Supramolecular complexes obtained from porphyrin-crown ether conjugates and a fullerene derivative bearing an ammonium unit

Article abstract of DOI:10.1016/j.tet.2005.07.120

A methanofullerene derivative with an ammonium subunit (1) has been prepared and its ability to form a supramolecular complex with a porphyrin-crown ether conjugate evidenced by NMR, UV-vis, electrospray mass spectrometry (ES-MS) and luminescence experime

Full text of DOI:10.1016/j.tet.2005.07.120

Tetrahedron 62 (2006) 1979–1987
Supramolecular complexes obtained from porphyrin–crown ether
conjugates and a fullerene derivative bearing an ammonium unit
a,
a
Nathalie Solladie, Mathieu E. Walther, Haiko Herschbach, Emmanuelle Leize,
b
b
*
´
Alain Van Dorsselaer,b, Teresa M. Figueira Duarte and Jean-Franc¸ois Nierengarten
c
c,
*
*
a
` `
Groupe de Synthese de Systemes Porphyriniques, Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne,
31077 Toulouse Cedex 4, France
Laboratoire de Spectrometrie de Masse Bio-organique, Ecole de Chimie, Polymeres et Materiaux (ECPM),
b
´
`
´
´
Universite Louis Pasteur and CNRS, 25 rue Becquerel, 67087 Strasbourg Cedex 2, France
´
c
` `
Groupe de Chimie des Fullerenes et des Systemes Conjugues, Laboratoire de Chimie de Coordination du CNRS,
205 route de Narbonne, 31077 Toulouse Cedex 4, France
Received 8 April 2005; revised 26 April 2005; accepted 30 April 2005
Available online 14 November 2005
Abstract—A methanofullerene derivative with an ammonium subunit (1) has been prepared and its ability to form a supramolecular
complex with a porphyrin–crown ether conjugate evidenced by NMR, UV–vis, electrospray mass spectrometry (ES-MS) and luminescence
experiments. Interestingly, in addition to the ammonium–crown ether recognition, intramolecular stacking of the fullerene moiety and the
porphyrin subunit has been evidenced. Due to this additional recognition element, the association constant for the supramolecular complex is
increased by two orders of magnitude when compared to the Ka values found for the complexation of 1 with benzo-18-crown-6. Finally, non-
covalent systems resulting from the association of cation 1 with porphyrin derivatives bearing two crown ether subunits have been
investigated. Intramolecular C60–porphyrin interactions have also been evidenced within these supramolecular complexes. As a result, the
2:1 complexes are very stable as shown by the ES-MS studies.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
accelerated charge separation and decelerated charge
recombination has been observed in a fullerene-based
acceptor–donor system when compared to the equivalent
benzoquinone-based system.4 This has been interpreted by
the smaller reorganization energy (l) of C60 compared with
those of small acceptors: the smaller reorganization energy
of C60 positions the photoinduced charge separation rate
upward along the normal region of the Marcus parabolic
curve, while forcing the charge recombination rate down-
ward in the inverted region. The efficient photogeneration of
long lived charge-separated states by photoinduced electron
transfer is of particular interest for solar energy conversion
and photovoltaic devices prepared from porphyrin–full-
erene systems have shown promising energy conversion
efficiencies.5
Owing to their particular electrochemical and electronic
properties, C60 and porphyrins are interesting building
blocks for the construction of new photochemical molecular
devices.1 Indeed, the synthesis of covalently linked
porphyrin–fullerene hybrids have generated significant
research efforts in the last few years.2,3 Their photophysical
properties have been studied in details and intramolecular
processes such as electron and energy transfer evidenced in
such multicomponent hybrid systems.2,3 Importantly,
excited-state dynamic investigations on C60–porphyrin
conjugates have revealed that the fullerene sphere is a
particularly interesting electron acceptor in artificial
photosynthetic models.4 The characteristics of C60 are
effectively in stark contrast with those of common acceptors
with smaller size such as benzoquinone. Actually,
Whereas research focused on covalently bound C60–
porphyrin derivatives has received considerable attention,
only a few related examples of non-covalent assemblies
have been described so far.6,7 In most cases, these non-
covalent assemblies have been obtained from a C60
derivative bearing a pyridyl moiety and a metalloporphyrin
through coordination to the metal ion.6 Due to the apical
Keywords: Binding studies; Crown ether; Fullerene; Porphyrin; Supra-
molecular chemistry.
