Biomimetic oxo-, dioxo- and oxo-peroxo-hydrazonato-vanadium(iv/v) complexes

Abstract

[VO(acac)₂] reacts with HL (HL is the hydrazone Hacpy-inh I, or Hacpy-bhz II; acpy = acetylpyridine, inh = isonicotinic acid hydrazide, bhz = benzoylhydrazide) in dry methanol to yield the oxovanadium(IV) complexes [VOL(acac)] (HL = I: 1, HL = II: 3). The dioxovanadium(V) complexes [VO₂L] (HL = I: 2, HL = II: 4) are obtained by aerial oxidation of 1 and 3 in methanol. Treatment of 1 and 3, or 2 and 4, with H₂O₂ yields the oxoperoxovanadium(V) complexes [VO(O₂)L] (HL = I: 5, HL = II: 6). In the presence of catechol or benzohydroxamic acid, 1 and 3 give the mixed chelate complexes [VOL(cat)] (HL = I: 7, HL = II: 8) or [VOL(bha)] (HL = I: 9, HL = II: 10). The peroxo complexes 5 and 6 undergo oxygen transfer reaction with PPh₃ in DMF. In DMF and DMSO, 7, 8, 9 and 10 slowly convert to the corresponding dioxo species 2 and 4. Acidification of 2 and 4 with HCl dissolved in methanol affords oxo–hydroxo complexes. Reaction of 7 with L-ascorbic acid yields 2. The crystal and molecular structures of 2 and 4 have been determined, confirming the ONN binding mode of I and II from their enolate form.