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 partici-pation 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 deproto-nation of the hydroxyl and elimination of metal electrophile by providing hydrogen protons, while Ag salts facilitate the intramolecular cyclization step by activating C---C 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.

Automated summary

This study simulated the different catalytic mechanisms of the reaction between CO2 and propargylic alcohol. It was found that metal-assisted catalytic system can enhance the conversion rate and product yield. The PA-activated mechanism was identified as the optimal reaction pathway with intramolecular cyclization as the rate-determining step. The combination of [Ch][Triz] and Ag salts played different roles in promoting the reaction steps.