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Sample records for n-heterocyclic carbene complexes

  1. Nickel N-heterocyclic carbene complexes in homogeneous catalysis

    Berding, Joris

    2009-01-01

    Described in this thesis are the investigations into the chemistry of N-heterocyclic carbene (NHC) ligands and transition-metal complexes thereof. Specifically, a variety of N-heterocyclic carbene complexes of nickel were prepared, characterized and used as catalysts in three types of homogeneous catalytic processes. First, nickel(II) complexes of monodentate NHC ligands were successfully used as catalysts in the hydrosilylation of internal alkynes. Second, nickel(II) complexes bearing bident...

  2. Synthesis and antimicrobial studies of silver N-heterocyclic carbene complexes bearing a methyl benzoate substituent

    Knapp, Amanda R.; Panzner, Matthew J.; Medvetz, Doug A.; Wright, Brian D.; Tessier, Claire A.; Wiley J. Youngs

    2010-01-01

    Due to the properties of silver as an antimicrobial, our research group has synthesized many different silver carbene complexes. Two new silver N-heterocyclic carbene complexes derived from 4,5-dichloroimidazole and theobromine bearing methyl benzoate substituents were synthesized by in situ carbene formation using silver acetate as the base in the reaction. The new compounds were fully characterized by several methods including NMR spectroscopy and X-ray crystallography. Preliminary antimicr...

  3. N-Heterocyclic carbenes as supporting ligands in transition metal complexes of N2.

    Ohki, Yasuhiro; Seino, Hidetake

    2016-01-01

    Recent developments have substantially expanded the scope of N-heterocyclic carbenes (NHCs) as ancillary ligands in coordination chemistry and homogeneous catalysis. This review provides a short overview of the emerging field of NHC-supported transition metal complexes of N2 and the possibilities to catalytically activate N2 in these complexes. PMID:26646731

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

    Dam, Johan Hygum; Osztrovszky, Gyorgyi; Nordstrøm, Lars Ulrik Rubæk; Madsen, Robert

    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...

  5. Gold (I) N-heterocyclic carbene complex inhibits mouse melanoma growth by p53 upregulation

    Nandy, Abhishek; Dey, Sumit Kumar; Das, Sujata; Munda, Rudra Narayan; Dinda, Joydev; Saha, Krishna Das

    2014-01-01

    Background Cancer treatment using gold (I) complexes is becoming popular. In this study, a gold (I) N-heterocyclic complex designated as complex 3 was synthesized, its cytotoxicity was examined, and its anti-melanoma activity was evaluated in vitro and in vivo. Methods Viability of cancer cells was determined by MTT assay upon treatment with various concentrations of a gold (I) N-heterocyclic carbene complex (complex 3) in a dose and time dependent manner. Mouse melanoma cells B16F10 were sel...

  6. Antimicrobial Studies of N-Heterocyclic Carbene Silver Complexes Containing Benzimidazol-2-ylidene Ligand

    Yetkin Gök; Yakup Sarı; Senem Akkoç; İlknur Özdemir; Selami Günal

    2014-01-01

    Seven novel 4-vinylbenzyl substituted N-heterocyclic carbene (NHC) silver complexes were synthesized from different benzimidazolium salts and silver (I) oxide in dichloromethane at room temperature. These new 4-vinylbenzyl substituted NHC silver complexes were characterized by spectroscopic (NMR, IR) and elemental analysis techniques. Using the agar dilution procedure, the antimicrobial activities of these synthesized new compounds were investigated against Gram (+)/(−) bacterial and fungal s...

  7. Synthesis and Properties of Chelating N-Heterocyclic Carbene Rhodium(I) Complexes: Synthetic Experiments in Current Organometallic Chemistry

    Mata, Jose A.; Poyatos, Macarena; Mas-Marza, Elena

    2011-01-01

    The preparation and characterization of two air-stable Rh(I) complexes bearing a chelating N-heterocyclic carbene (NHC) ligand is described. The synthesis involves the preparation of a Ag(I)-NHC complex and its use as carbene transfer agent to a Rh(I) precursor. The so obtained complex can be further reacted with carbon monoxide to give the…

  8. Bis-ligated Ti and Zr complexes of chelating N-heterocyclic carbenes

    El-Batta, Amer

    2011-07-01

    In this communication we report the synthesis of novel titanium and zirconium complexes ligated by bidentate "salicylaldimine-like" N-heterocyclic carbenes (NHC). Double addition of the NHC chelate to either TiCl4(thf)2 or ZrCl4 forms bis-ligated organometallic fragments with a distorted octahedral geometry. These complexes are rare examples of group IV transition-metal NHC adducts. Preliminary catalytic tests demonstrate that in the presence of methylaluminoxane (MAO) these complexes are useful initiators for the polymerization of ethylene and the copolymerization of ethylene with norbornene and 1-octene. © 2011 Elsevier B.V. All rights reserved.

  9. Hydroxo-rhodium-N-heterocyclic carbene complexes as efficient catalyst precursors for alkyne hydrothiolation

    Palacios, Laura; Artigas, Maria Jose; Polo, Víctor; FERNANDO J LAHOZ; Castarlenas, Ricardo; Pérez-Torrente, Jesús J.; LUIS A ORO

    2013-01-01

    The new Rh-hydroxo dinuclear complexes stabilized by an N-heterocyclic carbene (NHC) ligand of type [Rh(μ-OH)(NHC)(η2-olefin)] 2 (coe, IPr (3), IMes (4); ethylene, IPr (5)) are efficient catalyst precursors for alkyne hydrothiolation under mild conditions, presenting high selectivity toward α-vinyl sulfides for a varied set of substrates, which is enhanced by pyridine addition. The structure of complex 3 has been determined by X-ray diffraction analysis. Several intermediates relevant for the...

  10. Ruthenium(II) complexes of N-heterocyclic carbenes derived from imidazolium-linked cyclophanes.

    Caramori, Giovanni F; Garcia, Leone C; Andrada, Diego M; Frenking, Gernot

    2014-10-21

    The present work seeks to characterize, in the light of electronic structure calculations, an unusual metal-[(η(1)-NHC)2:(η(6)-arene)] bonding situation in a set of ruthenium(ii) complexes containing the ortho-xylylene-linked-bis(NHC)cyclophane ligand (NHC-cyclophane) (), which binds to the ruthenium center through two carbene carbons and one of the arene rings. The nature of ruthenium(ii)-[(η(1)-NHC)2:(η(6)-arene)] bonding was investigated in the light of EDA-NOCV, NBO and QTAIM analyses by adopting as a model compound. The interplay between the ortho-cyclophane scaffold with different families of five-membered carbenes, such as imidazole, , triazole-based NHCs (Enders' carbenes), , and P-heterocyclic carbenes (PHCs), , was investigated. The metal-[(η(1)-NHC)2:(η(6)-arene)] bonding situation was also extended to heavier analogues, such as N-heterocyclic silylenes (NHSi) and N-heterocyclic germylenes (NHGe), in order to address how the basicity of NHC, NHSi and NHGe is affected by the cyclophane framework. The results reveal that ruthenium(ii)-[(η(1)-NHC)2:(η(6)-arene)] is more covalently than electrostatically bonded and that the degree of covalence is larger in PHCs than in NHCs or Enders' carbenes. It is also revealed that the covalent character in the ruthenium(ii)-[(η(1)-NHGe)2:(η(6)-arene)] and ruthenium(ii)-[(η(1)-NHSi)2:(η(6)-arene)] bonds is larger than in ruthenium(ii)-[(η(1)-NHC)2:(η(6)-arene)]. PMID:25144142

  11. Synthesis of Complexes with Abnormal "Protic" N-Heterocyclic Carbenes.

    Jin, Hanpeng; Tan, Tristan Tsai Yuan; Hahn, F Ekkehardt

    2015-11-01

    Neutral 4-iodo-N-ethylimidazole 3 oxidatively adds to [Pt(PPh3)4] to give, in the presence of different tetraalkylammonium salts, complexes trans-[4], trans-[5], and trans-[6] containing an anionic C4-bound heterocycle with an unsubstituted ring-nitrogen atom. Complex trans-[4] reacts with the proton source NH4 I under protonation of the ring-nitrogen atom to produce complex trans-[7]I which bears an NH,NR-substituted aNHC ligand. The reaction of trans-[4] with CH3I yields the complex trans-[8]I which has a classical aNHC ligand with two alkylated ring-nitrogen atoms. PMID:26403225

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

    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.

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

    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 a...

  14. Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

    Zong Guan

    2014-04-01

    Full Text Available Deprotonation of indazolium salts at low temperatures gives N-heterocyclic carbenes of indazoles (indazol-3-ylidenes which can be trapped as rhodium complexes (X-ray analysis. In the absence of Rh, the indazol-3-ylidenes spontaneously dimerize under ring cleavage of one of the N,N-bonds and ring closure to an indazoleindole spiro compound which possesses an exocyclic imine group. The E/Z isomers of the imines can be separated by column chromatography when methanol is used as eluent. We present results of a single crystal X-ray analysis of one of the E-isomers, which equilibrate in solution as well as in the solid state. Heating of the indazoleindole spiro compounds results in the formation of quinazolines by a ring-cleavage/ring-closure sequence (X-ray analysis. Results of DFT calculations are presented.

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

    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

  16. An overview of N-heterocyclic carbenes

    Hopkinson, Matthew N.; Richter, Christian; Schedler, Michael; Glorius, Frank

    2014-06-01

    The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chemistry, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.

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

    Chandrakanta Dash; Mobin M Shaikh; Prasenjit Ghosh

    2011-03-01

    Two silver(I) complexes {[1-R-4-(-t4-butylacetamido)-1,2,4-triazol-5-ylidene]2Ag}+ Cl− [R = Et (1b), -Pr (2b)] of /-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 /-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 --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.

  18. Preparation of a N-Heterocyclic Carbene Nickel(II) Complex: Synthetic Experiments in Current Organic and Organometallic Chemistry

    Ritleng, Vincent; Brenner, Eric; Chetcuti, Michael J.

    2008-01-01

    A four-part experiment that leads to the synthesis of a cyclopentadienyl chloro-nickel(II) complex bearing a N-heterocyclic carbene (NHC) ligand is presented. In the first part, the preparation of 1,3-bis-(2,4,6-trimethylphenyl)imidazolium chloride (IMes[middle dot]HCl) in a one-pot procedure by reaction of 2,4,6-trimethylaniline with…

  19. Antimicrobial Properties of Some Bis(Iminoacenaphthene (BIAN)-Supported N-Heterocyclic Carbene Complexes of Silver and Gold

    Butorac, Rachel R; Alan H. Cowley; Al-Deyab, Salem S.

    2011-01-01

    The AgCl, AgOAc, AuCl, and AuOAc complexes of the new bis(imino)acenaphthene(BIAN)-supported N-heterocyclic carbene ligand and the precursor imidazolium salt have been investigated with respect to their antimicrobial activities against Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Psudomonas aeruginosa. The most active antimicrobial is the precursor imidazolium salt, which has a minimum inhibitory concentration (MIC) value of

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

    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.

  1. Lipophilicity-dependent ruthenium N-heterocyclic carbene complexes as potential anticancer agents.

    Lv, Gaochao; Guo, Liubin; Qiu, Ling; Yang, Hui; Wang, Tengfei; Liu, Hong; Lin, Jianguo

    2015-04-28

    Five Ru(II)-N-heterocyclic carbenes (NHC) (1-5) were synthesized by reacting the appropriately substituted imidazolium chlorides with Ag2O, forming the NHC-silver chloride in situ followed by transmetalation with dimeric p-cymene ruthenium(II) dichloride. All the complexes were characterized by NMR and ESI-MS, and complex 1 was also characterized by single-crystal X-ray diffraction. The IC50 values of these five complexes were determined by the MTT-based assay on four human cancer cell lines, SKOV-3 (ovarian), PC-3 (prostate), MDA-MB-231 (breast) and EC109 (esophagus). The cytotoxicities of these complexes changed from a moderate effect to a fine one, corresponding to the increasing lipophilicity order of the complex of 2 < 1 < 3 < 4 < 5 (0.91, 0.88, 1.36, 1.85 and 2.62 for 15 respectively). Complex 5 showed the most cytotoxicity with the IC50 values 10.3 0.3 ?M for SKOV-3, 2.9 0.1 ?M for PC-3, 8.2 0.6 ?M for MDA-MB-231, 6.4 0.2 ?M for EC109 cell lines. Due to the superior cytotoxicity of complex 5 against the PC-3 cell lines, further biological evaluations were carried out to elucidate its action mechanism. The morphologic changes and cell cycle analysis showed that complex 5 can inhibit PC-3 cell lines by inducing cell cycle arrest at the G2/M phase. The DNA binding experiments further demonstrate that complex 5 has a better binding ability for DNA (Kb = 2.2 10(6) M(-1)) than complexes 1-4 (3.8 10(5), 7.0 10(5), 5.7 10(5), and 1.9 10(5) respectively). PMID:25797411

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

    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

  3. Synthesis, characterization and antimicrobial activities of novel silver(I) complexes with coumarin substituted N-heterocyclic carbene ligands.

    Karata?, Mert Olgun; Olgundeniz, Begm; Gnal, Selami; zdemir, ?lknur; Al?c?, Blent; etinkaya, Engin

    2016-02-15

    Eight new coumarin substituted silver(I) N-heterocyclic carbene (NHC) complexes were synthesized by the interaction of the corresponding imidazolium or benzimidazolium chlorides and Ag2O in dichloromethane at room temperature. Structures of these complexes were established on the basis of elemental analysis, (1)H NMR, (13)C NMR, IR and mass spectroscopic techniques. The antimicrobial activities of carbene precursors and silver NHC complexes were tested against standard strains: Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and the fungi Candida albicans and Candida tropicalis. Results showed that all the compounds inhibited the growth of the all bacteria and fungi strains and some complexes performed good activities against different microorganisms. Among all the compounds, the most lipophilic complex bis[1-(4-methylene-6,8-dimethyl-2H-chromen-2-one)-3-(naphthalene-2-ylmethyl)benzimidazol-2-ylidene]silver(I) dichloro argentate (5e) was found out as the most active one. PMID:26740157

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

    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.

  5. Efficient Negishi coupling reactions of aryl chlorides catalyzed by binuclear and mononuclear nickel-N-heterocyclic carbene complexes.

    Xi, Zhenxing; Zhou, Yongbo; Chen, Wanzhi

    2008-11-01

    We describe the first nickel-N-heterocyclic carbene catalyzed Negishi cross-coupling reaction of a variety of unactivated aryl chlorides, heterocyclic chlorides, aryl dichlorides, and vinyl chloride. The mononuclear and binuclear nickel-NHC complexes supported by heteroarene-functionalized NHC ligands are found to be highly efficient for the coupling of unactivated aryl chlorides and organozinc reagents, leading to biaryls and terphenyls in good to excellent yields under mild conditions. For all aryl chlorides, the binuclear nickel catalysts show activities higher than those of mononuclear nickel complexes because of possible bimetallic cooperative effect. PMID:18841915

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

    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.

  7. Polymer-supported N-heterocyclic carbene-palladium complex for heterogeneous Suzuki cross-coupling reaction.

    Kim, Jong-Ho; Kim, Jung-Woo; Shokouhimehr, Mohammadreza; Lee, Yoon-Sik

    2005-08-19

    Poly(1-methylimidazoliummethyl styrene)-surface grafted-poly(styrene) resin was prepared for the first time as a polymer-supported N-heterocyclic carbene (NHC) precursor for palladium complex by suspension polymerization. To prepare this polymer-supported NHC precursor, 1-methyl-3-(4-vinylbenzyl)imidazolium hexafluorophosphate, [MVBIM][PF6-], was synthesized as a monomer and copolymerized with styrene and DVB in water. This polymer-supported NHC precursor with imidazolium as a ligand, which exists solely on the surface of the resin, was well characterized by FE-SEM, CLSM, and IR spectroscopy. The precursor containing imidazolium readily formed a stable complex with Pd(OAc)2, and this polymer-supported N-heterocyclic carbene-palladium complex exhibited excellent catalytic activity for Suzuki cross-coupling reaction in an aqueous medium. The catalyst was recovered quantitatively from the reaction mixture by simple filtration and was able to be reused for a number of recycles with consistent activity in all of the coupling reactions. PMID:16095291

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

    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 /-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.

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

    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.

  10. Cationic rhenium complexes ligated with N-heterocyclic carbenes - an overview.

    Hille, Claudia; Khn, Fritz E

    2015-12-14

    This review provides an overview of the currently known cationic rhenium NHC complexes. Synthesis, structures and properties are described. The title compounds are potential candidates for both catalytic and medical applications. Besides the variety of ancillary ligands, which are in some cases easily substituted, functionalization can be carried out in the side chain or at the backbone of the carbene ligand as well as - in the case of biscarbene ligands - at the bridging moiety. Cationic Re NHC complexes are promising precursors for radiopharmaceuticals and diagnostics - not only because of the possibility to radiolabel the metal (steps in this direction have been made and described already) - but rather the opportunity to link the complexes to biomolecules via the different possibilities provided by the ligands. The development of OLEDs based on luminescent Re(i) carbene complexes renders another potential application. PMID:26587970

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

    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.

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

    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.

  13. Tungsten(VI) N-Heterocyclic Carbene Complexes: Synthetic, Structural, and Computational Study

    2011-01-01

    The reaction of WOCl4 with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (Idipp) leads to an orange solid whose spectroscopic data are consistent with the 1:1 adduct [WOCl4(Idipp)]. Computational studies at the DFT level further support this formulation. Exposure of this compound to the atmosphere results in rapid hydrolysis to various imidazolium salts. If air diffuses very slowly into solutions of [WOCl4(Idipp)], it also undergoes slow hydrolysis to form [WO2Cl2(Idipp)]. This has been crystallographically characterized and is the first five-coordinate, 1:1 adduct of WO2Cl2. This complex has also been subject to DFT calculations, and its metalligand bonding has been explored. The carbenemetal interaction is primarily ?-donor in nature. The mechanism of the hydrolysis has also been probed by computational methods, revealing a plausible, low-energy reaction pathway. PMID:24882916

  14. Synthesis and Characterization of Ag(I) and Pd(II) Complexes with a Pyridine Substituted N-Heterocyclic Carbene Ligand

    We have used our new tridentate pyridine substituted N-heterocyclic carbene to generate an interesting trinuclear [((MepyCH2)2-Im)3Ag3]3+ complex, displaying very short Ag-Ag separations. A Pd(II)-NHC complex was prepared from [((MepyCH2)2-Im)3Ag3]3+ via a facile transmetallation, leading to a dimeric [(MepyCH2)2-ImPdCl]22+ complex. Future plans are underway for the survey of the potential applications of these new NHC complexes as luminesent materials or homogeneous catalysts. Since Arduengo's discovery of the first isolable free carbene in 1991, N-heterocyclic carbenes (NHC) have been extensively utilized as ligands for transition metals. NHC are generally more stable than two extreme types of carbenes, the Fischer and the Schrock carbenes. They are good ? donors like most tertiary phosphins, PR3, but the ?-bonding with the metal is rather weak. The thriving studies of NHC-coordinated metal complexes produced a wide range of applications from homogeneous catalysts to materials science

  15. Iridium(I) complexes with anionic N-heterocyclic carbene ligands as catalysts for the hydrogenation of alkenes in nonpolar media.

    Kolychev, Eugene L; Kronig, Sabrina; Brandhorst, Kai; Freytag, Matthias; Jones, Peter G; Tamm, Matthias

    2013-08-21

    A series of lithium complexes of anionic N-heterocyclic carbenes that contain a weakly coordinating borate moiety (WCA-NHC) was prepared in one step from free N-heterocyclic carbenes by deprotonation with n-butyl lithium followed by borane addition. The reaction of the resulting lithium-carbene adducts with [M(COD)Cl]2 (M = Rh, Ir; COD = 1,5-cyclooctadiene) afforded zwitterionic rhodium(I) and iridium(I) complexes of the type [(WCA-NHC)M(COD)], in which the metal atoms exhibit an intramolecular interaction with the N-aryl groups of the carbene ligands. For M = Rh, the neutral complex [(WCA-NHC)Rh(CO)2] and the ate complex (NEt4)[(WCA-NHC)Rh(CO)2Cl] were prepared, with the latter allowing an assessment of the donor ability of the ligand by IR spectroscopy. The zwitterionic iridium-COD complexes were tested as catalysts for the homogeneous hydrogenation of alkenes, which can be performed in the presence of nonpolar solvents or in the neat alkene substrate. Thereby, the most active complex showed excellent stability and activity in hydrogenation of alkenes at low catalyst loadings (down to 10 ppm). PMID:23883399

  16. Tunable and Efficient White Light Phosphorescent Emission Based on Single Component N-Heterocyclic Carbene Platinum(II) Complexes.

    Bachmann, Michael; Suter, Dominik; Blacque, Olivier; Venkatesan, Koushik

    2016-05-16

    A new class of cyclometalated pyridine N-heterocyclic carbene (NHC) Pt(II) complexes with electronically different alkyne derivatives (C≡CR; R = C6H4C(CH3)3 (1), C6H5 (2), C6H4F (3), C6H3(CF3)2 (4)) as ancillary ligands were synthesized, and the consequences of the electronic properties of the different substituted phenylacetylene ligands on the phosphorescent emission efficiencies were studied, where C≡CC6H4C(CH3)3 = 4-tert-butylphenylacetylene, C≡CC6H5 = phenylacetylene, C≡CC6H4F = 4-fluorophenylacetylene, and C≡CC6H3(CF3)2 = 3,5-bis(trifluoromethyl)phenylacetylene. Structural characterization, electrochemistry, and photophysical investigations were performed for all four compounds. Moreover, the emission quantum efficiencies and wavelength emission intensities of the complexes were also recorded in different weight percents in poly(methyl methacrylate) films (PMMA) and evaluated in the CIE-1931 chromaticity diagram. The square planar coordination geometry with the alkynyl ligands was corroborated for complexes 1, 2, and 3 by single crystal X-ray diffraction studies. These complexes show tunable monomeric high energy triplet emission and an additional concentration-dependent low-energy excimer-based phosphorescence. While adopting weight percent concentrations between 15 and 25%, the two emission bands covering the entire visible spectrum were obtained with these particular complexes displaying the properties of an efficient white light triplet emitter with excellent CIE-1931 coordinates (0.31, 0.33). On the basis of the high luminescent quantum efficiency of over 50% for white light emission, these compounds could be potentially useful for white organic light-emitting diodes (WOLEDs) based applications. PMID:27135529

  17. Synthesis, electronic structure, and magnetism of [Ni(6-Mes)2]+: a two-coordinate nickel(I) complex stabilized by bulky N-heterocyclic carbenes.

    Poulten, Rebecca C; Page, Michael J; Algarra, Andrs G; Le Roy, Jennifer J; Lpez, Isidoro; Carter, Emma; Llobet, Antoni; Macgregor, Stuart A; Mahon, Mary F; Murphy, Damien M; Murugesu, Muralee; Whittlesey, Michael K

    2013-09-18

    The two-coordinate cationic Ni(I) bis-N-heterocyclic carbene complex [Ni(6-Mes)2]Br (1) [6-Mes =1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene] has been structurally characterized and displays a highly linear geometry with a C-Ni-C angle of 179.27(13). Density functional theory calculations revealed that the five occupied metal-based orbitals are split in an approximate 2:1:2 pattern. Significant magnetic anisotropy results from this orbital degeneracy, leading to single-ion magnet (SIM) behavior. PMID:23971827

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

    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.

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

    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.

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

    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.

  1. 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

    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…

  2. Synthesis of N-heterocyclic carbene-PdCl2-(iso)quinoline complexes and their application in arylamination at low catalyst loadings.

    Liu, Feng; Zhu, Yi-Ran; Song, Lu-Gan; Lu, Jian-Mei

    2016-02-16

    A new type of N-heterocyclic carbene-PdCl2-(iso)quinoline complexes were successfully achieved in acceptable to good yields from easily available starting materials under mild conditions, and their structures were unambiguously confirmed using X-ray single crystal diffraction. Furthermore, their catalytic activity toward Buchwald-Hartwig arylamination of aryl chlorides with primary and secondary amines was fully tested. Under the optimal reaction conditions, the expected arylated amines can be obtained in high to excellent yields at low catalyst loadings (0.005-0.05 mol%). It may be worth noting here that comparison of these complexes with other well-defined and easily available NHC-Pd(ii) complexes bearing different N-containing ancillary ligands was also carried out, showing their superior catalytic activity over all others. PMID:26880100

  3. Solid-state structure, solution-state behaviour and catalytic activity of electronically divergent C,N-chelating palladium-N-heterocyclic carbene complexes.

    Chapman, Michael R; Lake, Benjamin R M; Pask, Christopher M; Nguyen, Bao N; Willans, Charlotte E

    2015-09-28

    A family of electronically diverse pyridyl- and picolyl-substituted imidazolium salts have been prepared and coordinated to palladium in a single step, to deliver a variety of palladium(ii)-N-heterocyclic carbene (NHC) complexes. Neutral Pd(NHC)X2, cationic [Pd(NHC)2X]X and dicationic [Pd(NHC)2]X2-type complexes have been isolated and fully characterised, with single-crystal X-ray analysis revealing a variety of coordination environments around the palladium centres. The pre-formed complexes have been employed in a model Suzuki-Miyaura cross-coupling reaction to yield a sterically congested tetra-ortho-substituted biaryl product, showcasing turnover numbers comparable to Pd-PEPPSI-IPr catalyst. PMID:26282010

  4. N-heterocyclic carbene catalyzed synthesis of oxime esters.

    Enders, Dieter; Grossmann, André; Van Craen, David

    2013-01-01

    A triazolium salt derived N-heterocyclic carbene catalyzes the redox esterification reaction between α-β-unsaturated aldehydes and oximes. The resulting saturated oxime esters were obtained in very good yields for a broad range of aliphatic, aromatic and heteroaromatic substrates. PMID:23104187

  5. Platinum complexes bearing normal and mesoionic N-heterocyclic carbene based pincer ligands: syntheses, structures, and photo-functional attributes.

    Naziruddin, Abbas Raja; Lee, Chen-Shiang; Lin, Wan-Jung; Sun, Bing-Jian; Chao, Kang-Heng; Chang, Agnes Hsiu Hwa; Hwang, Wen-Shu

    2016-04-01

    Platinum complexes featuring pyridine bis-N-heterocyclic-imidazol-2-ylidene/-mesoionic-triazol-5-ylidene donors as pincer ligands and chloro (-Cl), acetonitrile (-NCCH3) or cyano (-CN) groups as auxiliary ligands are prepared as highly strained organometallic phosphors. X-ray structures of four of these complexes confirm a distorted square planar geometry, where the pincer ligand and its mesityl wingtips occur in a twisted conformation to each other. Electrochemical and photophysical characterization have been carried out and the experimental results are interpreted with the aid of density functional theory calculations. Emission responses of complexes under exposure to different vapors and mechanical shear are reported. Notably, the platinum complex featuring pyridine bis-imidazol-2-ylidene and a weakly donating acetonitrile auxiliary ligand exhibited strong aquachromic and mechanochromic emission responses, showing color changes from sky blue to green or yellow-green. PMID:26947757

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

    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.

  7. Influence of bulky yet flexible N-heterocyclic carbene ligands in gold catalysis

    Alba Collado

    2015-10-01

    Full Text Available Three new Au(I complexes of the formula [Au(NHC(NTf2] (NHC = N-heterocyclic carbene bearing bulky and flexible ligands have been synthesised. The ligands studied are IPent, IHept and INon which belong to the ITent (Tent for tentacular family of NHC derivatives. The effect of these ligands in gold-promoted transformations has been investigated.

  8. Influence of bulky yet flexible N-heterocyclic carbene ligands in gold catalysis

    Collado, Alba; Patrick, Scott R; Gasperini, Danila; Meiries, Sebastien

    2015-01-01

    Summary Three new Au(I) complexes of the formula [Au(NHC)(NTf2)] (NHC = N-heterocyclic carbene) bearing bulky and flexible ligands have been synthesised. The ligands studied are IPent, IHept and INon which belong to the ITent (Tent for tentacular) family of NHC derivatives. The effect of these ligands in gold-promoted transformations has been investigated. PMID:26664600

  9. Synthesis and characterization of divalent manganese, iron, and cobalt complexes in tripodal phenolate/N-heterocyclic carbene ligand environments.

    K, Martina; Hohenberger, Johannes; Adelhardt, Mario; Zolnhofer, Eva M; Mossin, Susanne; Heinemann, Frank W; Sutter, Jrg; Meyer, Karsten

    2014-03-01

    Two novel tripodal ligands, (BIMPN(Mes,Ad,Me))(-) and (MIMPN(Mes,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 (1)H 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 (57)Fe Mssbauer 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 TIMEN(R) ligands, allow for side access of, e.g., organic substrates, to the reactive metal center. PMID:24299260

  10. Mild and selective H/D exchange at the β position of aromatic α-olefins by N-heterocyclic carbene-hydride-rhodium catalysts

    Giuseppe, Andrea di; Castarlenas, Ricardo; Pérez-Torrente, Jesús J.; FERNANDO J LAHOZ; Polo, Víctor; LUIS A ORO

    2011-01-01

    Pacman bites selectively! Stable rhodium(III)-N-heterocyclic carbene-hydride complexes (Pacman-like catalysts) are highly active and selective catalysts for H/D exchange at the β position of aromatic α-olefins (see picture). The interplay between bulky N-heterocyclic carbene and quinolinate ligands determines the size of the steric window responsible for this selectivity.

  11. Unexpected rearrangements in the synthesis of an unsymmetrical tridentate dianionic N-heterocyclic carbene

    Despagnet-Ayoub, Emmanuelle

    2013-01-01

    Starting from the same ethylenediamine species, three valuable carbene precursors were synthesized under differing conditions: a tridentate dianionic N-heterocyclic carbene bearing an aniline, a phenol and a central dihydroimidazolium salt, its benzimidazolium isomer by intramolecular rearrangement and a dicationic benzimidazolium-benzoxazolium salt by changing the Brønsted acid from HCl to HBF4. A DFT study was performed to understand the rearrangement pathway. The structure of a bis[(NCO)carbene] zirconium complex was determined. © 2013 The Royal Society of Chemistry.

  12. 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

    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.

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

    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.

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

    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…

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

    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

  16. Continuous-Flow N-Heterocyclic Carbene Generation and Organocatalysis.

    Di Marco, Lorenzo; Hans, Morgan; Delaude, Lionel; Monbaliu, Jean-Christophe M

    2016-03-18

    Two methods were assessed for the generation of common N-heterocyclic carbenes (NHCs) from stable imidazol(in)ium precursors using convenient and straightforward continuous-flow setups with either a heterogeneous inorganic base (Cs2 CO3 or K3 PO4 ) or a homogeneous organic base (KN(SiMe3 )2 ). In-line quenching with carbon disulfide revealed that the homogeneous strategy was most efficient for the preparation of a small library of NHCs. The generation of free nucleophilic carbenes was next telescoped with two benchmark NHC-catalyzed reactions; namely, the transesterification of vinyl acetate with benzyl alcohol and the amidation of N-Boc-glycine methyl ester with ethanolamine. Both organocatalytic transformations proceeded with total conversion and excellent yields were achieved after extraction, showcasing the first examples of continuous-flow organocatalysis with NHCs. PMID:26880372

  17. Ligand-controlled regioselectivity in the hydrothiolation of alkynes by rhodium N-heterocyclic carbene catalysts

    Giuseppe, Andrea di; Castarlenas, Ricardo; Pérez-Torrente, Jesús J.; Crucianelli, Marcello; Polo, Víctor; Sancho, Rodrigo; FERNANDO J LAHOZ; LUIS A ORO

    2012-01-01

    Rh-N-heterocyclic carbene compounds [Rh(μ-Cl)(IPr)(ν 2- olefin)] 2 and RhCl(IPr)(py)(ν 2-olefin) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-carbene, py = pyridine, olefin = cyclooctene or ethylene) are highly active catalysts for alkyne hydrothiolation under mild conditions. A regioselectivity switch from linear to 1-substituted vinyl sulfides was observed when mononuclear RhCl(IPr)(py)(ν 2- olefin) catalysts were used instead of dinuclear precursors. A complex interplay between electron...

  18. Mixed N-Heterocyclic Carbene-Bis(oxazolinyl)borato Rhodium and Iridium Complexes in Photochemical and Thermal Oxidative Addition Reactions

    Xu, Songchen [Ames Laboratory; Manna, Kuntal [Ames Laboratory; Ellern, Arkady [Ames Laboratory; Sadow, Aaron D [Ames Laboratory

    2014-12-08

    In order to facilitate oxidative addition chemistry of fac-coordinated rhodium(I) and iridium(I) compounds, carbene–bis(oxazolinyl)phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB(OxMe2)2(ImtBuH) (H[1]; OxMe2 = 4,4-dimethyl-2-oxazoline; ImtBuH = 1-tert-butylimidazole) and PhB(OxMe2)2(ImMesH) (H[2]; ImMesH = 1-mesitylimidazole), are deprotonated with potassium benzyl to generate K[1] and K[2], and these potassium compounds serve as reagents for the synthesis of a series of rhodium and iridium complexes. Cyclooctadiene and dicarbonyl compounds {PhB(OxMe2)2ImtBu}Rh(η4-C8H12) (3), {PhB(OxMe2)2ImMes}Rh(η4-C8H12) (4), {PhB(OxMe2)2ImMes}Rh(CO)2 (5), {PhB(OxMe2)2ImMes}Ir(η4-C8H12) (6), and {PhB(OxMe2)2ImMes}Ir(CO)2 (7) are synthesized along with ToMM(η4-C8H12) (M = Rh (8); M = Ir (9); ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate). The spectroscopic and structural properties and reactivity of this series of compounds show electronic and steric effects of substituents on the imidazole (tert-butyl vs mesityl), effects of replacing an oxazoline in ToM with a carbene donor, and the influence of the donor ligand (CO vs C8H12). The reactions of K[2] and [M(μ-Cl)(η2-C8H14)2]2 (M = Rh, Ir) provide {κ4-PhB(OxMe2)2ImMes′CH2}Rh(μ-H)(μ-Cl)Rh(η2-C8H14)2 (10) and {PhB(OxMe2)2ImMes}IrH(η3-C8H13) (11). In the former compound, a spontaneous oxidative addition of a mesityl ortho-methyl to give a mixed-valent dirhodium species is observed, while the iridium compound forms a monometallic allyl hydride. Photochemical reactions of dicarbonyl compounds 5 and 7 result in C–H bond oxidative addition providing the compounds {κ4-PhB(OxMe2)2ImMes′CH2}RhH(CO) (12) and {PhB(OxMe2)2ImMes}IrH(Ph)CO (13). In 12, oxidative addition results in cyclometalation of the mesityl ortho-methyl similar to 10, whereas the iridium compound reacts with the benzene solvent to give a rare crystallographically characterized cis-[Ir](H)(Ph) complex. Alternatively, the rhodium carbonyl 5 or iridium isocyanide {PhB(OxMe2)2ImMes}Ir(CO)CNtBu (15) reacts with PhSiH3 in the dark to form the silyl compound {PhB(OxMe2)2ImMes}RhH(SiH2Ph)CO (14) or {PhB(OxMe2)2ImMes}IrH(SiH2Ph)CNtBu (17). These examples demonstrate the enhanced thermal reactivity of {PhB(OxMe2)2ImMes}-supported iridium and rhodium carbonyl compounds in comparison to tris(oxazolinyl)borate, tris(pyrazolyl)borate, and cyclopentadienyl-supported compounds.

  19. Synthesis and behavior of novel sulfonated water-soluble N-heterocyclic carbene (η(4)-diene) platinum(0) complexes.

    Ruiz-Varilla, Andrea M; Baquero, Edwin A; Silbestri, Gustavo F; Gonzalez-Arellano, Camino; de Jesús, Ernesto; Flores, Juan C

    2015-11-14

    A series of water-soluble (NHC)Pt(0)(dvtms) and (NHC)Pt(0)(AE) complexes containing different sulfonated NHC ligands (dvtms = divinyltetramethyldisiloxane and AE = diallyl ether) are reported. The dvtms compounds have been found to be quite robust and to display some conformational rigidity, whereas their AE counterparts are less stable and more flexible. The catalytic evaluation of these complexes in the hydrosilylation of alkynes in water revealed no benefits in favor of the complexes containing the more labile spectator diene (AE), and a fairly regular catalytic behavior for all complexes that restricts the location of the sulfonate group to the proximity of the metal site. PMID:26346995

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

    Käß, Martina; Hohenberger, Johannes; Adelhardt, Mario; Zolnhofer, Eva M.; Mossin, Susanne; Heinemann, Frank W.; Sutter, Jörg; Meyer, Karsten

    2014-01-01

    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...

  1. An N-heterocyclic silylene-stabilized digermanium(0) complex.

    Shan, Yu-Liang; Yim, Wai-Leung; So, Cheuk-Wai

    2014-11-24

    The synthesis of an N-heterocyclic silylene-stabilized digermanium(0) complex is described. The reaction of the amidinate-stabilized silicon(II) amide [LSiN(SiMe3)2] (1; L=PhC(NtBu)2) with GeCl2⋅dioxane in toluene afforded the Si(II)-Ge(II) adduct [L{(Me3Si)2N}Si→GeCl2] (2). Reaction of the adduct with two equivalents of KC8 in toluene at room temperature afforded the N-heterocyclic carbene silylene-stabilized digermanium(0) complex [L{(Me3Si)2N}Si→Ge=Ge←Si{N(SiMe3)2}L] (3). X-ray crystallography and theoretical studies show conclusively that the N-heterocyclic silylenes stabilize the singlet digermanium(0) moiety by a weak synergic donor-acceptor interaction. PMID:25267490

  2. Improving Grubbs' II type ruthenium catalysts by appropriately modifying the N-heterocyclic carbene ligand.

    Vieille-Petit, Ludovic; Luan, Xinjun; Gatti, Michele; Blumentritt, Sascha; Linden, Anthony; Clavier, Hervé; Nolan, Steven P; Dorta, Reto

    2009-07-01

    The introduction of N-heterocyclic carbene ligands that incorporate correctly substituted naphthyl side chains leads to increased activity and stability in second generation ruthenium metathesis catalysts. PMID:19557281

  3. Luminescent platinum(II) complexes with functionalized N-heterocyclic carbene or diphosphine selectively probe mismatched and abasic DNA

    Fung, Sin Ki; Zou, Taotao; Cao, Bei; Chen, Tianfeng; To, Wai-Pong; Yang, Chen; Lok, Chun-Nam; Che, Chi-Ming

    2016-01-01

    The selective targeting of mismatched DNA overexpressed in cancer cells is an appealing strategy in designing cancer diagnosis and therapy protocols. Few luminescent probes that specifically detect intracellular mismatched DNA have been reported. Here we used Pt(II) complexes with luminescence sensitive to subtle changes in the local environment and report several Pt(II) complexes that selectively bind to and identify DNA mismatches. We evaluated the complexes' DNA-binding characteristics by ultraviolet/visible absorption titration, isothermal titration calorimetry, nuclear magnetic resonance and quantum mechanics/molecular mechanics calculations. These Pt(II) complexes show up to 15-fold higher emission intensities upon binding to mismatched DNA over matched DNA and can be utilized for both detecting DNA abasic sites and identifying cancer cells and human tissue samples with different levels of mismatch repair. Our work highlights the potential of luminescent Pt(II) complexes to differentiate between normal cells and cancer cells which generally possess more aberrant DNA structures. PMID:26883164

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

    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 c...

  5. Oxidation and β-Alkylation of Alcohols Catalysed by Iridium(I) Complexes with Functionalised N-Heterocyclic Carbene Ligands.

    Jiménez, M Victoria; Fernández-Tornos, Javier; Modrego, F Javier; Pérez-Torrente, Jesús J; Oro, Luis A

    2015-12-01

    The borrowing hydrogen methodology allows for the use of alcohols as alkylating agents for CC bond forming processes offering significant environmental benefits over traditional approaches. Iridium(I)-cyclooctadiene complexes having a NHC ligand with a O- or N-functionalised wingtip efficiently catalysed the oxidation and β-alkylation of secondary alcohols with primary alcohols in the presence of a base. The cationic complex [Ir(NCCH3 )(cod)(MeIm(2- methoxybenzyl))][BF4 ] (cod=1,5-cyclooctadiene, MeIm=1-methylimidazolyl) having a rigid O-functionalised wingtip, shows the best catalyst performance in the dehydrogenation of benzyl alcohol in acetone, with an initial turnover frequency (TOF0 ) of 1283 h(-1) , and also in the β-alkylation of 2-propanol with butan-1-ol, which gives a conversion of 94 % in 10 h with a selectivity of 99 % for heptan-2-ol. We have investigated the full reaction mechanism including the dehydrogenation, the cross-aldol condensation and the hydrogenation step by DFT calculations. Interestingly, these studies revealed the participation of the iridium catalyst in the key step leading to the formation of the new CC bond that involves the reaction of an O-bound enolate generated in the basic medium with the electrophilic aldehyde. PMID:26493780

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

    Thibault E. Schmid

    2015-09-01

    Full Text Available 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(picolinateRuCl(indenylidene complex 4a (SIPr = 1,3-bis(2-6-diisopropylphenylimidazolidin-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.

  7. New metathesis catalyst bearing chromanyl moieties at the N-heterocyclic carbene ligand

    Suchodolski, Szymon; Wojtkielewicz, Agnieszka; Morzycki, Jacek W

    2015-01-01

    Summary The synthesis of a new type of Hoveyda–Grubbs 2nd generation catalyst bearing a modified N-heterocyclic carbene ligands is reported. The new catalyst contains an NHC ligand symmetrically substituted with chromanyl moieties. The complex was tested in model CM and RCM reactions. It showed very high activity in CM reactions with electron-deficient α,β-unsaturated compounds even at 0 °C. It was also examined in more demanding systems such as conjugated dienes and polyenes. The catalyst is stable, storable and easy to purify. PMID:26877801

  8. Organometallic rhenium(III) chalcogenide clusters: coordination of N-heterocyclic carbenes.

    Durham, Jessica L; Wilson, Wade B; Huh, Daniel N; McDonald, Robert; Szczepura, Lisa F

    2015-07-01

    The preparation of rhenium based octahedral clusters containing N-heterocyclic carbenes is described. These represent the first examples of [M6(?3-Q)8](n+) or [M6(?3-X)8](n+) clusters to contain a carbene ligand of any type (NHC, Fischer or Schrock). Surprisingly, the NHC ligands attenuate their luminescent properties. PMID:26041404

  9. 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

    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°) 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.

  10. Annulated boron substituted N-heterocyclic carbenes: theoretical prediction of highly electrophilic carbenes.

    Bharadwaz, Priyam; Borthakur, Bitupon; Phukan, Ashwini K

    2015-11-14

    Theoretical calculations were carried out to understand the effect of annulation on the electronic and ligand properties of boron substituted N-heterocyclic carbenes (B-NHCs). Annulation results in a decrease in stability as indicated by the calculated values of singlet-triplet separations and stabilization energies as well as HOMO-LUMO gaps. Annulated B-NHCs are found to be weaker σ-donors but better π-acceptors than the parent ones. The decrease in σ-donation ability and the increase in π-accepting ability are further supported by the calculated values of proton affinities, nucleophilicity and electrophilicity indices as well as (31)P NMR chemical shifts of the corresponding NHC-PPh adducts. Most of the annulated B-NHCs are found to have significantly enhanced electrophilicity than the other known carbenes. PMID:26455836

  11. Direct estimate of the internal π-donation to the carbene centre within N-heterocyclic carbenes and related molecules

    Andrada, Diego M; Holzmann, Nicole; Hamadi, Thomas

    2015-01-01

    Summary Fifteen cyclic and acylic carbenes have been calculated with density functional theory at the BP86/def2-TZVPP level. The strength of the internal X→p(π) π-donation of heteroatoms and carbon which are bonded to the C(II) atom is estimated with the help of NBO calculations and with an energy decomposition analysis. The investigated molecules include N-heterocyclic carbenes (NHCs), the cyclic alkyl(amino)carbene (cAAC), mesoionic carbenes and ylide-stabilized carbenes. The bonding analysis suggests that the carbene centre in cAAC and in diamidocarbene have the weakest X→p(π) π-donation while mesoionic carbenes possess the strongest π-donation. PMID:26877795

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

    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.

  13. N-heterocyclic carbene-catalyzed internal redox reaction of alkynals: an efficient synthesis of allenoates.

    Zhao, Yu-Ming; Tam, Yik; Wang, Yu-Jie; Li, Zigang; Sun, Jianwei

    2012-03-16

    An efficient N-heterocyclic carbene (NHC)-catalyzed internal redox reaction of alkynals that bear a γ leaving group has been developed. This process provides a new access to a range of allenoates in good yields. Preliminary results demonstrate that the enantioselective variant can also be achieved. PMID:22352302

  14. N-Heterocyclic Carbene-Catalyzed Alcohol Acetylation: An Organic Experiment Using Organocatalysis

    Morgan, John P.; Shrimp, Jonathan H.

    2014-01-01

    Undergraduate students in the teaching laboratory have successfully used N-heterocyclic carbenes (NHCs) as organocatalysts for the acetylation of primary alcohols, despite the high water sensitivity of uncomplexed ("free") NHCs. The free NHC readily reacted with chloroform, resulting in an air- and moisture-stable adduct that liberates…

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

    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...

  16. Abnormal carbene-silicon halide complexes.

    Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; Schaefer, Henry F; Robinson, Gregory H

    2016-04-14

    Reaction of the anionic N-heterocyclic dicarbene (NHDC), [:C{[N(2,6-Pr(i)2C6H3)]2CHCLi}]n (1), with SiCl4 gives the trichlorosilyl-substituted (at the C4 carbon) N-heterocyclic carbene complex (7). Abnormal carbene-SiCl4 complex (8) may be conveniently synthesized by combining 7 with HCl·NEt3. In addition, 7 may react with CH2Cl2 in warm hexane, giving the abnormal carbene-complexed SiCl3(+) cation (9). The nature of the bonding in 9 was probed with complementary DFT computations. PMID:26605692

  17. N-heterocyclic carbenes (NHC) with 1,2,4-oxadiazole-substituents related to natural products: synthesis, structure and potential antitumor activity of some corresponding gold(I) and silver(I) complexes.

