Effects of axle-core, macrocycle, and side-station structures on the threading and hydrolysis processes of imine-bridged rotaxanes

Article abstract of DOI:10.1002/chem.201200837

Imine-bridged rotaxanes are a new type of rotaxane in which the axle and macrocyclic ring are connected by imine bonds. We have previously reported that in imine-bridged rotaxane 5, the shuttling motion of the macrocycle could be controlled by changing the temperature. In this study, we investigated how the axle and macrocycle structures affect the construction of the imine-bridged rotaxane as well as the dynamic equilibrium between imine-bridged rotaxane 5 and [2]rotaxane 7 by using various combinations of axles (1 A,B), macrocycles (2 a-e), and side-stations (XYL and TEG). In the threading process, the flexibility of the macrocycle and the substituent groups at the para position of the aniline moieties affect the preparation of the threaded imines. The size of the imine-bridging station and the macrocyclic tether affects the hydrolysis of the imine bonds under acidic conditions. Copyright

Full text of DOI:10.1002/chem.201200837

FULL PAPER
DOI: 10.1002/chem.201200837
Effects of Axle-Core, Macrocycle, and Side-Station Structures on the
Threading and Hydrolysis Processes of Imine-Bridged Rotaxanes
Hiroyoshi Sugino,[a] Hidetoshi Kawai,*[a, b] Takeshi Umehara,[a] Kenshu Fujiwara,[a] and
Takanori Suzuki*[a]
Abstract: Imine-bridged rotaxanes are
a new type of rotaxane in which the
axle and macrocyclic ring are connect-
ed by imine bonds. We have previously
reported that in imine-bridged rotax-
ane 5, the shuttling motion of the mac-
rocycle could be controlled by chang-
ing the temperature. In this study, we
investigated how the axle and macrocy-
cle structures affect the construction of
the imine-bridged rotaxane as well as
the dynamic equilibrium between
imine-bridged rotaxane 5 and [2]rotax-
ane 7 by using various combinations of
axles (1A,B), macrocycles (2a–e), and
side-stations (XYL and TEG). In the
threading process, the flexibility of the
macrocycle and the substituent groups
at the para position of the aniline moi-
eties affect the preparation of the
threaded imines. The size of the imine-
bridging station and the macrocyclic
tether affects the hydrolysis of the
imine bonds under acidic conditions.
Keywords: hydrolysis · imines · mo-
lecular devices · rotaxanes · supra-
molecular chemistry
Introduction
We previously reported a novel rotaxane synthesis in
which linking of the axle and the ring moieties was achieved
through imine bonds.[16–18] These bridged rotaxanes could be
readily obtained by threading an axle molecule with diform-
yl groups into a macrocyclic diamine, thus enabling imine
bonds to be formed between the axle and macrocycle mole-
cules, and then attaching end-cap groups. A unique tempera-
ture-dependent shuttling motion was observed when these
imine-bridged rotaxanes were converted into unbridged
[2]rotaxanes by cleavage/reformation of the imine bonds
under acidic conditions.
This successful example relies on the matching of the geo-
metries of the axle and the ring. In addition to exploring
how to exploit the generality of the imine-directed threading
methodology, it is also important that we study the size and
flexibility of the axle and ring. We should also determine
the effect of the substituent on the macrocycle, which can
stabilize/destabilize the imine bridge through electronic ef-
fects. We report herein the preparation of a series of imine-
bridged rotaxanes from the newly prepared hexahydropyr-
ene axle 1B and macrocycles 2c–e, along with their behav-
ior under acidic hydrolytic conditions. The core structures of
the newly prepared assemblies were designed so that they
are bulkier than those based on the hydrindacene axle
1A.[16a,b] Some of the new macrocycles were designed to
have an electron-donating/withdrawing substituent (2c: 4-
methoxyphenyl; 2d: 4-methoxycarbonylphenyl) at the para
position of the aniline moiety. The size of the inner cavity of
the macrocycle can be modified by altering the length and
flexibility of the tether units that connect the two aniline
moieties (2a: hexadiyne;[16a] 2b–d: hexamethylene; 2e: m-
xylylene; Scheme 1).
