Immobilized V-MIL-101 on modified Fe3O4 nanoparticles as heterogeneous catalyst for epoxidation of allyl alcohols and alkenes

Article abstract of DOI:10.1016/j.molcata.2014.12.004

As a new heterogeneous catalyst, Fe₃O₄ nanoparticles were prepared and modified with sodium silicate and (3-aminopropyl) trimethoxysilane (APTMS) followed by complexation with V-MIL-101 and designated as Fe₃O₄@SiO₂@APTMS@VMIL-101. It was characterized using FTIR, TEM, and VSM techniques. The Fe₃O₄@SiO₂@APTMS@VMIL-101 was found to successfully catalyze the epoxidation of allyl alcohols and alkenes with tert-butylhydroperoxide (TBHP) in moderate to high yields. The epoxidation of trans-stilbene, norbornen, cyclooctene, geraniol, trans-2-hexene-1ol and 1-octene-3-ol with 100% selectivity is promising. Investigation of the stability and reusability of Fe₃O₄@SiO₂@APTMS@V-MIL-101 revealed the heterogeneity character of the catalyst with no desorption during the course of epoxidation reactions. High yields, clean reactions, ease of catalyst separation and recyclability of the solid catalyst are some advantages of this method.

Full text of DOI:10.1016/j.molcata.2014.12.004

Accepted Manuscript
Title: Immobilized V-MIL-101 on modified Fe O
3
4
nanoparticles as heterogeneous catalyst for epoxidation of
allyl alcohols and alkenes
Author: Faezeh Farzaneh Yasaman Sadeghi
PII:
S1381-1169(14)00564-0
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2014.12.004
MOLCAA 9366
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
9-9-2014
13-11-2014
7-12-2014
Please cite this article as: Faezeh Farzaneh, Yasaman Sadeghi, Immobilized V-MIL-
01 on modified Fe3O4 nanoparticles as heterogeneous catalyst for epoxidation
1
of allyl alcohols and alkenes, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2014.12.004
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Manuscript Draft
Manuscript Number: MOLCAA-D-14-00826R1
Title: Immobilized V-MIL-101 on modified Fe3O4 nanoparticles as heterogeneous catalyst for
epoxidation of allyl alcohols and alkenes
Article Type: Research Paper
Section/Category: Supported homogeneous catalysis
Keywords: Epoxidation catalyst . Allylic alcohols. Oefins. V-MIL101. Magnetic nanoparticles
Corresponding Author: Prof. Faezeh Farzaneh,
Corresponding Author's Institution: University of Alzahra
First Author: Faezeh Farzaneh
Order of Authors: Faezeh Farzaneh; Yasaman Sadeghi
Abstract: As a new heterogeneous catalyst, Fe3O4 nanoparticles was prepared and modified with
sodium silicate and (3-aminopropyl) trimethoxysilane (APTMS) followed by complexation with V-MIL-
1
01 and designated as Fe3O4@SiO2@APTMS@VMIL-101. It was characterized using FTIR, TEM, and
VSM techniques. The Fe3O4@SiO2@APTMS@VMIL-101 was found to successfully catalyze the
epoxidation of allyl alcohols and alkenes with tert-butylhydroperoxide (TBHP) in moderate to high
yields. The epoxidation of trans-stilbene, norbornen, cyclooctene, geraniol, trans-2-hexene-1ol and 1-
octene-3-ol with 100% selectivity is promising. Investigation of the stability and reusability of
Fe3O4@SiO2@APTMS@V-MIL-101 revealed the heterogeneity character of the catalyst with no
desorption during the course of epoxidation reactions. High yields, clean reactions, ease of catalyst
separation and recyclability of the solid catalyst are some advantages of this method.

Cover Letter
Dear Mr. Editor
Attached, you will find my manuscript entitled Immobilized V-MIL-101 on modified Fe O
“
3
4
nanoparticles as heterogeneous catalyst for epoxidation of allyl alcohols and alkenes”. This
article is original, and has been written by the stated author who is aware of its content and
approve its submission. It has not published previously and is not under consideration for
publication elsewhere. On behalf of my co-worker, The novelty of this work is based on
immobilization of a type of MOF of vanadium on modified iron oxide nanoparticles as
heterogeneous catalyst. The high catalytic activity and selectivity for allyl alcohols and alkenes is
considerable. I would appreciate if you consider it for publication in Journal of Molecular
Catalysis A: Chemical.
With Best Regards
Faezeh Farzaneh
Professor of Chemistry
Department of Chemistry
Alzahra University
Vanak, Tehran, Iran
Faezeh_farzaneh@yahoo.com
Farzaneh@Alzahra.ac.ir

