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Guy Bertrand - One of the best experts on this subject based on the ideXlab platform.
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A crystalline monosubstituted Carbene
Nature Chemistry, 2018Co-Authors: Ryo Nakano, Rodolphe Jazzar, Guy BertrandAbstract:So far, monosubstituted Carbenes have only been spectroscopically characterized at very low temperatures. Now, it has been shown that a bulky, chemically inert, amino substituent is enough to tame the intrinsic tendency of Carbenes towards dimerization, enabling their isolation at room temperature. By flanking a Carbene carbon with two substituents, it is possible to synthesize persistent triplet Carbenes and isolable singlet Carbenes. Isolable singlet Carbenes are among the most powerful tools in chemistry, and they have even found medicinal and materials science applications. Between the rich chemistry of disubstituted Carbenes and the transient parent Carbene are the monosubstituted Carbenes that, so far, have only been observed in matrices at very low temperatures of just a few K. Herein, we describe the synthesis of a crystalline monosubstituted Carbene. The key for isolating such a species was to design the correct substituent, namely a benzo[ c ]pyrrolidino heterocycle, which can single-handedly tame the intrinsic tendency of Carbenes towards dimerization. The π-donor ability of the nitrogen atom, coupled with the steric bulk of chemically inert substituents at the two adjacent quaternary carbons, make these scaffolds very attractive for the isolation of a variety of other hitherto elusive electron-deficient species.
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A crystalline monosubstituted Carbene
Nature chemistry, 2018Co-Authors: Ryo Nakano, Rodolphe Jazzar, Guy BertrandAbstract:By flanking a Carbene carbon with two substituents, it is possible to synthesize persistent triplet Carbenes and isolable singlet Carbenes. Isolable singlet Carbenes are among the most powerful tools in chemistry, and they have even found medicinal and materials science applications. Between the rich chemistry of disubstituted Carbenes and the transient parent Carbene are the monosubstituted Carbenes that, so far, have only been observed in matrices at very low temperatures of just a few K. Herein, we describe the synthesis of a crystalline monosubstituted Carbene. The key for isolating such a species was to design the correct substituent, namely a benzo[c]pyrrolidino heterocycle, which can single-handedly tame the intrinsic tendency of Carbenes towards dimerization. The π-donor ability of the nitrogen atom, coupled with the steric bulk of chemically inert substituents at the two adjacent quaternary carbons, make these scaffolds very attractive for the isolation of a variety of other hitherto elusive electron-deficient species.
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Bicyclic (Alkyl)(amino)Carbenes (BICAACs): Stable Carbenes More Ambiphilic than CAACs
Journal of the American Chemical Society, 2017Co-Authors: Eder Tomás-mendivil, Rodolphe Jazzar, Max M. Hansmann, Cory M. Weinstein, Mohand Melaimi, Guy BertrandAbstract:A straightforward strategy allows for the synthesis of storable bicyclic (alkyl)(amino)Carbenes (BICAACs), which feature enhanced σ-donating and π-accepting properties compared to monocyclic (alkyl)(amino)Carbenes (CAACs). Due to the bicyclo[2.2.2]octane skeleton, the steric environment around the Carbene center is different from that of CAACs and similar to that observed in classical N-heterocyclic Carbenes. The different electronic properties of BICAACs as compared to CAACs allow for ligand exchange reactions not only at a metal center, but also at main group elements.
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Generalization of the Copper to Late‐Transition‐Metal Transmetallation to Carbenes beyond N‐Heterocyclic Carbenes
Chemistry (Weinheim an der Bergstrasse Germany), 2016Co-Authors: Yannick D. Bidal, Guy Bertrand, Mohand Melaimi, Orlando Santoro, David B. Cordes, Alexandra M. Z. Slawin, Catherine S. J. CazinAbstract:Carbene transition-metal complexes have become a prevalent family of catalysts enabling numerous organic transformations. Their facile synthetic access is a matter of great importance. To this end, the Cu(I) -NHC transfer methodology has emerged as a powerful alternative presenting attractive advantages over other methods. Herein, we report the remarkable ability of copper to transfer not only NHCs but also other types of Carbenes such as abnormal NHCs (aNHCs), cyclic (alkyl)(amino)Carbenes (CAACs), and mesoionic Carbenes (MICs) to various transition metal precursors.
