A NHC-Silyliumylidene Cation for Catalytic N‑Formylation of Amines Using Carbon Dioxide

This study describes the use of a silicon­(II) complex, namely, the NHC-silyliumylidene cation complex [(I_Me)₂SiH]I (1, I_Me = :C­{N­(Me)­C­(Me)}₂), to catalyze the chemoselective N-formylation of primary and secondary amines using CO₂ and PhSiH₃ under mild conditions to afford the corresponding formamides as a sole product (average reaction time: 4.5 h; primary amines, average yield: 95%, average TOF: 8 h^–1; secondary amines, average yield: 98%, average TOF: 17 h^–1). The activity of 1 and product yields outperform the currently available non-transition-metal catalysts used for this catalysis. Mechanistic studies show that the silicon­(II) center in complex 1 catalyzes the C–N bond formation via a different pathway in comparison with non-transition-metal catalysts. It sequentially activates CO₂, PhSiH₃, and amines, which proceeds via a dihydrogen elimination mechanism, to form formamides, siloxanes, and dihydrogen gas.