Kinetic and labeling studies of the formation and trapping reactions of dimethylgermylene

Article abstract of DOI:10.1021/om00110a004

The kinetics of the thermal decomposition of 7,7-dimethyl-1,4,5,6-tetraphenyl-7-germabenzonorbornadiene (1) have been studied in the presence of excess styrene, 2,3-dimethylbutadiene, and CCl₄. At 78.3°C the observed rate constant is 1.1 × 10^-3 s^-1 and is independent of the initial concentrations of 1 and the other reagents indicating a first-order, unimolecular decomposition. The same rate constant is also obtained without any added reagents. Activation parameters for the decomposition are ΔH^? = 27.8 ± 0.6 kcal/mol and ΔS? = 6.8 ± 1.6 eu. The parameters are consistent with rate-determining cleavage of a single bridgehead germanium-carbon bond to give a diradical intermediate. Generation of dimethylgermylene from 1 in the presence of excess (E)-2-deuteriostyrene yields cis and trans isomers of 2,5-dideuterio-11-dimethyl-3,4-diphenylgermacyclopentane. The site of the deuterium label is partially scrambled and can be rationalized by postulating acyclic diradical intermediates for the cycloaddition process.