Commercial Polymer Microsphere Grafted TBD-Based Ionic Liquids as Efficient and Low-Cost Catalyst for the Cycloaddition of CO2 with Epoxides

Development of efficient, cheap and recyclable catalysts for the synthesis of cyclic carbonates from CO 2 and epoxides is still a very attractive topic. Herein, the polymer grafted TBD-based ionic liquids (ILs) were fabricated from commercially available polystyrene (PS) and ingredients of the ILs, and used as heterogeneous catalysts for the conversion of CO 2 into cyclic carbonates in the absence of solvent and co-catalyst. To improve the catalytic performance, various substitutes (such as –COOH, –OH and –NH 2 ) were functionalized on the TBD cation. Among the as-obtained catalysts, carboxyl-containing catalyst (PS–[CETBD]Br) showed superior activity than others, which may be attributed to the stronger polarization capability of –COOH on the C–O bond of epoxide through the formed hydrogen bonding. Additionally, the combined synergistic effect of the nucleophilic attack by the halide anions also account for the facile ring-opening of epoxide. It is noted that CO 2 can be activated by the formation of carbamate between CO 2 and alkaline nitrogen of the TBD cations, thus facilitating the formation of cyclic carbonates. Moreover, the catalyst shows good chemical stability and catalytic reusability, which is very important for the practical conversion of CO 2 in chemical industry. Graphical Abstract