A biomimetic oxidation catalyzed by manganese(III) porphyrins and iodobenzene diacetate: Synthetic and mechanistic investigations

Abstract

With iodobenzene diacetate [PhI(OAc)2] as the oxygen source, manganese(III) porphyrin complexes exhibit remarkable catalytic activity toward the selective oxidation of alkenes and activated hydrocarbons. Conspicuous is the fact that the readily soluble PhI(OAc)2 in the presence of a small amount of water is more efficient than the commonly used PhIO and other oxygen sources under same catalytic conditions. High selectivity for epoxides and excellent catalytic efficiency with up to 10,000 TON have been achieved in alkene epoxidations. It was found that the reactivity of manganese(III) porphyrin catalysts was greatly affected by axial ligand and the weakly binding perchlorate gave the highest catalytic activity in the epoxidation of alkenes. A manganese(IV)-oxo porphyrin was detected in the reaction of the manganese(III) porphyrin and PhI(OAc)2. However, our catalytic competition and Hammett studies have suggested that the more reactive manganese(V)-oxo intermediate was favored as the premier active oxidant, even it is too short-lived to be produced in detectable concentrations.