Evidence of Fluoride Transfer from the Anion of [Zr[lcub]C5H3[SiMe2([eta]1-NtBu)]2[rcub]]+[RB(C6F5)3][minus] Complexes to the Zirconocenium CationFinancial support by the Spanish MEC (project MAT2004-02614) and DGUI/CM (program S/0505/PPQ-0328) is acknowleged. R[equals]Me, CH2Ph

generated by activation of the corresponding dialkyl compounds with B(C6F5)3 are active homogeneous catalysts for olefin polymerization. Weakly coordinating anions are required to minimize the ion-pairing interactions, which are crucial in determining the properties of the resulting polymeric materials and the characteristics of the polymerization processes. These counteranions frequently contain fluoroorganic moieties to reduce interactions by dissipating the negative charge and decreasing the nucleophilicity. However, [RB(C6F5)3] groups can still be responsible for deactivation processes. The carbon–fluorine bond is the strongest and least reactive bond found in organic molecules and its activation is a chemical challenge, whereas the boron–carbon bond is more reactive and C6F5 transfer to the cationic metal center is the most commonly observed deactivation pathway for [L2MR’][RB(C6F5)3] catalysts. [3] Ziegler and co-workers recently reported calculations on different competing thermal deactivation pathways for the [L2MR’][RB(C6F5)3] ion pair. [4]