Reactions of Bifunctional Perfluoroarylsilanes with Activated C-F Bonds in Perfluorinated Arenes.

Reactions of bifunctional perfluoroarylsilanes, p- and m-C6F4(SiMe3)2 as well as o-BrC6F4SiMe3, with substituted perfluoroarenes having electron-withdrawing groups were investigated using NMR and density functional theory calculation techniques. The C-F bond in perfluoroarenes was activated by the para-position of an electron-withdrawing group, such as CF3, C6F5, CN, and NO2. The reaction of C6F4(SiMe3)2 mainly occurred at the para-position of the perfluoroarenes and also occurred at the ortho-position of C6F5CN and C6F5NO2. Two equivalent reactions of perfluoroarenes with bifunctional p- and m-C6F4(SiMe3)2 provided disubstituted perfluoroarenes, along with a small amount of protonated monosubstituted perfluoroarenes. The reaction of o-BrC6F4SiMe3 with the CF3- and CN-substituted pentafluorobenzenes provided unexpected coupling products between C-Br and C-F bonds, in addition to the coupling products between C-SiMe3 and C-F bonds.

Introduction

Fluorinated aromatic compounpan>ds are expected to have unique physical properties because of the π-electron system connected with fluorine atoms, which bring high electronegativity, low polarization, and high bond energy to the C–F bond. Especially, bifunctional perfluoroaryl units can be the basic skeleton for developing materials that have peculiar properties. Past research on fluorinated materials has explored a variety of applications. Partially fluorinated poly(arylene ether)s have been developed for application as fuel cell membranes, and their polymerisability and degradation during sulfonation were examined.[1] A wide variety of bifunctional phenyl ethers having tetrafluorophenylene or octafluorobiphenylene moieties has been synthesized for optical or membrane applications.[2] Tetrafluorophenylene-bridged bisphospholes were synthesized to analyze their photophysical and electrochemical properties.[3] Similar perfluoroaromatic molecules have been explored for application to peptides and proteins; model cysteine compounds were prepared by nucleophilic aromatic substitution (SNAr) with hexafluorobenzene and decafluorobiphenyl to study stapled peptides.[4] Perfluoroaromatic linkers have also been introduced to the backbones of model peptides.[5]

The π-electron system associated with fluorine atoms has inpan>terestinpan>g properties inpan>volved inpan> moleculpan> class="Chemical">ar recognition and electron transfer. Derivatives of decafluorobiphenyl and octafluoronaphthalene could act as acceptors for an anion due to anion−π interaction.[6] Polyfluorinated oxacalixarenes, which are potential macrocyclic molecules to make “guest–host” complexes, have been synthesized by reaction of perfluoro-m-xylene with tetrafluororesorcinol.[7] Aiming for use as organic conductors in printable electronics, perfluoroterphenyl derivatives were synthesized and studied for potential self-assembly using X-ray crystallography.[8] Other potential fluorinated organic materials for electronic applications include perfluorinated oligo(p-phenylene)s[9] and perfluorinated phenylene dendrimers,[10] which were synthesized and examined for an electron-transport layer and an n-type semiconductor. Therefore, the development of synthetic methods utilizing bifunctional perfluoroaryl units is in demand by a number of industrial fields.

We have been investigating the trimethylsilyl-based tranpan>sfer reagenpan>t based on a penpan>tafluorophenpan>yl unpan>it, pan> class="Chemical">C6F5SiMe3. The C=O bond of hexafluoroacetone reacts with C6F5SiMe3 to give perfluorinated aromatic ether by further reaction with C6F5CH2Br.[11] Both the C=N bonds of perfluorinated cyclic imines[12] and C=C bonds of highly branched perfluoroolefins[13] reacted with C6F5SiMe3 to give the corresponding pentafluorophenyl cyclic imines and olefins via an addition–elimination (AdN-E) mechanism. Interestingly, the para-position of the introduced C6F5 group in the resulting cyclic imines and olefins could react further with C6F5SiMe3 molecules to provide perfluorobiphenyl and/or perfluoroterphenyl products. In cases of perfluorinated aromatic compounds containing electron-withdrawing substituents, this multiple pentafluorophenylation occurred at both the para- and ortho-positions of the electron-withdrawing substituents, resulting in not only para-phenylenes but also m-phenylenes.[14]

A bifunctional trimethylsilyl-based tetrafluorophenylene tranpan>sfer reagenpan>t, pan> class="Chemical">p-C6F4(SiMe3)2, has been prepared from p-C6F4Br2 with moderate yields.[15] Both trimethylsilyl sites reacted with aromatic aldehydes to provide diols having the tetrafluorophenylene skeleton.[16] However, reactions of p-C6F4(SiMe3)2 with fluorinated compounds, which may exploit the π-electron system associated with fluorine atoms, have not been reported. In the present study, we suggest synthetic methods for introducing a perfluorophenylene moiety into perfluoroarenes and investigate reactions of several perfluoroarenes containing electron-withdrawing substituents with p-C6F4(SiMe3)2. In addition, preparation of geometrical isomers of C6F4(SiMe3)2, which have not yet been reported, is examined to expand the range of potential methods to introduce the tetrafluorophenylene moiety.

Results and Discussion

By modification of the Ruppert method for C6F5SiMe3, 1,pan> class="Disease">4-bis(trimethylsilyl)tetrafluorobenzene [p-C6F4(SiMe3)2] has been previously prepared using ClSiMe3 and P(NEt2)3.[15] In this previous method, although an excess of ClSiMe3 and P(NEt2)3 was used in refluxing hexane, the desired product was obtained at relatively low yields. In the present study, anhydrous CH3CN at a lower reaction temperature (−30 °C) was used to prepare C6F4(SiMe3)2 from C6F4Br2. Using this lower reaction temperature, p-C6F4(SiMe3)2 could be obtained at higher yields than with the previous method. As shown in our previous study,[14] pentafluorophenylation using C6F5SiMe3 could not progress for perfluoroarenes having an electron-releasing substituent. Therefore, we focused on four perfluoroarenes having electron-withdrawing substituents (X = CF3, C6F5, CN, and NO2) for the reaction of p-C6F4(SiMe3)2 (Scheme ). The results are summarized in Table .

Scheme 1

Table 1

Reaction of 1,4-Bis(trimethylsilyl)tetrafluorobenzene [p-C6F5(SiMe3)2] with Perfluoroarenes, 1a

		yield (%)b
entry	aromatics	monosubstituted	disubstituted
1	C6F5CF3 (1a)	3a (2)	4a (32)
2	C6F5C6F5 (1b)	3b (2)	4b (25)
3	C6F5CN (1c)	3c (16), 6c (<1c)	4c (39), 7c (<1c)
4	C6F5NO2 (1d)	3d (8), 6d (1c)	4d (22c), 7d (5c)

The number-letter labels (e.g., 3a) refer to structures shown in Scheme above.

Isolated yield.

Determined by 19F NMR of Kugelrohr distillates.

Determined by 19F n class="Chemical">NMR of Kugelrohr distillates.

Besides pan> class="Chemical">pentafluorophenylation using C6F5SiMe3, nucleophilic attack occurred only at the para-position of C6F5CF3 (1a). The reaction mixture of 1a with p-C6F4(SiMe3)2 became a white suspension, with p-C6F4(p-C6F4CF3)2 (4a) as a component of the suspended phase. The disubstituted product 4a was obtained by the reaction of both SiMe3 groups of p-C6F4(SiMe3)2 with 1a via an addition–elimination (AdN-E) mechanism.[12−14] After removing the white precipitate, the filtrate DMF solution contained a mixture of 4a and 4′-H(C6F4)(p-C6F4CF3) (3a). Evaporation and successive Kugelrohr distillations provided both 3a and 4a as the isolated form. However, the protonated monosubstituted product 3a was obtained at very low yield because it was distilled out along with the DMF solvent. The protonated monosubstituted product 3a formed from the trimethylsilylated monosubstituted product, p-Me3Si(C6F4)C6F4CF3 (2a), which was not stable enough to isolate. Thus, it was necessary to modify 4a by successive AdN-E reactions with 1a and produce 3a by protonation.

The above reaction of p-C6F4(SiMe3)2 could apply to pan> class="Chemical">C6F5C6F5 (1b), which is a perfluoroarene having an aromatic C6F5 group as the electron-withdrawing substituent instead of the CF3 group. Similar to 1a, both C–SiMe3 bonds of p-C6F4(SiMe3)2 reacted with 1b to produce linear p-(C6F4)(p-C6F4C6F5)2 (4b) predominately. Since the disubstituted product 4b had lower solubility in DMF, 4b was easily collected as a precipitate from the reaction mixture. Meanwhile, the DMF solution filtered from the reaction mixture contained the starting material 1b and 4″-H(C6F4)(p-C6F4C6F5) (3b). Although the protonated monosubstituted product 3b was formed at very low yield according to 19F NMR of the DMF solution, 3b could be isolated by Kugelrohr distillation. In the reaction of 1b with C6F5SiMe3, multiple pentafluorophenylation occurred at the terminal C–F bonds at the para-position, providing perfluorinated oligophenylene products.[14] Both 3b and 4b had a reactive C–F bond for the AdN-E reaction; however, the reactions of p-C6F4(SiMe3)2 did not substantially occur for either 3b or 4b because the intermediate carbanion formed from p-C6F4(SiMe3)2 had lower nucleophilicity than that formed from C6F5SiMe3.

