Investigation of catalyst-transfer condensation polymerization for synthesis of poly(p-phenylenevinylene)

Article abstract of DOI:10.1002/pola.27281

Kumada-Tamao coupling polymerization of 1,4-dialkoxy-2-bromo-5-(2- chloromagnesiovinyl)benzene (1) and 1,4-dialkoxy-2-(2-bromovinyl)-5- chloromagnesiobenzene (2) with a Ni catalyst and Suzuki-Miyaura coupling polymerization of 2-{2-[(2,5-dialkoxy-4-iodophenyl)]vinyl}-4,4,5,5-tetramethyl- 1,3,2-dioxaborolane (3), its bromo counterpart 4, and 2,5-dialkoxy-4-(2- bromovinyl)phenylboronic acid (5) with a Pd initiator were investigated under catalyst-transfer condensation polymerization conditions for the synthesis of well-defined poly(p-phenylenevinylene) (PPV). The Kumada-Tamao polymerization of vinyl Grignard-type monomer 1 with Ni(dppp)Cl₂ at room temperature did not proceed, whereas aryl Grignard-type monomer 2 afforded oligomers of low molecular weight. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra of the polymer obtained from 2 implied that the Grignard end group reacted with tetrahydrofuran to terminate polymerization. On the other hand, Suzuki-Miyaura polymerization of vinyl boronic acid ester type monomers 3 and 4 and phenylboronic acid type monomer 5 with a Pd initiator and aqueous KOH at -20 °C to room temperature yielded the corresponding PPV with high molecular weight within a few minutes. However, the molecular weight distribution was broad, and MALDI-TOF mass spectra showed the peaks of polymers bearing no initiator unit at the chain end, as well as those of polymers with the initiator unit. These results indicated that intermolecular chain transfer of the Pd catalyst occurred. Dehalogenation and disproportionation of the growing end also took place as side reactions. 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2643-2653 The feasibility of catalyst-transfer condensation polymerization of phenylenevinylene type monomers was investigated for the synthesis of well-defined poly(phenylenevinylene) (PPV). Kumada-Tamao coupling polymerization with a Ni catalyst afforded PPV with low molecular weight. On the other hand, Suzuki-Miyaura coupling polymerization with a Pd catalyst yielded PPV with high molecular weight. However, the molecular weight distribution was broad, and the MALDI-TOF mass spectra showed the peaks of polymers bearing no initiator unit at the chain end. Copyright

Full text of DOI:10.1002/pola.27281

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Investigation of Catalyst-Transfer Condensation Polymerization for
Synthesis of Poly(p-phenylenevinylene)
Masataka Nojima, Yoshihiro Ohta, Tsutomu Yokozawa
Department of Material and Life Chemistry, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-Ku, Yokohama 221-8686,
Japan
Correspondence to: T. Yokozawa (E-mail: yokozt01@kanagawa-u.ac.jp)
Received 31 December 2013; accepted 30 May 2014; published online 00 Month 2014
DOI: 10.1002/pola.27281
ABSTRACT: Kumada-Tamao coupling polymerization of 1,4-dia-
lkoxy-2-bromo-5-(2-chloromagnesiovinyl)benzene (1) and 1,4-
dialkoxy-2-(2-bromovinyl)-5-chloromagnesiobenzene (2) with a
Ni catalyst and Suzuki-Miyaura coupling polymerization of 2-{2-
[(2,5-dialkoxy-4-iodophenyl)]vinyl}-4,4,5,5-tetramethyl-1,3,2-diox-
aborolane (3), its bromo counterpart 4, and 2,5-dialkoxy-4-(2-
tion of vinyl boronic acid ester type monomers 3 and 4 and
phenylboronic acid type monomer 5 with a Pd initiator and
aqueous KOH at 220 ꢀC to room temperature yielded the corre-
sponding PPV with high molecular weight within
a few
minutes. However, the molecular weight distribution was
broad, and MALDI-TOF mass spectra showed the peaks of poly-
mers bearing no initiator unit at the chain end, as well as those
of polymers with the initiator unit. These results indicated that
intermolecular chain transfer of the Pd catalyst occurred. Deha-
bromovinyl)phenylboronic acid (5) with
a Pd initiator were
investigated under catalyst-transfer condensation polymeriza-
tion conditions for the synthesis of well-defined poly(p-phenyl-
enevinylene) (PPV). The Kumada-Tamao polymerization of vinyl
Grignard-type monomer 1 with Ni(dppp)Cl2 at room tempera-
ture did not proceed, whereas aryl Grignard-type monomer 2
afforded oligomers of low molecular weight. Matrix-assisted
laser desorption ionization time-of-flight (MALDI-TOF) mass
spectra of the polymer obtained from 2 implied that the Gri-
gnard end group reacted with tetrahydrofuran to terminate
polymerization. On the other hand, Suzuki-Miyaura polymeriza-
logenation and disproportionation of the growing end also took
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place as side reactions. 2014 Wiley Periodicals, Inc. J. Polym.
Sci., Part A: Polym. Chem. 2014, 00, 000–000
KEYWORDS: catalyst-transfer condensation polymerization; cata-
lysts; conjugated polymers; Kumada-Tamao coupling reaction;
MALDI; poly(phenylenevinylene); Suzuki-Miyaura coupling
reaction
thermore, Pd-catalyzed Suzuki-Miyaura CTCP (Pd-CTCP) also
affords well-defined PF,12 PPP,13 and poly(3-hexylthiophene)
(P3HT).14 Recently, well-defined p-conjugated alternating
copolymers15 and poly(p-phenylene ethynylene)16 have been
synthesized by means of CTCP of biaryl and teraryl mono-
mers and a phenylacetylene monomer, respectively.
INTRODUCTION p-Conjugated polymers have received much
attention because of their applications in electronic devices,
including thin film transistors,1 organic light-emitting diodes
(OLEDs),2 and photovoltaic cells.3 Many p-conjugated poly-
mers have been conventionally synthesized by step-growth
polymerization; however, it is difficult to control the molecu-
lar weight and to obtain polymers with low polydispersity
using this method.4 However, development of chain-growth
condensation polymerization with a transition metal catalyst
has made it possible to synthesize well-defined p-conjugated
polymers.5,6 We have proposed that this polymerization
involves intramolecular catalyst transfer on the polymer
backbone.6 Ni-catalyzed Kumada-Tamao catalyst-transfer con-
densation polymerization (Ni-CTCP) affords well-defined pol-
y(alkylthiophene)s,7 polyfluorenes (PFs),8 polyphenylenes
(PPPs),9 poly(N-alkylpyrrole)s,10 and poly(2-alkoxypyridine-
3,5-diyl),11 and block copolymers consisting of these
p-conjugated polymers can also be obtained in one pot. Fur-
Among p-conjugated polymers, poly(p-phenylenevinylene)
(PPV) has been intensively investigated, especially for appli-
cation to OLEDs.2 Yu and Turner first succeeded in con-
trolled synthesis of PPV by ring-opening metathesis
polymerization of cyclophane monomers.17 Junkers and
coworkers18 conducted controlled anionic and radical poly-
merization of quinodimethanes containing a sulfinyl group,
followed by thermal elimination to obtain well-defined PPV.
