Investigation of catalyst-transfer condensation polymerization for the synthesis of n-type π-conjugated polymer, poly(2-dioxaalkylpyridine-3,6-diyl)

Article abstract of DOI:10.1002/pola.26152

Kumada-Tamao coupling polymerization of 6-bromo-3-chloromagnesio-2-(3-(2- methoxyethoxy)propyl)pyridine 1 with a Ni catalyst and Suzuki-Miyaura coupling polymerization of boronic ester monomer 2, which has the same substituted pyridine structure, with ^tBu₃PPd(o-tolyl)Br were investigated for the synthesis of a well-defined n-type π-conjugated polymer. We first carried out a model reaction of 2,5-dibromopyridine with 0.5 equivalent of phenylmagnesium chloride in the presence of Ni(dppp)Cl₂ and then observed exclusive formation of 2,5-diphenylpyridine, indicating that successive coupling reaction took place via intramolecular transfer of Ni(0) catalyst on the pyridine ring. Then, we examined the Kumada-Tamao polymerization of 1 and found that it proceeded homogeneously to afford soluble, regioregular head-to-tail poly(pyridine-2,5-diyl), poly(3-(2-(2-(methoxyethoxy)propyl) pyridine) (PMEPPy). However, the molecular weight distribution of the polymers obtained with several Ni and Pd catalysts was very broad, and the matrix-assisted laser desorption ionization time-of-flight mass spectra showed that the polymer had Br/Br and Br/H end groups, implying that the catalyst-transfer polymerization is accompanied with disproportionation. Suzuki-Miyaura polymerization of 2 with ^tBu₃PPd(o-tolyl)Br also afforded PMEPPy with a broad molecular weight distribution, and the tolyl/tolyl-ended polymer was a major product, again indicating the occurrence of disproportionation. Copyright

Full text of DOI:10.1002/pola.26152

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Investigation of Catalyst-Transfer Condensation Polymerization
for the Synthesis of n-Type p-Conjugated Polymer,
Poly(2-dioxaalkylpyridine-3,6-diyl)
Yutaka Nanashima, Rena Shibata, Ryo Miyakoshi, Akihiro Yokoyama, 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 13 April 2012; accepted 3 May 2012; published online
DOI: 10.1002/pola.26152
ABSTRACT: Kumada-Tamao coupling polymerization of 6-
distribution of the polymers obtained with several Ni and Pd
catalysts was very broad, and the matrix-assisted laser desorp-
tion ionization time-of-flight mass spectra showed that the
polymer had Br/Br and Br/H end groups, implying that the cata-
bromo-3-chloromagnesio-2-(3-(2-methoxyethoxy)propyl)pyridine
1
with a Ni catalyst and Suzuki-Miyaura coupling polymeriza-
tion of boronic ester monomer 2, which has the same substi-
t
tuted pyridine structure, with
3
Bu PPd(o-tolyl)Br were
lyst-transfer polymerization is accompanied with disproportio-
t
investigated for the synthesis of a well-defined n-type p-conju-
gated polymer. We first carried out a model reaction of 2,5-
dibromopyridine with 0.5 equivalent of phenylmagnesium
nation. Suzuki-Miyaura polymerization of 2 with Bu
3
PPd(o-
tolyl)Br also afforded PMEPPy with a broad molecular weight
distribution, and the tolyl/tolyl-ended polymer was a major
product, again indicating the occurrence of disproportionation.
VC 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem
2
chloride in the presence of Ni(dppp)Cl and then observed
exclusive formation of 2,5-diphenylpyridine, indicating that
successive coupling reaction took place via intramolecular
transfer of Ni(0) catalyst on the pyridine ring. Then, we exam-
ined the Kumada-Tamao polymerization of 1 and found that it
proceeded homogeneously to afford soluble, regioregular
head-to-tail poly(pyridine-2,5-diyl), poly(3-(2-(2-(methoxyethox-
y)propyl)pyridine) (PMEPPy). However, the molecular weight
000: 000–000, 2012
KEYWORDS: catalysts; catalyst-transfer condensation polymer-
ization; conjugated polymers; Kumada-Tamao coupling reac-
tion; living polymerization; MALDI; n-type p-conjugated
polymer; polypyridine
INTRODUCTION p-Conjugated polymers have received much
attention because of their application in electronic devices
polymers. The KTCTCP of acceptor monomers faces the fol-
lowing difficulties: (1) some electron-withdrawing groups
such as carbonyl group in acceptor monomers cannot toler-
ate the conditions used for the formation of Grignard mono-
mer; (2) the solubility of n-type p-conjugated polymers is
generally lower than that of p-type ones because acceptor
aromatics have stronger p–p stacking interaction than donor
aromatics; and (3) the weaker p-donation of the n-type poly-
mer backbone to Ni(0) catalyst may not sufficiently assist
intramolecular catalyst transfer. Kiriy and coworkers have
recently advanced this field and synthesized well-defined n-
type p-conjugated copolymers by means of Suzuki-Miyaura
1
2
such as thin-film transistors, organic light-emitting diodes,
3
and photovoltaic cells. Many p-conjugated polymers have
been conventionally synthesized by step-growth polymeriza-
tion, and therefore, it was difficult to control the molecular
4
,5
weight and to obtain polymers with low polydispersity.
However, the development of chain-growth condensation
polymerization with a transition metal catalyst has made it
6
,7
possible to synthesize well-defined p-conjugated polymers.
We have proposed that this polymerization involves intramo-
7
lecular catalyst transfer on the polymer backbone. Kumada-
Tamao
catalyst-transfer
condensation
polymerization
coupling polymerization of
monomer with a Pd catalyst and by means of an unusual
coupling polymerization of an anion radical of a thiophene-
a
fluorene-benzothiadiazole
(
KTCTCP) with a Ni catalyst yields well-defined poly(alkylth-
22
8
–16
17,18
19
iophene)s,
poly(N-alkylpyrrole)s,
gradient copolymers.
polyfluorenes,
polyphenylenes,
and
1
8,20
7
as well as block copolymers and
23
naphthalenediimide-thiophene monomer with a Ni catalyst,
2
1
both of which proceed in a chain-growth polymerization
manner, presumably via a catalyst-transfer mechanism. To
our knowledge, however, the KTCTCP of acceptor monomer
However, KTCTCP has been limited to the polymerization of
donor monomers for the synthesis of p-type p-conjugated
V
C
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SCHEME 1 Model reaction of 2,5-dibromopyridine with a half equivalent of phenylmagnesium chloride in the presence of
Ni(dppp)Cl
2
.
consisting of a single arene structure has not been reported.
