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

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Title: Design and synthesis of new C1 and C2-symmetric ansa-metallocene catalysts for isotactic-polypropylene formation
Author: Al-Bahily, Khalid A
Abstract: Several ansa C1 -symmetric cyclopentadienyl -fluorenyl metallocenes based on zirconium have been prepared with different substituents at position 3 on the cyclopentadienyl ring . Isotactic polypropylene production from these systems depends highly 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 showed good activity and produced high molecular weight of isotactic polypropylene . In terms of the tacticity of the polymers , metallocene 6 made the best isotactic polypropylene with ~88 % mmmm pentad content . Also , it has been found that if the size of this substituent is large as in 2 ,3 ,4 -trimethyl -3 -pentyl (metallocene 9 ) , then it will block the polymerization active site which will deactivate the metallocene . New synthetic pathways for the synthesis of cyclopentadienyl -fluorenyl metallocenes based on titanium have been achieved . Anchoring these types of ligands onto titanium by following the conventional method of using TiCl4 in the metallation step has failed for the production of Me2C (3 - (diphenylmethyl ) -C5H3 ) (C13H8 )TiCl2 (metallocene 12 ) , Ph2C (C5H4 ) (C13H8 )TiCl2 (metallocene 14 ) , and Ph2C (C5H4 ) (C13H8 )TiMe2 (metallocene 15 ) ; this is possibly due to the high reactivity of TiCl4 . Therefore , TiCl4 ? ?2THF has been prepared and used in that step to produce these new titanocenes with good yields . A new ansa -C2 -symmetric substituted bis -indenyl metallocene for isotactic polypropylene production has been successfully prepared . It is known that ansa -C2 - symmetric metallocenes are good catalysts for isotactic polypropylene production , but in general , their synthesis suffers from the production of the meso Cs -stereoisomer of these catalysts , which generally produces only atactic polypropylene . Therefore , the meso stereoisomers must be removed and this is considered a loss of the material that increases the cost of the catalysts . Addition of bulky substituents on the indenyl groups as 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 isotactic polypropylene with up to ~80 % mmmm pentad content .
URI: http : / /hdl .handle .net /1969 .1 /3061
Date: 2006-04-12

Citation

Design and synthesis of new C1 and C2-symmetric ansa-metallocene catalysts for isotactic-polypropylene formation. Available electronically from http : / /hdl .handle .net /1969 .1 /3061 .

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