Synthesis and temperature-induced morphological control in a hybrid porous iron-phosphonate nanomaterial and its excellent catalytic activity in the synthesis of benzimidazoles

Article abstract of DOI:10.1002/chem.201201350

A new organic-inorganic hybrid porous iron-phosphonate material, HPFP-1, has been synthesized under hydrothermal conditions by using hexamethylenediamine-N,N,N',N'-tetrakis-(methylphosphonic acid) (HDTMP) as the organophosphorus precursor. The morphology

Full text of DOI:10.1002/chem.201201350

FULL PAPER
DOI: 10.1002/chem.201201350
Synthesis and Temperature-Induced Morphological Control in a Hybrid
Porous Iron–Phosphonate Nanomaterial and Its Excellent Catalytic Activity
in the Synthesis of Benzimidazoles
[
a]
Arghya Dutta, John Mondal, Astam K. Patra, and Asim Bhaumik*
Abstract:
A
new organic–inorganic
synthesized at 443 K and 423 K were
semi-crystalline and showed rod-like-
and spherical morphological features,
respectively. SEM and TEM were em-
ployed to understand this change in
particle morphology depending on the
reaction temperature. Powder XRD
analysis suggested the formation of a
new tetragonal phase in HPFP-1 (a=
11.313, c=15.825 ꢀ; V=2025.659 ꢀ ).
3
hybrid porous iron–phosphonate mate-
rial, HPFP-1, has been synthesized
under hydrothermal conditions by
N -sorption analysis suggested the exis-
2
tence of supermicropores and interpar-
ticle mesopores in these materials. Ele-
mental- and thermal analyses, as well
as FTIR spectroscopy, were employed
to verify the composition and frame-
work bonding of the material. The
HPFP-1 material showed excellent cat-
alytic activity for the synthesis of ben-
zimidazole derivatives under mild
liquid-phase reaction conditions.
using
hexamethylenediamine-
N,N,N’,N’-tetrakis-(methylphosphonic
acid) (HDTMP) as the organophospho-
rus precursor. The morphology of this
material was found to be different at
three different temperatures. The ma-
terial that was synthesized at 453 K
showed a flake-like particle morpholo-
gy and the material was highly crystal-
line. Whereas, the materials that were
Keywords: benzimidazoles · heter-
ogeneous catalysis · iron · nanopar-
ticles
· organic–inorganic hybrid
composites
Introduction
the basic principles of natural enzymatic catalysis, in which
electrostatic-, hydrogen-bonding-, and covalent interactions
between the functional groups at fixed distances influence
Organic–inorganic hybrid porous materials have attracted
widespread attention by merging the mechanical properties
of inorganic solids with the versatile functionality of innu-
merable organic groups. The installation of organic function-
ality into the inorganic framework has made it possible to
extend the use of these materials into many emerging appli-
[4]
the reactivity of the catalysts.
Among the different types of porous materials that have
been developed, metal–phosphates hold great importance
[5]
[6]
for their applications in catalysis, ion-exchange, conduc-
[7]
[8]
tivity, lithium-ion batteries, etc. However, the catalytic
activities of these materials are restricted by low surface
area, the formation of large aggregated particles, small pore-
size, etc. Therefore, it is necessary to design suitable metal–
phosphonate-based catalysts that have uniform particle size
and readily accessible pore apertures. There have been re-
[1]
[2]
cations, such as medicine, optoelectronics, organocataly-
[
3]
sis, etc. Very soft- and sustainable synthesis conditions and
easily tunable topological- and chemical properties are the
main advantages of these porous hybrids. To make use of
these materials for different applications, well-defined- and
tunable chemical functions can be incorporated into porous
structures by judiciously choosing the organic building
blocks and conditions that could suit the formation of self-
assembled structures. Cooperative interactions between dif-
ferent functional groups that are precisely positioned at
well-defined sequences can greatly influence the rate of a
catalytic reaction and, by doing so, it is possible to mimic
[9]
ports of different transition-metal–phosphate nanoparticles
with well-defined morphologies and porosities. Of the tran-
sition metals, iron-containing catalysts are attracting increas-
ing attention for different chemical transformations owing
[10]
to its high abundance.
