High-valent metal-oxo complex

Two fundamentally different proposals for the mechanism of oxygen-atom transfer from high-valent metal oxo complexes have been considered. One proposal invokes substrate attack at both the metal and oxo centers to generate an oxametallacycle intermediate (3, Fig. 2). Such a mechanism was first advanced... 

Hydride Reduction of High-Valent Metal-Oxo Complexes by NADH Analogues... 

Fig ure 13.3 Biomimetic oxidation of organic compounds mediated by high-valent metal-oxo complexes. 

Makris TM, von Koenig K, Schlichting I, Sligar, SG (2006) The status of high-valent metal oxo complexes in the P450 cytochromes. Journal of Inorganic Biochemistry 100 507-518... 

The C—H bond can be activated by a metal complex, particularly when the complex plays the role of catalyst or photocatalyst. The reactions of hydrocarbons with metal complexes occur at low temperatures and can be selective. There are different pathways for C—H bond activation (i) by low-valence metal complexes, (ii) by high-valent metal-oxo compounds, (iii) by molecular oxygen and oxygen atom donors, (iv) by biological oxidation, or (v) by photocatalytic enhancement (21). 

J. Bernadou, A. Fabiano, A. Robert, B. Meunier, Redox tautomerism in high-valent metal-oxo-aquo complexes.Origin of the oxygen atom in epoxidation reactions catalyzed by water-soluble metalloporphyrins,/. Am. Chem. Soc. 116 (1994) 9375. 

Metal-peroxo intermediates of different structures were often implicated in the catalytic cycles of oxidative enzymes (see Figures 4.32 1.35 for representative examples). In most cases, however, these peroxo complexes are incompetent oxidants for native substrates. Instead, they undergo further reactions (usually, 0-0 bond cleavage that generates high-valent metal-oxo species) yielding more reactive, kinetically competent oxidants. Nevertheless, some peroxides can react with substrates in both enzymatic and synthetic systems. 

In the course of evolution. Nature has developed ways to mediate these oxidation processes precisely when and where they are required. For this purpose, 02 needs to be converted into formal singlet O-atom equivalents (O) e.g., (U -peroxo ligands, free or complexed peroxides, high-valent metal-oxo... 

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