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Sample records for n-heterocyclic carbene complexes

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

    Science.gov (United States)

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

    2015-06-01

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

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

    OpenAIRE

    Schuster, Oliver; Mercs, Laszlo; Albrecht, Martin

    2010-01-01

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

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

    OpenAIRE

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

    2013-01-01

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

  4. Copolymerization of cyclohexene oxide with CO2 catalyzed by tridentate N-heterocyclic carbene titanium(IV) complexes.

    Science.gov (United States)

    Quadri, Coralie C; Le Roux, Erwan

    2014-03-21

    A new class of complexes based on titanium(IV) bearing a bisanionic mer-tridentate N-heterocyclic carbene ligand were investigated for the copolymerization of cyclohexene oxide with CO2. Upon addition of [PPN]X' salts, all complexes were found to be active and highly selective toward the formation of poly(cyclohexene oxide-alt-carbon dioxide). PMID:24292280

  5. Synthesis and biological assays on cancer cells of dinuclear gold complexes with novel functionalised di(N-heterocyclic carbene) ligands.

    Science.gov (United States)

    Baron, Marco; Bellemin-Laponnaz, Stéphane; Tubaro, Cristina; Basato, Marino; Bogialli, Sara; Dolmella, Alessandro

    2014-12-01

    New dinuclear di(N-heterocyclic carbene) silver(I), gold(I) and gold(III) complexes have been synthesised and their antiproliferative effects towards various cancer cell lines have been screened. The di(N-heterocyclic carbene) ligands have a propylene linker between the carbene moieties and the imidazole backbone has been functionalised with a 1-benzyl- or 1-PEG-1,2,3-triazole ring (PEG=poly(ethylene glycol)) via a CuAAC (copper azido alkyne cycloaddition) reaction. The resulting gold(I) and gold(III) complexes display an antiproliferative activity superior to that of the unfunctionalised pristine complexes together with a higher selectivity towards cancerous cells with respect to healthy cells. PMID:25226437

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

    Directory of Open Access Journals (Sweden)

    Elzatahry AA

    2012-06-01

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

  7. Pyridine versus acetonitrile coordination in rhodium-N-heterocyclic carbene square-planar complexes.

    Science.gov (United States)

    Palacios, Laura; Di Giuseppe, Andrea; Castarlenas, Ricardo; Lahoz, Fernando J; Pérez-Torrente, Jesús J; Oro, Luis A

    2015-03-10

    Experimental and theoretical studies on the factors that control the coordination chemistry of N-donor ligands in square-planar complexes of the type RhCl(NHC)L(1)L(2) (NHC = N-heterocyclic carbene) are presented. The dinuclear complexes [Rh(?-Cl)(IPr)(?(2)-olefin)]2 {IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-carbene} have been reacted with different combinations of ligands including pyridine, acetonitrile, 2-pyridylacetonitrile, triphenylphosphine, tricyclohexylphosphine, carbon monoxide or molecular oxygen. In addition, the reactivity of RhCl(IPr)(PPh3)2 has also been studied. Pyridine preferentially coordinates trans to the carbene ligand whereas ?-acceptor ligands (olefin, CO or PPh3) are prone to bind cis to IPr and trans to chlorido, unless steric bulk hinders the coordination of the ligand (PCy3). In contrast, acetonitrile is more labile than pyridine but is able to form complexes coordinated cis-to-IPr. Molecular dioxygen also displaces the labile cyclooctene ligand in RhCl(IPr)(?(2)-coe)(py) to give a square-planar dioxygen adduct which can be transformed into a peroxo derivative by additional coordination of pyridine. Charge decomposition analysis (CDA) shows that ?-donation values are similar for coordination at cis- or trans-IPr positions, whereas efficient ?-backbonding is significantly observed at cis position being the favoured coordination site for ?-acceptor ligands. The Rh-IPr rotational barrier in a series of square-planar complexes has been analysed. It has been found that the main contribution is the steric hindrance of the ancillary ligand. The presence of a ?-donor ligand such as chlorido slows down the dynamic process. PMID:25714797

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-10-03

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

  9. N-heterocyclic carbene (NHC) complexes of group 4 transition metals.

    Science.gov (United States)

    Zhang, Dao; Zi, Guofu

    2015-04-01

    Since the discovery of a stable N-heterocyclic carbene (NHC), the use of NHCs in chemistry has developed rapidly over the past two decades. These interesting compounds are predominantly employed in organometallic chemistry as ligands for various metal centers, and as organocatalysts for a variety of transformations. In particular, the NHC transition metal complexes have received widespread attention, and significant progress has been made in the development of group 4 NHC-complexes in the last few years. These group 4 NHC-complexes are of interest because of their unique structural properties, and their potential application in organic transformations and catalysis. This review covers the superior design strategies for NHC ligands to stabilize early transition metals and well-defined group 4 metal complexes with mono- and multi-dentate NHC ligands. In this context, four types of NHC-complexes, i.e., carbon-functionalized NHCs, nitrogen-functionalized NHCs, oxygen-functionalized NHCs and nitrogen/oxygen-functionalized unsymmetric NHCs, are described. In addition, the use of group 4 NHC-complexes as catalysts in olefin (co)polymerization, ring-opening polymerization of rac-lactide, copolymerization of epoxides and CO2, as well as hydroamination/cyclization of aminoalkenes, is presented. Furthermore, limitations and challenges are discussed. PMID:25608933

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

    Directory of Open Access Journals (Sweden)

    Ting-Ting Gao

    2012-11-01

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

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

    Science.gov (United States)

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

    2015-05-20

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

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

    DEFF Research Database (Denmark)

    Dam, Johan Hygum; Osztrovszky, Gyorgyi

    2010-01-01

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

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

    Science.gov (United States)

    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 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

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

    OpenAIRE

    Maggi, Agnese; Madsen, Robert

    2011-01-01

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

  15. Synthesis from caffeine of a mixed N-heterocyclic carbene-silver acetate complex active against resistant respiratory pathogens.

    Science.gov (United States)

    Kascatan-Nebioglu, Aysegul; Melaiye, Abdulkareem; Hindi, Khadijah; Durmus, Semih; Panzner, Matthew J; Hogue, Lisa A; Mallett, Rebekah J; Hovis, Christine E; Coughenour, Marvin; Crosby, Seth D; Milsted, Amy; Ely, Daniel L; Tessier, Claire A; Cannon, Carolyn L; Youngs, Wiley J

    2006-11-16

    The bis(N-heterocyclic carbene) (NHC) silver complex, 3, with a methyl carbonate anion was formed from the reaction of the iodide salt of methylated caffeine, 1, with silver (I) oxide in methanol. Attempts to crystallize this complex from a mixture of common alcohols and ethyl acetate led to the formation of an NHC-silver acetate complex, 4. The more direct synthesis of 4 was accomplished by the in-situ deprotonation of 1 by silver acetate in methanol. Complex 4 demonstrated antimicrobial activity against numerous resistant respiratory pathogens from the lungs of cystic fibrosis (CF) patients including members of the Burkholderia cepacia complex that cause a high rate of mortality in patients with cystic fibrosis (CF). Application of this NHC silver complex to primary cultures of murine respiratory epithelial cells followed by microarray analysis showed minimal gene expression changes at the concentrations effective against respiratory pathogens. Furthermore, methylated caffeine without silver showed some antibacterial and antifungal activity. PMID:17154511

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

    Directory of Open Access Journals (Sweden)

    Dan Yuan

    2012-03-01

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

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

    DEFF Research Database (Denmark)

    Maggi, Agnese; Madsen, Robert

    2012-01-01

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

  18. An efficient N-heterocyclic carbene-ruthenium complex: application towards the synthesis of polyesters and polyamides.

    Science.gov (United States)

    Malineni, Jagadeesh; Keul, Helmut; Möller, Martin

    2015-03-01

    The ruthenium benzimidazolylidene-based N-heterocyclic carbene (NHC) complex 4 catalyzes the direct dehydrogenative condensation of primary alcohols into esters and primary alcohols in the presence of amines to the corresponding amides in high yields. This efficient new catalytic system shows a high selectivity towards the conversion of diols to polyesters and of a mixture of diols and diamines to polyamides. The only side product formed in this reaction is molecular hydrogen. Remarkable is the conversion of hydroxytelechelic polytetrahydrofuran (M¯n = 1000 g mol(-1) )-a polydispers starting material-into a hydrolytically degradable polyether with ester linkages (M¯n = 32 600 g mol(-1) ) and, in the presence of aliphatic diamines, into a polyether with amide linkages in the back bone (M¯n = 16 000 g mol(-1) ). PMID:25653190

  19. Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

    OpenAIRE

    Cristina Tubaro; Marco Baron; Andrea Biffis; Marino Basato

    2013-01-01

    Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC) ligands have been employed as catalysts in the intermolecular hydroarylation of alkynes with simple unfunctionalised arenes. Both mono- and dinuclear gold(III) complexes were able to catalyze the reaction; however, the best results were obtained with the mononuclear gold(I) complex IPrAuCl. This complex, activated with one equivalent of silver tetrafluoroborate, exhibited under acidic conditions at room temperature much high...

  20. Luminescent ruthenium(II) complex bearing bipyridine and N-heterocyclic carbene-based C?N?C pincer ligand for live-cell imaging of endocytosis.

    Science.gov (United States)

    Tsui, Wai-Kuen; Chung, Lai-Hon; Wong, Matthew Man-Kin; Tsang, Wai-Him; Lo, Hoi-Shing; Liu, Yaxiang; Leung, Chung-Hang; Ma, Dik-Lung; Chiu, Sung-Kay; Wong, Chun-Yuen

    2015-01-01

    Luminescent ruthenium(II)-cyanide complex with N-heterocyclic carbene pincer ligand C(?)N(?)C = 2,6-bis(1-butylimidazol-2-ylidene)pyridine and 2,2'-bipyridine (bpy) shows minimal cytotoxicity to both human breast carcinoma cell (MCF-7) and human retinal pigmented epithelium cell (RPE) in a wide range of concentration (0.1-500??M), and can be used for the luminescent imaging of endocytosis of the complex in these cells. PMID:25765974

  1. Luminescent Ruthenium(II) Complex Bearing Bipyridine and N-Heterocyclic Carbene-based C?N?C Pincer Ligand for Live-Cell Imaging of Endocytosis

    Science.gov (United States)

    Tsui, Wai-Kuen; Chung, Lai-Hon; Wong, Matthew Man-Kin; Tsang, Wai-Him; Lo, Hoi-Shing; Liu, Yaxiang; Leung, Chung-Hang; Ma, Dik-Lung; Chiu, Sung-Kay; Wong, Chun-Yuen

    2015-01-01

    Luminescent ruthenium(II)-cyanide complex with N-heterocyclic carbene pincer ligand C?N?C = 2,6-bis(1-butylimidazol-2-ylidene)pyridine and 2,2?-bipyridine (bpy) shows minimal cytotoxicity to both human breast carcinoma cell (MCF-7) and human retinal pigmented epithelium cell (RPE) in a wide range of concentration (0.1–500??M), and can be used for the luminescent imaging of endocytosis of the complex in these cells. PMID:25765974

  2. Magnesium and zinc complexes of functionalised, saturated N-heterocyclic carbene ligands: carbene lability and functionalisation, and lactide polymerisation catalysis.

    Science.gov (United States)

    Arnold, Polly L; Casely, Ian J; Turner, Zoë R; Bellabarba, Ronan; Tooze, Robert B

    2009-09-21

    The synthesis of magnesium and zinc complexes of bidentate anionic alkoxide ligands with saturated-backbone carbene groups is reported. Mono(ligand) and bis(ligand) complexes [M(L(R))N''](2) and [M(L(R))(2)] (M = Mg, Zn, N'' = N(SiMe(3))(2), L(R) = [OCMe(2)CH(2){CNCH(2)CH(2)NR}] R = (i)Pr, Mes, Dipp) have been isolated, and some structurally characterised and compared with the new unsaturated carbene complex [Mg(L)(2)]. Reactions with silyl halides show either addition across the metal carbene bond, or across the metal alkoxide bond, in accordance with the metals' electronegativity difference: the metal alkoxide bonds are stronger for Mg(II) complexes, for which the carbene is silylated to form zwitterionic [MgI(Me(3)SiL(R))N''] (Me(3)SiL(R) = OCMe(2)CH(2){Me(3)SiCNCH(2)CH(2)NR}) while the metal-bound alkoxide group is silylated in the Zn(II) complexes forming [ZnI(Me(3)SiOL(R))N''] (Me(3)SiOL(R) = Me(3)SiOCMe(2)CH(2){CNCH(2)CH(2)NR}). The proligand [HL(R)] is silylated at the alcohol group, forming the iodide salt [Me(3)SiOCMe(2)CH(2){HCNCH(2)CH(2)NR}]I.Preliminary results on the use of these complexes as initiators for the polymerisation of rac-lactide are reported, and suggest different initiation mechanisms are occurring for the two metals, in agreement with the different silylation reactivity observed. The polymerisation reactions are facile at room temperature even without an initiator, and yield polymers of reasonable molecular weight and heterotacticity and with good PDI. These are the first magnesium NHC complexes demonstrated to effect lactide polymerisation.Also, an adduct instead of the anticipated potassium alkoxycarbene is generated from the reaction of the proligand [HL(R)] with potassium amide KN''; this has been structurally characterised. PMID:20449168

  3. A cationic rhodium(I) N-heterocyclic carbene complex isolated as an aqua adduct

    OpenAIRE

    Ashley L. Huttenstine; Edward Rajaseelan; Oliver, Allen G; Rood, Jeffrey A.

    2011-01-01

    The title complex, aqua­[1,3-bis­(2,6-diiso­propyl­phen­yl)imid­az­ol-2-yl­idene](?4-cyclo­octa-1,5-diene)rhodium(I) tetra­fluor­ido­borate, [Rh(C8H12)(C27H36N2)(H2O)]BF4, exihibits a square-planar geometry around the Rh(I) atom, formed by a bidentate cyclo­octa-1,5-diene (cod) ligand, an N-heterocylcic carbene and an aqua ligand. The complex is cationic and a BF4 ? anion balances the charge. The structure exists as a hydrogen-bonded dimer in the solid state, formed via inte...

  4. Non-covalent interactions in coinage metal complexes of 1,2,4-triazole-based N-heterocyclic carbenes.

    Science.gov (United States)

    Turek, Jan; Panov, Illia; Švec, Petr; R?ži?ková, Zde?ka; R?ži?ka, Aleš

    2014-11-01

    Seven coinage metal(I) complexes bearing two different triazole-based N-heterocyclic carbene (NHC) ligands, [1-tert-butyl-4-{2-[(N,N-dimethylamino)methyl]phenyl}-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide and 1-tert-butyl-4-(4-methylphenyl)-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide], were synthesized and fully characterized in solution by NMR spectroscopy as well as in the solid state by X-ray diffraction techniques. Furthermore, the XRD analysis showed that the bidentate coordination of the amino group substituted NHC ligand, previously observed for rhodium and palladium complexes, does not take place in the solid state structure of Au(I) complexes with various halide ligands. Nevertheless, the formation of sets of two head-to-tail oriented monomers aggregated via a weak metallophilic contact was revealed for both NHC ligands as well as for all three coinage metals with different halides. These experimental data correlate quite well with the previously published theoretical study on related complexes. PMID:25189129

  5. Blue phosphorescent N-heterocyclic carbene chelated Pt(ii) complexes with an ?-duryl-?-diketonato ancillary ligand.

    Science.gov (United States)

    Ko, Soo-Byung; Park, Hee-Jun; Gong, Shaolong; Wang, Xiang; Lu, Zheng-Hong; Wang, Suning

    2015-04-29

    C^C* chelated Pt(ii) compounds that contain an N-heterocyclic carbene (NHC) donor have recently attracted great interest as blue or white phosphorescent emitters for organic light-emitting devices (OLEDs). To overcome the tendency for excimer formation in Pt(ii) compounds, an ?-duryl-?-diketonato ligand was selected as the ancillary ligand for blue phosphorescent C^C* chelated Pt(ii) compounds. Using this approach, a series of NHC-based C^C* chelated Pt(ii) compounds has been designed and synthesized. The chelate ligands used in the new C^C* chelated Pt(ii) compounds include 1-phenylimidazol-2-ylidene in , 1-phenyl-1,2,4-triazol-5-ylidene in , p-TMS-1-phenylimidazol-2-ylidene in , and p-TMS-1-phenyl-1,2,4-triazol-5-ylidene in . A single-crystal X-ray diffraction analysis revealed that the presence of the ?-duryl-?-diketonato ligand in the Pt(ii) compounds effectively suppresses the dimer formation in the crystal lattice. , , , and display blue phosphorescence at room temperature. The p-TMS substituted complex was found to display the most efficient blue phosphorescence at ?em = 468 nm with a ?PL of 0.68. Spectroscopic and computational studies established that the blue phosphorescence in the phenyl-imidazolylidene chelated complexes originates mainly from a (3)MLCT state while that in the phenyl-triazolylidene chelated compounds arises from a (3)ILCT state. Electroluminescent devices using and as the dopant were fabricated which display both monomer and exciplex emission, leading to pure white light electroluminescence with CIE coordinates of (0.32, 0.31). PMID:25501853

  6. N-alkyl functionalised expanded ring N-heterocyclic carbene complexes of rhodium(I) and iridium(I): structural investigations and preliminary catalytic evaluation

    OpenAIRE

    Dunsford, J. J.; Tromp, D. S.; Cavell, K. J.; Elsevier, C. J.; Kariuki, B. M.

    2013-01-01

    A series of new N-alkyl functionalised 6- and 7-membered expanded ring N-heterocyclic carbene (NHC) pro-ligands 3-6 and their corresponding complexes of rhodium(I) and iridium(I), [M(NHC)(COD)Cl] 7-14 and [M(NHC)(CO)(2)Cl] 15-22 are described. The complexes have been characterised by H-1 and C-13{H-1} NMR, mass spectrometry, IR and X-ray diffraction. It is noted from X-ray diffraction studies that the N-alkyl substituents are found to orientate themselves away from the metal centre due to unf...

  7. C^C* cyclometalated platinum(II) N-heterocyclic carbene complexes with a sterically demanding ?-diketonato ligand – synthesis, characterization and photophysical properties.

    Science.gov (United States)

    Tenne, M; Metz, S; Wagenblast, G; Münster, Ingo; Strassner, T

    2015-05-14

    Neutral cyclometalated platinum(ii) N-heterocyclic carbene complexes [Pt(C^C*)(O^O)] with C^C* ligands based on 1-phenyl-1,2,4-triazol-5-ylidene and 4-phenyl-1,2,4-triazol-5-ylidene, as well as acetylacetonato (O^O = acac) and 1,3-bis(2,4,6-trimethylphenyl)propan-1,3-dionato (O^O = mesacac) ancillary ligands were synthesized and characterized. All complexes are emissive at room temperature in a poly(methyl methacrylate) (PMMA) matrix with emission maxima in the blue region of the spectrum. High quantum efficiencies and short decay times were observed for all complexes with mesacac ancillary ligands. The sterically demanding mesityl groups of the mesacac ligand effectively prevent molecular stacking. The emission behavior of these emitters is in general independent of the position of the nitrogen in the backbone of the N-heterocyclic carbene (NHC) unit and a variety of substituents in 4-position of the phenyl unit, meta to the cyclometalating bond. PMID:25884050

  8. Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions

    Science.gov (United States)

    2013-01-01

    The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)2(IMes)(MeCN)2(R)]BF4 and [Ir(H)2(IMes)(py)2(R)]BF4 [py = pyridine; R = PCy3 or PPh3; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene and a phosphine, are used here to catalyze SABRE. They react with acetonitrile and pyridine to produce [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4 and [Ir(H)2(NCMe)(py)(IMes)(PCy3)]BF4, complexes that undergo ligand exchange on a time scale commensurate with observation of the SABRE effect, which is illustrated here by the observation of both pyridine and acetonitrile HP. In this study, the required symmetry breaking that underpins SABRE is provided for by the use of chemical inequivalence rather than the previously reported magnetic inequivalence. As a consequence, we show that the ligand sphere of the polarization transfer catalyst itself becomes hyperpolarized and hence that the high-sensitivity detection of a number of reaction intermediates is possible. These species include [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4, [Ir(H)2(MeOH)(py)(IMes)(PPh3)]BF4, and [Ir(H)2(NCMe)(py)2(PPh3)]BF4. Studies are also described that employ the deuterium-labeled substrates CD3CN and C5D5N, and the labeled ligands P(C6D5)3 and IMes-d22, to demonstrate that dramatically improved levels of HP can be achieved as a consequence of reducing proton dilution and hence polarization wastage. By a combination of these studies with experiments in which the magnetic field experienced by the sample at the point of polarization transfer is varied, confirmation of the resonance assignments is achieved. Furthermore, when [Ir(H)2(pyridine-h5)(pyridine-d5)(IMes)(PPh3)]BF4 is examined, its hydride ligand signals are shown to become visible through para-hydrogen-induced polarization rather than SABRE. PMID:24215616

  9. Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

    Science.gov (United States)

    Tubaro, Cristina; Baron, Marco; Basato, Marino

    2013-01-01

    Summary Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC) ligands have been employed as catalysts in the intermolecular hydroarylation of alkynes with simple unfunctionalised arenes. Both mono- and dinuclear gold(III) complexes were able to catalyze the reaction; however, the best results were obtained with the mononuclear gold(I) complex IPrAuCl. This complex, activated with one equivalent of silver tetrafluoroborate, exhibited under acidic conditions at room temperature much higher catalytic activity and selectivity compared to more commonly employed palladium(II) catalysts. Moreover, the complex was active, albeit to a minor extent, even under neutral conditions, and exhibited lower activity but higher selectivity compared to the previously published complex AuCl(PPh3). Preliminary results on intramolecular hydroarylations using this catalytic system indicate, however, that alkyne hydration by traces of water may become a serious competing reaction. PMID:23400639

  10. Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

    Directory of Open Access Journals (Sweden)

    Cristina Tubaro

    2013-02-01

    Full Text Available Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC ligands have been employed as catalysts in the intermolecular hydroarylation of alkynes with simple unfunctionalised arenes. Both mono- and dinuclear gold(III complexes were able to catalyze the reaction; however, the best results were obtained with the mononuclear gold(I complex IPrAuCl. This complex, activated with one equivalent of silver tetrafluoroborate, exhibited under acidic conditions at room temperature much higher catalytic activity and selectivity compared to more commonly employed palladium(II catalysts. Moreover, the complex was active, albeit to a minor extent, even under neutral conditions, and exhibited lower activity but higher selectivity compared to the previously published complex AuCl(PPh3. Preliminary results on intramolecular hydroarylations using this catalytic system indicate, however, that alkyne hydration by traces of water may become a serious competing reaction.

  11. N-Heterocyclic Carbene Complexes in other Transition Metal Mediated Reactions

    Science.gov (United States)

    Nixon, Tracy D.; Williams, Jonathan M. J.

    This chapter describes reactions involving NHC-transition metal complexes that have not been considered in previous chapters. The reactions are treated in six sections, presenting borrowing hydrogen reactions where C-C and C-N bonds are formed from alcohols in the first section. Then dehydration reactions either with or without coupling are discussed. The dynamic kinetic resolution of alcohols using a combination of NHC-TM catalysed racemisation coupled with enzyme-catalysed resolution is described. The next section considers the emerging area of dehydrogenation reactions, followed by a section discussing the isomerisation of alkene-containing substrates. The final section details hydrogen/deuterium exchange reactions within aryl and alkyl substrates.

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

    Science.gov (United States)

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

    2014-06-15

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

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

    Science.gov (United States)

    Ison, Elon A.; Ison, Ana

    2012-01-01

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

  14. Stepwise strategy to cyclometallated Pt(II) complexes with N-heterocyclic carbene ligands: a luminescence study on new ?-diketonate complexes.

    Science.gov (United States)

    Fuertes, Sara; García, Hector; Perálvarez, Mariano; Hertog, Wim; Carreras, Josep; Sicilia, Violeta

    2015-01-19

    The imidazolium salt 3-methyl-1-(naphthalen-2-yl)-1H-imidazolium iodide (2) has been treated with silver(I) oxide and [{Pt(?-Cl)(?(3)-2-Me-C3H4)}2] (?(3)-2-Me-C3H4 = ?(3)-2-methylallyl) to give the intermediate N-heterocyclic carbene complex [PtCl(?(3)-2-Me-C3H4)(HCC*-?C*)] (3) (HCC*-?C* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene). Compound 3 undergoes regiospecific cyclometallation at the naphthyl ring of the NHC ligand to give the five-membered platinacycle compound [{Pt(?-Cl)(CC*)}2] (4). Chlorine abstraction from 4 with ?-diketonate Tl derivatives rendered the corresponding neutral compounds [Pt(CC*)(L-O,O')] {L = acac (HL = acetylacetone) 5, phacac (HL = 1,3-diphenyl-1,3-propanedione) 6, hfacac (HL = hexafluoroacetylacetone) 7}. All of the compounds (3-7) were fully characterized by standard spectroscopic and analytical methods. X-ray diffraction studies were performed on 5-7, revealing short Pt-Pt and ?-? interactions in the solid-state structure. The influence of the R-substituents of the ?-diketonate ligand on the photophysical properties and the use of the most efficient emitter, 5, as phosphor converter has also been studied. PMID:25412763

  15. Reactivity of coordinatively unsaturated bis(N-heterocyclic carbene) Pt(II) complexes toward H(2). Crystal structure of a 14-electron Pt(II) hydride complex.

    Science.gov (United States)

    Rivada-Wheelaghan, Orestes; Roselló-Merino, Marta; Ortuño, Manuel A; Vidossich, Pietro; Gutiérrez-Puebla, Enrique; Lledós, Agustí; Conejero, Salvador

    2014-04-21

    The reactivity toward H2 of coordinatively unsaturated Pt(II) complexes, stabilized by N-heterocyclic carbene (NHC) ligands, is herein analyzed. The cationic platinum complexes [Pt(NHC')(NHC)](+) (where NHC' stands for a cyclometalated NHC ligand) react very fast with H2 at room temperature, leading to hydrogenolysis of the Pt-CH2 bond and concomitant formation of hydride derivatives [PtH(NHC)2](+) or hydrido-dihydrogen complexes [PtH(H2)(NHC)2](+). The latter species release H2 when these compounds are subjected to vacuum. The X-ray structure of complex [PtH(IPr)2][SbF6] revealed its unsaturated nature, exhibiting a true T-shaped structure without stabilization by agostic interactions. Density functional theory calculations indicate that the binding and reaction of H2 in complexes [PtH(H2)(NHC)2](+) is more favored for derivatives bearing aryl-substituted NHCs (IPr, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene and IMes = 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene) than for those containing tert-butyl groups (I(t)Bu). This outcome is related to the higher close-range steric effects of the I(t)Bu ligands. Accordingly, H/D exchange reactions between hydrides [PtH(NHC)2](+) and D2 take place considerably faster for IPr and IMes* derivatives than for I(t)Bu ones. The reaction mechanisms for both H2 addition and H/D exchange processes depend on the nature of the NHC ligand, operating through oxidative addition transition states in the case of IPr and IMes* or by a ?-complex assisted-metathesis mechanism in the case of I(t)Bu. PMID:24716606

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

    DEFF Research Database (Denmark)

    Ka?ß, Martina; Hohenberger, Johannes

    2014-01-01

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

  17. Macrophage and colon tumor cells as targets for a binuclear silver(I) N-heterocyclic carbene complex, an anti-inflammatory and apoptosis mediator.

    Science.gov (United States)

    Iqbal, Muhammad Adnan; Umar, Muhammad Ihtisham; Haque, Rosenani A; Khadeer Ahamed, Mohamed B; Asmawi, Mohd Zaini Bin; Majid, Amin Malik Shah Abdul

    2015-05-01

    Chronic inflammation intensifies the risk for malignant neoplasm, indicating that curbing inflammation could be a valid strategy to prevent or cure cancer. Cancer and inflammation are inter-related diseases and many anti-inflammatory agents are also used in chemotherapy. Earlier, we have reported a series of novel ligands and respective binuclear Ag(I)-NHC complexes (NHC=N-heterocyclic carbene) with potential anticancer activity. In the present study, a newly synthesized salt (II) and respective Ag(I)-NHC complex (III) of comparable molecular framework were prepared for a further detailed study. Preliminarily, II and III were screened against HCT-116 and PC-3 cells, wherein III showed better results than II. Both the compounds showed negligible toxicity against normal CCD-18Co cells. In FAM-FLICA caspase assay, III remarkably induced caspase-3/7 in HCT-116 cells most probably by tumor necrosis factor-alpha (TNF-?) independent intrinsic pathway and significantly inhibited in vitro synthesis of cytokines, interleukin-1 (IL-1) and TNF-? in human macrophages (U937 cells). In a cell-free system, both the compounds inhibited cyclooxygenase (COX) activities, with III being more selective towards COX-2. The results revealed that III has strong antiproliferative property selectively against colorectal tumor cells which could be attributed to its pro-apoptotic and anti-inflammatory abilities. PMID:25699476

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-06-07

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

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

    Science.gov (United States)

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

    2010-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    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(?4-C8H12) (3), {PhB(OxMe2)2ImMes}Rh(?4-C8H12) (4), {PhB(OxMe2)2ImMes}Rh(CO)2 (5), {PhB(OxMe2)2ImMes}Ir(?4-C8H12) (6), and {PhB(OxMe2)2ImMes}Ir(CO)2 (7) are synthesized along with ToMM(?4-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(?-Cl)(?2-C8H14)2]2 (M = Rh, Ir) provide {?4-PhB(OxMe2)2ImMes?CH2}Rh(?-H)(?-Cl)Rh(?2-C8H14)2 (10) and {PhB(OxMe2)2ImMes}IrH(?3-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 {?4-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.

  1. Highly efficient deep-blue emitters based on cis and trans N-heterocyclic carbene Pt(II) acetylide complexes: synthesis, photophysical properties, and mechanistic studies.

    Science.gov (United States)

    Zhang, Yuzhen; Blacque, Olivier; Venkatesan, Koushik

    2013-11-11

    We have synthesized cis and trans N-heterocyclic carbene (NHC) platinum(II) complexes bearing ?-alkynyl ancillary ligands, namely [Pt(dbim)2 (C?CR)2 ] [DBIM=N,N'-didodecylbenzimidazoline-2-ylidene; R=C6 H4 F (4), C6 H5 (5), C6 H2 (OMe)3 (6), C4 H3 S (7), and C6 H4 C?CC6 H5 (8)] and [Pt(ibim)2 (C?CC6 H5 )2 ] (9) (ibim=N,N'-diisopropylbenzimidazoline-2-ylidene), starting from [Pt(cod)(C?CR)2 ] (COD=cyclooctadiene) and 2?equivalents of [dbimH]Br ([ibimH]Br for complexes 9) in the presence of tBuOK and THF. Mechanistic investigations aimed at uncovering the cis to trans isomerization reaction have been performed on the representative cis complex 5?a [Pt(dbim)2 (C?CC6 H5 )2 ] and revealed the isomerization to progress smoothly in good yield when 5?a was treated with catalytic amounts of [Pt(cod)(C?CR)2 ] at 75?°C in THF or when 5?a was heated at 200?°C in the solid state under an inert atmosphere. Detailed examination of the reactions points to the possible involvement, in a catalytic fashion, of a solvent-stabilized Pt(II) dialkyne complex in the former case and a Pt(0) NHC complex in the latter case, for the transformation of the cis isomer to the corresponding trans complex. Thermal stability and the isomerization process in the solid state have been further investigated on the basis of TGA and DSC measurements. X-ray diffraction studies have been carried out to confirm the solid-state structures of 4?b, 5?a, 5?b, and 9?b. All of the synthesized dialkyne complexes 4-9 exhibit phosphorescence in solution, in the solid state at room temperature (RT), and also in frozen solvent glasses at 77?K. The emission wavelengths and quantum yields have been found to be highly tunable as a function of the alkynyl ligand. In particular, the trans isomer of complex 9 in a spin-coated film (10?wt?% in poly(methyl methacrylate), PMMA) exhibits a high phosphorescence quantum yield of 80?%, which is the highest reported for Pt(II) -based deep-blue emitters. Experimental observations and time-dependent density functional theory (TD-DFT) calculations are strongly indicative of the emission being mainly governed by metal-perturbed interligand ((3) IL) charge transfer. PMID:24108420

  2. Control of emission colour with N-heterocyclic carbene (NHC) ligands in phosphorescent three-coordinate Cu(I) complexes.

    Science.gov (United States)

    Krylova, Valentina A; Djurovich, Peter I; Conley, Brian L; Haiges, Ralf; Whited, Matthew T; Williams, Travis J; Thompson, Mark E

    2014-07-11

    A series of three phosphorescent mononuclear (NHC)-Cu(I) complexes were prepared and characterized. Photophysical properties were found to be largely controlled by the NHC ligand chromophore. Variation of the NHC ligand leads to emission colour tuning over 200 nm range from blue to red, and emission efficiencies of 0.16-0.80 in the solid state. PMID:24853355

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

    DEFF Research Database (Denmark)

    SØlvhØj, Amanda Birgitte; Madsen, Robert

    2011-01-01

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

  4. Organometallic rhenium(iii) chalcogenide clusters: coordination of N-heterocyclic carbenes.

    Science.gov (United States)

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

    2015-06-16

    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

  5. Calix[4]arenes with one and two N-linked imidazolium units as precursors of N-heterocyclic carbene complexes. Coordination chemistry and use in Suzuki-Miyaura cross-coupling.

    Science.gov (United States)

    Brenner, Eric; Matt, Dominique; Henrion, Mickaël; Teci, Matthieu; Toupet, Loïc

    2011-10-14

    The calix[4]arene-imidazolium salts 5-(3-butyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxy-calix[4]arene bromide (cone) (2), and 5,11-bis(3-alkyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxycalix[4]arene diiodide (cone) (R = methyl, 3a; R = n-butyl, 3b) have been synthesised. Reaction of 2 in dioxane with PdCl(2) in the presence of CsCO(3) and KBr (80 °C, 24 h) gives the carbene complex trans-[PdBr(2)(calix-monocarbene)(2)] (14), containing two N-heterocyclic carbene ligands derived from 2 (yield: 63%). Repeating the reaction in pyridine instead of dioxane gives the mixed pyridine-carbene complex trans-[PdBr(2)(calix-carbene)(pyridine)] (15) in 75% yield. Treatment of the bis-imidazolium salt 3a with [Pd(OAc)(2)] affords a chelate complex, trans-[PdI(2){calix-bis(carbene)}] (16), in which a metallo-(bis-carbene) fragment caps the upper rim of the calixarene basket. Complex 16, as well as its analogue 17, obtained from 3b, display apparent C(s)-symmetry in solution. This is not the case in the solid state, a single X-ray diffraction study carried out for 16 revealing a pinced cone structure for the calixarene skeleton, which reduces the symmetry to C(1). The chelate complex 17 shows poor activity in Suzuki-Miyaura cross-coupling of phenyl boronic acid and p-tolyl halides, an observation that suggests the presence of a strained metallocyclic unit preventing easy stereochemical rearrangement to an active species. Unlike 17, complexes 14 and 15 show good activities in cross-coupling. A comparative study using the carbene precursor 1-butyl-3-(2,6-diisopropylphenyl)imidazolium bromide (18), which is devoid of the receptor fragment, strongly suggests that the carbene ligands of 14 and 15 operate typically as bulky NHC-ligands. PMID:21879086

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

    KAUST Repository

    Manzini, Simone

    2015-03-01

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

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

    Directory of Open Access Journals (Sweden)

    Rob De Vreese

    2012-03-01

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

  8. Enantioselective all-carbon (4+2) annulation by N-heterocyclic carbene catalysis.

    Science.gov (United States)

    Candish, Lisa; Levens, Alison; Lupton, David W

    2014-10-15

    The enantioselective vinylogous Michael/aldol cascade is an underdeveloped approach to cyclohexenes. Herein we describe a highly enantioselective (most ? 98:2 er) and diastereoselective (all ? 15:1 dr) N-heterocyclic carbene catalyzed cycloisomerization of acyclic dienyl esters to cyclohexyl ?-lactones. Derivatizations avail cyclohexenes bearing four contiguous stereogenic centers, while mechanistic studies support olefin isomerization prior to cyclization. PMID:25252043

  9. Injection, transport, absorption and phosphorescence properties of a series of platinum (II) complexes with N-heterocyclic carbenes: a DFT and time-dependent DFT study.

    Science.gov (United States)

    Li, Leijiao; Liu, Xiaojuan; Feng, Jing; Song, Shuyan; Zhang, Hongjie

    2014-10-01

    The ground and excited states, charge injection/transport, and phosphorescence properties of five N?heterocyclic carbine-functionalized Pt(II) complexes were investigated by using the DFT method. By analyzing the nonradiative (k nr) rate constant and energies at [Formula: see text] and [Formula: see text] states, it is possible to forecast that BC5 with the pyrrole ligand has a higher phosphorescence quantum yield than any of the other four complexes. Thus, we consider that BC5 will be an efficient phosphorescent material that has balanced electron/hole-transport performance as well as high phosphorescence quantum yield. The calculated results indicate that, for the studied complexes, the nature of the ligand strongly affected the energy of the emissive state and was able to tune the emission color. We hope that our study will aid better understanding of the structure-property relationship of phosphorescent Pt (II) complexes and provide constructive information for designing novel and highly efficient OLED materials in the future. PMID:25227448

  10. Synthesis of ruthenium complexes having one or more N-heterocyclic carbene ligands supported on hybrid mesostructured silicas and their use in the hydrogenation of carbon dioxide

    OpenAIRE

    Baffert, Mathieu

    2011-01-01

    The goal of this PhD was to elaborate supported Ru-NHC catalytic materials based on hybrid organic-inorganic materials having imidazolium units perfectly distributed within a silica matrix. Passivation of these imidazolium materials followed by formation of NHC-carbene and reaction with [RuCl2(p-cymene)]2 provided these well-defined surface sites of general structures RuCl2(NHC)(L), where L was para-cymene (p-cymene) or THF depending on the reaction conditions, which could be further replaced...

  11. A theobromine derived silver N-heterocyclic carbene: synthesis, characterization, and antimicrobial efficacy studies on cystic fibrosis relevant pathogens.

    Science.gov (United States)

    Panzner, Matthew J; Hindi, Khadijah M; Wright, Brian D; Taylor, Jane B; Han, Daniel S; Youngs, Wiley J; Cannon, Carolyn L

    2009-09-21

    The increasing incidence of multidrug-resistant (MDR) pulmonary infections in the cystic fibrosis (CF) population has prompted the investigation of innovative silver based therapeutics. The functionalization of the naturally occurring xanthine theobromine at the N(1) nitrogen atom with an ethanol substituent followed by the methylation of the N(9) nitrogen atom gives the N-heterocyclic carbene precursor 1-(2-hydroxyethyl)-3,7,9-trimethylxanthinium iodide. The reaction of this xanthinium salt with silver acetate produces the highly hydrophilic silver carbene complex SCC8. The in vitro antimicrobial efficacy of this newly synthesized complex was evaluated with excellent results on a variety of virulent and MDR pathogens isolated from CF patients. A comparative in vivo study between the known caffeine derived silver carbene SCC1 and SCC8 demonstrated the ability of both complexes to improve the survival rates of mice in a pneumonia model utilizing the clinically isolated infectious strain of Pseudomonas aeruginosa PA M57-15. PMID:20449175

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

    Czech Academy of Sciences Publication Activity Database

    Turek, J.; Panov, I.; Horá?ek, Michal; ?ernošek, Z.; Pad?lková, Z.; R?ži?ka, A.

    2013-01-01

    Ro?. 32, ?. 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

  13. New aqua N-heterocyclic carbene Ru(II) complexes with two-electron process as selective epoxidation catalysts: an evaluation of geometrical and electronic effects.

    Science.gov (United States)

    Dakkach, Mohamed; Atlamsani, Ahmed; Parella, Teodor; Fontrodona, Xavier; Romero, Isabel; Rodríguez, Montserrat

    2013-05-01

    New ruthenium complexes with general formula [Ru(II)(T)(CN-Me)X](n+) (X = Cl(-) or H2O; T = 2,2':6',2?-terpyridine, trpy, or N,N-bis(2-pyridyl)ethylamine, bpea; CN-Me = N-methyl-N'-2-pyridylimidazolium) have been prepared. The complexes obtained have been characterized in solution by spectroscopic (1D- and 2D-NMR and UV-vis) techniques, mass spectrometry, and elemental analysis. The chloro complexes have also been characterized by X-ray diffraction analysis. The redox properties of all the compounds were studied by CV revealing, for the reported Ru-OH2 complexes, bielectronic Ru(IV/II) redox processes throughout a wide pH range. The catalytic activity of aquo complexes was evaluated in the epoxidation of olefins using PhIO as oxidant, displaying in general good yields and high selectivities for the epoxide product. The influence of electronic and geometrical factors on the spectroscopic and electrochemical properties as well as on the catalytic activity is discussed. PMID:23642180

  14. Accesses to electronic structures and the excited states of blue luminescent copper(I) complexes containing N-heterocyclic carbene ligands: a DFT/TDDFT exploitation.

    Science.gov (United States)

    Li, Qiang; Zhao, Feng; Xu, Shengxian; Xia, Hongying; Wang, Jinglan; Wang, Yibo

    2014-09-01

    The ground electronic states and photophysical properties of three designed Cu(I) complexes [Cu(ImNHC)(POP)](+) (1), [Cu(methyl-ImNHC)(POP)](+) (2), and [Cu(BenzImNHC)(POP)](+) (3); where [ImNHC?=?3-methyl-1-(pyridin-2-yl)-1H-imidazol-2-ylidene; methyl-ImNHC?=?3-methyl-1-(pyridin-2-ylmethyl)-1H-imidazol-2-ylidene; BenzImNHC?=?3-methyl-1-(pyridin-2-yl)-1H-benzimidazol-2-ylidene], have been investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The results reveal that the presence of the methylene spacer in the NHC ligands has a more direct effect on the distribution of frontier molecular orbitals while the elongation of ? conjugation provided by the fused imidazole in the NHC ligands has a negligible effect. The UV-vis absorption spectra of all the complexes are well produced by TD-DFT calculations based on the charge transfer amount calculations and the corresponding band assignments are discussed. Importantly, the triplet energy calculations demonstrated that complex 2 would be a highly efficient blue emitter with the deep-blue of 440 nm. PMID:25123713

  15. Photoswitchable organocatalysis: using light to modulate the catalytic activities of N-heterocyclic carbenes.

    Science.gov (United States)

    Neilson, Bethany M; Bielawski, Christopher W

    2012-08-01

    A 4,5-dithienylimidazolium salt was found to undergo electrocyclic isomerization upon exposure to UV radiation (?(irr) = 313 nm) under neutral and basic conditions; subsequent exposure to visible light reversed the reaction. Under ambient light and in the presence of base, the imidazolium species catalyzed transesterifications as well as amidations in a manner similar to those of previously reported N-heterocyclic carbene precatalysts. However, upon UV irradiation to effect the aforementioned photocyclization, the rate of the transesterification reaction between vinyl acetate and allyl alcohol was significantly attenuated (k(vis/UV) = 12.5), as was the rate of the condensation of ethyl acetate with aminoethanol (k(vis/UV) = 100). The rates of these reactions were successfully toggled between fast and slow states by alternating exposure to visible and UV light, respectively, thus demonstrating a rare example of a photoswitchable catalyst that operates via photomodulation of its electronic structure. PMID:22809240

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

    OpenAIRE

    Michael Nussbaum; Oliver Schuster; Martin Albrecht

    2014-01-01

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

  17. Synthesis of New Chiral N-Heterocyclic Carbenes and Abnormal Carbenes

    OpenAIRE

    Levy, Jean-Noel

    2011-01-01

    Chapter 1 Carbenes have fascinated organic chemists ever since the first evidence of their existence. The isolation and first crystallographic analysis of a stable NHC by Arduengo, in 1991, has had a major impact on the application of NHCs in chemistry. NHCs are widely used as ligands for transition metals, but also as catalysts in their own right. The aim of this project is to synthesise novel monodentate chiral NHCs 1 in order to induce a high level of stereocontrol in a s...

  18. A theobromine derived silver N-heterocyclic carbene: synthesis, characterization, and antimicrobial efficacy studies on cystic fibrosis relevant pathogens†

    OpenAIRE

    Panzner, Matthew J.; Hindi, Khadijah M.; Wright, Brian D.; Taylor, Jane B.; Han, Daniel S.; Youngs, Wiley J.; Cannon, Carolyn L.

    2009-01-01

    The increasing incidence of multidrug-resistant (MDR) pulmonary infections in the cystic fibrosis (CF) population has prompted the investigation of innovative silver based therapeutics. The functionalization of the naturally occurring xanthine theobromine at the N1 nitrogen atom with an ethanol substituent followed by the methylation of the N9 nitrogen atom gives the N-heterocyclic carbene precursor 1-(2-hydroxyethyl)-3,7,9-trimethylxanthinium iodide. The reaction of this xanthinium salt with...

  19. Palladium-catalyzed direct C2-arylation of an N-heterocyclic carbene: an atom-economic route to mesoionic carbene ligands.

    Science.gov (United States)

    Ghadwal, Rajendra S; Reichmann, Sven O; Herbst-Irmer, Regine

    2015-03-01

    Blocking the C2 position of an imidazole-derived classical N-heterocyclic carbene (NHC) with an aryl group is an essential strategy to establish a route to mesoionic carbenes (MICs), which coordinate to the metal via the C4 (or C5) carbon atom. An efficient catalytic route to MIC precursors by direct arylation of an NHC is reported. Treatment of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with an aryl iodide (RC6H4I) in the presence of 0.5?mol?% of [Pd2(dba)3] (dba = dibenzylideneacetone) precatalyst affords the C2-arylated imidazolium salts {IPr(C6H4R)}I (R = H, 4-Me, 2-Me, 4-OMe, 4-COOMe) in excellent (up to 92%) yields. Treatment of {IPr(C6H5)}I with CuI and KN(SiMe3)2 exclusively affords the MIC-copper complex [(IPrPh)CuI]. PMID:25639790

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

    Science.gov (United States)

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

    2015-02-01

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

  1. Planar N-heterocyclic carbene diarylborenium ions: synthesis by cationic borylation and reactivity with Lewis bases.

    Science.gov (United States)

    Farrell, Jeffrey M; Stephan, Douglas W

    2015-04-20

    The NHC-borane adduct (IBn)BH3 (1) (NHC= N-heterocyclic carbene; IBn=1,3-dibenzylimidazol-2ylidene) reacts with [Ph3 C][B(C6 F5 )4 ] through sequential hydride abstraction and dehydrogenative cationic borylation(s) to give singly or doubly ring closed NHC-borenium salts 2 and 3. The planar doubly ring closed product [C3 H2 (NCH2 C6 H4 )2 B][B(C6 F5 )4 ] is resistant to quaternization at boron by Et2 O coordination, but forms classical Lewis acid-base adducts with the stronger donors Ph3 P, Et3 PO, or 1,4-diazabicyclo[2.2.2]octane (DABCO). Treatment of 3 with tBu3 P selectively yields the unusual oligomeric borenium salt trans-[(C3 H2 (NCH2 C6 H4 )2 B)2 (C3 H2 (NCHC6 H4 )2 B)][B(C6 F5 )4 ] (7). PMID:25756464

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

    DEFF Research Database (Denmark)

    Makarov, Ilya; Fristrup, Peter

    2012-01-01

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

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

    Science.gov (United States)

    Nussbaum, Michael; Schuster, Oliver; Albrecht, Martin

    2013-12-16

    A ditopic benzobis(carbene) ligand precursor was prepared that contained a chelating pyridyl moiety to ensure co-planarity of the carbene ligand and the coordination plane of a bound octahedral metal center. Bimetallic ruthenium complexes comprising this ditopic ligand [L4Ru-C,N-bbi-C,N-RuL4] were obtained by a transmetalation methodology (C,N-bbi-C,N=benzobis(N-pyridyl-N'-methyl-imidazolylidene). The two metal centers are electronically decoupled when the ruthenium is in a pseudotetrahedral geometry imparted by a cymene spectator ligand (L4=[(cym)Cl]). Ligand exchange of the Cl(-)/cymene ligands for two bipyridine or four MeCN ligands induced a change of the coordination geometry to octahedral. As a consequence, the ruthenium centers, separated through space by more than 10 Å, become electronically coupled, which is evidenced by two distinctly different metal-centered oxidation processes that are separated by 134 mV (L4=[(bpy)2]; bpy=2,2'-bipyridine) and 244 mV (L4=[(MeCN)4]), respectively. Hush analysis of the intervalence charge-transfer bands in the mixed-valent species indicates substantial valence delocalization in both complexes (delocalization parameter ?=0.41 and 0.37 in the bpy and MeCN complexes, respectively). Spectroelectrochemical measurements further indicated that the mixed-valent Ru(II)/Ru(III) species and the fully oxidized Ru(III)/Ru(III) complexes gradually decompose when bound to MeCN ligands, whereas the bpy spectators significantly enhance the stability. These results demonstrate the efficiency of carbenes and, in particular, of the bbi ligand scaffold for mediating electron transfer and for the fabrication of molecular redox switches. Moreover, the relevance of spectator ligands is emphasized for tailoring the degree of electronic communication through the benzobis(carbene) linker. PMID:24218243

  4. N-Heterocyclic Carbene-Catalyzed Oxidative Annulations of ?,?-Unsaturated Aldehydes with Hydrazones: Selective Synthesis of Optically Active 4,5-Dihydropyridazin-3-ones and Pyridazin-3-ones.

