Metal oxygen species

Figure I. Metal-oxygen species a Fem, Co1" bTiIV, Vv, Nbv, Tav, CrVI, Movl, Wvl, Ru" IV, Osn-IV, Co111, Rhm, Ir1...

In general, the catalytic properties of transition metals for the oxidation of hydrocarbons are strongly governed by the existence and nature of the metal-oxygen intermediates. Among the various possible reactive intermediates, two families of metal-oxygen species emerge as the most important ones, i.e. metal peroxides and metal-oxo compounds. 

The polymerisation of alanine /V-carboxylic acid anhydride involves the participation of metal oxygen species which undergo decarboxylation yielding metal nitrogen propagating species. This may be shown schematically as follows ... 

A second way to overcome this spin conservation obstacle is via reaction of 302 with a paramagnetic (transition) metal ion, affording a superoxometal complex (Fig. 4.1, Reaction (3)). Subsequent inter- or intramolecular electron-transfer processes can lead to the formation of a variety of metal-oxygen species (Fig. 4.2) which may play a role in the oxidation of organic substrates. 

Chart 1 Wavenumber ranges in which 0-0 and M-0 stretching vibrations are normally observed for various metal oxygen species. 

The most notable reaction is that of metal-oxygen species with substrate. In the case of heme iron monooxygenases, high-valent iron-oxo species such as 3 or 4 in Fig. 5 are believed to react with substrates. On the other hand, both hydroperoxo (2) and 0x0 (3) are proposed for reactions by nonheme iron oxygenases. There are discussions on whether the iron-oxo species (3) is stabilized in the nonheme oxygenases in the absence of a porphyrin ligand which is effective to form 4. However, the iron-oxo species is attractive for explanation of the results obtained by monooxygenations by nonheme model iron systems. 

Metal-oxygen species in the enzymatic oxygenase system are usually too unstable to be identified, but formation of diamond shape p-peroxo species as an important active... 

Figure 7. Various metal-oxygen species formed in the absence or presence of metal ions.

Figure 18. Isolated catechol-metal-oxygen species [108-110].

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