Tri(alkylamino)cyclopropenium Acetate Ion Pair Catalysis for Reductive Functionalization of CO ₂ with Amines and Hydrosilane to <i>N</i> -Formamides and <i>N</i> -Methylamines

The catalytic reductive functionalization of CO2 offers a sustainable strategy for mitigating greenhouse gas emissions while producing value-added chemicals. Herein, a series of strained ion pair catalysts, tri(alkylamino)cyclopropenium acetate (TAC·AA), was designed to facilitate hierarchical CO2 reduction with amines using hydrosilane as the reductant. This system enables switchable transformations of CO2 into either N-formamides (2e– reduction) or N-methylamines (6e– reduction) by tuning the reaction conditions. At elevated CO2 pressure (0.5 MPa, 25 °C), 20 amines underwent efficient N-formylation, delivering products in quantitative yields (up to 99%). Strikingly, under reduced pressure (0.1 MPa) and elevated temperature (60 °C), 15 substrates attained complete N-methylation, achieving identical 99% yields with broad functional group tolerance. Control experiments, 1H NMR titrations, and GC–MS analyses confirmed that the key intermediate in this transformation is the aminal species rather than formamides. A dual-pathway mechanism was proposed where CO2 hydrosilylation generates silyl formate intermediates that either deliver formamides or undergo further reduction via aminal intermediates to methylamines, with selectivity governed by CO2 pressure and temperature.