A novel synthetic route to redox-active oligo(thio-1,4-phenylene) derivatives via a Michael-type addition

Article abstract of DOI:10.1246/bcsj.75.1827

N,N′-Diphenyl-1,4-benzoquinone diimine (PBI), which is the minimum redox-active unit of polyaniline, was reduced to N,N′-diphenyl-1,4-phenylenediamine (PDA) derivatives through Michael-type additions of some nucleophiles. The addition of thiophenol to PBI proceeded very rapidly. The polyaddition of PBI-endcapped monomers (P-2PBI, B-2PBI, and TB-2PBI) with thiobisbenzenethiol (TB) produced the novel thermostable oligo(thio-1,4-phenylene)s (OTP) having PDA units as a redox-active site (OTP-P-PDA, OTP-B-PDA, and OTP-PDA). This polymerization proceeded at room temperature without catalysts. OTP-P-PDA, one of the oligomers obtained, was found to have a moderate molecular weight (M_w 8400) and to possess good thermostability (Td_10% 400 °C). The polymerization based on Michael-type additions was also confirmed by NMR measurements. The oligomers obtained behaved as good electro-responsive materials. The redox process was determined by the slope of the Nernst plot that involved two electrons and two protons per PDA unit.

Full text of DOI:10.1246/bcsj.75.1827

c. Jpn.
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 1827–1832 (2002) 1827
e Chemical
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A Novel Synthetic Route to Redox-Active Oligo(thio-1,4-phenylene)
Derivatives via a Michael-Type Addition
Redox-Active Oligo(thio-1,4-phenylene)s
K. Yamamoto et al.
Kimihisa Yamamoto,* Masayoshi Higuchi, Toyohiko Nishiumi, and Hirokazu Takai
02
27
32
SJA8
09-2673
059
Department of Chemistry, Faculty of Science & Technology, Keio University, Yokohama 223-8522
(Received March 6, 2002)
N,Nꢀ-Diphenyl-1,4-benzoquinone diimine (PBI), which is the minimum redox-active unit of polyaniline, was re-
duced to N,Nꢀ-diphenyl-1,4-phenylenediamine (PDA) derivatives through Michael-type additions of some nucleophiles.
The addition of thiophenol to PBI proceeded very rapidly. The polyaddition of PBI-endcapped monomers (P-2PBI, B-
2PBI, and TB-2PBI) with thiobisbenzenethiol (TB) produced the novel thermostable oligo(thio-1,4-phenylene)s (OTP)
having PDA units as a redox-active site (OTP-P-PDA, OTP-B-PDA, and OTP-PDA). This polymerization proceeded at
room temperature without catalysts. OTP-P-PDA, one of the oligomers obtained, was found to have a moderate molecu-
lar weight (Mw 8400) and to possess good thermostability (Td10% 400 °C). The polymerization based on Michael-type
additions was also confirmed by NMR measurements. The oligomers obtained behaved as good electro-responsive ma-
terials. The redox process was determined by the slope of the Nernst plot that involved two electrons and two protons per
PDA unit.
02
02
3.3
.1
Redox-active macromolecules such as π-conjugated poly-
mers have received much attention as electrical materials,1 es-
pecially as electrodes in batteries and in capacitors, sensors,
and electronic displays. This is due to their properties of elec-
trically quick response. Up to now, π-conjugated polymers2
have been developed for this purpose due to their high electri-
cal conductivity. However, they generally lack the chemical
and thermal stability for these electrical applications. Thus,
thermostable polymers possessing redox activity and good re-
Scheme 1.
liability for long term use have been strongly desired for use in
electronic devices. One approach for obtaining the desired
polymer involves the introduction of a redox active site into a
thermostable aromatic polymer.3 Poly(thio-1,4-phenylene)
(PTP) is well known to exhibit good thermal stability, mold-
ability and chemical resistance and is an excellent engineering
plastic.4 However, it is a difficult polymer to synthesize under
mild conditions. Therefore, considerable effort has been exert-
ed in developing new synthetic methods for its preparation.5
Recently, polyaniline has been shown to react with nucleo-
philes such as amines and thiols at room temperature.6 This re-
action is noteworthy for the arylsulfide bond formation via nu-
cleophilic substitution of a thiol on the imine compounds.
