Application of an amino-functionalised metal-organic framework: An approach to a one-pot acid-base reaction

Article abstract of DOI:10.1039/c3ra44701d

The amino-functionalised metal-organic framework, MIL-101(Al)-NH ₂, has been synthesized by using a solvothermal method and employed as a bifunctional acid-base catalyst for a one-pot, sequential deacetalization-Knoevenagel condensation reaction. In preliminary studies, the abilities of MIL-101(Al)-NH₂ to serve as an acid and base catalyst were explored separately by two typical acid- and base-catalysed reaction, that is, deacetalization of benzaldehyde dimethylacetal and Knoevenagel condensation of benzaldehyde with malononitrile. MIL-101(Al)-NH₂ was found to catalyse each of these reactions with high efficiency. MIL-101(Al)-NH ₂ was then employed as a catalyst for the one-pot sequential deacetalization-Knoevenagel condensation reaction between benzaldehyde dimethylacetal and malononitrile. Benzylidenemalononitrile as the final product was successfully generated with a high yield via benzaldehyde over MIL-101(Al)-NH₂. In addition, the catalytic ability of MIL-101(Al)-NH₂ was demonstrated to be superior to those of conventional heterogeneous, homogeneous as well as other functionalised metal-organic framework catalysts. Finally, the results show that MIL-101(Al)-NH₂ can be reused as a catalyst for this process without significant loss of its activity. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ra44701d

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Application of an amino-functionalised metal-organic framework: An
approach to a one-pot acid-base reaction
Takashi Toyao, Mika Fujiwaki, Yu Horiuchi* and Masaya Matsuoka*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
The aminoꢀfunctionalised metalꢀorganic framework, MILꢀ101(Al)ꢀNH2, has been synthesized by using a
solvothermal method and employed as a bifunctional acidꢀbase catalyst for a oneꢀpot, sequential
deacetalizationꢀKnoevenagel condensation reaction. In preliminary studies, the abilities of MILꢀ101(Al)ꢀ
NH2 to serve as an acid and base catalyst were explored separately by two typical acidꢀ and baseꢀ
10 catalysed reaction, that is, deacetalization of benzaldehyde dimethylacetal and Knoevenagel condensation
of benzaldehyde with malononitrile. MILꢀ101(Al)ꢀNH2 was found to catalyse each of these reactions with
a high efficiency. MILꢀ101(Al)ꢀNH2 was then employed as a catalyst for the oneꢀpot sequential
deacetalizationꢀKnoevenagel condensation reaction between benzaldehyde dimethylacetal and
malononitrile. Benzylidenemalononitrile as the final product was successfully generated with a high yield
15 via benzaldehyde over MILꢀ101(Al)ꢀNH2. In addition, the catalytic ability of MILꢀ101(Al)ꢀNH2 was
demonstrated to be superior to those of conventional heterogeneous, homogeneous as well as other
functionalised metalꢀorganic framework catalysts. Finally, the results show that MILꢀ101(Al)ꢀNH2 can be
reused as a catalyst for this process without significant loss of its activity.
MOFs have been widely investigated as solid catalysts or catalyst
20 Introduction
supports for several organic transformations, such as
epoxidations,5 cycloadditions of CO2 with epoxides,6 aldol
condensations,7 Knoevenagel condensations8 and PaalꢀKnorr
45 reactions.9 In addition, because their topology and surface
functionalities can be readily tuned by modifying or varying the
core metalꢀoxo clusters and bridging organic linkers, MOFs have
emerged as interesting platforms for engineering molecular solids
to create multifunctional catalysts. Several multifunctional MOF
50 based catalytic systems have been devised10 so that reactions are
promoted by functionality in organic linkers or by coordinatively
unsaturated metal sites of MOFs. Moreover, catalytic sites in
these substances can be incorporated by using postsynthetic
modification of organic struts.
