Cationic quaternary ammonium-stabilized Nb oxoclusters catalyze reductive amination of carbon dioxide with hydrosilane

Abstract

The N-formylation of amines with CO2 and hydrosilanes is an emerging yet important reaction in fine chemical industry. Herein, we have reported a methyltrioctylammonium cation (TOMA) stabilized Nb oxocluster catalyst that can effectively realize two electron reduction of CO2 and form C-N bond simultaneously, leading to the corresponding formamides. The oxocluster catalyst exhibits excellent catalytic activity to transform secondary and primary amines into the corresponding formamides, with the conversion ranging from 81.5% to 99.2% under room temperature conditions. Furthermore, the Nb oxocluster catalyst shows the unique characteristics of ionic liquids, and it is highly robust and easy to be recycled for five times with negligible loss of catalytic activity. On the basis of the activity tests and structure characterization of Nb catalysts, it was found that TOMA cation played an important role in modulating the Nb oxocluster with high stability and uniform dispersion. The mechanism studies demonstrate that the formylation reaction proceeds through the formation of silyl formate intermediate rather than carbamate, and the Lewis base site of negative oxygen atoms from polyoxoniobate anions can exert a favorable impact on activation both CO2 and Si-H bond of PhSiH3, allowing that N-formylation reaction proceed smoothly under very mild reaction conditions.