A novel approach to bis(indolyl)methanes using nickel nanoparticles as a reusable catalyst under solvent-free conditions

Article abstract of DOI:10.2298/JSC120506076O

Nano-sized nickel as a catalyst has been developed for the electrophilic substitution reactions of indole with various aromatic aldehydes under solvent-free conditions to afford the corresponding bis(indolyl)methanes in high to excellent yields. The descr

Full text of DOI:10.2298/JSC120506076O

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J. Serb. Chem. Soc. 77 (0) 1–9 (2012)
JSCS–5378
UDC
Original scientific paper
Novel approach to bis(indolyl)methanes using nickel
nanoparticles as a reusable catalyst under solvent-free conditions
1
1
1
ABOLFAZL OLYAEI *, MOHSEN VAZIRI , REZA RAZEGHI ,
1
2
BAHAREH SHAMS and HASAN BAGHERI
1
Department of Chemistry, Payame Noor University, P. O. Box 19395-3697, Tehran, Iran and
2
Department of Chemistry, Islamic Azad University, Takestan Branch, Qazvin, Iran
(Received 6 May, revised 10 July 2012)
Abstract: A nanosized Nickel as catalyst has been developed for the
electrophilic substitution reactions of indole with various aromatic aldehydes
under solvent-free conditions to afford the corresponding bis(indolyl)methanes
in high to excellent yields. The described method has promising features such
as no hazardous organic solvents or catalysts, short reaction time, high product
yields, simple work-up procedure, reusable catalyst and easy product
separation without further purification with coulmn chromatography.
Keywords: indole; aldehyde; electrophilic substitution; Ni.
INTRODUCTION
The efficiency of heterogeneous catalysis in organic synthesis can be
improved by employing nanosized catalysts because of their extremely small size
and large surface to volume ratio. It has been recently demonstrated that Ni
nanoparticles as catalysts offer great opportunities for a wide range of
applications in organic synthesis and chemical manufacturing processes
1
including the chemoselective oxidative coupling of thiols , reduction of
2
-4
5
aldehydes and ketones , hydrogenation of olefins , and supports for hydrogen
6
adsorption . Thus, the remarkable catalytic activity and easy synthesis, simplicity
and reusability of the Ni nanoparticles encouraged us to utilize this as a catalyst
for the synthesis of bis(indolyl)methanes (BIM).
Development of bis(indolyl)alkane (BIA) derivatives has been of
considerable interest in organic synthesis because of their wide occurrence in
7
various natural products possessing biological activity and usefulness for drug
design. BIM are substances found in cruciferous that exhibit activity promoting
*
Corresponding author. E-mail: Olyaei_a@pnu.ac.ir
doi: 10.2298/JSC120506076O
1

2
OLYAEI et al.
8
beneficial estrogen metabolism and inducing apoptosis in human cancer cells .
Consequently, a number of synthetic methods for preparation of BIA derivatives
have been reported in the literature by reaction of indole with various aldehydes
9
-16
and ketones in the presence of either a Lewis acid or a protic acid . In recent
years, environmentally safer synthetic methods have received considerable
attention and some solvent-free protocols have been developed. Synthesis of
BIM under solvent-free conditions may be carried out using catalysts such as
17
2
18
using I
2 2
and ZrOCl ·8H O/silica gel . These previous methods involved
generally difficult handling, stoichiometric amount of catalyst may be needed,
and require tedious aqueous work-up, along with the use of environmentally
harmful organic solvents.
In view of the importance of BIA derivatives, we report herein the use of
1
9
nanosized nickel as catalyst in the reaction of indole with aromatic aldehydes
under solvent-free conditions. As such, our method provides the product via easy
work-up and is also in accord with green sustainable chemistry principles.
