Synthesis of wholly aromatic polymers possessing tetra-aryl-substituted vinylene units by palladium-catalyzed three-component coupling polymerization

Article abstract of DOI:10.1246/cl.2007.638

The synthesis of novel wholly aromatic poly(arylenevinylene)s containing tetra-aryl-substituted olefin units in the main chain by the three-component coupling polymerization of aryl dihalides, aryl diboronic acids, and acetylene derivatives is described. For instance, a polymer (M_n = 2600, M _w/M_n = 1.6) was obtained in a 76% yield by the polymerization of 1,4-diiodobenzene, diphenylacetylene, and 1,4- phenylenediboronic acid in DMF/H₂O at 100°C for 24 h in the presence of PdCl₂(PhCN)₂ (1 mol %) and KHCO₃. The obtained polymer is soluble in organic solvents such as CHCl₃, THF, and toluene, although it does not have any soft lateral segments. Copyright

Full text of DOI:10.1246/cl.2007.638

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38
Chemistry Letters Vol.36, No.5 (2007)
Synthesis of Wholly Aromatic Polymers Possessing Tetra-aryl-substituted Vinylene Units
by Palladium-catalyzed Three-component Coupling Polymerization
ꢀ
Kojiro Nakagawa and Ikuyoshi Tomita
Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering,
Tokyo Institute of Technology, Nagatuta-cho 4259-G1-9, Midori-ku, Yokohama 226-8502
(Received January 25, 2007; CL-070092; E-mail: tomita@echem.titech.ac.jp)
The synthesis of novel wholly aromatic poly(arylenevi-
derivatives containing tetra-aryl-substituted olefin units in the
main chain (Scheme 1).
nylene)s containing tetra-aryl-substituted olefin units in the
main chain by the three-component coupling polymerization of
aryl dihalides, aryl diboronic acids, and acetylene derivatives
is described. For instance, a polymer (Mn ¼ 2600, Mw=Mn ¼
On the basis of the palladium-catalyzed ternary coupling
reaction of aryl halides, internal alkynes, and arylboronic acids,5
the polymerization of 1, 2a, and 3 was carried out in DMF/H2O
ꢁ
1
:6) was obtained in a 76% yield by the polymerization of 1,4-
(v/v = 4/1) at 100 C for 24 h in the presence of PdCl2(PhCN)2
diiodobenzene, diphenylacetylene, and 1,4-phenylenediboronic
ꢁ
(1 mol %) and KHCO3 (2 equiv.). After the reaction, a polymer
4a was isolated by the precipitation with methanol as a yellow
powder in a 76% yield. In sharp contrast to the poor solubility
of the unsubstituted PPV ((–C6H4–CH=CH–)n), it was of fortu-
nate that the obtained polymer 4a exhibits good solubility in
common organic solvents such as THF, CHCl3, and toluene,
although 4a does not possess any soft lateral substituents. The
acid in DMF/H2O at 100 C for 24 h in the presence of
6
PdCl2(PhCN)2 (1 mol %) and KHCO3. The obtained polymer
is soluble in organic solvents such as CHCl3, THF, and toluene,
although it does not have any soft lateral segments.
Over the past few decades, a large number of studies on
-conjugated polymers have been carried out because of their
number average molecular weight (M ) of the polymer was
n
estimated to be 2600 from the GPC measurement. Under the
examined conditions, the polymer 4a precipitated out during
the polymerization, which might be the reason for the lower
molecular weight of the polymer.
ꢀ
characteristic properties. For instance, poly(phenylenevinylene)
1
(
of their potential applications in electroluminescence (EL) de-
PPV) and its derivatives have been paid much attention in view
2
vices. The transition metal-catalyzed polymerization systems
based on homo- and cross-coupling processes represent one of
Also, a polymer having methyl substitutents (4b, M ¼
n
2800, M =M ¼ 1:5) was obtained by the polymerization using
w
n
1
the most useful strategies for the preparation of ꢀ-conjugated
polymers, including PPV derivatives. In these cases, however,
di-p-tolylacetylene (2b) as an internal alkyne. The H NMR
spectrum of 4b was informative to estimate the composition
of the polymer. As shown in Figure 1, peaks for –C H – and
3
the structural design of monomers is essentially important
to overcome the poor processability and solubility of the
resulting polymers. We have been working on the development
and applications of three-component coupling polymerization
systems in which highly functionalized polymers having
6
4
–CH were observed, whose integral ratio (24:12) was in good
3
agreement with that expected from the objective structure.
Therefore, 4b was confirmed to be composed of the objective
tetra-aryl ethylene units. If the reaction of iodobenzene
(0.5 mmol), diphenylacetylene (1.5 mmol), and phenylboronic
acid (0.5 mmol) was carried out under the analogous conditions,
the Suzuki–Miyaura coupling product, biphenyl was not detect-
ed in the reaction mixture. In this case, tetraphenylethylene (5)
4
well-defined sequence are accessible from simple monomers.
