Synthesis of [1]rotaxane via covalent bond formation and its unique fluorescent response by energy transfer in the presence of lithium ion

Article abstract of DOI:10.1021/ja046929r

Although there have been a lot of reports on the synthesis and properties of [n]rotaxanes (mainly n = 2), only a few reports on the synthesis of [1]rotaxane has been published by Voegtle's group and others (see ref 5). Generally speaking, [1]rotaxane migh

Full text of DOI:10.1021/ja046929r

Published on Web 09/28/2004
Synthesis of [1]Rotaxane via Covalent Bond Formation and Its Unique
Fluorescent Response by Energy Transfer in the Presence of Lithium Ion
Kazuhisa Hiratani,*,† Maiko Kaneyama,† Yoshinobu Nagawa,‡ Emiko Koyama,‡ and
Masatoshi Kanesato‡
Department of Applied Chemistry, Utsunomiya UniVersity, 7-1-2 Youtou, Utsunomiya 321-8585, Japan,
and Nanoarchitectonics Research Center, National Institute of AdVanced Industrial Science and Technology,
Tsukuba Central 4, 1-1-1 Higashi, Tsukuba 305-8562, Japan
Received May 25, 2004; E-mail: hiratani@cc.utsunomiya-u.ac.jp
Scheme 1. Synthetic Strategy for [1]Rotaxane via Covalent Bond
Formation
Many kinds of supramolecular systems such as rotaxanes and
catenanes have been developed mainly by utilizing weak intermo-
lecular interactions such as hydrogen bonding,1 charge-transfer
phenomena,2 and intermolecular coordination with metal ions.3
Much attention has been paid to the development of these systems
from the viewpoint of topological interest and nanotechnology using
supramolecular systems.4 However, there are only a few reports
so far on the synthesis and properties of stark [1]rotaxanes.5
Recently, we reported a new synthetic method for [2]rotaxanes
via covalent bond formation.6 They can be obtained in high yields
by three steps starting from macrocyclic polyethers, i.e., tandem
Claisen rearrangement, diesterification, and aminolysis. To apply
covalent bond formation to the synthesis of a [1]rotaxane, we
designed a macrocyclic compound (1) having the phenylene part
substituted with an aldehyde group. Scheme 1 shows our strategy
for the synthesis of our [1]rotaxane. The most important step might
be the intramolecular bridging between the aldehyde part and one
of the phenolic hydroxy groups of 2.
According to the process, macrocyclic polyether (1) was prepared
from the reaction of the bis(naphthol) derivative and the diiodide
of oligoethylene glycol using a high-dilution method. The next step
was a tandem Claisen rearrangement.7 The rearranged product (2)
was obtained in excellent yield. The N-benzylaminomethyl deriva-
tive (3) was obtained by the reaction of 2 with benzylamine
followed by reduction of the imine with sodium boron hydride.
We prepared di(acid chloride)s (4: R ) (CH2)10) of dodecanoic
acid. In the presence of potassium tert-butyloxide, the equimolar
reaction of 3 with 4 gave bicyclic compound 5 (mixture of two
isomers) in 24% yield. Then, without separation of isomers, 5
was used in aminolysis with 9-(3-(aminopropyl)aminocarbonyl)-
anthracene (6), which was prepared by treating 9-chlorocarbonyl-
anthracene with 1,3-propylenediamine. Treatment of mixed isomers
of 5 with 6 in DMF at room temperature gave [1]rotaxane (7) and
a macrocycle with a long tail (8).8 These were separated by
preparative gel permeation chromatography (GPC). Compound 8
was prepared by another method to confirm the structure, that is,
the reaction of 3 with acid chloride having an anthryl end group
(9), which was prepared in the reaction of di(acid chloride) 4 with
6.9
Compounds 7 and 8 were confirmed to have the same parent
peak by ESI mass spectroscopy but also exhibited quite different
1H NMR spectra as shown in Figure 1. The NMR spectrum of 8
was the same as that of 8 prepared by the other reaction of 3 with
9 as described above. In the NMR of 7, some protons of the
oligomethylene moiety between anthryl and benzylamide moieties
Figure 1. 1H NMR (500 MHz) spectra of 7 and 8 in CDCl3 at 25 °C.
* Fax: +81-28-689-6146. Tel: +81-28-689-6146.
† Utsunomiya University.
of the macrocycle were observed to shift upfield compared with
that of 8. This means that some part of the oligomethylene is close
‡ National Institute of Advanced Industrial Science and Technology.
9
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J. AM. CHEM. SOC. 2004, 126, 13568-13569
10.1021/ja046929r CCC: $27.50 © 2004 American Chemical Society

