Gold(I)‐Thiolate Oligomers for Catalytic Hydrogenation of Nitroaromatics in Aqueous and Organic Medium

Thiolated gold nanoclusters (AuNCs) have been introduced to efficiently and selectively catalyze the hydrogenation of nitroaromatics due to the strong interaction of their S−Au‐S staple motifs with the nitro groups of nitroaromatics. However, without a gold core, gold(I)‐thiolate oligomers (AuSOs) with S−Au‐S staple motifs are rarely explored as catalysts for nitroaromatics. Here, we report a straightforward strategy for the synthesis of AuSOs through hydroxyl radical‐induced leaching of glutathione‐capped gold nanoparticles (GSH‐AuNPs). Raman spectroscopy and matrix‐assisted laser desorption/ionization‐time of flight mass spectrometry demonstrated that hydroxyl radical‐triggered etching of the GSH‐AuNPs resulted in the production of AuSOs, including Au4(GSH)7 and Au7(GSH)9. The AuSOs were found to catalyze NaBH4‐mediated hydrogenation of 4‐nitrophenol to 4‐aminophenol with a chemoselectivity of ∼100 % and a normalized rate constant (Knor) of 4.8×105 s− g−1. In addition to the high affinity of the S−Au−S staple motifs for 4‐nitrophenol, the unusual catalytic activity of the AuSOs was attributable to the fact that they efficiently catalyzed the production of H2 from NaBH4 and the reaction of dissolved oxygen and NaBH4. The chemoselectivity and applicability of the AuSOs were further verified by performing the catalytic reaction of methyl 2‐(2‐nitrophenyl) acetate or methyl 4‐nitrobenzoate with NaBH4. Gold(I)‐Thiolate Oligomers: A new class of gold‐based catalysts, prepared from the etching of glutathione‐capped gold nanoparticles with Fenton's reagent, for catalyzing NaBH4 reduction of nitroaromatics to aminoaromatics with high catalytic activity (normalized rate constant >105 S−1 g−1) and excellent chemoselectivity (∼100 %).