Abnormal bromination reaction selectivity of 5-diarylamino-2-methylbenzo[b] thiophene caused by a non-planar conjugated model: Synthesis and theoretical calculation

Article abstract of DOI:10.1016/j.molstruc.2012.07.054

5-Diarylamino-2-methylbenzo[b]thiophene was a new kind of triphenylamine-based charge-transporting material. For further modification of the compounds, bromination selectivity was studied through experiments and molecular simulation using Gaussian 09 program under B3LYP/6-311G (d, p) aided by Gaussian View 05 and Multiwfn Program. The results showed that bromination of 5-diarylamino-2-methyl-benzo[b]thiophene would occurred at an abnormal positions (4- and/or 4′-position) rather than at the normal position (3-position), which was different from those benzo[b]thiophene derivatives with simple 5-substitutes reported in literatures. The abnormal selectivity resulted from a special electron structure in which there was an interfinger-like frontier orbital or a special non-planar conjugated model. Electrons would be donated to the o- and p-positions of linked aromatic rings by this manner of electron delocalization, so that TPA unit rather than thiophene ring became the main factor in the selectivity, and reaction active energy at 4-position was lowest. The results were confirmed by the synthesis of three 4-Br and/or 4′-Br derivatives, compound 4, 5 and 6. Single crystal X-ray diffraction of compound 6 gave conclusive evidence on the abnormal selectivity.

Full text of DOI:10.1016/j.molstruc.2012.07.054

Journal of Molecular Structure 1032 (2013) 126–132
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
‘‘Abnormal’’ bromination reaction selectivity of 5-diarylamino-2-methylbenzo[b]
thiophene caused by a ‘‘non-planar’’ conjugated model: Synthesis and theoretical
calculation
b
a
b
Bian-Peng Wu a, , Mei-Li Pang , Ting-Feng Tan , Ji-Ben Meng
⇑
a School of Science, Tianjin Institute of Urban Construction, No. 26, Jinjing Road, Tianjin 300384, China
b Department of Chemistry, Nankai Univesity, No. 94, Weijin Road, Tianjin 300070, China
h i g h l i g h t s
"
"
"
"
"
The molecular simulation of TPA-based compounds having a benzo[b]thiopheng unit was performed.
‘‘Abnormal’’ bromination selectivity of the compounds was predicted.
Four new compounds were synthesized.
One of the ‘‘abnormal’’ products was characterized by single-crystal X-ray diffraction.
The primary cause for the ‘‘abnormal’’ selectivity was explained by a ‘‘non-planar’’ conjugated model.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 May 2012
Received in revised form 27 July 2012
Accepted 31 July 2012
Available online 10 August 2012
5-Diarylamino-2-methylbenzo[b]thiophene was a new kind of triphenylamine-based charge-transport-
ing material. For further modification of the compounds, bromination selectivity was studied through
experiments and molecular simulation using Gaussian 09 program under B3LYP/6-311G (d, p) aided
by Gaussian View 05 and Multiwfn Program. The results showed that bromination of 5-diarylamino-2-
methyl-benzo[b]thiophene would occurred at an ‘‘abnormal’’ positions (4- and/or 40-position) rather than
at the ‘‘normal’’ position (3-position), which was different from those benzo[b]thiophene derivatives with
simple 5-substitutes reported in literatures. The ‘‘abnormal’’ selectivity resulted from a special electron
structure in which there was an ‘‘interfinger-like’’ frontier orbital or a special ‘‘non-planar’’ conjugated
model. Electrons would be donated to the o- and p-positions of linked aromatic rings by this manner
of electron delocalization, so that TPA unit rather than thiophene ring became the main factor in the
selectivity, and reaction active energy at 4-position was lowest. The results were confirmed by the syn-
thesis of three 4-Br and/or 40-Br derivatives, compound 4, 5 and 6. Single crystal X-ray diffraction of com-
pound 6 gave conclusive evidence on the abnormal selectivity.
Keywords:
Benzothiophene
Triarylamine
Bromination
Molecular simulation
Electrophilic substitution
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
used in the preparation of photochromic materials [5–7] and phar-
maceutical intermediates [8].
