Some reactions of organogermanium compounds.

A comparative survey of published work on the reactions of organic derivatives of the Group IVB elements has been made, and the function of these elements in such reactions is discussed. The influence of the trimethylsilyl- and trimethyl- -germyl- substituents on the strengths of some carboxylic acids indicates that the inductive electron-releasing effect is slightly greater, and steric effects consider- -ably less, in the latter group. The alkaline cleavage of numerous tetra-organo- -silanes, -germanes, and -stannanes has been examined. The absolute and relative rates vary widely with the constitution of the compounds, but the germanes are generally much less reactive than the silanes, which are rather less reactive than the stannanes. The tetraorgano-stannanes are often less reactive than might be anticipated. The results are interpreted in terms of decreasing availability of the vacant d-orbitals for transition- state stabilisation as we descend Group IVB. The trimethylaralkyl-germanes and -silanes, especially the latter, are much more reactive than are the triethyl- analogues in nucleophilic cleavage, and this is shown to be a steric effect. Nuclear substituents influence the rates of cleavage of the benzyltrimethylstannanes in fair agreement with the predictions of the Hammett ?-p relationship. The simplest cleavage mechanism consistent with the results is a synchronous bimolecular nucleophilic (quasi-SN2) displacement at the metallic atom, although a mechanism involving the initial formation of a quinque- covalent intermediate cannot be excluded. The displacement of the chlorine atom of chloromethyl-trimethylmetallic compounds by the iodide and ethoxide ions has been studied kinetically. The results are in accordance with the bimolecular bridging mechanism of Eaborn and Jeffrey, and it is suggested that steric hindrance is largely responsible for the fact that the germane is slightly more reactive than the silane, but much less reactive than the stannane. Twenty-six new organometallic compounds are described.