Dynamic Open Coordination Cage from Nonsymmetrical Imidazole–Pyridine Ditopic Ligands for Turn-On/Off Anion Binding

Article abstract of DOI:10.1002/anie.201911097

This work demonstrates a new nonconventional ligand design, imidazole/pyridine-based nonsymmetrical ditopic ligands (1 and 1^S), to construct a dynamic open coordination cage from nonsymmetrical building blocks. Upon complex formation with Pd²⁺ at a 1:4 molar ratio, 1 and 1^S initially form mononuclear PdL₄ complexes (Pd²⁺(1)₄ and Pd²⁺(1^S)₄) without formation of a cage. The PdL₄ complexes undergo a stoichiometrically controlled structural transition to Pd₂L₄ open cages ((Pd²⁺)₂(1)₄ and (Pd²⁺)₂(1^S)₄) capable of anion binding, leading to turn-on anion binding. The structural transitions between the Pd₂L₄ open cage and the PdL₄ complex are reversible. Thus, stoichiometric addition (2 equiv) of free 1^S to the (Pd²⁺)₂(1^S)₄ open cage holding a guest anion ((Pd²⁺)₂(1^S)₄?G^?) enables the structural transition to the Pd²⁺(1^S)₄ complex, which does not have a cage and thus causes the release of the guest anion (Pd²⁺(1^S)₄+G^?).

Full text of DOI:10.1002/anie.201911097

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Accepted Article
Title: Dynamic Open Coordination Cage from Non-symmetrical
Imidazole-Pyridine Ditopic Ligands for Turn-On/Off Anion Binding
Authors: Daiji Ogata and Junpei Yuasa
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201911097
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10.1002/anie.201911097
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Dynamic Open Coordination Cage from Non-symmetrical
Imidazole-Pyridine Ditopic Ligands for Turn-On/Off Anion Binding
Daiji Ogata,[a] and Junpei Yuasa*[a]
Abstract: This work demonstrates a new non-conventional ligand design,
imidazole/pyridine-based non-symmetrical ditopic ligands (1 and 1S ), to
construct a dynamic open coordination cage from non-symmetrical building
constituents. Upon complex formation with Pd2+ at a 1:4 molar ratio, 1 and
1S initially form mononuclear PdL4 complexes (Pd2+(1)4 and Pd2+(1S)4)
without formation of
a cage. The PdL4 complexes undergo a
stoichiometrically controlled structural transition to Pd2L4 open cages
((Pd2+)2(1)4 and (Pd2+)2(1S)4) capable of anion binding, leading to turn-on
anion binding. The structural transitions between the Pd2L4 open cage and
the PdL4 complex are reversible. Thus, stoichiometric addition (2 eq) of free
1S to the (Pd2+)2(1S)4 open cage holding a guest anion ((Pd2+)2(1S)4·G–)
enables the structural transition to the Pd2+(1S)4 complex without the cage,
which causes the release of the guest anion (Pd2+(1S)4 + G–).
Symmetry is a common concept in science. Nature’s topology possesses
a high degree of symmetry, which is achieved mostly by self-assembly
of lower symmetric components. In supramolecular coordination
chemistry, symmetrical building blocks often drive a single and discrete
self-assembly with a static nature,[1] whose structure can often be
determined by X-ray crystallography. Conversely, non-symmetrical
building blocks are a challenging choice for building a discrete self-
assembly,[2–4] because these blocks give rise to statistical supramolecular
isomerization if no particular driving bias exists. Despite its difficulties,
there are advantages of self-assembly from non-symmetrical building
blocks, including a lack of symmetry in building components that
provide a non-dense packed structure with a rich space inside that is
available for open cage host-guest binding.[5–7] Moreover, the output
coordination cage may be highly dynamic, enabling turn-on/off binding
through stimuli-responsive structural transitions of the host cage. Such
controlled guest uptake and release is of potential interest but remains a
formidable challenge in host-guest chemistry.[8–12]
Scheme 1. a) Possible isomers of the M2L4 assembly from non-symmetrical ditopic
ligands. b) Summary of ligand design. c) Typical conformation of imidazole/pyridine-
based ditopic ligands and output coordination assemblies.
