Mild, safe, and versatile reagents for (CF2)n transfer and the construction of fluoroalkyl-containing rings

Article abstract of DOI:10.1021/om401016k

The preparation of new dizinc reagents [(MeCN)₂Zn((CF ₂)_n)₂Zn(MeCN)₂] (n = 3, 4, and 6) is reported. We show that the C4 reagent can readily transmetalate nickel to form a mononuclear perfluoronickelacycle. We also demonstrate that the reagents can be used to prepare novel fluoroorganics containing either perfluoroalkyl ring systems or perfluoroalkyl linked arenes under relatively mild conditions.

Full text of DOI:10.1021/om401016k

Article
pubs.acs.org/Organometallics
Mild, Safe, and Versatile Reagents for (CF2)n Transfer and the
Construction of Fluoroalkyl-Containing Rings
Peter T. Kaplan, Long Xu, Bo Chen, Katherine R. McGarry, Siqi Yu, Huan Wang, and David A. Vicic*
Department of Chemistry, Lehigh University, 6 E. Packer Avenue, Bethlehem, Pennsylvania 18015, United States
S
* Supporting Information
ABSTRACT: The preparation of new dizinc reagents
[(MeCN)2Zn((CF2)n)2Zn(MeCN)2] (n = 3, 4, and 6) is
reported. We show that the C4 reagent can readily
transmetalate nickel to form a mononuclear perfluoronickela-
cycle. We also demonstrate that the reagents can be used to
prepare novel fluoroorganics containing either perfluoroalkyl
ring systems or perfluoroalkyl linked arenes under relatively
mild conditions.
tetrafluoroethylene (TFE). They found that the resulting
metallacycle was extraordinarily stable and failed to release
carbon monoxide or fluorocarbon even after being treated with
bromine for 60 h at 50 °C.38 Such thermal stability contrasts
that seen for nonfluorinated iron carbonyl metallacycle
derivatives, which have been implicated as intermediates in
cyclopentanone formation.54,55
To our knowledge, the synthetic routes to well-defined
perfluorometallacyclopentanes all involve the oxidative cou-
pling of TFE, as outlined in eq 1.35,36,38,42−44,46,49,52,53,56 This
INTRODUCTION
■
Molecules and materials that contain sequential difluoro-
methylene groups are becoming increasingly important in
industry today. Repeating difluoromethylene groups can be
found in a diverse array of products, such as fluorinated
refrigerants, pharmaceuticals, pesticides, surfactants, polymers,
liquid crystals, anesthetics, blood substitutes, aerosol formula-
tions, and lubricants.1−27 While methods for incorporating
perfluoroalkyl, difluoromethyl, fluoromethyl, and isolated
difluoromethylene groups have advanced significantly in recent
years,28 reagents that can systematically incorporate repeating
difluoromethylene groups of various sizes have been slower to
develop. Radical-based reagents, which have their own
limitations, are perhaps the most successful synthons for such
functionalities to date.29−33
The (CF2)n functionality is also of interest to the synthetic
organic and organometallic communities as it is the backbone
of perfluoroalkyl-based metallacycles, the largest numbering
class of which are the perfluorometallacyclopentanes. Perfluor-
ometallacyclopentanes like those shown in Chart 1 have been
known since 1961.34−53 Stone and co-workers prepared the first
example (1) involving the reaction of iron pentacarbonyl with
oxidative coupling reaction appears to be common for other
late transition metals, as complexes 2−6 (Chart 1) are all
formed upon reaction of an appropriate metal precursor with
TFE. Such routes are problematic for discovery research today
as TFE has become increasingly unavailable for purchase due to
the explosion hazards associated with its handing.57−65 TFE can
be prepared inexpensively on a reasonable scale from the
thermal pyrolysis of waste polytetrafluoroethylene
(PTFE),66−69 but such routes typically involve temperatures
above 600 °C and the use of a quartz furnace connected to a
vacuum manifold. Moreover, the pyrolysis route does not
eliminate the detonation hazards accompanying the recon-
densed TFE or the problems associated with the acute toxicity
of octofluoroisobutylene,70−77 which can be formed as a
byproduct in the thermal degradation of PTFE.68,78,79 Other
methods exist to generate TFE more expensively on a small
Chart 1. Selected Known Examples of
Perfluorometallacyclopentanes
Received: October 17, 2013
Published: November 18, 2013
© 2013 American Chemical Society
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scale,80,81 but require gas handling techniques that can
complicate experimental protocols.
