Unidirectional Threading into a Bowl-Shaped Macrocyclic Trimer of Boron–Dipyrrin Complexes through Multipoint Recognition

Article abstract of DOI:10.1002/anie.201603821

Bowl-shaped macrocycles have the distinctive feature that their two sides are differentiated, and thus can be developed into elaborate hosts that fix a target molecule in a controlled geometry through multipoint interactions. We now report the synthesis of a bowl-shaped macrocyclic trimer of the boron–dipyrrin (BODIPY) complex and its unidirectional threading of guest molecules. Six polarized B^δ+?F^δ-bonds are directed towards the center of the macrocycle, which enables strong recognition of cationic guests. Specifically, the benzylbutylammonium ion is bound in a manner in which the benzyl group is located at the convex face of the bowl and the butyl group at its concave face. Furthermore, adrenaline was strongly captured on the convex side of the bowl by hydrogen bonding, Coulomb forces, and C?H???π interactions.

Full text of DOI:10.1002/anie.201603821

Angewandte
Communications
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International Edition: DOI: 10.1002/anie.201603821
German Edition: DOI: 10.1002/ange.201603821
Molecular Recognition
Hot Paper
Unidirectional Threading into a Bowl-Shaped Macrocyclic Trimer of
Boron–Dipyrrin Complexes through Multipoint Recognition
Takashi Nakamura, Gento Yamaguchi, and Tatsuya Nabeshima*
Abstract: Bowl-shaped macrocycles have the distinctive
feature that their two sides are differentiated, and thus can be
developed into elaborate hosts that fix a target molecule in
a controlled geometry through multipoint interactions. We now
report the synthesis of a bowl-shaped macrocyclic trimer of the
boron–dipyrrin (BODIPY) complex and its unidirectional
À
threading of guest molecules. Six polarized Bd+
F
d- bonds are
directed towards the center of the macrocycle, which enables
strong recognition of cationic guests. Specifically, the benzyl-
butylammonium ion is bound in a manner in which the benzyl
group is located at the convex face of the bowl and the butyl
group at its concave face. Furthermore, adrenaline was
strongly captured on the convex side of the bowl by hydrogen
À
bonding, Coulomb forces, and C H···p interactions.
U
nidirectional guest binding is an important and challeng-
ing topic, not only in terms of precise molecular recognition,
but also for the development of elaborate artificial nano-
machines that achieve regulated motions.[1] Macrocyclic
compounds have often been employed as components of
molecular machines, such as rotaxanes, and their shape is
a fundamental factor to create the functions.[2] In contrast to
planar molecules, nonplanar macrocyclic hosts can interact in
a different way with guests on the two sides. Classical
examples of nonplanar bowl-shaped macrocycles are cyclo-
dextrins[3] and calixarenes.[4] Their unsymmetrical structures
gave rise to unidirectional threading of designed axle
molecules of (pseudo)rotaxanes.[5,6] However, they often
suffer from inversion of the bowl because of their flexibility,
or from the two sides of the macrocycles being very similar.
These issues adversely affect the binding ability and precisely
regulated molecular motions.
Figure 1. a) Difference in shape of para-phenylene-linked cyclic dipyr-
rin/BODIPY trimers and meta-phenylene-linked ones. b) Meta-phenyl-
ene-linked L-shaped dipyrrin trimer 1 and bowl-shaped BODIPY trimer
2. TFA=trifluoroacetic acid, DDQ=2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone.
(ca. 1208)[10] instead of para-phenylene ones (ca. 1808)[9,11]
would result in trimeric macrocyclic frameworks with non-
planar, distorted shapes, because the sum of the interior
angles of the macrocycle would not be suitable for the
formation of planar polygons (Figure 1a). Herein, we report
the synthesis of a meta-phenylene-linked dipyrrin trimer 1,
and a bowl-shaped BODIPY trimer 2 formed by the reaction
of 1 with BF3·Et2O (Figure 1b). We also investigated the
ability of 2 to form an oriented [2]pseudorotaxane by
unidirectionally threading an ammonium guest.
