End-capping of a pseudorotaxane via diels-alder reaction for the construction of C60-terminated [2]rotaxanes

Article abstract of DOI:10.1021/ol048433k

(Chemical Equation Presented) The Diels-Alder reaction of various dienophiles such as C₆₀ with a pseudorotaxane having a sultine moiety afforded corresponding [2]-rotaxanes in moderate yields. The introduction of a porphyrin moiety on the wheel

Full text of DOI:10.1021/ol048433k

ORGANIC
LETTERS
2004
Vol. 6, No. 22
3957-3960
End-Capping of a Pseudorotaxane via
Diels Alder Reaction for the
−
Construction of C60-Terminated
[2]Rotaxanes
Hisahiro Sasabe,† Nobuhiro Kihara,*,† Yoshio Furusho,‡ Kazuhiko Mizuno,†
Akiya Ogawa,† and Toshikazu Takata*,§
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture
UniVersity, Sakai, Osaka 599-8531, Japan, Yashima Super-structured Helix Project,
JST, Moriyama-ku, Nagoya 552-8555, Japan, and Department of Organic and
Polymeric Materials, Tokyo Institute of Technology, O-okayama,
Meguro-ku, Tokyo 152-8552, Japan
kihara@chem.osakafu-u.ac.jp; ttakata@polymer.titech.ac.jp
Received August 9, 2004
ABSTRACT
The Diels
rotaxanes in moderate yields. The introduction of a porphyrin moiety on the wheel component considerably enhanced the efficiency of the
end-capping reaction with C60
−Alder reaction of various dienophiles such as C60 with a pseudorotaxane having a sultine moiety afforded corresponding [2]-
.
Buckminsterfullerene (C60) has been given much attention
as a potential component for innovative electronic and
photonic molecular devices because of its outstanding
electro- and photoactivity. Since interlocked compounds such
as rotaxanes and catenanes are believed to be superior
scaffolds for molecular devices,1 C60-containing interlocked
compounds are of great interest.2 However, a general method
for introducing C60 into interlocked compounds is limited,
probably due to the poor solubility of C60-containing
interlocked compounds and limited variations of C60 reac-
tions.
Rotaxanes with a sulfolene moiety as a diene precursor
reacted with C60 upon heating to afford C60-containing
rotaxanes. The method was effective in modifying the wheel
component in the rotaxane. However, the application of the
method to the end-capping of the pseudorotaxane formed in
situ in equilibrium between the axle and the wheel compo-
nents was quite limited because the decomposition of the
sulfolene moiety required very high temperatures. Therefore,
we focused our attention on the sultine group that decom-
poses at rather low temperatures to afford diene and
(2) (a) Diederich, F.; Dietrich-Buchecker, C.; Nierengarten, J.-F.; Sau-
vage, J.-P. J. Chem. Soc., Chem. Commun. 1995, 781. (b) Ashton, P. R.;
Diederich, F.; Go´mez-Lo´pez, M.; Nierengarten, J.-F.; Preece, J. A.; Raymo,
F. M.; Stoddart, J. F. Angew. Chem., Int. Ed. Engl. 1997, 36, 1448. (c)
Watanabe, N.; Kihara, N.; Furusho, Y.; Takata, T.; Araki, Y.; Ito, O. Angew.
Chem., Int. Ed. 2003, 42, 681. (d) Ros, T. D.; Guldi, D. M.; Morales, A.
F.; Leigh, D. A.; Prato, M.; Turco, R. Org. Lett. 2003, 5, 689. (e) Nakamura,
Y.; Minami, S.; Iizuka, K.; Nishimura, J. Angew. Chem., Int. Ed. 2003, 42,
3158. (f) Li, K.; Schuster, D. I.; Guldi, D. M.; Herranz, M. AÄ .; Echegoyen,
L. J. Am. Chem. Soc. 2004, 126, 3388. (g) Schuster, D. I.; Li, K.; Guldi, D.
M.; Ramey, J. Org. Lett., 2004, 6, 1919. (h) Sandanayaka, A. S. D.; Sasabe,
H.; Araki, Y.; Furusho, Y.; Ito, O.; Takata, T. J. Phys. Chem. A 2004, 108,
5145.
We have demonstrated that the Diels-Alder reaction is
an efficient method of introducing C60 into rotaxanes.2c,h
† Osaka Prefecture University.
‡ Yashima Super-structured Helix Project, JST.
§ Tokyo Institute of Technology.
(1) (a) Molecular Catenanes and Rotaxanes and Knots; Sauvage, J.-P.,
Dietrich-Buchecker, C., Eds.; Wiley-VCH: Weinheim, 1999. (b) Molecular
DeVices and Machines; Balzani, V.; Venturi, A.; Credi, A.; Wiley-VCH:
Weinheim, 2002. (c) Balzani, V.; Credi, A.; Raymo, F. M.; Stoddart, J. F.
Angew. Chem., Int. Ed. 2000, 39, 3348. (d) Balzani, V. Photochem.
Photobiol. Sci. 2003, 2, 459.
10.1021/ol048433k CCC: $27.50
© 2004 American Chemical Society
Published on Web 10/01/2004

