Using threading followed by shrinking to synthesize highly stable dialkylammonium-ion-based rotaxanes

Article abstract of DOI:10.1002/chem.201300049

Herein, we report a threading followed by shrinking approach for the synthesis of rotaxanes by using an oxygen-deficient macrocycle that contained two arylmethyl sulfone units and the dumbbell-shaped salt bis(3,5-dimethylbenzyl)ammonium tetrakis(3,5-trifluoromethylphenyl)borate as the host and guest components, respectively. The extrusion of SO₂ from both of the arylmethyl sulfone units of the macrocyclic component in the corresponding [2]pseudorotaxane resulted in a [2]rotaxane that was sufficiently stable to maintain its molecular integrity in CD₃SOCD₃ at 393 K for at least 5 h. Shrink wrap: A threading followed by shrinking method, which was used to extrude both arylmethyl sulfone motifs from the macrocyclic components of dialkylammonium-ion-based [2]pseudorotaxanes, afforded robust [2]rotaxanes that were sufficiently stable to maintain their molecular integrity in CD₃SOCD₃ at 393 K for at least 5 h (see figure). Copyright

Full text of DOI:10.1002/chem.201300049

FULL PAPER
DOI: 10.1002/chem.201300049
Using “Threading Followed by Shrinking” to Synthesize Highly Stable
Dialkylammonium-Ion-Based Rotaxanes
Liang-Yun Wang,[a] Jia-Ling Ko,[a] Chien-Chen Lai,[b] Yi-Hung Liu,[a]
Shie-Ming Peng,[a] and Sheng-Hsien Chiu*[a]
Abstract: Herein, we report a “thread-
ing followed by shrinking” approach
for the synthesis of rotaxanes by using
an “oxygen-deficient” macrocycle that
contained two arylmethyl sulfone units
as the host and guest components, re-
spectively. The extrusion of SO2 from
both of the arylmethyl sulfone units of
the macrocyclic component in the cor-
responding [2]pseudorotaxane resulted
in a [2]rotaxane that was sufficiently
stable to maintain its molecular
integrity in CD3SOCD3 at 393 K for at
least 5 h.
Keywords: rotaxanes · shrinking ·
and
the
dumbbell-shaped
salt
supramolecular
chemistry
·
bis(3,5-dimethylbenzyl)ammonium tet-
rakis(3,5-trifluoromethylphenyl)borate
synthetic methods · threading
Introduction
The potential applicability of rotaxanes as molecular actua-
tors and switches within mesoscale molecular electronic de-
vices has driven the development of new methods and pro-
cedures for their synthesis.[1] Over the past two decades,
“threading followed by stoppering”,[2] “clipping”,[3] and
“slippage”[4] have been the most widely used approaches for
the construction of interlocked molecules that perform vari-
ous functions (Figure 1). Although “threading followed by
swelling”[5] and “threading followed by shrinking”[6] strat-
egies have conceptually been suggested for many years,
their experimental realization was only recently demonstrat-
ed after several practical difficulties had been resolved. For
example, balancing the sizes of the macrocyclic component
and the termini of the dumbbell component—a major chal-
lenge when developing new “slippage” systems—is also a re-
quirement for successful “threading followed by swelling”
and “threading followed by shrinking” strategies, such that
the macrocyclic component can thread onto, but not slip off
from, the rod-like portion of the dumbbell-shaped compo-
nent prior to the onset of specific reactions to enlarge the
termini of the threadlike component (“swelling”) or to
shrink the size of the macrocyclic component (“shrinking”).
Figure 1. Schematic representation of various approaches for the synthe-
sis of rotaxanes.
The “shrinking” approach was first realized by employing a
Pd2+ ion to chelate a salophen moiety in the macrocyclic
unit of a corresponding [2]pseudorotaxane, thereby decreas-
ing the amount of free space in the complexed macrocycle
and interlocking the components of the [2]rotaxane.[6a] To
demonstrate the “shrinking” concept, which involves de-
creasing the number of atoms in the skeleton of the macro-
cyclic component, it was necessary to solve several other
problems in addition to that of balancing the sizes of the
macrocyclic and terminal components. When designing such
a system, the non-shrinking portion of the macrocycle
[a] L.-Y. Wang, J.-L. Ko, Y.-H. Liu, Prof. S.-M. Peng, Prof. S.-H. Chiu
Department of Chemistry and Center for Emerging Material and
Advanced Devices, National Taiwan University
No. 1, Sec. 4, Roosevelt Rd., Taipei, Taiwan 10617 (R.O.C.)
Fax : (+886)2-33661677
E-mail: shchiu@ntu.edu.tw
[b] Prof. C.-C. Lai
Institute of Molecular Biology, National Chung Hsing University and
Department of Medical Genetics, China Medical University Hospital
Taichung, Taiwan (R.O.C.)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300049.
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should be the primary source of stabilizing interactions
toward the threadlike component; if so, the variation in the
structure of the shrinking motif in the macrocyclic unit
would not significantly disrupt the stabilizing interactions in
the host/guest complex. In addition, the rate of shrinking of
the macrocycle in its complexed state should not be much
slower than that in its free state, thereby ensuring that the
pseudorotaxanes that are generated in solution do not disso-
ciate to overcome the decrease in concentration of the free
macrocycle. Moreover, because the recognition of the com-
ponents relies on weak noncovalent interactions, a mild
chemical reaction would be preferred for shrinking the ring
skeleton of the macrocyclic component to ensure that the
[2]pseudorotaxane does not undergo significant dissociation
in the presence of any undesired side products that may be
generated during the transformation.
Previously, we reported the preparation of a [2]rotaxane
by using a “threading follow by shrinking” approach that in-
volved the photoextrusion of SO2 from an arylmethyl sul-
fone motif in a penta(ethylene glycol)-containing macrocy-
cle.[6b] We suspected that performing the same photoextru-
sion reaction twice on a single macrocyclic component
would decrease the size of the resulting macrocycle even
further and, hence, result in [2]rotaxanes that were structur-
ally much more robust. Nevertheless, situating two aryl-
methyl sulfone motifs in a single macrocycle would presum-
ably hinder its binding ability to an ammonium-ion-contain-
ing dumbbell-shaped component. Because we have previ-
ously developed a successful “threading followed by swel-
ling” approach toward [2]rotaxanes, by using an “oxygen-
deficient” macrocycle (1)/dibenzylammonium ion molecular
recognition system with a cis-1-[(Z)-alk-1’-enyl]-2-vinylcy-
clopropane motif as the swellable terminal group,[5] we were
interested in realizing a “shrinking” approach that employed
macrocycle 1 (Scheme 1).
Herein, we report the use of an “oxygen-deficient” mac-
rocycle that contains two arylmethyl sulfone units for suc-
cessful “threading follow by shrinking” in conjunction with
a dumbbell-shaped salt, bis(3,5-dimethylbenzyl)ammonium
tetrakis(3,5-trifluoromethylphenyl)borate;
the
resulting
[2]rotaxane that is formed after SO2 has been extruded from
both of the arylmethyl sulfone motifs of the macrocyclic
component is sufficiently stable to maintain its molecular
integrity in CD3SOCD3 at 393 K for at least 5 h.
Results and Discussion
Previously, we have demonstrated that “oxygen-deficient”
macrocycle 1 is capable of forming a complex with dibenzyl-
ACHUTNGRENaUNG mmonium hexafluorophosphate ([DBA]CAHTUNGTRNE[NGUN PF6]) in CD3NO2
with an association constant (Ka) as high as 15000mÀ1
(Scheme 1).[7] Because the complexation of the DBA+ ion
+
À
with macrocycle 1 is mainly based on [N H···O] and
+
+
À
À
[N C H···O] hydrogen bonds and on [N H···p] and
+
+
À
[N C H···p] interactions between the CH2NH2 CH2 moiety
and the di(ethylene glycol) loop and its adjacent phenolic
units, respectively, in macrocycle 1, we suspected that intro-
duction of arylmethyl sulfone motifs into the para-xylene
motif of compound 1—a motif that is not involved signifi-
cantly in the stabilization of the complex—would result in
the formation of macrocycle 2, which would also be capable
of binding to the DBA+ ion.