developed imidazole-based ditopic ligands (type 2) consisting of ethynyl
spacers for supramolecular coordination systems we term “metal-ion
clipping (MIC)”.[17,18] During the course of our studies on MIC, we
realized intrinsic benefits of the imidazole-based ditopic ligands:
synthetic accessibility of the imidazole nitrogen side chain allows easy
introduction of chiral groups into the metal-coordination sites, which
gives rise to overall chirality in the output self-assembly.[18] Moreover,
because of the unique coordination vectors and conformational variety
of the ligand, the output self-assembly is often highly dynamic.[17,18] Thus,
herein, we designed new imidazole/pyridine-based ditopic ligands (type
3, 1S and 1) that are essentially non-symmetric (C1) when the imidazole
consists of a chiral pendant group (1S). At least three typical
conformations (perpendicular, parallel and antiparallel) exist in 1S and 1,
depending on the rotation around the ethynyl spacers (Scheme 1c). The
parallel geometry allows among the most appropriate coordination
vectors that provide a suitable driving bias to achieve a Pd2L4 open cage
(Scheme 1c; Figure S1).
UV/Vis absorption spectra of 1S with [Pd(CH3CN)4](BF4)2 showed
biphasic change with individual isosbestic points in response to the
molar ratio of [Pd2+]/[1S]0 = 0–0.24 and 0.26–1.0 (Figure 1a), indicating
a two-step self-assembly between 1S and Pd2+ (Scheme 2). The titration
plot provides an inflection point at [Pd2+]/[1S]0 = 0.25 and reaches
saturation at approximately [Pd2+]/[1S] = 0.50 (inset of Figure 1a),
suggesting assemblies with stoichiometry of [Pd2+]:[1S]0 = 1:4 and 1:2.
The same titration results can be reproduced with the achiral ligand (1)
and Pd2+ (Figure 1b).
Herein, we propose a new non-conventional ligand design for
creating a dynamic open coordination cage from non-symmetrical
building components. The present work focuses on a M2L4-type
coordination cage, which remains predominant and easy to design with
ditopic N-donor ligands (L) with a square–planar coordination metal (M
= PdII or PtII).[13] Despite its simplicity, four possible supramolecular
isomers are envisioned once non-symmetrical ditopic ligands are used
(Scheme 1a). Ditopic N-donor ligands have a common structural motif
consisting of two N-donor coordination sites connected by a central
linker through spacer units with a bite angle of a = 0–180˚ (Scheme
1b).[13–16] Among them, 3- or 4-pyridyl ditopic N-donor ligands (type 1)
are frequently used building blocks,[13–16] in which coordination vectors
of the 4-pyridyl ligand are fixed regardless of the ligand conformation.
Besides the pyridine-based ditopic ligands, we have extensively
[a]
D. Ogata, Dr. J. Yuasa
Department of Applied Chemistry,
Tokyo University of Science
1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
E-mail: yuasaj@rs.tus.ac.jp
Supporting information for this article is given via a link at the end of
the document.
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Figure 2. Positive ESI-MS spectra of 1S in acetonitrile (2.0 × 10−3 M) with the presence
of a) 0.25 and b) 0.50 equiv. of [Pd(CH3CN)4](BF4)2. Inset: Isotopically resolved signals
at a) m/z = 968.4 and the calculated isotopic distributions for [Pd(1S)4]2+, b) m/z = 510.7
Figure 1. UV/Vis absorption spectra of a) 1S and b) 1 (concentrations: 2.0 × 10−5 M) in
the presence of [Pd(CH3CN)4](BF4)2 ([0–0.24 equiv. (red lines); 0.26–1.0 equiv. (blue
lines)]. Insets: Plots of absorbance at 250 nm versus a) [Pd2+]/[1S]0 and b) [Pd2+]/[1]0.
and the calculated isotopic distributions for [(Pd)2(1S)4]4+
.
