Pascal Komorr

Chalcogenide radical cations are typically transient species. By one-electron oxidation of kinetically-stabilised arylchalcogenyl iodides, three stable representatives could be isolated and fully characterised.

Chalcogenide radical cations [R₂E]^•+ (E = S, Se, Te) are commonly short-lived intermediates of fundamental interest. Sulfide radical cations in particular are associated in vivo with oxidative stress and neuropathological processes. Having succeeded in the preparation of meta-terphenyl-based dichalcogenide radical cations [R₂E₂]^•+ (E = S, Se, Te), and a telluride analogue [R₂Te]^•+ in the past, we aimed to complete the series regarding sulfur and selenium. Here we report on the single-electron oxidation of diarylchalcogenides M^SFluindPhE (E = S, Se, Te; M^SFluind = dispiro[fluorene-9,3’-(1’,1’,7’,7’-tetramethyl-s-hydrindacen-4’-yl)-5’,9”-fluorene]) using XeF₂ in the presence of K[B(C₆F₅)₄], which afforded deeply coloured and isolable radical cation salts [M^SFluindPhE][B(C₆F₅)₄] (E = S, Se, Te). Structural and electronic properties were characterised by electron paramagnetic spectroscopy, cyclic voltammetry, optical absorption spectroscopy and single crystal X-ray diffraction (E = Se, Te), combined with extensive quantum mechanical computations.

The bulky aryl thiol, M^SFluindSH (1S), and aryl selenol, M^SFluindSeH (1Se), possessing a tetramethyl‐s‐hydrindacen‐4’‐yl‐(Rind)‐based substituent containing two fluorenyl groups in 9 and 9’‐positions, were prepared (M^SFluind=dispiro[fluorene‐9,3’‐(1’,1’,7’,7’‐tetramethyl‐s‐hydrindacene‐4’‐yl)‐5’,9’’‐fluorene]). The reaction of 1S and 1Se with Et₂Zn provided a monomeric zinc aryl thiolate, Zn(SM^SFluind)₂ (2S), and zinc aryl selenolate, Zn(SeM^SFluind)₂ (2Se), with essentially two‐coordinate zinc atoms.

Sterically encumbered bis(m‐terphenyl)chalcogenides, (2,6‐Mes₂C₆H₃)₂E (E=S, Se, Te) were obtained by the reaction of the chalcogen tetrafluorides, EF₄, with three equivalents of m‐terphenyl lithium, 2,6‐Mes₂C₆H₃Li. The single‐electron oxidation of (2,6‐Mes₂C₆H₃)₂Te using XeF₂/K[B(C₆F₅)₄] afforded the radical cation [(2,6‐Mes₂C₆H₃)₂Te][B(C₆F₅)₄] that was isolated and fully characterized. The electrochemical oxidation of the lighter homologs (2,6‐Mes₂C₆H₃)₂E (E=S, Se) was irreversible and impaired by rapid decomposition.