The crystal structures of 2,5-di(ethoxyphenyl)-3,6-dibromothieno[3,2-b]thiophene (I) and 2,5-di(ethoxyphenyl)-3,6-diphenylthieno[3,2-b]thiophene (II) have been studied in order to evaluate the planarity of these molecules. The aromatic systems introduced to the thieno[3,2-b]thiophene core structure show a degree of rotation from 30.94° to 66.56°. The crystal packing of (I) are characterized by π×××π stacking, while in (II), C-H×××p and C-H×××O interactions are observed

Dat, Nguyen Dang

Hien, Nguyen

Meervelt, Luc van

Ngan, Nguyen Bich

English

Vietnam Academy of Science and Technology: Journals Online

 Vietnam Journal of Chemistry, International Edition, 54(6): 672-677, 2016 
DOI: 10.15625/0866-7144.2016-00385 
672 
 
 
 
Structures of 2,5-diaryl- and 2,3,5,6-tetra[3,2-b]thiophene synthesized by 
the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction 
Nguyen Hien
1*
,
 
Nguyen Bich Ngan
1
, Nguyen Dang Dat
1
,
 
Luc van Meervelt
2
 
1
Faculty of Chemistry, Hanoi National University of Education 
2
Department of Chemistry, KU Leuven 
Received 10 August 2016; Accepted for publication 19 December 2016 
   
Abstract 
The crystal structures of 2,5-di(ethoxyphenyl)-3,6-dibromothieno[3,2-b]thiophene (I) and 2,5-di(ethoxyphenyl)-
3,6-diphenylthieno[3,2-b]thiophene (II) have been studied in order to evaluate the planarity of these molecules. The 
aromatic systems introduced to the thieno[3,2-b]thiophene core structure show a degree of rotation from 30.94  to 
66.56 . The crystal packing of (I) are characterized by π π stacking, while in (II), C-H  and C-H O interactions are 
observed. 
Keywords. thieno[3,2-b]thiophene, palladium-catalyzed, Suzuki-Miyaura, cross-coupling.  
 
1. INTRODUCTION 
 
Thieno[3,2-b]thiophene possesses a rigid 
structure and an extended π-conjugation. This 
electron-rich two annulated thiophene structure 
enable it to construct conjugated and low band gap 
organic semiconductors. Functionalized thieno[3,2-
b]thiophene units have been incorporated into, or 
designed as a part of the skeleton of conjugated 
oligomers and polymers to improve the electronic 
properties of the materials [1]. These kinds of 
materials were applied to produce high-performance 
organic field-effect transistors (OFETs) [2], organic 
light-emitting diodes (OLEDs) [3], and 
photovoltaics devices [4]. In fact, the performance of 
a functionalized material depends heavily on its 
molecular structure and the stacking motif. 
Therefore, design of functional molecular solid-state 
structures, or arrangements, through tuning of the 
intermolecular interactions is essential. 
One of the convenient methods for fine-tuning 
band gaps involves the arylation which promotes a 
greater conjugation in the ground state. This method 
is also employed for adjusting the band gap of 
organic materials and increasing intermolecular 
interactions in the solid state. The objective of this 
work was the partial and full functionalization of the 
thieno[3,2-b]thiophene ring starting from 2,3,5,6-
tetrabromothieno[3,2-b]thiophene [5] using the 
palladium-catalyzed Suzuki-Miyaura cross-coupling 
reaction [6]. Herein, the synthesis, the molecular and 
the crystal structures of the synthesized 2,5-
di(ethoxyphenyl)-3,6-dibromothieno[3,2-
b]thiophene (I) and 2,5-di(ethoxyphenyl)-3,6-
diphenylthieno[3,2-b]thiophene (II) will be 
discussed.
 
 
2. EXPERIMENTAL 
 
2.1. Chemicals 
Catalysts, solvents and other chemicals were 
purchased from Sigma-Aldrich or Merck and were 
used as received unless otherwise indicated. THF 
 VJC, 54(6) 2016                                                                                                                     Nguyen Hien, et al. 
673 
were refluxed over sodium wire in the presence of 
benzophenone as indicator and redistilled just before 
used. The Suzuki-Miyaura cross-coupling reactions 
were conducted under deaerated conditions.  
 
2.2. Instrumentation 
 
The 
1
H NMR and 
13
C NMR spectra were 
recorded on a Bruker Avance 500 NMR 
spectrometer in CDCl3. Chemical shift was reported 
in ppm units with tetramethylsilane (TMS) as 
internal reference. Splitting patterns are designated 
as s (singlet), d (doublet), t (triplet), q (quartet) and 
m (multiplet). X-ray measurements were performed 
on an Agilent SuperNova (single source at offset, 
Eos detector) diffractometer at the Department of 
Chemistry, KU Leuven, Belgium. 
 
