Results 211 to 220 of about 25,864 (264)
A Stable N-Heterocyclic Carbene with a Diboron Backbone
Journal of the American Chemical Society, 2005 The synthesis of a novel five-membered inorganic ring, a stable N-heterocyclic carbene with a diboron backbone, is reported. A pentacarbonyltungsten complex containing the new carbene is also described. Spectroscopic evidence indicates that the sterically encumbered carbene is a better sigma-donor than classical N-heterocyclic analogues, demonstrating ...
Krahulic, Kelly E. +3 more
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Are There Carbenes in N‐Heterocyclic Carbene Organocatalysis?
Angewandte Chemie International Edition, 2017AbstractAzolium cations are widely employed in organocatalysis to catalyse highly valuable synthetic processes in the presence of a base. These reactions are called “N‐heterocyclic carbene catalysis”, based on the assumption that they are initiated by the formation of a free carbene through deprotonation, which can then react with the substrates and ...
Sascha Gehrke, Oldamur Hollóczki
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An overview of N-heterocyclic carbenes
Nature, 2014The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes.
Matthew N, Hopkinson +3 more
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N‐Heterocyclic Carbenes as Organocatalysts
Angewandte Chemie International Edition, 2007AbstractOrganocatalyzed reactions represent an attractive alternative to metal‐catalyzed processes notably because of their lower cost and benign environmental impact in comparison to organometallic catalysis. In this context, N‐heterocyclic carbenes (NHCs) have been studied for their ability to promote primarily the benzoin condensation.
Nicolas, Marion +2 more
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A tropylium annulated N-heterocyclic carbene
Chemical Communications, 2020Derivatives of the cationic tropylium annulated imidazolylidene ITrop+ are obtained by hydride abstraction from related cycloheptatriene compounds.
Sebastian Appel +2 more
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2016
Abstract This review tries to shed light on the early history of different methods for the generation of N-heterocyclic carbenes (NHCs), i.e., the extrusion of heterocumulenes (decarboxylations) from suitable mesomeric betaines, deprotonations of hetarenium salts, α-eliminations, tautomerizations of mesomeric betaines, and reductive desulfurizations ...
Andreas Schmidt +2 more
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Abstract This review tries to shed light on the early history of different methods for the generation of N-heterocyclic carbenes (NHCs), i.e., the extrusion of heterocumulenes (decarboxylations) from suitable mesomeric betaines, deprotonations of hetarenium salts, α-eliminations, tautomerizations of mesomeric betaines, and reductive desulfurizations ...
Andreas Schmidt +2 more
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Angewandte Chemie International Edition in English, 1997
AbstractThe chemistry of N‐heterocyclic carbenes has long been limited to metal coordination compounds derived from azolium precursors, a development that was started by Öfele and Wanzlick in 1968. Since free carbenes are now available through the work of Arduengo (1991), a renaissance in this little‐recognized area of chemistry has occurred. A leading
Wolfgang A. Herrmann, Christian Köcher
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AbstractThe chemistry of N‐heterocyclic carbenes has long been limited to metal coordination compounds derived from azolium precursors, a development that was started by Öfele and Wanzlick in 1968. Since free carbenes are now available through the work of Arduengo (1991), a renaissance in this little‐recognized area of chemistry has occurred. A leading
Wolfgang A. Herrmann, Christian Köcher
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Journal of Organometallic Chemistry, 2000
Palladium(0) complexes of N-heterocyclic carbenes (NHC) are easily obtained starting from the free carbene and bis(tri-orthotolylphosphine)palladium(0) by ligand exchange. The complexes [(R)N(H)CC(H)N(R)C ‚„„„„„„„„„” ]2Pd of various 1,3-disubstituted imidazolin-2-ylidenes have been prepared by this method (R mesityl, t-Bu, i-Pr, cyclohexyl).
Volker P.W. Böhm +3 more
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Palladium(0) complexes of N-heterocyclic carbenes (NHC) are easily obtained starting from the free carbene and bis(tri-orthotolylphosphine)palladium(0) by ligand exchange. The complexes [(R)N(H)CC(H)N(R)C ‚„„„„„„„„„” ]2Pd of various 1,3-disubstituted imidazolin-2-ylidenes have been prepared by this method (R mesityl, t-Bu, i-Pr, cyclohexyl).
Volker P.W. Böhm +3 more
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2014
This chapter presents an overview of N-heterocyclic carbenes (NHCs) as chemical species. The electronic characteristics of these ligands are discussed, detailing how pπ–pπ delocalization and σ electron withdrawal stabilizes the carbene center. The bonding to metal centers is also discussed, whereby the potential for σ donation, π donation, and π ...
Nelson, David, Nolan, Steven
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This chapter presents an overview of N-heterocyclic carbenes (NHCs) as chemical species. The electronic characteristics of these ligands are discussed, detailing how pπ–pπ delocalization and σ electron withdrawal stabilizes the carbene center. The bonding to metal centers is also discussed, whereby the potential for σ donation, π donation, and π ...
Nelson, David, Nolan, Steven
openaire +4 more sources