Over the past two decades interlocked molecules have been
developed for use in molecular devices and materials.[1] In
particular, numerous rotaxanes and catenanes, which change
their shape and properties in response to external stimuli
such as a change in pH,[2,3] a change in the redox status,[4–7]
and irradiation with UV/Vis light,[8–10] have been designed
and prepared. For the effective generation of these mole-
cules, noncovalent interactions, such as hydrogen bond-
ing,[2,5,9,11] donor–acceptor interactions,[4,8] anion recogni-
tion,[12] metal coordination,[7,13] hydrophobic interac-
tions,[3,6,10,14] as well as covalent bond formation,[15,16] have
been used as the synthetic template. However, the range of
combinations is limited by the structure of the interacting
site because these noncovalent interactions are too particu-
lar to allow structural variation, especially with regard to
the distance and geometry between the interaction sites.
[a] H. Sugino, Prof. H. Kawai, Dr. T. Umehara, Prof. K. Fujiwara,
Prof. T. Suzuki
Department of Chemistry, Faculty of Science
Hokkaido University
Kita 10, Nishi 8, Kita-ku, Sapporo 060-0810 (Japan)
Fax : (+81)11-706-2714
E-mail: tak@sci.hokudai.ac.jp
[b] Prof. H. Kawai
Department of Chemistry, Faculty of Science
Tokyo University of Science
1-3 Kagurazaka, Shinjuku-ku, Tokyo, 162-8601 (Japan)
Fax : (+81)3-5228-8255
E-mail: kawaih@rs.tus.ac.jp
By comparing the threading and hydrolyzing behaviors of
these molecules with those of a previous example based on
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200837.
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Scheme 1. Structures of the axles 1A,B and macrocycles 2a–e.
the hydrindacene unit, we report herein on the general ap-
plicability of our method for preparing rotaxanes and the
scope and limitation for effective switching.
(2b).[16a,b] The formation of an imine bond between the axle
1A and the macrocycle 2e, which has a smaller cavity than
2a or 2b, also proceeded under similar conditions. These re-
sults seem to demonstrate that an imine-directed threading
Results and Discussion
Effects of the axle and macrocycle structures on the thread-
ing process: The effects of the core structure of the axles
were investigated with regard to their effects on the thread-
ing process. Threaded imines 3Aa–e and 3Ba,b were pre-
pared by threading and the formation of an imine bond be-
tween the axle 1A or 1B and macrocycles 2a–e under
acidic dehydrating conditions, that is, in benzene at reflux
with 4 ꢁ MS by the addition of trifluoroacetic acid (TFA;
Scheme 2).
X-ray analyses of imines 3Aa’ and 3Ab’ with a bromo-ter-
minated hydrindacene unit unambiguously revealed that the
hydrindacene axle passes through the macrocycle to create
Ci-symmetric 3Aa’ or 3Ab’ (Figure 1).
As shown in Table 1, the yields of the threaded imines
3Aa,b or 3Ba,b prepared from axles 1A and 1B are de-
pendent on the macrocycle structure rather than the axle
structure, which shows that the efficiency of threading is
similar for both rigid (2a)[16a] and flexible macrocycles
Scheme 2. Synthesis of threaded imines 3.
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Imine-Bridged Rotaxanes
FULL PAPER
method for the synthesis of rotaxane-type structures is gen-
erally applicable to macrocycles with cavities of different
sizes and axles with core structures that differ with regard to
bulkiness.
Next, the electronic effects of the substituents at the para
position of the aniline moieties were investigated.[19] Macro-
cycles 2c,d have electron-donating (4-methoxyphenyl: 2c)
and -withdrawing (4-methoxycarbonylphenyl: 2d) moieties
at this position, respectively. The higher yield of the thread-
ed form 3Ac suggests that an electron-donating group at the
para position of the aniline moieties favors imine-bond for-
mation. Thus, electronic effects of the substituent at this po-
sition can be considered to promote efficient imine-directed
threading by favoring the formation of imine bonds.
