Synthesis, optical properties, crystal structures and phase behaviour of symmetric, conjugated ethynylarene-based rigid rods with terminal carboxylate groups

Article abstract of DOI:10.1039/b413514h

Sonogashira cross-coupling reactions of 4-ethynylmethylbenzoate (1) with aryl halides gave 1,2-bis(4-carbomethoxyphenyl)ethyne (2), 1,4-bis(4- carbomethoxyphenylethynyl)benzene (3), 1,4-bis(4-carbomethoxyphenylethynyl) tetrafluorobenzene (4) and 9,10-bis(4-carbomethoxyphenylethynyl)anthracene (5), protected precursors to conjugated rigid rod bis(carboxylato) ligands. The compound 1,4-bis(4-carbomethoxyphenyl)butadiyne (6) was prepared by the oxidative homo-coupling of 1. The hydrolysis of 2 and 3 by NaOH in methanol gave the sodium salts of the respective carboxylate anions and subsequent treatment with HCl gave the corresponding free carboxylic acids. Compounds 2-6 were characterised by absorption, emission, IR, NMR and mass spectrometry and examined for liquid crystal phase behaviour by differential thermal analysis (DTA) and transmitted polarised light microscopy (TPLM). Compound 4 exhibited a nematic phase stable from 233.6 °C until decomposition at 320 °C. The single-crystal structures of 2, 5 and 6 were determined by X-ray diffraction at 110-160 K. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b413514h

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Synthesis, optical properties, crystal structures and phase behaviour of
symmetric, conjugated ethynylarene-based rigid rods with terminal
carboxylate groups
Tolulope M. Fasina,*ab Jonathan C. Collings,a Jacqueline M. Burke,a Andrei S. Batsanov,a
Richard M. Ward,a David Albesa-Jove´,a Laurent Porre`s,a Andrew Beeby,a Judith A. K. Howard,a
Andrew J. Scott,c William Clegg,c Stephen W. Watt,{d Christopher Viney{d and Todd B. Marder*a
Received 2nd September 2004, Accepted 26th October 2004
First published as an Advance Article on the web 24th November 2004
DOI: 10.1039/b413514h
Sonogashira cross-coupling reactions of 4-ethynylmethylbenzoate (1) with aryl halides gave
1,2-bis(4-carbomethoxyphenyl)ethyne (2), 1,4-bis(4-carbomethoxyphenylethynyl)benzene (3),
1,4-bis(4-carbomethoxyphenylethynyl)tetrafluorobenzene (4) and 9,10-bis(4-
carbomethoxyphenylethynyl)anthracene (5), protected precursors to conjugated rigid rod
bis(carboxylato) ligands. The compound 1,4-bis(4-carbomethoxyphenyl)butadiyne (6) was
prepared by the oxidative homo-coupling of 1. The hydrolysis of 2 and 3 by NaOH in methanol
gave the sodium salts of the respective carboxylate anions and subsequent treatment with HCl
gave the corresponding free carboxylic acids. Compounds 2–6 were characterised by absorption,
emission, IR, NMR and mass spectrometry and examined for liquid crystal phase behaviour by
differential thermal analysis (DTA) and transmitted polarised light microscopy (TPLM).
Compound 4 exhibited a nematic phase stable from 233.6 uC until decomposition at 320 uC. The
single-crystal structures of 2, 5 and 6 were determined by X-ray diffraction at 110–160 K.
metal-organic supramolecular assemblies. Recently, several
Introduction
groups reported the use of extended rod-like carboxylate
spacers such as 4,4-biphenyldicarboxylic acid,6 2,6-naphtha-
The molecular assembly of coordination polymers and
lenedicarboxylic acid,7 and systems containing fused rings1e in
supramolecules has provided a facile approach to novel
molecular materials for applications in catalysis, separations
the construction of a variety of 1D, 2D and 3D frameworks
and molecular recognition.1 Most of the initial research has
with novel topologies. Several phenylene–ethynylene-based
focused on the use of neutral, rigid N,N9-spacers such as
rigid rods with terminal carboxylic acid groups have been used
4,49-bipyridine and extended analogues.2 However, the poten-
in composite materials which incorporate regularly spaced
tial applications of many of the resulting structures have been
CdS and PbS nanoparticles, by reaction of their cadmium and
lead carboxylate salts with H2S.8a,b In addition, the photo-
restricted as they either contained interpenetrating networks or
have the anion clathrated within the cavities.
luminescence and lasing properties of thin films of substituted
The availability of two oxygen atoms and four electron pairs
oligo(phenylene–ethynylenes) bearing benzenecarboxylate end
groups have been examined,8c and liquid crystal phase
for ligation in carboxylate ligands allows for a variety of
coordination modes ranging from monodentate through chelat-
behaviour of luminescent bis(phenylethynyl)anthracenes bear-
ing long-chain carboxylate groups have been reported.8d
ing, bridging and even polydentate binding. This results in the
synthesis of polymers having a wider variety of topological
While most of the carboxylate ligands were used either as
arrangements.3 Furthermore, the use of anionic carboxylate
sodium salts or as the free acids, it has been shown with
ligands results in the formation of neutral metal complexes,
unsymmetrical ligands that esters do hydrolyse in situ to give
the acids when utilized under hydrothermal conditions.9 As
which eliminates the problem of counter-ion clathration.
Carboxylate chemistry has thus recently allowed the synthesis
of robust, porous materials with useful applications.4
part of an ongoing programme to examine the properties of
rigid rods based on the phenylene–ethynylene motif,2h,10 we
Benzene polycarboxylic acids, such as 1,2,4,5-benzene-
report herein the synthesis and characterisation of a series
tetracarboxylic acid,5a 1,3,5-benzenetricarboxylic acid,5b,c
of extended bis(carboxymethyl) compounds and their hydro-
1,4-benzenedicarboxylic acid,5d–f and the related [(4,49,40-
tricarboxydodecachlorotriphenyl)methyl radical (PTMTC)5g–j
lysed bis(carboxylic acids) containing rigid rod conjugated
backbones.
have been used as ligands in the formation of highly porous
Results and discussion
{ Present address: Department of Chemistry, University of
Cambridge, Lensfield Road, Cambridge, UK CB1 1EW.
