Synthesis and optical properties of 2,2'-biimidazole and benzo[d]imidazole derivatives: Changing π-conjugation by photoexcitation

Article abstract of DOI:10.3987/COM-13-S(S)12

1,1',5,5'-Tetraaryl-2,2'-biimidazole and benzo[d]imidazole derivatives were synthesized. Symmetrical and unsymmetrical benzo[d]imidazole derivatives could be obtained by the Pd-catalyzed coupling reaction between 2-iodo-benzo[d] imidazole and the correspo

Full text of DOI:10.3987/COM-13-S(S)12

HETEROCYCLES, Vol. 88, No. 1, 2014, pp. -. © 2014 The Japan Institute of Heterocyclic Chemistry
Received, 13th May, 2013, Accepted, 27th May, 2013, Published online, 31st May, 2013
DOI: 10.3987/COM-13-S(S)12
SYNTHESIS AND OPTICAL PROPERTIES OF 2,2′-BIIMIDAZOLE AND
BENZO[d]IMIDAZOLE DERIVATIVES: CHANGING π-CONJUGATION
BY PHOTOEXCITATION
Shoji Matsumoto,* Yu Zhao, and Motohiro Akazome
Department of Applied Chemistry and Biotechnology, Graduate School of
Engineering, Chiba University, 1-33 Yayoicho, Inageku, Chiba 263-8522, Japan;
E-mail: smatsumo@faculty.chiba-u.jp
Abstract – 1,1′,5,5′-Tetraaryl-2,2′-biimidazole and benzo[d]imidazole derivatives
were synthesized. Symmetrical and unsymmetrical benzo[d]imidazole derivatives
could be obtained by the Pd-catalyzed coupling reaction between
2-iodo-benzo[d]imidazole and the corresponding (benzo)imidazole anion.
Hypsochromic shifts in absorption and fluorescence spectra of
1,1′,5,5′-tetraaryl-2,2′-biazole were observed by switching pyrrole rings for
imidazole and benzo[d]imidazole rings, resulting in compounds with various
Stokes shifts. Based on the (TD)DFT calculation, it was reasoned that changing
the conformation of each single bond from a twisted to planar structure by
photoexcitation led to larger Stokes shifts.
INTRODUCTION
The expansion of the π-conjugation in one molecule by an external stimulus is an important feature in
various functional materials. The origin of the alternation of the π-conjugated system is divided broadly
into two categories: structural changes and conformational changes. For example, photochromic
compounds such as diarylethenes and spiropyranes, are categorized as structural changes and are used in
various fields where modifying the structure leads to a change in π-conjugation.1-5 Conformational
transformation to the extended π-conjugated system by the single-bond rotation is achieved by the addition
of metal ions to bidentate ligands;6 such changes can also be made without additives by photoexcitation.
For instance, twisted intramolecular charge transfer (TICT) can give rise to fluorescence quenching.7 TICT
is based on changing a planar molecule into a twisted structure between donor and acceptor components
This paper is dedicated to Professor Victor Snieckus on the occasion of his 77th birthday.

before and after photoexcitation.8
In studying the expansion of π-conjugation by photoexcitation, we have reported on the conformational
changes at 2,2′-bipyrrole single bonds of 1,1′,5,5′-tetraaryl-2,2′-bipyrrole derivatives.9 In these compounds,
the conformations of two pyrrole rings and between the pyrrole ring and the aryl group at the 5 and 5′
positions were twisted in the ground state. This structural change, from twisted to planar, and which
occurred by photo irradiation, gave
a
large Stokes shift. When pyrrole rings of
1,1′,5,5′-tetraphenyl-2,2′-bipyrrole (1) were replaced with imidazole rings, it was possible to increase the
planarity between the two azoles because of the decrease in steric hindrance derived from the hydrogen
atoms at the 3 and 3′ positions (Scheme 1). The effect of the replacement of the pyrrole rings with imidazole
on the planarization after photoexcitation is unknown.
