Base-0 free zirconocene cations

The above reactions are rather slow because the insertion reactivity is directly related to the rate of dissociation of the THF ligand, which is also present as the solvent. The most reactive cationic complexes are therefore base-free, i. e. they do not contain coordinating solvents or ligands. Logically, anion coordination is a problem in such systems. Ion pairing reduces the reactivity of the cationic zirconocenes, but in the presence of B(C6F5)4, RB(C6F5)3 (R = H, Me), or BARF", this interaction is only weak. 

Scheme 8.2. Synthetic access to base-free cationic zirconocenes.

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