Homogenous catalysis and heterogenous recycle: Cellulose-supported acetylacetonate ion pair catalyst for cycloaddition of carbon dioxide to epoxide

Designing catalysts that operate homogeneously during reactions while allowing heterogeneous recovery remains a significant challenge in carbon dioxide utilization. We developed a bifunctional cellulose-supported organocatalyst composed of an acetylacetonate anion and a protonated organic base for the cycloaddition of CO₂ with epoxide (CCE) reactions. 3-Acetylacetonate group was regioselectively anchored to C-6 position on cellulose backbone, then converted to acetylacetonate carbanion ion pair catalyst. An optimal cellulose-supported ion pair catalyst containing acetylacetonate carbanion (acac) and 1,8-diazabicyclo [5.4.0] undec-7-enium (DBUH), cell-acac-DBUH, achieved 95 % conversion and 98 % selectivity for CCE reaction of styrene oxide at 1.0 MPa CO₂, 120 °C in 8 h. NMR titrations verified H-bonding activation of the epoxide with DBUH, and formation of carbonate anion intermediate from acetylacetonate carbanion and CO₂; confirming the bifunctional catalytic mechanism. The excellent recyclability was attributable to temperature-induced aggregation and precipitation of the ion pair functioned cellulose, driven by electrostatic attractions between the cation and anion. The catalyst maintained high activity through five recycling cycles. This work offers a sustainable cellulose-based ion pair strategy combining homogeneous efficiency with heterogeneous recoverability for green CO₂ conversion.