A BOIMPY Dye Enables Multi‐Photoinduced Electron Transfer Catalysis: Reaching Super‐Reducing Properties
Amit Biswas, Simon Kolb, Sebastian H. Röttger, Arpan Das, Lukas J. Patalag, Partha Pratim Dey, Swagata Sil, Subir Maji, Soumi Chakraborty, Oliver S. Wenger, Anup Bhunia, Daniel B. Werz, Swadhin K. Mandal
Abstract
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. 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. Generally speaking, increased photon uptake leads to a more potent reductant. Here, we report the concept of multi-photoinduced electron transfer catalysis (>2 photons), termed multi-PET, which is enabled by photoinduced one-electron reductions of an organic dye. Further irradiation of the doubly reduced species leads to a photoexcited dianionic super-reductant, which is more potent than Li metal - one of the strongest chemical reductants known. This multi-photon process which is enabled by 390 nm LEDs allows the cleavage of strong carbon-fluorine 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 multi-PET for organic chemistry. In addition, multi-PET enabled Birch-type reductions. Spectroscopic, chemical and computational investigations are presented to gain mechanistic insights.