H5PW10V2O40/pyridino-SBA-15 as a highly recyclable, robust and efficient inorganic-organic hybrid material for the catalytic preparation of bis(indolyl)methanes

Article abstract of DOI:10.1016/j.molcata.2012.09.016

A highly well-organized heterogeneous protocol is developed for the simple synthesis of bis(indolyl)methanes by the effective mediation of an inorganic-organic hybrid material prepared by the chemically anchoring of H ₅PW₁₀V₂

Full text of DOI:10.1016/j.molcata.2012.09.016

Journal of Molecular Catalysis A: Chemical 366 (2013) 140–148
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
H PW V O /pyridino-SBA-15 as a highly recyclable, robust and efficient
5
10
2
40
inorganic–organic hybrid material for the catalytic preparation of
bis(indolyl)methanes
a,∗
b
a
b
b
Reza Tayebee , Mostafa M. Amini , Farzaneh Nehzat , Omid Sadeghi , Mahsa Armaghan
a
Department of Chemistry, School of Sciences, Hakim Sabzevari University, Sabzevar, Iran
Department of Chemistry, Shahid Beheshti University, G.C., Tehran, Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 August 2012
Received in revised form
A highly well-organized heterogeneous protocol is developed for the simple synthesis of
bis(indolyl)methanes by the effective mediation of an inorganic–organic hybrid material prepared by
the chemically anchoring of H5PW10V2O40 onto mesoporous silica (SBA-15). Standard characterization
data such as XRD, SEM, and FT-IR for the obtained catalyst verified that the ordered hexagonal mesoporous
structure of SBA-15 and the Keggin structure of tungstovanadophosphoricacid on pyridine modified SBA-
1
4 September 2012
Accepted 15 September 2012
Available online 24 September 2012
1
5 surface are preserved. Reusability experiments demonstrated that the active sites on the pyridine
modified SBA-15 mesoporous silica retained their structure after several cycles.
Keywords:
©
2012 Elsevier B.V. All rights reserved.
Hybrid material
Heteropolyacid
Keggin
Bis(indolyl)methane
Synthesis
1
. Introduction
groups to overcome the limitations involved in the separation
and recycling of the homogeneous catalysts. Several method-
ologies have been adopted in the literature for the synthesis
of inorganic–organic hybrid materials. Conventionally they are
immobilized/anchored on various organic polymers such as resins
[3,4], supported on inert porous solids such as alumina and sil-
ica [5,6] or encapsulated in the pores and cavities of microporous
and mesoporous materials such as zeolites, MCM-41, and SBA-15
[7–9].
As commented, immobilization of homogeneous catalyst onto
the porous material through chemical bonding is one of the most
powerful strategies to overcome the negative aspects of catalyst
leaching. To achieve this goal, it is necessary to use a linker with
chemical bonding between catalyst and support. Porous materials
have attracted the interest of scientific and technological societies
because of their ability to interact with atoms, ions and molecules
at surfaces, and forming a basis for the preparation of hetero-
geneous catalysts. Among various mesoporous molecular sieves,
SBA-15 mesoporous silica with uniform channels and narrow pore
size distributions has the ability to accommodate some of the huge
molecules such as heteropolyanionsonto the pores, thus, enable the
pore surfaces to be accessed in three dimensions in catalytic reac-
tions [10]. Mesoporous SBA-15 is a more attractive support than X-
and Y-type zeolites, and MCM-41 due to its better hydrothermal
stability, large pores up to approximately 30 nm, and thick walls
Heteropolyacids have attracted much attention during the
past decade because of their unique ensemble of properties. The
Keggin type vanadium substituted polyoxometalates have been
recognized as potent catalysts for many catalytic organic trans-
formations. They exhibit great advantages, and their catalytic
properties can be tuned by changing the identity of charge-
compensating counteractions, hetero-atoms, and framework metal
atoms. High solubility of these materials often makes their separa-
tion from the reaction mixture difficult. Therefore, immobilization
of the heteropolyacid on supports, with high surface area, improves
their catalytic performance in various liquid–solid heterogeneous
reactions. Although, physical adsorption of heteropolyacids via
encapsulation onto various supports and wet impregnation meth-
ods facilitated separation of the catalyst from the reaction mixture,
however, weak bonding interaction of heteropolyanion with the
support leads to partial leaching, especially with polar solvent
media [1,2].
Heterogenizations of heteropolyoxometalates through synthe-
sizing inorganic–organic hybrid materials have been an interesting
approach during the past years. This strategy enabled the research
∗ Corresponding author.
E-mail address: rtayebee@yahoo.com (R. Tayebee).
[
11].
1
381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.09.016

R. Tayebee et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 140–148
141
R
H
H
O
C
C
heterogenouscatalyst
HPA/TPI-SBA-15
+
2
SolventFree,100 oC
N
H
N
N
H
H
R
R=alkyl, halogen,hydroxyl,nitro,methoxy
Scheme 1.
