Light-Induced Single-Electron Transfer Processes involving Sulfur Anions as Catalysts

Abstract

Photoredox catalysis has evolved as an attractive approach to enable a wide variety of chemical reactions with high selectivity under mild conditions. The development of novel photocatalytic systems is key to obtaining new reactivity and improving their catalytic performances. In this context, cost-effective organic anion-based photocatalysts have recently attracted increasing interest. In particular, sulfur-based anionic catalysts are of interest due to their unique redox properties. This Perspective highlights and discusses recent advances in light-induced single-electron-transfer processes directly involving sulfur anions as catalysts. The content of this Perspective is organized along the different photoinduced electron-transfer pathways between catalysts and substrates.

Light-driven sp3-sp3 cross-coupling of carboxylic acids and alkyl halides over a Ni single-atom catalyst

“…4,5 The renewed interest in this catalytic methodology is owed to the mild reaction conditions employed, the robust functional group tolerance, and the possibility to access redox-neutral reaction routes unattainable with classical ionic chemistry triggered by thermal activation. 6,7 Besides, the use of visible light is seen as an ideal driving force for catalytic transformations, [8][9][10][11][12][13][14] in order to establish a greener chemical industry within the forthcoming decarbonization of our economy. 15 Despite the novelty of the approach, the method relies on the use of Ir or Ru-containing photocatalysts (chiefly, Ir[dF(CF3)ppy]2(dtbbpy)PF6 or Ru[dF(CF3)ppy]2(dtbbpy)PF6, where (dF(CF3)ppy = 2-(2,4difluorophenyl)-5-(trifluoromethyl)pyridine, and dtbbpy = 4,4′-di-tert-butyl-2,2'-bipyridine)), homogeneous Ni co-catalysts, and additional bipyridyl compounds for ligating the Ni centers, as summarized in Fig.…”

Metal-free photo-induced sulfidation of aryl iodide and other chalcogenation

“…In the past few years, the photoredox transition metal-catalyzed C-S cross-coupling between aryl halides and thiols/disulfides have been widely developed, in which a series of Cu, Ni, Pd, and Rh transition metals are still utilized as catalysts (Figure 2C). (Uyeda et al, 2013;Wang et al, 2013;Johnson et al, 2016;Jouffroy et al, 2016;Jouffroy et al, 2016;Oderinde et al, 2016;Li et al, 2020;Sandfort et al, 2020;Brahmachari et al, 2021;Qin et al, 2021;Yang et al, 2021) Meanwhile, A series of photo-induced transition-metal and photosensitizer free C−S cross-coupling methods has been developed (Bunnett and Creary, 1974;Liu et al, 2017;Pramanik et al, 2020;Dawei Cao et al, 2021;Nandy et al, 2021;Saroha et al, 2021;Shun Wang et al, 2021;Uchikura et al, 2021;Wang et al, 2022). For the metal-free synthesis of aryl sulfides, Hong and co-workers developed a convergent, organocatalytic visible-light-mediated process for the synthesis of diaryl sulfides (Hong et al, 2017).…”

Light‐Driven Hydrodefluorination of Electron‐Rich Aryl Fluorides by an Anionic Rhodium‐Gallium Photoredox Catalyst

“…[2] One exception is a pyridine-thiolate system that mediates the borylation of relatively inert aryl fluorides; however, the maximal turnovers attained was fewer than three. [9,10] To expand the substrate scope of transition-metal-based catalysts, judicious modifications of the ligand framework in the Ir(ppy) 3 progenitor can boost the overall chemical potential and improve reaction rates. For example, substituting a single ppy ligand with an electron-rich β-diketiminate ligand (NacNac) can increase the excited-state reduction strength by � 300 to 500 mV (Figure 1).…”