Superparamagnetic magnesium ferrite nanoparticles: A magnetically reusable and clean heterogeneous catalyst

Article abstract of DOI:10.1016/j.tetlet.2012.03.069

A highly efficient magnetically recoverable nano-catalyst was fabricated. The material synthesized has been fully characterized by vibrating sample magnetometry (VSM), X-ray powder diffraction, scanning and transmission electron microscopy, FT-IR, and the

Full text of DOI:10.1016/j.tetlet.2012.03.069

Tetrahedron Letters 53 (2012) 2959–2964
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Superparamagnetic magnesium ferrite nanoparticles: a magnetically
reusable and clean heterogeneous catalyst
Mehdi Sheykhan , Hossein Mohammadnejad , Jafar Akbari , Akbar Heydari a,
a,
b
a,
⇑
a
Chemistry Department, Tarbiat Modares University, PO Box 14155-4838, Tehran, Iran
Chemistry Department, Islamic Azad University, Saveh Branch, PO Box 39187-366, Saveh, Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A highly efficient magnetically recoverable nano-catalyst was fabricated. The material synthesized has
been fully characterized by vibrating sample magnetometry (VSM), X-ray powder diffraction, scanning
and transmission electron microscopy, FT-IR, and the Brunauer-Emmett–Teller (BET) isotherm method.
An investigation of its catalytic activity showed it to be a unique heterogeneous Lewis acid catalyst for
Received 28 January 2012
Revised 5 March 2012
Accepted 20 March 2012
Available online 28 March 2012
the synthesis of a-hydroxy and a-aminophosphonates, giving a total turnover number P450 for five con-
secutive runs. The catalyst is superparamagnetic having a ‘magnetization (left behind after an external
magnetic field is removed)’ to ‘magnetic saturation’ ratio of about 0.0008, and thus could be easily sep-
arated by the use of an external magnetic field and was not agglomerated by exposure to magnetic fields.
Ó 2012 Elsevier Ltd. All rights reserved.
Dedicated to memory of Hassan Tehrani
Moghadam.
Keywords:
Magnesium ferrite
Magnetic recovery
a
a
-Hydroxyphosphonate
-Aminophosphonate
Green catalysis
Magnetic nanoparticles have gained considerable interest in var-
of magnetic nanoparticles with tunable catalytic activity is of great
significance for both academia and industry. The cubic spinel ferrites
represent an important class of magnetic transition metal oxide
materials. Among ferrites, nano magnesium ferrite is very important
for its potential use in high-density recording media, adsorption,
ious disciplines such as ferrofluids, magnetic drug delivery, separa-
tions, magnetic high-density information storage, magnetic
1
–3
resonance imaging (MRI), and cancer hyperthermia treatment.
Magnetic nanoparticles are attractive catalysts since they can be
separated from the reaction medium after magnetization by an
external magnet. Magnetic separation is an intriguing alternative
to filtration or centrifugation as it prevents the loss of catalyst and
enhances reusability, rendering the catalyst cost-effective and is
promising for industrial applications.4 Clearly, the development
9
sensors and magnetic technologies, and has good photoelectrical
properties, low saturation magnetization, high resistivity and uni-
1
0
form and reproducible characteristics. A literature survey revealed
that few attempts have been made to prepare nano magnesium fer-
rite and to study its potential application in organic synthesis.
–8
Scheme 1. Synthesis of magnesium ferrite nanospheres.
⇑
Corresponding author. Tel.: +98 21 82883444; fax: +98 21 82883455.
E-mail address: akbar.heydari@gmx.de (A. Heydari).
Tel.: +98 21 82883444; fax: +98 21 82883455.
0
040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.03.069

2
960
M. Sheykhan et al. / Tetrahedron Letters 53 (2012) 2959–2964
a
b
d
c
e
f
2 4
Figure 1. (a) and (b) TEM micrographs, (c) and (d) SEM images, (e) FTIR spectrum and (f) XRD spectrum of the MgFe O nanospheres.
3 4
O
.15
In the past few years, highly efficient couplings catalyzed by
reported that such a coupling can also be catalyzed by Fe
Unfortunately, Fe nanoparticles are usually unstable and the
various nano magnetic catalysts have been described.1
1–14
Hu
3 4
O

