Hypervalency of Organogermanium Compounds-Scope and Limitation

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1 The structure of hypercoordinate organogermanium comounds in solid-ohase and in solution.The structure of 2-(2-t-butyl-5-oxo-1, 3, 2-oxathiagermolan-2-ylthio) acetic acid (1) and its phenyl derivative (2) and their pyridiumu salts (3) and (4) was investigated. In the solid phase, all compounds investigated were in trigonal bipyramidal structure.In solid-state, the two trigonal bipyramids are different while in solution these are equivalent in the NMR timescale. Thus, there is observed only one CH_2 proton and carbon signals, indicating a rapid exchange. Furthermore, the methylene peak split into two peaks, indicating a slow exchange. The barrier is ca 12 kcal mol^<-1>. We believe this exchange is Berry pseudorotation or turnstile rotation.2 Hypercoordinate structure of triarylgermanes.We prepared a variety of triarylgermanes with some ligands at ortho position such as chlorotris [2-(methoxymethyl) phenyl] germane and methyltris [2-(methoxymethyl)-phenyl] germane. Both compounds are pentavalent in a trigonal bipyramidal structure. The reason why such compounds did not show hexa or hepta coordination is not clear at all.3 Synthesis of novel hosts modified with germanium.We prepared a variety of novel organogermanium compounds as possible hosts for anions and neutral molecules. These include calixarenes with some side-chain containing germanium, azacrown with germanium-containing side-chain on nitrogen, and cyclophanes including germanium in the bridge.4 High-resolution solid-state ^<73>Ge NMR spectroscopy.We firstly observed germanium resonance of solid tetraphenylgermane in high-resolution condition. Ge-73 NMR may be a powerful tool for studying hyper valency of germanium.