Nestable Tetrakis(spiroborate) Nanocycles

Article abstract of DOI:10.1021/acs.orglett.5b00747

Multicomponent construction of the tetrakis(spiroborate) anionic nanocycles was achieved by reacting bis(dihydroxynaphthalene)s with tetrahydroxyanthraquinone in the presence of boric acid in a self-organized manner. These nanocycles exhibited selective molecular recognition behavior toward cationic guests such as methyl viologen derivatives. Formation of a supramolecular ring@ring and a guest@ring@ring structure was observed by combining the anionic nanocycle and the vinylogous analog of cyclobis(paraquat-p-phenylene). (Figure Presented).

Full text of DOI:10.1021/acs.orglett.5b00747

Letter
pubs.acs.org/OrgLett
Nestable Tetrakis(spiroborate) Nanocycles
,
†
‡
‡
‡
†
Hiroshi Danjo,* Yuhki Hashimoto, Yuki Kidena, Ayumi Nogamine, Kosuke Katagiri,
§
†
§
Masatoshi Kawahata, Toshifumi Miyazawa, and Kentaro Yamaguchi
†
‡
Department of Chemistry, and Graduate School of Natural Sciences, Konan University, 8-9-1 Okamoto, Higashinada, Kobe
6
58-8501, Japan
§
Kagawa School of Pharmaceutical Sciences, Tokushima Bunri University, 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan
*
S Supporting Information
ABSTRACT: Multicomponent construction of the tetrakis-
spiroborate) anionic nanocycles was achieved by reacting
(
bis(dihydroxynaphthalene)s with tetrahydroxyanthraquinone
in the presence of boric acid in a self-organized manner. These
nanocycles exhibited selective molecular recognition behavior
toward cationic guests such as methyl viologen derivatives.
Formation of a supramolecular ring@ring and a guest@ring@
ring structure was observed by combining the anionic
nanocycle and the vinylogous analog of cyclobis(paraquat-p-
phenylene).
hape-persistent macrocycles have been designed and
prepared for various purposes, including their use as
Spiroborate anionic nanocycles were prepared by mixing 1,4-
bis(1-(2,3-dihydroxynaphthyl))benzene (1a′), previously gen-
erated by deprotection of 1,4-bis(1-(2-methoxymethoxy-3-
hydroxynaphthyl))benzene (1a), and 2,3,6,7-tetrahydroxy-
anthraquinone (3) in the presence of 2 equiv of boric acid in
DMF at 150 °C (Scheme 1). The reversible formation of a
spiroborate linkage occurred, and tetrakis(spiroborate) nano-
cycle 4a·(Me NH ) was quantitatively obtained after repreci-
S
hosts for molecular recognition and the construction of porous
1
stacking structures. Particularly for molecular recognition, their
shape persistence plays an important role in the strict shape-
and size-selective guest inclusion. The cyclic structures are
usually constructed with a combination of rigid components,
such as aromatic rings and ethynylene linkages. Stoddart and
co-workers have continuously demonstrated that cyclobis-
2
2 4
pitation with diethyl ether. The preparation of the spiroborate
(
paraquat-p-phenylene) (blue box) and its derivatives act as
nanocycle 5a·(Me NH ) , which has a larger ring size, was also
2
2 4
good host molecules for the recognition of various electron-rich
achieved by the use of bis(4-(1-(2,3-dihydroxynaphthyl))-
phenyl)acetylene (2a′) instead of 1a′. In addition, the
tetrabutylated derivative of each nanocycle (4b·(Me NH )
2
aromatic compounds. In addition to the finely adjusted cavity
size, their tetracationic nature allows them to have strong
affinity toward electron-rich aromatic guests. To the best of our
knowledge, however, there are only a few examples of anionic
shape-persistent macrocycles that selectively recognize elec-
2
2 4
and 5b·(Me NH ) ) was prepared in a similar manner.
2
2 4
We have reported that cyclic spiroborate trimer rac-6·
Me NH ) was formed when 1a′ was treated with an
(
3
2
2 3
tron-deficient or cationic aromatic guests. The combination of
4b
equimolar amount of boric acid in DMF (Scheme 2). This
system involved only 1a′ as a sole bis(dihydroxyarene)
component and gave thermodynamically stable cyclic trimer
cationic and anionic macrocycles is expected to afford new
supramolecular higher-order architectures.