EXPERIMENTAL
All commercially available chemicals and reagents were used without further
purification. Melting points were determined with an Electrothermal model 9100 apparatus
1
and are uncorrected. IR spectra were recorded on a Shimadzu 4300 spectrophotometer. The H
1
3
6
and C NMR spectra were recorded in DMSO-d on Bruker DRX-500 Avance spectrometers.
Chemical shifts (δ) are reported in parts per million and are referenced to the NMR solvent.
Mass spectra of the products were obtained with an HP (Agilent Technologies) 5937 mass
selective detector. Elemental analyses were carried out by a CHN–O–Rapid Heraeus
elemental analyzer (Wellesley, MA).
General procedure for the synthesis of bis(indolyl)methanes 3
To a mixture of indole (2 mmol) and aromatic aldehyde (1 mmol) was added nickel
nanoparticle powder (10 mol %). The reaction mixture was magnetically stirred on a
o
preheated oil bath at 80 C for the appropriate time as indicated in Table 1. After completion
of the reaction, as indicated by TLC, the reaction mixture was cooled to room temperature.
Then, ethanol (5 mL) was added. Nanoparticles were recovered by centrifuging the organic
layer and reutilized for the same reaction. The solution was poured into water (50 mL). The
precipitate that formed was filtered, washed with water and dried. The crude product was
stirred for 5 min in boiling n-hexane and the resulting precipitate was filtered. The product 3
thus obtained was found to be pure upon TLC examination.
-
1
3
-((1H-Indole-3-yl)( phenyl)methyl)-1H-Indole (3a). IR (KBr, cm ): 3416, 1630, 1460,
-1 1
1
1
1
1
371, 1090, cm ; H NMR (500 MHz, DMSO-d
6
) δ: 5.68 (s, 1H, methine-H), 6.67-7.22 (m,
5H, Ar-H), 10.71 (s, 2H, indole-NH); C NMR (125 MHz, DMSO-d ) δ: 40.58, 112.33,
18.91, 119.03, 119.94, 121.73, 124.39, 124.66, 126.64, 127.48, 128.89, 129.15, 137.44,
45.83.
-((1H-Indole-3-yl)(4-nitrophenyl)methyl)-1H-Indole (3b). IR (KBr, cm ): 3425, 1590,
1
3
6
-1
3
-1 1
1
(
1
456, 1340, 1229, cm ; H NMR (500 MHz, DMSO-d
6
) δ: 5.89 (s, 1H, methine-H), 6.72-8.01
) δ: 40.35, 112.46,
17.55, 119.29, 119.78, 121.97, 124.28, 124.73, 127.24, 130.32, 137.47, 146.63, 154.00.
1
3
m, 14H, Ar-H), 10.79 (s, 2H, indole-NH); C NMR (125 MHz, DMSO-d
6

SYNTHESIS OF BIS(INDOLYL)METHANES
3
-
1
3
-((1H-Indole-3-yl)(3-nitrophenyl)methyl)-1H-Indole (3c). IR (KBr, cm ): 3405, 1525,
-1 1
1
(
1
1
458, 1351, 1045, cm ; H NMR (500 MHz, DMSO-d
6
) δ: 5.92 (s, 1H, methine-H), 6.72-8.30
m, 14H, Ar-H), 10.77(s, 2H, indole-NH); C NMR (125 MHz, DMSO-d ) δ: 39.97, 112.46,
17.82, 119.29, 119.79, 121.92, 121.98, 123.47, 124.75, 127.23, 130.46, 135.97, 137.49,
48.27, 148.67.
-((1H-Indole-3-yl)(2-nitrophenyl)methyl)-1H-Indole (3d). IR (KBr, cm ): 3415, 1574,
1
3
6
-
1
3
-1 1
1
(
1
461, 1350, 1227, cm ; H NMR (500 MHz, DMSO-d
m, 14H, Ar-H), 10.92 (s, 2H, indole-NH); C NMR (125 MHz, DMSO-d
6
6
) δ: 6.41 (s, 1H, methine-H), 6.77-7.87
) δ: 34.93, 112.51,
16.83, 119.37, 119.43, 122.03, 124.80, 124.99, 127.19, 128.39, 131.41, 133.38, 137.47,
1
3
1
38.55, 150.39.