Herein, we describe a novel synthetic method of redox-active
oligo(thio-1,4-phenylene)s (OTP) containing N,Nꢀ-diphenyl-
1,4-phenylenediamine (PDA) units;7 the yields, molecular
weight, thermostability, and redox properties of the oligomers
obtained were compared. The process involves a Michael-type
addition on the compounds having a double bond with an elec-
tron-attractive group.8
to N,Nꢀ-diphenyl-1,4-phenylenediamine (PDA) by chemical or
electrochemical oxidation/reduction as shown in Scheme 1.
PBI was reduced to PDA by a Michael-type addition of a nu-
cleophile at room temperature. Since PBI has a absorption at
450 nm based on CT, the reduction process is confirmed as the
decrease in the absorption of PBI in its UV-vis spectra. Initial-
ly, the Michael reaction of PBI with nucleophiles was investi-
gated in N-methyl-2-pyrrolidone (NMP) as the solvent. The
absorption at 450 nm gradually decreased with the addition of
the nucleophile. Kinetic analysis of the UV-vis spectra re-
vealed that thiols such as benzenethiol, hexadecanethiol, and
methanethiol reacted quantitatively with PBI. The reactions
were shown to obey pseudo-1st-order kinetics, where the rate
constants for benzenethiol, hexadecanethiol, and sodium meth-
oxide were found to be 3.4 × 10−3, 2.8 × 10−4, and 5.0 × 10−3
s−1, respectively. In contrast, the addition of aniline or phenol
to PBI was not observed due to its relatively low nucleophilici-
ty. As a result, thiols were found to be good nucleophiles for
PBI. During the addition of benzenethiol to PBI, a solvent ef-
fect was observed during the Michael reaction. The rate con-
stants in NMP, N,N-dimethylformamide (DMF), acetone, and
dichloromethane were determined to be 3.4 × 10−3, 4.8 ×
10−3, 1.1 × 10−2, and 1.3 × 10−2 sec−1, respectively. The rate
Results and Discussion
Michael-Type Additions of Nucleophiles to PBI.
N,Nꢀ-
Diphenyl-1,4-benzoquinone diimine (PBI), which is the mini-
mum redox-active unit of polyaniline, is reversibly converted

1828 Bull. Chem. Soc. Jpn., 75, No. 8 (2002)
Redox-Active Oligo(thio-1,4-phenylene)s
Scheme 2.
constant in dichloromethane is 4 times greater than that in
NMP. The reaction rapidly proceeds in a nonpolar solvent by
preventing the stabilization of the nucleophile by the solvation.
Control Reaction of PBI with Benzenethiol.
A control
reaction of PBI with benzenethiol was carried out in dichlo-
romethane for 2 h at room temperature (Scheme 2). The 2-
phenylthio-PDA (PDA-T) and 2,5-bis(phenylthio)-PDA (PDA-
2T) were isolated by silica gel column chromatography in 71
and 6% yields, respectively. The Michael-type addition of
benzenethiol to the quinone of PBI gave PDA-T. On the other
hand, PDA-2T was formed via the addition of benzenethiol to
PBI-T, which was the oxidized form of PDA-T. Since PDA-T
has a lower oxidation potential (0.23 V vs SCE at pH 1.3) than
that of PDA (0.28 V), some of the PBI acts as an oxidant of
PDA-T. As a result, PDA as the reduced form of PBI was de-
tected in a 17% yield in this reaction. In other words, more
than 94% of the PBI was converted to addition product in this
reaction. Diphenyl disulfide as a side product was detected
only in very small amounts based on HPLC. These results also
suggest that the nucleophilic addition proceeded quantitatively.
