The Pentafluorophenyl Group

Fluorine NMR data for a few representative examples of pentafluorophenyl compounds are given as follows, along with typical F-F coupling constants (Table 6.2).5 

It can be seen that electron-donating groups generally shield, and electron-withdrawing substituents generally deshield all of the fluorine 

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Tnmethylpentafluorophenylsilane reacts with ketones in the presence of cyamde ion to form the silyl eiher denved from the alkoxide created by the addition of the pentafluorophenyl amon to the carbonyl carbon [89] The nucleofugal character of the pentafluorophenyl group is significantly greater than that of the added cyamde ion so that the addihon proceeds under nearly neutral condmons (equation 73)... 

Pentafluorophenylcopper is representative of a series of fluori-nated organocopper compounds that are highly soluble in organic solvents, more thermally stable than their hydrocarbon analogs, and useful as synthetic intermediates. " Pentafluorophenylcopper has been used to introduce the pentafluorophenyl groups and as a reagent for an improved Ullman diphenyl ether synthesis. It is... 

The pentafluorophenyl group imparts greater crystallinity to the complexes and as a result many complexes have been studied by X-ray crystallography. Although vith other metal centers C Fs-CaFs or CfiFs-CfiHs n-n stacking interactions are observed [21, 22], there are not many examples in gold chemistry and they have been sho vn very recently [23]. 

The trinudear complex [Au3(p-triphos)(QF5)3] [97] in dichloromethane shows an absorption around 270 nm and in the solid state at room temperature the complex does not emit, even using an excitation frequency below 300 nm. At lower temperature (77 K) the complex emits with a maximum at 450 nm. Thus luminescence properties can be dramatically influenced by the pentafluorophenyl group which indicates its important contribution to the energy levels involved in the electronic transitions. 

The trinuclear complex [(Au2S2CNR2)] (PPh2)3CH Au(C6F5)] [102] (Figure 3.10) has an IR spectra that confirms the presence of the pentafluorophenyl group bonded to the Au(I) atom. The P H NMR spectrum shows a doublet at 43.6 ppm and a triplet at 41.2 ppm while the F H NMR spectrum shows the typical pattern for the pentafluorophenyl group bonded to the Au(I) atom. 

REAGENTS FOR THE INTRODUCTION OF THE PENTAFLUOROPHENYL GROUP INTO ORGANIC COMPOUNDS... 

The Pentafluorophenyl Group. Fluorine NMR chemical shifts for ortho, meta, and para fluorines can vary considerably (see Chapter 6 for more complete details). Scheme 3.59 provides data for one example, that of pentafluorotoluene. 

The pentafluorophenyl-group has an electronegativity value which has been estimated as being between that of chlorine and bromine so- 2). As would be expected, 3-pentafluorophenyltrifluorobenzyne (9) reacts with benzene to form the 1,4-cycloadduct in good yield 63>. 

The oxime nitrogen can also participate in cycloamination reactions to give pyrroles. Thus, treatment of oxime esters such as 185 with Pd(Ph3P)4 readily affords 186 [129]. The pentafluorophenyl group is necessary for good results otherwise a Beckmann rearrangement can unfavorably enter the picture. The oxime stereochemistry makes no difference on the outcome of the reaction. In addition to 186, pyrroles 187 and 188 were also prepared in this study (among others) [129]. 

Bis[l,2-phenylenebis(dimethylarsine)]gold(I) bis(pentafluorophenyl)aurate(I) is a white crystalline solid that melts at 178°C. It is soluble in acetone and dichloromethane, slightly soluble in diethyl ether, and insoluble in hexane. Its IR spectrum shows, along with those due to the pentafluorophenyl group (see Section B), strong absorptions at 745,590,435,365, and 350 cm "1 arising from the bis(arsine). In the cation the bis(arsine) acts as a chelate and therefore the cation contains a tetrahedral four-coordinated gold(I) atom.9... 

The Pentafluorophenyl Group Effects on Reactivity of Organic Compounds ... 

Finally, hydrazine reduction of [AuCl(C6F5)2(PPh3)] yields (255) [Au(C6F5)(PPh3)], and it was found in general that elimination of chloride occurs more readily upon reduction than loss of the pentafluorophenyl group does. 

In order to test the coordinative ability of the free sulfur atom of [Au3( ji-S2 C. Me2)2 p3-(PPh2)3CH CIO, it was treated with [Au(C6F5)(tht)]. However, this reaction, instead of promoting coordination of the new metallic center to the sulfur, results in the precipitation of gold(I) dimethyldithiocarbamate and the coordination of the pentafluorophenyl group to the gold center previously bonded to S2CNMe2, as shown in Eq. (36).123... 

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