Oxo-ferryl intermediate

In the field of enzyme catalysis, heme-proteins such as cytochrome P450, for example, exhibit both types of 0-0 bond cleavages in organic hydroperoxides and peroxy acids (178). Heterolytic cleavage of HOOH/ROOH yields H20 or the corresponding alcohol, ROH and a ferryl-oxo intermediate (Scheme 4). Homolytic 0-0 bond cleavage results in the formation of a hydroxyl (HO ) or an alkoxyl (RO ) radical and an iron-bound hydroxyl radical. 

The ring expansion of penicillin N to desacetoxycephalosporin is interesting as well. In spite of intensive efforts, this biosynthesis is stiU not completely clear. On the basis of substrate studies and kinetic investigations, it is assumed, that the chemistry of isopenicUlin N-synthase and expandase are alike and that the ring expansion also proceeds via a ferryl-oxo-intermediate, [41] and that a radical mechanism is involved as well. [42]... 

Despite the great variety of chemical transformations catalyzed by cytochromes P450, the vast majority of them are imdoubtedly driven by Compoimd I. This ferryl-oxo intermediate with a 7C-cation radical delocalized on the porphyrin is a very reactive species. All attempts to observe this species in a P450 system using atmospheric dioxygen have so far failed. However, important spectroscopic characterization and reactivity measirrements have been obtained by using the... 

While it is impossible to review individual metal-oxo complexes here, one recent dramatic development, discovery of ferryl(IV) nonheme complexes,57 58 deserves to be mentioned. Iron(IV)-oxo intermediates were known in heme chemistry for quite some time, but ferryl(IV) in nonheme systems became readily available and well characterized only very recently, when the X-ray structure of the Ferv=0 complex with tetramethylcyclam was determined,139 and several similar complexes were identified spectroscopically and crystallographically (Figure 4.36).57,58... 

EXAFS analysis of a peroxide compound of beef heart cytochrome c oxidase has also revealed the presence of a short Fe=0 bond with a bond length of 1.71 A [ 157]. A catalytic role for the ferryl-oxo species of cytochrome c oxidase has been postulated [158-161]. In this case, the prosthetic group is no longer protoporphyrin IX, but is instead heme a [162]. The observation of an Fe=0 bond for this intermediate of cytochrome oxidase further illustrates the generality of the short, 1.65 A, Fe =0 bond for high-valent oxo-iron states (Table 2). 

Oxidation of benzyl alcohol catalysed by chloroperoxidase exhibits a very high prochiral selectivity involving only the cleavage of the pro-S C-H bond. The reaction mechanism involved the transfer of a hydrogen atom to the ferryl oxygen of the iron-oxo complex. An a-hydroxy-carbon radical and the iron-hydroxy complex P-Fe -OH form. They may lead to the hydrated benzaldehyde or stepwise with the formation of the intermediate a-hydroxy cation. 

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