Foldamers in pseudo[2]rotaxanes and [2]rotaxanes: Tuning the switching kinetics and metastability

Article abstract of DOI:10.1016/j.tet.2011.10.116

Hydrogen bonded arylamide foldamers have been introduced in switchable pseudo[2]rotaxanes and [2]rotaxanes, which also include a cyclobisparaquat(p- phenylene) (CBPQT⁴⁺) ring and a 'dumbbell' containing tetrathiafulvalene (TTF) and 1,5-dioxynap

Full text of DOI:10.1016/j.tet.2011.10.116

Tetrahedron 68 (2012) 4517e4527
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Foldamers in pseudo[2]rotaxanes and [2]rotaxanes: tuning the switching kinetics
and metastability
,
a
b
,
c
c,
a
Kang-Da Zhang a, Xin Zhao a , Gui-Tao Wang , Yi Liu , Ying Zhang , Hao-Jie Lu , Xi-Kui Jiang ,
*
*
*
,c,
Zhan-Ting Li a
*
a State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Lu, Shanghai 200032, China
b The Molecular Foundry, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, USA
c Chemistry of Department, Fudan University, 220 Handan Road, Shanghai 200433, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 August 2011
Received in revised form 11 October 2011
Accepted 31 October 2011
Available online 6 November 2011
Hydrogen bonded arylamide foldamers have been introduced in switchable pseudo[2]rotaxanes and [2]
rotaxanes, which also include a cyclobisparaquat(p-phenylene) (CBPQT4þ) ring and a ‘dumbbell’ con-
taining tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP, for rotaxanes). The foldamer size
changes through folding and unfolding serve as a steric handle to modulate the mechanical movement of
the CBPQT4þ ring along the dumbbell of the pseudo[2]rotaxanes and [2]rotaxanes. By varying the
number of the repeating units in the foldamer, the kinetics of the solvent-dependent slippage/deslippage
of pseudo[2]rotaxanes and the switching of the ring between TTF and DNP of the [2]rotoxanes can be
tuned remarkably, with the time scope ranging from several minutes to several days, in twelve solvents
of varying polarity, which have been confirmed by the 1H NMR, UVevis spectroscopy, and cyclic vol-
tammogram experiments.
Keywords:
Foldamer
Hydrogen bond
Molecular device
Pseudorotaxane and rotaxane
Donoreacceptor interaction
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
redox-active tetrathiafulvalene (TTF), 1,5-dioxynaphthalene
(DNP), and cyclobis(paraquat-p-phenylene) (CBPQT4þ),7 which
[2]Rotaxanes are mechanically interlocked molecular architec-
tures that consist of a linear ‘dumbbell’ component threaded
through a macrocyclic ‘ring’ component.1 The dumbbell component
is typically equipped with bulky stoppers at both ends, with size
larger than that of the ring component to prevent its extrusion.2
have been sandwiched inside molecular switch tunnel junction
(MSTJ) devices in extended cross-bar networks.7b One issue asso-
ciated with these MSTJ devices is their short lifetime due to the
relaxation of the molecules from its metastable state co-
conformation (MSCC) to the ground state co-conformation
(GSCC). In order for these MSTJ devices to store information as
non-volatile memory, one has to generate a long-lived MSCC of the
[2]rotaxanes even after removal of the bias. This could be done by
introducing a barrier between the TTF and DNP units to slow down
the back shuttling of the CBPQT4þ ring from the DNP unit to the
neutral TTF unit. The barrier should be prudently adjusted, how-
ever, to an appropriate level such that the forward shuttling of the
CBPQT4þ ring from the oxidized TTF unit to the DNP unit is not
slowed down significantly. The medium itself can affect the barrier
for the original [2]rotaxanes, with the barrier energy being from
16 kcal/mol in solution to 18 kcal/mol in polymer gel and 21 kcal/
mol in the solid state device.8 More recently, charged spacer units
have been utilized to raise the barrier for the movement of the
CBPQT4þ ring by producing an electrostatic repulsion, and an ac-
tivation barrier in solution of 19 kcal/mol is reached when a bipyr-
idinium spacer is used.7b,9 Another desirable approach is the use of
deformable foldamer spacers as steric barriers to endow extra
stability for the MSCC.
Pseudo[2]rotaxanes
are
non-stoppered
counterparts
of
rotaxanesdi.e., threaded complexes in which the linear dumbbells
bear end groups that have smaller sizes than the ring components.3
One of the most important features of pseudo-[2]rotaxanes and [2]
rotaxanes is that their ring component can extrude or shuttle along
the linear dumbbell.4 When the dumbbell component is in-
corporated with two or more ‘stations’ with different recognition
strength, selective positioning of the ring component over the
stations can be realized to give molecular systems with multiple
states.5 In the past two decades, bi- and multi-stable supramolec-
ular systems of this kind have received great attention due to their
applications in the construction of molecular machines and devi-
ces.2b,6 Particularly, the potential application in high density mo-
lecular memories concerns bistable [2]rotaxanes incorporating
* Corresponding authors. Tel.: þ86 21 54925122; fax: þ86 21 64166128; e-mail
addresses: xzhao@mail.sioc.ac.cn (X. Zhao), ztli@mail.sioc.ac.cn (Z.-T. Li).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.10.116

4518
K.-D. Zhang et al. / Tetrahedron 68 (2012) 4517e4527
Foldamers are linear molecules or oligomers that adopt a sec-
state, and are shown to display half-lives ranging from 2.7 s to more
than 22 days, depending on the length of the foldamer segment and
the polarity of the medium.16 Based on these model pseudo[2]
rotaxane systems, we have extended our studies toward bistable [2]
rotaxanes, in which a foldamer segment is incorporated to connect
a TTF unit and a DNP unit in the dumbbell component.17 The fol-
damer segments as deformable spacers are shown to effectively
tune the shuttling of the CBPQT4þ ring between the TTF, in both its
neutral and oxidized forms, and DNP units.18 Consequently, the
lifetime of the post-oxidation MSCC in solution is dramatically
increased.19
ondary structure, typically a folded or helical one, stabilized by
discrete noncovalent interactions.10e12 The folding and unfolding
process is reversible, involving either energy release or consump-
tion. The folded states, like the helix of natural peptides, have an
apparent size larger than that of the extended ones. On the base of
this feature, we have recently utilized hydrogen bonded arylamide
foldamers to tune the dynamic mechanical property of methacry-
late copolymers.13 We conjectured that, if the apparent diameter of
the extended state of a foldamer is smaller than the internal di-
ameter of a macrocycle while the diameter of its folded state is
larger, it would be possible for the macrocycle to slip over the linear
foldamer when extended. However, the slippage should be de-
celerated compared to that over a similar but flexible molecule,
because it needs to, at least partially, break the noncovalent bonds
existing in the folded state. Since the length of foldamers can be
readily modulated by simply changing the number of their re-
peating units, the folded segments could be utilized as new mod-
ular stoppers or spaces for regulating the dynamic behavior of
pseudorotaxanes or rotaxanes.
Herein, we describe a systematic investigation of the kinetic
properties of two series of foldamer-containing interlocked species,
which are stabilized by the intermolecular donoreacceptor in-
teraction between the TTF unit and the CBPQT4þ ring.14,15 The first
series are pseudo[2]orotaxanes where a hydrogen bonding-driven
arylamide foldamer segment is attached as stopper at one of the
two ends of the dumbbell component. Three of these threaded
complexes can be isolated as stable pseudo[2]rotaxanes in the solid
2. Results and discussion
2.1. Design and synthesis
Chart 1 lists the structures of foldamer-containing pseudo-[2]
rotaxanes 1aed and bistable [2]rotaxanes 2a and 2b, and the cor-
responding dumbbell components 3aed, 4a, and 4b. We chose to
utilize the well-known TTF-CBPQT4þ donoreacceptor recognition
motif for the present study because (i) the donoreacceptor in-
teraction lives in both polar and less polar solvents, (ii) TTF unit has
reversible redox behavior, and (iii) the kinetics related to this motif
can be investigated using UVevis, 1H NMR, and cyclic voltammo-
gram techniques. Because the foldamer conformation is highly
solvent dependant, the solubility control was crucially important
for the investigation of the effect of the foldamer segments on the
ꢀ
dynamic properties of the threaded complexes. The large Frechet-
+
N
+
N
O
N
S
S
S
S
S
O
O
O
O
O
[G-3]O
O
O
O
S
H
O
O
n
Me
N
H
O
O
-
4PF6
N
N
+
1a: n = 0
1b: n = 1
1c: n = 2
1d: n = 3
O
O
+
Me
O
O
O
O
OMe
O
O
+
N
+
N
=
[G-3]
O
N
S
S
S
S
S
O
O
O
O
[G-3]O
O
O
O
O
S
H
O
O
O
n
Me
Me
H
O
N
N
-
2a: n = 0
2b: n = 1
4PF6
N
+
N
+
O
O
Me
O
H
H
N
O
O
O
O
OMe O
OMe O
O
O
O
O
O
S
S
H
N
[G-3]O
3a: n = 0
3b: n = 1
3c: n = 2
S
S
S
O
S
S
O
O
O
O
O
N
H
S
O
O
OMe OMe 3d: n = 3
n
n
H6
H7
O
O
H
N
[G-3]O
O
S
S
S
S
O
N
O
4a: n = 2
4b: n = 3
H
H3
H2
Chart 1. The structures of foldamer-containing pseudo[2]rotaxanes 1aed, bistable [2]rotaxanes 2a and 2b, and thread molecules 3aed, 4a and 4b.

K.-D. Zhang et al. / Tetrahedron 68 (2012) 4517e4527
4519
type G-3 dendron was thus introduced to one of the two ends of the
linear components to ensure good solubility for the tetracationic
interlocked molecules in both less polar and polar solvents.20,21
Foldamer segments of varying length are introduced to another
end of the linear components. There are a number of hydrogen
bonded folding patterns available as stopper groups. We chose the
3-amino-2-methoxybenzoic acid-derived foldamers22 because this
folding pattern survives a range of solvents,22b and in these fol-
damers, five repeating units form one turn,23 endowing short
oligomers with a large apparent size through folding. A systematic
investigation of the length-dependence of the dynamic property
would reveal their function as tunable steric barrier for controlling
the extrusion or slippage of the CBPQT4þ ring (Fig. 1). Molecular
modeling reveals that a single 2-methoxyl 1,3-benzamide re-
peating unit in the foldamer segment is not bulky enough to pre-
vent the extrusion of the CBPQT4þ ring, while the folded structure
as a whole is. The two oligo(ethylene glycol) chains linking the TTF
unit and the end groups are expected to strengthen the TTF-
CBPQT4þ complexation through the formation of intermolecular
CeH/O hydrogen bonds between the pyridinium protons and the
neighboring ether oxygen atoms.24 For [2]rotaxanes 2a and 2b, the
electron-rich DNP unit is incorporated in the dumbbell to form
a foldamer-bridged bistable system (Fig. 6, vide infra). The 1,3-
diisopropyl-phenoxyl group is used as the other stopper to pre-
vent the extrusion of the CBPQT4þ ring.25
Linear compounds 3aed were prepared according to the routes
shown in Scheme 1. Tetraglycol 5 was first reacted with [G-3]Br 620
in tetrahydrofuran (THF) in the presence of sodium hydride to give
7 in 94% yield. The alcohol was then treated with tosyl chloride in
dichloromethane in the presence of potassium hydroxide to pro-
duce 8 in 92% yield, which was transformed quantitatively into the
corresponding iodide 9 after treatment with sodium iodide in ac-
etone. Its reaction with 1026 in THF and methanol was activated by
cesium hydroxide to give 11 in 73% yield. Iodide 13, obtained from
treating tosylate 12 with sodium iodide in acetone, was subjected
to the reaction of 11 in the presence of cesium hydroxide to produce
14 in 80% yield. After hydrolysis in aqueous THF, the carboxylic acid
15 was first converted to carbamate, followed by coupling with
16aed,23a to produce 3aed in 52e70% yields.
