Oxidovanadium(IV) and dioxidovanadium(V) complexes of hydrazones of 2-benzoylpyridine and their catalytic applications

Reactions between the tridentate ONN donor ligands, Hbzpy-tch (I) and Hbzpy-inh (II), with [(VO)-O-IV(acac)(2)] in dry methanol give two different types of complexes, [(VO)-O-IV(acac)(bzpy-tch)] (1) and [(VO)-O-IV(OMe)(bzpyinh)] (2), respectively. Irrespective of their nature in methanol upon aerial oxidation and precipitation both yield dinuclear [{(VO)-O-V(bzpy-tch)}(2)(mu-O)(2)] (3) and [{(VO)-O-V(bzpy-inh)}(2)(-O)(2)] (4). Treatment of 1 or 2 in methanol with H2O2 yields the oxidomonoperoxidovanadium(V) complexes [{VVO(bzpy-tch)}(2)(mu-O-2)(2)] (5) and [(VO)-O-V(O-2)(bzpy-inh)] (6). Reactions of 3 and 4 with imidazolomethylpolystyrene cross-linked with 5% divinylbenzene (PS-im) in DMF give the polymer-supported PS-im[(VO2)-O-V(bzpy-inh)] (7) and PS-im [(VO2)-O-V(bzpy-tch)] (8). The compounds are characterized by various spectroscopic techniques and compounds 7 and 8 were also analyzed by thermal, atomic force microscopy (AFM), field-emission scanning electron micrographs (FE-SEM) as well as energy dispersive X-ray (EDAX) studies. The molecular structures of 3-5 and of [(VO)-O-V(O-2)(bzpy-inh)(H2O)]center dot 0.5MeOH (6a) were determined by single-crystal X-ray diffraction, confirming the mu-bis(O) and ONN binding mode in the dinuclear complexes 3 and 4, as well as the side-on coordination of the peroxido ligand in 5 and 6a. The polymer-grafted compounds 7 and 8 were used for the catalytic oxidation of isoeugenol using aqueous H2O2 as an oxidant. The intermediate peroxido species, expected to be involved during catalytic action, were also generated from solutions of 1-4 and studied by UV-Vis and V-51 NMR. The catalytic activity of the several systems was tested and the polymer-supported versions showed higher conversions than their neat counterparts. The polymer-supported complexes allow for recyclable catalytic systems, thus providing additional advantages over their homogeneous counterparts in terms of increased catalyst lifetime and easier separation from the reaction mixture.