Homochiral coordination polymers with nanotubular channels for enantioselective sorption of chiral guest molecules

Article abstract of DOI:10.1039/c3nj01058a

Two novel chiral coordination polymers were synthesized by treating C ₂-symmetric 2,2′-dihydroxy- and 2,2′-dimethoxy-1, 1′-binaphthalene-3,3′-dicarboxylic acids with Cu²⁺, in which sorption of some chiral β-lactam compounds in the fr

Full text of DOI:10.1039/c3nj01058a

NJC
View Article Online
View Journal | View Issue
LETTER
Homochiral coordination polymers with
nanotubular channels for enantioselective
sorption of chiral guest molecules†
Koichi Tanaka,*a Yuki Kikumoto,a Naoki Hotaa and Hiroki Takahashi*b
Cite this: New J. Chem., 2014,
38, 880
Received (in Montpellier, France)
5th September 2013,
Accepted 17th December 2013
DOI: 10.1039/c3nj01058a
www.rsc.org/njc
Two novel chiral coordination polymers were synthesized by treating
C2-symmetric 2,20-dihydroxy- and 2,20-dimethoxy-1,10-binaphthalene-
3,30-dicarboxylic acids with Cu2+, in which sorption of some chiral
b-lactam compounds in the frameworks occurred enantioselectively.
Porous coordination polymers (PCPs) or metal–organic frame-
works (MOFs) are hybrid crystalline solids with infinite network
structures built from organic bridging ligands and inorganic
nodes.1 These materials have shown promise in several applica-
tions, including gas storage,2 separation,3 luminescence,4 and
heterogeneous catalysis.5 Although
a number of rationally
designed homochiral PCPs with tunable structural features have
been reported recently, most homochiral PCPs are not sufficiently
robust for selective sorption or catalytic transformation of organic
molecules.6 Therefore, the synthesis of robust homochiral PCPs
with potential for application is still challenging. Recently, we
have reported the synthesis of homochiral PCPs constructed
from chiral BINOL dicarboxylic acids 1–3 and their effective
catalysis of the asymmetric ring-opening reaction of epoxides
with amines7 and alcohols8 under heterogeneous conditions,
as well as their use as chiral stationary phases for chiral HPLC.9
Herein, we report the syntheses and structures of two new
homochiral Cu-PCPs (R)-PCP-4a and (R)-PCP-4b constructed from
2,20-dihydroxy- (4a) and 2,20-dimethoxy-1,10-binaphthalene-3,30-
dicarboxylic acid (4b), and their enantioselective sorption of chiral
b-lactam compounds 5a–d.
The enantiopure ligand, 2,20-dihydroxy-1,10-binaphthalene-
3,30-dicarboxylic acid 4a, was prepared by optical resolution of
rac-4a through complexation with L-leucine methyl ester.10
Enantiopure 2,20-dimethoxy-1,10-binaphthalene-3,30-dicarboxylic
acid 4b was prepared according to a previously reported method.11
A mixture of enantiopure (R)-2,20-dihydroxy-1,10-binaphthalene-
3,30-dicarboxylic acid 4a (0.35 mmol), Cu(NO3)2ꢀ3H2O (0.70 mmol),
and pyridine (0.5 mL) in DMF (1 mL) and H2O (1 mL) was heated
in a glass tube at 80 1C for 24 h to produce (R)-PCP-4a as green
prisms. Similarly, (S)-PCP-4a was prepared using (S)-4a. The
product was characterized by infrared and circular dichroism
(CD) spectroscopy (Fig. S1 and S3, ESI†), thermogravimetric
analysis (Fig. S2 and S4, ESI†), and X-ray analysis. The enantio-
meric nature of (R)- and (S)-PCP-4a in the solid state was
demonstrated by the solid-state CD spectra, which were almost
mirror images of each other (Fig. S1, ESI†).
a Department of Chemistry and Materials Engineering, Faculty of Chemistry,
Materials and Bioengineering, Kansai University, Suita, Osaka 564-8680, Japan.
