N-Heterocyclic Carbene Coordinated Neutral and Cationic Heavier Cyclopropylidenes

Cyclopropylidene is a transient intermediate of the allene–propyne–cyclopropene isomerization. The incorporation of heavier Group 14 elements into the cyclopropylidene scaffold has to date been restricted to the formal replacement of the carbenic carbon atom by a base‐coordinated silicon(II) center. Herein we report the synthesis and characterization of NHC‐coordinated heavier cyclopropylidenes (Si2GeR3X, and Si3R3Br; X=Cl, Mes; R=Tip=2,4,6‐iPr3C6H2) in which the three‐membered ring is exclusively formed by silicon and germanium. In case of the chloro‐substituted Si2Ge‐cyclopropylidene, a stable heavier cycloprop‐1‐yl‐2‐ylidene cation is obtained by NHC‐induced chloride dissociation. He is heavy and he′s my brother: NHC‐coordinated cyclopropenylidene analogues with molecular scaffolds exclusively formed by heavier Group 14 elements are accessible from the corresponding vinylidene isomers by exchange of the NHC ligand for a smaller NHC. The residual chloride in one of these heavier cyclic carbenes can be expelled by a second equivalent of NHC to generate cationic derivatives of the imidazolium type.