A shuttling molecular machine with reversible brake function

Article abstract of DOI:10.1002/chem.200702001

Design, synthesis, and demonstration of a prototype of a shuttling molecular machine with a reversible brake function are reported. It is a photochemically and thermally reactive rotaxane composed of a dianthrylethane-based macrocycle as the ring component and a dumbbell shaped molecular unit with two, secondary ammonium stations separated by a phenylene spacer as the axle component. The rate of shuttling motion was shown to be reduced to less than 1 % (from 340 to <2.5 s^-1) by reducing the size of the ring component from 30-crown-8 to 24-crown-8 macrocycles upon photoirradiation. The ring component was turned back to 30-crown-8 by thermal ring opening, thus establishing a reversible brake function that works in response to photochemical and thermal stimuli.

Full text of DOI:10.1002/chem.200702001

FULL PAPER
DOI: 10.1002/chem.200702001
A Shuttling Molecular Machine with Reversible Brake Function
Keiji Hirose,* Yoshinobu Shiba, Kazuaki Ishibashi, Yasuko Doi, and Yoshito Tobe[a]
Abstract: Design, synthesis, and dem-
onstration of a prototype of a shuttling
molecular machine with a reversible
brake function are reported. It is a
photochemically and thermally reactive
nium stations separated by a phenylene
spacer as the axle component. The rate
of shuttling motion was shown to be re-
duced to less than 1% (from 340 to
<2.5s À1) by reducing the size of the
ring component from 30-crown-8 to
24-crown-8 macrocycles upon photoir-
radiation. The ring component was
turned back to 30-crown-8 by thermal
ring opening, thus establishing a rever-
sible brake function that works in re-
sponse to photochemical and thermal
stimuli.
rotaxane composed of
a dianthryl-
Keywords: crown compounds · mo-
lecular devices · noncovalent inter-
actions · photochromism · rotaxanes
ethane-based macrocycle as the ring
component and a dumbbell shaped mo-
lecular unit with two, secondary ammo-
Introduction
latter approach, continuous switching of solvent polarity
would, in practice, be difficult because a large volume of sol-
vent would accumulate if the polarity was changed in a re-
petitive manner.[7]
For the implementation and the development of artificial
molecular machines[1] and electronic devices at the nanome-
ter scale,[2] rotaxanes[3] are thought to be prime candidates.
The functions in these devices are based on relative motions,
such as shuttling[4] and circumrotation[5] in response to either
physical or chemical stimuli. For example, based on the dif-
ferences in conductivity caused by changes of sites on which
the ring component locates (station) in response to electrical
stimuli, molecular electronic devices have been developed.[6]
The positional control of ring molecules by shuttling motion
has been studied most extensively, in contrast to the rate-
control of shuttling motion. As a chemical approach to con-
trol the rate of shuttling motion, Schalley and co-workers re-
ported that complexation of the phenolic moiety of the axle
component of a rotaxane with a bulky base reduced its shut-
tling rate. Leigh and Stoddart suggested that the shuttling
rates of rotaxanes can be changed by exchanging the sol-
vents, which affects the interactions between the ring and
stations. In the former approach, repetitive switching of the
rates would be hindered by accumulation of products
formed by the complexation/decomplexation cycle. In the
Thus, construction of a braking system at a molecular
scale capable of reversible switching of rates by physical
stimuli has not been achieved.[8] Very recently, we reported
a substantial change of the slippage/deslippage rates of a
pseudorotaxane system caused by light and heat.[9] On the
basis of these results, we designed a rotaxane system that
has a reversible brake function for shuttling motion by uti-
lizing a size-changeable crown ether as the ring component.
Here we report the synthesis of the [2]rotaxane and quanti-
tative evaluation of the change of its shuttling rates by
1H NMR measurement.
Results and Discussion
Design of the rotaxane: Our concept for the control of the
shuttling motion is shown in Figure 1, which includes models
of [2]rotaxanes capable of changing the size of ring compo-
nents and their corresponding potential energy diagrams.
