Synthesis of poly(quinoxaline-2,3-diyl)s with alkoxy side chains by aromatizing polymerization of 4,5-dialkoxy-substituted 1,2-diisocyanobenzenes

Article abstract of DOI:10.1002/pola.24871

Poly(quinoxaline-2,3-diyl)s bearing alkoxy pendants was synthesized by living polymerization of 4,5-dialkoxy-3,6-dimethyl-1,2-diisocyanobenzenes, which were easily accessible from 3,6-dimethylcatechol, using organonickel complexes as initiators. Thermal p

Full text of DOI:10.1002/pola.24871

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Synthesis of Poly(quinoxaline-2,3-diyl)s with Alkoxy Side Chains by
Aromatizing Polymerization of 4,5-Dialkoxy-substituted 1,2-
Diisocyanobenzenes
Yuuya Nagata,1 Michinori Suginome1,2
1Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura,
Nishikyo-ku, Kyoto 615-8510 Japan
2JST, CREST, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
Correspondence to: M. Suginome (E-mail: suginome@sbchem.kyoto-u.ac.jp)
Received 23 May 2011; accepted 1 July 2011; published online 26 July 2011
DOI: 10.1002/pola.24871
ABSTRACT: Poly(quinoxaline-2,3-diyl)s bearing alkoxy pendants
was synthesized by living polymerization of 4,5-dialkoxy-3,6-di-
methyl-1,2-diisocyanobenzenes, which were easily accessible
from 3,6-dimethylcatechol, using organonickel complexes as
initiators. Thermal properties of the obtained polymers were
fully determined by thermogravimetric analysis and differential
scanning calorimetry, exhibiting strong dependence on their
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side chains. 2011 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 49: 4275–4282, 2011
KEYWORDS: alkoxy side chain; chiral; living polymerization;
polyaromatics; poly(quinoxaline-2,3-diyl)s; thermal properties
INTRODUCTION Much interest has focused on rigid-rod poly-
mers having fully aromatic backbone, such as poly(pheny-
lene)s, poly(thiophene)s, and poly(pyridine)s.1 Because of
their unique electronic, optical, chemical, and thermal prop-
erties, the polymers are regarded as a promising candidate
for electroluminescent,2 nonlinear optical,3 ion-conducting,4
and liquid crystalline5 materials. It is highly important to
explore new aromatic polymers with the development of
new polymerization reactions. Current efforts are being
made to utilize transition metal catalysts in polymerization,6
aiming at exploration of new polymer scaffolds with a fine
control of molecular weight and molecular weight
distribution.7
4,5-substituent of diisocyanobenzene, which are located at
the surrounding of the polymer backbone and determine the
properties of polymers, is critically important. We have so
far used alkoxymethyl groups as substituents at 4- and 5-
positions. We expected that introduction of alkoxy groups
directly to the quinoxaline rings would change the properties
of polymers and also make the synthesis of polymer much
easier. Although Reggelin et al.11 reported the synthesis of
poly(quinoxaline)s having alkoxy groups at the 6- and 7-
positions of the quinoxaline ring, the synthesis is limited to
5,8-dibromo- and 5,8-pyridyl-substituted derivatives, of
which properties and applicability have not been explored at
all in contrast to the 5,8-dialkyl derivatives. Furthermore, all
the polymerizations were carried out using organopalladium
initiators, whose activity has recently been recognized to be
much lower than the corresponding organonickel initiators
in the polymerization of 4,5-dialkoxymethyl-substituted 1,2-
diisocyanobenzenes. It seems to be important to see if the
organonickel complex serves as the superior initiators even
with 1,2-diisocyanobenzenes bearing alkoxy groups at the
4,5-positions. We, herein, report the nickel-mediated synthe-
sis of poly(quinoxaline)s bearing alkoxy pendants and their
thermal properties in comparison with poly(quinoxaline)s
previously reported. We also report on the formation of non-
racemic helical polyquinoxalines using a chiral organonickel
initiator.
We have developed a living polymerization of 1,2-diisocyano-
benzene derivatives with transition metal initiators.8 The po-
lymerization gives rigid aromatic polymers, poly(quinoxaline-
2,3-diyl)s, with narrow dispersities. Because of steric hin-
drance of the two substituents at the 5- and 8-positions of
the quinoxaline rings, the poly(quinoxaline)s form a rigid
helical structure.9 Quite recently, we have reported that sin-
gle-handed helical poly(quinoxaline-2,3-diyl) bearing metal-
binding sites serves as a highly efficient chiral ligand for
palladium-catalyzed asymmetric hydrosilylation.10 To explore
intriguing structure and functions of poly(quinoxaline-2,3-
diyl)s, it seems to be highly important to expand the scope
of the polymerization reaction. In particular, variation for the
Additional Supporting Information may be found in the online version of this article.
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SCHEME 1 Synthesis of 4,5-dialkoxy-substituted 1,2-diisocya-
nobenzene monomers 1a-e.
RESULTS AND DISCUSSION
Synthesis of new monomers 1a–e, which carry methyl
groups at 3- and 6-positions and alkoxy groups at 4- and 5-
positions of the benzene rings, is shown in Scheme 1. We
adopted 3,6-dimethylcathecol as a starting compound, which
can be prepared in multigram quantities from inexpensive
catechol, morpholine, and paraformaldehyde.12 In the first
step, various side chains were introduced onto the catechol
oxygen atoms through a Williamson ether synthesis. Thus,
the obtained compounds 3a–e were treated with fuming ni-
tric acid in acetic acid to yield dinitrobenzene derivatives
4a–e. The nitro groups were reduced quantitatively in the
presence of palladium on carbon under hydrogen atmos-
phere to amino groups, which were then formylated with an
excess amount of acetic formic anhydride to obtain diforma-
mide. Diisocyanobenzenes 1a–d were finally obtained after
dehydration with phosphoryl chloride (POCl3) in the pres-
ence of triethylamine. All moꢁnomers were stored under dry
nitrogen atmosphere at ꢀ20 C to avoid gradual decomposi-
tion. Monomer 1a showed a good crystallinity, affording sin-
gle crystals by recrystallization from hot hexane.