1
Fig. 1. The H NMR spectra (400 MHz, DMSO−d6) of (a)
PDA-T, (b) PDA-2T, (c) P-2PDA, (d) B-2PDA, (e) TB-
2PDA, and (f) OTP-PDA. The marked peaks (*) are as-
signed to amine protons.
1
The H-NMR spectrum of PDA-2T (Fig. 1b) supported the
symmetry of PDA di-substituted with phenylthio groups at
2,5- or 2,3-positions; the positions were decided to be 2,5-ones
by 1H-COSY and NOESY measurements. Nuclear Overhaus-
er effects (NOE) between the proton (a singlet peak at δ 6.98
ppm) on the central phenyl ring and the proton (δ 7.23 ppm) of
the thiophenylene ring at the o-position were observed. These
results provided support for the idea that the 2,3- and 2,6-
bis(phenylthio)-PDAs were difficult to form via this reaction.
Such results suggested that benzenethiol was preferentially
substituted at the 5-position of the central 1,4-benzoquinone
ring of PBI-T due to the steric hindrance and electron-donating
effect of the phenylthio group. This means that a Michael-type
addition should afford a linear thiophenylene polymer during
polymerization conditions.
Synthesis of Oligo(thio-1,4-phenylene) Derivatives via a
Michael-Type Addition. As a synthetic strategy for obtain-
ing thermostable polymers having PDAs as a redox unit, we
selected the Michael-type polyaddition of a dithiol to a PBI-
endcapped compound (Scheme 3). Three kinds of PBI-end-
capped monomers were obtained in 2 synthetic routes, as
shown in Scheme 4. As PDA-endcapped monomers, 1,4-PDA-
endcapped benzene (P-2PDA) and 4,4ꢀ-PDA-endcapped bi-
phenyl (B-2PDA) were synthesized via route 1. P-2PDA and
B-2PDA were synthesized in 80 and 77% yields, respectively,
through Suzuki coupling of the p-phenylenebis(dihydroxybo-
rane) or 4,4ꢀ-biphenyldiylbis(dihydroxyborane) with 2-bromo-
5-methyl-N,Nꢀ-diphenyl-1,4-phenylenediamine (PDA-Br).
Scheme 3.
The PDA-Br was obtained in 56% yield by the dehydration of
2-bromo-5-methyl-1,4-benzoquinone with aniline in the pres-
ence of titanium(Ⅳ) tetrachloride. 1,1ꢀ-PDA-endcapped 4,4ꢀ-
thiobis(benzenethiol) (TB-2PDA) was synthesized using route
2. TB-2PDA was synthesized in a 31% yield by the Michael-
type reaction of PBI (1.0 mmol) with TB (0.5 mmol). The
three kinds of PDA-endcapped monomers obtained, using both
routes, were quantitatively converted to the PBI-endcapped
monomers by oxidation with Ca(OCl)2. As shown in Scheme
5, the polymerization of the PBI-endcapped monomers with
TB proceeded in dichloromethane at room temperature for 24
h to give the corresponding oligomers (OTP-P-PDA, OTP-B-
PDA, and OTP-PDA). The orange color of the mixture disap-
peared during the polymerization due to the reduction of the
imine to the amine structure. The mixture was poured into
methanol to precipitate the oligomer. The oligomers were iso-
lated in 53–75% yields as white powders that were soluble in
dichloromethane, DMSO, THF and NMP. The yields, molecu-
lar weight (Mw and Mw/Mn), and thermostability (Td10% and Tg)
are summarized in Scheme 5.9 The oligomer obtained in a
higher yield (PTP-P-PDA, a 75% yield) showed higher mo-
lecular weight (Mw 8400) based on the general rule of polyad-
dition. The thermostability (Td10%) was enhanced up to 400 °C

K. Yamamoto et al.
Bull. Chem. Soc. Jpn., 75, No. 8 (2002) 1829
Scheme 5.
