Vanadium(V) complexes with chiral tridentate Schiff base ligands derived from 1S,2R(+)-2-amino-1,2-diphenylethanol and with acetohydroxamate co-ligand: Synthesis, characterization and catalytic activity in the oxidation of prochiral sulfides and olefins

Abstract

A series of vanadium(V) complexes with chiral tridentate Schiff base ligands were prepared. Five-coordinate complexes were obtained by a single condensation of 1S,2R(+)-2-amino-1,2-diphenylethanol with salicylaldehyde and its derivatives. Furthermore, six-coordinate complexes were synthesized with the same Schiff base ligands and also with monoanionic bidentate acetohydroxamate co-ligand. 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 analyses of the ligand, 1S,2R(+)-2-[(1-hydroxy-1,2-diphenylethyl)iminomethyl]-4-nitrophenol, 7, and its complex, (acetohydroxamato-κ2O,O′){1S,2R(+)-2-[(1-oxido-1,2-diphenylethyl)iminomethyl]-4-nitrophenolato-κ3N,O,O′}oxidovanadium(V), 7b, have been also performed. The five-coordinate vanadium(V) complexes have ability to catalyze the oxidation of prochiral sulfides [PhSR (R=Me, Bz)] in good yields and enantiomeric excesses. Moreover, catalytic activity of these complexes and also those derived from 1S,2S(−)-1,2-diphenyl-1,2-diaminoethane were tested in the oxidation of styrene and cyclohexene.