The investigation into the metal-coordinating compounds of 2,2′-biimidazoles have been reported.10
Recently, fluorescence sensing was achieved based on a polymer including the 2,2′-biimidazole structure
by Bai and co-workers.11 However, to the best of our knowledge, there is no report on the research into
structural changes of 2,2′-biimidazole derivatives under photoexcitation. Herein, we report the changes in
the Stokes shift of 2,2′-biimidazole and 2,2′-bibenzo[d]imidazole derivatives bearing phenyl rings at
nitrogen atoms under photoexcitation. We found that conformational changes between not only two azole
rings but also phenyl rings at the 5 (and 5') position and imidazole rings are necessary to realize greater
π-expansion.
Scheme 1. Proposed representation of the π-expansion of the 2,2′-bipyrrole and 2,2′-biimidazole
derivatives by photoexcitation
RESULTS AND DISCUSSION
We focused on those compounds bearing simple aryl substituents such as phenyl and naphthyl groups as
the target materials. We synthesized 1,1′,5,5′-tetraphenyl-2,2′-biimidazole (2), 1,1′-diphenyl-5,5′-

dinaphthyl-2,2′-biimidazole (3), 1,1′-diphneyl-2,2′-bibenzo[d]imidazole (4), and 1-phenyl-2-
(1,5-diphenylimidazol-2-yl)benzo[d]imidazole (5) to provide a sufficient variety of single-bond rotation
platforms to study (Scheme 2). The 2,2′-biimiazole structure was synthesized using the Cu mediated
coupling reaction of 2-iodo-1-phenylimidazole in a procedure reported by Park and Alper.12 Arylation at
the 5 and 5′ positions yielded 2 and 3 in a palladium-catalyzed coupling reaction.13 The position of phenyl
rings in 2 was determined by single crystal X-ray crystallographic analysis. Structure 4 was initially
obtained with only an 8% yield in the same procedure because the homo coupling reaction of
2-iodo-1-phenylbenzo[d]imidazole was inhibited. We then tried another approach with
2-iodo-1-phenylbenzo[d]imidazole and 2-lithiated 1-phenylbenzo[d]imidazole which returned 4 in 51%
yield.14,15 According to this procedure, we also obtained the unsymmetrical 5 with a yield of 47%.
Scheme 2. Synthesis of 2, 3, 4, and 5
The optical data of 1, 2, 3, 4, and 5 in THF are shown in Figure 1 and Table 1. The absorption (λmax) and
fluorescence (λem) peaks of 2 were both shifted to shorter wavelength (entries 1 and 2) compared with 1.
These shifts will be affected by the electronegativity of nitrogen atoms of 2 replacing the 3 and 3′ CH
positions in 1.16 Bathochromic shifts of λmax and λem were observed in the spectra of 3 bearing naphthyl

groups at 5 and 5′ positions (entry 3). This further suggests that absorption and emission are influenced
toward the edge of the substituents at 5 and 5′ positions. The shoulder peak (400 nm) was also observed in
the fluorescence spectrum of 3. By changing the imidazole group(s) to the benzo[d]imidazole, red shifts of
λmax were obtained in 4 and 5 as compared to 2 (entry 2 vs. 4 and 5). However, hypsochromic shifts of λem
were observed in 4 and 5 with respect to 2. All fluorescence quantum yields (ΦF) of (benzo)imidazole
derivatives were lower than that of 1.
