Transition Metal Chemistry
pyrrole-2-carboxaldehyde, 5-bromoindole-3-carboxalde-
hyde, thiophene-2-carboxaldehyde, o-phenylenediamine,
and 2-aminothiophenol were obtained either ꢀrom Sigma-
Aldrich Pvt. Ltd. or Avara chemicals, India, and used as
received. Inꢀrared spectra were recorded on a Shimadzu-IR
aꢂnity-1 spectrophotometer with sample prepared in KBr.
Yield and spectroscopic data oꢀ the selected compounds:
(a) 1-(4-chlorobenzyl)-2-(4-chlorophenyl)-1H-benzo[d]
imidazole (4ab): 0.014 g (8%); white solid;; FTIR (KBr,
−
1
1
cm ): 2906, 1698, 1527, 1082; H-NMR (CDCl , δ):
3
7.88 (d, 1H, J=7.8), 7.60 (d, 2H, J=8.1), 7.44 (m, 2H),
1
13
The H and C-NMR spectra were recorded on a Bruker
7.461–7.30 (m, 5H), 7.02 (d, 2H, J =7.8), 5.40 (s, 2H);
1
13
Avance 300 MHz spectrometer at 300.13 ( H), 75.47 MHz
C-NMR (CDCl , δ): 152.84, 143.05, 136.37, 135.90,
3
1
3
(
C) with SiMe as internal reꢀerences and coupling con-
134.63, 133.88, 130.45, 129.36, 129.13, 128.35, 127.26,
4
stants are given in Hertz. The mass spectral analysis was
123.47, 123.04, 120.18, 110.27, 47.76. ESI–MS: m/z
+
perꢀormed on Waters UPLC-MSMS (Xevo TQD) mass spec-
353.09 [M+H] .
6
trometer. The precursor complex [{(η -p-cymene)RuCl } ]
(b) 2-(5-bromo-1H-indol-3-yl)-1H-benzo[d]imidazole
2
2
1
[
44] was prepared by ꢀollowing a published procedure while
(4e): 0.118 g (75%): brown solid; H NMR (DMSO-d ,
6
the complex [RuCl(quinto)(p-cymene)] (I) [quinto=2-qui-
naldinato) was prepared by a slight modifcation oꢀ the
method reported earlier [45].
δ): 11.83 (s, 1H), 8.66 (s, 1H), 8.15 (s, 1H), 7.50 (t, 2H,
1
3
J=8.4), 7.34 (d, 1H, J=8.7), 7.16 (t, 2H, J=5.7); C-
NMR (DMSO-d , δ): 172.67, 149.27, 135.71, 127.84,
6
1
27.24, 125.31, 123.81, 114.50, 113.56, 106.65.
(
c) 2-(5-nitrothiophen-2-yl)-1H-benzo[d]imidazole (4 g):
Synthesis of [RuCl(quinto)(p‑cymene)] (I)
−1
0
2
1
7
1
1
2
.108 g (88%); Yellowsolid; FTIR (KBr cm ): 3103,
1
926, 1693, 1519, 1036, 744; H-NMR (DMSO-d , δ):
6
A round-bottom ꢃask was charged with [RuCl (p-cymene) ]
2
2 2
3.44 (s, 1H), 8.19 (d, 1H, J=4.5), 7.81 (d, 1H, J=4.2),
(
0.1 g, 0.163 mmol), quinaldic acid (0.056 g, 0.326 mmol)
1
3
.62 (m, 2H), 7.26 (m, 2H); C-NMR (DMSO-d , δ):
6
and NaOMe (0.02 g, 0.37 mmol).The resulting mixture was
stirred in methanol (40 ml) ꢀor 5 h at room temperature. The
red solution becomes cloudy as the reaction progress and
yellow solid appeared. The solid was collected and washed
with cold methanol and then with diethyl ether (2×10 ml)
72.45, 151.46, 145.08, 143.80, 141.21, 135.41, 131.46,
26.20, 124.59, 123.16, 119.75, 112.26. ESI–MS: m/z
+
46.14 [M+H] .