To date, more interest has been
paid to the synthesis of inorganic iron–phosphate-based
[11]
nanomaterials. However, there are much-fewer reports of
[12]
porous organic–inorganic hybrid iron–phosphonates.
Moreover, the morphology of these materials is also not
well-defined. Herein, we report, for the first time, a facile
one-pot synthesis and temperature-induced morphological
control in a hybrid porous iron–phosphonate material. The
conversion from semi-crystalline nanoparticles into crystal-
line flake-like morphology through nanorod-like particles
has been achieved very efficiently by changing the duration
and temperature of the reaction. This material shows excel-
lent catalytic activity for the synthesis of 2-arylbenzimid-
[
a] A. Dutta, J. Mondal, A. K. Patra, Prof. Dr. A. Bhaumik
Department of Materials Science
Indian Association for the Cultivation of Science
2
A and 2B Raja S. C. Mullick Road
Jadavpur, Kolkata 700 032 (India)
E-mail: msab@iacs.res.in
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201350.
Chem. Eur. J. 2012, 00, 0 – 0
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azoles from o-phenylenediamine and aromatic aldehydes.
The metal center and the organic functional groups that are
present in the framework play a synergistic role in catalyz-
ing the synthesis of the benzimidazoles. These benzimida-
zole derivatives have drawn immense attention because of
obtained. However, because of the low pH value (pHꢀ1) of
the solution, extended cross-linking that would lead to a
bulk material was prevented. When the solution was hydro-
thermally treated at 423 K for 24 h, spherical nanoparticles
were obtained. But, upon treatment of the solution at 443 K
for 24 h, 1D growth of the particles occurred, thus leading
to nanorods of a hybrid iron–phosphonate material. Further
growth of these nanorods at a slightly higher temperature,
453 K, afforded the material with a flake-like morphology.
In the FTIR spectrum of HPFP-1(F) (see the Supporting In-
[13]
their medicinal applications as antiviral-, antiulcer-, anti-
fungal-, antihypertensive-, anticancer-, and antihistamine
compounds. Apart from these applications, they are also im-
[
14]
portant intermediates in different organic reactions. Vari-
[15]
ous homogeneous catalytic methods have been reported
for the synthesis of benzimidazole derivatives. However, the
main drawback of these procedures is that these catalysts
cannot be reused in repeated cycles. Moreover, these meth-
ods suffer from low yields, long reaction times, the occur-
rence of side-reactions, and the need for harsh reaction con-
ditions. Therefore, it is essential to design an economically
cheap, reusable, and highly selective catalyst for this reac-
tion. A solid-supported homogeneous catalyst for the syn-
thesis of 2-arylbenzimidazole derivatives has previously
À1
formation, Figure S1), a sharp band at 1085 cm could be
observed, which could be attributed to the Fe-O-P stretching
À1
vibration. The weak shoulder band at 1000 cm could be
due to free PÀOH groups that are present in the material.
À1
The two weak bands at 1468 and 1431 cm , which corre-
spond to the CÀH bending- and PÀC stretching modes of
the methylphosphonic acid moiety, are also observed. A fur-
À1
ther two weak bands at 1385 and 1330 cm are attributable
to stretching vibrations of the P=O and CÀN covalent link-
[16]
À1
been reported.
However, in general, the major problem
ages. The small bands in the region 2850–3050 cm corre-
that is associated with these supported catalysts is the leach-
ing of the metal ions from the solid support. The non-uni-
formity of the active catalytic sites throughout the support is
another drawback of these catalysts. These problems can be
solved if the entire surface of the material acts as a catalyst.
Herein, the iron–phosphonate material that was used as the
catalyst (HPFP-1) was free from all of these problems. This
material has the further advantage of small particle size be-
cause small-sized particles eliminate the possibility of com-
positional differences between the surface and the bulk of
the material, thus making the catalytically active sites availa-
ble uniformly throughout the material.
spond to the CÀH stretching vibrations of methylene carbon
atoms in the organophosphorus ligand. The broad bands at
À1
around 3400 and 1630 cm are, respectively, due to asym-
metric OH stretching- and bending vibrations of the adsor-
bed water molecules.
