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There’s plenty of nitrogen to go around in cyclopentazole anion

Chemists make and purify an elusive all-nitrogen aromatic ring

by Bethany Halford
July 18, 2016 | A version of this story appeared in Volume 94, Issue 29

Nitrogen, unlike its next-door neighbor carbon, is not known for its propensity to form long chains or multiatom rings. But when strung together in these ways, polynitrogen compounds have applications as high-energy materials because they can break apart with explosive results. One such polynitrogen compound—the cyclopentazole anion—has long been sought because it is thought this molecule might be somewhat stable, thanks to its aromaticity. Previous studies identified the all-nitrogen five-membered ring in the gas phase, but no one has produced and directly detected the anion in solution—until now. Chemists at Hebrew University of Jerusalem, led by Yehuda Haas, report they were able to prepare the cyclopentazole ion by reducing phenyl­pentazole with sodium (shown) using tetrahydrofuran as a solvent. The researchers propose this produces the phenylpentazole radical anion, which then decomposes into the phenyl radical and cyclopentazole anion (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201605400). The cyclopentazole anion may be used in subsequent transformations, Haas and coworkers say. It is indefinitely stable at temperatures below –40 °C and even sticks around for a few minutes at room temperature.


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