-((1H-Indole-3-yl)(2-chlorophenyl)methyl)-1H-Indole (3e). IR (KBr, cm ): 3414, 1602,
-1
3
1
1
445, 1336, 1110; H NMR (500 MHz, DMSO-d
6
) δ: 6.10 (s, 1H, methine-H), 6.63-7.33 (m,
4H, Ar-H), 10.74 (s, 2H, indole-NH); C NMR (125 MHz, DMSO-d ) δ: 37.02, 112.46,
17.39, 119.27, 119.55, 121.90, 124.88, 127.38, 127.84, 128.60, 130.10, 131.09, 133.57,
1
3
1
1
6
1
37.52, 142.73.
-
1
3
-((1H-Indole-3-yl)(4-chlorophenyl)methyl)-1H-Indole (3f). IR (KBr, cm ): 3412, 1610,
1
1
487, 1455, 1012; H NMR (500 MHz, DMSO-d
6
) δ: 5.84 (s, 1H, methine-H), 6.82-7.36 (m,
1
3
14H, Ar-H), 10.91 (s, 2H, indole-NH); C NMR (125 MHz, DMSO-d ) δ: 22.94, 31.83,
6
1
12.38, 118.41, 119.11, 121.80, 124.49, 127.35, 128.85, 130.98, 131.14, 137.48, 144.89.
-1
3
-((1H-Indole-3-yl)(4-bromophenyl)methyl)-1H-Indole (3g). IR (KBr, cm ): 3409, 1600,
1
1
6
1
1
468, 1409, 1335, 1225, 1100; H NMR (500 MHz, DMSO-d
6
) δ: 5.69 (s, 1H, methine-H),
.68-7.31 (m, 14H, Ar-H), 10.8 (s, 2H, indole-NH); C NMR (125 MHz, DMSO-d ) δ: 39.90,
12.39, 118.30, 119.10, 119.61, 119.87, 121.79, 124.50, 127.33, 131.41, 131.76, 137.47,
45.34.
-((1H-Indole-3-yl)(4-hydroxyphenyl)methyl)-1H-Indole (3h). IR (KBr, cm ): 3410,
1
3
6
-
1
3
1
1
608, 1484, 1420, 1339, 1215, 1088; H NMR (500 MHz, DMSO-d ) δ: 5.57 (s, 1H, methine-
6
13
H), 6.50-7.20 (m, 14H, Ar-H), 8.99 (br, 1H, OH), 10.61 (s, 2H, indole-NH); C NMR (125
MHz, DMSO-d ) δ: 39.47, 112.25, 115.63, 115.79, 118.93, 119.55, 120.05, 121.64, 124.25,
27.54, 130.00, 130.12, 136.07, 137.47, 156.14.
-((1H-Indole-3-yl)(4-methylphenyl)methyl)-1H-Indole (3i). IR (KBr, cm ): 3403, 1600,
6
1
-
1
3
1
1
457, 1218, 1090; H NMR (500 MHz, DMSO-d
6
) δ: 5.64 (s, 1H, methine-H), 6.66-7.21 (m,
4H, Ar-H), 10.64 (s, 2H, indole-NH); C NMR (125 MHz, DMSO-d ) δ: 21.49, 40.58,
12.28, 118.97, 119.08, 120.00, 121.68, 124.34, 127.50, 129.05, 129.46, 135.42, 137.46,
42.82.