    Maftei, Catalin V; Fodor, Elena; Jones, Peter G; Freytag, Matthias; Franz, M Heiko; Kelter, Gerhard; Fiebig, Heinz-Herbert; Tamm, Matthias; Neda, Ion

    2015-08-28

    This work presents the synthesis, characterization and application of eleven new gold (I) complexes 13-23 with 1,2,4-oxadiazole-containing N-heterocyclic carbene (NHC) ligands and of the NHC silver(I) complex 24. The 1,2,4-oxadiazole unit, which can be found in a variety of biologically active natural products such as phidianidines or quisqualic acid, was incorporated, along with a variety of other biologically active moieties (anthracene, indole, 2-pyridine, 2,3,4,5-tetra-O-acetyl-D-glucopyranose, quincorine and quincoridine), in order to change the lipophilicity of the complexes, so that the transport of the active units (M-NHC) though the cell wall barrier is facilitated. The biological activity of the complexes was investigated. In vitro assessment of anti-tumor activity in a panel of 12 human tumor cell lines by a monolayer assay revealed impressive potency (mean IC50 < 0.1 μM) and tumor selectivity for 6 compounds, with individual IC50 values in the low nanomolar range. The solid state structures of compounds 13, 14, 15, 17, 18, 19 and 24 were determined by X-ray diffraction analyses. PMID:26185007

  18. A simple route to phosphamethine cyanines from S,N-heterocyclic carbenes.

    Binder, Justin F; Corrente, Andrea M; Macdonald, Charles L B

    2016-02-01

    Although salts of thiazolium cations are known, many readily prepared iodide salts have eluded spectroscopic and structural characterization; herein, data for a variety of such salts are reported. It has been demonstrated that thiazolium cations can be deprotonated to generate S,N-heterocyclic carbenes and their "electron rich olefin" dimers, but use of the former has been largely overshadowed by that of the more common N-heterocyclic carbenes. We report herein that the deprotonation of thiazolium iodides and their subsequent reaction with a conveniently prepared triphosphenium precursor grants phosphamethine cyanine cations with solid-state geometry and electronic structure unlike those of NHC-stabilized cations. Protection of the phosphorus atom in such ions with elemental sulfur provides an air- and moisture-stable dithiophosphinium salt. PMID:26536127

  19. An N-Heterocyclic Carbene/Lewis Acid Strategy for the Stereoselective Synthesis of Spirooxindole Lactones

    Dugal-Tessier, Julien; OBryan, Elizabeth A.; Schroeder, Thomas B. H.; Cohen, Daniel T.

    2012-01-01

    A cooperative catalysis approach for the enantioselective formal [3+2] addition of ?,?-unsaturated aldehydes to isatins has been developed. The N-heterocyclic carbene (NHC)-catalyzed homoenolate annulations of ?-aryl enals require the addition of lithium chloride for high levels of enantioselectivity. This NHC-catalyzed annulation provides efficient access to the 3-hydroxy indole skeleton and has been applied to the first eantioselective total synthesis of maremycin B. PMID:22489096

  20. Theoretical Insights on the Interaction of N-Heterocyclic Carbenes with Tetravalent Silicon Reagents.

    Pathak, Dipanjali; Deuri, Sanjib; Phukan, Prodeep

    2016-01-14

    Lewis acid-base type interaction between N-heterocyclic carbene (NHC) and tetravalent silicon reagent (SiR) has been investigated computationally. This NHC-Si interaction is of fundamental importance to the understanding of variety of NHC catalyzed organic transformations involving silicon compounds such as cyanosilylation, trifluoromethylsilylation, etc. Geometries of 24 NHCs, 10 silicon reagents, and their 61 Lewis acid-base complexes have been optimized using the B3LYP/6-31+G(d,p) and M05-2X/6-31+G(d,p) level of theory. The strength of NHC-Si interaction has been assessed in terms of binding energy of the complexes, charge transfer (CT) and the length of Si-CNHC bond. Energy decomposition analysis (EDA) and natural bond orbital (NBO) analysis at M052X/6-31+G(d,p) level of theory has been carried out to get a deeper understanding of the nature of bonding and charge delocalization. Proton affinity of the NHCs and fluoride affinity of the SiRs have been calculated and correlated with the binding energy of the resulting complexes. PMID:26654756

  1. Enantioselective N-Heterocyclic Carbene Catalyzed Diene Regenerative (4 + 2) Annulation.

    Levens, Alison; Zhang, Changhe; Candish, Lisa; Forsyth, Craig M; Lupton, David W

    2015-11-01

    An enantioselective N-heterocyclic carbene (NHC)-catalyzed diene regenerative (4 + 2) annulation has been achieved through the use of highly nucleophilic morpholinone-derived catalysts. The reaction proceeds with good to excellent yields, high enantioselectivity (most >92% ee), and good diastereoselectivity (most >7:1). The generality of the reaction is high, with 19 examples reported. The utility of the products has been examined with subsequent derivatization in Diels-Alder reactions using electron-poor dienophiles. Furthermore, interception of the proposed β-lactone intermediate has been achieved, allowing the synthesis of compounds bearing four contiguous stereocenters with high levels of enantio- and diastereoselectivity. PMID:26484753

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

    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.

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

    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.

  4. [CNN]-pincer nickel(II) complexes of N-heterocyclic carbene (NHC): synthesis and catalysis of the Kumada reaction of unactivated C-Cl bonds.

    Sun, Yunqiang; Li, Xiaoyan; Sun, Hongjian

    2014-07-01

    Three novel [CNN]-pincer nickel(ii) complexes with NHC-amine arms were synthesized in three steps. Complex was proven to be an efficient catalyst for the Kumada coupling of aryl chlorides or aryl dichlorides under mild conditions. PMID:24828414

  5. Pincer-CNC mononuclear, dinuclear and heterodinuclear Au(iii) and Pt(ii) complexes supported by mono- and poly-N-heterocyclic carbenes: synthesis and photophysical properties.

    Gonell, S; Poyatos, M; Peris, E

    2016-04-01

    A family of cyclometallated Au(iii) and Pt(ii) complexes containing a CNC-pincer ligand (CNC = 2,6-diphenylpyridine) supported by pyrene-based mono- or bis-NHC ligands have been synthesized and characterized, together with the preparation of a Pt-Au hetero-dimetallic complex based on a Y-shaped tris-NHC ligand. The photophysical properties of all the new species and of two related Ru(ii)-arene complexes were studied and compared. Whereas the pyrene-based complexes only exhibit emission in solution, those containing the Y-shaped tris-NHC ligand are only luminescent when dispersed in poly(methyl methacrylate) (PMMA). In particular, the pyrene-based complexes were found to be emissive in the range of 373-440 nm, with quantum yields ranging from 3.1 to 6.3%, and their emission spectra were found to be almost superimposable, pointing to the fluorescent pyrene-centered nature of the emission. This observation suggests that the emission properties of the pyrene fragment may be combined with some of the numerous applications of NHCs as supporting ligands allowing, for instance, the design of biological luminescent agents. PMID:26911885

  6. Application of the π-accepting ability parameter of N-heterocyclic carbene ligands in iridium complexes for signal amplification by reversible exchange (SABRE).

    van Weerdenburg, Bram J A; Eshuis, Nan; Tessari, Marco; Rutjes, Floris P J T; Feiters, Martin C

    2015-09-21

    The new π-accepting ability parameter (PAAP) appears to be the best tool to analyse the electronic properties of NHC ligands in [Ir(H)2(NHC)(Py)3](+) complexes for SABRE. Together with the buried volume, the efficiency of hyperpolarisation transfer in SABRE, depending on the exchange rate of pyridine, can be described. PMID:26243153

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

    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

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

  8. Amino Group Functionalized N-Heterocyclic 1,2,4-Triazole-Derived Carbenes: Structural Diversity of Rhodium(I) Complexes

    Turek, J.; Panov, I.; Horáček, Michal; Černošek, Z.; Padělková, Z.; Růžička, A.

    2013-01-01

    Roč. 32, č. 23 (2013), s. 7234-7240. ISSN 0276-7333 Institutional support: RVO:61388955 Keywords : TRANSITION-METAL COMPLEXES * BIFUNCTIONAL MECHANISM * TRANSFER HYDROGENATION Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.253, year: 2013

  9. Crystal structure of bis-(1,3-di-meth-oxy-imidazolin-2-yl-idene)silver(I) hexa-fluorido-phosphate, N-heterocyclic carbene (NHC) complex.

    Rietzler, Barbara; Laus, Gerhard; Kahlenberg, Volker; Schottenberger, Herwig

    2015-12-01

    The title salt, [Ag(C5H8N2O2)2]PF6, was obtained by deprotonation and metalation of 1,3-di-meth-oxy-imidazolium hexa-fluorido-phosphate using silver(I) oxide in methanol. The C-Ag-C angle in the cation is 178.1?(2), and the N-C-N angles are 101.1?(4) and 100.5?(4). The meth-oxy groups adopt an anti conformation. In the crystal, anions (A) are sandwiched between cations (C) in a layered arrangement {CAC} n stacked along [001]. Within a CAC layer, the hexafluoridophosphate anions accept several C-H?F hydrogen bonds from the cationic complex. PMID:26870450

  10. Crystal structure of bis(1,3-dimethoxyimidazolin-2-ylidene)silver(I) hexafluoridophosphate, N-heterocyclic carbene (NHC) complex

    Rietzler, Barbara; Laus, Gerhard; Kahlenberg, Volker; Schottenberger, Herwig

    2015-01-01

    The title salt, [Ag(C5H8N2O2)2]PF6, was obtained by deprotonation and metalation of 1,3-dimethoxyimidazolium hexafluoridophosphate using silver(I) oxide in methanol. The CAgC angle in the cation is 178.1?(2), and the NCN angles are 101.1?(4) and 100.5?(4). The methoxy groups adopt an anti conformation. In the crystal, anions (A) are sandwiched between cations (C) in a layered arrangement {CAC}n stacked along [001]. Within a CAC layer, the hexafluoridophosphate anions accept several CH?F hydrogen bonds from the cationic complex. PMID:26870450

  11. N-Heterocyclic-Carbene-Catalysed Diastereoselective Vinylogous Mukaiyama/Michael Reaction of 2-(Trimethylsilyloxy)furan and Enones

    Wang, Ying

    2015-10-15

    N-heterocyclic carbenes have been utilised as highly efficient nucleophilic organocatalysts to mediate vinylogous Mukaiyama/Michael reactions of 2-(trimethylsilyloxy)furan with enones to afford γ-substituted butenolides in 44-99% yield with 3:1-32:1 diastereoselectivity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Caffeine-based gold(I) N-heterocyclic carbenes as possible anticancer agents: synthesis and biological properties.

    Bertrand, Benoît; Stefan, Loic; Pirrotta, Marc; Monchaud, David; Bodio, Ewen; Richard, Philippe; Le Gendre, Pierre; Warmerdam, Elena; de Jager, Marina H; Groothuis, Geny M M; Picquet, Michel; Casini, Angela

    2014-02-17

    A new series of gold(I) N-heterocyclic carbene (NHC) complexes based on xanthine ligands have been synthesized and characterized by mass spectrometry, NMR, and X-ray diffraction. The compounds have been tested for their antiproliferative properties in human cancer cells and nontumorigenic cells in vitro, as well as for their toxicity in healthy tissues ex vivo. The bis-carbene complex [Au(caffein-2-ylidene)2][BF4] (complex 4) appeared to be selective for human ovarian cancer cell lines and poorly toxic in healthy organs. To gain preliminary insights into their actual mechanism of action, two biologically relevant in cellulo targets were studied, namely, DNA (more precisely a higher-order DNA structure termed G-quadruplex DNA that plays key roles in oncogenetic regulation) and a pivotal enzyme of the DNA damage response (DDR) machinery (poly-(adenosine diphosphate (ADP)-ribose) polymerase 1 (PARP-1), strongly involved in the cancer resistance mechanism). Our results indicate that complex 4 acts as an efficient and selective G-quadruplex ligand while being a modest PARP-1 inhibitor (i.e., poor DDR impairing agent) and thus provide preliminary insights into the molecular mechanism that underlies its antiproliferative behavior. PMID:24499428

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

    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 σ-basic/π-acid ligands, although they have been also shown to exhibit reasonable π-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.

  14. Superior Oxygen Stability of N-Heterocyclic Carbene-Coated Au Nanocrystals: Comparison with Dodecanethiol.

    Ling, Xiang; Schaeffer, Nicolas; Roland, Sylvain; Pileni, Marie-Paule

    2015-12-01

    The stability of Au nanocrystals (NCs) coated with different N-heterocyclic carbenes (NHCs) or dodecanethiol (DDT) to oxygen-based treatments was investigated. A dominant effect of the ligand type was observed with a significantly greater oxygen resistance of NHC-coated Au NCs compared to that of the thiol-based analogues. NHC-coated Au NCs are stable to 10 W oxygen plasma etching for up to 180 s whereas the integrity of DDT-coated Au NCs is strongly affected by the same treatment from 60-80 s. In the latter case, the average size of the NCs (from 2.6 to 6.3 nm) and the method of synthesis have no effect on the stability. NHC-coated Au NCs were found to generate of a smaller quantity of ligand-derived species under molecular oxygen treatment, which could account for the increased stability. PMID:26550843

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

    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 γ-alkyl and aryl-substituted deconjugated butenolides undergo vinylogous Michael addition with various α, β-unsaturated ketones, esters, or nitriles to afford γ,γ-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.

  16. A carbene-carbene complex equilibrium.

    Moss, Robert A; Wang, Lei; Odorisio, Christina M; Krogh-Jespersen, Karsten

    2010-08-11

    Phenylchlorocarbene, generated by laser flash photolysis of phenylchlorodiazirine, formed highly stable pi-type complexes with 1,3,5-trimethoxybenzene in pentane. The carbene and carbene complexes were in equilibrium. We measured the equilibrium constant (K = 1264 M(-1) at 294 K) and, from its temperature dependence, extracted the associated thermodynamic parameters: DeltaH(o) = -7.1 kcal/mol, DeltaS(o) = -10.2 eu, and DeltaG(o) = -4.1 kcal/mol. The carbene complexes were characterized by UV-vis spectroscopy and computational analysis. PMID:20681697

  17. An N-Heterocyclic Carbene as a Bidentate Hemilabile Ligand: A Synchrotron X-ray Diffraction and Density Functional Theory Study

    The N-heterocyclic carbene ligand IMes was shown by synchrotron crystallography and DFT computations to adopt a hemilabile bidentate coordination mode in CpM(CO)2(IMes)+B(C6F5)4- (M = Mo, W), with a C=C bond of one mesityl weakly coordinated to the metal.

  18. 25 years of N-heterocyclic carbenes: activation of both main-group element-element bonds and NHCs themselves.

    Würtemberger-Pietsch, Sabrina; Radius, Udo; Marder, Todd B

    2016-04-14

    N-Heterocyclic carbenes (NHCs) are widely used ligands and reagents in modern inorganic synthesis as well as in homogeneous catalysis and organocatalysis. However, NHCs are not always innocent bystanders. In the last few years, more and more examples were reported of reactions of NHCs with main-group elements which resulted in modification of the NHC. Many of these reactions lead to ring expansion and the formation of six-membered heterocyclic rings involving insertion of the heteroatom into the C-N bond and migration of hydrides, phenyl groups or boron-containing fragments. Furthermore, a few related NHC rearrangements were observed some decades ago. In this Perspective, we summarise the history of NHC ring expansion reactions from the 1960s till the present. PMID:26675582

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

    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.

  20. Cationic Silica-Supported N-Heterocyclic Carbene Tungsten Oxo Alkylidene Sites: Highly Active and Stable Catalysts for Olefin Metathesis.

    Pucino, Margherita; Mougel, Victor; Schowner, Roman; Fedorov, Alexey; Buchmeiser, Michael R; Copéret, Christophe

    2016-03-18

    Designing supported alkene metathesis catalysts with high activity and stability is still a challenge, despite significant advances in the last years. Described herein is the combination of strong σ-donating N-heterocyclic carbene ligands with weak σ-donating surface silanolates and cationic tungsten sites leading to highly active and stable alkene metathesis catalysts. These well-defined silica-supported catalysts, [(≡SiO)W(=O)(=CHCMe2 Ph)(IMes)(OTf)] and [(≡SiO)W(=O)(=CHCMe2 Ph)(IMes)(+) ][B(Ar(F) )4 (-) ] [IMes=1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene, B(Ar(F) )4 =B(3,5-(CF3 )2 C6 H3 )4 ] catalyze alkene metathesis, and the cationic species display unprecedented activity for a broad range of substrates, especially for terminal olefins with turnover numbers above 1.2 million for propene. PMID:26928967

  1. 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)

    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.

  2. Application of Chan-Lam cross coupling for the synthesis of N-heterocyclic carbene precursors bearing strong electron donating or withdrawing groups

    Huang, Liliang; He, Chengxiang; Sun, Zhihua

    2015-07-01

    Chan-Lam cross coupling allowed efficient synthesis of N,N’-disubstituted ortho-phenylene diamines bearing strong electron donating or withdrawing groups, such as nitro or methoxy groups, with moderate to high yields. These diamines can then be turned into N-heterocyclic carbene precursors after condensation with trimethyl orthoformate. The same strategy can also be utilized for the synthesis of N-monosubstituted aniline derivatives containing a functionalized ortho-aminomethyl group as intermediates for chiral 6-membered ring carbene precursors.

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

    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 ΔE 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.

  4. Synthesis and reactivity of cationic triruthenium clusters derived from 2-methyl- and 4-methylpyrimidines: from conventional cyclometalated ligands to novel types of N-heterocyclic carbenes.

    Cabeza, Javier A; García-Álvarez, Pablo; Pérez-Carreño, Enrique; Pruneda, Vanessa

    2013-03-01

    The methylation of the uncoordinated nitrogen atom of the cyclometalated triruthenium cluster complexes [Ru(3)(μ-H)(μ-κ(2)N(1),C(6)-2-Mepyr)(CO)(10)] (1; 2-MepyrH = 2-methylpyrimidine) and [Ru(3)(μ-H)(μ-κ(2)N(1),C(6)-4-Mepyr)(CO)(10)] (9; 4-MepyrH = 4-methylpyrimidine) gives two similar cationic complexes, [Ru(3)(μ-H)(μ-κ(2)N(1),C(6)-2,3-Me(2)pyr)(CO)(10)](+) (2(+)) and [Ru(3)(μ-H)(μ-κ(2)N(1),C(6)-3,4-Me(2) pyr)(CO)(10)](+) (9(+)), respectively, whose heterocyclic ligands belong to a novel type of N-heterocyclic carbenes (NHCs) that have the C(carbene) atom in 6-position of a pyrimidine framework. The position of the C-methyl group in the ligands of complexes 2(+) (on C(2)) and 9(+) (on C(4)) is of key importance for the outcome of their reactions with K[N(SiMe(3))(2)], K-selectride, and cobaltocene. Although these reagents react with 2(+) to give [Ru(3)(μ-H)(μ-κ(2)N(1),C(6)-2-CH(2)-3-Mepyr)(CO)(10)] (3; deprotonation of the C(2)-Me group), [Ru(3)(μ-H)(μ(3)-κ(3)N(1),C(5),C(6)-4-H-2,3-Me(2)pyr)(CO)(9)] (4; hydride addition at C(4)), and [Ru(6)(μ-H)(2){μ(6)-κ(6) N(1),N(1'),C(5),C(5'),C(6),C(6')-4,4'-bis(2,3-Me(2)pyr)}(CO)(18)] (5; reductive dimerization at C(4)), respectively, similar reactions with 9(+) have only allowed the isolation of [Ru(3)(μ-H)(μ(3)-κ(2)N(1),C(6)-2-H-3,4-Me(2)pyr)(CO)(9)] (11; hydride addition at C(2)). Compounds 3 and 11 also contain novel six-membered ring NHC ligands. Theoretical studies have established that the deprotonation of 2(+) and 9(+) (that have ligand-based LUMOs) are charge-controlled processes and that both the composition of the LUMOs of these cationic complexes and the steric protection of their ligand ring atoms govern the regioselectivity of their nucleophilic addition and reduction reactions. PMID:23335264

  5. Water-soluble IrIII N-heterocyclic carbene based catalysts for the reduction of CO2 to formate by transfer hydrogenation and the deuteration of aryl amines in water.

    Azua, Arturo; Sanz, Sergio; Peris, Eduardo

    2011-03-28

    Two new water-soluble [IrI(2)(AcO)(bis-NHC)] complexes (NHC=N-heterocyclic carbene) incorporating a sulfonate functionality have been synthesized. The two complexes have been tested in the reduction of CO(2) with H(2) and iPrOH, and their activity has been compared with similar species without the sulfonate moiety. In both reactions, the complex with the two abnormally bound NHCs shows the best catalytic efficiencies, due to the higher ?-electron-donor character of the ligand. Remarkably, the activities obtained for the reduction of CO(2) under the transfer hydrogenation conditions are the best reported to date in terms of TON value (max. TON=2700). The two new complexes have also shown very good activity in the selective deuteration of arylamines, a process that is known to proceed through a chelate assisted N-directed process. PMID:21365699

  6. Palladium N-Heterocyclic Carbene Precatalyst Site Isolated in the Core of a Star Polymer

    Bukhryakov, Konstantin V.

    2015-10-02

    An approach for supporting a Pd-NHC complex on a soluble star polymer with nanoscale dimensions is described. The resulting star polymer catalyst exhibits excellent activity in cross-coupling reactions, is stable in air and moisture, and is easily recoverable and recyclable. These properties are distinct and unattainable with the small-molecule version of the same catalyst. © 2015 American Chemical Society.

  7. Dearomatization Reactions of N-Heterocycles Mediated by Group 3 Complexes

    Miller, Kevin L [Univ. of California, Los Angeles, CA (United States); Williams, Bryan N [Univ. of California, Los Angeles, CA (United States); Benitez, Diego [California Inst. of Technology (CalTech), Pasadena, CA (United States); Carver, Colin T [Univ. of California, Los Angeles, CA (United States); Ogilby, Kevin R [Univ. of California, Los Angeles, CA (United States); Tkatchouk, Ekaterina [California Inst. of Technology (CalTech), Pasadena, CA (United States); Goddard, William A [California Inst. of Technology (CalTech), Pasadena, CA (United States); Diaconescu, Paula L [Univ. of California, Los Angeles, CA (United States)

    2010-01-13

    Group 3 (Sc, Y, Lu, La) benzyl complexes supported by a ferrocene diamide ligand are reactive toward aromatic N-heterocycles by mediating their coupling and, in a few cases, the cleavage of their C-N bonds. When these complexes reacted with 2,2'-bipyridine or isoquinoline, they facilitated the alkyl migration of the benzyl ligand onto the pyridine ring, a process accompanied by the dearomatization of the N-heterocycle. The products of the alkyl-transfer reactions act as hydrogen donors in the presence of aromatic N-heterocycles, ketones, and azobenzene. Experimental and computational studies suggest that the hydrogen transfer takes place through a concerted mechanism. An interesting disproportionation reaction of the dearomatized, alkyl-substituted isoquinoline complexes is also reported.

  8. Air-stable, convenient to handle Pd based PEPPSI (pyridine enhanced precatalyst preparation, stabilization and initiation) themed precatalysts of N/O-functionalized N-heterocyclic carbenes and its utility in Suzuki-Miyaura cross-coupling reaction.

    Ray, Lipika; Shaikh, Mobin M; Ghosh, Prasenjit

    2007-10-28

    Several new air-stable, convenient to handle and easily synthesized Pd based PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) type precatalysts supported over N/O-functionalized N-heterocyclic carbenes (NHC) namely, trans-[1-(benzyl)-3-(N-t-butylacetamido)imidazol-2-ylidene]Pd(pyridine)Cl2 (), trans-[1-(2-hydroxy-cyclohexyl)-3-(benzyl)imidazol-2-ylidene]Pd(pyridine)Cl2 () and trans-[1-(o-methoxybenzyl)-3-(t-butyl)imidazol-2-ylidene]Pd(pyridine)Br2 (), have been designed. Specifically, the Pd-NHC complexes, , and , were conveniently synthesized from their respective imidazolium halide salts by the reaction with PdCl2 in pyridine in presence of K2CO3 as a base. A new imidazolium chloride salt, 1-(benzyl)-3-(N-t-butylacetamido)imidazolium chloride () was synthesized by the alkylation reaction of benzyl imidazole with N-t-butyl-2-chloroacetamide. The molecular structures of the imidazolium chloride salt, , and the Pd-NHC complexes, , and , have been determined by X-ray diffraction studies. The density functional theory studies of the , and complexes were carried out to in order to gain insight about their structure, bonding and the electronic properties. The nature of the NHC-metal bond in these complexes was examined using Charge Decomposition Analysis (CDA), which revealed that the N-heterocyclic carbene ligands are effective sigma-donors. In addition, the catalysis studies revealed that the Pd-NHC complexes, , and , are effective catalysts for the Suzuki-Miyaura type C-C cross-coupling reactions. PMID:17928912

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

    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.

  10. Palladium-N-heterocyclic carbene (NHC)-catalyzed asymmetric synthesis of indolines through regiodivergent C(sp3)-H activation: scope and DFT study.

    Katayev, Dmitry; Larionov, Evgeny; Nakanishi, Masafumi; Besnard, Cline; Kndig, E Peter

    2014-11-10

    Two bulky, chiral, monodentate N-heterocyclic carbene ligands were applied to palladium-catalyzed asymmetric C-H arylation to incorporate C(sp(3))-H bond activation. Racemic mixtures of the carbamate starting materials underwent regiodivergent reactions to afford different trans-2,3-substituted indolines. Although this CAr-Calkyl coupling requires high temperatures (140-160?C), chiral induction is high. This regiodivergent reaction, when carried out with enantiopure starting materials, can lead to single structurally different enantiopure products, depending on the catalyst chirality. The C-H activation at a tertiary center was realized only in the case of a cyclopropyl group. No C-H activation takes place alpha to a tertiary center. A detailed DFT study is included and analyses of methyl versus methylene versus methine C-H activation is used to rationalize experimentally observed regio- and enantioselectivities. PMID:25262613

  11. Theoretical study on the effect of annelation and carbonylation on the electronic and ligand properties of N-heterocyclic silylenes and germylenes: carbene comparisons begin to break down.

    Guha, Ankur Kanti; Phukan, Ashwini K

    2014-05-01

    Quantum chemical calculations have been carried out to investigate the effect of annelation and carbonylation on the electronic and ligand properties of N-heterocyclic silylenes and germylenes. The thermodynamic stability of these ligands has been found to increase with annelation, while the reverse is true for carbonylation. This is in sharp contrast to N-heterocyclic carbenes (NHCs) where annelation leads to a decrease in their thermodynamic stabilities. Compared to nonannelated derivatives, annelated and carbonylated ones are found to be weaker σ donors but better π acceptors. The effect of carbonylation is more pronounced than annelation toward increasing the π acidity of these ligands. Carbonylation at the α-position with respect to the N atom attached to the Si/Ge center has been found to be the most effective way of enhancing the π acidity of these ligands. The computed natural charges reveal that electrophilicity increases upon both annelation and carbonylation. The calculated values of (31)P NMR chemical shifts of corresponding phosphinidene adducts of these ligands have been found to correlate well with the π acidity of these Si/Ge centers. PMID:24738711

  12. Homoleptic gold(i) N-heterocyclic allenylidene complexes: excited-state properties and lyotropic chromonics.

    Xiao, Xin-Shan; Zou, Chao; Guan, Xiangguo; Yang, Chen; Lu, Wei; Che, Chi-Ming

    2016-03-29

    A series of phosphorescent Au(i) bis(N-heterocyclic allenylidene) complexes, namely [Au([double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]CR(1)R(2))2](+)X(-), were synthesized and structurally characterized. These organometallic complexes exhibit panchromatic transient absorption upon electronic photo-excitation and can self-organize into lyotropic chromonic mesophases in aqueous solutions. PMID:26928852

  13. Stabilities of Immonium Ions Derived from N-Heterocyclic Carbenes Probed by Collision-Induced Dissociation Mass Spectrometry

    Polyakova, Svetlana; Kunetskiy, Roman Alexejevič; Schröder, Detlef

    -, č. 20 (2012), s. 3852-3862. ISSN 1434-193X Grant ostatní: European Research Council(XE) AdG HORIZOMS Institutional support: RVO:61388963 Keywords : carbenes * cations * collision-induced dissociation * density functional calculations * electrospray ionization * lipophilic cations * mass spectrometry * phase-transfer catalysis Subject RIV: CC - Organic Chemistry Impact factor: 3.344, year: 2012

  14. Proton-Transfer Polymerization by N-Heterocyclic Carbenes: Monomer and Catalyst Scopes and Mechanism for Converting Dimethacrylates into Unsaturated Polyesters

    Hong, Miao

    2016-01-18

    This contribution presents a full account of experimental and theoretical/computational investigations into the N-heterocyclic carbene (NHC)-catalyzed proton-transfer polymerization (HTP) that converts common dimethacrylates (DMAs) containing no protic groups into unsaturated polyesters. This new HTP proceeds through the step-growth propagation cycles via enamine intermediates, consisting of the proposed conjugate addition–proton transfer–NHC release fundamental steps. This study examines the monomer and catalyst scopes as well as the fundamental steps involved in the overall HTP mechanism. DMAs having six different types of linkages connecting the two methacrylates have been polymerized into the corresponding unsaturated polyesters. The most intriguing unsaturated polyester of the series is that based on the biomass-derived furfuryl dimethacrylate, which showed a unique self-curing ability Four MeO– and Cl–substituted TPT (1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene) derivatives as methanol insertion products, RxTPT(MeO/H) (R = MeO, Cl; x = 2, 3), and two free carbenes (catalysts), OMe2TPT and OMe3TPT, have been synthesized, while OMe2TPT(MeO/H) and OMe2TPT have also been structurally characterized. The structure/reactivity relationship study revealed that OMe2TPT, being both a strong nucleophile and a good leaving group, exhibits the highest HTP activity and also produced the polyester with the highest Mn, while the Cl–substituted TPT derivatives are least active and efficient. Computational studies have provided mechanistic insights into the tail-to-tail dimerization coupling step as a suitable model for the propagation cycle of the HTP. The extensive energy profile was mapped out and the experimentally observed unicity of the TPT-based catalysts was satisfactorily explained with the thermodynamic formation of key spirocyclic species.

  15. Proton-Transfer Polymerization by N-Heterocyclic Carbenes: Monomer and Catalyst Scopes and Mechanism for Converting Dimethacrylates into Unsaturated Polyesters.

    Hong, Miao; Tang, Xiaoyan; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene Y-X

    2016-02-17

    This contribution presents a full account of experimental and theoretical/computational investigations into the N-heterocyclic carbene (NHC)-catalyzed proton-transfer polymerization (HTP) that converts common dimethacrylates (DMAs) containing no protic groups into unsaturated polyesters. This new HTP proceeds through the step-growth propagation cycles via enamine intermediates, consisting of the proposed conjugate addition-proton transfer-NHC release fundamental steps. This study examines the monomer and catalyst scopes as well as the fundamental steps involved in the overall HTP mechanism. DMAs having six different types of linkages connecting the two methacrylates have been polymerized into the corresponding unsaturated polyesters. The most intriguing unsaturated polyester of the series is that based on the biomass-derived furfuryl dimethacrylate, which showed a unique self-curing ability. Four MeO- and Cl-substituted TPT (1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene) derivatives as methanol insertion products, (Rx)TPT(MeO/H) (R = MeO, Cl; x = 2, 3), and two free carbenes (catalysts), (OMe2)TPT and (OMe3)TPT, have been synthesized, while (OMe2)TPT(MeO/H) and (OMe2)TPT have also been structurally characterized. The structure/reactivity relationship study revealed that (OMe2)TPT, being both a strong nucleophile and a good leaving group, exhibits the highest HTP activity and also produced the polyester with the highest Mn, while the Cl-substituted TPT derivatives are least active and efficient. Computational studies have provided mechanistic insights into the tail-to-tail dimerization coupling step as a suitable model for the propagation cycle of the HTP. The extensive energy profile was mapped out, and the experimentally observed unicity of the TPT-based catalysts was satisfactorily explained with the thermodynamic formation of key spirocyclic species. PMID:26779897

  16. Insights Into the Carbene-Initiated Aggregation of [Fe(cot)2

    Lavallo, Vincent

    2010-11-25

    Carbenes attack! Stable carbenes react with [Fe(cot)2] in very different ways. Whereas the classical N-heterocyclic carbenes induce the formation of tetra- and trimetallic iron clusters, abnormal NHCs and carbocyclic carbenes (BACs) form mono- and bimetallic iron complexes. Cyclic (alkyl)(amino)carbenes (CAACs) react with [Fe(cot)2] in a completely different manner, namely through outersphere [4+1] cycloaddition.

  17. Unprecedented silicon(II)→calcium complexes with N-heterocyclic silylenes.

    Blom, Burgert; Klatt, Günter; Gallego, Daniel; Tan, Gengwen; Driess, Matthias

    2015-01-14

    The first N-heterocyclic silylene (NHSi) complexes of any s-block element to date are reported for calcium: [(η(5)-C5Me5)2Ca←:Si(O-C6H4-2-(t)Bu){(N(t)Bu)2CPh}] (6) and [(η(5)-C5Me5)2Ca←:Si(N(t)BuCH)2] (7). Complexes 6 and 7 are isolable in a facile way upon reaction of the corresponding free N-heterocyclic silylenes (NHSis) with [(η(5)-C5Me5)2Ca] (2). Complexes 6 and 7 were fully characterised by spectroscopic means and the single crystal X-ray diffraction analysis of 6 is also reported. Analysis of the bonding situation by DFT methods including a Bader Atoms in molecules (AIM) analysis is also reported. The bonding interaction between the Si and Ca centres in complexes 6 and 7 can best be viewed as σ-donor-acceptor interactions, with a considerable ionic contribution in the bond. The reactivity towards the oxygen containing substrates THF and benzophenone is also discussed. PMID:25382093

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

    İlknur 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.

  19. The influence of electron delocalization upon the stability and structure of potential N-heterocyclic carbene precursors with 1,3-diaryl-imidazolidine-4,5-dione skeletons

    Hobbs, Matthew; Forster, Taryn; Borau-Garcia, Javier; Knapp, Chrissy; TUONONEN, Heikki; Roesler, Roland

    2010-01-01

    Targeting N-heterocyclic carbenes (NHCs) with increased π-acceptor character featuring N-fluorophenyl substituents, the molecular 2-chloro-1,3-bis(fluorophenyl)imidazolidine-4,5-diones (1a–c) were isolated from the condensation of the corresponding formamidine with oxalyl chloride. These formal adducts of NHCs with hydrogen chloride demonstrated reactivity akin to that of alkyl halides: 1,3,1′,3′-tetrakis(2,6-dimethylphenyl)-[2,2′]diimidazolidinyl-4,5,4′,5′-tetraone (2b) was formed via the re...

  20. N-Heterocyclic carbenepalladium catalysts for the direct arylation of pyrrole derivatives with aryl chlorides

    Ismail zdemir

    2013-02-01

    Full Text Available New PdNHC complexes have been synthesized and employed for palladium-catalyzed direct arylation of pyrrole derivatives by using electron-deficient aryl chlorides as coupling partners. The desired coupling products were obtained in moderate to good yields by using 1 mol % of these air-stable palladium complexes. This is an advantage compared to the procedures employing air-sensitive phosphines, which have been previously shown to promote the coupling of aryl chlorides with heteroarenes.

  1. Addition of Small Electrophiles to N-Heterocyclic-Carbene-Stabilized Disilicon(0): A Revisit of the Isolobal Concept in Low-Valent Silicon Chemistry.

    Arz, Marius I; Straßmann, Martin; Geiß, Daniel; Schnakenburg, Gregor; Filippou, Alexander C

    2016-04-01

    Protonation and alkylation of (Idipp)Si═Si(Idipp) (1) afforded the mixed-valent disilicon(I)-borates [(Idipp)(R)Si(II)═Si(0)(Idipp)][B(Ar(F))4] (1R[B(Ar(F))4]; R = H, Me, Et; Ar(F) = C6H3-3,5-(CF3)2; Idipp = C[N(C6H3-2,6-iPr2)CH]2) as red to orange colored, highly air-sensitive solids, which were characterized by single-crystal X-ray diffraction, IR spectroscopy and multinuclear NMR spectroscopy. Dynamic NMR studies in solution revealed a degenerate isomerization (topomerization) of the "σ-bonded" tautomers of 1H[B(Ar(F))4], which proceeds according to quantum chemical calculations via a NHC-stabilized (NHC = N-heterocyclic carbene) disilahydronium ion ("π-bonded" isomer) and is reminiscent of the degenerate rearrangement of carbenium ions formed upon protonation of olefins. The topomerization of 1H[B(Ar(F))4] provides the first example of a reversible 1,2-H migration along a Si═Si bond observed in a molecular system. In contrast, 1Me[B(Ar(F))4] adopts a "rigid" structure in solution due to the higher energy required for the interconversion of the "σ-bonded" isomer into a putative NHC-stabilized disilamethonium ion. Addition of alkali metal borates to 1 afforded the alkali metal disilicon(0) borates 1M[BAr4] (M = Li, Ar = C6F5; M = Na, Ar = Ar(F)) as brown, air-sensitive solids. Single-crystal X-ray diffraction analyses and NMR spectroscopic studies of 1M[BAr4] suggest in concert with quantum chemical calculations that encapsulation of the alkali metal cations in the cavity of 1 predominantly occurs via electrostatic cation-π interactions with the Si═Si π-bond and the peripheral NHC aryl rings. Displacement of the [Si(NHC)] fragments by the isolobal fragments [PR] and [SiR](-) interrelates the cations [(NHC)(R)Si═Si(NHC)](+) to a series of familiar, multiply bonded Si and P compounds as verified by analyses of their electronic structures. PMID:26978031

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

    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 γ-methyl-α-methylene-γ-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.

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

    Zhang, Yuetao; Schmitt, Meghan; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene Y-X

    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 (I(t)Bu), 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 γ-methyl-α-methylene-γ-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 I(t)Bu. 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, I(t)Bu 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 M(n) = 70-85 kg/mol, regardless of the [MMBL]/[I(t)Bu] ratio employed. The I(t)Bu-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. PMID:24245532

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

    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)

  5. Enyne Metathesis Catalyzed by Ruthenium Carbene Complexes

    Poulsen, Carina Storm; Madsen, Robert

    Enyne metathesis combines an alkene and an alkyne into a 1,3-diene. The first enyne metathesis reaction catalyzed by a ruthenium carbene complex was reported in 1994. This review covers the advances in this transformation during the last eight years with particular emphasis on methodology develop...

  6. Cobalt and Iron Complexes with N-heterocyclic Ligands as Pyrolysis Precursors for Oxygen Reduction Catalysts

    Cobalt and Iron based catalysts for the Oxygen Reduction Reaction (ORR) are a promising alternative to the use of Pt in Polymer Electrolyte Fuel Cells (PEMFC). A systematic study on the influence of the nitrogenated ligand in the precursor complex on the ORR activity was performed. Several Fe and Co complexes were prepared with different N-heterocyclic ligands, namely: meso-tetra-(4-carboxyphenyl)-porphyrin (TCPP), N-methylimidazole (N-Me-Im), 3-amino-1,2,4-triazole-5-carboxylic acid (ATZC), 2,2′-bis(4,5-dimethylimidazole) (bis-Me-Im), phenanthroline (phen), 2-pyrazinecarboxylic acid (CO2-Pz), 3,6-di-2-pyridyl-1,2,4,5-tetrazine (DPTZ) and 2,4,6-tri(2-pyridyl)-s-triazine (TPTZ), adsorbed on a carbon substrate and submitted to thermal treatment. These ligands comprise five and six membered rings with one to four N-atoms. Key parameters such as the pyrolysis temperature, the complex load and the metal: ligand ratio were studied, in order to optimize the efficiency of the catalysts. The synthesized catalysts were characterized by several physical bulk and surface techniques, namely XRD, TGA, Raman spectroscopy, XPS, EDX and electron microscopies (SEM and TEM). The best catalyst was obtained from a Cobalt-phenanthroline precursor, adsorbed on a mesoporous carbon material, and pyrolyzed at 700 °C. The equilibrium potential was 0.90 V vs NHE (1.0 V for Pt), exchange current density 25 μA cm−2, Tafel slope was 90 mV dec−1, and 4.0 exchanged electrons, less than 9 % in H2O2 yield, and half wave potential only 80 mV lower than that of Platinum (10%). This catalyst exhibited the highest N content as determined by XPS. The electrochemical data of the prepared catalysts were analyzed in the context of the TGA, XRD and XPS information. A correlation between ORR activity and the N content (XPS) was found. This result strongly supports the model that proposes N atoms as the active sites, and provides a rational tool for designing new catalysts

  7. Cyclometalated Pd(II) and Ir(III) 2-(4-bromophenyl)pyridine complexes with N-heterocyclic carbenes (NHCs) and acetylacetonate (acac): synthesis, structures, luminescent properties and application in one-pot oxidation/Suzuki coupling of aryl chlorides containing hydroxymethyl.

    Xu, Chen; Li, Hong-Mei; Xiao, Zhi-Qiang; Wang, Zhi-Qiang; Tang, Si-Fu; Ji, Bao-Ming; Hao, Xin-Qi; Song, Mao-Ping

    2014-07-14

    A series of cyclopalladated 2-(4-bromophenyl)pyridine (bpp) complexes [Pd(bpp)(NHC)Cl] 1-3, [Pd(bpp)(acac)] 4, cyclometalated iridium(iii) complexes [Ir(bpp)2Cl]25 and [Ir(bpp)2(acac)] 6 have been synthesized and characterized. Their detailed structures have been determined by X-ray diffraction and many intermolecular C-HX (Cl, Br, ?) and ?? interactions were found in their crystals. Cyclometalated complexes 1-4 and 6 exhibit luminescence with emission peaks of 390-543 nm in dichloromethane solution under UV irradiation. Their application to coupling reactions of aryl chlorides containing hydroxymethyl was also investigated. An efficient 3/Cu cocatalyzed oxidation/Suzuki reaction for the synthesis of biarylaldehydes from chloro-phenylmethanol and arylboronic acids in air has been developed. In addition, a 6/3-cocatalyzed one-pot reaction of acetylferrocene, (2-amino-5-chlorophenyl)methanol, and arylboronic acids provided 6-aryl-2-ferrocenylquinolines in moderate to good yields. PMID:24878778

  8. Carbene insertion into a P-H bond: parent phosphinidene-carbene adducts from PH3 and bis(phosphinidene)mercury complexes.

    Bispinghoff, Mark; Tondreau, Aaron M; Grützmacher, Hansjörg; Faradji, Charly A; Pringle, Paul G

    2016-04-14

    PH3 reacts with the in situ generated N-heterocyclic carbene DippNHC* (DippNHC* = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) to give the phosphanyl-imidazolidine [(Dipp)NHC*-H]-[PH2]. Upon treatment with an ortho-quinone, [(Dipp)NHC*-H]-[PH2] is dehydrogenated to give the parent phosphinidene-carbene adduct (Dipp)NHC*[double bond, length as m-dash]PH. Alternative routes to [(Dipp)NHC*-H]-[PH2] and (Dipp)NHC*[double bond, length as m-dash]PH employ NaPH2 and (TMS)3P7 (TMS = trimethylsilyl), respectively, as phosphorus sources. The adduct (Dipp)NHC*[double bond, length as m-dash]PH and the related adduct (Dipp)NHC[double bond, length as m-dash]PH ((Dipp)NHC = bis(2,6-diisopropylphenyl)imidazol-2-ylidene) possessing an unsaturated NHC backbone both react with HgCl2 to give the bis(carbene-phosphinidenyl) complexes [((Dipp)NHC*[double bond, length as m-dash]P)2Hg] and [((Dipp)NHC[double bond, length as m-dash]P)2Hg]. PMID:26122315

  9. Hammett analysis of a family of carbene-carbene complex equilibria.

    Wang, Lei; Moss, Robert A; Thompson, Jack; Krogh-Jespersen, Karsten

    2011-03-01

    p-X-substituted phenylchlorocarbenes (X = NO(2), CF(3), Cl, H, Me, and MeO) form ?-type complexes with trimethoxybenzene in pentane. The carbenes and complexes are in equilibrium, and logarithms of the measured equilibrium constants are well correlated by Hammett ?(p) constants with ? = 2.48. The carbene complexes are characterized by UV-vis spectroscopy, and computational analysis is afforded by DFT calculations. PMID:21309524

  10. Reactions of aromatic N-heterocycles with a lutetium benzyl complex supported by a ferrocene-diamide ligand.

    Wong, Allison W; Miller, Kevin L; Diaconescu, Paula L

    2010-08-01

    A comparison between the reactivity behavior of two lutetium benzyl complexes supported by different ferrocene-diamide ligands towards aromatic N-heterocycles, such as 1-methylimidazole, isoquinoline, and pyridines, is presented. The two ferrocene-diamide ancillary ligands differ in their nitrogen-donor substituent: adamantyl for one and t-butyldimethylsilyl for the other. The synthesis and characterization of the adamantyl-derived complex 1(Ad)-DME are reported. The ring opening of 1-methylimidazole by the THF analogue of 1(Ad)-DME, 1(Ad)-THF, was observed, analogously to the ring opening of the same substrate by the lutetium benzyl complex supported by the silyl-substituted ligand. Also, analogous products were observed in the reactions with isoquinoline. PMID:20454748

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

    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 (λ max = 450 nm) with a high quantum yield (Φ em = 0.96). The X-ray crystal structure of this complex is characterized by a rather short intramolecular Au•••Au distance (3.272 Ǻ). 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.

  12. Stepwise and one-pot syntheses of Ir(III) complexes with imidazolium-based carbene ligands.

    Chien, Chih-Hsien; Fujita, Singo; Yamoto, Suguru; Hara, Takeshi; Yamagata, Tsuneaki; Watanabe, Masami; Mashima, Kazushi

    2008-02-21

    We report the preparation, crystal structure, electrochemistry, and emission properties of Ir(Cinsertion markC:)3, where Cinsertion markC: is an N-heterocyclic carbene ligand. Two synthetic approaches are introduced for generating Ir(III) complexes bearing imidazolium-based carbene ligands whose precursors are [pypiH2][Cl] (1a) (pyridyl[1,2-a]{2-phenylimidazol}-3-ylidene chloride) and [pympiH2][Cl] (1b) (pyridyl[1,2-a-{2-(p-methoxy)phenylimidazol}-3-ylidene chloride). The first method is a stepwise reaction: treatment of [Ir(mu-Cl)(COD)]2, where COD is 1,5-cyclooctadiene, with 4 equiv. of the corresponding carbene (Cinsertion markC:) ligands in the presence of an excess amount of sodium methoxide affords Ir(III) dimers [Ir(mu-Cl)(Cinsertion markC:)2]2 (2a, Cinsertion markC: = pypi(-); 2b, Cinsertion markC: = pympi(-)). These chloro-bridged dimers 2a and 2b react with the corresponding carbene (Cinsertion markC:) ligands to form the desired homoleptic compounds Ir(Cinsertion markC:)3 (3a, Cinsertion markC: = pypi(-); 3b, Cinsertion markC: = pympi(-)). The second method, using a one-pot reaction of [Ir(mu-Cl)(COD)]2 with 6 equiv. of the corresponding carbene (Cinsertion markC:) ligands 1a and 1b in the presence of excess amounts of Ag2O, affords Ir(Cinsertion markC:)3. The two methods are convenient and reproducible procedures for the synthesis of Ir(Cinsertion markC:)3. Complexes 3a and 3b are obtained as mixtures of meridional and facial isomers, which can be separated by recrystallization or flash column chromatography. PMID:18259625

  13. Application of imidazolinium salts and N-heterocyclic olefins for the synthesis of anionic and neutral tungsten imido alkylidene complexes.

