Aromatic with hexafluorobenzene

The reaction of the carbanion derived from diethyl methylphosphonate with perhalogenated aromatics may result in substitution of halide to yield perhaloaryl(hetaryl)methylphosphonates, which can be converted into tris- or bis-(perhaloaryl)methanes. Displacement of fluoride ion has been reported in the reaction of dimethoxycarbene with l-fluoro-2,4-dinitrobenzene and with hexafluorobenzene. The hydrodehalogenation of halogenated aryl ketones may be facilitated using hydrogen over a Pt/C catalyst. " ... 

Compound 311 formed stoichiometric co-crystals with perfuorinated aromatic molecules, hexafluorobenzene (BzF) and octafluoronaphthalene (NpF), by intermolecular Ar-ArF interactions, and 311 showed photochromic reactivity in the co-crystals as well as in the one-component crystal of 311. 

Anionic metal complexes can replace a fluorine in an aromatic substrate by nucleophilic aromatic substitution. King showed as early as 1964 that [Fe( 7 -G5H5)(CO)2] reacts with hexafluorobenzene to furnish [Fe( 7 -C5H5)(C6F5)(C0)2] (Scheme 9) Examples of nucleophilic attack may be disguised for instance, an anionic metal complex is formed m situ in the base-promoted reaction of [Rh(77 -C5Me5)(H)2(PMe3)]. ... 

Fluorinations of polyfluorobiphenyls with cobalt trifluoride (see Scheme 4), hexafluorobenzene with cobalt trifluoride ( cycIo-CeFi2, cyclo-CsFio at 100— 106 °C -t-cyclo-CsFio, perfluorocyclohexa-1,4-diene at 50 °C in the presence of CaClz), polynuclear aromatics with potassium tetrafluorocobaltate(iii) [e.g. (see also p. 57) pyrene - perfluoroperhydropyrene at 360—410 °C, decafluoro-... 

The most common types of aryl halides m nucleophilic aromatic substitutions are those that bear o ox p nitro substituents Among other classes of reactive aryl halides a few merit special consideration One class includes highly fluormated aromatic compounds such as hexafluorobenzene which undergoes substitution of one of its fluorines on reac tion with nucleophiles such as sodium methoxide... 

An interesting variant in which nucleophilic aromatic substitution is carried out on the crown nucleus rather than using the crown as nucleophile was reported by Haines . In this approach, hexafluorobenzene was stirred in 1,2-dimethoxyethane at room temperature with pentaethylene glycol and sodium hydride. A double nucleophilic aromatic substitution occurred affording 2, 3, 4 ,5 -tetrafluorobenzo-15-crown-5 as an oil in 38% yield. The reaction is illustrated below. 

The para-fluorine atoms on highly fluorinated aromatic compounds such as hexafluorobenzene or decafluorobiphenyl are activated and thus can go through aromatic nucleophilic substitution with bisphenols in an aprotic solvent at low temperatures (<80°C).121 123... 

A second fluorine substituent shields in the ortho- and especially in the para-position, but one in the meta-position deshields, with 1,3-5-trifluorobenzene having the most deshielded fluorines in a polyfluoro-aromatic system (Scheme 3.58). On the other hand, hexafluorobenzene has highly shielded fluorines. The fluorine spectra of these multifluoro-benzenes are second order in nature and their appearance is thus not generally predicable on the basis of first-order logic. 

One of us has used molecular polarization potentials (MPP) to study the interaction of aromatic molecules, including furan, thiophene, and pyridine with a positive unitary charge, these maps being powerful tools for the study of intermolecular interactions and chemical reactivity [129,130], This kind of study leads us to examine theoretically the problem of the interaction between cations and anions with aromatic rings. We were pioneers in proposing that, in parallel with cation-7i-systems (for instance, benzene), there should exists anion-perfhiorinated-7i-systems (for instance, hexafluorobenzene) [131]. These studies include tetrafluorofuran and tetrafluorothiophene (128, 129). Simultaneously, Mascal et al. [132] described the same phenomenon but with 1,3,5-triazine (130) and 2,4,6-trifluoro-l,3,5-triazine (131) as acid 7i-systems. The group of the University of Palma de Mallorca has published a large number of papers on this topic [133] that are well summarized in a two recent reviews [134,135],... 

