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.