Synthetic, Structural, and Physical Investigations of the Large Linear and Branched Oligogermanes Ph3GeGePh2GePh2GePh2H, Ge5Ph12, and (Ph3Ge)4Ge

The syntheses of two linear oligogermanes, Ph3GeGePh2GePh2GePh2H and Ge5Ph12, were achieved using a hydrogermolysis reaction starting with HPh2GeGePh2GePh2H. The preparation of the hydride-terminated tetragermane indicates that selectivity is possible using the hydrogermolysis reaction, which had not been observed previously. The structures of both of these compounds were determined, and they were also characterized by UV/visible spectroscopy and electrochemical methods (CV and DPV). The pentagermane Ge5Ph12 exhibits four irreversible oxidation waves in both its CV and DPV, as was observed for other aryl-substituted oligogermanes. The successful synthesis of the neopentane analogue (Ph3Ge)4Ge was also achieved by starting from GeH4 and Ph3GeCH2CN. This material was structurally characterized; the structure of (Ph3Ge)4Ge is highly sterically congested and contains long Ge–Ge single-bond distances that average 2.497(6) Å and exhibits an nearly idealized tetrahedral geometry at the central germanium atom with an average Ge–Ge–Ge bond angle of 109.49(2)°. The UV/visible spectrum of (Ph3Ge)4Ge exhibits a broad absorbance maximum centered at 250 nm, and DFT calculations indicate that this compound has a stabilized HOMO at −6.223 eV and a large HOMO–LUMO gap relative to those in other branched oligogermanes.