1H NMR analysis of porphyrin-stoppered rotaxanes: Effect of the porphyrin substituents on the macrocycle

Article abstract of DOI:10.1039/b403707c

Six kinds of porphyrin-stoppered rotaxanes were prepared by the combination of two threads (relatively longer and shorter) and three porphyrin rhodium chlorides having different substituents. The chemical shift changes in ¹H NMR spectra, due to the anisotropic shielding effects by the aromatic rings, enabled us to estimate the molecular structure. In the cases of the rotaxanes with relatively shorter thread, the conformation of the macrocycle proved to be affected by the substituents in the terminal porphyrin. This result suggests a mechanical interaction between the macrocycle and terminal porphyrin. This result will lead to novel designing of the molecular devices that can regulate the rotational motion of the macrocycle by the terminal porphyrin or transmit the rotational motion from the macrocycle to the terminal porphyrin.

Full text of DOI:10.1039/b403707c

View Article Online / Journal Homepage / Table of Contents for this issue
P A P E R
1H NMR analysis of porphyrin-stoppered rotaxanes: effect of the
porphyrin substituents on the macrocycley
Taichi Ikeda, Masumi Asakawa and Toshimi Shimizu*
Nanoarchitectonics Research Center, National Institute of Advanced Industrial Science and
Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
E-mail: tshmz-shimizu@aist.go.jp; Fax: þ81 298 61 4545; Tel: þ81 298 61 4544
Received (in Durham, UK) 10th March 2004, Accepted 28th April 2004
First published as an Advance Article on the web 15th June 2004
Six kinds of porphyrin-stoppered rotaxanes were prepared by the combination of two threads (relatively longer
and shorter) and three porphyrin rhodium chlorides having different substituents. The chemical shift changes in
1H NMR spectra, due to the anisotropic shielding effects by the aromatic rings, enabled us to estimate the
molecular structure. In the cases of the rotaxanes with relatively shorter thread, the conformation of the
macrocycle proved to be affected by the substituents in the terminal porphyrin. This result suggests a
mechanical interaction between the macrocycle and terminal porphyrin. This result will lead to novel
designing of the molecular devices that can regulate the rotational motion of the macrocycle by the terminal
porphyrin or transmit the rotational motion from the macrocycle to the terminal porphyrin.
preparations of porphyrin rhodium chlorides,6,8 two threads
Introduction
[relatively long (L) and short (S)]5,6 and porphyrin-stoppered
rotaxane5,6 are described in the references. All chemical
reagents and solvents were commercially available and used as
received. 1H and 13C NMR spectra were recorded on a Bruker
Interlocked molecules such as the rotaxanes and catenanes
have attracted increasing attention as new functional materials
having mechanical motion (translational or rotational motion)
between the components.1–4 The mechanical motions are
applicable to the molecular shuttles,1 molecular switches,2
molecular motors3 and molecular muscles.4 Recently, it has
been possible to prepare interlocked molecules through ther-
modynamically stable noncovalent bonds.5–7 Using this
approach, one can easily obtain interlocked molecules in high
yields. We have reported porphyrin-stoppered rotaxanes using
the axial coordination bond of porphyrin rhodium(III) chloride
and the host–guest system between the secondary ammonium
cation group and dibenzo-24-crown-8 (DB24C8).5,6 In the case
of 5,10,15,20-tetraphenylporphyrin (TPP) stoppered rotaxane,
we were able to analyze the molecular structure using X-ray
crystallography.6 As for other rotaxanes capped with
2,3,7,8,12,13,17,18-octaethylporphyrin (OEP) and 5,10,15,20-
tetra[3,5-di(tert-butyl)phenyl]porphyrin (TBPP) rhodium
chlorides, no single crystal was obtainable. Therefore, we
had no direct information on the molecular structure of these
porphyrin-stoppered rotaxanes using X-ray crystallography.
However, the chemical shift changes in 1H NMR spectra,
due to the anisotropic shielding effect by the porphyrin6,8
and the catechol rings of DB24C8, enabled us to estimate
the molecular structure. In this study, we analyzed six kinds
of porphyrin-stoppered rotaxanes using 1H NMR. On the
basis of this analysis, we discuss the effect of the porphyrin
substituents on the conformation of the macrocycle in
the rotaxane.