{ Present address: School of Engineering, University of California at
Owing to the potential reactivity of the acid group under the
Sonogashira cross-coupling reaction conditions, the com-
Merced, P.O. Box 2039, Merced, CA 95344, USA.
*Todd.Marder@durham.ac.uk (Todd B. Marder)
pounds were initially prepared as their methyl esters. This
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allowed for the isolation of the products in high yield by
passage through short silica gel columns with hot toluene,
and subsequent crystallisation upon cooling. The terminal
alkyne, 4-ethynyl(methylbenzoate) (1), used as precursor to
the conjugated systems, was prepared by a modification of
the literature procedure,11 involving the Sonogashira cross-
coupling of trimethylsilylacetylene (TMSA) to 4-iodo(methyl-
benzoate) at room temperature, followed by hydrodesilylation
using sodium carbonate in MeOH.
In addition, 1,4-bis(4-carbomethoxyphenyl)butadiyne 6 was
obtained in good yields via the oxidative homo-coupling of 1
using a stoichiometric amount of iodine in the presence of
catalytic Pd(PPh3)2Cl2 and CuI in triethylamine at room tem-
perature.15 This is also shown in Scheme 1. Compounds 3 and 6
have been previously reported, although no synthetic or charac-
terisation details were given.16 The esters 2 and 3 were converted
to the sodium salts of the corresponding acids via reaction
with NaOH, which were subsequently converted to the free acids
by treatment with HCl to give compounds 7 and 8 respectively.
Compounds 2–5 were synthesised via Sonogashira reactions
of 1 with the appropriate aryl halide using Pd(PPh3)2Cl2 and
CuI in triethylamine,12 as shown in Scheme 1. Thus,
4-iodo(methylbenzoate) was coupled with 1 at room tempera-
ture to give 2 in 91% yield. It was synthesised previously via a
one-pot coupling reaction involving 4-iodo(methylbenzoate)
and TMSA.13 Compounds 3 and 4 were prepared in 46
and 96% yields respectively by coupling of two equivalents of
Optical properties
The optical properties (absorption, fluorescence, quantum
yield and lifetime) of all compounds are presented in Table 1.
Compounds 2–4 display an intense absorption band in the UV
region. These chromophores are also highly fluorescent in the
UV, with quantum yields of up to 0.9. Compound 6 displays
similar UV absorption and fluorescence properties, but with a
defined vibrational substructure in absorption. This chromo-
phore shows a markedly lower quantum yield (1%) and a very
short fluorescence lifetime (70 ps), which are consistent with
the high non-radiative deactivation processes in diyne deriva-
tives.10e Lastly, compound 5 exhibits absorption and emission
in the visible range. Compared with the phenylene derivative 3,
this anthryl chromophore induces a smaller Stokes shift,
slightly lower quantum yield, and a fluorescence lifetime
reaching 2.7 ns.
1
to 1,4-diiodobenzene and 1,4-diiodotetrafluorobenzene,
respectively. Compound 5 was prepared via coupling of
two equivalents of 1 to the commercially available 9,10-
dibromoanthracene using the more active catalyst system
prepared in situ from Pd(PhCN)2Cl2 and the electron-rich
phosphine, PtBu3,14 which allowed the reaction to proceed at
room temperature in 80% yield. However, as the product was
often contaminated with traces of the mono-coupled material,
we chose to utilize samples prepared in similar yield but higher
purity from the more reactive 9,10-diiodoanthracene for
subsequent studies.
Scheme 1
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Table 1 Absorption and emission data for compounds 2–6 in acetonitrile, cyclohexane and dichloromethane
MeCN C6H12 CH2Cl2
e/cm21 lem e/cm21 lem
labs labs / Stokes
/
/
Stokes
labs
/
e/cm21 lem
/
Stokes
/
Cpd nm M21 t/ns nm M21 nm shift/cm21
nm shift/cm21
W
t/ns nm M21
nm shift/cm21
W
W
t/ns
a
2
3
4
5
304 41 700 330 2600
0.64 0.61 306
0.87 0.67 335
0.85 0.635 335
2.74 448
328 2200
362 2200
361 2150
482 1600
(400)
0.72 0.72 307 45 600 333 2500
0.70 0.64
0.91 0.68
0.86 0.62
0.64 2.67
a
a
a
a
a
a
332
331
(446)
473
322
364 2650
360 2400
483 (1700)
400
0.81
0.85
335 65 600 367 2600
334 43 500 364 2500
0.63 2.51 (451) 58 700 488 (1700)
478 400
326 48 200 355 2500
(472)
325
a
a
6
351 2600
0.006
—
352 2400
0.007
0.012 0.070
a
Not sufficiently soluble for accurate measurement of the extinction coefficient.
Crystal structures
benzene rings of the molecule are parallel but not coplanar,
˚
with an interplanar separation of 0.20 A. The same distortion
was observed in unsubstituted tolan,17 4,49-bis(methylamino-
carbonyl)tolan18 and 4-amino-49-nitrotolan,19 the last two
molecules also displaying nearly coplanar orientations of the
4,49-substituents. Molecules of 2 pack in layers parallel to the
(001) plane. Within a layer, the long axes of all molecules are
Compounds 2, 5 and 6 have been characterised by single-
crystal X-ray diffraction (Fig. 1). Molecule 2 has a crystal-
lographic inversion centre. The carboxy group is inclined by
only 5.6u to the plane of the benzene ring. The C(9)MC(99)
bond is tilted by 4.5u out of the latter plane, hence the two
Fig. 1 Molecular structures of 2, 5 (two independent molecules) and 6, showing displacement ellipsoids at the 50% probability level. Atoms
˚
generated by inversion centres are primed. Selected bond distances (A) in 2: C(6)–C(9) 1.433(2), C(9)–C(99) 1.199(3); in 5: C(6)–C(9) 1.439(2), C(9)–
C(10) 1.194(2), C(10)–C(11) 1.430(2), C(26)–C(29) 1.437(2), C(29)–C(30) 1.196(2), C(30)–C(31) 1.429(2); in 6: C(6)–C(9) 1.432(2), C(9)–C(10)
1.205(2), C(10)–C(11) 1.372(2), C(11)–C(12) 1.204(2), C(12)–C(13) 1.432(2).
