Facile synthesis, crystal structures, and high-spin cationic states of all-para-brominated oligo(N-phenyl-m-aniline)s

Article abstract of DOI:10.1021/jo0160571

Syntheses of both the dimer (3) and the trimer (4) of all-para-brominated poly(N-phenyl-m-aniline)s (2c) were achieved in a one-pot procedure from the parent nonbrominated oligomers and benzyltrimethylammonium tribromide [(BTMA)Br₃]. An X-ray crystallographic analysis revealed that 4 has a U-shaped structure, suggesting that 2c easily adopts helical structures. Furthermore, the redox properties were investigated by the UV-vis and EPR measurements. It was confirmed that the both 3 and 4 can be oxidized into the dications 3²⁺ and 4²⁺ with triplet spin-multiplicity.

Full text of DOI:10.1021/jo0160571

J . Org. Chem. 2002, 67, 491-498
491
F a cile Syn th esis, Cr ysta l Str u ctu r es, a n d High -Sp in Ca tion ic
Sta tes of All-pa r a -Br om in a ted Oligo(N-p h en yl-m -a n ilin e)s
Akihiro Ito,† Haruhiro Ino,† Kazuyoshi Tanaka,*,† Katsuichi Kanemoto,‡ and
Tatsuhisa Kato*,‡
Department of Molecular Engineering, Graduate School of Engineering, Kyoto University,
Sakyo-ku, Kyoto 606-8501, J apan, and Institute for Molecular Science,
Myodaiji, Okazaki 444-8585, J apan
a51053@sakura.kudpc.kyoto-u.ac.jp
Received August 25, 2001
Syntheses of both the dimer (3) and the trimer (4) of all-para-brominated poly(N-phenyl-m-aniline)s
(2c) were achieved in a one-pot procedure from the parent nonbrominated oligomers and
benzyltrimethylammonium tribromide [(BTMA)Br3]. An X-ray crystallographic analysis revealed
that 4 has a U-shaped structure, suggesting that 2c easily adopts helical structures. Furthermore,
the redox properties were investigated by the UV-vis and EPR measurements. It was confirmed
that the both 3 and 4 can be oxidized into the dications 32+ and 42+ with triplet spin-multiplicity.
In tr od u ction
It is well-known that triarylamines often give stable
cation radicals.1 In particular, tris(p-bromophenyl)-
aminium hexachloroantimonate (1+),2 generated by one-
electron oxidation of tris(p-bromophenyl)amine (TBPA,
1) using SbCl5, is one of the famous thermally stable
radicals and has long been used as a powerful one-
electron oxidant in organic synthetic chemistry.3
In view of their stability, triarylamine cation radicals
investigated in detail.5 However, the structural features
have not been clarified in their studies. On the other
hand, despite the stability of 1+, all-para-brominated
oligo(N-phenyl-m-aniline)s have not been hitherto pre-
pared to the best of our knowledge. In this paper, we
report on the synthesis, structures, and high-spin cationic
states of the dimer (3) and the trimer (4) of 2c, which
are expected to be thermally stable bis- and tris-cation
radicals.
have also become promising spin-containing molecular
units for exploitation of potential polymer-based organic
magnets. If such triarylamine cation radicals are con-
nected to each other via meta-linkage as shown below,
the resulting poly(cation radical) of poly(N-phenyl-m-
aniline) (2a ) is anticipated to have high-spin correlation,
leading to a polymer-based magnet.4 Therefore, chemical
and physical properties of oligo(N-phenyl-m-aniline)s and
their polycationic species are of interest from the view-
point of exploitation of organic high-spin polymers.
Recently, Hartwig and co-workers have succeeded in
preparation of several oligomers up to hexadecamer of
poly(N-anisyl-m-aniline)s (2b) and, furthermore, the
magnetic properties of their oxidized species have been
Resu lts a n d Discu ssion
Syn th esis. Synthesis of 3 and 4 was carried out by
the procedure shown in Scheme 1. The completely un-
substituted dimer and trimer, 5 and 6, were first pre-
pared using the Ullmann reaction from corresponding
arylamines and aryl halides. The selective bromination
at all para-positions succeeded by use of benzyltrimethy-
lammonium tribromide [(BTMA)Br3].6 Other powerful
brominating agents such as Br2 and tetrabutylammo-
† Kyoto University.
‡ Institute for Molecular Science.
(1) Forrester, A. R.; Hay, J . M.; Thomson, R. H. Organic Chemistry
of Stable Free Radicals; Academic Press: New York, 1968.
(2) Bell, F. A.; Ledwith, A.; Sherrington, D. C. J . Chem. Soc. 1969,
2720.
