Preparation, structural characterization of 1,2-digermacyclobut-3-enes, and their palladium-catalyzed insertion of alkynes

1,2-Digermacyclobut-3-enes were prepared by the treatment of Z-α,β-bis(chlorodialkylgermyl)ethenes with Na metal in boiling toluene and their structures were fully established by spectroscopic methods coupled with X-ray crystallography. In the presence of an appropriate catalyst, 1,2-digermacyclobut-3-enes reacted smoothly with alkynes to give the corresponding insertion products, 1,4-digermacyclohexa-2,5-dienes in moderate to good yields. Conventional complexes, such as [Pd(PPh₃)₄] and [Pt(PPh₃)₄], serve as efficient catalysts. The mechanism of the insertion reaction of alkynes into the germanium-germanium bond of 1,2-digermacyclobut-3-enes is discussed in terms of a key intermediate, a 1,4-digerma-2-buten-1,4-diylpalladium.