Some asymmetric organogermanium compounds.

The published information on the resolution of organosilicon, -germanium and -tin compounds is given together with a brief comparison of the bonding characteristics of these elements and a short review on organogermanium compounds. Several unsuccessful attempts were made to repeat the one reported resolution of an organogermanium compound, [viz., ethylisopropylphenylbromogermane by silver (+)-bromocamphor-sulphonate]. This reaction is discussed and the reasons for its failure are suggested. At least a partial resolution of p-ethylisopropylphenyl-germylbenzoic acid was obtained by recrystallisation of its salt with (-)-quinine from ethanol at 0°. The less-soluble material, on acid hydrolysis, gave a sample of solid germylbenzoic acid with a specific rotation of +0.38°. The acid obtained, similarly, from the mother-liquor had a small rotation of opposite sign (-0.14°). Samples of ethyl-1-naphthylphenylgermane with specific rotations of -8.75° and -9.53° respectively, were obtained by the lithium aluminium hydride reduction of the less-soluble (in pentane at low temperatures) diastereoisomers of ethyl-1-naphthylphenylgermanium (-)-menthoxide and ethyl-l-naphthyl-phenylgermanium (-)-phenylethoxide. These alkoxides had been prepared by reacting the sodium alcoholates with ethyl-1-naphthylphenylbromogermane. Reaction of these optically-active ethyl-l-naphthyl-phenylgermanes with chlorine (in carbon tetrachloride) gave the chlorogermanes [Et-l-NaphPhGeC1] with reversed sign of rotation viz., -1.52° and +1.75°. The sign of rotation was not changed when these chlorogermanes were reconverted into the germanes by lithium aluminium hydride reduction. However, considerable optical-activity was lost in these interconversions. These resolutions and interconversions are compared with those of similar organosilicon compounds. These resolutions gave the first reported optically-active organogermanium compounds free of resolving agent.