We set out to explore the KTCTCP of simple acceptor mono-
mers by focusing on the polymerization of pyridine mono-
mers, which can be formed, without decomposition, from
indicated that successive coupling reaction took place via
intramolecular transfer of Ni(0) catalyst on the pyridine ring
bearing no electron-donating alkoxy group, even though the
p-donation ability of pyridine is weaker than that of donor
monomers such as thiophene. Therefore, we expected that
the polymerization of para-substituted pyridine monomer
bearing an alkyl group would also proceed via a catalyst-
transfer chain-growth polymerization mechanism to yield
regioregular poly(pyridine-2,5-diyl) with well-defined molec-
ular weight and low polydispersity.
2
4
dihalopyridine with alkyl Grignard reagent. The polymer-
ization of 3-alkoxy-2-bromo-5-chloromagnesiopyridine
unfortunately afforded a polymer insoluble in the reaction
2
5
solvent, and we were not able to explore the KTCTCP. On
the other hand, the polymerization of 2-alkoxy-5-bromo-3-
chloromagnesiopyridine proceeded via a catalyst-transfer po-
lymerization mechanism to yield poly(2-(2-(2-methoxyethox-
y)ethoxy)pyridine-3,5-diyl) (m-PMEEOPy) with well-defined
Synthesis of Monomer Precursor
2
6
molecular weight and narrow polydispersity. However, this
polypyridine, in which the repeat unit is connected at the
Poly(2-alkylpyridine-3,6-diyl)s were reported to be synthe-
sized by means of Ni-catalyzed Kumada-Tamao coupling po-
2
4
3,5-position, like the meta-positions in a benzene ring, is an
lymerization in THF under reflux, but are not soluble in
2
7
nonconjugated polymer, and the electron-donating alkoxy
group decreases the electron acceptor nature of the pyridine
repeat unit. Accordingly, we should consider KTCTCP of
para-substituted pyridine monomer bearing an alkyl side
chain for the synthesis of well-defined n-type p-conjugated
polymers. In this article, we report an investigation of the
Kumada-Tamao coupling polymerization of 6-bromo-3-chlor-
omagnesio-2-(3-(2-methoxyethoxy)propyl)pyridine 1 with a
Ni catalyst to see whether the polymerization proceeds in a
controlled manner via a catalyst-transfer polymerization
mechanism. Furthermore, Suzuki-Miyaura coupling polymer-
THF at ambient temperature. We have found that diox-
aalkyl and trioxaalkyl groups are effective for increasing the
2
8
11
solubility of aromatic polyester
and polythiophene.
Therefore, we decided to examine the effect of introducing
methoxyethoxypropyl (MEP) groups into polypyridine. Mono-
mer precursor 3, 3,6-dibromo-2-(3-(2-methoxyethoxy)pro-
pyl)pyridine, was synthesized as shown in Scheme 2. Sono-
2
9
gashira coupling reaction
of commercially available 2-
amino-6-bromopyridine and 3-(2-methoxyethoxy)-1-propyne
4, which was easily obtained by Williamson ether synthesis
from 2-methoxyethanol and propargyl bromide, was carried
out with Pd and copper catalysts, and the resulting 2-amino-
6-(dioxaalkynyl)pyridine 5 was hydrogenated to afford 2-
amino-6-MEP-pyridine 6. The carbon adjacent to the MEP
group location in 6 was selectively brominated with 2,4,4,6-
ization of boronic acid ester monomer 2, having the same
t
substituted pyridine structure, with Bu PPd(o-tolyl)Br was
3
also investigated to evaluate side reactions associated with
this pyridine structure.
3
0
tetrabromo-2,5-cyclohexadienone. The amino group of the
obtained 7 was converted to bromine by treatment with Br2,
RESULTS AND DISCUSSION
HBr, and NaNO to yield the monomer precursor 3.
2
Model Reaction
We first examined whether the Ni catalyst would intramolec-
ularly walk on the acceptor pyridine ring between the para-
positions by means of a model reaction, as we had done in
our previous investigation of the KTCTCP of meta-substituted
pyridine monomer. Thus, 2,5-dibromopyridine was reacted
with a half equivalent of phenylmagnesium chloride in the
Polymerization from Dibromo Precursor 3
Monomer precursor 3 was converted to Grignard monomer
1 by treatment with 1 equivalent of isopropylmagnesium
i
chloride ( PrMgCl) in THF at room temperature for 24 h
2
6
1
(conversion of 3 ¼ 85%). It was confirmed by means of H
NMR and GC analysis that the bromine at the 3-position of 3
was exclusively converted to a chloromagnesio group. Poly-
merization of 1 was then carried out by the addition of
several Ni and Pd catalysts to the reaction mixture (Scheme 3
presence of a catalytic amount of Ni(dppp)Cl [dppp ¼ 1,3-
2
bis(diphenylphosphino)propane] in tetrahydrofuran (THF) at
ambient temperature. The products were analyzed by gas
chromatography (GC), GC-mass spectroscopy (GC-MS), and
and Table 1). First, Ni(dppp)Cl was evaluated, because it is a
2
1
H NMR spectroscopy, and it turned out that 2,5-diphenyl-
suitable Ni catalyst for the synthesis of well-defined poly
1
0
26
pyridine was quantitatively formed (Scheme 1). This result
(3-hexylthiophene) and m-PMEEOPy. The polymerization
2
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SCHEME 2 Synthesis of monomer precursor 3.
proceeded smoothly at room temperature, and the conver-
sion of 1 was 89% in 3 h. The obtained polymer had a very
broad polydispersity, and pure poly(3-(2-(2-(methoxyethox-
y)propyl)pyridine) (PMEPPy) was obtained by washing the
crude product with methanol to remove low-molecular-
weight oligomers (Fig. 1, entry 1). The obtained pure
PMEPPy was readily soluble in common organic solvents,
such as CHCl , CH Cl , and THF, as we had expected, but
affording polymers with low molecular weight (entries 7–9)
and broad polydispersity (entries 8 and 9). Pd catalysts were
also not effective for obtaining polymers with low polydis-
persity (entries 10–13). As Ni(dppp)Cl
lecular weight polymer, we further examined the polymeriza-
tion with Ni(dppp)Cl under various conditions. An increase
gave the highest mo-
2
2
in polymerization temperature from room temperature to 50
ꢀ
C resulted in broader polydispersity (entry 2). Polymeriza-
3
2
2
1
9,26
20
tion in the presence of LiCl
(entry 3) or dppp (entry
insoluble in hexane, diethyl ether, ethyl acetate, acetone, N,N-
dimethylformamide, and methanol. The regioregularity was
highly controlled as head-to-tail (HT) unit (Fig. 2). On the ba-
4) also did not afford polymer with low polydispersity.
