Electronically tuned triazole-derived mesoionic carbenes enhance the stability of Ag and Cu nanoparticles.

Stabilizing silver and copper nanoparticles remains a persistent challenge due to their rapid oxidation and surface degradation under ambient conditions. Ligand engineering offers a powerful strategy to control nanoparticle stability; however, N-heterocyclic carbenes (NHCs), including mesoionic NHCs (mNHCs), despite their strong metal-binding character, have shown limited success in stabilizing these oxidation-prone systems. Here, we report a new subclass of mNHCs based on carbonyl-conjugated 1,2,3-triazole scaffolds. Conjugation of an ester carbonyl group significantly enhances the π-acceptor character of the carbene while preserving strong σ-donation, as supported by DFT and EDA-NOCV analyses revealing increased π-backbonding and strengthened metal-carbene covalency relative to conventional triazole-derived mNHCs. These electronically tuned ligands enable the formation of highly robust silver nanoparticles with pronounced resistance to thermal, oxidative, and thiol-induced degradation, while extending the oxidative lifetime of copper nanoparticles by approximately fourfold compared to the existing NHC-stabilized systems. ATR-FTIR measurements further corroborate enhanced π-backbonding through characteristic carbonyl red-shifts upon metal coordination. Together, these findings demonstrate that electronic modulation of mNHCs provides a general strategy to control metal-ligand interactions at nanoparticle surfaces and thereby enhance the stability of coinage metal nanomaterials.