Iron porphyrins chemical oxidation

Despite uncertainties concerning the site of the first one-electron oxidation of Fe P, the second oxidation is thought to form a ferry 1 species, 0 = Fe P, which can oxidize or hydroxylate various organic compounds. In parallel with this chemistry of iron porphyrins, the oxidation of ruthenium and osmium porphyrins was studied by radiation chemical methods. 

The reduction ofsec-, and /-butyl bromide, of tnins-1,2-dibromocyclohexane and other vicinal dibromides by low oxidation state iron porphyrins has been used as a mechanistic probe for investigating specific details of electron transfer I .v. 5n2 mechanisms, redox catalysis v.v chemical catalysis and inner sphere v.v outer sphere electron transfer processes7 The reaction of reduced iron porphyrins with alkyl-containing supporting electrolytes used in electrochemistry has also been observed, in which the electrolyte (tetraalkyl ammonium ions) can act as the source of the R group in electrogenerated Fe(Por)R. ... 

Oxo-metal species participate in a wide range of biological and chemical oxidation reactions. Representative oxidizing enzyme, cytochrome P-450, which carries iron(III)-porphyrin complex as its active site, catalyzes various O-atom transfer reactions such as epoxidation, hydroxy-lation of C-H bond, and oxidation of sulfides. These reactions have been proven to proceed through cationic oxoiron(IV)-porphyrin species, which are generated by the oxidation of Fe(III) complex with molecular oxygen. This conversion from Fe(III) to 0=Fe(IV) species is a... 

Iron porphyrin complexes with axial (7-alkyl and (7-aryl groups have been prepared and fully characterized by several groups (17,18). Addition of a chemical oxidant to (19, 20), or electrochemical oxidation of (21), the low-spin iron(III)-alkyl (-aryl) porphyrins results in transient formation of an iron(IV) (7-alkyl (a-aryl) complex that undergoes reductive elimination to give the iron(II) N-substituted product as shown in Scheme 2. The iron(IV) intermediate has been directly observed by low temperature lH NMR spectroscopy (22) and spectroelectrochemistry (21). 

Oxidation of ]V-MeTTPFenCl (46, 52). Catalytic alkene oxidation by iron N-alkylporphyrins requires that the modified heme center can form an active oxidant, presumably at the HRP compound I level of oxidation. To show that iron N-alkyl porphyrins could form highly oxidized complexes, these reactive species were generated by chemical oxidation and examined by NMR spectroscopy. Reaction of the (N-MeTTP)FenCl with chlorine or bromine at low temperatures results in formation of the corresponding iron(III)-halide complex. Addition of ethyl- or t-butyl-hydroperoxide, or iodosylbenzene, to a solution of N-MeTTPFenCl at low temperatures has no effect on the NMR spectrum. However, addition of m-chloroperoxybenzoic acid (m-CPBA) results in the formation of iron(III) and iron(IV) products as well as porphyrin radical compounds that retain the N-substituent. 

The iron porphyrins and related compounds constitute an extremely important class of coordination complex due to their chemical behaviour and involvement in a number of vital biological systems. Over recent years a vast amount of work on them has been published. Chapter 21.1 deals with the general coordination chemistry of metal porphyrins, hydroporphyrins, azaporphyrins, phthalocyanines, corroles, and corrins. Low oxidation state iron porphyrin complexes are discussed in Section 44.1.4.5 and those containing nitric oxide in Section 44.1.4.7, while a later section in this chapter (44.2.9.2) is mainly concerned with iron(III) and higher oxidation state porphyrin complexes. Inevitably however, a considerable amount of information on iron(II) complexes is contained in that section as well as in Chapter 21.1. Therefore in order to prevent excessive duplication, the present section is restricted to highlighting some of the more important aspects of the coordination chemistry of the iron(II) porphyrins while the related unusually stable phthalocyanine complexes are discussed in the previous section. 

For the insertion of the iron ion into the porphyrin a variety of general procednres have been described and reviewed. In most cases, these methods lead to the formation of Fe complexes, which are then nsed to prepare Fe Fe, Fe, and Fe porphyrins. The most commonly employed methods for synthesizing Fe° porphyrins are described below. The preparation of the Fe° and Fe complexes from the iron(III) porphyrins by chemical or electrochemical means and the oxidized iron porphyrins (Fe° itt-cation radicals, Fe, Fe 7T-cation radicals, and Fe ) by chemically or electrochemically oxidizing the iron(III) porphyrins is described in more detail in the sections on the corresponding iron porphyrins below. Whereas Fe porphyrins can be photochemically rednced to Fe porphyrins, only a few examples of photooxidations of the iron center are known, which include laser photolysis of the co-condensation products of PFe at 15 K to produce... 

The oxidation of Fe(III)TMP(wi-chlorobenzoate) with 2 equivalents of mCPBA in toluene has been reported by Groves and Watanabe to give iron(III) porphyrin W-oxide (23, (89) Fig. 9). The reaction proceeded quantitatively only at low concentrations of the heme. The presence of an acid such as benzoic acid drastically depressed the formation of 23. The EPR spectrum, H NMR chemical shifts, and solution magnetic moment (5.4 /Zg) indicated that 23 was a high-spin ferric complex. Inspection of the reaction mechanism indicated that the reaction proceeded via the formation of the acylperoxo-iron(III) precursor 16, similar to the reaction carried out in dichloromethane. 

J. E. Bercaw, and H.B. Gray (1995). On the mechanism of catalytic alkene oxidation by molecular oxygen and halogenated iron porphyrins, J. Mol. Catal. A Chemical 104, LI 19-L122. 

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