RESULTS AND DISCUSSION
■
To circumvent the use of TFE in preparing perfluorometalla-
cyclopentanes, we sought to develop a new reagent that could
directly install a C4F8 group onto a metal precursor. In
particular, we wanted access to a difunctionalized perfluor-
obutane that could be used as a transmetalating agent.
Naumann and co-workers found that bis(n-perfluoroalkyl)zinc
complexes could be prepared by reacting diethyl zinc with 2
equiv of n-perfluoroalkyl iodide.82,83 We imagined that a
difunctionalized zinc derivative could also be prepared using
this method if 1,4-diiodooctafluorobutane was used as the
fluorinated substrate, as described in eq 2. A dinuclear structure
could be anticipated based on the work of Bickelhaupt with
nonfluorinated congeners.84 Indeed, upon addition of acetoni-
trile to a stirred mixture of 1,4-diiodooctafluorobutane and
diethyl zinc in hexanes, a white precipitate formed, which, by X-
ray crystallography, was confirmed to be complex 7 (Figure 1).
The method to prepare the bifunctionalized fluoroalkylzinc
reagents is general for other diiodoperfluoroalkanes, as rings
both smaller and larger than 7 can be prepared (eq 2). A crystal
structure of 8 has also been obtained (Figure 1) and confirms
its dinuclearity. Complex 8 is notable because this reagent can
potentially be used to prepare perfluorometallacyclobutanes,
which may be used to study and develop the yet unknown
perfluoroalkene metatheses reaction. The only example of a
perfluorometallacyclobutane reported to date was that synthe-
sized by Karel and co-workers41 and was generated by
decarbonylation of [(CO)4Fe(COCF2CF2CF2)]. The zinc
complex 8 is expected to provide entries to a diverse class of
new perfluorometallacyclobutanes through convenient trans-
metalation approaches.
The zinc complexes 7−9 were observed to slowly lose
HF2C−(CF2)n−CF2H upon dissolution in organic solvents.
The loss of HF2C−(CF2)n−CF2H was even observed after
monitoring the 19F NMR spectra of the zinc reagents before the
introduction of coordinating solvent. Nevertheless, the reagents
can effectively be used as CF2 transfer agents if handled
properly. For instance, complex 7 reacts readily with the nickel
precursor [(DME)NiBr2], as described in eq 3, to afford the
Figure 1. Top: ORTEP diagram of 7. Selected bond lengths (Å): Zn−
C1 2.032(4); Zn−C4 2.036(5); Zn−N2 2.077(4); Zn−N1 2.102(4).
Selected bond angles (deg): C1−Zn−C4 134.44(17); C1−Zn−N2
106.98(15); C4−Zn−N2 110.04(16); C1−Zn−N1 105.24(16); C4−
Zn−N1 96.14(17); N2−Zn−N1 96.37(14). Bottom: ORTEP diagram
of 8. The co-crystallized benzene has been omitted for clarity. Selected
bond lengths (Å): Zn1−C1 2.0248 (17); Zn1−N1 2.0835(16); Z1−
N2 2.1161(15). Selected bond angles (deg): C1−Zn1−N1 105.63(6);
C1−Zn1−N2 100.74(6); N1−Zn1−N2 93.86(6).
precursors to a variety of [LNi(Rf)2] derivatives.85 Indeed,
repeating the transmetalation in the presence of other
coligands, such as 2,6-dimethylphenyl isocyanide, leads to the
formation of 11 in 73% yield. Complex 11 has also been
structurally characterized, and selected bond lengths and angles
are provided in Figure 2.