Triphenyamine (TPA) is an important molecule which has a ba-
sic structure of charge-transport function. The compounds having
TPA unit are a kind of useful organic semiconductor materials in
the field of electro-luminescence [1]. However, TPA itself subjected
to greater limitations in actual applications for its low melt point,
no easy to form a film, easy to crystallize and be oxidized. The mol-
ecules modified with TPA unit could also be used as organic dye
[2]. A lot of research had focused on the modification of TPA
[3,4]. The compounds having benzo[b]thiophene unit were often
When TPA and benzo[b]thiophene units were combined in one
molecule, a new series of functional molecules were expected to
be obtained. 5-Diarylamino-2-methylbenzo[b]thiophene had been
prepared by introducing a diarylamino into the 5-position of 2-
methyl-benzo[b]thiophene in our previous works. According to
the experiments in literatures [9–18], 5-substituted-2-meth-
ylbenzo[b]thiophene derivatives (Fig. 1a) generally had a fixed ac-
tive position named as ‘‘normal’’ position (3-position of thiophene
ring), whatever the 5-substituent was electron-accepting or elec-
tron-donating group (Table 1) [9–18]. The relatively higher activity
of electrophilic substitution of thiophene ring may be the reasonable
explanation for the selectivity. In this paper, the bromination of
⇑
Corresponding author. Tel.: +86 22 23085199; fax: +86 22 23509933.
E-mail address: bianpeng-wu@163.com (B.-P. Wu).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.07.054

B.-P. Wu et al. / Journal of Molecular Structure 1032 (2013) 126–132
127
is expected to deduce reliable description of complex systems. The
researches on Fukui function, especially condensed Fukui function
(CFF) being used as reactive parameters, have attracted widespread
attentions [19]. CFF had been successfully applied to predict the ac-
tive sites of mono-substituted and di-substituted benzene in elec-
trophilic substitution of aromatic compounds, which is very
consistent with experiments and organic chemistry concepts
[20–22].
We performed the molecular simulation of 5-substituted-2-
methyl-benzo[b]thiophene using Gaussian 09 Program [23] aided
by Gaussian View 05 Software and Multiwfn Program [24]. Some
related compounds had been synthesized (Fig. 1b and c) and were
characterized by means of 1H NMR, 13C NMR and HRESI-MS. One
crystal structure was determined for further confirmation.
Fig. 1. 5-Substituted-2-methylbenzo[b]thiophene derivatives.
Table 1
Electrophilic substitution reactions of 5-substituted-2-methylbenzo[b]thiophene
reported in literatures.
–R
Bromination
Acetylation
Product (yield)
2. Results and discussion
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
½13; 14; 15ꢀ
pffiffiffiffiffiffiffiffi
½13ꢀ
pffiffiffiffiffiffi
–H
3-Br (63–95%), 3-acetyl (30–40%)
3-Br(b), 3-acetyl (77%)
3-Br(68%)
3-Br(b), 3-acetyl (93%)
3-Br(b)
3-Br(b)
½9ꢀ
pffiffiffiffiffiffiffiffi
½10ꢀ
–CH3
2.1. Molecular simulation
pffiffiffiffiffiffiffiffi
½16ꢀ
a
–OCH3
–Br
pffiffiffiffiffiffiffiffi
½12ꢀ
pffiffiffiffiffiffiffiffi
½11ꢀ
a
pffiffiffiffiffiffiffiffi
½17ꢀ
Theoretical calculations were performed by a fully first-princi-
ples scheme combining DFT with B3LYP/6-311G (d, p) method
[25]. Geometric optimizations and electronic structures are calcu-
lated using linear combinations of atomic orbitals as basis set.
Because the bromination of the title compounds occurred in the
aromatic ring of benzo[b]thiophene, the reaction belonged to elec-
trophilic substitution, and the distribution of electrons involved in
the reaction process would be the key to the question.
–COOCH3
–NH2ꢁHCl
–NO2
pffiffiffiffiffiffiffiffi
½18ꢀ
a
pffiffiffiffiffiffiffiffi
½19ꢀ
a
3-Br (64%)
a
Not reported.
b
Not given in abstract and original text not available for us.
5-diarylamino-2-methylbenzo[b]thiophene was investigated in or-
der to make additional modification of novel compounds.