Fig. 2. (a) Cyclic voltammograms of OTP-PDA coated on a
glassy carbon electrode in 0.2 M Na2SO4/H2SO4 aqueous
solution (pH 0.19) and the Nernst plots of (b) OTP-P-PDA,
(c) OTP-P-PDA, and (d) OTP-B-PDA.
Scheme 4.
by introduction of the p-terphenyl moiety into the main chain
of the oligomer without decrease in the solubility.
The NMR Measurements of the PDA-Endcapped Mono-
mers and Oligomers.10 In each oligomer, the presence of an
amino group (3386–3399 cm−1) was confirmed by its IR spec-
trum. Polymerization via the Michael-type addition was also
indicated from the 1H NMR measurements. PDA units, mono-
substituted at the 2-position, and PDA units di-substituted at
the 2,5-position, showed large differences in the chemical
shifts of the peaks assigned to the amine protons by exchange
with D2O. In the spectrum of mono-substituted PDA-T, two
peaks attributed to the two amine protons appeared at δ 8.06
and δ 7.32 ppm (Fig. 1a). Similar to the NMR of PDA-T, the
two peaks assigned to the 4 amine protons at δ 8.08 and δ 7.32
ppm were confirmed in the spectra of TB-2PDA (Fig. 1e). In
contrast, one peak assigned to the two amine protons appeared
at δ 7.43 ppm in the spectrum of di-substituted PDA-2T (Fig.
1b). These spectra show that a peak around 8.0 ppm in the
mono-substituted PDA unit is shifted to around 7.4 ppm in a
di-substituted one. This shift was also confirmed in the spectra
of P-2PDA and B-2PDA, that is, two peaks between 7.5–7.0
ppm appeared in each spectrum since P-2PDA and B-2PDA
have PDA units di-substituted by a methyl group and a phenyl
one at the 2,5-position (Figs. 1c and 1d). Therefore, the ab-
sence of peaks around 8.0 ppm in the spectrum of OTP-PDA
support the conclusion that the PDA units in TB-2PDA were
converted to di-substituted ones by polymerization based on
the Michael-type addition (Fig. 1f).
Electrochemical Property of Oligomers.
The electro-
chemical response of the oligomers was examined using the
electrode modified by the oligomer film (1.6 × 10−8 unit mol/
cm2) as shown in Fig. 2a. Three types of oligomers showed a
similar redox activity in an acidic medium (pH 0–4). The re-
dox potentials of OTP-P-PDA, OTP-B-PDA, and OTP-PDA
were observed at 0.45, 0.45, and 0.48 V vs SCE at pH 0.19, re-
spectively. The potentials are slightly different due to the dif-

1830 Bull. Chem. Soc. Jpn., 75, No. 8 (2002)
Redox-Active Oligo(thio-1,4-phenylene)s
°C) δ 145.92, 143.47, 139.53, 134.25, 133.92, 131.26, 130.42,
129.51, 129.01, 128.89, 128.38, 124.25, 119.42, 119.27, 118.24,
117.55, 116.04, 114.98; IR (KBr) 3389 (NH), 1496 cm−1(phenyl);
EI-MS m/z 368 [M]+; Anal. Calcd for C24H20N2S: C, 78.22; H,
5.47; N, 7.60%. Found: C, 77.84; H, 5.11; N, 7.35%. PDA-2T:
1H NMR (400 MHz, DMSO−d6, TMS standard, 30 °C) δ 7.43 (s,
2H), 7.33 (m, 8H), 7.23 (m, 2H), 7.09 (t, 4H, J = 7.81 Hz), 6.98
(s, 2H), 6.77 (d, 4H, J = 7.82 Hz), 6.72 (t, 2H, J = 7.32 Hz); 13
C
NMR (100 MHz, DMSO−d6, TMS standard, 30 °C) δ 144.28,
136.91, 133.90, 130.85, 129.56, 128.87, 127.61, 127.44, 123.79,
119.32, 116.15; IR (KBr) 3366 (NH), 1507 cm−1 (phenyl); EI-MS
m/z 476 [M]+; Anal. Calcd for C30H24N2S2: C, 75.59; H, 5.08; N,
5.88%. Found: C, 75.57; H, 4.71; N, 5.89%.
