Atomically Precise Alkynyl-Protected Metal Nanoclusters as a Model Catalyst: Observation of Promoting Effect of Surface Ligands on Catalysis by Metal Nanoparticles

Metal nanoclusters whose surface
ligands are removable while keeping
their metal framework structures intact are an ideal system for investigating
the influence of surface ligands on catalysis of metal nanoparticles.
We report in this work an intermetallic nanocluster containing 62
metal atoms, Au34Ag28(PhCC)34, and its use as a model catalyst to explore the importance of surface
ligands in promoting catalysis. As revealed by single-crystal diffraction,
the 62 metal atoms in the cluster are arranged as a four-concentric-shell
Ag@Au17@Ag27@Au17 structure. All
phenylalkynyl (PA) ligands are linearly coordinated to the surface
Au atoms with staple “PhCC–Au–CCPh”
motif. Compared with reported thiolated metal nanoclusters, the surface
PA ligands on Au34Ag28(PhCC)34 are readily removed at relatively low temperatures, while the metal
core remains intact. The clusters before and after removal of surface
ligands are used as catalysts for the hydrolytic oxidation of organosilanes
to silanols. It is, for the first time, demonstrated that the organic-capped
metal nanoclusters work as active catalysts much better than those
with surface ligands partially or completely removed.