Tungstate catalysis: pressure-switched 2- and 6-electron reductive functionalization of CO2 with amines and phenylsilane

Abstract

An efficient and environmentally benign tungstate catalyst for reductive functionalization of CO₂ with amines and phenylsilane was developed. By simply varying the pressure, 2-electron or 6-electron reduction of CO₂ was successfully achieved with simultaneous C–N bond formation, thus leading to the formation of formamides and methylamines, respectively. That is, secondary and primary amines furnished the corresponding methylamines or dimethylamines in excellent yields under atmospheric pressure of CO₂, while various formamides were formed in yields ranging from 52% to 98% when increasing the CO₂ pressure to 2 MPa. ¹H NMR studies and control experiments demonstrate that N-formylation proceeds through the formation of silyl formate, while N-methylation proceeds through an aminal intermediate generated by 4-electron reduction of CO₂.