Cyclotrigermenes

Cyclotrigermenes 7564 and 7664 also have a short intracyclic Ge = Ge double bond with a completely trigonal planar geometry. 

The absorption in the electronic spectrum lies in the normal range (Amax between 413 and 475 nm) (see Table I) for acyclic digermencs.60 63 75 A hypsochromic shift was observed for cyclotrigermene 75 (326 nm64). 

The first landmark was the successful synthesis and structural characterization of the cyclotrigermylium cations 2 and 19 by Sekiguchi and co-workers. This was achieved by reaction of trityl cation with the cyclotrigermenes 20 in the presence of weakly coordinating borate anions (Scheme 8). The trityl cation acts here as a one-electron oxidizing reagent and the resulting radical cation of 20 decomposes to the... 

Historically, the first solid state structure of a truly tricoordinated cation of the heavier group 14 elements (Si-Pb) was that of the cyclotrigermenium cation [((t-Bu3Si)Ge)3], 2 published in 1997. Cation 2 was prepared by one-electron oxidation of the cyclotrigermene 20 (E = Si) with trityl cation (see Scheme 8). " ... 

As illustrated in Scheme 10.6a, cyclometallenes react readily with chloro-carbons, e.g. CCI4, to give /ra i-l,2-dichloro derivatives. In an interesting extension of this type of reactivity, the treatment of a cyclotrigermene or... 

It should also be noted here that recent work in Japan has shown that a free germanium cation can be prepared and structurally characterized. Thus, the reaction of tetrakis (tri-z-butylsilyl)cyclotrigermene with trityl tetraphenylborate affords (t-Bu3SiGe)3+ BPI14 as a yellow crystalline solid. X-ray crystallography shows that there is no close interaction between the anion and the cation. The stability of the compound is presumably due not only to the steric protection afforded by the bulky t-BtcSi substituents, but also to the fact that it contains a 2jr-electron aromatic ring.198... 

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... 

TABLE 14. Parameters (bond length in pm, angle in deg) of cyclotrigermenes, cyclotristannenes and cyclotrigermenium cations ... 

Cyclotrigermenes were obtained from the reaction of metal-14 anions with tris(tri-r-butylsilyl)cyclotrigermenium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, the TFPB behaving as the leaving group (equation 156)168. The cyclotrigermene structure was established by X-ray determination. 

The synthesis of the first cyclotrisilenes has required a longer time than for the cyclotrigermenes due to the lack of suitable stable silylenes, in contrast, for example, to the well-known dichlorogermylene-dioxane complex25. Therefore, the preliminary preparation of the silylene precursors, which can generate silylenes in situ, was necessary for the successful synthesis of cyclotrisilenes. Until now, only two examples of cyclotrisilenes have been reported in the literature, of which only one was structurally characterized. 

FIGURE 2. ORTEP drawing of cyclotrigermene 5. Reprinted with permission from Reference 13. Copyright 1995 American Chemical Society... 

FIGURE 4. Reaction intermediate in the reaction of GeCbdioxane with /-HujSiNa in THF-t/g monitored by 29Si NMR spectroscopy formation of digermenoid 8 and its thermal transformation to a cyclotrigermene 7. Reprinted with permission from Reference 18. Copyright 2000 American Chemical Society... 

Oxidation of cyclotrigermenes — formation of the free germyl cation... 

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