The preparation of pure threaded complexes 1aed from 3aed
24
and CBPQT$4PF6 was then exploited. It was postulated that,
once the complexes were formed by the slippage of the CBPQT4þ
ring over the foldamer segment, the large G-3 dendron would
ensure good solubility for these complexes in less polar solvents.
Provided the reverse extrusion process was slow enough, one
could separate the pure complexes from the two free species by
simply making use of their difference in solubility. This was
proven the case for threaded complexes 1bed. The 1:1 mixtures
of threads 1bed with CBPQT$4PF6 in a minimal amount of ace-
tonitrile and acetone (1:2, v/v) were stirred for 48 h and then
concentrated at ambient temperature. The resulting green residue
was then triturated with a minimal amount of more polar ace-
tonitrile and water (1:4, v/v) to remove free CBPQT$4PF6. The
Fig. 1. Schematic representation depicting the foldamer-modulated extrusion (pseudo
[2]rotaxane decomplexation) or slippage (pseudo[2]-rotaxane formation) of the
CBPQT4þ ring from or onto a TTF-containing thread. The foldamer segment (red) in its
folded state has a large apparent size and must unfold into an extended conformation
in order for the CBPQT4þ ring to pass over.
Tetrahedron
TsCl, KOH, CH2Cl2
0 ºC, 12 h, 92%
NaH, THF
+
[G-3]
O
O
O
O
OH
[G-3]-Br
HO
O
O
5
O
OH
r.t., 5 h, 94%
6
7
NaI, acetone
[G-3]
O
O
O
O
OTs
[G-3]
O
O
O
O
I
reflux, 24 h, 100%
8
9
S
S
S
S
9, CsOH·H2O
S
S
S
S
CN
THF, MeOH
S
CN
[G-3]
O
O
O
O
S
S
10
NC
S
11
r.t., 16 h, 73%
O
O
NaI, acetone
11, CsOH·H2O, DMF, MeOH
reflux, 20 h, 96%
TsO
O
O
O
I
O
O
O
r.t., 6 h, 86%
OMe
OMe
12
13
O
LiOH·H2O, THF/H2O, r.t., 18 h, 100%
S
S
S
S
S
O
O
O
O
O
O
OMe
S
[G-3]
O
O
O
O
O
O
O
S
S
14
O
OMe
16a: n = 0
16b: n = 1
16c: n = 2
16d: n = 3
NH2
O
MeO2C
N
H
S
S
n
S
S
3a (70%)
3b (59%)
3c (53%)
3d (52%)
OMe
OH
[G-3]
O
15
ClCO2Et, MMP, CH2Cl2
r.t., 7-17 h, 52-70%
N
N
N
3b-d, acetone, MeCN
1b (28%)
1c (29%)
1d (53%)
-
4PF6
r.t., 48-72 h
N
CBPQT4+
Scheme 1. The synthesis of threads 3aed and pseudo[2]rotaxanes 1bed.

4520
K.-D. Zhang et al. / Tetrahedron 68 (2012) 4517e4527
remaining green solid was further triturated with a mixture of less
polar dichloromethane and petroleum ether (1:2, v/v) to remove
un-reacted threads 1bed. Threaded complexes 1bed could thus
be obtained as green solids in 28%, 29%, and 53% yields, re-
spectively, as confirmed by 1H NMR spectroscopy (vide infra). All
the three pseudorotaxanes remain as stable complexes in the solid
state.27 Pseudo[2]rotaxane 1a could not be isolated in its pure
interlocked form using the similar procedure as a result of fast
decomplexation.28
The synthetic routes for [2]rotaxanes 2a and 2b and dumbbells
4a and 4b are described in Scheme 2. Phenol 17 was first reacted
with 1,5-dibromopentane in acetonitrile to give compound 18 in
87% yield. The bromide was then treated with 1,5-
dihydroxynaphthalene in ethanol with potassium hydroxide as
base to afford 19 in 56% yield. This naphthol was further coupled
with bromide 20 in acetonitrile in the presence of potassium car-
bonate to produce 21 in 79% yield. Treatment of compound 21 with
hydrazine in ethanol quantitatively yielded 22, which was further
coupled with acid 23a and 23b23 to produce 24a and 24b in 78%
and dumbbell components were observed, but none of them were
from the individual free species, suggesting that they were com-
plexed, (ii) the two components existed in a 1:1 ratio, as indicated
by the relative intensity of their respective resonances. After
standing for a period of time, the resonances of the free compo-
nents appeared gradually, while those of the complexes di-
minished. Equilibria for 1c and 1d were reached after different
standing times. On the other hand, the 1H NMR spectrum of com-
plex 1b in acetonitrile-d3 recorded immediately after it was dis-
solved already exhibited the signals of both free and complexed 3b
and CBPQT$4PF6, reflecting that it underwent a more rapid
decomplexation process.
The slippage of the CBPQT4þ ring over the foldamer segments of
3aed to form the threaded complexes were also followed by re-
cording the 1H NMR spectra of their 1:1 solution in acetone-d6,
acetonitrile-d3, and DMSO-d6 at different time intervals. As
expected, the process was revealed to be time-dependent. The time
for reaching equilibrium increased with the elongation of the fol-
damer segment and was shorter in DMSO-d6 than in acetonitrile-d3
Pr-i
Pr-i
Pr-i
Br(CH2)5Br
naphthalene-1,5-diol
O
O
OH
Pr-i
O
K2CO3, MeCN
Br
KOH, EtOH
OH
reflux,12 h, 87%
reflux, 4 h, 56%
19
Pr-i
Pr-i
18
17
O
N
O
O
Pr-i
19, K2CO3, MeCN
O
O
Br
N
O
reflux, 20 h, 79%
20
21
Pr-i
O
OMe O
O2N
OH
N
H
23a: n = 1
23b: n = 2
Pr-i
OMe O
.
n
NH2NH2 H2O
NH2
O
O
O
EtOH, reflux, 3 h, 99%
EDCI, DMAP, THF, CHCl3
r.t., 3 h
22
Pr-i
O
OMe
OMe
Pr-i
H
H2, Pd-C, THF
40 ºC, 30 h
N
NO2
NH2
O
O
N
H
O
O
O
O
OMe
OMe
n
24a: n = 1 (78%)
24b: n = 2 (43%)
Pr-i
15, CBPQT·4PF6
O
Pr-i
ClCO2Et, NMM, CHCl3
H
N
2a (18%)
2b (20%)
4a (40%)
4b (38%)
O
O
+
N
H
r.t., 24 h
n
25a: n = 1 (96%)
25b: n = 2 (98%)
Pr-i
Scheme 2. The synthesis of [2]rotaxanes 2a and 2b and threads 4aed.
and 43% yields, respectively. Pd-catalyzed hydrogenation of the two
nitro compounds in THF and chloroform generated 25a and 25b in
nearly quantitative yields. The two amines were then coupled with
15, which was activated with ethyl chloroformate, in the presence
of CBPQT$4PF6 to produce both [2]rotaxanes 2a and 2b and
dumbbell 4a and 4b in moderate yields.
or acetone-d6. In all cases, the resonances of the pyridinium b-H of
the free and threaded CBPQT4þ ring did not overlap with others,
which were assigned by comparing the spectra with those of pure
CBPQT$4PF6 and previously reported related threaded systems.29
On the base of the relative intensities of these signals, we de-
termined the association constants (Ka) of the threaded complexes,
which, together with the calculated free energies of complexation
(D
Gꢀ), are provided in Table 1. The same results were obtained
2.2. Association constants of threaded complexes 1aed
starting from preformed complexes 1bed after the samples were
allowed to stand for enough time. The values are comparable to
those reported for other pseudo-[2]rotaxanes stabilized by the TTF-
CBPQT4þ donoreacceptor interactions,14 suggesting that the
The 1H NMR spectra of complexes 1c and 1d in acetonitrile-d3
displayed one set of signals, which was attributed to the pseudor-
otaxanes because (i) resonances corresponding to both CBPQT4þ
Table 1
The association constants (Ka) of pseudo[2]rotaxanes 1aed and the associated free energies (
D
Gꢀ) at 25 ꢀC
1a
1b
1c
1d
Ka (Mꢁ1
)
D
Gꢀ (kJ/mol)
Ka (Mꢁ1
)
D
Gꢀ (kJ/mol)
Ka (Mꢁ1
)
D
Gꢀ (kJ/mol)
Ka (Mꢁ1
)
D
Gꢀ (kJ/mol)
Acetonitrile-d3
Acetone-d6
DMSO-d6
1800
420
146
ꢁ18.6
ꢁ15.0
ꢁ12.3
752
258
157
ꢁ16.4
ꢁ13.8
ꢁ12.5
868
411
152
ꢁ16.8
ꢁ14.9
ꢁ12.4
576
187
120
ꢁ15.7
ꢁ13.0
ꢁ11.9

K.-D. Zhang et al. / Tetrahedron 68 (2012) 4517e4527
4521
foldamer segments did not play a significant role in determining
the thermodynamic stability of these pseudo[2]rotaxanes.
