Digermenes

A further interesting feature of the gallium phosphides and arsenides is that the former compounds are colorless whereas the latter range from yellow to orange. Color can arise from ir- ir transitions in main group compounds for example, in the disilylenes and digermenes R2E = ER2 (E = Si, Ge) in which the it- tt transitions occur at lower energy than... 

The photolysis of hexaarylcyclotrigermanes was used to synthesize the first stable digermenes. The photolyses are generally carried out at 254 nm in hydrocarbon solvents (e.g., cyclohexane or 3-methylpentane). Presumably, two equivalents of the cyclotrigermane form three equivalents of the digermene, the third equivalent being formed by dimerization of the diarylgermylene. 

Depending on the substituent, thermolysis of the three-membered ring may also yield the digermene, generally as an intermediate. Thermolysis of hexamesitylcyclotrigermane has been a particularly useful route to tetramesityldigermene.38... 

Attempts to form cyclotrigermanes (and, subsequently, digermenes see Section II.B.l) from the reductive cyclization of diaryldichlorogermanes and lithium naphthalenide (LiNp) with particularly bulky substituents on the aryl groups (i.e., isopropyl) led, instead, directly to the tetraaryldiger-menes by reductive coupling. 

Thia-, selena-, and telluradigermiranes have been synthesized by the addition of sulfur, selenium, or tellurium, respectively, to digermenes. 

It is interesting that the aryl groups in tetrakis(2,6-diethylphenyl)diger-mene do not shift under the same conditions or upon thermolysis, presumably because of steric hindrance. However, upon photolysis, tetrakis(2,6-diethylphenyl)digermene dissociates to the diarylgermylene.48... 

For the digermenes, Lappert later reported520 the full crystal structure of R2Ge=GeR2, R = Bsi and a refinement of the tin structure while Masamune has characterized the analog... 

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

Tetrakis(2,6-diethylphenyl)digermene 23 undergoes smooth cycloaddition with PhC CPh to yield a four-membered 1,2-digermacyclobutene ... 

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). 

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