    Science.gov (United States)

    Mao, Jian-Hui; Wang, Zi-Tian; Wang, Zhan-Yong; Cheng, Ying

    2015-06-19

    A novel and efficient method for the highly enantioselective synthesis of chiral 4,5-dihydropyridazin-3-one derivatives has been developed based on the chiral N-heterocyclic carbene-catalyzed oxidative annulation between ?,?-unsaturated aldehydes and hydrazones. Meanwhile, the selective synthesis of either 4,5-dihydropyridazin-3-ones or pyridazin-3-one derivatives from the same reactants has been achieved by simply varying catalytic and reaction conditions. PMID:26019007

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

    Science.gov (United States)

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

    2015-06-22

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

  6. Synthesis and Characterization of Di- and Tetracarbene Iron(II) Complexes with Chelating N-Heterocyclic Carbene Ligands and Their Application in Aryl Grignard–Alkyl Halide Cross-Coupling

    OpenAIRE

    Meyer, Steffen; Orben, Claudia Manuela; Demeshko, Serhiy; Dechert, Sebastian; Meyer, Franc

    2011-01-01

    A series of new and known bis(imidazolium) chloride and bromide salts bridged by either a methylene group (1?8, 10a,b) or an ethylene group (9a,b) and bearing different N substituents (Me, Et, Bn, tBu, Mes) have been reacted with [Fe{N(SiMe3)2}2]2 to yield the four-coordinate iron(II) complexes [LFeX2] (11?20; X = Cl, Br; L = chelating bis(imidazolylidene) ligand). Molecular structures of six of these complexes have been characterized by X-ray crystallography, and ...

  7. Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl

    Directory of Open Access Journals (Sweden)

    Hintermann Lukas

    2007-08-01

    Full Text Available Abstract The 1,3-diaryl-imidazolium chlorides IPr·HCl (aryl = 2,6-diisopropylphenyl, IMes·HCl (aryl = 2,4,6-trimethylphenyl and IXy·HCl (aryl = 2,6-dimethylphenyl, precursors to widely used N-heterocyclic carbene (NHC ligands and catalysts, were prepared in high yields (81%, 69% and 89%, respectively by the reaction of 1,4-diaryl-1, 4-diazabutadienes, paraformaldehyde and chlorotrimethylsilane in dilute ethyl acetate solution. A reaction mechanism involving a 1,5-dipolar electrocyclization is proposed.

  8. 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.

    Science.gov (United States)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    Miller, Kevin L; Williams, Bryan N; Benitez, Diego; Carver, Colin T; Ogilby, Kevin R; Tkatchouk, Ekaterina; Goddard, William A; Diaconescu, Paula L

    2010-01-01

    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.

  10. Catalytic hydrodechlorination of benzyl chloride promoted by Rh-N-heterocyclic carbene catalysts.

    Science.gov (United States)

    Lázaro, Guillermo; Polo, Víctor; Fernández-Alvarez, Francisco J; García-Orduña, Pilar; Lahoz, Fernando J; Iglesias, Manuel; Pérez-Torrente, Jesús J; Oro, Luis A

    2015-02-01

    The rhodium(I) complexes [Rh(Cl)(COD)(R-NHC-(CH2 )3 Si(OiPr)3 )] [COD=cyclooctadiene; R=2,6-diisopropylphenyl (1?a); n-butyl (1?b)] are effective catalyst precursors for the homogeneous hydrodechlorination of benzyl chloride using HSiEt3 as hydrogen source. This reaction is selective to the formation of toluene. However, in presence of a stoichiometric amount of potassium tert-butoxide (KtBuO) the formation of mixtures containing toluene together with 17-19?mol?% of the C--C homocoupling product, namely PhCH2 CH2 Ph, is observed. A mechanism proposal based on experimental insights and theoretical calculations at the DFT level that allows explanation of the experimental findings is included. Moreover, the heterogeneous catalytic system based on catalyst 1?a supported on MCM-41 has been demonstrated to be effective for the solvent-free hydrodechlorination of benzyl chloride using HSiEt3 and HSiMe(OSiMe3 )2 . PMID:25504980

  11. (C^C*) Cyclometalated binuclear N-heterocyclic biscarbene platinum(II) complexes--highly emissive phosphorescent emitters.

    Science.gov (United States)

    Tronnier, Alexander; Strassner, Thomas

    2013-07-21

    A series of bimetallic N-heterocyclic carbene (NHC) platinum(II) complexes with the general formula [Pt(NHC)(L)]2Ph were synthesized, which are composed of two [Pt(NHC)(L)] (L = acetylacetone, dipivaloylmethane or dimesitoylmethane; NHC = 3-methylimidazole or 3-benzylimidazole) fragments. Both fragments are cyclometalated to the same central phenyl ring in the para- or meta-position. All complexes have been fully characterized by standard techniques, two of them additionally by solid-state structures. Photoluminescence properties were investigated and very high quantum yields of 76-93% at room temperature have been observed. For a single-matrix device with an emitter concentration of 30%, a current efficiency of 25 cd A(-1), an external quantum efficiency of 8.5%, and a luminance efficiency of 10 lm W(-1) were achieved at 300 cd m(-2). Density functional theory (DFT) calculations were performed to support experimental data and gain further insight into the photoluminescence behaviour. PMID:23689316

  12. Dinuclear gold(I) complexes with propylene bridged N-heterocyclic dicarbene ligands: synthesis, structures, and trends in reactivities and properties.

    Science.gov (United States)

    Tubaro, Cristina; Baron, Marco; Costante, Michele; Basato, Marino; Biffis, Andrea; Gennaro, Armando; Isse, Abdirisak Ahmed; Graiff, Claudia; Accorsi, Gianluca

    2013-08-14

    Four novel dinuclear N-heterocyclic dicarbene gold(I) complexes with a propylene linker between the carbene moieties have been synthesized and their luminescence and electrochemical properties, together with their reactivity towards bromine oxidative addition, have been screened. All the complexes emit in the solid state in the blue-green spectral range (400-500 nm) with appreciable intensities (?(em) up to ?10%). In cyclic voltammetry, the Au(I)/Au(0) peak splits at low temperature into two separate peaks relative to the couples Au(I)-Au(I)/Au(I)-Au(0) and Au(I)-Au(0)/Au(0)-Au(0), thus indicating the presence of an Au···Au interaction in the dinuclear complex. Oxidative addition of bromine affords as a major or unique product Au(II)-Au(II) complexes most likely as a consequence of the interaction between the two gold centres favoured by the propylene linker. PMID:23788178

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

    Czech Academy of Sciences Publication Activity Database

    Polyakova, Svetlana; Kunetskiy, Roman Alexejevi?; Schröder, Detlef

    -, ?. 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. Ruthenium Nitrosyl Complexes with N-Heterocyclic Ligands.

    Science.gov (United States)

    Borges, Simone da S. S.; Davanzo, Celso U.; Castellano, Eduardo E.; Z-Schpector, Julio; Silva, Sebastião C.; Franco, Douglas W.

    1998-06-01

    A new route was developed for preparing a series of trans nitrosyl complexes of general formula trans-[Ru(NH(3))(4)L(NO)](BF(4))(3), where L = imidazole, L-histidine, pyridine, or nicotinamide. The complexes have been characterized by elemental analysis, molar conductance measurements, UV-visible, infrared, proton nuclear magnetic, and electron paramagnetic resonance spectroscopies, and electrochemical techniques. The compounds possess relatively high nu(NO) stretching frequencies indicating that a high degree of positive charge resides on the coordinated nitrosyl group. The nitrosyl complexes react with OH(-) according to the equation trans-[Ru(NH(3))(4)L(NO)](3+) + 2OH(-) right arrow over left arrow trans-[Ru(NH(3))(4)L(NO(2))](+) + H(2)O, with a K(eq) (at 25.0 degrees C in 1.0 mol/L NaCl) of 2.2 x 10(5), 5.9 x 10(7), 9.7 x 10(10), and 4.6 x 10(13) L(2) mol(-)(2) for the py, nic, imN, and L-hist complexes, respectively. Only one redox process attributed to the reaction [Ru(II)(NH(3))(4)L(NO(+))](3+) + e(-) right arrow over left arrow trans-[Ru(II)(NH(3))(4)L(NO(0))](2+) was observed in the range -0.45 to 1.20 V for all the nitrosyl complexes. Linear correlations are observed in plots of nu(NO) versus E(1/2) and of E(1/2) versus summation operatorE(L) showing that the oxidizing strength of the coordinated NO increases with increase in L pi-acidity. The crystal structure analysis of trans-[Ru(NH(3))(4)nicNO](2)(SiF(6))(3) shows that the mean Ru-N-O angle is very close to 180 degrees (177 +/- 1 degrees ) and the mean N-O distance is 1.17 +/- 0.02 Å, thus confirming the presence of the Ru(II)-NO(+) moiety in the nitrosyl complexes studied. PMID:11670402

  15. A diruthenium ?-carbido complex that shows singlet-carbene-like reactivity.

    Science.gov (United States)

    Takemoto, Shin; Ohata, Jun; Umetani, Kento; Yamaguchi, Masahiro; Matsuzaka, Hiroyuki

    2014-11-12

    Low-temperature deprotonation of the cationic ?-methylidyne complex [(Cp*Ru)2(?-NPh)(?-CH)][BF4] (Cp* = ?(5)-C5Me5) with KN(SiMe3)2 affords a thermally unstable ?-carbido complex [(Cp*Ru)2(?-NPh)(?-C)] (2), as evidenced by trapping experiments with elemental S or Se and (13)C NMR spectroscopic observation. The reactivity of 2 toward CO2, Ph2S(+)CH2(-), EtOH, and an intramolecular C-H bond indicates that the ?-carbido carbon in 2 has an ambiphilic (nucleophilic and electrophilic) nature consistent with the formulation of 2 as the first example of a transition-metal-substituted singlet carbene. DFT study suggests that the Ru substituents in 2 are stronger ?-donor and weaker ?-donor to the carbene center than amino substituents in N-heterocyclic carbenes. PMID:25365114

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

    Directory of Open Access Journals (Sweden)

    ?lknur Özdemir

    2010-04-01

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

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

    Science.gov (United States)

    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 ?-methyl-?-methylene-?-butyrolactone (MMBL). For MMA, there exhibits an exquisite selectivity of the NHC structure for the three types of reactions it promotes: enamine formation (single-monomer addition) by IMes, dimerization (tail-to-tail) by TPT, and polymerization by 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

  18. N-Heterocyclic carbene–palladium catalysts for the direct arylation of pyrrole derivatives with aryl chlorides

    Directory of Open Access Journals (Sweden)

    Ismail Özdemir

    2013-02-01

    Full Text Available New Pd–NHC 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.

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

    Gonell, Sergio; Poyatos, Macarena; Peris, Eduardo

    2014-07-28

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

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

    KAUST Repository

    Vummaleti, Sai V. C.

    2015-01-02

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

  2. A cationic zinc hydride cluster stabilized by an N-heterocyclic carbene: synthesis, reactivity, and hydrosilylation catalysis.

    Science.gov (United States)

    Rit, Arnab; Zanardi, Alessandro; Spaniol, Thomas P; Maron, Laurent; Okuda, Jun

    2014-11-24

    The trinuclear cationic zinc hydride cluster [(IMes)3Zn3H4(THF)](BPh4)2 (1) was obtained either by protonation of the neutral zinc dihydride [(IMes)ZnH2]2 with a Brønsted acid or by addition of the putative zinc dication [(IMes)Zn(THF)](2+). A triply bridged thiophenolato complex 2 was formed upon oxidation of 1 with PhS-SPh. Protonolysis of 1 by methanol or water gave the corresponding trinuclear dicationic derivatives. At ambient temperature, 1 catalyzed the hydrosilylation of aldehydes, ketones, and nitriles. Carbon dioxide was also hydrosilylated under forcing conditions when using (EtO)3SiH, giving silylformate as the main product. PMID:25257989

  3. Removing the sting from the tail: reversible protonation of scorpionate ligands in cobalt(II) tris(carbene)borate complexes.

    Science.gov (United States)

    Cowley, Ryan E; Bontchev, Ranko P; Duesler, Eileen N; Smith, Jeremy M

    2006-11-27

    Low-temperature deprotonation of the phenylborane dications, PhB(RIm)3OTf2 (R = tBu, Mes), followed by in situ reaction with CoCl2(thf)1.5, results in the formation of the four-coordinate complexes, kappa3-PhB(RIm)3CoCl, in which the metal is supported by tripodal N-heterocyclic carbene-based ligands. The chloride complexes are exceptionally sensitive to acid and can be reversibly protonated to form the zwitterions kappa2-{PhB(RIm)2(RIm.H)}CoCl2. This unexpected reactivity is attributed to the highly basic nature of the tris(carbene)borate ligands. Reaction of the chloride complexes with methylating reagents results in products that depend on the N-heterocyclic carbene substituent. For R = tBu, the four-coordinate high-spin complex, kappa3-PhB(tBuIm)3CoMe, is formed, while for R = Mes, reduction to a multitude of complexes occurs. PMID:17112274

  4. Syntheses, structural, computational, and thermal analysis of acid-base complexes of picric acid with N-heterocyclic bases.

    Science.gov (United States)

    Goel, Nidhi; Singh, Udai P

    2013-10-10

    Four new acid-base complexes using picric acid [(OH)(NO2)3C6H2] (PA) and N-heterocyclic bases (1,10-phenanthroline (phen)/2,2';6',2"-terpyridine (terpy)/hexamethylenetetramine (hmta)/2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz)) were prepared and characterized by elemental analysis, IR, NMR and X-ray crystallography. Crystal structures provide detailed information of the noncovalent interactions present in different complexes. The optimized structures of the complexes were calculated in terms of the density functional theory. The thermolysis of these complexes was investigated by TG-DSC and ignition delay measurements. The model-free isoconversional and model-fitting kinetic approaches have been applied to isothermal TG data for kinetics investigation of thermal decomposition of these complexes. PMID:24011225

  5. Enyne Metathesis Catalyzed by Ruthenium Carbene Complexes

    DEFF Research Database (Denmark)

    Poulsen, Carina Storm; Madsen, Robert

    2003-01-01

    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 development and synthetic applications.

  6. Uranium(IV) nucleophilic carbene complexes

    International Nuclear Information System (INIS)

    The mono-, bis-, and tris-carbene uranium complexes [Li(THF)2U(SCS)Cl3(THF)] (2a), [U(SCS)2(THF)2] (3a), and [{Li(OEt2)}2U(SCS)3] (1) were synthesized in good yields by reactions of UCl4 and the stoichiometric amount of Li2(SCS) [(SCS)2 = [Ph2P(dS)]2C2]. Complex 3a was also obtained by comproportionation reaction of 1 and 0.5 molar equiv of UCl4 and further reacted with 1 molar equiv of UCl4 to give the neutral mono-carbene [U(SCS)Cl2(THF)2] (5a). Treatment of U(NEt2)4 with H2C(Ph2PS)2 in THF led to a mixture of 3a and [U(SCS)(NEt2)2] (6), while the same reaction in Et2O gave the mixed alkyl-carbene compound [U(SCS)(SCHS)(NEt2)] (7) in 85% yield. The cationic uranium carbene complex [U(SCS)(NEt2)(THF)3][BPh4] (9) was isolated in almost quantitative yield from reaction of [U(NEt2)3][BPh4] and H2C(Ph2PS)2. Mono-carbenes 2a, 5a, and 9 were used as precursors for the synthesis of Cp and COT derivatives (Cp = C5H5, COT=C8H8). Treatment of 2a with 1 or 2 molar equiv of TlCp gave [Tl{U(Cp)(SCS)}2(?-Cl)3] (10) and [U(Cp)2(SCS)] (11) in 90% and 79% yield, respectively, whereas [U(Cp*)2(SCS)] (12) (Cp* = C5Me5) was obtained only by reaction of [U(Cp*)2Cl2] and Li2(SCS). Reactions of 5a or 9 with K2COT gave [U(COT)(SCS)(THF)] (13) in 78% and 99% yield, respectively. 2a, [Li(THF)(Et2O)U(SCS)(?-Cl)3]2 (2b), [U(SCS)2(py)2] 3 1.5py 3 0.5THF (3b 3 1.5py 3 0.5THF), [U(SCS){CS(Ph2PS)2}(py)] (4), 7.toluene, [Li(THF)2U(SCS)(NEt2)(?-O)]2 (8), 10.2 toluene, 11, 12, and 13.0.5 pentane were characterized by X-ray diffraction. The crystal data revealed that, in contrast to transition metal complexes, changes in the coordination sphere of the U(IV) center have little influence on the U(double bond)C bond. This feature was explained by DFT analysis of analogous U(IV) and Zr(IV) compounds [M(SCS1)Cl2(py)2] and [M(SCS1)(Cp)2] [M = U, Zr; SCS1 = C(H2PS)2]. Although the 5f orbitals are more radially contracted than the 6d atomic orbitals, the 5f AOs are lower in energy in uranium and can lead to greater angular overlaps in symmetry-constrained systems. As a result, the seven 5f orbitals play a 'buffer' role by engaging in covalent interactions with the carbon center to stabilize the nucleophilic carbene lone pairs. (authors)

  7. Axial ligand exchange of N-heterocyclic cobalt(III) Schiff base complexes: molecular structure and NMR solution dynamics.

    Science.gov (United States)

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

    2013-01-18

    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 protein, and consequently alters structure and causes inhibition. To guide the rational design of next generation agents, understanding the mechanism and dynamics of the ligand exchange process is essential. To investigate the lability, pH stability, and axial ligand exchange of these complexes in the absence of proteins, the pD- and temperature-dependent axial ligand substitution dynamics of a series of N-heterocyclic [Co(acacen)(X)(2)](+) complexes [where X = 2-methylimidazole (2MeIm), 4-methylimidazole (4MeIm), ammine (NH(3)), N-methylimidazole (NMeIm), and pyridine (Py)] were characterized by NMR spectroscopy. The pD stability was shown to be closely related to the nature of the axial ligand with the following trend toward aquation: 2MeIm > NH(3) ? 4MeIm > Py > Im > NMeIm. Reaction of each [Co(III)(acacen)(X)(2)](+) derivative with 4MeIm showed formation of a mixed ligand Co(III) intermediate via a dissociative ligand exchange mechanism. The stability of the mixed ligand adduct was directly correlated to the pD-dependent stability of the starting Co(III) Schiff base with respect to [Co(acacen)(4MeIm)(2)](+). Crystal structure analysis of the [Co(acacen)(X)(2)](+) derivatives confirmed the trends in stability observed by NMR spectroscopy. Bond distances between the Co(III) and the axial nitrogen atoms were longest in the 2MeIm derivative as a result of distortion in the planar tetradentate ligand, and this was directly correlated to axial ligand lability and propensity toward exchange. PMID:23282130

  8. Intramolecular cyclopropanation reactions of chromium (alkenyloxy)carbene complexes

    Energy Technology Data Exchange (ETDEWEB)

    Soederberg, B.C.; Hegedus, L.S. (Colorado State Univ., Fort Collins (United States))

    1990-12-01

    Chromium (aryl)(alkenyloxy)carbene complexes underwent intramolecualr cyclopropanation reactions under mild conditions. Evidence for the intervention of metathesis/readdition and for twist' addition followed by {beta}-hydride elimiantion/reductive elimination was obtained. Carbenes of this class, sufficiently stable to isolate, underwent facile photochemical intramolecualr cyclobutanone formation. Molecular structures were determined by {sup 1}H and {sup 13}C NMR spectroscopy.

  9. Directional properties of fluorenylidene moieties in unsymmetrically substituted N-heterocyclic carbenes. Unexpected CH activation of a methylfluorenyl group with palladium. Use in palladium catalysed Suzuki-Miyaura cross coupling of aryl chlorides.

    Science.gov (United States)

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

    2014-08-28

    Benzimidazolium salts having their two nitrogen atoms substituted by different 9-alkylfluorenyl groups ( and , alkyl(1)/alkyl(2) = Me/Et, Me/Pr, Me/n-Bu, Me/i-Pr, Me/Bn, Me/CH2SMe have been synthesised in high yields in two or three steps from N,N'-bis(9H-fluoren-9-ylidene)benzene-1,2-diamine (). The imidazolium salts were converted readily into the corresponding PEPPSI-type palladium complexes (PEPPSI = pyridine-enhanced precatalyst preparation stabilisation and initiation), while reaction of the methylthioether-substituted salt with PdCl2/K2CO3/pyridine afforded the palladacycle resulting from metallation of the methyl group attached to the fluorenylidene moiety. NMR and X-ray diffraction studies revealed that the carbene ligands in behave as clamp-like ligands, the resulting metal confinement arising from a combination of the orientational properties of the fluorenylidene moieties that push the alkyl groups towards the metal centre and attractive anagostic interactions involving CH2(fluorenyl) groups. Complexes were assessed in Suzuki-Miyaura cross-coupling reactions. Like their symmetrical analogues they displayed high activity in the coupling of phenyl boronic acid with p-tolylchloride but their performance remained slightly inferior to that of the related, symmetrical Et/Et complex . PMID:24927082

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

    OpenAIRE

    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 ...

  11. Formation of quinones, indanones and furans by the reaction of molybdenum carbene complexes with alkynes

    International Nuclear Information System (INIS)

    (Alkoxy)carbene complexes of molybdenum react with terminal alkynes to give carbene annulation of cycloaddition products, the skeleton of which depends on the carbene substitution pattern and the alkyne used. (CO)5Mo=C(OMe)-p-tol undergoes carbene annulation upon reaction with trimethylsilylacetylene leading to naphthoquinone after oxidative work-up. Similar products are obtained from (CO)5Mo=C(OMe)2-furyl and hex-1-yne or oct-1-yne. The reaction of these alkynes results in the formation of indanones as five-membered annulation products. In the presence of 3.3-dimethylbut-1-yne the (phenyl) carbene ligands act as a C1-synthon, which is incorporated into the furan cycloaddition products

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

    Czech Academy of Sciences Publication Activity Database

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

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

  13. Carbene complexes with two chromium central atoms: relationship between structure and redox properties.

    Czech Academy of Sciences Publication Activity Database

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

    Prague : International Society of Electrochemistry, 2012. [Annual ISE Meeting /63./. 19.08.2012-24.08.2012, Prague] Institutional support: RVO:61388955 Keywords : carbene complexes * redox properties * electrochemistry Subject RIV: CG - Electrochemistry

  14. Carbene-metal hydrides can be much less acidic than phosphine-metal hydrides: significance in hydrogenations.

    Science.gov (United States)

    Zhu, Ye; Fan, Yubo; Burgess, Kevin

    2010-05-01

    Acidities of iridium hydride intermediates were shown to be critical in some transformations mediated by the chiral analogues of Crabtree's catalyst, 1-3. To do this, several experiments were undertaken to investigate the acidities of hydrogenation mixtures formed using these iridium-oxazoline complexes. DFT calculations indicated that the acidity difference for Ir-H intermediates in these hydrogenations were astounding; iridium hydride from the N-heterocyclic carbene catalyst 1 was calculated to be around seven pK(a) units less acidic than those from the P-based complexes 2 and 3. Consistent with this, the carbene complex 1 was shown to be more effective for hydrogenations of acid-sensitive substrates. In deuteration experiments, less "abnormal" deuteration was observed, corresponding to fewer complications from acid-mediated alkene isomerization preceding the D(2)-addition step. Finally, simple tests with pH indicators provided visual evidence that phosphine-based catalyst precursors give significantly more acidic reaction mixtures than the corresponding N-heterocyclic carbene ones. These observations indicate carbene-for-phosphine (and similar) ligand substitutions may impact the outcome of catalytic reactions by modifying the acidities of the metal hydrides formed. PMID:20377250

  15. Substitution effects on the formation of T-shaped palladium carbene and thioketone complexes from Li/Cl carbenoids.

    Science.gov (United States)

    Molitor, Sebastian; Feichtner, Kai-Stephan; Kupper, Claudia; Gessner, Viktoria H

    2014-08-18

    The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd(0) precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moiety (by negative hyperconjugation effects) and the remaining negative charge at the carbenic carbon atom, isolation of a three-coordinate, T-shaped palladium carbene complex is possible. In contrast, insufficient charge stabilization results in the transfer of the sulfur of the thiophosphoryl moiety and thus in the formation of a thioketone complex. While the thioketones are stable compounds the carbene complexes are revealed to be highly reactive and decompose under elimination of Pd metal. Computational studies revealed that both complexes are formed by a substitution mechanism. While the ketone turned out to be the thermodynamically favored product, the carbene is kinetically favored and thus preferentially formed at low reaction temperatures. PMID:24664573

  16. Carbene complexes with two chromium central atoms: relationship between structure and redox properties.

    Czech Academy of Sciences Publication Activity Database

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

    Lisbon : Technical University of Lisbon, 2012. [International Conference on Organometallic Chemistry /25./. 02.09.2012-07.09.2012, Lisbon] Grant ostatní: GA MŠk(CZ) 21/2012 Institutional support: RVO:61388955 Keywords : carbene complexes * redox properties * chromium central atoms Subject RIV: CG - Electrochemistry

  17. Synthesis, characterization, and structural studies of multimetallic ferrocenyl carbene complexes of group VII transition metals.

    Science.gov (United States)

    Bezuidenhout, Daniela I; Lotz, Simon; Landman, Marilé; Liles, David C

    2011-02-21

    Fischer carbene complexes of the group VII transition metals (Mn and Re) containing at least two or three different transition metal substituents, all in electronic contact with the carbene carbon atom, were synthesized. The structural features and their relevance to bonding in the carbene multimetal compounds were investigated, as they represent indicators of possible reactivity sites in polymetallic carbene assemblies. For complexes of the type [ML(x){C(OR)R'}] (ML(x) = MnCp(CO)(2) or Re(2)(CO)(9)), ferrocenyl (Fc) was chosen as the R' substituent, while the OR substituent was systematically varied between an ethoxy or a titanoxy group, to yield the complexes 1a (ML(x) = MnCp(CO)(2), R = Et, R' = Fc), 2a (ML(x) = MnCp(CO)(2), R = TiCp(2)Cl, R' = Fc), 3a (ML(x) = Re(2)(CO)(9), R = Et, R' = Fc), and 4a (ML(x) = Re(2)(CO)(9), R = TiCp(2)Cl, R' = Fc). Direct lithiation of the ferrocene with n-BuLi/TMEDA at elevated temperatures, followed by the Fischer method of carbene preparation, resulted in formation of the novel biscarbene complexes with bridging ferrocen-1,1'-diyl (Fc') substituents [{?-Fe(C(5)H(4))(2)-C,C'}{C(OEt)ML(x)}(2)] (1b, ML(x) = MnCp(CO)(2); 3b, ML(x) = Re(2)(CO)(9)) or the unusual bimetallacyclic bridged biscarbene complexes [{?-TiCp(2)O(2)-O,O'}{?-Fe(C(5)H(4))(2)-C,C'}{CML(x)}(2)] (2b, ML(x) = MnCp(CO)(2); 4b, ML(x) = Re(2)(CO)(9)). The target compounds that were isolated displayed a variety of different geometric isomers and conformations. The greater reactivity of the binary dirhenium acylates in solution, compared to that of the cyclopentadienyl manganese acylate, resulted in a complex reaction mixture. Although the stabilization of hydroxycarbene or hydrido-acyl intermediates of dirhenium carbonyls could not be achieved, their existence in solution was confirmed by the isolation of [(?-H)(2)-(Re(CO)(4){C(O)Fc})(2)] (8), the unique dichloro-bridged biscarbene complex fac-[(?-Cl)(2)-(Re(CO)(3){C(OEt)Fc})(2)] (6), the known hydrido complex [Re(3)(CO)(14)H] (5), the acyl complex [Re(CO)(5){C(O)Fc}] (7), and the aldehyde-functionalized eq-[Re(2)(CO)(9){C(OTiCp(2)Cl)(Fc'CHO)}] (9). PMID:21250683

  18. Transfer Hydrogenation of Ketones and Activated Olefins Using Chelating NHC Ruthenium Complexes

    OpenAIRE

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

    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 ?,?-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,...

  19. Stabilization of Fully Reduced Iron–Sulfur Clusters by Carbene Ligation: The [FenSn]0 Oxidation Levels (n = 4, 8)

    OpenAIRE

    Deng, Liang; Holm, R. H.

    2008-01-01

    The all-ferrous [Fe4S4]0 state has been demonstrated in the fully reduced Fe protein of the Azotobacter vinelandii nitrogenase complex. We seek synthetic analogues of this state more tractable than the recently prepared but highly unstable cluster [Fe4S4(CN)4]4? (Scott, Berlinguette, Holm, and Zhou, Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 9741). The N-heterocyclic carbene 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (Pri2NHCMe2) has been found to stabilize the fully reduced clusters [Fe8...

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

    International Nuclear Information System (INIS)

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

  1. Synthesis and reactivity of metal carbene complexes with heterobiaryl spacer substituents

    OpenAIRE

    Lotz, Simon; Crause, Chantelle; Olivier, Andrew John; Liles, David C.; Go?rls, Helmar; Landman, Marile; Bezuidenhout, Daniela Ina

    2008-01-01

    Mono- and binuclear Fischer carbene complexes, [M(CO)5{C(OR)Ar-ArX}], X = H, {C(OR)M(CO)5}; M, M = W or Cr; R = Me, Et or (CH2)4OMe; Ar = thiophene, N-methylpyrrole or furan units 1–20, were synthesized. For this purpose, mono-, bi- or stepwise lithiated bithiophene, N,N-dimethylbipyrrole, thienylfuran and N-methyl(thienyl)pyrrole were reacted with chromium and tungsten hexacarbonyl precursors. Dilithiation in the 2- and 9-positions of N-methyl(thienyl)pyrrole could not be achieved. Alkylat...

  2. From spherical to leaf-like morphologies: tunable supramolecular assembly of alkynylgold(I) complexes through variations of the alkyl chain length.

    Science.gov (United States)

    Hong, Eugene Yau-Hin; Wong, Hok-Lai; Yam, Vivian Wing-Wah

    2015-04-01

    A series of luminescent polynuclear alkynylgold(I) complexes with different lengths of alkyl chains attached at the N-heterocyclic carbene moieties has been synthesised and demonstrated to display intriguing self-assembly behaviours through a cooperative growth mechanism. Variation of the alkyl chain length was found to cause drastic morphological differences in the aggregates and to strongly affect the thermodynamic parameters as revealed by the nucleation-elongation model. PMID:25707360

  3. Cationic iridium(III) complexes with two carbene-based cyclometalating ligands: cis versus trans isomers.

    Science.gov (United States)

    Monti, Filippo; La Placa, Maria Grazia I; Armaroli, Nicola; Scopelliti, Rosario; Grätzel, Michael; Nazeeruddin, Mohammad Khaja; Kessler, Florian

    2015-03-16

    A series of cationic iridium(III) complexes with two carbene-based cyclometalating ligands and five different N^N bipyridine and 1,10-phenanthroline ancillary ligands is presented. For the first time--in the frame of a rarely studied class of bis(heteroleptic) iridium complexes with two carbene-based cyclometalating ligands--a pair of cis and trans isomers has been isolated. All complexes (trans-1-5 and cis-3) were characterized by (1)H NMR, (13)C NMR, (31)P NMR, and HRMS (ESI-TOF); in addition, crystal structures of cis-3 and trans-4 are reported and discussed. Cyclic voltammetric studies show that the whole series exhibits highly reversible oxidation and reduction processes, suggesting promising potential for optoelectronic applications. Ground-state DFT and TD-DFT calculations nicely predict the blue shift experimentally observed in the room-temperature absorption and emission spectra of cis-3, compared to the trans complexes. In CH3CN, cis-3 displays a 4-fold increase in photoluminescence quantum yield (PLQY) with respect to trans-3, as a consequence of drastically slower nonradiative rate constant. By contrast, at 77 K, the emission properties of all the compounds, including the cis isomer, are much more similar, with a pronounced hypsochromic shift for the trans complexes. A similar behavior is found in solid state (1% w/w poly(methyl methacrylate) matrix), with all complexes displaying PLQY of ?70-80%, comparable emission lifetimes (? ? 1.3 ?s), and a remarkable rigidochromic shift. To rationalize the more pronounced nonradiative deactivation (and smaller PLQY) observed for photoexcited trans complexes, comparative temperature-dependent emission studies in the range of 77-450 K for cis-3 and trans-3 were made in propylene glycol, showing that solvation effects are primarily responsible for the observed behavior. PMID:25741900

  4. Stereoselectively fluorinated N-heterocycles: a brief survey

    Directory of Open Access Journals (Sweden)

    Xiang-Guo Hu

    2013-11-01

    Full Text Available The stereoselective incorporation of fluorine atoms into N-heterocycles can lead to dramatic changes in the molecules’ physical and chemical properties. These changes can be rationally exploited for the benefit of diverse fields such as medicinal chemistry and organocatalysis. This brief review will examine some of the effects that fluorine substitution can have in N-heterocycles, including changes to the molecules’ stability, their conformational behaviour, their hydrogen bonding ability, and their basicity. Finally, some methods for the synthesis of stereoselectively fluorinated N-heterocycles will also be reviewed.

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

    Science.gov (United States)

    Dahcheh, Fatme; Stephan, Douglas W

    2015-01-28

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

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

    Science.gov (United States)

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

    2015-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Stephan Hohloch

    2015-04-01

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

  8. Synthesis, structural characterization and thermal properties of copper and silver silyl complexes.

    Science.gov (United States)

    Sgro, Michael J; Piers, Warren E; Romero, Patricio E

    2015-02-28

    The synthesis of copper and silver silyl complexes containing either N-heterocyclic carbenes or nitrogen donors is described. Alterations made to both the neutral donor ligands as well as the silyl group provided access to a number of different compounds. Many of the complexes synthesized were studied in the solid state and the effect of the donor ligand on the final structure of the complexes was examined. The thermal properties of the complexes were explored using thermogravimetric analysis, differential scanning calorimetry and sublimations. Some of the complexes synthesized were demonstrated to be promising volatile metal precursors. PMID:25608661

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

    Science.gov (United States)

    van der Westhuizen, Belinda; Speck, J Matthäus; Korb, Marcus; Friedrich, Joachim; Bezuidenhout, Daniela I; Lang, Heinrich

    2013-12-16

    A series of ferrocenyl (Fc = ferrocenyl; fc = ferrocen-1,1'-diyl) and biferrocenyl (Bfc = 1',1?-biferrocenyl; bfc = 1',1?-biferrocen-1,1?-diyl) mono- and biscarbene tungsten(0) complexes of the type [(CO)5W?C(OMe)R] (1, R = Fc; 3, R = Bfc) and [(CO)5W?C(OMe)-R'-(OMe)C?W(CO)5] (2, R' = fc; 4, R' = bfc) were synthesized according to the classical synthetic methodology by reacting W(CO)6 with LiR (R = Fc, fc, bfc), followed by a subsequent alkylation using methyl trifluoromethanesulfonate. Electrochemical investigations were carried out on these complexes to get a closer insight into the electronic properties of 1-4. The ferrocenyl and biferrocenyl moieties in 1-4 show reversible one-electron redox events. It was further found that the Fischer carbene unit is reducible in an electrochemical one-electron transfer process. For the tungsten carbonyl moieties, irreversible oxidation processes were found. In addition, charge transfer studies were performed on 1-4 using in situ UV-vis-NIR and infrared spectroelectrochemical techniques. During the UV-vis-NIR investigations, typical low energy transitions for the mixed-valent biferrocenyl unit were found. A further observed high energy NIR absorption is attributed to a metal-metal charge transfer transition between the tungsten carbonyl fragment and the ferrocenyl/biferrocenyl group in the corresponding oxidized states, which can be described as class II systems according to Robin and Day. This assignment was verified by infrared spectroelectrochemical studies. The electrochemical investigations are supported by density functional theory calculations. The structural properties of 1-4 in the solid state were investigated by single-crystal X-ray diffraction studies showing no substituent effects on bond lengths and angles. The biferrocenyl derivatives exhibit syn-conformation of the ferrocenyl and carbene building blocks. PMID:24299202

  10. The fluxional amine gold(iii) complex as an excellent catalyst and precursor of biologically active acyclic carbenes.

    Science.gov (United States)

    Montanel-Pérez, Sara; Herrera, Raquel P; Laguna, Antonio; Villacampa, M Dolores; Gimeno, M Concepción

    2015-05-01

    A new amine gold(iii) complex [Au(C6F5)2(DPA)]ClO4 with the di-(2-picolyl)amine (DPA) ligand has been synthesised. In the solid state the complex has a chiral amine nitrogen because the ligand coordinates to the gold centre through one nitrogen atom from a pyridine and through the NH moiety, whereas in solution it shows a fluxional behaviour with a rapid exchange between the pyridine sites. This complex can be used as an excellent synton to prepare new gold(iii) carbene complexes by the reaction with isocyanide CNR. The resulting gold(iii) derivatives have unprecedented bidentate C^N acyclic carbene ligands. All the complexes have been spectroscopically and structurally characterized. Taking advantage of the fluxional behaviour of the amine complex, its catalytic properties have been tested in several reactions with the formation of C-C and C-N bonds. The complex showed excellent activity with total conversion, without the presence of a co-catalyst, and with a catalyst loading as low as 0.1%. These complexes also present biological properties, and cytotoxicity studies have been performed in vitro against three tumour human cell lines, Jurkat (T-cell leukaemia), MiaPaca2 (pancreatic carcinoma) and A549 (lung carcinoma). Some of them showed excellent cytotoxic activity compared with the reference cisplatin. PMID:25893402

  11. Simple synthesis of neutral and cationic Cu-NHC complexes.

    Science.gov (United States)

    Liu, Bo; Ma, Xueji; Wu, Feifei; Chen, Wanzhi

    2015-01-28

    A direct and practical synthetic route to N-heterocyclic carbene copper complexes of [(NHC)CuX] (X = halide) and [(NHC)2Cu]PF6 types using commercially available copper powder is described. A number of copper-NHC complexes have been obtained in a range of yields from 26 to 99%. The reactions take place in air without removal of moisture and oxygen, and the excess of copper powder can be easily removed via simple filtration after completion. The direct reactions of imidazolium salts and copper powder can also be performed in aqueous media avoiding tedious purification processes. The procedure is also suitable for gram-scale preparation. PMID:25479082

  12. Redox noninnocence of carbene ligands: carbene radicals in (catalytic) C-C bond formation.

    Science.gov (United States)

    Dzik, Wojciech I; Zhang, X Peter; de Bruin, Bas

    2011-10-17

    In this Forum contribution, we highlight the radical-type reactivities of one-electron-reduced Fischer-type carbenes. Carbene complexes of group 6 transition metals (Cr, Mo, and W) can be relatively easily reduced by an external reducing agent, leading to one-electron reduction of the carbene ligand moiety. This leads to the formation of "carbene-radical" ligands, showing typical radical-type reactivities. Fischer-type carbene ligands are thus clearly redox-active and can behave as so-called "redox noninnocent ligands". The "redox noninnocence" of Fischer-type carbene ligands is most clearly illustrated at group 9 transition metals in the oxidation state II+ (Co(II), Rh(II), and Ir(II)). In such carbene complexes, the metal effectively reduces the carbene ligand by one electron in an intramolecular redox process. As a result, the thus formed "carbene radicals" undergo a variety of radical-type C-C and C-H bond formations. The redox noninnocence of Fischer-type carbene ligands is not just a chemical curiosity but, in fact, plays an essential role in catalytic cyclopropanation reactions by cobalt(II) porphyrins. This has led to the successful development of new chiral cobalt(II) porphyrins as highly effective catalysts for asymmetric cyclopropanation with unprecedented reactivity and stereocontrol. The redox noninnocence of the carbene intermediates results in the formation of carbene-radical ligands with nucleophilic character, which explains their effectiveness in the cyclopropanation of electron-deficient olefins and their reduced tendency to mediate carbene dimerization. To the best of our knowledge, this represents the first example in which the redox noninnocence of a reacting ligand plays a key role in a catalytic organometallic reaction. This Forum contribution ends with an outlook on further potential applications of one-electron-activated Fischer-type carbenes in new catalytic reactions. PMID:21520926

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

    Science.gov (United States)

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

    2003-02-19

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

  14. Oxidative N-heterocyclic carbene catalyzed stereoselective annulation of simple aldehydes and 5-alkenyl thiazolones.

    Science.gov (United States)

    Lin, Li; Yang, Yuhong; Wang, Mei; Lai, Luhao; Guo, Yarong; Wang, Rui

    2015-05-11

    A highly diastereoselective annulation of simple aldehydes and 5-alkenyl thiazolones, via oxidative NHC catalysis has been developed. This strategy provides facile access to a diverse library of functionalized chiral thiazolo pyrones. Aerobic oxygen can also be applied as a secondary oxidant to avoid the use of stoichiometric organic or inorganic oxidants. PMID:25872611

  15. Palladium(ii) complexes with electron-poor, 4,5-disubstituted diimidazol-2-ylidene ligands: synthesis, characterization and catalytic activity.

    Science.gov (United States)

    Pinter, Piermaria; Biffis, Andrea; Tubaro, Cristina; Tenne, Mario; Kaliner, Maria; Strassner, Thomas

    2015-05-28

    Diimidazolium salts featuring different bridges between the imidazolium groups, as well as electron-withdrawing groups (chloride, cyanide) at the 4- and 5-position of the heterocyclic rings, have been successfully prepared. The diimidazolium salts serve as convenient precursors of di(N-heterocyclic carbene) ligands, which coordinate in a chelating fashion to palladium(ii) centres. The effect of the newly introduced electron-withdrawing groups on the spectroscopic and structural characteristics of the resulting complexes as well as on their reactivity as catalysts in a model alkyne hydroarylation reaction has been investigated and is discussed herein. PMID:25911982

  16. Traditional and ion-pair halogen-bonded complexes between chlorine and bromine derivatives and a nitrogen-heterocyclic carbene.

    Science.gov (United States)

    Donoso-Tauda, Oscar; Jaque, Pablo; Elguero, José; Alkorta, Ibon

    2014-10-01

    A theoretical study of the halogen-bonded complexes (A-X···C) formed between halogenated derivatives (A-X; A = F, Cl, Br, CN, CCH, CF3, CH3, H; and X = Cl, Br) and a nitrogen heterocyclic carbene, 1,3-dimethylimidazole-2-ylidene (MeIC) has been performed using MP2/aug'-cc-pVDZ level of theory. Two types of A-X:MeIC complexes, called here type-I and -II, were found and characterized. The first group is described by long C-X distances and small binding energies (8-54 kJ·mol(-1)). In general, these complexes show the traditional behavior of systems containing halogen-bonding interactions. The second type is characterized by short C-X distances and large binding energies (148-200 kJ·mol(-1)), and on the basis of the topological analysis of the electron density, they correspond to ion-pair halogen-bonded complexes. These complexes can be seen as the interaction between two charged fragments: A(-) and (+)[X-CIMe] with a high electrostatic contribution in the binding energy. The charge transfer between lone pair A(LP) to the ?* orbital of C-X bond is also identified as a significant stabilizing interaction in type-II complexes. PMID:25188812

  17. Dihydrogen activation by frustrated carbene-borane Lewis pairs: an experimental and theoretical study of carbene variation.

    Science.gov (United States)

    Kronig, Sabrina; Theuergarten, Eileen; Holschumacher, Dirk; Bannenberg, Thomas; Daniliuc, Constantin G; Jones, Peter G; Tamm, Matthias

    2011-08-01

    A variety of Lewis acid-base pairs consisting of tris(pentafluorophenyl)borane, B(C(6)F(5))(3), in combination with sterically demanding five- and six-membered N-heterocyclic carbenes (NHCs) of the imidazolin-2-ylidene, imidazolidin-2-ylidene, and tetrahydropyrimidin-2-ylidene types were investigated with respect to their potential to act as frustrated Lewis pairs (FLP) by reaction with dihydrogen (H(2)) and tetrahydrofuran (THF). A sufficient degree of "frustration" was usually established by introduction of a 1,3-di-tert-butyl or 1,3-diadamantyl carbene substitution pattern, which allows an unquenched acid-base reactivity and thus leads to heterolytic dihydrogen activation and ring-opening of THF. In contrast, 1,3-bis(2,6-diisopropylphenyl)-substituted carbenes showed ambiguous behavior, and the corresponding five-membered imidazolin-2-ylidene formed a stable carbene-B(C(6)F(5))(3) adduct, whereas fast C-F activation and formation of a zwitterionic pyrimidinium-fluoroborate was observed for the six-membered tetrahydropyrimidin-2-ylidene. A stable adduct was also isolated for the combination of the acyclic carbene bis(diisopropylamino)methylene with B(C(6)F(5))(3), and consequently no reactivity toward H(2) and THF was observed. To rationalize the reactivity of the carbene-borane Lewis pairs, the thermodynamics of adduct formation with B(C(6)F(5))(3) were calculated for 10 different carbenes; the stability (or instability) of these adducts can be used as a good measure of the degree of "frustration". PMID:21718018

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

    Science.gov (United States)

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

    2015-02-01

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

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

    Directory of Open Access Journals (Sweden)

    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 (110–130 °C to afford the corresponding 1,3-dienes in moderate yield (34–53%.

  20. The ketimide ligand is not just an inert spectator: heteroallene insertion reactivity of an actinide-ketimide linkage in a thorium carbene amide ketimide complex.

    Science.gov (United States)

    Lu, Erli; Lewis, William; Blake, Alexander J; Liddle, Stephen T

    2014-08-25

    The ketimide anion R2C=N(-) is an important class of chemically robust ligand that binds strongly to metal ions and is considered ideal for supporting reactive metal fragments due to its inert spectator nature; this contrasts with R2N(-) amides that exhibit a wide range of reactivities. Here, we report the synthesis and characterization of a rare example of an actinide ketimide complex [Th(BIPM(TMS)){N(SiMe3)2}(N=CPh2)] [2, BIPM(TMS)=C(PPh2NSiMe3)2]. Complex 2 contains Th=C(carbene), Th-N(amide) and Th-N(ketimide) linkages, thereby presenting the opportunity to probe the preferential reactivity of these linkages. Importantly, reactivity studies of 2 with unsaturated substrates shows that insertion reactions occur preferentially at the Th-N(ketimide) bond rather than at the Th=C(carbene) or Th-N(amide) bonds. This overturns the established view that metal-ketimide linkages are purely inert spectators. PMID:25044515

  1. Cobalt azide complexes with a tris(carbene)borate ligand scaffold.

    Science.gov (United States)

    Scepaniak, Jeremiah J; Margarit, Charles G; Bontchev, Ranko P; Smith, Jeremy M

    2013-09-01

    The four-coordinate Co(II) complex, (azido-?N)[1,1,',1''-(phenylboranetriyl)tris(3-tert-butyl-1H-imidazol-2-ylidene)]cobalt(II), [Co(C27H38BN6)(N3)], (1), denoted PhB(t-BuIm)3CoN3, was prepared by the reaction of the corresponding chloride complex with NaN3. One-electron oxidation results in the isolation of the five-coordinate Co(III) complex, bis(azido-?N)[1,1,',1''-(phenylboranetriyl)tris(3-tert-butyl-1H-imidazol-2-ylidene)]cobalt(III), [Co(C27H38BN6)(N3)2], (2), denoted PhB(t-BuIm)3Co(N3)2. Attempts to prepare cobalt nitrides by thermolysis or photolysis of these complexes were unsuccessful. PMID:24005501

  2. Reduction of chromium(0) and iron(0) aminocarbene complexes with heterocyclic substituents on the carbene carbon.

    Czech Academy of Sciences Publication Activity Database

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

    Prague : J. Heyrovský Instotute of Physical Chemistry, v.v.i, 2010 - (Hudská, V.; Ludvík, J.). s. 56 ISBN 978-80-87351-06-2. [The Heyrovský Discussion. Electrochemistry of Organic Molecules and Coordination Compounds /43./. 30.05.2010-03.06.2010, T?eš?] R&D Projects: GA AV ?R IAA400400813 Institutional research plan: CEZ:AV0Z40400503 Keywords : electrochemistry * aminocarbene complexes Subject RIV: CG - Electrochemistry

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

    Czech Academy of Sciences Publication Activity Database

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

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

  4. Syntheses of sterically shielded stable carbenes of the 1,2,4-triazole series and their corresponding palladium complexes: efficient catalysts for chloroarene hydrodechlorination.

