Improved catalytic performance of porous metal-organic frameworks for the ring opening of styrene oxide

Article abstract of DOI:10.1039/c7ce00528h

An emerging strategy to improve the performance of porous metal-organic framework (MOF) materials as heterogeneous catalysts is reported. The incorporation of the iron-substituted polyoxometalate (POM) TBA₄[PW₁₁Fe(H₂O)O

Full text of DOI:10.1039/c7ce00528h

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DOI: 10.1039/C7CE00528H
ARTICLE
Improved catalytic performance of porous metal-
organic frameworks for ring-opening of styrene
oxide†
Diana Julião‡, André D. S. Barbosa‡, Andreia F. Peixoto, Cristina Freire,
Baltazar de Castro, Salete S. Balula* and Luís Cunha-Silva*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
An emerging strategy to improve the performance of porous metal-organic framework (MOF)
materials as heterogeneous catalysts is reported. The incorporation of the iron-substituted
polyoxometalate (POM) TBA4[PW11Fe(H2O)O39] (PW11Fe) in the porous MOF NH2-MIL-101(Fe),
leading to a novel composite based MOF material, PW11Fe@NH2-MIL-101(Fe), revealed to be
a significant approach to increase the efficiency of the MOF material as regioselective catalyst
for ring-opening of styrene oxide with aniline. The conversion after 1 h of reaction using the
NH2-MIL-101(Fe) is 22% and augments to 100% when the PW11Fe@NH2-MIL-101(Fe) is
employed as catalyst. Noteworthy, the catalytic performance of this composite material is also
considerably better than that obtained with the respective physical mixture in similar conditions.
Furthermore, PW11Fe@NH2-MIL-101(Fe) revealed to be a remarkable selective heterogeneous
catalyst for the studied reaction (100% of selectivity to the 2-phenylamino-2-phenylethanol
isomer), with significant robustness and recycle ability.
attracted high scientific interest as heterogeneous catalysts
in numerous type of chemical reactions, as consequence of
Introduction
Metal–organic frameworks (MOFs), also known as
coordination networks or coordination polymers, are
crystalline materials based on metal centers or metallic
clusters interconnected by multidentate organic ligands to
form uni- (1D), bi- (2D) or three-dimensional (3D) infinite
structures.1-5 Their synthesis can be judiciously designed
and rationalized to obtain porous MOFs with specific
structures and topologies, large surface areas and tunable
pore features.6-8 These remarkable characteristics confer the
the immense possibility of combination of different active
sites (active metal centers and / or active functional organic
11, 25-28
linkers) in the same material.10,
More recently, the
porous MOFs have been explored as solid supports of
catalytic active species, for example metallic nanoparticles29-
31
,
metal oxides32-34
,
organometallic or coordination
36
complexes35,
, to prepare efficient and sustainable
heterogeneous catalysts in distinct reactions.
In particular, the MIL-101 family of MOF materials
reveal a porous 3D framework based in trimeric metal
building units, with general formula [M3X(H2O)2O(L)3]
porous MOFs a high potential for numerous applications,
14-18
principally catalysis.9-13, gas adsorption and separation
,
20
22
chemical sensing,19, 20 luminescence,19, drug delivery21,
∙
n
(H2O) (usually M=Cr(III), Fe(III) or Al(III), X− = F− or OH−,
and proton conduction23, 24. In particular, porous MOFs have
n
≈ 25 and L stands for amino- or 1,4-benzene-dicarboxylic
acid). These inorganic trimers are formed by three M(III)
centres with octahedral coordination environment {MO6}.
Adjacent octahedral moieties interconnect through the µ3-
O atom to originate the trimeric building unit which are
connected by the organic linkers (six ligands bonded at
each trimeric cluster), finally leading the porous 3D
framework material. This structural arrangement
REQUIMTE - LAQV & Department of Chemistry and Biochemistry,
Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal.
e-mails: sbalula@fc.up.pt and l.cunha.silva@fc.up.pt;
Tel: +351 220402576; Fax: +351 220402659
† Electronic Supplementary Information (ESI) available: additional relevant
figures, particularly UV-VIS and FTIR spectra, powder XRD patterns, SEM
images and 1H NMR spectrum. See DOI: 10.1039/x0xx00000x
‡ authors contributed equally as first authors.
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establishes a network of microporous channels (apertures
in the presence of aniline, 100% yield of 2-phenylamino-2-
View Article Online
of ca. 8.6 Å) inter-connecting two different mesoporous
phenylethanol could be achieved afteDrO1I:h1,0.i1n0s3t9e/aCd7CoE0f025428Hh
needed using the free MOF. Under these conditions, the
POM@MOFs showed high robustness and high recycle
capacity.
cages in a ratio of 2:1, with internal free diameters of ca
.
29 Å and 34 Å, respectively.37
The epoxide ring-opening reaction by amines is very
important since the resulting products, such as β-
aminoalcohols, possess
a considerable interest in the
preparation of biologically active compounds and synthetic
39
products in different chemical fields.38,
The β-
aminoalcohols are usually synthesized by the direct
aminolysis of epoxides. However, this reaction often
involves a large excess of amines and high temperatures, so
to promote useful modifications in habitual procedures,
,
44
homogeneous catalysts have been widely applied.40-43
Despite the effort to improve the epoxide ring-opening
reaction, most of the homogeneous catalysts used are
expensive, not efficient, toxic and instable. Some catalysts
showed excellent performance in aminolysis of different
kind of epoxides using mild conditions. Particularly, the
Figure 1. Schematic representation of the composite material
PW11Fe@MIL-101(Cr).
