Efficient N-formylation of carbon dioxide and amines with alkanolamine as eco-friendly catalyst under mild conditions

The catalytic fixation of greenhouse gas CO2 has been a hot topic of research, in which the reduction and functionalization of CO2 is important for application. In present work, cheap and readily available alkanolamines were used as efficient catalysts with phenylsilanes as reducing agents to achieve the N-formylation reaction by constructing C-N bonds via the reaction between CO2 and amines (aliphatic or aromatic amines) under mild conditions (40celciusand 0.1 MPa). Further studies showed that present catalytic system has wide substrates application. Mono-N-formylated compounds were obtained as main products with good to high yields for all amines. It is worthy noted that for p-aminobenzylamine containing two amino groups as substrate, both amino groups are formylated and N-formylation reaction occurs mainly in aliphatic amine with high electron cloud density. Scaleup research has been performed effectively with high conversion of amine (80%) to obtain the mono-formylated product selectively. Finally, the mechanism of the reaction between amine and CO2 is proposed via control experiments and spectra verification. Systematic mechanism studies have revealed that after polarization by polar solvent DMSO, N-methyldiethanolamine activates CO2 by forming internal salts, which are subsequently reduced by phenylsilanes to formoxysilane intermediates and finally to form N-formylated products.