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.