eventually chose the benzosultine group as a precursor of
diene that gives a highly reactive o-quinodimethane moiety.3
Here, we report a novel synthetic approach for preparing
[2]rotaxanes via Diels-Alder end-capping of a pseudo-
rotaxane having a sultine moiety on the axle terminus. The
effectiveness of this method is demonstrated by the introduc-
tion of C60 into the rotaxanes.
The combination of secondary ammonium salt and crown
ether such as dibenzo-24-crown-8 (DB24C8) has been
extensively studied as the easily accessible rotaxane system.4
Axle sec-ammonium salt 1a used in this work was prepared
as illustrated in Scheme 1. After protection of amino alcohol
Figure 1. Strategy toward the synthesis of C60-end-capped [2]-
rotaxane.
Scheme 1
ature, while at higher temperatures, the Cy group can intrude
into the DB24C8 cavity.8,9 Since the CPK model study
showed that the benzosultine moiety was as bulky as the Cy
group, we expected it to act as an end-cap for the DB24C8
wheel at ambient temperature. However, the addition of
DB24C8 to a suspension of 1.2 equiv of 1a in chloroform
at room-temperature resulted in the dissolution of 1a. The
complexation behavior between 1a and DB24C8 was dem-
onstrated by 1H NMR study in CDCl3/CD3CN, as shown in
Figure 2. When DB24C8 was added to a solution of 1a, a
new set of signals of the complex 1a‚DB24C8 immediately
appeared at room temperature.
Benzylic ammonium R-methylene proton signals of the
mixture were observed as complex multiplets at lower fields
than those of 1a, indicating the formation of pseudorotax-
ane.10 The benzosultine group behaved as a less bulky group
than the Cy group probably because of the flexible nature
of the SdO bond.
The pseudorotaxane structure was fixed by Diels-Alder
reaction with excess dimethyl fumarate in CHCl3 at 80 °C
in a sealed tube. The corresponding [2]rotaxane 7a was
obtained in 29% yield. Thus, a highly reactive o-quin-
odimethane intermediate was actually produced at 80 °C, at
which temperature the sulfolene group is thermally stable.
To estimate the effect of temperature, the stability constant
(Ka) of complex 1a‚DB24C8 was determined in CDCl3 by
1H NMR study.11 The apparent Ka was 189 ( 14 L mol-1 at
23 °C when [1a] ) 0.167 mol L-1. From the extrapolation
of the VT-NMR experiments, Ka at 80 °C was calculated as
38 ( 2 L mol-1, suggesting that ca. 75% of 1a formed the
complex with DB24C8. The results indicate that the ef-
ficiency of the Diels-Alder reaction of pseudorotaxane 1a‚
DB24C8 was merely ca. 40%, presumably because of the
steric bulkiness of the DB24C8 wheel of the pseudorotaxane.
Several rotaxanes were prepared by this method. [2]-
Rotaxane 7b was obtained in 28% yield when 1b was used
25 with a Boc group, acylation of 3 with 46 afforded ester 5.
The treatment of 5 with sodium hydroxymethanesulfinate
in the presence of a catalytic amount of tetrabutylammonium
bromide (TBAB) gave N-Boc sultine 6.3b The deprotection
of 6 with trifluoroacetic acid (TFA) proceeded smoothly. The
anion exchange with NH4PF6 afforded hexafluorophosphate
1a.7 1a was obtained as a mixture of the regioisomers of the
sultine moiety and was used without separation.
Stoddart and co-workers reported that the cyclohexyl (Cy)
group is larger than the cavity of DB24C8 at room temper-
(3) (a) Jarvis, W. F.; Hoey, M. D.; Finocchio, A. L.; Dittmer, D. C. J.
Org. Chem. 1988, 53, 5750. (b) Hoey, M. D.; Dittmer, D. C. J. Org. Chem.
1991, 56, 1947. (c) Segura, J. L.; Mart´ın, N. Chem. ReV. 1999, 99, 3199.
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Hubin, T. J.; Busch, D. H. Coord. Chem. ReV. 2000, 200-205, 5. (e) Takata,
T.; Kihara, N. ReV. Heteroat. Chem. 2000, 22, 197. (f) Kihara, N.; Takata,
T. J. Synth. Org. Chem. Jpn. 2001, 59, 206.
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N.; Stoddart, J. F.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1998,
120, 2297.
(9) Sohgawa, Y.-H.; Fujimori, H.; Shoji, J.; Furusho, Y.; Kihara, N.;
Takata, T. Chem. Lett. 2001, 774.
(10) (a) Ashton, P. R.; Campbell, P. J.; Chrystal, E. J. T.; Glink, P. T.;
Menzer, S.; Philp, D.; Spencer, N.; Stoddart, J. F.; Tasker, P. A.; Williams,
D. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 1865. (b) Cantrill, S. J.; Pease,
A. R.; Stoddart, J. F. J. Chem. Soc., Dalton Trans. 2000, 3715.
(11) Jones, J. W.; Gibson, H. W. J. Am. Chem. Soc. 2003, 125, 7001.
(7) Spectroscopic Data for 1a. Off-white solid. Mp: 93-97 °C. 1H
NMR (270 MHz, CD3CN): δ 7.92-7.83 (m, 2H), 7.46-7.37 (m, 4H),
7.32-7.28 (m, 1H), 6.99-6.97 (m, 3H), 5.29 (s, 2H), 5.16 (d, 1H, J )
14.0 Hz), 4.94 (d, 1H, J ) 14.0 Hz), 4.34-4.26 (m, 1H), 4.11 (s, 2H), 4.05
(s, 2H), 3.59 (d, 2H, J ) 15.8 Hz), 2.21 (s, 6H) ppm. FAB-MS (matrix;
mNBA): m/z ) 450.0 [M - PF6]+, 386.2 [M - PF6 - SO2]+. Anal. Calcd
for C26H28F6N1O4P1S1: C, 52.44; H, 4.74; N, 2.35; S, 5.38. Found: C,
52.66; H, 4.82; N, 2.27; S, 5.19.
3958
Org. Lett., Vol. 6, No. 22, 2004

