Herein, we uncover a hitherto hidden role of H-TEDA(BF4)2 – a cheap, stable, recoverable by-product of radical C(sp3)–H fluorinations using Selectfluor®. This forms a photoactive, mixed heteroaggregate with Selectfluor® which underlies the reactivity of visible light photochemical fluorination reactions of unactivated C(sp3)–H bonds. Where previous reports claim to be ‘photocatalytic’, reactions work without photocatalyst when H-TEDA(BF4)2 is dosed in at the start. Our results demonstrate that ‘photocatalysts’ are only necessary to generate a sufficient amount of nascent H-TEDA(BF4)2, whose heteroaggregate with Selectfluor® takes over as the main photoactive species. Mechanistic studies suggest the formation of a heterocomplex between H-TEDA(BF4)2 and Selectfluor® under photoirradiation, which generates TEDA•2+. A salient feature of our method is its flexibility to use the C(sp3)–H precursor substrate as the limiting reactant, simplifying isolations of products from unreacted precursors.

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