Series of Fluorinated Benzimidazole-Substituted Nitronyl Nitroxides: Synthesis, Structure, Acidity, Redox Properties, and Magnetostructural Correlations.

A special series of nitronyl nitroxides was synthesized: 2-(benzimidazol-2'-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1-imidazole-3-oxide-1-oxyls mono-, di-, tri-, or tetrafluorinated on the benzene ring. The structure of all paramagnets was unambiguously confirmed by single-crystal X-ray diffraction. It was found that in crystals, the radicals are assembled into chains due to intermolecular H-bonds between the benzimidazole moiety (H-bond donor) and the nitronyl nitroxide group or benzimidazole ring (H-bond acceptor).

Fluorinated Organic Paramagnetic Building Blocks for Cross-Coupling Reactions.

New stable polyfluorinated nitroxide radicals for use in cross-coupling reactions, namely, --butyl--oxyamino-2,3,5,6-tetrafluoro-4-iodobenzene and --butyl--oxyamino-2,3,5,6-tetrafluoro-4-ethynylbenzene, were prepared from perfluoroiodobenzene. The reaction of the polyfluoro derivative with -butylamine under autoclaving conditions leading to the formation of --butyl-2,3,5,6-tetrafluoro-4-iodoaniline proved to be the key stage of the whole process. The fluorinated -butyl iodophenyl nitroxide was found to form in a solid state via N-O···I halogen bonds, a one-dimensional assembly of the radicals.

Synthesis of Nitroxide Diradical Using a New Approach.

A new synthetic pathway to diradical organic systems is proposed. The effectiveness of this approach was exemplified by the synthesis of a new nitroxide diradical. An interaction of perfluorobiphenyl with lithium -butylamide, followed by oxidation of the thusly formed 4,4'-di--butyl-2,2',3,3',5,5',6,6'-octafluorobiphenyl-4,4'-diamine with -chloroperoxybenzoic acid, led to the polyfluorinated nitroxide diradical, ,'-(perfluorobiphenyl-4,4'-diyl)bis(--butyl(oxyl)amine), with a good total yield.

Aromatic S-Approach to Fluorinated Phenyl -Butyl Nitroxides.

The interaction of octafluorotoluene (), as well as pentafluorobenzonitrile () with -butylamine, followed by the oxidation of thus formed -butylanilines (,) with -chloroperoxybenzoic acid led to functionalized perfluorinated phenyl -butyl nitroxides [namely, 4-(--butyl(oxyl)amino)heptafluorotoluene () and 4-(--butyl(oxyl)amino)tetrafluorobenzonitrile ()] with nearly quantitative total yields. The molecular and crystal structures of nitroxide were proved by single crystal X-ray diffraction analysis. The radical nature of both nitroxides was confirmed by ESR data.

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.