Formation of porphyrin ferryl (FeO2+) complexes through the addition of nitrogen bases to peroxo-bridged iron(III) porphyrins

Chin, Daeje; Balch, Alan L.; Mar, Gerd N. La

doi:10.1021/ja00524a051

Cited by 132 publications

(77 citation statements)

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“…This is most certainly due to the increased stability ofhigh-valent metals when bound to highly basic oxo ligands. The reactivity of the iron(IV)-oxo species generated electrochemically is very similar to that reported for the iron(IV)-oxo species produced chemically (25)(26)(27)(28). The decomposition of the iron(IV)-oxo porphyrin at temperatures above -50'C shows that it is more chemically reactive than the iron(III) porphyrin ir-cation radical, even though the redox potential of the latter is more positive.…”

Section: Discussionsupporting

confidence: 75%

“…An iron(IV) porphyrin ir-cation radical has been isolated and characterized in the reaction of m-chloroperoxybenzoic acid or iodosylbenzene with 2-Cl at low temperature (26). Oxygenation of iron(II) porphyrins at low temperature results in a tk-peroxo dimer species, which decomposes to a monomeric iron(IV)-oxo porphyrin species upon addition of imidazole (27). More recently it has been shown that the iron(III) porphyrin ir-cation radical could be converted to the iron(IV) porphyrin by axial substitution of two methoxide anions for two perchlorate anions (25).…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Stabilization of higher-valent states of iron porphyrin by hydroxide and methoxide ligands: electrochemical generation of iron(IV)-oxo porphyrins.

Lee¹,

Calderwood²,

Bruice³

1985

Proc. Natl. Acad. Sci. U.S.A.

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An electrochemical study of hydroxide-and methoxide-ligated iron(II) tetraphenylporphyrins possessing ortho-phenyl substituents that block ,L-oxo dimer formation has been carried out. Ligation by these strongly basic oxyanions promotes the formation of iron(IV)-oxo porphyrins upon one-electron oxidation. Further one-electron oxidation of the latter provides the iron(IV)-oxo porphyrin ir-cation radical. (6), Mossbauer (7), ESR (8), and electron nuclear double resonance (ENDOR) (9) spectral data, compound I has been assigned the structure of a low-spin oxo-ligated iron(IV) porphyrin ir-cation radical. This same entity is suggested to serve as the oxygen transfer agent formed at the active site of the cytochrome P-450 enzymes (10, 11). One-electron reduction of the ir-cation radical of compound I results in the formation of an iron(IV)-oxo species termed compound 11 (12). Interestingly, compounds I and II of the peroxidases exhibit almost identical redox potentials (13).Only a few well-characterized model analogs of compounds I and II exist. These iron(IV) porphyrins have all been generated chemically at low temperatures. Until now, an iron(IV)-oxo porphyrin species has not been generated electrochemically. In the cyclic voltammogram of simple iron porphyrins, anodic sweeps beyond the iron(II)/iron(III) couple yield two reversible one-electron oxidation waves (32). Originally it was proposed that the first wave pertained to the iron(III)/iron(IV) couple and the second wave was due to porphyrin 1r-cation radical formation (14,15). This was shown to be incorrect in a report (16) which demonstrated that the redox potential of the first oxidation was independent of the many axial ligands employed (16) and that the physical properties of the oxidized species were consistent with an iron(III) porphyrin ir-cation radical structure (17). The second wave was attributed to an iron(III) porphyrin dication.In the literature, there is no mention of electrochemical investigations involving HO-, CH30-, etc. ligated iron porphyrins. This does not of course indicate an oversight (17) but simply reflects the instability, due to ,u-oxo dimer formation, of oxo-ligated iron(III) porphyrins. The inability to electrochemically generate a compound I or compound II analog could be due to the importance of oxo ligation to the stabilization of high-valent iron porphyrin species. It is well established that metals in their higher-valent oxidation states are generally stabilized by oxo ligation (18). Using sterically hindered porphyrins that are capable of hydroxide ligation, we have now been able to observe the electrochemical generation ofiron(IV)-oxo porphyrin species. In addition, the similarity of the iron(IV)-oxo and the porphyrin ir-cation redox potentials provides a rationale for the redox potentials of compounds I and II of the peroxidases. In the present study we describe the electrochemistry of porphyrins 1 to 5 when ligated to Cl-, HO-, and CH30 and discuss these results as they relate to studies involving the chemical ge...

