Monosilane SiH₄ is an industrial gas used for the production of silicon semiconductors. In contrast to its carbon analogue methane, SiH₄ can expand its coordination sphere, forming, e.g., the hypervalent six-coordinate anion [SiH₆]^2–. However, the isolation of [SiH₆]^2– in the condensed phase is challenging.

Jun Okuda, RWTH Aachen University, Germany, and colleagues have used a cyclen-derived macrocycle that can stabilize reactive metal hydrides of electropositive metals to “trap” [SiH₆]^2– in a dinuclear strontium complex (pictured). The complex was prepared via a reaction of the cationic benzyl complex [(Me₄TACD)Sr(CH₂Ph)][B(C₆H₃-3,5-Me₂)₄] (Me₄TACD = 1,4,7,10-tetramethyltetraazacyclododecane) with phenylsilane in tetrahydrofuran (THF).

When the complex decomposes, it releases H₂ to give a strontium complex with a silanide unit (SiH₃^–). An improved understanding of the reductive elimination of H₂ from hydrogen-rich silicon compounds could be useful, e.g., in the context of H₂ uptake and release in the hydrogen storage material K₄Si₄/KSiH₃. In reactions of the complex with a weak Brønsted acid, CO₂, or cyclooctatetraene, SiH₄ was released. This suggests that the synthesized complex can be considered an adduct of monosilane with two strontium hydride cations.

• Formation and Reactivity of a Hexahydridosilicate [SiH₆]²⁻ Coordinated by a Macrocycle‐Supported Strontium Cation,
  Jun Okuda, Thomas Höllerhage, Priyabrata Ghana, Thomas P. Spaniol, Ambre Carpentier, Laurent Maron, Ulli Englert,
  Angew. Chem. Int. Ed. 2021.
  https://doi.org/10.1002/anie.202115379