Digermanates

Figures Raman spectra of crystalline and glassy potassium digermanate showing comparison between crystal spectra and glass spectra.

It may ignite in air [1], particularly if air is admitted suddenly into the gas at reduced pressure [2], Although digermane and its homologues do not usually ignite on exposure to air, their autoignition temperatures appear to be about 50°C and combustion is rapid or explosive [3],... 

Table 15 lists bond parameters for the simple digermanes, distannanes, diplumbanes and mixed dinuclear species. Some disilanes and the gas-phase value for Ge2Hg are included for comparison. The set of Si—Ge examples has increased since Sheldrick s review, and all the other E—E combinations are now represented. 

PhCl2Ge)2 241.3 325 Ge-Ge in Ph3Ge2Cl3 is most readily cleaved of all mixed Cl/Ph digermanes... 

Bulky substituents confer stability on organogermanium compounds. Scheme 1 shows possible derivatization reactions for some substitued germanes and digermanes. Compounds d and e are obtained from reactions a and b3 as mixtures of diasteroisomers, however, reactions a3, b4 and b3 are more stereospecific. Compounds b-i in the scheme were characterized by H NMR spectra118. 

SCHEME 1. Derivatization reactions for germanes and digermanes stabilized by bulky substituent... 

Apart from the classic preparation of simple germanes Ge H2n+2 (where n = 2-5) from the hydrolysis of Mg2Ge201, the following solvent-free reaction202 gives satisfactory yields of digermanes ... 

After partial deary lation of the product obtained, using HBr, stereogenic germanium atoms are generated giving the d, l and meso forms of 1,2-diphenyl-1,2-dibromo-digermane, 102. 

Digermane hydrides are obtained by the following methods215. Reaction of R2GeH2 (where R = Ph or mesityl), with Me3CLi, produces R2GeHLi with 80 to 95% yields ... 

The latter, diarylhydrogermyllithium 103, reacts with PhGeClH2, and 1,1-diary 1-2-phenyl-digermane 104 is produced ... 

The unstable di- or triiodogermane can be converted into the bromide or chloride after reaction with the corresponding silver halides273. Silver halides can also be used for the preparation of digermane monohalides275 ... 

Reaction of GeBr4 with f-butyllithium gave a mixture of dibromo-di-t-butyl germane and l,l,2,2-tetrabromo-l,2-di-f-butyl-digermane, 114. 

The photochemistry of benzyl-substituted digermanes is thus basically the same as that observed for vinyl- and styryl-substituted digermanes reported in Section in. In comparison, the equivalent disilane compounds exhibit only Si—Si bond homolysis, with no Si—C cleavage or silylene formation39. 

TABLE 3. The product distribution obtained following photolysis of some digermanes in the presence of various trapping agents... 

Digermane Trapping agent Main products (yield %)... 

The photolysis of phenyl-substituted trigermanes yields both the digermanes and germylenes, as determined by trapping, matrix isolation and flash photolysis experiments74. The data presented indicate two independent photochemical processes as outlined in... 

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