When threaded imines 3Aa–e and 3Ba,b were subjected
to hydrolysis, the corresponding axles 1 and macrocycles 2
were both recovered quantitatively, which confirms the re-
versible formation/cleavage of the imine bonds in 3. Before
we studied the generation of [2]rotaxane 7, the imines 3
were converted into the imine-bridged rotaxanes 5 by at-
taching end-cap units 4a[16] (XYL) or 4b[16b] (TEG). Imine-
bridged rotaxane 5Aa,b-XYL and 5Aa–e-TEG with a hy-
drindacene core A and 5Ba,b-XYL with a hexahydropyrene
core B were prepared by attaching the end-cap units beyond
the xylylenyl (XYL) or triethylene glycolyl (TEG) side-sta-
tions in the corresponding threaded imines 3Aa–e and
3Ba,b (Scheme 3).
Figure 1. X-ray structures of bromo-terminated threaded imines 3Aa’[16a]
and 3Ab’. Hydrogen atoms and solvents have been omitted for clarity.
Effects of structure on the hydrolysis process: We investigat-
ed the effect of structure on the conversion of imine-bridged
rotaxanes 5 into [2]rotaxanes 7 under acidic hydrolytic con-
ditions (Scheme 4).
Table 1. Isolated yields of threaded imines 3.
Axle
Macrocycle
Isolated yields [%]
As previously reported, when TFA was added to a solu-
tion of 5Ab-XYL in CDCl3, a mixture of hydrolyzed [2]ro-
taxane [7Ab-XYL·2H]2+, mono-imine [6Ab-XYL·H]+, and
the starting diimine 5Ab-XYL were obtained, the diimine
being the major species in the equilibrated mixture. These
three species were observed as independent components,
and thus their rate of interconversion in this hydrolytic equi-
librium is slower than the NMR timescale. The equilibrium
1A
2a
2b
2c
2d
2e
2a
2b
3Aa
95
46
64
31
50
80
52
3Ab
3Ac
3Ad
3Ae
3Ba
3Bb
1B
Scheme 3. Introduction of end-cap units 4a and 4b onto the threaded imines 3Aa–e and 3Ba,b.
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H. Kawai, T. Suzuki et al.
Scheme 4. Generation of [2]rotaxanes 7 by the hydrolysis of imine bonds in 5.
ratio of 5Ab-XYL/[6Ab-XYL·H]+/[7Ab-XYL·2H]2+ was
42:35:23 at 233 K and 81:18:1 at 313 K (Scheme 5a).[16a,b]
Effect of core structure—A versus B: We investigated the
effect of the bulkiness of the axle core structures on the hy-
drolysis equilibrium by using imine-bridged rotaxanes 5Ab-
XYL and 5Bb-XYL. When TFA was added to a solution of
5Bb-XYL in wet C6D5Br, two sets of resonances for hydro-
lyzed [2]rotaxane [7Bb-XYL·2H]2+ and monoimine [6Bb-
XYL·H]+ were observed as an equilibrium mixture with the
starting diimine 5Bb-XYL (Figure 2a–f).[20,21]
In comparison with the hydrolysis equilibrium of hydrin-
dacene-type compound [7Ab-XYL·2H]2+, the proportion of
hexahydropyrene-type [2]rotaxane [7Bb-XYL·2H]2+ with
the bulkier core was higher than that of hydrindacene-type
[7Ab-XYL·2H]2+ (Scheme 5b). When this hydrolyzed
sample was cooled, the proportion of 5Bb-XYL decreased
and below 268 K the equilibrium ratio of 5Bb-XYL/[6Bb-
XYL·H]+/[7Bb-XYL·2H]2+ was 0:30:70 (Figure 2g; cf. the
equilibrium ratio of 50:42:8 for 5Ab-XYL/[6Ab-XYL·H]+
/[7Ab-XYL·2H]2+ at the same temperature).
value of DH for Bb-XYL is more negative than that for Ab-
XYL (DH=À6.0Æ0.4 for Ab, À9.0Æ1.3 kcalmolÀ1 for Bb).
