Synthesis of a soluble fullerene-rotaxane incorporating a furamide template

Article abstract of DOI:10.1016/j.tet.2005.07.123

The synthesis of a fullerene-rotaxane is described. The thread is constituted by a C₆₀ unit, which acts as a stopper, functionalized with a solubilizing side chain by 1,3 dipolar cycloaddition. The rotaxane is assembled by hydrogen bond-assiste

Full text of DOI:10.1016/j.tet.2005.07.123

Tetrahedron 62 (2006) 2003–2007
Synthesis of a soluble fullerene–rotaxane incorporating
a furamide template
Aurelio Mateo-Alonso and Maurizio Prato
*
Dipartimento di Scienze Farmaceutiche, Universit a` degli Studi di Trieste, Piazzale Europa 1, Trieste 34127, Italy
Received 21 June 2005; revised 18 July 2005; accepted 20 July 2005
Available online 14 November 2005
Abstract—The synthesis of a fullerene–rotaxane is described. The thread is constituted by a C60 unit, which acts as a stopper, functionalized
with a solubilizing side chain by 1,3 dipolar cycloaddition. The rotaxane is assembled by hydrogen bond-assisted synthesis using a
fumaramide template.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
In a collaborative work between Leigh’s group and our
3
group, a fullerene–rotaxane was assembled by clipping a
Rotaxanes have generated a lot of expectations due to their
benzylic amide macrocycle around a fullerene thread via
hydrogen bond-templated synthesis with a glycylglycine
template. C60 acted both as a stopper and an electroactive
unit. We decided to establish a straightforward synthetic
route to fullerene–rotaxanes containing a fumaramide
template that should establish the basis for the preparation
of supramolecular donor–acceptor systems. Fumaramides
have shown to be the best templates for closure of benzilic
1
,2
potential technological applications. They can be pre-
pared by means of different intermolecular interactions such
as hydrogen bonds,
3
–7
8
p-stacking, metal complexation.
9
The applicability of these systems can be enhanced when
using photo- and electroactive units like fullerenes. Owing
to the unique photochemical and electrochemical properties
1
0,11
of fullerene derivatives,
a wide variety of molecular
1
6
devices can be produced with diverse applicability,
including information storage, nanosensoring, conversion
of light into electric current. C60 has shown a great
efficiency as an electron acceptor in donor–acceptor
amide rotaxanes. They can be photochemically isomer-
1
ized leading to light driven molecular shuttles.
7–19
1
0,11
systems.
Since photoinduced electron transfer between
the donor and C60 can take place through space, they can be
connected by means of non-covalent interactions. An
example by Schuster and co-workers showed lifetimes up
2
. Results and discussion
1
2,13
The target thread displayed two stoppers, C60 on one side
0
to 32 ms in ZnP–C60 Sauvage-type rotaxanes.
Never-
and a 2,2 -diphenylethyl amide on the opposite side. These
stoppers have been shown to cooperate in the stabilization
theless, it has been reported that interlocked ZnP–C60 dyads
held together by hydrogen bonds have shown similar
16
of similar rotaxanes in the solid state by p-stacking. More
1
4
lifetimes to their covalently linked analogues. The nature
of the linker between the two units controls the distance, the
orientation and the electronic coupling between the two
units and thus, small structural variations can affect to the
lifetime of the charge-separated state. This has been
previously documented in covalently linked purpurin–C
importantly, a fumaramide template was placed in between
to direct the ring closure of the macrocycle around the
thread.
Our synthetic strategy was based on the preparation of a
fumaric acid derivative that contains the non-fullerenic
stopper. Then, it could be coupled by amidation with a
fullerene building block that displays a free amine
6
0
1
5
dyads. Therefore, it is worthy to explore different
interlocked systems not only to obtain higher lifetimes but
also to understand which are the structural factors that
control the efficiency of these systems.
(
Scheme 1). Fumaric acid monoethyl ester 1 was coupled
0
with 2, 2 -diphenylethylamine using the EDC/HOBt
couple. The ethyl ester 2 was hydrolyzed in the presence
of aqueous sodium hydroxide to yield the corresponding
Keywords: Supramolecular; Fullerene; Rotaxane; Hydrogen bond.
*
Corresponding author. Fax: C39 040 52572;
e-mail addresses: prato@units.it; prato@univ.trieste.it
1
8
acid 3.