Compared with those of 1a in the same solvent, the koff values of
1b decreased considerably, by as large as 58 to 365 times. The ex-
tent of rate drop became smaller from 1b to 1c, being 5 to 37 times,
and even smaller from 1c to 1d, being only two to five times. These
observations indicated that all the hydrogen bonded arylamide
units in the foldamer segments contributed in delaying the extru-
sion of CBPQT4þ, but not in a cooperative manner. Since the depth
of the CBPQT4þ ring is shorter than the width of the arylamide
repeat, for the longer foldamer segments in 1c and 1d, we proposed
that the extrusion of the CBPQT4þ ring does not require simulta-
neous breaking of all the hydrogen bonds. Instead, it should be
a multi-step process, which involved successive breaking of the
hydrogen bonds, probably mainly the six-membered ones, of one
arylamide unit after another from the TTF side. As illustrated in
Fig. 2, the extrusion of the CBPQT4þ ring only break the hydrogen
bonds of the arylamide unit close to the edges of its cavity, com-
mensurate with the conformational change of the encircled seg-
ment. The whole process is, to some extent, like removing a ring
from a curved, sticky finger over knuckles. The five-membered
NeH/O hydrogen bonds might survive, at least partially, during
the extrusion because the breaking of this series of hydrogen bonds
does not cause a size decrease, but would lead to the formation of
the cis conformation of the NeC(Ar) bond, which is unfavorable as
a result of the electrostatic repulsion between the neighboring C]
O and methoxyl oxygen atoms.
2.3. Extrusion kinetics of CBPQT4D of pseudo[2]rotaxanes
1aed
The above 1H NMR investigations revealed that foldamer-
capped pseudo[2]rotaxanes can exhibit [2]rotaxane-like charac-
ters, depending on the foldamer segments in the threads and the
media. To get deep insight into the effect of the foldamer segments
and the media on the dynamic properties of the threaded com-
plexes, a systematic kinetic investigation was performed. The TTF-
CBPQT4þ charge-transfer (CT) absorption, centered on 805 nm in
the UVevis spectra, was used as the probe.16 By monitoring the
decrease of this CT absorption with time, we obtained the rate
constants (koff) of the decomplexation of the pseudo[2]rotaxanes in
twelve solvents, from highly polar DMSO and DMF to less polar
chloroform, by assuming a first-order kinetics. The data, together
with the associated change of free energy and half-life values, are
listed in Table 2. The rates of decomplexation of pseudo[2]rotaxane
1a could not be determined using this method because the process
was too rapid to be monitored by the UVevis spectroscopy. Thus,
we first used the UVevis experiments to measure the rates of for-
mation (kon) of the pseudorotaxane from 3a and CBPQT$4PF6 in
polar DMSO, acetonitrile and acetone, and then calculated the koff
values in these solvents (0.058, 0.19, and 0.26 sꢁ1, respectively)
using the equation koff¼kon/K, where K was the association constant
of the complex (Table 1).30 The value in less polar solvents could not
be obtained due to the low solubility of CBPQT$4PF6.
It has been established that the donoreacceptor interactions
between the TTF and bipyridinium units become weakened pro-
nouncedly in less polar solvents due to the decrease of their
p-
stacking interation.31 The decomplexation of pseudo[2]rotaxanes
Table 2
The kinetic data for the extrusion of the CBPQT4þ ring over the foldamer segments in pseudo[2]rotaxanes 1bed at 25 ꢀC in different solvents
a
Solvent
3
bb
1b
1c
1d
koff (sꢁ1
)
D
Gs
Half-life
(s)
koff (sꢁ1
)
D
Gs
Half-life
(s)
koff (sꢁ1
)
D
Gs
Half-life
(s)
(kJ/mol)
(kJ/mol)
(kJ/mol)
DMSO
DMF
MeCN
PhCN
47.2
36.7
38.3
25.7
21.0
18.6
16.1
13.6
11.4
10.4
7.5
0.76
0.69
0.41
0.41
0.48
0.48
0.53
0.52
0.35
0
1.0ꢂ10ꢁ3
2.3ꢂ10ꢁ3
5.2ꢂ10ꢁ4
2.8ꢂ10ꢁ4
8.4ꢂ10ꢁ4
6.6ꢂ10ꢁ4
7.8ꢂ10ꢁ4
7.5ꢂ10ꢁ4
1.0ꢂ10ꢁ4
7.5ꢂ10ꢁ6
2.6ꢂ10ꢁ4
1.9ꢂ10ꢁ6
90
88
92
93
91
91
91
91
96
6.9ꢂ102
3.0ꢂ102
5.3ꢂ104
2.5ꢂ103
8.2ꢂ102
1.0ꢂ103
8.8ꢂ102
9.2ꢂ102
6.9ꢂ103
9.2ꢂ104
2.7ꢂ103
3.6ꢂ105
1.1ꢂ10ꢁ4
4.7ꢂ10ꢁ4
4.0ꢂ10ꢁ5
2.0ꢂ10ꢁ5
1.3ꢂ10ꢁ4
6.0ꢂ10ꢁ5
6.0ꢂ10ꢁ5
6.0ꢂ10ꢁ5
6.7ꢂ10ꢁ6
2.0ꢂ10ꢁ7
8.3ꢂ10ꢁ6
1.2ꢂ10ꢁ7
96
92
98
100
95
97
97
97
103
111
102
113
6.3ꢂ103
1.7ꢂ103
1.7ꢂ104
3.5ꢂ104
5.3ꢂ103
1.2ꢂ104
1.2ꢂ104
1.2ꢂ104
1.0ꢂ105
3.5ꢂ106
8.5ꢂ104
5.8ꢂ106
4.0ꢂ10ꢁ5
1.0ꢂ10ꢁ4
9.7ꢂ10ꢁ6
8.9ꢂ10ꢁ6
2.5ꢂ10ꢁ5
3.0ꢂ10ꢁ5
2.0ꢂ10ꢁ5
3.0ꢂ10ꢁ5
2.6ꢂ10ꢁ6
5.1ꢂ10ꢁ7c
2.1ꢂ10ꢁ6
3.6ꢂ10ꢁ7c
98
96
102
102
99
99
100
99
105
115
105
116
1.7ꢂ104
6.9ꢂ103
7.1ꢂ104
7.8ꢂ104
2.8ꢂ104
2.3ꢂ104
3.5ꢂ104
2.3ꢂ104
2.7ꢂ105
1.4ꢂ106c
3.3ꢂ105
1.9ꢂ106c
Acetone
Butanone
Cyclohexanone
Cyclopentanone
ClCH2CO2Et
ClCH2CH2Cl
THF
102
94
106
0.55
0.10
Chloroform
4.8
a
Dielectric constant of the solvent.
Scale of the solvent as a hydrogen bond acceptor.
Measured at 40 ꢀC.
b
c
As expected, the decomplexation of the pseudo[2]rotaxanes in
1bed was substantially slower in less polar solvents (such as
chloroform) than in polar solvents (such as DMSO and DMF), sug-
gesting that the increase of the free energy from a polar solvent to
a less polar solvent was obviously smaller than the increase of the
free energy of activation for the extrusion of the CBPQT4þ ring from
the linear component caused by the enhancement of the intra-
molecular hydrogen bonds of their foldamer segment in less polar
solvent. The fact that all the threaded complexes decomplexed even
in less polar solvents suggests that they are all pseudo[2]rotaxanes,
but have an increased character of [2]rotaxanes with the in-
troduction of longer foldamer segment in the threads. No linear
relationship is observed between the koff values and the dielectric
the same solvent decelerated with the elongation of the foldamer
segments and, for the same pseudo[2]rotaxane, accelerated with
the increase of the solvent polarity. For example, 1a decomposed
very quickly, with a half-life of as short as 2.7 s in acetone. In
contrast, 1d was much more stable in chloroform and 1,2-
dichloroethane. Indeed, it was found that even after standing for
4 days at ambient temperature, its CT absorption still exhibited no
perceptible decrease, indicating that it had a rotaxane-like char-
acter in these two solvents. It started to slowly decomplex at 40 ꢀC,
with the half-lives still being as long as 22 and 16 days (Table 2) in
the two solvents. Thus, by choosing foldamer segments of varying
length and solvents of different polarity, we could control the ex-
trusion of the CBPQT4þ ring from the threads in a remarkably long
span of time.
constant ( ) or the b scaledthe ability of a solvent as a hydrogen
3
bonding acceptor (Table 2).32 This observation is, however, not
unexpected considering that the TTF-CBPQT4þ donoreacceptor

4522
K.-D. Zhang et al. / Tetrahedron 68 (2012) 4517e4527
Tetrahedron
O
O
H
N
OMe O
S
S
S
S
S
O
O
N
H
S
N
H
N
H
S
S
S
S
S
O
N
OMe O
O
N
Me
H
S
H
Me
O
H
Me
O
Me
N
O
MeO
O
Me
H
N
O
O MeO
MeO
O
Me
O
H
O
O
N
N
H
OMe
O
O
Me
O
Me
O
N
H
N
O
OMe
O
O
N
H
OMe
N
H
H
OMe O
O
OMe
Me
OMe
O
N
H
O
H
N
S
S
S
S
S
S
S
S
S
S
S
S
Fig. 2. Proposed multi-step extrusion mechanism of the CBPQT4þ ring from the thread in 1d, which involves the breaking and re-formation of the six-membered intramolecular
NeH/O hydrogen bonds in the foldamer segments.
interactions and the intramolecular NeH/O hydrogen bonding of
the foldamer segment are dependent on multiple factors. It is
conducted for 3b by sonicating its solution in the mixture of CDCl3,
DMSO-d6, and D2O (47.5:47.5:5 v/v/v), which was monitored by 1H
NMR. After the disappearance of the amide signals, the pure sample
was separated and used to prepare pseudo[2]rotaxane 1b with
deuterated amide units. The koff values of this deuterated 1b in four
polar solvents were measured using UVevis spectroscopy and the
results listed in Table 3. It can be seen that the kinetic isotope effect
(KIE) increases notedly with the decrease of the solvent polarity,
supporting that the intramolecular NeH/O hydrogen bonding is
present in these solvents and plays its role in modulating the ex-
trusion of the CBPQT4þ ring.22b,33
noteworthy that the
3 value of THF is between those of chloroform
and 1,2-dichloroethane, but its
b
scale is much higher than those of
the two chlorinated solvents, which should account for the obser-
vation that the rates of decomplexation for all the pseudo[2]
rotaxanes in THF are substantially larger than those in the chlori-
nated solvents.
2.4. Kinetic isotope effect of the extrusion of CBPQT4D of 1b
Since the extrusion of the CBPQT4þ ring from the threads of the
pseudo[2]rotaxanes was highly dependent on the hydrogen
bonded foldamer segment of their thread component, this process
might exhibit a kinetic isotope effect (KIE) if the amide hydrogens
were exchanged to deuteriums. The zero-point free energy of the
resulting NeD/O deuterium bonding is expected to decrease with
respect to that of the NeH/O hydrogen bonding of the same amide
in the threaded state. During the extrusion process (Fig. 2), both the
hydrogen and deuterium bondings would be weakened or broken.