This indicates that imine-bridged 5Bb-XYL is thermody-
namically destabilized compared with 5Ab-XYL and that
steric repulsion between the axle core and the macrocycle in
the diACTHNURGTNEiNUG mine could be the major factor: Repulsion in 5Bb-
XYL is greater than that in 5Ab-XYL. Thus, [2]rotaxane
[7Bb-XYL·2H]2+ is the favored form, whereas in the case of
the less bulky hydrindacene-type compound, the diimine
form 5Ab-XYL is the favored form. This result suggests
that the bulkiness of the core structure in the axle is signifi-
cant for efficient hydrolysis of imine-bridged rotaxanes with
an XYL side-station.
Effect of side-station: We previously investigated the effect
of the side-station (XYL or TEG).[16a,b] In the case of 5Ab-
XYL with p-xylylene (XYL) side-stations, as mentioned
above (Scheme 5b), pure 5Ab-XYL in CDCl3 solution was
converted into a mixture of 5Ab-XYL, [6Ab-XYL·H]+, and
[7Ab-XYL·2H]2+ upon the addition of TFA. At equilibri-
um, the solution contained 23% of [2]rotaxane [7Ab-
XYL·2H]2+ at 233 K, and 1% at 313 K.[16a]
In the case of 5Ab-TEG with triethylene glycol ether
(TEG) side-stations, [2]rotaxane [7Ab-TEG·2H]2+ was ex-
clusively formed at 293 K in C6D5Br due to hydrogen bond-
ing between the ring part and the TEG units.[16b] Both
To explain the differences between 7Ab and 7Bb, we de-
termined the thermodynamic parameters DH and DS for the
equilibration between 5Ab and 7Ab, and 5Bb and 7Bb by
analyzing the vanꢂt Hoff plots (Figure 2h). The DS values
for both compounds are almost the same (DS=À26.0Æ1.4
for Ab, À28.6Æ4.5 calmolÀ1 KÀ1 for Bb). However, the
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Imine-Bridged Rotaxanes
FULL PAPER
Effect of spacer within the macrocycles: We investigated the
effects of different spacers in the macrocycles by comparing
the hydrolytic behavior of 5Aa,b,e-TEG/[7Aa,b,e-
TEG·2H]2+ (Scheme 6). Diimine 5Aa has a rigid hexadiyne
spacer whereas 5Ab has a flexible hexamethylene spacer.
Furthermore, 5Ae with a m-xylylene spacer has a smaller
cavity than either 5Aa,b.
[2]Rotaxane [7Ab-TEG·2H]2+ with
a hexamethylene
spacer was successfully generated from 5Ab-TEG under hy-
drolyzing conditions (shown above), and the macrocycle
unit shuttled between two TEG side-stations under acidic
hydrolyzing conditions.
In the case of 5Aa-TEG, however, hydrolyzed [2]rotaxane
[7Aa-TEG·2H]2+ was not observed in the 1H NMR spec-
trum, despite the assistance of the hydrogen-bonding station
(Scheme 6b). When TFA was added to a solution of 5Aa-
TEG, the signals assigned to 5Aa-TEG showed partial
broadening. When this sample was cooled to 248 K, four
doublets appeared around 5 ppm, which have been assigned
to the propargylic methylene protons in the macrocycle, and
no CHO signal was observed (see Figure S3 in the Support-
ing Information). This suggests that the vibrational motion
of the macrocycle around the threading unit (hindered rota-
tion)[16c] is slower than the NMR timescale at 248 K. Com-
parison of the results for Aa-TEG and Ab-TEG suggests
that the flexibility of the macrocycle is an important factor
in the efficient formation of a hydrogen bond with the TEG
side-station and therefore the formation of the hydrolyzed
[2]rotaxane 7.
