Quantification of Activated Single-Site Olefin Polymerization Catalysts on a Solid Support

Immobilized decamethylzirconocene methyl cation on a silica support was generated by treatment of Cp*2ZrMe2 with tethered borate activator [(SiO2)(x)(Al(iBu)(n)(OC6H4B(C6F5)(3))(2-n)][R2R'NH] (N-Et: R = R' = Et or N-Ph: R = Me; R' = Ph). The concentration of [Cp*2ZrMe](+) on the support was quantified using a newly developed and straightforward method that involves trapping and releasing the active species by subsequent treatment with vinyl methyl thioethers (CH2CH(CH2)(n)SMe, n = 1, 2) and ammonium bromide, [Bu4N]Br, followed by quantification using simple H-1 NMR spectroscopic tools. Reaction of [Cp*2ZrMe](+) with the trapping agent results in formation of stable metallacycle [Cp*Zr-2(CH2CHMe(CH2)(n)SMe)(+) (n = 1, 2); ion exchange in Cp*Zr-2(Br)(CH2CHMe(CH2)(n)SMe) (n = 1,2). This affords a measure for the number of ionic species that were initially present on the support. In this particular case, full conversion of the decamethyl zirconocene precursor to the corresponding cation, [Cp*2ZrMe](+), was observed. Whereas trapping with allyl methyl thioether renders a species that is not active in olefin polymerization catalysis, using butenyl methyl thioether as trapping agent provided a species that is catalytically active in the polymerization of olefins. Furthermore, this study shows that the fate of ionic [Cp*2ZrMe](+) is the same on the support as it is in solution phase.