Compounds of low-valent main group elements can have interesting reactivities and properties. Heavier analogues of vinylidenes (C=CH₂), for example, are interesting research targets. Digermenylidenes (R₂Ge=Ge:) are examples of this type of compound.

Thomas Müller, Carl von Ossietzky University of Oldenburg, Germany, and colleagues tried to synthesize heavy vinylidene analogues via a reaction of potassium salts of silole dianions with N-heterocyclic carbene (NHC)-stabilized germanium dichlorides. However, the desired products of the type R₂Si=Ge(NHC) were only observed as intermediates. The unexpected main products were siladigermiranes, which can be considered digermylenes that are part of a three-membered ring (pictured, R = Me/Et).

The products were obtained as deep green crystals after recrystallization, in yields of 23 % for the methyl-substituted compound and 64 % for the ethyl-substituted compound, respectively. X-ray diffraction (XRD) analysis showed that the compounds have long Ge–Ge bonds, which reduces ring strain and improves the stability of the compounds.

• Three-membered cyclic digermylenes stabilised by an N-heterocyclic carbene,
  Zhaowen Dong, Jan Mathis Winkler, Marc Schmidtmann, Thomas Müller,
  Chem. Sci. 2021.
  https://doi.org/10.1039/d1sc00956g