Corresponding authors. Tel.: C33 561 33 31 00; fax: C33 561 55 30 03;
e-mail addresses: solladie@lcc-toulose.fr; vandors@chimie.u-strasbg.fr;
jfnierengarten@lcc-toulouse.fr
*
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.07.120

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1980
binding on the porphyrin subunit, the attractive van der
Waals interaction of the fullerene sphere with the planar
p-surface of the porphyrin seen for several covalent C60–
porphyrin derivatives8 or in the solid state structures of
porphyrin–fullerene co-crystals9 is not possible in such
arrays. It can also be mentioned here that the p–p stacking
between C60 and porphyrin moieties is capable of enhancing
the efficiency of the end-capping reactions of pseudo-
rotaxanes and C60 thus leading to [2]-rotaxanes in higher
yields.10 As part of this research, we have recently shown
that p-stacking of the two chromophores can have a
dramatic effect on the recognition interactions in non-
covalent C60–porphyrin ensembles.7 Specifically, a supra-
molecular complex has been obtained from porphyrin–
crown ether conjugate 2 and methanofullerene derivative 1
bearing an ammonium function (Fig. 1). In addition to the
ammonium–crown ether interaction, intramolecular stack-
ing of the fullerene moiety and the porphyrin subunit has
been evidenced in the supramolecular system. Due to this
additional recognition element, the association constant (Ka)
for the complex obtained from 1 and 2 is increased by two
orders of magnitude when compared to Ka values previously
found for the complexation of 1 with other crown ether
derivatives. In this paper, we now report a full account on
this work. In addition, we also show that more complex
supramolecular systems are easily accessible by using
similar interactions as illustrated by the association of cation
1 with porphyrin derivatives 3 and 4 bearing two crown
ether subunits (Fig. 1).
2. Results and discussion
2.1. Synthesis
The synthesis of the functionalized methanofullerene
derivative 1 is depicted in Scheme 1. Commercially
available methyl 4-(aminomethyl)benzoate hydrochloride
was converted to its t-butylcarbonyl (Boc) derivative 5 as
previously reported.11 LiAlH4 reduction of compound 5
afforded compound 6 in 93% yield. Reaction of acid 712
with benzylic alcohol 6 under esterification conditions using
N,N0-dicyclohexylcarbodiimide (DCC) and 4-dimethyl-
aminopyridine (DMAP) led to malonic ester 8 in 78% yield.
The functionalization of C60 with 8 is based on the Bingel
reaction.13 Nucleophilic addition of a stabilized a-halo-
carbanion to the C60 core, followed by an intramolecular
nucleophilic substitution, leads to clean cyclopropanation of
C60.14 It has been shown that the a-halomalonate can be
generated in situ, and direct treatment of C60 with malonates
in the presence of I2 under basic conditions affords the
corresponding methanofullerenes in good yields.15 Treat-
ment of C60 with 8, iodine and 1,8-diazabicyclo[5.4.0]-
undec-7-ene (DBU) in toluene at room temperature afforded
methanofullerene 9 in 57% yield. Finally, removal of the
Boc group with CF3CO2H afforded the targeted derivative 1
as its trifluoroacetate salt in a quantitative yield.
The synthesis of the porphyrin–crown ether derivatives 2, 3,
and 4 is depicted in Scheme 2. Porphyrin 2 was obtained
Figure 1. Compounds 1–4.

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N. Solladie et al. / Tetrahedron 62 (2006) 1979–1987
1981
derivatives. Indeed, compounds 2, 3, and 4 were isolated
after tedious chromatographic purifications.
2.2. Binding studies
The ability of the fullerene derivative 1 to form
supramolecular complexes with crown ether derivatives
was first investigated with commercially available benzo-
18-crown-6 (14) by NMR studies. As shown in Figure 2, the
1H NMR spectra of 1 in CDCl3 showed dramatic changes
upon successive addition of 14. The complexation-induced
changes in chemical shifts were particularly important for
the aromatic protons of the 4-(aminomethyl)benzyl moiety
in 1 (Hc and Hd). Indeed, the signal of Hc–d in 1 was shifted
upfield when benzo-18-crown-6 (14) was added. The latter
observation maybe ascribed to the proximity of the aromatic
unit of guest 14 within the supramolecular complex
[(1)$(14)] in good agreement with the proposed structure.
