Abstract
Homoleptic cerous complexes Ce[N(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.
Highlights
Quinones are multifunctional organic molecules exhibiting intriguing redox behaviour.[1,2] Of particular note is their importance in biological electron–transfer processes (photosynthesis, respiration)[3] and in industrial catalysis (anthraquinone process for hydrogen peroxide production).[4]
Of particular note is their importance in biological electron–transfer processes[3] and in industrial catalysis.[4]
DHBQ was probed as a bridging redox-active ligand in bimetallic [LnCl2(thf)3]2(mbobq) (Ln 1⁄4 Y, Dy; bobq 1⁄4 2,5-bisoxide-1,4-benzoquinolato) to build single-molecule magnets.[12]
Summary
Quinones are multifunctional organic molecules exhibiting intriguing redox behaviour.[1,2] Of particular note is their importance in biological electron–transfer processes (photosynthesis, respiration)[3] and in industrial catalysis (anthraquinone process for hydrogen peroxide production).[4]. Scheme 1 Oxidation of trivalent cerium complexes with 1,4-quinone derivatives under formation of hydroquinolato-bridged ceric complexes.
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