Having established that the zinc reagents can be used as
effective transmetalating agents for nickel, we sought to provide
preliminary results for functionalizing organic diiodides to
novel organofluorine ring systems. Perfluoroalkyl zinc reagents
are known to be able to transmetalate copper to afford active
perfluoroalkylating agents,86,87 but there have been no reports
of ring-forming reactions using this methodology. In studies
using the new zinc reagents 7−9, we found that the variation in
fluoroalkyl chain length of the zinc reagents led to dramatic
differences in reactivity toward organic diiodides. For example,
the C3 zinc derivative 8 reacted cleanly with aryl diiodides in
the presence of CuCl/1,10-phenanthroline to afford the
fluoroalkyl ring-containing structures 12 and 13 (eq 5) in
46% and 93% yields, respectively. The higher yields obtained
with the more activated substrates like 2,3-diiodopyridine is not
unknown with zinc reagents. Kremlev and co-workers found
that [(DMF)2Zn(CF3)2] in combination with CuBr could
trifluoromethylate 2-iodopyridine in 93% yield, whereas
mononuclear metallacyclic complex 10 in 84% yield. A crystal
structure of 10 has been obtained (Figure 2), and the data
confirm that a monomeric nickel complex is produced.
Complex 10 represents a metallacyclic version of the recently
prepared [(MeCN)2Ni(Rf)2] complexes, which are convenient
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To determine the nature of the problem with the C4 derivative,
we explored whether or not the transmetalation of the
perfluoroalkyl group from zinc to copper was occurring. In
fact, mixing 4 equiv of CuCl with 7 in DMF led almost
instantaneously to the formation of a new species by 19F NMR
spectroscopy, with resonances appearing at δ −115.8 and
−139.5. We have determined by X-ray crystallography that this
new species is the unusual bis-cuprate 14 (eq 6, Figure 3).
Figure 2. Top: ORTEP diagram of 10. Selected bond lengths (Å):
Ni1−C1 1.893(5); Ni1−C4 1.887(5); Ni1−N1 1.903(5); Ni1−N2
1.898(5). Selected bond angles (deg): C4−Ni1−C1 86.7(2); C4−
Ni1−N2 91.5(2); C1−Ni1−N2 176.8(2); C4−Ni1−N1 177.7(2);
C1−Ni1−N1 91.3(2). Bottom: ORTEP diagram of 11. Selected bond
lengths (Å): Ni1−C5 1.870(5); Ni1−C14 1.870(4); Ni1−C4
1.933(5); Ni1−C1 1.937(4); C5−N1 1.158(6); C14−N2 1.155(6).
Selected bond angles (deg): C5−Ni1−C14 97.13(18); C5−Ni1−C4
89.52(19); C14−Ni1−C4 172.79(18); C5−Ni1−C1 175.51(19);
C14−Ni1−C1 87.36(19); C4−Ni1−C1 86.0(2); N1−C5−Ni1
176.1(4); N2−C14−Ni1 173.7(4).
Figure 3. ORTEP diagram of the dicuprate 14. The [Zn(DMF)6]
dication has been removed for clarity. Selected bond lengths (Å):
Cu1−C1 1.925(2); Cu1−C5 1.925(2); Cu1−Cu2 2.5481(4); Cu2−
C8 1.927(2); Cu2−C4 1.934(2). Selected bond angles (deg): C1−
Cu1−C5 173.67(9); C8−Cu2−C4 174.21(9).
Complex 14 is only the second bisperfluoroalkyl cuprate to be
structurally characterized88 and is the only such one that has a
dicopper and dianionic core. Isolation of 14 allowed us to study
its reactivity with aryl diiodides, and importantly, it was
determined that this bis-cuprate species is inactive in ring-
forming perfluoroalkylation reactions.
In attempts to achieve successful perfluoroalkylations with 7
by avoiding the formation of 14, we explored the effect of
additives. We found that addition of [NBu4]Br and DMPU
(DMPU = 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidi-
none) to zinc complex 7 before the introduction of copper to
the mixture indeed allowed access to the fluoroalkylated
products 15 and 16 (eq 7). As of yet, we do not fully
understand the mechanism by which these additives help the
reaction progress, although Organ and co-workers noted that
bromide may generate higher-order zincate complexes that are
effective transmetalating agents in certain Negishi reactions.89
Interestingly, the use of [NBu4]Br does not appear to influence
the reactivity of the C3 or the C6 zinc reagents.
reactions with aromatics containing electron-donating groups
like methyl or methoxy only afforded the trifluoromethyl
products in 2−4% yield.86 Similar, but suboptimal, yields for
the reaction described in eq 5 could be obtained if ligandless
CuCl was used as the copper source.
Surprisingly, when the C4 zinc derivative 7 was used to
perform similar perfluoroalkylation reactions with copper, only
trace amounts of ring-containing products could be detected.
