Photocatalytic Hydroxylation and Oxidative Coupling Reactions Mediated by Multinuclear Au(I) Supramolecular Clusters

Abstract

Polynuclear Au(I) cluster photocatalysts, known for their high activity and stability, hold substantial potential in organic synthetic chemistry. This study synthesized two Au(I) supramolecular cluster catalysts with different nuclearities: a tetranuclear cluster, C1 ([(dppmAu₂)₂L¹] • PF₆⁻), and a hexadecanuclear cluster, C2 [(dppmAu₂)₆(Au₄)(L¹)₄] • 4PF₆⁻, through a multicomponent stepwise self-assembly approach. Both cluster structures feature aurophilicity interaction motifs that endow them with exceptional photocatalytic performance, exhibiting optical band gaps of 2.27 eV and 2.41 eV, respectively. Upon photoexcitation, these clusters efficiently generate reactive oxygen species, significantly enhancing their photocatalytic efficacy for the oxidative hydroxylation of phenylboronic acids and oxidative coupling of benzylamines under mild conditions. Catalytic efficiencies exceeding 90 % were achieved. Turnover frequencies for C2 and C1 were measured at 52.045 h⁻¹ and 6.030 h⁻¹, respectively, representing the highest efficiencies reported for photocatalysts to date. Compared to C1, C2 exhibited superior photocatalytic activity, attributed to its higher photoelectric sensitivity and greater exposure of active metal sites. Using a combination of experimental data and density functional theory calculations, the plausible mechanisms were proposed for two photocatalytic reactions. This study demonstrates that the use of multicomponent cooperative self-assembly strategy to synthesize high-nuclearity Au(I) clusters offers innovative pathways for the development of efficient, green, light-driven organic synthesis.