(3) Dapperheld, S.; Steckhan, E.; Brinkhaus, K. G.; Esch, T. Chem.
Ber. 1991, 124, 2557-2567 and references therein.
(4) (a) Ito, A.; Ota, K.; Tanaka, K.; Yamabe, T.; Yoshizawa, K.
Macromolecules 1995, 28, 5618. (b) Yoshizawa, K.; Takata, A.; Tanaka,
K.; Yamabe, T. Polym. J . 1992, 24, 857.
(5) (a) Louie, J .; Hartwig, J . F. Macromolecules 1998, 31, 6737. (b)
Goodson, F. E.; Hauck, S. I.; Hartwig, J . F. J . Am. Chem. Soc. 1999,
121, 7527.
10.1021/jo0160571 CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/03/2002

492 J . Org. Chem., Vol. 67, No. 2, 2002
Ito et al.
F igu r e 1. Molecular structure of 5.
Sch em e 1. P r ep a r a tion of Com p ou n d s 3 a n d 4
nium tribromide [(TBA)Br3]7 were met with failure. The
brominated products 3 and 4 were isolated as single
crystals suitable for X-ray analysis by slow evaporation
of the solvent from the reaction mixture. The recrystal-
lization of 5 from CH2Cl2 gave colorless needles suitable
for X-ray crystallographic study. Single crystal of 6 was
unavailable despite our several attempts.
Molecu la r Str u ctu r es of 3-5. The crystal of 5
contains two crystallographically independent but con-
formationally same molecules owing to its space group
(Cc). The molecular structure of 5 (Figure 1) is very
similar to that of N,N,N′,N′,N′′,N′′-hexaphenyl-1,3,5-
triaminobenzene.8 As has been investigated by Veciana
and co-workers, triphenylmethyl-based molecules have
the combined helicity due to their propeller-like struc-
ture.9 The same structural characterization is applicable
to the present triphenylamine-based molecules. In 5, the
molecule adopts an approximate Cs conformation (in
other words, a meso (P*,M*) form). On the other hand,
the crystal of 3 contains dichloromethane, one of the
components of the mixed solvents, in ratio of 1:1 with 3,
as shown in Figure 2. Interestingly, 3 is approximately
C2-symmetric (in other words, either (P,P) or (M,M) form),
while the degree of off-coplanarity in each phenyl group
remains unchanged regardless of existence of bromo
substituents. Figure 3 shows two kinds of views of the
molecular structure of 4. The conformation of 4 is of
either (M,P,P) or (P,M,M) form. As is evident from Figure
3b, 4 favors a U-shape conformation. This closely relates
to the fact that a nonnegligible quantity of cyclic oligo-
mers were obtained in the preparation of poly(N-aryl-m-
aniline) by Hartwig’s group.5
Electr och em ica l Stu d ies. Redox behaviors of these
oligomers were studied by cyclic voltammetry (CV) at
room temperature. The electrochemical data for 3-6 and
their related triarylamines are summarized in Table 1.
(6) Kajigaeshi, S.; Kakinami, T.; Inoue, K.; Kondo, M.; Nakamura,
H.; Fujikawa, M.; Okamoto, T. Bull. Chem. Soc. J pn. 1988, 61, 597.
(7) (a) Berthelot, J .; Guette, C.; Essayegh, M.; Desbene, P. L.;
Basselier, J . J . Synth. Commun. 1986, 16, 1641. (b) Berthelot, J .;
Guette, C.; Essayegh, M.; Desbene, P. L.; Basselier, J . J . Can. J . Chem.
1989, 67, 2061.
(8) Yoshizawa, K.; Chano, A.; Ito, A.; Tanaka, K.; Yamabe, T.; Fujita,
H.; Yamauchi, J .; Shiro, M. J . Am. Chem. Soc. 1992, 114, 5994.
(9) (a) Veciana, J .; Rovira, C.; Crespo, M. I.; Armet, O.; Domingo,
V. M.; Palacio, F. J . Am. Chem. Soc. 1991, 113, 2552. (b) Veciana, J .;
Rovira, C.; Ventosa, N.; Crespo, M. I.; Palacio, F. J . Am. Chem. Soc.
1993, 115, 57. (c) Sedo´, J .; Ventosa, N.; Ruiz-Molina, D.; Mas, M.;
Molins, E.; Rovira, C.; Veciana, J . Angew. Chem., Int. Ed. Engl. 1998,
37, 330. (d) Ventosa, N.; Ruiz-Molina, D.; Sedo´, J .; Rovira, C.; Tomas,
X.; Andre´, J .-J .; Bieber, A.; Veciana, J . Chem. Eur. J . 1999, 5, 3533.
