The synthesis and crystal structures of halogenated tolans p-X-C 6H4-C≡C-C6F5 and p-X-C 6F4-C≡C-C6H5 (X = F, Cl, Br, I)

Article abstract of DOI:10.1039/b411191e

A series of halogenated, partially fluorinated tolans of general formula p-X-C₆H₄-C≡C-C₆F₅ [X = I (1), Br (2), Cl (3), F (4)] and p-X-C₆F₄-C≡C-C ₆H₅ [X = I (5), Br (6)] have been prepared via palladium-catalysed Sonogashira cross-coupling, or for X = Cl (7), by nucleophilic aromatic substitution reactions. The single-crystal X-ray structures of 1-3 and 5-6 have been determined. The structures reveal that the molecular packing is characterized by either arene-perfluoroarene interactions (3), or halogen - halogen interactions (isomorphous 1 and 2), or neither (isomorphous 5 and 6). The structure of 3 represents the first fully determined crystal structure of a compound that contains a halogen atom other than fluorine, in which arene -perfluoroarene interactions are present.

Full text of DOI:10.1039/b411191e

View Article Online / Journal Homepage / Table of Contents for this issue
A R T I C L E
The synthesis and crystal structures of halogenated tolans p-X–
C6H4–CC–C6F5 and p-X–C6F4–CC–C6H5 (X = F, Cl, Br, I)†
Jonathan C. Collings, Jacquelyn M. Burke, Philip S. Smith, Andrei S. Batsanov,
Judith A. K. Howard and Todd B. Marder*
Department of Chemistry, University of Durham, South Road, Durham, UK DH1 3LE.
E-mail: todd.marder@durham.ac.uk; Fax: +44(191)-334-4749; Tel: +44(191)-334-2037
Received 23rd July 2004, Accepted 13th September 2004
First published as an Advance Article on the web 8th October 2004
A series of halogenated, partially fluorinated tolans of general formula p-X–C6H4–CC–C6F5 [X = I (1), Br (2), Cl
(3), F (4)] and p-X–C6F4–CC–C6H5 [X = I (5), Br (6)] have been prepared via palladium-catalysed Sonogashira
cross-coupling, or for X = Cl (7), by nucleophilic aromatic substitution reactions. The single-crystal X-ray
structures of 1–3 and 5–6 have been determined. The structures reveal that the molecular packing is characterized
by either arene–perfluoroarene interactions (3), or halogen–halogen interactions (isomorphous 1 and 2), or neither
(isomorphous 5 and 6). The structure of 3 represents the first fully determined crystal structure of a compound that
contains a halogen atom other than fluorine, in which arene–perfluoroarene interactions are present.
(pentafluorophenylethynyl)tetrafluorobenzene.1 The complexes
1. Introduction
are stabilized via arene–perfluorarene interactions, which were
first discovered when it was found that an equimolar mixture
of benzene and hexafluorobenzene (HFB) forms a complex
with a melting point ca. 20 °C higher than either component.12
Subsequently, the crystal structures of this and other complexes,
containing either HFB or octafluoronaphthalene, have shown
them to be composed of infinite stacks of alternating arene
and perfluoroarene molecules.13 The arene–perfluoroarene
stacking motif also occurs in the crystal structures of partially
fluorinated molecules,14 as observed in the crystal structure of
(phenylethynyl)pentafluorobenzene, which consists of stacks
of parallel molecules in a head-to-tail arrangement, and simi-
larly, in the crystal structures of many 4-RO–C6F4–CC–C6H5
compounds.15
Fluorine substituents are also used to modify the liquid crys-
talline (LC) phase behaviour of mesogens. Several fluorinated
tolan and BPEB derivatives substituted by terminal alkoxy
chains have been observed to exhibit LC phases.16 Interestingly,
our BPEB binary complexes exhibit LC phase behaviour not
observed in the pure components, which is postulated to be a
result of the arene–perfluoroarene interactions.1,11
There are, as yet, no crystal structures featuring arene–per-
fluoroarene stacking between molecules which contain halogen
atoms other than fluorine. Therefore, it is not known what effect,
if any, their presence has on the arene–perfluoroarene interac-
tion. Herein we report the synthesis and crystal structures of
a series of selectively fluorinated tolans containing one other
halogen atom, with the general formulae p-X–C6H4–CC–C6F5
[X = I (1), Br (2), Cl (3), F (4)] and p-X–C6F4–CC–C6H5 [X = I
(5), Br (6), Cl (7)] as shown in Scheme 1. Compounds 5, 6, and
7 have been reported previously; 7 was prepared by nucleophilic
substitution at the para-position of chloropentafluorobenzene
by lithium phenylacetylide, and 5 and 6 were prepared via lithia-
tion at the C–Cl bond of 7, followed by reaction with iodine
and bromine, respectively.17 However, no experimental details
were given for these reactions, and the products were not fully
characterized. Additionally, 7 was synthesized by Sonogashira
coupling of an aryl triflate,18 although again, the compound was
not fully characterized.
The electronic, optical and liquid crystal properties of poly-
mers, oligomers, dendrimers and macrocycles based on the
arylene ethynylene motif,2 have led to interest in smaller arylene
ethynylene derivatives such as diphenylethynes (tolans) and
1,4-bis(phenylethynyl)benzenes (BPEBs). In this regard, we
have been carrying out a systematic examination of the syn-
thesis, structure and properties of tolans, BPEBs and 9,10-bis
(phenylethynyl)anthracenes (BPEAs), substituted with various
functional groups at the terminal positions.3
Their molecular structures are of particular importance,
especially in respect of their planarity. The dihedral angles
between the mean planes of the phenyl rings are determined by
the rotation about the carbon–carbon single bonds. This in turn
depends on the degree of conjugation between the two phenyl
rings through the carbon–carbon triple bond. The gas-phase
molecular structure of tolan, studied by electron diffraction
and electronic spectroscopy in supersonic jets, is consistent
with quasi-free ring rotation.4 However, tolan itself is planar in
the solid state.4a,5 Crystal structures of tolan derivatives reveal
a variety of dihedral angles between the arene rings, although
most are close to planar.6 Crystal packing forces are believed to
be responsible for the variation in conformations.