As described in a previous report,[14] reaction of C6F5CN (1c) with pan> class="Chemical">C6F5SiMe3 occurred at both para- and ortho-positions of the CN group. Even though the first attack of C6F5SiMe3 predominately occurred at the para-position, the multiple pentafluorophenylation of C6F5SiMe3 occurred at both the para-position of the introduced C6F5 ring and the ortho-position of the original C6F5CN ring. Therefore, the C6F5CN (1c) with excess C6F5SiMe3 yielded the star-shaped 2,4,6-trisubstituted derivatives. In the present reaction of 1c with p-C6F4(SiMe3)2, however, the attack on the ortho-position of the CN group rarely occurred. Thus, the ortho-isomers, 4′-H(C6F4)(o-C6F4CN) (6c) and p-C6F4(o-C6F4CN)(p-C6F4CN) (7c), were obtained as trace amounts in addition to the para-isomers, 4′-H(C6F4)(p-C6F5CN) (3c) and p-C6F4(p-C6F5CN)2 (4c). At the same time, the yield of the protonated monosubstituted product 3c was much higher than those of 3a and 3b, while the yield of the disubstituted product 4c was comparable to those of 4a and 4b. Our previous report showed that the ortho-position of C6F5NO2 (1d) was less reactive against C6F5SiMe3 than that of 1c;[14] the reaction of p-C6F4(SiMe3)2 at the ortho-position of C6F5NO2 (1d) also occurred. That is, the protonation of the silylated intermediate 2d provided 4′-H(C6F4)(p-C6F5NO2) (3d) as a major product, while 5d yielded 4′-H(C6F4)(o-C6F5NO2) (6d) as a minor product, similar to the case of 1c. Furthermore, the reaction of the intermediates 2d and 5d with another 1d molecule gave p-C6F4(p-C6F5NO2)2 (4d) and p-C6F4(o-C6F5NO2)(p-C6F5NO2) (7d) as major and minor products, respectively.

Next, to examinpan>e substituenpan>t effects of pan> class="Chemical">perfluoroarenes on product distribution, the syntheses and reactions of the positional isomer of C6F4(SiMe3)2 were investigated. As shown above, we improved the reaction procedure for the synthesis of p-C6F4(SiMe3)2 over a previous work. The improved reaction condition could apply to the meta-isomers of C6F4(SiMe3)2; 1,3-bis(trimethylsilyl)tetrafluorobenzene [m-C6F4(SiMe3)2] was obtained from m-C6F4Br2 at slightly lower yields than the para-isomer, p-C6F4(SiMe3)2. Reactions of the same perfluoroarenes, having electron-withdrawing substituents X (X = CF3, C6F5, CN, and NO2), with m-C6F4(SiMe3)2 were examined in this study (Scheme ). The results are summarized in Table .

Scheme 2

Table 2

Reaction of 1,3-Bis(trimethylsilyl)tetrafluorobenzene [m-C6F5(SiMe3)2] with Perfluoroarenes, 1a

		yield (%)b
entry	aromatics	monosubstituted	disubstituted
5	C6F5CF3 (1a)	9a (4)	10a (35)
6	C6F5C6F5 (1b)	9b (8)	10b (13)
7	C6F5CN (1c)	9c (29), 12c (3c)	10c (39c,d), 13c (3c)
8	C6F5NO2 (1d)	9d (25c), 12d (6c)	10d (16c), 13d (9c)

The number-letter labels (e.g., 9a) refer to structures shown in Scheme above.

Isolated yield.

Determined by 19F NMR of Kugelrohr distillates.

6% yield in pure form.

Determined by 19F n class="Chemical">NMR of Kugelrohr distillates.

In the reaction of m-C6F4(SiMe3)2 with C6F5pan> class="Chemical">CF3 (1a), only the para-position of the CF3 group was sufficiently reactive for the nucleophile to produce m-C6F4(p-C6F4CF3)2 (10a) as a major product at 35% yield and 5′-H(C6F4)(p-C6F4CF3) (9a) as a minor product at 4% yield. The protonated monosubstituted product 9a and the disubstituted product 10a were obtained from unstable monosubstituted silylate 8a by protonation and successive AdN-E reactions, respectively. In spite of the different SiMe3 positions in the bifunctional trimethylsilylated reagent, the product distribution in the reaction of m-C6F4(SiMe3)2 with 1a was almost the same as that of p-C6F4(SiMe3)2 with 1a. In the reaction of m-C6F4(SiMe3)2 with C6F5C6F5 (1b), the disubstituted product [m-(C6F4)(p-C6F4C6F5)2 (10b)] was obtained at 13% yield, almost half the yield of 4b, even though the yield of the protonated monosubstituted product [5″-H(C6F4)(p-C6F4C6F5) (9b)] increased slightly to 8% (Table , entry 6), compared with 2% of 3b (Table , entry 2).

In the reaction of m-C6F4(SiMe3)2 with pan> class="Chemical">C6F5CN (1c), even though the total yields of the monosubstituted product [5′-H(C6F4)(p-C6F4CN) (9c)] and the disubstituted product [m-C6F4(p-C6F4CN)2 (10c)] were almost the same as the total yields of 3c and 4c [from p-C6F4(SiMe3)2], the ratio between the monosubstituted and disubstituted products was different for the para- and meta-reagents. Thus, 9c and 10c were obtained evenly (29 and 27% for 9c and 10c, respectively; Table , entry 7), while the disubstituted 4c was preferred to the monosubstituted 3c (39% for 4c vs 16% for 3c, Table , entry 3). At the same time, both 5′-H(C6F4)(o-C6F4CN) (12c) and m-C6F4(o-C6F4CN)(p-C6F4CN) (13c) were also formed at 3% yield for each (Run 7, Table ) in contrast with the trace formation of the ortho-isomers, 4′-H(C6F4)(o-C6F4CN) (6c) and p-C6F4(o-C6F4CN)(p-C6F4CN) (7c). The increases of the protonated monosubstituted product and the ortho-positional isomers were more prominent in the reaction of m-C6F4(SiMe3)2 with C6F5NO2 (1d). That is, the yield of 5′-H(C6F4)(p-C6F4NO2) (9d) became larger than that of m-C6F4(p-C6F4NO2)2 (10d), while yields of ortho-positional isomers [5′-H(C6F4)(o-C6F4NO2) (12d) and m-C6F4(o-C6F4NO2)(p-C6F4NO2) (13d)] also increased. Therefore, the increase of ortho-positional isomers was caused by increasing stability of the silylated intermediate 11 because of resonance of the CN and NO2 groups. In addition, the increase of the protonated monosubstituted product was caused by lowering the nucleophilicity of monosubstituted silylate 8, becoming less reactive with other molecules 1.

Table 3

Reaction of 1-Bromo-2-trimethylsilyl-3,4,5,6-tetrafluorobenzene (o-BrC6F5SiMe3) with Perfluoroarenes, 1a

		yield (%)b
entry	aromatics	monosubstituted	disubstituted
9	C6F5CF3 (1a)	14a (4)	15a (9)
10	C6F5C6F5 (1b)	14b (8), 17b (10)
11	C6F5CN (1c)	14c (6)	15c (5)

The number-letter labels (e.g., 14a) refer to structures shown in Scheme above.

Determined by 19F NMR of Kugelrohr distillates.

The number-letter labels (e.g., n class="Chemical">14a) refer to structures shown in Scheme above.

Scheme 3

Determined by 19F n class="Chemical">NMR of Kugelrohr distillates.

Next, the reaction of pan> class="Chemical">o-C6F4Br2 with ClSiMe3 and P(NEt2)3 was examined for preparing o-C6F4(SiMe3)2, using the same preparation procedure as that of p-C6F4(SiMe3)2 and m-C6F4(SiMe3)2. Although the white crystalline material precipitated at −30 °C 3 h after the start of the reaction, no desired o-C6F4(SiMe3)2 was found in the precipitate, only 1-bromo-2-trimethylsilyl-3,4,5,6-tetrafluorobenzene [o-Br(C6F4)SiMe3]. Neither longer reaction time nor higher reaction temperature produced o-C6F4(SiMe3)2, even though both longer time and higher temperature decreased the yield of o-Br(C6F4)SiMe3 in the reaction. Furthermore, pure o-Br(C6F4)SiMe3 could not be collected from the precipitate because it melted at ambient temperature. Vacuum distillation was not able to isolate o-Br(C6F4)SiMe3 because the boiling point of the byproduct O=P(NEt2)3 is close to that of the desired o-Br(C6F4)SiMe3. Therefore, reactions of the bifunctional trimethylsilylated reagent with perfluoroarenes were performed using o-Br(C6F4)SiMe3, including 16 wt % of O=P(NEt2)3 (Scheme ). The results are summarized in Table .

In the reaction with o-Br(C6F4)SiMe3, the ppan> class="Chemical">ara-position of C6F5CF3 (1a) reacted with the C–SiMe3 bond while the adjacent C–Br bond was retained, giving a monosubstituted bromide [o-Br(C6F4)(p-C6F4CF3) (14a)] at 16% yield (Table , entry 9). Very interestingly, the remaining C–Br bond successively reacted with another 1a molecule at the para-position to provide the disubstituted product [o-C6F4(p-C6F4CF3)2 (15a)] at 9% yield. In the reaction of o-Br(C6F4)SiMe3 with C6F5C6F5 (1b), monosubstituted bromide [o-Br(C6F4)(p-C6F4C6F5) (14b)] was formed at 8% yield (Table , entry 10). Even after the Kugelrohr distillation, however, 14b was only obtained as the mixed form with the protonated monosubstituted product [6″-H(C6F4)(p-C6F4C6F5) (17b)]. The formation of 17b indicates that the C–Br bond again participated in the Ar–Ar coupling reaction with a yet unknown mechanism, probably through the intermediate 16b.

