Synthesis and Characterization of a 1,2-Digermabenzene

Abstract

A 1,2-digermabenzene bearing bulky substituents on its two germanium atoms was successfully synthesized and isolated as a stable, crystalline compound via the reaction of a digermyne precursor with 2 equiv of acetylene. Even though its molecular structure, which was revealed by X-ray crystallographic analysis, showed a trans-bent geometry for the Ge−Ge moiety, theoretical calculations suggested substantial levels of aromaticity.

Reaction of a Stable Digermyne with Acetylenes: Synthesis of a 1,2-Digermabenzene and a 1,4-Digermabarrelene

“…11,14,15 In the case of the carbon analogues, the trimerization of acetylene to afford a sixmembered cyclic π-conjugated system (i.e., an aromatic ring system) usually requires an appropriate transition-metal catalyst and severe conditions, as for example in the well-known Reppe reaction. In contrast, a cyclic six-membered π-conjugated aromatic ring system containing two heavier group 14 elements can be generated under ambient conditions in the absence of any transition-metal catalysts from the reaction of two molecules of acetylene and one heavier dimetallyne (vide supra).…”

“…The replacement of carbon atoms in the benzene ring with heavier group 14 elements, generating so-called heavy aromatics, 15 has generated much interest, even though this class of compounds is known to be highly susceptible towards auto-oligo-and polymerizations. So far, treatment of disilynes or digermynes with acetylene remains the only synthetic method to generate 1,2-disila-or 1,2-digermabenzenes.…”

“…So far, treatment of disilynes or digermynes with acetylene remains the only synthetic method to generate 1,2-disila-or 1,2-digermabenzenes. 11,14,15 Such transformations are not only of great interest due to their unique reactivity, but the resulting heavy aromatic systems that include two heavy atoms are also highly interesting with respect to structural aspects, such as bond-alternation, planarity of the aromatic ring, and other features that may be affected by the double-bond character of the E=E bonds.…”

“…15 However, this reaction also generated another unprecedented product, 1,4-digermabarrelene 14, which could be isolated and fully characterized. Herein, we report the reaction of the digermyne TbbGe¸GeTbb (2b) with acetylene in detail and we discuss the reaction mechanism on the basis of experimental and theoretical results.…”

“…After removing the solvent, signals for both 1,2-digermabenzene 13 and 1,4-digermabarrelene 14 were observed in the NMR spectra of the crude mixture, 15 and judging from their 1 H NMR spectra, yields of 61% (13) and 22% (14) were estimated (Scheme 3). Recrystallization of the crude mixture from benzene at room temperature afforded yellow crystals of 13 in 25% yield.…”