Catalytic Performance Of Dendritic Pyridineimine Transition Metal Catalysts In The Oligomerization Of Ethylene

In this paper,a dendritic pyridine imine ligand was synthesized with 1.0-generation polyamide-amine dendrimer moleculeand pyridine-2-carbaldehyde as raw materials by Schiff base reaction,and the a series of dendritic pyrimidin transition metal catalysts with different metal active centers were synthesized with dendritic pyridine imine ligand,CrCl₃·6H₂O,FeCl₂·6H₂O and CoCl₂·6H₂O by complex reaction.The synthesized dendritic pyridine imine ligand and the corresponding transition metal catalysts were analyzed by Fourier transform infrared spectroscopy?FT-IR?,ultraviolet-visible spectrophotometer?UV-Vis?,nuclear magnetic resonance spectroscopy?¹H NMR?and electrospray ionization mass spectrometry?ESI-MS?.Based on the synthesis and characterization of a series of dendritic pyrimidin imine transition metal catalysts,the catalysts were investigated for their ethylene oligomerization properties.The effects of solvent type,cocatalyst type,catalyst amount,reaction temperature,ethylene pressure and Al/M molar ratio on the catalytic activity of ethylene oligomerization and product distribution for the pyrimidin imine transition metal catalysts with different metal active center species were investigated in detail.The results showed that with the increase of reaction temperature,ethylene pressure and Al/M molar ratio,the catalytic ethylene oligomerization acticity of dendritic pyrimidin imine transition metal catalysts increased firstly and then decreased.When cyclohexane was used as solvent,MAO was used as cocatalyst,the catalyst activity was 3?mol,the reaction temperature was 25?,the ethylene pressure was 0.5 MPa,and the Al/M?Cr and Co?molar ratio was 500,The catalytic activity of the dendritic pyrimidin imine chromium and cobalt catalysts were reached up to 4.91×10⁴g/mol·Cr·h and 5.63×10⁴ g/mol·Co·h respectively,and the products were mainly C₆ and C_8,which were 73.9%and 61.94%.Under the same conditions,when the ethylene pressure was0.3 MPa,the catalyst activity of dendritic pyrimidin imine iron catalyst was 3.95×10⁴g/mol·Fe·h,and the products were mainly C₆ and C_8,which was 61.16%.In addition,the catalyzed ethylene oligomerization performance of dendritic pyrimidin imine transition metal catalysts was not only related to the solvent type,promoter type,catalyst amount,reaction temperature,ethylene pressure and Al/M molar ratio,but also was related to the type of active center.Under the same reaction conditions,the catalyst activity of dendritic pyrimidin imine cobalt was the highest,the catalyst activity of dendritic pyrimidin imine iron was the lowest,and the catalyst activity of dendritic pyrimidin imine chromium was moderate.