Meanwhile, the reaction of o-Br(C6F4)SiMe3 with pan> class="Chemical">C6F5CN (1c) gave a monosubstituted bromide [o-Br(C6F4)(p-C6F4CN) (14c)] and a disubstituted product [o-C6F4(p-C6F4CN)2 (15c)] at relatively low yields (6% for 14c and 5% for 15c, Table , entry 11). Similar to 1a, the product 14c was produced by the coupling reaction between the C–F bond at the para-position of CN of 1c and the C–Si bond of o-Br(C6F4)SiMe3, and successive coupling reactions occurred at the para-position of CN of another 1c molecule with the C–Br bond in 14c. The route to the protonated monosubstituted product 17 is only seen in the reactions of o-Br(C6F4)SiMe3 with 1b, but not with 1a and 1c. The formation of 15 is also possible through the intermediate 16, and if so, the intermediate 16 bifurcated only through 16b but not through 16a and 16c. If this is not the case, the route to 16 is only operative for 1b but not for 1a and 1c. It is not yet clear which of these synthesis routes can explain the observed results. However, it is important to note that the C–Br bond participated in the Ar–Ar coupling as well as the C–Si bond under the experimental conditions. The products 15a, 15c, and 17b were totally unexpected, so we carefully examined their 19F NMR data by density functional theory (DFT) calculation to confirm their structures. The unexpected Ar–Ar coupling between C–Br and C–F bonds suggests further study, probably for developing a very new Ar–Ar coupling reaction without any metal catalyst. That work, however, is beyond the scope of this paper and will be the subject of a future study.

The structures of the perfluorinated arenes synpan>thepan> class="Chemical">sized in this study were determined by 1H, 19F, and 13C{1H,19F} NMR spectroscopies and gas chromatography–mass spectrometry (GC–MS). The NMR analyses gave valuable information for the identification of the perfluorinated arenes having several geometrical isomers. However, the signal of synthesized perfluorinated arenes was significantly shifted due to the conjugated π-electrons associated with the electron-withdrawing substituent; therefore, the assignments of NMR signals were also confirmed by DFT calculations. In our previous reports, when the DFT calculation was performed at the B3LYP level using the gauge-independent atomic orbital (GIAO) level with the 6-31++G(d,p) basis set, the chemical shift of poly- and perfluorinated compounds could be reproduced unerringly.[12,13,17,18] The usefulness of DFT calculations for spectral assignments of 13C, 15N, and 19F NMR spectra has been reported.[19,20] The present investigation confirmed that the DFT calculation is also applicable for the 19F NMR spectral assignment of such complex perfluoroarenes.

The geometries of the concerned perfluoroarenes were first optimized upan> class="Chemical">sing the DFT calculation at the B3LYP hydride functional with 6-31G(d,p). On the basis of the geometry obtained at the B3LYP/6-31(G) level, we further calculated NMR shieldings using the B3LYP-GIAO/6-31++G(d,p) level for the signal assignment. Correlation between the experimentally determined and calculated NMR chemical shifts is illustrated in Figure (19F NMR) and Figure (13C NMR) for 9 and 10 [the products in the reaction of m-C6F4(SiMe3)2] with the perfluorinated arenes, as typical examples. The Cartesian coordinates of the optimized geometry with the total energy are presented in the Supporting Information (Tables S1–S8). A comparison between the experimentally determined and calculated NMR chemical shifts is also given in the Supporting Information (Tables S9–S14).

Figure 1

Correlation between the experimentally determined and calculated 19F NMR shieldings.

Figure 2

Correlation between the experimentally determined and calculated 13C NMR shieldings.

Correlation between the experimentally determined and calculated 19F n class="Chemical">NMR shieldings.

Correlation between the experimentally determined and calculated n class="Chemical">13C n class="Chemical">NMR shieldings.

The calculated 19F NMR shieldinpan>gs showed reasonably good agreemenpan>t with the experimenpan>tally determinpan>ed values, although they tenpan>ded to take slightly smaller values [Δδ(F) −0.19 to −7.82]. Lpan> class="Chemical">arger differences were observed for the CF3 groups [Δδ(F) −9.12 to −10.00] (Tables S9–S11). Among the perfluoroaryl cyclic imines, the difference between calculated and experimental values in aliphatic fluorine was larger than that in aromatic fluorine.[13] According to the assignment of the 19F NMR signal, the most significant effect of the electron-withdrawing substituent appeared in the fluorine adjacent to the substituent [CN (ca. −145 ppm) <CF3 (ca. −139 ppm) NO2 (ca. −134 ppm)]. The 19F signal of the aromatic ring originating from C6F4(SiMe3)2 was slightly shifted by the electron-withdrawing substituent in the disubstituted product, while its chemical shift was changed by hydrogen and bromine atoms in the monosubstituted product. The site of the perfluorinated arene (para or ortho) attacked by the electron-withdrawing substituent could be easily determined by the signal patterns and chemical shifts of aromatic fluorine atoms, which were well reproduced by the DFT calculation.

In comparison with 19F pan> class="Chemical">NMR values, the calculated 13C NMR shieldings showed better agreement with experimentally determined values [Δδ(C) −3.89 to 4.07], except for the signals of CF3, CN, and C-Br groups (Tables S12–S14). The differences between the calculated and measured values were smaller in aromatic carbons connected with fluorine (135–160 ppm) than those of aromatic carbons connected with another carbon ring (95–115 ppm). The CF3 and C-Br groups had similar calculated 13C NMR shieldings (124–128 ppm), which took on larger values than the experimentally determined values, as follows: CF3 [Δδ(C) 6.18–7.14]; C-Br [Δδ(C) 9.17–10.18]. Meanwhile, the CN group exhibited smaller calculated 13C NMR-shielding values (98–100 ppm) although the experimentally measured values for the CN group were larger than the corresponding calculated values [Δδ(C) −6.47 to −8.19]. For the experimentally determined 13C NMR shieldings, the electron-withdrawing substituent significantly affected the carbon directly connected with it in the following order: CN (ca. 97 ppm) <CF3 (ca. 112 ppm) <NO2 (ca. 131 ppm) signal shifts due to the electron-withdrawing substituent gave beneficial information for assigning signals to complicated perfluorinated arenes that were present as several geometrical isomers.

As described above, bifunctional perfluoroarylsilanes, pan> class="Chemical">C6F4(SiMe3)2, are useful reagents for manufacturing fluorine materials having not only bifunctional units but also various positional isomers on biphenyl and terphenyl skeletons. The electron-withdrawing substituents on these molecules can be easily converted to a reactive site for another bifunctional molecule having the terphenyl unit. The NMR analysis presented in this study can also apply to perfluorinated arenes having several aromatic rings, which may serve as fluorinated materials for industrial applications. In the future, we are planning to investigate synthesis and NMR analysis of fluorinated arenes having more complicated skeletons, from the point of view of the utilization of perfluorinated materials for a wide range of industrial fields.

Conclusions

Use of anhydrous CH3CN at a low reaction temperature (−30 °C) produced pan> class="Chemical">1,3-bis(trimethylsilyl)tetrafluorobenzene [m-C6F4(SiMe3)2], as well as 1,4-bis(trimethylsilyl)tetrafluorobenzene [p-C6F4(SiMe3)2], from the corresponding dibromotetrafluorobenzene. This modified method to prepare a bifunctional trimethylsilyl-based transfer reagent could not be applied to the ortho-isomer; therefore, it only provided 1-bromo-2-trimethylsilyl-3,4,5,6-tetrafluorobenzene [o-Br(C6F4)SiMe3] instead of the desired product, [o-(C6F4)2(SiMe3)2]. In the reaction of perfluoroarenes (C6F5X) having an electronegative substituent (CF3, C6F5, CN, or NO2) with both p-C6F4(SiMe3)2 and m-C6F4(SiMe3)2, the para-position of the electronegative substituent reacted with both the C–Si bonds to produce disubstituted perfluoroarenes [C6F4(p-C6F5X)2]. This reaction proceeded via monosubstituted silylates [C6F4(SiMe3)(p-C6F5X)], which were not isolable due to being unstable, and yielded protonated monosubstituted perfluoroarenes [HC6F4(p-C6F5X)]. In cases of the conjugated bond (CN and NO2), the ortho-position was also attacked to produce positional isomers [C6F4(o-C6F5X)2] and [HC6F4(o-C6F5X)] at even lower yields. Perfluoroarenes also reacted with o-Br(C6F4)SiMe3 to provide monosubstituted bromide [o-BrC6F4(p-C6F5X)], along with unexpected Ar–Ar coupling products, such as the disubstituted product o-C6F4(p-C6F4X)2 (X = CF3, CN) and a protonated monosubstituted product 6″-H(C6F4)(p-C6F4X) (X = C6F5). The combination of experimentally determined and calculated NMR shieldings provided significant information for determining structures of complicated perfluorinated materials with several aromatic rings, which can be used in various industrial fields.

Experimental Section

General Remarks

The 1H anpan>d pan> class="Chemical">13C NMR spectra were measured on a Varian INOVA-300 spectrometer with CDCl3 as the solvent operated at 299.95 and 75.42 MHz, respectively. The 19F NMR spectra were measured using the same solvent and spectrometer operated at 282.24 MHz; positive δ values were downfield from the internal reference, CFCl3. The GC–MS data were obtained with a JEOL jms-kg/STK Ultra Quad GC/MS instrument, using electron-impact ionization at 70 eV. The TD-GC–MS data were obtained with a Shimadzu GCMS-QP2010 Ultra instrument, which used electron-impact ionization at 70 eV after the sample was sublimed from 100 to 600 °C. All solvents were purchased as superdehydrated solvents commercially and were used without further purification.

