Synthesis of Genuine Germenyl Lithiums and the First Persistent Germenyl Radicals

The first isolated genuine germenyl lithiums (R₃ Si)(1-Ad)C=Ge(SiMetBu₂ )(Li⋅2 L) (R₃ Si=tBu₂ MeSi, L=THF (1 a), or L=12-crown-4 (1 b) and R₃ Si=tBuMe₂ Si, L=THF (2 a), or L=12-crown-4 (2 b)), were synthesized by reaction of the corresponding acyl germanes 3 and 4, respectively, with tBu₂ MeSiLi in THF at 70 °C. The novel 1 a and 2 b were characterized by NMR and UV/Vis spectroscopy, and also by X-ray crystallography (r(C=Ge)=1.865 Å for 1 a and 1.877 Å for 2 b). Nucleophilic addition reaction of 1 a with MeI and a C-H insertion reactions to the C=Ge bond of 1 a, 2 a and 2 b, are reported. Oxidation of 1 a and 2 b (toluene, 230 K) produces the first persistent germenyl radicals (R₃ Si)(1-Ad)C=Ge⋅-(SiMetBu₂ ) (R₃ Si=tBu₂ MeSi (13 a), R₃ Si=tBuMe₂ Si (13 b)), which were characterized by EPR spectroscopy (t_1/2 ≈30 min at 230 K, g=2.029, a_av (⁷³ Ge) is 55.0G for 13 a and 60.2G for 13 b). The experimental EPR parameters and DFT calculations indicate that 13 a and 13 b have a strongly bent structure at Ge (calc. ∡(C=Ge-Si)=136.7° (13 a), 135.9° (13 b)), and that the unpaired electron has a substantial s-character.