Synthesis, Structures, and Solution Dynamics of Tetrasubstituted Nine-Atom Germanium Deltahedral Clusters

Reported are the rational synthesis, structures, and solution dynamics of three tetrasubstituted and neutral Ge₉-based deltahedral clusters [Ge₉R₃R′]⁰, where R = Si­(SiMe₃)₃ and R′ = Et (<b>1</b>), Sn^<i>n</i>Bu₃ (<b>2</b>), or Tl (<b>3</b>). The first step of the synthesis is a reaction of an acetonitrile suspension of the intermetallic precursor compound K₄Ge₉ with {Si­(SiMe₃)₃}Cl which produces the trisubstituted monoanions [Ge₉{Si­(SiMe₃)₃}]⁻. A benzene suspension of the latter is then reacted with Sn^<i>n</i>Bu₃Cl or TlCp to produce <b>2</b> and <b>3</b>, respectively, while the same acetonitrile solution is reacted with EtBr in order to produce <b>1</b>. All three structures can be viewed as tricapped trigonal prisms of Ge₉ with the three “hypersilyl” substituents, Si­(SiMe₃)₃, <i>exo</i>-bonded to the capping atoms. The fourth substituent in <b>1</b>, the ethyl group, is <i>exo</i>-bonded to one of the six available Ge atoms with the Ge–C bond positioned radially to the Ge₉ core. In the case of <b>2</b>, on the other hand, the tin fragment is found above one of the triangular bases of the prism interacting with one or more Ge atoms in three crystallographically different molecules in the structure. Lastly, the Tl atom in the structure of <b>3</b> is found capping a pseudosquare face between two hypersilyl substituents. NMR spectroscopy indicates that all three compounds are dynamic at room temperature. Variable-temperature studies suggest that the process in <b>1</b> and <b>2</b> is intramolecular while the process in <b>3</b> involves dissociation of the Tl⁺ ion from the molecule followed by association at the same or another equivalent pseudosquare face of the molecule. Thus, the latter compound may be considered to a large extent to be ionic as it is made of a thallium cation and a trisubstituted cluster anion