Mechanism and Regioselectivity of C–N Bond Cleavage and Ring Expansion of N‑Heterocyclic Carbenes

We report here the theoretical analysis of the mechanism and regioselectivity of the direct insertion of silane moieties into the C–N bond of N-heterocyclic carbenes leading to eventual ring expansion and formation of diazasilinanes. Symmetrically and unsymmetrically substituted NHC have been considered to account for some experimental observations. These reaction steps include (1) Si–H bond activation of the silane at the NHC; (2) amide transfer to the silicon atom to yield a six-membered intermediate; (3) hydride or phenyl group transfer to the carbon atom to give the product. In addition, the computed results over a variety of silanes agree with experimental evidence and suggest that both steric and electronic effects play a crucial role in the regioselectivity outcome and the involvement of operative intermediates in the reaction pathway