E-mail: ktanaka@kansai-u.ac.jp
b Graduate School of Human and Environmental Studies, Kyoto University,
Kyoto 606-8501, Japan
† Electronic supplementary information (ESI) available: Synthesis of (R)-PCP-4a
and 4b, general procedure for guest sorption experiment and X-ray diffraction
study. CCDC 954513 and 954514. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c3nj01058a
A single crystal X-ray diffraction study revealed that (R)-PCP-4a
was formulated as [Cu((R)-4a)(Pyr)2(H2O)]ꢀ2DMFꢀH2O, which crystal-
lized in the trigonal system (space group P3221) (Fig. 1 and 2).‡
880 | New J. Chem., 2014, 38, 880--883
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
Letter
NJC
Fig. 3 ORTEP view of the molecular structure of (R)-PCP-4a with thermal
ellipsoids at 50%.
Fig. 1 ORTEP view of the molecular structure of (R)-PCP-4a with thermal
ellipsoids at 50%. The broken red and blue lines indicate inter and
intramolecular hydrogen bonds, respectively.
DMF (1 mL) and H2O (1 mL) was heated in a glass tube at 80 1C
for 24 h to produce (R)-PCP-2 as green prisms. (S)-PCP-4b was
similarly prepared using (S)-4b. The enantiomeric nature of (R)- and
(S)-PCP-4b in the solid state was also confirmed by the solid-state
CD spectra, which were almost mirror images (Fig. S2, ESI†).
A single crystal X-ray diffraction study revealed that (R)-PCP-4b
was formulated as [Cu((R)-4b)(Pyr)3]ꢀ0.5H2Oꢀ0.5DMF, which crystal-
lized in the space group C2221.‡ The asymmetric unit contained
two halves of Cu2+, two complete and two half molecules of
pyridine, a (R)-4b2ꢁ ion, two halves of water molecules, and one
half of a DMF molecule. The square pyramidal Cu2+ ion center was
coordinated by two monodentate (R)-4b2ꢁ ions and three pyridine
molecules (Fig. 3). A zigzag chain was formed by –[Cu(1)–(R)-4b–
Cu(2)–(R)-4b]– coordination and extended along the c-axis. The
apical position of the square pyramidal Cu2+ ions was occupied
by a nitrogen atom (dCu1–N1: 2.334(3) Å and dCu2–N3: 2.250(3) Å) of
pyridine. The torsion angles of O2–Cu1–N1–C25 and O5–Cu2–N3–
C33 were 167.81 and 137.61, respectively. The basal plane consisted
of two pyridine molecules and two (R)-4b2ꢁ ions.
The asymmetric unit contained one Cu2+, a pyridine, one half of a
ion of (R)-4a2ꢁ, two water molecules, and a DMF molecule. The
square pyramidal Cu2+ ion center was coordinated by two mono-
dentate (R)-4a2ꢁ ions, two pyridine molecules, and one water
molecule (Fig. 1). A helical chain was formed by –[Cu(1)–(R)-4a]3–
coordination and extended along the c-axis.
The apical position of square pyramidal Cu2+ was occupied by the
oxygen atom of the water molecule (dCu1–O3: 1.2987(19) Å), and the
basal plane consisted of two pyridine molecules and two (R)-4a2ꢁ
ions (Fig. 1). Intermolecular hydrogen bonds were formed between
the oxygen atom of DMF and the apical H2O molecule (OꢀꢀꢀO,
2.95 Å), and between a free H2O molecule and one of the oxygen
atoms of the carboxylates (OꢀꢀꢀO, 2.92 Å) (Fig. 1). The crystal had
channel structures extending along the c-axis, which contained DMF
and H2O molecules in a molar ratio of 2 : 1. The channel was
constructed by the three neighboring –[Cu(1)–(R)-4a]3– helical chains
around a threefold screw axis with a channel diameter of 6.1 Å. The
channel narrowed at the H2O molecule (Fig. 2).
The crystal had two different sizes of voids, highlighted as
circles in Fig. 4, which contained DMF and H2O molecules. The
large one had a channel structure running along the c-axis. The
channel was constructed by the basal ligands linked to Cu1,
with a diameter of 8.9–9.8 Å, whereas the small discrete cavity
was formed by the basal ligands connecting to Cu2. Water
molecules were densely packed in the small cavities.