FIGURE 1 ORTEP drawing of monomer 1a. Displacement ellip-
soids are drawn at the 50% probability level and H atoms are
shown as small spheres of arbitrary radii. Selected distances
ꢁ
˚
(A) and angles ( ) related with isocyano groups are as follows.
C1AN1: 1.165(3), N1AC5: 1.397(3), C2AN2: 1.161(3), N2AC6:
1.394(3), C13AN3: 1.166(4), N3AC17: 1.403(3), C14AN4:
1.163(3), N4AC18: 1.395(3), C1AN1AC5: 178.3(3), C2AN2AC6:
176.8(3), C13AN3AC17: 179.1(3), C14AN4AC18: 179.9(3).
monomers 1b–e also exhibited similar absorption peaks in
the range of 2116–2118 cmꢀ1. These values are significantly
smaller than those of aromatic monoisocyanides (2130–2140
cmꢀ1 16
indicating that the NBC bond was stretched in dii-
)
socyanobenzenes reported here. It should be noted here that
the NBC bond distance in 3,6-bis(4-methylphenyl)-1,2-diiso-
cyanobenzene is reported to be 1.147 Å,11 which is signifi-
cantly shorter than ordinary monoisocyanides, although we
can provide no clear explanation to the critical difference
between them.
ORTEP drawing of monomer 1a is shown in Figure 1. Two
independent molecules are observed in an asymmetric unit,
although they are almost structurally identical. Selected geo-
metric parameters related with the isocyano groups are sum-
marized in Figure 1. The NC bond distances (1.163–1.166 Å)
are slightly longer than those found in aromatic monoisocya-
nides (1.153–1.163 Å).13 It is known that the distance of
NBC bonds in monoisocyanobenzene derivatives is not
strongly influenced by the electronic density of the aromatic
ring (p-isocyanoaniline: 1.158 Å,14 pentafluorophenyl isocya-
nide: 1.159 Å15) or a methyl group at the ortho position
(2,4,6-trimethylphenyl isocyanide: 1.158 Å13). The elongation
of the NBC bond may arise from appreciable contributions
of a resonance structure containing C¼¼Nþ¼¼C form, which
reduces the NBC bond order (Fig. 2). This assumption is
supported by shortening of the bond distance between the
isocyano nitrogen and aromatic carbon atom (1.394–1.403 Å
in 1a vs. 1.407 Å in trimethylphenyl isocyanide). Infrared
spectroscopic study was also carried out on monomer 1a,
which showed a sharp absorption peak at 2117 cmꢀ1 origi-
nated from a stretching vibration of NBC bond. All other
Polymerizations of monomers 1a–e were carried out in the
presence of an organonickel initiator. After mixing a tetrahy-
drofuran (THF) solution of monomer 1a and a solution of
nickel complex in THF, the solution immediately turned tur-
bid with the formation of insoluble beige precipitates. The
methoxy group may be too short to dissolve the polyqui-
noxaline. In the polymerization of monomer 1b having
butoxy groups, the solubility of the formed polymer was
much improved, and the reaction mixture remained homoge-
neous until the end of the polymerization. The polymer 5b
FIGURE 2 Plausible resonance structures of diisocyanobenzene.
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TABLE 1 Polymerization of Diisocyanobenzene Derivatives with Alkoxy Chains in the Presence
of an Organonickel or Organopalladium Initiatora
Polymerb
c
c
Entries
Monomer (R)
x
(Yield/%)
Mn (ꢂ104)
Mw/Mn
d
d
1
1a (Me)
100
100
100
100
100
40
5a (–d)
–
–
2
1b (Bu)
5b (96)
5c (88)
5d (88)
5e (97)
5b40 (92)
5b60 (91)
5b80 (95)
5b (81)
5c (79)
3.26
2.77
3.69
2.72
1.19
1.99
2.85
2.30
3.41
1.14
1.30
1.74
1.13
1.08
1.09
1.16
1.50
1.62
3
1c (Oct)
4
1d (2-EtHexyl)
1e ((CH2)4Cl)
1b (Bu)
5
6
7
1b (Bu)
60
8
1b (Bu)
80
9e,f
10e,g
a
1b (Bu)
100
100
1c (Oct)
o-TolNiCl(PMe3)2 was used as an initiator unless otherwise noted.
b
All polymers named without superscripts are 100mer. Other polymers are named with superscripts which
refer to their degree of polymerization (40, 60, and 80).
c
Determined by gel permeation chromatography (GPC) calibrated with polystyrene standards.
d
The yield and the molecular weight were not determined because of its low solubility.
e
o-TolPdI(PMe2Ph)2 was used as an initiator instead of o-TolNiCl(PMe3)2. Reaction temperature was set at
50 ꢁC.
f
Reaction time was extended to 24 h.
g
Reaction time was extended to 72 h.
was obtained in almost quantitative yield with narrow mo-
lecular weight distribution (Mw/Mn ¼ 1.14). This suggests
that the polymerization proceeded in a living fashion as pre-
viously reported.9j Polymerization of monomer 1c having n-
octyloxy groups gave the corresponding polymer 5c with rel-
atively broad molecular weight distribution. Monomer 1d
with 2-ethylhexyloxy groups resulted in further broadening
of molecular weight distribution, probably because of steric
hindrance of the bulky side chains. Polymerization of mono-
mer 1e having chloroalkyl side chains, which would be uti-
lized for the introduction of functional groups after polymer-
ization, successfully proceeded without causing any side
reactions associated with the presence of the C(sp3)ACl
bond. In entries 2 and 6–8, polymerizations of monomer 1b
with varied monomer/initiator ratios were examined. As the
monomer/initiator ratio increased in the range of 40–100,
molecular weights of the obtained polymers were propor-
tionally increased with good polydispersity indexes (PDIs),
ranging between 1.08 and 1.16. Polymerizations of mono-
mers 1b and 1c were also carried out in the presence of an
organopalladium complex instead of the organonickel initia-
tor (entries 9 and 10). The palladium initiator required lon-
ger reaction time than the organonickel initiator. To achieve
full conversion of monomers 1b and 1c, it took 24 and 72 h,
respectively, even at elevated reaction temperature (50 ꢁC).
