Dianions arenes

The delocalised radical formed by protonation of the radical-anion is more easily reduced than the starting arene. For some polycyclic aromatic hydrocarbons, the redox potential for this radical species can be determined using a cyclic voltammetry technique [10]. Reduction in dimethylformamide is carried out to the potential for formation of the dianion. The dianion undergoes rapid monoprotonation and on the reverse sweep at a fast scan rate, oxidation of the monoanion to the radical can be observed. The radical intermediate from pyrene has E° = -1.15 V vs. see in dimethylformamide compared to E° = -2.13 V vs. see for pyrene,... 

H and C NMR spectra were applied to elucidate the electronic structure of the dianions in the dilithium arene compounds formed with anthracene, phenanthrene and 1,2,3,4-dibenzocyclooctatetraene (115). Although the three dianions have 16- 7r isoelec-tronic systems, the former two differ due to their charge distributiou, and 115 due to the steric strain in the cyclooctane ring, interfering with a coplanar configuration... 

Since different reactivity is observed for both the stoichiometric and the catalytic version of the arene-promoted lithiation, different species should be involved in the electron-transfer process from the metal to the organic substrate. It has been well-established that in the case of the stoichiometric version an arene-radical anion [lithium naph-thalenide (LiCioHg) or lithium di-ferf-butylbiphenylide (LiDTBB) for using naphthalene or 4,4 -di-ferf-butylbiphenyl (DTBB) as arenes, respectively] is responsible for the reduction of the substrate, for instance for the transformation of an alkyl halide into an alkyllithium . For the catalytic process, using naphthalene as the arene, an arene-dianion 2 has been proposed which is formed by overreduction of the corresponding radical-anion 1 (Scheme 1). Actually, the dianionic species 2 has been prepared by a completely different approach, namely by double deprotonation of 1,4-dihydronaphthalene, and its X-ray structure determined as its complex with two molecules of N,N,N N tetramethylethylenediamine (TMEDA). ... 

Herrera, R. P. Guijarro, A. Yus, M. Primary alkyl fluorides as regioselective alkylating reagents of lithium arene dianions. Easy prediction of regioselectivity by MO calculations on the dianion. Tetrahedron Lett. 2003, 44, 1313-1316. 

There is indirect evidence that in solution (see below) the 1,3-alternate conformer is in equilibrium with a cone conformer of idealized C4 symmetry (Fig. 15, a). The tetramer of Fig. 14 can be considered to be a metal analogue of a calix[4]arene [24], and this analogy includes also the propensity of this compound to coordinate metal ions. In fact, after further deprotonation of UrH- to the dianion Ur2-, the complex binds additional divalent cations to yield octanuclear species, [ (en)PtnM(Ur2, N(1),N(3),0(2), 0(4)) 4f+ with M = ds-(NH3)2Ptn, (en)Pt11, (H20)3Nin, (en)Pd11, and Cu11. The nitrate salts of these cations were isolated and the stmctures of the first... 

Partial oxidation of C2S4 proceeds with loss of sulfur and coupling to give the vinylidene dithiolate derivative of dmit2-. This planar dianion C4S62 is isolated as its blue-purple ELtN"1" salt (130). Treatment of this salt with metal halides affords di- and polymeric complexes, for example, [C4S6][RuCl(arene)]2 and the semiconducting [NK Seln (134) (Eq. 11). 

Subvalent germanium complexes combined with a dianionic calixarene ligand have been found. The reaction of / -tert-butylcalix[4] arene with MesSil in the presence of pyridine provides a useful synthetic route for [Butcalix ]H2. 

Lithium arene radical anions and dianions, [ArH2] Li and [ArH] 2 Li", can react with acidic hydrocarbons , alkyl halides or alkyl sulfides to form organolithiums via electron transfers. 

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