SiGe 2 and Ge 3 : Cyclic Digermenes that Undergo Unexpected Ring‐Expansion Reactions

The heavy cyclopropene analogues 1 H ‐siladigermirene R 4 SiGe 2 ( 1 a ) and 1 H ‐trigermirene R 4 Ge 3 ( 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 GeGe bond (bending angle 51.0(2)°). The interaction of 1 a and 1 b with CH 2 Cl 2 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=SiMe t Bu 2 ).