Generally, the atomic charge at any possible reactive site was
usually calculated to explain reaction selectivity of electrophilic
substitution. Mulliken atomic charge and NPA (natural population
analysis) charge are the two primary forms of atomic charge,
which results from two different theories and models. According
to the theory of molecular simulation, NPA atomic charge is more
reasonable than Mulliken atomic charge. After geometric
optimizations by Gaussian Program under proper level of calcula-
tion, NPA charge could be calculated. The larger negative value
would indicate greater activity in electrophilic substitution. Con-
clusions were relatively consistent with experiments and some
experiential laws based on electronic effects of substitutes for
some simple systems, such as mono-substituted benzene or
heterocyclic compounds [25]. But, it was not always the case,
especially for some rather complex systems.
In order to determine if the calculation method was appropriate
for 5-substituted-2-methylbenzo[b]thiophene system, some
compounds with simple substitutes were firstly selected for calcu-
lation. It was found that, if atomic charge was only taken for the
prediction of reaction selectivity, the conclusions were not satis-
factorily consistent with reported experiments, and sometimes
contradictory. Some data resulted from molecular simulation was
not listed in this paper. A reasonable explanation may be that
As it was known to us, amino or substituted amino was usually
strong active group for the electrophilic substitution of aromatic
ring. When diarylamino was attached to the 5-position of 2-meth-
ylbenzo[b]thiophene (Fig. 1b and c), a question would be put for-
ward: whether the reaction still had the ‘‘normal’’ position
selectivity as usual. Because there were two typical structure units
(TPA and benzo[b]thiophene units) in the molecule, it seemed
much more indecisive to predict the selectivity according to some
experiential laws in organic chemistry. Therefore, bromination
might form various products. Which was the main product in the
synthesis and whether it had the practical value? By this token,
it should be worth understanding the structure–activity relation-
ships of this molecular system both for theoretical research and de-
sign of new materials.
Semi-empirical method, such as resonance theory, and theoret-
ical calculations (molecular simulation) are the two ways to pre-
dict the selectivity of electrophilic substitution. For simple
aromatic systems, resonance theory can give reasonable prediction
according to the stability of resonance hybrid in most cases. Along
with the development of computational chemistry, theoretical cal-
culation based on existing basis sets instead of experiments in lab
Table 2
Electron distribution and the relatively more active sites.
–R
D
qi
Most active sites based on isosurface The sitesa related to
(fꢂ)
HOMO
C3/C4/C6/C7/C20/C30/C40
–CH3
–OCH3
–Br
ꢂ0.32682/ꢂ0.30156/ꢂ0.19631/ꢂ0.22757
ꢂ0.25060/ꢂ0.32376/0.143025/ꢂ0.209114
ꢂ0.12879/ꢂ0.12983/ꢂ0.03371/ꢂ0.09741
ꢂ0.13735/ꢂ0.17219/ꢂ0.13796/ꢂ0.10477/ꢂ0.17615/ꢂ0.08003/
ꢂ0.20716
3-
4-
3-
3-
3-
(4-)
–N, N-diphenylamino
40-, (20-)b, 4-,
4-, 40-, (20-, 6-)b
–N, N-bis(4-tert-butylphenyl)
amino
ꢂ0.13497/ꢂ0.17108/ꢂ0.14090/0.08192/ꢂ0.17125/ꢂ0.08552/–/
4-, (20-)b
4-, (40-, 20, 6-)b
a
Higher energy occupied MOs (related to more reactive site).
No product from experiment.
b

128
B.-P. Wu et al. / Journal of Molecular Structure 1032 (2013) 126–132
Fig. 3. Electron distribution of HOMO’s: (a) HOMO (orbital No. 56) of 5-Br
Fig. 2.
Dqi based on NPA of 5-substituted-2-methylbenzo[b]thiophene derivatives
derivative (isovalue = 0.015). (b) HOMO (orbital No. 47) of 5-OCH3 derivative
(isovalue = 0.020). (c) HOMO (orbital No. 83) of compound 2 (isovalue = 0.010). (d)
HOMO (orbital No. 115) of compound 3 (isovalue = 0.005).
(in atom unit). The circle marks are the more active sites according to experiments.