Scheme 6.
Synthesis of PDA-Br. Titanium tetrachloride (2.14 g, 11.3
mmol) was added in the chlorobenzene solution (40 mL) of
aniline (9.35 g, 0.100 mol) at 90 °C. 2-Bromo-5-methyl-p-benzo-
quinone (1.51 g, 5.68 mmol) dissolved in chlorobenzene (20 mL)
were added in the solution, and the mixture was stirred at 135 °C
for 24 h. The solution was filtrated and concentrated, and PDA-Br
(1.12 g, 3.18 mmol, 56%) was isolated by silica gel column chro-
matography (hexane:dichloromethane = 1:1, Rf = 0.52). PDA-
ferent substitutent groups on the PDA units. The redox cycles
were stable for more than one hundred scans. The oxidation
and reduction peak currents are proportional to the scan rate
during cyclic voltammetry. These results mean that excellent
redox activity was maintained even in the thiophenylene poly-
mers. The redox potentials depend on the pH of the mixture,
which means that the electron transfer process is associated
with proton transfer. On the basis of the Nernst plots, the slope
for the redox reaction of each oligomer was determined to be
ca. −60 mV/pH (Figs. 2b, 2c, and 2d). These results indicate
that the redox process involves two electron and two proton
transfers per PDA unit (Scheme 6). The oligomers promote a
two-electron transfer accompanied with a two-proton transfer,
thereby functioning as good electro-responsive materials.
1
Br: H NMR (400 MHz, DMSO−d6, TMS standard, 30 °C,) δ
7.40 (s, 1H), 7.35 (s, 1H), 7.34 (s, 1H), 7.19 (dd, J = 8.4, 8.4 Hz,
2H), 7.18 (dd, J = 8.4, 8.4 Hz, 2H), 7.15 (s, 1H), 6.88 (d, J = 8.4
Hz, 2H), 6.85 (d, J = 8.4 Hz, 2H), 6.76 (t, J = 8.4 Hz, 1H), 6.76
(t, J = 8.4 Hz, 1H); 13C NMR (100 MHz, DMSO−d6, TMS stan-
dard, 30 °C) δ 144.87, 144.76, 137.45, 135.09, 130.74, 128.89,
128.77, 124.72, 124.35, 118.77, 118.73, 115.73, 115.62, 114.00,
17.65; IR (KBr) 3404 (NH), 1597 cm−1 (phenyl); EI-MS m/z 352
[M]+, 354 [M + 2]+; Anal. Calcd for C19H17N2Br: C, 64.60; H,
4.85; N, 7.93%. Found: C, 64.78; H, 4.71; N, 7.81%.
Conclusion
Synthesis of P-2PDA. PDA-Br (353 mg, 1.00 mmol), 1,4-
phenylenebis(dihydroxyborane) (82.9 mg, 0.50 mmol), and
Pd(PPh3)4 (55.6 mg, 0.048 mmol) were dissolved in DMF (9 mL).
