Synthesis of TBAB‐based Deep Eutectic Solvents As the Catalyst in the Coupling Reaction Between CO2 and Epoxides under Ambient Temperature

The development of an efficient, easily prepared, and environmentally friendly catalyst is important for the coupling reaction between CO2 and epoxides. Herein, novel TBAB-based (tetrabutylammonium bromide, TBAB) deep eutectic solvents (DESs) have been applied in the transformation of CO2 and epoxides into cyclic carbonates with exhibit high activity and selectivity under mild conditions (25 degrees C, 8 bar CO2), The excellent activity and versatility of the TBAB-based DESs can be attributed to the hydrogen-bond interaction between the TBAB and citric acid. Due to hydrogen-bond interaction between -OH and Br-, the Br- becomes more flexible and facilitates the nucleophilic ring-opening process. The density functional theory (DFT) method has been used to explore the mechanism governing the CO2 cycloaddition reaction. DFT results imply that intramolecular hydrogen bonding and the flexible nucleophilic Br- anion can significantly accelerate the ring-opening process. Hence, the ring-closure reaction may be the rate-determining step in the CO2 cycloaddition reaction catalyzed by TBAB-based DESs. Both the experimental and computational results have demonstrated that the synergistic effect between the -OH and Br- in the TBAB-based DESs play a significant role in the acceleration of the ring-opening process of the CO2 cycloaddition reaction.