| Autor: |
Dragancea D; Institute of Chemistry, Academy of Sciences of Moldova , Academiei Str. 3, MD-2028 Chisinau, Moldova., Talmaci N; Institute of Chemistry, Academy of Sciences of Moldova , Academiei Str. 3, MD-2028 Chisinau, Moldova., Shova S; 'Petru Poni' Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, 700487 Iasi, Romania., Novitchi G; Laboratoire National des Champs Magnetiques Intenses-CNRS, Universite Joseph Fourier , 25 Avenue des Martyrs, 38042 Grenoble Cedex 9, France., Darvasiová D; Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology , Radlinského 9, 81237 Bratislava, Slovakia., Rapta P; Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology , Radlinského 9, 81237 Bratislava, Slovakia., Breza M; Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology , Radlinského 9, 81237 Bratislava, Slovakia., Galanski MS; Institute of Inorganic Chemistry, University of Vienna , Währinger Strasse 42, A-1090 Vienna, Austria., Kožı́šek J; Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology , Radlinského 9, 81237 Bratislava, Slovakia., Martins NM; Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade de Lisboa , Av. Rovisco Pais, 1049-001 Lisboa, Portugal., Martins LM; 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., Pombeiro AJ; Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade de Lisboa , Av. Rovisco Pais, 1049-001 Lisboa, Portugal., Arion VB; Institute of Inorganic Chemistry, University of Vienna , Währinger Strasse 42, A-1090 Vienna, Austria. |
| Abstrakt: |
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. |
