Asymmetric cycloaddition of CO2 and an epoxide using recyclable bifunctional polymeric Co(iii) salen complexes under mild conditions

Abstract

Bifunctional polymeric Co(III) salen complexes 1a–g derived from (1R,2R)-(−)-1,2-diaminocyclohexane and a triazine–piperazine core were synthesized and screened for the asymmetric cycloaddition reaction of CO₂ and an epoxide under mild conditions. A moderate K_rel value of 11.2 for the product propylene carbonate (ee = 74%) was obtained with catalyst 1e which does not require any external base as the co-catalyst. The polymeric Co(III)–CCl₃COO (1e) was efficiently recycled 10 times without any significant loss in activity under the present reaction conditions.