The Design, Synthesis Of New Co(Ⅱ), Ni(Ⅱ) Catalysts And Study Of Their Catalytic Activity For The Ethylene Oligomerization/Polymerization

This work aims to develop series of new transition metal catalysts for the ethylene oligmerization/polymerization at normal temperature and pressure on the basis of Brookhart type of bis(imino)pyridine ligand. For the first time we have modified the precursor of bis(imino)pyridine to synthesize three new compounds in one reaction pot, i.e. 2,6-diacetylpyridine (P1), 2-carbethoxyl-6-acetylpyridine (P2) and 2-carboxyl-6-acetyl-pyridine (P3), in which the 2-position of pyridine ring was substituted by the acetyl group, carbethoxyl group and carboxyl group respectively. Also their synthesis strategies and the mechanism were studied in detail. These three compounds were used as precursor to react with different aromatic amines and aliphatic amines to obtain eight series of new organic ligands and the corresponding Co(II), Ni(II) complexes, which were: the acetyl incorporated mono(imino)prydine L1-L5 (the corresponding Co(II), Ni(II) complexes 1-10), bis(imino)pyridine L6 (the corresponding Co(II), Ni(II) complexes 11-14), ketene pyridine L7-L8 (the corresponding Co(II), Ni(II) complexes 15-16), bis(imino)pyridine ring L9 (the corresponding Co(II), Ni(II) complexes 17-18), the carbethoxyl incorporated mono(imino)prydine L10-L15 (the corresponding Co(II), Ni(II) complexes 19-30), the aliphatic amine incorporated carboxamide L16-L18 (the corresponding Co(II), Ni(II) complexes 31-36), the aromatic amine incorporated carboxamide pyridine L19-L22 (the corresponding Co(II), Ni(II) complexes 37-44), the aromatic amine incorporated tert-carboximide pyridine L23-L30 (the corresponding Co(II) complexes 45-47). Totally, twenty organic compounds and forty one organometallics that had never been reported in literature were synthesized. The microwave irradiation facilitated the synthesis of the aforementioned compounds greatly, and provided multiform structures. All the compounds were determined by the element analysis, ¹H NMR, IR, and MS. The results suggest that the component of Co(II), Ni(II) complexes 1-10, 17-34, 37-47 are all in accordance with MLCl₂, 11-12 in accordance with MLSO₄, 13-14 in accordance with ML(NO₃)₂, 15-16, 35-36 in accordance with M₂LCl₄. The crystal structure of ligands L4, L16 and Ni(II), Zn(II) complexes were characterized by X-ray diffraction. The systematic studies were focused on the Co(II), Ni(II) complexes' catalytic activity for the ethylene oligomerization/polymerization. The correlation between catalytic activity of the catalyst and the electronic property of central metal, the ligand framework, as well as reaction condition were investigated. The experiments show that under the same reaction conditions the activities of Co(II) and Ni(II) complexes bearing the same ligand differ greatly. Generally, Co(II) catalysts are more inclined to yield polymer while Ni(II) catalyst inclined to afford oligomer. Furthermore, the activity of Co(II) catalysts are generally higher than that of Ni(II). The acetyl incorporated mono(imino)prydine Co(II) complexes show high ethylene polymerization activity up to 1.58×10⁵ g/mol-Co·h·atm (for 7/MAO catalyst system), while the Ni(II) catalysts give moderate oligomerization activity for ethylene and the fine selectivity for the a-olefin. The NO₃^- or SO₄^2- incorporated bis(imino)pyridine-Co(II) or Ni(II) complexes indicate lower ethylene oligomerization activities. Ketene pyridine, bis(imino)pyridine ring-Co(II) or Ni(II) complexes also can bring few oligomer and middling selectivity for the a-olefin. The carbethoxyl incorporated mono(imino)prydine Co(II) and Ni(II) complexes engender high ethylene oligomerization activity up to 5.80×10⁵ g/mol-Co·h·atm (for 23/MAO catalyst system) and good selectivity for the a-olefin C₄up to 86.8%. Aliphatic amine incorporated carboxamide mononuclear Co(II) and Ni(II) complexes are both inactive for the ethylene polymerization/oligomerization, while the dinucleus metal complexes generate some oligomers. Aromatic amine incorporated carboxamide pyridine-Co(II) and Ni(II) complexes both show low activities for ethylene oligomerization, but the Co(II) complexes behave few selectivity for C₄. The reaction conditions also have a great influence on the productivity of catalyst system. To study these effects, a series of experiments were undertaken under various reaction time, temperature and Al/M, from which the optimal reaction conditions have been established.