J. zyxwvutsrq Am. Chem. SOC. zyxwvu 1986, 108, zyxwvu 2603-2608 2603 Spectroscopic Studies of Phenyl Iron( IV) Porphyrin Complexes and Their Conversion into Iron( zyxw 11) N-Phenylporphyrins Alan L. Balch* and Mark W. Renner Contribution from the Department of Chemistry, University zyxw of California, Davis, California 9561 6. Received September zyxwv 3, 1985 Abstract: Oxidation of phenyl iron(II1) tetraarylporphyrin complexes with bromine in chloroform at -60 OC produces deep-red solutions whose zyxwvutsr IH and 2H NMR spectra indicate that they are the corresponding iron(1V) complexes. Characteristic IH NMR resonances include pyrrole protons at -60 to -70 ppm, iron phenyl resonances at ca. -300 ppm for the ortho protons, -50 to -75 ppm for the meta protons, ca. -100 ppm for the para protons, and ca. zyxwv +110 ppm for the para-methyl protons. The magnetic susceptibility of the iron(1V) species is 2.6 & 0.4 pLB. These aryl iron(1V) complexes are thermally unstable. When warmed, the aryl iron(1V) complex undergoes a clean reductive elimination to form the iron(I1) complex of the N-arylporphyrin. The electronic structure of the S = 1 iron(1V) complexes is consistent with an orbital occupany dx~*dxz1dyz1 with r-spin density transferred to the porphyrin and the axial phenyl group. The chemical characterization of the a-bonded phenyl iron(II1) porphyrin complexes 1 have received considerable attention. These low-spin complexes have been isolated from the reaction of phenylmagnesium bromide or phenyllithium with haloiron(II1) and have been subject to extensive characterization including both ‘H N M R spectroscopy” and X-ray crystallography.6 The destruction of hemoglobin and myoglobin by arylhydrazines in the presence of dioxygen leads to the precipitation of Heinz bodies and the formation of green pigments which have been identified as N - p h e n ~ l h e m e . ~ ~ Phenyl iron(II1) porphyrins have been demonstrated as intermediates in this process by both ‘H NMR * and by isolation, crystallization, and X-ray crystallography of phenylmyoglobin.12 Studies on models have demonstrated that the transfer of the phenyl group from iron to nitrogen occurs under oxidizing condition^.'^-'^ Electrochemical and optical spectroscopic studies have suggested that this process occurs via several intermediates as shown in Scheme I. This article is concerned with the first two steps in this scheme. Previous work involving spectroscopic studies of the iron( 11) and iron(II1) complexes of the N-substituted porphyrins has ap- peared.I6J7 Here we are particularly concerned with the direct (1) Clarke, D. A.; Grigg, R.; Johnson, A. W. J. Chem. SOC., Chem. Com- (2) Clarke, D. A.; Dolphin, D.; Grigg, R.; Johnson, A. W.; Pinnock, H. (3) Ogoshi, H.; Sugimoto, H.; Yoshida, 2.-I.; Kobayashi, H.; Sakai, H.; (4) Cocolios, P.; Laviron, E.; Guilard, R. J. Organomet. Chem. 1982, 228, (5) Cocolios, P.; Lagrange, G.; Guilard, R. J. Organomet. Chem. 1983, (6) Doppelt, P. Inorg. Chem. 1984, 23, 4009. (7) Saito, S.; Hano, H. A. Proc. Natl. Acad. Sci. U.S.A. 1981, 78, 5508. (8) Ortiz de Montellano, P. R.; Kunze, K. L. J. Am. Chem. Soc. 1981,103, (9) Augusto, 0.; Kunze, K. L.; Ortiz de Montellano, P. R. J. Biol. Chem. (10) Kunze, K. L.; Oritz de Montellano, P. R. J. Am. Chem. SOC. 1983, (1 1) Ortiz de Montellano, P. R.; Kerr, D. E. Biochemistry 1985, 24, 1147. (12) Ringe, D.; Petsko, G. A.; Kerr, D. 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One-electron oxidation of iron(II1) porphyrin halide complexes generally yields products which are now ac- knowledged to be iron(II1) complexes of oxidized porphyrin radicals.ls-26 Recently, however, the presence of the ( Fe’V0)2+ unit in the enzymatic intermediates, horseradish peroxidase compounds I and 11, has become established through comparitive studies on the actual enzyme intermediates and on synthetically prepared model compound^.^^-^^ The oxo ligand is particularly significant in stabilizing the high formal iron oxidation state, and the available evidence on the electronic structure, both from e~periment~~-~~ and the~ry,~~,~’ indicates that the unpaired electrons in these S = 1 species are localized on the Fe=O unit. The electronic distribution is altered when that oxo function is not present. 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