Figure 1a shows the larger ring (open-form) rotaxane and 1b
shows the smaller ring (closed-form) state, which are revers-
[a] Dr. K. Hirose, Y. Shiba, K. Ishibashi, Y. Doi, Prof. Dr. Y. Tobe
Division of Frontier Materials Science
A
Graduate School of Engineering Science, Osaka University
1–3 Machikaneyama, Toyonaka, Osaka 560–8531 (Japan)
Fax : (+81)6-6850-6229
component that has a symmetrical structure and is com-
posed of two stoppers, two stations, and one spacer. The po-
tential energy of the individual rotaxane depends on the po-
sition of the ring component. The steric barrier between the
ring component and the spacer is larger in the closed-form
E-mail: hirose@chem.es.osaka-u.ac.jp
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2008, 14, 3427 – 3433
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3427

(Scheme 1). In Scheme 2 the
structures of open and closed-
form ring molecules 3[9] and 4[9]
corresponding to 1 and 2, re-
spectively, are shown. The pho-
todimerization of the anthra-
cene units of 3 and the thermal
reversion of 4 to 3 cause a sub-
stantial change in their cavity
size, which is fully reversible.
The interconversion between
these two isomers proceeded
quantitatively and in 97.5%
durability after 10 cycles. The
closed-form ring molecule
4
forms a more stable complex
with dibenzylammonium hexa-
fluorophosphate than open-
form molecule 3. On the basis
Figure 1. Models of [2]rotaxanes and the corresponding energy diagrams of a shuttling machine with effective
brake function.
than in the open-form. Moreover, through the attractive in-
teractions between the ring components and the stations,
the closed-form rotaxane can be more stabilized than the
open-form. Consequently, the shuttling rate of the closed-
form rotaxane would be reduced more effectively than that
of the open-form.
of these results, we adopt 3 and 4 for the ring components
of rotaxanes 1 and 2. As the stopper, 3,5-bis(triisopropyl-
A
prevent deslipping of the axle component from the open-
form ring molecule 3 (30-crown-8 type).
To build a prototype of the shuttling molecular machine
with a reversible brake function, the following structural re-
quirements should be fulfilled; 1) a size-changeable ring
component, which responds to external stimuli, 2) an appro-
priate spacer, which acts as a small barrier to the open-form
ring and a large barrier to the closed-form ring, and 3) a sta-
tion, which interacts more strongly with the closed form ring
molecule than the open-form. As a rotaxane system, which
meets these requirements, we designed rotaxanes 1 and 2
consisting of a photochromic dianthrylethane-based ring
component[10] and a dumbbell shaped axle molecule with a
phenylene group and two secondary ammonium sites
Scheme 2. Reversible isomerization between open- (3) and closed- (4)
forms of ring molecules.
Preparation of rotaxane 1: The synthesis of rotaxane 1 was
carried out through two different routes, which are summar-
ized in Scheme 3 and Scheme 4. Diester 5 and the photocon-
trollable macrocycle 3, which were prepared according to
the literature,[7i,9] were used as starting materials in both
routes. As shown in Scheme 3, ammonium hexafluorophos-
phate 8 was prepared from diester 5 by reduction with
LAH, followed by salt formation with gaseous HCl and
anion exchange with NH4PF6. The closed-form ring mole-
cule 4, freshly prepared from the open-form compound 3 by
UV irradiation, was treated with 8 in CH2Cl2/CH3CN (1:1)
at 273 K to produce pseudorotaxane 9. Addition of anhy-
dride 10 and nBu3P[11] at 273 K, followed by purification
with preparative HPLC, furnished the open-form [2]ro-
taxane 1 via closed-form 2 (which opened during the isola-
tion procedure). However, the chemical yield of 1 was not
satisfactorily (<16% yield from 8), and 1 was contaminated
with a small amount of the corresponding [3]rotaxane. The
reasons for the low yield are attributed to low solubility of 8
in non-polar solvents, which reduced the extent of the for-
Scheme 1. The open- (1) and closed- (2) forms of the shuttling machine
with reversible brake function.
