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Synthesis, Characterization, Catalytic and Antiamoebic Activity of Vanadium Complexes of Binucleating Bis(dibasic tridentate ONS donor) Ligand Systems



[VIVO(acac)2] (acac = acetylacetonate) was treated with ligands CH2(H2L)2 in methanol heated at reflux to yield two neutral binuclear VIV complexes with the formula [CH2{VIVOL(H2O)}2], namely, 1 and 2. Ligands CH2(H2L)2I and II were derived from 5,5′-methylenebis(salicylaldehyde) and S-benzyldithiocarbazate [CH2(H2sal-sbdt)2, I] or S-methyldithiocarbazate [CH2(H2sal-smdt)2, II]. Aerial oxidation of 1 and 2 in the presence of KOH or CsOH·H2O resulted in the formation of dioxidovanadium(V) complexes, K2[CH2{VVO2(sal-sbdt)}2]·2H2O (3), Cs2[CH2{VVO2(sal-sbdt)}2]·2H2O (4), K2[CH2{VVO2(sal-smdt)}2]·2H2O (5) and Cs2[CH2{VVO2(sal-smdt)}2]·2H2O (6). The compounds were characterized in the solid state and in solution, namely, by spectroscopic techniques (IR, UV/Vis, EPR, 1H, 13C and 51V NMR spectroscopy). It is demonstrated that the VVO2 complexes 36 are efficient and selective towards the oxidative bromination by H2O2 of styrene to yield 1,2-dibromo-1-phenylethane, 1-phenylethane-1,2-diol and 2-bromo-1-phenylethane-1-ol, and of salicylaldehyde to yield 5-bromosalicylaldehyde, 3,5-dibromosalicylaldehyde and 2,4,6-tribromophenol; they therefore act as functional models of vanadium-dependent haloperoxidases. It is also shown that Cs2[CH2{VVO2(sal-sbdt)}2]·2H2O (4) and Cs2[CH2{VVO2(sal-smdt)}2]·2H2O (6) are catalyst precursors for the catalytic oxidation of styrene by peroxide to yield styrene oxide, benzaldehyde, 1-phenylethane-1,2-diol, benzoic acid and phenylacetaldehyde. Plausible intermediates involved in these catalytic processes were established by UV/Vis, EPR and 51V NMR spectroscopic studies. The VVO2 complexes along with ligands I and II were also screened against HM1:1MSS strains of Entamoeba histolytica; the IC50 values of compounds 3, 4 and 5 were significantly lower than that of metronidazole, thereby suggesting that they may be promising drugs for the treatment of amoebiasis.