Green Synthesis of Cyclic Carbonates from Epoxides and CO<inf>2</inf> Using Transition Metal Substituted Polyoxometalate-PDDA Hybrid Catalysts

Polyoxometalates can be tuned for specific catalytic property by substituting transition metal ions. We report the synthesis of hybrid materials of Cu2+, Co2+ and Ni2+ substituted phosphotungstates and poly(diallyldimethylammonium) chloride polymer (PDDA) for CO2 fixation. The in situ generated transition metal substituted polyoxometalates (TMS-POMs) are analyzed by FTIR, powder XRD, 31P NMR and SEM techniques. The hybrid TMS-POM materials are found to be good catalysts for converting epoxides to cyclic carbonates. Among these, PDDA-PWCo is the most efficient catalyst for cycloaddition of CO2 under solvent-free conditions at room temperature in shortest reaction time. Only 0.2 mol% of PDDA-PWCo is enough to deliver 100% conversion and selectivity to cyclic carbonates. This catalytic approach is employed for conversion of other cyclic, acyclic, and aromatic epoxides without using column purifications. Overall, the method of obtaining cyclic carbonates under green conditions using TMS-POMs-PDDA hybrid materials appears suitable for industrial applications. Graphical Abstract: [Figure not available: see fulltext.].