Figure 2. Partial 1H NMR spectra (CDCl3/CD3CN (2/1)) of (a) axle 1a and (b) a 1.0:1.2 mixture of 1a and DB24C8. Assignment of peaks
as “prime” denotes the protons in the pseudorotaxane.
as an axle. The reaction of 1a with dimethyl acetylenedi-
carboxylate in the presence of DB24C8 afforded [2]rotaxane
7c in 28% yield. These results show that the Diels-Alder
reaction of pseudorotaxane having an o-quinodimethane
moiety constitutes one of the general methods that can be
used to prepare various [2]rotaxanes, although the yield is
not very high.
in ODCB to give the corresponding C60-containing [2]-
rotaxane 7d12 in 33% yield (Scheme 2).
Scheme 2
The Diels-Alder end-capping protocol was applied to the
preparation of C60-containing [2]rotaxane. 1,2-Dichloroben-
zene (ODCB) was used as a solvent in which C60 was rather
soluble. The reaction of 1a with 1.5 equiv of C60 in the
presence of 2.0 equiv of DB24C8 at 80 °C was carried out
The structure of 7d was fully characterized by FAB-MS,
NMR, and IR spectra as well as by elemental analyses. When
4.0 equiv of DB24C8 was used, the yield of 7d decreased
to 17%. Thus, excess DB24C8 enhanced the polarity of the
system to decrease the Ka of the complex.13 It is noteworthy
that 7d is very soluble in ordinary organic solvents such as
(12) Typical Procedure. A mixture of 1a (54 mg, 0.09 mmol), DB24C8
(81 mg, 0.18 mmol), and C60 (97 mg, 0.14 mmol) in dry ODCB (1.0 mL)
under an argon atmosphere in the dark was slowly heated to 80 °C and
stirred at 80 °C for 12 h. The reaction mixture was directly chromatographed
(SiO2, eluent: toluene to CHCl3/methanol (90/10)) to collect a dark brown
band (118 mg), a part of which (107 mg) was further purified by preparative
GPC (eluent: CHCl3) to give 7d as a dark brown solid (46 mg, 33%). Mp:
180-182 °C. 1H NMR (400 MHz, CDCl3, 323 K): δ 8.37 (s, 1H), 8.27 (d,
1H, J ) 6.3 Hz), 7.79 (d, 1H, J ) 7.8 Hz), 7.56 (br, 2H), 7.37-7.35 (m,
4H), 6.88-6.76 (m, 11H), 5.35 (s, 2H), 4.82-4.48 (m, 8H), 4.12-4.09
(m, 8H), 3.82-3.71 (m, 8H), 3.51-3.46 (m, 8H), 2.13 (s, 6H) ppm. IR
(NaCl): 2922, 1716, 1504, 1455, 1253, 1210, 1180, 1123, 1102, 1056, 953,
842, 749, 557, 526 cm-1. FAB-MS (matrix: mNBA): m/z ) 1554.5 [M -
PF6]+. Anal. Calcd for C110H60F6N1O10P1‚(CHCl3)0.5: C, 75.39; H, 3.46;
N, 0.80. Found: C, 75.06; H, 3.56; N, 0.87.
Figure 3. [2]Rotaxanes 7a-c and axle 1b.
(13) Takata, T.; Kawasaki, H.; Kihara, N.; Furusho, Y. Macromolecules
2001, 34, 5449.
Org. Lett., Vol. 6, No. 22, 2004
3959

