Absolute rate constants for the reactions of germylene and dimethylgermylene with dimethylgermane: the deactivating effect of methyl groups in heavy carbenes

Gas-phase rate constants for the title reactions have been obtained by laser flash photolysis at 297 K, by use of photoprecursors, 3,4-dimethyl-1-germacyclopent-3-ene for GeH2 and pentamethyldigermane for GeMe2. The values obtained were (k (cm3 molecule−1 s−1)): (2.38±0.11)×10−10 for GeH2, (2.26±0.10)×10−13 for GeMe2. These results show that the insertion reaction of GeMe2 is 1050 times slower than that of GeH2 into the GeH bonds of Me2GeH2. This is explained in terms of a general mechanism involving an intermediate H-bridged complex, applicable to both silylene and germylene insertions. For the GeMe2 insertion, reactants are in equilibrium with the complex, which rearranges to the product in the rate controlling step.