A saddle-shaped macrocycle comprising 2,5-diphenylthiophene units

Article abstract of DOI:10.1246/cl.180187

2,5-Diphenylthiophene-based macrocycles were synthesized by Ni-mediated coupling of the corresponding building units. X-ray analysis revealed that the cyclic trimer had a saddle-shaped structure due to the steric demands of the biphenyl and thiophene-phen

Full text of DOI:10.1246/cl.180187

CL-180187
Received: March 4, 2018 | Accepted: March 27, 2018 | Web Released: April 7, 2018
A Saddle-shaped Macrocycle Comprising 2,5-Diphenylthiophene Units
Tetsuo Iwanaga,*1 Yuki Yamada,1 Tomokazu Yamauchi,2 Yohji Misaki,2 Masataka Inoue,1 and Haruo Yamada1
1Department of Chemistry, Faculty of Science, Okayama University of Science, 1-1 Ridaicho, Kita-ku, Okayama 700-0005, Japan
2Department of Applied Chemistry, Graduate School of Engineering, Ehime University,
3 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan
E-mail: iwanaga@chem.ous.ac.jp
2,5-Diphenylthiophene-based macrocycles were synthesized
by Ni-mediated coupling of the corresponding building units.
X-ray analysis revealed that the cyclic trimer had a saddle-
shaped structure due to the steric demands of the biphenyl and
thiophene-phenylene units, whereas DFT calculation showed
that the cyclic dimer had a rigid and almost coplanar structure
regardless of the steric hindrance between the benzene rings of
the biphenyl units. Moreover, the packing diagram of the cyclic
trimer showed alternating stacked layers of macrocycles and
solvent molecules.
Br
Br
Br
Na2S•9H2O
2steps
KOH
I
MeOH
120oC
2,2'-bipy
1,5-cod
Ni(cod)2
S
3
1 and 2
DMF:toluene (1:5)
reflux
Br
Br
Scheme 1. Synthesis of 2,5-diphenylthiophene-based macro-
cycles 1 and 2.
Keywords: Saddle-shaped macrocycle
| Diphenylthiophene |
Ni-mediated coupling
In the molecular design of π-conjugated compounds, cy-
clization and oligomerization of two or more arene units are one
promising approach for construction of fascinating functions.1
The structures and properties of these compounds can be
modified by varying the types and numbers of arene units and
the types of linkers. For example, the use of heteroaromatic
rings, such as thiophene, pyrrole, and furan, in oligoarene
derivatives considerably increases the number of possible
structures, which exhibit a variety of properties.2 In particular,
a large number of oligoarenes comprising thiophene units have
been extensively studied for the development of novel organic
macrocycle as well as cyclic dimer 2 by Ni-mediated coupling,
and their structures, electronic spectra, and electrochemical
properties were investigated.
2,5-Bis(3-bromophenyl)thiophene 3 as a building unit was
synthesized from 1-bromo-3-iodobenzene by Pd/Cu-catalyzed
Sonogashira-Glaser coupling followed by sulfide-mediated
cyclization (Scheme 1).5,7 This precursor was subjected to Ni-
mediated coupling under standard conditions.8 Compound 1 was
treated with Ni(cod)2 [cod = 1,5-cyclooctadiene] in the presence
of 2,2¤-bipyridine and cod in a DMF/toluene solution. The crude
product was purified by column chromatography to give cyclic
trimer 1 and cyclic dimer 2 in 64% and 1% yields both as
colorless solids (see Supporting Information). The low yield of
2 could be attributed to the large steric hindrance in the rigid
and small ring structure. The molecular ion peaks of 1 and 2
were observed at m/z 702.15 and 468.04 [M+], respectively. In
the 1H NMR spectrum of 1, the thiophene proton signal was
observed at δ 7.30 as a singlet, and the corresponding signal in
devices and supramolecular architectures.3 In
a previous
report, we synthesized 2,5-dianthrylthiophenes with a central
thiophene unit having two anthracene units, which revealed
characteristic structural and spectroscopic properties.4 Although
the parent 2,5-diphenylthiophene (DPT) unit is already known
(Figure 1),3b,5 DPT-based cyclic dimer
2 was previously
synthesized by Suzuki-Miyaura coupling and appears mainly
in patents for use in organic field-effect transistors.6 Herein, we
designed and synthesized cyclic trimer 1 as a new DPT-based
1
3 was observed at δ 7.29. The H NMR signal of 2 assignable
to the inner protons of the biphenylene units was observed
at ¤ 8.59, and it was shifted downfield compared with the
corresponding signals of 1 at ¤ 7.73. This value of 2 is attributed
to the ring current effect based on the almost coplanar structure
of biphenylene unit. Compound 1 gave eight aromatic signals in
the 13C NMR spectrum, which is consistent with the molecular
symmetry. Unfortunately, the solubility of 2 was too low to
measure its 13C NMR spectrum.
S
S
S
We obtained a good single crystal of 1 from p-xylene/
hexane for X-ray crystallography.9 The X-ray structure of 1 is
shown in Figure 2a. The cyclic framework of 1 adopts a saddle-
shaped structure of C1 symmetry. As cyclic trimer 1 comprises
three DPT units, its conformation can be characterized by the
dihedral angles between the phenylene planes and the thiophene
plane. The maximum and minimum of these values obtained
from the X-ray structure analyses of 1 are +54.0° and +5.1°,
respectively. The three biphenyl groups are considerably twisted
2
S
S
S
1
2,5-Diphenylthiophene
(DPT)
Figure 1. Structures of 2,5-diphenylthiophene (DPT) and
DPT-based macrocycles 1 and 2.
760 | Chem. Lett. 2018, 47, 760–762 | doi:10.1246/cl.180187
© 2018 The Chemical Society of Japan

