On the Origin of Nitrogen-Containing Promoters in the Cobalt-Catalyzed Methoxycarbonylation of Epoxides

The detailed promotion mechanism of nitrogenous compounds in the cobalt-catalyzed methoxycarbonylation of epoxides has not been studied to date. Herein, we present the intrinsic correlation between nitrogenous promoters and activity and selectivity in the alkoxycarbonylation of epoxides by a comprehensive in situ IR spectroscopy and DFT studies. In situ IR spectroscopy confirmed the acid-base neutralization of the nitrogenous promoters and HCo(CO)4, resulting in reduction of the acidity of the catalyst. With the reduced acid-derived activity for formation of ethers as by-products, the selectivity of desired esters was increased. DFT calculations showed that a nitrogenous base could facilitate the methanolysis of cobalt-acyl species with lowered activation energy, which is considered to be the rate-determining step in the catalytic cycle. As a result, the reaction activity towards carbonylation was also improved by nitrogenous promoters. The present studies will provide new insights to the long-term confusing problems in epoxides carbonylation.