To examine the cause of the uncontrolled polymerization, the
1
sis of assignment of the signals in the H NMR spectrum of
end groups of PMEPPy obtained by the polymerization of 3
2
4
i
poly(2-hexylpyridine-3,6-diyl), the a-CH signal of the MEP
2
with 1.0 equivalent of PrMgCl and Ni(dppp)Cl2 were ana-
group of the HT units of PMEPPy appeared at d ¼ 3.16,
lyzed by matrix-assisted laser desorption ionization time-of-
flight (MALDI-TOF) mass spectrometry with dithranol (1,8-
dihydroxy-9[10H]-anthracenone) as a matrix in the presence
of potassium trifluoroacetate as a cationizing agent. As
shown in Figure 4, the polymer provided three series of
peaks. The major peaks are consistent with the values calcu-
lated by using the formula 193.1n (repeat unit) þ 79.9 (Br)
whereas that of the head-to-head (HH) units appeared at d
¼
2.68 as a very small signal. The HT content of PMEPPy
was estimated as higher than 97% from the integral ratio of
the HT and HH signals. The UV–vis and photoluminescence
spectra of PMEPPy in CHCl3 are depicted in Figure 3. The
absorption maxima (kmax) and the photoluminescence max-
þ
ima (k
em) are similar to those of poly(2-hexylpyridine-
þ 1.0 (H) þ 39.1 (K ), where n is the number of repeat
max
3
1
3,6-diyl).
units. Therefore, one of the end groups of the polymer is a
bromine atom and the other is a hydrogen atom (designated
as Br/H). Moreover, the other two series of minor peaks
2
When Ni catalysts with different ligands, Ni(dppe)Cl (dppe
¼
1,2-bis(diphenyl-phosphino)ethane) (entry 5) and
þ
0
could be easily assigned to the K adducts of Br/Br- and H/
Ni(dppf)Cl (dppf ¼ 1,1 -bis(diphenylphosphino)-ferrocene)
2
H-ended polymers.
(
entry 6), were used, the products also showed broad poly-
dispersity. Ni(dcpe)Cl2 (dcpe ¼ 1,2-bis(dicyclohexylphosphi-
no)ethane) (entry 7), Ni(PPh ) Cl (entry 8), and
Ni(Bu P) Cl (entry 9) resulted in low conversion of 1,
It was reported that the MALDI-TOF mass spectra of poly
(3-alkylthiophene)s with broad polydispersity, which were
obtained by typical step-growth Ni-catalyzed polymerization
3
2
2
3
2
2
SCHEME 3 Polymerization of 1 for the synthesis of PMEPPy.
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a
TABLE 1 Polymerization of 1 with various catalysts
Crude Product
Purified Product
d
Temp.
Time
Conv. of
Regioregularity
ꢀ
b
c
c
Entry
Cat.
Additive
( C)
(h)
1(%)
M
n
(M /M
w n
)
M
n
(M
w
/M
n
)
(HT %)
e
1
2
3
4
5
6
7
8
9
Ni(dppp)Cl
2
–
–
rt
3
1
6
1
3
3
6
6
3
6
6
6
6
89
95
96
78
78
93
24
73
60
39
85
98
20
e
8400 (6.37)
6650 (10.5)
6000 (3.99)
4200 (12.3)
3500 (7.86)
8500 (6.75)
510 (1.03)
16,800 (7.49)
97
f
f
50
rt
–
–
g
f
f
LiCl
–
–
h
f
f
dppp
rt
–
–
e
e
Ni(dppe)Cl
2
–
–
–
–
–
–
–
–
–
rt
7,700 (3.48)
98
96
Ni(dppf)Cl
2
rt
13,500 (4.36)
f
f
Ni(dcpe)Cl
2
rt
–
–
Ni(PPh
Ni(Bu P)
Pd(dppp)Cl
3
)
2
Cl
2
rt
1500 (4.78)
2100 (2.72)
710 (1.89)
10,400 (1.97)
6,100 (1.74)
94
90
i
3
2
Cl
2
rt
f
f
10
11
12
13
a
2
rt
–
–
i
50
50
50
1300 (2.17)
2400 (1.96)
1850 (6.91)
1,940 (1.89)
76
f
f
Pd(dppe)Cl
2
–
–
t
f
f
Pd[( Bu
3
P)]
2
–
–
Polymerization of 1 was carried out by treatment of 3 with 1.0 equiv
Purified by washing with MeOH.
Not determined.
i
f
of PrMgCl, followed by addition of 1.8 mol % of Metal (ligand)Cl
b
2
.
g
h
i
Determined by GC.
LiCl equimolar to 3.
Dppp equimolar to catalyst.
Purified by HPLC.
c
Estimated by GPC based on polystyrene standards (eluent: THF)
d
1
Determined by H NMR.
of the corresponding chloromagnesio monomers, showed
three kinds of end groups corresponding to Br/H, Br/Br, and
lymerization: initiation from dibromo dimer, propagation via
intramolecular transfer of the Ni catalyst to the polymer end
group, and hydrolysis of the polymer-Ni(II)-Br end group
with hydrochloric acid, leading to the H end group. However,
the H end group might also be formed from the polymer-Ni-
H complex, which is generated by b-hydride elimination of
3
2
H/H. Therefore, one might suggest that the polymerization
of 1 had proceeded via a step-growth polymerization mecha-
nism. However, the molecular weight distribution of PMEPPy
obtained by the polymerization of 1 with Ni(dppp)Cl2 was
very much broader than that of polymers obtained by step-
growth polymerization, in which the molecular weight distri-
bution theoretically approaches 2 at high conversion. Fur-
thermore, the results of the model reaction indicated that
the Ni catalyst has a propensity for intramolecular transfer
on the pyridine ring. Accordingly, we consider that the for-
mation of the Br/H, Br/Br, and H/H end groups of PMEPPy
can be rationalized on the basis of catalyst-transfer polymer-
ization accompanied with side reactions as follows (Scheme
i
i
the polymer-Ni- Pr complex, because PrMgCl remained in
i
the reaction mixture; conversion of 3 to 1 with PrMgCl was
85% [Scheme 4(A)]. The Ni(0) generated by reductive elimi-
nation from the polymer-Ni-H would be inserted into the
CABr bond of monomer 1 and/or of polymer with H/Br
ends, followed by propagation and quenching with hydro-
chloric acid to afford polymer with H/H ends [Scheme
4(B,C)]. The Br/Br-ended polymers might be formed via dis-
proportionation between Br/Ni(II)Br-ended polypyridines,
followed by reductive elimination to afford coupled polymers
4). The Br/H end is generally formed by catalyst-transfer po-
i
FIGURE 1 GPC profiles of PMEPPy obtained by the polymerization of 1, formed by the reaction of 3 with 1.0 equivalent of PrMgCl,
2
with 1.8 mol % of Ni(dppp)Cl at room temperature for 3 h: (A) crude product and (B) purified product obtained by washing with
methanol.
