Dioxygen oxygen-atom transfer

Keywords Organometallics Dioxygen Early transition metals Oxygen atom transfer... 

The facile activation of dioxygen by these simple organometalHc complexes generates high-valent (V(V), Cr(V)) metal 0x0 complexes, which may undergo oxygen atom transfer reaction with organic substrates, and thus serve as catalysts for aerobic oxidations (Sect. 3.3). 

Such reactions are interesting as models for oxygen atom transfer in mechanisms of dioxygen activation by cytochrome P450 enzyme systems (49, 50, 51). 

Figure 9-28. The ring-opening oxidation of catechol by dioxygen in the presence of copper salts. The first step presumably involves an electron transfer type of process to generate the quinone, followed by the oxygen atom transfer in the second step.

Numerous other examples of reactions of this type have been described and a particularly dramatic example of a product derived from oxygen atom transfer to a co-ordinated ligand is seen in the reaction of the benzimidazole ligand 9.16 with dioxygen in the presence of a copper(i) catalysts. The isolated product of the reaction is the copper(n) complex of the benzimidazole-3-carboxylic acid, 9.17. 

The discovery of the ds and d10 metal ir-bonded dioxygen complexes (formally d6- and d8-peroxide systems), and the accompanying chemistry exemplified in Scheme 1, showed the possibility of attaining net oxygen-atom transfer to both inorganic and organic substrates. 

Oxygen Atom Transfer Catalysis and Dioxygen Activation... 

Biological systems activate ground-state dioxygen (302) for controlled energy transduction and chemical syntheses via electron-transfer and hydrogen-atom-transfer reduction to O2 -, HOO-, and HOOH. These reduction products are further activated with metalloproteins to accomplish oxygen atom-transfer chemistry. Conversely, green plants via photosystem II facilitate the oxidation of water to 02 (Chapter I),l... 

An interesting way to bypass the electronic noncomplementarity of typical reactions between transition metal ions or complexes and dioxygen is based on an oxygen atom transfer from an oxygen allotrope, ozone. This approach was very successful in generating aqueous ferryl, an otherwise hardly accessible species71 ... 

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