Synthesis and characterization of p-phenylenediamine derivatives bearing a thiadiazole unit

Article abstract of DOI:10.1016/S0040-4039(02)02315-8

New p-phenylenediamine derivatives bearing a thiadiazole unit were synthesized by palladium-catalyzed amination. Cyclic voltammetry revealed that the electrochemical properties depend on the position of the benzothiadiazole ring.

Full text of DOI:10.1016/S0040-4039(02)02315-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 9009–9013
Synthesis and characterization of p-phenylenediamine derivatives
bearing a thiadiazole unit
Mendra T. S. Ritonga, Hidehiro Sakurai and Toshikazu Hirao*
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Yamada-oka, Suita, Osaka 567-0871, Japan
Received 21 August 2002; revised 12 October 2002; accepted 17 October 2002
Abstract—New p-phenylenediamine derivatives bearing a thiadiazole unit were synthesized by palladium-catalyzed amination.
Cyclic voltammetry revealed that the electrochemical properties depend on the position of the benzothiadiazole ring. © 2002
Elsevier Science Ltd. All rights reserved.
The p-conjugated polymers have attracted much atten-
tion in the application to electrical materials depending
on their electrical properties.1 The oxidation states of
the p-conjugated polymers and oligomers interconvert
each other.2 For example, polyanilines exist in three
different discrete redox forms, which include a fully
reduced leucoemeraldine base form, a semioxidized
emeraldine one, and a fully oxidized pernigraniline
one.3 These properties are considered to permit the
construction of a catalytic system for oxidation reac-
tion. Polyanilines and polypyrroles serve as synthetic
metal catalysts under an oxygen atmosphere in the
dehydrogenative oxidation of benzylamines, 2-phenyl-
glycine, and 2,6-di-t-butylphenol.4 Similar catalysis is
also achieved with the quinonediimine derivatives.5
Two nitrogens of the quinonediimine moiety have been
revealed to be capable of participating in the complexa-
tion with transition metals.6
donor–acceptor polymer or oligomer may exhibit a
narrow band gap. However, most of these donor–
acceptor polymers comprise pyrrole, thiophene, or
phenylene as a donor unit. Introduction of acceptor
units like benzothiadiazole into an aniline oligomer
chain is expected to give a novel p-conjugated com-
pound, which exhibits different redox properties as
compared with those of aniline oligomers themselves.5
In this paper, we report the synthesis and characteriza-
tion of p-phenylenediamine derivatives bearing a thiadi-
azole unit. Not only the aniline analogue 1, but also 2
and 3 bearing the thiadiazole unit in a different position
were used in order to study the effect of the position on
an aniline oligomer chain (Scheme 1).
Synthetic routes to 1, 2 and 3 are shown in Scheme 2.
Amination of 4,7-dibromo-2,1,3-benzothiadiazole (4)10
was carried out by modifying a method reported for the
preparation of aniline oligomers by Buchwald et al.,11
Furthermore, control of the band gap of p-conjugated
polymers and oligomers is a research issue of ongoing
interest. Such control is essential for the desired electri-
cal and optical properties. Reduction of the band gap
to approximately zero is expected to afford a conduct-
ing polymer.7 One of the most successful approaches to
the low band gap polymers depends on an alternating
sequence of donor–acceptor units in the p-conjugated
polymer chain.8,9 2,1,3-Benzothiadiazole, which bears
two electron-withdrawing imine (CꢀN) nitrogens, is
known as a typical electron-accepting unit. When this
unit is combined with an electron-donating unit, the
Keywords: p-phenylenediamine; thiadiazole; redox; donor/acceptor.
* Corresponding author. Tel.: +81-6-6879-7413; fax: +81-6-6879-7415;
e-mail: hirao@chem.eng.osaka-u.ac.jp
Scheme 1. p-Phenylenediamine derivatives bearing a thiadia-
zole unit investigated in this study.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)02315-8

9010
M. T. S. Ritonga et al. / Tetrahedron Letters 43 (2002) 9009–9013
Scheme 2. Synthesis of aniline oligomers bearing a thiadiazole unit. Reagents and conditions: (a) 10 mol% Pd(OAc)2, 11 mol%
DPEphos, 2.8 equiv. t-BuONa, toluene, reflux, 27 h; (b) 10 mol% Pd(OAc)2, 11 mol% DPEphos, 2.8 equiv. t-BuONa, toluene,
reflux, 72 h; (c) 5 mol% Pd(OAc)2, 5.5 mol% DPEphos, 1.4 equiv. t-BuONa, toluene, 80°C, 20 h; (d) 5 mol% Pd(OAc)2, 5.5 mol%
DPEphos, 1.4 equiv. t-BuONa, toluene, reflux, 72 h.12
using
bis(2-(diphenylphosphino)phenyl)
ether
1 revealed two reversible one-electron oxidation pro-
cesses at +0.10 and +0.44 V (E1/2). The one-electron
reduction process was observed at −1.91 V (E1/2, Fig.