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Comparative reactivity of different types of stable cyclic and acyclic mono- and diamino Carbenes with simple organic substrates
Journal of the American Chemical Society, 2014Co-Authors: David Martin, Yves Canac, Vincent Lavallo, Guy BertrandAbstract:A series of stable Carbenes, featuring a broad range of electronic properties, were reacted with simple organic substrates. The N,N-dimesityl imidazolylidene (NHC) does not react with isocyanides, whereas anti-Bredt di(amino)Carbene (pyr-NHC), cyclic (alkyl)(amino)Carbene (CAAC), acyclic di(amino)Carbene (ADAC), and acyclic (alkyl)(amino)Carbene (AAAC) give rise to the corresponding ketenimines. NHCs are known to promote the benzoin condensation, and we found that the CAAC, pyr-NHC, and ADAC react with benzaldehyde to give the ketone tautomer of the Breslow intermediate, whereas the AAAC first gives the corresponding epoxide and ultimately the Breslow intermediate, which can be isolated. Addition of excess benzaldehyde to the latter does not lead to benzoin but to a stable 1,3-dioxolane. Depending on the electronic properties of Carbenes, different products are also obtained with methyl acrylate as a substrate. The critical role of the Carbene electrophilicity on the outcome of reactions is discussed.
Steven P. Nolan - One of the best experts on this subject based on the ideXlab platform.
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Carbenes : Synthesis, properties, and organometallic chemistry
Coordination Chemistry Reviews, 2008Co-Authors: Pierre De Frémont, Nicolas Marion, Steven P. NolanAbstract:Abstract Carbenes, thought of only as transient species for a long time, have become ubiquitous in organometallic chemistry. Their interaction with a metal center, which allows for their classification as a function of the nature of the Carbene–metal bond, has inspired the investigations of many research groups in every area of chemistry, from physical chemistry to organic synthesis. In this Review , we intend to give a general overview of Carbenes in a broad sense, discussing singlet and triplet Carbenes with all variations within these families. More precisely, we describe here, for Fischer- and Schrock-type Carbenes, N-heterocyclic Carbenes and non-stabilized ones, the different synthetic routes to both the immediate precursors of Carbenes and their metal complexes. Additionally, their steric and electronic properties are discussed in the light of both experimental and theoretical studies.
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transition metal systems bearing a nucleophilic Carbene ancillary ligand from thermochemistry to catalysis
Advances in Organometallic Chemistry, 2000Co-Authors: Laleh Jafarpour, Steven P. NolanAbstract:Publisher Summary Specific applications benefit from or require the use of sterically demanding phosphine ligation to stabilize reactive intermediates. Therefore, there is a need for strongly nucleophilic, bulky ligands that are resistant to oxidizing agents and form stable bonds with metals. The enthalpies of reaction can be converted to relative enthalpies of reaction on a mole of product basis by dividing the enthalpies by 4 which represents the number of bonds made in the course of reaction. The enthalpies of reaction for nucleophilic Carbenes depend on the stereoelectronic properties of the ligands affecting the availability of the Carbene lone pair. Increase in the steric congestion around the Carbene carbon atom hinders a closer approach of the ligand, therefore affording smaller metal-lone pair overlap. The nucleophilic Carbenes are phosphine-mimics but they are much more. They reside at the upper end of the Tolman electronic and steric parameter scales. Much remains to be explored with these ligands.
B. Riegel - One of the best experts on this subject based on the ideXlab platform.
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Carbene-Pnictinidene Adducts
Inorganic Chemistry, 1997Co-Authors: Anthony J. Arduengo, H. V. Rasika Dias, William J. Marshall, Joseph C. Calabrese, Alan H. Cowley, Jens R. Goerlich, B. RiegelAbstract:The syntheses, characterizations, and X-ray crystallographic structure determinations are described for adducts of stable nucleophilic Carbenes with pnictinidenes. The adducts between 1,3-dimesitylimidazol-2-ylidene and phenylphosphinidene, phenylarsinidene, (trifluoromethyl)phosphinidene, and (pentafluorophenyl)arsinidene are reported. These Carbene−pnictinidene adducts are formed by the direct reaction of a stable nucleophilic Carbene with the corresponding pnictinidene cyclic oligomers. The synthesis and structure of the adduct between 1,3-dimesitylimidazolin-2-ylidene and phenylphosphinidene from the reaction of 1,3-dimesitylimidazolin-2-ylidene with phenylphosphorus dichloride are also reported. These Carbene−pnictinidene adducts possess strongly polarized pnictinidene−Carbene bonds. The C−Pn−C angles are all typically small at 97−102°, and there is only a 4% shortening of the nominal PnC double bond compared to the Pn−C single bond to the second substituent on the pnictogen. The 31P NMR shifts of th...