Moreover, these polymerizations resulted in broader molecu-
lar weight distributions (Mw/Mn ¼ 1.50 and 1.62), suggest-
ing that the nickel initiator is more suitable for polymeriza-
tions of this type of diisocyanobenzene monomers (Table 1).
Polymers 5b–e showed good solubilities in common organic
solvents such as THF, chloroform, dichloromethane, and tolu-
ene. Polymers 5c and 5d were soluble even in nonpolar
hydrocarbons such as n-hexane and cyclohexane. On the
other hand, these polymers were insoluble in polar solvents
such as acetone, methanol, ethanol, and 2-propanol. The sol-
ubilities depended not only on the structures of the side
chains but also on their molecular weight. For instance, poly-
mers 5b40 and 5b60 were soluble in hexane, whereas poly-
mers 5b80 and 5b were insoluble.
Thermal properties of alkoxy-substituted polymers 5b–e are
summarized in Table 2. Propoxymethyl-substituted PQ was
also subjected to the measurement for comparison with
polymers 5b–e. They generally showed high thermal stability
with high decomposition temperatures (5% weight loss
measured by thermogravimetric analysis, TGA, 10 ꢁC/min,
dry nitrogen atmosphere) higher than 300 ꢁC. Polymers PQ
and 5b exhibited almost the same decomposition
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TABLE 2 Thermal Properties of Polymers PQ and 5b–e
Residue
at 500 ꢁC
(%)
Content
of Main
Chain (%)
a
b
Polymer
(R)
T5%
Tm
SCHEME 2 Synthesis of nonracemic polyquinoxalines (S,S)-PQ
and (S,S)-5b.
(ꢁC)
(ꢁC)
c
PQ
354.7
350.7
325.6
348.7
329.7
56.3
56.2
43.6
42.4
49.0
52.0
52.0
37.9
37.9
42.3
–
5b (Bu)
5c (Oct)
5d (2-EtHexyl)
5e ((CH2)4Cl)
a
161.6, 176.5
50.3, 116.4
149.6, 170.9
160.9, 182.7
tions about liquid crystalline properties of newly synthesized
polymers are currently underway.
Finally, we examined the synthesis of nonracemic polyqui-
noxalines using a chiral organonickel initiator, which has
been successful in inducing helical chirality to alkoxymethyl-
substituted polymer (S,S)-PQ (Scheme 2). Monomer 1b was
polymerized in the presence of a chiral organonickel com-
plex. The polymerization proceeded at room temperature,
affording (S,S)-5b in good yield (90%) with narrow disper-
sity (Mw/Mn ¼ 1.35). The polymer showed UV-vis (Figure 3)
and CD (Figure 4) spectra whose intensities can be well
comparable to that of (S,S)-PQ (80% screw-sense excess).
Although we have not determined the g value for 100% sin-
gle-handed structure for the alkoxy-substituted polyquinoxa-
lines, we could assume that the level of helix induction is
quite comparable to that of (S,S)-PQ.
Temperature for 5% weight loss as determined by TGA, 10 ꢁC/min.
Melting temperatures as determined by DSC, 10 ꢁC/min.
Small exothermic peak was observed at 175.3 ꢁC.
b
c
temperatures around 350 ꢁC. On the other hand, polymers
5c–e having longer side chain showed lower decomposition
temperatures. These results suggest that the thermal degra-
dation occurredꢁmainly at the side chains. Weights of TGA
residues at 500 C correspond roughly to the weight of their
main chains, being consistent with our assumption that the
thermal weight loss is because of the cleavage of the side
chains.
CONCLUSIONS
To analyze more detailed thermal properties, differential
scanning calorimetry (DSC) studies were carried out for
these polymers. To avoid an influence of thermal histories of
the polymers, all samples were heated to 200 ꢁC (10 ꢁC/
min), held at that temperature for 5 min, and then cooled to
40 ꢁC (10 ꢁC/min) just before the measurements. Measure-
ments were repeated twice, and it was confirmed that the
first scan was in complete agreement with the second scan.
Although polymers PQ and 5b showed comparable thermal
stability in the TGA measurements, a significant difference
between these polymers was observed in the DSC analyses.
Polymer PQ had no endothermic peaks during heating and
showed a small exothermic peak at 175.3 ꢁC, which might
arise from polymer crystallization. By contrast, polymer 5b
showed a clear melting peak at 161.6 ꢁC and a weak endo-
thermic peak at 176.5 ꢁC. This difference should be origi-
nated from higher flexibilities of butoxy groups in polymer
5b than propoxymethyl groups in polymer PQ. Polymer 5c
with longer alkoxy chain exhibited a lower melting point at
In summary, we have established the facile synthetic route
to o-diisocyanobenzene derivatives bearing alkoxy groups on
the quinoxaline rings. Crystal structure of 1,2-diisocyano-4,5-
dimethoxy-3,6-dimethylbenzene 1a revealed significantly lon-
ger isocyano CAN bond distance than that of monoisocyano-
benzenes. Polymerizations of these diisocyanobenzene mono-
mers proceeded in a living fashion in the presence of an
ꢁ
50.3 C. Polymer 5d bearing branched side chains showed a
higher melting temperature compared with polyꢁmer 5c with
ꢁ
weak endothermic peaks at 149.6 C and 170.9 C. Introduc-
tion of chlorine groups to side chains also influenced their
thermal properties. A weak endothermic peak at 160.9 ꢁC
and a strong peak at 182.7 ꢁC were observed for 5e. Note-
worthy, all the polymers showed multiple melting points,
which indicate liquid crystalline transition. Further investiga-
FIGURE 3 UV–visible absorption spectra of (S,S)-PQ (solid line,
9.25 ꢂ 10ꢀ5 mol/dm3) and (S,S)-5b (dotted line, 9.59 ꢂ 10ꢀ5
mol/dm3) in chloroform.
