Digermenes reactions

Digermenes undergo [2 + 2] cycloaddition with phenylacetylene, as shown in reaction 20125,126. 

Compound A was obtained from a reaction of tetrakis(2,6-diethylphenyl)digermene with an excess of DMSO in toluene. The molecular structures of both A and B were determined by single-crystal X-ray analyses (Figure 27). 

Reaction of the digermene 57 with diazomethane or trimethylsilyldiazomethane yields the azadigermiranes 58 via a [2+l]-cycloaddition (Equation (119)).158 Coupling of a cyclic carbene and a cyclic germylene furnishes the zwitter-ionic species 59 (Equation (120)).159... 

Transient digermene 86 was postulated as possible intermediate in the reaction of 1,2-dichlorodigermacyclobutane 87 with Mg/MgBr2 in the presence of an alkene, leading to the bicyclic compound 8878 [Eq. (17)]. However, an electron transfer reaction with the intermediate formation of a germyl radical is also a possibility.78 Similarly, transient 1,2-digermacyclobu-... 

Compounds with a Si=Si or Ge=Ge bond (i.e., disilenes and digermenes) can be isolated when the double bond contains bulky substituents. Only a few cycloaddition reactions with diazo compounds are known, and two reaction modes have been observed. One of the paths leads to the formation of disiliranes 184 (242) and digermiranes 185 (243) (Scheme 8.42), probably by ring contraction of an initially formed [3 + 2] cycloaddition product. The other path involves a 1,1-cycloaddition of the diazoalkane to give disilaaziridine 186 (244) and digermaazir-idine 187 (245). This nitrene-like reactivity is rather uncommon although some intramolecular examples are known (see Section 8.6.1). 

The reaction between a disilene (cis- and fra s-MePhSi=SiPhMe) and a silole (1,1-dimethyl-2,5-diphenylsilole) is a stereospecific Diels-Alder addition, as in the case of an ethylenic dienophile128. A digermene reacts in a similar way129. 

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