List of rewiewrs:
1
-
A. S. Aswar
Department of Chemistry, Sant Gadge Baba Amravati University, Amravati 444602, India
E_mail: anandaswar@yahoo.com
Expert in synthesis and catalytic reactions of transition metals with Schiff base complexe.
2
- Esther C.E. Rosenthal
Institut für Chemie, Technische Universität Berlin, Sekr. C 2, Straße des 17, Juni 135,
10623 Berlin, Germany
E-mail address: esther.rosenthal@tu-berlin.de (E.C.E. Rosenthal).
Expert in epoxidation reactions with catalysts.
3- Christopher W. Jones
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Dr., Atlanta,
GA 30332-0100, USA
E-mail address: cjones@chbe.gatech.edu (C.W. Jones).
Expert in catalytic activity of silica coated nanomagnet particles.
4
- Ramgopal Bhattacharyya,
aargibhatta@yahoo.com (R. Bhattacharyya).
Department of Chemistry, Jadavpur University, Jadavpur, Kolkata 700032, India
Expert in epoxidation reactions with catalysts using transition metal complexes ( Mo compounds).

Revision Note/Response to Reviewers
Ms. Ref. No.: MOLCAA-D-14-00826
Title: Immobilized V-MIL-101 on modified Fe3O4 nanoparticles as heterogeneous catalyst for
epoxidation of allyl alcohols and alkenes
Journal of Molecular Catalysis A: Chemical
Answer to the reviewer comments:
Reviewer #1: The manuscript presents the synthesis and application of
Fe3O4@SiO2@APTMs@V-MIL-101 for expoxidation reaction. This easily recoverable catalyst
shows several advantages as heterogeneous catalyst for liquid phase organic reaction. The
catalyst was well characterized and the results/discussion are well organized. It could be
recommended to the publication in JMC-A after clarifying following questions.
1
. The assignment of IR vibration bands in Fig. 1. The 1622 cm-1 band is assigned to Fe-O.
However, the vibration of adsorbed water appears at the same position in particular for
hydrophilic silica-containing materials. Similarly, the assignment of 3421 cma-1 band to Fe-OH
is also a matter of discussion.
The correction was made in Fig.1 and the text was modified accordingly, see last paragraph in
page 8.
2
. More clear SEM and TEM images are required to confirm the core-shell structure of the
materials. The images in Fig. 3 are poor in quality and lack a detailed description in the text.
The SEM image was transferred to the supplementary section and a TEM image with higher
quality was included in the main text with more explanation (see page 11) as bellow:
“
The SEM image of Fe O @SiO @APTMS@V-MIL-101 shows the formation of some
3 4 2
spherical particles with about 27-38 nm (see supplementary, Figure S2). The transmission
microscopy (TEM) image of Fe O @SiO @APTMS@VMIL101 is presented in Fig. 3. The
3
4
2
magnetic core shell nanoparticles (Fe O @SiO @APTMS@VMIL101) with about 8-10 nm in
3
4
2
diameter is evident in this Figure.”
3
.In Fig. 4, why conversion shows a maximum as the catalyst loading increases? The non-
productive decomposition of TBHP (possibly on Fe NPs) is not mentioned. Is abovementioned
phenomenon related to this issue?

As mentioned in the text, the product was characterized with comparison with that of authentic
sample. The yield was determined based on the limiting substrate (alkenes) consumption and not
with decomposition of the excess TBHP. Also, the conversion increase with increase in the
catalyst loading is expected.
4
. The authors should give a detailed discussion regarding to the solvent effects (page 14) on
both conversion and selectivity. I do not understand how boiling point affects the selectivity.
A new paragraph was included in page 14 (as bellow). Recall that the effect of ethanol and
chloroform on the reaction conversions were omitted since these two are similar respectively to
methanol and dichloromethate in solubility.
“As has been reported previously, solvent usually affect the conversion in homogeneous
catalysis systems [45]. In our heterogeneous catalysis system, the influence of different solvents
such as acetonitrile, methanol and dichloromethane is also observed although rather weaker
under optimum reaction conditions (Fig. 6). As is shown, a decrease in conversion is observed in
the order of acetonitrile methanol dichloromethane (Fig. 6). This trend is in the decreasing
order of dielectric constants as well as boiling points of these solvents. As has been explained
(vide infra), the transition state of the complexation of both hydroxyl and double bond groups to
vanadium center is more polar in comparison to that of reactants. Therefore, increasing the
polarity of the solvent is expected to increase the reaction rate. On the other hand, increasing the
solvent boiling point seems to increase the reaction rate constant based on the Arrhenius
equation. Moreover, since the one with the most transition state stabilization in acetonitrile reacts
with highest in the first step, undergoes reaction with the slowest rate in the second step in
which transfer of oxygen to the double bond occurs. Therefore, obtaining the highest selectivity
in acetonitrile is in accord with reactivity-selectivity principle[46].”
5
. It is known that NH2- coordinates to V as a Lewis base. This interaction will probably affect
the catalytic activity of V in the prepared catalyst. Therefore the authors are recommended to
compare the activity of core-shell Fe-Si-APTMs-V-MIL catalyst with that of pure V-MIL to see
whether this combination will deactivate the V sites.