In the same manner, a mixture of enantiopure (R)-2,20-
dimethoxy-1,10-binaphthalene-3,30-dicarboxylic acid 4b (0.35 mmol),
Cu(NO3)2 Cu(NO3)2ꢀ3H2O (0.70 mmol), and pyridine (0.5 mL) in
The Addison t parameters12 (t = 0 indicates ideal square
pyramidal geometry and t = 1 indicates ideal trigonal bipyramidal
geometry) indicated that the coordination sphere around Cu2+
in (R)-PCP-4a was nearly an ideal square pyramidal environment
and in (R)-PCP-4b was a distorted square pyramidal environment
(t = 0.04 for (R)-PCP-4a; t = 0.26 (Cu1), 0.20 (Cu2) for (R)-PCP-4b).
Owing to the distortion of the Cu ion geometry and the torsion
angle of the binaphthyl group (4a: C2–C1–C10–C20, ꢁ107.571; 4b:
C2–C1–C11–C12, ꢁ94.871), (R)-PCP-4a (helix) and 4b (zigzag) had
different chain structures (Fig. S3, ESI†).
The most valuable properties of the homochiral PCP arise from
the unique combination of its porosity and chirality. Thus, we
examined the enantioselective sorption of several chiral b-lactams
5a–d in (R)-PCP-4a and 4b. Crystalline evacuated or solvated
(R)-PCP-4a and 4b were stirred in a CH2Cl2 solution containing
a racemic mixture of b-lactams 5a–d for 24 h. The resulting
solid was collected by filtration and extracted with MeOH to
Fig. 2 The channel structures in (R)-PCP-4a crystal viewed down the
c-axis. The green, red and blue circles represent (R)-PCP-4a, DMF and
H2O molecules, respectively (H-atoms are omitted for clarity).
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 880--883 | 881

View Article Online
NJC
Letter
2,20-dimethoxy-1,10-binaphthalene-3,30-dicarboxylic acids, respec-
tively, with Cu2+ ions. These homochiral materials with nanotubular
channels exhibited enantioselective sorption of some chiral b-lactam
compounds. Studies to elucidate the mechanistic origin of the
enantioselectivity of guest sorption are in progress.
This study was supported by a Grant-in-Aid for Scientific Research
(C) (No.23550129) from The Ministry of Education, Culture, Sports,
Science and Technology (MEXT). The authors are grateful to
Prof. H. Tsue at Kyoto University for the BET measurement.
Experimental
Synthesis of [Cu((R)-4a)(Pyr)2(H2O)]ꢀ2DMFꢀH2O ((R)-PCP-4a)
A mixture of (R)-2,20-dihydroxy-1,10-binaphthyl-3,30-dicarboxylic
acid (4a)1 (13 mg, 0.035 mmol) and Cu(NO3)2ꢀ3H2O (17 mg,
0.07 mmol) was dissolved in DMF (1 mL) and H2O (1 mL), and
then pyridine (0.5 mL) was added to the solution. The solution was
heated in a glass tube at 80 1C for 24 h to give (R)-PCP-4a (16 mg) as
dark blue prisms. IR (KBr pellet, cmꢁ1): 3543, 2925, 1663, 1604,
1556, 1505, 1450, 1391, 1335, 1309, 1242, 1212, 1156, 1098, 1071,
1044, 1013, 961, 876, 808, 759, 702, 657, 624, 599.
Fig. 4 The channel structures in (R)-PCP-4b crystal viewed down the
c-axis. The green, red and blue circles represent (R)-PCP-4b, DMF and
H2O molecules, respectively (H-atoms are omitted for clarity).
Anal. calcd for C38H40CuN4O10: C, 58.79; H, 5.19; N, 7.22%.
Found: C, 60.10; H, 4.55; N, 6.24%.
