Digermenes preparation

Digermanes, unsymmetrically substituted, 3, 787 Digermenes, preparation, 3, 796 Digestion studies, stability, 12, 612-613 DIGISIM, in cyclic voltammetry, 1, 282-283 Digital simulations, in cyclic voltammetry, 1, 282 Dihalides, in chromium mononitrosyl complexes, 5, 302 Dihaloarenes, cross-coupling polymerization, 11, 659... 

The digermenes were the first stable doubly bonded germanium species to be prepared,3 5a 7,8 mainly by the routes displayed in Scheme 9. These routes have still been used during the past 4 years, but new ones have also been discovered. Depending on the method used and on the substituents on germanium, stable or transient digermenes have been obtained. 

When the earlier edition of this book was in preparation, no cyclic digermene or distannene was known. Meanwhile, several cyclotrigermenes and mixed Si/Ge heterocycles with Si=Si or Si=Ge bond have been synthesized by Sekiguchi s group. The... 

Weidenbruch and coworkers have recently succeeded in extending their chemistry of tetrasilabutadiene (vide supra) to its heavier congener, i.e. hexaaryltetragermabuta-1,3-diene 1008°. In this case, tetragermabutadiene 100 was prepared from digermene 4 via 99 by the synthetic method similar to that of its silicon analogue (Scheme 37)79. 

The lower heats of formation of silylenes compared with carbenes translate into somewhat lower, albeit similar, reactivity. There is a general lesson here that slowing down the reactions of carbene-like species makes possible processes like dimerization that are more or less impossible for carbenes. We have already seen that slowing down their rearrangements allows the observation of intermolecular reactions of alkylsilylenes not observed for alkylcarbenes. The dimerization of silylenes to disilenes, discovered in the gas phase [36], was employed to brilliant effect by West and coworkers in the condensed phase synthesis of isolable disilenes [37]. While these were not the first disilenes, silylene dimerization opened the way for the preparation of many new molecules, including digermenes from the dimerization of germylenes [38]. 

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