Herein, we wish to study the catalytic activity of different
heterogeneous catalysts prepared via wet impregnation method,
without chemical bonding, and with inorganic–organic hybrid
material synthesized by the chemical anchoring of a linker for
the generation of bis(indolyl)methanes. The preparation and
characterization of H5PW10V O immobilized onto amine- and
2.2. Synthesis of SBA-15 and pyrdine functionalized SBA-15
(TPI-SBA-15)
Mesoporous SBA-15 silica was prepared by the method as
described elsewhere [13]. For the preparation of pyridine function-
alized SBA-15, 1.0 g of SBA-15 was suspended in 50 ml toluene,
and the mixture was stirred for 1 h and then 2.0 g of TPI was
added and refluxed for 24 h. The white–brownish solid was
removed by filtration and was washed with toluene and ethanol
and then dried at room temperature. Synthesis of SBA-15 and
pyridine-functionalized material (TPI-SBA-15) were confirmed by
IR spectroscopy, low-angle X-ray diffraction and elemental anal-
ysis. Elemental and thermal analysis of TPI-SBA-15 sample gave
pyridine concentration of 1.92 mmol/g. A schematic diagram of
modified SBA-15 with TPI is shown in Scheme 2.
2
40
N-[3-(triethoxysilyl)propyl]isonicotinamide (TPI) modified meso-
porous silica surfaces (NH -SBA-15 and TPI-SBA-15) are studied,
2
and their catalytic performances are investigated. In this approach,
the catalyst HPA/TPI-SBA-15 applied as a highly efficient catalyst
for the above condensation reaction (Scheme 1). The heteroge-
neous nature and reusability of the immobilized catalyst were also
studied.
2
. Experimental
2
.3. Immobilization of 10-tungsto-2-vanadophosphoricacid on
2.1. Materials and methods
TPI-SBA-15
Reagents and starting materials were purchased from commer-
For immobilization of HPA on TPI-SBA-15, 50 ml of methanol
cial resources. All products were identified by comparison of their
spectral and physical data with those previously reported [19–23].
Progress of the reactions was monitored by TLC. Infrared spectra
were recorded (KBr pellets) on a 8700 Shimadzu Fourier Trans-
form spectrophotometer. 1H and C NMR spectra were recorded
on a Bruker AVANCE 300-MHz instrument using TMS as an internal
reference. Vanadium and molybdenum contents were determined
by ICP (Perkin Elmer Plasma 1000 Emission Spectrometer). X-ray
diffraction patterns were obtained on a STOE diffractometer with
Cu K␣ radiation. Electron microscopy was performed on a Phillips
XL-30 scanning electron microscope (SEM). The heteropolyacid cat-
alyst was prepared and characterized according to the literature
procedure [12].
solution containing 0.3 g of H5PW10V O ·30H O was added to a
2
40
2
freshly activated TPI-SBA-15 (0.70 g) and the mixture was refluxed
for 3 h. Then, the heterogeneous catalyst was filtered and extracted
in a soxhlet extractor using methanol as solvent for 12 h and
13
◦
thereafter was dried at 105 C in a vacuum oven (Scheme 3). The
combined filtrate after washing and soxhlation was subjected to
UV–vis analysis and found no characteristic bands for tungstodi-
vanadophosphoricacid (VHP). This clearly indicated retention of all
the VHPA in the pores of TPI-SBA-15. H5PW10V O loading on
2
40
TPI-SBA-15 was determined by measuring the amount of tung-
sten and vanadium in H5PW10V O40/TPI-SBA-15 (0.07 mmol/g,
2
0
.20 g/g) by inductively coupled plasma-atomic emission spec-
troscopy (ICP-AES). Moreover, ICP data clearly confirmed higher
OH
O
O
O
OH
+
+
O
NH
Si
Si
NH
OH EtO
2
H+
Toluene
O
OH
OH
OH
+
Si
N
H
EtO
Reflux
N
O
O
24h
EtO
+
O
+
OH
NH2
NH
OH
O
SBA-15
TPI
Scheme 2.

1
42
R. Tayebee et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 140–148
NMR, ı (ppm): 40.5, 111.8, 117.8, 119.4, 119.7, 122.1, 123.8, 124.4,
−
1
1
27.0, 129.9, 137.3, 146.7, 152.8. IR (KBr, cm ) ꢀmax: 736, 1086,
1
343, 1416, 1457, 1506, 1636, 3447.
2
.5.3. Bis(indolyl)-4-chlorophenylmethane
1
H NMR (CDCl , 300 MHz), ı (ppm): 5.82 (s, 1H), 6.54 (brs, 2H),
3
13
7
.0 (t, 2H), 7.15 (t, 2H), 7.25–7.35 (m, 8H), 7.81 (br, 2H, NH).
C
NMR, ı (ppm): 39.4, 111.2, 129.2, 129.4, 129.8, 122.0, 123.2, 126.4,
−
1
1
1
1
28.0, 130.0, 131.4, 136.2, 142.5. IR (KBr, cm ) ꢀmax: 667, 761, 856,
012, 1040, 1091, 1124, 1216, 1338, 1416, 1455, 1486, 1518, 1616,
726, 2853, 2925, 3011, 3056, 3413.