We focused on boron–difluoride complexes of dipyrrins
(BODIPY)[7] as a constituent unit of the macrocycles.[8] We
previously reported trimeric macrocycles of dipyrrin/
BODIPY linked through its 3,5-positions by para-phenylene
moieties.[9] The macrocycles had planar triangular shapes as
a corollary of the angle of each unit (Figure 1a). We
envisaged that the employment of meta-phenylene linkers
A dipyrrin trimer 1 was synthesized in 16% yield by the
TFA-catalyzed condensation of a 2,6-bis(2-pyrrolyl)anisole
(5) and mesitaldehyde. The 1H NMR spectrum of 1 recorded
at 238 K showed three signals for the methoxy protons, thus
suggesting that the cyclic trimer lost its apparent C3 symmetry
(Figure 2a,b). A single-crystal X-ray diffraction analysis
revealed the unique L-shaped structure of 1 (Figure 2c,d).
The two dipyrrin moieties (denoted as units 2 and 3 in
Figure 2a,b and depicted in blue and red, respectively) and
one methoxyphenyl ring (unit 3) deviated significantly from
the plane. Another characteristic is that one pyrrole ring of
[*] Dr. T. Nakamura, G. Yamaguchi, Prof. Dr. T. Nabeshima
Graduate School of Pure and Applied Sciences and Tsukuba Research
Center for Interdisciplinary Materials Science (TIMS)
University of Tsukuba
1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571 (Japan)
E-mail: nabesima@chem.tsukuba.ac.jp
Homepage: http://www.chem.tsukuba.ac.jp/nabesima/en/
index.html
1
a dipyrrin (unit 3) was inverted. All the H NMR signals of
1
1 were assigned on the basis of H-1H COSY and ROESY
NMR measurements (see Figures S4 and S5 in the Supporting
Information). Characteristic transannular ROE effects (e.g.
a3-b2’) indicated that the solution structure of 1 is basically the
same as that obtained by the X-ray analysis.
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under http://dx.doi.org/10.
1002/anie.201603821.
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rotation of the phenylene spacers was restricted by steric
À
hindrance of the B F units, thus the conformation was fixed
into a bowl shape. The central cavity was surrounded by F
atoms of the boron difluoride units. The distances between
any two of the three inner F atoms were 4.62–4.78 ꢀ. The two
sets of 1H signals (g,g’ and h,h’) of the mesityl groups did not
1
coalesce in the H NMR measurement at 1158C in 1,1,2,2-
[D2]tetrachloroethane, and no EXSY cross-peaks were
observed between them in the NOESY NMR spectrum at
the same temperature (mixing time, 1000 ms; see Figure S11).
This observation suggested that the rate of the bowl inversion
of 2 was slower than 0.02 sÀ1 at 1158C and its activation
energy (DG°) higher than 108 kJmolÀ1. The slow bowl
inversion renders 2 a promising candidate for a new kind of
nonplanar macrocyclic receptor.
The fluorine atoms of 2 accumulated in the cavity possess
d-
partial negative charges resulting from polarized Bd+
À
F
bonds (Figure 2h). This feature enables 2 to serve as an
excellent receptor for a cationic guest. Secondary ammonium
ions, in particular, were tightly bound to 2 to form a [2]pseu-
1
dorotaxane. A H NMR titration experiment of the tetrakis-
(3,5-bis(trifluoromethyl)phenyl)borate (TFPB) salt of the
dibutylammonium cation 6+ against 2 in CDCl3 unambigu-
ously determined its binding mode to be 2:6+ = 1:1 (Fig-
ure S13), and the binding constant (Ka [mÀ1]) was determined
to be logKa = 5.49(3) from a UV/Vis titration measurement
(Table 1, see Figures S14 and S15). Two sets of signals were
observed for the butyl groups of 6+ in the 1H NMR spectrum
of [6@2]+ (Figure 3c). This observation indicated that 6+
threaded through the bowl-shaped 2, with one butyl group
positioned on the concave face of 2, while the other was
positioned on its convex face. 1H-1H ROESY NMR measure-
ments of [6@2]+ (Figure 3a) showed ROE cross-peaks
between the protons of one butyl group (H5–H8) of axle 6+
and those of the meta-phenylene spacers (b,c) of the macro-
cyclic ring 2. Thus, the [2]pseudorotaxane formation shown in
Figure 3b was confirmed. Its formation was further supported
1
by a H DOSY NMR measurement, which gave the same
Figure 2. a,b) 1H NMR spectra of L-shaped dipyrrin trimer
diffusion coefficient for 6+ and 2 (D = 4.3 ꢁ 10À10 [m2 sÀ1];
Figure S19).
