One-pot installation of N-heterocyclic carbenes on gold nanoparticles through counterion-dependent mild-base...

N-heterocyclic carbene (NHC)-stabilized gold nanoparticles offer exceptional chemical and thermal stability, yet their installation typically requires multistep procedures, strong bases, or strictly inert conditions. We report a practical one-pot method that enables high-coverage NHC functionalization of gold nanoparticles using only imidazolium salts and a mild base. Systematic control experiments and spectroscopic analysis suggest a counterion-dependent mild-base activation pathway in which persistent HCO₃^-/CO₂-derived intermediates are not observed under the applied reaction conditions. Instead, the data are most consistent with the formation of an intermediate that, in proximity to the nanoparticle interface, decomposes to form an Au-C bond. Optimized reaction conditions enable quantitative ligand exchange while suppressing particle ripening. The method is tolerant to air and moisture and is applicable to a broad range of NHC precursors, including benzimidazolium, imidazolinium, and mesoionic carbenes, as well as to different nanoparticle systems based on gold, silver, and copper. These results provide a general and mild strategy for preparing robust NHC-functionalized nanomaterials.