Cu(hfac)2 Complexes with N-tert-Butyl-N-(1-alkyl-1H-pyrazole-5-yl)Hydroxylamines

The series of H5R N-tert-butyl-N-(1-alkyl-1H-pyrazole-5-yl)hydroxylamines (R = Me, iPr, nBu) (diamagnetic precursors of N5R 5-R-pyrazolyl-substituted tert-butylnitroxides) is expanded. It is established that the interaction of H5R with the copper(II) hexafluoroacetylacetonate Cu(hfac)2 leads to the formation of individual mononuclear complexes and their cocrystals with H5R. In the complexes, H5R are coordinated in a monodentate mode via an N atom of the pyrazole ring, and the OH groups form intermolecular hydrogen bonds. It is shown by cyclic voltammetry that the peak at 720-750 mV corresponding to one-electron H5R oxidation has a reduction response wave with a noticeably lower current, meaning that the process is partially reversible. Due to low values of potentials, the interaction with Cu(hfac)2 in the solution can lead to the oxidation of H5R by air oxygen and to the formation of complexes containing both H5R and N5R as ligands, thus allowing one to use the “one-pot” approach to prepare heterospin complexes with tert-butylnitroxides.