THE GE-H BOND-DISSOCIATION ENERGIES OF ORGANOGERMANES - A LASER-INDUCED PHOTOACOUSTIC STUDY

The Ge-H bond dissociation energies (BDE's) of several alkyl- and aryl-substituted germanium hydrides have been measured in hydrocarbon solution at room temperature by a photoacoustic technique. The BDE's of these hydrides are unaffected by alkyl substitution when compared to those for GeH4 and are in the range of 81.6-82.6 kcal/mol. Aryl substitution leads to a slightly weakened Ge-H bond (79.2-80.2 kcal/mol) in the cases of phenyl-, diphenyl-, and triphenylgermane. In an effort to further characterize the formation, spectral and decay properties of the germyl radicals some laser flash photolysis studies were carried out. The rate constants for hydrogen abstraction by tert-butoxy radicals were determined by nanosecond laser flash photolysis and fell in the range (0.7-4.4) X 10(8) M-1 s-1. The aryl-substituted germyl radicals add to the aromatic rings of the germane precursor. Diphenylgermyl radical adds to diphenylgermane with a rate constant of 2.9 X 10(5) M-1 s-1, while phenylgermyl radical adds to phenylgermane with a rate constant of 1.2 X 10(6) M-1 s-1.