Synthesis Of Zirconium And Hafnium Metal Catalysts Bearing Imine-amine Ligand And Their Application For Olefin Polymerization

Linear low density polyethylene(LLDPE)is a class of high-performance general-purpose plastics,exhibiting a unique set of properties and applications.Despite the many advances made in recent years,the production of new high-performance LLDPE remains a pressing task.This thesis includes two aspects of work:(1)A series of zirconium and hafnium complexes,[2,6-(R¹)₂-4-R²-C₆H₂-N-C(camphyl)=C(camphyl)-N-2,6-(R¹)₂-4-R²-C₆H₂]MMe₂(THF)(1-Zr:R¹=Me,R²=H,M=Zr;2-Zr:R¹=Me,R²=Me,M=Zr;1-Hf:R¹=Me,R²=H,M=Hf;2-Hf:R¹=Me,R²=Me,M=Hf),bearing bidentate NN ligands with the bulky camphyl backbone were synthesized by the stoichiometric reactions of?-diimine ligands with MMe₄(M=Hf or Zr).All Zr and Hf metal complexes were characterized by ¹H and ¹³C NMR spectroscopy,and the molecular structures of complexes 1-Zr and 1-Hf were determined by single-crystal X-ray diffraction.The results of structural analysis reveal that the original?-diimine ligand was selectively reduced into the ene-diamido form and generated an 1,3-diaza-2-metallocyclopentene ring in the metal complexes.Zr complexes 1-Zr and 2-Zr showed moderate activity(up to 388 kg(PE)·mol^-1(M)·h^-1),poor copolymerization ability,but unprecedented molecular weight capability toward ethylene/1-octene copolymerization.Therefore,copolymers with ultrahigh molecular weights(>600 or 337×104 g?mol^-1)were successfully synthesized by 1-Zr or 2-Zr,respectively,in the presence of[Ph₃C][B(C₆F₅)₄]as the cocatalyst.It is surprising that Hf complexes 1-Hf and 2-Hf showed negligible activity under otherwise identical conditions,revealing the great influence of metal centers on catalytic performances.(2)To synthesize?-olefin for use in comonomer,the bisphosphino-iminato ligands(syn-L and anti-L)were prepared to support the dinuclear nickel complexes(syn-Ni₂and anti-Ni₂).The Ni centers are successfully locked in relatively close proximity in syn-Ni₂(6.433(5)?),but much further apart in anti-Ni₂ because of the rigid anthracene skeleton.The mononuclear complex[Ni Br₂(C₁₄H₉-N=CH-C₆H₄-2-PPh₂)](Ni₁)was also prepared for control experiments.In the presence of Et Al Cl₂,syn-Ni₂ showed a remarkably high activity for ethylene dimerization(>90%)(up to 9.10×10⁶ g·mol^-1(Ni)·h^-1),which is approximately 1.5 and 3.3-fold higher than that of anti-Ni₂ or of mononuclear Ni₁.The redox properties of dinuclear complexes by cyclic voltammetry(CV)were distinguishing from that of mononuclear one,indicating the possible existence of cooperativity between two metal centers in dinuclear structures.Although the detailed mechanism has not been elucidated,cooperative effects favor isomerization of 1-butene,and dinuclear syn-Ni₂ and anti-Ni₂ exhibited higher selectivity for 2-butene than mononuclear Ni₁ under otherwise identical reaction conditions.