Nickel and Palladium Complexes of Pyridine-Phosphine Ligands Bearing Aromatic Substituents and Their Behavior as Catalysts in Ethene Oligomerization

Abstract

Bidentate pyridine-phosphine ligands 1 of general structure 2-aryl-6-[2-(diphenylphosphino)ethyl]pyridine were developed, in which the aryl group is phenyl (a), 1-naphthyl (b), 9-phenanthryl (c), 9-anthracyl (d), and ferrocenyl (e). The influence of these substituents on the nickel and palladium complexes of the ligands and their ethene oligomerization behavior was studied. The largest influence was observed in species with a square-planar surrounded metal center, whereas the nickel dichloride complexes 5 appeared as monometallic species with a tetrahedrally surrounded metal center. A classical binding mode of the ligand was not possible for the methylpalladium chloride complexes coordinated in a square-planar fashion. Instead, binuclear species in which two ligands span two metal centers were observed for 6a−d, and an undefined mixture of complexes was obtained for 6e. In contrast to these neutral palladium complexes, the cationic methylpalladium complexes 7, lacking the chloride anion, appear as well-de...