    Science.gov (United States)

    Glinyanaya, Nataliya V; Saberov, Vagiz Sh; Korotkikh, Nikolai I; Cowley, Alan H; Butorac, Rachel R; Evans, Daniel A; Pekhtereva, Tatyana M; Popov, Anatolii F; Shvaika, Oles P

    2014-11-21

    The new sterically shielded 1,3,4-trisubstituted 1,2,4-triazol-5-ylidenes 8b–d were synthesized by a three step method starting from 2-phenyl-1,3,4-oxadiazole. The syntheses of palladium complexes 9a–d and 10a–d (including the sterically shielded derivatives 9c,d and 10a–d) were carried out via the reactions of the stable carbenes 8a–d with palladium halogenide salts in THF or toluene solution. Complexes 9c,d and 10a–d were found to be excellent catalysts for the reductive dechlorination (hydrodechlorination) of p-dichlorobenzene. The structures of 8c, 9a,b, and 10a were determined by single-crystal X-ray diffraction. PMID:25030067

  5. Two 2D metal-organic frameworks based on N-heterocyclic and polycarboxylates ligands: Syntheses, structures, and photoluminescent properties

    Science.gov (United States)

    Yan, Li; Li, Chuanbi; Zhu, Dongsheng

    2013-02-01

    Two novel complexes constructed from aromatic acid and N-heterocyclic ligands have been synthesized by hydrothermal reaction: {[Mn(dipt)(BDC)3?H2O]n (1) [dipt = 2-(2,4-dichlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, BDC = terephthalic acid] and [Pb(dnpt)(BDC)2]n (2) [dnpt = 2-(4-nitrophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline]. Complexes 1 and 2 were characterized by elemental analysis, IR, single crystal X-ray diffraction and thermogravimetric analysis (TGA). The results suggest that complexes 1-2 exhibit 1D chain structure. The intermolecular C-H⋯O and N-H⋯O interactions extend the complexes into 2D networks, and the existing H-bonds further stabilized the title complexes, which can be proved by TGA experiment. Furthermore, the solid-state fluorescence spectrum of complexes 1 and 2 were also investigated, as well as the ligands dipt and dnpt.

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

    Directory of Open Access Journals (Sweden)

    Koichiro Oshima

    2009-08-01

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

  7. The development of nitro-Mannich/hydroamination cascades for the synthesis of substituted N-heterocycles

    OpenAIRE

    Barber, David M.; Dixon, Darren J.

    2013-01-01

    This thesis describes the development of nitro-Mannich/hydroamination cascade reactions for the synthesis of N-heterocycles, which are important motifs found in a variety of biologically active natural products and pharmaceuticals, such as atorvastatin (Lipitor®). Chapter 2 outlines the development of an efficient synthesis of 2,5-disubstituted pyrroles using a nitro-Mannich/hydroamination cascade. Starting from easily prepared N-protected imines and nitroalkyne substrates, a compatible ...

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

    OpenAIRE

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

    2013-01-01

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

  9. Ru(II) , Os(II) , and Ir(III) Complexes with Chelating Pyridyl-Mesoionic Carbene Ligands: Structural Characterization and Applications in Transfer Hydrogenation Catalysis.

    Science.gov (United States)

    Bolje, Aljoša; Hohloch, Stephan; van der Meer, Margarethe; Košmrlj, Janez; Sarkar, Biprajit

    2015-04-27

    Chelating ligands with one pyridine donor and one mesoionic carbene donor are fast establishing themselves as privileged ligands in homogeneous catalysis. The synthesis of several new Ir(III) -Cp*- and Os(II) -Cym complexes (Cp*=pentamethylcyclopentadienyl, Cym=p-cymene=4-isopropyl-toluene) derived from chelating pyridyltriazolylidenes where the additional pyridine donor was incorporated via the azide part of the triazole is presented. Furthermore, different 4-substituted phenylacetylene building blocks have been used to introduce electronic fine-tuning in the ligands. The ligands thus can be generally described as 4-(4-R-phenyl)-3-methyl-1-(pyridin-2-yl)-1H-1,2,3-triazol-5-ylidene (with R being H (L(1) ), Me (L(2) ), OMe (L(3) ), CN (L(4) ), CF3 (L(5) ), Br (L(6) ) or NO2 (L(7) )). The corresponding complexes (Ir-1 to Ir-7 and Os-1 to Os-7) were characterized by standard spectroscopic methods, and the expected three-legged, piano-stool type coordination was unambiguously confirmed by X-ray diffraction analysis of selected compounds. Together with Ru(II) analogues previously reported by us, a total of 21 complexes were tested as (pre)catalysts for the transfer hydrogenation of carbonyl groups, showing a remarkable reactivity even at very low catalyst loadings. The electronic effects of the ligands as well as different substrates were investigated. Some mechanistic elucidations are also presented. PMID:25752929

  10. Exploring the effect of axial ligand substitution (X = Br, NCS, CN) on the photodecomposition and electrochemical activity of [MnX(N-C)(CO)3] complexes.

    Science.gov (United States)

    Agarwal, Jay; Stanton Iii, Charles J; Shaw, Travis W; Vandezande, Jonathon E; Majetich, George F; Bocarsly, Andrew B; Schaefer Iii, Henry F

    2015-02-01

    The synthesis, electrochemical activity, and relative photodecomposition rate is reported for four new Mn(i) N-heterocyclic carbene complexes: [MnX(N-ethyl-N'-2-pyridylimidazol-2-ylidine)(CO)3] (X = Br, NCS, CN) and [MnCN(N-ethyl-N'-2-pyridylbenzimidazol-2-ylidine)(CO)3]. All compounds display an electrocatalytic current enhancement under CO2 at the potential of the first reduction, which ranges from -1.53 V to -1.96 V versus the saturated calomel electrode. Catalytic CO production is observed for all species during four-hour preparative-scale electrolysis, but substantial H2 is detected in compounds where X is not Br. All species eventually decompose under both 350 nm and 420 nm light, but cyanide substituted complexes (X = CN) last significantly longer (up to 5×) under 420 nm light as a result of a blue-shifted MLCT band. PMID:25501649

  11. A large perturbation on electronic and photophysical properties of Ir(III) carbene complexes caused by the variation of N-substitution in N,N?-heteroaromatic ligands

    Science.gov (United States)

    Liu, Yuqi; Si, Yanling; Wang, Ying; Wu, Zhijian

    2014-08-01

    DFT/TDDFT investigation was performed on the electronic and photophysical properties of blue-emitting Ir(III) carbene complexes (fpmi)3-xIr(N^N?)x (x = 1, 2) [fpmi = 1-(4-fluorophenyl)-3-methylimidazolin-2-ylidene-C,C2?, N^N? = 2-(1H-pyrazol-5-yl)pyridinato (1a(x = 1)/1a?(x = 2)); 2-(1H-imidazol-5-yl)pyridinato (1b/1b?); 2-(1H-imidazol-2-yl)pyridinato (1c/1c?); 2-(1H-1,2,4-triazol-5-yl)pyridinato (2a/2a?); 2-(1H-1,2,3-triazol-5-yl)pyridinato (2b/2b?); 2-(4H-1,2,4-triazol-3-yl)pyridinato (2c/2c?)]. The absorption intensities and band positions are obviously affected by the variation of N substitution in N^N? ligand. The emission properties show an apparent dependence on the solvent effects, and the N^N? ligand plays an important role in governing the emissive state. The pyrazolyl-pyridyl-based N^N? ligand is considered to be more beneficial for blue OLEDs emitters.

  12. Chemistry of diruthenium and dirhodium analogues of pentaborane(9): synthesis and characterization of metal n,s-heterocyclic carbene and B-agostic complexes.

    Science.gov (United States)

    Roy, Dipak Kumar; Mondal, Bijan; Anju, R S; Ghosh, Sundargopal

    2015-02-23

    Building upon our earlier results on the synthesis of electron-precise transition-metal-boron complexes, we continue to investigate the reactivity of pentaborane(9) and tetraborane(10) analogues of ruthenium and rhodium towards thiazolyl and oxazolyl ligands. Thus, mild thermolysis of nido-[(Cp*RuH)2B3H7] (1) with 2-mercaptobenzothiazole (2-mbtz) and 2-mercaptobenzoxazole (2-mboz) led to the isolation of Cp*-based (Cp* = ?(5)-C5Me5) borate complexes 5?a,b [Cp*RuBH3L] (5?a: L = C7H4NS2; 5?b: L = C7H4NOS)) and agostic complexes 7?a,b [Cp*RuBH2(L)2], (7?a: L = C7H4NS2; 7?b: L = C7H4NOS). In a similar fashion, a rhodium analogue of pentaborane(9), nido-[(Cp*Rh)2B3H7] (2) yielded rhodaboratrane [Cp*RhBH(L)2], 10 (L = C7H4NS2). Interestingly, when the reaction was performed with an excess of 2-mbtz, it led to the formation of the first structurally characterized N,S-heterocyclic rhodium-carbene complex [(Cp*Rh)(L2)(1-benzothiazol-2-ylidene)] (11) (L = C7H4NS2). Furthermore, to evaluate the scope of this new route, we extended this chemistry towards the diruthenium analogue of tetraborane(10), arachno-[(Cp*RuCO)2B2H6] (3), in which the metal center possesses different ancillary ligands. PMID:25537367

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

    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

  15. [Au(dien)(N-heterocycle)](3+): reactivity with biomolecules and zinc finger peptides.

    Science.gov (United States)

    Spell, Sarah R; Farrell, Nicholas P

    2015-01-01

    The reaction of [Au(dien)(N-heterocycle)](3+) (AuN4) coordination compounds with simple amino acids and zinc finger proteins is reported. Compared to [AuCl(dien)](2+), NMR studies show that the presence of a more substitution-inert N-donor as the putative leaving group slows the reaction with the sulfur-containing amino acids N-acetylmethionine (NAcMet) and N-acetylcysteine (NAcCys). Lack of ligand dissociation upon reaction with NAcCys indicates, to our knowledge, the first long-lived N-heterocycle-Au-S species in solution. Reactions with zinc finger proteins show a higher reactivity with the Cys3His zinc finger than with Cys2His2, likely due to the presence of fewer aurophilic cysteines in the latter. Of the Au(III) compounds studied, [Au(dien)(DMAP)](3+) (DMAP = 4-dimethylaminopyridine) appears to be the least reactive, with ESI-MS studies showing the presence of intact zinc fingers at initial reaction times. These results, in combination with previously reported characterization and pH dependency studies, will further aid in optimizing the structure of these AuN4 species to obtain a substitution-reactive yet selective compound for targeting zinc finger proteins. PMID:25531886

  16. Ruthenium(II) Complexes Containing Lutidine-Derived Pincer CNC Ligands: Synthesis, Structure, and Catalytic Hydrogenation of C?N bonds.

    Science.gov (United States)

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

    2015-05-11

    A series of Ru complexes containing lutidine-derived pincer CNC ligands have been prepared by transmetalation with the corresponding silver-carbene derivatives. Characterization of these derivatives shows both mer and fac coordination of the CNC ligands depending on the wingtips of the N-heterocyclic carbene fragments. In the presence of tBuOK, the Ru-CNC complexes are active in the hydrogenation of a series of imines. In addition, these complexes catalyze the reversible hydrogenation of phenantridine. Detailed NMR spectroscopic studies have shown the capability of the CNC ligand to be deprotonated and get involved in ligand-assisted activation of dihydrogen. More interestingly, upon deprotonation, the Ru-CNC complex 5?e(BF4 ) is able to add aldimines to the metal-ligand framework to yield an amido complex. Finally, investigation of the mechanism of the hydrogenation of imines has been carried out by means of DFT calculations. The calculated mechanism involves outer-sphere stepwise hydrogen transfer to the C?N bond assisted either by the pincer ligand or a second coordinated H2 molecule. PMID:25820229

  17. One-step synthesis of saturated spirocyclic N-heterocycles with stannyl amine protocol (SnAP) reagents and ketones.

    Science.gov (United States)

    Siau, Woon-Yew; Bode, Jeffrey W

    2014-12-24

    The combination of cyclic ketones and stannyl amine protocol (SnAP) reagents affords saturated, spirocyclic N-heterocycles under operationally simple reaction conditions. The resulting, N-unprotected spirocyclic amines are in great demand as scaffolds for drug discovery and development. The union of SnAP reagents and acyclic trifluoromethylketones yields ?-CF3 morpholines and piperazines. PMID:25482378

  18. Two alternative approaches to access mixed hydride-amido zinc complexes: synthetic, structural and solution implications.

    Science.gov (United States)

    Roberts, Andrew J; Clegg, William; Kennedy, Alan R; Probert, Michael R; Robertson, Stuart D; Hevia, Eva

    2015-04-21

    Using bis(amide) Zn(HMDS)2 (HMDS = 1,1,1,3,3,3-hexamethyldisilazide) as a precursor, this study explores the synthesis of N-heterocyclic carbene stabilized mixed amido-hydride zinc complexes using two alternative hydride sources, namely dimethylamine borane (DMAB) and phenylsilane PhSiH3. Hydride-rich zinc cluster Zn4(HMDS)2H6·2IPr () (IPr = 1,3-bis(2,6-di-isopropylphenyl)imidazol-2-ylidene), which can be envisaged as a co-complex of IPr·ZnH2 and (HMDS)ZnH, is obtained when DMAB is employed, with the concomitant formation of heteroleptic bis(amido)borane [HB(NMe2)(HMDS)] and H2 evolution. NMR studies in d8-THF show that although the bulky carbene IPr does not bind to the zinc bis(amide), its presence in the reaction media is required in order to stabilise . Reactions using the slightly less sterically demanding NHC IXy (IXy = 1,3-bis-(2,6-dimethylphenyl)imidazol-2-ylidene) led to the isolation and structural elucidation of the carbene adduct Zn(HMDS)2·IXy (). Contrastingly, mixtures of equimolar amounts of PhSiH3 and the zinc bis(amide) (60 °C, 3 h, hexane) afforded monomeric heteroleptic hydride (HMDS)ZnH·IPr (). NMR studies, including DOSY experiments, revealed that while the integrity of is retained in polar d8-THF solutions, in lower polarity C6D6 it displays a much more complex solution behaviour, being in equilibrium with the homoleptic species ZnH2·IPr, Zn(HMDS)2 and IPr. PMID:25846582

  19. Bespoke SnAP Reagents for the Synthesis of C-Substituted Spirocyclic and Bicyclic Saturated N-Heterocycles.

    Science.gov (United States)

    Geoghegan, Kimberly; Bode, Jeffrey W

    2015-04-17

    The precise placement of C-substituents on bicyclic and spirocyclic N-heterocycles is readily achieved by the combination of aldehydes and new SnAP reagents. The substituted SnAP reagents are readily prepared from simple starting materials and couple with a variety of aromatic and heteroaromatic aldehydes at room temperature under operationally simple conditions to deliver substituted morpholine and piperazine products. PMID:25822736

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

    OpenAIRE

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

    2011-01-01

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

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

    International Nuclear Information System (INIS)

    The comparative mineralization of eight polycyclic aromatic compounds in five soils collected from an abandoned coal tar refinery in eastern Ohio was determined. The soils showed differences only in total extractable hydrocarbon content of the soil chemical characteristics measured. The compounds studied included five polycyclic aromatic hydrocarbons (phenanthrene, anthracene, pyrene, and carcinogenic benz[a]anthracene and benzo[a]pyrene) and three N-heterocyclic aromatics (9H-carbazole, and carcinogenic 7H-dibenzo[c,g]carbazole and dibenz[a,j]acridine). Mineralization was measured by serum bottle radiorespirometry. Only phenanthrene, anthracene, pyrene, benz[a]anthracene, and carbazole were mineralized in the soils after 64 d. Two of the soils with eight to 15 times the hexane -extractable hydrocarbon content consistently showed more rapid initial rates and higher overall extents of mineralization compared to the other three soils. Overall extents of mineralization ranged from 38 to 55% for phenanthrene, 10 to 60% for anthracene, 25 to 70% for pyrene, background to 40% for benz[a]anthracene, and 25 to 50% for carbazole after 64 d. Extents of mineralization by indigenous soil microbiota appear to be more dependent on the chemical characteristics of the soil and not soil total biomass and activity. Cultures capable of degrading phenanthrene, anthracene, and pyrene were obtained following enrichment techniques. A Mycobacterium sp. capable of degrading these three compoup. 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

  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

    Energy Technology Data Exchange (ETDEWEB)

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

    International Nuclear Information System (INIS)

    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

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

    International Nuclear Information System (INIS)

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

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

    OpenAIRE

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

    2013-01-01

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

  6. TOF-SIMS analysis of N-heterocyclic compounds-implications for the Rosetta/COSIMA Mission

    Science.gov (United States)

    Le Roy, Léna; Briois, Christelle; Thirkell, Laurent; Cottin, Hervé; Fray, Nicolas; Poulet, Gilles; Hilchenbach, Martin

    The European Rosetta spacecraft launched on March 2004 will reach the comet 67/P-Churyumov-Gerasimenko in 2014 to perform the most exhaustive study ever achieved on comets (Glassmeier et al. 2007). The COmetary Secondary Ion Mass Analyser (COSIMA) carried on board will focus on chemical analysis of cometary dust grains collected in situ on a variety of metallic targets. COSIMA's goals are the in-situ characterisation of the atomic, molecular and isotopic composition of cometary dust grains. These analyses will provide inorganic and organic data about pristine solar system material (Kissel et al. 2007). COSIMA is a time-of-flight secondary ion mass spectrometer (TOF-SIMS) using an indium liquid metal ion source. Spectra inter-pretation of complex unknown samples with COSIMA instrument will be difficult due to the limited mass resolution (M/M of 2000 at m=100 amu) which excludes unambiguous compounds identification and requires preliminary work with reference samples. To help the interpretation of COSIMA spectra calibration laboratory work is in progress using the twin of the COSIMA flight instrument located at Katlenburg-Lindau (Germany) and the prototype of COSIMA in Orléans (France). Here we report the analysis of 100-400m deposits of organics performed with the COSIMA prototype based in Orléans. The organics are expected to be minor peaks, making their identification not simple. Nucleobase molecules, especially the purine bases, are among the building of the replicating molecules of life (DNA and RNA). Scour the universe in an attempt to find such a natural source of nucleobases is of fundamental significance in considerations of the origin of life (Lazcano Miller 1996) Therefore we focused our work on N-heterocyclic compounds which are believed to be present in comets or which belong to the chemical family of such molecules (Krueger Kissel 2006). Experiments have been performed on nine compounds: adenine, guanine, imidazole, 2-aminopyrimidine, cytosine, isocytosine, thymine, 4-aminopyrimidine and uracil. The first step was to characterize all these pure ni-trogenous organic molecules by their high statistics of positive and negative spectra. Deep examination has then been performed to look for peculiarity: we tried to differentiate i) the fragmentation peaks of a complex molecule from the quasi-molecular peak of pure compounds at the same mass and ii) characteristic features between isomers. For almost all compounds, highly intensive parent-like secondary ions of the general composition [M+H]+ or [M-H]-and characteristically large fragment ions correlated with functional groups were emitted. None possible ambiguities were revealed between the peaks from the actual molecule and the same one in a substructure form: they have two different spectral features. The two molecules were even distinguishable in binary mixture experiments. References: Glassmeier KH et al. (2007) Space Sci. Rev. 128, 1-21. Kissel J et al. (2007) Space Sci. Rev. 128, 823-867 Lazcano A Miller S.L. (1996) Cell 85, 793-798 Krueger F.R. Kissel J. (2006) Eds Springer, p 325-339

  7. Synthesis of a Simplified Version of Stable Bulky and Rigid Cyclic (Alkyl)(Amino)Carbenes (CAACs), and Catalytic Activity of the Ensuing Gold(I) Complex in the Three-Component Preparation of 1,2-Dihydroquinoline Derivatives

    OpenAIRE

    Zeng, Xiaoming; Frey, Guido D.; Kinjo, Rei; Donnadieu, Bruno; Bertrand, Guy

    2009-01-01

    A 95/5 mixture of cis and trans 2,4-dimethyl-3-cyclohexenecarboxaldehyde (trivertal), a common fragrance and flavor material produced in bulk quantities, serves as the precursor for the synthesis of a stable spirocyclic (alkyl)(amino)carbene, in which the 2-methyl-substituted cyclohexenyl group provides steric protection to an ensuing metal. The efficiency of this carbene as ligand for transition metal based catalysts is first illustrated by the gold(I) catalyzed hydroamination of internal al...

  8. ?-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.

    Science.gov (United States)

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

    2014-12-01

    Unlike the most of ?-alkoxy coordination in ?-hydroxycarboxylates to vanadium, novel ?-hydroxy coordination to vanadium(IV) has been observed for a series of chiral and achiral monomeric ?-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 [(?)VO(S-Hcitmal)(bpy)]·2H2O (5), [VO(H2cit)(phen)]2·6.5H2O (6), which were isolated from the reactions of vanadyl sulfate with ?-hydroxycarboxylates and N-heterocycle ligands in acidic solution. The complexes feature a tridentate citrate, malate or citramalate that chelates to vanadium atom through their ?-hydroxy, ?-carboxy and ?-carboxy groups; while the other ?-carboxylic acidic group of citrate is free to participate strong hydrogen bonds with lattice water molecule. The neutral ?-hydroxy group also forms strong intermolecular hydrogen bonds with water molecule and the negatively-charged ?-carboxy group in the environment. The inclusion of a hydrogen ion in ?-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-O?-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

  9. Structurally simple complexes of CO2.

    Science.gov (United States)

    Murphy, Luke J; Robertson, Katherine N; Kemp, Richard A; Tuononen, Heikki M; Clyburne, Jason A C

    2015-03-01

    The ability to bind CO2 through the formation of low-energy, easily-broken, bonds could prove invaluable in a variety of chemical contexts. For example, weak bonds to CO2 would greatly decrease the cost of the energy-intensive sorbent-regeneration step common to most carbon capture technologies. Furthermore, exploration of this field could lead to the discovery of novel CO2 chemistry. Reduction of complexed carbon dioxide might generate chemical feedstocks for the preparation of value-added products, particularly transportation fuels or fuel precursors. Implementation on a large scale could help to drastically reduce CO2 concentrations in the atmosphere. However, literature examples of weakly bonded complexes of CO2 are relatively few and true coordination complexes to a 'naked' CO2 fragment are nearly unheard of. In this review article, a variety of complexes of CO2 featuring diverse binding modes and reactivity will be examined. Topics covered include: (A) inclusion complexes of CO2 in porous materials. (B) Zwitterionic carbamates produced from the reaction of CO2 with polyamines. (C) Carbamate salts produced from reaction of CO2 with two equivalents of an amine. (D) Insertion products of CO2 into acid-base adducts (e.g., metal complexes). (E) Lewis acid-base activated CO2, such as frustrated Lewis pair complexes. (F) Simple base-CO2 adducts, wherein the base-CO2 bond is the only interaction formed. Complexes in the last category are of particular interest, and include imidazol-2-carboxylates (N-heterocyclic carbene adducts of CO2) as well as a few other examples that lie outside NHC chemistry. PMID:25601453

  10. Blue phosphorescent nitrile containing C^C* cyclometalated NHC platinum(II) complexes.

    Science.gov (United States)

    Tronnier, Alexander; Metz, Stefan; Wagenblast, Gerhard; Muenster, Ingo; Strassner, Thomas

    2014-02-28

    Since C^C* cyclometalated Pt(II) complexes with N-heterocyclic carbene (NHC) ligands have been identified as potential emitter materials in organic light-emitting devices (OLEDs), very promising results regarding quantum yields, colour and stability have been presented. Herein, we report on four nitrile substituted complexes with a chelating NHC ligand (1-(4-cyanophenyl)-3-isopropyl-1H-benzo[d]imidazole or 4-(tert-butyl)-1-(4-cyanophenyl)-3-methyl-1H-imidazole) and a bidentate monoanionic auxiliary ligand (acetylacetone or dimesitoylmethane). The complexes have been fully characterized including extensive 2D NMR studies (COSY, HSQC, HMBC, NOESY, (195)Pt NMR), three of them also by solid-state structures. Photophysical measurements in amorphous PMMA films and pure emitter films at room temperature reveal the impact of the mesityl groups in the auxiliary ligand, which led to a significant increase of the quantum yield, while the decay lifetimes decreased. The electron withdrawing nitrile groups shift the emission towards blue colour coordinates. PMID:24362536

  11. NaSH in the construction of thiophene ring fused with N-heterocycles: a rapid and inexpensive synthesis of novel small molecules as potential inducers of apoptosis.

    Science.gov (United States)

    Kolli, Sunder Kumar; Nakhi, Ali; Medishetti, Raghavender; Yellanki, Swapna; Kulkarni, Pushkar; Ramesh Raju, R; Pal, Manojit

    2014-09-15

    A facile construction of a thiophene ring fused with N-heterocycles has been achieved via the reaction of NaSH with 2-chloro-3-alkynyl quinoxalines/pyrazines leading to novel 2-substituted thieno[2,3-b]pyrazine/quinoxaline derivatives as potential inducers of apoptosis. Some of them showed encouraging pharmacological properties when tested in zebrafish. PMID:25168747

  12. A heteroleptic ferrous complex with mesoionic bis(1,2,3-triazol-5-ylidene) ligands: taming the MLCT excited state of iron(II).

    Science.gov (United States)

    Liu, Yizhu; Kjaer, Kasper S; Fredin, Lisa A; Chábera, Pavel; Harlang, Tobias; Canton, Sophie E; Lidin, Sven; Zhang, Jianxin; Lomoth, Reiner; Bergquist, Karl-Erik; Persson, Petter; Wärnmark, Kenneth; Sundström, Villy

    2015-02-23

    Strongly ?-donating N-heterocyclic carbenes (NHCs) have revived research interest in the catalytic chemistry of iron, and are now also starting to bring the photochemistry and photophysics of this abundant element into a new era. In this work, a heteroleptic Fe(II) complex (1) was synthesized based on sequentially furnishing the Fe(II) center with the benchmark 2,2'-bipyridine (bpy) ligand and the more strongly ?-donating mesoionic ligand, 4,4'-bis(1,2,3-triazol-5-ylidene) (btz). Complex?1 was comprehensively characterized by electrochemistry, static and ultrafast spectroscopy, and quantum chemical calculations and compared to [Fe(bpy)3](PF6)2 and (TBA)2[Fe(bpy)(CN)4]. Heteroleptic complex?1 extends the absorption spectrum towards longer wavelengths compared to a previously synthesized homoleptic Fe(II) NHC complex. The combination of the mesoionic nature of btz and the heteroleptic structure effectively destabilizes the metal-centered (MC) states relative to the triplet metal-to-ligand charge transfer ((3)MLCT) state in 1, rendering it a lifetime of 13?ps, the longest to date of a photochemically stable Fe(II) complex. Deactivation of the (3)MLCT state is proposed to proceed via the (3)MC state that strongly couples with the singlet ground state. PMID:25504660

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

    DEFF Research Database (Denmark)

    Liu, Yizhu; Kjær, Kasper Skov

    2015-01-01

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

  14. The inhibition of mild steel corrosion in phosphoric acid solutions by some N-heterocyclic compounds in the salt form

    International Nuclear Information System (INIS)

    The effect of some quaternary N-heterocyclic compounds on the corrosion of mild steel in solutions of phosphoric acid (H3PO4) has been investigated in relation to the concentration of the inhibitor and acid as well as temperature by various monitoring corrosion techniques. Surface morphology was studied by scanning electron microscopy (SEM). Results obtained revealed that these compounds are good mixed-type inhibitors without changing the mechanism of the corrosion process. In general, at constant acid concentration, inhibitor efficiency increased with concentration of the inhibitor. On the other hand, at constant inhibitor concentration, inhibitor efficiency decreased with concentration of the acid up to a critical concentration above which it started to increase. The studied compounds appeared to function through general adsorption following the thermodynamic-kinetic adsorption isotherm. The thermodynamic parameters were determined and discussed. A quantitative correlation between inhibitor structure and inhibition efficiency was discussed

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

    Science.gov (United States)

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

    2015-04-28

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

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

    Science.gov (United States)

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

    2014-12-01

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

  17. Biological variation in sensitivity to N-heterocyclic PAHs; effects of acridine on seven species of micro-algae.

    Science.gov (United States)

    Dijkman, N A; Van Vlaardingen, P L; Admiraal, W A

    1997-01-01

    The toxicity of the nitrogen (N) heterocyclic polyaromatic hydrocarbon (PAH) acridine was tested for seven species of microalgae: Scenedesmus acuminatus, Selenastrum capricornutum, Chlamydomonas eugametos, Staurastrum chaetoceras, Staurastrum manfeldtii, Navicula salinarum and Nitzschia sigma. The effect of acridine on the algae was studied in a 96-h growth test, in which growth rates were determined using cell numbers and biovolume. The obtained EC50 values (for growth rates based on cell numbers) ranged from 0.08 mg litre(-1) for N. sigma to 0.78 mg litre(-1) for C. eugametos and N. salinarum. Effect concentrations based on biovolume were slightly higher for most species. Metabolism of acridine was observed for one species (S. capricornutum), but this capacity did not result in a very different tolerance. Acridine toxicity was neither related to taxonomical background (green algae versus diatoms) nor to original habitat of the species (planktonic or benthic, eutrophic or oligo-mesotrophic). The presence of near-UV radiation during the incubation might explain the higher toxicity of acridine than is expected on basis of QSAR derived narcotic toxicity. PMID:15093480

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

    Scientific Electronic Library Online (English)

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

    2014-05-01

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

  19. Mousy off-flavor of wine: precursors and biosynthesis of the causative N-heterocycles 2-ethyltetrahydropyridine, 2-acetyltetrahydropyridine, and 2-acetyl-1-pyrroline by Lactobacillus hilgardii DSM 20176.

    Science.gov (United States)

    Costello, Peter J; Henschke, Paul A

    2002-11-20

    The N-heterocyclic bases, 2-ethyltetrahydropyridine (1), 2-acetyl-1-pyrroline (2), and 2-acetyltetrahydropyridine (3) are associated with the occurrence of mousy off-flavor in wine. The biosynthesis of these N-heterocycles by the wine lactic acid bacterium, Lactobacillus hilgardii DSM 20176, was studied by high-cell-density incubation in combination with a minimal chemically defined N-heterocycle assay medium. The key components of the defined N-heterocycle assay medium included D-fructose, ethanol, L-lysine, L-ornithine, and mineral salts. N-heterocycle formation was quantitatively determined by gas chromatography-mass spectrometry. The formation of 2 and 3 required the concomitant availability of a fermentable carbohydrate (D-fructose), ethanol, and iron (Fe(2+)). In addition, L-ornithine stimulated the formation of 2 and repressed 3 formation, whereas L-lysine stimulated the formation of 3 and repressed 2 formation. Incorporation of d(6)-ethanol into the acetyl side chain of 2 and 3, and of d(4)-acetaldehyde into the acetyl side chain of 3, confirmed that ethanol and acetaldehyde could serve as major side chain precursors. A pathway for the formation of 2 and 3 by heterofermentative lactic acid bacteria is proposed involving the interaction of accumulated C-2 intermediates from the heterolactic pathway and N-heterocyclic intermediates derived from the metabolism of L-ornithine and L-lysine. PMID:12428963

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

    Science.gov (United States)

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

    2014-06-01

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

  1. Synthesis of a simplified version of stable bulky and rigid cyclic (alkyl)(amino)carbenes, and catalytic activity of the ensuing gold(I) complex in the three-component preparation of 1,2-dihydroquinoline derivatives.

    Science.gov (United States)

    Zeng, Xiaoming; Frey, Guido D; Kinjo, Rei; Donnadieu, Bruno; Bertrand, Guy

    2009-06-24

    A 95/5 mixture of cis and trans 2,4-dimethyl-3-cyclohexenecarboxaldehyde (trivertal), a common fragrance and flavor material produced in bulk quantities, serves as the precursor for the synthesis of a stable spirocyclic (alkyl)(amino)carbene, in which the 2-methyl-substituted cyclohexenyl group provides steric protection to an ensuing metal. The efficiency of this carbene as ligand for transition metal based catalysts is first illustrated by the gold(I) catalyzed hydroamination of internal alkynes with secondary dialkyl amines, a process with little precedent. The feasibility of this reaction allows for significantly enlarging the scope of the one-pot three-component synthesis of 1,2-dihydroquinoline derivatives, and related nitrogen-containing heterocycles. Indeed, two different alkynes were used, which include an internal alkyne for the first step. PMID:19456108

  2. Thiophene decorated with Fischer carbene ligands

    OpenAIRE

    Jaarsveld, Nina A.; Liles, David C.; Lotz, Simon

    2010-01-01

    The activation of a section, or of all the carbons of thiophene by bromine in lithium–halogen exchange reactions, was implemented in a step-wise manner to facilitate the preparation of novel multiple Fischer carbene-bearing thiophene compounds.

  3. An intermediate cobalt(IV) nitrido complex and its N-migratory insertion product.

    Science.gov (United States)

    Zolnhofer, Eva M; Käß, Martina; Khusniyarov, Marat M; Heinemann, Frank W; Maron, Laurent; van Gastel, Maurice; Bill, Eckhard; Meyer, Karsten

    2014-10-22

    Low-temperature photolysis experiments (T = 10 K) on the tripodal azido complex [(BIMPN(Mes,Ad,Me))Co(II)(N3)] (1) were monitored by EPR spectroscopy and support the formation of an exceedingly reactive, high-valent Co nitrido species [(BIMPN(Mes,Ad,Me))Co(IV)(N)] (2). Density functional theory calculations suggest a low-spin d(5), S = 1/2, electronic configuration of the central cobalt ion in 2 and, thus, are in line with the formulation of complex 2 as a genuine, low-spin Co(IV) nitride species. Although the reactivity of this species precludes handling above 50 K or isolation in the solid state, the N-migratory insertion product [(NH-BIMPN(Mes,Ad,Me))Co(II)](BPh4) (3) is isolable and was reproducibly synthesized as well as fully characterized, including CHN elemental analysis, paramagnetic (1)H NMR, IR, UV-vis, and EPR spectroscopy as well as SQUID magnetization and single-crystal X-ray crystallography studies. A computational analysis of the reaction pathway 2 ? 3 indicates that the reaction readily occurs via N-migratory insertion into the Co-C bond (activation barrier of 2.2 kcal mol(-1)). In addition to the unusual reactivity of the nitride 2, the resulting divalent cobalt complex 3 is a rare example of a trigonal pyramidal complex with four different donor ligands of a tetradentate chelate-an N-heterocyclic carbene, a phenolate, an imine, and an amine-binding to a high-spin Co(II) ion. This renders complex 3 chiral-at-metal. PMID:25243488

  4. A Brief Survey of our Contribution to Stable Carbene Chemistry

    OpenAIRE

    Martin, David; Melaimi, Mohand; Soleilhavoup, Michele; Bertrand, Guy

    2011-01-01

    This personal account summarizes our work, beginning with the discovery of the first stable carbene in 1988 up until the recent isolation of mesoionic carbenes. It explains why we have moved our focus from acyclic to cyclic carbenes, and shows that these stable species are not limited to the role of ligand for transition metals, but that they are also powerful agents for the activation of small molecules, and for the stabilization of highly reactive diamagnetic and paramagnetic species.

  5. Effect of the functionalisation route on a Zr-MOF with an Ir-NHC complex for catalysis.

    Science.gov (United States)

    Carson, Fabian; Martínez-Castro, Elisa; Marcos, Rocío; Miera, Greco González; Jansson, Kjell; Zou, Xiaodong; Martín-Matute, Belén

    2015-06-23

    A new iridium N-heterocyclic carbene (NHC) metallolinker has been synthesised and introduced into a metal-organic framework (MOF), for the first time, via two different routes: direct synthesis and postsynthetic exchange (PSE). The two materials were compared in terms of the Ir loading and distribution using X-ray energy dispersive spectroscopy (EDS), the local Ir structure using X-ray absorption spectroscopy (XAS) and the catalytic activity. The materials showed good activity and recyclability as catalysts for the isomerisation of an allylic alcohol. PMID:26050822

  6. 'Carbene radicals' in Co(II)(por)-catalyzed olefin cyclopropanation.

    Science.gov (United States)

    Dzik, Wojciech I; Xu, Xue; Zhang, X Peter; Reek, Joost N H; de Bruin, Bas

    2010-08-11

    The mechanism of cobalt(II)-porphyrin-mediated cyclopropanation of olefins with diazoesters was studied. The first step--reaction of cobalt(II)-porphyrin with ethyl diazoacetate (EDA)--was examined using EPR and ESI-MS techniques. EDA reacts with cobalt(II)-porphyrin to form a 1:1 Co(por)(CHCOOEt) adduct that exists as two isomers: the 'bridging carbene' C' in which the 'carbene' is bound to the metal and the pyrrolic nitrogen of the porphyrin that has a d(7) configuration on the metal, and the 'terminal carbene' C in which the 'carbene' behaves as a redox noninnocent ligand having a d(6) cobalt center and the unpaired electron residing on the 'carbene' carbon atom. The subsequent reactivities of the thus formed 'cobalt carbene radical' with propene, styrene, and methyl acrylate were studied using DFT calculations. The calculations suggest that the formation of the carbene is the rate-limiting step for the unfunctionalized Co(II)(por) and that the cyclopropane ring formation proceeds via a stepwise radical process: Radical addition of the 'carbene radical' C to the C=C double bonds of the olefins results in formation of the gamma-alkyl radical intermediates D. Species D then easily collapse in almost barrierless ring-closure reactions (TS3) to form the cyclopropanes. This radical mechanism readily explains the high activity of Co(II)(por) species in the cyclopropanation of electron-deficient olefins such as methyl acrylate. PMID:20681723

  7. Heterogeneous catalysts for carbene insertion reactions

    OpenAIRE

    Fraile, Jose? M.; Mayoral, Jose? A.; Rolda?n, Marta

    2011-01-01

    Copper catalysts supported on silica or silica-alumina are used to promote the insertion of carbenes, coming from methyl phenyldiazoacetate and ethyl diazoacetate, into one C-H bond of THF, constituting the first example of this reaction promoted by a purely inorganic catalyst. Cu/SiO2-Al 2O3 leads to better results, regarding yield and catalyst recovery, than with Cu/SiO2. With the former, yields are similar or even slightly better than those reached in solution using Cu (OTf)2 as the cataly...

  8. Synthesis of Endohedral Metallofullerene Glycoconjugates by Carbene Addition

    Directory of Open Access Journals (Sweden)

    Takeshi Akasaka

    2011-11-01

    Full Text Available Endohedral metallofullerene glycoconjugates were synthesized under mild conditions by carbene addition using appropriate glycosylidene-derived diazirine with La2@Ih-C80. NMR spectroscopic studies revealed that the glycoconjugate consists of two diastereomers of [6,6]-open mono-adducts. The electronic properties were characterized using Vis/NIR absorption spectroscopy and electrochemical measurements. This study demonstrates that glycosylidene carbene is useful to incorporate carbohydrate moieties onto endohedral metallofullerene surfaces.

  9. Synthesis of Endohedral Metallofullerene Glycoconjugates by Carbene Addition

    OpenAIRE

    Takeshi Akasaka; Yutaka Maeda; Chika I. Someya; Takahiro Tsuchiya; Tsukasa Nakahodo; Michio Yamada

    2011-01-01

    Endohedral metallofullerene glycoconjugates were synthesized under mild conditions by carbene addition using appropriate glycosylidene-derived diazirine with La2@Ih-C80. NMR spectroscopic studies revealed that the glycoconjugate consists of two diastereomers of [6,6]-open mono-adducts. The electronic properties were characterized using Vis/NIR absorption spectroscopy and electrochemical measurements. This study demonstrates that glycosylidene carbene is useful to incorporate carbohydrate moie...

  10. Rhodium-mediated stereoselective polymerization of "carbenes".

    Science.gov (United States)

    Hetterscheid, Dennis G H; Hendriksen, Coen; Dzik, Wojciech I; Smits, Jan M M; van Eck, Ernst R H; Rowan, Alan E; Busico, Vincenzo; Vacatello, Michele; Van Axel Castelli, Valeria; Segre, Annalaura; Jellema, Erica; Bloemberg, Tom G; de Bruin, Bas

    2006-08-01

    Unprecedented rhodium-catalyzed stereoselective polymerization of "carbenes" from ethyl diazoacetate (EDA) to give high molecular mass poly(ethyl 2-ylidene-acetate) is described. The mononuclear, neutral [(N,O-ligand)M(I)(cod)] (M = Rh, Ir) catalytic precursors for this reaction are characterized by (among others) single-crystal X-ray diffraction. These species mediate formation of a new type of polymers from EDA: carbon-chain polymers functionalized with a polar substituent at each carbon of the polymer backbone. The polymers are obtained as white powders with surprisingly sharp NMR resonances. Solution and solid state NMR data for these new polymers reveal a highly stereoregular polymer, with a high degree of crystallinity. The polymer is likely syndiotactic. Material properties are very different from those of atactic poly(diethyl fumarate) polymer obtained by radical polymerization of diethyl fumarate. Other diazoacetates are also polymerized. Further studies are underway to reveal possible applications of these new materials. PMID:16866530

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

    Science.gov (United States)

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

    2015-07-01

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

  12. Bonding and reactivity of a ?-hydrido dicopper cation.

    Science.gov (United States)

    Wyss, Chelsea M; Tate, Brandon K; Bacsa, John; Gray, Thomas G; Sadighi, Joseph P

    2013-12-01

    A bent dicopper-hydride cation that has an N-heterocyclic carbene supporting ligand has a Cu-H-Cu angle of 122° in the solid state. Density functional theory suggests an open three-centered metal-hydrogen interaction. The hydride reacts readily with methanol and with carbon dioxide; insertion of phenylacetylene affords a gem-dicopper vinyl complex. PMID:24132865

  13. Gold(I)-Catalyzed Hydroarylation of Allenes with Indoles

    OpenAIRE

    Toups, Kristina L.; Liu, Gordon T.; Widenhoefer, Ross A.

    2007-01-01

    Reaction of a monosubstituted, 1,3-disubstituted, or tetrasubstituted allene with various indoles catalyzed by a 1:1 mixture of a gold(I) N-heterocyclic carbene complex and AgOTf at room temperature leads to hydroarylation with formation of 3-allyl-indoles in modest to good yield.

  14. Unsaturated carbone and allenylidene ruthenium complexes from alkynes

    International Nuclear Information System (INIS)

    The author's studies aimed at activation of terminal alkynes by metal complexes, reactivity patterns and selective preparations of unsaturated carbene, allenylidene and cumulenylidene derivatives of (arene)ruthenium complexes are reviewed. 48 refs

  15. Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-12-01

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

  16. Deprotonation of a Borohydride: Synthesis of a Carbene-Stabilized Boryl Anion**

    OpenAIRE

    Ruiz, David A.; Ung, Gaël; Melaimi, Mohand; Bertrand, Guy

    2013-01-01

    An acidic hydride! Thanks to the presence of a ?-acceptor cyclic (alkyl)(amino)carbene (CAAC) and of two electron-withdrawing nitrile groups, a borohydride reacts with a base to give a carbene-stabilized boryl anion, which reacts with carbon and metal electrophiles at the boron center.

  17. Experimental evidence for cobalt(III)-carbene radicals: key intermediates in cobalt(II)-based metalloradical cyclopropanation.

    Science.gov (United States)

    Lu, Hongjian; Dzik, Wojciech I; Xu, Xue; Wojtas, Lukasz; de Bruin, Bas; Zhang, X Peter

    2011-06-01

    New and conclusive evidence has been obtained for the existence of cobalt(III)-carbene radicals that have been previously proposed as the key intermediates in the underlying mechanism of metalloradical cyclopropanation by cobalt(II) complexes of porphyrins. In the absence of olefin substrates, reaction of [Co(TPP)] with ethyl styryldiazoacetate was found to generate the corresponding cobalt(III)-vinylcarbene radical that subsequently dimerizes via its ?-radical allylic resonance form to afford a dinuclear cobalt(III) porphyrin complex. X-ray structural analysis reveals a highly compact dimeric structure wherein the two metalloporphyrin units are arranged in a face-to-face fashion through a tetrasubstituted 1,5-hexadiene C(6)-bridge between the two Co(III) centers. The ?-radical allylic resonance form of the cobalt(III)-vinylcarbene radical intermediate could be effectively trapped by TEMPO via C-O bond formation to give a mononuclear cobalt(III) complex instead of the dimeric product. The allylic radical nature and related reactivity profile of the cobalt(III)-carbene radical, including its inability to abstract hydrogen atoms from toluene solvent, were established by DFT calculations. PMID:21563829

  18. Fire and ice: a gold(III) monohydride.

    Science.gov (United States)

    Hashmi, A Stephen K

    2012-12-21

    Good as gold: gold hydrides were long considered unstable. In the past few years reports have appeared on not only the stable NHC gold(I) monohydride complex 1 (see structure; NHC=N-heterocyclic carbene) but also a dinuclear gold(I) hydride and most recently the gold(III) monohydride complex 2 with a C-N-C pincer ligand. One can expect new and important impulses for inorganic and organometallic chemistry and homogeneous gold catalysis. PMID:23184856

  19. Transition metal-induced activation of alkynes leading to metal carbene species: synthetic application to new ?-conjugated molecules

    International Nuclear Information System (INIS)

    The in situ generation of furylcarbene complexes by means of transition metals was applied to catalytic carbene reactions, such as Wittig-type olefination and cycloisomerization reactions. In the presence of [Rh(OAc)2]2 as a catalyst and triphenylphosphine as a carbene accepter, carbonyl-ene-ynes 1a reacted with benzaldehyde to give a 2-styrylfuran derivative 3a. The reaction involving phosphine-ylide formation followed by Wittig-type olefination with aldehydes was applied to synthesis of furfurylidene-containing p-extended conjugated molecules. A Ruthenium catalyst underwent cycloisomerization of 1,2-bis(carbonylenyl)acetylene 10a,b to afford 2,2'-bifuran structures. The crystal structure of 5,5'-diphenyl-2,2'-bifuran 11b was determined by X-ray crystallography. The ORTEP drawings of 11b exhibited transoid and highly planar structure. The emission bands of the bisfuran 11b were observed at 414 and 440 nm, its quantum yield (84%) was higher than that of a similar 5,5'-diphenyl-2,2'-bithiophene

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

    DEFF Research Database (Denmark)

    HØj, Martin; Kvaskoff, David

    2014-01-01

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

  1. Activation of molecular hydrogen by a singlet carbene through quantum mechanical tunneling.

    Science.gov (United States)

    Henkel, Stefan; Sander, Wolfram

    2015-04-01

    Carbenes are among the few metal-free molecules that are able to activate molecular hydrogen. Whereas triplet carbenes have been shown to insert into H2 through a two-step mechanism that at low temperature is assisted by quantum mechanical tunneling (QMT), singlet carbenes insert in concerted reactions with considerable activation barriers, and are thus unreactive towards H2 at cryogenic temperatures. Here we show that 1-azulenylcarbene with a singlet ground state readily inserts into H2 , and that QMT governs the insertion into both H2 and D2 . This is the first example that shows that QMT can also be important for singlet carbenes inserting into dihydrogen. PMID:25690272

  2. C-H bond functionalization based on metal carbene migratory insertion.

    Science.gov (United States)

    Hu, Fangdong; Xia, Ying; Ma, Chen; Zhang, Yan; Wang, Jianbo

    2015-05-11

    Cross-coupling reactions involving metal carbene migratory insertion have been established as a new type of coupling reaction with diazo compounds as the reaction partners. Since 2011, an interesting development has been made in which the carbene migratory insertion process is successfully merged into C-H bond activations. Along this line, a series of investigations have been documented in the past few years. This feature article summarizes the developments in this area. PMID:25739369

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

    Directory of Open Access Journals (Sweden)

    Marilé 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(I–N-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 C—H...O hydrogen bond.

  4. Efficient Boron-Copper Additions to Aryl-Substituted Alkenes Promoted by NHC–Based Catalysts. Enantioselective Cu-Catalyzed Hydroboration Reactions

    OpenAIRE

    Lee, Yunmi; Hoveyda, Amir H.

    2009-01-01

    A Cu-catalyzed method for efficient boron-copper addition processes involving acyclic and cyclic disubstituted aryl olefins are reported. Reactions are promoted with 0.5–5 mol % of a readily available N-heterocyclic carbene (NHC) complex; the presence of MeOH promotes in situ protonation of the C–Cu bond and leads to efficient catalyst turnover, constituting a net Cu-catalyzed hydroboration process. Reactions proceed in >98:

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

    Czech Academy of Sciences Publication Activity Database

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

    2006-01-01

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

  6. trans-Bis{1-[2-(2,6-diisopropyl­anilino)phenyl]-3-isopropyl­imidazolin-2-ylidenyl-?C 2}diiodidopalladium(II) benzene disolvate

    OpenAIRE

    Daly, Christopher G.; Kuldip Singh; Cross, Warren B.

    2011-01-01

    In the title complex, [PdI2(C24H31N3)2]·2C6H6, the Pd2+ ion is located on an inversion centre in a slightly distorted square-planar geometry. The angle between the I2C2 square plane and the mean plane of the N-heterocyclic carbene ring is 79.8?(2)°, with I—Pd—C—N torsion angles of ?81.1?(6) and ?78.2?(5)°. The Pd—carbene and Pd—I distances are 2.016?(6) and ...

  7. Rotational spectrum and theoretical structure of the carbene HC4N

    Science.gov (United States)

    McCarthy, M. C.; Apponi, A. J.; Gordon, V. D.; Gottlieb, C. A.; Thaddeus, P.; Daniel Crawford, T.; Stanton, John F.

    1999-10-01

    Following a high-level coupled cluster calculation, the rotational spectrum of the bent HC4N singlet carbene was detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. The three rotational constants, the leading centrifugal distortion constants, and two nitrogen hyperfine coupling constants were determined to high accuracy. The rotational constants agree with those calculated ab initio to better than 0.5%. Like the isoelectronic C5H2 carbene of similar structure, HC4N was found to have fairly large centrifugal distortion and a large inertial defect. The calculated dipole moment of HC4N is 2.95 D.