-((1H-Indole-3-yl)(4-chlorol-3-nitrophenyl)methyl)-1H-Indole (3j). Yellow solid; Anal.
calcd for C23 : C, 68.74, H, 3.98, N, 10.46; found C, 68.83, H, 3.90, N, 10.51. IR
1
3
1
1
1
6
3
H
3 2
16ClN O
-
1
-1 1
(
1
KBr, cm ): 3400, 1574, 1471, 1350, 1225, cm ; H NMR (500 MHz, DMSO-d
6
) δ: 5.88 (s,
H, methine-H), 6.74-7.87 (m, 13H, Ar-H), 10.80 (s, 2H, indole-NH); C NMR (125 MHz,
) δ: 39.46, 112.49, 117.41, 119.36, 119.72, 122.03, 123.23, 124.82, 125.86, 127.13,
32.25, 134.57, 137.47, 147.25, 148.24.
-((1H-Indol-3-yl)(2-hydroxy-5-nitrophenyl)methyl)-1H-indole (3k). Yellow solid; Anal.
calcd for C23 : C, 72.06, H, 4.43, N, 10.96; found C, 71.96, H, 4.52, N, 11.01. IR (KBr,
1
3
DMSO-d
1
6
3
17 3 3
H N O
-1
-1 1
cm ): 3412, 1588, 1491, 1333, 1275, 1205 cm ; H NMR (500 MHz, DMSO-d
6
, δ / ppm): δ:
6
.05 (s, 1H, methine-H), 6.68-7.86 (m, 13H, Ar-H), 10.74 (s, 2H, indole-NH), 11.30 (br, 1H,
1
3
OH); C NMR (125 MHz, DMSO-d
6
, δ / ppm): 32.64, 112.46, 116.28, 117.57, 119.20,
1
19.51, 121.87, 124.47, 124.66, 125.78, 127.40, 133.21, 137.54, 140.24, 162.29; MS (m/z):
+
383 (M) , 265, 139, 130, 118, 117, 89.

4
OLYAEI et al.
3
-((1H-Indol-3-yl)(5-bromo-2-hydroxyphenyl)methyl)-1H-indole (3l). Pink solid; Anal.
calcd for C23H17BrN O: C, 66.18, H, 4.07, N, 6.71; found C, 66.24, H, 4.00, N, 6.80; IR (KBr,
2
-1
1
cm ): 3407, 1612, 1479, 1413, 1338, 1212, 1094; H NMR (500 MHz, DMSO-d
6
, δ / ppm):
6
.14 (s, 1H, methine-H), 6.76-7.35 (m, 13H, Ar-H), 9.76 (s, 1H, OH), 10.77 (s, 2H, indole-
1
3
NH); C NMR (125 MHz, DMSO-d
6
, δ / ppm) δ: 32.50, 110.74, 112.36, 118.10, 118.15,
1
4
19.08, 119.64, 121.78, 124.45, 127.53, 130.15, 132.30, 134.75, 137.45, 154.64; MS (m/z):
+
+
18 (M+2) , 416 (M) , 300, 298, 245, 243, 220, 117, 97.
-((1H-Indol-3-yl)(2-chloro-6-flourophenyl)methyl)-1H-indole (3m). Pink solid; Anal.
calcd for C23 : C, 73.69, H, 4.27, N, 7.47; found: C, 73.53, H, 4.35, N, 7.40; IR (KBr,
3
H16ClFN
2
-1
1
cm ): 3410, 1608, 1452, 1343, 1100; H NMR (500 MHz, DMSO-d , δ / ppm ): 6.40 (s, 1H,
methine-H), 6.88-7.37 (m, 13H, Ar-H), 10.89 (s, 2H, indole-NH); C NMR (125 MHz,
6
13
DMSO-d6, δ / ppm ): 36.45, 114.67, 117.58, 118.61, 118.79, 121.33, 121.52, 124.00, 126.82,
1
26.85, 128.87, 129.63, 131.92, 132.00, 133.14, 133.26, 136.52,139.30; MS (m/z): 376
+ +
(M+2) , 374 (M) , 337, 243, 222, 194, 117, 90, 89.