1). The electrochemical behavior of 1 in acetonitrile is
likely to be explained by A“B“C“D (E) shown in
Scheme 3.
(DPEphos)13 as a ligand. The reaction of 4 with aniline
(5) or 4-anilinoaniline (6) in refluxing toluene afforded
1 or 2 in 91% or 55% yield, respectively. For the
preparation of unsymmetrical pentamer 3, the amina-
tion of 4 with an equimolar amount of aniline was
performed at 80°C to give the mono-coupling product 7
selectively, followed by the coupling with 8.
The redox potentials from −2.2 to +1.4 V of 2 and 3 are
listed in Table 2. These electrochemical processes might
be accounted for as shown in Scheme 4. Reversible two
one-electron oxidation waves (B“C and C“D) and
one two-electron oxidation wave (D“E) were observed
with both compounds. The redox potentials were
almost the same for the oxidation processes, B“C and
C“D, of 2 and 3. On the other hand, the two-electron
oxidation wave of 3 appeared at +0.35 V (E1/2), which
is much lower than that of 2 (+0.62 V). This oxidation
corresponds to the formation of the fully oxidized form
E. Such lower potential E4 may be due to the structure
of the half-oxidized form D bearing the phenylenedi-
amine moiety, where the next-HOMO lies.
Table 1 lists the absorption maxima of 1–3 and the
related compounds 9 and 10. The absorption maximum
of 1 in CHCl3 was 522 nm, indicating that 1 has a small
HOMO–LUMO gap as compared with the thiophene
derivative 9, and has almost the same absorption maxi-
mum as observed with the pyrrole derivative 10, which
is known as the smallest HOMO–LUMO gap system in
these series.9e Furthermore, 2 showed a more red-
shifted absorption maximum at 550 nm. The absorp-
tion maximum of 3 was 546 nm between the values of
1 and 2. The red shift is considered to be related to the
donor–acceptor interaction and expanded conjugation.
Table 1. The absorption maxima of 1–3 and related com-
pounds
Chemical oxidation was also carried out. When 1 was
treated with 1.2 molar amounts of Ag2O in THF, the
Compound
1
2
3
9a
10a
umax (nm)b
522
550
546
447
532
a Ref. 9e.
b In CHCl3.
Figure 1. Cyclic voltammogram of 1 (1.0×10−3 M) in MeCN
(0.10 M Bu4NClO4) at a platinum working electrode with
scan rate=100 mV s−1 under an argon atmosphere.
The redox chemistry of 1, 2 and 3 was investigated by
cyclic voltammography. A scan from −2.2 to +1.2 V for

M. T. S. Ritonga et al. / Tetrahedron Letters 43 (2002) 9009–9013
Table 2. E1/2 values for the electrode processes of 1–3a
9011
Compound
E1 (V)
E2 (V)
E3 (V)
E4 (V)
1
2
3
−1.91
−1.95
−1.85
+0.10
−0.09
−0.08
+0.44
+0.18
+0.13
–
+0.62
+0.35
a 1.0×10−3 M in MeCN (0.10 M Bu4NClO4) at a platinum working
electrode with scan rate=100 mV s−1 (V versus Fc/Fc+) under an
argon atmosphere.
a half-oxidized form 12, which corresponds to D in the
redox cycle shown in Scheme 4. Because of the high
oxidation potential of 12, no further oxidation pro-
ceeded even though an excess amount of Ag2O was
added. On the other hand, the fully oxidized form 14
could be prepared with ease due to the low oxidation
potential. Actually, 3 was oxidized with an equimolar
amount of Ag2O to give 13, which was further trans-
ferred to 14 quantitatively by treatment of another
equimolar amount of Ag2O (Scheme 6).
Scheme 3. Plausible redox processes of 1.
(E,E)-quinonediimine derivative 11 was obtained quan-
titavely and no other isomers were detected (Scheme
5).14 Judging from Table 2, the behavior of 2 and 3 in
chemical oxidation are expected to be different. Oxida-
tion of 2 with an equimolar amount of Ag2O afforded
Scheme 5. Chemical oxidation of 1.12
Scheme 4. Plausible redox processes of 2 (left) and 3 (right).