NPA atomic charge of electrically neutral molecule (N electrons
system) could not be perfectly reasonable to describe the situation
when substrate was attacked by electrophillic reagents. The key
revealed that 4- (or 40) and 3-positions were really the competitive
sites in any way, and 4- (or 40-) position should be more active site
than 3-, except for 5-CH3 system. It seemed that the conclusion is
not exactly consistent with experiments (as shown in Table 1). In
this case, the frontier molecular orbital theory proposed by Fukui
could make some revision and gave a more reasonable conclusion
[26]. According to the theory, reaction selectivity should be related
to HOMO, LUMO and the orbits nearby. When the occupied orbit
held higher energy level and meanwhile distributed around the re-
lated atom, this atom would be most likely the reaction position
(Fig. 3). For 5-Br and 5-OCH3 systems, the activity of 3-position
comes from the distribution of HOMO in which heteroatom (S)
contributed more electron to 3-position. This is also the reason
for the higher activity of thiophene ring.
active intermediate in bromination was
properly represented by Nꢂ1 electrons system. In this situation,
the calculation using Fukui Function (fꢂ
(N) ꢂ (Nꢂ1) =
would be a better choice under the same level for the analysis of
electron density difference ( (N) and
) [25]. fꢂ,
(Nꢂ1) are Den-
sity Functions in three dimension. The (N) and
(Nꢂ1) presents
r-complex that was more
=
q
q
Dq)
D
q
q
q
q
q
the Density Function of the systems with N electrons and Nꢂ1
electrons, respectively. The reaction selectivity could be showed
in two ways as follows.
According to NBO (natural bond orbital) Theory [25], when the
Fukui Function converges to a single atom in the molecule, the va-
lue of fꢂ became the value of fiꢂðfiꢂ ¼ qiðNÞ ꢂ qiðN ꢂ 1ÞÞ, which is
equals to the difference (
Nꢂ1 electrons systems. The
charge were shown in Table 2 and Fig. 2. The calculation results
D
qi) of NPA atomic charge with N and
The isosurface and contour of f– could intuitively show the sites
with more net surplus of electronic distribution density. Electro-
philic reagent usually tends to attack at the site (marked with
D
qi calculated based on NPA atom
Fig. 4. Isosurface and contour of f– for compound 2 and 3. (a) The f– isosurface of compound 2, iso-value = 0.003, the yellow circle marks the possible reaction position or the
‘‘abnormal’’ reaction selectivity. (b) The f– iso-surface of compound 3, iso-value = 0.0026, the yellow circle marks the possible reaction position. (c) The contour (benzene ring)
of compound 2. (d) The f– contour (benzothiophene ring) of compound 3. (For interpretation of the references to color in this figure legend, the reader is referred to the web
version of this article.)

B.-P. Wu et al. / Journal of Molecular Structure 1032 (2013) 126–132
129
Fig. 5. Electron distribution of compound 2. (a) The isosurface of the ‘‘interfinger-
like’’ HOMO (orbital No. 83) of compound 2, isovalue = 0.004. (b) The tilt of the most
part of HOMO and the plane of benzo[b]thiophene when viewed at isovalue = 0.04.
(c) The tilt of the most part of HOMO and the plane (C17–C22, benzene ring) of one
of the two benzene rings when viewed at isovalue = 0.04; The tilt angle is about 45°.
Fig. 6. Total energy of r-complexes (in atom unit).
windmill-like structure, which had been confirmed by the X-ray
diffraction data of 2-methyl-4-bromo-5-bis(4-tertiary butyl-
phenyl) aminobenzo[b]thiophene 6 and some reported works.
The HOMO had 99.99% of p orbital component (Figs. 4c and 5a)
with 86.13% of occupation ratio, which was occupied by the lone
pair electrons of N atom. However, the occupation of N atom in
TPA was fairly lower. In other word, the N atom adopted sp2
hybridization and 13.87% of the occupation shared with other
atoms, so that the value of valence of the N atom was more than
(d) Electron delocalization through
p-orbits, isovalue = 0.023. (e) Electrostatic
potential map.
circle). For 5-diarylamino-2-methylbenzo[b]thiophene, there was
not only one possible site in the bromination. 4-, 40-, 3-, 20- and
6-positions were the competitive positions. In Fig. 4, it could be
found from the isosurface and contour of fꢂ that 6- and 3-positions
were less active, but 4-, 40- and 20-positions (o- and p-of the N
atom) more active. If the reaction was carried out at lower temper-
ature and lower active bromination reagent was used, more selec-
tivity would be expected. In this sense, reaction selectivity was
really ‘‘abnormal’’.
