In chemistry, the cyclopentadienyl anion or cyclopentadienide is an aromatic species with a formula of [C₅H₅]^-. Its name derives from the molecule cyclopentadiene. Salts of the cyclopentadienyl anion can be stable, e.g., Sodium cyclopentadienide. more complex coordination compounds are known as cyclopentadienyl complexes, such as metallocene