iron-substituted
polyoxometalate (POM)
(PW11Fe) revealed high
TBA4[PW11Fe(H2O)O39
]
,
performance as homogeneous catalyst in this reaction;42
nevertheless, its recover and recycle have serious
drawbacks. To overcome these limitations new strategies for
converting soluble POMs to solid materials that would be
stable in the liquid phase have been studied by many
research groups.33, 45-49 Various types of materials have been
used in the heterogenization of catalytically active species
resulting in efficient heterogeneous catalyst based
materials.50 The incorporation of POMs into porous MOFs
have demonstrated to decrease the reaction time, due to
concentration effect between the different components from
the catalytic reaction, resulting of the large cavities of
certain MOFs.33, 51
Experimental section
Materials and methods
All the reagents utilized in the syntheses and preparation
of the compounds and materials were used as received:
tetrabutylammonium bromide (TBA∙Br,
C16H36BrN, Alfa
Aesar, 98%), sodium tungstate dihydrate (Na2WO4∙2H2O,
Aldrich, ≥ 99.0%), sodium phosphate (Na3PO4, Aldrich,
96%), iron (III) chloride hexahydrate (FeCl3·6H2O, Merck,
p.a), chromium(III) nitrate nonahydrate [Cr(NO3)3.9H2O,
Aldrich, 99%], terephthalic acid (H2bdc, C8H6O2, Aldrich,
98%), 2-aminoterephthalic acid (NH2-H2bdc, C8H8NO2,
Aldrich, 99%) and dimethylformamide (C3H7NO, DMF, Fluka,
99.0%). Furthermore, the chemicals used in the catalytic
studies were used as purchased from commercial supplies
without any purification: acetonitrile (MeCN, CH3CN,
Panreac, 99.8%), aniline (C6H7N, Aldrich, 99%) and styrene
oxide (C8H8O, Aldrich, 97%), were also used as received.
Powder X-ray diffraction (XRD) patterns were collected
at room temperature on a on a Empyrean PANalytical
diffractometer (CuKα1,2 radiation, λ1 = 1.540598 Å and
λ2 = 1.544426 Å), equipped with an PIXcel 1D detector and a
flat-plate sample holder in a Bragg–Brentano para-focusing
optics configuration (45 kV, 40 mA). Intensity data were
obtained by the step-counting method (step 0.02º), in
continuous mode in the approximate range 3.0º ≤ 2θ ≤ 50º.
Following the recent investigation of our research group
in the design and application of advanced MOF-based
47,
materials as catalysts32-34,
52-57, two novel composites
were prepared by incorporation of PW11Fe into NH2-MIL-
101(Fe) and MIL-101(Cr) (denoted, respectively as
PW11Fe@NH2-MIL-101(Fe)
and
PW11Fe@MIL-101(Cr),
Figure 1), which were employed as heterogeneous catalysts
in the ring-opening of cycloalkene oxide. To date there are
only a report on the use of POM@MOFs as catalysts in the
ring-opening reaction of cycloalkene oxide in the presence
of methanol.58 Recently, we demonstrated that iron-based
MOFs behave as active and selective catalysts for this type of
reaction.57 This work presents a new synthetic strategic to
increase easily the catalytic performance of active MOFs by
encapsulating a POM guest. Using the POM@MOFs instead of
the free MOF structure, in the ring-opening of styrene oxide
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Infrared absorption spectra were recorded on
ARTICLE
a
and stirred at room temperature for 24 h (aVtielweAarstitc)le. OTnlhinee
DOI: 10.1039/C7CE00528H
PerkinElmer spectrum BX FTIR spectrometer equipped with
a Pike GldiATR device for measurements in attenuated total
reflectance (ATR) mode.
solid was filtered, washed scrupulously with MeCN and
dried in a desiccator over silica gel. The incorporation was
verified by the combination of several characterization
techniques, such as UV/Vis and FTIR spectroscopy, powder
XRD and ICP analysis. PW11Fe@NH2-MIL-101(Fe): Anal.
found (%): W, 9.29; Fe, 12.8; loading of PW11Fe: 0.046 mmol
g−1. Selected FTIR (cm–1): υ = 3466 (w), 3352 (w), 1576 (m),
1494 (w), 1424 (m), 1382 (vs), 1338 (m), 1256 (s), 1064
(w), 966 (w), 892 (w), 812 (w), 768 (m), 702 (w), 624 (w),
566 (w), 522 (w), 440 (w). PW11Fe@MIL-101(Cr): Anal.
W and Fe analysis was carried out by ICP-OES on a
Varian 820-MS at ”Universidade de Satiago de Compostela”.
Scanning electron microscopy (SEM) images were
performed in
a
high resolution scanning electron
microscope FEI Quanta 400 FEG ESEM. The energy-
dispersive X-ray spectroscopy (EDX) studies were recorded
in the same microscope working at 10 keV and using an
EDAX Genesis X4M microanalysis system. SEM and EDX
analysis were performed at “Centro de Materiais da
Universidade do Porto” (CEMUP, Porto, Portugal).
found (%): W, 22.2; loading of PW11Fe: 0.113 mmol g−1
.
Selected FTIR (cm-1): υ = 2342 (w), 1668 (w), 1628 (s), 1558
(w), 1506 (w), 1434 (vs), 1396 (w), 1064 (w), 960 (m), 886
(m), 814 (s), 746 (s), 666 (m), 588 (s), 516 (w), 418 (m).
GC-FID was performed in a Varian V3800 chromatograph
to monitor catalytic reactions and a Bruker 430-GC to follow
the reactions. In both experiments, hydrogen was the carrier
gas (55 cm3 s−1) and fused silica Supelco capillary columns
SPB-5 (30 m × 0.25 mm i.d.; 25 µm film thickness) were
used.
