Ligands dioxygen

The dioxygen ligand in mononuclear group VIII transition metal complexes. J. S. Valentine, Chem. Rev., 1973, 73, 235-245 (101). 

This review is particularly concerned with the bonding modes of the dioxygen ligand, and the factors affecting which of the various possible orientations it assumes in any particular complex. We shall therefore consider all previous work, from the earliest work on synthetic oxygen carriers, right up to the most recent studies on picket-fence and other synthetic porphyrins. All work concerned with an irreversible system will illustrate some principle appertaining to reversibility. On this basis we shall then attempt to provide a unified rationale for ... 

Type 1. Bridging adducts (see Fig. 2), where the dioxygen ligand is bridged between two metal atoms intermolecularly. Here, the metal dioxygen ratio is invariably 2 1. 

B. Theoretical Considerations Concerning the Orientation and Electronic Structure of the Dioxygen Ligand. 

We shall return to the discussion of the orientation and electronic structure of the dioxygen ligand during the next section which is primarily concerned with recent advances in the synthesis and physical characterization (particularly X-ray analysis) of oxygencarrying metal porphyrin model compounds. 

Dicobalt /it-peroxo complexes have been synthesized di-Co(III) species, [Co2(bpmp)(/r-02)(/z-CH3C02)](C104) 29, was reported by Kofod and coworkers. Di-Co(II) complex, 31 [Co2(/z-02)(oxapyme(N02)]+, has been prepared starting from the corresponding [Co2(/z- -02)(oxapyme)]+ species 30, as indicated in equation 13 . Both species were characterized in the solid state and interesting aspects of transformation of dioxygen ligand in bimetallic species were therefore explored. 

In these reactions triphenylphosphine was liberated, and the IR spectrum of the product showed that the dioxygen ligand was no longer present (absence of the strong 850 cm 1 bond). X-ray analyses showed a Rh P Cl ratio of 1 1 1 in these products. The presence of amine or amide ligands in the catalytic species was verified by IR, PMR, and elemental analysis. Despite this instrumental and analytical data, no reasonable formula can be proposed for any of these species. 

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