In the case of 5Ae-TEG, imine bonds were hydrolyzed
under similar hydrolytic conditions (Scheme 6c, Figure 3)
and [2]rotaxane [7Ae-TEG·2H]2+ was predominantly gener-
ated at 298 K. However, despite the presence of TEG side-
stations in 5Ae-TEG, monoimine [6Ae-TEG·H]+ was ob-
served in the hydrolyzed mixture at equilibrium. The less-fa-
vored 5Ae-TEG relative to [7Ae-TEG·2H]2+ may be attrib-
uted to the small size of the cavity of the macrocycle: The
multipoint hydrogen bonds formed between the ammonium
groups in the macrocycle and the TEG side-stations in the
axle in [7Ae-TEG·2H]2+ are not very strong because the
distance between the two amine parts in the macrocycle 2e
is somewhat shorter than the ideal value. In fact, the value
of DH for Ae-TEG determined from the vanꢂt Hoff plot is
less negative than that in Ab-TEG (DH=À10.7Æ0.7 for
Ae-TEG, À15.7Æ0.3 kcalmolÀ1 for Ab-TEG), as shown by
the shallower regression line for the plot (Figure 3h). The
value of DS for Ae-TEG is also less negative than that for
Ab-TEG (DS=À30.7Æ2.1 for Ae-TEG, À48.5Æ0.8 cal
molÀ1 KÀ1 for Ab-TEG), which indicates that enthalpic sta-
bilization and the loss of entropy due to hydrogen bon-
ding[16b] with the TEG side-stations is small for the macrocy-
cle Ae with the m-xylylene spacer.
Scheme 5. Hydrolytic equilibrium of imine-bridged rotaxanes 5, mono-
ACHTUNGTRENNUNGimines 6, and [2]rotaxanes 7. Equilibrium ratios were estimated by inte-
gration of the macrocyclic methylene protons in the 1H NMR spectra for
a) hydrindacene type Ab and b) hexahydropyrene type Bb.
imine-bond cleavage/hydrogen-bond formation and imine-
bond formation/hydrogen-bond cleavage are thermodynami-
cally matched processes.[19b] Thus, the TEG units form hy-
drogen bonds with the ammonium in the macrocycle
(Scheme 6) and serve as hydrogen-bonding stations. Upon
heating to 398 K under similar acidic conditions, imine-
bridged 5Ab-TEG was again formed by dehydration. The
equilibrium ratio of [2]rotaxane [7Ab-TEG·2H]2+ changed
drastically from 100:0 to 0:100 over a temperature range of
293 to 398 K (Scheme 6a).[16b]
These results suggest that the flexible hexamethylene
spacer in the macrocycle provides the best match for inter-
conversion between imine-bridged rotaxane 5 and [2]rotax-
ane 7.
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H. Kawai, T. Suzuki et al.
Figure 2. 1H NMR spectra (300 MHz, wet C6D5Br) of a) imine-bridged rotaxane 5Bb-XYL and b)–f) a hydrolyzed mixture containing 5Bb-XYL, mono-
ACHTUNGTRENNUNG
imine [6Bb-XYL·H]+, and [2]rotaxane [7Bb-XYL·2H]2+ recorded at b) 328, c) 308, d) 298, e) 283, and f) 268 K. g) Temperature-dependence of the
ratio of 5Bb-XYL, [6Bb-XYL·H]+, and [7Bb-XYL·2H]2+ at equilibrium in the hydrolyzed mixture in C6D5Br as estimated from the macrocyclic methyl-
1
ene protons in the H NMR spectra.[21] h) vanꢂt Hoff plots for the hydrolysis of 5Ab-XYL to 7Ab-XYL·2H2+ and 5Bb-XYL to 7Bb-XYL·2H2+
.
Electronic effects of the substituent on the macrocycle:
Imine-bond formation by the amine and hydrogen-bond for-
mation by the ammonium are affected by the electronic ef-
fects of the substituents.[19] In the threading process in our
rotaxane synthesis, imine-bond formation was favored by
the use of aniline derivatives with an electron-donating
group. Thus, we investigated the electronic effects of the
substituents on the macrocycle on the hydrolysis of the
imine bonds.
Under similar hydrolyzing conditions, imine-bridged ro-
taxanes 5Ab–d-TEG were converted into [2]rotaxanes
[7Ab–d-TEG·2H]2+ and their ratios at equilibrium were
found to be temperature-dependent (Figure 4). In each case,
we observed that the equilibrium ratio changed drastically
from 0:100 to 100:0 over the temperature range of 290 to
400 K. This temperature dependency is almost independent
of the presence of the 4-mehoxyphenyl or 4-methoxycarbo-
nylphenyl groups.