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M. T. S. Ritonga et al. / Tetrahedron Letters 43 (2002) 9009–9013
Scheme 6. Chemical oxidation of 2 and 3.12
In summary, we have established the synthesis of p-
phenylenediamine derivatives bearing a thiadiazole
unit, in which a small HOMO–LUMO gap system was
achieved. Cyclic voltammography indicates that the
electrochemical properties were related to the length of
the chain and the position of the benzothiadiazole ring.
(g) Hirao, T.; Fukuhara, S.; Otomaru, Y.; Moriuchi, T.
Synth. Met. 2001, 123, 373; (h) Moriuchi, T.; Bandoh, S.;
Miyaishi, M.; Hirao, T. Angew. Chem., Int. Ed. 2001, 40,
3042.
7. (a) Bredas, J. L.; Heeger, A. J.; Wudl, F. J. Chem. Phys.
1986, 85, 4673; (b) Bredas, J. L. Synth. Met. 1987, 17,
115.
8. (a) Yamamoto, T.; Maruyama, T.; Zhou, Z.-H.; Ito, T.;
Fukuda, T.; Yoneda, Y.; Begum, F.; Ikeda, T.; Sasaki,
S.; Takezoe, H.; Fukuda, A.; Kubota, K. J. Am. Chem.
Soc. 1994, 116, 4832; (b) Yamamoto, T.; Kanbara, T.;
Ooba, N.; Tomaru, S. Chem. Lett. 1994, 1709; (c)
Tanaka, S.; Yamashita, Y. Synth. Met. 1995, 69, 599; (d)
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; (e) Tanaka, S.; Yamashita, Y. Synth. Met. 1997,
84, 229; (f) Zhang, Q. T.; Tour, J. M. J. Am. Chem. Soc.
1997, 119, 5065; (g) Tanaka, S.; Yamashita, Y. Synth.
Met. 1997, 84, 229; (h) Zhang, Q. T.; Tour, J. M. J. Am.
Chem. Soc. 1998, 120, 5355; (i) Ng, S. C.; Ding, M.;
Chan, H. S. O.; Yu, W.-L. Macromol. Chem. Phys. 2001,
202, 8; (j) Tachibana, M.; Tanaka, S.; Yamashita, Y.;
Yoshizawa, K. J. Phys. Chem. B 2002, 106, 3549.
9. (a) Karikomi, M.; Kitamura, C.; Tanaka, S.; Yamashita,
Y. J. Am. Chem. Soc. 1995, 117, 6791; (b) Kitamura, C.;
Tanaka, S.; Yamashita, Y. Chem. Mater. 1996, 8, 570; (c)
van Mullekom, H. A. M.; Vekemans, J. A. J. M.; Meijer,
E. W. Chem. Commun. 1996, 2163; (d) Yamashita, Y.;
Ono, K.; Tomura, M.; Tanaka, S. Tetrahedron 1997, 53,
10169; (e) van Mullekom, H. A. M.; Vekemans, J. A. J.
M.; Meijer, E. W. Chem. Eur. J. 1998, 4, 1235; (f)
Raimundo, J. M.; Blanchard, P.; Brisset, H.; Akoudad,
S.; Roncali, J. Chem. Commun. 2000, 939; (g) Morikita,
T.; Yamaguchi, I.; Yamamoto, T. Adv. Mater. 2001, 13,
1862; (h) Jayakannan, M.; van Hal, P. A.; Janssen, R. A.
J. J. Polym. Sci. A 2002, 40, 2360; (i) Kitamura, C. Y.;
Saito, K.; Nakagawa, M.; Ouchi, M.; Yoneda, A.;
Yamashita, Y. Tetrahedron Lett. 2002, 43, 3373.
10. Pilgram, K.; Zupan, M.; Skiles, R. J. Heterocycl. Chem.
1970, 7, 629.
Acknowledgements
The use of the facilities of the Analytical Center, Fac-
ulty of Engineering, Osaka University is acknowledged.
We thank Ms. Toshiko Muneishi for the help of NMR
measurement. This work was partially supported by a
Grant-in-Aid for Scientific Research on Priority Areas
(No. 13128206) from the Ministry of Education, Sports,
Science and Technology, Japan.
