Activation-Reactivity Inversion in Au(I)-Complex-Photocatalyzed Borylation of Aryl Chlorides

Photocatalytic activation of aryl chlorides remains a challenge because productive bond cleavage depends not only on strong photoreducing power but also on efficient suppression of unproductive back-electron-transfer processes. Here we report a linear two-coordinate Au(I) complex that photocatalyzes the borylation of aryl chlorides, and provide a quantitative analysis of the kinetic factors governing the reactivity. For the majority of aryl chloride substrates tested, catalytic efficiency increased with the rate of photoinduced electron transfer and decreased with the rate of geminate charge recombination, consistent with the canonical kinetic model for typical photoredox catalysis. However, Lewis basic N -heteroaryl chlorides were catalytically inactive despite showing the most favorable electron-transfer kinetics. Spectroscopic, mass spectrometric, and computational studies revealed that the Lewis basic substrate coordinates to the Au(I) center and induces ligand substitution, generating a catalytically inactive species that abrogates the photoreductive pathway. These results demonstrate that substrate-induced catalyst speciation can override the intrinsic photoredox driving force and identify coordination lability as a critical, previously underappreciated determinant of photocatalytic reactivity. More broadly, this work exposes an intrinsic trade-off between photoreducing power and ligand stability in low-coordinate metal photocatalysts and establishes coordination robustness as a key design principle for catalytic activation of strong chemical bonds.