Mn^III Porphyrins: Catalytic Coupling of Epoxides with CO₂ under Mild Conditions and Mechanistic Considerations

Abstract

Abstract A series of 5,10,15,20‐tetrakis(2,3‐dichlorophenyl)porphyrinate complexes of manganese(III) [Mn III (T2,3DCPP)X] with six different axial ligands (X=NO 3 − , AcO − , IO 3 − , Br − , Cl − , HO − ) were investigated as catalysts in the cycloaddition reactions of CO 2 and styrene oxide (SO), under mild conditions, i. e., atmospheric pressure and 60 °C. [Mn III T(2,3DCPP)IO 3 ] showed the best catalytic performance, selectively producing the respective cyclic carbonate from diverse epoxides using tetrabutylammonium bromide as a nucleophile source. Mechanistic considerations were inferred from electronic spectra and spectrophotometric titrations, showing that there are a series of equilibriums involved in the formation of the catalytic active species. Stability constants for the proposed equilibrium models were determined using SQUAD software. A catalytic cycle has been proposed based on those observations.