692 | J. Mater. Chem., 2005, 15, 690–697
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parallel and are inclined by 67.5u to the layer plane, while
molecular planes contact face-to-edge at a dihedral angle of ca.
48u, i.e. they form a herringbone motif.
Table 2 Axial ratios and phase behaviour
Axial
ratio
Transitions
upon cooling
Cpd
Transitions upon heating
The unit cell of
5 contains two crystallographically
2
3
4
5
6
a
4.32
5.90
5.26
2.68
4.89
K 221.3 I
K (233.5)b deg
I 220.3 Ka
—
independent molecules, both of which lie on inversion centres.
The dihedral angle between the benzene and anthracene planes
is quite different in the two molecules, being 30.9 and 5.2u,
respectively, while the angle between the benzene and carboxy-
group planes is similar and small, 8.4 vs. 9.9u, and the CMC
bond is tilted out of the anthracene plane by 1.6 and 3.6u. In
9,10-bis(phenylethynyl)anthracene,10b the phenyl ring and the
CMC bond are inclined to the anthracene plane by 25.7 and
3.7u, respectively. The long axes of all molecules in the triclinic
structure of 5 are parallel within 0.3u, and their anthracene
planes are parallel within 3.6u. The anthracene moieties are
stacked in a brickwork pattern, with partial overlap between
their outlying rings and a mean interplanar separation of ca.
K1 216.7 K2 233.6 N 320 deg
K 291.1 I/deg
N 238.1 S/K2
—
K1 187.0 K2 (192.4)b
I
I (188.9)b
K
b
Metastable nematic phase forms on free cooling. Observed by
DTA only.
at 233.6 uC upon heating, which persisted until the sample
degraded at 320 uC, a range of over 80 uC. Upon cooling, the
nematic phase formed a transient smectic phase before
crystallising. It is interesting that 4, which has an axial ratio
of 5.26, exhibits mesophases whereas 3, with a larger axial
ratio of 5.90, does not. This is likely due to the enhanced
stability of the compound imparted by the four fluorine
substituents on the central ring which allows the mesophase to
˚
3.4 A.
Molecule 6 has no crystallographic symmetry and is
substantially non-planar. The two benzene rings form a
dihedral angle of 23.9u. The torsion angles between the
benzene rings and their carboxy substituents are larger than
in 2, viz. 10.4u around the C(2)–C(3) bond and 13.2u around
the C(16)–C(19) bond. It is noteworthy that the unsubstituted
1,4-diphenylbutadiyne is planar as a pure solid,20 in co-crystals
with perfluoro-1,4-diphenylbutadiyne,21 and in an acetylide
Cu4 cluster,22 whilst in 1,4-bis(4-nitrophenyl)butadiyne the
two benzene rings are perpendicular.23 However, the con-
formation has no appreciable effect on the bond distances in
the butadiyne moiety, which coincide, within experimental
error, in all diphenylbutadiyne derivatives, including 6. All
molecules in the triclinic structure of 6 have their long axes
parallel. The packing motif can be described as strongly
form below the degradation temperature. Compound
exhibited a metastable nematic phase upon cooling.
2
Conclusion
A series of conjugated rigid rods containing carboxylate end
groups have been prepared which are highly luminescent with
quantum yields up to 0.9. The 1,4-bis(4-carbomethoxyphenyl-
ethynyl)tetrafluorobenzene derivative displays
a nematic
mesophase over an 80 uC temperature range. Two of the
derivatives were converted to their free carboxylic acids via the
sodium salts. It is expected that these compounds will be of
considerable utility in the construction of extended solids
including transition metal carboxylates.
¯
slanted stacks running parallel to the [201] direction and
comprising a brickwork-type layer. The mean interplanar
˚
separation in a stack is ca. 3.4 A, and the shifts between
˚
adjacent molecules alternate between 5.6 and 7.8 A in the
Experimental
All reactions were performed under a dry N2 atmosphere using
standard Schlenk techniques. Et3N was freshly distilled from
CaH2 under N2 prior to use. NMR spectra were recorded on
Varian Mercury (1H at 200 MHz, 13C{1H} at 50 MHz,
19F{1H} at 188 MHz) or Bruker Avance (1H at 400 MHz,
13C{1H} at 100 MHz) spectrometers, in CDCl3, CD2Cl2, D2O
or d6-DMSO. Chemical shifts for 13C and 1H spectra are
given in ppm relative to SiMe4 as an external standard, using
the solvent or residual protons therein for reference; 19F
spectra are referenced to external CFCl3. FT-IR spectra were
recorded as Nujol mulls on a Perkin-Elmer 1600 FT-IR
spectrophotometer or a Bomen Michelson spectrophotometer.
UV-Vis absorption spectra were recorded on an ATI Unicam
UV-2 spectrophotometer. Steady state and time-resolved
fluorescence measurements were performed at room tempera-
ture in dilute solutions, with an absorbance of ,0.1, using a
Jobin-Yvon Horiba Fluorolog 3-22 Tau-3 spectrofluorimeter.