AVANCE 400 spectrometer (400 and 100 MHz for 1H and 13
C
NMR, respectively) with use of residual solvent as the internal
standard. 1H NMR and 13C NMR spectra were assigned using
2D COSY, ROESY, HMQC and HMBC. All NMR measure-
ments were conducted at 293 K.
Product characterization data
1
.
Rotaxane Rx(OEP L). Orange solid (Yield: 80%). H NMR
(400 MHz, CDCl3): d 0.12 (d, J ¼ 7.0 Hz, 2H, C11H), 1.19 (s,
3H, CaH3), 1.99 (t, 12H, CH3), 3.07 (m, 8H, CgH2), 3.45 (m,
8H, CbH2), 3.82 (m, 8H, CaH2), 4.11 (q, 8H, CH2), 4.21 (br,
2H, CbH2), 4.42 (br, 2H, CcH2), 5.50 (d, J ¼ 7.0 Hz, 2H,
C10H), 6.52 (m, 4H, C13H), 6.70 (m, 4H, C12H), 6.92 (d,
J ¼ 8.4 Hz, 2H, C3H), 7.04 (d, J ¼ 8.4 Hz, 2H, C6H), 7.06
(d, J ¼ 8.4 Hz, 2H, C2H), 7.37 (br, 2H, NH2), 7.41 (d,
J ¼ 8.4 Hz, 2H, C7H), 10.22 (s, 4H, CmesoH), 10.40 (s, 1H,
CONH). 13C NMR (100 MHz, CDCl3): d 19.0 (CH3), 20.5
(CH2), 31.6 (CaH3), 35.0 (C–CaH3), 52.3 (Cc), 52.6 (Cb), 68.5
(Ca), 70.3 (Cb), 70.7 (Cg), 98.2 (meso), 112.6 (C10), 113.1
(C13), 122.2 (C12), 125.8 (C2), 128.7 (C4), 128.8 (C7), 129.1
(C3, C6), 135.0 (C8), 135.2 (C5), 140.1 (a-pyrrole), 142.8 (b-pyr-
role), 145.3 (C9), 146.2 (C11), 147.6 (C14), 152.8 (C1), 166.5
=
(C O). Anal. Calcd for C86H104ClF3N7O11RhꢀH2O: C 63.56,
H 6.57, N 6.03; found: C 63.84, H 6.45, N 5.95%.
1
Rotaxane Rx(OEPꢀS). Orange solid (Yield: 75%). H NMR
(400 MHz, CDCl3): d 0.19 (d, J ¼ 6.8 Hz, 2H, C7H), 1.14 (s,
9H, CaH3), 1.92–2.02 (m, 12H, CH3), 2.21 (m, 4H, CgH2),
2.80 (overlapping, 8H, CgH2 and CbH2), 3.20 (br, 2H, CcH2),
3.24 (overlapping, 8H, CbH2 and CaH2), 3.60 (m, 4H, CaH2),
3.74 (br, 2H, CbH2), 4.09–4.18 (m, 8H, CH2), 4.80 (d,
J ¼ 6.8 Hz, 2H, C6H), 6.22 (m, 4H, C13H), 6.52 (br, 2H,
NH2), 6.68 (d, J ¼ 8.4 Hz, 2H, C3H), 6.71 (m, 4H, C12H),
6.96 (d, J ¼ 8.4 Hz, 2H, C2H), 10.26 (s, 4H, CmesoH). 13C
NMR (100 MHz, CDCl3): d 19.2 (CH3), 20.5 (CH2), 31.5
Experimental
General
OEP and TPP were purchased from Tokyo Chemical Industry
Co. TBPP was synthesized according to the literature.9 The
y Electronic supplementary information (ESI) available: chemical shift
data. See http://www.rsc.org/suppdata/nj/b4/b403707c/
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
870
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 8 7 0 – 8 7 3

View Article Online
(Ca), 35.0 (C–CaH3), 48.8 (Cc), 51.9 (Cb), 68.2 (Ca), 69.8 (Cb),
70.2 (Cg), 98.3 (meso), 112.9 (C13), 122.2 (C12), 122.5 (C6),
125.7 (C2), 128.2 (C4), 129.1 (C3), 140.0 (C5), 140.2 (a-pyrrole),
143.1 (b-pyrrole), 146.0 (C7), 147.0 (C14), 152.8 (C1). Anal.
