One-Pot Synthesis of Aldehydes or Alcohols from CO2 via Formamides or Silyl Formates

The solvent-free N-formylation of 2-(methylamino)pyridine with CO2 and phenylsilane was catalyzed by Cu(OAc)(2) alone to give N-methyl-N-(2-pyridyl)formamide called Comins-Meyers formamide. The X-ray crystallographic analysis of a copper complex revealed a paddle-wheel structure consisting of two copper ions bridged by four acetate ions with two molecules of 2-(methylamino)pyridine on both axial sites, which suggested (i) the improved solubility of the copper ion and (ii) the enhanced nucleophilicity of the acetate ion for the activation of phenylsilane. H-1 NMR spectra of benzene-d(6) solutions containing Cu(OAc)(2), 2-(methylamino)pyridine, and phenylsilane showed a singlet signal at 2.62 ppm, which was assigned to a catalytically active Cu-H species, and this signal disappeared upon exposure to CO2. Comins-Meyers formamide synthesized from 2-(methylamino)pyridine via the copper-catalyzed hydrosilylation of CO2 under solvent-free conditions was directly subjected to the Grignard reactions in THF for the one-pot synthesis of aldehydes or alcohols. On the other hand, silyl formates prepared from CO2 and phenylsilane using tetrabutylammonium acetate (TBAA) as an organocatalyst were also found to be good precursors of alcohols.

Automated summary

This study reported the solvent-free N-formylation reaction catalyzed by Cu(OAc)(2), which used CO2 and phenylsilane to react with 2-(methylamino)pyridine and produced N-methyl-N-(2-pyridyl)formamide. The improved solubility of copper ion and enhanced nucleophilicity of acetate ion played positive roles in the activation of phenylsilane.