The betaine adduct of N-heterocyclic carbene and carbodiimide (ICy·((p-tol))NCN) was found to be a very efficient ligand to prepare very small (1-1.3 nm) ruthenium nanoparticles (RuNPs). The coordination of the ligand on the metal surface takes place through the carbodiimide moiety. The resulting RuNPs led to decarbonylation of THF and showed size selectivity for styrene hydrogenation.