Catalytic studies
The ring-opening reactions of styrene oxide (Scheme 1)
were carried out in borosilicate 5 mL reaction vessel
equipped with
thermostated oil bath under air (atmospheric pressure),
using acetonitrile (MeCN) as the solvent at 80 C. In a typical
a magnetic stirrer and immersed in a
̊
Preparation of the materials
procedure the styrene oxide (1 mmol), aniline (0.9 mmol)
and the catalyst were dispersed in MeCN (1,5 mL).
Fe-substituted polyoxometalate. TBA salts of iron-
substituted POM, TBA4[PW11Fe(H2O)O39
] (PW11Fe), was
As the iron cation is the active catalytic center, all the
catalytic reactions were performed using a total of 50 µmol
synthesized according to reported procedures.59 The
compound was characterized by elemental and TGA
analysis, FTIR spectroscopy and powder XRD, unequivocally
confirming their preparation. Anal. Calcd. (%) for
of Fe-amount, what corresponded to use 0,025
g of
PW11Fe@NH2-MIL-101(Fe) and 0,442 g PW11Fe@MIL-
101(Cr) of composites. The most efficient heterogeneous
catalyst was recycled in consecutive cycles. At the end of
each reaction cycle, the composite was washed with MeCN
and dried at room temperature overnight. Then, the
recovered catalyst was reused in a new catalytic cycle
maintaining the previous experimental conditions. The
styrene oxide ring-opening reactions were monitored by GC
C
64H146N4O40PW11Fe (3720,90 gmol−1): C, 21.62; H, 3.72; N,
1.63. Found: C, 20.66; H, 3.95; N, 1.51. FTIR (cm-1): υ = 2962
(m), 2874 (w), 2360 (s), 2342 (s), 1484 (m), 1064 (s), 960
(s), 884 (s), 800 (vs), 668 (m), 594 (w), 516 (m), 374 (vs).
NH2-MIL-101(Fe). The porous MOF material NH2-MIL-
101(Fe) was prepared using the reported procedure.60 Anal.
found (%): Fe, 12.4. FTIR (cm−1): υ = 3460 (w), 3324 (w),
1652 (w), 1574 (s), 1496 (m), 1418 (m), 1382 (vs), 1338
(m), 1256 (s), 968 (w), 892 (w), 828 (m), 766 (w), 692 (w),
626 (w), 570 (w), 518 (w), 434 (w), 382 (m).
analysis and stopped when
a completed conversion of
aniline was observed or when the product yields remained
constant after two successive GC analyses. An aliquot was
taken directly from the reaction mixture with
a
MIL-101(Cr). The porous MOF MIL-101(Cr) was synthesized
employing the original method described by Férey and co-
workers.37 FTIR (cm-1): υ = 2976 (m), 2902 (m), 2360 (w),
1672 (w), 1632 (s), 1560 (m), 1510 (w), 1434 (vs), 1398
(w), 1076 (s), 1066 (w), 1050 (w), 884 (w), 834 (w), 810
(w), 746 (s), 714 (w), 668 (m), 588 (s), 468 (m).
microsyringe at regular intervals; the heterogeneous
catalysts were centrifuged and then the solution was
injected into the GC equipment for analysis of the starting
material and products. The reaction products were
identified 1HNMR spectroscopy.
Composite materials PW11Fe@MIL-101. The two
composite materials were prepared by adaptation of the
method previously reported.49 In brief, 0.6 g of the porous
support material, NH2-MIL-101(Fe) or MIL-101(Cr), were
added to a solution of PW11Fe in MeCN (10 mM in 13 mL)
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spectra of the MeCN solution after 24 hours of reaction show
View Article Online
DOI: 10.1039/C7CE00528H
a clear decrease of the absorbance in a typical absorption
band of the POM at ca. 250 nm (corresponds to the charge
transition from the bridging O-atoms to W-atoms) relatively
to the spectra of the initial POM solution. This observation
confirms the decrease in the amount of the PW11Fe in
solution, most probably due to its incorporation into the
porous MOFs. The composite materials were further
characterized by several techniques including FTIR
spectroscopy, powder XRD, metal analysis (ICP), scanning
electron microscopy (SEM) and energy-dispersive X-ray
spectroscopy (EDX).
(1)
(3)
(2)
Scheme 1. Ring-opening of styrene oxide with aniline.
Results and discussion
The presence of POM in the MIL-101 was initially
verified by FTIR spectroscopy, comparing the spectra of the
composite materials with the spectra of the POM and
respective solid support (Figures 2 and S2 in ESI). The FTIR
spectrum of the PW11Fe@NH2-MIL-101(Fe) reveals the
characteristic bands of the POM, namely ʋas(P−O) at
Catalysts preparation and characterization
The porous MOFs, NH2-MIL-101(Fe) and MIL-101(Cr), were
used as solid support for the incorporation of TBA salt of
iron-substituted POM, TBA4[PW11Fe(H2O)O39] (PW11Fe),
originating two unprecedented composite materials:
-
-
1
1064 cm 1, ʋas(W=O) at 966 cm and ʋas(W−O−W) at 896 cm-
1, as well as the vibrational modes of the MOF, namely the
asymmetric and symmetric ʋ(O−C−O) at 1496 cm-1 and 1418
cm-1 respectively (Figure 2). At 3466 cm-1 and 3352 cm-1 the
spectra of composite material also exhibits the asymmetric
and symmetric stretches associated amine groups and at
766 cm-1 the stretching mode of the aromatic rings δ(C−H)
was observed.61, 62 The characteristic bands of the PW11Fe in
the FTIR spectrum of PW11Fe@MIL-101(Cr) were observed
at 1064, 960 and 886 cm-1 and assigned to the P−O, W=O and
W−O−W stretching modes, respectively (Figure S2 in ESI).
