Synthesis And Catalytic Performance Of Dendritic Salicylaldimine Iron Catalysts In Ethylene Oligomerization

A series of 1.0G dendrimers with different length of alkyl chain in bridged groups were synthesized with aliphatic diamine,methacrylate and ethylenediamine as the raw materials.And then a series of dendritic salicylaldimine ligands were obtained through schiff base reaction between 1.0G dendrimers and salicylaldehyde.Finally,a series of dendritic salicylaldimine iron catalysts with different length of alkyl chain in bridged groups were synthesized through complexation reaction between dendritic salicylaldimine ligands and Fe Cl2·4H2O.The structures of 1.0G dendrimers,dendritic salicylaldimine ligands and the corresponding iron complexes were characterized by ultraviolet(UV)visible spectroscopy,fourier transform infrared(FT-IR),electrospray ionization mass spectrometry(ESI-MS)spectroscopy and nuclear magnetic resonance hydrogen(1H NMR)spectroscopy,and the results showed that the actual structure had achieved the goal for devised structure.Based on the synthesis and characterization of dendritic salicylaldimine iron catalysts,the catalytic performances for ethylene oligomerization were researched,and the effect of solvent,co-catalyst,reaction temperature,ethylene pressure and the amount of cocatalyst on catalytic activity and product selectivity were mainly investigated.The results showed that the dendritic salicylaldimine iron catalyst D6-Fe with hexamethylenediamine as bridged group had the biggest catalytic activity,researching up to 1.38×105g/(mol Fe·h)when toluene was used as solvent,MAO was used as cocatalyst,reaction temperature was 15℃,ethylene pressure was 0.5MPa and Al/Fe molar ratio was 1000,and the oligomers were mainly of low carbon number olefins C4 and C6,which content reached up to 85.72%.The catalytic property of dendritic salicylaldimine iron catalysts in ethylene oligomerization not only was relevant to catalytic system and catalytic process,but also was relevent to the structure of catalyst.The catalytic activity and selectivity of butene were all increase with the increase of the length of bridged group.In addition,under the same reaction consitions,catalytic activity and butene selectivity of iron catalyst were lower than cobalt catalyst and nickel catalyst when the ligand skeleton was the same.In addition,the apparent kinetic equations of dendritic salicylaldimine iron cataly sts D2-Fe,D4-Fe and D6-Fe were builded by investigating the effect of ethylene pressu re,catalyst concentration and reaction temperature on reaction rate.