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Chem. Eur. J. 2008, 14, 3427 – 3433

Molecular Shuttle with a Reversible Brake
FULL PAPER
Scheme 3. Synthesis of rotaxane 1.
mation of pseudorotaxane 9 during the capping reaction,
and the formation of a [3]rotaxane.
ring closure had proceeded efficiently. In addition, the
signal assigned to the benzylic protons of the axle compo-
nent (Hg, Hh, Hj, and Hk) of 1 appeared as a broad signal at
4.36 ppm, which was averaged on the NMR time-scale.
After the irradiation, the signal split into several signals in-
cluding those of Hg and Hh at 5.28 and 5.10 ppm. The signals
of Hj and Hk of 2 overlapped with the ethereal signals of the
ring component. The spectrum of 2 reverted to that of 1
completely after the NMR solution of 2 was left at room
temperature overnight. This implies that the thermal rever-
sion of 2 to 1 proceeds quantitatively. Hence, the evidence
for reversible switching between 1 and 2 by external stimuli,
photoirradiation and thermal heating, was thus established.
To improve the yield of 1, mono protected ammonium
hexafluorophosphate 13 was used as an alternative axle unit,
as shown in Scheme 4. Diester 5 was converted to the corre-
sponding amine 11 (47% yield), which, in turn, was reduced
with LAH to 12 (82%). Subsequent protonation gave the
mono protected ammonium hexafluorophosphate 13 (95%),
the solubility of which in nonpolar solvents was improved
compared to 8. The rotaxane formation was then carried out
in a mixed solvent consisting of CH2Cl2 and CH3CN in a
ratio of 2.4:1 in a similar manner as shown in Scheme 3.
After the purification by preparative HPLC, we obtained 15
(61%). Deprotection of the Boc group of 15 followed by
treatment with NH4PF6 afforded open-form rotaxane 1.
Determination of shuttling rates of open-form rotaxane 1
and closed-form rotaxane 2: To determine the rates of the
shuttling motion of rotaxane 1, VT-NMR spectra (Figures 3
and 4) were recorded. The rates of the shuttling motion of
rotaxane 1 were determined by the line-shape analysis of
their VT-NMR spectra in [D8]toluene and [D8]THF.[12]
Figure 5shows the partial experimental 1H NMR spectra of
the benzylic protons (Ha, Hb) on the axle component of
open-form rotaxane 1 at different temperatures together
with the simulated spectra assuming the rates shown. The ki-
Interconversion between open- and closed-form rotaxanes 1
1
and 2: The H NMR spectra of 1 and 2 in [D8]THF at 303 K
are shown in Figure 2. When a solution of 1 in [D8]THF im-
mersed in an ice bath was irradiated with a high-pressure
mercury lamp, the sharp singlet signal assigned to the ben-
zylic proton (Hi) of 1 at d=4.12 ppm disappeared. The dis-
appearance of this benzylic proton and the appearance of
the aliphatic proton of 2 at d=2.90 ppm indicated that the
Chem. Eur. J. 2008, 14, 3427 – 3433
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3429

K. Hirose et al.
the solutions were heated to
303 K in [D8]toluene and to
323 K in [D8]THF, respective-
ly.[13] Therefore, the maximum
estimated rates of shuttling
motion are k303 K <19 sÀ1 and
k
323 K <86 sÀ1,
respectively,
from the Gutowskiꢁs equation
calculated from the observed
Dn (the smallest difference be-
tween the resonance frequen-
cies of exchangeable protons
Ha and Hb in both solvents) of
2, as shown in Table 1.
As shown in Table 1, the
rate of shuttling of open-form
rotaxane 1 (k303 K =860 sÀ1) is
at least 45times faster than
that of closed-form rotaxane 2
(k303 K <19 sÀ1) in [D8]toluene.
The
[D8]THF is about 50 (k323 K
4500 sÀ1
vs.
switching
ratio
in
=
k
323 K <86 sÀ1).
These results clearly demon-
strate that the shuttling motion
was controlled very effectively
by changing the ring size of the
rotaxanes by using photochem-
Scheme 4. Alternative route for synthesis of rotaxane 1.
ical cycloaddition and thermal
reversion. In addition, the sol-
vent does not affect significantly the ratio of shuttling rates.
