Neutral and Cationic NHC-Coordinated Heavier Cyclopropylidenes

Cyclopropylidene as the smallest cyclic carbene with saturated backbone is a transient intermediate of the allene-propyne-cyclopropene isomerization. The incorporation of heavier Group 14 elements into the cyclopropylidene scaffold has so far been restricted to the replacement of the carbenic carbon atom by a intramolecularly base-coordinated silicon(II) center. Here 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 cyclic scaffold is exclusively formed of 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.