Hydrogen-Bonded Organic Frameworks Supported Au(I)/Au(0) Mixed-Valence Nanoparticles for Visible-Light-Driven Selective Oxidation of Sulfides

Selective oxidation of sulfides to sulfoxides is often plagued by overoxidation to sulfones and catalyst deactivation. Herein, we report a heterogeneous catalyst comprising Au(I)/Au(0) mixed-valence nanoparticles supported on hydrogen-bonded organic framework HOF-101 (AuNP@HOF-101). Using HAuCl₄ as the gold precursor, the π-conjugated framework of HOF-101 stabilizes Au(I) species, and controlled stepwise reduction with NaBH₄ spontaneously generates well-dispersed AuNPs (mean diameter 1.8 nm) with a stable Au(0)/Au(I) ratio of 72:28. The π···Au interactions stabilize the mixed-valence state against disproportionation. Under visible-light irradiation, HOF-101 generates singlet oxygen (¹O₂), while surface Au(I) sites anchor sulfides through soft acid-soft base interactions. Using methyl phenyl sulfide as a model substrate, AuNP@HOF-101 achieves 93.8% conversion with 98.2% sulfoxide selectivity under mild conditions (room temperature, O₂ atmosphere). The catalyst demonstrates broad substrate compatibility and excellent recyclability over ten cycles without significant activity loss or gold leaching (<0.3%). This work establishes a new paradigm for designing stable mixed-valence gold nanoparticle catalysts within HOFs for selective oxidation reactions.