Manganese(III) salen complex immobilized on Fe3O4 magnetic nanoparticles: The efficient, green and reusable nanocatalyst

Article abstract of DOI:10.1002/cjoc.201400007

A new Fe₃O₄ magnetic nanoparticles supported manganese salen complex was successfully prepared by attaching manganese acetates to a novel N,N′-bis(salicylidine)ethylenediamine ligand functionalized Fe₃O₄. The as-prepared catalyst was characterized by TGA, XRD, FTIR, VSM, and TEM. It was found to be an efficient catalyst for the synthesis of benzopyranopyrimidines in aqueous medium. High catalytic activity and ease of recovery from the reaction mixture using external magnet, and several reuse times without significant losses in performance are additional eco-friendly attributes of this catalytic system. Synthesis of benzopyranopyrimidines from salicylic aldehydes, malononitrile, and amine in the presence of Fe₃O₄SiO₂SalenMn MNPs. Copyright

Full text of DOI:10.1002/cjoc.201400007

FULL PAPER
DOI: 10.1002/cjoc.201400007
Manganese(III) Salen Complex Immobilized on Fe3O4 Magnetic
Nanoparticles: The Efficient, Green and Reusable
Nanocatalyst
Seyed Mohsen Sadeghzadeh,*,a Faeze Daneshfar,b and Maryam Malekzadehc
a Department of Chemistry, College of Sciences, Birjand University, P.O. Box 97175-615, Birjand, Iran
b Department of Physics, College of Sciences, Birjand University, P.O. Box 97175-614, Birjand, Iran
c Department of Chemistry, Payame Noor University, Tabas, Iran
A new Fe3O4 magnetic nanoparticles supported manganese salen complex was successfully prepared by at-
taching manganese acetates to a novel N,N'-bis(salicylidine)ethylenediamine ligand functionalized Fe3O4. The
as-prepared catalyst was characterized by TGA, XRD, FTIR, VSM, and TEM. It was found to be an efficient cata-
lyst for the synthesis of benzopyranopyrimidines in aqueous medium. High catalytic activity and ease of recovery
from the reaction mixture using external magnet, and several reuse times without significant losses in performance
are additional eco-friendly attributes of this catalytic system.
Keywords salen, nanocatalyst, benzopyranopyrimidine, green chemistry, solvent free
properties. Among the core-shell structured composites,
Introduction
the composites with magnetic core and functional shell
structures have received especial attention because of
their potential applications in catalysis, drug storage/
release, selective separation, chromatography, and
chemical or biologic sensors.[9-15] The magnetic core has
good magnetic responsibility, and can be easily mag-
netized. Therefore, the composites with magnetic core
can be conveniently collected, separated or fixed by
external magnet.
Control of selectivity, for example, chemo- and re-
gioselectivity, is among the most important objectives in
organic chemistry. For multicomponent reactions in-
volving the simultaneous molecular interaction of three
or more components, the issue of selectivity is of par-
ticular significance due to the high probability of several
potential parallel reaction pathways leading to different
product classes.[16-18] Many different process parameters
such as temperature, pressure, solvent, catalyst type, as
well as kinetic or thermodynamic control, and other
factors can be utilized to modulate the selectivity of
synthetic transformations.[19-24] In addition to these clas-
sical reaction parameters, the use of microwave irradia-
tion[25-28] or sonication[29-31] has provided additional op-
portunities to execute reactions and to tune selectivities
in organic synthesis. A challenging example in this
context is multicomponent condensation reactions of
2-hydroxybenzaldehyde (1), malononitrile (2), and
amine (3) which in general can lead to the formation of
Currently one of the most important synthetic ligand
systems, especially in the context of asymmetric cataly-
sis, are the tetradentate Schiff bases known as salen
(N,N'-bis(salicylaldehydo)ethylenediamine). In 1889,
while studying the effect of diamines on diketones,
Combes prepared the first salen ligand and its Cu com-
plex.[1] Since then, salen derivatives and their metal
complexes have been synthesised and characterized and
gradually their value as catalysts has become recog-
nised.[2] With the growth in interest in enantiomerically
pure compounds for the pharmaceutical and agro-
chemical industries, it is perhaps not surprising that in
the last decade attention has focused on chiral salen
ligands, and in particular on the use of their optically
pure metal complexes as asymmetric catalysts. Applica-
tions have grown rapidly and a broad range of asym-
metric catalyses have now been described including
oxidations, additions and reductions.