For instance, the palladium-catalyzed three-component coupling
polymerization of aromatic bisallenes, aryl dihalides, and
nucleophiles gives PPV derivatives possessing functional groups
originated from the nucleophilic components on each vinylene
unit.4
atives can be tuned by the nature of the functional substituents.
Herein, we would like to report a new palladium-catalyzed
three-component coupling polymerization of 1,4-diiodobenzene
was isolated in a 74% yield by SiO column chromatography
2
a–4d
The properties such as the solubility of the PPV deriv-
(eluent: hexane). This result further supported that the polymers
have the objective structure units.
As shown in Figures 2 and 3, the UV–vis absorption
maximum (ꢁmax) of 4a in a CHCl solution appeared at slightly
3
(1), internal alkynes (2a and 2b), and 1,4-phenylenediboronic
acid (3) as a novel synthetic method of a new class of PPV
longer wavelength (330 nm) in comparison with that of a model
compound, tetraphenylethylene (5, ꢁmax ¼ 310 nm). A yellow
transparent thin film with a thickness of about 20 mm was pre-
pared by coating the polymer 4a on glass substrate from a CHCl3
I
I
+
2
Ar
Ar
+
(HO)2B
B(OH)2
1
2a–2b
3
C6H4
CH3
CH3
CH3
Ar Ar
2
2
a :
b : Me
PdCl2(PhCN)2 (1 mol%)
KHCO3
DMF/H2O = (v / v = 4 / 1)
Me
1
00 °C, 24 h
Ar Ar
n
CH3
CH3
4a–4b
n
4
b
8
6
4
2
ppm
Scheme 1. Synthesis of wholly aromatic polymers possessing
tetra-aryl-substituted vinylene units.
1
Figure 1. H NMR spectrum of 4b.
Copyright ꢀ 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.5 (2007)
639
R. H. Baughman, Synth. Met. 1980, 1, 307. e) I. Murase,
T. Ohnishi, T. Noguchi, M. Hirooka, Polym. Commun.
5
(a)
(b)
4
a
(
ii)
1
979, 20, 1441.
2
3
J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N.
Marks, K. Mackay, R. H. Friend, P. L. Burns, A. B. Holmes,
Nature 1990, 347, 539.
a) A. Greiner, W. Heitz, Makromol. Chem., Rapid Commun.
1988, 9, 581. b) G. M. Farinola, F. Babudri, F. Naso, Y.
Dubistky, A. Zaopo, F. D’Amore, S. M. Pietralunga, Synth.
Met. 2003, 137, 1473.
a) N. Miyaki, I. Tomita, J. Kido, T. Endo, Macromolecules
1996, 29, 6685. b) N. Miyaki, I. Tomita, T. Endo, Chem.
Lett. 1997, 685. c) S. Kannoo, T. Saruhashi, S. Ishibe, K.
Nakagawa, I. Tomita, Polym. Bull. 2006, 57, 843. d) N.
Miyaki, I. Tomita, T. Endo, Macromolecules 1997, 30,
5
(i)
2
50
300
350
400
450
500
400
500
600
Wavelength / nm
Wavelength / nm
Figure 2. (a) UV–vis absorption spectra of 4a and 5 in CHCl3.
b) Photoluminescence spectra of 4a (c ¼ 12:5 mg/L, excited at
30 nm) in CHCl3 (i) and in a mixed solvent of CHCl3/MeOH
v/v = 30/70) (ii).
(
4
3
(
4
504. e) N. Miyaki, I. Tomita, T. Endo, J. Polym. Sci., Part
A: Polym. Chem. 1997, 35, 2097. f) N. Miyaki, I. Tomita, T.
Endo, J. Polym. Sci., Part A: Polym. Chem. 1997, 35, 1211.
g) S. Ishibe, I. Tomita, J. Polym. Sci., Part A: Polym. Chem.
2
005, 43, 3403.
5
6
C. Zhou, R. C. Larock, J. Org. Chem. 2005, 70, 3765.
A typical experimental procedure for the synthesis of 4a
is given as follows: to a test tube equipped with a magnetic
stirrer chip were added 1 (0.082 g, 0.25 mmol), 2a (0.267 g,
3
00
400
500
600
Wavelength / nm
Figure 3. UV–vis absorption and photoluminescence (excited
at 330 nm) spectra of 4a in the film.
