The versatile reactivity of disilenides, heavier analogues of vinyl anions, opened the door to novel heavier group 14 structure motifs with residual functionalities in the periphery around the SiSi moiety. The corresponding germanium analogue, digermenide Tip 2 GeGe(Tip)Li•dme 2 (Tip = 2,4,6-triisopropylphenyl, dme = 1,2-dimethoxyethane), has now been obtained from the reduction of Tip 2 GeCl 2 with 3.3 equiv of Li powder and a catalytic amount of naphthalene in dme at −70 °C. The lithium digermenide was characterized by NMR spectroscopy, UV/vis spectroscopy, X-ray diffraction, and DFT calculations. As proof of principle for its suitability for the nucleophilic transfer of the GeGe motif, the reaction with chlorosilanes leads to the unsymmetrically substituted digermenes Tip 2 GeGe(Tip)SiR 3 .

Tetrasiladigermatricyclohexanes in two isomeric forms (chair and doubly-bridged tetrahedron) are obtained by the reaction of MeLi with an α-chlorosilyl functionalized NHC-stabilized silagermenylidene. (29)Si NMR at low temperature proves the initial formation of a monomeric NHC-adduct of a disilenyl germylene followed by cyclisation to the isomeric heavy cyclopropene. Addition of an excess of NHC stabilizes the both intermediates and demonstrates the reversibility of rate-determining initial equilibria involving NHC dissociation. Finally, a mixture of two isomeric tricyclic Si4Ge2 species is obtained: at elevated temperature the chair isomer converts to the doubly edge-bridged tetrahedron.

An isolable NHC-coordinated disilenyl germylene RSi═SiR-GePh·NHC (5b: R = 2,4,6-triisopropylphenyl, NHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) is obtained from the reaction of the α-chloro silyl functionalized heavier vinylidene analogue R(Cl)Si-RSi═Ge·NHC with phenyllithium. The disilenyl germylene 5b isomerizes at 40 °C to the NHC-adduct of the corresponding heavier cyclopropylidene analogue 6b. Both 5b and 6b display near perfect regiodiscrimination in their reactions with phenylacetylene and xylyl isocyanide, affording in the case of each reagent two different regioisomers of NHC-coordinated cyclic germylenes. DFT calculations reveal that the Si═Si bond accounts for the high reactivity of 5b even at low temperature while in the case of cyclic 6b the low-valent germanium center requires a considerable thermal activation.

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