Asymmetric Metallocene Catalysts Based on Dibenzothiophene: A New Approach to High Molecular Weight Polypropylene Plastomers

Abstract

Synthesis and polymerization data of a series of new sulfur-containing C1-symmetric metallocenes, rac-[1-(9-η5-fluorenyl)-2-(2-methylbenzo[b]indeno[4,5-d]thiophen-1-η5-yl)ethane]zirconium dichloride (7a), rac-[1-(9-η5-fluorenyl)-2-(2-methylbenzo[b]indeno[4,5-d]thiophen-1-η5-yl)ethane]hafnium dichloride (7b), rac-[1-(9-η5-fluorenyl)-2-(2-methylbenzo[b]indeno[4,5-d]thiophen-1-η5-yl)ethane]hafnium dimethyl (7c), and rac-[1-(9-η5-fluorenyl)-2-(2-methylbenzo[b]indeno[4,5-d]thiophen-3-η5-yl)ethane]zirconium dichloride (8), are reported. The characteristic structural feature of these complexes is the 2-methyl-1H-benzo[b]indeno[4,5-d]thiophene moiety (3: MBIT), which was derived from dibenzothiophene. In the case of 7a−c the MBIT unit shows a “back” orientation, whereas in 8 it is directed to the “front” of the tetrahedral metallocene dichloride species, which was unambiguously illustrated by X-ray structure analysis. Propylene polymerization experiments revealed higher activity and stereoselectivity for 7a/MAO ...