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Chiral Ansa Zirconocene Compounds with [Me 2 Si] and [Me 4 Si 2 ] Bridges and with tert -Butyl Ring Substituents: Synthesis and Structural Characterization of the Racemo Complexes r ac - [Me 2 Si(C 5 H 2 -2,4-Bu t 2 ) 2 ]ZrCl 2 and r ac - [Me 4 Si 2 (C 5 H 2 -2,4-Bu t 2 ) 2 ]ZrCl 2…

2005; American Chemical Society; Volume: 24; Issue: 4 Linguagem: Inglês

10.1021/om049273j

1520-6041

C.E. Zachmanoglou, J.G. Melnick, B.M. Bridgewater, David G. Churchill, Gerard Parkin,

Synthesis and characterization of novel inorganic/organometallic compounds

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}.