Regioselective tetrametalation of ferrocene in a single reaction: Extension of s-block inverse crown chemistry to the d-block

s-Block metal inverse crowns constitute an emerging family of special compounds in which polymetallic amide cationic rings complex anionic guests. They are inverse crowns in the sense that their Lewis acidic/Lewis basic sites have been interchanged relative to those in conventional crown ether complexes, that is, here the metal atoms belong to the ring and not to the core. However, the chemistry controlling their formation goes far beyond that of simple macrocyclic host-guest combinations. It appears that a powerful ring template effect brings about the regioselective deprotonation of certain substrates to create and to encapsulate unusual anions, which are inaccessible through the use of mainstream bases. This field is currently being studied in the search for polymers with unusual properties (e.g., conductive, magnetic, electronic, optical). Also, following this first venture into organometallic chemistry the development prospects for inverse crown chemistry as a whole look decidedly bright with a vast pool of metallocenes now available as potential candidates for exploitation in this exciting new area.