Then, we measured the ESI mass of 1S in the presence of 0.25 and
0.50 equiv. of [Pd(CH3CN)4](BF4)2 in acetonitrile. At a molar ratio of
[Pd2+]/[1S]0 = 0.25, an intense single peak was observed at m/z = 968.4,
corresponding to [Pd(1S)4]2+ (Figure 2a); a clear indication of a
mononuclear 1:4 complex (Pd2+(1S)4) formed at [Pd2+]/[1S]0 = 0.25.
Conversely, at a molar ratio of [Pd2+]/[1S]0 = 0.50, the mass peak at m/z
= 968.4 corresponding to [Pd(1S)4]2+ completely disappeared with a
concomitant appearance of a new mass signal at m/z = 510.7, which is
assignable to the Pd2L4 assembly, [(Pd)2(1S)4]4+ (Figure 2b).
The PdL4 and Pd2L4 assemblies were then characterized by NMR
spectroscopy (Figure 3b–d). Peak assignments were performed by
1H,1H-COSY and ROESY cross-peak correlations (Figures S2–6). At
the molar ratio of [Pd2+]/[1] = 0.25, a upfield shift compared with that of
the free ligand (1) was observed for the pyridine (Ha and Hb). Conversely
the imidazole proton (Hj) showed a downfield, indicating that the
imidazole N-donor site preferentially coordinates Pd2+ in Pd2+(1)4. The
DFT calculations indicate that the PdL4 complex with the imidazole
coordinated is 19.0 kcal/mol lower in energy than that of the pyridine
coordinated (Figure S7). Although six stereoisomers of Pd2+(1)4 are
envisioned based on the ligand symmetry (Figure S8), the fine 1H NMR
spectrum at [Pd2+]/[1] = 0.25 (Figure 3d) indicates the preferential
formation of a single Pd2+(1)4 complex. The total number of NMR
resonances in the NMR spectrum due to Pd2+(1)4 was not changed
(Figure 3e vs. d), therefore the four 1 ligands served the same
coordination site. The imidazole and pyridine N-donor sites may have
different coordination affinities for Pd2+, hence the imidazole/pyridine-
based ditopic ligands (1 and 1S) initially formed the 1:4 complex at the
molar ratio of [Pd2+]/[1 or 1S]0 = 0.25 due to the preferential coordination
of one N-donor site (probably imidazole with higher affinity judging
from the competition experiments with the imidazole and pyridine
precursors, see Figure S9 and S10). This may be one reason that the
imidazole/pyridine-based ditopic ligands (1 and 1S) exhibited two-step
assembly with Pd2+ (Scheme 2). Increasing the molar ratio of [Pd2+]/[1]
from 0.25 to 0.50 resulted in downfield shifts of the pyridine protons Hb
and carbazole protons (Hc, Hd, He, Hf, Hg and Hh) (Figure 3d to c).
However, the total number of resonances in the NMR spectrum due to
(Pd2+)2(1)4 remained the same as that observed for the free ligand (Figure
3e vs. c). Therefore, the four 1 ligands bridged by two Pd2+ ions are
located in the same coordination environment. No appreciable minor
component was observed (Figure 3c), a clear indication that a single
isomer of (Pd2+)2(1)4 formed quantitatively at [Pd2+]/[1] = 0.50. The DFT
calculations indicate that the proposed Pd2L4 cage is 60.7–203.5
kcal/mol lower in energy than that of the other isomers (Figure S11). We
Scheme 2. Two-step self-assembly between top: 1S and Pd2+. Turn-on/off anion binding
through the structural transitions between (Pd2+)2(1S)4 and Pd2+(1S)4.
