Imidazole-Ti(Ⅳ) Complexes And Iminoamine Ni(Ⅱ) Complexes: Syntheses, Characterization And Catalytic Properties

The work of this thesis includes two parts: 1. Synthesis and ethylene polymerization behaviours of bidentate imidazole Ti(IV)/MAO catalysts. 2. Synthesis and norbornene polymerization behaviours ofβ-iminoamine Ni(II)/MAO catalysts.1. A series of 2,4,5-substituted 1H-imidazole ligands (LPB, LMB, LPE and LPH) were synthesized and characterized. Coordination of free 1H-imidazole ligands and lithium 1H-imidazol-1-ides with tetrachloride titanium gave corresponding Ti(IV) complexes of imidazoles (CS(PB), CS(MB), CS(PE), CD(PB)) and imidazol-1-yl (CS(PE-), CD(PB-),CD(MB-), CD(PH-)). In the presence of methylaluminoxane (MAO), the obtained Ti(IV) complexes were used as catalyst precursors for ethylene polymerizations. The results show that the obtained Ti(IV)/MAO catalysts produce ethylene polymers at a moderate activity level of 4.1～148.0 Kg(PE)·molTi^-1·h^-1 under optimal condition; Under same polymerization condition, the activities of mono- and bis- (imidazole) Ti(IV)/MAO catalysts are higher than that of corresponding mono- and bis- (imidazol-1-yl) Ti(IV)/MAO catalysts. The catalyst activities of Mono ligand Ti(IV)/MAO systems are higher than that of bis(ligand) systems. The catalyst activities increased continuously with the increasing Al/Ti ratios. The activities of (imidazole) Ti(IV)/MAO catalysts increase firstly then decreased gradually with the temperature increasing. The optimal polymerization temperatures are around 25 oC for CS(PB), CS(MB) and CS(PE)/MAO catalysts and 15 oC for CD(PB)/MAO catalyst. The catalyst activities of mono- or bis- (imidazol-1-yl) Ti(IV)/MAO systems are not sensitive to the temperature change. CD(PH-)/MAO was found inactive for ethylene polymerization. At optimal polymerization condition, the activity sequence of the obtained catalysts is CS(PB)> CD(PB)> CS(PE)> CS(PE-)> CD(MB-)> CD(PB-)> CS(MB)> CD(PH-).2.β-Iminoamine ligands and Ni(Ⅱ) complexes were synthesized and characterized. Singal-crystal structure displays that the six-membered chelate ring ofβ-iminoamine Ni(Ⅱ) complexes are less conjugated and adopt a folded conformation. 1H NMR studies revealed the same chelate ring conformation is retained in solution. In the presence of MAO,β-iminoamine Ni(Ⅱ) complexes were used as catalyst precursors for norbornene polymerization. The influences of temperature, Al/Ni ratios and precursor structure on polymerization behavior were examined. The results show theβ-iminoamine Ni(Ⅱ)/MAO catalysts gave soluble vinyl addition polymers at an activity level of 105 g(PNB)·molNi-1·h-1. Bulky A/MAO catalyst is relatively more active, whereas less bulky B/MAO catalyst produces higher molecular weight products. Optimal polymerization conditions are temperature 65-75oC and MAO 3.2-4mmol. The results suggest the cationic active species formed inβ-iminoamine Ni(Ⅱ)/MAO systems are liable to form inactive species with free TMA. The protruding and cationic natures of the active species would decrease instead of increase the catalyst activities.