Azaboratrane as an exceptionally potential organocatalyst for the activation of CO2 and coupling with epoxide

Abstract

• The energy barrier for the CO 2 activation in the presence of AZAB is 9.35 kcal/mol. Also, the activation step is the rate-determining step of the coupling reaction of CO 2 with ethylene oxide. • The rate constant for the activation step and TOF for the coupling reaction of CO 2 with ethylene oxide is 0.0898 L/mol/s, and 1.74 × 10 9 , respectively. • The activation energy decreases to a great extent in the presence of polar solvents. Consequently, the rate constant value for the activation step increases to 3.8 × 10 3 L/mol/s in acetonitrile. • The coupling of CO 2 with epichlorohydrin is kinetically and thermodynamically more feasible than other epoxides. Excessive use of fossil fuels resulted in a massive increase in CO 2 concentration in the atmosphere, which led to serious environmental issues. Thus, necessary steps need to be employed to alleviate the excessive amount of CO 2 from the atmosphere, and converting CO 2 into industrially valuable chemicals (e.g., cyclic carbonates) could be the best possible strategy. But the stability of the CO 2 molecule poses an extreme challenge in this approach. Owing to the thermodynamic stability of the CO 2 molecule, an exclusive bicyclic compound, azaboratrane (AZAB), has been theoretically investigated in the present work. The density functional theory (DFT) based studies were conducted to probe the catalytic action of the AZAB. The plausible mechanisms for the coupling reaction of CO 2 with epoxides were proposed and investigated. The effects of the solvents on the CO 2 coupling with epoxides in the presence of AZAB were also studied. Finally, a comparative analysis of different azatranes has been conducted to showcase the novelty of the presented catalyst. The result shows that the coupling reaction proceeds via CO 2 activation mechanism. The energy barrier for the activation was 9.35 kcal/mol, which further decreases to a great extent in the presence of highly polar solvents. Also, the calculated rate constant for the activation step was 0.08 L/mol/s. The rate constant tends to increase by increasing the temperature and polarity of the solvent. Thus, AZAB is found to be a potential catalyst for CO 2 activation and its coupling with epoxides.