Previously, we have reported that rac-2,2′,3,3′-tetrahydroxy-
3−
1
6
as the main product in low isolated yield (∼20%). By H
1
,1′-binaphthyl reacts with an equimolar amount of boric acid
3−
NMR monitoring, 1a′ was converted into 6 after stirring with
boric acid in DMF at 150 °C for 24 h, although some
byproducts were also formed (Figure 1). In contrast, sufficient
conversion into nanocycle 4a4 took place by the addition of an
equimolar amount (based on 1a′) of 3 and additional boric
acid, and 63 almost completely disappeared, indicating that the
in N,N′-dimethylformamide (DMF) to afford a cyclic trimeric
structure in a self-organized manner via the formation of
4
spiroborate linkages. The tris(spiroborate) cyclophane is
−
trianionic and sufficiently shape-persistent to form a rigid
triangular structure. As the next step, we intend to apply our
spiroborate strategy to the multicomponent construction of
supramolecular structures. Herein we present the preparation
of the shape-persistent spiroborate nanocycles by the use of two
different bis(dihydroxyarene) derivatives and boric acid. We
also demonstrate the construction of a Matryoshka-type,
nestable guest@ring@ring associate via the multilayered
molecular recognition of the spiroborate nanocycle and the
blue box derivatives.
−
4
−
construction of nanocycle 4a was more favorable than the
formation of cyclic trimer 6 . Rotational freedom of three 1a′
3−
3
−
would prevent the sufficient convergence into 6 , whereas the
intervention of 3 diminished the structural flexibility of the
Received: March 14, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.5b00747
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 1
1
Figure 1. Partial H NMR spectra (500 MHz, 25 °C in DMF-d ) of
7
(
a) 1a′ (40 mM); (b) 1a′ (40 mM) and B(OH) (40 mM) after
heating at 150 °C for 24 h; and (c) adding 3 (40 mM), and B(OH)
3
3
(
40 mM) to (b), and then heating at 150 °C for an additional 3 h. A
signal marked by a blue triangle was assigned to the proton derived
from 3.
4−
intermediates and led to the efficient formation of 4a . The
multicomponent construction of various spiroborate higher-
ordered structures can be realized by the rational design of
bis(dihydroxyarene) components.
4−
The precise structure of spiroborate nanocycle 4a was
determined by single crystal X-ray diffraction analysis in the
5
form of its tetra(n-butyl)ammonium (TBA) salt (Figure 2). It
Figure 2. Crystal structure of spiroborate nanocycle 4a·(TBA) . Top
4
+
(
(
a) and front (b) views. Counterions (TBA ) and solvent molecules
DMF) are omitted for clarity.
Scheme 2
was confirmed that 1a′ and 3 were alternatively bound through
a spiroborate linkage to form a rectangular macrocycle bearing
a thin box-shaped cavity. The distance between the centers of
the two anthraquinone units was estimated to be 7.7 Å, whereas
the distance between the two centroids of the upper and lower
4
−
naphthalene rings was found to be 8.7 Å. The cavity size of 4a
would be varied over a certain range and able to fit aromatic
guests.
The guest inclusion behavior of spiroborate nanocycle 4b4
−
was evaluated by the use of 1,2-bis(4-pyridyl)ethylene (7) and
2
+
1
,2-bis(4-(1-methylpyridinium))ethylene dication (8 ) as
electrically neutral and cationic guests, respectively (Figure
1
3
). In H NMR measurement, almost no interaction was
4−
observed between 4b and 7, whereas a significant upfield shift
and signal broadening were found upon mixing 8 and 4b in
2+
4−
DMSO-d , indicating selective molecular recognition of the
6
B
DOI: 10.1021/acs.orglett.5b00747
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Organic Letters
Letter
Figure 3. Chemical structure of 7, 8·(PF ) , 9·(TBA) , 10·(PF ) , and
6
2
2
6 4
1
1.
