氧桥联双核钛, 镍配合物的合成及催化制备双峰聚乙烯

To explore the potential of oxygen-bridged bisphosphinimine titanium and nickel complexes possessing bimetallic centers as catalysts for olefin polymerization, two oxygen-bridged diphosphorus compounds, named bis-(2-diphenylphosphino) phenylether(1a) and 9,9-dimethyl-4,6-bis(diphenylphosphino)xanthene(1b), were synthesized. After Staudinger reaction with Me₃SiN₃ in toluene under reflux, compound 1a with a flexible diphenyl ether bridge was converted into the bisphosphinimine precusor, while compound 1b with a rigid xanthene bridge was transformed into the monophosphinimine one. Subsequently, the dehalosilylation with CpTiCl₃ afforded the corresponding phosphinimine titanium complexes 3a and 3b, respectively. Single titanium center complex 3b further reacts with NiBr₂(DME) to translate into titaniumnickel heteronuclear bimetallic complex 4b. The structures of the complexes were characterized by ¹H, ¹³C, ³¹P NMR and elemental analyses. And the molecular structures of complexes 3a and 4b were further determined by single-crystal X-ray diffraction analysis. When activated by the methylaluminoxane(MAO), complexes 3a and 4b displayed high catalytic activity for ethylene polymerization. The bimetallic titanium complex 3a produced a wide molecular weight distribution polyethylene product, while the titanium-nickel heteronuclear bimetallic complex 4b gave rise to the bimodal polyethylene product.