These results show that the electron-donating/withdrawing
effects of the 4-methoxyphenyl/4-methoxycarbonylphenyl
groups only marginally influence the hydrogen bonding be-
tween the TEG side-station and macrocycle. In the case of
5Ac-TEG, an electron-donating group (4-methoxyphenyl)
would favor imine-bond formation (see Table 1; 3Ab vs.
3Ac), but the effects of the hydrogen bond would be ex-
ceeded by the electron-donating effect. Thus, the [2]rotax-
ane form [7Ac-TEG·2H]2+ is favored, as is the case in
[7Ab-TEG·2H]2+. Overall, the combination of a hexam-
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Imine-Bridged Rotaxanes
FULL PAPER
Scheme 6. Hydrolytic equilibrium of imine-bridged rotaxane 5, monoimine 6, and [2]rotaxane 7 with TEG side-stations and a) hexamethylene spacer Ab,
b) hexadiyne spacer Aa, and c) meta-xylylene spacer Ae. The equilibrium ratios were estimated by integration of the macrocyclic methylene protons in
1
the H NMR spectra in C6D5Br.[16b]
ethylene spacer and a TEG station is suitable for realizing
complete switching between a wide range of bridged rotax-
anes 5 and [2]rotaxanes 7.
turbing the hydrolysis process. We are currently constructing
more complex interlocked molecules, such as stretching
daisy chains, that respond to the hydrolysis/condensation of
imine bonds.
Conclusions
Experimental Section
We have shown that variation of the imine-bridging station,
side-station, and/or macrocycle structures all affect the
threading process of the axle in the macrocycle and the
process of hydrolysis to generate nonbridged [2]rotaxanes 7.
The electronic effects of the substituent groups on the mac-
rocycle have only marginal effects on the hydrolysis process,
which is useful for constructing advanced systems: Any sub-
stituent group can be introduced at this position without dis-
General: 1H and 13C NMR spectra were recorded on a JEOL AL-300
(1H/300 MHz, 13C/75 MHz) or a400 (1H/400 MHz, 13C/100 MHz) spec-
trometer. IR spectra were taken on a JASCO model FT/IR-230 infrared
spectrophotometer. Mass spectra were recorded on JEOL JMS-600 (EI),
JEOL JMS-T100GCV (FD), JMS-SX102A (FD, FAB) spectrometers.
Column chromatography was performed on silica gel I-6-40 (YMC, parti-
cle size 40-63 mm) and standardized aluminum oxide 90 (Merck, 63-200
mm), respectively. Thin-layer chromatography (TLC) was performed on
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H. Kawai, T. Suzuki et al.
Figure 3. 1H NMR spectra (300 MHz, wet C6D5Br) of a) imine-bridged rotaxane 5Ae-TEG and b)–f) a hydrolyzed mixture containing 5Ae-TEG, mono-
ACHTUNGTRENNUNG
imine [6Ae-TEG·H]+, and [2]rotaxane [7Ae-TEG·2H]2+ recorded at b) 403, c) 373, d) 333, e) 298, and f) 273 K. g) Temperature-dependence of the
ratio of 5Ae-TEG, [6Ae-TEG·H]+, and [7Ae-TEG·2H]2+ at equilibrium in the hydrolyzed mixture in C6D5Br, as estimated from the hydrindacene
methylene protons in the 1H NMR spectra.[21] h) vanꢂt Hoff plots for the hydrolysis of 5Ab-TEG to 7Ab-TEG·2H2+ and 5Ae-TEG to 7Ae-TEG·2H2+
.
silica gel 60 (Merck) of particle size 5-20 mm. Gel permeation chromatog-
raphy (GPC) was carried out on LC-908 (Japan Analytical Industry) with
JAIGEL 1H+2H, 2H+2.5H or 2.5H+3H columns eluted with CDCl3.