2.3. Synthesis and crystallization 
 
2.3.1. Synthesis of 2,5-di(ethoxyphenyl)-3,6-
dibromothieno[3,2-b]thiophene (I) 
 
Toluene (4 ml) was deoxygenated and saturated 
with argon by exchanging between vacuum and a 
stream of argon (3 times). 2,3,5,6-
Tetrabromothieno[3,2-b]thiophene (230 mg, 0.5 
mmol, 1.0 equiv) and Pd(Ph3P)4 (57.7 mg, 0.05 
mmol, 0.10 equiv) were dissolved in this solvent at 
60-70 
o
C. To the obtained solution was added H2O 
(1 ml), K3PO4 (212 mg, 1.0 mmol, 2.0 equiv), and 4-
ethoxyphenylboronic acid (182.6 mg, 2.2 equiv). 
The reaction was vigorously stirred under argon 
atmosphere at 110 
o
C until TLC (100 % n-hexane) 
showed the complete consumption of the starting 
material (about 8 hours). The reaction mixture was 
cooled by ice water. The white solid separated was 
filtered, washed several times with toluene and 
recrystallized from hot n-hexane:ethyl acetate (1:1, 
v/v) to give (I) (155.5 mg, yield 58 %) as white 
needles; mp 230-231 
o
C. 
1
H NMR (CDCl3, 500 
MHz): δ (ppm) 7.36 (t, J = 8.0 Hz, 1 H, aromatic), 
7.27 (m, 2 H, aromatic), 6.95 (m, 1 H, aromatic), 
4.10 (q, J = 7.0 Hz, 2 H, CH2), 1.45 (t, J = 7.0 Hz, 3 
H, CH3); 
13
C NMR (CDCl3, 125 MHz): δ (ppm) 
159.1 (C-O), 139.4, 138.8, 134.0, 129.8, 121.3, 
115.2, 114.9, 100.1, 63.6 (O-CH2), 14.8 (CH3). 
2.3.2. Synthesis of 2,5-di(ethoxyphenyl)-3,6-
diphenylthieno[3,2-b]thiophene (II) 
(I) (108 mg, 0.2 mmol) and Pd(Ph3P)4 (24 mg, 
0.02 mmol, 0.10 equiv) were dissolved in  toluene (4 
ml) that was degassed and saturated with argon. To 
the mixture were added phenylboronic acid (47 mg, 
0.44 mmol), K3PO4 (170 mg, 4.0 equiv) and distilled 
water (1 ml). The resulting mixture was refluxed at 
110 
o
C, during which the progress of the reaction 
was monitored by TLC (100 % n-hexane). After 8 h, 
phenylboronic acid (21 mg, 0.2 mmol) and 
Pd(Ph3P)4 (12 mg, 0.01 mmol, 0.05 equiv) were 
added; the mixture was further refluxed for 12 h. 
After the reaction was completed, the reaction 
mixture was diluted with 20 ml toluene, washed with 
water (3 times) and dried over anhydrous Na2SO4. 
(II) was isolated by column chromatography (n-
hexane:ethyl acetate 95:5, v/v) as a white solid (64 
mg, yield 60 %); mp 231-233 
o
C. (II) was further 
purified by recrystallized from n-hexane:ethyl 
acetate (3:1, v/v) solution. 
1
H NMR (CDCl3, 500 
MHz): δ (ppm) 7.48 (dd, J = 8.0 Hz and 1.0 Hz, 2 H, 
aromatic), 7.37 (dt, J = 8.0 Hz and 1.0 Hz, 2 H, 
aromatic), 7.33 (d, J = 8.5 Hz, 1 H, aromatic), 7.16 
(t, J = 8.0 Hz, 1 H, aromatic), 6.92 (td, J = 7.5 Hz 
and 0.5 Hz, 1 H, aromatic), 6.86 (m, 1 H, aromatic), 
6.79 (m, 1 H, aromatic), 3.86 (q, J = 7.0 Hz, 2 H, 
CH2), 1.13 (t, J = 7.0 Hz, 3 H, CH3). 
13
C NMR 
(CDCl3, 125 MHz): δ (ppm) 158.9 (C-O), 139.0, 
138.9, 135.7, 135.2, 130.8, 129.5, 129.1, 128.8, 
127.7, 121.6, 114.8, 114.6, 63.3 (O-CH2), 14.7 
(CH3). 
 
