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Carbene
Kinds of Carbene Terms modified by Carbene Selected AbstractsSynthesis, Cytotoxicity and Antibacterial Studies of p -Methoxybenzyl-Substituted and Benzyl-Substituted N-Heterocyclic Carbene,Silver ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2010Siddappa Patil Abstract p -Methoxybenzyl-substituted and benzyl-substituted N-heterocyclic carbene (NHC) [(3a,c) and (6a,c)] precursors were synthesised from the reaction of 1H -imidazole (1a), 4,5-dichloro-1H -imidazole (1b), and 1H -benzimidazole (1c) with p -methoxybenzyl bromide (2) and benzyl bromide (5). These NHC precursors were then treated with silver(I) acetate to yield the NHC,silver complexes [1,3-bis(4-methoxybenzyl)imidazol-2-ylidene]silver(I) acetate (4a), [4,5-dichloro-1,3-bis(4-methoxybenzyl)imidazol-2-ylidene]silver(I) acetate (4b), [1,3-bis(4-methoxybenzyl)benzimidazol-2-ylidene]silver(I) acetate (4c), (1,3-dibenzylimidazol-2-ylidene)silver(I) acetate (7a), (1,3-dibenzyl-4,5-dichloroimidazol-2-ylidene)silver(I) acetate (7b), and (1,3-dibenzylbenzimidazol-2-ylidene)silver(I) acetate (7c), respectively. The NHC precursor 3c, four NHC,silver complexes 4c and 7a,c were characterised by single-crystal X-ray diffraction method. The preliminary antibacterial activity of all the compounds was studied against Gram-negative bacteria Escherichia coli, and Gram-positive bacteria Staphylococcus aureus using the Kirby,Bauer disk-diffusion method. Almost all the NHC,silver complexes have shown high antibacterial activity compared to the NHC precursors. In addition, the NHC,silver complexes had their cytotoxicity investigated through MTT-based preliminary in vitro testing on the Caki-1 cell lines in order to determine their IC50 values. NHC,silver complexes 4a,c and 7a,c were found to have IC50 values of 7.3 (+/,6), 12.7(+/,3), 25.2 (+/,5), 2.5 (+/,3), 10.8 (+/,4) and 12.5 (+/,4) ,M respectively on the Caki-1 cell line. [source] Reprogramming of a Malonic N-Heterocyclic Carbene: A Simple Backbone Modification with Dramatic Consequences on the Ligand's Donor PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2010Vincent César Abstract Reaction of N,N, -dimesitylformamidine with dimethylmalonyl dichloride in dichloromethane in the presence of an excess of triethylamine gives the 2-chloro-4,5-dioxohexahydropyrimidine 1. The corresponding diamidocarbene 3 is generated in situ by further deprotonation with KHMDS at ,40 °C and identified by trapping with S8 to give the fully characterized (including X-ray structure) sulfur adduct 4. It also reacts with [RhCl(cod)]2 to yield the NHC complex [RhCl(3)(cod)] (5) (characterized also by X-ray structure). The donor properties of 3 were evaluated against the established IR [,(CO)] scale from [RhCl(3)(CO)2] (6). The average value of ,(CO) = 2045 cm,1 indicates that the diamidocarbene 3 is much less nucleophilic than structurally relevant six-membered NHCs including the anionic diaminocarbenes previously reported in our group. [source] Adducts of Aluminum and Gallium Trichloride with a N -Heterocyclic Carbene and an Adduct of Aluminum Trichloride with a ThioneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2004Andreas Stasch Abstract The reactions of AlCl3 and GaCl3 with 1,3,4,5-tetramethylimidazole-2-ylidene in toluene at room temperature affords the 1:1 adducts 5 and 6, respectively. The use of a bulky N -heterocyclic carbene (NHC) in toluene/THF and AlCl3 results in the formation of an imidazolium salt 7 with the tetrachloroaluminate anion. A 1:1 adduct 8 of 1,3,4,5-tetramethylimidazole-2(3H)-thione with AlCl3 is obtained in toluene. The crystal structures of 5·0.5C7H8, 7·THF and 8 were determined. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Towards Long-Living Metathesis Catalysts by Tuning the N-Heterocyclic Carbene (NHC) Ligand on Trifluoroacetamide-Activated Boomerang Ru ComplexesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2009Hervé Clavier Abstract The synthesis and characterization of three novel trifluoromethylamido-containing "boomerang" precatalysts bearing various N-heterocyclic carbene (NHC) ligands are reported. Comparative kinetic and stability studies show the significant effect of the NHC on the catalyst reaction profile. An investigation of the reaction scope for diverse metathesis transformations has allowed us to establish the influence of the NHC on catalyst activity, especially as a function of substrate steric bulk. The excellent stability of one of the novel precatalysts is disclosed, and allowed for its recovery at the end of catalytic reactions. Large-scale ring-closing metathesis, enyne-metathesis and cross-metathesis experiments have revealed the recoverability of the catalyst. ICP-MS analyses of the synthesized products reveal Ru contamination levels of less than 2.5 ppm.