Polysulfide Anions as Visible Light Photoredox Catalysts for Aryl Cross-Couplings

Abstract

Polysulfide anions are endowed with unique redox properties, attracting considerable attentions for their applications in alkali metals−sulfur batteries. However, the employment of these anionic species in redox catalysis for small molecule synthesis remains underdeveloped due to their moderate−poor electrochemical potential in the ground state, whereas some of them are characterized by photoabsorptions in visible spectral regions. Herein, we disclose the use of polysulfide anions as visible light photoredox catalysts for aryl cross-coupling reactions. The reaction design enables single-electron reduction of aryl halides upon the photoexcitation of tetrasulfide dianions (S 4 2− ). The resulting aryl radicals are engaged in (hetero)biaryl cross-coupling, borylation, and hydrogenation in a redox catalytic regime involving S 4• − /S 4 2− and S 3 • − /S 3 2− redox couples.

Electro‐mediated PhotoRedox Catalysis for Selective C(sp3)–O Cleavages of Phosphinated Alcohols to Carbanions

“…One solution is to generate photoexcitable radical ions by multi‐photon processes. [3] Such photoexcited radical ions are highly oxidizing[ 3a , 3b ] or reducing species,[ 3c , 3d , 3e , 3f , 3g , 3h ] leading to a significantly expanded redox “window” for activating inert substrates. Sacrificial redox additives (e.g.…”

Electro‐mediated PhotoRedox Catalysis for Selective C(sp3)–O Cleavages of Phosphinated Alcohols to Carbanions

“…One solution is to generate photoexcitable radical ions by multi‐photon processes [3] . Such photoexcited radical ions are highly oxidizing [3a,b] or reducing species, [3c–h] leading to a significantly expanded redox “window” for activating inert substrates. Sacrificial redox additives (e.g.…”

Leveraging of Sulfur Anions in Photoinduced Molecular Transformations

“…Chiba recently disclosed that these polysulfide anions could serve as visible-light photoredox catalysts to promote a series of aryl cross-coupling reactions. 44 For example, a heterobiaryl cross-coupling reaction between 4′-bromoacetophenone ( 10 ) and N -methylpyrrole ( 80 ) was promoted by a catalytic amount of K 2 S x in DMSO under irradiation with visible light (440 nm), affording biaryl 81 in good yield within 1.5 h ( Scheme 11 ). The process is proposed to be initiated by SET reduction of aryl bromide 10 by photoexcited S 4 2– to form the radical anion of aryl bromide 82 , which subsequently undergoes C–Br bond mesolysis to form aryl radical 83 .…”