Recently, synthetic organic chemists have given great attention to
the development of oneꢀpot, sequential organic reactions owing
to their comparably higher efficiencies, increased cost
effectiveness and reduced formation of waste materials.1 An
25 important goal in this area, is the development of new catalysts
having spatially isolated, multiple active sites so that they can
promote multiꢀstep reaction cascades. Among the various systems
designed to possess this capability, many of these are
homogeneous catalysts and, as a result, they generally suffer from
30 product contamination and limited recyclability.2 Furthermore,
catalytic acidꢀbase oneꢀpot reaction systems are hardly developed
in the homogeneous phase because the acid and base sites are
easily deactivated by each other. Therefore, the development of
multifunctional heterogeneous catalysts that promote oneꢀpot
35 reactions is currently receiving much attention.3
55
The coordinatively unsaturated metal sites within MOFs,
which can serve as catalytic centres, have been actively
investigated in recent years.11 These studies have shown that the
sites are capable of acting as Lewis acid catalysts for various
organic reactions. Because structural defects are thought to be
Metalꢀorganic frameworks (MOFs), also called porous
coordination polymers (PCPs), have gained recent interest
because of their several attractive properties, including high
specific surface areas, wellꢀordered porous structures and
40 structural designability.4 Because of these advantageous features,
60 responsible for catalysis by these MOFs, efforts have been made
to enhance activities by deliberately introducing defects.12
Although many reports exist describing the Lewis acidity of
MOFs, the Brønsted acidity of these substances has not been
studied greatly. However, very recently, Ameloot et al. reported
65 that Brønsted acid sites are present in MOFs and that they are
responsible for catalysis of the oligomerization of furfuryl
alcohol.13 The Brønsted acidities of MOFs are attributed to the
Department of Applied Chemistry, Graduate School of Engineering,
Osaka Prefecture University, 1-1, Gakuen-cho, Naka-ku, Sakai, Osaka
599-8531, Japan
E-mail:horiuchi@chem.osakafu-u.ac.jp; matsumac@chem.osakafu-u.ac.
jp; Fax: +81-72-254-9910; Tel: +81-72-254-9288
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presence of carboxylic acid moieties (–COOH groups) in the 55 Standard θ–2θ Xꢀray diffraction (XRD) data were recorded on a
organic linker existing on the outer surface of the particles and in
structural defects within the framework. Consequently, new
reactions and multiꢀstep processes that can be catalysed by
Brønsted acid sites present in MOFs would have great utility in
organic synthesis.
In the study described below, we examined the acid and base
properties of the aminoꢀfunctionalised MOF, MILꢀ101(Al)ꢀNH2,
in the context of catalysis of deacetalization and Knoevenagel
Shimadzu Xꢀray diffractmeter XRDꢀ6100 using Cu Kα radiation
(λ = 1.5406 Å). Nitrogen adsorptionꢀdesorption isotherms were
collected by using a BELꢀSORP mini (BEL Japan, Inc.) at 77 K.
FTꢀIR spectra were recorded in transmittance mode by a FTꢀIR
60 spectrophotometer equipped with a DTGS detector (JASCO
FT/IR 660Plus, resolution 4 cmꢀ1). Selfꢀsupporting pellets of the
samples were loaded in a specially constructed IR cell, which was
equipped with CaF2 windows. Thermogravimetric (TG) analysis
was carried out using a thermal analyser (Rigaku Termoplus
5
10 condensation reactions. It is wellꢀknown that deacetalization
reactions are catalysed by Brønsted acidic sites14 and 65 8120), with a heating rate of 10 K minꢀ1 in air. Scanning electron
Knoevenagel condensation reactions are catalysed by Brønsted
and Lewis base sites.15 The results show that the respective
reactions are successfully promoted by MILꢀ101(Al)ꢀNH2. The
15 possibility that the aminoꢀfunctionalised MOF can serve as a
bifunctional acidꢀbase catalyst has been demonstrated using a
oneꢀpot reaction producing benzylidenemalononitrile via
sequential deacetalization and Knoevenagel condensation
(Scheme 1). Finally, observations made in this effort show that
20 activity of MILꢀ101(Al)ꢀNH2 as acidꢀbase bifunctional catalysts
is superior to those of conventional heterogeneous, homogeneous
as well as other MOF catalysts.
microscope (SEM) images were obtained with a Hitachi Sꢀ4500.
