Facile access to molecular Zintl phases with tetra-anionic group 14 elements

The group 14 tetrel elements C, Si, Ge, Sn and Pb need to accommodate four additional electrons to reach a full valence shell. However, despite fulfillment of the octet rule, tetra-anionic tetrels are highly reactive anions. The considerable 4- charge on single atoms dictates their chemistry, making such anions strongly reducing, Brønsted basic or nucleophilic. Magnesium salts of the tetra-anionic tetrels are generally known as Zintl phases which, under forced conditions, are only accessible for the heavier tetrels (Mg2E, E = Si-Pb). Here we report facile full reduction of Si, Ge, Sn or Pb precursors to tetra-anions using a molecular Mg0 complex at room temperature. The solubilized nature of the reducing agent allows for formation of hydrocarbon-soluble Zintl phases under mild conditions. Encapsulation of the tetrel tetra-anions in a metalla crown, a ring of metal cations, significantly contributes to their stabilization.