Iron(II) and cobalt(II) 2-(benzimidazolyl)-6-(1-(arylimino)ethyl)pyridyl complexes as catalysts for ethylene oligomerization and polymerization

A series of iron(II) (7a-11a) and cobalt(II) (7b-11b) 2-(1-methyl-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridyl complexes were synthesized, as well as bidentate iron(II) and cobalt(II) complexes ligated by 2-(2-benzimidazolyl)-6-methylpyridine, 2-(carboethoxyl)-6-(2-benzimidazolyl)pyridine, and 2-(1-methyl-2-benzimidazolyl)-6-acetylpyridine. All organic compounds were fully characterized by NMR and IR spectroscopy and elemental analysis, while the metal complexes were carefully examined by IR spectroscopy and elemental analysis. Their molecular structures were determined by single-crystal X-ray diffraction analysis. The bidentate metal complexes display a distorted-tetrahedral coordination geometry; however, 2a is an exception, with a distorted-trigonal-bipyramidal geometry due to coordination of one DMF molecule. The X-ray crystallographic studies on all of the tridentate metal complexes revealed the coordination geometry as a distorted trigonal bipyramid. Upon activation with MAO or MMAO, the iron(II) 2-(2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridyl complexes showed high activities with good alpha-olefin selectivity, while the cobalt(II) analogues displayed moderate to good catalytic activities. However, other bidentate metal complexes showed considerable moderate catalytic activity. The oligomers and polyethylene waxes obtained were alpha-olefins, and the distribution of oligomers resembled Schulz-Flory rules with some exceptions. Various reaction parameters were investigated, and the results revealed that both the steric and electronic effects of ligands affect the catalytic activities of their metal complexes as well as the distribution of products.