In most cases, the N atom of amino group commonly tended to
stay in sp3 hybridization (triangle cone conformation) or in be-
tween sp3 and sp2 (such as in aniline). According to the calculation
results, 5-diarylamino-2-methyl-benzo[b]thiophene existed in
3, reaching 5.47. Except for the three
r-bond, there were some
additional bonds between the N atom and linked C atoms. It was
the main difference between diarylamino in TPA structure and
common amino. In 5-diarylamino-2-methylbenzo[b]-thiophene,
the N atom as a center and the three bonded C atoms lied in a plane
as show in Fig. 4. But, the three aromic rings and the center N atom
were in windmill-like conformation. In the HOMO shown in Fig. 5b
and c, there were about 45° tilt angle between the plane and linked
Scheme 1. Synthesis of related compounds.

130
B.-P. Wu et al. / Journal of Molecular Structure 1032 (2013) 126–132
aromic rings. As a result, the aromic rings were approximately ver-
tical. Viewed from the distribution of the orbit, it was even more
incredible that this type of orbit did not have face symmetry if
iso-value was made to enough small to show the more complete
view. So that, the HOMO was named ‘‘interfinger-like’’ orbit
(Fig. 5a). It seemed to be not easy to form normal p–
p conjugate.
In normal p– conjugate, the symmetry axis of p orbit and the aro-
p
matic ring ought to be perpendicular to each other so that the
greatest degree of overlap could achieve. It was absolutely not
the ordinary p–p conjugation. In other words, a special no-planar
conjugated model may exist in this system. In the model, electrons
could still delocalize among the three aromatic rings (Fig. 5d). As a
result, 4-, 6-, 20- and 40-positions all could gain the electron dona-
tion from N atom. These positions held more distribution of net
negative charge (Dqi) as shown in Figs. 3 and 4c and d. In addition,
the electrostatic potential map (Fig. 5e) also revealed that 4-posi-
tion is more vulnerable to be attacked by electrophillic reagent
than 3-position.
As it is known, the
formed in the process of electrophilic substitution. According to
Hammond Postulate, the energy level of -complex reflects the le-
vel of active energy. Active energy is the primary factor to deter-
mine the selectivity. The total energy of related -complexes can
be evaluated by calculation based on optimized structures
(Fig. 6). Compared with any other -complexes, 4-Br– -complex
r-complex was the active intermediate
r
Fig. 7. 1H NMR of compounds 2, 3, 4, 5, 6, 8 and 9 ꢃ the peaks resulting from the H’s
at 3-position; ꢃꢃ the peaks resulting from the H’s at 6- and 7-position; ꢃꢃꢃ the peaks
resulting from CHCl3.
r
r
r
had lowest energy (about -3837.55514 atom unit).
5, was obtained in petroleum ether. Compound 9 had also been
synthesized as a reference of 3-Br product. Due to the electron-
withdrawing effect of oxadiazole ring in 5-position, Br atom could
be introduce to 3-position (in thiophene ring) for certain. Its 1H
NMR, as a reference of 3-Br product, could be used to compare with
the 1H NMR of 4-Br products to confirm the position of Br atom.
1H NMR spectrums of related compounds (2–6) were shown in
Fig. 7. The three H protons at 6-, 7- and 3-positions were easy to be
distinguished. 6-H and 7-H gave two double peaks (marked ‘‘ꢃꢃ’’)
with a large interval. For example, compound 4 gave an interval
of 178.59 Hz and relatively large coupling constants (J = 8.39 Hz).
3-H was a ‘‘lone’’ proton and usually gave a single peak. In addition,
the peaks at about d = 2.6, derived from the H atoms at 2-CH3 of
thiophene rings, were split into a double peak for compounds 2–
6. It should be attributable to the coupling between the H atoms
at 2-CH3 and 3-H (4JH–H = 1–1.14 Hz). If the reaction occurred at
3-position, the coupling would disappear as shown in Fig. 7 (com-
pound 9). All the 4-Br products would retain the coupling.
2.2. Synthesis and structural characterization
In order to verify the calculation results, the bromination of 5-
diarylamino-2-methylbenzo[b]thiophene was carried out via
Scheme 1. Some substrates for bromination, 2-methyl-5-diphe-
nyl-amino benzo[b]thiophene (compound 2), 2-methyl-5-bis
(4-tert-butylphenyl)amino-benzothiophene (compound 3), and
2-(2-methylbenzo[b] thiophen-5-yl)-5-phenyl-1, 3, 4-oxadiazole
(compound 8) had been synthesized and characterized in our
previous works.