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monochromated MoKa radiation diffractometer with imaging
plate. A symmetry-related absorption correction was carried
out by using the program ABSCOR.17 The analysis was car-
ried out with direct methods (SHELX-9718 and SIR9219
)
using Yadokari-XG.20 The program ORTEP321 was used to
generate the X-ray structural diagrams. UV spectra were
recorded on a JASCO V-500 spectrometer. CD spectra were
recorded on a JASCO J-750 spectrometer. THF was dried and
deoxygenized using an alumina/catalyst column system
(GlassContour). Compound 2 (3,6-dimethylcatechol),12 acetic
formic anhydride,22 o-TolNiCl(PMe3)2,23 monomer Q,9b SSAr*-
NiCl(PMe3),9j and (g3-allyl)(g5-cyclopentadianyl)palladiu-
m(II)24 were prepared according to the reported procedures.
Dimethyl sulfoxide (DMSO), triethylamine, and POCl3 were
distilled, degassed, and stored under nitrogen. Other chemi-
cal reagents were purchased from the commercial sources
and were used without further purification.
FIGURE 4 CD spectra of (S,S)-PQ (solid line, 9.25 ꢂ 10ꢀ5 mol/
dm3) and (S,S)-5b (dotted line, 9.59
ꢂ
10ꢀ5 mol/dm3) in
chloroform.
Typical Procedure for the Synthesis of
Monomer 1 via 2, 3, and 4
Synthesis of 3b
ArNiCl(PMe3)2 complex as an initiator. The solubilities of the
polymers obtained here were strongly dependent on their
side chains and the degree of polymerization. The yielded
polymers 5b–e and the previously reported polymer PQ,
which has di(propoxymethyl) side chains, sꢁhowed similar
decomposition temperatures higher than 300 C. In contrast,
in DSC measurement, polyquinoxalines bearing alkoxy side
chains exhibited clear endothermic peaks, which were not
observed for polymer PQ. A chiral organonickel initiator was
used as an initiator for the polymerization of 1,2-diisocyano-
benzens, affording nonracemic polyquinoxaline bearing
alkoxy side chains in good yield with narrow dispersity. Poly-
merization of 1,2-diisocyanobenzenes bearing other func-
tional alkoxy side chains, introduction of optically active side
chains, and study on liquid crystalline properties of poly(qui-
noxaline)s are now being undertaken in this laboratory.
To a mixture of 2 (1.00 g, 7.24 mmol), potassium hydroxide
(3.25 g, 57.9 mmol), and 1-bromobutane (3.1 mL, 3.97 g,
29.0 mmol), DMSO (14.5 mL) was added at room tempera-
ture. The mixture was stirred at room temperature for 2 h.
Water (100 mL) was added to the reaction mixture, and
then organic materials were extracted with hexane (100 mL
ꢂ 2). The combined organic layer was washed with water
(100 mL ꢂ 3) and then brine (100 mL). The organic extract
was dried over Na2SO4, filtered, concentrated, and dried
under reduced pressure to give 3b as a colorless liquid,
which required no further purification (1.78 g, 98% yield).
1H NMR (CDCl3) d 6.79 (s, 2H), 3.93 (t, J ¼ 6.8 Hz, 4H), 2.22
(s, 6H), 1.78–1.71 (m, 4H), 1.56–1.46 (m, 4H), 0.98 (t, J ¼
7.4 Hz, 6H); 13C NMR (CDCl3) d 150.7, 129.8, 125.1, 72.6,
32.6, 19.4, 15.9, 14.0; IR (neat) 2958, 2872, 1492, 1464,
1426, 1379, 1279, 1215, 1161, 1080, 1029, 973, 841, 799
cmꢀ1; HRMS (EI) m/z calcd for C16H26O2 (Mþ): 250.1927,
found: 250.1933.
EXPERIMENTAL
All reactions were carried out under an atmosphere of nitro-
gen with magnetic stirring. 1H and 13C NMR spectra were
recorded on a Varian Mercury-VX 400, 400-MR, or JEOL
Synthesis of 4b
1
JNM-A500 spectrometer at an ambient temperature. H NMR
To fuming nitric acid (11.0 mL), an acetic acid (5.0 mL) soꢁlu-
tion of 3b (8.06 g, 29.0 mmol) was added dropwise at 0 C.
The cooling bath was removed, and the reaction mixture was
stirred at room temperature for 1 h. Water (100 mL) was
added to the reaction mixture, and organic materials were
extracted with Et2O (100 mL). The combined organic layer
was washed with water (100 mL) and then washed with
NaOH aq. (5 N, 100 mL ꢂ 2). The organic layer was washed
with water (100 mL ꢂ 3) and then brine (100 mL). The or-
ganic extract was dried over MgSO4, filtered, and concen-
trated under reduced pressure. The crude product was sub-
jected to silica gel chromatography (hexane/AcOEt ¼ 95/5),
giving 4b (5.99 g, 56% yield).