Effect of the pure V-MIL has been included in Tables 1 and 2 as catalyst 2.
6
. Graphic abstract is missing.
Graphical abstract was included as bellow.
Graphical abstract:
Immobilized V-MIL-101 on modified Fe O nanoparticles as heterogeneous
3
4
catalyst for oxidation of allyl alcohols and alkenes
Faezeh Farzaneh*, Yasaman Sadeghi
7
. Some language mistakes: Page 7 in the last sentence: ….. have been be responsible ……
The correction were made based on the recommendation.

*Graphical Abstract (for review)
Graphical abstract:
Immobilized V-MIL-101 on modified Fe O nanoparticles as heterogeneous
3
4
catalyst for oxidation of allyl alcohols and alkenes
Faezeh Farzaneh*, Yasaman Sadeghi

*Highlights (for review)
Highlights:
Fe O @SiO @APTMS@V-MIL-101 was prepared● The epoxidation of allyl alcohols and
3
4
2
alkenes were studied by the prepared catalyst ● The epoxidation of geraniol, trans-2-hexene
and 1-octene-3-ol with 100% conversion and selectivity is considerable● The epoxidation of
some alkenes with 100% selectivity is also promising.

*Manuscript
Click here to view linked References
Immobilized V-MIL-101 on modified Fe O nanoparticles as heterogeneous
3
4
catalyst for epoxidation of allyl alcohols and alkenes
Faezeh Farzaneh*, Yasaman Sadeghi
Department of Chemistry, Alzahra University, P.O.Box 1993891176, Vanak, Tehran, Iran
ABSTRACT
_
_______________________________________________________________________
As a new heterogeneous catalyst, Fe O nanoparticles was prepared and modified with
3
4
sodium silicate and (3-aminopropyl) trimethoxysilane (APTMS) followed by
complexation with V-MIL-101 and designated as Fe O @SiO @APTMS@VMIL-101. It
3
4
2
was
characterized
using
FTIR,
TEM,
and
VSM
techniques.
The
Fe O @SiO @APTMS@VMIL-101 was found to successfully catalyze the epoxidation
3
4
2
of allyl alcohols and alkenes with tert-butylhydroperoxide (TBHP) in moderate to high
yields. The epoxidation of trans-stilbene, norbornen, cyclooctene, geraniol, trans-2-
hexene-1ol and 1-octene-3-ol with 100% selectivity is promising. Investigation of the
stability and reusability of Fe O @SiO @APTMS@V-MIL-101 revealed the
3
4
2
heterogeneity character of the catalyst with no desorption during the course of
epoxidation reactions. High yields, clean reactions, ease of catalyst separation and
recyclability of the solid catalyst are some advantages of this method.
Keywords Epoxidation catalyst . Allylic alcohols. Alkenes. V-MIL101. Magnetic nanoparticles
_
____________________________________________________
Corresponding author. Tel.: +98-21-88258977; fax: +98-21-+98-21-8804134
E-mail address: faezeh_farzaneh@yahoo.com, Farzaneh@alzahra.ac.ir
*
1

1
. Introduction
Catalytic epoxidation of allyl alcohols and alkenes is an important synthetic method for
both industry and academics. The use of transition-metal complexes as catalysts for
epoxidation reactions is still interest because of their role in understanding of the
relevant biologically reactions [1]. Amongst which, study of the epoxidation of alkenes
and especially allyl alcohols catalyzed by vanadium complexes with different ligands is
of fundamental importance [2]. Utilization of oxovanadium(IV) compounds as oxidation
catalysts was first discovered by Sharpless [3] in regioselective epoxidation of allylic
alcohols with tert-butyl hydroperoxide as oxidant [4]. During the last decades, many
research works have been focused on the synthesis of different vanadium (IV) type
coordination compounds with Schiff base ligands as catalyst for epoxidation either in
homogeneous or heterogeneous environment [5-6].
Recently, metal–organic frameworks (MOFs) [7] have attracted considerable attention
for their potential applications in areas such as gas storage [8], separation [9], sensors
[
10], ion exchangers [11], catalysis [12], adsorption volatile organic compounds [13] and
drug delivery [14] due to their structures which contain large vacancies, high surface
areas, crystalline open structures, and tunable pore size by varying the type of metal
source or organic linkers [15].
The MIL-n family of materials (MIL: Materials of the Institute Lavoisier) are a group
of MOFs, originally developed by Férey’s group [16]. Different metal-MIL such as Cr-
MIL-101 [17], Fe-MIL-101 [18], Al-MIL-101 [19] and V-MIL-101 [20] have been
reported in this regard. The metal MIL-101 materials have a zeotype crystal structure
2