Fluoro-substituted annotated five-membered heterocycles are available via stepwise nucleophilic displacement reactions of perfluorinated or polyfluorinated aromatic compounds by 1,3-dinucleophiles. On reaction of hexafluorobenzene with the sodium salt of ethyl acetoacetate the 3-ethoxycarbonyl-2-methylcumarone is formed [64DOK( 158)926 69KGS778] (Scheme 29). 

Binary mixtures of benzene, 1,3,5-trifluorobenzene and hexafluorobenzene with ( jiTiim 11 PI G1 were modeled with MD simulations [122], The local ordering of the ions at an aromatic molecule was found to depend on the quadrupole moment of the aromatic species and to remain qualitatively the same on varying the mole fraction of the aromatic species. Interaction energies showed the most significant interactions to be between the aromatic molecule and the ions located at its equator [122],... 

Nucleophilic aromatic substitution of activated substrates (pentafluoropyridine, octafluorotoluene, hexafluorobenzene, metal arene jc-complexes) by anions of diethyl cyanomethylphosphonate has been achieved. The reaction is carried out with satisfactory yields in DMF, MeCN, or THF at room temperature in the presence of NaH, CsF, KjtX), or CS2CO3." In a similar manner, 3,6-dihalopyridazines react with sodium diethyl cyanomethylphosphonate in refluxing THF to give phosphonosubstituted pyridazines in 22-68% yields. ... 

Even if no —M electron-withdrawing substituents are present, however, aromatic fluorine can be replaced. The ease of this replacement increases with the degree of fluorination. Perfluoroaromatic compounds such as hexafluorobenzene or pentafluoropyridine are especially highly reactive toward a variety of nucleophiles (Scheme 2.40). 

This reaction pathway is usually favoured when an aromatic moiety and an alkene bear electron-withdrawing and electron-donating substituents, respectively (or vice versa). This addition involves a charge transfer and the course of the reaction is sensitive to the solvent polarity. Such a mechanism may resemble that of [2 + 2] photocycloaddition of alkenes to aji-unsaturated carbonyl compounds (Section 6.3.2). Scheme 6.81 shows examples of two intermolecular processes and one intramolecular [2 + 2] photocycloaddition reaction (a) crotononitrile (196) is added to anisole (197) to yield several stereoisomers of 198 in 38% chemical yield and with high regioselectivity, which is linked to bond polarization in the exciplex 818 (b) hexafluorobenzene (199) reacts with 1-ethynylbenzene (200) to form the bicyclo[4.2.0]octa-2,4,7-triene 201 in 86% yield 819 and (c) irradiation of 202 in methanol leads to the single photoproduct 203. 820... 

Perfluoroalkylation of arenes makes the aromatic ring electron deficient and thus it interacts with electron-rich arenes and Lewis bases. Figure 1.9 shows the TT-electron distribution on the hexafluorobenzene and benzene ring. Most of the TT-electrons in hexafluorobenzene are withdrawn from the aromatic ring by fluorine atoms to make the aromatic ring highly electron deficient, while the —-electrons in benzene are localized inside the ring. Thus both the benzenes interact attractively in a face-to-face manner [1]. 

Fluorocarbon compounds were radiolyzed to establish the existence and assess the role of valence tautomers in radiation chemistry. Dewar-octafluorotoluene and -decafluo-roxylene have been isolated and identified as products of the photolysis and radiolysis of their respective aromatic parent in condensed phase. Dewar hexafluorobenzene was irradiated to 10 Mrad doses and found to revert to its KekulS isomer with a G-value of 10, to polymerize with G 20, and, in addition, to give rise to a new isomer. The concept of an energy sink is introduced whereby part of the energy absorbed by an aromatic system is stored in the form of interconvertible valence isomers which react further to yield polymers or decay to the ground state. 

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