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Carbene-Pnictinidene Adducts
Inorganic chemistry, 1997Co-Authors: Anthony J. Arduengo, H. V. Rasika Dias, William J. Marshall, Joseph C. Calabrese, Alan H. Cowley, Jens R. Goerlich, B. RiegelAbstract:The syntheses, characterizations, and X-ray crystallographic structure determinations are described for adducts of stable nucleophilic Carbenes with pnictinidenes. The adducts between 1,3-dimesitylimidazol-2-ylidene and phenylphosphinidene, phenylarsinidene, (trifluoromethyl)phosphinidene, and (pentafluorophenyl)arsinidene are reported. These Carbene-pnictinidene adducts are formed by the direct reaction of a stable nucleophilic Carbene with the corresponding pnictinidene cyclic oligomers. The synthesis and structure of the adduct between 1,3-dimesitylimidazolin-2-ylidene and phenylphosphinidene from the reaction of 1,3-dimesitylimidazolin-2-ylidene with phenylphosphorus dichloride are also reported. These Carbene-pnictinidene adducts possess strongly polarized pnictinidene-Carbene bonds. The C-Pn-C angles are all typically small at 97-102 degrees, and there is only a 4% shortening of the nominal Pn=C double bond compared to the Pn-C single bond to the second substituent on the pnictogen. The (31)P NMR shifts of the phosphorus adducts suggest strongly shielded phosphorus centers in accord with the polarized structures.
Anthony J. Arduengo - One of the best experts on this subject based on the ideXlab platform.
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N-Heterocyclic Carbenes
Australian Journal of Chemistry, 2011Co-Authors: Anthony J. ArduengoAbstract:Scientific research offers many rewards and benefits that are highly sought in any activity – sharing ideas, interests, and experiences with like-minded individuals; the excitement of the quest for an understanding of the unknown and the function of the surrounding world; the satisfaction of achievement; and the generation of new knowledge uponwhich others may build. The study of the compounds with unusual valency has been and continues to be just such a productive and rewarding activity. In chemistry, the study of compounds with unusual valency offers researchers a rapid path ‘out of the box’ of the science’s conventional wisdom. The traditional grasp of how things are, how things function, and what one should anticipate from molecule–molecule interactions and reactions, or matter– energy interactions is best tested in this realm of the unusual. Accepted ideas are most easily pushed to their limits (and beyond) when applied to that which appears unusual by accepted standards. Carbenes fall within this area of compounds with unusual valency. These compounds contain a divalent carbon that, formally, violates the octet rule. Carbene chemistry has its roots in much simpler times when there was no real cause to be alarmed or concerned about such compounds because there was no octet rule to violate. Hence early chemical research seeking to isolate and study stable Carbenes was reasonable. The octet rule has its origins at the turn of the 20th century in Abegg’s rule and Lewis’s cubical atom. However, recognizable ‘Carbene’ research started some sixty five years earlier with the attempts of Dumas to isolate and characterize methylene (Scheme 1). The progress of Carbene research from its origins has been recounted elsewhere and is left to the reader to retrace in detail; here I only intend to briefly summarize those earlier events. The typically high reactivity of Carbenes and lack of suitable spectroscopy methods or laboratory techniques to handle these apparently transient species led to a widespread view that Carbenes were too reactive to be isolated as stable entities, but were, nonetheless, important intermediates in some chemical transformations. This view of extreme reactivity could be further supported by reliance on the octet rule. By the late 