Synthesis and characterization of the group 4 organometallic catalysts for olefin polymerization and novel silatranyl cobalt cluster

Abstract

The group 4 metallocene compounds have been becoming an important class of catalysts for the synthesis of organic molecules and polymers. The known organometallic chemistry of group 4 metals (Ti, Zr and Hf) has been largely developed by the use of cyclopentadienyl (or indenyl) and substituted cyclopentadienyl (or indenyl) ligand. The broader tunable feature of eletronic and steric factors in the cyclopentadienyl type ligands allows greater versatility in the design of catalytic systems that are able to give regio- and stereo-regular polyolefins. As part of our efforts in pursuing this matter, a new group 4 organometallic compounds were synthesized and the full characterizations including the molecular structure analysis were carried out. The catalytic activity of these complexes in olefin polymerization has been also examined. To study catalytic properties for styrene polymerization, the half-sandwich type titanium compound $(p-MePhC_5Me_4)TiCl_3$ (3) was synthesized by the reaction of the silylated Cp ligand $(p-MePhC_5Me_4)SiMe_3$ (2) with $TiCl_4$ in dichloromethane and the catalytic behavior of the compound 3 for styrene polymerization in the presence of excess amount of methylaluminoxane (MAO) has been carried out. This catalyst system produces a mixture of syndiotactic and atactic polystyrenes at 50℃. Treatment of 3 with stoichiometric amount of water gave oxo-bridged dinuclear titanium complex [$(p-MePhC_5Me_4)TiCl_2]_2$ ($μ_2$-O) (4) which was characterized by various spectroscopic means and single crystal X-ray diffraction study. We have also synthesized homoleptic titanium alkoxide compound bis (2,6-pyridinedimethoxy)titanium (5) and heteroleptic complex (2,6-pyridinedicarboxylate)(2,6-pyridinedimethoxy) titanium (6). Both titanium alkoxide compounds activated with MAO produce only atactic polystyrene, which differ from catalytic behavior of the general titanium alkoxide catalyst system. The molecular structure of 6 has been determined by X-ray cry...