When bromination was run at lower temperature with less ac-
tive reagents used, the selectivity of reaction could be clearly ob-
served. Under the condition of Br2/AlCl3, ꢂ10 °C and non-polar
solvent (CCl4), Br atoms were introduced in both 4- and 40-posi-
tions. Compound 4 was obtained as solid power. However, the
growth of its single crystalline was unsuccessful. For less active re-
agents (NBS), only 4-Br product (compound 5) was obtained as
sticky solid without complete solidification upon standing. But
the single crystalline of compound 6, an analogue of compound
In addition, the structure of compound 6 was characterized by
single crystal X-ray diffraction. It was found that Br atom was
linked with the C atom at 4-position (benzene ring) of benzo[b]
Fig. 8. (a) Molecular structure of compound 6 at 30% probability displacement ellipsoids. (b) Molecular packing of compound 6 viewed along a axis. Hydrogen bonds are
showed as dashed lines.

B.-P. Wu et al. / Journal of Molecular Structure 1032 (2013) 126–132
131
thiophene in Fig. 8. It presented the windmill-like structure, which
was also confirmed just as some previous studies [27]. The dihe-
dral angles of phenyl rings (C10–C15) and (C3–C8) with benzene
ring (C20–C25) are 59.7° and 79.9°, respectively. The thiophene
ring (C1–C4/S1) and phenyl ring (C3–C8) are almost coplanar with
their dihedral angle of only 1.8°, and the dihedral angles of phenyl
rings (C3–C8) and (C10–C15) are approximately vertical with their
dihedral angle of 90.5°, which is identical with theory calculation.
In the crystal structure of 6, molecules are linked through intermo-
lecular C14–H14ꢁ ꢁ ꢁS1 (ꢂx, y + 1/2, ꢂz) hydrogen bonds, forming
chains running along a axis (Fig. 8b). Crystallographic data for
the structures and the resulting table of crystalline data analysis
are available from Supplementary data.
concentrated to obtain a pale yellow solid (0.65 g, 67%), m.p
136.0–140.0 °C. Anal. Calcd. (%) for C21H17NS: C, 79.96; H, 5.43;
N, 4.44. Found (%): C, 79.82; H, 5.46; N, 4.47. 1H NMR (CDCl3,
300 MHz, 25 °C): d = 7.61 (d, J = 8.60 Hz, 1H), 7.38 (d, J = 2.05 Hz,
1H), 7.23 (m, 4H), 7.08 (dd, J = 8.45, 0.86 Hz, 4H), 7.05 (dd, JH–
H = 8.66, 2.17 Hz 1H), 6.98 (t, J = 7.33, 7.33 Hz 2H), 6.81 (s, 1H),
4
2.56 (d, JH–H = 0.98 Hz, 3H).
2-Methyl-N, N-diphenylbenzo[b]thiophen-5-amine
2 (0.1 g,
0.30 mmol), and anhydrous AlCl3 (44.6 mg) in CCl4 (8.0 mL) were
cooled to below ꢂ13 °C in ice-salt bath. A solution consisting of
Br2 (0.056 mL, 1.09 mmol) in CCl4 (10 mL) was added dropwise
slowly and stirred for 30 h. Then, the mixture was washed several
times with 10% aqueous sodium carbonate and water. The organic
phase was dried over magnesium sulfate and then concentrated
under reduced pressure. The crude product was purified by column
chromatography on silica gel with petroleum ether/CHCl3 (10:1) to
give slightly yellow solid (93.5 mg, yield 56.5%). Anal. Calcd. (%) for
3. Conclusions
When diarylamino was in the 5-position of benzothiophene,
molecular simulations and experiments had shown that bromina-
tion of the molecule was more possible to occur in 4- or 40-position,
rather than 3-position. Single crystal X-ray diffraction of com-
pound 6 had given conclusive evidence. The selectivity was
‘‘abnormal’’ for general 5-substituted-2-methyl-benzo[b]thio-
phene with simple 5-substitutes. In the molecules, the N atom in
TPA unit rather than thiophene ring may be the main factor for
the selectivity. The fundamental reason was that the HOMO of
the substrate held a special form of electron distribution around
N atom so that a special ‘‘non-planar’’ conjugated system formed.
The N atom adopted the configuration of the plane triangle (sp2
hybridization), instead of the triangular cone (sp3 hybridization).