References
1. (a) MacDiarmid, A. G.; Yang, L. S.; Huang, W. S.;
Humphrey, B. D. Synth. Met. 1987, 18, 393; (b) Ofer, D.;
Crooks, R. M.; Wrighton, M. S. J. Am. Chem. Soc. 1990,
112, 7869; (c) Gustafsson, G.; Cao, Y.; Treacy, G. M.;
Klavetter, F.; Colaneri, N.; Heeger, A. G. Nature 1992,
357, 477; (d) Bradley, D. D. C. Synth. Met. 1993, 54, 401;
(e) Miller, J. S. Adv. Mater. 1993, 5, 671; (f) Bloor, D.
Chem. Ber. 1995, 31, 385; (g) Jestin, I.; Frere, P.; Blan-
chard, P.; Roncali, J. Angew. Chem., Int. Ed. 1998, 37,
942 and references cited therein.
2. Kaplan, S.; Conwell, E. M.; Ritcher, A. F.; MacDiarmid,
A. G. Synth. Met. 1989, 29, E235.
3. Epstein, A. J.; Ginder, J. M.; Ritcher, A. F.; MacDi-
armid, A. G. In Conducting Polymers; Alcacer, L., Ed.;
Reidel: Holland, 1987; p. 121.
4. (a) Hirao, T.; Higuchi, M.; Ikeda, I.; Oshiro, Y. J. Chem.
Soc., Chem. Commun. 1993, 194; (b) Hirao, T.; Higuchi,
M.; Oshiro, Y.; Ikeda, I. Chem. Lett. 1993, 1889; (c)
Higuchi, M.; Ikeda, I.; Hirao, T. J. Org. Chem. 1997, 62,
1072.
11. Sadighi, J. P.; Singer, R. A.; Buchwald, S. L. J. Am.
5. Hirao, T.; Fukuhara, S. J. Org. Chem. 1998, 63, 7534.
6. (a) Higuchi, M.; Yamaguchi, S.; Hirao, T. Synlett 1996,
1213; (b) Higuchi, M.; Imoda, D.; Hirao, T. Macro-
molecules 1996, 29, 8277; (c) Higuchi, M.; Ikeda, I.;
Hirao, T. J. Org. Chem. 1997, 62, 1072; (d) Hirao, T.;
Yamaguchi, S.; Fukuhara, S. Tetrahedron Lett. 1999, 40,
3009; (e) Hirao, T.; Yamaguchi, S.; Fukuhara, S. Synth.
Met. 1999, 106, 67; (f) Moriuchi, T.; Bandoh, S.;
Miyaishi, M.; Hirao, T. Eur. J. Inorg. Chem. 2001, 651;
Chem. Soc. 1998, 120, 4960.
12. New compounds gave satisfactory spectroscopic data. 1:
1
mp 148–149°C; H NMR (CDCl3, 600 MHz) l 7.34 (dd,
J=8.4, 7.2 Hz, 4H), 7.24 (d, J=8.4 Hz, 4H), 7.21 (s, 2H),
6.99 (t, J=7.2 Hz, 2H), 6.68 (s, 2H); 13C NMR (CDCl3,
150 MHz) 109.2, 109.8, 118.2, 121.5, 128.0, 129.3, 142.1
ppm; IR (KBr, cm−1) 3394, 1599, 1523, 1475, 1428, 1385,
1300, 889, 756, 699, 431. Anal. calcd for C18H14N4S: C,

M. T. S. Ritonga et al. / Tetrahedron Letters 43 (2002) 9009–9013
9013
67.90; H, 4.43; N, 17.60; S, 10.07. Found: C, 67.89;
H, 4.71; N, 17.49; S, 10.11. HRMS (EI) calcd for
C18H14N4S: 318.0940. Found: 318.0941. 2: mp 140–
120.1, 120.2, 128.3, 128.8, 136.1, 136.9, 144.1, 148.9 ppm;
IR (KBr, cm−1) 3380, 3053, 2957, 2320, 1594, 1557, 1500,
1384, 1319, 1230, 1167, 1100, 1042, 833, 748, 696, 502,
420. HRMS (EI) calcd for C30H22N6S: 498.1626. Found:
498.1618. 13: mp 191–193°C; 1H NMR (CD2Cl2, 600
MHz) l 7.43 (dd, J=8.4, 7.2 Hz, 2H), 7.37–6.95 (m,
17H), 6.87 (t, J=7.2 Hz, 1H), 5.90 (br, 1H), 5.73 (br,
1H); 13C NMR (CD2Cl2, 150 MHz) 156.8, 155.9, 152.4,
149.8, 144.5, 141.6, 138.5, 136.1, 135.5, 129.6, 129.4,
127.0, 125.7, 125.3, 124.5, 122.0, 120.9, 120.5, 118.5,
116.8, 116.0, 104.0 ppm; IR (KBr, cm−1) 3379, 3025,
1599, 1507, 1294, 891, 819, 747, 695, 626, 503. HRMS
(EI) calcd for C30H22N6S: 498.1626. Found: 498.1612. 14:
mp 179–180°C; 1H NMR (CD2Cl2, 600 MHz) l 7.46–
7.35 (m, 4H), 7.26–6.94 (m, 12H), 6.91–6.75 (m, 4H); IR
(KBr, cm−1) 2924, 1653, 1602, 1559, 1507, 1302, 1163,
830, 745, 697. HRMS (EI) calcd for C30H20N6S:
496.1596. Found: 496.1580.
1
141°C; H NMR (CD2Cl2, 600 MHz) l 7.23 (dd, J=8.4,
7.2 Hz, 4H), 7.21 (d, J=8.7 Hz, 4H), 7.11 (d, J=8.7 Hz,
4H), 7.05 (s, 2H), 7.00 (d, J=8.4 Hz, 4H), 6.86 (t, J=7.2
Hz, 2H), 6.59 (s, 2H), 5.71 (s, 2H); 13C NMR (CD2Cl2,
150 MHz) 117.2, 118.6, 121.8, 123.9, 125.4, 125.6, 128.1,
129.3, 135.7, 142.1, 142.3, 150.0, 151.2, 155.8 ppm; IR
(KBr, cm−1) 3392, 3042, 2360, 1597, 1511, 1494, 1384,
1293, 1229, 1175, 1051, 889, 813, 748, 696, 511. Anal.
calcd for C30H24N6S: C, 71.98; H, 4.83; N, 16.79; S, 6.41.
Found: C, 71.70; H, 4.82; N, 16.64; S, 6.44. HRMS (EI)
calcd for C30H24N6S: 500.1783. Found: 500.1782. 3: mp
150–151°C; 1H NMR (CD2Cl2, 600 MHz) l 7.32–7.29
(m, 2H), 7.23–7.18 (m, 7H), 7.07–6.93 (m, 10H), 6.83 (t,
J=7.2 Hz, 1H), 6.61 (br, 2H), 5.65 (br, 2H); 13C NMR
(CD2Cl2, 150 MHz) 149.6, 148.8, 144.5, 142.6, 139.1,
138.1, 136.1, 134.6, 130.1, 129.0, 128.9, 126.4, 121.3,
120.9, 120.6, 119.3, 119.0, 118.2, 117.2, 115.5, 111.5,
106.6 ppm; IR (KBr, cm−1) 3388, 3027, 2362, 1737, 1596,
1513, 1294, 818, 748, 695, 485, 422. HRMS (EI) calcd for
C30H24N6S: 500.1783. Found: 500.1784. 11: mp 179–
13. Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C.
J.; van Leeuwen, P. W. N. M. Organometallics 1995, 14,
3081.
14. The geometry of 11 was determined by the nuclear Over-
hauser effect (NOE) between Ha and Hb, and the
2J(13C,15N) values15 of Ca and Cb (7.46 and 2.71 Hz,
respectively).
1
180°C; H NMR (CDCl3, 600 MHz) l 7.41 (dd, J=8.4,
7.2 Hz, 4H), 7.23 (t, J=7.2 Hz, 2H), 7.04 (s, 2H), 7.00 (d,
J=8.4 Hz, 4H); 13C NMR (CDCl3, 150 MHz) 120.6,
125.8, 126.2, 129.0, 148.8, 151.4, 155.4 ppm; IR (KBr,
cm−1) 3046, 2957, 1591, 1483, 1337, 1225, 1094, 825, 781,
724, 695, 498, 432. HRMS (EI) calcd for C18H12N4S:
1
316.0783. Found: 316.0784. 12: mp 193–194°C; H NMR
(CD2Cl2, 600 MHz) l 7.30 (dd, J=8.4, 7.2 Hz, 4H), 7.21
(s, 2H), 7.15 (d, J=8.7 Hz, 4H), 7.14 (d, J=8.4 Hz, 4H),
7.05 (d, J=8.7 Hz, 4H), 6.97 (t, J=7.2 Hz, 2H), 5.99 (s,
2H); 13C NMR (CD2Cl2, 150 MHz) 108.3, 115.8, 119.5,
15. Kalinowski, H.-O.; Berger, S.; Braun, S. Carbon-13 NMR
Spectroscopy; Wiley: Chichester, 1998; p. 572.