Highly Efficient Thiolate‐Based Ionic Liquid Catalysts for Reduction of CO₂: Selective N‐Functionalization of Amines to Form N‐Formamides and N‐Methylamines

Abstract

Developing efficient catalysts to convert CO2 into value‐added chemicals is valuable for reducing carbon emissions. Herein, a kind of novel thiolate‐based ionic liquid with sulfur as the active site was designed and synthesized, which served as highly efficient catalyst for the reductive functionalization of CO2 by amines and hydrosilane. By adjusting the CO2 pressure, various formamides and methylamines were selectively obtained in high yields. Remarkably, at the catalyst loading of 0.1 mol%, the N‐formylation reaction of N‐methylaniline exhibited an impressive turnover frequency (TOF) up to 600 h‐1. This IL catalyst displayed the highest activity compared to the reported non‐transition‐metal catalysts, which could be attributed to the multiple roles of the IL in activating hydrosilane, amine and CO2. In addition, control experiments and NMR monitoring experiments provided evidence that the reduction of CO2 by hydrosilane yielded formoxysilane intermediates that subsequently reacted with amines to form N‐formylated products. Alternatively, the formoxysilane intermediates could further react with hydrosilane and amine to produce 4‐electron‐reduced aminal products. These aminal products served as crucial intermediates in the N‐methylation reactions.