    Imbrich, Dominik A; Frey, Wolfgang; Naumann, Stefan; Buchmeiser, Michael R

    2016-05-01

    The synthesis, single crystal X-ray structure and activity in olefin metathesis of novel anionic tungsten imido alkylidene complexes [1,3-bis-(2,4,6-trimethylphenyl)imidazolinium](+) [W(N-2,6-iPr2C6H3)(CHCMe2Ph)(2,5-Me2Pyr)2Cl](-), [1,3-bis-(2,4,6-trimethylphenyl)imidazolinium](+) [W(N-2,6-iPr2C6H3)(CHCMe2Ph)(2,5Me2Pyr)2(OC6F5)](-), and [1,3-bis-(2,6-diisopropylphenyl)imidazolinium](+) [W(N-2,6-iPr2C6H3)(CHCMe2Ph)(2,5-Me2Pyr)Cl2](-) are reported. Additionally, the first example of a bis(N-heterocyclic olefinium) alkylidene tungstate, W(N-2,6-iPr2C6H3)(CHCMe2Ph)(2-methylene-1,3,4,5-tetramethyl-imidazoline)2(OTf)2, is described, including preparation, crystal structure and catalytic activity. PMID:27068323

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

    Chinnappan Sivasankar; Christina Baskaran; Ashoka G Samuelson

    2006-05-01

    Reaction of oligomeric Cu(I) complexes [Cu{-S-C(=NR)(O-Ar-CH3)}] 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.

  15. Electronic bond tuning with heterocyclic carbenes

    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.

  16. H(C)Ag: a triple resonance NMR experiment for (109) Ag detection in labile silver-carbene complexes.

    Weske, Sebastian; Li, Yingjia; Wiegmann, Sara; John, Michael

    2015-04-01

    In silver complexes, indirect detection of (109) Ag resonances via (1) H,(109) Ag-HMQC frequently suffers from small or absent JHAg couplings or rapid ligand dissociation. In these cases, it would be favourable to employ H(X)Ag triple resonance spectroscopy that uses the large one-bond JXAg coupling (where the donor atom of the ligand X is the relay nucleus). We have applied an HMQC-based version of the H(C)Ag experiment to a labile silver-NHC complex (NHC=N-heterocyclic carbene) at natural (13) C isotopic abundance and variable temperature. In agreement with simulations, H(C)Ag detection became superior to (1) H,(109) Ag-HMQC detection above -20?C. PMID:25641122

  17. 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

    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.

  18. Effects of Phosphine-Carbene Substitutions on the Electrochemical and Thermodynamic Properties of Nickel Complexes

    Galan, Brandon R.; Wiedner, Eric S.; Helm, Monte L.; Linehan, John C.; Appel, Aaron M.

    2014-05-12

    Nickel(II) complexes containing chelating N-heterocyclic carbene-phosphine ligands ([NiL2](BPh4)2, for which L = [MeIm(CH2)2PR2]) have been synthesized for the purpose of studying how this class of ligand effects the electrochemical properties compared to the nickel bis- diphosphine analogues. The nickel complexes were synthesized and characterized by x-ray crystallography and electrochemical methods. Based on the half wave potentials (E1/2), substitution of an NHC for one of the phosphines in a diphoshine ligand results in shifts in potential to 0.6 V to 1.2 V more negative than the corresponding nickel bis-diphosphine complexes. These quantitative results highlight the substantial effect that NHC ligands can have upon the electronic properties of the metal complexes. BRG, JCL, and AMA acknowledge the support by the US Department of Energy Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. MLH acknoledges the support of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

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

    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 π-accepting ability of NHCs, independent of their σ-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 δSe is correlated to the energy gap between a filled lone pair orbital on Se and the empty π* orbital corresponding to the Se–NHC bond. Bond energy decomposition analysis indicated no correlation between the orbital σ-contribution to bonding and the chemical shielding, while a good correlation was found between the π-contribution to bonding and the chemical shielding, confirming that this technique is indeed able to quantify the ability of NHCs to accept π-electron density. Calculations conducted on phosphinidene adducts yielded similar results. With the link between δSe and δP and π-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.

  20. Electron-rich N-heterocyclic silylene (NHSi)-iron complexes: synthesis, structures, and catalytic ability of an isolable hydridosilylene-iron complex.

    Blom, Burgert; Enthaler, Stephan; Inoue, Shigeyoshi; Irran, Elisabeth; Driess, Matthias

    2013-05-01

    The first electron-rich N-heterocyclic silylene (NHSi)-iron(0) complexes are reported. The synthesis of the starting complex is accomplished by reaction of the electron-rich Fe(0) precursor [(dmpe)2Fe(PMe3)] 1 (dmpe =1,2-bis(dimethylphosphino)ethane) with the N-heterocyclic chlorosilylene LSiCl (L = PhC(N(t)Bu)2) 2 to give, via Me3P elimination, the corresponding iron complex [(dmpe)2Fe(?:Si(Cl)L)] 3. Reaction of in situ generated 3 with MeLi afforded [(dmpe)2Fe(?:Si(Me)L)] 4 under salt metathesis reaction, while its reaction with Li[BHEt3] yielded [(dmpe)2Fe(?:Si(H)L)] 5, a rare example of an isolable Si(II) hydride complex and the first such example for iron. All complexes were fully characterized by spectroscopic means and by single-crystal X-ray diffraction analyses. DFT calculations further characterizing the bonding situation between the Si(II) and Fe(0) centers were also carried out, whereby multiple bonding character is detected in all cases (Wiberg Bond Index >1). For the first time, the catalytic activity of a Si(II) hydride complex was investigated. Complex 5 was used as a precatalyst for the hydrosilylation of a variety of ketones in the presence of (EtO)3SiH as a hydridosilane source. In most cases excellent conversions to the corresponding alcohols were obtained after workup. The reaction pathway presumably involves a ketone-assisted 1,2-hydride transfer from the Si(II) to Fe(0) center, as a key elementary step, resulting in a betaine-like silyliumylidene intermediate. The appearance of the latter intermediate is supported by DFT calculations, and a mechanistic proposal for the catalytic process is presented. PMID:23570308

  1. Group 1 and 2 cyclic (alkyl)(amino)carbene complexes.

    Turner, Zoë R; Buffet, Jean-Charles

    2015-08-01

    The first examples of cyclic (alkyl)(amino)carbene (CAAC) ligands bound to electropositive metal centres (K, Mg, Sr and Ba) have been isolated and characterised. Preliminary studies demonstrate that all complexes are active for polar monomer polymerisation under ambient conditions affording desirable hydroxyl-terminated telechelic polymers. PMID:26133112

  2. Ruthenium(II) and osmium(II) 1,2,3-triazolylidene organometallics: a preliminary investigation into the biological activity of 'click' carbene complexes.

    Kilpin, Kelly J; Crot, Stphanie; Riedel, Tina; Kitchen, Jonathan A; Dyson, Paul J

    2014-01-21

    Taking advantage of the facile and versatile synthetic properties of 'click' 1,2,3-triazolylidene N-heterocyclic carbenes (tzNHC's), a range of new organometallic Ru(II) and Os(II) arene complexes containing functionalised tzNHC ligands, [M(?(6)-p-cymene)(tzNHC)Cl2] [M = Ru(II), Os(II)], have been synthesised and fully characterised, including the X-ray crystal structure of one of the Os(II) complexes. The tzNHC ligands remain coordinated to the metal centres under relevant physiological conditions, and following binding to the model protein, ubiquitin. The in vitro cytotoxicity of the compounds towards human ovarian cancer cells is dependent on the substituent on the tzNHC ligand but is generally cancer cells over healthy cells (1.85 ?M in A2780 ovarian cancer cells versus 435 ?M in human embryonic kidney cells in one case). PMID:24201979

  3. Springloaded porphyrin NHC hybrid rhodium(III) complexes: carbene dissociation and oxidation catalysis

    Olguín, Juan; Müller-Bunz, Helge; Albrecht, Martin

    2014-01-01

    Porphyrin rhodium(III) complexes accommodate one or two NHC ligands in the apical position, which leads to severe porphyrin distortion and dearomatization. The strain in the bis(carbene) complex induces facile carbene dissociation and the formation of a catalytically active site for alcohol oxidation.

  4. Axial Ligand Exchange of N-heterocyclic Cobalt(III) Schiff Base Complexes: Molecular Structure and NMR Solution Dynamics

    Manus, Lisa M.; Holbrook, Robert J.; Atesin, Tulay A.; Heffern, Marie C.; Harney, Allison S.; Eckermann, Amanda L.; Meade, Thomas J.

    2013-01-01

    The kinetic and thermodynamic ligand exchange dynamics are important considerations in the rational design of metal-based therapeutics and therefore, require detailed investigation. Co(III) Schiff base complex derivatives of bis(acetylacetone) ethylenediimine [acacen] have been found to be potent enzyme and transcription factor inhibitors. These complexes undergo solution exchange of labile axial ligands. Upon dissociation, Co(III) irreversibly interacts with specific histidine residues of a ...

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

    Metelková, R.; Tobrman, T.; Hoskovcová, I.; Ludvík, Jiří

    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

  6. Synthesis and structure of novel triphenylarsine-substituted tungsten(0) Fischer carbene complexes

    Jansen van Rensburg, Armand; Landman, Maril; van Rooyen, Petrus H.; Conradie, Marrigje M.; Conradie, Jeanet

    2016-02-01

    X-ray crystal structure determination, as well as IR and NMR spectroscopy of four novel triphenylarsine-substituted tetracarbonyl tungsten(0) Fischer carbene complexes of general formula [(CO)4(AsPh3)WC(OEt)(Ar)], with Ar=2-thienyl (1), 2-furyl (2), 2-(N-methyl)pyrrolyl (3), 2,2?-bithienyl (4), revealed a cis-configuration for the substituted AsPh3 group relative to the carbene ligand for all four novel complexes. All X-ray structures showed that the W-C bond trans AsPh3carbenecomplex due to the different possible positions of the ligands and carbene substituents to each other, correlated with the experimental results.

  7. Iron in the Service of Chromium – the ortho-Benzannulation of trans, trans-Dienyl Fischer Carbene Complexes

    Lian, Yiqian; Wulff, William D.

    2005-01-01

    Chromium Fischer carbene complexes with trans, trans-dienyl substituents on the carbene carbon will react with diiron nonacarbonyl to give 2-alkoxycyclohexa-2,4-dienone iron tricarbonyl complexes and/or 2-alkoxyphenols in excellent yields. In the presence of silica gel or base, the cyclohexadienone complex will suffer loss of the iron and aromatization to give 2-alkoxyphenols. The formation of 2-alkoxyphenols from dienyl chromium carbene complexes is a known process (ortho-benzannulation) tha...

  8. A continuum of progress: applications of N-hetereocyclic carbene catalysis in total synthesis.

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

    2012-11-19

    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. These transformations employ typical as well as Umpolung types of bond disconnections and have served as the key step in several new total syntheses. This Minireview highlights these reports and captures the excitement and emerging synthetic utility of carbene catalysis in total synthesis. PMID:23074146

  9. A DFT and structural investigation of the conformations of Fischer carbene complexes

    Landman, Maril

    2015-09-01

    A set of different Fischer carbene complexes of group VI and VII metals, with varied heteroatom and heteroaromatic substituents on the carbene carbon atom, was studied. Density functional theory as well as single crystal diffraction techniques were employed to investigated the most stable conformation of these complexes. The complexes studied, [M(CO)4L{C(X)Z}], with L = PPh3 or CO, X = ethoxy (-OCH2CH3) or amino (-NH2 or NHCy) substituents as the heteroatom carbene substituents, Z = 2-furyl (-C4H3O), 2-thienyl (-C4H3S), 2-(N-methyl)pyrrolyl (-C4H3NCH3) as the second carbene substituent had their substituents varied systematically to give all the possible conformations of these complexes. The conformations of the complexes, in particular the relative orientations of the heteroatoms in the molecule (syn vs. anti), E/Z isomerism in the aminocarbene complexes and cis/trans isomerism in the ligand substituted complexes as well as various combinations of these aspects, were studied. In general, it was found that the most stable conformation theoretically as well as in the solid state for most of the complexes preferred the syn conformation. The Z-isomer is generally preferred over the E isomer while the cis is more predominant than the trans isomer. Using DFT and NBO calculations, explanations for the preferred conformations were explored. It was concluded that both steric and electronic factors influence the conformations of the carbene complexes, with the extent of contribution of these two factors varying for each of the different carbene substituents.

  10. Silver-Catalyzed Amidiniumation of Alkynes: Isolation of a Silver Intermediate, Synthesis of Enamine Amido Carbene Precursors, and an Unprecedented Umpolung of Propiolamide.

    Lv, Shichang; Wang, Jiwei; Zhang, Caiyun; Xu, Sheng; Shi, Min; Zhang, Jun

    2015-12-01

    A silver-catalyzed amidiniumation of N-propiolic formamidines for the synthesis of novel enamine amido carbene precursors is reported. Isolation of a first silver intermediate in silver-catalyzed amidiniumation of alkynes and other organogold intermediates supports our proposed mechanisms. Several control experiments reveal the unexpected effects of both HOTf and substrate substituents on the choice of either a ? or ?,??silver activation mode and the cyclization fashion. Bis(hydroxyimidazol)ium salts were obtained through an unprecedented umpolung of propiolamides. The byproduct Ag2 O as either an oxidant or silver source promotes the syntheses of N-heterocyclic carbene (NHC) precursors or Ag/NHC complexes. PMID:26473976

  11. 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

    Shawna L. Balof

    2015-10-01

    Full Text Available Three new ruthenium alkylidene complexes (PCy3Cl2(H2ITapRu=CHSPh (9, (DMAP2Cl2(H2ITapRu=CHPh (11 and (DMAP2Cl2(H2ITapRu=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.

  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.

    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. Flexible Structural Features of Pentafulvene Titanium Derivatives: Isolation and Characterization of NHC Complexes.

    Manßen, Manfred; Adler, Christian; Beckhaus, Rüdiger

    2016-03-18

    The reaction of η(5) ,η(1) -pentafulvene titanium complexes with the strong N-heterocyclic carbene (NHC) donor 1,3,4,5-tetramethylimidazole-2-ylidene, leads to the formation of isolable NHC titanium adducts, featuring a haptotropic shift of the pentafulvene ligand, proved by single crystal X-ray diffraction as well as NMR spectroscopy studies. PMID:26852891

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

    Liu, Yizhu; Kjær, Kasper Skov; Fredin, Lisa A.; Chabera, Pavel; Harlang, Tobias C. B.; Canton, Sophie E.; Lidin, Sven; Zhang, Jianxin; Lomoth, Reiner; Bergquist, Karl-Erik; Persson, Petter; Wärnmark, Kenneth; Sundström, Villy

    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...

  15. Recent Developments in the Chemistry of N-Heterocyclic Phosphines

    Gudat, Dietrich

    This chapter gives a survey on five- and six-membered phosphorus-nitrogen heterocyclic compounds whose rings combine a phosphazene (>N-P = N-) or phosphazane (>N-P(X)-N<) unit with an unsaturated C2 or C3 building block. Representatives contain structurally diverse species like aromatic 1,3,2-diazaphosphinines and (benzo)-1,3,2-diazaphospholes, cationic counterparts of subvalent main-group carbene analogues like 1,3,2-diazaphospholenium ions and phosphenium-diketiminates, and neutral heterocycles like 1,3,2-diazaphospholenes featuring unusual structures and reactivities. The exploration of these species developed rapidly in the last two decades in the wake of cutting edge research on multiple bonding and low coordination in the chemistry of heavier main-group elements, and the discovery of stable carbenes. This review summarizes the elaboration of synthetic approaches for different types of N-heterocyclic phosphine derivatives, discusses their characterization by physical and computational methods which furnished a thorough understanding of structure and bonding, and finally highlights accomplishments in the exploration of the chemical properties at the border of classical organic heterocyclic chemistry and molecular inorganic chemistry.

  16. Ru-Ag and Ru-Au dicarbene complexes from an abnormal carbene ruthenium system.

    Bitzer, Mario J; Pthig, Alexander; Jandl, Christian; Khn, Fritz E; Baratta, Walter

    2015-07-14

    Reaction of [Ru(OAc)2(PPh3)2] with a P-functionalized imidazolium bromide easily affords a cationic abnormal carbene Ru system. Metalation with Ag2O yields a Ru-Ag complex containing an anionic dicarbene ligand, while subsequent transmetalation with Au(tht)Cl leads to the corresponding Ru-Au system. The bimetallic complexes were characterized by single crystal X-ray diffraction and are the first examples of complexes bearing anionic dicarbene ligands connecting two different d-block elements. PMID:26053614

  17. Chiral PEPPSI Complexes: Synthesis, Characterization, and Application in Asymmetric Suzuki–Miyaura Coupling Reactions

    Benhamou, Laure

    2014-01-13

    PEPPSI complexes incorporating chiral N-heterocyclic carbene (NHC) ligands based on 2,2-dimethyl-1-(o-substituted aryl)propan-1-amines were synthesized. Two complexes, with one saturated and one unsaturated NHC ligand, were structurally characterized. The chiral PEPPSI complexes were used in asymmetric Suzuki-Miyaura reactions, giving atropisomeric biaryl products in modest to good enantiomeric ratios. © 2013 American Chemical Society.

  18. A two-color fluorogenic carbene complex for tagging olefins via metathesis reaction

    Wirtz, Marcel; Grüter, Andreas; Heib, Florian; Huch, Volker; Zapp, Josef; Herten, Dirk-Peter; Schmitt, Michael; Jung, Gregor

    2015-12-01

    We describe a fluorogenic ruthenium (II) carbene complex in which the chromophore is directly connected to the metal center. The compound introduces a boron dipyrromethene (BODIPY) moiety into target double bonds by metathesis. Tagging of terminal double bonds is demonstrated on immobilized styrene units on a glass surface. We also show that two compounds with distinguishable fluorescence properties are formed in the model reaction with styrene. The outcome of the metathesis reaction is characterized by 19F-NMR, optical spectroscopy, and, finally, single-molecule trajectories. This labeling scheme, in our perception, is of particular interest in the fields of interfacial science and biorthogonal ligation in combination with super-resolution imaging.

  19. N-Heterocyclic olefin stabilized boron dication.

    Lee, Wan-Hua; Lin, Ya-Fan; Lee, Gene-Hsiang; Peng, Shie-Ming; Chiu, Ching-Wen

    2016-04-14

    Boron mono- and di-cations featuring a nucleophilic N-heterocyclic olefin and the pentamethylcyclopentadienyl substituent have been prepared and structurally characterized. Experimental and theoretical investigations show that [η(5)-Cp*B-NHO](2+) is considerably more Lewis acidic than [η(5)-Cp*B-IMes](2+) due to the steric congestion imposed by the bent geometry of NHO around the central boron atom. PMID:26603655

  20. Transfer hydrogenation of ketones and activated olefins using chelating NHC ruthenium complexes

    Horn, Sabine; Gandolfi, Claudio; Albrecht, Martin, 1969-

    2011-01-01

    N-Heterocyclic carbene (NHC) ruthenium complexes consisting of different donor substituents attached to the NHC ligand efficiently catalyse the transfer hydrogenation of ketones and of activated olefins in α,β-unsaturated ketones to give saturated alcohols. The most active catalyst precursor contains a tethered olefin as a hemilabile donor site. This complex also converts nitriles and, depending on the reaction conditions, either benzylamines are produced by means of transfer hydrogenation, o...

  1. Suzuki–Miyaura cross-coupling reaction of 1-aryltriazenes with arylboronic acids catalyzed by a recyclable polymer-supported N-heterocyclic carbene–palladium complex catalyst

    Guangming Nan

    2010-06-01

    Full Text Available The Suzuki–Miyaura cross-coupling reaction of 1-aryltriazenes with arylboronic acids catalyzed by a recyclable polymer-supported Pd–NHC complex catalyst has been realized for the first time. The polymer-supported catalyst can be re-used several times still retaining high activity for this transformation. Various aryltriazenes were investigated as electrophilic substrates at room temperature to give biaryls in good to excellent yields and showed good chemoselectivity over aryl halides in the reactions.

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

    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

  3. Synthesis of phenanthrene derivatives through the net [5+5]-cycloaddition of prenylated carbene complexes with 2-alkynylbenzaldehyde derivatives

    Menon, Suneetha; Sinha-Mahapatra, Dilip; Herndon, James W.

    2007-01-01

    The reaction of prenylated carbene complexes and 2-alkynylbenzoyl derivatives has been investigated. Phenanthrene derivatives are produced if iodine is added prior to product isolation. Under these conditions alkyl migration reactions occur to form the observed products. The product yields are considerably higher using bis(prenylated) species owing to an increase in the effective molarity of dienophilic entities.

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

    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.

  5. Ruthenium(II) Complexes Containing Lutidine-derived Pincer CNC Ligands: Synthesis, Structure and Catalytic Hydrogenation of C=N bonds

    Hernández-Juárez, M.; López-Serrano, Joaquín; Lara, Patricia; Morales-Cerón, Judith; Vaquero, Mónica; Álvarez, Eleuterio; Salazar, Verónica; Suárez, Andrés

    2015-01-01

    A series of Ru complexes 3-5 containing lutidine-derived pincer CNC ligands have been prepared by transmetallation with the corresponding silver-carbene derivatives 2. Characterization of these derivatives shows both mer and fac coordination of the CNC ligands depending on the wingtips of the N-heterocyclic carbene fragments. Ru-CNC complexes 3-4 are active, in the presence of tBuOK, in the hydrogenation of a series of imines. In addition, these complexes also catalyze the reversible hydrogen...

  6. Stabilization of cyclic and acyclic carbon(0) compounds by differential coordination of heterocyclic carbenes: a theoretical assessment.

    Phukan, Ashwini K; Guha, Ankur Kanti

    2012-08-01

    Recently, donor stabilized divalent carbon(0) compounds have undergone intense experimental and theoretical investigation due to their strong electron rich character. In this Article, some new cyclic and acyclic carbon(0) compounds stabilized by differential coordination modes (such as abnormal, remote and a mixture of both) of N-heterocyclic carbenes are studied theoretically. The cyclic carbon(0) compounds proposed in this study are unusual in the sense that they contain a five membered ring consisting of only carbon atoms with a central carbon atom in the formal oxidation state of zero. All these compounds are found to be very strong nucleophiles which might have wide implications in catalysis. Calculation of first proton affinities of these molecules reveal that they are better ? donors than the carbon(0) compound supported by normal N-heterocyclic carbenes. Quantum chemical calculations indicate that these molecules possess very high donor-acceptor L ? C bond strengths and are thermodynamically stable. Calculation of the bond dissociation energies for the complexation of one and two molecules of AuCl indicates the possible isolation of their gem dimetalated derivatives. PMID:22717622

  7. Regarding the mechanism of olefin metathesis with sol-gel-supported Ru-based complexes bearing a bidentate carbene ligand. Spectroscopic evidence for return of the propagating Ru carbene.

    Kingsbury, Jason S; Hoveyda, Amir H

    2005-03-30

    Two isotopically and structurally labeled Ru-based carbenes (2-d4 and 13) have been prepared and attached to the surface of monolithic sol-gel glass. The resulting glass-supported complexes (18-dn and 19) exhibit significant catalytic activity in promoting olefin metathesis reactions and provide products of high purity. Through analysis of the derivatized glass pellets used in a sequence of catalytic ring-closing metathesis reactions mediated by various supported Ru carbenes, it is demonstrated that free Ru carbene intermediates in solution can be scavenged by support-bound styrene ether ligands prior to the onset of competing transition metal decomposition. The observations detailed herein provide rigorous evidence that the initially proposed release/return mechanism is, at least partially, operative. The present investigations shed light on a critical aspect of the mechanism of an important class of Ru-based metathesis complexes (those bearing a bidentate styrene ether ligand). PMID:15783234

  8. Role of gold(I) ?-oxo carbenes in the oxidation reactions of alkynes catalyzed by gold(I) complexes.

    Schulz, Ji?; Jakov, Lucie; Skrba, Anton; Roithov, Jana

    2014-08-13

    The gas phase structures of gold(I) complexes formed by intermolecular oxidation of selected terminal (phenylacetylene) and internal alkynes (2-butyne, 1-phenylpropyne, diphenylacetylene) were investigated using tandem mass spectrometry and ion spectroscopy in conjunction with quantum-chemical calculations. The experiments demonstrated that the primarily formed ?-gold(I) vinyloxypyridinium complexes readily undergo rearrangement, dependent on their substituents, to either gold(I) ?-oxo carbenenoids (a synthetic surrogate of the ?-oxo carbenes) or pyridine adducts of gold(I) enone complexes in the condensed phase and that the existence of naked ?-oxo carbenes is highly improbable. Isotopic labeling experiments performed with the reaction mixtures clearly linked the species that exist in solution to the ions transferred to the gas phase. The ions were then fully characterized by CID experiments and IRMPD spectroscopy. The conclusions based on the experimental observations perfectly correspond with the results from quantum-chemical calculations. PMID:25068382

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

    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.

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

    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.

  11. Effect of CO substitution on the redox properties of Fischer Mo(0) carbene complexes Mo(CO)5=C(Y)(2-Furyl), Y = OEt, NHCy or NH2

    Highlights: • Oxidation potential (CO)5Mo-carbene > (CO)4(PPh3)Mo-carbene > (CO)3(dppe)Mo-carbene • Different oxidation potential for fac and mer isomers • Different oxidation potential for cis and trans isomers • Lower oxidation potential for amino- than ethoxy carbenes - Abstract: An electrochemical study, complimented by a density functional theory study, on nine Mo(0) Fischer carbene complexes of the formula [(CO)3(L,L′)Mo=C(Y)(2-furyl)] with Y = OEt, NH2 or NHCy; L,L′ = CO,CO; PPh3,CO or dppe (diphenyl phosphinoethane), showed that the Mo-based oxidation process can be systematically tuned by the substitution of the CO groups: (most difficult to oxidize, largest oxidation potential Epa) [(CO)5Mo-carbene complex] > [(CO)4(PPh3)Mo-carbene complex] > [(CO)3(dppe)Mo-carbene complex]. The one-electron reduction of the complexes that is mainly localized on the carbene carbon, followed the same trend

  12. Bond Activation by Metal-Carbene Complexes in the Gas Phase.

    Zhou, Shaodong; Li, Jilai; Schlangen, Maria; Schwarz, Helmut

    2016-03-15

    "Bare" metal-carbene complexes, when generated in the gas phase and exposed to thermal reactions under (near) single-collision conditions, exhibit rather unique reactivities in addition to the well-known metathesis and cyclopropanation processes. For example, at room temperature the unligated [AuCH2](+) complex brings about efficient C-C coupling with methane to produce C2Hx (x = 4, 6), and the couple [TaCH2](+)/CO2 gives rise to the generation of the acetic acid equivalent CH2═C═O. Entirely unprecedented is the thermal extrusion of a carbon atom from halobenzenes (X = F, Cl, Br, I) by [MCH2](+) (M = La, Hf, Ta, W, Re, Os) and its coupling with the methylene ligand to deliver C2H2 and [M(X)(C5H5)](+). Among the many noteworthy C-N bond-forming processes, the formation of CH3NH2 from [RhCH2](+)/NH3, the generation of CH2═NH2(+) from [MCH2](+)/NH3 (M = Pt, Au), and the production of [PtCH═NH2](+) from [PtCH2](+)/NH3 are of particular interest. The latter species are likely to be involved as intermediates in the platinum-mediated large-scale production of HCN from CH4/NH3 (the DEGUSSA process). In this context, a few examples are presented that point to the operation of co-operative effects even at a molecular level. For instance, in the coupling of CH4 with NH3 by the heteronuclear clusters [MPt](+) (M = coinage metal), platinum is crucial for the activation of methane, while the coinage metal M controls the branching ratio between the C-N bond-forming step and unwanted soot formation. For most of the gas-phase reactions described in this Account, detailed mechanistic insight has been derived from extensive computational work in conjunction with time-honored labeling and advanced mass-spectrometry-based experiments, and often a coherent description of the experimental findings has been achieved. As for some transition metals, in particular those from the third row, the metal-carbene complexes can be formed directly from methane, coupling of the so-generated [MCH2] species with an inert molecule such as CH4, CO2, or NH3 constitutes a route to activate and functionalize methane under ambient conditions. Clearly, while these gas-phase studies cannot be translated directly to formally related processes in solution or those that occur at a surface, they nevertheless provide a conceptual mechanistic understanding and permit researchers to probe directly the remarkable intrinsic features of these elusive molecules and, in a broader context, help to identify the active site of a catalyst, the so-called "aristocratic atoms". PMID:26870872

  13. Understanding the Mechanism of the Divergent Reactivity of Non-Heteroatom-Stabilized Chromium Carbene Complexes with Furfural Imines: Formation of Benzofurans and Azetines.

    Funes-Ardoiz, Ignacio; González, Jairo; Santamaría, Javier; Sampedro, Diego

    2016-02-19

    The mechanisms of the reaction between non-heteroatom-stabilized alkynyl chromium carbene complexes prepared in situ and furfural imines to yield benzofurans and/or azetines have been explored by means of density functional theory method calculations. The reaction proceeds through a complex cascade of steps triggered by a nucleophilic addition of the imine nitrogen atom. The formation of two benzofuran regioisomers has been explained in terms of competitive nucleophilic attacks to different positions of the carbene complex. Each of these regioisomers can be obtained as the major product depending on the starting materials. The overall sequence could be controlled to yield benzofurans or azetines by adjusting the substituents present in the initial carbene complex. This mechanistic information allowed for the preparation of new benzofurans and azetinylcarbenes in good yields. PMID:26799934

  14. Characteristics and nature of the intermolecular interactions in boron-bonded complexes with carbene as electron donor: an ab initio, SAPT and QTAIM study.

    Esrafili, Mehdi D

    2012-05-01

    We report geometries, stabilization energies, symmetry adapted perturbation theory (SAPT) and quantum theory of atoms in molecules (QTAIM) analyses of a series of carbene-BX(3) complexes, where X = H, OH, NH(2), CH(3), CN, NC, F, Cl, and Br. The stabilization energies were calculated at HF, B3LYP, MP2, MP4 and CCSD(T)/aug-cc-pVDZ levels of theory using optimized geometries of all the complexes obtained from B3LYP/aug-cc-pVTZ. Quantitatively, all the complexes indicate the presence of B-C(carbene) interaction due to the short B-C(carbene) distances. Inspection of stabilization energies reveals that the interaction energies increase in the order NH(2) > OH > CH(3) > F > H > Cl > Br > NC > CN, which is the opposite trend shown in the binding distances. Considering the SAPT results, it is found that electrostatic effects account for about 50% of the overall attraction of the studied complexes. By comparison, the induction components of these interactions represent about 40% of the total attractive forces. Despite falling in a region of charge depletion with nabla(2)ρ(BCP) >0, the B-C(carbene) bond critical points (BCPs) are characterized by a reasonably large value of the electron density (ρ(BCP)) and H(BCP) kinetic energy density at BCP and the B-C(carbene) bond is a polar covalent bond. PMID:21877151

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

    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.

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

    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 β = 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, β = 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

  17. Steering S-H and N-H bond activation by a stable n-heterocyclic silylene: different addition of H(2)S, NH(3), and organoamines on a silicon(II) ligand versus its Si(II)-->Ni(CO)(3) complex.

    Meltzer, Antje; Inoue, Shigeyoshi; Präsang, Carsten; Driess, Matthias

    2010-03-10

    The strikingly different behavior of the ylide-like, N-heterocyclic silylene LSi: (5: L = CH[(C horizontal lineCH(2))CMe(NAr)(2)]; Ar = 2,6-(i)PrC(6)H(3)) versus its LSi-->Ni(CO)(3) complex 13 to activate E-H bonds (E = S, N) of small molecules is reported. Remarkably, conversion of 5 with hydrogen sulfide leads exclusively to the first isolable silathioformamide, L'Si( horizontal lineS)H (16: L' = CH[C(Me)NAr](2); Ar = 2,6-(i)PrC(6)H(3)) with a donor-supported Si horizontal lineS double bond and four-coordinate silicon. The latter result demonstrates the unusual ambivalent reactivity of 5 by combining two modes of reactivity involving S-H bond activation and subsequent 1,4- and 1,1-addition, respectively. In addition, 5 can serve as a ligand with well-balanced sigma-donor and pi-acceptor capabilities toward transition metals. This has been demonstrated by the isolable [Ni(0)(arene)] complexes 12a-e (arene = Me(n)C(6)H(6-n), n = 0-3), which are ideal precursors for the formation of the corresponding Ni(CO)(3) complex 13. The latter activates a S-H bond in hydrogen sulfide, too, but the presence of the Ni(CO)(3) moiety governs the formation of the complex 17, bearing an unprecedented beta-diketiminate silicon(II) thiol ligand: L'Si(SH): (L' = CH[C(Me)NAr](2); Ar = 2,6-(i)PrC(6)H(3)). Likewise, the Si(II)-->Ni(CO)(3) coordination in 13 steers exclusively 1,4-addition of ammonia, isopropylamine, and phenylhydrazine onto the silylene ligand 5, leading to the corresponding beta-diketiminate silicon(II) amide or hydrazide complexes L'Si(NHR)-->Ni(CO)(3) (23a-c: R = H, (i)Pr, N(H)Ph). IR measurements reveal that the carbonyl stretching frequencies of the Ni(CO)(3) moiety in 23a-c are shifted to even lower wavenumbers in comparison to those of NHCs or phosphines. In other words, the beta-diketiminate silicon(II) amide ligands in 23a-c represent the strongest donors in the series of N-heterocyclic silylenes reported as yet. PMID:20148586

  18. Investigation of the properties of 4,5-dialkylated N-heterocyclic carbenes

    Urban, S.; Tursky, Matyas; Frohlich, R.; Glorius, F.

    The investigation of the electronic and steric properties of 4,5-disubstituted imidazolylidenes is reported, as well as their successful application as organocatalysts in the formation of gamma-butyrolactones by conjugate Umpolung....

  19. Carbene-mediated self-assembly of diamondoids on metal surfaces

    Adhikari, Bibek; Meng, Sheng; Fyta, Maria

    2016-04-01

    N-heterocyclic carbenes (NHC)s are emerging as an alternative class of molecules to thiol-based self-assembled monolayers (SAMs), making carbene-based SAMs much more stable under harsh environmental conditions. In this work, we have functionalized tiny diamondoids using NHCs in order to prepare highly stable carbene-mediated diamondoid SAMs on metal substrates. Using quantum-mechanical simulations and two different configurations for the carbene-functionalized diamondoids attached on gold, silver, and platinum surfaces we were able to study in detail these materials. Specifically, we focus on the binding characteristics, stability, and adsorption of the NHC-mediated diamondoid SAMs on the metal surfaces. A preferential binding to platinum surfaces was found, while a modulation of the work function in all cases was clear. The surface morphology of all NHC-based diamondoid SAMs was revealed through simulated STM images, which show characteristic features for each surface.

  20. A general access to organogold(iii) complexes by oxidative addition of diazonium salts.

    Huang, Long; Rominger, Frank; Rudolph, Matthias; Hashmi, A Stephen K

    2016-05-11

    At room temperature under mild photochemical conditions, namely irradiation with a simple blue light LED, gold(i) chloro complexes of both phosphane and carbene ligands in combination with aryldiazonium salts afford arylgold(iii) complexes. With chelating P,N-ligands cationic six- or five-membered chelate complexes were isolated in the form of salts with weakly coordinating counter anions that were brought in from the diazonium salt. With monodentate P ligands or N-heterocyclic carbene ligands and diazonium chlorides neutral arylgold(iii) dichloro complexes were obtained. The coordination geometry was determined by X-ray crystal structure analyses of representative compounds, a cis arrangement of the aryl and the phosphane ligand at the square planar gold(iii) center is observed. PMID:27094217

  1. Stoichiometric sensitivity and structural diversity in click-active copper(I) N,S-heterocyclic carbene complexes.

    Han, Xiaoyan; Weng, Zhiqiang; Young, David James; Jin, Guo-Xin; Hor, T S Andy

    2014-01-21

    A series of novel Cu(I) N,S-heterocyclic carbene (NSHC) complexes [Cu(μ-Br)(NSHC)]2, [Cu(μ-X)(NSHC)]4 (X = Br or I), [(NSHC)2Cu(μ-Br)2Cu(NSHC)], and [(NSHC)2CuBr] have been isolated from in situ generated CuO(t)Bu and N-substituted benzothiazolium halides and characterized by X-ray crystallography. Five structural motifs were observed, viz. M(x)L(y) where x : y = 2 : 2, 4 : 4, 2 : 3, 1 : 2 and 2 : 4, with Cu···Cu separation traversing over a wide range of 2.5626(7) to 3.4725(7) Å distances. A preliminary investigation of the catalytic activity of these compounds indicated that the unusual mononuclear complex 6 [(NSHC)2CuBr] is an active catalyst for the Huisgen 1,3-dipolar cycloaddition of azide and alkynes while complexes 1-5 and 7 were marginally less active. PMID:24192930

  2. Synthesis, crystal, and biological activity of a novel carbene silver(I) complex with imidazole derivative

    Jiu-Fu, Lu, E-mail: jiufulu@163.com; Hong-Guang, Ge; Juan, Shi [Chemical Engineering College, Shaanxi University of Technology (China)

    2015-12-15

    Reaction of 2-(1-methyl-1,2-dihydroimidazol-3-yl)acetonitrile tetrafluoroborate with silver oxide in dichloromethane readily yields [Ag(DIM){sub 2}]BF{sub 4}, where DIM is 2-(1-methyl-1, 2-dihydroimidazol-3-yl)acetonitrile, representing a carbene organic ligand. The title compound was characterized by elemental analysis, IR, MS and single crystal X-ray diffraction. The crystal is of monoclinic system, space group C2/c with a = 14.010(18), b = 8.303(11), c = 14.936(20) Å, β = 93.910(4)°, V = 1639(4) Å{sup 3}, Z = 4, D{sub x} = 1.771 g/cm{sup 3}, F (000) = 864, µ(MoK{sub α}) = 1.278 mm{sup –1}. The final R{sup 1} = 0.0711 and wR{sup 2} = 0.1903 for reflections with I > 2σ(I). In addition, the preliminary biological test showed that the title compound had anti-fungus yeast activity.

  3. Synthesis, crystal, and biological activity of a novel carbene silver(I) complex with imidazole derivative

    Jiu-Fu, Lu; Hong-Guang, Ge; Juan, Shi

    2015-12-01

    Reaction of 2-(1-methyl-1,2-dihydroimidazol-3-yl)acetonitrile tetrafluoroborate with silver oxide in dichloromethane readily yields [Ag( DIM)2]BF4, where DIM is 2-(1-methyl-1, 2-dihydroimidazol-3-yl)acetonitrile, representing a carbene organic ligand. The title compound was characterized by elemental analysis, IR, MS and single crystal X-ray diffraction. The crystal is of monoclinic system, space group C2/ c with a = 14.010(18), b = 8.303(11), c = 14.936(20) Å, β = 93.910(4)°, V = 1639(4) Å3, Z = 4, D x = 1.771 g/cm3, F (000) = 864, µ(Mo K α) = 1.278 mm-1. The final R 1 = 0.0711 and wR 2 = 0.1903 for reflections with I > 2σ( I). In addition, the preliminary biological test showed that the title compound had anti-fungus yeast activity.

  4. Synthesis, crystal, and biological activity of a novel carbene silver(I) complex with imidazole derivative

    Reaction of 2-(1-methyl-1,2-dihydroimidazol-3-yl)acetonitrile tetrafluoroborate with silver oxide in dichloromethane readily yields [Ag(DIM)2]BF4, where DIM is 2-(1-methyl-1, 2-dihydroimidazol-3-yl)acetonitrile, representing a carbene organic ligand. The title compound was characterized by elemental analysis, IR, MS and single crystal X-ray diffraction. The crystal is of monoclinic system, space group C2/c with a = 14.010(18), b = 8.303(11), c = 14.936(20) Å, β = 93.910(4)°, V = 1639(4) Å3, Z = 4, Dx = 1.771 g/cm3, F (000) = 864, µ(MoKα) = 1.278 mm–1. The final R1 = 0.0711 and wR2 = 0.1903 for reflections with I > 2σ(I). In addition, the preliminary biological test showed that the title compound had anti-fungus yeast activity

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

    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.

  6. Rh-Catalyzed rearrangement of vinylcyclopropane to 1,3-diene units attached to N-heterocycles

    Alberto Brandi

    2011-03-01

    Full Text Available Dienes embedded in quinolizidine and indolizidine structures can be prepared in four steps from cyclic nitrones and bicyclopropylidene. The key intermediates ?-spirocyclopropanated N-heterocyclic ketones, generated via a domino 1,3-dipolar cycloaddition/thermal rearrangement sequence, were converted by Wittig methylenation to the corresponding vinylcyclopropanes (VCPs, which underwent rearrangement to 1,3-dienes in the presence of the Wilkinson Rh(I complex under microwave heating. The previously unexplored Rh(I-catalyzed opening of the VCP moiety embedded in an azapolycyclic system occurs at high temperature (110130 C to afford the corresponding 1,3-dienes in moderate yield (3453%.

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

    Vummaleti, Sai V. C.

    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) σ-bond, conferring carbocationic character (and reactivity) to the distal alkyne C atom. © 2014 American Chemical Society.

  8. Reductive dimerization of triruthenium clusters containing cationic aromatic N-heterocyclic ligands.

    Cabeza, Javier A; del Río, Ignacio; Pérez-Carreño, Enrique; Pruneda, Vanessa

    2010-05-10

    The cationic cluster complexes [Ru(3)(mu-H)(mu-kappa(2)N,C-L(1) Me)(CO)(10)](+) (1(+); HL(1) Me=N-methylpyrazinium), [Ru(3)(mu-H)(mu-kappa(2)N,C-L(2) Me)(CO)(10)](+) (2(+); HL(2) Me=N-methylquinoxalinium), and [Ru(3)(mu-H)(mu-kappa(2)-N,C-L(3) Me)(CO)(10)](+) (3(+); HL(3) Me=N-methyl-1,5-naphthyridinium), which contain cationic N-heterocyclic ligands, undergo one-electron reduction processes to become short lived, ligand-centered, trinuclear, radical species (1-3) that end in the formation of an intermolecular C--C bond between the ligands of two such radicals, thus leading to neutral hexanuclear derivatives. These dimerization processes are selective, in the sense that they only occur through the exo face of the bridging ligands of trinuclear enantiomers of the same configuration, as they only afford hexanuclear dimers with rac structures (C(2) symmetry). The following are the dimeric products that have been isolated by using cobaltocene as reducing agent: [Ru(6)(mu-H)(2){mu(6)-kappa(4)N(2),C(2)-(L(1) Me)(2)}(CO)(18)] (5; from 1(+)), [Ru(6)(mu-H)(2){mu(6)-kappa(4)N(2),C(2)-(L(2) Me)(2)}(CO)(18)] (6; from 2(+)), and [Ru(6)(mu-H)(2){mu(4)-kappa(8)N(2),C(6)-(L(3) Me)(2)}(CO)(18)] (7; from 3(+)). The structures of the final hexanuclear products depend on the N-heterocyclic ligand attached to the starting materials. Thus, although both trinuclear subunits of 5 and 6 are face-capped by their bridging ligands, the coordination mode of the ligand of 5 is different from that of the ligand of 6. The trinuclear subunits of 7 are edge-bridged by its bridging ligand. In the presence of moisture, the reduction of 3(+) with cobaltocene also affords a trinuclear derivative, [Ru(3)(mu-H)(mu-kappa(2)N,C-L(3') Me)(CO)(10)] (8), whose bridging ligand (L(3') Me) results from the formal substitution of an oxygen atom for the hydrogen atom (as a proton) that in 3(+) is attached to the C(6) carbon atom of its heterocyclic ligand. The results have been rationalized with the help of electrochemical measurements and DFT calculations, which have also shed light on the nature of the odd-electron species, 1-3, and on the regioselectivity of their dimerization processes. It seems that the sort of coupling reactions described herein requires cationic complexes with ligand-based LUMOs. PMID:20373311

  9. Two Equilibria of (N-Methyl-3-pyridinium)chlorocarbene, a Cationic Carbene.

    Cang, Hui; Moss, Robert A; Krogh-Jespersen, Karsten

    2016-02-11

    Equilibrium constants and the associated thermodynamic parameters are reported for the equilibria established between the cationic carbene (N-methyl-3-pyridinium)chlorocarbene tetrafluoroborate (MePyr(+)CCl BF4(-), 3) and 1,3,5-trimethoxybenzene (TMB) to form a carbene-TMB complex, as well as between carbene 3 and chloride ion to form the zwitterion, N-methyl-3-pyridinium dichloromethide (10). These equilibrium constants and thermodynamic parameters are contrasted with analogous data for several related carbenes, and the influence of the pyridinium unit in carbene 3 is thereby highlighted. Computational studies augment and elucidate the experimental results. PMID:26830199

  10. Synthesis and reactivity of fluorenyl-tethered N-heterocyclic stannylenes.

    Roselló-Merino, Marta; Mansell, Stephen M

    2016-04-14

    A fluorenyl (Fl) tethered diamine was synthesised by nucleophilic substitution of (bromoethyl)fluorene with a diisopropylphenyl (Dipp) substituted diamine to give FlC2H4N(H)C2H4N(H)Dipp (1a) in good yield (85%). Lithiation of 1a with n-BuLi proceeded with coordination of the Li cation to the aromatic fluorenide ring (2), and with subsequent equivalents of n-BuLi, the secondary amines were then sequentially deprotonated. A fluorenyl-tethered N-heterocyclic stannylene (NHSn) was synthesised from the reaction of 1a with SnN''2 {N'' = N(SiMe3)2} as a neutral dimeric species (5), and this was deprotonated with LiN'' to give the corresponding dianionic fluorenide-tethered NHSn (6). Reactions of [{Rh(cod)(μ-Cl)}2] with the mono-deprotonated ligand 2 led to the formation of a mixed-donor amide-amine Rh(i) compound (7), whereas reactions with the anionic NHSn 6 led to a Rh-fluorenyl complex of low stability with an uncoordinated pendent NHSn arm, which X-ray crystallography showed to be dimeric in the solid state. PMID:26757790

  11. Synthesis of tricyclic silicon-, germanium- and tin-containing tungsten carbene complexes [ButO)2(Cl)2W=CH]2EPh2 (E=Si, Ge, Sn). Crystal structure of [ButO)2(Cl)2W=CH]2SiPh2 complex

    Tungsten carbene complexes [ButO)2(Cl)2W=CH]2EPh2 (E=Si, Ge, Sn) were synthesized by the reaction of tricyclic carbin complexes Ph2E[C≡W(OBu1)3]2 with HCl. Tin-containing carbene complex is not thermally stable and identified in solution by 1H and 13C NMR spectroscopy. Silicon- and germanium-containing carbene complexes of tungsten were separated with high yields in the individual crystal state were identified by element analysis, IR- and 1H, 13C NMR-spectroscopy. Structure of silicon-containing complex [ButO)2(Cl)2W=CH]2SiPh2 were determined by X-ray diffraction. Silicon and tungsten atoms are deformed according to tetrahedral and tetragonal-pyramidal coordinations correspondingly

  12. 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

    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

  13. Iridium(I) N-Heterocyclic Carbene (NHC)/Phosphine Catalysts for Mild and Chemoselective Hydrogenation Processes.

    Kerr, William J; Mudd, Richard J; Brown, Jack A

    2016-03-24

    The directed chemoselective hydrogenation of olefins has been established by using iridium(I) catalysts, which feature a tuned NHC/phosphine ligand combination. This selective reduction process has been demonstrated in a wide array of solvents, including more environmentally acceptable media, also allowing further refinement of hydrogenation selectivity. PMID:26854284

  14. Toward new organometallic architectures: synthesis of carbene-centered rhodium and palladium bisphosphine complexes. stability and reactivity of [PC(BIm)PRh(L)][PF6] pincers.

