Study On Synthesis, And Catalysis Property Of Cyclopentadienyl Chromium Complexes Supported By2-lmidazole-Pyridine Ligands

Since Kaminsky and Sinn discovered that when a titanocene or zirconocenecatalyst system and methylaluminoxane （MAO） were mixed together, the catalystshowed remarkable ability for catalyzing the olefin polymerization, metallocenecatalyst using for olefin polymerization has become a researching hotspot. Presently,the polymerized product obtained by the metallocene catalyst could be extremelybroad, including linear high density polyethylene, linear low density polyethylene,syndiotactic, isotactic and atactic polypropylene, ethylene-styrene copolymer,syndiotactic polystyrene, cyclic olefin copolymers, etc. However, in order to achievea high catalytic activity of the metallocene catalyst, most of the catalyst system mustbe added to a certain amount of MAO or Ph₃C⁺B（C₆F₅）₄^–and Ph₃C⁺B[C₆H₃（CF₃）₂]₄^–etc. These cocatalysts are very expensive. In some catalytic systems, the costs ofcocatalyst are even higher than that of the main catalyst. Therefore, taking intoaccount the cost factor, the metallocene catalyst in the industrial application hasbeen largely limited. In reality, it is necessary to develop a system which maycatalyze the polymerization of olefin with a high activity to obtain a kind of highperformance product, and do not need a large amount of expensive co-catalyst at thesame time. In my article, we developed a homogenous olefin polymerization catalystsystem. In this system, the catalysts can be highly active to catalyze thepolymerization of olefins by simply adding a small amount of an aluminum alkyl ascocatalyst,By changing the substituent group on the imidazole ring, we synthesized fourkinds of2-inidazole-pyridine ligands （HL₁–HL₄）. By reacting with thecyclopentadienyl chromium or pentamethyl-cyclopentadienyl chromium complex,eight kinds of half-sandwich chromium complexes （1–8） were synthesized in a highyield, and were characterized by NMR and IR spectroscopy as well as elementalanalysis. Through the eight kinds of different complexes, we investigated in detail theeffects of kind of alkyl aluminum, amount of alkyl aluminum, temperatures andpolymerization time on the catalytical activity for ethylene polymerization. Thus wegot the optimal conditions for the catalysis polymerization of ethylene. Underspecific polymerization conditions, we compared the eight complexes’ performance,and investigated the causes of the differences between the catalysts’ activity.Experimental results show that under the room temperature, when activated by50-times amount of triethylaluminum, the catalyst2gave the highest catalyticactivity of3480kg PE mol Cr^–1h^–1. Among the homogeneous ethylene catalyticsystem activated by only a small amount of aluminum alkyl, one could reach thiskind of activity is already rare.As the nitrogen atom away from the central metal and the adjacent carbon atomson the imidazole ring formed a double bond, the electrical properties of the centralmetal could be significantly changed. Basing on this principle, the catalyst can beused in exploring the possibility of polymerization of propylene or ethylene andα-olefin copolymer only by the activation of small amount of aluminum alkyl.