Metallocene

A metallocene is a compound typically consisting of two cyclopentadienyl anions (C
₅H⁻
₅, abbreviated Cp) bound to a metal center (M) in the oxidation state II, with the resulting general formula (C₅H₅)₂M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride or vanadocene dichloride. Certain metallocenes and their derivatives exhibit catalytic properties, although metallocenes are rarely used industrially. Cationic group 4 metallocene derivatives related to [Cp₂ZrCH₃]⁺ catalyze olefin polymerization.

Some metallocenes consist of metal plus two cyclooctatetraenide anions (C
₈H²⁻
₈, abbreviated cot²⁻), namely the lanthanocenes and the actinocenes (uranocene and others).

Metallocenes are a subset of a broader class of compounds called sandwich compounds.^[1] In the structure shown at right, the two pentagons are the cyclopentadienyl anions with circles inside them indicating they are aromatically stabilized. Here they are shown in a staggered conformation.