Characterization of oxovanadium (IV)–Schiff-base complexes and those bound on resin, and their use in sulfide oxidation

Oxovanadium (IV)–Schiff-base complexes and those bound on Merrifield resin as a polymer support were prepared for their characterization and their use as catalyst in oxidation of methyl phenyl sulfide. Schiff bases were prepared with use of salicylaldehyde and 2,4-dihydroxybenzaldehyde as the aldehydes and 2-aminoethanol, L-phenylalaninol, L-histidinol, and L-phenylalanine as the counterparts. Oxovanadium (IV) complexes made up of these Schiff bases and those bound on the resin were spectroscopically characterized. The polymer-supported Schiff-base complexes in the presence of tertiary-butylhydroperoxide converted the sulfide to the corresponding sulfoxide in 80–90% yield in CDCl3 in 90 min. They afforded slightly lower rates of oxidation than the corresponding monomeric complexes. They converted the sulfide in a stereoselective manner yielding the sulfoxide in enantiomeric excess (the highest value of 40%). The polymer-supported complexes and the corresponding monomers achieved almost the same enatiometric excesses with each other.