Furthermore, Galvin and coworkers19 obtained well-defined
oligomers by means of stepwise synthesis, and they found
that OLED devices made from PPV with narrow polydisper-
sity showed better external quantum efficiency when
Additional Supporting Information may be found in the online version of this article.
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2014 Wiley Periodicals, Inc.
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EXPERIMENTAL
General
1H and 13C NMR spectra were obtained on JEOL ECA-500
and ECA-600 spectrometers. The internal standard for 1H
NMR spectra in CDCl3 was tetramethylsilane (0.00 ppm),
and the internal standard for 13C NMR spectra in CDCl3
was the midpoint of CDCl3 (77.0 ppm). All melting points
were measured with a Yanagimoto hot-stage melting point
apparatus without correction. Column chromatography was
performed on silica gel (Kieselgel 60, 230–400 mesh;
Merck) with a specified solvent. Commercially available
dehydrated tetrahydrofuran (THF, stabilizer-free; Kanto),
dehydrated diethyl ether (Kanto), dehydrated dichlorome-
thane (Kanto), and dehydrated N,N-dimethylformamide
(DMF) (Wako) were used as dry solvents. Isopropylmagne-
sium chloride (iPrMgCl; 2.0 M solution in THF and 2.0 M
solution in diethyl ether; Aldrich) were used as received.
2,5-Bis((2-ethylhexyl)oxy)-4-bromobenzaldehyde (8),22 2,5-
bis((2-ethylhexyl)oxy)-4-iodobenzaldehyde (9),23 1,4-bis((2-
ethylhexyl)oxy)-2,5-diiodobenzene (11),24 1-bromo-2,5-
bis((2-ethylhexyl)oxy)-4-iodobenzene (12),24 tBu3PPd(Ph)Br
SCHEME 1 Monomer design of phenylenevinylene-type mono-
mers 1–5.
compared with PPV with broad polydispersity. However,
these polymerization methods are generally unsuitable for
synthesizing p-conjugated block copolymers containing PPV.
If PPV could be synthesized by means of CTCP, it would be
easy to obtain well-defined p-conjugated block copolymers
of PPV and other p-conjugated polymers such as P3HT, open-
ing an entry into a new class of p-conjugated materials.
t
(6),25 and Bu3PPd(o-tolyl)Br (7)26 were prepared accord-
ing to the cited literature. The Mn and Mw/Mn values of
polymers were measured on a Tosoh HLC-8020 gel permea-
tion chromatography unit (eluent, THF; calibration, polysty-
rene standards) with two TSK-gel columns (23 Multipore
Mastrorilli and coworkers20 conducted Suzuki/Heck copoly-
merization of dibromofluorene and potassium vinyl trifluoro-
borate for the synthesis of poly(fluorenylene vinylene), and
they observed that the polymerization proceeded in a chain-
growth polymerization manner until the middle stage,
whereas the formed oligomers were coupled in a step-
growth polymerization manner in the final stage. In the cur-
rent work, we studied whether CTCP could be applied for
the synthesis of well-defined PPV in a more straightforward
way: polymerization of phenylenevinylene monomers. Thus,
we examined Ni-catalyzed Kumada-Tamao coupling polymer-
ization of 1 and 2 and Pd-catalyzed Suzuki-Miyaura coupling
polymerization of 3–5 (Scheme 1).
H
XL-M). Matrix-assisted laser desorption ionization time-of-
flight (MALDI-TOF) mass spectra were recorded on
a
Shimadzu/Kratos AXIMA-CFR plus in the reflectron ion
mode by use of a laser (k 5 337 nm). Dithranol (1,8-
dihydroxy-9[10H]-anthracenone) was used as the matrix for
the MALDI-TOF mass measurements.
Synthesis of 1-Bromo-2,5-bis[(2-ethylhexyl)oxy]-4-(2-
iodovinyl)benzene (10)
A round-bottomed flask equipped with a three-way stopcock
was heated under reduced pressure and then cooled to
room temperature under an argon atmosphere. Chromium
dichloride (3.700 g, 30.11 mmol) was placed in the flask,
and the atmosphere in the flask was replaced with argon. A
solution of 8 (2.207 g, 5.00 mmol) and iodoform (3.938 g,
10.12 mmol) in THF (10.0 mL) was added at 0 ꢀC, and the
mixture was stirred at 0 ꢀC for 2 h. The reaction was
quenched with saturated aqueous NaHCO3, and the mixture
was then poured into 250 mL of ethyl acetate and filtered
through Celite. The filtrate was extracted with ethyl acetate,
and the combined organic layers were washed with aqueous
Na2S2O3 and brine and dried over MgSO4. The solvent was
removed under reduced pressure in a rotary evaporator, and
the residue was purified by means of column chromatogra-
phy (SiO2 and hexane) to afford a mixture of geometric iso-
mers (E/Z 5 56/44) of 10 as a slightly yellow oil (1.788 g,
75%).
Monomers 1, 3, and 4 have metallated vinyl and halopheny-
lene moieties, whereas monomers 2 and 5 have metallated
phenylene and halovinyl moieties. van der Boom and
coworkers demonstrated that the reaction of Ni(PEt3)4 with
a bromostilbene derivative resulted in selective g2-C@C coor-
dination, which was kinetically preferable at low tempera-
ture, followed by intramolecular “ring walking” of the metal
center and intramolecular aryl-bromide bond activation,
which was thermodynamically preferable when the tempera-
ture was raised. This result was also supported by density
functional theory calculations.21
Therefore, we expected that the CTCP of 1–5 would pro-
ceed via transfer of the catalyst on both benzene rings and
carbon–carbon double bonds. However, this would be chal-
lenging, because intramolecular transfer of the catalyst
would need to be carried out at the same temperature as
the polymerization, in contrast to the above two-step
reaction.
