Protodefluorinated Selectfluor® heteroaggregate photoinduces direct C (sp3)–H fluorinations without photocatalyst

Herein, we uncover a hitherto hidden role of H-TEDA(BF4)2 - a cheap, stable, recoverable by-product of radical C(sp 3)-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(sp 3)-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 heteroaggregate between H-TEDA(BF4)2 and Selectfluor® under photoirradiation, which generates TEDA˙2+. A salient feature of our H-TEDA(BF 4) 2-promoted method is its flexibility to use the C(sp 3)-H precursor substrate as the limiting reactant, simplifying product isolations.