Aromatics, radical cation salts

The range of salts has been extended since the preliminary report. Utilization of the low-melting solvent SO2CIF has improved yields and provided access to less thermally stable perfluoro aromatic radical cation salts. Less powerful oxidizers than O2 salts are needed for the synthesis of CiqFs and polycyclic cation salts which have much higher thermal stability than their monocyclic relatives. The preparation and characterization of monocation salts derived from C P , QPs Cp3, and CioFg is reported here. The preparation and some properties of the pen-tafluoropyridine radical cation salts have been described elsewhere. ... 

Syathesis of Perfluoro Aromatic Radical Cation Salts. Hexafluoro-benzeae Hexafluoroiridate(V). Hexafluorobenzene (2.6 mmol) was dissolved in tungsten hexafluoride (2 mL) in a fused silica reactor to give a yellow-green solution. Iridium hexafluoride (2 mmol) was condensed into the reactor at 77 K. At about 273 K, the reaction mixture melted, and a bright orange solid rose to the surface of the WFg. The solvent and excess CgF were removed under vacuum at 298 K. The dry orange solid decomposed rapidly, producing volatile carbon fluorides. Some of the iridium was reduced to the metal. 

Three studies on radical cations discuss the characterization of polynuclear aromatic radical cation salts as organic metals (8), the reactions of cation radicals with neutral radicals (9), and the magnetic-electrical properties of perfluoroaromatic radical-cation salts (10). Chapters on polynuclear aromatic compounds in nonvolatile petroleum products (II) and in coal-based materials (12) present reviews of the subject and new findings. The remaining chapters in this book discuss the thermal conversion of polynuclear aromatic compounds to carbon (13), the nitration of pyrene by mixtures of N02 and N204 (14), the spectra, structures, and chromatographic retention times of large polycyclic aromatic hydrocarbons (15), the desulfurization of polynuclear thiophenes correlated with tt electron densities (16) and simple theoretical methods to predict and correlate polynuclear benzenoid aromatic hydrocarbon reactivities (IT). 

Particular attention has been given to the products of thermal decomposition of the radical cation salts and the products of F" attack, since the sets of products are related. Salts of the single-ring aromatics are thermally unstable at room temperature but can be kept below 258 K. Their thermal decomposition gives an equimolecular mixture of the parent fluoro aromatic and a perfluorocyclohexadtene. The initial dtene product is a specific isomer. This provides clean high-yield syntheses for those dienes and provides insight into the reaction mechanisms. 

AsFs or ReF , although not particularly powerful oxidizers, will generate radical cation salts from any of the multiring perfluoro (or perhydro) aromatics. 

In the case of the perfluorotoluene cation salts, both F attack and pyrolysis again yield half a mole of the parent fluoro aromatic molecule and half a mole of diene. But now the diene is wholly the 1,3-diene. These findings are essentially the same as those for the perfluoropyridine radical cation salts,where attack and pyrolysis produce half a mole each of C5NF5 and 1,3-C5NF7. With representation of the more electronegative centers (C CF3 and N) by E, the interaction is... 

The possibility of preparing radical-cation salts of these nonplanar aromatic compounds is an interesting prospect. Many of these compounds contain pyrene and perylene substructures, both of which form well-defined salts when the procedures outlined and reviewed in the chapter by Enkel-mann (8) are used. However, the morphologies of crystals of radical-cation salts derived from the nonplanar compounds are difficult to envisage. Consequently, one cannot be certain that the resulting salts will have useful conducting properties. 

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. 

RADICAL CATION SALTS OF SIMPLE AROMATICS -A FAMILY OF ORGANIC METALS... 

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... 

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