As a result, the difference between their zero-point free energies
should decrease, or even close to zero if they were broken com-
pletely, as shown in Fig. 3. To testify this, deuterium exchange was
Table 3
The kinetic data for the decomplexation of deuterated 1b at 25 ꢀC in different polar
solvents and the related kinetic isotope effect
DMF
MeCN
Acetone
THF
kD
2.1ꢂ10ꢁ3
6.1ꢂ10ꢁ4
3.7ꢂ10ꢁ4
1.7ꢂ10ꢁ4
KIEa
1.1
1.4
1.4
1.5
a
KIE represents the kH/kD ratio.
2.5. TTF redox chemistry and extrusion kinetics of the
CBPQT4D ring off pseudorotaxanes 1bed
Cyclic voltammetry (CV) was used to investigate the redox
property of the TTF unit in pseudo[2]rotaxanes 1bed in both less
polar chloroform and polar acetonitrile. The first oxidation poten-
tial of the three samples in chloroform was all 0.65 V, which was
larger than that (0.53 V) of control compound 3b,17 reflecting the
decreased electron-donating ability of the complexed TTF unit with
respect to the free one. The second oxidation potential of both
1bed and 3b in chloroform was all 0.84 V, implying that the for-
mation of radical cation TTFþꢃ had forced the CBPQT4þ ring of 1bed
to slip off the TTF unit and hence the CBPQT4þ ring did not affect the
TTF2þ dicationic ion formation. The electrochemical behavior is
quite different in acetonitrile. Pseudo[2]rotaxanes 1bed exhibited
only one oxidation process at 0.77 V, whereas 3b still gave rise to
two peaks at 0.44 and 0.78 V, respectively (Fig. 4). The CV of 1b
recorded in acetonitrile showed an additional weak broad peak at
0.44 V, assignable to the oxidation of free TTF unit. Such peak was
N-H
N-D
state of
extrusion
N-H
N-D
N-H
N-D
pseudorotaxane 1b
(threaded)
3b + CBPQT·4PF6
Fig. 3. The mechanism for the kinetic isotope effect of the decomplexation of
foldamer-derived pseudorotaxane 1b.

K.-D. Zhang et al. / Tetrahedron 68 (2012) 4517e4527
4523
Tetrahedron
(c)
(a)
(b)
0.5
0.0
0.5
0.5
0.0
0.0
-0.5
-0.5
-1.0
-1.5
-2.0
-0.5
-1.0
-1.5
0.44 V
-1.0
0.77 V
0.77 V
-1.5
0.78 V
-2.0
-0.5
0.0
0.5
E / V
1.0
1.5
0.0
0.5
E / V
1.0
1.5
0.0
0.5
E / V
1.0
1.5
(f)
(d)
0.5
0.0
(e)
1.0
0.5
2
0
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
0.44 V
0.44 V
-2
-4
-6
-0.5
-1.0
-1.5
1st cycle at 5 mV/s
2st cycle at 5 mV/s
2st cycle at 10 mV/s
2st cycle at 25 mV/s
2st cycle at 50 mV/s
2st cycle at 75 mV/s
2st cycle at 75 mV/s
2st cycle at 100 mV/s
2st cycle at 150 mV/s
2st cycle at 200 mV/s
2st cycle at 300 mV/s
2st cycle 400mV/s
0.77 V
-0.2
0.0
0.2
0.4
E / V
0.6
0.8
1.0
0.0
0.5
E / V
1.0
1.5
-0.2
0.0
0.2
0.4
E / V
0.6
0.8
1.0
Fig. 4. CVs (0.1 mM, scan rate¼10 mV/s) of (a) 3b, (bed) pseudo[2]rotaxanes 1bed in MeCN at 25 ꢀC, (e,f) CVs of bistable [2]rotaxane 2a (0.1 mM) at different scan rates in MeCN at
25 ꢀC. The Pt button and coil and Ag/AgCl electrodes were used as working, counter, and reference electrodes. n-Bu4N$PF6 (0.1 M) was used as the electrolyte.
not observed for 1c and 1d in acetonitrile and for all the three
pseudo[2]rotaxanes in chloroform. These results indicated that,
within the time scale of the electrochemical measurement, 1b al-
ready started to decomplex in acetonitrile but remained intact in
chloroform during the redox cycle, while 1c and 1d were more
stable in either solution conditions, which were consistent with the
above UVevis kinetic experiments.
CBPQT4+ CH
2
(
a)
complexes
(
b)
free
The redox-activated dynamic process was also investigated us-
ing the chemical oxidation/reduction methods. Adding 2.0 equiv of
Magic Blue ((4-BrC6H4)4NþSbCl6ꢁ)16,34 or 1.0 equiv of Fe(ClO4)3 to
the solution of pseudo[2]rotaxanes 1bed in acetonitrile resulted in
(
c)
29
the oxidation of the TTF unit to TTF2þ or TTFþ
.
The kinetics of
ꢃ
decomplexation of these oxidized pseudo[2]rotaxanes was then
investigated using the UVevis spectroscopy. By assuming a first-
order kinetic process for the extrusion of the CBPQT4þ ring over
the foldamer segment, we derived the koff values using the equation
koff¼[ln(C0/C)]/t, where C0 and C were the initial concentration and
the concentration of the threaded complexes at time t, which ap-
proximately equaled the time interval between the oxidation and
reduction of the sample. To reach the reduced state, the solutions of
the oxidized pseudo[2]rotaxanes were treated with an excess of
zinc powder. The recovered CT absorptions of the remaining
(
(
d)
e)
TTF-H
(cis/trans)
DNP
6.0
H-2/6
6.2
H-3/7
5.8
7.0
6.8
6.6
6.4
5.6
5.4 PPM
1
Fig. 5. Partial H NMR spectra (400 MHz, aceotonitrile-d3, 25 ꢀC) of (a) pseudo[2]ro-
taxane 1d, (b) 1d after Magic Blue (2.0 equiv) was added, (c) 1d recorded after zinc
powder (5.0 equiv) was added to the above solution of 1d and Magic Blue, which was
first allowed to stand for 5 min (without this reduction process, 1H NMR showed no
difference for the signals of the free and complexed CBPQT4þ ring), and (d) bistable [2]
rotaxane 2a and (e) 2a after Magic Blue (2.0 equiv) was added for 5 min. The con-
centration for 1d and 2a were kept at 2.0 mM.
pseudo-[2]rotaxanes were recorded, and the
C values were
obtained by comparing the absorptions with those of the initial
solutions. Alternatively, the C0/C could be obtained using the 1H
NMR spectroscopy by comparing the relative integrated intensity of
the CH2 signals of the free and complexed CBPQT4þ ring (Fig. 5aec).
The koff values of decomplexation were listed in Table 4. It can be
seen that, for the same pseudo[2]rotaxane, the koff values for the
oxidized complex are comparable and independent on the oxida-
tion state of TTF unit. Since the electrostatic repulsion between
TTF2þ and CBPQT4þ should be larger than that between TTFþꢃ and
CBPQT4þ, this observation supports that the energy barrier for ex-
trusion of the CBPQT4þ ring, after the first oxidation of TTF, was
predominantly controlled by its deslippage over the bulky foldamer
segment. This result may be attributed to the long linker between
the TTF and foldamer unit, which allowed the CBPQT4þ ring to
rapidly escape far away from the oxidized TTF unit. The corre-
sponding charge repulsion decayed exponentially to an in-
significant level when compared to the energy cost for the CBPQT4þ
Table 4
The kinetic data for the decomplexation of mono- (TTFþ ) and dioxidized (TTF
)
2þ
ꢃ
pseudorotaxanes 1bed in acetonitrile at 25 ꢀC, measured by the UVevis method
koff(TTFþ.
(sꢁ1
)
Half-life
(s)
koff(TTF2þ
(sꢁ1
)
Half-life
(s)
)
)
1b
1c
1d
1d
1d
0.11
0.016
0.0042
6.3
43
165
0.11
0.020
0.0042
0.0045a
0.0081b
6.3
37
165
154
66
Determined in acetonitrile-d3 using the 1H NMR method.
Value determined in acetone.
a
b

4524
K.-D. Zhang et al. / Tetrahedron 68 (2012) 4517e4527
ring slipping over the foldamer segment. On the other hand, the koff
values of the mono- and dioxidized 1bed in acetonitrile were
212e433 times higher than the values of the corresponding
unoxidized samples in the same solvent (Table 2). The kinetic sta-
bility in the unoxidized pseudo[2]rotaxanes was attributed to the
TTF-CBPQT4þ donoreacceptor interaction.
rotaxanes to TTF would lead to the formation of the MSCC (B, Fig. 6),
and the CBPQT4þ ring would slip back to the TTF side to form the
GSCC (B/A, Fig. 6). The last process is directly related to the life-
time of the MSCC and is critical for non-volatile molecular memory
with high metastability.
To get more insight into this last process, the CVs of the two
bistable [2]rotaxanes at varying scan rates in both acetonitrile and
chloroform were recorded. For the second scans, for 2a in aceto-
nitrile, at the slow scan rates of 5 and 10 mV/s, no peak was ob-
served at about 0.44 V, which is typical for the free TTF and, for
bistable [2]rotaxane 2a, associated with its MSCC. Within the range
of scan rates from 25 mV/s to 75 mV/s, this peak was observed and
intensified pronouncedly. This result indicates that even in solution
the MSCC of 2a had a relatively long lifetime at ambient tempera-
ture, which is comparable with that observed in
CBPQT4þeTTFeDNP-based rotaxanes entrapped in the solid-state
polymer.17b With the further increase of the scan rate from
100 mV/s to 400 mV/s, this peak still survived, but became weak-
ened, which might be attributed to the decreased C/D conversion
(Fig. 6) at increased scan rates. For 2a in chloroform and 2b in both
chloroform and acetonitrile, no peaks corresponding to the free TTF
unit were observed at different scan rates, which might reflect the
decreased C/D conversion as well as the increased stability of the
MSCC of the [2]rotaxanes.