In recent years, core–shell multi-components have
attracted intense attention because of their potential ap-
plications in catalysis.[3] Different from single-compo-
nent that can only supply people with one function, the
core-shell multi-components can integrate multiple
functions into one system for specific applications.[4-8]
Moreover, the interactions between different compo-
nents can greatly improve the performance of the multi-
components system and even generate new synergetic
* E-mail: sadeghzadeh_sm@yahoo.com; Tel.: 0098-561-2502065; Fax: 0098-561-2502065
Received January 1, 2014; accepted February 9, 2014; published online XXXX, 2014.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201400007 or from the author.
Chin. J. Chem. 2014, XX, 1—7
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Sadeghzadeh, Daneshfar & Malekzadeh
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several different tricyclic reaction products (Scheme 1)
due to the presence of at least three nonequivalent nu-
cleophilic reaction centers in the benzopyranopyrimi-
dines building block 4. Engaged in the development of
greener and sustainable pathways for organic transfor-
mations, nanomaterial, and nano-catalysis,[32-35] herein,
we report a simple and efficient synthesis of a nano-
ferrite-supported, magnetically recyclable, and inexpen-
sive manganese(III) catalyst and its application for the
synthesis of benzopyranopyrimidines.
trolled in the range 12≤pH≤13. (3) Different amount
of hydrazine hydrate (N2H4•H2O, 80% concentration)
was added to the above suspension. The reaction was
continued for about 24 h at room temperature. During
this period, the pH value was adjusted by NaOH and
kept in the range 12≤pH≤13. The black Fe3O4 NPs
were then rinsed several times with ionized water.
General procedure for the preparation of Fe3O4\
SiO2 nanoparticles
0.02 mol of Fe3O4 MNP was dispersed in a mixture
of 80 mL of ethanol, 20 mL of deioned water and 2.0
mL of 28 wt% concentrated ammonia aqueous solution
(NH3•H2O), followed by the addition of 0.20 g of tetra-
ethyl orthosilicate (TEOS). After vigorous stirring for
24 h, the final suspension was repeatedly washed, fil-
tered for several times and dried at 60 ℃ in the air.
Scheme 1 Synthesis of benzopyranopyrimidines from salicylic
aldehydes, malononitrile, and amine in the presence of Fe3O4\
SiO2\Salen\Mn MNPs
O
R
CN
Catalyst
r.t.
H
+
+
HN
CN
OH
R
General procedure for the preparation of compound
(A) nanoparticles
2
3
1
R
R
N
C
For synthesis of compound (A) MNP, 2 mmol of
Fe3O4\SiO2 MNPs were dispersed in a mixture of 80 mL
of ethanol, 20 mL of deioned water and 2.0 mL of 28
wt% concentrated ammonia aqueous solution (NH3•
H2O), followed by the addition of 20 mmol of ethyl
3,4-diaminobenzoate. After vigorous stirring for 24 h,
the magnetic Fe3O4\SiO2 nanoparticles were collected
by magnetic separation and washed with ethanol and
deionized water in sequence.
N
OH
O
N
4
Experimental
Materials and methods
Chemical materials were purchased from Fluka and
Merck in high purity. Melting points were determined in
open capillaries using an Electrothermal 9100 apparatus
and are uncorrected. FTIR spectra were recorded on a
VERTEX 70 spectrometer (Bruker) in the transmission
mode in spectroscopic grade KBr pellets for all the
powders. The particle size and structure were observed
by using a Philips CM10 transmission electron micro-
scope operating at 100 kV. Powder X-ray diffraction
data were obtained using Bruker D8 Advance model
with Cu Kα radiation. The thermogravimetric analysis
(TGA) was carried out on a NETZSCH STA449F3 at a
heating rate of 10 ℃•min−1 under nitrogen. The mag-
netic measurement was carried out in a vibrating sample
magnetometer (VSM) (4 inch, Daghigh Meghnatis Ka-
shan Co., Kashan, Iran) at room temperature. NMR
spectra were recorded in CDCl3 on a Bruker Avance
DRX-400 MHz instrument spectrometer using TMS as
internal standard. The purity determination of the prod-
ucts and reaction monitoring were accomplished by
TLC on silica gel polygram SILG/UV 254 plates.
General procedure for the preparation of Fe3O4\
SiO2\Salen (N,N'-bis(salicylidine)ethylenediamine)
nanoparticles
For synthesis of Fe3O4\SiO2\Salen MNPs, compound
(A) (4 g) was suspended in 600 mL of 0.1 mol•L－
1
toluene solution of salicylaldehyde and the colloidal
solution was refluxed for 24 h. The magnetic Fe3O4\
SiO2\Salen nanoparticles were collected by magnetic
separation and washed with ethanol and deionized water
in sequence.
