|M.Sc Student||Gornshtein Florina|
|Subject||Novel Group IV Organometallic Complexes: Synthesis,|
Characterization and Catalytic Activity
|Department||Department of Chemistry||Supervisor||Professor Moris Eisen|
|Full Thesis text|
During the last decade, an effort was made to develop a new generation of non-metallocene complexes providing an opportunity to create polymers with novel properties and uses.
In this research we report the synthesis and characterization of a novel zirconium(IV) dichloride complex ((CH3)3CCOCHCONEt2)2ZrCl2 (6) and three new neutral titanium(IV) dialkoxide complexes ((CH3)3CCOCHCONEt2)2Ti(OMe)2 (3), ((CH3)3CCOCHCONMe2)2Ti(OMe)2 (4), and (CH3COCHCONMe2)2Ti(OC(CH3)3)2 (5) produced during the attempts to synthesize the corresponding titanium diamido complexes presumably via an intra-molecular metathesis.
The molecular structures of complexes 3 and 5 have been confirmed by X-ray single-crystal diffraction studies. The molecular structure of complex 4 has been confirmed by NMR and 1H NOE measurements of the complex. In these complexes the metal is disposed in an octahedral environment with two chelating h2-b-ketoamidate and two alkoxide ligands.
Complexes 3 and 4 showed a dynamic behavior in solution and as dependence on temperature. This dynamic behavior is due to a disconnection and recoordination of the chelating ligands through the weaker Ti-O bond resulting in the formation of different octahedral stereoisomers in solution.
The catalytic activity of all the complexes in polymerization of propylene was studied under comparable conditions. When activated by MAO, the titanium complex 3 showed the highest catalytic activity. Furthermore, the influence of different MAO:catalyst ratios, polymerization times, temperatures, and solvents on the catalytic activity of complex 3 and the yield and molecular weights of the obtained polymers was also studied. The elastomeric properties of the polypropylene obtained using this complex as catalyst, are probably due to a dynamic interconversion between two of the six possible cis-octahedral C2-symmetry enantiomeric structures via an open C2v-symmetry intermediate complex, which is formed by an opening of at least one of the chelating b-ketoamidate ligands. The open intermediate complex is expected to produce atactic blocks, while the close complex should produce isotactic ones.
Additionally, it is known that alkoxide complexes can be utilized for the ring opening polymerization (ROP) of cyclic esters (such as lactones and lactides), therefore we have also studied the catalytic activity of these complexes in polymerization of e-caprolactone and rac-lactide.