Pentafluorophenyl rings

Perfluorinated compounds with a terminal C = C bond or internal C = C bond conjugated with the pentafluorophenyl ring react with an equimolar quantity of vanadiumf V) fluoride at - 20 C by adding fluorine atoms exclusively to the alkene bonds. 

Although none of them have been structurally characterized by X-ray diffraction, no intramolecular Au- -Au interaction is expected in these species because of the presence of a large number of pentafluorophenyl rings in each anion. Thus, in the crystal structure of the trinuclear starting methanide, which is less hindered, the shortest intramolecular Au- -Au separation is 6.10 A.90... 

Recently, Jen and coworkers developed a new class of molecular glasses based on the reversible self-assembly of aromatic/perfluoroaromatic (Ar-ArF) dendron-sub-stituted nonlinear high-p/i chromophores [156]. In these molecules (Fig. 4.27), both phenyl and pentafluorophenyl rings are incorporated as peripheral dendrons on the re-bridge and the donor-end of the chromophores Cl, C2, and C3. 

Au is linearly co-ordinated. Phenyl and pentafluorophenyl rings are planar... 

Fig. 30 CPK representation of the single-crystal X-ray structure of the pentafluorophenyl receptor. The receptor adopts in the solid-state a conformation that is adequate to interact simultaneously through hydrogen-bonding (sulfonamide NH) and anion-jt interaction with an halide located on top of the pentafluorophenyl ring...

Half-sandwich complexes of cobalt with intramolecular phosphorous coordination have been known for the cobalt atoms in oxidation state - -l and - -ll (see Sections 7.01.3.3 and 7.01.3.4). Butenschon has published a comprehensive review recently on cyclopentadienyl metal complexes bearing pendant phosphorous arsenic and sulphur ligands. Intramolecular coordination to the cobalt center via a substituted Cp ring also oecurred in a rare reaction which combined C-H and C-F activation at the same time, thus leading to the coupling between a pentafluorophenyl ring and a pentamethylcyclopentadienyl ring (see Scheme 10 above). 

The formation of ethyl cyano(pentafluorophenyl)acetate illustrates the intermolecular nucleophilic displacement of fluoride ion from an aromatic ring by a stabilized carbanion. The reaction proceeds readily as a result of the activation imparted by the electron-withdrawing fluorine atoms. The selective hydrolysis of a cyano ester to a nitrile has been described. (Pentafluorophenyl)acetonitrile has also been prepared by cyanide displacement on (pentafluorophenyl)methyl halides. However, this direct displacement is always aecompanied by an undesirable side reaetion to yield 15-20% of 2,3-bis(pentafluoro-phenyl)propionitrile. 

A key step in the synthesis of 13-membered meta ansa and 14-membered para ansa peptide alkaloids involves catalytic hydrogenolysis of carbobenzyl-oxypeptide pentafluorophenyl esters. The most suitable solvent is dioxane with addition of a catalytic amount of pyrrolidinopyridine and 2% ethanol. Temperature should not exceed 90°C. The authors believe that after deblocking, the amino function remains on the surface until ring formation with the activated carboxylic function is accomplished (/5/). 

Whereas the production of arylnitrenes by the deoxygenation of nitrosobenzenes or nitro-benzenes by trivalent phosphorus reagents and their subsequent intramolecular ring expansion to 3//-azepines are well-known processes, the corresponding intermolecular reactions to form 1//-azepines have been exploited only on rare occasions and appear to be of little preparative value. For example, the highly electrophilic pentafluorophenylnitrene, obtained by deoxygenation of pentafluoronitrosobenzene with triethyl phosphite in benzene solution, produced a low yield (2-10%) of l-(pentafluorophenyl)-l//-azepine, which was isolated as its [4 + 2] cycloadduct with ethenetetracarbonitrile.169 With anisole as the substrate l-(pentafluorophenyl)-l//-azepin-2(3//)-one (16% bp 128 —130 C/0.4 Torr) was obtained. 

The pentacyclic core 15 of more complicated manzamines was built up by a final ring closure of the thirteen-membered ring lactam in 50% yield. The tetracyclic system and the alkyne unit of the reactant 13 supposed a pre-orientation, an intermediately formed activated pentafluorophenyl ester 14 led to the desired... 

Magnetic nonequivalence is not uncommon, often deriving from the constraints of a ring, as in pentafluorophenyl derivatives or other symmetrically fluorine substituted ring systems such as those shown in Scheme 2.10. The fluorine and proton NMR spectra of 1,2-difluoroben-zene are both representative of the appearance of second order spectra of polyfluoroaromatics. They can be found in Chapter 3, Section 3.9.3. 

Homolytic ring opening of thietanes also resulted from reaction with pentafluorophenyl radicals, which were generated by photolysis of C Fj in the presence of Mc3SnSnMe3. 

Tris(pentafluorophenyl)boron [(CgF5)3B], a triarylboron bearing electron-withdrawing perfluorinated phenyl rings, was found to be much more powerful than (05115)36 as a Lewis acid accelerator for the present polymerization. When (0565)36 was added at room temperature to the polymerization system at an equimolar ratio of (0565)36 to the growing species 2, the polymerization took place rapidly with considerable heat evolution, attaining 100% monomer conversion within only about 10 min [6ig. 13 ( )]. This polymerization was estimated to be 150-times faster than that in the absence of (0565)36, and 12.5-times faster than that with (05115)36 as a Lewis acid under similar conditions. 

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