A new site-isolated acid-base bifunctional metal-organic framework for one-pot tandem reaction

Article abstract of DOI:10.1039/c4ra02683g

A highly porous and stable acid-base bifunctional metal-organic framework, MIL-101-NH₂-SO₃H, was prepared by direct solvothermal synthesis using two mixed (-NO₂, -SO₃H) terephthalate linkers followed by post-synthesis reduction to the NH₂ form, which showed excellent performance for a one-pot tandem deacetalization-nitroaldol reaction.

Full text of DOI:10.1039/c4ra02683g

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A new site-isolated acid-base bifunctional metal-
organic framework for one-pot tandem reaction
Cite this: DOI: 10.1039/x0xx00000x
a
b*
a*
Yu-Ri Lee, Young-Min Chung and Wha-Seung Ahn
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
A highly porous and stable acid-base bifunctional metal- solvothermal synthesis using two common organic linkers followed
by single step post-synthetic modification under mild reaction
organic framework, MIL-101-NH -SO H, was prepared by
2
3
conditions. This strategy is simple and can enable easier control over
the amount of Brønsted acid and base functions on its backbones.
Kitagawa and co-workers reported the preparation of MIL-101-
direct solvothermal synthesis using two mixed (-NO , -SO H)
2
3
terephthalate linkers followed by post-synthesis reduction to
the NH form, which showed excellent performance for a one-
2
SO H and MIL-101-NO2 using monosodium 2-sulfoterephthlate
3
pot tandem deacetalization-nitroaldol reaction.
(H BDC-SO Na) and 2-nitrobenzene-1,4-dicarboxylic acid (H BDC-
2
3
2
1
0,11
NO ), respectively, under similar synthesis conditions.
Because
2
The design of an efficient tandem catalyst closely mimicking H BDC-NO and H BDC-SO H are both moderately acidic, MIL-
2
2
2
3
nature’s multistep reaction cascades is one of the most fascinating 101 bearing both SO H and NO in a single structure was expected
3
2
but elusive challenges in the field of catalyst research. Although to form using a mixture of the two ligands. Subsequently, MIL-101-
several homogeneous catalysts combining chemically antagonistic NH -SO H bearing both Brønsted acid and base functions was
2
3
1
functions have been proposed, heterogeneous catalysts in principle prepared by reducing the NO groups in the product to NH by SnCl
2
2
2
appear to offer better opportunity to achieve high efficiency in a as described in Scheme 1. MIL-101, MIL-101-NH , and MIL-101-
2
tandem reaction by providing more effective site isolation of SO H were prepared for comparison using the methods reported
3
2
-4
10,12,13
different functions in a single system.
elsewhere.
Metal-organic frameworks (MOFs) or porous coordination
polymers (PCPs), in which metal ions or clusters are interconnected
by multidentate organic moieties through coordination bonding have
5
been studied extensively. In addition to their highly porous
structures, MOFs can be organic-functionalized easily either by
6
working directly or post-synthetically on the organic linkers. The
metal sites in the structure can also be functionalized by a post-
synthesis treatment because the removal of guest molecules
coordinated to the metal centres by vacuum or heating renders them
coordination-unsaturated sites (CUS) acting as a Lewis acid. The
high surface area and pore volume accompanied by the flexibility of
diverse organic functionalization in MOFs leads to the development
of useful multi-bifunctional MOF structures.
Recently, Li et al. reported the synthesis of bifunctional
chromium(III) terephthalate (MIL-101) having both Brønsted acid
and base sites via the three-step post-synthesis modification of MIL-
Scheme 1 Preparation of the site-isolated acid-base bifunctional
catalyst, MIL-101-NH -SO H.
7
-9
2
3
The X-ray powder diffraction patterns of MIL-101 and its -SO H,
3
-
NO and -NH mono-functionalized structures were all in good
2
2
†
10-13
agreements with those reported earlier (Fig. S1, ESI ).
