Substituent Effects in Digermanes: Electrochemical, Theoretical, and Structural Investigations

The
digermanes R3GeGePh3 (R3 = Bui3, Hexn3, (C18H37)3, or ButMe2) were synthesized using the
hydrogermolysis reaction, and the X-ray crystal structures of Bui3GeGePh3 and ButMe2GeGePh3 were determined.
The isobutyl-substituted digermane contains two independent molecules
in the unit cell with Ge–Ge bond distances of 2.4410(5) and
2.4409(5) Å, and ButMe2GeGePh3 has a Ge–Ge bond distance of 2.4255(3)
Å. These four digermanes and the four additional digermanes R3GeGePh3 (R3 = Me3, Bun3, Bus3, or PhMe2) were characterized by cyclic voltammetry,
differential pulse voltammetry, and linear sweep voltammetry in order
to determine the effects of varying substituent patterns on the oxidation
potential of these systems. Digermanes having more inductively donating
substituents exhibit more negative oxidation potentials than those
having less inductively donating substituents. Density functional
theory calculations were also performed on these eight systems, and
the energies of their frontier orbitals were determined. The energy
of the HOMO and LUMO in these systems was shown to depend on the electron-donating
ability of the organic substituents.