Synergistic electronegativity tuning in XH-Functionalized magnetic imidazolium zinc bromide ionic liquid catalysts for CO₂ cycloaddition to epoxides

The efficient and selective conversion of CO₂ into value-added chemicals remains a key challenge in the field of green catalysis. In this study, a series of magnetic nanoparticle-supported imidazolium zinc bromide ionic liquid catalysts (MPNPs-[ImC₂B][ZnBr₃], B = NH₂, OH, COOH, SH) functionalized with diverse hydrogen bond donor (HBD) groups were synthesized to investigate the influence of X–H electronegativity (X = N, O, S) on catalytic performance in the cycloaddition of CO₂ with epoxides. The designed catalysts integrate Lewis acidic Zn²⁺, Lewis basic Br⁻, and HBD within a single molecular framework, enabling intramolecular synergistic activation, where the X–H electronegativity modulates the hydrogen-bonding interaction and enhances epoxide ring opening. The catalyst also offers a high density of active centers, elevated activity, efficient dispersion, and magnetic recoverability within 30 s. Without solvents or co-catalysts, epoxide PO (12 mmol) and MPNPs-[ImC₂NH₂][ZnBr₃] (0.2 mol%) at 90 ℃ for 6 h, with a n_PO:n_CO2 ratio of 1:1.2, provided cyclic carbonate PC in 99.8 % yield and 100.0 % selectivity. Experimental studies and DFT calculations revealed that the enhanced catalytic activity is governed by the electron-withdrawing properties of the X–H unit, which fine-tunes the synergy among Zn²⁺, Br⁻, and X–H in stabilizing the transition state. These findings provide a deeper understanding of electronegativity-driven synergy in ionic liquid catalysts, offering a rational design strategy for efficient CO₂ transformation systems.