The association constant for the 1:1 complex based on the
Hb chemical shifts of 1 was determined as KaZ2100G
100 MK1, corresponding to a Gibbs free energy of
complexation DG0ZK4.5 kcal/mol. Identical results within
the error range were obtained when the complexation-
induced changes in chemical shifts were monitored for the
other protons of 1.
Scheme 1. Reagents and conditions: (i) LiAlH4, THF, 0 8C (93%); (ii)
DCC, DMAP, CH2Cl2, 0 8C to rt (78%); (iii) C60, I2, DBU, toluene, rt
(57%); (iv) CF3CO2H, CH2Cl2, rt (99%).
under the classical conditions developed by Lindsey.16
Condensation of aldehydes 1017 (1 equiv) and 12 (3 equiv)
with pyrrole (4 equiv) in CHCl3 in the presence of
BF3$Et2O as catalyst was followed by the oxidation of the
porphyrinogens by p-chloranil. Compound 2 was thus
obtained in 13% yield after purification.
The binding behavior of ammonium 1 to porphyrin 2 was
also investigated by H NMR titration in CDCl3 at 298 K.
1
1
As depicted in Figure 3A, the comparison between the H
NMR spectra of 1, 2 and mixtures of both components
revealed the apparition of new sets of signals as well as
complexation-induced changes in chemical shifts. This is
particularly visible for the pyrrolic protons of the porphyrin
moiety and the signals arising from the crown ether subunit.
The latter observations suggest the existence of two
conformers for the supramolecular complex obtained upon
association of the two components, one being in fast
exchange with uncomplexed 1 and 2 on the NMR time-
scale, the other one in slow exchange as shown in Figure 3B.
On the one hand, the initial ammonium–crown ether
association leading to conformer A is responsible for the
observed complexation-induced changes in chemical shifts
upon addition of ammonium 1 to solutions of 2. In principle,
association of the two molecular units should be possible by
p-stacking of the two chromophores only. However, no
significant changes in chemical shifts were observed in the
1H NMR spectrum of 1 upon addition of compound 9 thus
showing that the C60–porphyrin interaction does not take
place in the absence of ammonium–crown ether recognition.
Scheme 2. Reagents and conditions: (i) 12 (3 equiv), 11 (4 equiv),
BF3$Et2O, CHCl3, rt then p-chloranil, D (13%); (ii) BF3$Et2O, rt (69%);
(iii) 10, BF3$Et2O, CHCl3, rt then p-chloranil, D (2: 14%; 3: 11%; 4: 12%)
1
The selective preparation of trans-A2B2 porphyrin 3 was
attempted by the condensation of dipyrromethane 13 and
aldehyde 10. Compound 13 was obtained in a good yield by
acid catalyzed condensation of aldehyde 12 with an excess
pyrrole in solvent free conditions. Treatment of dipyrro-
methane 13 with aldehyde 10 in CHCl3 in the presence of a
catalytic amount of BF3$Et2O yielded a mixture of
porphyrins 2, 3, and 4. Indeed, under these conditions,
polypyrrolic rearrangement reactions took place as often
observed during the condensation of aldehydes with
5-substituted dipyrromethane derivatives containing an
unhired aryl substituent (lacking b-substituents).18 As a
result of this scrambling process, the desired trans-A2B2
porphyrin 3 was obtained together with other porphyrin
On the other hand, the new sets of signals seen in the H
NMR spectra correspond to conformer B. The dramatic up-
field shift observed for the pyrrolic protons in B must be the
result of the close proximity of the fullerene sphere
suggesting that supramolecule [(1)$(2)] adopts a confor-
mation in which the C60 subunit is located atop the
porphyrin macrocycle. Further evidence for C60–porphyrin
interactions came from UV–vis measurements. Addition of
increasing amount of 1 to a CH2Cl2 solution of 2 causes a
red shift of the Soret band, no further spectral changes being
observed beyond the addition of ca. 5 equiv of 1 (lmaxZ421
and 427 nm before and after addition of 1, respectively).