2.4. Structure solution and refinement 
 
The X-ray diffraction data were collected on an 
Agilent SuperNova diffractometer using mirror-
monochromated MoK  radiation (  = 0.71073 Å). 
Using Olex2 [7]. The structure was solved with the 
SHELXS [8] structure solution program using Direct 
Methods and refined by full-matrix least-squares 
methods based on F
2
 using SHELXL [9]. All non-
hydrogen atom parameters were refined 
anisotropically. All hydrogen atoms were placed in 
idealized positions and refined in riding mode with 
Uiso values assigned as 1.2 times those of the parent 
atoms (1.5 times for methyl groups), with a C–H 
distance of 0.95 (aromatic), 0.98 (methyl) or 0.99 Å 
(methylene). The crystal data, the data collection, 
and the structure refinement details are summarized 
in table 1. 
 
3. RESULTS AND DISCUSSION 
 
The molecular structures of the diaryl (I) and 
tetraaryl (II) derivatives of thieno[3,2-b]thiophene 
are shown in Fig. 1. The bond lengths and angles are 
in good agreement with the average values in the 
Cambridge Structure Database (CSD, version 5.37, 
November 2015) [10]. 
In order to enlarge the -conjugated system of 
 VJC, 54(6) 2016                                                                              Structures of 2,5-diaryl- and 2,3,5,6-tetra… 
674 
the thieno[3,2-b]thiophene, aromatic rings were 
introduced into the thieno[3,2-b]thiophene skeleton 
by Suzuki-Miyaura cross-coupling reactions. In 
these reactions, the site-selectivity at the C2 and C5 
positions was observed due to the effect of the 
sulphur heteroatom [10].  
 
Table 1: Crystal data, data collection and structure refinement parameters for (I) and (II) 
 (I) (II) 
CSD code CSD 1497991  CSD 1497992 
Chemical formula C22H18Br2O2S2 C34H28O2S2 
Mr 538.30 532.68 
Crystal system, space group Monoclinic, P21/n Triclinic, P-1 
Temperature (K) 100 100 
a, b, c (Å) 3.9155(3), 14.7861(11), 
17.4836(14) 
5.7894(5), 9.3851(11), 13.4001(14) 
, , (°) 90, 91.395(7), 90 82.144(9), 84.093(8), 75.788(9) 
V (Å
3
) 1011.92(13) 697.35(13) 
Z 2 1 
Radiation type  MoK  MoK  
 (mm
-1
)   4.23 0.22 
Crystal size (mm
3
) 0.3 × 0.1 × 0.1 0.45 × 0.12 × 0.08 
   
Data collection   
Tmin, Tmax 0.679, 1.000 0.638, 1.000 
No. of measured, independent 
and observed [I> 2 (I)] 
reflections 
10583, 2054, 1917 14116, 2842, 2541 
Rint 0.033 0.047 
(sin / )max (Å
-1
) 0.625 0.625 
   
Refinement   
R[F
2
> 2 (F
2
)], wR(F
2
), S 0.020, 0.048, 1.07 0.040, 0.104, 1.07 
No. of reflections 2054 2842  
No. of parameters  128 173 
max, min (e Å
-3
) 0.36, -0.25 0.47, -0.27 
 