AAS and elemental analysis of the iron–phosphonate ma-
terial show Fe, C, H, and N content of 26.74, 14.71, 3.51,
and 3.39 wt.%, respectively. This result suggests a Fe/C/N
molar ratio of 2:5:1 in the hybrid iron–phosphonate material
and it is in agreement with the calculated C/N molar ratio
of 5:1 in the organophosphorus ligand. The thermal stability
of the material was examined by using TG-DTA analysis
under a flow of N (see the Supporting Information, Fig-
2
ure S2). A sharp weight loss below 423 K was due to a loss
of moisture that was adsorbed on the surface of the materi-
al. In between 473 K and 1073 K, the material showed an
approximate 21% weight loss, which was very close to the
cumulative C, H, and N value (21.61 wt.%) obtained by ele-
mental analysis. These FTIR spectroscopic and thermal
analysis data semi-quantitatively show that the organophos-
phorus ligand, HDTMP, is present in the material and that
Results and Discussion
Synthesis and characterization: A solution of HDTMP was
added to an aqueous solution of FeCl during the synthesis
3
of these materials (Scheme 1). As soon as the solution of
the ligand had been added, a light-yellow precipitate was
the material can be formulated as Fe ACHTUNGTRNENUG( HDTMP)·xH O.
4 2
Microstructural analysis: FE-SEM and TEM images of
HPFP-1 were obtained to investigate the morphology of the
particle of these organic–inorganic hybrid materials
(
Figure 1). Figure 1a shows that the HPFP-1(NP) material is
composed of small spherical nanoparticles with a diameter
of 50–70 nm. These particles are aggregated throughout the
material, which gives rise to interparticle mesoporosity. The
magnified TEM image (Figure 1d) shows that some ran-
domly distributed worm-hole-like micropores are present in
the material. A rod-like morphology of HPFP-1(NR) is
clearly visible in Figure 1b; these nanorods are formed from
the 1D growth of the spherical nanoparticles at higher tem-
peratures. Both the FE-SEM (Figure 1b) and TEM images
(Figure 1e) show that the nanorods are about 500 nm in
Scheme 1. Hexamethylenediamine-N,N,N’,N’-tetrakis-(methylphosphonic
acid) (HDTMP).
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Hybrid Porous Iron–Phosphonate Nanomaterial
FULL PAPER
Figure 2. High-resolution TEM image (a) and corresponding FFT pattern
(
b) of HPFP-1(F).
Figure 1. SEM (a–c) and TEM images (d–f) of HPFP-1(NP), HPFP-
1
(NR), and HPFP-1(F), respectively.
length and the level of aggregation is also much lower com-
pared to the nanoparticles. When the reaction was carried
out at more-elevated temperatures, these nanorods fused to-
gether, thereby producing a flake-like morphology (Fig-
ure 1c,f). A schematic representation of the formation of
these materials is shown in Scheme 2. This temperature-
Figure 3. Wide-angle powder X-ray diffraction pattern of the HPFP-1
materials.
Scheme 2. Schematic representation of the formation of HPFP-1 materi-
als. Three different morphologies were obtained when the reaction was
performed at three different temperatures under hydrothermal condi-
tions.
pattern; interestingly, this diffraction pattern does not match
with any reported crystalline phase in the JCPDS database.
This experimental PXRD pattern was evaluated with re-
spect to its corresponding calculated PXRD pattern that
was obtained with Reflex, a software package for crystal-
structure determination. The lattice parameters and estimat-
ed standard deviation (ESD) values were obtained with the
CELSIZ program. This diffraction pattern was assigned with
regulated growth of the nanoparticles, which leads to differ-
ent morphologies of the particles, is a very facile process.
