Cyclopentadienyl Ligand
The alkali-metal cyclopentadienyl complexes react with various transition metal compounds to form a variety of complexes that are found throughout chemistry. The Cp ligand typically bonds to metals through all five carbon atoms, like in ferrocene, Fp ligand, ; chromocene, ; cobaltocene, ; and nickelocene, . When the Cp rings are mutually parallel the compound is known as a sandwich complex. This area of organometallic chemistry was first discovered in 1954 with the realization of the structure of ferrocene. Some metallocenes, notably rhodocene, and nickelocene, do exist in some forms where the metal-to-ring binding does not include all five ring atoms.
Other metals form bent structures, such as zirconocene dichloride, which is a catalyst for ethylene polymerization.
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