Synthesis of monodisperse oligo[(1,4-phenyleneethynylene)-alt-(2,5- thiopheneethynylene)]s

Article abstract of DOI:10.1081/SCC-200046517

The synthesis of monodisperse oligo[(1,4-phenyleneethynylene)-alt-(2,5- thioph-eneethynylene)]s using an iterative divergent/convergent doubling strategy based on Sonogashira coupling reaction was presented.

Full text of DOI:10.1081/SCC-200046517

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Synthesis of Monodisperse
Oligo[(1,4‐Phenyleneethynylene)‐A
Guorong Li a , Xianhong Wang a , Ji Li a , Xiaojiang
Zhao a & Fosong Wang a
a State Key Laboratory of Polymer Physics and
Chemistry , Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences and
Graduate School of the Chinese Academy of
Sciences , Changchun, 130022, China
Published online: 05 Aug 2006.
To cite this article: Guorong Li , Xianhong Wang , Ji Li ,
Xiaojiang Zhao & Fosong Wang (2005) Synthesis of Monodisperse
Oligo[(1,4‐Phenyleneethynylene)‐Alt‐(2,5‐Thiopheneethynylene)]s, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:1, 115-119, DOI: 10.1081/SCC-200046517
To link to this article: http://dx.doi.org/10.1081/SCC-200046517
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Synthetic Communicationsw, 35: 115–119, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200046517
Synthesis of Monodisperse
Oligo[(1,4-Phenyleneethynylene)-
Alt-(2,5-Thiopheneethynylene)]s
Guorong Li, Xianhong Wang, Ji Li,
Xiaojiang Zhao, and Fosong Wang
State Key Laboratory of Polymer Physics and Chemistry, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences and
Graduate School of the Chinese Academy of Sciences, Changchun, China
Abstract: The synthesis of monodisperse oligo[(1,4-phenyleneethynylene)-alt-(2,5-
thioph-eneethynylene)]s using an iterative divergent/convergent doubling strategy
based on Sonogashira coupling reaction was presented.
Keywords: Oligo[(1,4-phenyleneethynylene)-alt-(2,5-thiopheneethynylene)]s, iterative
divergent/convergent, sonogashira coupling reaction
INTRODUCTION
Conjugated oligomers of precise length and constitution have received con-
siderable attention both as models for analogous bulk polymers and as candi-
dates for molecular wires and molecular scale electronic devices.[1–3]
Monodisperse, well-defined oligo(1,4-phenyleneethynylene)s and oligo(2,5-thio-
pheneethynylene)s are of particular interest due to their linear conjugated
molecular structures as well as their interesting electronic characteristics.[4–17]
Different synthetic strategies and routes have been developed for
Received in Japan August 19, 2004
Address correspondence to Xianhong Wang, State Key Laboratory of Polymer
Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese
Academy of Sciences and Graduate School of the Chinese Academy of Sciences,
Changchun 130022, China. E-mail: xhwang@ciac.jl.cn

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G. Li et al.
preparing above oligomers by several groups. Tour et al. have demonstrated
an iterative divergent/convergent strategy to rapid synthesis of oligo(1,4-
phenyleneethynylene)s, oligo(2,5-thiopheneethynylene)s, and their block
cooligomers.[4,6,7,10–12] Later, they developed an in situ desilylation/
Pd-catalyzed coupling bidirectional synthesis strategy for the preparation of
oligo(1,4-phenyleneethynylene)s.[13] Godt et al. reported an alternative route
based on bromine-iodine selectivity of the Pd/Cu-catalyzed alkyne-aryl-
coupling to synthesis of oligo(1,4-phenyleneethynylene)s.[9] Recently, Chen
et al. described a new stepwise synthetic route for the preparation of
oligo(1,4-phenyleneethynylen-e)s with high purity.[18] To our knowledge,
there has not been any report on the preparation of oligo[(1,4-phenylene-
ethynylene)-alt-(2,5-thiopheneethynylene)]s up to now. We report here the
synthesis of soluble monodisperse oligo[(1,4-phenylene-ethynylene)-
alt-(2,5-thiopheneethynylene)]s by means of an iterative divergent/
convergent doubling strategy.
RESULTS AND DISCUSSION
The synthetic route is outlined in Scheme 1. Compound 1 was conveniently
synthesized according to previously reported procedure.[7] 4-iodoaniline was
converted to the diethyltriazene 2,[4,6] followed by coupling to trimethylsily-
lacetylene and then desilylation to afford 3 which was then coupled with 1 to
give 4, the desired “starting monomer” for the iterative divergent/convergent
doubling strategy. 4 was divided into two parts. One part was treated with base
to give the desilylation terminal alkyne 5, and the other was converted to the
aryl iodide 6 with methyl iodide. Then, 5 was coupled with 6 yielding
compound 7. Iteration of above reaction sequence doubled the molecular
length of compound 7 to afford 10, which was quite soluble in common
organic solvents such as THF, CHCl3, and so on. Both triazene- iodide conver-
sion and trimethylsilyl deprotection reactions were almost in quantitive
yields, and the coupling reactions were in high yields ( . 90%). Note that
any product bearing triazene in our present system was easily decomposed
on the silica gel! Fortunately, chromatographic purification on neutral
alumina has proven to be efficient.
In summary, first synthesis of monodisperse oligo[(1,4-phenylene-ethy-
nylene)-alt-(2,5-thiopheneethynylene)]s was reported in this communication.
EXPERIMENTAL
General Procedure for Iodide Formation from Triazenes
To a thick-walled flame-dried screw cap tube was added the corresponding
triazene and iodomethane (10 equiv). The tube was flushed with argon,

