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- (1H, 51V) and two-dimensional (COSY, gHSQC and NOESY) NMR spectra. The X-ray analysis of the complex, (benzohydroxamato-κ2O,O′){S(+)-2-[(1-oxido-3-methylpentyl)iminomethyl]phenolato-κ3N,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.

Graphical abstractA series of five-coordinate 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 with additional monoanionic bidentate benzohydroxamate co-ligand, were prepared and characterized. The five-coordinate vanadium(V) complexes have ability to catalyze the oxidation of prochiral sulfides to chiral sulfoxides. Catalytic activity of these complexes were also tested in the oxidation of styrene and cyclohexene.Figure optionsDownload full-size imageDownload as PowerPoint slide