The latter observation confirmed the existence of the C60–
porphyrin interactions in [(1)$(2)]. Effectively, red shifts in

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1982
b
C12H25O
Solv.
O
O
a
O
f
e
c
O
C
12H25O
d
O
O
O
O
c/d
e/f
b
CF3CO2
NH3
O
O
+
a
(e)
(d)
(c)
(b)
(a)
1
14
C12H25
O
O
O
O
O
O
H
N
H
C12H25O
O
O
H
O
O
O
CF3CO2
8
7
[(1).(14)]
δ (ppm)
Figure 2. 1H NMR spectra (300 MHz, CDCl3, 298 K) of 1 with 0 (a), 0.25 (b), 0.5 (c), 1.25 (d) and 2 equiv (e) of 14.
the Soret band have been observed for covalent C60–
porphyrin conjugates due to intramolecular p-stacking of
the two chromophores.8 As reported in detail in the
preliminary communication,7 the Ka value for the binding
of 1 to 2 was determined by a fluorescence titration. A
surprisingly high value for the association constant KaZ
375,000 MK1 was obtained. Effectively, the association
constant between porphyrin 2 and fullerene 1 is unexpect-
edly increased by two orders of magnitude when compared
to the Ka value found for the complexation of 1 with crown
ether 14. Such a stabilization of the supramolecular complex
formed between 1 and 2, which can be attributed to an
additional intramolecular interaction, provides further
evidence for the p-stacking of the fullerene moiety and
the porphyrin subunit in [(1)$(2)] suggested by the NMR
studies.
2.3. Mass spectrometric characterization
The supramolecular complexes obtained from fullerene
derivative 1 and the porphyrin–crown ether conjugate 2–4
were further characterized in the gas phase by electrospray
mass spectrometry (ES-MS). Unlike other mass spectro-
metric methods, ES-MS allows pre-existing ions in solution
to be transferred to the gas phase without fragmentation.
This soft ionization technique, mainly developed by Fenn
and co-workers,19 is now commonly applied to the study of
large non-covalent assemblies20 and appears as ideally
suited to characterize the non-covalent complexes formed
from 1 and 2–4. The positive ES mass spectrum (Fig. 4)
recorded from a 1:1 mixture of 1 and 2 displayed a singly
charged ion peak at m/zZ2587.2, which can be assigned to
the 1:1 complex after loss of the trifluoroacetate counter-
anion (calculated m/zZ2587.24).
The binding behavior of 1 to porphyrins 3 and 4 was also
investigated by H NMR in CDCl3 at 298 K. As discussed
1
As shown in Figure 5, the positive ES mass spectrum
obtained under mild conditions (extracting cone voltage
VcZ50 V) from a 2:1 mixture of 1 and 4 is characterized by
a doubly charged ion peak at m/zZ2055.2, which can be
assigned to the 2:1 complex after loss of the two
trifluoroacetate counteranions (calculated m/zZ2055.45).
The peak corresponding to the 1:1 complex could almost not
be detected under these conditions thus suggesting that the
self-assembled array [(1)$(3)2] is the most abundant species
in the analysed solution.
for the NMR binding studies of 1 to 2, apparition of new sets
of signals and complexation-induced changes in chemical
shifts were observed in the 1H NMR spectra of 3 and 4 upon
addition of ammonium 1 revealing the effective formation
of supramolecular structures. However, the interpretation of
the NMR spectra appeared difficult due to the possible
formation of 1:1 and 2:1 complexes. It must, however, be
noted that, as in the case of [(1)$(2)], intramolecular
C60–porphyrin interactions were evidenced for the
supramolecular complexes obtained from the association
of both 3 and 4 with ammonium 1. Effectively, some signals
corresponding to the pyrrolic protons were dramatically
ES-MS analysis of a 2:1 mixture of 1 and 3 gave similar
results. At low Vc, only the signal corresponding to the
supramolecular complex [(1)$(3)2] was observed (Fig. 6).
