Vanadium complexes having [(VO)-O-IV](2+) and [(VO2)-O-V](+) cores with binucleating dibasic tetradentate ligands: Synthesis, characterization, catalytic and antiamoebic activities

摘要

Binucleating hydrazones CH2(H(2)sal-bhz)(2) (I) and CH2(H(2)sal-fah)(2) (II), derived from 5,5'-methylbis(salicylaldehyde) and benzoylhydrazide or 2-furoylhydrazide, react with [VIVO(acac)(2)] to give dinuclear VIVO-complexes [CH2{(VO)-O-IV(sal-bhz)(H2O)}(2)] 1 and [CH2{(VO)-O-IV(sal-fah)(H2O)}(2)] 4, respectively. In the presence of KOH or CsOH center dot H2O, oxidation of 1 and 2 results in the formation of dioxidovanadium(V) complexes, K-2[CH2{(VO2)-O-V(sal-bhz)}(2)]center dot 2H(2)O 2, K-2[CH2{(VO2)-O-V(sal-fah)}(2)]center dot 2H(2)O 5, Cs-2[CH2{VVO2(sal-bhz)}(2)]center dot 2H(2)O 3 and Cs-2[CH2{VVO2(sal-fah)}(2)] center dot 2H(2)O 6. These complexes have alsobeen prepared by aerial oxidation of in situ prepared oxidovanadium(IV) complexes 1 and 4. The compounds were characterized by IR, electronic, EPR, H-1, C-13 and V-51 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 (VO2)-O-V-complexes were used to catalyze the oxidative bromination of salicylaldehyde, therefore acting as functional models of vanadium dependent haloperoxidases, in aqueous H2O2/KBr in the presence of HClO4 at room temperature. It is shown that the (VO)-O-IV-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 IC50 values are relatively high, the cell viability therefore not being much affected.