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Issue 19, 2013
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Synthesis, characterization and catalytic activity of copper(II) complexes containing a redox-active benzoxazole iminosemiquinone ligand

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Abstract

A tridentate benzoxazole-containing aminophenol ligand HLBAP was synthesized and complexed with CuII. The resulting CuII complexes were characterized by X-ray, IR, UV-vis-NIR spectroscopies, and magnetic susceptibility studies, demonstrating that the ligand is oxidized to the o-iminosemiquinone form [LBIS] in the isolated complexes. LBISCuIICl exhibits a distorted tetrahedral geometry, while LBISCuIIOAc is square pyramidal. In both solid state structures the ligand is coordinated to CuIIvia the benzoxazole, as well as the nitrogen and oxygen atoms from the o-iminosemiquinone moiety. The chloride, or acetate group occupies the fourth and/or fifth positions in LBISCuIICl and LBISCuIIOAc, respectively. Magnetic susceptibility measurements indicate that both complexes are diamagnetic due to antiferromagnetic coupling between the d9 CuII centre and iminosemiquinone ligand radical. Electrochemical studies of the complexes demonstrate both a quasi-reversible reduction and oxidation process for the Cu complexes. While LBISCuIIX (X = Cl) is EPR-silent, chemical oxidation affords a species with an EPR signal consistent with ligand oxidation to form a d9 CuII iminoquinone species. In addition, chemical reduction results in a CuII centre most likely bound to an amidophenoxide. Mild and efficient oxidation of alcohol substrates to the corresponding aldehydes was achieved with molecular oxygen as the oxidant and LBISCuIIX–Cs2CO3 as the catalyst.

Graphical abstract: Synthesis, characterization and catalytic activity of copper(ii) complexes containing a redox-active benzoxazole iminosemiquinone ligand

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Publication details

The article was received on 01 Jan 2013, accepted on 20 Feb 2013 and first published on 14 Mar 2013


Article type: Paper
DOI: 10.1039/C3DT00004D
Citation: Dalton Trans., 2013,42, 6829-6839
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    Synthesis, characterization and catalytic activity of copper(II) complexes containing a redox-active benzoxazole iminosemiquinone ligand

    S. E. Balaghi, E. Safaei, L. Chiang, E. W. Y. Wong, D. Savard, R. M. Clarke and T. Storr, Dalton Trans., 2013, 42, 6829
    DOI: 10.1039/C3DT00004D

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