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

The cydohexa-2,5-dien-1-yl group is established as a leaving group at silicon 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, [Ph3C](+) [B(C6F5)(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.