Sodium carbonate (2 M aq, 4.5 mL) was added in the solution, and
the solution was stirred at 70 °C for 16 h. Dichloromethane was
added in the reaction mixture; the dichloromethane solution was
washed with aqueous ammonium and brine, and dried over anhy-
drous sodium sulfate. P-2PDA (249 mg, 0.40 mmol, 80%) was
isolated by silica gel column chromatography (hexane : dichloro-
methane = 2:1, Rf = 0.47 in the solution of hexane:dichloro-
methane 1:1). P-2PDA: 1H NMR (400 MHz, THF−d8, TMS stan-
dard, 30 °C) δ 7.38 (s, 4H), 7.22 (s, 2H), 7.17 (s, 2H), 7.09 (dd, J
= 7.3, 7.3 Hz, 4H), 7.08 (dd, J = 7.3, 7.3 Hz, 4H), 6.85 (d, J =
7.3 Hz, 4H), 6.81 (d, J = 7.3 Hz, 4H), 6.67 (t, J = 7.3 Hz, 2H),
6.66 (t, J = 7.3 Hz, 2H), 6.51 (s, 2H), 6.29 (s, 2H), 2.20 (s, 2H);
13C NMR (100 MHz, THF−d8, TMS standard, 30 °C) δ 146.98,
146.85, 138.91, 137.35, 135.77, 133.34, 131.92, 129.61, 129.46,
129.42, 125.31, 124.86, 119.18, 119.00, 116.20, 116.11, 17.88; IR
(KBr) 3396 (NH), 1599 cm−1 (phenyl); EI-MS m/z 622 [M]+;
Anal. Calcd for C44H38N4: C, 84.85; H, 6.15; N, 9.00%. Found:
C, 84.40; H, 6.44; N, 8.74%.
Synthesis of OTP-P-PDA. Calcium hypochlorite (0.215 g,
1.50 mmol) was added to the dichloromethane solution (4 mL) of
P-2PDA (0.153 g, 0.245 mmol), and the solution was stirred at
room temperature for 4 h. The yellow color of the solution
changed to orange. P-2PBI (0.149 g, 98%, orange powder) was
isolated by filtration and concentration of the reaction mixture.
TB (50 mg, 0.2 mmol) dissolved in dichloromethane (25 mL) was
added to the dichloromethane solution (25 mL) of P-2PDI (0.124
g, 0.20 mmol) using a dropping funnel, and stirred at room tem-
Based on the rapid Michael-type addition of thiophenol to
N,Nꢀ-diphenyl-1,4-benzoquinone diimine (PBI), we estab-
lished a novel synthetic method for preparing oligo(thio-1,4-
phenylene) derivatives having redox-active N,Nꢀ-diphenyl-1,4-
phenylenediamine (PDA) units. This polyaddition proceeded
at room temperature without catalysts to give the oligomers
with moderate molecular weight and thermostability. The oli-
gomers obtained behaved as good electro-responsive materials,
and the redox process which involved two electrons and two
protons per PDA unit was determined by the slope of the
Nernst plot.
Experimental
Synthesis of PDA-T and PDA-2T.
N,Nꢀ-Diphenyl-1,4-ben-
zoquinone diimine (PBI, 129 mg, 0.500 mmol) dissolved in
dichloromethane (50 mL) was added to the dichloromethane solu-
tion (50 mL) of benzenethiol (55.1 mg, 0.500 mmol) using a drop-
ping funnel. The reaction mixture was stirred at room temperature
for 2 h. The orange color of the solution changed to yellow. The
solution was concentrated, and PDA-T (131 mg, 71%, brown vis-
cous liquid) and PDA-2T (11.3 mg, 6%, yellow crystals) were iso-
lated by silica gel column chromatography (hexane:dichloro-
1
methane = 3:1–1:1). PDA-T: H NMR (400 MHz, DMSO−d6,
TMS standard, 30 °C) δ 8.06 (s, 1H), 7.32 (s, 1H), 7.34 (m, 5H),
7.18 (d, 1H, J = 8.79 Hz), 7.14 (m, 4H), 6.97 (dd, 2H, J = 2.44,
8.79 Hz), 6.90 (d, 2H, J = 8.31 Hz), 6.86 (d, 1H, J = 2.44 Hz),
6.81 (d, 2H, J = 8.30 Hz), 6.74 (t, 1H, J = 7.81 Hz), 6.70 (t, 1H, J
= 7.32 Hz); 13C NMR (100 MHz, DMSO−d6, TMS standard, 30

K. Yamamoto et al.
Bull. Chem. Soc. Jpn., 75, No. 8 (2002) 1831
perature for 24 h. The orange color of the solution changed to
white. The reaction mixture was reprecipitated in methanol; OTP-
P-PDA (0.130 g, 75%, yellow powder) was isolated by filtration.
