Water-Soluble Palladium Nanoclusters as Catalysts in Ligand-Free Suzuki-Miyaura Cross-Coupling Reactions.

This Letter reports Pd-nanocluster catalysts and their formation in ligand-free Suzuki-Miyaura reactions with palladium-(II) nitrate as a precatalyst. The catalysts are water-soluble neutral Pd tetramer and trimer in their singlet electronic states, as identified by UV-vis absorption spectroscopy, and are formed by leaching of spherical Pd(0) nanoparticles with an average diameter of about 3 nm. The Pd(0) nanoparticles are produced by reducing palladium-(II) nitrate and characterized with transmission electron microscopy and Pd K-edge extended X-ray fine structure spectroscopy. The Pd-(II) reduction is induced by ethanol, enhanced by potassium hydroxide, and monitored with X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]