2
.5.4. Bis(indolyl)-2,6-dichlorophenylmethane
1
H NMR (CDCl , 300 MHz), ı (ppm): 6.58 (s, 1H), 6.68 (s, 2H),
3
6.86–7.03 (m, 7H), 7.09 (d, 2H, J = 7.8 Hz), 7.41 (d, 2H, J = 7.8 Hz),
7
.71 (br, NH). 13C NMR, ı (ppm): 37.2, 110.7, 114.4, 119.3, 119.6,
121.4, 121.8, 124.7, 127.2, 128.2, 128.6, 136.3, 138.7.
2
.5.5. Bis(indolyl)-2-nitrophenylmethane
1
H NMR (CDCl , 300 MHz), ı (ppm): 6.12 (s, 1H), 6.91 (s, 2H),
3
7
7
.08–7.17 (m, 4H), 7.29 (d, 2H, J = 7.8 Hz), 7.47 (d, 2H, J = 7.9 Hz),
.57–7.66 (m, 2H), 7.79–7.90 (m, 2H), 8.21 (d, 2H, J = 8.6 Hz).
Scheme 3.
amount of heteropolyacid is immobilized within the pyridine
functionalized support than bare SBA-15. Interestingly, the func-
tionalized mesoporous silica supported HPAs showed no leaching
after several hours contact with aqueous solution. The strong inter-
action between functionalized silica and HPA make it a suitable
homogeneous catalyst. As expected, TPI functional group improved
immobilization process and higher content of HPA was immobi-
lized within the functionalized support.
2.5.6. Bis(indolyl)-(1-methyl)methanediyl
1H NMR (CDCl3, 300 MHz), ı (ppm): ı 1.91 (d, 3H, J = 6.8 Hz), 4.50
(m, 1H), 6.85 (t, 2H, J = 6.8 Hz), 7.03 (m, 2H), 7.07 (t, 2H, J = 8 Hz), 7.25
−
1
(d, 2H, J = 8 Hz), 7.40 (d, 2H, J = 8 Hz), 7.84 (br, 2H). IR (KBr, cm
max: 3399, 3389, 2958.
)
ꢀ
2.5.7. Bis(indolyl)-cyclohexanediyl
1
H NMR (CDCl , 300 MHz), ı (ppm): ı 1.61 (m, 6H), 2.54 (m, 4H),
3
3
.25 (m, 1H), 4.60 (s, 1H), 6.89 (t, 2H, J = 7.2 Hz), 7.07 (m, 4H), 7.29
−
1
2.4. General procedure for the preparation of
(d, 2H, J = 8.1 Hz), 7.55 (d, 2H, J = 8.1 Hz), 7.92 (br, 2H). IR (KBr, cm
ꢀmax: 3450, 3030, 2929, 1658, 1550, 1461, 740.
)
bis-(indolyl)methanes
A mixture of carbonyl compound (1 mmol), indole (0.234 g,
2
.5.8. Bis(indolyl)-3,4-dimethoxyphenylmethane
2
mmol) and the desired amount of the heterogeneous catalyst, as
1
H NMR (CDCl , 300 MHz), ı (ppm): ı 3.76 (s, 3H), 3.85 (s, 3H),
3
◦
indicated in tables, was stirred at the elevated temperature (100 C)
for the appropriate reaction time. After completion of the reaction,
as indicated by TLC, acetonitrile (3 ml) was added to the reaction
mixture and the catalyst was filtered off. Then, silica gel (∼1 g) was
added to the filtrate, and after evaporation of the solvent, a dark
pinkish solid mixture was obtained. Purification of the product was
performed by a short column chromatography eluted with ethylac-
etate/petroleum ether (1/9) to give a pinkish solid product in high
yields. Products were known compounds and were identified by
means of IR and 1H NMR spectroscopy and/or comparison of their
melting points with those reported in the literature.
5
7
3
.83 (s, 1H), 6.65 (d, 2H), 6.78 (d, 2H), 7.0 (t, 3H), 7.17 (t, 2H),
.29–7.43 (m, 4H), 7.91 (br, NH, 2H). IR (KBr, cm ) ꢀmax: 3480,
020, 1604, 1512, 1456, 1418, 1336, 1216, 1091, 1033, 759.
−1
2.5.9. Bis(indolyl)-2-hydroxyphenylmethane
1
H NMR (CDCl , 300 MHz), ı (ppm): ı 3.79 (s, 1H), 5.83 (s, 1H),
3
6
7
1
.67 (d, 2H), 6.81 (d, 2H), 7.01 (t, J = 7.2 Hz, 2H), 7.28–7.46 (m, 6H),
−
1
.92 (br, s, NH, 2H). IR (KBr, cm ) ꢀmax: 3485, 3021, 2848, 1616,
517, 1465, 1411, 1326, 1221, 1094.
