Ethylene and Propylene Polymerization by a Series of Highly Electrophilic, Chiral Monocyclopentadienyltitanium Catalysts

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• 作者：Sean W. Ewart ; Mark J. Sarsfield ; Dusan Jeremic ; Tracey L. Tremblay ; Edan F. Williams ; and Michael C. Baird
• 刊名：Organometallics
• 出版年：1998
• 出版时间：April 13, 1998
• 年：1998
• 卷：17
• 期：8
• 页码：1502 - 1510
• 全文大小：135K
• 年卷期：v.17,no.8(April 13, 1998)
• ISSN：1520-6041

文摘

The compoundsCp*TiMe₂C₆F₅,Cp*TiMe₂OC₆F₅, andCp*TiMe₂Cl (Cp* =⁵-C₅Me₅) reactwith the borane B(C₆F₅)₃ to formthe thermally unstable, chiral complexesCp*TiMe(C₆F₅)(-Me)B(C₆F₅)₃,Cp*TiMe(OC₆F₅)(-Me)B(C₆F₅)₃,andCp*TiMeCl(-Me)B(C₆F₅)₃,respectively,which are similar to the knownCp*TiMe₂(-Me)B(C₆F₅)₃.All four -Me compounds behaveas sources of the highly electrophilic species[Cp*TiMeE]⁺ (E = Me, Cl,C₆F₅, OC₆F₅)whentreated with the borane, the last three being chiral, and all foursystems exhibit catalyticactivities for the polymerization of ethylene to high-molecular-weightpolyethylene. Despitethe chirality at titanium of three of the compounds, polymerization ofpropylene by all ofthem results in the formation of atactic, elastomeric polypropylene.NMR analyses of thepropylene polymers formed show that initiation involves 1,2-insertioninto a Ti-Me bond,and while propagation involves primarily head-to-tail 1,2-insertions,an unusually high (bymetallocene standards) proportion of the insertions also involves2,1-misinsertions butessentially no 1,3-enchainment. The major olefinic end groups arevinylidene (CH₂=CMe-), resulting from -hydrogen transfer following a 1,2-insertion, andvinyl (CH₂=CH-),resulting from -hydrogen transfer from the methyl group following a2,1-insertion or, morelikely, -methyl transfer following a 1,2-insertion. Smallamounts of internal olefins arealso formed via -hydrogen transfer following a 2,1-insertion.An EPR study of the Cp*TiMe₃/B(C₆F₅)₃ system in toluene indicatesthat <0.01% of the titanium is occasionally presentduring polymerization as a complex of titanium(III), suggestingthat a contribution tocatalysis by titanium(III) species is unlikely.