Synthesis and characterization of iron and cobalt dichloride bearing 2-quinoxalinyl-6-iminopyridines and their catalytic behavior toward ethylene reactivity

The 1-(6-(quinoxalin-2-yl)pyridin-2-yl)ethanone was synthesized in order to prepare a series of N-(1-(6-(quinoxalin-2-yl)pyridine-2-yl)ethylidene)benzenamines (L1–L7), which provided new alternative N∧N∧N tridentate ligands coordinating with iron(II) and cobalt(II) dichloride to form complexes of general formula LFeCl2 (1–7) and LCoCl2 (8–14). All organic compounds were fully characterized by NMR, IR spectroscopic and elemental analysis along with and magnetic susceptibilities and metal complexes were examined by IR spectroscopic and elemental analysis, while their molecular structures (L1, L4, 1, 4, 10, 13) were confirmed by single crystal X-ray diffraction analysis. Upon activation with methylaluminoxane (MAO), all iron complexes gave good catalytic activities for ethylene reactivity (oligomerization and polymerization), while their cobalt analogues showed moderate activities toward ethylene oligomerization with modified methylaluminoxane (MMAO). Various reaction parameters were investigated for better catalytic activities, the higher activities were observed at elevated ethylene pressure. The iron and cobalt complexes with para-methyl substituents of aryl group linked on imino group showed highest activity.

Graphical abstractThe 2-quinoxalinyl-6-iminopyridines and their iron(II) and cobalt(II) complexes were synthesized and full characterized. The molecular structures of (E)-N-(1-(6-(quinoxalin-2-yl)pyridin-2-yl)ethylidene)benzenamine and their metal complexes indicates rotations of the quinoxalinyl and imino-groups of ligand backbone during coordination, which suggests that the ligands form sterically-favored coordination with the metal center with the distorted trigonal-bipyramidal geometry. Upon activation with MAO, all iron complexes showed good catalytic activity for ethylene reactivity; while their cobalt analogues gave moderate to good activity for ethylene reactivity in the presence of MMAO.Figure optionsDownload full-size imageDownload as PowerPoint slide