Dioxygen bonding modes

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 ... 

Several dioxygen complexes of chromium featuring snperoxide (02 ) bound to Cr can be made by exposure of Cr precursors to 02. The first structurally characterized example of such an addnct that is, [TpiBu.Mecr(pz H)(02 )] -interestingly features the rare side-on bonding mode of the superoxide hgand. ... 

Currently, two geometrical structures for coordinated dioxygen are known—the side-on, which corresponds to a w-bonding mode, and the end-on, corresponding to a er-bonding mode, as seen in Fig. 41. 

Although the bulk of work with NOz as a ligand features Co111, nitrite can also be O- or N-bonded to Co11, and both modes have been observed in complexes formed by the reaction of several PR3 compounds with Co(N03)2, as well as in mixed nitro/nitroso complexes.375 The product Co(NO)(N02)(PEt3)2 reacts with dioxygen to form Co(N03)2 (OPEt3)2, a distorted octahedral structure with bidentate nitrate and cis phosphine oxides (102). 

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