A novel chiral porous metal-organic framework: Asymmetric ring opening reaction of epoxide with amine in the chiral open space

Article abstract of DOI:10.1039/b714083e

A novel chiral metal-organic framework, [Cu₂(5,5′-BDA) ₂] was synthesized by treating chiral 2,2′-dihydroxy-1, 1′-binaphthalene-5,5′-dicarboxylic acid (5,5′-H ₂BDA) with a Cu(ii) ion, in which the asymmetric ring opening r

Full text of DOI:10.1039/b714083e

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A novel chiral porous metal–organic framework: asymmetric ring
opening reaction of epoxide with amine in the chiral open spacew
Koichi Tanaka,*a Shinji Odaa and Motoo Shirob
Received (in Cambridge, UK) 12th September 2007, Accepted 3rd December 2007
First published as an Advance Article on the web 17th December 2007
DOI: 10.1039/b714083e
A novel chiral metal–organic framework, [Cu2(5,50-BDA)2] was
synthesized by treating chiral 2,20-dihydroxy-1,10-binaphtha-
lene-5,50-dicarboxylic acid (5,50-H2BDA) with a Cu(II) ion, in
which the asymmetric ring opening reaction of an epoxide with
amine proceeds efficiently under solvent-free conditions.
referred to that already known of 2 , by X-ray analysis of the
1 : 2 complex.z From the MeOH solution left after the
separation of the complex crystals, (S)-1 of 74% ee was
obtained. (S)-1 (74% ee) was then mixed with 1,4-diazabicy-
clo[3.3.3]octane (DABCO) in MeOH to give a 1 : 1 complex of
rac-1 and DABCO. From the filtrate left after separation of
the complex, (S)-1 of 499% ee was obtained in 32% yield.
The field of metal–organic frameworks (MOFs) has grown
explosively in recent years1 and numerous studies have been
reported owing to their potential applications in gas storage,2
separation3 and heterogeneous catalysis.4 While a large num-
bers of MOF are being discovered, so far only a few examples
of chiral MOF for enantioselective separations or heteroge-
neous asymmetric catalysis have been investigated.5 For
example, Lin et al. reported the enantioselective addition of
diethylzinc to 1-naphthaldehyde catalysed by a Ti modified
chiral MOF under heterogeneous conditions in high ee. Here,
we wish to report the synthesis of a novel chiral porous
metal–organic framework (3) through the reaction of
C2-symmetric 2,20-dihydroxy-1,10-binaphthalene-5,50-dicar-
boxylic acid (5,50-H2BDA, 1) and a Cu (II) ion and its function
as a chiral heterogeneous catalyst for the asymmetric ring
opening reaction of an epoxide with amine.
Treatment of enantiopure 5,50-H2BDA (R)-1 with
Cu(NO3)2 in aqueous MeOH solution by slow diffusion of
N,N-dimethylaniline at room temperature for several days
afforded [Cu2(5,50BDA)2(H2O)2] ꢀ MeOH ꢀ 2H2O, (R)-3, as
green needles in 33% yield. Similarly, (S)-3 was also prepared
using (S)-1. The product was characterized by IR and CD
spectroscopy, thermogravimetric analysis (TGA), and finally
X-ray analysis. The IR spectra of 3 exhibited peaks of nOH at
3367 and nCO2ꢁ at 1610 cmꢁ1, respectively. The enantiomeric
nature of (R)- and (S)-3 in the solid state was demonstrated by
solid-state CD spectra, which showed almost mirror image of
each other (Fig. 1).
