The Cyclohexadienyl-Leaving-Group Approach toward Donor-Stabilized Silylium Ions

Abstract

The cyclohexa-2,5-dien-1-yl group is established as a leaving group at silicon as an alternative to the Bartlett-Condon-Schneider silicon-to-carbon hydride transfer and the allyl-leaving-group approach to generate silylium ions. Hydride abstraction from the skipped diene unit employing trityl tetrakis(pentafluorophenyl)borate (1, [Ph 3 C] + [B(C 6 F 5) 4 ] -) yields the silicon cation along with benzene. Our investigations reveal that the presence of an internal or external donor group is mandatory to allow for the formation of intra- or intermolecularly stabilized silylium ions. If not, degradation of the precursor is observed as a result of the reaction of the allylic silane units with the released silylium ion. It is also shown that such allylic silanes do form remarkably stable alkyl-substituted carbenium ions when reacted stoichiometrically with benzene-stabilized silylium ions. (Chemical Equation Presented).