data are reported as follows: chemical shift in ppm down-
field from tetramethylsilane (d scale), multiplicity (s ¼ sin-
glet, d ¼ doublet, t ¼ triplet, m ¼ multiplet, and br ¼
broad), coupling constant (Hz), and integration. 13C NMR
chemical shifts are reported in ppm downfield from tetrame-
thylsilane (d scale). All 13C NMR spectra were obtained with
complete proton decoupling. IR spectra were obtained using
a Shimadzu FTIR-8400 FTIR spectrometer on NaCl plates or
in KBr pressed pellets. TGA was performed with Rigaku
Thermo Plus EVO II TG-DTA TG8120 at a heating rate of
10 ꢁC/min under nitrogen. DSC was recorded using ꢁRigaku
Thermo Plus EVO II DSC8230 at a heating rate of 10 C/min
under nitrogen. The GPC analysis was carried out with
TSKgel G4000HHR (CHCl3, polystyrene standards). Prepara-
tive GPC was performed on JAI LC-908 equipped with JAI-
GEL-1H and -2H columns in a series (CHCl3). X-ray diffrac-
tions were collected on a Rigaku R-AXIS RAPID-F graphite-
1H NMR (CDCl3) d 3.99 (t, J ¼ 6.4 Hz, 4H), 2.28 (s, 6H),
1.80–1.73 (m, 4H), 1.56–1.45 (m, 4H), 0.99 (t, J ¼ 7.4 Hz,
6H); 13C NMR (CDCl3) d 153.0, 140.3, 125.8, 73.7, 32.2, 19.2,
13.8, 11.8; IR (neat) 2959, 2938, 2877, 1539, 1468, 1356,
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1284, 1247, 1093, 1059, 1017, 939, 831, 788, 757 cmꢀ1
.
calcd for
435.2978.
C
26H40N2NaO2 ([MþNa]þ): 435.2982, found:
HRMS (EI) m/z calcd for C16H24N2O6 (Mþ): 340.1629, found:
340.1630.
Synthesis of 1e
Synthesis of 1b
Yield ¼ 67%. 1H NMR (CDCl3) d 3.96 (t, J ¼ 6.2 Hz, 4H),
3.62 (t, J ¼ 6.0 Hz, 4H), 2.34 (s, 6H) 2.03–1.93 (8H, m); 13C
NMR (CDCl3) d 172.0, 151.4, 128.7, 120.2, 72.9, 44.5, 29.2,
27.6, 12.8; IR (neat) 2958, 2876, 2118, 1570, 1444, 1384,
A mixture of 4b (5.99 g, 17.6 mmol) and 10 wt % Pd/C
(1.87 g, 1.76 mmol) in EtOH (17.6 mL) was stirred for 14.5
h under H2 atmosphere. The mixture was filtered through a
pad of Celite. The Celite pad was washed with EtOH (50
mL), and the filtrate was concentrated and dried under vac-
uum. The residue was dissolved in CH2Cl2 (88.0 mL), and
acetic formic anhydride (12.4 g, 140.9 mmol) was added to
the solution. After stirring at room temperature for 20 h, re-
moval of volatiles under reduced pressure gave a diformate
compound as a white powder (5.02 g). The diformate (2.00
g, 5.94 mmol) was suspended in CH2Cl2 (89 mL) and Et3N
(8.3 mL), and POCl3 (1.66 mL, 2.73 g, 17.8 mmol) was added
at 0 ꢁC to the suspension. After stirring for 1 h at 0 ꢁC, the
reaction mixture was washed with saturated NaHCO3 (50
mL ꢂ 2). The organic extract was dried over Na2SO4, filtered,
and concentrated under reduced pressure. The residue was
purified with silica gel column chromatography (hexane to
hexane/CH2Cl2 ¼ 50/50) to give 1b as a pale yellow liquid
(1.47 g, 70%).
1337, 1269, 1098, 1050, 967, 933, 726, 682, 652 cmꢀ1
;
HRMS (EI) m/z calcd for C18H22Cl2N2O2 (Mþ): 368.1053,
found: 368.1057.
o-TolPdI(PMe2Ph)2
To a solution of (g3-allyl)(g5-cyclopentadianyl)palladium(II)
(0.213 g, 1.00 mmol) in THF (10 mL), dimethylphenylphos-
phine (0.415 g, 3.00 mmol) was added at ꢀ78 ꢁC. After
15 min at ꢀ78 ꢁC, 2-iodotoluene (0.196 g, 0.90 mmol) was
added, and the mixture was heated at 50 ꢁC. After 3 h, all
volatiles were removed under vacuum, and the residue was
subjected to silica gel column chromatography (Hexane/
AcOEt ¼ 90/10), giving o-TolPdI(PMe2Ph)2 as a white pow-
der (0.261 g, 48%).
1H NMR (CDCl3) d 7.56–7.50 (4H, m) 7.37–7.29 (6H, m)
6.86–6.76 (3H, m) 6.76–6.69 (1H, m) 2.10 (3H, s) 1.62 (6H,
t, J ¼ 3.4 Hz) 1.43 (6H, t, J ¼ 3.4 Hz); 31P NMR (CDCl3) d
ꢀ10.33; IR (KBr) 3043, 2980, 2959, 2907, 2895, 2365,
1572, 1558, 1485, 1456, 1433, 1420, 1373, 1308, 1296,
1281, 1188, 1101, 1070, 1043, 1028, 1013, 999, 947, 903,
847, 739, 714, 690, 679, 644, 611 cmꢀ1; HRMS (ESI) m/z
calcd for C23H29IP2Pd (MþNaþ): 622.9716, found: 622.9702.
1H NMR (CDCl3) d 3.93 (t, J ¼ 6.8 Hz, 4H), 2.33 (s, 6H),
1.77–1.70 (m, 4H), 1.53–1.44 (m, 4H), 0.98 (t, J ¼ 7.2 Hz,
6H); 13C NMR (CDCl3) d 171.6, 151.7, 128.7, 119.9, 73.4,
32.2, 19.2, 13.9, 12.7; IR (neat) 2960, 2934, 2874, 2116,
1575, 1456, 1380, 1337, 1271, 1095, 1050, 946, 917, 739
cmꢀ1; HRMS (EI) m/z calcd for C18H24N2O2 (Mþ): 300.1832,
found: 300.1837.
