Strongly Reducing (Diarylamino)anthracene Catalyst for Metal-Free Visible-Light Photocatalytic Fluoroalkylation

Abstract

Well-defined 9,10-bis­(di­(p-tert-butylphenyl)­amino)­anthracene serves as a photocatalyst for radical fluoroalkylation under visible light irradiation. The diarylamine (Donor)–anthracene (π conjugated system)–diarylamine (Donor) scaffolds are easily accessed by typical palladium-catalyzed cross-coupling protocols of the corresponding halogenated anthracenes with various lithium diarylamides. The anthracene-based photocatalyst exhibits high reducing power, leading to generation of versatile fluoroalkyl radicals such as tri- and difluoroethyl and tri- and difluoromethyl radicals from the corresponding electron-accepting precursors. Catalyst design strongly influences the absorption capability of visible light and stability toward redox stimuli. The detailed mechanistic studies on the metal-free photocatalytic amino-trifluoroethylation of styrene with diphenyl­(2,2,2-trifluoroethyl)­sulfonium trifluoromethanesulfonate suggest that the reaction proceeds via catalytic radical processes rather than radical chain processes. In addition, the static quenching process is involved in the first single-electron-transfer (SET) process from the photocatalyst to the fluoroalkylating reagent. Furthermore, the 1e-oxidized cationic radical species of 9,10-bis­(di­(p-tert-butylphenyl)­amino)­anthracene, a key active catalytic species with long lifetime and a characteristic IVCT (Intervalence Charge Transfer) band in the near IR (NIR) region, is detected. From the viewpoint of elemental strategy initiative and green chemistry, the present noble metal-free organic photocatalytic system provides a pivotal technology to replace ruthenium- and iridium-based metal photocatalysis.

Synthesis, photophysical and electronic properties of tetra-donor- or acceptor-substitutedortho-perylenes displaying four reversible oxidations or reductions

“…In 1974, Dreeskamp, Koch and co-workers showed that the rate of ISC from the uorescent singlet to a triplet state can be increased in perylene by an intermolecular energy transfer to halogenated-naphthalene. 129,130,134 This precedence motivated us to take a closer look at our systems as the uorescence quantum yield of (DPA) 4 -Per is particularly low (4 ¼ 0.26) compared to perylene and triplet sensitizers are of great interest with many applications in phosphorescent materials, [135][136][137] phosphorescent bioimaging, 135,137,138 chemosensors, 135,137,139 photoinitiated polymerization, 137,140 photocatalysis, 137,[141][142][143][144] triplet-triplet annihilation based upconversion, 137,145,146 and oncological or antibacterial photodynamic therapy. 137,147,148 There are a few reports on triplet states of PDIs and these make use of bimolecular triplet sensitization, 149 incorporation of sulfur 150 or heavy metals such as Ir, 131,151,152 Pt, 153 Pd, 152,154 or Ru.…”

“…This intriguing property is interesting for applications including molecular switches, 161,162 receptors, 162,163 photoactive dyads 164 or photocatalysis. 143,165 The donor-substituted counterpart, (DPA) 4 -Per, can be oxidized up to ve times according to cyclic voltammetry studies a Excited at the respective l abs (max) of S 1 ) S 0 . b Pre-exponential factors B n scaled to 100 and given in parentheses.…”

Frontiers in Radical Fluoromethylation by Visible‐Light Organic Photocatalysis

“…In 2018, Eosin B‐catalyzed trifluoromethylation of coumarins 38 was reported by the Zhang and Deng group (Scheme a) . Koike and Akita group reported the keto‐trifluoromethylation of aromatic alkene 40 using 4 t Bu−BDA ((9,10‐bis( p ‐ t Bu−diphenylamino)anthracene)) (Scheme b) . In 2019, Zhang and Xu showed that 4CzIPN induces hydro‐trifluoromethylation of benzyl‐protected homoallylic alcohols and amines 42 concomitant with deprotection through HAT of the radical intermediate A (Scheme c) …”

“…In 2018, the Koike and Akita group found that the above‐mentioned BDA can induce the oxy‐trifluoromethylation of alkenoic acid 44 with the sulfonium‐type reagent 1 f (Scheme a) . In addition, the authors developed a sulfonium‐based CF 2 H reagent 2 e for photocatalytic difluoromethylation in 2017 .…”

“…In 2018, the Koike and Akita group found that the abovementioned BDA can induce the oxy-trifluoromethylation of alkenoic acid 44 with the sulfonium-type reagent 1 f (Scheme 15a). [49] In addition, the authors developed a sulfo-nium-based CF 2 H reagent 2 e for photocatalytic difluoromethylation in 2017. [50] The BDA derivative and perylene were good catalysts for the amino-difluoromethylation of aromatic alkenes 46, resulting in the synthesis of CF 2 HÀ amide compounds 47 (Scheme 15b).…”