2.5.10. Bis(indolyl)-2-methoxylphenylmethane
1
H NMR (CDCl , 90 MHz), ı (ppm): 3.82 (s, 3H), 6.32 (s, 1H), 6.61
3
2
2
2
.5. Spectral data for selected bis(indolyl)methanes
−
1
(s, 2H), 6.81–7.40 (m, ArH, 12H), 7.80 (br, NH, 2H). IR (KBr, cm
)
ꢀ
max: 3408, 3056, 2932, 1597, 1486, 1450, 1335, 1102, 745.
.5.1. Bis(indolyl)phenylmethane
1
H NMR (CDCl , 300 MHz), ı (ppm): 5.91 (s, 1H, CH), 6.68 (s,
3
2
.5.11. Bis (indolyl)-2-chlorophenylmethane
H), 7.10 (t, J = 7.3 Hz, 2H, arom), 7.22 (t, J = 7.3 Hz, 2H, arom), 7.23
1
H NMR (CDCl , 400 MHz), ı (ppm): 6.34 (s, 1H, Ar–CH), 6.66 (s,
(
t, J = 7.2 Hz, 1H, arom), 7.30–7.40 (m, 2H, arom), 7.35–7.45 (m, 4H,
3
13
2H), 7.02 (t, 2H, J¼8.0 Hz), 7.11–7.23 (m, 6H), 7.36–7.43 (m, 4H),
7
1417, 1455, 1616, 3052, 3412.
arom), 7.41 (d, J = 7.9 Hz, 2H, arom), 7.90 (s, br, 2H, NH). C NMR, ı
−
1
.96 (br, s, 2H, NH). IR (KBr, cm ) ꢀmax: 1010, 1037, 1093, 1337,
(
1
ppm): 40.6, 111.4, 119.7, 120.2, 120.4, 122.4, 124.1, 126.6, 127.5,
−1
28.6, 129.2, 137.1, 144.4. IR (KBr, cm ) ꢀmax: 760, 820, 890, 960,
1
080, 1200, 1410, 1640, 2380, 2880, 2900, 3340.
2
.5.12. Bis (indolyl)-3-methoxylphenylmethane
1
2
.5.2. Bis(indolyl)-4-nitrophenylmethane
H NMR (CDCl3, 400 MHz), ı (ppm): 3.76 (3H, s), 3.85 (3H, s), 5.83
1
H NMR (CDCl , 300 MHz), ı (ppm): 5.92 (s, 1H, CH), 6.63 (s, 2H),
(1H, s), 6.65 (2H, d), 6.78 (2H, d), 7.0 (3H, t), 7.17 (2H, t), 7.29–7.43
3
−
1
6
.91 (t, J = 7.3 Hz, 2H, arom), 7.08 (t, J = 7.3 Hz, 2H, arom), 7.25 (d,
(4H, m), 7.91 (2H, bs, NH). IR (KBr, cm ) ꢀmax: 3480, 3020, 1604,
13
J = 7.9 Hz, 2H, arom), 7.32 (d, J = 8.1 Hz, 2H, arom), 7.44 (d, J = 8.6 Hz,
2
1512, 1456, 1418, 1336, 1216, 1091, 1033, 759. C NMR, ı (ppm):
H, arom), 8.04 (d, J = 8.6 Hz, 2H, arom), 9.31 (s, br, 2H, NH). 13
C
147.4, 136.7, 127.1, 123.5,121.9, 119.8, 119.2, 112.3, 111, 55.8, 39.8.

R. Tayebee et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 140–148
143
Fig. 2. FT-IR spectrum of H5PW10V2O40.
The band at 998 cm 1 is due to the stretching vibration of W O ,
−
d
−
1
connecting with the terminal oxygen atoms. The band at 890 cm
was assigned to the stretching vibration of W Ob W, associated
with corner bridged oxygens, and the band at 778 cm comes from
the vibration of W Oc W, associated with side bridged oxygens.
From the IR spectrum of HPA/TPI-SBA-15, one can see a broad band
in the range of 1000–1250 cm , which reveals the strong interac-
tion of silica and heteropolyacid [16]. Actually, clear observation
of POM was hindered as a result of the strong background of silica
−
1
−
1
support. Owing to the overlap of the W
those of Si Si stretching vibrations of mesoporous supports,
only the bands corresponding to W W and W O are discern-
O W and P O bands with
O
O
able after immobilization within the support. Detection of bands
related to bulk HPA revealed that the Keggin structure is retained
after immobilization. However, a slight shift is evidenced as a result
of HPA interaction with functional groups of the support.
Fig. 1. FT-IR spectra of (A) SBA-15, (B) TPI-SBA-15, and (C) HPA/TPI-SBA-15.
