Significant proximity and cocatalyst effects in binuclear catalysis for olefin polymerization

We describe here the implementation of methylene-bridged binuclear "constrained geometry catalyst" (mu-CH2-3,3'){(eta(5)-indenyl)[1-Me2Si((BuN)-Bu-t)](ZrMe2)}(2) (C1-Zr-2) to produce high-M-w branched polyethylene. In ethylene homopolymerization, similar to 70x increases in molecular weight are achieved with (C1-Zr-2) vs (mu-CH2CH2-3,3'){(eta(5)-indenyl)[1-Me2Si((BuN)-Bu-t)](ZrMe2)}(2) (C2-Zr-2) under identical polymerization conditions using (Ph3C+)(2)[1,4-(C6F5)(3)BC6F4B(C6F5)(3)](2-) (B-2) as the cocatalyst for both. With MAO as the cocatalyst, similar to 600x increases in polyethylene molecular weight are achieved with (mu-CH2CH2-3,3'){(eta(5-) indenyl)[1-Me2Si((BuN)-Bu-t)](ZrCl2)}(2) (C2-Zr2Cl4) and (mu-CH2-3,3'){(eta(5)-indenyl)[1-Me2Si((BuN)-Bu-t)](ZrCl2)}(2) (C1-Zr2Cl4) vs mononuclear [1-Me2Si(3-ethylindenyl)((BuN)-Bu-t)]ZrCl2 (Zr1Cl2). In the ethylene + 1-hexene copolymerization, C1-Zr-2 enchains 3x more 1-hexene than does C2-Zr-2 under identical polymerization conditions (B-2 as cocatalyst). With MAO as the cocatalyst, C2-Zr2Cl4 enchains 3.5 x more, and C1-Zr2Cl4 4.2 x more, 1-hexene than does Zr1Cl2. When the polar solvent C6H5Cl 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.