Synthesis of π-conjugated polymers via regioregular organometallic polymers 2. Transformation of titanacyclopentadienecontaining polymer into poly(ρ-phenylene) derivative

Article abstract of DOI:10.1002/aoc.1593

The transformation of a regioregular organometallic polymer possessing titanacyclopentadiene-2,5-diyl units into a poly(ρ-phenylene) derivative by means of a novel polymer reaction method is described. The organotitianium polymer was prepared by the polymerization of 1,4-diethynyl-2,5- dioctyloxybenzene and a low-valent titanium complex, generated in situ from titanium(IV) isopropoxide and isopropylmagnesium chloride, and was subjected to the reaction with 3-bromo-1-propyne followed by the protonation. Consequently, a polymer consisting of the substituted phenylene-1,4-diyl units could be produced in a high yield,which is soluble in organic solvents such as chloroform. The number-average molecularweight and themolecular weight distribution of the polymer were estimated as 4800 and 1.8, respectively (GPC, polystyrene). The UV-vis absorption spectrum of the polymer exhibited the absorption maximum (λmax) at 329 nm, which was bathochromically shifted by 53 nm compared with that of a model compound, 1,4-bis(2-methoxyphenyl)-2- methylbenzene (λmax = 276 nm). Copyright

Full text of DOI:10.1002/aoc.1593

Full Paper
Received: 15 July 2009
Revised: 11 October 2009
Accepted: 26 October 2009
Published online in Wiley Interscience: 22 January 2010
(www.interscience.com) DOI 10.1002/aoc.1593
Synthesis of π-conjugated polymers via
regioregular organometallic polymers 2.
Transformation of titanacyclopentadiene-
containing polymer into poly(p-phenylene)
derivative
Tomoko Kino, Hiroki Nishiyama and Ikuyoshi Tomita∗
The transformation of a regioregular organometallic polymer possessing titanacyclopentadiene-2,5-diyl units into a poly(p-
phenylene) derivative by means of a novel polymer reaction method is described. The organotitianium polymer was prepared
by the polymerization of 1,4-diethynyl-2,5-dioctyloxybenzene and a low-valent titanium complex, generated in situ from
titanium(IV) isopropoxide and isopropylmagnesium chloride, and was subjected to the reaction with 3-bromo-1-propyne
followed by the protonation. Consequently, a polymer consisting of the substituted phenylene-1,4-diyl units could be produced
in a high yield, which is soluble in organic solvents such as chloroform. The number-average molecular weight and the molecular
weight distribution of the polymer were estimated as 4800 and 1.8, respectively (GPC, polystyrene). The UV–vis absorption
spectrum of the polymer exhibited the absorption maximum (λmax) at 329 nm, which was bathochromically shifted by 53 nm
c
compared with that of a model compound, 1,4-bis(2-methoxyphenyl)-2-methylbenzene (λmax = 276 nm). Copyright ꢀ 2010
John Wiley & Sons, Ltd.
Keywords: organometallic polymer; π-conjugated polymer; polymer reaction; poly(p-phenylene)
Introduction
In the course of our studies to evaluate the reactivity of the
organotitanium polymer (3) and to determine the possibility of
preparing π-conjugated materials possessing diverse main chain
functionality, we describe here the transformation into poly(p-
phenylene) derivative (4) using 3-bromo-1-propyne as a reagent
for the polymer reaction (Scheme 2). Properties of the poly(p-
phenylene) derivative obtained in the present method are also
discussed.
Organometallic polymers have been extensively studied with
expectation of their diverse applications to advanced func-
tional materials.[1] In addition, polymers possessing reactive
carbon–metal bonds are attractive candidates of reactive poly-
mers that serve as synthetic precursors for functional organic
and/or inorganic polymers applicable to many research fields.