2.6. Bistable [2]rotaxanes 2a and 2b
Since the dimeric and trimeric foldamer segments in pseudo[2]
rotaxanes 1b and 1c could provide an energy barrier for the
CBPQT4þ ring to extrude at a rate of 10ꢁ2e10ꢁ7 ꢁ1, we further
s
prepared bistable [2]rotaxanes 2a and 2b to study the foldamer-
tuned switching of the CBPQT4þ ring between the TTF and DNP
sites (Fig. 6). For most of previously reported TTF/DNPeCBPQT4þ
bistable [2]rotaxanes,17 the TTF and DNP sites are connected with
short chains, hence the shuttling of CBPQT4þ between the two sites
is usually rapid. Since TTF is more electron-rich than DNP, in a two-
state model, the equilibrium is always shifted toward the CBPQT4þ
ring encircling the TTF site to form GSCC, rather than toward the
The 1H NMR spectra in CD3CN showed that adding 2.0 equiv of
Magic Blue to the solution of the [2]rotaxanes resulted in the ap-
pearance of a new set of signals. For 2a, the two signals (at 5.78 and
5.89 ppm) of the protons of the TTF unit encapsulated in the
CBPQT4þ ring disappeared (Fig. 5d), while the signals of the H2/6
(at 6.16 and 6.20 ppm) and H3/7 (at 5.89 ppm) protons of the DNP
unit encapsulated in the CBPQT4þ ring emerged (see structure in
Chart 1 for numbering) (Fig. 5e).29 These results supported that the
CBPQT4þ ring had shuttled from the TTF side to the DNP side. In
separate UVevis experiments, both 2a and 2b were oxidized with
2.0 equiv of Fe(ClO4)3 in acetonitrile to produce doubly oxidized
TTF2þ. After standing for 50 min, the solutions were quickly treated
with an excess of zinc powder to reduce TTF2þ to TTF. The time-
dependent UVevis spectra of the solutions were then recorded,
which showed that the DNPeCBPQT4þ CT absorption gradually
decreased, while the TTFeCBPQT4þ CT absorption formed and in-
creased (Fig. 7). By assuming a first-order kinetics, we determined
the rate constants of the shuttling of the CBPQT4þ ring of 2a and 2b
Fig. 6. Schematic representation depicting the foldamer-tuned switching of the
CBPQT4þ ring between the TTF and DNP sites in bistable [2]rotaxanes 2a and 2b, with
2þ
the TTF unit being neutral (states A and B) or oxidized to TTFþ or TTF (states C and
ꢃ
D).
from the MSCC to the GSCC to be 1.1ꢂ10ꢁ2 and 7.4ꢂ10ꢁ4
s
ꢁ1, re-
CBPQT4þ ring encircling the DNP site to form the less stable MSCC.17
For foldamer-incorporated bistable [2]rotaxanes 2a and 2b, the
barrier energy for the shuttling of CBPQT4þ should be substantially
increased due to the hindrance of the foldamer segment. The 1H
NMR spectra of [2]rotaxanes 2a (Fig. 5d) and 2b in acetonitrile-d3
and acetone-d6 displayed one set of signals, suggesting that the
CBPQT4þ ring either shuttled rapidly between the TTF and DNP sites
(A4B, Fig. 6) or predominantly existed in the GSCC (A, Fig. 6). Since
the above kinetic investigation (Table 2) revealed that the slipping
rates of the CBPQT4þ ring over the dimeric (1b) and trimeric (1c)
foldamer segments were slow on the 1H NMR time scale, it was
reasonable to propose that the GSCC was formed predom-
inantly.Considering the TTF sides of their threads possess the same
structure, the rate constant of the shuttling of the CBPQT4þ ring in
[2]rotaxanes 2a and 2b from their GSCC to the MSCC should be
similar to the corresponding rate constant of decomplexation of
pseudo[2]rotaxanes 1b and 1c in the same solvent. Upon oxidation
spectively, which corresponded to half-lives of 66 and 930 s. Using
of the TTF unit to TTFþ or TTF2þ, the CBPQT4þ ring of the [2]
ꢃ
rotaxanes would be repelled to slip more rapidly over the foldamer
segment to encircle the DNP unit (C/D, Fig. 6), and the shuttling
rates should be comparable to the rates of decomplexation of the
corresponding oxidized pseudo-[2]rotaxanes 1b and 1c in the same
solvent (Table 4). Reduction of the TTFþꢃ or TTF2þ cation of the [2]
Fig. 7. The UVevis absorption spectra of the solution of bistable [2]rotaxane 2b in
acetonitrile at 25 ꢀC, obtained after zinc powder (5 equiv) was added to the solution of
its dioxidized sample. Inset: The plot of C/C0 versus the recording time (from 160 s to
12,300 s).

K.-D. Zhang et al. / Tetrahedron 68 (2012) 4517e4527
4525
the same method, the rate constant of the same process of 2a in
proton resonances of the deuterated solvents as the internal stan-
dards. UVevis spectra were recorded on a CARY 100 spectrometer;
Cyclic voltammetric measurements were carried out in a three-
electrode cell using a Pt button working electrode of 2 mm di-
ameter, a Pt wire counter electrode, and an Ag/AgCl reference
electrode on a computer-controlled CHI610D instrument. The
synthesis and characterization of compounds 7e11, 13, 3b, and 3c,
pseudorotaxanes 1b and 1c, compounds 18, 19, 21, 22, 24a, and 24b
have been described.19
chloroform was determined to be 9.9ꢂ10ꢁ6
s
ꢁ1, which corre-
sponded to a half-life of 19.5 h, 1064 times longer than that in
acetonitrile. The rate constants were all higher than the related koff
values of pseudo[2]rotaxanes 1b and 1c (Table 2), which was con-
sistent with the fact that the donoreacceptor interaction between
DNP and CBPQT4þ was weaker than that between TTF and CBPQT4þ
.
Since the foldamer segments were not symmetric, the energy
barrier experienced by CBPQT4þ ring from the two sides might be
slightly different, which should also contribute to the difference.
Remarkably, the solution of the MSCC of 2b in chloroform, obtained
4.1.1. Compound 3d. A suspension of 14 (0.15 g, 0.070 mmol) and
LiOH$H2O (0.16 g, 3.68 mmol) in THF (4 mL) and water (1 mL) was
stirred for 18 h and then acidified with aqueous HCl. The solvent
was removed and the resulting slurry triturated with CH2Cl2
(30 mL). The organic phase was successively washed with water
(30ꢂ2 mL) and brine (30 mL), dried over anhydrous Na2SO4, and
concentrated to give 15 as a yellow oil (0.15 g, 100%). Without fur-
ther purification, this acid was dissolved in CH2Cl2 (2 mL). To the
using the similar method, did not exhibit
a perceptible
TTFeCBPQT4þ CT band in the UVevis spectrum even after 3 days,
indicating that the foldamer segment can efficiently block the
conversion of MSCC to GSCC in less polar media.
3. Conclusion
We have demonstrated that hydrogen bonding-induced aryla-
mide foldamers can serve as deformable moiety in switchable
pseudorotaxanes and rotaxanes to modulate the switching kinetics
and metastability. The noncovalent nature of the folding confor-
mation in foldamers endows structural flexibility, making the fol-
damers versatile structural units to modulate the mechanical
movements of the CBPQT4þ ring along the dumbbell component.
By varying the number of the repeating units in the foldamer, the
kinetics of the solvent-dependent slippage/deslippage process of
pseudo-[2]rotaxanes can be tuned to cover a large span of more
than 7.0ꢂ105 times. Changing the oxidative state of the TTF unit
significantly increases the rate of the CBPQT4þ ring extruding off
the dumbbell. In bistable [2]rotaxanes where foldamer segments
are introduced to bridge a TTF unit and a DNP unit in the dumbbell,
the deformable sizes of the foldamers effectively serve as a steric
barrier to the relaxation from MSCC to GSCC. The lifetime of the
post-oxidation MSCC is thus dramatically increased. As shown in
the case for one [2]rotaxane in its metastable state in chloroform,
no relaxation to the ground state is observed even after 3 days! The
generation of such a long-lived MSCC in [2]rotaxanes holds great
promises for the application of these mechanically interlocked
molecules in non-volatile molecular memories.
The marriage of deformable foldamers and interlocked molec-
ular switches opens up the possibility of exploring more responsive
dynamic molecular materials. In principle, many other folding
patterns could be used for the similar purpose. The diversity of
folding patterns enables the future design of foldamer stoppers that
can operate in medium of discrete polarity or be modulated
chemically, photochemically or by molecular recognition.35e37 Be-
cause the foldamers tune the slippage of the ring through changing
their shape or conformation, which only involves the breaking of
noncovalent bonds, it is expected that longer foldamer segments
can be utilized to further increase the metastability, without
completely blocking the slippage of a properly sized ring over them.
Hence, this family of soft deformable foldamers also avoids the all-
or-nothing character displayed by most of the conventional
stoppers.
solution were added NMM (11.4
mL, 0.092 mmol) and ClCO2Et
(10.0
m
L, 0.076 mmol). After stirring for 1 h, a solution of 16d23b
(88 mg, 0.14 mmol) in CH2Cl2 (1 mL) was added and stirring was
continued for another 5 h. The solution was successively washed
with water (30 mLꢂ2) and brine (30 mL), dried over anhydrous
Na2SO4, and concentrated. The resulting residue was subject to
column chromatography (CHCl3) to give 3b as a pale yellow oil
(102 mg, 52%). Pale yellow solid. 1H NMR (400 MHz, CDCl3)
d: 10.10
(s, 1H), 9.88 (s, 1H), 9.83 (s, 1H), 8.96 (s, 1H), 8.78e8.89 (m, 3H), 8.46
(dd, J1¼8.2 Hz, J2¼1.2 Hz, 1H), 7.82e7.80 (m, 3H), 7.54 (dd,
J1¼6.4 Hz, J2¼1.6 Hz, 1H), 7.35e3.32 (m, 44H), 6.60e6.58 (m, 12H),
6.52 (d, J¼2.0 Hz, 2H), 6.48 (t, J¼2.0 Hz, 4H), 6.46 (br, 3H), 6.24 (d,
J¼1.2 Hz, 1H), 6.20 (s, 1H), 4.94 (s, 16H), 4.88 (br, 12H), 4.41 (s, 2H),
4.16 (s, 2H), 3.93 (s, 3H), 3.90 (s, 6H), 3.85 (s, 3H), 3.84 (s, 3H),
3.77e3.75 (m, 2H), 3.66e3.64 (m, 2H), 3.48e3.58 (m, 20H), 2.79 (t,
J¼6.4 Hz, 2H), 2.73e2.71 (m, 2H). 13C NMR (100 MHz, CDCl3)
d:
168.31, 165.78, 163.30, 163.24, 163.06, 160.24, 160.15, 160.07, 149.38,
147.78, 147.52, 147.41, 140.98, 139.45, 139.34, 136.89, 133.22, 132.43,
132.38, 131.34, 128.65, 128.06, 127.63,126.70,126.67, 126.49, 126.44,
126.39, 126.26, 125.90, 125.86, 125.76, 125.49, 125.07, 124.83,
124.55, 123.51, 123.07, 122.96, 122.93, 122.89, 112.43, 111.84, 111.80,
106.69, 106.55, 106.48, 101.68, 101.32, 73.13, 71.25, 71.05, 70.71,
70.59, 70.53, 70.44, 70.15, 70.05, 69.73, 69.66, 69.56, 63.14, 62.71,
62.54, 52.37, 35.23. MS (MALDI-TOF) m/z: 2819.2 [MþH]þ. HRMS
(MALDI-TOF): calcd for C160H154N4O31S6 [M]þ: 2818.8921. Found:
2818.8900.
