Complexation of triptycene-derived macrotricyclic host with bisparaquat derivative and self-folding guest: A switchable process controlled by K + ions

Article abstract of DOI:10.1002/cjoc.201300202

Triptycene-derived cylindrical macrotricyclic host with two dibenzo-30-crown-10 cavities could form stable 1:1 complexes with not only polyether linked bisparaquat derivative but also a self-folding A-D-A guest in solution and/or solid state. Moreover, it

Full text of DOI:10.1002/cjoc.201300202

FULL PAPER
DOI: 10.1002/cjoc.201300202
Complexation of Triptycene-Derived Macrotricyclic Host with
Bisparaquat Derivative and Self-Folding Guest: A Switchable
Process Controlled by K＋ Ions
Ying Han,a,b Jiabin Guo,a Jing Cao,a and Chuanfeng Chen*,a
a Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
b University of Chinese Academy of Sciences, Beijing 100049, China
Triptycene-derived cylindrical macrotricyclic host with two dibenzo-30-crown-10 cavities could form stable
1∶1 complexes with not only polyether linked bisparaquat derivative but also a self-folding A-D-A guest in solu-
tion and/or solid state. Moreover, it was found that switchable processes between the host and both the bisparaquat
derivative and the self-folding guest could be further controlled by potassium ions.
Keywords complexation, macrotricyclic host, paraquat, triptycene, switchable
Introduction
foldamers used as guests in host-guest systems were
reported.[8] This new host-guest complexation could
find potential applications in molecular assembly and
molecular machines.
In host-guest chemistry, it is always attractive and
challenging for a synthetic macrocyclic host with the
capability of binding different kinds of organic guests in
different complexation modes,[1,2] because such a syn-
thetic host could provide a lot of opportunities in mo-
lecular recognition and self-assembly. Moreover, a ma-
crocyclic host, which can encapsulate two or more
same[3] or different[4] guests inside its cavity, is also
powerful in developing various supramolecular systems
with specific structures and properties.
In previous work, we reported a novel triptycene-
derived macrotricyclic host 1[5] with two dibenzo-30-
crown-10 cavities and one central cavity, and found that
it could form 1∶2 stable complexes with two same
molecules of paraquat derivatives, such as 2.[6] As a
continuing work, we herein report the complexation of
the host 1 with guest 3 (Figure 1) in which two paraquat
subunits were linked by a flexible polyether chain, and a
self-folding A-D-A guest 4 which contains two paraquat
subunits and a naphthalene group. It was unexpectedly
found that host 1 and guest 3 could form a 1∶1 com-
plex 1·3 in both solution and solid state, in which the
guest adopts an ‘S’ conformation. Moreover, self-fold-
ing guest 4 could also be included in the cavity of host 1
to form a stable 1∶1 complex 1·4, and a potassium ion
controlled switchable process in the complex was
achieved as well. Although foldamers have attracted
much attention in the past two decades,[7] to our knowl-
edge, few examples on self-folding molecules or
Experimental
Melting points, taken on an electrothermal melting
point apparatus, are uncorrected. 1H NMR and 13C
NMR spectra were recorded on a DMX300 NMR.
Tetramethylsilane (TMS) was used as an internal stan-
dard, with chemical shifts expressed in parts per million
(ppm) downfield from the standard. MALDI-TOF mass
spectra were obtained on a BIFLEXIII mass spectrome-
ter. ESI mass spectra were obtained on a Finnigan Sur-
veyor MSQ Plus mass spectrometer. Elementary analy-
ses were performed in the Analytic Laboratory of this
Institute. Flash column chromatography was carried out
with silica gel (100－200 mesh). Other reagents and
solvents were purchased from common commercial
sources, and were used as received or purified by distil-
lation from appropriate drying agents.