We synthesized macrocycle 2 from di(ethylene glycol) in
five steps (Scheme 2). Alkylation of di(ethylene glycol) with
methyl 4-(bromomethyl)benzoate (3) gave diester 4, which
we reduced into the corresponding diol (5) by using LiAlH4.
We obtained dichloride 6 after treating diol 5 with N-chloro-
succinimide (NCS) and triphenylphosphine (PPh3); then, di-
chloride 6 underwent macrocyclization with 1,4-benzenedi-
methanethiol under basic conditions to afford macrocycle 7.
The use of meta-chloroperbenzoic acid (MCPBA) to oxidize
the two sulfide motifs of macrocycle 7 into sulfone units
gave macrocycle 2 (18% overall yield).
We irradiated (254 nm) a degassed solution of compound
2 in C6H6/CH2Cl2 (1:1) at 298 K for 90 min to confirm that
the shrinking of the ring skeleton of macrocycle 2, through
the extrusion of SO2, was possible. After four repeat experi-
ments, we isolated macrocycles 8 and 9, which resulting
from one and two successful photoextrusions, in 20–33%
and 26–38% yield, respectively, after column chromatogra-
phy on silica gel (Scheme 3). Having demonstrated that the
shrinking of the macrocyclic ring of compound 2 was possi-
ble under these conditions, we tested whether macrocycle 2
had reasonable binding affinity toward the DBA+ ion—a ne-
cessity if the shrinking reaction were to be applied to the
synthesis of rotaxanes.
We observed no evidence for the threading of [DBA]ACHTUNGTRENNUNG[PF6]
through macrocycle 2 in CD3CN or CD3NO2; because of the
poor solubility of this salt in less polar solvents (CDCl3,
CD2Cl2), we instead tested whether bis(para-tert-butyl)ben-
Scheme 1. Design of “shrinking” macrocycle 2 from macrocycle 1.
zylammonium hexafluorophosphate[8] ([10-H]
ACTHUNTRGENNG[U PF6]) would
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“Threading Followed by Shrinking” for Stable Rotaxanes
FULL PAPER
recognize macrocycle
CDCl3. However, the solubility
of compound [10-H][PF6] in
2
in
ACHTUNGTRENNUNG
CDCl3 remained limited, even
in the presence of an equimo-
lar amount of compound 2.
The complexation of com-
pound [10-H]ACHTNUTRGENNG[U PF6] with macro-
cycle 2 was weak in CDCl3/
CD3CN (8:2), with only negli-
gible changes in the 1H NMR
spectrum of their equimolar
(10 mm) mixture, even after
heating at 318 K for several
hours. We replaced the count-
AHCTUNGERTGeNNUN ranion of the threadlike
cation with an even more
weakly associated anion, tetra-
Scheme 2. Synthesis of macrocycle 2.
kis(3,5-trifluoromethylphenyl)-
borate (TFPB), with the ex-
pectation that the salt would be more soluble in CDCl3 or
CD2Cl2 and, therefore, that there would be stronger binding
between the [10-H]+ cation and macrocycle 2.[9] The
1H NMR spectrum of an equimolar (10 mm) mixture of mac-
rocycle 2 and threadlike salt [10-H]
CDCl3 at room temperature showed a migration of the sig-
nals of the free salt [10-H][TFPB] and the free macrocycle 2
ACHTUNGTREN[NUGN TFPB] (Scheme 4) in
AHCTUNGTRENNUNG
(Figure 2a–c). These shifted signals were presumably the
result of face-to-face association between the DBA+ and sul-
fone units of the threadlike salt and the macrocycle, respec-
tively, rather than from a rapidly exchanging threading/de-
Scheme 3. Shrinking of macrocycle 2 into macrocycles 8 and 9.
AHCTUNGTERGtNNUN hreading process, because we
observed the latter after heat-
ing the solution at 318 K for
12 h (Figure 2e). The intensity
of these new signals increased
with time, at the expense of
those of the free compounds
[10-H]ACHTNUTRGNEUNG[TFPB] and 2, becoming
predominant after 72 h. The
upfield shift of the signal of
the methylene protons adja-
+
cent to the NH2 center and
the signals of the OCH2CH2
protons of the macrocycle, rel-
ative to the respective signals
of their free species, were simi-
lar to those observed for the
[2]pseudorotaxanes that were
prepared from macrocycle 1
and DBA+ ions, thus suggest-
ing that the product was a
[2]rotaxane that had formed
through slippage (Scheme 4).
When we repeated this slip-
page experiment on a larger
scale and allowed the mixture
Scheme 4. Slippage synthesis of the [2]rotaxane [11-H]
anes [12-H][TFPB] and [13-H][TFPB].
ACHTUNGTREN[NGNU TFPB], followed by photoextrusion to give [2]rotax-
N
ACHTUNGTRENNUNG
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S.-H. Chiu et al.
[2]rotaxane [11-H]ACTHNUTRGNEUNG[TFPB] was not stable under the crystalli-
zation conditions, with its dissociation accelerated (in part)
by one of its components being needed for crystal packing.
After dissolving the slippage [2]rotaxane [11-H]ACTHNUGRTNEUNG[TFPB] in
a mixture of C6H6 and CH2Cl2 (1:1), we irradiated (254 nm)
the solution at 273 K. As expected, we obtained [2]rotax-
anes [12-H]ACTHNUTRGENNU[G TFPB] and [13-H]ACHTUNTGREN[NUNG TFPB], in 15 and 6% yield,
respectively, after column chromatography on silica gel; in
these interlocked molecules, the macrocyclic component had
been “shrunk” to give smaller macrocycles that correspond-
ed to compounds 8 and 9, after the extrusion of SO2 from
one and two of the sulfone units, respectively (Scheme 4).
The downfield and upfield shifts of the signals of the meth-
+
1
ylene protons adjacent to the NH2 centers in the H NMR
spectra of [2]rotaxanes [12-H][TFPB] and [13-H][TFPB],
[TFPB], respective-
A
ACHTUNGTRENNUNG
relative to that in the spectrum of [11-H]
G
+
À
ly (Figure 4), suggested that the [N C H···p] interactions of
1
Figure 2. Partial H NMR spectra (400 MHz, CDCl3, 298 K) of: a) macro-
cycle 2, b) threadlike salt [10-H][TFPB]; and their equimolar (10 mm)
AHCTUNGTRENNUNG
mixture after treatment at 298 K for: c) 0 h, and d) 6 h; or at 318 K for:
e) 12 h, and f) 72 h.
to equilibrate for three days, we obtained the corresponding
[2]rotaxane, [11-H]ACHTUNGTRENNUNG[TFPB], in 58% yield after column chro-
matography on silica gel.
We grew single crystals that were suitable for X-ray crys-
tallography through the liquid diffusion of hexanes into a
solution of compound [11-H]ACHTNUGTRNEUNG[TFPB] in CH2Cl2. The solid-
state structure in Figure 3[10,11] shows the expected [2]rotax-
ane geometry, in which the rod-like portion of the dumb-
bell-shaped component penetrates through the cavity of the
+
macrocyclic component, with the CH2NH2 unit interacting
with the oxygen atoms and the aromatic rings of the macro-
+
+
À
À
cyclic unit through possible [N H···O] and [N C H···p] hy-
drogen bonds. Notably, although we only performed the
crystallization of the purified slippage [2]rotaxane [11-H]-
Figure 4. Partial 1H NMR spectra (400 MHz, CDCl3, 298 K) of: a) slip-
ACHTUNGTRENNUNG
page [2]rotaxane [11-H]
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
A
U
+
the methylene protons adjacent to the NH2 ions first weak-
ened and then strengthened with each sequential extrusion
of a SO2 unit. We observed a similar trend in the migration
+
of the signal for the NH2 center, thus implying that the
+
À
strength of its [N H···O] hydrogen-bonding interactions
with the di(ethylene glycol) motif of the macrocyclic compo-
nent decreased in [2]rotaxane [12-H]
ACHTUNGTREN[NUNG TFPB] but increased
in [13-H][TFPB]. Thus, conformational preorganization ap-
AHCTUNGTRENNUNG
pears to be as important as the rigidity or ring size of the
+
macrocycles in their binding to the CH2 NH2CH2 center.