The bowl-shaped 2 has the potential to form an orientated
rotaxane with unsymmetrical axles by utilizing the difference
in the local environment of the convex and concave faces.
Benzylbutylammonium ion 3+ was chosen as the axle for this
purpose. The 1H NMR and UV/Vis titration experiments
1 (600 MHz, CDCl3, 238 K). c,d) The X-ray crystal structure of 1, with
ellipsoids at 50% probability. c) Top view. d) Side view. Hydrogen
atoms, solvents, and Mes groups are omitted for clarity. C: light green,
N: blue, O: red. e) 1H NMR (400 MHz) and f) 19F NMR (376 MHz)
spectra of bowl-shaped BODIPY trimer 2 (CDCl3, 298 K). g) The X-ray
crystal structure of 2, with ellipsoids at 50% probability. Hydrogen
atoms and solvent molecules are omitted for clarity. C: light green,
N: blue, O: red, B: pink, F: yellow-green. h) Electrostatic potential
surfaces of 2 obtained by DFT calculations at the B3LYP/6-31G* level
(the atomic coordinates of the crystal structure of 2 were used).
Table 1: Binding of ammonium guests to 2 (CHCl3 or CDCl3, 298 K).
Guest
labs [nm]
lem [nm]
logKa [log(mÀ1)]
The dipyrrin trimer 1 was converted into the BODIPY
trimer 2 in 79% yield on reaction with BF3·Et2O. Figure 2e
shows the 1H NMR spectrum of 2. Two signals were observed
for each proton of the mesityl groups (g,g’ and h,h’), which
suggests that 2 has C3v symmetry. The 19F NMR spectrum
showed two separated signals (À120.5, À148.9 ppm), which
also indicated that the two faces of the macrocycles were
differentiated (Figure 2 f). A single-crystal X-ray analysis of 2
clearly revealed the bowl-shaped macrocyclic structure (Fig-
ure 2g). The three BODIPY units were tilted by about 20–408
from the plane perpendicular to the apparent C3 axis. Free
none
3+
514
514
514
512
606
604
603
596
-
5.48(3)[a]
5.49(3)[a]
4.36(7)[a,c]
2.6(2)[d]
6.57(7)[a]
7.2(1)[a]
8.0(1)[b]
6+
7+
8+
–
–
[e]
[e]
9+
511
510
511
590
587
597
10+
4+
[a] Determined by UV/Vis titration. [b] Determined by competitive
1H NMR titration in the presence of 40 equiv of 3+. [c] No threading.
[d] Determined by 1H NMR titration. [e] Not measured.
2
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confirmed the 1:1 binding between 3+ and 2, with a binding
constant (logKa = 5.48(3)) similar to that of 6+ and 2
(Figures S21 and S22). The 1H NMR spectrum of [3@2]+
showed signals characteristic of 3+ threaded into 2. Remark-
ably, only one set of signals was observed for [3@2]+, which
suggests the selective formation of one conformational
isomer. Comparison of the 1H NMR chemical shifts of
[3@2]+ with those of [6@2]+ (Figure 3c,d) revealed that the
benzyl group of 3+ was on the convex side of 2, while the butyl
group of 3+ was contained within its concave cavity (Fig-
ure 3e). The selectivity of the threading direction was as high
as 97%, as determined from the integral ratios of the
1H NMR signals.
The recognition feature of the bowl-shaped BODIPY
trimer 2 was revealed by binding experiments with other
ammonium guests (Scheme 1, Table 1). The dibenzylammo-
Scheme 1. The investigated guests (used as TFPB salts). A racemic
dl-adrenaline 4+ was used in the experiment.
nium ion 7+ interacted with 2 (logKa = 4.36(7)) but did not
thread into it (Figure S24). It is considered that the benzyl
group of 7+ is too large to pass through the cavity of 2. The
binding of (admantylmethyl)butylammonium ion 8+ was also
weak (logKa = 2.6(2)), probably because the bulky adamantyl
group near the ammonium group destabilizes the formation
of the pseudorotaxane. Primary ammonium species, such as
benzylammonium ion 9+ and phenethylammonium ion 10+,
were more strongly bound (logKa = 6.57(7) and 7.2(1),
respectively) than the secondary ones (3+ and 6+). This
result is explained by the increased number of hydrogen
bonds between the ammonium NH group and the BODIPY
À
B F moieties.
