Ultra-small sugar-substituted N-heterocyclic carbene-protected palladium nanoparticles and catalytic activity

Ultra-small Pd nanoparticles (UNPs) represent a distinctive type of nanomaterial making them very attractive for a range of applications. Herein, chiral sugar-substituted N-heterocyclic carbenes (NHCs) with various lengths of alkyl chain (sugar-NHCs-(CnH2n+1)-C-n) were first used to prepare water-soluble Pd@NHCs-sugar UNPs via an efficient ligand-exchange strategy, which can be handled under air and are stable over 10 months. The Pd@NHCs-sugar UNPs were highly monodisperse, with tunable core diameters from 1.7 to 2.1 nm, and an effect of the particle size on the N-substituted aliphatic chains was observed. To investigate the accessibility of the surface, the Pd@NHCs-sugar UNPs were studied as catalysts for C-C coupling reaction in eco-friendly ethanol aqueous solution without any precipitation of metallic Pd. The presence of the longest aliphatic group in the Pd@NHCs-sugar UNPs imparts to them the highest catalyst activity (turnover number and turnover frequency up to 196 000 and 3 920 000 h(-1)).