Synthesis and Characterization of a Metalloid Ge₆ Cluster with Bulky Amide Ligands

This article details the synthesis and structural characterization of a new metalloid germanium cluster 3 with bulky amide ligands. The cluster features a Ge₆ core stabilized by four -N(Si^tBuMe₂)₂ ligands and was obtained via reduction of the amido trichlorogermane 2 using potassium chips in toluene. Single-crystal X-ray diffraction analysis revealed that the Ge₆ core adopts a butterfly-shaped geometry with a Ge-Ge dumbbell unit, which contains two unsubstituted germanium atoms exhibiting prominent lone-pair characteristics. The Ge₆ core can also be classified as a nido cluster, with a cluster-bonding-electron count of 16, perfectly satisfying the 2n + 4 electron-counting rule. Combining the structural features of this nido cluster with the bond length distribution in the folded four-membered ring suggests that the Ge4 ring features a certain degree of electron delocalization. Additionally, two bis(amido)-substituted germylenes (4 and 6) were isolated and structurally characterized. They exhibit analogous structural features, with each germanium center adopting a two-coordinate V-shaped configuration, the Ge-N bond lengths being very similar, and the nitrogen atoms adopting a planar triangular geometry. Notably, compound 6, bearing bulkier -N(SiⁱPr₃)₂ substituents, exhibits a significantly larger N-Ge-N bond angle (120.58°) compared to the corresponding value of 113.54° observed for compound 4 with -N(Si^tBuMe₂)₂ substituents. This clearly demonstrates that the steric bulk of the substituents exerts a remarkable influence on the molecular geometry and σ-donor ability of the lone pairs on germanium centers.