A DFT Study on the Mechanism of the Coupling Reaction between Chloromethyloxirane and Carbon Dioxide Catalyzed by Re(CO)5Br

Abstract

The detailed mechanism of the experimentally observed formation of five-membered cyclic carbonates in the coupling reaction between chloromethyloxirane and CO2 catalyzed by the Re(CO)5Br complex is revealed by means of density functional theory (DFT) calculations. All possible pathways are examined, and their corresponding energetics are demonstrated. Our calculations indicate that the real active catalyst is the unsaturated complex Re(CO)4Br rather than free radical species (Re(CO)5 or Br radicals). The preferred mechanism (path I) for the catalytic production of cyclic carbonates can be divided into three main stages involving epoxide oxidative addition, carbon dioxide insertion, and reductive elimination of cyclic carbonate, none of which contains significantly large barriers. Our results provide support for Jiang’s proposal that the reaction proceeds through the reactive oxametallacyclobutane 2b. Furthermore, we have found CO dissociation from 2b is an essential step, which facilitates CO2 coordinatio...