First of all, both 5 and 6 exhibited only one irreversible
oxidation wave. In the reverse scan, some new peaks
appeared in both 5 and 6, indicating the reduction process
of the redox-active products generated by the follow-up
reactions. Moreover, in 6, a new oxidation peak was
observed at the lower potential (+0.66 V vs SCE) in the
second sweep. In a cyclic voltammetric study of a series
of 1,3-bis(diarylamino)benzenes, the protecting substit-
uents on the both central and peripheral phenyl rings
are found to be important to stabilize the dicationic

All-para-Brominated Oligo(N-phenyl-m-aniline)s
J . Org. Chem., Vol. 67, No. 2, 2002 493
Ta ble 1. Red ox P oten tia ls of 3-6 a n d th e Rela ted
Tr ia r yla m in esa
compd
E1°′
E2°′
compd
E1°′
1
+1.18d
+1.12
+1.13
+0.92b
6
9
10
+0.93b
+1.18d
+1.32d
3c
4c
5
+1.24
+1.57b
a
0.1M n-Bu4NClO4 in CH2Cl2, potential vs SCE, Pt electrode,
b
25 °C, scan rate 100 mV/s. Peak potential (irreversible oxidation
process). c Measured in PhCN. See ref 11.
d
F igu r e 2. Molecular structure of 3.
F igu r e 4. Cyclic voltammetry of compounds 3 and 4 in PhCN
solution at room temperature with scan rate 100 mV/s.
in Figure 4, two reversible redox waves of 3 were
observed in benzonitrile solution, suggesting generation
of the corresponding monocation and dication. However,
4 showed only one pair of the reversible redox wave
despite having the three redox-active amino groups. In
cross-conjugated system like 3 and 4, we often observe
the simultaneous multielectron-transfer process. To iden-
tify whether the observed redox processes are one- or two-
electron transfer, we determined the number of removed
electrons by controlled-potential coulometry. As a result,
the reversible redox process in 4 turned out to be two-
electron-transfer process, while each redox wave in 3
turned out to be a one-electron oxidation process. From
the standard potential of the related compounds, 9 and
10,11 it can be deduced that the two-electron oxidation
F igu r e 3. (a) Molecular structure and (b) packing diagram
of 4.
species.10 In this respect, the redox irreversibility of 5
and 6 was expected to some extent. On the other hand,
it was found that the Br-substituted oligomers 3 and 4
satisfy the criterion of the redox reversibility. As shown
(10) Yano, M.; Sato, K.; Shiomi, D.; Ichimura, A.; Abe, K.; Takui,
T.; Itoh, K. Tetrahedron Lett. 1996, 37, 9207.
(11) Schmidt, W.; Steckhan, E. Chem. Ber. 1980, 113, 577.

494 J . Org. Chem., Vol. 67, No. 2, 2002
Ito et al.
F igu r e 6. UV-vis spectra of the SbCl5-oxidized species of (a)
5 and (b) 6 in CH2Cl2 at room temperature. The broken line
indicates the spectrum before oxidation.
F igu r e 5. UV-vis spectra of the TFAA-oxidized species of
(a) 5 and (b) 6 in CH2Cl2 at room temperature. The broken
line indicates the spectrum before oxidation. The arrows
designate the increase of the band at 1 h after addition of
TFAA.
of 4 comes from two peripheral triarylamine units. More-
over, although assignment for the higher irreversible
oxidation potential of 4 is unknown at the present stage,
it probably relates to oxidation of the central triarylamine
unit. Finally, it was confirmed that the second oxidation
wave of 4 is irreversible even at -40 °C.
F igu r e 7. EPR spectrum of the TFAA-oxidized species of 6
in CH2Cl2 at room temperature.
TFAA is a weak oxidant for 5 and 6. In contrast with
TFAA, when SbCl5 was used for oxidation of 5 and 6 in
a CH2Cl2/trifluoroacetic acid (TFA) ()3/1 (v/v)) mixture,
the oxidation process was accomplished immediately and,
moreover, the absorption spectra of the SbCl5-oxidized
species differed much from those of the TFAA-oxidized
ones (Figure 6). Note that the spectra of 5 (and 6) before
oxidation showed a single additional band at 394 nm (and
392 nm) probably owing to TFA. Upon addition of a few
drops of neat SbCl5, the band at about 390 nm decreased,
and new and broad bands appeared in the lower energy
region: 5, λmax ) 641 and 870 nm; 6, λmax ) 687 nm.
