Five- and six-coordinate vanadium(V) complexes with tridentate Schiff base ligands derived from S(+)-isoleucinol: Synthesis, characterization and catalytic activity in the oxidation of sulfides and olefins

A series of vanadium(V) complexes with chiral tridentate Schiff base ligands, obtained by a single condensation of S(+)-isoleucinol with salicylaldehyde and its derivatives, and also six-coordinate complexes with additional monoanionic bidentate benzohydroxamate co-ligand, were prepared. The complexes were characterized by elemental analysis and by their IR, CD, UV Vis, one- (H-1, V-51) and two-dimensional (COSY, gHSQC and NOESY) NMR spectra. The X-ray analysis of the complex, (benzohydroxamato-kappa O-2,O'){S(+)-2-[(1-oxido-3-methylpentyl)iminomethyl]Phenolato-kappa N-3,O,O']oxidovanadium(V), 1b, revealed a distorted octahedral VO(ONO)(OO) geometry. The five-coordinate vanadium(V) complexes have ability to catalyze the oxidation of sulfides [PhSR (R = Me, Bz)] using aqueous 30% H2O2 in good yields and enantiomeric excesses. Catalytic activity of these complexes were also tested in the oxidation of styrene and cyclohexene, using aqueous 30% H2O2 or tert-butyl hydroperoxide (TBHP) as oxidant. (C) 2013 Published by Elsevier Ltd.