Calcd for C79H99ClF3N6O10Rh: C 63.77, H 6.71, N 5.65;
found: C 64.04, H 6.89, N 5.34%.
difference in the chemical shifts between pseudo-Rx(L) and
Rx(XꢀY) [Dd ¼ dpseudo-Rx(L) ꢁ dRx(XꢀY)], which is a good probe
to analyze the conformational changes in the rotaxane.
First, we focused on the protons on the macrocycle. Fig. 2
shows the Dd values for each proton on the macrocycle (12,
13, a, b and g). In the cases of the rotaxanes with relatively
shorter thread [Rx(XꢀS)], two methylene protons on the same
carbon have different chemical shifts, because the intensity of
the shielding effect by the terminal porphyrin is significantly
different at the near and far side methylene protons (Fig. 3).6
Therefore, these protons were separately plotted in Fig. 2
(* and **).
In the cases of the rotaxanes with relatively longer thread
[Rx(XꢀL)], the Dd values for Rx(OEPꢀL) were larger than those
for the other two rotaxanes [Rx(TPPꢀL), Rx(TBPPꢀL)] because
four phenyl groups of TPP, which stand perpendicularly with
respect to the porphyrin core,6,10 weaken the shielding effect by
the porphyrin core. The Dd values for Rx(OEPꢀL) monotoni-
cally increase from the protons 12 to g, because the shielding
intensity by the terminal porphyrin increases from 12 to g.
The shielding intensity is the strongest at the porphyrin center,
and it decreases toward the periphery.8 As shown in Fig. 4,
the protons 12, 13, a, b and g gradually draw closer to
the porphyrin center. The Dd values for two rotaxanes
Rx(TPPꢀL) and Rx(TBPPꢀL) were almost the same, suggesting
that the conformations of the macrocycles in Rx(TPPꢀL) and
Rx(TBPPꢀL) should be almost the same. In rotaxanes
Rx(XꢀL), the affinity site of the thread and macrocycle, which
is the secondary ammonium cation group,11 is far from the
terminal porphyrin. Thus, it is considered that the substituents
of the porphyrins [ethyl-, phenyl- and 3,5-di(t-butyl)phenyl-]
have no effect on the conformation of the macrocycle.
Rotaxane Rx(TBPPꢀS). Purple solid (Yield: 25%). 1H NMR
(400 MHz, CDCl3): d 1.04 (d, J ¼ 7.0 Hz, 2H, C7H), 1.14 (s,
3H, CaH3), 1.51 (s, 9H, t-Bu), 2.51 (br, 4H, CgH2), 2.85 (br,
4H, CgH2), 2.97 (m, 4H, CbH2), 3.31 (m, 4H, CbH2), 3.31
(overlapping, 2H, CcH2), 3.36 (m, 4H, CaH2), 3.70 (m, 4H,
CaH2), 4.04 (s, 2H, CbH2), 5.07 (d, J ¼ 7.0 Hz, 2H, C6H),
6.19 (m, 4H, C13H), 6.67 (m, 4H, C12H), 6.90 (d, J ¼ 8.4
Hz, 2H, C3H), 7.00 (d, J ¼ 8.4 Hz, 2H, C2H), 7.80 (s, 4H,
C15H), 8.05 (s, 4H, C17H), 8.14 (s, 4H, C17H), 9.03 (s, 8H,
b-pyrrole). 13C NMR (100 MHz, CDCl3): d 31.6 (Ca), 32.2
(t-Bu), 35.0 (C–Ca ), 35.4 (t-Bu), 35.6 (t-Bu), 49.0 (Cc), 52.2
3
(Cb), 68.2 (Ca), 69.9 (Cb), 70.2 (Cg), 113.1 (C13), 121.5 (C15),
122.2 (C12), 122.8 (C6), 122.8 (meso), 125.7 (C2), 128.6 (C4),
129.4 (C17), 129.6 (C3), 131.5 (C17), 133.0 (b-pyrrole), 141.2
(C5), 141.6 (C18), 143.0 (a-pyrrole), 146.1 (C7), 147.0 (C14),
148.8 (C16), 149.7 (C16), 152.7 (C1). Anal. Calcd for
C119H147ClF3N6O10Rhꢀ2H2O: calcd C 69.62, H 7.41, N 4.09;
found: C 69.42, H 7.44, N 4.08%.