Our observation of reasonable (Ka =160mÀ1) binding affinity
of macrocycle 9 to [DBA]ACTHNUTRGNE[UNG PF6] in CDCl3/CD3CN (1:1), but
negligible binding affinities for macrocycles 2 and 8 to the
same salt, together with association constants of macrocycles
2 and 8 for alkyl-substituted salt [DBA]ACTHNUTRGNEG[NU TFPB] in CDCl3 of
5800 and 220mÀ1, respectively, are consistent with the trends
in the chemical-shift data for the signals of the main inter-
acting units of the corresponding [2]rotaxanes.[12] Our suc-
Figure 3. Ball-and-stick representation of the solid-state structure of the
slippage [2]rotaxane [11-H]+.
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“Threading Followed by Shrinking” for Stable Rotaxanes
FULL PAPER
cessful syntheses of [2]rotaxanes [12-H]
ACHTUNGTREN[NUGN TFPB] and [13-H]-
ACHTUNGTRENNUNG
(ESI) mass spectra of these compounds, which revealed in-
tense peaks at m/z 790.4567 and 726.4926 for ions [12-H]+
and [13-H]+, respectively. Thus, our spectroscopic data con-
firmed that it was indeed possible to shrink macrocycle 2
+
photochemically, whilst it encircled the NH2 center of a
DBA+ ion. Nevertheless, because the precursor that we used
to perform the “shrinking” process was slippage [2]rotaxane
[11-H]ACHTUNGTRENNUNG[TFPB], which was already a stable compound at
room temperature, our synthetic process was technically
“slippage followed by shrinking,” rather than “threading fol-
lowed by shrinking.” To truly realize this latter concept, we
required a suitable terminal group for the threadlike cation,
that is, one that would allow macrocycle 2 to freely associate
and disassociate, but not allow egress of its shrinking prod-
ucts (macrocycles 8 and/or 9).
Figure 5. 1H NMR spectra (400 MHz, CDCl3, 298 K) of: a) macrocycle 2,
b) an equimolar mixture of macrocycle
2
and threadlike salt
After some effort, we found that compound [14-H]-
G
E
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
[TFPB],[13] which featured terminal 3,5-dimethylphenyl
groups, could not penetrate through the internal cavities of
“shrunk” macrocycles 8 and 9, with no noticeable signals
that corresponded to [2]pseudorotaxanes appearing in the
1H NMR spectra of their equimolar mixtures (5 mm). In
contrast, an equimolar mixture of macrocycle 2 and thread-
Notably, the tert-butylphenyl and 3,5-dimethylphenyl moi-
eties are “reasonable” and “true” stopper units for DB24C8,
respectively, as evidenced from experimental observations
that DB24C8 only dissociated from the corresponding “ro-
taxanes” that featured the former stoppering units after the
like salt [14-H]
three sets of resonances (Figure 5b): One set for the free
macrocycle 2 (Figure 5a), one for the free salt [14-H][TFPB]
(Figure 5c), and one for the 1:1 complex that had formed
between compounds 2 and [14-H][TFPB]. The similar reso-
ACHTUNGTRENNUNG[TFPB] (5 mm) in CDCl3 at 298 K displayed
+
NH2 center had been acylated.[16] Based on those results,
C
one might suspect that the 3,5-dimethylphenyl group would
also be sterically bulkier and/or energetically less favorable
than the tert-butylphenyl group when passing through the
cavities of other macrocycles. However, in our case, we
found that the tert-butylphenyl group was a slippage stopper
for macrocycle 2, whereas the 3,5-dimethylphenyl group
could pass freely through it under similar conditions. We
suspect that the different macrocycles that were applied in
AHCTUNGTRENNUNG
lution of the originally overlapping signals for the protons of
the two methylene groups on the di(ethylene glycol) unit
into two separate multiplets and the significant upfield shifts
+
of the methylene protons adjacent to the NH2 centers of
the complex (Figure 5b) and of the slippage [2]rotaxane
+
A
U
these two examples and the acylation of the NH2 centers in
A
R
the cases of [2]rotaxanes that featured DB24C8 components
a
method,[14] we determined the
association constant (Ka) for
the interaction between macro-
cycle and threadlike salt
2
N
5 mm) to be 5800mÀ1.[15] The
observation that 3,5-dimethyl-
phenyl units could penetrate
through the cavity of the mac-
rocycle 2 at ambient tempera-
ture to form [2]pseudorotaxane
[2ꢀ14-H]
G
but
not
salt [14-H]ACHTUNGTRENNUNG[TFPB] would be an
ideal component for demon-
strating the “threading fol-
lowed by shrinking” concept
(Scheme 5).
Scheme 5. Synthesis of [2]rotaxanes [15-H]ACTHNUTRGNENG[U TFPB] and [16-H]ACHTUNGTNER[NUGN TFPB] by the macrocycle “shrinking” approach.
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S.-H. Chiu et al.
resulted in different types and strengths of noncovalent in-
teractions in the transition states for the dissociations of
these two systems, thereby resulting in different activation
energies for the same terminal functionality. For now, we
merely suggest that the potential energy for the threading
(or dethreading) of the terminus of a threadlike cation
through a macrocycle is related in a complex way to the
structures of the host and the guest and to the transition
state for the passage event, the noncovalent interactions of
which are hard to predict.[17]
CHCl3 solution of compound [16-H]ACTHNGUTERN[NUG PF6] (see below). The
solid-state structure shows[19] the expected geometry of the
[2]rotaxane, in which the dumbbell-shaped component is
penACTHUNRTGNEUNGetrated through the cavity of the macrocyclic compo-
+
nent, with the CH2NH2 units hydrogen bonded to the aro-
matic rings and the oxygen atoms of the macrocyclic unit
+
+
À
À
through possible [N H···O] and [N C H···p] hydrogen
bonds (Figure 6).
To test their stability, we dissolved [2]rotaxanes [15-H]-
ACHUTNGRENU[NG TFPB] and [16-H]ACHUTGNTREN[NUGN TFPB] in CD3SOCD3 and then heated
To test whether we could perform a true “threading fol-
lowed by shrinking” process, we prepared an equimolar
(32 mm) solution of macrocycle 2 and threadlike salt [14-H]-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
from the reaction mixture; instead, we isolated macrocycles
8 and 9 in 23 and 29% yield, respectively. We suspected that
we were generating an insufficient amount of the [2]pseu-
dorotaxane in solution; therefore, we performed the same
reaction under similar conditions, but changed the stoichi-
ometry of threadlike salt [14-H]
2:1 (64 mm:32 mm). Gratifyingly, after reapplying the reac-
tion conditions, we isolated the [2]rotaxanes [15-H][TFPB]
and [16-H][TFPB], which resulted from the extrusion of one
ACHTUNGERTN[NUNG TFPB] to macrocycle 2 to
Figure 6. Ball-and-stick representation of the solid-state structure of the
[2]rotaxane [16-H]+.
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
and two molecules of SO2, respectively, from the arylmethyl-
sulfone units of the macrocyclic component in 13 and 2%
yield, respectively (Table 1).[18] Changing the ratio of the sol-
vents in the “shrinking” reaction did not improve the yields,
the solutions at 343 K for 2 h whilst monitoring their
1H NMR spectra. No signals were observed that correspond-
ed to the free macrocycles or free dumbbell-shaped salt
but increasing the amount of threadlike salt [14-H]
G
ACHUTGTNREN[NUG 14-H]ACHTUNGTNER[NUGN TFPB], thus suggesting that the 3,5-dimethylphenyl
in the photoextrusion reaction mixture to up to four equiva-
lents (128 mm) improved the yield of [2]rotaxane [15-H]-
ACHTUNGTRENNUNG
group was a true stopper for both macrocycles 8 and 9 and
that the two [2]rotaxanes were reasonably robust under
these conditions. In contrast, we observed different behavior
when subsequently heating these two solutions at 373 K.
ACHTUNGTRENNUNG
extending the irradiation period did not significantly affect
the efficiency of the synthesis of the [2]rotaxane through
this “shrinking” process.
