|Ph.D Thesis||Department of Chemistry|
|Supervisor:||Prof. Eisen Moris|
An enormous progress was done, long since the Nobel Prize laureates Karl Ziegler and Giulio Natta first polymerized ethylene and propylene by heterogeneous titanium chloride catalyst. Since then, a variety of metallocene based homogeneous catalysts were developed. Beyond the metallocenes, new complexes were design containing a miscellany of ligands based on nitrogen, oxygen, phosphorous and sulfur atoms.
We have chosen to focus on a chiral benzamidinate ligand in a titanium complex with MAO (methyl alomoxane) as cocatalyst.
Our goal was to study the influence, if any, of a chiral ligand. The existence of a chiral ligand enabled us to receive a single diastereomer complex and not a racemic mixture at the metal center. Our assumption was that the existence of a chiral center will direct the approaching monomer to the active site in a specific way, which is energetically preferred from other naturally existing approaches for a prochiral monomer.
Two complexes were synthesized: [PhC(NTMS)(N-Myrtanyl)]TiCl3·THF and [PhC(NTMS)(N-Myrtanyl)]2TiCl2, and their catalytic activity was studied in the polymerization of propylene and styrene. The complexes showed a good catalytic activity. For propylene, the polymerization gives elastomeric polypropylene with significant stereoselectivity which was attributed to the existence of both, an isospecific site and an aspecific site.