Strategy of regulating the electrophilic/nucleophilic ability by ionic ratio in poly(ionic liquid)s to control the coupling reaction of epoxide

Abstract

Although poly(ionic liquid)s (PILs) have received extensive attention and research, the strategy for designing efficient PILs catalysts remains a challenge. This work reports a series of efficient PILs catalysts with increasing ionic ratio and various anion species to regulate electrophilic/nucleophilic ability, and explores the effect of the ionic ratio on the coupling reaction of propylene oxide (PO) with CO₂ or methanol. These PILs are synthesized by a quaternization reaction between poly(N-vinylimidazole) (PVIM) and dihaloalkanes, where the amount of crosslinker of dihaloalkanes controls the ionic ratio of PILs, further affecting their microcosmic environment, morphologies and properties. It is noteworthy that the ionic ratio with IL units and imidazoline group can work as a trigger and promoter in the coupling reaction of PO with CO₂ or methanol. The ionic ratio could open the reaction compared with the parent PVIM and the choice of anion could turn the reaction on or off. It suggested that the active microstructure and electrophilic/nucleophilic ability of PILs could be regulated by the ionic ratio. In these active sites, the IL units-connected imidazoline group could weaken the interaction of the cation–anion, giving enhanced leaving ability of the anion, contributing to the excellent catalytic performance.