We observed that the C6 zinc reagent, under conditions
screened thus far, does not lead to the formation of
perfluoroalkyl ring systems. However, reaction conditions
may be optimized to produced perfluoroalkyl linked arenes
such as 18 and 19 in moderate to good isolated yields (eq 8).
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The above reactions demonstrate that the new zinc reagents
described herein not only may be used to transmetalate nickel
but also may be used to generate perfluoroalkyl-based organic
ring systems and perfluoroalkyl linkers. Importantly, there have
been few reports to date of methods to prepare fused aryl/
fluoroalkyl ring systems of variable size. The most versatile
system we have found was that reported by Chen and co-
workers90,91 in which Cl(CF2)nI is first coupled to aryl iodides
using a superstoichiometric amount of copper metal to afford
Ar-(CF2)nCl. These Ar-(CF2)nCl products then undergo
intramolecular radical cyclizations upon reaction with
Na2S2O4 to afford fused ring systems. The method we are
reporting here is a complementary one that not only can form
fused ring systems under mild nonradical conditions but also
can be used to prepare transition-metal fluoroalkyl metalla-
cycles for developing potentially more sophisticated organo-
metallic transformations. The exploration of such trans-
formations is currently being pursued in our laboratories.
Crystal structures of 18 and 19 have been obtained, and the
ORTEP diagrams are shown in Figure 4.
CONCLUSIONS
■
In summary, a simple protocol to prepare bis(perfluoroalkyl)-
metallacyclic dizinc reagents has been established.92 The new
zinc reagents are bifunctionalized perfluoroalkyl groups that
may be used to transmetalate other metals and thereby transfer
the chain of repeating difluoromethylene groups. Given the
importance of transmetalation reactions in synthetic chemistry,
these new reagents can foreseeably be used in a variety of
transformations to install repeating difluoromethylene units in
both small and large molecules. Moreover, the reagent that we
demonstrated that could be used to prepare a perfluorome-
tallacyclopentane is anticipated to be helpful to smaller
laboratories that are less-equipped for generating and handling
perfluorinated gases, such as TFE, in order to study the
fundamental chemistry involving perfluorometallacyclopen-
tanes.
EXPERIMENTAL PROCEDURES
■
General Considerations. All manipulations were performed using
standard Schlenk and high-vacuum techniques or in a nitrogen-filled
glovebox. Solvents were purified by passing through activated alumina
and/or copper in a solvent purification system supplied by Pure
Process Technology. 1,4-Diiodooctafluorobutane and 1,6-diiododode-
cafluorohexane were purchased from SynQuest Laboratories, Inc. and
used without further purification. 1,3-Diiodohexafluoropropane was
prepared according to a previously published procedure.93 Solution 1H
NMR spectra were recorded at ambient temperature on a Bruker DRX
500 MHz spectrometer and referenced to residual proton solvent
signals. 13C NMR spectra were recorded on a Bruker NMR
spectrometer operating at 125 MHz and referenced to solvent signals.
19F spectra were recorded on the Bruker NMR spectrometer operating
at 470 MHz. A Bruker D8 Quest diffractometer was used for X-ray
crystal structure determinations. Mass spectral data were recorded on a
HP 5890 Series II Plus GC/MS.
Preparation of [(MeCN)2Zn((CF2)4)2Zn(MeCN)2] (7). An 8 mL
portion of a 1.0 M diethyl zinc solution in hexanes was prechilled in a
vial to −78 °C under a nitrogen atmosphere. 1,4-Diiodooctafluor-
obutane (3.64 g, 8 mmol) was diluted with 8 mL of pentane and was
also prechilled to −78 °C. The zinc solution was then added dropwise
to the 1,4-diiodooctafluorobutane solution at −78 °C. The reaction
vial was then stirred for 3 h at −20 °C. After 3 h, 4 mL of MeCN was
then added and the mixture was stirred vigorously for 1 h and then
warmed to room temperature. The pentane layer was decanted away,
and benzene was added to precipitate an off-white solid. The mixture
was stirred overnight, and then the solid was pumped dry on a high-
vacuum line. The product 7 was obtained in 86% yield as a white solid.
Figure 4. ORTEP diagrams of 18 (top) and 19 (bottom).
Experimental bond lengths and angles are provided in the Supporting
Information.
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19F NMR (CD3CN, 470 MHz): δ −125.5 (br s), −125.8 (br s). Anal.
