Niobium porphyrin complexes

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". ... 

Porphyrin derivatives of Nbv and Tav were first reported in 1972 and have since aroused increasing interest. Fluoride complexes MF3L were obtained from MC1S and the oc-taethylporphyrin in the presence of HF (L = OEP),321,322 Niobium chloride and bromide... 

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. 

The most studied of the Group 5 porphyrins have been compounds with vanadyl and niobium metal ions no electrochemical data have yet been reported for tantalum porphyrins. Vanadium porphyrins have been synthesized as both V(IV) and V(II) complexes. The vanadyl derivatives, represented as (P)VO, generally undergo well-defined reduction and oxidation reactions involving the porphyrin, macrocyle the lower oxidation state V(II) complexes have been prepared as (P)V (L) and (P)V (L)2 derivatives, where P = T(p-Me)PP or OEP and L = THE or PPhMe2, but these species have not been examined as to their electrochemical properties [7]. 

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