Efficient synthesis of substituted dithieno[2,3-b:3',2'-D]siloles and A 10- Membered silicon-bridged thiophene-based cyclophane

Article abstract of DOI:10.2174/157017811799304179

Two new substituted dithieno[2,3-b:3',2'-d]siloles, 7,7-diphenyl-2,5- bis(trimethylsilyl) dithieno[2,3-b:3',2'- d]silole (1) and 7,7-diphenyl-2,5- dichloro-dithieno[2,3-b:3',2'-d]silole (2) were synthesized in 79.4% and 31.6% yields, respectively via the

Full text of DOI:10.2174/157017811799304179

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Letters in Organic Chemistry, 2011, 8, 728-731
Efficient Synthesis of Substituted Dithieno[2,3-b:3',2'-d]siloles and A 10-
Membered Silicon-Bridged Thiophene-Based Cyclophane
Caiyun Zhao, Jianwu Shi, Chunli Li and Hua Wang*
Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng, 475004, P.R. China
Received June 16, 2011: Revised September 07, 2011: Accepted September 07, 2011
Abstract: Two new substituted dithieno[2,3-b:3',2'-d]siloles, 7,7-diphenyl-2,5-bis(trimethylsilyl) dithieno[2,3-b:3',2'-
d]silole (1) and 7,7-diphenyl-2,5-dichloro-dithieno[2,3-b:3',2'-d]silole (2) were synthesized in 79.4% and 31.6% yields,
respectively via the cross-coupling of 1,4-dilithiobutadienes with dichlorodiphenylsilane. An unexpected tetrachloro-
substituted 10-membered silicon-bridged thiophene-based cyclophane (3) was obtained in a high yield as 46.9% when the
cross-coupling of 1,4-dilithiobutadiene reacted with dichlorodimethylsilane. In addition, the crystal structures of title
compounds are described.
Keywords: Cross-coupling, dithieno[2,3-b:3',2'-d]silole, heterocycles, silicon-bridged thiophene-based cyclophane.
In recent years, particular attention has been paid to
dithienosilole (DTS)-based polymers, promising functional
organic materials in devices such as light-emitting diodes
[1], field effect transistors [2], polymer solar cells [3], and
dye sensitive solar cells (DSSCs) [4]. Among the DTS
derivatives, great interest has been focused on dithieno[3,2-
b:2',3'-d]silole (4) during the last twenty years. However, as
one of the isomeric DTSs, there are few reports about the
derivatives based on dithieno[2,3-b:3',2'-d]silole (5). Iyoda
reported the preparation of 7,7-dimethyl-dithieno[2,3-b:3',2'-
d]silole in good yields by using palladium-catalyzed
intramolecular cross-coupling of organostannyl species [5a]
or using CuCl2-mediated cyclization of organozinc species
[5b]. In our recent work, we have reported the synthesis
of 7,7-dimethyl-2,5-bis(trimethylsilyl)-dithieno[2,3-b:3',2'-d]
silole in 81% yield by using 2,2'-dilithium-5,5'-bis(trimethyl-
silyl)-3,3'-bithiophene with dichlorodimethylsilane and its
halogenation ring opening in the presence of NXS (X = Cl,
Br, I) [6].
silyl)dithieno[2,3-b:3',2'-d]silole (8, 81.0%), in which dichlo-
rodimethylsilane was used instead of dichlorodiphenylsilane
[6]. Due to the presence of the two TMS groups, 7 has a very
good solubility and there was no solubility problem in both
Br/Li-exchange and subsequent ring close reaction. On the
other hand, the TMS groups in 7 also prevent the possible
side reactions occurred at the acidic ꢀ positions of thiophene
during the Br/Li-exchange reaction. Based on such factors
from the structure of 7, our method offers a practical route to
both 1 and 8 in good yields.
When TMS groups were replaced with Cl groups in 2,2'-
dibromo-5,5'-dichloro-3,3'-bithiophene (9) [8], after double
Br/Li exchange and quenching with dichlorodiphenylsilane,
2 could be obtained in 31.6% isolated yield. However, 7,7-
dimethyl-2,5-dichlorodithieno[2,3-b:3',2'-d]silole (10) can
not be obtained when dichlorodimethylsilane is used for the
formation of silole ring. Instead of 10, an unexpected 10-
membered silicon-bridged thiophene-based cyclophane (3)
was generated in pretty good yield (46.9%, Scheme 3).
Herein, we try to report the synthesis of dithieno[2,3-
Compared with the case in Schemes 2 and 3, when the
starting material was changed from 7 to 9, and the TMS
groups (EDG, electron donating group) in 7 were replaced
with Cl groups (EWG, electron withdrawing group) in 9.
After Br/Li exchange, the stability of dianion 9 is better than
that of dianion 7, which means that nucleophilicity of
dianion 9 is worse than that of dianion 7. As a result, the
yield of formation of 1 is much higher than that of 2 when
the dianions were quenched with dichlorodiphenylsilane.
b:3',2'-d]silole
based
derivatives,
7,7-diphenyl-2,5-
bis(trimethylsilyl)dithieno[2,3-b:3',2'-d]silole (1) and 7,7-
diphenyl-2,5-dichloro-dithieno[2,3-b:3',2'-d]silole (2) via the
cross-coupling of 1,4-dilithiobutadienes with dichloro-
diphenyl-silane. In addition, an unexpected tetrachloro-
substituted 10-membered silicon-bridged thiophene-based
cyclophane (3) was obtained when 1,4-dilithiobutadiene
reacted with dichlorodimethylsilane.
The synthetic route to 1 is shown in Scheme 2. The
efficient synthesis of 2,2'-dibromo-5,5'-bis(trimethylsilyl)-
3,3'-bithiophene (7) was reported in our previous work [7].
With 7 as starting material, after double Br/Li-exchange, the
reaction mixture was quenched with dichlorodiphenylsilane
to generate 1 in 79.4 % isolated yield (Scheme 2). Same case
happened in the formation of 7,7-dimethyl-2,5-bis(trimethyl-
The formation of two C-Si bonds for silole ring should be
carried out step by step. With the weaker nucleophilicity,
dianion 9 attacked Si atom of dichlorodimethylsilane, the
main product is unexpectedly 3, a silicon-bridged thiophene-
based 10-membered ring cyclophane, instead of expected 10.
The yield of 46.9% in forming 3 is much higher than that of
normal formation of macrocylces in organic synthesis. The
formation of 3 is different from the case of dianion 7
reacting with dichlorodimethylsilane or dichlorodiphenyl-
silane to generate dithieno[2,3-b:3',2'-d]siloles, 8 and 1. On
*Address correspondence to this author at the Key Lab for Special
Functional Materials of Ministry of Education, Henan University, Kaifeng,
475004, P. R. China; Tel: 86-378-3897112; Fax: (+86)-378-3881358;
E-mail: hwang@henu.edu.cn
1875-6255/11 $58.00+.00
© 2011 Bentham Science Publishers