1H NMR (500 MHz, CDCl3): d 5 7.58 (d, J 5 14.9 Hz, 1 H),
7.49 (s, 1 H), 7.36 (d, J 5 8.6 Hz, 1 H), 7.06 (s, 1 H), 7.05 (s,
1 H), 6.94 (d, J 5 14.9 Hz, 1 H), 6.79 (s, 1 H), 6.56 (d, J 5 8.6
Hz, 1 H), 3.93–3.78 (m, 4 H), 1.72–1.67 (m, 2 H), 1.60–1.20
2
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(m, 16 H), 0.98–0.82 (m, 12 H); 13C NMR (126 MHz, CDCl3):
d 5 188.9, 155.9, 150.0, 124.2, 121.1, 118.3, 110.3, 72.1,
72.7, 39.4, 39.3, 30.5, 30.4, 29.03, 28.99, 23.93, 23.87, 22.99,
22.96, 14.05, 14.03, 11.1.
room temperature under an argon atmosphere. Diiodoben-
zene 11 (46.14 g, 78.73 mmol), dichlorobis(triphenylphos-
phine)palladium (2.79 g, 3.97 mmol), and copper(I) iodide
were placed in the flask, and the atmosphere in the flask
was replaced with argon. Dry DMF (220 mL), distilled trie-
thylamine (19 mL), and trimethylsilylacetylene (13.5 mL,
93.50 mmol) were added into the flask via a syringe, and
the mixture was stirred at room temperature for 24 h. The
reaction was quenched with saturated aqueous NH4Cl, and
the aqueous layer was extracted with ethyl acetate. The com-
bined organic layers were washed with water, dried over
anhydrous MgSO4, and concentrated in vacuo. The residue
was purified by means of column chromatography (SiO2 and
hexane) to afford 13 as a yellow oil (14.19 g, 32%).
Synthesis of 1-(2,2-Dibromovinyl)-2,5-bis[(2-
ethylhexyl)oxy]-4-iodobenzene (10)
A round-bottomed flask equipped with a three-way stopcock
was heated under reduced pressure and then cooled to room
temperature under an argon atmosphere. Iodobenzaldehyde 9
(0.243 g, 0.50 mmol) and triphenylphosphine (0.276 g, 1.05
mmol) were placed in the flask, and the atmosphere in the
flask was replaced with argon. Dry dichloromethane (1.1 mL)
was added into the flask via a syringe, and the mixture was
ꢀ
stirred at 210 C. A solution of carbon tetrabromide (0.187 g,
1H NMR (600 MHz, CDCl3): d 5 7.24 (s, 1 H), 6.82 (s, 1 H),
3.86–3.78 (m, 4 H), 1.75–1.70 (m, 2 H), 1.60–1.26 (m, 17 H),
0.97–0.87 (m, 13 H), 0.24 (s, 9 H); 13C NMR (150 MHz,
CDCl3): d 5 155.0, 151.7, 123.3, 115.8, 113.2, 100.8, 99.2,
87.6, 72.1, 71.9, 39.6, 39.4, 30.51, 30.46, 29.1, 29.0, 23.95,
23.86, 23.1, 23.0, 14.1, 11.3, 11.2, 0.08.
0.57 mmol) in dry dichloromethane (1.1 mL) was added drop-
wise at 210 ꢀC over about 90 min with stirring under dry
ꢀ
nitrogen. Stirring was continued at 210 C for 6 h, and then
the reaction was quenched with saturated aqueous NaHCO3.
The aqueous layer was extracted with dichloromethane. The
combined organic layers were washed with brine, dried over
anhydrous MgSO4, and concentrated in vacuo. The residue
was purified by means of column chromatography (SiO2, hex-
ane) to afford 10 as a slightly yellow oil (0.216 g, 67%).
Synthesis of 4-Bromo-2,5-bis[(2-ethylhexyl)oxy]-1-(2-
trimethylsilylethynyl)benzene (14)
The desired 14 (0.153 g, 0.45 mmol) was obtained in 90%
yield from 12 (0.270 g, 0.50 mmol) in a similar manner to
that described for the synthesis of 13 from 11.
1H NMR (500 MHz, CDCl3): d 5 10.42 (s, 1 H), 7.31 (s, 1 H),
7.24 (s, 1 H), 3.93–3.89 (m, 4 H), 1.79–1.74 (m, 2 H), 1.58–
1.24 (m, 16 H), 0.96–0.87 (m, 12 H); 13C NMR (126 MHz,
CDCl3): d 5 188.9, 155.9, 150.0, 124.2, 121.1, 118.3, 110.3,
72.1, 72.7, 39.4, 39.3, 30.5, 30.4, 29.03, 28.99, 23.93, 23.87,
22.99, 22.96, 14.05, 14.03, 11.1.
1H NMR (500 MHz, CDCl3): d 5 7.03 (s, 1 H), 6.93 (s, 1 H),
3.87–3.79 (m, 4 H), 1.76–1.71 (m, 2 H), 1.62–1.23 (m, 21 H),
0.99–0.83 (m, 13 H), 0.24 (s, 9 H); 13C NMR (126 MHz,
CDCl3): d 5 154.9, 149.3, 117.54, 117.47, 113.5, 112.2, 100.6,
99.0, 72.3, 71.9, 39.6, 39.4, 30.5, 29.1, 29.0, 23.87, 23.86,
23.1, 23.0, 14.10, 14.08, 11.3, 11.1.
Synthesis of (E)-1-(2-Bromovinyl)-2,5-bis[(2-
ethylhexyl)oxy]-4-iodobenzene (20)
A Schlenk flask was heated under reduced pressure and then
cooled to room temperature under an argon atmosphere. The
obtained 10 (0.139 g, 0.22 mmol) and diethyl phosphite
(0.102 g, 7.40 mmol) were placed in the flask, and the atmos-
phere in the flask was replaced with argon. Distilled triethyl-
amine (0.4 mL) was added via a syringe, and the mixture was
Synthesis of 1,4-Bis[(2-ethylhexyl)oxy]-2-ethynyl-5-
iodobenzene (15)
Tetrabutylammonium fluoride (1.0
M solution in THF,
51.5 mL, 51.5 mmol) was added to a solution of 13 (26.03 g,
46.77 mmol) in THF (400 mL) at room temperature, and the
whole mixture was stirred at room temperature for 14 h.
Then, ethyl acetate was added, and the mixture was washed
with water and saturated aqueous NH4Cl, dried over anhy-
drous MgSO4, and concentrated in vacuo. The residue was
purified by means of column chromatography (SiO2, hexane)
to afford 15 as a reddish brown oil (20.64 g, 94%).