including two kinds of cages. They have multiple transition metal sites and large surface
areas, which can be activated by heating in vacuum [21]. MIL-101 materials have been
used as adsorbents, column packing materials and catalysts [22-23].
Due to easier recovery and recycling of reaction catalysts in the heterogeneous
processes, most efforts have been focused towards the heterogeneous processes or
heterogenization of homogeneous catalysts. Therefore, different solid supports such as
microporous [24-25] or mesoporous materials [26], polymers [27-28], silica and silicate
layers [29] and magnetic nano particles [30] have been used. The Fe O nanoparticles are
3
4
known as excellent supports for heterogenization of homogeneous catalysts by
immobilization of homogeneous catalysts on their surfaces. Notably, functionalized
MNPs have recently been employed as catalysts for different organic reactions [31-35].
Preparation of immobilized V-MIL-101 on modified iron oxide nanomagnetic particles
and application as heterogeneous epoxidation catalyst is described in this presentation. To
the best of our knowledge, there has been no report on the immobilization of MOF on
modified Fe O nanoparticles in literature.
3
4
2
. Experimental
2
.1. Materials
All materials were of commercial reagent grade and used without further purification.
Acetonitrile, vanadium(III) chloride (VCl ), N,N-dimethylformamide (DMF), methanol,
3
terephthalic acid, norbornene, cyclohexene, styrene, -methylstyrene, trans-stilbene,
cinnamyl alcohol, sodium chloride (NaCl), trans-2-hexen-1-ol, 1-octene-3-ol, sodium
3

silicate (Na SiO ), ferric chloride (FeCl ), ferrous chloride tetrahydrate (FeCl .4H O),
2
3
3
2
2
ammonium
hydroxide
(25%),
hydrochloric
acid,
glycerol
and
3-
aminopropyltrimethoxysilane (APTMS) and tert-butyl hydroperoxide (TBHP, 80% )
were obtained from Merck Chemical Company. Cyclooctene and geraniol were
purchased from Sigma and Aldrich respectively.
2
.2. Characterization
FT-IR spectra were recorded on a Bruker Tensor 27 FT-IR spectrometer using KBr
-1
pellets over the range of 4,000–400 cm . Transmission electron microscopy (TEM)
images were taken by Zeiss-EM10C-100 KV. Scanning electron micrograph (SEM)
images were taken by XL-30 Phillips (1992). Magnetic susceptibility measurements were
carried out using a vibrating sample magnetometer (VSM) (BHV-55, Riken, Japan) in the
magnetic field range of -8000 Oe to 8000 Oe at room temperature. Vanadium and iron
were determined by atomic absorption on a Chermo double beam instrument.
Epoxidation products were analyzed by GC and GC-Mass using Agilent 6890 series with
a FID detector, HP-5, 5% phenylmethylsiloxane capillary and Agilent 5973 network,
mass selective detector, HP-5 MS 6989 network GC system.
2
.3. Preparation of magnetic nanoparticles ( Fe O : MNPs)
3 4
The magnetite nanoparticles (Fe O : MNPs) was prepared according to the previously
3
4
reported method [35] with some modifications. A solution of FeCl .4H O (0.86 g) and
2
2
FeCl (1.40 g) in deionized water (40 mL) was stirred at 85 for 30 minutes under
3
4

nitrogen gas. Upon addition of ammonium hydroxide (25 %, 3 mL), the solution color
turned from light brown to black. After stirring for 20 minutes under these conditions, the
solution was cooled to room temperature followed by filtration. The magnetite
precipitate was washed twice with H O and sodium chloride (0.02M) solution.
2
2
.3.1. Coating magnetic nanoparticles with silica (Fe O @SiO )
3 4 2
A mixture of sodium silicate (9.50 g in 50 mL deionized water) containing MNPs (1.00
g) of nanoparticles was stirred for 30 min at room temperature and 20 min at 80˚ C. The
solution pH was then adjusted at 6–7 using dilute HCl (2M) solution. The precipitate
(
Fe O @SiO ) was separated and washed several times with H O by magnetic
3
4
2
2
decantation followed by dispersion in 50 mL of methanol.
2
.3.2. Functionalization of silica coated nanoparticles with APTMS
Fe O @SiO @APTMS)
(
3
4
2
Glycerol (20 mL) was added to a suspension of Fe O @SiO (2 g in methanol (20 mL)
3
4
2
and H O (0.13 mL) and the resultant mixture was kept under ultrasound for 30 min.
2
Then, 3-aminopropyltrimethoxysilane (APTMS) (0.84 mL) was added to the resultant
solution, followed by heating at reflux at 80–90 for 3 h. The obtained modified
nanomagnetic as nanospheres was washed with deionized water and methanol
respectively and then dried at room temperature.
2
.4. Preparation of V-MIL-101
5