Under more brutal conditions (VcZ180 V), the spectrum
was still dominated by the doubly charged ion peak at m/zZ
2055.6 but a singly charged ion peak attributed to the 1:1
complex was also observed at m/zZ2709.6 (calculated
m/zZ2709.28). The intensity of the latter signal is increased
1
up-field shifted in the H NMR spectra of 3 and 4 upon
addition of methanofullerene 1. Furthermore, by adding
increasing amount of 1 to CH2Cl2 solutions of 3 and 4, the
characteristic red shift of the Soret band due to the
C60–porphyrin interactions was observed in the UV–vis
spectra.

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N. Solladie et al. / Tetrahedron 62 (2006) 1979–1987
1983
Solv.
A
(a)
pyrrolic H
(b)
(c)
(d)
8
6
4
δ (ppm)
1 + 2
B
Fast
OR
O
O
O
Ar
O
OR
O
O
O
N
Ar
H
HN
N
O
N
H
NH
H
A
O
O
CF3CO2
Ar
Slow
RO
O
O
RO
O
O
Ar
O
O
N
H
Ar
HN
N
O
N
H
NH
O
H
O
O
Ar
B
CF3CO2
Figure 3. (A) 1H NMR spectra (CDCl3, 300 MHz, 298 K) of 1 (a), 2 (d), a 2:1 mixture of 1 and 2 (b) and a 1:1 mixture of 1 and 2 (c); the signals of the pyrrolic
protons of B are highlighted. (B) Schematic representation of the two conformers of the supramolecular complex obtained upon association of 1 and 2. A is in
fast exchange with uncomplexed 1 and 2 on the NMR time-scale and B in slow exchange.
as the Vc value is increased, thus the peak corresponding to
[(1)$(3)] must result from the fragmentation of the 2:1
supramolecular complex [(1)$(3)2] initially present in
solution. A similar behavior was also observed for the ES
mass spectra of the 2:1 mixture of 1 and 4 recorded at
various Vc values. In both cases, the fragmentation is still
limited thus showing the high stability of the non-covalent
arrays [(1)$(3)2] and [(1)$(4)2]. This observation further
corroborates the existence of intramolecular stacking
interactions between the fullerene moiety and the porphyrin
subunit in [(1)$(3)2] and [(1)$(4)2] as suggested by the NMR
and UV–vis data.
2.4. Preliminary fluorescence studies
The complexation between 1 and 2–4 was finally
investigated in CH2Cl2 by luminescence studies. A large
decrease in intensity of the characteristic porphyrin
emission was observed when the fullerene ammonium salt
1 was added to a CH2Cl2 solution of 2, 3 or 4. This decrease
can be attributed, at least in part, to the reabsorption of the
porphyrin luminescence by the fullerene derivative 1.
However, experiments carried out in parallel with mixtures
of 2, 3 or 4 and methanofullerene 9, which are not able to
form a supramolecular complex show that the decrease in

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N. Solladie et al. / Tetrahedron 62 (2006) 1979–1987
1984
Figure 4. ES mass spectrum (VcZ20 V) recorded from an equimolar mixture (10K5 M) of 1 and 2 in CH2Cl2.
luminescence intensity could mainly originate from an
intramolecular photoinduced process in the supramolecular
C60–porphyrin conjugates. Further evidence for an intra-
molecular quenching of the porphyrin excited-state by the
fullerene moiety in [(1)$(2)], [(1)$(3)2] and [(1)$(4)2] was
obtained from the following experiments. Addition of DBU
to mixtures of 1 and 2, 3 or 4 in CH2Cl2 causes an increase
of the porphyrin emission. Actually, the fluorescence
intensity of the resulting solution was found to be similar
to that of the reference solution containing 9 and 2, 3 or 4. In
other words, the treatment with a base deprotonates the
ammonium moiety of 1 and, thereby, disrupts the non-
covalent bonding interactions that brought the components
together. Addition of trifluoroacetic acid to the CH2Cl2
solution regenerates the ammonium center, thus allowing
the formation of the supramolecular complexes, and the
luminescence intensity of final solution is the same as that of
the starting mixture of 1 and 2, 3 or 4. The observed
decrease in luminescence intensity originates from either
energy or electron transfer from the photoexcited porphyrin
to the C60 acceptor in the supramolecular complexes. Steady
state measurements are not sufficient to determine the nature
of the quenching because the residual porphyrin emission
overlaps the much weaker fullerene emission, thus
prohibiting clean excitation spectroscopy. Detailed photo-
physical studies are currently under investigation and will
be reported in due time.