ꢀ
stirred at 80 C for 8 h. The reaction was quenched with 1 M
HCl, and the aqueous layer was extracted with dichlorome-
thane. The combined organic layers were washed with brine,
dried over anhydrous MgSO4, and concentrated in vacuo. The
residue was purified by means of column chromatography
(SiO2 and hexane) to afford 20, including a trace of geometric
isomer as a slightly yellow oil (0.110 g, 90%).
1H NMR (600 MHz, CDCl3): d 5 7.28 (s, 1 H), 6.85 (s, 1 H), 3.84
(d, J 5 6.2 Hz, 2 H), 3.82 (d, J5 6.2 Hz, 2 H), 3.27 (s, 1 H), 1.74 (m,
J 5 6.2 Hz, 2 H), 1.59–1.27 (m, 16 H), 0.95–0.87 (m, 12 H); 13C
NMR (150 MHz, CDCl3): d 5 155.1, 151.7, 123.6, 116.2, 112.2,
88.0, 81.7, 79.7, 72.3, 72.1, 39.40, 39.35, 30.5, 30.4, 29.03, 29.01,
23.9, 23.8, 23.01, 23.00, 14.08, 14.05, 11.2, 11.1.
1H NMR (500 MHz, CDCl3): d 5 10.42 (s, 1 H), 7.31 (s, 1 H),
7.24 (s, 1 H), 3.93–3.89 (m, 4 H), 1.79–1.74 (m, 2 H), 1.58–
1.24 (m, 16 H), 0.96–0.87 (m, 12 H); 13C NMR (126 MHz,
CDCl3): d 5 188.9, 155.9, 150.0, 124.2, 121.1, 118.3, 110.3,
72.1, 72.7, 39.4, 39.3, 30.5, 30.4, 29.03, 28.99, 23.93, 23.87,
22.99, 22.96, 14.05, 14.03, 11.1.
Synthesis of 1,4-Bis[(2-ethylhexyl)oxy]-2-ethynyl-5-
bromobenzene (16)
The desired 16 (0.124 g, 0.28 mmol) was obtained in 95%
yield from 14 (0.270 g, 0.50 mmol) in a similar manner to
that described for the synthesis of 15 from 13.
Synthesis of 2,5-Bis[(2-ethylhexyl)oxy]-4-iodo-1-(2-
trimethylsilylethynyl)benzene (13)
A round-bottomed flask equipped with a three-way stopcock
was heated under reduced pressure and then cooled to
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1H NMR (500 MHz, CDCl3): d 5 7.07 (s, 1 H), 6.96 (s, 1 H),
3.85–3.80 (m, 4 H), 3.83 (s, 1 H), 1.78–1.72 (m, 2 H), 1.58–
1.25 (m, 17 H), 0.97–0.85 (m, 12 H); 13C NMR (126 MHz,
CDCl3): d 5 154.9, 149.4, 118.0, 117.8, 113.9, 111.2, 81.5,
79.5, 72.32, 72.26, 39.4, 39.3, 30.4, 29.0, 23.86, 23.84, 23.0,
14.0, 11.1.
solution in THF, 2.4 mL, 4.8 mmꢀol) was added via a syringe,
and stirring was continued at 0 C for 2 h. A solution of trii-
sopropyl borate (1.825 g, 9.70 mmol) in dry THF (12 mL)
was added via a syringe at 278 ꢀC. After 2 h, the reaction
mixture was warmed to room temperature and stirred for
an additional 1.5 h. Then, the reaction was quenched with
1 M HCl, and the aqueous layer was extracted with diethyl
ether. The combined organic layers were washed with satu-
rated aqueous NaHCO3 and brine, dried over anhydrous
Na2SO4, and concentrated in vacuo. The residue was recrys-
tallized from hexane ꢀto give (E)-5 as a white solid (1.413 g,
61%): mp 80.5–83.0 C.
Synthesis of (E)-2-{2-[(2,5-Bis((2-ethylhexyl)oxy)-4-
iodophenyl)]vinyl}-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (3)
A Schlenk flask was heated under reduced pressure and
then cooled to room temperature under an argon atmos-
phere. To
a solution of diisopinocampheylborane (4.95
1H NMR (600 MHz, CDCl3): d 5 7.33 (s, 1 H), 7.31 (d,
J 5 14.0 Hz, 1H), 7.02 (d, J 5 14.0 Hz, 1H), 6.79 (s, 1 H), 5.80
(s, 2H), 3.94–3.90 (m, 4 H), 1.78–1.72 (m, 2 H), 1.56–1.27
(m, 16 H), 0.97–0.88 (m, 12 H); 13C NMR (150 MHz, CDCl3):
d 5 158.1, 150.5, 133.1, 128.3, 119.7, 110.0, 109.4, 71.4,
71.2, 39.54, 39.50, 30.73, 30.66, 29.08, 29.02, 24.10, 24.07,
23.01, 22.94, 14.05, 14.01, 11.16, 11.09.
mmol), prepared from BH3-SMe2 (0.47 mL, 4.95 mmol) and
a-pinene (1.387 g, 10.18 mmol) in THF (2.5 mL), a solution
of 15 (3.637 g, 7.51 mmol) in THF (3.7 mL) was added at
235 ꢀC. The mixture was stirred for 6.5 h at 0 ꢀC, and a
solution of acetaldehyde (3.0 mL, 53.12 mmol) in THF
(2.5 mL) was added. This mixture was refluxed for 12 h,
cooled to room temperature, and concentrated in vacuo.
After the addition of a solution of pinacol (0.779 g, 6.59
mmol) in THF (2.0 mL), the reaction mixture was stirred for
13 h at room temperature and concentrated in vacuo. The
resulting residue was purified by means of column chroma-
tography (SiO2, hexane/triethylamine/ethyl acetate 5 50/1/
1) to afford (E)-3 as a brownish-red oil (0.253 g, 55%).