There are several reports of inorganic iron–phosphate nano-
[17]
[18]
[19]
particles, -nanorods, and other morphologies. More-
over, although there have been reports of changes in the
crystallographic phase and subsequent morphology of the
products on changing the reaction temperature through con-
a
new tetragonal phase, where a=11.313 ꢀ and c=
15.825 ꢀ. The unit-cell parameters with estimated standard
deviations and hkl values for different planes are listed in
Table 1. Very small deviations in these values indicate that
the calculated values are fitted well with the experimental
data. The HPFP-1(NP) material that was synthesized at
423 K only shows two sharp diffraction peaks, which corre-
spond to the (001) and (100) planes. In the case of the
HPFP-1(NR) material, the intensity of the (001) diffraction
peak becomes stronger than the intensity of the (100) plane,
which indicates the 1D growth of the particles along the
[20]
ventional heating or microwave irradiation,
to date, the
temperature-induced control of the morphology of hybrid
iron–phosphonate materials is unprecedented. The HPFP-
1(F) material also shows good crystallinity. High-resolution
TEM (Figure 2a) shows the crystal fringes; the correspond-
ing FFT pattern is shown in Figure 2b. These crystal planes
are correlated with the wide-angle XRD pattern of the ma-
terial.
[21]
c axis, thus leading to the formation of nanorods. Howev-
er, in the diffraction pattern of HPFP-1(F), the (113), (220),
and other peaks also become strong, owing to growth of the
particles along all directions, with the extra energy at elevat-
Powder X-ray diffraction: Wide-angle powder X-ray diffrac-
tion patterns of the HPFP-1 materials are shown in Figure 3.
HPFP-1(F) shows multiple diffraction peaks in the PXRD
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A. Bhaumik et al.
Table 1. Unit-cell parameters of HPFP-1(F).
which is unusual for type-II isotherms. The occurrence of
such hysteresis loops is due to mesoporosity, which origi-
nates from the interparticle void spaces. The pore-size distri-
butions of the materials (Figure 5) show that there is meso-
3
V (ESD) [ꢀ ]
2025.659 (6.824)
tetragonal
phase
Parameters
Deviation
a=11.313 ꢀ
c=15.825 ꢀ
0.0226
0.0141
h
k
l
2q
d [ꢀ]
0
1
1
0
0
1
2
2
3
3
3
4
1
3
4
3
5
0
0
0
0
0
1
2
2
1
1
1
0
0
2
2
0
2
1
0
1
2
3
3
0
1
0
1
2
0
6
4
3
6
0
5.610
7.830
9.58
15.7533
11.2912
9.2321
7.8861
5.1974
4.4952
4.1104
3.8619
3.5604
3.481
3.3036
2.8149
2.5765
2.4488
2.2814
2.1536
2.0923
11.22
17.06
19.75
21.62
23.03
25.01
25.59
26.99
31.79
34.82
36.7
Figure 5. Pore-size distribution of the HPFP-1 materials following the
NLDFT method.
39.5
41.95
43.24
porosity in all three samples. However, the materials that
were synthesized at higher temperatures, that is, HPFP-
1(NR) and HPFP-1(F), showed supermicroporosity as well
as mesoporosity. At higher temperatures, when the particles
grow to form nanorods and nanoflakes, the degree of cross-
linking also increases and the supermicroporosity could orig-
inate from this cross-linking in the framework. The HPFP-
1(NP) material shows a H1 hysteresis loop, which is typical-
ly due to the agglomeration of approximately spherical par-
ed reaction temperatures. This observation matches well
with the morphology of the material (Figure 1).
N -adsorption/desorption study: The N -adsorption/desorp-
2
2
tion isotherms of the HPFP-1 materials are shown in
Figure 4. These isotherms are classified as type II according
to IUPAC nomenclature. In the intermediate relative-pres-
[23]
sure region (P/P =0.05–0.3), there is a gradual increase in
ticles.
