WorldWideScience

Sample records for n-heterocyclic carbene complexes

  1. N-heterocyclic carbene-phosphinidyne transition metal complexes.

    Science.gov (United States)

    Doddi, Adinarayana; Bockfeld, Dirk; Bannenberg, Thomas; Jones, Peter G; Tamm, Matthias

    2014-12-01

    The N-heterocyclic carbene-phosphinidene adduct IPr?PSiMe3 is introduced as a synthon for the preparation of terminal carbene-phosphinidyne transition metal complexes of the type [(IPr?P)MLn ] (MLn =(?(6) -p-cymene)RuCl) and (?(5) -C5 Me5 )RhCl). Their spectroscopic and structural characteristics, namely low-field (31) P?NMR chemical shifts and short metal-phosphorus bonds, show their similarity with arylphosphinidene complexes. The formally mononegative IPr?P ligand is also capable of bridging two or three metal atoms as demonstrated by the preparation of bi- and trimetallic RuAu, RhAu, Rh2 , and Rh2 Au complexes. PMID:25287885

  2. Dioxygen adducts of rhodium N-heterocyclic carbene complexes.

    Science.gov (United States)

    Keske, Eric C; Zenkina, Olena V; Asadi, Ali; Sun, Hongsui; Praetorius, Jeremy M; Allen, Daryl P; Covelli, Danielle; Patrick, Brian O; Wang, Ruiyao; Kennepohl, Pierre; James, Brian R; Crudden, Cathleen M

    2013-05-28

    Rhodium complexes functionalized by N-heterocyclic carbene ligands react with dioxygen to form adducts. Depending on the specifics of the ancillary ligands, oxygen binds to Rh either as a peroxide to form a fully oxidized Rh(III) complex, or as singlet dioxygen in a Rh(I) square planar complex. We have shown through analysis of a series of compounds, some previously published and some novel, that the presence of additional ligands that would support the formation of an octahedral geometry, as typically found with Rh(III) complexes, is critical for formation of the peroxide. In addition, we have demonstrated through DFT studies, that the potential energy surface with regard to the O-O bond length is relatively shallow, which provides a rationale for the distribution of bond lengths observed for apparently similar complexes analyzed by crystallography. PMID:23440044

  3. N-Heterocyclic carbene metal complexes in medicinal chemistry.

    Science.gov (United States)

    Oehninger, Luciano; Rubbiani, Riccardo; Ott, Ingo

    2013-03-14

    Metal complexes with N-heterocyclic carbene (NHC) ligands are widely used in chemistry due to their catalytic properties and applied for olefin metathesis among other reactions. The enhanced application of this type of organometallics has over the last few years also triggered a steadily increasing number of studies in the fields of medicinal chemistry, which take advantage of the fascinating chemical properties of these complexes. In fact it has been demonstrated that metal NHC complexes can be used to develop highly efficient metal based drugs with possible applications in the treatment of cancer or infectious diseases. Complexes of silver and gold have been biologically evaluated most frequently but also platinum or other transition metals have demonstrated promising biological properties. PMID:23223752

  4. Homobimetallic Ruthenium-N-Heterocyclic Carbene Complexes For Olefin Metathesis

    Science.gov (United States)

    Sauvage, Xavier; Demonceau, Albert; Delaude, Lionel

    In this chapter, the synthesis and catalytic activity towards olefin metathesis of homobimetallic ruthenium (Ru)-alkylidene, -cyclodiene or -arene complexes bearing phosphine or N-heterocyclic carbene (NHC) ligands are reviewed. Emphasis is placed on the last category of bimetallic compounds. Three representatives of this new type of molecular scaffold were investigated. Thus, [(p-cymene)Ru(m-Cl)3RuCl (h2-C2H4)(L)] complexes with L = PCy3 (15a), IMes (16a), or IMesCl2 (16b) were prepared. They served as catalyst precursors for cross-metathesis (CM) of various styrene derivatives. These experiments revealed the outstanding aptitude of complex 16a (and to a lesser extent of 16b) to catalyze olefin metathesis reactions. Contrary to monometallic Ru-arene complexes of the [RuCl2(p-cymene)(L)] type, the new homobimetallic species did not require the addition of a diazo compound nor visible light illumination to initiate the ring-opening metathesis of norbornene or cyclooctene. When diethyl 2,2-diallylmalonate and N,N-diallyltosylamide were exposed to 16a,b, a mixture of cycloisomerization and ring-closing metathesis (RCM) products was obtained in a nonselective way. Addition of phenylacetylene enhanced the metathetical activity while completely repressing the cycloisomerization process.

  5. Methanol dehydrogenation by iridium N-heterocyclic carbene complexes.

    Science.gov (United States)

    Campos, Jesús; Sharninghausen, Liam S; Manas, Michael G; Crabtree, Robert H

    2015-06-01

    A series of homogeneous iridium bis(N-heterocyclic carbene) catalysts are active for three transformations involving dehydrogenative methanol activation: acceptorless dehydrogenation, transfer hydrogenation, and amine monoalkylation. The acceptorless dehydrogenation reaction requires base, yielding formate and carbonate, as well as 2-3 equivalents of H2. Of the few homogeneous systems known for this reaction, our catalysts tolerate air and employ simple ligands. Transfer hydrogenation of ketones and imines from methanol is also possible. Finally, N-monomethylation of anilines occurs through a "borrowing hydrogen" reaction. Notably, this reaction is highly selective for the monomethylated product. PMID:25615426

  6. The Potential of N-Heterocyclic Carbene Complexes as Components for Electronically Active Materials

    OpenAIRE

    Schuster, Oliver; Mercs, Laszlo; Albrecht, Martin

    2010-01-01

    The application of N-heterocyclic carbene complexes as active sites in materials other than catalysis has been remarkably scarce. Inspired by the — often misleading — ‘carbene’ label, which implies a substantial degree of M=C ? bonding, we have been interested in evaluating the potential of N-heterocylclic carbene complexes as building blocks for constructing electronically active materials. Electron mobility via the metal-carbon bond has been investigated in monometallic imidazol-2-ylidene c...

  7. T-Shaped Platinum(II) Complexes Stabilised by Bulky N-Heterocyclic Carbene Ligands

    OpenAIRE

    Rivada-Wheelaghan, Orestes; Donnadieu, Bruno; Maya, Celia; Conejero Iglesias, Salvador

    2010-01-01

    Pt to a T! Treating bulky N-heterocyclic carbene (NHC) ligands with [PtMe3I]4 results in rapid elimination of ethene and formation of [PtMeI(NHC)2] complexes. These complexes are suitable materials for the synthesis of T-shaped platinum(II) complexes stabilised by agostic interactions. X-ray structure determination of one of these complexes shows a rather long ? agostic interaction.

  8. Gold(I Complexes of N-Heterocyclic Carbene Ligands Containing Benzimidazole: Synthesis and Antimicrobial Activity

    Directory of Open Access Journals (Sweden)

    ?lknur Özdemir

    2010-03-01

    Full Text Available Gold(I N-heterocyclic carbene (NHC complexes were obtained in good yields from the corresponding silver complexes by treatment with [AuCl(PPh3] following the commonly used silver carbene transfer route. The silver complexes were synthesized from the benzimidazolium halide salts by the in situ reactions with Ag2O in dichloromethane as a solvent at room temperature. All gold complexes have been characterized by 1H-NMR, 13C-NMR and IR spectroscopy and elemental analysis. Au-NHC complexes were evaluated for their in vitro antimicrobial activity against a variety of Gram-positive and Gram-negative bacteria and fungal species.

  9. Alkyne-Azide Cycloaddition Catalyzed by Silver Chloride and “Abnormal” Silver N-Heterocyclic Carbene Complex

    OpenAIRE

    Aldo I. Ortega-Arizmendi; Eugenia Aldeco-Pérez; Erick Cuevas-Yañez

    2013-01-01

    A library of 1,2,3-triazoles was synthesized from diverse alkynes and azides using catalytic amounts of silver chloride instead of copper compounds. In addition, a novel “abnormal” silver N-heterocyclic carbene complex was tested as catalyst in this process. The results suggest that the reaction requires only 0.5% of silver complex, affording 1,2,3-triazoles in good yields.

  10. Alkyne-Azide Cycloaddition Catalyzed by Silver Chloride and “Abnormal” Silver N-Heterocyclic Carbene Complex

    Science.gov (United States)

    Ortega-Arizmendi, Aldo I.; Aldeco-Pérez, Eugenia; Cuevas-Yañez, Erick

    2013-01-01

    A library of 1,2,3-triazoles was synthesized from diverse alkynes and azides using catalytic amounts of silver chloride instead of copper compounds. In addition, a novel “abnormal” silver N-heterocyclic carbene complex was tested as catalyst in this process. The results suggest that the reaction requires only 0.5% of silver complex, affording 1,2,3-triazoles in good yields. PMID:24307866

  11. Backbone tuning in indenylidene–ruthenium complexes bearing an unsaturated N-heterocyclic carbene

    Directory of Open Access Journals (Sweden)

    César A. Urbina-Blanco

    2010-11-01

    Full Text Available The steric and electronic influence of backbone substitution in IMes-based (IMes = 1,3-bis(2,4,6-trimethylphenylimidazol-2-ylidene N-heterocyclic carbenes (NHC was probed by synthesizing the [RhCl(CO2(NHC] series of complexes to quantify experimentally the Tolman electronic parameter (electronic and the percent buried volume (%Vbur, steric parameters. The corresponding ruthenium–indenylidene complexes were also synthesized and tested in benchmark metathesis transformations to establish possible correlations between reactivity and NHC electronic and steric parameters.

  12. Electronic structure and ionization energies of palladium and platinum N-heterocyclic carbene complexes.

    OpenAIRE

    Green, JC; Herbert, BJ

    2005-01-01

    Density functional methods have been used to calculate the geometries, electronic structure and ionization energies (IE) of N-heterocyclic carbene complexes of palladium and platinum, [M(CN2R2C2H2)2](M = Pd, Pt; R = H, Me, Bu t). Agreement with X-ray structures (R = Bu t) was good. Calculated IE agreed well with the photoelectron (PE) spectra (R = Bu t); metal bands were calculated to be within 0.25 eV of the experimental values, whereas the higher lying ligand bands deviated by up to 0.9 eV....

  13. Biscarbene palladium(II) complexes. reactivity of saturated versus unsaturated N-heterocyclic carbenes.

    Science.gov (United States)

    Fu, Ching-Feng; Lee, Chun-Chin; Liu, Yi-Hung; Peng, Shie-Ming; Warsink, Stefan; Elsevier, Cornelis J; Chen, Jwu-Ting; Liu, Shiuh-Tzung

    2010-03-15

    A series of designed palladium biscarbene complexes including saturated and unsaturated N-heterocyclic carbene (NHC) moieties have been prepared by the carbene transfer methods. All of these complexes have been characterized by (1)H and (13)C NMR spectroscopy as well as X-ray diffraction analysis. The reactivity of Pd-C((saturated NHC)) is distinct from that of Pd-C((unsaturated NHC)). The Pd-C((saturated NHC)) bonds are fairly stable toward reagents such as CF(3)COOH, AgBF(4) and I(2), whereas Pd-C((unsaturated NHC)) bonds are readily cleaved under the similar conditions. Notably, the catalytically activity of these palladium complexes on Suzuki-Miyaura coupling follows the order: (sat-NHC)(2)PdCl(2) > (sat-NHC)(unsat-NHC)PdCl(2 )> (unsat-NHC)(2)PdCl(2). PMID:20143789

  14. Cationic bis-N-heterocyclic carbene (NHC) ruthenium complex: structure and application as latent catalyst in olefin metathesis.

    Science.gov (United States)

    Rouen, Mathieu; Queval, Pierre; Falivene, Laura; Allard, Jessica; Toupet, Loïc; Crévisy, Christophe; Caijo, Frédéric; Baslé, Olivier; Cavallo, Luigi; Mauduit, Marc

    2014-10-13

    An unexpected cationic bis-N-heterocyclic carbene (NHC) benzylidene ether based ruthenium complex (2 a) was prepared through the double incorporation of an unsymmetrical unsaturated N-heterocyclic carbene (U2 -NHC) ligand that bore an N-substituted cyclododecyl side chain. The isolation and full characterization (including X-ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2 a displayed interesting latent behavior during ring-closing metathesis, which could be "switched on" under acidic conditions. PMID:25212827

  15. Cationic bis-N-heterocyclic carbene (NHC) ruthenium complex: Structure and application as latent catalyst in olefin metathesis

    KAUST Repository

    Rouen, Mathieu

    2014-09-11

    An unexpected cationic bis-N-heterocyclic carbene (NHC) benzylidene ether based ruthenium complex (2 a) was prepared through the double incorporation of an unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligand that bore an N-substituted cyclododecyl side chain. The isolation and full characterization (including X-ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2 a displayed interesting latent behavior during ring-closing metathesis, which could be "switched on" under acidic conditions.

  16. N-Heterocyclic Carbene Complexes in Olefin Metathesis

    Science.gov (United States)

    Luan, Xinjun; Dorta, Reto; Leitgeb, Anita; Slugovc, Christian; Tiede, Sascha; Blechert, Siegfried

    Olefin metathesis is now a synthetic tool found ubiquitously in various fields involving synthesis. Of its many variations, three are prominently used: (1) catalytic ring closing metathesis (RCM) is an extremely powerful method for the construction of carbon-carbon double bonds in organic chemistry; (2) ring opening metathesis polymerisation (ROMP) where polymers are formed by use of the energy released from cyclic strain; and (3) cross metathesis (CM) where non-cyclic partners are coupled through C-C double bond formation. These important transformations and variations on these themes mediated by second generation ruthenium complexes bearing a NHC ligand will be presented in the following sections.

  17. Ruthenium indenylidene complexes bearing N-alkyl/N-mesityl-substituted N-heterocyclic carbene ligands.

    Science.gov (United States)

    Yu, Baoyi; Hamad, Fatma B; Sels, Bert; Van Hecke, Kristof; Verpoort, Francis

    2015-07-14

    We report on the synthesis and characterization of second generation ruthenium indenylidene catalysts bearing unsymmetrical N-heterocyclic carbene (NHC) ligands denoted as RuCl2(3-phenyl-1-indenylidene)(1-mesityl-3-R-4,5-dihydroimidazol-2-ylidene)(PCy3), in which R is methyl 8a, octyl 8b or cyclohexyl 8c. The characterization of 8a-c was performed by NMR spectroscopy, elemental analysis, IR, HRMS and single-crystal X-ray diffraction analysis. In addition, the catalytic activity of the obtained initiators was evaluated in various representative metathesis reactions. The results reveal that the complexes 8a-c, bearing an N-alkyl side on the NHC, show a faster catalytic initiation than the reference complex 2. Complex 8a, which performs the best among the investigated indenylidene complexes, exhibits slower initiation but better overall efficiency than its benzylidene analogue 1c, especially in a low catalyst loading. PMID:26052999

  18. The Crystallographic and Quantum Mechanical Analysis of some Pd(II) N-heterocyclic carbene Complexes

    International Nuclear Information System (INIS)

    Because of their extraordinary properties, N-heterocyclic carbenes (NHC) have found access to a great variety of catalytic processes which include C-C coupling reactions, formation of furans, cyclopropanation, olefin metathesis, hydroformylation, polymerization and hydrosilylation reactions. In this study, molecular and crystal structures of Pd(II) NHC complexes have been determined by single crystal x-ray diffraction technique. In addition, molecular geometries of all complexes under study were optimized at the B3LYP level of density functional theory (DFT) and the effective core potentials of Hay and Wadt with LanL2DZ basis set were used. In order to investigate binding orbitals of metal and charge transfer mechanism occurred in NHC ring, natural bond orbital (NBO) analyses were performed at the B3LYP/LanL2DZ level on the basis of the optimized ground state for complexes

  19. Biological Screening of Newly Synthesized BIAN N-Heterocyclic Gold Carbene Complexes in Zebrafish Embryos.

    Science.gov (United States)

    Farooq, Muhammad; Taha, Nael Abu; Butorac, Rachel R; Evans, Daniel Anthony; Elzatahry, Ahmed A; Elsayed, Elsayed Ahmed; Wadaan, Mohammad A M; Al-Deyab, Salem S; Cowley, Alan H

    2015-01-01

    N-Heterocyclic carbene (NHC) metal complexes possess diverse biological activities but have yet to be extensively explored as potential chemotherapeutic agents. We have previously reported the synthesis of a new class of NHC metal complexes N-heterocyclic with acetate [IPr(BIAN)AuOAc] and chloride [IPr(BIAN)AuCl] ligands. In the experiments reported herein, the zebrafish embryos were exposed to serial dilutions of each of these complexes for 10-12 h. One hundred percent mortality was observed at concentrations ?50 µM. At sub-lethal concentrations (10-30 µM), both compounds influenced zebrafish embryonic development. However, quite diverse categories of abnormalities were found in exposed embryos with each compound. Severe brain deformation and notochord degeneration were evident in the case of [IPr(BIAN)AuOAc]. The zebrafish embryos treated with [IPr(BIAN)AuCl] exhibited stunted growth and consequently had smaller body sizes. A depletion of 30%-40% glutathione was detected in the treated embryos, which could account for one of the possible mechanism of neurotoxicity. The fact that these compounds are capable of both affecting the growth and also compromising antioxidant systems by elevating intracellular ROS production implies that they could play an important role as a new breed of therapeutic molecules. PMID:26501273

  20. Nanofiber composites containing N-heterocyclic carbene complexes with antimicrobial activity

    Directory of Open Access Journals (Sweden)

    Elzatahry AA

    2012-06-01

    Full Text Available Ahmed A Elzatahry1,4, Abdullah M Al-Enizi1, Elsayed Ahmed Elsayed2,5, Rachel R Butorac3, Salem S Al-Deyab1, Mohammad AM Wadaan2, Alan H Cowley31Petrochemical Research Chair, Department of Chemistry, 2Chair of Advanced Proteomics & Cytomics Research, Faculty of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia; 3Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, TX, USA; 4Institute of Advanced Technology and New Materials, City for Scientific Research and Technology Applications, New Borg Alrab, Alexandria, Egypt; 5Natural & Microbial Products Department, National Research Centre, Dokki, Cairo, EgyptAbstract: This report concerns nanofiber composites that incorporate N-heterocyclic carbenes and the use of such composites for testing antimicrobial and antifungal activities. The nanofiber composites were produced by electrospinning mixtures of the gold chloride or gold acetate complexes of a bis(iminoacenaphthene (BIAN-supported NHC with aqueous solutions of polyvinyl alcohol (PVA. The products were characterized by scanning-electron microscopy, which revealed that nanofibers in the range of 250–300 nm had been produced. The biological activities of the nanofiber composites were tested against two Gram-positive bacteria, six Gram-negative bacteria, and two fungal strains. No activity was evident against the fungal strains. However, the gold chloride complex was found to be active against all the Gram-positive pathogens and one of the Gram-negative pathogens. It was also found that the activity of the produced nanofibers was localized and that no release of the bioactive compound from the nanofibers was evident. The demonstrated antimicrobial activities of these novel nanofiber composites render them potentially useful as wound dressings.Keywords: nanofiber, electrospinning, N-Heterocyclic carbene, biopolymer, antimicrobial

  1. N-Heterocyclic Carbene-Phosphinidene Complexes of the Coinage Metals.

    Science.gov (United States)

    Doddi, Adinarayana; Bockfeld, Dirk; Nasr, Alexandre; Bannenberg, Thomas; Jones, Peter G; Tamm, Matthias

    2015-11-01

    Coinage metal complexes of the N-heterocyclic carbene-phosphinidene adduct IPr?PPh (IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were prepared by its reaction with CuCl, AgCl, and [(Me2 S)AuCl], which afforded the monometallic complexes [(IPr?PPh)MCl] (M=Cu, Ag, Au). The reaction with two equivalents of the metal halides gave bimetallic [(IPr?PPh)(MCl)2 ] (M=Cu, Au); the corresponding disilver complex could not be isolated. [(IPr?PPh)(CuOTf)2 ] was prepared by reaction with copper(I) trifluoromethanesulfonate. Treatment of [(IPr?PPh)(MCl)2 ] (M=Cu, Au) with Na(BAr(F) ) or AgSbF6 afforded the tetranuclear complexes [(IPr?PPh)2 M4 Cl2 ]X2 (X=BAr(F) or SbF6 ), which contain unusual eight-membered M4 Cl2 P2 rings with short cuprophilic or aurophilic contacts along the chlorine-bridged M???M axes. Complete chloride abstraction from [(IPr?PPh)(AuCl)2 ] was achieved with two equivalents of AgSbF6 in the presence of tetrahydrothiophene (THT) to form [(IPr?PPh){Au(THT)}2 ][SbF6 ]2 . The cationic tetra- and dinuclear complexes were used as catalysts for enyne cyclization and carbene transfer reactions. PMID:26365325

  2. Luminescence Studies of the Intracellular Distribution of a Dinuclear Gold(I) N-Heterocyclic Carbene Complex

    Energy Technology Data Exchange (ETDEWEB)

    Barnard, Peter J.; Wedlock, Louise E.; Baker, Murray V.; Berners-Price, Susan J.; Joyce, David A.; Skelton, Brian W.; Steer, James H. (UWA)

    2008-10-03

    A bidentate cyclophane N-heterocyclic carbene ligand has been used to synthesize a new dinuclear Au{sup I} complex of the formula [Au{sub 2}L{sub 2}]{sup 2+}. The short Au {hor_ellipsis} Au distance imposed by the rigid cyclophane ligand leads to a red-shifted luminescence profile that enables the complex to be used as a luminescent probe for distribution studies in single living cancer cells.

  3. Silver complexes of 1,2,4-triazole derived N-heterocyclic carbenes: Synthesis, structure and reactivity studies

    Indian Academy of Sciences (India)

    Chandrakanta Dash; Mobin M Shaikh; Prasenjit Ghosh

    2011-03-01

    Two silver(I) complexes {[1-R-4-($N$-t4-butylacetamido)-1,2,4-triazol-5-ylidene]2Ag}+ Cl? [R = Et (1b), -Pr (2b)] of $N/O$-functionalized N-heterocyclic carbenes derived from 1,2,4-triazoles are reported. The silver complexes, 1b and 2b, have been synthesized from the reaction of the $N/O$-functionalized triazolium chloride salts namely, 1-R-4-(N-t-butylacetamido)-1,2,4-triazolium chloride [R = Et (1a), -Pr (2a)] by treatment with Ag2O in 53-56% yield. The 1,2,4-triazolium chloride salts 1a and 2a were prepared by the alkylation reaction of 1-R-1,2,4-triazole (R = Et, -Pr) with $N-t$-butyl-2-chloro acetamide in 47-63% yield. The molecular structures of the silver(I) complexes, 1b and 2b, have been determined by X-ray diffraction studies. The density functional theory studies on the silver 1b and 2b complexes suggest that the 1,2,4-triazole derived N-heterocyclic carbenes to be strong ?donating ligands similar to the now much recognized imidazolebased N-heterocyclic carbenes. The reactivity studies with (SMe2)AuCl and (SMe2)CuBr indicated the silver complexes, 1b and 2b, to be good transmetallating agents.

  4. N-Heterocyclic carbene–palladium(II-1-methylimidazole complex catalyzed Mizoroki–Heck reaction of aryl chlorides with styrenes

    Directory of Open Access Journals (Sweden)

    Ting-Ting Gao

    2012-11-01

    Full Text Available A well-defined N-heterocyclic carbene–palladium(II-1-methylimidazole [NHC-Pd(II-Im] complex 1 was found to be an effective catalyst for the Mizoroki–Heck reaction of a variety of aryl chlorides with styrenes. Both activated and deactivated aryl chlorides work well to give the corresponding coupling products in good to excellent yields by using tetrabutylammonium bromide (TBAB as the ionic liquid.

  5. Cationic tungsten-oxo-alkylidene-N-heterocyclic carbene complexes: highly active olefin metathesis catalysts.

    Science.gov (United States)

    Schowner, Roman; Frey, Wolfgang; Buchmeiser, Michael R

    2015-05-20

    The synthesis, structure, and olefin metathesis activity of the first neutral and cationic W-oxo-alkylidene-N-heterocyclic carbene (NHC) catalysts are reported. Neutral W-oxo-alkylidene-NHC catalysts can be prepared in up to 90% isolated yield. Depending on the ligands used, they possess either an octahedral (Oh) or trigonal bipyramidal ligand sphere. They can be activated with excess AlCl3 to form cationic olefin metathesis-active W-complexes; however, these readily convert into neutral chloro-complexes. Well-defined, stable cationic species can be prepared by stoichiometric substitution of one chloro ligand in the parent, neutral W-oxo-alkylidene-NHC complexes with Ag(MeCN)2B(Ar(F))4 or NaB(Ar(F))4; B(Ar(F))4 = B(3,5-(CF3)2-C6H3)4. They are highly active olefin metathesis catalysts, allowing for turnover numbers up to 10,000 in various olefin metathesis reactions including alkenes bearing nitrile, sec-amine, and thioether groups. PMID:25938340

  6. Amide Synthesis from Alcohols and Amines Catalyzed by Ruthenium N-Heterocyclic Carbene Complexes

    DEFF Research Database (Denmark)

    Dam, Johan Hygum; Osztrovszky, Gyorgyi

    2010-01-01

    The direct synthesis of amides from alcohols and amines is described with the simultaneous liberation of dihydrogen. The reaction does not require any stoichiometric additives or hydrogen acceptors and is catalyzed by ruthenium N-heterocyclic carbene complexes. Three different catalyst systems are presented that all employ 1,3-diisopropylimidazol-2-ylidene (IiPr) as the carbene ligand. In addition, potassium tert-butoxide and a tricycloalkylphosphine are required for the amidation to proceed. In the first system, the active catalyst is generated in situ from [RuCl2(cod)] (cod = 1,5-cyclooctadiene), 1,3-diisopropylimidazolium chloride, tricyclopentylphosphonium tetrafluoroborate, and base. The second system uses the complex [RuCl2(IiPr)(p-cymene)] together with tricyclohexylphosphine and base, whereas the third system employs the Hoveyda-Grubbs 1st-generation metathesis catalyst together with 1,3-diisopropylimidazolium chloride and base. A range of different primary alcohols and amines have been coupled in thepresence of the three catalyst systems to afford the corresponding amides in moderate to excellent yields. The best results are obtained with sterically unhindered alcohols and amines. The three catalyst systems do not show any significant differences in reactivity, which indicates that the same catalytically active species is operating. The reaction is believed to proceed by initial dehydrogenation of the primary alcohol to the aldehyde that stays coordinated to ruthenium and is not released into the reaction mixture. Addition of the amine forms the hemiaminal that undergoes dehydrogenation to the amide. A catalytic cycle is proposed with the {(IiPr)Ru-II} species as the catalytically active components.

  7. Palladium complexes of a new type of N-heterocyclic carbene ligand derived from a tricyclic triazolooxazine framework

    Indian Academy of Sciences (India)

    Manoj Kumar Gangwar; Alok Ch Kalita; Prasenjit Ghosh

    2014-09-01

    A new type of tricyclic triazolooxazine derived N-heterocyclic carbene precursors were developed by the alkylation reaction of a tricyclic triazolooxazine framework. In particular, the reaction of 5a,6,7,8,9,9ahexahydro-4-benzo[][1,2,3]triazolo[1,5-][1,4]oxazine with methyl iodide and ethyl iodide yielded the tricyclic triazolooxazine derived N-heterocyclic carbene precursors, (1?2)a, in 67?84% yield. The tricyclic triazolooxazinium iodide salts, (1?2)a, underwent metallation in a straight forward manner upon treatment with PdCl2 in the presence of K2CO3 in pyridine to give the trans-{3-(R)-5a,6,7,8,9,9a-hexahydro-4-benzo[][1,2,3]triazolo[1,5-][1,4]oxazin-4-ylidene} PdI2(pyridine) [R = Me (1b), Et (2b)] complexes in 23?25% yield. The new tricyclic triazolooxazine derived N-heterocyclic carbene moiety, as stabilized upon binding to palladium in the (1?2)b complexes, was structurally characterized by the X-ray single crystal diffraction studies.

  8. Electrochemiluminescent ruthenium(II) N-heterocyclic carbene complexes: a combined experimental and theoretical study.

    Science.gov (United States)

    Barbante, Gregory J; Francis, Paul S; Hogan, Conor F; Kheradmand, Peyman R; Wilson, David J D; Barnard, Peter J

    2013-07-01

    A series of four Ru(II) complexes of the form [Ru(bpy)2(C(^)N)](2+) (where C(^)N is a bidentate pyridine-functionalized imidazolylidene- or benzimidazolylidene-based N-heterocyclic carbene (NHC) ligand and bpy is 2,2'-bipyridine) have been synthesized using a Ag(I) transmetalation protocol from the Ru(II) precursor compound, Ru(bpy)2Cl2. The synthesized azolium salts and Ru(II) complexes were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, cyclic voltammetry, and electronic absorption and emission spectroscopy. The molecular structures for two benzimidazolium salts and three Ru(II) complexes were determined by single crystal X-ray diffraction. The complexes display photoluminescence within the range 611-629 nm, with the emission wavelength of the benzimidazolylidene containing structures, slightly blue-shifted relative to the imidazolylidene containing complexes. All complexes exhibited a reversible, one-electron oxidation, which is assigned to the Ru(2+/3+) redox couple. When compared to [Ru(bpy)3](2+), complexes of imidazolylidene containing ligands were oxidized at more negative potentials, while those of the benzimidazolylidene containing ligands were oxidized at more positive potentials. All four complexes exhibited moderately intense electrochemiluminescence (ECL) with the obtained ECL spectra closely resembling the photoluminescence spectra. The ability to predictably fine-tune the highest occupied molecular orbital (HOMO) level of the Ru(II) complexes via the flexible synthetic strategy offered by NHCs is valuable for the design of ECL-based multiplexed detection strategies. PMID:23772555

  9. Rhenium complexes of bidentate, bis-bidentate and tridentate N-heterocyclic carbene ligands.

    Science.gov (United States)

    Chan, Chung Ying; Barnard, Peter J

    2015-11-28

    A series of eight Rhenium(i)-N-heterocyclic carbene (NHC) complexes of the general form [ReCl(CO)3(C^C)] (where C^C is a bis(NHC) bidentate ligand), [ReCl(CO)3(C^C)]2 (where C^C is a bis-bidentate tetra-NHC ligand) and [Re(CO)3(C^N^C)](+)[X](-) (where C^N^C is a bis(NHC)-amine ligand and the counter ion X is either the ReO4(-) or PF6(-)) have been synthesised using a Ag2O transmetallation protocol. The novel precursor imidazolium salts and Re(i) complexes were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy and the molecular structures for two imidazolium salt and six Re(i) complexes were determined by single crystal X-ray diffraction. These NHC ligand systems are of interest for possible applications in the development of Tc-99m or Re-186/188 radiopharmaceuticals and as such the stability of two complexes of the form [ReCl(CO)3(C^C)] and [Re(CO)3(C^N^C)][ReO4] were evaluated in ligand challenge experiments using the metal binding amino acids l-histidine or l-cysteine. These studies showed that the former was unstable, with the chloride ligand being replaced by either cysteine or histidine, while no evidence for transchelation was observed for the latter suggesting that bis(NHC)-amine ligands of this type may be suitable for biological applications. PMID:26477971

  10. Synthesis and characterization of an iron complex bearing a cyclic tetra-N-heterocyclic carbene ligand: An artifical heme analogue?

    KAUST Repository

    Anneser, Markus R.

    2015-04-20

    An iron(II) complex with a cyclic tetradentate ligand containing four N-heterocyclic carbenes was synthesized and characterized by means of NMR and IR spectroscopies, as well as by single-crystal X-ray structure analysis. The iron center exhibits an octahedral coordination geometry with two acetonitrile ligands in axial positions, showing structural analogies with porphyrine-ligated iron complexes. The acetonitrile ligands can readily be substituted by other ligands, for instance, dimethyl sulfoxide, carbon monoxide, and nitric oxide. Cyclic voltammetry was used to examine the electronic properties of the synthesized compounds. © 2015 American Chemical Society.

  11. Ruthenium and osmium complexes of dihydroperimidine-based N-heterocyclic carbene pincer ligands.

    Science.gov (United States)

    McQueen, Caitlin M A; Hill, Anthony F; Ma, Chenxi; Ward, Jas S

    2015-12-21

    The reactions of N,N'-bis(phosphinomethyl)dihydroperimidine pro-ligands H2C(NCH2PR2)2C10H6 (R = Cy 1a, R = Ph 1b) with [RuCl2(PPh3)3] give markedly different products. Chelate-assisted double C-H activation in the former affords the perimidinylidene-based N-heterocyclic carbene (per-NHC) pincer complex [RuCl2(OC4H8){?(3)-P,C,P'-C(NCH2PCy2)2C10H6}] (2), while the latter reaction provides the asymmetric PNP-coordinated complex [RuCl2(PPh3){?(3)-P,N,P'-CH2(NCH2PPh2)2C10H6}] (3), in which no C-H activation has occurred. Subsequent reactions of the per-NHC complex 2 with carbon monoxide and mesityl isocyanide readily displaced the labile THF ligand to afford the complexes [RuCl2(CA){?(3)-P,C,P'-C(NCH2PCy2)2C10H6}] (A = O 4, A = NC6H2Me35). Double C-H activation of 1a and 1b was significantly more facile on reaction with [OsCl2(PPh3)3], providing the per-NHC complexes [OsHCl(PPh3){?(3)-P,C,P'-C(NCH2PR2)2C10H6}] (R = Cy 7a, R = Ph 7b, respectively), each as two isomers. The reactions of 1b with [Ru2(?-Cl)2Cl2(?-C6H3Me3)2] or [AuCl(THT)] (THT = tetrahydrothiophene) provide the bimetallic complexes [Ru2{?-H2C(NCH2PPh2)2C10H6}Cl4(?-C6H3Me3)2] (8) and [Au2{?-H2C(NCH2PPh2)2C10H6}Cl2] (9) without C-H activation occurring. PMID:26492361

  12. Dehydrogenative Synthesis of Imines from Alcohols and Amines Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex

    DEFF Research Database (Denmark)

    Maggi, Agnese; Madsen, Robert

    2012-01-01

    A new method for the direct synthesis of imines from alcohols and amines is described where hydrogen gas is liberated. The reaction is catalyzed by the ruthenium N-heterocyclic carbene complex [RuCl2(IiPr)(p-cymene)] in the presence of the ligand DABCO and molecular sieves. The imination can be applied to a variety of primary alcohols and amines and can be combined with a subsequent addition reaction. A deuterium labeling experiment indicates that the catalytically active species is a ruthenium ...

  13. Synthesis, characterization, and reactivity of furan- and thiophene-functionalized bis(n-heterocyclic carbene) complexes of iron(II)

    KAUST Repository

    Rieb, Julia

    2014-09-15

    The synthesis of iron(II) complexes bearing new heteroatom-functionalized methylene-bridged bis(N-heterocyclic carbene) ligands is reported. All complexes are characterized by single-crystal X-ray diffraction (SC-XRD), nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis. Tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (2a) and tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenethiophene)methane]iron(II) hexafluorophosphate (2b) were obtained by aminolysis of [Fe{N(SiMe3)2}2(THF)] with furan- and thiophene-functionalized bis(imidazolium) salts 1a and 1b in acetonitrile. The SC-XRD structures of 2a and 2b show coordination of the bis(carbene) ligand in a bidentate fashion instead of a possible tetradentate coordination. The four other coordination sites of these distorted octahedral complexes are occupied by acetonitrile ligands. Crystallization of 2a in an acetone solution by the slow diffusion of Et2O led to the formation of cisdiacetonitriledi[ bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (3a) with two bis(carbene) ligands coordinated in a bidentate manner and two cis-positioned acetonitrile molecules. Compounds 2a and 2b are the first reported iron(II) carbene complexes with four coordination sites occupied by solvent molecules, and it was demonstrated that those solvent ligands can undergo ligand-exchange reactions.

  14. Ruthenium complexes of chelating amido-functionalized N-heterocyclic carbene ligands: Synthesis, structure and DFT studies

    Indian Academy of Sciences (India)

    Sachin Kumar; Anantha Narayanan; Mitta Nageswar Rao; Mobin M Shaikh; Prasenjit Ghosh

    2011-11-01

    Synthesis, structure and density functional theory (DFT) studies of a series of new ruthenium complexes, [1-(R)-3--(benzylacetamido)imidazol-2-ylidene]RuCl(-cymene) [R = Me (1c), -Pr (2c), CH2Ph (3c); -cymene = 4--propyltoluene] supported over $N/O$-functionalized N-heterocyclic carbene (NHC) ligands are reported. In particular, the ruthenium (1-3)c complexes were synthesized from the respective silver complexes, [1-(R)-3--(benzylacetamido)imidazol-2-ylidene]2Ag+Cl? [R = Me (1b), -Pr (2b), CH2Ph (3b)] by the treatment with [Ru(-cymene)Cl2]2 in 65-76% yields. The molecular structures of (1-3)c revealed the chelation of the N-heterocylic carbene ligand through the carbene center and an amido sidearm of the ligand in all of the three complexes. The density functional theory studies on the ruthenium (1-3)c complexes indicated strong binding of the NHC ligand to the metal center as was observed from the deeply buried NHC-Ru -bonding molecular orbitals.

  15. Sulfur-Functionalized N-Heterocyclic Carbene Complexes of Pd(II: Syntheses, Structures and Catalytic Activities

    Directory of Open Access Journals (Sweden)

    Dan Yuan

    2012-03-01

    Full Text Available N-heterocyclic carbenes (NHCs can be easily modified by introducing functional groups at the nitrogen atoms, which leads to versatile coordination chemistry as well as diverse catalytic applications of the resulting complexes. This article summarizes our contributions to the field of NHCs bearing different types of sulfur functions, i.e., thioether, sulfoxide, thiophene, and thiolato. The experimental evidence for the truly hemilabile coordination behavior of a Pd(II thioether-NHC complex has been reported as well. In addition, complexes bearing rigid CSC-pincer ligands have been synthesized and the reasons for pincer versus pseudo-pincer formation investigated. Incorporation of the electron-rich thiolato function resulted in the isolation of structurally diverse complexes. The catalytic activities of selected complexes have been tested in Suzuki-Miyaura, Mizoroki-Heck and hydroamination reactions.

  16. Dehydrogenative Synthesis of Imines from Alcohols and Amines Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex

    DEFF Research Database (Denmark)

    Maggi, Agnese; Madsen, Robert

    2012-01-01

    A new method for the direct synthesis of imines from alcohols and amines is described where hydrogen gas is liberated. The reaction is catalyzed by the ruthenium N-heterocyclic carbene complex [RuCl2(IiPr)(p-cymene)] in the presence of the ligand DABCO and molecular sieves. The imination can be applied to a variety of primary alcohols and amines and can be combined with a subsequent addition reaction. A deuterium labeling experiment indicates that the catalytically active species is a ruthenium dihydride. The reaction is believed to proceed by initial dehydrogenation of the alcohol to the aldehyde, which stays coordinated to ruthenium. Nucleophilic attack of the amine affords the hemiaminal, which is released from ruthenium and converted into the imine.

  17. Cyclopentadienyl molybdenum(II/VI) N-heterocyclic carbene complexes: Synthesis, structure, and reactivity under oxidative conditions

    KAUST Repository

    Li, Shenyu

    2010-04-26

    A series of N-heterocyclic carbene (NHC) complexes CpMo(CO) 2(NHC)X (NHC = IMe = 1,3-dimethylimidazol-2-ylidene, X = Br, 1; NHC = 1,3-dipropylimidazol-2-ylidene, X = Br, 2; NHC = IMes = 1,3-bis(2,4,6- trimethylphenyl)imidazol-2-ylidene, X = Br, 3; NHC = IBz = 1,3-dibenzylimidazol- 2-ylidene, X = Br, 4a, and X = Cl, 4b; NHC = 1-methyl-3-propylimidazol-2- ylidene, X = Br, 5) and [CpMo(CO)2(IMes)(CH3CN)][BF 4] (6) have been synthesized and fully characterized. The stability of metal-NHC ligand bonds in these compounds under oxidative conditions has been investigated. The thermally stable Mo(VI) dioxo NHC complex [CpMoO 2(IMes)][BF4] (9) has been isolated by the oxidation of the ionic complex 6 by TBHP (tert-butyl hydrogen peroxide). Complex 6 can be applied as a very active (TOFs up to 3400 h-1) and selective olefin epoxidation catalyst. While under oxidative conditions (in the presence of TBHP), compounds 1-5 decompose into imidazolium bromide and imidazolium polyoxomolybdate. The formation of polyoxomolybdate as oxidation products had not been observed in a similar epoxidation catalyzed by Mo(II) and Mo(VI) complexes. DFT studies suggest that the presence of Br- destabilizes the CpMo(VI) oxo NHC carbene species, consistent with the experimental observations. © 2010 American Chemical Society.

  18. Stereoelectronic effects in C-H bond oxidation reactions of Ni(I) N-heterocyclic carbene complexes.

    Science.gov (United States)

    Poulten, Rebecca C; López, Isidoro; Llobet, Antoni; Mahon, Mary F; Whittlesey, Michael K

    2014-07-21

    Activation of O2 by the three-coordinate Ni(I) ring-expanded N-heterocyclic carbene complexes Ni(RE-NHC)(PPh3)Br (RE-NHC = 6-Mes, 1; 7-Mes, 2) produced the structurally characterized dimeric Ni(II) complexes Ni(6-Mes)(Br)(?-OH)(?-O-6-Mes')NiBr (3) and Ni(7-Mes)(Br)(?-OH)(?-O-7-Mes')NiBr (4) containing oxidized ortho-mesityl groups from one of the carbene ligands. NMR and mass spectrometry provided evidence for further oxidation in solution to afford bis-?-aryloxy compounds; the 6-Mes derivative was isolated, and its structure was verified. Low-temperature UV-visible spectroscopy showed that the reaction between 1 and O2 was too fast even at ca. -80 °C to yield any observable intermediates and also supported the formation of more than one oxidation product. Addition of O2 to Ni(I) precursors containing a less electron-donating diamidocarbene (6-MesDAC, 7) or less bulky 6- or 7-membered ring diaminocarbene ligands (6- or 7-o-Tol; 8 and 9) proceeded quite differently, affording phosphine and carbene oxidation products (Ni(O?PPh3)2Br2 and (6-MesDAC)?O) and the mononuclear Ni(II) dibromide complexes (Ni(6-o-Tol)(PPh3)Br2 (10) and (Ni(7-o-Tol)(PPh3)Br2 (11)) respectively. Electrochemical measurements on the five Ni(I) precursors show significantly higher redox potentials for 1 and 2, the complexes that undergo oxygen atom transfer from O2. PMID:24972307

  19. Multicomponent synthesis of unsymmetrical unsaturated N-heterocyclic carbene precursors and their related transition-metal complexes

    KAUST Repository

    Queval, Pierre

    2013-12-04

    A low-cost, modular, and easily scalable multicomponent procedure affording access in good yields and excellent selectivity (up to 93 %) to a wide range of (a)chiral unsymmetrical 1-aryl-3-cycloalkyl-imidazolium salts is disclosed. Electronic and steric properties of the corresponding unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligands were evaluated and evidenced strong electron donor ability, high steric discrimination, and modular steric demand. A low-cost, modular, and easily scalable multicomponent procedure, affording access to a wide range of (a)chiral unsymmetrical 1-aryl-3-cycloalkyl- imidazolium salts in good yields and excellent selectivities, is disclosed. Electronic and steric properties of the corresponding unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligands were evaluated and evidenced strong electron-donor ability, high steric discrimination, and modular steric demand. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. A new tridentate pincer phosphine/n-heterocyclic carbene ligand: palladium complexes, their structures, and catalytic activities.

    Science.gov (United States)

    Lee, Hon Man; Zeng, Jing Yao; Hu, Ching-Han; Lee, Ming-Tsung

    2004-10-18

    A new imidazolium salt, 1,3-bis(2-diphenylphosphanylethyl)-3H-imidazol-1-ium chloride (2), for the phosphine/N-heterocyclic carbene-based pincer ligand, PC(NHC)P, and its palladium complexes were reported. The complex, [Pd(PC(NHC)P)Cl]Cl (4), was prepared by the common route of silver carbene transfer reaction and a novel direct reaction between the ligand precursor, PC(NHC)P.HCl and PdCl(2) without the need of a base. Metathesis reactions of 4 with AgBF(4) in acetonitrile produced [Pd(PC(NHC)P)(CH(3)CN)](BF(4))(2) (5). The same reaction in the presence of excess pyridine gave [Pd(PC(NHC)P)(py)](BF(4))(2) (6). The X-ray structure determination on 4-6 revealed the chiral twisting of the central imidazole rings from the metal coordination plane. In solution, fast interconversion between left- and right-twisted forms occurs. The twisting reflects the weak pi-accepting property of the central NHC in PC(NHC)P. The uneven extent of twisting among the three complexes further implies the low rotational barrier about the Pd-NHC bond. Related theoretical computations confirm the small rotational energy barrier about the Pd-NHC bond (ca. 4 kcal/mol). Catalytic applications of 4 and 5 have shown that the complexes are modest catalysts in Suzuki coupling. The complexes were active catalysts in Heck coupling reactions with the dicationic complex 5 being more effective than the monocationic complex 4. PMID:15476383

  1. N-Heterocyclic carbene stabilized Ag-P nanoclusters.

    Science.gov (United States)

    Khalili Najafabadi, Bahareh; Corrigan, John F

    2015-01-14

    The N-heterocyclic carbene (NHC) 1,3-di-isopropylbenzimidazole-2-ylidene ((i)Pr2-bimy) is found to be an excellent ligand for the stabilization of silver-phosphorus polynuclear complexes. The straightforward preparation and characterization of the clusters [Ag12(PSiMe3)6((i)Pr2-bimy)6] (1) and [Ag26P2(PSiMe3)10((i)Pr2-bimy)8] (2) are described, representing the first examples of such structurally characterized, higher nuclearity complexes obtained using this class of ligands. PMID:25415342

  2. Carbon monoxide induced reductive elimination of disulfide in an N-heterocyclic carbene (NHC)/thiolate dinitrosyl iron complex (DNIC).

    Science.gov (United States)

    Pulukkody, Randara; Kyran, Samuel J; Bethel, Ryan D; Hsieh, Chung-Hung; Hall, Michael B; Darensbourg, Donald J; Darensbourg, Marcetta Y

    2013-06-01

    Dinitrosyliron complexes (DNICs) are organometallic-like compounds of biological significance in that they appear in vivo as products of NO degradation of iron-sulfur clusters; synthetic analogues have potential as NO storage and releasing agents. Their reactivity is expected to depend on ancillary ligands and the redox level of the distinctive Fe(NO)2 unit: paramagnetic {Fe(NO)2}(9), diamagnetic dimerized forms of {Fe(NO)2}(9) and diamagnetic {Fe(NO)2}(10) DNICs (Enemark-Feltham notation). The typical biological ligands cysteine and glutathione themselves are subject to thiolate-disulfide redox processes, which when coupled to DNICs may lead to intricate redox processes involving iron, NO, and RS(-)/RS•. Making use of an N-heterocyclic carbene-stabilized DNIC, (NHC)(RS)Fe(NO)2, we have explored the DNIC-promoted RS(-)/RS• oxidation in the presence of added CO wherein oxidized {Fe(NO)2}(9) is reduced to {Fe(NO)2}(10) through carbon monoxide (CO)/RS• ligand substitution. Kinetic studies indicate a bimolecular process, rate = k [Fe(NO)2](1)[CO](1), and activation parameters derived from kobs dependence on temperature similarly indicate an associative mechanism. This mechanism is further defined by density functional theory computations. Computational results indicate a unique role for the delocalized frontier molecular orbitals of the Fe(NO)2 unit, permitting ligand exchange of RS• and CO through an initial side-on approach of CO to the electron-rich N-Fe-N site, ultimately resulting in a 5-coordinate, 19-electron intermediate with elongated Fe-SR bond and with the NO ligands accommodating the excess charge. PMID:23668326

  3. Bulky N-Phosphino-Functionalized N-Heterocyclic Carbene Ligands: Synthesis, Ruthenium Coordination Chemistry, and Ruthenium Alkylidene Complexes for Olefin Metathesis.

    Science.gov (United States)

    Brown, Christopher C; Rominger, Frank; Limbach, Michael; Hofmann, Peter

    2015-11-01

    Ruthenium chemistry and applications in catalytic olefin metathesis based on N-phosphino-functionalized N-heterocyclic carbene ligands (NHCPs) are presented. Alkyl NHCP Ru coordination chemistry is described, and access to several potential synthetic precursors for ruthenium alkylidene complexes is outlined, incorporating both trimethylsilyl and phenyl alkylidenes. The Ru alkylidene complexes are evaluated as potential olefin metathesis catalysts and were shown to behave in a latent fashion. They displayed catalytic activity at elevated temperatures for both ring closing metathesis and ring opening metathesis polymerization. PMID:26479425

  4. Ruthenium-based complexes containing a benzimidazolium tag covalently connected to N-heterocyclic carbene ligands: environmentally friendly catalysts for olefin metathesis transformations.

    Science.gov (United States)

    Klu?iar, Marek; Grela, Karol; Mauduit, Marc

    2013-05-28

    Two ruthenium-based pre-catalysts containing an ionic tag covalently connected to a N-heterocyclic carbene (NHC) ligand are reported. These novel complexes, bearing a polar benzimidazolium group, are air-stable and can be easily prepared from commercially available reagents. The quaternary benzimidazolium tag allows the efficient separation of ruthenium waste from the metathesis product after reaction. Application in several olefin metathesis transformations leads to desired products of high purity, which exhibit ruthenium contamination levels as low as 1 ppm after simple filtration through a pad of silica gel. PMID:23360984

  5. A RhIII-N-heterocyclic carbene complex from metal-metal singly bonded [RhII?RhII] precursor

    Indian Academy of Sciences (India)

    Arup Sinha; Abir Sarbajna; Shrabani dinda; Jitendra K Bera

    2011-11-01

    Metal-metal singly bonded [Rh2(CO)4(acac)2][OTf]2 (1) has been synthesized and characterized by spectroscopic and analytical techniques. A density functional theory (DFT) optimized structure has been computed for the unbridged centro-symmetric structure. Reaction of 1 with PIN.HBr results in the [Rh(PIN)2(H2O)Br][OTf]2 (2) in high yield. The reaction involves metal-oxidation from RhII to RhIII accompanied by the metal-metal bond cleavage. The X-ray structure of 2 has been determined which reveals the incorporation of two N-heterocyclic carbene (NHC) ligands to each rhodium. This work demonstrates the general utility of the metal-metal bonded compounds for the easy synthesis of metal-NHC compounds.

  6. Synthesis and characterization of a cationic phthalimido-functionalized N-heterocyclic carbene complex of palladium(II) and its catalytic activity

    KAUST Repository

    Goh, Li Min Serena

    2014-01-29

    A cationic phthalimido-functionalized N-heterocyclic carbene (NHC) palladium(II) complex has been synthesized from [3-methyl-1-(2?- phthalimidoethyl)imidazolium] hexafluorophosphate ([NHCMe,PhtH] PF6) by transmetalation and isolated in 67 % yield. The title complex has been applied as catalyst in the Suzuki-Miyaura cross-coupling reaction under benign aqueous conditions. The catalyst is active without any observable initiation period. High average turnover frequencies (TOFs) of up to 55000 h-1 have been reached with catalyst concentrations as low as 0.01 mol-%. A cationic phthalimido-functionalized N-heterocyclic carbene (NHC) palladium(II) complex has been prepared in high yield. The complex was activated instantly, without an initiation period, in the Suzuki-Miyaura cross-coupling reaction under benign aqueous aerobic conditions. Turnover frequencies (TOFs) up to 55000 h-1, were achieved with 0.01 mol-% of the complex. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Chemistry of Iron N -heterocyclic carbene complexes: Syntheses, structures, reactivities, and catalytic applications

    KAUST Repository

    Riener, Korbinian

    2014-05-28

    Iron is the most abundant transition metal in Earth\\'s crust. It is relatively inexpensive, not very toxic, and environmentally benign. Undoubtedly, due to the involvement in a multitude of biological processes, which heavily rely on the rich functionalities of iron-containing enzymes, iron is one of the most important elements in nature. Additionally, three-coordinate iron complexes have been reported during the past several years. In this review, the mentioned iron NHC complexes are categorized by their main structure and reactivity attributes. Thus, monocarbene and bis-monocarbene complexes are presented first. This class is subdivided into carbonyl, nitrosyl, and halide compounds followed by a brief section on other, more unconventional iron NHC motifs. Subsequently, donor-substituted complexes bearing bi-, tri-, tetra-, or even pentadentate ligands and further pincer as well as scorpionato motifs are described.

  8. Conformations of N-Heterocyclic Carbene Ligands in Ruthenium Complexes Relevant to Olefin Metathesis

    OpenAIRE

    Stewart, Ian C.; Benitez, Diego; O'Leary, Daniel J.; Tkatchouk, Ekaterina; Day, Michael W; Goddard, William A., III; Grubbs, Robert H

    2009-01-01

    The structure of ruthenium-based olefin metathesis catalyst 3 and model ?-complex 5 in solution and in the solid state are reported. The N-tolyl ligands, due to their lower symmetry than the traditional N-mesityl substituents, complicate this analysis, but ultimately provide explanation for the enhanced reactivity of 3 relative to standard catalyst 2. The tilt of the N-tolyl ring provides additional space near the ruthenium center, which is consistent with the enhanced reactivity of 3 towards...

  9. Binuclear luminescent silver(I) - N-heterocyclic carbene complex derived from 1-picolyl-3-pyrimidylbenzimidazoliumhexaflurophosphate

    Science.gov (United States)

    Adhikary, Sirsendu Das; Seth, Saikat Kumar; Senapati, Manas Ranjan; Dinda, Joydev

    2013-06-01

    Starting from the novel proligand 1-picolyl-3-pyrimidylbenzimidazoliumhexaflurophosphate (1), the binuclear silver (I) complex (2) has been synthesized and both the compounds (1-2) have been characterized by different spectroscopic techniques. Finally, the solid state structure of 2 has been determined by single crystal X-ray diffraction studies. The role of non-covalent ?-? stacking interactions in stabilizing the self-assembly process appears to be of great importance in the title complex. Additional weak forces like C-H⋯? and anion⋯? interactions are also found to be operating in 2. A rare combination of these interactions in 2, of the type C-H⋯?/?⋯?/?⋯H-C and anion⋯?/?⋯?/?⋯anion, is observed, and this unusual supramolecular network is fully described here. Moreover, the proligand 1 is non-luminescent at room temperature in acetonitrile whereas complex 2 is luminescent. Closed shell d10-d10 interactions of Ag(I) is expected to be the sources of luminescence.

  10. Conformations of N-Heterocyclic Carbene Ligands in Ruthenium Complexes Relevant to Olefin Metathesis

    Science.gov (United States)

    Stewart, Ian C.; Benitez, Diego; O'Leary, Daniel J.; Tkatchouk, Ekaterina; Day, Michael W.; Goddard, William A.; Grubbs, Robert H.

    2009-01-01

    The structure of ruthenium-based olefin metathesis catalyst 3 and model ?-complex 5 in solution and in the solid state are reported. The N-tolyl ligands, due to their lower symmetry than the traditional N-mesityl substituents, complicate this analysis, but ultimately provide explanation for the enhanced reactivity of 3 relative to standard catalyst 2. The tilt of the N-tolyl ring provides additional space near the ruthenium center, which is consistent with the enhanced reactivity of 3 towards sterically demanding substrates. Due to this tilt, the more sterically accessible face bears the two methyl substituents of the N-aryl rings. These experimental studies are supported by computational studies of these complexes by DFT. The experimental data provides a means to validate the accuracy of the B3LYP and M06 functionals. B3LYP provides geometries that match X-ray crystal structural data more closely, though it leads to slightly less (?0.5 kcal mol?1) accuracy than M06 most likely because it underestimates attractive non-covalent interactions. PMID:19146414

  11. Antibacterial properties of water-soluble gold(I) N-heterocyclic carbene complexes.

    Science.gov (United States)

    Fernández, Gabriela A; Vela Gurovic, María S; Olivera, Nelda L; Chopa, Alicia B; Silbestri, Gustavo F

    2014-06-01

    The antibacterial properties of water-soluble gold(I) complexes [1-methyl-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C1), [1-mesityl-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C2), [1-(2,6-diisopropylphenyl)-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C3) and [1,3-bis(2,6-diisopropyl-4-sodiumsulfonatophenyl)imidazol-2-ylidene]gold(I) chloride (C4) and the respective ligands were assessed by agar diffusion and broth macrodilution methods against Gram-positives Staphylococcus aureus, Enterococcus faecalis and Micrococcus luteus and the Gram-negative bacteria Yersinia ruckeri, Pseudomonas aeruginosa and Escherichia coli. Viability after treatments was determined by direct plate count. The bactericidal activity displayed by C1 and C3 was comparable to that of AgNO3. PMID:24662463

  12. Synthesis of the first radiolabeled 188Re N-heterocyclic carbene complex and initial studies on its potential use in radiopharmaceutical applications.

    Science.gov (United States)

    Wagner, Thomas; Zeglis, Brian M; Groveman, Sam; Hille, Claudia; Pöthig, Alexander; Francesconi, Lynn C; Herrmann, Wolfgang A; Kühn, Fritz E; Reiner, Thomas

    2014-06-15

    A novel approach towards the synthesis of radiolabeled organometallic rhenium complexes is presented. We successfully synthesized and analyzed the first (188)Re-labeled N-heterocyclic biscarbene complex, trans-dioxobis(1,1'-methylene-bis(3,3'-diisopropylimidazolium-2-ylidene))(188)rhenium(V) hexafluorophosphate ((188)Re-4) via transmetalation using an air-stable and moisture-stable silver(I) biscarbene complex. In order to assess the viability of this complex as a potential lead structure for in vivo applications, the stability of the (188)Re-NHC complex was tested in physiologically relevant media. Ultimately, our studies illustrate that the complex we synthesized dissociates rapidly and is therefore unsuitable for use in radiopharmaceuticals. However, it is clear that the transmetalation approach we have developed is a rapid, robust, and mild method for the synthesis of new (188)Re-labeled carbene complexes. PMID:24889257

  13. Synthesis of Well-Defined Copper "N"-Heterocyclic Carbene Complexes and Their Use as Catalysts for a "Click Reaction": A Multistep Experiment that Emphasizes the Role of Catalysis in Green Chemistry

    Science.gov (United States)

    Ison, Elon A.; Ison, Ana

    2012-01-01

    A multistep experiment for an advanced synthesis lab course that incorporates topics in organic-inorganic synthesis and catalysis and highlights green chemistry principles was developed. Students synthesized two "N"-heterocyclic carbene ligands, used them to prepare two well-defined copper(I) complexes and subsequently utilized the complexes as…

  14. Influence of pyrazolate vs N-heterocyclic carbene ligands on the slow magnetic relaxation of homoleptic trischelate lanthanide(III) and uranium(III) complexes.

    Science.gov (United States)

    Meihaus, Katie R; Minasian, Stefan G; Lukens, Wayne W; Kozimor, Stosh A; Shuh, David K; Tyliszczak, Tolek; Long, Jeffrey R

    2014-04-23

    Two isostructural series of trigonal prismatic complexes, M(Bp(Me))3 and M(Bc(Me))3 (M = Y, Tb, Dy, Ho, Er, U; [Bp(Me)](-) = dihydrobis(methypyrazolyl)borate; [Bc(Me)](-) = dihydrobis(methylimidazolyl)borate) are synthesized and fully characterized to examine the influence of ligand donor strength on slow magnetic relaxation. Investigation of the dynamic magnetic properties reveals that the oblate electron density distributions of the Tb(3+), Dy(3+), and U(3+) metal ions within the axial ligand field lead to slow relaxation upon application of a small dc magnetic field. Significantly, the magnetization relaxation is orders of magnitude slower for the N-heterocyclic carbene complexes, M(Bc(Me))3, than for the isomeric pyrazolate complexes, M(Bp(Me))3. Further, investigation of magnetically dilute samples containing 11-14 mol % of Tb(3+), Dy(3+), or U(3+) within the corresponding Y(3+) complex matrix reveals thermally activated relaxation is favored for the M(Bc(Me))3 complexes, even when dipolar interactions are largely absent. Notably, the dilute species U(Bc(Me))3 exhibits Ueff ? 33 cm(-1), representing the highest barrier yet observed for a U(3+) molecule demonstrating slow relaxation. Additional analysis through lanthanide XANES, X-band EPR, and (1)H NMR spectroscopies provides evidence that the origin of the slower relaxation derives from the greater magnetic anisotropy enforced within the strongly donating N-heterocyclic carbene coordination sphere. These results show that, like molecular symmetry, ligand-donating ability is a variable that can be controlled to the advantage of the synthetic chemist in the design of single-molecule magnets with enhanced relaxation barriers. PMID:24650296

  15. N-heterocyclic carbene copper(I) catalysed N-methylation of amines using CO2

    KAUST Repository

    Santoro, Orlando

    2015-09-30

    The N-methylation of amines using CO2 and PhSiH3 as source of CH3 was efficiently performed using a N-heterocyclic carbene copper(I) complex. The methodology was found compatible with aromatic and aliphatic primary and secondary amines. Synthetic and computational studies have been carried out to support the proposed reaction mechanism for this transformation.

  16. Frustrated N-heterocyclic carbene-silylium ion Lewis pairs.

    Science.gov (United States)

    Silva Valverde, Miguel F; Theuergarten, Eileen; Bannenberg, Thomas; Freytag, Matthias; Jones, Peter G; Tamm, Matthias

    2015-05-28

    The reaction of the N-heterocyclic carbene 1,3-di-tert-butyl-4,5-dimethylimidazolin-2-ylidene () with trimethylsilyl iodide, triflate and triflimidate [Me3SiX, X = I, CF3SO3 (OTf), (CF3SO2)2N (NTf2)] by mixing the neat, liquid starting materials afforded the corresponding 2-(trimethylsilyl)imidazolium salts [()SiMe3]X as highly reactive, white crystalline solids. Only the triflimidate (X = NTf2) proved to be stable in solution and could be characterized by means of NMR spectroscopy (in C6D5Br) and X-ray diffraction analysis, whereas dissociation into free and Me3SiOTf was observed for the triflate system, in agreement with the trend derived by DFT calculations; the iodide was too insoluble for characterization. The compounds [()SiMe3]X showed the reactivity expected for frustrated carbene-silylium pairs, and treatment with carbon dioxide, tert-butyl isocyanate and diphenylbutadiyne gave the 1,2-addition products [()CO2SiMe3]X (X = I, OTf, NTf2), [()C(NtBu)OSiMe3]OTf and [()C(Ph)C(SiMe3)CCPh]OTf, respectively. Upon reaction with [AuCl(PPh3)], metal-chloride bond activation was observed, with formation of the cationic gold(i) complexes [()Au(PPh3)]X (X = OTf, NTf2). PMID:25912291

  17. Synthesis and Characterization of Divalent Manganese, Iron, and Cobalt Complexes in Tripodal Phenolate/N-Heterocyclic Carbene Ligand Environments

    DEFF Research Database (Denmark)

    Ka?ß, Martina; Hohenberger, Johannes

    2014-01-01

    Two novel tripodal ligands, (BIMPNMes,Ad,Me)? and (MIMPNMes,Ad,Me)2–, combining two types of donor atoms, namely, NHC and phenolate donors, were synthesized to complete the series of N-anchored ligands, ranging from chelating species with tris(carbene) to tris(phenolate) chelating arms. The complete ligand series offers a convenient way of tuning the electronic and steric environment around the metal center, thus, allowing for control of the complex’s reactivity. This series of divalent complexes of Mn, Fe, and Co was synthesized and characterized by 1H NMR, IR, and UV/vis spectroscopy as well as by single-crystal X-ray diffraction studies. Variable-temperature SQUID magnetization measurements in the range from 2 to 300 K confirmed high-spin ground states for all divalent complexes and revealed a trend of increasing zero-field splitting |D| from Mn(II), to Fe(II), to Co(II) complexes. Zero-field 57Fe Mo?ssbauer spectroscopy of the Fe(II) complexes 3, 4, 8, and 11 shows isomer shifts ? that increase gradually as carbenes are substituted for phenolates in the series of ligands. From the single-crystal structure determinations of the complexes, the different steric demand of the ligands is evident. Particularly, the molecular structure of 1?in which a pyridine molecule is situated next to the Mn–Cl bond?and those of azide complexes 2, 4, and 6 demonstrate the flexibility of these mixed-ligand derivatives, which, in contrast to the corresponding symmetrical TIMENR ligands, allow for side access of, e.g., organic substrates, to the reactive metal center.

