Acyclic Germylones: Congeners of Allenes with a Central Germanium Atom

The cyclic alkyl­(amino) carbene (cAAC:)-stabilized acyclic germylones (Me2-cAAC:)2Ge (1) and (Cy2-cAAC:)2Ge (2) were prepared utilizing a one-pot synthesis of GeCl2(dioxane), cAAC:, and KC8 in a 1:2:2.1 molar ratio. Dark green crystals of compounds 1 and 2 were produced in 75 and 70% yields, respectively. The reported methods for the preparation of the corresponding silicon compounds turned out to be not applicable in the case of germanium. The single-crystal X-ray structures of 1 and 2 feature the C–Ge–C bent backbone, which possesses a three-center two-electron π-bond system. Compounds 1 and 2 are the first acyclic germylones containing each one germanium atom and two cAAC: molecules. EPR measurements on compounds 1 and 2 confirmed the singlet spin ground state. DFT calculations on 1/2 revealed that the singlet ground state is more stable by ∼16 to 18 kcal mol–1 than that of the triplet state. First and second proton affinity values were theoretically calculated to be of 265.8 (1)/267.1 (2) and 180.4 (1)/183.8 (2) kcal mol–1, respectively. Further calculations, which were performed at different levels suggest a singlet diradicaloid character of 1 and 2. The TD-DFT calculations exhibit an absorption band at ∼655 nm in n-hexane solution that originates from the diradicaloid character of germylones 1 and 2.以1:2:2.1的摩尔比，将二氧六环合二氯化锗（GeCl₂(dioxane)）、环烷基(氨基)卡宾（cyclic alkyl(amino) carbene，缩写cAAC）与KC8进行一锅法合成，得到了cAAC稳定的无环锗宾类化合物：(Me₂-cAAC:)₂Ge（1）与(Cy₂-cAAC:)₂Ge（2）。化合物1和2的深绿色晶体产率分别为75%与70%。此前报道的对应硅基化合物的制备方法，在锗体系中并不适用。单晶X射线衍射结构分析表明，化合物1和2的C–Ge–C骨架呈弯曲构型，且具有三中心两电子π键体系。化合物1和2是首例每分子包含一个锗原子与两个cAAC配体的无环锗宾类化合物。对化合物1和2的电子顺磁共振（Electron Paramagnetic Resonance, EPR）测试证实其基态为单重自旋态。对1和2的密度泛函理论（Density Functional Theory, DFT）计算结果显示，单重基态较三重基态稳定约16至18 kcal mol⁻¹。理论计算得到的第一和第二质子亲和能分别为265.8（1）/267.1（2）和180.4（1）/183.8（2） kcal mol⁻¹。在不同理论级别下开展的进一步计算表明，化合物1和2具有单重双自由基特征。含时密度泛函理论（Time-Dependent Density Functional Theory, TD-DFT）计算结果显示，在正己烷溶液中，化合物1和2在约655 nm处存在吸收带，该吸收源于锗宾类化合物的双自由基特征。