This observation is supported by the SEM image
0
N -uptake. This increase could be attributed to multilayer
shown in Figure 1a. However, in the case of HPFP-1(NR),
owing to the formation of nanorods, the interparticle aggre-
gation is relatively weak and, hence, the hysteresis loop is
also narrower. The BET surface area of HPFP-1(NP) is also
higher than that of HPFP-1(NR). Because of densification
at higher temperature, the surface area of HPFP-1(F) is the
lowest. The adsorption isotherm of HPFP-1(F) shows a H3
hysteresis loop, which does not show any limiting adsorption
at high relative pressure. The desorption branch of this hys-
teresis does not level off at relative pressures that are close
to the saturation vapor pressure. This H3 hysteresis loop is a
signature of aggregated plate-like particles that have slit-like
2
adsorption, which corresponds to the presence of mesopores
[22]
in the materials. Moreover, these isotherms show that the
materials adsorb large amounts of nitrogen at high P/P0
values, thus indicating interparticle porosity. In the desorp-
tion branch, all three isotherms show a hysteresis loop,
[24]
pores. From the SEM and TEM images of HPFP-1(F), we
found that the material was composed of plate-like particles.
The surface area-, pore-size-, and pore-volume data are
summarized in Table 2.
Benzimidazole synthesis: The catalytic activity of the HPFP-
1
(NP) catalyst was investigated in one-pot condensation re-
actions for the synthesis of benzimidazole derivatives by the
reaction between o-phenylenediamine and aromatic alde-
hydes that contain various electron-donating- and electron-
withdrawing groups (Table 3). The HPFP-1(NP) catalyst
shows high reactivity at room temperature and the reaction
only takes 2–4 h to proceed to completion. The elemental
Figure 4. N
2
-adsorption/desorption isotherm of HPFP-1 materials. The
À1
adsorbed volume was shifted by 45 and 10 ccg for HPFP-1(NP) and
HPFP-1(NR), respectively. Filled symbols represent the adsorption
points whereas empty symbols correspond to the desorption points.
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Hybrid Porous Iron–Phosphonate Nanomaterial
Table 2. Physicochemical properties of HPFP-1 materials.
FULL PAPER
yields, irrespective of the substituents on the ben-
Sample
BET surface
Pore size
(by NLDFT) [nm]
Pore volume zaldehyde moiety, the interactions between the cat-
2
À1
À1
area [m g
]
A
H
U
G
R
N
U
G
A[ ccg
H
U
G
R
N
U
G
]
alyst and the carbonyl oxygen seem to be strong
enough to subsidize the effect of the substituents.
In the next step, the amine groups of o-phenylene-
diamine are attached onto the carbonyl carbon. The
tertiary amine groups that are
HPFP-1(NP)
HPFP-1(NR)
HPFP-1(F)
153.6
121.0
58.0
4.5
3.1, 5.4
1.6, 5.4
0.35
0.20
0.08
present in the hybrid frame-
work help to eliminate the pro-
Table 3. Synthesis of 2-arylbenzimidazoles catalyzed by HPFP-1.
Entry
Aromatic
aldehyde
Benzimidazole
t
Yield
[%]
M.p. [8C]
(Lit. M.p.)
TOF
ACHTUNGENTRNUNG[ h ]
[
a]
[b]
À1 [c]
tons in the subsequent water-re-
moval step. Thus, this synergis-
tic effect of the Fe center and
the tertiary amine groups cata-
lyze the synthesis of benzimida-
zole derivatives. We wanted to
investigate the role of the mor-
phology- and surface area of
the material in determining cat-
alytic activity. Because the reac-
tion with p-nitrobenzaldehyde
showed the highest yield when
HPFP-1(NP) was used as the
catalyst, the same reaction was
chosen to check the catalytic
activity of HPFP-1(NR) and
HPFP-1(F). In both cases, the
reaction was performed for 4 h
and HPFP-1(NR) afforded
[h]
1
3
2
3
4
90
92
88
90
288 (289–291)
211.2
323.9
206.5
158.4
2
3
4
328 (327)
298 (299–300)
224 (224–226)
5
3
87
332 (330)
204.2
4
4% yield whilst HPFP-1(F)
[
[
[
[
d]
e]
f]
6
7
8
9
4
4
7
6
44
30
328 (327)
77.4
52.8
55.3
–
gave 30% yield. Furthermore,
we found that the yield of the
product also decreased with de-
creasing surface area of the cat-
alyst. Again, because HPFP-
328 (327)
1
(NP) is composed of nano-
sized spherical particles, the
porous framework is more ac-
cessible for this material. In
HPFP-1(NR), the aggregation
is much lower and, in HPFP-
55
–
–
g]
trace
1
(F), the highly dense plate-like
[
a] Reaction conditions: ArÀCHO (1.0 equiv), o-phenylenediamine (1.0 equiv), T=298 K, catalyst (30 mg),
particles hinder the mass-trans-
port through the porous chan-
nels. The catalytic activity of
our hybrid iron–phosphonate
catalyst was verified by per-
forming the reaction without
EtOH (5 mL). [b] Yield of the isolated pure product. [c] Turn over frequency (TOF)=(moles of substrate con-
2
verted per mole of iron per hourꢂ10 ). [d] Reaction was carried out with HPFP-1(NR) as the catalyst. [e] Re-
action was carried out with HPFP-1(F) as the catalyst. [f] Reaction was carried out in the presence of FeCl
g] Reaction was carried out in the absence of a catalyst.
