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

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, [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.