confirmed that almost the same chemical shifts as (Pd2+)2(1)4 can be
obtained when the chiral ligand (1S) is examined (Figure 3c vs. 3b). NOE
correlations were observed between the pyridine proton Ha and the
carbazole proton Hd, and between the pyridine proton Hb and the
carbazole protons Hc and Hd (Figure 3a dashed arrows; see Figure S5),
whereas free 1S has no NOE cross-peak between these protons (Figure
S6). The energy-minimized structure of a (Pd2+)2(1S)4 open cage
(obtained by molecular mechanics) explains why the pyridine protons
(Ha and Hb) and the carbazole protons (Hc and Hd) are located in close
proximity (Figure 3a, dashed arrows), which is consistent with the NOE
cross-peak analysis. Conversely, NMR signal splitting was observed in
the pyridine proton Ha and the imidazole proton Hi when the methyl
group at the imidazole nitrogen of the achiral ligand 1 was replaced with
the chiral alkyl group (1 → 1S, Figure 3c → 3b). The NMR signal
splitting can be attributed to the existence of two diastereomers for
(Pd2+)2(1S)4 with opposite chiral configurations, whose population ratio
was determined to be 55:45 by the integration ratio of signals “i” (Figure
3b). The two diastereomers are in slow exchange on the NMR time scale,
which was confirmed by various temperature (VT) 1H NMR
experiments (Figure S12). Consequently, comparison of the NMR data
(1 vs. 1S) indicates inherent chirality for (Pd2+)2(1)4 and (Pd2+)2(1S)4,
which might arise from ligand-to-ligand steric repulsion between the
pyridine protons “Ha” and between the imidazole protons “Hi” (solid
arrows in Figure 3a and S13), which forces the two aromatic rings to
adopt a twisting position and therefore cause geometric strain that breaks
the mirror image symmetry.
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Figure 4. Solution structures of a) (Pd2+)2(1S)4 and b) (Pd2+)2(1S)4·ReO4 exploited by NMR
analysis. c) Chemical shifts of Ha, Hb, Hc, Hd and Hj vs. [ReO4–]. Theoretical curves were
obtained based on the 1:1 binding model. d) Job plot analysis between (Pd2+)2(1S)4 and
NBu4ReO4, where x = [ReO4–]/([(Pd2+)2(1S)4] + [ReO4–]). e) Stacked 1H NMR spectra of
(Pd2+)2(1S)4 (5.0 × 10–4 M) in the presence of NBu4ReO4 in CD3CN at 298 K.
Figure 3. a) Solution structure of (1S)4(Pd2+
) determined by NMR analysis. Solid and
2
dashed arrows indicate suggested steric hindrance and NOE correlations, respectively.
1H NMR spectra b) 1S (2.0 × 10–3 M) in the presence of Pd2+ (1.0 × 10–3 M). c,d) 1 (2.0 ×
10–3 M) in the presence of c) Pd2+ (1.0 × 10–3 M) and d) Pd2+ (5.0 × 10–4 M). e) 1 (2.0 ×
10–3 M) in the absence of Pd2+ in CD3CN at 298 K. The small peak annotated by an
asterisk originates from the palladium agent.
The NMR-based determination of (Pd2+)2(1)4 and (Pd2+)2(1S)4
suggests an open cage inside (Figure 4a) to binding with anions (G– =
BF4 , PF6 , ClO4 , ReO4 and SbF6 ).[19–21] Figure 4e shows the 1H NMR
titration of (Pd2+)2(1S)4 with successive additions of NBu4ReO4, wherein
particularly, we observed a notable downfield shift of the pyridine
proton “Hb” (blue triangle) with a concomitant upfield shift of the
carbazole proton “Hd” (green square). The NMR titration data can be
fitted by nonlinear fitting based on the 1:1 host-guest binding model
(Figure 4c),[10c] which yields an association constant (Ka) of (7.6 ± 0.8)
× 102 M–1 (see also Figures S14–17). The 1:1 binding model was also
supported by job plot analysis (Figure 4d). Noteworthy, the initially
formed mononuclear Pd2+(1S)4 complex never exhibited such NMR peak
shifts even with the addition of NBu4ReO4 (Figure 4c black triangles;
Figure S18). Thus, the stoichiometry-driven structural transition of
Pd2+(1S)4 into the (Pd2+)2(1S)4 open cage is able to turn-on anion binding
(Scheme 2).