M. Sheykhan et al. / Tetrahedron Letters 53 (2012) 2959–2964
2961
coagulation of the nanoparticles during the reaction is frequently
unavoidable. From our ongoing program on the applications of
magnetic nanomaterials,1
MgFe magnetic nanospheres with tunable diameters in the
range of 100–180 nm and their application in organic synthesis
6–19
we report herein the synthesis of
2 4
O
as highly efficient recyclable catalysts in
ophosphonate preparation.
a-hydroxy- and a-amin-
The nanospheres of MgFe
tation method using FeCl
Á6H
as raw materials in the presence of multiwall carbon nanotubes
O
2 4
were prepared by the co-precipi-
3
2
O, FeCl O, and Mg(OAc) Á4H
2
Á4H
2
2
2
O
2
0
(Scheme 1).
Magnesium ferrite nanospheres were synthesized according to
the procedure shown in Scheme 1. The nanoparticles of magne-
sium ferrite synthesized were fully characterized by TEM
(
Fig. 1a,b), SEM (Fig. 1c,d), FT-IR (Fig. 1e) and XRD (Fig. 1f). Both
Figure 3. The isotherm plot of the catalyst.
SEM and TEM indicated that the synthetic magnesium ferrite was
present as uniform nanospheres and the size of the nanospheres
was about 150 nm. The FT-IR spectrum of MgFe
2
O
4
synthesized
the adsorption–desorption gas. The N adsorption–desorption iso-
therm (Fig. 3) is not reversible due to capillary condensation. The
2
À1
in the range 400–4000 cm is shown in Figure 1e. The spectrum
shows two characteristic intense absorption bands corresponding
to the vibrations of tetrahedral and octahedral complexes at
surface area was calculated using the BET method, and a value of
2
À1
53.0 m g was found. The synthetic material indicated a type
(IV) nitrogen adsorption–desorption isotherm (Fig. 3). Barrett–Joy-
ner–Halenda (BJH) pore size analysis confirms mesoporosity and
shows the radii of pores to be about 2.71 nm. Also, the total pore
À1
À1
21
5
65 cm
and 428 cm , respectively.
All organic functional
groups including carboxy, hydroxy, and methyl groups were re-
moved from the structure during the hydrolysis and combustion
processes. The presence of the Mg2 ionic state in A-sites (tetrahe-
dral sites) caused the generation of a long shoulder. The appear-
ance of the normal mode of vibration corresponded to the
+
3
À1
volume from BET was 0.1588 cm g (see Figs. S2–S8 in Supple-
mentary data).
It is of great importance that a catalyst should possess sufficient
magnetic and superparamagnetic properties for its practical appli-
cation. Magnetic hysteresis measurements on MgFe O were con-
À1
tetrahedral cluster (565 cm ) with a wavenumber higher than
À1
that of the octahedral cluster (428 cm ) which could be due to
2
4
its shorter bond length. It is worthwhile to note that there is a clear
ducted in an applied magnetic field at room temperature, with
the field sweeping from À8000 to +8000 Oersted. As shown in Fig-
ure 4, the hysteresis loop for the samples was completely revers-
ible. The ratio of remanence (retentivity, Mr) on magnetic
increase in the value of
pared with its bulk version (406 cm ). This is due to the re-distri-
t
2
of the present nano MgFe
2
O
4
when com-
À1
bution of cations among the A- and B-sites when the nanoparticle
3+
material is prepared. In fact, replacement of Fe ions of smaller ra-
saturation (M ) for the catalyst was about 0.0008, confirming its
s
2
+
dii with Mg ions in the A-site may occur and the frequencies of
vibrations changed due to the change in the bond lengths of the
superparamagnetic nature. The catalyst showed high permeability
in magnetization and high reversibility in the hysteresis loop,
ensuring that no aggregation was imposed on the nanospheres in
the magnetic fields. The value of magnetic saturation for MgFe O
9
occupied ions.
The MgFe
characterization with XRD, Figure 1f. Diffraction peaks at around
1.3, 35.2, 41.5, 43.2, 50.5, 63.2, 67.5, 74.3, 85.0, and 88.9 corre-
sponded to the (111), (220), (311), (222), (400), (422), (511),
440), (620), and (533) planes. The diffraction peaks observed
agree well with that of the cubic structure of MgFe (magnesium
2 4
O synthesized was subjected to further structural
2
4
À1
was 6.00 emu g at room temperature (Fig. 4).
-Hydroxy- and -aminophosphonates are useful building
2
a
a
blocks and represent an important class of biologically active
(
2 4
O
ferrite) (JCPDS card No. 36-0398). No other phase except the mag-
nesium ferrite was detectable. The measurements were carried out
on a Philips X’Pert diffractometer with CoKa radiation.
The histogram (Fig. 2) obtained from 50 nanoparticles, con-
firmed the fact that the size of the distribution was a narrow nor-
mal one with a 145 nm average value.
The surface area measurements of the synthetic ferrite were
evaluated on Micromeritics, ASAP 2000 equipment, using N as
2
Figure 4. The vibrating sample magnetometer curve of synthesized magnesiofer-
rite nanospheres at room temperature shows that the hysteresis loop for the sample
is completely reversible.
OH
O
O
P
OCH
MgFe O , 1 mol%
2
4
O
+
OCH3
R
P
R
H
H
°
35 C
3
H CO
OCH3
3
1
2
3
2 4
Figure 2. The histogram generated from the sizes of the MgFe O nanospheres
using the SEM image.
Scheme 2. Catalytic synthesis of a-hydroxyphosphonates.

