Dioxo- and Oxovanadium(V) Complexes of Biomimetic Hydrazone ONO Donor Ligands: Synthesis, Characterisation, and Reactivity

Abstract

The dioxovanadium(V) complexes M[VO2(L)solv] (2, 5, 6) have been isolated along with dimeric, oxo-bridged monooxovanadium complexes with the formula [{VOL}2µ-O] (1, 4), and characterised by their spectral and thermogravimetric properties and reactivity patterns. H2L is the hydrazone H2{(R-sal)-iNH} [sal derives from salicylaldehyde (R = H) or p-Cl-salicylaldehyde (R = Cl)] or H2hap-iNH, where hap is the o-hydroxyacetophenone moiety, and iNH 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 methanol or DMSO in the respective solutions as shown by 51V NMR. Treatment of the dimeric (1 and 4) or anionic complexes (2a and 5) with H2O2 yielded (unstable) oxoperoxovanadium complexes K[VO(O2)L] (7, 8). Acidification of 1 and 4 afforded oxohydroxo complexes. When compound 2a is dissolved in methanol, it is partly deoxygenated to form [VO(OMe)(HOMe)L] (9), the crystal and molecular structures of which have been determined, confirming the ONO binding mode of L in its enolate form.