“Spring-loaded” mechanism for chemical fixation of carbon dioxide with epoxides

Carbon dioxide (CO2) fixation into valuable chemicals is of great significance, but a molecular level rational design of catalysts remains a challenge. Herein, based on the proposal of a "spring-loaded" mechanism, a family of phenolic hydroxyl imidazolium salt-based ionic liquids was designed for CO2 cycloaddition with epoxides into cyclic carbonates. The cation-anion interaction intensity was finely modulated through tailoring the position of the hydroxyl group. The moderate intensity endows superior nucleophilic leaving ability of the I− anion to provide strong C···I interaction for the rate-determining ring-opening step. The synergy of nucleophilic attack by the I− anion, electrophilic attack by a hydroxyl group, and corresponding stabilization effect enabled a high yield within a short reaction time, even at room temperature and atmospheric conditions. A volcano-type regulation of the spring-loaded mechanism was unraveled, revealing the crucial parameter in the designation of high-performing catalyst for CO2 transformation via cycloaddition.