General procedure for the preparation of Fe3O4\
SiO2\Salen\Mn nanoparticles
Fe3O4\SiO2\Salen (0.45 g) was added to an excess of
pyridine dissolved in dichloromethane/ionic liquid, to
which Mn(OAc)2 (0.65 g) was subsequently added. pH
was maintained at 9 by addition of sodium borohydride.
The reaction mixture was kept under magnetic stirring
overnight. The final particle was separated from the so-
lution by applying a magnetic field, washed three times
with water to remove any ions present, and dried under
vacuum.[36]
General procedure for the preparation of Fe3O4 na-
noparticles
General procedure for the synthesis of benzopyrano-
pyrimidines
The synthesis procedure for the preparation of Fe3O4
nanoparticles is illustrated as follows: (1) 0.01 mol
FeCl2•4H2O and 0.03 mol FeCl3•6H2O were dissolved
in 200 mL distilled water, followed by the addition of
PEG (1.0 g, MW 6000). (2) Sodium hydroxide (NaOH)
was added to the solution and the pH value was con-
2-Hydroxybenzaldehyde (2 mmol), malononitrile (1
mmol), amine (1 mmol) and Fe3O4\SiO2\Salen\Mn
MNPs (0.0008 g) were stirred at room temperature un-
der solvent-free conditions for the appropriate time.
2
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Manganese(III) Salen Complex Immobilized on Fe3O4 Magnetic Nanoparticles
Upon completion, the progress of the reaction was mon-
The structural properties of synthesized Fe3O4\SiO2\
itored by TLC. When the reaction was completed, EtOH
was added to the reaction mixture and the Fe3O4\
SiO2\Salen\Mn MNPs was separated by external magnet.
Then the solvent was removed from solution under re-
duced pressure and the resulting product was purified by
recrystallization using ethanol.
Salen\Mn MNP were analyzed by X-ray power diffrac-
tion (XRD). As shown in Figure 2, XRD patterns of the
synthesized Fe3O4\SiO2\Salen\Mn nanoparticle display
several relatively strong reflection peaks in the 2θ re-
gion of 20°－70°, which is quite similar to those of
Fe3O4 nanoparticles reported by other groups. The dis-
cernible six diffraction peaks in Figure 2a can be in-
dexed to (220), (311), (400), (422), (511), and (440)
which match well with the database of magnetite in
JCPDS (JCPDS card No. 19-0629) file. Besides the
peak of iron oxide, the XRD pattern of Fe3O4\SiO2
core-shell nanoparticles presented a broad featureless
XRD peak at low diffraction angle, which corresponded
to the amorphous state SiO2 shells (Figure 2b) (JCPDS
card No. 29-0085). Figure 2c shows a typical XRD pat-
tern of the Fe3O4\SiO2\Salen\Mn MNP.
Results and Discussion
The first step in the accomplishment of this goal was
the synthesis and functionalization of magnetic nano-
particles (Figure 1). The catalyst was prepared by soni-
cating nano-ferrites with salen [which acts as a robust
anchor and avoids Mn(III)] in absolute MeOH, followed
by addition of Mn(OAc)2. Material with Mn(III) on the
functionalized nano-ferrites was obtained in excellent
yield. The synthesized Fe3O4\SiO2\Salen\ Mn MNP was
then characterized by different methods such as XRD,
TEM, VSM, FTIR and TGA.
Tetraethyoxysilane
Fe3O4
Fe3O4
+
OH
O
O
O
Si
O
NH2
NH2
NH2
NH2
Fe3O4
O
EtO
O
O
Figure 2 XRD analysis of (a) Fe3O4, (b) Fe3O4\SiO2, and (c)
Fe3O4\SiO2\Salen\Mn.
(A)
O
NH2
NH2
The successful synthesis of the Fe3O4\SiO2\Salen\
Mn nanoparticles was confirmed by the FTIR spectra
(Figure 3). The peaks at 3415 cm−1 and 590 cm−1 appear
in all the FTIR spectra, which are assigned to the －OH
group and the Fe－O group, respectively (Figure 3a). In
FTIR spectra of the Fe3O4\SiO2 MNPs, the absorption
intensity of Fe－O group decreases with the addition of
silica portion and a strong absorption intensity of the
Si–O–Si group appears at 1090 cm−1 owing to the silica
coat (Figure 3b). Peaks appeared at 3120, 2930, 1720,
and 1610 cm−1 are due to the stretching of the C－H
aromatic group, the C－H aliphatic group, C＝O group,
and C＝N group in the Fe3O4\SiO2\Salen\Mn MNP,
respectively (Figure 3c).
