Direct catalytic access to N-silylated enamines from enolizable imines and hydrosilanes by base-free dehydrogenative Si-N coupling

Abstract

A procedure for the synthesis of otherwise difficult-to-make N-silylated enamines, that is masked enamines derived from primary amines, is reported. The approach is based on formation of a silyliminium ion and subsequent abstraction of the acidified α-proton rather than α-deprotonation of the enolizable imine followed by reaction with an electrophilic silicon reagent. The silicon electrophile, stabilized by a sulfur atom, is generated by cooperative activation of an Si-H bond at the Ru-S bond of a tethered ruthenium(II) thiolate complex. After transfer of the silicon cation onto the imine nitrogen atom, the remaining ruthenium(II) hydride fulfills the role of the base. Deprotonation and release of dihydrogen close the catalytic cycle. The net reaction is a dehydrogenative Si-N coupling of enolizable imines and hydrosilanes.

Keywords: SiH bond activation; chemoselectivity; dehydrogenative coupling; enamine compounds; homogeneous catalysis.