Substitution of a Fluorine Atom in Perfluorobenzonitrile by a Lithiated Nitronyl Nitroxide

A 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (1) lithium derivative was found to react with perfluorobenzonitrile (2) substituting its para-fluorine atom to form 2-(4-cyanotetrafluorophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl (3), a new nitronyl nitroxide containing a multifunctional framework of strong electron-withdrawing nature. This result shows the possibility of obtaining multifunctional nitronyl nitroxides via the interaction of paramagnetic lithium derivatives as C-nucleophiles with polyfluoroarenes activated for nucleophilic substitution. The reaction regioselectivity is supported by the data of quantum-chemical calculations, which also show that the reaction follows a concerted pathway without formation of an intermediate. Reduction of nitronyl nitroxide 3 in system NaNO₂-AcOH yielded corresponding iminonitroxide 4. Characterization of persistent radicals 3 and 4 obtained by the S_N^F synthetic strategy includes X-ray crystal structures, electron spin resonance data, and static magnetic-susceptibility measurements. X-ray diffraction analysis of both nitronyl nitroxide and iminonitroxide revealed a complete match of the parameters of their crystal lattices.