V-MIL-101 was prepared according to the procedure described previously [20]. VCl3
0.20 g) and terephthalic acid (0.17 g) were dissolved in DMF (2 mL) in a 10 mL Pyrex
(
tube. The tube was sealed and heated in autoclave at 150 °C for 24 h. After cooling to the
room temperature, the green precipitate was filtered, washed with DMF and dried in air.
V-MIL-101 with formula [V OCl(C H NO) (C H O ) ]·3.1C H NO·10H O·0.1C H O
3
3
7
2
8
4
4 3
3
7
2
-
8
6
4
1
was obtained. Anal. Calc.: for C40.1H68.1ClN O V ( M=1265.96 gMol ) : C 41.72,
5.1
28.5
3
H 4.56, N 9.80 : found C 41.74, H 4.72, N 9.85% .
2
. 5. Immobilization of V-MIL-101 onto (Fe O @SiO @APTMS@VMIL101)
3 4 2
To a stirring solution of V-MIL-101 (0.08 g in 16 mL DMF), Fe O @
3
4
SiO @APTMS (0.19 g) was added and the mixture heated at 90˚ C for 24 h. The solid
2
was then magnetically separated and washed twice with DMF. After drying of the solid at
room temperature, Fe O @SiO @APTMS@V-MIL-101 was obtained as a brown solid.
3
4
2
2
.6. Catalytic epoxidation, general procedure:
All epoxidation reactions of the allyl alcohols (geraniol, cinnamyl alcohol, trans-2-
hexen-1-ol and 1-octene-3-ol) and alkenes (norbornene, cyclohexene, cyclooctene,
styrene, -methylstyrene and trans-stilbene) were carried out in a round bottom flask
equipped with a magnetic stirrer and a water-cooled condenser. Typically,
Fe O @SiO @APTMS@V-MIL-101 (containing %2.5 V) (40 mg) designated as catalyst
3
4
2
6

1
in acetonitril (5 mL), and substrate (20 mmol in 5 mL acetonitrile) were mixed. TBHP
(24 mmol) was then added and the mixture was heated at reflux for several hours. After
separation of the catalyst by means of an external magnet, the filtrate plus authentic
samples were subjected to GC and GC-Mass analyses.
3
. Results and discussion
3
.1. Catalyst synthesis and characterization
The V-MIL-101 (V-MOF) was prepared under hydrothermal conditions (Scheme 1a).
The catalyst was synthesized by preparation of Fe O magnetic nanopartcles (MNPs) by
3
4
precipitation of iron(II) and iron(III) ions using sodium silicate in acidic solution [36] and
subsequent coating of Fe O with silica to Fe O /SiO core–shell particles (scheme1b).
3
4
3
4
2
The coating procedure was carried out for two reasons. First, the SiO shell can
2
effectively prevent the aggregation and chemical degradation of the Fe O nanoparticles
3
4
in a harsh liquid environment. Second, the surface Si–OH groups can be modified by
functionalization with desired organic groups. Therefore, the surface was then
functionalized with APTMS [37] and the vanadium MOF was finally immobilized on the
modified iron oxide and designated as MNPs@SiO @APTMS@V-MIL-101 (scheme
2
1
c). Recently, the experimental and theoretical studies on the adsorption of pyridine on
MIL-101 has shown that the substitution occurred by removal of one water molecule (as
solvent) coordinated to the Cr-MIL-101) [38]. Based on this result, it seemed that the
nitrogen of immobilized amine group should have been responsible for removing one
DMF molecule (as solvent) coordinated to the V-MIL-101.
7

Scheme 1. (a) Preparation of V-MIL-101, and (b) and (c) preparation steps of
Fe O @SiO @APTMS@V-MIL-101.
3
4
2
The FT-IR spectra of Fe O , Fe O @SiO , Fe O @SiO @APTMS, V-MIL-101 and
3
4
3
4
2
3
4
2
Fe O @SiO @APTMS@ V-MIL-101 before and after using as catalyst are shown in
3
4
2
Fig.1a-f, respectively. For Fe O magnetic nanoparticles (MNPs), observing a broad peak
3
4
-1
with relatively low intensity centered at the regions 3421 and 1622 cm should be
attributed to the Fe-OH groups of the surface or the adsorbed water stretching and
-1
bending vibrations. The peak at 583 cm is also attributed to the Fe–O vibrations [37, 39,
4
0] (Fig. 1a).
8

After modification of MNPs with sodium silicate designated as MNPs @SiO2 ,
a
-1
relatively strong peak is observed at 1100 cm in its spectrum due to Si–O–Si and Si–OH
stretching vibrations (Fig 1b) [41]. In the
Fig. 1. The FTIR spectra: (a) Fe O , (b) Fe O @SiO , (c) Fe O @SiO @APTMS, (d) V-
3
4
3
4
2
3
4
2
MIL-101, (e) Fe O @SiO @APTMS@V-MIL-101 before using and (f) after using as
3
4
2
catalyst.
spectrum of functionalized MNPs@SiO2 with APTMS (designated as
-1
MNPs@SiO @APTMS), two bands appearing at 2870 and 2920 cm are related to the
2
C–H stretching vibrations (Fig 1c) [42]. The FT-IR spectrum of V-MIL-101 shown in
Fig. 1d is consistent with those reported previously [37]. It shows vibrations
-1
-1
corresponding to 1660-1650 cm
(DMF), 1440, 1620 cm
(COO symmetric and
-1
asymmetric), weak bands in the spectral region of 700–400 cm most likely due to in-
-1
-1
plane and out-of plane bending modes of COO groups [41], 1520 cm (C=C), 940 cm
9

