Highly active Mn(III) meso-tetrakis(2,3-dichlorophenyl)porphyrin catalysts for the cycloaddition of CO2 with epoxides

Abstract A new free-base porphyrin, meso -tetrakis(2,3-dichlorophenyl)porphyrin, (H 2 T2,3-DCPP) and the respective manganese(III) complexes [Mn III (T2,3-DCPP)X] with six different axial ligands (NO 3 − , AcO − , IO 3 − , Br − , Cl − , HO − ) were synthesized and characterized. The molecular structure of [Mn III (T2,3-DCPP)Cl] was also confirmed by single crystal X-ray diffraction. The complexes, when combined with tetrabutylammonium halides as nucleophile source cocatalysts, were highly active catalysts in the solvent-free cycloaddition reactions of carbon dioxide with styrene oxide, selectively producing the respective cyclic carbonate. The complex [Mn III (T2,3-DCPP)Cl] was used to evaluate a series of parameters in the system and efficiently catalyzed the transformation of various epoxides using TBAI as cocatalyst, 30 bar of CO 2 at 100 °C, producing nearly quantitative conversions in most of the cases. Remarkable TON values of 500,000 and 434,780 were achieved, respectively, for propylene oxide and styrene oxide using [Mn III (T2,3-DCPP)Cl] as catalyst. Recycling experiments were conducted and the system maintains high conversion rates after eight runs, which indicated a high stability and reusability of the catalyst.