The rate of shuttling of closed-form 2 was also estimated
by saturation transfer experiments.[14] As a result, the shut-
tling rate of rotaxane 2 at 273 K in [D8]THF was estimated
to be <2.3 sÀ1. The rate constant of 1, k273 K =340 sÀ1, at the
same temperature in [D8]THF was calculated from the ki-
netic parameters obtained from the VT-NMR shown in
Table 1. These results also demonstrate that the rate of shut-
tling was reduced substantially to less than 1% (from 340 to
Figure 2. Partial 1H NMR spectra (400 MHz) of open- (1, upper) and
closed-form (2, lower) 2-station [2]rotaxanes recorded in [D8]THF at
303 K.
netic parameters were determined from the Eyring plot
listed in Table 1. On the other hand, the shuttling rates of
closed-form rotaxane 2 could not be determined in the same
manner. The room-temperature spectra of 2 indicate that
the shuttling motion is slow on the NMR time scale and that
the coalescence of the split signals was not observed when
Figure 3. Experimental (left) and simulated (right) partial VT-NMR
(270 MHz) spectra of protons Ha and Hb of 1 in [D8]toluene. The corre-
sponding temperatures and exchange rates are indicated.
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Chem. Eur. J. 2008, 14, 3427 – 3433

Molecular Shuttle with a Reversible Brake
FULL PAPER
spectral analyses were performed by means of a JEOL JMS-DX303HF
for EI and FAB ionization. The LD TOF mass measurements were per-
formed by means of a Shimadzu/Kratos AXIMA-CFR spectrometer. Ele-
mental analyses were carried out by using a Perkin–Elmer 2400II ana-
lyzer. UV-visible spectra were recorded by using a Hitachi U-3310 spec-
trometer in acetonitrile. Preparative HPLC separation was undertaken
with a JAI LC-908 chromatograph by using 600 mm”20 mm JAIGEL-
1H and 2H GPC columns with CHCl3 as an eluent. Solvents were dried
(drying agent in parentheses) and distilled prior to use: THF (sodium
benzophenone ketyl), CH3CN, CH2Cl2 (CaH2). Compounds 3, 5 and 10
were prepared according to the literature, respectively.[7i,9]
Synthesis of 7: To a suspension of LAH (770 mg, 20.3 mmol) in dry THF
(100 mL) was added slowly a solution of 5 (2.20 g, 5.09 mmol) in dry
THF (50 mL) over 13 min. After 1.5 h stirring at room temperature,
water (10 mL) was added slowly at 58C. The reaction mixture was fil-
tered through a pad of Celite by suction. The solvent of the combined fil-
trate was evaporated off. The residue was washed with aqueous solution
of 20% KOH (50 mL), extracted with diethyl ether, and the extract was
dried over anhydrous MgSO4. The removal of the solvent under reduced
pressure gave crude 6 (2.89 g) as a pale yellow oil. Introduction of a HCl
gas into a solution of 6 in THF (150 mL) gave 7 as a white powder. Fil-
tration by suction, washing with THF, and drying under reduced pressure
gave 7 (2.11 g, 92% yield for 2 steps). Thus obtained 7 was employed for
anion exchange reaction to 8 without further purification. m.p. 225–
Figure 4. Experimental (left) and simulated (right) partial VT-NMR
(270 MHz) spectra of protons Ha, and Hb of 1 in [D8]THF. The corre-
sponding temperatures and exchange rates are indicated.
Table 1. Rates of shuttling and the corresponding kinetic parameters of 1
and 2.
solvent
Tc [K] Dn [Hz]
DH°
DS°
k [sÀ1
]
1
2308C (decomp.); H NMR (270 MHz, D2O, 30 8C): d=7.54 (s, 4H), 7.48
A
]
[JKÀ1 molÀ1
]
(s, 8H), 4.68 (s, 4H), 4.32 (s, 4H), 4.31 ppm (s, 4H); IR (KBr): n˜ =3366
(br), 2992, 2940, 2788, 2716, 2592, 2364, 1557, 1457, 1417, 1217, 1021, 976,
848 cmÀ1; MS (FAB): m/z: 377.2 (MÀHClÀCl)+.
