Alcohol promoted N-methylation of anilines with CO2/H2 over a cobalt catalyst under mild conditions

Abstract

N-Methylation of amines with CO₂/H₂ to N-methylamines over non-noble metal catalysts is very interesting but remains challenging. Herein, we present an alcohol (e.g., ethanol) promoted strategy for the N-methylation of anilines with CO₂/H₂ with high efficiency under mild conditions (e.g., 125 °C), which is achieved over a cobalt catalytic system composed of Co(OAc)₂·4H₂O, triphos and Sn(OTf)₂. This catalytic system has a broad substrate scope and is tolerant toward a wide range of anilines and N-methyl anilines, and a series of N,N-dimethyl anilines were obtained in high yields. Mechanism investigation indicates that the alcohol solvent shifts the equilibrium of CO₂ hydrogenation by forming an alkyl formate, which further reacts with the amine to produce N-formamide, and Sn(OTf)₂ promotes the deoxygenative hydrogenation of N-formamides to afford N-methylamines. This is the first example of the N-methylation of amines with CO₂/H₂ over a cobalt catalytic system, which shows comparable performance to the reported Ru catalysts and may have promising applications.