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Synthesis and Characterization of Pyrazolyl-Functionalized Imidazolium-Based Ionic Liquids and Hemilabile (Carbene)palladium(II) Complex Catalyzed Heck ReactionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2007Ruihu Wang Abstract Neat reactions of 1-(pyrazolylmethyl)imidazole with an excess of alkyl or polyfluoroalkyl halides at 100 °C followed by subsequent metathetical reactions with LiN(SO2CF3)2 or KPF6 at 25 °C gave rise to a series of monoquaternary salts 3a,3k. These salts can be also prepared through treatment of 1-alkylimidazole with 1-(chloromethyl)pyrazole hydrochloride in the presence of base, followed by anion exchange with LiN(SO2CF3)2 or KPF6. Their phase-transition temperature, thermal stability, density and solubility in common solvents have been investigated. Most of the bis(trifluoromethanesulfon)amide salts are room-temperature ionic liquids. The effect of anions and of alkyl substituents bonded to the imidazolium cation on the physicochemical properties was examined. Using 3-butyl-1-(pyrazolylmethyl)imidazolium chloride (2d), the precursor of 3-butyl-1-(pyrazolylmethyl)imidazolium bis(trifluoromethanesulfon)amide (3d), as a reactant, a hemilabile (N-heterocyclic carbene)palladium(II) complex 4 was synthesized through a (carbene)silver(I) transfer reagent. It was characterized by single-crystal X-ray diffraction analysis. The catalytic activity and recyclability of 4 in 3d were preliminarily evaluated by consecutive Heck reactions using different substrates. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis, Structural Diversity, and Ligand-Transfer Potential of (Carbene)copper(I) ComplexesHELVETICA CHIMICA ACTA, Issue 6 2009Galmari Venkatachalam Abstract Copper(I) complexes comprising different N-heterocyclic carbene ligands were prepared via in situ deprotonation and metallation. Depending on the wingtip groups on the carbene ligand (alkyl vs. aryl, chelating or monodentate), a variety of different structural motifs were identified, such as a trigonal planar geometry (alkyl wingtips) and an unprecedented see-saw-type structure (pyridinyl wingtip groups). While aryl wingtip groups increase the stability of the complexes, alkyl substituents induce rapid demetallation in the presence of moisture. The reactivity of these complexes was used to establish a carbene-transfer protocol, which is illustrated by the formation of new cyclic thiourea compounds (transfer to sulfur) and new (carbene)ruthenium(II) complexes (transfer to ruthenium). This suggests that (carbene)copper(I) complexes could become valuable alternatives to (carbene)silver(I) complexes for synthesizing (carbene)metal systems via transmetallation. [source] Microwave-Assisted Synthesis of N-Heterocyclic Carbene- Palladium(II) ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010Abstract The microwave-assisted synthesis of two different types of N-heterocyclic carbene-palladium(II) complexes, (NHC)Pd(acac)Cl (NHC=N-heterocyclic carbene; acac=acetylacetonate) and (NHC)PdCl2(3-chloropyridine), has been carried out. A drastic reduction in reaction times (20 to 88 times faster, depending on the complex) was observed when compared to the previously described, conventionally-heated synthesis of these complexes. The protocol also allowed for the synthesis of (IPr)Pd(acac)Cl [IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] on a 5-mmol scale in 30,min, with the reactants loaded in air. [source] Ferrocene Redox Controlled Reversible Immobilization of Ruthenium Carbene in Ionic Liquid: A Versatile Catalyst for Ring-Closing MetathesisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Guiyan Liu Abstract A ferrocene-tagged ruthenium carbene 15 that can be reversibly