Selective N-formylation/N-methylation of amines and N-formylation of amides and carbamates with carbon dioxide and hydrosilanes: promotion of the basic counter anions of the zinc catalyst

Abstract

A catalyst composed of commercially available Zn(OAc)₂ and 1,10-phenanthroline (phen) was effective in the N-formylation/N-methylation of amines using CO₂ as the C1 source in the presence of hydrosilanes. An equimolar reaction of N-methylaniline with PhSiH₃ under a CO₂ atmosphere yielded the N-formylation product in 92% yield at 25 °C. Scale-up of the reaction using 10 mmol substrate was also successful in affording the desired product in 83% yield (1.1 g). This catalyst exhibits a high thermal stability and a turnover number (TON) of 385 000 at 150 °C. In addition, the reaction of N-methylaniline in the presence of excess Ph₂SiH₂ produced N,N-dimethylaniline. Furthermore, our catalytic protocol was developed for the N-formylation of amides and carbamates, which have smaller pK_a values and lower reactivities than the corresponding amines. The present Zn(OAc)₂/phen catalyst was found to show versatility in the conversion of CO₂ and amines into several functionalized organic chemicals under mild conditions. We propose that the basic counter anion (i.e., the acetate) of the catalyst activates both the Si–H and N–H bonds.