Table 1 Enantioselective sorption of racemic guest b-lactams 5a–d
Synthesis of [Cu((R)-4b)(Pyr)3]ꢀ0.5DMFꢀ0.5H2O ((R)-PCP-4b)
A mixture of (R)-2,20-dihydroxy-1,10-binaphthyl-3,30-dicarboxylic
acid (4b)2 (13 mg, 0.035 mmol) and Cu(NO3)2ꢀ3H2O (17 mg,
0.07 mmol) was dissolved in DMF (1 mL) and H2O (1 mL), and
then pyridine (0.5 mL) was added to the solution. The solution
was heated in a glass tube at 80 1C for 24 h to give (R)-PCP-4b
(16 mg) as blue needles. IR (KBr pellet, cmꢁ1): 3606, 2938, 1663,
1604, 1487, 1446, 1407, 1373, 1330, 1237, 1217, 1150, 1097,
1068, 1041, 1006, 915, 813, 793, 757, 697, 637, 619, 597.
Anal. calcd for C40.5H35.5CuN3.5O7: C, 65.14; H, 4.79; N,
6.56%. Found: C, 63.42; H, 4.91; N, 6.06%.
Eea (%)
Entry
Guest
(R)-PCP-4a
(R)-PCP-4b
1b
2c
3c
4c
5c
5a
5a
5b
5c
5d
3 (R)
20 (R)
3
12
2
13 (R)
10 (R)
29
40
26
a
b
c
Determined by HPLC. Evacuated PCP. Solvated PCP.
Notes and references
retrieve the adsorbed enantioenriched b-lactams. The enantiomeric
excess (ee) values for the adsorbed guests were found to be 20% for
(R)-PCP-4a and 10% for (R)-PCP-4b, with the (R)-enantiomer in
excess for both cases. As shown in Table 1, (R)-PCP-4b showed a
relatively high enantioselectivity compared to (R)-PCP-4b, except for
entry 2. It should also be noted that the as-synthesized solvated PCP
showed higher enantioselectivity than the evacuated PCP. Although
the enantioselectivity was modest (B40% ee), these results suggest
that (R)-PCP-4a and 4b may be useful for the separation or
purification of such compounds.
X-ray powder diffraction (PXRD) indicated that (R)-PCP-4a
remained highly crystalline after sorption experiments, while
(R)-PCP-4b changes to an amorphous solid (Fig. S8, ESI†). After
removal of included solvents, however, the evacuated (R)-PCP-4a
and 4b exhibited a small BET surface area of 0.481 m2 gꢁ1 and
1.29 m2 gꢁ1, respectively (Fig. S9, ESI†).
‡ Crystal data for (R)-PCP-4a: C38H40CuN4O10, M = 776.28, trigonal, a =
8.89960(10) Å, b = 8.89960(10) Å, c = 39.5773(11) Å, a = 90.001, b = 90.001,
g = 120.001, V = 2714.68(11) Å3, T = 123(2) K, space group P3221, Z = 3,
26 777 reflections measured, 4148 independent reflections (Rint
=
0.0561). The final R1 and wR(F2) values were 0.0524 (I > 2s(I)) and
0.1377 (I > 2s(I)), respectively. The final R1 and wR(F2) values were
0.0558 (all data) and 0.1453 (all data), respectively. The goodness of fit
on F2 was 1.124. Flack parameter = 0.03(2). Crystal data for (R)-PCP-4b:
C40.5H35.5CuN3.5O7, M = 746.76, orthorhombic, a = 22.934(4) Å, b =
30.885(5) Å, c = 10.5055(18) Å, a = 90.001, b = 90.001, g = 90.001, V =
7441(2) Å3, T = 100(2) K, space group C2221, Z = 8, 30 654 reflections
measured, 8488 independent reflections (Rint = 0.0435). The final R1 and
wR(F2) values were 0.0535 (I > 2s(I)) and 0.1495 (I > 2s(I)), respectively.
The final R1 and wR(F2) values were 0.0587 (all data) and 0.1539 (all data),
respectively. The goodness of fit on F2 was 1.110. Flack parameter =
0.028(15). CCDC 954513 and 954514.