C O M M U N I C A T I O N S
Scheme 2. Behavior of Energy Transfer of [1]Rotaxane Due to
Schematic Host-Guest Interaction
Figure 2. Fluorescence spectra of 7 (5.0 × 10-6 M) in CH2Cl2/CH3CN
(9/1); excitation wavelength ) 285 nm, which originally excited naphthalene
ring (see ref 10).
to the aromatic rings and affected by the ring current. On the other
hand, the NMR spectrum of 8 shows usual chemical shifts compared
to those of 3 as the macrocycle part and 9 as the long chain part.
In addition, the GPC peak due to compound 8 was observed to
flow faster than that of compound 7, although both parent peaks in
the ESI mass are the same. This means that the molecular volume
of 7 is apparently smaller than that of 8 in GPC. From these results
it is presumed that 7 is a macrocycle through which a long chain
threads, whereas 8 is a macrocycle having a long and unthreaded
molecular chain as shown in Scheme 1. In addition, thermal
isomerization of 7 to form 8 did not occur. Heating 7 in dimethyl
sulfoxide at 160 °C for 0.5 h and at 100 °C for 5 h gave no new
product, and both NMR spectra were the same as that for starting
compound 7. This means that [1]rotaxane 7 is not isomerized to 8
under those conditions.
increase only in the presence of lithium ions, which might make it
a candidate for a lithium ion-sensing agent.
Acknowledgment. K.H. would like to thank the Ministry of
Education, Culture, Sports, Science and Technology (MEST) for
partial support through a Grant-in-Aid for Scientific Research (No.
14540526).
Supporting Information Available: Electronic supplementary
information (ESI): 1H and 13C NMR spectra and ESI-mass data for
[1]rotaxane 7, crownophane 8, and the complex of 7 with lithium ion
(PDF). This material is available free of charge via the Internet at http://
pubs.acs.org.
[1]Rotaxane (7) might have a three-dimensionally small cavity
constructed by both the ring and the chain connected with the
macrocycle. The inside of the cavity, which is surrounded by several
ether-oxygens and amide groups, is expected to catch a small cation
among electron-deficient species such as metal ions and onium ions
as shown in Scheme 2.
References
(1) Vo¨gtle, F.; Meier, S.; Hoss, R. Angew. Chem., Int. Ed. Engl. 1992, 31,
1619. Hunter, C. A. J. Am. Chem. Soc. 1992, 114, 5303. Johnston, A. G.;
Leigh, D. A.; R. J. Pritchard, R. J.; Deegan, M. D. Angew. Chem., Int.
Ed. Engl. 1995, 34, 1209.
(2) Ortholand, J. Y.; Slawin, A. M. Z.; Spensor, N.; Stoddart, J. F.; Williams,
D. J. Angew. Chem., Int. Ed. Engl. 1989, 28, 5091.
Alkali metal ions as guest species were investigated for this
experiment. Among them, only lithium ion can change the chemical
shifts of 7 in the NMR spectrum in CDCl3. On the other hand,
compound 8 has no response (no change of the spectrum) when
adding alkali metal ions. This means that [1]rotaxane (7) can work
as a host molecule toward lithium guest ions. The fluorescence
spectrum was measured in CH2Cl2 + CH3CN (9:1) in both the
presence and absence of alkali metal ions. The energy transfer from
naphthalene to anthryl groups was observed in both cases when
irradiated at 285 nm in CHCl3;10 that is, the emittance from 400 to
500 nm based on the anthryl group was observed. Figure 2 shows
the fluorescence spectrum of 7 with and without alkali ion. Only
lithium ion drastically enhanced the fluorescence intensity, while
the other cations did not change the spectrum. The association
constant was estimated by changing the concentration ratio of the
cation toward [1]rotaxane (7). The association constant (Ka) of 7
toward lithium ion is 8.4 ( 0.3 × 103, with a ratio of complexation
of 1:1. Surprisingly, there is no detectable value of Ka for any other
