Metallocenes, like ferrocene cannot be nitrated. Why?

Explanation:

Metallocenes are cyclic organometallic compounds with a double pentadienyl structure consisting of a metal atom in between the two structures. In ferrocene, Fe is the metal in between the two pentadienyl structures.

Nitration reaction is the reaction of nitric acid in the presence of sulphuric acid. When metallocenes, (e.g. ferrocene) are being treated with this stong oxidizing agent (nitric acid), oxidation of organometallic compound takes place. When this oxidation occurs, it oxidizes the oxidation state of the Fe metal from +2 to +3 in ferrocene, and it becomes unstable. Then, as a result, the whole metallocene structure gets destroyed.