3
.
[
iron content in the catalyst was determined by AAS analy-
sis. The Fe content in this HPFP-1 material is 26.74%. From
these data, it is clear that the one-pot condensation reaction
is equally tolerant of both electron-donating- and electron-
withdrawing substituents on the aromatic ring. A possible
mechanism for this reaction is shown in Scheme 3. In this
mechanism, the Fe center of the catalyst coordinates to the
carbonyl oxygen atom of the aromatic aldehyde, similar to
Lewis acid sites, thereby activating the carbonyl carbon
any catalyst. When the reaction was carried out in the ab-
sence of a catalyst (Table 3, entry 9), no benzimidazole
product was obtained, even after a prolonged reaction time.
On the other hand, in a control experiment when a homoge-
neous phase of FeCl was used as the catalyst under opti-
3
mized conditions at 298 K, only 55% yield of the benzimi-
dazole (Table 3, entry 8) was obtained. Singh et al. also re-
[15a]
ported
the FeCl -catalyzed synthesis of benzimidazoles at
3
higher temperatures to obtain better yields. However, the
reusability of this homogeneous catalyst was limited and its
[25]
atom.
Because all of the reactions give almost-equal
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A. Bhaumik et al.
the conversion after 2 h (75.2
and 76.5% yield at 2 and 4 h,
respectively) and there were no
detectable Fe in the reaction
mixture. This result suggested
that no leaching of Fe occurred
during the course of the reac-
tion because, otherwise, the
conversion would have in-
creased considerably and the
filtrate would contain dissolved
Fe. Thus, the catalytic pathway
described herein over HPFP-1
is purely heterogeneous in
nature.
Scheme 3. Plausible mechanism for the synthesis of benzimidazoles. In this mechanism, the iron center in the
catalyst activates the aromatic aldehyde and facilitates the attack of the amine. The tertiary amine groups in
the catalyst help to eliminate the protons in the water-removal step. Again, the iron center activates the mole-
cule for the second attack of the amine. Thus, the cooperative involvement of iron and the tertiary amines in
the catalyst catalyzes the synthesis of benzimidazole derivatives.
Conclusion
Herein, we have shown that a
new organic–inorganic hybrid
separation from reaction medium was also a serious prob-
lem. The TOFs for the synthesis of benzimidazole catalyzed
by HPFP-1(NP) catalyst are summarized in Table 3.
porous iron–phosphonate material can be synthesized under
one-pot hydrothermal conditions. Nanoparticle-, nanorod-,
and flake-like morphologies of this material can be obtained
by simply tuning the reaction temperature. PXRD results
show that the HPFP-1(F) material is crystalline and forms a
From the recycling-efficiency test, we found that this
hybrid iron–phosphonate catalyst could be recycled and
reused in a further four cycles without any significant loss of
catalytic activity, which clearly indicates that the catalyst is
purely heterogeneous in nature. We plotted the recycling ef-
ficiency of the HPFP-1(NP) catalyst for four consecutive
catalytic cycles in the condensation reaction between ben-
zaldehyde and o-phenylenediamine (Figure 6). To test for
new tetragonal phase. N -adsorption/desorption experiments
2
show that these materials are porous, with pore-sizes in the
range of supermicroporous and mesoporous regions. Meso-
pores in these materials originate from interparticle porosity.