1
2
1
2
[D8]toluene
[D8]toluene >303
[D8]THF
[D8]THF
266
–
8.4
–
37Æ4
nd[a]
À65Æ17
860Æ270[b]
<19[b,c]
nd[a]
243
>323
36Æ2
À65Æ8
nd[a]
4500Æ300[d]
Synthesis of 8: Addition of a solution of NH4PF6 (6.01 g, 36.9 mmol) in
H2O (10 mL) into a solution of 7 (900 mg, 2.00 mmol) in H2O (20 mL) re-
sulted in a suspension. The precipitates were collected by suction filtra-
tion. Recrystalization from CH3CN/Et2O gave 8 (1.07 g, 80% yield) as
colorless crystals. m.p. 2608C (decomp.); 1H NMR (270 MHz, CD3CN,
308C): d=7.51 (s, 4H), 7.43 (s, 8H), 4.61 (s, 4H), 4.26 (s, 4H), 4.24 ppm
(s, 4H); 13C NMR (75.5 MHz, [D6]DMSO, 308C): d=129.69, 129.65,
129.5, 129.3, 127.5, 126.4, 62.5, 50.2, 49.9 ppm; IR (KBr): n˜ =3379 (br),
3249, 3227, 2994, 2945, 2789, 2714, 1582, 1416, 838, 758 cmÀ1; MS (FAB):
m/z: 522.9 (MÀPF6)+, 378.2 (MÀ2PF6)+; elemental analysis calcd (%)
for C24H30F12N2O2P2: C 43.12, H 4.52, N 4.19; found: C 42.91, H 4.53, N
4.12.
39
nd[a]
<86[d,c]
[a] Not determined. [b] at 303 K. [c] Maximum rates estimated from the
Gutowskiꢁs equation, assuming that the coalescence was observed at
each temperature. [d] at 323 K.
<2.3 sÀ1) by changing the size of the ring component from
30-crown-8 to 24-crown-8 type macrocycles.
Conclusion
Synthesis of rotaxane 1 from 8: A solution of crown ether 3 (70.0 mg,
93.0 mmol) in benzene (7 mL) was placed in a Pyrex tube and was well
degassed by bubbling dry argon. Then, the solution was irradiated by
using a 500 W high pressure mercury lamp for 10 min in an ice bath.
After irradiation, the solvent was evaporated off with cooling. The fresh-
ly prepared 4 in CH2Cl2/CH3CN (1:1) (400 mL) was mixed with secondary
We have synthesized 2-station [2]rotaxanes that have a di-
anthrylethane moiety in the ring unit of which size could be
A
changed reversibly and quantitatively by intramolecular
photochemical cycloaddition and thermal reversion. Sub-
stantial differences between the shuttling rates of the open-
and closed-form rotaxanes were observed, demonstrating
that the shuttling motion was controlled effectively by the
external stimuli. These results clearly demonstrate the po-
tential of the brake function of the present system for appli-
cations in the control of shuttling and other motions direct-
ed toward the construction of artificial molecular
ammonium hexafluorophosphate
8 (60.1 mg, 89.9 mmol) in CH3CN
(200 mL) and acid anhydride 10 (165mg, 194 mmol) in CH2Cl2 (200 mL) in
an ice-salt bath. Resulted precipitates were dissolved by the addition of
CH2Cl2 (100 mL) and CH3CN (100 mL). Then, 40 mol% of nBu3P (9 mL,
36 mmol) was added to the mixture under a N2 atmosphere. After stirring
for 5.5h in the ice-salt bath and 0.5h at room temperature, the solvent
was evaporated. Preparative HPLC separation of the products gave 1
(33.1 mg, 16% yield) as a yellow powder. MS (MALDI-TOF): m/z:
2061.7 (MÀPF6)+; 2715.9 ([3]rotaxane-HPF6-PF6).