Figure 1. UV-VIS absorption (bold line; 3.0 × 10-5 M in THF) and fluorescence (narrow line; 3.0 × 10-7 M
in THF, excited at λmax) spectra of 1 (blue line), 2 (red line), 3 (purple line), 4 (green line), and 5
(orange line)
Table 1. Optical properties of 1-5
Absorptiona
λmax (nm) ε (M-1 cm-1)
Fluorescenceb
Stokes shift
Δλ (nm)d Δν (cm-1)e
Entry Compound
c
λem (nm)
416
ΦF
1
2
3
4
5
1
2
3
4
5
303
287
312
292
298
24,000
24,800
31,400
19,200
20,400
0.60
0.37
113
110
8,965
9,654
397
400(sh), 421 0.38
88, 109 7,051, 8,298
371
386
0.23
0.55
79
88
7,292
7,650
a
b
c
Measured in THF (3.0 × 10-5 M). Measured in THF (3.0 × 10-7 M) excited at λmax
. Determined by p-terphenyl in
cyclohexane as a standard (ΦF=0.87, excited at 265 nm). d Δλ = λem – λmax. e Δν = 1/λmax – 1/λem.
In the case of the 2,2′-bipyrrole compounds, we rationalized that the planar structure in the excited state
could be investigated by analyzing the Stokes shift; when planarity in the excited state is increased, a larger
Stokes shift should be obtained.9 We therefore focused on the Stokes shifts of compounds 1-5 summarized
in Table 1. When the pyrrole structure was switched for imidazole, a larger Stokes shift was obtained in
terms of energy (entries 1 and 2), although similar wavelengths were observed (1, 113 nm (8,965 cm-1); 2,
110 nm (9,654 cm-1)). This result was unexpected, in which a smaller change was expected in the case of 2

because of the increased planarity of 2,2′-biazole in the ground state. A smaller energy change between the
ground state and excited state (Δν = 8,298 cm-1) was obtained in 3 (entry 3). Furthermore, 4 and 5 also had
smaller Stokes shifts than 2 (entry 2 vs. 4 and 5). A smaller value of Δν (7,292 cm-1) was obtained in 4 than
in 5, which possessed phenyl substituents at position 5 and allowed comparison with 2. This implies that the
conformational change at the bi(benzo)imidazole moiety as well as at the phenyl rings substituted at 5 (and
5′) position(s) are effective in lengthening emission wavelengths. The value obtained for 4 is still larger
than the Stokes shift obtained from the 2,2′-bipyrrole compounds with fixed planar structures via
intramolecular hydrogen bonding (65 nm (4,475 cm-1) and 55 nm (3,964 cm-1)).17 Therefore,
conformational changes are possible even in 4.
We also measured the absorption and fluorescence spectra of 1 and 2 in MeCN and EtOH (Figure 2 and
Table 2). The λem of 1 changed substantially by varying the solvent, whereas the λmax was within 4 nm
(entries 1, 2, and 3). This compared to a larger change of λmax in 2 (~13 nm), which had a smaller change
of λem between solvents. These results suggest that the compounds have different polarities in the ground
and excited states. Compound 1, bearing the 2,2′-bipyrrole unit, is polar in its excited state, whereas 2,
having 2,2′-biimidazole moiety, is polar in its ground state. However, the difference of Stokes shift
between 1 and 2 were consistent in all three solvents: larger Stokes shifts in terms of energy were
obtained for 2 in every solvent.
Figure 2. UV-Vis absorption (bold line; 3.0 × 10-5 M) and fluorescence (narrow line; 3.0 × 10-7 M,
excited at λmax) spectra of a) 1 and b) 2 in THF (blue line), MeCN (red line), and EtOH (green
line)

Table 2. Optical properties of 1 and 2 in various solvents
Absorptiona
λmax (nm) ε (M-1 cm-1)
Fluorescenceb
λem (nm)
416
Stokes shift
Δλ (nm)c Δν (cm-1)d
Entry
Compound
Solvent
1
2
3
4
5
6
1
1
1
2
2
2
THF
MeCN
EtOH
THF
303
300
299
287
282
274
24,000
20,800
22,000
24,800
22,800
24,500
113
121
114
110
112
118
8,965
9,580
9,232
9,654
10,080
10,986
421
413
397
MeCN
EtOH
394
392
a Concentration: 3.0 × 10-5 M. b Concentration: 3.0 × 10-7 M. Excited at λmax. c Δλ = λem – λmax. d Δν 1/λmax – 1/λem.
