Ligand-free Suzuki–Miyaura coupling using ruthenium(0) nanoparticles and a continuously irradiating microwave system†
We developed a conceptually and methodologically novel ruthenium(0) nanoparticle catalyst, sulfur-modified Au-supported ruthenium nanoparticles (SARu). SARu is easily prepared through a three-step procedure involving simultaneous in situ metal nanoparticle and nanospace organization. This unique method does not require any conventional preformed template to immobilize and stabilize metal nanoparticles. SARu is an ideal ruthenium catalyst for liquid-phase combinatorial synthesis because it repeatedly catalyzes ligand-free Suzuki–Miyaura coupling of aryl halides, including aryl chlorides, with arylboronic acids with low Ru leaching. Physical analysis of SARu showed that the active species in these reactions were ruthenium (0) nanoparticles with a size of 1–3 nm. Also, we developed a continuously irradiating microwave methodology, which can first time discriminate the heating effect and the microwave effect in microwave experiments.