Compared to the synthesis of metallocene cations, metallocene anions have remained far less explored with only a handful of synthetically isolated compounds. As metallocene anions require a formal +I metal oxidation state, group 1 metallocenes represent the simplest metallocene anions. Since the +I oxidation state is most stable for alkali metals, the synthesis of group 1 metallocene anions is not dependent on any reducing agents or bulky Cp substituents. In contrast, the unstable nature of d-block metallocene anions not only demands harsh reducing agents for their synthesis, but also the stabilization of these highly reactive anionic species. Recent approaches, such as the isolation of the derivatized manganocene, ferrocene and cobaltocene anion, have demonstrated the efficiency of bulky substituents in stabilizing the reactive metal center.