Polymerization of α-olefins with pyridylamidohafnium catalysts:: Living behavior and unexpected isoselectivity from a Cs-symmetric catalyst precursor

The olefin polymerization behavior of pyridylamidohafnium catalysts bearing a methylene bridge between the pyridine and amido ligand components was analyzed. The pyridylimine ligand precursors were prepared via a Schiff base condensation between 4phenyl-2-pyridine carbdxaldehyde and the aniline. It was found that the reduction of the pyridylimines with LiAlH4 or NaBH3CN gave the pyrdylamine ligands in yields from 82 to 90%. It was also found that the isoselectivity for propylene polymerization (and presumably 1-hexene polymerization) resulted from an enantiomorphic site control mechanism, which was highly unusual in light of the generally accepted symmetry rules for olefin polymerization catalysts.