Cyclooctatetraene, anions from

The anion from one electron transfer is probably an intermediate. Simple alkenes do not form such stable dianions, but some conjugated derivatives do form dianions as with cyclooctatetraene forming dianion with alkali metals. 

The Hiickel rule predicts aromaticity for the six-7c-electron cation derived from cycloheptatriene by hydride abstraction and antiaromaticity for the planar eight-rc-electron anion that would be formed by deprotonation. The cation is indeed very stable, with a P Cr+ of -1-4.7. ° Salts containing the cation can be isolated as a product of a variety of preparative procedures. On the other hand, the pK of cycloheptatriene has been estimated at 36. ° This value is similar to those of normal 1,4-dienes and does not indicate strong destabilization. Thus, the seven-membered eight-rc-electron anion is probably nonplanar. This would be similar to the situation in the nonplanar eight-rc-electron hydrocarbon, cyclooctatetraene. 

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... 

A single-electron transfer from cyclooctatetraene dipotassium (C8H8K2) to 2- and 4-nitrostilbenes in THF leads to the formation of paramagnetic potassium salts of the anion-radicals. In this solvent, the salts exist as coordination complexes (Scheme 3.43). 

Electro-optical modulators are other examples whose efficiency is enhanced in the presence of ion-radicals. These devices are based on the sandwich-type electrode structures containing organic layers as the electron/hole-injecting layers at the interface between the electrode and the emitter layer. The presence of ion-radicals lowers the barrier height for the electron or hole injection. Anion-radicals (e.g., anion-radicals from 4,7-diphenyl-l,10-phenanthroline—Kido and Matsumoto 1998 from tetra (arylethynyl) cyclooctatetraenes—Lu et al. 2000 from bis (1-octylamino) perylene-3,4 9,10-bis (dicarboximide)s— Ahrens et al. 2006) or cation-radicals (e.g., cation-radicals from a-sexithienyl—Kurata et al. 1998 l,l-diphenyl-2-[phenyl-4-A/,A- /i(4 -methylphenyl)] ethylene— Umeda et al. 1990, 2000), all of them are electron or hole carriers. 

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 triplet-sensitized photoreaction in the crystalline state has been achieved by using crystalline organic salts which were prepared from cationic sensitizers and an anionic reactant (Scheme 40) [73]. Thus, upon selective excitation of the sensitizer these salts or hydrogen-bonded complex gave two dibenzosemi-bullvalenes through triplet-triplet energy transfer to the reactant, A dibenzo-cyclooctatetraene, which is a product of direct (singlet state) irradiation, was not produced. 

It was seen earlier that cyclooctatetraene, 3, is a non-planar, nonaromatic compound. The addition of 2 rc-electron converts this system to the di-anion 65, and the new species appears to be planar and highly resonance stabilized. The protons of this 107t8C system resonate at r 4.3 190,208) (there is a discrepancy in some early work 20 )), the charge-corrected value being x 1.8, which is clearly in an aromatic region. The 13C chemical shift 192> of +42.5 ppm from benzene is also as expected, the calculated value being +40 ppm. ... 

In 1945 Michael J. S. Dewar suggested that the tropylium ion (the cation derived from cycloheptatriene) should also be aromatic (Figure 9). This was confirmed in 1954 since then, the dianion of butadiene and the dication of cyclooctatetraene have also been shown to be aromatic. Like benzene, all four of these ions are planar rings with six tt electrons. According to Hiickel s rule the cyclopropene cation should also exhibit aromaticity, and it does. (In this case n = 0, and 4n + 2 = 2.) The planar anion of cyclononatetraene and the dianion of cyclooctatetraene should also be aromatic (n = 2, and 4n + 2 = 10), and both of them are. 

Cocondensation of La, Ce, Nd, or Er metal atoms with cyclooctatetraene at — 196°C yielded dinuclear complexes of the formula [CgHgR(THF)2][R(CgHg)2] after extraction with tetrahydrofuran (De Kock et al., 1978). The structure of the neodymium complex (fig. 23, table 15) shows two cyclooctatetraene rings in the anion, which are neither equidistant from the neodymium atom, nor p allel. The neodymium atom in the cation is asymmetrically located with respect to the central cyclooctatetraene ring with neodymium-carbon distances between 2.68 and 4.63 A (Ely et al., 1976 De Kock et al., 1978). 

The bis([8]annulene)lanthanate(III) anions which are complexed by an [8]annulenelanthanate(III) cation are the only other class of complexes which contain two [8]annulene dianions in a sandwich arrangement about a lanthanide(III) ion. This class was first reported for the cerium(III) ion, from the reduction of a cerium(IV) alkoxide with triethylaluminum in the presence of cyclooctatetraene.3 ... 

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