-1
(
V-O) and the weak bands appearing at 887 and 764 cm relating to the stretching
vibrations of C–C groups and the out-of-plane deformation vibrations of benzene ring C–
-1
H groups [42]. Observation of bands at 948 and 610 cm in the spectrum of
MNPs@SiO @APTMS@V-MIL-101, attributed to the V=O and COO vibrations, are
2
consistent with the immobilization of V-MIL-101 on the modified
MNPs@SiO @APTMS nanoparticles (Fig 1d,f) [20,41-43].
2
The X-ray diffraction powder pattern (XRD) of Fe O @SiO @APTMS@V-MIL-101
3
4
2
is shown in Figure 1S (see supplementary). The diffraction peaks can be assigned to the
planes of spinel structured (JCPDSNo.19-0629) [35,42].
The magnetic properties of the prepared nanomaterials were investigated by means of
vibrating sample magnetometry (VSM). Data obtained for the hysteresis loops of the
materials at room temperature (Fig. 2) exhibits magnetization curves of MNPs,
MNPs@APTMS and MNPs@APTMS@V-MIL-101 either before or after use as catalyst.
Whereas the magnetization curve of Fe O nanopaticles showed no remanence effect
3
4
(superparamagnetic property) with saturation magnetization of about 25 emu/g (Fig 2a),
superparamagnetic behavior decreased to saturation magnetization of about 12 emu/g
after coating of the magnetite nanoparticles with amino–silane (Fig. 2b). Based on the
obtained difference, coupling of a rather small amount of amino–silane to the magnetic
nanospheres surface is concluded. Afterward, by means of amino-silica nanoparticles
surface modification with V-MIL-101, the exhibited superparamagnetic properties was
found to decrease to saturation magnetization of about 11emu/g. Recall that the
superparamagnetic properties of MNPs@APTMS@V-MIL-101 is critical in preventing
aggregation and enabling it to redisperse rapidly upon removing the magnet. The
1
0

superparamagnetic properties of MNPs@APTMS@V-MIL-101 before and after using as
epoxidation catalysts are shown in Fig. 2c and 2d respectively [41, 42 and 44]. With such
high magnetization property of MNPs@APTMS@V-MIL-101 after using as catalyst, the
catalyst could be easily separated from solution under an external magnetic field.
Fig. 2. Magnetization curves: (a) Fe O , (b) Fe O @SiO @APTMS, (c)
3
4
3
4
2
Fe O @SiO @APTMS@V-MIL-101 before using and (d) after using as
3
4
2
catalyst.
The SEM image of Fe O @SiO @APTMS@V-MIL-101 shows the formation of some
3
4
2
spherical particles with about 27-38 nm (see supplementary, Figure S2). The transmission
microscopy (TEM) image of Fe O @SiO @APTMS@VMIL101 is presented in Fig. 3.
3
4
2
The magnetic core shell nanoparticles (Fe O @SiO @APTMS@VMIL101) with about
3
4
2
8
-10 nm in diameter is evident in this Figure.
1
1

Fig. 3. TEM image of Fe O @SiO @APTMS@V-MIL-101.
3
4
2
3
.2. Catalytic studies
The catalytic performance of V-MIL-101 and Fe O @SiO @APTMS@V-MIL-101
3
4
2
were studied in the epoxidation of norbornene as the representative substrate using TBHP
as oxidant. In order to find the optimum reaction conditions, the effect of various
reaction parameters such as the amount of catalyst, reaction time and solvent were
evaluated (Figs. 4, 5 and 6) respectively.
As indicated in Fig. 4, increasing the amount of Fe O @SiO @APTMS@V-MIL-101
3
4
2
catalyst from 10 to 40 mg increases the conversion from 50 to 70% with 100%
selectivity.
1
2

Similarly, increasing the reaction time from 16 to 24 h using 40 mg of catalyst was
found to increase the norbornene conversion from 48 to 70% with 100% selectivity (Fig.
5
). When epoxidation of norbornene was carried out in the presence of V-MIL-101, 93%
conversion with 95% selectivity was observed within 14 h and using 20 mg of the
catalyst.
Fig. 4. Conversion and selectivity of norbornene with different amount of
Fe O @SiO @APTMS@V-MIL- 101 as catalyst.
3
4
2
1
3

