Intramolecular synergistic catalysis for asymmetric alternating copolymerization of CO2 and meso-epoxides

Asymmetric alternating copolymerization of meso-epoxides and carbon dioxide (CO2) is an efficient route to produce isotactic polycarbonates with main-chain chirality involving two contiguous stereogenic centers. Based on multi-chiral induction and bimetallic synergistic catalysis, herein, we design novel binaphthol-linked dinuclear aluminum complexes bearing quaternary ammonium salts anchored on the ligand with multiple chiralities for asymmetric copolymerization of CO2 and meso-epoxides, affording the completely alternating polycarbonates with up to 99% enantioselectivity. Also, they are discovered to be highly active and enantioselective in catalyzing alternating copolymerization of phthalic anhydride and meso-epoxides in a controlled manner. The linked-chain length and steric hindrance at the para-position on the phenolate moieties of the ligand have significant effects on both activity and enantioselectivity. Notably, the bifunctional, multichiral complexes prove to be highly enantioselective and selective even at a low catalyst loading of 20 ppm, indicating an intramolecular synergistic effect between the tethered quaternary ammonium salts and the metallic ions.

Automated summary

This study demonstrates the asymmetric alternating copolymerization of CO2 and meso-epoxides to produce isotactic polycarbonates with main-chain chirality. The designed binaphthol-linked dinuclear aluminum complexes exhibit high enantioselectivity and activity in catalyzing the copolymerization. The length of the linked chains and steric hindrance on the ligand's phenolate moieties significantly affect the catalyst's performance.