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.07.123

2004
A. Mateo-Alonso, M. Prato / Tetrahedron 62 (2006) 2003–2007
O
O
O
EDC/HOBt
DCM
NaOH
EtO
EtO
HO
Ph
Ph
OH
N
H
N
H
MeOH/H O
2
O
O
Ph
O
Ph
1
2
3
Scheme 1.
C60 was functionalized through [3C2] cycloaddition using
an azomethine ylide generated in situ by condensation
between aminoacid 4 and formaldehyde giving the
previously activated using the EDC/HOBt couple.
The reaction afforded the desired thread 10, which was
soluble in chloroform and was fully characterized by NMR,
MS, IR and UV–vis-NIR. A purity O98% was observed by
HPLC using toluene/iPrOH 99:1 as eluent. The chromato-
gram showed a single peak corresponding to thread 10 with
a retention time of 31 min.
2
0
monoadduct 5, as previously reported by our group
Scheme 2). Then, the amino group was deprotected
(
yielding the ammonium salt 7. The acid 3 was activated in
the presence of EDC and HOBt and coupled with the
fullerene salt 7 using pyridine as solvent, leading to the
corresponding fullerene thread 9. The thread 9 showed to
be insoluble in chloroform or DMSO and could only be
characterized by mass spectroscopy. The solubility of the
thread in non-disrupting hydrogen bond solvents, such as
chloroform, is one of the most important requirements for
the preparation of this type of rotaxanes. However, rotaxane
formation was attempted using thread 9 under the
Rotaxane 11 was assembled by slow addition of isophthal-
oyl chloride and p-xylylenediamine in the presence of NEt3
(
formation of the rotaxane 11 was confirmed both by NMR
Scheme 3). It was purified by flash chromatography. The
1
(
checked by HPLC showing a single peak at 29 min and a
H NMR, COSY) and MS. The purity of rotaxane 11 was
1
purity O98%. The H NMR spectrum of rotaxane 11 in
3
previously reported conditions, but after the addition of
the macrocycle precursors no reaction was observed.
CDCl3 shows an upfield shift of the protons on the
fumaramide double bond (from 6.88 to 5.74 ppm), which
is more pronounced in pyridine-d (from 7.76 to 6.22 ppm)
5
These results clearly show that the combination of fullerenes
and fumaramides gave highly insoluble molecules in
chlorinated solvents. To overcome this problem, a solubi-
lizing chain was introduced. This was easily achieved by
functionalization of C60 using 1,3 dipolar cycloaddition
(
Figure 1, signals A and B). This effect proved not only the
formation of the rotaxane but also that the macrocycle laid
on the fumaramide template. The shifting observed is
caused by the shielding of the benzylic aromatic rings on the
macrocycle over the thread due to anisotropy. The spectrum
(
Scheme 2). The cycloaddition was carried out using again
2
0
of rotaxane 11 in CDCl displays a shifting of the amide
3
aminoacid 4 and decanal instead of formaldehyde,
introducing a hydrocarbon chain in the fulleropyrrolidine
ring. This chain should increase the solubility in chloroform,
but also should allow the clipping of the rotaxane since the
hydrocarbon chain is pretty flexible. The reaction gave the
fullerene building block 6, which was deprotected using
diluted TFA. The ammonium salt 8 was dissolved in
pyridine and allowed to react with acid 3, which was
protons (Figure 1, signals C and D) to the aromatic region.
This effect was observed more clearly in pyridine-d , where
the amide protons on the thread 10 appeared more downfield
5
(9.82 and 9.51 ppm) due to hydrogen bonding with the
solvent. The spectrum of rotaxane 11 in pyridine-d showed
5
the amide protons of the template shifted even more
downfield (10.72 and 10.53 ppm).
R
O
H
NHBoc
N
N
HO
NHBoc
∆
TFA, DCM
4
Toluene
O
H
R
5
6
R = H
R = (CH ) CH
3
2
8
R
R
O
H
N
NH
3
N
N
N
H
3, EDC, HOBt
O
Py, DCM
7
8
R = H
R = (CH ) CH
9
R = H
10 R = (CH ) CH
3
2
8
3
2 8
Scheme 2.

A. Mateo-Alonso, M. Prato / Tetrahedron 62 (2006) 2003–2007
2005
d
b
O
O
a
O
O
N
N
H
H
E+G
N
f
c
D
H
N
Cl
Cl
O
O
H
N
K
F
N
N
H
e
N
G
J+L
A+B
I
NH
2
O
O
O
M+N
C
H
H
H
1
0
11
N
N
O
O
H N
2
NEt , CHCl
3
3
Scheme 3.