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1
ꢀ
3
at 25 C.
FIGURE 2 H NMR spectrum of PMEPPy (M
n
¼ 16,800, M /M
w n
¼ 7.49) in CDCl
[
Scheme 4(D)]. The small peak in the higher molecular
1.8 mol % of Ni(dppp)Cl to the reaction mixture. However,
2
weight region in the gel permeation chromatography (GPC)
elution curve of the obtained polymer could be due to this
disproportionation product.
the polymerization proceeded slowly, and the GPC profile of
the products showed a very broad polydispersity [Fig. 5(A)].
This presumably arises from aggregation of Grignard mono-
mer 1, as in the case of the polymerization of p-phenylene
monomer and m-pyridine monomer. Accordingly, the po-
lymerization of 1 with Ni(dppp)Cl2 was carried out in the
presence of 1.0 equivalent of LiCl. This caused the polymer-
ization to proceed more quickly; however, the molecular
weight distribution of the obtained polymer was as broad as
that of the polymer obtained from precursor 3 [Fig. 5(B)].
Polymerization from Bromiodo Precursor 8
1
9
26
i
If unreacted PrMgCl does not remain in the reaction mix-
ture, the complicated mechanisms described above would be
simplified and it might be possible to establish a more pre-
cise polymerization mechanism of 1. Therefore, we used 6-
bromo-2-MEP-3-iodopyridine 8 as a monomer precursor
instead of dibromo precursor 3, hoping for quantitative gen-
eration of Grignard monomer 1 via a more facilitated magne-
sium-iodo exchange reaction. Indeed, the reaction of 8 with
The MALDI-TOF mass spectrum of PMEPPy obtained at 1 h
(M
n
¼ 10,300, M
w
/M
n
¼ 4.35) contained one major series of
i
ꢀ
þ
1
.0 equivalent of PrMgCl in THF at 0 C for 5 min quantita-
peaks, corresponding to the K adducts of the Br/Br-ended
polymer, accompanied by two minor series of peaks (Fig. 6).
The two minor series of peaks correspond to the K adducts
tively yielded Grignard monomer 1 (100% conversion of 8
as determined by analytical GC). The polymerization of 1
was then carried out at room temperature by the addition of
þ
þ
of PMEPPy with Br/H ends and the Na adducts of PMEPPy
FIGURE 3 (A) UV–vis spectrum and (B) photoluminescence (PL) spectrum of PMEPPy in chloroform solution (ꢁ10ꢂ5 M).
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FIGURE 4 MALDI-TOF mass spectra of PMEPPy obtained by the polymerization of 1, formed by the reaction of 3 with 1.0 equiva-
i
lent of PrMgCl, with 1.8 mol % of Ni(dppp)Cl
2
at room temperature for 1 h (M
n
¼ 5100, M
w
/M
n
¼ 3.14).
SCHEME 4 Proposed mechanism of production of (A) Br/H, (B and C) H/H and (D) Br/Br-ended PMEPPy by the polymerization of 1,
i
2
formed by the reaction of 3 with PrMgCl, with Ni(dppp)Cl .
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i
FIGURE 5 GPC profiles of PMEPPy obtained by the polymerization of 1, formed by the reaction of 8 with 1.0 equivalent of PrMgCl,
with 1.8 mol % of Ni(dppp)Cl
2
(A) in the absence of LiCl at room temperature for 1 and 24 h (M
n
¼ 1300, M
w
/M
n
¼ 4.49) and (B) in
the presence of 1.0 equivalent of LiCl at room temperature for 1 h (M
n
¼ 10,300, M
w
/M
n
¼ 4.35).
with Br/Br ends. Peaks due to H/H-ended polymers were
not observed in this case, implying that the formation of the
H/H-ended polymer involves the reaction of the polymer-
portionation occurred continually from the initial stage of
polymerization. Thus, the polymerization of with
1
Ni(dppp)Cl proceeds essentially via an intramolecular cata-
2
i
Ni(II)-Br end group with residual PrMgCl. Accordingly, the
lyst-transfer polymerization mechanism to afford PMEPPy
with Br/H ends after hydrolysis of the polymer-Ni-Br com-
plex; however, disproportionation reaction continually occurs
to afford PMEPPy with Br/Br ends, as well as Ni(II) and
Ni(0) complex, which can initiate the polymerization from 1
and insert into the terminal CABr bond, followed by repro-
pagation, respectively (Scheme 5). The tendency for occur-
rence of disproportionation in the polymerization of pyridine
monomer 1, in contrast to the absence of disproportionation
main product was PMEPPy with Br/Br ends, which was pre-
sumably formed via disproportionation, as discussed in the
previous section.
We next followed the time course of the polymerization to
clarify when PMEPPy with Br/Br ends was formed. The GPC
profiles of the products showed two peaks from the begin-
ning, and both peaks were shifted toward the higher molecu-
lar weight region with increasing reaction time [Fig. 7(A)]. In
the MALDI-TOF mass spectra, the major peaks were always
those of the Br/Br-ended polymers from the early stage to
the final stage [Fig. 7(B)]. This result indicated that dispro-
8
19
20
in the KTCTCP of thiophene, phenylene, pyrrole, and
2
6
even 2-alkoxy-5-bromo-3-chloromagnesiopyridine
mono-
mers, can presumably be attributed to coordination of the
pyridine nitrogen adjacent to carbon-Ni-Br end to the Ni in
FIGURE 6 MALDI-TOF mass spectra of PMEPPy obtained by the polymerization of 1, formed by the reaction of 8 with 1.0 equiva-
i
lent of PrMgCl, with 1.8 mol % of Ni(dppp)Cl
/M
¼ 4.35).
