Oxido-bridged dinuclear vanadium(V) Schiff base complexes derived from 1R,2S(−)-norephedrine: Synthesis, structure, characterization and catalytic studies

Abstract

A series of vanadium(V) complexes with chiral tridentate Schiff base ligands, obtained by a single condensation of 1R,2S(−)-norephedrine with salicylaldehyde and its derivatives, were prepared. The complexes were characterized by elemental analysis and by their IR, CD, UV–Vis, 1D (1H, 51V) and 2D (COSY, gHSQC) NMR spectra. The X-ray analysis of μ-oxido-bis({1R,2S(−)-2-[(1-oxido-1-phenylpropyl)iminomethyl]-3,5-dimethoxyphenolato-κ3N,O,O′}oxidovanadium(V)), V2O3(C18H19NO4)2, 4, revealed oxido-bridged dinuclear structure with, unexpectedly, two five-coordinate square-pyramidal geometries about metal atoms. The two O-bonded oxidovanadium units are in the twist-angular configuration with the VV–O–VV angle of 108.75(8)° and V–O distances of 1.802(2) and 1.818(2)Å. The vanadium(V) complexes have ability to catalyze the oxidation of sulfides [PhSR (R=Me, Bz)] in good yields and enantiomeric excesses, utilizing aqueous 30% H2O2 or cumene hydroperoxide (CHP) as oxidant.