(a)
(c)
A+B
A+B
I+K
G F
FGIJK
E
O
C+D
O
C+D
L
M+N
L
M
N
J
(b)
(d)
e
b
b c d
c+d
f
f
a
9
8
7
6
5
4
3
2
1
10
ppm
8
7
6
5
4
3
2
1
ppm
1
5 5
Figure 1. H NMR (400 MHz) of (a) thread 10 in CDCl3j, (b) rotaxane 11 in CDCl3j, (c) thread 10 in pyridine-d and (d) rotaxane 11 in pyridine-d . The peaks
highlighted correspond to the residual solvent peaks.
On the other hand the UV–vis-NIR spectra of thread 10 and
rotaxane 11 did not show any major differences.
4. Experimental
4.1. General
3
. Conclusions
NMR spectra were recorded on a Varian Gemini-200
200 MHz) or on a Jeol (400 MHz) at room temperature in
CDCl (unless otherwise stated). Chemical shifts reported in
ppm are referred to TMS. Infrared spectra were recorded on
a Jasco FTIR-200 spectrometer. Mass Spectroscopy:
Electrospray (ES-MS) experiments were recorded at
Universit a` degli Studi di Trieste on a Perkin-Elmer API1
at 5600 eV. UV–vis-NIR measurements were recorded on a
Varian 5000 UV–vis-NIR spectrometer. HPLC experiments
were carried out using a semipreparative Phenomenex
(
Fullerene–rotaxane 11 was assembled by hydrogen bond-
directed synthesis using a fumaramide template. The
insolubility of the fumaramide template together with C60
was overcome by the introduction of a solubilizing
hydrocarbon chain. This required the preparation of a
novel fullerene building block by 1,3-dipolar cycloaddition.
The solubilization of the new thread in chloroform allowed
the preparation of the rotaxane.
3

2006
A. Mateo-Alonso, M. Prato / Tetrahedron 62 (2006) 2003–2007
˚
Prodigy 5 mm silica 100 A column and a Waters 996
photodiode detector. Toluene/iPrOH 99:1 was used as the
mobile phase. Flow rate gradient 0–1 mL/min (0–3 min),
followed by a constant flow rate of 1 mL/min (3–57 min).
Commercially available products were used without further
142.52, 142.49, 142.12, 142.08, 142.06, 142.03, 141.99,
141.96, 141.95, 141.91, 141.69, 141.63, 141.13, 140.09,
139.80, 139.55, 136.78, 136.01, 135.40, 135.32, 77.25, 76.51,
66.48, 51.70, 31.91, 31.48, 30.15, 29.70, 29.58, 29.30, 28.52,
27.60, 22.72, 14.19. IR (NaCl): 3356, 2922, 2849, 1701, 1498,
C
purification. Anhydrous CHCl stabilized with amylenes
3
1461, 1363, 1248, 1168. MS: 1034 (MCH) .
was purchased from Aldrich and used as received.
4
.1.4. Fullerene thread 10. Fullerene 6 (120 mg,
0
monoethyl ester (2). Fumaric acid monoethyl ester
4
.1.1. Fumaric acid mono-2,2 -diphenylethylamide
0.116 mmol) was dissolved in DCM (3 mL) and TFA
(3 mL) was added in small portions. The resulting solution
was stirred at room temperature for 3 h. The solvent was
evaporated under vacuum. The residue was then dissolved
0
.39 mmol), HOBt (170 mg, 1.39 mmol) were stirred at
(
200 mg, 1.39 mmol), 2,2 diphenylethylamine (274 mg,
1
1
8
room temperature in DCM (10 mL). EDC (275, 1.39 mmol)
was added in small portions and the resulting solution was
stirred at room temperature for 20 h. The solution was taken
up with AcOEt (50 mL) and was washed with aqueous HCl
in pyridine (anhydrous, 12 mL). Then a solution of acid 3
(51 mg, 0.172 mmol), EDC (36 mg, 0.172 mmol), HOBt
(25 mg, 0.182 mmol) in DCM (12 mL), which was
previously stirred for 15 min, was added to the fullerene
solution. The resulting solution was stirred at room
temperature for 15 min. The solution was washed with
aqueous HCl (0.5 N, 50 mL!2), aqueous NaHCO (satu-
3
rated, 50 mL!2) and brine (50 mL). The organic phase was
dried over MgSO and the solvent was evaporated under
(
0.5 N, 50 mL), aqueous NaHCO (saturated, 50 mL) and
3
brine (50 mL). The organic phase was dried over MgSO4
and the solvent was evaporated under vacuum yielding the
desired product (423 mg, 93%).
