Tetrachlorophthalimides as Organocatalytic Acceptors for Electron Donor–Acceptor Complex Photoactivation

Abstract

Excitation of photoactive electron donor−acceptor (EDA) complexes is an effective way to generate radicals. Applications in a catalytic regime typically use catalytic donors. Herein, we report that readily available electron-poor tetrachlorophthalimides can act as effective organocatalytic acceptors to trigger the formation of EDA complexes with a variety of radical precursors not amenable to previous catalytic methods. Excitation with visible light generates carbon radicals under mild conditions. The versatility of this EDA complex catalytic platform allowed us to develop mechanistically distinct radical reactions, including in combination with a cobalt-based catalytic system. Quantum yield measurements established that a closed catalytic cycle is operational, which hints at the ability of tetrachlorophthalimides to readily turn over and govern each catalytic cycle.

Recent Advances in Employing Catalytic Donors and Acceptors in Electron Donor–Acceptor Complex Photochemistry

“…Recently, Melchiorre and co-workers have reported that readily available electron-deficient tetrachlorophthalimides can act as catalytic acceptors in EDA complex photochemistry for Giese-type reactions . Their strategy is compatible with a variety of radical precursors including dihydropyridines (DHPs), alkylsilicates, and organotrifluoroborates.…”

“…The quantum yield (Φ) of the reaction was measured to be 0.04, consistent with a closed catalytic cycle. The authors were also successful in combining EDA photocatalysis with cobaloxime catalysis to perform Heck-type cross-coupling reactions …”

“…Recently, Melchiorre and co-workers have reported that readily available electrondeficient tetrachlorophthalimides can act as catalytic acceptors in EDA complex photochemistry for Giese-type reactions. 69 Their strategy is compatible with a variety of radical precursors including dihydropyridines (DHPs), alkylsilicates, and organotrifluoroborates. The redox-neutral catalytic cycle is initiated via the formation of EDA complex M between N-phenyltetrachlorophthalamide 67 and the radical precursor (Scheme 14).…”

Electron donor–acceptor complex-catalyzed photoredox reactions mediated by DIPEA and inorganic carbonates

“…3 a ,5 Since 2019, the EDA catalysis strategy, i.e. EDA complex-mediated radical generation with catalytic amounts of electron donors 6–9 or acceptors, 10 has emerged as a rapidly growing subfield. Since the donor or acceptor catalyst functions through the association with leaving group-bearing moieties, the EDA catalysis approach is selective and efficient as was demonstrated in the pioneering studies.…”

Direct photolysis of 4-tert-alkyl-1,4-dihydropyridines under blue-light irradiation for the generation of tertiary alkyl radicals

“…UV-vis studies also demonstrated that an electron donor–acceptor (EDA) complex between the DHP anion and the Michael acceptor was unlikely under our reaction conditions (see ESI†). 24…”