Compounds 4,[8] 5[9] and 6[3j] were prepared accord-
ing to the published procedures
Synthesis of compound 3 A mixture of compound
5 (0.377 g, 0.75 mmol) and 1-(2-methoxyethyl)-4,4'-
bipyridine hexafluorophosphate 6 (0.54 g, 1.5 mmol) in
CH3CN (30 mL) was refluxed for 72 h. The resulting
mixture was concentrated under reduced pressure, and
yellow oil was obtained, which was dissolved in acetone
*
E-mail: cchen@iccas.ac.cn
Received March 14, 2013; accepted April 21, 2013; published online April 29, 2013.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201300202 or from the author.
Chin. J. Chem. 2013, 31, 607—611
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Han et al.
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H3
H2
+
N
2PF6
+
N
O
O
-
H1
2
10 H11
H8
H
O
O
H9
O
O
O
O
O O
O
+
N
+
N
O
O
O
O
O
O
O
H13
H14
O O
H12
O
O
O
O
O
O
O
O
O
N+
N+
-O
4PF6
1
4
H4
H6 H7
H5
+
N
4PF6
+
N
+
N
O
O
+
N
O
O
O
-
3
Figure 1 Structures and proton designations of host 1, and guests 2－4.
Scheme 1 Synthesis of guest 3
and then treated with NH4PF6. After the solution was
stirred at ambient temperature until clear, the solvent
was removed, and the solid precipitate was collected by
filtration, washed with water, and then dried under vac-
uum to yield 0.76 g (87%) of compound 3 as a pale yel-
TsCl/Et3N/DMAP/CH2Cl2
HO
O
OH
O
O
90%
+
O
N
N
1
low solid. M.p.: 183－185 ℃. H NMR (300 MHz,
-
PF6
6
CD3COCD3-d6) δ: 3.37 (s, 6H), 3.58 (dd, J＝5.6, 3.3 Hz,
4H), 3.69 (dd, J＝5.6, 3.3 Hz, 4H), 4.00－4.10 (m, 4H),
4.10－4.20 (m, 4H), 5.03－5.20 (m, 4H), 8.79 (d, J＝
5.7 Hz, 8H), 9.34 (d, J＝5.6 Hz, 8H). 13C NMR (75
MHz, CD3COCD3-d6) δ: 59.1, 62.7, 69.8, 70.9, 71.0,
71.2, 127.7, 127.8, 147.4, 151.2. ESI-MS m/z: 440.7
[M − 2PF− ]2＋ , 245.9 [M − 3PF− ]3＋ , 148.0 [M−
TsO
O
OTs
3
O
O
CH3CN
87%
5
reacted with 1-(2-methoxyethyl)-4-(pyridin-4-yl)pyri-
dinium 6 to afford compound 3 in 87% yield. Com-
pound 3 was characterized by H NMR, 13C NMR, MS
1
6
6
4PF− ]4＋ . Anal. calcd for C34H46F24N4O5P4•H2O: C
spectrum, and elemental analysis.
6
34.36, H 4.07, N 4.71; found C 34.03, H 3.90, N 4.87.
Complexation between triptycene-derived macrotri-
cyclic host and guest 3
Crystal data for complex 1·3 CCDC 932062,
C
114H114F24N6O25P4, Mw＝2578.23, crystal size 0.20×
0.15×0.1 mm3, monoclinic, space group P2(1)/n, a＝
16.591(3) Å, b＝20.184(4) Å, c＝19.083(4) Å, α＝90°,
β＝94.52(3)°, γ＝90°, V＝6370(2) Å3, Z＝2, Dc＝1.344
Mg/m3, T＝173(2) K, μ＝0.163 mm−1, 11449 reflec-
tions measured, 11146 unique (Rint＝0.1844), final R
indices [I＞2σ(I)]: R1＝0.1934, wR2＝0.4488, R indices
(all data): R1＝0.2561, wR2＝0.4853.