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Section: Discussionsupporting

confidence: 75%

Section: Discussionmentioning

confidence: 99%

Stabilization of higher-valent states of iron porphyrin by hydroxide and methoxide ligands: electrochemical generation of iron(IV)-oxo porphyrins.

Lee¹,

Calderwood²,

Bruice³

1985

Proc. Natl. Acad. Sci. U.S.A.

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“…The redox potential of 1 is significantly higher than those of the l-oxo dinuclear metalloporphyrins measured under the same conditions (E f (V vs Ag/ AgCl): 2, 0.38 [34] ; 3, 0.51 [34] ; 4, a -0.09 [29] ). On the other hand, it has been reported [44,45] that [(pc)Fe II ] is almost quantitatively oxidized by O 2 to 1 without the formation of partially reduced oxygen species such as H 2 O 2 . Indeed, our previous study on the electrochemical reduction of O 2 catalyzed by [(pc)Fe] adsorbed at an electrode surface revealed [33] that most of O 2 molecules (84%) are reduced by four electrons into H 2 O.…”

Section: Structural Analysis Of Polypyrrole Prepared By the O 2 -Oxidmentioning

confidence: 99%

Oxidative Polymerization of Pyrrole Promoted by Four-Electron Transfer to O2: Catalysis of O2-Oxidation byμ-Oxo Dinuclear Complexes with Macrocyclic Ligands

Oyaizu

Haryono

Shinoda

et al. 2001

Macromol. Chem. Phys.

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“…Fe(IV)-oxo intermediates containing neutral porphyrin rings have also been prepared (25a-c, 26, and 27) ( Figure 9), and were first observed in the decomposition of (η 1 :η 2 -peroxo)diiron intermediates [75,76]. More recently, electrochemical preparation of 27 has been achieved by the one-electron oxidation of the Fe(III)-OH precursor [77].…”

Section: Fe(iv)-oxo Intermediatesmentioning

confidence: 99%

Transition Metal Complexes and the Activation of Dioxygen

Yee

Tolman

2014

Metal Ions in Life Sciences

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In order to address how diverse metalloprotein active sites, in particular those containing iron and copper, guide O₂binding and activation processes to perform diverse functions, studies of synthetic models of the active sites have been performed. These studies have led to deep, fundamental chemical insights into how O₂coordinates to mono- and multinuclear Fe and Cu centers and is reduced to superoxo, peroxo, hydroperoxo, and, after O-O bond scission, oxo species relevant to proposed intermediates in catalysis. Recent advances in understanding the various factors that influence the course of O₂activation by Fe and Cu complexes are surveyed, with an emphasis on evaluating the structure, bonding, and reactivity of intermediates involved. The discussion is guided by an overarching mechanistic paradigm, with differences in detail due to the involvement of disparate metal ions, nuclearities, geometries, and supporting ligands providing a rich tapestry of reaction pathways by which O₂is activated at Fe and Cu sites.

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Formation of porphyrin ferryl (FeO2+) complexes through the addition of nitrogen bases to peroxo-bridged iron(III) porphyrins

Cited by 132 publications

References 0 publications

Stabilization of higher-valent states of iron porphyrin by hydroxide and methoxide ligands: electrochemical generation of iron(IV)-oxo porphyrins.

Stabilization of higher-valent states of iron porphyrin by hydroxide and methoxide ligands: electrochemical generation of iron(IV)-oxo porphyrins.

Oxidative Polymerization of Pyrrole Promoted by Four-Electron Transfer to O2: Catalysis of O2-Oxidation byμ-Oxo Dinuclear Complexes with Macrocyclic Ligands

Transition Metal Complexes and the Activation of Dioxygen

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