    Plikhta, Andriy; Pthig, 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

  15. Enantioselective Construction of Quaternary N-Heterocycles by Palladium-Catalyzed Decarboxylative Allylic Alkylation of Lactams

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

    2011-01-01

    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 manuscript, we describe the highly enantioselective palladium-catalyzed decarboxylative allylic alkylation of readily available lactams to form 3,3,-disubstituted pyrrolidinones, piperidinones, caprolactams, and structurally related lacta...

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

    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)

  17. Binding of molecular oxygen by an artificial heme analogue: investigation on the formation of an Fe–tetracarbene superoxo complex

    Anneser, Markus R.

    2016-02-26

    The dioxygen reactivity of a cyclic iron(II) tetra–NHC-complex (NHC: N-heterocyclic carbene) is investigated. Divergent oxidation behavior is observed depending on the choice of the solvent (acetonitrile or acetone). In the first case, exposure to molecular oxygen leads to an oxygen free Fe(III) whereas in the latter case an oxide bridged Fe(III) dimer is formed. In acetone, an Fe(III)-superoxide can be trapped, isolated and characterized as intermediate at low temperatures. An Fe(III)–O–Fe(III) dimer is formed from the Fe(III) superoxide in acetone upon warming and the molecular structure has been revealed by single crystal X-ray diffraction. It is shown that the oxidation of the Fe(II) complex in both solvents is a reversible process. For the regeneration of the initial Fe(II) complex both organic and inorganic reducing agents can be used.

  18. Binding of molecular oxygen by an artificial heme analogue: investigation on the formation of an Fe-tetracarbene superoxo complex.

    Anneser, Markus R; Haslinger, Stefan; Pöthig, Alexander; Cokoja, Mirza; D'Elia, Valerio; Högerl, Manuel P; Basset, Jean-Marie; Kühn, Fritz E

    2016-04-12

    The dioxygen reactivity of a cyclic iron(ii) tetra-NHC-complex (NHC: N-heterocyclic carbene) is investigated. Divergent oxidation behavior is observed depending on the choice of the solvent (acetonitrile or acetone). In the first case, exposure to molecular oxygen leads to an oxygen free Fe(iii) whereas in the latter case an oxide bridged Fe(iii) dimer is formed. In acetone, an Fe(iii)-superoxide can be trapped, isolated and characterized as intermediate at low temperatures. An Fe(iii)-O-Fe(iii) dimer is formed from the Fe(iii) superoxide in acetone upon warming and the molecular structure has been revealed by single crystal X-ray diffraction. It is shown that the oxidation of the Fe(ii) complex in both solvents is a reversible process. For the regeneration of the initial Fe(ii) complex both organic and inorganic reducing agents can be used. PMID:26952651

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

    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.

  20. Ionic Liquids as Carbene Catalyst Precursors in the One-Pot Four-Component Assembly of Oxo Triphenylhexanoates (OTHOs

    Anton Axelsson

    2015-11-01

    Full Text Available Ionic liquids (ILs are a convenient and inexpensive source of N-heterocyclic carbenes (NHCs. In this study, dialkyl imidazolium-based ILs are used as carbene precursors in a four-component synthesis of oxo triphenylhexanoates (OTHOs, where it was found that IL outperformed commonly used NHC precatalysts in terms of reaction efficiency. The reaction is highly stereoselective, delivering the anti-diastereomer (20:1 dr, and the OTHOs can be obtained in high-to-excellent yields. By virtue of the four-component reaction-setup, facile construction of the OTHO scaffold with a diverse set of functional groups (21 examples can be achieved. In the context of sustainability, the IL can be recovered and reused several times without affecting selectivity or yield. Moreover, most compounds can be isolated by precipitation and filtration, mitigating the use of solvent-demanding chromatography.

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

    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.

  2. Enantioselective Construction of Quaternary N-Heterocycles by Palladium-Catalyzed Decarboxylative Allylic Alkylation of Lactams

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

    2011-01-01

    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 manuscript, we describe the highly enantioselective palladium-catalyzed 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 envision 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 employed in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures. PMID:22270628

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

    Behenna, Douglas C.

    2011-12-18

    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. © 2012 Macmillan Publishers Limited. All rights reserved.

  4. Low-spin hexacoordinate Mn(III): synthesis and spectroscopic investigation of homoleptic tris(pyrazolyl)borate and tris(carbene)borate complexes.

    Forshaw, Adam P; Smith, Jeremy M; Ozarowski, Andrew; Krzystek, J; Smirnov, Dmitry; Zvyagin, S A; Harris, T David; Karunadasa, Hemamala I; Zadrozny, Joseph M; Schnegg, Alexander; Holldack, Karsten; Jackson, Timothy A; Alamiri, Ahmad; Barnes, Diane M; Telser, Joshua

    2013-01-01

    Three complexes of Mn(III) with "scorpionate" type ligands have been investigated by a variety of physical techniques. The complexes are [Tp(2)Mn]SbF(6) (1), [Tp(2)*Mn]SbF(6) (2), and [{PhB(MeIm)(3)}(2)Mn](CF(3)SO(3)) (3a), where Tp(-) = hydrotris(pyrazolyl)borate anion, Tp*(-) = hydrotris(3,5-dimethylpyrazolyl)borate anion, and PhB(MeIm)(3)(-) = phenyltris(3-methylimidazol-2-yl)borate anion. The crystal structure of 3a is reported; the structures of 1 and 2 have been previously reported, but were reconfirmed in this work. The synthesis and characterization of [{PhB(MeIm)(3)}(2)Mn]Cl (3b) are also described. These complexes are of interest in that, in contrast to many hexacoordinate (pseudo-octahedral) complexes of Mn(III), they exhibit a low-spin (triplet) ground state, rather than the high-spin (quintet) ground state. Solid-state electronic absorption spectroscopy, SQUID magnetometry, and high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy were applied. HFEPR, in particular, was useful in characterizing the S = 1 spin Hamiltonian parameters for complex 1, D = +19.97(1), E = 0.42(2) cm(-1), and for 2, D = +15.89(2), E = 0.04(1) cm(-1). In addition, frequency domain Fourier-transform THz-EPR spectroscopy, using coherent synchrotron radiation, was applied to 1 only and gave results in good agreement with HFEPR. Variable-temperature dc magnetic susceptibility measurements of 1 and 2 were also in good agreement with the HFEPR results. This magnitude of zero-field splitting (zfs) is over 4 times larger than that in comparable hexacoordinate Mn(III) systems with S = 2 ground states. Complexes 3a and 3b (i.e., regardless of counteranion) have a yet much larger magnitude zfs, which may be the result of unquenched orbital angular momentum so that the spin Hamiltonian model is not appropriate. The triplet ground state is rationalized in each complex by ligand-field theory (LFT) and by quantum chemistry theory, both density functional theory and unrestricted Hartree-Fock methods. This analysis also shows that spin-crossover behavior is not thermally accessible for these complexes as solids. The donor properties of the three different scorpionate ligands were further characterized using the LFT model that suggests that the tris(carbene)borate is a strong ?-donor with little or no ?-bonding. PMID:23259486

  5. Lewis Acid Binding and Transfer as a Versatile Experimental Gauge of the Lewis Basicity of Fe(0) , Ru(0) , and Pt(0) Complexes.

    Braunschweig, Holger; Brunecker, Carina; Dewhurst, Rian D; Schneider, Christoph; Wennemann, Benedikt

    2015-12-21

    A number of zerovalent ruthenium tri- and tetracarbonyl complexes of the form [Ru(CO)5-n Ln ] (n=1, 2) with neutral phosphine or N-heterocyclic carbene donor ligands have been treated with the Lewis acids GaCl3 and Ag(+) to form a range of metal-only Lewis pairs (MOLPs). The spectroscopic and structural parameters of the adducts are compared to each other and to related iron carbonyl based MOLPs. The Lewis basicity of the original Ru(0) complexes is gauged by transfer experiments, as well as through the degree of pyramidization of the bound GaCl3 units and the RuM bond lengths. The work shows the benefits of the MOLP concept as one of the few direct experimental gauges of metal basicity, and one that can allow comparisons between metal complexes with different metal centers and ligand sets. PMID:26555043

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

    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 < CO < PF3 < NO(+). Electron-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. PMID:26174521

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

    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.

  8. Dicationic sulfur analogues of N-heterocyclic silylenes and phosphenium cations.

    Martin, Caleb D; Jennings, Michael C; Ferguson, Michael J; Ragogna, Paul J

    2009-01-01

    DABling with sulfur: Sulfur(II) dications can be prepared using alpha-diimines to stabilize the positive charge (see scheme; DAB = diazabutadiene, Dipp = 2,6-diisopropylphenyl, OTf = CF(3)SO(3)). The bonding is best described as that of a N,N-chelated sulfur(II) dication; these species represent the first sulfur-based structural mimics of N-heterocyclic silylene compounds and phosphenium cations. PMID:19137516

  9. Reversible Carbene Formation in the Ionic Liquid 1-Ethyl-3-Methylimidazolium Acetate by Vaporization and Condensation.

    Kar, Bishnu Prasad; Sander, Wolfram

    2015-12-01

    The role of N-heterocyclic carbenes in the chemistry of ionic liquids based on imidazolium salts has long been discussed. Here, we present experimental evidence that 1-ethyl-3-methylimidazolium-2-ylidene (EMIm) can coexist with its protonated imidazolium cation (EMImH(+) ) at low temperatures. If the vapor of the ionic liquid [EMImH(+) ][AcO(-) ] is trapped in solid argon or nitrogen at 9 K, only acetic acid (AcOH) and the carbene, but no ionic species, are found by IR spectroscopy. This indicates that during the evaporation of [EMImH(+) ][AcO(-) ] proton transfer occurs to form the neutral species. If the vapor of [EMImH(+) ][AcO(-) ] is trapped at 9 K as film in the absence of a host matrix, a solid consisting of EMImH(+) , EMIm, AcO(-) , and AcOH is formed. During warming to room temperature the proton transfer in the solid to form back the IL [EMImH(+) ][AcO(-) ] can be monitored by IR spectroscopy. This clearly demonstrates that evaporation and condensation of the IL [EMImH(+) ][AcO(-) ] results in a double proton transfer, and the carbene EMIm is only metastable even at low temperatures. PMID:26376583

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

    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)

  11. Activation of Si-H bonds across the nickel carbene bond in electron rich nickel PCcarbeneP pincer complexes.

    LaPierre, Etienne A; Piers, Warren E; Spasyuk, Denis M; Bi, David W

    2016-01-14

    Silicon-hydrogen bonds are shown to add to a nickel carbon double bond to yield nickel ?-silylalkyl hydrido complexes. Kinetic and isotope labeling studies suggest that a concerted 4-centred addition across the Ni[double bond, length as m-dash]C bond is operative rather than a mechanism involving Si-H oxidative addition. This constitutes an example of Si-H bond activation via ligand cooperativity. PMID:26650257

  12. Tip-induced gating of molecular levels in carbene-based junctions

    Foti, Giuseppe; Vázquez, Héctor

    2016-03-01

    We study the conductance of N-heterocyclic carbene-based (NHC) molecules on gold by means of first-principles calculations based on density-functional theory and non-equilibrium Green’s functions. We consider several tip structures and find a strong dependence of the position of the NHC molecular levels with the atomistic structure of the tip. The position of the lowest unoccupied molecular orbital (LUMO) can change by almost 0.8 eV with tip shape. Through an analysis of the net charge transfer, electron redistribution and work function for each tip structure, we rationalize the LUMO shifts in terms of the sum of the work function and the maximum electrostatic potential arising from charge rearrangement. These differences in the LUMO position, effectively gating the molecular levels, result in large conductance variations. These findings open the way to modulating the conductance of NHC-based molecular circuits through the controlled design of the tip atomistic structure.

  13. Tip-induced gating of molecular levels in carbene-based junctions.

    Foti, Giuseppe; Vzquez, Hctor

    2016-03-29

    We study the conductance of N-heterocyclic carbene-based (NHC) molecules on gold by means of first-principles calculations based on density-functional theory and non-equilibrium Green's functions. We consider several tip structures and find a strong dependence of the position of the NHC molecular levels with the atomistic structure of the tip. The position of the lowest unoccupied molecular orbital (LUMO) can change by almost 0.8 eV with tip shape. Through an analysis of the net charge transfer, electron redistribution and work function for each tip structure, we rationalize the LUMO shifts in terms of the sum of the work function and the maximum electrostatic potential arising from charge rearrangement. These differences in the LUMO position, effectively gating the molecular levels, result in large conductance variations. These findings open the way to modulating the conductance of NHC-based molecular circuits through the controlled design of the tip atomistic structure. PMID:26891059

  14. N-Methylphthalimide-substituted benzimidazolium salts and PEPPSI Pd–NHC complexes: synthesis, characterization and catalytic activity in carbon–carbon bond-forming reactions

    Gök, Yetkin; İlhan, İlhan Özer

    2016-01-01

    Summary A series of novel benzimidazolium salts (1–4) and their pyridine enhanced precatalyst preparation stabilization and initiation (PEPPSI) themed palladium N-heterocyclic carbene complexes [PdCl2(NHC)(Py)] (5–8), where NHC = 1-(N-methylphthalimide)-3-alkylbenzimidazolin-2-ylidene and Py = 3-chloropyridine, were synthesized and characterized by means of 1H and 13C{1H} NMR, UV–vis (for 5–8), ESI-FTICR-MS (for 2, 4, 6–8) and FTIR spectroscopic methods and elemental analysis. The synthesized compounds were tested in Suzuki–Miyaura cross-coupling (for 1–8) and arylation (for 5–8) reactions. As catalysts, they demonstrated a highly efficient route for the formation of asymmetric biaryl compounds even though they were used in very low loading. For example, all compounds displayed good catalytic activity for the C–C bond formation of 4-tert-butylphenylboronic acid with 4-chlorotoluene. PMID:26877810

  15. New vistas in N-heterocyclic silylene (NHSi) transition-metal coordination chemistry: syntheses, structures and reactivity towards activation of small molecules.

    Blom, Burgert; Stoelzel, Miriam; Driess, Matthias

    2013-01-01

    This account is a review on the synthesis and transition-metal coordination chemistry of N-heterocyclic silylenes (NHSi's) over the last 20 years till the present time (2012). Recently, fascinating and novel synthetic methods have been developed to access transition-metal-NHSi complexes as an emerging class of compounds with a wealth of intriguing reactivity patterns. The striking influence of coordinating NHSi's to transition-metal complex fragments affording different reactivities to the "free" NHSi is a connecting theme ("leitmotif") throughout the review, and highlights the potential of these compounds which lie at the interface of contemporary main-group and classical organometallic chemistry towards new molecular catalysts for small-molecule activation. PMID:23229274

  16. Utilization of N-X bonds in the synthesis of N-heterocycles.

    Minakata, Satoshi

    2009-08-18

    Nitrogen-containing heterocycles--such as aziridines, pyrrolidines, piperidines, and oxazolines--frequently show up as substructures in natural products. In addition, some of these species show potent biological activities. Therefore, researchers would like to develop practical and convenient methods for constructing these heterocycles. Among the available methods, the transfer of N(1) units to organic molecules, especially olefins, is a versatile method for the synthesis of N-heterocycles. This Account reviews some of our recent work on the synthesis of N-heterocycles using the N-X bond. A nitrogen-halogen bond bearing an electron-withdrawing group on the nitrogen can be converted to a halonium ion. In the presence of C-C double bonds, these species produce three-membered cyclic halonium intermediates, which can be strong electrophiles and can produce stereocontrolled products. N-Halosuccinimides are representative sources of halonium ions, and the nitrogen of succinimide is rarely used in organic synthesis. If the nitrogen could act as a nucleophile, after releasing halonium ions to C-C double bonds, we expect great advances would be possible in the stereoselective functionalization of olefins. We chose N-chloro-N-sodio-p-toluenesulfonamide (chloramine-T, CT), an inexpensive and commercially available reagent, as our desired reactant. In the presence of a catalytic amount of CuCl or I(2) and AgNO(3), we achieved the direct aziridination of olefins with CT. The reaction catalyzed by I(2) could be carried out in water or silica-water as a green process. The reaction of iodoolefins with CT gave pyrrolidine derivatives under extremely mild conditions with complete stereoselectivity. We also extended the utility of the N-chloro-N-metallo reagent, which is often unstable and difficult to work with. Although CT does not react with electron-deficient olefins without a metal catalyst or an additive, we found that N-chloro-N-sodiocarbamates react with electron-deficient olefins in the presence of a phase transfer catalyst to give the corresponding aziridines. We also used this method to synthesize asymmetric aziridines using quaternary cinchona alkaloid catalysts. We also developed a facile synthetic method for preparing N-heterocycles that involves the in situ generation of an N-X bond using tert-butyl hypochlorite or tert-butyl hypoiodite (tert-BuOI). Treatment of alkenylamides containing an active hydrogen on the nitrogen with tert-BuOI led to the production of various N-heterocycles via intramolecular cyclization. Iodination of readily available sulfonamides or carboxamides with tert-BuOI generated reactive N-iodinated amides, which smoothly reacted with olefins to give aziridines or oxazolines. The reaction of fullerene, C(60), with CT also led to aziridination: the resulting aziridinofullerene underwent a unique rearrangement to an azafulleroid. Chlorination of readily available amide derivatives with tert-BuOCl, followed by a reaction with C(60) in the presence of an organic base, afforded aziridinofullerenes with various substituents on the nitrogen. The results in this Account contribute to the development of convenient methods for constructing simple and useful heterocycles. PMID:19480410

  17. H-D exchange in metal carbene complexes: Structure of cluster (μ-H)(μ-OCD3)Os3(CO)9{:C(CD3)NC2H8O}

    Savkov, Boris; Maksakov, Vladimir; Kuratieva, Natalia

    2015-10-01

    X-ray and spectroscopic data for the new complex (μ-H)(μ-OCH3)Os3(CO)9{:C(CD3)NC2H8O} (2) obtained in the reaction of the (μ-H)(μ-Cl)Os3(CO)9{:C(CH3)NC2H8O} (1) with NaOCD3 in CD3OD solution are reported. It is shown that cluster 1 has the property of CH-acidity inherent of Fisher type carbenes. This had demonstrated using hydrogen deuterium exchange reaction in the presence of a strong base. Bridging chlorine to metoxide ligand substitution takes place during the reaction. The molecular structure of 2 is compared with known analogues.

  18. Imidazolium Ionic Liquids, Imidazolylidene Heterocyclic Carbenes, and Zeolitic Imidazolate Frameworks for CO2 Capture and Photochemical Reduction.

    Wang, Sibo; Wang, Xinchen

    2016-02-01

    Imidazolium ionic liquids (ILs), imidazolylidene N-heterocyclic carbenes (NHCs), and zeolitic imidazolate frameworks (ZIFs) are imidazolate motifs which have been extensively investigated for CO2 adsorption and conversion applications. Summarized in this minireview is the recent progress in the capture, activation, and photochemical reduction of CO2 with these three imidazolate building blocks, from homogeneous molecular entities (ILs and NHCs) to heterogeneous crystalline scaffolds (ZIFs). The developments and existing shortcomings of the imidazolate motifs for their use in CO2 utilizations is assessed, with more of focus on CO2 photoredox catalysis. The opportunities and challenges of imidazolate scaffolds for future advancement of CO2 photochemical conversion for artificial photosynthesis are discussed. PMID:26683833

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

    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.

  20. Biochemical Interpretation of Quantitative Structure-Activity Relationships (QSAR) for Biodegradation of N-Heterocycles : A Complementary Approach to Predict Biodegradability

    Philipp, Bodo; Hoff, Malte; Germa, Florence; Schink, Bernhard; Beimborn, Dieter; Mersch-Sundermann, Volker

    2007-01-01

    Prediction of the biodegradability of organic compounds is an ecologically desirable and economically feasible tool for estimating the environmental fate of chemicals. We combined quantitative structure-activity relationships (QSAR) with the systematic collection of biochemical knowledge to establish rules for the prediction of aerobic biodegradation of N-heterocycles. Validated biodegradation data of 194 N-heterocyclic compounds were analyzed using the MULTICASE-method which delivered two QS...

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

    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. Study of the factors supporting the selective complexation of the trivalent lanthanide and actinide ions; Etude des facteurs favorisant la complexation selective des ions lanthanides et actinides trivalents

    Mehdoui, T

    2005-09-15

    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{sup +} 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)

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

    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

  4. Investigation on reactivity of non-classical carbenes with sterically hindered Lewis acid, B(C6F5)3 under inert and open conditions

    Arunabha Thakur; Pavan K Vardhanapu; Gonela Vijaykumar; Sushil Ranjan Bhatta

    2016-04-01

    Reactions of B(C6F5)3 with abnormal N-heterocyclic carbene (NHC), L1 and cyclic (alkyl)(amino) carbene (AAC), L2 in the presence of moisture as well as in its absence, have been investigated in toluene. Reaction of NHC with 1 equivalent of B(C6F5)3 under inert condition produced classical Lewis acid-base adduct, [L1.B(C6F5)3], 1. Further, probing the same reaction with cyclic (alkyl)(amino) carbene (AAC), having different electronic property, led to the isolation of [L2.B(C6F5)3], 2 under inert condition. Interestingly, reaction of NHC or AAC with 1 equivalent of B(C6F5)3 in the presence of moisture resulted in water splitting leading to the formation of [L1-H][(OH)B(C6F5)3], 3 and [L2-H][(OH)B(C6F5)3, 4. All these compounds (1-4) were characterized in solution by 1H, 13C, 19F and 11B NMR spectroscopy. Additionally, the solid-state structures were unambiguously established by crystallographic analysis of compounds 1-4.

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

    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)

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

    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 α-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

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

    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 (λ(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

  8. Coordinatively unsaturated ruthenium complexes as efficient alkyneazide cycloaddition catalysts

    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-κ2-phosphazide complex, Cp*Ru(κ2- 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.

  9. A Comparison of the Stability and Reactivity of Diamido- and Diaminocarbene Copper Alkoxide and Hydride Complexes.

    Collins, Lee R; Riddlestone, Ian M; Mahon, Mary F; Whittlesey, Michael K

    2015-09-28

    The mononuclear N-heterocyclic carbene (NHC) copper alkoxide complexes [(6-NHC)CuOtBu] (6-NHC = 6-MesDAC (1), 6-Mes (2)) have been prepared by addition of the free carbenes to the tetrameric tert-butoxide precursor [Cu(OtBu)]4, or by protonolysis of [(6-NHC)CuMes] (6-NHC = 6-MesDAC (3), 6-Mes (4)) with tBuOH. In contrast to the relatively stable diaminocarbene complex 2, the diamidocarbene derivative 1 proved susceptible to both thermal and hydrolytic ring-opening reactions, the latter affording [(6-MesDAC)Cu(OC(O)CMe2C(O)N(H)Mes)(CNMes)] (6). The intermediacy of [(6-MesDAC)Cu(OH)] in this reaction was supported by the generation of Cu2O as an additional product. Attempts to generate an isolable copper hydride complex of the type [(6-MesDAC)CuH] by reaction of 1 with Et3SiH resulted instead in migratory insertion to generate [(6-MesDAC-H)Cu(P(p-tolyl)3)] (9) upon trapping by P(p-tolyl)3. Migratory insertion was also observed during attempts to prepare [(6-Mes)CuH], with [(6-Mes-H)Cu(6-Mes)] (10) isolated, following a reaction that was significantly slower than in the 6-MesDAC case. The longer lifetime of [(6-Mes)CuH] allowed it to be trapped stoichiometrically by alkyne, and also employed in the catalytic semi-reduction of alkynes and hydrosilylation of ketones. PMID:26310393

  10. From Silylone to an Isolable Monomeric Silicon Disulfide Complex.

    Xiong, Yun; Yao, Shenglai; Mller, Robert; Kaupp, Martin; Driess, Matthias

    2015-08-24

    The synthesis and characterization of the first bis-N-heterocyclic carbene stabilized monomeric silicon disulfide (bis-NHC)SiS2 2 (bis-NHC=H2 C[{NC(H)C(H)N(Dipp)}C:]2 , Dipp=2,6-iPr2 C6 H3 ) is reported. Compound 2 is prepared in 89?% yield from the reaction of the zero-valent silicon complex ('silylone') 1 [(bis-NHC)Si] with elemental sulfur. Compound 2 can react with GaCl3 in acetonitrile to give the corresponding (bis-NHC)Si(S)S?GaCl3 Lewis acid-base adduct 3 in 91?% yield. Compound 3 is also accessible through the reaction of the unprecedented silylone-GaCl3 adduct [(bis-NHC)Si?GaCl3 ] 4 with elemental sulfur. Compounds 2, 3, and 4 could be isolated and characterized by elemental analyses, HR-MS, IR, (13) C- and (29) Si-NMR spectroscopy. The structures of 3 and 4 could be determined by single-crystal X-ray diffraction analyses. DFT-derived bonding analyses of 2 and 3 exhibited highly polar Si-S bonds with moderate p? -p? bonding character. PMID:26148938

  11. Structural, spectral and magnetic studies of two Co(II)-N-heterocyclic diphosphonates based on multinuclear units

    Zhao, Chen; Ma, Kui-Rong; Zhang, Yu; Kan, Yu-He; Li, Rong-Qing; Hu, Hua-You

    2016-01-01

    Two examples of Co(II)-N-heterocyclic coordination polymers based on 1-hydroxyethylidenediphosphonic acid (H5L = CH3C(OH)(PO3H2)2), namely 0.5(H3NCH2CH2NH3)[Co6(Cl2)(H3L)2(H2L)(HL)(2,2?-bipy)6] 1 and 2(NH4)[Co3(HL)2(H2O)2(phen)2]2(H2O) 2, have been solvothermally obtained by introducing the second ligands 2,2?-bipyridine/1,10-phenanthroline (2,2?-bipy/phen) and characterized by powder X-ray diffraction (PXRD), elemental analysis, IR, TG-DSC. The single-crystal X-ray diffractions show that compound 1 possesses a 0-D structure with hexa-nuclear cluster [Co6(O-P-O)8] built through single/double O-P-O bridges and compound 2 displays a 1-D ladder-like chain structure with magnetic topology building blocks [Co4(O-P-O)4]n. Then H-bonding and ?-? stacking interactions further expand the two low-dimensional structures into three-dimensional supramolecular frameworks. Fluorescent measurements reveal that both the maximum emission peaks of 1-2 are centered at 423 nm, mainly deriving from intraligand ?*-? transition state of N-heterocyclic ligand 2,2?-bipy/phen, respectively. Magnetism data indicate that 1 exhibits antiferromagnetic behavior within hexa-nuclear Co(II) clusters, while 2 shows weak ferromagnetic interactions in 1-D topology Co(II)-chain, showing promising potential as magnetic materials.

  12. Luminescent pillared LnIII–ZnII heterometallic coordination frameworks with two kinds of N-heterocyclic carboxylate ligands

    In our efforts toward rational design and systematic synthesis of ‘pillar-layer’ structure coordination frameworks, four new LnIII–ZnII heterometallic coordination polymers (CPs) based on two kinds of N-heterocyclic carboxylic ligands with formula ([LnZn(L1)2(L2)(H2O)m]·nH2O)∞ (Ln=La (1), Eu (2), Gd (3) and Dy (4), m=3 (for 1) and 2 (for 2–4), n=8 (for 1) and 7 (for 2–4), H2L1=pyridine-2,3-dicarboxylate acid, HL2=isonicotinic acid), have been synthesized under hydrothermal reaction of Ln2O3, ZnO, H2L1 and HL2. CP 1 has a three-dimensional (3D) structure with a (3,6)-connected sit topology network, while CPs 2–4 are isostructural with 3D single-node pcu alpha-Po topology network. Also, luminescent properties of these CPs have also been investigated. The emission of 1 and 3 should be attributed to the coordination-perturbed ligand-centered luminescence and the emission spectra of 2 and 4 show the characteristic bands of the corresponding LnIII ions. - Graphical abstract: Four new 3D LnIII–ZnII coordination frameworks with “pillar-layer” sit or pcu alpha-Po topology have been successfully obtained. Moreover, the photoluminescent properties of compounds 1–4 have also been investigated. - Highlights: • Four new LnIII–ZnII heterometallic coordination frameworks with two types of topologies have been synthesized. • Metal oxides and two kinds of N-heterocyclic carboxylate ligands were used for the construction of targeted coordination polymers. • The luminescent properties of the coordination polymers are investigated

  13. Room-temperature Kumada cross-coupling of unactivated aryl chlorides catalyzed by N-heterocylic carbene-based nickel(II) complexes.

    Xi, Zhenxing; Liu, Bin; Chen, Wanzhi

    2008-05-16

    The Kumada cross-coupling reaction of a variety of unactivated aryl chlorides, vinyl chlorides, and heteroaryl chlorides catalyzed by nickel(II) complexes containing pyridine-functionalized NHC ligands is described. The catalysts are so active that the reactions proceed at room temperature in excellent yields. PMID:18412386

  14. Preparation of phenalenes and hydronaphthacenes through tandem alkyne Fischer-carbene complex coupling and inter- or intramolecular Diels-Alder reactions

    Patti, Rajesh Kumar; Duan, Shaofeng; Wang, Zhipeng; Herndon, James W.

    2011-01-01

    The rapid construction of phenalenes through the reaction of 8-alkynyltetralones with Fischer carbine complexes followed by either inter- or an intramolecular Diels-Alder reaction is presented. As a showcase of the synthetic utility of this process, the rapid construction of polycyclic ring systems containing the tetracycline core has been demonstrated through an iterative application of this reaction sequence.

  15. Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes

    2016-01-01

    Summary Bearing the versatility of N-heterocyclic carbene (NHC) ligands, here density functional theory (DFT) calculations unravel the capacity of coordination of a deprotonated NHC ligand (pNHC) to generate a doubly C2,N3-bridged dinuclear complex. Here, in particular the discussion is based on the combination of the deprotonated 1-arylimidazol (aryl = mesityl (Mes)) with [M(cod)(μ-Cl)] (M = Ir, Rh) generated two geometrical isomers of complex [M(cod){µ-C3H2N2(Mes)-κC2,κN3}]2). The latter two isomers display conformations head-to-head (H-H) and head-to-tail (H-T) of C S and C 2 symmetry, respectively. The isomerization from the H-H to the H-T conformation is feasible, whereas next substitutions of the cod ligand by CO first, and PMe3 later confirm the H-T coordination as the thermodynamically preferred. It is envisaged the exchange of the metal, from iridium to rhodium, confirming here the innocence of the nature of the metal for such arrangements of the bridging ligands. PMID:26877814

  16. Re(I) NHC Complexes for Electrocatalytic Conversion of CO2.

    Stanton, Charles J; Machan, Charles W; Vandezande, Jonathon E; Jin, Tong; Majetich, George F; Schaefer, Henry F; Kubiak, Clifford P; Li, Gonghu; Agarwal, Jay

    2016-03-21

    The modular construction of ligands around an N-heterocyclic carbene building block represents a flexible synthetic strategy for tuning the electronic properties of metal complexes. Herein, methylbenzimidazolium-pyridine and methylbenzimidazolium-pyrimidine proligands are constructed in high yield using recently established transition-metal-free techniques. Subsequent chelation to ReCl(CO)5 furnishes ReCl(N-methyl-N'-2-pyridylbenzimidazol-2-ylidine)(CO)3 and ReCl(N-methyl-N'-2-pyrimidylbenzimidazol-2-ylidine)(CO)3. These Re(I) NHC complexes are shown to be capable of mediating the two-electron conversion of CO2 following one-electron reduction; the Faradaic efficiency for CO formation is observed to be >60% with minor H2 and HCO2H production. Data from cyclic voltammetry is presented and compared to well-studied ReCl(2,2'-bipyridine)(CO)3 and MnBr(2,2'-bipyridine)(CO)3 systems. Results from density functional theory computations, infrared spectroelectrochemistry, and chemical reductions are also discussed. PMID:26950549

  17. 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.

    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

  18. 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 )

    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 π-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, δ(Cr,X) increases with the decrease of the π-donor character of the X group

  19. Electron pairing analysis of the Fischer-type chromium-carbene complexes (CO){sub 5}Cr=C(X)R (X=H, OH, OCH{sub 3}, NH{sub 2}, NHCH{sub 3} and R=H, CH{sub 3}, CH=CH{sub 2}, Ph, C-CH )

    Poater, Jordi; Cases, Montserrat; Fradera, Xavier; Duran, Miquel; Sola, Miquel

    2003-10-15

    The electron-pair density distributions of a series of 25 Fischer carbene complexes of the type (CO){sub 5}Cr=C(X)R (X=H, OH, OCH{sub 3}, NH{sub 2}, NHCH{sub 3} and R=H, CH{sub 3}, CH=CH{sub 2}, 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 {pi}-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, {delta}(Cr,X) increases with the decrease of the {pi}-donor character of the X group.

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

    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.

  1. Carbenes in matrices: reactions and rearrangements

    Sander, W. W.; Patyk, A.; Bucher, G.

    1990-05-01

    Carbenes and silylenes with a variety of substituents have been isolated and characterized in low temperature matrices. Reactions of these species with small molecules, especially 3O 2, have been studied. The structure of the primary addition products as well as the reactivity as a function of the spin-state (triplet T or singlet S) is discussed.

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

    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

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

    Esquivel, Dolores; De Canck, Els [Center for Ordered Materials, Organometallics and Catalysis, Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, 9000 Ghent (Belgium); Jiménez-Sanchidrián, César [Department of Organic Chemistry, Nanochemistry and Fine Chemistry Research Institute (IUIQFN), Faculty of Sciences, University of Córdoba, Campus de Rabanales, Marie Curie Building, Ctra. Nnal. IV, km 396, 14071 Córdoba (Spain); Romero-Salguero, Francisco J., E-mail: qo2rosaf@uco.es [Department of Organic Chemistry, Nanochemistry and Fine Chemistry Research Institute (IUIQFN), Faculty of Sciences, University of Córdoba, Campus de Rabanales, Marie Curie Building, Ctra. Nnal. IV, km 396, 14071 Córdoba (Spain); Van Der Voort, Pascal, E-mail: pascal.vandervoort@ugent.be [Center for Ordered Materials, Organometallics and Catalysis, Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-S3, 9000 Ghent (Belgium)

    2014-11-14

    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 N{sub 2} 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, {sup 13}C and {sup 29}Si 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.

  4. Unveiling the Importance of π-Stacking in Borrowing-Hydrogen Processes Catalysed by Iridium Complexes with Pyrene Tags.

    Ruiz-Botella, Sheila; Peris, Eduardo

    2015-10-19

    This work describes the preparation of a series of pyrene-tagged N-heterocyclic carbene complexes of iridium, and their use in two benchmark borrowing hydrogen reactions: the reduction of ketones by transfer hydrogenation and the β-alkylation of secondary alcohols with primary alcohols. The detailed study of these homogeneously catalysed reactions reveals several important implications regarding the strong influence of the pyrene tags in the catalysts. First, the catalytic activity is partially inhibited by addition of an external amount of pyrene, but only when pyrene-tagged catalysts and aromatic substrates are used. Second, the rate order of the reaction is highly dependent on the nature of the substrates and the ligand. When pyrene-tagged catalysts and aromatic substrates are used, the reaction follows a zero-order dependence on the concentration of the substrate. All other combinations afford a second-order rate in the substrates. And third, the presence or absence of the pyrene functionality in the catalyst also influences the reaction order with respect to the concentration of the catalyst. Pyrene-containing catalysts display a fractional rate order of below 1. Finally, two pyrene-tagged catalysts were supported onto reduced-graphene oxide (rGO), and used as heterogeneous catalysts. While the dimetallic catalyst was effectively recycled 12 times, the monometallic catalyst maintained its activity for only three runs. PMID:26471441

  5. Oxo-Centered Mixed-Ligand Triruthenium Complexes Having Redox-Active N-Methyl-4,4'-bipyridinium Ions (mbpy(+)). Reversible Multistep Electrochemical Properties of [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](2+) and [Ru(III)(3)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(L)](3+) (L = H(2)O and N-Heterocyclic Ligands).

    Abe, Masaaki; Sasaki, Yoichi; Yamada, Yasuko; Tsukahara, Keiichi; Yano, Shigenobu; Yamaguchi, Tadashi; Tominaga, Masato; Taniguchi, Isao; Ito, Tasuku

    1996-11-01

    A new series of oxo-centered acetate-bridged triruthenium comlexes having two redox-active N-methyl-4,4'-bipyridinium ions (mbpy(+)) have been prepared, and their reversible multistep and multielectron electrochemical properties are reported: [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](2+) and [Ru(III)(3)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(L)](3+) (L = H(2)O, pyrazine (pz), pyridine (py), imidazole (Him), and 4-(dimethylamino)pyridine (dmap)). Among these series, the CO complex, [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](ClO(4))(2).2DMF (1b.2DMF) was structurally characterized by X-ray crystallography. 1b.2DMF crystallizes in the monoclinic space group P2(1)/m (No. 11) with a = 8.740(6) Å, b = 32.269(6) Å, c = 10.276(4) Å, beta = 103.37(5) degrees, V = 2820(2) Å(3), Z = 2, d(calcd) = 1.636 g cm(-)(3), and R = 0.071 (R(w) = 0.074) for 5277 independent reflections (|F(o)| > 3sigma(|F(o)|). The (CO)Ru.Ru distance (3.410(2) Å) is appreciably longer than the other Ru.Ru distance (3.276(2) Å), indicating that the trinuclear core is in the valence-trapped Ru(III)(2)Ru(II)(CO) oxidation state. The cyclic voltammogram of [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](PF(6))(2) (1a) shows a total of seven reversible one-electron redox steps at E(1/2) = +0.90, +0.26, -1.07, -1.17, -1.56, -1.97, and -2.32 V and one irreversible step at E(pc) = -2.99 V vs Fc/Fc(+) in a 0.1 M [(n-C(4)H(9))(4)N]PF(6)-CH(3)CN solution (M = mol dm(-)(3)). All of the waves are clearly assignable to the triruthenium "Ru(3)(&mgr;(3)-O)" core-based or mbpy(+) ligand-based processes. The splitting of each ligand-based redox processes (mbpy(+)/mbpy(*) and mbpy(*)/mbpy(-)) into two one-electron steps indicates that electronic interactions between two terminal ligands occur through the triruthenium cluster core. Other mixed-ligand Ru(III)(3) analogs also show multistep redox behavior involving a total of eight or nine electrons. While the extent of interactions between ligands is much smaller than that found in the CO complex, it is systematically changed by the nature of L; with more basic L, interactions between two mbpy(+) ligands become larger. PMID:11666835

  6. Dancing with Energetic Nitrogen Atoms: Versatile N-Functionalization Strategies for N-Heterocyclic Frameworks in High Energy Density Materials.

    Yin, Ping; Zhang, Qinghua; Shreeve, Jean'ne M

    2016-01-19

    Nitrogen-rich heterocycles represent a unique class of energetic frameworks featuring high heats of formation and high nitrogen content, which have generated considerable research interest in the field of high energy density materials (HEDMs). Although traditional C-functionalization methodology of aromatic hydrocarbons has been fully established, studies on N-functionalization strategies of nitrogen-containing heterocycles still have great potential to be exploited by virtue of forming diverse N-X bonds (X = C, N, O, B, halogen, etc.), which are capable of regulating energy performance and the stability of the resulting energetic compounds. In this sense, versatile N-functionalization of N-heterocyclic frameworks offers a flexible strategy to meet the requirements of developing new-generation HEDMs. In this Account, the role of strategic N-functionalization in designing new energetic frameworks, including the formation of N-C, N-N, N-O, N-B and N-halogen bonds, is emphasized. In the family of N-functionalized HEDMs, energetic derivatives, by virtue of forming N-C bonds, are the most widely used type due to the good nucleophilic capacity of most heterocyclic backbones. Although introduction of carbon tends to decrease energetic performance, significant improvement in material sensitivity makes this strategy attractive for safety concerns. More importantly, most "explosophores" can be readily introduced into the N-C linkage, thus providing a promising route to various HEDMs. Formation of additional N-N bonds typically gives rise to higher heats of formation, implying the potential enhancement in detonation performance. In many cases, the increased hydrogen bonding interactions within N-N functionalized heterocycles also improve thermal stability accordingly. Introduction of a single N,N'-azo bridge into several azole moieties leads to an extended nitrogen chain, demonstrating a new strategy for designing high-nitrogen compounds. The strategy of N-O functionalization has become an increasingly efficient tool for exploring new HEDMs with both high energy and low sensitivity. As a highly dense building block, introduction of oxygen not only improves density significantly but also gives rise to a better oxygen balance. Furthermore, the N-O functionalized strategy is highly suitable for a broad variety of N-heterocycles including five-membered azoles and six-membered azines. Newly explored N-halogen and N-B functionalization strategies have endowed the resulting HEDMs with some new energetic characteristics. Typical examples include the N-halogenated fused triazole and FOX-7 as potential hypergolic oxidizers with very short ignition delay times. In addition, some exploratory studies of N-B functionalized heterocycles have expanded energetic applications as hypergolic ionic liquids, green pyrotechnic colorants, and high-oxygen carriers. Overall, flexible N-functionalization methodologies involving different N-X bond formation have not only provided an efficient approach to diverse energetic ingredients but also expanded the application scope of energetic materials. Discussion and perspectives of N-functionalized protocols are given to summarize possible structure-property correlations, thus providing efficient guidelines for future design of new HEDMs. PMID:26717271

  7. NHC rhodium complexes as potential prosthetic groups for mAb radiolabeling with astatine

    Full text of publication follows. Aim: Astatine-211 is the most promising alpha emitter for radioimmunotherapy. However, its clinical development is hampered by the in vivo de-astatination observed with radiolabelled antibody fragments. An astatinated N-heterocyclic carbene (NHC) Rhodium complex has been tested as a model to investigate the benefit of prosthetic groups from the Rhodium-NHC family to improve the radiolabeling stability of antibodies fragments. Methods: wet harvested At-211 in diisopropyl ether was used. Firstly, astatine was reduced with cysteine. Then, astatide was incubated with a chlorinated Rh-NHC complex to allow the formation of the astatinated analogue. Reaction conditions have been optimized for these two steps. Astatide reactivity has also been compared with the iodide (I-125) one. Serum stability of the astatinated complex has been evaluated. Results: quantitative formation of astatide was observed when cysteine amounts higher than 46.2 nmol/μl of astatine solution were added. Nucleophilic substitution kinetics showed that high radiolabeling yields were obtained for 15 min at 60 C. degrees (88%) or 5 min at 100 C. degrees (95%). The new compound was detected using chromatographic analyses, in good agreement with the cold iodinated rhodium complex characteristics. The radioiodinated complex has also been easily obtained from the same precursor (5 min. at 100 C. degrees, up to 85%) using [125I]NaI as a radiotracer. In vitro stability of the astatinated complex was controlled after 15 h. incubation in human serum at 4 C. degrees and 37 C. degrees. No degradation was observed, indicating a good chemical and enzymatic stability. Conclusion: the astatinated complex was obtained in good yield and exhibits good chemical and enzymatic stability. These preliminary results demonstrate the interest of this new radiolabeling methodology. (authors)

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

    Hadad, C. Z., E-mail: cacier.hadad@udea.edu.co [Grupo de Química-Física Teórica, Instituto de Química, Universidad de Antioquia, A. A. 1226 Medellín (Colombia); Jenkins, Samantha [College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha, Hunan 410081 (China); Flórez, Elizabeth [Departamento de Ciencias Básicas, Universidad de Medellín, Carrera 87 N° 30-65, Medellín (Colombia)

    2015-03-07

    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.

  9. Trimethoxybenzene complexes of pentafluorophenylchlorocarbene.

    Wang, Lei; Moss, Robert A; Krogh-Jespersen, Karsten

    2011-07-21

    Pentafluorophenylchlorocarbene, generated by laser flash photolysis (LFP) of pentafluorophenylchlorodiazirine, formed ?-type complexes with 1,3,5-trimethoxybenzene in pentane. The carbene and carbene complexes were in equilibrium with K = 3.21 10(5) M(-1) at 294 K. From the temperature dependence of K, ?H = -10.2 kcal/mol, ?S = -9.5 eu, and ?G = -7.4 kcal/mol at 298 K. The carbene complexes were characterized by UV-vis spectroscopy and computational analysis. PMID:21696161

  10. Consecutive Cycloaddition/S(N)Ar/Reduction/Cyclization/Oxidation Sequences: A Copper-Catalyzed Multicomponent Synthesis of Fused N-Heterocycles.

