EXCEPTIONALLY PERSISTENT NITROGEN-CENTERED FREE-RADICALS - PREPARATION, ISOLATION, AND MOLECULAR-STRUCTURE OF N-(ARYLTHIO)-2,4,6-TRIPHENYLANILINO RADICALS

The preparation, isolation, molecular structure, and ESR spectra of N-(arylthio)-2,4,6-triphenylanilino radicals 2 are described. Radicals 2 have been prepared by oxidation of N-(arylthio)-2,4,6-triphenylaniline (1) with PbO2 and studied by ESR spectroscopy. The radical solutions (benzene) were greenish blue or yellowish green, absorbing in the visible region at 513-535 and 626-644 nm. The radicals persist over a long period with only a slight or no decomposition, even in the presence of atmospheric oxygen, and have shown no tendency to dimerize, even at low temperatures. These properties have permitted us to isolate 2 as pure radical crystals and to determine the molecular structure of 2e by single-crystal X-ray analysis. The ESR spectrum of 2 consists of a broad 1:1:1 triplet (alpha-N, 0.890-0.896 mT), and hyperfine splittings due to protons were completely unresolved. However, on deuteriation of the 2,4,6-triphenyl groups on the anilino group, hyperfine splittings due to the anilino meta (0.133-0.134) and the arylthiyl ortho protons (0.088 mT) were found. Furthermore, at high gain satellite lines due to S-33 isotopes (0.51 mT) at natural abundance were detected. On the basis of these ESR results the spin density distribution in 2 is elucidated.