Quantum Chemical Study of the Reaction of 3-(Trimethylsilyl)cyclohexa-1,4-dienes with B(C6F5)3

The reaction of 3-(trimethylsilyl)cyclohexa-1,4-diene with tris(pentafluorophenyl)borane, B(C6F5)(3), has been investigated by using the M06-2X DFT method with the PCM model. The Lewis acid B(C6F5)(3) is most likely to abstract a hydrogen at the C-6 position in 3-(trimethylsilyl)cyclohexa-1,4-diene from the face opposite to the SiMe3 group. The product complex of the abstraction easily dissociates into [SiMe3(C6H6)](+) and [HB(C6F5)(3)]- or a loosely bound ion pair in dichloromethane. The dissociated ions give the complex in another structure from which the reagent, Me3SiHB(C6F5)(3), for the following hydrosilylation reaction is generated. The calculations suggest that the transformation to the complex structure that leads to the key reagent is more difficult in toluene and in benzene and is very difficult in n-pentane. The mechanism of hydrosilylation of alkenes is discussed, estimating the Lewis acidity of the silicon center in Me3SiHB(C6F5)(3), Me3SiH, and SiMe3(+).