A Phosphinonitronyl Nitroxide

Abstract Nitronyl nitroxides are widely used in chemistry, physics, and materials science because of their inherently high reactivity and magnetic activity, but the synthesis of C(2)‐organoelement derivatives is still a challenge. This paper describes effective synthesis and properties of the first nitronyl nitroxide carrying an additional redox‐active phosphine group, namely 1,3,5,7‐tetramethyl‐8‐(4,4,5,5‐tetramethyl‐4,5‐dihydro‐1 H ‐imidazole‐3‐oxide‐1‐oxyl‐2‐yl)‐2,4,6‐trioxa‐8‐phosphaadamantane. This phosphinonitronyl nitroxide was prepared by reacting lithiated nitronyl nitroxide with 8‐bromo‐1,3,5,7‐tetramethyl‐2,4,6‐trioxa‐8‐phosphaadamantane. The paramagnet was characterized by cyclic voltammetry and electron spin resonance (ESR), infrared, and UV/vis spectroscopy supported by quantum chemical calculations. Molecular and crystal structure of the phosphinonitronyl nitroxide was established by X‐ray structural analysis. ESR spectroscopy and density functional theory (DFT) calculations proved spin delocalization onto the phosphorus atom. According to the cyclic‐voltammetry data, oxidation of the phosphinonitronyl nitroxide takes place quasi‐reversibly at E 1/2  = 0.76 V, and its reduction occurs chemically and electrochemically reversibly at E 1/2 = −0.95 V (rel. Ag/AgCl).