Cerium–quinone redox couples put under scrutiny. Issue 4 (8th December 2020)

• Record Type: Journal Article
• Authors: Bayer, Uwe; Werner, Daniel; Berkefeld, Andreas; Maichle-Mössmer, Cäcilia; Anwander, Reiner
• Is Part Of: Chemical science. Volume 12:Issue 4(2021)
• Page Start: 1343
• Page End: 1351
• Publication Date: 2020-12-08
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0sc04489j
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Para -quinones reveal distinct reactivity towards homoleptic cerous silylamide and siloxide complexes depending on both their oxidizing power and the supporting ligand L. Abstract : Homoleptic cerous complexes Ce[N(SiMe3 )2 ]3, [Ce{OSi(O t Bu)3 }3 ]2 and [Ce{OSi i Pr3 }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 (Cl4 BQ) readily form hydroquinolato-bridged ceric complexes of the composition [(Ce IV L3 )2 (μ2 -O2 C6 R4 )]. Less oxidising quinones like 2, 5-di- tert -butyl-1, 4-benzoquinone ( t Bu2 BQ) 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 (Me4 BQ) afford cerous semiquinolates of the type [(Ce III L2 (thf)2 )(μ2 -O2 C6 Me4 )]2 . All complexes were characterised by X-ray diffraction, 1 H, 13 C{ 1 H} and 29 Si NMR spectroscopy, DRIFT spectroscopy, UV-Vis spectroscopy and CV measurements. The species putatively formed during the electrochemical reduction of [Ce IV {N(SiMe3 )2 }3 ]2 (μ2 -O2 C6 H4 ) could be mimicked by chemical reduction with Co II Cp2 yielding [(Ce III {N(SiMe3 )2 }3 )2 (μ2 -O2 C6 H4 )][Co III Cp2 ]2 .