Preparation and catalysis of ethyleneoligomerization by diphenyl-methylene-bridging pyridine-imide two-center Ni catalyst
A two-center Ni catalyst for ethylene oligomerization was prepared using 4,4'-diaminodiphenylmethane,pyridine-2-formaldehyde and nickel chloride hexahydrate as raw materials.The structures of the ligands and catalysts were analyzed by infrared spectroscopy(FTIR),ultraviolet spectroscopy(UV-vis),hydrogen nuclear magnetic resonance spectroscopy(1 H NMR)and electrospray ionization mass spectrometry(ESI-MS),and the catalytic performance was evaluated by ethylene oligomerization experiment.The results showed that polymerization conditions and catalyst structure have great influence on the performance of ethylene oligomerization catalyzed by two-center Ni catalyst.Using cyclohexane as solvent and modified methylaluminoxane(MMAO)as cocatalyst,the catalytic activity of the methyl-substituted diphenyl methylene bribed bicentral Ni catalyst was the highest when the reaction temperature was 25 ℃,n(Al)∶n(Ni)=1 000,the ethylene pressure was 0.5 MPa,the amount of the main catalyst was 3 μmol and the reaction time was 45 min.The maximum value was 7.61 × 104 g/(mol Ni·h)and the selectivity of butene was 72.58％.In addition,the mechanism of ethylene oligomerization catalyzed by diphenylmethylene-brided pyridinimide two-center Ni catalyst was deduced.
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