Elemental analyses were taken on a Yanako MT-6 CHN recorder at the
Center for Instrumental Analysis of Hokkaido University. Reactions
were carried out under an argon atmosphere.
Preparation of threaded imine 3Bb: TFA (2 drops, ca. 20 mL, 0.26 mmol)
was added to a mixture of 1B (60 mg, 73 mmol) and 2b (55 mg, 77 mmol)
in benzene. The mixture was heated at reflux for 28 h with stirring under
dehydrating conditions (Soxhlet apparatus with a thimble filter contain-
ing 4 ꢁ MS), and additional TFA (2 drops, ca. 20 mL, 0.26 mmol) was
added to the mixture every 15 h. After the reaction mixture had cooled
to room temperature, it was filtered through aluminum oxide. The crude
product obtained by concentrating the filtrate was purified by GPC sepa-
ration (1H+2H) to give 3Bb (57 mg, 52%) as a white solid. M.p. 193.0–
195.08C (dec.); 1H NMR (300 MHz, CDCl3): d=7.26–6.68 (m, 44H),
4.20–4.00 (m, 8H), 3.24 (d, J=15.9 Hz, 4H), 3.08 (d, J=15.9 Hz, 4H),
1.88–1.60 (m, 16H), 0.98 (s, 18H), 0.20 ppm (s, 12H); 13C NMR (75 MHz,
CDCl3): d=169.48, 157.36, 155.05, 141.71, 139.27, 133.76, 133.68, 132.66,
131.74, 130.95, 128.90, 128.87, 127.92, 127.04, 126.65, 123.99, 120.03,
114.36, 68.12, 47.56, 38.10, 29.15, 26.00, 25.68, 18.21, À4.40 ppm; IR
2,6-Bis(4-bromophenyl)-1,2,3,5,6,7-hexahydro-s-indacene-2,6-dicarbalde-
hyde (1A’), 2,6-bis(4-bromophenyl)-1,2,3,5,6,7-hexahydro-s-indacene-2,6-
dicarbaldehyde (1A),[16a] macrocycles 2a,[16a] 2b,[16a] threaded imine
3Aa’,[16a] a-[4-{tris(4’-tert-butylbiphenyl-4-yl)methyl}phenoxy]-a’-bromo-
p-xylene (4a),[16a] and 1-{tris(4’-tert-butylbiphenyl-4-yl)methyl}-4-{2-[2-(2-
iodoethoxy)ethoxy]ethoxy}-benzene (4b)[16b] were prepared by following
the known procedures. All commercially available compounds were used
without further purification unless otherwise indicated.
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Imine-Bridged Rotaxanes
FULL PAPER
Figure 4. Temperature dependence of the ratio of imine-bridged rotaxanes 5-TEG and [2]rotaxanes [7-TEG·2H]2+ at equilibrium, as estimated from the
1
macrocyclic methylene protons in the H NMR spectra in C6D5Br. a) Hydrogen (R=H), b) 4-methoxyphenyl (R=4-MeOC6H4-), and c) 4-methoxycarbo-
nylphenyl (R=4-MeOCOC6H4-) groups were attached at the para position of the aniline moieties.[21]
(KBr): n˜ =3031, 2929, 2857, 1655, 1607, 1510, 1496, 1471, 1459, 1401,
1252, 1172, 1034, 1002, 914, 825, 782, 758, 538 cmÀ1; LRMS (FD): m/z
(%): 1513 (35) [M+3]+, 1512 (71) [M+2]+, 1511 (100) [M+1]+, 1510 (85)
[M]+; HRMS (FD): calcd. for C102H106N2O6Si2: 1510.7589 [M]+; found:
1510.7593.
Acknowledgements
We acknowledge financial support from the Global COE Program (Proj-
ect No. B01: Catalysis as the Basis for Innovation in Materials Science)
from MEXT. H.K. also thanks the JST PRESTO project. We are grateful
to E. Fukushi, Y. Takata and K. Watanabe of the GC-MS and NMR Lab-
oratory, Graduate School of Agriculture, Hokkaido University for the
mass spectrometric analyses.