Calcd (found) for C16H12F16N4Zn2: C, 27.65 (27.76); H, 1.74 (1.88).
The C4F8 zinc derivative decomposes slowly in the solution state but is
stable in the solid state.
Isolation of Dicuprate Complex 14 for Structural Character-
ization. The zinc complex 7 (1.05 g, 1.51 mmol) and copper chloride
(300 mg, 3.03 mmol) were dissolved in 4 mL of DMF and stirred for 3
h at room temperature. The mixture was checked by 19F NMR, and it
was determined that 63.3% conversion to the cuprate species occurred.
The mixture was filtered through a 0.2 μm PTFE filter, and the yellow
solution was placed in a vial. Ether was layered on top of the yellow
solution and placed in a −35 °C freezer overnight to form colorless
crystals. 19F NMR (DMF-d7, 470 MHz): δ −115.75 (br s, 4F),
−139.48 (br s, 4f). Crystals decompose upon extended time under
vacuum. Anal. Calcd (found) for C26H42Cu2F16N6O6Zn: C, 30.29
(29.72); H, 4.11 (4.01).
Preparation of 1,1,2,2,3,3,4,4-Octafluoro-1,2,3,4-tetrahydro-
naphthalene (15). The zinc complex 7 (34.75 mg, 0.05 mmol) was
dissolved in 0.8 mL of DMF and 0.4 mL of DMPU. Tetra-n-
butylammonium bromide (32.24 mg, 0.10 mmol) was then added,
followed by sequential addition of copper chloride (9.9 mg, 0.10
mmol) and 1,2-diiodobenzene (32.99 mg, 0.10 mmol). A 0.012 mL
portion of trifluorotoluene (0.098 mmol) was syringed into the vial as
the internal standard. The solution was then transferred to a J-Young
NMR tube, sealed, and heated for 3 h at 100 °C. The NMR yield of 15
was 28%. 19F NMR (ethyl ether, 470 MHz): δ −103.6 (br s, 4F),
−135.7 (br s, 4F). EI MS: m/z = 276.
Preparation of [(MeCN)2Zn((CF2)3)2Zn(MeCN)2] (8). A volume
of 5 mL (5.00 mmol) of a 1.0 M diethyl zinc solution in hexanes was
added to a prechilled vial (−78 °C) under a nitrogen atmosphere and
diluted with 5 mL of pentane. A mass of 2 g (5 mmol) of 1,3-
diiodohexafluoropropane was added slowly, and the whole solution
was stirred in a nitrogen-filled glovebox cold well at −78 °C for 8 h
and gradually warmed to room temperature. Then 4 mL of acetonitrile
was added at room temperature and the mixture was stirred for 12 h.
After decanting the top pentane/hexane layer, 10 mL of diethyl ether
was added to the acetonitrile layer, and the whole solution was put in
the fridge in a glovebox (−35 °C) for recrystallization. The white
crystals were collected by filtration, and they were dried on a high-
vacuum line overnight to give an 82% product yield. 19F NMR
(CD3CN, 470 MHz): δ −126.2 (s), −136.8 (s). Anal. Calcd (found)
for C14H12F12N4Zn2: C, 28.26 (28.29); H, 2.03 (2.32).
Preparation of [(MeCN)2Zn((CF2)6)2Zn(MeCN)2] (9). A 4 mL
portion of a 1.0 M solution of ZnEt2 in hexanes was transferred into an
empty vial, diluted with 4 mL of pentane, and cooled to −78 °C. In
another vial, 4 mmol (2.206 g) of diiodododecafluorohexane was
dissolved into 4 mL of pentane. The diiodododecafluorohexane
solution was then added dropwise to the ZnEt2 solution at −78 °C and
then stirred for 3 h at −20 °C. Then 4 mL of acetonitrile was added
dropwise to the solution. The resulting mixture was left to stir
vigorously overnight at room temperature. The solution was pumped
dry for 2 days on a high-vacuum line, yielding an off-white powder
(86%). 19F NMR (CD3CN, 470 MHz): δ −122.1 (br s), −123.0 (br
s). −123.3 (br s). Anal. Calcd (found) for C20H12F24N4Zn2: C, 26.84
(26.97); H, 1.35 (1.39).
