Naphthalene cation salt

Eberson and Radner (19-23) have explored some of the scope of the reaction of N02 with ArH +. They prepared the solid hexafluorophosphates of the naphthalene cation radical and some methylnaphthalene cation radicals, for example, C10H8,+PF6, and carried out reactions of the solid salts with N02 in dichloromethane at temperatures near-25 °C (19-23). Reaction was found to occur according to equation 12. The results of their reactions are summarized in Table I (19). This table also lists the results of nitrating the parent hydrocarbons by the conventional route (N02 + ) and with N204. The results prompted Eberson and Radner to dismiss the possibility that conventional nitration of these compounds was preceded by electron transfer (equations 11 and 12), because the proportions of isomers from the reaction of ArH + with N02 were quite different from those from the reactions of ArH with N02+ and with N204. Eberson and Radner set out to determine whether or not the conventional nitration of naphthalene and methylnaph-thalenes involved the electron-transfer step. In so doing they became, to our knowledge, the first to show that a neutral radical (N02) will react with an aromatic cation radical. 

The stability of radical-cation salts varies from rapid decomposition in air (e.g., naphthalene salts) to stability for several months under ambient conditions (e.g., perylene and decacyclene salts). The stability correlates with the oxidation potential As a rule of thumb, salts of extendend aromatic systems are more stable than those of smaller ones, and salts of the ideal 2 1 composition are more stable than those of other compositions. 

As it was first shown on naphthalene radical cation salts of various aromatic hydrocarbons can be prepared by anodic oxydation and subsequent crystallization in solvents like methylenechloride, chlorobenzene, 1,1,2-trichloroethane or THF if an electrolyte like NR4X with suitable anions X is present (R n-hutyl X BF4, C104, PF5 , AsF6% SbF6, ...) l... 

Another view has recently been proposed by Wegner.Naphthalene and other simple aromarics can be oxidize electrochemi-cally to form monomelic radial cat n salts (Ar. X ) which have conductivities of 10 to 10 s/cm. The crystal structures of these reveal that the aromatic moieties form stacks, along which the charges and the electrons are presumably delocalized. The structure is formally analogous to that deduced for oxidized (doped) polyacetylene in which the polyene chains are arranged in stacks. This leads to the idea that intermolecular delocalization is the important feature which leads to high conductivity. Other data are consistent with this rationale. Biphenyl and terphenyl radical cation salts have crystal structures very similar to that of oxidized (doped) poly(p-phenylene lO). In the older literature oligoanilines (26) are reported upon iodine treatment to yield conductivities up to 1 s/cm the aniline moieties are stacked in these materials as well. Poly(N-vinyl-carbazole) (27) forms radical cation structures by oxidation with... 

The room temperature conductivity of polycrystalline samples of the naphthalene cation radical salts lies between 0.1 and 1 (Q cm) . Single crystals measured along the stack direction show a conductivity of several 100 (Q cm) depending on the quality of the crystals and to some extent on the nature of the counterions, solvent inclusion etc. The naphthalin cation radical salts can be stored for sometime at room temperature, if moisture is excluded. The corresponding radical ion complexes of perylene, pyrene, fluoranthene, and other arenes of higher number of fused rings exhibit a much greater stability and can be handled under normal laboratory conditions. 

The X-ray crystal structures of the two isomeric naphthalene cations 107 and 108 as PF6 salts have been determined, and represent the first reported X-ray structures of [Fe(naphthalene)Cp] cations. 

Salts of diazonium ions with certain arenesulfonate ions also have a relatively high stability in the solid state. They are also used for inhibiting the decomposition of diazonium ions in solution. The most recent experimental data (Roller and Zollinger, 1970 Kampar et al., 1977) point to the formation of molecular complexes of the diazonium ions with the arenesulfonates rather than to diazosulfonates (ArN2 —0S02Ar ) as previously thought. For a diazonium ion in acetic acid/water (4 1) solutions of naphthalene derivatives, the complex equilibrium constants are found to increase in the order naphthalene < 1-methylnaphthalene < naphthalene-1-sulfonic acid < 1-naphthylmethanesulfonic acid. The sequence reflects the combined effects of the electron donor properties of these compounds and the Coulomb attraction between the diazonium cation and the sulfonate anions (where present). Arenediazonium salt solutions are also stabilized by crown ethers (see Sec. 11.2). 

Nitration can be catalyzed by lanthanide salts. For example, the nitration of benzene, toluene, and naphthalene by aqueous nitric acid proceeds in good yield in the presence of Yb(03SCF3)3.5 The catalysis presumably results from an oxyphilic interaction of nitrate ion with the cation, which generates or transfers the N02+ ion.6 This catalytic procedure uses a stoichiometric amount of nitric acid and avoids the excess strong acidity associated with conventional nitration conditions. 

The authors proposed the following picture of the silylene anion-radical formation. Treatment of the starting material by the naphthalene anion-radical salt with lithium or sodium (the metals are denoted here as M) results in two-electron reduction of >Si=Si< bond with the formation of >SiM—MSi< intermediate. The existence of this intermediate was experimentally proven. The crown ether removes the alkali cation, leaving behind the >Si - Si< counterpart. This sharply increases electrostatic repulsion within the silicon-silicon bond and generates the driving force for its dissociation. In a control experiment, with the alkali cation inserted into the crown ether, >Si — Si< species does dissociate into two [>Si ] particles. 

A similar situation is observed in the case of the cation-radical derived from dimethylhexa-phenyl diphosphafnlveninm dication as a resnlt of redaction of the latter by the sodinm salt of the naphthalene anion-radical (Biaso et al. 2006). According to ESR, x-ray experimental data, and results of DFT calculations, the diphosphafnlveninm cation-radical detains the excess electron density within the exocyclic double bond (see Scheme 3.41). Stabilization is gained by conjngation with the two pentavalent phosphorus atoms. Biaso et al. (2006) rationalize the electronic strnctnre throngh two valence-isomeric fluidic forms of the distonic type. 

A few examples in which aromatic cation radicals have been isolated as crystalline salts, actually consist of mixed valence units. For example, crystal structure analysis showed that the naphthalene radical cation (NAP) + forms a mixed valence dimer (NAPy4 in which the two components are arranged face to face in n-stacks with an interplanar separation significantly closer than van der Waals contacts. Such an intermolecular organization arises from the sponta-... 

The only competing reaction in interactions of 2-benzopyrylium salts with active methylene compounds is the formation of naphthalene 229, which is constructed with participation of the 1-methyl group of the ben-zo[c]pyrylium cation (90KGS315). 

The platinum-catalysed intramolecular domino annulation reaction of o-alkynylben-zaldehydes has been described as a versatile approach to naphthalenes with annulated carbocycles or heterocycles of various sizes (Scheme 32).94 A plausible mechanism for the platinum(II)-catalysed annulation reaction shows that the double annulation process most probably proceeds through the benzopyrylium cation (117), which results from the nucleophilic attack of the carbonyl oxygen at the alkyne, activated by the Lewis-acidic platinum salt. A subsequent intramolecular Huisgen-type 3 + 2-cycloaddition of the second alkyne is assumed to generate intermediate (118). Rearrangement to (119) and the formal 4 + 2-cycloaddition product (118) leads to the aromatized final (116), liberating the active catalyst. In the case of FeCl3 as the Lewis acid, we assume that intermediate (118) is oxidatively transformed to (121). 

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