Cyclooctatetraene anion radical

ESR cavity produces a signal (nonuplet, ajj = 3,23 G), which indicates eight equivalent protons. When bicyclo [6.1.0] nonatriene (196) was reduced in the ESR cavity the spectra of the cyclononatriene radical anion (197) and of the methyl-cyclooctatetraene radical anion (198 Eq. (251) ) were observed. 

In contrast with the cyclooctatetraene radical anion, the present radical anions appear to be in equilibrium with the parent dehydroannulenes. This may be due to the fact that, unlike cyclooctatetraene,... 

The NMR spectrum indicates a planar aromatic structure. It has been demonstrated that the dianion is more stable than the radical anion formed by one-electron reduction, since the radical anion disproportionates to cyclooctatetraene and the dianion ... 

Our success in super-stabilization of cation 6 led us to the preparation of a higher homologue, that is, cyclooctatetraene (COT), fully annelated with BCO units 9 (9). As compared with a large number of studies on its radical anion or dianions, the studies on the cationic species of COT have been quite limited. There have been only one study by Olah and Paquette on the substituted COT dication (70), which is a typical 6n Hiickel aromatic system, and few sporadic studies on radical cations, which involve indirect spectral observations, such as electronic spectra in Freon matrix at low temperature (77,72) and constant-flow ESR study (13). 

Pairs of radical ions of like charge also react by electron transfer (i.e., they disproportionate). One classic example involves reduction of tetraphenylethylene and subsequent ET between two tetraphenylethylene anions. A more recent interesting example is that of cyclooctatetrene radical anion 148 . Alkali metals readily reduce the nonplanar cyclooctatetraene, generating a persistent planar radical anion... 

D. A. Hrovat, J. H. Hammons, C. D. Stevenson, and W. T. Borden, Calculations of the Equilibrium Isotope Effects on the Reductions of Benzene-dg and Cyclooctatetraene-dg, J. Am. Chem. Soc. 1997,119, 9523. B3LYP/6-31+G calculations on the title compounds and on the radical anions formed from them show that the very large difference between the equilibrium isotope effects, found by Stevenson, is due to an inverse isotope effect on the planarization of the COT ring. This explanation was subsequently confirmed by KIE measurements, carried out by C. D. Stevenson, E. C. Brown, D. A. Hrovat, and W. T. Borden, Isotope Effects on the Ring Inversion of Cyclooctatetraene, J. Am. Chem. Soc. 1998, 120, 8864. 

A cell (Fig. 54) that allowed the precise control of potential and current was designed by Goldberg and Bard, who also demonstrated the advantage of combining ESR spectroscopy with electrochemical techniques such as CA, CV, and chronopotentiometry [366]. The latter approach was taken in a study of the reduction of cyclooctatetraene (COT) in which it was demonstrated that the COT radical anion is stable in the presence of tetra-butylammonium ion, which had been a matter of dispute in previous work [378] (Fig. 55). 

Vincow and Concepcion reported a convenient approacii to the synthesis of the radical anion of 5, by the reduction of the syn [2+2] dimer of cyclooctatetraene (11) [81]. It was found that when 11 is reduced by an alkali metal at room temperature,... 

Cyclooctatetraene and some of its derivatives are electrochemically reducible in dry degassed DMF containing BU4NCIO4 as the supporting electrolyte. The first reduction peak potentials which are required to form the corresponding anion radical are shown in Table 824, though a further reaction of the intermediates is not known. 

Dick turned up some interesting chemistry of caprolactam and its O-alkyl imino ethers. He and collaborators went on to explore the chemistry of allene, for example, its reactions with acetylene, carbon monoxide, and tetrafluo-roethylene. He did extensive work on the chemistry of cyclooctatetraene and of ferrocene. In the cyanocarbon area he collaborated on studies of the anion radical of tetracyanoethylene, that is, tetracyanoethylene bearing an extra electron. He was author or coauthor of 45 papers and 16 U.S. Patents that came out of the Central Research Department. 

Cyclooctatetraene was reduced electrochemically to cyclooctatetraenyl dianion. In DMF the product is mostly (92%) 1,3,5-cyclooctatriene at —1.2 V. If the potential is lowered the main product is 1,3,6-cyclooctatriene. Previous experiments, in which the anion radical was found to be disproportionated, were explained on the basis of reactions of the cyclooctatetraene dianion with alkali metal ions to form tightly bound complexes, or with water to form cyclooctatrienes. The first electron transfer to cyclooctatetraene is slow and proceeds via a transition state which resembles planar cyclooctatetraene102. 

Let us compare anion-radicals with dianions, which are definitely stronger bases. For example, the cyclooctatetraene dianion (CgHg ) accepts protons even from solvents such as dimethylsulfoxide (DMSO) and V,V-dimethylformamide. The latter is traditionally qualified as an aprotic solvent. In this solvent, the cyclooctatetraene dianion undergoes protonation resulting in the formation of cyclooctatrienes (Allendoerfer and Rieger 1965) + 2H+ CgHjo. It is seen that... 

The behavior of the same azoxybenzene is studied in homogeneous conditions— when the dipotassium salt of cyclooctatetraene dianion (CgHgKj) acts as a dissolved electrode. In this case, the reduction of azoxybenzene stops at the very first stage, that is, after the transfer of one electron only (Todres et al. 1975). The initial one-electron reduction produces the azoxybenzene anion-radicals, which are not reduced further despite the presence of residual electron donor in the solution. The ESR method does not reveal these anion-radicals although one-electron oxidation by phenoxyl radicals quantitatively regenerates azoxybenzene and produces the corresponding potassium phenolate molecules in a quantitative yield. Treatment with water leads to a 100% yield of azobenzene (Scheme 2.14). 

The diamagnetic complex is not reduced further by the cyclooctatetraene dianion. This prevents the conversion of the azoxybenzene anion-radicals into azodianions. Potassium cation plays an important role in this limitation of the reduction process, which, generally, proceeds readily (the... 

In the case of cyclooctatetraene, an electron prefers the isotopicaUy heavier material. At 173 K, the equilibrium constant for -F C Dg = CgHg + CgDg was found to be 1.16 (Stevenson 2007). However, when this anion-radical reacts with cyclooctatetraene dianion (not with the anion-radical), the transferred electrons prefer the isotopicaUy lighter material (Stevenson et al. 1990,1992) as follows CgHg -F = CgHg -F CgDg. The semiempirical quantum chemical consideration led to the... 

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