Interestingly, adrenaline 4+ was bound the strongest of the
investigated ammonium guests. The interaction was so strong
that its association constant (logKa = 8.0(1)) could not be
determined by ordinary UV titration experiments; it was thus
determined by a competition experiment in the presence of an
excess amount of 3+ (Figure S34). Since the binding of
secondary ammonium species is generally weaker than
primary ones (Table 1), it is remarkable that adrenaline 4+
(secondary ammonium) exhibited such a strong association
constant. The detailed structure of the adrenaline/macrocycle
Figure 3. a) 1H-1H ROESY NMR spectrum of [6@2](TFPB) (CDCl3,
600 MHz, 263 K). b) The structure of [6@2]+ obtained by DFT calcu-
lations at the B3LYP/6-31G* level. The Mes groups and hydrogen
atoms are omitted for clarity. C of 2: light green; C of 6: magenta, O:
red, N: blue, B: pink, F: yellow-green. Pairs of protons between which
ROE cross-peaks were observed are highlighted. c,d) 1H NMR spectra
of [2]pseudorotaxanes (600 MHz, 263 K, CDCl3): c) [6@2](TFPB),
d) [3@2](TFPB). e) Schematic representation of the unidirectional
threading of benzylbutylammonium ion 3+ into the bowl-shaped
BODIPY trimer 2. f–h) The structure of [4@2]+ obtained by DFT
calculations at the B3LYP/6-31G* level. C of 2: light green, C of 4:
black, O: red, N: blue, B: pink, F: yellow-green, H: white. Mes groups
are omitted for clarity. f) Pairs of 1H-1H atoms between which cross-
peaks were observed in the ROESY NMR spectrum (Figure S35).
g) Pairs of 19F-1H atoms between which cross-peaks were observed in
the HOESY NMR spectrum (Figure S36). h) Intermolecular interac-
tions between adrenaline 4+ and BODIPY trimer 2. i,j) Comparison of
the intermolecular hydrogen bonding of adrenaline 4+ with i) BODIPY
trimer 2 and j) a b2-adrenaergic receptor protein.[12]
1
complex was unambiguously determined by H-1H ROESY
and 19F-1H HOESY NMR measurements, together with the
structure obtained by DFT calculations (Figure 3 f,g). As in
the case of benzylbutylammonium ion 3+, the benzene ring of
4+ was positioned at the convex face of 2, and the methyl
group of 4+ at the concave face. Several intermolecular
interactions contributed to the strong binding of 4+ (Fig-
ure 3h): 1) Hydrogen bonding between the ammonium NH
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group of 4+ and the BODIPY B F groups; 2) hydrogen
bonding between the hydroxy group of 4+ and the BODIPY
À
[4] A. Ikeda, S. Shinkai, Chem. Rev. 1997, 97, 1713.
[5] a) M. R. Craig, M. G. Hutchings, T. D. W. Claridge, H. L.
Anderson, Angew. Chem. Int. Ed. 2001, 40, 1071; Angew.
Chem. 2001, 113, 1105; b) Q.-C. Wang, D.-H. Qu, J. Ren, K.
Chen, H. Tian, Angew. Chem. Int. Ed. 2004, 43, 2661; Angew.
Chem. 2004, 116, 2715; c) D.-H. Qu, Q.-C. Wang, J. Ren, H. Tian,
Org. Lett. 2004, 6, 2085; d) Q.-C. Wang, X. Ma, D.-H. Qu, H.
Tian, Chem. Eur. J. 2006, 12, 1088; e) T. Oshikiri, Y. Takashima,
H. Yamaguchi, A. Harada, J. Am. Chem. Soc. 2005, 127, 12186;
f) H. Yamaguchi, T. Oshikiri, A. Harada, J. Phys. Condens.
Matter 2006, 18, S1809; g) T. Oshikiri, Y. Takashima, H.
Yamaguchi, A. Harada, Chem. Eur. J. 2007, 13, 7091; h) T.
Oshikiri, H. Yamaguchi, Y. Takashima, A. Harada, Chem.
Commun. 2009, 5515; i) J. W. Park, H. J. Song, Org. Lett. 2004, 6,
4869; j) J. W. Park, H. J. Song, H.-J. Chang, Tetrahedron Lett.