  8. Rhodium (II) carbene C-H insertion in water and catalyst reuse

    International Nuclear Information System (INIS)

    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 Rh2(OAc)4. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutilization. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-07-31

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

  10. Reactivity of Cationic Agostic and Carbene Structures Derived from Platinum(II) Metallacycles.

    Science.gov (United States)

    Campos, Jesús; Ortega-Moreno, Laura; Conejero, Salvador; Peloso, Riccardo; López-Serrano, Joaquín; Maya, Celia; Carmona, Ernesto

    2015-06-01

    This paper describes the formation of new platinacyclic complexes derived from the phosphine ligands PiPr2 Xyl, PMeXyl2 , and PMe2 Ar?Xyl?2 (Xyl=2,6-Me2 C6 H3 and Ar?Xyl?2=2,6-(2,6-Me2 C6 H3 )2 -C6 H3 ) as well as reactivity studies of the trans-[Pt(C^P)2 ] bis-metallacyclic complex 1?a derived from PiPr2 Xyl. Protonation of compound 1?a with [H(OEt2 )2 ][BArF ] (BArF =B[3,5-(CF3 )2 C6 H3 ]4 ) forms a cationic ?-agostic structure 4?a, whereas ?-hydride abstraction employing [Ph3 C][PF6 ] produces a cationic platinum carbene trans-[Pt{PiPr2 (2,6-CH(Me)C6 H3 }{PiPr2 (2,6-CH2 (Me)C6 H3 }][PF6 ] (8). Compounds 4?a and 8 react with H2 to yield the same 1:3 equilibrium mixture of 4?a and trans-[PtH(PiPr2 Xyl)2 ][BArF ] (6), in which one of the phosphine ligands participates in a ?-agostic interaction. DFT calculations reveal that H2 activation by 8 occurs at the highly electrophilic alkylidene terminus with no participation of the metal. The two compounds 4?a and 8 experience C-C coupling reactions of a different nature. Thus, 4?a gives rise to complex trans-[PtH{(E)-1,2-bis(2-(PiPr2 )-3-MeC6 H3 )CH?CH}] (7) that contains a tridentate diphosphine-alkene ligand, through agostic C?H oxidative cleavage and C-C reductive coupling steps, whereas the C-C coupling reaction in 8 involves classical migratory insertion of its [Pt?CH] and [Pt?CH2 ] bonds promoted by platinum coordination of CO or CNXyl. The mechanisms of the C?C bond-forming reactions have also been investigated by computational methods. PMID:25959723

  11. (Aminocarbene)(divinyltetramethyldisiloxane)iron(0) compounds: a class of low-coordinate iron(0) reagents.

    Science.gov (United States)

    Zhang, Hezhong; Ouyang, Zhenwu; Liu, Yuesheng; Zhang, Qiang; Wang, Lei; Deng, Liang

    2014-08-01

    The combined use of aminocarbene and divinyltetramethyldisiloxane (dvtms) as supporting ligands enables the access of unprecedented low-coordinate iron(0) alkene compounds [L(n)Fe(?(2):?(2)-dvtms)] (L=N-heterocyclic carbene (NHC) or cyclic (alkyl)(amino)carbene (CAAC), n=1 or 2) from the reactions of FeCl2 with alkali-metal reducing agents, free aminocarbene ligands, and dvtms. The iron(0) species deliver their {L(n)Fe(0)} fragments to perform redox reactions with Ph2SiH2, S8, Se, and DippN3, furnishing novel aminocarbene-supported iron(IV) silylene, all-ferrous iron-sulfur/selenium cubanes, and bis(imido)iron(IV) compounds. These conversions demonstrate the potential synthetic utility of the carbene-supported iron(0) complexes as a valuable class of low-coordinate iron(0) reagents. PMID:24961207

  12. Explicit role of dynamical and nondynamical electron correlation on singlet-triplet splitting in carbenes

    Energy Technology Data Exchange (ETDEWEB)

    Seal, Prasenjit [Department of Chemistry, University of Calcutta, 92, A.P.C. Ray Road, Kolkata - 700 009 (India); Chakrabarti, Swapan [Department of Chemistry, University of Calcutta, 92, A.P.C. Ray Road, Kolkata - 700 009 (India)], E-mail: swapanchem@yahoo.co.in

    2007-02-14

    Density functional theoretical studies have been performed on carbene systems to determine the singlet-triplet splitting and also to explore the role of electron correlation. Using an approximate method of separation of dynamical and nondynamical correlation, it is found that dynamical and nondynamical electron correlation stabilizes the singlet state relative to the triplet for halo carbenes in both BLYP and B3LYP methods. Calculations performed on higher homologues of methylene suggest that beyond CH(CH{sub 3}), both the electron correlations have leveling effect in stabilizing the singlet state relative to the triplet. It has also been observed while dynamical electron correlation fails to provide any substantial degree of stabilization to the singlet states of higher homologues of methylene in B3LYP method, an opposite trend is observed for nondynamical counterpart. Among the larger systems studied (9-triptycyl)({alpha}-naphthyl)-carbene has the highest stability of the triplet state whereas bis-imidazol-2-ylidenes has the most stable singlet state. Interestingly, the values of the dynamical electron correlation for each state of each system studied are different for the two methods used. The reason behind this apparent discrepancy lies in the fact that the coefficients of the LYP part in B3LYP and BLYP functionals are different.

  13. Explicit role of dynamical and nondynamical electron correlation on singlet-triplet splitting in carbenes

    International Nuclear Information System (INIS)

    Density functional theoretical studies have been performed on carbene systems to determine the singlet-triplet splitting and also to explore the role of electron correlation. Using an approximate method of separation of dynamical and nondynamical correlation, it is found that dynamical and nondynamical electron correlation stabilizes the singlet state relative to the triplet for halo carbenes in both BLYP and B3LYP methods. Calculations performed on higher homologues of methylene suggest that beyond CH(CH3), both the electron correlations have leveling effect in stabilizing the singlet state relative to the triplet. It has also been observed while dynamical electron correlation fails to provide any substantial degree of stabilization to the singlet states of higher homologues of methylene in B3LYP method, an opposite trend is observed for nondynamical counterpart. Among the larger systems studied (9-triptycyl)(?-naphthyl)-carbene has the highest stability of the triplet state whereas bis-imidazol-2-ylidenes has the most stable singlet state. Interestingly, the values of the dynamical electron correlation for each state of each system studied are different for the two methods used. The reason behind this apparent discrepancy lies in the fact that the coefficients of the LYP part in B3LYP and BLYP functionals are different

  14. A theoretical study of the mechanism of the addition reaction between carbene and azacyclopropane

    Directory of Open Access Journals (Sweden)

    XIAOJUN TAN

    2010-05-01

    Full Text Available The mechanism of the addition reaction between carbene and azacyclopropane was investigated using the second-order Moller–Plesset perturbation theory (MP2. By using the 6-311+G* basis set, geometry optimization, vibrational analysis and the energy properties of the involved stationary points on the potential energy surface were calculated. From the surface energy profile, it can be predicted that there are two reaction mechanisms. The first one (1 is carbene attack at the N atom of azacyclopropane to form an intermediate, 1a (IM1a, which is a barrier-free exothermic reaction. Then, IM1a can isomerize to IM1b via a transition state 1a (TS1a, in which the potential barrier is 30.0 kJ/mol. Subsequently, IM1b isomerizes to a product (Pro1 via TS1b with a potential barrier of 39.3 kJ/mol. The other one (2 is carbene attack at the C atom of azacyclopropane, firstly to form IM2 via TS2a, the potential barrier is 35.4 kJ/mol. Then IM2 isomerizes to a product (Pro2 via TS2b with a potential barrier of 35.1 kJ/mol. Correspondingly, the reaction energy for the reactions (1 and (2 is –478.3 and –509.9 kJ/mol, respectively. Additionally, the orbital interactions are also discussed for the leading intermediate.

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

    Scientific Electronic Library Online (English)

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

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

  16. Pd-catalyzed cross-coupling of terminal alkynes with ene-yne-ketones: access to conjugated enynes via metal carbene migratory insertion.

    Science.gov (United States)

    Xia, Ying; Liu, Zhen; Ge, Rui; Xiao, Qing; Zhang, Yan; Wang, Jianbo

    2015-06-30

    A novel strategy for alkyne-alkyne cross-coupling has been developed under the palladium catalysis. In this reaction, ene-yne-ketones are employed as carbene precursors, which couple with terminal alkynes through the metal carbene migratory insertion process. Furan-substituted enynes are obtained in good yields and in a stereoselective manner. PMID:26077197

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-01-30

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

  18. Highvalent and organometallic technetium and rhenium compounds

    International Nuclear Information System (INIS)

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

  19. rac-cis-Dicarbonyl­chlorido{1-[2-(diphenyl­phosphanyl-?P)benz­yl]-3-(phenyl-?C 1)imidazol-2-yl­idene-?C 2}ruthenium(II) dichloro­methane monosolvate

    OpenAIRE

    Domski, Gregory J.; Pecak, Wiktoria H.; Swenson, Dale C.

    2012-01-01

    In the title compound, [Ru(C28H22N2P)Cl(CO)2]·CH2Cl2, the RuII atom exhibits a distorted octa­hedral coordination geometry. The N-phenyl group of the ligand has undergone orthometalation; as a result, the tridentate phosphane-functionalized N-heterocyclic carbene ligand is coordinating in a meridional fashion. This complex is of inter­est with respect to transfer hydrogenation catalysis and also provides an example of C—H activation behavior in late transition metal complexes. The dichlo...

  20. rac-cis-Dicarbonylchlorido{1-[2-(diphenylphosphanyl-κP)benzyl]-3-(phenyl-κC1)imidazol-2-ylidene-κC2}ruthenium(II) dichloromethane monosolvate

    OpenAIRE

    Domski, Gregory J.; Pecak, Wiktoria H.; Swenson, Dale C.

    2012-01-01

    In the title compound, [Ru(C28H22N2P)Cl(CO)2]·CH2Cl2, the RuII atom exhibits a distorted octahedral coordination geometry. The N-phenyl group of the ligand has undergone orthometalation; as a result, the tridentate phosphane-functionalized N-heterocyclic carbene ligand is coordinating in a meridional fashion. This complex is of interest with respect to transfer hydrogenation catalysis and also provides an example of C—H activation behavior in late transition metal complexes...

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

    CERN Document Server

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

    2015-01-01

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

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

    Science.gov (United States)

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

    2015-04-21

    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

  3. 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

    Directory of Open Access Journals (Sweden)

    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°.

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

    DEFF Research Database (Denmark)

    NordstrØm, Lars Ulrik Rubæk; Vogt, Henning

    2008-01-01

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

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

    Scientific Electronic Library Online (English)

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

    2009-09-01

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

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

    Czech Academy of Sciences Publication Activity Database

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

    2014-01-01

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

  7. Gas-phase synthesis of charged copper and silver Fischer carbenes from diazomalonates: mechanistic and conformational considerations in metal-mediated wolff rearrangements.

    Science.gov (United States)

    Julian, Ryan R; May, Jeremy A; Stoltz, Brian M; Beauchamp, J L

    2003-04-16

    Copper(I) and silver(I) Fischer carbenes are synthesized in the gas phase. Various diazomalonate-based compounds with an attached metal ion are introduced into the gas phase by electrospray ionization and subjected to collisional activation. Loss of N(2) generates a metastable Fischer carbene, which subsequently undergoes Wolff rearrangement and loss of CO. Further excitation leads to the loss of another CO molecule and the generation of a stable Fischer carbene. Isotopically labeled compounds are utilized to confirm the assignment of the products resulting from this process. DFT calculations are used to evaluate various mechanistic possibilities and to quantitatively assess the energetics of reactants and products. Silver(I) is shown to be more effective in facilitating Wolff rearrangement than copper(I), although both are more effective when compared to spectator charges such as sodium or a fixed quaternary nitrogen. Carbenes are not produced when copper(II), nickel(II), or a proton is used to form a quasi-molecular ion from the diazomalonate carbene precursor. Finally, trapping of the Fischer carbene by various functional groups attached through the open coordination site of the metal is investigated. PMID:12683818

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

    Czech Academy of Sciences Publication Activity Database

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

    2013-01-01

    Ro?. 117, ?. 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

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

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xianping.

    1990-09-21

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

  10. Palladium-Catalyzed Tandem Carbene Migratory Insertion and Intramolecular Cyclization: Synthesis of Chromeno[4,3-b]chromene Compounds.

    Science.gov (United States)

    Shang, Xue Song; Li, Nian Tai; Siyang, Hai Xiao; Liu, Pei Nian

    2015-05-01

    Chromeno[4,3-b]chromene is a ubiquitous structural motif found in various pharmaceuticals and biologically active compounds. A concise palladium-catalyzed reaction of vinyl iodides and salicyl N-tosylhydrazones has been achieved to afford a series of compounds containing the chromeno[4,3-b]chromene scaffold in moderate to high yield. This tandem reaction involves palladium(II) carbene migratory insertion and intramolecular cyclization assisted by an O nucleophile and tolerates various functional groups. PMID:25880468

  11. Synthesis and reactions of cyclovalence isomers of azo-keto-carbenes

    International Nuclear Information System (INIS)

    Novel types of cycloaddition products with an azomethine imine functionality have been prepared from ?-azo-?'-diazo ketones with a carbon chain of variable length between the azo- and the keto-group; the reaction is induced by catalytical amounts of rhodium(II) acetate and occurs with the concomitant extrusion of dinitrogen. The synthesis of these cyclic azomethine imines succeeded in the course of the intramolecular reaction of the azo nitrogen atoms with a carbene/carbenoid carbon atom, in situ generated from the ?-diazoketone functionality; this is a novel cyclization reaction. Some of the resulting cyclization products are stable and have been isolated, others could only be trapped with dipolarophiles as [3+2] cycloadducts. The ring-size of the heterocyclic products depends on the one hand on the length of the carbon-chain (for n = 0, 1, 2) between the carbonyl carbon atom and the quaternary aliphatic or aromatic carbon atom that blocks the tautomerization of the azo-group in the starting material. On the other hand, the ring size depends on which of the two nitrogen atoms of the azo-group undergoes the ring closure with the carbene/carbenoid carbon atom generated from the ?-diazoketon functionality in the course of the reaction. By far the most serious problem in the preparation of the cyclic azomethine imines is the synthesis of the required ?-azo-?'-diazo ketones. A so far unknown property of the azo-group is its intramolecularly directed nucleophilicity olecularly directed nucleophilicity toward ketenes, which emerge from acid chlorides and anhydrides, or from ?-diazo ketones in the course of the Wolff rearrangement. This complicated the approach to the required ?-azo-?'-diazo ketones via these functionalities as precursors and with the desired chain length between the azo- and diazo-keto-groups. Nevertheless, these problems could be overcome by using alternative strategies. Utilizing ?-azo-?'-diazo ketones a largely commonly applicable approach to endocyclic and N-exocyclic azomethine imines was worked out, which results from the so far unknown intramolecular reaction of azo-nitrogen atoms on carbenoids (rhodium-stabilized carbenes). Work up and isolation of the different reaction products turned out not to be without difficulty. Most of the novel and in solution partly unstable compounds that were characterized in this thesis would not have been isolable in the conventional manner (chemical separation processes, column chromatography). However, this has been managed by employing the radial chromatography upon optimizing some parameters; apparently, this is a not widely known chromatographic separation method that enables fast separations with high efficiency. To clarify the question, why only certain azomethine imines react with special dipolarophiles, quantum-mechanical calculations of the reactants' frontier orbitals have been carried out; this resulted in a satisfactory concordance with the FMO theory by Fukui. Likewise, molecular calculations rationalize the observed stereo- and regioselectivity as well as the kinetic and thermodynamic reaction control in the course of cycloaddition reactions of azomethine imines. (author)

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

    Directory of Open Access Journals (Sweden)

    Nuno R. Candeias

    2007-01-01

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

  13. Carbene supported dimer of heavier ketenimine analogue with p and si atoms.

    Science.gov (United States)

    Roy, Sudipta; Dittrich, Birger; Mondal, Totan; Koley, Debasis; Stückl, A Claudia; Schwederski, Brigitte; Kaim, Wolfgang; John, Michael; Vasa, Suresh Kumar; Linser, Rasmus; Roesky, Herbert W

    2015-05-20

    A cyclic alkyl(amino) carbene (cAAC) stabilized dimer [(cAAC)Si(P-Tip)]2 (2) (Tip = 2,4,6-triisopropylphenyl) is reported. 2 can be considered as a dimer of the heavier ketenimine (R2C?C?N-R) analogue. The dark-red rod-shaped crystals of 2 were synthesized by reduction of the precursor, cAAC-dichlorosilylene-stabilized phosphinidene (cAAC)SiCl2?P-Tip with sodium napthalenide. The crystals of 2 are storable at room temperature for several months and stable up to 215 °C under an inert atmosphere. X-ray single-crystal diffraction revealed that 2 contains a cyclic nonplanar four-membered SiPSiP ring. Magnetic susceptibility measurements confirmed the singlet spin ground state of 2. Cyclic voltammetry of 2 showed a quasi-reversible one-electron reduction indicating the formation of the corresponding radical anion 2(•-), which was further characterized by EPR measurements in solution. The electronic structure and bonding of 2 and 2(•-) were studied by theoretical calculations. The experimentally obtained data are in good agreement with the calculated values. PMID:25919008

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

    Science.gov (United States)

    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

  15. Rapid Generation and Safe Use of Carbenes Enabled by a Novel Flow Protocol with In-line IR spectroscopy.

    Science.gov (United States)

    Müller, Simon T R; Murat, Aurélien; Maillos, Delphine; Lesimple, Patrick; Hellier, Paul; Wirth, Thomas

    2015-05-01

    A powerful new continuous process for the formation and use of donor/acceptor-substituted carbenes is described. The safety profile of diazo group transfer on methyl phenylacetate was determined including kinetic studies in batch and in flow using in-line IR analysis. Batch work-up and liquid chromatography were circumvented by developing an optimized liquid/liquid flow separation method providing aryl diazoacetates in high purity. Fast screening of reaction conditions in flow with in-line IR analysis allowed rapid reaction optimization. Finally, a multistep process of diazo group transfer, extraction, separation and subsequent diazo decomposition combined with multiple X?H insertion reactions was established. PMID:25808068

  16. Synthesis and characterisation of the aminocarbene complexes [(eta(5)-C5H5)Fe(CO)(PPh3){=C(NHR2)(CH2R1)}]+BF4- [R-1 = H, Me or Pr; R-2 = H, Me, Et, CHMe2, CH2Ph, CH(Me)Ph, CH2CH=CH2 or CH2CH2OH

    OpenAIRE

    Davies, SG; Edwards, AJ; JONES, S; Metzler, MR; YANADA, K; YANADA, R

    1998-01-01

    A number of secondary aminocarbenes of the type (RS)-[(?5-C5H5)Fe(CO)(PPh 3){=C(CH2R1)(NHR2)}] +BF4- were synthesised in very good yield [66-99%, R1 = H, Me or Pr; R2 = H, Me, Et, CHMe2, CH2Ph, CH(Me)Ph, CH2CH=CH2 or CH2CH2OH]. The absolute configuration of one of the carbenes was established by a single-crystal X-ray diffraction experiment. The chemistry of the carbene complexes was investigated.

  17. Theoretical studies of the insertion of carbenes in the zeolite framework: modification of the acidity and creation of chiral sites

    Scientific Electronic Library Online (English)

    Maria Beatriz S., Mota; Nilton, Rosenbach Jr.; Claudio J. A., Mota.

    1021-10-01

    Full Text Available Foi realizado um estudo teórico da inserção de carbenos (CH2 e CHCHO) na estrutura cristalina da zeólita Y. O método our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) M062x/6-31G(d,p):PM6 foi utilizado para descrever a inserção do metileno (CH2) nas ligações T-O (T = Si [...] ou Al) da rede resultando em quatro estruturas isômeras. Em todos os casos os cálculos indicaram uma alta exotermicidade para a inserção do metileno na rede cristalina, independentemente da multiplicidade do carbeno (singlete ou triplete). A inserção na ligação O-H ácida para formar um grupo metóxi adsorvido foi o processo mais favorável, mas este caminho não ocorre se a inserção é feita na zeólita desprotonada. A inserção do formil-carbeno (CHCHO) cria centros quirais na estrutura cristalina. A acidez da zeólita após a inserção dos carbenos foi calculada usando a energia de desprotonação. Os cálculos predizem a possibilidade de desenvolver zeólitas ácidas com centros quirais, que poderiam imitar enzimas, especialmente para uso em processos de química fina e transformação de biomassa. Abstract in english A theoretical study of the insertion of carbenes (CH2, CHCHO) in the framework structure of zeolite Y was carried out. The "our own n-layered integrated molecular orbital and molecular mechanics" (ONIOM) scheme M062x/6-31G(d,p):PM6 was used to describe the insertion of methylene (CH2) in the T-O bon [...] ds (T = Si, Al) of the framework yielding four isomeric structures. In all cases, calculations indicated a high exothermic process for the insertion of methylene in the framework, regardless of the spin multiplicity of the carbene (singlet or triplet). Insertion into the acidic O-H bond to afford an adsorbed methoxy group was the most favourable process, but this pathway does not occur if insertion is carried out on the deprotonated zeolite. Insertion of formylcarbene (CHCHO) creates chiral sites in the framework. The acidity of the zeolite structures after carbene insertion was calculated by means of the deprotonation energy. The calculations predicted the possibility of designing acidic zeolites with chiral sites that could mimic enzymes, especially for uses in fine chemical processes and biomass transformations.

  18. rac-cis-Dicarbonylchlorido{1-[2-(diphenylphosphanyl-?Pbenzyl]-3-(phenyl-?C1imidazol-2-ylidene-?C2}ruthenium(II dichloromethane monosolvate

    Directory of Open Access Journals (Sweden)

    Gregory J. Domski

    2012-09-01

    Full Text Available In the title compound, [Ru(C28H22N2PCl(CO2]·CH2Cl2, the RuII atom exhibits a distorted octahedral coordination geometry. The N-phenyl group of the ligand has undergone orthometalation; as a result, the tridentate phosphane-functionalized N-heterocyclic carbene ligand is coordinating in a meridional fashion. This complex is of interest with respect to transfer hydrogenation catalysis and also provides an example of C—H activation behavior in late transition metal complexes. The dichloromethane solvent molecule is disordered over two sets of sites with an occupancy ratio of 0.873?(14:0.127?(14.

  19. Antileishmanial activity of ruthenium(II)tetraammine nitrosyl complexes.

    Science.gov (United States)

    Pereira, José Clayston Melo; Carregaro, Vanessa; Costa, Diego Luís; da Silva, João Santana; Cunha, Fernando Q; Franco, Douglas Wagner

    2010-09-01

    The complexes trans-[Ru(NO)(NH(3))(4)L](X)(3) (X = BF(4)(-), PF(6)(-) or Cl(-) and L = N-heterocyclic ligands, P(OEt)(3), SO(3)(-2)), and [Ru(NO)Hedta)] were shown to exhibit IC(50pro) in the range of 36 (L = imN) to 5000 microM (L = imC). The inhibitory effects of trans-[Ru(NO)(NH(3))(4)imN](BF(4))(3) and of the Angeli's salt on the growth of the intramacrophage amastigote form studied were found to be similar while the trans-[Ru(NH(3))(4)imN(H(2)O)](2+) complex was found not to exhibit any substantial antiamastigote effect. The trans-[Ru(NO)(NH(3))(4)imN](BF(4))(3) compound, administered (500 nmol kg(-1) day(-1)) in BALB/c mice infected with Leishmania major, was found to exhibit a 98% inhibition on the parasite growth. Furthermore, this complex proved to be at least 66 times more efficient than glucantime in in vivo experiments. PMID:20598778

  20. Catalyst-controlled reverse selectivity in C-C bond formation: NHC-Cu-catalyzed ?-selective allylic alkylation with organolithium reagents.

    Science.gov (United States)

    Pizzolato, Stefano F; Giannerini, Massimo; Bos, Pieter H; Fañanás-Mastral, Martín; Feringa, Ben L

    2015-05-11

    An efficient and highly ?-selective copper-catalyzed allylic alkylation of allylic halides with organolithium reagents is presented. The use of N-heterocyclic carbenes as ligands is key to reverse the common ?-selectivity of this transformation and gives rise to the corresponding linear products with high levels of regioselectivity. PMID:25872468

  1. C?H alkenylations with alkenyl acetates, phosphates, carbonates, and carbamates by cobalt catalysis at 23?°c.

    Science.gov (United States)

    Moselage, Marc; Sauermann, Nicolas; Richter, Sven C; Ackermann, Lutz

    2015-05-18

    Inexpensive cobalt catalysts with N-heterocyclic carbene ligands enable direct arene alkenylations with easily accessible alkenyl acetates through regioselective C?H/C?O functionalizations in a stereoconvergent fashion. The versatile cobalt catalyst was broadly applicable and thus also allowed for the efficient conversion of alkenyl phosphates, carbonates, and carbamates at ambient temperature. PMID:25864965

  2. Cu-catalyzed formal methylative and hydrogenative carboxylation of alkynes with carbon dioxide: efficient synthesis of ?,?-unsaturated carboxylic acids.

    Science.gov (United States)

    Takimoto, Masanori; Hou, Zhaomin

    2013-08-19

    The sequential hydroalumination or methylalumination of various alkynes catalyzed by different catalyst systems, such those based on Sc, Zr, and Ni complexes, and the subsequent carboxylation of the resulting alkenylaluminum species with CO2 catalyzed by an N-heterocyclic carbene (NHC)-copper catalyst have been examined in detail. The regio- and stereoselectivity of the overall reaction relied largely on the hydroalumination or methylalumination reactions, which significantly depended on the catalyst and alkyne substrates. The subsequent Cu-catalyzed carboxylation proceeded with retention of the stereoconfiguration of the alkenylaluminum species. All the reactions could be carried out in one-pot to afford efficiently a variety of ?,?-unsaturated carboxylic acids with well-controlled configurations, which are difficult to construct by previously reported methods. This protocol could be practically useful and attractive because of its high regio- and stereoselectivity, simple one-pot reaction operation, and the use of CO2 as a starting material. PMID:23852827

  3. PHOTOFRAGMENTATION VOLTAMMETRY STUDIES OF THE AMINOCARBENE COMPLEXES [(ETA(5)-C5H5)FE(CO)(L)(=C(NHR(1))(R(2))]BF4 [L = PPH3, P(P-TOL)3, R(1) = ME, CH2PH, R(2) = ME, BU

    OpenAIRE

    Davies, S.; Metzler, M.; Watkins, W.; Compton, R; Booth, J.; EKLUND, J

    1993-01-01

    The synthesis of the complexes [(?5-C5H5)Fe(CO)(L){=C(NHR 1)(R2)}]BF4 [L = PPh3, P(p-Tol)3; R1 = Me, CH2Ph; R2 = Me, Bu] is described. Photofragmentation voltammetry is used to demonstrate that the primary photoprocess is loss of the phosphine ligand in all four carbene complexes. A common intermediate is observed when the analogous aminocarbenes are studied.

  4. Formation of the first derivatives of praseodymium-containing metallofullerenes via regioselective carbene addition to Pr rate at C{sub 2v}(9)-C{sub 82}

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Qin; Li, Hui; Wang, Yan; Lian, Yongfu [Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin (China)

    2014-12-01

    The first derivatives of praseodymium-containing metallofullerenes are formed through regioselective cycloaddition of adamantylidene carbene to Pr rate at C{sub 2v}(9)-C{sub 82}, and two isomers out of the 35 possible monoadducts are successfully isolated. Optical adsorption and electrical chemistry characterizations indicate that the electronic property of Pr rate at C{sub 2v}(9)-C{sub 82} is largely pertained in these derivatives, since their ?-electron systems are not altered markedly. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  5. Air-Stable (CAAC)CuCl and (CAAC)CuBH4 Complexes as Catalysts for the Hydrolytic Dehydrogenation of BH3 NH3.

    Science.gov (United States)

    Hu, Xingbang; Soleilhavoup, Michèle; Melaimi, Mohand; Chu, Jiaxiang; Bertrand, Guy

    2015-05-11

    The first stable copper borohydride complex [(CAAC)CuBH4 ] [CAAC=cyclic(alkyl)(amino)carbene] bearing a single monodentate ligand was prepared by addition of NaBH4 or BH3 NH3 to the corresponding [(CAAC)CuCl] complex. Both complexes are air-stable and promote the catalytic hydrolytic dehydrogenation of ammonia borane. The amount of hydrogen released reaches 2.8 H2 /BH3 NH3 with a turnover frequency of 8400?mol?H?2?molcat (-1) ?h(-1) at 25?°C. In a fifteen-cycle experiment, the catalyst was reused without any loss of efficiency. PMID:25802096

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

    International Nuclear Information System (INIS)

    The aim of this work is to study the complexation of f-elements in solution by ligands incorporating N-heterocyclic donors. These ligands display interesting properties for the selective separation of An(III)/Ln(III) have been studied to obtain a better understanding of the coordination properties with f-elements and to develop more selective extractants. The hepta-dentate ligand tpaam shows an affinity for Ln(III) similar to the tetradentate ligand tpa in water even when the three additional amide groups are bonded to the metal. Even though the complexation with tpa is exothermic, that with tpaam is endothermic with a more positive entropy. The dehydration of the cation disfavours the formation of Ln(III) complexes with ligands containing weak donors. The analysis of the solution paramagnetic relaxation times of the tpaam complexes is in agreement with data in the solid-state. There is little difference between the formation constants of the Ln3+ complexes with different ligands (tpaam, tpzen, tpa and tpza) as determined by UV-vis spectrophotometry in anhydrous acetonitrile. The limitations encountered during this study are intrinsic to the ligands studied. The preliminary study of two tetrapodal ligands containing acid and pyridine groups (Lpy)or pyrazine (Lpz) show the formation of 1:1 complexes in water. Analysis of the formation constants of the corresponding Gd(III) complexes shows that replacement of a pyridine group by pyrazine result in a loss of stability of 1.6 logarithmic units. (author)

  7. Zirconoxycarbene complexes of ruthenium - reduction of coordinated CO in the reaction of a Zr-Ru compound with H2

    International Nuclear Information System (INIS)

    Compounds have been synthesized with directly bonded early and late transition metals such as Cp2Zr[Ru(CO)2Cp]2 in the hope of cleaving the metal-metal bond with H2. The resulting mixture containing reactive hydridic M-H and acidic M-H units might be a powerful reducing system for polar molecules including CO. Evidence is presented for a circuitous stepwise conversion of the complex into Ru-H and Zr-H units and for the reduction of coordinated CO to a formyl or zirconoxy carbene group. 8 references, 1 figure

  8. Carbene reactions. Pt. 5

    International Nuclear Information System (INIS)

    Thermal cleavage of spiro[norbornadiene-7,2'-oxiranes] respectively after 14C labelling of the corresponding compound which was labelled by 14C at the methylen-group, generates ketenes probably via carbenaoxiranes. An equilibration carbenaoxirane reversible oxirene could not be detected. (orig./HK)

  9. THEORETICAL STUDY OF THE MECHANISM OF CYCLOADDITION REACTION BETWEEN DICHLORO-SILYLENE CARBENE(CL2SI=C:) AND ACETONE

    Scientific Electronic Library Online (English)

    XIUHUI, LU; PINGPING, XIANG; LEYI, SHI; JUNFENG, HAN; ZHENXIA, LIAN.

    Full Text Available The mechanism of the cycloaddition reaction between singlet dichloro-silylene carbene and acetone has been investigated with DFT, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations a [...] re calculated by CCSD(T)//B3LYP/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The channel (I) consists of two steps: (1) the two reactants firstly form a four-membered ring intermediate through a barrier-free exothermic reaction of 307.1 kJ/mol; (2) four-membered ring intermediate then isomerizes to a CH3-transfer product via a transition state with energy barrier of 11.3 kJ/mol. The process of channel (II) is as following: on the basis of four-membered ring intermediate created between the two reactants, four-membered ring intermediate further reacts with acetone to form the intermediate through a barrier-free exothermic reaction of 165.8 kJ/mol; Then, intermediate isomerizes to a silicic bis-heterocyclic product via a transition state, for which the barrier is 57.6 kJ/mol.

  10. Gold-catalyzed Intermolecular [4C + 3C] Cycloaddition Reactions.

    Science.gov (United States)

    Gung, Benjamin W; Bailey, Lauren N; Wonser, Josh

    2010-04-28

    In the presence of the N-heterocyclic carbene gold catalyst (NHC-AuIPr, 7), propargyl esters 1a-f and 13 undergo a [4C + 3C] cycloaddition reaction with cyclopentadiene and furan under mild conditions. The evidence suggests the formation of the seven-membered ring occurs by a direct cycloaddition process, rather than a stepwise cyclopropanation/Cope rearrangement sequence. PMID:20352055

  11. Asymmetric Pd-NHC*-catalyzed coupling reactions

    OpenAIRE

    Kundig, Ernst Peter; Jia, Yixia; Katayev, Dmitry; Nakanishi, Masafumi

    2012-01-01

    Very high asymmetric inductions result in the Pd-catalyzed intramolecular arylation of amides to give 3,3-disubstituted oxindoles when new in situ-generated chiral N?heterocyclic carbene (NHC*) ligands are employed. Structural studies show that conformational locking to minimize allylic strain is the key to understanding the function of these ligands. New applications of these ligands in the frontier area of asymmetric coupling reactions involving C(sp3)–H bonds are detailed. Highly enant...

  12. Towards electrically conductive, self-healing materials

    OpenAIRE

    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 subsequentl...

  13. A Facile Route to C2-Substituted Imidazolium Ionic Liquids

    OpenAIRE

    Handy, Scott T.; Elliot Ennis

    2009-01-01

    A convenient route for the preparation of C2-substituted imidazolium ionic liquids is reported. This method involves the alkylation of N-heterocyclic carbenes, which are readily generated from the C2-unsubstituted imidazolium ionic liquids. It works well for non-functionalized alkyl chlorides, and less well for alkyl bromides and iodides, likely due to competing elimination reactions. The resulting C2-substituted salts can be transformed into ionic liquids via standard anion metathesis reacti...

  14. Enantioselective ?-Protonation by a Cooperative Catalysis Strategy

    Science.gov (United States)

    Wang, Michael H.; Cohen, Daniel T.; Schwamb, C. Benjamin; Mishra, Rama K.; Scheidt, Karl A.

    2015-01-01

    An enantioselective N-heterocyclic carbene (NHC)-catalyzed ?-protonation through the orchestration of three distinct organocatalysts has been developed. This cooperative catalyst system enhances both yield and selectivity, compared to only the NHC-catalyzed process. This new method allows for the efficient conversion of a large scope of aryl-oxobutenoates to highly enantioenriched succinate derivatives and demonstrates the benefits of combining different activation modes in organocatalysis. PMID:25929160

  15. A Facile Route to C2-Substituted Imidazolium Ionic Liquids

    Directory of Open Access Journals (Sweden)

    Scott T. Handy

    2009-06-01

    Full Text Available A convenient route for the preparation of C2-substituted imidazolium ionic liquids is reported. This method involves the alkylation of N-heterocyclic carbenes, which are readily generated from the C2-unsubstituted imidazolium ionic liquids. It works well for non-functionalized alkyl chlorides, and less well for alkyl bromides and iodides, likely due to competing elimination reactions. The resulting C2-substituted salts can be transformed into ionic liquids via standard anion metathesis reactions.

  16. Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl2(P-P)(N-N)] type complexes

    International Nuclear Information System (INIS)

    The substitution reactions [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, where P.P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2' -bipyridine, 4,4' L-dimethoxy-2,2' L- bipyridine, 4,4' L-dimethylpyridine-2,2' L-bipyridine and 4,4' L-dichloro-2,2' L-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pKa of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the 31P{1H} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF6, there are two doublets with ?? < 1. This is consistent with products formed by dissociation of the chloride trans to one of the phosphorus atoms in the precursors. (author)

  17. Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl{sub 2}(P-P)(N-N)] type complexes

    Energy Technology Data Exchange (ETDEWEB)

    Monteiro, Marcos C.R.; Machado, Sergio de Paula, E-mail: sergiopm@iq.ufrj.b [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Inst. de Quimica; Nascimento, Fabio B.; Valle, Eliana M.A.; Batista, Alzir A. [Universidade Federal de Sao Carlos (UFSCAR), Sao Carlos, SP (Brazil). Dept. de Quimica; Ellena, Javier; Castellano, Eduardo E. [Universidade de Sao Paulo (IFSC/USP), Sao Carlos, SP (Brazil). Inst. de Fisica

    2010-07-01

    The substitution reactions [RuCl{sub 2}(P-P)(N-N)] + L {yields} [RuCl(L)(P-P)(N-N)]{sup +} + Cl{sup -}, where P.P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2' -bipyridine, 4,4' L-dimethoxy-2,2' L- bipyridine, 4,4' L-dimethylpyridine-2,2' L-bipyridine and 4,4' L-dichloro-2,2' L-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pK{sub a} of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the {sup 31}P{l_brace}{sup 1}H{r_brace} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF{sub 6}, there are two doublets with {Delta}{sigma} < 1. This is consistent with products formed by dissociation of the chloride trans to one of the phosphorus atoms in the precursors. (author)

  18. Inhibition of oxidative metabolism of tocopherols with ?-N-heterocyclic derivatives of vitamin E

    OpenAIRE

    Ohnmacht, Stephan; Nava, Phillip; West, Ryan; Parker, Robert; Atkinson, Jeffrey

    2008-01-01

    The oxidative metabolism of tocopherols and tocotrienols by monooxygenases is a key factor in the plasma and tissue clearance of forms of vitamin E other than ?-tocopherol. It is well known that a commonly ingested form of vitamin E, ?-tocopherol, has greatly reduced plasma half life (faster clearance) than ?-tocopherol. The tocotrienols are metabolized even faster than ?-tocopherol. Both ?-tocopherol and ?- and ?-tocotrienol possess intriguing biological activities that are different ...

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

    Science.gov (United States)

    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.

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

    International Nuclear Information System (INIS)

    Electron transmission spectroscopy is used to study transient negative ions or shape resonances in various benzene derivatives. Because of the long lifetime of these ions (? > 10-14 S) the vibrational structure of their first two electronic states is observed superposed on the total electron cross section curves in the energy range 0-6 eV and the corresponding adiabatic electron affinities are determined. The comparison of the first electron affinity with the first ionization potential and the energy on the first excited state of each of the derivatives is used to characterize the 'donor' substituents on the benzene ring. As a complementary study, these derivatives are studied in the liquid phase using polarography (cyclic voltametry). The linear correlation established between polarographic potentials measured in dimethyl formamide and the electron affinities was used to deduce electron affinities for several molecules which are difficult to measure in the gas phase. (author)

  1. N-Heterocyclic compounds as radioprotectors. 1. 2-Pyridinemethanethiol, 2-pyrazinemethanethiol and related compounds

    International Nuclear Information System (INIS)

    2-Pyridinemethanethiol 1, which is structurally related to cysteamine, showed good radioprotective potency in mice, but 2-pyrazine-methanethiol 9 was inactive. Certain derivatives of 1 and 9 that were synthesised were radioprotective. The 3 isomeric mercaptopyridines showed activity. Further study of N-heteroaromatic compounds as radioprotectors is indicated. An improved method for the preparation of 9 is described

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

    International Nuclear Information System (INIS)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  4. Effects of N-heterocyclic polyaromatic hydrocarbons on survival, reproduction, and biochemical parameters in Daphnia magna.

    Czech Academy of Sciences Publication Activity Database

    Feldmanová, Marie; Hilscherová, Klára; Maršálek, Blahoslav; Bláha, Lud?k

    2006-01-01

    Ro?. 21, ?. 4 (2006), s. 425-431. ISSN 1520-4081 R&D Projects: GA ?R(CZ) GA525/03/0367 Institutional research plan: CEZ:AV0Z60050516 Keywords : N- PAH s * Daphnia magna * biomarkers Subject RIV: EF - Botanics Impact factor: 1.582, year: 2006

  5. Selective Biodegradation of S and N Heterocycles by a Recombinant Rhodococcus erythropolis Strain Containing Carbazole Dioxygenase

    OpenAIRE

    YU, BO; Xu, Ping; ZHU, SHANSHAN; Cai, Xiaofeng; Wang, Ying(School of Physics, Shandong University, Jinan, 250100, PR China); Li, LI; Li, Fuli; Liu, Xiaoyong; Ma, Cuiqing

    2006-01-01

    The carbazole dioxygenase genes were introduced into a dibenzothiophene degrader. The recombinant Rhodococcus erythropolis SN8 was capable of efficiently degrading dibenzothiophene and carbazole simultaneously. SN8 could also degrade various alkylated derivatives of carbazole and dibenzothiophene in FS4800 crude oil by just a one-step bioprocess.

  6. Organic-Inorganic Hybrid Silica Material Derived from a Monosilylated Grubbs-Hoveyda Ruthenium Carbene as a Recyclable Metathesis Catalyst

    Directory of Open Access Journals (Sweden)

    Michel Wong Chi Man

    2010-08-01

    Full Text Available The synthesis of a monosilylated Grubbs-Hoveyda ruthenium alkylidene complex is described, as well as the preparation and characterization of the corresponding material by sol-gel cogelification with tetraethoxysilane (TEOS and the assay of this recyclable supported catalyst in ring-closing diene and enyne metathesis reactions under thermal and microwave conditions.

  7. Organic-Inorganic Hybrid Silica Material Derived from a Monosilylated Grubbs-Hoveyda Ruthenium Carbene as a Recyclable Metathesis Catalyst

    OpenAIRE

    Michel Wong Chi Man; Ramón Alibés; Xavier Cattoën; Guadalupe Borja; Roser Pleixats

    2010-01-01

    The synthesis of a monosilylated Grubbs-Hoveyda ruthenium alkylidene complex is described, as well as the preparation and characterization of the corresponding material by sol-gel cogelification with tetraethoxysilane (TEOS) and the assay of this recyclable supported catalyst in ring-closing diene and enyne metathesis reactions under thermal and microwave conditions.

  8. Palladium-Catalyzed Heck Coupling Reaction of Aryl Bromides in Aqueous Media Using Tetrahydropyrimidinium Salts as Carbene Ligands

    Directory of Open Access Journals (Sweden)

    ?smail Özdemir

    2010-01-01

    Full Text Available An efficient and stereoselective catalytic system for the Heck cross coupling reaction using novel 1,3-dialkyl-3,4,5,6-tetrahydropyrimidinium salts (1, LHX and Pd(OAc2 loading has been reported. The palladium complexes derived from the salts 1a-f prepared in situ exhibit good catalytic activity in the Heck coupling reaction of aryl bromides under mild conditions.

  9. Coordination and activation of Al-H and Ga-H bonds.

    Science.gov (United States)

    Abdalla, Joseph A B; Riddlestone, Ian M; Turner, Joshua; Kaufman, Paul A; Tirfoin, Remi; Phillips, Nicholas; Aldridge, Simon

    2014-12-22

    The modes of interaction of donor-stabilized Group?13 hydrides (E=Al, Ga) were investigated towards 14- and 16-electron transition-metal fragments. More electron-rich N-heterocyclic carbene-stabilized alanes/gallanes of the type NHC?EH3 (E=Al or Ga) exclusively generate ?(2) complexes of the type [M(CO)4 (?(2)-H3 E?NHC)] with [M(CO)4 (COD)] (M=Cr, Mo), including the first ?(2) ?-gallane complexes. ?-Diketiminato ('nacnac')-stabilized systems, {HC(MeCNDipp)2 }EH2 , show more diverse reactivity towards Group?6 carbonyl reagents. For {HC(MeCNDipp)2 }AlH2, both ?(1) and ?(2) complexes were isolated, while [Cr(CO)4 (?(2)-H2 Ga{(NDippCMe)2 CH})] is the only simple ?(2) adduct of the nacnac-stabilized gallane which can be trapped, albeit as a co-crystallite with the (dehydrogenated) gallylene system [Cr(CO)5 (Ga{(NDippCMe)2 CH})]. Reaction of [Co2 (CO)8] with {HC(MeCDippN)2 }AlH2 generates [(OC)3 Co(?-H)2 Al{(NdippCme)2 CH}][Co(CO)4] (12), which while retaining direct Al?H interactions, features a hitherto unprecedented degree of bond activation in a ?-alane complex. PMID:25358970

  10. Reactions of ruthenium Cp phosphine complex with 4,4-disubstituted-1,6-enynes: effect of methyl substituents in the olefinic fraction.

    Science.gov (United States)

    Chung, Chia-Pei; Chen, Chien-Chih; Lin, Ying-Chih; Liu, Yi-Hong; Wang, Yu

    2009-12-30

    We studied chemical reactions of Cp(PPh(3))(2)RuCl with nine 1,6-enyne compounds (1-4, 8, 12, 19, 21, and 22) in which the triple bond is associated with propargylic alcohol and the olefinic group has various substituted methyl groups. For the enyne compounds 1-3 with no substituted methyl group, the reaction takes place at the propargylic alcohol first giving the allenylidene complex 6 which could undergo a skeletal rearrangement to yield the disubstituted vinylidene complex 7. By changing the propargylic alcohol to propargylic ether, the reaction gives the carbene complex 10 as the major product and the butadiene complex 9 by a cyclization reaction as the minor product. For enyne 12 with two methyl groups at the terminal carbon of the olefinic part, formation of either of the carbene complexes 15 and 16 with a substituted cyclopentenyl ring at Calpha or the vinylidene complex 17 is controlled by the use of solvent. For the formation of 15 and 16, a C-C bond-forming cyclization reaction is proposed to occur at Cbeta in an intermediate where the triple bond is pi-coordinated. However, for the vinylidene intermediate, the reaction may proceed by the formation of the allenylidene, which undergoes a retro-ene reaction to bring about cleavage of the dimethyl substituted allyl group giving 17. For two enynes 21 and 22 where each olefinic portion is internally substituted with one methyl group, two vinylidene complexes 23 and 24 each with a five-membered ring bonded at Cbeta are isolated. The reaction proceeds via formation of an allenylidene intermediate followed by a cyclization at Cgamma. Stabilization of the cationic charge by the presence of methyl subsituents clearly controls the reaction pathway to give different products. These chemical reactions and their mechanisms are corroborated by structure determinations of five ruthenium complexes using single crystal X-ray diffraction analysis. PMID:19954195

  11. Ruthenium carbenes supported on mesoporous silicas as highly active and selective hybrid catalysts for olefin metathesis reactions under continuous flow.