1 For reviews, see: (a) M. Eddaoudi, D. B. Moler, H. Li,
B. Chen, T. M. Reineke, M. O’Keeffe and O. M. Yaghi, Acc.
Chem. Res., 2001, 34, 319; (b) G. Ferey, C. Mellot-Draznieks,
C. Serre and F. Millange, Acc. Chem. Res., 2005, 38, 217;
(c) R. J. Hill, D. L. Long, N. R. Champness, P. Hubberstey
In conclusion, we synthesized two novel chiral PCPs
(R)-PCP-4a and 4b by treating C2-symmetric 2,20-dihydroxy- and
882 | New J. Chem., 2014, 38, 880--883
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
Letter
and M. Schroder, Acc. Chem. Res., 2005, 38, 335; (d) Z. Wang,
NJC
5 For reviews, see: (a) L. Ma, C. Abney and W. Lin, Chem. Soc.
Rev., 2009, 38, 1248; (b) A. Dhakshinamoorthy and
H. Garcia, Chem. Soc. Rev., 2012, 41, 5262.
6 For reviews, see: (a) L. Ma, C. Abney and W. Lin, Chem. Soc.
Rev., 2009, 38, 1248; (b) Y. Liu, W. Xuan and Y. Cui, Adv.
Mater., 2010, 22, 4112; (c) J. Falkowski, S. Liu and W. Lin, Isr.
J. Chem., 2012, 52, 591; (d) M. Yoon, R. Srirambalaji and
K. Kim, Chem. Rev., 2012, 112, 1196.
G. Chen and K. Ding, Chem. Rev., 2009, 109, 322;
(e) J. P. John, J. Perman and M. Zaworotko, Chem. Soc.
Rev., 2009, 38, 1400; ( f ) W. L. Leong and J. J. Vittal, Chem.
Rev., 2011, 111, 688; (g) D. Zhao, D. J. Timmons,
D. Yuan and H. Zhou, Acc. Chem. Res., 2011, 44, 123;
(h) T. R. Cook, Y. Zheng and P. J. Stang, Chem. Rev., 2013,
113, 734.
2 For reviews, see: (a) L. J. Murray, M. Dinca and J. R. Long,
Chem. Soc. Rev., 2009, 38, 1294; (b) A. Phan, C. J. Doonan,
F. J. Uribe-Romo, C. B. Knobler, M. O’Keeffe and
O. M. Yaghi, Acc. Chem. Res., 2010, 43, 58; (c) H. Wu,
Q. Gong, D. H. Olson and J. Li, Chem. Rev., 2012, 112, 836.
3 For reviews, see: (a) K. S. Suslick, P. Bhyrappa, J. H. Chou,
7 K. Tanaka, S. Oda and M. Shiro, Chem. Commun., 2008, 820.
8 (a) K. Tanaka and K. Otani, New J. Chem., 2010, 34, 2389;
(b) K. Tanaka, K. Otani, T. Murase, S. Nishihote and
Z. Urbanczyk-Lipkowska, Bull. Chem. Soc. Jpn, 2012, 85, 709.
9 K. Tanaka, T. Muraoka, D. Hirayama and A. Ohnish, Chem.
Commun., 2012, 48, 8577.
M. E. Kosal, S. Nakagaki, D. W. Smithenry and S. R. Wilson, 10 D. J. Cram, R. C. Hegeson, S. C. Peacock, L. J. Kaplan,
Acc. Chem. Res., 2005, 38, 283; (b) B. Chen, S. Xiang and
G. Qian, Acc. Chem. Res., 2010, 43, 1115; (c) J. Li, J. Sculley
and H. Zhou, Chem. Rev., 2012, 112, 869.
L. A. Domeier, P. Moreau, K. Koga, J. M. Mayer, Y. Chao,
M. G. Siegel, D. H. Hoffman, G. Dotsevi and Y. Sogah, J. Org.
Chem., 1978, 43, 1930.
4 For reviews, see: (a) M. D. Allendorf, C. A. Bauer, 11 P. K. Baruah, R. Gonnade, P. R. Rajamohanan, H. Hofmann
R. K. Bhakta and R. J. T. Houk, Chem. Soc. Rev., 2009, and G. J. Sanjayan, J. Org. Chem., 2007, 72, 5077.
38, 1330; (b) J. Rocha, L. D. Carlos, F. A. A. Paz and 12 A. W. Addison and N. Rao, J. Chem. Soc., Dalton Trans.,
D. Ananias, Chem. Soc. Rev., 2011, 40, 926. 1984, 1349.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 880--883 | 883