3.1.2. X-ray diffraction study
Low-angle powder X-ray diffraction (XRD) patterns of pure,
functionalized, and H5PW10V O
trated in Fig. 3. The results showed that the samples are of a high
degree of order in a hexagonal close-packed lattice. As can be seen,
containing SBA-15 are illus-
3
3
3
. Results and discussion
2
40
.1. Structural characterization of the hybrid material
◦
all patterns showed an intense reflection (1 0 0) at about 2ꢁ = 1.5 ,
.1.1. FT-IR spectroscopy
SBA-15 mesoporous silica was functionalized with pyridine by
treating with TPI in refluxing toluene. The TPI was anchored to the
mesoporous silica surface by condensation of the silanol groups of
mesoporous silica and the ethoxy groups of TPI. The incorporation
of the pyridine moieties on the mesoporous material was confirmed
by FT-IR. The characteristic stretching vibration bands of pyridine
−
1
at 1655 and 1560 and organosilane at 2981 cm in the FT-IR spec-
tra (Fig. 1) of the grafted material confirmed the presence of TPI
group on the surface of the mesoporous silica. Furthermore, the
Si
O Si, Si O and SiO H stretching vibration bands of mesoporous
−
1
silica appeared at 1060, 958, and 3000–3500 cm , respectively.
−1
The broad band in the 3500–3700 cm region can be attributed to
the symmetrical stretching vibration modes of the adsorbed water
molecules.
The structure of Keggin HPA anion consists of a PO tetrahedron
4
that surrounded by four W O9 groups formed by the edge sharing
3
octahedron. These groups are connected to each other by corner-
sharing oxygen atoms [14]. This structure gives rise to different
types of oxygen atoms, being responsible for the fingerprint IR
−
1
bands of the Keggin anion between 1100 and 500 cm (Fig. 2). The
four distinct bands belonging to the Keggin structure were centered
−1
−1
at 1088, 998, 890, and 778 cm [15]. The band at 1088 cm was
assigned to the symmetric stretching vibration of PO tetrahedron.
Fig. 3. Low-angle X-ray diffraction patterns of SBA-15, TPI-SBA-15 and HPA/TPI-
SBA-15.
4

1
44
R. Tayebee et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 140–148
Fig. 4. X-ray diffraction patterns of H5PW10V2O40 (a), and H5PW10V2O40/TPI-SBA-15 (b).
which indicates that the mesoporous structure of SBA-15 after
functionalization with TPI and immobilization of H5PW10V O
3.2. Studying catalytic activity of some inorganic–organic hybrid
materials
2
40
remained intact. The slight shift of the characteristic reflection of
SBA-15 in low-angle XRD pattern indicates that the H5PW10V O
Table
1 shows the catalytic activity of some prepared
2
40
mostly occupied mesoporous channels. Furthermore, for further
characterization, the wide-angle XRD patterns of H5PW10V O
H5PW10V O supported inorganic–organic hybrid materials for
2
40
the synthesis of bis(idolyl)phenylmthane. Clearly, the support
material and the amine linker (TPI and/or Pip.) strongly affected the
efficacy of the heterogeneous catalyst. The results demonstrated
that pyridine-modified SBA-15 is a superior carrier with respect to
MCM-41 with the same organic modifier attached to the desired
2
40
before and after immobilization were recorded (Fig. 4a and b,
respectively). The diffraction peaks of H5PW10V O with d values
2
40
of 8.76, 6.15, 5.01, 4.33, 3.87, 3.52, 3.26, 3.05, 2.87, 2.73, 2.60, 2.39,
◦
◦
2
.22, 2.03, 1.97, 1.88, 1.72, and 1.54 A in the 2ꢁ range of 10–80
are in accordance with JCPDS for this compound [17]. Interestingly,
the H5PW10V O diffraction peaks after incorporation on TPI-SBA-
heteropolyacid catalyst H5PW10V O40. The first produced 84% of
2
product after 25 min (entry 2); whereas, the latter yielded the same
amount after 60 min (entry 1). Effect of the amine linker on the
catalytic efficacy was also investigated. Results revealed that TPI
liker (84% after 25 min) behaved distinctly better than NHCl (86%
after 150 min, entry 4). Finally, it was found that piperazine linked
to NHCl linker supported on SiO2 (mesh, 230–400, 5–15 ␮m) acti-
vated the heterogeneous catalyst and reduced the reaction time
2
40
◦
1
5 collapsed and only a broad peak at about 20 is visible which
indicated H5PW10V O is well dispersed onto SBA-15 mesoporous
2
40
silica, and it is a suitable heterogeneous catalyst for a wide variety
of catalytic applications. This is in accordance with XRD pattern of
heteropolyanions in other supports [17].
∼
50%. The first showed 85% of product after 80 min; whereas, SiO2-
3
.1.3. SEM studies
The SEM micrographs of TPI-SBA-15 and H5PW10V O40/TPI-
NHCl-H5PW10V O produced comparable conversion in 150 min
2
40
2
(entry 4).