Fluorescence quantum yields were determined at room
temperature, relative to double matched standards [quinine
sulfate in 0.1 M H2SO4 and 2,29-(1,4-phenylene)bis(5-phenyl-
oxazole) in cyclohexane],26 and refractive index correction was
performed.27 Fluorescence lifetimes were recorded operating in
the phase-modulation mode. The phase shift and modulation
directions almost parallel to the long molecular axes.
…
The closest intermolecular (C)H O contacts in structures 2
˚
(2.67–2.70 A), 5 (2.59–2.69 A) and 6 (2.45–2.68 A) are close to
˚
˚
24
the sum of the van der Waals radii (2.68 A) and, according
˚
to MO calculations, are well within the range of stabilising
2
C(sp )–H O interactions (weak hydrogen bonds), which
…
25
have a potential minimum at 2.58 A. However, structure 6
˚
…
also contains an exceptionally short contact C(18)–H O(49)
˚
(x + 1, y, z) of 2.22 A, which nearly corresponds to the E 5 0
point of the calculated potential curve25 and the lower edge
24
…
of the observed distribution of (C)H O distances, i.e. to
the border between stabilising and destabilising repulsive
interactions.
Phase behaviour
The phase behaviour of compounds 2–6 was studied using
differential thermal analysis (DTA) and transmitted polarised
light microscopy (TPLM). The phase transition data are given
in Table 2. Compounds 4 and 6 show two distinct crystalline
phases upon heating. Only compound 4 was found to exhibit
any stable liquid crystal mesophases: a nematic phase appeared
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were recorded over the frequency range 1–300 MHz, and the
data fitted using the Jobin-Yvon software package. Mass
spectra were recorded on an HP 5971 Mass Selective Detector
attached to an HP 5890 GC using a 5% Ph-methylsiloxane
coated capillary column with UHP helium as the carrier gas.
Elemental analyses were obtained from M-H-W Laboratories,
Phoenix, Arizona and the University of Durham. All organic
reagents were obtained from commercial sources and tested for
purity by GC–MS prior to use.
under N2 was added Et3N (50 mL) via syringe. The reaction
mixture was stirred overnight at room temperature. The
resulting precipitate was collected by filtration, washed with
water and dissolved in hot toluene. The hot toluene solution
was filtered through a short pad of silica gel (70–230 mesh).
Cooling of the toluene solution gave the desired compound as
small, white crystals. Yield 0.36 g (46%), mp 234 uC (decomp.).
1
IR (cm21) 1718 (CO). H NMR (CDCl3): d 3.92 (s, 6H), 7.55
(d, 4H), 8.00 (m, 4H), 7.47 (s, 4H). MS (EI), m/z (rel.): 395
(32), 394 (100), 363 (33), 276 (17), 166 (17). Anal. calc. for
C26H18O4: C, 79.17; H, 4.60. Found: C, 79.38; H, 4.62%.
Synthesis
4-Ethynyl(methylbenzoate) (1)11. A degassed solution of
trimethylsilylacetylene (8.98 g, 91.6 mmol) in Et3N (20 mL)
was transferred via cannula into a Schlenk flask containing
4-iodo(methylbenzoate) (20 g, 76.3 mmol), CuI (0.29 g,
1.52 mmol) and Pd(PPh3)2Cl2 (1.07g, 1.52 mmol) in Et3N
(400 mL). The reaction mixture was stirred at room
temperature for 2 h. The solvent was removed in vacuo, and
the residue dissolved in hexane and purified by passage
through a short column of silica gel (70–230 mesh). The crude
product was recrystallised from hexane. Yield 17.2 g (97%).
The above product (15.5 g, 66.8 mmol) was mixed with
anhydrous sodium carbonate in MeOH (120 mL). The
reaction mixture was stirred at room temperature for 3 h
under N2. The solvent was removed under reduced pressure
and the crude 4-ethynyl(methylbenzoate) was purified by
dissolution in hexane and passage through a short column of
silica gel (70–230 mesh). Recrystallisation from hexane
afforded pale yellow crystals.28 Yield 8.70 g (81%), mp 93–
94 uC (lit.11 92.5–93.5 uC). IR (cm21) 3239 (CH), 2103 (CC)
1,4-Bis(4-carbomethoxyphenylethynyl)-2,3,5,6-tetrafluoro-
benzene (4). Et3N (40 mL) was added via a cannula to a
degassed mixture of 4-ethynyl(methylbenzoate) (0.384 g,
2.4 mmol), 1,4-diiodotetrafluorobenzene (0.402 g, 1.0 mmol),
Pd(PPh3)2Cl2 (0.0337 g, 0.048 mmol), CuI (0.0091, 0.048 mmol)
in a Schlenk flask. The reaction mixture was heated to reflux
for 3 h. The resulting precipitate was collected by filtration,
washed with water and dissolved in hot toluene, and the hot
toluene solution was filtered through a short pad of silica gel
(70–230 mesh). Cooling of the toluene solution gave the
desired compound as small, white crystals. Yield 0.45 g (96%),
1
mp 233–235 uC. IR (cm21) 1719 (CO). H NMR (CDCl3): d
3.92 (s, 6H), 7.61 (m, 4H), 8.02 (m, 4H). 19F{1H} NMR
(CDCl3): d 2147 (s). MS (EI), m/z (rel.): 467 (28), 466 (100),
436 (16), 435 (62), 348 (18), 202 (22). Anal. calc. for
C26H14F4O4: C, 66.96; H, 3.03. Found: C, 66.91; H, 2.97%.
9,10-Bis(4-carbomethoxyphenylethynyl)anthracene (5).
A
Schlenk flask was charged with 9,10-diiodoanthracene
(0.430 g, 1.0 mmol), 4-ethynyl(methylbenzoate) (0.384 g,
2.4 mmol), Pd(PPh3)2Cl2 (0.014 g, 0.02 mmol), CuI (0.004 g,
0.02 mmol) and evacuated and purged with N2 three times.
Dry triethylamine (40 mL) was added via cannula under N2.
The reaction mixture was stirred at room temperature for 3 h.