In particular, organometallic polymers possessing reactive func-
tions in the main chain are attractive for attaining novel
macromolecular design of the target polymers with unique
functions in the main chain. Recently, polymers containing re-
active organometallic building blocks such as organoboron,[2]
cobaltacyclopentadiene,[3] zirconacyclopentadiene,[4] titana-
cyclobutene[5] and titanacyclopentadiene[6,7] in the main chain
have been prepared and they have been applied as powerful syn-
thetic precursors for main chain functionalized materials. Through
our studies on the reactive organometallic polymers, it turned out
that the control of regioregularity of the main chain connection at
each metallacycle unit is an important point to obtain novel func-
tional materials such as π-conjugated polymers via the reactive
polymers. Previously, we reported the synthesis of a regioregular
organotitanium polymer (3) by the regiospecific metallacycliza-
tion of a diethynylbenzene derivative (1) and a low-valent titanium
complex (2), generated in situ from titanium(IV) isopropoxide
[Ti(OPri)4] and isopropylmagnesium chloride (iPrMgCl), and the
polymer was converted into novel π-conjugated polymers con-
taining 1,3-butadiene-1,4-diyl units (4) (Scheme 1).[7]
Experimental
Materials
A
diethyl ether solution of iPrMgCl was prepared from
2-chloropropane and magnesium in diethyl ether. Ti(OPri)4 was
distilled and stored under argon. 1,4-Dioctyloxybenzene was pre-
pared from hydroquinone and 1-bromooctane and purified by
recrystallization from ethanol. 3-Bromo-1-propyne was distilled
under argon. Diethyl ether was dried over sodium benzophenone
∗
Correspondence to: Ikuyoshi Tomita, Tokyo Institute of Technology, Depart-
ment of Electronic Chemistry, Interdisciplinary Graduate School of Science
and Engineering, Nagatsuta-cho 4259-G1-9, Midori-ku, Yokohama 226-8502,
Japan. E-mail: tomita@echem.titech.ac.jp
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, Japan
c
Appl. Organometal. Chem. 2010, 24, 558–562
Copyright ꢀ 2010 John Wiley & Sons, Ltd.

Synthesis of π-conjugated polymers
C8H17
O
iPrO OPri
Ti
C8H17
O
Et2O
Ti(OPri)2
+
n
-78 °C ~ -50 °C
OC8H17
OC8H17
1
2
3
C8H17
O
X
X
HCl or I2
n
-50 °C ~ r.t.
OC8H17
4 (X = H or I)
Scheme 1. Synthetic route for diene-containing π-conjugated polymers (4).
Ti(OPri)2Br
Me
C8H17O
C8H17O
H3O+
HC≡CCH2Br
-50 °C ~ r.t.
3
n
n
OC8H17
OC8H17
5
Scheme 2. Synthetic route for a poly(p-phenylene) derivative (5) by the reaction of 3 with 3-bromo-1-propyne.
ketyl and distilled under argon. All reagents used for precipitation
and analyses were used without further purification.
and 1,4-diiodo-2,5-dioctyloxybenzene (5.9 g, 10 mmol), were
added diiospropylamine (40 ml) and tetrahydrofuran (15 ml), and
the mixture was stirred for 30 min at ambient temperature.
Then, trimethylsilylacetylene (2.5 g, 25 mmol) was added and
the mixture was heated under gentle reflux overnight. After
the addition of benzene (100 ml), the mixture was washed
with brine and the organic layer was dried over magnesium
sulfate. 1,4-Bis(trimethylsilylethynyl)-2,5-dioctyloxybenzene was
obtained in a quantitative yield (4.8 g, 10 mmol) by SiO2 column
chromatography (eluent: benzene).
1H-NMR (300 MHz, CDCl3, δ in ppm) 0.25 [s, 18H, -Si(CH3)3], 0.88
(t, J = 6.2 Hz, 6H, -CH3), 1.25–1.53 [20H, -OCH2CH2(CH2)5-], 1.78
(m, 4H, -OCH2CH2-), 3.94 (t, J = 6.3 Hz, 4H, -OCH2CH2-), 6.89 (s, 2H,
-C6H2-).
To a methanol (20 ml) solution of 1,4-bis(trimethylsilylethynyl)-
2,5-dioctyloxybenzene (4.8 g, 10 mmol), a methanol solution of
potassium hydroxide (1.0 M, 12 ml) was added and the mixture
was stirred at ambient temperature for 4 h. Then, diethyl ether
(20 ml) was added and the mixture was washed with water. The
organic layer was collected and dried over magnesium sulfate.
1,4-Diethynyl-2,5-dioctyloxybenzene (1) was isolated in a 77%
yield (2.6 g, 7.7 mmol) by SiO2 column chromatography (eluent:
hexane).
1H-NMR (300 MHz, CDCl3, δ in ppm) 0.88 (t, J = 5.7, 6H, -CH3),
1.28–1.54 [20H, -OCH2CH2(CH2)5-], 1.79 (m, 4H, -OCH2CH2-), 3.33
(s, 2H, -C CH), 3.96 (t, J = 7.2 Hz, 4H, -OCH2-), 6.95 (s, 2H, -C6H2-).
13C-NMR (75 MHz, CDCl3, δ in ppm) 14.1, 22.6, 25.9, 29.1, 29.2,
29.3, 31.7, 69.7, 79.8, 82.4, 113.3, 117.8, 154.0.
