Synthesis of Cp Complexes
Most cyclopentadienyl complexes are prepared by treating a metal halide with sodium cyclopentadienide (NaCp). For the preparation of some particularly robust complexes, cyclopentadiene is employed in the presence of a conventional base such as NaOH. Specialized alternatives to NaCp include trimethylsilyl cyclopentadiene (CpSiMe3) and thallium cyclopentadienide (CpTl) in an ethereal solvent. Most Cp complexes have various other ligands besides a cyclopentadienyl ligand, such as carbonyl, halogen, alkyl, and so on. Biscyclopentadienyl complexes are called metallocenes. It is often the case that these complexes are thermally stable, and they are used for various catalysts. For example, some of the early transition metal complexes, such as Cp2TiCl2 and Cp2ZrCl2 with aluminoxane as a co-catalyst, can catalyze olefin polymerization. Such species are called Kaminsky-type catalysts.
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