With the guests in hand, the complexation between
host 1 and guest 3 in solution was then investigated. As
1
shown in Figure 2, the H NMR spectrum of a 1∶1
mixture of 1 and 3 in CD3CN/CDCl3 (1∶1, V∶V) ex-
hibited great difference from those for 1 and 3. The H1
proton signal of the benzene ring in 1 showed an obvi-
ous upfield shift, which might be attributed to the π-π
interaction between the electron-rich triptycene moiety
and the electron-poor paraquat moieties. Similarly, the
protons H4, H5, H6 and H7 also shifted upfield due to
their positions in the shield region of the aromatic rings
of host 1. These observations indicated that host 1 and
guest 3 formed a stable complex, and both of the
paraquat rings in 3 were included in the cavity of 1.
Furthermore, a quantitative estimate between 1 and 3
was determined by the 1H NMR spectroscopic titrations.
Consequently, a 1∶1 complex 1·3 was formed by
Results and Discussion
Synthesis of guest 3
Synthesis of guest 3 was outlined in Scheme 1.
Starting from the tetraethylene glycol, the bisparaquat
derivative 3 linked by a polyether chain was conven-
iently synthesized in two steps. First, reaction of the
tetraethylene glycol and tosyl chloride in the presence of
Et3N and DMAP gave compound 5, which was then
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Chin. J. Chem. 2013, 31, 607—611

Complexation of Triptycene-Derived Macrotricyclic Host with Bisparaquat Derivative
C－H…O hydrogen bonding interactions between the
protons of the guest and the polyether oxygen atoms of
the DB30C10 moiety with the distances of 2.55 (c), 2.42
(d), 2.63 (e), 2.45 (f), 2.26 (g), 2.50 (h), 2.64 (i), and
2.62 Å (j), respectively. These multiple intermolecular
interactions might play an important role in formation of
complex 1·3.
Complexation between triptycene-derived macrotri-
cyclic host and self-folding A-D-A guest 4
Formation of complex 1·3 stimulated us to further
design and synthesize guest 4 containing two paraquat
subunits and a naphthalene group, and investigated the
complexation between host 1 and guest 4. Similar to
Figure 2 Partial 1H NMR spectra (300 MHz, 298 K, CD3CN∶
CDCl3＝1∶1, V∶V) of (a) free 1, (b) 1 and 1.0 equiv. of 3, (c)
free 3. [1]0＝3.0 mmol/L.
1
that of 1 and 3, the H NMR spectral experiments (Fig-
ure 4) showed that a stable 1∶1 complex between host
1 and guest 4 in solution was formed, and the com-
plexation between 1 and 4 was also a fast exchange
process. Correspondingly, the H1 proton signal of the
benzene ring in 1 showed an upfield shift, while the H8,
H9, H10 and H11 proton signals of the bipyridinium, and
the H12, H13 and H14 proton signals of the naphthalene
group in guest 4 all shifted upfield as well, which were
attributed to their positions in the shield region of the
aromatic rings of host 1. Moreover, the association con-
stant for 1·4 was calculated to be 1.00(±0.03)×103
L•mol−1.[10] The 2D ROESY spectral experiment of
complex 1·4 was further carried out to investigate the
interactions between the two components. The results[10]
showed that the NOE effects between protons H8, H11 of
the guest and the crown protons of the host were ob-
served, respectively, which suggested that self-folding
A-D-A guest 4 could be included in the cavity host 1,
and the bipyridinium ring of 4 might be more closed to
the crown ether units of 1.
monitoring the changes of the chemical shift of proton
H1. Accordingly, the average association constant Kav
for the 1∶1 complex 1·3 was calculated to be 1.39
(±0.04)×103 L•mol−1.[10,11]
Formation of complex 1·3 was also supported by the
electrospray ionization mass spectrum (ESI-MS).[10] As
a result, the strong peaks at m/z 1103.6, 687.4, 479.6 for
[1⋅ 3 − 2PF− ]2＋ , [1⋅ 3 − 3PF− ]3＋ , [1⋅ 3 − 4PF− ]4＋ , re-
6
6
6
spectively, were observed, which was consistent with
formation of complex 1·3.