Synthesis of Monodisperse Oligomers
117
Scheme 1.
sealed, and heated to 1208C overnight. The reaction was cooled to room temp-
erature, and the solvent was removed in vacuo. The crude product was then
filtered through a plug of silica gel with ethyl acetate.
General Procedure for Desilylation of Alkynes
The silylated alkyne was dissolved in methanol and dichloromethane.
Potassium carbonate (2 equiv) was then added, and the reaction was stirred
overnight. The reaction mixture was subjected to an aqueous workup and
the aqueous layer was extracted with dichloromethane. After drying the

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G. Li et al.
combined organic layers over magnesium sulfate, the solvent was removed
in vacuo. The product was used without further purification.
General Procedure for Sonogashira Coupling Reaction
To a flame-dried vessel were added the alkyne, the iodo compound (1.0 equiv
based on per alkyne), bis(dibenzylideneacetone)palladium(0) (5 mol % per
alkyne), triphenylphosphine(25 mol % per alkyne), copper(I) iodide (10 mol
% per alkyne), and THF/Et3N (2:1) at room temperature under argon. The
vessel was sealed and allowed to stir at room temperature for 2 days. The
reaction mixture was then subjected to an aqueous workup and the aqueous
layer was extracted three times with dichloromethane. After drying the
combined organic layers over magnesium sulfate, the solvent was removed
in vacuo to afford a crude product, which was then purified by column
chromatography (neutral alumina, 200–300 mesh).
Spectral data for oligomers:
Oligomer 4. 1H NMR (CDCl3, 600 MHz): d7.45 (d, J ¼ 8.4 Hz, 2H), 7.39
(d, J ¼ 8.4 Hz, 2H), 6.98 (s, 1H), 3.77 (q, J ¼ 7.2 Hz, 4H), 2.65 (t, J ¼ 7.8 Hz,
2H), 1.60 (p, J ¼ 7.2 Hz, 2H), 1.35 (sext, J ¼ 7.2 Hz, 2H), 1.27 (br s, 6H), 0.94
(t, J ¼ 7.2 Hz, 3H), 0.26 (s, 9H); 13C NMR (CDCl3, 150 MHz): d151.27,
148.64, 132.34, 132.18, 123.44, 120.44, 120.25, 118.69, 101.82, 97.05,
94.33, 82.39, 32.16, 32.05, 29.05, 22.18, 13.91, 13.81; LDI-MS: 436 (Mþ),
407 (M - C2H5), 363 (M - TMS), 336 (M – Et2N3).
Oligomer 7. 1H NMR (CDCl3, 600 MHz): d7.48 (d, J ¼ 8.4 Hz, 2H), 7.46
(s, 4H), 7.40 (d, J ¼ 8.4 Hz, 2H), 7.03 (s, 1H), 7.01 (s, 1H), 3.77
(q, J ¼ 7.2 Hz, 4H), 2.72 (t, J ¼ 7.2 Hz, 2H), 2.65 (t, J ¼ 7.2 Hz, 2H), 1.65–
1.59 (m, 4H), 1.41–1.34 (m, 4H), 1.26 (br s, 6H), 0.97–0.93 (m, 6H), 0.26
(s, 9H); 13C NMR (CDCl3, 150 MHz): d151.24, 148.63, 148.00, 132.91,
132.48, 132.12, 131.28, 131.11, 124.02, 123.07, 122.56, 122.41, 120.41,
120.18, 119.10, 118.59, 102.25, 96.80, 95.71, 94.89, 93.30, 84.70, 84.44,
82.38, 32.19, 32.07, 31.99, 29.16, 29.04, 28.98, 22.20, 22.13, 14.10, 13.87,
13.78; LDI-MS: 698 (Mþ), 669 (M–C2H5), 598 (M–Et2N3).
1
Oligomer 10. H NMR (CDCl3, 600 MHz): d7.49–7.47 (m, 14H), 7.40
(d, J ¼ 8.4 Hz, 2H), 7.09 (s, 2H), 7.05 (s, 1H), 7.02 (s, 1H), 3.78
(q, J ¼ 7.2 Hz, 4H), 2.75–2.72 (m, 6H), 2.66 (t, J ¼ 7.2 Hz, 2H), 1.69–1.57
(m, 8H), 1.41–1.32 (m, 8H), 1.27–1.20 (m, 6H), 0.98–0.94 (m, 12H), 0.26
(s, 9H); 13C NMR (CDCl3, 150 MHz): d151.32, 148.70, 148.12, 133.23,
133.01, 132.56, 132.19, 131.37, 131.23, 124.09, 123.20, 123.17, 123.04,
122.98, 122.65, 122.61, 122.56, 122.46, 120.45, 120.30, 120.05, 120.01,
119.16, 118.67, 102.35, 96.80, 96.10, 95.73, 94.90, 93.84, 93.78,
93.24, 84.81, 84.71, 84.51, 84.28, 84.21, 82.39, 32.24, 32.04, 29.21,
29.04, 22.25, 22.18, 13.90, 13.80; LDI-MS: MALDI-MS: 1223 (Mþ), 1123
(M–Et2N3).