Tolans that crystallise in non-centrosymmetric space
groups are useful for second harmonic generation (SHG).7
Recently, non-centrosymmetric crystal structures have been
reported for tolans with a terminal alkyne substituent, and
these have been shown to have large SHG activities.8 Another
aspect of the crystallography of tolans is polymorphism,
one particularly interesting compound in this regard being
4-methoxy-4-nitrotolan, which exhibits at least three
polymorphs depending on the solvent from which it is grown.
Although at least two of these polymorphs are centrosymmetric,
one polymorph is non-centrosymmetric and is therefore
potentially suitable for SHG.9 Thus, even in dipolar systems, a
variety of packing arrangements may be close in energy.
Fluorine substituents are often used to modify the structural,
electronic and optical properties of molecules. We have thus
begun to synthesise selectively fluorinated tolans and BPEBs
and to evaluate their properties.10 We have recently shown
that 1,4-bis(phenylethynyl)tetrafluorobenzene forms a 1:1
complex with 1,4-bis(pentafluorophenylethynyl)benzene,11 and
1,4-bis(phenylethynyl)benzene forms a 2:1 complex with 1,4-bis-
2. Results and discussion
2.1 Synthesis
Cross-coupling reactions were carried out under standard
Sonogashira conditions, using a catalyst system composed of
† Arene–Perfluoroarene Interactions in Crystal Engineering, Part 12.
For Part 11 see ref. 1.
3 1 7 2
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 1 7 2 – 3 1 7 8
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

View Article Online
Scheme 1 The synthesis of 1–7.
Pd(PPh3)2Cl2 and CuI, each in 1% molar ratio compared to the
aryl halide. A slight excess (1.2 equivalents) of the appropriate
phenylacetylene was employed. Some of the reactions took
place at room temperature, although several needed some ad-
ditional heating to proceed to completion. All of the reactions
were performed in dry, deoxygenated amine solvents, with tri-
ethylamine being used in preference to diisopropylamine for all
reactions involving reagents with a pentafluorophenyl group, in
order to avoid possible nucleophilic substitution at the para posi-
tion by a secondary amine.19 The progress of the reactions was
monitored by GC-MS, which could also detect the formation of
any side-products. In most cases, trace amounts of butadiynes
were observed, consistent with them being formed only in the
catalyst initiation step.3a
The 1-halogeno-4-(pentafluorophenylethynyl)benzenes (1–4)
were prepared (Scheme 1) by the coupling of pentafluorophenyl-
acetylene with the appropriate aryl halide. Pentafluorophenyl-
acetylene can be obtained in respectable yields from the
base-induced hydrodesilation of its trimethylsilylated precursor,
which is, in turn, obtained from the Sonogashira cross-coupling
of trimethylsilylacetylene (TMSA) to iodopentafluorobenzene.20
For the synthesis of 1, a threefold excess of 1,4-diiodobenzene
was used relative to pentafluorophenylacetylene, in order to
minimize the formation of 1,4-bis(pentafluorophenylethynyl)-
benzene, arising from coupling at both iodo positions. A similar
strategy was employed previously in the synthesis of 1-iodo-
4-(phenylethynyl)benzene.21 The product was separated from
unreacted 1,4-diiodobenzene and 1,4-bis(pentafluorophenyl-
ethynyl)benzene, and much of the diiodobenzene was recovered,
by column chromatography and recrystallisation, although the
yield was very low. This can be attributed to the electron-with-
drawing nature of the pentafluorophenylethynyl moiety which
therefore serves as an activating group. This makes the product
more susceptible to further coupling, resulting in an increased
amount of 1,4-bis(pentafluorophenylethynyl)benzene, and a
decreased yield of product.
benzene respectively to phenylacetylene. Here, as in the synthesis
of 1, a three-fold excess of the dihalogenotetrafluorobenzene
was used for similar reasons to those outlined above, and the
products were separated from the remaining starting materi-
als by column chromatography. However, these reactions gave
respectable yields of product with only small amounts of 1,4-
(phenylethynyl)tetrafluorobenzene being produced, which is
probably due to the products being less reactive towards further
coupling than the starting material because of the phenylethynyl
group being a weaker electron acceptor than the pentafluoro-
phenylethynyl group.
It was initially decided to attempt the synthesis of com-
pound 7 analogously by cross-coupling phenylacetylene to
1-bromo-4-chlorotetrafluorobenzene. However, the resulting
reaction was shown by GC-MS to produce a mixture of 7 and
4-phenylethynyl-2,3,5,6-tetrafluorobenzene, arising from hydro-
dehalogenation of the chloro group. Hydrodehalogenation
has been observed previously in these cross-couplings,3a and
seems to be particularly prevalent for highly fluorinated aryl
halides. As the side-product was not easily separated from the
product by either column chromatography or recrystallisation,
it was decided to resort to the original method16 of adding
chloropentafluorobenzene to lithium phenylacetylide at low
temperature. This produced a clean product although the yield
was rather low.
2.2 Crystal structures
The structures of compounds 1, 2, 3, 5 and 6 were determined
from single-crystal X-ray diffraction data collected at 100–120 K
(Table1);wecouldnotobtainsatisfactorycrystalsof compounds
4 and 7. Each structure contains one molecule per asymmetric
unit, shown in Fig. 1. In molecule 3, the two benzene rings
form a dihedral angle (s in Table 2) of 3.4°, similar to 4.8° in
PhCCC6F5.15 In the other four compounds the twist is larger,
s = 9.4 to 15.7°. Unlike PhCCC6F5 and tolan itself, molecules
1–3 also show a substantial deviation from linearity, as indicated
by the angle (u in Table 2) between the vectors C(1)C(4) and
C(9)C(12). Molecules 5 and 6, however, remain practically
linear. The bond distances are unexceptional.