Fig. 5. Conversion and selectivity of norbornene at different times
in the presence of Fe O @SiO @APTMS@V-MIL-101.
3
4
2
As has been reported previously, solvent usually affect the conversion in
homogeneous catalysis systems [45]. In our heterogeneous catalysis system, the influence
of different solvents such as acetonitrile, methanol and dichloromethane is also observed
although rather weaker under optimum reaction conditions (Fig. 6). As is shown, a
decrease in conversion is observed in the order of acetonitrile
methanol >
dichloromethane (Fig. 6). This trend is in the decreasing order of dielectric constants as
well as boiling points of these solvents. As has been explained (vide infra), the transition
state of the complexation of both hydroxyl and double bond groups to vanadium center is
more polar in comparison to that of reactants. Therefore, increasing the polarity of the
solvent is expected to increase the reaction rate. On the other hand, increasing the solvent
boiling point seems to increase the reaction rate constant based on the Arrhenius
equation. Moreover, since the one with the most transition state stabilization in
acetonitrile reats with highest in the first step, undergoes reaction with the slowest rate in
the second step in which transfer of oxygen to the double bond occurs. Therefore,
1
4

obtaining the highest selectivity in acetonitrile is in accord with reactivity-selectivity
principle [46].
Fig. 6. The effect of solvent on the conversion and selectivity of norbornene using
Fe O @SiO @APTMS@V-MIL-101 as catalyst.
3
4
2
Whereas epoxidation reactions were generally efficient using TBHP as oxidant,
hydrogen peroxide (H O ) proved to be inefficient under optimized conditions. This
2
2
might be related to the more electrophilic character of the peroxide oxygen in TBHP.
In order to determine the general applicability of the Fe O @SiO @APTMS@V-MIL-
3
4
2
1
01 catalyst, epoxidation reactions of other olefins such as trans-stilbene, norbornene,
cyclooctene , cyclohexene, α- methylstyrene and styrene under optimized epoxidation
conditions were also studied (Table 1).When Fe O @SiO @APTMS@V-MIL-101 (1)
3
4
2
was used as catalyst, the conversions were 20 to 75-% with 70 to 100% selectivities
1
5

Table 1
Results obtained for epoxidation of different alkenes in the presence of Fe O @SiO @APTMS@V-MIL-
3
4
2
1
01 (1)and V-MIL-101 (2).
a
Entry
Substrate conversion
Product selectivity
b
Epoxide % (TON) Epoxide % (TON)
Catalyst 1 (%)
Catalyst 2 (%)
Catalyst 1
Catalyst 2
1
trans-stilbene
7
5
95
1
00 (45)
100 (20)
95 (392)
2
3
4
norbornene
93
7
5
2
100 (853)
cyclooctene
0
35
1
8
00 (592)
90 (148)
40 (346)
cyclohexene
4 82
c
6 (403)
3
5
6
-
5
methylstyrene
2
60
9
8 (296)
78 (253)
55 (317)
syrene
d
2
0
75
70 (237)
a
Reaction conditions: catalyst 1: 40 mg , catalyst 2: 20 mg), substrate (20 mmol, for trans-stilbene, 1 mmol
was used), TBHP (24 mmol), solvent (acetonitril, 5 ml, reflux at 80 ˚C), time (for 1: 24 h , for 2 : 14 h).
TON is the mmol of products to mmol of vanadium present in catalyst.
A mixture of 2-cyclohexene-1-ol and 2-cyclohexene-1-one (14%) were also identified as byproduct.
Benzaldehyde (30%) was also identified as byproduct.
b
c
d
1
6

toward the corresponding epoxides (Table 1). As seen in Table 1, The trans-stilbene,
norbornene and cyclooctene are quantitatively converted to the corresponding epoxides
with 100% selectivity, (entries 1-3, Table 1). Moreover, the selectivities were found to be
higher in the presence of catalyst 1 (Table 1). In the cases of styrene and cyclohexene,
benzaldeyde, and a mixture of other oxidation products were also obtained in addition to
the corresponding epoxides (Table 1).
Particularly significant are the epoxidation results of trans-silbene and norbornene
which afforded the corresponding epoxides in high yields (Table 1, entries 1 and 2). The
high selectivities might be attributed to the alkene structures in which no other oxidation
routes are available in these cases. On the other hand, whereas cyclooctene exclusively
gives the corresponding epoxide, cyclohexene undergoes allylic oxidation and
epoxidation, concomitantly (Table 1, entries 3 and 4). Such difference may have arisen
from cyclooctene chair conformation in which the double bond is in one plane and all
other carbons are in another plane [47]. Therefore, the allylic hydrogens of cyclooctene
are less reactive in comparison to that of cyclohexene with half-chair conformation [48].
Finally, compared to α- methylstyrene which affords epoxide in about 98% yield (Table
1
, entry 5), styrene gives styrene epoxide and benzaldehyde (Table 1, entry 6) in 70%
yield. As observed previously by us and others, styrene epoxide partly undergoes further
oxidation to benzaldehyde as the main byproduct [49].
The epoxidation results of various allyl alcohols such as geraniol, trans-2-hexene-1-ol,
1
-octene-3-ol, and cinnamyl alcohol with catalysts 1 and 2 as heterogeneous and
homogeneous catalysts, respectively under optimized reaction conditions are given in
Table 2.
1
7