4.1.2. Compound 3a. Pale yellow solid. 1H NMR (400 MHz, CDCl3)
d:
9.16 (s, 2H), 8.60 (d, J¼8.0 Hz, 1H), 7.59 (d, J¼8.0 Hz, 1H), 7.43e7.31
(m, 40H), 7.18 (t, J¼8.0 Hz, 1H), 6.70e6.69 (m, 12H), 6.62e6.61 (m,
2H), 6.59e6.58 (m, 4H), 6.57e6.56 (m, 3H), 6.37e6.36 (m, 2H), 5.04
(s, 16H), 4.98 (s, 12H), 4.51 (s, 2H), 3.94 (s, 3H), 3.90 (s, 3H),
3.80e3.78 (m, 2H), 3.75e3.73 (m, 2H), 3.66e3.61 (m, 20H),
2.93e2.89 (m, 4H). 13C NMR (100 MHz, CDCl3)
d: 168.2, 165.9, 160.3,
160.2, 160.1, 149.4, 141.1, 139.5, 139.4, 136.9, 132.3, 128.7, 128.1, 127.7,
126.7 (d), 126.3, 124.5, 124.4, 123.9, 123.0 (d), 122.9, 112.4, 112.3,
112.2, 112.1, 106.7, 106.6, 106.5, 101.7 (d), 101.4, 73.2, 71.4, 71.1, 70.8
(d), 70.7, 70.6 (d), 70.2, 70.1, 69.8, 69.7, 69.6, 62.3, 52.4, 35.3. MS
(MALDI-TOF) m/z: 2371.8 [M]þ. HRMS (MALDI-TOF): calcd for
C136H133NO25S6 [M]þ: 2373.7491. Found: 2373.7460.
4. Experimental section
4.1. General methods
4.1.3. Pseudorotaxane 1d. A solution of 3d (29 mg, 0.01 mmol) and
CBPQT$4PF6 (11 mg, 0.01 mmol) in acetone (0.25 mL) and aceto-
nitrile (0.25 mL) was stirred for 36 h and then concentrated. The
resulting green solid was dissolved in acetonitrile (10 mL) and to
the solution added water (40 mL) quickly. The formed dark green
solid was filtrated and washed with aqueous acetonitrile (20%,
20 mLꢂ4) and ether (10 mL). The solid was then triturated with
All reagents and chemicals were obtained from commercial
sources and used without further purification unless otherwise
noted. The solvents have been purified by standard procedures
before use. The 1H and 13C NMR spectra were recorded on Varian
Mercury 300 or 400 MHz spectrometers in the indicated solvents.
Chemical shifts are expressed in parts per million (d) using residual

4526
K.-D. Zhang et al. / Tetrahedron 68 (2012) 4517e4527
CH2Cl2 (15 mL) and the insoluble solid was removed by filtration,
which was CBPQT$4PF6 as evidenced by 1H NMR. The solution was
again concentrated and the resulting residue triturated succes-
sively with a mixture of CH2Cl2 and PE (1:2, 10 mLꢂ4) to remove
free 3d. The solid was then dried in vacuo to give pure 1d as
69.0, 68.9, 69.8 (d), 67.4, 64.2, 61.8, 61.4, 39.1, 34.7, 34.3, 29.6, 26.4,
25.7, 25.6, 23.0, 22.4. MS (ESI): 900.12 [Mꢁ4PF6]4þ, 1249.05
[Mꢁ3PF6]3þ. HRMS (ESI): calcd for C218H227N7O29S6 [Mꢁ4PF6]4þ
:
899.6207. Found: 899.6200. Thread 4a. 1H NMR (400 MHz, CDCl3)
d: 10.03 (s, 1H), 9.00 (s, 1H), 8.71 (d, J¼8.0 Hz, 1H), 8.51 (d, J¼8.0 Hz,
a green solid (21 mg, 53%). 1H NMR (400 MHz, CD3CN)
d
: 10.09 (s,
1H), 7.90e7.84 (m, 3H), 7.69 (d, J¼8.0 Hz, 1H), 7.40e7.29 (m, 44H),
7.09 (s, 3H), 6.83 (t, J¼8.4 Hz, 2H), 6.67 (s, 12H), 6.60 (s, 2H), 6.56 (s,
4H), 6.53 (s, 3H), 6.31 (s, 1H), 6.30 (s, 1H), 5.00 (s, 16H), 4.95 (s,
12H), 4.49 (s, 2H), 4.20 (s, 2H), 4.17 (t, J¼6.0 Hz, 2H), 4.10 (t,
J¼5.6 Hz, 2H), 3.92 (s, 3H), 3.85 (s, 3H), 3.82e3.79 (m, 4H), 3.74 (br,
2H), 3.66e3.54 (m, 20H), 3.49e3.45 (m, 2H), 3.35e3.31 (m, 2H),
2.88e2.84 (m, 4H), 2.03e1.89 (m, 6H), 1.83e1.80 (m, 2H), 1.63e1.62
(m, 2H), 1.54e1.52 (m, 2H), 1.44e1.26 (m, 14H), 1.23 (d, J¼7.2 Hz,
1H), 9.92 (br, 2H), 8.87 (d, J¼6.0 Hz, 8H), 8.82 (s, 1H), 8.67 (d,
J¼8.0 Hz, 1H), 8.59 (br, 2H), 8.31 (d, J¼8.0 Hz, 1H), 7.83 (br, 8H),
7.74e7.69 (m, 3H), 7.54 (s, 8H), 7.50e7.46 (m, 1H), 7.42e7.39 (m,
1H), 7.33e7.15 (m, 43H), 6.59e6.56 (m, 8H), 6.54e6.53 (m, 4H),
6.49e6.44 (m, 6H), 6.41e6.36 (m, 3H), 5.93 (d, J¼13 Hz, 1H), 5.82
(d, J¼17 Hz, 1H), 5.60e5.53 (m, 8H), 4.96e4.93 (m, 16H), 4.89e4.84
(m, 12H), 4.25 (s, 2H), 4.08e4.50 (m, 2H), 3.93 (s, 3H), 3.90e3.86
(m, 6H), 3.81e3.80 (m, 6H), 3.71e3.61 (m, 16H), 3.57 (br, 2H), 3.50
(br, 2H), 3.48e3.40 (m, 4H), 2.96e2.90 (m, 4H). MS (ESI) m/z:
835.54 [Mꢁ4PF6]4þ, 1162.04 [Mꢁ3PF6]3þ, [Mꢁ2PF6]2þ 1185.54.
12H). 13C NMR (100 MHz, CDCl3)
d: 168.2, 165.3, 163.0, 160.2, 160.1,
160.0, 154.7 (d), 153.4, 147.4, 147.1, 141.9, 140.9, 139.4, 139.3, 136.8,
132.1, 131.2, 128.6, 128.1, 127.6, 127.2, 126.8 (d), 126.6 (d), 126.5,
126.4, 125.9, 125.7, 125.4, 125.2, 125.1, 124.5, 124.0, 123.9, 123.1,
123.0 (d), 122.9, 114.2, 114.1, 112.5, 111.8, 106.6, 106.5, 106.4, 105.3,
101.6, 101.5, 101.2, 74.8, 73.1, 71.2, 71.0, 70.7 (d), 70.6, 70.5, 70.1,
70.0, 69.8, 69.6, 69.5. 68.2, 68.0, 62.7, 62.5, 40.0, 35.2, 30.4, 29.8,
29.7, 29.5, 29.4 (d), 27.2, 26.5, 26.3, 24.2, 23.1. MS (MALDI-TOF) m/z:
3078.2 [M]þ. HRMS (MALDI-TOF): calcd for C182H195N3O29S6:
3078.2201 [M]þ. Found: 3078.2228.
HRMS (ESI): calcd for C196H186F12N8O31P2S6 [Mꢁ2PF6]2þ
:
1814.5416]. Found: 1814.5417.
4.1.4. Bistable [2]rotaxane 2a and thread 4a. A suspension of 24a
(35 mg, 0.033 mmol) and Pd/C (10%, 30 mg) in THF (5 mL) was
stirred at 40 ꢀC under the atmosphere of hydrogen for 30 h and
then cooled. The solid was removed by filtration and the filtrate
concentrated to give 25a as a sticky oil (33 mg, 96%). Without
further purification, this amine was dissolved in chloroform (1 mL)
for the next step. To a solution of 15 (70 mg, 0.033 mmol) in
4.1.5. Bistable [2]rotaxane 2b. Green solid. 1H NMR (400 MHz,
CD3COCD3) d: 10.08 (s, 1H), 10.04 (s, 1H), 9.35 (br, 8H), 8.96 (s, 1H),
chloroform (2 mL) were added NMM (5.3
m
L, 0.043 mmol) and
8.54e8.52 (m, 1H), 8.48 (d, J¼6.8 Hz, 1H), 8.31e8.25 (m, 9H), 7.78
(br, 8H), 7.70e7.62 (m, 5H), 7.31e7.14 (m, 45H), 7.07 (t, J¼8.0 Hz,
1H), 6.98e6.90 (m, 3H), 6.83e6.76 (m, 2H), 6.60 (br, 8H), 6.56 (s,
4H), 6.50 (br, 6H), 6.44 (s, 1H), 6.31 (s, 2H), 6.09 (d, J¼13.6 Hz, 1H),
6.01 (d, J¼13.6 Hz, 1H), 5.87 (s, 8H), 4.94 (s, 16H), 4.90 (s, 8H), 4.85
(s, 4H), 4.19 (s, 2H), 4.09 (t, J¼6.0 Hz, 2H), 4.06 (s, 2H), 4.00 (d,
J¼6.0 Hz, 2H), 3.91 (br, 6H), 3.82 (s, 3H), 3.73e3.66 (m, 14H), 3.62
(s, 4H), 3.58e3.52 (m, 2H), 3.50e3.46 (m, 2H), 3.43e3.35 (m, 6H),
3.30e3.27 (m, 2H), 3.26e3.19 (m, 2H), 3.02e2.95 (m, 4H),
1.85e1.70 (m, 8H), 1.53e1.50 (m, 2H), 1.43e1.40 (m, 2H), 1.30e1.15
ClCO2Et (4.7 L, 0.039 mmol). The solution was stirred for 1 h and
m
then concentrated. The resulting slurry was dissolved in THF
(2 mL) and the insoluble residue removed by filtration. The filtrate
was concentrated again and the resulting orange oil dissolved in
acetone (0.6 mL) and acetonitrile (0.3 mL). CBPQT$4PF6 (34 mg,
0.031 mmol) and the above solution of 25a were added and the
mixture stirred for 24 h and then concentrated to afford a dark
green solid. The residue was supersonicated in CH2Cl2 (12 mL) and
PE (18 mL) for 2 h and then insoluble green residue removed by
filtration. The resulting green solid was dissolved in acetonitrile
(10 mL). Water (40 mL) was added dropwise and the formed pre-
cipitate filtrated out again and washed with acetonitrile and water
(100 mL, 1:4) thoroughly. The solid was dissolved in a solution of
NH4PF6 (0.10 g) in acetone (5 mL) and the solution was concen-
trated. The resulting slurry was triturated with water (10 mL). The
insoluble green residue was filtrated out again, washed with water
(10 mLꢂ3) and ether (5 mL) and dried in vacuo to afford 2a as
a green solid (24 mg, 18%). The filtrate of CH2Cl2 and PE was con-
centrated with a rotavapor and the resulting residue subjected to
column chromatography (n-hexane/chloroform 1:1) to give 4a as
an orange solid foam (40 mg, 40%). [2]Rotaxane 2a. 1H NMR
(m, 14H), 1.06 (d, J¼6.8 Hz, 12H). 13C NMR (100 MHz, CD3COCD3)
d:
167.8, 165.2, 162.7, 162.4, 159.7, 159.6, 159.4, 154.1, 153.1, 147.5, 147.4,
146.7, 145.5, 145.4, 144.3, 141.1, 140.7, 139.3, 136.8, 135.9 (d), 132.1,
131.8, 131.1, 131.0, 130.5, 128.6, 127.9, 127.7, 127.3, 127.1, 126.7, 126.6,
126.3, 125.5, 125.4, 125.3, 124.7 (d), 124.5, 124.4, 124.1, 123.9, 123.8,
123.7, 123.3, 122.1, 119.8, 119.6, 119.3, 119.0, 118.7, 113.4, 113.3, 108.4,
108.3 (d), 107.9, 106.0, 104.9 (d), 100.6, 100.2, 74.0, 71.6, 70.4, 70.0,
69.8, 69.7, 69.5 (d), 69.4, 69.2, 69.0, 68.9, 68.8, 67.4, 64.2, 62.3, 61.9,
61.4, 39.1, 34.7, 34.3, 29.6, 26.4, 25.7, 25.6, 23.0, 22.4. HRMS (ESI):
calcd for C226H234N8O31S6 [Mꢁ4PF6]4: 936.8826. Found: 936.8671.