2006, 47, 3831; k) C. Casati, P. Franchi, R. Pievo, E. Mezzina, M.
Lucarini, J. Am. Chem. Soc. 2012, 134, 19108; l) Y. Akae, Y.
Koyama, S. Kuwata, T. Takata, Chem. Eur. J. 2014, 20, 17132;
m) Y. Akae, Y. Koyama, H. Sogawa, Y. Hayashi, S. Kawauchi, S.
Kuwata, T. Takata, Chem. Eur. J. 2016, 22, 5335.
[6] a) A. Arduini, F. Calzavacca, A. Pochini, A. Secchi, Chem. Eur.
J. 2003, 9, 793; b) A. Arduini, R. Bussolati, A. Credi, G. Faimani,
S. Garaudꢂe, A. Pochini, A. Secchi, M. Semeraro, S. Silvi, M.
Venturi, Chem. Eur. J. 2009, 15, 3230; c) A. Arduini, R.
Bussolati, A. Credi, S. Monaco, A. Secchi, S. Silvi, M. Venturi,
Chem. Eur. J. 2012, 18, 16203; d) A. Arduini, R. Bussolati, A.
Credi, A. Secchi, S. Silvi, M. Semeraro, M. Venturi, J. Am. Chem.
Soc. 2013, 135, 9924; e) C. Gaeta, F. Troisi, P. Neri, Org. Lett.
2010, 12, 2092; f) C. Talotta, C. Gaeta, Z. Qi, C. A. Schalley, P.
Neri, Angew. Chem. Int. Ed. 2013, 52, 7437; Angew. Chem. 2013,
125, 7585; g) C. Gaeta, C. Talotta, L. Margarucci, A. Casapullo,
P. Neri, J. Org. Chem. 2013, 78, 7627; h) R. Ciao, C. Talotta, C.
Gaeta, L. Margarucci, A. Casapullo, P. Neri, Org. Lett. 2013, 15,
5694; i) C. Gaeta, C. Talotta, P. Neri, Chem. Commun. 2014, 50,
9917.
[7] A. Loudet, K. Burgess, Chem. Rev. 2007, 107, 4891.
[8] a) C. Ikeda, T. Nabeshima, Chem. Commun. 2008, 721; b) T.
Sakida, S. Yamaguchi, H. Shinokubo, Angew. Chem. Int. Ed.
2011, 50, 2280; Angew. Chem. 2011, 123, 2328; c) Y. Yu, N.
Bogliotti, J. Tang, J. Xie, Eur. J. Org. Chem. 2013, 7749; d) T.
Nabeshima, M. Yamamura, G. J. Richards, T. Nakamura, J.
Synth. Org. Chem. Jpn. 2015, 73, 1111.
[9] a) C. Ikeda, N. Sakamoto, T. Nabeshima, Org. Lett. 2008, 10,
4601; b) N. Sakamoto, C. Ikeda, T. Nabeshima, Chem. Commun.
2010, 46, 6732.
[10] a) R. J. P. Corriu, G. Bolin, J. J. E. Moreau, C. Vernhet, J. Chem.
Soc. Chem. Commun. 1991, 211; b) F. H. Carrꢂ, R. J. P. Corriu,
G. Bolin, J. J. E. Moreau, C. Vernhet, Organometallics 1993, 12,
2478; c) J. L. Sessler, D. An, W.-S. Cho, V. Lynch, M. Marquez,
Chem. Eur. J. 2005, 11, 2001; d) J. Setsune, K. Watanabe, J. Am.
Chem. Soc. 2008, 130, 2404; e) J. Setsune, K. Yamato, Chem.
Commun. 2012, 48, 4447.
[11] J. Setsune, M. Toda, T. Yoshida, Chem. Commun. 2008, 1425.
