Perfluoroarenes

Perfluoroarenes also undergo facile and selective monosubstitution with hydroxyl-amine. This reaction is general and proceeds with different Ai-alkylhydroxylamines and a number of perfluorinated arenes (e.g. 29, equation 19) and pentafluoropyridine. 

The elimination of only one fluorine of unsubstituted perfluoroarencs yielding monothiolated pentafluorobenzenes and heptafluoronaphthalenes is rather difficult to perforin. The reactivity of the respective perfluoroarenes is not very high and because of enhanced reactivity of fluorine in position 4 (benzene) or 6 (naphthalene) of the mono(alkylsulfanyl) compounds, the reaction tends to proceed further. When perfluorobenzene is reacted with the hydrosulfide anion, the pcrfluorobenzenethiolate anion formed is a very strong competitor to the hydrosulfidc anion ... 

Thiophene-perfluoroarene copolymers have been described (06JA2536). Absorptions in the range 334—360 were reported. 

Condensation of enamines with perfluoroarenes, such as perfluorobenzene, perfluor-otoluene, bromopentafluorobenzene and perfluoropyridine, leads after hydrolysis to the formation of a-perfluoroaryl ketones137. C-Arylation may be followed by intramolecular N-arylation thus leading to fluorinated tetrahydrocarbazoles (Scheme 51). The C-versus-N initial arylation ratio is very dependent on the amine moiety and was best for diethylamine enamines. 

Fluoride activation of Si-C bonds toward electrophiles has recently been exploited to synthesise alternating thiophene-perfluoroarene copolymers without using transition metal catalysis. This has the advantage of leading to products that are devoid of even traces of metal residues <2006JA2536>. Here the electrophiles are perfluoroarenes (ttF) the potential nucleophilic sites are the 2- and 5-positions of 3,4-dibutoxy-2,5-bis(trimethylsilyl)thiophene. The reaction is initiated with catalytic fluoride ion, which is regenerated with each C-C bond formed (Equation 106). 

C F bond activation is atttacting increasing interest in coimection with green chemistry. Perfluoroarenes are more reactive than the corresponding perfluoroalkanes, possibly because of the easier access to the C-F bond in CeFg versus C6F12. Photochemical routes are common as in equation (22). ... 

Similar structures have been observed for a variety of other arene-perfluoroarene complexes [15], indicating that this kind of interaction is a generally occurring phenomenon for this type of structure [18], Evidence based on structural [17] and spectroscopic data [19[, and on quantum chemical calculations [20] (Figure 1.8) indicates, that the observed arene-perfluoroarene interactions are mainly the consequence of strong quadrupolar electrostatic attraction [21]. 

The remarkably low reactivity of tetrafluoroparacyclophane (29) to Friedel-Crafts acylation in comparison with para-xylene indicates the deactivation of the nonfluorinated aromatic ring of 29 because of electron-deficiency due to a through-space polarization (Scheme 1.33) [26]. The tt-tt stacking interaction between arenes and perfluoroarenes has been employed for modification of the liquid crystals [27]. 

Perfluoroarenes were also found to be highly reactive coupling partners in intermolecular direct arylation [68, 69]. A wide range of aryl halides can be employed, including heterocycles such as pyridines, thiophenes, and quinolines. A fluorinated pyridine substrate may also be cross-coupled in high yield and it was also found that the site of arylation preferentially occurs adjacent to fluorine substituents when fewer fluorine atoms are present. Interestingly, the relative rates established from competition studies reveal that the rate of the direct arylation increases with the amount of fluorine substituents on the aromatic ring. In this way, it is inversely proportional to the arene nucleophilicity and therefore cannot arise from an electrophilic aromatic substitution type process (Scheme 7). 

Week, M. et al.. Influence of perfluoroarene-arene interactions on the phase behavior of... 

N-Arylation. Amines are perfluoroarylated with perfluoroarenes in THE The amino group is attached to the p-position in the reaction involving perfluorotoluene or pentafluoropyridine. Generally, primary amines are more reactive but secondary amines also undergo perfluoroarylation at a higher temperature and with added triethylamine. 

A few solvents exhibit intermediate properties. For example, both BTF (Ref. 22) and F-626 (Ref. 23 see Section 3.1) are able to dissolve appreciable quantities of both fluorous and non-fluorous solutes. Other solvents are often mistakenly assumed to be fluorous. Of these, the most important are perfluoroarenes such as hexafluo-robenzene. The arene tt clouds and sp carbon-fluorine bonds lead to significant intermolecular bond dipoles, induced dipoles and quadrupolar interactions with non-fluorous molecules. ... 

Coliings, J.C. Roscoe. K.P. Robins. E.G. Batsanov, A.S. Stimson. L.M. Howard, J.A.K. Clark, S.J. Marder. T.B. Arene-perfluoroarene interactions in crystal engineering 8 Structures of 1 1 complexes of hexafluorobenzene with fused-ring polyaromatic hydrocarbons. New J. Chem. 2002. 26. 1740-1746. 

Generation of perfluoroaryl radicals under mild conditions Perfluoroarenes... 

Figure 8,6 Monomer molecular orbital contour plots of the HOMO and LUMO orbitals of FTF, TFTFT and TFT. Reprinted with permission from S. E. Koh, B. Delley, J. E. Medvedeva, A. Facchetti, A. J. Freeman, T. J. Marks and M. A. Ratner, Quantum chemical analysis of electronic structure and n- and p-type charge transport in perfluoroarene-modified oligothiophene semiconductors, J. Phys. Chem. B, 110, 24361 24370 (2006), Copyright 2006 American Chemical Society...

A. Facchetti, M.-H. Yoon, C. L. Stem, H. E. Katz, T. J. Marks, Building blocks for n-type organic electronics regiochemicaUy modulated inversion of majority carrier sign in perfluoroarene-modified polythiophene semiconductors, Angew. Chem. Int. Ed., 42, 3900-3903 (2003). 

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