These findings clearly indicate the formation of highly
π-conjugated compounds by the follow-up reactions. The
corroborating evidence was obtained from the EPR
spectrum of the oxidized solution (Figure 7). The observed
quintet spectrum was typical for benzidine cation radical
with an unpaired electron equally coupled to two nitrogen
atoms (aN ) 0.43 mT).12 This suggests that the further
UV-Visible a n d EP R Sp ectr a of Oxid ized Sp e-
cies. As has been described in the preceding section, it
was found that the generated cation radicals 5+ and 6+
are unstable and, subsequently, the follow-up reactions
occur. Hence, the oxidation process of 5 and 6 was
monitored by UV-vis spectroscopy. First of all, we
selected trifluoroacetic anhydride, TFAA, as an oxidant.
The neutral 5 (and 6) were colorless in a CH2Cl2 solution
that exhibits a single band at λmax ) 297 nm (and 299
nm). Next, the solution of 5 (and 6) was treated with neat
TFAA. After the addition of TFAA, two bands appeared
gradually: 5, λmax ) 379 and 569 nm; 6, λmax ) 377 and
588 nm (Figure 5). The slow oxidation indicates that
(12) (a) Dollish, F. R.; Hall, W. K. J . Phys. Chem. 1965, 69, 2127.
(b) Seo, E. T.; Nelson, R. F.; Fritsch, J . M.; Marcoux, L. S.; Leedy, D.
W.; Adams, R. N. J . Am. Chem. Soc. 1966, 88, 3498.

All-para-Brominated Oligo(N-phenyl-m-aniline)s
J . Org. Chem., Vol. 67, No. 2, 2002 495
Sch em e 2. Sch em a tic Oxid a tion P a th w a y of 4
oligomerization reactions between the generated cation
radicals 5+ (and 6+) took place because of their high spin
density at the ortho- and para-ring positions.13 Of the
resulting products, those containing benzidine moieties
are more easily oxidized than the parent 5 (and 6) and,
finally, undergo further oxidation to the benzidine cation
radical exhibiting the above-mentioned characteristic
EPR spectrum (Scheme 2). The appearance of the differ-
ent absorption spectra due to the different oxidants is
probably ascribed to the resulting oligomerized products.
Contrary to 5 and 6, the above oligomerization reaction
is difficult for all-para-brominated oligomers 3 and 4.
J udging from the oxidation potentials of 3 and 4, SbCl5
is pertinent to oxidize these compounds. Addition of less
than 1 equiv of SbCl5 into a CH2Cl2 solution of 3 (and 4)
yielded a blue solution showing a single EPR signal
without any hyperfine structures [∆Bpp ) 1.52 mT for
3+ (∆Bpp ) 1.57 mT for 4+)]. As shown in Figure 8, the
resulting solution for 3+ (and 4+) showed a single broad
band at 779 nm (790 nm), which is clearly different from
the spectra for the oxidized products of 5 (and 6). This
suggests that the cation radical of the all-para-bromi-
nated 3 (and 4) was highly stable at room temperature
in accordance with the results of the CV studies. Actually,
both 3+ and 4+ were isolated from the CH2Cl2 solution
by adding diethyl ether. However, we have not hitherto
succeeded in obtaining single crystals suitable for the
X-ray diffraction study.
As a result of the CV measurements, 3 and 4 are
expected to generate the di- or trication by excess of
SbCl5. The resulting EPR spectra in frozen CH2Cl2
solution of 3 (and 4) showed a similar single signal with
broad line width compared with 3+ (and 4+) [∆Bpp ) 1.95
mT for 3 (∆Bpp ) 2.80 mT for 4)] (Figure 9). More
noteworthy is that, in both samples, a weak transition
was observed in the ∆mS ) (2 region, clearly indicating
the presence of high-spin species. To identify the spin
multiplicity of this species, we adopted the pulsed EPR
method on the basis of the the fact that the magnetic
moments with distinct spin quantum numbers (S) precess
with their specific nutation frequency (ωn) in the presence
of a microwave irradiation field (B1) and a static magnetic
field (B0).14 If the microwave irradiation field (ω1 ) -γeB1)
is weak enough compared with the fine-structure param-
eter (ωD in units of frequency), the nutation frequency
(13) (a) Ito, A.; Miyajima, H.; Yoshizawa, K.; Tanaka, K.; Yamabe,
T. J . Org. Chem. 1997, 62, 38. (b) Ito, A.; Ono, Y.; Tanaka, K. J . Org.
Chem. 1999, 64, 8236.

496 J . Org. Chem., Vol. 67, No. 2, 2002
Ito et al.
F igu r e 9. EPR spectra of (a) 3 and (b) 4 oxidized by excess
SbCl5 in CH2Cl2 at 123 K. Inset: Spectra for the forbidden
∆mS ) (2 transition at 123 K.
