Dicationic Porous Poly(Ionic Liquid)s with Hydrogen Bond Donors for Efficient Catalytic Conversion of CO2 under Mild Conditions.

Abstract

The formation of cyclic carbonates by coupling CO2 with epoxides offers a practical way of upgrading the surplus CO2 that has accumulated in the atmosphere, and thus helps to mitigate global warming. Because CO2 is intrinsically robust thermodynamically and sluggish kinetically, however, this transformation usually demands harsh conditions. Herein, a family of porous poly(ionic liquid)s denoted bAm-PIL-x (bAm = bis-amide) was constructed by radical copolymerization of an imidazolium-based ionic liquid monomer (tVIm-IL) and a quaternary ammonium-based ionic liquid monomer (tQAm-IL) in the presence of N,N'-methylenebisacrylamide as the cross-linker. These polymers combine a moderate specific surface area, pores spanning several size regimes, and a pronounced affinity for CO2, which makes them well suited to both capturing and converting CO2. Applied to the coupling of CO2 with epoxides under solvent-free, metal-free, and cocatalyst-free conditions, bAm-PIL-2 delivered excellent performance at a mild 80 °C and 1.0 bar. The catalyst was readily regenerated and recycled, and it accepted a wide range of epoxide substrates. Density functional theory (DFT) calculations together with in situ infrared spectroscopy were used to probe how the catalyst, the epoxides, and CO2 interact, and on this basis a plausible reaction mechanism for the cycloaddition is proposed. The present findings offer meaningful guidance for designing highly efficient catalysts for CO2 conversion.