2
in the presence of 1.0 equivalent of LiCl at room temperature for 1 h (M
n
¼ 10,300,
M
w
n
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FIGURE 7 (A) GPC profiles and (B) MALDI-TOF mass spectra of PMEPPy obtained by the polymerization of 1, formed by the reac-
i
2
tion of 8 with 1.0 equivalent of PrMgCl, with 1.8 mol % of Ni(dppp)Cl in the presence of 1.0 equivalent of LiCl at room tempera-
ture for (a) 15 min (M
n
¼ 8440, M
w
/M
n
¼ 2.16), (b) 30 min (M
n
¼ 12,240, M /M
w n
¼ 3.13), (c) 45 min (M
n
¼ 13,690, M
w
/M
n
¼ 3.79),
and (d) 60 min (M
n
¼ 13,100, M
w
/M
n
¼ 4.29).
t
another pyridine-Ni-Br end, as shown in complex X in
Scheme 5.
2 with Bu PPd(o-tolyl)Br was carried out in the presence of
3
CsF/18-crown-6 in THF containing a small amount of water
at room temperature according to the Suzuki-Miyaura cata-
lyst-transfer condensation polymerization protocols for the
synthesis of poly(p-phenylene)
Scheme 6). The GPC profile of PMEPPy obtained up to 3
min had a relatively high molecular weight and a narrow
molecular weight distribution; however, a peak in the low-
molecular-weight region appeared at 5 min. After 15 min,
the GPC showed a bimodal distribution, and then the two
peaks merged into one broad peak at 24 h [Fig. 8(A)]. We
also followed the polymerization by using MALDI-TOF mass
spectrometry to check the polymer end groups [Fig. 8(B)].
The polymer obtained at 3 min had mainly tolyl groups at
both ends, whereas the polymer with tolyl/Br ends became
the main product at 15 min. The polymer obtained after 24
Suzuki-Miyaura Coupling Polymerization of 2
3
4
35
We speculated that disproportionation occurred in the
Kumada-Tamao coupling polymerization of 1 because the
nitrogen adjacent to carbon-Ni-Br coordinates to the Ni of
another propagating end, that is, 6-bromopyridine monomers
would be unsuitable for catalyst-transfer condensation poly-
merization, even though the catalyst can walk on the pyri-
dine ring. We were next interested to see whether similar
disproportionation would take place in the Suzuki-Miyaura
coupling polymerization of a boronic ester monomer having
the same pyridine structure with a Pd catalyst.
and polythiophene
(
The corresponding pinacol boronate monomer 2 was synthe-
3
3
sized from 3 by a standard method. The polymerization of
i
SCHEME 5 Proposed polymerization mechanism of 1, formed by the reaction of 8 with PrMgCl, with Ni(dppp)Cl
2
.
8
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SCHEME 6 Polymerization of 2 for the synthesis of PMEPPy.
h again had tolyl/tolyl ends. PMEPPy with tolyl/tolyl ends
would have been formed via disproportionation. Conse-
quently, it turns out that the unsatisfactory catalyst-transfer
polymerization of 1 and 2 is due to disproportionation aris-
ing from the 6-bromopyridine structure of the monomers.
with a specified solvent. Commercially available dehydrated
THF (stabilizer-free; Kanto) and dehydrated dichloromethane
(Kanto) were used as dry solvents. The conversion of mono-
mer was determined by analytical GC performed on a Shi-
madzu GC-2010 gas chromatograph equipped with a Restek
dimethypolylsiloxane fluid Rtx-1 column (15 m) and a flame
ionization detector. GC mass spectra were obtained on a Shi-
madzu GC-MS-QP5050A with a Restek dimethypolylsiloxane
EXPERIMENTAL
General
1
13
fluid Rtx-1 column (30 m). The Mn and M /M values of
H and C NMR spectra were obtained on JEOL ECA-500
w
n
1
polymers were measured on a Tosoh HLC-8020 GPC unit
eluent, THF; calibration, polystyrene standards) with two
and ECA-600 spectrometers. The internal standards for
H
(
NMR spectra in CDCl3 and DMSO-d6 were tetramethylsilane
0.00 ppm) and the midpoint of CD H (2.50 ppm), respec-
TSK gel columns (2ꢃ Multipore H -M). MALDI-TOF mass
(
2
XL
1
3
spectra were recorded on a Shimadzu/Kratos AXIMA-CFR
plus in the reflectron ion mode by use of a laser (k ¼ 337
nm). Dithranol was used as the matrix for the MALDI-TOF
mass measurements. UV–vis spectra were measured on a
Shimadzu UV-1800 spectrophotometer. Photoluminescence
was measured on a Shimadzu RF-5300 spectrophotometer.
tively, and the internal standards for C NMR spectra in
CDCl and DMSO-d were the midpoints of CDCl (77.0 ppm)
3
6
3
and CD3 (39.8 ppm), respectively. All melting points were
measured with a Yanagimoto hot-stage melting point appara-
tus without correction. Column chromatography was per-
formed on silica gel (Kieselgel 60, 230–400 mesh; Merck)
FIGURE 8 (A) GPC profiles and (B) MALDI-TOF mass spectra of PMEPPy obtained by the polymerization of 2 with 4.8 mol % of
t
Bu
3
PPd(o-tolyl)Br at room temperature for (a) 3 min (M
¼ 4100, M /M ¼ 1.86), and (d) 24 h (M ¼ 6000, M
n
¼ 3550, M
/M
¼ 2.05).
w
/M
n
¼ 1.64), (b) 5 min (M
n
¼ 3700, M /M
w n
¼ 1.72), (c) 15 min
(
M
n
w
n
n
w
n
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Synthesis of 2,5-Diphenylpyridine
propargyl bromide (16.75 g, 140.8 mmol) in dry THF (15
mL) was then added and stirring was continued at 0 C for
4 h. The reaction was quenched with ice water, and the or-
ganic layer was extracted with diethyl ether. The combined
ꢀ
All glass apparatus were dried before use. The addition of
reagents into a reaction flask and the withdrawal of a small
aliquot 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.
organic layers were dried over MgSO . The solvent was
4
removed under reduced pressure in a rotary evaporator, and
the residue was purified by means of distillation (18 mmHg,
ꢀ
58.0–58.5 C) to afford 4 as a colorless oil (10.08 g, 79%).
