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

The synthesis (4ad) and structure (4a,c) of the four crystalline, water-stable, hydrocarbon- and perfluorocarbon (PFC)-soluble fluorous zirconocene(IV) dichloride precatalysts [Zr{η5-C5H4SiMe3-n(RF)n}2Cl2] (n = 1, RF = CH2CH2C6F13 (4a), C8F17 (4b), CH2C6F5 (4c); n = 3, RF = 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 4ad, 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.