Both
MIL-101-NO -SO H and MIL-101-NH -SO H also showed similar
2
3
2
3
14
XRD patterns to that of simulated MIL-101 suggesting that the
fundamental MIL-101 structure was kept intact during the post-
1
01: i) BOC(N-tert-butoxy carbonyl)-protected amino group grafting
synthesis reduction of NO2 groups by SnCl . Table 1 lists the
2
on the CUS, ii) direct sulfonation of the phenylene backbone with
8
specific surface area and pore volume of the materials and Figs. S2
chlorosulfonic acid, and iii) BOC de-protection. Although the
†
and S3, ESI shows the N adsorption–desorption isotherms and pore
2
catalyst exhibited useful catalytic properties in a one pot tandem
reaction, the catalyst preparation process was difficult and lengthy.
An acid treatment for the direct sulfonation of the organic linkers
may also give rise to undesirable deformation of the MOF structure.
This paper proposes an alternative synthetic route for the
introduction of site-isolated acid and base sites in MIL-101: direct
size distributions of the functionalized MIL-101 series. As expected,
both the surface area and pore volume decreased after the
incorporation of additional NH and/or SO H groups into the MIL-
2
3
13,15
1
01 structure.
Although dual functionalization resulted in more
significant reduction of the total pore volume, MIL-101-NH -SO H
2
3
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†
still remained highly porous, even in the presence of both NH and ESI . While high population of weak-medium acidity was detected
2
2
SO H groups in the phenylene backbones. These values (2320 m /g, in MIL-101, the number of strong acid sites increased further in both
.39 cm /g) were significantly higher than those reported by Li et al. MIL-101-SO H and MIL-101-NH -SO H, which clearly suggests
that the newly introduced SO H group in the MIL-101 structure
Elemental analysis (Table S1, ESI ) showed that the dual- enhanced the acid strength of the catalyst.
functionalized MIL-101-NH -SO H contained approximately 30%
3
3
1
3
2
3
2
3
8
using their 3-step synthesis approach (638 m /, 0.18 cm /g).
3
†
2
3
sulfonic acid and 50% primary amine groups compared to the Table 2 Acid amounts of MIL-101 and its functionalized structure
corresponding amounts in the mono-functionalized MIL-101-SO H based on NH -TPD analysis
3
3
and MIL-101-NH , respectively.
Acid amount (mmol/g)
2
Catalyst
a
b
c
Total
0.380
1.042
0.321
Weak-medium
Strong
0.118
0.663
0.132
0.291
Table 1 Specific surface area and pore volume of MIL-101and its
functionalized structures
MIL-101
MIL-101-SO H
MIL-101-NH2
0.262
0.378
0.189
0.412
3
Surface area
Pore volume
(cm /g)
Catalyst
2
3
(m /g)
MIL-101-NH -SO H
0.704
2
b
3
MIL-101
3442
2090
1870
2190
2320
2.06
1.69
1.48
1.37
1.39
a
c
3
73~723K; 373~593K; 593~723K.
MIL-101-SO H
3
MIL-101-NH2
The catalytic properties of MIL-101-NH -SO H were evaluated
2
3
MIL-101-NO -SO H
2
3
by examining the one-pot tandem conversion of benzaldehyde-
dimethylacetal (1) to trans-1-nitro-2-phenylethylene (3): the acid-
catalyzed deacetalization of compound 1 to benzaldehyde 2,
followed by the Henry condensation of compound 2 with
nitromethane to compound 3 in the presence of a base catalyst.
Initially, two different kinds of ion-exchange resin catalysts with
either pure Brønsted acid or base sites were tested (Table S2, ESI ).