Each structure contains infinite stacks of molecules, running
parallel to the crystal axis y, and with interplanar separations
(d in Table 3) characteristic of close contact of aromatic mol-
ecules. Nevertheless, these five structures present three different
packing motifs, as illustrated by Figs. 2 and 3. The monoclinic
The synthesis of compounds 2–4 was more straightforward, as
the bromo-, chloro-, and fluoro- groups present did not undergo
coupling to pentafluorophenylacetylene under the reaction con-
ditions. Therefore, an excess of the aryl halide starting material
was not required, no significant amounts of side products were
generated, and purification required only recrystallisation in
order to obtain analytically pure samples in good yields.
The synthesis of 5 and 6 was achieved by the coupling of
1,4-diiodotetrafluorobenzene and 1,4-dibromotetrafluoro-
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 1 7 2 – 3 1 7 8
3 1 7 3

View Article Online
Table 1 Crystal data and structure refinement parameters
Compound
1
2
3
5
6
Formula
Formula weight
T/K
Crystal system
Space group
a/Å
b/Å
c/Å
C14H4F5I
394.07
105(2)
Monoclinic
P21/c (#14)
21.417(7)
4.9672(16)
11.692(4)
90
92.288(5)
90
1242.9(7)
4
C14H4F5Br
347.08
100(2)
Monoclinic
P21/c (#14)
20.517(1)
5.181(1)
11.254(1)
90
96.922(1)
90
1187.6(1)
4
C14H4F5Cl
302.62
110(2)
Triclinic
P1 (#2)
6.076(1)
7.488(1)
13.168(1)
85.343(1)
86.054(1)
83.332(1)
592.1(1)
2
C14H5F4I
376.08
100(2)
Monoclinic
P21/n (#14)
12.668(2)
5.074(1)
18.833(3)
90
93.703(4)
90
1208.1(3)
4
C14H5F4Br
329.09
120(2)
Monoclinic
P21/n (#14)
12.752(1)
4.966(1)
18.367(1)
90
93.231(2)
90
1161.3(2)
4
a/°
b/°
c/°
V/Å3
Z
qcalcd/g cm−3
2.106
2.62
1.941
3.51
1.698
0.37
2.068
2.68
1.882
3.57
l/mm−1
Transmission range
Total reflections
Unique refls.
Refined parameters
Rint
0.30–0.88
11360
2850
181
0.052
0.053
0.143
0.23–0.84
10137
2697
197
0.039
0.030
0.082
0.81–0.98
6110
2698
181
0.016
0.030
0.088
0.62–0.78
11022
2769
172
0.039
0.027
0.057
0.77–1.00
11716
2548
192
0.089
0.037
0.083
R [F, I > 2r(I)]
wR (F2, all data)
Table 2 Intramolecular parameters
Table 3 Intermolecular packing parametersa
Bond lengths/Å
Angles/°
Compound
d/Å
h/°
x/°
Compound
C(4)–C(7)
C(7)C(8)
C(8)–C(9)
s
u
1
2
3
5
6
3.43
3.46
3.38
3.48
3.38
46.3
48.1
25.5
46.7
46.2
87.5
83.8
0
86.5
87.5
1
2
3
5
6
1.430(8)
1.438(3)
1.433(2)
1.438(4)
1.435(5)
1.205(9)
1.203(4)
1.195(2)
1.175(4)
1.191(5)
1.420(8)
1.432(3)
1.423(2)
1.446(4)
1.436(5)
9.4
15.7 10.6
3.4
13.1
12.8
6.9
4.8
1.4
1.4
a For uniformity, the molecular plane is defined as the mean plane of all
carbon atoms, ignoring halogens and H atoms.
Fig. 1 The molecular structures of 1, 2, 3, 5 and 6 with thermal ellipsoids drawn at 50% probability level.
(space group P21/c) crystal structures of compounds 1 and 2
are very similar and can be regarded as isomorphous with the
bromine–iodine substitution. In the same way, compound 5 is
isomorphous with 6, both crystallising in the monoclinic space
group P21/n. In these four structures, the adjacent molecules in
a stack are related by the b translation and therefore are strictly
parallel, and all interplanar separations along a stack are sym-
metrically equivalent. The stack is strongly slanted, as indicated
by the ‘offset angle’ (h in Table 3) between the direction of the
stack and the normal to the molecular planes. The offsets in
structures 1, 2, 5 and 6 are similar in both magnitude and di-
rection, so that the CC bond of each molecule is sandwiched
between a C–C bond of a benzene ring on one side and a C–C
bond of a fluorinated benzene ring on the other (Fig. 2). Thus,
there is no overlap between parallel arene and perfluoroarene
rings, which is the structure-defining synthon in practically
all molecular arene:perfluoroarene complexes13 and in most
arylene–ethynylene ‘rods’ containing both fluorinated and non-
fluorinated rings.15
Although the directions of all stacks in each structure are
parallel, the planes of molecules from adjacent stacks are almost
perpendicular (dihedral angle x in Table 3). The inter-stack
3 1 7 4
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 1 7 2 – 3 1 7 8

View Article Online
Fig. 2 Overlap of molecules in the stacks for 1 (similar with 2), 3 and
5 (similar with 6). H atoms are omitted.
packing motif can be best described as ‘flattened herringbone’.22
In structures 1 and 2 adjacent stacks are related via a 21 screw
axis and their molecules contact head-to-head (Fig. 3), giving
rise to an infinite zig-zag chain of (interstack) contacts II
(3.744 Å) or BrBr (3.557 Å). These contacts are shorter than
twice the (isotropic) van der Waals radii of iodine (4.06 Å) and
bromine (3.74 Å), respectively,23 and have the characteristic
“L-shape” of the C–XX–C moiety, with one C–XX angle
close to 180° (167.4° in 1, 163.6° in 2) and the other close to 90°
(95.6° in 1 and 85.5° in 2). In contrast, in structures 5 and 6,
adjacent stacks are related via a glide plane and their molecules
contact head-to-tail, which precludes any close proximity bet-
ween iodine or bromine atoms.
