Oxoiron porphyrins

It was later discovered that the reactive intermediates in the iron porphyrin model systems were high-valent oxoiron porphyrin complexes. A green oxoiron(IV) porphyrin cation radical species (13) has been well characterized by various spectroscopic techniques, including visible spectroscopy, NMR, EPR, Mossbauer, and EXAFS (Figure 1.11) . It has recently been shown by Nam and Que that the oxygen-atom transfer from certain iodosylarenes is reversible with some iron porphyrins. For the case of 1,2-difluoro-4-iodobenzene both an oxoferryl species and an iodosyl-ferric species were observed to be in equilibrium . 

Although many high valent oxoiron porphyrins have been prepared there have been veiy few mechanistic studies of oxidations by these models for HRP compounds I and This can largely be attributed to the low stability of such species which has... 

Theoretical consideration of stereoselective epoxidation with oxoiron porphyrins has lead to the remarkable conclusion that oxygen is inserted into the iron-nitrogen bond and the alkene is coordinated in a perpendicular orientation with respect to the iron-oxygen bond [64]. 

Oxoiron(V) porphyrins—red in color—an isoelectronic form of oxoiron(IV) porphyrin cation radicals—green—have been proposed (references 55a-c), although the density functional theory calculations have indicated that there are no true oxoiron(V) porphyrins (references 55d-f). Further spectroscopic studies are necessary to confirm the existence of this intermediate. 

This hydroxylation-induced intramolecular migration, known as the NIH shift, was explained by the involvement of arene oxides formed by the attack of electrophilic oxoiron(V) porphyrin on the aromatic ring.753 Intermediate 98 was also suggested to be formed in hydroxylation by the Fenton and related reagents in aprotic media after initial oxidation with an oxoiron(V) complex followed by electron transfer.744 754... 

The prostnetic group of these enzymes contains an iron(III)porphyrin complex and the active oxidant can be formally regarded as a high-valent oxoiron(V)-... 

In order to explain their high activity and stability it was postulated that polyhalogenation of the porphyrin ring system not only stabilizes the latter towards oxidative destruction but also stabilizes the oxoiron intermediate with respect to p-oxo dimer formation. In principle, it should also be possible to design stable solid catalysts capable of mediating analogous selective oxidations in the liquid phase. 

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... 

Oxoiron(IV) tefraphenylchlorin complexes have been prepared as the first models of a reaction intermediate in the catalytic cycle of cytochrome d Optical absorption spectra show a characteristic red-shified band at 630 nm as observed in the oxoferryl intermediate of cytochrome d, and the proton NMR spectra of the N-Melm complex exhibit very small hyperfine shifts of the pyrrole protons, as is true for oxoferryl porphyrin complexes. The pyrroline protons of the saturated pyrrole ring show unusual splitting into upheld and downfield resonances. The N-Melm complex also shows normal Fe =0 stretching frequencies as compared to the corresponding oxoferryl porphyrin complexes. And finally, for iron porphycenes, both peroxo and ferryl intermediates have been detected by H NMR spectroscopy during the oxygenation of the Fe complexes. ... 

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