    Jia, Feng-Cheng; Xu, Cheng; Zhou, Zhi-Wen; Cai, Qun; Li, Deng-Kui; Wu, An-Xin

    2015-06-01

    A highly efficient multicomponent domino protocol has been developed for the synthesis of 5-phenyl-[1,2,3]triazolo[1,5-c]quinazolines from simple and readily available (E)-1-bromo-2-(2-nitrovinyl)benzenes, aldehydes, and sodium azide. This elegant domino process involved consecutive [3 + 2] cycloaddition, copper-catalyzed S(N)Ar, reduction, cyclization, and oxidation sequences. Notably, sodium azide acted as a dual nitrogen source in the construction of this novel fused N-heterocycle. PMID:25996444

  11. NHC→SiCl4 : an ambivalent carbene-transfer reagent.

    Böttcher, Tobias; Steinhauer, Simon; Lewis-Alleyne, Lesley C; Neumann, Beate; Stammler, Hans-Georg; Bassil, Bassem S; Röschenthaler, Gerd-Volker; Hoge, Berthold

    2015-01-01

    The addition of BCl3 to the carbene-transfer reagent NHC→SiCl4 (NHC=1,3-dimethylimidazolidin-2-ylidene) gave the tetra- and pentacoordinate trichlorosilicon(IV) cations [(NHC)SiCl3 ](+) and [(NHC)2 SiCl3 ](+) with tetrachloroborate as counterion. This is in contrast to previous reactions, in which NHC→SiCl4 served as a transfer reagent for the NHC ligand. The addition of BF3 ⋅OEt2 , on the other hand, gave NHC→BF3 as the product of NHC transfer. In addition, the highly Lewis acidic bis(pentafluoroethyl)silane (C2 F5 )2 SiCl2 was treated with NHC→SiCl4 . In acetonitrile, the cationic silicon(IV) complexes [(NHC)SiCl3 ](+) and [(NHC)2 SiCl3 ](+) were detected with [(C2 F5 )SiCl3 ](-) as counterion. A similar result was already reported for the reaction of NHC→SiCl4 with (C2 F5 )2 SiH2 , which gave [(NHC)2 SiCl2 H][(C2 F5 )SiCl3 ]. If the reaction medium was changed to dichloromethane, the products of carbene transfer, NHC→Si(C2 F5 )2 Cl2 and NHC→Si(C2 F5 )2 ClH, respectively, were obtained instead. The formation of the latter species is a result of chloride/hydride metathesis. These compounds may serve as valuable precursors for electron-poor silylenes. Furthermore, the reactivity of NHC→SiCl4 towards phosphines is discussed. The carbene complex NHC→PCl3 shows similar reactivity to NHC→SiCl4 , and may even serve as a carbene-transfer reagent as well. PMID:25363673

  12. Catalytic Transformation of Aldehydes with Nickel Complexes through ?(2) Coordination and Oxidative Cyclization.

    Hoshimoto, Yoichi; Ohashi, Masato; Ogoshi, Sensuke

    2015-06-16

    Chemists no longer doubt the importance of a methodology that could activate and utilize aldehydes in organic syntheses since many products prepared from them support our daily life. Tremendous effort has been devoted to the development of these methods using main-group elements and transition metals. Thus, many organic chemists have used an activator-(aldehyde oxygen) interaction, namely, ?(1) coordination, whereby a Lewis or Brnsted acid activates an aldehyde. In the field of coordination chemistry, ?(2) coordination of aldehydes to transition metals by coordination of a carbon-oxygen double bond has been well-studied; this activation mode, however, is rarely found in transition-metal catalysis. In view of the distinctive reactivity of an ?(2)-aldehyde complex, unprecedented reactions via this intermediate are a distinct possibility. In this Account, we summarize our recent results dealing with nickel(0)-catalyzed transformations of aldehydes via ?(2)-aldehyde nickel and oxanickelacycle intermediates. The combination of electron-rich nickel(0) and strong electron-donating N-heterocyclic carbene (NHC) ligands adequately form ?(2)-aldehyde complexes in which the aldehyde is highly activated by back-bonding. With Ni(0)/NHC catalysts, processes involving intramolecular hydroacylation of alkenes and homo/cross-dimerization of aldehydes (the Tishchenko reaction) have been developed, and both proceed via the simultaneous ?(2) coordination of aldehydes and other ? components (alkenes or aldehydes). The results of the mechanistic studies are consistent with a reaction pathway that proceeds via an oxanickelacycle intermediate generated by the oxidative cyclization with a nickel(0) complex. In addition, we have used the ?(2)-aldehyde nickel complex as an effective activator for an organosilane in order to generate a silicate reactant. These reactions show 100% atom efficiency, generate no wastes, and are conducted under mild conditions. PMID:25955708

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

    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

  14. Heterogeneous SnCl2/SiO2 versus Homogeneous SnCl2 Acid Catalysis in the Benzo[N,N]-heterocyclic Condensation

    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 SnCl2·2H2O was finally selected. Among various solid supports activated with SnCl2, heterogeneous SnCl2/SiO2 proved to be the most effective and significantly higher conversions were achieved compared to SnCl2·2H2O itself. The results of TG-DTA and BET indicated that dispersed SnCl2 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

  15. Luminescent pillared Ln{sup III}–Zn{sup II} heterometallic coordination frameworks with two kinds of N-heterocyclic carboxylate ligands

    Liu, Sui-Jun; Jia, Ji-Min; Cui, Yu; Han, Song-De; Chang, Ze, E-mail: changze@nankai.edu.cn

    2014-04-01

    In our efforts toward rational design and systematic synthesis of ‘pillar-layer’ structure coordination frameworks, four new Ln{sup III}–Zn{sup II} heterometallic coordination polymers (CPs) based on two kinds of N-heterocyclic carboxylic ligands with formula ([LnZn(L1){sub 2}(L2)(H{sub 2}O){sub m}]·nH{sub 2}O){sub ∞} (Ln=La (1), Eu (2), Gd (3) and Dy (4), m=3 (for 1) and 2 (for 2–4), n=8 (for 1) and 7 (for 2–4), H{sub 2}L1=pyridine-2,3-dicarboxylate acid, HL2=isonicotinic acid), have been synthesized under hydrothermal reaction of Ln{sub 2}O{sub 3}, ZnO, H{sub 2}L1 and HL2. CP 1 has a three-dimensional (3D) structure with a (3,6)-connected sit topology network, while CPs 2–4 are isostructural with 3D single-node pcu alpha-Po topology network. Also, luminescent properties of these CPs have also been investigated. The emission of 1 and 3 should be attributed to the coordination-perturbed ligand-centered luminescence and the emission spectra of 2 and 4 show the characteristic bands of the corresponding Ln{sup III} ions. - Graphical abstract: Four new 3D Ln{sup III}–Zn{sup II} coordination frameworks with “pillar-layer” sit or pcu alpha-Po topology have been successfully obtained. Moreover, the photoluminescent properties of compounds 1–4 have also been investigated. - Highlights: • Four new Ln{sup III}–Zn{sup II} heterometallic coordination frameworks with two types of topologies have been synthesized. • Metal oxides and two kinds of N-heterocyclic carboxylate ligands were used for the construction of targeted coordination polymers. • The luminescent properties of the coordination polymers are investigated.

  16. A cyclic (alkyl)(amido)carbene: synthesis, study and utility as a desulfurization reagent.

    McCarty, Zachary R; Lastovickova, Dominika N; Bielawski, Christopher W

    2016-04-01

    The synthesis and study of a cyclic (alkyl)(amido)carbene is described. The carbene was found to undergo C-H insertion at low temperatures, formed cyclopropenes upon exposure to alkynes, and facilitated desulfurization reactions. Spectroscopic studies revealed that the carbene is strongly π-accepting but retains a complimentary degree of σ-donating properties. PMID:27010415

  17. What have we learnt about heavy carbenes through laser flash photolysis studies?

    Becerra, Rosa; Walsh, Robin

    2007-06-14

    Time resolved gas-phase kinetic studies have contributed a great deal of fundamental information about the reactions and reactivity of heavy carbenes (silylenes, germylenes and stannylenes) during the past two decades. In this article we trace the development of our understanding through the mechanistic themes of intermediate complexes, third body assisted associations, catalysed reactions, non-observed reactions and substituent effects. Ab initio (quantum chemical) calculations have substantially assisted mechanistic interpretation and are discussed where appropriate. Trends in reactivity are identified and some signposts to future studies are indicated. This review, although detailed, is not comprehensive. PMID:17538727

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

    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. Cyclic (Amino)(aryl)carbenes (CAArCs) as Strong ?-Donating and ?-Accepting Ligands for Transition Metals.

    Rao, Bin; Tang, Huarong; Zeng, Xiaoming; Liu, Liu; Melaimi, Mohand; Bertrand, Guy

    2015-12-01

    Cyclic (amino)(aryl)carbenes (CAArCs) result from the replacement of the alkyl substituent of cyclic (alkyl)(amino) carbenes (CAACs) by an aryl group. This structural modification leads to enhanced electrophilicity of the carbene center with retention of the high nucleophilicity of CAACs, and therefore CAArCs feature a small singlet-triplet gap. The isoindolium precursors are readily prepared in good yields, and deprotonation at low temperature, in the presence of [RhCl(cod)]2 and [(Me2 S)AuCl] lead to air-stable rhodium and gold CAArC-supported complexes, respectively. The rhodium complexes promote the [3+2] cycloaddition of diphenylcyclopropenone with ethyl phenylpropiolate, and induce the addition of 2-vinylpyridine to alkenes by CH activation. The gold complexes allow for the catalytic three-component preparation of 1,2-dihydroquinolines from aniline and phenyl acetylene. These preliminary results illustrate the potential of CAArC ligands in transition-metal catalysis. PMID:26457345

  20. α-Hydroxy coordination of mononuclear vanadyl citrate, malate and S-citramalate with N-heterocycle ligand, implying a new protonation pathway of iron-vanadium cofactor in nitrogenase.

    Chen, Can-Yu; Chen, Mao-Long; Chen, Hong-Bin; Wang, Hongxin; Cramer, Stephen P; Zhou, Zhao-Hui

    2014-12-01

    Unlike the most of α-alkoxy coordination in α-hydroxycarboxylates to vanadium, novel α-hydroxy coordination to vanadium(IV) has been observed for a series of chiral and achiral monomeric α-hydroxycarboxylato vanadyl complexes [VO(H2cit)(bpy)]·2H2O (1), [VO(Hmal)(bpy)]·H2O (2), [VO(H2cit)(phen)]·1.5H2O (3), [VO(Hmal)(phen)]·H2O (4), and [(Δ)VO(S-Hcitmal)(bpy)]·2H2O (5), [VO(H2cit)(phen)]2·6.5H2O (6), which were isolated from the reactions of vanadyl sulfate with α-hydroxycarboxylates and N-heterocycle ligands in acidic solution. The complexes feature a tridentate citrate, malate or citramalate that chelates to vanadium atom through their α-hydroxy, α-carboxy and β-carboxy groups; while the other β-carboxylic acidic group of citrate is free to participate strong hydrogen bonds with lattice water molecule. The neutral α-hydroxy group also forms strong intermolecular hydrogen bonds with water molecule and the negatively-charged α-carboxy group in the environment. The inclusion of a hydrogen ion in α-alkoxy group results in the formation of a series of neutral complexes with one less positive charge. There are two different configurations of citrate with respect to the trans-position of axial oxo group, where the complex with trans-hydroxy configuration seems more stable with less hindrance. The average bond distances of V-Ohydroxy and V-Oα-carboxy are 2.196 and 2.003Å respectively, which are comparable to the VO distance (2.15Å) of homocitrate in FeV-cofactor of V-nitrogenase. A new structural model is suggested for R-homocitrato iron vanadium cofactor as VFe7S9C(R-Hhomocit) (H4homocit=homocitric acid) with one more proton in homocitrate ligand. PMID:25240212

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

    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

  2. Adsorbed States of phosphonate derivatives of N-heterocyclic aromatic compounds, imidazole, thiazole, and pyridine on colloidal silver: comparison with a silver electrode.

    Podstawka, Edyta; Olszewski, Tomasz K; Boduszek, Bogdan; Proniewicz, Leonard M

    2009-09-01

    Here, we report a systematic surface-enhanced Raman spectroscopy (SERS) study of the structures of phosphonate derivatives of the N-heterocyclic aromatic compounds imidazole (ImMeP ([hydroxy(1H-imidazol-5-yl)methyl]phosphonic acid) and (ImMe)(2)P (bis[hydroxy-(1H-imidazol-4-yl)-methyl]phosphinic acid)), thiazole (BAThMeP (butylaminothiazol-2-yl-methyl)phosphonic acid) and BzAThMeP (benzylaminothiazol-2-yl-methyl)phosphonic acid)), and pyridine ((PyMe)(2)P (bis[(hydroxypyridin-3-yl-methyl)]phosphinic acid)) adsorbed on nanometer-sized colloidal particles. We compared these structures to those on a roughened silver electrode surface to determine the relationship between the adsorption strength and the geometry. For example, we showed that all of these biomolecules interact with the colloidal surface through aromatic rings. However, for BzAThMeP, a preferential interaction between the benzene ring and the colloidal silver surface is observed more so than that between the thiazole ring and this substrate. The PC(OH)C fragment does not take part in the adsorption process, and the phosphonate moiety of ImMeP and (ImMe)(2)P, being removed from the surface, only assists in this process. PMID:19670840

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

    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...

  4. Synthesis of a sterically modulated pyridine-NHC palladium complex and its reactivity towards ethylene

    Khlebnikov, Vsevolod; Meduri, Angelo; Mller-Bunz, Helge; Milani, Barbara; Albrecht, Martin

    2012-01-01

    A new cationic pyridine-carbene palladium complex has been prepared that features a C,N-bidentate coordinating ligand with a shielded pyridine and a sterically less protected carbene moiety; evaluation of this complex in ethylene polymerization revealed competitive reductive elimination processes and provides guidelines for further catalyst design.

  5. Solvent mimicry with methylene carbene to probe protein topography.

    Gmez, Gabriela Elena; Monti, Jos Luis E; Mundo, Mariana Roco; Delfino, Jos Mara

    2015-10-01

    The solvent accessible surface area (SASA) of the polypeptide chain plays a key role in protein folding, conformational change, and interaction. This fundamental biophysical parameter is elusive in experimental measurement. Our approach to this problem relies on the reaction of the minimal photochemical reagent diazirine (DZN) with polypeptides. This reagent (i) exerts solvent mimicry because its size is comparable to water and (ii) shows scant chemical selectivity because it generates extremely reactive methylene carbene. Methylation gives rise to the EM (extent of modification) signal, which is useful for scrutinizing the conformational change triggered by Ca(2+) binding to calmodulin (CaM). The increased EM observed for the full protein is dominated by the enhanced exposure of hydrophobic area in Ca(2+)-CaM. Fragmentation allowed us to quantify the methylene incorporation at specific sites. Peptide 91-106 reveals a major reorganization around the calcium 151 binding site, resulting in local ordering and a greater exposure of the hydrophobic surface. Additionally, this technique shows a high sensitivity to probe recognition between CaM and melittin (Mel). The large decrease in EM indicates the occlusion of a significant hydrophobic area upon complexation. Protection from labeling reveals a larger involvement of the N-terminal and central regions of CaM in this interaction. Despite its smaller size, Mel's differential exposure can also be quantified. Moreover, MS/MS fragmentation realizes the goal of extending the resolution of labeled sites at the amino acid level. Overall, DZN labeling emerges as a useful footprinting method capable of shedding light on physiological conformational changes and interactions. PMID:26348271

  6. The reactions of anthronylidene carbene with some heterocyclic compounds

    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)

  7. Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

    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.

  8. Efficient Domino Hydroformylation/Benzoin Condensation: Highly Selective Synthesis of ?-Hydroxy Ketones.

    Dong, Kaiwu; Sang, Rui; Soule, Jean-Francois; Bruneau, Christian; Franke, Robert; Jackstell, Ralf; Beller, Matthias

    2015-12-01

    An improved domino hydroformylation/benzoin condensation to give ?-hydroxy ketones has been developed. Easily available olefins are smoothly converted into the corresponding ?-hydroxy ketones in high yields with excellent regioselectivities. Key to success is the use of a specific catalytic system consisting of a rhodium/phosphine complex and the CO2 adduct of an N-heterocyclic carbene. PMID:26503672

  9. Assembly of functionalized carbocycles or N-heterocycles through a domino electrocyclization-[1,2] migration reaction sequence.

    Jana, Navendu; Driver, Tom G

    2015-10-14

    The development of processes that streamline the synthesis of complex, functionalized carbocycles and heterocycles remains a hotly pursued topic because their scaffolds are present in a range of bioactive molecules and electronic materials. Although the Nazarov reaction has emerged to be useful in the synthesis of carbocycles and heterocycles, using an electrocyclization to trigger a migration remains underdeveloped. By constructing several bonds in one operation, domino reaction sequences are particularly effective at improving the efficiency of synthesis. The use of transition metal catalysts has the potential to render these processes stereoselective. This review examines the use of electrocyclization-[1,2] migrations to construct molecules and is organized by the type of ring constructed and the order of the two steps in this process. PMID:26275170

  10. A very peculiar family of N-heterocyclic phosphines: unusual structures and the unique reactivity of 1,3,2-diazaphospholenes.

    Gudat, D

    2016-04-14

    This Perspective gives an account of the peculiar electronic and molecular structures of N-heterocyclic phosphines featuring either a single 1,3,2-diazaphospholene (DAP) ring with an exocyclic P-substituent X or two DAP rings linked by a P-P bond (bis-diazaphospholenyls), respectively, and their impact on the chemical properties of these molecules. The bonding situation in simple DAPs is epitomized by strong hyperconjugation between endocyclic π-type electrons and the exocyclic P-X bond. This interaction may induce a perceptible ionic polarization of the P-X bond which can persist even in the limit of a vanishing electronegativity gradient between P and X, and becomes visible in unusual geometric distortions of molecular structures and a unique chemical behaviour. Structural distortions are particularly evident in bond lengthening effects in P-halogen and P-phosphino derivatives R2P-DAP (with R2P ≠ DAP) which span the whole range from covalent molecules to contact ion pairs with a close relation to frustrated Lewis-pairs. The most significant impact on the chemical properties is found for P-phosphino- and P-hydrogen derivatives where reactions at substantially accelerated rates or totally new reaction modes can be observed, and new stoichiometric and first catalytic processes exploiting these features are currently emerging. The recently discovered bis-diazaphospholenyls differ from the simple derivatives as their central bond remains unpolarised as a consequence of the symmetric molecular structure. The occurrence of low-energy P-P bond homolysis that was nonetheless observed in one case is according to the results of thermochemical studies of P-P bond fission reactions attributable to the effects of steric congestion and induces chemical reactivity that can be considered complementary to that of the simple R2P-DAPs. Some concluding remarks will pay attention to a facet of DAP reactivity that has so far been widely neglected but is currently receiving increasing attention, namely well-defined ring-opening processes. PMID:26863391

  11. Computational Investigations of Potential Energy Function Development for Metal--Organic Framework Simulations, Metal Carbenes, and Chemical Warfare Agents

    Cioce, Christian R.

    Metal-Organic Frameworks (MOFs) are three-dimensional porous nanomaterials with a variety of applications, including catalysis, gas storage and separation, and sustainable energy. Their potential as air filtration systems is of interest for designer carbon capture materials. The chemical constituents (i.e. organic ligands) can be functionalized to create rationally designed CO2 sequestration platforms, for example. Hardware and software alike at the bleeding edge of supercomputing are utilized for designing first principles-based molecular models for the simulation of gas sorption in these frameworks. The classical potentials developed herein are named PHAST --- Potentials with High Accuracy, Speed, and Transferability, and thus are designed via a "bottom-up" approach. Specifically, models for N2 and CH4 are constructed and presented. Extensive verification and validation leads to insights and range of applicability. Through this experience, the PHAST models are improved upon further to be more applicable in heterogeneous environments. Given this, the models are applied to reproducing high level ab initio energies for gas sorption trajectories of helium atoms in a variety of rare-gas clusters, the geometries of which being representative of sorption-like environments commonly encountered in a porous nanomaterial. This work seeks to push forward the state of classical and first principles materials modeling. Additionally, the characterization of a new type of tunable radical metal---carbene is presented. Here, a cobalt(II)---porphyrin complex, [Co(Por)], was investigated to understand its role as an effective catalyst in stereoselective cyclopropanation of a diazoacetate reagent. Density functional theory along with natural bond order analysis and charge decomposition analysis gave insight into the electronics of the catalytic intermediate. The bonding pattern unveiled a new class of radical metal---carbene complex, with a doublet cobalt into which a triplet carbene sigma donates, and subsequent back-bonding occurs into a pi* antibonding orbital. This is a different type of interaction not seen in the three existing classes of metal-carbene complexes, namely Fischer, Schrock, and Grubbs. Finally, the virtual engineering of enhanced chemical warfare agent (CWA) detection systems is discussed. As part of a U.S. Department of Defense supported research project, in silico chemical modifications to a previously synthesized zinc-porphyrin, ZnCS1, were made to attempt to achieve preferential binding of the nerve agent sarin versus its simulant, DIMP (diisopropyl methylphosphonate). Upon modification, a combination of steric effects and induced hydrogen bonding allowed for the selective binding of sarin. The success of this work demonstrates the role that high performance computing can play in national security research, without the associated costs and high security required for experimentation.

  12. Ligands rock & roll: stepwise twisting of two cis-coordinated lopsided N-heterocycles in an octahedral bis(2-phenylazopyridine)-ruthenium(II) complex with seven atropisomers.

    Velders, Aldrik H; Hotze, Anna C G; Reedijk, Jan

    2005-02-01

    1H NMR data of alpha-[Ru(azpy)2(MeBim)2](PF6)2 (azpy=2-phenylazopyridine, MeBim=1-methylbenzimidazole), 2, revealed the presence of a total of seven atropisomers at -95 degrees C: three head-to-tail, HT, isomers (A, C, and D), and four head-to-head, HH, isomers which, due to the presence of an intrinsic C2 axis in the alpha-[Ru(azpy)2] moiety, are two sets of identical pairs (B/B and E/E). The NMR data of 2 represent a unique example of a coordination compound that shows a variable temperature (VT) behavior with more, well-defined steps of slow-to-fast exchange of its atropisomers. At 65 degrees C, all atropisomers are in fast exchange; on lowering the temperature the sharp signals first broaden (at room temperature) and consecutively split up into two sets of relatively sharp signals, in slow exchange, at about 0 degrees C (D, 40 %, and the coalesced signals of ABBCEE, 60 %). Upon further cooling, the set of peaks belonging to D remain sharp until the lowest recording temperatures. The signals of the other set of resonances, on the other hand, first broaden again and then separate into two sets of broad peaks (C/E/E and A) and one set of sharp peaks (B and B in fast exchange); on lowering the temperature even more, these signals broaden once again and finally, at -95 degrees C, are split up into a total of four sets of signal (A, B/B, C, and E/E). At low temperatures, ROESY experiments revealed that atropisomerization occurs through the synchronous rotation of both MeBim ligands in the interconversion of the two "identical" HH atropisomers B and B, as well as in the interconversion between C and E/E. The HH rotamers B/B furthermore exhibit a slow-to-fast exchange atropisomerization behavior that is observed independently from the other dynamic processes in this compound. The versatile cis bifunctional binding of the DNA model bases (MeBim ligands) in 2 parallels the observation of alpha-[Ru(azpy)2Cl2] which shows extraordinarly high cytotoxicity against tumor cell lines. PMID:15643666

  13. Propane activation by palladium complexes with chelating bis(NHC) ligands and aerobic cooxidation.

    Munz, Dominik; Strassner, Thomas

    2014-02-24

    The development of efficient aerobic oxidation methods remains a challenge for the selective functionalization of C-H bonds in alkanes. Herein we report the development of a C-H functionalization procedure for propane by using a palladium catalyst with chelating bis(N-heterocyclic carbene) ligands in trifluoroacetic acid together with a vanadium co-catalyst. Halides play a decisive role in the reaction. The experimental results are presented together with supporting kinetic data and an isotope effect. The reaction can be run with dioxygen as the oxidant if vanadium salts and halides are present in the reaction mixture. Experimental as well as computational results favor a mechanism involving C-H activation by palladium(II), followed by oxidation to palladium(IV) by bromine. PMID:24482080

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

    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

  15. CO2 binding in the (quinoline-CO2)− anionic complex

    We have studied the (quinoline-CO2)− anionic complex by a combination of mass spectrometry, anion photoelectron spectroscopy, and density functional theory calculations. The (quinoline-CO2)− anionic complex has much in common with previously studied (N-heterocycle-CO2)− anionic complexes both in terms of geometric structure and covalent bonding character. Unlike the previously studied N-heterocycles, however, quinoline has a positive electron affinity, and this provided a pathway for determining the binding energy of CO2 in the (quinoline-CO2)− anionic complex. From the theoretical calculations, we found CO2 to be bound within the (quinoline-CO2)− anionic complex by 0.6 eV. We also showed that the excess electron is delocalized over the entire molecular framework. It is likely that the CO2 binding energies and excess electron delocalization profiles of the previously studied (N-heterocycle-CO2)− anionic complexes are quite similar to that of the (quinoline-CO2)− anionic complex. This class of complexes may have a role to play in CO2 activation and/or sequestration

  16. Protein Footprinting by Carbenes on a Fast Photochemical Oxidation of Proteins (FPOP) Platform

    Zhang, Bojie; Rempel, Don L.; Gross, Michael L.

    2016-03-01

    Protein footprinting combined with mass spectrometry provides a method to study protein structures and interactions. To improve further current protein footprinting methods, we adapted the fast photochemical oxidation of proteins (FPOP) platform to utilize carbenes as the footprinting reagent. A Nd-YAG laser provides 355 nm laser for carbene generation in situ from photoleucine as the carbene precursor in a flow system with calmodulin as the test protein. Reversed-phase liquid chromatography coupled with mass spectrometry is appropriate to analyze the modifications produced in this footprinting. By comparing the modification extent of apo and holo calmodulin on the peptide level, we can resolve different structural domains of the protein. Carbene footprinting in a flow system is promising.

  17. Probing Protein Surface with a Solvent Mimetic Carbene Coupled to Detection by Mass Spectrometry

    Gmez, Gabriela E.; Mundo, Mariana R.; Craig, Patricio O.; Delfino, Jos M.

    2012-01-01

    Much knowledge into protein folding, ligand binding, and complex formation can be derived from the examination of the nature and size of the accessible surface area (SASA) of the polypeptide chain, a key parameter in protein science not directly measurable in an experimental fashion. To this end, an ideal chemical approach should aim at exerting solvent mimicry and achieving minimal selectivity to probe the protein surface regardless of its chemical nature. The choice of the photoreagent diazirine to fulfill these goals arises from its size comparable to water and from being a convenient source of the extremely reactive methylene carbene (:CH2). The ensuing methylation depends primarily on the solvent accessibility of the polypeptide chain, turning it into a valuable signal to address experimentally the measurement of SASA in proteins. The superb sensitivity and high resolution of modern mass spectrometry techniques allows us to derive a quantitative signal proportional to the extent of modification (EM) of the sample. Thus, diazirine labeling coupled to electrospray mass spectrometry (ESI-MS) detection can shed light on conformational features of the native as well as non-native states, not easily addressable by other methods. Enzymatic fragmentation of the polypeptide chain at the level of small peptides allows us to locate the covalent tag along the amino acid sequence, therefore enabling the construction of a map of solvent accessibility. Moreover, by subsequent MS/MS analysis of peptides, we demonstrate here the feasibility of attaining amino acid resolution in defining the target sites.

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

    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

  19. Stabilization of carbenes via α-ylide substitutions: a computational quest for new divalents at DFT.

    Haerizade, Bibi Narjes; Kassaee, Mohammad Zaman; Koohi, Maryam; Ghavami, Monire; Zandi, Hassan

    2014-01-01

    In our continued quest for novel stable carbenes, silylenes, and germylenes, here we compare and contrast multiplicities and relative stabilities of carbenes affected with four different α-ylides. The latter include carbon, immonium, phosphorus, and sulfur ylides substituted at the alpha positions of carbenes with acyclic, cyclic and cyclicunsaturated structural frameworks. Related thermodynamic data are calculated at B3LYP/6-311++G**//B3LYP/6-31+G* and B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G* levels. Investigations reveal the enlargement of the singlet-triplet energy gaps (ΔΕs-t) in the order of immonium > phosphorus > sulfur > carbon. The observed trend, which is taken as an indication of stability, is thoroughly analyzed by applying appropriate isodesmic reactions which differentiate the substituent effects on each of our singlet or triplet carbene. The effect of unsaturation is also probed in each series of the ylide carbenes. The reactivity of the species is discussed in terms of nucleophilicity and electrophilicity. PMID:24807316

  20. Rhodium, iridium and nickel complexes with a 1,3,5-triphenylbenzene tris-MIC ligand. Study of the electronic properties and catalytic activities

    Carmen Mejuto; Beatriz Royo; Gregorio Guisado-Barrios; Eduardo Peris

    2015-01-01

    The coordination versatility of a 1,3,5-triphenylbenzene-tris-mesoionic carbene ligand is illustrated by the preparation of complexes with three different metals: rhodium, iridium and nickel. The rhodium and iridium complexes contained the [MCl(COD)] fragments, while the nickel compound contained [NiCpCl]. The preparation of the tris-MIC (MIC = mesoionic carbene) complex with three [IrCl(CO)2] fragments, allowed the estimation of the Tolman electronic parameter (TEP) for the ligand, which was...

  1. Fullerene–Carbene Lewis Acid–Base Adducts

    Li, Huaping

    2011-08-17

    The reaction between a bulky N-heterocylic carbene (NHC) and C60 leads to the formation of a thermally stable zwitterionic Lewis acid-base adduct that is connected via a C-C single bond. Low-energy absorption bands with weak oscillator strengths similar to those of n-doped fullerenes were observed for the product, consistent with a net transfer of electron density to the C60 core. Corroborating information was obtained using UV photoelectron spectroscopy, which revealed that the adduct has an ionization potential ∼1.5 eV lower than that of C60. Density functional theory calculations showed that the C-C bond is polarized, with a total charge of +0.84e located on the NHC framework and -0.84e delocalized on the C 60 cage. The combination of reactivity, characterization, and theoretical studies demonstrates that fullerenes can behave as Lewis acids that react with C-based Lewis bases and that the overall process describes n-doping via C-C bond formation. © 2011 American Chemical Society.

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

    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

  3. Metal-Mediated Couplings of Primary Alcohols with Amines and Carbohydrates

    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 alcoho...

  4. 1,3-Bis(2,4,6-trimethylphenyl-3H-imidazol-1-ium tetraoxidorhenate(VII

    Maril Landman

    2011-12-01

    Full Text Available The title compound, (C21H25N2[ReO4], was formed as the unexpected product in an attempted synthesis of a rhenium(IN-heterocyclic carbene (NHC complex. The compound has crystallographic mirror symmetry with both the cation and the tetrahedral anion located across a mirror plane. The cation and anion are linked by a CH...O hydrogen bond.

  5. N-(2,4,6-Trimethylphenylformamide

    David C. Liles

    2011-01-01

    Full Text Available The title compound, C10H13NO, was obtained as the unexpected, almost exclusive, product in the attempted synthesis of a manganese(I–N-heterocyclic carbene (NHC complex. The dihedral angle between the planes of the formamide moiety and the aryl ring is 68.06 (10°. In the crystal, molecules are linked by N—H...O hydrogen bonds, forming infinite chains along the c axis.

  6. Diazirine-modified gold nanoparticle: template for efficient photoinduced interfacial carbene insertion reactions.

    Ismaili, Hossein; Lee, Soo; Workentin, Mark S

    2010-09-21

    Photolysis of a 3-aryl-3-(trifluoromethyl)diazirine-modified monolayer-protected gold nanoparticles (2-C(12)MPNs), with a core size of 1.8 ± 0.3 nm, in the presence of model carbene trapping reagents leads to efficient, essentially quantitative, modification of the interface via carbene insertion reactions. The utility of carbene insertion reactions as a general approach for the modification of Au-MPNs to provide a breadth of new structures available was demonstrated using acetic acid, methanol, benzyl alcohol, phenol, benzylamine, methyl acrylate, and styrene (10a-g, respectively) as electrophilic carbene trapping agents to form the corresponding modified 3a-g-C(12)MPNs. The 1.8 ± 0.3 nm gold nanoparticles bearing a diazirine group (2-C(12)MPNs) were synthesized using the ligand exchange reaction with the requisite 3-aryl-3-(trifluoromethyl)diazirinealkylthiol. The 2-C(12)MPNs and the resulting products of the reaction on the MPN (3a-g-C(12)MPN) were fully characterized by IR, (1)H NMR, and (19)F NMR spectroscopy and, when applicable, transmission electron microscopy (TEM). Verification for the 3a-g-C(12)MPNs was accomplished by comparison of the spectral data to those of obtained for the photoreactions of 3-(3-methoxyphenyl)-3-(trifluoromethyl)-3H-diazirine as a model with 10a-g. PMID:20735050

  7. Intramolecular transannulation of alkynyl triazoles via alkyne-carbene metathesis step: access to fused pyrroles.

    Shi, Yi; Gevorgyan, Vladimir

    2013-10-18

    An intramolecular Rh-catalyzed transannulation reaction of alkynyl triazoles has been developed. This method allows efficient construction of various 5,5-fused pyrroles, including tetrahydropyrrolo and spiro systems. The method demonstrates excellent functional group compatibility. A rhodium carbene-alkyne metathesis mechanism is proposed for this transformation. PMID:24093728

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

    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.

  9. Selenophene transition metal complexes

    White, C.J.

    1994-07-27

    This research shows that selenophene transition metal complexes have a chemistry that is similar to their thiophene analogs. Selenophene coordination has been demonstrated and confirmed by molecular structure in both the {eta}{sup 5}- and the {eta}{sup 1}(Se)-coordination modes. The reaction chemistry of selenophene complexes closely resembles that of the analogous thiophene complexes. One major difference, however, is that selenophene is a better donor ligand than thiophene making the selenophene complexes more stable than the corresponding thiophene complexes. The {sup 77}Se NMR chemical shift values for selenophene complexes fall within distinct regions primarily depending on the coordination mode of the selenophene ligand. In the final paper, the C-H bond activation of {eta}{sup 1}(S)-bound thiophenes, {eta}{sup 1}(S)-benzothiophene and {eta}{sup 1}(Se)-bound selenophenes has been demonstrated. The deprotonation and rearrangement of the {eta}{sup 1}(E)-bound ligand to the carbon bound L-yl complex readily occurs in the presence of base. Reprotonation with a strong acid gives a carbene complex that is unreactive towards nucleophilic attack at the carbene carbon and is stable towards exposure to air. The molecular structure of [Cp(NO)(PPh{sub 3})Re(2-benzothioenylcarbene)]O{sub 3}SCF{sub 3} was determined and contains a Re-C bond with substantial double bond character. Methyl substitution for the thienylcarbene or selenylcarbene gives a carbene that rearranges thermally to give back the {eta}{sup 1}(E)-bound complex. Based on these model reactions, a new mechanism for the H/D exchange of thiophene over the hydrodesulfurization catalyst has been proposed.

  10. Thiazolium carbene catalysts for the fixation of CO2 onto amines.

    Das, Shoubhik; Bobbink, Felix D; Bulut, Safak; Soudani, Mylne; Dyson, Paul J

    2016-02-11

    The catalytic N-formylation and N-methylation of amines using CO2 as the carbon source represents a facile and sustainable approach for the synthesis of pharmaceuticals and natural products. Herein, we describe highly effective and inexpensive thiazolium carbene-based catalysts derived from vitamin B1 for the N-formylation and N-methylation of amines, using polymethylhydrosiloxane (PMHS) as a reducing agent, which operate under ambient conditions. PMID:26739571

  11. Role of quantum mechanical tunneling on the ?-effect of silicon on carbenes in 3-trimethylsilylcyclobutylidene.

    Karmakar, Sharmistha; Datta, Ayan

    2014-03-01

    Quantum mechanical tunneling (QMT) is increasingly being realized as an important phenomenon that can enhance the rate of reactions even at room temperature. Recently, the ability of a trimethylsilane (TMS) group to activate 1,3-H shift to a carbene from a ?-position has been demonstrated. Direct dynamical calculations (using canonical varitational transition state theory) inclusive of small curvature tunneling (CVT-SCT) show that QMT plays a decisive role in such 1,3-hydrogen migration in both the presence and absence of TMS. The presence of a TMS group reduces the activation energy of 1,3-H shift reaction via 1,3-equatorial interaction of the TMS group with the carbene. Tunneling across the smaller barrier enhances the overall forward rate of the reaction. The Arrhenius plot for the reaction shows substantial curvature in comparison to the CVT mechanism at room temperature. Arrhenius plots for the kinetic isotope effects (KIEs) for the ?-deuterated and per deuterated 3-trimethylsilylcyclobutylidene also show strong deviations from the classical over the barrier mechanism. The magnitude of the KIE is suggestive of QMT from the vibrational excited states of the carbenes. PMID:24467461

  12. The cycloadditions of various substituted carbenes, silylenes, and germylenes onto the diamond (100) surface: a theoretical exploration.

    Xu, Yi-Jun; Zhang, Yong-Fan; Li, Jun-Qian

    2006-07-20

    The cycloadditions of 21 singlet substituted carbenes, silylenes, and germylenes onto the diamond (100) surface have been theoretically studied by means of density functional theory coupled with effective cluster models. The calculated reaction energies and reaction pathways have disclosed that the substituents play an important effect on the reaction profiles for the additions of carbenes, silylenes, and germylenes onto the diamond (100) surface. Our theoretical investigations illustrate that, irrespective of carbenes, silylenes, and germylenes, the cycloadditions of those with electropositive substituents (such as H and CH(3)) onto diamond (100) are much more favorable than those with electronegative and pi-donating substituents (such as F and NH(2)) both thermodynamically and kinetically. In broad perspective, we believe that a similar reactivity trend can also be extended to that of Si (100), Ge (100), fullerene, single-walled carbon nanotube, disilenes, digermenes, silenes, and germenes because all of these materials feature an analogous bonding motif. PMID:16836344

  13. Lutidine-derived Ru-CNC hydrogenation pincer catalysts with versatile coordination properties

    Filonenko, Georgy A.; Cosimi, Elena; Lefort, Laurent; Conley, Matthew P.; Copéret, Christophe; Lutz, Martin|info:eu-repo/dai/nl/304828971; Hensen, Emiel J.M.; Pidko, Evgeny A.

    2014-01-01

    Lutidine-derived bis-N-heterocyclic carbene (NHC) ruthenium CNC-pincer complexes (Ru-CNC's) were prepared. Depending on the synthetic procedure, normal (1, 2) or mixed normal/abnormal NHC-complexes (3) are formed. In the presence of phosphazene base, Ru-CNC complexes activate nitriles to give ketimino compounds 4-6. Nitrile adduct 4 shows reactivity toward strong bases to yield dearomatized complex 7, which heterolytically activates H2 to form the bis-hydrido complex 8. Finally, these Ru-CNC'...

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

    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.

  15. Vanadium(IV/V) complexes of Triapine and related thiosemicarbazones: Synthesis, solution equilibrium and bioactivity.

    Kowol, Christian R; Nagy, Nóra V; Jakusch, Tamás; Roller, Alexander; Heffeter, Petra; Keppler, Bernhard K; Enyedy, Éva A

    2015-11-01

    The stoichiometry and thermodynamic stability of vanadium(IV/V) complexes of Triapine and two related α(N)-heterocyclic thiosemicarbazones (TSCs) with potential antitumor activity have been determined by pH-potentiometry, EPR and (51)V NMR spectroscopy in 30% (w/w) dimethyl sulfoxide/water solvent mixtures. In all cases, mono-ligand complexes in different protonation states were identified. Dimethylation of the terminal amino group resulted in the formation of vanadium(IV/V) complexes with considerably higher stability. Three of the most stable complexes were also synthesized in solid state and comprehensively characterized. The biological evaluation of the synthesized vanadium complexes in comparison to the metal-free ligands in different human cancer cell lines revealed only minimal influence of the metal ion. Thus, in addition the coordination ability of salicylaldehyde thiosemicarbazone (STSC) to vanadium(IV/V) ions was investigated. The exchange of the pyridine nitrogen of the α(N)-heterocyclic TSCs to a phenolate oxygen in STSC significantly increased the stability of the complexes in solution. Finally, this also resulted in increased cytotoxicity activity of a vanadium(V) complex of STSC compared to the metal-free ligand. PMID:26349014

  16. A Serine-Substituted P450 Catalyzes Highly Efficient Carbene Transfer to Olefins In Vivo

    Coelho, Pedro S; Wang, Z. Jane.; Ener, Maraia E.; Baril, Stefanie A.; Kannan, Arvind A.; Arnold, Frances H; Brustad, Eric M

    2013-01-01

    Genetically encoded catalysts for non-natural chemical reactions will open new routes to sustainable production of chemicals. We designed a unique serine-heme ligated cytochrome “P411” that catalyzes efficient and selective carbene transfers from diazoesters to olefins in intact Escherichia coli cells. The mutation C400S in cytochrome P450BM3 gives a signature ferrous-CO Soret peak at 411 nm, abolishes monooxygenation activity, raises the resting state FeIII/II reduction potential, and signif...

  17. NHC-based pincer ligands: carbenes with a bite.

    Andrew, Rhiann E; González-Sebastián, Lucero; Chaplin, Adrian B

    2016-01-19

    In this frontier article we overview the emergence and scope of NHC-based CCC and CNC pincer systems, i.e. complexes containing mer-tridentate ligands bearing two NHC donor groups, comment on their effectiveness in applications, and highlight areas for future development and exploitation. PMID:26673868

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

    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.

  19. Reductive Cyclopropanations Catalyzed by Dinuclear Nickel Complexes.

    Zhou, You-Yun; Uyeda, Christopher

    2016-02-01

    Dinuclear Ni complexes supported by naphthyridine-diimine (NDI) ligands catalyze the reductive cyclopropanation of alkenes with CH2 Cl2 as the methylene source. The use of mild terminal reductants (Zn or Et2 Zn) confers significant functional-group tolerance, and the catalyst accommodates structurally and electronically diverse alkenes. Mononickel catalysts bearing related N chelates afford comparatively low cyclopropane yields (≤20 %). These results constitute an entry into catalytic carbene transformations from oxidized methylene precursors. PMID:26822193

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

    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.

  1. Highvalent and organometallic technetium and rhenium compounds

    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.

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

    Kvapilová, Hana; Hoskovcová, Irena; Ludvík, Jiří; Záliš, Stanislav

    2014-01-01

    Roč. 33, č. 18 (2014), s. 4964-4972. ISSN 0276-7333 R&D Projects: GA MŠk LD14129; GA ČR 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

  3. Group 4 Transition-Metal Complexes of an Aniline–Carbene–Phenol Ligand

    Despagnet-Ayoub, Emmanuelle

    2013-05-24

    Attempts to install a tridentate aniline-NHC-phenol (NCO) ligand on titanium and zirconium led instead to complexes resulting from unexpected rearrangement pathways that illustrate common behavior in carbene-early- transition-metal chemistry. © 2013 American Chemical Society.

  4. A stable dimer of SiS2 arranged between two carbene molecules.

    Mohapatra, Chandrajeet; Mondal, Kartik Chandra; Samuel, Prinson P; Keil, Helena; Nieptter, Benedikt; Herbst-Irmer, Regine; Stalke, Dietmar; Dutta, Sayan; Koley, Debasis; Roesky, Herbert W

    2015-09-01

    The Me-cAAC:-stabilized dimer of silicon disulfide (SiS2 ) has been isolated in the molecular form as (Me-cAAC:)2 Si2 S4 (2) at room temperature [Me-cAAC:=cyclic alkyl(amino) carbene]. Compound 2 has been synthesized from the reaction of (Me-cAAC:)2 Si2 with elemental sulfur in a 1:4 molar ratio under oxidative addition. This is the smallest molecular unit of silicon disulfide characterized by X-ray crystallography, electron ionization mass spectrometry, and NMR spectroscopy. Structures with three sulfur atoms arranged around a silicon atom are known; however, 2 is the first structurally characterized silicon-sulfur compound containing one terminal and two bridging sulfur atoms at each silicon atom. Compound 2 shows no decomposition after storing for three months in an inert atmosphere at ambient temperature. The bonding of 2 has been further studied by theoretical calculations. PMID:26179976

  5. Highly stereoselective synthesis of cyclopentanes bearing four stereocentres by a rhodium carbene-initiated domino sequence.

    Parr, Brendan T; Davies, Huw M L

    2014-01-01

    Stereoselective synthesis of a cyclopentane nucleus by convergent annulation constitutes a significant challenge for synthetic chemists. Although a number of biologically relevant cyclopentane natural products are known, more often than not, the cyclopentane core is assembled in a stepwise manner because of the lack of efficient annulation strategies. Here we report the rhodium-catalysed reactions of vinyldiazoacetates with (E)-1,3-disubstituted 2-butenols generate cyclopentanes, containing four new stereogenic centres with very high levels of stereoselectivity (99% ee, >97: 3 dr). The reaction proceeds by a carbene-initiated domino sequence consisting of five distinct steps: rhodium-bound oxonium ylide formation, [2,3]-sigmatropic rearrangement, oxy-Cope rearrangement, enol-keto tautomerization and finally an intramolecular carbonyl ene reaction. A systematic study is presented detailing how to control chirality transfer in each of the four stereo-defining steps of the cascade, consummating in the development of a highly stereoselective process. PMID:25082301

  6. Possible formation of crystalline sodium carbene carbonate Na2(CO)CO3 at high pressure

    Combined experimental and ab-initio computational studies suggest that at pressures above 20 GPa and temperatures above 1500 K sodium formate deprotonizes under formation of Na+2 [C=O| CO32-]. This new compound involves mesomeric C-O bonds with carbonate plus carbene units as limiting states and CO2 chains as intermediate. Sodium is six-fold coordinated by O-atoms. The formation of this new compound implies nucleophilic addition as reaction mechanism which is consistent with previously observed reduced stability of the H-O bond at these high pressures. The findings suggest further that the sextet state of carbon is energetically less unfavourable at high pressure than at ambient pressure.

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

    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.

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

    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. A spectroscopic study of the reaction of the carbene, tetrabromocyclopentadienylidene, with O 2 in low temperature matrices

    Dunkin, Ian R.; McCluskey, Adam

    1994-01-01

    The photolysis of tetrabromodiazocyclopentadiene ( 2) in low temperature Ar and N 2 matrices generates the carbene, tetrabromocyclopentadienylidene ( 3). In O 2-doped matrices, ( 3) reacts with oxygen yielding first tetrabromocyclopentadienone O-oxide ( 4), identification of which was aided by experiments with isotopically labelled oxygen, and then tetrabromocyclopentadienone ( 5) and tetrabromo-α-pyrone ( 6). The matrix uv-visible and infrared absorption spectra of tetrabromocyclopentadienone O-oxide ( 4) are reported.

  10. A Broadly Applicable NHC–Cu-Catalyzed Approach for Efficient, Site-, and Enantioselective Coupling of Readily Accessible (Pinacolato)alkenylboron Compounds to Allylic Phosphates and Applications to Natural Product Synthesis

    Gao, Fang; Carr, James L.; Hoveyda, Amir H.