4
1
8 1
Mp 111–112 8C (Mp 112–113 8C). H NMR (200 MHz):
.34–7.19 (m, 10H, Ar), 6.77 (d, JZ14.4 Hz, 1H,
HC]CH), 6.72 (d, JZ14.4 Hz, 1H, HC]CH), 5.80–5.65
vacuum. The crude was purified by flash chromatography
(CHCl ) yielding the desired product (117 mg, 83%).
7
3
1
(
m, 1H, NH), 4.30–4.15 (m, 3H, OCOCH CH and CHPh ),
H NMR (400 MHz, CDCl ): 7.4–7.2 (m, 10H, Ar); 6.99
3
2
3
2
4
OCOCH CH ).
.01 (dd, JZ8.0, 5.7 Hz, OCNHCH ), 1.31 (t, JZ7.0 Hz,
(d, 1H, JZ14.82 Hz, CH]CH); 6.77 (d, 1H, JZ14.82 Hz,
CH]CH); 6.70–6.60 (m, 1H, CONH); 5.73 (t, 1H,
2
2
3
JZ5.88 Hz, CONH); 4.90 (d, 1H, JZ10.25 Hz, H ); 4.28
E
2
.1.2. Fullerene thread 9. Fullerene 7 (25 mg, 27 mmol)
0
4
was dissolved in pyridine (anhydrous, 2.5 mL). Then a
(t, 1H, JZ6.63 Hz, CH
2H, JZ5.89, 7.76 Hz, H
(m, 2H, H ); 3.20–3.10 (m, 1H, H
2.45–2.35 (m, 1H, H ); 1.83 (q, 2H, JZ7.85 Hz, H
(m, 17H). H NMR (400 MHz, pyridine-d ): 9.82 (t, 1H,
F
Ph
); 3.97–3.90 (m, 1H, H
); 2.55–2.45 (m, 1H, H
); 1.7–0.8
2
);4.25–4.15(m, 2H, H
); 3.75–3.60
);
G
);4.00(dd,
I
J
1
8
solution of acid 3 (16 mg, 54 mmol), EDC (11 mg,
4 mmol), HOBt (7 mg, 54 mmol) in CH Cl (5 mL),
K
L
M
5
N
O
2
2
1
which was previously stirred for 15 min, was added over
the fullerene solution. The resulting solution was stirred at
room temperature for 15 min. The solution was washed with
5
JZ5.59 Hz, CONH); 9.51 (t, 1H, JZ5.62 Hz, CONH); 7.88
(d, 1H JZ14.98 Hz, CH]CH); 7.64 (d, 1H, JZ14.98 Hz,
aqueous HCl (0.5 N, 50 mL!2), aqueous NaHCO (satu-
3
CH]CH); 7.50–7.10 (m, 10H, Ar); 4.62 (t, 2H, H
1H, JZ5.58 Hz, CH Ph ); 4.30–4.10 (m, 4H, H
4.05–3.90 (m, 1H, m, 1H, H ); 3.40–3.25 (m, 1H, m, 1H,
CH ); 1.96 (q, 2H, JZ7.60 Hz,
); 1.5–0.6 (m, 17H). C NMR (50 MHz, pyridine-d ):
G
); 4.38 (t,
rated, 50 mL!2) and brine (50 mL). The organic phase was
dried over MgSO and the solvent was evaporated under
F
2
I
CH );
K
4
J
vacuum. The crude was purified by flash chromatography
(
H
H
L
); 2.60–2.40 (m, 2H, H
M
N
1
3
toluene/iPrOH 8:2) and by reprecipitation (CHCl /MeOH
3
O
5
9
1
:1/ether) yielding the desired product (25 mg, 85%). MS:
086 (MCH) .
