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 [cAAC(Me)] (cAAC(Me)=:C(CMe2)(2)(CH2) NAr, Ar=2,6-iPr(2)C(6)H(3)) with H2SiI2 in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAAC(Me))(2)Si:(center dot)]I-+(-) (1) (1), which features a cationic cAAC-silicon(I) radical, and [cAAC(Me) -H]I-+(-). In addition, the reaction of the NHC-iodosilicon(I) dimer [I-Ar(I)Si:](2) (I-Ar=:C{N(Ar)CH}(2)) with 4 equiv of I-Me (:C{N(Me)CMe}(2)), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(I-Me)(2)SiH]I-+(-) (2) comprising the first NHC-parent-silyliumylidene cation. Its further reaction with fluorobenzene afforded the C-Ar-H bond activation product [1-F-2-I-Me-C6H4]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.