Although the SO H-bound catalyst converted compound
MIL-101-NH -SO H
2
3
The FT-IR spectra of MIL-101-SO H (Fig. 1a), MIL-101-NO -
3
2
SO H (Fig. 1b), and MIL-101-NH -SO H (Fig. 1c) showed bands at
3
2
3
-
1
ca. 1188 and 1080 cm due to the stretching modes of SO H moiety
3
1
6
-1
with double-bond character (O=S=O). The band at ca. 1025 cm
†
was assigned to the stretching vibration of a S-O single bond. The IR
absorption band positions of the sulfonic acid in the MIL-101
derivatives were identical to the features of the free ligand,
1
3
exclusively to 2 (entry 1), the NH -bound catalyst did not promote
2
the same reaction (entry 2). On the other hand, the base catalyst
converted compound 2 completely to compound 3 (entry 3). These
results showed that the acid and base sites independently catalyze the
first and the second steps of the tandem reaction, respectively.
17
indicating that the sulfonate oxygen was not bound to Cr. In the
-
1
case of MIL-101-NO -SO H, the peak observed at 1542 cm was
2
3
18
assigned to the asymmetric –NO2 stretching vibration. The
characteristic peak of the NO2 groups in combination with the
stretching band for the SO H groups shows that both nitrogen
dioxide and sulfonic acid groups exist in the MIL-101 structure.
3
Table 3 Catalytic performance of the MIL-101 series for one-pot
a
tandem reaction
After reduction, the ν(NO2)asym peak disappeared and was replaced
O
NO2
OCH3
-
1
Acid Cat.
2 CH OH
Base Cat
+ CH NO
H O
by the stretching bands of amine group (ν=3486 and 3366 cm ),
-
3
2
3
OCH3
H
-
2
indicating the complete reduction of NO groups to NH . ν(NH )
2
2
2 asym.
1
2
3
and ν(NH2)sym. bands were also detected in MIL-101-NH . The FT-
2
Conv. of Selectivity (%)
IR spectrum of the MIL-101-NH -SO H clearly showed the
Entry Catalyst
2
3
1
(%)
2
3
existence of both SO H and NH groups in the MIL-101 structure.
3
2
1
2
3
MIL-101
52.4
100
93.8
95.6
3.6
6.2
MIL-101-SO H
4.4
3
MIL-101-NH2
71.2
96.4
MIL-101-SO H +
MIL-101-NH2
3
4
b
100
100
48.0
0.7
52.0
99.3
5
a
MIL-101-NH -SO H
2
3
Reaction conditions: catalyst (0.05 g), benzaldehydedimethyl-
acetal (1 mmol), o-xylene (0.1 g), nitromethane (5 ml), 323 K, 6h;
b
physical mixture (1:1 w/w), extended run (12h).
The conversion and product selectivity of the tandem reaction
were strongly dependent on the functionalization of MIL-101, as
shown in Table 3. Bare MIL-101 exhibited moderate activity and ca.
5
2% of 1 was converted. The high selectivity to 2 suggests that the
Lewis acidic CUS in MIL-101 catalyzed the first step of the tandem
reaction (entry 1). In the presence of MIL-101-SO H catalyst, the
3
conversion of 1 reached 100% with high selectivity to 2. The
enhanced catalytic activity must be due to the incorporation of new
Brønsted acid sites combined with the existing Lewis acid chromium
sites (entry 2). The minor formation of 3 suggests that weak basic
Fig. 1 IR spectra of MIL-101 and its functionalized forms; (a) MIL-
01-SO H, (b) MIL-101- NO -SO H, (c) MIL-101-NH -SO H, (d)
1
3
2
3
2
3
MIL-101-NH , and (e) MIL-101.
19
2
sites exist in MIL-101.
The catalytic activity of the MIL-101-NH was superior to that of
MIL-101, and the selectivity to 3 was dramatically improved to 96.4%
2
To measure the acid strength of the catalysts, NH -TPD analysis
was performed and the result was shown in Table 2 and Fig. S4,
3
2
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(
entry 3), suggesting that the Lewis acid metal centres and base sites
M. E. Davis, Angew. Chem. Int. Ed., 2006, 45, 6332; (c) N. T. S.
Phan, C. S. Gill, J. V. Nguyen, Z. J. Zhang and C. W. Jones, Angew.