  18. Ruthenium olefin metathesis catalysts featuring unsymmetrical N-heterocyclic carbenes.

    Science.gov (United States)

    Paradiso, Veronica; Bertolasi, Valerio; Costabile, Chiara; Grisi, Fabia

    2015-12-22

    New ruthenium Grubbs' and Hoveyda-Grubbs' second generation catalysts bearing N-alkyl/N-isopropylphenyl N-heterocyclic carbene (NHC) ligands with syn or anti backbone configuration were obtained and compared in model olefin metathesis reactions. Different catalytic efficiencies were observed depending on the size of the N-alkyl group (methyl or cyclohexyl) and on the backbone configuration. The presence of an N-cyclohexyl substituent determined the most significant reactivity differences between catalysts with syn or anti phenyl groups on the backbone. In particular, anti catalysts proved highly efficient, especially in the ring-closing metathesis (RCM) of encumbered diolefins, while syn catalysts showed low efficiency in the RCM of less hindered diolefins. This peculiar behavior, rationalized through DFT studies, was found to be related to the high propensity of these catalysts to give nonproductive metathesis events. Enantiopure anti catalysts were also tested in asymmetric metathesis reactions, where moderate enantioselectivities were observed. The steric and electronic properties of unsymmetrical NHCs with the N-cyclohexyl group were then evaluated using the corresponding rhodium complexes. While steric factors proved unimportant for both syn and anti NHCs, a major electron-donating character was found for the unsymmetrical NHC with anti phenyl substituents on the backbone. PMID:26608162

  19. Structure, bonding and energetics of N-heterocyclic carbene (NHC) stabilized low oxidation state group 2 (Be, Mg, Ca, Sr and Ba) metal complexes: A theoretical study

    Indian Academy of Sciences (India)

    Ashim Baishya; V Rao Mundlapati; Sharanappa Nembenna; Himansu S Biswal

    2014-11-01

    A series of N-heterocyclic carbene stabilized low oxidation state group 2 metal halide and hydrides with metal-metal bonds ([L(X) M-M(X) L]; L = NHC ((CHNH)2C:), M = Be, Mg, Ca, Sr and Ba, and X = Cl or H) has been studied by computational methods. The main objective of this study is to predict whether it is possible to stabilize neutral ligated low oxidation state alkaline-earth metal complexes with metal-metal bonds. The homolytic metal-metal Bond Dissociation Energy (BDE) calculation, Natural Bond Orbital (NBO) and Energy Decomposition Analyses (EDA) on density functional theory (DFT) optimized [L(X)M-M(X)L] complexes revealed that they are as stable as their -diketiminate, guanidinate and -diimine counterparts. The optimized structures of the complexes are in trans-linear geometries. The bond order analyses such as Wiberg Bond Indices (WBI) and Fuzzi Bond Order (FBO) confirm the existence of single bond between two metal atoms, and it is covalent in nature.

  20. Visible-Light Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic Carbene-Isoquinoline Complex

    Energy Technology Data Exchange (ETDEWEB)

    Thoi, VanSara; Kornienko, Nick; Margarit, C; Yang, Peidong; Chang, Christopher

    2013-06-07

    The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni(Prbimiq1)]2+ (1c, where Prbimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (Ecat = 1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s1, respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion.

  1. Visible-light photoredox catalysis: selective reduction of carbon dioxide to carbon monoxide by a nickel N-heterocyclic carbene-isoquinoline complex.

    Science.gov (United States)

    Thoi, V Sara; Kornienko, Nikolay; Margarit, Charles G; Yang, Peidong; Chang, Christopher J

    2013-09-25

    The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene-amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni((Pr)bimiq1)](2+) (1c, where (Pr)bimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (E(cat) = -1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s(-1), respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion. PMID:24033186

  2. The Depolymerization of Poly(Ethylene Terephthalate) (PET) Using N-Heterocyclic Carbenes from Ionic Liquids

    Science.gov (United States)

    Kamber, Nahrain E.; Tsujii, Yasuhito; Keets, Kate; Waymouth, Robert M.; Pratt, Russell C.; Nyce, Gregory W.; Hedrick, James L.

    2010-01-01

    The depolymerization of the plastic polyethylene terephthalate (PET or PETE) is described in this laboratory procedure. The transesterification reaction used to depolymerize PET employs a highly efficient N-heterocyclic carbene catalyst derived from a commercially available imidazolium ionic liquid. N-heterocyclic carbenes are potent nucleophilic…

  3. Olefin Metathesis With Ruthenium-Arene Catalysts Bearing N-Heterocyclic Carbene Ligands

    Science.gov (United States)

    Delaude, Lionel; Demonceau, Albert

    In this chapter, we summarize the main results of our investigations on the ring-opening metathesis polymerization (ROMP) of cyclooctene catalyzed by various ruthenium (Ru)-arene complexes bearing imidazolin-2-ylidene, imidazolidin- 2-ylidene, or triazolin-5-ylidene ligands. Three major findings emerged from this study. First, we underscored the intervention of a photochemical activation step due to visible light illumination. Second, we established that the presence of an endocyclic double bond in the carbene ligand central heterocycle was not crucial to achieve high catalytic efficiencies. Third, we demonstrated that ortho-metallation of the N-heterocyclic carbene (NHC) ligand by the Ru center led to inactive catalysts.

  4. Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines

    Science.gov (United States)

    Chung, Lai-Hon; Lo, Hoi-Shing; Ng, Sze-Wing; Ma, Dik-Lung; Leung, Chung-Hang; Wong, Chun-Yuen

    2015-01-01

    Iridium(III) hydrido complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-butylimidazolin-2-ylidene)phenyl anion (C1^C^C1) or 1,3-bis(3-butylbenzimidazolin-2-ylidene)phenyl anion (C2^C^C2) and aromatic diimine (2,2?-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4?-dimethyl-2,2?-bipyridine (Me2bpy), or dipyrido-[3,2-f:2?,3?-h]-quinoxaline (dpq)) in the form of [Ir(C^C^C)(N^N)(H)]+ have been prepared. Crystal structures for these complexes show that the Ir–CNHC distances are 2.043(5)–2.056(5) Å. The hydride chemical shifts for complexes bearing C1^C^C1 (?20.6 to ?20.3?ppm) are more upfield than those with C2^C^C2 (?19.5 and ?19.2?ppm), revealing that C1^C^C1 is a better electron donor than C2^C^C2. Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (??=?340–530?nm (????103?dm3 mol?1 cm?1)) originate from a d?(IrIII)????*(N^N) metal-to-ligand charge transfer transition, where the d?(IrIII) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellow-spectral region (553–604?nm in CH3CN and CH2Cl2) upon photo-excitation with quantum yields of 10?3–10?1. PMID:26487542

  5. Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines

    Science.gov (United States)

    Chung, Lai-Hon; Lo, Hoi-Shing; Ng, Sze-Wing; Ma, Dik-Lung; Leung, Chung-Hang; Wong, Chun-Yuen

    2015-10-01

    Iridium(III) hydrido complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-butylimidazolin-2-ylidene)phenyl anion (C1^C^C1) or 1,3-bis(3-butylbenzimidazolin-2-ylidene)phenyl anion (C2^C^C2) and aromatic diimine (2,2?-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4?-dimethyl-2,2?-bipyridine (Me2bpy), or dipyrido-[3,2-f:2?,3?-h]-quinoxaline (dpq)) in the form of [Ir(C^C^C)(N^N)(H)]+ have been prepared. Crystal structures for these complexes show that the Ir–CNHC distances are 2.043(5)–2.056(5) Å. The hydride chemical shifts for complexes bearing C1^C^C1 (?20.6 to ?20.3?ppm) are more upfield than those with C2^C^C2 (?19.5 and ?19.2?ppm), revealing that C1^C^C1 is a better electron donor than C2^C^C2. Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (??=?340–530?nm (????103?dm3 mol?1 cm?1)) originate from a d?(IrIII)????*(N^N) metal-to-ligand charge transfer transition, where the d?(IrIII) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellow-spectral region (553–604?nm in CH3CN and CH2Cl2) upon photo-excitation with quantum yields of 10?3–10?1.

  6. Neutral and Cationic Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes: Reactivity in Selected Olefin Metathesis Reactions and Immobilization on Silica.

    Science.gov (United States)

    Sen, Suman; Schowner, Roman; Imbrich, Dominik A; Frey, Wolfgang; Hunger, Michael; Buchmeiser, Michael R

    2015-09-21

    The synthesis and single-crystal X-ray structures of the novel molybdenum imido alkylidene N-heterocyclic carbene complexes [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf)2] (3), [Mo(N-2,6-Me2C6H3)(IMes)(CHCMe2Ph)(OTf)2] (4), [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf){OCH(CF3)2}] (5), [Mo(N-2,6-Me2C6H3)(CH3CN)(IMesH2)(CHCMe2Ph)(OTf)](+)BArF(-) (6), [Mo(N-2,6-Cl2C6H3)(IMesH2)(CHCMe3)(OTf)2] (7) and [Mo(N-2,6-Cl2C6H3)(IMes)(CHCMe3)(OTf)2] (8) are reported (IMesH2=1,3-dimesitylimidazolidin-2-ylidene, IMes=1,3-dimesitylimidazolin-2-ylidene, BArF(-)=tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate, OTf=CF3SO3(-)). Also, silica-immobilized versions I1 and I2 were prepared. Catalysts 3-8, I1 and I2 were used in homo-, cross-, and ring-closing metathesis (RCM) reactions and in the cyclopolymerization of ?,?-diynes. In the RCM of ?,?-dienes, in the homometathesis of 1-alkenes, and in the ethenolysis of cyclooctene, turnover numbers (TONs) up to 100,000, 210,000 and 30,000, respectively, were achieved. With I1 and I2, virtually Mo-free products were obtained (<3?ppm Mo). With 1,6-hepta- and 1,7-octadiynes, catalysts 3, 4, and 5 allowed for the regioselective cyclopolymerization of 4,4-bis(ethoxycarbonyl)-1,6-heptadiyne, 4,4-bis(hydroxymethyl)-1,6-heptadiyne, 4,4-bis[(3,5-diethoxybenzoyloxy)methyl]-1,6-heptadiyne, 4,4,5,5-tetrakis(ethoxycarbonyl)-1,7-octadiyne, and 1,6-heptadiyne-4-carboxylic acid, underlining the high functional-group tolerance of these novel Group?6 metal alkylidenes. PMID:26249141

  7. Latent ruthenium–indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand

    Science.gov (United States)

    Schmid, Thibault E; Modicom, Florian; Dumas, Adrien; Borré, Etienne; Toupet, Loic

    2015-01-01

    Summary A silver-free methodology was developed for the synthesis of unprecedented N-heterocyclic carbene ruthenium indenylidene complexes bearing a bidentate picolinate ligand. The highly stable (SIPr)(picolinate)RuCl(indenylidene) complex 4a (SIPr = 1,3-bis(2-6-diisopropylphenyl)imidazolidin-2-ylidene) demonstrated excellent latent behaviour in ring closing metathesis (RCM) reaction and could be activated in the presence of a Brønsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM) and enyne metathesis reactions. PMID:26425213

  8. Latent ruthenium-indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand.

    Science.gov (United States)

    Schmid, Thibault E; Modicom, Florian; Dumas, Adrien; Borré, Etienne; Toupet, Loic; Baslé, Olivier; Mauduit, Marc

    2015-01-01

    A silver-free methodology was developed for the synthesis of unprecedented N-heterocyclic carbene ruthenium indenylidene complexes bearing a bidentate picolinate ligand. The highly stable (SIPr)(picolinate)RuCl(indenylidene) complex 4a (SIPr = 1,3-bis(2-6-diisopropylphenyl)imidazolidin-2-ylidene) demonstrated excellent latent behaviour in ring closing metathesis (RCM) reaction and could be activated in the presence of a Brønsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM) and enyne metathesis reactions. PMID:26425213

  9. Dehydrogenative Coupling of Primary Alcohols To Form Esters Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex

    DEFF Research Database (Denmark)

    SØlvhØj, Amanda Birgitte; Madsen, Robert

    2011-01-01

    The ruthenium complex [RuCl2(IiPr)(p-cymene)] catalyzes the direct condensation of primary alcohols into esters and lactones with the release of hydrogen gas. The reaction is most effective with linear aliphatic alcohols and 1,4-diols and is believed to proceed with a ruthenium dihydride as the catalytically active species.

  10. Structural variation, dynamics, and catalytic application of palladium(II) complexes of di-N-heterocyclic carbene-amine ligands.

    Science.gov (United States)

    Houghton, Jennifer; Dyson, Gavin; Douthwaite, Richard E; Whitwood, Adrian C; Kariuki, Benson M

    2007-07-28

    A series of palladium(II) complexes incorporating di-NHC-amine ligands has been prepared and their structural, dynamic and catalytic behaviour investigated. The complexes [trans-(kappa(2)-(tBu)CN(Bn)C(tBu))PdCl(2)] (12) and [trans-(kappa(2)-(Mes)CN(H)C(Mes))PdCl(2)] (13) do not exhibit interaction between the amine nitrogen and palladium atom respectively. NMR spectroscopy between -40 and 25 degrees C shows that the di-NHC-amine ligand is flexible expressing C(s) symmetry and for 13 rotation of the mesityl groups is prevented. In the related C(1) complex [(kappa(3)-(tBu)CN(H)C(tBu))PdCl][Cl] (14) coordination of NHC moieties and amine nitrogen atom is observed between -40 and 25 degrees C. Reaction between 12-14 and two equivalents of AgBF(4) in acetonitrile gives the analogous complexes [trans-(kappa(2)-(tBu)CN(Bn)C(tBu))Pd(MeCN)(2)][BF(4)](2) (15), [trans-(kappa(2)-(Mes)CN(H)C(Mes))Pd(MeCN)(2)][BF(4)](2) (16) and [(kappa(3)-(tBu)CN(H)C(tBu))Pd(MeCN)][BF(4)](2) (17) indicating that ligand structure determines amine coordination. The single crystal X-ray structures of 12, 17 and two ligand imidazolium salt precursors (tBu)C(H)N(Bn)C(H)(tBu)][Cl](2) (2) and [(tBu)C(H)N(H)C(H)(tBu)][BPh(4)](2) (4) have been determined. Complexes 12-14 and 15-17 have been shown to be active precatalysts for Heck and hydroamination reactions respectively. PMID:17622424

  11. Accessing Sodium Ferrate Complexes Containing Neutral and Anionic N-Heterocyclic Carbene Ligands: Structural, Synthetic, and Magnetic Insights.

    Science.gov (United States)

    Maddock, Lewis C H; Cadenbach, Thomas; Kennedy, Alan R; Borilovic, Ivana; Aromí, Guillem; Hevia, Eva

    2015-09-21

    This study reports the synthesis and single-crystal X-ray crystallographic, NMR spectroscopic, and magnetic characterization of a series of sodium ferrates using bis(amide) Fe(HMDS)2 as a precursor (HMDS = 1,1,1,3,3,3-hexamethyldisilazide). Reaction with sodium reagents NaHMDS and NaCH2SiMe3 in hexane afforded donor-solvent-free sodium ferrates [{NaFe(HMDS)3}?] (1) and [{NaFe(HMDS)2(CH2SiMe3)}?] (2), respectively, which exhibit contacted ion pair structures, giving rise to new polymeric chain arrangements made up of a combination of inter- and intramolecular Na···Me(HMDS) electrostatic interactions. Addition of the unsaturated NHC IPr (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) to 1 and 2 caused deaggregation of their polymeric structures to form discrete NHC-stabilized solvent-separated ion pairs [Na(IPr)2](+)[Fe(HMDS)3](-) (3) and [(THF)3·NaIPr](+)[Fe(HMDS)2CH2SiMe3](-) (4), where in both cases, the NHC ligand coordinates preferentially to Na. In contrast, when IPr is sequentially reacted with the single-metal reagents NaCH2SiMe3 and Fe(HMDS)2, the novel heteroleptic ferrate (THF)3Na[:C{[N(2,6-(i)Pr2C6H3)]2CHCFe(HMDS)2}] (5) is obtained. This contains an anionic NHC ligand acting as an unsymmetrical bridge between the two metals, coordinating through its abnormal C4 position to Fe and its normal C2 position to Na. The formation of 5 can be described as an indirect ferration process where IPr is first metalated at the C4 position by the polar sodium alkyl reagent, which in turn undergoes transmetalation to the more electronegative Fe(HMDS)2 fragment. Treatment of 5 with 1 molar equiv of methyl triflate (MeOTf) led to the isolation and structural elucidation of the neutral abnormal NHC (aNHC) tricoordinate iron complex [CH3C{[N(2,6-iPr2C6H3)]2CHCFe(HMDS)2}] (6) with the subsequent elimination of NaOTf, disclosing the selectivity of complex 5 to react with this electrophile via its C2 position, leaving its Fe-C4 and Fe-N bonds intact. The magnetic susceptibility properties of compounds 1-6 have been examined. This study revealed a drastic change of magnetic susceptibility in replacing a pure ? donor from an idealized trigonal coordination environment by an NHC ? donating character. PMID:26331635

  12. Synthesis of the first radiolabeled 188Re N-heterocyclic carbene complex and initial studies on its potential use in radiopharmaceutical applications

    OpenAIRE

    Wagner, Thomas; Zeglis, Brian M; Groveman, Sam; Hille, Claudia; Pöthig, Alexander; Francesconi, Lynn C.; Herrmann, Wolfgang A.; Fritz E. Kühn; Reiner, Thomas

    2014-01-01

    A novel approach towards the synthesis of radiolabeled organometallic rhenium complexes is presented. We successfully synthesized and analyzed the first 188Re-labeled N-heterocyclic biscarbene complex, trans-dioxobis(1,1?-methylene-bis(3,3?-diisopropylimidazolium-2-ylidene))188rhenium(V) hexafluorophosphate (188Re-4) via transmetalation using an air-stable and moisture-stable silver(I) biscarbene complex. In order to assess the viability of this complex as a potential lead structure for in vi...

  13. Comproportionation of Cationic and Anionic Tungsten Complexes Having an N-Heterocyclic Carbene Ligand to Give the Isolable 17-Electron Tungsten Radical, CpW(CO)2(IMes)•

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, John A.; Franz, James A.; van der Eide, Edwin F.; Walter, Eric D.; Petersen, Jeffrey L.; DuBois, Daniel L.; Bullock, R. Morris

    2011-09-21

    A series consisting of a tungsten anion, radical and cation, supported by the N-heterocyclic carbene IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and spanning formal oxidation states W(0), W(I) and W(II), has been synthesized, isolated, and characterized. Reaction of the hydride CpW(CO)2(IMes)H with KH and 18 crown 6 gives the tungsten anion [CpW(CO)2(IMes)]-[K(18 crown 6)]+. The crystal structure of this complex shows that the K+ interacts not only with the oxygen atoms in the crown ether, but also with the carbonyl oxygens. The electrochemical oxidation of [CpW(CO)2(IMes)]- in acetonitrile is fully reversible (E½ = ?1.65 V vs Cp2Fe+•/0) at all scan rates, indicating that CpW(CO)2(IMes)• is a persistent radical. Hydride transfer from CpW(CO)2(IMes)H to Ph3C+PF6 affords [cis-CpW(CO)2(IMes)(MeCN)]+PF6 . Comproportionation of [CpW(CO)2(IMes)]- with [CpW(CO)2(IMes)(MeCN)]+ gives the 17-electron tungsten radical CpW(CO)2(IMes)•. This complex shows paramagnetically shifted resonances in 1H NMR spectra and has been characterized by IR spectroscopy, low-temperature EPR spectroscopy, and X-ray diffraction. CpW(CO)2(IMes)• is very stable with respect to disproportionation and dimerization. NMR studies of degenerate electron transfer between CpW(CO)2(IMes)• and [CpW(CO)2(IMes)]- are reported. DFT calculations were carried out on CpW(CO)2(IMes)H, as well as on related complexes bearing NHC ligands with N,N´ substituents Me [CpW(CO)2(IMe)H] or H [CpW(CO)2(IH)H] to compare to the experimentally studied IMes complexes with mesityl substituents. These calculations reveal W H homolytic bond dissociation energies (BDEs) to decrease with increasing steric bulk of the NHC ligand, from 67 for CpW(CO)2(IH)H to 64 for CpW(CO)2(IMe)H to 63 kcal/mol for CpW(CO)2(IMes)H. The calculated spin density at W for CpW(CO)2(IMes)• is 0.63. The W radicals CpW(CO)2(IMe)• and CpW(CO)2(IH)• are calculated to form weak W W bonds. The weakly bonded complexes [CpW(CO)2(IMe)]2 and [CpW(CO)2(IH)]2, are predicted to have W-W BDEs of 6 and 18 kcal/mol, respectively, and to dissociate readily to the W-centered radicals CpW(CO)2(IMe)• and CpW(CO)2(IH)•. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  14. Comproportionation of cationic and anionic tungsten complexes having an N-heterocyclic carbene ligand to give the isolable 17-electron tungsten radical CpW(CO)2(IMes)(•).

    Science.gov (United States)

    Roberts, John A S; Franz, James A; van der Eide, Edwin F; Walter, Eric D; Petersen, Jeffrey L; DuBois, Daniel L; Bullock, R Morris

    2011-09-21

    A series consisting of a tungsten anion, radical, and cation, supported by the N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and spanning formal oxidation states W(0), W(I), and W(II), has been synthesized, isolated, and characterized. Reaction of the hydride CpW(CO)(2)(IMes)H with KH and 18-crown-6 gives the tungsten anion [CpW(CO)(2)(IMes)](-)[K(18-crown-6)](+). Electrochemical oxidation of [CpW(CO)(2)(IMes)](-) in MeCN (0.2 M (n)Bu(4)N(+)PF(6)(-)) is fully reversible (E(1/2) = -1.65 V vs Cp(2)Fe(+•/0)) at all scan rates, indicating that CpW(CO)(2)(IMes)(•) is a persistent radical. Hydride transfer from CpW(CO)(2)(IMes)H to Ph(3)C(+)PF(6)(-) in MeCN affords [cis-CpW(CO)(2)(IMes)(MeCN)](+)PF(6)(-). Comproportionation of [CpW(CO)(2)(IMes)](-) with [CpW(CO)(2)(IMes)(MeCN)](+) gives the 17-electron tungsten radical CpW(CO)(2)(IMes)(•). This complex shows paramagnetically shifted resonances in the (1)H NMR spectrum and has been characterized by IR spectroscopy, low-temperature EPR spectroscopy, and X-ray diffraction. CpW(CO)(2)(IMes)(•) is stable with respect to disproportionation and dimerization. NMR studies of degenerate electron transfer between CpW(CO)(2)(IMes)(•) and [CpW(CO)(2)(IMes)](-) are reported. DFT calculations were carried out on CpW(CO)(2)(IMes)H, as well as on related complexes bearing NHC ligands with N,N' substituents Me (CpW(CO)(2)(IMe)H) or H (CpW(CO)(2)(IH)H) to compare to the experimentally studied IMes complexes with mesityl substituents. These calculations reveal that W-H homolytic bond dissociation energies (BDEs) decrease with increasing steric bulk of the NHC ligand, from 67 to 64 to 63 kcal mol(-1) for CpW(CO)(2)(IH)H, CpW(CO)(2)(IMe)H, and CpW(CO)(2)(IMes)H, respectively. The calculated spin density at W for CpW(CO)(2)(IMes)(•) is 0.63. The W radicals CpW(CO)(2)(IMe)(•) and CpW(CO)(2)(IH)(•) are calculated to form weak W-W bonds. The weakly bonded complexes [CpW(CO)(2)(IMe)](2) and [CpW(CO)(2)(IH)](2) are predicted to have W-W BDEs of 6 and 18 kcal mol(-1), respectively, and to dissociate readily to the W-centered radicals CpW(CO)(2)(IMe)(•) and CpW(CO)(2)(IH)(•). PMID:21786753

  15. N, N?-Olefin functionalized Bis-Imidazolium Pd(II) chloride N-Heterocyclic carbene complex builds a supramolecular framework and shows catalytic efficacy for `C–C' coupling reactions

    Indian Academy of Sciences (India)

    Gourisankar Roymahapatra; Tapastaru Samanta; Saikat Kumar Seth; Ambikesh Mahapatra; Shyamal Kumar Chattopadhyay; Joydev Dinda

    2015-06-01

    The ligand 3,3?-(-phenylenedimethylene)bis{1-(2-methylallyl)} imidazolium bromide (1) and its Palladium(II) N-heterocyclic carbene (NHC) complex (3) has been synthesized and characterized by several spectroscopic techniques and the solid-state structure of 3 has been determined by single crystal X-ray diffraction studies. The Pd(II) complex possesses ring head to tail – stacking interactions (3.767 A$^{\\circ}$) through imidazole rings. Complex 3 catalyzes Suzuki-Miyaura `C–C' coupling reaction. DFT calculations have been used to understand the HOMO/LUMO energy and hence the stability and reactivity of Pd(II) complex in syn and anti-configuration.

  16. Hydrogen-bonding pincer complexes with two protic N-heterocyclic carbenes from direct metalation of a 1,8-bis(imidazol-1-yl)carbazole by platinum, palladium, and nickel.

    Science.gov (United States)

    Marelius, David C; Darrow, Evan H; Moore, Curtis E; Golen, James A; Rheingold, Arnold L; Grotjahn, Douglas B

    2015-07-27

    Pincer protic N-heterocyclic carbene (PNHC) complexes were synthesized by direct metalation, the formation of a metal carbon bond from an unfunctionalized C?H bond in a single synthetic step. Significantly, direct metalation succeeded even for a first-row metal, nickel. The chloride complexes were isolated and then converted to the acetate, triflate, or in the platinum case, a hydride analogue. Crystal structures and (1) H, (13) C, and (15) N?NMR data, as well as IR spectra, document the effects of intramolecular hydrogen bonding and the planar but flexible pincer framework. Anti-Markovnikov addition of O?H bonds to alkynes, including catalyzed alkyne hydration, were demonstrated on the Pt triflate analog. PMID:26134355

  17. Evaluation of an olefin metathesis pre-catalyst with a bulky and electron-rich N-heterocyclic carbene

    KAUST Repository

    Manzini, Simone

    2015-03-01

    The commercially-available metathesis pre-catalyst M23 has been evaluated alongside new complex [RuCl2((3-phenyl)indenylidene)(PPh3)(SIPrOMe)] (1), which bears a para-methoxy-substituted N-heterocyclic carbene ligand. Several model metathesis reactions could be conducted using only parts-per-million levels of ruthenium catalyst. The effects of the different NHC ligands on reactivity have been explored.

  18. N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis

    Directory of Open Access Journals (Sweden)

    Rob De Vreese

    2012-03-01

    Full Text Available The interplay between metals and N-heterocyclic carbenes (NHCs has provided a window of opportunities for the development of novel catalytic strategies within the past few years. The recent successful combination of Brønsted acids with NHCs has added a new dimension to the field of cooperative catalysis, enabling the stereoselective synthesis of functionalized pyrrolidin-2-ones as valuable scaffolds in heterocyclic chemistry. This Commentary will briefly highlight the concept of N-heterocyclic carbene/Brønsted acid cooperative catalysis as a new and powerful methodology in organic chemistry.

  19. A Tungsten Complex with a Bidentate, Hemilabile N-Heterocyclic Carbene Ligand, Facile Displacement of the Weakly Bound W-(C=C) Bond, and the Vulnerability of the NHC Ligand Toward Catalyst Deactivation During Ketone Hydrogenation

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Fan; Dioumaev, Vladimir K.; Szalda, David J.; Hanson, Jonathan; Bullock, R. Morris

    2007-09-24

    The initial reaction observed between N-heterocyclic carbene IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO)2(PPh3)H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMes)H]+[CpM(CO)2(PPh3)]– . At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO)2(PR3)H (M = Mo, W; R = Me, Ph) produces CpM(CO)2(IMes)H. Hydride transfer from CpW(CO)2(IMes)H to Ph3C+B(C6F5)4- gives CpW(CO)2(IMes)+B(C6F5)4- which was crystallographically characterized using x-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H2, THF, ketones or alcohols. Reaction of CpW(CO)2(IMes)+ with H2 gives the dihydride complex [CpW(CO)2(IMes)(H)2]+. Addition of Et2CH–OH to CpW(CO)2(IMes)+B(C6F5)4- gives the alcohol complex [CpM(CO)2(IMes)(Et2CH–OH)]+[B(C6F5)4]– which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H2 to the ketone complex [CpW(CO)2(IMes)(Et2C=O)]+[B(C6F5)4]– produces an equilibrium with the dihydride [CpW(CO)2(IMes)(H)2]+ (Keq = 1.1 ? 103 at 25 °C). The tungsten ketone complex [CpW(CO)2(IMes)(Et2C=O)]+[B(C6F5)4]– serves as a modest catalyst for hydrogenation of Et2C=O to Et2CH–OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]+B(C6F5)4-, indicating that these catalysts with N-heterocyclic carbenes ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

  20. Synthesis of Enantioenriched ?,?-Disubstituted Cyclopentenes Catalyzed by N-Heterocyclic Carbenes

    OpenAIRE

    Phillips, Eric M.; Wadamoto, Manabu; Scheidt, Karl A.

    2009-01-01

    The desymmetrization of 1,3-diketones using N-heterocyclic carbenes results in the formation of highly enantioenriched cyclopentenes in good yield. The reaction proceeds through a catalytic intramolecular aldol reaction and subsequent ?-lactone formation. The expulsion of carbon dioxide at mild reaction temperatures affords the cyclopentene products.

  1. Bis-N-heterocyclic Carbene Aminopincer Ligands Enable High Activity in Ru-Catalyzed Ester Hydrogenation.

    Science.gov (United States)

    Filonenko, Georgy A; Aguila, Mae Joanne B; Schulpen, Erik N; van Putten, Robbert; Wiecko, Jelena; Müller, Christian; Lefort, Laurent; Hensen, Emiel J M; Pidko, Evgeny A

    2015-06-24

    Bis-N-heterocyclic carbene (NHC) aminopincer ligands were successfully applied for the first time in the catalytic hydrogenation of esters. We have isolated and characterized a well-defined catalyst precursor as a dimeric [Ru2(L)2Cl3]PF6 complex and studied its reactivity and catalytic performance. Remarkable initial activities up to 283,000 h(-1) were achieved in the hydrogenation of ethyl hexanoate at only 12.5 ppm Ru loading. A wide range of aliphatic and aromatic esters can be converted with this catalyst to corresponding alcohols in near quantitative yields. The described synthetic protocol makes use of air-stable reagents available in multigram quantities, rendering the bis-NHC ligands an attractive alternative to the conventional phosphine-based systems. PMID:26052835

  2. Main-chain organometallic polymers comprising redox-active iron(II) centers connected by ditopic N-heterocyclic carbenes

    OpenAIRE

    Mercs, Laszlo; Neels, Antonia; Stoeckli-Evans, Helen; Albrecht, Martin

    2009-01-01

    Main-chain organometallic polymers were synthesized from bimetallic iron(II) complexes containing a ditopic N-heterocyclic carbene (NHC) ligand [(cp)(CO)LFe(NHC?NHC)Fe(cp)(CO)L]X? (where NHC?NHC represents a bridging dicarbene ligand, L = I? or CO). Addition of a diimine ligand such as pyrazine or 4,4?-bipyridine, interconnected these bimetallic complexes and gave the corresponding co-polymers containing iron centers that are alternately linked by a dicarbene and a diimine ligand. Diimine coo...

  3. Catalytic Dynamic Kinetic Resolutions with N-Heterocyclic Carbenes: Asymmetric Synthesis of Highly Substituted ?-Lactones

    OpenAIRE

    Cohen, Daniel T.; Eichman, Chad C.; Phillips, Eric M.; Zarefsky, Emily R.; Scheidt, Karl A.

    2012-01-01

    An N-heterocyclic carbene (NHC)-catalyzed dynamic kinetic resolution of racemic ?-substituted ?-keto esters has been developed. This method relies on the epimerization of an NHC-enol intermediate before subsequent aldol/acylation events. Highly substituted ?-lactones are produced in good yield (50–88%) with good to excellent diastereoselectivity (5:1 to 20:1 dr) and excellent enantioselectivity (up to 99% ee).

  4. Mechanistic Investigation of the Ruthenium–N-Heterocyclic-Carbene-Catalyzed Amidation of Alcohols and Amines

    DEFF Research Database (Denmark)

    Makarov, Ilya; Fristrup, Peter; Madsen, Robert

    2012-01-01

    The mechanism of the ruthenium–N-heterocyclic-carbene-catalyzed formation of amides from alcohols and amines was investigated by experimental techniques (Hammett studies, kinetic isotope effects) and by a computational study by using dispersion-corrected density functional theory (DFT/ M06). The Hammett study indicated that a small positive charge builds-up at the benzylic position in the transition state of the turnover-limiting step. The kinetic isotope effect was determined to be 2.29ACHTUNGT...

  5. N-heterocyclic carbene organocatalytic reductive ?,?-coupling reactions of nitroalkenes via radical intermediates.

    Science.gov (United States)

    Du, Yu; Wang, Yuhuang; Li, Xin; Shao, Yaling; Li, Guohui; Webster, Richard D; Chi, Yonggui Robin

    2014-11-01

    An unprecedented N-heterocyclic carbene catalytic reductive ?,?-carbon coupling of ?,?-nitroalkenes, by using an organic substrate to mimic the one-electron oxidation role of the pyruvate ferredoxin oxidoreductase (PFOR) in living systems, has been developed. The reaction goes through a radical anion intermediate generated under a catalytic redox process. For the first time, the presence of radical anion intermediate in NHC organocatalysis is observed and clearly verified. PMID:25343564

  6. Expanding the catalytic activity of nucleophilic N-heterocyclic carbenes for transesterification reactions.

    Science.gov (United States)

    Nyce, Gregory W; Lamboy, Jorge A; Connor, Eric F; Waymouth, Robert M; Hedrick, James L

    2002-10-17

    [reaction: see text] Currently, there is a renewed interest in reactions that are catalyzed by organic compounds. Typical organic catalysts for acylation or transesterification reactions are based on either nucleophilic tertiary amines or phosphines. This communication discusses the use of nucleophilic N-heterocyclic carbenes as efficient transesterification catalysts. These relatively unexplored and highly versatile organic catalysts were found to be mild, selective, and more active than traditional organic nucleophiles. PMID:12375894

  7. Expanded ring N-heterocyclic carbene adducts of group 15 element trichlorides: synthesis and reduction studies.

    Science.gov (United States)

    Sidiropoulos, Anastas; Osborne, Brooke; Simonov, Alexandr N; Dange, Deepak; Bond, Alan M; Stasch, Andreas; Jones, Cameron

    2014-10-21

    Reactions of the expanded ring N-heterocyclic carbene, 6-Dip (:C{N(Dip)CH2}2CH2, Dip = 2,6-diisopropylphenyl), with group 15 element trichlorides have yielded the monomeric complexes, [(6-Dip)ECl3] (E = P, As or Sb), two examples of which (E = P and Sb) have been crystallographically characterised. Reduction of [(6-Dip)PCl3] with KC8 yielded the unusual tetraphosphorus dicationic complex, [(6-Dip)2(?-P4)]Cl2, the X-ray crystal structure of which shows it to be an ion-separate salt. The compound can also be prepared from the direct reaction of excess 6-Dip with PCl3. Treatment of the cyclic amidinium salt, [6-MesH]Br (6-MesH = [HC{N(Mes)CH2}2CH2](+), Mes = mesityl) with KC8, leads to reductive coupling of the heterocycle and formation of the hindered bis(hexahydropyrimidine), (6-MesH)2. An X-ray crystallographic analysis of (6-MesH)2 shows the compound to have a long central C-C bond, while an electrochemical analysis reveals it to undergo an irreversible two-electron oxidation in dichloromethane solutions. PMID:25166429

  8. Ruthenium(II) and osmium(II) complexes bearing bipyridine and the N-heterocyclic carbene-based C^N^C pincer ligand: an experimental and density functional theory study.

    Science.gov (United States)

    Chung, Lai-Hon; Cho, Ka-Sin; England, Jason; Chan, Siu-Chung; Wieghardt, Karl; Wong, Chun-Yuen

    2013-09-01

    Ruthenium(II) and osmium(II) complexes [M(C^N^C)(N^N)L](n+) (L = Cl(-), n = 1; L = CH3CN, t-BuNC, n = 2) containing a neutral tridentate N-heterocyclic carbene (NHC)-based pincer ligand, either 2,6-bis(1-butylimidazol-2-ylidene)pyridine (C(1)^N^C(1)) or 2,6-bis(3-butylbenzimidazol-2-ylidene)pyridine (C(2)^N^C(2)), and a neutral 2,2'-bipyridine-type aromatic diimine have been prepared. Investigations into the effects of varying M (Ru and Os), C^N^C, N^N, and L on the structural, electrochemical, absorption, and emission characteristics associated with [M(C^N^C)(N^N)L](n+) are presented. Interestingly, spectroscopic findings and time-dependent density functional theory (TD-DFT) calculations in this work support a d?(Ru(II)/Os(II)) ? ?*(N^N) metal-to-ligand charge transfer (MLCT) assignment for the lowest-energy transition in [M(C^N^C)(N^N)L](n+) and not a d?(Ru(II)/Os(II)) ? ?*(C^N^C) MLCT assignment. This is in stark contrast to [Ru(tpy)(bpy)Cl](+) and [Os(tpy)(bpy)Cl](+) (tpy = 2,2':6',2?-terpyridine, bpy = 2,2'-bipyridine) for which the lowest-energy transitions are assigned as d?(Ru/Os) ? ?*(tpy) MLCT transitions. [Ru(II)(C^N^C)(N^N)L](n+) is emissive with emission maxima of around 600-700 nm observed upon photoexcitation of their d?(Ru(II)) ? ?*(N^N) MLCT bands. The electronic structures for [Ru(C^N^C)(N^N)Cl](0) have also been probed by spectroelectrochemistry, electron paramagnetic resonance (EPR) spectroscopy, and DFT calculations, which reveal that the lowest unoccupied molecular orbitals (LUMOs) for [Ru(C^N^C)(N^N)Cl](+) are N^N-based. PMID:23952294

  9. An Isolable, Photoswitchable N-Heterocyclic Carbene: On-Demand Reversible Ammonia Activation.

    Science.gov (United States)

    Teator, Aaron J; Tian, Yuan; Chen, Mu; Lee, Jeehiun K; Bielawski, Christopher W

    2015-09-21

    The first isolable, photoswitchable N-heterocyclic carbene was synthesized and found to undergo reversible electrocyclic isomerization upon successive exposure to UV and visible radiation. The UV-induced ring closure afforded substantial changes to the electronic structure of the dithienylethene-based NHC, as evidenced by changes in the corresponding UV/Vis absorption and (13) C?NMR spectra. Likewise, molecular orbital calculations revealed diminished electron density at the carbene nucleus upon photocyclization, consistent with the enhanced electrophilicity displayed by the ring-closed form. The photoswitchable NHC was successfully switched between its ring-opened and ring-closed states with high fidelity over multiple cycles. Furthermore, the ring-closed isomer was found to undergo facile N?H bond activation, allowing for the controlled capture and release of ammonia upon cycling between its isomeric states. PMID:26274507

  10. Synthesis of chiral mono(N-heterocyclic carbene palladium and gold complexes with a 1,1'-biphenyl scaffold and their applications in catalysis

    Directory of Open Access Journals (Sweden)

    Min Shi

    2011-05-01

    Full Text Available Axially chiral mono(NHC–Pd(II and mono(NHC–Au(I complexes with one side shaped 1,1'-biphenyl backbone have been prepared from chiral 6,6'-dimethoxybiphenyl-2,2'-diamine. The complexes were characterized by X-ray crystal structure diffraction. The Pd(II complex showed good catalytic activities in the Suzuki–Miyaura and Heck–Mizoroki coupling reactions, and the (S-Au(I complexes also showed good catalytic activities in the asymmetric intramolecular hydroamination reaction to give the corresponding product in moderate ee.

  11. Adjusting the DNA Interaction and Anticancer Activity of Pt(II) N-Heterocyclic Carbene Complexes by Steric Shielding of the Trans Leaving Group.

    Czech Academy of Sciences Publication Activity Database

    Muenzner, J.K.; Rehm, T.; Biersack, B.; Casini, A.; de Graaf, I.; Worawutputtapong, P.; Noor, A.; Kempe, R.; Brabec, Viktor; Kašpárková, Jana; Schobert, R.

    2015-01-01

    Ro?. 58, ?. 15 (2015), s. 6283-6292. ISSN 0022-2623 R&D Projects: GA ?R(CZ) GA14-21053S Institutional support: RVO:68081707 Keywords : PLATINUM COMPLEXES * CANCER -CELLS * CISPLATIN Subject RIV: BO - Biophysics Impact factor: 5.447, year: 2014

  12. Well-defined indium(III)N-heterocyclic carbene complexes with triflate ligands: structural models for the In(OTf)3 catalyst.

    OpenAIRE

    Cotgreave, JH; Colclough, D; Kociok-Köhn, G; Ruggiero, G.; Frost, CG; Weller, AS

    2004-01-01

    Reaction of 1,3-dimesitylimidazolium chloride [IMesH]Cl with InMe3 results in (IMes)InMe2Cl, which on treatment with one equivalent of TMS-OTf affords (IMes)InMe2(OTf), which can be converted to the bistriflate complex (IMes)In(Me)(OTf)2 on addition of HOTf.

  13. Amine-N-heterocyclic carbene cascade catalysis for the asymmetric synthesis of fused indane derivatives with multiple chiral centres.

    Science.gov (United States)

    Jia, Zhi-Jun; Jiang, Kun; Zhou, Qing-Qing; Dong, Lin; Chen, Ying-Chun

    2013-07-01

    An aminocatalytic asymmetric Diels-Alder reaction of 2,4-dienals and labile 1-indenones in situ generated from 3-bromo-1-indanones was developed, producing highly fused indane products with multiple chiral centres followed by a cascade N-heterocyclic carbene-mediated benzoin condensation. PMID:23712483

  14. Enantioselective Synthesis of Chromanones Bearing Quaternary Substituted Stereocenters Catalyzed by (1R)-Camphor-Derived N-Heterocyclic Carbenes.

    Science.gov (United States)

    Rafi?ski, Zbigniew; Kozakiewicz, Anna

    2015-08-01

    A catalytic asymmetric intramolecular crossed-benzoin reaction for the synthesis of chromanones by novel camphor-derived N-heterocyclic carbenes is described. The corresponding chromanones bearing quaternary stereogenic centers were isolated in high yields with high to excellent enantioselectivity. PMID:26161638

  15. Optimized Syntheses of Cyclopentadienyl Nickel Chloride Compounds Containing "N"-Heterocyclic Carbene Ligands for Short Laboratory Periods

    Science.gov (United States)

    Cooke, Jason; Lightbody, Owen C.

    2011-01-01

    Experiments are described for the preparation of imidazolium chloride precursors to "N"-heterocyclic carbenes and their cyclopentadienyl nickel chloride derivatives. The syntheses have been optimized for second- and third-year undergraduate laboratories that have a maximum programmed length of three hours per week. The experiments are flexible and…

  16. Main-chain organometallic polymers comprising redox-active iron(II) centers connected by ditopic N-heterocyclic carbenes.

    Science.gov (United States)

    Mercs, Laszlo; Neels, Antonia; Stoeckli-Evans, Helen; Albrecht, Martin

    2009-09-21

    Main-chain organometallic polymers were synthesized from bimetallic iron(ii) complexes containing a ditopic N-heterocyclic carbene (NHC) ligand [(cp)(CO)LFe(NHC approximately NHC)Fe(cp)(CO)L]X(2) (where NHC approximately NHC represents a bridging dicarbene ligand, L = I(-) or CO). Addition of a diimine ligand such as pyrazine or 4,4'-bipyridine, interconnected these bimetallic complexes and gave the corresponding co-polymers containing iron centers that are alternately linked by a dicarbene and a diimine ligand. Diimine coordination depended on the wingtip groups at the carbene ligands and was accomplished either by photolytic activation of a carbonyl ligand from the cationic [Fe(cp)(NHC)(CO)(2)](+) precursor (alkyl wingtips) or by AgBF(4)-mediated halide abstraction from the neutral complex [FeI(cp)(NHC)(CO)] (mesityl wingtips). Remarkably, the polymeric materials were substantially more stable than the related bimetallic model complexes. Electrochemical analyses indicated metal-metal interactions in the pyrazine-containing polymers, whereas in 4,4'-bipyridine-linked systems the metal centers were electronically decoupled. PMID:20449160

  17. Tuning and Quantifying Steric and Electronic Effects of N-Heterocyclic Carbenes

    KAUST Repository

    Falivene, Laura

    2014-07-12

    This chapter states that the main handles for tuning steric and electronic effects are the substituents on N atoms, the nature of the C4-C5 bridge (either saturated or unsaturated), and the substituents on the C4 and C5 atoms. The initial intuition that steric properties of N-heterocyclic carbenes (NHCs) could be modulated and could impact catalytic behavior stimulated the development of steric descriptors to quantify the steric requirement of different NHCs and, possibly, to compare them with tertiary phosphines. NHCs can be classified as typically strong ?-basic/?-acid ligands, although they have been also shown to exhibit reasonable ?-basic properties. This electronic modularity allows NHC ligands to adapt flexibly to different chemical environments represented by a transition metal and the other ligands. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved.

  18. Unveiling the peculiar hydrogen bonding behavior of solvated N-heterocyclic carbenes.

    Science.gov (United States)

    Hollóczki, Oldamur

    2016-01-01

    To investigate the hydrogen bonding and its dynamics of N-heterocyclic carbenes (NHCs) in solution, a molecular mechanical force field was fitted for the homologous series of 1,3-dialkylimidazol-2-ylidenes. During the exploration of the potential energy surface of the water/1,3-dimethylimidazol-2-ylidene system, it was observed for the first time that the carbene is prone to interaction with hydrogen bond donor molecules also from the rather unusual "on top" orientation, where the direction of the interplay is perpendicular to the plane of the NHC's ring. The fitting of the force field parameters for imidazol-2-ylidenes was found to be the best in the case of a two-site model, which reproduces not only the strength, but also the direction dependency of hydrogen bonding. With the aid of this tool, curious, hitherto unknown types of hydrogen bonding could be unveiled for NHCs. In the case of non-hydrogen bonding solvents, carbenes tend to form short lived, but structurally influental hydrogen bonds between each other via ring hydrogen atoms and the divalent carbon atoms. The chemically highly important hydrogen bond dynamics of NHCs was found to be facilitated by three center hydrogen bonding, where two alcohol molecules bind to a carbene, which is allowed only by the aforementioned relatively strong interaction between the NHC and the hydrogen bond donor in the "on top" orientation. The latter finding has significant effects on processes that involve this kind of replacement, such as the selective transesterification reactions, and the mechanism of proton exchange on azolium rings. PMID:26592182

  19. "Hummingbird" behaviour of N-heterocyclic carbenes stabilises out-of-plane bonding of AuCl and CuCl units.

    Science.gov (United States)

    Teci, Matthieu; Brenner, Eric; Matt, Dominique; Gourlaouen, Christophe; Toupet, Loic

    2015-07-27

    An N-heterocyclic carbene substituted by two expanded 9-ethyl-9-fluorenyl groups was shown to bind an AuCl unit in an unusual manner, namely with the Au?X rod sitting out of the plane defined by the heterocyclic carbene unit. As shown by X-ray studies and DFT calculations, the observed large pitch angle (21°) arises from an easy displacement of the gold(I) atom away from the carbene lone-pair axis, combined with the stabilisation provided by weak CH???Au interactions involving aliphatic and aromatic H atoms of the NHC wingtips. Weak, intermolecular Cl???H bonds are likely to cooperate with the H???Au interactions to stabilise the out-of-plane conformation. A general belief until now was that tilt angles in NHC complexes arise mainly from steric effects within the first coordination sphere. PMID:26130507

  20. Efficient electronic communication of two ruthenium centers through a rigid ditopic N-heterocyclic carbene linker

    OpenAIRE

    Michael Nussbaum; Oliver Schuster; Martin Albrecht

    2014-01-01

    A ditopic benzobis(carbene) ligand precursor was prepared that contained a chelating pyridyl moiety to ensure co-planarity of the carbene ligand and the coordination plane of a bound octahedral metal center. Bimetallic ruthenium complexes comprising this ditopic ligand [L?Ru-C,N-bbi-C,N-RuL?] were obtained by a transmetalation methodology (C,N-bbi-C,N=benzobis(N-pyridyl-N?-methyl-imidazolylidene). The two metal centers are electronically decoupled when the ruthenium is in a pseudotetrahedral ...

  1. Enantioselective sulfonation of enones with sulfonyl imines by cooperative N-heterocyclic-carbene/thiourea/tertiary-amine multicatalysis.

    Science.gov (United States)

    Jin, Zhichao; Xu, Jianfeng; Yang, Song; Song, Bao-An; Chi, Yonggui Robin

    2013-11-18

    Many hands make light work: In an organocatalytic asymmetric sulfonation of enones, the activation of a sulfonyl imine by an N-heterocyclic carbene (NHC) catalyst led to the release of a sulfinic anion, which underwent nucleophilic addition to the enone. The enantioselectivity of the process was controlled by a chiral thiourea/amine co-catalyst through anion recognition and hydrogen-bonding interactions. Tol=p-tolyl. PMID:24115649

  2. N-Heterocyclic Carbene-Catalysed Diastereoselective Vinylogous Michael Addition Reaction of gamma-Substituted deconjugated Butenolides

    KAUST Repository

    Guo, Hao

    2015-11-16

    An efficient N-heterocyclic carbene (NHC)-catalysed vinylogous Michael addition of deconjugated butenolides was developed. In the presence of 5 mol% of the NHC catalyst, both ?-alkyl and aryl-substituted deconjugated butenolides undergo vinylogous Michael addition with various ?, ?-unsaturated ketones, esters, or nitriles to afford ?,?-disubstituted butenolides containing adjacent quaternary and tertiary carbon centers in good to excellent yields with excellent diastereoselectivities. In this process, the free carbene is assumed to act as a strong Brønsted base to promote the conjugate addition.

  3. Spherical core-shell magnetic particles constructed by main-chain palladium N-heterocyclic carbenes

    Science.gov (United States)

    Zhao, Huaixia; Li, Liuyi; Wang, Jinyun; Wang, Ruihu

    2015-02-01

    The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs.The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs. Electronic supplementary information (ESI) available: The additional SEM images, IR spectra, TG-MS curves, Solid state 13C NMR spectra, XPS spectra and XRD spectra of palladium NHC particles. See DOI: 10.1039/c4nr07330d

  4. Anti-Markovnikov Hydroheteroarylation of Unactivated Alkenes with Indoles, Pyrroles, Benzofurans, and Furans Catalyzed by a Nickel-N-Heterocyclic Carbene System.

    Science.gov (United States)

    Schramm, York; Takeuchi, Makoto; Semba, Kazuhiko; Nakao, Yoshiaki; Hartwig, John F

    2015-09-30

    We report the catalytic addition of C-H bonds at the C2 position of heteroarenes, including pyrroles, indoles, benzofurans, and furans, to unactivated terminal and internal alkenes. The reaction is catalyzed by a combination of Ni(COD)2 and a sterically hindered, electron-rich N-heterocyclic carbene ligand or its analogous Ni(NHC)(arene) complex. The reaction is highly selective for anti-Markovnikov addition to ?-olefins, as well as for the formation of linear alkylheteroarenes from internal alkenes. The reaction occurs with substrates containing ketones, esters, amides, boronate esters, silyl ethers, sulfonamides, acetals, and free amines. PMID:26334367

  5. Mechanistic Investigation of the Ruthenium–N-Heterocyclic-Carbene-Catalyzed Amidation of Alcohols and Amines

    DEFF Research Database (Denmark)

    Makarov, Ilya; Fristrup, Peter

    2012-01-01

    The mechanism of the ruthenium–N-heterocyclic-carbene-catalyzed formation of amides from alcohols and amines was investigated by experimental techniques (Hammett studies, kinetic isotope effects) and by a computational study by using dispersion-corrected density functional theory (DFT/ M06). The Hammett study indicated that a small positive charge builds-up at the benzylic position in the transition state of the turnover-limiting step. The kinetic isotope effect was determined to be 2.29ACHTUNGTRENUNG(!0.15), which suggests that the breakage of the C"H bond is not the rate-limiting step, but that it is one of several slow steps in the catalytic cycle. Rapid scrambling of hydrogen and deuterium at the a position of the alcohol was observed with deuterium-labeled substrates, which implies that the catalytically active species is a ruthenium dihydride. The experimental results were supported by the characterization of a plausible catalytic cycle by using DFT/M06. Both cisdihydride and trans-dihydride intermediates were considered, but when the theoretical turnover frequencies (TOFs) were derived directly from the calculated DFT/M06 energies, we found that only the trans-dihydride pathway was in agreement with the experimentally determined TOFs.

  6. A monotopic aluminum telluride with an Al=Te double bond stabilized by N-heterocyclic carbenes

    Science.gov (United States)

    Franz, Daniel; Szilvási, Tibor; Irran, Elisabeth; Inoue, Shigeyoshi

    2015-01-01

    Aluminum chalcogenides are mostly encountered in the form of bulk aluminum oxides that are structurally diverse but typically consist of networks with high lattice energy in which the chalcogen atoms bridge the metal centres. This makes their molecular congeners difficult to synthesize because of a pronounced tendency for oligomerization. Here we describe the isolation of the monotopic aluminum chalcogenide (LDipN)AlTe(LEt)2 (LDip=1,3-(2,6-diisopropylphenyl)-imidazolin-2-imine, LEt=1,3-diethyl-4,5-dimethyl-imidazolin-2-ylidene). Unique features of (LDipN)AlTe(LEt)2 are the terminal position of the tellurium atom, the shortest aluminum–tellurium distance hitherto reported for a molecular complex and the highest bond order reported for an interaction between these elements, to the best of our knowledge. At elevated temperature (LDipN)AlTe(LEt)2 equilibrates with dimeric {(LDipN)AlTe(LEt)}2 in which the chalcogen atoms assume their common role as bridges between the metal centres. These findings demonstrate that (LDipN)AlTe(LEt)2 comprises the elusive Al=Te double bond in the form of an N-heterocyclic carbene-stabilized species. PMID:26612781

  7. A Stable Planar-Chiral N-Heterocyclic Carbene with a 1,1'-Ferrocenediyl Backbone.

    Science.gov (United States)

    Petrov, Alex R; Derheim, Anatoli; Oetzel, Jan; Leibold, Michael; Bruhn, Clemens; Scheerer, Stefan; Oßwald, Steffen; Winter, Rainer F; Siemeling, Ulrich

    2015-07-01

    This paper focuses on the stable, ferrocene-based N-heterocyclic carbene (NHC) rac-[Fe{(?(5)-t-BuC5H3)NpN}2C:] (A'-Np, Np = neopentyl), which is planar-chiral due to the two tert-butyl substituents in 3,3'-positions. A'-Np was synthesized in nine steps starting from 1,1'-di-tert-butylferrocene (1), the first step being its 3,3'-dilithiation to afford rac-[Fe(?(5)-t-BuC5H3Li)2] (rac-fc'Li2, 2). The structures of rac-fc'(SiMe3)2 (3), rac-fc'Br2 (4), rac-fc'(N3)2 (5), and the immediate carbene precursor [A'-NpH]BF4 were determined by single-crystal X-ray diffraction (XRD). The chemical properties of A'-Np were found to be very similar to those of its tert-butyl-free congener A-Np, both being ambiphilic NHCs with rather high calculated HOMO energies (ca. -4.0 eV) and low singlet-triplet gaps (ca. 35 kcal/mol). A Tolman electronic parameter value of 2050 cm(-1) was derived from IR data of cis-[RhCl(A'-Np)(CO)2], indicating the high donicity of A'-Np as a ligand. Consistent with its ambiphilic nature, A'-Np was found to react readily with carbon monoxide, affording the betainic enolate (A'-Np)2CO as four stereoisomers, viz. (RpRp-A'-Np)?C(O(-))(RpRp-A'-Np(+)), (SpSp-A'-Np)?C(O(-))(SpSp-A'-Np(+)), (RpRp-A'-Np)?C(O(-))(SpSp-A'-Np(+)), and (SpSp-A'-Np)?C(O(-))(RpRp-A'-Np(+)). The former two isomers were structurally characterized as a racemic compound by single-crystal XRD. A'-Np was found to react swiftly with dichloromethane, affording the addition product A'-NpH-CHCl2 in a reaction that is unprecedented for diaminocarbenes. A-NpH-CHCl2 was obtained analogously. Both compounds were structurally characterized by single-crystal XRD. An electrochemical investigation of A'-Np by cyclic and square wave voltammetry revealed a reversible oxidation of the carbene at a half-wave potential of -0.310 vs ferrocene/ferrocenium (THF/NBu4PF6). The electrochemical data previously published for A-Np were identified to be incorrect, since unnoticed hydrolysis of the NHC had taken place, affording A-Np(H2O). The hydrolysis products of A-Np and A'-Np were found to be reversibly oxidized at half-wave potentials of -0.418 and -0.437 V, respectively. PMID:26098133

  8. Dynamic Behavior of N-Heterocyclic Carbene Boranes: Boron-Carbene Bonds in B,B-Disubstituted N,N-Dimethylimidazol-2-ylidene Boranes Have Substantial Rotation Barriers.

    Science.gov (United States)

    Damodaran, Krishnan; Li, Xiben; Pan, Xiangcheng; Curran, Dennis P

    2015-05-01

    Dynamic NMR spectroscopy has been used to measure rotation barriers in five B,B-disubstituted 1,3-dimethylimidazol-2-ylidene boranes. The barriers are attributed to the sp(2)-sp(3) bond between C(1) of the N-heterocyclic carbene ring and the boron atom. Bonds to boron atoms bearing a thexyl (1,1,2-trimethylpropyl) group show especially high barriers, ranging from 75-86 kJ mol(-1). 2-Isopropyl-1,3,5-trimethylbenzene is used as a comparable to help understand the nature and magnitude of the barriers. PMID:25843519

  9. N-Heterocyclic carbene-catalyzed cascade reaction of 2-aroylvinylcinnamaldehydes with 2-aroylvinylchalcones: rapid assembly of six contiguous stereogenic centers with high diastereoselectivity.

    Science.gov (United States)

    Fan, Xing-Wen; Cheng, Ying

    2014-01-01

    N-Heterocyclic carbene-catalyzed reaction of 2-aroylvinylcinnamaldehydes with 2-aroylvinylchalcones proceeded via a triple Michael addition and intramolecular lactonization cascade to produce novel 9-(2-aroyl-3-aroylmethyl-1-indanyl)-3-arylindeno[2,1-c]pyran-1-ones in good yields with high diastereoselectivity. This reaction constructed six contiguous stereogenic centers in a single reactive event. Among 32 possible diastereoisomers that contain six stereocenters, only two diastereoisomers were detected with diastereomeric ratios being 10?:?1-28?:?1. This work opens up a new avenue for the synthesis of complex indane derivatives, a type of compound that has been reported to possess various biological and pharmaceutical activities. PMID:24202128

  10. The 1:1 co-crystallization of enantiomers of an arene-tethered and ortho-metallated N-heterocyclic carbene ruthenium(II) half-sandwich complex: Synthesis, structural characterization and theoretical study

    Science.gov (United States)

    Karab?y?k, Hasan; K?l?nçarslan, Rafet; Aygün, Muhittin; Çetinkaya, Bekir; García-Granda, Santiago

    2008-01-01

    The reaction of [RuCl 2( p-cymene)] 2 with in situ deprotonated NHC precursor 1,3-bis(biphenyl-2-yl)imidazolinium chloride was carried out in p-xylene at 140 °C to produce ?2, in which the NHC moiety acts as a tridentate C,C',C''-ligand. The complex 2 was characterized by NMR spectroscopy and X-ray crystallographic study. Crystallographic analysis combined with computational study regarding the compound, 1-[? 6-(2'-biphenyl)]-3-[2-phenyl-1,2-phenylene]imidazolidin-2-ylidenechlororuthenium(II), 2, reveals that its metal-centered enantiomers are co-crystallized in 1:1 ratio and NHC frame possessing a tridentate coordination mode consists of ?-donation of the carbene carbon, ? 6-arene tethering of terminal biaryl and ? 1-coordination of the biphenyl ring at 2-position. Enantiomers of the complex are packed as asymmetric dimers in solid state formed by C-H⋯Cl type weak H-bonds and C-H⋯? type interactions giving rise to asymmetric chains. Both interactions serve to stabilization of the extended structure.

  11. Grubbs–Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids

    Science.gov (United States)

    Koy, Maximilian; Altmann, Hagen J; Autenrieth, Benjamin; Frey, Wolfgang

    2015-01-01

    Summary The novel dicationic metathesis catalyst [(RuCl2(H2ITapMe2)(=CH–2-(2-PrO)-C6H4))2+ (OTf?)2] (Ru-2, H2ITapMe2 = 1,3-bis(2’,6’-dimethyl-4’-trimethylammoniumphenyl)-4,5-dihydroimidazol-2-ylidene, OTf? = CF3SO3 ?) based on a dicationic N-heterocyclic carbene (NHC) ligand was prepared. The reactivity was tested in ring opening metathesis polymerization (ROMP) under biphasic conditions using a nonpolar organic solvent (toluene) and the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM+][BF4 ?]. The structure of Ru-2 was confirmed by single crystal X-ray analysis. PMID:26664582

  12. Grubbs-Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids.

    Science.gov (United States)

    Koy, Maximilian; Altmann, Hagen J; Autenrieth, Benjamin; Frey, Wolfgang; Buchmeiser, Michael R

    2015-01-01

    The novel dicationic metathesis catalyst [(RuCl2(H2ITapMe2)(=CH-2-(2-PrO)-C6H4))(2+) (OTf(-))2] (Ru-2, H2ITapMe2 = 1,3-bis(2',6'-dimethyl-4'-trimethylammoniumphenyl)-4,5-dihydroimidazol-2-ylidene, OTf(-) = CF3SO3 (-)) based on a dicationic N-heterocyclic carbene (NHC) ligand was prepared. The reactivity was tested in ring opening metathesis polymerization (ROMP) under biphasic conditions using a nonpolar organic solvent (toluene) and the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM(+)][BF4 (-)]. The structure of Ru-2 was confirmed by single crystal X-ray analysis. PMID:26664582

  13. Density Functional Study on [3+2]-Dipolar Cycloaddition Reaction of the N-heterocyclic Carbene Boryl Azide with Olefins

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xinghui; Wang, Ketai; Niu, Teng; Li, Shanshan [Lanzhou Univ. of Arts and Science, Lanzhou (Korea, Republic of)

    2014-05-15

    The cycloaddition reactions of the N-heterocyclic carbene boryl azide with methyl acrylate, butenone, and hexafluoropropene have been investigated theoretically. Solvent effects on these reactions have been explored by calculation that included a polarizable continuum model (PCM) for the solvent (C6H6). The title reaction could produce 4- and 5-substituted 1,2,3-triazolines, respectively. The reaction systems have the higher chemical reactivity with the low barriers and could be favored. Yet the smaller differences have been found to occur in energetics, and the cycloaddition reactions occur for s-trans conformations over s-cis conformations. The calculations indicated that the cycloaddition reaction of the alkenes have certain regioselectivity.