immobilized in an ionic liquid (IL) via the controlled oxidation and reduction of a ferrocene tag was prepared. This offers a new strategy which uses redox chemistry to control immobilization and to recycle both the catalyst and the IL. In this experiment, 11 recycles were performed for the ring-closing metathesis (RCM) of a substrate using 16 as the catalyst in an ionic liquid (IL). More importantly, after the reaction was completed, the ruthenium catalyst was easily separated from the supporting IL by just adding decamethylferrocene (DMFc) to reduce the cationic ferrocene and then extracting it with benzene. Thus, this recycle system offers an easy way to recycle both the ruthenium catalyst and the IL. [source] Das Maß aller Ringe , N-heterocyclische CarbeneANGEWANDTE CHEMIE, Issue 39 2010Dipl.-Chem. Abstract Die Quantifizierung und Variation der charakteristischen Eigenschaften von Ligandenklassen ist ein spannendes und lohnenswertes Forschungsgebiet. N-heterocyclische Carbene (NHCs) sind dabei wegen ihres Elektronenreichtums und ihrer Struktur von besonderem Interesse. Deshalb haben NHCs weite Verbreitung als Liganden in der Übergangsmetallkatalyse und der Organometallchemie sowie auch direkt in der Organokatalyse gefunden. Hier wird ein Überblick über die physikochemischen Daten (Elektronik, Sterik, Bindung) von NHCs gegeben, die für das Design, die Anwendung und das mechanistische Verständnis dieser Verbindungen in der Katalyse nützlich sind. [source] Crystalline 1H -1,2,3-Triazol-5-ylidenes: New Stable Mesoionic Carbenes (MICs),ANGEWANDTE CHEMIE, Issue 28 2010Gregorio Guisado-Barrios Dr. Mit einem Klick zu MICs: Eine kurze modulare Synthese führt zu neuartigen stabilen Heterocyclen mit einem freien Elektronenpaar an einem Kohlenstoffzentrum. Diese mesoionischen Verbindungen sind bessere Donoren als klassische N-heterocyclische Carbene, und sie sind durch Deprotonierung der konjugierten Säuren mit vergleichsweise milden Basen zugänglich. [source] Copper-Free Asymmetric Allylic Alkylation with Grignard Reagents,ANGEWANDTE CHEMIE, Issue 19 2010Olivier Jackowski Dr. AAA,lternative: Die Titelreaktion mit Allylbromiden verläuft unter Katalyse durch N-heterocyclische Carbene. Die Reaktion ergibt gute Enantioselektivitäten und mitunter eine hervorragende ,-Regioselektivität, insbesondere beim Aufbau quartärer Stereozentren. [source] Steering the Surprisingly Modular ,-Acceptor Properties of N-Heterocyclic Carbenes: Implications for Gold Catalysis,ANGEWANDTE CHEMIE, Issue 14 2010Manuel Alcarazo Dr. Geben und nehmen: Die ,-Akzeptoreigenschaften N-heterocyclischer Carbene (NHCs) werden oft als vernachlässigbar angesehen, können aber bis zu dem Punkt erhöht werden, an dem sie das Katalyseverhalten von Gold-NHC-Komplexen zu dominieren beginnen (siehe Schema). Da es leichter zu sein scheint, die ,-Acidität von NHCs einzustellen als ihre ,-Donoreigenschaften, muss die allgemeine Einschätzung dieser wichtigen Hilfsliganden revidiert werden. [source] Addition of Carbene to the Equator of C70 To Produce the Most Stable C71H2 Isomer: 2,aH -2(12)a-Homo(C70 - D5h(6))[5,6]fullerene,ANGEWANDTE CHEMIE, Issue 5 2010Bao Li Dr. Endlich ist es gelungen, das schwer fassbare thermodynamisch stabilste Isomer von C71H2 (siehe Struktur) zu synthetisieren, und zwar durch Addition von CH2 an eine äquatoriale Bindung von C70,, und damit an eine Stelle, an der eine solche Reaktion kinetisch ungünstig ist. Rechnungen zufolge ist die verwendete pyrogene Synthesemethode der Grund, dass die Reaktanten die höhere Aktivierungsbarriere bei äquatorialer Addition überwinden können. [source] Abnormal Reactivity of an N-Heterocyclic Carbene (NHC) with a Phosphaalkene: A Route to a 4-Phosphino-Substituted NHC,ANGEWANDTE CHEMIE, Issue 52 2009Joshua Ein freches NHC: Ein stabiles N-heterocyclisches Carben (NHC) reagiert mit einem Phosphaalken nicht wie erwartet an der 2-Position, sondern an der 4-Position und liefert so ein neuartiges 4-phosphanylsubstituiertes NHC, das als difunktioneller Ligand für Gold(I) fungiert. Der Reaktionsmechanismus wurde mithilfe von Dichtefunktionalrechnungen untersucht. [source] Reduction of Transition-Metal-Coordinated Carbon Monoxide by a Rare-Earth Hydride Cluster: Isolation of Well-Defined Heteromultimetallic Oxycarbene, Oxymethyl, Carbene, and