Catalytic reactions
Deacetalization reaction: The reactions were carried out in
liquid phase in a 35 ml glass reactor. A solution of benzaldehyde
70 dimethylacetal (1 mmol) and 1, 4ꢀdioxane (4 ml) was stirred at
363 K with 100 mg of the catalysts in powder form. The
progression of the reaction was monitored by using gas
chromatography (Shimadzu GCꢀ14B with a flame ionization
detector) equipped with an InertCap ®1 capillary column.
75
Knoevenagel condensation reaction: The reactions were carried
out in liquid phase in a 35 ml glass reactor. A solution of
benzaldehyde (1 mmol), malononitrile (5 mmol) and 1, 4ꢀdioxane
(4 ml) was stirred at 363 K with 100 mg of the catalysts in
80 powder form. The progression of the reaction was monitored by
using gas chromatography (see above).
25
One-pot deacetalization-Knoevenagel condensation reaction:
The reactions were carried out in liquid phase in a 35 ml glass
85 reactor. A solution of benzaldehyde dimethylacetal (1 mmol),
malononitrile (5 mmol) and 1, 4ꢀdioxane (4 ml) were stirred at
363 K with 100 mg of the catalysts in powder form. The
progression of the reaction was monitored by using gas
chromatography (see above).
30 Scheme 1. Oneꢀpot deacetalizationꢀKnoevenagel condensation reaction.
Experimental
Materials
2ꢀAminoꢀbenzenedicarboxylic
acid
(H2BDCꢀNH2),
1,4ꢀ
90
Reusability of the catalyst was studied as follows. After the
first run, the catalyst was washed three times with 1, 4ꢀdioxane,
dried at 313 K in air and reused for the next run. The above
procedure was repeated three times.
35 benzenedicarboxylic acid (H2BDC), N’Nꢀdimethylformamide
(DMF), ZrCl4, Cr(NO3)3ꢁ9H2O, NaOH, HCl, methanol, acetone,
triethylamine and 1, 4ꢀdioxane were purchased from Nacalai
Tesque Inc. 1,3,5ꢀBenzenetricarboxylic acid (H2BTC),
malononitrile, benzaldehyde and benzaldehyde dimethylacetal
40 were purchased from Tokyo Chemical Industry Co., Ltd.
AlCl3ꢁ6H2O, Al(NO3)3ꢁ9H2O, Cu(NO3)3ꢁ3H2O and MgO were
purchased from Kishida Chemical Co., Ltd. Al2O3 was purchased
from Evonik. HY zeolite (SiO2 / Al2O3 = 30) was purchased from
ZEOLYST. All materials were used as received without
45 purification.
Results and discussion
95 The aminoꢀfunctionalised MOF catalyst, MILꢀ101(Al)ꢀNH2, was
prepared from AlCl3ꢁ6H2O and H2BDCꢀNH2 by using the
previously described solvothermal method.16 XRD and N2
adsorptionꢀdesorption measurements were performed to confirm
the formation of the MOF structure. Figure 1 shows an XRD
100 pattern of MILꢀ101(Al)ꢀNH2. Although the diffraction pattern
does not perfectly match the diffraction pattern previously
reported, the pattern can be attributable to a MILꢀ101 type
structure.17 In addition, because no diffraction patterns
corresponding to the bulk Al2O3 are observed, it is confirmed that
105 crystalline Al2O3 are not formed in MILꢀ101(Al)ꢀNH2. Figure 2
represents N2 adsorptionꢀdesorption isotherm of MILꢀ101(Al)ꢀ
NH2. This isotherm shows the wellꢀknown characteristic steps of
the MILꢀ101 type structure. The changes present in isotherm
correspond to filling only the superoctahedra at low relative
110 pressures (P/P0 < 0.05) and, as the pressure increases, medium
Catalysts preparation
MILꢀ101(Al)ꢀNH2 was synthesized using the previouslyꢀreported
method.16 The mixture of AlCl3ꢁ6H2O (0.51 g), H2BDCꢀNH2
(0.56 g) and DMF (40 ml) was subjected to solvothermal reaction
50 conditions in a Teflonꢀlined stainless steel autoclave for 40 h at
403 K under autogenous pressure. The generated precipitate was
separated by filtration, washed repeatedly with acetone and dried
under vacuum for 3 h at room temperature.