1
Figure 4. Partial H NMR spectra (500 MHz, 25 °C in DMSO-d ) of
6
cationic guest (Figure S1). The upfield shift of the
anthraquinone proton signals and the downfield shift of the
(
a) 5b·(Me NH ) (0.5 mM); (b) 10·(PF ) (0.5 mM); (c) 11 (0.5
2 2 4 6 4
mM); (d) 10·(PF ) (0.5 mM) and 11 (0.5 mM); (e) 5b·(Me NH )
6
4
2
2
4
4−
phenylene proton signals were also observed for 4b , implying
(
0.5 mM) and 10·(PF ) (0.5 mM); and (f) 5b·(Me NH ) (0.5 mM),
6 4 2 2 4
4
−
2+
that nanocycle 4b recognized 8 inside the cavity. This is
also supported by the fact that a only small upfield shift and
broadening was observed when 8·(PF ) was treated with
1
0·(PF ) (0.5 mM), and 11 (0.5 mM). Signals marked by an asterisk
6 4
(*) are assigned to impurities.
6
2
acyclic bis(spiroborate) 9·(TBA) , probably indicating the
shift of the methylene proton signals of 104+ was preserved
2
existence of electrostatic and weak π−π interactions (Figure
S2). The cyclic structure would be essential for sufficient host−
guest interaction. According to the Job plot, the association
4+
after the addition of 11. These data implied that 10 was
4−
incorporated into the cavity of 5b while keeping its
association with 11. This was confirmed by an NOESY
ratio of 4b4 and 8 was estimated to be 1:2 (Figure S3). The
−
2+
experiment, in which multiple correlations were observed
4
−
width of the cavity of 4b was estimated to be ca. 18 Å and
enough to incorporate two 8 . The electrostatic balancing also
4−
4+
4+
between 5b and 10 , and 10 and 11 in their 1:1:1 mixture
2
+
(
(
Figure S6). The cold spray ionization mass spectrometry
might cause this stoichiometry.
CSI-MS) experiment also supported their multicomponent
4
−
Spiroborate nanocycle 5 possessed a larger ring size and
was expected to exhibit different molecular recognition
7
association behavior. When a mixture of 5b·(Me NH ) , 10·
(
2
2 4
PF ) , and 11 in DMF/MeOH was sprayed in the positive-ion
6 4
4−
behavior from 4 . The distance between the two anthraqui-
mode at rt, a series of signals corresponding to the 1:1:1
none units of spiroborate nanocycle 54 was estimated to be ca.
−
4−
4+
complex of 5b , 10 , and 11 were detected (Figure S7).
1
4−16 Å by a provisional molecular modeling study, which
4−
4+
The complexation mode of 5a , 10 , and 11 was
would be suitable for the incorporation of three aromatic
planes. According to this estimation, we tried to employ the
vinylogous analog of the blue box (10 ) as a guest, which was
proven to well recognize aromatic compounds in its electron-
deficient cavity to form three-layered tetracationic aromatic
unambiguously determined by X-ray crystallographic analysis
(
Figure 5). The Matryoshka-type, nestable guest@ring@ring
4
+
2c
6
1
stacks (Figure 3). By H NMR measurement, it was confirmed
4
+
that the proton signals of both 10 and naphthalene (11) were
shifted when the two compounds were mixed in DMSO-d6,
indicating that their association took place (Figure 4d). The
precise structure of the associate was determined by single
crystal X-ray diffraction analysis, showing that 11 was
4
+
incorporated inside the cavity of 10 (Figure S5). It was also
found that 104 acted as a guest for the tetraanionic spiroborate
+
4
−
nanocycle. In the presence of 5b , All the proton signals of
1
4+
0 , including the methylene protons located outside its cavity,
were shifted upfield while keeping the symmetricity of the
spectrum (Figure 4e). A further upfield shift (h and i) and
Figure 5. Crystal structure of 11@10@5a. Top (a) and front (b)
views shown by stick model, and (c) bird’s eye view shown by a space
filling model. 5a , 10 , and 11 are drawn in red, blue, and green,
respectively. Solvent molecules (DMF) and excess 11 are omitted for
clarity.
4+
4
−
4+
slight downfield shift (k) of the proton signals of 10 , similar
to those in Figure 4d, were observed when 11 was added to the
mixture of 5b4 and 10 (Figure 4f). In addition, the upfield
−
4+
C
DOI: 10.1021/acs.orglett.5b00747
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Organic Letters
Letter
structure was constructed to afford a pentalayered aromatic
4416−4439. (d) Iyoda, M.; Yamakawa, J.; Rahman, M. J. Angew.