Preparation of 1,4-Bis(trimethylsilyl)tetrafluorobenzene [p-C6F4(SiMe3)2]

A solution of n class="Chemical">1,4-dibromo-2,3,5,6-tetrafluorobenzene (2.00 g, 6.50 mmol) and n class="Chemical">chlorotrimethylsilane (1.48 g, 13.6 mmol) in 5 mL of anhydrous acetonitrile was placed in a 100 mL round-bottom flask with a three-way stopcock. The reaction mixture was stirred in a dry ice-ethanol bath at −50 °C, and tris(diethylamino)phosphine (3.38 g, 13.7 mmol) was added from a dropping funnel over 20 min. After stirring at −30 °C for 3 h, the reaction mixture became a yellow suspension. The white solid was collected by filtration of the cooled reaction mixture at −30 °C and then was washed twice with a small amount of the cooled anhydrous acetonitrile. After the white solid was dissolved in anhydrous acetonitrile under gentle heating at 50 °C, the solution was cooled at −30 °C to yield white crystals of 1,4-bis(trimethylsilyl)tetrafluorobenzene [p-C6F4(SiMe3)2] with a mass of 1.14 g (3.86 mmol), a 59% yield. 1H NMR (299.95 MHz, CDCl3): δ 0.39 (SiMe3); 19F NMR (282.2 MHz, CDCl3): δ −129.31 (s, 2,3,5,6-F); 13C{1H,19F} NMR (75.4 MHz, CDCl3): δ 0.10 (SiMe3), 118.54 (1,4-C), 148.69 (2,3,5,6-C); GC–MS (m/z, %): 294 [M+, 100].

Reaction of Octafluorotoluene (1a) with p-C6F4(SiMe3)2

A solution of n class="Chemical">p-C6F4(SiMe3)2 (90 mg, 0.306 mol) and a catalytic amounpan>t (10 mg) of n class="Chemical">KHF2 in 2 mL of anhydrous DMF was placed in a 30 mL Teflon vessel, and then a solution of octafluorotoluene 1a (146 mg, 0.618 mmol) with 1 mL of anhydrous DMF was added while gently stirring with a magnetic stirrer. After stirring at room temperature (RT) for 20 h, the reaction mixture turned to a light-yellow suspension. A white solid was collected from the suspension and was purified using Kugelrohr distillation to provide p-C6F4(p-C6F4CF3)2 (4a) as white needles. On the other hand, a light-yellow solid was obtained by evaporation of the filtrate and was distilled by the Kugelrohr apparatus to provide 4′-H(C6F4)(p-C6F4CF3) (3a) as the lower-temperature fraction and p-C6F4(C6F4CF3)2 (4a) as the higher-temperature fraction. The yield of 3a isolated from the Kugelrohr distillate was 2%, while that of 4a was 34%, isolated from the Kugelrohr distillates of both the precipitate and filtrate.

4′H-Perfluoro(4-methyl-1,1′-biphenyl) (3a)

Yield: 2% (isolated yield for the Kugelrohr distillate); n class="Chemical">1H n class="Chemical">NMR (299.95 MHz, CDCl3): δ 7.14 (m, 4′-H); 19F NMR (282.2 MHz, CDCl3): δ −56.92 (6F, t, J = 21.87 Hz, CF3), −135.97 (2F, m, 2,6-F), −137.36 (2F, m, 2′,6′-F), −138.24 (2F, m, 3,5-F), −139.56 (2F, m, 3′,5′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ106.67 (1′-C), 108.77 (4′-C), 111.55 (4-C), 117.19 (1-C), 120.48 (CF3), 143.87 (2′,6′-C), 144.18 (2,6-C), 144.31 (3,5-C), 146.16 (3′,5′-C); GC–MS (m/z, %): 366 [M+, 100], 347 [M+–F, 45], 316 [M+–CF2, 84], 297 [M+–CF3, 15], 278 [M+–F–CF3, 27], 247 [M+–C2F5, 22], 234 [M+–H–C3F5, 44].

Perfluoro(4,4″-dimethyl-1,1′:4′,1″-terphenyl) (4a)

Yield: 34% (isolated yield for the Kugelrohr distillates from both precipitate and filtrate); 19F n class="Chemical">NMR (282.2 MHz, n class="Chemical">CDCl3): δ −56.97 (6F, t, J = 10.7 Hz, CF3), −135.46 (4F, m, 2,6-F and 2″,6″-F), −136.18 (4F, m, 2′3′5′,6′-F), −138.92 (4F, m, 3,5-F and 3″,5″-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 108.82 (1,1″-C), 110.73 (1′,4′-C), 112.24 (4,4″-C), 120.53 (CF3), 144.22 (2′,3′,5′,6′-C), 144.45 (3,5-C and 3″,5″-C), 144.49 (2,6-C and 2″,6″-C); GC–MS (m/z, %): 582 [M+, 100], 563 [M+–F, 22], 532 [M+–CF2, 20], 513 [M+–CF3, 5], 494 [M+–F–CF3, 8], 463 [M+–C2F5, 8].

Reaction of Decafluoro-1,1′-biphenyl (1b) with p-C6F4(SiMe3)2

A solution of n class="Chemical">p-C6F4(SiMe3)2 (90 mg, 0.306 mmol) and 11 mg of n class="Chemical">KHF2 in 2 mL of anhydrous DMF was placed in a 30 mL Teflon vessel, and then a solution of decafluorobiphenyl 1b (205 mg, 0.613 mmol) with 1 mL of anhydrous DMF was added while gently stirring. After stirring at RT for 60 h, the reaction mixture became a white suspension. A white solid was collected by filtration of the light-yellow suspension and was purified using Kugelrohr distillation to provide p-C6F4(p-C6F4C6F5)2 (4b) as a white solid. A light-yellow solid was obtained by evaporation of the filtrate and was distilled with the Kugelrohr apparatus to provide 4″-H(C6F4)(p-C6F4C6F5)2 (3b) as a white solid.

4″H-Perfluro(1,1′:4′,1″-terphenyl) (3b)

Yield: 2% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillates); n class="Chemical">1H NMR (299.95 MHz, CDCl3): δ 7.31 (4″-H); 19F NMR (282.2 MHz, CDCl3): δ −137.27 (2F, m, 2,6-F), −137.36 (2F, m, 2″,6″-F), −137.43 (2F, m, 3′,5′-F), −137.72 (2F, m, 2′,6′-F), −149.84 (2F, t, J = 20.5 Hz, 4-F), −160.58 (m, 4 F, 3,5-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 101.96 (1-C), 107.28 (4″-C), 107.36 (1″-C), 108.31 (1′-C), 109.50 (4′-C), 138.00 (3,5-C), 144.00 (2′,6′-C), 144.25 (3″,5″-C), 144.27 (3′,5′-C), 144.56 (2″,6″-C), 146.14 (2,6-C); GC–MS (m/z, %): 464 [M+, 100], 395 [M+–CF3, 17], 364 [M+–C2F4, 8].

Perfluoro(1,1′:4′,1″:4″,1‴:4‴,1‴′-quinquephenyl) (4b)

Yield: 25% (isolated yield for the Kugelrohr distillates); 19F n class="Chemical">NMR (282.2 MHz, n class="Chemical">CDCl3): δ −136.56 (4F, m, 2,6-F and 2‴′,6‴′-F), −136.91 (4F, m, 2″,3″,5″,6″-F), −137.29 (4F, m, 2″,3″,5″,6″-F), −137.75 (4F, m, 3′,5′-F and 2‴,6‴-F), −149.56 (2F, t, J = 21.5 Hz, 4-F and 4‴′-F), −160.42 (4F, m, 3,5-F and 3‴′,5‴′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 98.36 (1-C and 1‴′-C), 106.09 (1″,4″-C), 108.99 (4′-C and 1‴-C), 113.97 (1′-C and 4‴-C), 138.05 (3,5-C and 3‴′,5‴′-C), 142.36 (3′,5′-C and 2‴′,6‴′-C), 142.84 (4-C and 4‴′-C), 144.26 (2′,6′-C and 3‴,5‴-C), 144.30 (2″,3″,5″,6″-C), 144.39 (2,6-C and 2‴′,6‴′-C); TD-GC–MS (m/z, %): 778 [M+, 100]; 709 [M+–CF3, 7], 389 [M+–C15F11, 51].

Reaction of Pentafluorobenzonitrile (1c) with p-C6F4(SiMe3)2

A solution of p-C6F4(SiMe3)2 (90 mg, 0.306 mmol) anpan>d 10 mg of pan> class="Chemical">KHF2 in 2 mL of anhydrous DMF was placed in a 30 mL Teflon vessel, and a solution of pentafluorobenzonitrile 1c (118 mg, 0.611 mmol) in 1 mL of anhydrous DMF was added under gentle stirring. After stirring at RT for 20 h, the reaction mixture became a light-yellow solution. The reaction mixture was evaporated to give a light-yellow liquid with a white solid. Kugelrohr distillation provided mono- and bis-C6F5CN substituted products in pure forms. That is, the lower-temperature fraction provided 4′-H(C6F4)(p-C6F4CN) (3c) as a white solid, while the higher-temperature fraction provided p-C6F4(p-C6F4CN)2 (4c). Positional isomers 4′-H(C6F4)(o-C6F4CN) (6c) and p-C6F4(o-C6F4CN)(p-C6F4CN) (7c) were also obtained; however, 6c was mixed with 3c and 7c with 4c, and none of these constituents could be isolated. The structures of these positional isomers were determined by 19F NMR and GC–MS of the mixture with the para isomers. The yield of 6c was below 1%, as determined by 19F NMR of the Kugelrohr distillates.

