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

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Summary

Introduction

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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