165.74, 165.62, 157.49, 156.04, 154.77, 147.69, 147.66,
147.42, 147.35, 147.07, 146.83, 146.78, 146.73, 146.71,
C
146.58, 146.55, 146.51, 146.48, 146.34, 146.25, 145.93,
4
.1.3. Fullerene building block 6. A solution of C
145.89, 145.83, 145.77, 145.73, 145.31, 145.14, 145.04,
145.01, 143.82, 143.66, 143.20, 142.95, 142.92, 142.76,
142.69, 142.65, 142.58, 142.41, 142.35, 140.74, 140.70,
140.46, 140.25, 137.76, 134.93, 134.35, 134.22, 129.42,
129.05, 127.37, 77.50, 72.39, 51.70, 32.65, 30.91, 30.55,
30.39, 30.35, 30.12, 28.14, 23.54, 14.87. IR (NaCl): 3745,
3288, 3079, 2921, 2850, 2360, 1630, 1544, 1456, 1338, 1189,
6
0
2
0
(
237 mg, 0.312 mmol), aminoacid 4 (50 mg, 0.313 mmol)
and decanal (244 mg, 1.560 mmol) were sonicated for
0 min in toluene (240 mL). Then the solution was refluxed
3
for 25 min. The solvent was evaporated by vacuum
distillation. The residue was purified by flash chromato-
graphy (toluene), unreacted C60 was eluted followed by the
desired product. This was further purified by reprecipitation
C
748. MS: 1212 (MCH) . UV–vis-NIR (THF, lmax): 255,
292, 320, 431, 704.
using CHCl /MeOH (120 mg, 37%).
3
1
H NMR (200 MHz): 5.29 (br s, 1H, NH); 4.96 (d, 1H,
JZ10.4 Hz, C –CH –N); 4.34 (d, 1H, JZ5.8 Hz,
4.1.5. Rotaxane 11. A solution of p-xylylenediamine
(144 mg, 1.050 mmol) in CHCl (anhydrous, 40 mL) and
6
0
2
3
C –CHR–N); 4.27 (d, 1H, JZ10.4 Hz, C –CH –N);
a separate solution of isophthaloyl chloride (213 mg,
1.050 mmol) in CHCl (anhydrous, 40 mL) were added
6
0
60
2
3
NCH CH H N); 2.62–2.25 (m, 2H, C –CH–CH );
.82–3.55 (m, 3H, NCH CH H N); 3.18–3.12 (m, 1H,
2
a
b
3
dropwise, simultaneously for 4 h to a stirred solution of the
thread 10 (85 mg, 0.070 mmol) in CHCl3 (anhydrous,
150 mL) containing NEt3 (153 mL, 2.100 mmol) under
argon. After the addition, the reaction mixture was stirred
overnight at room temperature. The solution was filtered
through Celite, concentrated to dryness and
2
a
b
60
2
1
3
2.00–0.85 (m, 26H). C NMR (50 MHz): 156.15, 155.98,
154.80, 153.34, 147.04, 147.02, 146.37, 146.35, 146.13,
146.11, 146.03, 145.92, 145.88, 145.85, 145.83, 145.55,
145.53, 145.42, 145.22, 145.16, 145.14, 145.12, 145.05,
144.55, 144.41, 144.30, 144.28, 143.08, 142.97, 142.53,

A. Mateo-Alonso, M. Prato / Tetrahedron 62 (2006) 2003–2007
2007
chromatographed (CHCl ), giving unreacted thread (33 mg)
3
5. Leigh, D. A.; Murphy, A.; Smart, J. P.; Slawin, A. M. Z.
and rotaxane 11 (30 mg, 25% yield).
Angew. Chem., Int. Ed. 1997, 36, 728–732.
6
. Hubner, G. M.; Glaser, J.; Seel, C.; Vogtle, F. Angew. Chem.,
Int. Ed. 1999, 38, 383–386.
1
H NMR (400 MHz, CDCl ): 8.37 (s, 2H, H ); 8.11 (d, 4H,
a
3
JZ8.30 Hz, H ); 7.69–7.59 (m, 4H, NH ); 7.59 (t, 2H,
7. Martinez-Diaz, M. V.; Spencer, N.; Stoddart, J. F. Angew.
Chem., Int. Ed. 1997, 36, 1904–1907.
b
c
JZ7.94 Hz, H ); 7.30–7.20 (m, 10H, Ar); 7.70–7.10 (m,
d
2
H, H CH ); 6.98 (s, 8H, H ); 5.82 (d, 1H, JZ14.77 Hz,
8. Anelli, P. L.; Ashton, P. R.; Ballardini, R.; Balzani, V.;
Delgado, M.; Gandolfi, M. T.; Goodnow, T. T.; Kaifer, A. E.;
Philp, D.; Pietraszkiewicz, M.; Prodi, L.; Reddington, M. V.;
Slawin, A. M. Z.; Spencer, N.; Stoddart, J. F.; Vicent, C.;
Williams, D. J. J. Am. Chem. Soc. 1992, 114, 193–218.