H
Fe3O4
+
2
O
OH
O
(A)
N
N
OH
OH
Mn(OAc)2
Fe3O4
O
O
(B)
The size and structure of the Fe3O4\SiO2\Salen\Mn
MNP were also evaluated using transmission electron
microscopy (TEM) (Figure 4). The average size of
Fe3O4 MNPs is about 15－20 nm (Figure 4a). After be-
ing coated with a silica layer, the typical core-shell
structure of the Fe3O4\SiO2 MNPs can be observed. The
dispersity of Fe3O4\SiO2 MNPs is also improved, and
the average size increases to about 20－25 nm (Figure
4b). The TEM image of the Fe3O4\SiO2\Salen\Mn
MNPs is shown in Figure 4c. The functionalization of
N
Mn
O
N
Fe3O4
O
N
O
O
(C)
Figure
1
Schematic illustration of the synthesis for
Fe3O4\SiO2\Salen\Mn nanoparticles.
Chin. J. Chem. 2014, XX, 1—7
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Sadeghzadeh, Daneshfar & Malekzadeh
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lowed by a second peak at 420－460 ℃, corresponding
to the loss of the organic spacer group.
The magnetic properties of the nanoparticles were
characterized using a vibrating sample magnetometer
(VSM). The magnetization curves of the obtained nano-
composite registered at 300 K show that nearly no re-
sidual magnetism is detected (Figure 5b), which means
that the nanocomposite exhibited the paramagnetic
characteristics. Magnetic measurement shows that pure
Fe3O4, and Fe3O4\SiO2\Salen\Mn MNPs have saturation
magnetization values of 60.2, and 33.2 emu/g respec-
tively. These nanocomposites with paramagnetic char-
acteristics and high magnetization values can quickly
respond to the external magnetic field and quickly re-
disperse once the external magnetic field is removed.
The result reveals that the nanocomposites exhibit good
magnetic responsibility, which suggests a potential ap-
plication for targeting and separation.
Figure 3 FTIR spectra of (a) Fe3O4, (b) Fe3O4\SiO2, (c)
Fe3O4\SiO2\Salen\Mn.
Figure 5 (a) TGA diagram of nano catalysis; (b) Room-tem-
perature magnetization curves of the nano catalysis.
The catalytic potential of the Fe3O4\SiO2\Salen\Mn
MNPs was evaluated in condensation reactions. At first,
the reaction of salicylic aldehydes, diemthyl amine, and
malononitrile was chosen as a model reaction to opti-
mize the reaction conditions such as the amount of the
catalyst, temperature, time, and solvent (Table 1). It was
found that the best yield of the product was obtained at
room temperature under solvent-free conditions in the
presence of 0.0008 g of Fe3O4\SiO2\Salen\Mn MNPs for
50 min (Table 1, Entry 13). Three separated reactions
were examined in the absence of any catalyst and in the
presence of Fe3O3 and Fe3O4\SiO2\Salen MNPs. The
results of these studies showed that any amount of the
desired product was not formed (Table 1, Entries 15－
17). A similar reaction in the presence of Mn(OAc)2 as a
Figure 4 TEM images of (a) Fe3O4 MNPs, (b) Fe3O4\SiO2
MNPs, (c) Fe3O4\SiO2\Salen\Mn MNPs, and (d) Fe3O4\SiO2\
Salen\Mn MNPs after seven reuses.
the Fe3O4\SiO2\Salen\Mn MNPs does not result in the
change of the morphology and size of the obtained
Fe3O4\SiO2 MNPs. The thermal behavior of Fe3O4\SiO2\
Salen\Mn MNP is shown in Figure 5a. A significant
decrease in the weight percentage of the Fe3O4\SiO2\
Salen\Mn MNP at about 130 ℃ is related to desorption
of water molecules from the catalyst surface. This was
evaluated to be 1%－3% according to the TG analysis.
In addition, the analysis showed two other decreasing
peaks. The first peak appears at temperature around 250
－280 ℃ due to the decomposition of Mn. This is fol-
4
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Manganese(III) Salen Complex Immobilized on Fe3O4 Magnetic Nanoparticles
Table 1 Optimization of the reaction conditions for the synthesis of benzopyranopyrimidine in terms of temperature, catalyst amount,
time and product yield
Entry
Catalyst
Solvent
－
Temp./℃
r.t.