We grew single crystals suitable for X-ray crystallography
through the liquid diffusion of diisopropyl ether into a
[2]Rotaxane [15-H]
cycle 8 and dumbbell-shaped salt [14-H]
compound [16-H][TFPB] remained intact after 5 h (Fig-
ure 7c). We observed no dissociation in the H NMR spectra
of [2]rotaxane [16-H][TFPB] when we continued to heat its
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
1
AHCTUNGTRENNUNG
solution at 393 K for a further 5 h.[20] This result
supports our original hypothesis that the shrinking
of the ring twice could generate a more stable and
robust rotaxane with an even smaller interlocked
macrocyclic component (Scheme 6).
Table 1. “Threading followed by shrinking” of macrocycle 2 and threadlike salt
ACHTUNGTRENNUNG[14-H]ACHTUNGTRENNUNG
[TFPB] under various conditions.[a]
Entry
Thread
[equiv]
Solvent system
(CH2Cl2/C6H6)
t [min]
G
[16-H]+
ACHTUNGTRENNUNG
A
[%]
[%]
We suspect that the low yield of [2]rotaxane
A
ACHTUNGTRENN[UNG TFPB] from the “shrinking” process was
1
2
3
4
5
6
7
8
1
2
2.2
2.2
3
4
5
4
1:1
1:1
3:2
2:3
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
60
60
60
60
60
60
60
120
–
13
7
<1
2
3
2
4
4
3
3
2
AHCTUNGTRENNUNG
3
sion reaction proceeds through the photochemical
cleavage of one of the C S bonds of the arylme-
thylsulfone into two radicals, the extrusion of SO2
by dissociating the other C S bond in the same
manner, and the recombination of the two benzylic
radicals to form a new C C bond. Thus, if the
time interval that is required for homolytic dissoci-
13
17
14
10
20
19
20
19
À
À
9[b]
10[b]
11[b]
12[b]
4 (=2+2)
4 (=2+1+1)
4 (=2+1+1)
4 (=2+2)
60 (=30+30)
60 (=30+15+15)
60 (=20+20+20)
80 (=40+40)
2
2
3
[21]
À
À
ation of the second C S bond and the recombina-
tion of the two benzyl radicals after breaking the
[a] The concentration of macrocycle 2 was fixed at 32 mm. [b] The threadlike salt was
added in portions; the solution was irradiated for the indicated time intervals.
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“Threading Followed by Shrinking” for Stable Rotaxanes
FULL PAPER
À
first C S bond are sufficiently
long enough to allow for the
dissociation of the originally
interlocked dumbbell-shaped
ion from the open-chain
podand-type host, recombina-
tion of the two radicals might
result in the formation of the
macrocycle in its free state. To
verify this hypothesis, we ex-
changed the counteranion of
[2]rotaxane [15-H]
[TFPB] for
À
PF6 and ClÀ. We found that
[2]rotaxanes [15-H]
[15-H][PF6] both underwent
successful photoextrusions,
ACHTUNGTRENN[UNG TFPB] and
AHCTUNGTRENNUNG
with shrinkage of their origi-
nally interlocked macrocycles,
thus giving their corresponding
[2]rotaxanes,
[16-H]ACHTUNGTRENNUNG[TFPB]
and [16-H][PF6], in 28 and
AHCTUNGTRENNUNG
1
Figure 7. Partial H NMR spectra (400 MHz, CD3SOCD3, 298 K) of: a) [2]rotaxane [16-H]
[TFPB], and the so-
22% yield, respectively. In
contrast, the 1H NMR spec-
trum of the irradiated [2]rotax-
ane [15-H][Cl] featured no de-
ACHTUNGTRENNUNGlution after sequential heating at: b) 343 K for 2 h, c) 373 K for 5 h, d) 383 K for 5 h, and e) 393 K for 5 h.
tectable signals for the corresponding [2]rotaxane, [16-H]
[Cl]; indeed, we isolated its free macrocycle (9) in 76%
yield after column chromatography on silica gel. This result
+
suggests that strong ion-pairing of the NH2 center with the
ClÀ anion—an interaction that has previously been applied
to operate a molecular switch that was comprised of a
crown ether-like macrocycle and
a diACHTUNGTNRUEGNalkylammonium
ion[22]—significantly decreases the stability of the complex
between the dumbbell-shaped ion and the open-chain free
radical intermediate that were formed from the macrocyclic
component, thereby resulting in the dissociation of the com-
plex, even though such ion-pairing would not dissociate the
components of the interlocked [2]rotaxane [15-H][Cl] be-
cause of its bulky 3,5-dimethylphenyl stoppers. Although re-
combination of the two benzylic radicals that are generated
from the extrusion of SO2 from a diarylmethyl sulfone may
be sufficiently rapid to retain a certain degree of chirality at
the benzylic carbon atom,[21] we conclude that, when the
counteranion is ClÀ, the total time interval between the
À
À
cleavage of the first C S bond and the formation of the C
C bond from the two benzylic radicals must be longer than
the time that is required for the dissociation of the thread-
like salt from the podand-like open-chain host, otherwise
the reaction yield would not differ from those with TFPB
À
and PF6 as the counteranions. In other words, this experi-
ment supports an open-chain mechanism for the extrusion
of SO2 from diarylmethyl sulfones. Thus, the relatively low
yields when synthesizing [2]rotaxane [16-H]+ by using this
approach presumably result from the difficulty of perform-
ing two successful extrusion and interlocking processes from
the starting [2]pseudorotaxane. To enhance the efficiency of
future rotaxane syntheses through such a “shrinking” ap-
Scheme 6. Anion effect in transforming [2]rotaxane [16-H]+ into [15-H]+
.
Chem. Eur. J. 2013, 00, 0 – 0
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S.-H. Chiu et al.
which was then filtered. The filtrate was concentrated under reduced
pressure and purified by column chromatography on silica gel (CH2Cl2/
MeOH, 95:5) to afford a colorless oil (0.70 g, 81% yield). 1H NMR
(400 MHz, CDCl3): d=3.57–3.71 (m, 8H), 4.55 (s, 4H), 4.65 (s, 4H), 7.28
(d, J=8 Hz, 4H), 7.32 ppm (d, J=8 Hz, 4H); 13C NMR (100 MHz,
CDCl3): d=64.2, 69.1, 70.3, 72.7, 126.7, 127.6, 137.0, 140.3 ppm; HRMS
(ESI): m/z calcd for C20H26NaO5: 369.1678 [M+Na]+; found: 369.1675.
proach (i.e., one in which cleavage of the macrocyclic struc-
ture of the complexed ring is unavoidable), it might be nec-
essary to enhance the binding affinity of the corresponding
open-chain podand to the guest unit or to decrease the life-
times of the open-chain intermediates.
AHCTUNGTRENNUNG
Dichloride 6: Diol 5 (0.7 g, 2.02 mmol), NaHCO3 (1.71 g, 20.35 mmol),
PPh3 (1.6 g, 6.10 mmol), and NCS (0.81 g, 6.06 mmol) were mixed in
CH2Cl2 (31 mL) at 08C and the mixture was stirred for 40 min before
being quenched through the addition of a saturated aqueous solution of
NaHCO3 (10 mL). The organic layer was separated and the aqueous
layer was extracted again with CH2Cl2 (30 mL). The organic layers were
combined, dried (MgSO4), concentrated under reduced pressure, and pu-
rified by column chromatography on silica gel (EtOAc/hexanes, 4:6) to
afford a colorless oil (0.47 g, 61% yield). 1H NMR (400 MHz, CDCl3):
d=3.60–3.69 (m, 8H), 4.55 (s, 4H), 4.56 (s, 4H), 7.31 (d, J=8.8 Hz, 4H),
7.34 ppm (d, J=8.8 Hz, 4H); 13C NMR (100 MHz, CDCl3): d=45.9, 69.5,
70.6, 72.6, 127.8, 128.5, 136.6, 138.6 ppm; HRMS (ESI): m/z calcd for
C20H25Cl2O3: 383.1181 [M+H]+; found: 383.1144.