–
–
–
–
–
Figure 5. a) 1H NMR spectrum of (Pd2+)2(1S)4 (1.0 × 10–3 M) in the presence of NBu4ReO4
(1.0 × 10–3 M), which was measured after successive addition of b) 2 equiv. (toward
(Pd2+)2(1S)4) of 1S and c) 1 equiv. (toward Pd2+(1S)4) of Pd2+ in CD3CN at 298 K. The small
peaks annotated by asterisks originate from the free 1S ligand.
re-assembly into the (Pd2+)2(1S)4 coordination cage and reuptake of the
guest anion (Scheme 2).
In conclusion, we have successfully demonstrated the availability of
a new ligand design for achieving a dynamic open coordination cage
from non-symmetrical components. Using appropriate coordination
vectors, non-symmetrical ditopic ligands (1 and 1S) consisting of
imidazole and pyridine N-donors successfully self-assembled into a
Pd2L4 open cage whose structure is inherently chiral and has an open
cage available for anion binding. The Pd2L4 open cage is highly dynamic
and capable of transition to a PdL4 complex without a cage property
under stoichiometric control. Therefore, the anion-binding ability of the
coordination cage can be turned on and off by simply adjusting the
component ratio ([Pd]:[L]), enabling controlled guest anion uptake and
release through the stoichiometry-driven structural transitions of the host
cage. The ligand design can be applied widely for fine-tuning
coordination cages to afford turn-on/off guest binding switchability.
1
–
The H NMR spectrum of (Pd2+)2(1S)4 in the presence of ReO4
dramatically changed to that of the mononuclear Pd2+(1S)4 complex by
the stoichiometric addition of 2 equiv. (toward (Pd2+)2(1S)4) of free 1S
(Figure 5a to b). This event is attributed to the structural transition of the
(Pd2+)2(1S)4 coordination cage into the Pd2+(1S)4 complex without a cage,
therefore releasing the guest anion bound inside the open cage of
Pd2+(1S)4 (Scheme 2). The original 1H NMR spectrum of (Pd2+)2(1S)4 is
almost recovered by the stoichiometric addition of 1 equiv. (toward
Pd2+(1S)4) of [Pd(CH3CN)4](BF4)2 into the resulting solution of Pd2+(1S)4
containing ReO4– (Figure 5b to c). Therefore, Pd2+(1S)4 is capable of
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O. Aleveque, E. Levillain, M. Allain, J. Arago, E. Orti, S. Goeb, M.
Salle, Angew. Chem. Int. Ed. 2017, 56, 16272.
Acknowledgments
This work was partly supported by JSPS KAKENHI Grant
Numbers 19H02693, 19K22207, and 19H04596 in Scientific
Research on Innovative Areas “Coordination Asymmetry”, Grant-
in-Aid for the ASAHI Glass Foundation. We thank the Edanz
Group (www.edanzediting.com/ac) for editing a draft of this
manuscript.
[12]
a) X. Bai, C. Jia , Y. Zhao, D. Yang, S.-C. Wang, A. Li, Y.-T. Chan,
Y.-Y. Wang, X.-J. Yang, B. Wu, Angew. Chem. Int. Ed. 2018, 57,
1851; b) S. Hiraoka, K. Harano, M. Shiro, M. Shionoya, Angew. Chem.
Int. Ed. 2005, 44, 2727.
[13]
[14]
A. Schmidt, A. Casini, F. E. Kühn, Coord. Chem. Rev. 2014, 275, 19.
a) D. Fujita, K. Suzuki, S. Sato, M. Yagi-Utsumi, Y. Yamaguchi, N.
Mizuno, T. Kumasaka, M. Takata, M. Noda, S. Uchiyama, K. Kato, M.
Fujita, Nat. Commun. 2012, 3, 1093; b) J. Bunsen, J. Iwasa, P.
Bonakdarzadeh, E. Numata, K. Rissanen, S. Sato, M. Fujita, Angew.
Chem., Int. Ed. 2012, 51, 3161; c) Q.-F. Sun, T. Murase, S. Sato, M.