General methods
2
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sites.14 On the other hand, Knoevenagel condensation reactions
are catalysed over Brønsted and Lewis base sites.15 Therefore,
60 this study was conducted to investigate the activities of the
respective Brønsted acid and base sites in MILꢀ101(Al)ꢀNH2. For
comparison purposes, the activities of MILꢀ101(Al)ꢀNH2 in these
reactions were compared to those of HY zeolite (SiO2/Al2O3 =
30) and MgO, which are conventional acid and base catalysts,
65 respectively. As shown in Fig. 3, inspection of the time courses
for the production of benzaldehyde in deacetalization reactions of
benzaldehyde dimethylacetal shows that MILꢀ101(Al)ꢀNH2 and
HY zeolite serve as efficient catalysts for this process while
benzaldehyde is not generated when MgO is used. The results
70 suggest that carboxylic acid groups (–COOH) present on outer
surfaces or at defect sites in MILꢀ101(Al)ꢀNH2 act as effective
Brønsted acids.
5
10
15
Fig. 1. XRD pattern of MILꢀ101(Al)ꢀNH2.
Subsequently, Knoevenagel condensation reactions of
benzaldehyde with malononitrile were carried out using MILꢀ
75 101(Al)ꢀNH2, HY zeolite and MgO. The time courses displayed
in Fig. 4 demonstrate that MILꢀ101(Al)ꢀNH2 is an effective
catalyst of this reaction, whereas MgO has a lower activity and
the reaction does not proceed when HY zeolite is employed.
These findings suggest that the –NH2 groups in MILꢀ101(Al)ꢀ
80 NH2 act as base sites to promote the Knoevenagel condensation
reaction. Furthermore, it is noteworthy that the reaction rate for
MILꢀ101(Al)ꢀNH2 is much higher than that for MgO. This result
20
25
30
85
Fig. 2. N2 adsorptionꢀdesorption isotherm of MILꢀ101(Al)ꢀNH2.
90
(P/P0 = 0.15) and large cavities of the MOF become filled. By
using the BET (BrunauerꢀEmmettꢀTeller) method to treat the N2
adsorption data, the specific surface area of MILꢀ101(Al)ꢀNH2
35 was calculated to be 800 m2gꢀ1. This value is lower than the one
previously reported,16 indicating that some structural defects exist
in the sample of MILꢀ101(Al)ꢀNH2 prepared in this study.
Despite leading to a low specific surface area of this material, the
structural defects can be key features required to develop
40 catalysts which exhibit better performances, as suggested by
Corma et al.18
95
Fig. 3. Time course of the deacetalization reaction over MILꢀ101(Al)ꢀ
NH2 (●), HY zeolite (■) and MgO (◆).
In order to further confirm the structural features, FTꢀIR and
TG analyses were performed (see Figs. S1 and S2 in the
Supporting Information). The FTꢀIR spectrum of MILꢀ101(Al)ꢀ
45 NH2 shows bands corresponding to the symmetric and
asymmetric stretching of primary amines (3408 and 3521 cmꢀ1),
indicating that the –NH2 groups are free without coordination. As
shown in Fig. S2, MILꢀ101(Al)ꢀNH2 releases water followed by
desorption of some DMF and decomposes at temperatures above
50 650 K. This result indicates high thermal stability of MILꢀ
101(Al)ꢀNH2 prepared in this study.
