Assist Prof. Mizuhata, Y.; Ms. Fujimori, S.; Assoc Prof. Sasamori, T.; Prof. Tokitoh, N.
(Organoelement Chemistry, Division of Synthetic Chemistry)
Benzene is the simplest aromatic compound and known as the basic skeleton in many organic compounds. It has been extensively studied not only from the industrial aspect such as petroleum chemistry but also the fundamental one as the most basic skeleton showing “aromaticity” since the beginning of organic chemistry.
“Heavy benzenes” in which the carbon atom(s) of the benzene ring is replaced by high-period group 14 element(s), that is, “heavy element” (silicon, germanium, tin, and lead), have attracted much attention from the interest of its aromaticity experimentally and theoretically. However, these compounds are extremely high-reactive species, e.g., silabenzene (HSiC5H5) in which one of the skeletal carbon atom of the benzene ring is replaced by a silicon atom, is known to decompose by self-oligomerization reaction even at very low temperature of –200 ºC. We have already succeeded in the synthesis and isolation of a series of “heavy benzenes” as stable compounds even at room temperature by taking advantage of kinetic stabilization afforded by a very bulky substituent, Tbt group (see the figure), to prevent the self-oligomerization. Although these compounds are found to have “aromaticity” and unique electronic state, the existence of the bulky substituent necessary for stabilization makes it difficult to develop their further applications.
In this study, we have reported the formation of germabenzenylpotassium 1 as an isolable compound together with the elimination of the Tbt group during the reduction of the stable germabenzene 2 having a Tbt group on the germanium atom and a t-butyl group on the adjacent carbon atom with potassium graphite (KC8). Compound 1 can be regarded as the anion retaining the germabenzene skeleton, i.e., a germanium analog of a phenyl anion (⊝C6H5). From both experimental and theoretical points of view, compound 1 shows not only the aromatic character but also the contribution of the canonical structure of divalent species (germylene), which is negligible in the case of phenyl anion, clearly showing the effect of substitution with germanium (heavy element).
Compound 1 can be expected as a useful reagent to introduce a germabenzene skeleton, and we have already succeeded in the synthesis of several types of new germabenzenyl derivatives. The findings of this research are expected to contribute to the design and development of novel functional molecules incorporating a germabenzene ring.
Mizuhata, Y.; Fujimori, S.; Sasamori, T.; Tokitoh, N., Germabenzenylpotassium: A Germanium Analogue of a Phenyl Anion, Angew. Chem. Int. Ed., 56, 4588–4592 (2017).
Published 8 March 2017
Inside Cover: Angew. Chem. Int. Ed., 56, 4364 (2017).