The Al(iii)-based polydentate chelate complex catalyzed cycloaddition of carbon dioxide and epoxides: synthetic optimization and mechanistic study

Abstract

Aimed at greenhouse gas CO₂ high value-added utilization, a N,N′-(propane-1,3-diyl)dipicolinamide (PPPA) supported Al(III) metal–organic polydentate chelate complex (Al-PPPA) was designed and used to efficiently catalyze CO₂ to cyclic carbonates. The substrate conversion and product selectivity were more than 95% and 98%, respectively, at 120 °C and 2 MPa CO₂ without the presence of a co-catalyst. After 5 times of recycling, the substrate conversion was no less than 88%, which indicated the excellent thermal stability and reusability of the catalyst. Simultaneously, the catalyst showed a widely universal range of substrates including olefin chains, phenyl chains, internal epoxides and fluorine-containing epoxides. Furthermore, the plausible mechanism of the CO₂ cycloaddition reaction was explored by employing in situ IR technology. The ring opening of PO, CO₂ activation and the formation of the final products were examined visually. This work supplies a new route for the theoretical and experimental exploration of new catalyst design and process understanding for efficient greenhouse gas reuse.