Ring expansion of a ring expanded carbene

Abstract

Reaction of phenylsilane with the ring expanded carbene 6-Mes results in facile Si-H oxidative addition to the carbenic carbon at room temperature. Heating the resultant diorganosilane product induces ring expansion through silicon to carbon migration of either the Si-H or Si-Ph bonds.

Versatile chemistry of six-membered NHC with boranes: bromination at sp3 borane, activation of the B–H bond of HBpin, and ring expansion of NHC

“…23 While the ring expansion of 5-NHCs in the presence of s/p-block hydrides is well established, [29][30][31][32][33] there is only one literature precedence of the ring expansion of 6-SIMes to a seven-membered ring in the presence of PhSiH 3 , which required 3 days and 110 °C. 34 Though we did not perform any theoretical studies, we can speculate from the literature that the mechanism proceeds via the initial coordination of the NHC to the boron center of 9-BBN (6a). 28 Afterwards, the hydrogen atom attached to the boron atom migrates to the electron-deficient carbene carbon atom.…”

Unraveling differences in aluminyl and carbene coordination chemistry: bonding in gold complexes and reactivity with carbon dioxide

“…15 Another particularly interesting feature of carbenes is that their electronic properties can be sizably modulated by applying selected modications on their structure. [14][15][16] For instance, the nucleophilicity of carbenes can be enhanced by modifying the size of the ring, where, in the socalled Ring Expanded N-Heterocyclic carbenes (RENHCs), 17,18 the wider N-C-N angle of six-and seven-membered NHCs corresponds to an increase of the p-character of the lone pair, which, in turn, destabilizes the HOMO and enhances its nucleophilic behavior. 16,19 Analogously, as it has been reported for anti-Bredt carbenes, 20 a pyramidalized N substituent, due to a reduced N-to-C p-donation, is able to decrease the LUMO energy enhancing their electrophilicity.…”

Theoretical Investigation of Hydride Insertion into N‐Heterocyclic Carbenes Containing N, P, C, O and S Heteroatoms

“…[14] We have recently also reported the ring expansion of an already ring-expanded carbene. [15] Previous synthetic and theoretical studies have focused on the interaction between elemental hydrides and NHCs, with less effort directed towards the effect of the carbene on the ringinsertion pathway. We have previously investigated the effect of varying the heterocyclic N substituents, [8] concluding that H substituents are too small to provide experimentally relevant results, while CH3 provides analogous results to experimentally relevant Ph and bulky Ar groups.…”