Germyl Mesolytic Dissociations in the Allylgermane and Penta-2,4-dienylgermane Radical Anions. A Theoretical Study

In CH2CHCH2 GeH3.- two stable structures have a trigonal bipyramidal arrange-ment around Ge, with the extra electron in equatorial (tbp eq) or axial (tbp ax) position. In CH2(CH)3CH2 GeH3.- only tbp ax is found, while a second structure with a tetrahedral germyl group has the extra electron on the conjugated ? system. C Ge bond cleavage yields allyl/ pentadienyl radicals plus germide. Both dissociation reactions require 4-6 kcal mol-1, less than the analogous C and Si systems (ca. 30 and 14 kcal mol-1, respectively). Fragmentation is dramatically activated with respect to homolysis in the corresponding neutrals. The wavefunction is dominated by one single configuration at all distances, in contrast with homolytic cleavage, in which two configurations are important. C Ge bond dissociation is at variance also with heterolysis, due to spin recoupling of one of the C Ge bond electrons with the originally unpaired electron.