Mechanochemically immobilized supported ionic liquid catalysts enable atmospheric-pressure cycloaddition of CO₂ with epoxides

The conversion of carbon dioxide into value added chemicals is a promising strategy for advancing carbon circularity, yet the development of recyclable catalysts that remain highly active under atmospheric CO 2 pressure without solvents or co-catalysts remains a significant challenge. Herein, we report a mechanochemically synthesized supported ionic liquid catalyst, N(CH 3 ) 2 -[Im][Br]@SiO 2 , that combines the catalytic efficiency of imidazolium ionic liquids with the practical advantages of heterogeneous catalysis. Solid-state 29 Si CP-MAS NMR spectroscopy, supported by Gaussian peak deconvolution and quantitative integration analysis of the T- and Q-type silicon species, confirmed the successful covalent immobilization of the ionic liquid on the silica surface via formation of Si-O-Si(C) linkages, producing an efficient catalyst for the solvent free cycloaddition of CO 2 with epoxides. Under atmospheric CO 2 pressure, the catalyst achieves 99% conversion of epichlorohydrin with 99% yield of chloromethyl ethylene carbonate at 120 °C after 12 h without the need for additional co-catalysts. The high activity originates from cooperative activation of the epoxide through hydrogen bonding by the acidic C2-H proton of the imidazolium cation together with nucleophilic ring opening by the bromide anion. The catalyst retains high activity over five consecutive reaction cycles and exhibits broad substrate scope, delivering consistently high conversions and cyclic carbonate yields (>95%) for structurally diverse epoxides. This work demonstrates that mechanochemical immobilization provides an effective platform for designing recoverable supported ionic liquid catalysts that overcome the traditional trade-off between catalytic performance and recyclability, offering a practical route towards low pressure CO 2 utilization and sustainable cyclic carbonate synthesis.