Oxygenation of saturated and unsaturated hydrocarbons with sodium periodate catalyzed by manganese(III) tetra-arylporphyrins, to study the axial ligation of imidazole

Competitive oxygenation of cyclooctene and tetralin with sodium periodate catalyzed by Mn(III)(TPP)OAc, TPP = meso-tetraphenylporphyrin; Mn(III) (TNP)OAc, TNP = meso-tetrakis(1-naphthyl) porphyrin; Mn(III) (TMP)OAc, TMP = meso-tetrakis(2,4,6-trimethyl-phenyl)porphyrin; Mn(III) (TDCPP)OAc, TDCPP = meso-tetrakis(2,6-dichlorophenyl) porphyrin, and Mn(III) (TPNMe2-TFPP)OAc, TPNMe2- TFPP = meso-tetrakis(para-NMe2-tetrafluorophenyl)porphyrin, was carried out in the presence or absence of imidazole. This study showed that, in the absence of imidazole, selectivity for epoxide formation was high with electron-rich catalysts such as Mn(TPP)OAc, Mn(TNP)OAc and Mn(TMP)OAc, but low with electron-deficient catalysts such as Mn(TDCPP)OAc and Mn(TPNMe2-TFPP)OAc. Presumably, not only the axial ligation of imidazole to the four-coordinate Mn(III)-center, but also the steric and electronic influences of aryl-substituents on the porphyrin periphery affect the selectivity of the catalytic oxidation reaction.