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

Abstract

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.

Donor-acceptor molecular oligogermanes: Novel properties and structural aspects

“…As it was stated earlier for linear Ge5Ph12, the Ge-Ge bond length in the centre of the molecule is slightly longer than at the ends due to steric reasons (2.4359(6) and 2.4397(6) for end and 2.4549(6) and 2.47001(6) for central) [25] , but in 4 this difference is almost negligeable. This could bebe explained by the presence of methyl groups instead of phenyl groups.…”

σ-Bond electron delocalization of branched oligogermanes and germanium containing oligosilanes

“…Although there are several reports concerned with UV–Vis absorption properties of oligogermanes [23–26,44–51] it is difficult to make comparisons. Many of the studied compounds contain aryl substituents which interact with the σ-conjugated system [26] .…”

“…However, the use of different substitution patterns and also different polymerization degrees complicates a reliable comparison. While recent progress in the synthesis of oligogermanes [18–24] has provided ready access to oligogermanes many of these contain chromophoric substituents [22–27] , complicating UV spectroscopic analysis. The use of isostructural oligomeric silanes, germanes, and germanium containing silanes should help to obtain a more accurate estimation of the influence of silicon and germanium on the nature of σ-bond electron delocalization.…”

A luminescent and dichroic hexagermane

“…5 and exhibits five resolved oxidation waves, all of which are irreversible. The first oxidation wave for 1 is at 1100 mV and is at a less positive potential than that found for the 20 suggesting that the s-based HOMO of 1, which is presumed to be the source of the electron lost during the oxidation event, is destabilized relative to that of Ge 5 Ph 12 . The first oxidation wave for 1 is at 1100 mV and is at a less positive potential than that found for the 20 suggesting that the s-based HOMO of 1, which is presumed to be the source of the electron lost during the oxidation event, is destabilized relative to that of Ge 5 Ph 12 .…”