Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 25, Issue 46, Pages 10858-10865Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201902238
Keywords
aromaticity; density functional calculations; germacyclopentadienyl anion; germanium; X-ray diffraction
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Funding
- DFG through its Major Research Instrumentation Program [INST 184/108-1 FUGG]
- Ministry of Science and Culture (MWK) of the Lower Saxony State
- state of Lower Saxony for a Georg Lichtenberg Scholarship
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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 eta(5)-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.
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