Prior to exploring applications to oneꢀpot reactions, separate
deacetalization of benzaldehyde dimethylacetal and Knoevenagel
condensation of benzaldehyde with malononitrile were performed
55 over MILꢀ101(Al)ꢀNH2 as test reactions. Both reactions are
widely used in organic chemistry.19 In general, deacetalization
100
105
110
Fig. 4. Time course of the Knoevenagel condensation reaction over MILꢀ
reactions are wellꢀknown to be catalysed over Brønsted acidic 115 101(Al)ꢀNH2 (
●
), HY zeolite (■) and MgO (◆).
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is attributable to the presence of –NH2 groups in MILꢀ101(Al)ꢀ
the oneꢀpot benzylidenemalononitrile forming process.
NH2. It is wellꢀknown that the Knoevenagel condensation 60 Observation made in additional studies show that Al2O3 does not
reaction undergoes through the formation of imine intermediate
on the catalysts containing organic amines, followed by the
addition of active methylene group.20 Therefore, it can be
considered that the reaction is promoted more efficiently over
promote this reaction, suggesting that possible impurities in MILꢀ
101(Al)ꢀNH2 comprised of aluminum oxide are not responsible
for the observed catalytic activity (entry 4). Also, the oneꢀpot
reaction takes place when a mixture of HY zeolite and MgO is
5
MILꢀ101(Al)ꢀNH2 with –NH2 groups than over MgO. As 65 utilized (entry 5), but the reaction rate is much lower than that of
explored above, the results emanating from the above effort show
that MILꢀ101(Al)ꢀNH2 possesses both Brønsted acid and base
10 sites that serve as catalysts for respective deacetalization and
Knoevenagel condensation reactions.
the MILꢀ101(Al)ꢀNH2 catalysed process. These facts suggest that
MILꢀ101(Al)ꢀNH2 behaves as an efficient bifunctional acidꢀbase
catalyst compared to conventional solid catalysts.
In addition, homogeneous catalysts such as HCl and
The potential use of MILꢀ101(Al)ꢀNH2 as a bifunctional acidꢀ 70 triethylamine were used for the oneꢀpot reaction. The presence of
base catalyst for oneꢀpot reactions was investigated next. For this
purpose, MILꢀ101(Al)ꢀNH2 was employed to promote the
15 benzylidenemalononitrile (3a) forming reaction between
benzaldehyde dimethylacetal and malononitrile that takes place
the acid catalyst (HCl) leads to quantitative deprotonation of
dimethylacetal to benzaldehyde but does not lead to the formation
of 3a (entry 6). On the other hand, the starting substrate remains
unchanged when using triethylamine as a catalyst even after 3 h
through sequential deacetalization and Knoevenagel condensation 75 (entry 7). Furthermore, the reaction hardly occurs even the first
processes. Inspection of the time course of the process displayed
in Fig. 5 shows that benzylidenemalononitrile is efficiently
20 generated from benzaldehyde dimethylacetal (1a) via a pathway
involving initial formation of benzaldehyde (2a), and that the
yield of 3a reaches 94% after a 3 h reaction time. It is also shown
that the reaction does not take place in the absence of a catalyst
(entry 17 in Table 1). These observations clearly demonstrate that
25 MILꢀ101(Al)ꢀNH2 serves as an effective bifunctional acidꢀbase
catalyst for the sequential deacetalization and Knoevenagel
condensation reaction.
step of the reaction when the mixture of HCl and triethylamine is
employed as the catalyst (entry 8). In the homogeneous systems,
acid and base catalysts are easily neutralised, resulting in the
deactivation of the catalysts.
