Dioxygen niobium complexes

Dioxygen binds to metal porphyrins in the three expected modes, i.e. u-superoxo, peroxo and bridging peroxo. In contrast to die simple complexes discussed previously, dioxygen coordination occurs with a wide range of transition metals from titanium and niobium through to the Group VIII metals. 

No dioxygen adducts of vanadium porphyrins have been reported. However, a niobium(IV) porphyrin, NbBr2TPP, has recently been reported to react with dioxygen. Characterization was based upon ESR data. A 10-line signal g — 2.002), due to weak coupling to the Nb nucleus (/ = f), was seen. This implied a superoxo-type complex. IR data are consistent with the superoxo formalism showing Vo o = 1220cm". ... 

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