Compound (I) crystallizes in space group P21/n, 
while (II) crystallizes in space group P-1. Both 
compounds have an inversion centre located in the 
middle of the C1-C1
i
 bond in (I) and C2-C2
ii
 bond in 
(II) (Symmetry codes: (i) -x, -y + 1, -z + 1; (ii) -x + 
1, -y + 1, -z; Fig. 1). As a result, the asymmetric unit 
consists of one half of the molecule, the second half 
being generated by an inversion centre. The fused 
thiophene rings in both structures are planar (r.m.s. 
deviation = 0.002 Å for (I) and 0.001 Å for (II)). 
The introduced phenyl rings are non-planar with the 
core structure. In (I), the dihedral angle between the 
thieno[3,2-b]thiophene ring and the ethoxyphenyl 
ring is 46.93(8) . The rotation is to reduce the 
repulsion between Br1 H5 and S1 H9, that is in 
good agreement with the case of 3,6-dibromo-2(4-
tert-butylphenyl)-5-(4-methylstyryl)thieno[3,2-
b]thiophene [12]. In (II), the dihedral angles 
between the thieno[3,2-b]thiophene ring and the two 
phenyl rings are 31.24(6)  and 66.61(7) , 
respectively. In addition, in this compound, the 
ethoxyphenyl ring is almost perpendicular to the 
phenyl ring (the dihedral angle between both rings is 
64.09(8) ). Only one tetra-substituted thieno[3,2-
b]thiophene structure similar to (II) is present in the 
CSD: 2,3,5,6-tetraphenylthieno[3,2-b]thiophene 
(refcode WEXBOS, [12]). In that case, the 2,5-
phenyl rings and the 3,6-phenyl rings are rotated out 
of the plane of the thieno[3,2-b]thiophene ring by 
dihedral angles of 35.31(7) and 59.38(6) , 
respectively. Possibly, the ethoxy-substituted phenyl 
groups force the un-substituted ones to rotate less 
from the core structure, while they themselves are 
twisted more The packing of (I) shows -  stacking 
between the 4-ethoxyphenyl rings [Cg1 Cg1
i
 = 
3.9155(3) Å; Cg1 is the centroid of the C4-C9 ring; 
symmetry code: (i) x + 1, y, z; Fig. 2a]. A weak C-
Br  interaction is observed [C2-Br1 Cg1
ii
; 
 VJC, 54(6) 2016                                                                                                                     Nguyen Hien, et al. 
675 
Br1 Cg1
ii
 = 3.9290(9) Å; symmetry code: (ii) -x + 1, -y + 1, -z + 1].  
 
 
 
 
(I)  
(II) 
Figure 1: Molecular structures of (I) and (II), showing the atom-labelling schemes. Displacement ellipsoids 
are drawn at the 50% probability level. [Symmetry codes: (i) -x, -y + 1, -z + 1; (ii) -x + 1, -y + 1, -z] 
 
Due to the presence of the four bulky 
substituents, the packing of (II) shows no -  
stacking (Fig. 2b), which is in agreement with the 
analogous structure 2,3,5,6-tetraphenylthieno[3,2-
b]thiophene [12]. C-H O interactions are present in 
the crystal packing resulting in a chain of molecules 
in the (204) plane. Parallel chains of the molecules 
are linked by C-H  interactions with the ethoxy-
substituted phenyl groups (table 2, Fig. 2b). 
Possible intermolecular S S interactions which 
could increase the electronic transport between 
neighboring molecules are not observed in the 
crystal packing of both (I) and (II). 
 
Table 2: Hydrogen bond geometry (Å, °) for (II) 
D-H A D-H H A D A D-H A 
C14-H14 O17
i
 0.95 2.54 3.476(2) 168 
C6-H6 Cg1
ii
 0.95 2.67 3.515(2) 148 
C19-H19C Cg2
iii
 0.98 2.87 3.697(2) 143 
Symmetry codes: (i) -x - 1, -y - 1, -z - 1; (ii) x + 1, y, z; (iii) -x, -y + 1, -z + 1. 
 
4. CONCLUSION 
 
In conclusion, the crystal structures of a 2,5-
diaryl- and a 2,3,5,6-tetraayl derivatives of 
thieno[3,2-b]thiophene were recorded and analyzed. 
The results showed that the phenyl rings introduced 
into the thieno[3,2-b]thiophene core structure 
undergo a degree of rotation from 30.94  to 66.56 . 
In addition, π π stacking is the dominant 
arrangement in the crystal packing of (I). On the 
other hand, C-H  and C-H O interactions are 
observed in the crystal structure of (II). 
Intermolecular S S interactions which could 
increase the electronic transport between 
neighboring molecules are not found in the crystal 
packing of both (I) and (II). Attempts to planarize 
the introduced aromatic rings with the thieno[3,2-
b]thiophene by the FeCl3-oxidation reaction are in 
progress in our laboratory and will be reported in 
near future.  
 
Acknowledgements. This research is funded by the 
Vietnam National Foundation for Science and 
Technology Development (NAFOSTED) under 
grand number 104.01-2012.26. The authors thank 
VLIR-UOS (project ZEIN2014Z182) for financial 
support and the Hercules Foundation for supporting 
the purchase of the diffractometer through project 
AKUL/09/0035. 
 
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676 
 
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Corresponding author: Nguyen Hien 
Faculty of Chemistry 
Hanoi National University of Education 
136, Xuan Thuy, Cau Giay, Hanoi 
E-mail: hiennguyendhsphn@gmail.com; Telephone: 0983825316.  


Structures of 2,5-diaryl- and 2,3,5,6-tetra[3,2-b]thiophene synthesized by the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction

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Structures of 2,5-diaryl- and 2,3,5,6-tetra[3,2-b]thiophene synthesized by the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction

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