New bulky phosphino-pyridine ligands. Palladium and nickel complexes for the catalytic polymerization and oligomerization of ethylene

Two bulky phosphino-pyridine ligands (6-mesityl-2-((diarylphosphino)methyl)pyridine, Psimilar toN) were successfully prepared by means of Suzuki coupling of mesitylboronic acid with 6-bromo-2-picoline followed by phosphinylation. These ligands readily form the palladium and nickel complexes upon treatment with (COD)PdMeCl and (DME)NiBr2, respectively. These Psimilar toN chelating Pd(II) and Ni(II) complexes were characterized by both spectral data and X-ray crystallography. The coordination geometry around the metal center is square planar for the Pd(II) complexes and tetrahedral for the Ni(II) complexes. The cationic methylpalladium(II) complexes showed poor activity in the catalytic polymerization of ethylene, but the nickel complexes were highly active with the activation of MAO. The nickel complexes catalyzed the polymerization of ethylene with an Al/Ni ratio of 150, whereas di- and trimerization was observed when the Al/Ni ratio is 500. The obtained polyethylenes are highly crystalline.