General Procedure for Kumada-Tamao Coupling
Polymerization
All glass apparatus were dried prior to use. Addition of
reagents to a reaction flask and withdrawal of a small ali-
quot of the reaction mixture for analysis were carried out
via a syringe from a three-way stopcock under a stream of
nitrogen. A round-bottomed flask equipped with a three-way
stopcock containing lithium chloride (0.2 mmol) was heated
under reduced pressure and then cooled to room tempera-
ture under an argon atmosphere. Monomer precursor 10 or
20 (0.2 mmol) was placed in the flask, and the atmosphere in
the flask was replaced with argon. Dry THF (1.0 mL) was
added to the flask via a syringe, and the mixture was stirred
1H NMR (600 MHz, CDCl3): d 5 7.69 (d, J 5 18.5 Hz, 1 H),
7.24 (s, 1 H), 6.98 (s, 1 H), 6.14 (d, J 5 18.5 Hz, 1 H), 3.84–
3.60 (m, 4 H), 1.79–1.71 (m, 2 H), 1.62–1.18 (m, 37 H),
0.99–0.84 (m, 16 H); 13C NMR (150 MHz, CDCl3): d 5 152.2,
151.6, 143.6, 127.8, 123.9, 109.6, 87.4, 83.2, 72.3, 72.1,
39.43, 39.41, 30.6, 30.5, 29.04, 29.03, 27.8, 23.99, 23.94,
23.06, 22.98, 14.09, 14.08, 11.2.
i
at 0 ꢀC. PrMgCl (2.0 M solution in THF, 0.1 mL, 0.2 mmol)
Synthesis of (E)-2-{2-[4-Bromo-(2,5-bis((2-
ethylhexyl)oxy)phenyl)]vinyl}-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (4)
The desired 4 (1.462 g, 2.63 mmol) was obtained in 35%
yield from 16 (3.274 g, 7.50 mmol) in a similar manner to
that described for the synthesis of 3 from 15.
was added via a syringe, and stirring was continued. A sus-
pension of Ni catalyst (0.010 mmol, 5.0 mol %) in dry THF
(1.0 mL) was added via a syringe, and stirring was contin-
ued at room temperature. After 24–60 h, 5 M hydrochloric
acid was added. The mixture was extracted with chloroform,
and the organic layer was washed with water, dried over
anhydrous MgSO4, and concentrated under reduced pressure
to give PPV.
1H NMR (500 MHz, CDCl3): d 5 7.69 (d, J 5 18.6 Hz, 1 H),
7.09 (s, 1 H), 7.06 (s, 1 H), 6.13 (d, J 5 18.6 Hz, 1 H), 3.86–
3.60 (m, 4 H), 1.81–1.72 (m, 2 H), 1.59–1.19 (m, 28 H),
0.99–0.84 (m, 12 H); 13C NMR (126 MHz, CDCl3): d 5 151.3,
149.8, 143.4, 126.8, 117.9, 113.2, 111.2, 83.2, 77.2, 773,
77.2, 39.40, 39.35, 30.6, 30.5, 29.6, 29.0, 24.83, 24.79, 24.0,
23.9, 23.03, 22.98, 14.08, 11.16, 11.12.
General Procedure for Suzuki-Miyaura Coupling
Polymerization
All glass apparatus were dried prior to use. Addition of
reagents into a reaction flask and withdrawal of a small ali-
quot of the reaction mixture for analysis were carried out
via a syringe from a three-way stopcock under a stream of
nitrogen. A round-bottomed flask equipped with a three-way
stopcock was heated under reduced pressure and then
cooled to room temperature under an argon atmosphere.
Monomer 3, 4, or 5 (0.1 mmol), base (0.45 mmol), and dried
18-crown-6 (0.8 mmol) were placed in the flask, and the
atmosphere in the flask was replaced with argon. Dry THF
(7.5 mL) and distilled water (0.5 mL) were added to the
flask via a syringe, and the mixture was degassed with
Synthesis of (E)-4-(2-Bromovinyl)-2,5-bis[(2-
ethylhexyl)oxy]phenylboronic Acid (5)
A round-bottomed flask equipped with a three-way stopcock
was heated under reduced pressure and then cooled to
room temperature under an argon atmosphere. Bromoviny-
liodobenzene 20 (2.716 g, 4.80 mmol) was placed in the
flask, and the atmosphere in the flask was replaced with
argon. Dry THF (24 mL) was added to the flask via a
i
ꢀ
syringe, and the mixture was stirred at 0 C. PrMgCl (2.0 M
4
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SCHEME 2 Synthesis of monomer precursors 10–20 and monomers 3–5.
argon. This mixture was added to a solution of 6 or 7 (0.005
mmol, 5.0 mol %) in dry THF (5.0 mL, degassed with argon),
via a cannula, and the reaction mixture was stirred at room
temperature. After 24–170 h, 1 M hydrochloric acid was
added. The mixture was extracted with chloroform, and the
organic layer was washed with water, dried over anhydrous
MgSO4, and concentrated under reduced pressure to give
PPV.
introduced into all the monomers. Iodovinyl bromobenzene
10 was synthesized by the reaction of 8, which was obtained
according to the reported method,22 with CrCl2 and iodo-
form.27 The obtained 10 is a mixture of trans and cis forms,
which could not be separated, and thus, this mixture was
used for polymerization. Bromovinyl iodobenzene 20 was
prepared from 4-iodobenzaldehyde 9.23 Wittig-type reaction
of 9 with CBr4 afforded dibromovinyl compound 10, which
was then subjected to reaction with diethyl phosphite in trie-
thylamine, affording 20 with high (E) selectivity.28
RESULTS AND DISCUSSION
In contrast to Grignard-type monomers, boronic acid or bor-
onic acid ester monomers are generally stable in air and can
be isolated. Vinyl boronic acid ester monomers 3 and 4 were
prepared by introduction of an ethynyl group into 11 and
12,24 followed by hydroboration of the ethynyl group.29 Phe-
nylboronic acid monomer 5 was obtained by selective bora-
tion of iodine of 20 via iodo-Grignard exchange reaction.
Synthesis of Monomer Precursors and Monomers
For a comprehensive study of CTCP leading to PPV, we pre-
pared monomer precursors 10 and 20 for Ni-CTCP and mono-
mers 3–5 for Pd-CTCP according to Scheme 2.
The iodine atom in 10 and 20 was expected to undergo selec-
tive Grignard-halogen exchange reaction to generate Grignard
monomers containing bromine atom in a similar manner to
that in which bromothiophene Grignard monomers were
generated from bromoiodothiophenes in Ni-CTCP.7(a–d) To
increase the solubility of PPV, 2-ethylhexyloxy groups were
Kumada-Tamao Coupling Polymerization of 1 and 2
When the same p-conjugated polymers are synthesized via
Ni-CTCP and via Pd-CTCP, Ni-CTCP generally affords
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reductive elimination occurs with concomitant generation of
a Ni(0) complex, which is inserted into the intramolecular
CABr bond. In the case of 1, however, diene was formed by
initiation. This would strongly coordinate to the Ni catalyst,
which might be responsible for inhibiting polymerization
(Scheme 4).