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at the organic linkers catalyze the one-pot tandem reaction
consecutively. The concentration of 2 remained low because of the
fast conversion of 2 to 3, which also led to the high conversion of 1.
No reaction was reported in the presence of MIL-101-NH prepared
by the post-synthesis grafting of amine groups onto the Cr metal
3
4
5
S. Shylesh, A. Wagener, A. Seifert, S. Ernst and W. R. Thiel, Angew.
Chem. Int. Ed., 2010, 49, 184.
2
8
sites. It is likely that most of the Lewis acid sites were blocked by
N. R. Shiju, A. H. Alberts, S. Khalid, D. R. Brown and G.
Rothenberg, Angew. Chem. Int. Ed., 2011, 50, 9615.
the grafting of the base amine groups on the CUS, which would
prevent the acid-catalyzed reaction of 1 to 2. It is also worth noting
that the use of a physical mixture of acid- and base-functionalized
MIL-101 catalysts was not effective to enhance the selectivity of 3
(a) O. M. Yaghi, M. O’Keeffe, N. W. Ockwig, H. K. Chae, M.
Eddaoudi and J. Kim, Nature 2003, 423, 705; (b) M. P. Suh, H. J.
Park, T. K. Prasad and D. W. Lim, Chem. Rev., 2012, 112, 782; (c) J.
R. Li, J. Sculley and H. C. Zhou, Chem. Rev., 2012, 112, 869; (d) L.
E. Kreno, K. Leong, O. K. Farha, M. Allendorf, R. P. V. Duyne and
J. T. Hupp, Chem. Rev., 2012, 112, 1105; (e) J. Lee, O. K. Farha, J.
Roberts, K. A. Scheidt, S. T. Nguyen and J. T. Hupp, Chem. Soc.
Rev., 2009, 38, 1450; (f) M. K. Bhunia, S. K. Das, M. M. Seikh, K. V.
(
entry 4). In the case of MIL-101-NH -SO H, the complete
2 3
conversion of 1 with very high selectivity to 3 (>99%) was achieved
entry 5). The excellent performance of the MIL-101-NH -SO H in
(
2
3
the reaction clearly shows that the introduction of both Brønsted acid
and base sites on the organic linkers without any reduction in CUS at
the metal centres is a highly efficient design for the site isolation of
antagonistic functions in a single system. The overall reaction
mechanism could be proposed, as shown in Scheme S1, ESI . As
summarized in Table S3, ESI , MIL-101-NH -SO H showed high
catalytic activity than the bifunctional MIL-101 prepared by the
three-step post-synthesis modification, or previously reported
bifunctional mesoporous silica, PMO-NH -SO H, HPA-NH -SBA-
1
†
Domasevitch and A. Bhaumik, Polyhedron, 30, 2218.
†
6
(a) T. Ahnfeldt, D. Gunzelmann, J. Wack, J. Senker and N. Stock,
CrystEngComm, 2012, 14, 4126; (b) M. Kim, J. F. Cahill, H. Fei, K.
A. Prather and S. M. Cohen, J. Am. Chem. Soc., 2012, 134, 18082; (c)
S. M. Cohen, Chem. Rev., 2012, 112, 970.
2
3
8
3
2
3
2
4
20
5, and AB-MCM-41.
The stability of the catalyst, MIL-101-NH -SO H, was tested by
7
8
9
F. Vermoortele, R. Ameloot, A. Vimont, C. Serre and D. De Vos,
Chem. Commun., 2011, 47, 1521.
2
3
performing repeated reaction cycles under the reaction conditions.
At the end of each reaction cycle, the catalyst was recovered by
filtration, and then washed, dried and reused. As shown in Fig. S5,
B. Li, Y. Zhang, D. Ma, L. Li, G. Li, G. Li, Z. Shi and S. Feng, Chem.
Commun., 2012, 48, 6151.
