Direct Catalytic Access to N-Silylated Enamines from Enolizable Imines and Hydrosilanes by Base-Free Dehydrogenative SiN Coupling

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 ion 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. Silicon IN, hydrogen OUT: N‐Silylated enamines are protected enamines derived from combinations of primary rather than secondary amines and enolizable carbonyl compounds. This rare class of compounds is now directly available from imines by a dehydrogenative SiN coupling. The catalyst generates the silicon electrophile by SiH bond activation and also acts as a base after transfer of the silicon electrophile onto the imine nitrogen atom (see scheme, ArF=3,5‐bis(trifluoromethyl)phenyl, Si=R3Si=triorganosilyl).