  14. Density Functional Study on [3+2]-Dipolar Cycloaddition Reaction of the N-heterocyclic Carbene Boryl Azide with Olefins

    International Nuclear Information System (INIS)

    The cycloaddition reactions of the N-heterocyclic carbene boryl azide with methyl acrylate, butenone, and hexafluoropropene have been investigated theoretically. Solvent effects on these reactions have been explored by calculation that included a polarizable continuum model (PCM) for the solvent (C6H6). The title reaction could produce 4- and 5-substituted 1,2,3-triazolines, respectively. The reaction systems have the higher chemical reactivity with the low barriers and could be favored. Yet the smaller differences have been found to occur in energetics, and the cycloaddition reactions occur for s-trans conformations over s-cis conformations. The calculations indicated that the cycloaddition reaction of the alkenes have certain regioselectivity

  15. Steric and electronic parameters of a bulky yet flexible N-heterocyclic carbene: 1,3-bis(2,6-bis(1-ethylpropyl)phenyl)imidazol-2-ylidene (IPent)

    KAUST Repository

    Collado, Alba

    2013-06-10

    The free N-heterocyclic carbene IPent (1; IPent = 1,3-bis(2,6-bis(1- ethylpropyl)phenyl)imidazol-2-ylidene) was prepared from the corresponding imidazolium chloride salt (2). The steric and electronic parameters of 1 were determined by synthesis of the gold(I) chloride complex [Au(IPent)Cl] (3) and the nickel-carbonyl complex [Ni(IPent)(CO)3] (4), respectively. 3 and 4 were fully characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction studies on single crystals. © 2013 American Chemical Society.

  16. How does the addition of steric hindrance to a typical N-heterocyclic carbene ligand affect catalytic activity in olefin metathesis?

    OpenAIRE

    Poater Teixidor, Albert; Falivene, Laura; Urbina-Blanco, Cesar A.; Manzini, Simone; Steven P. Nolan; Cavallo, Luigi

    2013-01-01

    Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in ...

  17. An Electronic Rationale for Observed Initiation Rates in Ruthenium-Mediated Olefin Metathesis: Charge Donation in Phosphine And N-Heterocyclic Carbene Ligands

    Energy Technology Data Exchange (ETDEWEB)

    Getty, K.; Delgado-Jaime, M.U.; Kennepohl, P.

    2009-06-01

    Ru K-edge XAS data indicate that second generation ruthenium-based olefin metathesis precatalysts (L = N-heterocyclic carbene) possess a more electron-deficient metal center than in the corresponding first generation species (L = tricyclohexylphosphine). This surprising effect is also observed from DFT calculations and provides a simple rationale for the slow phosphine dissociation kinetics previously noted for second-generation metathesis precatalysts.

  18. Nitrenium ions and trivalent boron ligands as analogues of N-heterocyclic carbenes in olefin metathesis: a computational study.

    Science.gov (United States)

    Pazio, A; Wo?niak, K; Grela, K; Trzaskowski, B

    2015-11-18

    We used the density functional theory to evaluate the suitability of nitrenium ions and trivalent boron ligands as analogues of N-heterocyclic carbenes in ruthenium-based metathesis catalysts. We demonstrate that these analogues induce only minor structural changes in Hoveyda-Grubbs-like precatalysts, but have major impact on precatalyst initiation. Nitrenium ion-modified precatalysts are characterized by a weak Ru-N bond resulting in a relatively strong Ru-O bond and large free energy barriers for initiation, making them good candidates for efficient latent Ru-based catalysts. On the other hand the trivalent boron ligand, bearing a formal -1 charge, binds strongly to the ruthenium ion, weakening the Ru-O bond and facilitating its dissociation, to promote fast reaction initiation. We show that the calculated bond dissociation energy of the Ru-C/N/B bond may serve as an accurate indicator of the Ru-O bond strength and the rate of metathesis initiation. PMID:26525899

  19. From the N-Heterocyclic Carbene-Catalyzed Conjugate Addition of Alcohols to the Controlled Polymerization of (Meth)acrylates.

    Science.gov (United States)

    Ottou, Winnie Nzahou; Bourichon, Damien; Vignolle, Joan; Wirotius, Anne-Laure; Robert, Fredéric; Landais, Yannick; Sotiropoulos, Jean-Marc; Miqueu, Karinne; Taton, Daniel

    2015-06-22

    Among various N-heterocyclic carbenes (NHCs) tested, only 1,3-bis(tert-butyl)imidazol-2-ylidene (NHC(tBu) ) proved to selectively promote the catalytic conjugate addition of alcohols onto (meth)acrylate substrates. This rather rare example of NHC-catalyzed 1,4-addition of alcohols was investigated as a simple means to trigger the polymerization of both methyl methacrylate and methyl acrylate (MMA and MA, respectively). Well-defined ?-alkoxy poly(methyl (meth)acrylate) (PM(M)A) chains, the molar masses of which could be controlled by the initial [(meth)acrylate]0/[ROH]0 molar ratio, were ultimately obtained in N,N-dimethylformamide at 25?°C. A hydroxyl-terminated poly(ethylene oxide) (PEO-OH) macro-initiator was also employed to directly access PEO-b-PMMA amphiphilic block copolymers. Investigations into the reaction mechanism by DFT calculations revealed the occurrence of two competitive concerted pathways, involving either the activation of the alcohol or that of the monomer by NHC(tBu) . PMID:26013759

  20. Electrogenerated N-heterocyclic carbene: N-acylation of chiral oxazolidin-2-ones in ionic liquids

    International Nuclear Information System (INIS)

    An electrochemical procedure for the N-acylation of chiral oxazolidin-2-ones, in the absence of volatile molecular organic solvents, has been set up via electrolyses of ionic liquid [bmim]BF4 containing oxazolidin-2-ones followed by addition of saturated or unsaturated anhydrides. N-acyloxazolidin-2-ones were isolated in good to elevated yields. The electrochemically induced N-acylation of chiral oxazolidin-2-ones occurs with total retention of the absolute configuration of all the chiral atoms. The electrogenerated carbene (1-butyl-3-methyl-1H-imidazol-2-ylidene) has been indicated as the base involved in the deprotonation of chiral oxazolidin-2-ones

  1. Copper and Silver Carbene Complexes without Heteroatom-Stabilization: Structure, Spectroscopy, and Relativistic Effects.

    Science.gov (United States)

    Hussong, Matthias W; Hoffmeister, Wilhelm T; Rominger, Frank; Straub, Bernd F

    2015-08-24

    Salts of a copper and a silver carbene complex were prepared from dimesityl diazomethane, made possible by the steric shielding of the N-heterocyclic carbene (NHC) ancillary ligand IPr**. The mint-green complex [IPr**Ag=CMes2 ](+) [NTf2 ](-) is the first isolated silver carbene complex without heteroatom donor substituents. Single-crystal X-ray diffraction provides evidence for a predominant carbenoid character, and supports the postulation of such reactive species as intermediates in silver-catalyzed C-H activation reactions. The greenish yellow copper carbene complex [IPr**Cu=CMes2 ](+) [NTf2 ](-) has spectroscopic properties in between the isostructural silver complex and the already reported emerald green gold carbene complex. A comparison in the Group?11 series indicates that relativistic effects are responsible for the strong ??bond and the significant ??back-bonding in the gold carbene moiety. PMID:26189567

  2. ?-face donation from the aromatic N-substituent of N-heterocyclic carbene ligands to metal and its role in catalysis

    KAUST Repository

    Credendino, Raffaele

    2012-05-16

    In this work, we calculate the redox potential in a series of Ir and Ru complexes bearing a N-heterocyclic carbene (NHC) ligand presenting different Y groups in the para position of the aromatic N-substituent. The calculated redox potentials excellently correlate with the experimental ?E 1/2 potentials, offering a handle to rationalize the experimental findings. Analysis of the HOMO of the complexes before oxidation suggests that electron-donating Y groups destabilize the metal centered HOMO. Energy decomposition of the metal-NHC interaction indicates that electron-donating Y groups reinforce this interaction in the oxidized complexes. Analysis of the electron density in the reduced and oxidized states of representative complexes indicates a clear donation from the C ipso of the N-substituents to an empty d orbital on the metal. In case of the Ru complexes, this mechanism involves the Ru-alkylidene moiety. All of these results suggest that electron-donating Y groups render the aromatic N-substituent able to donate more density to electron-deficient metals through the C ipso atom. This conclusion suggests that electron-donating Y groups could stabilize higher oxidation states during catalysis. To test this hypothesis, we investigated the effect of differently donating Y groups in model reactions of Ru-catalyzed olefin metathesis and Pd-catalyzed C-C cross-coupling. Consistent with the experimental results, calculations indicate an easier reaction pathway if the N-substituent of the NHC ligand presents an electron-donating Y group. © 2012 American Chemical Society.

  3. How does the addition of steric hindrance to a typical N-heterocyclic carbene ligand affect catalytic activity in olefin metathesis?

    Science.gov (United States)

    Poater, Albert; Falivene, Laura; Urbina-Blanco, César A; Manzini, Simone; Nolan, Steven P; Cavallo, Luigi

    2013-05-28

    Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in mind that there is a significant structural difference between both ligands in different olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance. PMID:23455458

  4. How does the addition of steric hindrance to a typical N-heterocyclic carbene ligand affect catalytic activity in olefin metathesis?

    KAUST Repository

    Poater, Albert

    2013-01-01

    Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in mind that there is a significant structural difference between both ligands in different olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance. © 2013 The Royal Society of Chemistry.

  5. Catalisadores contendo carbenos n-heterocíclicos como ligantes: propriedades, sínteses, aplicações e comparação com outros ligantes Catalysts containing n-heterocyclic carbenes as ligands: properties, syntheses, applications and comparison with other catalysts

    Directory of Open Access Journals (Sweden)

    Julio Cezar Pastre

    2008-01-01

    Full Text Available N-heterocyclic carbenes (NHCs have become of considerable importance in modern organometallic chemistry and homogeneous catalysis. There are several advantages in the use NHCs over their phosphorus analogues, which explains the enormous development of NHC ligands in the field of organometallic catalysis in the past few years. In this article, we present an overview of the importance of the catalysts containing NHC ligands, their synthesis, some pertinent synthetic applications, and a brief comparison with other catalysts.

  6. Highly stereoselective synthesis of 1,2,3-trisubstituted indanes via oxidative N-heterocyclic carbene-catalyzed cascades.

    Science.gov (United States)

    Biswas, Anup; De Sarkar, Suman; Fröhlich, Roland; Studer, Armido

    2011-09-16

    Three stereocenters are formed in the carbene catalyzed cascade reaction of enals with various ?-diketones to give the corresponding indane derivatives with excellent stereoselectivities. The products are readily transformed to the corresponding 1,2,3-trisubstituted indane derivatives, which represent privileged substructures in medicinal chemistry. PMID:21863845

  7. Six-Membered N-Heterocyclic Carbenes with a 1,1?-Ferrocenediyl Backbone : Bulky Ligands with Strong Electron-Donor Capacity and Unusual Non-Innocent Character

    OpenAIRE

    Siemeling, Ulrich; Färber, Christian; Leibold, Michael; Bruhn, Clemens; Mücke, Philipp; Winter, Rainer; Sarkar, Biprajit; von*Hopffgarten, Moritz; Frenking, Gernod

    2009-01-01

    AbstractThe stable, crystalline N-heterocyclic diaminocarbene fc[N(CH2tBu)-C-N(CH2tBu)] (2d, fc = 1,1?-ferrocenediyl) was prepared by deprotonation of its formamidinium precursor fc[N(CH2tBu)-CH-N(CH2tBu)][BF4] (1d) and used for the preparation of the 16 valence electron complexes [Mo(2d)(CO)4], [RhCl(2d)(cod)] (cod = 1,5-cyclooctadiene) and [RhCl(2d)(CO)2]. 1d, 2d and [RhCl(2d)(cod)] were structurally characterised by single-crystal X-ray diffraction studies. The electrochemical properties o...

  8. Catalisadores contendo carbenos n-heterocíclicos como ligantes: propriedades, sínteses, aplicações e comparação com outros ligantes / Catalysts containing n-heterocyclic carbenes as ligands: properties, syntheses, applications and comparison with other catalysts

    Scientific Electronic Library Online (English)

    Julio Cezar, Pastre; Carlos Roque Duarte, Correia.

    Full Text Available [...] Abstract in english N-heterocyclic carbenes (NHCs) have become of considerable importance in modern organometallic chemistry and homogeneous catalysis. There are several advantages in the use NHCs over their phosphorus analogues, which explains the enormous development of NHC ligands in the field of organometallic cata [...] lysis in the past few years. In this article, we present an overview of the importance of the catalysts containing NHC ligands, their synthesis, some pertinent synthetic applications, and a brief comparison with other catalysts.

  9. Synthesis, spectroscopic studies and reactivity of triphenylphosphine ruthenium (II) complexes with N-heterocyclic ligands

    International Nuclear Information System (INIS)

    Reported is the chemistry of triphenylphosphine ruthenium (II) complexes of general formula RuCl2(PPh3)2L2 and RuCl2(PPh3)2A, obtained from the reaction of RuCl2(PPh3)3 with N-heterocyclic ligands L, or A (of ambidentate nature). The electronic spectra exhibit two strong metal-to-ligand charge-transfer bands, ascribed to the b1(dxz)->b1(pi) and a2(dxy)->a2(pi) transitions, and a third, weak band ascribed to the b2(dyz)->a2(pi) transition. The electronic states and the vibrational modes of the complexes were characterized by means of their resonance Raman and infrared absorption spectra. Thermogravimetric and thermodifferential analysis indicated that the melting process is succeeded by an exothermic reaction, and that the weigh loss starts to occur only after this step. The complexes dissociated in CHCl3 solution, showing preferential labilization of the phosphine ligands, as in the case of the hydrogenation catalyst Ru(PPh3)3Cl2. In the presence of CO, RuCl2(CO)2L2 complexes were gennerated. Several derivatives were isolated and characterized. (author)

  10. Organocatalytic conjugate-addition polymerization of linear and cyclic acrylic monomers by N-heterocyclic carbenes: Mechanisms of chain initiation, propagation, and termination

    KAUST Repository

    Zhang, Yuetao

    2013-11-27

    This contribution presents a full account of experimental and theoretical/computational investigations into the mechanisms of chain initiation, propagation, and termination of the recently discovered N-heterocyclic carbene (NHC)-mediated organocatalytic conjugate-addition polymerization of acrylic monomers. The current study specifically focuses on three commonly used NHCs of vastly different nucleophilicity, 1,3-di-tert-butylimidazolin-2-ylidene (ItBu), 1,3- dimesitylimidazolin-2-ylidene (IMes), and 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4- triazol-5-ylidene (TPT), and two representative acrylic monomers, the linear methyl methacrylate (MMA) and its cyclic analog, biomass-derived renewable ?-methyl-?-methylene-?-butyrolactone (MMBL). For MMA, there exhibits an exquisite selectivity of the NHC structure for the three types of reactions it promotes: enamine formation (single-monomer addition) by IMes, dimerization (tail-to-tail) by TPT, and polymerization by ItBu. For MMBL, all three NHCs promote no dimerization but polymerization, with the polymerization activity being highly sensitive to the NHC structure and the solvent polarity. Thus, ItBu is the most active catalyst of the series and converts quantitatively 1000-3000 equiv of MMBL in 1 min or 10 000 equiv in 5 min at room temperature to MMBL-based bioplastics with a narrow range of molecular weights of Mn = 70-85 kg/mol, regardless of the [MMBL]/[ItBu] ratio employed. The ItBu-catalyzed MMBL polymerization reaches an exceptionally high turnover frequency up to 122 s -1 and a high initiator efficiency value up to 1600%. Unique chain-termination mechanisms have been revealed, accounting for the production of relative high-molecular-weight linear polymers and the catalytic nature of this NHC-mediated conjugate-addition polymerization. Computational studies have provided mechanistic insights into reactivity and selectivity between two competing pathways for each NHC-monomer zwitterionic adduct, namely enamine formation/dimerization through proton transfer vs polymerization through conjugate addition, and mapped out extensive energy profiles for chain initiation, propagation, and termination steps, thereby satisfactorily explaining the experimental observations. © 2013 American Chemical Society.

  11. Pyrene-based bisazolium salts: from luminescence properties to janus-type bis-N-heterocyclic carbenes.

    Science.gov (United States)

    Gonell, Sergio; Poyatos, Macarena; Peris, Eduardo

    2014-07-28

    A series of pyrene-based bisazolium salts have been obtained starting from 4,5,9,10-tetrabromo-2,7-di-tert-butylpyrene. The synthetic procedure to the pyrene-bisazoliums (PBIs) reveals an unexpected behavior, as a consequence of the presence of the alkyl groups (alkyl=Me, Et, n-Pr, and n-Bu) coming from the trisalkoxyformate in the final products, instead of the expected tBu of tAmyl groups from the starting tetra-aminated pyrenes. All bisazoliums show fluorescence properties, with emissions in the range of 370-420?nm, and quantum yields ranging from 0.29 to 0.41. The PBIs were used as bis-NHC precursors in the preparation of a series of dirhodium and diiridium complexes, which have been fully characterized. The electrochemical studies on selected dimetallic complexes reveal that the electronic communication between the metals through the polyaromatic linker is negligible. PMID:24753109

  12. Synthesis of functionalised N-heterocyclic carbene ligands bearing a long spacer and their use in olefin metathesis.

    Science.gov (United States)

    Ko?nik, Wioletta; Grela, Karol

    2013-05-28

    A synthetic route to backbone functionalised imidazolinium salts-NHC ligand precursors has been developed. These tagged NHC ligands can be used to obtain a homogeneous Hoveyda-type catalyst (19) containing a quaternary ammonium group on a C-8 long spacer. Products of olefin metathesis reactions promoted by complex 19 can be readily purified from Ru-residues by filtration of the reaction mixture through a small amount of silica gel. PMID:23463014

  13. N-Heterocyclic Carbene-Copper-Catalyzed Group-, Site-, and Enantioselective Allylic Substitution with a Readily Accessible Propargyl(pinacolato)boron Reagent: Utility in Stereoselective Synthesis and Mechanistic Attributes.

    Science.gov (United States)

    Shi, Ying; Jung, Byunghyuck; Torker, Sebastian; Hoveyda, Amir H

    2015-07-22

    The first instances of catalytic allylic substitution reactions involving a propargylic nucleophilic component are presented; reactions are facilitated by 5.0 mol % of a catalyst derived from a chiral N-heterocyclic carbene (NHC) and a copper chloride salt. A silyl-containing propargylic organoboron compound, easily prepared in multigram quantities, serves as the reagent. Aryl- and heteroaryl-substituted disubstituted alkenes within allylic phosphates and those with an alkyl or a silyl group can be used. Functional groups typically sensitive to hard nucleophilic reagents are tolerated, particularly in the additions to disubstituted alkenes. Reactions may be performed on the corresponding trisubstituted alkenes, affording quaternary carbon stereogenic centers. Incorporation of the propargylic group is generally favored (vs allenyl addition; 89:11 to >98:2 selectivity); 1,5-enynes can be isolated in 75-90% yield, 87:13 to >98:2 SN2'/SN2 (branched/linear) selectivity and 83:17-99:1 enantiomeric ratio. Utility is showcased by conversion of the alkynyl group to other useful functional units (e.g., homoallenyl and Z-homoalkenyl iodide), direct access to which by other enantioselective protocols would otherwise entail longer routes. Application to stereoselective synthesis of the acyclic portion of antifungal agent plakinic acid A, containing two remotely positioned stereogenic centers, by sequential use of two different NHC-Cu-catalyzed enantioselective allylic substitution (EAS) reactions further highlights utility. Mechanistic investigations (density functional theory calculations and deuterium labeling) point to a bridging function for an alkali metal cation connecting the sulfonate anion and a substrate's phosphate group to form the branched propargyl addition products as the dominant isomers via Cu(III) ?-allyl intermediate complexes. PMID:26172476

  14. Synthesis and Antimicrobial Activity of Novel Ag-N-Hetero-cyclic Carbene Complexes

    Directory of Open Access Journals (Sweden)

    ?lknur Özdemir

    2010-04-01

    Full Text Available A series of imidazolidinium ligand precursors are metallated with Ag2O to give silver(I N-heterocyclic carbene complexes. All compounds were fully characterized by elemental analyses, 1H-NMR, 13C-NMR and IR spectroscopy techniques. All compounds studied in this work were screened for their in vitro antimicrobial activities against the standard strains: Enterococcus faecalis (ATCC 29212, Staphylococcus aureus (ATCC 29213, Escherichia coli (ATCC 25922, Pseudomonas aeruginosa (ATCC 27853 and the fungi Candida albicans and Candida tropicalis. The new imidazolidin-2-ylidene silver complexes have been found to display effective antimicrobial activity against a series of bacteria and fungi.

  15. What can NMR spectroscopy of selenoureas and phosphinidenes teach us about the ?-accepting abilities of N-heterocyclic carbenes?

    KAUST Repository

    Vummaleti, Sai V. C.

    2015-01-02

    The electronic nature of the interaction of NHCs with metal centres is of interest when exploring their properties, how these properties influence those of metal complexes, and how these properties might depend on ligand structure. Selenourea and phosphinidene complexes have been proposed to allow the measurement of the ?-accepting ability of NHCs, independent of their ?-donating ability, via the collection of 77Se or 31P NMR spectra, respectively. Herein, the synthesis and characterisation of selenoureas derived from a range of imidazol-2-ylidenes, 4,5-dihydroimidazol-2-ylidenes and triazol-2-ylidenes are documented. Computational studies are used to explore the link between the shielding of the selenium centre and the electronic properties of the NHCs. Results show that ?Se is correlated to the energy gap between a filled lone pair orbital on Se and the empty ?* orbital corresponding to the Se–NHC bond. Bond energy decomposition analysis indicated no correlation between the orbital ?-contribution to bonding and the chemical shielding, while a good correlation was found between the ?-contribution to bonding and the chemical shielding, confirming that this technique is indeed able to quantify the ability of NHCs to accept ?-electron density. Calculations conducted on phosphinidene adducts yielded similar results. With the link between ?Se and ?P and ?-back bonding ability clearly established, these compounds represent useful ways in which to fully understand and quantify this aspect of the electronic properties of NHCs.

  16. Highly selective biaryl cross-coupling reactions between aryl halides and aryl Grignard reagents: a new catalyst combination of N-heterocyclic carbenes and iron, cobalt, and nickel fluorides.

    Science.gov (United States)

    Hatakeyama, Takuji; Hashimoto, Sigma; Ishizuka, Kentaro; Nakamura, Masaharu

    2009-08-26

    Combinations of N-heterocyclic carbenes (NHCs) and fluoride salts of the iron-group metals (Fe, Co, and Ni) have been shown to be excellent catalysts for the cross-coupling reactions of aryl Grignard reagents (Ar(1)MgBr) with aryl and heteroaryl halides (Ar(2)X) to give unsymmetrical biaryls (Ar(1)-Ar(2)). Iron fluorides in combination with SIPr, a saturated NHC ligand, catalyze the biaryl cross-coupling between various aryl chlorides and aryl Grignard reagents in high yield and high selectivity. On the other hand, cobalt and nickel fluorides in combination with IPr, an unsaturated NHC ligand, exhibit interesting complementary reactivity in the coupling of aryl bromides or iodides; in contrast, with these substrates the iron catalysts show a lower selectivity. The formation of homocoupling byproducts is suppressed markedly to less than 5% in most cases by choosing the appropriate metal fluoride/NHC combination. The present catalyst combinations offer several synthetic advantages over existing methods: practical synthesis of a broad range of unsymmetrical biaryls without the use of palladium catalysts and phosphine ligands. On the basis of stoichiometric control experiments and theoretical studies, the origin of the unique catalytic effect of the fluoride counterion can be ascribed to the formation of a higher-valent heteroleptic metalate [Ar(1)MF(2)]MgBr as the key intermediate in our proposed catalytic cycle. First, stoichiometric control experiments revealed the stark differences in chemical reactivity between the metal fluorides and metal chlorides. Second, DFT calculations indicate that the initial reduction of di- or trivalent metal fluoride in the wake of transmetalation with PhMgCl is energetically unfavorable and that formation of a divalent heteroleptic metalate complex, [PhMF(2)]MgCl (M = Fe, Co, Ni), is dominant in the metal fluoride system. The heteroleptic ate-complex serves as a key reactive intermediate, which undergoes oxidative addition with PhCl and releases the biaryl cross-coupling product Ph-Ph with reasonable energy barriers. The present cross-coupling reaction catalyzed by iron-group metal fluorides and an NHC ligand provides a highly selective and practical method for the synthesis of unsymmetrical biaryls as well as the opportunity to gain new mechanistic insights into the metal-catalyzed cross-coupling reactions. PMID:19639999

  17. Pyridine substituted N-heterocyclic carbene ligands as supports for Au(I)-Ag(I) interactions: formation of a chiral coordination polymer.

    Science.gov (United States)

    Catalano, Vincent J; Malwitz, Mark A; Etogo, Anthony O

    2004-09-01

    Reaction of 1,3-bis(2-pyridinylmethyl)-1H-imidazolium tetrafluoroborate, [H(pyCH(2))(2)im]BF(4), with silver oxide in dichloromethane readily yields [Ag((pyCH(2))(2)im)(2)]BF(4), 1.BF(4)(). 1.BF(4) is converted to the analogous Au(I)-containing species, [Au((pyCH(2))(2)im)(2)]BF(4), 3, by a simple carbene transfer reaction in dichloromethane. Further treatment with two equivalents of AgBF(4) produces the trimetallic species [AuAg(2)((pyCH(2))(2)im)(2)(NCCH(3))(2)](BF(4))(3), 4, which contains two silver ions each coordinated to the pyridine moieties on one carbene ligand and to an acetonitrile molecule in a T-shaped fashion. Monometallic [Ag((py)(2)im)(2)]BF(4), 5, and [Au((py)(2)im)(2)]BF(4), 6, are made analogously to 1.BF(4) and 3 starting from 1,3-bis(2-pyridyl)-imidazol-2-ylidene tetrafluoroborate, [H(py)(2)im]BF(4). Addition of excess AgBF(4) to 6 yields the helical mixed-metal polymer, ([AuAg((py)(2)im)(2)(NCCH(3))](BF(4))(2))(n), 7 which contains an extended Au(I)-Ag(I) chain with short metal-metal separations of 2.8359(4) and 2.9042(4) A. Colorless, monometallic [Hg((pyCH(2))(2)im)(2)](BF(4))(2), 8, is easily produced by refluxing [H(pyCH(2))(2)im)]BF(4) with Hg(OAc)(2) in acetonitrile. The related quinolyl-substituted imidazole, [H(quinCH(2))(2)im]PF(6), is produced analogously to [H(pyCH(2))(2)im]BF(4). [Hg((quinCH(2))(2)im)(2)](PF(6))(2), 9, is isolated in good yield as a white solid from the reaction of Hg(OAc)(2) and [H(quinCH(2))(2)im]PF(6). The reaction of [H(quinCH(2))(2)im]PF(6) with excess Ag(2)O produces the triangulo-cluster [Ag(3)((quinCH(2))(2)im)(3)](PF(6))(3), 11. All of these complexes were studied by (1)H NMR spectroscopy, and complexes 3-9 were additionally characterized by X-ray crystallography. These complexes are photoluminescent in the solid state and in solution with spectra that closely resemble those of the ligand precursor. PMID:15332824

  18. Blue-emitting dinuclear N-heterocyclic dicarbene gold(I) complex featuring a nearly unit quantum yield

    KAUST Repository

    Baron, Marco

    2012-02-06

    Dinuclear N-heterocyclic dicarbene gold(I) complexes of general formula [Au 2(RIm-Y-ImR) 2](PF 6) 2 (R = Me, Cy; Y = (CH 2) 1-4, o-xylylene, m-xylylene) have been synthesized and screened for their luminescence properties. All the complexes are weakly emissive in solution whereas in the solid state some of them show significant luminescence intensities. In particular, crystals or powders of the complex with R = Me, Y = (CH 2) 3 exhibit an intense blue emission (? max = 450 nm) with a high quantum yield (? em = 0.96). The X-ray crystal structure of this complex is characterized by a rather short intramolecular Au•••Au distance (3.272 ?). Time dependent density functional theory (TDDFT) calculations have been used to calculate the UV/vis properties of the ground state as well as of the first excited state of the complex, the latter featuring a significantly shorter Au•••Au distance. © 2012 American Chemical Society.

  19. Synthesis and Applications of Bidentate N-heterocyclic Mono- and Biscarbene Ligands

    OpenAIRE

    Jokic, Nadezda

    2011-01-01

    Bridge functionalized chelate bis-N-heterocyclic carbene (bis-NHC) rhodium(I) and palladium(II) complexes of the general formula (bis-NHC)Rh(COD)PF6 and Pd(bis-NHC)Br2, having a hydroxyl functional group attached to the bridging moiety were prepared and characterized including single crystal X-ray analysis for Rh(bis-(Me-NHC)(COD)PF6, Rh(bis-(Et-NHC)(COD)PF6, Pd(bis-(MeNHC))Br2. The bis-NHC rhodium complexes were examined in hydrosilylation and transfer hydrogenation reactions. The bis-NHC p...

  20. Interpretation of electronic spectra of ruthenium nitroso complexes with N-heterocyclic ligands

    International Nuclear Information System (INIS)

    Relaying on ab initio and semiempirical CINDO/CI calculations of free ligands L and complexes trans-[Ru(NO)(NH3)4(L)]3+ (L=pyridine, pyrazine, nicotinamide, l-histidine, imidazole), electronic absorption spectra of nitroso complexes with nitrogen-containing heterocyclic ligands L have been analyzed. Spectral manifestations of strong covalent bond Ru-NO was pointed out and the conclusion was made about advisability of presentation of Ru and NO oxidation states in grouping RuNO3+ as Ru(III) and NO0. Introduction of nitroso group into inner coordination sphere of Ru(II) complexes with nitrogen-containing heterocyclic ligands results in essential rearrangement of the entire structure and deprives ligands L of their ability to manifest chromophore properties

  1. Facile Thermal W-W Bond Homolysis in the N-Heterocyclic Carbene-Containing Tungsten Dimer [CpW(CO)2(IMe)]2

    Energy Technology Data Exchange (ETDEWEB)

    van der Eide, Edwin F.; Liu, Tianbiao L.; Camaioni, Donald M.; Walter, Eric D.; Bullock, R. Morris

    2012-03-05

    The thermal W-W bond homolysis in [CpW(CO)2(IMe)]2 (IMe = 1,3-dimethylimidazol-2-ylidene) was investigated and was found to occur to a large extent compared to other tungsten dimers such as [CpW(CO)3]2. CpW(CO)2(IMe)H was prepared by heating a solution of [IMeH]+[CpW(CO)2(PMe3)]?, and exists in solution as a mixture of interconverting cis and trans isomers. The carbene rotation in CpW(CO)2(IMe)H was explored by DFT calculations, and low enthalpic barriers (< 3.5 kcal mol?1) are predicted. CpW(CO)2(IMe)H has pKaMeCN = 31.5(3) and deprotonation with KH gives K+[CpW(CO)2(IMe)]? (• MeCN). Hydride abstraction from CpW(CO)2(IMe)H with Ph3C+PF6? in the presence of a coordinating ligand L (MeCN or THF) gives [CpW(CO)2(IMe)(L)]+PF6?. Electrochemical measurements on the anion [CpW(CO)2(IMe)]? in MeCN, together with digital simulations, give an E1/2 of ?1.54(2) V vs Cp2Fe+/0 for the [CpW(CO)2(IMe)]•/? couple. A thermochemical cycle provides the solution bond dissociation free energy of the W-H bond of CpW(CO)2(IMe)H as 61.3(6) kcal mol?1. In the electrochemical oxidation of [CpW(CO)2(IMe)]?, reversible dimerization of the electrogenerated radical CpW(CO)2(IMe)• occurs, and digital simulation provides kinetic and thermodynamic parameters for the monomer-dimer equilibrium: kdimerization ~ 2.5 ? 104 M?1 s?1, khomolysis ~ 0.5 s?1 (i.e., Kdim ~ 5 ? 104 M?1). Reduction of [CpW(CO)2(IMe)(MeCN)]+PF6? with cobaltocene gives the dimer [CpW(CO)2(IMe)]2, which in solution exists as a mixture of anti and gauche rotomers. As expected from the electrochemical experiments, the dimer is in equilibrium with detectable amounts of CpW(CO)2(IMe)•. This species was observed by IR spectroscopy, and its presence in solution is also in accordance with the observed reactivity toward 2,6-di-tert-butyl-1,4-benzoquinone, chloroform and dihydrogen. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences and Geosciences. Pacific Northwest National Laboratory is a multiprogram national laboratory operated for DOE by Battelle. The EPR studies were performed at EMSL, a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research located at Pacific Northwest National Laboratory.

  2. The isolation of [Pd{OC(O)H}(H)(NHC)(PR3)] (NHC = N-heterocyclic carbene) and its role in alkene and alkyne reductions using formic acid

    KAUST Repository

    Broggi, Julie

    2013-03-27

    The [Pd(SIPr)(PCy3)] complex efficiently promotes a tandem process involving dehydrogenation of formic acid and hydrogenation of C-C multiple bonds using H2 formed in situ. The isolation of a key catalytic hydridoformatopalladium species, [Pd{OC(O)H}(H)(IPr)(PCy 3)], is reported. The complex plays a key role in the Pd(0)-mediated formation of hydrogen from formic acid. Mechanistic and computational studies delineate the operational role of the palladium complex in this efficient tandem sequence. © 2013 American Chemical Society.

  3. A Continuum of Progress: Applications of N-Hetereocyclic Carbene Catalysis in Total Synthesis

    OpenAIRE

    Izquierdo, Javier; Hutson, Gerri E.; Cohen, Daniel T.; Scheidt, Karl A.

    2012-01-01

    N-Heterocyclic carbene (NHC) catalyzed transformations have emerged as powerful tactics for the construction of complex molecules. Since Stetter’s report in 1975 of the total synthesis of cis-jasmon and dihydrojasmon by using carbene catalysis, the use of NHCs in total synthesis has grown rapidly, particularly over the last decade. This renaissance is undoubtedly due to the recent developments in NHC-catalyzed reactions, including new benzoin, Stetter, homoenolate, and aroylation processes. T...

  4. Electronic bond tuning with heterocyclic carbenes

    KAUST Repository

    Falivene, Laura

    2013-01-01

    We discuss the impact of the nature of the heterocyclic carbene ring, when used as a complex forming ligand, on the relative stability of key intermediates in three typical Ru, Pd and Au promoted reactions. Results show that P-heterocyclic carbenes have a propensity to increase the bonding of the labile ligand and of the substrate in Ru-promoted olefin metathesis, whereas negligible impact is expected on the stability of the ruthenacycle intermediate. In the case of Pd cross-coupling reactions, dissociation of a P-heterocyclic carbene is easier than dissociation of the N-heterocyclic analogue. In the case of the Au-OH synthon, the Au-OH bond is weakened with the P-heterocyclic carbene ligands. A detailed energy decomposition analysis is performed to rationalize these results. © 2013 The Royal Society of Chemistry.

  5. Synthesis, spectroscopic characterization and electronic structure of some new Cu(I) carbene complexes

    Indian Academy of Sciences (India)

    Chinnappan Sivasankar; Christina Baskaran; Ashoka G Samuelson

    2006-05-01

    Reaction of oligomeric Cu(I) complexes [Cu{$\\mu$-S-C(=NR)(O-Ar-CH3)}]$_n$ with Lewis acids gave Cu(I) carbene complexes, which were characterized by 1H and 13C NMR spectroscopy. Cu(I) carbene complexes could be directly generated from RNCS, Cu(I)-OAr and Lewis acids; this method can be used to prepare Cu(I) carbene complexes with different substitutents on the carbene carbon. The complexes were unreactive towards olefins and do not undergo cyclopropanation. Electronic structure calculations (DFT) show that the charge on the carbene carbon plays an important role in controlling the reactivity of the carbene complex.

  6. Self-assembly of copper(II) complexes with a dibasic tridentate ligand and monodentate N-heterocycles: structural, magnetic and EPR studies

    Science.gov (United States)

    Das, Sunirban; Pal, Samudranil

    2005-05-01

    Three ternary copper(II) complexes of general formula [Cu(bhac)(hc)], with a tridentate Schiff base, acetylacetone benzoylhydrazone (H 2bhac) and monodentate N-heterocycles (hc=pyrazole, imidazole and pyridine), have been synthesized. Elemental analysis, various forms of spectroscopy (infrared, electronic absorption and EPR), cyclic voltammetry, cryomagnetic measurements and X-ray crystallography were used for the characterization of the complexes. Analytical data, infrared and electronic spectral features and molar conductivity values are consistent with the proposed molecular formulae and the +2 oxidation state of the metal ion in these complexes. In each complex, the enolate-O, the imine-N and the deprotonated amide-O donor tridentate ligand (bhac 2-) and the sp 2 N donor heterocycle form an O 2N 2 square-plane around the metal ion. The whole molecule of none of the complexes is perfectly planar because of different orientation of the phenyl ring plane of the tridentate ligand and that of the heterocycle ring plane with respect to the plane containing rest of the molecule. In the solid state, the complexes having the pyrazole and the pyridine as the heterocyclic ligand, exist as centrosymmetric dimeric species due to very weak apical coordination of the metal bound enolate-O. The complex of imidazole has no such apical coordination and exists as a monomer. In the crystal lattice, the molecules of these complexes are involved in a variety of intermolecular non-covalent interactions such as O-H⋯O, N-H⋯O, N-H⋯N, C-H⋯? and ?⋯?. Self-assembly via these interactions lead to a one-dimensional arrangement of [Cu(bhac)(Hpyrz)]·C 2H 5OH, a two-dimensional layered structure of [Cu(bhac)(Himdz)] and a three-dimensional network of [Cu(bhac)(py)]. Cryomagnetic and EPR spectral measurements indicates weak antiferromagnetic spin-exchange in all the three complexes.

  7. Water-soluble tetrapodal N, O ligands incorporating soft N-heterocycles for the selective complexation of Am(III) over Ln(III)

    International Nuclear Information System (INIS)

    A series of four water-soluble N, O-tetrapodal ligands derived from ethylenediamine, bearing hard acetate groups and soft N-heterocycles, either pyridine or pyrazine, was developed to study the impact of the softness of N-donors on the complexation properties with trivalent f ions. Two novel ligands of enhanced soft character, bearing three pyridines (L3py) or three pyrazines (L3pz), were synthesized and the related lanthanide complexes were studied in solution. The ligand containing three pyridyl-methyl moieties L3py gives complexes with a coordination similar to EDTA, i.e. a hexa-dentate coordination mode as indicated by NMR and luminescence decays (q = 3) and stability constants in the range log ?110 = 6.99-9.3 (La-Lu). On the other hand, the softest molecule L3pz forms much less stable complexes with log ?110 = 4.0-4.4 (La-Eu). The selective back-extraction of Am(III) from organic solutions containing 4f and 5f elements was tested with the four water-soluble complexing agents. The ligand L3pz demonstrates poor stripping ability and selectivity. In contrast, the three ligands Lpy, Lpz and L3py give interesting back-extraction results with Eu/Am separation factors ranging from 36 to 46, which are significantly higher than with HEDTA. This exemplifies the role of the N-hetero-cycle softness in enhancing the separation between Am(III) and Eu(III). Interestingly, the pyrazine-based ligand, Lpz, demonstrates the best stripping properties, with a distribution factor that approaches that of HEDTA in the same conditions (DAm?0.3). This molecule is a good compromise between softness and hardness and forms complexes still stable at pH 3 due to its low basicity. (authors)

  8. Experimental and Computational Studies on the Mechanism of N-Heterocycle C-H Activation by Rh(I)/PCy3

    OpenAIRE

    Wiedemann, Sean H.; Lewis, Jared C.; Ellman, Jonathan A.; Bergman, Robert G.

    2006-01-01

    Evidence is presented for a proposed mechanism of C-H activation of 3-methyl-3,4-dihydroquinazoline (1) by (PCy3)2RhCl. One intermediate (3), a coordination complex of 1 with (PCy3)2RhCl, was identified along the path to the Rh-N-heterocyclic carbene product of this reaction (2). Isotopic labeling and reaction-rate studies were used to demonstrate that C-H activation takes place intramolecularly on the reaction coordinate between 3 and 2. Computational studies corroborate the proposed mechani...

  9. Stability constants of Ni(II)- and Cu(II)-N-heterocycle complexes according to spectrophotometric data

    Science.gov (United States)

    Badhe, Samata; Tekade, Pradip; Bajaj, Sonal; Thakare, Shrikant

    2015-12-01

    The interaction of Ni(II) and Cu(II) with ethyl 4-(4-hydroxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine- 5-carboxylate [Ligand 1], 4-(1H-benzimidazol-2-yl)phenol [Ligand 2], and 2-(3-phenylamino- 4,5-dihydro-1,2-oxazol-5-yl)phenol [Ligand 3] have been studied by spectrophotometric technique at 0.01 M ionic strength and 28°C in 70% dioxane—water mixture. The data obtained were used to estimate the stability constant of these ligands. Spectrophotometric investigation of Ni(II) and Cu(II) complexes with these ligands shows 1: 1 complex formation. The formation of complexes has been studied by Job's variation method. The values of conditional stability constants of Cu(II) complexes are greater than the corresponding Ni(II) complexes. The greater value of stability constant of Cu(II) complexes may be due to the fact of more stable nature of Cu(II). The value of stability constant of Cu(II)—Ligand 2 complex is greater than that of Cu(II)-Ligand 1 and Cu(II)-Ligand 3. The same of Ni(II)-Ligand 3 complex is greater than that of Ni(II)-Ligand 1 and Ni(II)-Ligand 2.

  10. Syntheses and structural characterizations of 24-membered dimetal (Mn, Ni, Fe) macrocyclic complexes and the C-S bond formation between acetylacetone and a mercapto N-heterocycle.

    Science.gov (United States)

    Zhang, Xiaofeng; Chen, Hui; Ma, Chengbing; Chen, Changneng; Liu, Qiutian

    2006-09-01

    An organic ligand 2,5-di(3-pentanedionylthio)-1,3,4-thiadiazole (H2L) reacts with metal (Mn, Ni, Fe) salts, resulting in 24-membered dimetal macrocyclic complexes [MnL(H2O)(dmso)](2).2dmso, [NiL(H2O)(dmf)](2).2dmf, [MnL(dmf)2]2 and [Fe2L2(solvent)2(SO4)] (solvent=dmso; H2O ; dmf). Di-manganese macrocyclic complexes [MnL(dmf)(dmso)]2 and [MnL(H2O)2](2).6H2O can also be obtained directly by aerobic assembly reaction of MnCl2, dipotassium 1,3,4-thiadiazole-2,5-dithiolate (K2tdadt) and acetylacetone (H2acac) in various solvents, accompanying a C-S bond formation between acetylacetone and the mercapto N-heterocycle. Disulfide has been considered as the intermediate in the assembly reaction. Meanwhile an assembly reaction including MnCl2, 2-mercaptobenzimidazole and H2acac has produced an organic compound 2-(3-pentanedionylthio)benzimidazole with a new C-S bond. These dimetal complexes have similar macrocyclic structures, in which solvent molecules and sulfate coordinate to the octahedral metal in trans-configuration, whereas a pair of water molecules are located in octahedral cis-positions for owing to a small steric effect. A host cavity of sufficiently large size exists in the macrocyclic structure to trap the solvent molecules and the sulfate anion. The IR spectra have been used to assign the solvent molecules trapped and the sulfate anion which is shown as a bridged bidentate ligand. Thermal analyses show the stability of the macrocyclic backbone below 200 degrees C and gradual release processes of the trapped solvent molecules. Decomposition and oxidation of the dimetal macrocycle backbone occur at 300-500 degrees C, resulting in a metal sulfate. Further decomposition led to metal oxide at 500-600 degrees C. PMID:17028714

  11. Fischer carbene complexes with two chromium centers as potential molecular wires.

    Czech Academy of Sciences Publication Activity Database

    Metelková, R.; Tobrman, T.; Hoskovcová, I.; Ludvík, Ji?í

    Lausanne : International Society of Electrochemistry, 2014. ise142050. [Annual Meeting of the International Society of Electrochemistry /65./. 31.08.2014-05.09.2014, Lausanne] Institutional support: RVO:61388955 Keywords : Fiescher carbene complexes * electron transfer * electrochemistry Subject RIV: CG - Electrochemistry

  12. Hexacoordinate Ru-based olefin metathesis catalysts with pH-responsive N-heterocyclic carbene (NHC) and N-donor ligands for ROMP reactions in non-aqueous, aqueous and emulsion conditions.

    Science.gov (United States)

    Balof, Shawna L; Nix, K Owen; Olliff, Matthew S; Roessler, Sarah E; Saha, Arpita; Müller, Kevin B; Behrens, Ulrich; Valente, Edward J; Schanz, Hans-Jörg

    2015-01-01

    Three new ruthenium alkylidene complexes (PCy3)Cl2(H2ITap)Ru=CHSPh (9), (DMAP)2Cl2(H2ITap)Ru=CHPh (11) and (DMAP)2Cl2(H2ITap)Ru=CHSPh (12) have been synthesized bearing the pH-responsive H2ITap ligand (H2ITap = 1,3-bis(2',6'-dimethyl-4'-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene). Catalysts 11 and 12 are additionally ligated by two pH-responsive DMAP ligands. The crystal structure was solved for complex 12 by X-ray diffraction. In organic, neutral solution, the catalysts are capable of performing standard ring-opening metathesis polymerization (ROMP) and ring closing metathesis (RCM) reactions with standard substrates. The ROMP with complex 11 is accelerated in the presence of two equiv of H3PO4, but is reduced as soon as the acid amount increased. The metathesis of phenylthiomethylidene catalysts 9 and 12 is sluggish at room temperature, but their ROMP can be dramatically accelerated at 60 °C. Complexes 11 and 12 are soluble in aqueous acid. They display the ability to perform RCM of diallylmalonic acid (DAMA), however, their conversions are very low amounting only to few turnovers before decomposition. However, both catalysts exhibit outstanding performance in the ROMP of dicyclopentadiene (DCPD) and mixtures of DCPD with cyclooctene (COE) in acidic aqueous microemulsion. With loadings as low as 180 ppm, the catalysts afforded mostly quantitative conversions of these monomers while maintaining the size and shape of the droplets throughout the polymerization process. Furthermore, the coagulate content for all experiments stayed <2%. This represents an unprecedented efficiency in emulsion ROMP based on hydrophilic ruthenium alkylidene complexes. PMID:26664616

  13. A correlation between redox behaviour of Fischer-type carbene complexes and their structure and reactivity.

    Czech Academy of Sciences Publication Activity Database

    Hoskovcová, I.; Dvo?ák, D.; Ludvík, Ji?í; Záliš, Stanislav

    Bratislava : Slovak Technical University Press, 2007 - (Melník, M.; Šima, J.; Tatarko, M.), s. 1-15 R&D Projects: GA ?R GA203/04/0487 Institutional research plan: CEZ:AV0Z40400503 Keywords : Fischer-type carbene complexes * correlation * electrochemical measurements Subject RIV: CG - Electrochemistry

  14. Abstraction of methyl from neutral Fischer-type carbene complexes: A new site for nucleophilic attack

    Energy Technology Data Exchange (ETDEWEB)

    Toomey, L.M.; Atwood, J.D. [State Univ. of New York, Buffalo, NY (United States)

    1997-02-04

    Reactions of Fischer-type carbene complexes, M(CO){sub 5}(C(OMe)pH) (M = Cr, W), with metal carbonyl anions (M`{sup -} = CpFe(CO){sub 2}{sup -@}, Re(CO){sub 5}{sup -}, Mn(CO){sub 4}PPh{sub 3}{sup -}, Co(CO){sub 3}PPh{sub 3}{sup -}, Cp{sup *}Cr(CO){sub 3}{sup -}, CpMo(CO){sub 3}{sup -}) result in demethylation of the carbene complexes. The products are M(CO){sub 5}C(O)Ph{sup -} and M`-Me, characterized by infrared and NMR spectroscopy. A slower rate for reaction with W(CO){sub 5}(C(OEt)Ph) in comparison to the methyl analogue is consistent with nucleophilic attack of the metal carbonyl anion on the methyl of the methoxy group of the carbene. This is a new type of nucleophilic attack of a Fischer-type carbene. 22 refs., 1 fig., 1 tab.

  15. Synthesis of axially chiral gold complexes and their applications in asymmetric catalyses

    OpenAIRE

    Sun, Yin-wei; XU, QIN; SHI, MIN

    2013-01-01

    Several novel chiral N-heterocyclic carbene and phosphine ligands were prepared from (S)-BINOL. Moreover, their ligated Au complexes were also successfully synthesized and characterized by X-ray crystal diffraction. A weak gold-? interaction between the Au atom and the aromatic ring in these gold complexes was identified. Furthermore, we confirmed the formation of a pair of diastereomeric isomers in NHC gold complexes bearing an axially chiral binaphthyl moiety derived from the hindered rotat...

  16. Mutagenic activity of some platinum and ruthenium complexes with N-heterocyclic ligands in salmonella typhimurium Ta 1530 and Ta 98

    International Nuclear Information System (INIS)

    The mutagenic activity of some platinum and ruthenium complexes with 2,2'-biquinoline (b iq) and 2-(2' -pyridyl) quinoline (p q) was examined in strains of salmonella typhimurium Ta 1530 and Ta 98. The complexes cis-[Pt(Nn)X2)] (Nn=b iq, X=CI; Nn=p q, X=CI, Br), Pt3(b iq)2I6 and me r-[Ru(b iq)2CI3].2H2O exhibit significant mutagenic activity while me r-[Ru(p q)CI3(C2H5OH)], [Ru(p q)CI4]. 3a-2a and [Ru(p q) (DMSO)2CI2].0.5H2O show much weaker mutagenic activity. the platinum complexes appear to be more active via induction of frameshift than base substitution mutation while me r-[Ru(b iq)2CI3].2H2O is highly mutagenic via base substitution. (authors). 16 refs., 2 tabs

  17. Salicylaldimine Ruthenium Alkylidene Complexes: Metathesis Catalysts Tuned for Protic Solvents

    OpenAIRE

    Binder, Joseph B.; Guzei, Ilia A.; Raines, Ronald T.

    2007-01-01

    Tuning the electronic and steric environment of olefin metathesis catalysts with specialized ligands can adapt them to broader applications, including metathesis in aqueous solvents. Bidentate salicylaldimine ligands are known to stabilize ruthenium alkylidene complexes, as well as allow ring-closing metathesis in protic media. Here, we report the synthesis and characterization of exceptionally robust olefin metathesis catalysts bearing both bidentate salicylaldimine and N-heterocyclic carben...

  18. Synthesis of hydronaphthalenes through coupling of enyne carbonyl compounds that contain pendant alkene groups with Fischer carbene complexes

    OpenAIRE

    Kumar-Patti, Rajesh; Duan, Shaofeng; Camacho-Davila, Alejandro; Waynant, Kris; Dunn, Kenneth A.; Herndon, James W.

    2010-01-01

    The coupling of enyne carbonyl compounds that contain pendant alkene groups with Fischer carbene complexes to afford furans that contain pendant alkene groups is described. Subsequent intramolecular Diels-Alder reactions are effective in select cases, resulting in hydronaphthalene systems after dehydration. Although the Diels-Alder event is thermodynamically unfavorable, the overall transformation of alkene-furans to dihydronaphthalenes is a favorable process.

  19. Tandem olefin metathesis/hydrogenation at ambient temperature: activation of ruthenium carbene complexes by addition of hydrides.

    Science.gov (United States)

    Schmidt, Bernd; Pohler, Michael

    2003-07-21

    Sodium hydride activates ruthenium carbene complexes to catalyze hydrogenation reactions subsequent to ring closing olefin metathesis. Under these conditions, hydrogenation of cyclopentenols proceeds smoothly at ambient temperature and under 1 atm of hydrogen in toluene. An alternative protocol was developed that involves the formation of hydrogen in situ by reaction of excess sodium hydride with protic functional groups and water. PMID:12956069

  20. Synthesis of Naphthalenes through Three-Component Coupling of Alkynes, Fischer Carbene Complexes, and Benzaldehyde Hydrazones via Isoindole Intermediates

    OpenAIRE

    Duan, Shaofeng; Sinha-Mahapatra, Dilip K.; Herndon, James W.

    2008-01-01

    The synthesis of naphthalene derivatives through three-component coupling of 2-alkynylbenzaldehyde hydrazones with carbene complexes and electron-deficient alkynes has been examined. The reaction involves formation of an isoindole derivative, followed by intramolecular Diels–Alder reaction, followed by nitrene extrusion. The reaction was highly regioselective using unsymmetrical alkynes.

  1. Synthesis of naphthalenes through three-component coupling of alkynes, Fischer carbene complexes, and benzaldehyde hydrazones via isoindole intermediates.

    Science.gov (United States)

    Duan, Shaofeng; Sinha-Mahapatra, Dilip K; Herndon, James W

    2008-04-17

    The synthesis of naphthalene derivatives through three-component coupling of 2-alkynylbenzaldehyde hydrazones with carbene complexes and electron-deficient alkynes has been examined. The reaction involves formation of an isoindole derivative, followed by intramolecular Diels-Alder reaction, followed by nitrene extrusion. The reaction was highly regioselective using unsymmetrical alkynes. PMID:18351767

  2. Theoretical tools to distinguish O-ylides from O-ylidic complexes in carbene-solvent interactions.

    Science.gov (United States)

    Gómez, Sara; Restrepo, Albeiro; Hadad, C Z

    2015-11-25

    In this paper, we report the geometries and properties of 48 molecular species located on the MP2/6-311++G(d,p) PES of the fluorocarbene-(methanol)3 system. The structures were found by a combination of a stochastic search method, using a modified Metropolis acceptance test, and some hand constructed very symmetrical structures. We use several theoretical descriptors to categorize these species, focusing our attention on the interaction between the carbene carbon and the methanol oxygen, CcO, because this is the key interaction in the formation of O-ylides, ether products, and O-ylidic solvation complexes. These descriptors include natural charges and natural bond orbitals (NBO), CcO bond orders, CcO distances, energetic stabilities, and properties at bond critical points. Accordingly, the isomers were divided into four groups: ethers, fluorocarbene-methanol O-ylides, O-ylidic carbene-solvent complexes and hydrogen bonded carbene-solvent complexes. We found that the possibility of forming H-bonds among solvent molecules and between the carbene carbon and the hydrogen of the solvent molecule affects the stability, structure and nature of CcO interactions in O-ylides and O-ylidic complexes to the point of generating some diffuse borderlines between these two kinds of species. We determined which set of theoretical tools is suitable to better distinguish between them. Additionally, we clarify the nature of the relevant interactions in these species. PMID:26568481

  3. Bis-mixed-carbene ruthenium-thiolate-alkylidene complexes: synthesis and olefin metathesis activity.

    Science.gov (United States)

    Dahcheh, Fatme; Stephan, Douglas W

    2015-01-28

    A series of bis-carbene Ru-hydride species, including (IMes)(Im(OMe)2)(PPh3)RuHCl (1) and (SIMes)(Me2Im(OMe)2)(PPh3)RuHCl (2) were prepared and subsequently shown to react with aryl-vinyl-sulfides to give the bis-carbene-alkylidene complexes: Im(OMe)2(SIMes)RuCl(SR)(=CHCH3) (R = p-FC6H4 (3), p-(NO2)C6H4 (4)), Im(OMe)2(IMes)RuCl(=CHCH3)(SPh) (5), Me2Im(OMe)2(SIMes)RuCl(=CHCH3)(SPh) (6), Im(OMe)2(SIMes)(F5C6S)RuCl(=CHR) (R = C4H9 (9), C5H11 (10)). The activity of these species in the standard Grubbs' tests for ring-opening metathesis polymerization, ring-closing and cross-metathesis are reported. Although these thiolate derivatives are shown to exhibit modest metathesis activities, the reactivity is enhanced in the presence of BCl3. PMID:25462569

  4. Metallocene carbene chemistry

    International Nuclear Information System (INIS)

    A review of chemical properties of group IV element chamfered metallocenes Cp2M (M=Ti, Zr, Hf) is presented. It is shown that specific features of their stereoelectronic structure and clearly pronounced oxophily of M metals permit using the complexes as components of reaction systems involving carbenes. The use of ruthenium carbene complexes for realizing the catalytic metathesis of lateral olefin substituents in the chamfered metallocenes is described by way of example

  5. Correlations and Contrasts in Homo- and Heteroleptic Cyclic (Alkyl)(amino)carbene-Containing Pt(0) Complexes.

    Science.gov (United States)

    Arnold, Nicole; Braunschweig, Holger; Brenner, Peter B; Celik, Mehmet Ali; Dewhurst, Rian D; Haehnel, Martin; Kramer, Thomas; Krummenacher, Ivo; Marder, Todd B

    2015-08-24

    An improved synthetic route to homoleptic complex [Pt(CAAC(Me))2] (CAAC = cyclic (alkyl)(amino)carbenes) and convenient routes to new heteroleptic complexes of the form [Pt(CAAC(Me))(PR3)] are presented. Although the homoleptic complex was found to be inert to many reagents, oxidative addition and metal-only Lewis pair (MOLP) formation was observed from one of the heteroleptic complexes. The spectroscopic, structural, and electrochemical properties of the zero-valent complexes were explored in concert with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. The homoleptic [Pt(CAAC)2] and heteroleptic [Pt(CAAC)(PR3)] complexes were found to be similar in their spectroscopic and structural properties, but their electrochemical behavior and reactivity differ greatly. The unusually strong color of the CAAC-containing Pt(0) complexes was investigated by TD-DFT calculations and attributed to excitations into the LUMOs of the complexes, which are predominantly composed of bonding ? interactions between Pt and the CAAC carbon atoms. PMID:26241579

  6. Total synthesis of the calphostins: application of fischer carbene complexes and thermodynamic control of atropisomers.

    Science.gov (United States)

    Merlic, C A; Aldrich, C C; Albaneze-Walker, J; Saghatelian, A; Mammen, J

    2001-02-23

    The total syntheses of the potent protein kinase C inhibitors calphostins A, B, C, and D as well as a variety of structural analogues are reported. An aminobenzannulation reaction of an enantiopure chromium Fischer carbene complex is utilized to prepare a pentasubstituted naphthylamine. After optimization of side-chain substituents, conversion of the naphthylamine to an o-naphthoquinone was followed by biomimetic oxidative dimerization using trifluoroacetic acid and air yielding a 1:2 P/M mixture of atropisomeric perylenequinones. Thermal equilibration to a 3:1 P:M atropisomeric ratio and separation of the perylenequinones followed by side chain desymmetrization and functionalization led to the total synthesis of enantio- and diastereomerically pure calphostin C in only twelve steps from commercially available starting materials. In addition, calphostins A, B, D, and several structural analogues were prepared to evaluate biological activities. PMID:11312960

  7. One-pot three-component synthesis of quinoxaline and phenazine ring systems using Fischer carbene complexes

    OpenAIRE

    Priyabrata Roy; Binay Krishna Ghorai

    2010-01-01

    One-pot three-component coupling of o-alkynylheteroaryl carbonyl derivatives with Fischer carbene complexes and dienophiles leading to the synthesis of quinoxaline and phenazine ring systems has been investigated. This involves the generation of furo[3,4-b]pyrazine and furo[3,4-b]quinoxaline as transient intermediates, which were trapped with Diels–Alder dienophiles. This is the first report on furo[3,4-b]pyrazine intermediates.

  8. One-pot three-component synthesis of quinoxaline and phenazine ring systems using Fischer carbene complexes

    Directory of Open Access Journals (Sweden)

    Priyabrata Roy

    2010-05-01

    Full Text Available One-pot three-component coupling of o-alkynylheteroaryl carbonyl derivatives with Fischer carbene complexes and dienophiles leading to the synthesis of quinoxaline and phenazine ring systems has been investigated. This involves the generation of furo[3,4-b]pyrazine and furo[3,4-b]quinoxaline as transient intermediates, which were trapped with Diels–Alder dienophiles. This is the first report on furo[3,4-b]pyrazine intermediates.

  9. C-H activation in Ir(III) and N-demethylation in Pt(II) complexes with mesoionic carbene ligands: examples of monometallic, homobimetallic and heterobimetallic complexes.

    Science.gov (United States)

    Maity, Ramananda; Tichter, Tim; van der Meer, Margarethe; Sarkar, Biprajit

    2015-11-14

    Mononuclear Pt(II) and the first dinuclear Pt(II) complexes along with a cyclometalated heterobimetallic Ir(III)/Pd(II) complex bearing mesoionic carbene donor ligands are presented starting from the same bis-triazolium salt. The mononuclear Pt(II) complex possesses a free triazole moiety which is generated from the corresponding triazolium salt through an N-demethylation reaction, whereas the mononuclear Ir(III) complex features an unreacted triazolium unit. PMID:26443200

  10. Copper(I) complexes of mesoionic carbene: structural characterization and catalytic hydrosilylation reactions.

    Science.gov (United States)

    Hohloch, Stephan; Duecker, Fenja Leena; van der Meer, Margarethe; Sarkar, Biprajit

    2015-01-01

    Two series of different Cu(I)-complexes of "click" derived mesoionic carbenes are reported. Halide complexes of the type (MIC)CuI (with MIC = 1,4-(2,6-diisopropyl)-phenyl-3-methyl-1,2,3-triazol-5-ylidene (for 1b), 1-benzyl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene (for 1c)) and cationic complexes of the general formula [Cu(MIC)2]X (with MIC =1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene, X = CuI2- (for 2á), 1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene, X = BF4- (for 2a), 1,4-(2,6-diisopropyl)phenyl-3-methyl-1,2,3-triazol-5-ylidene, X = BF4- (for 2b), 1-benzyl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene, X = BF4- (for 2c)) have been prepared from CuI or [Cu(CH3CN)4](BF4) and the corresponding ligands, respectively. All complexes were characterized by elemental analysis and standard spectroscopic methods. Complexes 2á and 1b were studied by single-crystal X-ray diffraction analysis. Structural analysis revealed 2á to adopt a cationic form as [Cu(MIC)2](CuI2) and comparison of the NMR spectra of 2á and 2a confirmed this conformation in solution. In contrast, after crystallization complex 1b was found to adopt the desired neutral form. All complexes were tested for the reduction of cyclohexanone under hydrosilylation condition at elevated temperatures. These complexes were found to be efficient catalysts for this reaction. 2c was also found to catalyze this reaction at room temperature. Mechanistic studies have been carried out as well. PMID:25911966

  11. Copper(I Complexes of Mesoionic Carbene: Structural Characterization and Catalytic Hydrosilylation Reactions

    Directory of Open Access Journals (Sweden)

    Stephan Hohloch

    2015-04-01

    Full Text Available Two series of different Cu(I-complexes of “click” derived mesoionic carbenes are reported. Halide complexes of the type (MICCuI (with MIC = 1,4-(2,6-diisopropyl-phenyl-3-methyl-1,2,3-triazol-5-ylidene (for 1b, 1-benzyl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene (for 1c and cationic complexes of the general formula [Cu(MIC2]X (with MIC =1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene, X = CuI2? (for 2á, 1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene, X = BF4? (for 2a, 1,4-(2,6-diisopropylphenyl-3-methyl-1,2,3-triazol-5-ylidene, X = BF4? (for 2b, 1-benzyl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene, X = BF4? (for 2c have been prepared from CuI or [Cu(CH3CN4](BF4 and the corresponding ligands, respectively. All complexes were characterized by elemental analysis and standard spectroscopic methods. Complexes 2á and 1b were studied by single-crystal X-ray diffraction analysis. Structural analysis revealed 2á to adopt a cationic form as [Cu(MIC2](CuI2 and comparison of the NMR spectra of 2á and 2a confirmed this conformation in solution. In contrast, after crystallization complex 1b was found to adopt the desired neutral form. All complexes were tested for the reduction of cyclohexanone under hydrosilylation condition at elevated temperatures. These complexes were found to be efficient catalysts for this reaction. 2c was also found to catalyze this reaction at room temperature. Mechanistic studies have been carried out as well.