†
ESI , the conversion and selectivity remained almost identical after 5
(a) R. Srirambalaji, S. Hong, R. Natarajan, M. Yoon, R. Hota, Y.
Kim, Y. H. Ko and K. Kim, Chem. Commun., 2012, 48, 11650; (b) A.
Dhakshinamoorthy, M. Alvaro and H. Garcia, Adv. Synth. Catal.,
recycles. The XRD pattern and FT-IR spectrum of the solid catalyst
after reuse were also indistinguishable from that of the fresh catalyst.
In summary, this paper reported the synthesis of a simple site-
isolated acid-base bifunctional metal-organic framework MIL-101-
NH -SO H containing sulfonic acid and amine groups without any
2
010, 352, 171; (c) E. P. Mayoral and J. Cejka, ChemCatChem, 2011,
3, 157.
2
3
1
0 G. Akiyama, R. Matsuda, H. Sato, M. Takata and S. Kitagawa, Adv.
Mater., 2011, 23, 3294.
reduction of the unsaturated Lewis acid sites at the metal centres.
XRD, BET surface area measurements, FT-IR spectroscopy, and
elemental analysis confirmed that the –SO H and –NH groups had 11 G. Akiyama, R. Matsuda, H. Sato, A. Hori, M. Takata and S.
3
2
been incorporated successfully without deteriorating the porous
nature of the parent MIL-101 structure significantly. MIL-101-NH2-
Kitagawa, Micropor. Mesopor. Mater., 2012, 157, 89.
2 J. Kim, Y. R. Lee and W.-S. Ahn, Chem. Commun., 2013, 49, 7647.
3 D. Jiang, L. L. Keenan, A. D. Burrows and K. J. Edler, Chem.
Commun., 2012, 48, 12053.
1
1
SO H exhibited excellent catalytic performance for the one-pot
3
tandem reaction of benzaldehydedimethylacetal to trans-1-nitro-2-
phenylethylene under mild reaction conditions.
This research was supported by Basic Science Research Program 14 G. Férey, C. M. Drazniekes, C. Serre, F. Millange, J. Dutour, S.
through the National Research Foundation of Korea (NRF) funded
by the Ministry of Education, Science and Technology (NRF-
Surblé and I. Margiolaki, Science 2005, 309, 2040.
1
5 M. G. Goesten, J. J. Alcaniz, E. V. R. Fernandez, K. B. S. S. Gupta, E.
2
013R1A1A4A01006480; 2013005862)
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77.
6 D. S. Warren and A. J. McQuillan, J. Phys. Chem. B, 2008, 112
0535.
,
1
Notes and references
1
1
1
1
,
a
Department of Chemistry and Chemical Engineering, Inha University,
1
Incheon 402-751, Korea.
7 M. L. Foo, S. Horike, T. Fukushima, Y. Hijikata, Y. Kubota, M.
E-mail: whasahn@inha.ac.kr; Tel: +82-32-860-7466
Takataf and S. Kitagawa, Dalton Trans., 2012, 41, 13791.
b
Department of Nano & Chemical Engineering, Kunsan National
8 A. Modrow, D. Zargarani, R. Herges and N. Stock, Dalton Trans.
012, 41, 8690.
9 Y. K. Hwang, D. Y. Hong, J. S. Chang, S. H. Jhung, Y. K. Seo, J.
,
University, 558 Daehak-ro, Kunsan, Jeollabuk-Do, 573-701, Korea.
E-mail: ymchung@kunsan.ac.kr; Tel: +82-63-469-4774
2
†
Electronic Supplementary Information (ESI) available: Experimental
Kim, A. Vimont, M. Daturi, C. Serre and G. Férey, Angew. Chem. Int.
Ed., 2008, 47, 4144.
details and additional data. See DOI: 10.1039/c000000x/
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