Results and discussion
Six kinds of porphyrin-stoppered rotaxanes were prepared by
the combination of two threads [relatively longer (L) and
shorter (S)] and three porphyrins (OEP, TPP and TBPP).
DB24C8 was used as the macrocycle. Rx(OEPꢀS) represents
OEP-stoppered rotaxane consisting of the macrocycle
DB24C8 and thread S (Fig. 1). All of the rotaxanes excluding
Rx(TBPPꢀS) were obtainable in high yields (70%–80%).
On the other hand, the results for the rotaxanes with rela-
tively shorter thread [Rx(XꢀS)] were complicated. The Dd
values for the rotaxane Rx(OEPꢀS) monotonically increase from
the protons 12 to g (average Dd value of near and far sides
methylene protons), suggesting that the conformations of the
macrocycles in Rx(OEPꢀL) and Rx(OEPꢀS) should be almost
the same. Interestingly, the plots of Rx(TPPꢀS) and
Rx(TBPPꢀS) were completely different from each other. In par-
ticular, the Dd values for the catechol protons in Rx(TBPPꢀS)
In the previous study,6 we confirmed that the pseudo-rotax-
ane with relatively longer thread [pseudo-Rx(L): inclusion
complex without porphyrin stopper] was a slow exchange
system on the NMR timescale, indicating that the mixture
containing the thread and macrocycle afforded two sets of
peaks assignable to free and inclusion complex species in the
1H NMR spectrum. From the comparison of 1H NMR spectra
for the rotaxane and pseudo-Rx(L), we confirmed the shielding
effect by the terminal porphyrin, that is, all of the peaks
assigned to the macrocycle and thread shifted up-field after
introduction of the terminal porphyrin. We calculated the
Fig. 2 Chemical shift change for each proton on the macrocycle. The
Dd values were calculated from the chemical shift difference between
pseudo-rotaxane
and
porphyrin-stoppered
rotaxane
(Dd ¼
dpseudo-Rx(L) ꢁ dRx(XꢀY)). * and ** are Dd values for near and far side
methylene protons with respect to the terminal porphyrin, respectively.
Open triangle (N): Rx(OEPꢀS), open square (K): Rx(TPPꢀS), open cir-
cle (X): Rx(TBPPꢀS), closed triangle (/): Rx(OEPꢀL), closed square
(L): Rx(TPPꢀL), closed circle (S): Rx(TBPPꢀL). The plots of
Rx(TPPꢀL) and Rx(TBPPꢀL) are overlapped.
Fig. 1 Chemical structure of the components of porphyrin-stoppered
rotaxanes and numbering for 1H NMR assignment.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 8 7 0 – 8 7 3
871

View Article Online
Fig. 3 Schematic illustration of the methylene protons on the macro-
cycle (DB24C8). In the rotaxane with relatively shorter thread, two
methylene protons on the same carbon located at opposite sides are
assigned to different peaks in 1H NMR spectrum.
Fig. 5 Chemical shift change for each proton on the thread. The Dd
were larger than those in Rx(TPPꢀS), indicating less contribu-
tion of the deshielding effect by four phenyl groups of TBPP.
The macrocycle has fast rotational conformation exchange
between the conformations (A) and (B) (Fig. 4). Since the
exchange rate between these two conformations is fast on the
NMR timescale, the weight-averaged chemical shifts attributa-
ble to two conformations are observed in the 1H NMR spectra.
X-Ray crystallographic data for Rx(TPPꢀS) suggest that
Rx(TPPꢀS) prefer conformation (B) due to aromatic CH–p
interaction between the catechol rings and phenyl groups of
TPP.6 In the case of Rx(TBPPꢀS), we can easily assume that
bulky t-butyl groups of TBPP sterically hinder conformation
(B). As a consequence, the rotaxane Rx(TBPPꢀS) is considered
to prefer conformation (A). In conformation (A), the catechol
protons and the methylene protons g are under the shielding
effect of the porphyrin core, and the methylene protons a
and b are under the deshielding effect of four phenyl groups
[Fig. 4 (A)]. This situation is in good agreement with the
results, as shown in Fig. 2. Namely, the up-field shift of the
catechol protons and methylene protons g for Rx(TBPPꢀS)
was larger than that for Rx(TPPꢀS), indicating that these
protons are under the shielding effect. It should be noted that
the near side methylene protons to the terminal porphyrin a
and g do not follow our interpretation. In comparison with
the far side methylene protons, the near side methylene pro-
tons are found to be more sensitive to the change in distance
from the terminal porphyrin.6 Thus, the effect of the conforma-
tion exchange between (A) and (B) may be easily compensated
by a small distance change from the terminal porphyrin.
