The effect of metal silver(I) salt on CO2 conversion to α-alkylidene cyclic carbonates: A DFT study

The cycloaddition of CO2 with propargylic alcohol (PA) catalyzed by ILs has evoked great interest in the past few decades. Recent research found that metal-assisted catalytic system can achieve higher CO2 conversion and product yield than pure IL. However, the microscopic mechanisms of different catalytic systems have not been investigated in detail. In this study, considering activation sequences of the reactants, various reaction routes of PA-activated mechanism and CO2-activated mechanism in the catalytic system with or without metal participation were simulated respectively. The PA-activated mechanism was found to be the optimal path for the carboxylative cyclization of PA with CO2, and intramolecular cyclization was the rate-determining step. Due to the synergistic catalytic effect of [Ch][Triz] and AgNO3 in the reaction, the activation Gibbs free energy of 14.2 kcal/mol in metal-assisted system is lower than that in pure IL (24.9 kcal/mol). [Ch][Triz] promotes deprotonation of the hydroxyl and elimination of metal electrophile by providing hydrogen protons, while Ag salts facilitate the intramolecular cyclization step by activating CC triple bond of the substrate. Simultaneously, the influence of cations in ionic liquids is analyzed, and it is found that the weak interaction between CO2 and cations can indirectly affect the active center through electronic effects.