Abstract
The oxidation of olefins and organic sulfides with tetra-n-butylammonium periodate (TBAP) in the presence of a Mn(III) complex from a series of partially and fully brominated meso-tetraphenylporphyrins, MnTPPBrx(OAc) (x=0, 2, 4, 6 and 8) has been studied in a comparative manner. With the exception of MnTPPBr2(OAc), the half-wave potential for the Mn(III)/Mn(II) metal-centered process was gradually shifted to higher values on going from MnTPP(OAc) to MnTPPBr8(OAc). However, a complex order has been observed for the catalytic activity of the complexes; while the stability of the Mn–porphyrins towards oxidative degradation under the reaction conditions decreases in the order MnTPPBr8(OAc)>MnTPP(OAc)>MnTPPBr6(OAc)>MnTPPBr2(OAc)>MnTPPBr4(OAc), their catalytic activity has been found to follow the order MnTPPBr8(OAc)≪MnTPP(OAc)⩽MnTPPBr6(OAc)<MnTPPBr2(OAc)⩽MnTPPBr4(OAc). The maximum conversion (42%) was obtained in the case of MnTPPBr4(OAc) and the minimum conversion (14%) is related to MnTPPBr8(OAc). Oxidation of methyl phenyl sulfide with TBAP in a 1:1 molar ratio leads to the following pattern of catalytic activity for the used Mn–porphyrins: MnTPPBr4(OAc)>MnTPP(OAc)>MnTPPBr2(OAc)⩾MnTPPBr6(OAc)≫MnTPPBr8(OAc). The highest methyl phenyl sulfide conversion is 69% at room temperature.
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