Preparation of 5,5,6,6,7,7,8,8-Octafluoro-5,6,7,8-tetrahydro-
quinoline (16). The zinc complex 7 (34.8 mg, 0.05 mmol) was
weighed into in a 20 mL vial and dissolved in 0.8 mL of DMF. Tetra-n-
butylammonium bromide (32.24 mg, 0.10 mmol) was added, followed
by the addition of copper chloride (9.9 mg, 0.10 mmol) and 2,3-
diiodopyridine (33.09 mg, 0.10 mmol). A 0.012 mL portion of
trifluorotoluene (0.098 mmol) was syringed into the vial as the
internal standard. The solution was transferred to a J-Young NMR
tube, sealed, and then heated for 3 h at 100 °C. The NMR yield of 16
1
was 90%. H NMR (CDCl3, 500 MHz): δ 9.05 (d, J = 4.7 Hz, 1H),
8.23 (d, J = 8.2 Hz, 1H), 7.76 (dd, J = 8.2, 4.7 Hz, 1H). 19F NMR
(CDCl3, 470 MHz): δ −105.9 (s, 2F), −111.6 (s, 2F), −135.6 (s, 2F),
−136.0 (s, 2F). EI MS: m/z = 277.
Preparation of [(MeCN)2Ni(C4F8)] (10). Zinc complex 7 (251 mg,
0.32 mmol), freshly crystallized from benzene, was dissolved in 8 mL
of MeCN and was then immediately added dropwise to a stirred
mixture of [(DME)NiBr2] (202 mg, 0.65 mmol) in 4 mL of
acetonitrile. The mixture was stirred for 3 h at room temperature, and
then the volatiles were removed under vacuum. The nickel complex
was extracted from the residue with benzene, and this benzene
solution was filtered and then dried under vacuum to yield an orange
solid. Yield of 10: 84%. X-ray quality crystals were grown from THF/
ether. 19F NMR (CD3CN, 470 MHz): δ −106.0 (s), −139.4 (s). Anal.
Calcd (found) for C8H6F8N2Ni: C, 28.19 (27.85); H, 1.77 (1.88).
Preparation of [(2,6-Dimethylphenyl isocyanide)2Ni(C4F8)]
(11). [(MeCN)2Ni(C2F4)] (10) (131 mg, 0.38 mmol) was dissolved
in 10 mL of THF, and then 110 mg (0.83 mmol) of 2,6-
dimethylphenyl isocyanide was immediately added. The mixture was
stirred for 3 h at room temperature, and then the volatiles were
removed under vacuum. The nickel complex was washed with pentane
Preparation of 17. A 4 mL portion of a 1.0 M solution of ZnEt2 in
hexanes was transferred into an empty vial, diluted with 4 mL of
pentane, and cooled to −78 °C under a nitrogen atmosphere. In
another vial, 4 mmol (2.2160 g) of diiodododecafluorohexane was
dissolved into 4 mL of pentane. The diiodododecafluorohexane
solution was then added dropwise to the ZnEt2 solution at −78 °C and
then stirred overnight at room temperature. A 2 mL portion of DMPU
was then added dropwise to the solution. The resulting mixture was
left to stir vigorously overnight at room temperature. After removing
the pentane layer, the product was precipitated from the solution by
slowly adding 8 mL of Et2O. Filtration and evaporation on a high-
vacuum line afforded 17 (2.3017 g, 92%) as a white solid. 19F NMR
(471 MHz, DMF-d7): δ −121.42, −123.55, −124.79. Anal. Calcd
(found) for C36H48F24N8O4Zn2: C, 34.77 (34.19); H, 3.89 (3.89).
Preparation of 18. To a resealable pressure tube were added
[(DMPU)2Zn((CF2)6)2Zn(DMPU)2] (62.4 mg, 0.05 mmol), CuCl
(19.9 mg, 0.2 mmol), diiodobenzene (99.0 mg, 0.3 mmol), and
DMPU (1 mL) sequentially in a glovebox at room temperature. The
resulting mixture was sealed and quickly submerged in an oil bath
preheated to 110 °C. After 19 h, the mixture was cooled to room
temperature and purified by chromatography on silica gel (eluent: n-
hexane/ethyl acetate = 1/0 to 20/1) to afford 2,2′-(perfluorohexane-
1,6-diyl)bis(iodobenzene) (36.0 mg, 51%, white solid). 1H NMR
(CDCl3, 500 MHz): δ 8.09 (d, J = 7.85 Hz, 1H), 7.58 (d, J = 7.85 Hz,
1H), 7.48 (t, J = 7.85 Hz, 1H), 7.19 (t, J = 7.74 Hz, 1H). 19F NMR
(CDCl3, 470 MHz): δ −107.1 (s), −119.8 (s), −122.4 (s). Anal. Calcd
(found) for C18H8F12I2: C, 30.62 (30.72); H, 1.14 (1.22).