F igu r e 8. UV-vis spectra of (a) 3 and (b) 4 oxidized by less
than 1 equiv of SbCl5 in CH2Cl2 at room temperature.
for a transition from |S, MS to |S, MS +1 is expressed
in good approximation as
ωn ) [S(S + 1) - MS(MS + 1)]1/2ω1
(1)
indicating that ωn can be scaled with the spin quantum
numbers S and MS in a unit of ωn ()ω1) for the doublet
species. Figure 10 shows the relation between the EPR
spectra observed at 5 K and its transient nutation spectra
in a 2-D contour representation. Namely, the projection
on the magnetic field axis roughly corresponds to the
usual EPR spectrum, while the projection on the fre-
quency axis corresponds to the nutation spectrum. The
intense peak observed at 341.0 mT (341.5 mT) is expected
to be the |1/2, +1/2 T |1/2, -1/2 transition of the doublet
species 3+ (4+) and had the nutation frequency of 30.0
MHz (30.0 MHz), indicating ω1 ) 30 MHz. On the other
hand, two peaks at 332.5 and 351.0 mT (339.5 and 344.5
mT) had the same nutation frequency of 43.8 MHz (43.9
MHz), suggesting the presence of a high-spin cationic
species of 3 (4). Here, the frequency ratio (ωn/ω1) of 43.8/
30.0 (43.9/30.0) is in good agreement with the ratio of
x
2 expected for |1, 0 T |1, (1 transition of the triplet
(14) For determination of spin-multiplicity for high-spin molecules
by using pulsed EPR technique, see: (a) Isoya, J .; Kanda, H.; Norris,
J . R.; Tang, J .; Bowman, M. K. Phys. Rev. 1990, B41, 3905. (b)
Astashkin, A. V.; Schweiger, A. Chem. Phys. Lett. 1990, 174, 595. (c)
Sato, K.; Yano, M.; Furuichi, M.; Shiomi, D.; Takui, T.; Abe, K.; Itoh,
K.; Higuchi, A.; Katsuma, K.; Shirota, Y. J . Am. Chem. Soc. 1997, 119,
6607. (d) Bock, H.; Gharagozloo-Hubmann, K.; Sievert, M.; Prisner,
T.; Havlas, Z. Nature 2000, 404, 267.
F igu r e 10. Field-swept electron spin nutation spectra of (a)
3 and (b) 4 oxidized by excess SbCl5 in CH2Cl2 at 5 K. ω1
corresponds to 30 MHz.

All-para-Brominated Oligo(N-phenyl-m-aniline)s
J . Org. Chem., Vol. 67, No. 2, 2002 497
F igu r e 11. Pulse sequence for the measurements of the electron spin nutation spectrum.
Ta ble 2. Su m m a r y of Cr ysta l Da ta , Da ta Collection , a n d Refin em en t P a r a m eter s for 3-5
3
4
5
formula
Mr
C
31H20Br6N2Cl2
C42H24Br9N3
1289.81
C60H48N4
825.07
970.84
cryst habit
cryst size (mm)
cryst system
space group
cell consts
a (Å)
colorless plate
0.91 × 0.24 × 0.06
monoclinic
P21/n
colorless plate
0.63 × 0.15 × 0.06
triclinic
colorless prismatic
0.50 × 0.45 × 0.30
monoclinic
P1h
Cc
16.003(4)
11.986(5)
18.377(4)
92.79(1)
109.68(2)
100.85(2)
3319(1)
4
1.943
74.65
1856.00
55.0
10.558(2)
20.992(3)
10.298(2)
25.192(2)
9.811(2)
19.412(5)
b (Å)
c (Å)
R (deg)
â (deg)
106.41(2)
104.48(1)
γ (deg)
V (Å3)
2137.7(7)
2
2.004
84.98
1224.00
50.0
4645(1)
8
2.359
1.37
3488.00
55.0
Z
Dcalcd (g cm-3
)
µ (mm-1
F(000)
2θmax
)
no. of reflcns
measd
8272
6392
4467
unique
Rint
7994
0.072
5947
0.053
4345
0.031
Params
R (Rw)
390
511
578
0.063 (0.069) [I > 3.00σ(I)]
1.10
0.075 (0.082) [I > 3.00σ(I)]
0.95
0.056 (0.031) [I > 2.00σ(I)]
0.15
max ∆F (e Å-3
)
state from eq 1. As a result, the high-spin species
generated by excess of SbCl5 can be regarded as 32+ (42+).