Efficient Synthesis of Substituted Dithieno[2,3-b:3',2'-d]siloles
Letters in Organic Chemistry, 2011, Vol. 8, No. 10
729
Cl
Cl
TMS
TMS
Cl
Cl
S
S
S
S
Me
Me
Me
Me
Si
Si
S
S
S
S
Si
Si
Ph
Ph
Ph
Ph
Cl
Cl
1
2
3
S
S
S
S
Me
Me
Me
Me
Si
Si
S
S
Si
Si
H2
H2
S
S
4
5
6
Scheme 1. The molecular structures of 1-6.
TMS
TMS
TMS
TMS
TMS
TMS
n-BuLi
n-BuLi
Ph2SiCl2
S
S
S
S
S
S
Si
Si
Me2SiCl2
Br
Br
Me
8, 81.0%
Scheme 2. The synthetic route to 1 and 8.
Cl
Cl
Ph
Me
Ph
7
1, 79.4%
Cl
Cl
Cl
Cl
n-BuLi
n-BuLi
Ph2SiCl2
S
S
S
S
S
S
X
Si
Si
Me2SiCl2
Br
Br
Me
Ph
Me
Ph
9
2, 31.6%
10
n-BuLi
n-BuLi
Me2SiCl2
Ph2SiCl2
X
Cl
Cl
Cl
Cl
Cl
S
S
S
S
S
S
Ph
Ph
Ph
Ph
Me
Me
Me
Me
Si
Si
Si
Si
S
S
Cl
Cl
Cl
11
3, 46.9%
Scheme 3. The synthetic route to 2 and 3.
one hand, the absence of 10 means that the macrocyclic
structure of 3 is more stable than that of 10 in the
nucleophilic reaction of dianion 9 with of dichlorodimethyl-
silane. On the other hand, the nucleophilic reaction of
dianion 9 with dichlorodiphenylsilane, which bears bulky
phenyl groups, can not generate macrocyclic compound 11,
but only 2 in low yield (Scheme 3).
first step was Br/Li exchange of bis(3-bromothiophen-2-
yl)dimethylsilane to form the aryl lithium species; the second
step was the aryl lithium species combined with CuCN to
afford the Lipshutz cuprate and the last step was the Lipshutz
cuprate oxidated by 1,4-benzoquinone to result in target
compound 6. Compared with the Iyoda method, our method
for making 3 is more facile. In addition, the structure of 3 is
obviously different from that of 6.
Another silicon-bridged thiophene-based 10-membered
ring cyclophane, 6 (Scheme 1) was reported by Iyoda [9] in
18-50% yield. In his work, three steps were involved. The
The structure of 2 was confirmed by single crystal X-ray
analysis (Fig. 1). In the structure of 2, the frame of