20th century, the view of Carbenes was beginning to change again. Experimental techniques had improved substantially and new spectroscopic techniques, beyond the reach of early Carbene researchers, were becoming common-place. There was hope that transient Carbene species could at least be captured briefly and studied if not placed in a bottle. Beginning in 1960Wanzlick reported the chemistry of imidazolines and (to a lesser extent) imidazoles in the quest for stable Carbenes. Unfortunately, Wanzlick’s efforts were contemporaneous with other rather spectacular experimental mishaps that laid false claims to the isolation of simple singlet Carbenes. Wanzlick’s experiments were perhaps nearly capable of producing a ‘bottle-able’ Carbene, but the scientific environment and culture in his time was still not welcoming to his views. Publications suggesting flaws or oversights in his work kept a truly ‘bottle-able’ Carbene just beyond the community’s grasp. Nonetheless, Wanzlick, Ofele, Lappert, Huttner and others published chemistry that showed that in situ generated imidazol(in)-2-ylidenes give rise to interesting new compounds (Scheme 2). Chemistry of themain group elements sulfur and phosphorus opened another opportunity to approach the quest for Carbenes. Seppelt and Bertrand employed the elements of sulfur and phosphorus to construct molecules in which the conceptual ‘resonance’ relationship between a-diCarbenes and acetylenes could be perturbed by the introduction of the heavier main group elements. These pioneering studies provided thiaacetylenes and phosphaacetylenes that exhibited ‘Carbene-like’
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Carbene ADDUCTS OF DIMETHYLCADMIUM
Zeitschrift für Naturforschung B, 1999Co-Authors: Anthony J. Arduengo, Fredric Davidson, Jens R. Goerlicha, William J. MarshallAbstract:The first examples of Carbene-cadmium complexes are reported from the reactions of a variety of imidazol-2-ylidenes or imidazolin-2-ylidenes with dimethylcadmium. Four new Carbene complexes are characterized by NMR spectroscopy (¹H , ¹³C and ¹¹³Cd). The cadmium centers are strongly shifted downfield (100 -150 ppm) by interaction with the Carbenes. X-ray structures are reported for three Carbene-cadmium 1:1 adducts. The cadmium centers exhibit distorted trigonal-planar geometries in which the Carbene ligands have an average 18.2 pm longer bond distance to cadmium compared to the methyl groups. The planes of cadmium coordination are twisted with respect to the plane of the imidazole ring. The more basic imidazolin-2-ylidene is shown to displace imidazol-2-ylidenes from the cadmium center.
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Carbene-Pnictinidene Adducts
Inorganic Chemistry, 1997Co-Authors: Anthony J. Arduengo, H. V. Rasika Dias, William J. Marshall, Joseph C. Calabrese, Alan H. Cowley, Jens R. Goerlich, B. RiegelAbstract:The syntheses, characterizations, and X-ray crystallographic structure determinations are described for adducts of stable nucleophilic Carbenes with pnictinidenes. The adducts between 1,3-dimesitylimidazol-2-ylidene and phenylphosphinidene, phenylarsinidene, (trifluoromethyl)phosphinidene, and (pentafluorophenyl)arsinidene are reported. These Carbene−pnictinidene adducts are formed by the direct reaction of a stable nucleophilic Carbene with the corresponding pnictinidene cyclic oligomers. The synthesis and structure of the adduct between 1,3-dimesitylimidazolin-2-ylidene and phenylphosphinidene from the reaction of 1,3-dimesitylimidazolin-2-ylidene with phenylphosphorus dichloride are also reported. These Carbene−pnictinidene adducts possess strongly polarized pnictinidene−Carbene bonds. The C−Pn−C angles are all typically small at 97−102°, and there is only a 4% shortening of the nominal PnC double bond compared to the Pn−C single bond to the second substituent on the pnictogen. The 31P NMR shifts of th...
