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

Synthesis and polymerization data of a series of new sulfur-containing C 1 -symmetric metallocenes, rac -[1-(9-η 5 -fluorenyl)-2-(2-methylbenzo[ b ]indeno[4,5- d ]thiophen-1-η 5 -yl)ethane]zirconium dichloride ( 7a ), rac -[1-(9-η 5 -fluorenyl)-2-(2-methylbenzo[ b ]indeno[4,5- d ]thiophen-1-η 5 -yl)ethane]hafnium dichloride ( 7b ), rac -[1-(9-η 5 -fluorenyl)-2-(2-methylbenzo[ b ]indeno[4,5- d ]thiophen-1-η 5 -yl)ethane]hafnium dimethyl ( 7c ), and rac -[1-(9-η 5 -fluorenyl)-2-(2-methylbenzo[ b ]indeno[4,5- d ]thiophen-3-η 5 -yl)ethane]zirconium dichloride ( 8 ), are reported. The characteristic structural feature of these complexes is the 2-methyl-1 H -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 compared to 8 /MAO. The catalysts 7a, 8 /MAO were found to operate under different polymerization mechanisms indicated by a diverse correlation of tacticity and polymerization temperature. Crystalline, flexible polypropylenes with tacticities ranging from 65 ≤ [mmmm] ≤ 90 and molecular weights up to 2 × 10 5 g mol - 1 were obtained for 7a /MAO, whereas experiments using 8 /MAO produced low tacticity, waxy materials. To achieve ultrahigh molecular weight isotactic polypropylene plastomers ( M w up to 1.5 × 10 6 g mol - 1 ), further investigations on the hafnium dimethyl complex 7c /[(C 6 H 5 ) 3 C + ][(C 6 F 5 ) 4 B - ] in liquid propylene were performed.