Diarylnitroxide Diradicals: Low-Temperature Oxidation of Diarylamines to Nitroxides

A low temperature method, in which the progress of the oxidation of secondary diarylamines with DMDO at low temperatures is monitored by magnetic resonance spectroscopy (EPR and NMR) and magnetic studies by a Superconducting Quantum Interference Device (SQUID), is developed for preparation of the first <i>m</i>-phenylene based diarylnitroxide diradical. EPR spectroscopy and magnetic studies (SQUID) indicate that the diradical in the dichloromethane matrix predominantly adopts anticonformation (<b>2A-anti</b>) and possesses triplet ground state. Similar oxidation experiments for conformationally constrained aza[1<sub>4</sub>]metacyclophane provide evidence for the formation of small amounts of the corresponding diarylnitroxide diradical. Both diarylnitroxide diradicals could only be detected at low temperatures (−80 °C and below).