3. Conclusions
A methanofullerene derivative bearing an ammonium unit
(1) was synthesized. Its ability to form supramolecular
complexes with crown ether derivatives was first evidenced
with commercially available benzo-18-crown-6 (14) by
NMR studies. The value found for the association constant
is quite low (2100 MK1 in CDCl3 at 298 K) but consistent
with association constants already reported for supramole-
cular associates resulting from ammonium–crown ether
interactions.20d,21 The assembly of the C60–ammonium
+
Figure 5. ES mass spectrum (VcZ50 V) recorded from a 2:1 mixture of 1 and 4 in CH2Cl2.

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N. Solladie et al. / Tetrahedron 62 (2006) 1979–1987
1985
+
Figure 6. ES mass spectra recorded at different Vc from a 2:1 mixture of 1 and 3 in CH2Cl2.
cation 1 with a porphyrin derivative bearing one crown ether
moiety (2) was also investigated. The NMR and UV–vis
binding studies revealed an interesting behavior. Effec-
tively, in addition to the ammonium–crown ether recog-
nition, intramolecular stacking of the fullerene moiety and
the porphyrin subunit has been evidenced. Due to this
additional recognition element, the association constant for
the supramolecular complex is increased by two orders of
magnitude when compared to the Ka values found for the
complexation of 1 with crown ether 14. Finally, more
complex non-covalent systems resulting from the asso-
ciation of cation 1 with porphyrin derivatives 3 and 4 bearing
two crown ether subunits were investigated. Intramolecular
C60–porphyrin interactions have also been evidenced within
the resulting supramolecular complexes. As a result, the 2:1
complexes are very stable as shown by the ES-MS studies.
These supramolecular arrays containing two fullerene
subunits appear to be particularly interesting candidates
for photophysical studies. Effectively, the beneficial effect
resulting from the presence of a second fullerene moiety on
the properties of C60-dumbbells has been recently high-
lighted by Martin and co-workers.22
were prepared as previously reported. All reactions were
performed in standard glassware under an inert Ar
atmosphere. Evaporation and concentration were done at
water aspirator pressure and drying in vacuo at 10K2 Torr.
Column chromatography: silica gel 60 (230–400 mesh,
0.040–0.063 mm) was purchased from Merck. Thin-layer
chromatography (TLC) was performed on glass sheets
coated with silica gel 60 F254 purchased from Merck,
visualization by UV light. UV–vis spectra were recorded on
a Hitachi U-3000 spectrophotometer. NMR spectra were
recorded on a Bruker AC 300 with solvent peaks as
reference. Elemental analyses were performed by the
analytical service at the Institut Charles Sadron, Strasbourg.
4.1.1. Compound 6. A 1 M LiAlH4 solution in dry THF
(4 mL, 4.0 mmol) was added dropwise to a stirred solution
of 5 (0.9 g, 3.39 mmol) in dry THF (100 mL) at 0 8C. The
resulting mixture was stirred for 5 h at 0 8C, then MeOH was
carefully added. The resulting mixture was filtered (Celite)
and evaporated. Column chromatography (SiO2, CH2Cl2/
2% MeOH) yielded 6 (0.75 g, 93%) as a colorless glassy
1
product. H NMR (300 MHz, CDCl3): 7.31 (AB, JZ7 Hz,
4H), 4.83 (broad s, 1H), 4.69 (d, JZ6 Hz, 2H), 4.31 (d, JZ
6 Hz, 2H), 1.67 (broad s, 1H), 1.46 (s, 9H); 13C NMR
(75 MHz, CDCl3): 155.9, 140.0, 138.2, 127.6, 127.2, 79.5,
64.9, 44.3, 28.3. Anal. Calcd for C13H19O3N: C 65.80,
H 8.07, N 5.90. Found: C 66.52, H 8.18, N 6.03.