Therefore, it was found that the broad EPR spectra
shown in Figure 9 should be viewed as overlap of the
doublet and triplet spectra. The reason the quartet state
expected for 43+ was not observed is probably due to
weakness of the oxidant employed. It is noteworthy that
the D values of 32+ and 42+, which cannot be determined
from the usual EPR measurements (Figure 9), can be
approximately estimated to be 9.25 and 2.25 mT from
the peak-to-peak width at ωn ) ca. 44 MHz. From these
values, the average distances between two radical centers
of 32+ and 42+ are roughly calculated to be 6.7 and 10 Å,
respectively, by using the so-called point dipole ap-
proximation. The estimated distance of 6.7 Å is a little
longer than the distance between two nitrogen atoms in
3. On the other hand, 10 Å is in good agreement with
the distance between the two peripheral nitrogen atoms
if 42+ adopts an expanded conformation in contrast to the
U-shape conformation of the X-ray structure. This sug-
gests that the positive charge in 42+ is localized on the
two peripheral triphenylamino moieties and, moreover,
42+ adopts a linear conformation so as to diminish the
intramolecular Coulomb repulsion.
the Br-unsubstituted 5 and 6 caused complicated follow-
up reactions toward a mixture of the higher oligomeric
products containing benzidine cation radical moieties. On
the other hand, the Br-substituted 3 and 4 gave ther-
mally stable and isolable cation radicals. Furthermore,
it was confirmed that the oxidation of 3 and 4 in CH2Cl2
with an excess of SbCl5 generates the high-spin bis-cation
radicals 32+ and 42+. The reason for difficulty of additional
electron removal from 42+ resides probably on the in-
crease of oxidation potentials due to polybromo substitu-
tions.
Exp er im en ta l Section
Gen er a l P r oced u r es. Commercial grade reagents were
used without further purification. Elemental analyses were
performed by Microanalytical Center, Kyoto University.
P h ysica l Mea su r em en ts. The CV measurements were
performed with a combination of Hokuto-Denko HA-305 po-
tentiostat, HB-104 function generator, and Yokogawa 3025 XY
recorder with a three-electrode cell using Pt wires as the
working and the counter electrodes and an Ag/0.01 M AgNO3
(MeCN) as the reference electrode in a solution of 0.25 mM of
5 (or 6) and 0.1 M n-Bu4NClO4 in CH2Cl2 (25 °C, scan rate
100 mV s-1). On the other hand, a BAS CV-50W voltammetric
analyzer was employed for the CV and coulometry measure-
ments of 3 and 4 in PhCN (0.4 mM). The observed potentials
were corrected with reference to ferrocene added as an internal
standard after each measurement. UV-vis spectra were
recorded on a Shimadzu UV-2200 spectrometer. EPR spectra
were measured using a J EOL J ES-RE-2X X-band spectrom-
eter. Pulsed EPR measurements were carried out on a Bruker
ELEXES E580 X-band FT ESR spectrometer. The microwave
pulse sequence used is shown in Figure 11. For the transient
nutation experiment, the two-pulse electron spin-echo signal
S(t1) was detected by increasing the width (t1) of the nutation
Con clu sion s
We have shown that the use of (BTMA)Br3 leads
selectively and completely to Br substitution at all the
para positions of oligo(N-phenyl-m-aniline)s. The U-
shaped structure of 4 suggests that the polymerization
process to poly(N-aryl-m-aniline)s entails the formation
of cyclic oligomers and, moreover, the resulting polymer
readily adopts helical structures. The oxidized species of

498 J . Org. Chem., Vol. 67, No. 2, 2002
Ito et al.
pulse. We employed phase cycles to suppress unwanted signals
and artifacts which arise from an inaccurate pulse length. The
observed signal S(t1, B0) as a function of the external magnetic
field B0 is converted into a nutation frequency domain S(ωN,
B0) spectrum by Fourier transformation along the t1 direction,
as shown in Figure 10.
stand for 1 day. The precipitated white crystals were filtered
out, and the inorganic impurity was washed out with a
quantity of water. The resulting crystals were, furthermore,
washed with a portion of CHCl3. Colorless plates (0.47 g, 67%)
1
were obtained. Mp: 271-272 °C. H NMR (CDCl3, 270 MHz)
[δ (ppm)]: 5.30 (s, 1H), 6.78 (d, J ) 8.8 Hz, 8H); 7.33 (d, J )
8.8 Hz, 8H); 7.89 (s, 1H). 13C NMR (CDCl3, 67.5 MHz) [δ
(ppm)]: 115.7, 120.7, 119.9, 123.6, 132.4, 132.7, 139.7, 145.0,
145.5. Anal. Calcd for C30H18N2Br6‚C1H2Cl2: C, 38.35; H, 2.08;
N, 2.89. Found: C, 38.14; H, 2.11; N, 2.85.
