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(TFPPBr_8) [H2TFPPBr_8, β-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(TFPPBr_8)Cl occurs through a radical-chain mechanism in which the radicals are generated by oxidation and reduction of alkyl hydroperoxides.
© 1994 American Association for the Advancement of Science. Received 28 December 1993; accepted 1 April 1994. We thank J. E. Lyons, P. E. Ellis, W. P. Schaefer, E. R. Birnbaum, and T. Takeuchi for helpful discussions. Supported by the U.S. Department of Energy, Morgantown Energy Technology Center, and the Sun Company. M.W.G. acknowledges an NIH postdoctoral fellowship.