2
,5-Dibromopyridine (0.477 g, 2.01 mmol) was placed in the
1
H NMR (600 MHz, CDCl ): d ¼ 4.21 (d, J ¼ 2.4 Hz, 2 H),
3
flask, and the atmosphere in the flask was replaced with ar-
gon. Dry THF (5.0 mL) was added into the flask via a sy-
ringe, and the mixture was stirred at 0 C. To this mixture,
3
.71–3.69 (m, 2 H), 3.59–3.57 (m, 2 H), 3.40 (s, 3 H), 2.40 (t,
13
J ¼ 2.4 Hz, 1 H); C NMR (151 MHz, CDCl ): d ¼ 79.5, 74.5,
3
ꢀ
7
1.6, 68.9, 59.0, 58.4.
phenylmagnesium chloride (2.0 M solution in THF, 2.2 mL,
4
.40 mmol) was added via a syringe, and then a suspension
Synthesis of 2-Amino-6-[3-(2-methoxyethoxy)-1-
propynyl]pyridine (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. 2-Amino-6-
bromopyridine (18.65 g, 107.8 mmol), triphenylphosphine
of Ni(dppp)Cl (5.9 mg, 0.0109 mmol, 0.54 mol %) in dry
2
THF (5.0 mL) was added via a syringe at room temperature.
After 3 h, the reaction was quenched with water, and the or-
ganic layer was extracted with dichloromethane. The com-
bined organic layers were dried over MgSO . The solvent
was removed under reduced pressure by rotary evaporator,
and the residue was purified by means of column chroma-
4
(
2.88 g, 11.0 mmol), cuprous iodide (2.03 g, 10.7 mmol), and
bis(triphenylphosphine)palladium dichloride (3.78 g, 5.4
mmol) were placed in the flask, and the atmosphere in the
flask was replaced with argon. Dry THF (350 mL) was added
into the flask via a syringe, and the mixture was stirred at
room temperature. Next, triethylamine (22.0 mL, 158.5
mmol) and a solution of 3 (15.39 g, 129.4 mmol) in dry THF
tography (SiO
pyridine as a pale yellow solid (0.270 g, 58%).
2
, hexane/EtOAc ¼ 8/1) to afford 2,5-diphenyl-
1
H NMR (600 MHz, CDCl ): d ¼ 8.94 (d, J ¼ 2.4 Hz, 1 H),
3
8
7
.04 (d, J ¼ 8.3 Hz, 2 H), 7.96 (dd, J ¼ 2.4 and 8.3 Hz, 1 H),
.82 (d, J ¼ 8.3 Hz, 1 H), 7.63 (d, J ¼ 8.3 Hz, 2 H), 7.52–7.48
13
(
22.0 mL) were added via a syringe, and stirring was contin-
(m, 4 H), 7.45–7.40 (m, 2 H); C NMR (151 MHz, CDCl ): d
3
ued at room temperature for 23 h. The reaction was
quenched with aqueous 3 M HCl solution, and the aqueous
layer was washed with dichloromethane and then made
basic to around pH 14 with aqueous 10% NaOH solution.
The organic layer was extracted with dichloromethane, and
¼
156.2, 148.1, 139.0, 137.7, 135.1, 134.9, 129.1, 129.0,
28.8, 128.0, 127.0, 126.8, 120.3.
1
Model Reaction
All glass apparatus were dried before use. The addition of
reagents into a reaction flask and the withdrawal of a small
aliquot 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.
the combined organic layers were dried over MgSO . The
4
solvent was removed under reduced pressure in a rotary
evaporator, and the residue was purified by means of column
chromatography (SiO , hexane/EtOAc ¼ 4/1) to afford 5 as a
2
pale brown oil (4.179 g, 68%).
1
H NMR (600 MHz, CDCl
.83 (d, J ¼ 7.2 Hz, 1 H), 6.46 (d, J ¼ 8.2 Hz, 1 H), 4.56 (br
s, 2 H), 4.43 (s, 2 H), 3.77–3.75 (m, 2 H), 3.60–3.59 (m, 2 H),
3
): d ¼ 7.38 (t, J ¼ 7.7 Hz, 1 H),
2,5-Dibromopyridine (0.237 g, 1.00 mmol) and naphthalene
6
(
used as an internal standard for GC analysis, 25.9 mg, 0.20
mmol) were placed in the flask, and the atmosphere in the
flask was replaced with argon. Dry THF (5.0 mL) was added
into the flask via a syringe, and the mixture was stirred at 0
1
3
3
1
.40 (s, 3 H); C NMR (151 MHz, CDCl ): d ¼ 158.1, 140.5,
3
37.8, 117.7, 108.7, 85.9, 84.0, 71.7, 69.1, 59.0, 58.9.
ꢀ
C. To this mixture, phenylmagnesium chloride (2.0 M solu-
Synthesis of 2-Amino-6-[3-(2-methoxyethoxy)
propyl]pyridine (6)
tion in THF, 0.26 mL, 0.52 mmol) was added via a syringe,
and then a suspension of Ni(dppp)Cl (3.4 mg, 0.0063 mmol,
2
A mixture of 5% Pd/C (4.87 g, 5.0 mol %), 5 (4.18 g, 20.2
mmol), and ethyl acetate (200 mL) was stirred at room tem-
perature for 4 h under a hydrogen atmosphere. The reaction
mixture was filtered through Celite, and the filtrate was con-
centrated under vacuum. The residue was recrystallized
0
.63 mol %) in dry THF (5.0 mL) was added via a syringe at
room temperature. The reaction was allowed to proceed for
h followed by quenching in water. The organic layer was
3
extracted with diethyl ether and subjected to GC and GC-MS
analyses to determine the product composition and
distribution.
from dichloromethane–hexane to give 6 as a white solid
ꢀ
(
7.81 g, 80%): mp ¼ 64.9–66.1 C.
1
Synthesis of 3-(2-Methoxyethoxy)-1-propyne (4)
H NMR (600 MHz, CDCl ): d ¼ 7.32 (t, J ¼ 7.7 Hz, 1 H),
3
A solution of 2-methoxyethanol (9.66 g, 126.9 mmol) in dry
THF (150 mL) was mixed with a suspension of NaH (60% in
oil, 6.02 g, 150 mmol), and the reaction mixture was stirred
6.51 (d, J ¼ 7.5 Hz, 1 H), 6.31 (d, J ¼ 7.9 Hz, 1 H), 4.38 (br
s, 2 H), 3.59–3.57 (m, 2 H), 3.55–3.53 (m, 2 H), 3.50 (t, J ¼
6.7 Hz, 2 H), 3.39 (s, 3 H), 2.67 (t, J ¼ 7.7 Hz, 2 H), 1.99
ꢀ
13
at 0 C for 1 h under an argon atmosphere. A solution of
(quint, J ¼ 7.2 Hz, 2 H); C NMR (150 MHz, CDCl ): d ¼
3
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1
2
60.3, 158.0, 138.0, 112.8, 105.7, 72.0, 70.8, 70.0, 59.0, 34.5,
9.4.
