title: Vanadium(V) Complexes with Substituted 1,5-bis(2-hydroxybenzaldehyde)carbohydrazones and Their Use As Catalyst Precursors in Oxidation of Cyclohexane.
abstract: Six dinuclear vanadium(V) complexes have been synthesized: NH4[(VO2)2((H)LH)] (NH4[1]), NH4[(VO2)2((t-Bu)LH)] (NH4[2]), NH4[(VO2)2((Cl)LH)] (NH4[3]), [(VO2)(VO)((H)LH)(CH3O)] (4), [(VO2)(VO)((t-Bu)LH)(C2H5O)] (5), and [(VO2)(VO)((Cl)LH)(CH3O)(CH3OH/H2O)] (6) (where (H)LH4 = 1,5-bis(2-hydroxybenzaldehyde)carbohydrazone, (t-Bu)LH4 = 1,5-bis(3,5-di-tert-butyl-2-hydroxybenzaldehyde)carbohydrazone, and (Cl)LH4 = 1,5-bis(3,5-dichloro-2-hydroxybenzaldehyde)carbohydrazone). The structures of NH4[1] and 4-6 have been determined by X-ray diffraction (XRD) analysis. In all complexes, the triply deprotonated ligand accommodates two V ions, using two different binding sites ONN and ONO separated by a diazine unit -N-N-. In two pockets of NH4[1], two identical VO2(+) entities are present, whereas, in those of 4-6, two different VO2(+) and VO(3+) are bound. The highest oxidation state of V ions was corroborated by X-ray data, indicating the presence of alkoxido ligand bound to VO(3+) in 4-6, charge density measurements on 4, magnetic susceptibility, NMR spectroscopy, spectroelectrochemistry, and density functional theory (DFT) calculations. All four complexes characterized by XRD form dimeric associates in the solid state, which, however, do not remain intact in solution. Compounds NH4[1], NH4[2], and 4-6 were applied as alternative selective homogeneous catalysts for the industrially significant oxidation of cyclohexane to cyclohexanol and cyclohexanone. The peroxidative (with tert-butyl hydroperoxide, TBHP) oxidation of cyclohexane was performed under solvent-free and additive-free conditions and under low-power microwave (MW) irradiation. Cyclohexanol and cyclohexanone were the only products obtained (high selectivity), after 1.5 h of MW irradiation. Theoretical calculations suggest a key mechanistic role played by the carbohydrazone ligand, which can undergo reduction, instead of the metal itself, to form an active reduced form of the catalyst.
authors: Institute of Chemistry, Academy of Sciences of Moldova , Academiei Str. 3, MD-2028 Chisinau, Moldova.
authors: Diana
authors: D
authors: Dragancea
authors: Institute of Chemistry, Academy of Sciences of Moldova , Academiei Str. 3, MD-2028 Chisinau, Moldova.
authors: Natalia
authors: N
authors: Talmaci
authors: "Petru Poni" Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, 700487 Iasi, Romania.
authors: Sergiu
authors: S
authors: Shova
authors: Laboratoire National des Champs Magnetiques Intenses-CNRS, Universite Joseph Fourier , 25 Avenue des Martyrs, 38042 Grenoble Cedex 9, France.
authors: Ghenadie
authors: G
authors: Novitchi
authors: Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology , Radlinského 9, 81237 Bratislava, Slovakia.
authors: Denisa
authors: D
authors: Darvasiová
authors: Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology , Radlinského 9, 81237 Bratislava, Slovakia.
authors: Peter
authors: P
authors: Rapta
authors: Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology , Radlinského 9, 81237 Bratislava, Slovakia.
authors: Martin
authors: M
authors: Breza
authors: Institute of Inorganic Chemistry, University of Vienna , Währinger Strasse 42, A-1090 Vienna, Austria.
authors: Mathea Sophia
authors: MS
authors: Galanski
authors: Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology , Radlinského 9, 81237 Bratislava, Slovakia.
authors: Jozef
authors: J
authors: Kožı́šek
authors: Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade de Lisboa , Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
authors: Nuno M R
authors: NM
authors: Martins
authors: Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade de Lisboa , Av. Rovisco Pais, 1049-001 Lisboa, Portugal.|Chemical Engineering Department, Instituto Superior de Engenharia de Lisboa, Instituto Politécnico de Lisboa , R. Conselheiro Emídio Navarro, 1959-007 Lisboa, Portugal.
authors: Luísa M D R S
authors: LM
authors: Martins
authors: Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade de Lisboa , Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
authors: Armando J L
authors: AJ
authors: Pombeiro
authors: Institute of Inorganic Chemistry, University of Vienna , Währinger Strasse 42, A-1090 Vienna, Austria.
authors: Vladimir B
authors: VB
authors: Arion