A DFT Study of the Conversion of CO₂ in Dimethylcarbonate Catalyzed by Sn(IV) Alkoxides

Density functional theory (DFT) calculations of intermediates and transition states of the reaction between CO₂ and methanol over different R₂Sn(OCH₃)₂ catalysts (R = alkyl, phenyl and halogens) were carried out. The interaction of the CO₂ molecule with the tin catalyst was controlled by the entropic term, being disfavored at room temperature and atmospheric pressure. On the other hand, the insertion of the CO₂ molecule into the Sn–OCH₃ bond is thermodynamic favorable for all the catalysts studied. The computed free-energy of activation varied with the nature of the substituent R. Phenyl groups exhibit the smallest barrier, whereas halogen atoms the highest. Alkyl groups present intermediate barriers. The results are in agreement with recent experimental results that indicated a higher turnover number (TON) for dimethylcarbonate (DMC) formation when Ph₂SnO was used as catalyst. The whole mechanistic scheme was then computed for phenyl and methyl as substituents, considering a dimer tin species.

CO₂; dimethylcarbonate; tin alkoxides; DFT