Various MOF catalysts such as MILꢀ53(Al)ꢀNH2, MILꢀ53(Al),
MILꢀ101(Cr)ꢀNH2, MILꢀ101(Cr), ZrꢀMOFꢀNH2, ZrꢀMOF, Cuꢀ
MOF and CaꢀMOF21 were also employed for the oneꢀpot reaction
(entry 9–16).22 Among the catalysts explored in this study, MILꢀ
101(Al)ꢀNH2 was found to exhibit the highest catalytic activity
80
85
90
Table 1. Oneꢀpot deacetalizationꢀKnoevenagel condensation
reaction using various catalystsa.
30
35
Entry Catalyst
Conv. (%) Yield (%)
2a
3a
1
2
3
MILꢀ101(Al)ꢀNH2
HY zeolite
MgO
100
88
7
6
79
6
94
9
1
40
4
5
6
7
Al2O3
14
67
100
3
1
3
20
5
2
8
HY zeolite + MgOb
HClc
39
95
1
Fig. 5. Time course of the oneꢀpot deacetalizationꢀKnoevenagel
condensation
reaction
over
MILꢀ101(Al)ꢀNH2;
benzaldehyde
).
dimethylacetal (◆), benzaldehyde (■), benzylidenemalononitrile (
●
Triethylaminec
8
HCl + Triethylamined 15
5
45
9
MILꢀ53(Al)ꢀNH2
MILꢀ53(Al)
MILꢀ101(Cr)ꢀNH2
MILꢀ101(Cr)
ZrꢀMOFꢀNH2
ZrꢀMOF
CuꢀMOF
CaꢀMOF
No catalyst
100
81
9
2
19
75
57
69
34
0
18
5
For comparison purposes, conventional solid and
homogeneous as well as other MOF catalysts were applied for
this oneꢀpot acidꢀbase reaction with the results summarized in
Table 1. When HY zeolite is used as the catalyst (entry 2), the
50 second step, involving Knoevenagel condensation of
benzaldehyde with malononitrile, does not take place efficiently.
As a result, only benzaldehyde is produced because HY zeolite
only serves as an acid catalyst for the deacetalization step. In
addition, when MgO is employed (entry 3), the reaction between
55 the acetal and malononitrile does not occur because the first step
in the pathway does not take place. These results clearly
demonstrate that the existence of both acid and base sites, like
those found in MILꢀ101(Al)ꢀNH2, are necessary for promotion of
10
11
12
13
14
15
16
17
14
86
60
99
85
79
38
2
84
38
23
26
7
2
2
a
Reaction conditions: Benzaldehyde dimethylacetal (1 mmol),
95 malononitrile (5 mmol), 1, 4ꢀdioxane (4 mL), catalyst (100 mg), 363 K, 3
h. b The mixture of HY zeolite (50 mg) and MgO (50 mg) was employed
as the catalyst. c 0.1 mmol of the catalyst was used. d The mixture of HCl
(0.1 mmol) and triethylamine (0.1 mmol) was employed as the catalyst.
4
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for the oneꢀpot reaction. This result is attributable to the presence
catalysts.
of –NH2 groups and its large pore size (window size = 1.2 ×
1.6Å).16 Specifically, the –NH2 groups promote the second
condensation step of the reaction, and the large pore sizes enable
facile diffusion of the substrates and products. Although MILꢀ
101(Cr)ꢀNH2 has both –NH2 groups and the same pore size as
60
Finally, recycling experiments were carried out for the
evaluation of the reusability of MILꢀ101(Al)ꢀNH2. The catalyst
after the reaction for 3 h was washed with 1, 4ꢀdioxane, dried at
313 K and then reused for the next run. As shown in Fig. 6, MILꢀ
101(Al)ꢀNH2 can be reused at least three times with the retention
5
MILꢀ101(Al)ꢀNH2, its catalytic activity is lower than that of MILꢀ 65 of high catalytic activity and selectivity.
