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Table 1 Diels–Alder reactions of 9-hydroxyanthracene and N-substituted maleimides
Yield (%)
Entry
R
Temp (1C)
With MOF
Without
1
2
40
50
86
77
22
10
Fig. 4 Proposed mechanism for the catalytic Diels–Alder reaction.
encapsulation and reorganization of the reactants, respectively, prior
to product formation. Such pre-organization in confined space
decreases the activation energy of the reaction by stabilizing the
transition state through p–p interaction (Fig. 4).
3
4
50
40
65
80
8
In conclusion, a highly porous electron rich MOF-1 has been
synthesized using a p-electron rich tetracarboxylic acid. The high
surface area and electron rich nature of the pore ensured high
affinity towards aromatic reactants through p–p interaction. In
particular, it shows effective catalytic Diels–Alder reactions under
mild reaction conditions within porous nano-channels. Moreover,
less reactive poly-aromatic maleimides undergo excellent conversion
in the presence of MOF-1a even using low boiling solvents. Aliphatic
reactants have been shown to have lower reactivity than aromatic
reactants due to their weaker interaction with the MOF. Finally, the
heterogeneous nature and high thermal stability under the reaction
conditions were successfully utilized for many catalytic cycles.
Authors are grateful to the Department of Science and Technology
(DST), India, for financial support and B.G. thanks the Indian Institute
of Science for the Bristol Mayer Squibb Fellowship and research grant.
15
5
6
7
40
40
40
82
85
75
17
15
10
8
9
40
45
80
70
17
10
Notes and references
10
11
45
50
60
65
13
7
1 (a) K. Kim, Nat. Chem., 2009, 1, 603; (b) G. Ferey, Chem. Soc. Rev., 2008,
37, 191; (c) O. M. Yaghi, Nat. Mater., 2007, 6, 92; (d) N. L. Toh,
N. Nagarithinum and J. J. Vittal, Angew. Chem., Int. Ed., 2005, 44, 2237;
(e) L. Pan, H. Liu, X. Lei, X. Huang, D. H. Olson, N. Turro and J. Li, Angew.
Chem., Int. Ed., 2003, 42, 542; ( f ) L. J. Murray, M. Dinca and J. R. Long,
Chem. Soc. Rev., 2009, 38, 1294; (g) J. Y. Lee, O. K. Farha, J. Roberts,
K. A. Scheidt, S. T. Nguyen and J. T. Hupp, Chem. Soc. Rev., 2009, 38, 1450;
(h) A. Lan, K. Li, H. Wu, D. H. Olson, T. J. Emge, W. Ki, M. Hong and J. Li,
Angew. Chem., Int. Ed., 2009, 48, 2334; (i) B. Gole, A. K. Barand and
P. S. Mukherjee, Chem. Commun., 2011, 47, 12137; ( j) S. Leininger,
B. Olenyuk and P. J. Stang, Chem. Rev., 2000, 100, 853; (k) T. K. Maji,
G. Mostafa, R. Matsuda and S. Kitagawa, J. Am. Chem. Soc., 2005,
127, 17152; (l) X. Xu, M. Nieuwienhuyzen and S. L. James, Angew. Chem.,
Int. Ed., 2002, 41, 764.
catalyst. This clearly reflects the potential of MOF-1a as a hetero-
geneous catalyst for the Diels–Alder reactions (ESI†). All the products
were purified using column chromatography and characterized
using NMR spectroscopy and ESI-HRMS (ESI†). The catalyst was
separated by filtration and washed several times with ethanol. It is
noteworthy that the recovered catalyst was activated every time prior
to further use. The catalytic activity of MOF-1a remains almost the
same even after three different cycles and PXRD of the recovered
catalyst (ESI†) showed it to be quite stable under the reaction
conditions and can be used for further catalytic cycles.
2 (a) M. Yoon, R. Srirambalaji and K. Kim, Chem. Rev., 2012, 112, 1196;
(b) F. Song, C. Wang, J. M. Falkowski, L. Ma and W. Lin, J. Am. Chem.
Soc., 2010, 132, 15390.
3 (a) C. D. Wu and W. Lin, Angew. Chem., Int. Ed., 2007, 46, 1075;
(b) G. Q. Kong, S. Ou, C. Zou and C. D. Wu, J. Am. Chem. Soc., 2012,
134, 19851; (c) J. M. Falkowski, C. Wang, S. Liu and W. Lin, Angew.
Chem., Int. Ed., 2011, 50, 8674; (d) A. Shultz, A. A. Sarjeant, O. K. Farha,
J. T. Hupp and S. T. Nguyen, J. Am. Chem. Soc., 2011, 133, 13252.
4 (a) M. Yoshizawa, M. Tamura and M. Fujita, Science, 2006, 312, 251;
(b) T. Murase, S. Horiuchi and M. Fujita, J. Am. Chem. Soc., 2010, 132, 2866.
The above-mentioned catalytic reactions presumably involve a
three-step mechanism: encapsulation of the reactants, reorganiza-
tion and adduct formation. After adduct formation, the product is
released from MOF-1a as the initial planar 1a becomes bent (after
product formation) and thereby weakens the p–p interaction with
the walls of the MOF, which makes it difficult for the product to stay 5 A. Z. Fadhel, P. Pollet, C. L. Liottaand and C. A. Eckert, Molecules,
2010, 15, 8400.
in the confined space of the MOF. The enhanced catalytic activity
using MOF-1a could be attributed to the reduction of entropy loss
6 K. C. Nicolaou, S. A. Snyder, T. Montagnon and G. Vassilikogiannakis,
Angew. Chem., Int. Ed., 2002, 41, 1668.
(DS) and activation energy of such addition reactions due to 7 K. Ikemoto, Y. Inokuma and M. Fujita, J. Am. Chem. Soc., 2011, 133, 16806.
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 7439--7441 7441