Synthesis And Catalytic Behavior Of 2-(1H-2-benzimidazolyl)-6-(1-arylimino)Ethyl)Pyridine And 2-alkoxyimidate-1,10-phenanthroline Metal Complexes

This dissertation focuses on designing and synthesis of transition metalcomplexes as catalysts for ethylene activation. 2-(1H-2-benzimidazolyl)-6-[1-(arylimino) ethyl]pyridines ligands and their corresponding iron, cobalt and nickelcomplexes were successfully prepared. Upon activation with aluminum compounds,these complexes are active for ethylene oligomerization and/or polymerization. Therelationship between ligand environment and catalytic activity were elucidated.Additionally, the reaction parameters, such as the reaction temperature, cocatalyst, theamount of cocatalyst and ethylene pressure etc were systemically studied. Manganese,cobalt and nickel complexes bearing 1,10-phenanthroline derivatives have beensynthesized and characterized, the relation between the products and reactionconditions have been studied, their catalytic behavors upon oligomerization ofethylene have been elucidated. Four main parts are included in this dissertation.First in Chapterl,the progress of catalysts used in polymerization and /oroligomerization of ethylene is summarized, especially transition metal complexes.In chapter 2, a series of tridentate N^N^N iron(â…¡) and cobalt(â…¡) dichloridecomplexes bearing 2-(1H-2-benzimidazolyl)-6-[1-(arylimino)ethyl]pyridines weresynthesized and characterized. Single crystal X-ray diffraction studies ofrepresentative examples of the cobalt and iron complexes confirm distortedbipyramidal geometry around the metal center. Upon coordination of a methanolsolvent molecule a geometry change to a distorted octahedron has been observed. Thesteric and electronic effects on catalytic activity are evaluated for differentsubstituents in the arylimino part of the ligand. On treatment with MAO or MMAO,the iron (â…¡) complexes exhibited good activities of up to 10⁶ g·mol^-1(Fe)·h^-1 forethylene oligomerization and moderate activities for polymerization, meanwhilecobalt (â…¡) complexes showed moderate activities for ethylene dimerization. The bestactivities were observed with iron complexes with bulky iPr groups in the aryl moiety.In comparison to the analogues containing2-(1-alkyl-2-benzimidazolyl)-6-[1-(arylimino)ethyl]pyridines, the iron complexesbearing 2-(1H-2-benzimidazolyl)-6-1-(arylimino)ethyl)pyridines showed betteractivity towards ethylene reactivity.In Chapter 3, a series of tridentate N^N^N nickel complexes bearing 2-(1H-2-benzimidazolyl)-6-[1-(arylimino)ethyl]pyridines was synthesized and characterized. The molecular structures of complexes 3-1a, 3-1d and 3-2c were determined with thesingle crystal diffraction, and these were found to have six coordinate distortedoctahedral geometry around the Ni center. On treatment with Et₂AlCl, all nickelcomplexes exhibited good catalytic activities up to 10⁶ g·mol^-1(Ni)·h^-1 for ethyleneoligomerization with major dimerization. The steric and electronic effects on catalyticactivities of metal complexes as well as the influence of various reaction parameterswere carefully investigated.In Chapter 4, the methyl and ethyl carboxyimidate complexes of manganese,cobalt and nickel have been synthesized by the reaction of 2-cyano-1,10-phenanthroline with metal dichloride in the corresponding alcohol. Somecomplexes have been confirmed by single crystal X-ray diffraction analysis. Themolecular structures of methoxyimidate complexes demonstrate a centrosymmetricdimeric structure, whereas the ethoxyimidate complexes are mononuclear. Moreover,the reaction in non-protonic solvent resulted in the formation of nitrile metalcomplexes, in which the metal center was coordinated by two ligands and twochlorides. All the complexes were evaluated in the catalytic oligomerization ofethylene with alkylaluminums as cocatalyst. Manganese complexes were less active,cobalt complexes showed low to moderate catalytic activities, and nickel complexesgave moderate to good catalytic activities.