Time/min
70
Catalyst amount/g
0.001
Yielda/%
96
1
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
Fe3O4\SiO2\Salen\Mn
－
2
H2O
EtOH
THF
CH2Cl2
n-Hexane
－
r.t.
70
0.001
23
3
r.t.
70
0.001
48
4
r.t.
70
0.001
37
5
r.t.
70
0.001
24
6
r.t.
70
0.001
14
7
80
70
0.001
96
8
－
90
70
0.001
96
9
－
100
r.t.
70
0.001
96
10
－
60
0.001
96
11
－
r.t.
50
0.001
96
12
－
r.t.
40
0.001
73
13
－
r.t.
50
0.0008
0.0006
0.0008
0.0008
0.0008
0.0008
96
14
－
r.t.
50
75
15
－
r.t.
50
－
16
Fe3O4
－
r.t.
50
－
17
18
Fe3O4\SiO2\Salen
Mn(OAc)2
－
r.t.
50
－
－
r.t.
50
69
a Isolated yields.
non-supported catalyst gave the desired product in
moderate yield (69%) due to the formation of by-prod-
ucts (Table 1, Entry 18). This result indicated that the
catalytic efficiency of Mn(OAc)2 was increased by im-
mobilization onto Fe3O4.
Table 2 Comparison of the catalytic activity of Fe3O4\SiO2\
Salen\Mn MNPs with that of Salen\Mn
Yielda/%
Entry Reaction time/min
Fe3O4\SiO2\Salen\Mn Salen\Mn
1
2
3
4
5
30
40
50
60
70
67
73
96
96
96
64
71
91
95
98
The catalytic activity of the Fe3O4\SiO2\Salen\Mn
MNPs was compared with that of the Salen\Mn. For this
purpose, the reactions were carried out separately at
room-temperature under solvent-free conditions with
both the catalysts for the appropriate time (Table 2). The
aliquots of the reaction mixture were collected periodi-
cally at an interval of 10 min. Table 2 shows the varia-
tion of the yields of benzopyranopyrimidine with time,
when Fe3O4\SiO2\Salen\Mn MNPs and Salen\Mn were
employed as catalysts. It is evident that, the catalytic
activity of the Fe3O4\SiO2\Salen\Mn MNPs is similar to
the Salen\Mn. After 50 min, Fe3O4\SiO2\Salen\Mn
MNPs showed 96% preparation of benzopyranopyrimi-
dine as compared to 91% with Salen\Mn. After 70 min,
yield of the product in the presence of Fe3O4\SiO2\
Salen\Mn MNPs is fixed at 96%, but Salen\Mn MNPs
showed 98% preparation of benzopyranopyrimidine.
The nano-sized particles increase the exposed surface
area of the active component of the catalyst, thereby
enhancing the contact between reactants and catalyst
dramatically and mimicking the homogeneous catalysts.
Also, the activity and selectivity of nano-catalyst can be
manipulated by tailoring chemical and physical proper-
ties like size, shape, composition and morphology.
After optimization of the reaction conditions, to de-
lineate this approach, particularly in regard to library
a Isolated yields.
construction, this methodology was evaluated by using
different amines, variety of different substituted 2-hy-
droxybenzaldehyde and of malononitrile in the presence
of Fe3O4\SiO2\Salen\Mn MNPs under similar conditions.
As can be seen from Table 3, electronic effects and the
nature of substituents on the amines and 2-hydroxyben-
zaldehyde did not show strongly obvious effects in
terms of yields under the reaction conditions. The
four-component cyclocondensation reaction proceeded
smoothly. High yields and excellent TONs and TOFs
were achieved in all the cases.
Mechanistically, the reaction occurs via initial for-
mation of arylidenemalononitrile 5 by the Knoevenagel
condensation between 1 and 2 followed by subsequent
Pinner reaction (5→6). Next, the cyano group of inter-
mediate 6 can be attacked by the amine 3 to produce
intermediate 7. Finally, amine 7 reacts with another
molecule of salicylic aldehyde 1 followed by proton
transfer to afford the product 4 (Scheme 2).