Instrumentation
Nuclear magnetic resonance spectra were obtained on a Jeol
ECP300spectrometer(300and75 MHzfor1HNMRand13CNMR,re-
spectively). Gelpermeationchromatography(GPC)measurements
were performed on a Shimadzu LC-10AS liquid chromatograph
equipped with Tosoh TSK-gel GMHHR-M tandem columns using
chloroform (CHCl3) as an eluent at 35 ◦C. Polystyrene standards
were used for the calibration. Thermogravimetic analyses (TGA)
were performed on a Shimadzu TGA-50 instrument. Differential
scanning calorimetric (DSC) measurements were carried out on a
Shimadzu DSC-60 instrument. TGA and DSC measurements were
performed under nitrogen at the scan rate of 10 ◦C/min. Ultravio-
let–visible (UV–vis) spectra and photoluminescence spectra were
measured in CHCl3 on a Shimadzu UV-3100PC spectrometer and
a Shimadzu RF-5300PC spectrometer, respectively.
Synthesis of 1,4-Diethynyl-2,5-dioctyloxybenzene (1)
To a 200 ml round bottom flask containing 1,4-dioctyloxybenzene
(5.0 g, 15 mmol), were added iodine (3.1 g, 24.3 mmol), periodic
acid monohydrate (1.4 g, 6.0 mmol), acetic acid (45 ml), water
(8 ml) and concentrated sulfuric acid (1.7 ml), and the mixture
was heated under gentle reflux overnight. After the addition of
aqueoussodiumthiosulfate, themixturewasextractedthreetimes
with hexane. The intermediate, 1,4-diiodo-2,5-dioctyloxybenzene,
was obtained in a 78% yield (7.19 g, 11.7 mmol) by recrystallization
from ethanol.
IR (KBr disk, cm−1) 3287, 2926, 2872, 2852, 1637, 1543, 1500,
1469, 1385, 1273, 1219, 1199, 1039, 999, 860, 761, 727, 671,
648, 526.
Likewise, 2-ethynylanisole was obtained by the reaction
of 2-iodoanisole with trimethylsilylacetylene followed by the
deprotection of the trimethylsilyl group.
1H-NMR (300 MHz, CDCl3, δ in ppm) 3.30 (s, 1H, -C CH), 3.86 (s,
3H, -OCH3), 6.84–6.91 (2H, aromatic), 7.29 (m, 1H, aromatic), 7.45
(d, J = 7.2 Hz, 1H, aromatic).
1H-NMR (300 MHz, CDCl3, δ in ppm) 0.88 (t, J = 6.8 Hz, 6H, -CH3),
1.29–1.50 [20H, -OCH2CH2(CH2)5-], 1.80 (m, 3H, -OCH2CH2-), 3.92
(t, J = 6.5 Hz, 4H, -OCH2CH2-), 7.17 (s, 2H, -C6H2-).
Introduction of two ethynyl groups were performed by the
Sonogashira coupling reaction.[8] To a 100 ml round bottom
flask containing copper(I) iodide (0.04 g, 0.05 mmol), palladium(II)
chloride(0.02 g, 0.1 mmol), triphenylphosphine(0.05 g, 0.1 mmol),
c
Appl. Organometal. Chem. 2010, 24, 558–562
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
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T. Kino, H. Nishiyama and I. Tomita
13C-NMR (75 MHz, CDCl3, δ in ppm) 55.8, 80.1, 81.1, 110.6, 111.1,
120.4, 130.3, 134.1, 160.6.
IR (KBr disk, cm−1) 3285, 3074, 3007, 2964, 2945, 2914, 2837,
2542, 2106, 2065, 1909, 1597, 1575, 1491, 1464, 1435, 1290, 1253,
1178, 1163, 1111, 1047, 1024, 937, 814, 754, 653, 614, 582, 569.
13C-NMR (75 MHz, CDCl3, δ in ppm) 20.0, 55.3, 55.4, 110.6, 111.1,
120.4, 120.7, 126.6, 128.3, 128.4, 129.6, 130.6, 130.7, 130.9, 131.1,
136.3, 137.2, 137.3, 156.5, 156.7.
IR (KBr disk, cm−1) 2961, 2928, 2833, 1595, 1579, 1483, 1460,
1431, 1392, 1292, 1234, 1174, 1159, 1118, 1049, 1022, 1005, 939,
889, 852, 829, 787, 754, 679, 619, 580.
