Abstract
New stable polyfluorinated nitroxide radicals for use in cross-coupling reactions, namely, N-tert-butyl-N-oxyamino-2,3,5,6-tetrafluoro-4-iodobenzene and N-tert-butyl-N-oxyamino-2,3,5,6-tetrafluoro-4-ethynylbenzene, were prepared from perfluoroiodobenzene. The reaction of the polyfluoro derivative with tert-butylamine under autoclaving conditions leading to the formation of N-tert-butyl-2,3,5,6-tetrafluoro-4-iodoaniline proved to be the key stage of the whole process. The fluorinated tert-butyl iodophenyl nitroxide was found to form in a solid state via N–O···I halogen bonds, a one-dimensional assembly of the radicals. The acceptor role of the nitroxide group in the halogen bonding changes to a donor role when the nitroxide reacts with Cu(hfac)2. In the last case, zero-dimensional assembly prevails, giving a three-spin complex with axial coordinated nitroxide groups and, as a consequence, causing ferromagnetic intramolecular exchange interactions between Cu(II) and radical spins.
Highlights
Introduction tertButylarylnitroxides and corresponding polynitroxides are an important class of paramagnets that have been actively used in different fields of research
Because the above-mentioned polyfluorinated tert-butylarylnitroxides satisfy all these requirements, within the framework of this work, we studied the possibility of obtaining their iodo and ethynyl derivatives that may be subjected to the Sonogashira cross-coupling reaction
The use of tert-butylamine under autoclaving conditions at 120 ◦ C led to the substitution of the fluorine atom in perfluoroiodobenzene and the formation of N-tert-butyl-2,3,5,6-tetrafluoro-4-iodoaniline (1) in a high yield
Summary
Butylarylnitroxides and corresponding polynitroxides are an important class of paramagnets that have been actively used in different fields of research. The oxidation of N-tert-butylanilines is performed to obtain nitroxide radicals [1,2]. We proposed a new synthetic approach to obtaining functionalized tertbutylphenylnitroxides 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]. The nitroxides of this type can serve as paramagnetic building blocks for diverse applications
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