SBA-15 are shown in Fig. 5a and b, respectively. SEM micrographs
show both materials have similar texture and there is no sig-
nificant difference and also indicated that the H5PW10V O is
2
40
3.3. Studying the catalytic activity of support material SBA-15
and withTPI linker
well dispersed in TPI-SBA-15 and can be used as a hetero-
geneous catalyst. Furthermore, the intense diffraction at about
◦
2
ꢁ = 2 in the low-angle X-ray diffraction patterns of all sam-
Table 2 describes the catalytic activity of H PW V O40, TPI-
5
10
2
ples confirmed that the mesoporous structures of SBA-15 after
functionalization with TPI and immobilization of HPA are well
maintained.
SBA-15, and SBA-15 fragments, separately, in the preparation of
bis(indolyl)phenylmethane under the standard reaction condition
reported in this work. H PW V O was solely effective in the
5
10
2
40

R. Tayebee et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 140–148
145
Table 1
Comparing the catalytic activity of some prepared inorganic–organic hybrid materials bearing H5PW10V2O40 for the synthesis of bis(idolyl)phenylmthane.
Entry
Catalyst
Catalyst (g)
H5PW10V2O40 (mmol)
Time (min)
Yield (%)
−
−
−
−
3
3
3
3
1
2
3
4
MCM-41-TPI-H5PW10V2O40
SBA-15-TPI-H5PW10V2O40
SiO2-NHCl-Pip-H5PW10V2O40
SBA-15-NHCl-H5PW10V2O40
0.009
0.02
0.011
0.015
10
10
10
10
60
25
80
84
84
85
86
150
◦
Benzaldehyde (1 mmol), indole (2 mmol) and the desired amount of the heterogeneous catalyst, as indicated in table, was stirred at 120 C for the appropriate reaction time.
After completion, the product was worked up as described in Section 2.2.
Table 2
sufficient to obtain 84% of conversion after short time 25 min (entry
Studying the catalytic activity of H5PW10V2O40, TPI-SBA-15, and SBA-15 in the
preparation of bis(indolyl)phenylmethane.
9
). It is noticeable that free carrier material has also shown some
catalytic activity in the desired reaction. SBA-15 and pyridine mod-
ified TPI-SBA-15 produced 55 and 45% of conversion after 60 and
Entry
Catalyst
Catalyst
mg)
Time
(min)
Yield
(%)
(
8
0 min (entries 7 and 8, respectively). Obviously, modification of
5
6
7
8
9
H5PW10V2O40
H5PW10V2O40
SBA-15
SBA-15-TPI
H5PW10V2O40/TPI-SBA-15
56
3
20
20
20
15
40
60
80
25
84
65
55
45
84
SBA-15 with pyridine decreased its catalytic activity.
3.4. Studying effect of different supporting materials
Reaction condition is described in Section 2.
To compare the role of amine linker on the efficiency of the
catalytic system, heterogenization of H5PW10V O was carried
2
40
out via physical absorption on three important carriers including
synthetic route and 0.056 g (2 mol%) of this catalyst produced 84%
of product after 15 min (entry 5); whereas, 0.003 g (∼0.1 mol%) of
this catalyst led to 65% of conversion after 40 min (entry 6). Using
SBA-15, MCM-41, and ZrO (Table 3). These three catalytic systems
2
based on the desired heteropolyacid and carriers were prepared
according to the conventional wet-impregnation method. SBA-15,
as a mesoporous hexagonal silica with large pores, thick walls, and
high hydrothermal stability would act as a promising catalyst sup-
port. Furthermore, its large internal surface area allows dispersion
inorganic–organic hybrid of H5PW10V O40/TPI-SBA-15 (0.02 g),
2
which was included only 3 mg of the desired heteropolyacid, was
of a large number of the catalytically active H5PW10V O40. MCM-41
2
is a class of mesoporous silica tube-like materials with a hexagonal
arrangement of uniformly sized one-dimensional mesoporous. This
material has high thermal and hydrothermal stability, pores with
uniform size and shape, large surface areas, and high hydropho-
bicity and acidity; therefore, these compounds are of interest as
sorbents and solid support in catalysis [18]. According to these com-
ments, results confirmed that SBA-15 is the best carrier and led to
8
8% yield after 15 min (entry 11). MCM-41 was also effective and
produced the same result after somewhat longer time 35 min (entry
2). Notably, ZrO showed the least activity with 71% of conversion
1
2
after 45 min (entry 13). Meanwhile, homogeneous unsupported
H5PW10V O gave only 50% yield after 40 min (entry 10).
2
40
Although, the surface area of H5PW10V O
increases after
2
40
immobilization onto the solid carriers and good results were
obtained, however, leaching of the heteropolyacid during work up
by using polar reaction media and poor catalytic reusability of the
above physically adsorbed catalysts would be an important limiting
problem in practical applications and covalent bonding of the het-
eropolyacid to the carrier surface via an organic linker would be a
promising solution.
To study leaching of H5PW10V O from the surface of SBA-
2
40
1
5, reusability of H5PW10V O40/SBA-15 was investigated. Although
2
this catalyst led to 88% of conversion in the first run after 15 min,
however, catalytic efficiency of the protocol was decreased signifi-
cantly in the next runs by using the recycled H5PW10V O40/SBA-15
2
Table 3
Studying the catalytic activity of some important classical supports obtained via
physical adsorption of HPA on the carrier.