Compound 3, although chemically analogous to 1 and 2, crys-
tallises in a very different motif: adjacent molecules in a stack are
related via inversion centres and therefore are antiparallel rather
than parallel. The offset angle is much smaller than in 1 and 2
(and also in 5 and 6). Thus, the structure contains mixed stacks
of alternating arene and perfluoroarene rings. Although there
are two symmetrically non-equivalent interplanar separations
in the stack, in fact they are almost equal. The shortest ClCl
separation of 3.927 Å is much greater than twice the van der
Waals radius of Cl (3.52 Å), while the contacts ClF(11) (x,
y, z − 1) of 3.29 Å and ClF(13) (x − 1, y, z − 1) of 3.21 Å are
close to the sum of van der Waals radii (1.76 + 1.46 = 3.22 Å).
The structure being triclinic (space groupP1), molecular planes
in adjacent stacks are parallel. In fact, the structure of 3 is iso-
morphous with that of PhCCC6F5,with a substitution of one
Cl atom for F.15
As mentioned previously, co-crystallization of an arene and
a perfluoroarene containing one benzene ring or one aromatic
condensed system each, always leads to the motif of mixed stacks
with alternating arene and perfluoroarene moieties contacting
face-to-face (with some offset), although pure components
display herring bone motifs without any stacking. The stacking
mode is probably due largely to electrostatic interactions.13c This
motif has also been observed in a number of rod-like molecules
containing arene and perfluoroarene groups.1,11,14a,15 Given that
structure 3 displays this ‘normal’ synthon, one has to explain
the absence of this synthon in other structures. A plausible
explanation for 1 and 2 seems to be the prevalence of II
Fig. 3 Crystal packing of 1, 3 and 5 (H atoms are omitted).
and BrBr interactions. Short contacts of precisely this type
between atoms of halogens (and especially heavier halogens)
have been known for a long time and often attributed to rela-
tively strong interactions (‘secondary bonds’, charge-transfer,
or quasi-covalent interactions).24–26 One of the favoured models
invokes weak donor–acceptor interactions between the relatively
electron-deficient ‘polar’ part of the halogen atom (close to the
continuation of the covalent bond) and electron-rich orbitals
normal to this bond. Unfortunately, while structural data on
halogen–halogen contacts are abundant, reliable information
about the energy and character of the bonding is not. Most of
the observed geometrical effects can be rationalised simply by
postulating anisotropic shapes of the halogen atoms, flattened
at the ‘pole’ (i.e. along the continuation of the covalent bond).
The corresponding system of anisotropic van der Waals radii27
would suggest for 1 and 2 II and BrBr contact distances of
ca. 3.9 and 3.4 Å, respectively, of which the latter (although not
the former) is shorter than the observed distance. A thorough
crystallographic and ab initio study28 of ClCl contacts in
chlorinated hydrocarbons proved specific attractive interactions
to be negligible and the van der Waals repulsion anisotropic.
Similar work for bromo and iodo derivatives remains to be
undertaken, although the higher polarisability of these atoms
makes attractive interactions much more likely. Although this
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 1 7 2 – 3 1 7 8
3 1 7 5

View Article Online
1
give colourless plates. Yield: 0.72 g (18%), m.p. 95–96 °C. H
agrees with our present observations (II and BrBr but not
ClCl interactions supplanting arene–perfluoroarene interac-
tions as the structure-defining factor), more thorough and
extensive investigation is obviously necessary, the more so as
neither halogen–halogen nor arene–perfluoroarene interactions
are realised in structures 5 and 6.
NMR (200 MHz): d 7.74 (m, 2H), 7.29 (m, 2H). 19F{1H} NMR
(188 MHz): d −136.2 (m, 2F), −152.5 (m, 1F), −162.0 (m, 2F).
13C{1H} NMR (125 MHz): d 147.1 (d of m, C–F, JCF = 250 Hz),
141.5 (d of m, C–F, JCF = 255 Hz), 137.8 (d of m, C–F,
JCF = 250 Hz), 137.7 (C–H), 133.2 (C–H), 120.9 (Cipso of arene
ring), 100.5 (CC), 100.0 (m, Cipso of fluoroarene ring), 96.0
(C–I), 74.4 (CC). MS (EI) m/z (rel): 394 (m+, 100), 266 (10),
248 (10), 217 (10). Anal. Calcd. for C14H4F5I: C 42.67, H 1.02;
Found: C 42.45, H 0.98%.
3. Conclusions
A series of 1-halogeno-4-(pentafluorophenyl–ethynyl)benzenes
and 1-halogeno-4-(phenylethynyl)tetrafluorobenzenes have
been synthesized. In all but one case this was achieved by
palladium-catalyzed Sonogashira cross-coupling. In the case
of 1-chloro-4-(pentafluorophenylethynyl)benzene, nucleophilic
attack on chloropentafluorobenzene by lithium phenylacetylide
was used. The single crystal structures of five of the com-
pounds have been solved from X-ray diffraction data. The
molecules show three types of packing motif, one dominated
by halogen–halogen interactions, the second dominated by
arene–perfluoroarene interactions, and the third in which nei-
therarepresent.Thestructureof 1-chloro-4-(pentafluorophenyl-
ethynyl)benzene is the first fully determined crystal structure of
a compound that contains a halogen atom other than fluorine,
in which arene–perfluoroarene interactions are present.