The orbit that the lone pair of the N atom occupied was not a pure
p-orbital, but a unique ‘‘interfinger-like’’ orbit. Electrons were do-
nated to the o- and p-position of linked aromatic rings by this man-
ner of electron delocalization, so that 4- or 40-position became the
C
21H14Br3NS: C, 45.68; H, 2.56; N, 2.54; Found (%): C, 47.01; H,
2.60; N, 2.45. 1H NMR (CDCl3, 300 MHz, 25 °C): d = 7.38 (dd,
J = 178.59, 8.38 Hz, 2H), 7.29 (d, J = 8.92 Hz, 2H), 7.29 (q, J = 5.28,
5.28, 5.28 Hz, 2H), 7.17–7.13 (m, 1H), 6.83 (d, J = 8.92 Hz, 2H),
4
6.83 (q, J = 5.27, 5.27, 5.26 Hz, 2H), 2.61 (d, JH–H = 1.14 Hz, 3H).
HS-ESIMS: m/z 548.8397, found 549.8473 (M + H+, 100%).
4.2.2. 4-Bromo-N, N-diphenyl-2-methylbenzo[b]thiophen-5-amine 5
N-bromosuccinimide (NBS) (3.9 g, 21.7 mmol) was dissolved in
a solution of acetated acid (45.0 mL) and CHCl3 (80.0 mL). 2-
methyl-N,
N-diphenylbenzo[b]thiophen-5-amine
2
(5.0 g,
15.9 mmol) in a solution of CHCl3 (150 mL) was added drop-wised
to the above solution below ꢂ13 °C in 1 h. The result mixture was
washed with water and neutralized with sodium carbonate to ba-
sicity. After concentration, the crude solid was purified by column
chromatography on silica gel with petroleum ether (60–90 °C) to
give colorless sticky compound 5 (6.1 g, yield 97.3%). Anal. Calcd.
(%) for C21H16BrNS: C, 63.96; H, 4.09; N, 3.55; Found (%): C,
63.80; H, 4.00; N, 3.60. 1H NMR (CDCl3, 300 MHz, 25 °C): d = 7.60
(d, J = 8.40 Hz, 1H, Ar–H), 7.34–7.24 (m, 4H, Ar–H), 7.22–7.19 (d,
J = 8.39 Hz, 4H, Ar–H), 7.06–7.00 (m, 4H, Ar–H), 6.93–6.91 (dd,
more active site. According to calculation, 4-Br-r-complex con-
tained the lowest energy, where 4-Br product would be the main
product controlled by reaction kinetics factors.
4
4. Experimental
2H, Ar–H), 6.80 (s, 1H, Ar–H), 2.56 (d, JH–H = 1.14 Hz, 3H, –CH3).
HS-ESIMS: m/z 393.0187, found 394.0262 (M + H+, 100%).
4.1. Materials and measurements
4.2.3. 4-Bromo-5-bis(4-tert-butylphenyl)-2-methylbenzo[b]thio-
phene amine 6
All chemicals were commercially available with AR grade and
used without further purification. The melting point was deter-
mined by an XPR-201 microscopic melting apparatus and uncor-
rected. Elemental analysis was performed on Elementar Vario EL
apparatus. 1H NMR spectra were recorded on a Bruker AV300
instrument at 300 MHz in CDCl3. HRMS were recorded on Finnigan
MAT 95 mass spectrometer.
Firstly, 5-bis(4-tert-butylphenyl)-2-methylbenzo-[b]thiophene
amine
3 was prepared by the reaction of 5-amine-2-meth-
ylbenzo[b]thiophene 1 with 1-tert-butyl-4-iodo-benzene in 1, 2-
dichlorobenzene. 1-tert-butyl-4-iodobenzene was commercially
available or prepared from 4-tert-butylaniline. 5-amine-2-meth-
ylbenzo[b]thiophene was synthesized as a flake crystal (m.p. 56–
58 °C) through several steps from 4-aminobenzenethiol [30–32].