N,N,N′,N′-Tetr a p h en yl-1,3-ben zen ed ia m in e (5). Diphe-
nylamine (8.60 g, 50.8 mmol), 1,3-dibromobenzene (6.00 g, 25.4
mmol), CuI (0.48 g, 2.5 mmol), 18-crown-6 (0.66 g, 2.5 mmol),
and K2CO3 (7.00 g, 50.6 mmol) were heated together at 200
°C for 24 h with stirring under N2 atmosphere. The reaction
mixture was poured into ethyl acetate, and the inorganic
impurity was removed by filtration. After evacuation of ethyl
acetate, the remaining mixture was column-chromatographed
on silica gel (eluent: n-hexane) to afford 5 (Rf ) 0.37) as a
4,4′,4′′,6,6′-P en t a b r om o-3,3′-b is[b is(4-b r om op h en yl)-
a m in o]tr ip h en yla m in e (4). To a mixed solution (CH2Cl2, 5
mL; MeOH, 2 mL) of 6 (0.26 g, 0.45 mmol) was added K2CO3
(0.55 g, 4.0 mmol) and then a mixed solution (CH2Cl2, 5 mL;
MeOH, 2 mL) of benzyltrimethylammonium tribromide (1.58
g, 4.05 mmol) dropwise with stirring. After being stirred for 1
h until the orange color faded away, the reaction mixture was
allowed to stand for 1 day. After evaporation of the solvent,
the residue was separated into the aqueous and CH2Cl2 layers.
The CH2Cl2 solution was dried over MgSO4. After evaporation
of the solvent, the resulting yellow solids were recrystallized
from CH2Cl2-MeOH (5:2). Yellow plates (0.37 g, 64%) were
obtained. Mp: 257-258 °C. 1H NMR (CDCl3, 270 MHz) [δ
(ppm)]: 6.60 (d, J ) 8.6 Hz, 2H), 6.64 (s, 2H), 6.71 (d, J ) 8.9
Hz, 8H), 7.27 (d, J ) 8.6 Hz, 2H), 7.30 (d, J ) 8.9 Hz, 8H);
7.80 (s, 2H). 13C NMR (CDCl3, 67.5 MHz) [δ (ppm)]: 115.7,
116.1, 118.3, 118.8, 123.2, 123.7, 129.7, 132.3, 139.6, 140.5,
144.5, 144.9, 145.0, 145.2. Anal. Calcd for C42H24N3Br9: C,
39.11; H, 1.88; N, 3.26; Br, 55.76. Found: C, 38.78; H, 1.72;
N, 3.09; Br, 58.09.
X-r a y Str u ctu r a l An a lysis of 3-5. Single-crystal diffrac-
tion experiments were carried out at room temperature on a
Rigaku AFC7R four-circle diffractometer equipped with graph-
ite-monochromated Mo KR radiation using the ω 2θ scan
technique. The data were corrected for Lorentz and polariza-
tion effects. In addition, a ψ-scan empirical absorption was
applied for 3 and 4 (several reflections; minimum, maximum
transmission 0.23, 1.00 for 3 and 0.47, 1.00 for 4). The
structures were solved by direct methods using SHELXS 8615
(for 3 and 4) and SAPI 9116 (for 5), expanded using DIRDIF92.17
The non-hydrogen atoms were refined by full-matrix least-
squares analysis with the anisotropic thermal parameters.
After several cycles of refinements, the position of the H atoms
were calculated and fixed. All the calculations were performed
using teXsan crystallographic software package of Molecular
Structure Corp.18 Crystal data and experimental details are
listed in Table 2. Full structural information has been depos-
ited with the Cambridge Crystallographic Data Centre.19
1
white solid in 27% yield. Mp: 140-141 °C. H NMR (CDCl3,
300 MHz) [δ (ppm)]: 6.65 (dd, 2H), 6.87 (t, 1H); 6.95 (tt, 4H);
7.05 (m, 9H); 7.20 (m, 8H). 13C NMR (CDCl3, 75 MHz) [δ
(ppm)]: 118.3, 119.7, 122.6, 124.0, 129.1, 129.7, 147.5, 148.5.
Anal. Calcd for C30H24N2: C, 87.35; H, 5.86; N, 6.79. Found:
C, 87.27; H, 5.65; N, 6.76.
