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 [(IMe)2SiH]I (1, IMe = :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.