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Issue 43, 2016
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Vanadium(IV and V) complexes of pyrazolone based ligands: Synthesis, structural characterization and catalytic applications

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Abstract

The ONO donor ligands obtained from the condensation of 4-benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-one (Hbp) with benzoylhydrazide (H2bp-bhz I), furoylhydrazide (H2bp-fah II), nicotinoylhydrazide (H2bp-nah III) and isonicotinoylhydrazide (H2bp-inh IV), upon treatment with [VIVO(acac)2], lead to the formation of [VIVO(bp-bhz)(H2O)] 1, [VIVO(bp-fah)(H2O)] 2, [VIVO(bp-nah)(H2O)] 3 and [VIVO(bp-inh)(H2O)] 4, respectively. At neutral pH the in situ generated aqueous K[H2VVO4] reacts with ligands I and II, forming potassium salts, K(H2O)2[VVO2(bp-bhz)] 5 and K(H2O)2[VVO2(bp-fah)] 6, while ligands III and IV give neutral complexes, [VVO2(Hbp-nah)] 9 and [VVO2(Hbp-inh)] 10, respectively. Acidification of aqueous solutions of 5 and 6 with HCl also gives neutral complexes [VVO2(Hbp-bhz)] 7 and [VVO2(Hbp-fah)] 8, respectively. Complexes 1–4, upon slow aerial oxidation in methanol, convert into monooxidovanadium(V) complexes, [VVO(bp-bhz)(OMe)] 11, [VVO(bp-fah)(OMe)] 12, [VVO(bp-nah)(OMe)] 13 and [VVO(bp-inh)(OMe)] 14, respectively. All complexes were characterized by various spectroscopic techniques like FT-IR, UV-visible, EPR (for complexes 1–4) and NMR (1H, 13C and 51V), elemental analysis, thermogravimetry and single crystal X-ray diffraction (for complexes 510 and 12). In the solid state, all complexes characterized by X-ray diffraction show the metal ion 5-coordinated in a distorted square pyramidal geometry. Complexes 11–14 were tested as catalysts for the one-pot three-component (ethylacetoacetate, benzaldehyde and ammonium acetate) dynamic covalent assembly, via Hantzsch reaction, using hydrogen peroxide as oxidant in solution and under solvent-free conditions. The complexes are also active catalysts for the oxidation of tetralin to tetralone with H2O2 as oxidant. The influence of the amounts of catalyst and oxidant, and solvent, temperature and time on the catalyzed reactions was investigated.

Graphical abstract: Vanadium(iv and v) complexes of pyrazolone based ligands: Synthesis, structural characterization and catalytic applications

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Publication details

The article was received on 01 Sep 2016, accepted on 15 Sep 2016 and first published on 15 Sep 2016


Article type: Paper
DOI: 10.1039/C6DT03425J
Citation: Dalton Trans., 2016,45, 17343-17364
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    Vanadium(IV and V) complexes of pyrazolone based ligands: Synthesis, structural characterization and catalytic applications

    M. R. Maurya, B. Sarkar, F. Avecilla and I. Correia, Dalton Trans., 2016, 45, 17343
    DOI: 10.1039/C6DT03425J

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