Efficient fixation of CO₂into carbonates by tertiary N-functionalized poly(ionic liquids): Experimental-theoretical investigation

The efficiency and versatility of catalysts in the multi-step reaction of carbonates with carbon dioxide (CO₂) as raw material are barely satisfactory. Herein, ternary copolymerized bifunctional poly(ionic liquid)s (TBPILs) rich in hydroxyls, halogen anions and tertiary N were fabricated via free radical copolymerization. Due to the ingenious modification of tertiary N in the polymeric framework to form multi-site activation with hydroxyls and halogen anions, the specific activity of TBPILs reached to 17.87 mmol_SCm^-2_catalh^-1in CO₂cycloaddition reaction. Meanwhile, for the transesterification reaction of cyclic carbonates with methanol, by the introduction of tertiary N, the yield of dimethyl carbonate increased from trace to 80.31 % in the absence of any solvent or co-catalyst. Density functional theory calculations, combined with electrostatic potential and average local ionization energy analyses confirmed the dual roles of tertiary N in the formation of carbonates by CO₂. This work provides an originality idea to design high-efficiency catalysts for CO₂insertion into carbonates, and study the effects of basic sites on CO₂conversion.