New thiosemicarbazide and dithiocarbazate based oxidovanadium(iv) and dioxidovanadium(v) complexes. Reactivity and catalytic potential

Abstract

The Schiff bases {H3dfmp-(smdt)2} (I), {H3dfmp-(sbdt)2} (II) and {H3dfmp-(tsc)2} (III) are synthesized by reaction of 2,6-diformyl-4-methylphenol (H3dfmp) and S-methyldithiocarbazate (smdt), S-benzyldithiocarbazate (sbdt) and thiosemicarbazide (tsc), respectively. Addition of [VIVO(acac)2] to solutions of these compounds in methanol leads to the formation of the oxidovanadium(iv) complexes [VIVO{Hdfmp-(smdt)2(CH3OH)}] (1), [VIVO{Hdfmp-(sbdt)2(CH3OH)}] (2) and [VIVO{Hdfmp-(tsc)2(CH3OH)}] (3). All these VIVO-compounds can be oxidized to the corresponding dioxidovanadium(v) (VVO2) complexes in methanolic solution upon aerial oxidation in the presence of KOH. The isolated compounds are K[VVO2{Hdfmp-(smdt)2}] (4), K[VVO2{Hdfmp-(sbdt)2}] (5) and K[VVO2{Hdfmp-(tsc)2}] (6). The Cs+ salts of these complexes i.e. Cs[VVO2{Hdfmp-(smdt)2}] (7), Cs[VVO2{Hdfmp-(sbdt)2}] (8) and Cs[VVO2{Hdfmp-(tsc)2}] (9) are prepared similarly in the presence of CsOH. All these compounds are characterized by various spectroscopic techniques like FT-IR, UV-visible, and 1H and 51V NMR and thermal studies. IR spectral data confirm the coordination of ligands through the azomethine nitrogen, the sulphur and the phenolic oxygen atoms to the metal. These complexes show excellent catalytic activity and selectivity for the oxidation of benzyl alcohol and ethylbenzene in the presence of H2O2 as an oxidant. Various parameters such as the amount of catalyst and oxidant, reaction time, reaction temperature and solvent were taken into consideration to optimize these catalytic oxidations. Compound 7 was also remarkably efficient and selective in the catalytic oxidation of primary and secondary alcohols to the corresponding aldehyde/ketone, as well as of several aromatic compounds such as toluene, benzene, cumene and tetralin. This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.