OTP-P-PDA: 1H NMR (400 MHz, DMSO−d6, TMS standard, 30
°C) δ 7.40–6.29 (m), 2.39–2.14 (m); IR (KBr) 3399 (NH), 1491
cm−1 (phenyl).
Anal. Calcd for C48H38N4S3: C, 75.16; H, 4.99; N, 7.31%. Found:
C, 75.11; H, 4.69; N, 7.06%.
Synthesis of OTP-PDA. Calcium hypochlorite (0.172 g,
1.20 mmol) was added to the dichloromethane solution (4 mL) of
TB-2PDA (0.153 g, 0.20 mmol), and the solution was stirred at
room temperature for 4 h. The yellow color of the solution
changed to orange. The reaction mixture was reprecipitated in
water; TB-2PBI (99%, orange powder) was isolated by filtration
and concentration of the reaction mixture. TB (50 mg, 0.2 mmol)
dissolved in dichloromethane (25 mL) was added to the dichlo-
romethane solution (25 mL) of the TB-2PBI using a dropping fun-
nel. The solution was stirred at room temperature for 24 h. The
orange color of the solution changed to white. The reaction mix-
ture was reprecipitated in methanol; OTP-PDA (60%, yellow pow-
Synthesis of B-2PDA. PDA-Br (353 mg, 1.00 mmol), 4,4ꢀ-
biphenyldiylbis(dihydroxyborane) (121 mg, 0.50 mmol), and
Pd(PPh3)4 (55.6 mg, 0.048 mmol) were dissolved in 1,2-
dimethoxyethane (9 mL). Sodium carbonate (2 M aq, 4.5 mL)
was added in the solution, and the solution was stirred at 70 °C for
16 h. Dichloromethane was added in the reaction mixture; the
dichloromethane solution was washed with aqueous ammonia and
brine, and dried over anhydrous sodium sulfate. B-2PDA (0.269
g, 77%) was isolated by silica gel column chromatography
(hexane:dichloromethane = 2:1, Rf = 0.26 in the solution of
1
der) was isolated by filtration. OTP-PDA: H NMR (400 MHz,
DMSO−d6, TMS standard, 30 °C) δ 7.45–6.62 (m); IR (KBr)
1
hexane:dichloromethane = 1:1). B-2PDA: H NMR (400 MHz,
3386 (NH), 1495 cm−1 (phenyl).
THF−d8, TMS standard, 30 °C) δ 7.60 (d, J = 8.0 Hz, 4H), 7.47
(d, J = 8.0 Hz, 4H), 7.25 (s, 2H), 7.22 (s, 2H), 7.10 (dd, J = 8.0,
8.0 Hz, 4H), 7.10 (dd, J = 8.0, 8.0 Hz, 4H), 6.90 (d, J = 8.0 Hz,
4H), 6.82 (d, J = 8.0 Hz, 4H), 6.69 (t, J = 8.0 Hz, 2H), 6.67 (t, J
= 8.0 Hz, 2H), 6.55 (s, 2H), 6.36 (s, 2H), 2.21 (s, 2H); 13C NMR
(100 MHz, THF−d8, TMS standard, 30 °C) δ 146.23, 139.11,
138.62, 136.65, 135.07, 132.52, 131.34, 129.33, 128.75, 128.68,
126.95, 126.51, 124.69, 124.23, 118.40, 118.23, 115.37, 115.30,
17.16; IR (KBr) 3389 (NH), 1599 cm−1 (phenyl); MALDI-TOF-
MS m/z 698 [M]+; Anal. Calcd for C50H42N4: C, 85.93; H, 6.06;
N, 8.02%. Found: C, 85.77; H, 6.00; N, 7.74%.