  12. Structurally Characterized Cationic Silver(I) and Ruthenium(II)carbene complexes of 1,2,3-Triazol-5-ylidenes

    OpenAIRE

    Cai, Jiajia; Yang, Xiaoping; Arumugam, Kuppuswamy; Bielawski, Christopher W.; Jonathan L. Sessler

    2011-01-01

    A novel 1,3,4-substituted 1,2,3-triazolium salt was found to function as an effective precursor for the synthesis of the first structurally characterized cationic silver(I) and ruthenium(II)carbene complexes of overall 1:2 ligand-to-metal stoichiometry. The Ag(I) complex crystallized in the form of an eight silver atom-containing cluster, whereas the Ru(II) complex proved to be a discrete species and was found to be capable of initiating the ring-opening metathesis polymerization of norbornen...

  13. Density functional computations of the cyclopropanation of ethene catalyzed by iron (II) carbene complexes Cp(CO)(L)Fe?CHR, L D CO, PMe3, R D Me, OMe, ph, CO2Me

    Science.gov (United States)

    Wang, Fen; Meng, Qingxi; Li, Ming

    Density functional theory has been used to study the Fe-catalyzed cyclopropanation of Fe-carbene complexes with ethene. All the intermediates and transition states were optimized completely at the B3LYP/6-31+G(d,p) level. Calculation results confirm that the cyclopropanation of Fe-carbene complexes with ethene involves the two reaction paths I and II. In the reaction path I, the double bond of ethene attacks directly on the carbene carbon of Fe-carbene complexes to generate the cyclopropane. In the reaction path II, ethene substitution for PMe3 or CO in the Fe-carbene complexes leads to the complexes M2; and the attack of one carbon of ethene on the carbene carbon results in the complexes M3 with a Fe bond C bond C bond C four-membered ring, and then generates the cyclopropane via the elimination reaction. For Fe-carbene complexes A, C, D, E, and H, the main reaction mode is the reaction path I; for Fe-carbene complexes B, F, and G, the main reaction mode is the reaction path II.0

  14. Comprehensive Thermochemistry of W-H Bonding in the Metal Hydrides CpW(CO)2(IMes)H, [CpW(CO)2(IMes)H]•+, and [CpW(CO)2(IMes)(H)2]+. Influence of an N-Heterocyclic Carbene Ligand on Metal Hydride Bond Energies

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, John A.; Appel, Aaron M.; DuBois, Daniel L.; Bullock, R. Morris

    2011-09-21

    A free energy map interconnecting nine tungsten complexes has been determined based on chemical equilibria and electrochemical data in MeCN solution (T = 22 °C). Homolytic W-H bond dissociation free energies (BDFEs) are 59.3(3) kcal mol?1 for CpW(CO)2(IMes)H and 59(1) kcal mol?1 for the dihydride [CpW(CO)2(IMes)(H)2]+. For the radical cation, [CpW(CO)2(IMes)H]•+, W-H bond homolysis to generate the 16-electron cation [CpW(CO)2(IMes)]+ is followed by MeCN uptake, with free energies for these steps being 51(1) kcal mol?1 and ?16.9(5) kcal mol?1 respectively. Based on these two steps, the free energy change for conversion of [CpW(CO)2(IMes)H]•+ to [CpW(CO)2(IMes)(MeCN)]+ in MeCN is 34(1) kcal mol?1. The pKa of CpW(CO)2(IMes)H in MeCN was determined to be 31.9(1), significantly higher than the 26.6 reported for the related phosphine complex, CpW(CO)2(PMe3)H. This difference is attributed to the electron donor strength of IMes far exceeding that of PMe3. The pKa values for [CpW(CO)2(IMes)H]•+ and [CpW(CO)2(IMes)(H)2]+ were determined to be 6.3(5) and 6.3(8), much closer to the pKa values reported for the PMe3 analogs. The free energy of hydride abstraction from CpW(CO)2(IMes)H is 74(1) kcal mol?1, and the resultant [CpW(CO)2(IMes)]+ cation is significantly stabilized by binding MeCN to form [CpW(CO)2(IMes)(MeCN)]+, giving a hydride donor ability of 57(1) kcal mol?1. Electrochemical oxidation of [CpW(CO)2(IMes)]? shows a fully reversible wave (E° = ?1.65 V vs. Cp2Fe+/0 in MeCN), and CpW(CO)2(IMes)H is reversibly oxidized (E° = ?0.13(3) V) at high scan rates (800 V s?1). High pressure NMR experiments provide an estimate of ?G° = 10.3(4) kcal mol?1 for the displacement of MeCN by H2 for [CpW(CO)2(IMes)(MeCN)]+ to give [CpW(CO)2(IMes)(H)2]+.

  15. Comprehensive thermochemistry of W-H bonding in the metal hydrides CpW(CO)2(IMes)H, [CpW(CO)2(IMes)H](•+), and [CpW(CO)2(IMes)(H)2]+. Influence of an N-heterocyclic carbene ligand on metal hydride bond energies.

    Science.gov (United States)

    Roberts, John A S; Appel, Aaron M; DuBois, Daniel L; Bullock, R Morris

    2011-09-21

    The free energies interconnecting nine tungsten complexes have been determined from chemical equilibria and electrochemical data in MeCN solution (T = 22 °C). Homolytic W-H bond dissociation free energies are 59.3(3) kcal mol(-1) for CpW(CO)(2)(IMes)H and 59(1) kcal mol(-1) for the dihydride [CpW(CO)(2)(IMes)(H)(2)](+) (where IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), indicating that the bonds are the same within experimental uncertainty for the neutral hydride and the cationic dihydride. For the radical cation, [CpW(CO)(2)(IMes)H](•+), W-H bond homolysis to generate the 16-electron cation [CpW(CO)(2)(IMes)](+) is followed by MeCN uptake, with free energies for these steps being 51(1) and -16.9(5) kcal mol(-1), respectively. Based on these two steps, the free energy change for the net conversion of [CpW(CO)(2)(IMes)H](•+) to [CpW(CO)(2)(IMes)(MeCN)](+) in MeCN is 34(1) kcal mol(-1), indicating a much lower bond strength for the 17-electron radical cation of the metal hydride compared to the 18-electron hydride or dihydride. The pK(a) of CpW(CO)(2)(IMes)H in MeCN was determined to be 31.9(1), significantly higher than the 26.6 reported for the related phosphine complex, CpW(CO)(2)(PMe(3))H. This difference is attributed to the electron donor strength of IMes greatly exceeding that of PMe(3). The pK(a) values for [CpW(CO)(2)(IMes)H](•+) and [CpW(CO)(2)(IMes)(H)(2)](+) were determined to be 6.3(5) and 6.3(8), much closer to the pK(a) values reported for the PMe(3) analogues. The free energy of hydride abstraction from CpW(CO)(2)(IMes)H is 74(1) kcal mol(-1), and the resultant [CpW(CO)(2)(IMes)](+) cation is significantly stabilized by binding MeCN to form [CpW(CO)(2)(IMes)(MeCN)](+), giving an effective hydride donor ability of 57(1) kcal mol(-1) in MeCN. Electrochemical oxidation of [CpW(CO)(2)(IMes)](-) is fully reversible at all observed scan rates in cyclic voltammetry experiments (E° = -1.65 V vs Cp(2)Fe(+/0) in MeCN), whereas CpW(CO)(2)(IMes)H is reversibly oxidized (E° = -0.13(3) V) only at high scan rates (800 V s(-1)). For [CpW(CO)(2)(IMes)(MeCN)](+), high-pressure NMR experiments provide an estimate of ?G° = 10.3(4) kcal mol(-1) for the displacement of MeCN by H(2) to give [CpW(CO)(2)(IMes)(H)(2)](+). PMID:21780811

  16. Aerosolized antimicrobial agents based on degradable dextran nanoparticles loaded with silver carbene complexes

    KAUST Repository

    Ornelas-Megiatto, Cátia

    2012-11-05

    Degradable acetalated dextran (Ac-DEX) nanoparticles were prepared and loaded with a hydrophobic silver carbene complex (SCC) by a single-emulsion process. The resulting particles were characterized for morphology and size distribution using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The average particle size and particle size distribution were found to be a function of the ratio of the organic phase to the surfactant containing aqueous phase with a 1:5 volume ratio of Ac-DEX CH2Cl2 (organic):PBS (aqueous) being optimal for the formulation of nanoparticles with an average size of 100 ± 40 nm and a low polydispersity. The SCC loading was found to increase with an increase in the SCC quantity in the initial feed used during particle formulation up to 30% (w/w); however, the encapsulation efficiency was observed to be the best at a feed ratio of 20% (w/w). In vitro efficacy testing of the SCC loaded Ac-DEX nanoparticles demonstrated their activity against both Gram-negative and Gram-positive bacteria; the nanoparticles inhibited the growth of every bacterial species tested. As expected, a higher concentration of drug was required to inhibit bacterial growth when the drug was encapsulated within the nanoparticle formulations compared with the free drug illustrating the desired depot release. Compared with free drug, the Ac-DEX nanoparticles were much more readily suspended in an aqueous phase and subsequently aerosolized, thus providing an effective method of pulmonary drug delivery. © 2012 American Chemical Society.

  17. Carbene complexes of zirconium. Synthesis, structure, and reactivity with carbon monoxide to affort coordinated ketene

    International Nuclear Information System (INIS)

    Treatment of Cp2Zr(L)(CO) (Cp = C5H5; L = PMe3, CO) with Cp*2ZrH2 (Cp* = C5Me5) affords zirconium oxycarbene complexes, Cp2(L)Zr double bond CHO single bond Zr(X)Cp*2 (L = PMe3, X = H, I; L = CO, X = H), that represent some of the first examples of group 4 metal-to-carbon multiple bonding. The first X-ray diffraction structure determination of a zirconium carbene complex, that of Cp(PMe3)Zr double bond CHO single bond Zr(H)Cp*2.C6H6, is reported (C2/c, a = 27.318 (4) A, b = 19.895 (3) A, c = 19.932 (5) A ? = 132.188 (10)0, Z = 8) and shows a very short Zr-C bond length of 2.117 (7) A. Treatment of Cp2(CO)Zr double bond CHO single bond Zr(H)Cp*2 with CH3 I or Cp2(PMe3)Zr double bond CHO single bond Zr(I)Cp*2 with CO affords the zirconium substituted enediolate zirconacycle, Cp*2ZrOCH double bond C(Zr(I)Cp2)O, which has been characterized by an X-ray diffraction study (P21/c, a = 15.866 (4) A, b = 10.673 (3) A, c = 20.561 (4) A, ? = 105.5 (2)0, Z = 4). This complex most likely forms by coupling of the zirconoxycarbene and a carbonyl to give a metal-coordinated ketene intermediate that subsequently rearranges to the isolated product. An isotopic crossover experiment has demonstrated that the new carbon-carbon bond is formed in an intramolecular coupling step. The ketene intermediate can be trapped by dissolving Cp2(CO)Zr double bond CHO single bond Zr(H)Cp*2 in pyridine, giving Cp2(py)Zr(O double bond C double bond CHOZr(I)Cp*2). Treatment of the isolated ketene complex with CH3I in benzene gives the enediolate zirconocycle; in pyridine Cp2(py)Zr(O double bond C double bond CHOZr(I)Cp*2) can be observed spectroscopically. 38 references, 4 figures, 5 tables

  18. Chemistry of N,S-Heterocyclic Carbene and Metallaboratrane Complexes: A New ?(3) -BCC-Borataallyl Complex.

    Science.gov (United States)

    Roy, Dipak Kumar; De, Anangsha; Panda, Subhankar; Varghese, Babu; Ghosh, Sundargopal

    2015-09-21

    A high-yielding synthetic route for the preparation of group?9 metallaboratrane complexes [Cp*MBH(L)2 ], 1 and 2 (1, M=Rh, 2, M=Ir; L=C7 H4 NS2 ) has been developed using [{Cp*MCl2 }2 ] as precursor. This method also permitted the synthesis of an Rh-N,S-heterocyclic carbene complex, [(Cp*Rh)(L2 )(1-benzothiazol-2-ylidene)] (3; L=C7 H4 NS2 ) in good yield. The reaction of compound 3 with neutral borane reagents led to the isolation of a novel borataallyl complex [Cp*Rh(L)2 B{CH2 C(CO2 Me)}] (4; L=C7 H4 NS2 ). Compound 4 features a rare ?(3) -interaction between rhodium and the B-C-C unit of a vinylborane moiety. Furthermore, with the objective of generating metallaboratranes of other early and late transition metals through a transmetallation approach, reactions of rhoda- and irida-boratrane complexes with metal carbonyl compounds were carried out. Although the objective of isolating such complexes was not achieved, several interesting mixed-metal complexes [{Cp*Rh}{Re(CO)3 }(C7 H4 NS2 )3 ] (5), [Cp*Rh{Fe2 (CO)6 }(?-CO)S] (6), and [Cp*RhBH(L)2 W(CO)5 ] (7; L=C7 H4 NS2 ) have been isolated. All of the new compounds have been characterized in solution by mass spectrometry, IR spectroscopy, and (1) H, (11) B, and (13) C?NMR spectroscopies, and the structural types of 4-7 have been unequivocally established by crystallographic analysis. PMID:26251213

  19. Ruthenium Olefin Metathesis Catalysts Bearing Carbohydrate-Based N-Heterocyclic Carbenes

    OpenAIRE

    Keitz, Benjamin K.; Grubbs, Robert H

    2010-01-01

    Ru-based olefin metathesis catalysts containing carbohydrate-derived NHCs from glucose and galactose were synthesized and characterized by NMR spectroscopy. 2D-NMR spectroscopy revealed the presence of Ru-C (benzylidene) rotamers at RT and the rate of rotation was measured using magnetization transfer and VT-NMR spectroscopy. The catalysts were found to be effective at ring-opening metathesis polymerization (ROMP), ring closing metathesis (RCM), cross metathesis (CM), and asymmetric ring open...

  20. Ruthenium Olefin Metathesis Catalysts Bearing Carbohydrate-Based N-Heterocyclic Carbenes

    Science.gov (United States)

    Keitz, Benjamin K.; Grubbs, Robert H.

    2010-01-01

    Ru-based olefin metathesis catalysts containing carbohydrate-derived NHCs from glucose and galactose were synthesized and characterized by NMR spectroscopy. 2D-NMR spectroscopy revealed the presence of Ru-C (benzylidene) rotamers at RT and the rate of rotation was measured using magnetization transfer and VT-NMR spectroscopy. The catalysts were found to be effective at ring-opening metathesis polymerization (ROMP), ring closing metathesis (RCM), cross metathesis (CM), and asymmetric ring opening cross metathesis (AROCM) and showed surprising selectivity in both CM and AROCM. PMID:21603126

  1. Group 6 heteroatom- and non-heteroatom-stabilized carbene complexes. beta,beta'- and alpha,beta,beta'-annulation reactions of cyclic enamines.

    Science.gov (United States)

    Barluenga, José; Ballesteros, Alfredo; Bernardo De La Rúa, Ramón; Santamaría, Javier; Rubio, Eduardo; Tomás, Miguel

    2003-02-19

    Cyclization reactions of group 6 Fischer carbene complexes with cyclopentanone and cyclohexanone enamines are described. Enamine 3a undergoes thermal alpha,beta,beta'-annulation with alkenylcarbene complexes 1 and 2 (THF, 60 degrees C), affording semibullvalenes 5. The metalate intermediates 6, resulting from beta,beta'-annulation of the enamines 3a and 4a, were quantitatively formed by running the reaction in hexane at room temperature. Acid-promoted demetalation of 6 afforded endo-2-bicyclo[3.2.1]octen-8-ones 7 and endo/exo-2-bicyclo[3.3.1]nonen-9-ones 8 (endo/exo = 5:1). Using (S)-methoxymethylpyrrolidine-derived enamines 3b and 4b,c allowed highly enantioenriched cycloadducts endo-(+)-7 as well as endo-(-)-8 and exo-(-)-8 to be accessed. The non-heteroatom-stabilized carbene complex 10 was formed from complex 6 by Me(3)SiOTf-promoted elimination of the methoxy group, characterized by (13)C NMR, and transformed into the organic compounds 7, 7-d, and 11 as well as into bicyclo[3.2.1]octan-2,8-diones 14 and cycloheptanones 15. On the basis of this sequence, enantioenriched cycloheptanones (+)-15 were efficiently prepared in one pot from carbene complexes 2 and enamine 3b (51-55% yield, 91-96% ee). Extension of this work to simple Fischer carbene complexes 16 allowed an appropriate way to generate the nonstabilized pentacarbonyl[(phenyl(alkyl)carbene]tungsten complex 17 to be designed, for which the thermal and chemical behavior leading to compounds 18-21 is described. PMID:12580610

  2. Amine-catalyzed coupling of aldehydes and ketenes derived from Fischer carbene complexes: formation of beta-lactones and enol ethers.

    Science.gov (United States)

    Merlic, Craig A; Doroh, Brandon C

    2003-07-25

    Aldehydes react with ketenes generated from photolysis of Fischer chromium carbene complexes to generate either beta-lactones or enol ethers resulting from decarboxylation of beta-lactones. The reaction is catalyzed by tertiary amines and can occur with diastereoselectivity greater than 20:1 with DMAP as the catalyst. PMID:12868950

  3. Exploring new generations of ruthenium olefin metathesis catalysts: the reactivity of a bis-ylidene ruthenium complex by DFT.

    Science.gov (United States)

    Poater, Albert; Credendino, Raffaele; Slugovc, Christian; Cavallo, Luigi

    2013-05-28

    Density functional theory calculations were used to predict the behaviour of a potential novel architecture of olefin metathesis catalysts, in which one of the neutral ligands of classical Ru-based catalysts, e.g. a phosphine or an N-heterocyclic carbene, is replaced by an alkylidene group. Introduction of a second alkylidene ligand favors dissociation of the remaining phosphine and the overall energy profile for the metathesis using ethylene as the probe substrate reveals that the proposed bis-alkylidene complexes might match the requirements of a good performing olefin metathesis catalyst. PMID:23426093

  4. Exploring new generations of ruthenium olefin metathesis catalysts: The reactivity of a bis-ylidene ruthenium complex by DFT

    KAUST Repository

    Poater, Albert

    2013-01-01

    Density functional theory calculations were used to predict the behaviour of a potential novel architecture of olefin metathesis catalysts, in which one of the neutral ligands of classical Ru-based catalysts, e.g. a phosphine or an N-heterocyclic carbene, is replaced by an alkylidene group. Introduction of a second alkylidene ligand favors dissociation of the remaining phosphine and the overall energy profile for the metathesis using ethylene as the probe substrate reveals that the proposed bis-alkylidene complexes might match the requirements of a good performing olefin metathesis catalyst. © 2013 The Royal Society of Chemistry.

  5. Redox Non–innocence of a N–heterocyclic Nitrenium Cation Bound to a Nickel–Cyclam Core

    OpenAIRE

    Heims, Florian; Pfaff, Florian Felix; Abram, Sarah-Luise; Erik R. Farquhar; Bruschi, Maurizio; Greco, Claudio; Ray, Kallol

    2013-01-01

    The redox properties of Ni complexes bound to a new ligand [DMC–nit]+, where a N–heterocyclic nitrenium group is anchored on a 1,4,8,11–tetraazacyclotetradecane backbone, have been examined using spectroscopic and DFT methods. Ligand based [Ni(DMC–nit)]2+/+ reduction and metal based [Ni(DMC–nit)]2+/3+ oxidation processes have been established for the [Ni(DMC–nit)]+/2+/3+ redox series, which represents the first examples of nitrenium nitrogen (Nnit) bound first row transition metal complexes. ...

  6. Electronic structure and slow magnetic relaxation of low-coordinate cyclic alkyl(amino) carbene stabilized iron(I) complexes.

    Science.gov (United States)

    Samuel, Prinson P; Mondal, Kartik Chandra; Amin Sk, Nurul; Roesky, Herbert W; Carl, Elena; Neufeld, Roman; Stalke, Dietmar; Demeshko, Serhiy; Meyer, Franc; Ungur, Liviu; Chibotaru, Liviu F; Christian, Jonathan; Ramachandran, Vasanth; van Tol, Johan; Dalal, Naresh S

    2014-08-27

    Cyclic alkyl(amino) carbene stabilized two- and three-coordinate Fe(I) complexes, (cAAC)2FeCl (2) and [(cAAC)2Fe][B(C6F5)4] (3), respectively, were prepared and thoroughly studied by a bouquet of analytical techniques as well as theoretical calculations. Magnetic susceptibility and Mössbauer spectroscopy reveal the +1 oxidation state and S = 3/2 spin ground state of iron in both compounds. 2 and 3 show slow magnetic relaxation typical for single molecule magnets under an applied direct current magnetic field. The high-frequency EPR measurements confirm the S = 3/2 ground state with a large, positive zero-field splitting (?20.4 cm(-1)) and reveal easy plane anisotropy for compound 2. CASSCF/CASPT2/RASSI-SO ab initio calculations using the MOLCAS program package support the experimental results. PMID:25072104

  7. Cyclic alkyl amino carbene (CAAC) ruthenium complexes as remarkably active catalysts for ethenolysis.

    Science.gov (United States)

    Marx, Vanessa M; Sullivan, Alexandra H; Melaimi, Mohand; Virgil, Scott C; Keitz, Benjamin K; Weinberger, David S; Bertrand, Guy; Grubbs, Robert H

    2015-02-01

    An expanded family of ruthenium-based metathesis catalysts bearing cyclic alkyl amino carbene (CAAC) ligands was prepared. These catalysts exhibited exceptional activity in the ethenolysis of the seed-oil derivative methyl oleate. In many cases, catalyst turnover numbers (TONs) of more than 100,000 were achieved, at a catalyst loading of only 3?ppm. Remarkably, the most active catalyst system was able to achieve a TON of 340,000, at a catalyst loading of only 1?ppm. This is the first time a series of metathesis catalysts has exhibited such high performance in cross-metathesis reactions employing ethylene gas, with activities sufficient to render ethenolysis applicable to the industrial-scale production of linear ?-olefins (LAOs) and other terminal-olefin products. PMID:25522160

  8. Structural diversity of late transition metal complexes with flexible tetra-NHC ligands.

    Science.gov (United States)

    Weiss, Daniel T; Altmann, Philipp J; Haslinger, Stefan; Jandl, Christian; Pöthig, Alexander; Cokoja, Mirza; Kühn, Fritz E

    2015-11-14

    The synthesis of copper, gold, nickel, palladium, platinum, and iron complexes with open chain tetra-N-heterocyclic carbene (NHC) ligands via transmetalation using silver NHC complexes is presented. The obtained complexes show differing coordination geometries depending on both ligand structure and metal. While the complexes of the coinage metals form di- or tetranuclear structures, the group 10 metal complexes exhibit a distorted square planar coordination geometry at the metal centers. In the case of iron an enhanced flexibility of the ligand - caused by a longer alkyl bridge - leads to octahedral complexes with a sawhorse-type coordination by the tetracarbene ligand and two cis acetonitrile ligands. To the best of our knowledge, this is the first known example of a tetracarbene ligand in sawhorse-type coordination within an octahedral coordination sphere. The remaining cis-labile sites are prone to exchange reactions as shown by addition of trimethylphosphine. PMID:26216511

  9. Correlations between electrochemical and spectrochemical parameters of ruthenium sulfoxides series with N-heterocyclic

    International Nuclear Information System (INIS)

    A systematic study of Ru Cl sub(2) (DMSO) sub(2) L sub(2) derivates, where L = N-heterocyclic base is described, contributing for a best understanding of chemical behaviour and electronic structure of the ruthenium sulfoxides. The correlations between the electrochemical and the spectroscopical parameters of the serie are presented with more emphasis. (author)

  10. Amides of gold(I) diphosphines prepared from N-heterocyclic sources and their in vitro and in vivo screening for anticancer activity

    OpenAIRE

    Horvath, Ulrike E.I.; Dobrza?ska, Liliana; Strasser, Christoph E.; Bouwer, Wilna; Joone, Gisela; Jansen van Rensburg, Constance E.; Cronje, Stephanie; Raubenheimer, Helgard G.

    2012-01-01

    A series of new neutral mononuclear or dinuclear gold(I) complexes and a cyclic cationic tetranuclear amidogold(I) complex comprising of the phosphines 1,2- bis(dimethylphosphino)ethane (dmpe), ?-1,2–bis(diphenylphosphino)ethane (dppe), ?-1,3- bis(diphenylphosphino)propane (dppp), ?-1,5-bis(diphenylphosphino)pentane (dpppe), ?-1,6- bis(diphenylphosphino)hexane (dpph) or trimethylphosphine, and several N-heterocyclic ring systems (imidazolate, pyrazolate, 1,2,3-triazolate, 1,2,4...

  11. Synthesis of axially chiral gold complexes and their applications in asymmetric catalyses

    Science.gov (United States)

    Sun, Yin-wei

    2013-01-01

    Summary Several novel chiral N-heterocyclic carbene and phosphine ligands were prepared from (S)-BINOL. Moreover, their ligated Au complexes were also successfully synthesized and characterized by X-ray crystal diffraction. A weak gold-? interaction between the Au atom and the aromatic ring in these gold complexes was identified. Furthermore, we confirmed the formation of a pair of diastereomeric isomers in NHC gold complexes bearing an axially chiral binaphthyl moiety derived from the hindered rotation around C–C and C–N bonds. In the asymmetric intramolecular hydroamination reaction most of these chiral Au(I) complexes showed good catalytic activities towards olefins tethered with a NHTs functional group to give the corresponding product in moderate yields and up to 29% ee. PMID:24204435

  12. Synthesis of axially chiral gold complexes and their applications in asymmetric catalyses

    Directory of Open Access Journals (Sweden)

    Yin-wei Sun

    2013-10-01

    Full Text Available Several novel chiral N-heterocyclic carbene and phosphine ligands were prepared from (S-BINOL. Moreover, their ligated Au complexes were also successfully synthesized and characterized by X-ray crystal diffraction. A weak gold-? interaction between the Au atom and the aromatic ring in these gold complexes was identified. Furthermore, we confirmed the formation of a pair of diastereomeric isomers in NHC gold complexes bearing an axially chiral binaphthyl moiety derived from the hindered rotation around C–C and C–N bonds. In the asymmetric intramolecular hydroamination reaction most of these chiral Au(I complexes showed good catalytic activities towards olefins tethered with a NHTs functional group to give the corresponding product in moderate yields and up to 29% ee.

  13. On the reactivity and stability of electrogenerated N-heterocyclic carbene in parent 1-butyl-3-methyl-1H-imidazolium tetrafluoroborate: Formation and use of N-heterocyclic carbene-CO2 adduct as latent catalyst

    International Nuclear Information System (INIS)

    A simple electrolysis (under galvanostatic conditions) of the room temperature ionic liquid 1-butyl-3-methyl-1H-imidazolium tetrafluoroborate, BMIm-BF4, yields, after bubbling CO2 into the catholyte, the adduct NHC-CO2. The considerable stability of this NHC-CO2 adduct, at room temperature, in the parent ionic liquid as solvent, has been compared with the one of free NHC in the same BMIm-BF4. The BMIm-BF4 solution containing NHC-CO2 adduct, suitably triggered (US irradiation or 120 °C), is able to release free NHC. The NHC-CO2 adduct usefulness has been demonstrated using it as efficient latent catalyst, in BMIm-BF4 as solvent, in the benzoin condensation and in the oxidative esterification of cinnamaldehyde with benzyl alcohol

  14. Saturated and unsaturated (hydrotris(3,5-dimethylpyrazolyl)borato)tungsten(II) carbene complexes

    Energy Technology Data Exchange (ETDEWEB)

    Feng, S.G.; White, P.S.; Templeton, J.L. [Univ. of North Carolina, Chapel Hill, NC (United States)

    1992-04-08

    Reaction of [Tp{prime}(CO){sub 2} W(PhC{sub 2}H)][BF{sub 4}] (Tp{prime} = hydrotris(3,5-dimethylpyrazolyl)borato) with PhC{sub 2}H or reaction of Tp{prime}(CO)IW(PhC{sub 2}R) (R = H, Me) with PhC{sub 2}H/AgBF{sub 4} generates cationic bisalkyne complexes [Tp{prime}(CO)W(PhC{sub 2}H)-(PhC{sub 2}R)][BF{sub 4}]. NMR and crystal data suggest that the two alkyne ligands donate a total of six electrons to the metal with phenyl groups distal to each other. Crystals of the bis(phenylacetylene) complex belong to the monoclinic space group P2{sub 1}/n, Z = 4.

  15. Iron(0) Aminocarbene Complexes Bearing Heterocyclic Substituent on Carbene Carbon Atom: Electrochemistry and Reactivity.

    Czech Academy of Sciences Publication Activity Database

    Hoskovcová, I.; Zv??inová, R.; Dvo?ák, D.; Záliš, Stanislav; Ludvík, Ji?í

    Lausanne : International Society of Electrochemistry, 2008, 080898-080898. [Annual Meeting of the International Society of Electrochemistry /59./. Seville (ES), 07.09.2008-12.09.2008] R&D Projects: GA AV ?R IAA400400813 Institutional research plan: CEZ:AV0Z40400503 Keywords : electrochemistry * reactivity * iron aminocarbene complexes Subject RIV: CG - Electrochemistry http://www.uco.es/electroquimica-rseq/Circular_Seville08.pdf

  16. Catalytic Asymmetric ?-Acylation of Tertiary Amines Mediated by a Dual Catalysis Mode: N-Heterocyclic Carbene and Photoredox Catalysis

    OpenAIRE

    DiRocco, Daniel A.; Rovis, Tomislav

    2012-01-01

    Cross-coupling reactions are some of the most widely utilized methods for C-C bond formation; however, the requirement for pre-activated starting materials still presents a major limitation. Methods that take direct advantage of the inherent reactivity of the C-H bond offer an efficient alternative to these methods, negating the requirement for substrate pre-activation. In this process two chemically distinct activation events culminate in the formation of the desired C-C bond with loss of H2...

  17. Synthesis, characterization and luminescence studies of gold(I–NHC amide complexes

    Directory of Open Access Journals (Sweden)

    Adrián Gómez-Suárez

    2013-10-01

    Full Text Available A flexible, efficient and straightforward methodology for the synthesis of N-heterocyclic carbene gold(I–amide complexes is reported. Reaction of the versatile building block [Au(OH(IPr] (1 (IPr = 1,3-bis(2,6-diisopropylphenylimidazol-2-ylidene with a series of commercially available (heteroaromatic amines leads to the synthesis of several [Au(NRR’(IPr] complexes in good yields and with water as the sole byproduct. Interestingly, these complexes present luminescence properties. UV–vis and fluorescence measurements have allowed the identification of their excitation and emission wavelengths (?max. These studies revealed that by selecting the appropriate amine ligand the emission can be easily tuned to achieve a variety of colors, from violet to green.

  18. Deconstructing selectivity in the gold-promoted cyclization of alkynyl benzothioamides to six-membered mesoionic carbene or acyclic carbene complexes

    KAUST Repository

    Vummaleti, Sai Vikrama Chaitanya

    2014-05-02

    We demonstrate that the experimentally observed switch in selectivity from 5-exo-dig to 6-endo-dig cyclization of an alkynyl substrate, promoted by Au I and AuIII complexes, is connected to a switch from thermodynamic to kinetic reaction control. The AuIII center pushes alkyne coordination toward a single Au-C(alkyne) ?-bond, conferring carbocationic character (and reactivity) to the distal alkyne C atom. © 2014 American Chemical Society.

  19. Enantioselective construction of quaternary N-heterocycles by palladium-catalysed decarboxylative allylic alkylation of lactams

    Science.gov (United States)

    Behenna, Douglas C.; Liu, Yiyang; Yurino, Taiga; Kim, Jimin; White, David E.; Virgil, Scott C.; Stoltz, Brian M.

    2012-02-01

    The enantioselective synthesis of nitrogen-containing heterocycles (N-heterocycles) represents a substantial chemical research effort and resonates across numerous disciplines, including the total synthesis of natural products and medicinal chemistry. In this Article, we describe the highly enantioselective palladium-catalysed decarboxylative allylic alkylation of readily available lactams to form 3,3-disubstituted pyrrolidinones, piperidinones, caprolactams and structurally related lactams. Given the prevalence of quaternary N-heterocycles in biologically active alkaloids and pharmaceutical agents, we envisage that our method will provide a synthetic entry into the de novo asymmetric synthesis of such structures. As an entry for these investigations we demonstrate how the described catalysis affords enantiopure quaternary lactams that intercept synthetic intermediates previously used in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures.

  20. Fluorocarbon and hydrocarbon N-heterocyclic (C5-C7) imidazole-based liquid crystals.

    Science.gov (United States)

    Chen, Hongren; Hong, Fengying; Shao, Guang; Hang, Deyu; Zhao, Lei; Zeng, Zhuo

    2014-12-01

    By using three synthetic protocols, a series of fluorocarbon and hydrocarbon N-heterocyclic imidazole-based liquid crystals (LCs) and related imidazolium-based ionic liquid crystals (ILCs) have been prepared. The ring size of the N-heterocycle and the length of the N-terminal chain (on the imidazolium unit in the ILCs) were modified, and the influence of these structural parameters on liquid-crystal phases was investigated by means of polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). These new ILCs exhibit a disordered smectic phase (SmA), good thermal stabilities, a broad smectic phase range, a high dipole moment, relatively low melting points, but high clearing points and strong emission fluorescence relative to imidazole-based LCs. These encouraging results have led us to believe these fluorocarbon and hydrocarbon N-heterocyclic imidazole-based LCs and related imidazolium-based ILCs could be used as new liquid-crystalline materials. PMID:25256069

  1. Making oxidation potentials predictable: coordination of additives applied to the electronic fine tuning of an iron(II) complex.

    Science.gov (United States)

    Haslinger, Stefan; Kück, Jens W; Hahn, Eva M; Cokoja, Mirza; Pöthig, Alexander; Basset, Jean-Marie; Kühn, Fritz E

    2014-11-01

    This work examines the impact of axially coordinating additives on the electronic structure of a bioinspired octahedral low-spin iron(II) N-heterocyclic carbene (Fe-NHC) complex. Bearing two labile trans-acetonitrile ligands, the Fe-NHC complex, which is also an excellent oxidation catalyst, is prone to axial ligand exchange. Phosphine- and pyridine-based additives are used for substitution of the acetonitrile ligands. On the basis of the resulting defined complexes, predictability of the oxidation potentials is demonstrated, based on a correlation between cyclic voltammetry experiments and density functional theory calculated molecular orbital energies. Fundamental insights into changes of the electronic properties upon axial ligand exchange and the impact on related attributes will finally lead to target-oriented manipulation of the electronic properties and consequently to the effective tuning of the reactivity of bioinspired systems. PMID:25333790

  2. Making oxidation potentials predictable: Coordination of additives applied to the electronic fine tuning of an iron(II) complex

    KAUST Repository

    Haslinger, Stefan

    2014-11-03

    This work examines the impact of axially coordinating additives on the electronic structure of a bioinspired octahedral low-spin iron(II) N-heterocyclic carbene (Fe-NHC) complex. Bearing two labile trans-acetonitrile ligands, the Fe-NHC complex, which is also an excellent oxidation catalyst, is prone to axial ligand exchange. Phosphine- and pyridine-based additives are used for substitution of the acetonitrile ligands. On the basis of the resulting defined complexes, predictability of the oxidation potentials is demonstrated, based on a correlation between cyclic voltammetry experiments and density functional theory calculated molecular orbital energies. Fundamental insights into changes of the electronic properties upon axial ligand exchange and the impact on related attributes will finally lead to target-oriented manipulation of the electronic properties and consequently to the effective tuning of the reactivity of bioinspired systems.

  3. Quantum-chemical investigation of the nature of metal-carbene and metal-olefin bonds in complexes [ClnM(C2H4)]- (M=Mo,Pd)

    International Nuclear Information System (INIS)

    On the basis of electron structure calculation using Huckel method comparative investigation of the nature of metal-ethylidene and metal-ethylene bonds in complexes [Cl5Mo(C2H4)]- and [Cl3Pd(C2H4)]-, and also carbene complex stability regarding olefine izomerization is carried out. It is shown that metal-ethylidene bond in the above complexes is stronger than metal-ethylene one, and Mo(4)-ethylidene bond is stronger than Pd(2)-ethylidene one. It is supposed that relative stability of alkylidene structures may be one of the reasons of catalytic activity of Mo(4) compounds in olefine metathesis and oligomerization reactions in which carbene complex is considered as an intermediate

  4. Contrasting electronic requirements for C?H binding and C?H activation in d(6) half-sandwich complexes of rhenium and tungsten.

    Science.gov (United States)

    Thenraj, Murugesan; Samuelson, Ashoka G

    2015-09-15

    A computational study of the interaction half-sandwich metal fragments (metal?=?Re/W, electron count?=?d(6) ), containing linear nitrosyl (NO(+) ), carbon monoxide (CO), trifluorophosphine (PF3 ), N-heterocyclic carbene (NHC) ligands with alkanes are conducted using density functional theory employing the hybrid meta-GGA functional (M06). Electron deficiency on the metal increases with the ligand in the order NHC withdrawing ligands like NO(+) lead to more stable alkane complexes than NHC, a strong electron donor. Energy decomposition analysis shows that stabilization is due to orbital interaction involving charge transfer from the alkane to the metal. Reactivity and dynamics of the alkane fragment are facilitated by electron donors on the metal. These results match most of the experimental results known for CO and PF3 complexes. The study suggests activation of alkane in metal complexes to be facile with strong donor ligands like NHC. © 2015 Wiley Periodicals, Inc. PMID:26174521

  5. Synthesis of Aryliron Complexes [CpFe(CO2Ar] by Palladium-Catalyzed Reactions of [CpFe(CO2I] with Arylzinc, -Boron, or -Indium Reagents

    Directory of Open Access Journals (Sweden)

    Koichiro Oshima

    2009-08-01

    Full Text Available Transmetalation between [CpFe(CO2I] and arylzinc iodide-lithium chloride complexes proceeds in the presence of catalytic amounts of palladium acetate and N,N,N’,N’-tetramethyl-1,2-cyclohexanediamine to yield the corresponding aryliron complexes [CpFe(CO2Ar]. Phenylation of [CpFe(CO2I] also takes place when triphenylindium is used under similar conditions. Arylboronic acids undergo arylation in the presence of cesium carbonate and a palladium-N-heterocyclic carbene complex, PEPPSI. The present methods are useful for the facile synthesis of various functionalized [CpFe(CO2Ar]. The products [CpFe(CO2Ar] represent an interesting class of aryl metals that undergo several transformation.

  6. Gold(I)-phosphine-N-heterocycles: biological activity and specific (ligand) interactions on the C-terminal HIVNCp7 zinc finger.

    Science.gov (United States)

    Abbehausen, Camilla; Peterson, Erica J; de Paiva, Raphael E F; Corbi, Pedro P; Formiga, André L B; Qu, Yun; Farrell, Nicholas P

    2013-10-01

    The syntheses and the characterization by chemical analysis, (1)H and (31)P NMR spectroscopy, and mass spectrometry of a series of linear triphenylphosphine gold(I) complexes with substituted N-heterocycle ligands (L), [(PPh3)Au(I)(L)](+), is reported. The reaction of [(PPh3)Au(L)](+) (L = Cl(-) or substituted N- heterocyclic pyridine) with the C-terminal (Cys3His) finger of HIVNCp7 shows evidence by mass spectrometry (ESI-MS) and (31)P NMR spectroscopy of a long-lived {(PPh3)Au}-S-peptide species resulting from displacement of the chloride or pyridine ligand by zinc-bound cysteine with concomitant displacement of Zn(2+). In contrast, reactions with the Cys2His2 finger-3 of the Sp1 transcription factor shows significantly reduced intensities of {(PPh3)Au} adducts. The results suggest the possibility of systematic (electronic, steric) variations of "carrier" group PR3 and "leaving" group L as well as the nature of the zinc finger in modulation of biological activity. The cytotoxicity, cell cycle signaling effects, and cellular accumulation of the series are also reported. All compounds display cytotoxicity in the micromolar range upon 96 h continuous exposure to human tumor cells. The results may have relevance for the reported inhibition of viral load in simian virus by the gold(I) drug auranofin. PMID:24063530

  7. From bis(N-Alkylimidazole) to bis(NH–NHC) in rhenium carbonyl complexes

    OpenAIRE

    Huertos, Miguel A.; Pérez, Julio; Riera, Lucía

    2010-01-01

    Two birds, one stone: A deprotonation–protonation sequence using only one molar equivalent of base and acid transforms two N-alkylimidazole molecules into N-heterocyclic carbene ligands (see scheme; black?C, gray?H, green?F, blue?N, red?O, cyan?Re, yellow?S).

  8. Structure and bonding in neutral and cationic 14-electron gold alkyne pi complexes.

    Science.gov (United States)

    Flügge, Susanne; Anoop, Anakuthil; Goddard, Richard; Thiel, Walter; Fürstner, Alois

    2009-08-24

    Cyclododecyne (5) as a prototype unstrained alkyne was coordinated to either the neutral [AuCl] fragment or to two different cationic [Au(NHC)](+) entities (NHC = N-heterocyclic carbene), and the resulting complexes 6, 8, and 10 were characterized by X-ray crystallography and NMR spectroscopy. Since the structure of cyclododecyne in the solid state could also be obtained after in situ crystallization, a comparison was possible that provides insights into structural changes imposed on the alkyne by the different gold fragments. These data are interpreted on the basis of a DFT analysis of the bonding situation in the individual compounds, which provides insights into the very first elementary step common to many gold-catalyzed transformations. PMID:19569141

  9. Crystalline 1H-1,2,3-Triazol-5-ylidenes: New Stable Mesoionic Carbenes (MICs)**

    OpenAIRE

    Guisado-Barrios, Gregorio; Bouffard, Jean; Donnadieu, Bruno; Bertrand, Guy

    2010-01-01

    Until recently, the availability of neutral carbon-based ?1C ligands was limited to carbon monoxide, isocyanides, and carbenes. Compared to phosphorus-based ligands, carbenes tend to bind more strongly to metal centers, avoiding the necessity for the use of excess ligand in catalytic reactions. The corresponding complexes are often less sensitive to air and moisture, and are remarkably resistant to oxidation.[1] As the robustness of carbene complexes is largely due to the presence of strong c...

  10. Toward New Organometallic Architectures: Synthesis of Carbene-Centered Rhodium and Palladium Bisphosphine Complexes. Stability and Reactivity of [PC(BIm)PRh(L)][PF6] Pincers.

    Science.gov (United States)

    Plikhta, Andriy; Pöthig, Alexander; Herdtweck, Eberhardt; Rieger, Bernhard

    2015-10-01

    In this article, we report the synthesis of a tridentate carbene-centered bisphosphine ligand precursor and its complexes. The developed four-step synthetic strategy of a new PC(BIm)P pincer ligand represents the derivatization of benzimidazole in the first and third positions by (diphenylphosphoryl)methylene synthone, followed by phosphine deprotection and subsequent insertion of a noncoordinating anion. The obtained ligand precursor undergoes complexation, with PdCl2 and [?-OCH3Rh(COD)]2 smoothly forming the target organometallics [PC(BIm)PPdCl][PF6] and [PC(BIm)PRh(L)][PF6] under mild hydrogenation conditions. A more detailed study of the rhodium complexes [PC(BIm)PRh(L)][PF6] reveals significant thermal stability of the PC(BIm)PRh moiety in the solid state as well as in solution. The chemical behavior of 1,3-bis(diphenylphosphinomethylene)benzimidazol-2-ylrhodium acetonitrile hexafluorophosphate has been screened under decarbonylation, hydrogenation, and hydroboration reaction conditions. Thus, the PC(BIm)PRh(I) complex is a sufficiently stable compound, with the potential to be applied in catalysis. PMID:26390389

  11. Metal–metal interaction in Fischer carbene complexes : a study of ferrocenyl and biferrocenyl tungsten alkylidene complexes

    OpenAIRE

    van der Westhuizen, Belinda; Speck, J. Matthaus; Korb, Marcus; Friedrich, Joachim; Bezuidenhout, Daniela Ina; Lang, Heinrich

    2013-01-01

    A series of ferrocenyl (Fc = ferrocenyl; fc = ferrocen-1,1'-diyl) and biferrocenyl (Bfc = 1',1''-biferrocenyl; bfc = 1',1''-biferrocen-1,1'''-diyl) mono- and biscarbene tungsten(0) complexes of the type [(CO)5W=C(OMe)R] (1, R = Fc; 3, R = Bfc) and [(CO)5W=C(OMe)-R'-(OMe)C=W(CO)5] (2, R' = fc; 4, R' = bfc) were synthesized according to the classical synthetic methodology by reacting W(CO)6 with LiR (R = Fc, fc, bfc), followed by a subsequent alkylation using methyl trifluoromethane...

  12. Spectroscopic and electrochemical correlations in triangular ruthenium clusters containing N-heterocyclic ligands

    International Nuclear Information System (INIS)

    A series of clusters of general formula [Ru sub(3) O (OOCCH sub(3)) sub(6) L sub(3)] sup(+), where L = N-heterocyclic ligands, were synthesized and characterized based on elemental analysis. UV-VIS and IR spectra. Voltametric studies revealed the existence of up to six acessible oxidation states, with a high degree of electronic delocalization. The Ru sub(3) O trigonal center possesses many delocalized electrons and can be visualized as a source of electrons. The ligands coordinated to the clusters tune their redox potentials, determine the differences in their electronic spectra, and are responsible for the special conditions required for their synthesis. (author)

  13. The first resonance hybrid of silyl-carbene and pyridyl-silylene complexes. Formation by Aryl C-H bond activation of DMAP [4-(dimethylamino)pyridine] on a silylene complex

    International Nuclear Information System (INIS)

    Treatment of a tungsten bis(silyl) complex Cp*W{?3-(Si,Si,O)-xantsil}(CO)(H) [xantsil=(9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)] with 4-(dimethylamino)pyridine (DMAP) causes ortho-metallation in a DMAP-stabilized silylene complex that is generated from the bis(silyl) complex through silicon-to-tungsten 1,2-methyl migration and methane elimination. Resulting W-Si-N-C four-membered metallacycle Cp*W[?3(Si,Si,C)-(SiMe2){SiMe(NC5H3NMe2)}-(C15H12O)](CO)(H) can be regarded as the resonance hybrid of silyl-carbene an pyridyl-silylee complexes. (author)

  14. Properties and reactions of manganese methylene complexes in the gas phase. The importance of strong metal: carbene bonds for effective olefin metathesis catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Stevens, A.E.; Beauchamp, J.L.

    1979-10-10

    In this communication the formation, properties and reactions of the gas phase carbenes MnCH/sub 2//sup +/, (CO)/sub 5/MnCH/sub 2//sup +/, and (CO)/sub 4/MnCH/sub 2//sup +/ are described. Reported results include observation of metathesis and abstraction reactions of the methylene ligand with olefins and the first experimental determination of metal-carbene bond dissociation energies. Important points are that: (a) metal-methylene bond energies are extremely strong; and (b) the Mn/sup +/-methylene bond energy is decreased substantially on addition of five carbonyls to the metal center. If the metal-carbene bond energy exceeds 100 kcal/mol, then transfer of the carbene to an olefin to give a cyclopropane or new olefin will be endothermic and thus will not compete with the metathesis reaction. In order to avoid low turnover numbers resulting from consumption of carbene intermediates, strong metal-carbene bonds are a desirable feature of practical metathesis catalysts. (DP)

  15. Formation and Reactions of Tetracarbonyl Intermediates of the Fischer Carbene Complex (CO)5W=C(OMe)Ph : A Laser Flash Photolysis Study Using Time-Resolved Infrared and UV/Vis Spectroscopy

    OpenAIRE

    Gut, Hans-Peter; Welte, Nicolas; Link, Uwe; Fischer, Helmut; Steiner, Ulrich

    2000-01-01

    The results of nanosecond laser flash photolysis (XeCl excimer irradiation at 308 nm) of the Fischer carbene complex [(CO)5W=C(OMe)Ph] (CZ) in di-n-butyl ether and n-hexane are reported. Spectrokinetical detection of the intermediates was based on transient absorptions simulaneously recorded in the UV/vis and the IR spectral regions. The primary photoproducts are the unstable isomer CE produced with a quantum yield of about 30% and a tetracarbonyl complex I-S, probably of structure [(CO)4(S)W...

  16. Formation and photostability of N-heterocycles in space. I. The effect of nitrogen on the photostability of small aromatic molecules

    Science.gov (United States)

    Peeters, Z.; Botta, O.; Charnley, S. B.; Kisiel, Z.; Kuan, Y.-J.; Ehrenfreund, P.

    2005-04-01

    Nitrogen-containing cyclic organic molecules (N-heterocycles) play important roles in terrestrial biology, for example as the nucleobases in genetic material. It has previously been shown that nucleobases are unlikely to form and survive in interstellar and circumstellar environments. Also, they were found to be unstable against ultraviolet (UV) radiation. However, nucleobases were detected in carbonaceous meteorites, suggesting their formation and survival is possible outside the Earth. In this study, the nucleobase precursor pyrimidine and the related N-heterocycles pyridine and s-triazine were tested for UVstability. All three N-heterocycles were found to photolyse rapidly and their stability decreased with an increasing number of nitrogen atoms in the ring. The laboratory results were extrapolated to astronomically relevant environments. In the diffuse interstellar medium (ISM) these N-heterocycles in the gas phase would be destroyed in 10-100years, while in the Solar System at 1AU distance from the Sun their lifetime would not extend beyond several hours. The only environment where small N-heterocycles could survive, is in dense clouds. Pyridine and pyrimidine, but not s-triazine, could survive the average lifetime of such a cloud. The regions of circumstellar envelopes where dust attenuates the UVflux, may provide a source for the detection of N-heterocycles. We conclude that these results have important consequences for the detectability of N-heterocycles in astronomical environments.

  17. Construction of porous cationic frameworks by crosslinking polyhedral oligomeric silsesquioxane units with N-heterocyclic linkers

    Science.gov (United States)

    Chen, Guojian; Zhou, Yu; Wang, Xiaochen; Li, Jing; Xue, Shuang; Liu, Yangqing; Wang, Qian; Wang, Jun

    2015-06-01

    In fields of materials science and chemistry, ionic-type porous materials attract increasing attention due to significant ion-exchanging capacity for accessing diversified applications. Facing the fact that porous cationic materials with robust and stable frameworks are very rare, novel tactics that can create new type members are highly desired. Here we report the first family of polyhedral oligomeric silsesquioxane (POSS) based porous cationic frameworks (PCIF-n) with enriched poly(ionic liquid)-like cationic structures, tunable mesoporosities, high surface areas (up to 1,025?m2 g?1) and large pore volumes (up to 0.90?cm3 g?1). Our strategy is designing the new rigid POSS unit of octakis(chloromethyl)silsesquioxane and reacting it with the rigid N-heterocyclic cross-linkers (typically 4,4?-bipyridine) for preparing the desired porous cationic frameworks. The PCIF-n materials possess large surface area, hydrophobic and special anion-exchanging property, and thus are used as the supports for loading guest species PMo10V2O405? the resultant hybrid behaves as an efficient heterogeneous catalyst for aerobic oxidation of benzene and H2O2-mediated oxidation of cyclohexane.

  18. Cyclic (alkyl)(amino)carbenes (CAACs): stable carbenes on the rise.

    Science.gov (United States)

    Soleilhavoup, Michèle; Bertrand, Guy

    2015-02-17

    CONSPECTUS: Carbenes are compounds that feature a divalent carbon atom with only six electrons in its valence shell. In the singlet state, they possess a lone pair of electrons and a vacant orbital and therefore exhibit Lewis acidic and Lewis basic properties, which explains their very high reactivity. Following the preparation by our group in 1988 of the first representative, a variety of stable carbenes are now available, the most popular being the cyclic diaminocarbenes. In this Account, we discuss another class of stable cyclic carbenes, namely, cyclic (alkyl)(amino)carbenes (CAACs), in which one of the electronegative and ?-donor amino substituents of diaminocarbenes is replaced by a ?-donating but not ?-donating alkyl group. As a consequence, CAACs are more nucleophilic (?-donating) but also more electrophilic (?-accepting) than diaminocarbenes. Additionally, the presence of a quaternary carbon in the position ? to the carbene center provides steric environments that differentiate CAACs dramatically from all other ligands. We show that the peculiar electronic and steric properties of CAACs allow for the stabilization of unusual diamagnetic and paramagnetic main group element species. As examples, we describe the preparation of room temperature stable phosphorus derivatives in which the heteroatom is in the zero oxidation state, nucleophilic boron compounds, and phosphorus-, antimony-, boron-, silicon-, and even carbon-centered neutral and cationic radicals. CAACs are also excellent ligands for transition metal complexes. The most recent application is their use for the stabilization of paramagnetic complexes, in which the metal is often in a formal zero oxidation state. Indeed, bis(CAAC)M complexes in which the metal is gold, copper, cobalt, iron, nickel, manganese, and zinc have been isolated. Depending on the metal, the majority of spin density can reside either on the metal or on the carbene carbons and the nitrogen atoms of the CAAC ligand. In contrast to diaminocarbenes, the higher basicity of CAACs makes them poor leaving groups, and thus they cannot be used for classical organocatalysis. However, because of their superior electrophilicity and smaller singlet-triplet gap, CAACs can activate small molecules at room temperature, such as CO, H2, and P4, as well as enthalpically strong bonds, such as B-H, Si-H, N-H, and P-H. Lastly, excellent results have been obtained in palladium, ruthenium, and gold catalysis. CAAC-metal complexes are extremely thermally robust, which allows for their utilization in harsh conditions. This property has been used to perform a variety of gold-catalyzed reactions in the presence of basic amines, including ammonia and hydrazine, which usually deactivate catalysts. PMID:25515548

  19. Mineralization of polycyclic and n-heterocyclic aromatic compounds in hydrocarbon-contaminated soils

    International Nuclear Information System (INIS)

    The comparative mineralization of eight polycyclic aromatic compounds in five soils collected from an abandoned coal tar refinery in eastern Ohio was determined. The soils showed differences only in total extractable hydrocarbon content of the soil chemical characteristics measured. The compounds studied included five polycyclic aromatic hydrocarbons (phenanthrene, anthracene, pyrene, and carcinogenic benz[a]anthracene and benzo[a]pyrene) and three N-heterocyclic aromatics (9H-carbazole, and carcinogenic 7H-dibenzo[c,g]carbazole and dibenz[a,j]acridine). Mineralization was measured by serum bottle radiorespirometry. Only phenanthrene, anthracene, pyrene, benz[a]anthracene, and carbazole were mineralized in the soils after 64 d. Two of the soils with eight to 15 times the hexane -extractable hydrocarbon content consistently showed more rapid initial rates and higher overall extents of mineralization compared to the other three soils. Overall extents of mineralization ranged from 38 to 55% for phenanthrene, 10 to 60% for anthracene, 25 to 70% for pyrene, background to 40% for benz[a]anthracene, and 25 to 50% for carbazole after 64 d. Extents of mineralization by indigenous soil microbiota appear to be more dependent on the chemical characteristics of the soil and not soil total biomass and activity. Cultures capable of degrading phenanthrene, anthracene, and pyrene were obtained following enrichment techniques. A Mycobacterium sp. capable of degrading these three compounds was isolated and reintroduced into two of the soils, resulting in mineralization enhanced above that of the indigenous soil microbial population. These data indicate that the future success of bioremediation methods relies on the characterization of environmental parameters affecting microbial degradation as well as the isolation of microbial populations that can reduce toxicity in the environment

  20. Use of a Bidentate Ligand Featuring an N-Heterocyclic Phosphenium Cation (NHP(+)) to Systematically Explore the Bonding of NHP(+) Ligands with Nickel.

    Science.gov (United States)

    Bezpalko, Mark W; Foxman, Bruce M; Thomas, Christine M

    2015-09-01

    A novel bidentate ligand featuring an N-heterocyclic phosphenium cation (NHP(+)) linked to a phosphine side arm is used to explore the coordination chemistry of NHP(+) ligands with nickel. Direct P-Cl bond cleavage from a chlorophosphine precursor [PP]-Cl (1) by Ni(COD)2 affords the asymmetric bimetallic complex [Cl2Ni(?-PP)2Ni] (2) via a nonoxidative process. Abstraction of the halide with either NaBPh4 or K[B(C6F5)4] prior to metal coordination to form the free phosphenium ligand [PP](+) in situ, followed by coordination to Ni(COD)2, afforded the halide-free Ni(0) complexes [(PP)Ni(COD)] [B(C6F5)4] (4) and [(PP)Ni(COD)][BPh4] (5). Chloride abstraction from 1 is problematic in the presence of a PF6(-) counterion, however, as evident by the formation of [(PP)Ni(PP-F)][PF6] (3). The COD ligand in 5 can be readily displaced with PMe3 or PPh3 to afford [(PP)NiL2][BPh4] (L = PMe3 (6), PPh3 (7)). Complexes 2-7 feature planar geometries about the NHP(+) phosphorus atom and unusually short Ni-P distances, indicative of multiple bonding resulting from both P ? Ni ? donation and Ni ? P ? backbonding. This bonding description is supported by theoretical studies using natural bond orbital analysis. PMID:26302438

  1. Novel Synthesis of 3-Phenyl-chromen-4-ones Using N-Heterocyclic Carbene as Organocatalyst: An Efficient Domino Catalysis Type Approach

    Energy Technology Data Exchange (ETDEWEB)

    Mishra, Priya; Singh, Sarita; Ankit, Preyas; Fatma, Shahin; Singh, Divya; Singh, Jagdamba [Univ. of Allahabad, Allahabad (India)

    2013-04-15

    Herein is reported a simple and efficient synthesis of isoflavones starting from various substituted phenacyl bromides and salicylaldehydes in presence of NHC. The mechanism involved domino catalysis type approach with consumption and regeneration of catalyst in two catalytic cycles. This method proved to be very lucrative and gives very good yield. The method described here represents an environmentally benign alternative to classical approach.

  2. N-heterocyclic carbene-catalyzed tandem aza-benzoin/Michael reactions: on site reversal of the reactivity of N-Boc imines.

    Science.gov (United States)

    Wu, Ke-Jia; Li, Gong-Qiang; Li, Yi; Dai, Li-Xin; You, Shu-Li

    2011-01-01

    A tandem NHC-catalyzed aza-benzoin/Michael reaction has been developed as a method to efficiently produce dihydroindenones and pyrrolidinone-containing tricycles. The novel reaction pattern involves tert-butyl aryl(tosyl)methylcarbamates reacting as both electrophile and nucleophile on the same carbon. PMID:20953492

  3. Study of the factors supporting the selective complexation of the trivalent lanthanide and actinide ions

    International Nuclear Information System (INIS)

    In order to obtain clear-cut information on the factors which favour the discrimination between trivalent actinides and lanthanides, we investigated the complexation of the tris(cyclopentadienyl) Ce(III) and U(III) compounds, (RCp)3M (R = tBu, SiMe3), with a series of monocyclic azines with distinct Lewis basicity and reduction potential. Coordination of pyrazine and 4,4' and 2,2'-bipyridines on the (RCp)3M complexes has also been studied. Of major interest is the reversible oxidation of the (RCp)3U species into the uranium(IV) [(RCp)3U]2(pyz) complexes by pyrazine. The presence of cooperativity in the binding of the cyclopentadienyl groups by U(III), due to late appearance of back-bonding, leads to a greater stabilization of the uranium(III) complexes. Complexation of the species Cp*2MI (M = Ce, U) by 2,2'-bipyridine, phenanthroline and ter-pyridine affords the adducts [Cp*2M(L)]I. For L = bipy and terpy, these compounds are reduced into Cp*2M(L). The magnetic data for [Cp*2M(terpy)]I and Cp*2M(terpy) are consistent with Ce(III) and U(III) species, with the formulation Cp*2MIII(terpy). An electron transfer reaction between these species was observed in NMR. Reactions of the [Cp*2M(terpy)]I and Cp*2M(terpy) complexes with H and H+ donor reagents lead to a clear differentiation of these trivalent ions. We studied the coordination of the stable N-heterocyclic carbene and isonitrile molecules on (RCp)3M and Cp*2MI; competition reactions and comparison of the crystal structures of the carbene compounds reveal the much better affinity of the NHC and tBuNC ligands for the 5f rather than for the 4f ion. (authors)

  4. Efficient Removal of Ruthenium Byproducts from Olefin Metathesis Products by Simple Aqueous Extraction

    Science.gov (United States)

    Hong, Soon Hyeok; Grubbs, Robert H.

    2008-01-01

    Simple aqueous extraction removed ruthenium byproducts efficiently from ring-closing metathesis (RCM) reactions catalyzed by a PEG-supported N-heterocyclic carbene-based ruthenium complex. PMID:17428062

  5. Gold(I)-Catalyzed Hydration of Allenes

    OpenAIRE

    Zhang, Zhibin; Du Lee, Seong; Fisher, Aaron S.; Widenhoefer, Ross A.

    2009-01-01

    A gold(I) N-heterocyclic carbene complex catalyzes the intermolecular hydration of allenes to form allylic alcohols in modest yield with selective delivery of water to the terminal carbon atoms of the allenyl moiety.

  6. Protonolysis of a Ruthenium-Carbene Bond and Applications in Olefin Metathesis

    Science.gov (United States)

    Keitz, Benjamin K.; Bouffard, Jean; Bertrand, Guy; Grubbs, Robert H.

    2011-01-01

    The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Brønsted acid results in protonolysis of the Ru-MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicate a rate-determining protonation step to generate the metathesis active species. The NHC/MIC catalyst was found to have activity exceeding current commercial ruthenium catalysts. PMID:21574621

  7. Protonolysis of a Ruthenium-Carbene Bond and Applications in Olefin Metathesis

    OpenAIRE

    Keitz, Benjamin K.; Bouffard, Jean; Bertrand, Guy; Grubbs, Robert H

    2011-01-01

    The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Brønsted acid results in protonolysis of the Ru-MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicate a rate-determining protonation step to generate the metathesis active species. The NHC/MIC catalyst was found to have activity exceeding current commercial ruthenium catalysts.

  8. Exploring new generations of ruthenium olefin metathesis catalysts: the reactivity of a bis-ylidene ruthenium complex by DFT

    OpenAIRE

    Poater Teixidor, Albert; Credendino, Raffaele; Slugovc, Christian; Cavallo, Luigi

    2013-01-01

    Density functional theory calculations were used to predict the behaviour of a potential novel architecture of olefin metathesis catalysts, in which one of the neutral ligands of classical Ru-based catalysts, e. g. a phosphine or an N-heterocyclic carbene, is replaced by an alkylidene group. Introduction of a second alkylidene ligand favors dissociation of the remaining phosphine and the overall energy profile for the metathesis using ethylene as the probe substrate reveals that the proposed ...

