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. 2025 Sep 15;64(38):e202513772.
doi: 10.1002/anie.202513772. Epub 2025 Aug 7.

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

Affiliations

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

Falk Ebeler et al. Angew Chem Int Ed Engl. .

Abstract

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).

Keywords: Carbene; Cluster; Diradicaloid; Germanium; Main group; Stretched bond.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic illustration of cyclobutanediyls I‐C, bicyclo[1.1.0]butanes II‐C, and their heavier Group 14 congeners II‐ESB and II‐ELB, featuring a bridgehead short‐bond (SB) and long‐bond (LB), respectively (substituents omitted except R for II‐E). Niecke's diradicaloid III and selected germanium diradicaloids IVVII. Representative examples of germanium diradicaloid (propellane‐type) cluster compounds IXXIII.
Figure 2
Figure 2
a) Synthesis of compound 2. b) Donor–acceptor perspective for 2. c) Solid‐state molecular structure of 2. Aryl groups are shown as wireframes and H atoms are omitted for clarity. Thermal ellipsoids are shown at 50%. Selected bond lengths (Å) and angles (°): C2─C3 1.373(4), Ge1─C2 1.944(3), Ge2─C3 1.995(3), Ge1─Cl1 2.112(1), Ge1─Cl3 2.117(1), Ge2─Cl4 2.164(1), Ge2─Cl5 2.337(1); C3─C2─Ge1 129.0(2), C2─C3─Ge2 130.7(2), C2─Ge1─Cl1 116.1(1), C3─Ge2─Cl4 124.2(1), C3─Ge2─Cl5 85.0(1), Cl5─Ge2─Cl6 177.3(1).
Scheme 1
Scheme 1
a) Synthesis of compound [(ADC)Ge2]2 (3). b) An alternative canonical form of 3.
Figure 3
Figure 3
Solid‐state molecular structure of 3. Aryl groups are shown as wireframe models. H atoms and minor occupied disordered atoms as well as solvent molecules are omitted for clarity. Ellipsoids are shown at 50% (Selected bond lengths and angles are given in Table 1).
Figure 4
Figure 4
a) Molecular graph of 3 obtained from QTAIM analysis (PBE0/def2‐TZVPP). The small green, red, and blue spheres indicate BCPs (bond critical points), RCPs (ring critical points), and CCP (cage critical point), with electron density (ρ(rBCP) in a. u.) and Laplacian of electron density (∇2 ρ(r) in a. u.) (in parentheses). Contour plots of ∇2 ρ(r) (solid lines correspond to positive values and dashed to negative values) for the b) Ge3─C35─C36─Ge4 c) Ge1─Ge4─Ge2, and (d) Ge1─C2─C3─Ge2 planes.
Figure 5
Figure 5
a) Selected molecular orbitals (with energies in eV at PBE0/def2‐TZVPP) for 3. b) FOD plot (isosurfaces 0.007 a.e. in yellow) for 3.
Figure 6
Figure 6
CAS(2,2) orbitals for 3 according to SS‐CASSCF calculations [occupation number].
Scheme 2
Scheme 2
a) Selected canonical structures (A, B, and C) for 3. b) Reactions of 3 with TEMPO and Fe2(CO)9 to 4 and 5, respectively.
Figure 7
Figure 7
Solid‐state molecular structures 4 and 5. Aryl groups are shown as wireframes and H atoms and occupied disordered atoms are omitted for clarity. Thermal ellipsoids are shown at 50%. Selected bond lengths (Å) and angles (°) for 4: Ge1─O1 1.858(1), Ge1─Ge3 2.568(1), Ge2─Ge4 2.529(1), Ge1⋯Ge2 3.337(1), Ge3⋯Ge4 3.302(2); Ge1─Ge4─Ge2 82.4(1); for 5: Ge1⋯Ge2 3.482(1), Ge1─Ge4 2.462(1), Ge1─Ge3 2.594(1), Ge3─Ge4 2.967(1), Ge1─Fe1 2.360(1), Ge2─Fe2 2.363(4); Ge1─Ge4─Ge2 87.4(1), Ge1─Ge4─Ge3 56.2(1), Ge1─Ge3─Ge4 52.0(1), Ge4─Ge1─Ge3 71.8(1), Ge3─Ge4─C36 65.7(2), Ge2─Ge4─Ge3─Ge1 117.3(1).

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