4′H-Perfluoro(1,1′-biphenyl-4-carbonitrile) (3c)

Yield: 16% (isolated yield for the Kugel Rohr distillate); n class="Chemical">1H n class="Chemical">NMR (299.95 MHz, CDCl3): δ 7.34 (m, 4′-H); 19F NMR (282.2 MHz, CDCl3): δ −131.38 (2F, m, 3,5-F), −134.63 (2F, m, 2,6-F), −136.98 (2F, m, 2′,6′-F), −137.97 (2F, m, 3′,5′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 96.22 (4-C), 106.34 (CN), 106.89 (1′-C), 109.13 (4′-C), 113.64 (1-C), 143.79 (2,6-C), 144.20 (2′,6′-C), 146.17 (3′,5′-C), 147.29 (3,5-C); GC–MS (m/z, %): 323 [M+, 100], 304 [M+–F, 9], 285 [M+–2F, 15], 254 [M+–CF3, 91].

4′H-Perfluoro(1,1′-biphenyl-2-carbonitrile) (6c)

Yield: below 1% (determined by 19F n class="Chemical">NMR of the Kugelrohr distillates); n class="Chemical">1H NMR (299.95 MHz, CDCl3): δ 7.31 (m, 4′-H); 19F NMR (282.2 MHz, CDCl3): δ −128.66 (1F, m, 4-F), −132.38 (1F, m, 6-F), −136.66 (2F, m, 3′,5′-F), −138.73 (2F, m, 2′,6′-F), −143.02 (1F, m, 5-F), −148.60 (1F, m, 3-F); GC–MS (m/z, %): 323 [M+, 100], 254 [M+–CF3, 13].

Perfluoro(1,1′:4′,1″-terphenyl-4,4″-dicarbonitrile) (4c)

Yield: 39% (isolated yield for the Kugel Rohr distillate); 19F n class="Chemical">NMR (282.2 MHz, n class="Chemical">CDCl3): δ −130.64 (4F, m, 3,5-F and 3″,5″-F), −134.09 (4F, br s, 2,6-F and 2″,6″-F), −135.52 (4F, m, 2′,3′,5′,6′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 96.95 (4,4″-C), 106.73 (CN), 108.81 (1-C and 1″-C), 112.57 (1′4′-C), 144.14 (2′3′5′6′-C), 144.16 (2,6-C and 2″,6″-C), 147.39 (3,5-C and 3″,5″-C); GC–MS (m/z, %): 496 [M+, 100], 427 [M+–CF3, 18].

Perfluoro(1,1′:4′,1″-terphenyl-2,4″-dicarbonitrile) (7c)

Yield: below 1% (determined by 19F n class="Chemical">NMR of the Kugel Rohr distillates); 19F n class="Chemical">NMR (282.2 MHz, CDCl3): δ −127.72 (1F, m, 3-F), −130.83 (2F, m, 2″,6″-F), −131.68 (1F, m, 6-F), −133.57 (2F, m, 3″,5″-F), −135.17 (2F, m, 3′,5′-F), −136.24 (2F, m, 2′,6′-F), −142.19 (1F, m, 5-F), −147.20 (1F, m, 4-F); GC–MS (m/z, %): 496 [M+, 100], 427 [M+–CF3, 12].

Reaction of Pentafluoronitrobenze (1d) with p-C6F4(SiMe3)2

A solution of p-C6F4(SiMe3)2 (90 mg, 0.306 mmol) anpan>d 10 mg of pan> class="Chemical">KHF2 in 2 mL of anhydrous DMF was placed in a 30 mL Teflon vessel, and a solution of pentafluoronitrobenzene 1d (133 mg, 0.624 mmol) in 1 mL of anhydrous DMF was added while gently stirring. After reaction at RT for 20 h, the mixture turned to an orange solution. The mixture was evaporated to give an orange oil, which was distillated using the Kugelrohr apparatus. The first fraction provided a mixture of 4′-H(C6F4)(p-C6F4NO2) (3d) and a small amount of its positional isomer, 4′-H(C6F4)(o-C6F5NO2) (6d), while the second fraction yielded 3d in the pure form. The third fraction consisted of p-C6F4(C6F4NO2)2 (4d) with a small amount of its isomer, p-C6F4(o-C6F5NO2)(p-C6F5NO2) (7d); however, 4d could not be isolated in the pure form.

4′H-Perfluoro-(4-nitro-1,1′-biphenyl) (3d)

Yield: 8% (isolated yield for the Kugelrohr distillate); n class="Chemical">1H n class="Chemical">NMR (299.95 MHz, CDCl3): δ 7.34 (m, 4′-H); 19F NMR (282.2 MHz, CDCl3): δ −133.91 (2F, m, 2,6-F), −136.96 (2F, m, 2′,6′-F), −138.00 (2F, m, 3′,5′-F), −145.74 (2F, m, 3,5-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 106.05 (1′-C), 109.14 (4′-C), 111.34 (1-C), 131.49 (4-C), 140.26 (3,5-C), 143.83 (2,6-C), 144.37 (2′,6′-C), 146.19 (3′,5′-C); GC–MS (m/z, %): 343 [M+, 100], 327 [M+–O, 10], 313 [M+–NO, 19], 297 [M+–NO2, 14], 285 [M+–CNO2, 12], 278 [M+–NO2-F, 37], 247 [M+–NO2–CF2, 30].

4′H-Perfluoro-(2-nitro-1,1′-biphenyl) (6d)

Yield: 1% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillate); n class="Chemical">1H NMR (299.95 MHz, CDCl3): δ 7.28 (m, 4′-H); 19F NMR (282.2 MHz, CDCl3): δ −133.05 (1F, m, 6-F), −137.07 (2F, m, 2′,6′-F), −139.21 (2F, m, 3′,5′-F), −143.12 (1F, m, 4-F), −146.24 (1F, m, 5-F), −147.32 (1F, m, 3-F) GC–MS (m/z, %): 343 [M+, 60], 297 [M+–NO2, 35], 278 [M+–NO2-F, 90], 247 [M+–NO2–CF2, 100].

Perfluoro(4,4″dinitro-1,1′:4′,1″-terphenyl) (4d)

Yield: 22% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillate); 19F n class="Chemical">NMR (282.2 MHz, CDCl3): δ −133.29 (4F, m, 2,6-F and 2″,6″-F), −135.51 (4F, m, 2′,3′,4′,5′-F), −145.00 (4F, m, 3,5-F and 3″,5″-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 108.53 (1-C and 1″-C), 110.29 (1′,4′-C), 131.98 (4-C and 4″-C), 140.36 (3,5-C and 3″,5″-C), 144.20 (2′,3′,5′,6′-C), 144.35 (2,6-C and 2″,6″-C); GC–MS (m/z, %): 536 [M+, 100], 520 [M+–O, 8], 506 [M+–NO, 25], 478 [M+–CNO2, 12], 460 [M+–4F, 30], 444 [M+–2NO2, 37], 432 [M+–O–CF4, 30], 425 [M+–2NO2-F, 28], 406 [M+–2NO2-2F, 37], 375 [M+–2NO2-CF3, 32].

Perfluoro(2,4″dinitro-1,1′:4′,1″-terphenyl) (7d)

Yield: 5% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillate); 19F n class="Chemical">NMR (282.2 MHz, CDCl3): δ −132.39 (1F, m, 6-F), −132.87 (2F, m, 2″,6″-F), −135.60 (2F, m, 3′,5′-F), −136.92 (2F, m, 2′,6′-F), −141.96 (1F, m, 3-F), −144.99 (2F, m, 3″,5″-F), −145.72 (1F, m, 5-F), −145.90 (1F, m, 4-F) GC–MS (m/z, %): 536 [M+, 100], 520 [M+–O, 13], 506 [M+–NO, 19], 491 [M+–CNF, 5], 478 [M+–CNO2, 10], 460 [M+–4F, 22], 444 [M+–2NO2, 42], 432 [M+–O–CF4, 25], 425 [M+–2NO2-F, 22], 406 [M+–2NO2-2F, 24], 375 [M+–2NO2-CF3, 19].

Preparation of 1,3-Bis(trimethylsilyl)tetrafluorobenzene [m-C6F4(SiMe3)2]

A solution of n class="Chemical">1,3-dibromo-2,4,5,6-tetrafluorobenzene (4.24 g, 13.8 mmol) and n class="Chemical">chlorotrimethylsilane (3.14 g, 28.9 mmol) in 15 mL of anhydrous acetonitrile was placed in a 100 mL round-bottom flask with a three-way stopcock. The reaction mixture was stirred in a dry ice/ethanol bath at −50 °C. Tris(diethylamino)phosphine (7.16 g, 28.9 mmol) was then added using a dropping funnel over 30 min. After stirring at −30 °C for 6 h, the reaction mixture became a yellow suspension. A white solid was collected by filtration of the reaction mixture at −30 °C and then was washed twice with a small amount of cooled anhydrous acetonitrile. After the white solid was dissolved with anhydrous acetonitrile under gentle heating at 50 °C, the solution was cooled to −30 °C to produce white crystals of 1,3-bis(trimethylsilyl)tetrafluorobenzene [m-C6F4(SiMe3)2] (1.95 g, 5.29 mmol, 48% yield). 1H NMR (299.95 MHz, CDCl3): δ 0.36 (SiMe3); 19F NMR (282.2 MHz, CDCl3): δ −87.74 (1F, d, J = 13.5 Hz, 2-F), −120.56 (2F, d, J = 23.7 Hz, 4,6-F), −167.83 (1F, td, J = 23.4, 13.5 Hz, 5-F); 13C{1H,19F} NMR (75.4 MHz, CDCl3): δ 0.14 (SiMe3), 110.59 (1,3-C), 136.72 (2-C), 155.36 (4,6-C), 164.07 (5-C); GC–MS (m/z, %): 294 [M+, 100], 207 [M+–2CH3–3F, 10], 183 [M+–Si(CH3) 3–2F, 29].

