Cerium–quinone redox couples put under scrutiny |
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| Authors: | Uwe Bayer Daniel Werner Andreas Berkefeld Ccilia Maichle-Mssmer Reiner Anwander |
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| Institution: | Institut für Anorganische Chemie, Eberhard Karls Universität Tübingen (EKUT), Auf der Morgenstelle 18, 72076 Tübingen Germany, [http://uni-tuebingen.de/syncat-anwander] |
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| Abstract: | Homoleptic cerous complexes CeN(SiMe3)2]3, Ce{OSi(OtBu)3}3]2 and Ce{OSiiPr3}3]2 were employed as thermally robust, weakly nucleophilic precursors to assess their reactivity towards 1,4-quinones in non-aqueous solution. The strongly oxidizing quinones 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or tetrachloro-1,4-benzoquinone (Cl4BQ) readily form hydroquinolato-bridged ceric complexes of the composition (CeIVL3)2(μ2-O2C6R4)]. Less oxidising quinones like 2,5-di-tert-butyl-1,4-benzoquinone (tBu2BQ) tend to engage in redox equilibria with the ceric hydroquinolato-bridged form being stable only in the solid state. Even less oxidising quinones such as tetramethyl-1,4-benzoquinone (Me4BQ) afford cerous semiquinolates of the type (CeIIIL2(thf)2)(μ2-O2C6Me4)]2. All complexes were characterised by X-ray diffraction, 1H, 13C{1H} and 29Si NMR spectroscopy, DRIFT spectroscopy, UV-Vis spectroscopy and CV measurements. The species putatively formed during the electrochemical reduction of CeIV{N(SiMe3)2}3]2(μ2-O2C6H4) could be mimicked by chemical reduction with CoIICp2 yielding (CeIII{N(SiMe3)2}3)2(μ2-O2C6H4)]CoIIICp2]2. Para-quinones reveal distinct reactivity towards homoleptic cerous silylamide and siloxide complexes depending on both their oxidizing power and the supporting ligand L. |
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