1-Bromo-4-(pentafluorophenylethynyl)benzene (2). Ca. 150 ml
of triethylamine was added to a 250 ml Schlenk flask containing
1-bromo-4-iodobenzene (2.82 g, 10 mmol), Pd(PPh3)2Cl2 (0.07 g,
0.1 mmol) and CuI (0.02 g, 0.1 mmol). Pentafluorophenyl-
acetylene (2.30 g, 12 mmol) was added dropwise by pipette
under N2 purge. The reaction mixture was stirred for 4 h at room
temperature, then filtered through a coarse sinter, and was evap-
orated to dryness in vacuo. The crude residue was extracted with
hexane, filtered through a 3 cm thick silica pad, and the filtrate
evaporated under reduced pressure. The residue was re-crystal-
lised from hexane to give the pure product as colourless cubes.
1
Yield: 2.80 g (85%), m.p. 103–104 °C. H NMR (200 MHz): d
7.53 (m, 2H), 7.44 (m, 2H). 19F{1H} NMR (188 MHz): d −136.2
(m, 2F) −152.5 (m, 1F, F) −162.0 (m, 2F, F). 13C{1H} NMR
(125 MHz): d 147.1 (d of m, C–F, JCF = 252 Hz), 141.5 (d of m,
C–F, JCF = 254 Hz), 137.7 (d of m, C–F, JCF = 250 Hz), 133.2
(C–H), 131.9 (C–H), 124.2 (C–Br), 120.9 (Cipso of arene ring),
100.3 (CC), 100.0 (m, Cipso of fluoroarene ring), 74.2 (CC).
MS (EI) m/z (rel): 348 (m+, 94), 346 (100), 266 (74), 248 (82), 247
(39), 241 (22), 240 (30), 217 (79), 216 (36), 173 (26). Anal. Calcd.
for C14H4F5Br: C 48.45, H 1.16; Found: C 48.48, H 1.14%.
4. Experimental
4.1 Synthesis and characterisation
All reactions were carried out under a dry N2 atmosphere using
standard Schlenk techniques, although once the reactions were
complete, further procedures were carried out without any
precautions against air. Triethylamine and diisopropylamine
were distilled from CaH2 under N2 and THF was distilled over
Na/benzophenone under N2, prior to use. All other solvents
were GPR grade and used without further purification or
drying. Pentafluorophenylacetylene was prepared using a modi-
fied literature procedure.20 The catalyst precursor Pd(PPh3)2Cl2
was prepared via the literature procedure.29 All other reagents
were obtained from commercial suppliers and used without
further purification.
1-Chloro-4-(pentafluorophenylethynyl)benzene (3). Ca. 50 ml
of triethylamine was added to a 100 ml Schlenk flask containing
1-chloro-4-iodobenzene (0.48 g,
2 mmol), Pd(PPh3)2Cl2
(0.014 g, 0.02 mmol) and CuI (0.004 g, 0.02 mmol). Penta-
fluorophenylacetylene (0.46 g, 2.4 mmol) was added by pipette
to the mixture under N2 purge. The reaction mixture was allowed
to stir for 3 h at room temperature, and was then heated at 60 °C
for 1 h. It was subsequently filtered through a coarse sinter, and
then evaporated to dryness in vacuo. The crude residue was
extracted with hexane, filtered through a 3 cm silica pad, and the
filtrate evaporated under reduced pressure. The residue was re-
crystallised from hexane to give the product as colourless needles.
Yield: 0.46 g (85%), m.p. 99–100 °C. 1H NMR (200 MHz): d 7.51
(m, 2H), 7.37 (m, 2H). 19F{1H} NMR (188 MHz): d −136.3 (m,
2F, F), −152.6 (m, 1F, F), −162.0 (m, 2F, F). 13C{1H} NMR
(125 MHz): d 147.1 (d of m, C–F, JCF = 253 Hz), 141.6 (d of m,
Proton and 19F NMR spectra were recorded on a Varian
Mercury spectrometer at 200 MHz and 188 MHz respectively in
CDCl3. The chemical shifts are reported in ppm and referenced
to the internal standards SiMe4 and CFCl3 respectively. 13C
NMR experiments were performed on a Varian spectrometer at
125 MHz with chemical shifts referenced to SiMe4. MS analy-
ses were performed on a Hewlett-Packard 5890 Series II gas
chromatograph with a 5971A MSD mass selective ion detector
and a 12 m fused silica (5% cross-linked phenylmethylsilicone)
capillary column, under the following operating conditions:
injector temperature 250 °C, detector temperature 270 °C, the
oven temperature was ramped from 70 °C to 270 °C at the rate
20 °C min−1. UHP helium was used as the carrier gas. Elemental
analyses were performed using an Exeter Analytical CE-440
analyzer at the University of Durham. Melting points were ob-
tained using a Laboratory Devices Mel-Temp II equipped with
a Fluke 51 digital thermometer, and are uncorrected.
C–F, JCF = 254 Hz), 137.7 (d of m, C–F JCF = 250 Hz), 135.9
,
(C–Cl), 133.1 (C–H), 129.0 (C–H), 120.2 (Cipso of arene ring),
100.5 (CC), 100.2 (m, Cipso of fluoroarene ring), 74.2 (CC).
MS (EI) m/z (rel): 304 (m+, 31), 302 (100), 266 (15), 248 (21),
217 (19), 216 (12). Anal. Calcd. for C14H4F5Cl: C 55.54, H 1.32,
Found: C 55.56, H 1.24%.