The mixture was filtered, and the residue was dissolved in hot
toluene and filtered through a 2 cm pad of neutral alumina.
The filtrate was cooled to give orange/red crystals of the
product. Yield: 0.40 g, (81%), mp 288–290 uC. IR (cm21) 1716
(CO). 1H NMR (CDCl3): d 3.95 (s, 6H), 7.64 (m, 4H), 7.82 (m,
4H), 8.11 (m, 4H), 8.67 (m, 4H). MS (EI), m/z (rel.): 495 (39),
494 (100), 435 (8), 373 (9), 187 (15). Anal. calc. for C34H22O4:
C, 82.58; H, 4.48. Found: C, 82.43; H, 4.70%.
1
1703 (CLO), 1284 (COC). H NMR (CDCl3): d 3.26 (1H, s,
CCH), 3.91 (3H, s, CO2CH3), 7.51–7.59 (2H, m, ArH), 7.97–
8.00 (2H, m, ArH). 13C{1H} NMR (CDCl3): d 166.4 (CO),
132.1, 130.0, 129.6, 126.7, 82.8, 80.0, 52.2 (OCH3). MS (EI),
m/z (rel.): 160 (M+, 55), 129 (M+ 2 CH3O, 100), 101 (54), 75
(27), 51 (10).
1,2-Bis(4-carbomethoxyphenyl)ethyne (2)13. Et3N was trans-
ferred via syringe into a Schlenk flask containing 4-ethynyl-
(methylbenzoate) (2.30 g, 14.4 mmol), 4-iodo(methylbenzoate)
(3.14 g, 12.0 mmol), CuI (0.046 g, 0.24 mmol) and
Pd(PPh3)2Cl2 (0.17 g, 0.24 mmol). The reaction mixture was
stirred at room temperature for 2 h after which the solvent was
removed in vacuo. The residue was dissolved in hot toluene and
passed through a short pad of silica gel (70–230 mesh). The
compound was obtained as colourless crystals on removal of
toluene. Yield: 3.2 g (91%), mp 218–220 uC (lit.13 219–223 uC).
IR (cm21) 1718 (CO). 1H NMR (CD2Cl2): d 3.90 (6H, s,
CO2CH3), 7.63 (4H, m, ArH), 8.02 (4H, m, ArH). 13C{1H}
NMR (CD2Cl2): d 52.5 (OCH3), 91.5 (CC), 127, 129, 130, 133,
(ArC), 166 (CO). MS (EI), m/z (rel.): 295 (16), 294 (82), 264
(19), 263 (100), 176 (29). Anal. calc. for C18H14O4: C, 73.46; H,
4.79. Found: C, 73.56; H, 4.80%.
1,4-Bis(4-carbomethoxyphenyl)butadiyne (6). To a solution
i
of 4-ethynyl(methylbenzoate) (1.08 g, 6.74 mmol) in Pr2NH
(250 mL) under N2 were added CuI (0.064 g, 0.34 mmol),
Pd(PPh3)2Cl2 (0.095 g, 0.135 mmol) and iodine (0.985 g,
3.88 mmol) while stirring. After vigorous stirring for 6 h, the
solvent was removed in vacuo, and the residue was dissolved in
hot toluene and purified by passage through a short column of
silica gel (70–230 mesh). After removal of the toluene the
residue was dissolved in CH2Cl2 (100 mL) and washed with
saturated Na2S2O3 (3 6 50 mL), and the organic layer was
dried over MgSO4. Removal of the solvent and recrystallisa-
tion from toluene gave the desired compound as a white
powder. Yield 0.80 g (75%), mp 190–191 uC. IR (cm21) 1928
(CC). 1H NMR (CDCl3): d 3.93 (s, 6H), 7.58 (m, 4H), 8.02 (m,
1,4-Bis(4-carbomethoxyphenylethynyl)benzene (3). To
a
Schlenk flask containing 4-ethynyl(methylbenzoate) (0.768 g,
4.80 mmol), 1,4-diiodobenzene (0.660 g, 2.00 mmol), CuI
(0.008 g, 0.042 mmol) and Pd(PPh3)2Cl2 (0.028 g, 0.040 mmol)
694 | J. Mater. Chem., 2005, 15, 690–697
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4H). 13C{1H} NMR (CDCl3): d 52.3 (OCH3), 76.2, 81.9 (CC),
126.1, 129.6, 130.6, 132.5 (ArC), 166.2 (CO). MS (EI), m/z
(rel.): 318 (100), 287 (72), 200 (18), 128 (14). Anal. calc. for
C20H14O4: C, 75.46; H, 4.43. Found: C, 75.46; H, 4.48%.
Table 3 Crystal data and experimental parameters for X-ray diffrac-
tion studies
Compound
2
5
6
Formula
Formula weight
T/K
C
294.29
160
18H14O4
C34H22O4
494.52
110
C20H14O4
318.31
120
1,2-Bis(4-benzoic acid)ethyne (7)29. Compound 2 (0.95 g,
3.23 mmol) was dissolved in 40 mL of a 10% solution of
NaOH in methanol. The reaction mixture was heated to reflux
for 24 h, and allowed to cool. The sodium salt was filtered off
as a white precipitate and dried in vacuo. Yield: 0.88 g (88%).
1H NMR (D2O): d 7.48 (d, 4H), 7.70 (d, 4H).