Methyl Complexes,ANGEWANDTE CHEMIE, Issue 42 2009Yasumasa Takenaka Dr. Der vierkernige Yttrium-Polyhydrid-Komplex 1 reduziert koordiniertes CO in Übergangsmetallkomplexen unter Bildung neuartiger Oxycarben-, Oxymethyl-, Carbenoxo- und Methyloxo-Heterometallkomplexe (siehe Schema). Das Reaktionsmuster hängt von der Art der Übergangsmetallcarbonylkomplexe ab. [source] Hauptgruppenmetallcluster stabilisiert durch N-heterocyclische CarbeneANGEWANDTE CHEMIE, Issue 37 2009Robert Wolf Dr. Carben als Schlüssel: Die Verwendung eines N-heterocyclischen Carbenliganden eröffnet den Zugang zum neutralen, oktaedrischen closo -Cluster 1, dem Prototyp einer neuen Klasse von Carben-stabilisierten Hauptgruppenmetallclustern. Quantenchemische Methoden sind erforderlich, um die Bindungsverhältnisse in solchen Clustern zu verstehen und systematische Zusammenhänge aufzudecken. [source] ChemInform Abstract: Rational Exploration of N-Heterocyclic Carbene (NHC) Palladacycle Diversity: A Highly Active and Versatile Precatalyst for Suzuki,Miyaura Coupling Reactions of Deactivated Aryl and Alkyl Substrates.CHEMINFORM, Issue 39 2010Guang-Rong Peh Abstract A small library of NHC-palladacycles is prepared by heating readily available palladacycle acetates with imidazolium salts. [source] ChemInform Abstract: Homogeneous, Anaerobic (N-Heterocyclic Carbene),Pd or ,Ni Catalyzed Oxidation of Secondary Alcohols at Mild Temperatures.CHEMINFORM, Issue 4 2010Christophe Berini Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Towards Long-Living Metathesis Catalysts by Tuning the N-Heterocyclic Carbene (NHC) Ligand on Trifluoroacetamide-Activated Boomerang Ru Complexes.CHEMINFORM, Issue 2 2010Herve Clavier Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Asymmetric Transfer Hydrogenation Catalyzed by a Novel Planar Chiral N-Heterocyclic Carbene,Rhodium(I) Complex.CHEMINFORM, Issue 35 2009Ru Jiang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Ruthenium(II) Complexes Bearing a Pyridyl-Supported Pyrazolyl,N-Heterocyclic Carbene (NNC) Ligand and Their Catalytic Activity in the Transfer Hydrogenation of Ketones.CHEMINFORM, Issue 14 2009Fanlong Zeng Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: N-Heterocyclic Carbene,Acetylamide Palladium Complexes and Their Catalytic Activities in Heck,Mizoroki Reactions.CHEMINFORM, Issue 3 2009Tao Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Nucleophilic Carbene and HOAt Relay Catalysis in an Amide Bond Coupling: An Orthogonal Peptide Bond Forming Reaction.CHEMINFORM, Issue 14 2008Harit U. Vora Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Unexpected Solvent-Induced cis/trans Isomerization and Catalytic Application of a Bis-bidentate Nickel(II) Complex with N-Heterocyclic Carbene and Amido Functionalities.CHEMINFORM, Issue 13 2008Chuang-Yi Liao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] (N-Heterocyclic Carbene)Gold(I)-Catalyzed Cycloisomerization of Cyclohexadienyl Alkynes to Tetracyclo[3.3.0.02,8.04.6]octanes.CHEMINFORM, Issue 48 2007Soo Min Kim Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] All-Carbon Quaternary Stereogenic Centers by Enantioselective Cu-Catalyzed Conjugate Additions Promoted by a Chiral N-Heterocyclic Carbene.CHEMINFORM, Issue 23 2007M. Kevin Brown Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Palladium-N-heterocyclic Carbene, an Efficient Catalytic System for the Carbonylative Cross-Coupling of Pyridine Halides with Boronic Acids.CHEMINFORM, Issue 21 2007Eddy Maerten Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis and Characterization of Pyrazolyl-Functionalized Imidazolium-Based Ionic Liquids and Hemilabile (Carbene)palladium(II) Complex Catalyzed Heck Reaction.CHEMINFORM, Issue 18 2007Ruihu Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Easily Prepared Air- and Moisture-Stable Pd,NHC (NHC: N-Heterocyclic Carbene) Complexes: A Reliable, User-Friendly, Highly Active Palladium Precatalyst for the Suzuki,Miyaura Reaction.CHEMINFORM, Issue 43 2006Christopher J. O'Brien Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Highly Efficient Trialkylsilylcyanation of Aldehydes, Ketones and Imines Catalyzed by a Nucleophilic N-Heterocyclic Carbene.CHEMINFORM, Issue 41 2006Taichi Kano Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] | |||||||||||||||||||||||||||||||