1-Fluoro-4-(pentafluorophenylethynyl)benzene (4). Ca. 50 ml
of triethylamine was added to a 100 ml Schlenk flask containing
1-Iodo-4-(pentafluorophenylethynyl)benzene (1). Ca. 300 ml of
triethylamine was added to a 500 ml Schlenk flask containing
1,4-diiodobenzene (9.90 g, 30 mmol), Pd(PPh3)2Cl2 (0.07 g,
0.1 mmol) and CuI (0.02 g, 0.1 mmol). Pentafluorophenyl-
acetylene (2.30 g, 12 mmol) was added dropwise by pipette
under N2 purge and the reaction mixture was stirred for 4 h at
60 °C. The reaction mixture was filtered through a coarse sinter,
and then evaporated to dryness in vacuo. The crude residue was
extracted with hexane, filtered through a 3 cm silica pad, and
the filtrate evaporated under reduced pressure. The residue was
purified via column chromatography on silica with cyclohexane
as the eluent, to obtain 5.50 g of recovered 1,4-diodobenzene,
and the product, which was re-crystallised from hexane to
1-fluoro-4-iodobenzene (0.44 g,
2 mmol), Pd(PPh3)2Cl2
(0.014 g, 0.02 mmol) and CuI (0.004 g, 0.02 mmol). Penta-
fluorophenylacetylene (0.46 g, 2.4 mmol) was added by pipette
under N2 purge. The reaction mixture was stirred for 3 h at room
temperature, and was then heated at reflux for 2 h. It was then
filtered through a coarse sinter, and evaporated to dryness in
vacuo. The crude residue was extracted with hexane, filtered
through a 3 cm silica pad, and the filtrate evaporated under
reduced pressure. The residue was re-crystallised from hexane
to give the product as colourless crystals. Yield: 0.45 g (79%),
1
m.p. 82–83 °C. H NMR (200 MHz): d 7.57 (m, 2H), 7.09 (m,
2H). 19F{1H} NMR (188 MHz): d −108.8 (m, 1F), −136.5 (m,
3 1 7 6
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 1 7 2 – 3 1 7 8

View Article Online
2F), −153.0 (m, 1F), −162.1 (m, 2F). 13C{1H} NMR (125 MHz):
d 163.3 (d, C–F, JCF = 255 Hz), 147.1 (d, C–F, JCF = 255 Hz),
141.5 (d, C–F, JCF = 250 Hz), 137.6 (d, C–F, JCF = 250 Hz),
134.0 (C–H), 117.6 (Cipso of arene ring), 116.0 (m, C–H), 100.4
(CC), 100.1 (m, Cipso of fluoroarene ring), 72.8 (CC). MS
(EI), m/z (rel): 286 (m+, 100), 266 (7), 255 (11), 235 (9), 217 (8),
216 (8). Anal. Calcd. for C14H4F6: C 58.74, H 1.40; Found: C
58.87, H 1.42%.
through a 3 cm thick silica pad. The filtrate was evaporated
under reduced pressure to leave a white residue, which was re-
crystallised from hexane to give the product as a white powder.
Yield: 1.04 g (37%), m.p. 95–96 °C. 1H NMR (200 MHz): d 7.59
(m, 2H), 7.38 (m, 3H). 19F{1H} NMR (188 MHz): d −136.3 (m,
2F), −141.7 (m, 2F). MS (EI) m/z (rel): 286 (m+, 33), 285 (16),
284 (100), 248 (10). Anal. Calcd. for C14H5F4Cl: C 58.93, H 1.91;
Found: C 58.76, H 1.56%.
1-Iodo-4-(phenylethynyl)tetrafluorobenzene (5). Ca. 300 ml
of diisopropylamine was added to a 500 ml Schlenk flask
containing 1,4-diiodotetrafluorobenzene (12.06 g, 30 mmol),
Pd(PPh3)2Cl2 (0.07 g, 0.1 mmol) and CuI (0.02 g, 0.1 mmol).
Phenylacetylene (1.22 g, 12 mmol) was added dropwise by
pipette under a N2 purge. The reaction mixture was allowed
to stir for 4 h. The reaction mixture was filtered through a
coarse sinter, and was then evaporated to dryness in vacuo.
The crude residue was extracted with hexane and filtered
through a 3 cm silica silica pad, and the filtrate evaporated
under reduced pressure. The residue was purified via column
chromatography using hexane as the eluent, to obtain 6.40 g
of recovered 1,4-diodotetrafluorobenzene, and the product,
which was re-crystallised from hexane to give colourless needles.
4.2 Crystallography
Diffraction quality crystals were obtained by re-crystallisation
from n-hexane or by slow evaporation of dichloromethane
solutions. X-Ray diffraction experiments were carried out on
Bruker 3-circle diffractometers equipped with a SMART 1000
or (for 6) SMART 6000 CCD area –detector, using graphite-
monochromated Mo-Ka radiation (λ = 0.71073 Å). The low
temperature of the crystals was maintained using Cryostream
(Oxford Cryosystems) open-flow N2 cryostats. Several runs of
narrow (0.3°) x scans covered the full sphere of the reciprocal
space to 2h = 55° (for 6, 2h = 54°). Reflection intensities
were corrected for absorption by a semi-empirical method
based on multiple scans of identical reflections and Laue
equivalents.30 The structures were solved by direct methods,
and refined by full-matrix least squares on F2 of all the data,
using SHELXTL software.31 Non-H atoms were refined in
anisotropic approximation, H atoms were refined in isotropic
approximation (in 2 and 6) or treated as ‘riding’ in idealised
positions. The crystal data and experiment details are listed in
Table 1.
1
Yield: 2.70 g (72%), m.p. 123–124 °C. H NMR (200 MHz): d
7.60 (m, 2H), 7.40 (m, 3H). 19F{1H} NMR (188 MHz): d −137.5
(m, 2F), −159.3 (m, 2F). 13C{1H} NMR (125 MHz): d 148.3 (d
of m, C–F, JCF = 253 Hz), 145.8 (d of m, C–F, JCF = 256 Hz),
132.2 (C–H), 130.0 (C–H), 128.8 (C–H), 121.8 (Cipso of arene
ring), 102.8 (CC), 100.3 (m, Cipso of fluoroarene ring), 74.7
(CC), 73.1 (m, C–I). MS (EI), m/z (rel): 377 (26), 376 (m+, 100),
248 (11). Anal. Calcd. for C14H5F4I: C 44.71, H 1.34; Found: C
44.51, H 1.30%.
CCDC
reference
numbers
245721–245725.
See
http://www.rsc.org/suppdata/ob/b4/b411191e/ for crystallo-
graphic data in .cif or other electronic format.
