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

The digermanes R3GeGePh3 (R-3 = Bu-3(i), Hex(3)(n), (C18H37)(3), or (BuMe2)-Me-t) were synthesized using the hydrogermolysis reaction, and the X-ray crystal structures of (Bu3GeGePh3)-Ge-i and (BuMe2GeGePh3)-Me-t 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) degrees, and (BuMe2GeGePh3)-Me-t has a Ge-Ge bond distance of 2.4255(3) degrees. These four digennanes and the four additional digerrnanes R3GeGePh3 (R-3 = Me-3, Bu-3(n), Bu-3(s), 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 substitu,ents.