3,3′-Din itr otr ip h en yla m in e (7). 3-Iodonitrobenzene (6.22
g, 25.0 mmol), aniline (1.00 g, 10.7 mmol), CuI (0.48 g, 2.5
mmol), 18-crown-6 (0.53 g, 2.0 mmol), K2CO3 (3.45 g, 25.0
mmol), and o-dichlorobenzene (5 mL) were heated together at
180 °C for 24 h with stirring under N2 atmosphere. The
reaction mixture was poured into ethyl acetate, and the
inorganic impurity was removed by filtration. After evacuation
of ethyl acetate, the remaining mixture was column-chromato-
graphed on silica gel (eluent: 1:4 ethyl acetate-n-hexane) to
afford 7 (Rf ) 0.53) as a brown solid in 45% yield. 1H NMR
(CDCl3, 90 MHz) [δ (ppm)]: 7.08-7.40 (m, 9H), 7.88 (m, 4H).
Anal. Calcd for C18H13N3O4: C, 64.47; H, 3.91; N, 12.53.
Found: C, 64.60; H, 3.79; N, 12.56.
3,3′-Dia m in otr ip h en yla m in e (8). 7 (1.47 g, mmol) dis-
solved in MeCN (35 mL) at 50 °C was added quickly into a
hot solution (ca. 50 °C) of SnCl2 in concentrated HCl (24 mL)
with stirring. After being stirred for 1 h at ca. 60 °C, the
resulting mixture was made alkaline enough so as not to
deposit inorganic white colloids and extracted with Et2O. The
Et2O solution was dried over MgSO4. After column chroma-
tography on silica gel (eluent: 1:1 ethyl acetate-n-hexane), 8
(Rf ) 0.51) was obtained as a white solid (yield 89%). 1H NMR
(CDCl3, 90 MHz) [δ (ppm)]: 3.90 (br s, 4H), 5.93-7.27 (m,
13H). Anal. Calcd for C18H17N3: C, 78.52; H, 6.22; N, 15.26.
Found: C, 78.03; H, 6.58; N, 15.12.
3,3′-Bis(d ip h en yla m in o)tr ip h en yla m in e (6). 8 (0.73 g,
2.7 mmol), iodobenzene (10.8 g, 53.0 mmol), CuI (1.00 g, 5.2
mmol), and K2CO3 (1.50 g, 10.9 mmol) were heated together
at 180 °C for 64 h with stirring under N2 atmosphere. The
reaction mixture was poured into ethyl acetate, and the
inorganic impurity was removed by filtration. After evacuation
of ethyl acetate, the remaining mixture was column-chromato-
graphed on silica gel (eluent: 1:9 ethyl acetate-n-hexane) to
afford 6 (Rf ) 0.77) as a pale yellow solid in 38% yield. Mp:
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research from the Ministry
of Education, Science, and Culture of J apan.
J O0160571
1
121-122 °C. H NMR (CDCl3, 270 MHz) [δ (ppm)]: 6.66 (m,
(15) Sheldrick, G. M. SHELXS 86, Program for the Solution of
Crystal Structures, University of Go¨ttingen, 1986; Acta Crystallogr.,
Sect. A 1990, 46, 467.
(16) Hai-Fu, F. SAPI91, Structure Analysis Programs with Intel-
ligent Control; Rigaku Corp.: Tokyo, J apan, 1991.
(17) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits J . M. M.; Smykalla, C. DIRDIF
program system; Technical Report of the Crystallography Laboratory,
University of Nijmegen: Nijmegen, The Netherlands, 1992.
(18) TEXSAN 1.8, Crystal Structure Analysis Package; Molecular
Structure Corp.: The Woodlands, TX, 1997.
(19) Supplementary publication nos. CCDC-167826 (3), -167825 (4),
and -167824 (5) can be obtained on request from the Director,
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB12 1E2, U.K.
4H), 6.84-7.22 (m, 29H). 13C NMR (CDCl3, 67.5 MHz)
[δ (ppm)]: 118.5, 118.6, 119.9, 122.4, 122.7, 123.5, 124.1, 129.0,
129.1, 129.7, 147.3, 147.5, 148.3, 148.6. Anal. Calcd for
C
42H33N3: C, 87.01; H, 5.74; N, 7.25. Found: C, 86.50; H, 5.99;
N, 7.08.
4,6-Dib r om o-1,3-b is[b is(4-b r om op h en yl)a m in o]b en -
zen e (3). To a mixed solution (CH2Cl2 5 mL, MeOH 2 mL) of
5 (0.30 g, 0.73 mmol) was added K2CO3 (0.60 g, 4.4 mmol) and
then a mixed solution (CH2Cl2, 5 mL; MeOH, 2 mL) of
benzyltrimethylammonium tribromide (1.70 g, 4.36 mmol)
dropwise with stirring. After being stirred for 1 h until the
orange color faded away, the reaction mixture was allowed to