To support this speculation, model reaction of phenylmagne-
sium bromide and 4-bromotoluene was carried out in the
presence of 5 mol % of Ni(dppp)Cl2 and (1E,3E)-1,4-diphe-
nylbuta-1,3-diene as a diene, resulting in no progress of the
reaction (Supporting Information Fig. S1). In addition, it has
been reported that Kumada-Tamao coupling reaction of vinyl
Grignard reagents exhibits relatively low reactivity.31
SCHEME 3 Polymerization of 1 and 2 for the synthesis of PPV.
polymers with lower polydispersity and higher molecular
weight. For example, P3HT obtained with Ni-CTCP and with
Pd-CTCP
showed
Mn 5 17,200,
Mw/Mn 5 1.26
and
We next examined polymerization of aryl Grignard monomer 2.
Precursor 20 was converted to 2 by treatment with 1 equiv of
Mn 5 10,900, Mw/Mn 5 1.56, respectively.7(c),14 To understand
the reason for these results, Nakamura and coworkers30
investigated kinetic isotope effects in oxidative addition of
haloarenes to Ni and Pd(0) catalyst and carried out theoreti-
cal calculations, and they concluded that the key irreversible
processes are p-complexation with the Ni catalyst and oxida-
tive addition to the Pd catalyst following p-complexation,
respectively. In other words, once a Ni/haloarene p-complex
forms, it does not dissociate and proceeds quickly to the oxi-
dative addition step in an intramolecular manner. On the
other hand, the Pd catalyst can dissociate from the Pd/hal-
oarene p-complex. These results account for the better
control in Ni-CTCP. Accordingly, Grignard-type phenylenevi-
nylene monomers 1 and 2 were first polymerized under
Ni-CTCP conditions (Scheme 3). To our knowledge, there
is no previous report of PPV synthesis even by means of
i
PrMgCl in THF at 0 C (conversion of 20 5 100%). Polymeriza-
tion of 2 was then carried out by the addition of Ni(dppp)Cl2
to the reaction mixture at room temperature to afford an
oligomer (Mn 51990, Mw/Mn 5 1.37; Table 1, Entry 1). In an
attempt to obtain high-molecular-weight PPV, the polymeriza-
tion was conducted with several Ni catalysts having different
ligands; however, oligomers of similar molecular weight were
obtained (Table 1, Entries 2–5).
ꢀ
These results implied that termination reactions occur in
this polymerization. Accordingly, the polymer end groups
were analyzed by means of MALDI-TOF mass spectrometry
using dithranol (1,8-dihydroxy-9[10H]-anthracenone) as a
matrix. The spectrum of polymer obtained with Ni(dppp)Cl2
showed several series of peaks (Fig. 1). The major peaks
can be assigned to polymer in which one end group is THF
and the other is a bromine atom (designated as THF/Br). It
has already been reported that electron-rich aryl Grignard
reagents react with THF through a radical pathway.32 Peaks
due to THF/H-ended polymers were also observed. There
were also two other series of minor peaks assignable to
Br/Br- and Br/H-ended polymers, as well as a number of
peaks that could not be assigned. If Ni-CTCP proceeds, the
propagating end group should be PPV-Ni-Br, which cannot
react with THF. Therefore, the THF-ended polymer was pre-
sumably generated by reaction of THF with Grignard-ended
polymer formed through a conventional step-growth poly-
merization mechanism.
conventional
polycondensation.
Ni-catalyzed
Kumada-Tamao
coupling
Monomer precursor 10 was converted to Grignard monomer
1 by treatment with 1 equiv of PrMgCl in THF at room tem-
i
perature for 3 h (conversion of 10 5 90%). It was confirmed
by means of 1H NMR and GC analysis that the iodine at the
C@C of 10 was exclusively converted to a chloromagnesio
group. Polymerization of 1 was then carried out by the addi-
tion of Ni(dppp)Cl2, which is suitable for the synthesis of
well-defined P3HT, to the reaction mixture; however, poly-
merization of 1 did not proceed. In the initiation step of Ni-
CTCP, Ni(dppp)Cl2 reacts with 2 equiv of monomers, and
SCHEME 4 Proposed initiation reaction mechanism of 1 with Ni catalyst.
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TABLE 1 Polymerization of 2 with various catalystsa
Entry
Solvent
Catalyst
Time (h)
Temperature (ꢀC)
Mn (Mw/Mn)b
1
2
3
4
5
6
THF
THF
THF
THF
THF
Et2O
Ni(dppp)Cl2
Ni(dppf)Cl2
Ni(dppe)Cl2
Ni(PPh3)Cl2
Ni(dppp)Cl2
Ni(dppp)Cl2
60
24
24
24
24
24
Room temperature
Room temperature
Room temperature
Room temperature
70
1,990 (1.37)
1,850 (1.35)
2,140 (1.34)
2,050 (1.40)
1,670 (1.25)
1,860 (1.56)
Room temperature
a
b
Polymerization of 2 ([2]0 5 0.1 M) was carried out by the treatment of
20 with 1.0 equiv of iPrMgCl in the presence of LiCl, followed by the
addition of 5.0 mol % of catalyst.
Estimated by gel permeation chromatography based on polystyrene
standards (eluent: THF).
The polymerization was also carried out in diethyl ether
instead of THF; however, similar oligomers were obtained
(Entry 6). The MALDI-TOF mass spectrum did not show
peaks of polymer ends reacted with diethyl ether (see Sup-
porting Information Fig. S2); however, multiple unknown
series of peaks were observed. Consequently, we concluded
that elementary Kumada-Tamao coupling reaction using Ni-
CTCP was not suitable for the synthesis of PPV.
Polymerization of 3 with a Pd initiator 6 ([3]0/[6]0 5 20)
was first carried out in the presence of CsF/18-crown-6 in
THF containing a small amount of water at room tempera-
ture, in a similar manner to the case of Pd-CTCP for the syn-
thesis of well-defined PPP13 and P3HT.14 However, the
polymerization was considerably slower than Pd-CTCP lead-
ing to PPP and P3HT, and 3 remained even after 6 days,
resulting in the formation of oligomer (Table 2, Entry 1). The
polymerization of 3 was then carried out at 60 ꢀC or with
higher monomer concentration (from 8.33 3 1023 M to 2.50
3 1022 M); however, high-molecular-weight polymer was
not obtained (Table 2, Entries 2 and 3). The MALDI-TOF
mass spectra of the obtained oligomer (Table 2, Entry 2)
showed two series of peaks: one is oligomer with a phenyl
group from the Pd initiator 6 at one end, and the other is
oligomer with boronic acid pinacol ester or boronic acid
group, formed by hydrolysis of the ester, at one end (Sup-
porting Information Fig. S3). This result indicated that Pd-
CTCP proceeded concomitantly with intermolecular transfer
of the catalyst (chain transfer).
