Syntheses of iron, cobalt, chromium, copper and zinc complexes with bulky bis(imino)pyridyl ligands and their catalytic behaviors in ethylene polymerization and vinyl polymerization of norbornene

The syntheses, characterization, and ethylene and norbornene polymerization behaviors of iron, cobalt, chromium, copper and zinc complexes (3–7b) bearing chelating bulky 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine ligand (1) or 2,6-bis[1-(2,5-ditertbutylphenylimino)ethyl]pyridine ligand (2) are reported. X-ray diffraction study of the cobalt complex (4) shows the geometry of the cobalt center to be distorted trigonal bipyramid. Treatment of the iron, cobalt 2,6-bis[1-(2,5-ditertbutylphenylimino)ethyl pyridine complexes (3 and 4) with methylaluminoxane (MAO) lead to a highly active ethylene polymerization catalysts converting ethylene to highly linear polyethylene (PE), while the corresponding chromium complex (5) is disclosed as moderate catalytic activity for the polymerization of ethylene. The specific catalytic activities were evaluated at different temperature and Al/M (M = Fe, Co and Cr) ratio. In addition, the complexes 3–5 and corresponding compounds of FeCl2, CoCl2(THF)1.5 and CrCl3(THF)3 can also catalyze vinyl polymerization of norbornene activated with MAO and show good activities. However, the copper and zinc complexes (6a–7b) showed no active in ethylene and norbornene polymerization in the presence of MAO.

Graphical abstractThe syntheses, characterization and ethylene and norbornene polymerization behaviors of iron, cobalt, chromium, copper, and zinc complexes (3–7b) bearing chelating bulky 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine ligand (1) or 2,6-bis[1-(2,5-ditertbutylphenylimino)ethyl]pyridine ligand (2) are reported. And the cobalt complex 4 was characterized by the X-ray diffraction. Except copper and zinc complexes (6a–7b), the other complexes (3–5) show good activities in ethylene and vinyl norbornene polymerization. It is interested that FeCl2, CoCl2(THF)1.5 and CrCl3(THF)3 can catalyse vinyl polymerization of norbornene activated with MAO and show good activities.Figure optionsDownload full-size imageDownload as PowerPoint slide