Formation of Dimethyl Carbonate from CO₂ and Methanol Catalyzed by Me₂SnO: A Density Functional Theory Approach

The conversion of CO₂ into dimethyl carbonate (DMC) is an environmental and industrial appealing topic because it contributes to reduce the emissions of CO₂ and to increase its use as raw material. In the present study we employed the CAM-B3LYP/def2-SVP DFT approach to evaluate the thermodynamic and kinetic parameters for the catalytic conversion of CO₂ and methanol into DMC. Starting with the activation of four methanol molecules by the [Me₂SnO]₂ dimer, we computed all the stationary points along the pathway to convert CO₂ and methanol into the DMC. The capture of two CO₂ molecules is promoted by an alkoxitin intermediate, in an exothermic process, with low activation energy. Formation of a first DMC occurs after an intramolecular rerrangement involving a tetrahedral intermediate. The formation of a second DMC may occur either in a process similar to the first one or by dimerization of the hemicarbonate formed after releasing the first DMC. In this pathway, the [Me₂(OH)SnO(OMe)SnMe₂]₂ complex is formed. This complex is less reactive than [Me₂Sn(OMe)₂]₂ but still conserves the catalytic activity. Identification of this mechanism suggests that the catalytic action of Me₂SnO can be improved by modulating the formation of the final [Me₂(OH)SnO(OMe)SnMe₂]₂ complex.