Are Gitonic Dications Really Stable and Visible? Revisiting o,o-Diprotonated Dications of the Nitro Group

Abstract

We revisited the chemistry of gitonic dications of the nitro group using a combination of experimental, spectroscopic, and computational techniques to settle this long-standing dispute over the notion of superelectrophiles. The o,o-diprotonated species, long considered to be exceptionally stable and long-lived, was not spectroscopically detectable in a solution of 1-nitronaphthalene or β-nitrostyrene in trifluoromethanesulfonic acid (TFSA). Further, the addition of a dinuclear dianion based on monocarba-closo-dodecaborate to 1-nitronaphthalene in TFSA gave the o-monoprotonated salt, as determined by single-crystal X-ray analysis, whereas a proton-bridged half-cation was confirmed to be the dominant species in solution.