  9. Asymmetric catalytic cascade reactions for constructing diverse scaffolds and complex molecules.

    Science.gov (United States)

    Wang, Yao; Lu, Hong; Xu, Peng-Fei

    2015-07-21

    With the increasing concerns about chemical pollution and sustainability of resources, among the significant challenges facing synthetic chemists are the development and application of elegant and efficient methods that enable the concise synthesis of natural products, drugs, and related compounds in a step-, atom- and redox-economic manner. One of the most effective ways to reach this goal is to implement reaction cascades that allow multiple bond-forming events to occur in a single vessel. This Account documents our progress on the rational design and strategic application of asymmetric catalytic cascade reactions in constructing diverse scaffolds and synthesizing complex chiral molecules. Our research is aimed at developing robust cascade reactions for the systematic synthesis of a range of interesting molecules that contain structural motifs prevalent in natural products, pharmaceuticals, and biological probes. The strategies employed to achieve this goal can be classified into three categories: bifunctional base/Brønsted acid catalysis, covalent aminocatalysis/N-heterocyclic carbene catalysis, and asymmetric organocatalytic relay cascades. By the use of rationally designed substrates with properly reactive sites, chiral oxindole, chroman, tetrahydroquinoline, tetrahydrothiophene, and cyclohexane scaffolds were successfully assembled under bifunctional base/Brønsted acid catalysis from simple and readily available substances such as imines and nitroolefins. We found that some of these reactions are highly efficient since catalyst loadings as low as 1 mol % can promote the multistep sequences affording complex architectures with high stereoselectivities and yields. Furthermore, one of the bifunctional base/Brønsted acid-catalyzed cascade reactions for the synthesis of chiral cyclohexanes has been used as a key step in the construction of the tetracyclic core of lycorine-type alkaloids and the formal synthesis of ?-lycorane. Guided by the principles of covalent aminocatalysis and N-heterocyclic carbene catalysis, we synthesized chiral piperidine, indole, and cyclobutane derivatives. The synthesis of chiral cyclobutanes and pyrroloindolones showed unprecedented reactivity of substrates and catalysts. The development of the strategy of asymmetric organocatalytic relay cascades has provided a useful tool for the controlled synthesis of specific diastereomers in complex molecules. This Account gives a panoramic view and the logic of our research on the design, development, and applications of asymmetric catalytic cascade reactions that will potentially provide useful insights into exploring new reactions. PMID:26099943

  10. Bidentate NHC^pyrozolate ligands in luminescent platinum(II) complexes.

    Science.gov (United States)

    Naziruddin, Abbas Raja; Galstyan, Anzhela; Iordache, Adriana; Daniliuc, Constantin G; Strassert, Cristian A; De Cola, Luisa

    2015-05-14

    A bidentate C^N donor set derived from an N-heterocyclic carbene (NHC) precursor linked to a trifluoromethyl (CF3) functionalized pyrazole ring is described for the first time. The ligands have been employed to prepare four new phosphorescent complexes by the coordination of platinum(II) centres bearing cyclometalated phenyl-pyridine/triazole-pyridine chelates. The electronic and steric environments of these complexes were tuned through the incorporation of suitable substituents in the phenyl-pyridine/triazole-pyridine ligands, wherein the position of the phenyl-ring substituent (a CF3 group) also directs the selective adoption of either a trans or a cis configuration between the C(NHC) and the C(phenyl) donor atoms. Molecular structures obtained by X-ray diffraction for three of the complexes confirm a distorted square-planar configuration around the platinum centre, and DFT calculations show that the substituents have a significant influence on the energies of the frontier orbitals. Moreover, a platinum(II) complex featuring the new bidentate NHC^pyrazolate ligand and a bulky adamantyl functionalized pyridine-triazole luminophore was observed to be highly emissive and exhibiting a sky-blue luminescence (?(Em) = 470 nm) with photoluminescence quantum yields as high as 50% in doped PMMA matrices. A complete photophysical investigation of all of the complexes in solution as well as in the solid state is herein reported. PMID:25616069

  11. Magnetic properties of 1 : 4 complexes of CoCl2 and pyridines carrying carbenes (S(0) = 4/2, 6/2, and 8/2) in diluted frozen solution; influence of carbene multiplicity on heterospin single-molecule magnets.

    Science.gov (United States)

    Karasawa, Satoru; Nakano, Kimihiro; Tanokashira, Jun-ichi; Yamamoto, Noriko; Yoshizaki, Takahito; Koga, Noboru

    2012-11-28

    The microcrystalline sample of a parent complex, [CoCl(2)(py)(4)], showed a single-molecule magnet (SMM) behavior with an effective activation barrier, U(eff)/k(B), of 16 K for reversal of the magnetism in the presence of a dc field of 3 kOe. Pyridine ligands having 2-4 diazo moieties, DYpy; Y = 2, 3l, 3b, and 4, were prepared and confirmed to be quintet, septet, septet, and nonet in the ground state, respectively, after irradiation. The 1 : 4 complexes, CoCl(2)(DYpy)(4); Y = 2, 3l, 3b, and 4 in frozen solutions after irradiation showed the magnetic behaviors of SMMs with total spin multiplicity, S(total) = 17/2, 25/2, 25/2, and 33/2, respectively. Hysteresis loops depending on the temperature were observed and the values of coercive force, H(c), at 1.9 K were 12, 8.4, 11, and 8.1 kOe for CoCl(2)(CYpy)(4); Y = 2, 3l, 3b, and 4, respectively. In dynamic magnetic susceptibility experiments, ac magnetic susceptibility data obeyed the Arrhenius law to give U(eff)/k(B) values of 94, 92, 93, and 87 K for CoCl(2)(CYpy)(4); Y = 2, 3l, 3b, and 4, respectively, while the relaxation times for CoCl(2)(CYpy)(4); Y = 2 and 3l, obtained by dc magnetization decay in the range of 3.5-1.9 K slightly deviated downward from Arrhenius plots on cooling. The dynamic magnetic behaviors for CoCl(2)(CYpy)(4) including [CoCl(2)(py)(4)] and CoCl(2)(C1py)(4) suggested that the generated carbenes interacted with the cobalt ion to increase the relaxation time, ?(q), due to the spin quantum tunneling magnetization, which became larger with increasing S(total) of the complex. PMID:22898723

  12. Coordinatively unsaturated ruthenium complexes as efficient alkyneazide cycloaddition catalysts

    KAUST Repository

    Lamberti, Marina

    2012-01-23

    The performance of 16-electron ruthenium complexes with the general formula Cp*Ru(L)X (in which L = phosphine or N-heterocyclic carbene ligand; X = Cl or OCH2CF3) was explored in azidealkyne cycloaddition reactions that afford the 1,2,3- triazole products. The scope of the Cp*Ru(PiPr 3)Cl precatalyst was investigated for terminal alkynes leading to new 1,5-disubstituted 1,2,3-triazoles in high yields. Mechanistic studies were conducted and revealed a number of proposed intermediates. Cp*Ru- (PiPr3)(2-HCCPh)Cl was observed and characterized by 1H, 13C, and 31P NMR at temperatures between 273 and 213 K. A rare example of N,N-?2-phosphazide complex, Cp*Ru(?2- iPr3PN3Bn)Cl, was fully characterized, and a single-crystal X-ray diffraction structure was obtained. DFT calculations describe a complete map of the catalytic reactivity with phenylacetylene and/or benzylazide. © 2012 American Chemical Society.

  13. A Heteroleptic Ferrous Complex with Mesoionic Bis(1,2,3-triazol-5-ylidene) Ligands: Taming the MLCT Excited State of Iron(II)

    DEFF Research Database (Denmark)

    Liu, Yizhu; Kjær, Kasper Skov

    2015-01-01

    Strongly sigma-donating N-heterocyclic carbenes (NHCs) have revived research interest in the catalytic chemistry of iron, and are now also starting to bring the photochemistry and photophysics of this abundant element into a new era. In this work, a heteroleptic Fe-II complex (1) was synthesized based on sequentially furnishing the Fe-II center with the benchmark 2,2-bipyridine (bpy) ligand and the more strongly sigma-donating mesoionic ligand, 4,4-bis(1,2,3-triazol-5-ylidene) (btz). Complex1 was comprehensively characterized by electrochemistry, static and ultrafast spectroscopy, and quantum chemical calculations and compared to [Fe(bpy)(3)](PF6)(2) and (TBA)(2)[Fe(bpy)(CN)(4)]. Heteroleptic complex1 extends the absorption spectrum towards longer wavelengths compared to a previously synthesized homoleptic Fe-II NHC complex. The combination of the mesoionic nature of btz and the heteroleptic structure effectively destabilizes the metal-centered (MC) states relative to the triplet metal-to-ligand charge transfer ((MLCT)-M-3) state in 1, rendering it a lifetime of 13ps, the longest to date of a photochemically stable Fe-II complex. Deactivation of the (MLCT)-M-3 state is proposed to proceed via the (MC)-M-3 state that strongly couples with the singlet ground state.

  14. Coal-Tar-Sealcoated Parking Lots: "Hot spots" of PAHs and N-heterocycles to Urban Streams and Lakes Result in "Hot Moments" of Toxicity

    Science.gov (United States)

    Mahler, B. J.; Van Metre, P. C.; Ingersoll, C.; Kunz, J. L.

    2014-12-01

    Coal-tar (CT) sealcoat, a potent source of polycyclic aromatic hydrocarbons (PAHs) and N-heterocycles, is applied to asphalt pavement of parking lots and driveways in many parts of the U.S. and Canada every 1 to 5 years. We measured the chemistry and toxicity of unfiltered runoff resulting from rain events simulated from 5 hours to 111 days after application of CT or asphalt (AS) sealcoat. PAHs and N-heterocycles were measured by GC/EIMS. Toxicity tests were done with Ceriodaphnia dubia and Pimephales promelas exposed 48 hours to undiluted and diluted (1 part runoff 9 parts control water) runoff under ambient lighting. Organisms were then transferred to fresh control water and subjected to a 4-hour pulse of ultraviolet radiation (UVR). Concentrations of 2- and 3-ringed PAHs and N-heterocycles in CT runoff, initially high (sum of 6 PAHs, 220 ?g/L; sum of 7 N-heterocycles, 904 ?g/L), decreased rapidly, whereas concentrations of 4-, 5- and 6-ringed PAHs more than doubled by 7 days after application (sum of 9 PAHs, 378 ?g/L) and remained elevated 111 days after application (sum of 9 PAHs, 283 ?g/L). Concentrations of PAHs and N-heterocycles in AS sealcoated runoff followed a similar pattern, but were ~10 times lower than those in CT runoff; concentrations in a sample of runoff from unsealed asphalt pavement were near or less than the detection limit. Organisms exposed to samples of undiluted CT-runoff collected during the 36 days following CT sealcoat application (no UVR exposure) experienced 100% mortality. Mortality (as much as 100%) of organisms exposed to the 10% dilution of CT runoff or to undiluted AS runoff occurred only with UVR; mortality of organisms exposed to the 10% solution of AS runoff and UVR was minimal. Results demonstrate that freshly CT-sealed parking lots and driveways are "hot spots" of PAH and N-heterocycle contamination and that prolonged "hot moments" of toxicity follow CT sealcoat application.

  15. Cyclometallated platinum(II) complexes containing NHC ligands: synthesis, characterization, photophysics and their application as emitters in OLEDs.

    Science.gov (United States)

    Solomatina, A I; Krupenya, D V; Gurzhiy, V V; Zlatkin, I; Pushkarev, A P; Bochkarev, M N; Besley, N A; Bichoutskaia, E; Tunik, S P

    2015-04-28

    A series of square planar [Pt(N^C)(NHC)L] complexes containing cyclometallated N^C ligands (phenylpyridine and benzoquinoline) and N-heterocyclic carbene (NHC)--N^C = 2-phenylpyridine, 7,8-benzoquinoline; NHC = 1,3-dibenzylbenzimidazolium, 1,3-diethylbenzimidazolium, 1,3-dibenzylimidazolium; L = Cl, Br, -C2Ph--have been synthesized in moderate to good yields. The complexes obtained were characterized using chemical analysis, MS-ESI spectrometry, NMR spectroscopy and X-ray crystallography. The complexes display moderate to strong phosphorescence in solution (Q.Y. 0.3-7.9%) and in the solid state (Q.Y. 2.7-16.0%), which is related to metal modulated intraligand ?-?* transitions located at the aromatic system of cyclometallated ligands with some contribution of the MLCT excited state. Emission lifetimes fall in the range of 0.2-1.5 ?s in solution and amount up to 13 ?s in the solid state. Analysis of the spectroscopic data together with the density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations clearly support this assignment and show negligible contribution of the auxiliary ligands to the emissive excited states. The compounds obtained were also used to prepare organic light emitting diode (OLED) devices, which display good luminance efficiency emitting in the green area of the visible spectrum. PMID:25482398

  16. Utility of Bifunctional N-Heterocyclic Phosphine (NHP)-Thioureas for Metal-Free Carbon-Phosphorus Bond Construction toward Regio- and Stereoselective Formation of Vinylphosphonates.

    Science.gov (United States)

    Mulla, Karimulla; Aleshire, Kyle L; Forster, Paul M; Kang, Jun Yong

    2016-01-01

    An efficient and practical protocol for completely regioselective and highly stereoselective synthesis of vinyldiazaphosphonates from N-heterocyclic phosphine (NHP) and allenes via phospha-Michael/intramolecular nucleophilic substitution reaction has been developed. This transformation enabled the synthesis of valuable densely functionalized vinyldiazaphosphonates with a ?-, ?-unsaturated ester moiety under mild reaction conditions. Synthetic utility of vinyldiazaphosphonates was demonstrated by a series of synthetic manipulations. PMID:26639442

  17. Pyrrole PMOs, incorporating new N-heterocyclic compounds on an ethene-PMO through Diels–Alder reactions

    International Nuclear Information System (INIS)

    The ethenylene bridges on the walls of an ethenylene-bridged periodic mesoporous organosilica were successfully modified with a variety of pyrrole derivatives – pyrrole, methylpyrrole, dimethylpyrrole, trimethylpyrrole and 1-phenylpyrrole – through Diels–Alder reactions. X-ray diffraction measurements and N2 adsorption–desorption analysis confirmed the preservation of the ordering and mesoporosity of the parent material as well as the decoration of the pores with the surface Diels–Alder adducts. Moreover, other techniques such as DRIFT, 13C and 29Si nuclear magnetic resonances revealed the formation of the surface N-heterocyclic compounds at the parent ethenylene sites. - Highlights: • Chemical modification of the double bonds on an ethene-PMO through the Diels–Alder reaction. • A family of pyrrole derivatives act as dienes in the Diels–Alder reaction. • Well-ordering and mesoporosity are retained after the post-functionalization. • N-containing compounds on the surface of ethene-PMO are present after the Diels–Alder reaction

  18. Microwave-assisted synthesis of N-heterocycles and their evaluation using an acetylcholinesterase immobilized capillary reactor

    Scientific Electronic Library Online (English)

    Diego P., Sangi; Julia L., Monteiro; Kenia L., Vanzolini; Quezia B., Cass; Marcio W., Paixão; Arlene G., Corrêa.

    2014-05-01

    Full Text Available Os etenoditioacetais polarizados são conhecidos como importantes intermediários em muitos processos de síntese. Neste trabalho, reporta-se a anelação livre de metal de transição de 1,1-bis(tiometil)-2-nitroetileno com hidroxilalquilaminas e alquildiaminas. Esta metodologia permite a síntese direta d [...] e N-heterociclos tais como imidazolidinas, oxazolidinas e benzoxazóis sob irradiação de micro-ondas. Estes compostos foram avaliados como inibidores da acetilcolinesterase usando um reator capilar contendo a enzima imobilizada acoplado a um espectrômetro de massas. Abstract in english Polarized ketene dithioketals have been recognized as useful building blocks in many synthetic operations. In this work, a transition-metal-free annulations of 1,1-bis(thiomethyl)-2-nitroethylene with hydroxylalkylamines or alkyldiamines have been reported. This methodology provides a directed appro [...] ach to N-heterocycles, e.g., imidazolidines, oxazolidines and benzoxazoles under microwave conditions. These compounds were evaluated as acetylcholinesterase inhibitors by using an enzyme immobilized capillary reactor-tandem mass spectrometry.

  19. Mesoionic Carbene-Gold(I) Catalyzed Bis-Hydrohydrazination of Alkynes with Parent Hydrazine.

    Science.gov (United States)

    Tolentino, Daniel R; Jin, Liqun; Melaimi, Mohand; Bertrand, Guy

    2015-10-01

    A novel synthetic route gives access to mesoionic carbene and cyclopropenylidene supported gold chloride complexes. The corresponding cationic MIC-gold complex obtained by chloride abstraction allows for the first transition metal-catalyzed functionalization of both nitrogens of parent hydrazine. PMID:25597889

  20. Influence of ionic liquids on the syntheses and structures of Mn(ii) coordination polymers based on multidentate N-heterocyclic aromatic ligands and bridging carboxylate ligands.

    Science.gov (United States)

    Qin, Jian-Hua; Wang, Hua-Rui; Pan, Qi; Zang, Shuang-Quan; Hou, Hongwei; Fan, Yaoting

    2015-10-28

    Seven Mn(ii) coordination polymers, namely {[Mn2(ptptp)Cl2(H2O)3]·H2O}n (1), {[Mn(?-ptptp)3]2[Mn3(?3-Cl)]2}·2Cl·16H2O (2), {[Mn2(ptptp)(ip)2(H2O)3]·H2O}n (3), {[Mn2(ptptp)(5-CH3-ip)2(H2O)3]·H2O}n (4), {[Mn4(ptptp)(5-Br-ip)3(H2O)3]·4H2O}n (5), {[Mn2(ptptp)(Hbtc)(H2O)2]·2H2O}n (6) and {[Mn2(ptptp)(tdc)(H2O)2]·1.5H2O}n (7), have been prepared based on multidentate N-heterocyclic aromatic ligands and bridging carboxylate ligands (H2ptptp = 2-(5-{6-[5-(pyrazin-2-yl)-1H-1,2,4-triazol-3-yl]pyridin-2-yl}-1H-1,2,4-triazol-3-yl)pyrazine; R-isophthalic acids, H2ip-R: R = -H (3), -CH3 (4), -Br (5); H3btc = trimesic acid (6); H2tdc = thiophene-2,5-dicarboxylic acid (7)), in order to further probe the multiple roles of [RMI]Br ionic liquids in the hydro/solvothermal synthesis (RMI = 1-alkyl-3-methylimidazolium, R = ethyl, or propyl, or butyl). The successful syntheses of complexes 2-6 suggest that in hydro/solvothermal synthesis the addition of a small amount of [RMI]Br plays a crucial role. Complex 1 exhibits single right-handed helices constructed by ptptp ligands and Mn(ii) ions. Complex 2 possesses octanuclear helicate structures in which two propeller-shaped [Mn(?-ptptp)3](4-) units embrace two [Mn3(?3-Cl)](5+) cluster cores inside. Complexes 3 and 4 are isostructural and display a 1D double chain formed by two kinds of pseudo meso-helices: (Mn-ptptp)n and (Mn-5-R-ip)n. Complex 5 has a 2D structure containing 1D Mn(ii) ion chains formed through carboxylates and [ptptp](2-)-N,N bridges. Complex 6 shows a 2D structure formed by a meso-helix (Mn-ptptp)n and the partly deprotonated Hbtc ligands. Complex 7 features a heterochiral [2 + 2] coaxially nested double-helical column formed by using the outer double-helices (Mn-ptptp)n as a template to encapsulate the inner double-helices (Mn-tdc)n with opposite orientation. All complexes were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, single-crystal X-ray crystallography and powder X-ray diffraction. The magnetic properties of 1-7 were also investigated. PMID:26394243

  1. Ruthenium—Arene Complexes Derived from NHC•CO2 and NHC•CS2 Zwitterionic Adducts and Their Use in Olefin Metathesis

    Science.gov (United States)

    Delaude, Lionel; Demonceau, Albert

    A range of imidazol(in)ium-2-carboxylates and -dithiocarboxylates bearing alkyl or aryl groups on their nitrogen atoms were prepared by reacting the corresponding N-heterocyclic carbenes (NHCs) with either carbon dioxide or carbon disulfide. All the zwitterionic products were characterized by various analytical techniques, including thermogravimetric analysis (TGA). Their ability to act as NHC ligand precursors for in situ catalytic applications was investigated in the ruthenium-promoted ring-opening metathesis polymerization (ROMP) of cyclo-octene. Upon exposure to the [RuCl2(p-cymene)]2 dimer, the NHC CO2 adducts readily dissociated to generate [RuCl2(p-cymene)(NHC)] complexes that were highly active catalyst precursors for olefin metathesis. Conversely, the NHC CS2 betaines retained their zwitterionic nature and led to new cationic complexes of the [RuCl(p-cymene)(NHC CS2)]+PF6 - type that were devoid of any significant catalytic activity in the reaction under consideration

  2. Nitrogen heterocyclic carbene containing pentacoordinate iron dicarbonyl as a [Fe]-hydrogenase active site model.

    Science.gov (United States)

    Jiang, Shuang; Zhang, Tianyong; Zhang, Xia; Zhang, Guanghui; Li, Bin

    2015-10-14

    A novel pentacoordinate mono iron dicarbonyl complex bearing a nitrogen heterocyclic carbene ligand was reported as a model of a [Fe]-hydrogenase active site, which exhibits interesting proton coupled CO binding reactivity, electro-catalytic proton reduction and catalytic transfer hydrogenation reactivity. PMID:26369379

  3. Electron pairing analysis of the Fischer-type chromium-carbene complexes (CO)5Cr=C(X)R (X=H, OH, OCH3, NH2, NHCH3 and R=H, CH3, CH=CH2, Ph, C-CH )

    International Nuclear Information System (INIS)

    The electron-pair density distributions of a series of 25 Fischer carbene complexes of the type (CO)5Cr=C(X)R (X=H, OH, OCH3, NH2, NHCH3 and R=H, CH3, CH=CH2, Ph, C-CH) are analyzed using the Atoms in Molecules theory. Localization and delocalization indices are used to characterize the electron pairing taking place in the Cr=C---X moiety in these complexes. Electron delocalization between the Cr and C atoms and between the C atom and the X group are related to the ?-donor strength of the X group and the degree of back-donation between the chromium pentacarbonyl and the carbene fragments. The results obtained with the Atoms in Molecules theory complement those obtained in a previous study by means of energy and charge decomposition analyses. Electron delocalization between the Cr atom and the X group is consistent with the hypothesis of a weak 3-center 4-electron bonding interaction in the Cr=C-X group of atoms. Except for X=H, ?(Cr,X) increases with the decrease of the ?-donor character of the X group

  4. Magnetic properties of 1:2 mixed cobalt(II) salicylaldehyde Schiff-base complexes with pyridine ligands carrying high-spin carbenes (Scar = 2/2, 4/2, 6/2, and 8/2) in dilute frozen solutions: role of organic spin in heterospin single-molecule magnets.

    Science.gov (United States)

    Karasawa, Satoru; Nakano, Kimihiro; Yoshihara, Daisuke; Yamamoto, Noriko; Tanokashira, Jun-ichi; Yoshizaki, Takahito; Inagaki, Yuji; Koga, Noboru

    2014-06-01

    The 1:2 mixtures of Co(p-tolsal)2, p-tolsal = N-p-tolylsalicylideniminato, and diazo-pyridine ligands, DXpy; X = 1, 2, 3l, 3b, and 4, in MTHF solutions were irradiated at cryogenic temperature to form the corresponding 1:2 cobalt-carbene complexes Co(p-tolsal)2(CXpy)2, with Stotal = 5/2, 9/2, 13/2, 13/2, and 17/2, respectively. The resulting Co(p-tolsal)2(CXpy)2, X = 1, 2, 3l, 3b, and 4, showed magnetic behaviors characteristic of heterospin single-molecule magnets with effective activation barriers, Ueff/kB, of 40, 65, 73, 72, and 74 K, for reorientation of the magnetic moment and temperature-dependent hysteresis loops with a coercive force, Hc, of ?0, 6.2, 10, 6.5, and 9.0 kOe at 1.9 K, respectively. The relaxation times, ?Q, due to a quantum tunneling of magnetization (QTM) were estimated to be 1.6 s for Co(p-tolsal)2(C1py)2, ?2.0 × 10(3) s for Co(p-tolsal)2(C2py)2, and >10(5) s for Co(p-tolsal)2(CXpy)2; X = 3b, 3l, and 4. In heterospin complexes, organic spins, carbenes interacted with the cobalt ion to suppress the QTM pathway, and the ?Q value increased with increasing the Stotal values. PMID:24816331

  5. Carbene formation upon reactive dissolution of metal oxides in imidazolium ionic liquids.

    Science.gov (United States)

    Wellens, Sil; Brooks, Neil R; Thijs, Ben; Meervelt, Luc Van; Binnemans, Koen

    2014-03-01

    Metal oxides were found to dissolve in different imidazolium ionic liquids with a hydrogen atom in the C2 position of the imidazolium ring, but not if a methyl substituent was present in the C2 position. The crystal structure of the product that crystallised from an ionic liquid containing dissolved silver(i) oxide showed that this was a silver(i) carbene complex. The presence of carbenes in solution was proven by (13)C NMR spectroscopy and the reactions were also monitored by Raman spectroscopy. The dissolution of other metal oxides, namely copper(ii) oxide, zinc(ii) oxide and nickel(ii) oxide, was also studied in imidazolium ionic liquids and it was found that stable zinc(ii) carbenes were formed in solution, but these did not crystallise under the given experimental conditions. A crystalline nickel(ii) carbene complex could be obtained from a solution of nickel(ii) chloride dissolved in a mixture of 1-butyl-3-methylimidazolium and 1-ethyl-3-methylimidazolium acetate. PMID:24390601

  6. Mechanism of Copper-Catalyzed Hydroalkylation of Alkynes: An Unexpected Role of Dinuclear Copper Complexes.

    Science.gov (United States)

    Suess, Alison M; Uehling, Mycah R; Kaminsky, Werner; Lalic, Gojko

    2015-06-24

    This article describes a mechanistic study of copper-catalyzed hydroalkylation of terminal alkynes. Relying on the established chemistry of N-heterocyclic carbene copper hydride (NHCCuH) complexes, we previously proposed that the hydroalkylation reaction proceeds by hydrocupration of an alkyne by NHCCuH followed by alkylation of the resulting alkenylcopper intermediate by an alkyl triflate. NHCCuH is regenerated from NHCCuOTf through substitution with CsF followed by transmetalation with silane. According to this proposal, NHCCuH must react with an alkyne faster than with an alkyl triflate to avoid reduction of the alkyl triflate. However, we have determined that NHCCuH reacts with alkyl triflates significantly faster than with terminal alkynes, strongly suggesting that the previously proposed mechanism is incorrect. Additionally, we have found that NHCCuOTf rapidly traps NHCCuX (X = F, H, alkenyl) complexes to produce (NHCCu)2(?-X)(OTf) (X = F, H, alkenyl) complexes. In this article, we propose a new mechanism for hydroalkylation of alkynes that features dinuclear (NHCCu)2(?-H)(OTf) (X = F, H, alkenyl) complexes as key catalytic intermediates. The results of our study establish feasible pathways for the formation of these intermediates, their ability to participate in the elementary steps of the proposed catalytic cycle, and their ability to serve as competent catalysts in the hydroalkylation reaction. We also provide evidence that the unusual reactivity of the dinuclear complexes is responsible for efficient hydroalkylation of alkynes without concomitant side reactions of the highly reactive alkyl triflates. PMID:26042355

  7. Water-Soluble Iridium-NHC-Phosphine Complexes as Catalysts for Chemical Hydrogen Batteries Based on Formate.

    Science.gov (United States)

    Horváth, Henrietta; Papp, Gábor; Szabolcsi, Roland; Kathó, Ágnes; Joó, Ferenc

    2015-09-21

    Molecular hydrogen, obtained by water electrolysis or photocatalytic water splitting, can be used to store energy obtained from intermittent sources such as wind and solar power. The storage and safe transportation of H2 , however, is an open and central question in such a hydrogen economy. Easy-to-synthesize, water-soluble iridium-N-heterocyclic carbene-phosphine (Ir(I) -NHC-phosphine) catalysts show unprecedented high catalytic activity in dehydrogenation of aqueous sodium formate. Fast reversible generation and storage of hydrogen can be achieved with these catalysts by a simple decrease or increase in the hydrogen pressure, respectively. PMID:26289830

  8. Heterogeneous SnCl{sub 2}/SiO{sub 2} versus Homogeneous SnCl{sub 2} Acid Catalysis in the Benzo[N,N]-heterocyclic Condensation

    Energy Technology Data Exchange (ETDEWEB)

    Darabi, Hossein Reza; Aghapoor, Kioumars; Mohsenzadeh, Farshid; Jalali, Mohammad Reza; Talebian, Shiva; Ebadi-Nia, Leila [Nano and Organic Synthesis Lab, Chemistry and Chemical Engineering Research Center of Iran, Tehran (Iran, Islamic Republic of); Khatamifar, Ehsan; Aghaee, Ali [Shifa Pharmed Industrial Group Co., Karaj (Iran, Islamic Republic of)

    2011-01-15

    The scope of homogeneous Lewis acid-catalyzed benzo[N,N]-heterocyclic condensation was expanded to include the use of various metal salts not reported in the literature and SnCl{sub 2}·2H{sub 2}O was finally selected. Among various solid supports activated with SnCl{sub 2}, heterogeneous SnCl{sub 2}/SiO{sub 2} proved to be the most effective and significantly higher conversions were achieved compared to SnCl{sub 2}·2H{sub 2}O itself. The results of TG-DTA and BET indicated that dispersed SnCl{sub 2} coordinates with surface hydroxyl groups of silica leading to formation of stable Lewis acid sites. Low catalyst loading, operational simplicity, practicability and applicability to various substrates render this eco-friendly approach as an interesting alternative to previously applied procedures.

  9. Unusual solvation through both p-orbital lobes of a carbene carbon

    Science.gov (United States)

    Hadad, C. Z.; Jenkins, Samantha; Flórez, Elizabeth

    2015-03-01

    As a result of a configurational space search done to explain the experimental evidence of transient specific solvation of singlet fluorocarbene amide with tetrahydrofuran, we found that the most stable structures consist in a group in which each oxygen of two tetrahydrofuran molecules act as electron donor to its respective empty p-orbital lobe of the carbene carbon atom, located at each side of the carbene molecular plane. This kind of species, which to our knowledge has not been reported before, explains very well the particular experimental characteristics observed for the transient solvation of this system. We postulate that the simultaneous interaction to both p-orbital lobes seems to confer a special stability to the solvation complexes, because this situation moves away the systems from the proximity of the corresponding transition states for the ylide products. Additionally, we present an analysis of other solvation complexes and a study of the nature of the involved interactions.

  10. Supported ruthenium-carbene catalyst on ionic magnetic nanoparticles for olefin metathesis.

    Science.gov (United States)

    Chen, Shu-Wei; Zhang, Zhi-Cheng; Ma, Miaofeng; Zhong, Chong-Min; Lee, Sang-gi

    2014-10-01

    The Grubbs-Hoveyda ruthenium-carbene complex has been covalently immobilized on ionic magnetic nanoparticles utilizing an imidazolium salt linker. The supported catalyst exhibited excellent catalytic activity for ring-closing metathesis (RCM) and cross-metathesis (CM) in the presence of less than 1 mol % of ruthenium. The catalysts can easily be recovered magnetically and reused up to seven times with minimal leaching of ruthenium species. PMID:25215600

  11. A highly efficient catalyst for selective oxidative scission of olefins to aldehydes: abnormal-NHC-Ru(II) complex in oxidation chemistry.

    Science.gov (United States)

    Daw, Prosenjit; Petakamsetty, Ramu; Sarbajna, Abir; Laha, Siladitya; Ramapanicker, Ramesh; Bera, Jitendra K

    2014-10-01

    The utility and selectivity of the catalyst [Ru(COD)(L(1))Br2] (1) bearing a fused ?-conjugated imidazo[1,2-a][1,8]naphthyridine-based abnormal N-heterocyclic carbene ligand L(1) is demonstrated toward selective oxidation of C?C bonds to aldehydes and C?C bonds to ?-diketones in an EtOAc/CH3CN/H2O solvent mixture at room temperature using a wide range of substrates, including highly functionalized sugar- and amino acid-derived compounds. PMID:25237828

  12. A persistent (amino)(ferrocenyl)carbene†‡

    OpenAIRE

    DeHope, Alan; Mendoza-Espinosa, Daniel; Donnadieu, Bruno; Bertrand, Guy

    2011-01-01

    Deprotonation of N,N-diisopropyl-C-ferrocenylaldiminium triflate 2 cleanly leads to the corresponding 1,2-diamino-1,2-diferrocenylethene 3, the dimer of the desired (amino)(ferrocenyl)carbene. Fulvene 6, obtained by addition of the lithium salt of tetramethylcyclopentadiene to methoxyformamidinium methylsulfate 5, reacts with dicarbonylcyclopentadienylbromoiron(II), and with a mixture of FeCl2 and Cp* lithium salt, affording the corresponding tetramethylferrocenylaldiminium salt 7, and noname...

  13. Application of chitosan and its N-heterocyclic derivatives for preconcentration of noble metal ions and their determination using atomic absorption spectrometry.

    Science.gov (United States)

    Azarova, Yu A; Pestov, A V; Ustinov, A Yu; Bratskaya, S Yu

    2015-12-10

    Chitosan and its N-heterocyclic derivatives N-2-(2-pyridyl)ethylchitosan (2-PEC), N-2-(4-pyridyl) ethylchitosan (4-PEC), and N-(5-methyl-4-imidazolyl) methylchitosan (IMC) have been applied in group preconcentration of gold, platinum, and palladium for subsequent determination by atomic absorption spectroscopy (AAS) in solutions with high background concentrations of iron and sodium ions. It has been shown that the sorption mechanism, which was elucidated by XPS, significantly influences the sorption capacity of materials, the efficiency of metal ions elution after preconcentration, and, as a result, the accuracy of metal determination by AAS. We have shown that native chitosan was not suitable for preconcentration of Au(III), if the elution step was used as a part of the analysis scheme. The group preconcentration of Au(III), Pd(II), and Pt(IV) with subsequent quantitative elution using 0.1M HCl/1M thiourea solution was possible only on IMC and 4-PEC. Application of IMC for analysis of the national standard quartz ore sample proved that gold could be accurately determined after preconcentration/elution with the recovery above 80%. PMID:26428172

  14. Kinetic Selectivity of Olefin Metathesis Catalysts Bearing Cyclic (Alkyl)(Amino)Carbenes

    OpenAIRE

    Anderson, Donde R.; Ung, Thay; Mkrtumyan, Garik; Bertrand, Guy; Grubbs, Robert H; Schrodi, Yann

    2008-01-01

    The evaluation of ruthenium olefin metathesis catalysts 4–6 bearing cyclic (alkyl)(amino)carbenes (CAACs) in the cross-metathesis of cis-1,4-diacetoxy-2-butene (7) with allylbenzene (8) and the ethenolysis of methyl oleate (11) is reported. Relative to most NHC-substituted complexes, CAAC-substituted catalysts exhibit lower E/Z ratios (3:1 at 70% conversion) in the cross-metathesis of 7 and 8. Additionally, complexes 4–6 demonstrate good selectivity for the formation of terminal olefins versu...

  15. Allene formation by gold catalyzed cross-coupling of masked carbenes and vinylidenes

    OpenAIRE

    Lavallo, Vincent; Frey, Guido D.; Kousar, Shazia; Donnadieu, Bruno; Bertrand, Guy

    2007-01-01

    Addition of a sterically demanding cyclic (alkyl)(amino)carbene (CAAC) to AuCl(SMe2) followed by treatment with [Et3Si(Tol)]+[B(C6F5)4]? in toluene affords the isolable [(CAAC)Au(?2-toluene)]+[B(C6F5)4]? complex. This cationic Au(I) complex efficiently mediates the catalytic coupling of enamines and terminal alkynes to yield allenes and not propargyl amines as observed with other catalysts. Mono-, di-, and tri-substituted enamines can be used, as well as aryl-, alkyl-, and trimethylsilyl-subs...

  16. Microwave-assisted syntheses of N-heterocycles using alkenone-, alkynone- and aryl-carbonyl O-phenyl oximes: formal synthesis of neocryptolepine.

    Science.gov (United States)

    Portela-Cubillo, Fernando; Scott, Jackie S; Walton, John C

    2008-07-18

    This research aimed to provide a new and "clean" synthetic method that would enable both known and novel N-heterocycles to be prepared efficiently. O-Phenyl oximes were found to be excellent precursors for iminyl radicals with a variety of acceptor side chains. Dihyropyrroles were made in good yields from O-phenyl oximes containing pent-4-ene acceptors. The analogous process with a hex-5-enyl acceptor did not yield a dihydropyridine, probably because the 6-exo-trig ring closure of the iminyl radical was too slow to compete with H-atom abstraction. The iminyl radical from a precursor with a pent-4-yne type side chain underwent ring closure followed by rearrangement to afford a pyrrole derivative. Suitably substituted iminyl radicals ring closed readily onto aromatic acceptors, thus enabling several polycyclic systems to be accessed. Quinolines were made from 3-phenylpropanones via their O-phenyl oximes. Syntheses of phenanthridines starting from 2-formylbiphenyls were particularly efficient, and this approach enabled the natural product trisphaeridine to be made. Starting from 2-phenylnicotinaldehyde derivatives, ring closures of the derived iminyl radicals onto the phenyl rings yielded benzo[h][1,6]naphthyridines. Similarly, ring closure onto a phenyl ring from a benzothiophene-based iminyl yielded a benzo[b]thieno[2,3-c]quinoline. By way of contrast, iminyl radical ring closure onto pyridine rings was not observed. However, iminyl radicals did cyclize onto indoles, enabling indolopyridines to be prepared. The latter route was exploited in a short formal synthesis of neocryptolepine starting from 2-((1H-indol-3-yl)methyl)cyclohexanone. PMID:18549288

  17. Catalyst Design and Optimization within a Framework of Green Chemistry

    OpenAIRE

    Tosh, Evangeline

    2009-01-01

    This thesis is divided into two main parts. The first, being the evaluation of existing catalytic reactions under the modern aspects of “Green Chemistry”. Energy conservation, atom economy, minimization of waste, side product recycling and use of renewable feedstocks were optimized in systems evaluated, and comparisons to previously know systems made. The second part is focused on carbocyclic carbene synthesis and application of carbocyclic and remote N-heterocyclic carbene complexes in C-N...

  18. Energy Transfer in a Hybrid Ir(III) Carbene-Pt(II) Acetylide Assembly for Efficient Hydrogen Production.

    Science.gov (United States)

    Yu, Zhen-Tao; Yuan, Yong-Jun; Chen, Xin; Cai, Jian-Guang; Zou, Zhi-Gang

    2015-07-01

    A new heterometallic supramolecular complex, consisting of an iridium carbene-based unit appended to a platinum terpyridine acetylide unit, representing a new Ir(III) -Pt(II) structural motif, was designed and developed to act as an active species for photocatalytic hydrogen production. The results also suggested that a light-harvesting process is essential to realize the solar-to-fuel conversion in an artificial system as illustrated in the natural photosynthetic system. PMID:26096270

  19. Kinetic Selectivity of Olefin Metathesis Catalysts Bearing Cyclic (Alkyl)(Amino)Carbenes

    Science.gov (United States)

    Anderson, Donde R.; Ung, Thay; Mkrtumyan, Garik; Bertrand, Guy; Grubbs, Robert H.; Schrodi, Yann

    2008-01-01

    The evaluation of ruthenium olefin metathesis catalysts 4–6 bearing cyclic (alkyl)(amino)carbenes (CAACs) in the cross-metathesis of cis-1,4-diacetoxy-2-butene (7) with allylbenzene (8) and the ethenolysis of methyl oleate (11) is reported. Relative to most NHC-substituted complexes, CAAC-substituted catalysts exhibit lower E/Z ratios (3:1 at 70% conversion) in the cross-metathesis of 7 and 8. Additionally, complexes 4–6 demonstrate good selectivity for the formation of terminal olefins versus internal olefins in the ethenolysis of 11. Indeed, complex 6 achieved 35 000 TONs, the highest recorded to date. CAAC-substituted complexes exhibit markedly different kinetic selectivity than most NHC-substituted complexes. PMID:18584055

  20. Synthesis, characterization, and electrochemical properties of diiron propaneditellurolate (PDTe) complexes as active site models of [FeFe]-hydrogenases.

    Science.gov (United States)

    Song, Li-Cheng; Li, Qian-Li; Feng, Zhan-Heng; Sun, Xiao-Jing; Xie, Zhao-Jun; Song, Hai-Bin

    2013-02-01

    Parent complex (?-PDTe)Fe(2)(CO)(6) (1, PDTe = ?-TeCH(2)CH(2)CH(2)Te-?) is prepared via a new synthetic route involving the reaction of (?-Te(2))Fe(2)(CO)(6) with Et(3)BHLi, followed by treatment of (?-LiTe)(2)Fe(2)(CO)(6) with Br(CH(2))(3)Br in a 43% yield. Further reactions of 1 with 1 equiv of monophosphines in the presence of the decarbonylating agent Me(3)NO afford the corresponding monophosphine-substituted complexes (?-PDTe)Fe(2)(CO)(5)(L) (2, L = PPh(3); 3, PPh(2)H; 4, PMe(3)) in 37%-47% yields, whereas the N-heterocyclic carbene I(Mes)-monosubstituted complex (?-PDTe)Fe(2)(CO)(5)(I(Mes)) (5) can be prepared in a 26% yield by treatment of 1 with the in situ generated I(Mes) from the 1,3-bis(mesityl)imidazolium salt I(Mes)·HCl and n-BuLi. While the diphosphine-bridged single-butterfly complexes (?-PDTe)Fe(2)(CO)(4)(dppm) (6) and (?-PDTe)Fe(2)(CO)(4)(dppn) (7) can be prepared in 28% and 21% yields by treatment of 1 with 1 equiv of the corresponding diphosphines in refluxing xylene, treatment of 1 with 0.5 equiv of diphosphines in the presence of Me(3)NO results in the formation of the corresponding diphosphine-bridged double-butterfly complexes [(?-PDTe)Fe(2)(CO)(5)](2)(dppp) (8), [(?-PDTe)Fe(2)(CO)(5)](2)(dppb) (9), and [(?-PDTe)Fe(2)(CO)(5)](2)(dppf) (10) in 25-37% yields. All the new substituted model complexes 2-10 are characterized by combustion analysis and spectroscopy, and particularly for 2, 3, 5, and 7-10, by X-ray crystallography. In addition, a comparative study on the electrochemical and electrocatalytic properties of the PDTe-type model complexes 1 and 7 with their corresponding selenium and sulfur analogs are reported. PMID:23143609

  1. The reactions of anthronylidene carbene with some heterocyclic compounds

    International Nuclear Information System (INIS)

    The action of the anthronylidene carbene, generated by photochemical decomposition of 9-diazo 10-anthron, on four heterocyclic compounds (furan, thiophene, 1-methyl-pyrrole and 2,5-dihydrofuran) has been examined. Two classical carbene reactions have been observed: the addition on double bond (furan, thiophene, 1-methylpyrrole) and hydrogen atom abstraction of the heterocyclic compound (2,5-dihydrofuran). In the case of furan and thiophene, the cyclo-propanic compound resulting from the addition is spontaneously transformed into an ethylenic derivative by valence isomerization. The furan derivative undergoes a cis-trans isomerization, while the thiophene one undergoes an extra carbene attack. In the case of 1-methylpyrrole, the corresponding cyclo-propanic compound undergoes a ring cleavage, followed by a hydrogen atom migration leading to the formation of a substituted anthron. Only an allylic hydrogen atom selective abstraction of heterocyclic compound takes place in the reaction of anthronylidene carbene with 2,5-dihydrofuran. The asymmetrical coupling of radicals so obtained yields the corresponding substituted anthron. (author)

  2. Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

    Energy Technology Data Exchange (ETDEWEB)

    Gottlieb, C.A.; Thaddeus, P. [Harvard Univ., Cambridge, MA (United States)

    1993-12-01

    Highly reactive carbenes and carbon-chain radicals are studied at millimeter wavelengths by observing their rotational spectra. The purpose is to provide definitive spectroscopic identification, accurate spectroscopic constants in the lowest vibrational states, and reliable structures of the key intermediates in reactions leading to aromatic hydrocarbons and soot particles in combustion.

  3. Nitrene-carbene-carbene rearrangement. Photolysis and thermolysis of tetrazolo[5,1- a ]phthalazine with formation of 1-phthalazinylnitrene, o-cyanophenylcarbene, and phenylcyanocarbene

    DEFF Research Database (Denmark)

    Høj, Martin; Kvaskoff, David; Wentrup, Curt

    2014-01-01

    1-Azidophthalazine 9A is generated in trace amount by mild FVT of tetrazolo[5,1-a]phthalazine 9T and is observable by its absorption at 2121 cm-1 in the Ar matrix IR spectrum. Ar matrix photolysis of 9T/9A at 254 nm causes ring opening to generate two conformers of (o-cyanophenyl) diazomethane 11 (2079 and 2075 cm-1), followed by (o-cyanophenyl)carbene 312, cyanocycloheptatetraene 13, and finally cyano(phenyl)carbene 314 as evaluated by IR spectroscopy. The two carbenes 312 and 314 were observed...

  4. Thermally Stable, Latent Olefin Metathesis Catalysts

    OpenAIRE

    Thomas, Renee M.; Fedorov, Alexey; Keitz, Benjamin K.; Grubbs, Robert H

    2011-01-01

    Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to i...

  5. Crystalline Cyclic (Alkyl)(amino)carbene-tetrafluoropyridyl Radical.

    Science.gov (United States)

    Styra, Steffen; Melaimi, Mohand; Moore, Curtis E; Rheingold, Arnold L; Augenstein, Timo; Breher, Frank; Bertrand, Guy

    2015-06-01

    A stable cyclic (alkyl)(amino)carbene (CAAC) 1 inserts into the para-CF bond of pentafluoropyridine, and after fluoride abstraction, the iminium-pyridyl adduct [3](+) was isolated. A cyclic voltammetry study shows a reversible three-state redox system involving [3](+) , [3](?) , and [3](-) . The CAAC-pyridyl radical [3](?) , obtained by reduction of [3](+) with magnesium, has been spectroscopically and crystallographically characterized. In contrast to the lack of ? communication between the CAAC and the pyridine units in cation [3](+) , the unpaired electron of [3](?) is delocalized over an extended ? system involving both heterocycles. PMID:25925367

  6. Stable P-Heterocyclic Carbenes: Scope and Limitations

    OpenAIRE

    Jason D. Masuda; Martin, David; Lyon-Saunier, Celine; Baceiredo, Antoine; Gornitzka, Heinz; Donnadieu, Bruno; Bertrand, Guy

    2007-01-01

    The conjugate acids (PHCH +s) of P-heterocyclic carbenes (PHCs) are prepared by formal [3+2] cycloaddition of a 1,3-diphosphaallyl or 1,3-phosphinophosphenium cation with various nitriles. The effect of the phosphorus substituent on the fate of the cyclization and on that of the counteranion and base in the subsequent deprotonation reaction are reported. Two PHCs that are indefinitely stable in the solid state are described. In solution, one of them, made from acetonitrile, undergoes a facile...

  7. Thin films of molecular materials synthesized from fisher's carbene ferrocenyl: Film formation and electrical properties

    International Nuclear Information System (INIS)

    The synthesis of materials from Fisher's carbene ferrocenyl of the elements chromium, molybdenum and tungsten was carried out. The Fisher's compounds that were synthesized included the following combinations of two different metallic atoms: iron with chromium, iron with molybdenum and iron with tungsten. The molecular solids' preparation was done in electro-synthesis cells with platinum electrodes. Thin films were prepared by vacuum thermal evaporation on quartz substrates and crystalline silicon wafers. Pellets and thin films from these compounds were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy, atomic force microscopy and ellipsometry. The powder and thin films synthesized from these materials show the same intra-molecular bonds shown by infrared spectroscopy results, suggesting that thermal evaporation does not alter these bonds in spite of the thin films being amorphous, in contrast with other bimetallic complexes where material decomposition occurs. The differences in the conductivity values of the prepared films are very small, so they may be attributed to the different metallic ions employed in each case. The tungsten complex exhibits a higher conductivity than the molybdenum and chromium complexes at room temperature. Electrical conductivity values found for thin films are higher than for pellets made of the same molecular materials

  8. The Effects of NHC-Backbone Substitution on Efficiency in Ruthenium-based Olefin Metathesis

    OpenAIRE

    Kuhn, Kevin M.; Bourg, Jean-Baptiste; Chung, Cheol K.; Virgil, Scott C; Grubbs, Robert H

    2009-01-01

    A series of ruthenium olefin metathesis catalysts bearing N-heterocyclic carbene (NHC) ligands with varying degrees of backbone and N-aryl substitution have been prepared. These complexes show greater resistance to decomposition through C–H activation of the N-aryl group, resulting in increased catalyst lifetimes. This work has utilized robotic technology to examine the activity and stability of each catalyst in metathesis, providing insights into the relationship between ligand architecture ...

  9. Comparing Ru and Fe-catalyzed olefin metathesis.

    Science.gov (United States)

    Poater, Albert; Chaitanya Vummaleti, Sai Vikrama; Pump, Eva; Cavallo, Luigi

    2014-08-01

    Density functional theory calculations have been used to explore the potential of Fe-based complexes with an N-heterocyclic carbene ligand, as olefin metathesis catalysts. Apart from a less endothermic reaction energy profile, a small reduction in the predicted upper energy barriers (? 2 kcal mol(-1)) is calculated in the Fe catalyzed profile with respect to the Ru catalysed profile. Overall, this study indicates that Fe-based catalysts have the potential to be very effective olefin metathesis catalysts. PMID:24821502

  10. Design and Synthesis of Ruthenium based Olefin Metathesis Catalysts

    OpenAIRE

    Singstad, Åsmund

    2010-01-01

    The present Master thesis seeks to develop new unsymmetrical ruthenium-based olefin metathesis catalysts and therein a better understanding of olefin metathesis catalysis with unsymmetrical active complexes. Such catalysts have a potential for chemoselectivity and in best case, stereoselectivity. Two different classes of catalysts, coordinated by a hemilabile amine ligand and by a novel N-heterocyclic carbene (NHC) ligand respectively, have been investigated. Two new amine-based olefin metath...

  11. Tandem isomerization/telomerization of long chain dienes

    OpenAIRE

    AlexeiLapkin; LauraTorrente Murciano; KingsleyCavell

    2014-01-01

    The first example of a tandem reaction involving double-bond migration in combination with telomerization is reported. Homogeneous and heterogeneous Ru catalysts were employed as isomerisation catalysts, and telomerization was realized using a homogeneous Pd(0) precursor complex with a N-heterocyclic carbene (IMes) ligand. Overall conversions approaching 60 % were achieved with the best selectivity to telomerization products of 91% attained at 11 % conversion. Conversion was markedly higher ...

  12. Frustrated Lewis pair activation of an N-sulfinylamine: a source of sulfur monoxide.

    Science.gov (United States)

    Longobardi, Lauren E; Wolter, Vanessa; Stephan, Douglas W

    2015-01-12

    Inter- and intramolecular P/B frustrated Lewis pairs are shown to react with an N-sulfinylamine to form PNSOB linakages. These species can be regarded as phosphinimine-borane-stabilized sulfur monoxide complexes, and indeed these species act as sources of SO, effecting the oxidation of PPh3 and delivering SO to [RhCl(PPh3)3] and an N-heterocyclic carbene. PMID:25376102

  13. Nitrene-carbene-carbene rearrangement. Photolysis and thermolysis of tetrazolo[5,1- a ]phthalazine with formation of 1-phthalazinylnitrene, o-cyanophenylcarbene, and phenylcyanocarbene

    DEFF Research Database (Denmark)

    HØj, Martin; Kvaskoff, David

    2014-01-01

    1-Azidophthalazine 9A is generated in trace amount by mild FVT of tetrazolo[5,1-a]phthalazine 9T and is observable by its absorption at 2121 cm-1 in the Ar matrix IR spectrum. Ar matrix photolysis of 9T/9A at 254 nm causes ring opening to generate two conformers of (o-cyanophenyl) diazomethane 11 (2079 and 2075 cm-1), followed by (o-cyanophenyl)carbene 312, cyanocycloheptatetraene 13, and finally cyano(phenyl)carbene 314 as evaluated by IR spectroscopy. The two carbenes 312 and 314 were observed by ESR spectroscopy (D|hc = 0.5078, E|hc = 0.0236 and D|hc = 0.6488, E|hc = 0.0195 cm-1, respectively). The rearrangement of 12 â., 13 â., 14 constitutes a carbene-carbene rearrangement. 1-Phthalazinylnitrene 310 is observed by means of its UV-vis spectrum in Ar matrix following FVT of 9 above 550 C. Rearrangement to cyanophenylcarbenes also takes place on FVT of 9 as evidenced by observation of the products of ring contraction, viz., fulvenallenes and ethynylcyclopentadienes 16-18. Thus the overall rearrangement 10 ?11 ? 12 â., 13 â., 14 can be formulated. © 2013 American Chemical Society.

  14. M(0) - Aminocarbene complexes (M = Cr, W, Fe): Redox Behavior Tuned by Metal and/or ligand modification.

    Czech Academy of Sciences Publication Activity Database

    Hoskovcová, I.; Rohá?ová, J.; Dvo?ák, D.; Ludvík, Ji?í

    2006-01-01

    Ro?. 2, ?. 23 (2006), s. 87-95. ISSN 1938-5862 R&D Projects: GA ?R GA203/04/0487 Institutional research plan: CEZ:AV0Z40400503 Keywords : carbene complexes * electrochemistry Subject RIV: CG - Electrochemistry

  15. Generation of Rhodium(I) Carbenes from Ynamides and Their Reactions with Alkynes and Alkenes

    OpenAIRE

    Liu, Renhe; Winston-McPherson, Gabrielle N.; Yang, Zhong-Yue; Zhou, Xin; Song, Wangze; Ilia A. Guzei; Xu, Xiufang; Tang, Weiping

    2013-01-01

    Rh(I) carbenes were conveniently generated from readily available ynamides. These metal carbene intermediates could undergo metathesis with electron-rich or neutral alkynes to afford 2-oxo-pyrrolidines or be trapped by tethered alkenes to yield 3-azabicyclo[3.1.0]hexanes, a common skeleton in numerous bioactive pharmaceuticals. Although the scope of the former is limited, the latter reaction tolerates various substituted alkenes.

  16. The reactivity game: theoretical predictions for heavy atom tunneling in adamantyl and related carbenes.

    Science.gov (United States)

    Kozuch, S

    2014-05-01

    The possibility of carbon atom tunneling at cryogenic temperatures for carbene-based ring expansion of adamantane analogues calls for a delicate balance of reactivity to experimentally detect the transpiring reaction. An overly reactive carbene will precipitously decay; an excessively stable carbene will not tunnel. Nevertheless, the factors that affect the quantum-mechanical tunneling (QMT) reactivity - mass, barrier height and width - are strikingly different from the classical "over the barrier" thermal mechanism. Herein, comparisons with experimental values and predictions on measurable rate constants for novel carbene systems are presented by way of small curvature tunneling (SCT) computations. Adamantane, noradamantane and bisnoradamantane have a significantly different C-C bond strain and reactivity, which can be modulated by tinkering with the carbene substituent atom (H, Cl or F) to obtain an observable lifetime of the reactant. The influence of barrier heights and widths, kinetic isotope effects (KIEs), the detection of the tunneling-determining atoms (TDA) and the comparisons with hydrogen-based reactions are discussed with the objective of finding the physical limits for QMT. PMID:24590008

  17. Carbene vs olefin products of C-H activation on ruthenium via competing alpha- and beta-H elimination.

    Science.gov (United States)

    Kuznetsov, Vladimir F; Abdur-Rashid, Kamaluddin; Lough, Alan J; Gusev, Dmitry G

    2006-11-01

    Bulky pincer complexes of ruthenium are capable of C-H activation and H-elimination from the pincer ligand backbone to produce mixtures of olefin and carbene products. To characterize the products and determine the mechanisms of the C-H cleavage, reactions of [RuCl(2)(p-cymene)](2) with N,N'-bis(di-tert-butylphosphino)-1,3-diaminopropane (L1) and 1,3-bis(di-tert-butylphosphinomethyl)cyclohexane (L2) were studied using a combination of X-ray crystallography, NMR spectroscopy, and DFT computational techniques. The reaction of L1 afforded a mixture of an alkylidene, a Fischer carbene, and two olefin isomers of the 16-e monohydride RuHCl[(t)Bu(2)PNHC(3)H(4)NHPBu(t)(2)] (2), whereas the reaction of L2 gave two olefin and two alkylidene isomers of 16-e RuHCl[2,6-(CH(2)PBu(t)(2))(2)C(6)H(8)] (3), all resulting from dehydrogenations of the ligand backbone of L1 and L2. The key intermediates implicated in the C-H activation reactions were identified as 14-electron paramagnetic species RuCl(PCP), where PCP = cyclometalated L1 or L2. Thus the alpha- and beta-H elimination reactions of RuCl(PCP) involved spin change and were formally spin-forbidden. Hydrogenation of 2 and 3 afforded 16-electron dihydrides RuH(2)Cl(PCP) distinguished by a large quantum exchange coupling between the hydrides. PMID:17076513

  18. Chemical functionalization of graphene by carbene cycloaddition: A density functional theory study

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • The reaction process of graphene functionalization with CCl2 group in atomic scales was studied. • The potential candidate carbenes CR2 (R = H, F, CN, NO20, NO290, CH3, OCH3, CCH, C6H5) were separately combined with graphene. • The functionalization of graphene nanoribbon with dichlorocarbene group was investigated. • The electronic properties of graphene functionalized by carbene groups were discussed. - Abstract: In this work, we have systematically studied the structural, energetic and electronic properties of graphene functionalized with carbene groups by using density functional theory. Introducing a low concentration of CCl2 group in graphene was studied in detail by DFT, and closed cyclopropane-like three-membered ring structure was formed, meanwhile, the potential candidate carbene groups CR2 (R = H, F, CH3, CN, NO2, OCH3, CCH, C6H5) were added to graphene sheet, and CR2 (R = H, NO2, CH3) groups were expected to be good reactive species to covalently modify graphene. The graphene functionalization with carbene groups above can open graphene's band gap. More CCl2 molecules were added to graphene, and different concentrations of CCl2 group can tune graphene's band gap. In addition, the addition of CCl2 group to graphene edges was investigated, and the stronger binding energy was found. Multiple CCl2 molecules preferred to be bound with the same edge of graphene nanoribbon. This work provides an insight into the detailed molecular mechanism of graphene functionalization with carbene groups

  19. The influence of anionic ligands on stereoisomerism of Ru carbenes and their importance to efficiency and selectivity of catalytic olefin metathesis reactions.

    Science.gov (United States)

    Torker, Sebastian; Khan, R Kashif M; Hoveyda, Amir H

    2014-03-01

    Investigations detailed herein provide insight regarding the mechanism of stereochemical inversion of stereogenic-at-Ru carbene complexes through a nonolefin metathesis-based polytopal rearrangement pathway. Computational analyses (DFT) reveal that there are two key factors that generate sufficient energy barriers that are responsible for the possibility of isolation and characterization of high-energy, but kinetically stable, intermediates: (1) donor-donor interactions that involve the anionic ligands and the strongly electron donating carbene groups and (2) dipolar effects arising from the syn relationship between the anionic groups (iodide and phenoxide). We demonstrate that a Brønsted acid lowers barriers to facilitate isomerization, and that the positive influence of a proton source is the result of its ability to diminish the repulsive electronic interactions originating from the anionic ligands. The implications of the present studies regarding a more sophisticated knowledge of the role of anionic units on the efficiency of Ru-catalyzed olefin metathesis reactions are discussed. The electronic basis for the increased facility with which allylic alcohols participate in olefin metathesis processes will be presented as well. Finally, we illustrate how a better understanding of the role of anionic ligands has served as the basis for successful design of Ru-based Z-selective catalysts for alkene metathesis. PMID:24533571

  20. Thin films of molecular materials synthesized from fisher's carbene ferrocenyl: Film formation and electrical properties

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Vergara, M.E. [Coordinacion de Ingenieria Mecatronica. Escuela de Ingenieria, Universidad Anahuac del Norte. Avenida Lomas de la Anahuac s/n, Col. Lomas Anahuac, 52786, Huixquilucan (Mexico)], E-mail: elena.sanchez@anahuac.mx; Ortiz, A. [Instituto de Investigaciones en Materiales. Universidad Nacional Autonoma de Mexico. A. P. 70-360, 04510, Mexico, DF (Mexico); Alvarez-Toledano, C.; Moreno, A. [Instituto de Quimica, Universidad Nacional Autonoma de Mexico. Circuito Exterior, Ciudad Universitaria, 04510, Mexico, DF (Mexico); Alvarez, J.R. [Instituto Tecnologico y de Estudios Superiores de Monterrey, Campus Ciudad de Mexico. Calle del Puente 222, Col. Ejidos de Huipulco, 14380, Mexico, DF (Mexico)

    2008-07-31

    The synthesis of materials from Fisher's carbene ferrocenyl of the elements chromium, molybdenum and tungsten was carried out. The Fisher's compounds that were synthesized included the following combinations of two different metallic atoms: iron with chromium, iron with molybdenum and iron with tungsten. The molecular solids' preparation was done in electro-synthesis cells with platinum electrodes. Thin films were prepared by vacuum thermal evaporation on quartz substrates and crystalline silicon wafers. Pellets and thin films from these compounds were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy, atomic force microscopy and ellipsometry. The powder and thin films synthesized from these materials show the same intra-molecular bonds shown by infrared spectroscopy results, suggesting that thermal evaporation does not alter these bonds in spite of the thin films being amorphous, in contrast with other bimetallic complexes where material decomposition occurs. The differences in the conductivity values of the prepared films are very small, so they may be attributed to the different metallic ions employed in each case. The tungsten complex exhibits a higher conductivity than the molybdenum and chromium complexes at room temperature. Electrical conductivity values found for thin films are higher than for pellets made of the same molecular materials.

  1. Palladation of diimidazolium salts at the C4 position: access to remarkably electron-rich palladium(II) centers

    OpenAIRE

    Heckenroth, Marion; Kluser, Evelyne; Neels, Antonia; Albrecht, Martin

    2008-01-01

    Palladation of C2-protected diimidazolium salts with Pd(OAc)? afforded complexes comprising C4-bound N-heterocyclic dicarbene ligands. The reactivity of these complexes towards Lewis acids (AgBF?, AgOAc) and Brønsted acids (H?SO?, H?PO?, HOAc) revealed that abnormal C4 bonding of the carbenes markedly increases the nucleophilicity of the coordinated palladium center as compared to C2 bonding. Despite its formal +2 charge, the palladium center in these complexes is best described as a Lewis ba...

  2. [PdA (IPr*) (cinnamyl)Cl]: An efficient pre-catalyst for the preparation of tetra-ortho-substituted biaryls by Suzuki-Miyaura cross-coupling

    KAUST Repository

    Chartoire, Anthony

    2012-03-13

    The bigger the better: The new well-defined [Pd(IPr*)(cin)Cl] pre-catalyst is described (see scheme). This complex proves to be highly active in the Suzuki-Miyaura cross-coupling for the synthesis of tetra-ortho- substituted biaryls under mild conditions. IPr* is reported as the largest N-heterocyclic carbene (NHC) to date for [Pd(NHC)(cin)Cl] complexes, explaining the high reactivity observed for this complex in this challenging transformation. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Synthesis of Heavy Fluorous Ruthenium Metathesis Catalysts Using the Stereoselective Addition of Polyfluoroalkyllithium to Sterically Hindered Diimines.

    Czech Academy of Sciences Publication Activity Database

    Hošek, J.; Rybá?ková, M.; ?ejka, J.; Cva?ka, Josef; Kví?ala, J.

    2015-01-01

    Ro?. 34, ?. 13 (2015), s. 3327-3334. ISSN 0276-7333 Institutional support: RVO:61388963 Keywords : ring-closing metathesis * form tetrasubstituted olefins * N-heterocyclic carbene Subject RIV: CC - Organic Chemistry Impact factor: 4.126, year: 2014

  4. Synthesis of a Benzodiazepine-derived Rhodium NHC Complex by C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Bergman, Roberg G.; Gribble, Jr., Michael W.; Ellman, Jonathan A.

    2008-01-30

    The synthesis and characterization of a Rh(I)-NHC complex generated by C-H activation of 1,4-benzodiazepine heterocycle are reported. This complex constitutes a rare example of a carbene tautomer of a 1,4-benzodiazepine aldimine stabilized by transition metal coordination and demonstrates the ability of the catalytically relevant RhCl(PCy{sub 3}){sub 2} fragment to induce NHC-forming tautomerization of heterocycles possessing a single carbene-stabilizing heteroatom. Implications for the synthesis of benzodiazepines and related pharmacophores via C-H functionalization are discussed.

