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

• Published in: Organometallics 2009-06, Vol.28 (11), p.3264-3271
• Main Authors: Flapper, Jitte, van Leeuwen, Piet W. N. M, Elsevier, Cornelis J, Kamer, Paul C. J
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om9000378

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-defined, monomeric complexes. When the nickel complexes 5a−d were activated with MAO, they catalyzed the oligomerization of ethene with a maximum turnover frequency of 11 × 103 mol ethene per mol nickel per hour, whereas 5e showed no activity. Selectivities for butenes were between 93 and 97 mol %, with a maximum 1-butene content of 93%. The catalytic behavior is different from that of the nickel complex lacking an aromatic group at the ligand, again showing the influence of these substituents. The palladium complexes 7 were hardly active in ethene oligomerization, giving very small amounts of oligomers.