Novel functionalized guanidinium ionic liquids: Efficient acid-base bifunctional catalysts for CO₂ fixation with epoxides

A series of functional guanidinium-based ionic liquids (FGBILs) that contain both Lewis acid and basic sites was prepared by a simple method, and used as catalysts for the synthesis of cyclic carbonates through the cycloaddition of CO₂ to epoxides in the absence of co-catalyst and solvent. Propylene oxide conversion was near completion at 130 C and 2.5 MPa in 2 h when [TMGC₂H₄NH₂]Br was used as catalyst. The effects of functional groups and counter anions on catalytic performance were investigated. The synergistic effect of polarization by hydrogen bonding and the nucleophilic attack by bromide anion account for the facile ring-opening of epoxide. Furthermore, the protocol is applicable to a variety of terminal epoxides, producing the corresponding cyclic carbonates in high yield and selectivity. It is envisaged that the metal- and solvent-free process using a single catalyst has high potential for large-scale fixation of CO₂.