Dioxo- and oxovanadium(V) complexes of biomimetic hydrazone ONO donor ligands: Synthesis, characterisation, and reactivity

The dioxovanadium(V) complexes M[VO2(L)solv] (2, 5, 6) have been isolated a long with dimeric, ore-bridged monooxovanadium complexes with the formula [ {VOL}(2)mu -O] (1, 4), and characterised by their spectral and thermogravim etric properties and reactivity patterns. H2L is the hydrazone H-2{(R-sal)- iNH} [sal derives from salicylaldehyde (R = H) or p-CI-salicylaldehyde (R = CI)] or H(2)hap-iNH, where hap is the o-hydroxyacetophenone moiety, and iN H stands for isonicotinic acid hydrazide. In the isolated potassium (M = K) complexes 2a, 5 and 6, solv is a water molecule, which was exchanged for m ethanol or DMSO in the respective solutions as shown by V-51 NMR. Treatment of the dimeric (1 and 4) or anionic complexes (2a and 5) with H2O2 yielded (unstable) oxoperoxovanadium complexes K[VO(O-2)L] (7, 8). Acidification o f 1 and 4 afforded oxohydroxo complexes. When compound 2a is dissolved in m ethanol, it is partly deoxygenated to form [VO(OMe)(HOMe)L] (9), the crysta l and molecular structures of which have been determined, confirming the ON O binding mode of L in its enolate form.