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

Abstract

Abstract[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)2 I 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 3–6 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.