1
and pumped dry under vacuum to yield a yellow solid. 73% yield. H
NMR (toluene-d8, 500 MHz): δ 6.60 (t, J = 7.6, 1H), 6.40 (d, J = 7.6,
2H), 1.87 (s, 6H). 19F NMR (THF, 470 MHz): δ −100.1 (s, 2F),
−139.3 (s, 2F). Anal. Calcd (found) for C22H18F8N2Ni: C, 50.71
(50.92); H, 3.48 (3.58).
Preparation of 1,1,2,2,3,3-Hexafluoro-2,3-dihydro-1H-in-
dene (12) and 5,5,6,6,7,7-Hexafluoro-6,7-dihydro-5H-
cyclopenta[b]pyridine (13). Copper(I) chloride (10 mg, 0.1
mmol) and 1,10-phenanthroline (18 mg, 0.1 mmol) were dissolved
in 1 mL DMF, and the solution was stirred for 30 min at room
temperature. Zinc complex 8 (30 mg, 0.05 mmol) and 1,2-
diiodobenzene (32 mg, 0.1 mmol) were added to the solution, and
the whole mixture was transferred to a J-Young NMR tube, sealed, and
heated to 90 °C for 16 h. NMR yields were based on trifluorotoluene
as an internal standard: 46% yield for 12. 19F NMR (470 MHz,
CDCl3) δ −108.45 (t, J = 5.0 Hz, 4F), −133.05 (quint, J = 4.3 Hz, 2F).
EI MS: m/z = 226. Compond 13 was prepared in an analogous
manner (yield: 93%). 19F NMR (470 MHz, MeCN-d3): δ −108.21 (s,
2F), −114.44 (s, 2F), −132.19 (quint, J = 4.3 Hz, 2F). EI MS: m/z =
227.
Preparation of 19. To a resealable pressure tube were added
[(DMPU)2Zn((CF2)6)2Zn(DMPU)2] (62.1 mg, 0.05 mmol), CuCl
(19.7 mg, 0.2 mmol), 4-iodo-1,1′-biphenyl (56.2 mg, 0.2 mmol), and
DMPU (1 mL) sequentially in a glovebox at room temperature. The
resulting mixture was sealed and quickly submerged in an oil bath
preheated to 110 °C. After 17 h, the mixture was cooled to room
temperature and purified by chromatography on silica gel (eluent: n-
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hexane/ethyl acetate = 1/0 to 20/1) to afford 4,4″-(perfluorohexane-
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1
1,6-diyl)di-1,1′-biphenyl (48.5 mg, 80%): white solid. H NMR (500
MHz, CDCl3): δ 7.41 (t, J = 7.3 Hz, 2H), 7.48 (t, J = 8.0 Hz, 4H), 7.62
(d, J = 7.0 Hz, 4H), 7.67 (d, J = 8.4 Hz, 4H), 7.71 (d, J = 8.2 Hz 4 H).
19F NMR (471 MHz, CDCl3): δ −111.48, −122.26, −122.79.
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ASSOCIATED CONTENT
* Supporting Information
■
S
Crystallographic information files (CIF) and selected NMR
spectral data. This material is available free of charge via the
Internet at http://pubs.acs.org.
(28) Liang, T.; Neumann, C. N.; Ritter, T. Angew. Chem., Int. Ed.
2013, 8214.
AUTHOR INFORMATION
■
(29) Chernykh, Y.; Hlat-Glembova, K.; Klepetarova, B.; Beier, P. Eur.
J. Org. Chem. 2011, 2011, 4528.
(30) Chernykh, Y.; Opekar, S.; Klepetarova, B.; Beier, P. Synlett 2012,
Notes
The authors declare no competing financial interest.
23, 1187.
ACKNOWLEDGMENTS
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