Preparation of imine-bridged rotaxane 5Bb-XYL: Tetrabutylammonium
fluoride (TBAF; 1.0m solution in THF, 33 mL, 33 mmol) was added to a
solution of 3Bb (25 mg, 17 mmol) in dry DMF (1.5 mL) and dry THF
(4.0 mL) at room temperature under an argon atmosphere. After stirring
the mixture for 15 min, Cs2CO3 (27 mg, 83 mmol) and 4a (38 mg,
41 mmol) were added. The mixture was stirred for 23 h at room tempera-
ture before being poured into water. The aqueous mixture was extracted
with CHCl3 and the extract was washed with water and brine, dried over
MgSO4, and then filtered. The crude product was separated by GPC
(2H+2.5H) to give 5Bb-XYL (18 mg, 38%) as a white solid. M.p. 244–
2468C (dec.); 1H NMR (300 MHz, C6D6): d=7.63–7.20 (m, 64H), 7.09–
6.87 (m, 44H), 6.77 (d, J=8.8 Hz, 8H), 4.73 (s, 4H), 4.69 (s, 4H), 3.88
(m, 8H), 3.45 (d, J=16.1 Hz, 4H), 3.17 (d, J=16.1 Hz, 4H), 1.80–1.52
(m, 8H), 1.40–1.26 (m, 8H), 1.23 ppm (s, 54H); 13C NMR (100 MHz,
CDCl3): d=158.08, 157.35, 156.82, 151.01, 150.14, 145.77, 139.76, 139.31,
139.13, 138.37, 137.69, 136.89, 136.74, 133.75, 133.47, 132.65, 132.26,
131.72, 131.44, 130.94, 128.85, 128.02, 127.82, 127.69, 127.09, 126.66,
126.58, 126.35, 125.92, 125.66, 124.00, 121.50, 121.30, 114.84, 114.35,
113.62, 69.76, 69.67, 68.12, 63.64, 47.54, 38.08, 34.51, 31.35, 29.14,
26.00 ppm; IR (KBr): n˜ =3027, 2951, 2885, 1607, 1510, 1494, 1460, 1396,
1369, 1292, 1240, 1175, 1109, 1003, 816, 763, 565, 532 cmÀ1; LRMS (FD):
m/z (%): 2957.8 (28), 2954.5 (100) [M]+, 732.4 (27); HRMS (FD): calcd.
for C216H202N2O8: 2951.5461 [M]+; found: 2951.5447; elemental analysis
calcd (%) for C216H202N2O8·2CH3CH2OH: C 86.75, H 7.08, N 0.92; found:
C 86.91, H 7.43, N 0.94.
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Chem. Eur. J. 2012, 00, 0 – 0
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Imine-Bridged Rotaxanes
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[20] When a small amount of TFA (0.08% v/v) was added to the solution
of 5Ab-XYL in wet CDCl3, the dynamic equilibrium in Figure 2 was
observed. However, when a large excess of TFA (>1% v/v) was
added, hydrolysis of the imine bonds was not observed. This obser-
vation resembles the results observed by Giuseppone and Lehn.[19b]
[21] We have checked that the equilibrium ratio of 5/ACTHNGUTERNNUG
[7·2H]2+ was main-
tained for several cycles of the heating/cooling process. Although
evaporation of water upon heating during the VT-NMR process
cannot be completely ruled out, such a change did not affect the re-
sults over repeated experiments.
Received: March 13, 2012
Revised: June 6, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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H. Kawai, T. Suzuki et al.
Threading macrocycles: Variation of
the imine-bridging station, side-station,
and/or macrocycle structures all affect
the threading process of the axle in the
macrocycle and the hydrolysis generat-
ing nonbridged [2]rotaxane (see
scheme).
Supramolecular Chemistry
H. Sugino, H. Kawai,* T. Umehara,
K. Fujiwara, T. Suzuki* ..... &&&& — &&&&
Effects of Axle-Core, Macrocycle, and
Side-Station Structures on the
Threading and Hydrolysis Processes of
Imine-Bridged Rotaxanes
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www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!