To further investigate the large Stokes shift in 2, we examined the structures in the ground and excited
states using density functional theory (DFT) with the B3LYP/6-31+G** level on the Gaussian09
program.18,19 The excited structures were optimized by time-dependent DFT (TDDFT) (nstate=5). The
dihedral angles of relevant positions are summarized in Table 3. All compounds showed greater planarity in
the excited state than in the ground state, as evidenced by a decrease in the dihedral angle upon excitation.
As expected, the dihedral angle between the two imidazole rings of 2 (33.50° for N4′-C5-C6-N7) was
smaller than that for 1 (47.01° for C4′-C5-C6-N7) in the ground state (entry 1 vs. 2). The conformational
change however, between the two heteroaromatic rings in the ground and excited states was lower in 2
(23.07°) as compared with 1 (26.13°), which contradicts results from the Stokes shifts analysis. We
therefore considered all dihedral angles along the long axis of the compounds and found that changes in
dihedral angles at 5 and 5′ are more planar in 2 (18.2°) than in 1 (11.2°). The total difference of
dihedral-angle change of 2 from the ground to the excited state (AGS–AES) is larger than that of 1, leading to
improved π-conjugation that is consistent with the larger Stokes shift observed spectroscopically.20 This
was further supported from the HOMO and LUMO orbital energies (Figure 3). The narrower HOMO and
LUMO energies in the excited state as compared to the ground state (ΔE) was observed in 1 and 2, which
may explain the fluorescence at longer wavelength than the absorption peak. The difference between the
ΔE values for the ground and excited states (ΔΔE) of 2 is larger than that of 1 (1.3344 eV and 0.9018 eV,
respectively), which would suggest that a larger Stokes shift of 2 would be observed. Additionally, every
HOMO and LUMO orbital of 1 and 2 spreads to phenyl rings at the 5 and 5' positions. Further, not only the
single bond between two azole rings but also that between phenyl and azole rings showed double bond
character in the LUMO orbital. Taking all of these information together, the larger Stokes shift was
attributed to efficient planarization, which spread to the edge substituents in an extended π-conjugation
network.

Table 3. Dihedral angle of the ground and excited state optimized by (TD)DFT calculation
Dihedral angle (°)
Sum of dihedral angle (°)
Ground state Excited state
Position of
Entry Compound
A –A (°)
GS ES
Ground statea Excited stateb
dihedral angle
(AGS)a
(AES)b
C1-C2-C3-N4
C4′-C5-C6-N7
N7-C8-C9-C10
C1-C2-C3-N4
N4′-C5-C6-N7
N7-C8-C9-C10
C1-C2-C3-N4
N4′-C5-C6-N7
N7-C8-C9-C10
N4′-C5-C6-N7
C1-C2-C3-N4
N4′-C5-C6-N7
40.57
47.01
40.57
41.61
33.50
41.61
43.61
30.12
36.25
17.47
42.40
27.33
29.34
20.88
29.32
23.43
10.43
23.42
25.52
7.18
1
2
3
1
2
3
128.15
79.54
48.61
59.44
56.80
116.72
109.98
57.28
53.18
20.48
9.45
4
5
4
5
17.47
69.73
9.45
8.02
19.85
8.68
28.53
41.20
a
b
The structure was optimized by DFT/B3LYP/6-31+G** level.
TDDFT/B3PLY/6-31+G** level using nstate=5.