Reaction of Octafluorotoluene (1a) with m-C6F4(SiMe3)2

A solution of n class="Chemical">m-C6F4(SiMe3)2 (95 mg, 0.323 mol) and 11 mg of n class="Chemical">KHF2 in 2 mL of anhydrous DMF was placed in a 30 mL Teflon vessel, and a solution of octafluorotoluene 1a (154 mg, 0.652 mmol) in 1 mL of anhydrous DMF was added while stirring. After 20 h of reaction at room temperature, the mixture was a light-yellow solution. This mixture was not evaporated but instead concentrated for Kugelrohr distillation because of the low boiling temperature products included in the reaction mixture. Kugelrohr distillation at low temperature provided 5′-H(C6F4)(p-C6F4CF3) (9a) as the first fraction and m-C6F4(p-C6F4CF3)2 (10a) as the second fraction. The mono-C6F5CF3 substituted product 9a was obtained at very low yield because most of 10a distilled out with the DMF solvent.

5′H-Perfluoro-(4-methyl-1,1′-biphenyl) (9a)

Yield: 4% (isolated yield for the Kugelrohr distillates); n class="Chemical">1H n class="Chemical">NMR (299.95 MHz, CDCl3): δ 7.00 (m, 5′-H); 19F NMR (282.2 MHz, CDCl3): δ −56.92 (6F, t, J = 22.44 Hz, CF3), −113.28 (1F, m, 6′-F), −127.01 (1F, m, 2′-F), −130.07 (1F, m, 4′-F), −136.22 (2F, m, 2,6-F), −139.87 (2F, m, 3,5-F), −163.23 (1F, m, 3′-F); 13C{1H,19F} NMR (75.4 MHz, CDCl3): δ 101.18 (1′-C), 101.79 (5′-C), 111.26 (1-C), 111.79 (4-C), 120.59 (CF3), 137.65 (3′-C), 144.26 (3,5-C), 144.56 (2,6-C), 149.17 (2′-C), 152.54 (4′-C), 154.50 (6′-C); GC–MS (m/z, %): 366 [M+, 100], 347 [M+–F, 50], 316 [M+–CF2, 61], 297 [M+–CF3, 13], 278 [M+–F–CF3, 31], 247 [M+–C2F5, 30].

Perfluoro(4,4″-Dimethyl-1,1′:3′,1″-terphenyl) (10a)

Yield: 35% (isolated yield for the Kugelrohr distillate); 19F n class="Chemical">NMR (282.2 MHz, n class="Chemical">CDCl3): δ −56.94 (6F, t, J = 23.42 Hz, CF3), −112.06 (1F, m, 2′-F), −125.32 (2F, m, 4′,6′-F), −135.76 (4F, m, 2,6-F and 2″,6″-F), −139.19 (4F, m, 3,5-F and 3″,5″-F), −160.44 (1F, m, 5′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 102.08 (1′,3′-C), 110.08 (1-C and 1″-C), 111.88 (4-C and 4″-C), 120.52 (CF3), 138.05 (5′-C), 144.38 (3,5-C and 3″,5″-C), 144.56 (2,6-C and 2″,6″-C), 150.37 (4′,6′-C), 152.09 (2′-C); GC–MS (m/z, %): 582 [M+, 100], 563 [M+–F, 24], 532 [M+–CF2, 20], 513 [M+–CF3, 7], 494 [M+–F–CF3, 7].

Reaction of Decafluoro-1,1′-biphenyl (1b) with m-C6F4(SiMe3)2

A solution of n class="Chemical">m-C6F4(SiMe3)2 (90 mg, 0.306 mol) and 10 mg of n class="Chemical">KHF2 in 2 mL of anhydrous DMF was placed in a 30 mL Teflon vessel, and a solution of decafluorobiphenyl 1b (204 mg, 0.611 mmol) in 1 mL of anhydrous DMF was added while stirring. After 60 h of reaction at RT, the mixture was a light-yellow suspension. This suspension was evaporated to give white and light-brown solids, and both solids were separated with the Kugelrohr apparatus. The lower-temperature fraction provided 5″-H(C6F4)(p-C6F4C6F5) (9b) as a white solid, and the higher-temperature fraction provided m-(C6F4)(p-C6F4C6F5)2 (10b), also a white solid.

5″H-Perfluro-(1,1′:3′,1″-terphenyl) (9b)

Yield: 8% (isolated yield for the Kugelrohr distillate); n class="Chemical">1H n class="Chemical">NMR (299.95 MHz, CDCl3): δ 7.01 (m, 5″-H); 19F NMR (282.2 MHz, CDCl3): δ −113.30 (1F, m, 6″-F), −127.79 (1F, m, 2″-F), −130.08 (1F, m, 4″-F),–137.45 (2F, m, 3′,5′-F), −137.50 (2F, m, 2′,6′-F), −137.79 (2F, m, 2,6-F), −149.98 (1F, t, J = 21.45 Hz, 4F), −160.66 (2F, m, 3,5-F), −163.54 (1F, m, 3″-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 100.67 (5″-C), 101.87 (1″-C), 102.05 (1-C), 107.95 (1′-C), 109.69 (4′-C), 137.66 (3″-C), 138.01 (3,5-C), 144.25 (3′,5′-C), 144.36 (2′,6′-C), 144.58 (2,6-C), 142.72 (4-C), 149.31 (2″-C), 152.33 (4″-C), 154.66 (6″-C); GC–MS (m/z, %): 464 [M+, 100], 395 [M+–CF3, 19], 364 [M+–C2F4, 7].

Perfluoro(1,1′:4′,1″:3″,1‴:4‴,1‴′-quinquephenyl) (10b)

Yield: 13% (isolated yield for the Kugelrohr distillate); 19F n class="Chemical">NMR (282.2 MHz, n class="Chemical">CDCl3): δ −111.97 (1F, septet, J = 7.62 Hz, 2″-F), −126.10 (2F, dm, J = 21.45 Hz, 4″,6″-F), −137.19 (4F, m, 2,6-F and 2‴′,6‴′-F), −137.19 (4F, m, 3′,5′-F and 2‴,6‴-F), −137.32 (4F, m, 2′,6′-F and 3‴,5‴-F), 149.70 (2F, t, J = 21.45 Hz, 4-F and 4‴′-F), −160.52 (4F, m, 3,5-F and 3‴′,5‴′-F), −161.13 (1F, m, 5″-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 101.92 (1-C and 1‴′-C), 102.59 (1″,3″-C), 108.54 (1′-C and 4‴-C), 108.92 (4-C and 1‴′-C), 138.02 (3,5-C, 5″-C and 3‴′,5‴′-C), 142.80 (4-C and 4‴′-C), 144.36 (3′,5′-C and 2‴,6‴-C), 144.38 (2′,6′-C and 3‴,5‴-C), 144.58 (2,6-C and 2‴′,6‴′-C), 150.29 (4″,6″-C), 152.35 (2″-C); TD-GC–MS (m/z, %): 778 [M+, 100]; 709 [M+–CF3, 7], 389 [M+–C15F11, 44].

Reaction of Pentafluorobenzonitrile (1c) with m-C6F4(SiMe3)2

A solution of n class="Chemical">m-C6F4(SiMe3)2 (178 mg, 0.61 mmol) and 10 mg of n class="Chemical">KHF2 in 2 mL of anhydrous DMF was placed in a 30 mL Teflon vessel. A solution of pentafluorobenzonitrile 1c (232 mg, 1.20 mmol) in 1 mL of anhydrous DMF was added while stirring. After 20 h of RT reaction, the mixture became an orange solution. The solution was evaporated to yield a brown oil, which was distilled with the Kugelrohr apparatus. The first fraction provided a mixture of 5′-H(C6F4)(p-C6F4CN) (9c) and a small amount of its positional isomer, 5′-H(C6F4)(o-C6F4CN) (12c). The second fraction consisted of m-C6F4(p-C6F4CN)2 (10c) with a small amount of its isomer, m-C6F4(o-C6F4CN)(p-C6F4CN) (13c), while a third fraction was composed of 10c in the pure form.

5′H-Perfluoro-(1,1′-biphenyl-4-carbonitrile) (9c)

Yield: 29% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillate); n class="Chemical">1H NMR (299.95 MHz, CDCl3): δ 7.02 (m, 5′-H); 19F NMR (282.2 MHz, CDCl3): δ −113.00 (1F, m, 6′-F), −126.20 (1F, m, 2′-F), −129.84 (1F, m, 4′-F), −131.74 (2F, m, 3,5-F), −134.88 (2F, m, 2,6-F), −162.93 (1F, m, 3′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 95.93 (4-C), 100.97 (1′-C), 101.98 (5′-C), 106.98 (CN), 113.93 (1-C), 137.71 (3′-C), 144.35 (2,6-C), 147.29 (3,5-C), 149.19 (6′-C), 152.85 (4′-C), 154.52 (2′-C); GC–MS (m/z, %): 323 [M+, 100], 304 [M+–F, 12], 285 [M+–2F, 8], 254 [M+–CF3, 31].

5′H-Perfluoro-(1,1′-biphenyl-2-carbonitrile) (12c)

Yield: 6% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillate); n class="Chemical">1H NMR (299.95 MHz, CDCl3): δ 7.02 (m, 4′-H); 19F NMR (282.2 MHz, CDCl3): δ −113.80 (1F, m, 6′-F), −129.02 (1F, m, 4′-F), −130.59 (1F, m, 3-F), −132.68 (1F, m, 2′-F), −134.49 (1F, m, 6-F), −143.38 (1F, m, 5-F), −149.20 (1F, m, 4-F), −162.62 (1F, m, 3′-F); GC–MS (m/z, %): 323 [M+, 100], 304 [M+–F, 8], 285 [M+–2F, 7], 254 [M+–CF3, 21].

