Novel Group Ⅳ 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 for a-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 half-zirconocene complexes with imino-quinolinol ligands, titanium complexes containing double-duty [O-N N-] ligands; group IV metal complexes containing a tetradentate dianionic [O, S, S, O] carborane ligand; nickel complexes with carborane [S, C] or [S, 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. The full dissertation was summarized as follows:1. A series of half-zirconocene complexes with imino-quinolinol ligands have been synthesized and characterized. The catalytic behaviors of these complexes toward ethylene polymerization were investigated in the presence of methylaluminoxane (MAO) as a cocatalyst. The catalytic behaviors were highly affected by the substituent in both cyclopentadienyl and imino-quinolinol ligands. Cp analogue complexes CpZr[O N NR]Cl2exhibited high activities up to1.34×107g PE-mol Zr-1·h-1, whereas Cp*analogue complexes Cp*Zr[O N NR]Cl2also showed moderate activities for ethylene polymerization. The bulky and donation substituents on the ligands in the ortho-position seem to be important for high catalytic activity. These zirconium precatalysts exhibited excellent thermal stability at80℃.2. A new type of double-duty tridentate [O, N, N] ligands were easily prepared in one step based on corresponding imino-quinolinol ligands. When deprotonated by NaH, such ligands can be used as tridentate monoanionic ligands to synthesize trichlorotitanium complexes. While deprotonated by "BuLi, it can be used as tridentate dianionic ligand to synthesize dichlorotitanium complexes. The molecular structures of double-duty tridentate [O, N, N] ligand and one of trichlorotitanium complexes have been characterized by single X-ray diffraction analysis. The local atomic environment and charge state of Ti in two titanium complexes were investigated by X-ray absorption spectroscopy. When activated by excess methylaluminoxane (MAO), these titanium complexes can be used as catalysts for ethylene polymerizaiton and exhibited different catalytic behaviors. Titanium complexes bearing second amine ligand is more active than the titanium complex bearing imine ligand. In addition, the bulky and donation substituents on second amine analogue ligand enhance the activity of its precatalyst.3. we have introduced a new class of easily accessible group IV metal complexes containing a novel o-carborane bridged [OSSO]-type tetradentate ligand which are structurally well-characterized single-site catalyst precursors for ethylene (co)polymerization. A combination of X-ray crystallographic and X-ray absorption spectroscopy studies confirm the nature of these group IV metal complexes. For the first time, group IV metal complexes bearing o-carborane bridged [OSSO]-type tetradentate ligand exhibit good activity toward ethylene polymerization and ethylene copolymerization with1-hexene. In the copolymerization of ethylene with1-hexene, linear low-density polyethylene (LLDPE) was abtained and contain12.7mol%1-hexene incorporation.4. we have introduced a new class of easily accessible half-sandwich zirconium complex containing a novel o-carborane [S, S, O] tridentate ligand which are structurally well-characterized single-site catalyst precursors for ethylene (co)polymerization. A combination of DFT calculations, elemental and NMR analyses confirm the nature of half-sandwich zirconium complex. For the first time, half-sandwich zirconium complex bearing o-carborane [S, S, O] tridentate ligand exhibit good activity toward ethylene polymerization and ethylene copolymerization. In the copolymerization of ethylene with1-hexene or polar olefins, we found that good activities were achieved with low incorporation ratio of the polar olefins. These results maybe due to that carborane tridentate ligand contain a highly electron-deficient carborane moiety, which should enhance the Lewis acidity of the central metal ion, thus increase the activity of the resulting zirconium complex. The steric hindrance caused by Cp (cyclopentadienyl) and tBu groups protect the active species and results in high activity and long lifetime. But in ethylene copolymerization, crowded steric hindrance may results in low comonomer incorporation. In addition, the good solubility of zirconium complex with carborane ligand backbone is benefit for high catalytic activity.5. The o-carborane [S, C] ligand1[1-(2’-(S)PPh2)-o-carborane] was prepared by the monophosphino o-carborane reacted with elemental sulfur in the presence of Et3N. Ligand1was lithiated with n-BuLi and then reacted with (Ph)3PNi(Ph)Cl2, Ni(PPh.3)Cl2,(DME)NiBr2respectively to give the same mononuclear Ni complex {[1-(2’-(S)PPh2)-o-carborane]2Ni}(2). Additionally, the lithium salt of ligand1was treated with elemental sulfur then reacted with (Ph)3PNi(Ph)Cl2affording mononuclear Ni complex3{[1-S-(2’-(S)PPh2)-o-carborane]2Ni}. Ni complexes2and3were characterized by IR,1H NMR spectroscopy and elemental analysis. In addition, an X-ray structure analysis was performed on complex2, where the o-carborane[S, C] ligand1was found to coordinate in a bidentate mode. EXAFS spectroscopy performed on complex3described the similar coordination chemistry with complex2. Two nickel complexes with carborane [S, C] or [S, S] ligands shows moderate catalytic activities for the additon polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst. Catalytic activities, molecular weights, and molecular weight distributions of polynorbornene (PNB) have been investigated onder the various reaction conditions.