Dioxygen nitrogen donor ligands

Although a wide variety of nitrogen donor ligands exist in transition-metal complexes, relatively few general types have been employed in those complexes that have been found to activate dioxygen. Generally, the ligands are at least bidentate, and often are multidentate. 

Another notable example of the anomalous behavior of imidazole ligands is the kinetic tram effect observed for the rates of substitution of 02 for CO in the hemes Fe(TPP)02L ([29], M = Fe, X = 02, L = Py, Pip, or l-Melm) according to Eq.(4)and Table 8 30). One of the three nitrogen donors in question, l-Melm, stabilizes the dioxygen adduct in a manner not to be expected from its basicity. The substitution is clearly of the SN1 type, the elimination of the 02 molecule being the rate-determining step. 

While the hemochromes are substitutionally labile, their autoxidation ultimately producing p-oxo complexes of the type [Fe2(P)2]0 accompanied with the loss of the nitrogen donor axial ligands, the ruthenochromes and osmo-chromes are stable. Autoxidation occurs in an outer-sphere electron transfer, e.g. from Os(II) to a dioxygen molecule, see Sect. 3.22. 

Often, bis(p-oxo) copper compounds are stabilized by didentate ligands generating square planar Cu (0)2 complexes favorable for d copper(III) ion (1). Removal of a third nitrogen donor often can change the dioxygen adduct produced from a side-on peroxo isomer to a bis(p-oxo) compound. For example, the copper(I) complex of the tridentate pyridyl amine ligand. 

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