Fujita, Angew. Chem. Int. Ed. 2011, 50, 10318; d) Q.-F. Sun, J. Iwasa,
D. Ogawa, Y. Ishido, S. Sato, T. Ozeki, Y. Sei, K. Yamaguchi, M.
Fujita, Science, 2010, 328, 1144.
Keywords: anion binding • chirality • coordination cage • dynamic
assembly • host-guest systems
[1]
[2]
a) R. Chakrabarty, P. S. Mukherjee, P. J. Stang, Chem. Rev. 2011,
111, 6810; b) M. Han, D. M. Engelhard, G. H. Clever, Chem. Soc.
Rev. 2014, 43, 1848.
a) L. Zhao, B. H. Northrop, Y.-R. Zheng, H.-B. Yang, H. J. Lee, Y. M.
Lee, J. Y. Park, K.-W. Chi, P. J. Stang, J. Org. Chem. 2008, 73, 6580;
b) Y.-R. Zheng, B. H. Northrop, H.-B. Yang, L. Zhao, P. J. Stang, J.
Org. Chem. 2009, 74, 3554; c) S. Ghosh, P. S. Mukherjee, Inorg.
Chem. 2009, 48, 2605;
[15]
[16]
a) J. E. M. Lewis, A. B. S. Elliott, C. J. McAdam, K. C. Gordon, J. D.
Crowley, Chem. Sci. 2014, 5, 1833; b) S. M. Jansze, M. D. Wise, A.
V. Vologzhanina, R. Scopelliti, K. Severin, Chem. Sci. 2017, 8, 1901;
c) R. Sekiya, M. Fukuda, R. Kuroda, J. Am. Chem. Soc. 2012, 134,
10987.
[3]
a) O. Jurček , P. Bonakdarzadeh, E. Kalenius, J. M. Linnanto, M.
Groessl, R. Knochenmuss, J. A. Ihalainen, K. Rissanen, Angew.
Chem. Int. Ed. 2015, 54, 15462; b) S. Kumar Sen, R. Natarajan, Inorg.
Chem. 2019, 58, 7180.
a) G. H. Clever, P. M. Punt, Acc. Chem. Res. 2017, 50, 2233; b) S.
Löffler, J. Lübben, L. Krause, D. Stalke, B. Dittrich, G. H. Clever, J.
Am. Chem. Soc. 2015, 137, 1060. c) D. Preston, J. E. Lewis, J. D.
Crowley, J. Am. Chem. Soc. 2017, 139, 2379.
[4]
[5]
[6]
X. N. Gao, A. Y. Fu, Y. Y. Wang, Inorg. Chem. 2016, 55, 4330.
K. Harris, D. Fujita, M. Fujita, Chem. Commun. 2013, 49, 6703.
D. Zhang, T. K. Ronson, J. R. Nitschke, Acc. Chem. Res. 2018, 51,
2423.
[17]
[18]
a) N. Inukai, T. Kawai, J. Yuasa, Chem. Eur. J. 2014, 20, 15159; b)
Y. Imai, T. Kawai, J. Yuasa, Chem. Commun. 2015, 51, 10103.
a) Y. Imai, Y. Nakano, T. Kawai, J. Yuasa, Angew. Chem. Int. Ed.
2018, 57, 8973; b) Y. Imai, J. Yuasa, Chem. Sci. 2019, 10, 4236; c)
Y. Imai, J. Yuasa, Chem. Commun. 2019, 55, 4095; d) K. Nonomura,
J. Yuasa, Inorg. Chem. 2019, 58, 6474.
[7]
a) K. Matsumoto, S. Kusaba, Y. Tanaka, Y. Sei, M. Akita, K. Aritani,
M. Haga, M. Yoshizawa, Angew. Chem. Int. Ed. 2019, 58, 8463; b) S.
Kai, M. Nakagawa, T. Kojima, X. Li, M. Yamashina, M. Yoshizawa, S.