Polymerization of Monomer 1a
Other diisocyanobenzenes 1a, 1c, 1d, and 1e were prepared
according to the procedure for 1b.
A THF solution of o-TolNiCl(PMe3)2 (37.3 mmol/L, 124.0 lL,
4.6 lmol) was added to a solution of 1a (0.100 g, 0.463
mmol) in THF (13.8 mL) with vigorous stirring. The reaction
mixture immediately turned turbid with the formation of in-
soluble beige precipitates. After 3 h, monomer 1a was com-
pletely disappeared. The obtained precipitates were not solu-
ble in any common solvents.
Synthesis of 1a
Yield ¼ 73%. 1H NMR (CDCl3) d 3.84 (6H, s), 2.34 (6H, s);
13C NMR (CDCl3) d 171.9, 152.2, 128.6, 100.6, 60.6, 12.5; IR
(KBr) 3004, 2948, 2117, 1577, 1462, 1406, 1339, 1275,
1095, 1047, 979, 963, 906, 817, 771 cmꢀ1; HRMS (EI) m/z
calcd for C12H12N2O2 (Mþ): 216.0893, found: 216.0899.
Polymer 5b
A THF solution of o-TolNiCl(PMe3)2 (37.3 mmol/L, 76.7 lL,
2.9 lmol) was added to a solution of 1b (85.9 mg, 0.286
mmol) in THF (8.5 mL) with vigorous stirring. After 3 h,
NaBH4 (10.8 mg, 0.286 mmol) was added to the reaction
mixture and stirred for 1 h. Water (20 mL) and CH2Cl2 (50
mL) was added, and organic materials were extracted with
CH2Cl2. The organic layer was collected and dried over
Na2SO4. The crude material obtained by evaporation of sol-
vent was purified by preparative GPC, giving polymer 5b as
a beige solid (82.8 mg, 96% yield). 1H NMR (CDCl3) d 4.00
(2H, br s), 3.85 (2H, br s), 2.17 (6H, br s), 1.74 (4H, br s),
1.51–1.45 (4H, m), 0.96 (6H, t, J ¼ 7.2 Hz). GPC (CHCl3, g/
mol): Mn ¼ 3.26 ꢂ 104, Mw/Mn ¼ 1.14.
Synthesis of 1c
Yield ¼ 80%. 1H NMR (CDCl3) d 3.92 (t, J ¼ 6.8 Hz, 4H),
2.33 (s, 6H), 1.78–1.71 (m, 4H), 1.49–1.39 (m, 4H), 1.33–
1.18 (m, 18H), 0.89 (t, J ¼ 7.0 Hz, 6H); 13C NMR (CDCl3) d
171.6, 151.7, 128.7, 119.9, 73.7, 31.8, 30.4, 30.2, 29.4, 29.2,
26.0, 22.6, 14.1, 12.7. IR (neat) 2956, 2927, 2855, 2116,
1456, 1379, 1338, 1269, 1095, 1049, 963, 919, 722 cmꢀ1
;
HRMS (EI) m/z calcd for C26H40N2O2 (Mþ): 412.3084, found:
412.3083.
Synthesis of 1d
Yield ¼ 75%. 1H NMR (CDCl3) d 3.82–3.75 (m, 4H), 2.33 (s,
6H), 1.78–1.72 (m, 2H), 1.59–1.23 (m, 16H), 0.96–0.88 (m,
12H); 13C NMR (CDCl3) d 171.6, 151.9, 128.6, 119.9, 40.5,
30.2, 29.1, 23.6, 23.0, 14.1, 12.7, 11.1; IR (neat) 2960, 2931,
2873, 2858, 2116, 1700, 1457, 1380, 1338, 1295, 1269,
1169, 1113, 1094, 1048, 962, 811 cmꢀ1; HRMS (EI) m/z
Other polymers 5c–e, 5b40, 5b60, 5b80, and PQ were pre-
pared according to the procedure for polymer 5b. (S,S)-PQ
and (S,S)-5b were prepared according to the procedure for
polymer 5b using SSAr*NiCl(PMe3) as an initiator.
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ARTICLE
Polymer 5c
to the reaction mixture, and the reaction mixture was stirred
for 12 h. Water (20 mL) and CH2Cl2 (20 mL) were added,
and organic materials were extracted. After the organic layer
was collected by using a phase separation filter and dried
over Na2SO4, solvents were removed under reduced pres-
sure. The crude product was purified by preparative GPC,
giving polymer 5b as a beige solid (40.6 mg, 81% yield).
1H NMR (CDCl3) d 4.00 (2H, br s), 3.85 (2H, br s), 2.18 (6H,
br s), 1.75 (4H, br s), 1.54–1.46 (4H, m), 0.96 (6H, t, J ¼ 7.2
Hz); GPC (CHCl3, g/mol): Mn ¼ 2.30 ꢂ 104, Mw/Mn ¼ 1.50.
1
Yield ¼ 88%. H NMR (CDCl3) d 4.03 (2H, br s), 3.82 (2H, br
s), 2.19 (6H, br s), 1.79 (4H, br s), 1.44 (4H, br s), 1.27
(16H, br s), 0.90–0.84 (6H, m); GPC (CHCl3, g/mol): Mn
¼
2.77 ꢂ 104, Mw/Mn ¼ 1.30.
Polymer 5d
1
Yield ¼ 88%. H NMR (CDCl3) d 3.75 (4H, br s), 2.13 (6H, br
s), 1.70–1.20 (18H, m), 0.84 (12H, br s); GPC (CHCl3, g/mol):
Mn ¼ 3.69 ꢂ 104, Mw/Mn ¼ 1.74.
Polymer 5e
1
Yield ¼ 97%. H NMR (CDCl3) d 3.97 (2H, br s), 3.90 (2H, br
5c Obtained by Palladium-Initiated Polymerization
s), 3.60 (4H, br s), 2.17 (6H, br s), 1.94 (8H, br s); GPC
By the same procedure as that used for polymerization of
(CHCl3, g/mol): Mn ¼ 2.72 ꢂ 104, Mw/Mn ¼ 1.33.