Suzuki-Miyaura Coupling Polymerization of 3 and 4
Pd-CTCP proceeds under less basic conditions when com-
pared with Ni-CTCP, and stable arylpalladium(II) halide com-
plex can be used as an externally added initiator.12 Moreover,
Pd-catalyzed cross-coupling polymerization is more common
for the synthesis of PPV than Ni-catalyzed polymerization,33
and Suzuki-Miyaura coupling polymerization with a conven-
tional Pd catalyst is often used.34 Accordingly, we next exam-
ined Pd-CTCP for the synthesis of well-defined PPV. The
polymerization of vinylboronic acid ester monomers 3 and 4
is described in this section, and the polymerization of phe-
nyleneboronic acid monomer 5 in the following section
(Scheme 5).
We next examined various bases. Common bases for Suzuki-
Miyaura coupling reaction, such as K2CO3, K3PO4, and KOH,
FIGURE 1 MALDI-TOF mass spectra of products obtained by
the polymerization of 2 with 5.0 mol % of Ni(dppp)Cl2 in THF
([2]0 5 0.1 M) at room temperature for 60 h (Mn 5 1990, Mw/
Mn 5 1.37). [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
SCHEME 5 Polymerization of 3–5 for the synthesis of PPV.
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TABLE 2 Polymerization of 3 or 4 with 5.0 mol % of 6 and various bases
Entry
Monomer
Base
Temperature (ꢀC)
Time
Mn (Mw/Mn)
1a
2a
3
3
3
3
3
3
3
3
3
4
4
CsF/18-crown-6
CsF/18-crown-6
CsF/18-crown-6
K2CO3
Room temperature
60
144 h
144 h
24 h
2,630 (2.91)c
2,630 (4.53)c
3,410 (2.61)c
1,120 (1.06)c
1,160 (1.08)c
2,400 (1.73)c
5,940 (2.00)
6,320 (2.06)
9,580 (2.26)
6,410 (2.68)
9,450 (2.59)
3b
4b
5b
6b
7b
8b
9b
10b
11b
Room temperature
Room temperature
Room temperature
Room temperature
Room temperature
0
128 h
126 h
79 h
K3PO4
KOH
KOH/18-crown-6
KOH/18-crown-6
KOH/18-crown-6
KOH/18-crown-6
KOH/18-crown-6
5 min
5 min
30 min
5 min
30 min
220
Room temperature
220
a
c
[3]0 5 8.33 3 1023 M.
[3 or 4]0 5 2.50 3 1022 M.
Monomer remained.
b
did not work well, and monomer remained (Table 2, Entries
4–6). However, when KOH was used in combination with 18-
crown-6, the polymerization became dramatically fast, and
monomer 3 was consumed within 5 min. The molecular
weight was increased, but the molecular weight distribution
was broad (Table 2, Entry 7). Anticipating that polymeriza-
tion would be better controlled at low temperature, we con-
ducted polymerization at 0 and 220 ꢀC. The polymerization
In the spectrum of PPV obtained at 5 min, two major series
of peaks corresponding to polymer with a phenyl group at
one end and an iodine atom at the other (Ph/I) and to Ph/
H-ended polymer were observed. Several other minor series
of peaks were assigned to polymers ended with (boronic
acid ester)/H or I, B(OH)2/H or I, and H/H, which would not
have been initiated by the Pd complex 6. In the polymeriza-
tion for 30 min, the polymer ends surprisingly became
almost uniform as Ph/H. These results implied that the poly-
merization of 3 was initiated by the Pd catalyst 6 and pro-
ceeded with intermolecular transfer of the Pd catalyst to
afford boron-ended polymer. In the final stage, the boron-
ended polymer reacted with Ph/I-ended polymer, followed
by deiodination of the polymer end group to yield PPV with
Ph/H. Deiodination in Pd-catalyzed Suzuki-Miyaura coupling
polymerization has been reported by Janssen and
coworkers.35
ꢀ
at 0 C was still fast, being completed within 5 min, but the
polydispersity was broad (Table 2, Entry 8). The polymeriza-
tion proceeded even at 220 ꢀC, and the Mn reached about
9600. Unfortunately, however, the polydispersity was more
than 2.0 (Table 2, Entry 9).
To see how the polymerizꢀation proceeded, the end groups of
the PPV obtained at 220 C for 5 min and 30 min were ana-
lyzed by MALDI-TOF mass spectrometry (Fig. 2).
FIGURE 2 MALDI-TOF mass spectra of products obtained by the polymerization of 3 in the presence of KOH/18-crown-6 and
5.0 mol % of 6 in THF ([3]0 5 2.50 3 1022 M) and water at 220 ꢀC for (a) 5 min (Mn 5 4360, Mw/Mn 5 2.03) and (b) 30 min
(Mn 5 9580, Mw/Mn 5 2.26).
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Moreover, the polymerization of 3 was carried out with
bis[tris(tert-butyl)phosphine]palladium(0) instead of
vinylborane, analogously with the low reactivity of vinyl Gri-
gnard reagent in Kumada-Tamao coupling reaction.31 On the
other hand, monomer 5 bearing the boronic acid group on
the benzene ring is expected to undergo polymerization
with CsF, because the monomer leading to well-defined
PPP with CsF has the same phenylboronic acid moiety.13
In the polymerization of 5, tBu3PPd(o-tolyl)Br (7) was
used as an initiator instead of 6, as the phenyl group,
which is introduced at the polymer end group from 6, and
bromine is sometimes difficult to distinguish in MALDI-
TOF mass spectra due to the similar molecular weights of
the phenyl group and bromine atom. Thus, polymerization
of 5 was carried out with the Pd initiator 7 in the pres-
ence of CsF/18-crown-6 at room temperature in a similar
manner to the case of polymerization of 3 and 4. Contrary
to our expectation, however, the polymerization was slow,
and 5 remained even after a week. When KOH/18-crown-6
was used, the polymerization was completed within 2.5
min to yield high-molecular-weight PPV with a broad
molecular weight distribution (Table 3). The different reac-
tivity of 5 from the PPP monomer can presumably be
accounted for by the different electron density of the ben-
zene ring conjugated with a carbon–carbon double bond at
the para position.
6
under similar conditions. This Pd catalyst would not intro-
duce a terminal group, such as the phenyl group in the
case of 6, but would afford polymer with boron/I ends
during polymerization, which should result in higher
molecular weight polymer via coupling reaction between
these polymers. However, the molecular weight and
molecular weight distribution were similar to those in the
case of the polymerization with 6 (Fig. 3). Furthermore,
not iodine but hydrogen atom was present at one end
of the obtained polymer. These results suggested that
the molecular weight and molecular weight distribution
in the polymerization of 3 with 6 were governed by
deiodination.