Synthesis of Poly(p-phenylene) Derivative (5)
To a 50 ml flask containing 1 (0.167 g, 0.43 mmol) in diethyl ether
Results and Discussion
i
(20 ml), were added Ti(OPri)4 (0.178 g, 0.63 mmol) and PrMgCl
(1.0 M, 1.3 ml, 1.3 mmol) at −78 ◦C under argon. After stirring
for 30 min at that temperature and then at −50 ◦C for 12 h, a
diethyl ether (0.13 ml) solution of 3-bromo-1-propyne (0.060 g,
0.50 mmol) was added and the mixture was warmed slowly to
ambient temperature. After the addition of a methanol solution
of hydrochloric acid (1.0 M, 0.50 ml, 0.50 mmol), the mixture was
kept stirring for an additional 1 h. Then water (10 ml) was added
and the mixture was extracted with CHCl3. The organic layer was
collected and dried over magnesium sulfate. The polymer (5) was
obtained in a 78% yield (0.15 g) by precipitation into methanol.
1H-NMR(300 MHz,CDCl3,δ inppm)0.84(br,6H,-CH3),1.22–1.85
[br, 24H, -OCH2(CH2)6-], 2.23 (br, 3H, Ar-CH3), 3.96 (br, 4H, -OCH2-),
7.05–7.71 (5H, aromatic).
Sato et al. has described that the transformation of titanacy-
clopentadiene derivatives, obtained by the cyclization of 2 and
1,6-heptadiyne derivatives, with 3-bromo-1-propyne proceeds
smoothly to give benzene derivatives.[9] In order to make sure
the effective nature of the present process, a model experiment
was performed using a titanacycle derived from 2-ethynylanisole
(Scheme 3). That is, a 2,5-diaryltitanacyclopentadiene derivative
was prepared by the reaction of 2-ethynylanisole and the low-
valent titanium complex (2), generated from Ti(OPri)4 and iPrMgCl,
at −78 to −50 ◦C for 12 h[10] and the titanacycle was subjected to
the reaction with 3-bromo-1-propyne at −50 ◦C and the mixture
was warmed up gradually to ambient temperature. It was found
that the reaction took place nicely to give an objective p-terphenyl
derivative (6), 1,4-bis(2-methoxyphenyl)-2-methylbenzene, in a
high yield (88%) after isolation with column chromatography.
The high efficiency of the model reaction prompted us to
carry out the polymer reaction under the same conditions. As
a titanacyclopentadiene-containing polymer, we employed 3
which is obtainable from the diethynylbenzene derivative having
solubilizing soft alkoxy substituents (1) and 2 as we described
previously[6,11] and3wasreacteddirectlywith3-bromo-1-propyne
at −50 ◦C to ambient temperature. As a result, a polymer (5) was
isolated in a 78% yield by precipitation into methanol (Scheme 2).
The polymer (5) is soluble in organic solvents such as chloroform
anddichloromethane.Thenumber-averagemolecularweight(Mn)
and the molecular weight distribution (MW/Mn) of the polymer
were estimated as 4800 and 1.8, respectively (GPC, with respect to
polystyrene standards).
13C-NMR (75 MHz, CDCl3, δ in ppm) 14.1, 21.4, 22.6, 25.9, 26.2,
29.2, 29.3, 31.8, 68.1, 125.3, 128.2, 128.8, 137.8, 150.5.
IR (KBr disk, cm−1) 2926, 2854, 1685, 1608, 1560, 1467, 1377,
1261, 1205, 1028, 866, 802, 721, 669, 528.
Synthesis of 1,4-Bis(2-methoxyphenyl)-2-methylbenzene (6)
To a 50 ml flask containing 2-ethynylanisole (0.155 g, 1.20 mmol)
in diethyl ether, were added Ti(OPri)4 (0.235 g, 0.83 mmol) and
iPrMgCl (1.0 M, 1.6 mmol, 1.6 ml) at −78 ◦C under argon. After
stirring for 30 min at that temperature and then at −50 ◦C for 12 h,
a diethyl ether (0.13 ml) solution of 3-bromo-1-propyne (0.074 g,
0.625 mmol) was added and the mixture was warmed slowly to
ambient temperature. After the addition of a methanol solution
of hydrochloric acid (1.0 M, 0.63 ml, 0.63 mmol), the mixture was
kept stirring for an additional 1 h and was washed with brine. The
organic layer was collected and dried over magnesium sulfate. A
p-terphenyl derivative (6) was obtained as yellow oil in an 88%
yield (0.16 g, 0.53 mmol) by column chromatography on Al2O3
(eluent: benzene).