dry ether (20.0 mL) was added via a syringe. The mixture
was stirred at room temperature for 1 h, then the reaction
was quenched with water, and the organic layer was
extracted with diethyl ether. The combined organic layers
Synthesis of 6-Amino-3-bromo-2-[3-(2-methoxyethoxy)
propyl]pyridine (7)
To a solution of 6 (7.71 g, 36.7 mmol) in dry dichlorome-
thane (100 mL) at 0 C, 2,4,4,6-tetrabromo-2,5-cyclohexadie-
none (17.5 g, 42.6 mmol) was slowly added. The mixture
were dried over MgSO . The solvent was removed under
4
reduced pressure by rotary evaporator, and the residue was
ꢀ
purified by means of column chromatography (SiO , hexane/
2
EtOAc ¼ 4/1), followed by Kugelrohr distillation (0.04
ꢀ
was stirred at 0 C for 6 h. The reaction was quenched with
ꢀ
mmHg, 110–115 C) to afford 8 as a colorless oil (2.85 g,
aqueous 3 M HCl solution, and the aqueous layer was
washed with dichloromethane and then made basic to
around pH 14 with aqueous 10% NaOH solution. The or-
ganic layer was extracted with dichloromethane, and the
7
1%).
1
H NMR (600 MHz, CDCl ): d ¼ 7.86 (d, J ¼ 8.2 Hz, 1 H),
3
7
.03 (d, J ¼ 8.2 Hz, 1 H), 3.61–3.60 (m, 2 H), 3.59–3.54 (m,
4
7
H), 3.39 (s, 3 H), 3.00 (t, J ¼ 7.8 Hz, 2 H), 2.03 (quint, J ¼
combined organic layers were dried over MgSO . The solvent
4
1
3
.8 Hz, 2 H); C NMR (151 MHz, CDCl ): d ¼ 164.2, 148.6,
3
was removed under reduced pressure in a rotary evaporator,
and the residue was recrystallized from dichloromethane–
141.2, 126.9, 94.4, 71.9, 70.4, 69.9, 59.1, 37.4, 28.3.
hexane to give 7 as a white solid (9.13 g, 86%): mp ¼
Synthesis of 6-Bromo-2-[3-(2-methoxyethoxy)propyl]
pyridin-3-yl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (2)
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. Dibromopyri-
dine 3 (3.54 g, 10.0 mmol) was placed in the flask, and the
atmosphere in the flask was replaced with argon. Dry diethyl
ether (30.0 mL) was added into the flask via a syringe, and
ꢀ
1
09.7–110.8 C.
1
H NMR (600 MHz, CDCl ): d ¼ 7.46 (d, J ¼ 8.4 Hz, 1 H),
3
6
.23 (d, J ¼ 8.4 Hz, 1 H), 4.47 (br s, 2 H), 3.61–3.59 (m, 2
H), 3.57–3.53 (m, 4 H), 3.39 (s, 3 H), 2.82 (t, J ¼ 7.2 Hz, 2
1
3
H), 1.99 (quint, J ¼ 7.2 Hz, 2 H); C NMR (151 MHz, CDCl ):
3
d ¼ 158.0, 156.9, 141.5, 108.5, 107.7, 72.0, 70.8, 69.9, 59.0,
3
3.7, 28.2.
ꢀ
the mixture was stirred at ꢂ78 C. Then, n-butyl lithium (1.6
Synthesis of 3,6-Dibromo-2-[3-(2-methoxyethoxy)
propyl]pyridine (3)
A mixture of 7 (0.98 g, 3.39 mmol) and bromine (0.53 mL,
M in hexane, 7.5 mL, 12.0 mmol) was added via a syringe,
ꢀ
and stirring was continued at ꢂ78 C for 3 h. To this mix-
ture, a solution of triisopropyl borate (2.29 g, 12.2 mmol) in
dry ether (10.0 mL) was added via a syringe. The mixture
was stirred at room temperature for 2 h, then a solution of
pinacol (1.61 g, 13.7 mmol) in dry ether (10.0 mL) was
added, and after 5 min, acetic acid (0.60 mL, 10.5 mmol)
was added. Stirring was continued at room temperature for
1
0.0 mmol) in aqueous 48% HBr solution (5.5 mL) was
ꢀ
stirred at 0 C for 0.5 h. An aqueous solution (3.0 mL) of
NaNO (0.72 g, 10.0 mmol) was added to the reaction mix-
2
ꢀ
ꢀ
ture at 0 C, and stirring was continued at 0 C for 4 h. The
resulting solution was neutralized with aqueous 10% NaOH
solution and extracted with dichloromethane. The combined
2
h. The reaction was quenched with water, and the organic
organic layers were washed with aqueous 10% Na S O so-
2
2
3
layer was extracted with diethyl ether. The combined organic
lution and water and dried over MgSO . The solvent was
4
layers were dried over MgSO . The solvent was removed
4
removed under reduced pressure in a rotary evaporator, and
the residue was purified by means of column chromatogra-
under reduced pressure in a rotary evaporator, and the resi-
due was purified by means of Kugelrohr distillation (0.07–
ꢀ
phy (SiO
2
, hexane/EtOAc ¼ 3/1) to afford 3 as a pale yellow
0
.09 mmHg, 142–144 C) to afford 2 as a colorless oil (2.56
oil (1.03 g, 86%).
g, 64%).
1
1
H NMR (600 MHz, CDCl ): d ¼ 7.62 (d, J ¼ 8.2 Hz, 1 H),
3
H NMR (600 MHz, CDCl ): d ¼ 7.84 (d, J ¼ 7.9 Hz, 1 H),
3
7
4
7
.18 (d, J ¼ 8.2 Hz, 1 H), 3.61–3.59 (m, 2 H), 3.58–3.54 (m,
7
.29 (d, J ¼ 7.9 Hz, 1 H), 3.59–3.52 (m, 6 H), 3.38 (s, 3 H),
H), 3.39 (s, 3 H), 2.99 (t, J ¼ 7.7 Hz, 2 H), 2.05 (quint, J ¼
3
.08 (t, J ¼ 7.6 Hz, 2 H), 2.00–1.95 (m, 2 H), 1.34 (s, 12 H);
1
3
1
3
.7 Hz, 2 H); C NMR (151 MHz, CDCl ): d ¼ 161.5, 142.2,
3
C NMR (151 MHz, CDCl ): d ¼ 164.9, 146.0, 143.9, 124.6,
3
1
39.7, 126.8, 120.3, 72.0, 70.5, 70.0, 59.1, 33.8, 27.9.