2
962
M. Sheykhan et al. / Tetrahedron Letters 53 (2012) 2959–2964
Table 1
Synthesis of
a
-hydroxyphosphonates in the presence of a catalytic amount of MgFe
2
O
4
nanospheres
Time (h)
Yield 3a (%)
TON
92
TOF (h
46
À1
)
Entry
a
R
Product
OH
O
Ph
Ph
P
2
2
92
H CO OCH3
3
OH
O
b
c
3
4-CH C
6
H
4
P
88
83
88
83
44
83
OCH3
H CO
3
OCH3 OH
O
3
2-CH OC
6
H
4
1
P
H CO
OCH3
3
OH
O
d
Furyl
P
1
2
82
75
82
75
82
OCH
O
3
OCH
3
OH
O
e
Cinnamyl
P
H CO
37.5
OCH3
3
a
Isolated yield.
compounds, and their synthesis has received considerable inter-
NH2
22–27
est.
These methods include the use of various Bronsted acids
O
O
P
2
8–30
MgFe O , 1 mol%
2
4
NH
and Lewis acids as catalysts.
However, all of them have limita-
2
R1
R2
+
+
R
H
OCH
3
O
tions because of the hygroscopic features of imines. We tested a
one-pot procedure using superparamagnetic MgFe nanospheres
as a catalyst. In the presence of 1 mol % of MgFe the two and three
35 °C
R1
OCH
3
P
2 4
O
OCH3
H CO
3
2 4
O
4
5
2
6
component coupling reactions involving carbonyl compounds,
amines, and dialkyl phosphite resulted in the corresponding
Scheme 3. Catalytic synthesis of a-aminophosphonates.
Table 2
One-pot synthesis of
a-aminophosphonates in the presence of MgFe
2
O
4
nanospheres as the catalyst
R1/R2
Product
Time (h)
Yield 6a (%)
TON
TOF (h )
À1
Entry
Ph
NH
O
4 (92,91,91,91)b
(average:92)
9
a
Ph/H
2
2
94 (Total TON: 91.8 Â 5 = 459)
47 (Total TOF: 459/2 = 229.5)
P
OCH
OCH
3
3
Ph
NH
O
b
c
4-CH
2-CH
3
C
6
H
4
/H
P
90
90
91
45
OCH
3
OCH
3
H C
3
Ph
NH
O
3
OC
6
H
4
/H
P
1
91
91
OCH
3
OCH
3
OCH
3
Ph
NH
O
d
e
4-Cl-C
6
H
4
/H
2
2
87
85
43.5
42
23
21
P
OCH3
OCH
3
Cl
Ph
NH
O
4-(CH
3
)
2
N–C
6
H
4
/H
P
OCH3
OCH
3
(H C) N
3 2

