Dual ionic liquids containing Bi-bridged bromide dizinc anion immobilized on CoFe₂O₄@polystyrenes: Intramolecular multicenter synergism and regulation for CO₂ cycloaddition

The synthesis of cyclic carbonates via CO₂ cycloaddition holds significant promise in reducing CO₂ concentrations. The dizinc bromide ionic liquid, with an intramolecular Bi-bridged bromide dizinc anion structure, was constructed. This dual ionic liquid was immobilized on the surface of CoFe₂O₄@polystyrenes to prepare the MPNPs-[ImC_nZ][ZnBr₃]₂ catalysts with high activity, moderate reaction conditions, good stability, and easy separation and recovery. Without solvents or co-catalysts, a 99.5% propylene oxide conversion and a 100.0% cyclic carbonates selectivity was obtained. Experimental studies and DFT calculations pointed that the appropriate alkyl chain length between the bis-imidazolium cations facilitated the formation of [ZnBr₃]₂. The synergistic effect between this dimer and the bis-imidazolium cations made MPNPs-[ImC₂Im][ZnBr₃]₂ an efficient catalyst for CO₂ cycloaddition owning to the intramolecular electronic effect and spatial effect. The catalyst integrates the advantages of bimetal halide ionic liquid, intramolecular multicentral synergy, and efficient separation and recovery, opening up a novel avenue for industrial applications.