2-Oxazoline/benzoxazole-1,10-phenanthrolinylmetal (iron, cobalt or nickel) dichloride: Synthesis, characterization and their catalytic reactivity for the ethylene oligomerization

Series of 2-benzoxazole-1,10-phenanthrolines (L1–L4) and 2-oxazoline-1,10-phenanthrolines (L5–L8) were synthesized and used as tridentate N^N^N ligands in coordinating with metal (nickel, cobalt or iron) chlorides. Their metal complexes, nickel(II) (Ni1–Ni8), cobalt(II) (Co1–Co8) and iron(II) (Fe1–Fe8), were characterized by elemental and IR spectroscopic analyses. The molecular structures of the ligand L2 and the complexes Ni3, Co1, Co3 and Fe2 have been determined by the single-crystal crystallography. The nickel complex Ni3 and iron complex Fe2 display an octahedral geometry, whereas cobalt complex Co1 is with a distorted bipyramidal geometry and Co3 as square pyramidal geometry. At 10 atm ethylene, all the complexes showed good activities in ethylene dimerization upon activation with appropriate aluminum cocatalysts; the nickel complexes gave the activity up to 3.11 × 106 g mol−1(Ni) h−1 upon activation with diethylaluminum chloride (Et2AlCl), meanwhile the cobalt and iron complexes showed activities up to 1.51 × 106 g mol−1(Co) h−1 and 1.89 × 106 g mol−1(Fe) h−1, individually, upon activation with modified methylaluminoxane (MMAO).