Revisiting the 2-imino-1,10-phenanthrolylmetal precatalyst in ethylene oligomerization: Benzhydryl-modified cobalt(II) complexes and their dimerization of ethylene

Abstract

The ortho-benzhydryl substituted 2-imino-1,10-phenanthrolylcobalt(II) dichlorides Co1-Co8 have been prepared by the direct reaction of the corresponding compartmental ligands L1–L8 and cobalt(II) chloride with good yields. All the organic compounds (L1–L8) have been fully characterized by FT-IR, 1H/13C NMR spectroscopy and elemental analysis, and their corresponding cobalt complexes (Co1–Co8) have been characterized by FT-IR spectroscopy and elemental analysis, along with the single crystal X-ray diffraction for the representative complexes Co3, Co7 and Co8. On treatment with modified methylaluminoxane (MMAO), all the cobalt complexes Co1-Co8 display good activities (up to 3.25 × 105 g mol−1 (Co) h−1 at 50 °C) toward ethylene dimerization (C4 ranging from 92 to 100%), along with minor hexenes, in which the selectivity of 2-butene ranges from 55 to 84.4%. In comparison with their previous analogues, the current precatalysts bear bulkier substituents which are not beneficial to ethylene oligomerization.