Entry
Catalyst (10 mg)
HPA
Time (min)
Yield
(%)
(
mmol)
−
−
−
−
3
3
3
3
10
11
12
13
H5PW10V2O40
10
10
10
10
40
15
35
45
50
88
89
71
H5PW10V2O40/SBA-15
H5PW10V2O40/MCM-41
H5PW10V2O40/ZrO2
Fig. 5. SEM micrographs of TPI-SBA-15 (a) and H5PW10V2O40/TPI-SBA-15 (b).
Reaction condition is described in Section 2.

1
46
R. Tayebee et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 140–148
Table 4
Synthesis of various bis(indolyl)methane derivatives in the presence of H5PW10V2O40/TPI-SBA-15 under solvent free condition.
Entry
Substrate
Product
Time (min)
Yield (%)
M.P.
Refs.
[19]
Cl
H
H
Cl
C
1
4
C
30
85
76–77
O
N
H
N
H
H
NO2
H
C
O
C
1
5
15
95
220–222
[20]
NO2
N
N
H
H
Cl
H
H
C
C
O
1
6
20
88
108–109
[20]
Cl
N
N
H
H
H
OH
H
C
C
O
1
7
40
92
98
[21]
OH
N
N
H
H
H
H
C
C
1
8
25
84
149–150
[22]
O
N
N
H
H
MeO
MeO
H
OMe
MeO
C
H
O
1
9
C
30
75
195
[23]
N
N
H
H
H
H
C
C
O
Me
2
0
2h
64
95–97
[23]
Me
N
N
H
H

R. Tayebee et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 140–148
147
Table 4 (Continued)
Entry
Substrate
Product
Time (min)
Yield (%)
M.P.
Refs.
O2N
H
H
O2N
C
2
1
C
30
87
217–222
[23]
O
N
H
N
H
H
MeO
H
C
C
O
2
2
20
78
195
[23]
OMe
N
N
H
H
H
H
C
C
O
2
3
OMe
20
66
139–141
[23]
OMe
N
N
H
H
Reaction condition is described in Section 2.
(
Fig. 6). This finding clearly proved leaching of the HPA from the
(Table 4). Findings confirmed that this method is effective for a wide
range of aldehydes. However, aldehyds bearing electron withdraw-
ing groups were slightly more effective than aldehyds with electron
rich substituents. Aliphatic aldehyde, isopropyl aldehyde, achieved
the corresponding bis(indolyl)methane with <35% yields after long
time 3 h.
surface of SBA-15 during work up as the result of washing the
reused catalyst with CH CN. Although, leaching problem would be
decreased by washing the reused catalyst with less polar solvents,
however, H5PW10V O40/SBA-15 is not a promising proposal for the
3
2
preparation of the title compounds.
3.5. Synthesis of different bis(indolyl)methanes
3.6. Comparing the catalytic activity of H5PW10V2O40/TPI-SBA-15
In order to prove the applicability of this protocol, a series of
heterogeneous system with other reported catalysts
structurally diverse aromatic and aliphatic aldehydes bearing elec-
tron withdrawing and electron donating substituents were tested
in the reaction with indole under standard reaction conditions
The superiority of the present protocol was studied over
reported methodologies by comparing the obtained results with
those reported previously (Table 5). The reaction of benzaldehyde
with indole for the synthesis of bis(3-indolyl)methane was selected
as a model reaction and the comparison was in terms of mol% of
the catalysts, temperature, reaction time, and percentage yields. It
seems that the present protocol is superior over reported method-
ologies considering reaction time, catalyst mol%, ease of work-up,
and catalyst recycling.
3.7. Studying reusability of H5PW10V2O40/TPI-SBA-15
In order to prove the reusability of H5PW10V O40/TPI-SBA-15, it
2
was separated from the reaction mixture and washed with CH CN.
3
The catalyst was dried and activated in a vacuum oven for 4 h. The
recycled catalyst was reused for a new reaction with benzaldehyde.
The catalyst was found to be reusable for at least 10 cycles with-
out considerable loss of activity (Fig. 7). The chemical binding of
H5PW10V O to the surface of solid support by the mediation of
2
40
the TPI linker is responsible for the high reusability of the catalyst.
Apparently, besides the surface area, particle size, pore structure
and distribution of the protons of HPAs, which are usually referred
to as the elements of tertiary structure [27], the nature of supports
Fig. 6. Reusability study of H5PW10V2O40/SBA-15 in the condensation of benzalde-
hyde with indole under the optimized reaction conditions.

1
48
R. Tayebee et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 140–148
Table 5
Comparison of the catalytic efficiency of H5PW10V2O40/TPI-SBA-15 heterogeneous system with some reported catalysts.
Entry
Catalyst
Catalyst mol%
Time
Yield (%)
84
Condition
Refs.