Hiraoka, Chem. Eur. J. 2018, 24, 3965; c) D. Samanta, S. Mukherjee,
Y. P. Patil, P. S. Mukherjee, Chem.–Eur. J. 2012, 18, 12322; d) M. D.
Wise, J. J. Holstein, P. Pattison, C. Besnard, E. Solari, R. Scopelliti,
G. Bricogne, K. Severin, Chem. Sci. 2015, 6, 1004.
[19]
a) M. D. Johnstone, E. K. Schwarze, J. Ahrens, D. Schwarzer, J. J.
Holstein, B. Dittrich, F. M. Pfeffer, G. H. Clever, Chem.–Eur. J. 2016,
22, 10791; b) D. A. McMorran, P.J. Steel, Angew. Chem. Int. Ed.
1998, 37, 3295; c) P.J. Steel, D. A. McMorran, Chem. Asian J. 2019,
14, 1098; d) L.-P. Zhou, Q.-F. Sun, Chem. Commun. 2015, 51,
16767; e) D. P. August, G. S. Nichol, P. J. Lusby, Angew. Chem. Int.
Ed. 2016, 55, 15022.
[8]
[9]
a) A. J. McConnell, C. S. Wood, P. P. Neelakandan, J. R. Nitschke,
Chem. Rev. 2015, 115, 7729; b) T. Y. Kim, R. A. S. Vasdev, D.
Preston, J. D. Crowley, Chem.–Eur. J. 2018, 24, 14878.
a) R. Li, J. J. Holstein, W. G. Hiller, J. Andréasson, G. H. Clever, J.
Am. Chem. Soc. 2019, 141, 2097; b) M. Han, R. Michel, B. He, Y.-S.
Chen, D. Stalke, M. John, G. H. Clever, Angew. Chem. Int. Ed. 2013,
52, 1319; c) L. Catti, N. Kishida, T. Kai, M. Akita, M. Yoshizawa,
Nature Commun. 2019, 10, 1948.
[20]
[21]
Clever et al. reported the dimeric intercatenated coordination cage of
Pd2L4 (Pd4L8) having the outer two pockets to bind anions, whose
(first) binding constant to ReO4– is larger than that of our coordination
cage, see: S. Freye, R. Michel, D. Stalke, M. Pawliczek, H.
Frauendorf, G. H. Clever, J. Am. Chem. Soc. 2013, 135, 8476.
Upon addition of chloride and bromide anions, the coordination cage
was decomposed into the free ligand (Figure S19). The precipitation
was generated by the presence of the sulfate anion. The Ka value for
PF6– binding (6.2 ± 1.0) × 10 M–1 (Figure S14) was smaller than that
[10]
[11]
a) W. Cullen, S. Turega, C. A. Hunter, M. D. Ward, Chem. Sci. 2015,
6, 625; b) J. E. M. Lewis, E. L. Gavey, S. A. Cameron, J. D. Crowley,
Chem. Sci. 2012, 3, 778; c) A. M. Castilla , T. K. Ronson, J. R.
Nitschke, J. Am. Chem. Soc. 2016, 138, 2342.
–
of ReO4 (Ka = (7.6 ± 0.8) × 102 M–1). We attribute this tendency to
a) V. Croue, S. Goeb, G. Szaloki, M. Allain, M. Salle, Angew. Chem.
Int. Ed. 2016, 55, 1746; b) G. Szaloki, V. Croue, V. Carre, F. Aubriet,
−
the better match of the shape as well as volume of ReO4 with the
inner open cage.
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10.1002/anie.201911097
Angewandte Chemie International Edition
COMMUNICATION
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COMMUNICATION
Non-symmetrical ditopic ligands (L)
drive formation of a dynamic Pd2L4
open cage that is capable of turn-on
and -off anion binding through
Daiji Ogata, and Junpei Yuasa*
Page No. – Page No.
Dynamic Open Coordination Cage
from Non-symmetrical Imidazole-
Pyridine Ditopic Ligands for Turn-
On/Off Anion Binding
stoichiometry-driven
structural
transitions of the host cage.
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