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Carbene-Pnictinidene Adducts
Inorganic chemistry, 1997Co-Authors: Anthony J. Arduengo, H. V. Rasika Dias, William J. Marshall, Joseph C. Calabrese, Alan H. Cowley, Jens R. Goerlich, B. RiegelAbstract:The syntheses, characterizations, and X-ray crystallographic structure determinations are described for adducts of stable nucleophilic Carbenes with pnictinidenes. The adducts between 1,3-dimesitylimidazol-2-ylidene and phenylphosphinidene, phenylarsinidene, (trifluoromethyl)phosphinidene, and (pentafluorophenyl)arsinidene are reported. These Carbene-pnictinidene adducts are formed by the direct reaction of a stable nucleophilic Carbene with the corresponding pnictinidene cyclic oligomers. The synthesis and structure of the adduct between 1,3-dimesitylimidazolin-2-ylidene and phenylphosphinidene from the reaction of 1,3-dimesitylimidazolin-2-ylidene with phenylphosphorus dichloride are also reported. These Carbene-pnictinidene adducts possess strongly polarized pnictinidene-Carbene bonds. The C-Pn-C angles are all typically small at 97-102 degrees, and there is only a 4% shortening of the nominal Pn=C double bond compared to the Pn-C single bond to the second substituent on the pnictogen. The (31)P NMR shifts of the phosphorus adducts suggest strongly shielded phosphorus centers in accord with the polarized structures.
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Carbene adducts of magnesium and zinc
Journal of Organometallic Chemistry, 1993Co-Authors: Anthony J. Arduengo, Fredric Davidson, H. V. Rasika Dias, R.l. HarlowAbstract:Abstract The syntheses and characterizations of adducts of dialkylmagnesium and dialkylzinc with nucleophilic Carbenes are described. These Carbene adducts are available directly from the reaction of the stable nucleophilic Carbenes 1,3-dimesitylimidazol-2-ylidene or 1,3-di(1-adamantyl)imidazol-2-ylidene and the dialkylmetal compounds. The X-ray crystal structures of the 1,3-di(1-adamantyl)imidazol-2-ylidene · diethylzinc adduct and 1,3-dimesitylimidazol-2-ylidene · diethylmagnesium are reported. The adamantyl substituted Carbene gave a monomeric metal adduct whereas the mesityl substituted Carbene shows a structure with bridging alkyl groups.
Ryo Nakano - One of the best experts on this subject based on the ideXlab platform.
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A crystalline monosubstituted Carbene
Nature Chemistry, 2018Co-Authors: Ryo Nakano, Rodolphe Jazzar, Guy BertrandAbstract:So far, monosubstituted Carbenes have only been spectroscopically characterized at very low temperatures. Now, it has been shown that a bulky, chemically inert, amino substituent is enough to tame the intrinsic tendency of Carbenes towards dimerization, enabling their isolation at room temperature. By flanking a Carbene carbon with two substituents, it is possible to synthesize persistent triplet Carbenes and isolable singlet Carbenes. Isolable singlet Carbenes are among the most powerful tools in chemistry, and they have even found medicinal and materials science applications. Between the rich chemistry of disubstituted Carbenes and the transient parent Carbene are the monosubstituted Carbenes that, so far, have only been observed in matrices at very low temperatures of just a few K. Herein, we describe the synthesis of a crystalline monosubstituted Carbene. The key for isolating such a species was to design the correct substituent, namely a benzo[ c ]pyrrolidino heterocycle, which can single-handedly tame the intrinsic tendency of Carbenes towards dimerization. The π-donor ability of the nitrogen atom, coupled with the steric bulk of chemically inert substituents at the two adjacent quaternary carbons, make these scaffolds very attractive for the isolation of a variety of other hitherto elusive electron-deficient species.
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A crystalline monosubstituted Carbene
Nature chemistry, 2018Co-Authors: Ryo Nakano, Rodolphe Jazzar, Guy BertrandAbstract:By flanking a Carbene carbon with two substituents, it is possible to synthesize persistent triplet Carbenes and isolable singlet Carbenes. Isolable singlet Carbenes are among the most powerful tools in chemistry, and they have even found medicinal and materials science applications. Between the rich chemistry of disubstituted Carbenes and the transient parent Carbene are the monosubstituted Carbenes that, so far, have only been observed in matrices at very low temperatures of just a few K. Herein, we describe the synthesis of a crystalline monosubstituted Carbene. The key for isolating such a species was to design the correct substituent, namely a benzo[c]pyrrolidino heterocycle, which can single-handedly tame the intrinsic tendency of Carbenes towards dimerization. The π-donor ability of the nitrogen atom, coupled with the steric bulk of chemically inert substituents at the two adjacent quaternary carbons, make these scaffolds very attractive for the isolation of a variety of other hitherto elusive electron-deficient species.