Conclusion
We have demonstrated that a “threading followed by shrink-
ing” strategy can be applied to the synthesis of stable molec-
ular rotaxanes from derivatives of macrocycle 1. We ob-
tained a relatively low yield of the [2]rotaxane [16-H]-
ACHTUNGTRENNUNG[TFPB] as a result of the need to perform two open-chain
SO2-extrusion reactions with sufficiently long-living free-
radical intermediates, thereby providing the weakly associat-
ed dumbbell-shaped cation and the open-chain podand-type
host with sufficient time to dissociate. Nevertheless, by twice
shrinking the size of the macrocyclic component, the result-
Macrocycle 7: A solution of KOH (0.24 g, 4.28 mmol) in EtOH (95%,
725 mL) was added to a solution of dichloride 6 (0.47 g, 1.20 mmol) and
1,4-benzenedimethanethiol (0.20 g, 1.20 mmol) in toluene (241 mL) over
a period of 8 h. Then, the mixture was stirred at RT for 16 h. After con-
centrating under reduced pressure, the residue was purified by column
chromatography on silica gel (CH2Cl2/MeOH, 98:2) to afford a white
solid (0.50 g, 87% yield). M.p. 77–798C; 1H NMR (400 MHz, CDCl3):
d=3.52 (s, 4H), 3.58 (s, 4H), 3.60–3.68 (m, 8H), 4.54 (s, 4H), 7.06 (s,
4H), 7.06 (d, J=8 Hz, 4H), 7.24 ppm (d, J=8 Hz, 4H); 13C NMR
(100 MHz, CDCl3): d=34.6, 35.1, 69.4, 70.7, 72.5, 127.3, 129.0, 129.1,
136.6, 136.9, 137.2 ppm; HRMS (ESI): m/z calcd for C28H32NaO3S2:
503.1691 [M+Na]+; found: 503.1638.
ing [2]rotaxane, [16-H]ACTHNUTRGNE[NUG TFPB], incorporated the much
smaller (25 atom) macrocycle 9 as one of its interlocked
components, thereby providing a system that maintained its
molecular integrity in CD3SOCD3 at 393 K for at least 5 h.
We hope that this method will be added to the repertoire of
reactions that are available to the synthetic chemist for the
construction of complicated and robust interlocking
structures.
Macrocycle 2: MCPBA (1.05 g, 4.20 mmol) was added to solution of mac-
rocycle 7 (0.50 g, 1.04 mmol) in CH2Cl2 (10 mL) at 08C and the mixture
was stirred for 30 min. After partitioning between CH2Cl2 (40 mL) and a
saturated aqueous solution of NaHCO3 (2ꢁ20 mL), the organic phase
was dried (MgSO4) and concentrated under reduced pressure; the residue
was purified by column chromatography on silica gel (CH2Cl2/MeOH,
98:2) to afford a white solid (0.45 g, 79% yield). M.p. 241–2438C;
1H NMR (400 MHz, CDCl3): d=3.64–3.72 (m, 8H), 4.08 (s, 4H), 4.12 (s,
4H), 4.59 (s, 4H), 7.16–7.22 (m, 8H), 7.37 ppm (d, J=8 Hz, 4H);
13C NMR (100 MHz, CDCl3): d=58.0, 58.2, 69.9, 70.7, 72.2, 126.4, 127.5,
129.0, 130.6, 131.2, 139.8 ppm; HRMS (ESI): m/z calcd for
C28H32NaO7S2: 567.1487 [M+Na]+; found: 567.1455.
Experimental Section
General: All glassware, stirrer bars, syringes, and needles were either
oven- or flame-dried prior to use. All reagents were obtained from com-
mercial sources, unless otherwise indicated. Anhydrous CH2Cl2 and
MeCN were obtained by distillation from CaH2 under N2. The reactions
were conducted under N2 or Ar atmospheres. Thin layer chromatography
(TLC) was performed on Merck 0.25 mm silica gel (Merck Art. 5715).
Column chromatography was performed on Kieselgel 60 (Merck, 70–
230 mesh). Melting points were determined on a Fargo MP-2D melting-
point apparatus. For NMR spectroscopy, the deuterated solvent was used
as the lock, whilst either the residual protons in the solvent or TMS were
employed as an internal standard. Chemical shifts are reported in parts
per million (ppm). Multiplicities are given as s (singlet), d (doublet),
t (triplet), q (quartet), m (multiplet), or br (broad).
General method for the photoextrusion process: The photoextrusion re-
action was performed on a Rayonet RPR-200 photoreactor that con-
tained 16 35 W, 254 nm lamps; the reaction mixture was placed in a
quartz apparatus that was equipped with an internal cold finger.
Macrocycles 8 and 9: Macrocycle 2 (54 mg, 0.1 mmol) was dissolved in a
degassed mixture of CH2Cl2 and benzene (1:1, 10 mL) and then irradiat-
ed (254 nm) for 1.5 h. The organic solvents were evaporated under re-
duced pressure and the residue was purified by column chromatography
on silica gel (EtOAc/hexanes, 1:9 to 3:7) to afford macrocycle 8 as a
white solid (15.8 mg, 33% yield) and macrocycle 9 as a white solid
(14.2 mg, 34% yield).
Macrocycle 8: M.p. 131–1338C; 1H NMR (400 MHz, CDCl3): d=2.87–
2.98 (m, 4H), 3.60–3.73 (m, 8H), 3.90 (s, 2H), 4.00 (s, 2H), 4.53 (s, 2H),
4.59 (s, 2H), 6.84–6.88 (m, 4H), 7.05–7.11 (m, 4H), 7.16 (d, J=8 Hz,
2H), 7.33 ppm (d, J=8 Hz, 2H); 13C NMR (100 MHz, CDCl3): d=37.1,
56.4, 57.8, 69.2, 69.7, 70.4, 70.9, 71.8, 73.1, 125.4, 126.3, 127.2, 127.5, 128.9,
129.7, 129.9, 130.6, 136.0, 139.4, 139.6, 141.7 ppm (one signal is missing,
possibly because of signal overlap); HRMS (ESI): m/z calcd for
C28H32NaO5S: 503.1868 [M+Na]+; found: 503.1853.
Diester 4: NaH (60%, 1.09 g, 27.3 mmol) was added to a solution of
di(ethylene glycol) (1.11 g, 10.0 mmol) in THF (105 mL) and then the
mixture was heated at reflux for 30 min before the addition of methyl
4-(bromomethyl)benzoate (5.27 g, 23.0 mmol). After heating at reflux for
16 h, the mixture was concentrated under reduced pressure and the
yellow residue was partitioned between CH2Cl2 (50 mL) and water
(30 mL). The organic layer was dried (MgSO4), concentrated under re-
duced pressure, and purified by column chromatography on silica gel
(EtOAc/hexanes, 3:7) to afford
a colorless oil (2.09 g, 52% yield).
1H NMR (400 MHz, CDCl3): d=3.60–3.69 (m, 8H), 3.86 (s, 6H), 4.58 (s,
4H), 7.36 (d, J=8 Hz, 4H), 7.95 ppm (d, J=8 Hz, 4H); 13C NMR
(100 MHz, CDCl3): d=51.9, 69.8, 70.6, 72.5, 127.0, 129.2, 129.5, 143.5,
166.7 ppm; HRMS (ESI): m/z calcd for C22H26NaO7: 425.1577 [M+Na]+;
found: 425.1533.
Macrocycle 9: M.p. 110–1128C; 1H NMR (400 MHz, CDCl3): d=2.79–
2.93 (m, 8H), 3.65–3.73 (m, 8H), 4.56 (s, 4H), 6.74 (d, J=8 Hz, 4H), 6.75
(s, 4H), 7.13 ppm (d, J=8 Hz, 4H); 13C NMR (100 MHz, CDCl3): d=
37.0, 37.1, 69.5, 71.0, 72.9, 126.8, 128.8, 129.0, 135.7, 138.1, 140.0 ppm;
Diol 5: A solution of diester 4 (1.00 g, 2.48 mmol) in THF (10 mL) was
slowly added to
a suspension of LAH (0.24 g, 6.32 mmol) in THF
(30 mL) at 08C and then the mixture was heated at reflux for 3 h. After
cooling to RT, water (5 mL) and MgSO4 (1 g) were added to the mixture,
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“Threading Followed by Shrinking” for Stable Rotaxanes
FULL PAPER
HRMS (ESI): m/z calcd for C28H32NaO3: 439.2249 [M+Na]+; found:
439.2175.
161.7 ppm (q, 1J
254.1909 [M]+; found: 254.1879.