Chin. J. Chem. 2014, XX, 1—7
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5

Sadeghzadeh, Daneshfar & Malekzadeh
Table 3 Synthesis of benzopyranopyrimidines derivatives catalyzed by Fe3O4\SiO2\Salen\Mn MNPsa
FULL PAPER
Entry Aldehyde Amine Product Yieldb/% TON
Entry
Aldehyde
Amine Product Yieldb/% TON
TOF/h
TOF/h−1
O
O
O
Me
HN
HN
H
H
1
2
96[37] 96×104 115×104
5
93[37] 93×104 112×104
94[37] 94×104 113×104
4a
4b
4e
4f
N
Me
Et
H
OH
OH
O
O
Me
Br
95[37] 95×104 114×104
6
7
HN
H
H
Et
Me
OH
O
OH
O
H
H
3
82[37] 82×104 98×104
95[37] 95×104 114×104
4c
4g
N
N
OH
H
H
OH
OMe
CH3
O
4
95
95×104 114×104
H
4d
N
H
OH
a Reaction condition: 2-hydroxybenzaldehyde (2 mmol), malononitrile (1 mmol), amine (1 mmol) and Fe3O4\SiO2\Salen\Mn MNPs
(0.0008 g) at room-temperature. b Yield refers to isolated product.
Scheme 2 A possible mechanism for the one-pot reaction for synthesis of benzopyranopyrimidines
Fe3O4
Fe3O4
O
O
O
O
N
O
N
O
N
Mn
O
N
Mn
O
+
O
N
N
C
CN
R
CN
H
N
+
HN
C
OH
CN
N
O
NH
R
OH
N
3
O
1
2
6
5
O
Mn
N
N
Fe3O4
O
O
O
O
Fe3O4
N
N
O
Mn
O
O
N
R
R
R
R
R
R
N
+H
O
N
C
N
C
C
NH
N
OH
H
N
H
OH
O
NH
HO
N
O
N
1
7
4
6
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Chin. J. Chem. 2014, XX, 1—7

Manganese(III) Salen Complex Immobilized on Fe3O4 Magnetic Nanoparticles
Figure 6 (a) Reuses performance of the catalysts; (b) FT-IR spectrum of recovered Fe3O4\SiO2\Salen\Mn MNPs.
[5] Liu, B.; Zeng, H. C. Small 2005, 1, 566.
[6] Cao, J.; Sun, J. Z.; Hong, J.; Li, H. Y.; Chen, H. Z.; Wang, M. Adv.
Mater. 2004, 16, 84.
[7] Sun, X. M.; Li, Y. D. Angew. Chem., Int. Ed. 2004, 43, 597.
It is important to note that the magnetic property of
Fe3O4\SiO2\Salen\Mn MNPs facilitates its efficient re-
covery from the reaction mixture during work-up pro-
cedure. The activity of the recycled catalyst was also
examined under the optimized conditions. After the
completion of reaction, the catalyst was separated by an
[8] Wang, Q. B.; Liu, Y.; Ke, Y. G.; Yan, H. Angew. Chem., Int. Ed. 2008,
47, 316.
[9] Lyon, J. L.; Fleming, D. A.; Stone, M. B.; Schiffer, P.; Williams, M.
external magnet, washed with methanol and dried at the
pump. The recovered catalyst was reused for seven
consecutive cycles without any significant loss in cata-
lytic activity (Figure 6a).
The recyclability test was stopped after seven runs.
Comparison of TEM images (Figure 4d) and FT-IR
spectra of used catalyst (Figure 6b) with those of the
fresh catalyst (Figure 3 and 4a) showed that the mor-
phology and structure of Fe3O4\SiO2\Salen\Mn MNPs
remained intact after seven recoveries.
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Conclusions
In summary, Fe3O4\SiO2\Salen\Mn MNP as a new
magnetic nanoparticles catalyst was synthesized directly
through reaction of Mn(OAc)2 complex supported on
Fe3O4\SiO2\Salen MNP. The synthesized Fe3O4\SiO2\
Salen\Mn MNP was used as a magnetically recyclable
heterogeneous catalyst for the efficient one-pot synthe-
sis of benzopyranopyrimidines from the reaction of
2-hydroxybenzaldehyde, malononitrile, and amine with
high product yields. The catalytic research on novel ap-
proaches toward nanomaterials should be improved to
enhance organic synthesis. For that purpose, nanoparti-
cles catalyst provides a new way for continuous proc-
esses, because of its simple recyclability. From a scien-
tific point, our results expand the application of nano-
particles. This catalyst should be helpful to the devel-
opment of new catalytic systems.
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(Pan, B.; Fan, Y.)
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