Next, we focused on the protons on the thread. In the case
of the thread, we especially focused on the protons around
the secondary ammonium cation group (3, b, c and 6) because
these protons are sensitive to the conformational changes of
DB24C8 due to the (de)shielding effect of the catechol rings.
In the Dd plot for the rotaxanes with relatively longer thread
[Rx(XꢀL)], the result was almost the same as that discussed
above (Fig. 5). The Dd values for Rx(OEPꢀL) were larger than
values were calculated from the chemical shift difference bet-
ween pseudo-rotaxane and porphyrin-stoppered rotaxane (Dd ¼
dpseudo-Rx(L) ꢁ dRx(XꢀY)). Open triangle (N): Rx(OEPꢀS), open square
(K): Rx(TPPꢀS), open circle (X): Rx(TBPPꢀS), closed triangle (/):
Rx(OEPꢀL), closed square (L): Rx(TPPꢀL), closed circle (S):
Rx(TBPPꢀL). The plots of Rx(TPPꢀL) and Rx(TBPPꢀL) are overlapped.
those for the other two rotaxanes and the Dd values for
Rx(TPPꢀL) and Rx(TBPPꢀL) were almost the same.
In the case of the rotaxanes with relatively shorter thread
[Rx(XꢀS)], we found an interesting result in the comparison
of Rx(TPPꢀS) and Rx(TBPPꢀS). At the t-butyl side (3
and b), the Dd values for Rx(TPPꢀS) were larger than those
for Rx(TBPPꢀS). In contrast, the Dd values for the rotaxane
Rx(TBPPꢀS) were larger than those for the rotaxane
Rx(TPPꢀS) at the porphyrin side (c and 6). Two possible inter-
pretations are proposed. One is that the location of the macro-
cycle would change toward the t-butyl side and the protons at
this side (3 and 6) would be influenced by the stronger shield-
ing effect of the catechol rings. The other is that the macrocycle
would be in a V-shaped conformation in Rx(TBPPꢀS) and two
catechol rings sandwich the pyridine group (Fig. 6). The latter
case is supported by the up-field shift of the catechol rings in
Rx(TBPPꢀS) (Fig. 2). It should be noted that the Dd values
for the catechol protons in Rx(TBPPꢀS) were larger than those
in Rx(OEPꢀS), suggesting that the catechol rings in
Rx(TBPPꢀS) are under a stronger shielding effect than those
in Rx(OEPꢀS). It was considered that the large up-field shift
of the catechol rings in Rx(TBPPꢀS) could be attributed
to two factors, namely, contribution of conformation (A)
Fig. 6 Schematic illustration of the V-shaped conformation of the
macrocycle in rotaxane Rx(TBPPꢀS). The white and gray arrows
represent the deshielding and shielding effect by the aromatic planes,
respectively.
Fig. 4 Schematic illustration of two conformations arising from the
rotational conformation exchange of the macrocycle in rotaxane.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
872
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 8 7 0 – 8 7 3

View Article Online
(Fig. 4) and the V-shaped conformation of the macrocycle
(Fig. 6). Conformation (A) enables the V-shaped conforma-
tion of the macrocycle. In conformation (B), the V-shaped
conformation would be sterically hindered by the bulky t-butyl
groups of TBPP. We considered that the conformation change
of the thread would be negligible, because the thread S is very
short and the interlocked macrocycle hinders a large confor-
mational change of the thread.
References
´
R. A. Bissell, E. Cordova, A. E. Kaifer and J. F. Stoddart, Nature,
1
´
1994, 369, 133; M.-V. M. Dıaz, N. Spencer and J. F. Stoddart,
Angew. Chem., Int. Ed. Engl., 1997, 36, 1904; P. R. Ashton,
R. Ballardini, V. Balzani, A. Credi, K. R. Dress, E. Ishow,
C. J. Kleverlaan, O. Kocian, J. A. Preece, N. Spencer, J. F.
Stoddart, M. Venturi and S. Wenger, Chem. Eur. J., 2000, 6, 3558;
A. S. Lane, D. A. Leigh and A. Murphy, J. Am. Chem. Soc., 1997,
119, 11 092; G. Bottari, F. Dehez, D. A. Leigh, P. J. Nash, E. M.
