Adamantyl-Substituted Triplet Diradical: Synthesis, Structure, Redox and Magnetic Properties

A stable diradical 2-{N-[(3s,5s,7s)-adamantyl-1]-N-oxylamino}-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl—a heteroatomic analogue of trimethylenemethane—has been synthesized by reacting lithiated 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl with 1-nitroso-adamantane, followed by oxidation of the intermediate hydroxylamine. According to X-ray diffraction data, the dihedral angle between the planes of paramagnetic moieties in the paramagnet is close to 60°. Magnetochemical measurements have shown that the energy gap between the triplet and singlet states (2J/k_B; H = –2JS_1/2S_1/2) in the diradical is 880 K. The EPR spectrum of the diradical was simulated using the parameters: S = 1, g_xx = 2.007, g_yy = 2.005, g_zz = 2.006, D = 825 MHz, E = 60 MHz. According to the data of cyclic voltammetry in the anodic region, the diradical undergoes electrochemical oxidation at potentials of 0.79, 1.63, 1.89, and 2.25 V, the first process being chemically and electrochemically reversible. In the cathodic region, the diradical is reduced quasi-reversibly at –1.18 and irreversibly at –2.59 V.