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

The 2-azaphenalenyl radical <b>2</b> has been synthesized and characterized by ESR spectroscopy. Variable-temperature ESR measurements were carried out on both the phenalenyl (<b>1</b>) and the 2-azaphenalenyl (<b>2</b>) radicals. The phenalenyl radical <b>1</b> 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 <b>1</b> was obtained in CCl<sub>4</sub> (11.34 ± 0.11 kcal/mol) and toluene (9.8 ± 0.7 kcal/mol). The 2-azaphenalenyl radical <b>2</b> does not show a propensity to dimerize over the measurable temperature range (220−330 K), but does so in the presence of Cu(hfac)<sub>2</sub> (hfac = hexafluoroacetylacetonate). The latter complex was characterized by X-ray crystallography.