Chiral Ansa Zirconocene Compounds with [Me2Si] and [Me4Si2] Bridges and with tert-Butyl Ring Substituents: Synthesis and Structural Characterization of t
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- 作者：Cary E. Zachmanoglou ; Jonathan G. Melnick ; Brian M. Bridgewater ; David G. Churchill ; and Gerard Parkin
- 刊名：Organometallics
- 出版年：2005
- 出版时间：February 14, 2005
- 年：2005
- 卷：24
- 期：4
- 页码：603 - 611
- 全文大小：242K
- 年卷期：v.24,no.4(February 14, 2005)
- ISSN：1520-6041
文摘
A series of chiral ansa zirconocene compounds that feature (i) [Me2Si] and [Me4Si2] bridgesand (ii) two tert-butyl substituents on each cyclopentadienyl ring, namely, rac-[Me2Si(CpBut2)2]ZrCl2, rac-[Me2Si(CpBut2)2]Zr(Ph)Cl, rac-[Me2Si(CpBut2)2]ZrMe2, rac-[Me2Si(CpBut2)2]Zr(CO)2, rac-[Me4Si2(CpBut2)2]ZrCl2, and rac-[Me4Si2(CpBut2)2]Zr(CO)2, has been synthesized. In each case,the complex exists as the racemo isomer due to inter-ring steric interactions between theBut substituents proximal to the ansa bridge that destabilize the meso isomer. rac-[Me4Si2(CpBut2)2]ZrCl2 is the first structurally characterized ansa zirconocene complex with a [Me4Si2] bridge that adopts a racemo geometry. IR spectroscopic studies on the dicarbonylcomplexes (Cp1,3-But2)2Zr(CO)2, rac-[Me2Si(CpBut2)2]Zr(CO)2, and rac-[Me4Si2(CpBut2)2]Zr(CO)2demonstrate that the [Me2Si] and [Me4Si2] ansa bridges have opposite electronic influencesin this system, with the [Me2Si] bridge exerting an electron-withdrawing effect and the [Me4Si2] bridge exerting an electron-donating effect. The [Me2Si] and [Me4Si2] bridges also exerta different influence with respect to olefin polymerization, with {rac-[Me2Si(CpBut2)2]ZrCl2/MAO} being a more active catalyst system for polymerization of ethylene than is either{(Cp1,3-But2)2ZrCl2/MAO} or {rac-[Me4Si2(CpBut2)2]ZrCl2/MAO}.