    2014-01-01

    A set of protocols for catalytic enantioselective allylic substitution (EAS) reactions that allow for additions of alkenyl units to readily accessible allylic electrophiles is disclosed. Transformations afford 1,4-dienes that contain a tertiary carbon stereogenic site and are promoted by 1.0–5.0 mol % of a copper complex of an N-heterocyclic carbene (NHC). Aryl- as well as alkyl-substituted electrophiles bearing a di- or trisubstituted alkene may be employed. Reactions can involve a variety o...

  11. Chimie de coordination de carbènes N-hétérocycliques substitués par des groupements alkyfluorényle : interactions faibles, effets stériques, catalyse

    Teci, Matthieu

    2015-01-01

    This thesis deals with a series of N-heterocyclic carbene ligands (NHCs) in which the N atoms bear expanded alkylfluorenyl (AF) substituents. Special focus has been put on the steric properties of these new ligands, as well as their influence on catalytic reactions involving Pd and Cu centres.The first part of this work describes the synthesis of a series of AF-substituted azolium salts suitable for the preparation of palladium PEPPSI-NHC complexes. These turned out to be very active in Suzuk...

  12. Comparing Ru and Fe-catalyzed olefin metathesis

    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.

  13. Utilisation of water soluble iridium catalysts for signal amplification by reversible exchange.

    Fekete, M; Gibard, C; Dear, G J; Green, G G R; Hooper, A J J; Roberts, A D; Cisnetti, F; Duckett, S B

    2015-05-01

    The catalytic hyperpolarisation of pyridine, 3-hydroxypyridine and oxazole by the Signal Amplification By Reversible Exchange (SABRE) process is achieved by a series of water soluble iridium phosphine and N-heterocyclic carbene dihydride complexes. While the efficiency of the SABRE process in methanol-d4 solution or ethanol-d6 solution is high, with over 400-fold (1)H polarisation of pyridine being produced by [Ir(H)2(NCMe)(py)(IMes)(monosulfonated-triphenylphosphine)]BF4, changing to a D2O or a D2O-ethanol solvent mixture leads to dramatically reduced activity which is rationalised in terms of low H2 solubility. PMID:25823378

  14. Crystal structure of {3-[3,5-bis(2,6-dimethylphenyl-1,2-phenylene]-1-(2,6,2??,6??-tetramethyl-1,1?:3?,1??-terphenyl-5?-ylimidazol-2-ylidene}chlorido(?6-p-cymeneruthenium(II benzene disolvate

    Shohei Sase

    2014-12-01

    Full Text Available The title compound, [Ru(C47H43N2Cl(C10H14]2C6H6, crystallized with two independent molecules of benzene. One of the N-aryl moieties of the N-heterocyclic carbene (NHC ligand underwent cyclometallation to form a five-membered ruthenacycle. The complex has a three-legged piano-stool structure with two C atoms incorporated in the five-membered ruthenacycle and a Cl atom as legs. The ruthenacycle is essentially coplanar with the imidazole ring of the NHC ligand, making a dihedral angle of 0.85?(8.

  15. Encapsulating Inorganic Acetylene, HBNH, Using Flanking Coordinative Interactions.

    Swarnakar, Anindya K; Hering-Junghans, Christian; Nagata, Koichi; Ferguson, Michael J; McDonald, Robert; Tokitoh, Norihiro; Rivard, Eric

    2015-09-01

    A stable donor-acceptor coordination complex of the elusive parent inorganic iminoborane HBNH (a structural analogue of acetylene) is reported. This species was generated via thermally induced N2 elimination/1,2-H migration from a hydrido(azido)borane adduct NHC?BH2N3 (NHC=N-heterocyclic carbene) in the presence of a fluorinated triarylborane. The mechanism of this process was also investigated by computational and isotopic labeling studies. This transformation represents a new and potentially modular route to unsaturated inorganic building blocks for advanced material synthesis. PMID:26214271

  16. Gold( i )-catalysed dehydrative formation of ethers from benzylic alcohols and phenols

    Veenboer, Richard M. P.

    2015-01-01

    © The Royal Society of Chemistry 2015. We report the cross-dehydrative reaction of two alcohols to form unsymmetrical ethers using NHC-gold(i) complexes (NHC = N-heterocyclic carbene). Our progress in developing this reaction into a straightforward procedure is discussed in detail. The optimised methodology proceeds under mild reaction conditions and produces water as the sole by-product. The synthetic utility of this environmentally benign methodology is exemplified by the formation of a range of new ethers from readily available phenols bearing electron withdrawing substituents and secondary benzylic alcohols with various substituents. Finally, we present experimental results to account for the chemoselectivity obtained in these reactions.

  17. Complexity

    Gershenson, Carlos

    2011-01-01

    The term complexity derives etymologically from the Latin plexus, which means interwoven. Intuitively, this implies that something complex is composed by elements that are difficult to separate. This difficulty arises from the relevant interactions that take place between components. This lack of separability is at odds with the classical scientific method - which has been used since the times of Galileo, Newton, Descartes, and Laplace - and has also influenced philosophy and engineering. In recent decades, the scientific study of complexity and complex systems has proposed a paradigm shift in science and philosophy, proposing novel methods that take into account relevant interactions.

  18. Carbene Reactions

    Hoffmann, R. W.; Barth, W.; Carlsen, Lars; Egsgaard, Helge

    The gas-phase thermolysis of the norbornadienespirodithiolane S-oxides (5) and (7) led to benzene, ethylene, and carbon disulphide as the major products, possibly involving carbon disulphide oxides as intermediates. Thermolyses of the related sulphones (9) or (14) led to completely different...

  19. Electronic Excitations in Fischer-Type Cr and W Aminocarbene Complexes: A Combined ab Initio and Experimental Study

    Kvapilová, Hana; Hoskovcová, Irena; Kayanuma, M.; Daniel, CH.; Záliš, Stanislav

    2013-01-01

    Roč. 117, č. 45 (2013), s. 11456-11463. ISSN 1089-5639 R&D Projects: GA MŠk LD11086 Institutional support: RVO:61388955 Keywords : METAL CARBENE COMPLEXES * FLASH-PHOTOLYSIS * BASIS-SETS Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.775, year: 2013

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

    Hoskovcová, I.; Roháčová, J.; Dvořák, D.; Ludvík, Jiří

    2006-01-01

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

  1. Preparing Gold(I) for Interactions with Proton Donors: The Elusive [Au]???HO Hydrogen Bond.

    Groenewald, Ferdinand; Dillen, Jan; Raubenheimer, Helgard G; Esterhuysen, Catharine

    2016-01-01

    MP2 and DFT calculations with correlation consistent basis sets indicate that isolated linear anionic dialkylgold(I) complexes form moderately strong (ca. 10?kcal?mol(-1) ) Au???H hydrogen bonds with single H2 O molecules as donors in the absence of sterically demanding substituents. Relativistic effects are critically important in the attraction. Such bonds are significantly weaker in neutral, strong ?-donor N-heterocyclic carbene (NHC) complexes (ca. 5?kcal?mol(-1) ). The overall association (>11?kcal?mol(-1) ), however, is strengthened by co-operative, synergistic classical hydrogen bonding when the NHC ligands bear NH units. Further manipulation of the interaction by ligands positioned trans to the carbene, is possible. PMID:26695099

  2. Insero C-H de carbenides de rdio em gua e reutilizao do catalisador Rhodium (II carbene C-H insertion in water and catalyst reuse

    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.

  3. Rhodium (II) carbene C-H insertion in water and catalyst reuse; Insercao C-H de carbenoides de rodio em agua e reutilizacao do catalisador

    Candeias, Nuno R.; Gois, Pedro M.P.; Afonso, Carlos A.M. [Instituto Superior Tecnico, Lisboa (Portugal)]. E-mail: carlosafonso@ist.utl.pt

    2007-07-01

    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-ethoxycarbonyl acetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst Rh{sub 2}(OAc){sub 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. (author)

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

    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 α-H and β-H abstraction. © 2011 American Chemical Society.

  5. Palladium-Catalyzed Intermolecular Carbene Insertion Prior to Intramolecular Heck Cyclization: Synthesis of 2-Arylidene-3-aryl-1-indanones.

    Arunprasath, Dhanarajan; Muthupandi, Pandi; Sekar, Govindasamy

    2015-11-01

    A domino process that converges the migratory insertion of carbene with a Heck reaction has been established as a versatile tool for the synthesis of 2-arylidene-3-aryl-1-indanones from very stable and easily accessible N-tosylhydrazones and 2'-iodochalcones. The reaction selectively proceeds through 5-exo-trig cyclization and delivers the products selectively with the E configuration of the double bond in excellent yields. The one-pot synthesis of 2-arylidene-3-aryl-1-indanones involving in situ synthesis of both 2'-iodochalcones and N-tosylhydrazones has also been demonstrated. PMID:26501560

  6. Nearly degenerate isomers of C(BH)2: cumulene, carbene, or carbone?

    Barua, Shiblee R; Allen, Wesley D; Kraka, Elfi; Jerabek, Paul; Sure, Rebecca; Frenking, Gernot

    2013-11-18

    The ground electronic state of C(BH)2 exhibits both a linear minimum and a peculiar angle-deformation isomer with a central B-C-B angle near 90. Definitive computations on these species and the intervening transition state have been executed by means of coupled-cluster theory including single and double excitations (CCSD), perturbative triples (CCSD(T)), and full triples with perturbative quadruples (CCSDT(Q)), in concert with series of correlation-consistent basis sets (cc-pVXZ, X=D, T, Q, 5, 6; cc-pCVXZ, X=T, Q). Final energies were pinpointed by focal-point analyses (FPA) targeting the complete basis-set limit of CCSDT(Q) theory with auxiliary core correlation, relativistic, and non-Born-Oppenheimer corrections. Isomerization of the linear species to the bent form has a minuscule FPA reaction energy of 0.02 kcal mol(-1) and a corresponding barrier of only 1.89 kcal mol(-1). Quantum tunneling computations reveal interconversion of the two isomers on a timescale much less than 1 s even at 0 K. Highly accurate CCSD(T)/cc-pVTZ and composite c~CCSDT(Q)/cc-pCVQZ anharmonic vibrational frequencies confirm matrix-isolation infrared bands previously assigned to linear C(BH)2 and provide excellent predictions for the heretofore unobserved bent isomer. Chemical bonding in the C(BH)2 species was exhaustively investigated by the atoms-in-molecules (AIM) approach, molecular orbital plots, various population analyses, local mode vibrations and force constants, unified reaction valley analysis (URVA), and other methods. Linear C(BH)2 is a cumulene, whereas bent C(BH)2 is best characterized as a carbene with little carbone character. Weak B-B attraction is clearly present in the unusual bent isomer, but its strength is insufficient to form a CB2 ring with a genuine boron-boron bond and attendant AIM bond path. PMID:24123325

  7. Singlet-triplet energy gap in halogen-substituted carbenes and silylenes: a difference-dedicated configuration interaction calculation

    García, V. M.; Castell, O.; Reguero, M.; Caballol, R.

    Ab initio calculations including correlation energy are reported on a series of halogen-substituted carbenes and silylenes: CH2, CHF, CF2, CHCl, CCl2, CHBr, CBr2, SiH2, SiHF, SiF2, using the difference-dedicated configuration interaction method. All these compounds with the exception of CH2 have singlet ground states. The singlet-triplet energy differences are in very good agreement with experiment when available, as well as with other high level calculations. The singlet-triplet separation is also determined in trifluoromethyl carbenes, CHCF3, CFCF3, CClCF3 and CBrCF3. The CF3 substituent has little influence on the energy gap since CHCF3 like CH2 has a triplet ground state, with a gap of 11·1 kcal mol-1, and CFCF3, CClCF3 and CBrCF3 have singlet ground states, like CHF, CHCl and CHBr, with gaps of -17·6, -5·4, and -3·5 kcal mol-1.

  8. Synthesis, characterization and cytotoxic activities of the [RuCl2(NO)(dppp)(L)]PF6 complexes.

    Golfeto, Camilla C; Von Poelhsitz, Gustavo; Selistre-de-Araújo, Heloísa S; de Araujo, Márcio P; Ellena, Javier; Castellano, Eduardo E; Lopes, Luiz G L; Moreira, Icaro S; Batista, Alzir A

    2010-05-01

    The synthesis and characterization of ruthenium compounds of the type [RuCl(2)(NO)(dppp)(L)]PF(6) [dppp=1,3-bis(diphenylphosphino)propane; L=pyridine, 4-methylpyridine, 4-phenylpyridine and dimethyl sulfoxide] are described. The complexes were characterized by elemental analysis, UV/Vis and infrared spectroscopy, cyclic voltammetry, and X-ray crystallography for the complexes with the pyridine and 4-methylpyridine ligands. In vitro evaluation of these nitrosyl complexes revealed cytotoxic activity from 7.1 to 19.0 microM against the MDA-MB-231 breast tumor cells and showed that, in this case, they are more active than the reference metallodrug cisplatin. The 1,3-bis(diphenylphosphino)propane and the N-heterocyclic ligands alone failed to show cytotoxic activities at the concentrations tested (maximum concentration utilized=200 microM). PMID:20117840

  9. Metal Complexes of Quinolone Antibiotics and Their Applications: An Update

    Valentina Uivarosi

    2013-09-01

    Full Text Available Quinolones are synthetic broad-spectrum antibiotics with good oral absorption and excellent bioavailability. Due to the chemical functions found on their nucleus (a carboxylic acid function at the 3-position, and in most cases a basic piperazinyl ring (or another N-heterocycle at the 7-position, and a carbonyl oxygen atom at the 4-position quinolones bind metal ions forming complexes in which they can act as bidentate, as unidentate and as bridging ligand, respectively. In the polymeric complexes in solid state, multiple modes of coordination are simultaneously possible. In strongly acidic conditions, quinolone molecules possessing a basic side nucleus are protonated and appear as cations in the ionic complexes. Interaction with metal ions has some important consequences for the solubility, pharmacokinetics and bioavailability of quinolones, and is also involved in the mechanism of action of these bactericidal agents. Many metal complexes with equal or enhanced antimicrobial activity compared to the parent quinolones were obtained. New strategies in the design of metal complexes of quinolones have led to compounds with anticancer activity. Analytical applications of complexation with metal ions were oriented toward two main directions: determination of quinolones based on complexation with metal ions or, reversely, determination of metal ions based on complexation with quinolones.

  10. Theoretical description of metal-ligand bonding within f-element complexes: A successful and necessary interplay between theory and experiment

    Maldivi, P.; Petit, L.; Vetere, V. [CEA Grenoble, Dept. de Recherche Fondamentale sur la Matiere Condensee, Laboratoire de reconnaissance ionique, DRFMC/SCIB (LCIB, UMR E 3 CEA-UJF), 38 (France); Petit, L.; Adamo, C. [Ecole Nationale Superieure de Chimie de Paris, Laboratoire d' electrochimie et de chimie analytique, CNRS UMR-7575, 75 - Paris (France)

    2007-10-15

    The quantum chemical study presented here shows various aspects of the bonding of lanthanide (La{sup 3+}, Gd{sup 3+}) and actinide (U{sup 3+}, Am{sup 3+}, Cm{sup 3+}) ions with N-heterocyclic ligands (poly-azines, BTP: bis(1,2,4-triazinyl)-2,6-pyridine). Several families of complexes, differing by their coordination sphere, have been examined. Clearly, the lanthanide complexes always show a purely ionic bonding. The behaviour of U(III) is also well defined with a more or less strong back bonding interaction whatever the complex is. In contrast, the heavy actinides (Am{sup 3+} and Cm{sup 3+}) are changeable, with a weak covalent character, going from donation to back donation, depending on the coordination sphere of the complex. (authors)

  11. Electroinduced Carbene Formation in the Cathodic Reduction of 1,2-Dicarbonyl Compounds via Electron-Transfer to the Solvent

    Graphical abstract: Display Omitted -- Highlights: •Electron-transfer reaction in solution from the substrate dianion to the solvent. •To our knowledge, it is the first time that a carbene is generated by an electron-transfer in solution process. •1,1-Dichloroethyl radical and methyl-chlorocarbene as involved intermediates. •The stereochemistry of the radical anion intermediate governs the reaction pathway. •Electroinduced effect of reversible electroactive systems is presented. -- Abstract: Electrochemical reduction of 9,10-phenanthrenequinone, benzil and acenaphthenequinone in 1,1,1-trichloroethane (TCE)/TBAP under constant potential conditions provides an interesting entry to new coupling products through an electron-transfer reaction in solution to the chlorinated solvent. This electroinduced reaction points out the differences in the reaction pathway followed by these 1,2-dicarbonyl compounds depending on their geometry. The intermediates nature and their behavior, both in solution and at the electrode surface, are discussed

  12. Design and synthesis of ruthenium(II) OCO pincer type NHC complexes and their catalytic role towards the synthesis of amides

    Muthukumaran Nirmala; Periasamy Viswanathamurthi

    2016-01-01

    The present contribution describes the synthesis and characterization of a family of robust ruthenium complexes, supported by a tridentate pincer ligand of the type bis-phenolate--heterocyclic carbene [Bu(OCO)2−] (NHC). Ruthenium(II) complexes (1-3) bearing bis-phenolate--heterocyclic carbene ligand were synthesized in good yields by the reaction of imidazolinium proligand (HL) with metal precursors [RuHCl(CO)(EPh3)2(B)] (E = P or As; B = PPh3, AsPh3 or Py) by transmetalation from the corresponding silver carbene complex. All the Ru(II)-NHC complexes have been characterized by elemental analyses, spectroscopic methods as well as ESI mass spectrometry. Based on the spectral results, an octahedral geometry was assigned for all the complexes. The tridentate nature of the Bu(OCO)2− ligand as well as some level of steric protection provided by the Bu groups may rationalize the excellent stability of the Ru-Ccarbene bond in the present systems. Moreover, for the explorations of catalytic potential of the synthesized compounds, all the three [Ru-NHC] complexes (1-3) were tested as catalysts for amidation of alcohols with amines. Notably, the complex 1 was found to be very efficient and versatile catalyst towards amidation of a wide range of alcohols with amines.

  13. Nuevos alquinil complejos y carbenos N-Heterocclicos de oro(I). Autoensamblaje de complejos heteronucleares usando metaligandos de oro(I)= New alkynyl and N-Heterocyclic gold(I) complexes. Self-assembly of heteronuclear complexes usin gold(I) metallaligands

    Cmara Hernndez, Vernica

    2013-01-01

    Objetivos: Los objetivos planteados para esta tesis han sido la sntesis y caracterizacin de nuevos alquinil complejos y carbenos N-Heterocclicos (NHC) de oro(I), as como la utilizacin de algunos de estos complejos como metalaligandos en reacciones de ensamblaje de nuevos complejos heteronucleares. Tambin nos planteamos llevara a cabo estudios estructurales de los nuevos complejos preparados, as como estudios de su comportamiento en disolucin, y sus propiedades fotofsicas. Meto...

  14. A mesoionic bis(Py-tzNHC) palladium(ii) complex catalyses "green" Sonogashira reaction through an unprecedented mechanism.

    Gazvoda, Martin; Virant, Miha; Pevec, Andrej; Urankar, Damijana; Bolje, Aljoa; Ko?evar, Marijan; Komrlj, Janez

    2016-01-28

    A novel bis(pyridyl-functionalized 1,2,3-triazol-5-ylidene)-palladium(ii) complex [Pd(Py-tzNHC)2](2+) catalyses the copper-, amine-, phosphine-, and additive-free aerobic Sonogashira alkynylation of (hetero)aryl bromides in water as the only reaction solvent. The catalysis proceeds along two connected Pd-cycles with homogeneous bis-carbene Pd(0) and Pd(II) species, as demonstrated by electrospray ionization mass spectrometry. PMID:26575368

  15. 3,3′-Di-n-butyl-1,1′-(p-phenylenedimethylenediimidazolium bis(hexafluorophosphate

    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...π interaction further stabilizes the crystal structure.

  16. Cis/trans Coordination in olefin metathesis by static and molecular dynamic DFT calculations

    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.

  17. Nanostructured Thin Films Obtained from Fischer Aminocarbene Complexes

    Rosa E. Lazo-Jiménez; M. Carmen Ortega-Alfaro; José G. López-Cortés; Cecilio Alvarez-Toledano; José Á. Chávez-Carvayar; Jordi Ignés-Mullol; Maykel González-Torres; Pilar Carreón-Castro

    2016-01-01

    The synthesis of four amphiphilic organometallic complexes with the general formula RC = M(CO)5NH(CH2)15CH3, where R is a ferrocenyl 2(a-b) or a phenyl 4(a-b) group as a donor moiety and a Fischer carbene of chromium (0) or tungsten (0) as an acceptor group, are reported. These four push-pull systems formed Langmuir (L) monolayers at the air-water interface, which were characterized by isotherms of surface pressure versus molecular area and compression/expansion cycles (hysteresis curves); Br...

  18. Molecular electrocatalysts for the hydrogen production from iron based hydrogenases; Electrocatalyseurs moleculaires pour la production d'hydrogene inspires des hydrogenases a fer

    Gloaguen, F.; Capon, J.F.; Schollhammer, Ph.; Talarmin, J. [Laboratoire de Chimie, Electrochimie Moleculaires et Chimie Analytique, UMR CNRS 6521 UBO, 29 - Brest (France)

    2005-07-01

    The complex type [Fe{sub 2}(CO){sub 6}({mu}-SRS)] are structural analogue of the active site of iron hydrogenases constituted of a dinuclear entity and diatomic ligands CO and CN. The today knowledge on the electrocatalytic activity of some of these organometallic complexes towards the proton reduction in hydrogen{sup 1,2,3}, makes possible the elaboration of bio inspired electrocatalysts. Studies must now be realized to better understand the reduction processes of the iron dinuclear complexes with and without acids. In this framework the authors synthesized series of complexes type [Fe{sub 2}(CO){sub 6-n} L{sub n}({mu}-E-CH{sub 2}-X-CH{sub 2}-E)] (n=0,1 or 2; L=carbene N-heterocyclic; E=S or P(Ph); X= CH{sub 2}, C{sub 6}H{sub 4} or NR). (A.L.B.)

  19. Molecular electrocatalysts for the hydrogen production from iron based hydrogenases

    The complex type [Fe2(CO)6(μ-SRS)] are structural analogue of the active site of iron hydrogenases constituted of a dinuclear entity and diatomic ligands CO and CN. The today knowledge on the electrocatalytic activity of some of these organometallic complexes towards the proton reduction in hydrogen1,2,3, makes possible the elaboration of bio inspired electrocatalysts. Studies must now be realized to better understand the reduction processes of the iron dinuclear complexes with and without acids. In this framework the authors synthesized series of complexes type [Fe2(CO)6-n Ln(μ-E-CH2-X-CH2-E)] (n=0,1 or 2; L=carbene N-heterocyclic; E=S or P(Ph); X= CH2, C6H4 or NR). (A.L.B.)

  20. Mild and Complete Carbonyl Ligand Scission on a Mononuclear Transition Metal Complex.

    Braunschweig, Holger; Celik, Mehmet Ali; Dewhurst, Rian D; Kachel, Stephanie; Wennemann, Benedikt

    2016-04-11

    The complete scission of the carbon-oxygen bond of carbon monoxide, while frequently observed on bulk metals and with bimetallic and cluster transition metal complexes, is unknown with monometallic systems. Reaction of a zerovalent iron bis(borylene) complex with a cyclic (alkyl)(amino)carbene revealed a highly selective intramolecular cleavage of the C-O bond of a carbonyl ligand at room temperature, leading to the formation of a highly unusual iron complex containing a base-stabilized (bora)alkylideneborane ligand. DFT investigation of the reaction mechanism suggested that the two Lewis acidic borylene boron atoms cooperate to cleave the C-O multiple bond. PMID:26990148

  1. Metallacumulenes and carbide complexes. Final performance report

    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.

  2. Synthesis and structure determination of a stable organometallic uranium(V) imine complex and its isolobal anionic U(IV)-ate complex

    The reaction of one equivalent of Cp*2UCl2 with 2-(trimethylsilyl-imino)-1,3-di-tert-butyl-imidazoline in boiling toluene afforded a one electron oxidation of the uranium metal and the opening of the N-heterocyclic ring, resulting in the formation of an organometallic uranium(V) imine complex. This complex crystallized with one molecule of toluene in the unit cell, and its solid-state structure was determined by X-ray diffraction analysis. When the same reaction was performed in perdeuterated toluene, a myriad of organometallic complexes were obtained, however, when equimolar amounts of water were used in toluene, the same complex was obtained, and its solid state characterization shows two independent molecules in the unit cell with an additional water molecule. For comparison of the geometric parameters, the corresponding isolobal anionic uranium(IV) complex [Cp*2UCl3]- was synthesized by the reaction of Cp*2UCl2 with 1,3-di-tert-butyl-imidazolium chloride, and the resulting U(IV)-ate complex was characterized by X-ray diffraction analysis. (authors)

  3. Synthesis of novel synthetic intermediates from the reaction of benzimidazole and triazole carbenes with ketenimines and their application in the construction of spiro-pyrroles.

    Mo, Jun-Ming; Ma, Yang-Guang; Cheng, Ying

    2009-12-01

    2-(2-Alkoxycarbonyl-1-arylamino-1-propenyl)benzimidazolium and 5-(2-alkoxycarbonyl-1-arylamino-1-propenyl)triazolium salts were synthesized in good yields from the reaction of benzimidazole and triazole carbenes with ketenimines. Upon treatment with a base, both salts were converted into novel 1,3-dipoles which underwent [3+2] cycloaddition reactions with electron-deficient alkynes and allenes to produce benzimidazole-spiro-pyrroles or triazole-spiro-pyrroles. This work provides novel synthons for the construction of multifunctional spiro-pyrrole derivatives that are not easy accessible by other synthetic methods and are potentially amenable to further transformations. PMID:19907793

  4. Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase

    Bittner, Dror M.; Zaleski, Daniel P.; Tew, David P.

    2016-01-01

    Abstract Carbenes of platinum and palladium, PtC3 and PdC3, were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and ab initio calculations confirm that both molecules are linear. The geometry of PtC3 was accurately determined by fitting to the experimental moments of inertia of twenty‐six isotopologues. The results are consistent with the proposal of an autogenic isolobal relationship between O, Au+, and Pt atoms. PMID:26879473

  5. (Bis{2-[3-(2,4,6-trimethyl­benz­yl)imid­azolin-2-yliden-1-yl-κC 2]-4-methyl­phenyl}amido-κN)chloridopalladium(II)

    Guan-Jun Cheng; Wei Wei; Chuang Zhou; Mei-Ming Luo

    2010-01-01

    The coordination geometry about the Pd centre in the title compound, [Pd(C40H42N5)Cl], is approximately square-planar. The CNC pincer-type N-heterocyclic carbene ligand binds to the Pd atom in a tridentate fashion by the amido N atom and the two carbene atoms and generates two six-membered chelate rings, completing the coordination.

  6. Structures, Electronics, and Reactivity of Strained Phosphazane Cages: A Combined Experimental and Computational Study.

    Roth, Torsten; Vasilenko, Vladislav; Wadepohl, Hubert; Wright, Dominic S; Gade, Lutz H

    2015-08-01

    A series of formamidine-bridged P2N2 cages have been prepared. Upon deprotonation, these compounds serve as valuable precursors to hybrid N-heterocyclic carbene ligands, whereas direct metalation gives rearranged dimetallic complexes as a result of cleavage of the formamidine bridge. The latter metal complexes contain an intact cyclophosphazane moiety that coordinates two distinct metal centers in a monodentate and a chelating fashion. A computational study has been carried out to elucidate the bonding within the P2N2 framework as well as the reactivity patterns. Natural bond orbital analysis indicates that the cage motif is poorly described by localized Lewis structures and that negative hyperconjugation effects govern the stability of the bicyclic framework. The donor capacity of the cyclophosphazane unit was assessed by inspection of the frontier molecular orbitals, highlighting the fact that ?-back-donation from the metal fragments is crucial for effective metal-ligand binding. PMID:26181231

  7. Cationic Tungsten(VI) Penta-Methyl Complex: Synthesis, Characterization and its Application in Olefin Metathesis Reaction

    Dey, Raju

    2016-04-13

    Tungsten-hexa-methyl readily reacts with B(C6F5)3 in dichloromethane and generates the corresponding well-defined cationic tungsten-penta-methyl complex which was identified precisely by 1H NMR, 13C NMR, 1H-13C NMR correlation spectroscopy. Unlike WMe6, this cationic complex has low energy barrier to form tungsten carbene intermediate, which was further supported by the fact that WMe6 alone has no activity in olefin metathesis reaction whereas the cationic complex shows catalytic activity for self-metathesis of 1-octene.

  8. Catalytic α-arylation of imines leading to N-unprotected indoles and azaindoles

    Marelli, Enrico

    2016-03-30

    A Palladium-N-heterocyclic carbene-catalyzed methodology for the synthesis of substituted, N-unprotected indoles and azaindoles is reported. The protocol permits access to various, highly substituted members of these classes of compounds. Although two possible reactions pathways (deprotonative and Heck-like) can be proposed, control experiments, supported by computational studies, point towards a deprotonative mechanism being operative.

  9. NHC-catalysed highly selective aerobic oxidation of nonactivated aldehydes

    Lennart Möhlmann; Stefan Ludwig; Siegfried Blechert

    2013-01-01

    This publication describes a highly selective oxidation of aldehydes to the corresponding acids or esters. The reaction proceeds under metal-free conditions by using N-heterocyclic carbenes as organocatalysts in combination with environmentally friendly oxygen as the terminal oxidation agent.

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

    Hošek, J.; Rybáčková, M.; Čejka, J.; Cvačka, Josef; Kvíčala, J.

    2015-01-01

    Roč. 34, č. 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

  11. Triruthenium and triosmium carbonyl clusters containing chiral bidentate NHC-thiolate ligands derived from levamisole.

    Cabeza, Javier A; da Silva, Iván; del Río, Ignacio; Sánchez-Vega, M Gabriela

    2006-09-01

    The trinuclear complexes [M3(mu-Cl)(mu-S approximately CH)(CO)9] (M=Ru, Os; S approximately CH=1-ethylenethiolate-3-H-4-(S)-phenylimidazolin-2-ylidene) and [M3(mu-H)(mu-S approximately CMe)(CO)9] (M=Ru, Os; S approximately CMe=1-ethylenethiolate-3-methyl-4-(S)-phenylimidazolin-2-ylidene) have been prepared by treating [Ru3(CO)12] and [Os3(CO)10(MeCN)2] with levamisolium chloride or [M3(mu-H)(CO)11]- with methyl levamisolium triflate, respectively. The chiral N-heterocyclic carbene-thiolate ligands S approximately CH and S approximately CMe arise from the oxidative addition of the C-S bond of levamisolium or methyl levamisolium cations to anionic trinuclear clusters. PMID:17028704

  12. Cytotoxic potency of self-assembled Ruthenium(II-NHC complexes with pincer type 2, 6-bis(N-methylimidazolylidene/benzimidazolylidenepyrazine ligands

    Gourisannkar Roymahapatra

    2015-01-01

    Full Text Available Objective: To study the cytotoxic potency of self-assembled Ruthenium(II-NHC complexes with 2,6-di-(N-methylimidazolylidene/benzimidazolylidenepyrazine ligands. Materials and Methods: Ru(II-N-heterocyclic (Ru-NHC complexes, Bis-[2,6-di-(N-methylimidazol-2-ylidenepyrazine]ruthenium(II hexaflurophosphate (3, Bis-[2,6-di-(N-methylbenzimidazol-2-ylidenepyrazine]ruthenium(II hexaflurophosphate (4 have been synthesized from corresponding ligands 2,6-di-(N-methylimidazoliumpyrazine dichloride (1; 2,6-di-(N-methylbenzimidazoliumpyrazine dichloride (2. Complexes were studied to determine their pro-apoptotic activity against HCT15 and Hep2 cell lines, and antimicrobial activity against Pseudomonas aeruginosa, Staphylococcus epidermidis and Candida albicans. Results: Both, complex 3 and 4, formed a nanosphere structure in aqueous growth medium. Cytotoxicity study revealed that complex 3 was more effective than complex 4. Complexes mainly target cellular DNA and bacterial cell wall. Conclusion: This is the first report on the formation of nanoball structure of Ru(II-NHC complexes. Thus, complex 3 provides a new insight to develop antitumor or antimicrobial drug.

  13. Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation.

    Herzberger, Jana; Niederer, Kerstin; Pohlit, Hannah; Seiwert, Jan; Worm, Matthias; Wurm, Frederik R; Frey, Holger

    2016-02-24

    The review summarizes current trends and developments in the polymerization of alkylene oxides in the last two decades since 1995, with a particular focus on the most important epoxide monomers ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO). Classical synthetic pathways, i.e., anionic polymerization, coordination polymerization, and cationic polymerization of epoxides (oxiranes), are briefly reviewed. The main focus of the review lies on more recent and in some cases metal-free methods for epoxide polymerization, i.e., the activated monomer strategy, the use of organocatalysts, such as N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) as well as phosphazene bases. In addition, the commercially relevant double-metal cyanide (DMC) catalyst systems are discussed. Besides the synthetic progress, new types of multifunctional linear PEG (mf-PEG) and PPO structures accessible by copolymerization of EO or PO with functional epoxide comonomers are presented as well as complex branched, hyperbranched, and dendrimer like polyethers. Amphiphilic block copolymers based on PEO and PPO (Poloxamers and Pluronics) and advances in the area of PEGylation as the most important bioconjugation strategy are also summarized. With the ever growing toolbox for epoxide polymerization, a "polyether universe" may be envisaged that in its structural diversity parallels the immense variety of structural options available for polymers based on vinyl monomers with a purely carbon-based backbone. PMID:26713458

  14. Efficient Covalent Bond Formation in Gas-Phase Peptide-Peptide Ion Complexes with the Photoleucine Stapler

    Shaffer, Christopher J.; Andrikopoulos, Prokopis C.; Řezáč, Jan; Rulíšek, Lubomír; Tureček, František

    2016-01-01

    Noncovalent complexes of hydrophobic peptides GLLLG and GLLLK with photoleucine (L*) tagged peptides G(L* n L m )K (n = 1,3, m = 2,0) were generated as singly charged ions in the gas phase and probed by photodissociation at 355 nm. Carbene intermediates produced by photodissociative loss of N2 from the L* diazirine rings underwent insertion into X-H bonds of the target peptide moiety, forming covalent adducts with yields reaching 30%. Gas-phase sequencing of the covalent adducts revealed preferred bond formation at the C-terminal residue of the target peptide. Site-selective carbene insertion was achieved by placing the L* residue in different positions along the photopeptide chain, and the residues in the target peptide undergoing carbene insertion were identified by gas-phase ion sequencing that was aided by specific 13C labeling. Density functional theory calculations indicated that noncovalent binding to GL*L*L*K resulted in substantial changes of the (GLLLK + H)+ ground state conformation. The peptide moieties in [GL*L*LK + GLLLK + H]+ ion complexes were held together by hydrogen bonds, whereas dispersion interactions of the nonpolar groups were only secondary in ground-state 0 K structures. Born-Oppenheimer molecular dynamics for 100 ps trajectories of several different conformers at the 310 K laboratory temperature showed that noncovalent complexes developed multiple, residue-specific contacts between the diazirine carbons and GLLLK residues. The calculations pointed to the substantial fluidity of the nonpolar side chains in the complexes. Diazirine photochemistry in combination with Born-Oppenheimer molecular dynamics is a promising tool for investigations of peptide-peptide ion interactions in the gas phase.

  15. Efficient Covalent Bond Formation in Gas-Phase Peptide-Peptide Ion Complexes with the Photoleucine Stapler

    Shaffer, Christopher J.; Andrikopoulos, Prokopis C.; Řezáč, Jan; Rulíšek, Lubomír; Tureček, František

    2016-04-01

    Noncovalent complexes of hydrophobic peptides GLLLG and GLLLK with photoleucine (L*) tagged peptides G(L* n L m )K (n = 1,3, m = 2,0) were generated as singly charged ions in the gas phase and probed by photodissociation at 355 nm. Carbene intermediates produced by photodissociative loss of N2 from the L* diazirine rings underwent insertion into X-H bonds of the target peptide moiety, forming covalent adducts with yields reaching 30%. Gas-phase sequencing of the covalent adducts revealed preferred bond formation at the C-terminal residue of the target peptide. Site-selective carbene insertion was achieved by placing the L* residue in different positions along the photopeptide chain, and the residues in the target peptide undergoing carbene insertion were identified by gas-phase ion sequencing that was aided by specific 13C labeling. Density functional theory calculations indicated that noncovalent binding to GL*L*L*K resulted in substantial changes of the (GLLLK + H)+ ground state conformation. The peptide moieties in [GL*L*LK + GLLLK + H]+ ion complexes were held together by hydrogen bonds, whereas dispersion interactions of the nonpolar groups were only secondary in ground-state 0 K structures. Born-Oppenheimer molecular dynamics for 100 ps trajectories of several different conformers at the 310 K laboratory temperature showed that noncovalent complexes developed multiple, residue-specific contacts between the diazirine carbons and GLLLK residues. The calculations pointed to the substantial fluidity of the nonpolar side chains in the complexes. Diazirine photochemistry in combination with Born-Oppenheimer molecular dynamics is a promising tool for investigations of peptide-peptide ion interactions in the gas phase.

  16. Complexation of trivalent cationic lanthanides by N.O donor ligands: physico-chemical studies of the association and selectivity in solution

    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)

  17. Fac-mer equilibria of coordinated iminodiacetate (ida2-) in ternary CuII(ida)(H-1B)- complex formation (B = imidazole, benzimidazole) in aqueous solution

    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 ± 1° at a fixed ionic strength, = 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 (log 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) complex to form the ternary Cu(ida) (H-1B)- complexes.

  18. Copper Complexes with NH-Imidazolyl and NH-Pyrazolyl Units and Determination of Their Bond Dissociation Gibbs Energies.

    Wilting, Alexander; Kgler, Merle; Siewert, Inke

    2016-02-01

    We synthesized two dinuclear copper complexes, which have ionizable N imidazole and N pyrazole protons in the ligand, respectively, and determined the BDFE of the hypothetical H atom transfer reactions Cu(II)(LH-1) + H() ? Cu(I)(L) in MeOH/H2O (BDFE: bond dissociation Gibbs (free) energy). The ligands have two adjacent N,N',O-binding pockets, which differ in one N-heterocycle: L(a) has an imidazole unit and L(c), a pyrazole unit. The copper(II) complexes of L(a) and L(c) have been characterized, and the substitution pattern has only little influence on the structural properties. The BDFEs of the hypothetical PCET reactions have been determined by means of the species distribution and the redox potentials of the involved species in MeOH/H2O (80/20 by weight). The pyrazole copper complex 3 exhibits a lower BDFE than the isoelectronic imidazole copper complex 1 (1, 292(3) kJ mol(-1); 3, 279(1) kJ mol(-1)). The difference is mainly caused by the higher acidity of the N pyrazole proton of 3 compared to the N imidazole proton of 1. The redox potentials of 1 and 3 are very similar. PMID:26788812

  19. Equilibrium between a cyclotrisilene and an isolable base adduct of a disilenyl silylene

    Cowley, Michael J.; Huch, Volker; Rzepa, Henry S.; Scheschkewitz, David

    2013-10-01

    In organic chemistry, compounds with adjacent alkene and carbene functionalities (vinyl carbenes) are studied widely as fleeting intermediates and in the coordination sphere of transition metals. Stable derivatives of vinyl carbenes remain elusive, including the corresponding heavier group 14 homologues. Here we report the isolation and full characterization of a base-stabilized silicon version of a vinyl carbene that features a silicon-silicon double bond as well as a silylene functionality, coordinated by an N-heterocyclic carbene (NHC). In solution, the intensely green disilenyl silylene adduct exists in equilibrium with the corresponding silicon analogue of a cyclopropene and free NHC, which was quantified by nuclear magnetic resonance spectroscopy and ultraviolet-visible spectroscopy. The reversibility of this process raises exciting possibilities for the preparation of extended conjugated ? systems of silicon.

  20. A quantitative structure-activity approach for lipophilicity estimation of antitumor complexes of different metals using microemulsion electrokinetic chromatography.

    Foteeva, Lidia S; Trofimov, Denis A; Kuznetsova, Olga V; Kowol, Christian R; Arion, Vladimir B; Keppler, Bernhard K; Timerbaev, Andrei R

    2011-06-01

    Microemulsion electrokinetic chromatography (MEEKC) offers a valuable tool for the rapid and highly productive determination of lipophilicity for metal-based anticancer agents. In this investigation, the MEEKC technique was applied for estimation of n-octanol-water partition coefficient (logP(oct)) of a series of antiproliferative complexes of gallium(III) and iron(III) with (4)N-substituted α-N-heterocyclic thiosemicarbazones. Analysis of relationships between the experimental logP(oct) and the retention factors of compounds showed their satisfactory consistency in the case of single metal sets, as well as for both metals. Since none of available calculation programs allows for evaluating the contribution of central metal ion into logP(oct) (i.e. ΔlogP(oct)) of complexes of different metals, this parameter was measured experimentally, by the standard 'shake-flask' method. Extension of the logP(oct) programs by adding ΔlogP(oct) data resulted in good lipophilicity predictions for the complexes of gallium(III) and iron(III) included in one regression set. Comparison of metal-thiosemicarbazonates under examination in terms of logP(oct) vs. antiproliferative activities (i.e. 50% inhibitory concentration in cancer cells) provided evidence that their cytotoxic potency is associated with the ability to cross the lipid bilayer of the cell-membrane via passive diffusion. PMID:21382684

  1. Rhodium, iridium and nickel complexes with a 1,3,5-triphenylbenzene tris-MIC ligand. Study of the electronic properties and catalytic activities

    Mejuto, Carmen; Royo, Beatriz

    2015-01-01

    Summary The coordination versatility of a 1,3,5-triphenylbenzene-tris-mesoionic carbene ligand is illustrated by the preparation of complexes with three different metals: rhodium, iridium and nickel. The rhodium and iridium complexes contained the [MCl(COD)] fragments, while the nickel compound contained [NiCpCl]. The preparation of the tris-MIC (MIC = mesoionic carbene) complex with three [IrCl(CO)2] fragments, allowed the estimation of the Tolman electronic parameter (TEP) for the ligand, which was compared with the TEP value for a related 1,3,5-triphenylbenzene-tris-NHC ligand. The electronic properties of the tris-MIC ligand were studied by cyclic voltammetry measurements. In all cases, the tris-MIC ligand showed a stronger electron-donating character than the corresponding NHC-based ligands. The catalytic activity of the tri-rhodium complex was tested in the addition reaction of arylboronic acids to α,β-unsaturated ketones. PMID:26734104

  2. Modulating NHC catalysis with fluorine

    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 β-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.

  3. Pyridylidene ligand facilitates gold-catalyzed oxidative C–H arylation of heterocycles

    Hata, Kazuhiro; Ito, Hideto

    2015-01-01

    Summary Triaryl-2-pyridylidene effectively facilitates the gold-catalyzed oxidative C–H arylation of heteroarenes with arylsilanes as a unique electron-donating ligand on gold. The employment of the 2-pyridylidene ligand, which is one of the strongest electron-donating N-heterocyclic carbenes, resulted in the rate acceleration of the C–H arylation reaction of heterocycles over conventional ligands such as triphenylphosphine and a classical N-heterocyclic carbene. In situ observation and isolation of the 2-pyridylidene-gold(III) species, as well as a DFT study, indicated unusual stability of gold(III) species stabilized by strong electron donation from the 2-pyridylidene ligand. Thus, the gold(I)-to-gold(III) oxidation process is thought to be facilitated by the highly electron-donating 2-pyridylidene ligand. PMID:26877796

  4. New cadmium(II) halides modified by N-heterocyclic molecules

    Wang, Tie-Gang; Li, Su; Yu, Jie-Hui; Xu, Ji-Qing

    2015-03-01

    Under the solvothermal condition, the reaction of CdI2, bpp and KI at pH = 8 afforded compound [CdI2(bpp)] (bpp = 1,2-bis(4-pyridyl)propane) 1, while at the ambient conditions, the reactions of CdX2, dabco and KX at pH = 4-5 produced compounds [H2(dabco)][CdBr4]H2O (dabco = 1,4-diazabicyclo[2,2,2]octane) 2 and [(Hdabco)CdI3] 3. X-ray single-crystal diffraction analysis reveals that (i) compound 1 possesses a one-dimensional (1-D) zigzag chain structure. The large volume bpp molecule controls the Cd2+ ion to adopt a tetrahedral geometric configuration; (ii) both compounds 2 and 3 are mononuclear. Interestingly, in the same pH environments, dabco was in situ diprotonated in compound 2, while dabco was in situ monoprotonated in compound 3. The templating effect as well as the X- ion maybe plays a key role in the protonated degree for dabco in an acidic environment. The photoluminescence analysis indicates that compound 1 emits the strong green light, which should be attributed to a combination of two types of charge transfers: the charge transfer between Cd2+ and I-; the charge transfer between Cd2+ and bpp.

  5. New iodocuprates(I) with N-heterocyclic molecules as the cations

    Zhao, Jin-Jing; Zhang, Xiao; Wang, Yan-Ning; Jia, Hong-Li; Yu, Jie-Hui; Xu, Ji-Qing

    2013-11-01

    Under the hydrothermal conditions, the reactions between CuI, KI and bp/bpp (bp=4,4?-bipiperidine, bpp=1,3-bis(4-piperidyl)propane) in an acidic alcohol solution produced three new organically templated iodocuprates(I) as [H2bp]2[Cu2I6] 1, [tmbp][Cu2I4] 2 and [tmbpp] 2 [Cu4I8]2H2O 3 (tmbp2+=N,N,N?,N?-tetramethyl-4,4?-bipiperidinium; tmbpp2+=N,N,N?,N?-tetramethyl-1,3-bis(4-piperidyl)propane dication). X-ray analysis revealed that (i) tmbp2+ and tmbpp2+ in compounds 2 and 3 originated from the complete N-alklation of bp/bpp with CH3OH; (ii) templated by H2bp2+, the inorganic anion [Cu2I6]2- of 1 possesses a dinuclear structure, whereas templated by tmbp2+, the inorganic anion [Cu2I4]2- of 2 exhibits a one-dimensional (1D) chain structure; (iii) templated by tmbpp2+, the inorganic anion [Cu4I8]4- of 3 shows a cubane-like structure modified by four terminal I- ions. The photoluminescence analysis indicates that compounds 1 and 2 emit blue light, while compound 3 emits green light.

  6. [Design, synthesis and antiproliferative activities of artemisinin derivatives substituted by N-heterocycles].

