Aromatic SNF-Approach to Fluorinated Phenyl tert-Butyl Nitroxides

Abstract

The interaction of octafluorotoluene (1a), as well as pentafluorobenzonitrile (1b) with tert-butylamine, followed by the oxidation of thus formed tert-butylanilines (2a,b) with meta-chloroperoxybenzoic acid led to functionalized perfluorinated phenyl tert-butyl nitroxides [namely, 4-(N-tert-butyl(oxyl)amino)heptafluorotoluene (3a) and 4-(N-tert-butyl(oxyl)amino)tetrafluorobenzonitrile (3b)] with nearly quantitative total yields. The molecular and crystal structures of nitroxide 3a were proved by single crystal X-ray diffraction analysis. The radical nature of both nitroxides was confirmed by ESR data. The interaction of Cu(hfac)2 with the obtained nitroxides 3a,b gave corresponding trans-bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)bis{4-(N-tert-butyl(oxyl)amino)perfluoroarene-κO}copper (II) complexes ([Cu(hfac)2(3a)2] and [Cu(hfac)2(3b)2]). X-ray crystal structure analysis showed square bipyramid coordination of a centrally symmetric Cu polyhedron with the axial positions occupied by oxygen atoms of the nitroxide groups. Magnetic measurements revealed intramolecular ferromagnetic exchange interactions between unpaired electrons of Cu(II) ions and paramagnetic ligands, with exchange interaction parameters JCu–R reaching 53 cm−1.

Fluorinated Organic Paramagnetic Building Blocks for Cross-Coupling Reactions

“…It was revealed that radical 4 crystallizes in the orthorhombic Pbca space group ( Table 1 ). Bond lengths of the tert -butylnitroxide moiety ( Table 2 ) are fully consistent with those of previously described radicals of this family [ 3 ]. The nitroxide groups in diradical 4 are twisted at a large angle (~64°) relative to the aromatic ring.…”

“…Recently, we proposed a new synthetic approach to obtaining functionalized tert -butylphenylnitroxides by sequential substitution of a fluorine atom in polyfluorinated arenes with tert -butylamine or lithium tert -butylamide and oxidation of resultant N - tert -butylanilines with meta -chloroperoxybenzoic acid ( m -CPBA). This approach has been found to generate nitroxide mono- and diradicals in high yields ( Figure 1 ) [ 3 , 4 ]. Moreover, it turned out that polyfluorinated tert -butylarylnitroxides are much stable than nonfluorinated analogs.…”

Synthesis of Nitroxide Diradical Using a New Approach

“…Diradical 3 crystallizes in the monoclinic P2 1 /c space group. Bond lengths of the tert-butylnitroxide moiety are completely compatible with those of previously described radicals of this family [25]. The nitroxide groups in diradical 3 are twisted by different and large angles (~65 • and~70 • ) relative to the aromatic rings, as are the aromatic rings toward each other (~53 • , Figure 3a).…”

“…Diradical 3 featured an irreversible oxidation wave with E 1/2 ≈ 0.98 V, which was assigned to the oxidation of the nitroxide radicals into the corresponding oxoammonium cations. On the cathodic side, nitroxide diradical 3 also showed irreversible redox at −1.43 V. The redox potentials of diradical 3 are very close to those of fluorinated phenyl-tert-butylnitroxides reported by us previously [25].…”

“…The polyradicals thus obtained have been effectively used for the construction of molecular magnets capable of cooperative magnetic ordering at 3.4-46 K [21][22][23][24]. Realizing that the advances in the synthesis of nitroxide multi-spin molecules would be crucial for the further development of advanced organic magnetic materials and devices, we recently developed a new synthetic approach to functionalized tert-butylphenylnitroxides via substitution of a fluorine atom in polyfluorinated arenes by tert-butylamine with subsequent oxidation of the obtained tert-butylanilines with meta-chloroperoxybenzoic acid (m-CPBA) [25].…”