|Ph.D Student||Aharonovich Sinai|
|Subject||Hetero-aza-allyl Complexes of Li, Ti, Zr, and V:|
Structure, Reactivity and Catalytic Propylene
|Department||Department of Chemistry||Supervisor||Professor Moris Eisen|
|Full Thesis text|
In the wake of the Nobel-winning discovery of Ziegler and Natta six decades ago, many new early transition metal catalysts for the polymerization of α olefins were developed based on the cyclopentadienyl ligands, and since the early 90's also based on different other ligands, among them the amidinate. This work was partly inspired by the significantly different catalytic behavior of two benzamidinate titanium catalysts differentiated only by the identity of the para substituent on the aromatic ring (H or Me). The substituent effect on the polymerization catalysis using titanium and zirconium arylamidinates was studied by preparing a library of arylamidinates with differently substituted aromatic rings as carbon substituents. Using Linear Free Energy Relationship and NOE studies the active species in the polymerization was characterized, and we have shown for the titanium complexes that the substituent can hinder the chain termination reaction by its steric bulk alone. When the chain termination is completely suppressed, the polymerization is said to be "living", and a precise control over the molecular weight and the composition of the polymer can be achieved. We were also intrigued by the notion suggested by Fujita et. al. that a close pendant fluorine atom can also induce living polymerization by competing with the metallic center over interaction with the β hydrogen of the growing chain. In order to check the generality of this idea, we have prepared two perfluorinated zirconium benzimidazolate complexes, which have F-Zr distances similar to the ones in Fujita's catalysts, and examined their activity in the polymerization of propylene. Another goal was to expand the scope of metal centers supported by the amidinate ligand for use in α olefin polymerization to vanadium (V). To this end, we have synthesized and studied the structure, reactivity and olefin polymerization abilities of mono- and bis-amidinate imidovanadium (V) complexes, and found conditions in which reduction of the metal to V (IV) or amidinate formation can occur. Finally, during the preparation of the transition metal amidinates we were exposed to the interesting and diverse coordination chemistry and reactivity of the lithium arylamidinates, which serves as starting materials for the preparation of many amidinate complexes and also organo-nitrogen compounds. We report in this publication our study of the substituent effects, and mechanistic studies of the amidinate and benzimidazolate formation from nitriles and amides, and also the structure and reactivity of the lithium aryl amidinates.