Deprotonation from Diphenylsilane with Organosilyllithium Agents

In contrast to their carbon analogs, there are only a few reports on deprotonation from silanes. This is because the normal polarization of a Si-H bond is Si(delta+)-H(delta-), while that of a C-H bond is C(delta-)-H(delta+). From a bond orbital perspective, a sigma*CH orbital has greater expansion on hydrogen, while a sigma*SiH orbital has greater expansion on Si. Thus, the lone pair of a base mainly attacks hydrogen of a C-H bond for deprotonation, but adds to the silicon atom of a Si-H bond. Previous reports showed that the assistance of negative hyperconjugation between the lone pair of the silyl anion and sigma* orbitals on silyl substituent(s) or an intramolecular chelating group (a pincer ligand) is necessary for deprotonation from silanes. In fact, Kira et al. found that treatment of diphenylsilane with t-butyllithium or LDA resulted in nucleophilic substitution, not deprotonation, only to eliminate a hydride as a leaving group. Recently, we developed a silicon-homologation reaction by a deprotonation-nucleophilic substitution sequence. In that reaction, we assumed that dispro-portionation led to alkoxysilyllithium or a silenoid species generated in situ. We expected that a disproportionation approach could be applied to the deprotonation of monosilanes, such as diphenylsilane. Here we report the first successful approach to the deprotonation of monosilanes with no intramolecular chelation.