The W and Fe analysis further support the presence of the
PW11Fe in the respective composite materials, revealing a
PW11Fe loading of 0.046 and 0.113 mmol g−1 in
PW11Fe@NH2-MIL-101(Fe)
and
PW11Fe@MIL-101(Cr).
These materials were prepared by the impregnation
method, which has been largely employed and it is well
32-34, 47, 52, 55, 56
established in our group.
Initially, the
incorporation of the PW11Fe in the MIL-101 frameworks was
monitored by UV-Vis spectroscopy (Figure S1 in the
Electronic Supplementary Information, ESI). The UV-Vis
PW11Fe@NH2-MIL-101(Fe)
respectively.
and
PW11Fe@MIL-101(Cr),
Figure 2. FTIR spectra of the PW11Fe, the support NH2-MIL-101(Fe)
and the composite, before (PW11Fe@NH2-MIL-101(Fe)) and after
catalytic use (PW11Fe@NH2-MIL-101(Fe)_ac, recovered after the 3rd
reaction cycle).
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ARTICLE
PW11Fe@NH2-MIL-101(Fe) does not reveaVlieweArxtitcelenOsnilvinee
changes relatively to that of the “DfOreI:e1”0.1s0o39li/dC7CsEu0p0p5o28rHt,
indicating that the global crystalline structure of the solid
support is maintained after the incorporation of the PW11Fe
(Figure 3). The powder XRD pattern of the PW11Fe@MIL-
101(Cr) shows significant differences with respect with the
difractogram of the MIL-101(Cr) support. Some relevant
peaks that do not match with those of PW11Fe emerged
between ca. 5º and 8º (2θ) in the diffraction pattern of the
composite material. This type of changes were already
observed and reported for related composite materials
63
based in MIL-101(Cr).47,
Bromberg and co-workers
concluded that these emerged peaks are in fact not “new”,
since the Bragg peak positions are consistent with the unit
cell of MIL-101 family. These unmodified MOFs possess
those peaks with null or very weak intensity. The
incorporation of the POM in porous framework affects the
electron density of the crystal structure of MIL-101, creating
the observed diffracted intensity at these positions.63 The
absence of diffraction peaks corresponding to PW11Fe in the
powder XRD pattern of the two composite materials
suggests that the POM is incorporated in the solid support in
a random dispersed form. In fact, the incorporation of the
PW11Fe in the porous framework of the two distinct support
materials, NH2-MIL-101(Fe) and MIL-101(Cr), doesn’t
causes degradation and/or collapse of their structure.
Figure 3. Powder XRD patterns of the PW11Fe, the solid support
NH2-MIL-101(Fe) and the composite material before PW11Fe@NH2-
MIL-101(Fe) and after the 3rd catalytic use PW11Fe@NH2-MIL-
101(Fe)_ac.
The integrity of the MOF structure in the composite
materials was confirmed by powder XRD (Figures 3 and S3
in ESI). The diffraction pattern of the composite material
(a)
(b)
(c)
4 µm
5 µm
5 µm
Figure 4. SEM images of solid support NH2-MIL-101(Fe) (a), and the composite material before PW11Fe@NH2-MIL-101(Fe) (b) and
after the 3rd catalytic use catalytic use PW11Fe@NH2-MIL-101(Fe)_ac (c).
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View Article Online
DOI: 10.1039/C7CE00528H
ARTICLE
Catalytic studies
W
The ring-opening reaction of styrene oxide in the presence
of aniline was catalyzed by two different Fe-MOFs based
heterogeneous catalysts: PW11Fe@MIL-101(Cr) and
PW11Fe@NH2-MIL-101(Fe). All the reactions were
performed using a total amount of 50 µmol of Fe and using
MeCN as solvent. A blank reaction was performed without
catalyst. In this case the aniline and the styrene oxide were
not consumed during 2 h of reaction.
Fe
O
In our previous work, it was demonstrated that the
support NH2-MIL-101(Fe) is an active heterogeneous
catalyst for the ring-opening of cyclohexene oxide in the
presence of aniline, achieving 87% of conversion after 24 h
at 80 ºC.57 In this work, the same Fe-MOF support material
was used as heterogeneous catalyst for the ring-opening of
styrene oxide in the presence of aniline and close complete
conversion was also obtained later than 24 h. However, after
the first hour only 22% of conversion was achieved, which
indicates that the Fe center in the MOF framework presents
a small catalytic activity in this type of reaction. In fact the
activity of the Fe centers in the MOF structure can be
dependent to the presence of surface defects, which
originate more active unsaturated Fe metal centers. The
catalytic activity of MIL-101(Cr) was also investigated and
no reaction occurred during the first 5 h of reaction.
W
O
Fe
Figure 5. EDX elemental mapping images for the composite
material before PW11Fe@NH2-MIL-101(Fe) (top) and after the
3rd catalytic use PW11Fe@NH2-MIL-101(Fe)_ac (bottom).
In order to increase the catalytic efficiency of the NH2-
MIL-101(Fe), a strategic method based in the encapsulation
of a catalytic active guest (PW11Fe) into its cavities, forming
the novel composite PW11Fe@NH2-MIL-101(Fe) was
performed. Also, to evaluate the catalytic participation of the
Fe centers from the MOF framework, the same active guest
PW11Fe was also encapsulated into the MIL-101(Cr)
structure, PW11Fe@MIL-101(Cr).
The SEM images of the composite materials
PW11Fe@MIL-101 show the same type of particles of the
solid supports (Figures
4 and S4 in ESI). The similar
morphology showed by the different materials, together
with the XRD patterns previously discussed, are a indication
that the main features of the crystalline structure of the
solid supports are maintained unchanged after the
incorporation of the POM. Additionally, the elemental
mapping images reveal the presence and
a uniform
distribution of W, confirming unequivocally the
homogeneous incorporation of PW11Fe in the composite
material (Figure 5).
