Theoretical study of TBD-catalyzed carboxylation of propylene glycol with CO2

The mechanisms for the reaction of propylene glycol (PG) with CO₂ catalyzed by 1,5,7-triazabicyclo4.4.0]dec-5-ene (TBD) were theoretically investigated by density functional theory (DFT) method at the B3LYP/6-311++G(d,p) level. Through analyzing the optimized structures and energy profiles along the reaction paths, the PG-activated route was identified as the most probable reaction path, in which the rate-determining step was the nucleophilic attack of one of the O atoms in CO₂ on the hydroxyl linked C atom in PG with energy barrier 56.96 kcal/mol. The catalytic role of TBD could be considered as a proton bridge activated by the synergistic action of its N atoms.