Applications Of Ni(?) And Pd(?) Catalysts In Olefin Polymerization

In this graduate dissertation,we designed and synthesized a series of a-diimine ligands with different substituents on the acenaphthyl backbone.The corresponding Ni(II)and Pd(II)complexes were prepared and characterized by nuclear magnetic resonance,mass spectra,X-ray single crystal diffraction and elemental analysis.Then we used them in ethylene polymerization and copolymerization with methyl acrylate and explored the tensile property of the polyethylene product.In addition,we studied the redox controlled norbornene,polar norbornene and alkyne polymerization using palladium complexes(NHC)Pd(allyl)Cl(NHC =1,3-Ar2-napthoquinimidazolylidene).1.A series of a-diimine ligands with different substituents on the acenaphthyl backbone were synthesized and characterized.The corresponding Ni(?)and Pd(?)complexes were prepared and used in ethylene polymerization and copolymerization with methyl acrylate.In ethylene polymerization,these Ni(?)complexes showed activities of up to 1.6 × 107 g/(mol Ni·h),generating polyethylene with molecular weight(Mn)of up to 4.2 ×105.Interestingly,these Ni(II)complexes behave very similarly in ethylene polymerization except for the complex with two methoxy substituents on the ortho position of the acenaphthyl backbone,in which case about three times higher polyethylene molecular weight and much lower branching density were observed.The ligand substituent effect is much more dramatic for the Pd(?)complexes.In ethylene polymerization,activities of up to 1.7 × 104 g/(mol Pd·h)and polyethylene molecular weight(Mn)of up to 4.7×104 could be obtained.Again,the Pd(?)complex with two methoxy substituents on the ortho position of the acenaphthyl backbone demonstrated much higher activity and generated polyethylene with about three times higher molecular weight than the classic Pd(?)complex.Similar trend was maintained in ethylene-methyl acrylate copolymerization.2.Two palladium complexes(NHC)Pd(allyl)CI(NHC =1,3-Ar2-napthoquinimidazolylidene,Ar = 2,6-Me2-C6H3,2,6-iPr2-C6H3)bearing a redox-active naphthoquinone moiety,were prepared and characterized.Electro-chemistry cyclic voltammetry and NMR studies showed that the palladium complexes could be easily reduced and re-oxidized using CoCp2 and[FeCp2][BAF](BAF = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate)regents.The properties of these neutral and reduced palladium complexes in norbornene,5-norbornene-2-yl acetate and 1-chloro-l-octyne polymerization were studied.The neutral complexes were active in all of these polymerization reactions in the presence of Na[BAF].In contrast,the reduced analogues showed very low activity under the same conditions.As such,switchable polymerization could be realized in this catalytic system.