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ARTICLE
MIL-101(Fe) (containing 49 µmol of Fe in
View Article Otnhlinee
100
90
80
70
60
50
40
30
20
10
0
DOI: 10.1039/C7CE00528H
framework) is added to 1 µmol PW11Fe system, the
activity increased but not as much as the composite
PW11Fe@NH2-MIL-101(Fe) system (Figure 7). These
results indicate that the support NH2-MIL-101(Fe) has
an important influence in the activity of the active
PW11Fe guest, in addition to the confinement effect
conferred by the MOF cavities.
PWPW11FFee@@NNHH2--MMIILL--110011((FFee))
11
2
PW11Fe@MIL-101(Cr)
PW11Fe@MIL-101(Cr)
PW11Fe
PW11Fe
NNHH2-M-MILI-L1-0110(1F(Fe)e)
2
100
90
0
10
20
30
40
50
60
PW11Fe@NH2-MIL-101(Fe)
80
Time (min)
70
60
Figure 6. Kinetic profile for the ring-opening reaction of
styrene oxide with aniline using various Fe-based catalysts (50
µmol of total Fe) at 80 °C, in MeCN (solvent).
PW11Fe + NH2-MIL-101(Fe)
50
40
PW11Fe
30
The results displayed in Figure 6 demonstrate that the
composite PW11Fe@NH2-MIL-101(Fe) is significantly
more active than the support NH2-MIL-101(Fe), using in
both reactions a total of 50 µmol of Fe. In fact, using the
heterogeneous PW11Fe@NH2-MIL-101(Fe) catalyst it is
possible to achieve complete conversion after 1 h of
reaction. The same conversion was obtained by the
homogeneous PW11Fe; however, this presents the
various disadvantages associated to the homogeneous
catalysts, i.e. the impossibility of recovery from the
reaction medium and recyclability. Using the
heterogeneous PW11Fe@NH2-MIL-101(Fe) catalyst,
after 1 h the catalyst could be isolated from reaction, the
solvent could be evaporated and the products could be
easily recovered. Comparing the catalytic activity of the
PW11Fe@NH2-MIL-101(Fe) and the PW11Fe@MIL-
101(Cr), when in both cases a total of 50 µmol of Fe
were used, it is possible to observe the superior
catalytic activity of the PW11Fe@NH2-MIL-101(Fe)
composite, demonstrating that the Fe centers in the
MOF framework have an important contribution to
achieve the complete conversion of the styrene oxide
ring-opening reaction in the presence of aniline.
20
PW11Fe@MIL-101(Cr)
10
0
0
10
20
30
40
50
60
Time (min)
Figure 7. Kinetic profile for the ring-opening of styrene oxide
with aniline in the presence of various Fe-based catalysts, using
1 µmol of PW11Fe, MeCN as solvent at 80 °C.
The efficiency of the catalyst was also analyzed by its
capacity to trail the reaction to produce mostly a single
product. An efficient catalyst need to be highly selective.
Both
composites
PW11Fe@NH2-MIL-101(Fe)
and
PW11Fe@MIL-101(Cr) presented 96 % of selectivity for the
2-phenylamino-2-phenylethanol (isomer 3 in scheme 1),
according to Lewis acid catalyzed SN1 ring opening
mechanism at the end of the reaction, i.e. after 1 h (Figures 5
64,50
and 7).
No differences in the selectivity were also found
for the active support NH2-MIL-101(Fe) and for the
homogeneous catalyst PW11Fe (selectivity of 98 for
%
isomer 3). The product 2-phenylamino-2-phenylethanol was
isolated by column chromatography and identified by 1H
NMR (Figure S5 in ESI). 62, 65
In view of such excellent catalytic performance of the
PW11Fe@NH2-MIL-101(Fe) composite, the recycle capacity
and the stability of this composite was investigated. At the
end of each reaction cycle, the solid catalyst was recovered
from reaction by centrifugation, washed thoroughly with
MeCN, dried at room temperature and reused in a new
catalytic cycle maintaining the experimental conditions.
To better understand the contribution of the NH2-
MIL-101(Fe) support to the high catalytic activity of the
composite PW11Fe@NH2-MIL-101(Fe),
a comparative
study was performed between this composite and the
guest compound PW11Fe in equal amounts (1 µmol). As
expected, the styrene oxide conversion decreased when
a lower amount (1 µmol; Figure 7) of the homogeneous
catalyst PW11Fe was used, relatively to the result
obtained with higher quantity (50 µmol; Figure 6).
Therefore, the 1 µmol of PW11Fe encapsulated into NH2-
MIL-101(Fe) support is much more active than the free
PW11Fe (Figure 7). Additionally, when the support NH2-
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100
90
80
70
60
50
40
30
20
10
partial loss in crystallinity was expected, as verified in
View Article Online
previous literature regarding the DsOoIl:i1d0.10s3u9p/Cp7oCrEt0.507528IHn
addition, the SEM/EDX techniques were also used to study
the morphology and chemical composition of PW11Fe@NH2-
MIL-101(Fe)-ac. SEM images (Figure 4) reveal a similar
morphology to the as-prepared crystalline composed with
no evidence of degradation. EDX mapping images of
PW11Fe@NH2-MIL-101(Fe)-ac (Figure 5) also show an
identical chemical composition to the sample before
catalysis. Thus, the characterization data points out to the
high robustness of the PW11Fe@NH2-MIL-101(Fe)
heterogeneous catalyst suggested by the structural
preservation of the material after catalytic use.