ꢁ
1b, 1c (50.0 mg, 0.121 mmol) was polymerized at 50 C for
72 h in THF (2.8 mL) with a THF solution of o-TolPdI(P-
Me2Ph)2 (41.4 mmol/L, 29.3 lL, 1.2 lmol), giving 5c in 79%
Polymer 5b40
1
Yield ¼ 92%. H NMR (CDCl3) d 4.00 (2H, br s), 3.84 (2H, br
1
yield. H NMR (CDCl3) d 4.04 (2H, br s), 3.84 (2H, br s), 2.18
s), 2.50–1.90 (6H, m), 1.90–1.62 (4H, m), 1.57–1.32 (4H, m),
1.07–0.84 (6H, m), small peaks originated from end-group
were observed in 9.95 and 7.84–7.12 ppm; GPC (CHCl3, g/
mol): Mn ¼ 1.19 ꢂ 104, Mw/Mn ¼ 1.08.
(6H, br s), 1.80 (4H, br s), 1.44 (4H, br s), 1.27 (16H, br s),
0.98–0.74 (6H, m); GPC (CHCl3, g/mol): Mn ¼ 3.41 ꢂ 104,
Mw/Mn ¼ 1.62.
Polymer 5b60
1
Yield ¼ 91%. H NMR (CDCl3) d 4.00 (2H, br s), 3.84 (2H, br
This work was supported by a Grant-in-Aid for Scientific
Research from MEXT.
s), 2.18 (6H, br s), 1.90–1.62 (4H, m), 1.60–1.30 (4H, m),
0.96 (6H, t, J ¼ 7.2 Hz), small peaks originated from end-
group were observed in 9.95 and 7.84–7.10 ppm; GPC
(CHCl3, g/mol): Mn ¼ 1.99 ꢂ 104, Mw/Mn ¼ 1.09.
REFERENCES AND NOTES
Polymer 5b80
1 (a) Tour, J. M. Adv Mater 1994, 6, 190–198; (b) Berresheim,
1
Yield ¼ 95%. H NMR (CDCl3) d 4.01 (2H, br s), 3.85 (2H, br
A. J.; Muller, M.; Mullen, K. Chem Rev 1999, 99, 1747–1786; (c)
¨
¨
Roncali, J. Chem Rev 1992, 92, 711–738; (d) Yamamoto, T.;
Maruyama, T.; Zhou, Z.-H.; Ito, T.; Fukuda, T.; Yoneda, Y.;
Begum, F.; Ikeda, T.; Sasaki, S. J Am Chem Soc 1994, 116,
4832–4845.
s), 2.18 (6H, br s), 1.75 (4H, br s), 1.60–1.30 (4H, m), 0.96
(6H, t, J ¼ 7.2 Hz), small peaks originated from end-group
were observed in 9.95 and 7.84–7.12 ppm; GPC (CHCl3, g/
mol): Mn ¼ 2.85 ꢂ 104, Mw/Mn ¼ 1.16.
2 (a) Akcelrud, L. Prog Polym Sci 2003, 28, 875–962; (b) Pere-
pichka, I. F.; Perepichka, D. F.; Meng, H.; Wudl, F. Adv Mater
2005, 17, 2281–2305.
Polymer PQ
1
Yield ¼ 93%. H NMR (CDCl3) d 4.66 (2H, br s), 4.57 (2H, br
3 (a) Nalwa, H. S. Adv Mater 1993, 5, 341–358; (b) Yamamoto,
T.; Zhou, Z.-H.; Kanbara, T.; Shimura, M.; Kizu, K.; Maruyama,
T.; Nakamura, Y.; Fukuda, T.; Lee, B.-L.; Ooba, N.; Tomaru, S.;
Kurihara, T.; Kaino, T.; Kubota, K.; Sasaki, S. J Am Chem Soc
1996, 118, 10389–10399.
s), 3.46 (2H, br s), 2.35 (6H, br s), 1.85–1.56 (4H, m), 0.90
(6H, t, J ¼ 7.0 Hz), small peaks originated from end-group
were observed in 10.06 and 7.87–7.09 ppm; GPC (CHCl3, g/
mol): Mn ¼ 3.49 ꢂ 104, Mw/Mn ¼ 1.06.
Polymer (S,S)-PQ
4 (a) Lauter, U.; Meyer, W. H.; Wegner, G. Macromolecules
1997, 30, 2092–2101; (b) Meyer, W. H. Adv Mater 1998, 10,
439–448; (c) Wenzl, F. P.; Mauthner, G.; Collon, M.; List, E. J.
W.; Suess, C.; Haase, A.; Jakopic, G.; Somitsch, D.; Knoll, P.;
Bouguettaya, M.; Reynolds, J. R.; Leising, G. Thin Solid Films
2003, 433, 287–291.
1
Yield ¼ 90%. H NMR (CDCl3) d 4.66 (2H, br s), 4.56 (2H, br
s), 3.47 (2H, br s), 2.35 (6H, br s), 1.59 (4H, br m), 0.90 (6H,
t, J ¼ 7.0 Hz), small peaks originated from end-group were
observed in 10.06 and 7.72–6.54 ppm; GPC (CHCl3, g/mol):
Mn ¼ 3.83 ꢂ 104, Mw/Mn ¼ 1.36.
5 (a) Chen, S. H.; Conger, B. M.; Mastrangelo, J. C.; Kende, A.
S.; Kim, D. U. Macromolecules 1998, 31, 8051–8057; (b) Knaa-
pila, M.; Ruokolainen, J.; Torkkeli, M.; Serimaa, R.; Horsburgh,
L.; Monkman, A. P.; Bras, W.; ten Brinke, G.; Ikkala, O. Synth
Met 2001, 121, 1257–1258; (c) Chen, L.; Chen, Y.; Yao, K.; Zhou,
W.; Li, F.; Chen, L.; Hu, R.; Tang, B. Z. Macromolecules 2009,
42, 5053–5061.