    Zuo, Zhi-zhong; Zhong, Hang; Cai, Ting; Bao, Yu; Liu, Zhi-qiang; Liu, Dan; Zhao, Lin-xiang

    2015-07-01

    Increasing attention has been focused on the antitumor activity of artemisinin derivatives in recent years, for artemisinin had been reported to have cytotoxic effects against HL-60, P388 and MCF-7 tumor cells. We report here the synthesis and evaluation for antitumor activity of a series of artemisinin-ether derivatives bearing tetrahydropyrrole, morpholine, piperidine, substituted piperidines and azoles with various linkers. Sixteen 10-O-substituted dihydroartemisinin derivatives were designed and synthesized, all of which have never been reported in literatures and whose antiproliferative effects on human breast cancer MCF-7, MCF-7/Adr and HL-60 cells were determined by MTT assay or direct cell counting. Each of these artemisinin derivatives possessed better effects than dihydroartemisinin evidently against HL-60 and MCF-7 cells growth, while less potent than doxorubicin. All target compounds exhibited significantly improved potency compared to DHA and doxorubicin on the doxorubicin-resistant MCF-7/Adr cells, so did they in their sensitive counterparts MCF-7 cells. Among them, compounds GF02, GH04 and ZH04 showed strong activity against these three cell lines growth. Further research is undergoing. PMID:26552149

  7. Synthesis and in Vitro Antimicrobial Evaluation of New N-Heterocyclic Diquaternary Pyridinium Compounds

    Bianca Furdui; Georgiana Parfene; Ioana Otilia Ghinea; Rodica Mihaela Dinica; Gabriela Bahrim; Martine Demeunynck

    2014-01-01

    A series of bis-pyridinium quaternary ammonium salts (bis-PyQAs) with different aryl and heteroaryl moieties were synthesized and their antimicrobial activity investigated. The inhibition effect of the compounds was evaluated against bacteria, molds and yeasts; the activities were expressed as the minimum inhibitory concentrations (MIC). The relationships between the structure descriptors (logP, polarizability, polar surface area (2D), van der Waals area (3D)) and the biological activity of t...

  8. New iodocuprates(I) with N-heterocyclic molecules as the cations

    Under the hydrothermal conditions, the reactions between CuI, KI and bp/bpp (bp=4,4?-bipiperidine, bpp=1,3-bis(4-piperidyl)propane) in an acidic alcohol solution produced three new organically templated iodocuprates(I) as [H2bp]2[Cu2I6] 1, [tmbp][Cu2I4] 2 and [tmbpp] 2 [Cu4I8]2H2O 3 (tmbp2+=N,N,N?,N?-tetramethyl-4,4?-bipiperidinium; tmbpp2+=N,N,N?,N?-tetramethyl-1,3-bis(4-piperidyl)propane dication). X-ray analysis revealed that (i) tmbp2+ and tmbpp2+ in compounds 2 and 3 originated from the complete N-alklation of bp/bpp with CH3OH; (ii) templated by H2bp2+, the inorganic anion [Cu2I6]2? of 1 possesses a dinuclear structure, whereas templated by tmbp2+, the inorganic anion [Cu2I4]2? of 2 exhibits a one-dimensional (1D) chain structure; (iii) templated by tmbpp2+, the inorganic anion [Cu4I8]4? of 3 shows a cubane-like structure modified by four terminal I? ions. The photoluminescence analysis indicates that compounds 1 and 2 emit blue light, while compound 3 emits green light. - Graphical abstract: By employing hydrothermal in situ N-alkylation of bp/bpp with CH3OH, three new organically templated iodocuprates(I) were obtained. Display Omitted - Highlights: Three new organically templated iodocuprates(I) were reported. Cations tmbp2+ and tmbpp2+ originated from in situ alkylation of bp/bpp with CH3OH. H+ and I? play a key role in alkylation of bp/bpp with CH3OH. Photoluminescence emission for iodocuprates(I) is related to CuCu interaction

  9. N-Heterocyclic compounds as radioprotectors II. Derivatives of pyridine and pyrimidine containing thiol precursors

    Pyridine and 4-substitued pyrimidine derivatives incorporating a sulphur functional side-group were evaluated as potential radioprotective agents by screening tests in mice. 2-(2-Pyridyl)ethanethiol and its derivatives showed some radioprotective action when administered intraperitoneally, but all were inferior to 2-pyridinemethanethiol. They showed no protection when administered orally. Substitution of the pyridine ring by chlorine gave compounds which also showed inferior radioprotective properties to those demonstrated by 2-pyridinemethanethiol. Corresponding phosphorothioates also exhibited little activity. The pyrimidine derivatives showed protection of a low order

  10. Transient negative ions in benzene. Some N-heterocyclic and mono-substituted derivatives

    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 (τ > 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)

  11. Structures and Chemical Equilibria of Some N-Heterocycles Containing Amide Linkages

    N. H. Abd El Moneim

    2003-05-01

    Full Text Available Structures and chemical equilibria of 5-carboxy-2-thiouracil (1, 5,6-diphenyl-3-hydroxy-1,2,4-triazine (2, 1-phenyl-3-methyl-5-pyrazolone (3 and 2-mercapto-4,6-dimethylpyrimidine hydrochloride (4 are reported. Their electronic transitions are assigned and pK values are evaluated and discussed.

  12. A study of the resistance of some N-heterocycles (BTPS) to radiolysis

    Full text of publication follows. One option for the selective extraction of trivalent minor actinides within highly active effluents coming from the PUREX process could be as follows: firstly, to co-extract trivalent actinides [An(III)Am(III) and Cm(III)] and also lanthanides [Ln(III)] from the PUREX raffinates; secondly, to separate An(III) from Ln(III) by means of selective extractants. Although efficient extractants for the co-extraction of An(III) and Ln(III) have been developed, selective extractants for An(III) are still required. The various tetra-alkyl substituted BTP molecules, which have been studied within the FP5 European integrated project PARTNEW have been shown to be too sensitive towards acidic hydrolysis and alpha-radiolysis for the development of an An(III)/Ln(III) separation process. Other extracting molecules have been developed within the framework of the FP6 European Integrated Project EUROPART. These molecules include some nitrogen heterocycles. This paper presents some of the basic research carried out in order to improve the resistance of the chosen molecules towards radiolytic degradation. Attempts to improve their extraction properties by the addition of synergists, which usually avoid third-phase formation and improve the kinetics of extraction, will be outlined. It appears that some reagents are not only more selective towards An(III) than tetra-alkyl substituted BTPs, but also more resistant to radiolysis. The carbon atoms on the alpha positions of their triazinyl rings are fully substituted, thus preventing oxidation and nitration of the alkyl groups. Although none of the presently studied ligands has yet met the requirements of a process development strategy, huge improvements have been made in the field of nitrogen heterocycles since the first reference molecule, tetra-n-propyl-bis-triazinyl-pyridine (nPr-BTP), was first chosen in 1998 to demonstrate the scientific feasibility of An(III)/Ln(III) separation from highly active waste of medium acidity ([HNO3] > 0.5 mol/L). Many of these developments have taken place within European research programmes. (authors)

  13. A novel stereoselective synthesis of N-heterocycles by intramolecular hydrovinylation

    Bothe, Ulrich; Rudbeck, H. C.; Tanner, David Ackland; Johannsen, Mogens

    2001-01-01

    A novel method for the synthesis of bicyclic amines has been developed. Cyclisation of 1,6-dienes by intramolecular hydrovinylation in the presence of catalytic amounts of allylpalladium chloride dimer afforded bicyclic amines in one step. Added phosphines, silver salts, as well as the nature of ...

  14. New iodocuprates(I) with N-heterocyclic molecules as the cations

    Zhao, Jin-Jing [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China); Zhang, Xiao [State Key Lab of Urban Water Resource and Environment (SKLUWRE) and Academy of Fundamental and Interdisciplinary Science, Harbin Institute of Technology, Harbin, Heilongjiang 150080 (China); Wang, Yan-Ning; Jia, Hong-Li [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China); Yu, Jie-Hui, E-mail: jhyu@jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China); Xu, Ji-Qing, E-mail: xjq@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun, Jilin 130023 (China)

    2013-11-15

    Under the hydrothermal conditions, the reactions between CuI, KI and bp/bpp (bp=4,4′-bipiperidine, bpp=1,3-bis(4-piperidyl)propane) in an acidic alcohol solution produced three new organically templated iodocuprates(I) as [H{sub 2}bp]{sub 2}[Cu{sub 2}I{sub 6}] 1, [tmbp][Cu{sub 2}I{sub 4}] 2 and [tmbpp] 2 [Cu{sub 4}I{sub 8}]·2H{sub 2}O 3 (tmbp{sup 2+}=N,N,N′,N′-tetramethyl-4,4′-bipiperidinium; tmbpp{sup 2+}=N,N,N′,N′-tetramethyl-1,3-bis(4-piperidyl)propane dication). X-ray analysis revealed that (i) tmbp{sup 2+} and tmbpp{sup 2+} in compounds 2 and 3 originated from the complete N-alklation of bp/bpp with CH{sub 3}OH; (ii) templated by H{sub 2}bp{sup 2+}, the inorganic anion [Cu{sub 2}I{sub 6}]{sup 2−} of 1 possesses a dinuclear structure, whereas templated by tmbp{sup 2+}, the inorganic anion [Cu{sub 2}I{sub 4}]{sup 2−} of 2 exhibits a one-dimensional (1D) chain structure; (iii) templated by tmbpp{sup 2+}, the inorganic anion [Cu{sub 4}I{sub 8}]{sup 4−} of 3 shows a cubane-like structure modified by four terminal I{sup −} ions. The photoluminescence analysis indicates that compounds 1 and 2 emit blue light, while compound 3 emits green light. - Graphical abstract: By employing hydrothermal in situ N-alkylation of bp/bpp with CH{sub 3}OH, three new organically templated iodocuprates(I) were obtained. Display Omitted - Highlights: • Three new organically templated iodocuprates(I) were reported. • Cations tmbp{sup 2+} and tmbpp{sup 2+} originated from in situ alkylation of bp/bpp with CH{sub 3}OH. • H{sup +} and I{sup −} play a key role in alkylation of bp/bpp with CH{sub 3}OH. • Photoluminescence emission for iodocuprates(I) is related to Cu···Cu interaction.

  15. Towards electrically conductive, self-healing materials

    Williams, Kyle A.; Boydston, Andrew J.; Bielawski, Christopher W.

    2007-01-01

    A novel class of organometallic polymers comprising N-heterocyclic carbenes and transition metals was shown to have potential as an electrically conductive, self-healing material. These polymers were found to exhibit conductivities of the order of 10−3 S cm−1 and showed structurally dynamic characteristics in the solid-state. Thin films of these materials were cast onto silicon wafers, then scored and imaged using a scanning electron microscopy (SEM). The scored films were subsequently healed...

  16. Synthesis of 3-fluoro-3-aryl oxindoles: Direct enantioselective α arylation of amides

    Wu, Linglin

    2012-02-06

    Modus operandi: Catalytic access to the title compounds through a new asymmetric α-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.

  17. Modulating NHC catalysis with fluorine

    Rey, Yannick P; Ryan Gilmour

    2013-01-01

    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 β-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 editi...

  18. Heterolysis of Dihydrogen by Silver Alkoxides and Fluorides.

    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

  19. Asymmetric NHC-catalyzed aza-Diels-Alder reactions: Highly enantioselective route to α-amino acid derivatives and DFT calculations

    Yang, Limin

    2014-08-01

    A facile N-heterocyclic carbene catalytic enantioselective aza-Diels-Alder reaction of oxodiazenes with α-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.

  20. Ultrasmall NHC-coated gold nanoparticles obtained through solvent free thermolysis of organometallic Au(i) complexes.

    Crespo, Julin; Guari, Yannick; Ibarra, Alfonso; Larionova, Joulia; Lasanta, Tania; Laurencin, Danielle; Lpez-de-Luzuriaga, Jos M; Monge, Miguel; Olmos, M Elena; Richeter, Sbastien

    2014-11-14

    Ultrasmall gold nanoparticles (Au UNPs) represent a unique class of nanomaterials making them very attractive for certain applications. Herein, we developed an organometallic approach to the synthesis of Au UNPs stabilized with the C18H37-NHC ligand by the solvent free thermolysis of [RMIM][Au(C6F5)2] () or [Au(C6F5)(RNHC)] () (with R = C18H37-), by controlling the reactivity of pentafluorophenyl ligands as deprotonating or reductive elimination agents; Au UNPs can be achieved by solvent free thermolysis. Pentafluorophenyl Au(i) complexes and are synthesized from the corresponding ionic and neutral precursors. The presence of long alkyl chain imidazolium or carbene species in the complexes makes them to behave as isotropic liquids at moderate temperatures. The use of multinuclear NMR allows the description of the mechanism of formation of the UNPs as well as the surface state of the UNPs. PMID:25245422

  1. Bimetallic Cu(i) complex with a pyridine-bridged bis(1,2,3-triazole-5-ylidene) ligand.

    Iwasaki, Haruka; Teshima, Yuta; Yamada, Yuji; Ishikawa, Ryuta; Koga, Yuji; Matsubara, Kouki

    2016-04-01

    A dinuclear copper(i) complex bearing a mesoionic carbene ligand has been prepared from the corresponding silver analogue and its structure determined spectroscopically. The results revealed that two Cu(i) halide salt molecules were bound to the carbon atoms of the pyridine-bridged bis(triazolylidene) moieties rather than the pyridine. Cyclic voltammogram measurements revealed that the two Cu(i) centres underwent a stepwise oxidation, suggesting that both the triazolylidene rings of the ligand could be on the same expanded π-conjugated system. The catalytic hydroboration of styrene derivatives with bis(pinacolato)diborane in the presence of this complex allowed for the β-selective formation of the corresponding alkylboronate esters. PMID:26928475

  2. Copper(I) Complexes of Zwitterionic Imidazolium-2-Amidinates, a Promising Class of Electroneutral, Amidinate-Type Ligands.

    Mrquez, Astrid; vila, Elena; Urbaneja, Carmen; lvarez, Eleuterio; Palma, Pilar; Cmpora, Juan

    2015-11-16

    The first complexes containing imidazolium-2-amidinates as ligands (betaine-type adducts of imidazolium-based carbenes and carbodiimides, NHC-CDI) are reported. Interaction of the sterically hindered betaines ICyCDI(DiPP) and IMeCDI(DiPP) [both bearing 2,6-diisopropylphenyl (DiPP) substituents on the terminal N atoms] with Cu(I) acetate affords mononuclear, electroneutral complexes 1a and 1b, which contain NHC-CDI and acetate ligands terminally bound to linear Cu(I) centers. In contrast, the less encumbered ligand ICyCDI(p-Tol), with p-tolyl substituents on the nitrogen donor atoms, affords a dicationic trigonal paddlewheel complex, [Cu2(?-ICyCDI(p-Tol))3](2+)[OAc(-)]2 (2-OAc). The nuclear magnetic resonance (NMR) resonances of this compound are broad and indicate that in solution the acetate anion and the betaine ligands compete for binding the Cu atom. Replacing the external acetate with the less coordinating tetraphenylborate anion provides the corresponding derivative 2-BPh4 that, in contrast with 2-OAc, gives rise to sharp and well-defined NMR spectra. The short Cu-Cu distance in the binuclear dication [Cu2(?-ICyCDI(p-Tol))3](2+) observed in the X-ray structures of 2-BPh4 and 2-OAc, ca. 2.42 , points to a relatively strong "cuprophilic" interaction. Attempts to force the bridging coordination mode of IMeCDI(DiPP) displacing the acetate anion with BPh4(-) led to the isolation of the cationic mononuclear derivative [Cu(IMeCDI(DiPP))2](+)[BPh4](-) (3b) that contains two terminally bound betaine ligands. Compound 3b readily decomposes upon being heated, cleanly affording the bis-carbene complex [Cu(IMe)2](+)[BPh4(-)] (4) and releasing the corresponding carbodiimide (C(?N-DiPP)2). PMID:26517572

  3. Toward fluorine-free blue-emitting cationic iridium complexes: to generate emission from the cyclometalating ligands with enhanced triplet energy.

    He, Lei; Wang, Zhen; Duan, Lian; Yang, Chunpeng; Tang, Ruiren; Song, Xiangzhi; Pan, Chunyue

    2016-04-01

    A route toward fluorine-free blue-emitting cationic iridium complexes, to generate emission from the cyclometalating ligands with enhanced triplet energy, has been proposed and demonstrated. Attaching electron-donating groups to the pyridine moieties of the ppy-type cyclometalating ligands (Hppy is 2-phenylpyridine) enhances the triplet ((3)π-π*) energy of the ligand, and the use of electron-rich or non-conjugated ancillary ligands ensures that the emission is generated from the (3)π-π* states of cyclometalating ligands. By this molecular design, [Ir(buoppy)2(pzpy)]PF6 (1) and [Ir(buoppy)2(bim-cb)]PF6 (2) have been developed, with 4-butoxy-2-phenylpyridine (buoppy) as the cyclometalating ligand and electron-rich 2-(1H-pyrazol-1-yl)pyridine (pzpy) or non-conjugated N-heterocyclic dicarbene (bim-cb) as the ancillary ligands. Complexes 1 and 2 give emission with major emission peaks around 465 nm, which is among the bluest reported for fluorine-free cationic iridium complexes. For both complexes, the emission is generated from the (3)π-π* states centered on buoppy. For complex 1, the charge-transfer (Ir/buoppy → pzpy) state is dominated by non-radiative deactivation and it behaves as a non-radiative deactivation channel for the emissive buoppy-centered (3)π-π* states which lies close to the charge-transfer state in energy. Such a non-radiative deactivation channel is largely suppressed in the rigid matrix, and is eliminated in complex 2 with a non-conjugated dicarbene ancillary ligand. PMID:26918443

  4. Nanostructured Thin Films Obtained from Fischer Aminocarbene Complexes

    Rosa E. Lazo-Jiménez

    2016-03-01

    Full Text Available The synthesis of four amphiphilic organometallic complexes with the general formula RC = M(CO5NH(CH215CH3, where R is a ferrocenyl 2(a-b or a phenyl 4(a-b group as a donor moiety and a Fischer carbene of chromium (0 or tungsten (0 as an acceptor group, are reported. These four push-pull systems formed Langmuir (L monolayers at the air-water interface, which were characterized by isotherms of surface pressure versus molecular area and compression/expansion cycles (hysteresis curves; Brewster angle microscopic images were also obtained. By using the Langmuir–Blodgett (LB method, molecular monolayers were transferred onto glass substrates forming Z-type multilayers. LB films were characterized through ultraviolet-visible spectroscopy, atomic force microscopy and X-ray diffraction techniques. Results indicated that films obtained from 2b complex [(Ferrocenyl(hexadecylaminemethylidene] pentacarbonyl tungsten (0 are the most stable and homogeneous; due to their properties, these materials may be incorporated into organic electronic devices.

  5. Complex Beauty

    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 philosophical, cultural ...

  6. Stabilization of a Silaaldehyde by its ?(2) Coordination to Tungsten.

    Fukuda, Tetsuya; Hashimoto, Hisako; Sakaki, Shigeyoshi; Tobita, Hiromi

    2016-01-01

    Treatment of pyridine-stabilized silylene complexes [(?(5) -C5 Me4 R)(CO)2 (H)W?SiH(py)(Tsi)] (R=Me, Et; py=pyridine; Tsi=C(SiMe3 )3 ) with an N-heterocyclic carbene (Me) I(i) Pr (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) caused deprotonation to afford anionic silylene complexes [(?(5) -C5 Me4 R)(CO)2 W?SiH(Tsi)][H(Me) I(i) Pr] (R=Me (1-Me); R=Et (1-Et)). Subsequent oxidation of 1-Me and 1-Et with pyridine-N-oxide (1?equiv) gave anionic ?(2) -silaaldehydetungsten complexes [(?(5) -C5 Me4 R)(CO)2 W{?(2) -O?SiH(Tsi)}][H(Me) I(i) Pr] (R=Me (2-Me); R=Et (2-Et)). The formation of an unprecedented W-Si-O three-membered ring was confirmed by X-ray crystal structure analysis. PMID:26768821

  7. Unique Properties and Reactivity of Electrophilic Metal Centers Supported by Ferrocene Diamide Ligands

    Miller, Kevin L

    2014-01-01

    The work reported herein represents various studies of group 3 metal complexes supported by ferrocene diamide ligands. Chapter 1 is a brief introduction and survey of relevant literature, and it outlines the reasoning behind the study of these compounds. Chapter 2 details the synthesis of Sc, Y, Lu, and La benzyl complexes supported by a ferrocene diamide ligand, and their reactions with aromatic N-heterocycles. The group 3 metal complexes facilitate an alkyl migration to the N-heterocycles, ...

  8. Investigations into the Antibacterial Activity of the Silver-Based Antibiotic Drug Candidate SBC3

    Matthias Tacke

    2012-11-01

    Full Text Available The synthesis of N-heterocyclic carbene (NHC silver(I acetate complexes with varying lipophilic benzyl-substituents at the 1 and 3 positions starting from 4,5-diphenylimidazole, opened a new class of antibiotic drug candidates. These NHC-silver(I acetate derivatives exhibit interesting structural motifs in the solid state and proved to be soluble and stable in biological media. The leading candidate, SBC3, which was known to exhibit good antibacterial activity in preliminary Kirby-Bauer tests, was tested quantitatively using minimum inhibitory concentrations. NHC-silver(I acetate complexes were found to have MIC values ranging from 20 to 3.13 μg/mL for a variety of Gram-positive, Gram-negative and mycobacteria tested. These values represent good antibiotic activities against potential pathogens when compared to clinically approved antibiotics. Most striking is the fact that SBC3 is active against methicillin-resistant Staphylococcus aureus with a MIC value of 12.5 μg/mL.

  9. Deep blue phosphorescent organic light-emitting diodes with very high brightness and efficiency

    Lee, Jaesang; Chen, Hsiao-Fan; Batagoda, Thilini; Coburn, Caleb; Djurovich, Peter I.; Thompson, Mark E.; Forrest, Stephen R.

    2016-01-01

    The combination of both very high brightness and deep blue emission from phosphorescent organic light-emitting diodes (PHOLED) is required for both display and lighting applications, yet so far has not been reported. A source of this difficulty is the absence of electron/exciton blocking layers (EBL) that are compatible with the high triplet energy of the deep blue dopant and the high frontier orbital energies of hosts needed to transport charge. Here, we show that N-heterocyclic carbene (NHC) Ir(III) complexes can serve as both deep blue emitters and efficient hole-conducting EBLs. The NHC EBLs enable very high brightness (>7,800 cd m-2) operation, while achieving deep blue emission with colour coordinates of [0.16, 0.09], suitable for most demanding display applications. We find that both the facial and the meridional isomers of the dopant have high efficiencies that arise from the unusual properties of the NHC ligand--that is, the complexes possess a strong metal-ligand bond that destabilizes the non-radiative metal-centred ligand-field states. Our results represent an advance in blue-emitting PHOLED architectures and materials combinations that meet the requirements of many critical illumination applications.

  10. Enthalpies of ligand substitution for [Mo(η5C5H5)(CO)2(NO)] – The role of π-bonding effects in metal–ligand bond strengths

    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 π∗ orbitals is an important part of complex stability. • FTIR studies show shifts to lower wavenumbers of ν-CO and ν-NO. • Structural studies show lengthening of the C-O and N-O bonds. - Abstract: Enthalpies of ligand substitution for [Mo(η5-C5H5)(CO)2(NO)] producing [Mo(η5-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(η5-C5H5)(CO)(NO)] has a vacant site containing strongly π-accepting carbonyl and nitrosyl ligands and this is shown to influence the stability of the product complex. Infrared studies of both νCO and νNO show that metal-to-ligand backbonding increases in the order P(OMe)3 3 5-C5H5)(CO)(IPr)(NO)] and [Mo(η5-C5H5)(CO)(SIPr)(NO)] are reported

  11. Mild partial deoxygenation of esters catalyzed by an oxazolinylborate-coordinated rhodium silylene.

    Xu, Songchen; Boschen, Jeffery S; Biswas, Abhranil; Kobayashi, Takeshi; Pruski, Marek; Windus, Theresa L; Sadow, Aaron D

    2015-09-28

    An electrophilic, coordinatively unsaturated rhodium complex supported by borate-linked oxazoline, oxazoline-coordinated silylene, and N-heterocyclic carbene donors [{?(3)-N,Si,C-PhB(Ox(Me2))(Ox(Me2)SiHPh)Im(Mes)}Rh(H)CO][HB(C6F5)3] (, Ox(Me2) = 4,4-dimethyl-2-oxazoline; Im(Mes) = 1-mesitylimidazole) is synthesized from the neutral rhodium silyl {PhB(Ox(Me2))2Im(Mes)}RhH(SiH2Ph)CO () and B(C6F5)3. The unusual oxazoline-coordinated silylene structure in is proposed to form by rearrangement of an unobserved isomeric cationic rhodium silylene species [{PhB(Ox(Me2))2Im(Mes)}RhH(SiHPh)CO][HB(C6F5)3] generated by H abstraction. Complex catalyzes reductions of organic carbonyl compounds with silanes to give hydrosilylation products or deoxygenation products. The pathway to these reactions is primarily influenced by the degree of substitution of the organosilane. Reactions with primary silanes give deoxygenation of esters to ethers, amides to amines, and ketones and aldehydes to hydrocarbons, whereas tertiary silanes react to give 1,2-hydrosilylation of the carbonyl functionality. In contrast, the strong Lewis acid B(C6F5)3 catalyzes the complete deoxygenation of carbonyl compounds to hydrocarbons with PhSiH3 as the reducing agent. PMID:26278517

  12. Dual Catalysis for Selective Ring-Opening Polymerization of Lactones: Evolution toward Simplicity.

    Naumann, Stefan; Scholten, Philip B V; Wilson, James A; Dove, Andrew P

    2015-11-18

    Much work has been directed to the design of complex single-site catalysts for ring-opening polymerization (ROP) to enhance both activity and selectivity. More simply, however, cooperative effects between Lewis acids and organocatalytic nucleophiles/Lewis bases provide a powerful alternative. In this study we demonstrate that the combination of N-heterocyclic carbenes, 1,8-diazabicycloundec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP) with simple Lewis acids enables the ROP of the macrolactone pentadecalactone in a rapid and efficient manner. Remarkably, regardless of the nature of the nucleophile, the order of activity was observed to be MgX2 ? YCl3 ? AlCl3 and MgI2 > MgBr2 > MgCl2 in every case. The minimal influence of the organobase on polymerization activity allows for the use of simple and inexpensive precursors. Furthermore, extension of the study to other cyclic (di)ester monomers reveals the choice of Lewis acid to lead to monomer selective ROP activity and hence control over copolymer composition by choice of Lewis acid. This approach could lead to the realization of complex polymer structures with tunable physical properties from simple catalyst combinations. PMID:26505677

  13. Activity of rhodium-catalyzed hydroformylation: added insight and predictions from theory.

    Sparta, Manuel; Børve, Knut J; Jensen, Vidar R

    2007-07-11

    We have performed a density functional theory investigation of hydroformylation of ethylene for monosubstituted rhodium-carbonyl catalysts, HRh(CO)3L, where the modifying ligand, L, is a phosphite (L = P(OMe)3, P(OPh)3, or P(OCH2CF3)3), a phosphine (L = PMe3, PEt3, PiPr3, or PPh3), or a N-heterocyclic carbene (NHC) based on the tetrahydropyrimidine, imidazol, or tetrazol ring, respectively. The study follows the Heck and Breslow mechanism. Excellent correspondence between our calculations and existing experimental information is found, and the present results constitute the first example of a realistic quantum chemical description of the catalytic cycle of hydroformylation using ligand-modified rhodium carbonyl catalysts. This description explains the mechanistic and kinetic basis of the contemporary understanding of this class of reaction and offers unprecedented insight into the electronic and steric factors governing catalytic activity. The insight has been turned into structure-activity relationships and used as guidelines when also subjecting to calculation phosphite and NHC complexes that have yet to be reported experimentally. The latter calculations illustrate that it is possible to increase the electron-withdrawing capacity of both phosphite and NHC ligands compared to contemporary ligands through directed substitution. Rhodium complexes of such very electron-withdrawing ligands are predicted to be more active than contemporary catalysts for hydroformylation. PMID:17555314

  14. Shell crosslinked nanoparticles carrying silver antimicrobials as therapeutics†

    Li, Yali; Hindi, Khadijah; Watts, Kristin M.; Taylor, Jane B.; Zhang, Ke; Li, Zicheng; Hunstad, David A.; Cannon, Carolyn L.; Wiley J. Youngs; Wooley, Karen L.

    2009-01-01

    Amphiphilic polymer nanoparticles loaded with silver cations or/and N-heterocyclic carbene–silver complexes were assessed as antimicrobial agents against Gram-negative pathogens Escherichia coli and Pseudomonas aeruginosa.

  15. Trianionic pincer and pincer-type metal complexes and catalysts.

    O'Reilly, Matthew E; Veige, Adam S

    2014-09-01

    Trianionic pincer and pincer-type ligands are the focus of this review. Metal ions from across the periodic table, from main group elements, transition metals, and the rare earths, are combined with trianionic pincer ligands to produce some of the most interesting complexes to appear in the literature over the past decade. This review provides a comprehensive examination of the synthesis, characterization, properties, and catalytic applications of trianionic pincer metal complexes. Some of the interesting applications employing trianionic pincer and pincer-type complexes include: (1) catalyzed aerobic oxidation, (2) alkene isomerization, (3) alkene and alkyne polymerization, (4) nitrene and carbene group transfer, (5) fundamental transformations such as oxygen-atom transfer, (6) nitrogen-atom transfer, (7) O2 activation, (8) C-H bond activation, (9) disulfide reduction, and (10) ligand centered storage of redox equivalents (i.e. redox active ligands). Expansion of the architecture, type of donor atoms, chelate ring size, and steric and electronic properties of trianionic pincer ligands has occurred rapidly over the past ten years. This review is structured according to the type of pincer donor atoms that bind to the metal ion. The type of donor atoms within trianionic pincer and pincer-type ligands to be discussed include: NCN(3-), OCO(3-), CCC(3-), redox active NNN(3-), NNN(3-), redox active ONO(3-), ONO(3-), and SNS(3-). Since this is the first review of trianionic pincer and pincer-type ligands, an emphasis is placed on providing the reader with in-depth discussion of synthetic methods, characterization data, and highlights of these complexes as catalysts. PMID:24927219

  16. Group 4 Metalloporphyrin diolato Complexes and Catalytic Application of Metalloporphyrins and Related Transition Metal Complexes

    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.

  17. Managing Complexity

    Maylath, Bruce; Vandepitte, Sonia; Minacori, Patricia; Isohella, Suvi; Mousten, Birthe; Humbley, John

    2013-01-01

    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 workplaces of language service providers. © Association of Teachers of Technical Writing....

  18. From silicon(II)-based dioxygen activation to adducts of elusive dioxasiliranes and sila-ureas stable at room temperature

    Xiong, Yun; Yao, Shenglai; Müller, Robert; Kaupp, Martin; Driess, Matthias

    2010-07-01

    Dioxygen activation for the subsequent oxygenation of organic substrates that involves cheap and environmentally friendly chemical elements is at the cutting edge of chemical research. As silicon is a non-toxic and highly oxophilic element, the use of silylenes could be attractive for facile dioxygen activation to give dioxasiliranes with a SiO2-peroxo ring as versatile oxo-transfer reagents. However, the latter are elusive species, and have been generated and studied only in argon matrices at -233 °C. Recently, it was demonstrated that unstable silicon species can be isolated by applying the concept of donor-acceptor stabilization. We now report the first synthesis and crystallographic characterization of dioxasiliranes stabilized by N-heterocyclic carbenes that feature a three-membered SiO2-peroxide ring, isolable at room temperature. Unexpectedly, these can undergo internal oxygen transfer in toluene solution at ambient temperature to give a unique complex of cyclic sila-urea with C=O --> Si=O interaction and the shortest Si=O double-bond distance reported to date.

  19. Medical Complex

    Kumaraswamy, Mohan

    2002-01-01

    One element of the CIVCAL project Web-based resources containing images, tables, texts and associated data on the construction of the Medical Complex. This project covers the construction of a new Hong Kong University Medical Complex on Sassoon Road, Pokfulam. The complex will comprise two buildings, one will house laboratories and a car park, while the other will contain lecture halls

  20. Alkane metathesis with the tantalum methylidene [(≡SiO)Ta(=CH2)Me2]/[(≡SiO)2Ta(=CH2)Me] generated from well-defined surface organometallic complex [(≡SiO)TaVMe4

    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.

  1. Communication complexity and information complexity

    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.).

  2. Ternary complexes

    The stability constants of mixed pyridine dicarboxylic-dicarboxylic acid complexes of uranyl ion have been determined at 300C and ionic strength ? = 0.1 M(NaCLO4). The pyridine dicarboxylic used is quinolinic and the dicarboxylic acids are malonic, succinic, itaconic, glutaric and adipic acid. In all these systems the ternary complexes were more stable than the corresponding binary complexes. The stabilities of the ternary complexes depend on the nature of the donor atoms, size of the chelate ring and steric hindrance in one of the binary complexes. (author)

  3. Complexity Plots

    Thiyagalingam, Jeyarajan

    2013-06-01

    In this paper, we present a novel visualization technique for assisting the observation and analysis of algorithmic complexity. In comparison with conventional line graphs, this new technique is not sensitive to the units of measurement, allowing multivariate data series of different physical qualities (e.g., time, space and energy) to be juxtaposed together conveniently and consistently. It supports multivariate visualization as well as uncertainty visualization. It enables users to focus on algorithm categorization by complexity classes, while reducing visual impact caused by constants and algorithmic components that are insignificant to complexity analysis. It provides an effective means for observing the algorithmic complexity of programs with a mixture of algorithms and black-box software through visualization. Through two case studies, we demonstrate the effectiveness of complexity plots in complexity analysis in research, education and application. © 2013 The Author(s) Computer Graphics Forum © 2013 The Eurographics Association and Blackwell Publishing Ltd.

  4. Aesthetic complexity

    Svozil, Karl

    2005-01-01

    Aesthetics, among other criteria, can be statistically examined in terms of the complexity required for creating and decrypting a work of art. We propose three laws of aesthetic complexity. According to the first law of aesthetic complexity, too condensed encoding makes a decryption of a work of art impossible and is perceived as chaotic by the untrained mind, whereas too regular structures are perceived as monotonous, too orderly and not very stimulating. Thus a necessary condition for an ar...

  5. Engaging complexity

    Gys M. Loubser

    2014-01-01

    Full Text Available In this article, I discuss studies in complexity and its epistemological implications for systematic and practical theology. I argue that engagement with complexity does not necessarily assurea non-reductionist approach. However, if complexity is engaged transversally, it becomes possible to transcend reductionist approaches. Moreover, systematic and practical the ologians can draw on complexity in developing new ways of understanding and, therefore, new ways of describing the focus, epistemic scope and heuristic structures of systematic and practical theology. Firstly, Edgar Morin draws a distinction between restricted and general complexity based on the epistemology drawn upon in studies in complexity. Moving away from foundationalist approaches to epistemology, Morin argues for a paradigm of systems. Secondly,I discuss Kees van Kooten Niekerk�s distinction between epistemology, methodology andontology in studies in complexity and offer an example of a theological argument that drawson complexity. Thirdly, I argue for the importance of transversality in engaging complexity by drawing on the work of Wentzel van Huyssteen and Paul Cilliers. In conclusion, I argue that theologians have to be conscious of the epistemic foundations of each study in complexity, and these studies illuminate the heart of Reformed theology.Intradisciplinary and/or interdisciplinary implications: Therefore, this article has both intradisciplinary and interdisciplinary implications. When theologians engage studies incomplexity, the epistemological roots of these studies need to be considered seeing thatresearchers in complexity draw on different epistemologies. Drawing on transversality wouldenhance such considerations. Furthermore, Edgar Morin�s and Paul Cilliers� approach tocomplexity will inform practical and theoretical considerations in church polity and unity.

  6. Switchable selectivity in an NHC-catalysed dearomatizing annulation reaction

    Guo, Chang; Fleige, Mirco; Janssen-Mller, Daniel; Daniliuc, Constantin G.; Glorius, Frank

    2015-10-01

    The development of general catalytic methods for the regio- and stereoselective construction of chiral N-heterocycles in a diversity-oriented fashion remains a formidable challenge in organic synthesis. N-heterocyclic carbene (NHC) catalysis has been shown to produce a variety of outcomes, but control of the reactivity has rarely been demonstrated. Here we report a switchable catalytic activation of enals with aromatic azomethine imines that provides high selectivity using NHC organocatalysts. The original selectivity corresponds to the acidity of the base used in the reaction. The catalytically generated chiral homoenolate or enol intermediate undergoes enantioselective annulation with electrophiles such as N-iminoquinolinium ylides, N-iminoisoquinolinium ylides and ?-N-iminocarboline ylides. The good-to-high overall yields, high regioselectivities and excellent enantioselectivities observed are controlled by the catalyst and reaction conditions.

  7. Designing Complexity

    Glanville, Ranulph

    2007-01-01

    This article considers the nature of complexity and design, as well as relationships between the two, and suggests that design may have much potential as an approach to improving human performance in situations seen as complex. It is developed against two backgrounds. The first is a world view that derives from second order cybernetics and radical…

  8. Complex derivatives

    Battiston, Stefano; Caldarelli, Guido; Georg, Co-Pierre; May, Robert; Stiglitz, Joseph

    2013-03-01

    The intrinsic complexity of the financial derivatives market has emerged as both an incentive to engage in it, and a key source of its inherent instability. Regulators now faced with the challenge of taming this beast may find inspiration in the budding science of complex systems.

  9. Designing Complexity

    Glanville, Ranulph

    2007-01-01

    This article considers the nature of complexity and design, as well as relationships between the two, and suggests that design may have much potential as an approach to improving human performance in situations seen as complex. It is developed against two backgrounds. The first is a world view that derives from second order cybernetics and radical

  10. Hamiltonian complexity

    In recent years we have seen the birth of a new field known as Hamiltonian complexity lying at the crossroads between computer science and theoretical physics. Hamiltonian complexity is directly concerned with the question: how hard is it to simulate a physical system? Here I review the foundational results, guiding problems, and future directions of this emergent field.

  11. Microwave-Assisted Synthesis of N-Heterocyclic Compounds [Sntese de Compostos N-Heterociclos Empregando Micro-ondas

    Diego P. Sangi

    2010-12-01

    Full Text Available Association of biological activity with heterocyclic motifs is well known and is important from drug discovery viewpoint. This article gives an account of the recent applications of microwaves in the synthesis of biologically active heterocyclic compounds from the literature and also from our research group.

  12. Toxic effects and oxidative stress in higher plants exposed to polycycylic aromatic hydrocarbons and their N-heterocyclic derivatives

    Pašková, V.; Hilscherová, Klára; Feldmanová, Marie; Bláha, Luděk

    2006-01-01

    Roč. 25, č. 12 (2006), s. 3238-3245. ISSN 0730-7268 Institutional research plan: CEZ:AV0Z60050516 Keywords : toxic effects * oxidative stress Subject RIV: EF - Botanics Impact factor: 2.202, year: 2006

  13. Reactions of Stable N-Heterocyclic Silylenes with Ketones and 3,5-Di-tert-butyl-o-benzoquinone

    Azhakar, Ramachandran; Ghadwal, Rajendra S.; Roesky, Herbert W.; Hey, Jakob; Stalke, Dietmar

    2011-01-01

    The reactions of L [PhC(NtBu)2SiCl] and L0 [CH{(Cd CH2)(CMe)(2,6-iPr2C6H3N)2}Si] with monoketones and quinone have been examined. The reaction of L with 2-adamantanone furnishes a [1 + 2] cycloaddition product 1, whereas with 3,5-di-tert-butyl-o-benzoquinone leads to the [1 + 4] cycloaddition product 2. The treatment of L0 with 3,5-di-tertbutyl- o-benzoquinone gives [1 + 4] cycloaddition product 3, and the reaction with acylferrocene yields compound 4. Compounds 1 4 were ch...

  14. AN EFFICIENT AQUEOUS N-HETEROCYCLIZATION OF ANILINE DERIVATIVES: MICROWAVE-ASSISTED SYNTHESIS OF N-ARYL AZACYCLOALKANES

    N-aryl azacycloalkanes, an important class of building blocks in natural product and pharmaceuticals, are synthesized via an efficient and simple eco-friendly protocol that involves double N-alkylation of aniline derivatives. The reaction is accelerated by exposure to microwaves ...

  15. AN EFFICIENT AND SIMPLE AQUEOUS N-HETEROCYCLIZATION OF ANILINE DERIVATIVES: MICROWAVE-ASSISTED SYNTHESIS OF N-ARYL AZACYCLOALKANES

    An efficient and clean synthesis of N-aryl azacycloalkanes from alkyl dihalides and aniline derivatives has been achieved using microwave irradiation in an aqueous potassium carbonate medium. The phase separation can simplify the product isolation and reduce usage of vol...

  16. Communication Complexity

    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 al...

  17. Complex variables

    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

  18. Complex Covariance

    Frieder Kleefeld

    2013-01-01

    Full Text Available According to some generalized correspondence principle the classical limit of a non-Hermitian quantum theory describing quantum degrees of freedom is expected to be the well known classical mechanics of classical degrees of freedom in the complex phase space, i.e., some phase space spanned by complex-valued space and momentum coordinates. As special relativity was developed by Einstein merely for real-valued space-time and four-momentum, we will try to understand how special relativity and covariance can be extended to complex-valued space-time and four-momentum. Our considerations will lead us not only to some unconventional derivation of Lorentz transformations for complex-valued velocities, but also to the non-Hermitian Klein-Gordon and Dirac equations, which are to lay the foundations of a non-Hermitian quantum theory.

  19. Carney Complex

    ... of hands, feet, and face due to a pituitary tumor Testicular neoplasm called large cell calcifying Sertoli cell ... in people with Carney complex include adrenocortical carcinoma , pituitary gland tumors , thyroid , colorectal , liver and pancreatic cancers . Ovarian cancer ...

  20. Decomposition Complexity

    Shen, Alexander

    2010-01-01

    We consider a problem of decomposition of a ternary function into a composition of binary ones from the viewpoint of communication complexity and algorithmic information theory as well as some applications to cellular automata.

  1. Tableau complexes

    Knutson, Allen; Miller, Ezra; Yong, Alexander

    2005-01-01

    Let X,Y be finite sets and T a set of functions from X -> Y which we will call "tableaux". We define a simplicial complex whose facets, all of the same dimension, correspond to these tableaux. Such "tableau complexes" have many nice properties, and are frequently homeomorphic to balls, which we prove using vertex decompositions. In our motivating example, the facets are labeled by semistandard Young tableaux, and the more general interior faces are labeled by Buch's set-valued semistandard ta...

  2. Unusual carbon monoxide activation, reduction, and homologation reactions of 5f-element organometallics: the chemistry of carbene-like dihaptoacyls

    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 β-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

  3. Lutetium-methanediide-alkyl complexes: synthesis and chemistry.

    Li, Shihui; Wang, Meiyan; Liu, Bo; Li, Lei; Cheng, Jianhua; Wu, Chunji; Liu, Dongtao; Liu, Jingyao; Cui, Dongmei

    2014-11-17

    The first four-coordinate methanediide/alkyl lutetium complex (BODDI)Lu2 (CH2 SiMe3 )2 (?2 -CHSiMe3 )(THF)2 (BODDI=ArNC(Me)CHCOCHC(Me)NAr, Ar=2,6-iPr2 C6 H3 ) (1) was synthesized by a thermolysis methodology through ?-H abstraction from a Lu-CH2 SiMe3 group. Complex 1 reacted with equimolar 2,6-iPrC6 H3 NH2 and Ph2 C+O to give the corresponding lutetium bridging imido and oxo complexes (BODDI)Lu2 (CH2 SiMe3 )2 (?2 -N-2,6-iPr2 C6 H3 )(THF)2 (2) and (BODDI)Lu2 (CH2 SiMe3 )2 (?2 -O)(THF)2 (3). Treatment of 3 with Ph2 C=O (4?equiv) caused a rare insertion of Lu-?2 -O bond into theC=O group to afford a diphenylmethyl diolate complex 4. Reaction of 1 with PhN=C=O (2?equiv) led to the migration of SiMe3 to the amido nitrogen atom to give complex (BODDI)Lu2 (CH2 SiMe3 )2 -?-{PhNC(O)CHC(O)NPh(SiMe3 )-?(3) N,O,O}(THF) (5). Reaction of 1 withtBuN=C formed an unprecedented product (BODDI)Lu2 (CH2 SiMe3 ){?2 -[?(2) :?(2) -tBuN=C(=CH2 )SiMe2 CHC=NtBu-?(1) N]}(tBuN=C)2 (6) through a cascade reaction of N=C bond insertion, sequential cyclometalative ?-(sp(3) )-H activation, C=C bond formation, and rearrangement of the newly formed carbene intermediate. The possible mechanistic pathways between 1, PhN=C=O, and tBuN=C were elucidated by DFT calculations. PMID:25284379

  4. Complex analysis

    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...

  5. Holographic Complexity

    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. Holographic complexity

    Alishahiha, Mohsen

    2015-12-01

    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 codimension one time slice in the bulk geometry enclosed by the extremal codimension two hypersurface appearing in the computation of the holographic entanglement entropy. The proportionally constant, up to a numerical order of 1 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 models. We also explore a possible relation between the defined quantity and fidelity appearing in quantum information literature.

  7. Phosphine modified cobalt hydroformylation

    Rensburg, H. van; Tooze, R.P.; Foster, D.F. [Sasol Technology UK, St. Andrews (United Kingdom); Janse van Rensburg, W. [Sasol Technology, Sasolburg (South Africa)

    2006-07-01

    An ongoing challenge in phosphine modified cobalt hydroformylation is the fundamental understanding of the electronic and steric properties of phosphine ligands that influence the selectivity and activity of the catalytic reaction. A series of acyclic and cyclic phosphines have been prepared and tested in phosphine modified cobalt hydroformylation of 1-octene. Molecular modelling on a series of phospholanes showed some interesting theoretical and experimental correlations. We also evaluated the use of N-heterocyclic carbenes as an alternative for phosphines in modified cobalt hydroformylation. (orig.)

  8. Iron-catalyzed coupling of aryl sulfamates and aryl/vinyl tosylates with aryl Grignards.

    Agrawal, Toolika; Cook, Silas P

    2014-10-01

    The iron-catalyzed coupling of aryl sulfamates and tosylates with aryl Grignard reagents is reported for the first time. The methodology employs air-stable, low-cost FeF3·3H2O and the N-heterocyclic carbene ligand IPr·HCl as the preligand to form a long-lived catalyst upon treatment with aryl Grignards. The reaction provides a range of cross-coupled products in good-to-excellent yields. In contrast to previous reports with aryl chlorides, these reactions proceed with low levels of Grignard homocoupling regardless of the iron source. PMID:25230097

  9. 5-Azido-4-dimethylamino-1-methyl-1,2,4-triazolium Hexafluoridophosphate and Derivatives

    Gerhard Laus

    2016-02-01

    Full Text Available 5-Azido-4-(dimethylamino-1-methyl-1,2,4-triazolium hexafluoridophosphate was synthesized from the corresponding 5-bromo compound with NaN3. Reaction with bicyclo[2.2.1]hept-2-ene yielded a tricyclic aziridine, addition of an N-heterocyclic carbene resulted in a triazatrimethine cyanine, and reduction with triphenylphosphane gave the 5-amino derivative. The crystal structures of three nitrogen-rich salts were determined. Thermoanalysis of the cationic azide and triazene showed exothermal decomposition. The triazene exhibited negative solvatochromism in polar solvents involving the dipolarity π* and hydrogen-bond donor acidity α of the solvent.