The enantiopure ligand, 5,50-H2BDA (1) was prepared by
optical resolution of rac-16 through complexation with cinch-
onidine. When a solution containing a 1 : 2 mixture of rac-1
and cinchonidine (2) in MeOH was kept at room temperature,
a 1 : 2 complex of (R)-1 of 91% ee and 2 was obtained as
colorless prisms. Recrystallization of the complex from MeOH
gave almost pure 1 : 2 complex crystals, which upon decom-
position with dil. HCl afforded (R)-1 of 499% ee in 35%
yield. The absolute configuration of (R)-1 was determined,
A single crystal X-ray diffraction study revealed that (R)-3 is
formulated as [Cu2(5,50BDA)2(H2O)2] ꢀ MeOH ꢀ 2H2O which
crystallized in a space group P21(#4).y (Fig. 2) In (R)-3, each
Cu(II) ion is coordinated by four carboxylate oxygen atoms of
(R)-1 and each pair of Cu(II) ions is bridged by four carbox-
ylate groups to form 2D dinuclear square grid coordination
networks with a Cuꢀ ꢀ ꢀCu distance of 15.62(2) A; the void
space is filled by one MeOH and two H2O guest molecules
through hydrogen bonding. The 2D square grids stuck to form
layers along the b-axis. (Fig. 3) Thermogravimetric analysis
(TGA) of (R)-3 showed that 19.5% of its mass is lost in
the temperature range 25–120 1C, corresponding to the loss
of all solvent molecules per formula unit. N2 adsorption
a Department of Chemistry and Materials Engineering, Faculty of
Chemistry, Materials and Bioengineering, Kansai University, Suita,
Osaka 564-8680, Japan. E-mail: ktanaka@ipcku.kansai-u.ac.jp;
Fax: +81-06-6368-0861; Tel: +81-06-6368-0861
b Rigaku X-ray Laboratory, 3-9-12 Matsubara-choAkishima, Tokyo
196-8666, Japan. E-mail: shiro@rigaku.co.jp
w Electronic supplementary information (ESI) available: Optical re-
solution of 1, synthesis of 3 and general procedure for the asymmetric
ring-opening reaction of epoxide, and Fig. S1–S4. See DOI: 10.1039/
b714083e
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Fig. 3 Crystal structure of (R)-3 viewed down the c-axis.
Fig. 1 CD spectra of (R)- and (S)-3 as Nujol mulls.
measurements indicated that an evacuated sample of (R)-3 had
BET surface area of 1.71 m2 gꢁ1
.
X-ray powder diffraction (XRPD) patterns for (R)-3 are
shown in Fig. 4. After removal of the guest MeOH and water
in vacuo, the crystalline (R)-3 changes to an amorphous solid.
Interestingly, however, the evacuated solid (R)-3 readily ad-
sorbs the guest MeOH and water to form the original crystal-
line phase upon exposure to their vapours.
The catalytic activity of (R)-3 toward asymmetric ring
opening reactions of epoxides with aromatic amines was
examined. (Table 1) For example, when a solution of a
mixture of cyclohexene oxide (4a), aniline (5a) and 0.05 equiv.
of evacuated (R)-3 was stirred at 25 1C for 48 h in toluene, an
optically active b-amino alcohol (6a) of 40% ee was obtained
in 47% yield. Similarly, cyclopentene oxide (4b) reacted with
5a to give an optically active 6b of 43% ee in 15% yield. After
the experiments, the crystals of (R)-3 were recovered by simple
filtration and reused in the next cycles of the reaction without
appreciable loss of reactivity and enantioselectivity. It is
interesting to note that remarkable improvements both in
the reactivity and enantioselectivity were achieved when the
Fig. 4 XRPD patterns of (R)-3 before (bottom) and after (middle)
the removal of guest methanol and water and after exposure of
evacuated solid to methanol and water vapours (top).
Table 1 Asymmetric ring-opening reaction of epoxide with amine
Catalyst
Epoxide Amine Solvent Time/h Yield (%) Ee (%)a
(R)-3
(R)-3
(R)-3
(R)-3
4a
4b
4a
4b
5a
5a
5a
5a
5a
5a
5b
5c
Toluene 48
Toluene 48
None 24
None 24
None 24
None 24
None 24
None 24
54
15
51
30
3
1
3
13
45
43
51
50
2
0
2
0
(S)-BINOLb 4a
(S)-BINOL 4b
(R)-3
(R)-3
a
4a
4a
Fig. 2 2D chiral open framework of (R)-3 viewed down the b-axis.
b
Determined by HPLC. 2,20-Dihydroxy-1,10-binaphthalene.
(all the solvent molecules are omitted for clarity).