1st cycle
2nd cycle
3rd cycle
Leaching
0
0
10
20
30
Time (min)
40
50
60
Figure 8. Kinetic profile for the ring-opening reaction of
styrene oxide in the presence of aniline, for three consecutive
reaction cycles catalyzed by PW11Fe@NH2-MIL-101(Fe) (50
µmol of total Fe, 1 µmol of PW11Fe).
Concluding remarks
The recyclability data for PW11Fe@NH2-MIL-101(Fe) is
displayed in Figure 8. It is possible to verify a high capacity
of recyclability of this composite since complete consume of
aniline was achieved for the three consecutive cycles after
only 1 h. A slightly increase of activity is observed for the
second and the third cycles, what can be associated to some
structural reorganization occurred during the first cycle to
form a more active catalytic composite. Furthermore, in
order to evaluate the stability of the composite and to
investigate the possibility of active centers loss, a leaching
test was performed. In this experiment, the solid was
removed from the reaction mixture after 10 min of its
initiation; following the analysis of the filtrate for more 50
A
tactical approach to activate widely the catalytic
performance of the MOF structures to form novel
heterogeneous catalysts for the ring-opening reaction of
styrene oxide in the presence of aniline was reported. The
highly active composites were prepared by the simple
encapsulation of iron-substituted POM PW11Fe into NH2-
MIL-101(Fe) and MIL-101(Cr) large porous cavities. The
composites PW11Fe@NH2-MIL-101(Fe) and PW11Fe@MIL-
101(Cr) revealed high efficiency and notably selectivity to
the 2-phenylamino-2-phenylethanol isomer (isomer 3 in
scheme 1) after
1
h
of reaction. Both composites
and PW11Fe@MIL-101(Cr)
PW11Fe@NH2-MIL-101(Fe)
presented 96 % of selectivity for the 2-phenylamino-2-
phenylethanol, according to Lewis acid catalyzed SN1 ring
opening mechanism at the end of the reaction, i.e. after 1 h
(Figures 5 and 7). No differences in the selectivity were
found for the active support NH2-MIL-101(Fe) and for the
min. Figure
8 presents the results obtained from the
leaching test, which indicates that the reaction practically
stopped after the solid removal. This behavior demonstrates
the heterogeneity of the PW11Fe@NH2-MIL-101(Fe)
composite and the absence of loss of active Fe species.
homogeneous catalyst PW11Fe (selectivity of 98
isomer 3).
% for
The materials PW11Fe@NH2-MIL-101(Fe) showed
higher catalytic performance than the PW11Fe@MIL-
101(Cr), what is due to the catalytic activity attributed to
the Fe centers of the NH2-MIL-101(Fe) framework, as well
as to the mutual activation occurred between the PW11Fe
guest and the NH2-MIL-101(Fe) support, promoted by the
effective interaction of the guest and the MOF framework.
Furthermore, when the catalytic activity of the isolated
guest PW11Fe and the free support NH2-MIL-101(Fe) were
analyzed separately and also in a physical mixture, their
performance was appreciably inferior of the composite
material PW11Fe@NH2-MIL-101(Fe). The high robustness
and stability of the composite material was confirmed
through characterization after catalytic use.
Catalyst material stability
The structural stability of the PW11Fe@NH2-MIL-101(Fe)
catalyst
was
evaluated
through
the
extensive
characterization of the solid recovered after the catalytic use
(PW11Fe@NH2-MIL-101(Fe)-ac). FTIR data of the composite
after catalytic use (Figure 2) show that the characteristic
bands of the material remain unaltered. In particular, no
changes are observed in the bands assigned to the active
guest PW11Fe stretching modes (1000-850 cm-1), suggesting
that the PW11Fe structure is also preserved after catalytic
use. The powder XRD patterns before and after catalytic use
(Figure 3) reveal the maintenance of the main diffraction
peaks, accompanied with a slight decrease of peak intensity
in the 5°-10° range, as well as at 20°, 24° and 29°. This
8 | CrystEngComm, 2017, 00, 1-8
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Following the promising results obtained, further work
will be developed using this and other Fe-MOFs based
composites as heterogeneous catalysts, to enlarge the
success application of these heterogeneous catalysts to the
valuable ring-opening reactions. A large number of epoxide
compounds and several distinct amines will be evaluated
to verify that this procedure based in MOF materials
represents a reliable methodology for a broad epoxide
aminolysis system.
7. D. P. Cai, B. Liu, D. D. Wang, L. L. Wang, Y. Liu, B. H. Qu, X.
View Article Online
C. Duan, Q. H. Li and T. H. Wang, J. MDatOeIr: .10C.h10e3m9/.CA7,C2E0001562,84H,
183-192.
8. C. Wang, T. Zhang and W. B. Lin, Chem. Rev., 2012, 112,
1084-1104.
9. D. Farrusseng, S. Aguado and C. Pinel, Angew. Chem. Int.
Edit., 2009, 48, 7502-7513.
10. A. Corma, H. Garcia and F. Xamena, Chem. Rev., 2010,
110, 4606-4655.
11. J. W. Liu, L. F. Chen, H. Cui, J. Y. Zhang, L. Zhang and C. Y.
Acknowledgements
Su, Chem. Soc. Rev., 2014, 43, 6011-6061.
Funding agencies and projects: the work was co-
12. E. Gkaniatsou, C. Sicard, R. Ricoux, J. P. Mahy, N. Steunou
financed by UE, FEDER - Fundo Europeu de Desenvolvimento
and C. Serre, Mater. Horizons, 2017, 4, 55-63.
Regional and COMPETE 2020
– Programa Operacional
13. Y. B. Huang, J. Liang, X. S. Wang and R. Cao, Chem. Soc.
Rev., 2017, 46, 126-157.