Table 2
Results obtained for epoxidation of different allyl alcohols in the presence of Fe O @SiO @APTMS@V-
3
4
2
MIL-101 (1)and V-MIL-101 (2).
a
Entry
Substrate conversion
Product selectivity
b
Epoxide % (TON) Epoxide % (TON)
Catalyst 1 (%)
Catalyst 2 (%)
Catalyst 1
Catalyst 2
Geraniol
1
100
97
1
1
00 (1185)
95 (409)
trans-2-hexen-1-ol
2
3
4
100
85
00 (1185)
95 (359)
1-octene-3-ol
8
0
45
75
1
7
00 (948)
0 (711)
80 (190)
45 (317)
cyclohexene
0
6
a
Reaction conditions: catalyst 1: 40 mg , catalyst 2: 20 mg), substrate (20 mmol, for trans-stilbene, 1 mmol
was used), TBHP (24 mmol), solvent (acetonitril, 5 ml, reflux at 80 ˚C), time (for 1: 24 h , for 2 : 14 h).
TON is the mmol of products to mmol of vanadium present in catalyst.
b
1
8

Obtaining 100% conversion and selectivity for geraniol and trans-2-hexene-1-ol with
catalyst 1 is promising. In the case of catalyst 2, the conversion and selectivities were
found to be 45 to 97% and 45 to 95%, respectively. The higher activity of allyl alcohols
may be due to the initial complexation of both hydroxyl and double bond groups to
vanadium center [50]. It was also found that the epoxidation conversion of geraniol either
with Fe O @SiO @APTMS or using no catalyst (blank) were 8 and 5%, respectively.
3
4
2
These results clearly indicate the key role of the immobilized V-MIL-101 on the
modified iron nanoparticles as catalyst in epoxidation reaction.
In order to make insight into the reaction mechanism, epoxidation of trans-2-hexene-1-
ol was carried out in the presence of diphenylamine as a radical scavenger. Observation
of no inhibition indicated that oxidation does not occur through a radical mechanism.
Based on sharpless suggestion [51], both the allylic OH and double bond as well as the
hydroperoxide seem to initially coordinate to the metal center. Subsequently, transfer of
oxygen form the generated peroxo intermediate to the double bond affords the
corresponding epoxide product [51].
The stability of the magnetically recovered Fe O @SiO @APTMS@V-MIL-101 has
3
4
2
been investigated by recycling the recovered catalyst and determination of the vanadium
content using atomic absorption spectroscopy. Compared to the iron and
vanadiumcontents of 13.51 and 2.15% in the fresh catalyst, these two were found to be
1
3.50 and 2.11 %, in the used catalyst. Therefore, the vanadium content present in the
filtrate should not have been significant and no catalytic activity was also observed in
using filtrate solution.
1
9

The reusability of the catalyst after recovery by magnetic decantation was examined
with geraniol as a model for five runs. As indicated in Fig. 7, a decrease in conversion
from 100 to 98% without any changes in selectivities was observed.
Fig. 7. The effect of recycling of catalyst (Fe O @SiO @APTMS@V-
3
4
2
MIL-101) on epoxidation of geraniol.
As shown before, the FTIR and VSM spectra of catalyst before and after using as
catalyst are similar. Comparison of the prepared immobilized V-MIL-101 nanaocatalyst
with some other previously reported V-MILs and V-MIL-47 [52] as catalyst for
epoxidation of cyclohexene, it seems, the extent of applicability, reusability and stability
of immobilized one is more than homogeneous (V-MIL 101) catalyst.
4
. Conclusions
2
0

In this study, V-MIL-101 immobilized on the modified iron oxide nanomagnet and
designated as Fe O @SiO @APTMS@V-MIL-101, was characterized with FT-IR, XRD,
3
4
2
VSM and TEM techniques. This compound was found to successfully catalyze the
epoxidation of alkenes and allyl alcohols in moderate to high yields. It was also found
that the selectivity and TON number of immobilized V-MIL-101 was higher than that of
unimmobilized or homogeneous systems. Study of the catalyst reusability revealed that at
least five epoxidation runs could be carried out without significant reduction in catalytic
activity. Based on the promising advantages of magnetic nanoparticles in comparison to
those of conventional catalyst supports, utilization of Fe O @SiO @APTMS@V-MIL-
3
4
2
1
01 opens a new route to the immobilization of MOFs compounds for making new
catalysis systems. This method provides several advantages including high yield, clean
reaction, ease of catalyst separation and recyclability of the solid catalyst. Compared to
the reported TONs in the conventional catalysis systems, the high TONs obtained in this
research for immobilized V-MIL-101 on modified Fe O nanoparticles are promising.
3
4
Acknowledgments
The authors would appreciate the Alzahra University for financial support.
References:
[
[
1] K.A. Joergensen, Chem. Rev. 89 (1989) 431-458.
2] José A.L. da Silva, João J.R. Fraústo da Silva, Armando J.L. Pombeiro
Coord. Chem. Rev. 255 (2011) 2232– 2248.
[
3] T. Katsuki, K.B. Sharpless, J.Am. Chem. Soc.102 (1980) 5974-5976.
2
1