Complexes with dioxygen

The preliminary formation of metal-dioxygen complex was postulated in the mechanisms discussed earlier. However, a series of metal complexes were synthesized that form stable complexes with dioxygen. These complexes were studied as individual compounds. A few of them are given in Table 10.7. 

Chelate Complexes that form Complexes with Dioxygen... 

Kinetic Parameters for the Reactions of [FeL(DTBC)] Complexes with Dioxygen in Different Solvents (29)a... 

Fig. 11. Volume profile for the reaction of the Cu(I) complex with dioxygen.

In order to account for the reactivity of these complexes with dioxygen one must at first look at the cyclic voltammetric responses reported in Figure 24. 

Fig. 10. Water-free iron complex with dioxygen placed above the cofactor (5a) and the transition state for dioxygen coordination to iron (TS[5a-6a] ). Distances are given in angstroms.

The metals which form this type of complex by reaction with dioxygen are mainly the later second and third row transition series metals, notably Ru°, Os°, Rh1, Ir1, Pt° and Pd°. It is not surprising to see metals noted for their ability to undergo oxidative addition reactions amongst those which form this type of mononuclear dioxygen complex as a formal two-electron reduction of dioxygen is required for complex formation. The other metals known to form mononuclear peroxo-type complexes with dioxygen are Ni°, Co1 and one example of Co . 

The reaction of both complexes with dioxygen was explored, affording in the case of 410 an intractable mixture. However, 409 reacts to afford the Pd(IV) nitrate complex TpPd(K2-CH2CMe2-<)-C6H4)0N02 (511,... 

Figure 9-33. Sometimes the reaction of copper complexes with dioxygen can have dramatic consequences ...

Becker, M., Schindler, S., Karlin, K. D., etal., Intramolecular ligand hydroxylation Mechanistic high-pressure studies on the reaction of a dinuclear copper complex with dioxygen. Inorg. Chem. 1999, 38, 1989-1995. 

Oxidants that operate according to this one-electron oxidation mechanism include potassium ferricyanide in alkaline solution, cobalt, copper complexes with dioxygen, and some enzymes. 

The unique versatility of ruthenium as an oxidation catalyst continues to provide a stimulus for research on a variety of oxidative transformations. Its juxtaposition in the periodic table and close similarity to the biological redox elements, iron and manganese, coupled with the accessibility of various high-valent oxo species by reaction of lower-valent complexes with dioxygen make ruthenium an ideal candidate for suprabiotic catalysis. 

The activation of On by Co, Mn, and Mo porphyrins has been studied theoretically by Witko and coworkers [568]. In the case of the Co porphyrin, the active forms of the catalyst are found to include an end-on complex with dioxygen and the hydroperoxo form, but not an oxo O=Co(porph) complex because water will not easily dissociate. In the case of the Mn porphyrin, the side-on, hydroperoxo, and 0X0 types of ligands are possible. In the case of the Mo porphyrin, all forms, the side-on, end-on, hydroperoxo, and oxo forms, are possible. 

REACTIONS OF MONONUCLEAR METAL COMPLEXES WITH DIOXYGEN 121... 

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