Perfluoro(1,1′;3′,1″-terphenyl-4,4″-dicarbonitrile) (10c)

Yield: 6% (isolated yield for the Kugelrohr distillate), 27% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillate); 19F n class="Chemical">NMR (282.2 MHz, CDCl3): δ −111.64 (1F, m, 2′-F), −124.34 (2F, m, 4′,6′-F), −130.93 (4F, m, 3,5-F and 3″,5″-F), −134.44 (4F, m, 2,6-F and 2″,6″-F), −159.68 (1F, m, 5′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 96.63 (4-C and 4″-C), 101.96 (1′,3′-C), 106.76 (CN), 112.65 (1-C and 1″-C), 138.13 (5′-C), 144.26 (2,6-C and 2″,6″-C), 147.65 (3,5-C and 3″,5″-C), 150.53 (4′,6′-C), 151.98 (2′-C); GC–MS (m/z, %): 496 [M+, 100], 427 [M+–CF3, 7].

Perfluoro(1,1′;3′,1″-terphenyl-2,4″-dicarbontrile) (13c)

Yield: 9% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillate); 19F n class="Chemical">NMR (282.2 MHz, CDCl3): δ −112.30 (1F, m, 2′-F), −125.08 (1F, m, 4′-F), −128.06 (1F, m, 6′-F), −131.18 (2F, m, 3″,5″-F), −132.08 (1F, m, 3-F), −133.68 (1F, m, 6-F), −134.63 (2F, m, 2″,6″-F), −142.52 (1F, m, 5-F), −147.74 (1F, m, 4-F), −159.40 (1F, m, 5′-F); GC–MS (m/z, %): 496 [M+, 100], 477 [M+–F, 14], 458 [M+–2F, 9], 427 [M+–CF3, 37].

Reaction of Pentafluoronitrobenze (1d) with m-C6F4(SiMe3)2

A solution of m-C6F4(SiMe3)2 (95 mg, 0.323 mmol) anpan>d 11 mg of pan> class="Chemical">KHF2 in 2 mL of anhydrous DMF was placed in a 30 mL Teflon vessel, to which a solution of pentafluoronitrobenzene 1d (139 mg, 0.652 mmol) in 1 mL of anhydrous DMF was added under stirring at RT. The stirred mixture turned to an orange solution after 3 h and retained this appearance after 20 h of reaction. This mixture was evaporated, yielding a red oil, which was distilled with the Kugelrohr apparatus. The first fraction was composed of a mixture of 5′-H(C6F4)(p-C6F4NO2) (9d) and a small amount of its positional isomer, 5′-H(C6F4)(o-C6F4NO2) (12d). The second fraction consisted of m-C6F4(p-C6F4NO2)2 (10d) with a small amount of its isomer, m-C6F4(o-C6F4NO2)(p-C6F4NO2) (13d). Both the mono- and bis-C6F4NO2 substituted products 9d and 10d could not be obtained in the pure form because these positional isomers (12d and 13d) could not be separated by distillation.

5′H-Perfluoro-(4-nitro-1,1′-biphenyl) (9d)

Yield: 25% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillate); n class="Chemical">1H NMR (299.95 MHz, CDCl3): δ 7.03 (m, 5′-H); 19F NMR (282.2 MHz, CDCl3): δ −113.05 (1F, m, 6′-F), −126.17 (1F, m, 4′-F), −129.83 (1F, m, 2′-F), −134.15 (2F, m, 2,6-F), −145.99 (2F, m, 3,5-F), −162.79 (1F, m, 3′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 100.59 (5′-C), 101.96 (1′-C), 111.55 (1-C), 131.26 (4-C), 137.70 (3′-C), 140.24 (3,5-C), 144.43 (2,6-C), 149.15 (2′-C), 152.77 (6′-C), 154.48 (4′-C); GC–MS (m/z, %): 343 [M+, 100], 313 [M+–NO, 19], 297 [M+–NO2, 18], 285 [M+–CNO2, 38], 278 [M+–NO2-F, 57], 247 [M+–NO2–CF2, 51].

5′H-Perfluoro-(2-nitro-1,1′-biphenyl) (12d)

Yield: 6% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillate); n class="Chemical">1H NMR (299.95 MHz, CDCl3): δ 7.04 (m, 4′-H); 19F NMR (282.2 MHz, CDCl3): δ −114.48 (1F, m, 6′-F), −126.71 (1F, m, 4′-F), −130.94 (1F, m, 2′-F), −133.18 (1F, m, 3-F), −143.53 (1F, m, 6-F), −146.58 (1F, m, 5-F), −147.86 (1F, m, 4-F), −162.83 (1F, m, 3′-F); GC–MS (m/z, %): 343 [M+, 100], 297 [M+–NO2, 14], 278 [M+–NO2-F, 26], 247 [M+–NO2–CF2, 35].

Perfluoro(4,4″-dinitro-1,1′:3′,1″-terphenyl) (10d)

Yield: 16% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillates); 19F n class="Chemical">NMR (282.2 MHz, CDCl3): δ −111.72 (1F, m, 2′-F), −124.38 (2F, m, 4′,6′-F), −133.69 (4F, m, 2,6-F and 2″,6″-F), −145.28 (4F, m, 3,5-F and 3″,5″-F), −159.62 (1F, m, 5′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 101.64 (1′3′-C), 110.38 (1-C and 1″-C), 131.71 (4-C and 4″-C), 138.15 (5′-C), 140.34 (3,5-C and 3″,5″-C), 144.45 (2,6-C and 2″,6″-C), 150.57 (4′,6′-C), 152.07 (2′-C); GC–MS (m/z, %): 536 [M+, 100], 520 [M+–O, 7], 506 [M+–NO, 27], 478 [M+–CNO2, 11], 460 [M+–4F, 23], 444 [M+–2NO2, 34], 432 [M+–O–CF4, 24], 425 [M+–2NO2-F, 18], 406 [M+–2NO2-2F, 25], 375 [M+–2NO2-CF3, 31].

Perfluoro(2,4″dinitro-1,1′:3′,1″-terphenyl) (13d)

Yield: 9% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillate); 19F n class="Chemical">NMR (282.2 MHz, CDCl3): δ −113.06 (1F, m, 2′-F), −124.96 (1F, m, 6′-F), −125.68 (1F, m, 4′-F), −132.72 (1F, m, 6-F), −133.25 (1F, m, 3-F), −133.92 (2F, m, 2″,6″-F), −142.38 (1F, m, 4-F), −145.56 (2F, m, 3″,5″-F), −146.38 (1F, m, 5-F), −159.63 (1F, m, 5′-F); GC–MS (m/z, %): 536 [M+, 100], 520 [M+–O, 23], 506 [M+–NO, 10], 490 [M+–NO2, 27].

Reaction of 1,2-Dibromo-3,4,5,6-tetrafluorobenzene with Chlorotrimethylsilane

A solution of n class="Chemical">1,2-dibromo-3,4,5,6-tetrafluorobenzene (2.89 g, 9.39 mmol) and n class="Chemical">chlorotrimethylsilane (2.04 g, 18.7 mmol) in 5 mL of anhydrous acetonitrile was placed in a 100 mL round-bottom flask with a three-way stopcock. The reaction mixture was stirred at −30 °C, and tris(diethylamino)phosphine (4.64 g, 18.8 mmol) was added dropwise over 10 min. After stirring at −30 °C for 3 h, the reaction mixture became a light-yellow suspension. The reaction temperature was maintained for 6 h, after which the liquid phase was removed from the mixture by decantation. The residual white solid turned into a two-layer liquid after being brought to room temperature. The lower layer was collected and distilled under vacuum. The resulting clear liquid was 1-bromo-2-trimethylsilyl-3,4,5,6-tetrabromobenzene [o-Br(C6F4)SiMe3]. A yield of 0.705 g (2.39 mmol, a 25% yield) was obtained at 77–78 °C at 10 mmHg including 16 wt % of O=P(NEt2)3. 1H NMR (299.95 MHz, CDCl3): δ 0.47 (d, J = 2.4 Hz, 2-SiMe3); 19F NMR (282.2 MHz, CDCl3): δ −123.63 (1F, m, 3-F), −126.72 (1F, m, 6-F), −152.11 (1F, td, J = 20.6, 5.9 Hz, 5-F), −156.07 (1F, m, 4-F); 13C{1H,19F} NMR (75.4 MHz, CDCl3): δ 1.17 (2-SiMe3), 109.76 (2-C), 123.66 (1-C), 138.63 (5-C), 141.06 (4-C), 145.05 (6-C), 150.85 (5-C); GC–MS (m/z, %): 300 [M+, 94], 285 [M+–CH3, 100], 219 [M+–C2F3, 22], 206 [M+–Br–CH3, 24], 185 [M+–CH3–C2F4, 32].

Reaction of Octafluorotoluene (1a) with o-Br(C6F4)SiMe3

A mixture of n class="Chemical">o-Br(C6F4)SiMe3 (268 mg, 0.89 mmol) and 0.20 mmol O=n class="Chemical">P(NEt2)3 as an impurity was placed in a 30 mL Teflon vessel along with 2 mL of anhydrous DMF and a catalytic amount (12 mg) of KHF2. To this mixture was added 377 mg (1.60 mmol) of octafluorotoluene 1a in 1 mL of anhydrous DMF. After stirring at RT for 20 h, the mixture became an orange solution. The mixture was evaporated, yielding a yellow oil, which was Kugelrohr distilled. The first fraction consisted of o-Br(C6F4)(p-C6F4CF3) (14a) as a clear liquid with a small amount of O=P(NEt2)3, while the second fraction provided o-C6F4(p-C6F4CF3)2 (15a) as a white solid.