101(Al)ꢀNH2 (entry 11). To clarify the origin of the difference in
the activity, SEM observations were conducted, as displayed in
10 Fig. S3. The large particle size ranging from 200 nm to 400 nm is
observed for MILꢀ101(Al)ꢀNH2 compared to the particle size of
MILꢀ101(Cr)ꢀNH2 (50–100 nm). Since the Brønsted acidities are
attributed to –COOH groups in the organic linker existing on the
outer surface of the particles and in structural defects within the
15 framework, the small particles are expected to be favorable for
the reaction. On the other hand, however, these SEM images also
reveal that MILꢀ101(Al)ꢀNH2 has lower crystallinity than MILꢀ
101(Cr)ꢀNH2, suggesting that larger amounts of structural defects
exist in MILꢀ101(Al)ꢀNH2. Therefore, the results of the oneꢀpot
20 reaction can be rationalized by the amount of structural defects.
As a consequence, MILꢀ101(Al)ꢀNH2 exhibits better performance
in the oneꢀpot reaction. Interestingly, MOF catalysts possessing –
NH2 groups not only promote the Knoevenagel condensation
reaction but also catalyse the first deacetalization step more
25 efficiently than those without primary amine moieties (entry 9, 11,
13). This outcome is associated with the cooperative effect of
acid and base groups that lead to acceleration of the aldehyde
forming process. In addition, it should be noted that the
condensation step of the reaction is catalysed by some MOF
30 catalysts that do not contain –NH2 groups (entry 12, 14). In
general, Knoevenagel condensation reactions are promoted by not
only base catalysts but also Lewis acid catalysts.23 As mentioned
in the introduction, it has been widely studied that coordinatively
unsaturated metal sites of MOFs can act as Lewis acid catalysts.
35 These facts suggest that coordinatively unsaturated metal sites of
MOFs catalyse the second step of the reaction, resulting in the
Conclusions
The results of the investigation described above show that the
aminoꢀfunctionalised MOF, MILꢀ101(Al)ꢀNH2, serves as
a
70 bifunctional acidꢀbase catalyst. The initial studies reveal that
MILꢀ101(Al)ꢀNH2 promotes both the deacetalization of
benzaldehyde dimethylacetal and Knoevenagel condensation of
benzaldehyde with malononitrile. Moreover, owing to the
presence of Brønsted acid and base sites, MILꢀ101(Al)ꢀNH2
75 promotes the oneꢀpot reaction of benzaldehyde dimethylacetal
and malononitrile to produce benzylidenemalononitrile. In
addition, the results show that MILꢀ101(Al)ꢀNH2 exhibits higher
catalytic activities than conventional heterogeneous acid and base
as well as various MOF catalysts for the oneꢀpot acidꢀbase
80 reaction. Lastly, MILꢀ101(Al)ꢀNH2 can be recycled at least three
times without significant loss of its catalytic activity. The
observations made in this effort suggest new possibilities to
design catalysts for oneꢀpot reactions utilizing MOF materials.
Ackowledgements
85 The present work is supported by a GrantꢀinꢀAid for Scientific
Research (KAKENHI) from Ministry of Education, Culture,
Sports, Science and Technology of Japan (No. 21550192). The
authors thank Prof. M. Tatsumisago, Dr. A. Hayashi and Mr. T.
Matsuyama for TG analysis. T. T. thanks the JSPS Research
90 Fellowships for Young Scientists.
Notes and references
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Fig. 6. Recycling tests for the oneꢀpot deacetalizationꢀKnoevenagel
condensation reaction over MILꢀ101(Al)ꢀNH2. Reaction conditions:
Benzaldehyde dimethylacetal (1 mmol), malononitrile (5 mmol), 1, 4ꢀ
dioxane (4 mL), catalyst (100 mg), 363 K, 3 h.
55 formation of 3a as the final product. From these comparison
studies, it was revealed that the activity of MILꢀ101(Al)ꢀNH2 as
an acidꢀbase bifunctional catalyst is superior to those of
conventional heterogeneous, homogeneous as well as other MOF
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6
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