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.