Bicyclo[1.1.0]tetragermane-2,4-diide Diradicaloid

The synthesis, structure, and reactivity of the bicyclo[1.1.0]tetragermane-2,4-diide compound [(ADC)Ge₂]₂ (3), which features a Ge₄ core bridged by two anionic dicarbene frameworks (ADC = PhC{N(Dipp)C}₂; Dipp = 2,6-iPr₂C₆H₃), are reported. Treatment of an alkyne-functionalized amidine Me₃SiC≡CN(Dipp)C(Ph)═N(Dipp) (1) with GeCl₄ affords [(ADC)GeCl₃(GeCl₄)] (2). KC₈ reduction of 2 yields 3 as a Venetian red crystalline solid. DFT calculations reveal a singlet ground state for 3 with the singlet-triplet energy gap of 14 kcal mol^-1. CASSCF (complete active space self-consistent field) calculations suggest a modest diradical character (β = 9%) for 3. Compound 3 readily reacts with TEMPO (2,2,6,6-tetramethylpiperidinyloxyl) to yield the Ge─Ge bond-cleaved product, [(ADC)Ge(Ge-TEMPO)]₂ (4). Treatment of 3 with Fe₂(CO)₉ gives [(ADC)Ge(Ge{Fe(CO)₄})]₂ (5).