[2]Rotaxanes [15-H][TFPB] and [16-H]
0.194 mmol) and dumbbell-shaped salt [14-H]ACHTUNGTRENNUNG
0.387 mmol) were dissolved in a degassed mixture of CH2Cl2 and ben-
zene (1:1, 6 mL) and then irradiated (254 nm) at 273 K for 40 min. After
ACHTUGNRTEN(NNUG C,B)=50 Hz); HRMS (ESI): m/z calcd for C18H24N:
Dumbbell-shaped salt [10-H]
methyl)phenyl] borate (NaTFPB, 444 mg, 0.501 mmol) was added to a
solution of compound [10-H][PF6] (228 mg, 0.501 mmol) in MeOH. The
A
N
A
ACHTUNGTRENNUNG
R
mixture was concentrated under reduced pressure and the residue was
partitioned between CH2Cl2 (20 mL) and deionized water (10 mL). The
organic phase was dried (MgSO4) and concentrated under reduced pres-
sure to afford a yellow oil (563 mg, 96% yield). 1H NMR (400 MHz,
CDCl3): d=1.28 (s, 18H), 4.07 (t, J=6 Hz, 4H), 7.16 (d, J=8.4 Hz, 4H),
7.45 (d, J=8.4 Hz, 4H), 7.51 (s, 4H), 7.67 ppm (s, 8H); 13C NMR
the addition of another portion of compound [14-H]ACTHNUTRGNE[NUG TFPB] (432 mg,
0.387 mmol), the mixture was irradiated at 273 K for a further 40 min.
The organic solvents were evaporated under reduced pressure and the
residue was purified by column chromatography on silica gel (CH2Cl2/
hexanes, 6:4 to 8:2) to afford [2]rotaxane [15-H]
ACHTUNGERTN[NUNG TFPB] as a yellow solid
(100 MHz, CDCl3): d=30.8, 34.9, 52.7, 117.6, 124.6, 124.6 (q, 1J
271 Hz), 127.4, 128.9, 128.9 (q, 2J
(C,F)=31 Hz), 134.8, 155.6, 161.7 ppm
(q, 1J
(C,B)=50 Hz); HRMS (ESI): m/z calcd for C22H32N: 310.2535
[M]+; found: 310.2510.
[2]Rotaxane [11-H][TFPB]:
1.05 mmol) and dumbbell-shaped salt [10-H]
ACHTUNGTRNE(NUNG C,F)=
(58.4 mg, 19% yield). [2]Rotaxane [16-H][TFPB] was also obtained, after
further purification by column chromatography on silica gel (CH2Cl2/hex-
anes, 2:8), as a white solid (8.5 mg, 3% yield).
[TFPB]: M.p. 152–1548C; 1H NMR (400 MHz,
Compound [15-H]ACTHNUTRGNEUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
G
A
solution of macrocycle
2 (574 mg,
CDCl3): d=2.33 (s, 12H), 2.61–2.77 (m, 4H), 2.93–3.07 (m, 8H), 3.28–
3.33 (m, 2H), 3.58–3.63 (m, 2H), 3.88 (s, 2H), 4.22 (s, 2H), 4.33 (s, 2H),
4.37 (s, 2H), 6.54–6.70 (br, 2H), 6.60 (s, 4H), 6.82 (d, J=7.6 Hz, 2H),
6.91 (d, J=7.6 Hz, 2H), 6.96 (d, J=7.6 Hz, 2H), 6.98 (d, J=7.6 Hz, 2H),
7.06 (s, 2H), 7.19 (d, J=8 Hz, 2H), 7.32 (d, J=7.6 Hz, 2H), 7.49 (s, 4H),
AHCTUNGTRENNUNG
0.498 mmol) in CHCl3 (16 mL) was stirred at 458C for 3 days and then
the organic solvent was evaporated under reduced pressure. The residue
was purified by column chromatography on silica gel (CH2Cl2/hexanes,
1
7.68 ppm (s, 8H); 13C NMR (100 MHz, CDCl3): d=21.1, 35.2, 36.0, 52.2,
9:1) to afford a white solid (499 mg, 58% yield). M.p. 97–998C; H NMR
1
(400 MHz, CDCl3): d=1.31 (s, 18H), 2.25–2.33 (m, 4H), 2.79–2.86 (m,
4H), 3.46–3.53 (m, 4H), 3.84 (s, 4H), 4.08 (s, 4H), 4.44 (s, 4H), 6.75–6.89
(br, 2H), 6.93 (d, J=8 Hz, 4H), 6.93 (d, J=8.4 Hz, 4H), 7.16 (d, J=
8 Hz, 4H), 7.41 (d, J=8.4 Hz, 4H), 7.49 (s, 4H), 7.56 (s, 4H), 7.67 ppm
(s, 8H); 13C NMR (100 MHz, CDCl3): d=31.0, 34.7, 51.4, 56.9, 61.1, 69.0,
58.0, 61.0, 69.2, 69.9, 70.8, 70.9, 74.1, 74.4, 117.4, 123.6, 124.6 (q, J
N
2
271 Hz), 126.7, 128.4, 128.9 (q, J
ACHTUNGTRENUN(NG C,F)=31 Hz), 129.2, 129.4, 129.7, 130.0,
130.3, 130.3, 131.3, 131.4, 133.1, 134.8, 137.0, 138.8, 141.7, 141.7,
1
161.7 ppm (q, J
734.3874 [M]+; found: 734.3854.
Compound [16-H]
[TFPB]: M.p. 170–1728C; 1H NMR (400 MHz,
CATHNUGTREN(NUNG C,B)=50 Hz); HRMS (ESI): m/z calcd for C46H56NO5S:
70.7, 74.1, 117.4, 124.5 (q, 1J
128.9 (q, 2J
(C,F)=31 Hz), 128.8, 129.7, 131.8, 132.0, 134.8, 136.6, 153.2,
161.7 ppm (q, 1J
(C,B)=50 Hz); HRMS (ESI): m/z calcd for
C50H64NO7S2: 854.4124 [M]+; found: 854.4101.
[2]Rotaxanes [12-H][TFPB] and [13-H][TFPB]: [2]Rotaxane [11-H]-
[TFPB] (119 mg, 0.069 mmol) was dissolved in a degassed mixture of
ACHTUNGTRENUN(NG C,F)=271 Hz), 125.7, 127.0, 127.2, 127.9,
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
CDCl3): d=1.86 (t, J=6.4 Hz, 4H), 2.34 (s, 12H), 3.00–3.04 (m, 4H),
3.05–3.16 (m, 8H), 3.51–3.57 (m, 4H), 4.04 (s, 4H), 6.37 (s, 4H), 6.66 (d,
J=7.6 Hz, 4H), 6.99–7.19 (m, 12H), 7.50 (s, 4H), 7.69 ppm (s, 8H);
13C NMR (100 MHz, CDCl3): d=21.2, 32.9, 33.3, 51.2, 68.9, 70.7, 74.3,
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
117.4, 124.6 (q, 1J(C,F)=271 Hz), 125.5, 128.3, 128.8, 128.9 (q, 2J
ACTHNUGTRENNUGN ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
CH2Cl2 and benzene (1:1, 2 mL) and then irradiated (254 nm) at 273 K
for 20 min. The organic solvents were evaporated under reduced pressure
and the residue was purified by column chromatography on silica gel
AHCTUNGTRENNUNG
(CH2Cl2/hexanes, 1:4 to 1:1) to afford compound [13-H]ACHTUNGTRENNUNG
yellow oil (7.01 mg, 6% yield) and compound [12-H]CAHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
oil (16.9 mg, 15% yield).
ACHTUNGTRENNUNG
Compound [12-H]ACHTUNGTRENNUNG
[TFPB]: 1H NMR (400 MHz, CDCl3): d=1.32 (s,
was repeated a further nine times with each successive filtrate. An aque-
ous solution of HCl (1m, 0.03 mL) was added to the final filtrate and the
organic phase was separated and concentrated under reduced pressure.