3
-((1H-Indol-3-yl)(2-benzyloxyphenyl)methyl)-1H-indole (3n). White solid; Anal. calcd
-1
for C30
H
24
N
2
O: C, 84.11, H, 5.60, N, 6.54; found C, 84.17, H, 5.65, N, 6.48.IR (KBr, cm ):
1
3
CH
411, 1589,1447, 1340, 1221, 1091; H NMR (500 MHz, DMSO-d , δ / ppm): 5.14 (s, 2H, O-
6
13
2
-), 6.34 (s, 1H, methine-H), 6.79-7.38 (m, 19H, Ar-H), 10.79 (s, 2H, indole-NH);
, δ / ppm): 34.99, 72.40, 114.52, 115.45, 120.88, 121.22, 122.01,
23.40, 123.91, 126.79, 129.89, 130.03, 130.22, 130.59, 131.29, 132.23, 136.39, 139.70,
C
NMR (125 MHz, DMSO-d
6
1
1
+
40.50, 158.38; MS (m/z):428 (M) , 337, 243, 130, 117, 92, 91.
RESULTS AND DISCUSSION
In continuation of our work on the development of solvent-free conditions in
2
0-24
one-pot, multi component reactions
, we observed that the treatment of indole
with aromatic aldehydes in the presence of nickel catalyst under solvent-free
conditions afforded the corresponding BIM derivatives. As a model reaction, the
reaction of indole (2 mmol) with benzaldehyde (1 mmol) was initially examined
o
at 70-120 C in the presence of nanosized Nickel powder (10 mol %) as catalyst
under solvent-free conditions. Our investigation demonstrated that the best result
o
was obtained when temperature was fixed at 80 C and the reaction was
completed in 1 hour. Thereby, an excellent yield of bis(indolyl)phenylmethane
(3a) was obtained (95%). To determine the appropriate concentration of the
catalyst Ni nanoparticles, we have investigated that the model reaction of
benzaldehyde and indole at different concentrations of Ni nanoparticles. This
indicated that 10 mol % of nanosized Ni produces the best results with respect to
product yield (Table I).
In order to show the general applicability of the method for other substrates
and derivatives, the same reaction conditions can be applied. Reactions of 2
equiv indole and 1 equiv aromatic aldehydes 2 in the presence of nickel
o
nanoparticle catalyst under solvent-free conditions at 80 C in appropriate times
(see Table II) directly afforded BIM derivatives (3a-n) with good to excellent
yields (Scheme). The reaction times and yields of the synthesized BIM

SYNTHESIS OF BIS(INDOLYL)METHANES
5
derivatives have been shown in Table 2. As shown in Table 2, yields are almost
quantitative in most cases.
We found that aromatic aldehydes with electron donating and electron
withdrawing groups were converted to the corresponding products within some
hours. We have examined the recovery and reusability of the catalyst. The
catalyst was recovered by a simple work-up using the centrifugation method and
reused during four consecutive runs without any apparent loss of activity for the
same reaction. It is noteworthy that the yield of the product in the second, third,
and fourth uses was almost the same as that in the first run.
1
13
All products were well characterized by H NMR, C NMR, FTIR, mass
spectra, elemental analyses and melting point. To the best of our knowledge,
synthesis of compounds 3j-n has not previously been reported in literature. The
1
H NMR spectra of compounds 3j-n are shown a sharp singlet for the indole-NH
at about δ 10.80 ppm. The methine protons appeared as singlet at about δ 6.20
and aromatic protons displayed in the region of 6.68-7.86 ppm. Hydroxyl protons
in the compounds 3k and 3l were observed at δ 11.30 and 9.76 ppm, respectively.
1
3
The C NMR, FTIR, mass spectra and elemental analyses confirmed the
structures of synthesized compounds.