1-Bromo-4-(phenylethynyl)tetrafluorobenzene (6). Ca. 300 ml
of diisopropylamine was added to a 500 ml Schlenk flask
containing 1,4-dibromotetrafluorobenzene (9.24 g, 30 mmol),
Pd(PPh3)2Cl2 (0.07 g, 0.1 mmol) and CuI (0.02 g, 0.1 mmol).
Phenylacetylene (1.22 g, 12 mmol) was added dropwise by
pipette under N2 purge. The reaction mixture was allowed to
stir for 4 h, and was then filtered through a coarse sinter, and the
filtrate evaporated to dryness in vacuo. The crude residue was
extracted with hexane, filtered through a 3 cm silica pad, and
the filtrate evaporated under reduced pressure. The residue was
purified via column chromatography using hexane as the eluent,
to obtain 4.30 g of recovered 1,4-dibromotetrafluorobenzene,
and the product, which was re-crystallised from hexane to give
Acknowledgements
We thank EPSRC for research support, for postgraduate
studentships (JCC, JMB, PSS) and for a Senior Research
Fellowship (JAKH). We also thank Ms. Jaroslava Dostal for
performing the elemental analyses.
References
1 S. W. Watt, C. Dai, A. J. Scott, J. M. Burke, R. Ll. Thomas,
J. C. Collings, C. Viney, W. Clegg and T. B. Marder, Angew. Chem.,
Int. Ed., 2004, 43, 3061.
2 (a) U. H. F. Bunz, Chem. Rev., 2000, 100, 1605; (b) R. Giesa, J.
Macromol. Sci., Rev. Macromol. Chem. Phys., 1996, C36, 631;
(c) J. M. Tour, Chem. Rev., 1996, 96, 537; (d) J. S. Moore, Acc. Chem.
Res., 1997, 30, 402.
1
colourless needles. Yield: 2.12 g (65%), m.p. 100–101 °C. H
NMR (200 MHz): d 7.60 (m, 2H), 7.40 (m, 3H). 19F{1H} NMR
(188 MHz): d −134.2 (m, 2F), −136.3 (m, 2F). 13C{1H} NMR
(125 MHz): d 148.1 (d of m, C–F, JCF = 254 Hz), 145.6 (d of m,
C–F, JCF = 250 Hz), 131.9 (C–H), 129.7 (C–H), 128.5 (C–H),
121.5 (Cipso of arene ring), 102.9 (CC), 100.3 (m, Cipso of
fluoroarene ring), 74.0 (CC). MS (EI), m/z (rel): 330 (31), 328
(m+, 100), 248 (57), 230 (36), 229 (21), 199 (29). Anal. Calcd. for
C14H5F4Br: C 51.17, H 1.52; Found: C 51.32, H 1.54%.
3 (a) P. Nguyen, Z. Yuan, L. Agocs, G. Lesley and T. B. Marder,
Inorg. Chim. Acta, 1994, 220, 289; (b) P. Nyugen, S. Todd,
D. Van den Biggelar, N. J. Taylor, T. B. Marder, F. Wittmann and
R. H. Friend, Synlett, 1994, 299; (c) P. Nguyen, G. Lesley, C. Dai,
N. J. Taylor, T. B. Marder, V. Chu, C. Viney, I. Ledoux and J. Zyss,
in Applications of Organometallic Chemistry in the Preparation
and Processing of Advanced Materials, ed. J. F. Harrod and R. M.
Laine, Kluwer Academic, Dordrecht, 1995, p. 333; (d) P. Nguyen,
G. Lesley, T. B. Marder, I. Ledoux and J. Zyss, Chem. Mater., 1997,
9, 406; (e) M. Biswas, P. Nguyen, T. B. Marder and L. R. Khundkar,
J. Phys. Chem. A, 1997, 101, 1689; (f) A. Beeby, K. Findlay, P. J. Low
and T. B. Marder, J. Am. Chem. Soc., 2002, 124, 8280; (g) A. Beeby,
K. S. Findlay, P. J. Low, T. B. Marder, P. Matousek, A. W. Parker,
S. R. Rutter and M. Towrie, Chem. Commun., 2003, 2406.
4 (a) A. V. Abramenkov, A. Almenningen, B. N. Cyvin, S. J. Cyvin,
T. Jonvik, L. L. S. Khaikin, C. Romming and L. V. Vilkov, Acta
Chem. Scand. Ser. A, 1988, 42, 674; (b) K. Okuyama, T. Hasegawa,
T. Ito and N. Mikami, J. Phys. Chem., 1984, 88, 1711.
5 A. Mavridis and I. Moustakali-Mavridis, Acta Crystallogr., Sect. B,
1977, 33, 3612.
6 G. R. Desiraju and T. S. R. Krishna, J. Chem. Soc., Chem. Commun.,
1988, 192.
7 (a) A. E. Stiegman, E. Graham, K. J. Perry, L. R. Khundkar,
L.-T. Cheng and J. W. Perry, J. Am. Chem. Soc., 1991, 113, 7658;
(b) C. Dehu, F. Meyers and J.-L. Bredas, J. Am. Chem. Soc., 1993,
115, 6198.
1-Chloro-4-(phenylethynyl)tetrafluorobenzene (7). Ca. 50 ml
of dry THF was added to a three-necked 250 ml flask equipped
with a dropping funnel. Phenylacetylene (1.02 g, 10 mmol) was
added via pipette to the flask under N2 purge. A 6.5 ml aliquot
of a 1.6 M solution of n-butyllithium in hexanes was added via
cannula to the dropping funnel under nitrogen. The butyllithium
solution was then added dropwise to the reaction mixture
at −78 °C, and the reaction was stirred for 1 h. Chloropenta-
fluorobenzene (2.02 g, 10 mmol) was added under nitrogen
purge. The mixture was allowed to warm to room temperature,
and was observed to darken progressively. After 24 h, the reaction
mixture was filtered through a 3 cm silica pad with diethyl ether,
and the filtrate was evaporated under reduced pressure to leave a
dark residue. The residue was extracted with hexane and filtered
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 1 7 2 – 3 1 7 8
3 1 7 7

View Article Online
8 M. Ohkita, T. Suzuki, K. Nakatani and T. Tsuji, Chem. Commun.,
2001, 1454.