The residue was partitioned between CH2Cl2 (20 mL) and water (10 mL)
and then the organic phase was dried (MgSO4) and concentrated under
reduced pressure. The residue was purified by column chromatography
on silica gel (CH2Cl2/MeOH, 92:8) to afford a colorless oil (22.9 mg,
18H), 2.74 (t, J=6.6 Hz, 4H), 2.85–2.93 (m, 2H), 2.96–3.08 (m, 6H),
3.27–3.34 (m, 2H), 3.52–3.59 (m, 2H), 3.87 (s, 2H), 4.24 (s, 2H), 4.27 (s,
2H), 4.35 (s, 2H), 6.48–6.68 (br, 2H), 6.82 (d, J=8 Hz, 2H), 6.91–7.01
(m, 10H), 7.13 (d, J=8 Hz, 2H), 7.28 (d, J=8 Hz, 2H), 7.44 (d, J=
8.4 Hz, 4H), 7.49 (s, 4H), 7.68 ppm (s, 8H); 13C NMR (100 MHz,
CDCl3): d=31.1, 34.8, 35.0, 35.8, 51.9, 58.3, 60.9, 69.2, 69.8, 70.6, 70.8,
74.1, 74.2, 117.4, 123.5, 124.5 (q, 1J
128.9, 128.9 (q, 2J
(C,F)=31 Hz), 129.2, 129.4, 129.7, 130.3, 130.3, 131.4,
133.1, 134.8, 137.1, 141.5, 141.8, 153.7, 161.7 ppm (q, 1J
(C,B)=50 Hz);
HRMS (ESI): m/z calcd for C50H64NO5S: 790.4504 [M]+; found: 790.4567.
Compound [13-H]
[TFPB]: 1H NMR (400 MHz, CDCl3): d=1.34 (s,
ACHTUNGTRNE(NUNG C,F)=271 Hz), 125.9, 126.9, 128.4,
1
98% yield). H NMR (400 MHz, CDCl3): d=2.37 (s, 12H), 2.66–2.86 (m,
ACHTUNGTRENNUNG
4H), 2.93–3.03 (m, 4H), 3.06–3.13 (m, 2H), 3.13–3.20 (m, 2H), 3.38–3.47
(m, 2H), 3.67–3.74 (m, 2H), 3.92 (s, 2H), 4.37 (s, 2H), 4.63 (s, 2H), 4.82
(s, 2H), 6.66 (s, 4H), 6.79–6.86 (m, 4H), 6.95 (d, J=8 Hz, 2H), 7.01–7.07
(m, 4H), 7.14 (d, J=8 Hz, 2H), 7.59 ppm (d, J=7.6 Hz, 2H); 13C NMR
(100 MHz, CDCl3): d=21.4, 35.4, 36.0, 52.1, 58.6, 61.0, 69.5, 70.0, 70.8,
71.2, 74.0, 74.6, 125.0, 127.0, 128.4, 128.8, 129.3, 130.0, 130.1, 130.5, 131.1,
131.9, 133.2, 136.2, 138.4, 140.6, 141.5 ppm (one signal was missing, possi-
bly because of signal overlap); HRMS (ESI): m/z calcd for C46H56NO5S:
734.3878 [M]+; found: 734.3897.
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
18H), 1.83–1.91 (m, 4H), 2.87–2.94 (m, 4H), 3.04–3.16 (m, 8H), 3.47–
3.54 (m, 4H), 4.00 (s, 4H), 6.67 (d, J=8 Hz, 4H), 6.76 (d, J=8 Hz, 4H),
7.06 (d, J=8 Hz, 4H), 7.07 (s, 4H), 7.09–7.22 (br, 2H), 7.44 (d, J=8 Hz,
4H), 7.50 (s, 4H), 7.68 ppm (s, 8H); 13C NMR (100 MHz, CDCl3): d=
31.2, 32.9, 33.3, 34.8, 50.9, 68.7, 70.6, 74.3, 117.4, 124.5 (q, 1J
N
2
271 Hz), 125.7, 127.0, 127.5, 128.2, 128.9, 128.9 (q, J
G
G
ACHTUNGTRENNUNG
132.9, 134.8, 137.8, 142.3, 153.3, 161.7 ppm (q, 1J
(ESI): m/z calcd for C50H64NO3: 726.4886 [M]+; found: 726.4926.
Dumbbell-shaped salt [14-H][TFPB]: NaTFPB (895 mg, 1.01 mmol) was
added to a solution of compound [14-H][PF6] (403 mg, 1.01 mmol) in
ACHTUNGTREN(NUGN C,B)=50 Hz); HRMS
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
aqueous solution of HCl (1m, 0.03 mL) and a saturated aqueous solution
of NH4PF6 (5 mL) were added to the final filtrate and the organic phase
was separated and concentrated under reduced pressure. The residue was
partitioned between CH2Cl2 (20 mL) and water (10 mL) and then the or-
ganic phase was dried (MgSO4) and concentrated under reduced pres-
sure. The residue was purified by column chromatography on silica gel
(CH2Cl2/MeOH, 95:5) to afford a yellow solid (20.4 mg, 80% yield). M.p.
100–1028C; 1H NMR (400 MHz, CDCl3): d=2.37 (s, 12H), 2.62–2.80 (m,
4H), 2.93–3.03 (m, 4H), 3.03–3.10 (m, 2H), 3.10–3.16 (m, 2H), 3.39–3.46
AHCTUNGTRENNUNG
MeOH, which was then concentrated under reduced pressure. The resi-
due was partitioned between CH2Cl2 (20 mL) and deionized water
(10 mL). The organic phase was dried (MgSO4) and concentrated under
reduced pressure to afford a yellow solid (1.06 g, 94% yield). M.p. 134–
1358C; 1H NMR (400 MHz, CDCl3): d=2.27 (s, 12H), 4.01 (t, J=6 Hz,
4H), 6.80 (s, 4H), 7.11 (s, 2H), 7.50 (s, 4H), 7.68 ppm (s, 8H); 13C NMR
(100 MHz, CDCl3): d=20.9, 52.9, 117.5, 124.6 (q, 1J
ACHTUNGTRENNUNG
2
5
126.6, 127.7, 128.9 (q, JACHTUNGTRENNUNG
Chem. Eur. J. 2013, 00, 0 – 0
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S.-H. Chiu et al.
(m, 2H), 3.65–3.73 (m, 2H), 3.92 (s, 2H), 4.34 (s, 2H), 4.36 (s, 2H), 4.42
(s, 2H), 6.66 (s, 4H), 6.82 (d, J=8 Hz, 2H), 6.86 (d, J=7.6 Hz, 2H), 6.96
(d, J=7.6 Hz, 2H), 7.01 (d, J=8 Hz, 2H), 7.04 (s, 2H), 7.18 (d, J=
7.6 Hz, 2H), 7.43 ppm (d, J=7.6 Hz, 2H); 13C NMR (100 MHz, CDCl3):
d=21.2, 35.4, 36.1, 52.1, 57.5, 60.9, 69.3, 69.8, 70.9, 71.2, 74.0, 74.4, 124.6,
126.8, 128.5, 129.0, 129.3, 129.9, 130.3, 130.3, 130.5, 131.1, 131.5, 133.3,
136.7, 138.6, 140.9, 141.5 ppm; HRMS (ESI): m/z calcd for C46H56NO5S:
734.3878 [M]+; found: 734.3896.
McGrier, M. Frasconi, A. A. Sarjeant, J. F. Stoddart, Org. Lett. 2012,
14, 5188–5191; g) V. Blanco, A. Carlone, K. D. Hꢂnni, D. A. Leigh,
B. Lewandowski, Angew. Chem. 2012, 124, 5256–5259; Angew.
Chem. Int. Ed. 2012, 51, 5166–5169; h) C.-F. Chang, C.-J. Chuang,
C.-C. Lai, Y.-H. Liu, S.-M. Peng, S.-H. Chiu, Angew. Chem. 2012,
124, 10241–10245; Angew. Chem. Int. Ed. 2012, 51, 10094–10098;
i) Y. Abe, H. Okamura, K. Nakazono, Y. Koyama, S. Uchida, T.
Takata, Org. Lett. 2012, 14, 4122–4125; j) Y.-C. You, M.-C. Tzeng,
C.-C. Lai, S.-H. Chiu, Org. Lett. 2012, 14, 1046–1049; k) C. Roche,
A. Sour, J.-P. Sauvage, Chem. Eur. J. 2012, 18, 8366–8376; l) Z.
Zhang, C. Han, G. Yu, F. Huang, Chem. Sci. 2012, 3, 3026–3031;
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Yamafuji, H. Kayama, T. Yamagishi, J. Am. Chem. Soc. 2012, 134,
20322–20325.
