Acyclic Germylones: Congeners of Allenes with a Central Germanium Atom

Abstract

The cyclic alkyl­(amino) carbene (cAAC:)-stabilized acyclic germylones (Me₂-cAAC:)₂Ge (<b>1</b>) and (Cy₂-cAAC:)₂Ge (<b>2</b>) 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 <b>1</b> and <b>2</b> 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 <b>1</b> and <b>2</b> feature the C–Ge–C bent backbone, which possesses a three-center two-electron π-bond system. Compounds <b>1</b> and <b>2</b> are the first acyclic germylones containing each one germanium atom and two cAAC: molecules. EPR measurements on compounds <b>1</b> and <b>2</b> confirmed the singlet spin ground state. DFT calculations on <b>1</b>/<b>2</b> 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 (<b>1</b>)/267.1 (<b>2</b>) and 180.4 (<b>1</b>)/183.8 (<b>2</b>) kcal mol^–1, respectively. Further calculations, which were performed at different levels suggest a singlet diradicaloid character of <b>1</b> and <b>2</b>. The TD-DFT calculations exhibit an absorption band at ∼655 nm in <i>n</i>-hexane solution that originates from the diradicaloid character of germylones <b>1</b> and <b>2</b>