Significant Proximity and Cocatalyst Effects in Binuclear Catalysis for Olefin Polymerization

We describe here the implementation of methylene-bridged binuclear “constrained geometry catalyst” (μ-CH 2 -3,3‘){(η 5 -indenyl)[1-Me 2 Si( t BuN)](ZrMe 2 )} 2 (C1-Zr 2 ) to produce high- M w branched polyethylene. In ethylene homopolymerization, ∼70× increases in molecular weight are achieved with(C1-Zr 2 ) vs (μ-CH 2 CH 2 -3,3‘){(η 5 -indenyl)[1-Me 2 Si( t BuN)](ZrMe 2 )} 2 (C2-Zr 2 ) under identical polymerization conditions using(Ph 3 C + ) 2 [1,4-(C 6 F 5 ) 3 BC 6 F 4 B(C 6 F 5 ) 3 ] 2- (B 2 ) as the cocatalyst for both. With MAO as the cocatalyst, ∼600× increases in polyethylene molecular weight are achieved with (μ-CH 2 CH 2 -3,3‘){(η 5 -indenyl)[1-Me 2 Si( t BuN)](ZrCl 2 )} 2 (C2-Zr 2 Cl 4 ) and (μ-CH 2 -3,3‘){(η 5 -indenyl)[1-Me 2 Si( t BuN)](ZrCl 2 )} 2 (C1-Zr 2 Cl 4 ) vs mononuclear [1-Me 2 Si(3-ethylindenyl)( t BuN)]ZrCl 2 (Zr 1 Cl 2 ). In the ethylene + 1-hexene copolymerization, C1-Zr 2 enchains 3× more 1-hexene than does C2-Zr 2 under identical polymerization conditions (B 2 as cocatalyst). With MAO as the cocatalyst, C2-Zr 2 Cl 4 enchains 3.5× more, and C1-Zr 2 Cl 4 4.2× more, 1-hexene than does Zr 1 Cl 2 . When the polar solvent C 6 H 5 Cl is used as the polymerization medium, dramatic compression in the dispersion of polymerization activities and molecular weights is found. Both homopolymerization and copolymerization results argue that achievable Zr−Zr spatial proximity significantly influences chain transfer rates and selectivity for comonomer enchainment and that such proximity effects are highly cocatalyst and solvent sensitive.