Synthesis of Monodisperse Oligomers
ACKNOWLEDGMENT
119
This work was supported by National Science Fund for Distinguished Young
Scholars (No. 20225414).
REFERENCES
1. Tour, J. M. Chem. Rev. 1996, 96, 537.
2. Martin, R. E.; Diederich, F. Angew. Chem. Int. Ed. 1999, 38, 1350.
3. Yang, X. W.; Yuan, L. H.; Yamato, K.; Brown, A. L.; Feng, W.; Furukawa, M.;
Zeng, X. C.; Gong, B. J. Am. Chem. Soc. 2004, 126, 3148.
4. Schumm, J. S.; Pearson, D. L.; Tour, J. M. Angew. Chem. Int. Ed. 1994, 33, 1360.
5. Bumm, L. A.; Arnold, J. J.; Cygan, M. T.; Dunbar, T. D.; Burgin, T. P.; Jones, L.;
Allara, D. L.; Tour, J. M.; Weiss, P. S. Science 1996, 271, 1705.
6. Jones, L.; Schumm, J. S.; Tour, J. M. J. Org. Chem. 1997, 62, 1388.
7. Pearson, D. L.; Tour, J. M. J. Org. Chem. 1997, 62, 1376.
8. Reed, M. A.; Zhou, C.; Muller, C. J.; Burgin, T. P.; Tour, J. M. Science 1997, 278,
252.
9. Ziener, U.; Godt, A. J. Org. Chem. 1997, 62, 6137.
10. Huang, S. L.; Tour, J. M. Polym. Prep. 1998, 525.
11. Chen, J.; Reed, M. A.; Rawlett, A. M.; Tour, J. M. Science 1999, 286, 1550.
12. Huang, S. L.; Tour, J. M. J. Am. Chem. Soc. 1999a, 121, 4908.
13. Huang, S. L.; Tour, J. M. J. Org. Chem. 1999b, 64, 8898.
14. Huang, S. L.; Tour, J. M. Tetrahedron Lett. 1999c, 40, 3347.
15. Donhauser, Z. J.; Mantooth, B. A.; Kelly, K. F.; Bumm, L. A.; Monell, J. D.;
Stapleton, J. J.; Price, D. W.; Rawlett, A. M.; Allara, D. L.; Tour, J. M.;
Weiss, P. S. Science 2001, 292, 2303.
16. Fan, F. R. F.; Yang, J.; Cai, L.; Price, D. W., Jr.; Dirk, S. M.; Kosynkin, D. V.;
Yao, Y.; Rawlett, A. M.; Tour, J. M.; Bard, A. J. J. Am. Chem. Soc. 2002, 124,
5550.
17. Stewart, M. P.; Maya, F.; Kosynkin, D. V.; Dirk, S. M.; Stapleton, J. J.;
McGuiness, C. L.; Allara, D. L.; Tour, J. M. J. Am Chem. Soc. 2004, 126, 370.
18. Zhou, C. Z.; Liu, T. X.; Xu, J. M.; Chen, Z. K. Macromolecules 2003, 36, 1457.