Structure and Reactivity of Cationic Zirconocenes

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. 

The aforementioned reactive cationic zirconocene species can react with chlorinated solvents by chloride abstraction. However, an even more pronounced property of cationic zirconocenes is their ability to abstract and bind fluoride. Cationic complexes [Cp2ZrMe(thf)]+ are unstable with BF4 and PF6 counterions [14], and the reaction of Cp2ZrCl2 with AgBF4 directly affords Cp2ZrF2 [7]. The use of Cp2ZrCl2/AgC104 as an 

The usual precursor Cp2ZrCl2 is a commercially available crystalline solid that is slightly sensitive to moisture and light. Some monosubstituted (ligands RC5H4 R = Me, iPr, wBu, tBu) and polysubstituted zirconocenes (Me2C5H3, Me5C5) as well as the indenyl- and the 2-methylindenyl complex, all of which are homoleptic, are also commercially available. 

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