Design and synthesis of new C1 and C2-symmetric ansa-metallocene catalysts for isotactic-polypropylene formation

摘要

Several ansa C1-symmetric cyclopentadienyl-fluorenyl metallocenes based onzirconium have been prepared with different substituents at position 3 on thecyclopentadienyl ring. Isotactic polypropylene production from these systems dependshighly on the size of these substituents. Therefore, large groups such as 1-methyl-4-tbutylcyclohexyl(metallocene 6), 1-methyl-cyclohexyl (metallocene 7), 1,3,3,5-tetramethylcyclohexyl (metallocene 8), and 2,3,4-trimethyl-3-pentyl (metallocene 9)have been investigated. In combination with methylaluminoxane (MAO), they showedgood activity and produced high molecular weight of isotactic polypropylene. In termsof the tacticity of the polymers, metallocene 6 made the best isotactic polypropylenewith ~88% mmmm pentad content. Also, it has been found that if the size of thissubstituent is large as in 2,3,4-trimethyl-3-pentyl (metallocene 9), then it will block thepolymerization active site which will deactivate the metallocene.New synthetic pathways for the synthesis of cyclopentadienyl-fluorenylmetallocenes based on titanium have been achieved. Anchoring these types of ligandsonto titanium by following the conventional method of using TiCl4 in the metallationstep has failed for the production of Me2C(3-(diphenylmethyl)-C5H3)(C13H8)TiCl2(metallocene 12), Ph2C(C5H4)(C13H8)TiCl2 (metallocene 14), andPh2C(C5H4)(C13H8)TiMe2 (metallocene 15); this is possibly due to the high reactivity ofTiCl4. Therefore, TiCl4??2THF has been prepared and used in that step to produce thesenew titanocenes with good yields.A new ansa-C2-symmetric substituted bis-indenyl metallocene for isotacticpolypropylene production has been successfully prepared. It is known that ansa-C2-symmetric metallocenes are good catalysts for isotactic polypropylene production, but ingeneral, their synthesis suffers from the production of the meso Cs-stereoisomer of thesecatalysts, which generally produces only atactic polypropylene. Therefore, the mesostereoisomers must be removed and this is considered a loss of the material thatincreases the cost of the catalysts. Addition of bulky substituents on the indenyl groupsas in Me2Si(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)2ZrCl2 (metallocene 5)has prevented the meso stereoisomer production. 5/MAO produces isotacticpolypropylene with up to ~80% mmmm pentad content.