  5. Synthesis of a Benzodiazepine-derived Rhodium NHC Complex by C-H Bond Activation

    OpenAIRE

    Gribble, Michael W.; Ellman, Jonathan A.; Bergman, Robert G.

    2008-01-01

    The synthesis and characterization of a Rh(I)-NHC complex generated by C-H activation of 1,4-benzodiazepine heterocycle are reported. This complex constitutes a rare example of a carbene tautomer of a 1,4-benzodiazepine aldimine stabilized by transition metal coordination and demonstrates the ability of the catalytically relevant RhCl(PCy3)2 fragment to induce NHC-forming tautomerization of heterocycles possessing a single carbene-stabilizing heteroatom. Implications for the synthesis of benz...

  6. Towards New Generations of Metathesis Metal-Carbene Pre-catalysts

    Science.gov (United States)

    Allaert, Bart; Dieltiens, Nicolai; Stevens, Chris; Drozdzak, Renata; Dragutan, Ileana; Dragutan, Valerian; Verpoort, Francis

    : A short general introduction combined with some historical milestones in the field of olefin metathesis is presented followed by an overview of recent representatives of metal carbene initiators. This paper attempts to relief the many superb contributions and overwhelming work invested in intelligent design and innovative synthesis in this area. Despites of recent advances there is still a great interest in the generation of new, better performing, and more environment friendly metathesis.

  7. Fischer carbene catalysis of alkynol cycloisomerization: Application to the synthesis of the altromycin B disaccharide

    Science.gov (United States)

    Koo, BonSuk

    2015-01-01

    The tungsten-catalyzed cycloisomerization of alkynyl alcohols can be conducted without using photochemistry, using a stable tungsten Fischer carbene as the precatalyst for this transformation. A variety of alkynyl alcohols undergo cycloisomerization under these conditions to provide endocyclic enol ethers of 5, 6, and 7-membered ring sizes. The utility of this method is further demonstrated in the stereoselective synthesis of the disaccharide substructure of altromycin B. PMID:17385878

  8. DFT STUDY ON THE MECHANISM OF THE ADDITION REACTION BETWEEN CARBENE AND GLYCINE

    Scientific Electronic Library Online (English)

    XIAOJUN, TAN; WEIHUA, WANG; PING, LI; JINSONG, GU; GUORONG, WANG; DANGSHENG, WANG; TAO, LI.

    Full Text Available The mechanism of addition reaction between the singlet carbene and glycine has been investigated at the B3LYP/6-311+G* level of theory, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. Computational results suggest that ther [...] e are two reaction pathways (1) and (2) during the addition process. In the pathway (1), carbene attacks the C=O bond from the H¹C¹C² side of glycine to form an intermediate (IM1), which is a barrier-free exothermic reaction. Then, IM1 isomerizes to a product (Pro1) via a transition state (TS1) with a potential barrier of 25.7 kJ/mol. Similarly, in the pathway (2), carbene attacks the C=O bond from the H²C¹C² side of glycine to form an intermediate IM2. Subsequently, IM2 isomerizes to Pro2 via TS2, where the Pro2 and Pro1 are enantiomers actually. The calculated potential barrier of 51.3 kJ/mol is higher than that of the pathway (1). Correspondingly, the reaction energy for the both pathways is -258.5 kJ/mol. Additionally, the atoms in molecules (AIM) theory has also been performed to characterize the bonding interaction and structural features for the addition reaction.

  9. Ruthenium-Aryloxide Catalysts for Olefin Metathesis

    Science.gov (United States)

    Monfette, Sebastien; Blacquiere, Johanna M.; Conrad, Jay C.; Beach, Nicholas J.; Fogg, Deryn E.

    : Advances in design of ruthenium aryloxide catalysts for olefin metathesis are described. The target complexes are accessible on reaction of RuCl2(NHC)(py)2 (CHPh) (NHC - N-heterocyclic carbene) with electron-deficient, monodentate aryl- oxides, or aryloxides that yield small, rigid chelate rings. The best of these catalysts offer activity comparable to or greater than that of the parent chloride (Grubbs) systems in ring-closing metathesis (RCM). Preliminary studies of the electronic nature of the Ru-X bond suggest that the metal center is more electropositive in the aryloxide complexes than in the Grubbs systems.

  10. Cycloalkyl-based unsymmetrical unsaturated (U?)-NHC ligands: flexibility and dissymmetry in ruthenium-catalysed olefin metathesis.

    Science.gov (United States)

    Rouen, Mathieu; Borré, Etienne; Falivene, Laura; Toupet, Loic; Berthod, Mikaël; Cavallo, Luigi; Olivier-Bourbigou, Hélène; Mauduit, Marc

    2014-05-21

    Air-stable Ru-indenylidene and Hoveyda-type complexes bearing new unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligands combining a mesityl unit and a flexible cycloalkyl moiety as N-substituents were synthesised. Structural features, chemical stabilities and catalytic profiles in olefin metathesis of this new library of cycloalkyl-based U2-NHC Ru complexes were studied and compared with their unsymmetrical saturated NHC-Ru homologues as well as a set of commercially available Ru-catalysts bearing either symmetrical SIMes or IMes NHC ligands. PMID:24647372

  11. Cycloalkyl-based unsymmetrical unsaturated (U2)-NHC ligands: Flexibility and dissymmetry in ruthenium-catalysed olefin metathesis

    KAUST Repository

    Rouen, Mathieu

    2014-01-01

    Air-stable Ru-indenylidene and Hoveyda-type complexes bearing new unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligands combining a mesityl unit and a flexible cycloalkyl moiety as N-substituents were synthesised. Structural features, chemical stabilities and catalytic profiles in olefin metathesis of this new library of cycloalkyl-based U2-NHC Ru complexes were studied and compared with their unsymmetrical saturated NHC-Ru homologues as well as a set of commercially available Ru-catalysts bearing either symmetrical SIMes or IMes NHC ligands. © 2014 the Partner Organisations.

  12. Transition Metal Catalyzed Reactions for Forming Carbon–Oxygen and Carbon–Carbon Bonds

    DEFF Research Database (Denmark)

    Sølvhøj, Amanda Birgitte

    2015-01-01

    Dehydrogenative ester formation with a ruthenium NHC complex A new atom-economical methodology for synthesizing esters by the dehydrogenative coupling of primary alcohols was developed. The reaction is catalyzed by the ruthenium N-heterocyclic carbene complex RuCl2(IiPr)(p-cymene). By screening the effect of different additives, solvents and loadings on the selfcondensation of pentanol, the optimal reaction conditions were found to be 2.5 mol % of RuCl2(IiPr)(p-cymene), 4.5 mol % of PCy3 and 10 ...

  13. Highvalent and organometallic technetium and rhenium compounds

    International Nuclear Information System (INIS)

    Diagnostic methods in nuclear medicine allow a detailed description of morphological organ structures and their function. The beta emitting isotope Tc-99 has optimal physical properties (140 keV gamma rays, half-life 6 h) and is therefore used for radiopharmaceuticals. The thesis is concerned with the search for new technetium complexes and their reproducible production. The (TcO3) core is of main interest. The second part of the thesis deals with organometallic technetium and rhenium complexes with carbonyl ligands and N-heterocyclic carbenes that show stability in aerobic aqueous solutions.

  14. E-Selective Semi-Hydrogenation of Alkynes by Heterobimetallic Catalysis.

    Science.gov (United States)

    Karunananda, Malkanthi K; Mankad, Neal P

    2015-11-25

    A unique cooperative H2 activation reaction by heterobimetallic (NHC)M'-MCp(CO)2 complexes (NHC = N-heterocyclic carbene, M' = Cu or Ag, M = Fe or Ru) has been leveraged to develop a catalytic alkyne semi-hydrogenation transformation. The optimal Ag-Ru catalyst gives high selectivity for converting alkynes to E-alkenes, a rare selectivity mode for reduction reactions with H2. The transformation is tolerant of many reducible functional groups. Computational analysis of H2 activation thermodynamics guided rational catalyst development. Bimetallic alkyne hydrogenation and alkene isomerization mechanisms are proposed. PMID:26550848

  15. Amide Synthesis from Alcohols and Amines by the Extrusion of Dihydrogen

    DEFF Research Database (Denmark)

    NordstrØm, Lars Ulrik Rubæk; Vogt, Henning

    2008-01-01

    An environmentally friendly method for synthesis of amides is presented where a simple ruthenium catalyst mediates the direct coupling between an alcohol and an amine with the liberation of two molecules of dihydrogen. The active catalyst is generated in situ from an easily available ruthenium complex, an N-heterocyclic carbene and a phosphine. The reaction allows primary alcohols to be coupled with primary alkyamines to afford the corresponding secondary amides in good yields. The amide formation presumably proceeds through a catalytic cycle where the intermediate aldehyde and hemiaminal are both coordinated to the metal catalyst.

  16. Comparing Ru and Fe-catalyzed olefin metathesis

    KAUST Repository

    Poater, Albert

    2014-01-01

    Density functional theory calculations have been used to explore the potential of Fe-based complexes with an N-heterocyclic carbene ligand, as olefin metathesis catalysts. Apart from a less endothermic reaction energy profile, a small reduction in the predicted upper energy barriers (? 2 kcal mol -1) is calculated in the Fe catalyzed profile with respect to the Ru catalysed profile. Overall, this study indicates that Fe-based catalysts have the potential to be very effective olefin metathesis catalysts. This journal is © the Partner Organisations 2014.

  17. Tandem isomerization/telomerization of long chain dienes

    Science.gov (United States)

    Torrente-Murciano, Laura; Nielsen, David J.; Cavell, Kingsley J.; Lapkin, Alexei A.

    2014-01-01

    The first example of a tandem reaction involving double-bond migration in combination with telomerization is reported. Homogeneous and heterogeneous Ru catalysts were employed as isomerization catalysts, and telomerization was realized using a homogeneous Pd(0) precursor complex with a N-heterocyclic carbene (IMes) ligand. Overall conversions approaching 60% were achieved with the best selectivity to telomerization products of 91% attained at 11% conversion. Conversion was markedly higher in the presence of longer-chain alcohol (1-butanol) as the nucleophile (telogen). PMID:24982855

  18. Theoretical Predictions of Redox Potentials of Fischer-Type Chromium Anninocarbene Complexes.

    Czech Academy of Sciences Publication Activity Database

    Kvapilová, Hana; Hoskovcová, Irena; Ludvík, Ji?í; Záliš, Stanislav

    2014-01-01

    Ro?. 33, ?. 18 (2014), s. 4964-4972. ISSN 0276-7333 R&D Projects: GA MŠk LD14129; GA ?R GA13-04630S Institutional support: RVO:61388955 Keywords : standard hydrogen electrode * density functional theory * metal carbene complexes Subject RIV: CG - Electrochemistry Impact factor: 4.126, year: 2014

  19. Electronic spectra of linear HC5H and cumulene carbene H2C5

    Science.gov (United States)

    Steglich, Mathias; Fulara, Jan; Maity, Surajit; Nagy, Adam; Maier, John P.

    2015-06-01

    The 1 3 ?u - ? X 3 ?g - transition of linear HC5H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC2n+1H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the 1 1 A 1 ? X ˜ 1 A 1 transition of the cumulene carbene pentatetraenylidene H2C5 (B).

  20. Electronic spectra of linear HC$_5$H and cumulene carbene H$_2$C$_5$

    CERN Document Server

    Steglich, M; Maity, S; Nagy, A; Maier, J P

    2015-01-01

    The $1 ^3\\Sigma_u^- \\leftarrow X^3\\Sigma_g^-$ transition of linear HC$_5$H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC$_{2n+1}$H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the $1 ^1 A_1 \\leftarrow X ^1 A_1$ transition of the cumulene carbene pentatetraenylidene H$_2$C$_5$ (B).

  1. Electronic spectra of linear HC5H and cumulene carbene H2C5.

    Science.gov (United States)

    Steglich, Mathias; Fulara, Jan; Maity, Surajit; Nagy, Adam; Maier, John P

    2015-06-28

    The 1(3)?u (-)?X(3)?g (-) transition of linear HC5H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC2n+1H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the 1(1)A1?X˜(1)A1 transition of the cumulene carbene pentatetraenylidene H2C5 (B). PMID:26133432

  2. Synthesis of cis - and trans-diisothiocyanato-bis(NHC) complexes of nickel(II) and applications in the Kumada-Corriu reaction

    KAUST Repository

    Jothibasu, Ramasamy

    2010-09-13

    Metathetical reaction of AgSCN with a series of trans-dihalido-bis(carbene) nickel(II) complexes in CH3CN readily afforded the novel diisothiocyanato-bis(carbene) complexes [Ni(NCS)2(NHC)2] (trans-2a, NHC = 1,3-diisopropylbenzimidazolin-2-ylidene; trans-2b, NHC = 1,3-diisobutylbenzimidazolin-2-ylidene; trans-2c, NHC = 1,3- dibenzylbenzimidazolin-2-ylidene; cis-2d, NHC = 1,3-di(2-propenyl) benzimidazolin-2-ylidene; cis-2e, NHC = 1-propyl-3-methylbenzimidazolin-2- ylidene) as greenish-yellow powders in moderate to good yields. While dihalido-bis(carbene) Ni(II) complexes exclusively form trans-complexes, a trans-cis isomerization occurs upon halido-isothiocyanato exchange with complexes bearing less bulky carbene ligands, i.e., cis-2d/e. DFT calculations indicated that this isomerization can be attributed to a reduced energy difference between trans- and cis-isomers of diisothiocyanato complexes. All complexes have been characterized by multinuclear NMR spectroscopy, ESI mass spectrometry, and X-ray diffraction analysis. A catalytic study revealed that cis-complexes generally exhibit greater activities in the Kumada-Corriu coupling reaction. © 2010 American Chemical Society.

  3. Surface Characterization and in situ Protein Adsorption Studies on Carbene-Modified Polymers.

    Science.gov (United States)

    Nelson, Geoffrey W; Parker, Emily M; Singh, Kulveer; Blanford, Christopher F; Moloney, Mark G; Foord, John S

    2015-10-13

    Polystyrene thin films were functionalized using a facile two-step chemical protocol involving carbene insertion followed by azo-coupling, permitting the introduction of a range of chemical functional groups, including aniline, hexyl, amine, carboxyl, phenyl, phosphonate diester, and ethylene glycol. X-ray photoelectron spectroscopy (XPS) confirmed the success of the two-step chemical modification with a grafting density of at least 1/10th of the typical loading density (10(14)-10(15)) of a self-assembled monolayer (SAM). In situ, real-time quartz crystal microbalance with dissipation (QCM-D) studies show that the dynamics of binding of bovine serum albumin (BSA) are different at each modified surface. Mass, viscoelastic, and kinetic data were analyzed, and compared to cheminformatic descriptors (i.e., c log P, polar surface area) typically used for drug discovery. Results show that functionalities may either resist or adsorb BSA, and uniquely influence its adsorption dynamics. It is concluded that carbene-based surface modification can usefully influence BSA binding dynamics in a manner consistent with, and more robust than, traditional systems based on SAM chemistry. PMID:26391812

  4. Carbene Spin Multiplicity in Solution Probed Using Time-Resolved EPR Spectroscopy

    Scientific Electronic Library Online (English)

    Jin, Wang; Natalia V., Lebedeva; Matthew S., Platz; Malcolm D. E., Forbes.

    2009-09-01

    Full Text Available Espectroscopia de resonancia paramagnética electrónica (EPR por las siglas en inglés) fue utilizada para detectar los radicales libres formados mediante reacciones de abstracción de átomos de hidrógeno de diversos carbenos generados fotoquímicamente en soluciones de n-hexano y a temperatura ambiente [...] . En particular, se describe el análisis de tres carbenos que fueron generados por fotoexcitación de un bifenilo con dos grupos diazo. Se identificaron señales EPR de dos radicales alquilo y uno bencílico. La estructura de dichos radicales se confirmó mediante un proceso de simulación computacional utilizando parámetros espectroscópicos (factores-g, constantes de acoplamiento hiperfino) reportados en la literatura. Experimentos previos de absorción óptica han llevado a la conclusión de que los carbenos estudiados presentan un estado basal de tipo triplete, lo que se confirma al observar las señales EPR de emisión a campo bajo pero de absorción a campo alto. Además, se encontró que los espectros presentan un espín fuertemente polarizado como consecuencia de un mecanismo CIDEP, y que la intensidad de las señales está relacionada con los rendimientos cuánticos asociados a la producción de los carbenos iniciales. Como era de esperarse, un tercer sustrato, que reacciona vía una reacción concertada de tipo Wolff a través de un reordenamiento del intermediario singulete producido en el estado excitado, no dio lugar a ninguna señal EPR. Así mismo, cuando las reacciones de los tres carbenos se llevan a cabo en acetonitrilo, la multiplicidad del espín se invierte de modo que se genera un estado basal.singulete, por lo que no se observan señales EPR. Los resultados descritos en este trabajo son consistentes con aquellos obtenidos mediante fotólisis láser. Abstract in english Time-resolved (CW) EPR spectroscopy at X-band has been used to detect free radicals created by H-atom abstraction reactions of photochemically generated carbenes in n-hexadecane solutions at room temperature. Three different carbenes were studied, formed via loss of nitrogen after photo-excitation o [...] f a substituted biphenyl diazo precursor. The TREPR signals from two different alkyl radicals and the benzylic-type radical from the carbene are detected for two of the three diazo substrates. The radicals were unambiguously identified by spectral simulation using literature parameters (g-factors and hyper-fine coupling constants). Previous transient optical absorption spectroscopy experiments have concluded that these two carbenes have triplet ground states, which is confirmed by the low field emissive, high field absorptive phase of the TREPR signals reported here. The spectra are strongly spin polarized by the Radical Pair Mechanism of CIDEP, and their overall intensities track with the measured quantum yields for carbene production. A third substrate, known to react via a concerted Wolff reaction or excited state rearrangement via a singlet state, showed no TREPR signal, as expected. Reactions run in acetonitrile, where the spin multiplicity is reversed to give a singlet ground state, did not lead to detectable TREPR signals for all three substrates. The observations are consistent with previously published laser flash photolysis results.

  5. Ruthenium Carbene Mediated Metathesis of Oleate-Type Fatty Compounds

    OpenAIRE

    Vosloo, Manie H. C.; Segakweng, Constance K.; Bassie B. Marvey

    2008-01-01

    The complexes RuCl2(PCy3)2(=CHPh), 1, and RuCl2(PCy3)(H2IMes)(=CHPh), 2, proved to be active catalysts for the self-metathesis of oleate-type fatty compounds containing the ester, hydroxyl, epoxy and carboxylic acid functional groups. At elevated reaction temperatures 2 showed a higher activity, stability and lower selectivity for primary metathesis products compared to 1. A profound influence of organic functional groups on catalyst activity and selectivity was found and from relative activi...

  6. Ruthenium Carbene Mediated Metathesis of Oleate-Type Fatty Compounds

    Directory of Open Access Journals (Sweden)

    Manie H. C. Vosloo

    2008-04-01

    Full Text Available The complexes RuCl2(PCy32(=CHPh, 1, and RuCl2(PCy3(H2IMes(=CHPh, 2, proved to be active catalysts for the self-metathesis of oleate-type fatty compounds containing the ester, hydroxyl, epoxy and carboxylic acid functional groups. At elevated reaction temperatures 2 showed a higher activity, stability and lower selectivity for primary metathesis products compared to 1. A profound influence of organic functional groups on catalyst activity and selectivity was found and from relative activities and selectivities 2 has proved to be more resistant to deactivation by polar functional groups and more inclined to promote double bond isomerisation than 1. The observed catalyst deactivation by oxygen-containing functional groups could be attributed to a phosphine displacement side reaction.

  7. Studies of the mechanism of the olefin metathesis reaction and the process of active site formation on photoreduced molybdenum-silicate catalysts. I. Mechanism of formation of molybdenum-carbene intermediates

    Energy Technology Data Exchange (ETDEWEB)

    Elev, I.V.; Shelimov, B.N.; Kazanskii, V.B.

    1987-10-01

    The products of the initial stages of the reaction of ethylene and propylene with Mo/sup 4 +/ ions in photoreduced molybdenum-silicate olefin metathesis catalysts have been studied by mass spectroscopy. The reaction of C/sub 2/H/sub 4/ with Mo/sup 4 +/ has been found to yield propylene, whereas interaction of C/sub 3/H/sub 6/ with Mo/sup 4 +/ gives a superequilibrium concentration of butenes and a small amount of pentenes. A significant kinetic isotope effect for the metathesis reaction was observed upon substitution of C/sub 3/H/sub 6/ by C/sub 3/D/sub 6/. The results can be interpreted in terms of a stepwise mechanism involving carbene intermediates, which are formed via isomerization of surface-bound ..pi..-complexes of olefins with Mo/sup 4 +/ ions as a result of intramolecular 1,2-H atom transfer.

  8. A search for thermal isomerization of olefins to carbenes: Thermal generations of the silicon-nitrogen double bond

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xianping.

    1990-09-21

    The first part of this thesis will search for the thermal isomerization of olefins to carbenes which is predicted to be a high energy process by calculations and has only been observed in a few strained olefins. The possibility of thermal isomerization of simple olefins to carbenes will be explored. Substitution of a silyl group on the double bond of an olefin allows a potential intermediate which has a {beta}-radical to the silyl group during the cis-trans isomerization. The effects of a trimethylsilyl group on this isomerization are the subject of this study. The second part of this thesis will include the generation and chemistry of intermediates containing a silicon-nitrogen double bond. The isomerization of parent silanimine to the aminosilylene was calculated to be a high energy process. New approaches to the silicon-nitrogen double bond will also be presented. 92 refs., 12 figs., 11 tabs.

  9. Inserção C-H de carbenóides de ródio em água e reutilização do catalisador Rhodium (II) carbene C-H insertion in water and catalyst reuse

    OpenAIRE

    Nuno R. Candeias; Gois, Pedro M.P.; Afonso, Carlos A.M.

    2007-01-01

    A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II) catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonylacetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst Rh2(OAc)4. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutiliz...

  10. Inserção C-H de carbenóides de ródio em água e reutilização do catalisador Rhodium (II carbene C-H insertion in water and catalyst reuse

    Directory of Open Access Journals (Sweden)

    Nuno R. Candeias

    2007-01-01

    Full Text Available A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonylacetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst Rh2(OAc4. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutilization.

  11. Inserção C-H de carbenóides de ródio em água e reutilização do catalisador / Rhodium (II) carbene C-H insertion in water and catalyst reuse

    Scientific Electronic Library Online (English)

    Nuno R., Candeias; Pedro M. P., Gois; Carlos A. M., Afonso.

    Full Text Available [...] Abstract in english A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II) catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonylacetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst [...] Rh2(OAc)4. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutilization.

  12. Production of propylene from 1-butene on highly active "bi-functional single active site" catalyst: Tungsten carbene-hydride supported on alumina

    KAUST Repository

    Mazoyer, Etienne

    2011-12-02

    1-Butene is transformed in a continuous flow reactor over tungsten hydrides precursor W-H/Al2O3, 1, giving a promising yield into propylene at 150 °C and different pressures. Tungsten carbene-hydride single active site operates as a "bi-functional catalyst" through 1-butene isomerization on W-hydride and 1-butene/2-butenes cross-metathesis on W-carbene. This active moiety is generated in situ at the initiation steps by insertion of 1-butene on tungsten hydrides precursor W-H/Al2O3, 1 followed by ?-H and ?-H abstraction. © 2011 American Chemical Society.

  13. A highly conjugated benzimidazole carbene-based ruthenium sensitizer for dye-sensitized solar cells.

    Science.gov (United States)

    Ho, Shih-Yu; Su, Chaochin; Li, Chung-Yen; Prabakaran, Kumaresan; Shen, Ming-Tai; Chen, Ying-Fan; Chang, Wei-Chun; Tingare, Yogesh S; Akula, Suribabu; Tsai, Sheng-Han; Li, Wen-Ren

    2013-09-01

    A new type of carbene-based ruthenium sensitizer, CB104, with a highly conjugated ancillary ligand, diphenylvinylthiophene-substituted benzimidazolepyridine, was designed and developed for dye-sensitized solar cell applications. The influence of the thiophene antenna on the performance of the cell anchored with CB104 was investigated. Compared with the dye CBTR, the conjugated thiophene in the ancillary ligand of CB104 enhanced the molar extinction coefficient of the intraligand ?-?* transition and the intensity of the lower energy metal-to-ligand charge-transfer band. However, the incident photon-to-current conversion efficiency spectrum of the cell anchored with CB104 (0.15?mM) showed a maximum of 63?% at 420?nm. The cell sensitized with the dye CB104 attained a power conversion efficiency of 7.30?%, which was lower than that of the cell with nonconjugated sensitizer CBTR (8.92?%) under the same fabrication conditions. The variation in the performance of these two dyes demonstrated that elongating the conjugated light-harvesting antenna resulted in the reduction of short-circuit photocurrent density, which might have been due to the aggregation of dye molecules. In the presence of a coabsorbate, chenodeoxycholic acid, the CB104-sensitized cell exhibited an enhanced photocurrent density and achieved a photovoltaic efficiency of 8.36?%. PMID:23832840

  14. Catalytic Enantioselective Olefin Metathesis in Natural Product Synthesis. Chiral Metal-Based Complexes that Deliver High Enantioselectivity and More

    OpenAIRE

    Hoveyda, Amir H.; Malcolmson, Steven J.; Meek, Simon J.; Zhugralin, Adil R.

    2010-01-01

    Chiral olefin metathesis catalysts enable chemists to access enantiomerically enriched small molecules with high efficiency; synthesis schemes involving such complexes can be substantially more concise than those that would involve enantiomerically pure substrates and achiral Mo alkylidenes or Ru-based carbenes. The scope of research towards design and development of chiral catalysts is not limited to discovery of complexes that are merely the chiral versions of the related achiral variants. ...

  15. Nucleophilic addition of amines to ruthenium carbenes: ortho-(alkynyloxy)benzylamine cyclizations towards 1,3-benzoxazines.

    Science.gov (United States)

    González-Rodríguez, Carlos; Suárez, José Ramón; Varela, Jesús A; Saá, Carlos

    2015-02-23

    A new ruthenium-catalyzed cyclization of ortho-(alkynyloxy)benzylamines to dihydro-1,3-benzoxazines is reported. The cyclization is thought to take place via the vinyl ruthenium carbene intermediates which are easily formed from [Cp*RuCl(cod)] and N2 CHSiMe3 . The mild reaction conditions and the efficiency of the procedure allow the easy preparation of a broad range of new 2-vinyl-2-substituted 1,3-benzoxazine derivatives. Rearrangement of an internal C(sp) in the starting material into a tetrasubstituted C(sp(3) ) atom in the final 1,3-benzoxazine is highly remarkable. PMID:25640908

  16. Domino Michael addition-carbene rearrangement-cyclization reaction of 1-alkynyl(aryl)-lambda3-bromanes with 2-mercapto-1,3-benzazoles.

    Science.gov (United States)

    Ochiai, Masahito; Tada, Norihiro

    2005-10-28

    Exposure of 1-alkynyl[p-(trifluoromethyl)phenyl](tetrafluoroborato)-lambda3-bromanes to 2-mercaptobenzimidazole or benzothiazole in dichloromethane at 0 degrees C under argon resulted in a domino Michael addition-carbene rearrangement-cyclization reaction to produce directly tricyclic heterocycles in high yields, whereas the reaction with 2-mercaptobenzoxazole afforded 1-alkynyl sulfides. PMID:16220178

  17. Cis/trans Coordination in olefin metathesis by static and molecular dynamic DFT calculations

    KAUST Repository

    Poater, Albert

    2014-05-25

    In regard to [(N-heterocyclic carbene)Ru]-based catalysts, it is still a matter of debate if the substrate binding is preferentially cis or trans to the N-heterocyclic carbene ligand. By means of static and molecular dynamic DFT calculations, a simple olefin, like ethylene, is shown to be prone to the trans binding. Bearing in mind the higher reactivity of trans isomers in olefin metathesis, this insight helps to construct small alkene substrates with increased reactivity. © 2014 Springer Science+Business Media New York.

  18. 3,3?-Di-n-butyl-1,1?-(p-phenylenedimethylenediimidazolium bis(hexafluorophosphate

    Directory of Open Access Journals (Sweden)

    Rosenani A. Haque

    2010-04-01

    Full Text Available The asymmetric unit of the title N-heterocyclic carbene compound, C22H32N42+·2PF6?, consists of one half of the N-heterocyclic carbene dication and one hexafluorophosphate anion. The dication lies across a crystallographic inversion center. The imidazole ring is twisted away from the central benzene ring, making a dihedral angle of 76.23?(6°. The hexafluorophosphate anions link the cations into a three-dimensional network via intermolecular C—H...F hydrogen bonds. A weak C—H...? interaction further stabilizes the crystal structure.

  19. Theoretical studies of the insertion of carbenes in the zeolite framework: modification of the acidity and creation of chiral sites

    Scientific Electronic Library Online (English)

    Maria Beatriz S., Mota; Nilton, Rosenbach Jr.; Claudio J. A., Mota.

    2014-06-01

    Full Text Available Foi realizado um estudo teórico da inserção de carbenos (CH2 e CHCHO) na estrutura cristalina da zeólita Y. O método our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) M062x/6-31G(d,p):PM6 foi utilizado para descrever a inserção do metileno (CH2) nas ligações T-O (T = Si [...] ou Al) da rede resultando em quatro estruturas isômeras. Em todos os casos os cálculos indicaram uma alta exotermicidade para a inserção do metileno na rede cristalina, independentemente da multiplicidade do carbeno (singlete ou triplete). A inserção na ligação O-H ácida para formar um grupo metóxi adsorvido foi o processo mais favorável, mas este caminho não ocorre se a inserção é feita na zeólita desprotonada. A inserção do formil-carbeno (CHCHO) cria centros quirais na estrutura cristalina. A acidez da zeólita após a inserção dos carbenos foi calculada usando a energia de desprotonação. Os cálculos predizem a possibilidade de desenvolver zeólitas ácidas com centros quirais, que poderiam imitar enzimas, especialmente para uso em processos de química fina e transformação de biomassa. Abstract in english A theoretical study of the insertion of carbenes (CH2, CHCHO) in the framework structure of zeolite Y was carried out. The "our own n-layered integrated molecular orbital and molecular mechanics" (ONIOM) scheme M062x/6-31G(d,p):PM6 was used to describe the insertion of methylene (CH2) in the T-O bon [...] ds (T = Si, Al) of the framework yielding four isomeric structures. In all cases, calculations indicated a high exothermic process for the insertion of methylene in the framework, regardless of the spin multiplicity of the carbene (singlet or triplet). Insertion into the acidic O-H bond to afford an adsorbed methoxy group was the most favourable process, but this pathway does not occur if insertion is carried out on the deprotonated zeolite. Insertion of formylcarbene (CHCHO) creates chiral sites in the framework. The acidity of the zeolite structures after carbene insertion was calculated by means of the deprotonation energy. The calculations predicted the possibility of designing acidic zeolites with chiral sites that could mimic enzymes, especially for uses in fine chemical processes and biomass transformations.

  20. Mono- and Bimetallic Ruthenium—Arene Catalysts for Olefin Metathesis: A Survey

    Science.gov (United States)

    Borguet, Yannick; Sauvage, Xavier; Demonceau, Albert; Delaude, Lionel

    In this chapter, we summarize the main achievements of our group toward the development of easily accessible, highly efficient ruthenium—arene catalyst precursors for olefin metathesis. Major advances in this field are presented chronologically, with an emphasis on catalyst design and mechanistic details. The first part of this survey focuses on monometallic complexes with the general formula RuCl2(p-cymene)(L), where L is a phosphine or N-heterocyclic carbene ancillary ligand. In the second part, we disclose recent developments in the synthesis and catalytic applications of homobimetallic ruthenium—arene complexes of generic formula (p-cymene)Ru(?-Cl)3RuCl(?2-C2H4)(L) and their derivatives resulting from the substitution of the labile ethylene moiety with vinylidene, allenylidene, or indenylidene units

  1. rac-cis-Dicarbonylchlorido{1-[2-(diphenylphosphanyl-?Pbenzyl]-3-(phenyl-?C1imidazol-2-ylidene-?C2}ruthenium(II dichloromethane monosolvate

    Directory of Open Access Journals (Sweden)

    Gregory J. Domski

    2012-09-01

    Full Text Available In the title compound, [Ru(C28H22N2PCl(CO2]·CH2Cl2, the RuII atom exhibits a distorted octahedral coordination geometry. The N-phenyl group of the ligand has undergone orthometalation; as a result, the tridentate phosphane-functionalized N-heterocyclic carbene ligand is coordinating in a meridional fashion. This complex is of interest with respect to transfer hydrogenation catalysis and also provides an example of C—H activation behavior in late transition metal complexes. The dichloromethane solvent molecule is disordered over two sets of sites with an occupancy ratio of 0.873?(14:0.127?(14.

  2. Diastereotopic group selectivity and chemoselectivity of alkylidene carbene reactions on 8-oxabicyclo[3.2.1]- oct-6-ene ring systems.

    Science.gov (United States)

    Munro, Kevin R; Male, Louise; Spencer, Neil; Grainger, Richard S

    2013-10-21

    ?-Hydroxyalkylidene carbenes, generated from thermolysis of ?,?-epoxy-N-aziridinylimines, undergo diastereotopic group selective 1,5 C–H insertion reactions on 2,4-dimethyl-8-oxabicyclo[3.2.1]oct-6-ene ring systems. Protection of a tertiary alcohol at C-3 of the bridged oxabicycle as a trimethylsilyl ether reverses the sense of diastereoselectivity. 1,5 C–H insertion into a methine adjacent to an OBn group, 1,5 O–R insertion into a tertiary alcohol (R = H) or silylether (R = TMS) at C-3 to form spirocyclic dihydrofurans, 1,2-rearrangement to an alkyne and fragmentation to a ketone are competing major pathways for 2-benzyloxy-substituted 8-oxabicyclo[3.2.1]oct-6-ene systems. Dihydrofuran formation is shown to be a result of substitution on the oxabicyclic ring system through comparison with other methods of alkylidene carbene formation. PMID:24175334

  3. Synthesis, structure and electrochemistry of Fischer alkoxy- and aminocarbene complexes of tungsten : the use of DFT to predict and understand oxidation and reduction potentials

    OpenAIRE

    Landman, Marilé; Pretorius, René; Buitendach, Blenerhassitt E.; van Rooyen, Petrus H.; Conradie, Jeanet

    2013-01-01

    Reactions of Fischer alkoxycarbene complexes [W(CO)5{C(OEt)Ar}], Ar = thienyl (1) or furyl (2), with ethylene diamine lead to the formation of two different reaction products: an aminolysis product (5 or 6) where the ethoxy substituent of the carbene ligand is replaced by the ethylene diamine moiety, as well as a chelated product where aminolysis and substitution of one carbonyl ligand had taken place, yielding 7 or 8. Aminolysis of 1 and 2 with cyclohexyl amine (CHA) pro...

  4. Metallacumulenes and carbide complexes. Final performance report

    Energy Technology Data Exchange (ETDEWEB)

    Selegue, J.P.

    1992-12-31

    We investigated many aspects of transition metal complexes of carbon-rich ligands, including cumulated transition metal carbene complexes of the types vinylidene (M=C=CR{sub 2})(M = Fe, Ru, Os, Mo, W), allenylidene (M=C=C=CR{sub 2}), and butatrienylidene (M=C=C=CR{sub 2}), as well as ``naked`` carbon ligands C{sub 1}, C{sub 2}, and C{sub 3}. In the last 3 years, we began to put some effort into studying the fullerenes. Finally, we investigated initial aspects of the coordination chemistry of thiophenes, from the perspectives of (1) modeling the transition- metal-catalyzed hydrodesulfurization of fossil fuels and (2) development of metal-doped, polythiophene-based polymers.

  5. Weakly Stabilized Primary Borenium Cations and their Dicationic Dimers

    OpenAIRE

    Prokofjevs, Aleksandrs; Kampf, Jeff W; Solovyev, Andrey; Curran, Dennis P; Vedejs, Edwin

    2013-01-01

    Hydride abstraction from monocationic hydride bridged salts [H(H2B–L)2]+ [B(C6F5)4]? (L = Lewis base) generates an observable primary borenium cation for L = iPr2NEt, but with L = Me3N, Me2NPr, or several N-heterocyclic carbenes, highly reactive dicationic dimers are formed.

  6. Weakly stabilized primary borenium cations and their dicationic dimers.

    Science.gov (United States)

    Prokofjevs, Aleksandrs; Kampf, Jeff W; Solovyev, Andrey; Curran, Dennis P; Vedejs, Edwin

    2013-10-23

    Hydride abstraction from monocationic hydride bridged salts [H(H2B-L)2](+) [B(C6F5)4]¯ (L = Lewis base) generates an observable primary borenium cation for L = iPr2NEt, but with L = Me3N, Me2NPr, or several N-heterocyclic carbenes, highly reactive dicationic dimers are formed. PMID:24087933

  7. Enantioselective Intramolecular Hydroacylation of Unactivated Alkenes: An NHC-Catalyzed Robust and Versatile Formation of Cyclic Chiral Ketones.

    Science.gov (United States)

    Janssen-Müller, Daniel; Schedler, Michael; Fleige, Mirco; Daniliuc, Constantin G; Glorius, Frank

    2015-10-12

    A highly enantioselective intramolecular N-heterocyclic carbene (NHC)-catalyzed hydroacylation reaction gives access to a range of cyclic ketones from unactivated olefin-substituted aldehydes (up to 99?% ee). Remarkably, aliphatic aldehydes were also transformed efficiently in an NHC-catalyzed hydroacylation reaction for the first time. PMID:25776819

  8. The Effects of NHC-Backbone Substitution on Efficiency in Ruthenium-based Olefin Metathesis

    Science.gov (United States)

    Kuhn, Kevin M.; Bourg, Jean-Baptiste; Chung, Cheol K.; Virgil, Scott C.; Grubbs, Robert H.

    2009-01-01

    A series of ruthenium olefin metathesis catalysts bearing N-heterocyclic carbene (NHC) ligands with varying degrees of backbone and N-aryl substitution have been prepared. These complexes show greater resistance to decomposition through C–H activation of the N-aryl group, resulting in increased catalyst lifetimes. This work has utilized robotic technology to examine the activity and stability of each catalyst in metathesis, providing insights into the relationship between ligand architecture and enhanced efficiency. The development of this robotic methodology has also shown that, under optimized conditions, catalyst loadings as low as 25 ppm can lead to 100% conversion in the ring-closing metathesis of diethyl diallylmalonate. PMID:19351207

  9. The stabilization of gallane and indane by a ring expanded carbene.

    Science.gov (United States)

    Leverett, Anthony R; McKay, Alasdair I; Cole, Marcus L

    2015-01-14

    7Dipp Complexes of the group 13 binary hydrides GaH3 and InH3 have been prepared. Both adducts possess excellent thermal stability in the solid state but decompose readily in solution at ambient temperature. The presence of short M-H···H-CAlkyl distances in the structures of both [MH3(7Dipp)] complexes is discussed. PMID:25428184

  10. Fac-mer equilibria of coordinated iminodiacetate (ida2-) in ternary CuII(ida)(H-1B)- complex formation (B = imidazole, benzimidazole) in aqueous solution

    Indian Academy of Sciences (India)

    Susmita Bandyopadhyay; G N Mukherjee

    2003-08-01

    pH potentiometric and spectrophotometric investigations on the complex formation equilibria of CuII with iminodiacetate (ida2-) and heterocyclic N-bases, viz. imidazole and benzimidazole (B), in aqueous solution in binary and ternary systems using different molar ratios of the reactants indicated the formation of complexes of the types, Cu(ida), Cu(ida)(OH)-, (ida)Cu(OH)Cu(ida)-, Cu(B)2+, Cu(H-1B)+, Cu(ida)(H-1B)-, (ida)Cu(B)Cu(ida) and (ida)Cu(H-1B)Cu(ida)-. Formation constants of the complexes at $25 \\pm 1^\\circ$ at a fixed ionic strength, $I = 0.1$ mol dm-3 (NaNO3) in aqueous solution were evaluated and the complex formation equilibria were elucidated with the aid of speciation curves. Departure of the experimental values of the reproportionation constants ($\\Delta \\log K_{\\text{Cu}}$) of ternary Cu(ida)(H-1B)- complexes from the statistically expected values, despite their formation in appreciable amounts at equilibrium, were assigned to fac(f)-mer(m) equilibria of the ida2- ligand coordinated to CuII, as the N-heterocyclic donors, (H-1B)-, coordinate trans- to the N-(ida2-) atom in the binary Cu(ida)$_f$ complex to form the ternary Cu(ida)$_m$(H-1B)- complexes.

  11. Complexation of trivalent cationic lanthanides by N.O donor ligands: physico-chemical studies of the association and selectivity in solution

    International Nuclear Information System (INIS)

    The aim of this work is to study the complexation of f-elements in solution by ligands incorporating N-heterocyclic donors. These ligands display interesting properties for the selective separation of An(III)/Ln(III) have been studied to obtain a better understanding of the coordination properties with f-elements and to develop more selective extractants. The hepta-dentate ligand tpaam shows an affinity for Ln(III) similar to the tetradentate ligand tpa in water even when the three additional amide groups are bonded to the metal. Even though the complexation with tpa is exothermic, that with tpaam is endothermic with a more positive entropy. The dehydration of the cation disfavours the formation of Ln(III) complexes with ligands containing weak donors. The analysis of the solution paramagnetic relaxation times of the tpaam complexes is in agreement with data in the solid-state. There is little difference between the formation constants of the Ln3+ complexes with different ligands (tpaam, tpzen, tpa and tpza) as determined by UV-vis spectrophotometry in anhydrous acetonitrile. The limitations encountered during this study are intrinsic to the ligands studied. The preliminary study of two tetrapodal ligands containing acid and pyridine groups (Lpy)or pyrazine (Lpz) show the formation of 1:1 complexes in water. Analysis of the formation constants of the corresponding Gd(III) complexes shows that replacement of a pyridine group by pyrazine result in a loss of stability of 1.6 logarithmic units. (author)

  12. Transient negative ions in benzene. Some N-heterocyclic and mono-substituted derivatives

    International Nuclear Information System (INIS)

    Electron transmission spectroscopy is used to study transient negative ions or shape resonances in various benzene derivatives. Because of the long lifetime of these ions (? > 10-14 S) the vibrational structure of their first two electronic states is observed superposed on the total electron cross section curves in the energy range 0-6 eV and the corresponding adiabatic electron affinities are determined. The comparison of the first electron affinity with the first ionization potential and the energy on the first excited state of each of the derivatives is used to characterize the 'donor' substituents on the benzene ring. As a complementary study, these derivatives are studied in the liquid phase using polarography (cyclic voltametry). The linear correlation established between polarographic potentials measured in dimethyl formamide and the electron affinities was used to deduce electron affinities for several molecules which are difficult to measure in the gas phase. (author)

  13. Asymmetric hydrogenation of imines, enamines and N-heterocycles using phosphoramidite ligands

    OpenAIRE

    Mrsic, Natasa,

    2010-01-01

    De asymmetrische hydrogenerings (AH) reactie vertegenwoordigt een veelzijdige, schone en atoom efficiënte methode voor de synthese van enantiozuivere verbindingen. De focus van dit onderzoek lag op de AH van imines en enamines, met name in heteroaromatische verbindingen. De reden hiervoor is dat deze structuren veelvuldig voorkomen in geneesmiddelen en fysiologisch actieve verbindingen. Dit proefschrift beschrijft het gebruik van Iridium complexen van op binol gebaseerde fosforamidiet liga...

  14. Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl2(P-P)(N-N)] type complexes

    International Nuclear Information System (INIS)

    The substitution reactions [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, where P.P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2' -bipyridine, 4,4' L-dimethoxy-2,2' L- bipyridine, 4,4' L-dimethylpyridine-2,2' L-bipyridine and 4,4' L-dichloro-2,2' L-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pKa of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the 31P{1H} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF6, there are two doublets with ?? < 1. This is consistent with products formed by dissociation of the chloride trans to one of the phosphorus atoms in the precursors. (author)

  15. Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl{sub 2}(P-P)(N-N)] type complexes

    Energy Technology Data Exchange (ETDEWEB)

    Monteiro, Marcos C.R.; Machado, Sergio de Paula, E-mail: sergiopm@iq.ufrj.b [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Inst. de Quimica; Nascimento, Fabio B.; Valle, Eliana M.A.; Batista, Alzir A. [Universidade Federal de Sao Carlos (UFSCAR), Sao Carlos, SP (Brazil). Dept. de Quimica; Ellena, Javier; Castellano, Eduardo E. [Universidade de Sao Paulo (IFSC/USP), Sao Carlos, SP (Brazil). Inst. de Fisica

    2010-07-01

    The substitution reactions [RuCl{sub 2}(P-P)(N-N)] + L {yields} [RuCl(L)(P-P)(N-N)]{sup +} + Cl{sup -}, where P.P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2' -bipyridine, 4,4' L-dimethoxy-2,2' L- bipyridine, 4,4' L-dimethylpyridine-2,2' L-bipyridine and 4,4' L-dichloro-2,2' L-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pK{sub a} of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the {sup 31}P{l_brace}{sup 1}H{r_brace} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF{sub 6}, there are two doublets with {Delta}{sigma} < 1. This is consistent with products formed by dissociation of the chloride trans to one of the phosphorus atoms in the precursors. (author)

  16. Modulating NHC catalysis with fluorine

    Directory of Open Access Journals (Sweden)

    Yannick P. Rey

    2013-12-01

    Full Text Available Fluorination often confers a range of advantages in modulating the conformation and reactivity of small molecule organocatalysts. By strategically introducing fluorine substituents, as part of a ?-fluoroamine motif, in a triazolium pre-catalyst, it was possible to modulate the behaviour of the corresponding N-heterocyclic carbene (NHC with minimal steric alterations to the catalyst core. In this study, the effect of hydrogen to fluorine substitution was evaluated as part of a molecular editing study. X-ray crystallographic analyses of a number of derivatives are presented and the conformations are discussed. Upon deprotonation, the fluorinated triazolium salts generate catalytically active N-heterocyclic carbenes, which can then participate in the enantioselective Steglich rearrangement of oxazolyl carbonates to C-carboxyazlactones (e.r. up to 87.0:13.0.

  17. Transient Palladadiphosphanylcarbenes: Singlet Carbenes with an “Inverse” Electronic Configuration (p?2 instead of ?2) and Unusual Transannular Metal–Carbene Interactions (?C?pd Donation and ?Pd?C Back-donation)

    OpenAIRE

    Vignolle, Joan; Gornitzka, Heinz; Maron, Laurent; Schoeller, Wolfgang W.; Bourissou, Didier; Bertrand, Guy

    2007-01-01

    Upon treatment with [PdCl(allyl)]2, asymmetrically substituted ?, ??-diphosphanyl diazo compounds eliminate dinitrogen to afford C-chlorodiphosphanylmethanide complexes in high yields. In the presence of a chloride-abstracting agent, such as sodium tetraphenylborate, the C-chlorodiphosphanylmethanide complexes react with pyridine and trimethylphosphine, readily affording the corresponding nitrogen and phosphorus ylides. The postulated intermediate in this process, namely palladadiphosphanylca...

  18. Synthesis of 3-fluoro-3-aryl oxindoles: Direct enantioselective ? arylation of amides

    KAUST Repository

    Wu, Linglin

    2012-02-06

    Modus operandi: Catalytic access to the title compounds through a new asymmetric ?-arylation protocol is reported (see scheme). These products are formed in good yields and excellent enantioselectivities by using a new and easily synthesized chiral N-heterocyclic carbene (NHC) ligand. Advanced DFT calculations reveal the properties of the NHC ligand and the mode of operation of the catalyst. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Chelated Ruthenium Catalysts for Z-Selective Olefin Metathesis

    Science.gov (United States)

    Endo, Koji; Grubbs, Robert H.

    2011-01-01

    We report the development of ruthenium-based metathesis catalysts with chelating N-heterocyclic carbene (NHC) ligands which catalyze highly Z-selective olefin metathesis. A very simple and convenient synthetic procedure of such a catalyst has been developed. An intramolecular C-H bond activation of the NHC ligand, which is promoted by anion ligand substitution, forms the appropriate chelate for stereo- controlled olefin metathesis. PMID:21563826

  20. Application of Olefin Cross Metathesis in Natural Product Syntheses

    OpenAIRE

    Dewi-Wülfing, Purnama

    2005-01-01

    Olefin cross metathesis (CM) is a powerful coupling method, thanks to the development of the new catalysts bearing N-heterocyclic carbene ligand, which increased the efficiency and the selectivity of the reaction. In the first part of the dissertation, the sequential CM – reductive cyclization method was introduced, followed by its application in the syntheses of three natural products. CM between enones or enediones with allyl- or homoallylamines give exclusively E-substituted enones, which ...

  1. Chelated Ruthenium Catalysts for Z-Selective Olefin Metathesis

    OpenAIRE

    ENDO, KOJI; Grubbs, Robert H

    2011-01-01

    We report the development of ruthenium-based metathesis catalysts with chelating N-heterocyclic carbene (NHC) ligands which catalyze highly Z-selective olefin metathesis. A very simple and convenient synthetic procedure of such a catalyst has been developed. An intramolecular C-H bond activation of the NHC ligand, which is promoted by anion ligand substitution, forms the appropriate chelate for stereo- controlled olefin metathesis.

  2. Improved Ruthenium Catalysts for Z-Selective Olefin Metathesis

    OpenAIRE

    Keitz, Benjamin K.; ENDO, KOJI; Patel, Paresma R.; Herbert, Myles B.; Grubbs, Robert H

    2011-01-01

    Several new C-H activated ruthenium catalysts for Z-selective olefin metathesis have been synthesized. Both the carboxylate ligand and the aryl group of the N-heterocyclic carbene have been altered and the resulting catalysts were evaluated using a range of metathesis reactions. Substitution of bidentate with monodentate X-type ligands led to a severe attenuation of metathesis activity and selectivity, while minor differences were observed between bidentate ligands within the same family (e.g...

  3. Synthesis of azoimidazolium dyes with nitrous oxide.

    Science.gov (United States)

    Tskhovrebov, Alexander G; Naested, Lara C E; Solari, Euro; Scopelliti, Rosario; Severin, Kay

    2015-01-19

    A new method for the synthesis of industrially important azoimidazolium dyes is presented. The procedure is based on a reagent which is rarely used in the context of synthetic organic chemistry: nitrous oxide ("laughing gas"). N2O is first coupled to N-heterocyclic carbenes. Subsequent reaction with aromatic compounds through an AlCl3-induced C-H activation process provides azoimidazolium dyes in good yields. PMID:25420599

  4. Heterolysis of Dihydrogen by Silver Alkoxides and Fluorides.

    Science.gov (United States)

    Tate, Brandon K; Nguyen, Jenna T; Bacsa, John; Sadighi, Joseph P

    2015-07-01

    Alkoxide-bridged disilver cations react with dihydrogen to form hydride-bridged cations, releasing free alcohol. Hydrogenolysis of neutral silver fluorides affords hydride-bridged disilver cations as their bifluoride salts. These reactions proceed most efficiently when the supporting ligands are expanded N-heterocyclic carbenes (NHCs) derived from 6- and 7-membered cyclic amidinium salts. Kinetics studies show that silver fluoride hydrogenolysis is first-order in both silver and dihydrogen. PMID:26059331

  5. Enantioselective NHC-Catalyzed Redox [4 + 2]-Hetero-Diels-Alder Reactions Using ?,?-Unsaturated Trichloromethyl Ketones as Amide Equivalents.

    Science.gov (United States)

    Attaba, Nassilia; Taylor, James E; Slawin, Alexandra M Z; Smith, Andrew D

    2015-10-01

    ?,?-Unsaturated trichloromethyl ketones are suitable ?,?-unsaturated amide and ester equivalents in N-heterocyclic carbene (NHC)-catalyzed redox hetero-Diels-Alder reactions with azolium enolates generated from ?-aroyloxyaldehydes. The initially formed syn-dihydropyranone products can be isolated or can undergo ring-opening with benzylamine followed by aminolysis of the resulting CCl3 ketone to form a range of diamides with high diastereo- and enantioselectivity (up to >95:5 dr and >99% ee). PMID:26344498

  6. Asymmetric NHC-catalyzed aza-Diels-Alder reactions: Highly enantioselective route to ?-amino acid derivatives and DFT calculations

    KAUST Repository

    Yang, Limin

    2014-08-01

    A facile N-heterocyclic carbene catalytic enantioselective aza-Diels-Alder reaction of oxodiazenes with ?-chloroaldehydes as dienophile precursors is reported, with excellent enantioselectivity (ee > 99%) and excellent yield (up to 93%). DFT study showed that cis-TSa, formed from a top face approach of oxodiazene to cis-IIa, is the most favorable transition state and is consistent with the experimental observations. © 2014 American Chemical Society.

  7. Activation et transfert de l'oxygène moléculaire catalysés par les complexes des métaux de transition Activation and Tranfer of Molecular Oxygen Catalyzed by Transition Metal Complexes

    Directory of Open Access Journals (Sweden)

    Nimoun H.

    2006-11-01

    Full Text Available Cet article tente de rationaliser les différents processus par lesquels les complexes des métaux de transition permettent d'activer l'oxygène moléculaire et de le transférer sélectivement sur des substrats définis. Après un bref rappel des propriétés de l'oxygène moléculaire et de ses associations possibles avec les métaux, nous distinguons trois voies essentielles par les-quelles l'oxygène peut être activé a Les oxydations catalysées par les complexes de type peroxo dans lesquelles substrat et oxygène sont coordinés ensemble sur le même métal formant intermédiairement un peroxométallocycle. b Les oxydations catalysées par les complexes superoxo dans lesquelles l'attaque du substrat s'effectue sur l'oxygène coordiné au métal. c Les oxydations catalysées par les complexes oxo dans lesquelles ces derniers ont un comportement carbénique. This article attempts to make a rational explanation of the different processes by which transition metal complexes can be used to activate molecular oxygen and selectively transfer it on specific substrates. After a brief review of the properties of molecular oxygen and of its possible associations with metals, a distinction is made between three basic ways of activating oxygen: a Oxidations catalyzed by peroxo-type complexes in which substrate and oxygen are both coordinated on the saure metal forming transiently a peroxometallocycle. b Oxidations catalyzed by superoxo complexes in which the substrate attacks the coordinated oxygen. c Oxidations catalyzed by oxo complexes in which these oxo complexes have a carbenic behavior.

  8. Ruthenium-catalyzed olefin metathesis accelerated by the steric effect of the backbone substituent in cyclic (alkyl)(amino) carbenes.

    Science.gov (United States)

    Zhang, Jun; Song, Shangfei; Wang, Xiao; Jiao, Jiajun; Shi, Min

    2013-10-21

    Three ruthenium complexes bearing backbone-monosubstituted CAACs were prepared and displayed dramatic improvement in catalytic efficiency not only in RCM reaction but also in the ethenolysis of methyl oleate, compared to those bearing backbone-disubstituted CAACs. PMID:24013192

  9. Organic-Inorganic Hybrid Silica Material Derived from a Monosilylated Grubbs-Hoveyda Ruthenium Carbene as a Recyclable Metathesis Catalyst

    OpenAIRE

    Michel Wong Chi Man; Ramón Alibés; Xavier Cattoën; Guadalupe Borja; Roser Pleixats

    2010-01-01

    The synthesis of a monosilylated Grubbs-Hoveyda ruthenium alkylidene complex is described, as well as the preparation and characterization of the corresponding material by sol-gel cogelification with tetraethoxysilane (TEOS) and the assay of this recyclable supported catalyst in ring-closing diene and enyne metathesis reactions under thermal and microwave conditions.

  10. Organic-Inorganic Hybrid Silica Material Derived from a Monosilylated Grubbs-Hoveyda Ruthenium Carbene as a Recyclable Metathesis Catalyst

    Directory of Open Access Journals (Sweden)

    Michel Wong Chi Man

    2010-08-01

    Full Text Available The synthesis of a monosilylated Grubbs-Hoveyda ruthenium alkylidene complex is described, as well as the preparation and characterization of the corresponding material by sol-gel cogelification with tetraethoxysilane (TEOS and the assay of this recyclable supported catalyst in ring-closing diene and enyne metathesis reactions under thermal and microwave conditions.

  11. Catalytic Enantioselective Olefin Metathesis in Natural Product Synthesis. Chiral Metal-Based Complexes that Deliver High Enantioselectivity and More

    Science.gov (United States)

    Malcolmson, Steven J.; Meek, Simon J.; Zhugralin, Adil R.

    2012-01-01

    Chiral olefin metathesis catalysts enable chemists to access enantiomerically enriched small molecules with high efficiency; synthesis schemes involving such complexes can be substantially more concise than those that would involve enantiomerically pure substrates and achiral Mo alkylidenes or Ru-based carbenes. The scope of research towards design and development of chiral catalysts is not limited to discovery of complexes that are merely the chiral versions of the related achiral variants. A chiral olefin metathesis catalyst, in addition to furnishing products of high enantiomeric purity, can offer levels of efficiency, product selectivity and/or olefin stereoselectivity that are unavailable through the achiral variants. Such positive attributes of chiral catalysts (whether utilized in racemic or enantiomerically enriched form) should be considered as general, applicable to other classes of transformations. PMID:19967680

  12. Palladium-Catalyzed Heck Coupling Reaction of Aryl Bromides in Aqueous Media Using Tetrahydropyrimidinium Salts as Carbene Ligands

    Directory of Open Access Journals (Sweden)

    ?smail Özdemir

    2010-01-01

    Full Text Available An efficient and stereoselective catalytic system for the Heck cross coupling reaction using novel 1,3-dialkyl-3,4,5,6-tetrahydropyrimidinium salts (1, LHX and Pd(OAc2 loading has been reported. The palladium complexes derived from the salts 1a-f prepared in situ exhibit good catalytic activity in the Heck coupling reaction of aryl bromides under mild conditions.

  13. Thermally Stable, Latent Olefin Metathesis Catalysts

    Science.gov (United States)

    Thomas, Renee M.; Fedorov, Alexey; Keitz, Benjamin K.

    2011-01-01

    Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C, and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 hours. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C, and exhibited a long catalyst lifetime in solution at elevated temperatures. PMID:22282652

  14. Enthalpies of ligand substitution for [Mo(?5C5H5)(CO)2(NO)] – The role of ?-bonding effects in metal–ligand bond strengths

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Enthalpies of ligand substitution are measured for Mo(C5H5)(CO)2(NO). • Phosphines and N-heterocyclic carbenes are stronger ligands and displace CO. • Backbonding to ?? orbitals is an important part of complex stability. • FTIR studies show shifts to lower wavenumbers of ?-CO and ?-NO. • Structural studies show lengthening of the C-O and N-O bonds. - Abstract: Enthalpies of ligand substitution for [Mo(?5-C5H5)(CO)2(NO)] producing [Mo(?5-C5H5)Mo(CO)(L)(NO)] have been measured by solution calorimetry at 30 °C in THF for L = P(OMe)3 2 2Ph 3 (SIPr = 1,3-bis(2,6-bis(diisopropylphenyl)imidazolinylidene; IPr = 1,3-bis(2,6-bis(diisopropylphenyl)-imidazol-2-ylidene)). The accepting metal fragment [Mo(?5-C5H5)(CO)(NO)] has a vacant site containing strongly ?-accepting carbonyl and nitrosyl ligands and this is shown to influence the stability of the product complex. Infrared studies of both ?CO and ?NO show that metal-to-ligand backbonding increases in the order P(OMe)3 3 5-C5H5)(CO)(IPr)(NO)] and [Mo(?5-C5H5)(CO)(SIPr)(NO)] are reported

  15. Ruthenium carbenes supported on mesoporous silicas as highly active and selective hybrid catalysts for olefin metathesis reactions under continuous flow.

    Science.gov (United States)

    Bru, Miriam; Dehn, Richard; Teles, J Henrique; Deuerlein, Stephan; Danz, Manuel; Müller, Imke B; Limbach, Michael

    2013-08-26

    In the search for a highly active and selective heterogenized metathesis catalyst, we systematically varied the pore geometry and size of various silica-based mesoporous (i.e., MCM-41, MCM-48, and SBA-15) and microporous (ZSM-5 and MWW) versus macroporous materials (D11-10 and Aerosil 200), besides other process parameters (temperature, dilution, and mean residence time). The activity and, especially, selectivity of such "linker-free" supports for ruthenium metathesis catalysts were evaluated in the cyclodimerization of cis-cyclooctene to form 1,9-cyclohexadecadiene, a valuable intermediate in the flavor and fragrance industry. The optimized material showed not only exceptionally high selectivity to the valuable product, but also turned out to be a truly heterogeneous catalyst with superior activity relative to the unsupported homogeneous complex. PMID:23852995

  16. Spin-spin contributions to the zero-field splitting tensor in organic triplets, carbenes and biradicals-a density functional and ab initio study.

    Science.gov (United States)

    Sinnecker, Sebastian; Neese, Frank

    2006-11-01

    An evaluation study for the direct dipolar electron spin-spin (SS) contribution to the zero-field splitting (ZFS) tensor in electron paramagnetic resonance (EPR) spectroscopy is presented. Calculations were performed on a wide variety of organic systems where the SS contribution to the ZFS dominates over the second-order spin-orbit coupling (SOC) contribution. Calculations were performed using (hybrid) density functional theory (DFT), as well as complete active space self-consistent field (CASSCF) wave functions. In the former case, our implementation is an approximation, because we use the two-particle reduced spin-density matrix of the noninteracting reference system. In the latter case, the SS contribution is approximated by a mean-field method which, nevertheless, gives accurate results, compared to the approximation free computation of the SS part in a CASSCF framework. For the case of the triplet dioxygen molecule, it was shown that restricted open-shell density functional theory (RODFT), as well as CASSCF, can provide accurate spin-spin couplings while spin-unrestricted DFT leads to much larger errors. Furthermore, 15 organic radicals, including several 1,3 and 1,5 diradicals, dinitroxide biradicals, and even a chlorophyll a model system, were examined as test cases to demonstrate the accuracy and efficiency of our approach within a DFT framework. Accurate D values with root-mean-square deviations of 0.0035 cm(-1) were obtained. Furthermore, all trends, including those due to substituent effects, were correctly reproduced. In a different set of calculations, the polyacenes benzene, naphthalene, anthracene, and tetracene were studied. Applying DFT, the absolute D values were noticeably underestimated, but it was possible to correctly reproduce the trend to smaller D values with larger size of the systems. Finally, it was demonstrated that our approach is also well-suited for the study of carbenes. The smaller organic radicals of this work were also studied, through the use of CASSCF wave functions. This was a special advantage in the case of the triplet polyacenes, where the CASSCF approach gave better results than the DFT method. In comparing spin-restricted and spin-unrestricted results, it was shown through a natural orbital analysis and comparison to high-level ab initio calculations that even small amounts of spin polarization introduced by the unrestricted calculations lead to large deviations between the unrestricted Kohn-Sham (UKS) and restricted open-shell Kohn-Sham (ROKS) approaches. It is challenging to understand why the ROKS results show much better correlation with the experimental data. PMID:17078624

  17. Complex Beauty

    OpenAIRE

    Franceschet, Massimo

    2014-01-01

    Complex systems and their underlying convoluted networks are ubiquitous, all we need is an eye for them. They pose problems of organized complexity which cannot be approached with a reductionist method. Complexity science and its emergent sister network science both come to grips with the inherent complexity of complex systems with an holistic strategy. The relevance of complexity, however, transcends the sciences. Complex systems and networks are the focal point of a philos...

