Counterion-enabled divergent reactivity in dinuclear gold photoredox catalysis

Tuning the electronics of photocatalysts is crucial for controlling the reactivity pathways in photoredox catalysis. While the key approaches like ligand engineering and donor-acceptor modulation are crucial, they invariably require multistep synthesis for the generation of a photocatalyst library. Counterions are inherent to all cationic photocatalysts but interestingly, their potential to influence reactivity has been overlooked. Herein, we demonstrate an unforeseen reactivity control that uses counterions to tune electronics in dinuclear-gold-photoredox catalysis. The photoexcited [Auᴵ–Auᴵ]²⁺ complex selectively reduces S(VI)-Cl bonds, whereas halide addition generates a potent reductant [Au¹⁄²–Au¹⁄²]⁺, capable of reducing otherwise unreactive S(VI)-F bonds. A successful application of this concept has been demonstrated in the alkene functionalization using sulfonyl chlorides and sulfonyl fluorides. Detailed mechanistic studies provided the first experimental evidence for the [Au¹/²–Au¹/²]⁺ species, which had been proposed earlier but never been experimentally validated.