An approach to fluorinated phthalonitriles containing a nitronyl nitroxide or iminonitroxide moiety

A 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl lithium derivative was found to react with perfluorophthalonitrile with formation of 2-(3,4-dicyano-2,5,6-trifluorophenyl)- (1) and 2-(2-amino-4,5-dicyano-3,6-difluorophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl (2). The yields of 1 were near 15% independently of reaction time (from 2 to 6 h), whereas the yields of 2 considerably increased from a trace amount to 20%. Both nitronyl nitroxides were reduced to the corresponding iminonitroxides in the presence of NaNO₂/AcOH with yields 80–95%. Molecular and crystal structures of the obtained nitroxides were solved by monocrystal X-ray diffraction analysis, and the nature of the radical was ascertained by electron spin spectroscopy (ESR) and SQUID magnetometry. Static magnetochemical measurements of 1 revealed domination of the ferromagnetic exchange interactions between the odd electrons of the paramagnetic centres. The exchange interactions probably proceed via short intermolecular contacts (3.021(3) and 3.05(2) Å) between the nitroxide O atoms and cyanide C atoms. Structural characteristics of the prepared nitroxides make them valuable precursors for the synthesis of paramagnetic macrocycles, which may serve as building blocks in the field of molecular magnetism.