2-(1H-2-Benzimidazolyl)-6-(1-(arylimino)ethyl)pyridyl Iron(II) and Cobalt(II) Dichlorides: Syntheses, Characterizations, and Catalytic Behaviors toward Ethylene Reactivity

A series of tridentate N̂N̂N iron(II) and cobalt(II) dichloride complexes bearing 2-(1 H -2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines were synthesized and characterized by elemental and spectroscopic analyses. Single-crystal X-ray diffraction studies of representative examples of the cobalt and iron complexes confirm distorted bipyramidal geometry around the metal center. Upon coordination of a methanol solvent molecule, a geometry change to distorted octahedral was observed. The steric and electronic effects on catalytic activity are evaluated for different substituents in the arylimino part of the ligand: Me, Et, i Pr, Cl, and Br in ortho - and Me and H in para -position. On treatment with methylaluminoxane (MAO) or modified MAO (MMAO), the iron(II) complexes exhibited good activities of up to 10 6 g·mol −1 (Fe)·h −1 for ethylene oligomerization and moderate activities for polymerization, while cobalt(II) complexes showed moderate activities for ethylene dimerization. The best activities were observed with iron complexes with bulky i Pr groups in the aryl moiety. In comparison to the analogues containing the 2-(1-alkyl-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines, the iron complexes bearing 2-(1 H -2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines showed the best activity toward ethylene reactivity.