Expecting that dehalogenation of bromine would be sup-
pressed, when compared with iodine, we next attempted
the polymerization of bromo monomer 4 instead of iodo
monomer 3. The polymerization of 4 was still fast: 4 was
consumed within 5 min at room temperature and within
30 min at 220 ꢀC (Table 2, Entries 10 and 11). The
obtained polymers showed similar molecular weight and
polydispersity. The MALDI-TOF mass spectra showed major
Ph/Br peaks and minor Ph/H, Bpin (boronic acid ester)/
Br, and B(OH)2/Br peaks in the middle stage and uniform
Ph/H peaks in the final stage (Supporting Information Fig.
S4). Consequently, it turned out that dehalogenation was
not suppressed under this condition even when the halo-
gen atom in the monomer was changed from iodine to
bromine.
The MALDI-TOF mass spectra of PPV obtained by the use of
CsF/18-crown-6 as a base showed tolyl/tolyl, tolyl/Br, tolyl/
H, H/Br, and H/H peaks (Fig. 4). As described above, poly-
mers with tolyl/Br and tolyl/H ends would be obtained by
initiation with the Pd initiator 7, and polymers with H/Br
and H/H ends would be formed by intermolecular transfer
of the Pd catalyst to monomer. The tolyl/tolyl-ended poly-
mer is unique to the polymerization of 1–5 and can be
accounted for by disproportion of tolyl-ended PPV-Pd(II)Br
to PdBr2 and (tolyl-ended PPV)2Pd(II), affording PPV with
tolyl/tolyl ends via reductive elimination (Scheme 6). The
tendency for occurrence of disproportionation in the
polymerization of monomer 5, in contrast to monomers 3
and 4, can presumably be attributed to p-electron coordina-
tion of C@C adjacent to the Pd-Br end to the Pd in another
C@C-Pd-Br end (Scheme 6). This disproportionation was
supported by model reaction of (E)-(2-bromovinyl)benzene and
Pd(PtBu3)2, yielding (1E,3E)- 1,4-diphenylbuta-1,3-diene via
disproportionation of PhCH@CH-Pd(PtBu3)-Br complex (Sup-
porting Information).
Suzuki-Miyaura Coupling Polymerization of 5
The polymerization of 3 and 4 required a stronger base,
KOH, contrary to the case of Pd-CTCP with CsF for the syn-
thesis of PPP13 and P3HT,14 and we considered that the
strong base might induce dehalogenation. The low reactivity
of 3 with CsF was presumably due to the low reactivity of
Such disproportionation was also observed in the synthesis
of poly[2-(dioxalkyl)pyridine-3,6-diyl] in Ni- and Pd-CTCP
under similar conditions, owing to coordination of pyridine
nitrogen adjacent to the carbon-M-Br (M 5 Ni or Pd) end to
the M in another pyridine-M-Br end.26 Consequently, it
turns out that disproportionation of the vinylene-Pd-Br
propagating end is liable to occur in Suzuki-Miyaura cou-
pling polymerization of 5. The MALDI-TOF mass spectrum
of the polymer obtained with KOH/18-crown-6 did not
show a bromine atom end, indicating that debromination
also occurred when strong base was used (Supporting
Information Fig. S5).
FIGURE 3 Gel permeation chromatography profiles of PPV
obtained by the polymerization of 3 in the presence of KOH/18-
crown-6 and 5.0 mol % of 6 or bis[tri(tert-butylphosphine)]pal-
ladium(0) in THF ([3]0 5 2.50 3 1022 M) and water at room tem-
perature: (1) 6 for 5 min (Mn 5 5940, Mw/Mn 5 2.00) and (2)
bis[tri(tert-butylphosphine)]palladium(0) for 5 min (Mn 5 6320,
Mw/Mn 5 2.01).
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TABLE 3 Polymerization of 5 with 5.0 mol % of 7 and various bases
Entry
Base
Temperature
Time
Mn (Mw/Mn)
1
2
CsF/18-crown-6
KOH/18-crown-6
Room temperature
Room temperature
170 h
1,700 (2.16)a
9,870 (3.75)
2.5 min
a
Monomer remained.
FIGURE 4 MALDI-TOF mass spectra of PPV obtained by the polymerization of 5 in the presence of CsF/18-crown-6 and 5.0 mol %
of 7 in THF ([5]0 5 8.33 3 1023 M) and water at room temperature for 170 h (Mn 5 1700, Mw/Mn 5 2.16): (a) whole spectrum and (b)
magnification of the spectrum between m/z 5 2150–2550.
CONCLUSIONS
the Pd catalyst and dehalogenation of the polymer terminal
halogen. In the case of polymerization of 5, disproportiona-
tion of the polymer-Pd-Br complex took place, probably due
to p-electron coordination of the carbon–carbon double bond
(C@C) adjacent to the Pd-Br end to the Pd in another C@C-
The feasibility of Ni-CTCP (Kumada-Tamao coupling polymer-
ization) and Pd-CTCP (Suzuki-Miyaura coupling polymeriza-
tion) for the synthesis of well-defined PPV was investigated.
In Ni-CTCP, vinyl Grignard type monomer 1 did not undergo
Pd-Br end. Therefore, controlled synthesis of PPV by means
polymerization, whereas aryl Grignard type monomer 2
of Pd-CTCP turned out to be difficult, even though high-
afforded oligomers with low molecular weight. The MALDI-
molecular-weight PPV was obtained. We are now investigat-
TOF mass spectra indicated that the Grignard end group
ing the reason why intermolecular transfer of the catalyst
reacted with THF as a reaction solvent to terminate polymer-
ization. In Pd-CTCP, vinyl boronic acid ester type monomers
3 and 4 and phenylboronic acid type monomer 5 underwent
very fast polymerization in the presence of KOH/18-crown-6
occurs in the polymerization of monomers containing C@C,
and we are also examining other coupling polymerization
methods for the synthesis of well-defined PPV.
to afford high-molecular-weight PPV with a broad molecular
weight distribution. The MALDI-TOF mass spectra of the
polymers obtained from 3 and 4 indicated that polymeriza-
ACKNOWLEDGMENTS
tion was accompanied with intermolecular chain transfer of
This study was supported by a Grant in Aid (No. 24550141) for
Scientific Research from Japan Society for the Promotion of
Science (JSPS) and a Scientific Frontier Research Project Grant
from the Ministry of Education, Science, Sport and Culture,
Japan (MEXT).
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