The structural elucidation of the polymer (5) was performed by
the 1H NMR and 13C NMR spectra in comparison with those of
1
the model compound (6). In the H NMR spectrum of 6, a peak
assignable to the methyl protons attached to the benzene ring
is observable at 2.18 ppm besides two peaks for the methoxy
protons at 3.77 ppm and 3.82 ppm (Fig. 1a). The integral ratio of
the peak of the methyl protons and those of the methoxy protons
1H-NMR (300 MHz, CDCl3, δ in ppm) 2.18 (s, 3H, Ar–CH3), 3.77 (s,
3H, -OCH3), 3.82 (s, 3H, -OCH3), 6.94–7.04 (4H, aromatic), 7.18–7.41
(7H, aromatic).
iPrO
OPri
Et2O
Ti
Ti(OPri)2
+
2
-78 °C ~ -50 °C
MeO
OMe
OMe
Ti(OPri)2Br
Me
H3O+
HC≡CCH2Br
-50 °C ~ r.t.
MeO
OMe
MeO
OMe
6
Scheme 3. Synthetic route for a terphenyl derivative (6) via a 2,5-diaryltitanacyclopentadiene derivative.
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 558–562

Synthesis of π-conjugated polymers
c
a
CH3
d
b
(a)
a
CH3
(b)
CH3 CH2 CH2
O
6
n
OCH3 CH O
OC8H17
c3
b
5
6
b, c
a
c
d
aromatic
b
aromatic
a
*
8
7
6
5
4
3
2
1
0
8
7
6
5
4
3
2
1
0
ppm
ppm
Figure 1. 1H NMR spectra of a terphenyl derivative (6) (a) and a poly(p-phenylene) derivative (5) (b).
in CHCl3 exhibited the absorption maximum (λmax) and its onset
(λonset) at 276 nm and 375 nm, respectively. In the case 5, the
absorption peak appeared at longer wavelength region where the
λmax andλonset areobservableat329and500 nm, respectively. The
clear bathochromic shift is also observable in the emission spectra.
In the photoluminescence spectrum of 5, the emission maximum
was found at 445 nm, while that of 6 appeared at 407 nm.
Conclusions
A poly(p-phenylene) derivative was successfully prepared by
means of the polymer reaction of a regioregular organometallic
polymer (3) containing titanacyclopentadiene units in the main
chain. The effective nature of the transformation process was
supported by the high efficiency of the model reaction and
by the spectroscopic analyses. The polymer exhibited the
π-conjugated character judging from the absorption and the
emission spectra. On the basis of the present polymer reaction
process, the diverse molecular design of the repeating structure of
the polymer was attained from simple monomer structures. Also,
the use of other electrophilic reagents for the polymer reactions
might give versatile main chain functionalized macromolecules.
Further synthetic studies utilizing the organotitanium polymers
are currently being investigated and the results will be published
in the forthcoming papers.
Figure 2. UV–visspectraof6(a) and5(b), andphotoluminescencespectra
of 6 (c) and 5 (d) (measured in CHCl3).
(3.0 : 6.0) is in good accordance with the proposed structure (3 : 6).
In the case of the polymer (5), the peaks for the methyl protons
and methylenes adjacent to the oxygen are observable at 2.23 and
at 3.96 ppm as broad signals (Fig. 1b). In the 13C NMR spectrum of
6, the methyl substituent attached to the benzene ring is observed
at 20.0 ppm and the peaks for two methoxy moieties appear at
55.3 and 55.4 ppm. In the case of 5, the corresponding peaks are
clearly observable at 21.4 and at 68.1 ppm, respectively.
The thermal stability of the polymer (5) was evaluated by
its TGA, where the temperature for 10% weight loss (Td10) was
observed at 305 ◦C, which was in good agreement with the
reported decomposition temperatures for the alkoxy-substituted
poly(p-phenylene)s.[12] TheDSCanalysisof5wasperformedbelow
its decomposition temperature, from which the glass transition
temperature (Tg) was observed at 58.4 ◦C.
Acknowledgments
This work was partly supported by a Grant-in-Aid for Science
Research in a Priority Area ‘Super-Hierarchical Structures’ from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan. The financial support of the New Energy and Industrial
Technology Development Organization (NEDO) of Japan is
gratefully acknowledged.
The polymer 5 was found to have the extended π-conjugated
system along the backbone as supported by its UV–vis spectrum
in comparison with that of the terphenyl derivative (6) as a model
compound (Fig. 2). That is, the absorption spectrum of 6 measured
c
Appl. Organometal. Chem. 2010, 24, 558–562
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/aoc

T. Kino, H. Nishiyama and I. Tomita
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 558–562