    Science.gov (United States)

    Bru, Miriam; Dehn, Richard; Teles, J Henrique; Deuerlein, Stephan; Danz, Manuel; Müller, Imke B; Limbach, Michael

    2013-08-26

    In the search for a highly active and selective heterogenized metathesis catalyst, we systematically varied the pore geometry and size of various silica-based mesoporous (i.e., MCM-41, MCM-48, and SBA-15) and microporous (ZSM-5 and MWW) versus macroporous materials (D11-10 and Aerosil 200), besides other process parameters (temperature, dilution, and mean residence time). The activity and, especially, selectivity of such "linker-free" supports for ruthenium metathesis catalysts were evaluated in the cyclodimerization of cis-cyclooctene to form 1,9-cyclohexadecadiene, a valuable intermediate in the flavor and fragrance industry. The optimized material showed not only exceptionally high selectivity to the valuable product, but also turned out to be a truly heterogeneous catalyst with superior activity relative to the unsupported homogeneous complex. PMID:23852995

  12. Enthalpies of ligand substitution for [Mo(?5C5H5)(CO)2(NO)] – The role of ?-bonding effects in metal–ligand bond strengths

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Enthalpies of ligand substitution are measured for Mo(C5H5)(CO)2(NO). • Phosphines and N-heterocyclic carbenes are stronger ligands and displace CO. • Backbonding to ?? orbitals is an important part of complex stability. • FTIR studies show shifts to lower wavenumbers of ?-CO and ?-NO. • Structural studies show lengthening of the C-O and N-O bonds. - Abstract: Enthalpies of ligand substitution for [Mo(?5-C5H5)(CO)2(NO)] producing [Mo(?5-C5H5)Mo(CO)(L)(NO)] have been measured by solution calorimetry at 30 °C in THF for L = P(OMe)3 2 2Ph 3 (SIPr = 1,3-bis(2,6-bis(diisopropylphenyl)imidazolinylidene; IPr = 1,3-bis(2,6-bis(diisopropylphenyl)-imidazol-2-ylidene)). The accepting metal fragment [Mo(?5-C5H5)(CO)(NO)] has a vacant site containing strongly ?-accepting carbonyl and nitrosyl ligands and this is shown to influence the stability of the product complex. Infrared studies of both ?CO and ?NO show that metal-to-ligand backbonding increases in the order P(OMe)3 3 5-C5H5)(CO)(IPr)(NO)] and [Mo(?5-C5H5)(CO)(SIPr)(NO)] are reported

  13. Borylene complexes (BH)L2 and nitrogen cation complexes (N+)L2: isoelectronic homologues of carbones CL2.

    Science.gov (United States)

    Celik, Mehmet Ali; Sure, Rebecca; Klein, Susanne; Kinjo, Rei; Bertrand, Guy; Frenking, Gernot

    2012-04-27

    Quantum chemical calculations using DFT (BP86, M05-2X) and ab initio methods (CCSD(T), SCS-MP2) have been carried out on the borylene complexes (BH)L(2) and nitrogen cation complexes (N(+))L(2) with the ligands L=CO, N(2), PPh(3), NHC(Me), CAAC, and CAAC(model). The results are compared with those obtained for the isoelectronic carbones CL(2). The geometries and bond dissociation energies of the ligands, the proton affinities, and adducts with the Lewis acids BH(3) and AuCl were calculated. The nature of the bonding has been analyzed with charge and energy partitioning methods. The calculated borylene complexes (BH)L(2) have trigonal planar coordinated boron atoms which possess rather short B-L bonds. The calculated bond dissociation energies (BDEs) of the ligands for complexes where L is a carbene (NHC or CAAC) are very large (D(e) =141.6-177.3 kcal mol(-1)) which suggest that such species might become isolated in a condensed phase. The borylene complexes (BH)(PPh(3))(2) and (BH)(CO)(2) have intermediate bond strengths (D(e) =90.1 and 92.6 kcal mol(-1)). Substituted homologues with bulky groups at boron which protect the boron atom from electrophilic attack might also be stable enough to become isolated. The BDE of (BH)(N(2))(2) is much smaller (D(e) =31.9 kcal mol(-1)), but could become observable in a low-temperature matrix. The proton affinities of the borylene complexes are very large, particularly for the bulky adducts with L=PPh(3), NHC(Me), CAAC(model) and CAAC and thus, they are superbases. All (BH)L(2) molecules bind strongly AuCl either ?(1) (L=N(2), PPh(3), NHC(Me), CAAC) or ?(2) (L=CO, CAAC(model)). The BDEs of H(3)B-(BH)L(2) adducts which possess a hitherto unknown boron?boron donor-acceptor bond are smaller than for the AuCl complexes. The strongest bonded BH(3) adduct that might be isolable is (BH)(PPh(3))(2)-BH(3) (D(e) =36.2 kcal mol(-1)). The analysis of the bonding situation reveals that (BH)-L(2) bonding comes mainly from the orbital interactions which has three major contributions, that is, the donation from the symmetric (?) and antisymmetric (?(||)) combination of the ligand lone-pair orbitals into the vacant MOs of BH L?(BH)?L and the L?(BH)?L ? backdonation from the boron lone-pair orbital. The nitrogen cation complexes (N(+))L(2) have strongly bent L-N-L geometries, in which the calculated bending angle varies between 113.9° (L=N(2)) and 146.9° (L=CAAC). The BDEs for (N(+))L(2) are much larger than those of the borylene complexes. The carbene ligands NHC and CAAC but also the phosphane ligands PPh(3) bind very strongly between D(e) =358.4 kcal mol(-1) (L=PPh(3)) and D(e) =412.5 kcal mol(-1) (L=CAAC(model)). The proton affinities (PA) of (N(+))L(2) are much smaller and they bind AuCl and BH(3) less strongly compared with (BH)L(2). However, the PAs (N(+))L(2) for complexes with bulky ligands L are still between 139.9 kcal mol(-1) (L=CAAC(model)) and 168.5 kcal mol(-1) (L=CAAC). The analysis of the (N(+))-L(2) bonding situation reveals that the binding interactions come mainly from the L?(N(+))?L donation while L?(N(+) )?L ? backdonation is rather weak. PMID:22434609

  14. Synthesis, in vitro and in vivo characterization of rhenium tricarbonyl complexes with different bifunctional tridentate ligands

    International Nuclear Information System (INIS)

    Discovery of new chelating ligands that bind technetium/rhenium strongly is a priority in the quest toward the design and development of site specific radiopharmaceuticals. The current study on the application of Tc/Re carbonyls in radiopharmaceuticals has been focused on the utility of specific tridentate ligand systems for achieving kinetic inertness and in vivo stability. In this paper, (Bis (2-pyridylmethyl)-amino)-ethylamine(1) (Fig. 1), (Bis (2-pyridylmethyl)-amino)-acetic acid (2) (Fig. 1), L(6-amino-hexyl)-pyridyl-2-methyl- amino-acetic acid (3) (Fig. 2), and picolylamine diacetic acid (4) (Fig. 3) that possessed an NNN, NNO and NOO donor atom sets were synthesized, which can be a good selection for these requirements. The Re(I)-complexes of above four ligands were prepared in good yield with [NEt4]2[ReBr3(CO)3] in water at 75 degree C for 3 h. The complexes were characterized by elemental analysis and spectroscopic methods. The 188Re(I)-complexes of Four ligands were carried out by incubating the fac- [188Re(CO)3(H2O)3]+ fragment for 60 min at 75 degree C in PBS buffer (0.1 M NaCl/0.05 M sodium phosphate buffered, pH 7.4) under nitrogen. After cooling in ice bath, complexes formations were monitored by HPLC. The HPLC analysis demonstrated that the reaction produces in the complex 1 with yield greater than 95% and its retention times was 7.5 min, whichand its retention times was 7.5 min, which is stable for more than 12 h in human serum, and the complex 2 with yield 93% is stable for more than 8 h in human serum, its retention times was 15.5 min, and the complex 3 with yield 90% is stable for more than 10 h in human serum, its retention times was 15.4 min, while the complex 4 with yields more than 92% can be stable 10 h in human serum and its retention time was 15.6 min respectively. The identity of the 188Re-complexes were proved by comparative HPLC studies using samples of the well characterized thenium(I) complexes as reference. In vivo biodistribution studies at 24 hour post-injection were carried out in normal, white mice. The biodistribution data are shown in table 1. The data show: the major part of the complexes cleared efficiently from the blood pool (0.09-0.67%); No organs (apart from liver and kidneys) or tissue was specifically targeted; Low activity (0.25-0.93%) found in the stomach indicated the good in vivo stability of the complexes. In conclusion, four ligands react with fac- [M(CO)3(H2O)3]+ (M=188Re, Re) fragment resulting in four single stable complexes, M(CO)3(1), M(CO)3(2), M(CO)3(3) and M(CO)3(4), containing aromatic N-heterocycles. These ligand systems are attractive for functionalization purposes of biological vectors since they are easy to synthesize. The corresponding complexes with fac-[M(CO)3(H2O)3]+ are in vivo and vitro stable. Thus the proposed strategy of attaching M(CO)3(1), M(CO)3(2), M(CO)3(3) and M(CO)3(4) complexes is promising for labeling of biomolecules. The approach is worthy of further investigation.

  15. Alkane metathesis with the tantalum methylidene [(?SiO)Ta(?CH2)Me2]/[(?SiO)2Ta(?CH2)Me] generated from well-defined surface organometallic complex [(?SiO)Ta(V)Me4].

    Science.gov (United States)

    Chen, Yin; Abou-hamad, Edy; Hamieh, Ali; Hamzaoui, Bilel; Emsley, Lyndon; Basset, Jean-Marie

    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. PMID:25557135

  16. Group 4 Metalloporphyrin diolato Complexes and Catalytic Application of Metalloporphyrins and Related Transition Metal Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Guodong Du

    2004-12-19

    In this work, the first examples of group 4 metalloporphyrin 1,2-diolato complexes were synthesized through a number of strategies. In general, treatment of imido metalloporphyrin complexes, (TTP)M=NR, (M = Ti, Zr, Hf), with vicinal diols led to the formation of a series of diolato complexes. Alternatively, the chelating pinacolate complexes could be prepared by metathesis of (TTP)MCl{sub 2} (M = Ti, Hf) with disodium pinacolate. These complexes were found to undergo C-C cleavage reactions to produce organic carbonyl compounds. For titanium porphyrins, treatment of a titanium(II) alkyne adduct, (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh), with aromatic aldehydes or aryl ketones resulted in reductive coupling of the carbonyl groups to produce the corresponding diolato complexes. Aliphatic aldehydes or ketones were not reactive towards (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh). However, these carbonyl compounds could be incorporated into a diolato complex on reaction with a reactive precursor, (TTP)Ti[O(Ph){sub 2}C(Ph){sub 2}O] to provide unsymmetrical diolato complexes via cross coupling reactions. In addition, an enediolato complex (TTP)Ti(OCPhCPhO) was obtained from the reaction of (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh) with benzoin. Titanium porphyrin diolato complexes were found to be intermediates in the (TTP)Ti=O-catalyzed cleavage reactions of vicinal diols, in which atmospheric oxygen was the oxidant. Furthermore, (TTP)Ti=O was capable of catalyzing the oxidation of benzyl alcohol and {alpha}-hydroxy ketones to benzaldehyde and {alpha}-diketones, respectively. Other high valent metalloporphyrin complexes also can catalyze the oxidative diol cleavage and the benzyl alcohol oxidation reactions with dioxygen. A comparison of Ti(IV) and Sn(IV) porphyrin chemistry was undertaken. While chelated diolato complexes were invariably obtained for titanium porphyrins on treatment with 1,2-diols, the reaction of vicinal diols with tin porphyrins gave a number of products, including mono-, bis-alkoxo, and chelating diolato complexes, depending on the identity of diols and the stoichiometry employed. It was also found that tin porphyrin complexes promoted the oxidative cleavage of vicinal diols and the oxidation of {alpha}-ketols to {alpha}-diketones with dioxygen. In extending the chemistry of metalloporphyrins and analogous complexes, a series of chiral tetraaza macrocyclic ligands and metal complexes were designed and synthesized. Examination of iron(II) complexes showed that they were efficient catalysts for the cyclopropanation of styrene by diazo reagents. Good yields and high diastereoselectivity were obtained with modest enantioselectivity. A rationalization of the stereoselectivity was presented on the basis of structural factors in a carbene intermediate.

  17. Microwave-Assisted Synthesis of N-Heterocyclic Compounds [Síntese de Compostos N-Heterociclos Empregando Micro-ondas

    Directory of Open Access Journals (Sweden)

    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.

  18. Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes

    Directory of Open Access Journals (Sweden)

    Werner Bonrath

    2008-01-01

    Full Text Available Non-conventional techniques, such as microwave (MW and power ultrasound(US as well as combined MW/US irradiation, have been used to promote one-potsynthesis of second-generation ionic liquids (ILs, cutting down reaction times andimproving yields. However, the use of chloroalkanes in the alkylation of N-heterocyclesrequires more drastic conditions if results are to match those obtained with more reactivealkyl halides. The present paper describes a series of MW- or MW/US-promoted ILpreparations starting from chloroalkanes and classic heterocycles (1-methylimidazole,pyridine and 1-methylpyrrolidine. When reactions were carried out under conventionalheating in an oil bath they required longer reaction times and gave poorer yields. 1H-NMRanalysis and ion-exchange chromatography showed that the present solventless procedureafforded ILs of satisfactory purity. The observed high yields (usually 70-98% isolated,and short reaction times showed that a straightforward access to ILs can be also achievedwith the use of alkyl chlorides, resulting in a considerable reduction of costs.

  19. Toxicity and modulations of biomarkers in Xenopus laevis embryos exposed to polycyclic aromatic hydrocarbons and their N-heterocyclic derivatives.

    Czech Academy of Sciences Publication Activity Database

    Buryšková, B.; Hilscherová, Klára; Bláha, Lud?k; Maršálek, Blahoslav; Holoubek, I.

    2006-01-01

    Ro?. 21, ?. 1 (2006), s. 590-598. ISSN 1520-4081 Institutional research plan: CEZ:AV0Z60050516 Keywords : PAH -s * N- PAH s * Xenopus laevis Subject RIV: EF - Botanics Impact factor: 1.582, year: 2006

  20. Complex chemistry

    International Nuclear Information System (INIS)

    This book introduces complex chemistry with ten chapters, which include development of complex chemistry on history coordination theory and Warner's coordination theory and new development of complex chemistry, nomenclature on complex with conception and define, chemical formula on coordination compound, symbol of stereochemistry, stereo structure and isomerism, electron structure and bond theory on complex, structure of complex like NMR and XAFS, balance and reaction on solution, an organo-metallic chemistry, biology inorganic chemistry, material chemistry of complex, design of complex and calculation chemistry.

  1. Spin-state energetics and spin-crossover behavior of pseudotetrahedral cobalt(III)-imido complexes. The role of the tripodal supporting ligand.

    Science.gov (United States)

    Wasbotten, Ingar H; Ghosh, Abhik

    2007-09-17

    DFT calculations have underscored the importance of the tripodal supporting ligand in tuning the spin-state energetics of pseudotetrahedral transition metal imido complexes. In particular, we have focused on Co(III)-imido complexes, where our best estimate (OLYP) of the singlet-triplet splitting varies from 0.75 eV for a trisphosphine complex (1) and 0.3 eV for a tris(N-heteroyclic-carbene) complex (2) to essentially 0.0 eV for a hydrotris(pyrazolyl)borate (3) complex. The experimentally studied analogues of 1, 2, and 3 all exhibit S = 0 ground states; however, the experimental analogue of 3 exhibits spin-crossover behavior due to a low-lying S = 1 state. Interestingly, whereas all the pure functionals examined successfully predict nearly equienergetic singlet end triplet states for 3, the hybrid functionals B3LYP and O3LYP exhibit a clear (and incorrect) preference for the S = 2 state. In addition, we have also carried out an exploratory survey of Cr(III), Mn(III), and Fe(III) imido complexes with trisphosphine and hydrotris(pyrazolyl)borate (Tp) supporting ligands. Among the more interesting predictions of this study is that an FeIII(Tp)(imido) species should exhibit a high-spin S = 5/2 ground state, which would be unique for an iron-imido complex. PMID:17713903

  2. Stille Catalyst-Transfer Polycondensation Using Pd-PEPPSI-IPr for High-Molecular-Weight Regioregular Poly(3-hexylthiophene).

    Science.gov (United States)

    Qiu, Yunyan; Mohin, Jacob; Tsai, Chia-Hua; Tristram-Nagle, Stephanie; Gil, Roberto R; Kowalewski, Tomasz; Noonan, Kevin J T

    2015-05-01

    A commercially available palladium N-heterocyclic carbene (Pd-NHC) precatalyst is used to initiate chain-growth polymerization of 2-bromo-3-hexyl-5-trimethylstannylthiophene. The molecular weight of the resultant poly(3-hexylthiophene) can be modulated (7 to 73 kDa, ? = 1.14 to 1.53) by varying the catalyst concentration. Mass spectrometry data confirm control over the polymer end groups and (1) H NMR spectroscopy reveals that the palladium catalyst is capable of "ring-walking". A linear relationship between Mn and monomer conversion is observed. Atomic force microscopy and X-ray scattering verify the regioregular nature of the resultant polythiophene. PMID:25757046

  3. A Pt/sup II/-alkane complex with pentacoordinated carbon as the first intermediate of reactions of oxidation and multiple H/D exchange of alkanes in aqueous solutions of Pt/sup II/-Pt/sup IV/ chlorides

    International Nuclear Information System (INIS)

    The activation of alkanes and cycloalkanes (RH = C/sub n/H/sub n/) in the system Pt/sup II/-Pt/sup IV/-Cl--D+-D2O leads to products of oxidation and multiple H/D exchange (C/sub n/H/sub m-i/D/sub i/). We found that under conditions of competition of exchange and oxidation of cyclohexane, the parameter M0 = i (the average number of D atoms in the exchange product at the initial moment) increases with increasing concentration of D+, while the mechanism requires a decrease in M0 with increasing [D+]. This result permits an assured selection in favor of the alkane-alkyl mechanism rather than the alkyl-carbene mechanism, and made it possible to conclude that the first kinetically significant intermediate of the reaction is the Pt/sup II/-alkane complex

  4. Stereochemical aspects of nucleophilic addition reactions to alkoxycarbene cations of the iron chiral auxiliary [(eta(5)-C5H5)Fe(CO)(PPh3)

    OpenAIRE

    Davies, SG; Fletcher, AM; Maberly, TR; Thomson, JE

    2013-01-01

    Alkoxy carbene complexes incorporating the iron chiral auxiliary [(?5-C5H5)Fe(CO)(PPh3)] were prepared in good yields from either the corresponding acyl complexes or methoxymethyl complex of the auxiliary. A range of nucleophilic addition reactions to these alkoxy carbene complexes showed moderate to high diastereoselectivities and the reactive conformations of the carbene complexes under these conditions are discussed. © 2013 The Royal Society of Chemistry and the Centre National de la Rec...

  5. Metal-ligand cooperation on a diruthenium platform: selective imine formation through acceptorless dehydrogenative coupling of alcohols with amines.

    Science.gov (United States)

    Saha, Biswajit; Rahaman, S M Wahidur; Daw, Prosenjit; Sengupta, Gargi; Bera, Jitendra K

    2014-05-19

    Metal-metal singly-bonded diruthenium complexes, bridged by naphthyridine-functionalized N-heterocyclic carbene (NHC) ligands featuring a hydroxy appendage on the naphthyridine unit, are obtained in a single-pot reaction of [Ru2(CH3COO)2(CO)4] with 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (BIN?HBr) or 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (PIN?HBr), TlBF4, and substituted benzaldehyde containing an electron-withdrawing group. The modified NHC-naphthyridine-hydroxy ligand spans the diruthenium unit in which the NHC carbon and hydroxy oxygen occupy the axial sites. All the synthesized compounds catalyze acceptorless dehydrogenation of alcohols to the corresponding aldehydes in the presence of a catalytic amount of weak base 1,4-diazabicyclo[2.2.2]octane (DABCO). Further, acceptorless dehydrogenative coupling (ADHC) of the alcohol with amines affords the corresponding imine as the sole product. The substrate scope is examined with 1 (BIN, p-nitrobenzaldehyde). A similar complex [Ru2(CO)4(CH3COO)(3-PhBIN)][Br], that is devoid of a hydroxy arm, is significantly less effective for the same reaction. Neutral complex 1?a, obtained by deprotonation of the hydroxy arm in 1, is found to be active for the ADHC of alcohols and amines under base-free conditions. A combination of control experiments, deuterium labeling, kinetic Hammett studies, and DFT calculations support metal-hydroxyl/hydroxide and metal-metal cooperation for alcohol activation and dehydrogenation. The bridging acetate plays a crucial role in allowing ?-hydride elimination to occur. The ligand architecture on the diruthenium core causes rapid aldehyde extrusion from the metal coordination sphere, which is responsible for exclusive imine formation. PMID:24715433

  6. Lutetium-methanediide-alkyl complexes: synthesis and chemistry.

    Science.gov (United States)

    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

  7. Gold-catalyzed cycloisomerization of 1,7-enyne esters to structurally diverse cis-1,2,3,6-tetrahydropyridin-4-yl ketones.

    Science.gov (United States)

    Rao, Weidong; Sally; Koh, Ming Joo; Chan, Philip Wai Hong

    2013-04-01

    A synthetic method that relies on gold(I)-catalyzed cycloisomerization of 1,7-enyne esters to prepare highly functionalized cis-1,2,3,6-tetrahydropyridin-4-yl ketone derivatives in good to excellent yields and as a single regio-, diastereo-, and enantiomer is described. By taking advantage of the distinctive differences in the electronic and steric properties between an NHC (NHC = N-heterocyclic carbene) and phosphine ligand in the respective gold(I) complexes, a divergence in product selectivity was observed. In the presence of [PhCNAuIPr](+)SbF6(-) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) as the catalyst, tandem 1,3-acyloxy migration/6-exo-trig cyclization/1,5-acyl migration of the substrate was found to selectively occur to give the ?-diketone-substituted 1,2,3,6-tetrahydropyridine adduct. In contrast, reactions with the gold(I) phosphine complex [MeCNAu(JohnPhos)](+)SbF6(-) (JohnPhos = (1,1'-biphenyl-2-yl)-di-tert-butylphosphine) as the catalyst was discovered to result in preferential 1,3-acyloxy migration/6-exo-trig cyclization/hydrolysis of the 1,7-enyne ester and formation of the cis-1,2,3,6-tetrahydropyridin-4-yl ketone derivative. The utility of this piperidine forming strategy as a synthetic tool that makes use of 1,7-enyne esters was exemplified by its application to the synthesis of an enantiopure analogue of the bioactive 2,3,4,4a,5,9b-hexahydroindeno[1,2-c]pyridine family of compounds. PMID:23458312

  8. Carney Complex

    Science.gov (United States)

    ... Carney complex; if a patient has a PRKAR1A mutation and one of the above tumors or other conditions, then he or she is diagnosed with Carney complex. Genetic testing for the newer genes, PRKACA, PRKACB, PDE11A , and PDE8B , is not yet commercially ...

  9. Complex derivatives

    Science.gov (United States)

    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.

  10. Designing Complexity

    Science.gov (United States)

    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…

  11. Development of novel catalysts for the photocatalytic hydrogen formation

    Energy Technology Data Exchange (ETDEWEB)

    Pilz, Thomas David

    2011-11-16

    For future conversion of sunlight into chemical energy, intramolecular systems for artifical photosynthesis were developed in several stages. This comprised the fabrication of novel ligands and the resulting charge transfer chromophores (Ru(bpy)3-type) and/or catalytically active complexes (Pt, Pd). These were combined into heteronuclear diades consisting of covalently bonded functional subunits. In particular, the chromophores and catalysis centers were bridged so that their individual properties were retained while their individual functions were combined into a supramolecular photocatalyst. This makes it possible to reduce protons to hydrogen on these catalysts when exposed to light. As bridging units, oligodentate ligands were produced and used that can coordinate the active metal centers via bipyridines and N-heterocyclic carbenes (NHC). A number of such heterobimetal complexes, their initial compounds and appropriate reference compounds were produced, characterized, and compared. Apart from structural, photophysical and electrochemical analyses, also successful catalysis experiment were carried out with the manufactured photocatalysts for light-induced hydrogen production from water. Further representative control experiments and dynamic light scattering analyses were carried out in order to gain deeper understanding of the processes going on during catalysis. By comparing the properties of the fabricated catalysts with selected reference compounds, information was obtained on the structure-property relationships of the systems. (orig.) [German] Fuer die zukuenftige Umwandlung von Sonnenlicht in chemische Energie wurden schrittweise intramolekular arbeitende Systeme fuer eine artifizielle Photosynthese aufgebaut. Dabei wurde eine Anzahl von neuen Liganden und den resultierenden Charge-Transfer-Chromophoren (Ru(bpy)3-artig) bzw. katalyseaktiven Komplexen (Pt, Pd) hergestellt. Diese wurden zu heteronuklearen Diaden zusammengefuegt, welche aus kovalent verbundenen Funktionsuntereinheiten bestehen. Insbesondere wurden Chromophor und Katalysezentrum so miteinander verbrueckt, dass ihre individuellen Eigenschaften weiterbestehen, ihre Einzelfunktionen aber im Zusammenspiel als supramolekularer Photokatalysator fungieren. Somit wird es moeglich unter Lichteinstrahlung die Reduktion von Protonen zu Wasserstoff an diesen Katalysatoren durchzufuehren. Als Brueckeneinheit wurden dafuer oligodentate Liganden hergestellt und verwendet, die ueber Bipyridine und N-heterozyklische Carbene (NHC) die aktiven Metallzentren koordinieren koennen. Eine Anzahl solcher heterobimetallischen Komplexe, deren Ausgangsverbindungen sowie geeignete Referenzverbindungen wurden hergestellt, charakterisiert und miteinander verglichen. Neben strukturellen, photophysikalischen und elektrochemischen Analysen wurden zusaetzlich erfolgreich Katalyseexperimente mit den erzeugten Photokatalysatoren zur lichtgetriebenen Wasserstoffentwicklung aus Wasser durchgefuehrt. Ebenso wurden repraesentative Kontrollexperimente und zusaetzliche Analysen mittels dynamischer Lichtstreuung ausgefuehrt, um ein tiefergehendes Verstaendnis von den Prozessen waehrend der Katalyse zu erhalten. Durch Vergleich der Eigenschaften der hergestellten Katalysatoren mit ausgewaehlten Referenzverbindungen konnten zudem weitere Aussagen ueber Struktur-Eigenschafts-Beziehungen der Systeme abgeleitet werden. (orig.)

  12. Complex variables

    CERN Document Server

    Fisher, Stephen D

    2012-01-01

    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

  13. Complexity International

    Science.gov (United States)

    Complexity International (CI) is an electronic journal devoted to "the field of complex systems, the generation of complex behaviour from the interaction of multiple parallel processes." The journal covers a wide variety of topics, including genetic algorithms, neural networks, and chaos theory. Because much of the focus is based on technological imitation of biological processes, some of the papers are closely tied to the life sciences. Volumes are added to on a continual basis as papers are accepted. Due to the lengthy acceptance process, it is especially useful that the CI Web site offers drafts of current submissions.

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

    DEFF Research Database (Denmark)

    Maggi, Agnese; Madsen, Robert

    2012-01-01

    The work presented in this thesis was performed at the Department of Chemistry of the Technical University of Denmark during a three year Ph.D. program. The thesis involves two distinct Projects related to organometallic and carbohydrate chemistry. Project 1: Dehydrogenative synthesis of imines from alcohols and amines catalyzed by a ruthenium N-heterocyclic carbene complex. The successful method development and application of a convenient and direct (one step) synthesis of imines from alcohols and amines is described. The developed method provides quick andextended access to structurally diverse and synthetically important imines. The reaction is catalyzed by the ruthenium N-heterocyclic carbene complex [RuCl2(IiPr)(p-cymene)] (3) and proceeds in the presence of the ligand DABCO and molecular sieves with concomitant extrusion of water and hydrogen. A range of different primary alcohols and amines have been coupled in the presence of the catalyst to afford the corresponding imines in moderate to good yields.Optically pure amines gave the corresponding imines without any sign of racemization. Moreover, the one-pot diastereoselective addition of different organometallic reagents to the imine, obtained from the coupling between benzyl alcohol and (R)-1-phenylethylamine, was performed. To address specifics of the reaction mechanism, different experiments with deuterium-labeled benzyl alcohol were carried out indicating that that the catalytically active species is a ruthenium dihydride. The reaction is proposed to proceed by initial dehydrogenation of the alcohol to the aldehyde, which stays coordinated to the ruthenium centre. Then, nucleophilic attack of the amine affords the hemiaminal, which is released from ruthenium and converted into the imine. Project 2: Tin-mediated regioselective 6-O-glycosylations of unprotected phenyl 1-thioglycopyranosides Chemical glycosylation is of outstanding importance to access biologically relevant carbohydrate structures, but classical methods suffer from the disadvantage of extensive protecting group manipulations. Thus, approaches to reduce the number of steps connected to chemical synthesis are highly important. In this thesis approaches to the regioselective glycosylation of fully unprotected phenyl 1-thio-glycopyranoside acceptors via tin activation are described. Tin-mediated Koenigs-Knorr glycosylation of phenyl 1-thio-?-D-glucopyranoside (28), phenyl 1-thio-?-Dgalactopyranoside (32) and phenyl 1-thio-?-D-mannopyranoside (33) with different bromide donors afforded the corresponding (1?6) linked disaccharides in good to moderate yields. The disaccharides obtained from the first coupling can be activated as donors for subsequent tinmediated glycosylation reactions. The activation has been performed following two different strategies. The first involved one-step activation with a thiophilic reagent, while the second employed a two-step activation which entailed first formation of a glycosyl halide, and then activation with a halophilic reagent. This last approach is of particular interest; in fact, thioglycosides can be used as acceptors enabling an iterative oligosaccharide synthesis. Following these strategies a number of different trisaccharides have been successfully synthesized.

  15. Tribotesting Complex

    International Science & Technology Center (ISTC)

    Development of Methodological Basis and Creation of a Branch Tribotesting Complex Intended for High-Temperature Friction and Wear Testing of Metallurgical Equipment Tool Specimens with the Aim of Enhancement of Equipment and Tool Wear Resistance

  16. Complex Covariance

    Directory of Open Access Journals (Sweden)

    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.

  17. Experimental and theoretical study of the kinetics of dissociation in cis-[RuCl2(P-P)(N-N)] type complexes

    Scientific Electronic Library Online (English)

    Marcos C. R., Monteiro; Fabio B., Nascimento; Eliana M. A., Valle; Javier, Ellena; Eduardo E., Castellano; Alzir A., Batista; Sergio de Paula, Machado.

    1992-19-01

    Full Text Available As reações de substituição [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, onde P-P = 1,4-bis(difenilfosfino)butano e N-N = 2,2´-bipiridina, 4,4´-dimetóxi-2,2´-bipiridina, 4,4´-dimetil-2,2´-bipiridina e 4,4´-dicloro-2,2´-bipiridina, L = piridina (py) ou 4-metilpiridina (4-pic), foram estudadas s [...] ob condições de pseudo-primeira ordem. As reações ocorrem por um mecanismo dissociativo e as constantes de velocidade nas reações de substituição aumentam com o aumento do pKa dos ligantes N-heterocíclicos e com a diminuição dos potenciais de oxidação do centro metálico. Quanto mais alta é a porcentagem de participação dos orbitais atômicos d do metal na formação do HOMO, conforme calculado pelo método DFT, mais fácil é a dissociação do cloreto da esfera de coordenação do complexo. Nos espectros de 31P{¹H} RMN da série de complexos de fórmula geral [RuCl(L)(P-P)(N-N)]PF6, há dois dubletos com ?? Abstract in english The substitution reactions [RuCl2(P-P)(N-N)] + L ? [RuCl(L)(P-P)(N-N)]+ + Cl-, where P-P = 1,4-bis(diphenylphosphino)butane and N-N = 2,2´-bipyridine, 4,4´-dimethoxy-2,2´-bipyridine, 4,4´-dimethylpyridine-2,2´-bipyridine and 4,4´-dichloro-2,2´-bipyridine, L = pyridine (py) or 4-methylpyridine (4-pic [...] ), were studied under pseudo-first order conditions. The reactions proceeded by means of a dissociative mechanism. The rate constants of the substitution reactions increased as the pKa of the N-heterocyclic ligands increased and as the oxidation potential of the metal center decreased. The greater the participation of the atomic d orbitals of the metal in the HOMO, according to DFT calculations, the easier is the dissociation of the chloride from the coordination sphere of the complex. In the 31P{¹H} NMR spectra of the series of complexes of general formula [RuCl(L)(P-P)(N-N)]PF6, there are two doublets with ??

  18. Nucleophilic substitution in ionizable Fischer thiocarbene complexes: steric effect of the alkyl substituent on the heteroatom.

    Science.gov (United States)

    Andrada, Diego M; Zoloff Michoff, Martin E; de Rossi, Rita H; Granados, Alejandro M

    2015-03-10

    A detailed kinetic study has been carried out for the aminolysis of ionizable Fischer thiocarbene complexes (CO)5M[double bond, length as m-dash]C(SR)CH3 (M = Cr, W; R = iPr, nBu, cHex, tBu) with five primary amines and one secondary amine in aqueous acetonitrile solutions (50% MeCN-50% water (v/v)). The observed rate constants for the reaction with primary amines showed a first-order dependence on the amine concentration, while with morpholine, the rate constant has second-order dependence. The general base catalysis process was confirmed by the variation of the rate constants with the concentration of an external catalyst and the pH. The results agree with a stepwise mechanism where the nucleophilic addition to the carbene carbon to produce a tetrahedral intermediate () is the first step, followed by a rapid deprotonation of to form the anion which leads to the products by general-acid catalysed leaving group (-SR) expulsion. In general, it was found that the chromium complexes are less reactive than the tungsten analogues. The obtained Brønsted parameters for the nucleophilic addition (?nuc) indicate that C-N bond formation has made little progress at the transition state. By using Charton's correlation, the role that the steric factor plays throughout the mechanism has been unraveled. The nucleophilic addition to the thiocarbenes is less sensitive to steric effects than the alkoxycarbenes regardless of the nature of the metal centre. Conversely, the steric effects on the general-base catalysis can be strong depending on the volume of the catalyst and the metal centre. On the basis of the structure-reactivity coefficients ? and ? and comparison with alkoxycarbene complexes, esters and thiolesters, insights into the main factors ruling the reactivity in terms of transition state imbalances are discussed. PMID:25698135

  19. Complex analysis

    CERN Document Server

    Freitag, Eberhard

    2005-01-01

    The guiding principle of this presentation of ``Classical Complex Analysis'' is to proceed as quickly as possible to the central results while using a small number of notions and concepts from other fields. Thus the prerequisites for understanding this book are minimal; only elementary facts of calculus and algebra are required. The first four chapters cover the essential core of complex analysis: - differentiation in C (including elementary facts about conformal mappings) - integration in C (including complex line integrals, Cauchy's Integral Theorem, and the Integral Formulas) - sequences and series of analytic functions, (isolated) singularities, Laurent series, calculus of residues - construction of analytic functions: the gamma function, Weierstrass' Factorization Theorem, Mittag-Leffler Partial Fraction Decomposition, and -as a particular highlight- the Riemann Mapping Theorem, which characterizes the simply connected domains in C. Further topics included are: - the theory of elliptic functions based on...

  20. Communication Complexity

    OpenAIRE

    Pa?lvo?lgyi, Do?mo?to?r

    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...

  1. Complex Networks

    CERN Document Server

    Evsukoff, Alexandre; González, Marta

    2013-01-01

    In the last decade we have seen the emergence of a new inter-disciplinary field focusing on the understanding of networks which are dynamic, large, open, and have a structure sometimes called random-biased. The field of Complex Networks is helping us better understand many complex phenomena such as the spread of  deseases, protein interactions, social relationships, to name but a few. Studies in Complex Networks are gaining attention due to some major scientific breakthroughs proposed by network scientists helping us understand and model interactions contained in large datasets. In fact, if we could point to one event leading to the widespread use of complex network analysis is the availability of online databases. Theories of Random Graphs from Erdös and Rényi from the late 1950s led us to believe that most networks had random characteristics. The work on large online datasets told us otherwise. Starting with the work of Barabási and Albert as well as Watts and Strogatz in the late 1990s, we now know th...

  2. Investigation of Complex Iron Surface Catalytic Chemistry Using the ReaxFF Reactive Force Field Method

    Science.gov (United States)

    Zou, Chenyu; Van Duin, Adri

    2012-12-01

    To demonstrate the feasibility of classical reactive dynamics for studying complex surface chemistry, we performed a series of five reactive molecular dynamics simulations addressing the carbon monoxide methanation and the hydrocarbon chain initiation using the ReaxFF reactive force field method. We found that the catalytic surface hydrogenation initiates from the undissociated CO molecules absorbed on the surface of the catalyst as described in the oxygenate mechanism. This process leads to the generation of surface absorbed CH X - groups, which initiates the synthesis of methane and the hydrocarbon chain growth. Direct hydrogenation of the surface carbide was not observed in the simulation. Coordination analysis of the carbon atoms in the system provides possible explanations in that the surface carbon atoms are further stabilized by the surface deformation of the iron catalyst at elevated temperatures. Results from the simulations also indicated that the surface CH- could dissociate into surface carbon atoms or be further hydrogenated into CH2- radicals, which is an important intermediate species in the synthesis of methane as well as the chain initiation. Results from the C-C coupling simulation suggested the preference of coupling between CH- and CH2- groups, which agrees with the alkenyl scheme of the carbene mechanism. The overall results agree with the available experimental observations and quantum mechanics (QM) study. Furthermore, these simulations indicate the possible cooperation among different mechanisms and prove the serviceability of the ReaxFF method for studying the complex heterogeneous catalytic system. These simulations have also allowed us to evaluate the accuracy of the current ReaxFF Fe/C/O/H description, providing crucial information regarding areas where further improvement is required.

  3. Managing Complexity

    Energy Technology Data Exchange (ETDEWEB)

    Chassin, David P.; Posse, Christian; Malard, Joel M.

    2004-08-01

    Physical analogs have shown considerable promise for understanding the behavior of complex adaptive systems, including macroeconomics, biological systems, social networks, and electric power markets. Many of today’s most challenging technical and policy questions can be reduced to a distributed economic control problem. Indeed, economically-based control of large-scale systems is founded on the conjecture that the price-based regulation (e.g., auctions, markets) results in an optimal allocation of resources and emergent optimal system control. This paper explores the state of the art in the use physical analogs for understanding the behavior of some econophysical systems and to deriving stable and robust control strategies for them. In particular we review and discussion applications of some analytic methods based on the thermodynamic metaphor according to which the interplay between system entropy and conservation laws gives rise to intuitive and governing global properties of complex systems that cannot be otherwise understood.

  4. Managing Complexity

    CERN Document Server

    Chassin, D P; Posse, C; Chassin, David P.; Malard, Joel; Posse, Christian

    2004-01-01

    Physical analogs have shown considerable promise for understanding the behavior of complex adaptive systems, including macroeconomics, biological systems, social networks, and electric power markets. Many of today's most challenging technical and policy questions can be reduced to a distributed economic control problem. Indeed, economically-based control of large-scale systems is founded on the conjecture that the price-based regulation (e.g., auctions, markets) results in an optimal allocation of resources and emergent optimal system control. This paper explores the state of the art in the use physical analogs for understanding the behavior of some econophysical systems and deriving stable and robust control strategies for them. In particular we review and discuss applications of some analytic methods based on a thermodynamic metaphor according to which the interplay between system entropy and conservation laws gives rise to intuitive and governing global properties of complex systems that cannot be otherwis...

  5. Electrochemistry of Fischer alkoxycarbene complexes of chromium: The use of density functional theory to predict and understand oxidation and reduction potentials

    International Nuclear Information System (INIS)

    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 ELUMO–3.44 (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 1–5 lays within a narrow potential range of 0.43–0.50 V vs. Fc/Fc+, is Cr-based and is mainly sensitive to the electrophilic character of the heteroarene ring directly attached to the carbene carb

  6. Managing Complexity

    OpenAIRE

    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 a...

  7. Complex mortgages

    OpenAIRE

    Amromin, Gene; Huang, Jennifer; Sialm, Clemens; Zhong, Edward

    2010-01-01

    Complex mortgages became a popular borrowing instrument during the bullish housing market of the early 2000s but vanished rapidly during the subsequent downturn. These non-traditional loans (interest only, negative amortization, and teaser mortgages) enable households to postpone loan repayment compared to traditional mortgages and hence relax borrowing constraints. At the same time, they increase household leverage and heighten dependence on mortgage refinancing to escape changes in contract...

  8. Complex Microfluidics

    OpenAIRE

    Wunderlich, Bernhard

    2013-01-01

    The dynamics of complex fluids in microchannels was studied both experimentally and theoretically. Single molecule dynamics of semiflexible actin filaments was observed in shear flow and could be quantitatively described by a telescopic rod model based on forcebalances. Novel microfluidic rheometers for differential measurements of the shear- and extensional viscosity of non-Newtonian fluids were developed and tested. Pressure and velocity fields of oscillatory flows in viscoelastic microch...

  9. Complex Networks

    International Nuclear Information System (INIS)

    Complex Networks have become a quite successful approach to analyse the structure and dynamics of systems with many interacting elements. These elements (often denoted as agents) are represented by the nodes of a network, whereas their interaction is described by the links between nodes. Statistical physics has mostly focused on the topology of such networks, emphasizing the fact that interaction occurs not necessarily via a mean field or on a regular lattice. Instead, the heterogeneity in interaction plays an important role to understand the growth of real networks. A more refined view on complex networks has to take into account that both interactions and nodes can follow their own dynamics. This has a considerably impact on the systemic properties, in particular on the occurrence of phase transitions. The term 'systemic risk' denotes such a phase transition. The breakdown of a whole system can be described as a macroscopic property which emerges from the nonlinear interactions between nodes, conditional on the eigendynamics of the nodes. The talk will present different examples of growing complex networks ranging from Open Source Software to Economic Networks. It addresses the impact of topology, weighted links, dynamics of links and nodes on the emergence of systemic properties, such as robustness or adaptivity. (author)

  10. Complex Systems

    CERN Document Server

    Smith, J B

    2003-01-01

    The study of Complex Systems is considered by many to be a new scientific field, and is distinguished by being a discipline that has applications within many separate areas of scientific study. The study of Neural Networks, Traffic Patterns, Artificial Intelligence, Social Systems, and many other scientific areas can all be considered to fall within the realm of Complex Systems, and can be studied from this new perspective. The advent of more capable computer systems has allowed these systems to be simulated and modeled with far greater ease, and new understanding of computer modeling approaches has allowed the fledgling science to be studied as never before. The preliminary focus of this paper will be to provide a general overview of the science of Complex Systems, including terminology, definitions, history, and examples. I will attempt to look at some of the most important trends in different areas of research, and give a general overview of research methods that have been used in parallel with computer mo...

  11. Complex variables

    CERN Document Server

    Flanigan, Francis J

    2010-01-01

    A caution to mathematics professors: Complex Variables does not follow conventional outlines of course material. One reviewer noting its originality wrote: ""A standard text is often preferred [to a superior text like this] because the professor knows the order of topics and the problems, and doesn't really have to pay attention to the text. He can go to class without preparation."" Not so here-Dr. Flanigan treats this most important field of contemporary mathematics in a most unusual way. While all the material for an advanced undergraduate or first-year graduate course is covered, discussion

  12. Complex dynamics

    CERN Document Server

    Carleson, Lennart

    1993-01-01

    Complex dynamics is today very much a focus of interest. Though several fine expository articles were available, by P. Blanchard and by M. Yu. Lyubich in particular, until recently there was no single source where students could find the material with proofs. For anyone in our position, gathering and organizing the material required a great deal of work going through preprints and papers and in some cases even finding a proof. We hope that the results of our efforts will be of help to others who plan to learn about complex dynamics and perhaps even lecture. Meanwhile books in the field a. re beginning to appear. The Stony Brook course notes of J. Milnor were particularly welcome and useful. Still we hope that our special emphasis on the analytic side will satisfy a need. This book is a revised and expanded version of notes based on lectures of the first author at UCLA over several \\Vinter Quarters, particularly 1986 and 1990. We owe Chris Bishop a great deal of gratitude for supervising the production of cour...

  13. Cosmic Complexity

    Science.gov (United States)

    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

  14. Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, Jared; Bergman, Robert; Ellman, Jonathan

    2008-02-04

    Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct funtionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes their work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. They initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. They then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, they discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. They then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy{sub 3}){sub 2}] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazolein, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy{sub 3}){sub 2} fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, they developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including azoles, azolines, dihydroquinazolines, pyridines, and quinolines, with a wide range of functionalized olefins. They demonstrated the utility of this methodology in the synthesis of natural products, drug candidates, and other biologically active molecules. In addition, they developed conditions to directly arylate these heterocycles with aryl halides. The initial conditions that used PCy{sub 3} as a ligand were successful only for aryl iodides. However, efforts designed to avoid catalyst decomposition led to the development of ligands based on 9-phosphabicyclo[4.2.1]nonane (Phoban) that also facilitated the coupling of aryl bromides. They then replicated the unique coordination environment, stability, and catalytic activity of this complex using the much simpler tetrahydrophosphepine ligands and developed conditions that coupled aryl bromides bearing diverse functional groups without the use of a glovebox or purified reagents. With further mechanistic inquiry, they anticipate that researchers will better understand the details of the aforementioned Rh-catalyzed C-H bond functionalization reactions, resulting in the design of more efficient and robust catalysts, expanded substrate scope, and new transformations.

  15. Complex silumins

    Directory of Open Access Journals (Sweden)

    S. Pietrowski

    2007-09-01

    Full Text Available Purpose: The study presents the results of investigations carried out on silumins with additions of Mg, Ni, Cu, Cr, Mo and W. The silumins containing Mg, Cu and Ni are well-known and commonly used in construction of machines and equipment.Design/methodology/approach: Additions of Cr, Mo and W have not been thoroughly investigated yet. They are considered a new family of innovative cast aluminium alloys.Findings: In Al-Si systems they form silicides, like Cr3Si, Mo3Si, W3Si and intermetallic phases of Al13Cr4Si4, Al12Mo, Al12W and AlWSi. The silicides crystallise in cubic lattice of parameters similar to aluminium and silicon.Research limitations/implications: Therefore they can act as crystallisation substrates and occur as separate phases. The examinations under the microscope and X-ray microanalysis of the linear and point distribution of elements confirmed the presence of the above mentioned phases. A combination of two elements, e.g. Cr and Mo, or Cr and W, was observed to cause the formation of complex silicide layers of Mo3Si and (Cr, Mo3Si, or Cr3Si as well as (W, Cr3Si.Originality/value: The presence of the silicides has been indicated as a possible source of the refinement of ?(Al and ?(Si phases. The precipitations of these phases and of the intermetallic phases favour a high degree of the silumins hardening. A characteristic feature is the fact that nucleation and crystallisation of the successive phases takes place at the phase boundaries formed between the previously precipitated phase and solid solution ?. The studies carried out so far have indicated that in complex silumins at high temperatures crystallise the silicides and peritectic phases of Al12W, AlWSi, Al12Mo and Al13Cr4Si4. Phases ? or ? are the next ones to crystallise, followed by complex eutectic ? + ? +Al(Si, Cr, Mo, W, Fe. Further crystallise the phases of Mg2Si, Al3Ni and Al2Cu. The silumins presented here are characterised by high mechanical properties: Rp0,2=320-420MPa, Rm =400-520MPa, A5=0.5-5.0% and elevated hardness of 145-210HB. Further investigations will be carried out to optimise the chemical composition of silumins and the precipitation hardening process parameters to produce alloys characterised by optimum combination of strength, ductility and hardness.

  16. Hydroamination reactions of alkynes with ortho-substituted anilines in ball mills: synthesis of benzannulated N-heterocycles by a cascade reaction.

    Science.gov (United States)

    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

  17. Synthesis of 5- and 6-N-heterocyclic methylenebisphosphonate derivatives and evaluation of their cytogenetic activity in normal human lymphocyte cultures.

    Science.gov (United States)

    Abdou, Wafaa M; Kamel, Azza A; Khidre, Rizk E; Geronikaki, Athina; Ekonomopoulou, Maria T

    2012-05-01

    Methods for the preparation of various aminomethylene bisphosphonates were developed. The required bisphosphonates were obtained by applying tetraethyl methylenebisphosphonate reagent to different types of oxazinones and the relevant Schiff base derivatives. Based on the prediction results (Pass program), we further estimated the sister chromatid exchange frequency and proliferation rate index values of human lymphocyte cultures after the administration of four newly synthesized bisphosphonates in order to evaluate their cytotoxic/cytostatic and possible antineoplastic potency. The results showed that all four bisphosphonates cause a dose-dependent increase in sister chromatid exchange frequency, followed by a decrease in proliferation rate index in both experiments compared to the control. PMID:22243546

  18. Practical Iron- and Cobalt-Catalyzed Cross-Coupling Reactions between N-Heterocyclic Halides and Aryl or Heteroaryl Magnesium Reagents.

    Science.gov (United States)

    Kuzmina, Olesya M; Steib, Andreas K; Fernandez, Sarah; Boudot, Willy; Markiewicz, John T; Knochel, Paul

    2015-05-26

    The reaction scope of iron- and cobalt-catalyzed cross-coupling reactions in the presence of isoquinoline (quinoline) in the solvent mixture tBuOMe/THF has been further investigated. Various 2-halogenated pyridine, pyrimidine, and triazine derivatives were arylated under these mild conditions in excellent yields. The presence of isoquinoline allows us to perform Fe-catalyzed cross-coupling reactions between 6-chloroquinoline and aryl magnesium reagents. Furthermore, it was found that the use of 10?% N,N-dimethylquinoline-8-amine increases the yields of some Co-catalyzed cross-coupling reactions with chloropyridines bearing electron-withdrawing substituents. PMID:25899175

  19. AQUEOUS N-HETEROCYCLIZATION OF PRIMARY AMINES AND HYDRAZINES WITH DIHALIDES: MICROWAVE-ASSISTED SYNTHESES OF N-AZACYCLOALKANES, ISOINDOLE, PYRAZOLE, PYRAZOLIDINE AND PHTHALAZINE DERIVATIVES

    Science.gov (United States)

    The synthesis of nitrogen-containing heterocycles from alkyl dihalides (ditosylates) and primary amines and hydrazines via a simple and efficient cyclocondensation in alkaline aqueous medium that occurs under microwave irradiation is described. This improved greener synthetic met...

  20. A novel binuclear ruthenium complex: spectroscopic and electrochemical characterization, and formation of Langmuir and Langmuir-Blodgett films

    Scientific Electronic Library Online (English)

    Karen, Wohnrath; Poliana M. dos, Santos; B., Sandrino; Jarem R., Garcia; Alzir A., Batista; Osvaldo N., Oliveira Jr.

    1634-16-01

    Full Text Available O complexo [{RuCl3(dppb)}2(µ-4,4'-bipy)] (dppb = PPh2(CH2)4PPh2; 4,4'-bipy= 4,4'-bipiridil) foi obtido por meio da reação entre 4,4'-bipiridina e mer-[RuCl3(dppb)].H2O, em bom rendimento. As características do complexo binuclear obtido, estudadas por medidas de FT-IR, UV-Vis, EPR e análise elementar [...] foram similares às do complexo [RuCl3(dppb)L] (L= N-heterociclo). [{RuCl3(dppb)}2(µ-4,4'-bipy)] é solúvel em solventes fracamente polares, facilitando a sua utilização para produzir filmes de Langmuir e Langmuir-Blodgett (LB). Enquanto que filmes cast e o complexo em solução são vermelhos, filmes LB são azul-esverdeados, provavelmente devido à oxidação da bisfosfina. A natureza nanoestruturada dos filmes LB, se manifestou nas medidas eletroquímicas, já que estes filmes exibem maior corrente de pico do que os filmes cast e dip-coated. As respostas eletroquímicas destes filmes são caracterizadas pelo processo RuIII RuIII/RuII RuII, o qual difere do complexo em solução. Neste último caso, um processo irreversível é observado devido à formação de novas espécies. A eletroatividade dos filmes LB/[{RuCl3(dppb)}2(µ-4,4' -bipy)] indica a possibilidade de utilização em dispositivos eletroquímicos. Abstract in english [{RuCl3(dppb)}2(µ-4,4'-bipy)] was prepared from the reaction of the 4,4'-bipyridine and mer-[RuCl3(dppb)].H2O, in good yield. The characteristics of the binuclear complex studied with FT-IR, UV-Vis, EPR and elemental analysis were similar to those of the [RuCl3(dppb)L] (L= N-heterocycle). [{RuCl3(dp [...] pb)}2(µ-4,4'-bipy)] is soluble in weakly polar organic solvents, facilitating its use in the production of Langmuir and Langmuir-Blodgett (LB) films production. While the cast films and the complex in solution were red, the LB films were green-bluish, probably due to oxidation of the bisphosphine. The nanostructured nature of the LB films was manifested in electrochemical measurements, as these films exhibited higher peak currents than cast or dip-coated films. For all films, the electrochemical response was dominated by the RuIII RuIII/RuII RuII process, which differed from that of the binuclear compound. For the latter, an irreversible process appeared due to formation of new species. The electroactivity of LB films from [{RuCl3(dppb)}2(µ-4,4'-bipy)] also pointed to their possible use in electrochemical devices.

