The (Me5C5)Si+ cation:: A stable derivative of HSi+

The reaction of decamethylsilicocene, (Me-5 C-5)(2)Si, with the proton-transfer reagent Me5C5H2+ B(C6F5)(4)- produces the salt (Me5C5)Si+ B(C6F5)(4)- (2), which can be isolated as a colorless solid that is stable in the absence of air and moisture. The crystal structure reveals the presence of a cationic pi complex with an eta(5)-pentamethylcyclopentadienyl ligand bound to a bare silicon center. The Si-29 nuclear magnetic resonance at very high field (delta = -400.2 parts per million) is typical of a pi complex of divalent silicon. The (eta(5)-Me5C5)Si+ cation in 2 can be regarded as the "resting state" of a silyliumylidene-type (eta(1)-Me5C5)Si+ cation. The availability of 2 opens new synthetic avenues in organosilicon chemistry. For example, 2 reacted with lithium bis(trimethylsilyl)amide to give the disilene E-{(eta(1)-Me5C5)[N(SiMe3)(2)]Si}(2) (3).