Competitividade Internacionalização (POCI-01-0145-
e
FEDER-007265) through PT 2020 and by national funds
through the FCT / MCTES - Fundação para a Ciência e a
Tecnologia / Ministério da Ciência, Tecnologia e Ensino
14. B. Li, H. L. Wang and B. L. Chen, Chem. Asian J., 2014, 9,
1474-1498.
Superior for the research centre REQUIMTE
- LAQV
15. J. R. Li, R. J. Kuppler and H. C. Zhou, Chem. Soc. Rev., 2009,
38, 1477-1504.
(UID/QUI/50006/2013).
Individual grants: additional thanks to the FCT / MCTES
for the PhD fellowships SFRH/BD/95574/2013 (to ADSB),
SFRH/BD/102783/2014 (to DJ), and the Post-doctoral
16. J. R. Li, Y. G. Ma, M. C. McCarthy, J. Sculley, J. M. Yu, H. K.
Jeong, P. B. Balbuena and H. C. Zhou, Coord. Chem. Rev.,
2011, 255, 1791-1823.
grants
SFRH/BPD/72126/2010
(to
AFP)
and
SFRH/BPD/111899/2015 (to LCS).
17. J. R. Li, J. Sculley and H. C. Zhou, Chem. Rev., 2012, 112,
869-932.
It is not possible to compare the activity of two different
catalysts (PW12 and PW11Fe) in two different reactions
(methanolysis and aminolysis of epoxides, respectively).
18. J. Liu, P. K. Thallapally, B. P. McGrail, D. R. Brown and J.
Liu, Chem. Soc. Rev., 2012, 41, 2308-2322.
19. L. E. Kreno, K. Leong, O. K. Farha, M. Allendorf, R. P. Van
Duyne and J. T. Hupp, Chem. Rev., 2012, 112, 1105-1125.
References
1. S. L. James, Chem. Soc. Rev., 2003, 32, 276-288.
20. F. Y. Yi, D. X. Chen, M. K. Wu, L. Han and H. L. Jiang,
ChemPlusChem, 2016, 81, 675-690.
2. J. L. C. Rowsell and O. M. Yaghi, Microporous Mesoporous
Mat., 2004, 73, 3-14.
21. W. Cai, C.-C. Chu, G. Liu and Y.-X. J. Wang, Small, 2015, 11,
4806-4822.
3. D. Maspoch, D. Ruiz-Molina and J. Veciana, Chem. Soc. Rev.,
2007, 36, 770-818.
22. J. Della Rocca, D. Liu and W. Lin, Accounts Chem. Res.,
2011, 44, 957-968.
4. S. Kitagawa and R. Matsuda, Coord. Chem. Rev., 2007, 251,
23. S. Horike, D. Umeyama and S. Kitagawa, Accounts Chem.
Res., 2013, 46, 2376-2384.
2490-2509.
5. D. J. Tranchemontagne, J. L. Mendoza-Cortes, M. O'Keeffe
24. M. Yoon, K. Suh, S. Natarajan and K. Kim, Angew. Chem.
Int. Edit., 2013, 52, 2688-2700.
and O. M. Yaghi, Chem. Soc. Rev., 2009, 38, 1257-1283.
6. O. K. Farha and J. T. Hupp, Accounts Chem. Res., 2010, 43,
25. A. H. Chughtai, N. Ahmad, H. A. Younus, A. Laypkov and F.
1166-1175.
Verpoort, Chem. Soc. Rev., 2015, 44, 6804-6849.
26. A. Dhakshinamoorthy, M. Opanasenko, J. Cejka and H.
Garcia, Catal. Sci. Technol., 2013, 3, 2509-2540.
This journal is © The Royal Society of Chemistry 2017
CrystEngComm, 2017, 00, 1-8 | 9
Please do not adjust margins

Please do not adjust margins
CrystEngComm
Page 10 of 11
ARTICLE
CrystEngComm
27. M. Yoon, R. Srirambalaji and K. Kim, Chem. Rev., 2012,
112, 1196-1231.
45. N. V. Maksimchuk, K. A. Kovalenko, S. S. Arzumanov, Y. A.
View Article Online
DOI: 10.1039/C7CE00528H
Chesalov, M. S. Melgunov, A. G. Stepanov, V. P. Fedin and
O. A. Kholdeeva, Inorg. Chem., 2010, 49, 2920-2930.
28. Y. Liu, W. M. Xuan and Y. Cui, Adv. Mater., 2010, 22, 4112-
4135.
46. R. Canioni, C. Roch-Marchal, F. Secheresse, P. Horcajada,
C. Serre, M. Hardi-Dan, G. Ferey, J.-M. Greneche, F.
Lefebvre, J.-S. Chang, Y.-K. Hwang, O. Lebedev, S. Turner
and G. Van Tendeloo, J. Mater. Chem., 2011, 21, 1226-
1233.
29. H. L. Liu, L. N. Chang, C. H. Bai, L. Y. Chen, R. Luque and Y.
W. Li, Angew. Chem. Int. Edit., 2016, 55, 5019-5023.
30. Q. H. Yang, Q. Xu, S. H. Yu and H. L. Jiang, Angew. Chem.
Int. Edit., 2016, 55, 3685-3689.
47. S. Ribeiro, A. D. S. Barbosa, A. C. Gomes, M. Pillinger, I. S.
Goncalves, L. Cunha-Silva and S. S. Balula, Fuel Processing
Technology, 2013, 116, 350-357.
31. P. Falcaro, R. Ricco, A. Yazdi, I. Imaz, S. Furukawa, D.
Maspoch, R. Ameloot, J. D. Evans and C. J. Doonan, Coord.
Chem. Rev., 2016, 307, 237-254.
