Theoretical study on the mechanism of nickel(0)-mediated coupling between carbon dioxide and epoxyethane

The mechanism of the Ni-mediated coupling reaction of CO2 with epoxyethane has been extensively investigated by the density functional theory (DFT) calculations. All the possible pathways are examined, and their corresponding energetics are demonstrated. On the basis of the comparison of three mechanisms, it is determined that the preferred mechanism for the catalytic production of cyclic carbonate can be divided into three main steps involving epoxide oxidative addition, carbon dioxide insertion, and reductive elimination of cyclic carbonate (route I-C), none of which contains significantly large barriers. The overall reaction is exothermic and the rate-determining step is associated with the reductive elimination of cyclic carbonate from the six-membered metallacyclic intermediate 15. All reaction pathways with solvent effects taken into consideration have been studied by means of a PCM-UAHF model. The calculations indicate that the introduction of solvent effects does not change the general trends for the reaction potential energy surfaces. Our results provide a theoretical support for the reaction mechanism proposed from previous experimental observations. At the same time, the present theoretical study gives a clear profile for the cycloaddition of carbon dioxide with epoxyethane promoted by (Ph3P)(2)Ni. (C) 2009 Elsevier B.V. All rights reserved.