Insight into the reversible behavior of Lewis–Brønsted basic poly(ionic liquid)s in one-pot two-step chemical fixation of CO2 to linear carbonates

Abstract

The multi-step reaction of CO₂ over basic catalysts significantly improves the diversity of products, vividly embodying the ability of green chemistry to turn waste into treasure. However, under a Lewis acidic CO₂ atmosphere, the activity maintenance of the multi-step reaction puts forward higher requirements for the reversible regeneration ability of the basic catalysts. Novel Lewis–Brønsted binary basic poly(ionic liquid)s (LB-PILs) were successfully developed through a radical copolymerization followed by ion-exchange strategy, and were applied to the two-step synthesis of dimethyl carbonate (DMC) by coupling CO₂ cycloaddition and CH₃OH transesterification without any cocatalyst. Relying on the activation of CO₂ by Lewis basic tertiary N and the thermal recovery of nucleophilic HCO₃⁻ to stronger Brønsted basic OH⁻ with the help of temperature control in CH₃OH transesterification, the LB-PILs presented high activity, stable repeatability and linear carbonate universality. In situ IR analysis and Knoevenagel condensation, combined with theoretical calculations, provided reliable support for the ingenious incorporation of reversible regeneration of basic catalysts in a Lewis acidic CO₂ atmosphere and multi-step coupling reaction process of CO₂.