cations.
The three-dimensionally small cavity formed seems to recognize
lithium ion with the smallest ion radius among alkali metal ions.
The NMR study of the complex of 7 with lithium ions supports
the interaction of lithium ion with the polyether and amide-carbonyl
oxygen atoms. Complexation with lithium ion is presumed to result
in the uptake of a lithium ion into the cavity with high selectivity.
The uptake might restrain the movement of the threaded chain
moiety and the anthryl group and approximate the distance between
naphthyl and anthryl groups eventually to suppress the quenching
phenomenon.
(3) Dietrich-Buchecker, C.; Sauvage, J.-P.; Tetrahedron Lett. 1983, 24, 5091.
(4) Molecular Catenanes, Rotaxanes and Knots, A Journey Through the World
of Molecular Topology; Sauvage, J.-P., Dietrich-Buchecker, C., Eds.;
Wiley-VCH: Weinheim, 1999.
(5) Rotaxanes: (a) Jaeger, R.; Haendel, F.; Harren, J.; Rissanen, K.; Vo¨gtle,
F. Liebigs Ann. 1996, 1201. (b) Ruter, C.; Wienand, W.; Schmuck, C.;
Vo¨gtle, F. Chem. Eur. J. 2001, 7, 1728. (c) Fukuhara, G.; Fujimoto, T.;
Kaneda, T. Chem. Lett. 2003, 32, 536. Pseudo[1]rotaxanes: (d) Ashton,
P. R.; Ballardini, R.; Balzani, V.; Boyd, S. E.; Credi, A.; Gandolfi, M.
T.; Gomez-Lopez, M.; Iqbal, S.; Philp, D.; Preece, J. A.; Prodi, L.; Ricketts,
H. G.; Stoddart, J. F.; Tolley, M. S.; Venturi, M.; White, A. J. P.; Williams,
D. J. Chem. Eur. J. 1997, 3, 152. (e) Chen, Z.; Bradshaw, J. S.; Habata,
Y.; Lee, M. L. J. Heterocycl. Chem. 1997, 34, 983.
(6) Hiratani, K.; Suga, J.; Nagawa, Y.; Houjou, H.; Tokuhisa, H.; Numata,
M.; Watanabe, K. Tetrahedron Lett. 2002, 43, 5747.
(7) (a) Hiratani, K.; Kasuga, K.; Goto, M.; Uzawa, H. J. Am. Chem. Soc.
1997, 119, 12677. (b) Hiratani, K.; Uzawa, H.; Kasuga, K.; Kambayashi,
H. Tetrahedron Lett. 1997, 38, 8993.
(8) Synthesis of 7 and 8: Compound 5 (80 mg, 0.086 mmol) was dissolved
in 10 mL of anhydrous DMF, and then amine 6 (95 mg, 0.34 mmol) was
added. The solution was stirred at room temperature under an argon
atmosphere for 5 days. After removal of DMF under vacuum, the residue
was submitted to gel permeation chromatography. Mainly, three peaks in
GPC were collected. The first elute (21 mg; 20% yield) and the second
elute (45 mg; 45% yield) have the same molecular weight (found: 1214.7
(+H+); calcd: 1213.60). The third one was excess amine 6. The NMR,
IR, and ESI-mass spectra of the first and second elutes by GPC were
measured.
(9) NMR spectra of the first elute (8) and the second elute (7) are shown in
Figure 1.
(10) Synthesis of 8 by another method: To diacid dichloride 4 (47 mg, 0.18
mmol) in 80 mL of anhydrous THF were added compound 3 (0.13 g,
0.18 mmol) and triethylamine (18 mg, 0.18 mmol). The solution was
stirred at ice-water temperature for 2 h. Then, to the solution were added
amine 6 (73 mg, 0.26 mmol) and triethylamine (18 mg, 0.18 mmol) at
room temperature for 2 h. After removal of THF, the residue was submitted
to column chromatography with chloroform and then GPC for isolation
of 8 (30 mg; 14% yield). The 1H NMR spectrum of the product was
identified to the second elute described above (see ref 8).
(11) When irradiated at 285 nm, the maximum of the wavelength in the
fluorescence spectrum should be originally observed at 342 nm on the
basis of the naphthalene ring; see: Ishow, E.; Credi, A.; Balzani, V.;
Spadola, F.; Mandolini, L. Chem. Eur. J. 1999, 5, 984.
Thus, we synthesized novel [1]rotaxanes via covalent bond
formation in three steps starting with crownophane 2 having two
hydroxy groups. Compound 7 exhibited a fluorescence intensity
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