Enantioselective Resolution Copolymerization of Racemic 2,3-Disubstituted cis-Epoxides with CO2 Mediated by Binuclear Cobalt(III) Catalyst

Main observation and conclusion Enantioselective resolution copolymerization of racemic internal epoxides with carbon dioxide (CO2) is a challenging issue because of their poor reactivity and complicated regio/stereoselectivity. Herein, we describe the first enantioselective resolution copolymerization of racemic aromatic 2,3-disubstituted cis-epoxides and CO2 using enantiopure dinuclear cobalt(III) complexes as catalyst under mild conditions, affording the corresponding polycarbonates with completely alternating structure and good enantioselectivity in the range of 70% to 97% ee. The isotactic polycarbonate from beta-methylstyrene oxide is a typical semicrystalline material, possessing a melting point of 241 C-o; while other isotactic-enriched copolymers from 2,3-disubstituted cis-epoxides bearing a substitute group on the aromatic ring are amorphous, having glass transition temperatures between 86 C-o and 124 C-o. Interestingly, the copolymer selectivity is correlated well with the Hammett substituent constant, and the highest polymer selectivity of 98% was found in the system using the epoxides bearing an electron-donating group on the benzene ring. [GRAPHICS] .

Automated summary

The enantioselective resolution copolymerization of racemic aromatic 2,3-disubstituted cis-epoxides and CO2 using enantiopure dinuclear cobalt(III) complexes as catalyst yielded polycarbonates with completely alternating structure and good enantioselectivity in the range of 70% to 97% ee. The copolymer selectivity is correlated well with the Hammett substituent constant, and the highest polymer selectivity of 98% was found in the system using the epoxides bearing an electron-donating group on the benzene ring.