(
(
d) 2-(3-methylthiophen-2-yl)-1H-benzo[d]imidazole
−
1
4 h): 0.066 g (57%); Brown solid; FTIR (KBr cm ):
and dried under vacuum. Yield 0.129 g (81%); Yellow
1
3
047, 2924, 1720, 1562, 1068, 746; H NMR (DMSO-d ,
1
6
solid; HNMR (CDCl , δ): 8.59 (d, 1H, J = 8.7), 8.40 (d,
3
δ): 12.41 (s, 1H), 7.56 (m, 3H), 7.18 (d, 2H, J=4.2), 7.05
1
H, J=8.3), 8.23 (d, 1H, J=8.4), 8.02–7.97 (m, 2H), 7.79
1
3
(
d, 1H, J=4.8), 2.58 (m, 3H); C-NMR (DMSO-d , δ):
6
(
d, 1H, J=14.7), 5.74 (d, 1H, J=5.8), 5.54 (d, 2H, J=6),
1
1
47.46, 138.12, 135.16, 132.30, 127.43, 122.78, 118.95,
5
.42 (d, 1H, J=6), 2.61 (m, 1H), 2.26 (s, 3H), 1.11 (d, 3H,
+
11.80, 15.91; ESI–MS: m/z 215.16 [M+H] .
J=6.9), 1.00 (d, 3H, J=6.9).
(
(
e) 2-(5-methylthiophen-2-yl)-1H-benzo[d]imidazole
−
1
4ia):0.061 g (53%), Brown solid; FTIR (KBr cm ):
1
Representative procedure for the synthesis
of 2‑arylbenzimidazoles/2‑arylbenzothiazoles
with ruthenium(II)‑catalyst (I) in water
3024, 2936, 1712, 1570, 746; H NMR (DMSO-d , δ):
6
12.81 (s, 1H), 7.59 (m, 3H), 7.17 (d, 2H, J= 6.3), 6.90
1
3
(s, 1H), 2.50 (s, 3H); C-NMR (DMSO-d , δ): 147.57,
6
1
44.03, 142.92, 135.09, 131.03, 127.34,127.10, 122.89,
A
S chle nck tube wa s cha rge d w it h 1,
-phenylenediamine/2-aminothiophenol (0.5 mmol), alde-
hyde (0.5 mmol) and ruthenium(II) catalyst (I) (0.011 g,
.025 mmol). Then 2 ml oꢀ distilled water was added to
the tube and sealed. The reaction mixture was stirred at
00 °C under nitrogen atmosphere on a magnetic stirrer
or about 16 h. The reaction mixture was cooled to room
122.09, 118.81, 111.38, 15.53.
2
(ꢀ) 2-(5-methylthiophen-2-yl)-1-((5-methylthiophen-2-yl)
methyl)-1H-benzo[d]imidazole (4ib): 0.01 g (6%), light
−1
0
brown solid; FT-IR (KBr cm ): 2928, 1716, 1516, 1058,
1
742; H NMR (CDCl , δ): 7.82 (d, 1H, J=8.4), 7.38–7.29
3
1
(m, 4H), 6.81 (m, 1H), 6.70–6.59 (m, 2H), 5.82 (s, 2H),
1
3
ꢀ
2.56 (s, 3H), 2.42 (s, 3H); C-NMR (CDCl , δ):147.82,
3
temperature and extracted with ethyl acetate (3 × 10 ml).
The combined organic ꢀractions was evaporated to dryness
using a rotary evaporator and the residue thus obtained was
purifed by column chromatography over silica gel column
using petroleum ether and ethyl acetate as eluents. The
spectroscopic data oꢀ the known synthesized compounds
were well-matched with the reported values [50] (see sup-
plementary material).
143.79, 143.08, 136.36, 135.92, 129.44, 128.30, 126.21,
125.36, 125.07, 122.96, 122.77, 119.76, 109.85, 44.16,
+
15.33, 15.25; ESI–MS: m/z 325.0495 [M+H] .
(g) 2-(5-methylꢀuran-2-yl)-1-((5-methylꢀuran-2-yl)
methyl)-1H-benzo[d]imidazole (4 kb): yellow
1
solid;0.025 g (17%); H-NMR(CDCl , δ): 7.79 (d,
3
2H, J = 5.1), 7.50 (d, 1H, J = 4.8), 7.29 (m, 2H), 7.11
(s, 1H), 6.21 (s, 1H), 6.14 (s, 1H), 5.88 (s, 1H), 5.55
1
3