acetone, acetonitrile, chloroform, and THF, whereas most
C60-derivatives are insoluble in these solvents.
Scheme 3
If the wheel component can attract the dienophile, the
rotaxane yield may increase by the cooperative effect
between the components. Since various C60 receptors have
been prepared using porphyrin as a C60-attractive group,14
a
novel crown ether 8 having zinc porphyrinate (ZnP) moiety
was prepared. The pseudorotaxane prepared from 1a and 8
was reacted with 2.0 equiv of C60 in ODCB. The corre-
sponding [2]rotaxane 9 was obtained in 46% yield (Scheme
3). The apparent Ka of 1a and 8 determined as described
above was 37 ( 3 L mol-1 in CDCl3 at 80 °C ([1a] ) 90
mM). Since pseudorotaxane 1a‚8 is as stable as la‚DB24C8,
the clear increase in the yield of 9 can be explained by the
attractive interaction between C60 and the ZnP moiety that
accelerated the Diels-Alder reaction to enhance the ef-
ficiency of the end-cap.
In summary, we have demonstrated that the benzosultine
group is a useful functional group for the end-capping of
pseudorotaxane with a highly reactive o-quinodimethane
generated at lower temperatures (80 °C) at the axle end. The
Diels-Alder reaction of various dienophiles such as C60 with
pseudorotaxane afforded corresponding [2]rotaxanes in mod-
erate yields. The introduction of a porphyrin moiety on the
wheel considerably enhanced the efficiency of the end-
capping reaction with C60.
Acknowledgment. This work was financially supported
from the Grant-in-Aid for Scientific Research from the
Ministry of Education, Science, Sports, Culture, and Tech-
nology.
(14) (a) Tashiro, K.; Aida, T.; Zheng, J.-Y.; Kinbara, K.; Saigo, K.;
Sakamoto, S.; Yamaguchi, K. J. Am. Chem. Soc. 1999, 121, 9477. (b) Zheng,
J.-Y.; Tashiro, K.; Hirabayashi, Y.; Kinbara, K.; Saigo, K.; Aida, T.;
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Burgess, M.; Boyd, P. D. W. J. Am. Chem. Soc. 2000, 122, 10704. (e)
Ayabe, M.; Ikeda, A.; Kubo, Y.; Takeuchi, M.; Shinkai, S. Angew. Chem.,
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Supporting Information Available: Spectroscopic data
for compounds 7a-c and 9. This material is available free
of charge via the Internet at http://pubs.acs.org.
OL048433K
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Org. Lett., Vol. 6, No. 22, 2004