Chiral <i>Ansa</i> Zirconocene Compounds with [Me<sub>2</sub>Si] and [Me<sub>4</sub>Si<sub>2</sub>] Bridges and with <i>tert</i>-Butyl Ring Substituents: Synthesis and Structural Characterization of the <i>Racemo</i> Complexes <i>r</i><i>ac</i><i>-</i>[Me<sub>2</sub>Si(C<sub>5</sub>H<sub>2</sub>-2,4-Bu<sup>t</sup><sub>2</sub>)<sub>2</sub>]ZrCl<sub>2</sub> and <i>r</i><i>ac</i><i>-</i>[Me<sub>4</sub>Si<sub>2</sub>(C<sub>5</sub>H<sub>2</sub>-2,4-Bu<sup>t</sup><sub>2</sub>)<sub>2</sub>]ZrCl<sub>2</sub>
收藏资源简介：
A series of chiral ansa zirconocene compounds that feature (i) [Me2Si] and [Me4Si2] bridges and (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 the But 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 dicarbonyl complexes (Cp1,3-But2)2Zr(CO)2, rac-[Me2Si(CpBut2)2]Zr(CO)2, and rac-[Me4Si2(CpBut2)2]Zr(CO)2 demonstrate that the [Me2Si] and [Me4Si2] ansa bridges have opposite electronic influences in 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 exert a 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}.