Crystal system
Space group
Orthorhombic
Pbca
Triclinic
¯
P1
Triclinic
¯
P1
˚
a/A
7.1061(8)
5.9558(7)
34.129(4)
90
90
90
1444.4(3)
4
1.353
0.096
56.5
8196
1667
102
0.026
1365
7.225(1)
11.660(1)
15.381(1)
77.343(1)
83.037(1)
72.026(1)
1200.5(1)
2
1.368
0.089
55
12 771
5483
349
7.0249(5)
10.4613(8)
11.7016(8)
75.204(3)
72.585(3)
75.457(3)
779.0(1)
2
1.357
0.095
61
6778
4305
273
0.022
3456
0.055
0.141
˚
b/A
˚
c/A
a/u
b/u
c/u
The sodium salt was dissolved in water, and the solution
acidified with HCl. The turbid solution was cooled and filtered
and the solid was dried in vacuo to give 1,2-bis(4-benzoic
3
˚
V/A
Z
Dc/g cm23
1
acid)ethyne as a white powder. Yield: 0.48 g (64%). H NMR
m/mm21
(d6-DMSO): d 7.69 (d, 4H), 7.97 (d, 4H).
2hmax/u
Total reflections
Unique reflections
Parameters
1,4-Bis(4-carboxyphenylethynyl)benzene (8). Compound 3
(0.50 g, 1.27 mmol) was dissolved in 60 mL of a 20% solution
of NaOH in methanol. The reaction mixture was heated to
reflux for 24 h, and allowed to cool. The sodium salt was
filtered off as a white precipitate and washed with methanol
and the solid was dried in vacuo. Yield: 0.38 g (73%).
Rint
0.021
4026
0.040
0.120
Reflections I . 2s(I)
R [F, I . 2s(I)]
wR (F2, all data)
0.041
0.112
The sodium salt was dissolved in distilled water and acidified
with HCl. The turbid solution was cooled in ice and filtered
Thermographs were displayed on a PC and analysed using
Mettler FP99 system software (version 1). All heating and
cooling operations were carried out at 10 uC min21 and the
onset temperature was determined for all transitions.
1
and dried in vacuo to give the diacid. Yield 0.26 g (77%). H
NMR (DMSO): d 7.67 (overlapped s and d, 8H), 7.96 (d, 4H).
X-Ray crystallography
Prior to loading, the samples were crushed to a fine powder
using a mortar and pestle. Aluminium sample and reference
pans (25 ml) were hermetically sealed with aluminium lids using
a Perkin-Elmer press to give a cold weld capable of with-
standing pressures of up to 2 atm. Sample analysis was
conducted as follows: the pan containing the sample was
weighed and then placed in the appropriate compartment of
the DTA; sample and reference pans were equilibrated at 50 uC;
both were heated, at 10 uC min21 to at least 5 uC above the
sample’s clearing/degradation temperature and cooled to 50 uC
at the same rate before finally being returned to ambient
temperature; the sample pan was then re-weighed. This
sequence was carried out six times for each sample.
Compound 2 was crystallised by slow evaporation of a hexane
solution, compound 5 from hot CHCl3, and compound 6 by
slow evaporation of a benzene solution. X-Ray diffraction
data were collected on Bruker 3-circle diffractometers
with SMART 1K CCD area detectors (for 2 and 5) or a
ProteumM APEX CCD area detector (for 6), using graphite-
˚
monochromated Mo-Ka radiation (l 5 0.71073 A) from a
sealed tube (for 2 and 5) or a 60W microfocus Bede
MicrosourceH with glass polycapillary optics (for 6). The low
temperature of the crystals was maintained using Cryostream
(Oxford Cryosystems) open-flow N2 cryostats. The structures
were solved by direct methods and refined by full-matrix least
squares against F2 of all data, using SHELXTL30 software. All
C and O atoms were refined in anisotropic approximation,
with H atoms ‘riding’ in idealized positions (2 and 5) or refined
in isotropic approximation (6). Crystal data and experimental
details are listed in Table 3.
Transmitted polarised light microscopy (TPLM)
An Olympus BH-2 transmitted polarised light microscope was
used to identify the phase transitions detected by differential
thermal methods. A Linkam THMS 600 heating/freezing stage
and TP 92 temperature programmer/controller were used to
enable observation of sample microstructures in situ at
elevated temperatures.
CCDC reference numbers 249324–249326. See http://
www.rsc.org/suppdata/jm/b4/b413514h/ for crystallographic
data in .cif or other electronic format.
To identify phase transitions, samples in powder form were
held between BDH borosilicate coverslips (22 6 22 mm;
thickness No. 1). The glass was first cleaned by immersing in
concentrated nitric acid for 1 h, followed by thorough rinsing
in de-ionised water and then acetone. Following this, the clean
coverslips were air-dried under a dust cover. Heating and
cooling rates of 10 uC min21 were typical and a dry N2 purge
was provided through the sample chamber at ca. 30 mL min21
in an attempt to limit sample oxidation.
Differential thermal analysis (DTA)
A Mettler FP900 Thermosystem, consisting of a Mettler FP90
control processor linked to an FP84 sample hot stage, was
used to locate possible liquid crystal transitions in samples
having an approximate mass of 5 mg. The calorimeter
was calibrated with an indium standard. Experiments were
conducted in an environment of dry nitrogen, delivered
through a cold finger at a flow rate of ca. 30 mL min21
.
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C. Rovira and J. Veciana, Nature Mater., 2003, 2, 190; (i)
Acknowledgements
D. Maspoch, J. Vidal-Gancedo, D. Ruiz-Molina, C. Rovira and
J. Veciana, J. Phys. Chem. Solids, 2004, 65, 819; (j) D. Maspoch,
D. Ruiz-Molina, K. Wurst, C. Rovira and J. Veciana, Chem.
Commun., 2004, 1164.
6 L. Pan, N. Ching, X. Huang and J. Li, Inorg. Chem., 2000, 39,
5333; N. L. Rosi, M. Eddaoudi, J. Kim, M. O’Keeffe and
O. M. Yaghi, Angew. Chem., Int. Ed., 2002, 41, 284; J. Tao, X. Yin,
R. Huang, L. Zheng and S. W. Ng, Inorg. Chem. Commun., 2002,
5, 975.
