Dinuclear vanadium, copper, manganese and titanium complexes containing O,O,N-dichelating ligands: Synthesis, crystal structure and catalytic activity

O,O,N- or O,N-dichelating ligands, H4L1, H4L2, derived from new bis(hydroxybenzylidene)-substituted terephthalo and oxalo hydrazides were prepared and characterized by FT-IR and NMR spectroscopy (H4L1 = dicondensation of salicylaldehyde and terephthalic acid dihydrazide, H4L2 = dicondensation of salicylaldehyde and oxalic acid dihydrazide). [{VO2}2(H2L1)] (1), [{Cu(CH3OH)}2(L1)] (2), [{Mn(CH3OH)}2(L1)] (3) and [TiO(H3L1)2] (4) complexes of the potentially hexadentate 2[ONO] donor hydrazone ligand [L1]4− were synthesized by reaction of the appropriate metal salts with H4L1. The complexes [{VO(CH3O)(CH3OH)}2(L2)] (5), [{Cu(CH3OH)}2(L2)] (6), [{Mn(H2O)2(CH3OH)}2(L2)] (7) and [{TiO(CH3OH)}2(L2)]·2H2O (8) were synthesized by the reaction of corresponding metal salts with H4L2. All complexes were characterized by microanalyses, FT-IR, UV–Vis and NMR spectroscopic methods. The crystal structures of 1 and 5 were established by X-ray analyses. Compound 1 is a one-dimensional coordination polymer. The catalytic potential of the complexes was evaluated for oxidation of hydrocarbons including cycloalkenes, cyclic alkanes and benzylalcohol using H2O2 as terminal oxidant. Of the studied aroylhydrazone complexes, 4 showed the best selectivity and activity as catalyst.