The structure was optimized by
Figure 3. Orbitals and energies of HOMO and LUMO of a) 1 and b) 2, estimated by DFT (left) and TDDFT
(nstate=5) (right) calculated for structure optimization at the B3LYP/6-31+G** level

The order of the Stokes shift in imidazole derivatives, 2, 3, 4, and 5, is consistent with that of the differences
in the dihedral angles (AGS–AES) (Table 1 and Table 3). The smaller Stokes shift and dihedral angels of 3
were consistent with the observed Stokes shift and dihedral angles of 2 (entry 2 vs. 3 in Table 1 and Table
3).21 Furthermore, the planarity between two (benzo)imidazole rings of 4 and 5 was increased in the ground
state (entry 2 vs. 4 and 5 in Table 3), which led to the bathochromic shift of λmax (entry 2 vs. 4 and 5 in Table
1). Furthermore, the small Stokes shift was also observed in 4 and 5, because of small AGS–AES caused by
both the small change of the dihedral angle between two (benzo)imidazole rings and the decrease in the
number of freely rotating single bonds (three in 2 and 3, whereas there are only two in 5 and one in 4).
In conclusion, we synthesized the 1,1′,5,5′-tetraaryl-2,2′-biimidazole and benzo[d]imidazole derivatives
using the Pd-catalyzed coupling reaction. Hypsochromic shifts in absorption and fluorescence peaks were
obtained by switching pyrrole rings for imidazole rings (1 vs. 2), which led to a larger Stokes shift of 2 as
compared to 1. From (TD)DFT calculations, a large change of the sum of dihedral angles in the long axis
was important to give the larger Stokes shift, and the decrease in the number of the freely rotating single
bond was also influenced in the decrease of the Stokes shift. Those findings will be useful in designing
compounds having large Stokes shifts, which is important for functional materials such as wavelength
conversion materials.
EXPERIMENTAL
Melting points were determined with Yanaco MP-J3 and values were uncorrected. NMR spectra were
recorded at 300 MHz (proton) and at 75 MHz (carbon-13) on Varian GEMINI 2000 spectrometer with
TMS or CDCl3 as internal standard. J-Values are given in Hz. UV-Vis spectra were measured on a JASCO
V570 spectrophotometer. Fluorescence spectra were measured on a JASCO FP-6600 spectrofluorometer.
Elemental analyses (EA) were carried out on a Perkin-Elmer 2400CHN or an Exeter Analytical, Inc.
CE-440F in Center for Analytical Instrumentation of Chiba University. Mass spectra were carried out on a
JEOL JMS-AX500, a JMS-HX110, or THERMO Fisher Exactive in Center for Analytical Instrumentation
of Chiba University. Anhydrous THF was distilled from sodium benzophenone ketyl immediately prior to
use. Anhydrous DMF was distilled from P2O5 under reduced pressure and was stored with MS 4 Å. The
reactions were performed under argon atmosphere otherwise noted.
Synthesis of 1,1'-Diphenyl-2,2'-biimidazole: To a solution of 1-phenylimidazole22 (0.781 g, 5.42 mmol)
in THF (10 mL) was dropwisely added n-BuLi (3.8 mL, 1.8 M in hexane, 2.1 mmol) at -30 °C. After being
stirred for 30 min at that temperature, to the solution was added iodine (1.55 g, 6.11 mmol) at that
temperature. The reaction mixture was warmed up to room temperature and stirred for additional 1 h. After
quenched with saturated Na2S2O3 (5 mL), the mixture was extracted with EtOAc (5 mL × 3). The combined

organic layer was washed with brine (10 mL) and dried over MgSO4. After evaporation in vacuo, the
residual mixture was dissolved in DMF (6 mL). To that solution was added Cu powder (0.701 g, 11.0
atom-equivalents). After being stirred for 5 h at 90 °C, the reaction mixture was cooled to room temperature,
and was added 28% aqueous NH3 (70 mL). After being stirred for 1 h to dissolve the excess amount of Cu
powder, the mixture was extracted with EtOAc (5 mL × 5). The combined organic layer was washed with
brine (10 mL) and dried over MgSO4. After evaporation in vacuo, the residual mixture was recrystallized
from hexane and acetone to give 1,1'-diphenyl-2,2'-biimidazole (0.593 g, 2.07 mmol) in 77% yield as
colorless plate crystals: mp = 155.5–156.5 °C; 1H NMR (300 MHz, CDCl3) δ 6.71 (diffused d, J = 7.6 Hz,
4H), 7.05 (d, J = 1.2 Hz, 2H), 7.11–7.23 (m, 6H), 7.25 (d, J = 1.2 Hz, 2H); 13C NMR (75 MHz, CDCl3) δ
121.0, 123.7, 127.3, 128.9, 129.8, 136.9, 137.3. Anal. Calcd for C18H14N4·0.1H2O: C, 75.03; H, 4.97; N,
