Vanadium complexes having [VIVO]2+ and [V VO2]+ cores with binucleating dibasic tetradentate ligands: Synthesis, characterization, catalytic and antiamoebic activities

Abstract

Binucleating hydrazones CH2(H2sal-bhz)2 (I) and CH2(H2sal-fah)2 (II), derived from 5,5′-methylbis(salicylaldehyde) and benzoylhydrazide or 2-furoylhydrazide, react with [VIVO(acac)2] to give dinuclear V IVO-complexes [CH2{VIVO(sal-bhz)(H 2O)}2] 1 and [CH2{VIVO(sal-fah) (H2O)}2] 4, respectively. In the presence of KOH or CsOH·H2O, oxidation of 1 and 2 results in the formation of dioxidovanadium(v) complexes, K2[CH2{VVO 2(sal-bhz)}2]·2H2O 2, K 2[CH2{VVO2(sal-fah)} 2]·2H2O 5, Cs2[CH2{V VO2(sal-bhz)}2]·2H2O 3 and Cs2[CH2{VVO2(sal-fah)} 2]·2H2O 6. These complexes have also been prepared by aerial oxidation of in situ prepared oxidovanadium(iv) complexes 1 and 4. The compounds were characterized by IR, electronic, EPR, 1H, 13C and 51V NMR spectroscopy, elemental analyses and thermogravimetric patterns. Single crystal X-ray analysis of 3 confirms the coordination of the ligand in the dianionic (ONO2-) enolate tautomeric form. The VVO2-complexes were used to catalyze the oxidative bromination of salicylaldehyde, therefore acting as functional models of vanadium dependent haloperoxidases, in aqueous H2O 2/KBr in the presence of HClO4 at room temperature. It is shown that the VIVO-complexes [CH2{VIVO(sal- bhz)(H2O)}2] 1 and [CH2{VIVO(sal- fah)(H2O)}2] 4 are catalyst precursors for the catalytic oxidation of organic sulfides using aqueous H2O2. Plausible intermediates involved in these catalytic processes are established by UV-Vis, EPR and 51V NMR studies. The vanadium complexes along with ligands I and II are also screened against HM1:1MSS strains of Entamoeba histolytica, the results showing that the IC50 values of compounds 3 and 6 are lower than that of metronidazole. The toxicity studies against human cervical (HeLa) cancer cell line also showed that although compounds 3 and 6 are more toxic than metronidazole towards this cell line, the corresponding IC 50 values are relatively high, the cell viability therefore not being much affected. © The Royal Society of Chemistry 2010.