8
4.1, 71.9, 70.9, 69.6, 58.9, 34.2, 30.5, 24.7, 24.6.
Synthesis of 6-Bromo-3-iodo-2-[3-(2-methoxyethoxy)
propyl]pyridine (8)
Polymerization
Synthesis of HT-PMEPPy
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. Dibromopyri-
dine 3 (3.54 g, 10.0 mmol) was placed in the flask, and the
atmosphere in the flask was replaced with argon. Dry diethyl
ether (30.0 mL) was added into the flask via a syringe, and
Kumada-Tamao Coupling Polymerization. All glass appa-
ratus were dried before use. The addition of reagents into a
reaction flask and the withdrawal of a small aliquot 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 (24.7 mg, 0.65 mmol) was heated
under reduced pressure and then cooled to room tempera-
ture under an argon atmosphere. Monomer precursor 8
(0.220 g, 0.55 mmol) was placed in the flask, and the
ꢀ
the mixture was stirred at ꢂ78 C. Then, n-butyl lithium (1.6
M in hexane, 7.5 mL, 12.0 mmol) was added via a syringe,
ꢀ
and stirring was continued at ꢂ78 C for 3 h. To this mix-
ture, a solution of 1,2-diiodoethane (3.13 g, 11.1 mmol) in
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atmosphere in the flask was replaced with argon. Dry THF
groups were formed from the early stage to the final stage,
implying that the polymerization proceeds via an intramolecu-
lar catalyst-transfer polymerization mechanism to afford
PMEPPy with Br/H ends; however, disproportionation occurs
to afford PMEPPy with Br/Br ends. The tendency for dispro-
portionation in the polymerization of pyridine monomer 1 is
presumably attributable to coordination of the nitrogen in the
pyridine-Ni-Br end to the Ni in another pyridine-Ni-Br end.
Suzuki-Miyaura coupling polymerization of pinacol boronate
monomer 2 with a Pd catalyst was also accompanied with dis-
proportionation. We are investigating catalyst-transfer conden-
sation polymerization of other acceptor monomers, with the
aim of synthesizing well-defined n-type p-conjugated polymers.
(
2.6 mL) was added into the flask via a syringe, and the mix-
ꢀ
i
ture was stirred at 0 C. To this mixture, PrMgCl (2.0 M so-
lution in THF, 0.28 mL, 0.56 mmol) was added via a syringe,
and stirring was continued at room temperature for 10 min
(
conversion of 8 to 1 was 100% by analytical GC). A suspen-
sion of Ni(dppp)Cl2 (5.1 mg, 0.0094 mmol, 1.83 mol %) in
dry THF (2.6 mL) was added via a syringe, and stirring was
continued at room temperature. After 1 h, 5 M hydrochloric
acid was added, and then the aqueous layer was made basic
to around pH 14 with 10% aqueous NaOH. The mixture was
extracted with dichloromethane, and the organic layer was
washed with water, dried over anhydrous MgSO , and con-
4
centrated under reduced pressure. The residue was washed
well with methanol and collected by suction filtration to give
HT-PMEPPy (M ¼ 13,800, M /M ¼ 5.71) as a white solid.
ACKNOWLEDGMENTS
n
w
n
This study was partially supported by a grant-in-aid (No.
21350067) for Scientific Research from Japan Society for the
Promotion of Science and a Scientific Frontier Research Project
Grant from the Ministry of Education, Science, Sports and Cul-
ture, Japan.
1
H NMR (600 MHz, CDCl ): d ¼ 7.90 (br s, 1 H), 7.49 (br s,
3
1
H), 3.57-3.51 (m, 6 H), 3.37 (s, 3 H), 3.16 (br s, 2 H) 2.17
(
br s, 2 H).
Suzuki-Miyaura Coupling Polymerization. All glass appa-
ratus were dried before use. The addition of reagents into a
reaction flask and the withdrawal of a small aliquot of the reac-
tion mixture for analysis were carried out via a syringe from a
three-way stopcock under a stream of nitrogen. A round-bot-
tomed flask equipped with a three-way stopcock was heated
under reduced pressure and then cooled to room temperature
under an argon atmosphere. Monomer 2 (40.0 mg, 0.100
mmol), dried CsF (68.6 mg, 0.452 mmol), and dried 18-crown-
REFERENCES AND NOTES
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6
7
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0.0048 mmol, 4.8 mol %) in dry THF (5.0 mL), degassed with
Ed.; Wiley-CH: Weinheim, 2010; pp 35–58.
argon, via a cannula, and the reaction mixture was stirred at
room temperature. After 24 h, 5 M hydrochloric acid was
added, and the aqueous layer was made basic to around pH 14
with 10% aqueous NaOH. The mixture was extracted with
dichloromethane, and the organic layer was washed with water,
8
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dried over anhydrous MgSO , and concentrated under reduced
4
pressure to give PMEPPy (M ¼ 6000, M /M ¼ 2.05).
11 Adachi, I.; Miyakoshi, R.; Yokoyama, A.; Yokozawa, T. Mac-
romolecules 2006, 39, 7793–7795.
n
w
n
CONCLUSIONS
1
2 Sheina, E. E.; Liu, J.; Iovu, M. C.; Laird, D. W.; McCullough,
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-bromo-3-chloromagnesio-2-(3-(2-methoxyethoxy)propyl)-
1
6
pyridine 1 with a Ni catalyst as an extension of catalyst-
transfer condensation polymerization for the synthesis of
well-defined n-type p-conjugated polymers was investigated.
We first demonstrated the occurrence of intramolecular
transfer of Ni(0) catalyst on the pyridine ring by means of a
model reaction of 2,5-dibromopyridine with 0.5 equivalent of
1
1
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phenylmagnesium chloride in the presence of Ni(dppp)Cl ; this
2
1
reaction afforded 2,5-diphenylpyridine exclusively. However,
the Kumada-Tamao polymerization of 1 afforded polypyridine,
PMEPPy, with very broad polydispersity with several kinds of
1
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Ni catalysts, including Ni(dppp)Cl . The MALDI-TOF mass spec-
tra indicated that PMEPPy molecules with Br/Br and Br/H end
2
19 Miyakoshi, R.; Shimono, K.; Yokoyama, A.; Yokozawa, T.
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