Synthesis Of Aminothiophene Phosphorus Ligand And Its Application In Catalyzing Oligomerization Of Ethylene

Linear?-olefin is an important chemical raw material,and the selective oligomerization of ethylene to produce?-olefin with specific carbon number has become an important development direction in the future.In recent years,the high activity and high selectivity exhibited by Cr-based catalysts in the selective oligomerization of ethylene to produce linear?-olefins have received extensive attention from academia and industry.PNP ligands have been extensively studied in chromium-catalyzed selective oligomerization of ethylene to produce?-olefins.Numerous studies have shown that the ligand structure plays a decisive role in catalyst performance.Due to the special structure of the multi-site PNP ligand,a unique coordination pattern may be formed during the coordination with the chromium center,which affects the catalytic performance.Therefore,this paper mainly carried out the research work in the following aspects:Multi-site PNP ligands L1?L3?L5?L6were synthesized by using aminophenol and aminothiophenol substrates and diphenylphosphorus chloride respectively.The structure of each ligand was determined by analysis means such as ¹H NMR and ¹³C NMR.The above ligands are combined with chromium salts and a co-catalyst methylaluminoxane?MAO?to form a catalyst for catalyzing the oligomerization of ethylene.By changing the reaction conditions such as solvent,reaction temperature,Al/Cr molar ratio,ethylene pressure,etc.,its influence on the catalytic reaction was investigated.Through comparative experiments,the effect of ligand structure on catalytic performance was investigated.Experimental results show:When the solvent is cyclohexane,the reaction temperature is 50?,the reaction pressure is 2.5MPa,and the Al/Cr molar ratio is 700,the ligand L6/Cr?III?/MAO catalytic system activity can reach 1.92×10⁶g/?mol Cr·h?,the ligand L5/Cr?III?/MAO catalytic system has a selectivity to 1-octene up to 57.53%.Through the density functional theory calculation?DFT?,the selectivity of the catalytic system composed of the ligands L4?L6 was simulated.The calculation results show that the three catalytic systems are mainly based on the selectivity of 1-octene.