Racemization germanium compounds

Already partially resolved methyl-1-naphthylphenylgermanium hydride ([otp°° + 10) could also be separated on column A into two fractions characterized by [a] g5 = + 80 and —42 respectively. Partial resolution could even be obtained for the configuration-ally less stable methyl-1 -naphthylphenylgermanium chloride if the elution was carried out with diethyl ether 53), which is much less nucleophilic towards germanium than methanol, which causes the racemization of this compound. 

Other transition metal anions fail in giving the expected compounds . Germanium halides react more easily but are useless for the preparation of optically active compounds. Indeed, optically active bromo-germanes are not known, and chlorogermanes rapidly racemize in ether or tetrahydrofuran. ... 

Consequently, the ionization process is a specific phenomenon caused by the lability of the Si-Br or Si-I bonds and the affinity of silicon for oxygen not all racemization processes involve ionic 1 1 adducts. Moreover, the case of the tin compounds shows that the ability to undergo racemization is connected with the ability to increase coordination number. Thus, since silicon, germanium, and tin compounds show similar conductimetric and kinetic behavior, we may conclude that racemization and nucleophilic substitution are both activated by nucleophiles and involve a coordination extension process as shown in Scheme 67. However, existence of the siliconium ion 209 cannot be excluded in the case of bromosilanes. 

Various germatranes have been prepared. Substituted benzyloxymethyl-germanes rearrange thermally to the Ge-O compound more slowly than Si, and racemic organo-germanium and -tin compounds have been resolved by inclusion chromatography on microcrystalline cellulose triacetate. ... 

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