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8
stack. All the longitudinal axes of the two anthraquinone
4
−
(2) (a) Odell, B.; Reddington, M. V.; Slawin, A. M. Z.; Spencer, N.;
Stoddart, J. F.; Williams, D. J. Angew. Chem., Int. Ed. Engl. 1988, 27,
moieties of 5a , the two vinylenebispyridinium moieties of
4+
1
0 , and 11 were almost parallel, and the distance of each pair
1
547−1550. (b) Ashton, P. R.; Odell, B.; Reddington, M. V.; Slawin,
A. M. Z.; Stoddart, J. F.; Williams, D. J. Angew. Chem., Int. Ed. Engl.
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of the adjacent aromatic planes was ca. 3.5 Å, which would be
suitable for aromatic π−π interaction. In addition, the π−π and
methylene CH−π interactions between the diphenylethynyl
1
́
linkage of 5a4 and the p-xylylene linkage of 10 , and the
−
4+
aromatic CH−π interactions between the p-xylylene linkage of
̌
4+
10
and 11, were also found. Those interactions would be
Giesener, M. A.; McGrier, P. L.; Bruns, C. J.; Stern, C. L.; Sarjeant, A.
important for the parallel association of 11@10@5a.
A.; Stoddart, J. F. J. Am. Chem. Soc. 2013, 135, 183−192.
(3) (a) McCord, D. J.; Small, J. H.; Greaves, J.; Van, Q. N.; Shaka, A.
In summary, we have reported the preparation of shape-
4−
4−
J.; Fleischer, E. B.; Shea, K. J. J. Am. Chem. Soc. 1998, 120, 9763−9770.
b) Abrahams, B. F.; Price, D. J.; Robson, R. Angew. Chem., Int. Ed.
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persistent tetraanionic spiroborate nanocycles 4 and 5 by
reacting bis(dihydroxynaphthalene) (1,2) with tetrahydroxy-
anthraquinone 3 in the presence of boric acid in a self-
(
2
̈
4
−
organized manner. Spiroborate nanocycle 4b exhibited
1
molecular recognition ability toward cationic aromatic guest
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+
4−
8
, whereas no interaction was observed between 4b and
9
803.
4−
electrically neutral guest 7. Spiroborate nanocycle 5 , bearing a
larger ring size, also showed inclusion behavior toward its
cationic guest. The vinylogous analog of cyclobis(paraquat-p-
(4) (a) Danjo, H.; Hirata, K.; Yoshigai, S.; Azumaya, I.; Yamaguchi,
K. J. Am. Chem. Soc. 2009, 131, 1638−1639. (b) Danjo, H.; Mitani, N.;
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phenylene) 104 was incorporated into 5 to form 10@5, a
+
4−
(
5) CCDC-1045666 (10@5b), 1045667 ([11@10]·(PF ) ),
6 4
supramolecular ring@ring structure. Furthermore, a three-
4
−
4+
1045668 (11@10@5), 1045669 (4a·(TBA) ), and 1045670 (9·
4
component association was realized by mixing 5 , 10 , and
naphthalene (11) to form 11@10@5 as a Matryoshka-type,
nestable guest@ring@ring supramolecular structure. The
formation of these associates was observed in solution and
the solid state by NMR, CSI-MS, and X-ray crystallographic
analyses.
(
TBA) ) contain the supplementary crystallographic data for this
2
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ASSOCIATED CONTENT
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0]·(PF ) , 10@5b, and 11@10@5a in the form of single-
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AUTHOR INFORMATION
Corresponding Author
■
4
(
*E-mail: danjo@konan-u.ac.jp.
L.; Sarjeant, A. A.; Cao, D.; Stoddart, J. F. Chem.Eur. J. 2012, 18,
Notes
202−212.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by The Hirao Taro Foundation of the
Konan University Association for Academic Research. We
thank Drs. G. Ueno, N. Mizuno, and S. Baba (Japan
Synchrotron Radiation Research Institute (JASRI)) for
invaluable help in data collection in the X-ray analysis of 9·
(
TBA) , [11@10]·(PF ) , 10@5b, and 11@10@5a. The
2 6 4
synchrotron radiation experiment was performed at the
BL26B2 and BL38B1 stations of SPring-8 with the approval
of JASRI (Proposal Nos. 2014A1214 and 2014B1423).
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DOI: 10.1021/acs.orglett.5b00747
Org. Lett. XXXX, XXX, XXX−XXX