Construction of bicarbonate-porous poly(ionic liquid)s for cycloaddition of CO2 and epoxides under mild conditions

The utilization of carbon dioxide (CO2) as a C1 building block to synthesize cyclic carbonates represents an environmentally and sustainably viable approach. Nevertheless, the preparation of metal- and halogen-free porous materials remains a promising avenue for the cycloaddition reaction. In this context, we have designed a bicarbonate-porous poly(ionic liquid)s (PEI/PS-HCO3) catalyst with a mesoporous structure for the construction of multiple active sites through quaterisation and ion exchange. The as-prepared PEI/PS-HCO3 catalyst exhibited excellent catalytic activity for the synthesis of cyclic carbonates, with yields of up to 93% under metal-, solvent- and halogen-free conditions. Furthermore, the catalyst exhibited excellent reusability by washing with anhydrous ethanol. The feasible reaction mechanism was proposed. The interaction of dual hydrogen bond donors (amine groups and [HCO3](-) anion) with epichlorohydrin (ECH) via hydrogen bonding results in the polarisation of the epoxide C-O bond. Amine groups, also acting as Lewis base sites, captured CO2 to produce carbamates ([NH-COO](-)). The nucleophilic [HCO3](-) attacked the less sterically hindered beta-carbon atom of epichlorohydrin (ECH). This protocol provides a novel strategy for the preparation of halogen-free catalysts.