Synthesis of 11: A solution of amine 5 (1.42 g, 3.28 mmol), di-tert-butyl
dicarbonate (Boc2O) (711 mg, 3.26 mmol), and N, N-dimethylaminopyri-
dine (DMAP) (18 mg, 16 mmol) in CH2Cl2 (25mL) was stirred at room
temperature for 2 h. After evaporation of the solvent, chromatography
on silica gel (eluent: hexane/ethyl acetate) gave 11 (818 mg, 47%) as a
pale yellow oil. 1H NMR (400 MHz, CDCl3, 308C): d=8.02–7.97 (m,
4H), 7.42 (d, J=8.5Hz, 2H), 7.30–7.17 (m, 6H), 4.44 (brs, 2H), 4.38 (brs,
2H), 3.91 (s, 3H), 3.90 (s, 3H), 3.86 (s, 2H), 3.79 (s, 2H), 1.48 ppm (s,
9H); 13C NMR (100 MHz, CDCl3, 308C): d=166.9, 166.8, 155.8, 145.6,
139.2, 136.4, 129.8, 129.7, 129.1, 128.8, 128.3, 128.1, 127.9, 127.6, 127.1,
80.4, 52.9, 52.8, 52.1, 52.0, 49.5, 28.5 ppm; IR (neat): n˜ =3334 (br), 2977,
2952, 2842, 1723, 1694, 1612, 1456, 1435, 1408, 1366, 1281, 1164, 1111,
machines.[15]
Experimental Section
General: H NMR (270, 300, or 400 MHz) and 13C NMR (67.5, 75.0, 100,
or 125.6 MHz) spectra were recorded by using a Varian Unity-Inova 500,
a JEOL JNM-AL-400, a Varian Mercury 300, or a JEOL JNM-GSX-270
spectrometer. The chemical shifts of 1H NMR and 13C NMR signals are
quoted relative to tetramethylsilane or residual solvent. IR spectra were
recorded as a KBr disk by using a JASCO FTIR-410 spectrometer. Mass
1
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3431

K. Hirose et al.
1019, 755 cmÀ1; MS (FAB): m/z: 532.9 (M+H)+; HRMS (FAB): m/z: for
C31H37N2O6: calcd: 533.2652; found: 533.2668.
yellow powder. m.p. 137–1408C; 1H NMR (270 MHz, CDCl3, 308C): d=
8.21 (d, J=1.0 Hz, 4H), 7.97 (d, J=8.6 Hz, 4H), 7.84 (brs, 2H), 7.63 (brs,
4H), 7.57 (d, J=8.9 Hz, 4H), 7.53–7.43 (m, 8H), 7.05–7.00 (m, 4H),
6.88–6.82 (m, 4H), 6.71–6.59 (m, 4H), 5.40 (s, 4H), 4.19–3.98 (m, 20H),
3.67 (br, 8H), 3.51 (br, 4H), 3.43 (br, 4H), 1.43 (heptet, J=7.3 Hz, 12H),
1.07 ppm (d, J=7.3 Hz, 72H); 13C NMR (100 MHz): d=167.0, 153.5,
148.8, 147.0, 146.5, 136.4, 134.1, 130.7, 129.1, 128.8, 128.1, 127.9, 124.5,
124.2, 124.1, 123.6, 121.9, 121.8, 112.4, 74.0, 71.1, 70.5, 70.4, 69.6, 68.4,
65.9, 31.6, 26.6, 18.6, 10.8 ppm; IR (KBr): n˜ =3067 (br), 2944, 2866, 1720,
1505, 1459, 1268, 1131, 844 cmÀ1; MS (FAB): m/z: 1963.2 (MÀ2PF6)+; el-
emental analysis calcd (%) for C122H166O12N2F12P2Si4: C 64.98, H 7.42, N
1.24; found: C 64.92, H 7.34, N 1.17.
