title: Vanadium-induced formation of thiadiazole and thiazoline compounds. Mononuclear and dinuclear oxovanadium(v) complexes with open-chain and cyclized thiosemicarbazone ligands.
abstract: Reactions of the salicylaldehyde 4-phenylthiosemicarbazone (H(2)L) with selected vanadium(iv) and vanadium(v) precursors ([VO(acac)(2)], [VO(OAc)(2)], VOSO(4), [V(2)O(4)(acac)(2)]) were investigated under aerobic conditions in different alcohols (methanol, ethanol, propanol). In all examined cases mononuclear alkoxo vanadium(v) complexes [VOL(OR)] (1) (OR = OMe, OEt, OPr) were isolated as major products. On prolonged standing, mother liquids afforded dinuclear vanadium(v) complexes [V(2)O(3)(L(cycl))(2)(OR)(2)] (3) (OR = OMe, OEt, OPr), where L(cycl)(-) represents 1,3,4-thiadiazole ligand, formed by vanadium-induced oxidative cyclization of H(2)L. When [VO(acac)(2)] or [V(2)O(4)(acac)(2)] were used as precursors, in addition to products 1 and 3, a thiazoline derivative HL(acac)(cycl) (2) was isolated. This compound, formed by a reaction between acetylacetone and H(2)L, represented the second type of cyclic product. The products were characterized by IR and NMR spectroscopies, TG analysis, and in some cases by single-crystal X-ray diffraction. To the best of our knowledge, compounds [V(2)O(3)(L(cycl))(2)(OR)(2)] represent the first structurally characterized dinuclear vanadium(v) complexes with a thiadiazole moiety acting as a bridging ligand. Complexes 1 and 3, when dissolved in an appropriate alcohol, underwent substitution of the alkoxo ligand as confirmed by XRPD. The kinetics of reactions in methanolic solutions was qualitatively studied by UV-Vis and ESMS spectrometries. Under the experimental conditions applied, a relatively slow formation of the mononuclear complex [VOL(OMe)] and an even slower formation of the cyclic species 2 were observed, whereas the presence of dinuclear compound [V(2)O(3)(L(cycl))(2)(OMe)(2)] in the reaction mixture could not be detected.
authors.affiliation: Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, 10000, Zagreb, Croatia.
authors.forename: Mirta
authors.initials: M
authors.lastname: Rubcić
authors.forename: Dalibor
authors.initials: D
authors.lastname: Milić
authors.forename: Gordan
authors.initials: G
authors.lastname: Horvat
authors.forename: Ivica
authors.initials: I
authors.lastname: Dilović
authors.forename: Nives
authors.initials: N
authors.lastname: Galić
authors.forename: Vladislav
authors.initials: V
authors.lastname: Tomisić
authors.forename: Marina
authors.initials: M
authors.lastname: Cindrić
mesh_terms: D018360:Crystallography, X-Ray; D008024:Ligands; D015394:Molecular Structure; D013830:Thiadiazoles / Q000138:chemical synthesis*; D053778:Thiazolidines / Q000138:chemical synthesis*; D013882:Thiosemicarbazones / Q000737:chemistry*; D014638:Vanadates / Q000737:chemistry*; D014639:Vanadium / Q000737:chemistry*
chemical_list: D008024:Ligands; D013830:Thiadiazoles; D053778:Thiazolidines; D013882:Thiosemicarbazones; D014639:Vanadium; D014638:Vanadates