730 Letters in Organic Chemistry, 2011, Vol. 8, No. 10
Zhao et al.
dithienosilole shows slight torsion. The crystal of 2 belongs
to monoclinic, space group P2 (1). The torsional angle
between two thiophene rings is 10.1° (C4-C2-C6-C8) and
the dihedral angle between the two thiophene rings is 7.3°.
The two benzene rings are out of the plane of dithienosilole.
The dihedral angles between the plane of the dithienosilole
and the two planes of the benzene rings are 64.5° and 83.2°,
respectively and meanwhile the dihedral angle between the
two benzene planes is 66.0°.
The efficient synthesis of the dithieno[2,3-b:3',2'-d]siloles
makes them possible to be used as the building blocks in the
application of organic functional materials, such as organic
semiconductor, OLED, etc. More interesting is that we
provide an efficient method for making a new tetrachloro-
substituted 10-membered silicon-bridged thiophene-based
cyclophane, 3, which might show its application as a new
type of host molecule in supramolecular chemistry.
EXPERIMENTAL
Preparation of 1
In a Schlenk flask, a solution of 7 (477.3 mg, 1.02 mmol)
in anhyd THF (20 mL) was added under Ar, then n-BuLi
(2.57 M, 0.83 mL, 2.1 equiv) was added dropwise at –78 °C.
After keeping at –78 °C for 2 h, Ph2SiCl2 (0.24 mL, 1.12
mmol, 1.1 equiv) was added, then the reaction mixture was
warmed slowly to ambient temperature and heated at 120 °C
overnight. After quenching with H2O (20 mL), the reaction
mixture was extracted with CHCl3 (3 ꢀ 20 mL) and then the
organic layer was washed with sat. NaHCO3 (40 mL) and
H2O (2 ꢀ 30 mL). After drying over MgSO4, the solvent was
removed in vacuo. The residue was purified by column
chromatography on silica gel with PE (60–90 °C) as eluent
to yield 1 (397.1 mg, 79.4 %) as a white solid. Mp: 149-150
ꢀ. 1H NMR (400 MHz, CDCl3) ꢁ 7.68 (dd, J1=8.0Hz,
J2=1.6Hz, 2H), 7.46 (s, 1H), 7.35-7.43(m, 3H), 0.36 (s, 1H);
13CNMR(100 MHz, CDCl3): ꢁ 154.68, 152.60, 138.59,
135.33, 131.61, 130.32, 128.14, 128.11, 0.02; HRMS (TOF
MS EI+) m/z calcd for [C26H30S2Si3] 490.1097 (Exact Mass),
found 490.1102. IR (KBr): 3060.7, 3001.7, 2954.6, 2887.7,
1657.6, 1658.9, 1484.7, 1429.7 (C-H) cm–1.
Fig. (1). Molecular structure and conformation for 2. Carbon,
silicon, chlorine and sulfur atoms are depicted with thermal
ellipsoids set at 50% probability level and all hydrogen atoms are
omitted for clarity.
The structure of 3 was also confirmed by single crystal
X-ray analysis (Fig. 2). The crystal of 3 belongs to
monoclinic, space group P1. In 3, the central 10-membered
ring has a “U”-shaped cycle containing both convex and
concave U-shapes linked together. The average dihedral
angle between the two thiophene rings in the bithienyl unit is
66.8°. The two homochiral bithienyl moieties of 3 have
transoid conformation. The torsional angles between the
neighboring thiophene rings are 109.3° (C4-C3-C14-C13)
and 111.9° (C5- C6-C10-C9). Two oppositing thiophenes
have an average dihedral angle of 19.4°.
Preparation of 2 and 3
2 and 3 were prepared from 9, respectively according to
the method used for the preparation of 1 from 7. For 2, the
reaction was carried out on 165.2 mg scale of 9, 55.6 mg
1
(31.6 %) of 2 was obtained. Mp: 191-193ꢀ . H NMR (400
MHz, CDCl3) ꢁ 7.63-7.62 (m, 2 H), 7.48 (t, J=7.2 Hz, 1 H),
7.40 (t, J=7.2 Hz, 2 H), 7.14 (s, 1H); 13CNMR(100 MHz,
CDCl3): ꢁ 151.19, 139.39, 135.27, 130.89, 130.03, 129.94,
128.40, 121.53; HRMS (TOF MS EI+) m/z calcd for
In summary, we have successfully synthesized
disubstituted dithieno[2,3-b:3',2'-d]siloles, 1 and 2 by the
cross-coupling of 1,4-dilithiobutadienes with dichlorosilane.
(a) side view
(b) crystal packings
Fig. (2). Molecular structure and conformation for 3: (a) side view; Carbon, silicon and sulfur atoms are depicted with thermal ellipsoids set
at 50% probability level and all hydrogen atoms are omitted for clarity. (b) crystal packings in monoclinic, space group P1.

