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 SNF 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.