Fortunately, we obtained the single crystal of com-
plex 1·3, and its X-ray crystal structure provided further
evidence for formation of complex 1·3. As shown in
Figure 3, guest 3 was included in the central cavity of
host 1 to form a 1∶1 complex, which is consistent with
that in solution. In complex 1·3, host 1 adopts a sym-
metrical conformation, while the guest molecule existed
as an S-type structure with two paraquat moieties situ-
ated at the sides of the crown ether moieties of the host,
respectively. The complex was stabilized by multiple
non-covalent interactions, including the multiple C－
H…π interactions between the protons of ether chain of
3 and the aromatic rings of the triptycene skeleton of 1
with the distances of 2.88 (a), and 2.76 Å (d); multiple
Figure 4 Partial 1H NMR spectra (300 MHz, 298 K, CD3CN∶
CDCl3＝1∶1, V∶V) of (a) free 1, (b) 1 and 1.0 equiv. of 4, (c)
free 4. [1]0＝3.0 mmol/L.
The ESI-MS of complex 1·4[10] showed the strong
peaks at m/z 536.82 and 763.93 for [1·4− 4PF− ]4＋ and
6
[1·4− 3PF− ]3＋ , respectively, which provided another
6
evidence for formation of the complex.
Figure 3 Side view (a) and top view (b) of the crystal structure
of complex 1·3. Dotted lines denote the non-covalent interactions.
In addition, we also tried to obtain the single crystal
of complex 1·4 suitable for X-ray diffraction analysis
for several times, but they were all unsuccessful. Instead,
Solvent molecules, PF− counterions, and hydrogen atoms not
6
involved in the non-covalent interactions are omitted for clarity.
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© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Han et al.
FULL PAPER
we obtained the crystal structure of guest 4,[8] which
showed that it adopts an S-type self-folding structure
stabilized by a couple of C－H…F interactions between
the methylene protons of the linked ether chain and the
fluorine atoms, and also the anion-π interactions be-
rived macrotricyclic host 1 with two dibenzo-30-crown-
10 cavities could form stable 1∶1 complexes with not
only the bisparaquat derivative 3 linked by a polyether
chain in both solution and solid state, but also a self-
folding A-D-A guest 4. Moreover, potassium ion con-
trolled switchable processes between the host and both
bisparaquat derivative 3 and the self-folding guest were
also achieved. Based on these developed host-guest
systems, our further studies will focus on the applica-
tions of the novel synthetic host in molecular assembly
and molecular machines, which are now in progress.
tween PF− and two bipyridinium rings of 4. This spe-
6
cific self-folding structure benefited it to be included by
host 1 with a large central cavity.
K＋ ion-controlled binding and release of the guest in
the complex
Moreover, we also investigated the potassium ions
controlled switchable process between the host and the
Acknowledgement
1
self-folding guest by a series of H NMR experiments
(Figure 5). Consequently, it was found that the 1H NMR
spectrum of a 1∶1 mixture of 1 and guest 4 showed
formation of complex 1·4. When six equivalents of
KPF6 was added to the above solution, the proton sig-
nals of the complex totally disappeared, while the pro-
ton signals of guest 4 and the aromatic proton signals of
the host all shifted downfield almost to the original po-
sitions (Figure 5c). These indicated that complexation
between the crown ethers and the potassium ions oc-
curred, which resulted in the release of the cationic or-
ganic guest 4 from the cavity of the host. When 8
equivalents of 18-crown-6 was then added to the above
system, it was found that the proton signals of complex
1·4 recovered (Figure 5d), suggesting complex 1·4
formed again. Thus, the release and binding process of
the self-folding A-D-A guest 4 in the complex could be
easily controllable switched by addition and removal of
the potassium ions. Similarly, K＋ ion-controlled bind-
ing and release of guest 3 in complex 1·3 was also
found.[10]
We thank the National Natural Science Foundation
of China (Nos. 20972162, 91127009), and the National
Basic Research Program (No. 2011CB932501) for fi-
nancial support.
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