−
3
◦
◦
24
25
26
27
28
29
H5PW10V2O40/TPI-SBA-15
H6P2W18O62
ZrOCl2·8H2O
TiO2(nano)
LiClO4
La(PFO)3
10
2
25 min
15 min
40 min
12 h
5 h
30 min
Solvent free/100
Solvent free/120
Solvent free/50
CH2Cl2/r.t
CH3CN/r.t
CH3CN/r.t
C
C
This work
[23]
[24]
[25]
[26]
>80
◦
5
84
64
90
90
C
10
10
5
[19]
Acknowledgements
Partial financial support from the Research Councils of Hakim
Sabzevari University and Shahid Beheshti University is greatly
appreciated. Special thanks to Vahid Tayebee for English editing
of the manuscript.
References
[
[
[
[
[
[
[
[
1] M. Faraj, C. Hill, J. Chem. Soc. Chem. Commun. (1987) 1487.
2] J.M. Thomas, Nature 314 (1985) 669.
3] D.C. Bailey, S.H. Langer, Chem. Rev. 81 (1981) 109.
4] D.E. Devos, P.A. Jacobs, Catal. Today 57 (2000) 105.
5] M.J. Naughton, R.S. Drago, J. Catal. 155 (1995) 383.
6] J.P. Arhancet, M.E. Davis, J.S. Merola, B.E. Hanson, Nature 339 (1989) 454.
7] G.A. Ozin, C. Gil, Chem. Rev. 89 (1989) 1749.
8] R. Grommen, P. Manikandan, Y. Gao, T. Shane, J.J. Shane, R.A. Schoonheydt, B.M.
Weckhuysen, D. Goldfarb, J. Am. Chem. Soc. 122 (2000) 11488.
9] E. Byambajav, Y. Ohtsuka, Appl. Catal. A: Gen. 252 (2003) 193.
[
[10] J. Parmentier, S. Saadhallah, M. Reda, J. Phys. Chem. Solids 65 (2004) 139.
[11] F. Ying, J. Li, C. Huang, W. Weng, H. Wan, Catal. Lett. 115 (2007).
[12] E.R. Cadot, A.T.M. Thouvenot, G. Herve, Inorg. Chem. 31 (1992) 4128.
[13] D. Zhao, Q. Huo, J. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem. Soc. 120 (1998)
6024.
Fig. 7. Yield% as a function of reusability of H5PW10V2O40/TPI-SBA-15 in the con-
densation of benzaldehyde with indole under the optimized reaction conditions.
[14] M.T. Pope, Heteropoly and Isopoly Oxometalates, Springer-Veriag, Berlin, 1983,
p. 8.
[
15] P. Karandikar, K.C. Dhanya, S. Deshpande, Catal. Commun. 5 (2004) 69.
and interaction of HPAs with support is very influential on catalytic
activity.
[16] H.-J. Kim, Y.-G. Shul, H. Han, Appl. Catal. A: Gen. 299 (2006) 46.
[
17] A. Tarlani, M. Abedini, A. Nemati, M. Khabaz, M.M. Amini, J. Colloid Interface
Sci. 303 (2006) 32.
[
18] Q.-Y. Liu, W.-L. Wu, J. Wang, X.-Q. Ren, Y.-R. Wang, Micropor. Mesopor. Mater.
76 (2004) 51.
4
. Conclusions
[
[
[
19] L. Wang, J.H. Han, T. Sheng, J.Z. Fan, X. Tang, Synlett (2005) 337.
20] N. Azizi, L. Torkian, M.R. Saidi, J. Mol. Catal. A: Chem. 275 (2007) 109.
21] S. Sobhani, J. Organomet. Chem. 694 (2009) 3027.
A two-step synthesis has been employed to synthesize a new
type of H5PW10V O on TPI functionalized SBA-15. Evidence for
[22] O.R. Sullivan, Chem. Ind. (1972) 849.
[23] A. Kamal, A.A. Qureshi, Tetrahedron 19 (1963) 513.
2
40
the chemical bonding of the heteropolyacid clusters to the SBA-15
surface was provided by several analytical techniques. The pyri-
dine group anchored on the SBA-15 surface and heteropolyacid
clusters dispersed well on the TPI-functionalized SBA-15 surface
through strong bond. The major advantages of the supported HPA
cluster over pure homogeneous HPA were the increased reactiv-
ity of the inorganic–organic hybrid material, easy separation, high
reusability, and fast recovery of the material.
[
[
[
[
24] H. Firouzabadi, N. Iranpoor, A.M. Jafarpour, A. Jafari, J. Mol. Catal. A: Chem. 253
(
2006) 249.
25] M.L. Kantam, S. Laha, J. Yadav, B. Sreedhar, Tetrahedron Lett. 47 (2006)
6213.
26] J.S. Yadav, B.V. Subba Reddy, V.S.R. Murthy, G. Mahesh Kumar, C. Madan, Syn-
thesis (2001) 783.
27] E. Rafiee, Z. Zolfagharifar, M. Joshaghani, S. Eavani, Appl. Catal. A: Gen. 365
(2009) 287.