Rigid-Flexible Binuclear Catalysts: Boosting Activity for Copolymerization of CO2 and Propylene Oxide

Abstract

Inspired by natural enzymes, synergy is widely utilized in small molecule recognition and transformation, but has not been fully explored in polymer synthesis. Herein, we present an enzyme-mimicking catalyst design strategy for constructing rigid-flexible binuclear catalysts (RFBCs), aiming to boost the copolymerization of CO₂ and propylene oxide (PO). The key design strategy of RFBCs is to boost intramolecular synergy by spatial proximity of active sites imposed by rigid skeleton, while a flexible linker affords dynamic interactions of active centers. The optimal catalyst Nap-Al₂, featured with rigid naphthalene skeleton grafting two adjacent aluminum porphyrins through soft alkyl chains, exhibits outstanding catalytic performance (5000 h^–1) outperforming the previously reported polymeric catalysts (3100 h^–1) under similar conditions. Moreover, Nap-Al₂ exhibits great thermal stability at high temperatures up to 140 °C. A comprehensive catalytic cycle based on dynamic synergy has been proposed, taking into account the key intermediates involved in the copolymerization of CO₂/PO. Overall, we present that the construction of RFBCs for designing enzyme-mimicking catalysts is not only suitable for the ROCOP of CO₂/PO but also conducive to future investigation for related polymerization processes, such as the ring-opening of lactones.