19.44. Found: C, 75.03; H, 5.06; N, 19.47.
Synthesis of 1,1',5,5'-Tetraphenyl-2,2'-biimidazole (2): K2CO3 (0.277 mmol, 2.00 mmol) (preheated in
vacuo at 120 °C for 2 h), 1,1'-diphenyl-2,2'-biimidazole (0.143 g, 0.499 mmol), bromobenzene (0.331 g,
2.11 mmol), Pd(OAc)2 (22.3 mg, 0.0993 mmol), and PPh3 (52.4 mg, 0.200 mmol) were dissolved in DMF
(2.5 mL). After being stirred for 48 h at 140 °C, the reaction mixture was cooled to room temperature. After
addition of brine (10 mL), the mixture was extracted with CHCl3 (10 mL × 4). The combined organic layer
was washed with brine (10 mL) and dried over MgSO4. After evaporation in vacuo, the residual mixture
was subjected to column chromatography on silica-gel (hexane : EtOAc = 1 : 1) to give 2 (0.197 g, 0.449
mmol) in 89% yield. Rercrystallization from hexane and CHCl3 gave colorless needle crystals: mp =
281.8–282.4 °C; 1H NMR (300 MHz, CDCl3) δ 6.74 (d, J = 7.3 Hz, 4H), 7.01 (m, 4H), 7.10–7.23 (m, 12H),
7.31 (s, 2H); 13C NMR (75 MHz, CDCl3) δ 127.1, 127.4, 127.8, 128.2, 128.2, 128.5, 128.8, 129.4, 134.1,
136.0, 139.4. Anal. Calcd for C30H22N4·0.5H2O: C, 80.51; H, 5.18; N, 12.52. Found: C, 80.59; H, 5.03; N,
12.55.
Synthesis of 5,5'-Di(naphthalen-2-yl)-1,1'-diphenyl-2,2'-biimidazole (3): The titled compound was
prepared with 1,1'-diphenyl-2,2'-biimidazole and 2-bromonaphthalene for 72 h in 43% yield according to a
procedure mentioned in 2: colorless powder; mp = 275.7–277.3 °C (hexane –CHCl3); 1H NMR (300 MHz,
CDCl3) δ 6.83 (d, J = 7.5 Hz, 4H), 7.06 (dd, J = 1.6 and 8.5 Hz, 2H), 7.14 (t, J = 7.8 Hz, 4H), 7.21 (t, J = 7.1
Hz, 2H), 7.39-7.43 (m, 6H), 7.54 (s, 2H), 7.61 (s, 2H), 7.62-7.64 (m, 2H), 7.70-7.73 (m, 2H); 13C NMR (75
MHz, CDCl3) δ 125.9, 126.2, 126.3, 126.8, 127.1, 127.2, 127.5, 127.8, 127.9, 128.9 (large intensity), 129.0,
132.3, 133.1, 134.2, 136.1, 139.6. Anal. Calcd for C38H26N4·0.25H2O: C, 84.03; H, 4.92; N, 10.32. Found:
C, 84.21; H, 4.77; N, 10.40.