Efficient Synthesis of Substituted Dithieno[2,3-b:3',2'-d]siloles
Letters in Organic Chemistry, 2011, Vol. 8, No. 10
731
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[C20H12Cl2S2Si] 413.9527 (Exact Mass), found 413.9531. IR
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1
Mp: 263-264 ꢀ. H NMR (400 MHz, CDCl3) ꢀ 6.72 (s,
1H), 0.40 (s, 1H); 13CNMR(100 MHz, CDCl3): ꢀ 144.81,
134.76, 132.73, 129.88, 0.82; HRMS (TOF MS EI+) m/z
calcd for [C20H16Cl4S4Si2] 579.8428 (Exact Mass), found
579.8433. IR (KBr): 3088.2, 2978.1, 2954.6, 2899.5 (C-H)
cm–1.
[2]
Crystal Data for 2 and 3
Crystal Data for 2:
M = 415.43, C20H12Cl2S2Si,
monoclinic, space group P2 (1), a = 6.6297 (12) Å, b =
12.109 (2) Å, c = 11.969 (2) Å, ꢀ = 90°, ꢁ = 100.072 (2)°, ꢂ
= 90°, V = 946.1(3) Å3, Z = 2, Dcalcd = 1.458 Mg/cm3. A
colorless crystal of dimensions 0.41 ꢁ 0.38 ꢁ 0.36 mm was
used for measurement at 296 (2) K with the ꢃ scan mode on
a Bruker Smart APEX diffractometer with CCD detector
using Mo–Ka radiation (ꢄ = 0.71073 Å). The data were
corrected for Lorentz and polarization effects and absorption
corrections were performed using SADABS [a] program.
The crystal structures were solved using the SHELXTL [b]
program and refined using full matrix least squares. The
positions of hydrogen atoms were calculated theoretically
and included in the final cycles of refinement in a riding
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space group P1, a = 10.456 (2) Å, b = 18.845 (4) Å, c =
13.6551(3) Å, ꢀ = 90°, ꢁ = 106.440 (2)°, ꢂ = 90°, V =
2580.6(9) Å3, Z = 4, Dcalcd = 1.499 Mg/cm3. A colorless
crystal of dimensions 0.41 ꢁ 0.37 ꢁ 0.35 mm was used for
measurement at 296 (2) K. The structure was solved by the
same methods as used for 2. The final cycle of fullmatrix
least-squares refinement was based on 4781 observed
reflections [I >2s(I)] and 275 variable parameters with R1 =
0.0390, wR2 = 0.0809.
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ACKNOWLEDGEMENTS
This work was supported by the NSFC (20972041,
50803015, 20672028), Program for Innovation Scientists and
Technicians Troop Construction Projects of Henan Province
(104100510011) and Program for SBGJ090506.
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SUPPLEMENTARY MATERIAL
Supplementary material is available on the publishers
Web site along with the published article.
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