Si(II) Cation-Promoted Formation of an Abnormal NHC-Bound Silylene and a cAAC-Silanyl Radical Ion.

The reaction of amidinatosilylene LSi(:)Cl [L = PhC(NBu)] with N-heterocyclic carbene I [:C{N(Ar)CH}, where Ar = 2,6-PrCH] and NaOTf in tetrahydrofuran (THF) facilely afforded a silicon(II) cation [LSi(:)-I]OTf (), where I isomerizes to abnormal N-heterocyclic carbene I, coordinating to the silicon(II) center. Its Ge homologue, [LGe(:)-I]OTf (), was also accessed via the same protocol. For the formation of , we propose that an -generated Si(II) cation [LSi(:)] under the treatment of LSi(:)Cl with NaOTf may isomerize I in THF. In contrast, the replacement of I with cyclic alkyl(amino) carbene (cAAC) furnished a cAAC-silanyl radical ion LSi(H)-cAAC [], which may undergo an abstraction of the H radical from THF. All of the products were characterized by nuclear magnetic resonance spectroscopy, electron paramagnetic resonance, and X-ray crystallography, and their bonding scenarios were investigated by density functional theory calculations. These studies provide new perspective on carbene-silicon chemistry.