Studies On Synthesis Of Novel N,N Bidentate Chromium Complexes And Its Performance In Ethylene Oligomerization

In this dissertation,a series of chromium complexes with the different substituted groups were synthesized,using hyperbranched macromolecules and phenoxy groups as bridging groups by catalytic modification of their amino groups.The characterization results of ultraviolet,Fourier transform infrared,nuclear magnetic resonance,and carbon spectra,electrospray ionization mass spectrometry and elemental analysis proved the structures of hyperbranched pyrimide and phenoxy-bridged pyrimidine ligands and chromium complexes were consistent with the theoretical design structures.Based on the synthesis and characterization,a series of hyperbranched bridged pyrimide and phenoxy bridged pyrimide chromium complexes for ethylene oligomerization with different substituted groups were studied.The effects of polymeric reaction system and operation process on the oligomerization activity and the product distribution were investigated in detail.The experimental results show that all hyperbranched bridged pyrimide and phenoxy bridged pyrimide chromium complexes with different substituent groups have moderate performance for ethylene oligomerization using MAO as co-catalyst and toluene as solvent.Among them,the catalytic activity of catalyst C1 with hyperbranched macromolecules as the bridging group is higher than that of catalyst C2.The optimal reaction conditions for catalyzing ethylene oligomerization were as follows:the reaction temperature was 65°C,the reaction pressure was 4 MPa,the molar ratio of Al/Cr was 300 and the reaction time was 30 min.The catalytic activity of the catalyst Cr1 based on phenoxy group is higher than that of Cr2-Cr4.The optimal reaction conditions for catalyzing ethylene oligomerization were as follows:the reaction temperature was 50°C,the reaction pressure is 1 MPa,the molar ratio of Al/Cr was 300 and the reaction time was 30 min.The catalytic activities of catalysts C1 and Cr1 were 1.26×10⁵g/（mol（Cr）·h）and 2.93×10⁵g/（mol（Cr）·h）,respectively.The selectivity of C₈in the oligomerization products was 57.13%and 55.34%.Hyperbranched bridged pyrimide and phenoxy-bridged pyrimide chromium complexes with different substituent groups catalyzed the oligomerization of ethylene,which showed the better catalytic performance of chromium catalysts.With the increase of the steric hindrance of the catalyst with hyperbranched macromolecules and phenoxy as the bridging group,the catalytic activity of ethylene oligomerization and the selectivity to C₈in the oligomerization products gradually decreased,of which the highest catalytic activity and selectivity of C₈were C1 and Cr1.