Chlorine-Substituted Germabenzene: Generation and Application as a Precursor for Aryl-Substituted Germabenzenes

The Reduction of Metallabenzenes: Different Scenarios Highly Dependent on the Central Group 14 Elements, Si vs. Ge

In order to synthesize a silabenzenyl anion, in which the anionic carbon atom of a phenyl anion was replaced with a silicon atom, the reductive dearylation reaction of 1-Tbt-2-tert-butyl-silabenzene (Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl) with KC8 was attempted. Unexpectedly, this reaction resulted in the formation of a dianion species without the elimination of the Tbt group. This is totally different from the reactions of Tbt-substituted germa- or stannabenzene with KC8 , which resulted in the formation of the corresponding heavy analogues of phenyl anion, together with the elimination of Tbt group. Experimental and theoretical investigation revealed that one of the protons of the o-benzyl positions of the Tbt group was abstracted by the negatively charged silicon atom of an in-situ generated intermediate. Compared with the previously reported germanium system, the contrasting results indicate that the central heavy group 14 element has a great influence on the elimination step of the Tbt group.

Recent progress in the chemistry of heavy aromatics

The aromaticity and synthetic application of "heavy benzenes", i.e., benzenes containing a heavier Group 14 element (Si, Ge, Sn, and Pb) in place of skeletal carbon, have been the targets of many theoretical and synthetic studies. Although the introduction of a sterically demanding substituent enabled us to synthesize and isolate heavy aromatic species as a stable compound by suppressing their high reactivity and tendency to polymerize, the existence of a protection group is an obstruction to the development of functional materials based on heavy aromatics. This review will delineate the most recent topics in the chemistry of heavy aromatics, i.e., the chemistry of "metallabenzenyl anions", which are the heavier Group 14 element analogs of phenyl anions stabilized by taking advantage of charge repulsion instead of steric protection.

Heavier element-containing aromatics of [4n+2]-electron systems

While the implication of the aromaticity concept has been dramatically expanded to date since its emergence in 1865, the classical [4n+2]/4n-electron counting protocol still plays an essential role in evaluating the aromatic nature of compounds. Over the last few decades, a variety of heavier heterocycles featuring the formal [4n+2] π-electron arrangements have been developed, which allows for assessing their aromatic nature. In this review, we present recent developments of the [4n+2]-electron systems of heavier heterocycles involving group 13-15 elements. The synthesis, spectroscopic data, structural parameters, computational data, and reactivity are introduced.

Potassium Salts of 2,5-Bis(trimethylsilyl)-Germolide: Switching between Aromatic and Non-Aromatic States

The reduction of a 1-mesityl-2,5-bis-trimethylsilylchlorogermole 8 with KC₈ is reported. While the reaction with one equivalent of KC₈ gave the dimer with a Ge-Ge bond 10, excess of KC₈ (four equivalents) resulted in the formation of the potassium salt of the germole dianion, 11 with reductive cleavage of the Ge-C bond. Careful reduction with two equivalents of KC₈ in THF provided the potassium salt of the planar germolide 5. Its solid-state structure revealed contact ion pairs with the potassium ion η⁵ -coordinated to the germacyclopentadienide ring. The molecular structure of the anion indicates a high degree of cyclic electron delocalization, in agreement with results from DFT calculations. Separation of the ion pair by complexation of the potassium ions with 18-crown-6 triggers the isomerization to germolide 6, which is characterized by a pyramidal coordination sphere of the germanium atom and a localized diene structure. The isomers 5 and 6 represent a rare example for a structurally manifested switch between a non-aromatic and an aromatic state induced by an external stimulus, in this case the complexation of the counter cation.