9 (a) T. Kurihara, H. Tabei and T. Kaino, J. Chem. Soc., Chem.
Commun., 1987, 959; (b) H. Tabei, T. Kurihara and T. Kaino, Appl.
Phys. Lett., 1987, 59, 1855; (c) C. Wang, J. Feng and C. Yu, J. Beijing
Inst. Technol., 1996, 5, 27; (d) C. Dai, A. J. Scott, W. Clegg, G. Cross
and T. B. Marder, unpublished results.
J. Wen, Chin. J. Chem., 1994, 12, 169; (f) J. Wen, M. Q. Tian and
Q. Chen, Liq. Cryst., 1994, 16, 445.
17 M. R. Wiles and A. G. Massey, Tetrahedron Lett., 1967, 5137.
18 Q.-Y. Chen and Z.-T. Li, J. Chem. Soc., Perkin Trans. 1, 1992,
2931.
19 P. Tarrant, in Fluorine Chemistry Reviews, ed. P. Tarrant, Marcel
Dekker, New York, vol. 7, 1974.
10 C. Dai, A. J. Scott, W. Clegg, S. W. Watt, C. Viney and T. B. Marder,
unpublished results.
11 C. Dai, P. Nguyen, T. B. Marder, A. J. Scott, W. Clegg and C. Viney,
Chem. Commun., 1999, 2494.
20 Y. Zhang and J. Wen, Synthesis, 1990, 727.
21 J. Kajanus, S. B. van Berlekom, B. Albinsson and J. Martensson,
Synthesis, 1999, 1155.
22 G. R. Desiraju and A. Gavezzotti, Acta Crystallogr., Sect. B, 1989,
45, 473.
23 R. S. Rowland and R. Taylor, J. Phys. Chem., 1996, 100, 7384.
24 H. A. Bent, Chem. Rev., 1968, 68, 587.
25 G. R. Desiraju, Crystal Engineering. The Design of Organic Solids,
Elsevier, Amsterdam, 1989.
26 (a) N. Ramasubbu, R. Parthasarathy and P. Murray-Rust, J. Am.
Chem. Soc., 1986, 108, 4308; (b) R. Pedireddi, D. S. Reddy, S. Goud,
D. C. Craig, A. D. Rae and G. R. Desiraju, J. Chem. Soc., Perkin
Trans. 2, 1994, 2353.
27 S. C. Nyburg and C. H. Faerman, Acta Crystallogr., Sect. B, 1985,
41, 274.
28 S. L. Price, A. J. Stone, J. Lucas, R. S. Rowland and A. E. Thornley,
J. Am. Chem. Soc., 1994, 116, 4910.
29 (a) R. F. Heck, Palladium Reagents in Organic Synthesis, Academic
Press, London, 1985, p. 18; (b) L. Brandsma, S. F. Vasilevsky and
H. D. Verruijsse, Application of Transition Metal Catalysts in
Organic Synthesis, Springer, Berlin, 1988, p. 179.
30 G. M. Sheldrick, SADABS: Program for scaling and correction of
area detector data, ver. 2.03, Bruker AXS, Madison, Wisconsin,
USA, 2001.
31 G. M. Sheldrick, SHELXTL, An integrated system for solving
refining and displaying crystal structures from diffraction data, ver.
5.10, Bruker Analytical X-ray Systems, Madison, Wisconsin, USA,
1997.
12 C. R. Patrick and G. S. Prosser, Nature, 1960, 187, 1021.
13 (a) J. H. Williams, J. K. Cockcroft and A. N. Fitch, Angew. Chem.,
Int. Ed. Engl., 1992, 31, 1655; (b) T. Dahl, Acta Chem. Scand. Ser.
A, 1988, 42, 1; (c) J. Potenza and D. Mastropaolo, Acta Crystal-
logr., Sect. B, 1975, 31, 2527; (d) J. C. Collings, K. P. Roscoe,
R. Ll. Thomas, A. S. Batsanov, L. M. Stimson, J. A. K. Howard
and T. B. Marder, New J. Chem., 2001, 25, 1410; (e) J. C. Collings,
K. P. Roscoe, E. G. Robins, A. S. Batsanov, L. M. Stimson,
J. A. K. Howard, S. J. Clark and T. B. Marder, New J. Chem., 2002,
26, 1740.
14 (a) G. W. Coates, A. R. Dunn, L. M. Henling, D. A. Dougherty
and R. H. Grubbs, Angew. Chem., Int. Ed. Engl., 1997, 36, 248;
(b) C. P. Brock, D. G. Naae, N. Goodhand and T. A. Hamor, Acta
Crystallogr., Sect. B, 1978, 34, 3691; (c) V. R. Vangala, A. Nangia
and V. M. Lynch, Chem. Commun., 2002, 1304.
15 C. E. Smith, P. S. Smith, R. L. Thomas, E. G. Robins, C. Dai,
A. J. Scott, S. Borwick, A. S. Batsanov, S. W. Watt, S. J. Clark,
C. Viney, J. A. K. Howard, W. Clegg and T. B. Marder, J. Mater.
Chem., 2004, 14, 413.
16 (a) J. Wen, M. Tian, H. Yu, Z. Guo and Q. Chen, J. Mater. Chem.,
1994, 4, 327; (b) J. Wen, M. Q. Tian and Q. Chen, J. Fluorine
Chem., 1994, 68, 117; (c) J. Wen, Y. L. Xu and Q. Chen, J. Fluorine
Chem., 1994, 68, 15; (d) Y. L. Xu, W. L. Wang, Q. Chen and J. Wen,
Liq. Cryst., 1994, 15, 915; (e) Y. L. Xu, W. L. Wang, Q. Chen and
3 1 7 8
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 1 7 2 – 3 1 7 8