1
mmol), DMF (4 mL), and H2O (1 mL). The mixture was
.5 mmol), 3 (0.041 g, 0.25 mmol), KHCO3 (0.050 g, 0.50
ꢁ
stirred at 100 C for 10 min. Then, a DMF solution of
PdCl2(PhCN)2 (0.025 M, 0.20 mL, 0.0050 mmol) was added
solution. The UV–vis absorption spectrum of the film was
almost identical to that measured in a dilute CHCl3 solution.
Upon irradiation of UV–vis light, this film emits green light
ꢁ
and the mixture was stirred at 100 C for 24 h. After pouring
into brine (10 mL), the aqueous phase was extracted three
times with CHCl3 (5 mL each). After drying over magnesi-
um sulfate, the organic solution was concentrated and was
(
ꢁ
em, max ¼ 525 nm), although only very weak fluorescence
could be detected in a dilute CHCl3 solution. However, it is
of note that the corresponding emission was observable in a
solution of a mixed solvent containing a considerable amount
of poor solvent (e.g., CHCl3/MeOH mixed solvent, v/v = 30/
precipitated into a large excess amount of methanol to give
1
4
a in a 76% yield (0.096 g). H NMR (300 MHz, CDCl3,
13
ꢂ) 6.19–8.04 (–C6H5 and –C6H4–, 28H).
C NMR
7
0) although 4a could be dissolved completely under the exam-
(
75 MHz, CDCl3, ꢂ) 126.0, 126.5, 127.2, 127.7, 130.8,
ined conditions (Figures 2 and 3). By increasing the content
of the poor solvent, the interaction between the polymer chains
becomes much stronger than that in a solution without poor
solvents. We assume that the fluorescence observed in the film
and in the presence of poor solvents is due to the suppression
1
31.3, 131.8, 138.4, 139.4, 140.7, 142.1, 142.8, 143.7. IR
ꢂ1
(
neat, cm ) 3056, 3027, 1803, 1665, 1597, 1491, 1443,
1
8
400, 1345, 1275, 1181, 1111, 1074, 1030, 1005, 976, 909,
10, 733, 698. 4b: from 1 (0.082 g, 0.25 mmol), 2b
(
8
(
0.309 g, 1.5 mmol), and 3 (0.041 g, 0.25 mmol); Yield
1
7
of the twisting vibration of the aromatic rings in 4a.
2% (0.115 g); H NMR (300 MHz, CDCl3, ꢂ) 1.72–2.40
13
In summary, a new class of wholly aromatic polymers
having PPV backbone and the aryl substituents on the vinylene
units was obtained by the palladium-catalyzed three-component
coupling polymerization of 1,4-diiodobenzene, internal alkynes,
and 1,4-phenylenediboronic acid. On the basis of the present
polymerization method, a variety of fully substituted poly(aryl-
enevinylene)s are expected to be produced by the simple mono-
mer design. Thus, the synthesis and properties of a series of
polymers are currently being investigated.
–CH3, 12H), 6.53–7.82 (–C6H4–, 24H).
C NMR
(
75 MHz, CDCl3, ꢂ) 21.2, 125.9, 127.2, 131.3, 131.9,
1
36.0, 138.2, 139.3, 139.6, 140.2, 140.9, 142.3, 143.3. IR
ꢂ1
(neat, cm ) 3025, 2992, 2920, 2866, 1905, 1794, 1655,
1607, 1508, 1487, 1449, 1404, 1273, 1182, 1113, 1020,
1005, 965, 909, 816, 768, 733.
7
8
The similar fluorescent behavior has also been reported
in the cases of 5 and a polymer having analogous fully
substituted vinylene structure. See Refs. 8 and 9.
a) S. Sharafy, K. A. Muszkat, J. Am. Chem. Soc. 1971, 93,
4119. b) P. F. Barbara, S. D. Rand, P. M. Rentzepis, J.
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S. A. Jonker, J. M. Warman, M. P. de Haas, M. J. W.
Vermeulen, W. F. Jager, B. de Lange, B. L. Feringa, R. W.
Fessenden, J. Am. Chem. Soc. 1993, 115, 3286.
References and Notes
1
a) T. Ito, H. Shirakawa, S. Ikeda, J. Polym. Sci., Polym.
Chem. Ed. 1974, 12, 11. b) A. F. Diaz, K. K. Kanazawa,
G. P. Gardini, J. Chem. Soc., Chem. Commun. 1979, 14,
635. c) T. Yamamoto, K. Sanechika, A. Yamamoto, J.
Polym. Sci., Polym. Lett. Ed. 1980, 18, 9. d) L. W.
Schacklette, R. R. Chance, D. M. Ivory, G. G. Miller,
9
D. M. Johansson, M. Theander, O. Ingan a¨ s, M. R. Anderson,
Synth. Met. 2000, 113, 293.
Published on the web (Advance View) April 14, 2007; doi:10.1246/cl.2007.638