SiGe2 and Ge3: Cyclic Digermenes that Undergo Unexpected Ring‐Expansion Reactions

The heavy cyclopropene analogues 1H-siladigermirene R4SiGe2 (1 a) and 1H-trigermirene R4Ge3 (1 b) have been obtained, and the X-ray crystal structure of 1 a shows that it forms an isosceles triangle with a highly trans-bent endocyclic GeGe bond (bending angle 51.0(2)°). The interaction of 1 a and 1 b with CH2Cl2 unexpectedly affords the unusual four-membered-ring compounds 2 a and 2 b as a result of ring expansion (see scheme: E=Si, Ge; R=SiMetBu2).