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reaction was carried out under solvent-free conditions. For
example, the reaction of 4a with 5a without using toluene
afforded 6a of 51% ee in 51% yield. Similarly, 4b was
converted to 6b in 30% yield and 50% ee under solvent-free
conditions. In contrast, when the reaction was performed
using (S)-BINOL as catalyst instead of (R)-3, no reactivity
and enantioselectivity were observed (Table 1). It was also
found that the reaction is very sensitive to the structure of
nucleophile. In this case of the reactions between cyclohexene
oxide (4a) and o- (5b) or p-methylaniline (5c) under the same
conditions, the conversion as well as the enantioselectivity
dropped dramatically.
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In summary, a novel chiral metal–organic framework has
been synthesized and structurally characterized. In the pre-
sence of the chiral metal–organic framework, asymmetric ring
opening reactions of epoxides with amines proceeded to give
optically active b-amino alcohols under solvent-free condi-
tions. Continued efforts to apply this strategy to other asym-
metric reactions are presently under way.
Notes and references
.
z X-ray single crystal diffraction data for (R)–1 2 was collected on a
Rigaku RAXIS RAPID imaging plate diffractometer using Cu Ka
radiation. Crystal data: formula C62H74N4O14, formula weight
1099.28, space group P21212(#18), a = 13.7716(6), b = 15.0164(7),
c = 15.8042(8) A, V = 3268.3(3) A3, Z = 2, r = 1.117 g cmꢁ3, 2ymax
= 136.51, R1 = 0.1250 (calculated on F2 for 2503 reflections with I 4
2s(I)), wR2 = 0.3256 (calculated on F for 3303 reflections), GOF =
4 (a) B. Gomez-Lor, E. Guttierez-Puebla, M. Iglesias, M. Monge, C.
Ruiz-Valero and N. Snejko, Chem. Mater., 2005, 17, 2568; (b) K.
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7
1.066. The structure was solved by SHELXS97 and refined by
SHELXL97 8. The molecule of 1 lies on a 2-fold axis in the crystal.
The absolute configuration of 1 was determined based on that of 2.
CCDC 660911. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/b714083e
y X-ray single crystal diffraction data for (R)-3 was collected on a
Rigaku RAXIS RAPID imaging plate diffractometer using Mo Ka
5 (a) O. R. Evans, H. L. Ngo and W. Lin, J. Am. Chem. Soc.,
2001, 123, 10395; (b) Y. Cui, O. R. Evance, L. H. Ngo,
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Commun., 2003, 994; (d) D. Bradshaw, T. J. Prior, E. J. Cussen,
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2006, 2563.
radiation. Crystal data: formula C45H36Cu2O19
1007.86, space group P21(#4), a = 15.620(5), b = 11.377(4), c =
15.620(5) A, b = 94.88(5)1, V = 2766(2) A, Z = 2, r = 1.210 g cmꢁ3
, formula weight
,
2ymax = 50.01, R1 = 0.0745 (for 6750 reflections with I 4 2s(I)), wR2
= 0.1946 (for 8263 reflections), GOF = 1.039, Flack parameter =
ꢁ0.05(2) (refined using 3212 Friedel pairs). The structure was solved
by SHELXS97 and refined by SHELXL97. The absolute configuration
was determined based on the Flack parameter. At the first stage of the
structure analysis, it was suggested that the unit cell corresponded to
C-centered orthorhombic cell and its space group was C2221(#20).
After successive trials were failed in the structure determination, we
supposed that the compound might be crystallized in merohedrally
twinning form with two domains of the space group P21(#4). The unit
cell transformation matrix was 0.5 0.5 0 0 0 1 ꢁ0.5 0.5 0 (according to
the representation in SHELXL). The structures composed of the two
domains related by the matrix of 0 0 ꢁ1 0 ꢁ1 0 ꢁ1 0 0 was successfully
solved and refined to R1 = 0.0751. The twin fraction at the last stage
of the refinement was 0.510(3). CCDC 660912. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b714083e
6 K. Tanaka, H. Takano and Z. Lipkowska, J. Inc. Phenom., 2006,
56, 281.
7 G. M. Sheldrick, SHELXS97, Program for the Solution of Crystal
Structures, University of Gottingen, Germany, 1997.
8 G. M. Sheldrick, SHELXL97, University of Gottingen, Germany,
1997.
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This journal is The Royal Society of Chemistry 2008
822 | Chem. Commun., 2008, 820–822