This material shows very good catalytic activity for the syn-
thesis of benzimidazole derivatives from various substituted
aromatic aldehydes and o-phenylenediamine. This simple
and convenient catalytic process for the synthesis of benzi-
midazoles could open up new avenues for the use of hybrid
porous metal–phosphonates in the synthesis of organic fine
chemicals.
Experimental Section
Synthesis: HPFP-1 samples were synthesized by using anhydrous iron-
AHCTUNGERTNNUNG( III) chloride (Merck) and a 25% aqueous solution of hexamethylenedia-
mine-N,N,N’,N’-tetrakis-(methylphosphonic acid) (HDTMP, Fluka). The
reagents were used without further purification. In a typical synthesis,
3
FeCl (1.63 g, 10 mmol) was dissolved in distilled water (10 g) and a 25%
aqueous solution of HDTMP (5 g, 2.54 mmol) was added dropwise. The
solution was stirred for 30 min and hydrothermally treated in a steel-
lined Teflon autoclave in three different batches: The first batch, which
was labeled HPFP-1(NP), yielded nanoparticles when the solution was
kept at 423 K for 24 h. The second batch, which was labeled HPFP-
Figure 6. Catalytic-recycling efficiency of the HPFP-1(NP) material.
any leaching of iron into the reaction mixture during the
catalytic reactions, a control experiment was performed by
taking the condensation reaction between benzaldehyde and
o-phenylenediamine as a representative case. After 2 h, the
catalyst was removed from the reaction mixture and the
mixture was allowed to stir for a further 2 h under identical
reaction conditions. We observed that there was almost no
increase in the yield of the product after 4 h compared to
1
(NR), yielded nanorod-like particles when the solution was treated at
443 K for 24 h. The third batch, which was labeled HPFP-1(F), yielded
flake-like particles when the solution was heated at 453 K for 48 h. Final-
ly, the products were collected by filtration and dried at RT.
General procedure for the synthesis of 2-arylbenzimidazoles: In a typical
synthesis,
a mixture of o-phenylenediamine (1 mmol, 108 mg; Loba
Chemie) and benzaldehyde (1 mmol, 106 mg; Loba Chemie) was stirred
in EtOH (5 mL) in the presence of the HPFP-1(NP) catalyst (30 mg) in
air at RT for 5 h (monitored by TLC). After the reaction was complete,
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Hybrid Porous Iron–Phosphonate Nanomaterial
FULL PAPER
the catalyst was filtered and the EtOH was removed under vacuum.
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2
Cl
2
(20 mL) and washed
2
SO and
4
1
13
from EtOH to afford pure 2-phenylbenzimidazole. The H and C NMR
spectroscopic data of this product were in good agreement with those of
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[
[
Characterization: Elemental analysis was carried out on a Shimadzu AA-
6
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Received: April 20, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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ÞÞ
These are not the final page numbers!

A. Bhaumik et al.
Morphology under control: An new
organic–inorganic hybrid porous iron–
phosphonate material was synthesized
under hydrothermal conditions by
using HDTMP as an organophospho-
rus precursor. This material showed
nanosphere-, nanorod-, and flake-like
particle morphologies at different tem-
peratures. Nanospheres of the HPFP-1
material showed the highest catalytic
activity in the synthesis of benzimida-
zoles from aromatic aldehydes and o-
phenylenediamine.
Hybrid Composites
A. Dutta, J. Mondal, A. K. Patra,
A. Bhaumik* .................. &&&& — &&&&
Synthesis and Temperature-Induced
Morphological Control in a Hybrid
Porous Iron–Phosphonate Nanomate-
rial and Its Excellent Catalytic Activity
in the Synthesis of Benzimidazoles
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ÝÝ
These are not the final page numbers!