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Issue 40, 2015
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Vanadium(V) complexes of a tripodal ligand, their characterisation and biological implications

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Abstract

The reaction of the tripodal tetradentate dibasic ligand 6,6′-(2-(pyridin-2-yl)ethylazanediyl)bis(methylene)bis(2,4-di-tert-butylphenol), H2L1I, with [VIVO(acac)2] in CH3CN gives the VVO-complex, [VVO(acac)(L1)] 1. Crystallisation of 1 in CH3CN at ∼0 °C gives dark blue crystals of 1, while at room temperature it affords dark green crystals of [{VVO(L1)}2μ-O] 3. Upon prolonged treatment of 1 in MeOH, [VVO(OMe)(MeOH)(L1)] 2 is obtained. All three complexes were analysed by single-crystal X-ray diffraction, depicting a distorted octahedral geometry around vanadium. In the reaction of H2L1 with VIVOSO4 partial hydrolysis of the tripodal ligand results in the elimination of the pyridyl fragment of L1 and the formation of H[VVO2(L2)] 4 containing the ONO tridentate ligand 6,6′-azanediylbis(methylene)bis(2,4-di-tert-butylphenol), H2L2II. Compound 4, which was not fully characterised, undergoes dimerization in acetone yielding the hydroxido-bridged [{VVO(L2)}2μ-(OH)2] 5 having a distorted octahedral geometry around each vanadium. In contrast, from a solution of 4 in acetonitrile, the dinuclear compound [{VVO(L2)}2μ-O] 6 is obtained, with a trigonal bipyramidal geometry around each vanadium. The methoxido complex 2 is successfully employed as a functional catechol-oxidase mimic in the oxidation of catechol to o-quinone under air. The process was confirmed to follow a Michaelis–Menten type kinetics with respect to catechol, the Vmax and KM values obtained being 7.66 × 10−6 M min−1 and 0.0557 M, respectively, and the turnover frequency is 0.0541 min−1. A similar reaction with the bulkier 3,5-di-tert-butylcatechol proceeded at a much slower rate. Complex 2 was also used as a catalyst precursor for the oxidative bromination of thymol in aqueous medium. The selectivity shows quite interesting trends, namely when not using excess of the primary oxidizing agent, H2O2, the para mono-brominated product corresponds to ∼93% of the products and no dibromo derivative is formed.

Graphical abstract: Vanadium(v) complexes of a tripodal ligand, their characterisation and biological implications

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Publication details

The article was received on 17 Jul 2015, accepted on 30 Aug 2015 and first published on 04 Sep 2015


Article type: Paper
DOI: 10.1039/C5DT02716K
Author version available: Download Author version (PDF)
Citation: Dalton Trans., 2015,44, 17736-17755
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    Vanadium(V) complexes of a tripodal ligand, their characterisation and biological implications

    M. R. Maurya, B. Uprety, F. Avecilla, P. Adão and J. Costa Pessoa, Dalton Trans., 2015, 44, 17736
    DOI: 10.1039/C5DT02716K

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