  1. An electrochemical alternative strategy to the synthesis of {beta}-lactams

    Energy Technology Data Exchange (ETDEWEB)

    Sotgiu, G. [Dip. Elettronica Applicata, Universita di Roma Tre, via Vasca Navale 84, I-00146 Roma (Italy)], E-mail: achille.inesi@uniroma1.it; Chiarotto, I.; Feroci, M. [Dip. Ingegneria Chimica, Materiali, Materie Prime e Metallurgia, Universita ' La Sapienza' , via Castro Laurenziano, 7, I-00161 Roma (Italy); Orsini, M. [Dip. Elettronica Applicata, Universita di Roma Tre, via Vasca Navale 84, I-00146 Roma (Italy); Rossi, L. [Dip. Chimica, Ingegneria Chimica e Materiali, Universita degli Studi, I-67040, Monteluco di Roio, L' Aquila (Italy); Inesi, A. [Dip. Ingegneria Chimica, Materiali, Materie Prime e Metallurgia, Universita ' La Sapienza' , via Castro Laurenziano, 7, I-00161 Roma (Italy)], E-mail: sotgiu@uniroma3.it

    2008-11-15

    Electrochemically induced cyclization of bromoamides to {beta}-lactams has been achieved in room-temperature ionic liquids (RTILs). The use of volatile, organic solvents (VOCs) and of supporting electrolytes may be avoided. Proton exchange reaction between amide substrates and suitable electrogenerated bases gives rise to a C{sub 4} carbanion which undergoes cyclization to {beta}-lactam via intramolecular nucleophilic substitution (C{sub 3}-C{sub 4} bond formation). {beta}-Lactams have been isolated in good to elevated yields. The 'non innocent' nature of the RTILs (imidazolium-based salts) is considered. Proton exchange reaction between N-dialkylimidazolium cation and EGB yielding N-heterocyclic carbene is discussed.

  2. An electrochemical alternative strategy to the synthesis of {beta}-lactams. Part 3 [1]. Room-temperature ionic liquids vs molecular organic solvents

    Energy Technology Data Exchange (ETDEWEB)

    Sotgiu, G.; Orsini, M. [Dip. Elettronica Applicata, Universita di Roma Tre, via Vasca Navale 84, I-00146 Roma (Italy); Chiarotto, I.; Feroci, M.; Inesi, A. [Dip. Ingegneria Chimica, Materiali, Materie Prime e Metallurgia, Universita ' ' La Sapienza' ' , via Castro Laurenziano, 7, I-00161 Roma (Italy); Rossi, L. [Dip. Chimica, Ingegneria Chimica e Materiali, Universita degli Studi, I-67040, Monteluco di Roio, L' Aquila (Italy)

    2008-11-15

    Electrochemically induced cyclization of bromoamides to {beta}-lactams has been achieved in room-temperature ionic liquids (RTILs). The use of volatile, organic solvents (VOCs) and of supporting electrolytes may be avoided. Proton exchange reaction between amide substrates and suitable electrogenerated bases gives rise to a C{sub 4} carbanion which undergoes cyclization to {beta}-lactam via intramolecular nucleophilic substitution (C{sub 3}-C{sub 4} bond formation). {beta}-Lactams have been isolated in good to elevated yields. The 'non innocent' nature of the RTILs (imidazolium-based salts) is considered. Proton exchange reaction between N-dialkylimidazolium cation and EGB yielding N-heterocyclic carbene is discussed. (author)

  3. 1-n-Butyl-3-methylimidazolium-2-carboxylate: a versatile precatalyst for the ring-opening polymerization of ?-caprolactone and rac-lactide under solvent-free conditions

    Directory of Open Access Journals (Sweden)

    Astrid Hoppe

    2013-04-01

    Full Text Available The ring-opening polymerization of ?-caprolactone (?-CL and rac-lactide (rac-LA under solvent-free conditions and using 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO2 as precatalyst is described. Linear and star-branched polyesters were synthesized by successive use of benzyl alcohol, ethylene glycol, glycerol and pentaerythritol as initiator alcohols, and the products were fully characterized by 1H and 13C{1H} NMR spectroscopy, gel permeation chromatography (GPC, and differential scanning calorimetry (DSC. BMIM-2-CO2 acts as an N-heterocyclic carbene precursor, resulting from in situ decarboxylation, either by heating under vacuo (method A or by addition of NaBPh4 (method B. Possible catalytic and deactivation mechanisms are proposed.

  4. Unexpected drastic decrease in the excited-state electronic communication between porphyrin chromophores covalently linked by a palladium(II) bridge.

    Science.gov (United States)

    Abdelhameed, Mohammed; Karsenti, Paul-Ludovic; Langlois, Adam; Lefebvre, Jean-François; Richeter, Sébastien; Ruppert, Romain; Harvey, Pierre D

    2014-09-26

    A dyad built up of a zinc(II) porphyrin and the corresponding free base, [Zn-Fb], fused to N-heterocyclic carbene (NHCs) ligands, respectively acting as singlet energy donor and acceptor, and a bridging trans-PdI2 unit, along with the corresponding [Zn-Zn] and [Fb-Fb] dimers were prepared and investigated by absorption and emission spectroscopy and density functional computations. Despite favorable structural and spectroscopic parameters, unexpectedly slow singlet energy transfer rates are measured in comparison with the predicted values by the Förster theory and those observed for other structurally related dyads. This observation is rationalized by the lack of large molecular orbital (MO) overlaps between the frontier MOs of the donor and acceptor, thus preventing a double electron exchange through the trans-PdI2 bridge, and by an electronic shielding induced by the presence of this same linker preventing the two chromophores to fully interact via their transition dipoles. PMID:25123591

  5. Chemoselective reduction of the carbonyl functionality through hydrosilylation: integrating click catalysis with hydrosilylation in one pot.

    Science.gov (United States)

    Roy, Sudipta Raha; Sau, Samaresh Chandra; Mandal, Swadhin K

    2014-10-01

    Herein we report the chemoselective reduction of the carbonyl functionality via hydrosilylation using a copper(I) catalyst bearing the abnormal N-heterocyclic carbene 1 with low (0.25 mol %) catalyst loading at ambient temperature in excellent yield within a very short reaction time. The hydrosilylation reaction of ?,?-unsaturated carbonyl compounds takes place selectively toward 1,2-addition (C?O) to yield the corresponding allyl alcohols in good yields. Moreover, when two reducible functional groups such as imine and ketone groups are present in the same molecule, this catalyst selectively reduces the ketone functionality. Further, 1 was used in a consecutive fashion by combining the Huisgen cycloaddition and hydrosilylation reactions in one pot, yielding a range of functionalized triazole substituted alcohols in excellent yields. PMID:25188382

  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.).

    Science.gov (United States)

    Yang, Ya-Xiu; Li, Yongxin; Ganguly, Rakesh; So, Cheuk-Wai

    2015-07-01

    The reaction of [LCH2] (, 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 (), Zr ()] and [1,3-C6H4(PhPS)(PhP)CH2]. The reactions appear to proceed through the formation of metal bis(carbene) complexes, [LC[double bond, length as m-dash]M[double bond, length as m-dash]CL], which then undergo an intermolecular sulphur transfer reaction with the P[double bond, length as m-dash]S bond of [LCH2] to form and , and the byproduct is [1,3-C6H4(PhPS)(PhP)CH2]. In addition, the reaction of , [CH2(PPh2S)2] () and M(NMe2)4 in refluxing toluene gave a mixture of [{LC(S)}M(NHMe2){C(PPh2S)2}] [M = Hf (), Zr ()], [1,3-C6H4(PhPS)(PhP)CH2] and [CH2(PPh2S)(PPh2)]. Moreover, the intermolecular sulfur transfer reaction is evidenced by the reaction of the tin(ii) 1,3-benzodi(thiophosphinoyl)methandiide complex [{?-1,3-C6H4(PhPS)2C}Sn]2 () with two equivalents of elemental sulfur in CH2Cl2 at ambient temperature to give [{1,3-C6H4(PhPS)2CS}2Sn] (). Compounds , , , , and were characterized by NMR spectroscopy and X-ray crystallography. PMID:26079794

  7. Generalized complex geometry

    CERN Document Server

    Gualtieri, M

    2007-01-01

    Generalized complex geometry, introduced by Hitchin, encompasses complex and symplectic geometry as its extremal special cases. We explore the basic properties of this geometry, including its enhanced symmetry group, elliptic deformation theory, relation to Poisson geometry, and local structure theory. We also define and study generalized complex branes, which interpolate between flat bundles on Lagrangian submanifolds and holomorphic bundles on complex submanifolds.

  8. Complex submanifolds of almost complex Euclidean Spaces

    OpenAIRE

    Di Scala, Antonio Jose

    2010-01-01

    We prove that a compact Riemann surface can be realized as a pseudo-holomorphic curve of $(\\mathbb{R}^4,J)$, for some almost complex structure $J$ if and only if it is an elliptic curve. Furthermore we show that any (almost) complex $2n$-torus can be holomorphically embedded in $(\\mathbb{R}^{4n},J)$ for a suitable almost complex structure $J$. This allows us to embed any compact Riemann surface in some almost complex Euclidean space and to show many explicit examples of almo...

  9. Iron- and Cobalt-Catalyzed Alkene Hydrogenation: Catalysis with Both Redox-Active and Strong Field Ligands.

    Science.gov (United States)

    Chirik, Paul J

    2015-06-16

    The hydrogenation of alkenes is one of the most impactful reactions catalyzed by homogeneous transition metal complexes finding application in the pharmaceutical, agrochemical, and commodity chemical industries. For decades, catalyst technology has relied on precious metal catalysts supported by strong field ligands to enable highly predictable two-electron redox chemistry that constitutes key bond breaking and forming steps during turnover. Alternative catalysts based on earth abundant transition metals such as iron and cobalt not only offer potential environmental and economic advantages but also provide an opportunity to explore catalysis in a new chemical space. The kinetically and thermodynamically accessible oxidation and spin states may enable new mechanistic pathways, unique substrate scope, or altogether new reactivity. This Account describes my group's efforts over the past decade to develop iron and cobalt catalysts for alkene hydrogenation. Particular emphasis is devoted to the interplay of the electronic structure of the base metal compounds and their catalytic performance. First generation, aryl-substituted pyridine(diimine) iron dinitrogen catalysts exhibited high turnover frequencies at low catalyst loadings and hydrogen pressures for the hydrogenation of unactivated terminal and disubstituted alkenes. Exploration of structure-reactivity relationships established smaller aryl substituents and more electron donating ligands resulted in improved performance. Second generation iron and cobalt catalysts where the imine donors were replaced by N-heterocyclic carbenes resulted in dramatically improved activity and enabled hydrogenation of more challenging unactivated, tri- and tetrasubstituted alkenes. Optimized cobalt catalysts have been discovered that are among the most active homogeneous hydrogenation catalysts known. Synthesis of enantiopure, C1 symmetric pyridine(diimine) cobalt complexes have enabled rare examples of highly enantioselective hydrogenation of a family of substituted styrene derivatives. Because improved hydrogenation performance was observed with more electron rich supporting ligands, phosphine cobalt(II) dialkyl complexes were synthesized and found to be active for the diastereoselective hydrogenation of various substituted alkenes. Notably, this class of catalysts was activated by hydroxyl functionality, representing a significant advance in the functional group tolerance of base metal hydrogenation catalysts. Through collaboration with Merck, enantioselective variants of these catalysts were discovered by high throughput experimentation. Catalysts for the hydrogenation of functionalized and essentially unfunctionalized alkenes have been discovered using this approach. Development of reliable, readily accessible cobalt precursors facilitated catalyst discovery and may, along with lessons learned from electronic structure studies, provide fundamental design principles for catalysis with earth abundant transition metals beyond alkene hydrogenation. PMID:26042837

  10. Complex Multiplicative Calculus

    CERN Document Server

    Bashirov, Agamirza

    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 realization of the ordinary calculus. In particular, the Cauchy formula of complex calculus disappears in multiplicative complex calculus.

  11. Ab initio investigation of surface adsorption phenomena: from pyridine gold complexes to larger system

    Energy Technology Data Exchange (ETDEWEB)

    Mollenhauer, Doreen; Floss, Johannes; Voloshina, Elena; Paulus, Beate [Institut fuer Chemie und Biochemie - Physikalische und Theoretische Chemie, Freie Universitaet Berlin, Takustrasse 3, 14195 Berlin (Germany)

    2010-07-01

    The investigation of the adsorption of organic molecules on metal substrates plays an important role for the understanding of multivalent interactions. Due to the enhancement of the adsorption new architectures of multivalent molecules can appear on metal surfaces. Taking into account recent molecular electronic experiments involving molecules linked via N-heterocycles to gold electrodes and nanoclusters, pyridine derivates are seen to be interesting objects for theoretical studies. The interaction of the parent compound pyridine and some substituted derivates with a single gold atom has been investigated. Different quantum-chemical methods and basis sets have been used to find a reliable description. We plan to extend our studies to gold clusters, gold nanoparticles and para-linked pyridine derivates. The main purpose is to analyze the nature of multivalent bonding in comparison to monovalent interaction.

  12. Complex Multiplicative Calculus

    OpenAIRE

    Bashirov, Agamirza; Riza, Mustafa

    2011-01-01

    In the present paper we extend the concepts of multiplicative de- rivative and integral to complex-valued functions of complex variable. Some drawbacks, arising with these concepts in the real case, are explained satis- factorily. Properties of complex multiplicative derivatives and integrals are studied. In particular, the fundamental theorem of complex multiplicative calculus, relating these concepts, is proved. It is shown that complex multi- plicative calculus is not jus...

  13. Visualization of Complex Systems

    OpenAIRE

    Viste, Magnhild

    2008-01-01

    Complex systems are difficult to understand. To aid understanding of complex dynamic systems the field of system dynamics has developed a set of visualization methods for graphic representation of the simulation models of complex systems. The resulting visualizations, however, may sometimes be difficult to understand for audiences without a background in the scientific investigation of complex dynamic systems. It is therefore necessary to find new ways of representing complex s...

  14. Protein Complexes in Bacteria

    Science.gov (United States)

    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 species. For instance, of 285 “gold standard” protein complexes in E. coli, less than 10% are fully conserved among a set of 7 distantly-related bacterial “model” species. Complex conservation follows one of three models: well-conserved complexes, complexes with a conserved core, and complexes with partial conservation but no conserved core. Expanding the comparison to 894 distinct bacterial genomes illustrates fractional conservation and the limits of co-conservation among components of protein complexes: just 14 out of 285 model protein complexes are perfectly conserved across 95% of the genomes used, yet we predict more than 180 may be partially conserved across at least half of the genomes. No clear relationship between gene essentiality and protein complex conservation is observed, as even poorly conserved complexes contain a significant number of essential proteins. Finally, we identify 183 complexes containing well-conserved components and uncharacterized proteins which will be interesting targets for future experimental studies. PMID:25723151

  15. Lanthanide acylpyrazolonates: synthesis, properties and structural features

    Science.gov (United States)

    Belousov, Yu A.; Drozdov, Andrey A.

    2012-12-01

    Data concerning synthesis and structural features of lanthanide acylpyrazolonates including tris-complexes, heteroligand complexes with aromatic N-heterocycles and phosphorus-containing ligands and anionic tetrakis-complexes are summarized. The effect of substituents in the acyl moiety on the structural and luminescence properties of the compounds is considered. The key features of acylpyrazolonate coordination polymers and bis(acylpyrazolonates) of rare earth elements are discussed. The bibliography includes 71 references.

  16. Quantum Complex Minkowski Space

    OpenAIRE

    Jakimowicz, Grzegorz; Odzijewicz, Anatol

    2005-01-01

    The complex Minkowski phase space has the physical interpretation of the phase space of the scalar massive conformal particle. The aim of the paper is the construction and investigation of the quantum complex Minkowski space.

  17. Quantum Communication Complexity

    OpenAIRE

    Klauck, Hartmut

    2000-01-01

    This paper surveys the field of quantum communication complexity. Some interesting recent results are collected concerning relations to classical communication, lower bound methods, one-way communication, and applications of quantum communication complexity.

  18. Oligocyclopentadienyl transition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    de Azevedo, Cristina G.; Vollhardt, K. Peter C.

    2002-01-18

    Synthesis, characterization, and reactivity studies of oligocyclopentadienyl transition metal complexes, namely those of fulvalene, tercyclopentadienyl, quatercyclopentadienyl, and pentacyclopentadienyl(cyclopentadienyl) are the subject of this account. Thermal-, photo-, and redox chemistries of homo- and heteropolynuclear complexes are described.

  19. Complexity Simplicity Simplexity

    OpenAIRE

    Cunha, Miguel Pina E.; Rego, Arme?nio

    2008-01-01

    “In the midst of order, there is chaos; but in the midst of chaos, there is order”, John Gribbin wrote in his book Deep Simplicity (p.76). In this dialectical spirit, we discuss the generative tension between complexity and simplicity in the theory and practice of management and organization. Complexity theory suggests that the relationship between complex environments and complex organizations advanced by the well-known Ashby’s law, may be reconsidered: only simple organization provide...

  20. Complexity Near Horizons

    CERN Document Server

    Halyo, Edi

    2015-01-01

    We generalize the concept of complexity near horizons to all nondegenerate black holes. For Schwarzschild black holes, we show that Rindler observers see a complexity change of $S$ during proper time $1/\\kappa$ which corresponds to the creation of a causal patch with proper length $1/\\kappa$ inside the horizon. We attempt to describe complexity in the horizon CFT and the Euclidean picture.

  1. ?-Alkyl and ?-aryl complexes

    International Nuclear Information System (INIS)

    Methods of preparation, solubility, reactivity, as well as molecular and crystal structure of ?-alkyl and ?-aryl complexes of rare earths of different composition are described. Di- and trisubstituted alkyl (aryl)lanthanides, their halogen derivatives of RLnHal type, afe-complexes, complexes of Cp2LnR type and ilide derivatives are considered in particular. 173 refs.; 17 figs.; 12 tabs

  2. Lanthanide complexes with pivaloylacetone

    International Nuclear Information System (INIS)

    Complexes Ln(pa)3·2H2O (Ln=La, Gd, Lu, Hpa - pivaloylacetone) are synthesized and investigated by the methods of element, IR spectroscopic and thermal analyses. Behaviour of the complexes during heating in vacuum is compared with such one for acetylacetonates and dipivaloylmethanates. Structure of the complexes in solution is studied by 1H NMR and MALDI-MS

  3. Complex Systems + Systems Engineering = Complex Systems Engineeri

    OpenAIRE

    Abbott, Russ

    2006-01-01

    One may define a complex system as a system in which phenomena emerge as a consequence of multiscale interaction among the system's components and their environments. The field of Complex Systems is the study of such systems--usually naturally occurring, either bio-logical or social. Systems Engineering may be understood to include the conceptualising and building of systems that consist of a large number of concurrently operating and interacting components--usually includin...

  4. Synthesis, structural characterization, reactivity, and catalytic properties of copper(I) complexes with a series of tetradentate tripodal tris(pyrazolylmethyl)amine ligands.

    Science.gov (United States)

    Haldón, Estela; Delgado-Rebollo, Manuela; Prieto, Auxiliadora; Alvarez, Eleuterio; Maya, Celia; Nicasio, M Carmen; Pérez, Pedro J

    2014-04-21

    Novel tris(pyrazolylmethyl)amine ligands Tpa(Me3), Tpa*(,Br), and Tpa(Br3) have been synthesized and structurally characterized. The coordination chemistries of these three new tetradentate tripodal ligands and the already known Tpa and Tpa* have been explored using different copper(I) salts as starting materials. Cationic copper(I) complexes [Tpa(x)Cu]PF6 (1-4) have been isolated from the reaction of [Cu(NCMe)4]PF6 and 1 equiv of the ligand. Complexes 2 (Tpa(x) = Tpa*) and 3 (Tpa(x) = Tpa(Me3)) have been characterized by X-ray studies. The former is a 1D helical coordination polymer, and the latter is a tetranuclear helicate. In both structures, the Tpa(x) ligand adopts a ?(2):?(2):?(1)-coordination mode. However, in solution, all of the four complexes form fluxional species. When CuI is used as the copper(I) source, neutral compounds 5-8 have been obtained. Complexes 6-8 exhibit a 1:1 metal-to-ligand ratio, whereas 5 presents 2:1 stoichiometry. Its solid-state structure has been determined by X-ray diffraction, revealing its 3D polymeric nature. The polymer is composed by the assembly of [Tpa2Cu4I4] units, in which Cu4I4 presents a step-stair structure. The Tpa ligands bridge the Cu4I4 clusters, adopting also a ?(2):?(2):?(1)-coordination mode. As observed for the cationic derivatives, the NMR spectra of 5-8 show the equivalence of the three pyrazolyl arms of the ligands in these complexes. The reactivities of cationic copper(I) derivatives 1-4 with PPh3 and CO have been explored. In all cases, 1:1 adducts [Tpa(x)CuL]PF6 [L = PPh3 (9-11), CO (12-15)] have been isolated. The crystal structure of [Tpa*Cu(PPh3)]PF6 (9) has been obtained, showing that the coordination geometry around copper(I) is trigonal-pyramidal with the apical position occupied by the tertiary amine N atom. The Tpa* ligand binds the Cu center to three of its four N atoms, with one pyrazolyl arm remaining uncoordinated. In solution, the carbonyl adducts 13-15 exist as a mixture of two isomers; the four- and five-coordinate species can be distinguished by means of their IR ?CO stretching bands. Finally, the catalytic activities of complexes 1-4 have been demonstrated in carbene- and nitrene-transfer reactions. PMID:24697594

  5. Complex variables I essentials

    CERN Document Server

    Solomon, Alan D

    2013-01-01

    REA's Essentials provide quick and easy access to critical information in a variety of different fields, ranging from the most basic to the most advanced. As its name implies, these concise, comprehensive study guides summarize the essentials of the field covered. Essentials are helpful when preparing for exams, doing homework and will remain a lasting reference source for students, teachers, and professionals. Complex Variables I includes functions of a complex variable, elementary complex functions, integrals of complex functions in the complex plane, sequences and series, and poles and r

  6. Quantum State Complexity Measure

    CERN Document Server

    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.

  7. Semicarbazonas e tiossemicarbazonas: o amplo perfil farmacológico e usos clínicos

    OpenAIRE

    Beraldo Heloisa

    2004-01-01

    This article shows that thiosemicarbazones, semicarbazones and their metal complexes can exhibit target selectivity along with a wide pharmacological profile. Complexes of thiosemicarbazones with cytotoxic or antitumoral activity are presented, some of which show activity against cisplatinum-resistant cells. The inhibition mechanism of the enzyme ribonucleoside diphosphate reductase (RDR), involved in DNA syntheses, by alpha(N)-heterocyclic thiosemicarbazones is discussed. The encouraging res...

  8. Semicarbazonas e tiossemicarbazonas: o amplo perfil farmacológico e usos clínicos Semicarbazones and thiosemicarbazones: their wide pharmacological profile and clinical applications

    OpenAIRE

    Heloisa Beraldo

    2004-01-01

    This article shows that thiosemicarbazones, semicarbazones and their metal complexes can exhibit target selectivity along with a wide pharmacological profile. Complexes of thiosemicarbazones with cytotoxic or antitumoral activity are presented, some of which show activity against cisplatinum-resistant cells. The inhibition mechanism of the enzyme ribonucleoside diphosphate reductase (RDR), involved in DNA syntheses, by alpha(N)-heterocyclic thiosemicarbazones is discussed. The encouraging res...

  9. Nickel Catalysis: Synergy between Method Development and Total Synthesis.

    Science.gov (United States)

    Standley, Eric A; Tasker, Sarah Z; Jensen, Kim L; Jamison, Timothy F

    2015-05-19

    Nickel(0) catalysts have proven to be powerful tools for multicomponent coupling reactions in our laboratories over the past 15 years. This interest was originally sparked by the ubiquity of allylic alcohol motifs in natural products, such as (-)-terpestacin, which we envisioned assembling by the coupling of two ? components (alkyne and aldehyde) with concomitant reduction. Mechanistic investigations allowed us to elucidate several modes of controlling the regioselectivity and stereoselectivity in the oxidative cyclization, and these insights enabled us to leverage combinations of alkenes and phosphine ligands to direct regioselective outcomes. The initial success in developing the first intermolecular reductive alkyne-aldehyde coupling reaction launched a series of methodological investigations that rapidly expanded to include coupling reactions of alkynes with other electrophilic ? components, such as imines and ketones, as well as electrophilic ? components, such as epoxides. Aziridines proved to be more challenging substrates for reductive coupling, but we were recently able to demonstrate that cross-coupling of aziridines and alkylzinc reagents is smoothly catalyzed by a zero-valent nickel/phenanthroline system. Moreover, the enantioselective alkyne-aldehyde coupling and the development of novel P-chiral ferrocenyl ligands enabled the total synthesis of (-)-terpestacin, amphidinolides T1 and T4, (-)-gloeosporone, and pumiliotoxins 209F and 251D. We subsequently determined that alkenes could be used in place of alkynes in several nickel-catalyzed reactions when a silyl triflate activating agent was added. We reason that such an additive functions largely to enhance the electrophilicity of the metal center by coordination to the electrophilic ? component, such that less nucleophilic alkene ? donors can undergo productive combination with nickel complexes. This activation manifold was further demonstrated to be effective for alkene-aldehyde couplings. In a related manner, electrophilic promoters were also successfully employed for allylic substitution reactions of allylic carbonates with simple alkenes and in the Mizoroki-Heck reaction of both benzyl and aryl electrophiles. In these instances, it is proposed that counterion exchange from a more strongly coordinating anion to the weakly or noncoordinating triflate counterion enables reaction at an electrophilic Ni(II) center rather than by coordination to one of the coupling components. Mechanistic insights also played an important role in the development of mixed N-heterocyclic carbene/phosphite ligand systems to overcome challenges in regioselective alkene-aldehyde coupling reactions. We hope that, taken together, the body of work summarized in this Account demonstrates the constructive interplay among total synthesis, methodological development, and mechanistic investigation that has driven our research program. PMID:25905431

  10. Taurid meteor complex

    Science.gov (United States)

    Bu?ek, M.; Porub?an, V.

    2014-07-01

    Structure of the autumnal part of the Taurid meteor complex based on photographic, radio and video meteor orbits is investigated and presented. Potential filaments or sub-streams to be associated with the complex were searched for utilizing the Southworth-Hawkins D-criterion. Altogether fourteen filaments or sub-streams associated with the complex were separated, with the length of the complex exceeding 100 degrees. Central part of the complex is formed by four the most dense filaments, the Northern and Southern Taurids, Southern Piscids and Omicron Orionids. The most probable bodies genetically related to the complex besides 2P/Encke are 2005 UY6, 2005 TF50 and 2007 RU17.

  11. On Complex Random Variables

    Directory of Open Access Journals (Sweden)

    Anwer Khurshid

    2012-07-01

    Full Text Available Normal 0 false false false EN-US X-NONE X-NONE In this paper, it is shown that a complex multivariate random variable  is a complex multivariate normal random variable of dimensionality if and only if all nondegenerate complex linear combinations of  have a complex univariate normal distribution. The characteristic function of  has been derived, and simpler forms of some theorems have been given using this characterization theorem without assuming that the variance-covariance matrix of the vector  is Hermitian positive definite. Marginal distributions of  have been given. In addition, a complex multivariate t-distribution has been defined and the density derived. A characterization of the complex multivariate t-distribution is given. A few possible uses of this distribution have been suggested.

  12. Measuring static complexity

    Directory of Open Access Journals (Sweden)

    Ben Goertzel

    1992-03-01

    Full Text Available The concept of “pattern” is introduced, formally defined, and used to analyze various measures of the complexity of finite binary sequences and other objects. The standard Kolmogoroff-Chaitin-Solomonoff complexity measure is considered, along with Bennett's ‘logical depth’, Koppel's ‘sophistication'’, and Chaitin's analysis of the complexity of geometric objects. The pattern-theoretic point of view illuminates the shortcomings of these measures and leads to specific improvements, it gives rise to two novel mathematical concepts--“orders” of complexity and “levels” of pattern, and it yields a new measure of complexity, the “structural complexity”, which measures the total amount of structure an entity possesses.

  13. Simplicial complexes of graphs

    CERN Document Server

    Jonsson, Jakob

    2008-01-01

    A graph complex is a finite family of graphs closed under deletion of edges. Graph complexes show up naturally in many different areas of mathematics, including commutative algebra, geometry, and knot theory. Identifying each graph with its edge set, one may view a graph complex as a simplicial complex and hence interpret it as a geometric object. This volume examines topological properties of graph complexes, focusing on homotopy type and homology. Many of the proofs are based on Robin Forman's discrete version of Morse theory. As a byproduct, this volume also provides a loosely defined toolbox for attacking problems in topological combinatorics via discrete Morse theory. In terms of simplicity and power, arguably the most efficient tool is Forman's divide and conquer approach via decision trees; it is successfully applied to a large number of graph and digraph complexes.

  14. Complex Systems and Dependability

    CERN Document Server

    Zamojski, Wojciech; Sugier, Jaroslaw

    2012-01-01

    Typical contemporary complex system is a multifaceted amalgamation of technical, information, organization, software and human (users, administrators and management) resources. Complexity of such a system comes not only from its involved technical and organizational structure but mainly from complexity of information processes that must be implemented in the operational environment (data processing, monitoring, management, etc.). In such case traditional methods of reliability analysis focused mainly on technical level are usually insufficient in performance evaluation and more innovative meth

  15. Physics of Complex Plasmas.

    OpenAIRE

    Su?tterlin, Robert

    2010-01-01

    Physics of complex plasmas is a wide and varied field. In the context of this PhD thesis I present the major results from my research on fundamental properties of the plasma sheath, the plasma dust interaction, non-Hamiltonian dynamics, and on non-equilibrium phase transitions, using complex plasmas as a model system. The first chapter provides a short overview of the development of physics of Complex Plasmas. From fundamental plasma physics, properties of dust in plasmas, to the exception...

  16. Quantum Computational Complexity

    OpenAIRE

    Watrous, John

    2008-01-01

    This article surveys quantum computational complexity, with a focus on three fundamental notions: polynomial-time quantum computations, the efficient verification of quantum proofs, and quantum interactive proof systems. Properties of quantum complexity classes based on these notions, such as BQP, QMA, and QIP, are presented. Other topics in quantum complexity, including quantum advice, space-bounded quantum computation, and bounded-depth quantum circuits, are also discussed.

  17. Complex Composite Odontome

    OpenAIRE

    Mahesh Gabhane; Meena Kulkarni; Aarti Mahajan; Arpan Shah,

    2010-01-01

    Complex composite odontoma was described as a distinct entity for the first time by Broca in 1866. This lesion takes place because dental components are laid down in a disorganized manner, due to failure of normal morphodifferentiation. The difference between complex and composite odontomas is arbitrary, being based on the preponderance of well-organized denticles as opposed to a preponderance of disorganized dental tissues rather than on any absolute difference. In complex odontoma individua...

  18. Engineering Complex Tissues

    OpenAIRE

    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 osteoge...

  19. Ion-molecule collision complexes

    Energy Technology Data Exchange (ETDEWEB)

    Klots, C.E.

    1978-01-01

    A summary of ideas emerging at the workshop on ion-molecule collision complexes is given and covers the direct observation of colision complexes, unimolecular reactions of collision complexes, and the direct preparation of collision complexes. 31 references. (JFP)

  20. Synthesis, Structure, and Reactivity ofbis(1,2,4-tri-t-butylcyclopentadienyl) Complexes of Cerium

    Energy Technology Data Exchange (ETDEWEB)

    Werkema, Evan L.

    2005-05-19

    The sterically demanding 1,2,4-tri-t-butylcyclopentadienylligand (1,2,4-(Me3C)3C5H2, hereafter Cp') has been used to preparemonomeric cerium metallocenes, Cp 2CeX (X = Cl, I, OSO2CF3), which areused to synthesize the benzyl, Cp'2CeCH2C6H5. The benzyl is a usefulstarting material for preparing other complexes in the Cp'2CeZ system (Z= BF4, F, NH2, C6H5, H). X-ray crystal structures of Cp'2CeOSO2CF3,Cp'2CeF, Cp'2CeCH2C6H5, and Cp'2CeH are presented. The benzyl slowlydecomposes in solution to toluene and a metallacycle,[Cp'][(Me3C)2C5H2(CMe2CH2)]Ce. The ring CMe3 groups of both themetallacycle and the hydride, Cp'2CeH, can be fully deuterated byprolonged exposure to C6D6, providing a useful labeling tool inmechanistic studies.The hydride activates C-F and/or C-H bonds influorobenzenes, C6HxF6-x , x = 0-5. The reactions are selective, with theselectivity depending on the presence of two fluorines ortho to thereaction site more than on the type of bond activated. Complexes of thetype Cp'2CeC6HxF5-x , x = 0-4, are formed as intermediates, which slowlydecompose in solution to Cp'2CeF and fluorobenzynes, C6HxF4-x, x = 0-4,which are trapped. The rate at which Cp'2CeC6HxF5-x complexes decomposeincreases as the number of fluorines decreases. Complexes with oneortho-fluorine decompose much faster than those with two ortho-fluorines.The metallacycle activates only C-H bonds in fluorobenzenes, permittingthe synthesis of specific Cp'2CeC6HxF5-x complexes. The crystal structureof Cp'2CeC6F5 is presented. The hydride and the metallacycle react withfluoromethanes, CH4-xFx, x = 1-3, through postulated Cp'2CeCH3-xFxintermediates to generate Cp'2CeF and other products. The other products,CH4, tri-t-butylbenzenes, tri-t-butylfluorobenzenes, and a presumedmetallocene cerium fluoride with one Cp' and one (Me2EtC)(Me3C)2C5H2ligand, suggest a decomposition pathway for Cp'2CeCH3-xFx , x = 1-3, thatinvolves carbenes or carbenoids, which are trapped. The hydridepolymerizes ethylene, but hydrogenates other olefins. The metallacycleactivates C-H bonds in olefins and aromatics to generate new complexeswith Ce-C bonds. The hydride reacts with one equivalent of CO in pentaneto generate (Cp'2Ce)2CH2O, whose crystal structure shows the presence ofa bridging dianionic formaldehyde ligand. (Cp'2Ce)2CH2O reacts H2 to givethe hydride and Cp'2CeOMe, or with a mixture of H2 and CO to generateCp'2CeOMe exclusively. (Cp'2Ce)2CH2O or the hydride can react with anadditional equivalent of CO to generate dimeric enediolate,(Cp'2CeCHO)2.

  1. Introductory complex analysis

    CERN Document Server

    Silverman, Richard A

    1984-01-01

    A shorter version of A. I. Markushevich's masterly three-volume Theory of Functions of a Complex Variable, this edition is appropriate for advanced undergraduate and graduate courses in complex analysis. Numerous worked-out examples and more than 300 problems, some with hints and answers, make it suitable for independent study. 1967 edition.

  2. Urban research and complexity

    OpenAIRE

    Pumain, Denise

    1998-01-01

    This chapter is at first an attempt to identify the sources of complexity in the urban realm. A second step is to present various modelling approaches referring to the new paradigm of complexity, from a review of the literature in urban geography, urban planning and urban economics until 1998.

  3. Visual Complexity: A Review

    Science.gov (United States)

    Donderi, Don C.

    2006-01-01

    The idea of visual complexity, the history of its measurement, and its implications for behavior are reviewed, starting with structuralism and Gestalt psychology at the beginning of the 20th century and ending with visual complexity theory, perceptual learning theory, and neural circuit theory at the beginning of the 21st. Evidence is drawn from…

  4. An Unusual Complex Odontoma

    OpenAIRE

    Kodali, Rama Mohan; Venkat suresh, B.; Ramanjaneya Raju, P.; Vora, Sambhav K.

    2010-01-01

    Odontoma, complex type is an agglomerate of all the dental tissues that are characterized by normal histodifferentiation but abnormal morphodifferentiation producing little or no resemblance to normal tooth form. They are usually asymptomatic but often associated with eruption disturbances. An interesting case of unusually large complex odontoma that was associated with pain and an impacted as well as missing molar is reported.

  5. The complexity of science

    Directory of Open Access Journals (Sweden)

    H.P.P. (Hennie Lótter

    1999-03-01

    Full Text Available In this article an alternative philosophy of science based on ideas drawn from the study of complex adaptive systems is presented. As a result of the enormous expansion in scientific disciplines, and the number of scientists and scientific institutions in the twentieth century, I believe science can be characterised as a complex system. I want to interpret the processes of science through which scientists themselves determine what is regarded as good science. This characterisation of science as a complex system can supply an answer to the question why the sciences have been so successful in solving growing numbers of problems and correcting their own mistakes. I utilise components of complexity theory to explain and interpret science as a complex system. I first explain the concept of complexity in ordinary language. The explanation of science as a complex system starts with a definition of the basic rules guiding the behaviour of science as a complex system. Next, I indicate how various sciences have resulted through the implementation of these rules in the study of a specific aspect of reality. The explanation of the growth of science through evolutionary adaptation and learning forms the core o f the article.

  6. Bacterial formate hydrogenlyase complex.

    Science.gov (United States)

    McDowall, Jennifer S; Murphy, Bonnie J; Haumann, Michael; Palmer, Tracy; Armstrong, Fraser A; Sargent, Frank

    2014-09-23

    Under anaerobic conditions, Escherichia coli can carry out a mixed-acid fermentation that ultimately produces molecular hydrogen. The enzyme directly responsible for hydrogen production is the membrane-bound formate hydrogenlyase (FHL) complex, which links formate oxidation to proton reduction and has evolutionary links to Complex I, the NADH:quinone oxidoreductase. Although the genetics, maturation, and some biochemistry of FHL are understood, the protein complex has never been isolated in an intact form to allow biochemical analysis. In this work, genetic tools are reported that allow the facile isolation of FHL in a single chromatographic step. The core complex is shown to comprise HycE (a [NiFe] hydrogenase component termed Hyd-3), FdhF (the molybdenum-dependent formate dehydrogenase-H), and three iron-sulfur proteins: HycB, HycF, and HycG. A proportion of this core complex remains associated with HycC and HycD, which are polytopic integral membrane proteins believed to anchor the core complex to the cytoplasmic side of the membrane. As isolated, the FHL complex retains formate hydrogenlyase activity in vitro. Protein film electrochemistry experiments on Hyd-3 demonstrate that it has a unique ability among [NiFe] hydrogenases to catalyze production of H2 even at high partial pressures of H2. Understanding and harnessing the activity of the FHL complex is critical to advancing future biohydrogen research efforts. PMID:25157147

  7. Role of the cocatalyst in the copolymerization of CO2 and cyclohexene oxide utilizing chromium salen complexes.

    Science.gov (United States)

    Darensbourg, Donald J; Mackiewicz, Ryan M; Rodgers, Jody L

    2005-10-12

    The mechanism of the copolymerization of cyclohexene oxide and carbon dioxide to afford poly(cyclohexylene)carbonate catalyzed by (salen)CrN3 (H2salen = N,N,'-bis(3,5-di-tert-butylsalicylidene)-1,2-ethylene-diimine) in the presence of a broad range of cocatalysts has been studied. We have previously established the rate of copolymer formation to be very sensitive to both the electron-donating ability of the salen ligand and the [cocatalyst], where N-heterocyclic amines, phosphines, and ionic salts were effective cocatalysts. Significant increases in the rate of copolymerization have been achieved with turnover frequencies of approximately 1200 h(-1), thereby making these catalyst systems some of the most active and robust thus far uncovered. Herein we offer a detailed explanation of the role of the cocatalyst in the copolymerization of CO2 and cyclohexene oxide catalyzed by chromium salen derivatives. A salient feature of the N-heterocyclic amine- or phosphine-cocatalyzed processes is the presence of an initiation period prior to reaching the maximum rate of copolymerization. Importantly, this is not observed for comparable processes involving ionic salts as cocatalysts, e.g., PPN+ X-. In these latter cases the copolymerization reaction exhibits ideal kinetic behavior and is proposed to proceed via a reaction pathway involving anionic six-coordinate (salen)Cr(N3)X- derivatives. By way of infrared and 31P NMR spectroscopic studies, coupled with in situ kinetic monitoring of the reactions, a mechanism of copolymerization is proposed where the neutral cocatalysts react with CO2 and/or epoxide to produce inner salts or zwitterions which behave in a manner similar to that of ionic salts. PMID:16201825

  8. Complexity and behavioral economics.

    Science.gov (United States)

    Rosser, J Barkley; Rosser, Marina V

    2015-04-01

    This paper will consider the relationship between complexity economics and behavioral economics. A crucial key to this is to understand that Herbert Simon was both the founder of explicitly modern behavioral economics as well as one of the early developers of complexity theory. Bounded rationality was essentially derived from Simon's view of the impossibility of full rationality on the part of economic agents. Modern complexity theory through such approaches as agent-based modeling offers an approach to understanding behavioral economics by allowing for specific behavioral responses to be assigned to agents who interact within this context, even without full rationality. Other parts of modern complexity theory are considered in terms of their relationships with behavioral economics. Fundamentally, complexity provides an ultimate foundation for bounded rationality and hence the need to use behavioral economics in a broader array of contexts than most economists have thought appropriate. PMID:25783044

  9. Exponential Random Simplicial Complexes

    CERN Document Server

    Zuev, Konstantin; Krioukov, Dmitri

    2015-01-01

    Exponential random graph models have attracted significant research attention over the past decades. These models are maximum-entropy ensembles under the constraints that the expected values of a set of graph observables are equal to given values. Here we extend these maximum-entropy ensembles to random simplicial complexes, which are more adequate and versatile constructions to model complex systems in many applications. We show that many random simplicial complex models considered in the literature can be casted as maximum-entropy ensembles under certain constraints. We introduce and analyze the most general random simplicial complex ensemble $\\mathbf{\\Delta}$ with statistically independent simplices. Our analysis is simplified by the observation that any distribution $\\mathbb{P}(O)$ on any collection of objects $\\mathcal{O}=\\{O\\}$, including graphs and simplicial complexes, is maximum-entropy under the constraint that the expected value of $-\\ln \\mathbb{P}(O)$ is equal to the entropy of the distribution. W...

  10. Method for Preparation of Amides from Alcohols and Amines by Extrusion of Hydrogen

    DEFF Research Database (Denmark)

    Vogt, Henning Technical University of Denmark,

    The present invention relates to a method for preparation of carboxamides using alcohols and amines as starting materials in a dehydrogenative coupling reaction catalyzed by a ruthenium N-heterocyciic carbene (NHC) complex, which may be prepared in situ.

  11. Simplicity, Complexity and Modelling

    CERN Document Server

    Christie, Mike; Dawid, Philip; Senn, Stephen S

    2011-01-01

    Several points of disagreement exist between different modelling traditions as to whether complex models are always better than simpler models, as to how to combine results from different models and how to propagate model uncertainty into forecasts. This book represents the result of collaboration between scientists from many disciplines to show how these conflicts can be resolved. Key Features: Introduces important concepts in modelling, outlining different traditions in the use of simple and complex modelling in statistics. Provides numerous case studies on complex modelling, such as clima

  12. Simplicity, complexity and modelling

    CERN Document Server

    Christie, Mike; Dawid, Philip; Senn, Stephen S

    2011-01-01

    Several points of disagreement exist between different modelling traditions as to whether complex models are always better than simpler models, as to how to combine results from different models and how to propagate model uncertainty into forecasts. This book represents the result of collaboration between scientists from many disciplines to show how these conflicts can be resolved. Key Features: Introduces important concepts in modelling, outlining different traditions in the use of simple and complex modelling in statistics. Provides numerous case studies on complex modelling, such as c

  13. Managing Complex Projects

    CERN Document Server

    Kerzner, Harold

    2010-01-01

    Discover how you can apply the Kerzner Approach® to successfulLy manage the most challenging and complex projects. Managing complex projects not only takes know-how on the part of project managers, but it also requires that they be willing and able to adapt to change, harness their ability to innovate at a moment's notice, and summon their determination to see a job to completion. This is the book that makes sense out of the complexities that plague today's project managers. It clearly lays out a blueprint to demystify what can be an overwhelming process into manageable strategies that, if cul

  14. Complex rotation numbers

    OpenAIRE

    Buff, Xavier; Goncharuk, Nataliya

    2013-01-01

    We investigate the notion of complex rotation number which was introduced by V.I.Arnold in 1978. Let $f: \\mathbb R/\\mathbb Z \\to \\mathbb R/\\mathbb Z$ be an orientation preserving circle diffeomorphism and let $\\omega \\in \\mathbb C/\\mathbb Z$ be a parameter with positive imaginary part. Construct a complex torus by glueing the two boundary components of the annulus $\\{z \\in \\mathbb C/\\mathbb Z \\mid 0< \\Im(z)< \\Im({\\omega})\\}$ via the map $f+{\\omega}$. This complex torus is is...

  15. Electromeric Rhodium Radical Complexes

    OpenAIRE

    F.F. Puschmann; J. Harmer; Stein, D; H. R\\xfcegger; de Bruin, B; H. Gr\\xfctzmacher

    2010-01-01

    "Chemical Equation Presented" Radical changes: One single P-Rh-P angle determines whether the odd electron in the paramagnetic complex [Rh(trop2PPh)(PPh3)] is delocalized over the whole molecule (see picture, blue) or is localized on the P - Rh unit (red). The two energetically almost degenerate electromers exist in a fast equilibrium, and the "red" complex has the highest spin density at Rh of all low valent Rh complexes observed to date. © 2010 Wiley-VCH Verlag GmbH and Co. KGaA.

  16. Nuclear power complex

    International Nuclear Information System (INIS)

    The current state and trends of development of the nuclear power complex are described on the national scale and within the framework of CMEA. The nuclear power complex is defined as an interbranch system with strong material and information linkages. A detailed analysis is presented of the management system and especially its decision-making stage. The characteristics are described of applied research and of technical and economic research relations. The problems are discussed of research management within a research institute. The management laws are applied to the entire branch and complex and are generalized for international scientific and technical cooperation. (M.D.)

  17. Equivariant topological complexity

    CERN Document Server

    Colman, Hellen

    2012-01-01

    We define and study an equivariant version of Farber's topological complexity for spaces with a given compact group action. This is a special case of the equivariant sectional category of an equivariant map, also defined in this paper. The relationship of these invariants with the equivariant Lusternik-Schnirelmann category is given. Several examples and computations serve to highlight the similarities and differences with the non-equivariant case. We also indicate how the equivariant topological complexity can be used to give estimates of the non-equivariant topological complexity.

  18. Complexity and sustainability

    CERN Document Server

    Wells, Jennifer

    2012-01-01

    Complex dynamic system studies have been studied explicitly in the natural sciences, and most only implicitly throughout other fields. Yet much great social theory and philosophy is in fact based in complexity, and important concepts like postmodernism, risk, and collapse all stem from complexity. Six key terms are explored: nonlinearity, feedbacks, thresholds, hierarchies, emergence and self-organization, and dozens of related principles are discussed, with a focus on uncertainty, risk, vulnerability, learning, strategy, resilience, collapse and sustainability. The book surveys the role of

  19. Vincristine Lipid Complex Injection

    Science.gov (United States)

    ... to change your dose of vincristine lipid complex injection.you should know that vincristine may interfere with the normal menstrual cycle (period) in women and may temporarily or permanently stop sperm production in men. Tell your doctor if you ...

  20. Transcription Elongation Complex Stability

    Science.gov (United States)

    Liu, Xiaoqing; Martin, Craig T.

