Trianion radical

In the case of 1,8-diphenylnaphthalene, there is an interesting difference in the spin states of the anion-radical on one hand, and of the trianion-radical on the other. In the anion-radical, the main contonr for spin distribntion is the naphthalene framework. In the trianion-radical, the naphthalene n system bears two electrons (nonassociated with any bond), whereas the third (unpaired) electron oscillates between 1 and 8-phenyl snbstitnents (Gerson and Hnber 1987). 

Tetracyanoqninodimethide is able to give both anion-radical and dianion. It is nnable to form the trianion-radical. However, with widespread n-electron contonr, the trianion-radical exists—snch... 

Distribution of spin density in the framework of trianion-radicals allows determining whether or not there is some conjugation between substituents at different sites. For example, reduction of dinitro spiro(indoline-benzopyran) with potassium tert-butoxide in DMSO proceeds according to Scheme 1.40 (Alberti et al. 1995). 

The radical anion and the triradical anion of 43 are both paramagnetic species and can be detected by EPR. The EPR spectrum of the radical anion of 43 shows an 11-line hyperfine pattern for the ten equivalent protons76. The trianion radical of 43 shows a highly resolved EPR spectrum where additional 7Li (and 6Li) couplings are evident74,76b. 

Further reduction of the dianions, 482- and 492-, with lithium metal gave the corresponding trianion radicals, but in contrast to the reduction of 43, the reduction could not be made to proceed further. This behavior can be explained by the tendency of 434 to dimerize, unlike the tetraanions of 48 and 49. When the reduction is performed with potassium metal, both 48 and 49 yield tetraanions (484 /4K+, 494 /4K+). The tetraanion 484 /4K+... 

Dianion Radicals, Trianion Radicals, and Multianion Radicals... 

The experimental data available for reduced coraimulene suggest that only tetralithio-1 exists as a dimer while the other observed species - from monoanion radicals to trianion radicals - exist as monomers in ether solutions. Interestingly, octalithio-59 (two tetranions tethered by an octamethylene chain) was found to... 

Paradoxically, although they are electron-rich, S-N compounds are good electron acceptors because the lowest unoccupied molecular orbitals (LUMOs) are low-lying relative to those in the analogous carbon systems. For example, the ten r-electron [SsNs] anion undergoes a two-electron electrochemical reduction to form the trianion [SsNs] whereas benzene, the aromatic hydrocarbon analogue of [SsNs], forms the monoanion radical [CeHg] upon reduction. ... 

Oxidaton of heme goes through the biliverdin species. Octaethylbiliverdin can exist in coordinated form as the fully reduced trianion (OEB)3-, as the two-electron-oxidized monoanion (OEBox), or as the one-electron-oxidized radical (OEB-)2-. Nickel forms complexes with all three moieties, [Nin(OEB)]ra with n I 1, 0, and -1 (689).1787 The most highly oxidized species [Ni(OEBox)]I3 could be crystallized. The structure shows a helical coordination of the linear tetrapyrrole ligand around nickel with Ni—N distances of 1.867 A and 1.879 A. 

Fig. 22. ESR spectra of the radical anion, dianion and radical trianion of 2.4.6-triphenyl- -phosphorin...

A third electron is then transferred from the contact with the K—Na alloy, forming the paramagnetic radical trianion 67. The phosphorus coupling constant in 67 of dp = 4,6 was calculated from the ESR spectmm of 2.4.6-tris-pentadeutero-phenyl-X -phosphorin. 

If a solution of the radical trianion <57 (prepared by the K/Na method) is titrated with a solution of the X -phosphorin 22, then upon addition of one aliquot of 22 to 2 aliquots of 67 no ESR signal can be seen (formation of the dianion 66). Continuation of the titration results in the appearance of an ESR signal due to the radical anion 65 (flp = 32,4 Gauss), which reaches maximum intensity after addition of one equivalent of 22. 

Of course, in all of these experiments sealed, high-vacuum glass systems with complete exclusion of air and moisture have to be employed. Under such conditions the results are easily reproducible the radical ions themselves are indeed very stable. The radical mono-anion 65 is best prepared by first reducing all the way to the radical trianion 67, and then adding the double amount of starting solution of 2.4.6-triphenyl-X -phosphorin. 

Tri-tert-butyl-X -phosphorin 24 in THF could not be reduced to a radical trianion with K/Na. Only the doublet of the radical monoanion can be seen in the ESR spectrum (Cp = 27,8 Gauss). Good resolution of the hyperfme structure of the signals was not obtained. 

X -phosphorins have physical properties which are rather similar to those of pyridines. But the chemistry of X -phosphorins is very different, due mainly to the phosphorus atom which can easily lose one electron to produce a stable radical cation, or accept one or more electrons to yield a radical anion, dianion or radical trianion. Nucleophiles add to stable X -phosphorin anions. In contrast to pyridine chemistry, no stable X -phosphorinium compound (corresponding to a N-alkyl-pyridinium salt) could be isolated. Instead the electron shell of phosphorus is enlarged by addition of an electrophile yielding a X -phosphorine derivative. 

Synthesis of the closely related acyclic (19) and macrocyclic (20) polyradicals has recently been reported (Figure 5.1).1231 The -conjugated carbanions (e.g., the calix[4]-arene-based tetraanion and the related calix[3]arene-based trianion) were synthesized and studied.1241 Oxidation of these tetra- and tri-anions gave the corresponding tetra- and tri-radicals, respectively. It has been shown in closely related systems that it is not the shape or overall geometric symmetry of the molecules, but rather it is the juxtaposition of the carbenic centers within the jt-cross-conjugated structure, that is most important in determining the spin multiplicity of the alternant hydrocarbon molecule.1251... 

The first stage of this unusual reaction involves debenzylation of the substrate to form 2-aminobenzimidazole polyaniones. The formation of 2,2 -azobenzimida-zolone is the result of autooxidation of 2-aminobenzimidazole di- and trianiones, when 2-nitrobenzimidazole is formed on oxidizing of radical anions [660]. 

The electrochemical reduction process of 1-methyl-3,5-dinitro-l, , 4-triazole is unusually proceeded ESR spectrum of its radical trianion in acetonitrile is identified [853] (Scheme 3.20). 

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