The development of an efficient, easily prepared, and environmentally friendly catalyst is important for the coupling reaction between CO 2 and epoxides. Herein, novel TBAB-based (tetrabutylammonium bromide, TBAB) deep eutectic solvents (DESs) have been applied in the transformation of CO 2 and epoxides into cyclic carbonates with exhibit high activity and selectivity under mild conditions (25 °C, 8 bar CO 2 ), 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 À OH and Br À , the Br À 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 CO 2 cycloaddition reaction. DFT results imply that intramolecular hydrogen bonding and the flexible nucleophilic Br À anion can significantly accelerate the ring-opening process. Hence, the ring-closure reaction may be the rate-determining step in the CO 2 cycloaddition reaction catalyzed by TBAB-based DESs. Both the experimental and computational results have demonstrated that the synergistic effect between the À OH and Br À in the TBAB-based DESs play a significant role in the acceleration of the ring-opening process of the CO 2 cycloaddition reaction.
With the consumption of fossil fuels, the level of CO2 in the atmosphere is growing rapidly, which leads to global warming. Hence, the chemical conversion of CO2 into high value-added products is one of the most important approaches to reducing CO2 emissions. Due to being simple, inexpensive and environmentally friendly, the direct synthesis of cyclic carbonates from olefins and CO2 is a promising project for industrial application. In this review, we discuss the design of the homogeneous and heterogeneous catalytic system for the synthesis of cyclic carbonates from the reaction of olefins and CO2. Usually, the catalyst contains the epoxidation active site and the cycloaddition active site, which could achieve the oxidation of oleifins and the CO2-insert, respectively. This review will provide a comprehensive overview of the direct synthesis of cyclic carbonates from olefins and CO2 catalyzed by homogeneous and heterogeneous catalysts. The focus mainly lies on the rational fabrication of multifunctional catalysts, and provides a new perspective for the design of catalysts.
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