M. Sheykhan et al. / Tetrahedron Letters 53 (2012) 2959–2964
2963
Table 2 (continued)
À1
Entry
R1/R2
Product
Time (h)
2
Yield 6a (%)
TON
40
TOF (h
)
Ph
NH
CH3
O
Ph
f
Ph-CH
2
/CH
3
81
20
P
OCH3
OCH
3
Ph
S
NH
O
g
2-Thienyl/H
1
2
88
89
44
44
22
P
OCH
OCH
3
3
Ph
NH
O
P
OCH
h
–(CH
)
2 5
–
44.5
OCH
3
3
a
Isolated yield.
Results of five consecutive runs.
b
analysis) associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.tetlet.2012.03.069.
References and notes
1
2
.
.
Speliotis, D. E. J. Magn. Magn. Mater. 1999, 193, 29–35.
Bulte, J. W. M.; De Cuyper, M. D.; Despres, Frank, J. A. J. Magn. Magn. Mater.
1
999, 194, 204–209.
Corot, C.; Robert, P.; Idee, J. M.; Port, M. Adv. Drug Delivery Rev. 2006, 58, 1471–
504.
Teunissen, W.; De Groot, F. M. F.; Geus, J.; Stephan, O.; Tence, M.; Colliex, C. J.
Catal. 2001, 204, 169–174.
3
.
.
1
4
Figure 5. The recycling of catalyst in
a-aminophosphonate synthesis for entry a;
5. Stevens, P. D.; Fan, J.; Gardimalla, H. M. R.; Yen, M.; Gao, T. Org. Lett. 2005, 7,
carried out at 35 oC for 2 h.
2085–2087.
6.
Gardimalla, H. M. R.; Mandal, D.; Stevens, P. D.; Yen, M.; Gao, Y. Chem. Commun.
005, 4432–4434.
2
3
1
a
-hydroxyphosphonates (Scheme 2, Table 1) and
a
-aminophos-
7. Lu, A.-H.; Schmidt, W.; Matoussevitch, N.; Bönnemann, H.; Spliethoff, B.;
3
2
phonates (Scheme 3, Table 2), respectively. To test the reusability
of the catalyst we decanted the vessel using an external magnet and
the retained catalyst was washed with diethyl ether to remove the
residual product, dried, and used in a subsequent reaction. The reac-
tion of benzaldehyde, aniline, and dimethyl phosphite resulted in
Tesche, B.; Bill, E.; Kiefer, W.; Schuth, F. Angew. Chem., Int. Ed. 2004, 43, 4303–
4306.
8
9
.
.
Zheng, Y.; Stevens, P. D.; Gao, Y. J. Org. Chem. 2006, 71, 537–542.
Pradeep, A.; Priyadharsini, P.; Chandrasekaran, G. J. Magn. Magn. Mater. 2008,
320, 2774–2779.
1
1
0. Smit, J.; Wijin, H. P. J. Ferrites, Philips Technical Library; John Wiley & Sons: New
York, 1959.
1. Stevens, P. D.; Li, G.; Fan, J.; Yen, M.; Gao, Y. Chem. Commun. 2005, 4435–4437.
thecorresponding a-aminophosphonatein 94%isolatedyield. Infive
consecutive runs, the isolated yields remained similar with no
detectable loss, 94%, 92%, 91%, 91% and 91%. The average yield of
the reaction was 92% (Fig. 5). Also, the total turnover number was
up to 450 and there was no considerable loss of activity.
To check leaching, after 20 min from initiation, the vessel was
decanted using an external magnet and the supernatant was tested
for activity. No product was observed by TLC after 4 h. This con-
firmed that there was no contribution of homogeneous catalysis
in this reaction.
12. Akbari, J.; Heydari, A.; Kalhor, H. R.; Azizian Kohan, S. J. Comb. Chem. 2010, 12,
37–140.
3. Luo, S.; Zheng, X.; Xu, H.; Mi, X.; Zhang, L.; Cheng, J. P. Adv. Synth. Catal. 2007,
49, 2431–2434.
14. Stevens, P. D.; Fan, J.; Gardimalla, H. M. R.; Yen, M.; Gao, Y. Org. Lett. 2005, 7,
085–2088.
1
1
3
2
1
1
5. Hu, A.; Yee, G. T.; Lin, W. J. Am. Chem. Soc. 2005, 127, 12486–12487.
6. Sheykhan, M.; Ma’mani, L.; Ebrahimi, A.; Heydari, A. J. Mol. Catal. A: Chem. 2011,
335, 253–261.
1
1
7. Ma’mani, L.; Sheykhan, M.; Heydari, A. Appl. Catal., A: Gen. 2011, 395, 34–38.
8. Ma’mani, L.; Sheykhan, M.; Heydari, A.; Faraji, M.; Yamini, Y. Appl. Catal., A: Gen.
2
010, 377, 64–69.
19. Ma’mani, L.; Heydari, A.; Sheykhan, M. Appl. Catal., A: Gen. 2010, 384, 122–127.
20. A solution was prepared from FeCl O (368 mg, 1.85 mmol) and FeCl Á6H
Á4H
1 g, 3.7 mmol) in deionized H O (30 mL) under an Ar atmosphere, and 200 mg
of multiwall carbon nanotubes (MWCNT) were added. After 10 min, 25%
aqueous NH (10 mL) was added at room temperature and the solution stirred
The synthetic method presented required only a small amount
of non-toxic MgFe
2
O
4
as catalyst (1 mol %). Recycling of the cata-
2
2
3
2
O
(
2
lyst over five subsequent runs was accomplished without signifi-
cant reduction of yields. The superparamagnetic magnesium
ferrite prepared showed high stability retaining excellent activity
even after several reaction runs.
3
with vigorous mechanical stirring (700 rpm). The dropping rate was controlled
with a constant dropper at 2 mL/min resulting in small uniform particles of
Fe
10 mL) was added dropwise to the suspension. The precipitate of Mg(OH)
was formed by adding 1 M aqueous NaOH to the solution. The co-precipitated
powder was washed with deionized H O, filtered, dried and calcined at 550 °C
3
O
4
. After 20 min, Mg(OAc)
2
Á4H
2 2
O (750 mg, 3.5 mmol) in deionized H O
(
2
Acknowledgements
2
for 6 h. The crystal phase of material synthesized was characterized by X-ray
diffraction. The size, homogeneity and surface morphology of the powders
were studied by SEM and TEM. The specific surface area of the powders was
The authors would like to acknowledge the financial support
provided by Tarbiat Modares the University for carrying out this
research.
2
measured using the BET method with N adsorption.
2
2
1. Modi, K. B.; Chhantbar, M. C.; Joshi, H. H. Ceram. Int. 2006, 32, 111–114.
2. de Noronha, R. G.; Romão, C. C.; Fernandes, A. C. Catal. Commun. 2011, 12, 337–
340.
Supplementary data
2
3. Merino, P.; Marques-Lopez, E.; Herrera, R. P. Adv. Synth. Catal. 2008, 350, 1195–
1
208.
Supplementary data (original Brunauer-Emmett–Teller (BET),
Barret–Joyner–Halenda (BJH) and nitrogen adsorption–desorption
2
4. Tang, J.; Wanga, L.; Wang, W.; Zhang, L.; Wu, S.; Mao, D. J. Fluorine Chem. 2011,
132, 102–106.

