Group-V a Porphyrins

As with the titanium porphyrins, these complexes occur as vanadyl complexes with an axial oxo group and produce a normal electronic spectrum which changes to a hematin spectrum when trifluoroacetic acid is added [Bonnett (9)]. The vanadyl porphyrins contain a single unpaired electron (/i=l,4B.M.) and their esr spectra have been studied in some detail [Kivelson (113a), Roberts (152)]. The rich redox chemistry of the inorganic vanadium salts is not reflected in the vanadyl porphyrins, where the +4 state seems to be exceptionally stable. 

Both diamagnetic metalloporphyrins have been synthesized with three monovalent ligands in the +5 state and have normal electronic spectra (NbOEPF3 569 (24,000)532(8,300)403(186,000) TaOEPF3 576 (27,000) 528 (8,300) 399 (174,00)] [Buckler (27)]. 

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