Trapping a Silicon(I) Radical with Carbenes: A Cationic cAAC-Silicon(I) Radical and an NHC-Parent-Silyliumylidene Cation.

The trapping of a silicon(I) radical with N-heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAACMe ] (cAACMe =:C(CMe2 )2 (CH2 )NAr, Ar=2,6-iPr2 C6 H3 ) with H2 SiI2 in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAACMe )2 Si:. ]+ I- (1), which features a cationic cAAC-silicon(I) radical, and [cAACMe -H]+ I- . In addition, the reaction of the NHC-iodosilicon(I) dimer [IAr (I)Si:]2 (IAr =:C{N(Ar)CH}2 ) with 4 equiv of IMe (:C{N(Me)CMe}2 ), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(IMe )2 SiH]+ I- (2) comprising the first NHC-parent-silyliumylidene cation. Its further reaction with fluorobenzene afforded the CAr -H bond activation product [1-F-2-IMe -C6 H4 ]+ I- (3). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1. Compounds 1-3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X-ray crystallography.