We thank One NorthEast for funding through the
Nanotechnology UIC Programme (T. B. M., J. A. K. H. and
A. B.), EPSRC for research support (W. C.), postgraduate
studentships (J. M. B. and A. J. S.), and a Senior Research
Fellowship (J. A. K. H.), the University of Durham for a Sir
Derman Christopherson Foundation Fellowship (T. B. M.),
the Royal Society for a Developing World Study Visit award
(T. M. F.), and Heriot-Watt University for a postgraduate
studentship (S. W. W.).
7 D. Min, S. S. Yoon, C. Lee, C. Y. Lee, M. Suh, Y.-J. Hwang,
W. S. Han and S. W. Lee, Bull. Korean Chem. Soc., 2001, 22, 531.
8 (a) V. Hensel, A. Godt, R. Popovitz-Biro, H. Cohen, T. R. Jensen,
K. Kjaer, I. Weissbuch, E. Lifshitz and M. Lahav, Chem. Eur. J.,
2002, 8, 1413; (b) R. Buller, H. Cohen, E. Minkin, R. Popovitz-
Biro, E. Lifshitz and M. Lahav, Adv. Funct. Mater., 2002, 12, 713;
(c) T. Maillou, J. Le Moigne, V. Dumarcher, L. Rocha, B. Geoffroy
and J.-M. Nunzi, Adv. Mater., 2002, 14, 1297; (d) R. Gimene´z,
M. Pin˜ol and J. L. Serano, Chem. Mater., 2004, 16, 1377.
9 W. Lin, L. Ma and O. R. Evans, Chem. Commun., 2000, 2263;
W. Lin, M. E. Chapman, Z. Wang and G. T. Yee, Inorg. Chem.,
2000, 39, 4169; O. R. Evans and W. Lin, Chem. Mater., 2001, 13,
2705.
10 (a) P. Nguyen, Z. Yuan, L. Agocs, G. Lesley and T. B. Marder,
Inorg. Chim. Acta, 1994, 220, 289; (b) P. Nguyen, S. Todd, D. Van
den Biggelaar, 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, J. F. Harrod
and R. M. Laine, eds., NATO ASI Ser. E, Kluwer Academic
Publishers, Dordrecht, 1995, vol. 297, pp. 333–347; (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) C. Dai,
P. Nguyen, T. B. Marder, A. J. Scott, W. Clegg and C. Viney,
Chem. Commun., 1999, 2493; (g) A. Beeby, K. Findlay, P. J. Low
and T. B. Marder, J. Am. Chem. Soc., 2002, 124, 8280; (h) 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; (i)
C. E. Smith, P. S. Smith, R. Ll. Thomas, E. G. Robins,
J. C. Collings, 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; (j) 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; (k) For a review of other work, see: U. H. F. Bunz,
Chem. Rev., 2000, 100, 1605.
11 W. B. Austin, N. Bilow, W. J. Kelleghan and K. S. Y. Lau, J. Org.
Chem., 1981, 46, 2280.
12 K. Sonogashira, Y. Tohda and N. Hagihara, Tetrahedron Lett.,
1975, 4467.
13 M. J. Mio, L. C. Kopel, J. B. Braun, T. L. Gadzikwa, K. L. Hull,
R. G. Brisbois, C. J. Markworth and P. A. Grieco, Org. Lett.,
2002, 4, 3199; A. P. Rudenko and A. V. Vasil’ev, Russ. J. Org.
Chem., 1995, 31, 1360.
14 T. Hundertmark, A. F. Littke, S. L. Buchwald and G. C. Fu, Org.
Lett., 2000, 2, 1729.
15 Q. Liu and D. J. Burton, Tetrahedron Lett., 1997, 38, 4371.
16 H. Matsubara, T. Shimura, A. Hasegawa, M. Semba, K. Asano
and K. Yamamoto, Chem. Lett., 1998, 1099.
17 A. Mavridis and I. Moustakali-Mavridis, Acta Crystallogr., Sect.
B, 1977, 33, 3612; A. V. Abramenkov, A. Almenningen,
B. N. Cyvin, S. J. Cyvin, T. Jonvik, L. S. Khaikin, C. Rømming
and L. V. Vilkov, Acta Chem. Scand. Ser. A, 1988, 42, 674;
I. E. Zanin, M. Yu. Antipin and Yu. T. Struchkov,
Kristallografiya, 1991, 36, 411.
18 F. D. Lewis, J.-S. Yang and C. L. Stern, J. Am. Chem. Soc., 1996,
118, 2772.
19 E. M. Graham, V. M. Miskowski, J. W. Perry, D. R. Coulter,
A. E. Stiegman, W. P. Schaefer and R. E. Marsh, J. Am. Chem.
Soc., 1989, 111, 8771.
Tolulope M. Fasina,*ab Jonathan C. Collings,a Jacqueline M. Burke,a
Andrei S. Batsanov,a Richard M. Ward,a David Albesa-Jove´,a
Laurent Porre`s,a Andrew Beeby,a Judith A. K. Howard,a
Andrew J. Scott,c William Clegg,c Stephen W. Watt,{d
Christopher Viney{d and Todd B. Marder*a
aDepartment of Chemistry, University of Durham, South Road, Durham,
UK DH1 3LE. E-mail: Todd.Marder@durham.ac.uk;
Fax: +44(191)-384-4737; Tel: +44(191)-334-2037
bDepartment of Chemistry, University of Lagos, Lagos, Nigeria
cSchool of Natural Sciences (Chemistry), University of Newcastle upon
Tyne, Newcastle upon Tyne, UK NE1 7RU
dDepartment of Chemistry, School of Engineering and Physical Sciences,
Heriot-Watt University, Riccarton, Edinburgh, UK EH14 4AS
References
1 (a) B. F. Hoskins and R. Robson, J. Am. Chem. Soc., 1990, 112,
1546; (b) D. Braga, F. Grepioni and G. R. Desiraju, Chem. Rev.,
1998, 98, 1375; (c) J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh,
Y. J. Jeon and K. Kim, Nature, 2000, 404, 982; (d) S. Leninger,
B. Olenyuk and P. J. Stang, Chem. Rev., 2000, 100, 853; (e)
M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keeffe
and O. M. Yaghi, Science, 2002, 295, 469.