9. Diederich, F.; Dietrich-Buchecker, C. O.; Nierengarten, J.-F.;
Sauvage, J. P. J. Chem. Soc., Chem. Commun. 1995, 781–782.
0. Tagmatarchis, N.; Prato, M. Organofullerene materials. In
Fullerene-Based Materials; Prassides, K., Ed.; Structure and
Bonding; Springer Verlag: Berlin, 2004; Vol. 109, pp 1–39.
1. Mateo-Alonso, A.; Tagmatarchis, N.; Prato, M. In Fullerenes
and Their Derivatives; Gogotsi, Y. Ed.; Handbook in
Nanomaterials; CRC, 2006, in press.
C
D
e
CH]CH); 5.67 (d, 1H, JZ14.77 Hz, CH]CH); 4.80 (d,
H, JZ10.64 Hz, H ); 4.55–4.35 (m, 8H, H ); 4.22 (t, 1H,
1
E
f
JZ4.75 Hz, CH Ph ); 4.19–4.10 (m, 5H, H CH CH );
3
F
2
I
J
K
.15–3.05 (m, 1H, H ); 2.60–2.40 (m, 1H, H ); 2.40–2.20
L M
(
m, 1H, H ); 1.85–1.75 (m, 2H, H ); 1.5–0.7 (m, 17H).
N O
1
H NMR (400 MHz, pyridine-d ): 10.75 (t, 1H, JZ5.15 Hz,
5
1
1
1
CONH); 10.53 (t, 1H, JZ5.50 Hz, CONH); 8.45 (dt, 4H
JZ7.76 and 1.82 Hz, H ); 8.25–8.15 (m, 4H, H ); 7.59
b
c
(
t, 2H, JZ7.76 Hz, H ); 7.40–7.15 (m, Ar); 6.28 (d, 1H,
d
JZ14.91 Hz, CH]CH); 6.17 (d, 1H, JZ14.91 Hz,
CH]CH); 4.85–4.60 (m, 8H, H ), 4.51 (t, 2H, JZ7.94 Hz,
H ); 4.31 (t, 1H, JZ5.63 Hz, CH Ph ); 4.30–4.00 (m, 5H,
H , H , H ); 3.35–3.25 (m, 1H, H ); 2.55–2.45 (m, 1H, H );
2
1
1
4
f
G
F
2
2. Li, K.; Bracher, P. J.; Guldi, D. M.; Herranz, M. A.;
Echegoyen, L.; Schuster, D. I. J. Am. Chem. Soc. 2004, 126,
I
K
J
L
M
.45–2.35 (m, 1H, H ); 1.9 (q, 2H, JZ7.96 Hz, H );
N O
9
156–9157.
.4–0.6 (m, 17H). IR (NaCl): 2360, 1639, 1525, 466. MS:
744 (MCH) . UV–vis-NIR (THF, lmax): 249, 292, 320,
31, 703.
C
13. Li, K.; Schuster, D. I.; Guldi, D. M.; Herranz, M. A.;
Echegoyen, L. J. Am. Chem. Soc. 2004, 126, 3388–3389.
1
1
4. Watanabe, N.; Kihara, N.; Furusho, Y.; Takata, T.; Araki, Y.;
Ito, O. Angew. Chem., Int. Ed. 2003, 42, 681–683.
5. Ohkubo, K.; Kotani, H.; Shao, J. G.; Ou, Z. P.; Kadish, K. M.;
Li, G. L.; Pandey, R. K.; Fujitsuka, M.; Ito, O.; Imahori, H.;
Fukuzumi, S. Angew. Chem., Int. Ed. 2004, 43, 853–856.
Acknowledgements
This work has been supported by the EU (RTN EMMMA),
Universit a` di Trieste and MIUR (PRIN 2004, prot.
2
Dr. Giovanni Bottari for help and useful comments. We also
thank Dr. Fabio Hollan for the mass measurements.
16. Gatti, F. G.; Leigh, D. A.; Nepogodiev, S. A.; Slawin,
A. M. Z.; Teat, S. J.; Wong, J. K. Y. J. Am. Chem. Soc. 2001,
123, 5983–5989.
004035502). We are grateful to Dr. Tatiana Da Ros and
17. Altieri, A.; Bottari, G.; Dehez, F.; Leigh, D. A.; Wong,
J. K. Y.; Zerbetto, F. Angew. Chem., Int. Ed. 2003, 42,
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296–2300.
8. Bottari, G.; Leigh, D. A.; Perez, E. M. J. Am. Chem. Soc. 2003,
25, 13360–13361.
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