´
Perez, J. K. Y. Wong and F. Zerbetto, Angew. Chem., Int. Ed.,
2003, 42, 5886; J. P. Collin, P. Gavina and J. P. Sauvage, New
J. Chem., 1997, 21, 525; N. Armaroli, V. Balzani, J. P. Collin,
P. Gavina, J. P. Sauvage and B. Ventura, J. Am. Chem. Soc.,
1999, 121, 4397; H. Murakami, A. Kawabuchi, K. Kottoo,
M. Kunitake and N. Nakashima, J. Am. Chem. Soc., 1997, 119,
7605.
Y. Chen, G. Jung, D. A. A. Ohlberg, X. Li, D. R. Stewart,
J. O. Jeppesen, K. A. Nielsen, J. F. Stoddart and R. S. Williams,
Nanotechnology, 2003, 14, 462; A. R. Pease, J. O. Jeppesen,
J. F. Stoddart, Y. Luo, C. P. Collier and J. R. Heath, Acc. Chem
Res., 2001, 34, 433.
D. A. Leigh, J. K. Y. Wong, F. Dehez and F. Zerbetto, Nature,
2003, 424, 174.
M. C. Jimenez, C. D. Buchecker and J. P. Sauvage, Angew.
Chem., Int. Ed., 2000, 39, 3284.
M. Asakawa, T. Ikeda, N. Yui and T. Shimizu, Chem. Lett.,
2002, 174.
T. Ikeda, M. Asakawa, M. Goto, Y. Nagawa and T. Shimizu,
Eur. J. Org. Chem., 2003, 3744.
Conclusion
From the analysis of the shielding effect, we were able to dis-
cuss the conformation of the macrocycle in the rotaxanes. All
rotaxanes with relatively longer thread Rx(XꢀL) were found to
be in the same conformation. However, the conformations of
the macrocycle were different in the rotaxanes with relatively
shorter thread Rx(XꢀS). In Rx(OEPꢀS), the conformation of
the macrocycle might be almost the same as Rx(OEPꢀL). It
is considered that the rotaxanes Rx(TBPPꢀS) and Rx(TPPꢀS)
prefer conformations (A) and (B) shown in Fig. 4, respectively.
Moreover, the macrocycle in Rx(TBPPꢀS) might be in a V-
shaped conformation. The lower yield of Rx(TBPPꢀS) (25%)
in comparison with other rotaxanes (70%–80%) suggests that
the steric interaction between the macrocycle and terminal por-
phyrin possibly destabilizes rotaxane formation. In other
words, the macrocycle mechanically interacts with TBPP in
Rx(TBPPꢀS), which is an important aspect in designing mole-
cular devices that can regulate the rotational motion of the
macrocycle by the terminal porphyrin or transmit the rota-
tional motion from the macrocycle to the terminal porphyrin.
2
3
4
5
6
7
M. Fujita, N. Fujita, K. Ogura and K. Yamaguchi, Nature, 1999,
400, 52; C. D. Buchecker, B. Colasson, M. Fujita, A. Hori,
N. Geum, S. Sakamoto, K. Yamaguchi and J. P. Sauvage,
J. Am. Chem. Soc., 2003, 125, 5717.
H. Ogoshi, J. Setsume, T. Omura and Z. Yoshida, J. Am. Chem.
Soc., 1975, 97, 6461.
8
9
H. Tamiaki, S. Suzuki and K. Maruyama, Bull. Chem. Soc. Jpn.,
1993, 66, 2633.
Acknowledgements
10 G. B. Jameson, J. P. Collman and R. Boulatov, Acta Crystallogr.,
Sect. C, 2001, 57, 406.
11 S. J. Cantrill, A. R. Pease and J. F. Stoddart, J. Chem. Soc.,
Dalton Trans., 2000, 3715; T. Takata and N. Kihara, Rev.
Heteroatom. Chem., 2000, 22, 197.
This study was supported by the Industrial Technology
Research Grant Program of the New Energy and Industrial
Technology Development Organization (NEDO) of Japan.
T h i s j o u r n a l i s Q T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w . J . C h e m . , 2 0 0 4 , 2 8 , 8 7 0 – 8 7 3
873