Transformations of spirogermabifluorene upon reduction with alkali metals

•The reduction reactions of spirogermabifluorene were studied.•Stepwise Ge–C bond cleavages occur upon reduction.•An aromatic germanium containing dianion is the final reduction product.•X-ray diffraction study revealed 1D polymeric chain for the sodium adduct.•Spirogermane shows different reactivity compared to the isostructural spirosilane.

Spirogermabifluorene (C24H16Ge, 1) and the anionic products of its reduction with alkali metals were prepared and investigated by single-crystal X-ray diffraction. A monoanionic intermediate product of the reduction, formed upon the cleavage of a Ge–C bond and proton abstraction from the solvent, was isolated in the form of the cesium salt, [Cs+(diglyme)(C12H8GeC12H9−)] (2). Structural investigation of 2 revealed the presence of a tricoordinated germanium center and complexation of the cesium cation by two aromatic moieties. The reduction of 1 with an excess of alkali metals leads to the cleavage of the second Ge–C bond with subsequent elimination of biphenyl to give the C12H8Ge2− dianion which was crystallized as the sodium adduct, [{Na+(THF)}2(C12H8Ge2−)] (3). The structural elucidation for complex 3 shows η3- and η5-coordinations of the sodium ions to the π-system of dianions. The resulting Na⋯C and Na⋯Ge contacts along with the Na⋯OTHF interactions lead to the formation of the zigzag polymeric chains in the crystal lattice of 3.

Graphical abstractThe graphic shows the transformation of spirogermanium compound upon reduction into mono and dianions.Figure optionsDownload full-size imageDownload as PowerPoint slide