Reduced-Phenalenyl-Based Molecule as a Super Electron Donor for Radical-Mediated C–N Coupling Catalysis at Room Temperature

We demonstrate that an in situ generated di-reduced phenalenyl (PLY) species accumulates sufficiently high energy and acts as a super electron donor to generate aryl radicals from aryl halides to accomplish Buchwald–Hartwig-type C–N cross-coupling reactions at room temperature. This catalytic protocol does not require any external stimuli such as heat, light, or cathodic current. This protocol shows a wide variety of substrate scope covering different genres of aryl and heteroaryl halides with various aromatic as well as aliphatic amines and late-stage functionalization of the well-known natural products. The control experiments, along with extensive density functional theory (DFT) calculations, unveil that the aryl radical is generated by a single electron transfer from the di-reduced PLY to the aryl halide substrate. The aryl radical acts as an electrophile and binds with amine, leading to the chemically driven radical-mediated C–N cross-coupling under transition-metal-free conditions

Triple-photoinduced electron transfer (tri-PET) catalysis for activation of super strong bonds

Single electron redox processes allow the formation of highly reactive radicals – valuable intermediates that enable unique transformations in organic chemistry (1,2). An established concept to create radical intermediates is photoexcitation of a catalyst to a higher energy intermediate, subsequently leading to a photoinduced electron transfer (PET) with a reaction partner (3–7). The known concept of consecutive photoinduced electron transfer (con PET) leads to catalytically active species even higher in energy by the uptake of two photons (8). This process has already been used widely for catalytic reductions; however, limitations towards strong bonds and electron rich substrates remain (9,10). Generally speaking, increased photon uptake leads to a more potent reductant. Here, we introduce triple-photoinduced electron transfer catalysis, termed tri-PET, enabled by the three-photon uptake of a dye molecule leading to an excited dianionic super-reductant which is more potent than Li metal (11) – one of the strongest chemical reductants known. Irradiation of the metal-free catalyst by violet light enables the cleavage of strong carbon-fluoride bonds and reduction of other halides even in very electron-rich substrates. The resulting radicals are quenched by hydrogen atoms or engaged in carbon-carbon and carbon-phosphorus bond formations, highlighting the utility of tri-PET for organic chemistry. Thorough spectroscopic, chemical and computational investigations are presented to understand this novel mode of photoredox catalysis. The existence of the dianion which takes up a third photon when irradiated was proven by X-ray diffraction analysis