[12] A. M. Ring, A. Manglik, A. C. Kruse, M. D. Enos, W. I. Weis,
K. C. Garcia, B. K. Kobilka, Nature 2013, 502, 575.
À
B F groups; 3) Coulomb interaction between the cationic
d-
ammonium group NH2+ of 4+ and the polarized Bd+ F bonds
À
À
of BODIPY; and 4) C H···p interactions between the ben-
zene ring of 4+ and the m-Ph spacer of 2. In terms of points (1)
and (2), one BF2 moiety undergoes a double hydrogen
bonding with the hydroxy and ammonium groups of 4+
(Figure 3h,i). This hydrogen bonding was supported by
1
strong correlations between the corresponding H-19F pairs
in the 19F-1H HOESY NMR (Figure S36) as well as no
chemical exchange of the ammonium and hydroxy protons
with H2O in the ROESY NMR spectrum (Figure S35). This
multiple hydrogen bonding is reminiscent of the recognition
mode of adrenaline 4+ by the aspartic acid and asparagine
residues in the natural b2-adrenergic receptor protein (Fig-
ure 3j).[12] Several artificial host molecules aiming at recog-
nition of adrenaline 4+ and other phenethylamine derivatives
have been reported, but it has been difficult to achieve
selective recognition through multiple intermolecular inter-
actions modes.[13] In this sense, 2 is a fresh departure from
simple artificial macrocycles that recognize guests through
nonselective interactions.
In conclusion, the L-shaped dipyrrin macrocycle 1 and
bowl-shaped BODIPY macrocycle 2 were synthesized and
their unique shapes were unambiguously determined by
various NMR techniques and single-crystal X-ray diffraction
measurements. 2 formed an oriented [2]pseudorotaxane by
unidirectionally threading ammonium guests such as benzyl-
butylammonium ion 3+ and adrenaline 4+. Multiple inter-
action modes, such as hydrogen bonding with the BODIPY
B F bonds and C H···p interactions with the aromatic
scaffold, are key to realizing the significantly strong and
regiospecific binding. This research should contribute to the
design of functional host molecules utilizing multiple inter-
action modes. In addition, the bowl-shaped ring, whose two
faces are desymmetrized, has the potential to realize one-way
movement of a molecular machine along the axle fueled by
random thermal energy. The study of such sophisticated
molecular devices is now in progress.
À
À
Acknowledgements
This research was supported by JSPS KAKENHI Grant
Numbers JP15H00723 and JP15H00914.
Keywords: boron · host–guest systems · macrocycles ·
[13] a) T. Schrader, J. Org. Chem. 1998, 63, 264; b) M. Herm, T.
Schrader, Chem. Eur. J. 2000, 6, 47; c) O. Molt, D. Rꢃbeling, G.
Schꢄfer, T. Schrader, Chem. Eur. J. 2004, 10, 4225; d) S.
Kolusheva, O. Molt, M. Herm, T. Schrader, R. Jelinek, J. Am.
Chem. Soc. 2005, 127, 10000; e) M. Maue, T. Schrader, Angew.
Chem. Int. Ed. 2005, 44, 2265; Angew. Chem. 2005, 117, 2305;
f) H. Kawai, R. Katoono, K. Fujiwara, T. Tsuji, T. Suzuki, Chem.
Eur. J. 2005, 11, 815; g) O. Danylyuk, V. P. Fedin, V. Sashuk,
Chem. Commun. 2013, 49, 1859.
molecular recognition · supramolecular chemistry
[1] a) V. Balzani, A. Credi, F. M. Raymo, J. F. Stoddart, Angew.
Chem. Int. Ed. 2000, 39, 3348; Angew. Chem. 2000, 112, 3484;
b) A. Harada, Acc. Chem. Res. 2001, 34, 456.
[2] a) E. R. Kay, D. A. Leigh, F. Zerbetto, Angew. Chem. Int. Ed.
2007, 46, 72; Angew. Chem. 2007, 119, 72; b) M. Xue, Y. Yang, X.
Chi, X. Yan, F. Huang, Chem. Rev. 2015, 115, 7398.
Received: April 20, 2016
[3] J. Szejtli, Chem. Rev. 1998, 98, 1743.
Published online: && &&, &&&&
4
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Communications
Molecular Recognition
T. Nakamura, G. Yamaguchi,
T. Nabeshima*
&&&& — &&&&
Unidirectional Threading into a Bowl-
Shaped Macrocyclic Trimer of Boron–
Dipyrrin Complexes through Multipoint
Recognition
Going in to bowl: A bowl-shaped macro-
cyclic trimer of a boron–dipyrrin complex
has been synthesized in which six polar-
are strongly captured from the convex
side of the macrocycle by hydrogen
À
bonding, Coulomb forces, and C H···p
À
ized B F bonds are directed towards the
interactions and thread unidirectionally
through the complex.
center of the macrocycle for strong
recognition. Cationic ammonium guests
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