Novel Titanium, Zirconium And Late Transtion Metal Catalysts For Olefin Polymerization

The field of olefin polymerization catalysis has experienced Ziegler-Natta catalysts, metallocene catalysts and post-metallocene catalysts periods. Ziegler-Natta catalysts showed poor stereoselectivity forα-olefin polymerization. The high oxophilicity of early transition metal catalysts causes the active centre of metallocene catalyst to be poisoned by most functionalized olefins which contain O, S or N heteroatoms. A large amount of MAO or expensive fluorinated borate is generally required as cocatalyst for obtaining high activity. There is a great need to develop new catalyst systems which can provide high activity, high stereoselectivity, with no need of large amounts of expensive cocatalyst and good functional-group tolerance ability. In this dissertation, a series of novel titanium and zirconium(Ⅳ) complexes bearing [N, O, S] ligands, [N, O] ligands, [N, N, S] ligands were synthesized and characterized. The effects of catalyst structures, molar ratio of catalyst/cocatalyst, reaction temperature on polymerization reaction have been discussed in detail. Moreover, a series of novel functionalized metallacycles were prepared and their reactions were investigated. We tried to put nickel and palladium catalyst in the metallacycles and tested the new catalysts for olefin polymerization. The full dissertation was summarized as follows:1. A series of novel titanium and zirconium complexes bearing [N, O, S] tridentate ligands have been synthesized by the reaction of Ti(OPri)4 or TiCl4 or Zr(OPri)4·iPrOH and ligands in toluene at -78℃. The molecular structures of the titanium and zirconium complexes have been confirmed by single crystal X-ray analysis. It can be learned that when the substituent near to phenoxy is varied from H to But, both monomeric and dimeric, including oxygen-and sulfur-bridged titanium complexes were synthesized, reflecting that the steric hindrance plays a significant role on the geometry of complexes. When activated by excess methylaluminoxane (MAO), some complexes can be used as catalysts for ethylene polymerization. The activity of titanium chloride complexes are higher than those of their analogous alkoxide complexes. The highest activity can reach ca.106 gPE·molTi-1·h-1, and the Mv of the polymer achieves 106 gmol-1. Moreover, alkoxide titanium complexes can be applied for ROP ofε-Caprolactone. The conversion can reach 90% under mild conditions and the Mw is about 104 gmol-1.2. A series of novel titanium and zirconium complexes bearing heterocycle-containing [N, O] bidentate ligands have been synthesized by the reaction of TiCl4(THF)2, ZrCl4 and the corresponding ligands in THF at -78℃. The molecular structures of one ligand and five complexes have been confirmed by single crystal X-ray analysis. From the crystal structures of titanium and zirconium complexes with the same ligands, we can learn that the size of coordination metal and the steric hindrance both play a significant role on the geometry of complexes. Capture of the intermediate zirconium complex help understand the process of the reactions. When activated by excess methylaluminoxane (MAO), these complexes can be used as catalysts for ethylene polymerization. Zirconium complexes usually are more active towards ethylene polymerization than the corresponding titanium complexes, and the highest activity of zirconium complex reaches 5.2×105 gPE·molZr-1·h-1, the PE obtained has high molecular weight (3.0×105 gmol-1). The steric effect on ethylene polymerization is also studied.3. Three novel titanium complexes have been prepared by the reation of TiCl4 and the corresponding [N, N, S] ligands. The molecular structures of two ligands have been confirmed by single crystal X-ray analysis. When activated by excess methylaluminoxane (MAO), these complexes can be used as catalysts for ethylene polymerization with good activity (about 106 gPE·molTi-1·h-1). The effects of steric factor, the temperature, and the ratio of Al/Ti on ethylene polymerization have been systematically studied.4. Novel tetra-nuclear iridium metallacycle and bi-nuclear rhodium, ruthenium metallacycles have been synthesized by the reaction of 4-pyridyl dithioether and half-sandwich bimetal complexes. Nickel and palladium catalysts for olefin polymerization were tried to put into the flexible tetra-nuclear iridium metallacycle. Further research was done on the reaction of the obtained metallacycles. Two homo-trinuclear metallacycles and four hetero-trinuclear metallacycles were sequentially prepared. Different conformations of the tetra-nuclear iridium complex were discovered due to different guest solvent molecules.5. Novel half-sandwich ruthenium metallacycle containing functionalized rigid 3-pyridyl-α-diimine unit have been synthesized. NiBr2·DME and (COD)PdMeCl was used to combine with theα-diimine part, which was existed in the metallacycle, respectively. The obtained novel nickel catalyst was applied for ethylene and norbornene polymerization with moderate to good activity. While the palladium catalyst can be used for norbornene polymerization with good activity. The effects of the ratio of Al/M and polymerization temperature on the polymerization behavior were investigated.