Identifying the True Catalyst: A Mn(II) Salt versus Mn(II) Complexes in Epoxidation with m-Chloroperbenzoic Acid

The oxidant meta-chloroperbenzoic acid (m-CPBA) is used widely for the epoxidation of alkenes, yet its efficiency is often limited under ambient conditions. In this study we investigate the catalytic activity of a Mn(II) salt and mononuclear Mn(II) complexes, two of which are reported here for the first time, in the epoxidation of alkenes with m-CPBA under ambient conditions. Time-resolved Raman spectroscopy was used to monitor substrate conversion, oxidant consumption, and product formation. The data reveal that simple Mn(II) salts exhibit significantly higher catalytic activity than Mn(II) complexes, indicating that ligand coordination inhibits the reactivity of the manganese centre. The catalytic efficiency of Mn(II) perchlorate was particularly notable, achieving near-complete oxidation of styrene within minutes under mild conditions. Furthermore, epoxidation of a range of alkenes demonstrated that Mn(II) salts provide broad substrate scope and high selectivity. These findings suggest that simple Mn(II) salts can serve as highly efficient and cost-effective catalysts in alkene epoxidations with m-CPBA.