Enantioselective Resolution Copolymerization of Racemic cis-Epoxides and Cyclic Anhydrides Mediated by Multichiral Bimetallic Chromium Complexes

Enantioselective resolution copolymerization of racemic epoxides is a powerful strategy for the production of optically active polymers with main-chain chirality and highly enantioenriched epoxides. However, a deep investigation on unsymmetrically disubstituted cis-epoxides for the preparation of chiral polymers is scanty because of their limited reactivity and complex regio- and stereo-selectivity. In this contribution, we report the highly enantioselective resolution copolymerization of racemic cis-disubstituted epoxides with cyclic anhydrides mediated by multichiral bimetallic chromium complexes. Up to 36 examples of cis-disubstituted epoxides, including conjugated alicyclic epoxides, aliphatic epoxides, aromatic epoxides, and ether-containing epoxides, were employed to the enantioselective copolymerization with cyclic anhydrides under mild conditions. Optically active polyesters with enantiomeric excess (ee) up to 96% were obtained, while unreacted enantiopure epoxides were isolated with up to 97% ee. The steric hindrance and electronic properties of the substituent groups in the epoxide monomers considerably affect the regioselectivity during the ring-opening process. The diverse structures of cis-disubstituted epoxides are beneficial for preparing various chiral copolymers with excellent functionality and tunable properties.