Fluorous Zirconocene(IV) Complexes and Their Olefin Polymerization Activity in Toluene and Fluorous Biphasic Solvent Systems^†

The synthesis (4a−d) and structure (4a,c) of the four crystalline, water-stable, hydrocarbon- and perfluorocarbon (PFC)-soluble fluorous zirconocene(IV) dichloride precatalysts [Zr{η⁵-C₅H₄SiMe_3-n(R_F)_n}₂Cl₂] (n = 1, R_F = CH₂CH₂C₆F₁₃ (4a), C₈F₁₇ (4b), CH₂C₆F₅ (4c); n = 3, R_F = CH₂C₆F₅ (4d)), possessing one to three fluorous alkyl or aryl groups attached to the cyclopentadienyl ligand through a silicon atom and an additional methylene (4c,d) or ethylene (4a) spacer or no spacer at all (4b), are reported. A nonfluorous analogue of 4a, [Zr{η⁵-C₅H₄SiMe₂C₈H₁₇}₂Cl₂] (4e), was prepared for comparison, and 4a was easily converted to its dimethyl derivative [Zr{η⁵-C₅H₄SiMe₂CH₂CH₂C₆F₁₃}₂Me₂] (5a). The ethylene polymerization activities of the zirconocene dichlorides were compared to those of the known bis{(trimethylsilyl)cyclopentadienyl}zirconium dichloride [Zr{η⁵-C₅H₄SiMe₃}₂Cl₂] (4f), in both toluene and fluorous biphasic solvent (FBS) systems. In the case of 4b a PE with a bimodal molecular weight distribution and a significantly lower molecular weight was obtained. Polymerization data and polymer properties for 4a−d, compared to data for 4f, show a marked influence of the fluorous groups and the alkyl spacer (e.g. methylene in 4c or ethylene in 4a). FBS conditions result in PE with a higher average molecular weight. Evidence on the nature of the active species formed when these precatalysts were treated with an excess of methylaluminoxane (MAO) is presented.