HRMS (ESI): calcd for C226H234F6N8O31PS6 [Mꢁ3PF6]3þ: 1297.4984.
Found: 1297.4784. Thread 4b. Orange solid in 15% yield. 1H NMR
(400 MHz, CD3COCD3)
d: 10.05 (s, 1H), 9.31 (br, 8H), 8.90 (s, 1H),
(CDCl3, 400 MHz) d: 9.86 (s, 1H), 9.78 (s, 1H), 8.92 (s, 1H), 8.70 (d,
8.45 (d, J¼7.6 Hz, 1H), 8.32e8.15 (m, 9H), 7.77 (s, 8H), 7.70e7.60 (m,
4H), 7.31e7.10 (m, 44H), 7.04 (t, J¼8.4 Hz, 1H), 6.98e6.90 (m, 3H),
6.83e6.77 (m, 2H), 6.60 (s, 8H), 6.56 (s, 4H), 6.49 (br, 6H), 6.43 (br,
1H), 6.33 (s, 2H), 6.06 (d, J¼12.8 Hz, 1H), 5.96 (d, J¼13.6 Hz, 1H),
5.85 (br, 8H), 4.93 (s, 16H), 4.89 (s, 8H), 4.84 (s, 4H), 4.20 (s, 2H),
4.08 (t, J¼6.0 Hz, 2H), 4.05 (s, 2H), 3.99 (t, J¼6.0 Hz, 2H), 3.83e3.81
(m, 6H), 3.75e3.66 (m, 12H), 3.63 (s, 4H), 3.57e3.55 (m, 2H),
3.50e3.48 (m, 2H), 3.44e3.37 (m, 6H), 3.32e3.29 (m, 2H),
3.24e3.20 (m, 2H), 3.05e3.00 (m, 2H), 2.99e2.94 (m, 2H),
1.87e1.68 (m, 8H), 1.54e1.49 (m, 2H), 1.46e1.40 (m, 2H), 1.32e1.16
J¼8.0 Hz, 1H), 8.63 (d, J¼7.6 Hz, 1H), 8.44 (d, J¼7.6 Hz, 1H),
7.82e7.50 (m, 4H), 7.59 (d, J¼7.6 Hz, 1H), 7.38e7.18 (m, 46H), 7.08
(t, J¼6.0 Hz, 1H), 7.02 (br, 3H), 6.79e6.72 (m, 2H), 6.59 (br, 12H),
6.51 (br, 2H), 6.48 (br, 4H), 6.45 (br, 3H), 6.24 (d, J¼2.0 Hz, 1H), 6.20
(s, 1H), 4.93 (s, 16H), 4.88 (br, 12H), 4.41 (s, 2H), 4.15 (s, 2H), 4.10 (t,
J¼6.0 Hz, 2H), 4.03 (t, J¼6.0 Hz, 2H), 3.89 (s, 3H), 3.88 (s, 3H), 3.79
(s, 3H), 3.78e3.65 (m, 6H), 3.60e3.45 (m, 20H), 3.44e3.38 (m, 2H),
3.29e3.23 (m, 2H), 2.82e2.70 (m, 4H), 2.00e1.70 (m, 8H),
1.60e1.42 (m, 4H), 1.35e1.70 (m, 14H), 1.15 (d, J¼6.8 Hz, 12H). 13C
NMR (DMSO-d6, 100 MHz) d: 168.3, 165.7, 163.4, 162.9, 159.5, 159.4,
(m, 14H), 1.06 (d, J¼6.8 Hz, 12H). 13C NMR (100 MHz, CD3COCD3)
d:
159.3, 153.9, 152.9, 148.5, 147.9, 147.1, 141.1, 140.9, 139.3, 139.2,
136.8, 131.8, 131.5, 131.1, 130.1, 128.3, 128.1, 127.8, 127.7, 127.6, 127.2,
125.9, 125.8 (d), 125.3, 125.2 (d), 124.8, 124.5, 124.3, 124.2, 123.7,
123.6, 123.1 (d), 122.6, 113.3 (d), 111.0 (d), 110.9 (d), 106.4, 106.1,
105.6, 105.5, 101.0, 100.7, 74.2, 71.7, 70.4, 70.0, 69.7, 69.6 (d), 69.5,
69.2, 69.0 (d), 68.7, 68.6, 67.6, 62.6, 62.1, 61.7, 34.6, 30.2, 29.6, 28.9
(d), 28.7, 28.5 (d), 26.4, 25.7, 25.6, 23.8, 22.5. MS (MALDI-TOF) m/z:
167.8, 165.4, 162.1, 159.7, 159.6, 159.4, 154.1, 153.0, 147.4, 146.6,
145.4, 144.3, 141.1, 140.7, 139.3, 136.8, 135.9, 131.7, 131.1, 130.5, 128.5,
127.9, 127.7, 127.3, 127.1, 126.3 (d), 126.0, 125.9, 125.5, 124.7 (d),
124.5, 124.3, 124.0, 123.9, 123.5, 123.3, 122.0, 119.7, 119.6, 119.3,
119.0, 113.4, 113.2, 108.3, 108.2, 107.9 (d), 106.0, 104.9 (d), 100.6,
100.2, 74.0, 71.6, 70.4, 70.0, 69.9, 69.8, 69.6 (d), 69.5, 69.4 (d), 69.2,

K.-D. Zhang et al. / Tetrahedron 68 (2012) 4517e4527
4527
3227.3 [M]þ. HRMS (MALDI-TOF): calcd for C190H202N4O31S6 [M]þ:
3227.2677. Found: 3227.2652.
Becher, J.; Stoddart, J. F. Angew. Chem., Int. Ed. 2001, 40, 1216e1221; (b)
Steuerman, D. W.; Tseng, H.-R.; Peters, A. J.; Flood, A. H.; Jeppesen, J. O.; Nielsen,
K. A.; Stoddart, J. F.; Heath, J. R. Angew. Chem., Int. Ed. 2004, 43, 6486e6491; (c)
Flood, A. H.; Peters, A. J.; Vignon, S. A.; Steuerman, D. W.; Tseng, H.-R.; Kang, S.;
Heath, J. R.; Stoddart, J. F. Chem.dEur. J. 2004, 10, 6558e6564.
Acknowledgements
18. For examples, of controllable shuttling of rotaxanes, see (a) Kang, S.; Vignon, S.
A.; Tseng, H. R.; Stoddart, J. F. Chem.dEur. J. 2004, 10, 2555e2564; (b) Nygaard,
S.; Laursen, B. W.; Flood, A. H.; Hansen, C. N.; Jeppesen, J. O.; Stoddart, J. F. Chem.
Commun. 2006, 144e146; (c) Jeppesen, J. O.; Nygaard, S.; Vignon, S. A.; Stoddart,
We thank NSFC (20732007, 20921091, 20872167, 20974118), and
STCSM (10PJ1412200 and 09XD1405300) for financial support.
ꢀ
J. F. Eur. J. Org. Chem. 2005, 196e220; (d) Alvarez-Perez, M.; Goldup, S. M.; Leigh,
D. A.; Slawin, A. M. Z. J. Am. Chem. Soc. 2008, 130, 1836e1838.
19. A preliminary communication has been reported, see: Zhang, K.-D.; Zhao, X.;
Wang, G.-T.; Liu, Y.; Zhang, Y.; Lu, H.-J.; Jiang, X.-K.; Li, Z.-T. Angew. Chem., Int. Ed.
2011, 50, 9866e9870.
References and notes
1. (a) Schill, G. Catenanes, Rotaxanes, and Knots; Academic: New York, NY, 1971;
192; (b) Molecular Catenanes, Rotaxanes and Knots: a Journey through the World
of Molecular Topology; Sauvage, J.-P., Dietrich-Buchecker, C., Eds.; Wiley-VCH:
Weinheim, 1999; p 368.
2. (a) Amabilino, D. B.; Stoddart, J. F. Chem. Rev. 1995, 95, 2725e2828; (b) Sauvage,
J.-P. Acc. Chem. Res. 1998, 31, 611e619.
3. (a) Glink, P. T.; Schiavo, C.; Stoddart, J. F.; Williams, D. J. Chem. Commun. 1996,
1483e1490; (b) Harada, A.; Hashidzume, A.; Yamaguchi, H.; Takashima, Y.
Chem. Rev. 2009, 109, 5974e6023.
ꢀ
20. Hawker, C. J.; Frechet, M. J. J. Am. Chem. Soc. 1990, 112, 7638e7647.
ꢀ
21. Amabilino, D. B.; Ashton, P. R.; Balzani, V.; Brown, C. L.; Credi, A.; Frechet, J. M. J.;
Leon, J. W.; Raymo, F. M.; Spencer, N.; Stoddart, J. F.; Venturi, M. J. Am. Chem. Soc.