  18. Tuning the catalytic properties of rare earth borohydrides for the polymerisation of isoprene.

    Science.gov (United States)

    Bonnet, Fanny; Jones, Chloe E; Semlali, Sanaa; Bria, Marc; Roussel, Pascal; Visseaux, Marc; Arnold, Polly L

    2013-01-21

    Previous results obtained for the cis-polymerisation of isoprene with scandium half-sandwich complex Cp*Sc(BH(4))(2)(THF) 1a were extended to its neodymium analog. The X-ray structure of the already reported neodymium monomer compound Cp*Nd(BH(4))(2)(THF)(2) 1b is presented. Cp*Nd(BH(4))(2)(THF)(2)/[CPh(3)][B(C(6)F(5))(4)]/Al((i)Bu)(3) catalytic system was found to be very active and stereoselective towards isoprene polymerisation, leading to highly 1,4-cis polyisoprene up to 92%. The effect on isoprene polymerisation of the addition of a NHC molecule to Cp*Ln(BH(4))(2)(THF)(n) pre-catalyst (Cp* = ?(5)-C(5)Me(5), Ln = Sc, n = 1, 1a; Nd, n = 2, 1b; Sm, n = 2, 1c) or to a trisborohydride Ln(BH(4))(3)(THF)(n) (Ln = Sc, n = 1.5, 2a; Nd, n = 3, 2b; Sm, n = 3, 2c) was also studied. Several NHC ligands were assessed: the classical [1-C{(N(t)BuCH)}(2)] (L(1)) and functional N-heterocyclic carbenes, two amino-tethered HNBu(t)CH(2)CH(2)[1-C{N(CHCH)NR}] (HL(2-R)) (R = (t)Bu, Mes (Mes = 2,4,6-Me(3)-C(6)H(2))) and the hydroxyl-tethered HOCMe(2)CH(2)[1-C{N(CHCH)N(i)Pr}] (HL(3)). Neodymium-based complex (L(2-tBu))Nd(BH(4))(2)(THF)(2) 3 could be isolated and characterized. With some of the catalytic combinations tested, the introduction of the NHC ligand in the coordination sphere of the complex induces a switch of the stereoselectivity of the resulting polymer. Scandium complex 2a, which produces mainly 1,4-cis polyisoprene when associated to a borate activator and aluminum alkyl, leads to 1,4-trans polymer up to 94% regular when HL(2-tBu) carbene is added to the same reaction mixture. This result is the only example of highly trans-polyisoprene synthesized with a scandium based catalyst. Coordination of the carbene moiety to the rare earth centre is confirmed by NMR studies on paramagnetic neodymium pre-catalysts. PMID:23202137

  19. Synthesis, in vitro and in vivo characterization of rhenium tricarbonyl complexes with different bifunctional tridentate ligands

    International Nuclear Information System (INIS)

    Discovery of new chelating ligands that bind technetium/rhenium strongly is a priority in the quest toward the design and development of site specific radiopharmaceuticals. The current study on the application of Tc/Re carbonyls in radiopharmaceuticals has been focused on the utility of specific tridentate ligand systems for achieving kinetic inertness and in vivo stability. In this paper, (Bis (2-pyridylmethyl)-amino)-ethylamine(1) (Fig. 1), (Bis (2-pyridylmethyl)-amino)-acetic acid (2) (Fig. 1), L(6-amino-hexyl)-pyridyl-2-methyl- amino-acetic acid (3) (Fig. 2), and picolylamine diacetic acid (4) (Fig. 3) that possessed an NNN, NNO and NOO donor atom sets were synthesized, which can be a good selection for these requirements. The Re(I)-complexes of above four ligands were prepared in good yield with [NEt4]2[ReBr3(CO)3] in water at 75 degree C for 3 h. The complexes were characterized by elemental analysis and spectroscopic methods. The 188Re(I)-complexes of Four ligands were carried out by incubating the fac- [188Re(CO)3(H2O)3]+ fragment for 60 min at 75 degree C in PBS buffer (0.1 M NaCl/0.05 M sodium phosphate buffered, pH 7.4) under nitrogen. After cooling in ice bath, complexes formations were monitored by HPLC. The HPLC analysis demonstrated that the reaction produces in the complex 1 with yield greater than 95% and its retention times was 7.5 min, which is stable for more than 12 h in human serum, and the complex 2 with yield 93% is stable for more than 8 h in human serum, its retention times was 15.5 min, and the complex 3 with yield 90% is stable for more than 10 h in human serum, its retention times was 15.4 min, while the complex 4 with yields more than 92% can be stable 10 h in human serum and its retention time was 15.6 min respectively. The identity of the 188Re-complexes were proved by comparative HPLC studies using samples of the well characterized thenium(I) complexes as reference. In vivo biodistribution studies at 24 hour post-injection were carried out in normal, white mice. The biodistribution data are shown in table 1. The data show: the major part of the complexes cleared efficiently from the blood pool (0.09-0.67%); No organs (apart from liver and kidneys) or tissue was specifically targeted; Low activity (0.25-0.93%) found in the stomach indicated the good in vivo stability of the complexes. In conclusion, four ligands react with fac- [M(CO)3(H2O)3]+ (M=188Re, Re) fragment resulting in four single stable complexes, M(CO)3(1), M(CO)3(2), M(CO)3(3) and M(CO)3(4), containing aromatic N-heterocycles. These ligand systems are attractive for functionalization purposes of biological vectors since they are easy to synthesize. The corresponding complexes with fac-[M(CO)3(H2O)3]+ are in vivo and vitro stable. Thus the proposed strategy of attaching M(CO)3(1), M(CO)3(2), M(CO)3(3) and M(CO)3(4) complexes is promising for labeling of biomolecules. The approach is worthy of further investigation.

  20. O uso de cálculos teóricos como ferramenta para a detecção de moléculas no meio interestelar: o caso dos carbenos CnNH (n=1, 3 e 5 Use of theoretical calculations as a tool for the detection of molecules in the interestellar medium: the case of the c n nh (n= 1, 3 and 5 carbenes

    Directory of Open Access Journals (Sweden)

    João Bosco P. da Silva

    1997-10-01

    Full Text Available This work reviews some applications of ab initio molecular orbital calculations to the elucidation of structures of interstellar molecules. The case of the CnNH (n=1, 3 and 5 carbenes is extensively analyzed and discussed. Theoretical conformational analysis and predicted values for the rotational constants and dipole moments of the singlet state of C5NH are reported for the first time and a comparison is performed with results previously obtained for C3NH and CNH.

  1. Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes

    OpenAIRE

    Werner Bonrath; Julien Estager; Jean-Marc Lévêque; Luisa Boffa; Emanuela Calcio Gaudino; Giancarlo Cravotto

    2008-01-01

    Non-conventional techniques, such as microwave (MW) and power ultrasound(US) as well as combined MW/US irradiation, have been used to promote one-potsynthesis of second-generation ionic liquids (ILs), cutting down reaction times andimproving yields. However, the use of chloroalkanes in the alkylation of N-heterocyclesrequires more drastic conditions if results are to match those obtained with more reactivealkyl halides. The present paper describes a series of MW- or MW/US-promoted ILpreparati...

  2. Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes

    Directory of Open Access Journals (Sweden)

    Werner Bonrath

    2008-01-01

    Full Text Available Non-conventional techniques, such as microwave (MW and power ultrasound(US as well as combined MW/US irradiation, have been used to promote one-potsynthesis of second-generation ionic liquids (ILs, cutting down reaction times andimproving yields. However, the use of chloroalkanes in the alkylation of N-heterocyclesrequires more drastic conditions if results are to match those obtained with more reactivealkyl halides. The present paper describes a series of MW- or MW/US-promoted ILpreparations starting from chloroalkanes and classic heterocycles (1-methylimidazole,pyridine and 1-methylpyrrolidine. When reactions were carried out under conventionalheating in an oil bath they required longer reaction times and gave poorer yields. 1H-NMRanalysis and ion-exchange chromatography showed that the present solventless procedureafforded ILs of satisfactory purity. The observed high yields (usually 70-98% isolated,and short reaction times showed that a straightforward access to ILs can be also achievedwith the use of alkyl chlorides, resulting in a considerable reduction of costs.

  3. Group 4 Metalloporphyrin diolato Complexes and Catalytic Application of Metalloporphyrins and Related Transition Metal Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Guodong Du

    2004-12-19

    In this work, the first examples of group 4 metalloporphyrin 1,2-diolato complexes were synthesized through a number of strategies. In general, treatment of imido metalloporphyrin complexes, (TTP)M=NR, (M = Ti, Zr, Hf), with vicinal diols led to the formation of a series of diolato complexes. Alternatively, the chelating pinacolate complexes could be prepared by metathesis of (TTP)MCl{sub 2} (M = Ti, Hf) with disodium pinacolate. These complexes were found to undergo C-C cleavage reactions to produce organic carbonyl compounds. For titanium porphyrins, treatment of a titanium(II) alkyne adduct, (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh), with aromatic aldehydes or aryl ketones resulted in reductive coupling of the carbonyl groups to produce the corresponding diolato complexes. Aliphatic aldehydes or ketones were not reactive towards (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh). However, these carbonyl compounds could be incorporated into a diolato complex on reaction with a reactive precursor, (TTP)Ti[O(Ph){sub 2}C(Ph){sub 2}O] to provide unsymmetrical diolato complexes via cross coupling reactions. In addition, an enediolato complex (TTP)Ti(OCPhCPhO) was obtained from the reaction of (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh) with benzoin. Titanium porphyrin diolato complexes were found to be intermediates in the (TTP)Ti=O-catalyzed cleavage reactions of vicinal diols, in which atmospheric oxygen was the oxidant. Furthermore, (TTP)Ti=O was capable of catalyzing the oxidation of benzyl alcohol and {alpha}-hydroxy ketones to benzaldehyde and {alpha}-diketones, respectively. Other high valent metalloporphyrin complexes also can catalyze the oxidative diol cleavage and the benzyl alcohol oxidation reactions with dioxygen. A comparison of Ti(IV) and Sn(IV) porphyrin chemistry was undertaken. While chelated diolato complexes were invariably obtained for titanium porphyrins on treatment with 1,2-diols, the reaction of vicinal diols with tin porphyrins gave a number of products, including mono-, bis-alkoxo, and chelating diolato complexes, depending on the identity of diols and the stoichiometry employed. It was also found that tin porphyrin complexes promoted the oxidative cleavage of vicinal diols and the oxidation of {alpha}-ketols to {alpha}-diketones with dioxygen. In extending the chemistry of metalloporphyrins and analogous complexes, a series of chiral tetraaza macrocyclic ligands and metal complexes were designed and synthesized. Examination of iron(II) complexes showed that they were efficient catalysts for the cyclopropanation of styrene by diazo reagents. Good yields and high diastereoselectivity were obtained with modest enantioselectivity. A rationalization of the stereoselectivity was presented on the basis of structural factors in a carbene intermediate.

  4. Hydride-alkenylcarbyne to alkenylcarbene transformation in bisphosphine-osmium complexes.

    Science.gov (United States)

    Bolaño, Tamara; Castarlenas, Ricardo; Esteruelas, Miguel A; Modrego, F Javier; Oñate, Enrique

    2005-08-10

    The elongated dihydrogen complex [formula: see text](1) reacts with 1,1-diphenyl-2-propyn-1-ol and 2-methyl-3-butyn-2-ol to give the hydride-hydroxyvinylidene-pi-alkynol derivatives [OsH{=C=CHC(OH)R2}{eta2-HC(triple bond)CC(OH)R2}(PiPr3)2]BF4 (R = Ph (2), Me (3)), where the pi-alkynols act as four-electron donor ligands. Treatment of 2 and 3 with HBF(4) and coordinating solvents leads to the dicationic hydride-alkenylcarbyne compounds [OsH((triple bond)CCH=CR2)S2(PiPr3)2][BF4]2 (R = Ph, S = H(2)O (4), CH(3)CN (5); R = Me, S = CH(3)CN (6)), which in acetonitrile evolve into the alkenylcarbene complexes [Os(=CHCH=CR2)(CH3CN)3(PiPr3)2][BF4](2) (R = Ph (7), Me (8)) by means of a concerted 1,2-hydrogen shift from the osmium to the carbyne carbon atom. Treatment of 2-propanol solutions of 5 with NaCl affords OsHCl2((triple bond)CCH=CPh2)(PiPr3)2 (10), which reacts with AgBF(4) and acetonitrile to give [OsHCl((triple bond)CCH=CPh2)(CH3CN)(PiPr3)2]BF(4) (11). In this solvent complex 11 is converted to [OsCl(=CHCH=CPh2)(CH3CN)2(PiPr3)2]BF(4) (12). Complex 5 reacts with CO to give [Os(=CHCH=CPh2)(CO)(CH3CN)2(PiPr3)2][BF(4)](2) (15). DFT calculations and kinetic studies for the hydride-alkenylcarbyne to alkenylcarbene transformation show that the difference of energy between the starting compounds and the transition states, which can be described as eta(2)-carbene species [formula: see text] increases with the basicity of the metallic center. The X-ray structures of 4 and 7 and the rotational barriers for the carbene ligands of 7, 8, and 12 are also reported. PMID:16076226

  5. Alkane metathesis with the tantalum methylidene [(?SiO)Ta(=CH2)Me2]/[(?SiO)2Ta(=CH2)Me] generated from well-defined surface organometallic complex [(?SiO)TaVMe4

    KAUST Repository

    Chen, Yin

    2015-01-21

    By grafting TaMe5 on Aerosil700, a stable, well-defined, silica-supported tetramethyl tantalum(V) complex, [(?SiO)TaMe4], is obtained on the silica surface. After thermal treatment at 150 °C, the complex is transformed into two surface tantalum methylidenes, [(?SiO)2Ta(=CH2)Me] and [(?SiO)Ta(=CH2)Me2], which are active in alkane metathesis and comparable to the previously reported [(?SiO)2TaHx]. Here we present the first experimental study to isolate and identify a surface tantalum carbene as the intermediate in alkane metathesis. A systematic experimental study reveals a new reasonable pathway for this reaction.

  6. Communication complexity and information complexity

    Science.gov (United States)

    Pankratov, Denis

    Information complexity enables the use of information-theoretic tools in communication complexity theory. Prior to the results presented in this thesis, information complexity was mainly used for proving lower bounds and direct-sum theorems in the setting of communication complexity. We present three results that demonstrate new connections between information complexity and communication complexity. In the first contribution we thoroughly study the information complexity of the smallest nontrivial two-party function: the AND function. While computing the communication complexity of AND is trivial, computing its exact information complexity presents a major technical challenge. In overcoming this challenge, we reveal that information complexity gives rise to rich geometrical structures. Our analysis of information complexity relies on new analytic techniques and new characterizations of communication protocols. We also uncover a connection of information complexity to the theory of elliptic partial differential equations. Once we compute the exact information complexity of AND, we can compute exact communication complexity of several related functions on n-bit inputs with some additional technical work. Previous combinatorial and algebraic techniques could only prove bounds of the form theta( n). Interestingly, this level of precision is typical in the area of information theory, so our result demonstrates that this meta-property of precise bounds carries over to information complexity and in certain cases even to communication complexity. Our result does not only strengthen the lower bound on communication complexity of disjointness by making it more exact, but it also shows that information complexity provides the exact upper bound on communication complexity. In fact, this result is more general and applies to a whole class of communication problems. In the second contribution, we use self-reduction methods to prove strong lower bounds on the information complexity of two of the most studied functions in the communication complexity literature: Gap Hamming Distance (GHD) and Inner Product mod 2 (IP). In our first result we affirm the conjecture that the information complexity of GHD is linear even under the uniform distribution. This strengthens the O(n) bound shown by Kerenidis et al. (2012) and answers an open problem by Chakrabarti et al. (2012). We also prove that the information complexity of IP is arbitrarily close to the trivial upper bound n as the permitted error tends to zero, again strengthening the O(n) lower bound proved by Braverman and Weinstein (2011). More importantly, our proofs demonstrate that self-reducibility makes the connection between information complexity and communication complexity lower bounds a two-way connection. Whereas numerous results in the past used information complexity techniques to derive new communication complexity lower bounds, we explore a generic way, in which communication complexity lower bounds imply information complexity lower bounds in a black-box manner. In the third contribution we consider the roles that private and public randomness play in the definition of information complexity. In communication complexity, private randomness can be trivially simulated by public randomness. Moreover, the communication cost of simulating public randomness with private randomness is well understood due to Newman's theorem (1991). In information complexity, the roles of public and private randomness are reversed: public randomness can be trivially simulated by private randomness. However, the information cost of simulating private randomness with public randomness is not understood. We show that protocols that use only public randomness admit a rather strong compression. In particular, efficient simulation of private randomness by public randomness would imply a version of a direct sum theorem in the setting of communication complexity. This establishes a yet another connection between the two areas. (Abstract shortened by UMI.).

  7. Managing Complexity

    DEFF Research Database (Denmark)

    Maylath, Bruce; Vandepitte, Sonia; Minacori, Patricia; Isohella, Suvi; Mousten, Birthe; Humbley, John

    2013-01-01

    This article discusses the largest and most complex international learning-by-doing project to date- a project involving translation from Danish and Dutch into English and editing into American English alongside a project involving writing, usability testing, and translation from English into Dutch and into French. The complexity of the undertaking proved to be a central element in the students' learning, as the collaboration closely resembles the complexity of international documentation workpl...

  8. The activation mechanism of Fe-based olefin metathesis catalysts

    Science.gov (United States)

    Poater, Albert; Pump, Eva; Vummaleti, Sai Vikrama Chaitanya; Cavallo, Luigi

    2014-08-01

    Density functional theory calculations have been used to describe the first turnover for olefin metathesis reaction of a homogenous Fe-based catalyst bearing a N-heterocyclic carbene ligand with methoxyethene as a substrate. Equal to conventional Ru-based catalysts, the activation of its Fe congener occurs through a dissociative mechanism, however with a more exothermic reaction energy profile. Predicted upper energy barriers were calculated to be on average ?2 kcal/mol more beneficial for Fe catalyzed metathesis. Overall, this present computational study emphasises on advantages of Fe-based metathesis and gives a potential recipe for the design of an efficient Fe-based olefin metathesis catalysts.

  9. Highly Active Chiral Ruthenium Catalysts for Asymmetric Ring-Closing Olefin Metathesis

    OpenAIRE

    Funk, Timothy W.; Berlin, Jacob M.; Grubbs, Robert H

    2006-01-01

    The synthesis of olefin metathesis catalysts containing chiral, monodentate N-heterocyclic carbenes and their application to asymmetric ring-closing metathesis (ARCM) is reported. These catalysts retain the high levels of reactivity found in the related achiral variants (1a and 1b). Using the parent chiral catalysts 2a and 2b and derivatives that contain steric bulk in the meta positions of the N-bound aryl rings (catalysts 3-5), five- through seven-membered rings were formed in up to 92% ee....

  10. Hybrid ruthenium ROMP catalysts based on an engineered variant of ?-barrel protein FhuA ?CVF(tev) : effect of spacer length.

    Science.gov (United States)

    Sauer, Daniel F; Bocola, Marco; Broglia, Claudio; Arlt, Marcus; Zhu, Lei-Lei; Brocker, Melanie; Schwaneberg, Ulrich; Okuda, Jun

    2015-01-01

    A biohybrid ring-opening olefin metathesis polymerization catalyst based on the reengineered ?-barrel protein FhuA ?CVF(tev) was chemically modified with respect to the covalently anchored Grubbs-Hoveyda type catalyst. Shortening of the spacer (1,3-propanediyl to methylene) between the N-heterocyclic carbene ligand and the cysteine site 545 increased the ROMP activity toward a water-soluble 7-oxanorbornene derivative. The cis/trans ratio of the double bond in the polymer was influenced by the hybrid catalyst. PMID:25425216

  11. Nickel(0)-catalyzed enantioselective annulations of alkynes and arylenoates enabled by a chiral NHC ligand: efficient access to cyclopentenones.

    Science.gov (United States)

    Ahlin, Joachim S E; Donets, Pavel A; Cramer, Nicolai

    2014-11-24

    Cyclopentenones are versatile structural motifs of natural products as well as reactive synthetic intermediates. The nickel-catalyzed reductive [3+2] cycloaddition of ?,?-unsaturated aromatic esters and alkynes constitutes an efficient method for their synthesis. Here, nickel(0) catalysts comprising a chiral bulky C1-symmetric N-heterocyclic carbene ligand were shown to enable an efficient asymmetric synthesis of cyclopentenones from mesityl enoates and internal alkynes under mild conditions. The bulky NHC ligand provided the cyclopentenone products in very high enantioselectivity and led to a regioselective incorporation of unsymmetrically substituted alkynes. PMID:25258104

  12. Cobalt-catalyzed ortho alkylation of aromatic imines with primary and secondary alkyl halides.

    Science.gov (United States)

    Gao, Ke; Yoshikai, Naohiko

    2013-06-26

    We report here cobalt-N-heterocyclic carbene catalytic systems for the ortho alkylation of aromatic imines with alkyl chlorides and bromides, which allows the introduction of a variety of primary and secondary alkyl groups at room temperature. The stereochemical outcomes of the reaction of secondary alkyl halides suggest that the present reaction involves single-electron transfer from a cobalt species to the alkyl halide to generate the corresponding alkyl radical. A cycloalkylated product obtained by this method can be transformed into unique spirocycles through manipulation of the directing and cycloalkyl groups. PMID:23758603

  13. O uso de cálculos teóricos como ferramenta para a detecção de moléculas no meio interestelar: o caso dos carbenos CnNH (n=1, 3 e 5) / Use of theoretical calculations as a tool for the detection of molecules in the interestellar medium: the case of the c n nh (n= 1, 3 and 5) carbenes

    Scientific Electronic Library Online (English)

    João Bosco P. da, Silva; Benício B., Neto; Mozart N., Ramos.

    1997-10-01

    Full Text Available [...] Abstract in english This work reviews some applications of ab initio molecular orbital calculations to the elucidation of structures of interstellar molecules. The case of the CnNH (n=1, 3 and 5 ) carbenes is extensively analyzed and discussed. Theoretical conformational analysis and predicted values for the rotational [...] constants and dipole moments of the singlet state of C5NH are reported for the first time and a comparison is performed with results previously obtained for C3NH and CNH.

  14. Complex variables

    CERN Document Server

    Fisher, Stephen D

    1999-01-01

    The most important topics in the theory and application of complex variables receive a thorough, coherent treatment in this introductory text. Intended for undergraduates or graduate students in science, mathematics, and engineering, this volume features hundreds of solved examples, exercises, and applications designed to foster a complete understanding of complex variables as well as an appreciation of their mathematical beauty and elegance. Prerequisites are minimal; a three-semester course in calculus will suffice to prepare students for discussions of these topics: the complex plane, basic

  15. Softball Complex

    Science.gov (United States)

    Ellis, Jim

    1977-01-01

    The Parks and Recreation Department of Montgomery, Alabama, has developed a five-field softball complex as part of a growing community park with facilities for camping, golf, aquatics, tennis, and picnicking. (MJB)

  16. Tribotesting Complex

    International Science & Technology Center (ISTC)

    Development of Methodological Basis and Creation of a Branch Tribotesting Complex Intended for High-Temperature Friction and Wear Testing of Metallurgical Equipment Tool Specimens with the Aim of Enhancement of Equipment and Tool Wear Resistance

  17. Complex Philosophy

    OpenAIRE

    Gershenson, Carlos

    2001-01-01

    We present several philosophical ideas emerging from the studies of complex systems. We make a brief introduction to the basic concepts of complex systems, for then defining "abstraction levels". These are useful for representing regularities in nature. We define absolute being (observer independent, infinite) and relative being (observer dependent, finite), and notice the differences between them. We draw issues on relative causality and absolute causality among abstraction...

  18. Stereochemical aspects of nucleophilic addition reactions to alkoxycarbene cations of the iron chiral auxiliary [(eta(5)-C5H5)Fe(CO)(PPh3)

    OpenAIRE

    Davies, SG; Fletcher, AM; Maberly, TR; Thomson, JE

    2013-01-01

    Alkoxy carbene complexes incorporating the iron chiral auxiliary [(?5-C5H5)Fe(CO)(PPh3)] were prepared in good yields from either the corresponding acyl complexes or methoxymethyl complex of the auxiliary. A range of nucleophilic addition reactions to these alkoxy carbene complexes showed moderate to high diastereoselectivities and the reactive conformations of the carbene complexes under these conditions are discussed. © 2013 The Royal Society of Chemistry and the Centre National de la Reche...

  19. Communication Complexity

    CERN Document Server

    Pálvölgyi, Dömötör

    2010-01-01

    The first section starts with the basic definitions following mainly the notations of the book written by E. Kushilevitz and N. Nisan. At the end of the first section I examine tree-balancing. In the second section I summarize the well-known lower bound methods and prove the exact complexity of certain functions. In the first part of the third section I introduce the random complexity and prove the basic lemmas about it. In the second part I prove a better lower bound for the complexity of all random functions. In the third part I introduce and compare several upper bounds for the complexity of the identity function. In the fourth section I examine the well-known Direct-sum conjecture. I introduce a different model of computation then prove that it is the same as the original one up to a constant factor. This new model is used to bound the Amortized Time Complexity of a function by the number of the leaves of its protocol-tree. After this I examine the Direct-sum problem in case of Partial Information and in ...

  20. Assessing the ligand properties of 1,3-dimesitylbenzimidazol-2-ylidene in ruthenium-catalyzed olefin metathesis.

    Science.gov (United States)

    Borguet, Yannick; Zaragoza, Guillermo; Demonceau, Albert; Delaude, Lionel

    2013-05-28

    The deprotonation of 1,3-dimesitylbenzimidazolium tetrafluoroborate with a strong base afforded 1,3-dimesitylbenzimidazol-2-ylidene (BMes), which was further reacted in situ with rhodium or ruthenium complexes to afford three new organometallic products. The compounds [RhCl(COD)(BMes)] (COD is 1,5-cyclooctadiene) and cis-[RhCl(CO)2(BMes)] were used to probe the steric and electronic parameters of BMes. Comparison of the percentage of buried volume (%V(Bur)) and of the Tolman electronic parameter (TEP) of BMes with those determined previously for 1,3-dimesitylimidazol-2-ylidene (IMes) and 1,3-dimesitylimidazolin-2-ylidene (SIMes) revealed that the three N-heterocyclic carbenes (NHCs) had very similar profiles. Nonetheless, changes in the hydrocarbon backbone subtly affected the stereoelectronic properties of these ligands. Accordingly, the corresponding [RuCl2(PCy3)(NHC)(=CHPh)] complexes displayed different catalytic behaviors in the ring-closing metathesis (RCM) of ?,?-dienes. In the benchmark cyclization of diethyl 2,2-diallylmalonate, the new [RuCl2(PCy3)(BMes)(=CHPh)] compound (1d) performed slightly better than the Grubbs second-generation catalyst (1a), which was in turn significantly more active than the related [RuCl2(PCy3)(IMes)(=CHPh)] initiator (1b). For the formation of a model trisubstituted cycloolefin, complex 1d ranked in-between catalyst precursors 1a and 1b, whereas in the RCM of tetrasubstituted cycloalkenes it lost its catalytic efficiency much more rapidly. PMID:22990296

  1. Stereolability of Chiral Ruthenium Catalysts With Frozen NHC Ligand Conformations Investigated by Dynamic-HPLC.

    Science.gov (United States)

    Menta, Sergio; Pierini, Marco; Cirilli, Roberto; Grisi, Fabia; Perfetto, Alessandra; Ciogli, Alessia

    2015-10-01

    The stereolability of chiral Hoveyda-Grubbs II type ruthenium complexes bearing N-heterocyclic carbene (NHC) ligands with Syn-phenyl groups on the backbone and Syn- or Anti-oriented o-tolyl N-substituents was studied by resorting to dynamic high-performance liquid chromatography (D-HPLC). A complete chromatographic picture of the involved stereoisomers (four for Anti- and two for Syn-complexes) was achieved at very low temperatures (-53°C and -40°C respectively), at which the NHC-Ru bond rotations were frozen out. Inspection of the chromatographic profiles recorded at higher temperatures revealed the presence of plateau zones between the couples of either Syn or Anti stereoisomers, attesting to the active interconversion between the eluted species. Such dynamic chromatograms were successfully simulated through procedures based on both theoretical plate and classical stochastic models. The good superimposition achieved between experimental and simulated chromatographic profiles allowed determination of the related isomerization energy barriers (?Gisom (#) ), all derived by rotation around the NHC-Ru bond. The obtained diastereomerization barriers between the Anti isomers were found in very good agreement with those previously measured by experimental nuclear magnetic resonance (NMR) and assessed through Density Functional Theory (DFT) calculations. With the same approach, for the first time we also determined the enantiomerization barrier of the Syn isomer. Focused changes to the structure of complex Syn, studied by a molecular modeling approach, were found suitable to strongly reduce the stereolability arising from rotation around the NHC-Ru bond. Chirality 27:685-692, 2015. © 2015 Wiley Periodicals, Inc. PMID:26250890

  2. Complex analysis

    CERN Document Server

    Freitag, Eberhard

    2005-01-01

    The guiding principle of this presentation of ``Classical Complex Analysis'' is to proceed as quickly as possible to the central results while using a small number of notions and concepts from other fields. Thus the prerequisites for understanding this book are minimal; only elementary facts of calculus and algebra are required. The first four chapters cover the essential core of complex analysis: - differentiation in C (including elementary facts about conformal mappings) - integration in C (including complex line integrals, Cauchy's Integral Theorem, and the Integral Formulas) - sequences and series of analytic functions, (isolated) singularities, Laurent series, calculus of residues - construction of analytic functions: the gamma function, Weierstrass' Factorization Theorem, Mittag-Leffler Partial Fraction Decomposition, and -as a particular highlight- the Riemann Mapping Theorem, which characterizes the simply connected domains in C. Further topics included are: - the theory of elliptic functions based on...

  3. Complex Systems

    Science.gov (United States)

    Bossomaier, Terry R. J.; Green, David G.

    2000-07-01

    This book explores the exciting new field of complexity. It features in-depth coverage of important theoretical areas, including fractals, chaos, nonlinear dynamics, artificial life, and self organization. It also provides overviews of complexity in several applied areas, including parallel computation, control systems, neural systems, and ecosystems. Contributors examine some of the properties that best characterize complex systems, including algorithmic richness, nonlinearity, and abundant interactions between components. In this way the book draws themes, especially the ideas of connectivity and natural computation, that reveal deep, underlying similarities among phenomena that have formerly been treated as completely distinct. Researchers in a wide array of fields, including ecology, neuroscience, computer science, and mathematics, will find this volume to be a fascinating collection of ideas.

  4. Communication Complexity

    OpenAIRE

    Pálvölgyi, Dömötör

    2010-01-01

    The first section starts with the basic definitions following mainly the notations of the book written by E. Kushilevitz and N. Nisan. At the end of the first section I examine tree-balancing. In the second section I summarize the well-known lower bound methods and prove the exact complexity of certain functions. In the first part of the third section I introduce the random complexity and prove the basic lemmas about it. In the second part I prove a better lower bound...

  5. Holographic Complexity

    CERN Document Server

    Alishahiha, Mohsen

    2015-01-01

    For a field theory with a gravitational dual, following Susskind's proposal we define holographic complexity for a subsystem. The holographic complexity is proportional to the volume of a co-dimension one time slice in the bulk geometry enclosed by the extremal co-dimension two hyper-surface appearing in the computation of the holographic entanglement entropy. The proportionally constant, up to a numerical order of one factor is G R where G is the Newton constant and R is the curvature of the space time. We study this quantity in certain holographic model. We also explore a possible relation between the defined quantity and fidelity appearing in quantum information literature.

  6. Complex Networks

    CERN Document Server

    Evans, T S

    2004-01-01

    An outline of recent work on complex networks is given from the point of view of a physicist. Motivation, achievements and goals are discussed with some of the typical applications from a wide range of academic fields. An introduction to the relevant literature and useful resources is also given.

  7. Complex Networks

    CERN Document Server

    Evsukoff, Alexandre; González, Marta

    2013-01-01

    In the last decade we have seen the emergence of a new inter-disciplinary field focusing on the understanding of networks which are dynamic, large, open, and have a structure sometimes called random-biased. The field of Complex Networks is helping us better understand many complex phenomena such as the spread of  deseases, protein interactions, social relationships, to name but a few. Studies in Complex Networks are gaining attention due to some major scientific breakthroughs proposed by network scientists helping us understand and model interactions contained in large datasets. In fact, if we could point to one event leading to the widespread use of complex network analysis is the availability of online databases. Theories of Random Graphs from Erdös and Rényi from the late 1950s led us to believe that most networks had random characteristics. The work on large online datasets told us otherwise. Starting with the work of Barabási and Albert as well as Watts and Strogatz in the late 1990s, we now know th...

  8. Complex networks

    OpenAIRE

    EVANS, TS

    2004-01-01

    An outline of recent work on complex networks is given from the point of view of a physicist. Motivation, achievements and goals are discussed with some of the typical applications from a wide range of academic fields. An introduction to the relevant literature and useful resources is also given.

  9. Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl2(P-P)(N-N)] type complexes

    Scientific Electronic Library Online (English)

    Marcos C. R., Monteiro; Fabio B., Nascimento; Eliana M. A., Valle; Javier, Ellena; Eduardo E., Castellano; Alzir A., Batista; Sergio de Paula, Machado.

    Full Text Available As reações de substituição [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, onde P-P = 1,4-bis(difenilfosfino)butano e N-N = 2,2´-bipiridina, 4,4´-dimetóxi-2,2´-bipiridina, 4,4´-dimetil-2,2´-bipiridina e 4,4´-dicloro-2,2´-bipiridina, L = piridina (py) ou 4-metilpiridina (4-pic), foram estudadas s [...] ob condições de pseudo-primeira ordem. As reações ocorrem por um mecanismo dissociativo e as constantes de velocidade nas reações de substituição aumentam com o aumento do pKa dos ligantes N-heterocíclicos e com a diminuição dos potenciais de oxidação do centro metálico. Quanto mais alta é a porcentagem de participação dos orbitais atômicos d do metal na formação do HOMO, conforme calculado pelo método DFT, mais fácil é a dissociação do cloreto da esfera de coordenação do complexo. Nos espectros de 31P{¹H} RMN da série de complexos de fórmula geral [RuCl(L)(P-P)(N-N)]PF6, há dois dubletos com ?? Abstract in english The substitution reactions [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, where P-P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2´-bipyridine, 4,4´-dimethoxy-2,2´-bipyridine, 4,4´-dimethylpyridine-2,2´-bipyridine and 4,4´-dichloro-2,2´-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic [...] ), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pKa of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the 31P{¹H} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF6, there are two doublets with ??

  10. Gold-catalyzed cycloisomerization of 1,7-enyne esters to structurally diverse cis-1,2,3,6-tetrahydropyridin-4-yl ketones.

    Science.gov (United States)

    Rao, Weidong; Sally; Koh, Ming Joo; Chan, Philip Wai Hong

    2013-04-01

    A synthetic method that relies on gold(I)-catalyzed cycloisomerization of 1,7-enyne esters to prepare highly functionalized cis-1,2,3,6-tetrahydropyridin-4-yl ketone derivatives in good to excellent yields and as a single regio-, diastereo-, and enantiomer is described. By taking advantage of the distinctive differences in the electronic and steric properties between an NHC (NHC = N-heterocyclic carbene) and phosphine ligand in the respective gold(I) complexes, a divergence in product selectivity was observed. In the presence of [PhCNAuIPr](+)SbF6(-) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) as the catalyst, tandem 1,3-acyloxy migration/6-exo-trig cyclization/1,5-acyl migration of the substrate was found to selectively occur to give the ?-diketone-substituted 1,2,3,6-tetrahydropyridine adduct. In contrast, reactions with the gold(I) phosphine complex [MeCNAu(JohnPhos)](+)SbF6(-) (JohnPhos = (1,1'-biphenyl-2-yl)-di-tert-butylphosphine) as the catalyst was discovered to result in preferential 1,3-acyloxy migration/6-exo-trig cyclization/hydrolysis of the 1,7-enyne ester and formation of the cis-1,2,3,6-tetrahydropyridin-4-yl ketone derivative. The utility of this piperidine forming strategy as a synthetic tool that makes use of 1,7-enyne esters was exemplified by its application to the synthesis of an enantiopure analogue of the bioactive 2,3,4,4a,5,9b-hexahydroindeno[1,2-c]pyridine family of compounds. PMID:23458312

  11. Managing Complexity

    CERN Document Server

    Chassin, D P; Posse, C; Chassin, David P.; Malard, Joel; Posse, Christian

    2004-01-01

    Physical analogs have shown considerable promise for understanding the behavior of complex adaptive systems, including macroeconomics, biological systems, social networks, and electric power markets. Many of today's most challenging technical and policy questions can be reduced to a distributed economic control problem. Indeed, economically-based control of large-scale systems is founded on the conjecture that the price-based regulation (e.g., auctions, markets) results in an optimal allocation of resources and emergent optimal system control. This paper explores the state of the art in the use physical analogs for understanding the behavior of some econophysical systems and deriving stable and robust control strategies for them. In particular we review and discuss applications of some analytic methods based on a thermodynamic metaphor according to which the interplay between system entropy and conservation laws gives rise to intuitive and governing global properties of complex systems that cannot be otherwis...

  12. Managing Complexity

    Energy Technology Data Exchange (ETDEWEB)

    Chassin, David P.; Posse, Christian; Malard, Joel M.

    2004-08-01

    Physical analogs have shown considerable promise for understanding the behavior of complex adaptive systems, including macroeconomics, biological systems, social networks, and electric power markets. Many of today’s most challenging technical and policy questions can be reduced to a distributed economic control problem. Indeed, economically-based control of large-scale systems is founded on the conjecture that the price-based regulation (e.g., auctions, markets) results in an optimal allocation of resources and emergent optimal system control. This paper explores the state of the art in the use physical analogs for understanding the behavior of some econophysical systems and to deriving stable and robust control strategies for them. In particular we review and discussion applications of some analytic methods based on the thermodynamic metaphor according to which the interplay between system entropy and conservation laws gives rise to intuitive and governing global properties of complex systems that cannot be otherwise understood.

  13. Complex Systems

    CERN Document Server

    Smith, J B

    2003-01-01

    The study of Complex Systems is considered by many to be a new scientific field, and is distinguished by being a discipline that has applications within many separate areas of scientific study. The study of Neural Networks, Traffic Patterns, Artificial Intelligence, Social Systems, and many other scientific areas can all be considered to fall within the realm of Complex Systems, and can be studied from this new perspective. The advent of more capable computer systems has allowed these systems to be simulated and modeled with far greater ease, and new understanding of computer modeling approaches has allowed the fledgling science to be studied as never before. The preliminary focus of this paper will be to provide a general overview of the science of Complex Systems, including terminology, definitions, history, and examples. I will attempt to look at some of the most important trends in different areas of research, and give a general overview of research methods that have been used in parallel with computer mo...

  14. Unusual carbon monoxide activation, reduction, and homologation reactions of 5f-element organometallics: the chemistry of carbene-like dihaptoacyls

    International Nuclear Information System (INIS)

    This article reviews recent results on the chemical, spectral and structural properties of bis(pentamethylcyclopentadienyl) thorium and uranium dihaptoacyl complexes produced by migratory insertion of carbon monoxide into actinide-carbon sigma bonds. The high coordinative unsaturation and oxygen affinity of the ligation environment produces a marked perturbation of the bonding and reactivity toward that of a coordinated oxycarbene: M(eta2-OCR). Reactivity patterns observed include hydrogen atom and trimethylsilyl migration to the acyl carbon, as well as coupling with additional carbon monoxide to produce a dimeric complex of the enedionediolate ligand, OC(R)(anti O)C=C(anti O)(R)CO. The dihaptoacyls insert into the Th-H bond of ]Th[(CH3)5C5]2H2]2. For Th[(CH3)5C5]2[eta2-COCH2C(CH3)3]Cl, this results, via ?-hydride elimination, in catalytic isomerization to Th[(CH3)5C5]2-[trans-OC(H)=C(H)C(CH3)3]. In the presence of hydrogen gas, the hydride catalytically hydrogenates the dihaptoacyls to alkoxides (M(eta2-COR)?M-OCH2R). Mechanistic studies include kinetic measurements as well as isotopic labelling and stereochemical analysis. 102 references

  15. Development of novel catalysts for the photocatalytic hydrogen formation

    Energy Technology Data Exchange (ETDEWEB)

    Pilz, Thomas David

    2011-11-16

    For future conversion of sunlight into chemical energy, intramolecular systems for artifical photosynthesis were developed in several stages. This comprised the fabrication of novel ligands and the resulting charge transfer chromophores (Ru(bpy)3-type) and/or catalytically active complexes (Pt, Pd). These were combined into heteronuclear diades consisting of covalently bonded functional subunits. In particular, the chromophores and catalysis centers were bridged so that their individual properties were retained while their individual functions were combined into a supramolecular photocatalyst. This makes it possible to reduce protons to hydrogen on these catalysts when exposed to light. As bridging units, oligodentate ligands were produced and used that can coordinate the active metal centers via bipyridines and N-heterocyclic carbenes (NHC). A number of such heterobimetal complexes, their initial compounds and appropriate reference compounds were produced, characterized, and compared. Apart from structural, photophysical and electrochemical analyses, also successful catalysis experiment were carried out with the manufactured photocatalysts for light-induced hydrogen production from water. Further representative control experiments and dynamic light scattering analyses were carried out in order to gain deeper understanding of the processes going on during catalysis. By comparing the properties of the fabricated catalysts with selected reference compounds, information was obtained on the structure-property relationships of the systems. (orig.) [German] Fuer die zukuenftige Umwandlung von Sonnenlicht in chemische Energie wurden schrittweise intramolekular arbeitende Systeme fuer eine artifizielle Photosynthese aufgebaut. Dabei wurde eine Anzahl von neuen Liganden und den resultierenden Charge-Transfer-Chromophoren (Ru(bpy)3-artig) bzw. katalyseaktiven Komplexen (Pt, Pd) hergestellt. Diese wurden zu heteronuklearen Diaden zusammengefuegt, welche aus kovalent verbundenen Funktionsuntereinheiten bestehen. Insbesondere wurden Chromophor und Katalysezentrum so miteinander verbrueckt, dass ihre individuellen Eigenschaften weiterbestehen, ihre Einzelfunktionen aber im Zusammenspiel als supramolekularer Photokatalysator fungieren. Somit wird es moeglich unter Lichteinstrahlung die Reduktion von Protonen zu Wasserstoff an diesen Katalysatoren durchzufuehren. Als Brueckeneinheit wurden dafuer oligodentate Liganden hergestellt und verwendet, die ueber Bipyridine und N-heterozyklische Carbene (NHC) die aktiven Metallzentren koordinieren koennen. Eine Anzahl solcher heterobimetallischen Komplexe, deren Ausgangsverbindungen sowie geeignete Referenzverbindungen wurden hergestellt, charakterisiert und miteinander verglichen. Neben strukturellen, photophysikalischen und elektrochemischen Analysen wurden zusaetzlich erfolgreich Katalyseexperimente mit den erzeugten Photokatalysatoren zur lichtgetriebenen Wasserstoffentwicklung aus Wasser durchgefuehrt. Ebenso wurden repraesentative Kontrollexperimente und zusaetzliche Analysen mittels dynamischer Lichtstreuung ausgefuehrt, um ein tiefergehendes Verstaendnis von den Prozessen waehrend der Katalyse zu erhalten. Durch Vergleich der Eigenschaften der hergestellten Katalysatoren mit ausgewaehlten Referenzverbindungen konnten zudem weitere Aussagen ueber Struktur-Eigenschafts-Beziehungen der Systeme abgeleitet werden. (orig.)

  16. Complex variables

    CERN Document Server

    Flanigan, Francis J

    2010-01-01

    A caution to mathematics professors: Complex Variables does not follow conventional outlines of course material. One reviewer noting its originality wrote: ""A standard text is often preferred [to a superior text like this] because the professor knows the order of topics and the problems, and doesn't really have to pay attention to the text. He can go to class without preparation."" Not so here-Dr. Flanigan treats this most important field of contemporary mathematics in a most unusual way. While all the material for an advanced undergraduate or first-year graduate course is covered, discussion

  17. Metal-Mediated Couplings of Primary Alcohols with Amines and Carbohydrates

    DEFF Research Database (Denmark)

    Maggi, Agnese; Madsen, Robert

    2012-01-01

    The work presented in this thesis was performed at the Department of Chemistry of the Technical University of Denmark during a three year Ph.D. program. The thesis involves two distinct Projects related to organometallic and carbohydrate chemistry. Project 1: Dehydrogenative synthesis of imines from alcohols and amines catalyzed by a ruthenium N-heterocyclic carbene complex. The successful method development and application of a convenient and direct (one step) synthesis of imines from alcohols and amines is described. The developed method provides quick andextended access to structurally diverse and synthetically important imines. The reaction is catalyzed by the ruthenium N-heterocyclic carbene complex [RuCl2(IiPr)(p-cymene)] (3) and proceeds in the presence of the ligand DABCO and molecular sieves with concomitant extrusion of water and hydrogen. A range of different primary alcohols and amines have been coupled in the presence of the catalyst to afford the corresponding imines in moderate to good yields.Optically pure amines gave the corresponding imines without any sign of racemization. Moreover, the one-pot diastereoselective addition of different organometallic reagents to the imine, obtained from the coupling between benzyl alcohol and (R)-1-phenylethylamine, was performed. To address specifics of the reaction mechanism, different experiments with deuterium-labeled benzyl alcohol were carried out indicating that that the catalytically active species is a ruthenium dihydride. The reaction is proposed to proceed by initial dehydrogenation of the alcohol to the aldehyde, which stays coordinated to the ruthenium centre. Then, nucleophilic attack of the amine affords the hemiaminal, which is released from ruthenium and converted into the imine. Project 2: Tin-mediated regioselective 6-O-glycosylations of unprotected phenyl 1-thioglycopyranosides Chemical glycosylation is of outstanding importance to access biologically relevant carbohydrate structures, but classical methods suffer from the disadvantage of extensive protecting group manipulations. Thus, approaches to reduce the number of steps connected to chemical synthesis are highly important. In this thesis approaches to the regioselective glycosylation of fully unprotected phenyl 1-thio-glycopyranoside acceptors via tin activation are described. Tin-mediated Koenigs-Knorr glycosylation of phenyl 1-thio-?-D-glucopyranoside (28), phenyl 1-thio-?-Dgalactopyranoside (32) and phenyl 1-thio-?-D-mannopyranoside (33) with different bromide donors afforded the corresponding (1?6) linked disaccharides in good to moderate yields. The disaccharides obtained from the first coupling can be activated as donors for subsequent tinmediated glycosylation reactions. The activation has been performed following two different strategies. The first involved one-step activation with a thiophilic reagent, while the second employed a two-step activation which entailed first formation of a glycosyl halide, and then activation with a halophilic reagent. This last approach is of particular interest; in fact, thioglycosides can be used as acceptors enabling an iterative oligosaccharide synthesis. Following these strategies a number of different trisaccharides have been successfully synthesized.

  18. Complex dynamics

    CERN Document Server

    Carleson, Lennart

    1993-01-01

    Complex dynamics is today very much a focus of interest. Though several fine expository articles were available, by P. Blanchard and by M. Yu. Lyubich in particular, until recently there was no single source where students could find the material with proofs. For anyone in our position, gathering and organizing the material required a great deal of work going through preprints and papers and in some cases even finding a proof. We hope that the results of our efforts will be of help to others who plan to learn about complex dynamics and perhaps even lecture. Meanwhile books in the field a. re beginning to appear. The Stony Brook course notes of J. Milnor were particularly welcome and useful. Still we hope that our special emphasis on the analytic side will satisfy a need. This book is a revised and expanded version of notes based on lectures of the first author at UCLA over several \\Vinter Quarters, particularly 1986 and 1990. We owe Chris Bishop a great deal of gratitude for supervising the production of cour...

  19. Complex silumins

    Directory of Open Access Journals (Sweden)

    S. Pietrowski

    2007-09-01

    Full Text Available Purpose: The study presents the results of investigations carried out on silumins with additions of Mg, Ni, Cu, Cr, Mo and W. The silumins containing Mg, Cu and Ni are well-known and commonly used in construction of machines and equipment.Design/methodology/approach: Additions of Cr, Mo and W have not been thoroughly investigated yet. They are considered a new family of innovative cast aluminium alloys.Findings: In Al-Si systems they form silicides, like Cr3Si, Mo3Si, W3Si and intermetallic phases of Al13Cr4Si4, Al12Mo, Al12W and AlWSi. The silicides crystallise in cubic lattice of parameters similar to aluminium and silicon.Research limitations/implications: Therefore they can act as crystallisation substrates and occur as separate phases. The examinations under the microscope and X-ray microanalysis of the linear and point distribution of elements confirmed the presence of the above mentioned phases. A combination of two elements, e.g. Cr and Mo, or Cr and W, was observed to cause the formation of complex silicide layers of Mo3Si and (Cr, Mo3Si, or Cr3Si as well as (W, Cr3Si.Originality/value: The presence of the silicides has been indicated as a possible source of the refinement of ?(Al and ?(Si phases. The precipitations of these phases and of the intermetallic phases favour a high degree of the silumins hardening. A characteristic feature is the fact that nucleation and crystallisation of the successive phases takes place at the phase boundaries formed between the previously precipitated phase and solid solution ?. The studies carried out so far have indicated that in complex silumins at high temperatures crystallise the silicides and peritectic phases of Al12W, AlWSi, Al12Mo and Al13Cr4Si4. Phases ? or ? are the next ones to crystallise, followed by complex eutectic ? + ? +Al(Si, Cr, Mo, W, Fe. Further crystallise the phases of Mg2Si, Al3Ni and Al2Cu. The silumins presented here are characterised by high mechanical properties: Rp0,2=320-420MPa, Rm =400-520MPa, A5=0.5-5.0% and elevated hardness of 145-210HB. Further investigations will be carried out to optimise the chemical composition of silumins and the precipitation hardening process parameters to produce alloys characterised by optimum combination of strength, ductility and hardness.

  20. Theoretical research on the effect of regulated ?-conjugation on the photophysical properties of Ir(III) complexes.

    Science.gov (United States)

    Xie, Li-Ming; Bai, Fu-Quan; Li, Wei; Zhang, Zhi-Xiang; Zhang, Hong-Xing

    2015-04-21

    In this work, the effect of regulated host and auxiliary ligand ?-conjugation on the photophysical properties of a series of Ir(III) carbene complexes is examined by using the start-of-the-art theoretical methods. According to our results, all of the lowest-lying and strongest absorption peaks can be assigned as having a mixed ligand-to-ligand/metal-to-ligand charge transfer (LLCT/MLCT) character, but the different ways of introducing phenyl have a great effect on the absorption wavelength variation. In addition, the charge transfer characteristics of lowest-lying emission have some minute differences. In addition, when the extended ?-conjugation is broken, the emission wavelength can be effectively retained due to the similar emission charge transfer related electronic density distribution of occupied molecular orbitals and unoccupied molecular orbitals. However, the larger ?-conjugation can give rise to remarkably blue-shifted emission. This blue-shifted emission can be attributed to the alteration in the transition character due to intense interactions between nearly degenerate unoccupied molecular orbitals. Through the evaluation of the spin-orbit coupling (SOC) effect, we can gain a deeper understanding of the radiative decay rate processes. These results reveal that the larger ?-conjugation can also lead to higher quantum efficiency due to the larger radiative decay and the smaller nonradiative decay rate. Our theoretical studies highlight the role of ?-conjugation of the host and auxiliary ligand, and thus, can pave the way for the design of novel and efficient blue phosphorescent materials. PMID:25785669

  1. Investigation of Complex Iron Surface Catalytic Chemistry Using the ReaxFF Reactive Force Field Method

    Science.gov (United States)

    Zou, Chenyu; Van Duin, Adri

    2012-12-01

    To demonstrate the feasibility of classical reactive dynamics for studying complex surface chemistry, we performed a series of five reactive molecular dynamics simulations addressing the carbon monoxide methanation and the hydrocarbon chain initiation using the ReaxFF reactive force field method. We found that the catalytic surface hydrogenation initiates from the undissociated CO molecules absorbed on the surface of the catalyst as described in the oxygenate mechanism. This process leads to the generation of surface absorbed CH X - groups, which initiates the synthesis of methane and the hydrocarbon chain growth. Direct hydrogenation of the surface carbide was not observed in the simulation. Coordination analysis of the carbon atoms in the system provides possible explanations in that the surface carbon atoms are further stabilized by the surface deformation of the iron catalyst at elevated temperatures. Results from the simulations also indicated that the surface CH- could dissociate into surface carbon atoms or be further hydrogenated into CH2- radicals, which is an important intermediate species in the synthesis of methane as well as the chain initiation. Results from the C-C coupling simulation suggested the preference of coupling between CH- and CH2- groups, which agrees with the alkenyl scheme of the carbene mechanism. The overall results agree with the available experimental observations and quantum mechanics (QM) study. Furthermore, these simulations indicate the possible cooperation among different mechanisms and prove the serviceability of the ReaxFF method for studying the complex heterogeneous catalytic system. These simulations have also allowed us to evaluate the accuracy of the current ReaxFF Fe/C/O/H description, providing crucial information regarding areas where further improvement is required.

  2. AQUEOUS N-HETEROCYCLIZATION OF PRIMARY AMINES AND HYDRAZINES WITH DIHALIDES: MICROWAVE-ASSISTED SYNTHESES OF N-AZACYCLOALKANES, ISOINDOLE, PYRAZOLE, PYRAZOLIDINE AND PHTHALAZINE DERIVATIVES

    Science.gov (United States)

    The synthesis of nitrogen-containing heterocycles from alkyl dihalides (ditosylates) and primary amines and hydrazines via a simple and efficient cyclocondensation in alkaline aqueous medium that occurs under microwave irradiation is described. This improved greener synthetic met...

  3. A new two-dimensional ZnII coordination polymer constructed by a multidentate N-heterocyclic ligand and 5-carboxybenzene-1,3-dicarboxylate.

    Science.gov (United States)

    Huang, Qiu-Ying; Yang, Yi; Meng, Xiang-Ru

    2015-08-01

    In the coordination polymer, poly[[{?-1-[(1H-benzimidazol-2-yl)methyl]-1H-imidazole-?(2)N:N'}(?-5-carboxybenzene-1,3-dicarboxylato-?(2)O(1):O(3))zinc(II)] dimethylformamide monosolvate pentahydrate], {[Zn(C9H4O6)(C11H10N4)]·C3H7NO·5H2O}n, the Zn(II) ion is coordinated by two N atoms from two symmetry-related 1-[(1H-benzimidazol-2-yl)methyl]-1H-imidazole (bmi) ligands and two O atoms from two symmetry-related 5-carboxybenzene-1,3-dicarboxylate (Hbtc(2-)) ligands in a slightly distorted tetrahedral geometry. The Zn(II) ions are bridged by Hbtc(2-) and bmi ligands, leading to a 4-connected two-dimensional network with the topological notation (4(4).6(2)). Adjacent layers are further connected by 12 kinds of hydrogen bonds and also by ?-? interactions, resulting in a three-dimensional supramolecular architecture in the solid state. PMID:26243418

  4. A Dual Independence Complex

    OpenAIRE

    Waßmer, Arnold Johannes

    2005-01-01

    In the present work we apply the concept of duality to the simplicial complex of independent (stable) sets of graphs, the so called independence complex. We prove that this complex can be dualized for the case of paths and cycles. The result is a dual independence complex, which is a regular cell complex with surprising structures. Although it contains the same topological information as the non-dual complex its homeomorphism type is "nicer". The independence complex of a cycle, for example, ...

  5. Mastering the reactivity of gold (i) carbenes

    OpenAIRE

    López Carrillo, Verónica

    2010-01-01

    Esta tesis doctoral se ha centrado en el estudio experimental de la ciclación catalizada por oro de 1,5-eninos con un grupo electroatractor en la posición alílica que permite obtener selectivamente 1,4-dienos o biciclo[3.1.0]hexenes modulando la electrofilia del catalizador. Mecanísticamente es una ciclación 5-endo-dig en la que se forma un ciclopropil carbeno de Au como intermedio, que a su vez puede reaccionar in situ con nucleófilos como H2O, ROH, aldehídos ó nucleófilos carbonados. Tambié...

  6. Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, Jared; Bergman, Robert; Ellman, Jonathan

    2008-02-04

    Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct funtionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes their work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. They initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. They then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, they discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. They then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy{sub 3}){sub 2}] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazolein, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy{sub 3}){sub 2} fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, they developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including azoles, azolines, dihydroquinazolines, pyridines, and quinolines, with a wide range of functionalized olefins. They demonstrated the utility of this methodology in the synthesis of natural products, drug candidates, and other biologically active molecules. In addition, they developed conditions to directly arylate these heterocycles with aryl halides. The initial conditions that used PCy{sub 3} as a ligand were successful only for aryl iodides. However, efforts designed to avoid catalyst decomposition led to the development of ligands based on 9-phosphabicyclo[4.2.1]nonane (Phoban) that also facilitated the coupling of aryl bromides. They then replicated the unique coordination environment, stability, and catalytic activity of this complex using the much simpler tetrahydrophosphepine ligands and developed conditions that coupled aryl bromides bearing diverse functional groups without the use of a glovebox or purified reagents. With further mechanistic inquiry, they anticipate that researchers will better understand the details of the aforementioned Rh-catalyzed C-H bond functionalization reactions, resulting in the design of more efficient and robust catalysts, expanded substrate scope, and new transformations.

  7. Complex fuzzy normal subgroup

    Science.gov (United States)

    Al-Husban, Abdallah; Salleh, Abdul Razak; Hassan, Nasruddin

    2015-09-01

    In this paper, we continue the study of complex fuzzy groups by introducing the notion of complex fuzzy normal subgroup based on complex fuzzy space as a generalisation of fuzzy normal subgroup in the sense of Dib.

  8. A novel binuclear ruthenium complex: spectroscopic and electrochemical characterization, and formation of Langmuir and Langmuir-Blodgett films

    Scientific Electronic Library Online (English)

    Karen, Wohnrath; Poliana M. dos, Santos; B., Sandrino; Jarem R., Garcia; Alzir A., Batista; Osvaldo N., Oliveira Jr.

    2006-12-01

    Full Text Available O complexo [{RuCl3(dppb)}2(µ-4,4'-bipy)] (dppb = PPh2(CH2)4PPh2; 4,4'-bipy= 4,4'-bipiridil) foi obtido por meio da reação entre 4,4'-bipiridina e mer-[RuCl3(dppb)].H2O, em bom rendimento. As características do complexo binuclear obtido, estudadas por medidas de FT-IR, UV-Vis, EPR e análise elementar [...] foram similares às do complexo [RuCl3(dppb)L] (L= N-heterociclo). [{RuCl3(dppb)}2(µ-4,4'-bipy)] é solúvel em solventes fracamente polares, facilitando a sua utilização para produzir filmes de Langmuir e Langmuir-Blodgett (LB). Enquanto que filmes cast e o complexo em solução são vermelhos, filmes LB são azul-esverdeados, provavelmente devido à oxidação da bisfosfina. A natureza nanoestruturada dos filmes LB, se manifestou nas medidas eletroquímicas, já que estes filmes exibem maior corrente de pico do que os filmes cast e dip-coated. As respostas eletroquímicas destes filmes são caracterizadas pelo processo RuIII RuIII/RuII RuII, o qual difere do complexo em solução. Neste último caso, um processo irreversível é observado devido à formação de novas espécies. A eletroatividade dos filmes LB/[{RuCl3(dppb)}2(µ-4,4' -bipy)] indica a possibilidade de utilização em dispositivos eletroquímicos. Abstract in english [{RuCl3(dppb)}2(µ-4,4'-bipy)] was prepared from the reaction of the 4,4'-bipyridine and mer-[RuCl3(dppb)].H2O, in good yield. The characteristics of the binuclear complex studied with FT-IR, UV-Vis, EPR and elemental analysis were similar to those of the [RuCl3(dppb)L] (L= N-heterocycle). [{RuCl3(dp [...] pb)}2(µ-4,4'-bipy)] is soluble in weakly polar organic solvents, facilitating its use in the production of Langmuir and Langmuir-Blodgett (LB) films production. While the cast films and the complex in solution were red, the LB films were green-bluish, probably due to oxidation of the bisphosphine. The nanostructured nature of the LB films was manifested in electrochemical measurements, as these films exhibited higher peak currents than cast or dip-coated films. For all films, the electrochemical response was dominated by the RuIII RuIII/RuII RuII process, which differed from that of the binuclear compound. For the latter, an irreversible process appeared due to formation of new species. The electroactivity of LB films from [{RuCl3(dppb)}2(µ-4,4'-bipy)] also pointed to their possible use in electrochemical devices.

  9. Complex Multiplicative Calculus

    OpenAIRE

    Bashirov, Agamirza; Riza, Mustafa

    2011-01-01

    In the present paper we extend the concepts of multiplicative de- rivative and integral to complex-valued functions of complex variable. Some drawbacks, arising with these concepts in the real case, are explained satis- factorily. Properties of complex multiplicative derivatives and integrals are studied. In particular, the fundamental theorem of complex multiplicative calculus, relating these concepts, is proved. It is shown that complex multi- plicative calculus is not jus...

  10. Hyper Space Complex Number

    OpenAIRE

    Tan, Shanguang

    2007-01-01

    A new kind of numbers called Hyper Space Complex Numbers and its algebras are defined and proved. It is with good properties as the classic Complex Numbers, such as expressed in coordinates, triangular and exponent forms and following the associative and commutative laws of addition and multiplication. So the classic Complex Number is developed from in complex plane with two dimensions to in complex space with N dimensions and the number system is enlarged also.

  11. Preparation and reactivity of diazoalkane complexes of ruthenium stabilised by an indenyl ligand.

    Science.gov (United States)

    Albertin, Gabriele; Antoniutti, Stefano; Castro, Jesús; Dottorello, Gianluca

    2015-05-21

    Diazoalkane complexes [Ru(?(5)-C9H7)(N2CAr1Ar2)(PPh3)L]BPh4 (1-3) [L = PPh3, P(OMe)3, P(OEt)3; Ar1 = Ar2 = Ph; Ar1 = Ph, Ar2 = p-tolyl; Ar1Ar2 = C12H8 fluorenyl] were prepared by allowing chloro-complexes [RuCl(?(5)-C9H7)(PPh3)L] to react with an excess of diazoalkane in ethanol. Complexes 1-3 reacted with ethylene CH2=CH2 (1 atm) and maleic anhydride [ma, CH=CHCO(O)CO] to afford ?(2)-alkene complexes [Ru(?(5)-C9H7)(?(2)-CH2=CH2)(PPh3)L]BPh4 (4, 5) and [Ru(?(5)-C9H7){?(2)-CH=CHCO(O)CO}(PPh3)L]BPh4 (7). Further, complexes 1-3 underwent cycloaddition with acrylonitrile CH2=C(H)CN, giving 1H-pyrazoline derivatives [Ru(?(5)-C9H7){?(1)-N=C(CN)CH2C(Ar1Ar2)NH}(PPh3)L]BPh4 (6). Treatment of diazoalkane complexes 1-3 with acetylene CH[triple bond, length as m-dash]CH under mild conditions (1 atm, room temperature) led to dipolar cycloaddition, affording 3H-pyrazole complexes [Ru(?(5)-C9H7)-{?(1)-N=NC(Ar1Ar2)CH=CH}(PPh3)L]BPh4 (8), whereas reaction with terminal alkynes RC?CH (R = Ph, p-tolyl, Bu(t)) gave vinylidene derivatives [Ru(?(5)-C9H7){=C=C(H)R}(PPh3)L]BPh4 (9). The latter reacted with nucleophiles such as amines and alcohols to give amino- and alkoxy-carbene derivatives [Ru(?(5)-C9H7){=C(NHPr(n))(CH2Ph)}(PPh3)L]BPh4 (11) and [Ru(?(5)-C9H7){=C(CH3)(OEt)}(PPh3)L]BPh4 (10), respectively. In addition, complexes 9 reacted with phenylhydrazine to afford nitrile derivatives [Ru(?(5)-C9H7)(N[triple bond, length as m-dash]CCH2R)(PPh3)L]BPh4 (12) and phenylamine, whereas the reaction with water led to hydrolysis of the alkyne and formation of carbonyl complexes [Ru(?(5)-C9H7)(CO)(PPh3)L]BPh4 (13). Lastly, treatment of vinylidene complexes with the phosphines PPh3 and P(OMe)3 afforded alkenylphosphonium derivatives [Ru(?(5)-C9H7){C(H)=C(R)PPh3}(PPh3)L]BPh4 (14) and [Ru(?(5)-C9H7){C(R)=C(H)P(OMe)3}(PPh3)L]BPh4 (15), respectively. Compound [Ru(?(5)-C9H7){C(H)=C(H)PPh3}(PPh3)L]BPh4 (16) was also prepared. The complexes were characterised by spectroscopy (IR and NMR) and X-ray crystal structure determinations of [Ru(?(5)-C9H7){N2C(C12H8)}(PPh3){P(OEt)3}]BPh4 (3c), [Ru(?(5)-C9H7){=C=C(H)Ph}(PPh3){P(OEt)3}]BPh4 (9d) and [Ru(?(5)-C9H7){C(H)=C(Ph)PPh3}(PPh3){P(OEt)3}]BPh4 (14d). PMID:25913868

  12. Complex Elliptic Pendulum

    OpenAIRE

    Bender, Carl M.; Hook, Daniel W; Kooner, Karta

    2009-01-01

    This paper briefly summarizes previous work on complex classical mechanics and its relation to quantum mechanics. It then introduces a previously unstudied area of research involving the complex particle trajectories associated with elliptic potentials.

