Popis: |
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) MnTPP(OAc) > MnTPPBr2(OAc) ⩾ MnTPPBr6(OAc) ≫ MnTPPBr8(OAc). The highest methyl phenyl sulfide conversion is 69% at room temperature. |