Vanadium complexes having [VIVO]2+ and [VVO2]+cores with binucleating dibasic tetradentate ligands: Synthesis, characterization, catalytic and antiamoebic activities

Abstract

Binucleating hydrazones CH(2)(H(2)sal-bhz)(2) (I) and CH(2)(H(2)sal-fah)(2) (II), derived from 5,5'-methylbis(salicylaldehyde) and benzoylhydrazide or 2-furoylhydrazide, react with [V(IV)O(acac)(2)] to give dinuclear V(IV)O-complexes [CH(2){V(IV)O(sal-bhz)(H(2)O)}(2)] 1 and [CH(2){V(IV)O(sal-fah)(H(2)O)}(2)] 4, respectively. In the presence of KOH or CsOH.H(2)O, oxidation of 1 and 2 results in the formation of dioxidovanadium(v) complexes, K(2)[CH(2){V(V)O(2)(sal-bhz)}(2)].2H(2)O 2, K(2)[CH(2){V(V)O(2)(sal-fah)}(2)].2H(2)O 5, Cs(2)[CH(2){V(V)O(2)(sal-bhz)}(2)].2H(2)O 3 and Cs(2)[CH(2){V(V)O(2)(sal-fah)}(2)].2H(2)O 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, (1)H, (13)C and (51)V NMR spectroscopy, elemental analyses and thermogravimetric patterns. Single crystal X-ray analysis of 3 confirms the coordination of the ligand in the dianionic (ONO(2-)) enolate tautomeric form. The V(V)O(2)-complexes were used to catalyze the oxidative bromination of salicylaldehyde, therefore acting as functional models of vanadium dependent haloperoxidases, in aqueous H(2)O(2)/KBr in the presence of HClO(4) at room temperature. It is shown that the V(IV)O-complexes [CH(2){V(IV)O(sal-bhz)(H(2)O)}(2)] 1 and [CH(2){V(IV)O(sal-fah)(H(2)O)}(2)] 4 are catalyst precursors for the catalytic oxidation of organic sulfides using aqueous H(2)O(2). Plausible intermediates involved in these catalytic processes are established by UV-Vis, EPR and (51)V 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 IC(50) 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.