Imidazole and related heterocyclic ligand complexes of oxovanadium(IV)—potential models for the reduced vanadium site of the seaweed bromoperoxidases

Abstract We have used the model compound approach to comment on the structural hypotheses that in reduced bromoperoxidase (BPO) the vanadium is coordinated by at least one imidazole-type nitrogen donor and possibly a phenolate-type oxygen donor. We report here the synthesis and spectroscopic characterization of representative examples of three classes of oxovanadium(IV)—imidazole complexes (i) [VO(acac) 2 (imid)], where acac = 2,4-pentanedionate and imid = N- or 2-substituted imidazole. (ii) [VO(imid) 4 Cl] + , which is stabilized in solution in the presence of excess imid. (iii) [VO(ON) 2 ], where (ON) = , n = 0 or 1, and E = O, S, NH, NMe. It is the complexes of type (iii) above which most closely resemble the non-axial nature of ESR spectrum of the reduced BPO enzymes.