48. J. Juan-Alcaniz, M. G. Goesten, E. V. Ramos-Fernandez, J.
32. C. M. Granadeiro, A. D. S. Barbosa, S. Ribeiro, I. C. M. S.
Santos, B. de Castro, L. Cunha-Silva and S. S. Balula,
Catalysis Science & Technology, 2014, 4, 1416-1425.
Gascon and F. Kapteijn, New J. Chem., 2012, 36, 977-987.
49. N. V. Maksimchuk, M. N. Timofeeva, M. S. Melgunov, A. N.
Shmakov, Y. A. Chesalov, D. N. Dybtsev, V. P. Fedin and O.
A. Kholdeeva, J. Catal., 2008, 257, 315-323.
33. C. M. Granadeiro, A. D. S. Barbosa, P. Silva, F. A. A. Paz, V.
K. Saini, J. Pires, B. de Castro, S. S. Balula and L. Cunha-
Silva, Appl. Catal. A - Gen., 2013, 453, 316-326.
50. C. L. Hill, J. Mol. Catal. A - Chem., 2007, 262, 2-6.
51. J. Juan-Alcaniz, J. Gascon and F. Kapteijn, J. Mater. Chem.,
2012, 22, 10102-10118.
34. C. M. Granadeiro, L. S. Nogueira, D. Juliao, F. Mirante, D.
Ananias, S. S. Balula and L. Cunha-Silva, Catal. Sci.
Technol., 2016, 6, 1515-1522.
52. D. M. Fernandes, A. D. S. Barbosa, J. Pires, S. S. Balula, L.
Cunha-Silva and C. Freire, ACS Appl. Mater. Interfaces,
2013, 5, 13382-13390.
35. X. L. Li, R. Van Zeeland, R. V. Maligal-Ganesh, Y. C. Pei, G.
Power, L. Stanley and W. Y. Huang, ACS Catal., 2016, 6,
6324-6328.
53. C. M. Granadeiro, M. Karmaoui, E. Correia, D. Juliao, V. S.
Amaral, N. J. O. Silva, L. Cunha-Silva and S. S. Balula, Rsc
Advances, 2015, 5, 4175-4183.
36. A. B. Redondo, F. L. Morel, M. Ranocchiari and J. A. van
Bokhoven, ACS Catal., 2015, 5, 7099-7103.
54. C. M. Granadeiro, S. O. Ribeiro, M. Karmaoui, R. Valenca, J.
C. Ribeiro, B. de Castro, L. Cunha-Silva and S. S. Balula,
Chem. Commun., 2015, 51, 13818-13821.
37. G. Férey, C. Mellot-Draznieks, C. Serre, F. Millange, J.
Dutour, S. Surblé and I. Margiolaki, Science, 2005, 309,
2040-2042.
55. C. M. Granadeiro, P. Silva, V. K. Saini, F. A. A. Paz, J. Pires,
L. Cunha-Silva and S. S. Balula, Catal. Today, 2013, 218–
219, 35-42.
38. A. V. Narsaiah, D. Sreenu and K. Nagaiah, Synth. Commun.,
2006, 36, 3183-3189.
39. N. Azizi, B. Mirmashhori and M. R. Saidi, Catal. Commun.,
2007, 8, 2198-2203.
56. S. Ribeiro, C. M. Granadeiro, P. Silva, F. A. Almeida Paz, F.
F. de Biani, L. Cunha-Silva and S. S. Balula, Catalysis
Science & Technology, 2013, 3, 2404-2414.
40. S. R. Roy, A. Nijamudheen, A. Pariyar, A. Ghosh, P. K.
Vardhanapu, P. K. Mandal, A. Datta and S. K. Mandal, ACS
Catal., 2014, 4, 4307-4319.
57. A. D. S. Barbosa, D. Julião, D. M. Fernandes, A. F. Peixoto,
C. Freire, B. de Castro, C. M. Granadeiro, S. S. Balula and L.
Cunha-Silva, Polyhedron, 2017, 127, 464 - 470.
41. N. Aramesh, B. Yadollahi and V. Mirkhani, Inorg. Chem.
Commun., 2013, 28, 37-40.
58. L. H. Wee, F. Bonino, C. Lamberti, S. Bordiga and J. A.
42. H. Danafar and B. Yadollahi, Catal. Commun., 2009, 10,
Martens, Green Chem., 2014, 16, 1351-1357.
842-847.
59. L. I. Kuznetsova, L. G. Detusheva, M. A. Fedotov and V. A.
43. S. Tobisch, Chem.-Eur. J., 2015, 21, 6765-6779.
Likholobov, J. Mol. Catal. A - Chem., 1996, 111, 81-90.
44. M. Distaso and E. Quaranta, J. Catal., 2008, 253, 278-288.
60. S. Bauer, C. Serre, T. Devic, P. Horcajada, J. Marrot, G.
Férey and N. Stock, Inorg. Chem., 2008, 47, 7568-7576.
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ARTICLE
61. P. Serra-Crespo, E. V. Ramos-Fernandez, J. Gascon and F.
View Article Online
DOI: 10.1039/C7CE00528H
Kapteijn, Chem. Mater., 2011, 23, 2565-2572.
62. Y. Lin, C. Kong and L. Chen, RSC Adv., 2012, 2, 6417-6419.
63. L. Bromberg, Y. Diao, H. Wu, S. A. Speakman and T. A.
Hatton, Chem. Mater., 2012, 24, 1664-1675.
64. Shivani, B. Pujala and A. K. Chakraborti, J. Org. Chem.,
2007, 72, 3713-3722.
65. F. Ulgheri, G. Orrù, M. Crisma and P. Spanu, Tetrahedron
Letters, 2004, 45, 1047-1050.
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