6
5
4
3
2
1
0
(b)
(a)
+23.0
+54.0
-41.6
-21.6
-28.1
-17.4
+33.0
-28.4
-33.0
28.4
-33.0
+33.0
+5.1
-29.5
+60.2
250
300
350
400
450
500
550
Wavelength /nm
Figure 4. Absorption (solid lines) and fluorescence (dashed
lines) spectra of 1 (red) and DPT (blue) in CHCl3.
Figure 2. Molecular structures of 1 and 2. Dihedral angles
(°) of thiophene-phenylene rings (red numbers) and biphenyl
moieties (blue numbers) are shown. (a) X-ray structure of 1
recrystallized from p-xylene/hexane. Solvent molecules are
omitted for clarity. (b) Calculated structure of 2 at the B3LYP/
6-311G(d,p) level.
1
DPT
y
x
2
1.5
1
0.5
0
Potential /V (vs. Fc/Fc+)
Figure 5. Differential pulse voltammograms of 1 and DPT in
CH2Cl2.
The electronic spectra of 1 and DPT were measured in
CHCl3. In the UV-vis spectra (Figure 4), compound 1 gave an
absorption at -max 317 nm at the p-band, whereas the corre-
sponding band at the longest wavelength was observed at 327 nm
for DPT. The absorption band of 1 is blue-shifted by 10 nm
relative to that of the parent DPT because the π-conjugation
through the whole molecule is diminished by the saddle-shaped
structure. In the fluorescence spectra, compound 1 gave an
emission band at 399 nm with a fluorescence quantum yield Φf
of 0.14, whereas the emission peak of DPT was observed at
392 nm with a quantum yield Φf of 0.12. The large Stokes shift
of 1 (82 nm, 6480 cm¹1) was attributed to a significant structural
difference between the excited state and the ground state.
The oxidation potentials of 1 and DPT were investigated by
cyclic voltammetry. Compound 1 exhibited some obscure redox
waves in CH2Cl2 with nBu4NPF6 as the supporting electrolyte at
room temperature (Figure S1). In order to determine the correct
potentials, we performed differential pulse voltammetry under
the same conditions, and the results are shown in Figure 5. The
first oxidation peak (E1ox) of 1 was found at 0.93 V (vs. Fc/Fc+),
which was weak and complicated. This potential occurs almost
at the same potential as that of DPT (0.92 V), which can be
attributed to the independent HOMO of the DPT unit in the
macrocyclic framework (Figure S2).
Figure 3. Packing diagram of 1 along the a axis. Typical
C-H£π contacts and π£π interactions are shown as red broken
lines and blue broken line, respectively. x: 3.33 ¡, y: 2.87 ¡.
Solvent molecules are shown in purple for clarity.
from the planar conformation due to steric hindrance. The
packing diagram of the cyclic trimer 1 showed alternating
stacked layers of macrocycles and solvent molecules. Intermo-
lecular C-H£π interactions rather than π£π interactions are
dominant, and the shortest H£π distance is 3.33 ¡ (Figure 3).
No sulfur atoms have any significant intermolecular contacts
because they face toward the inside of the macrocycle.
The optimized structure of cyclic dimer 2 was calculated
at the B3LYP/6-311G(d,p) level of theory (Figure 2b).10 The
calculation gave a C2h symmetry with dihedral angles of «28.4°
(biphenyl) and «33.0° (thiophene-phenyl). These structural data
suggest that 2 exhibits pseudo-planarity as well as a large
surface area. This structural feature should be a major reason for
the low solubility due to effective intermolecular stacking in the
solid state.
Chem. Lett. 2018, 47, 760–762 | doi:10.1246/cl.180187
© 2018 The Chemical Society of Japan | 761

In summary, 2,5-diphenylthiophene-based macrocycles 1
and 2 were successfully synthesized by Ni-mediated coupling.
We could only evaluate the properties of cyclic trimer 1 by
spectroscopic and electrochemical measurements. X-ray analysis
and DFT calculations revealed that cyclic trimer 1 had a saddle-
shaped structure depending on the steric hindrance between the
biphenyl and thiophene-phenylene units. The structures of DPT-
based cyclic oligomers are attractive for the design of molecular
devices based on twisted π-conjugated macrocycles. Further
studies focusing on the synthesis of higher cyclic oligomers
introducing the soluble substitution as well as their applications
in organic electronic devices are in progress.
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This work was partly supported by Grant for Promotion of
OUS Research Projects. The authors thank Prof. Shinji Toyota
of Tokyo Institute of Technology and Prof. Kan Wakamatsu of
Okayama University of Science for helpful discussion, and Mr.
Naoto Asano for his technical assistance.
Supporting Information is available on http://dx.doi.org/
10.1246/cl.180187.
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ꢀ
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c = 14.277(2) ¡, ¡ = 79.069(4), ¢ = 81.974(5), £ =
¹3
82.994(5)°, V = 2094.6(5) ¡3, Z = 2, Dc = 1.283 g cm
,
®(Mo Kα) = 0.216 mm¹1. Number of data 9433, number
of data used 6618 [I > 2.0σ(I)], R1 = 0.0549, wR2 =
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3
762 | Chem. Lett. 2018, 47, 760–762 | doi:10.1246/cl.180187
© 2018 The Chemical Society of Japan