Synthesis, Characterization, and Coordination Chemistry of the 2-Azaphenalenyl Radical

The 2-azaphenalenyl radical 2 has been synthesized and characterized by ESR spectroscopy. Variable-temperature ESR measurements were carried out on both the phenalenyl (1) and the 2-azaphenalenyl (2) radicals. The phenalenyl radical 1 has the known propensity to dimerize at temperatures below 20 °C, but unexpectedly less so than originally reported. The first experimental measurement of bond dissociation enthalpy for the dimerization of the phenalenyl radical 1 was obtained in CCl₄ (11.34 ± 0.11 kcal/mol) and toluene (9.8 ± 0.7 kcal/mol). The 2-azaphenalenyl radical 2 does not show a propensity to dimerize over the measurable temperature range (220−330 K), but does so in the presence of Cu(hfac)₂ (hfac = hexafluoroacetylacetonate). The latter complex was characterized by X-ray crystallography.