[(Me3Si)Si]3EtGe9Pd(PPh3), a Pentafunctionalized Deltahedral Zintl Cluster: Synthesis,Structure, and Solution Dynamics

The title compound, which has a ten‐atom deltahedral cluster core of Ge₉Pd, was synthesized through insertion of Pd(PPh₃) into the tetrasubstituted nona‐germanium cluster [(Me₃Si)Si]₃EtGe₉ through a reaction of the latter with Pd(PPh₃)₄. This first reaction of neutral tetrasubstituted nine‐atom clusters shows that they retain reactivity despite their neutral charge. The Ge₉Pd core is the first that incorporates a 5‐connected transition metal other than from Group VI, a noble metal in this case. Single‐crystal X‐ray diffraction shows that the ten‐atom core is a closo‐cluster with the expected shape of a bicapped square antiprism. ¹H and ¹³C NMR spectroscopy show that, in contrast to the parent tetra‐substituted [(Me₃Si)Si]₃EtGe₉, the new compound does not exhibit dynamics. Relativistic DFT calculations are used to explain the differences.     

Elusive Zintl Ions [μ‐HSi4]3− and [Si5]2− in Liquid Ammonia: Protonation States,Sites, and Bonding Situation Evaluated by NMR and Theory

The existence of [μ‐HSi₄]^3? in liquid ammonia solutions is confirmed by ¹H and ²⁹Si NMR experiments. Both NMR and quantum chemical calculations reveal that the H atom bridges two Si atoms of the [Si₄]^4? cluster, contrary to the expectation that it is located at one vertex Si of the tetrahedron. The calculations also indicate that in the formation of [μ‐HSi₄]^3?, protonation is driven by a high charge density and an increase of electron delocalization compared to [Si₄]^4?. Additionally, [Si₅]^2? was detected for the first time and characterized by NMR. Calculations show that it is resistant to protonation, owing to a strong charge delocalization, which is significantly reduced upon protonation. Thus, our methods reveal three silicides in liquid ammonia: unprotonated [Si₅]^2?, terminally protonated [HSi₉]^3?, and bridge‐protonated [μ‐HSi₄]^3?. The protonation trend can be roughly predicted by the difference in charge delocalization between the parent compound and the product, which can be finely tuned by the presence of counter ions in solution.