2-Methylbenzo[b]thiophen-5-amine 1 (0.5 g, 3.06 mmol), 1-
tert-butyl-4-iodobenzene (1.9 g, 7.30 mmol), 1,2-dichlorobenzene
(10 mL), fresh treated Cu power (0.84 g, 200 mesh), fine power of
anhydrous potassium carbonate (3.64 g) and 18-crown-6
(0.174 g) were added to 50 mL three-necked flask equipped with
mechanical stirrer. The reaction mixture was stirred in N2 for
48 h under reflux. The mixture was filtrated under vacuum and
washed twice with hot 1, 2-dichlorobenzene. After steam distilla-
tion, residue 2-dichlorobenzene were removed. The resulting solid
(1.45 g) was dissolved in petroleum ether (70 mL, 60–90 °C), then
treated with aluminum oxide microspheres, and concentrated to
obtain a pale yellow solid 3 (0.81 g, 62%), m.p 160–164 °C. Anal.
Calcd. (%) for C29H33NS: C, 81.45; H, 7.78; N, 3.28. Found (%): C,
79.82; H, 7.97; N, 3.33. 1H NMR (CDCl3, 300 MHz, 25 °C): d = 7.56
(d, J = 8.58 Hz, 1H), 7.35 (d, J = 2.03 Hz, 1H), 7.23–7.17 (m, 4H),
7.03 (dd, J = 8.59, 2.15 Hz, 1H), 7.01–6.94 (m, 4H), 6.79 (s, 1H),
X-ray diffraction data were collected using a Bruker SMART-
1000 CCD area detector equipped with a graphite mono-chroma-
tized Mo K
a (0.71073 Å) radiation at 113(2) K. The structure was
solved by direct methods and refined on F2 by full-matrix least-
squares procedure with SHELXS-97 [28] and SHELXL-97 [29]. All
hydrogen atoms were located in a difference Fourier map and their
geometry was idealized, and refined by a riding model.
4.2. Bromination of 5-substituted-2-methylbenzo[b]thio-phene
4.2.1. 4-Bromo-N, N-bis(4-bromophenyl)-2-methylbenzo[b]thio-
phen-5-amine 4
Firstly, 5-diphenyl-2-methylbenzo[b]thiophene-amine 2 was
prepared through the reaction of 2-methylbenzo[b]-thiophen-5-
amine 1 (0.5 g, 3.06 mmol) with iodobenzene (1.5 g, 7.35 mmol)
in 1, 2-dichlorobenzene. Iodobenzene was commercially available.
The residue was treated with aluminum oxide microspheres and

132
B.-P. Wu et al. / Journal of Molecular Structure 1032 (2013) 126–132
4
2.54 (d, JH–H = 1.03 Hz, 3H), 1.29 (d, J = 4.88 Hz, 19H). HS-ESIMS:
m/z 427.2334, found 428.2404 (M + H+, 100%).
fax: (internet) +44 1223 336 033; email: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.2012.
07.054.
N-bromosuccinimide (NBS) (2.14 g, 16.5 mmol) was dissolved
in a solution of acetated acid and CHCl3. 2-methyl-5-bis(4-tertiary
butylphenyl) amine-benzothiophene (5.0 g, 11.7 mmol) in CHCl3
was added drop-wised to the above solution at below ꢂ13 °C in
1 h. The result mixture was washed with water and neutralized
with sodium carbonate to basicity. After concentration, the crude
solid was recrystallized in CHCl3 to obtain pale yellow compound
6 (5.1 g, yield 86%), m.p. 199.5–202.8 °C. The pale yellow single
crystal of 6 with long stick was obtained in petroleum ether at
room temperature for 2 weeks. Anal. Calcd. (%) for C29H32BrNS: C,
68.76; H, 6.37; N, 2.77. Found (%): C, 68.48; H, 6.24; N, 2.65. 1H
NMR (CDCl3, 300 MHz, 25 °C): d = 7.63 (d, J = 8.39 Hz, 1H), 7.22–
7.11 (m, 6H, Ar–H), 6.89 (d, J = 8.66 Hz, 4H, Ar–H), 2.59
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Acknowledgments
This work was financially supported by Grants from the Natural
Science Foundation of Tianjin (09JCYBJC06000), the Open Fund to
Large-scale Equipment of Tianjin Urban Construction Institute,
and the National Natural Science Foundation of China (Nos.
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Appendix A. Supplementary material
13C NMR data of compounds are available as the supplementary
data associated with this article can be found online. Crystallo-
graphic data for the structures reported have been deposited with
the Cambridge Crystallographic Data Centre (CCDC No. 852439).
These data can be obtained free of charge from www.ccdc.cam.
ac.uk/conts/retrieving.html or from the Cambridge Crystallo-
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