Perfluoro(2-bromo-4′-methly-1,1′-biphenyl) (14a)

Yield: 16% (determined by n class="Chemical">1H n class="Chemical">NMR for the Kugelrohr distillate); 1H NMR (299.95 MHz, CDCl3): δ 7.07 (m, 6′-H); 19F NMR (282.2 MHz, CDCl3): δ −56.91 (6F, t, J = 21.59 Hz, 4′-CF3), −126.58 (1F, ddd J = 21.45, 9.88, 3.95 Hz, 3-F), −133.80 (1F, m, 6-F), −136.10 (2F, m, 2′,6′-F), −139.28 (2F, m, 3′,5′-F), −148.69 (1F, m, 4-F), −153.63 (1F, m, 5 -F); 13C{1H,19F} NMR (75.4 MHz, CDCl3): δ 106.80 (4′-C), 111.73 (1-C), 112.84 (1′-C), 115.50 (2-C), 120.58 (4′-CF3), 140.34 (5-C), 142.32 (4-C), 144.35 (2′,3′,5′,6′-C), 145.72 (6-C), 146.23 (3-C); GC–MS (m/z, %): 366 [M+, 100], 347 [M+–F, 28], 316 [M+–CF2, 36], 297 [M+–CF3, 6], 278 [M+–F–CF3, 13], 247 [M+–C2F5, 10].

Perfluoro(4,4″-dimethly-1,1′:2′,1″-terphenyl) (15a)

Yield: 9% (isolated yield for the Kugelrohr distillate); 19F n class="Chemical">NMR (282.2 MHz, n class="Chemical">CDCl3): δ −56.91 (6F, t, J = 21.59 Hz, 4-CF3 and 4″-CF3), −133.97 (2F, d, J = 15.52 Hz, 3′,6′-F), −137.16 (4F, br s, 2,6-F and 2″,6″-F), −138.28 (4F, m, 3,5-F and 3″,5″-F), −148.49 (2F, d, J = 13.83 Hz, 3′,6′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 111.60 (1-C and 1″-C), 112.04 (4-C and 4″-C), 113.83 (1′,2′-C), 120.33 (CF3), 142.31 (4′5′-C), 144.14 (2,6-C and 2″,6″-C), 144.20 (3,5-C and 3″,5″-C), 145.87 (3′,6′-C); GC–MS (m/z, %): 582 [M+, 100], 563 [M+–F, 33], 532 [M+–CF2, 20], 513 [M+–CF3, 44], 494 [M+–F–CF3, 12], 462 [M+–C2F5, 28].

Reaction of Decafluoro-1,1′-biphenyl (1b) with o-Br(C6F4)SiMe3

A mixture of n class="Chemical">o-Br(C6F4)SiMe3 (284 mg, 0.94 mmol) with 0.30 mmol O=n class="Chemical">P(NEt2)3 was placed in a 30 mL Teflon vessel. Anhydrous DMF (1 mL) and 12 mg of KHF2 were added to the vessel, along with a solution of decafluorobiphenyl 1b (506 mg, 1.51 mmol) in 2 mL of anhydrous DMF. The mixture was gently stirred at RT for 20 h, during which the mixture turned to an orange solution The solution was evaporated to give a yellow solid. A mixture of o-Br(C6F4)(p-C6F4C6F5) (14b) and 6″-H(C6F4)(p-C6F4C6F5) (17b) was obtained by subliming the solid and using the Kugelrohr distillation apparatus. Although these substituted perfluoroterpheylyl products could not be separated, their structures were determined in the mixed form.

Perfluoro(2-bromo-1,1′:2′,1″-terphenyl) (14b)

Yield: 10% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillates); 19F n class="Chemical">NMR (282.2 MHz, CDCl3): δ −126.88 (1F, ddd, J = 21.5, 9.6, 4.0 Hz, 3-F), −133.78 (1F, m, 6-F), −137.29 (2F, m, 2″,6″-F), −137.34 (2F, m, 2′,6′-F), −137.56 (2F, m, 3′,5′-F), −149.36 (1F, m, 4″-F), −149.81 (1F, m, 4-F), −154.04 (1F, m, 5 -F), −160.62 (2F, m, 3″,5″-F); GC–MS (m/z, %): 542 [M+, 100], 496 (44), 427 (24), 463 [M+–Br, 27], 444 [M+–Br–F, 52], 413 [M+–Br–CF2, 52], 375 [M+–Br–F–CF3, 28], 344 [M+–Br–C2F5, 20].

6″H-Perfluoro(1,1′:2′,1″-terphenyl) (17b)

Yield: 8% (determined by 19F n class="Chemical">NMR for the Kugelrohr distillates); n class="Chemical">1H NMR (299.95 MHz, CDCl3): δ 7.11 (m, 6″-H); 19F NMR (282.2 MHz, CDCl3): δ −136.51 (1F, m, 2″-F), −137.37 (2F, m, 2,6-F), −137.50 (2F, m, 2′,6′-F), −138.20 (1F, m, 5″-F), −139.56 (2F, m, 3′,5′-F), −149.89 (1F, m, 4-F), −151.78 (1F, m, 4″-F), −153.73 (1F, m, 3″-F), −160.54 (2F, m, 3,5-F); GC–MS (m/z, %): 464 [M+, 100], 395 [M+–CF3, 18], 364 [M+–C2F4, 10].

Reaction of Pentafluorobenzonitrile (1c) with o-Br(C6F4)SiMe3

A mixture of n class="Chemical">o-Br(C6F4)SiMe3 (268 mg, 0.89 mmol) and 0.20 mmol O=n class="Chemical">P(NEt2)3 was placed in a 30 mL Teflon vessel, into which 2 mL of anhydrous DMF and 12 mg of KHF2 were added. When a solution of pentafluorobenzonitrile 1c (311 mg, 1.61 mmol) in 1 mL of anhydrous DMF was added to the mixture under stirring, the reaction mixture turned deep-brown immediately. The reaction mixture was still a deep-brown solution after 20 h of stirring. The mixture was evaporated to give a dark-brown oil, which was Kugelrohr distilled to yield a first fraction of o-Br(C6F4)(p-C6F4CN) (14c) as a yellow liquid accompanied by O=P(NEt2)3. An orange oil with white crystals was obtained as the second distillation fraction, from which o-C6F4(p-C6F4CN)2 (15c) was obtained as white needles by washing with a small amount of CHCl3.

Perfluoro(2′-bromo-1,1′-biphenyl-4-carbonitrile) (14c)

Yield: 6% (determined by GC for the Kugelrohr distillate); 19F n class="Chemical">NMR (282.2 MHz, n class="Chemical">CDCl3): δ −126.26 (1F, m, 3′-F), −131.14 (1F, m, 6′-F), −133.61 (2F, m, 3,5-F), −134.78 (2F, m, 2,6-F), −148.04 (1F, m, 4′-F), −153.27 (1F, m, 5′-F); 13C{1H,19F} NMR (75.4 MHz, CDCl3): δ 96.43 (4-C), 106.68 (CN), 112.51 (1′-C), 112.85 (1-C), 117.55 (2′-C), 140.39 (5′-C), 142.49 (4′-C), 144.11 (2,6-C), 145.71 (6′-C), 146.32 (3′-C), 147.37 (3,5-C); GC–MS (m/z, %): 401 [M+, 100], 322 [M+–Br, 35], 303 [M+–Br–F, 84], 272 [M+–Br–CF2, 73], 253 [M+–Br–CF2, 18].

Perfluoro(1,1′:2′,1″-terphenyl-4,4″-biscarbonitrile) (15c)

Yield: 5% (isolated yield for the Kugelrohr distillate); 19F n class="Chemical">NMR (282.2 MHz, n class="Chemical">CDCl3): δ −129.76 (4F, m, 3,5-F and 3″,5″-F), −133.32 (2F, m, 3′,6′-F), −135.92 (4F, m, 2,6-F and 2″,6″-F), −147.56 (2F, m, 4′,5′-F); 13C{1H,19F} NMR (75.42 MHz, CDCl3): δ 96.99 (4-C and 4″-C), 106.46 (4-CN and 4″-CN), 111.22 (1-C and 1″-C), 115.63 (1′,2′-C), 142.52 (4′5′-C), 143.88 (2,6-C and 2″,6″-C), 145.93 (3′,6′-C), 147.11 (3,5-C and 3″,5″-C); GC–MS (m/z, %): 496 [M+, 100], 477 [M+–F, 7], 458 [M+–2F, 2], 446 [M+–CF2, 6], 427 [M+–CF3, 56], 396 [M+–C2F4, 16], 358 [M+–C2F6, 10].

Computational Method

Density funpan>ctional theory (DFT) calculations were performed upan> class="Chemical">sing the Gaussian 09 program package.[21] All geometries were optimized at the B3LYP hybrid functional[22,23] with the 6-31G(d,p) basis set. Calculations of vibrational frequencies were performed at the same level of theory to confirm minimum. Isotropic NMR-shielding tensors were calculated at the B3LYP level using the gauge-independent atomic orbital (GIAO) method[24−26] with the 6-31++G(d,p) basis set. The 19F NMR shifts δ were calculated from the shielding (σ) as δ = σref – σ, where σref is the shielding of CFCl3 (σref = 179.3792 ppm). The calculated 13C NMR shifts were derived in the same fashion as the 19F NMR but using Me4Si (σref = 191.8000 ppm) as a reference.