  10. [Cu(NHC)]-Catalyzed C-H Allylation and Alkenylation of both Electron-Deficient and Electron-Rich (Hetero)arenes with Allyl Halides.

    Xie, Weilong; Chang, Sukbok

    2016-01-01

    New reactivity of a [Cu(NHC)] (NHC=N-heterocyclic carbene) catalyst is disclosed for the efficient C-H allylation of polyfluoroarenes using allyl halides in benzene at room temperature. The same catalyst system also promotes an isomerization-induced alkenylation of initially the generated allyl arenes when the reaction is run in tetrahydrofuran. Significantly, not only electron-deficient but also electron-rich (hetero)arenes undergo this double-bond migration process, thus leading to alkenylated products. The present system features mild reaction conditions, broad scope with respect to the arene substrates and allyl halide reactants, good functional-group tolerance, and high stereoselectivity. PMID:26695120

  11. Asymmetric, Three-Component, One-Pot Synthesis of Spiropyrazolones and 2,5-Chromenediones from Aldol Condensation/NHC-Catalyzed Annulation Reactions.

    Wang, Lei; Li, Sun; Chauhan, Pankaj; Hack, Daniel; Philipps, Arne R; Puttreddy, Rakesh; Rissanen, Kari; Raabe, Gerhard; Enders, Dieter

    2016-04-01

    A novel one-pot, three-component diastereo- and enantioselective synthesis of spiropyrazolones has been developed involving the aldol condensation of an enal to generate α,β-unsaturated pyrazolones, which react with a second equivalent of enal through an N-heterocyclic carbene (NHC)-catalyzed [3+2] annulation. The desired spirocyclopentane pyrazolones are obtained in moderate to good yields and good to excellent stereoselectivities. Alternatively, starting from cyclic 1,3-diketones, 2,5-chromenediones are available through [2+4] annulation. PMID:26864437

  12. 1-Benzyl-3-phenylimidazolium hexafluorophosphate

    Ping Jiang

    2009-09-01

    Full Text Available in the title compound, C16H15N2+PF6?, a precursor of N-heterocyclic carbene, the phenyl and benzyl rings are twisted away from the central imidazolium ring system, making dihedral angles of 70.30?(8 and 32.03?(10, respectively. The crystal structure is stabilized by CH...F hydrogen bonds. Furthermore, PF...? interactions involving imidazolium rings are observed [F...? = 2.9857?(16, P...? = 4.1630?(16?, PF...? = 127.92?(6].

  13. Synthesis and reactivity of electron poor allenes: formation of completely organic frustrated Lewis pairs.

    Palomas, David; Holle, Sigrid; Inés, Blanca; Bruns, Hans; Goddard, Richard; Alcarazo, Manuel

    2012-08-14

    The synthesis of several electron poor allenes bearing electron withdrawing substituents is described and their use as Lewis acids in the field of frustrated Lewis pair (FLP) chemistry reported. At room temperature the combination of N-heterocyclic carbenes (NHC) with the allenes under study invariably afforded the corresponding Lewis adducts; however, at -78 °C this reaction is in most of the cases inhibited and kinetically induced organic FLPs are formed. Under these conditions the activation of S-S bonds in disulfides has been achieved in excellent yields. PMID:22526755

  14. Amorphic complexity

    Fuhrmann, G.; Gröger, M.; Jäger, T.

    2016-02-01

    We introduce amorphic complexity as a new topological invariant that measures the complexity of dynamical systems in the regime of zero entropy. Its main purpose is to detect the very onset of disorder in the asymptotic behaviour. For instance, it gives positive value to Denjoy examples on the circle and Sturmian subshifts, while being zero for all isometries and Morse-Smale systems. After discussing basic properties and examples, we show that amorphic complexity and the underlying asymptotic separation numbers can be used to distinguish almost automorphic minimal systems from equicontinuous ones. For symbolic systems, amorphic complexity equals the box dimension of the associated Besicovitch space. In this context, we concentrate on regular Toeplitz flows and give a detailed description of the relation to the scaling behaviour of the densities of the p-skeletons. Finally, we take a look at strange non-chaotic attractors appearing in so-called pinched skew product systems. Continuous-time systems, more general group actions and the application to cut and project quasicrystals will be treated in subsequent work.

  15. Managing Complexity

    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 Dut...

  16. Complex Networks

    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...

  17. Complex Philosophy

    Gershenson, C

    2001-01-01

    As science, knowledge, and ideas evolve and are increased and refined, the branches of philosophy in charge of describing them should also be increased and refined. In this work we try to expand some ideas as a response to the recent approach from several sciences to complex systems. Because of their novelty, some of these ideas might require further refinement and may seem unfinished, but we need to start with something. Only with their propagation and feedback from critics they might be improved. We make a brief introduction to complex systems, for then defining abstraction levels. Abstraction levels represent simplicities and regularities in nature. We make an ontological distinction of absolute being and relative being, and then discuss issues on causality, metaphysics, and determinism.

  18. Managing Complexity

    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.

  19. Managing Complexity

    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...

  20. Time complexity and gate complexity

    We formulate and investigate the simplest version of time-optimal quantum computation theory (TO-QCT), where the computation time is defined by the physical one and the Hamiltonian contains only one- and two-qubit interactions. This version of TO-QCT is also considered as optimality by sub-Riemannian geodesic length. The work has two aims: One is to develop a TO-QCT itself based on a physically natural concept of time, and the other is to pursue the possibility of using TO-QCT as a tool to estimate the complexity in conventional gate-optimal quantum computation theory (GO-QCT). In particular, we investigate to what extent is true the following statement: Time complexity is polynomial in the number of qubits if and only if gate complexity is also. In the analysis, we relate TO-QCT and optimal control theory (OCT) through fidelity-optimal computation theory (FO-QCT); FO-QCT is equivalent to TO-QCT in the limit of unit optimal fidelity, while it is formally similar to OCT. We then develop an efficient numerical scheme for FO-QCT by modifying Krotov's method in OCT, which has a monotonic convergence property. We implemented the scheme and obtained solutions of FO-QCT and of TO-QCT for the quantum Fourier transform and a unitary operator that does not have an apparent symmetry. The former has a polynomial gate complexity and the latter is expected to have an exponential one which is based on the fact that a series of generic unitary operators has an exponential gate complexity. The time complexity for the former is found to be linear in the number of qubits, which is understood naturally by the existence of an upper bound. The time complexity for the latter is exponential in the number of qubits. Thus, both the targets seem to be examples satisfyng the preceding statement. The typical characteristics of the optimal Hamiltonians are symmetry under time reversal and constancy of one-qubit operation, which are mathematically shown to hold in fairly general situations.

  1. Managing Complexity

    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 allocati...

  2. Tuning the Electronic Structure of Fe(II) Polypyridines via Donor Atom and Ligand Scaffold Modifications: A Computational Study.

    Bowman, David N; Bondarev, Alexey; Mukherjee, Sriparna; Jakubikova, Elena

    2015-09-01

    Fe(II) polypyridines are an important class of pseudo-octahedral metal complexes known for their potential applications in molecular electronic switches, data storage and display devices, sensors, and dye-sensitized solar cells. Fe(II) polypyridines have a d(6) electronic configuration and pseudo-octahedral geometry and can therefore possess either a high-spin (quintet) or a low-spin (singlet) ground state. In this study, we investigate a series of complexes based on [Fe(tpy)2](2+) (tpy = 2,2';6',2″-terpyridine) and [Fe(dcpp)2](2+) (dcpp = 2,6-bis(2-carboxypyridyl)pyridine). The ligand field strength in these complexes is systematically tuned by replacing the central pyridine with five-membered (N-heterocyclic carbene, pyrrole, furan) or six-membered (aryl, thiazine-1,1-dioxide, 4-pyrone) moieties. To determine the impact of ligand substitutions on the relative energies of metal-centered states, the singlet, triplet, and quintet states of the Fe(II) complexes were optimized in water (PCM) using density functional theory at the B3LYP+D2 level with 6-311G* (nonmetals) and SDD (Fe) basis sets. It was found that the dcpp ligand scaffold allows for a more ideal octahedral coordination environment in comparison to the tpy ligand scaffold. The presence of six-membered central rings also allows for a more ideally octahedral coordination environment relative to five-membered central rings, regardless of the ligand scaffold. We find that the ligand field strength in the Fe(II) polypyridines can be tuned by altering the donor atom identity, with C donor atoms providing the strongest ligand field. PMID:26295275

  3. Complex variables

    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

  4. Complex dynamics

    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...

  5. Cosmic Complexity

    Mather, John C.

    2012-01-01

    What explains the extraordinary complexity of the observed universe, on all scales from quarks to the accelerating universe? My favorite explanation (which I certainty did not invent) ls that the fundamental laws of physics produce natural instability, energy flows, and chaos. Some call the result the Life Force, some note that the Earth is a living system itself (Gaia, a "tough bitch" according to Margulis), and some conclude that the observed complexity requires a supernatural explanation (of which we have many). But my dad was a statistician (of dairy cows) and he told me about cells and genes and evolution and chance when I was very small. So a scientist must look for me explanation of how nature's laws and statistics brought us into conscious existence. And how is that seemll"!gly Improbable events are actually happening a!1 the time? Well, the physicists have countless examples of natural instability, in which energy is released to power change from simplicity to complexity. One of the most common to see is that cooling water vapor below the freezing point produces snowflakes, no two alike, and all complex and beautiful. We see it often so we are not amazed. But physlc!sts have observed so many kinds of these changes from one structure to another (we call them phase transitions) that the Nobel Prize in 1992 could be awarded for understanding the mathematics of their common features. Now for a few examples of how the laws of nature produce the instabilities that lead to our own existence. First, the Big Bang (what an insufficient name!) apparently came from an instability, in which the "false vacuum" eventually decayed into the ordinary vacuum we have today, plus the most fundamental particles we know, the quarks and leptons. So the universe as a whole started with an instability. Then, a great expansion and cooling happened, and the loose quarks, finding themselves unstable too, bound themselves together into today's less elementary particles like protons and neutrons, liberating a little energy and creating complexity. Then, the expanding universe cooled some more, and neutrons and protons, no longer kept apart by immense temperatures, found themselves unstable and formed helium nuclei. Then, a little more cooling, and atomic nuclei and electrons were no longer kept apart, and the universe became transparent. Then a little more cooling, and the next instability began: gravitation pulled matter together across cosmic distances to form stars and galaxies. This instability is described as a "negative heat capadty" in which extracting energy from a gravitating system makes it hotter -- clearly the 2nd law of thermodynamics does not apply here! (This is the physicist's part of the answer to e e cummings' question: what is the wonder that's keeping the stars apart?) Then, the next instability is that hydrogen and helium nuclei can fuse together to release energy and make stars burn for billions of years. And then at the end of the fuel source, stars become unstable and explode and liberate the chemical elements back into space. And because of that, on planets like Earth, sustained energy flows support the development of additional instabilities and all kinds of complex patterns. Gravitational instability pulls the densest materials into the core of the Earth, leaving a thin skin of water and air, and makes the interior churn incessantly as heat flows outwards. And the heat from the sun, received mostly near the equator and flowing towards the poles, supports the complex atmospheric and oceanic circulations. And because or that, the physical Earth is full of natural chemical laboratories, concentrating elements here, mixing them there, raising and lowering temperatures, ceaselessly experimenting with uncountable events where new instabilities can arise. At least one of them was the new experiment called life. Now that we know that there are at least as many planets as there are stars, it is hard to imagine that nature's ceasess experimentation would not be able to produce life elsewhere -- but we don't know for sure. And life went on to cause new Instabilities, constantly evolving, with living things in an extraordinary range of environments, changing the global environment, with boom-and-bust cycles. with predators for every kInd of prey, with criminals for every possible crime, with governments to prevent them, and instabilities of the governments themselves. One of the instabilities Is that humans demand new weapons and new products of all sort, leading to serious investments in science and technology. So the natural/human world of competition and combat is structured to lead to advanced weaponry and cell phones. So here we are In 2012, with people writing essays and wondering whether their descendents will be artificial life forms travelling back into space. And, pondering what are the origins of those forces of nature that give rise to everything. Verllnde has argued that gravitation, the one force that has so far resisted our efforts at a Quantum description, is not even a fundamental force, but is itself it a statistical force, like osmosis. What an amazing turn of events! But after all I've just said, I should not be surprised a bit.

  6. Cosmic Complexity

    Mather, John C.

    2012-01-01

    What explains the extraordinary complexity of the observed universe, on all scales from quarks to the accelerating universe? My favorite explanation (which I certainty did not invent) ls that the fundamental laws of physics produce natural instability, energy flows, and chaos. Some call the result the Life Force, some note that the Earth is a living system itself (Gaia, a "tough bitch" according to Margulis), and some conclude that the observed complexity requires a supernatural explanation (of which we have many). But my dad was a statistician (of dairy cows) and he told me about cells and genes and evolution and chance when I was very small. So a scientist must look for me explanation of how nature's laws and statistics brought us into conscious existence. And how is that seemll"!gly Improbable events are actually happening a!1 the time? Well, the physicists have countless examples of natural instability, in which energy is released to power change from simplicity to complexity. One of the most common to see is that cooling water vapor below the freezing point produces snowflakes, no two alike, and all complex and beautiful. We see it often so we are not amazed. But physlc!sts have observed so many kinds of these changes from one structure to another (we call them phase transitions) that the Nobel Prize in 1992 could be awarded for understanding the mathematics of their common features. Now for a few examples of how the laws of nature produce the instabilities that lead to our own existence. First, the Big Bang (what an insufficient name!) apparently came from an instability, in which the "false vacuum" eventually decayed into the ordinary vacuum we have today, plus the most fundamental particles we know, the quarks and leptons. So the universe as a whole started with an instability. Then, a great expansion and cooling happened, and the loose quarks, finding themselves unstable too, bound themselves together into today's less elementary particles like protons and neutrons, liberating a little energy and creating complexity. Then, the expanding universe cooled some more, and neutrons and protons, no longer kept apart by immense temperatures, found themselves unstable and formed helium nuclei. Then, a little more cooling, and atomic nuclei and electrons were no longer kept apart, and the universe became transparent. Then a little more cooling, and the next instability began: gravitation pulled matter together across cosmic distances to form stars and galaxies. This instability is described as a "negative heat capadty" in which extracting energy from a gravitating system makes it hotter -- clearly the 2nd law of thermodynamics does not apply here! (This is the physicist's part of the answer to e e cummings' question: what is the wonder that's keeping the stars apart?) Then, the next instability is that hydrogen and helium nuclei can fuse together to release energy and make stars burn for billions of years. And then at the end of the fuel source, stars become unstable and explode and liberate the chemical elements back into space. And because of that, on planets like Earth, sustained energy flows support the development of additional instabilities and all kinds of complex patterns. Gravitational instability pulls the densest materials into the core of the Earth, leaving a thin skin of water and air, and makes the interior churn incessantly as heat flows outwards. And the heat from the sun, received mostly near the equator and flowing towards the poles, supports the complex atmospheric and oceanic circulations. And because or that, the physical Earth is full of natural chemical laboratories, concentrating elements here, mixing them there, raising and lowering temperatures, ceaselessly experimenting with uncountable events where new instabilities can arise. At least one of them was the new experiment called life. Now that we know that there are at least as many planets as there are stars, it is hard to imagine that nature's ceasess experimentation would not be able to produce life elsewhere

  7. Cosmic Complexity

    Mather, John C.

    2012-01-01

    What explains the extraordinary complexity of the observed universe, on all scales from quarks to the accelerating universe? My favorite explanation (which I certainty did not invent) ls that the fundamental laws of physics produce natural instability, energy flows, and chaos. Some call the result the Life Force, some note that the Earth is a living system itself (Gaia, a "tough bitch" according to Margulis), and some conclude that the observed complexity requires a supernatural explanation (of which we have many). But my dad was a statistician (of dairy cows) and he told me about cells and genes and evolution and chance when I was very small. So a scientist must look for me explanation of how nature's laws and statistics brought us into conscious existence. And how is that seemll"!gly Improbable events are actually happening a!1 the time? Well, the physicists have countless examples of natural instability, in which energy is released to power change from simplicity to complexity. One of the most common to see is that cooling water vapor below the freezing point produces snowflakes, no two alike, and all complex and beautiful. We see it often so we are not amazed. But physlc!sts have observed so many kinds of these changes from one structure to another (we call them phase transitions) that the Nobel Prize in 1992 could be awarded for understanding the mathematics of their common features. Now for a few examples of how the laws of nature produce the instabilities that lead to our own existence. First, the Big Bang (what an insufficient name!) apparently came from an instability, in which the "false vacuum" eventually decayed into the ordinary vacuum we have today, plus the most fundamental particles we know, the quarks and leptons. So the universe as a whole started with an instability. Then, a great expansion and cooling happened, and the loose quarks, finding themselves unstable too, bound themselves together into today's less elementary particles like protons and neutrons, liberating a little energy and creating complexity. Then, the expanding universe cooled some more, and neutrons and protons, no longer kept apart by immense temperatures, found themselves unstable and formed helium nuclei. Then, a little more cooling, and atomic nuclei and electrons were no longer kept apart, and the universe became transparent. Then a little more cooling, and the next instability began: gravitation pulled matter together across cosmic distances to form stars and galaxies. This instability is described as a "negative heat capadty" in which extracting energy from a gravitating system makes it hotter -- clearly the 2nd law of thermodynamics does not apply here! (This is the physicist's part of the answer to e e cummings' question: what is the wonder that's keeping the stars apart?) Then, the next instability is that hydrogen and helium nuclei can fuse together to release energy and make stars burn for billions of years. And then at the end of the fuel source, stars become unstable and explode and liberate the chemical elements back into space. And because of that, on planets like Earth, sustained energy flows support the development of additional instabilities and all kinds of complex patterns. Gravitational instability pulls the densest materials into the core of the Earth, leaving a thin skin of water and air, and makes the interior churn incessantly as heat flows outwards. And the heat from the sun, received mostly near the equator and flowing towards the poles, supports the complex atmospheric and oceanic circulations. And because or that, the physical Earth is full of natural chemical laboratories, concentrating elements here, mixing them there, raising and lowering temperatures, ceaselessly experimenting with uncountable events where new instabilities can arise. At least one of them was the new experiment called life. Now that we know that there are at least as many planets as there are stars, it is hard to imagine that nature's ceasess experimentation would not be able to produce life elsewhere -- but we don't know for sure. And

  8. Complex silumins

    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 α(Al and β(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 α. 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 α or β are the next ones to crystallise, followed by complex eutectic α + β +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.

  9. Advances in nickel-catalyzed cycloaddition reactions to construct carbocycles and heterocycles.

    Thakur, Ashish; Louie, Janis

    2015-08-18

    Transition-metal catalysis has revolutionized the field of organic synthesis by facilitating the construction of complex organic molecules in a highly efficient manner. Although these catalysts are typically based on precious metals, researchers have made great strides in discovering new base metal catalysts over the past decade. This Account describes our efforts in this area and details the development of versatile Ni complexes that catalyze a variety of cycloaddition reactions to afford interesting carbocycles and heterocycles. First, we describe our early work in investigating the efficacy of N-heterocyclic carbene (NHC) ligands in Ni-catalyzed cycloaddition reactions with carbon dioxide and isocyanate. The use of sterically hindered, electron donating NHC ligands in these reactions significantly improved the substrate scope as well as reaction conditions in the syntheses of a variety of pyrones and pyridones. The high reactivity and versatility of these unique Ni(NHC) catalytic systems allowed us to develop unprecedented Ni-catalyzed cycloadditions that were unexplored due to the inefficacy of early Ni catalysts to promote hetero-oxidative coupling steps. We describe the development and mechanistic analysis of Ni/NHC catalysts that couple diynes and nitriles to form pyridines. Kinetic studies and stoichiometric reactions confirmed a hetero-oxidative coupling pathway associated with this Ni-catalyzed cycloaddition. We then describe a series of new substrates for Ni-catalyzed cycloaddition reactions such as vinylcyclopropanes, aldehydes, ketones, tropones, 3-azetidinones, and 3-oxetanones. In reactions with vinycyclopropanes and tropones, DFT calculations reveal noteworthy mechanistic steps such as a C-C σ-bond activation and an 8π-insertion of vinylcyclopropane and tropone, respectively. Similarly, the cycloaddition of 3-azetidinones and 3-oxetanones also requires Ni-catalyzed C-C σ-bond activation to form N- and O-containing heterocycles. PMID:26200651

  10. Electrochemistry of Fischer alkoxycarbene complexes of chromium: The use of density functional theory to predict and understand oxidation and reduction potentials

    Highlights: Synthesis, crystal structure and electrochemical study of Fischer ethoxycarbenes. Density functional theory (DFT) calculated energies of Fischer ethoxycarbenes. DFT understanding of oxidation and reduction centre of Fischer ethoxycarbenes. Relationship between first oxidation and first reduction potential and DFT calculated energies. -- Abstract: The electrochemical behaviour of a series of Fischer ethoxycarbene complexes of the type [(CO)5Cr=C(OEt)R] with R = 2-thienyl (1), 2-furyl (2), 2-(N-methylpyrrolyl) (3), N-methyl-2-(2?-thienyl)pyrrole) (4) and 2,2?-thienylfuran (5), is investigated by means of cyclic voltammetry. Results show that the first one electron reduction process is sensitive to the energy, shape and distribution of the LUMO orbital, leading to a linear relationship between the formal reduction potential and the LUMO energy: E0?(Ccarbene) = 0.70 ELUMO3.44 (R2 = 1.00) which is valid over a large potential range. The dimeric heteroarene substituents of 4 and 5 lead to enhanced stabilization of the reduced complexes 4 and 5, making another one electron reduction possible. The formal reduction potential, E0?(Cr) of the first oxidation process of 15 lays within a narrow potential range of 0.430.50 V vs. Fc/Fc+, is Cr-based and is mainly sensitive to the electrophilic character of the heteroarene ring directly attached to the carbene carbon

  11. A broadly applicable NHC-Cu-catalyzed approach for efficient, site-, and enantioselective coupling of readily accessible (pinacolato)alkenylboron compounds to allylic phosphates and applications to natural product synthesis.

    Gao, Fang; Carr, James L; Hoveyda, Amir H

    2014-02-01

    A set of protocols for catalytic enantioselective allylic substitution (EAS) reactions that allow for additions of alkenyl units to readily accessible allylic electrophiles is disclosed. Transformations afford 1,4-dienes that contain a tertiary carbon stereogenic site and are promoted by 1.0-5.0 mol % of a copper complex of an N-heterocyclic carbene (NHC). Aryl- as well as alkyl-substituted electrophiles bearing a di- or trisubstituted alkene may be employed. Reactions can involve a variety of robust alkenyl-(pinacolatoboron) [alkenyl-B(pin)] compounds that can be either purchased or prepared by various efficient, site-, and/or stereoselective catalytic reactions, such as cross-metathesis or proto-boryl additions to terminal alkynes. Vinyl-, E-, or Z-disubstituted alkenyl-, 1,1-disubstituted alkenyl-, acyclic, or heterocyclic trisubstituted alkenyl groups may be added in up to >98% yield, >98:2 SN2':SN2, and 99:1 enantiomeric ratio (er). NHC-Cu-catalyzed EAS with alkenyl-B(pin) reagents containing a conjugated carboxylic ester or aldehyde group proceed to provide the desired 1,4-diene products in good yield and with high enantioselectivity despite the presence of a sensitive stereogenic tertiary carbon center that could be considered prone to epimerization. In most instances, the alternative approach of utilizing an alkenylmetal reagent (e.g., an Al-based species) represents an incompatible option. The utility of the approach is illustrated through applications to enantioselective synthesis of natural products such as santolina alcohol, semburin, nyasol, heliespirone A, and heliannuol E. PMID:24467274

  12. Investigating the pharmacokinetics and biological distribution of silver-loaded polyphosphoester-based nanoparticles using (111) Ag as a radiotracer.

    Aweda, Tolulope A; Zhang, Shiyi; Mupanomunda, Chiedza; Burkemper, Jennifer; Heo, Gyu Seong; Bandara, Nilantha; Lin, Mai; Cutler, Cathy S; Cannon, Carolyn L; Youngs, Wiley J; Wooley, Karen L; Lapi, Suzanne E

    2015-05-30

    Purified (111) Ag was used as a radiotracer to investigate silver loading and release, pharmacokinetics, and biodistribution of polyphosphoester-based degradable shell crosslinked knedel-like (SCK) nanoparticles as a comparison to the previously reported small molecule, N-heterocyclic silver carbene complex analog (SCC1) for the delivery of therapeutic silver ions in mouse models. Biodistribution studies were conducted by aerosol administration of (111) Ag acetate, [(111) Ag]SCC1, and [(111) Ag]SCK doses directly into the lungs of C57BL/6 mice. Nebulization of the (111) Ag antimicrobials resulted in an average uptake of 1.07 ± 0.12% of the total aerosolized dose given per mouse. The average dose taken into the lungs of mice was estimated to be 2.6 ± 0.3% of the dose inhaled per mouse for [(111) Ag]SCC1 and twice as much dose was observed for the [(111) Ag]SCKs (5.0 ± 0.3% and 5.9 ± 0.8% for [(111) Ag]aSCK and [(111) Ag]zSCK, respectively) at 1 h post administration (p.a.). [(111) Ag]SCKs also exhibited higher dose retention in the lungs; 62-68% for [(111) Ag]SCKs and 43% for [(111) Ag]SCC1 of the initial 1 h dose were observed in the lungs at 24 h p.a.. This study demonstrates the utility of (111) Ag as a useful tool for monitoring the pharmacokinetics of silver-loaded antimicrobials in vivo. PMID:25952472

  13. A Dual Independence Complex

    Wamer, 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, ...

  14. On Wagoner complexes

    Essert, Jan

    2009-01-01

    Wagoner complexes are simplicial complexes associated to groups with spherical root data. They admit interesting homotopy groups related to integral group homology. We give a general definition of Wagoner complexes, exhibit some simple properties and calculate low homotopy groups. In addition, we give a definition of affine Wagoner complexes related to groups admitting a root datum with valuation.

  15. Complexes of connected graphs

    Vassiliev, V. A.

    2014-01-01

    Graphs with given k vertices generate an (acyclic) simplicial complex. We describe the homology of its quotient complex, formed by all connected graphs, and demonstrate its applications to the topology of braid groups, knot theory, combinatorics, and singularity theory. The multidimensional analogues of this complex are indicated, which arise naturally in the homotopy theory, higher Chern-Simons theory and complexity theory.

  16. Complexity of 4-Manifolds

    Costantino, Francesco

    2006-01-01

    We define and study a notion of complexity for smooth, closed and orientable $4$-manifolds. This notion, based on the theory of Turaev shadows, represents the $4$-dimensional analogue of Matveev's complexity of $3$-manifolds. We classify complexity $0$ and $1$ four manifolds and provide examples of manifolds of higher complexity.

  17. Complex Multiplicative Calculus

    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 just another realizat...

  18. The management of complexity

    Hundsnes, Tore

    2000-01-01

    The complex structure of many business environments, and indeed many corporations or organizations operating in them, implies great challenges for managers. What sources generate this complexity, and how can it be managed? Chaos theory and complexity theory represents new perspectives on how to understand the dynamics and behavior of complex adaptive systems, and why it is difficult to predict their future state. These systems create, or inhibit several sources of complexity for managers. Sev...

  19. Hyper Space Complex Number

    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.

  20. Protein Complexes in Bacteria

    Caufield, J. Harry; Abreu, Marco; Wimble, Christopher; Uetz, Peter

    2015-01-01

    Large-scale analyses of protein complexes have recently become available for Escherichia coli and Mycoplasma pneumoniae, yielding 443 and 116 heteromultimeric soluble protein complexes, respectively. We have coupled the results of these mass spectrometry-characterized protein complexes with the 285 gold standard protein complexes identified by EcoCyc. A comparison with databases of gene orthology, conservation, and essentiality identified proteins conserved or lost in complexes of other spe...

  1. Complex networks analysis of language complexity

    Amancio, Diego R; Oliveira, Osvaldo N; Costa, Luciano da F; 10.1209/0295-5075/100/58002

    2013-01-01

    Methods from statistical physics, such as those involving complex networks, have been increasingly used in quantitative analysis of linguistic phenomena. In this paper, we represented pieces of text with different levels of simplification in co-occurrence networks and found that topological regularity correlated negatively with textual complexity. Furthermore, in less complex texts the distance between concepts, represented as nodes, tended to decrease. The complex networks metrics were treated with multivariate pattern recognition techniques, which allowed us to distinguish between original texts and their simplified versions. For each original text, two simplified versions were generated manually with increasing number of simplification operations. As expected, distinction was easier for the strongly simplified versions, where the most relevant metrics were node strength, shortest paths and diversity. Also, the discrimination of complex texts was improved with higher hierarchical network metrics, thus point...

  2. Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

    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.

  3. Evolution of biological complexity.

    Adami, C; Ofria, C; Collier, T C

    2000-04-25

    To make a case for or against a trend in the evolution of complexity in biological evolution, complexity needs to be both rigorously defined and measurable. A recent information-theoretic (but intuitively evident) definition identifies genomic complexity with the amount of information a sequence stores about its environment. We investigate the evolution of genomic complexity in populations of digital organisms and monitor in detail the evolutionary transitions that increase complexity. We show that, because natural selection forces genomes to behave as a natural "Maxwell Demon," within a fixed environment, genomic complexity is forced to increase. PMID:10781045

  4. Hydroamination reactions of alkynes with ortho-substituted anilines in ball mills: synthesis of benzannulated N-heterocycles by a cascade reaction.

    Weiße, Maik; Zille, Markus; Jacob, Katharina; Schmidt, Robert; Stolle, Achim

    2015-04-20

    It was demonstrated that ortho-substituted anilines are prone to undergo hydroamination reactions with diethyl acetylenedicarboxylate in a planetary ball mill. A sequential coupling of the intermolecular hydroamination reaction with intramolecular ring closure was utilized for the syntheses of benzooxazines, quinoxalines, and benzothiazines from readily available building blocks, that is, electrophilic alkynes and anilines with OH, NH, or SH groups in the ortho position. For the heterocycle formation, it was shown that several stress conditions were able to initiate the reaction in the solid state. Processing in a ball mill seemed to be advantageous over comminution with mortar and pestle with respect to process control. In the latter case, significant postreaction modification occurred during solid-state analysis. Cryogenic milling proved to have an adverse effect on the molecular transformation of the reagents. PMID:25766865

  5. Design, synthesis, and biological evaluation of 6alpha- and 6beta-N-heterocyclic substituted naltrexamine derivatives as mu opioid receptor selective antagonists.

    Li, Guo; Aschenbach, Lindsey C; Chen, Jianyang; Cassidy, Michael P; Stevens, David L; Gabra, Bichoy H; Selley, Dana E; Dewey, William L; Westkaemper, Richard B; Zhang, Yan

    2009-03-12

    Opioid receptor selective antagonists are important pharmacological probes in opioid receptor structural characterization and opioid agonist functional study. Thus far, a nonpeptidyl, highly selective and reversible mu opioid receptor (MOR) antagonist is unavailable. On the basis of our modeling studies, a series of novel naltrexamine derivatives have been designed and synthesized. Among them, two compounds were identified as leads based on the results of in vitro and in vivo assays. Both of them displayed high binding affinity for the MOR (K(i) = 0.37 and 0.55 nM). Compound 6 (NAP) showed over 700-fold selectivity for the MOR over the delta receptor (DOR) and more than 150-fold selectivity over the kappa receptor (KOR). Compound 9 (NAQ) showed over 200-fold selectivity for the MOR over the DOR and approximately 50-fold selectivity over the KOR. Thus these two novel ligands will serve as leads to further develop more potent and selective antagonists for the MOR. PMID:19199782

  6. Design, Synthesis, and Biological Evaluation of 6α- and 6β-N-Heterocyclic Substituted Naltrexamine Derivatives as μ Opioid Receptor Selective Antagonists

    Li, Guo; Aschenbach, Lindsey C.; Chen, Jianyang; Cassidy, Michael P.; Stevens, David L.; Gabra, Bichoy H.; Selley, Dana E.; Dewey, William L.; Westkaemper, Richard B.; Zhang, Yan

    2009-01-01

    Opioid receptor selective antagonists are important pharmacological probes in opioid receptor structural characterization and opioid agonist functional study. Thus far, a nonpeptidyl, highly selective and reversible μ opioid receptor (MOR) antagonist is unavailable. On the basis of our modeling studies, a series of novel naltrexamine derivatives have been designed and synthesized. Among them, two compounds were identified as leads based on the results of in vitro and in vivo assays. Both of them displayed high binding affinity for the MOR (Ki = 0.37 and 0.55 nM). Compound 6 (NAP) showed over 700-fold selectivity for the MOR over the δ receptor (DOR) and more than 150-fold selectivity over the κ receptor (KOR). Compound 9 (NAQ) showed over 200-fold selectivity for the MOR over the DOR and approximately 50-fold selectivity over the KOR. Thus these two novel ligands will serve as leads to further develop more potent and selective antagonists for the MOR. PMID:19199782

  7. Design, Synthesis, and Biological Evaluation of 6α- and 6β-N-Heterocyclic Substituted Naltrexamine Derivatives as μ Opioid Receptor Selective Antagonists

    Li, Guo; Aschenbach, Lindsey C.; Chen, Jianyang; Cassidy, Michael P.; Stevens, David L.; Gabra, Bichoy H.; Selley, Dana E; Dewey, William L.; Westkaemper, Richard B.; Zhang, Yan

    2009-01-01

    Opioid receptor selective antagonists are important pharmacological probes in opioid receptor structural characterization and opioid agonist functional study. Thus far, a nonpeptidyl, highly selective and reversible μ opioid receptor (MOR) antagonist is unavailable. On the basis of our modeling studies, a series of novel naltrexamine derivatives have been designed and synthesized. Among them, two compounds were identified as leads based on the results of in vitro and in vivo assays. Both of t...

  8. AQUEOUS N-HETEROCYCLIZATION OF PRIMARY AMINES AND HYDRAZINES WITH DIHALIDES: MICROWAVE-ASSISTED SYNTHESES OF N-AZACYCLOALKANES, ISOINDOLE, PYRAZOLE, PYRAZOLIDINE AND PHTHALAZINE DERIVATIVES

    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...

  9. Quantum Communication Complexity

    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.

  10. Irinotecan Lipid Complex Injection

    Irinotecan lipid complex is used in combination with other medications to treat pancreatic cancer that has spread to other parts of ... after treatment with other chemotherapy medications. Irinotecan lipid complex is in a class of antineoplastic medications called ...

  11. Vincristine Lipid Complex Injection

    Vincristine lipid complex is used to treat a certain type of acute lymphoblastic leukemia (ALL; a type of cancer of the ... two different treatments with other medications. Vincristine lipid complex is in a class of medications called vinca ...

  12. Doxorubicin Lipid Complex Injection

    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 (a ...

  13. Mycobacterium Avium Complex (MAC)

    ... Select a Language: Fact Sheet 514 Mycobacterium Avium Complex (MAC) WHAT IS MAC? HOW DO I KNOW ... THE BOTTOM LINE WHAT IS MAC? Mycobacterium Avium Complex (MAC) is a serious illness caused by common ...

  14. Cytarabine Lipid Complex Injection

    Cytarabine lipid complex is used to treat lymphomatous meningitis (a type of cancer in the covering of the spinal cord and brain). Cytarabine lipid complex is in a class of medications called antimetabolites. ...

  15. Daunorubicin Lipid Complex Injection

    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 ...

  16. Oligocyclopentadienyl transition metal complexes

    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. Chiral lutetium benzamidinate complexes.

    Benndorf, Paul; Jenter, Jelena; Zielke, Larissa; Roesky, Peter W

    2011-03-01

    Enantiomerically pure lutetium complexes were synthesized as the first rare earth metal complexes containing a chiral amidinate ligand. The catalytic activity and the enantioselectivity in hydroamination reactions were studied. PMID:21173978

  18. Phospholylsamarium(III) complexes

    Gosink, H.J.; Nief, F.; Ricard, L.; Mathey, F. [Ecole Polytechnique, Palaiseau (France)

    1995-03-15

    Here, the authors report the chemical preparation and crystal structure of the first examples of phospholylsamarium(III) complexes. These complexes were analyzed characterized by NMR spectroscopy and X-ray spectroscopy.

  19. Evolution of Biological Complexity

    Adami, Christoph; Ofria, Charles; Collier, Travis C.

    2000-01-01

    In order to make a case for or against a trend in the evolution of complexity in biological evolution, complexity needs to be both rigorously defined and measurable. A recent information-theoretic (but intuitively evident) definition identifies genomic complexity with the amount of information a sequence stores about its environment. We investigate the evolution of genomic complexity in populations of digital organisms and monitor in detail the evolutionary transitions that increase complexit...

  20. Complexity and Fisher information

    Binder, P.-M.

    2000-04-01

    The connection between an observer-based theory of measurement and a hierarchical classification of complex systems in terms of topological exponents is discussed. This leads to generalized definitions of complexity that capture different aspects of the structure of the trajectory space of complex systems.

  1. Oxidative degradation of the organometallic iron(II) complex [Fe{bis[3-(pyridin-2-yl)-1H-imidazol-1-yl]methane}(MeCN)(PMe3)](PF6)2: structure of the ligand decomposition product trapped via coordination to iron(II).

    Haslinger, Stefan; Pthig, Alexander; Cokoja, Mirza; Khn, Fritz E

    2015-12-01

    Iron is of interest as a catalyst because of its established use in the Haber-Bosch process and because of its high abundance and low toxicity. Nitrogen-heterocyclic carbenes (NHC) are important ligands in homogeneous catalysis and iron-NHC complexes have attracted increasing attention in recent years but still face problems in terms of stability under oxidative conditions. The structure of the iron(II) complex [1,1'-bis(pyridin-2-yl)-2,2-bi(1H-imidazole)-?N(3)][3,3'-bis(pyridin-2-yl-?N)-1,1'-methanediylbi(1H-imidazol-2-yl-?C(2))](trimethylphosphane-?P)iron(II) bis(hexafluoridophosphate), [Fe(C17H14N6)(C16H12N6)(C3H9P)](PF6)2, features coordination by an organic decomposition product of a tetradentate NHC ligand in an axial position. The decomposition product, a C-C-coupled biimidazole, is trapped by coordination to still-intact iron(II) complexes. Insights into the structural features of the organic decomposition products might help to improve the stability of oxidation catalysts under harsh conditions. PMID:26632838

  2. Complex variables I essentials

    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

  3. Heuristic dynamic complexity coding

    korupa, Jozef; Slowack, Jrgen; Mys, Stefaan; Lambert, Peter; Van de Walle, Rik

    2008-04-01

    Distributed video coding is a new video coding paradigm that shifts the computational intensive motion estimation from encoder to decoder. This results in a lightweight encoder and a complex decoder, as opposed to the predictive video coding scheme (e.g., MPEG-X and H.26X) with a complex encoder and a lightweight decoder. Both schemas, however, do not have the ability to adapt to varying complexity constraints imposed by encoder and decoder, which is an essential ability for applications targeting a wide range of devices with different complexity constraints or applications with temporary variable complexity constraints. Moreover, the effect of complexity adaptation on the overall compression performance is of great importance and has not yet been investigated. To address this need, we have developed a video coding system with the possibility to adapt itself to complexity constraints by dynamically sharing the motion estimation computations between both components. On this system we have studied the effect of the complexity distribution on the compression performance. This paper describes how motion estimation can be shared using heuristic dynamic complexity and how distribution of complexity affects the overall compression performance of the system. The results show that the complexity can indeed be shared between encoder and decoder in an efficient way at acceptable rate-distortion performance.

  4. Photocytotoxic lanthanide complexes

    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.

  5. Quantum State Complexity Measure

    Campbell, Yuri

    2011-01-01

    The complexity measures role has become much clearer in recent years as they help to better understand complex systems dynamical behavior. Even though the large number of measures proposed to tackle this issue for classical systems, for quantum systems only Kolmogorov's algorithm complexity extensions have been proposed. Hence, the present approach makes use of a new and mathematically well-established complexity measure for classical systems and extends it to assess quantum states complexity as well. Then the proposed extension is applied to a mixed state constructed with a W-state together with controlled white noise, showing a convex behavior of quantum state complexity. Thus, this reinforces the differences from previous known quantum complexities.

  6. 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(-)).

    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 [{μ-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

  7. Simplicial complexes of graphs

    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.

  8. Complex Systems and Dependability

    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

  9. Quantum Computational Complexity

    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.

  10. Complex Correspondence Principle

    Bender, C; Hook, D. W.; Meisinger, P. N.; Wang, Q-H

    2009-01-01

    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 domain. The associat...

  11. Engineering Complex Tissues

    Mikos, Antonios G.; Herring, Susan W.; OCHAREON, PANNEE; Elisseeff, Jennifer; Lu, Helen H.; Kandel, Rita; Schoen, Frederick J.; Toner, Mehmet; Mooney, David; Atala, Anthony; Van Dyke, Mark E.; Kaplan, David; Vunjak-Novakovic, Gordana

    2006-01-01

    This article summarizes the views expressed at the third session of the workshop “Tissue Engineering—The Next Generation,” which was devoted to the engineering of complex tissue structures. Antonios Mikos described the engineering of complex oral and craniofacial tissues as a “guided interplay” between biomaterial scaffolds, growth factors, and local cell populations toward the restoration of the original architecture and function of complex tissues. Susan Herring, reviewing osteogenesis and ...

  12. How evolution guides complexity

    LARRY S. YAEGER

    2009-01-01

    Long-standing debates about the role of natural selection in the growth of biological complexity over geological time scales are difficult to resolve from the paleobiological record. Using an evolutionary model—a computational ecosystem subjected to natural selection—we investigate evolutionary trends in an information-theoretic measure of the complexity of the neural dynamics of artificial agents inhabiting the model. Our results suggest that evolution always guides complexity change, just n...

  13. Quantum Certificate Complexity

    Aaronson, Scott

    2002-01-01

    Given a Boolean function f, we study two natural generalizations of the certificate complexity C(f): the randomized certificate complexity RC(f) and the quantum certificate complexity QC(f). Using Ambainis' adversary method, we exactly characterize QC(f) as the square root of RC(f). We then use this result to prove the new relation R0(f) = O(Q2(f)^2 Q0(f) log n) for total f, where R0, Q2, and Q0 are zero-error randomized, bounded-error quantum, and zero-error quantum query complexities respec...

  14. Phospholyl-uranium complexes

    After having reported a bibliographical study on penta-methylcyclopentadienyl uranium complexes, and a description of the synthesis and radioactivity of uranium (III) and (IV) boron hydrides compounds, this research thesis reports the study of mono and bis-tetramethyl-phospholyl uranium complexes comprising chloride, boron hydride, alkyl and alkoxide ligands. The third part reports the comparison of structures, stabilities and reactions of homologue complexes in penta-methylcyclopentadienyl and tetramethyl-phospholyl series. The last part addresses the synthesis of tris-phospholyl uranium (III) and (IV) complexes.

  15. Complex hyperbolic triangle groups

    Schwartz, R E

    2003-01-01

    The theory of complex hyperbolic discrete groups is still in its childhood but promises to grow into a rich subfield of geometry. In this paper I will discuss some recent progress that has been made on complex hyperbolic deformations of the modular group and, more generally, triangle groups. These are some of the simplest nontrivial complex hyperbolic discrete groups. In particular, I will talk about my recent discovery of a closed real hyperbolic 3-manifold which appears as the manifold at infinity for a complex hyperbolic discrete group.

  16. Nuclear weapons complex

    In this book, GAO characterizes DOE's January 1991 Nuclear Weapons Complex Reconfiguration Study as a starting point for reaching agreement on solutions to many of the complex's safety and environmental problems. Key decisions still need to be made about the size of the complex, where to relocate plutonium operations, what technologies to use for new tritium production, and what to do with excess plutonium. The total cost for reconfiguring and modernizing the complex is still uncertain, and some management issues remain unresolved. Congress faces a difficult task in making test decisions given the conflicting demands for scarce resources in a time of growing budget deficits and war in the Persian Gulf

  17. Conducting metal dithiolate complexes

    Underhill, A. E.; Ahmad, M. M.; Turner, D. J.; Clemenson, P. I.; Carneiro, K.; Yueqiuan, S.; Mortensen, Kell

    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......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...

  18. Simplicial Complexes of Graphs

    Jonsson, Jakob

    2005-01-01

    Let G be a finite graph with vertex set V and edge set E. A graph complex on G is an abstract simplicial complex consisting of subsets of E. In particular, we may interpret such a complex as a family of subgraphs of G. The subject of this thesis is the topology of graph complexes, the emphasis being placed on homology, homotopy type, connectivity degree, Cohen-Macaulayness, and Euler characteristic. We are particularly interested in the case that G is the complete graph on V. Monotone graph p...

  19. Berger Engineering Complex

    Federal Laboratory Consortium — Description/History: Engineering laboratory The Berger Lab Complex is a multi-purpose building with professional office, 100 seat auditorium, general purpose labs,...

  20. Gold trifluoromethyl complexes.

    Gil-Rubio, Juan; Vicente, José

    2015-12-01

    This article reviews the synthesis, reactivity and applications of gold trifluoromethyl complexes, which are the only isolated perfluoroalkyl complexes of gold. The most reported examples are neutral Au(i) complexes of the type [Au(CF3)L], whereas only two Au(ii) trifluoromethyl complexes have been reported, both being diamagnetic and containing a strong Au-Au bond. A number of Au(iii) trifluoromethyl complexes have been prepared by oxidative addition of halogens or iodotrifluoromethane to Au(i) complexes or, in a few cases, by transmetallation reactions. Owing to the limitations of the available synthetic methods, a lower number of examples is known, particularly for the oxidation states (ii) and (iii). Gold trifluoromethyl complexes present singular characteristics, such as thermal stability, strong Au-C bonds and, in some cases, reactive α-C-F bonds. Some of the Au(iii) complexes reported, show unusually easy reductive elimination reactions of trifluoromethylated products which could be applied in the development of gold-catalyzed processes for the trifluoromethylation of organic compounds. PMID:26169553