Substituent Effects in the Catalytic Propylene Polymerization Promoted by Titanium (IV) amidinate Complexes
Written by Sinai Aharonovich
Sinai Aharonovich, Moshe Kapon, Mark Botoshanski, and Moris S. Eisen
Schulich Department of Chemistry and Institute of Catalysis Science and Technology,Technion – Israel Institute of Technology, Haifa 32000, Israel
The amidinates, N(R1)C(R2)NR3, are important members of the non-metallocene ligands used in olefin polymerization catalysis. Since the electronic and steric properties of the ancillary ligands are known to affect key catalytic parameters such as the catalytic activity and microstructure of the polymers, we were interested in examining the influence of the amidinate carbon substituent on the catalytic behavior of the titanium amidinates and on the polymer microstructure. Seven different substituted bis[N, N’- bis(trimethylsilyl)arylamidinato] titanium dichlorides and the analogous 2-furyl and 2-pyridyl complexes were synthesized and characterized.
These complexes were active in the polymerization of propylene after their activation with methylalumoxane (MAO). The resulted elastomeric polypropylene can be fractionalized into a major, elastomeric fraction and a minor, isotactic fraction. Unexpectedly, we have found, using linear free energy relationship studies, that the termination rate for the elastomeric fraction is strictly related only to the steric bulk of the aromatic substituent. In this presentation we will discuss how the seemingly remote aromatic substituents affect the catalysis.