Polymer (S,S)-5b
1
Yield ¼ 90%. H NMR (CDCl3) d 4.00 (2H, br s), 3.84 (2H, br
s), 2.17 (6H, br s), 1.75 (4H, br s), 1.60–1.30 (4H, m), 0.96
(6H, t, J ¼ 7.2 Hz), small peaks originated from end-group
were observed in 9.95 and 8.06–6.55 ppm; GPC (CHCl3, g/
mol): Mn ¼ 3.53 ꢂ 104, Mw/Mn ¼ 1.35.
6 (a) Yamamoto, T. Macromol Rapid Commun 2002, 23,
583–606; (b) Babudri, F.; Farinola, G. M.; Naso, F. J Mater
Chem 2004, 14, 11–34; (c) Cheng, Y.-J.; Luh, T.-Y. J Organomet
Chem 2004, 689, 4137–4148; (d) Coady, D. J.; Khramov, D. M.;
Norris, B. C.; Tennyson, A. G.; Bielawski, C. W. Angew Chem
Int Ed 2008, 48, 5187–5190; (e) Wu, Z.-Q.; Ono, R. J.; Chen, Z.;
Li, Z.; Bielawski, C. W. Polym Chem 2011, 2, 300–302; (f) Wu,
5b Obtained by Palladium-Initiated Polymerization
A THF solution of o-TolPdI(PMe2Ph)2 (41.4 mmol/L, 40.3 lL,
1.7 lmol) was added to a solution of 1b (50.0 mg, 0.166
mmol) in THF (4.9 mL) with vigorous stirring. After stirring
at 50 ꢁC for 24 h, NaBH4 (6.3 mg, 0.242 mmol) was added
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2011, 49, 4275–4282
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ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Z.-Q.; Ono, R. J.; Chen, Z.; Bielawski, C. W. J Am Chem Soc
2010, 132, 14000–14001.
12 Fields, D. L.; Miller, J. B.; Reynolds, D. D. J Org Chem 1964,
29, 2640–2647.
7 (a) Yokozawa, T.; Yokoyama, A. Chem Rev 2009, 109,
5595–5619; (b) Yokozawa, T. In Conjugated Polymer Synthesis;
Chujo, Y., Ed.; Wiley-CH: Weinheim, 2010; Chapter 2, pp 35–58.
13 Fernandes, M. A.; Layh, M.; Omondi, B. Acta Crystallogr
Sect C Cryst Struct Commun 2002, 58, 384–385.
14 Britton, D. J Chem Crystallogr 1993, 23, 689–690.
8 Ito, Y.; Ihara, E.; Murakami, M.; Shiro, M. J Am Chem Soc
15 Lentz, D.; Preugschat, D. Acta Crystallogr, Sect C: Cryst
1990, 112, 6446–6447.
Struct Commun 1993, 49, 52–54.
9 (a) Ito, Y.; Ihara, E.; Murakami, M. Angew Chem Int Ed Engl
1992, 31, 1509–1510; (b) Ito, Y.; Ihara, E.; Uesaka, T.; Murakami,
M. Macromolecules 1992, 25, 6711–6713; (c) Ito, Y.; Kojima, Y.;
Murakami, M. Tetrahedron Lett 1993, 34, 8279–8282; (d) Ito, Y.;
Kojima, Y.; Murakami, M.; Suginome, M. Bull Chem Soc Jpn
1997, 70, 2801–2806; (e) Ito, Y.; Ohara, T.; Shima, R.; Suginome,
M. J Am Chem Soc 1996, 118, 9188–9189; (f) Ito, Y.; Miyake, T.;
Hatano, S.; Shima, R.; Ohara, T.; Suginome, M. J Am Chem
Soc 1998, 120, 11880–11893; (g) Ito, Y.; Miyake, T.; Ohara, T.;
Suginome, M. Macromolecules 1998, 31, 1697–1699; (h) Ito, Y.;
Miyake, T.; Suginome, M. Macromolecules 2000, 33,
4034–4038; (i) Suginome, M.; Collet, S.; Ito, Y. Org Lett 2002, 4,
351–354; (j) Yamada, T.; Noguchi, H.; Nagata, Y.; Suginome, M.
J Polym Sci A Polym Chem 2010, 48, 898–904.
16 Cotton, F. A.; Zingales, F.
351–355.
J Am Chem Soc 1961, 83,
17 Higashi, T. ABSCOR. Program for Absorption Correction;
Rigaku Corporation: Japan, 1995.
18 Sheldrick, G. M. SHELX-97. Programs for Crystal Structure
Analysis; University of Gottingen: Germany, 1997.
¨
19 Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.;
Spagna, R. J Appl Cryst 1999, 32, 115–119.
20 Wakita, K. Yadokari-XG. Program for Crystal Structure Anal-
ysis; 2000.
21 Farrugia, L. J. J Appl Cryst 1997, 30, 565.
22 Krimen, L. I. Org Synth Coll 1988, 6, 8.
10 (a) Yamamoto, T.; Suginome, M. Angew Chem Int Ed 2009,
48, 539–542; (b) Yamamoto, T.; Yamada, T.; Nagata, Y.; Sugi-
nome, M. J Am Chem Soc 2010, 132, 7899–7901.
23 (a) Carmona, E.; Paneque, M.; Poveda, M. L. Polyhedron
1989, 8, 285–291; (b) Ito, Y.; Ihara, E.; Murakami, M. Polym J
1992, 24, 297–299.
11 Reggelin, M.; Scholz, J.; Hamburger, M. J Polym Sci A
Polym Chem 2009, 47, 4830–4839.
24 Tatsuno, Y.; Yoshida, T.; Otsuka, S. Inorg Synth 1979, 19,
220–223.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2011, 49, 4275–4282