Room-Temperature Long-Lived Radical Cations of Monocyclic Arenes Obtained by NbF5 Acting as Oxidising Agent and Counterion Precursor

The direct observation of long-lived carbocations has represented a fascinating topic for chemists. In this context, the preparation of fairly stable radical cations by one-electron oxidation of monocyclic aromatic molecules is still a difficult task. In the course of our studies on the chemistry of the pentahalides of niobium and tantalum, we have found that room-temperature long-lived radical cation salts of monocyclic arenes can be prepared according to the reaction: 3NbF5 + Arene → [Arene][Nb2F11] + NbF4. The driving force of this unexpected redox process is supplied mainly by the interaction established between the anion [Nb2F11] and the -density of the cation. X-Ray structure of very rare radical cation salt isolated in the solid state at room temperature (Figure 1) and unprecedented EPR identification of a [C6H6]•+ salt as a non-transient species in solution at room temperature (Figure 2) are shown.