    2009-01-01

    Transcription machinery from a variety of organisms shows striking mechanistic similarity. Both multi- and single subunit RNA polymerases have evolved an 8–10-base pair RNA-DNA hybrid as a part of a stably transcribing elongation complex. Through characterization of halted complexes that can readily carry out homopolymeric slippage synthesis, this study reveals that T7 RNA polymerase elongation complexes containing only a 4-base pair hybrid can nevertheless be more stable than those with the normal 8-base pair hybrid. We propose that a key feature of this stability is the topological threading of RNA through the complex and/or around the DNA template strand. The data are consistent with forward translocation as a mechanism to allow unthreading of the topological lock, as can occur during programmed termination of transcription. PMID:19846559

  1. Pigment-protein complexes

    Energy Technology Data Exchange (ETDEWEB)

    Siegelman, H W

    1980-01-01

    The photosynthetically-active pigment protein complexes of procaryotes and eucaryotes include chlorophyll proteins, carotenochlorophyll proteins, and biliproteins. They are either integral components or attached to photosynthetic membranes. Detergents are frequently required to solubilize the pigment-protein complexes. The membrane localization and detergent solubilization strongly suggest that the pigment-protein complexes are bound to the membranes by hydrophobic interactions. Hydrophobic interactions of proteins are characterized by an increase in entropy. Their bonding energy is directly related to temperature and ionic strength. Hydrophobic-interaction chromatography, a relatively new separation procedure, can furnish an important method for the purification of pigment-protein complexes. Phycobilisome purification and properties provide an example of the need to maintain hydrophobic interactions to preserve structure and function.

  2. The Complex Bateman Equation

    OpenAIRE

    Fairlie, D. B.; Leznov, A. N.

    1999-01-01

    The general solution to the Complex Bateman equation is constructed. It is given in implicit form in terms of a functional relationship for the unknown function. The known solution of the usual Bateman equation is recovered as a special case.

  3. Network Complexity of Foodwebs

    CERN Document Server

    Standish, Russell K

    2010-01-01

    In previous work, I have developed an information theoretic complexity measure of networks. When applied to several real world food webs, there is a distinct difference in complexity between the real food web, and randomised control networks obtained by shuffling the network links. One hypothesis is that this complexity surplus represents information captured by the evolutionary process that generated the network. In this paper, I test this idea by applying the same complexity measure to several well-known artificial life models that exhibit ecological networks: Tierra, EcoLab and Webworld. Contrary to what was found in real networks, the artificial life generated foodwebs had little information difference between itself and randomly shuffled versions.

  4. Radiotherapy Complex for Oncology

    International Science & Technology Center (ISTC)

    Researches at a Choice and Substantiation of Basic Physical and Technical Parameters as well as Basic Decisions of Experimental Therapeutic Complex with New Ecologically Safe Sources of Gamma Radiation Intending to Increase an Efficiency of Brachytherapy in Oncology

  5. Daunorubicin Lipid Complex Injection

    Science.gov (United States)

    ... lipid complex is used to treat advanced Kaposi's sarcoma (a type of cancer that causes abnormal tissue ... are pregnant, plan to become pregnant, or are breast-feeding. You should not become pregnant while you ...

  6. Coxeter-like complexes

    Directory of Open Access Journals (Sweden)

    Eric Babson

    2004-12-01

    Full Text Available Motivated by the Coxeter complex associated to a Coxeter system (W,S, we introduce a simplicial regular cell complex ?(G,S with a G-action associated to any pair (G,S where G is a group and S is a finite set of generators for G which is minimal with respect to inclusion. We examine the topology of ?(G,S, and in particular the representations of G on its homology groups. We look closely at the case of the symmetric group S n minimally generated by (not necessarily adjacent transpositions, and their type-selected subcomplexes. These include not only the Coxeter complexes of type A, but also the well-studied chessboard complexes.

  7. Complex Regional Pain Syndrome

    Science.gov (United States)

    ... across the country. NINDS-supported scientists are studying new approaches to treat CRPS and intervene more aggressively after traumatic injury to lower the chances of developing the disorder. NIH Patient Recruitment for Complex Regional Pain Syndrome Clinical Trials At ...

  8. On scattered subword complexity

    CERN Document Server

    Kása, Zoltán

    2011-01-01

    Special scattered subwords, in which the gaps are of length from a given set, are defined. The scattered subword complexity, which is the number of such scattered subwords, is computed for rainbow words.

  9. Cousin complexes and applications

    OpenAIRE

    Jafari, Raheleh

    2011-01-01

    In this thesis, the class of modules whose Cousin complexes have finitely generated cohomologies are studied as a subclass of modules which have uniform local cohomological annihilators and it is shown that these two classes coincide over local rings with Cohen-Macaulay formal fibres. This point of view enables us to obtain some properties of modules with finite Cousin complexes and find some characterizations of them. In this connection we discuss attached prime ideals of...

  10. Proteins and Complexity

    Science.gov (United States)

    Murray, Joelle; Gibbon, Dana; Runyon, Alissa; Bajracharya, Arun

    2015-03-01

    A protein's tertiary structure determines its function in living organisms. The different functions proteins serve necessitate variety in native structures. How is variation in tertiary structure created from a common set of amino acids and molecular forces? In other words, what generates complexity in structures across all types of native proteins? To explore this question, a simple HP model of protein folding was explored for evidence of self-organized criticality, a potential generator of complexity.

  11. Operationalizing career complexity

    OpenAIRE

    Strunk, Guido

    2009-01-01

    There are a growing number of studies describing developments in the labour market, in employer-employee relationships, and in individual careers in a very similar way. The discussion about work force flexibility and the challenges for HRM to handle scattered arrangements is often justified by a growing complexity caused by the driving forces of globalization, virtualization, demographic developments or changes in values. However, so far there is no empirical evidence for that complexity hypo...

  12. Complex logistics audit system

    Directory of Open Access Journals (Sweden)

    Zuzana Marková

    2010-02-01

    Full Text Available Complex logistics audit system is a tool for realization of logistical audit in the company. The current methods for logistics auditare based on “ad hok” analysis of logisticsl system. This paper describes system for complex logistics audit. It is a global diagnosticsof logistics processes and functions of enterprise. The goal of logistics audit is to provide comparative documentation for managementabout state of logistics in company and to show the potential of logistics changes in order to achieve more effective companyperformance.

  13. Weakly complex homogeneous spaces

    OpenAIRE

    Moroianu, Andrei; Semmelmann, Uwe

    2012-01-01

    We complete our recent classification of compact inner symmetric spaces with weakly complex tangent bundle by filling up a case which was left open, and extend this classification to the larger category of compact homogeneous spaces with positive Euler characteristic. We show that a simply connected compact equal rank homogeneous space has weakly complex tangent bundle if and only if it is a product of compact equal rank homogeneous spaces which either carry an invariant alm...

  14. Advances in network complexity

    CERN Document Server

    Dehmer, Matthias; Emmert-Streib, Frank

    2013-01-01

    A well-balanced overview of mathematical approaches to describe complex systems, ranging from chemical reactions to gene regulation networks, from ecological systems to examples from social sciences. Matthias Dehmer and Abbe Mowshowitz, a well-known pioneer in the field, co-edit this volume and are careful to include not only classical but also non-classical approaches so as to ensure topicality. Overall, a valuable addition to the literature and a must-have for anyone dealing with complex systems.

  15. Programming Complex Systems

    OpenAIRE

    Maymin, Philip

    1997-01-01

    Classical programming languages cannot model essential elements of complex systems such as true random number generation. This paper develops a formal programming language called the lambda-q calculus that addresses the fundamental properties of complex systems. This formal language allows the expression of quantumized algorithms, which are extensions of randomized algorithms in that probabilities can be negative, and events can cancel out. An illustration of the power of qu...

  16. Discrete Complex Analysis

    OpenAIRE

    Mercat, Christian

    2009-01-01

    My present interest is in Discrete Differential Geometry, especially applied to Computer Graphics, but it stems from Discrete Complex Analysis and Integrable Models, which has been my main subject of study during the past 6 years. The intention is to translate the best part of the theory of surfaces and complex analysis to the era of computers and discrete surfaces. This XIXth century theory, paved the way to the world of engineering marvels of the XXth century. Its discrete counterpart would...

  17. Markets and complexity

    OpenAIRE

    Kasimatis, Nikolaus

    2008-01-01

    This paper extends the model developed in “Complexity and Competition” (Gale and Sabourian, Econometrica 2005). In that paper, decentralized finite markets are treated as extensive-form matching and bargaining games. In these games there are many inefficient outcomes supported by subgame perfect equilibria. GS introduce an equilibrium refinement in which players maintain an aversion to complexity and show that such a refinement eliminates non-competitive outcomes. We admit more general en...

  18. Complex/Symplectic Mirrors

    International Nuclear Information System (INIS)

    We construct a class of symplectic non-Kaehler and complex non-Kaehler string theory vacua, extending and providing evidence for an earlier suggestion by Polchinski and Strominger. The class admits a mirror pairing by construction. Comparing hints from a variety of sources, including ten-dimensional supergravity and KK reduction on SU(3)-structure manifolds, suggests a picture in which string theory extends Reid's fantasy to connect classes of both complex non-Kaehler and symplectic non-Kaehler manifolds

  19. Complex Systems: A Survey

    OpenAIRE

    Newman, M. E. J.

    2011-01-01

    A complex system is a system composed of many interacting parts, often called agents, which displays collective behavior that does not follow trivially from the behaviors of the individual parts. Examples include condensed matter systems, ecosystems, stock markets and economies, biological evolution, and indeed the whole of human society. Substantial progress has been made in the quantitative understanding of complex systems, particularly since the 1980s, using a combination...

  20. Complex logistics audit system

    OpenAIRE

    Zuzana Marková; Dušan Malindžák

    2010-01-01

    Complex logistics audit system is a tool for realization of logistical audit in the company. The current methods for logistics auditare based on “ad hok” analysis of logisticsl system. This paper describes system for complex logistics audit. It is a global diagnosticsof logistics processes and functions of enterprise. The goal of logistics audit is to provide comparative documentation for managementabout state of logistics in company and to show the potential of logistics changes in order...

  1. Complex Networks and Graphs

    Science.gov (United States)

    Complex Systems Science Laboratory,

    Students learn about complex networks and how to represent them using graphs. They also learn that graph theory is a useful mathematical tool for studying complex networks in diverse applications of science and engineering, such as neural networks in the brain, biochemical reaction networks in cells, communication networks, such as the internet, and social networks. Topics covered include set theory, defining a graph, as well as defining the degree of a node and the degree distribution of a graph.

  2. Organotin complexes with phosphines

    International Nuclear Information System (INIS)

    A series of organotin complexes was prepared involving phosphines bonded to the organotin moiety. The series include derivatives of SnClxPh4-x (where x varied from zero to four with the phosphines Ph3P, (Ph2P)CH2, (Ph2P)2(CH2)2, cis-(Ph2P)CH2, and CH3C(CH2PPh2)3. A host of new complexes was obtained, showing different stoichiometries, bonding modes, and coordination numbers around the tin atom. These complexes were characterized by several different chemical and physical methods. The 119Sn Moessbauer parameters varied differently. Whereas isomer shift values did not great variation for each group of complexs with the same organotin parent (SnClxPh4-x), reflecting a small change in s charge distribution on the Sn atom upon complexation, quadrupole splitting results varied widely, however, when the parent organotin compound was wholly symmetric (SnCl4 and SnPPh4), the complexes also tended to show quadrupole splitting values approaching zero. (author)

  3. Algorithmic Relative Complexity

    Directory of Open Access Journals (Sweden)

    Daniele Cerra

    2011-04-01

    Full Text Available Information content and compression are tightly related concepts that can be addressed through both classical and algorithmic information theories, on the basis of Shannon entropy and Kolmogorov complexity, respectively. The definition of several entities in Kolmogorov’s framework relies upon ideas from classical information theory, and these two approaches share many common traits. In this work, we expand the relations between these two frameworks by introducing algorithmic cross-complexity and relative complexity, counterparts of the cross-entropy and relative entropy (or Kullback-Leibler divergence found in Shannon’s framework. We define the cross-complexity of an object x with respect to another object y as the amount of computational resources needed to specify x in terms of y, and the complexity of x related to y as the compression power which is lost when adopting such a description for x, compared to the shortest representation of x. Properties of analogous quantities in classical information theory hold for these new concepts. As these notions are incomputable, a suitable approximation based upon data compression is derived to enable the application to real data, yielding a divergence measure applicable to any pair of strings. Example applications are outlined, involving authorship attribution and satellite image classification, as well as a comparison to similar established techniques.

  4. Ecology, Complexity, and Metaphor

    Science.gov (United States)

    JAMES D. PROCTOR and BRENDON M. H. LARSON (; )

    2005-12-01

    This peer-reviewed article from Bioscience is about Ecology, Complexity and Metaphor.Complexity has recently risen to prominence in ecology as part of a broader interest that suggests its status is something more than just a scientific theory or property of reality. It may be helpful to consider complexity, and related terms such as "self-organization," as recent metaphors deployed to advance knowledge on fundamental questions in ecology, including the relationship between parts and wholes, and between order and disorder. Though not commonly viewed as such, metaphors are an indispensable component of science, and should not be appraised as true or false, but rather in terms of how they help or hinder knowledge. By understanding metaphor as a necessary ally and not a threat to ecological knowledge, we may enrich our contextual understanding of complexity while continuing to invoke it in useful ways. The special section introduced by this article features essays by two prominent experts in ecology, complexity, and metaphor: science studies scholar Evelyn Fox Keller and theoretical ecologist Simon Levin

  5. Complexity: The bigger picture

    CERN Document Server

    Vicsek, Tamás

    2010-01-01

    If a concept is not well defined, there are grounds for its abuse. This is particularly true of complexity, an inherently interdisciplinary concept that has penetrated very different fields of intellectual activity from physics to linguistics, but with no underlying, unified theory. Complexity has become a popular buzzword used in the hope of gaining attention or funding -- institutes and research networks associated with complex systems grow like mushrooms. Why and how did it happen that this vague notion has become a central motif in modern science? Is it only a fashion, a kind of sociological phenomenon, or is it a sign of a changing paradigm of our perception of the laws of nature and of the approaches required to understand them? Because virtually every real system is inherently extremely complicated, to say that a system is complex is almost an empty statement - couldn't an Institute of Complex Systems just as well be called an Institute for Almost Everything? Despite these valid concerns, the world is ...

  6. Quantum Complexity in Graphene

    Science.gov (United States)

    Baskaran, G.

    Carbon has a unique position among elements in the periodic table. It produces an allotrope, graphene, a mechanically robust two dimensional semimetal. The multifarious properties that graphene exhibits has few parallels among elemental metals. From simplicity, namely carbon atoms connected by pure sp2 bonds, a wealth of novel quantum properties emerge. In classical complex systems such as a spin glass or a finance market, several competing agents or elements are responsible for unanticipated and difficult to predict emergent properties. The complex (sic) structure of quantum mechanics is responsbile for an unanticipated set of emergent properties in graphene. We call this quantum complexity. In fact, most quantum systems, phenomena and modern quantum field theory could be viewed as examples of quantum complexity. After giving a brief introduction to the quantum complexity we focus on our own work, which indicates the breadth in the type of quantum phenomena that graphene could support. We review our theoretical suggestions of, (i) spin-1 collective mode in netural graphene, (ii) relativistic type of phenomena in crossed electric and magnetic fields, (iii) room temperature superconductivity in doped graphene and (iv) composite Fermi sea in neutral graphene in uniform magnetic field and (v) two-channel Kondo effect. Except for the relativistic type of phenomena, the rest depend in a fundamental way on a weak electron correlation that exists in the broad two-dimensional band of graphene.

  7. Complexity of Networks

    CERN Document Server

    Standish, R K

    2005-01-01

    Network or graph structures are ubiquitous in the study of complex systems. Often, we are interested in complexity trends of these system as it evolves under some dynamic. An example might be looking at the complexity of a food web as species enter an ecosystem via migration or speciation, and leave via extinction. In this paper, a complexity measure of networks is proposed based on the {\\em complexity is information content} paradigm. To apply this paradigm to any object, one must fix two things: a representation language, in which strings of symbols from some alphabet describe, or stand for the objects being considered; and a means of determining when two such descriptions refer to the same object. With these two things set, the information content of an object can be computed in principle from the number of equivalent descriptions describing a particular object. I propose a simple representation language for undirected graphs that can be encoded as a bitstring, and equivalence is a topological equivalence....

  8. Cancer and bone: a complex complex.

    Science.gov (United States)

    van Driel, Marjolein; van Leeuwen, Johannes P T M

    2014-11-01

    Primary and secondary bone cancers are rare events. However, once settled, a complex process is started involving an extensive amount of factors and interactions. The bone micro-environment is a preferential site for (metastatic) tumor cells to enter, stay, colonize and expand. The fact that the tumor cells affect the complete bone environment involving many cell types and regulatory pathways to stimulate their own growth and escape from therapy is devastating for the patient. Many efforts have been made to get more insight into the mechanisms underlying the communication between bone cells and cancer cells and progress is made in therapeutic interventions. This review will discuss the biological mechanisms of primary bone malignancies (osteosarcoma, Ewing's sarcoma, chondrosarcoma, multiple myeloma) and secondary bone malignancies (bone metastases) and therapeutic interventions. PMID:25046842

  9. Beyond Complex Numbers

    CERN Document Server

    Abubakr, M

    2007-01-01

    There has been always an ambiguity in division when zero is present in the denominator. So far this ambiguity has been neglected by assuming that division by zero as a non-allowed operation. In this paper, I have derived the new set of numbers by considering that a number divided by zero gives rise to "a beyond complex number". This is very similar to the way imaginary numbers are defined. It was only after considering i = sqrt(-1), we have been able to deduce all the laws for imaginary numbers. Similarly here, I have considered "a number when divided by zero gives rise to a beyond complex number". This is the introduction paper to this "beyond complex numbers" containing the algebra of it.

  10. Introduction to Complex Plasmas

    CERN Document Server

    Bonitz, Michael; Ludwig, Patrick

    2010-01-01

    Complex plasmas differ from traditional plasmas in many ways: these are low-temperature high pressure systems containing nanometer to micrometer size particles which may be highly charged and strongly interacting. The particles may be chemically reacting or be in contact with solid surfaces, and the electrons may show quantum behaviour. These interesting properties have led to many applications of complex plasmas in technology, medicine and science. Yet complex plasmas are extremely complicated, both experimentally and theoretically, and require a variety of new approaches which go beyond standard plasma physics courses. This book fills this gap presenting an introduction to theory, experiment and computer simulation in this field. Based on tutorial lectures at a very successful recent Summer Institute, the presentation is ideally suited for graduate students, plasma physicists and experienced undergraduates.

  11. Modeling Complex Time Limits

    Directory of Open Access Journals (Sweden)

    Oleg Svatos

    2013-01-01

    Full Text Available In this paper we analyze complexity of time limits we can find especially in regulated processes of public administration. First we review the most popular process modeling languages. There is defined an example scenario based on the current Czech legislature which is then captured in discussed process modeling languages. Analysis shows that the contemporary process modeling languages support capturing of the time limit only partially. This causes troubles to analysts and unnecessary complexity of the models. Upon unsatisfying results of the contemporary process modeling languages we analyze the complexity of the time limits in greater detail and outline lifecycles of a time limit using the multiple dynamic generalizations pattern. As an alternative to the popular process modeling languages there is presented PSD process modeling language, which supports the defined lifecycles of a time limit natively and therefore allows keeping the models simple and easy to understand.

  12. Control of complex systems

    CERN Document Server

    Albertos, Pedro; Blanke, Mogens; Isidori, Alberto; Schaufelberger, Walter; Sanz, Ricardo

    2001-01-01

    The world of artificial systems is reaching complexity levels that es­ cape human understanding. Surface traffic, electricity distribution, air­ planes, mobile communications, etc. , are examples that demonstrate that we are running into problems that are beyond classical scientific or engi­ neering knowledge. There is an ongoing world-wide effort to understand these systems and develop models that can capture its behavior. The reason for this work is clear, if our lack of understanding deepens, we will lose our capability to control these systems and make they behave as we want. Researchers from many different fields are trying to understand and develop theories for complex man-made systems. This book presents re­ search from the perspective of control and systems theory. The book has grown out of activities in the research program Control of Complex Systems (COSY). The program has been sponsored by the Eu­ ropean Science Foundation (ESF) which for 25 years has been one of the leading players in stimula...

  13. Emergy and ecosystem complexity

    Science.gov (United States)

    Ulgiati, Sergio; Brown, Mark T.

    2009-01-01

    The question "What drives complexity?" is addressed in this paper. To answer this question, we explore the way energy and material resources of different quality flow through ecosystems and support, directly and indirectly, ecosystems growth and development. Processes of resource transformation throughout the ecosystem build order, cycle materials, generate and sustain information. Energy drives all these processes and energetic principles explain much of what is observed, including energy degradation according to the laws of thermodynamics. Emergy, a quantitative measure of the global environmental work supporting ecosystem dynamics, is used here in order to provide a deeper understanding of complexity growth and decline in ecosystems. Ecosystem complexity is discussed in this paper in relation to changes in structure, organization and functional capacity, as explained by changes in emergy, empower, and transformity.

  14. Can Complexity be Planned?

    Directory of Open Access Journals (Sweden)

    Ilona Koutny

    2015-04-01

    Full Text Available The long accepted complexity invariance of human languages has become controversial within the last decade. In investigations of the problem, both creole and planned languages have often been neglected. After a presentation of the scope of the invariance problem and the proposition of the natural to planned language continuum, this article will discuss the contribution of planned languages. It will analyze the complexity of Esperanto at the phonological, morphological, syntactic and semantic levels, using linguistic data bases. The role of the L2 speech community and development of the language will also be taken into account when discussing the endurance of the same level of simplicity of this planned international language. The author argues that complexity can be variable and to some extent planned and maintained.

  15. BRAND program complex

    International Nuclear Information System (INIS)

    A description is given of the structure, input procedure and recording rules of initial data for the BRAND programme complex intended for the Monte Carlo simulation of neutron physics experiments. The BRAND complex ideology is based on non-analogous simulation of the neutron and photon transport process (statistic weights are used, absorption and escape of particles from the considered region is taken into account, shifted readouts from a coordinate part of transition nucleus density are applied, local estimations, etc. are used). The preparation of initial data for three sections is described in detail: general information for Monte Carlo calculation, source definition and data for describing the geometry of the system. The complex is to be processed with the BESM-6 computer, the basic programming lan-- guage is FORTRAN, volume - more than 8000 operators

  16. Complex-Valued Autoencoders

    CERN Document Server

    Baldi, Pierre; Lu, Zhiqin

    2011-01-01

    Autoencoders are unsupervised machine learning circuits whose learning goal is to minimize a distortion measure between inputs and outputs. Linear autoencoders can be defined over any field and only real-valued linear autoencoder have been studied so far. Here we study complex-valued linear autoencoders where the components of the training vectors and adjustable matrices are defined over the complex field with the $L_2$ norm. We provide simpler and more general proofs that unify the real-valued and complex-valued cases, showing that in both cases the landscape of the error function is invariant under certain groups of transformations. The landscape has no local minima, a family of global minima associated with Principal Component Analysis, and many families of saddle points associated with orthogonal projections onto sub-space spanned by sub-optimal subsets of eigenvectors of the covariance matrix. The theory yields several iterative, convergent, learning algorithms, a clear understanding of the generalizatio...

  17. Synchronization in complex networks

    Energy Technology Data Exchange (ETDEWEB)

    Arenas, A.; Diaz-Guilera, A.; Moreno, Y.; Zhou, C.; Kurths, J.

    2007-12-12

    Synchronization processes in populations of locally interacting elements are in the focus of intense research in physical, biological, chemical, technological and social systems. The many efforts devoted to understand synchronization phenomena in natural systems take now advantage of the recent theory of complex networks. In this review, we report the advances in the comprehension of synchronization phenomena when oscillating elements are constrained to interact in a complex network topology. We also overview the new emergent features coming out from the interplay between the structure and the function of the underlying pattern of connections. Extensive numerical work as well as analytical approaches to the problem are presented. Finally, we review several applications of synchronization in complex networks to different disciplines: biological systems and neuroscience, engineering and computer science, and economy and social sciences.

  18. Localizations on Complex Networks

    CERN Document Server

    Zhu, Guimei; Yin, Chuanyang; Li, Baowen

    2011-01-01

    We study the structural characteristics of complex networks using the representative eigenvectors of the adjacent matrix. The probability distribution function of the components of the representative eigenvectors are proposed to describe the localization on networks where the Euclidean distance is invalid. Several quantities are used to describe the localization properties of the representative states, such as the participation ratio, the structural entropy, and the probability distribution function of the nearest neighbor level spacings for spectra of complex networks. Whole-cell networks in the real world and the Watts-Strogatz small-world and Barabasi-Albert scale-free networks are considered. The networks have nontrivial localization properties due to the nontrivial topological structures. It is found that the ascending-order-ranked series of the occurrence probabilities at the nodes behave generally multifractally. This characteristic can be used as a structural measure of complex networks.

  19. Emergent Complex Network Geometry

    CERN Document Server

    Wu, Zhihao; Rahmede, Christoph; Bianconi, Ginestra

    2014-01-01

    Networks are mathematical structures that are universally used to describe a large variety of complex systems such as the brain or the Internet. Characterizing the geometrical properties of these networks has become increasingly relevant for routing problems, inference and data mining. In real growing networks, topological, structural and geometrical properties emerge spontaneously from their dynamical rules. Nevertheless we still miss a model in which networks develop an emergent complex geometry. Here we show that a single two parameter network model, the growing geometrical network, can generate complex network geometries with non-trivial distribution of curvatures, combining exponential growth and small-world properties with finite spectral dimensionality. In one limit, the non-equilibrium dynamical rules of these networks can generate scale-free networks with clustering and communities, in another limit planar random geometries with non-trivial modularity. Finally we find that these properties of the geo...

  20. Philosophy of complex systems

    CERN Document Server

    2011-01-01

    The domain of nonlinear dynamical systems and its mathematical underpinnings has been developing exponentially for a century, the last 35 years seeing an outpouring of new ideas and applications and a concomitant confluence with ideas of complex systems and their applications from irreversible thermodynamics. A few examples are in meteorology, ecological dynamics, and social and economic dynamics. These new ideas have profound implications for our understanding and practice in domains involving complexity, predictability and determinism, equilibrium, control, planning, individuality, responsibility and so on. Our intention is to draw together in this volume, we believe for the first time, a comprehensive picture of the manifold philosophically interesting impacts of recent developments in understanding nonlinear systems and the unique aspects of their complexity. The book will focus specifically on the philosophical concepts, principles, judgments and problems distinctly raised by work in the domain of comple...

  1. Complex Systems: A Survey

    CERN Document Server

    Newman, M E J

    2011-01-01

    A complex system is a system composed of many interacting parts, often called agents, which displays collective behavior that does not follow trivially from the behaviors of the individual parts. Examples include condensed matter systems, ecosystems, stock markets and economies, biological evolution, and indeed the whole of human society. Substantial progress has been made in the quantitative understanding of complex systems, particularly since the 1980s, using a combination of basic theory, much of it derived from physics, and computer simulation. The subject is a broad one, drawing on techniques and ideas from a wide range of areas. Here I give a survey of the main themes and methods of complex systems science and an annotated bibliography of resources, ranging from classic papers to recent books and reviews.

  2. Modeling Complex Systems

    CERN Document Server

    Boccara, Nino

    2010-01-01

    Modeling Complex Systems, 2nd Edition, explores the process of modeling complex systems, providing examples from such diverse fields as ecology, epidemiology, sociology, seismology, and economics. It illustrates how models of complex systems are built and provides indispensable mathematical tools for studying their dynamics. This vital introductory text is useful for advanced undergraduate students in various scientific disciplines, and serves as an important reference book for graduate students and young researchers. This enhanced second edition includes: . -recent research results and bibliographic references -extra footnotes which provide biographical information on cited scientists who have made significant contributions to the field -new and improved worked-out examples to aid a student’s comprehension of the content -exercises to challenge the reader and complement the material Nino Boccara is also the author of Essentials of Mathematica: With Applications to Mathematics and Physics (Springer, 2007).

  3. Complexity and Philosophy

    CERN Document Server

    Heylighen, F; Gershenson, C; Cilliers, Paul; Gershenson, Carlos; Heylighen, Francis

    2006-01-01

    The science of complexity is based on a new way of thinking that stands in sharp contrast to the philosophy underlying Newtonian science, which is based on reductionism, determinism, and objective knowledge. This paper reviews the historical development of this new world view, focusing on its philosophical foundations. Determinism was challenged by quantum mechanics and chaos theory. Systems theory replaced reductionism by a scientifically based holism. Cybernetics and postmodern social science showed that knowledge is intrinsically subjective. These developments are being integrated under the header of "complexity science". Its central paradigm is the multi-agent system. Agents are intrinsically subjective and uncertain about their environment and future, but out of their local interactions, a global organization emerges. Although different philosophers, and in particular the postmodernists, have voiced similar ideas, the paradigm of complexity still needs to be fully assimilated by philosophy. This will thr...

  4. Study of antiorbital complexes

    CERN Document Server

    Lusztig, G

    2009-01-01

    Let E be a finite dimensional vector space over an algebraic closure of a finite field with a given linear action of a connected linear algebraic group K and let E' be the dual space. A complex of l-adic sheaves on E is said to be orbital if it is a simple perverse sheaf whose support is a single K-orbit. A complex of l-adic sheaves on E is said to be biorbital if it is orbital and if its Deligne Fourier transform is orbital on E'. In this paper we study examples of biorbital complexes arising in the case where E is an eigenspace of a semisimple automorphism of a reductive Lie algebra.

  5. Complex Aperture Networks

    CERN Document Server

    Owladeghaffari, Hamed

    2009-01-01

    A complex network approach on a rough fracture is developed. In this manner, some hidden metric spaces (similarity measurements) between apertures profiles are set up and a general evolutionary network in two directions (in parallel and perpendicular to the shear direction) is constructed. Evaluation of the emerged network shows the connectivity degree (distribution) of network, after a transition step; fall in to the stable states which are coincided with the Gaussian distribution. Based on this event and real observations of the complex network changes, an algorithm (COmplex Networks on Apertures: CONA) is proposed in which evolving of a network is accomplished using preferential detachments and attachments of edges (based on a competition and game manner) while the number of nodes is fixed. Also, evolving of clustering coefficients and number of edges display similar patterns as well as are appeared in shear stress, hydraulic conductivity and dilation changes, which can be engaged to estimate shear strengt...

  6. Interdisciplinary Symposium on Complex Systems

    CERN Document Server

    Rössler, Otto; Zelinka, Ivan

    2015-01-01

    The book you hold in your hands is the outcome of the “2014 Interdisciplinary Symposium on Complex Systems” held in the historical city of Florence. The book consists of 37 chapters from 4 areas of Physical Modeling of Complex Systems, Evolutionary Computations, Complex Biological Systems and Complex Networks. All 4 parts contain contributions that give interesting point of view on complexity in different areas in science and technology. The book starts with a comprehensive overview and classification of complexity problems entitled Physics in the world of ideas: Complexity as Energy”  , followed by chapters about complexity measures and physical principles, its observation, modeling and its applications, to solving various problems including real-life applications. Further chapters contain recent research about evolution, randomness and complexity, as well as complexity in biological systems and complex networks. All selected papers represent innovative ideas, philosophical overviews and state-of-the-...

  7. Complex variables II essentials

    CERN Document Server

    Solomon, Alan D

    2013-01-01

    REA's Essentials provide quick and easy access to critical information in a variety of different fields, ranging from the most basic to the most advanced. As its name implies, these concise, comprehensive study guides summarize the essentials of the field covered. Essentials are helpful when preparing for exams, doing homework and will remain a lasting reference source for students, teachers, and professionals. Complex Variables II includes elementary mappings and Mobius transformation, mappings by general functions, conformal mappings and harmonic functions, applying complex functions to a

  8. Is Communication Complexity Physical?

    CERN Document Server

    Marcovitch, Samuel

    2007-01-01

    Recently, Brassard et. al. conjectured that the fact that the maximal possible correlations between two non-local parties are the quantum-mechanical ones is linked to a reasonable restriction on communication complexity. We provide further support for the conjecture in the multipartite case. We show that any multipartite communication complexity problem could be reduced to triviality, had Nature been more non-local than quantum-mechanics by a quite small gap for any number of parties. Intriguingly, the multipartite nonlocal-box that we use to show the result corresponds to the generalized Bell inequality that manifests maximal violation in respect to a local hidden-variable theory.

  9. Simulations with Complex Measure

    CERN Document Server

    Markham, J F

    1996-01-01

    A method is proposed to handle the sign problem in the simulation of systems having indefinite or complex-valued measures. In general, this new approach, which is based on renormalisation blocking, is shown to yield statistical errors smaller than the crude Monte Carlo method using absolute values of the original measures. The improved method is applied to the 2D Ising model with temperature generalised to take on complex values. It is also adapted to implement Monte Carlo Renormalisation Group calculations of the magnetic and thermal critical exponents.

  10. Complexity, time and music

    OpenAIRE

    Boon, Jean Pierre

    2009-01-01

    The concept of complexity as considered in terms of its algorithmic definition proposed by G.J. Chaitin and A.N. Kolmogorov is revisited for the dynamical complexity of music. When music pieces are cast in the form of time series of pitch variations, concepts of dynamical systems theory can be used to define new quantities such as the {\\em dimensionality} as a measure of the {\\em global temporal dynamics} of a music piece, and the Shanon {\\em entropy} as an evaluation of its...

  11. Theories of computational complexity

    CERN Document Server

    Calude, C

    1988-01-01

    This volume presents four machine-independent theories of computational complexity, which have been chosen for their intrinsic importance and practical relevance. The book includes a wealth of results - classical, recent, and others which have not been published before.In developing the mathematics underlying the size, dynamic and structural complexity measures, various connections with mathematical logic, constructive topology, probability and programming theories are established. The facts are presented in detail. Extensive examples are provided, to help clarify notions and constructions. The lists of exercises and problems include routine exercises, interesting results, as well as some open problems.

  12. Real and complex analysis

    CERN Document Server

    Apelian, Christopher

    2009-01-01

    The Spaces R, Rk, and CThe Real Numbers RThe Real Spaces RkThe Complex Numbers CPoint-Set Topology Bounded SetsClassification of Points Open and Closed SetsNested Intervals and the Bolzano-Weierstrass Theorem Compactness and Connectedness Limits and Convergence Definitions and First Properties Convergence Results for SequencesTopological Results for Sequences Properties of Infinite SeriesManipulations of Series in RFunctions: Definitions and Limits DefinitionsFunctions as MappingsSome Elementary Complex FunctionsLimits of FunctionsFunctions: Continuity and Convergence Continuity Uniform Contin

  13. Complex Gaussian Multiplicative Chaos

    Science.gov (United States)

    Lacoin, Hubert; Rhodes, Rémi; Vargas, Vincent

    2015-07-01

    In this article, we study complex Gaussian multiplicative chaos. More precisely, we study the renormalization theory and the limit of the exponential of a complex log-correlated Gaussian field in all dimensions (including Gaussian Free Fields in dimension 2). Our main working assumption is that the real part and the imaginary part are independent. We also discuss applications in 2 D string theory; in particular we give a rigorous mathematical definition of the so-called Tachyon fields, the conformally invariant operators in critical Liouville Quantum Gravity with a c = 1 central charge, and derive the original KPZ formula for these fields.

  14. Luminescent macrocyclic lanthanide complexes

    Science.gov (United States)

    Raymond, Kenneth N; Corneillie, Todd M; Xu, Jide

    2014-05-20

    The present invention provides a novel class of macrocyclic compounds as well as complexes formed between a metal (e.g., lanthanide) ion and the compounds of the invention. Preferred complexes exhibit high stability as well as high quantum yields of lanthanide ion luminescence in aqueous media without the need for secondary activating agents. Preferred compounds incorporate hydroxy-isophthalamide moieties within their macrocyclic structure and are characterized by surprisingly low, non-specific binding to a variety of polypeptides such as antibodies and proteins as well as high kinetic stability. These characteristics distinguish them from known, open-structured ligands.

  15. The ?-Catenin Destruction Complex

    OpenAIRE

    Stamos, Jennifer L.; Weis, William I.

    2013-01-01

    The Wnt/?-catenin pathway is highly regulated to insure the correct temporal and spatial activation of its target genes. In the absence of a Wnt stimulus, the transcriptional coactivator ?-catenin is degraded by a multiprotein “destruction complex” that includes the tumor suppressors Axin and adenomatous polyposis coli (APC), the Ser/Thr kinases GSK-3 and CK1, protein phosphatase 2A (PP2A), and the E3-ubiquitin ligase ?-TrCP. The complex generates a ?-TrCP recognition site by phosphor...

  16. Spin-glass complexity.

    Science.gov (United States)

    Crisanti, A; Leuzzi, L; Parisi, G; Rizzo, T

    2004-03-26

    We study the quenched complexity in spin-glass mean-field models satisfying the Becchi-Rouet-Stora-Tyutin supersymmetry. The outcome of such study, consistent with recent numerical results, allows, in principle, to conjecture the absence of any supersymmetric contribution to the complexity in the Sherrington-Kirkpatrick model. The same analysis can be applied to any model with a full replica symmetry breaking phase, e.g., the Ising p-spin model below the Gardner temperature. The existence of different solutions, breaking the supersymmetry, is also discussed. PMID:15089702

  17. Plasma Membrane Receptor Complexes

    OpenAIRE

    Aker, J. C. M.; Vries, S. C.

    2008-01-01

    Recent data on the plasma membrane (PM)-located LRR-RLKs (for Leu-rich repeat receptor-like kinases) BRI1 (for brassinosteroid insensitive 1) and the coreceptors BAK1 (for BRI1-associated kinase 1) and SERK1 (for somatic embryogenesis receptor-like kinase 1) that participate in the perception of brassinosteroids (BRs) suggest that they are organized into heterooligomeric protein complexes. Other components of this complex include members of the 14-3-3 family, and, in the case of SERK1, the ki...

  18. Applied complex variables

    CERN Document Server

    Dettman, John W

    2012-01-01

    Analytic function theory is a traditional subject going back to Cauchy and Riemann in the 19th century. Once the exclusive province of advanced mathematics students, its applications have proven vital to today's physicists and engineers. In this highly regarded work, Professor John W. Dettman offers a clear, well-organized overview of the subject and various applications - making the often-perplexing study of analytic functions of complex variables more accessible to a wider audience. The first half of Applied Complex Variables, designed for sequential study, is a step-by-step treatment of fun

  19. Complex matrix model duality

    Energy Technology Data Exchange (ETDEWEB)

    Brown, T.W.

    2010-11-15

    The same complex matrix model calculates both tachyon scattering for the c=1 non-critical string at the self-dual radius and certain correlation functions of half-BPS operators in N=4 super- Yang-Mills. It is dual to another complex matrix model where the couplings of the first model are encoded in the Kontsevich-like variables of the second. The duality between the theories is mirrored by the duality of their Feynman diagrams. Analogously to the Hermitian Kontsevich- Penner model, the correlation functions of the second model can be written as sums over discrete points in subspaces of the moduli space of punctured Riemann surfaces. (orig.)

  20. Tevatron's complex collider cousins

    CERN Multimedia

    Fischer, W

    2004-01-01

    Letter referring to Schwarzschild's story "Disappointing performance and tight budgets confront Fermilab with tough decisions" and contesting that the Tevatron is not the most complex accelerator operating. They use the examples of CERN's SPS collider, HERA at DESY and the RHIC at Brookhaven (1/4 page)

  1. Diagonalization in proof complexity.

    Czech Academy of Sciences Publication Activity Database

    Krají?ek, Jan

    2004-01-01

    Ro?. 182, ?. 1 (2004), s. 181-192. ISSN 0016-2736 R&D Projects: GA AV ?R IAA1019401; GA MŠk LN00A056 Institutional research plan: CEZ:AV0Z1019905 Keywords : circuit complexity * NP * propositional proof system Subject RIV: BA - General Mathematics Impact factor: 0.394, year: 2004

  2. Complex Game Design Modeling

    OpenAIRE

    Narayanasamy, Viknashvaran; Wong, Kok Wai; Rai, Shri; Chiou, Andrew

    2010-01-01

    This paper looks at the game design and engineering approach to model the game design. The game modeling framework discussed in this paper could be a systematic alternative for implementing in the game engine architecture. The suggested game modeling framework incorporates structural game component, temporal game component and boundary game component frameworks. It is suitable to model most complex games and game engines.

  3. Drawing with Complex Numbers

    OpenAIRE

    Eastwood, Michael; Penrose, Roger

    2000-01-01

    It is not commonly realized that the algebra of complex numbers can be used in an elegant way to represent the images of ordinary 3-dimensional figures, orthographically projected to the plane. We describe these ideas here, both using simple geometry and setting them in a broader context.

  4. Nitrido complexes of technetium

    International Nuclear Information System (INIS)

    In this report synthesis, characterization and chemical behaviour of coordination compounds of the element technetium are reported containing a geminal nitrogen ligand. In addition, an evaluation of the in-vitro behaviour of the complexes is given as well as a list of all literature to this matter. (author)

  5. Modular Isogeny Complexes

    OpenAIRE

    Rezk, Charles

    2011-01-01

    We describe a vanishing result on the cohomology of a cochain complex associated to the moduli of chains of finite subgroup schemes on elliptic curves. These results have applications to algebraic topology, in particular to the study of power operations for Morava E-theory at height 2.

  6. Energy momentum complex

    Scientific Electronic Library Online (English)

    Gamal G.L., Nashed.

    2010-09-01

    Full Text Available We show that the definition of the energy- momentum complex given by Møller using Weitzenböck space- time in the calculations of gravitational energy gives results which are different from those obtained from other definitions given in the framework of general relativity. [...

  7. Power grid complexity

    CERN Document Server

    Mei, Shengwei; Cao, Ming

    2011-01-01

    This book introduces self-organized criticality (SOC) theory and complex network theory and applies them to power systems. It examines four blackout models based on SOC theory and studies the SOC of power systems at both the macroscopic and microscopic levels.

  8. Complex Regional Pain Syndrome

    Science.gov (United States)

    Complex regional pain syndrome (CRPS) is a chronic pain condition. It causes intense pain, usually in the arms, hands, legs, or feet. It may happen ... move the affected body part The cause of CRPS is unknown. There is no specific diagnostic test. ...

  9. Symmetry in Complex Networks

    Directory of Open Access Journals (Sweden)

    Angel Garrido

    2011-01-01

    Full Text Available In this paper, we analyze a few interrelated concepts about graphs, such as their degree, entropy, or their symmetry/asymmetry levels. These concepts prove useful in the study of different types of Systems, and particularly, in the analysis of Complex Networks. A System can be defined as any set of components functioning together as a whole. A systemic point of view allows us to isolate a part of the world, and so, we can focus on those aspects that interact more closely than others. Network Science analyzes the interconnections among diverse networks from different domains: physics, engineering, biology, semantics, and so on. Current developments in the quantitative analysis of Complex Networks, based on graph theory, have been rapidly translated to studies of brain network organization. The brain's systems have complex network features—such as the small-world topology, highly connected hubs and modularity. These networks are not random. The topology of many different networks shows striking similarities, such as the scale-free structure, with the degree distribution following a Power Law. How can very different systems have the same underlying topological features? Modeling and characterizing these networks, looking for their governing laws, are the current lines of research. So, we will dedicate this Special Issue paper to show measures of symmetry in Complex Networks, and highlight their close relation with measures of information and entropy.

  10. The CERN accelerator complex

    CERN Multimedia

    Haffner, Julie

    2013-01-01

    The LHC is the last ring (dark grey line) in a complex chain of particle accelerators. The smaller machines are used in a chain to help boost the particles to their final energies and provide beams to a whole set of smaller experiments, which also aim to uncover the mysteries of the Universe.

  11. The CERN accelerator complex

    CERN Multimedia

    Christiane Lefèvre

    2008-01-01

    The LHC is the last ring (dark grey line) in a complex chain of particle accelerators. The smaller machines are used in a chain to help boost the particles to their final energies and provide beams to a whole set of smaller experiments, which also aim to uncover the mysteries of the Universe.

  12. Complex Digital Visual Systems

    Science.gov (United States)

    Sweeny, Robert W.

    2013-01-01

    This article identifies possibilities for data visualization as art educational research practice. The author presents an analysis of the relationship between works of art and digital visual culture, employing aspects of network analysis drawn from the work of Barabási, Newman, and Watts (2006) and Castells (1994). Describing complex network…

  13. On Descriptive Complexity, Language Complexity and GB

    CERN Document Server

    Rogers, J

    1995-01-01

    We introduce $L^2_{K,P}$, a monadic second-order language for reasoning about trees which characterizes the strongly Context-Free Languages in the sense that a set of finite trees is definable in $L^2_{K,P}$ iff it is (modulo a projection) a Local Set---the set of derivation trees generated by a CFG. This provides a flexible approach to establishing language-theoretic complexity results for formalisms that are based on systems of well-formedness constraints on trees. We demonstrate this technique by sketching two such results for Government and Binding Theory. First, we show that {\\em free-indexation\\/}, the mechanism assumed to mediate a variety of agreement and binding relationships in GB, is not definable in $L^2_{K,P}$ and therefore not enforcible by CFGs. Second, we show how, in spite of this limitation, a reasonably complete GB account of English can be defined in $L^2_{K,P}$. Consequently, the language licensed by that account is strongly context-free. We illustrate some of the issues involved in estab...

  14. Modelling Complexity in Musical Rhythm

    CERN Document Server

    Liou, C Y; Lee, C Y; Liou, Cheng-Yuan; Wu, Tai-Hei; Lee, Chia-Ying

    2007-01-01

    This paper constructs a tree structure for the music rhythm using the L-system. It models the structure as an automata and derives its complexity. It also solves the complexity for the L-system. This complexity can resolve the similarity between trees. This complexity serves as a measure of psychological complexity for rhythms. It resolves the music complexity of various compositions including the Mozart effect K488. Keyword: music perception, psychological complexity, rhythm, L-system, automata, temporal associative memory, inverse problem, rewriting rule, bracketed string, tree similarity

  15. Software Complexity Methodologies & Software Security

    OpenAIRE

    Masoud Rafighi; Nasser Modiri

    2011-01-01

    It is broadly clear that complexity is one of the software natural features. Software natural complexity and software requirement functionality are two inseparable part and they have special range. measurement complexity have explained with using the MacCabe and Halsted models and with an example discuss about software complexity in this paper Flow metric information Henry and Kafura, complexity metric system Agresti-card-glass, design metric in item’s level have compared and peruse then ca...

  16. Submanifolds of generalized complex manifolds

    OpenAIRE

    Ben-Bassat, Oren; Boyarchenko, Mitya

    2003-01-01

    The main goal of our paper is the study of several classes of submanifolds of generalized complex manifolds. Along with the generalized complex submanifolds defined by Gualtieri and Hitchin (we call these ``generalized Lagrangian submanifolds'' in our paper), we introduce and study three other classes of submanifolds. For generalized complex manifolds that arise from complex (resp., symplectic) manifolds, all three classes specialize to complex (resp., symplectic) submanifol...

  17. Actinide porphyrin complexes

    Energy Technology Data Exchange (ETDEWEB)

    Milam, S.N.

    1989-01-01

    The first bis(porphyrin)actinide complexes have been prepared by reaction of M(NEt{sub 2}){sub 4} (where M = Th, U) with H{sub 2}TPP or H{sub 2}OEP. The coordination geometry of (TPP){sub 2}Th is a distorted square-prism where the thorium center is displaced 1.47 {angstrom} from each of the porphyrin N{sub 4} planes; the porphyrin planes are separated by 2.94 {angstrom}. The porphyrin macrocycles, held in such close proximity, interact electronically as shown by a shift in the porphyrin Soret band to higher energy and unusually facile oxidation processes relative to related monoporphyrin complexes. Oxidation of (TPP){sub 2}M yields porphyrin-based radical cation complexes ((TPP){sub 2}M{sup +})(SbCl{sub 6}{sup {minus}}) and dicationic complexes, ((TPP){sub 2}M{sup 2+}) (SbCl{sub 6}{sup {minus}}){sub 2}. The porphyrin planes of ((TPP){sub 2}Th{sup +})(SbCl{sub 6}{sup {minus}}) are separated by 2.89 {angstrom}, this separation is slightly less than that of (TPP){sub 2}Th. The EPR spectrum of ((TPP){sub 2}Th{sup +})(SbCl{sub 6}{sup {minus}}) is that of a simple organic radical (g = 2.0016) while the uranium complex shows unusual signals at g{sub para} = 3.175 and g{sub perp} = 1.343. SQUID measurements on ((TPP){sub 2}Th{sup +}) (SbCl{sub 6}{sup {minus}}) suggest that above 70 K there are thermally populated excited state(s) with f-orbital character. Above 200 K, ((TPP){sub 2}U{sup +})(SbCl{sub 6}{sup {minus}}) apparently adopts S = 3/2 spin state(s), but below 70 K the spin state appears to be S = 1/2. This behavior may be due to antiferromagnetic coupling of the porphyrin radical to the f{sup 2} U{sup IV} center. The dicationic complex ((TPP){sub 2}Th{sup 2+})(SbCl{sub 6}{sup {minus}}){sub 2} is essentially diamagnetic.