  13. Doxorubicin Lipid Complex Injection

    Science.gov (United States)

    Doxorubicin lipid complex is used to treat ovarian cancer that has not improved or that has worsened after treatment with other medications. Doxorubicin lipid complex is also used to treat Kaposi's sarcoma ( ...

  14. Daunorubicin Lipid Complex Injection

    Science.gov (United States)

    Daunorubicin lipid complex is used to treat advanced Kaposi's sarcoma (a type of cancer that causes abnormal tissue to ... body) related to acquired immunodeficiency syndrome (AIDS). Daunorubicin lipid complex is in a class of medications called ...

  15. Vincristine Lipid Complex Injection

    Science.gov (United States)

    Vincristine lipid complex is used to treat a certain type of acute lymphoblastic leukemia (ALL; a type of cancer ... least two different treatments with other medications. Vincristine lipid complex is in a class of medications called ...

  16. Oligocyclopentadienyl transition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    de Azevedo, Cristina G.; Vollhardt, K. Peter C.

    2002-01-18

    Synthesis, characterization, and reactivity studies of oligocyclopentadienyl transition metal complexes, namely those of fulvalene, tercyclopentadienyl, quatercyclopentadienyl, and pentacyclopentadienyl(cyclopentadienyl) are the subject of this account. Thermal-, photo-, and redox chemistries of homo- and heteropolynuclear complexes are described.

  17. Quantum Communication Complexity

    OpenAIRE

    Klauck, Hartmut

    2000-01-01

    This paper surveys the field of quantum communication complexity. Some interesting recent results are collected concerning relations to classical communication, lower bound methods, one-way communication, and applications of quantum communication complexity.

  18. On Wagoner complexes

    OpenAIRE

    Essert, Jan

    2009-01-01

    Wagoner complexes are simplicial complexes associated to groups of Kac-Moody type. They admit interesting homotopy groups which are related to integral group homology if the root datum is of 2-spherical type. We give a general definition of Wagoner complexes, exhibit some simple properties and calculate low dimensional homotopy groups. In addition, we give a definition of affine Wagoner complexes related to groups admitting a root datum with valuation.

  19. Measuring semantic complexity

    CERN Document Server

    Zadrozny, W

    1995-01-01

    We define {\\em semantic complexity} using a new concept of {\\em meaning automata}. We measure the semantic complexity of understanding of prepositional phrases, of an "in depth understanding system", and of a natural language interface to an on-line calendar. We argue that it is possible to measure some semantic complexities of natural language processing systems before building them, and that systems that exhibit relatively complex behavior can be built from semantically simple components.

  20. On Complex Random Variables

    OpenAIRE

    Anwer Khurshid; Zuhair A. Al-Hemari; Shahid Kamal

    2012-01-01

    In this paper, it is shown that a complex multivariate random variable  is a complex multivariate normal random variable of dimensionality if and only if all nondegenerate complex linear combinations of  have a complex univariate normal distribution. The characteristic function of  has been derived, and simpler forms of some theorems have been given using this characterization theorem without assuming that the variance-covariance matrix of the vector  is Hermitian posit...

  1. Discrete Morse Complexes

    OpenAIRE

    Chari, Manoj K.; Joswig, Michael

    2000-01-01

    We investigate properties of the set of discrete Morse functions on a simplicial complex as defined by Forman. It is not difficult to see that the pairings of discrete Morse functions of a finite simplicial complex again form a simplicial complex, the discrete Morse complex. It turns out that several known results from combinatorial topology and enumerative combinatorics, which previously seemed to be unrelated, can be re-interpreted in the setting of these discrete Morse co...

  2. Complexity and Transition Management

    OpenAIRE

    Rotmans, J.; Loorbach, D.A.

    2009-01-01

    This article presents a framework, transition management, for managing complex societal systems. The principal contribution of this article is to articulate the relationship between transition management and complex systems theory. A better understanding of the dynamics of complex, adaptive systems provides insight into the opportunities, limitations, and conditions under which it is possible to influence such systems. Transition management is based on key notions of complex systems theory, s...

  3. Complexity of Counting CSP with Complex Weights

    CERN Document Server

    Cai, Jin-Yi

    2011-01-01

    We give a complexity dichotomy theorem for the counting Constraint Satisfaction Problem (#CSP in short) with complex weights. To this end, we give three conditions for its tractability. Let F be any finite set of complex-valued functions, then we prove that #CSP(F) is solvable in polynomial time if all three conditions are satisfied; and is #P-hard otherwise. Our complexity dichotomy generalizes a long series of important results on counting problems: (a) the problem of counting graph homomorphisms is the special case when there is a single symmetric binary function in F; (b) the problem of counting directed graph homomorphisms is the special case when there is a single not-necessarily-symmetric binary function in F; and (c) the standard form of #CSP is when all functions in F take values in {0,1}.

  4. Lanthanide complexes with pivaloylacetone

    International Nuclear Information System (INIS)

    Complexes Ln(pa)3·2H2O (Ln=La, Gd, Lu, Hpa - pivaloylacetone) are synthesized and investigated by the methods of element, IR spectroscopic and thermal analyses. Behaviour of the complexes during heating in vacuum is compared with such one for acetylacetonates and dipivaloylmethanates. Structure of the complexes in solution is studied by 1H NMR and MALDI-MS

  5. Complex variables I essentials

    CERN Document Server

    Solomon, Alan D

    2013-01-01

    REA's Essentials provide quick and easy access to critical information in a variety of different fields, ranging from the most basic to the most advanced. As its name implies, these concise, comprehensive study guides summarize the essentials of the field covered. Essentials are helpful when preparing for exams, doing homework and will remain a lasting reference source for students, teachers, and professionals. Complex Variables I includes functions of a complex variable, elementary complex functions, integrals of complex functions in the complex plane, sequences and series, and poles and r

  6. Photocytotoxic lanthanide complexes

    Indian Academy of Sciences (India)

    Akhtar Hussain; Akhil R Chakravarty

    2012-11-01

    Lanthanide complexes have recently received considerable attention in the field of therapeutic and diagnostic medicines. Among many applications of lanthanides, gadolinium complexes are used as magnetic resonance imaging (MRI) contrast agents in clinical radiology and luminescent lanthanides for bioanalysis, imaging and sensing. The chemistry of photoactive lanthanide complexes showing biological applications is of recent origin. Photodynamic therapy (PDT) is a non-invasive treatment modality of cancer using a photosensitizer drug and light. This review primarily focuses on different aspects of the chemistry of lanthanide complexes showing photoactivated DNA cleavage activity and cytotoxicity in cancer cells. Macrocyclic texaphyrin-lanthanide complexes are known to show photocytotoxicity with the PDT effect in near-IR light. Very recently, non-macrocyclic lanthanide complexes are reported to show photocytotoxicity in cancer cells. Attempts have been made in this perspective article to review and highlight the photocytotoxic behaviour of various lanthanide complexes for their potential photochemotherapeutic applications.

  7. Instability of metal 1,3-benzodi(thiophosphinoyl)methandiide complexes: formation of hafnium, tin and zirconium complexes of 1,3-benzodi(thiophosphinoyl)thioketone dianionic ligand [1,3-C6H4(PhPS)2CS](2(-)).

    Science.gov (United States)

    Yang, Ya-Xiu; Li, Yongxin; Ganguly, Rakesh; So, Cheuk-Wai

    2015-07-28

    The reaction of [LCH2] (1, L = 1,3-C6H4(PhPS)2) and M(NMe2)4 (M = Hf, Zr) in toluene at 110 °C afforded a mixture of group 4 metal complexes [{LC(S)}2M] [M = Hf (2), Zr (3)] and [1,3-C6H4(PhPS)(PhP)CH2]. The reactions appear to proceed through the formation of metal bis(carbene) complexes, [LC=M=CL], which then undergo an intermolecular sulphur transfer reaction with the P=S bond of [LCH2] to form 2 and 3, and the byproduct is [1,3-C6H4(PhPS)(PhP)CH2]. In addition, the reaction of 1, [CH2(PPh2S)2] (4) and M(NMe2)4 in refluxing toluene gave a mixture of [{LC(S)}M(NHMe2){C(PPh2S)2}] [M = Hf (5), Zr (6)], [1,3-C6H4(PhPS)(PhP)CH2] and [CH2(PPh2S)(PPh2)]. Moreover, the intermolecular sulfur transfer reaction is evidenced by the reaction of the tin(ii) 1,3-benzodi(thiophosphinoyl)methandiide complex [{?-1,3-C6H4(PhPS)2C}Sn]2 (7) with two equivalents of elemental sulfur in CH2Cl2 at ambient temperature to give [{1,3-C6H4(PhPS)2CS}2Sn] (8). Compounds 2, 3, 5, 6, and 8 were characterized by NMR spectroscopy and X-ray crystallography. PMID:26079794

  8. Assessing physiological complexity.

    Science.gov (United States)

    Burggren, W W; Monticino, M G

    2005-09-01

    Physiologists both admire and fear complexity, but we have made relatively few attempts to understand it. Inherently complex systems are more difficult to study and less predictable. However, a deeper understanding of physiological systems can be achieved by modifying experimental design and analysis to account for complexity. We begin this essay with a tour of some mathematical views of complexity. After briefly exploring chaotic systems, information theory and emergent behavior, we reluctantly conclude that, while a mathematical view of complexity provides useful perspectives and some narrowly focused tools, there are too few generally practical take-home messages for physiologists studying complex systems. Consequently, we attempt to provide guidelines as to how complex systems might be best approached by physiologists. After describing complexity based on the sum of a physiological system's structures and processes, we highlight increasingly refined approaches based on the pattern of interactions between structures and processes. We then provide a series of examples illustrating how appreciating physiological complexity can improve physiological research, including choosing experimental models, guiding data collection, improving data interpretations and constructing more rigorous system models. Finally, we conclude with an invitation for physiologists, applied mathematicians and physicists to collaborate on describing, studying and learning from studies of physiological complexity. PMID:16109885

  9. Recollement and Tilting Complexes

    CERN Document Server

    Miyachi, J

    2002-01-01

    First, we study recollement of a derived category of unbounded complexes of modules induced by a partial tilting complex. Second, we give equivalent conditions for $P^{\\centerdot}$ to be a recollement tilting complex, that is, a tilting complex which induces an equivalence between recollements $\\{\\cat{D}_{A/AeA}(A), \\cat{D}(A), \\cat{D}(eAe)}$ and $\\{\\cat{D}_{B/BfB}(B), \\cat{D}(B), \\cat{D}(fBf)}$, where e, f are idempotents of A, B, respectively. In this case, there is an unbounded bimodule complex $\\varDelta^{\\centerdot}_{T}$ which induces an equivalence between $\\cat{D}_{A/AeA}(A)$ and $\\cat{D}_{B/BfB}(B)$. Third, we apply the above to a symmetric algebra A. We show that a partial tilting complex $P^{\\centerdot}$ for A of length 2 extends to a tilting complex, and that $P^{\\centerdot}$ is a tilting complex if and only if the number of indecomposable types of $P^{\\centerdot}$ is one of A. Finally, we show that for an idempotent e of A, a tilting complex for eAe extends to a recollement tilting complex for A, ...

  10. Improved Ruthenium Catalysts for Z-Selective Olefin Metathesis

    Science.gov (United States)

    Keitz, Benjamin K.; Endo, Koji; Patel, Paresma R.; Herbert, Myles B.; Grubbs, Robert H.

    2011-01-01

    Several new C-H activated ruthenium catalysts for Z-selective olefin metathesis have been synthesized. Both the carboxylate ligand and the aryl group of the N-heterocyclic carbene have been altered and the resulting catalysts were evaluated using a range of metathesis reactions. Substitution of bidentate with monodentate X-type ligands led to a severe attenuation of metathesis activity and selectivity, while minor differences were observed between bidentate ligands within the same family (e.g. carboxylates). The use of nitrato-type ligands, in place of carboxylates, afforded a significant improvement in metathesis activity and selectivity. With these catalysts, turnover numbers approaching 1000 were possible for a variety of cross-metathesis reactions, including the synthesis of industrially-relevant products. PMID:22097946

  11. The activation mechanism of Fe-based olefin metathesis catalysts

    KAUST Repository

    Poater, Albert

    2014-08-01

    Density functional theory calculations have been used to describe the first turnover for olefin metathesis reaction of a homogenous Fe-based catalyst bearing a N-heterocyclic carbene ligand with methoxyethene as a substrate. Equal to conventional Ru-based catalysts, the activation of its Fe congener occurs through a dissociative mechanism, however with a more exothermic reaction energy profile. Predicted upper energy barriers were calculated to be on average ?2 kcal/mol more beneficial for Fe catalyzed metathesis. Overall, this present computational study emphasises on advantages of Fe-based metathesis and gives a potential recipe for the design of an efficient Fe-based olefin metathesis catalysts. © 2014 Elsevier B.V.

  12. Ring-Closing and Cross-Metathesis with Artificial Metalloenzymes Created by Covalent Active Site-Directed Hybridization of a Lipase.

    Science.gov (United States)

    Basauri-Molina, Manuel; Verhoeven, Dide G A; van Schaik, Arnoldus J; Kleijn, Henk; Klein Gebbink, Robertus J M

    2015-10-26

    A series of Grubbs-type catalysts that contain lipase-inhibiting phosphoester functionalities have been synthesized and reacted with the lipase cutinase, which leads to artificial metalloenzymes for olefin metathesis. The resulting hybrids comprise the organometallic fragment that is covalently bound to the active amino acid residue of the enzyme host in an orthogonal orientation. Differences in reactivity as well as accessibility of the active site by the functionalized inhibitor became evident through variation of the anchoring motif and substituents on the N-heterocyclic carbene ligand. Such observations led to the design of a hybrid that is active in the ring-closing metathesis and the cross-metathesis of N,N-diallyl-p-toluenesulfonamide and allylbenzene, respectively, the latter being the first example of its kind in the field of artificial metalloenzymes. PMID:26346291

  13. Ni-Catalyzed Alkenylation of Ketone Enolates under Mild Conditions: Catalyst Identification and Optimization.

    Science.gov (United States)

    Grigalunas, Michael; Ankner, Tobias; Norrby, Per-Ola; Wiest, Olaf; Helquist, Paul

    2015-06-10

    A procedure for Ni-catalyzed cross-coupling of ketone enolates with alkenyl halides has been developed. Intermolecular coupling of aromatic and aliphatic ketone lithium enolates with a variety of alkenyl halides is achieved in the presence of Ni(cod)2 catalyst (5 mol %), an N-heterocyclic carbene (NHC) ligand, and LiI (10 mol %) at 6-22 °C for 0.5-12 h with yields of up to 90%. During the initial development of this reaction, a misleading result with respect to the actual active catalyst was obtained using commercially available Q-Phos ligand, which was found to contain a trace of Pd metal contaminant sufficient to catalyze the reaction. However, under the final conditions optimized for Ni(cod)2 in the presence of an NHC ligand, Pd was incompetent as a catalyst. PMID:26024472

  14. Ligand-controlled regiodivergent nickel-catalyzed annulation of pyridones.

    Science.gov (United States)

    Donets, Pavel A; Cramer, Nicolai

    2015-01-01

    The 1,6-annulated 2-pyridone motif is found in many biologically active compounds and its close relation to the indolizidine and quinolizidine alkaloid core makes it an attractive building block. A nickel-catalyzed C-H functionalization of 2-pyridones and subsequent cyclization affords 1,6-annulated 2-pyridones by selective intramolecular olefin hydroarylation. The switch between the exo- and endo-cyclization modes is controlled by two complementary sets of ligands. Irrespective of the ring size, the regioselectivity during the cyclization is under full catalyst control. Simple cyclooctadiene promotes an exo-selective cyclization, whereas a bulky N-heterocyclic carbene ligand results in an endo-selective mode. The method was further applied in the synthesis of the lupin alkaloid cytisine. PMID:25378295

  15. 1-n-Butyl-3-methylimidazolium-2-carboxylate: a versatile precatalyst for the ring-opening polymerization of ?-caprolactone and rac-lactide under solvent-free conditions

    Directory of Open Access Journals (Sweden)

    Astrid Hoppe

    2013-04-01

    Full Text Available The ring-opening polymerization of ?-caprolactone (?-CL and rac-lactide (rac-LA under solvent-free conditions and using 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO2 as precatalyst is described. Linear and star-branched polyesters were synthesized by successive use of benzyl alcohol, ethylene glycol, glycerol and pentaerythritol as initiator alcohols, and the products were fully characterized by 1H and 13C{1H} NMR spectroscopy, gel permeation chromatography (GPC, and differential scanning calorimetry (DSC. BMIM-2-CO2 acts as an N-heterocyclic carbene precursor, resulting from in situ decarboxylation, either by heating under vacuo (method A or by addition of NaBPh4 (method B. Possible catalytic and deactivation mechanisms are proposed.

  16. Visible Light Mediated Reductive Cleavage of C-O Bonds Accessing ?-Substituted Aryl Ketones.

    Science.gov (United States)

    Speckmeier, Elisabeth; Padié, Clément; Zeitler, Kirsten

    2015-10-01

    C-O ?-bonds in multifaceted benzoin derivatives can be effectively cleaved as acetates using catalytic amounts of [Ru(bpy)3]Cl2 as photoredox catalyst in combination with Hantzsch ester and triethylamine as a sacrificial electron donor. This mild and operationally simple method is applicable to a great variety of substrates. Homo- and cross-benzoins, which are easily accessed by NHC (N-heterocyclic carbene) catalysis, with both electron-withdrawing and electron-donating substituents, including aryl halogenides, can be employed. The deoxygenated counterparts are isolated in good to excellent yields. These broadly accessible, ?-substituted (nonsymmetric) aryl ketones are versatilely applicable for further transformations as illustrated by the syntheses of 2-arylbenzofurans. PMID:26372674

  17. Catalytic Kinetic Resolution of Disubstituted Piperidines by Enantioselective Acylation: Synthetic Utility and Mechanistic Insights.

    Science.gov (United States)

    Wanner, Benedikt; Kreituss, Imants; Gutierrez, Osvaldo; Kozlowski, Marisa C; Bode, Jeffrey W

    2015-09-01

    The catalytic kinetic resolution of cyclic amines with achiral N-heterocyclic carbenes and chiral hydroxamic acids has emerged as a promising method to obtain enantio-enriched amines with high selectivity factors. In this report, we describe the catalytic kinetic resolution of disubstituted piperdines with practical selectivity factors (s, up to 52) in which we uncovered an unexpected and pronounced conformational effect resulting in disparate reactivity and selectivity between the cis- and trans-substituted piperidine isomers. Detailed experimental and computational studies of the kinetic resolution of various disubstituted piperidines revealed a strong preference for the acylation of conformers in which the ?-substituent occupies the axial position. This work provides further experimental and computational support for the concerted 7-member transition state model for acyl transfer reagents and expands the scope and functional group tolerance of the secondary amine kinetic resolution. PMID:26308097

  18. Simplicial complexes of graphs

    CERN Document Server

    Jonsson, Jakob

    2008-01-01

    A graph complex is a finite family of graphs closed under deletion of edges. Graph complexes show up naturally in many different areas of mathematics, including commutative algebra, geometry, and knot theory. Identifying each graph with its edge set, one may view a graph complex as a simplicial complex and hence interpret it as a geometric object. This volume examines topological properties of graph complexes, focusing on homotopy type and homology. Many of the proofs are based on Robin Forman's discrete version of Morse theory. As a byproduct, this volume also provides a loosely defined toolbox for attacking problems in topological combinatorics via discrete Morse theory. In terms of simplicity and power, arguably the most efficient tool is Forman's divide and conquer approach via decision trees; it is successfully applied to a large number of graph and digraph complexes.

  19. Measuring static complexity

    Directory of Open Access Journals (Sweden)

    Ben Goertzel

    1992-03-01

    Full Text Available The concept of “pattern” is introduced, formally defined, and used to analyze various measures of the complexity of finite binary sequences and other objects. The standard Kolmogoroff-Chaitin-Solomonoff complexity measure is considered, along with Bennett's ‘logical depth’, Koppel's ‘sophistication'’, and Chaitin's analysis of the complexity of geometric objects. The pattern-theoretic point of view illuminates the shortcomings of these measures and leads to specific improvements, it gives rise to two novel mathematical concepts--“orders” of complexity and “levels” of pattern, and it yields a new measure of complexity, the “structural complexity”, which measures the total amount of structure an entity possesses.

  20. Randomised Individual Communication Complexity.

    Czech Academy of Sciences Publication Activity Database

    Buhrman, H.; Koucký, Michal; Vereshchagin, N.K.

    Maryland : IEEE Computer Society Press, 2008, s. 321-331. ISBN 978-0-7695-3169-4. [IEEE Conference on Computational Complexity 2008. College Park (US), 23.06.2008-26.06.2008] R&D Projects: GA ?R GP201/07/P276 Institutional research plan: CEZ:AV0Z10190503 Keywords : randomized individual communication complexity * round complexity Subject RIV: BA - General Mathematics

  1. Reduced Complexity Sphere Decoding

    OpenAIRE

    Li, Boyu; Ayanoglu, Ender

    2009-01-01

    In Multiple-Input Multiple-Output (MIMO) systems, Sphere Decoding (SD) can achieve performance equivalent to full search Maximum Likelihood (ML) decoding, with reduced complexity. Several researchers reported techniques that reduce the complexity of SD further. In this paper, a new technique is introduced which decreases the computational complexity of SD substantially, without sacrificing performance. The reduction is accomplished by deconstructing the decoding metric to de...

  2. Complex Correspondence Principle

    OpenAIRE

    Bender, C. M.; Hook, D. W.; Meisinger, P. N.; Q. H. Wang

    2010-01-01

    Quantum mechanics and classical mechanics are two very different theories, but the correspondence principle states that quantum particles behave classically in the limit of high quantum number. In recent years much research has been done on extending both quantum mechanics and classical mechanics into the complex domain. This letter shows that these complex extensions continue to exhibit a correspondence, and that this correspondence becomes more pronounced in the complex do...

  3. Genetics of complex diseases*

    OpenAIRE

    Motulsky, Arno G.

    2006-01-01

    Approaches to the study of the genetic basis of common complex diseases and their clinical applications are considered. Monogenic Mendelian inheritance in such conditions is infrequent but its elucidation may help to detect pathogenic mechanisms in the more common variety of complex diseases. Involvement by multiple genes in complex diseases usually occurs but the isolation and identification of specific genes so far has been exceptional. The role of common polymorphisms as indicators of dise...

  4. Quantum Bounded Query Complexity

    OpenAIRE

    Buhrman, Harry; van Dam, Wim

    1999-01-01

    We combine the classical notions and techniques for bounded query classes with those developed in quantum computing. We give strong evidence that quantum queries to an oracle in the class NP does indeed reduce the query complexity of decision problems. Under traditional complexity assumptions, we obtain an exponential speedup between the quantum and the classical query complexity of function classes. For decision problems and function classes we obtain the following result...

  5. Complex diffusion coatings

    International Nuclear Information System (INIS)

    Modern notions in the field of theory and practice of the obtaining of complex diffusion coatings are presented. Rational procedures carbo-chromizing, chromo-nitridation, chromo-boriding and titaniding to obtain the surfaces with special physicochemical properties for the use under complex conditions of exploitaion are presented. The results of metallographical, physical, chemical, mechanical and other methods of investigation of complex coatings are given. Examples of the application of such coatings and modern equipment for their obtaining are described

  6. Complex Systems and Dependability

    CERN Document Server

    Zamojski, Wojciech; Sugier, Jaroslaw

    2012-01-01

    Typical contemporary complex system is a multifaceted amalgamation of technical, information, organization, software and human (users, administrators and management) resources. Complexity of such a system comes not only from its involved technical and organizational structure but mainly from complexity of information processes that must be implemented in the operational environment (data processing, monitoring, management, etc.). In such case traditional methods of reliability analysis focused mainly on technical level are usually insufficient in performance evaluation and more innovative meth

  7. Quantum Computational Complexity

    OpenAIRE

    Watrous, John

    2008-01-01

    This article surveys quantum computational complexity, with a focus on three fundamental notions: polynomial-time quantum computations, the efficient verification of quantum proofs, and quantum interactive proof systems. Properties of quantum complexity classes based on these notions, such as BQP, QMA, and QIP, are presented. Other topics in quantum complexity, including quantum advice, space-bounded quantum computation, and bounded-depth quantum circuits, are also discussed.

  8. Management of complex fisheries

    DEFF Research Database (Denmark)

    Frost, Hans Staby; Andersen, Peder; Hoff, Ayoe

    2013-01-01

    The purpose of this paper is to demonstrate how fisheries economics management issues or problems can be analyzed by using a complex model based on conventional bioeconomic theory. Complex simulation models contain a number of details that make them suitable for practical management advice, including taking into account the response of the fishermen to implemented management measures. To demonstrate the use of complex management models this paper assesses a number of second best management schem...

  9. Prime discriminant simplicial complex.

    Science.gov (United States)

    Zhang, Junping; Xie, Ziyu; Li, Stan Z

    2013-01-01

    The structure representation of data distribution plays an important role in understanding the underlying mechanism of generating data. In this paper, we propose the prime discriminant simplicial complex (PDSC) by utilizing persistent homology to capture such structures. Assuming that each class is represented with a prime simplicial complex, we classify unlabeled samples based on the nearest projection distances from the samples to the simplicial complexes. We also extend the extrapolation ability of these complexes with a projection constraint term. Experiments in simulated and practical datasets indicate that, compared with several published algorithms, the proposed PDSC approaches achieve promising performance without losing structure representation. PMID:24808213

  10. Interplay of donor-acceptor interactions in stabilizing boron nitride compounds: insights from theory.

    Science.gov (United States)

    Momeni, Mohammad R; Shulman, Lisa; Rivard, Eric; Brown, Alex

    2015-07-01

    The stability of a variety of linear and cyclic (BN)n (n = 1-3) adducts with N-heterocyclic carbene (ImMe2; ImMe2 = [(HCNMe)2C:]), N-heterocyclic olefin (ImMe2CH2) and Wittig (Me3PCH2) donors has been examined using M05-2X/cc-pVTZ computations. The strength and nature of the bonds have been investigated using natural bond orbital (NBO) and atoms-in-molecules (AIM) analyses. Complementary energy decomposition analysis (EDA-NOCV) has been carried out based on BP86/TZ2P computations. In agreement with NBO and AIM analyses, the orbital interaction energy obtained from EDA contributes at least 50% to the total attractive interactions for the carbon-boron bonds indicating their largely covalent nature. The feasibility of isolating monomeric (BN)n units using a donor/acceptor protocol was also investigated in a series of adducts of the general form: LB·(BN)n·BH3 and LB·(BN)n·W(CO)5 (n = 1-3; LB = Lewis bases). Moreover, EDA-NOCV analysis of ImMe2·BN·W(CO)5 and ImMe2·B3N3·W(CO)5 shows that the carbene-boron bonds are stronger in the presence of W(CO)5 as a Lewis acid mainly because of a dramatic decrease in the amount of Pauli repulsion rather than an increase in the electrostatic/orbital attraction terms. PMID:26051266

  11. Urban research and complexity

    OpenAIRE

    Pumain, Denise

    1998-01-01

    This chapter is at first an attempt to identify the sources of complexity in the urban realm. A second step is to present various modelling approaches referring to the new paradigm of complexity, from a review of the literature in urban geography, urban planning and urban economics until 1998.

  12. Individual Communication Complexity

    OpenAIRE

    Buhrman, Harry; Klauck, Hartmut; Vereshchagin, Nikolai; Vitanyi, Paul

    2003-01-01

    We initiate the theory of communication complexity of individual inputs held by the agents, rather than worst-case or average-case. We consider total, partial, and partially correct protocols, one-way versus two-way, with and without help bits. The results are expressed in trems of Kolmogorov complexity.

  13. Introductory complex analysis

    CERN Document Server

    Silverman, Richard A

    1984-01-01

    A shorter version of A. I. Markushevich's masterly three-volume Theory of Functions of a Complex Variable, this edition is appropriate for advanced undergraduate and graduate courses in complex analysis. Numerous worked-out examples and more than 300 problems, some with hints and answers, make it suitable for independent study. 1967 edition.

  14. Conducting metal dithiolate complexes

    DEFF Research Database (Denmark)

    Underhill, A. E.; Ahmad, M. M.; Turner, D. J.; Clemenson, P. I.; Carneiro, K.; Yueqiuan, S.; Mortensen, Kell

    1985-01-01

    Further work on the chemical composition of the one-dimensional metallic metal dithiolene complex Li-Pt(mnt) is reported. The electrical conduction and thermopower properties of the nickel and palladium complexes are reported and compared with those of the platinum compound

  15. Bacterial formate hydrogenlyase complex.

    Science.gov (United States)

    McDowall, Jennifer S; Murphy, Bonnie J; Haumann, Michael; Palmer, Tracy; Armstrong, Fraser A; Sargent, Frank

    2014-09-23

    Under anaerobic conditions, Escherichia coli can carry out a mixed-acid fermentation that ultimately produces molecular hydrogen. The enzyme directly responsible for hydrogen production is the membrane-bound formate hydrogenlyase (FHL) complex, which links formate oxidation to proton reduction and has evolutionary links to Complex I, the NADH:quinone oxidoreductase. Although the genetics, maturation, and some biochemistry of FHL are understood, the protein complex has never been isolated in an intact form to allow biochemical analysis. In this work, genetic tools are reported that allow the facile isolation of FHL in a single chromatographic step. The core complex is shown to comprise HycE (a [NiFe] hydrogenase component termed Hyd-3), FdhF (the molybdenum-dependent formate dehydrogenase-H), and three iron-sulfur proteins: HycB, HycF, and HycG. A proportion of this core complex remains associated with HycC and HycD, which are polytopic integral membrane proteins believed to anchor the core complex to the cytoplasmic side of the membrane. As isolated, the FHL complex retains formate hydrogenlyase activity in vitro. Protein film electrochemistry experiments on Hyd-3 demonstrate that it has a unique ability among [NiFe] hydrogenases to catalyze production of H2 even at high partial pressures of H2. Understanding and harnessing the activity of the FHL complex is critical to advancing future biohydrogen research efforts. PMID:25157147

  16. Leading healthcare in complexity.

    Science.gov (United States)

    Cohn, Jeffrey

    2014-12-01

    Healthcare institutions and providers are in complexity. Networks of interconnections from relationships and technology create conditions in which interdependencies and non-linear dynamics lead to surprising, unpredictable outcomes. Previous effective approaches to leadership, focusing on top-down bureaucratic methods, are no longer effective. Leading in complexity requires leaders to accept the complexity, create an adaptive space in which innovation and creativity can flourish and then integrate the successful practices that emerge into the formal organizational structure. Several methods for doing adaptive space work will be discussed. Readers will be able to contrast traditional leadership approaches with leading in complexity. They will learn new behaviours that are required of complexity leaders, along with challenges they will face, often from other leaders within the organization. PMID:25815410

  17. Real and complex analysis

    CERN Document Server

    Apelian, Christopher

    2009-01-01

    Unlike other undergraduate-level texts, Real and Complex Analysis develops both the real and complex theory together. It takes a unified, elegant approach to the theory that is consistent with the recommendations of the MAA’s 2004 Curriculum Guide. By presenting real and complex analysis together, the authors illustrate the connections and differences between these two branches of analysis right from the beginning. This combined development also allows for a more streamlined approach to real and complex function theory. Enhanced by more than 1,000 exercises, the text covers all the essential topics usually found in separate treatments of real analysis and complex analysis. Ancillary materials are available on the book’s website.

  18. [Complexity: an introduction].

    Science.gov (United States)

    Gómez, Carlos Alberto Palacio; Jaramillo, Francisco Luis Ochoa

    2011-01-01

    Complexity appears in the twentieth century as a way to understand many phenomena that are perceived as chaotic and complex from classical thought, which still persist in our way of explaining the world. Its purpose is to study the complex and adaptive systems that are sensitive to initial conditions. Some of the characteristics of complex thought are systemic perspective, autopoiesis, self-organization, emergent properties, unpredictability of the systems, analogic thought, and the complementarity of the phenomena, among others. Living systems respond to a complex logic, and in that sense, our vision of human populations and patients, and how we try to solve problems and human diseases, should be open to the possibilities that arise from this form of understand the world. PMID:21503430

  19. Low-valent cobalt catalysis: new opportunities for C-H functionalization.

    Science.gov (United States)

    Gao, Ke; Yoshikai, Naohiko

    2014-04-15

    Rapid progress in the fields of organometallic chemistry and homogeneous catalysis has made it possible for synthetic chemists to consider using ubiquitous yet unreactive C-H bonds as starting points to construct complex organic molecules. However, a majority of the C-H functionalization reactions currently in use require noble transition metal catalysts and harsh reaction conditions, so researchers have placed a priority on the development of mild and cost-effective catalysts. Given this situation, we wondered whether earth-abundant first-row transition metals could emulate the reactivity of a noble transition metal catalyst and carry out similar C-H functionalization reactions at a lower cost and under milder conditions. We also wondered whether we could use first-row transition metals to achieve hitherto unknown, but useful, C-H functionalization reactions. This Account summarizes our research on the development of three different types of C-H functionalization reactions using low-valent cobalt catalysts: (1) hydroarylation of alkynes and olefins, (2) ortho C-H functionalization with electrophiles, and (3) addition of arylzinc reagents to alkynes involving 1,4-cobalt migration. Although synthetic chemists have previously paid little attention to cobalt in designing catalytic C-H functionalization reactions, earlier studies, particularly those on stoichiometric cyclometalation, inspired us as we developed the hydroarylation and ortho C-H functionalization reactions. In these transformations, we combined a cobalt precatalyst, a ligand (such as phosphine or N-heterocyclic carbene (NHC)), and Grignard reagent to generate low-valent cobalt catalysts. These novel catalysts promoted a series of pyridine- and imine-directed hydroarylation reactions of alkynes and olefins at mild temperatures. Notably, we observed branched-selective addition to styrenes, which highlights a distinct regioselectivity of the cobalt catalyst compared with typical rhodium and ruthenium catalysts. The combination of a cobalt-NHC catalyst and a Grignard reagent allows directed aromatic C-H functionalizations with electrophiles such as aldimines, aryl chlorides, and alkyl chlorides or bromides. This second reaction has a particularly broad scope, allowing us to introduce secondary alkyl groups at the ortho position of aryl imines, a difficult reaction to carry out by other means. Serendipitously, we found that a cobalt-Xantphos complex catalyzed the third type of C-H functionalization: the addition of an arylzinc reagent to an alkyne to afford ortho-alkenylarylzinc species through a 1,4-cobalt migration. This "migratory arylzincation" allowed us to quickly construct a diverse group of functionalized benzothiophenes and benzoselenophenes. Collectively, our studies of cobalt catalysis have provided cost-effective catalysts and milder conditions for existing C-H functionalizations and have led to some unprecedented, attractive chemical transformations. PMID:24576170

  20. Synchronization in complex dynamical networks coupled with complex chaotic system

    Science.gov (United States)

    Wei, Qiang; Xie, Cheng-Jun; Wang, Bo

    2015-11-01

    This paper investigates synchronization in complex dynamical networks with time delay and perturbation. The node of complex dynamical networks is composed of complex chaotic system. A complex feedback controller is designed to realize different component of complex state variable synchronize up to different scaling complex function when complex dynamical networks realize synchronization. The synchronization scaling function is changed from real field to complex field. Synchronization in complex dynamical networks with constant delay and time-varying coupling delay are investigated, respectively. Numerical simulations show the effectiveness of the proposed method.

  1. Simplicity, complexity and modelling

    CERN Document Server

    Christie, Mike; Dawid, Philip; Senn, Stephen S

    2011-01-01

    Several points of disagreement exist between different modelling traditions as to whether complex models are always better than simpler models, as to how to combine results from different models and how to propagate model uncertainty into forecasts. This book represents the result of collaboration between scientists from many disciplines to show how these conflicts can be resolved. Key Features: Introduces important concepts in modelling, outlining different traditions in the use of simple and complex modelling in statistics. Provides numerous case studies on complex modelling, such as c

  2. Nuclear power complex

    International Nuclear Information System (INIS)

    The current state and trends of development of the nuclear power complex are described on the national scale and within the framework of CMEA. The nuclear power complex is defined as an interbranch system with strong material and information linkages. A detailed analysis is presented of the management system and especially its decision-making stage. The characteristics are described of applied research and of technical and economic research relations. The problems are discussed of research management within a research institute. The management laws are applied to the entire branch and complex and are generalized for international scientific and technical cooperation. (M.D.)

  3. Complexity and sustainability

    CERN Document Server

    Wells, Jennifer

    2012-01-01

    Complex dynamic system studies have been studied explicitly in the natural sciences, and most only implicitly throughout other fields. Yet much great social theory and philosophy is in fact based in complexity, and important concepts like postmodernism, risk, and collapse all stem from complexity. Six key terms are explored: nonlinearity, feedbacks, thresholds, hierarchies, emergence and self-organization, and dozens of related principles are discussed, with a focus on uncertainty, risk, vulnerability, learning, strategy, resilience, collapse and sustainability. The book surveys the role of

  4. Measuring static complexity

    OpenAIRE

    Ben Goertzel

    1992-01-01

    The concept of “pattern” is introduced, formally defined, and used to analyze various measures of the complexity of finite binary sequences and other objects. The standard Kolmogoroff-Chaitin-Solomonoff complexity measure is considered, along with Bennett's ‘logical depth’, Koppel's ‘sophistication'’, and Chaitin's analysis of the complexity of geometric objects. The pattern-theoretic point of view illuminates the shortcomings of these measures and leads to specific improvem...

  5. Managing Complex Projects

    CERN Document Server

    Kerzner, Harold

    2010-01-01

    Discover how you can apply the Kerzner Approach® to successfulLy manage the most challenging and complex projects. Managing complex projects not only takes know-how on the part of project managers, but it also requires that they be willing and able to adapt to change, harness their ability to innovate at a moment's notice, and summon their determination to see a job to completion. This is the book that makes sense out of the complexities that plague today's project managers. It clearly lays out a blueprint to demystify what can be an overwhelming process into manageable strategies that, if cul

  6. Parameterized complexity theory

    CERN Document Server

    Flum, Jorg; Salomaa, Arto

    2006-01-01

    Parameterized complexity theory is a recent branch of computational complexity theory that provides a framework for a refined analysis of hard algorithmic problems. The central notion of the theory, fixed-parameter tractability, has led to the development of various new algorithmic techniques and a whole new theory of intractability. This book is a state-of-the-art introduction into both algorithmic techniques for fixed-parameter tractability and the structural theory of parameterized complexity classes, and it presents detailed proofs of recent advanced results that have not appeared in book

  7. Modelling Complexity in Musical Rhythm

    OpenAIRE

    Liou, Cheng-Yuan; Wu, Tai-Hei; Lee, Chia-Ying

    2007-01-01

    This paper constructs a tree structure for the music rhythm using the L-system. It models the structure as an automata and derives its complexity. It also solves the complexity for the L-system. This complexity can resolve the similarity between trees. This complexity serves as a measure of psychological complexity for rhythms. It resolves the music complexity of various compositions including the Mozart effect K488. Keyword: music perception, psychological complexity, rhy...

  8. Complexity at mesoscopic lengthscale.

    Science.gov (United States)

    Egami, T

    2015-09-01

    Modern materials are often complex in the structure at mesoscale. The method of pair-density function (PDF) is a powerful tool to characterize mesoscopic structure, bridging short- and long-range structures. PMID:26306189

  9. Applications over Complex Lagrangians

    OpenAIRE

    TEKKOYUN, Mehmet; Ozusaglam, Erdal; Gorgulu, Ali

    2009-01-01

    In this paper, Lagrangian formalisms of Classical Mechanics was deduced on Kaehlerian manifold being geometric model of a generalized Lagrange space.Then, it was given two applications of complex Euler-Lagrange equations on mechanics system.

  10. Aluminium complex in coal.

    Czech Academy of Sciences Publication Activity Database

    Straka, Pavel

    2007-01-01

    Ro?. 4, ?. 3 (2007), s. 67-74. ISSN 1214-9705 R&D Projects: GA AV ?R IAA300460702 Institutional research plan: CEZ:AV0Z30460519 Keywords : aluminium * complex * solid-state Subject RIV: DD - Geochemistry

  11. Bitter Sweetness of Complexity

    Science.gov (United States)

    Horst, A. K.; Wagener, C.

    Glycosylation of proteins, lipids and mucins has gained increasing complexity in the course of evolution. Metazoans and mammals exhibit extensively exploited pathways of N-glycan biosynthesis, with unique features that are not found in plants or protozoans.

  12. A complex legacy

    Science.gov (United States)

    Moore, Cristopher

    2011-11-01

    In his tragically short life, Alan Turing helped define what computing machines are capable of, and where they reach inherent limits. His legacy is still felt every day, in areas ranging from computational complexity theory to cryptography and quantum computing.

  13. On scattered subword complexity

    CERN Document Server

    Kása, Zoltán

    2011-01-01

    Special scattered subwords, in which the gaps are of length from a given set, are defined. The scattered subword complexity, which is the number of such scattered subwords, is computed for rainbow words.

  14. Complex Flow Workshop Report

    Energy Technology Data Exchange (ETDEWEB)

    none,

    2012-05-01

    This report documents findings from a workshop on the impacts of complex wind flows in and out of wind turbine environments, the research needs, and the challenges of meteorological and engineering modeling at regional, wind plant, and wind turbine scales.

  15. Multiparty Quantum Communication Complexity

    CERN Document Server

    Van Dam, W; Tapp, A; Dam, Wim van; Hoyer, Peter; Tapp, Alain

    1999-01-01

    Quantum entanglement cannot be used to simulate communication among remote parties, but it can reduce the communication needed for some problems. Let each out of $k$ parties hold some partial input data to some fixed $k$-variable function $f$. The communication complexity of $f$ is the minimum number of classical bits required to be broadcasted for every party to know the value of $f$ on their inputs. We show that, for a particular function $F$, if the parties share prior quantum entanglement, then the communication complexity of $F$ is exactly $k$. On the other hand, we also show that, if no entangled particles are provided, then the classical communication complexity of $F$ is roughly $k \\log_2 k$. In terms of the number of parties, this proves for the first time a communication complexity separation better than a constant number of bits.

  16. Single Neuron Complex Dynamics.

    Czech Academy of Sciences Publication Activity Database

    Andrej, Ladislav

    1996-01-01

    Ro?. 2, ?. 4 (1996). ISSN 1355-8250. [Toward a Science of Consciousness. Tuscon, 00.00.1996] Keywords : non-monotone transfer function * chaotic activity of single neuron * complexity of spikes timing

  17. Radiotherapy Complex for Oncology

    International Science & Technology Center (ISTC)

    Researches at a Choice and Substantiation of Basic Physical and Technical Parameters as well as Basic Decisions of Experimental Therapeutic Complex with New Ecologically Safe Sources of Gamma Radiation Intending to Increase an Efficiency of Brachytherapy in Oncology

  18. Interaction of Triapine and related thiosemicarbazones with iron(III)/(II) and gallium(III): a comparative solution equilibrium study†

    OpenAIRE

    Enyedy, Éva A.; Primik, Michael F.; Kowol, Christian R.; Arion, Vladimir B.; Kiss, Tamás; Keppler, Bernhard K.

    2011-01-01

    Stoichiometry and stability of GaIII, FeIII, FeII complexes of Triapine and five related ?-N heterocyclic thiosemicarbazones with potential antitumor activity have been determined by pH-potentiometry, UV-vis spectrophotometry, 1H NMR spectroscopy, and spectrofluorimetry in aqueous solution (with 30% DMSO), together with the characterization of the proton dissociation processes. Additionally, the redox properties of the iron complexes were studied by cyclic voltammetry at various pH values. Fo...

  19. Models complexity measurement

    OpenAIRE

    Rezaei, Hengameh

    2011-01-01

    The demand for measuring the quality aspects and need for higher maintainability and understandability of the models are increasing within the field of software engineering and management. Among these, complex models are of special interest for designers as they are more correlated to the eventual reliability of the system and therefore are considered very important. This study presents a method for measuring the complexity of existing software models in Ericsson seeking to raise the maintain...

  20. A complexity reliability model.

    OpenAIRE

    Norman SCHNEIDEWIND; Hinchey, Mike

    2009-01-01

    A model of software complexity and reliability is developed. It uses an evolutionary process to transition from one software system to the next, while complexity metrics are used to predict the reliability for each system. Our approach is experimental, using data pertinent to the NASA satellite systems application environment. We do not use sophisticated mathematical models that may have little relevance for the application environment. Rather, we tailor our approach to the software ...

  1. Complex Systems: A Survey

    OpenAIRE

    Newman, M. E. J.

    2011-01-01

    A complex system is a system composed of many interacting parts, often called agents, which displays collective behavior that does not follow trivially from the behaviors of the individual parts. Examples include condensed matter systems, ecosystems, stock markets and economies, biological evolution, and indeed the whole of human society. Substantial progress has been made in the quantitative understanding of complex systems, particularly since the 1980s, using a combination...

  2. Synchronization in complex networks

    OpenAIRE

    Arenas, Alex; Diaz-Guilera, Albert; Kurths, Jurgen; Moreno, Yamir; Zhou, Changsong

    2008-01-01

    Synchronization processes in populations of locally interacting elements are in the focus of intense research in physical, biological, chemical, technological and social systems. The many efforts devoted to understand synchronization phenomena in natural systems take now advantage of the recent theory of complex networks. In this review, we report the advances in the comprehension of synchronization phenomena when oscillating elements are constrained to interact in a complex...

  3. Advances in network complexity

    CERN Document Server

    Dehmer, Matthias; Emmert-Streib, Frank

    2013-01-01

    A well-balanced overview of mathematical approaches to describe complex systems, ranging from chemical reactions to gene regulation networks, from ecological systems to examples from social sciences. Matthias Dehmer and Abbe Mowshowitz, a well-known pioneer in the field, co-edit this volume and are careful to include not only classical but also non-classical approaches so as to ensure topicality. Overall, a valuable addition to the literature and a must-have for anyone dealing with complex systems.

  4. Complex logistics audit system

    Directory of Open Access Journals (Sweden)

    Zuzana Marková

    2010-02-01

    Full Text Available Complex logistics audit system is a tool for realization of logistical audit in the company. The current methods for logistics auditare based on “ad hok” analysis of logisticsl system. This paper describes system for complex logistics audit. It is a global diagnosticsof logistics processes and functions of enterprise. The goal of logistics audit is to provide comparative documentation for managementabout state of logistics in company and to show the potential of logistics changes in order to achieve more effective companyperformance.

  5. Conversation, coupling and complexity

    DEFF Research Database (Denmark)

    Fusaroli, Riccardo; Abney, Drew; Bahrami, Bahador; Kello, Chris; Tylén, Kristian

    2013-01-01

    We investigate the linguistic co-construction of interpersonal synergies. By applying a measure of coupling between complex systems to an experimentally elicited corpus of joint decision dialogues, we show that interlocutors’ linguistic behavior displays increasing signature of multi-scale coupling, known as complexity matching, over the course of interaction. Furthermore, we show that stronger coupling corresponds with more effective interaction, as measured by collective task performance.

  6. Complex Strategic Choices

    DEFF Research Database (Denmark)

    Leleur, Steen

    2012-01-01

    Effective decision making requires a clear methodology, particularly in a complex world of globalisation. Institutions and companies in all disciplines and sectors are faced with increasingly multi-faceted areas of uncertainty which cannot always be effectively handled by traditional strategies. Complex Strategic Choices provides clear principles and methods which can guide and support strategic decision making to face the many current challenges. By considering ways in which planning practices ...

  7. Algorithmic Relative Complexity

    OpenAIRE

    Daniele Cerra; Mihai Datcu

    2011-01-01

    Information content and compression are tightly related concepts that can be addressed through both classical and algorithmic information theories, on the basis of Shannon entropy and Kolmogorov complexity, respectively. The definition of several entities in Kolmogorov’s framework relies upon ideas from classical information theory, and these two approaches share many common traits. In this work, we expand the relations between these two frameworks by introducing algorithmic cross-complexity ...

  8. Carney complex and lentiginosis

    OpenAIRE

    Horvath, Anelia; Stratakis, Constantine A,

    2009-01-01

    Initially described as the ‘complex of myxomas, spotty skin pigmentation and endocrine overactivity,’ Carney complex (CNC) is known as an autosomal dominant multiple neoplasia syndrome involving skin and cardiac myxomas, pigmented skin lesions and endocrine tumors. Pigmented cutaneous manifestations in CNC are important diagnostically because they can be used for the early detection of the disease and, thus, the prevention of life-threatening complications of CNC related to heart myxomas and ...

  9. Multivariate multiscale complexity analysis

    OpenAIRE

    Ahmed, Mosabber Uddin

    2012-01-01

    Established dynamical complexity analysis measures operate at a single scale and thus fail to quantify inherent long-range correlations in real world data, a key feature of complex systems. They are designed for scalar time series, however, multivariate observations are common in modern real world scenarios and their simultaneous analysis is a prerequisite for the understanding of the underlying signal generating model. To that end, this thesis first introduces a notion of mult...

  10. Synthesis, Structure, and Reactivity ofbis(1,2,4-tri-t-butylcyclopentadienyl) Complexes of Cerium

    Energy Technology Data Exchange (ETDEWEB)

    Werkema, Evan L.

    2005-05-19

    The sterically demanding 1,2,4-tri-t-butylcyclopentadienylligand (1,2,4-(Me3C)3C5H2, hereafter Cp') has been used to preparemonomeric cerium metallocenes, Cp 2CeX (X = Cl, I, OSO2CF3), which areused to synthesize the benzyl, Cp'2CeCH2C6H5. The benzyl is a usefulstarting material for preparing other complexes in the Cp'2CeZ system (Z= BF4, F, NH2, C6H5, H). X-ray crystal structures of Cp'2CeOSO2CF3,Cp'2CeF, Cp'2CeCH2C6H5, and Cp'2CeH are presented. The benzyl slowlydecomposes in solution to toluene and a metallacycle,[Cp'][(Me3C)2C5H2(CMe2CH2)]Ce. The ring CMe3 groups of both themetallacycle and the hydride, Cp'2CeH, can be fully deuterated byprolonged exposure to C6D6, providing a useful labeling tool inmechanistic studies.The hydride activates C-F and/or C-H bonds influorobenzenes, C6HxF6-x , x = 0-5. The reactions are selective, with theselectivity depending on the presence of two fluorines ortho to thereaction site more than on the type of bond activated. Complexes of thetype Cp'2CeC6HxF5-x , x = 0-4, are formed as intermediates, which slowlydecompose in solution to Cp'2CeF and fluorobenzynes, C6HxF4-x, x = 0-4,which are trapped. The rate at which Cp'2CeC6HxF5-x complexes decomposeincreases as the number of fluorines decreases. Complexes with oneortho-fluorine decompose much faster than those with two ortho-fluorines.The metallacycle activates only C-H bonds in fluorobenzenes, permittingthe synthesis of specific Cp'2CeC6HxF5-x complexes. The crystal structureof Cp'2CeC6F5 is presented. The hydride and the metallacycle react withfluoromethanes, CH4-xFx, x = 1-3, through postulated Cp'2CeCH3-xFxintermediates to generate Cp'2CeF and other products. The other products,CH4, tri-t-butylbenzenes, tri-t-butylfluorobenzenes, and a presumedmetallocene cerium fluoride with one Cp' and one (Me2EtC)(Me3C)2C5H2ligand, suggest a decomposition pathway for Cp'2CeCH3-xFx , x = 1-3, thatinvolves carbenes or carbenoids, which are trapped. The hydridepolymerizes ethylene, but hydrogenates other olefins. The metallacycleactivates C-H bonds in olefins and aromatics to generate new complexeswith Ce-C bonds. The hydride reacts with one equivalent of CO in pentaneto generate (Cp'2Ce)2CH2O, whose crystal structure shows the presence ofa bridging dianionic formaldehyde ligand. (Cp'2Ce)2CH2O reacts H2 to givethe hydride and Cp'2CeOMe, or with a mixture of H2 and CO to generateCp'2CeOMe exclusively. (Cp'2Ce)2CH2O or the hydride can react with anadditional equivalent of CO to generate dimeric enediolate,(Cp'2CeCHO)2.

  11. Nickel Catalysis: Synergy between Method Development and Total Synthesis.

    Science.gov (United States)

    Standley, Eric A; Tasker, Sarah Z; Jensen, Kim L; Jamison, Timothy F

    2015-05-19

    Nickel(0) catalysts have proven to be powerful tools for multicomponent coupling reactions in our laboratories over the past 15 years. This interest was originally sparked by the ubiquity of allylic alcohol motifs in natural products, such as (-)-terpestacin, which we envisioned assembling by the coupling of two ? components (alkyne and aldehyde) with concomitant reduction. Mechanistic investigations allowed us to elucidate several modes of controlling the regioselectivity and stereoselectivity in the oxidative cyclization, and these insights enabled us to leverage combinations of alkenes and phosphine ligands to direct regioselective outcomes. The initial success in developing the first intermolecular reductive alkyne-aldehyde coupling reaction launched a series of methodological investigations that rapidly expanded to include coupling reactions of alkynes with other electrophilic ? components, such as imines and ketones, as well as electrophilic ? components, such as epoxides. Aziridines proved to be more challenging substrates for reductive coupling, but we were recently able to demonstrate that cross-coupling of aziridines and alkylzinc reagents is smoothly catalyzed by a zero-valent nickel/phenanthroline system. Moreover, the enantioselective alkyne-aldehyde coupling and the development of novel P-chiral ferrocenyl ligands enabled the total synthesis of (-)-terpestacin, amphidinolides T1 and T4, (-)-gloeosporone, and pumiliotoxins 209F and 251D. We subsequently determined that alkenes could be used in place of alkynes in several nickel-catalyzed reactions when a silyl triflate activating agent was added. We reason that such an additive functions largely to enhance the electrophilicity of the metal center by coordination to the electrophilic ? component, such that less nucleophilic alkene ? donors can undergo productive combination with nickel complexes. This activation manifold was further demonstrated to be effective for alkene-aldehyde couplings. In a related manner, electrophilic promoters were also successfully employed for allylic substitution reactions of allylic carbonates with simple alkenes and in the Mizoroki-Heck reaction of both benzyl and aryl electrophiles. In these instances, it is proposed that counterion exchange from a more strongly coordinating anion to the weakly or noncoordinating triflate counterion enables reaction at an electrophilic Ni(II) center rather than by coordination to one of the coupling components. Mechanistic insights also played an important role in the development of mixed N-heterocyclic carbene/phosphite ligand systems to overcome challenges in regioselective alkene-aldehyde coupling reactions. We hope that, taken together, the body of work summarized in this Account demonstrates the constructive interplay among total synthesis, methodological development, and mechanistic investigation that has driven our research program. PMID:25905431

  12. Controllability of Complex Networks

    Science.gov (United States)

    Liu, Yang; Slotine, Jean-Jacques; Barabasi, Albert-Laszlo

    2011-03-01

    The ultimate proof of our understanding of natural or technological systems is reflected in our ability to control them. While control theory offers mathematical tools to steer engineered systems towards a desired state, we lack a general framework to control complex self-organized systems, like the regulatory network of a cell or the Internet. Here we develop analytical tools to study the controllability of an arbitrary complex directed network, identifying the set of driver nodes whose time-dependent control can guide the system's dynamics. We apply these tools to real and model networks, finding that sparse inhomogeneous networks, which emerge in many real complex systems, are the most difficult to control. In contrast, dense and homogeneous networks can be controlled via a few driver nodes. Counterintuitively, we find that in both model and real systems the driver nodes tend to avoid the hubs. We show that the robustness of control to link failure is determined by a core percolation problem, helping us understand why many complex systems are relatively insensitive to link deletion. The developed approach offers a framework to address the controllability of an arbitrary network, representing a key step towards the eventual control of complex systems.

  13. Algorithmic Relative Complexity

    Directory of Open Access Journals (Sweden)

    Daniele Cerra

    2011-04-01

    Full Text Available Information content and compression are tightly related concepts that can be addressed through both classical and algorithmic information theories, on the basis of Shannon entropy and Kolmogorov complexity, respectively. The definition of several entities in Kolmogorov’s framework relies upon ideas from classical information theory, and these two approaches share many common traits. In this work, we expand the relations between these two frameworks by introducing algorithmic cross-complexity and relative complexity, counterparts of the cross-entropy and relative entropy (or Kullback-Leibler divergence found in Shannon’s framework. We define the cross-complexity of an object x with respect to another object y as the amount of computational resources needed to specify x in terms of y, and the complexity of x related to y as the compression power which is lost when adopting such a description for x, compared to the shortest representation of x. Properties of analogous quantities in classical information theory hold for these new concepts. As these notions are incomputable, a suitable approximation based upon data compression is derived to enable the application to real data, yielding a divergence measure applicable to any pair of strings. Example applications are outlined, involving authorship attribution and satellite image classification, as well as a comparison to similar established techniques.

  14. Complexity of Networks

    CERN Document Server

    Standish, R K

    2005-01-01

    Network or graph structures are ubiquitous in the study of complex systems. Often, we are interested in complexity trends of these system as it evolves under some dynamic. An example might be looking at the complexity of a food web as species enter an ecosystem via migration or speciation, and leave via extinction. In this paper, a complexity measure of networks is proposed based on the {\\em complexity is information content} paradigm. To apply this paradigm to any object, one must fix two things: a representation language, in which strings of symbols from some alphabet describe, or stand for the objects being considered; and a means of determining when two such descriptions refer to the same object. With these two things set, the information content of an object can be computed in principle from the number of equivalent descriptions describing a particular object. I propose a simple representation language for undirected graphs that can be encoded as a bitstring, and equivalence is a topological equivalence....

  15. Complexity: The bigger picture

    CERN Document Server

    Vicsek, Tamás

    2010-01-01

    If a concept is not well defined, there are grounds for its abuse. This is particularly true of complexity, an inherently interdisciplinary concept that has penetrated very different fields of intellectual activity from physics to linguistics, but with no underlying, unified theory. Complexity has become a popular buzzword used in the hope of gaining attention or funding -- institutes and research networks associated with complex systems grow like mushrooms. Why and how did it happen that this vague notion has become a central motif in modern science? Is it only a fashion, a kind of sociological phenomenon, or is it a sign of a changing paradigm of our perception of the laws of nature and of the approaches required to understand them? Because virtually every real system is inherently extremely complicated, to say that a system is complex is almost an empty statement - couldn't an Institute of Complex Systems just as well be called an Institute for Almost Everything? Despite these valid concerns, the world is ...

  16. Complexity, time and music

    CERN Document Server

    Boon, Jean Pierre

    2009-01-01

    The concept of complexity as considered in terms of its algorithmic definition proposed by G.J. Chaitin and A.N. Kolmogorov is revisited for the dynamical complexity of music. When music pieces are cast in the form of time series of pitch variations, concepts of dynamical systems theory can be used to define new quantities such as the {\\em dimensionality} as a measure of the {\\em global temporal dynamics} of a music piece, and the Shanon {\\em entropy} as an evaluation of its {\\em local dynamics}. When these quantities are computed explicitly for sequences sampled in the music literature from the 18th to the 20th century, no indication is found of a systematic increase in complexity paralleling historically the evolution of classical western music, but the analysis suggests that the fractional nature of art might have an intrinsic value of more general significance.

  17. Complex Systems: A Survey

    CERN Document Server

    Newman, M E J

    2011-01-01

    A complex system is a system composed of many interacting parts, often called agents, which displays collective behavior that does not follow trivially from the behaviors of the individual parts. Examples include condensed matter systems, ecosystems, stock markets and economies, biological evolution, and indeed the whole of human society. Substantial progress has been made in the quantitative understanding of complex systems, particularly since the 1980s, using a combination of basic theory, much of it derived from physics, and computer simulation. The subject is a broad one, drawing on techniques and ideas from a wide range of areas. Here I give a survey of the main themes and methods of complex systems science and an annotated bibliography of resources, ranging from classic papers to recent books and reviews.

  18. Emergent Complex Network Geometry

    CERN Document Server

    Wu, Zhihao; Rahmede, Christoph; Bianconi, Ginestra

    2014-01-01

    Networks are mathematical structures that are universally used to describe a large variety of complex systems such as the brain or the Internet. Characterizing the geometrical properties of these networks has become increasingly relevant for routing problems, inference and data mining. In real growing networks, topological, structural and geometrical properties emerge spontaneously from their dynamical rules. Nevertheless we still miss a model in which networks develop an emergent complex geometry. Here we show that a single two parameter network model, the growing geometrical network, can generate complex network geometries with non-trivial distribution of curvatures, combining exponential growth and small-world properties with finite spectral dimensionality. In one limit, the non-equilibrium dynamical rules of these networks can generate scale-free networks with clustering and communities, in another limit planar random geometries with non-trivial modularity. Finally we find that these properties of the geo...

  19. Complex Aperture Networks

    CERN Document Server

    Owladeghaffari, Hamed

    2009-01-01

    A complex network approach on a rough fracture is developed. In this manner, some hidden metric spaces (similarity measurements) between apertures profiles are set up and a general evolutionary network in two directions (in parallel and perpendicular to the shear direction) is constructed. Evaluation of the emerged network shows the connectivity degree (distribution) of network, after a transition step; fall in to the stable states which are coincided with the Gaussian distribution. Based on this event and real observations of the complex network changes, an algorithm (COmplex Networks on Apertures: CONA) is proposed in which evolving of a network is accomplished using preferential detachments and attachments of edges (based on a competition and game manner) while the number of nodes is fixed. Also, evolving of clustering coefficients and number of edges display similar patterns as well as are appeared in shear stress, hydraulic conductivity and dilation changes, which can be engaged to estimate shear strengt...

  20. Thiosemicarbazone complexes of technetium

    International Nuclear Information System (INIS)

    One aproach to the design of new sup(99m)Tc-radiopharmaceuticals consists in the preparation of bifunctional radio-pharmaceuticals [1]. In this approach, a bifunctional molecule is synthesized which possesses a chelating functional group (capable of forming a stable complex with sup(99m)Tc) attached to a second functional group which is expected to have a useful biological distribution. Thiosemicarbazones are compounds that possess great chelating capacity [2] and are easily obtainable by condensation of the theosemicarbazide (H2N-NH-CS-NH2) or substituted thiosemicarbazide with the carbonyl groups of aldehydes or ketones. Consequently transformation of molecules of biological interest that the carbonyl group possess in thiosemicarbazones is simple and these modified molecules could act a bifunctional radiopharmaceuticals. For this reason a series of thiosemicarbazone complexes of 99Tc was prepared. This is the first report on technetium complexes with thiosemicarbazones. (orig.)