A Spatially Separated Germylene-Carbene Compound for Site-Selective Small-Molecule Activation

We report the synthesis and characterization of a spatially separated germylene-carbene compound (1) via a salt elimination strategy between an (amidinato)chlorogermylene and a deprotonated N-heterocyclic carbene. Compound 1 exhibits excellent site-selective reactivity, engaging in small-molecule activation at either germylene or the carbene center, depending on the nature of the reactant. Isocyanates, isothiocyanates, BH₃·SMe₂, and GeCl₂·dioxane undergo preferential activation at the carbene site, yielding novel addition and coordination products. Reactions with two equiv of S₈ and BH₃·SMe₂ also led to 2-fold addition products, both on germylene and on the carbene center. However, the reaction with one equivalent of mesitylazide selectively occurs on germylene instead of carbene, forming an imidogermane compound. Addition of the second equivalent of mesitylazide resulted in formation of an imidogermane-triazene compound via azide addition to carbene without N₂ loss. DFT calculations reveal that HOMO and HOMO-2 are primarily associated with carbene carbon and the σ-type lone pairs on the Ge atom, respectively, separated by a small energy gap. Natural population analysis indicates a more negative charge on the carbene carbon, consistent with its higher nucleophilicity toward electrophiles. The LUMO, localized on the Ge 4p orbital, supports the observed germylene reactivity with azides through nucleophilic addition pathways.