Malononitrile carbanion functioned cellulose bridging homogeneous catalysis and heterogeneous recycling in CO2 fixation

The development of catalyst that workable homogeneously in reaction and recoverable heterogeneously in separation remains a challenge. We designed functionalized cellulose featuring malononitrile carbanion ion pair as a bifunctional catalyst for the cycloaddition of CO₂ to epoxides (CCE) reactions. The malononitrile (MNH) group was regioselectively anchored on the C-6 position of the anhydrous glucose unit of the cellulose backbone (Cell-MNH), and subsequently deprotonated with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) yielding catalyst Cell-[MN][DBUH], which exhibited excellent catalytic activity in CCE reactions of styrene oxide under conditions of 120 °C, 1.0 MPa, and 8 h, with catalyst loading of 1.5 mol%, achieving a yield of 93% and a selectivity of 94%. A bifunctional catalytic mechanism was proposed in which the carbanion attacked the CO₂ and the 1,8-diazabicyclo[5.4.0]undec-7-enium (DBUH) as an H-bond donor activated the epoxide. NMR titration experiments validated the role of DBUH in coordinating to epoxide through hydrogen bonding, and 13 C NMR spectra revealed a carbonate intermediate derived from malononitrile carbanion and CO 2 . The catalyst was homogeneous at 120 °C during the reaction but precipitated upon cooling due to the inter-chain attractions of the positive and negative ions, allowing easy filtration and recycling. The catalyst maintained robust by yields of 82%–97% and selectivity of 92%–99% through five recycles. This lignocellulose-based ion pair organocatalyst enables efficient homogeneous catalysis with heterogeneous recovery, offering potential design and broad applicability.