The Direct Non-Perturbing Leaching Test in the Phosphine-Free Suzuki-Miyaura Reaction Catalyzed by Palladium Nanoparticles

The aryl halides normally unreactive in the reaction with phenylboronic acid in the presence of a palladium nanoparticle catalyst were shown to become involved, if a more reactive aryl iodide is simultaneously participating in the process. The involvement phenomenon can be interpreted as a direct evidence of the formation of smaller and more reactive palladium nanoparticles through leaching from the initial nanocatalyst. The involvement test was applied both to free unsupported Pd nanoparticles and supported species, thus exhibiting essentially the same character of evolutions of various nanomaterials during the catalytic transformation associated with leaching of reactive species from the initial particles. The system allows for concurrent processing of less reactive aryl bromides and even chlorides together with much more reactive aryl iodides. The interpretation of the observed phenomena and implications for practical realization of nanoparticle catalysts are discussed.