Synthesis of 12: Into a suspension of LAH (200 mg, 5.27 mmol) in THF
(30 mL) was added a solution of 11 (710 mg, 5.09 mmol) in THF (10 mL)
dropwise during 3 min at À108C. After 30 min stirring at room tempera-
ture, water was added slowly. The solvent was evaporated off, and the
residue was extracted with diethyl ether. The extract was washed with
10% KOH aqueous solution and dried over anhydrous MgSO4. Evapora-
tion of the solvent gave 12 as a pale yellow oil (520 mg, 82%). Amine 12
was employed for anion exchange reaction to 13 without further purifica-
tion. 1H NMR (400 MHz, CDCl3, 308C): d=7.33 (s, 4H), 7.29–7.25(m,
4H), 7.15(brs, 4H), 4.67 (s, 2H), 4.64 (s, 2H), 4.39 (brs, 2H), 4.33 (brs,
2H), 3.80 (s, 2H), 3.77 (s, 2H), 1.49 ppm (s, 9H); 13C NMR (100 MHz,
CDCl3, 308C): d=155.9, 139.9, 139.8, 139.0, 138.6, 137.3, 136.8, 128.4,
128.3, 128.1, 127.6, 127.13, 127.09, 80.1, 65.1, 65.0, 52.8, 52.7, 49.3, 49.0,
Synthesis of the closed-form rotaxane 2: A solution of rotaxane
1
(6.5mg, 2.9 mmol) in [D8]THF (700 mL) was placed in a Pyrex NMR tube
and was well degassed by a bubbling of dry argon for 45min. Then, the
solution was irradiated using a 500 W high pressure mercury lamp for
10 min. After irradiation, the reaction mixture was immediately chilled to
08C to avoid thermal reversion reaction. 1H NMR (400 MHz, [D8]THF,
08C): d=8.29 (d, J=1.0 Hz, 2H), 8.25(d, J=1.0 Hz, 2H), 8.12 (brs, 2H),
7.87 (d, J=11 Hz, 2H), 7.78 (d, J=7.9 Hz, 4H), 7.74–7.68 (m, 8H), 7.52
(d, J=7.8 Hz, 2H), 7.38 (d, J=8.1 Hz, 2H), 7.05–6.94 (m, 6H), 6.87 (d,
J=6.8 Hz, 2H), 6.81–6.70 (m, 8H), 6.67–6.55 (m, 4H), 5.40, (s, 2H), 5.33
(s, 2H), 5.28 (br, 2H), 5.10 (br, 2H), 4.24–3.36 (m, 26H), 2.90 (s, 4H),
1.52–1.43 (m, 12H), 1.08 ppm (d, J=7.6 Hz, 72H).
28.5ppm; IR (neat): n˜ =3384 (br), 3054, 3009, 2977, 2928, 2867, 1682,
N
1457, 1411, 1365, 1245, 1163, 732 cmÀ1; MS (FAB): m/z: 477.0 (M+H)+;
HRMS (FAB): m/z: for C29H37N2O4: calcd: 477.2753; found: 477.2621.
Synthesis of 13: Into a solution of amine 12 (340 mg, 713 mmol) and
NH4PF6 (122 mg, 748 mmol) in CH3CN (8 mL), argon gas was vigorously
bubbled for 2 h. Then the solvent was removed by evaporation, and the
residue was extracted with acetone/CH2Cl2 (1:1). The extract was washed
with water and dried over anhydrous MgSO4. Evaporation of the solvent
gave 13 (420 mg, 95%) as a colorless foam. m.p. 78–81 8C; 1H NMR
(270 MHz, CD3CN, 308C): d=7.43 (s, 4H), 7.38 (d, J=8.2 Hz, 2H), 7.29–
7.25(m, 4H), 7.18 (d, J=7.9 Hz, 2H), 4.61 (d, J=5.4 Hz, 2H), 4.53 (s,
2H), 4.41 (brs, 4H), 4.21 (s, 2H), 4.20 (s, 2H), 3.28 (t, J=5.4 Hz, 1H),
1.43 ppm (s, 9H); 13C NMR (100 MHz, CD3CN): d=156.6, 144.7, 141.8,
138.0, 131.1, 131.0, 130.0, 129.9, 129.0, 128.5, 128.1, 127.9, 118.2, 80.8,
64.5, 64.1, 52.1, 52.0, 28.6 ppm; IR (KBr): n˜ =3587, 3357 (br), 3244, 2978,
2934, 2878, 2825, 1662, 1464, 1415, 1368, 1250, 1163, 848 cmÀ1; MS
(MALDI-TOF): m/z: 477.1 (MÀPF6)+; elemental analysis calcd (%) for
C29H37F6N2O4P: C 55.95, H 5.99, N 4.50; found: C 55.92, H 5.93, N 4.73.
