powerful oxidizing Properties of a Planar [8]Annulene: Tetrakis(perfluorocyclobuta)cyclooctatetraene~1) and Its Radical Anion

摘要

The central eight-membered ring of tetrakis(perfluorocyclobuta)cyclooctatetraene (1) is flat both in the crystal and in solution, but tetrakis*perfluorocyclopenta)cyclooctatetraene (2) assumes a tub shape similar to that of parent cyclooctatetraene. This stericaly induced structural difference strongly affects the physical properties of compounds 1 and 2. The first and second reduciton potentials of 1 in solution, + 0.79 and +0.14 V vs. SCE, are considerably more positive than the corresponding values, +0.20 and -0.21 V, f 2. Accordingly, mere contact with Hg metal in N,N-dimethylformamide converts 1 to an unusualy stable radical anion 1~.- that is persistent in air. The temperature-independent coupling constant, a_F = +-0.320 mT, of the sixteen equivalent #beta#-~19F-nuclei in 1~.- is much smaller tan teh expected value, and the g factor of 1~.- is markedly lower than those generally found for structurally related raidcal anions. In contrast, the characteristic data for 2~.-, generated from 2 with K metal in 1,2-dimethyoxyethane, comply with the expected data. The coupling constants a_F=+-0.97 and +0.935 mT, each of eight #beta#-~19F-nuclei in 2~.-, average +-0.9051 mT upon raising the temperature from 220 to 260 K. The gas-phase electro affinity of 1,A=3.4+-0.2 eV, which was estimated fromt eh reduction potential in solution and from charge-transfer absorption spectra obtained from a series fo methylated benzenes and naphthalenes, is among the highest known for neutral orgaic molecules.