Ion Pair Functionalized Cellulosic Organocatalysts Bridging Homogeneous Catalysis and Heterogeneous Recycle for Fixation of CO ₂

Designing a catalytic system that combines the high catalytic efficiency and well-defined mechanism of homogeneous catalysts with the recoverability of heterogeneous catalysts remains a significant challenge in the field of carbon dioxide (CO 2 ) utilization. This study designed an ion pair functionalized cellulosic organocatalyst for the cycloaddition of CO 2 to epoxide (CCE) reactions. The catalyst functions homogeneously at elevated temperatures while self-precipitating under ambient conditions upon completion of the reaction. C-6 of the anhydrous glucose unit on the cellulose backbone was anchored with pyridinol (PyOH), a precatalyst group, and a super strong base guanidine abstracts the hydroxy proton, thereby rendering a guanidinium pyridinolate ion pair organocatalyst. A typical cellulose-supported catalyst, Cell-4-PyO − ·TBDH +, incorporating an ion pair of 4-PyO − and TBDH +, exhibited excellent catalytic performance in the CCE reaction, delivering 96% conversion with 98% selectivity within 12 h at 120 °C and 1.0 MPa CO 2 using 0.5 mol % catalyst loading. 1 H NMR titration and 13 C NMR CO 2 adsorption experiments confirmed the activations of both the epoxide and CO 2 by the ion pair. The catalytic process operates through a dual activation pathway, in which TBD-H + activates the oxygen atom of the epoxide via bidentate hydrogen bonding, while pyridinolate activates CO 2 to form a carbonate anion that attacks the epoxide. Cell-4-PyO − ·TBDH + exhibited excellent solubility in the reaction system at 120 °C, allowing it to function as a homogeneous catalyst; upon CO 2 release and subsequent temperature reduction, the catalyst gradually underwent aggregation. The catalytic system retained high activity and selectivity over seven consecutive cycles, with yields of 91−98% and selectivities of 95−99%. The superior recyclability can be attributed to temperature-dependent variations in intermolecular distances together with strengthened hydrogen bonding between ion pairs, leading to catalyst flocculation and phase separation. This work introduces a general strategy for bio-based polymer cellulose-supported ion pair catalysts that combine homogeneous catalysis with heterogeneous recycling, advancing the green utilization of CO 2 .