Effects of Ligand Substitutions on the Rotation Rate of Indenyl Ligands in Bis(2-arylindenyl)zirconocenes by NMR Line-Shape Analysis and Relaxation in the Rotating Frame

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• 作者：Gregg M. Wilmes ; Marcia B. France ; Stephen R. Lynch ; and Robert M. Waymouth
• 刊名：Organometallics
• 出版年：2004
• 出版时间：May 10, 2004
• 年：2004
• 卷：23
• 期：10
• 页码：2405 - 2411
• 全文大小：89K
• 年卷期：v.23,no.10(May 10, 2004)
• ISSN：1520-6041

文摘

Unbridged bis(2-arylindenyl)metallocene complexes, such as bis(2-phenylindenyl)zirconiumdichloride (1a), when treated with appropriate activators are active catalyst precursors forthe production of elastomeric polypropylene. The proposed mechanism for polymerizationinvolves isomerization of the catalyst between geometries of differing stereoselectivity on atime scale slower than polymer chain growth. As the rotation of the 2-arylindenyl ligand isproposed to result in the different catalyst geometries, the rate at which this rotation occursis of interest for the interpretation of the behavior of these complexes. A series of zirconocenes{bis(2-phenylindenyl)zirconium dimethyl (1b), bis(2-phenylindenyl)zirconium dibenzyl (1c),bis(2-(3,5-di-tert-butylphenyl)indenyl)zirconium dimethyl (2b), and bis(2-(3,5-di-tert-butylphenyl)indenyl)zirconium dibenzyl (2c)}, varying both in the indenyl ligand frameworkand the mages/gifchars/sigma.gif" BORDER=0 >-ligand, has been synthesized. The rotation rates of the methyl-substitutedmetallocenes are too fast to be determined by standard NMR techniques such as EXSY,line-shape analysis, or magnetization transfer experiments. On-resonance spin-latticerelaxation in the rotating frame (T_{1mages/gifchars/rho.gif" BORDER=0 >}) has been used to determine the rate of rotation of thearyl ligands in 1b, 1c, and 2b and allowed comparison with the rates obtained for thebenzylated species by line-shape analysis. The nature of both the mages/gifchars/pi.gif" BORDER=0 > and the mages/gifchars/sigma.gif" BORDER=0 > ligand systemsaffects the rate, with sterically bulky substituents resulting in slower rotation. The effect ofthe mages/gifchars/sigma.gif" BORDER=0 > ligand is substantially stronger than that of the mages/gifchars/pi.gif" BORDER=0 > ligand.