Powerful oxidizing properties of a planar [8]annulene: Tetrakis(perfluorocyclobuta)cyclooctatetraene and its radical anion

The central eight-membered ring of tetrakis(perfluorocyclobuta)cyclooctatet raene (1) is flat both in the crystal and in solution, but tetrakis(perfluo rocyclopenta)cyclooctatetraene (2) assumes a tub shape similar to that of p arent cyclooctatetraene. This sterically induced structural difference stro ngly affects the physical properties of compounds 1 and 2. The first and se cond reduction 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 , of 2. Accordingly, mere contact with Hg metal in N,N-dimethylformamide co nverts 1 to an unusually stable radical anion 1(.-) that is persistent in a ir. The temperature-independent coupling constant, a(F) = + 0.320 mT, of th e sixteen equivalent beta-F-19-nuclei in 1(.-) is much smaller than the exp ected value, and the g factor of 1(.-) is markedly lower than those general ly found for structurally related radical anions. In contrast, the characte ristic data for 2(.-), generated from 2 with K metal in 1,2-dimethoxyethane , comply with the expected data. The coupling constants a(F) = +0.976 and 0.935 mT, each of eight beta-F-19-nuclei in 2(.-), average +0.951 mT upon r aising the temperature from 220 to 260 K. The gas-phase electron affinity o f 1, A = 3.4 +/- 0.2 eV, which was estimated from the reduction potential i n solution and from charge-transfer absorption spectra obtained from a seri es of methylated benzenes and naphthalenes, is among the highest known for neutral organic molecules.