CONCLUSIONS
In summary, we have found for the first time that Ni in the form of
nanoparticles, is a potential alternative to the use of noble-metal-based catalysts
for the synthesis of BIM derivatives. Compared to the other previously reported
procedures in literature, the present method provides some advantages such as
omitting organic solvent, efficient and experimental simplicity, compatibility
with various functional groups, generality, clean, easy work-up and high yields.
Moreover, there is no need for dry solvents or protecting gas atmospheres.
Product purification by column chromatography is not necessary and catalyst can
be easily recovered from the reaction mixture by simple centrifugation.
Acknowledgment. The authors thank the Research Council of Payame Noor University
for financial support.
И З В Н Д
МНВ ОПИРСТО РИМСЕЗИ БИР(ИМДНКИК)ЛЕСАМА ТОНСПЕБНЛ МАМНЧЕРСИЦА
МИЙКА ЙАН ЙАСАКИЗАСНПА БЕЗ ОПИРТРСВА ПАРСВАПАЧА
1
1
1
1
2
ABOLFAZL OLYAEI , MOHSEN VAZIRI , REZA RAZEGHI , BAHAREH SHAMS и HASAN BAGHERI
1
2
Department of Chemistry, Payame Noor University, P.O. Box 19395-3697, Tehran, Iran и Department of
Chemistry, Islamic Azad University, Takestan Branch, Qazvin, Iran
Пазвијеме рт мамнцерсихе мийка йнје рт тонспебљеме йан йасакизаснп т пеайхији
екейспнуикме рторсистхије имднка и пазкицисиф апнласицмиф акдефида т ндртрсвт
парсвапаца. Дибијеми рт ндгнвапајтћи бир(имднкик)лесами т днбпнл дн ндкицмнл
опимнрт. Опедмнрси нве леснде рт ндртрсвн нпгамрйиф парсвапаца, йпасйн пеайхинмн

6
OLYAEI et al.
впеле, вирнй опимнр опнизвнда пеайхије, једмнрсавам онрстоай нбпаде пеайхинме
рлече, нкайчамн изнкнвање опнизвнда и лнгтћмнрс пегемепахије и вичерсптйе
тоноспебе йасакизаснпа.
(Опилљемн 6. лаја, певидипамн 10. јтка 2012)
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SYNTHESIS OF BIS(INDOLYL)METHANES
7
TABLE I. Comparison of the amount of Ni and yields for the synthesis of
BIM.
Entry
Catalyst/ mol %
Time/ min
Yield, %
1
2
3
4
5
1
90
90
90
60
60
55
65
70
84
95
2.5
5.0
7.5
10
TABLE II. Ni nanoparticles-catalyzed synthesis of BIM under solvent-free conditions at 80 ° C.
o
M.P ( C)
Found
Entry
Ar
Products
Time/ minYield/ %
Reported [Lit.]
1
2
3
4
5
6
7
8
9
C
6
H
5
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
60
20
30
60
95
92
89
88
91
90
88
85
85
89
94
88
92
88
148-150
220-22
264-265
137-139
74-75
149-150 [25]
217-220 [25]
265-566 [26]
139-141 [27]
70-71 [25]
76-77 [25]
110-112 [28]
122-124 [25]
4-NO
3-NO
2-NO
2-ClC
4-ClC
4-BrC
4-OHC
4-CH
4-Cl-3-NO
2-OH-5-NO
2-OH-5-BrC
2-Cl-6-FC
2-OCH PhC
2
2
2
C
C
C
6
6
6
H
H
H
4
4
4
6
H
H
4
20
6
4
100
100
120
90
70
20
110
60
70
80-82
6
H
4
116-117
136-137
96-97
183-184
194-196
141-142
94-95
6
H
4
3
C
6
H
4
93-94 [25]
1
0
2
C
6
H
3
-
-
-
-
-
1
1
2
C
6
H
3
1
1
1
2
3
4
6
H
3
6
H
3
2
6
H
5
206-208
Scheme. Synthesis of bis(indolyl)methanes.