Digermenes stable

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. 

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. 

Four new stable digermenes 66-69 were synthesized from dichlorogermanes and sodium in toluene or lithium naphthalenide (Scheme 10). 66 and 68 have been characterized by X-ray61 (see Section III,B,1). 66-6851 keep their digermene structure in solution, in contrast to 6960 (probably the E isomer due to the steric hindrance in the Z isomer), for which an interconversion with the corresponding germylene was observed. 

On the other hand, (2-f-Bu-4,5,6-Me3C6H)2Ge=Ge(2-f-Bu-4,5,6-Me3CgH)2 41 was also synthesized as a stable digermene and was characterized by X-ray crystallography20. In solution digermene 41 reacted with benzil to afford 42, which is a [4 + l]cycloadduct... 

We want to use this knowledge to tell us something about R2M=MR2 and RM=MR, about which we know considerably less. Maybe this information will help chemists make digermenes and distan-nenes that will retain their structures in solution or the gas phase. Maybe it will aid in the synthesis of stable triply bonded compounds of silicon and germanium, or hexasilabenzene ... 

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