Electrochemistry of perfluorotetracyclobuta-1,3,5,7-cyclooctatetraene, a powerful neutral organic oxidant

Abstract

The electrochemistry of perfluorotetracyclobuta-l,3,5,7-cyclooctatetraene (1) (a flat cyclooctatetraene) shows two reversible one-electron reductions at 0.79 and 0.14 V vs. SCE. The apparent electron-transfer rate constant for the first reduction is 0.07 ± 0.02 cm/s. The first reduction potential of 1 is more than 2.3 V positive of cyclooctatetraene (COT), and the apparent rate constant is more than an order of magnitude higher. It is suggested that the larger electron transfer rate constant for 1 compared with COT is due to the lower molecular reorganization energy required to reach the transition state for electron transfer. The unusually positive reduction potential of 1 is probably due at least in part to the 16 fluorine atoms.We report our findings on the electrochemistry of perfluorotetracyclobuta-1,3,5,7-cyclooctatetraene,1 1, which is one of the most powerful neutral organic oxidants known, reducing at positive 0.79 V vs. SCE.

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

“…These values are narrower and larger than those of 3-11. It is interesting to note that 12 has an extraordinarily low reduction potential ( +0.79 V vs SCE; +0.33 V vs Fc/Fc + ) owing to lowering of the LUMO level by planarization of COT ring and the accumulated electron-withdrawing effects of sixteen fluorine atoms [79]. Figure 9.…”

Powerful Oxidizing Properties of a Planar [8]Annulene: Tetrakis(perfluorocyclobuta)cyclooctatetraene and Its Radical Anion

“…The cyclic voltammogram of 1 exhibits two reversible reduction waves at E 1 1a2 0.79 and E 2 1a2 0.14 V vs. SCE [13]. The first of them is by 2.4 V more positive than the corresponding potential of COT at À 1.61 V. This finding can be rationalized by the cooperative inductive and conformational effects of perfluorocyclobutane annelation: because neutral 1 already has a planar geometry, little reorganization energy is required for electron transfer.…”

“…Comparison of the first reduction potentials, E 1/2 , of 1 ( 0.79 V [13]) and 2 ( 0.20 V) with the corresponding value for COT (À 1.61 V [13]) indicates that the shift by 1.8 V on going from COT to 2 is due to the annelation by the electronattracting perfluoroalkane ring. A further change of 0.6 V, on passing from 2 to 1, is attributed to the structural change, as 1 needs not be flattened on conversion to its radical anion 1 .À .…”

“…Flanking each hyperfine line, two pairs of satellites with a relative intensity of ca. 4% indicated an interaction with two sets of eight equivalent 13 Cisotopes. The pertinent coupling constants j a C j were 0.191 AE 0.001 mT and 0.135 AE 0.001 mT, whereby the lines associated with the smaller j a C j value were markedly broadened upon lowering the temperature.…”

“…The reduction potentials of 2 were measured by cyclic voltammetry at room temperature. Like 1 [13], compound 2 displays two reversible Radical Anions. Reduction of compounds 1 and 2 to their radical anions was carried out with K in 1,2-dimethoxyethane (DME), either by a direct contact with the metallic mirror or indirectly by the method of solvated electrons [18].…”