Synthesis of 2-Iodo-1-phenylbenzo[d]imidazole: To a solution of 1-phenylbenzo[d]imidazole23 (1.55 g,
7.98 mmol) in THF (25 mL) was dropwisely added sec-BuLi (10.0 mL, 1.0 M in cyclohexane/hexane, 10
mmol) at -60 °C. After being stirred for 30 min at that temperature, to the solution was added iodine (2.35 g,

9.26 mmol) at that temperature. The reaction mixture was warmed up to room temperature and stirred for
additional 2.5 h. After quenched with saturated Na2S2O3 (5 mL), the mixture was extracted with EtOAc (10
mL × 3). The combined organic layer was washed with brine (20 mL) and dried over MgSO4. After
evaporation in vacuo, the residual mixture was subjected to column chromatography on silica-gel (hexane :
EtOAc = 2 : 1) to give 2-iodo-1-phenylbenzo[d]imidazole (1.97 g, 6.15 mmol) in 77% yield as colorless
solid: mp = 162.2–163.2 °C (hexane-CHCl3); 1H NMR (300 MHz, CDCl3) δ 7.14 (d, J = 7.8 Hz, 1H), 7.19
(t, J = 6.9 Hz, 1H), 7.26 (dt, J = 1.6 and 7.5 Hz, 1H), 7.40 (diffused dd, J = 3.4 and 7.6 Hz, 2H), 7.59 (m, 3H),
13
7.78 (d, J = 7.9 Hz, 1H); C NMR (75 MHz, CDCl3) δ 103.5, 110.2, 119.2, 122.7, 123.6, 128.2, 129.5,
129.7, 136.7, 137.5, 145.4. Anal. Calcd for C13H9IN2: C, 48.77; H, 2.83; N, 8.75. Found: C, 48.82; H, 2.81;
N, 8.60.
Synthesis of 1,1'-Diphenyl-2,2'-bibenzo[d]imidazole (4): To a solution of 1-phenylbenzo[d]imidazole23
(0.293 g, 1.51 mmol) in THF (4 mL) was dropwisely added sec-BuLi (1.8 mL, 1.0 M in
cyclohexane/hexane, 10 mmol) at -60 °C. After being stirred for 1 h at that temperature, the mixture was
added to a solution of Pd(PPh3)4 (12.2 mg, 0.0106 mmol) and 2-iodo-1-phenylbenzo[d]imidazole (0.358 g,
1.12 mmol) in THF (3 mL) at -60 °C. After being stirred for 48 h at 50 °C, the reaction mixture was cooled
to room temperature. After addition of H2O (10 mL), the mixture was extracted with EtOAc (10 mL × 3).
The combined organic layer was washed with brine (20 mL) and dried over MgSO4. After evaporation in
vacuo, the residual mixture was subjected to column chromatography on silica-gel (hexane : EtOAc = 2 : 1)
to give 4 (0.197 g, 0.510 mmol) in 51% yield. Rercrystallization from hexane and THF gave colorless plate
crystals: mp = 173.3–173.8 °C; 1H NMR (300 MHz, CDCl3) δ 6.85 (diffused d, J = 7.0 Hz, 4H), 7.20-7.33
(m, 10H), 7.37 (dt, J = 1.7 and 6.6 Hz, 2H), 7.93 (d, J = 7.9 Hz, 2H); 13C NMR (75 MHz, CDCl3) δ 110.6,
121.1, 123.3, 124.4, 125.6, 127.8, 129.5, 135.3, 135.4, 143.0, 143.1. HRMS (FAB): Calcd for C26H19N4
([M+H]+): 387.1610. Found: 387.1617. Anal. Calcd for C26H18N4: C, 80.81; H, 4.69; N, 14.50. Found: C,
80.50; H, 4.46; N, 14.38.
