As most polymerisations are carried out in aromatic solvents the formation of arene adducts has been suggested. These adducts would then be in equilibrium with other dormant states and active states of the catalytic process (cf. Scheme 2).
In order to investigate these possible adducts zirconocene compounds with one or two phenyl groups tethered to the Cp-moiety have been prepared. Activation of these compounds indeed lead to the formation of zirconocene cations and dications as demonstrated by NMR experiments (cf. Scheme 3). The dication is the first example of a zirconocene intramolecular stabilised by phenyl interaction.
Recently, we have extended these models and have exchanged the brigding carbon with silicon. The effect is quite dramatic: we not only observe the cation with coordinated phenyl group, but also the well known inner-coordination-sphere compound with a Zr-Me-BX3 bridge. Both compounds are in exchange with each other, as demonstrated by low temperatur NMR experiments.
More detailed results of my research can be found in the talk section.
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last changed: 25.06.2006