1996, 118, 12012e12020.
22. (a) Hou, J.-L.; Yi, H.-P.; Shao, X.-B.; Li, C.; Wu, Z.-Q.; Jiang, X.-K.; Wu, L.-Z.; Tung,
C.-H.; Li, Z.-T. Angew. Chem., Int. Ed. 2006, 45, 796e800; (b) Yi, H.-P.; Wu, J.;
Ding, K.-L.; Jiang, X.-K.; Li, Z.-T. J. Org. Chem. 2007, 72, 870e877.
23. (a) Qin, B.; Chen, X. Y.; Fang, X.; Shu, Y. Y.; Yip, Y. K.; Yan, Y.; Pan, S. Y.; Ong, W.
Q.; Ren, C. L.; Su, H. B.; Zeng, H. Q. Org. Lett. 2008, 10, 5127e5130; (b) Yan, Y.;
Qin, B.; Ren, C. L.; Chen, X. Y.; Yip, Y. K.; Ye, R. J.; Zhang, D. W.; Su, H. B.; Zeng, H.
Q. J. Am. Chem. Soc. 2010, 132, 5869e5879; (c) Qin, B.; Ren, C. L.; Ye, R. J.; Sun, C.;
Chiad, K.; Chen, X. Y.; Li, Z.; Xue, F.; Su, H. B.; Chass, G. A.; Zeng, H. Q. J. Am.
Chem. Soc. 2010, 132, 9564e9566; (d) Qin, B.; Ong, W. Q.; Ye, R. J.; Du, Z. Y.;
Chen, X. Y.; Yan, Y.; Zhang, K.; Su, H. B.; Zeng, H. Q. Chem. Commun. 2011,
5419e5421; (e) Qin, B.; Sun, C.; Liu, Y.; Shen, J.; Ye, R. J.; Zhu, J.; Duan, X.-F.;
Zeng, H. Q. Org. Lett. 2011, 13, 2270e2273.
24. Anelli, P. L.; Ashton, P. R.; Ballardini, R.; Balzani, V.; Delgado, M.; Gandolfi, M. T.;
Goodnow, T. T.; Kaifer, A. E.; Philp, D.; Pietraszkiewicz, M.; Prodi, L.; Red-
dington, M. V.; Slawin, A. M. Z.; Spencer, N.; Stoddart, J. F.; Vicent, C.; Williams,
D. J. J. Am. Chem. Soc. 1992, 114, 193e218.
25. Liu, Y.; Flood, A. H.; Bonvallet, P. A.; Vignon, S. A.; Northrop, B. H.; Tseng, H.-R.;
Jeppesen, J. O.; Huang, T. J.; Brough, B.; Baller, M.; Magonov, S.; Solares, S. D.;
Goddard, W. A.; Ho, C.-M.; Stoddart, J. F. J. Am. Chem. Soc. 2005, 127, 9745e9759.
26. Jia, C.; Zhang, D.; Xu, W.; Zhu, D. Org. Lett. 2001, 3, 1941e1944.
27. The samples of 1bed were found stable at room temperature after two months.
The 1H NMR spectra of their suspended solution in CDCl3 did not exhibit the
signals of free 3bed, and the thin layer chromatography (TLC) did not show the
spot of free 3bed either.
28. The 1:1 mixture of 3a and CBPQT$4PF6 in acetonitrile/acetone (1:2, v/v) quickly
turned from orange to blue, indicating the formation of the threaded complex.
However, the trituration of the concentrated residue with acetonitrile/water (1:
4, v/v) or dichloromethane/petroleum ether (1:2, v/v) caused complete re-
moval of CBPQT$4PF6 and 3a, respectively, indicating that pseudorotaxane 1a
decomplexed rapidly within the operation time.
4. (a) Crowley, J. D.; Goldup, S. M.; Lee, A.-L.; Leigh, D. A.; McBurney, R. T. Chem.
Soc. Rev. 2009, 38, 1530e1541; (b) Silvi, S.; Venturi, M.; Credi, A. J. Mater. Chem.
2009, 19, 2279e2294; (c) Stoddart, J. F. Chem. Soc. Rev. 2009, 38, 1802e1820; (d)
Durot, S.; Reviriego, F.; Sauvage, J.-P. Dalton Trans. 2010, 39, 10557e10570.
ꢀ
5. (a) Bissell, R. A.; Cordova, E.; Kaifer, A. E.; Stoddart, J. F. Nature 1994, 369,
133e137; (b) Altieri, A.; Gatti, F. G.; Kay, E. R.; Leigh, D. A.; Martel, D.; Paolucci,
F.; Slawin, A. M. Z.; Wong, J. K. Y. J. Am. Chem. Soc. 2003, 125, 8644e8654; (c)
Collin, J. P.; Gavina, P.; Heitz, V.; Sauvage, J.-P. Eur. J. Inorg. Chem. 1998, 1e14.
ꢀ
ꢀ
6. (a) Balzani, V.; Gomez-Lopez, M.; Stoddart, J. F. Acc. Chem. Res. 1998, 31,
405e414; (b) Harada, A. Acc. Chem. Res. 2001, 34, 456e464; (c) Kay, E. R.; Leigh,
D. A. Top. Curr. Chem. 2005, 262, 133e177; (d) Tian, H.; Wang, Q.-C. Chem. Soc.
Rev. 2006, 35, 361e374; (e) Balzani, V.; Credi, A.; Venturi, M. Chem. Soc. Rev.
2009, 38, 1542e1550.
7. (a) Pease, A. R.; Jeppesen, J. O.; Stoddart, J. F.; Luo, Y.; Collier, C. P.; Heath, J. R.
Acc. Chem. Res. 2001, 34, 433e444; (b) Trabolsi, A.; Fahrenbach, A. C.; Dey, S. K.;
Share, A. I.; Friedman, D. C.; Basu, S.; Gasa, T. B.; Khashab, N. M.; Saha, S.;
Aprahamian, I.; Khatib, H. A.; Flood, A. H.; Stoddart, J. F. Chem. Commun. 2010,
871e873.
8. (a) Flood, A. H.; Stoddart, J. F.; Steuerman, D. W.; Heath, J. R. Science 2004, 306,
2055e2056; (b) Choi, J. W.; Flood, A. H.; Steuerman, D. W.; Nygaard, S.;
Braunschweig, A. B.; Moonen, N. N. P.; Laursen, B. W.; Luo, Y.; Delonno, E.;
Peters, A. J.; Jeppesen, J. O.; Xe, K.; Stoddart, J. F.; Heath, J. R. Chem.dEur. J. 2006,
12, 261e279.
9. Li, H.; Zhao, Y.-L.; Fahrenbach, A. C.; Kim, S.-Y.; Paxton, W. F.; Stoddart, J. F. Org.
Biomol. Chem. 2011, 9, 2240e2250.
10. Foldamers: Structure, Properties and Applications; Hecht, S., Huc, I., Eds.; Wiley-
VCH: Weinheim, 2007; p 456.
11. (a) Gong, B. Chem.dEur. J. 2001, 7, 4336e4342; (b) Huc, I. Eur. J. Org. Chem. 2004,
17e29; (c) Gong, B. Acc. Chem. Res. 2008, 41, 1376e1386; (d) Saraogi, I.; Ham-
ilton, A. D. Chem. Soc. Rev. 2009, 38, 1726e1743; (e) Guichard, G.; Ivan Huc, I.
Chem. Commun. 2011, 5933e5941.
12. (a) Li, Z.-T.; Hou, J.-L.; Li, C.; Yi, H.-P. Chem.dAsian J. 2006, 1, 766e778; (b) Li, Z.-
T.; Hou, J.-L.; Li, C. Acc. Chem. Res. 2008, 41, 1343e1353; (c) Zhao, X.; Li, Z.-T.
Chem. Commun. 2010, 1601e1616.
29. Tseng, H. R.; Vignon, S. A.; Stoddart, J. F. Angew. Chem., Int. Ed. 2003, 42,
1491e1495.
30. Ashton, P. R.; Baxter, I.; Fyfe, M. C. T.; Raymo, F. M.; Spencer, N.; Stoddart, J. F.;
White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1998, 120, 2297e2307.
31. Chiang, P.-T.; Cheng, P.-N.; Lin, C.-F.; Liu, Y.-H.; Lai, C.-C.; Peng, S.-M.; Chiu, S.-H.
Chem.dEur. J. 2006, 12, 865e876.
32. Reichardt, C. Solvents and Solvent Effects in Organic Chemistry; Wiley-VCH:
Weinheim, 2003; 653.
13. Shi, Z.-M.; Huang, J.; Ma, Z.; Guan, Z.; Li, Z.-T. Macromolecules 2010, 43,
33. (a) Parra, R. D.; Zeng, H.; Zhu, J.; Zheng, C.; Zeng, X. C.; Gong, B. Chem.dEur. J.
6185e6192.
ꢀ
2001, 7, 4352e4357; (b) Jiang, H.; Leger, J. M.; Guionneau, P.; Huc, I. Org. Lett.
14. Philp, D.; Slawin, A. M. Z.; Spencer, N.; Stoddart, J. F.; Williams, D. J. J. Chem. Soc.,
Chem. Commun. 1991, 1584e1586.
2004, 6, 2985e2988; (c) Li, F.; Gan, Q.; Xue, L.; Wang, Z.-M.; Jiang, H. Tetra-
hedron Lett. 2009, 50, 2367e2369.
15. Li, Z.-T.; Stein, P. C.; Svenstrup, N.; Lund, K. H.; Becher, J. Angew. Chem., Int. Ed.
Engl. 1995, 34, 2524e2528.
34. Connelly, N. G.; Geiger, W. Chem. Rev. 1996, 96, 877e910.
35. Kanamori, D.; Okamura, T.-A.; Yamamoto, H.; Ueyama, N. Angew. Chem., Int. Ed.
2005, 44, 969e972.
36. Yu, Z.; Hecht, S. Angew. Chem., Int. Ed. 2011, 50, 1640e1643.
37. Hou, J.-L.; Shao, X.-B.; Chen, G.-J.; Zhou, Y.-X.; Jiang, X.-K.; Li, Z.-T. J. Am. Chem.
Soc. 2004, 126, 12386e12394.
16. A pseudorotaxane consisting of a MeS-bearing TTF-DNP thread and a CBPQT4þ
ring had been reported to have a rotaxane-like character, see: Jeppesen, J. O.;
Becher, J.; Stoddart, J. F. Org. Lett. 2002, 4, 557e560.
17. For examples, of bistable rotaxanes based on the CBPQT4þ ring and TTF and
DNP-containing dumbbell component, see: (a) Jeppesen, J. O.; Perkins, J.;