Mechanism of Catalytic Oxygenation of Alkanes by Halogenated Iron Porphyrins

Halogenation of an iron porphyrin causes severe saddling of the macrocyclic structure and a large positive shift in the iron(III)/(II) redox couple. Although pre-halogenated iron(II) porphyrins such as Fe(TFPPBr8) [H2TFPPBr8, beta-octabromo-tetrakis(pentafluorophenyl)-porphyrin] are relatively resistant to autoxidation, they rapidly reduce alkyl hydroperoxides. These and related reactivity studies suggest that catalysis of alkane oxygenation by Fe(TFPPBr8)Cl occurs through a radical-chain mechanism in which the radicals are generated by oxidation and reduction of alkyl hydroperoxides.