Unraveling the Mechanism of a Co(−I)–Ga Photoreductant in the Catalytic Hydrodefluorination of Electron-Rich Fluoroarenes

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Abstract
Strong photoreductants based on first-row transition metals are rare. We report an anionic heterobimetallic Co(-I)-Ga complex, [(H2)CoGa(N(o-(NCH2PiPr2)C6H4)3)]- ([2-H2]-), that catalyzes the hydrodefluorination of electron-rich fluoroarenes under violet light irradiation (390 nm), in the presence of stoichiometric alkoxide base, substoichiometric crown ether, and 1 atm H2. The photodissociation of H2 from [2-H2]- to form the 'naked' Co(-I) species [2]- was observed by ultrafast transient absorption spectroscopy. In combination with its reactivity profile, [2]- is proposed to be photoexcited to form an active photoreductant that reduces fluoroarenes via outer-sphere single-electron transfer. Detailed mechanistic studies suggest that the resultant Co(0) complex (2ox-H2), which is characterized by EPR spectroscopy, re-enters the catalytic cycle via a putative anionic Co(0) hydride intermediate [2ox-H]-. To the best of our knowledge, this is the first example of a 3d metal photoredox catalyst for C-F bond activation.
Funding Information
  • German research council (DFG) (521217569)
  • National Science Foundation (NSF) (2102095)

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