High-valent metal-oxo complexes are vital, susceptive oxidants in enzymatic and synthetic catalytic oxidations. In the following investigation, three electron-withdrawing and one electron-donating porphyrin-manganese(III) complexes were synthesized and spectroscopically characterized. Employing the mild oxidant iodobenzene diacetate, manganese(IV)-oxo intermediates, i.e. [MnIV(Por)O] (Por = porphyrin ligand), were chemically generated. Moreover, the same [MnIV(Por)O] can be produced through a photochemical approach by visible light irradiation of the photo-labile manganese(III) chlorate precursors. The kinetics of oxygen atom transfer (OAT) reactions with organic substrates by these chemically-generated [MnIV(Por)O] were studied in CH3CN solutions. As a result, the apparent second-order rate constants for sulfoxidations by these active oxo species were on average a magnitude larger than the rates for epoxidation of the aryl alkenes. The comprehensive kinetic studies will be discussed, which will contribute insights into the transient oxidants in oxidation reactions where physical reactive intermediates are not observable.

Oxidation kinetics of porphyrin-manganese(IV)-oxo intermediates generated by chemical and photochemical methods

2019 Spring National Meeting

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