Synthesis, structure, and electrochemistry of nitronyl nitroxide-substituted 1,4-naphthoquinone

A method for the synthesis of naphthoquinone with an additional redox-active paramagnetic group, namely, 2-bromo-3-(4-(4,4,5,5-tetramethyl-3-oxide-1-oxylimidazolidin-2-yl)phenoxy)naphthalene-1,4-dione, was developed by reacting 1,2-dibromonaphtho-quinone with 2-(4-hydroxyphenyl)-4,4,5,5-tetramethyl-2-imidazoline-3-oxide-1-oxyl in DMF in the presence of K 2 CO 3 . The molecular and crystal structure of the paramagnetic compound was solved using an X-ray diffraction analysis. According to the data of cyclic voltammetry the oxidation of the nitroxide group in spin-labeled naphthoquinone occurs reversibly at E 1/2 = 0.513 V ( vs . Ag/AgCl), and its reduction proceeds at a peak potential of −1.33 V and exhibits a corresponding oxidation peak. The electrochemical activity of the naphthoquinone fragment manifests itself in the cathode region and is expressed as a group of two successive peaks at potentials of −0.72 and −1.49 V, the first of which has the characteristics of a quasi-reversible process, the second one also exhibits a corresponding oxidation wave.