2 (a) R. W. Gable, B. F. Hoskins and R. Robson, J. Chem. Soc.,
Chem. Commun., 1990, 1677; (b) M. Fujita, Y. J. Kwon,
M. Miyazawa and K. Ogura, J. Chem. Soc., Chem. Commun.,
1994, 1977; (c) F. Robinson and M. J. Zaworotko, J. Chem. Soc.,
Chem. Commun., 1995, 2413; (d) L. R. MacGillivray,
S. Subramanian and M. J. Zaworotko, J. Chem. Soc., Chem.
Commun., 1994, 1325; (e) N. Masciocchi, P. Cairati, L. Carlucci,
G. Mezza, G. Ciani and A. Sironi, J. Chem. Soc., Dalton Trans.,
1996, 2739; (f) M.-L. Tong, X.-M. Chen, X.-L. Yu and
T. C. W. Mak, J. Chem. Soc., Dalton Trans., 1998, 5; (g)
P. J. Hagrman, D. Hagrman and J. Zubieta, Angew. Chem., Int.
Ed., 1999, 38, 2639; (h) T. M. Fasina, J. C. Collings, D. P. Lydon,
D. Albesa-Jove, A. S. Batsanov, J. A. K. Howard, P. Nguyen,
M. Bruce, A. J. Scott, W. Clegg, S. W. Watt, C. Viney and
T. B. Marder, J. Mater. Chem., 2004, 14, 2395.
3 C. N. R. Rao, S. Natarajan and R. Vaidhyanathan, Angew. Chem.,
Int. Ed., 2004, 43, 1466.
4 M. O’Keeffe, M. Eddaoudi, H. Li, T. Reineke and O. M. Yaghi,
J. Solid State Chem., 2000, 152, 3; W. Mori and S. Takamizawa,
J. Solid State Chem., 2000, 152, 120; M. Eddaoudi, J. Kim,
D. Vodak, A. Sudik, J. Wachter, M. O’Keeffe and O. M. Yaghi,
Proc. Natl. Acad. Sci. USA, 2002, 99, 4900; T. Ohmura, W. Mori,
M. Hasegawa, T. Takei, T. Ikeda and E. Hasegawa, Bull. Chem.
Soc. Jpn., 2003, 76, 1387.
5 (a) O. M. Yaghi, C. E. Davis, G. Li and H. Li, J. Am. Chem. Soc.,
1997, 119, 2861; (b) S. S.-Y. Chui, S. M.-F. Lo, J. P. H. Charmant,
A. G. Orpen and I. D. Williams, Science, 1999, 283, 1148; (c)
T. M. Reineke, M. Eddaoudi, M. Fehr, D. Kelly and O. M. Yaghi,
J. Am. Chem. Soc., 1999, 121, 1651; (d) T. M. Reineke,
M. Eddaoudi, M. O’Keeffe and O. M. Yaghi, Angew. Chem., Int.
Ed., 1999, 38, 2590; (e) L. Pan, N. Zheng, Y. Wu, S. Han, R. Yang,
X. Huang and J. Li, Inorg. Chem., 2001, 40, 828; (f) K. Seki and
W. Mori, J. Phys. Chem. B, 2002, 106, 1380; (g) D. Maspoch,
N. Domingo, D. Ruiz-Molina, K. Wurst, N. Domingo,
M. Cavallini, F. Tejada, C. Rovira and J. Veciana, Angew.
Chem., Int. Ed., 2004, 43, 1828; (h) D. Maspoch, D. Ruiz-Molina,
K. Wurst, N. Domingo, M. Cavallini, F. Biscarini, J. Tejada,
20 J. K. D. Surette, M.-A. MacDonald, M. J. Zaworotko and
R. D. Singer, J. Chem. Crystallogr., 1994, 24, 715; F. R. Fronczek
and M. S. Erickson, J. Chem. Crystallogr., 1995, 25, 737.
696 | J. Mater. Chem., 2005, 15, 690–697
This journal is ß The Royal Society of Chemistry 2005

View Online
21 G. W. Coates, A. R. Dunn, L. M. Henling, D. A. Dougherty and
R. H. Grubbs, Angew. Chem., Int. Ed. Engl., 1997, 36, 248.
22 M. G. B. Drew, F. S. Esho and S. M. Nelson, J. Chem. Soc., Chem.
Commun., 1982, 1347.
23 J. J. Mayerle, T. C. Clarke and K. Bredfeldt, Acta Crystallogr.,
Sect. B, 1979, 35, 1519.
24 R. S. Rowland and R. Taylor, J. Phys. Chem., 1996, 100, 7384. All
26 A. T. R. Williams, S. A. Winfield and J. N. Miller, Analyst, 1983,
108, 1067.
27 J. N. Demas and G. A. Crosby, J. Phys. Chem., 1971, 75, 991.
28 For the crystal and molecular structure of 1, see: C. Dai, Z. Yuan,
J. C. Collings, T. M. Fasina, R. Ll. Thomas, K. P. Roscoe,
L. M. Stimson, D. S. Yufit, A. S. Batsanov, J. A. K. Howard and
T. B. Marder, CrystEngComm, 2004, 6, 184.
˚
calculations presume the idealized C–H bond distance of 1.08 A.
25 J. van de Bovenkamp, J. M. Matxain, F. B. van Duijneveldt and
T. Steiner, J. Phys. Chem. A, 1999, 103, 2784.
29 B. H. Lee and C. S. Marvel, J. Polym. Sci., 1982, 20, 393.
30 SHELXTL, ver. 6.12, Bruker AXS, Madison, Wisconsin, USA,
2001.
This journal is ß The Royal Society of Chemistry 2005
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