Group 10 Metal Complexes with Chelating Macrocyclic Dicarbene Ligands Bearing a 2,6-Lutidinyl Bridge: Synthesis, Reactivity, and Catalytic Activity

Palladium(II) and platinum(II) complexes of the title ligands have been prepared; the two carbene moieties of the ligand coordinate to the metal in cis fashion, while the bridging pyridyl group remains outside the metal coordination sphere but close to the metal center. In this peculiar situation, the pyridyl group can assist the oxidation of the metal center to the +IV oxidation state upon coordination to the metal in the product. Furthermore, the pyridyl group is found to promote the catalytic role of the palladium(II) complexes in copper- and amine-free Sonogashira reactions.