Mechanochemical Synthesis of a Sodium Anion Complex [Na+(2,2,2-cryptand)Na–] and Studies of Its Reactivity: Two-Electron and One-Electron Reductions

Group 1 metal molecular chemistry is dominated by a +1 oxidation state, while a 0 oxidation state is widespread in the metals. A more exotic, yet still available, oxidation state of group 1 metal is −1, i.e., alkalide. Reported as early as the 1970s, the alkalides appear in every modern inorganic chemistry textbook as an iconic chemical curiosity, yet their reactivity remains unexplored. This is due to their synthetic hurdles. In this work, we report the first facile synthesis of the archetypical alkalide complex, [Na⁺(2,2,2-cryptand)Na^–], which allows us to unveil a versatile reactivity profile of this once exotic species.

Group 1 metal anions, i.e., alkalides, have been textbook iconic chemical curiosities since their landmark, yet technically demanding, synthesis reported first in the 1970s. Despite being known for decades, the reactivity of alkalides has been barely studied due to their poor accessibility. Herein, we report the first facile synthesis of the archetypical alkalide, a sodium sodide [Na⁺(2,2,2-cryptand)Na⁻] (1), enabled by mechanochemical ball milling. Studies of the reactivity of 1 unveil a versatile profile, including one-electron and two-electron reductions.