Synthesis
of
1-Phenyl-2-(1-phenylimidazol-2-yl)benzo[d]imidazole: To
a
solution of
1-phenylimidazole22 (0.526 g, 3.65 mmol) in THF (8 mL) was dropwisely added n-BuLi (2.7 mL, 1.6 M in
hexane, 4.3 mmol) at -78 °C. After being stirred for 1 h at that temperature, the mixture was added to a
solution of Pd(PPh3)4 (12.2 mg, 0.0106 mmol) and 2-iodo-1-phenylbenzo[d]imidazole (0.358 g, 1.12
mmol) in THF (3 mL) at -78 °C. After being stirred for 72 h at 50 °C, the reaction mixture was cooled to
room temperature. After addition of H2O (10 mL), the mixture was extracted with EtOAc (10 mL × 3). The
combined organic layer was washed with brine (20 mL) and dried over MgSO4. After evaporation in vacuo,
the residual mixture was subjected to column chromatography on silica-gel (hexane : EtOAc = 2 : 1) to give
1-phenyl-2-(1-phenylimidazol-2-yl)benzo[d]imidazole (0.375 g, 1.11 mmol) in 56% yield.
Rercrystallization from hexane and CHCl3 gave colorless prism crystals: mp = 175.0–176.8 °C; 1H NMR

(300 MHz, CDCl3) δ 6.77 (d, J = 7.5 Hz, 2H), 6.81 (d, J = 7.0 Hz, 2H), 7.10–7.37 (m, 11H), 7.90 (d, J = 7.8
Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 110.5, 120.9, 121.9, 123.1, 124.0 (large height), 125.6, 127.6, 129.2,
129.3, 130.4, 135.1, 135.6, 137.0, 137.2, 143.1, 143.3. HRMS (FAB): Calcd for C22H17N4 ([M+H]+):
337.1453. Found: 337.1449.
Synthesis of 2-(1,5-Diphenylimidazol-2-yl)-1-phenylbenzo[d]imidazole (5): The titled compound was
prepared with 1-phenyl-2-(1-phenylimidazol-2-yl)benzo[d]imidazole and half equivalent of corresponding
reagents for 46 h in 47% yield according to a procedure mentioned in 2: colorless powder; mp =
202.3–203.9 °C (hexane-EtOAc); 1H NMR (300 MHz, CDCl3) δ 6.68 (d, 2H, J = 7.6 Hz), 6.94 (m, 2H),
7.00–7.09 (m, 4H), 7.16–7.36 (m, 10H), 7.39 (s, 1H), 7.87 (d, 1H, J = 7.8 Hz); 13C NMR (75 MHz, CDCl3)
δ 110.5, 120.7, 123.0, 125.8, 126.8, 127.6, 127.9, 128.3 (large intensity), 128.9, 129.07, 129.13, 129.3,
134.7, 135.1, 135.66, 135.69, 138.9, 142.9, 143.4. HRMS (FAB): Calcd for C26H19N4 ([M+H]+): 413.1766.
Found: 413.1779. Anal. Calcd for C26H18N4·0.09EtOAc: C, 81.02; H, 4.97; N, 13.33. Found: C, 81.01; H,
4.92; N, 13.13.
X-Ray Crystallography: X-Ray diffraction data for the crystal was measured on a Bruker APEXII CCD
diffractometer with graphite monochromated Mo Kα (λ=1.54178 Å). The structure was solved by a direct
method SHELXS-9724 and refined by SHELXL-9724 in a computer program package from Bruker AXS.
Hydrogen atoms are calculated in appropriate position.
2: C30H22N4, Mr=438.52, monoclinic, P21/n, T=173 K, a=5.9583(4) Å, b=11.7853(8) Å, c=15.8218(10) Å,
β=92.3750(10)°, V=1110.06(13) Å3, Z=2, Dc= 1.312 g cm-3, R1=0.0383, wR2=0.0847. Deposition number
CCDC-940241
for
2.
Free
copies
of
the
data
can
be
obtained
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge, Crystallographic Data Centre,
12 Union Road, Cambridge, CB2 1EZ, UK, Fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
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