2
2
964
M. Sheykhan et al. / Tetrahedron Letters 53 (2012) 2959–2964
5. Miller, D. J.; Hammond, S. M.; Anderluzzi, D.; Bugg, T. D. H. J. Chem. Soc., Perkin
Trans. 1 1998, 131–142.
by TLC, the catalyst was removed using a magnet, washed with Et
to reuse. The organic phase was concentrated under reduced pressure and all
the products isolated gave satisfactory spectral data ( H NMR and C NMR)
compared with those reported in the literature.
2
O and dried
1
13
26. Meyer, J. H.; Barlett, P. A. J. Am. Chem. Soc. 1998, 120, 4600–4609.
27. Yokomatsu, T.; Yoshida, Y.; Shibuya, S. J. Org. Chem. 1994, 59, 7930–7933.
28. Bhagat, S. S.; Chakraborti, A. K. J. Org. Chem. 2007, 72, 1263–1270. and
references cited therein.
32. To a mixture containing the aldehyde (1.0 mmol) and amine (1.0 mmol) at
2 4
room temperature, MgFe O (2 mg, 1 mol %) was added (Scheme 3, Table 2)
2
3
9. Paraskar, A. S.; Sudalai, A. Arkivoc 2006, x, 183–189.
0. Ghosh, R.; Maiti, S.; Chakraborty, A.; Maiti, D. J. Mol. Catal. A: Chem. 2004, 210,
and the mixture stirred. After 10 min, dimethyl phosphite (1.1 mmol) was
added; the reaction proceeded at 35 °C. Completion of the reaction was
5
3–57.
2
indicated by TLC. The catalyst was removed using a magnet, washed with Et O
3
1. To a mixture of the aldehyde (1.0 mmol) and a catalytic amount of MgFe
2
O
4
and dried to reuse. The organic phase was concentrated under 1reduced
pressure and all the products isolated gave satisfactory spectral data ( H NMR
and 13C NMR) compared with those reported in the literature.
(
(
2 mg, 1 mol %) at room temperature was added dimethyl phosphate
1.1 mmol) and the mixture stirred at 35 °C. After completion, as indicated