Theoretical study on the mechanism of the cycloaddition reaction of CO2 and epichlorohydrin catalyzed by a triazine-based polymer with TBAI co-catalyst
The increase in CO2 emissions poses a major threat to the environment.The cycloaddition reaction of CO2 and epoxides can be catalyzed using nitrogen-and halogen-containing organocatalysts.The detailed reaction mechanism of the addition of CO2 and epichlorohydrin(ECH)to cyclic carbonate catalyzed by a composite catalytic system(Cat-Ⅰ)of a triazine-based polymer catalyst and a tetrabutylammonium iodide(TBAI)co-catalyst has been calculated using the ω B97XD/def2-TZVP//ω B97XD/def2-SVP method in conjunction with the SMD solvation model.Calculated results show that the ECH-first-activation path is the lowest energy path for the target reaction with the catalysis of Cat-Ⅰ.In the catalytic process with Cat-Ⅰ,the C-O bonds in ECH are activated by the hydrogen-bond donor of the imidogen group,and the synergistic effects of strong nucleophilicity and dissociative ability of I-promote the reaction.The turnover frequency(TOF)-determining intermediate(TDI)is the starting reactants,and the TOF-determining transition state(TDTS)is the transition state of the step of the cyclization of the carbonic hemiester.The apparent free energy barrier for the catalysis of Cat-Ⅰ is 33.54 kcal/mol,being 16.55 kcal/mol lower than that for Cat without co-catalyst.Which are in line with the experimental observation of the 100％and 70％conversions for the reaction in the conditions of 1.02 atm pressure and 105℃,catalyzed by the triazine-based polymer catalyst with or without TBAI co-catalyst,respectively.
DFTCO2 conversionorganocatalystTOF-determining states(TDI and TDTS)
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