Dinuclear Oxidovanadium(IV) and Dioxidovanadium(V) Complexes of 5,5′‐Methylenebis(dibasic tridentate) Ligands: Synthesis, Spectral Characterisation, Reactivity, and Catalytic and Antiamoebic Activities

The synthesis of dinuclear oxidovanadium(IV) and dioxidovanadium(V) complexes of two hydrazones [CH 2 (H 2 sal‐nah) 2 ( I ) and CH 2 (H 2 sal‐inh) 2 ( II )] derived from 5,5′‐methylenebis(salicylaldehyde) [CH 2 (Hsal) 2 ] and nicotinic acid hydrazide (nah) or isonicotinic acid hydrazide (inh) is described. The compounds were characterised in the solid state and in solution, namely by spectroscopic techniques (IR, UV/Vis, EPR, 1 H, 13 C and 51 V NMR). It has been demonstrated that the dioxidovanadium(V) complexes K 2 [CH 2 {V V O 2 (sal‐nah)} 2 ] · 2H 2 O ( 3 ), Cs 2 [CH 2 {V V O 2 (sal‐nah)} 2 ] · 2H 2 O ( 4 ) and Cs 2 [CH 2 {V V O 2 (sal‐inh)} 2 ] · 2H 2 O ( 5 ) of I and II are active in the oxidative bromination of salicylaldehyde by H 2 O 2 , therefore acting as functional models of vanadium‐dependenthaloperoxidases, and it has also been shown that the corresponding oxidovanadium(IV) complexes [CH 2 {V IV O(sal‐nah)(H 2 O)} 2 ] ( 1 ) and [CH 2 {V IV O(sal‐inh)(H 2 O)} 2 ] ( 2 ) are catalyst precursors for the catalytic oxidation, by peroxide, of methyl phenyl sulfide and diphenyl sulfide, yielding the corresponding sulfoxide and sulfone. Plausible intermediates involved in these catalytic processes are established by UV/Vis, EPR and 51 V NMR studies. The dioxidovanadium(V) complexes along with ligands I and II were also screened against HM1:1MSS strains of Entamoeba histolytica . The results showed that the IC 50 values of compounds 3 and 5 are lower than the IC 50 value of metronidazole. The toxicity studies against human cervical (HeLa) cell lines showed that compounds 3 and 5 are not much toxic but are more toxic than metronidazole. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)