This work was partially supported by Grants-in-Aid for Sci-
entific Research (Nos. 11555253, 11136245, and 11167273)
from the Ministry of Education, Science, Sports and Culture, ;
by a Kanagawa Academy of Science and Technology research
Grant (Project No. 23); by the Kawakami foundation; and by a
Grant-in-Aid for Unique Development for Technology from
the Science and Technology Agency.
References
Synthesis of OTP-B-PDA. Calcium hypochlorite (0.215 g,
1.50 mmol) was added to the dichloromethane solution (4 mL) of
B-2PDA (0.175 g, 0.250 mmol), and the solution was stirred at
room temperature for 4 h. The yellow color of the solution
changed to orange. B-2PBI (0.170 g, 98%, orange powder) was
isolated by filtration and concentration of the reaction mixture.
TB (50 mg, 0.2 mmol) dissolved in dichloromethane (25 mL) was
added to the dichloromethane solution (25 mL) of B-2PDI (0.140
g, 0.20 mmol) using a dropping funnel. The solution was stirred
at room temperature for 24 h. The orange color of the solution
changed to white. The reaction mixture was reprecipitated in
methanol; OTP-B-PDA (0.113 g, 53%, yellow powder) was isolat-
1
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ed by filtration. OTP-B-PDA: H NMR (400 MHz, DMSO−d6,
TMS standard, 30 °C) δ 7.75–6.32 (m), 2.25–2.07 (m); IR (KBr)
3388 (NH), 1490 cm−1 (phenyl).
Synthesis of TB-2PDA. PDI (0.260 g, 1.00 mmol) dissolved
in dichloromethane (100 mL) was added to the dichloromethane
solution (50 mL) of TB (0.123 g, 0.50 mmol) using an additional
funnel. The reaction mixture was stirred at room temperature for
2 h. The orange color of the solution changed to yellow. The so-
lution was concentrated, and TB-2PDA (112 mg, 31%, brown yel-
low solid) was isolated by silica gel column chromatography
(hexane:dichloromethane = 3:1–1:1). TB-2PDA: 1H NMR (400
MHz, DMSO−d6, TMS standard, 30 °C) δ 8.08 (s, 2H), 7.32 (s,
2H), 7.28 (d, 4H, J = 8.31 Hz), 7.23 (d, 4H, J = 8.31 Hz), 7.17 (d,
2H, J = 8.30 Hz), 7.13 (t, 4H, J = 7.32 Hz), 7.11 (t, 4H, J = 7.32
Hz), 7.00 (dd, 2H, J = 2.45, 8.79 Hz), 6.92 (d, 4H, J = 7.32 Hz),
6.91 (d, 2H, J = 2.45 Hz), 6.79 (d, 4H, J = 7.81 Hz), 6.74 (t, 2H,
J = 7.32 Hz), 6.68 (t, 2H, J = 7.32 Hz); 13C NMR (100 MHz,
DMSO−d6, TMS standard, 30 °C) δ 145.76, 143.39, 139.53,
134.33, 134.25, 133.28, 131.54, 131.44, 129.19, 129.00, 128.84,
124.27, 119.87, 119.35, 118.27, 117.94, 116.17, 115.00; IR (KBr)
3390 (NH), 1499 cm−1 (phenyl); FAB-MS m/z 767 [M+1]+;
3
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7
8
9
High molecular weight polymers were not obtained in the
reaction, because a part of the PBI-type monomers were reduced
to PDA-type by the reaction with PDA units of the oligomers,
similar to the case of the control reaction of PBI with benzenethi-
ol. Therefore, both ends of the obtained oligomers are considered
to be thiol groups.
6
a) C.-C. Han and R.-C. Jeng, Chem. Commun., 1997, 553.
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10 The PDA units of the compounds obtained are gradually
oxidized to PBI in the air with moisture, but they are stable over 6
months in a refrigerator.