What is implied by the term superaromatic as applied to the

What is implied by the term \"superaromatic\" as applied to the reactivity of ferrocene toward electrophilic aromatic substitution? How can this be used to explain the fact that no Lewis acid catalyst is required during the Friedel-Crafts acylation of ferrocene?

Solution

Ferrocene itself consists of two cyclopentadiene anions with an iron (II) cation sandwiched between them. Its reactivity is similar to that of benzene, but it is a stronger nucleophile in Friedel-Crafts reactions since each ring has 6 ? electrons distributed over 5 carbon atoms compared to 6 carbon atoms in benzene. Its enhanced nucleophilicity relative to benzene allows us to use a milder acid catalyst, phosphoric acid, to run the reaction.
Your instructor will discuss with you the specifics of the mechanism to transform ferrocene into monoacetylferrocene.
The attachment of an acetyl group on ferrocene deactivates the compound towards further substutition, but because ferrocene is generally much more nucleophilic than benzene (it is referred to as a