  18. Preparation and reactivity of diazoalkane complexes of ruthenium stabilised by an indenyl ligand.

    Science.gov (United States)

    Albertin, Gabriele; Antoniutti, Stefano; Castro, Jesús; Dottorello, Gianluca

    2015-05-01

    Diazoalkane complexes [Ru(?(5)-C9H7)(N2CAr1Ar2)(PPh3)L]BPh4 () [L = PPh3, P(OMe)3, P(OEt)3; Ar1 = Ar2 = Ph; Ar1 = Ph, Ar2 = p-tolyl; Ar1Ar2 = C12H8 fluorenyl] were prepared by allowing chloro-complexes [RuCl(?(5)-C9H7)(PPh3)L] to react with an excess of diazoalkane in ethanol. Complexes reacted with ethylene CH2[double bond, length as m-dash]CH2 (1 atm) and maleic anhydride [ma, CH[double bond, length as m-dash]CHCO(O)CO] to afford ?(2)-alkene complexes [Ru(?(5)-C9H7)(?(2)-CH2[double bond, length as m-dash]CH2)(PPh3)L]BPh4 (, ) and [Ru(?(5)-C9H7){?(2)-CH[double bond, length as m-dash]CHCO(O)CO}(PPh3)L]BPh4 (). Further, complexes underwent cycloaddition with acrylonitrile CH2[double bond, length as m-dash]C(H)CN, giving 1H-pyrazoline derivatives [Ru(?(5)-C9H7){?(1)-N[double bond, length as m-dash]C(CN)CH2C(Ar1Ar2)NH}(PPh3)L]BPh4 (). Treatment of diazoalkane complexes with acetylene CH[triple bond, length as m-dash]CH under mild conditions (1 atm, room temperature) led to dipolar cycloaddition, affording 3H-pyrazole complexes [Ru(?(5)-C9H7)-{?(1)-N[double bond, length as m-dash]NC(Ar1Ar2)CH[double bond, length as m-dash]CH}(PPh3)L]BPh4 (), whereas reaction with terminal alkynes RC[triple bond, length as m-dash]CH (R = Ph, p-tolyl, Bu(t)) gave vinylidene derivatives [Ru(?(5)-C9H7){[double bond, length as m-dash]C[double bond, length as m-dash]C(H)R}(PPh3)L]BPh4 (). The latter reacted with nucleophiles such as amines and alcohols to give amino- and alkoxy-carbene derivatives [Ru(?(5)-C9H7){[double bond, length as m-dash]C(NHPr(n))(CH2Ph)}(PPh3)L]BPh4 () and [Ru(?(5)-C9H7){[double bond, length as m-dash]C(CH3)(OEt)}(PPh3)L]BPh4 (), respectively. In addition, complexes reacted with phenylhydrazine to afford nitrile derivatives [Ru(?(5)-C9H7)(N[triple bond, length as m-dash]CCH2R)(PPh3)L]BPh4 () and phenylamine, whereas the reaction with water led to hydrolysis of the alkyne and formation of carbonyl complexes [Ru(?(5)-C9H7)(CO)(PPh3)L]BPh4 (). Lastly, treatment of vinylidene complexes with the phosphines PPh3 and P(OMe)3 afforded alkenylphosphonium derivatives [Ru(?(5)-C9H7){C(H)[double bond, length as m-dash]C(R)PPh3}(PPh3)L]BPh4 () and [Ru(?(5)-C9H7){C(R)[double bond, length as m-dash]C(H)P(OMe)3}(PPh3)L]BPh4 (), respectively. Compound [Ru(?(5)-C9H7){C(H)[double bond, length as m-dash]C(H)PPh3}(PPh3)L]BPh4 () was also prepared. The complexes were characterised by spectroscopy (IR and NMR) and X-ray crystal structure determinations of [Ru(?(5)-C9H7){N2C(C12H8)}(PPh3){P(OEt)3}]BPh4 (), [Ru(?(5)-C9H7){[double bond, length as m-dash]C[double bond, length as m-dash]C(H)Ph}(PPh3){P(OEt)3}]BPh4 () and [Ru(?(5)-C9H7){C(H)[double bond, length as m-dash]C(Ph)PPh3}(PPh3){P(OEt)3}]BPh4 (). PMID:25913868

  19. Minimum Complexity Pursuit

    CERN Document Server

    Jalali, Shirin

    2011-01-01

    The fast growing field of compressed sensing is founded on the fact that if a signal is 'simple' and has some 'structure', then it can be reconstructed accurately with far fewer samples than its ambient dimension. Many different plausible structures have been explored in this field, ranging from sparsity to low-rankness and to finite rate of innovation. However, there are important abstract questions that are yet to be answered. For instance, what are the general abstract meanings of 'structure' and 'simplicity'? Do there exist universal algorithms for recovering such simple structured objects from fewer samples than their ambient dimension? In this paper, we aim to address these two questions. Using algorithmic information theory tools such as Kolmogorov complexity, we provide a unified method of describing 'simplicity' and 'structure'. We then explore the performance of an algorithm motivated by Ocam's Razor (called MCP for minimum complexity pursuit) and show that it requires $O(k\\log n)$ number of samples...

  20. Gold Thione Complexes

    Directory of Open Access Journals (Sweden)

    Francesco Caddeo

    2014-08-01

    Full Text Available The reaction of the ligand Et4todit (4,5,6,7-Tetrathiocino-[1,2-b:3,4-b']-diimidazolyl-1,3,8,10-tetraethyl-2,9-dithione with gold complexes leads to the dinuclear gold(I complexes [{Au(C6F5}2(Et4todit] and [Au(Et4todit]2(OTf2, which do not contain any gold-gold interactions, or to the gold(III derivative [{Au(C6F53}2(Et4todit]. The crystal structures have been established by X-ray diffraction studies and show that the gold centers coordinate to the sulfur atoms of the imidazoline-2-thione groups.

  1. Stable generalized complex structures

    CERN Document Server

    Cavalcanti, Gil R

    2015-01-01

    A stable generalized complex structure is one that is generically symplectic but degenerates along a real codimension two submanifold, where it defines a generalized Calabi-Yau structure. We introduce a Lie algebroid which allows us to view such structures as symplectic forms. This allows us to construct new examples of stable structures, and also to define period maps for their deformations in which the background three-form flux is either fixed or not, proving the unobstructedness of both deformation problems. We then use the same tools to establish local normal forms for the degeneracy locus and for Lagrangian branes. Applying our normal forms to the four-dimensional case, we prove that any compact stable generalized complex 4-manifold has a symplectic completion, in the sense that it can be modified near its degeneracy locus to produce a compact symplectic 4-manifold.

  2. Some uranium halide complexes

    International Nuclear Information System (INIS)

    Uranium halide complex salts [MeEtim]X (where[MeEtim] 1-methyl-3-ethyl-imidazolium; X-Cl, Br, I) have been used for synthesis of room temperature ionic liquids AlX3 [Me Etim]X. The crystal structure of [MeEtim]I revealed significant H bonding between cation and anion. This interaction, detected here for the first time, is important for the structure of these ionic liquids which are efficient solvents for studying electrochemical and spectroscopic properties of novel uranium halide complex salts. The cyclic voltammogram of [UO2X4]2- salts showed irreversible and reversible reduction processes. X-ray structural analysis of this salt showed tetragonal symmetry and no evidence of H bonds between anions and cations. The X-ray structure of a pseudo-halide compound [U(NCS)]4- showed significant cation-anion bonding. (U.K.)

  3. Complexities and futures?

    Directory of Open Access Journals (Sweden)

    John Urry

    2011-09-01

    Full Text Available Physical and social worlds are full of change, paradox and contradiction. There are no simple, unchangingstable states or states to which there is equilibrium-establishing movement. The “normal” state isnot one of balance and equilibrium. Any system is “complex”. Policies never straightforwardly restoreequilibrium. The equilibrium models dominant in most economic system analyses, especially generalequilibrium models, can be critiqued since they ignore the huge array of positive feedbacks. Thus, systems should be viewed as dynamic and processual, demonstrating the power of the second law of thermodynamics, in which physical and social systems are seen as moving towards entropy. Systems can be broadly viewed as unpredictable, open rather than closed, with energy and matter flowing in and out. Systems are characterised by a lack of proportionality or “non-linearity” between the apparent “causes” and “effects” of events and processes. Various implications for thinking futures are examined in the light of this complex systems thinking.

  4. Polystochastic Models for Complexity

    CERN Document Server

    Iordache, Octavian

    2010-01-01

    This book is devoted to complexity understanding and management, considered as the main source of efficiency and prosperity for the next decades. Divided into six chapters, the book begins with a presentation of basic concepts as complexity, emergence and closure. The second chapter looks to methods and introduces polystochastic models, the wave equation, possibilities and entropy. The third chapter focusing on physical and chemical systems analyzes flow-sheet synthesis, cyclic operations of separation, drug delivery systems and entropy production. Biomimetic systems represent the main objective of the fourth chapter. Case studies refer to bio-inspired calculation methods, to the role of artificial genetic codes, neural networks and neural codes for evolutionary calculus and for evolvable circuits as biomimetic devices. The fifth chapter, taking its inspiration from systems sciences and cognitive sciences looks to engineering design, case base reasoning methods, failure analysis, and multi-agent manufacturing...

  5. Physics and complexity.

    OpenAIRE

    Sherrington, D.

    2010-01-01

    This paper is concerned with complex macroscopic behaviour arising in many-body systems through the combinations of competitive interactions and disorder, even with simple ingredients at the microscopic level. It attempts to indicate and illustrate the richness that has arisen, in conceptual understanding, in methodology and in application, across a large range of scientific disciplines, together with a hint of some of the further opportunities that remain to be tapped. In d...

  6. Architecture of Glaciotectonic Complexes

    OpenAIRE

    Schack Pedersen, Stig A.

    2014-01-01

    Glaciotectonic studies are an integrated part of the Quaternary geological research carried out by the Danish geological survey. Almost all the hilly areas in Denmark were created or affected by glaciotectonic deformations, and the features are included in the mapping of surface near deposits. For the mapping and support of constructing 3D geological models a classification of architecture of glaciotectonic complexes is suggested. The important elements for classification of architecture are ...

  7. Processes on Complex Networks

    Science.gov (United States)

    Complex Systems Science Laboratory,

    Building on their understanding of graphs, students are introduced to random processes on networks. They walk through an illustrative example to see how a random process can be used to represent the spread of an infectious disease, such as the flu, on a social network of students. This demonstrates how scientists and engineers use mathematics to model and simulate random processes on complex networks. Topics covered include random processes and modeling disease spread, specifically the SIR (susceptible, infectious, resistant) model.

  8. Modeling Complex Systems

    International Nuclear Information System (INIS)

    This book by Nino Boccara presents a compilation of model systems commonly termed as 'complex'. It starts with a definition of the systems under consideration and how to build up a model to describe the complex dynamics. The subsequent chapters are devoted to various categories of mean-field type models (differential and recurrence equations, chaos) and of agent-based models (cellular automata, networks and power-law distributions). Each chapter is supplemented by a number of exercises and their solutions. The table of contents looks a little arbitrary but the author took the most prominent model systems investigated over the years (and up until now there has been no unified theory covering the various aspects of complex dynamics). The model systems are explained by looking at a number of applications in various fields. The book is written as a textbook for interested students as well as serving as a comprehensive reference for experts. It is an ideal source for topics to be presented in a lecture on dynamics of complex systems. This is the first book on this 'wide' topic and I have long awaited such a book (in fact I planned to write it myself but this is much better than I could ever have written it!). Only section 6 on cellular automata is a little too limited to the author's point of view and one would have expected more about the famous Domany-Kinzel model (and more accurate citation!). In my opinion this is one of the best textbooks published during the last decst textbooks published during the last decade and even experts can learn a lot from it. Hopefully there will be an actualization after, say, five years since this field is growing so quickly. The price is too high for students but this, unfortunately, is the normal case today. Nevertheless I think it will be a great success! (book review)

  9. Languages, decidability, and complexity.

    Czech Academy of Sciences Publication Activity Database

    Haar, S.; Masopust, Tomáš

    1. London : Springer, 2013 - (Seatzu, C.; Silva, M.; van Schuppen, J.), s. 23-43 ISBN 978-1-4471-4275-1. - (Lecture Notes in Control and Information Sciences. 433) R&D Projects: GA ?R GPP202/11/P028 Grant ostatní: European Commission(XE) EU.ICT.DISC 224498 Institutional support: RVO:67985840 Keywords : Automata theory * decidability * complexity Subject RIV: BA - General Mathematics http://link.springer.com/chapter/10.1007/978-1-4471-4276-8_2

  10. Complexity in fluids

    International Nuclear Information System (INIS)

    Fluids are basically very simple things. The fluids encountered all the time - air, water, milk, coffee, etc. - are undramatic. One blob of a given fluid looks much like any other, except for such gross properties as volume or mass. Of course, blobs of fluid come in different shapes. However, it's easy to change the shape of a blob of fluid, with the result that we rarely think of the shape of a fluid blob as a defining property. In fact, a blob that starts with one shape can be deformed into almost any other shape, with arbitrarily small input of energy. When one talks about lumps of a solid, in contrast, shape is important. This is because it takes work, i.e., energy, to change the shape of a solid. Making a small deformation from some rest configuration takes a small amount of energy, and a large deformation takes a lot of energy. Sometimes, as in idealized elastic systems, the required energy goes to infinity as the deformation becomes unbounded. Real solids usually break if you deform them enough; all subsequent deformations cost no energy. Basically, a finite deformation requires finite energy. Complexity arises in fluid systems because the shape of a blob of fluid is indeterminate. Nothing prevents an initially simple fluid blob from deforming into the weirdest shape imaginable. It is the absence of any kind of blob-shape constraint that allows complexity to enter fluid science. During these lectures the author briefly describes a few areas in which complexity describes a few areas in which complexity arises and has to be dealt with. These lectures will be roughly divided as follows: (1) physical and mathematical description of fluids and flows; (2) flow transport and ergodic theory; (3) magnetic dynamos and related problems; (4) flow instabilities; (5) turbulence

  11. Iodine complexes with triethylamine

    International Nuclear Information System (INIS)

    Electron- and IR spectra have been used to study complexing of triethylamine with molecular iodine in heptane, tetrahydrofuran, 1, 4-dioxane, acetonitrile, benzene and toluene with a wide variatian in components concentration. In ternary systems of triethylamine-iodine-solvent, iodine molecules react with triethylamine molecules and form salts of the ((Csub(2)Hsub(5))sub(3)NxHJsub(2n+1)) composition (n=0, 1, 2...) where n depends on the ratio of concentrations of components in the system

  12. Arithmetic of Complex Manifolds

    CERN Document Server

    Lange, Herbert

    1989-01-01

    It was the aim of the Erlangen meeting in May 1988 to bring together number theoretists and algebraic geometers to discuss problems of common interest, such as moduli problems, complex tori, integral points, rationality questions, automorphic forms. In recent years such problems, which are simultaneously of arithmetic and geometric interest, have become increasingly important. This proceedings volume contains 12 original research papers. Its main topics are theta functions, modular forms, abelian varieties and algebraic three-folds.

  13. Dynamics of complex flow

    International Nuclear Information System (INIS)

    Problems of the flow of complex suspensions or melt materials and powders are classified according to the existence of exact formulations and of useful models. Regimes of interest are classified into dilute, entangled, and packed, and the difficulties and successes of the different types of objects and the different types of regimes are studied. Particular notice is taken of situations where a phase change is found between regimes

  14. NDT for Complex Projects

    Science.gov (United States)

    Carnevale, Mario

    2013-04-01

    Non-destructive testing of structures composed of various types of materials is performed using a variety of methods. Most commonly, electromagnetic and acoustic methods are used to perform this task. Advances in computer software and electro-mechanical hardware have resulted in semi-automated systems for performing simple low-cost in-situ concrete testing. These systems are designed to be operated by anyone who can read a manual and push the right buttons. Although useful in many circumstances, we ask: "What happens when concrete structures are not simple and are too complex to be analyzed by these semi-automated systems and, most importantly, by minimally trained operators?" Many infrastructure projects are boldly pushing the limit of traditional engineering design. As structures become more complex, the methods and techniques used to evaluate these structures must also evolve. A first step towards adapting geophysical methods to evaluate complex structures is to develop pre-investigation conceptual models of possible responses that structures will have to available geophysical methods. This approach is important for designing the geometry and data acquisition parameters necessary for achieving the desired results. Examples of case by case assessments of the application of GPR to concrete investigations are examined. These include complex concrete wall structures, soil tunnel structures, and airport runways. HGI's adaption of ground penetrating radar (GPR) and seismic methods for assessing the substrate of a heavily reinforced concrete structure up to seven feet thick is reviewed. A range of GPR antenna frequencies were used to image the concrete and the underlying material. Time and frequency domain GPR analyses where used in the assessment. A multi-channel seismic survey using a roll-along data collection technique was used to assess the resonant frequency of the concrete structure, the nature of the underlying medium, and behavior of the structural system.

  15. Quantum Hamiltonian Complexity

    OpenAIRE

    Gharibian, Sevag; Huang, Yichen; Landau, Zeph; Shin, Seung Woo

    2014-01-01

    We survey the growing field of Quantum Hamiltonian Complexity, which includes the study of Quantum Constraint Satisfaction. In particular, our aim is to provide a computer science-oriented introduction to the subject in order to help bridge the language barrier between computer scientists and physicists in the field. As such, we include the following in this paper: (1) The motivations and history of the field, (2) a glossary of condensed matter physics terms explained in com...

  16. Fluorido complexes of technetium

    International Nuclear Information System (INIS)

    Fluorine chemistry has received considerable interest during recent years due to its significant role in the life sciences, especially for drug development. Despite the great nuclear medicinal importance of the radioactive metal technetium in radiopharmaceuticals, its coordination chemistry with the fluorido ligand is by far less explored than that of other ligands. Up to now, only a few technetium fluorides are known. This thesis contains the synthesis, spectroscopic and structural characterization of novel technetium fluorides in the oxidation states ''+1'', ''+2'', ''+4'' and ''+6''. In the oxidation state ''+6'', the fluoridotechnetates were synthesized either from nitridotechnetic(VI) acid or from pertechnetate by using reducing agent and have been isolated as cesium or tetraethylammonium salts. The compounds were characterized spectroscopically and structurally. In the intermediate oxidation state ''+4'', hexafluoridotechnetate(IV) was known for long time and studied spectroscopically. This thesis reports novel and improved syntheses and solved the critical issues of early publications such as the color, some spectroscopic properties and the structure of this key compound. Single crystal analyses of alkali metal, ammonium and tetramethylammonium salts of hexafluoridotechnetate(IV) are presented. In aqueous alkaline solutions, the ammonium salt of hexafluoridotechnetate(IV) undergoes hydrolysis and forms an oxido-bridged dimeric complex. It is the first step hydrolysis product of hexafluoridotechnetate(IV) and was characterized by spectroscopic and crystallographic methods. Low-valent technetium fluorides with the metal in the oxidation states of ''+2'' or ''+1'' are almost unknown. A detailed description of the synthesis and characterization of pentafluoridonitrosyltechnetate(II) is presented. The complex was isolated as alkali metal salts, and spectroscopic as well as structural features of the complexes are presented. Different salts of the trans-tetraamminefluoridonitrosyltechnetium(I) cation were prepared via a facile route and were characterized by spectroscopic and crystallographic methods. Ligand exchange reactions of the nitrosyltechnetium complexes are presented.

  17. Equivariant topological complexity

    OpenAIRE

    Colman, Hellen; Grant, Mark

    2012-01-01

    We define and study an equivariant version of Farber's topological complexity for spaces with a given compact group action. This is a special case of the equivariant sectional category of an equivariant map, also defined in this paper. The relationship of these invariants with the equivariant Lusternik-Schnirelmann category is given. Several examples and computations serve to highlight the similarities and differences with the non-equivariant case. We also indicate how the e...

  18. Complexity Science for Simpletons

    OpenAIRE

    Feinstein C. A.

    2006-01-01

    In this article, we shall describe some of the most interesting topics in the subject of Complexity Science for a general audience. Anyone with a solid foundation in high school mathematics (with some calculus) and an elementary understanding of computer programming will be able to follow this article. First, we shall explain the significance of the P versus NP problem and solve it. Next, we shall describe two other famous mathematics problems, the Collatz 3n+1 Conjecture an...

  19. Feline respiratory disease complex.

    Science.gov (United States)

    Cohn, Leah A

    2011-11-01

    Feline respiratory disease complex (FRDC) refers to the characteristic acute presentation of a contagious respiratory or ocular disease caused by one or multiple pathogens. Environmental and host factors impact the transmission, clinical presentation, preventive strategy, and treatment of affected cats. The FRDC is especially problematic in settings where large numbers of cats cohabit, including animal shelters, catteries, and semi-feral colonies. Although elimination of FRDC is an unrealistic goal, improved understanding can lead to strategies to minimize disease impact. PMID:22041216

  20. Localizations on Complex Networks

    OpenAIRE

    Zhu, Guimei; Yang, Huijie; Yin, Chuanyang; Li, Baowen

    2011-01-01

    We study the structural characteristics of complex networks using the representative eigenvectors of the adjacent matrix. The probability distribution function of the components of the representative eigenvectors are proposed to describe the localization on networks where the Euclidean distance is invalid. Several quantities are used to describe the localization properties of the representative states, such as the participation ratio, the structural entropy, and the probabil...

  1. Carney complex (CNC)

    OpenAIRE

    Bertherat Jérôme

    2006-01-01

    Abstract The Carney complex (CNC) is a dominantly inherited syndrome characterized by spotty skin pigmentation, endocrine overactivity and myxomas. Skin pigmentation anomalies include lentigines and blue naevi. The most common endocrine gland manifestations are acromegaly, thyroid and testicular tumors, and adrenocorticotropic hormone (ACTH)-independent Cushing's syndrome due to primary pigmented nodular adrenocortical disease (PPNAD). PPNAD, a rare cause of Cushing's syndrome, is due to prim...

  2. Volatile uranyl hexafluoroacetoacetonate complexes

    International Nuclear Information System (INIS)

    A composition of matter is described, characterized by the formula UO2(CF3COCHCOCF3).L where L is a ligand selected from isopropanol, ethanol, isobutanol, tert-butanol, methanol, tetrahydrofuran, acetone, dimethylformamide, n-propanol and ethyl acetate. A process for producing the complex comprises reacting uranyl chloride with a hexafluoroacetylacetonate dissolved in a ligand L: experimental details are given. (U.K.)

  3. Modeling Complex Systems

    Energy Technology Data Exchange (ETDEWEB)

    Schreckenberg, M [Fachbereich Physik, Duisburg-Essen University, D-47048 Duisburg (Germany)

    2004-10-08

    This book by Nino Boccara presents a compilation of model systems commonly termed as 'complex'. It starts with a definition of the systems under consideration and how to build up a model to describe the complex dynamics. The subsequent chapters are devoted to various categories of mean-field type models (differential and recurrence equations, chaos) and of agent-based models (cellular automata, networks and power-law distributions). Each chapter is supplemented by a number of exercises and their solutions. The table of contents looks a little arbitrary but the author took the most prominent model systems investigated over the years (and up until now there has been no unified theory covering the various aspects of complex dynamics). The model systems are explained by looking at a number of applications in various fields. The book is written as a textbook for interested students as well as serving as a comprehensive reference for experts. It is an ideal source for topics to be presented in a lecture on dynamics of complex systems. This is the first book on this 'wide' topic and I have long awaited such a book (in fact I planned to write it myself but this is much better than I could ever have written it{exclamation_point}). Only section 6 on cellular automata is a little too limited to the author's point of view and one would have expected more about the famous Domany-Kinzel model (and more accurate citation{exclamation_point}). In my opinion this is one of the best textbooks published during the last decade and even experts can learn a lot from it. Hopefully there will be an actualization after, say, five years since this field is growing so quickly. The price is too high for students but this, unfortunately, is the normal case today. Nevertheless I think it will be a great success{exclamation_point} (book review)

  4. The Atomic complex

    International Nuclear Information System (INIS)

    The political aspects of the growth of the two facets of the atomic complex have been dealt with in a distinct manner. Hence, this treatise is divided into two parts -two historical accounts- the first 'The explosion' dealing with the arm and the second 'The combustion' linked to the first part and devoted to the production of recoverable energy. Each part seeks to give an overall view of the unfolding of this extraordinary adventure whilst reserving a special destiny to the French aspects

  5. Complex regional pain syndrome

    OpenAIRE

    Moesker, A.

    2011-01-01

    Complex regional pain syndrome (CRPS) previously known as reflex sympathetic dystrophy is a chronic neurological disorder involving the limbs characterized by disabling pain, swelling, vasomotor instability, sudomotor abnormality, and impairment of motor function. CRPS is not uncommon after hand surgery and may complicate post-operative care. There is no specific diagnostic test for CRPS and the diagnosis is based on history, clinical examination, and supportive laboratory findings. Recent mo...

  6. The SEA complex – the beginning

    Directory of Open Access Journals (Sweden)

    Dokudovskaya S. S.

    2012-07-01

    Full Text Available The presence of distinctive internal membrane compartments, dynamically connected via selective transport pathways, is a hallmark of eukaryotic cells. Many of the proteins required for formation and maintenance of these compartments share an evolutionary history. We have recently identified a new conserved protein complex – the SEA complex – that possesses proteins with structural characteristics similar to the membrane coating complexes such as the nuclear pore complex (NPC, the COPII vesicle coating complex and HOPS/CORVET tethering complexes. The SEA complex in yeast is dynamically associated to the vacuole. The data on the function of the SEA complex remain extremely limited. Here we will discuss a possible role of the SEA complex based on the data from genetic assays and a number of functional studies in both yeast and other eukaryotes.

  7. Keynes, Hayek and Complexity

    Science.gov (United States)

    Ormerod, Paul

    In the spirit of the overall topic of the conference, in this paper I consider the extent to which economic theory includes elements of the complex systems approach. I am setting to one side here the developments over the past decade in applying complex systems analysis to economic problems. This is not because this recent work is not important. It most certainly is. But I want to argue that there is a very distinct tradition of what we would now describe as a complex systems approach in the works of two of the greatest economists of the 20th century. There is of course a dominant intellectual paradigm within economics, that known as `neo-classical'economics. This paradigm is by no means an empty box, and is undoubtedly useful in helping to understand how some aspects of the social and economic worlds work. But even in its heyday, neo-classical economics never succeeded by its empirical success in driving out completely other theoretical approaches, for its success was simply not sufficient to do so. Much more importantly, economics over the past twenty or thirty years has become in an increasing state of flux.

  8. Emergent Complex Network Geometry

    Science.gov (United States)

    Wu, Zhihao; Menichetti, Giulia; Rahmede, Christoph; Bianconi, Ginestra

    2015-01-01

    Networks are mathematical structures that are universally used to describe a large variety of complex systems such as the brain or the Internet. Characterizing the geometrical properties of these networks has become increasingly relevant for routing problems, inference and data mining. In real growing networks, topological, structural and geometrical properties emerge spontaneously from their dynamical rules. Nevertheless we still miss a model in which networks develop an emergent complex geometry. Here we show that a single two parameter network model, the growing geometrical network, can generate complex network geometries with non-trivial distribution of curvatures, combining exponential growth and small-world properties with finite spectral dimensionality. In one limit, the non-equilibrium dynamical rules of these networks can generate scale-free networks with clustering and communities, in another limit planar random geometries with non-trivial modularity. Finally we find that these properties of the geometrical growing networks are present in a large set of real networks describing biological, social and technological systems. PMID:25985280

  9. Relations between semidualizing complexes

    CERN Document Server

    Frankild, Anders J; Taylor, Amelia

    2007-01-01

    We study the following question: Given two semidualizing complexes B and C over a commutative noetherian ring R, does the vanishing of Ext^n_R(B,C) for n>>0 imply that B is C-reflexive? This question is a natural generalization of one studied by Avramov, Buchweitz, and Sega. We begin by providing conditions equivalent to B being C-reflexive, each of which is slightly stronger than the condition Ext^n_R(B,C)=0 for all n>>0. We introduce and investigate an equivalence relation \\approx on the set of isomorphism classes of semidualizing complexes. This relation is defined in terms of a natural action of the derived Picard group and is well-suited for the study of semidualizing complexes over nonlocal rings. We identify numerous alternate characterizations of this relation, each of which includes the condition Ext^n_R(B,C)=0 for all n>>0. Finally, we answer our original question in some special cases.

  10. Complexity: an internet resource for analysis of DNA sequence complexity

    Science.gov (United States)

    Orlov, Y. L.; Potapov, V. N.

    2004-01-01

    The search for DNA regions with low complexity is one of the pivotal tasks of modern structural analysis of complete genomes. The low complexity may be preconditioned by strong inequality in nucleotide content (biased composition), by tandem or dispersed repeats or by palindrome-hairpin structures, as well as by a combination of all these factors. Several numerical measures of textual complexity, including combinatorial and linguistic ones, together with complexity estimation using a modified Lempel–Ziv algorithm, have been implemented in a software tool called ‘Complexity’ (http://wwwmgs.bionet.nsc.ru/mgs/programs/low_complexity/). The software enables a user to search for low-complexity regions in long sequences, e.g. complete bacterial genomes or eukaryotic chromosomes. In addition, it estimates the complexity of groups of aligned sequences. PMID:15215465

  11. Polyhydride complexes for hydrogen storage

    Energy Technology Data Exchange (ETDEWEB)

    Jensen, C.M. [Univ. of Hawaii, Honolulu, HI (United States)

    1995-09-01

    Polyhydride metal complexes are being developed for application in hydrogen storage. Efforts have focused on developing complexes with improved available hydrogen weight percentages. We have explored the possibility that complexes containing aromatic hydrocarbon ligands could store hydrogen at both the metal center and in the ligands. We have synthesized novel indenyl hydride complexes and explored their reactivity with hydrogen. The reversible hydrogenation of [IrH{sub 3}(PPh{sub 3})({eta}{sup 5}-C{sub 10}H{sub 7})]{sup +} has been achieved. While attempting to prepare {eta}{sup 6}-tetrahydronaphthalene complexes, we discovered that certain polyhydride complexes catalyze both the hydrogenation and dehydrogenation of tetrahydronaphthalene.

  12. Shapes of interacting RNA complexes

    DEFF Research Database (Denmark)

    Fu, Benjamin Mingming; Reidys, Christian

    2014-01-01

    Shapes of interacting RNA complexes are studied using a filtration via their topological genus. A shape of an RNA complex is obtained by (iteratively) collapsing stacks and eliminating hairpin loops.This shape-projection preserves the topological core of the RNA complex and for fixed topological genus there are only finitely many such shapes. Our main result is a new bijection that relates the shapes of RNA complexes with shapes of RNA structures. This allows to compute the shape polynomial of RNA complexes via the shape polynomial of RNA structures. We furthermore present a linear time uniform sampling algorithm for shapes of RNA complexes of fixed topological genus.

  13. Complexity: an internet resource for analysis of DNA sequence complexity

    OpenAIRE

    Orlov, Y. L.; Potapov, V. N.

    2004-01-01

    The search for DNA regions with low complexity is one of the pivotal tasks of modern structural analysis of complete genomes. The low complexity may be preconditioned by strong inequality in nucleotide content (biased composition), by tandem or dispersed repeats or by palindrome-hairpin structures, as well as by a combination of all these factors. Several numerical measures of textual complexity, including combinatorial and linguistic ones, together with complexity estimation using a modified...

  14. Magnesium hydrides and the dearomatisation of pyridine and quinoline derivatives.

    Science.gov (United States)

    Hill, Michael S; Kociok-Köhn, Gabriele; MacDougall, Dugald J; Mahon, Mary F; Weetman, Catherine

    2011-12-14

    Reactions of the ?-diketiminato n-butyl magnesium complex, [HC{(Me)CN(2,6-(i)Pr(2)C(6)H(3))}(2)Mg(n)Bu], with a range of substituted pyridines and fused-ring quinolines in the presence of PhSiH(3) has been found to result in dearomatisation of the N-heterocyclic compounds. This reaction is proposed to occur through the formation of an unobserved N-heterocycle-coordinated magnesium hydride and subsequent hydride transfer via the C2-position of the heterocycle prior to hydride transfer to the C4-position and formation of thermodynamically-favoured magnesium 1,4-dihydropyridides. This reaction is kinetically suppressed for 2,6-dimethylpyridine while the kinetic product, the 1,2-dihydropyridide derivative, was isolated through reaction with 4-methylpyridine (4-methylpyridine), in which case the formation of the 1,4-dihyropyridide is prevented by the presence of the 4-methyl substituent. X-ray structures of the products of these reactions with 4-methylpyridine, 3,5-dimethylpyridine and iso-quinoline comprise a pseudo-tetrahedral magnesium centre while the regiochemistry of the particular dearomatisation reaction is determined by the substitution pattern of the N-heterocycle under observation. The compounds are all air-sensitive and exposure of the magnesium derivatives of dearomatised pyridine and 4-dimethylaminopyridine (DMAP) to air resulted in ligand rearomatisation and the formation of dimeric ?(2)-?(2)-?(2)-peroxomagnesium compounds which have also been subject to analysis by single crystal X-ray diffraction analysis. An unsuccessful extension of this chemistry to N-heterocycle hydrosilylation is suggested to be a consequence of the low basicity of the silane reagent in comparison to the pyridine substrates which effectively impedes any further interaction with the magnesium centres. PMID:21986998

  15. Cohomology of a Quaternionic Complex

    OpenAIRE

    Horan, Robin

    1995-01-01

    We investigate the cohomology of a certain elliptic complex defined on a compact quaternionic-K\\"{a}hler manifold with negative scalar curvature. We show that this particular complex is exact, with the possible exception of one term.

  16. Theory of Complex Scattering Lengths

    CERN Document Server

    Hussein, M S

    2000-01-01

    We derive a generalized Low equation for the T-matrix appropriate for complex atom-molecule interaction. The properties of this new equation at very low enegies are studied and the complex scattering length and effective range are derived.

  17. Sensemaking: a complexity perspective

    Directory of Open Access Journals (Sweden)

    Timothy Lynam

    2015-03-01

    Full Text Available Our intent was to provide a methodological overview of the primary data collection process in support of the other articles in this special issue. We documented and illustrated the use of a data collection and analysis suite, SenseMaker, that was designed to collect and work with narrative fragments. The approach presented adds a new and inherently mixed tool to the mixed methods toolbox. Despite its novelty and potential utility, little has been written in the academic literature on the application of SenseMaker to complex problems. To the best of our knowledge, the approach has not been used in relation to climate change or climate change adaptation and has not been presented in the mixed methods literature. We sought to contribute to filling this gap through describing the approach used to generate the data that underpin the articles in this special feature. Our purpose was to illustrate some of the potential and most notable challenges of using the SenseMaker data collection and analysis process in a complex domain through examining adaptation to climate change. Our overview was not exhaustive but rather sought to highlight capabilities and challenges through examining experiences of adaptation from a stages of change perspective. SenseMaker provides a remarkably powerful tool for the capture of micronarratives of complex phenomena such as climate change. The capacity to have respondents interpret, i.e., make sense of, their own narratives is an important innovation that provides one plausible solution to the problem of analysts coding narratives. Analytically, however, SenseMaker is relatively weak for those seeking strong statistical support for analyses and provides no capability for analyzing the narratives themselves.

  18. Kinetics of complex plasmas

    CERN Document Server

    Sodha, Mahendra Singh

    2014-01-01

    The presentation in the book is based on charge balance on the dust particles, number and energy balance of the constituents and atom-ion-electron interaction in the gaseous plasma. Size distribution of dust particles, statistical mechanics, Quantum effects in electron emission from and accretion on dust particles and nonlinear interaction of complex plasmas with electric and electromagnetic fields have been discussed in the book. The book introduces the reader to basic concepts and typical applications. The book should be of use to researchers, engineers and graduate students.

  19. Relations between semidualizing complexes

    OpenAIRE

    Frankild, Anders J.; Sather-wagstaff, Sean; Taylor, Amelia

    2007-01-01

    We study the following question: Given two semidualizing complexes B and C over a commutative noetherian ring R, does the vanishing of Ext^n_R(B,C) for n>>0 imply that B is C-reflexive? This question is a natural generalization of one studied by Avramov, Buchweitz, and Sega. We begin by providing conditions equivalent to B being C-reflexive, each of which is slightly stronger than the condition Ext^n_R(B,C)=0 for all n>>0. We introduce and investigate an equivalence relation...

  20. Homology of perfect complexes

    OpenAIRE

    Avramov, L. L.; Buchweitz, R. -o; Iyengar, S. B.; Miller, C.

    2006-01-01

    It is proved that the sum of the Loewy lengths of the homology modules of a finite free complex F over a local ring R is bounded below by a number depending only on R. This result uncovers, in the structure of modules of finite projective dimension, obstructions to realizing R as a closed fiber of some flat local homomorphism. Other applications include, as special cases, uniform proofs of known results on free actions of elementary abelian groups and of tori on finite CW co...

  1. Characterizing biomaterial complexity

    Directory of Open Access Journals (Sweden)

    L.A. Clifton

    2009-07-01

    Full Text Available Biomaterials research will always require a range of techniques to examine structure and function on a range of length scales and in a range of settings. Neutron scattering provides a unique way of disentangling the molecular and structural complexity of biomaterials through study of the constituent components. We examine how the technique has been used to study surface immobilized proteins and lipid films, floating lipid bilayers as mimics of in vitro planar membranes, and formation of fibres from solution by insects and spiders.

  2. Complexity Science for Simpletons

    Directory of Open Access Journals (Sweden)

    Feinstein C. A.

    2006-07-01

    Full Text Available In this article, we shall describe some of the most interesting topics in the subject of Complexity Science for a general audience. Anyone with a solid foundation in high school mathematics (with some calculus and an elementary understanding of computer programming will be able to follow this article. First, we shall explain the significance of the P versus NP problem and solve it. Next, we shall describe two other famous mathematics problems, the Collatz 3n+1 Conjecture and the Riemann Hypothesis, and show how both Chaitin's incompleteness theorem and Wolfram's notion of "computational irreducibility" are important for understanding why no one has, as of yet, solved these two problems.

  3. Fluorido complexes of technetium

    Energy Technology Data Exchange (ETDEWEB)

    Mariappan Balasekaran, Samundeeswari

    2013-07-04

    Fluorine chemistry has received considerable interest during recent years due to its significant role in the life sciences, especially for drug development. Despite the great nuclear medicinal importance of the radioactive metal technetium in radiopharmaceuticals, its coordination chemistry with the fluorido ligand is by far less explored than that of other ligands. Up to now, only a few technetium fluorides are known. This thesis contains the synthesis, spectroscopic and structural characterization of novel technetium fluorides in the oxidation states ''+1'', ''+2'', ''+4'' and ''+6''. In the oxidation state ''+6'', the fluoridotechnetates were synthesized either from nitridotechnetic(VI) acid or from pertechnetate by using reducing agent and have been isolated as cesium or tetraethylammonium salts. The compounds were characterized spectroscopically and structurally. In the intermediate oxidation state ''+4'', hexafluoridotechnetate(IV) was known for long time and studied spectroscopically. This thesis reports novel and improved syntheses and solved the critical issues of early publications such as the color, some spectroscopic properties and the structure of this key compound. Single crystal analyses of alkali metal, ammonium and tetramethylammonium salts of hexafluoridotechnetate(IV) are presented. In aqueous alkaline solutions, the ammonium salt of hexafluoridotechnetate(IV) undergoes hydrolysis and forms an oxido-bridged dimeric complex. It is the first step hydrolysis product of hexafluoridotechnetate(IV) and was characterized by spectroscopic and crystallographic methods. Low-valent technetium fluorides with the metal in the oxidation states of ''+2'' or ''+1'' are almost unknown. A detailed description of the synthesis and characterization of pentafluoridonitrosyltechnetate(II) is presented. The complex was isolated as alkali metal salts, and spectroscopic as well as structural features of the complexes are presented. Different salts of the trans-tetraamminefluoridonitrosyltechnetium(I) cation were prepared via a facile route and were characterized by spectroscopic and crystallographic methods. Ligand exchange reactions of the nitrosyltechnetium complexes are presented.

  4. Automatic Complexity Analysis

    DEFF Research Database (Denmark)

    Rosendahl, Mads

    1989-01-01

    One way to analyse programs is to to derive expressions for their computational behaviour. A time bound function (or worst-case complexity) gives an upper bound for the computation time as a function of the size of input. We describe a system to derive such time bounds automatically using abstract interpretation. The semantics-based setting makes it possible to prove the correctness of the time bound function. The system can analyse programs in a first-order subset of Lisp and we show how the system also can be used to analyse programs in other languages.

  5. Complex Sleep Apnea Syndrome

    OpenAIRE

    Wang J.; Wang Y; Feng J; By, Chen; Cao J

    2014-01-01

    Juan Wang,1,* Yan Wang,1,* Jing Feng,1,2 Bao-yuan Chen,1 Jie Cao1 1Respiratory Department of Tianjin Medical University General Hospital, Tianjin, People's Republic of China; 2Division of Pulmonary and Critical Care Medicine, Duke University Medical Center, Durham, NC, USA *The first two authors contributed equally to this work Abstract: Complex sleep apnea syndrome (CompSAS) is a distinct form of sleep-disordered breathing characterized as central sleep apnea (CSA), and presents in obstr...

  6. Complexity in Managing Modularization

    DEFF Research Database (Denmark)

    Hansen, Poul H. Kyvsgård; Sun, Hongyi

    2011-01-01

    In general, the phenomenon of managing modularization is not well known. The cause-effect relationships between modularization and realized benefits are complex and comprehensive. Though a number of research works have contributed to the study of the phenomenon of efficient and effective modularization management it is far from clarified. Recognizing the need for further empirical research, we have studied 40 modularity cases in various companies. The studies have been designed as long-term studies leaving time for various types of modularization benefits to emerge. Based on these studies we have developed a framework to support the heuristic and iterative process of planning and realizing modularization benefits.

  7. Oedipus Complex in Literature Works

    OpenAIRE

    Yan Liu; Chencheng Wang

    2011-01-01

    In psychoanalytic theory, Oedipus complex denotes the emotions and ideas that the mind keeps in the unconscious, via dynamic repression, that concentrate upon a boy's desire to sexually possess his mother (Freud.1900). In the course of his psychosexual development, the complex is the boy's phallic stage formation of a discrete sexual identity; a girl's analogous experience is the Electra complex. Freud first mentioned the Oedipus complex in 1897. After his father's death, he began to make sel...

  8. Computationally Tractable Pairwise Complexity Profile

    OpenAIRE

    Bar-Yam, Yavni; Harmon, Dion; Bar-Yam, Yaneer

    2012-01-01

    Quantifying the complexity of systems consisting of many interacting parts has been an important challenge in the field of complex systems in both abstract and applied contexts. One approach, the complexity profile, is a measure of the information to describe a system as a function of the scale at which it is observed. We present a new formulation of the complexity profile, which expands its possible application to high-dimensional real-world and mathematically defined syste...

  9. Complexity, Information and Biological Organisation

    OpenAIRE

    Attila Grandpierre

    2005-01-01

    Regarding the widespread confusion about the concept and nature of complexity, information and biological organization, we look for some coordinated conceptual considerations corresponding to quantitative measures suitable to grasp the main characteristics of biological complexity. Quantitative measures of algorithmic complexity of supercomputers like Blue Gene/L are compared with the complexity of the brain. We show that both the computer and the brain have a more fundamental, dynamic comple...

  10. The Complex System in Babel

    OpenAIRE

    Dwi Setiawan; Liliek Soelistyo

    2008-01-01

    This article discusses how the plot of Babel reflects the principles of the quantum-physic theory of complex system such as complexity, indeterminacy and non-linearity. In terms of complexity, the movie exposes more than two distinct subplots with their subcomponents. Yet, every subplot is only meaningful when it is mentally put in relation to the others. Due to its complexity, it is highly difficult for the audience and the characters of Babel to determine the meaning or the significance of ...

  11. Pseudo-complex general relativity

    International Nuclear Information System (INIS)

    An algebraic extension of General Relativity is presented, which introduces pseudo-complex coordinates. We give a short review on the properties of pseudo-complex variables and their advantage of their use in field theory. Afterwards we extend General Relativity to pseudo-complex variables. The projection to real results is described and in particular the pseudo-complex Schwarzschild solution is discussed. (author)

  12. Boundary complexes and weight filtrations

    CERN Document Server

    Payne, Sam

    2011-01-01

    We study the dual complexes of boundary divisors in log resolutions of compactifications of algebraic varieties and show that the homotopy types of these complexes are independent of all choices. Inspired by recent developments in nonarchimedean geometry, we consider relations between these boundary complexes and weight filtrations on singular cohomology and cohomology with compact supports, and give applications to dual complexes of resolutions of isolated singularities that generalize results of Stepanov and Thuillier.

  13. Generalized complex structures on nilmanifolds

    OpenAIRE

    Cavalcanti, Gil R.; Gualtieri , Marco

    2004-01-01

    We show that all 6-dimensional nilmanifolds admit generalized complex structures. This includes the five classes of nilmanifold which admit no known complex or symplectic structure. Furthermore, we classify all 6-dimensional nilmanifolds according to which of the four types of left-invariant generalized complex structure they admit. We also show that the two components of the left-invariant complex moduli space for the Iwasawa manifold are no longer disjoint when they are vi...

  14. Box complexes, neighborhood complexes, and the chromatic number

    CERN Document Server

    Csorba, P; Schurr, I; Wassmer, A; Csorba, Peter; Lange, Carsten; Schurr, Ingo; Wassmer, Arnold

    2003-01-01

    Lovasz's striking proof of Kneser's conjecture from 1978 using the Borsuk--Ulam theorem provides a lower bound on the chromatic number of a graph. We introduce the shore subdivision of simplicial complexes and use it to show an upper bound to this topological lower bound and to construct a strong Z_2-deformation retraction from the box complex (in the version introduced by Matousek and Ziegler) to the Lovasz complex. In the process, we analyze and clarify the combinatorics of the complexes involved and link their structure via several ``intermediate'' complexes.

  15. Persistent Homology of Complex Networks

    OpenAIRE

    Horak, Danijela; Maletic, Slobodan; Rajkovic, Milan

    2008-01-01

    Long lived topological features are distinguished from short lived ones (considered as topological noise) in simplicial complexes constructed from complex networks. A new topological invariant, persistent homology, is determined and presented as a parametrized version of a Betti number. Complex networks with distinct degree distributions exhibit distinct persistent topological features. Persistent toplogical attributes, shown to be related to robust quality of networks, also...

  16. Canberra Deep Dish Communications Complex

    Science.gov (United States)

    1990-01-01

    View of Canberra 70m (230 ft.) antenna with flags from the three Deep Space Network sites. The Canberra Deep Space Communications Complex, located outside Canberra, Australia, is one of the three complexes which comprise NASA's Deep Space Network. The other complexes are located in Goldstone, California, and Madrid, Spain.

  17. Kolmogorov complexity as a language

    CERN Document Server

    Shen, Alexander

    2011-01-01

    The notion of Kolmogorov complexity (=the minimal length of a program that generates some object) is often useful as a kind of language that allows us to reformulate some notions and therefore provide new intuition. In this survey we provide (with minimal comments) many different examples where notions and statements that involve Kolmogorov complexity are compared with their counterparts not involving complexity.

  18. Tate Resolutions and Weyman Complexes

    OpenAIRE

    Cox, David; Materov, Evgeny

    2009-01-01

    We construct generalized Weyman complexes for coherent sheaves on projective space and describe explicitly how the differential depend on the differentials in the correpsonding Tate resolution. We apply this to define the Weyman complex of a coherent sheaf on a projective variety and explain how certain Weyman complexes can be regarded as Fourier-Mukai transforms.

  19. Organometallic Complexes of Graphene

    CERN Document Server

    Sarkar, Santanu; Bekyarova, Elena; Haddon, Robert C

    2013-01-01

    We demonstrate the organometallic hexahapto complexation of chromium with graphene, graphite and carbon nanotubes. All of these extended periodic pi-electron systems exhibit some degree of reactivity toward the reagents CrCO)6 and (eta6-benzene)Cr(CO)3, and we are able to demonstrate the formation of (eta6-rene)Cr(CO)3 or (eta6-arene)2Cr, where arene = single-walled carbon nanotubes (SWNT), exfoliated graphene (XG), epitaxial graphene (EG) and highly-oriented pyrolytic graphite (HOPG). We find that the SWNTs are the least reactive presumably as a result of the effect of curvature on the formation of the hexahapto bond; in the case of HOPG, (eta6-HOPG)Cr(CO)3 was isolated while the exfoliated graphene samples were found to give both (eta6-graphene)2Cr, and (eta6-graphene)Cr(CO)3 structures. We report simple and efficient routes for the mild decomplexation of the graphene-chromium complexes which appears to restore the original pristine graphene state. This study represents the first example of the use of graph...

  20. Deformable Simplicial Complexes

    DEFF Research Database (Denmark)

    Misztal, Marek Krzysztof

    2010-01-01

    In this dissertation we present a novel method for deformable interface tracking in 2D and 3D|deformable simplicial complexes (DSC). Deformable interfaces are used in several applications, such as fluid simulation, image analysis, reconstruction or structural optimization. In the DSC method, the interface (curve in 2D; surface in 3D) is represented explicitly as a piecewise linear curve or surface. However, the domain is also subject to discretization: triangulation in 2D; tetrahedralization in 3D. This way, the interface can be alternatively represented as a set of edges/triangles separating triangles/tetrahedra marked as outside from those marked as inside. Such an approach allows for robust topological adaptivity. Among other advantages of the deformable simplicial complexes there are: space adaptivity, ability to handle and preserve sharp features, possibility for topology control. We demonstrate those strengths in several applications. In particular, a novel, DSC-based fluid dynamics solver has been developed during the PhD project. A special feature of this solver is that due to the fact that DSC maintains an explicit interface representation, surface tension is more easily dealt with. One particular advantage of DSC is the fact that as an alternative to topology adaptivity, topology control is also possible. This is exploited in the construction of cut loci on tori where a front expands from a single point on a torus and stops when it self-intersects.