Chemistry of hydrazonato oxovanadium(V) alkoxides derived from dihydric/monohydric alcohols

The reaction of bis(acetylacetonato)oxovanadium(IV) with benzoylhydrazones of benzoylacetone and salicylaldehyde - H(2)babh and H(2)sabh, respectively - with ethane-1,2-diol (H(2)ed) in acetone solution has afforded the alkoxides (VO)-O-V(babh)(Hed) and (VO)-O-V(sabh)(Hed) in which the Hed(-) ligand is chelated both in the solid state and in solution. In methanol solution (no H(2)ed added) five-coordinated (VO)-O-V(babh)(OMe) and six-coordinated (VO)-O-V(sabh)(OMe)(OHMe) are formed. Aerial oxygen is the oxidant (V-IV --> V-V) in the synthesis. The X-ray structures of VO(babh)(Hed) and VO(sabh)(OMe)(OHMe) are reported. In the VO5N coordination sphere the alcohol oxygen lies trans to the oxo oxygen. The general V-O bond length order is oxo < alkoxidic < phenoxidic < enolato < alcoholic. The complexes are mononuclear but intermolecular O-H ... N hydrogen bonding afford dimers. The Hed(-) complexes represent authentic examples of rare oxovanadium species incorporating ethane-1,2-diol chelation uncomplicated by alkoxide bridging. The complexes have low V(V)/V(IV) reduction potentials (E-1/2, -0.3 to -0.2 V) corresponding to stabilization of the pentavalent state. The methylene protons of Hed(-) in the complexes are inequivalent in solution (H-1 NMR). Crystal data: VO(babh)(Hed): monoclinic, space group P2(1)/c, a = 11.260(6), b = 7.672(3), c = 21.072(8) Angstrom, beta = 91.95(4)degrees, V = 1820(1.4) Angstrom(3), Z = 4, R = 4.12%, R-w = 4.67%; VO(sabh)(OMe)(OHMe): monoclinic, space group P2(1)/c, a = 8.170(4), b = 16.984(10), c = 12.242(7) Angstrom, beta = 104.24(4)degrees, V = 1646(1.6) Angstrom(3), Z = 4, R = 3.64%, R-w = 4.71%. (C) 1997 Elsevier Science S.A.