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
aqueous solution of HCl (1m, 0.01 mL) and a saturated aqueous solution
of NH4PF6 (2 mL) were added to the final filtrate and the organic phase
was separated and concentrated under reduced pressure. The residue was
partitioned between CH2Cl2 (20 mL) and water (10 mL) and then the or-
ganic phase was dried (MgSO4) and concentrated under reduced pres-
sure. The residue was purified by column chromatography on silica gel
(CH2Cl2/MeOH, 95:5) to afford a white solid (4.59 mg, 51% yield). M.p.
232–2338C; 1H NMR (400 MHz, CDCl3): d=1.99 (t, J=6 Hz, 4H), 2.38
(s, 12H), 3.01–3.15 (m, 8H), 3.25–3.35 (m, 4H), 3.64–3.74 (m, 4H), 4.09
(s, 4H), 6.31 (s, 4H), 6.61 (d, J=7.6 Hz, 4H), 6.95 (d, J=7.6 Hz, 4H),
7.03 (s, 2H), 7.08 (s, 4H), 7.20–7.30 ppm (br, 2H); 13C NMR (100 MHz,
CDCl3): d=21.4, 33.2, 33.2, 50.9, 69.2, 71.0, 74.2, 125.7, 128.4, 128.6,
129.2, 130.2, 130.6, 133.2, 138.0, 138.3, 141.5 ppm; HRMS (ESI): m/z
calcd for C46H56NO3: 670.4260 [M]+; found: 670.4283.
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A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
solved in a degassed mixture of CH2Cl2 and benzene (1:1, 1.8 mL) and
then irradiated (254 nm) at 273 K for 30 min. The organic solvents were
evaporated under reduced pressure and the residue was purified by
column chromatography on silica gel (CH2Cl2/hexanes, 4:6) to afford
compound [16-H]
[16-H][PF6] (through shrinking of the macrocyclic component of [15-H]-
[PF6]): [2]Rotaxane [15-H][PF6] (10 mg, 0.01 mmol) was dissolved in a
ACHTUNGTRENNUNG[TFPB] (7.7 mg, 28% yield).
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
degassed mixture of CH2Cl2 and benzene (1:1, 1 mL) and then irradiated
(254 nm) at 273 K for 30 min. The organic solvents were evaporated
under reduced pressure and the residue was purified by column chroma-
tography on silica gel (CH2Cl2/MeOH, 95:5) to afford compound [16-H]-
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ACHTUNGTRENNUNG[PF6] (2 mg, 22% yield).
Acknowledgements
This study was supported by the National Science Council of Taiwan
(NSC-100-2119M-002-026 and NSC-101-2628M-002-010) and by National
Taiwan University (NTU-101-R890913).
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“Threading Followed by Shrinking” for Stable Rotaxanes
FULL PAPER
[10] CCDC-917835 ([11-H]
G
E
[17] For other discussions and studies about the threading process, see:
a) T. Clifford, A. Abushamleh, D. H. Busch, Proc. Natl. Acad. Sci.
USA 2002, 99, 4830–4836; b) H. W. Gibson, N. Yamaguchi, L. M.
Hamilton, J. W. Jones, J. Am. Chem. Soc. 2002, 124, 4653–4665;
c) C.-J. Chuang, M.-L. Yen, C.-C. Lai, Y.-H. Liu, S.-M. Peng, S.-H.
Chiu, Chem. Commun. 2013, 49, 4199–4201.
[18] From most of these reactions, we isolated macrocycles 8 and 9 as
the major byproducts; the starting free macrocycle (2) was not com-
pletely consumed and we could recycle the dumbbell-shaped salt
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
[11] Crystal data for [11-H]
[C32H12BF24][CH2Cl2]; Mr =2347.95; colorless columnar crystals; tri-
clinic; space group P1; a=14.4985(3), b=17.7566(3), c=
T
24.1925(5) ꢄ; V=5966.4(2) ꢄ3; 1calcd =1.307 gcmÀ3
1.134 mmÀ1; T=200(2) K; 21747 independent reflections; F2 refine-
ment; R1 =0.0906 and wR2 =0.2558.
[14-H]ACTHNGUTERN[UNG TFPB] after ion-exchange and chromatography processes.
However, increasing the irradiation time not only resulted in the re-
cycling of much less of the free macrocycle (2) but also lower yields
of the desired [2]rotaxanes; see Table 1, entries 7 and 8.
[12] The binding constants were determined based on an integration of
the slowly exchanging signals in the 1H NMR spectra of equimolar
mixtures
dimethylbenzylammonium)]
isopropylbenzylammonium)]
[13] For the synthesis of [14-H]
Glink, J. F. Stoddart, Chem. Eur. J. 2003, 9, 4046–4054.
[14] For a description of the single-point method, see: a) P. R. Ashton,
E. J. T. Chrystal, P. T. Glink, S. Menzer, C. Schiavo, N. Spencer, J. F.
Stoddart, P. A. Tasker, A. J. P. White, D. J. Williams, Chem. Eur. J.
1996, 2, 709–728; b) P. R. Ashton, M. C. T. Fyfe, S. K. Hickingbot-
tom, J. F. Stoddart, A. J. P. White, D. J. Williams, J. Chem. Soc.
Perkin Trans. 2 1998, 2117–2128.
[15] Because the degree of ion pairing between the dialkylammonium
ion and its counteranion would depend on the concentration, the
value of Ka as determined in this manner is merely a “ballpark”
figure; for a discussion of a method for more precisely determining
these values, see: W. J. Jones, H. W. Gibson, J. Am. Chem. Soc. 2003,
125, 7001–7004.
(5 mm)
of
[TFPB] and macrocycle 8/
[TFPB].
[PF6], see: M. Horn, J. Ihringer, P. T.
macrocycle
2/
G
[19] Crystal data for [16-H]
CATHGNURTENU[NGN PF6]: [C46H56O3N]AHCTNURGTEG[NNNU PF6]CATHNUGTERN[NUGN CHCl3]; Mr =935.26;
¯
G
ACHTUNGTRENNUNG
colorless columnar crystals; triclinic; space group P1; a=11.5164(7),
E
b=12.4216(6),
c=17.7638(8) ꢄ;
V=2374.9(2) ꢄ3;
1calcd =
G
1.308 gcmÀ3; m(CuKa)=1.134 mmÀ1; T=200(2) K; 8625 independent
ACTHNGUTERNNUG
reflections; F2 refinement; R1 =0.0851 and wR2 =0.2652.
[20] We observed small and complicated signals when we heated the so-
AHCTUNGERTGlNNUN ution at 403 K for 5 h (see the Supporting Information), presumably
because of decomposition of the [2]rotaxane, rather than its dissoci-
ation.
[21] R. S. Givens, B. Hrinczenko, J. H.-S. Liu, B. Matuszewski, J. Tholen-
Collison, J. Am. Chem. Soc. 1984, 106, 1779–1789.
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Lin, C.-C. Lai, Y.-H. Liu, S.-M. Peng, S.-H. Chiu, Chem. Eur. J.
2007, 13, 4350–4355.
Received: January 7, 2013
Revised: March 28, 2013
Published online: && &&, 0000
[16] Y. Tachibana, N. Kihara, Y. Furusho, T. Takata, Org. Lett. 2004, 6,
4507–4509.
Chem. Eur. J. 2013, 00, 0 – 0
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S.-H. Chiu et al.
Rotaxanes
L.-Y. Wang, J.-L. Ko, C.-C. Lai,
Y.-H. Liu, S.-M. Peng,
S.-H. Chiu* .................... &&&& — &&&&
Using “Threading Followed by
Shrinking” to Synthesize Highly Stable
Dialkylammonium-Ion-Based Rotax-
anes
Shrink wrap: A “threading followed by
shrinking” method, which was used to
extrude both arylmethyl sulfone motifs
from the macrocyclic components of
dialkylammonium-ion-based [2]pseu-
dorotaxanes, afforded robust [2]rotax-
anes that were sufficiently stable to
maintain their molecular integrity in
CD3SOCD3 at 393 K for at least 5 h
(see figure).
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These are not the final page numbers!