Ferrocene

"Ferrocene is an organometallic compound with the formula Fe(C₅H₅)₂. It is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central metal atom. Such organometallic compounds are also known as sandwich compounds.^[2] The rapid growth of organometallic chemistry is often attributed to the excitement arising from the discovery of ferrocene and its many analogues."