Acknowledgements
This work was supported by the Izumi Science and Technology Founda-
tion and a Grant-in-Aid for Scientific Research from the Ministry of
Education, Culture, Sports, Science and Technology of Japan. K.I. ex-
presses his special thanks for the Global COE (Center of Excellence)
Program “Global Education and Research Center for Bio-Environmental
Chemistry” of Osaka University.
Synthesis of rotaxane 15: A solution of crown ether 3 (130 mg, 173 mmol)
in benzene (10 mL) was placed in a Pyrex tube and was well degassed by
bubbling dry argon. Then, the solution was irradiated using a 500 W high
pressure mercury lamp for 20 min in an ice bath. After irradiation, the
solvent was evaporated off with cooling. The freshly prepared 4 in
CH2Cl2 (300 mL) was mixed with secondary ammonium hexafluorophos-
phate 13 (90.1 mg, 145 mmol) in CH3CN (125 mL), and a solution of anhy-
dride 10 (270 mg, 319 mmol) in CH2Cl2 (250 mL) in an ice-salt bath. Then,
40 mol% of nBu3P (15 mL, 58 mmol) was added to the mixture under a
N2 atmosphere. After stirring for 6.5h in an ice-salt bath, the solvent was
evaporated. Subsequent preparative HPLC separation gave 15 (194 mg,
61% yield) as a yellow foam. m.p. 115–1188C; 1H NMR (270 MHz,
CDCl3, 308C): d=8.20 (s, 4H), 7.98 (br, 2H), 7.97 (d, J=9.1 Hz, 4H),
7.84 (brs, 1H), 7.82 (brs, 1H), 7.55 (d, J=8.7 Hz, 4H), 7.50–7.35 (m, 8H),
7.25–7.21 (m, 8H), 6.99 (br, 4H), 6.92 (br, 4H), 6.77–6.73 (m, 2H), 6.60–
6.57 (m, 2H), 5.38 (s, 2H), 5.34 (s, 2H), 4.38 (br, 8H), 4.14 (br, 4H),
4.05–4.04 (m, 4H), 3.95–3.94 (m, 4H), 3.77–3.59 (m, 16H), 1.47 (s, 9H),
1.47–1.37 (m, 12H), 1.07 (d, J=7.2 Hz, 36H), 1.05ppm (d, J=7.4 Hz,
36H); 13C NMR (125.6 MHz): d=167.2, 167.0, 155.9, 148.9, 147.2, 147.0,
146.5, 140.0, 138.3, 136.5, 136.4, 135.7, 134.3, 134.1, 130.7, 130.5, 129.8,
129.4, 129.3, 129.0, 128.2, 128.1, 12803, 128.02, 127.5, 124.6, 124.2, 123.6,
121.9, 121.8, 112.3, 80.4, 73.9, 71.2, 70.5, 70.2, 69.6, 68.2, 66.0, 65.6, 52.6,
49.1, 28.4, 26.5, 18.51, 18.49, 10.8, 10.7 ppm; IR (KBr): n˜ =3133, 3066,
2943, 2889, 2866, 1720, 1696, 1461, 1268, 1250, 1130, 882, 843 cmÀ1; MS
(MALDI-TOF): m/z: 2061.7 (MÀPF6)+; elemental analysis calcd (%) for
C127H173O14N2F6PSi4: C 69.05, H 7.89, N 1.27; found: C 68.96, H 7.99, N
1.37.
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68.4 mmol) in CH2Cl2 (4 mL) was added
a
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3432
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[12] To avoid the decomposition of 1, the solvent for the irradiation with
high pressure mercury lamp was limited. For this reaction [D8]THF
and [D8]toluene were chosen as suitable polar and less polar sol-
vents.
[13] The temperature for the VT-NMR measurement was limited be-
cause the cycloreversion of the closed-form rotaxane 2 started to
occur at higher temperatures during the measurement.
[14] Details of the saturation transfer experiment are given in Supporting
Information.
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A
Received: December 19, 2007
Published online: March 3, 2008
Chem. Eur. J. 2008, 14, 3427 – 3433
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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