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

Abstract

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 heteroaggregate between H-TEDA(BF₄)₂ and Selectfluor® under photoirradiation, which generates TEDA˙²⁺. A salient feature of our H-TEDA(BF₄)₂-promoted method is its flexibility to use the C(sp³)–H precursor substrate as the limiting reactant, simplifying product isolations.