In conclusion, this work paves the way toward the
construction of new stable non-covalent supramolecular
arrays combining porphyrin and fullerene units. Upon a
suitable choice of the molecular components, new supra-
molecular architectures displaying interesting photoinduced
intercomponent processes can be envisaged. Work in this
direction is under progress in our laboratories.
4.1.2. Compound 8. DCC (2.57 g, 12.6 mmol) was added to
a stirred solution of 6 (0.745 g, 3.14 mmol), 7 (1.94 g,
3.45 mmol) and DMAP (0.153 g, 1.26 mmol) in CH2Cl2
(100 mL) at 0 8C. After 1 h, the mixture was allowed to
slowly warm to room temperature (within 1 h), then stirred
for 12 h, filtered and evaporated to dryness. Column
chromatography (SiO2, CH2Cl2/hexane 4:1) yielded 8
(1.93 g, 78%) as a colorless oil. 1H NMR (300 MHz,
CDCl3): 7.28 (AB, JZ7 Hz, 4H), 6.46 (d, JZ2 Hz, 2H),
6.41 (t, JZ2 Hz, 1H), 5.16 (s, 2H), 5.09 (s, 2H), 4.84 (broad
s, 1H), 4.31 (d, JZ6 Hz, 2H), 3.91 (t, JZ7 Hz, 4H), 3.47 (s,
4. Experimental
4.1. General
Reagents and solvents were purchased as reagent grade and
used without further purification. THF was distilled over
sodium benzophenone ketyl. Compounds 5,11 7,12 and 1017

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N. Solladie et al. / Tetrahedron 62 (2006) 1979–1987
1986
2H), 1.75 (m, 4H), 1.44 (s, 9H), 1.30 (m, 36H), 0.88 (t, JZ
7 Hz, 6H); 13C NMR (75 MHz, CDCl3): 166.2, 160.4,
155.8, 139.3, 137.1, 134.3, 128.6, 127.6, 106.4, 101.1, 79.5,
68.1, 67.2, 66.9, 44.3, 41.5, 31.9, 29.65, 29.6, 29.5, 29.4,
29.3, 29.2, 28.4, 26.0, 22.7, 14.1.
6 Hz, 2H), 3.93 (m, 2H), 3.85 (m, 4H), 3.79 (m, 6H), 1.54 (s,
36H), 1.53 (s, 18H), K2.69 (broad s, 2H).
4.1.6. Compound 13. A 3.2 M solution of BF3$OEt2
(0.28 mL) in CHCl3 was added to a stirred mixture of 12
(804 mg, 3.68 mmol) and pyrrole (10 mL, 36.6 mmol) at
room temperature under argon. After 2 h, the resulting dark
brown solution was evaporated. The residue was dissolved
in CH2Cl2, washed with a 1 M aqueous NaOH solution (2!
) and evaporated. Column chromatography (SiO2, hexane/
CH2Cl2/Et3N 94:5:1) gave 13 (848 mg, 69%) as a brown oil.
1H NMR (CDCl3, 300 MHz): 7.87 (broad s, 2H), 7.49 (t, JZ
2 Hz, 1H), 7.22 (d, JZ2 Hz, 2H), 6.73 (m, 2H), 6.29 (m,
2H), 6.06 (m, 2H), 5.52 (s, 1H), 1.46 (s, 18H).
4.1.3. Compound 9. DBU (0.16 mL, 1.04 mmol) was added
to a stirred solution of C60 (300 mg, 0.41 mmol), I2 (116 mg,
0.45 mmol) and 8 (326 mg, 0.41 mmol) in toluene (500 mL)
at room temperature. The solution was stirred for 12 h at
room temperature, filtered through a short plug of SiO2
(toluene) and evaporated. Column chromatography (SiO2,
CH2Cl2/hexane 7:3) yielded 9 (0.71 g, 57%) as a dark brown
solid. UV–vis (CH2Cl2): 256 (125,500), 325 (35,900), 425
(3300), 688 (190); 1H NMR (300 MHz, CDCl3): 7.35 (AB,
JZ7 Hz, 4H), 6.56 (d, JZ2 Hz, 2H), 6.42 (t, JZ2 Hz, 1H),
5.47 (s, 2H), 5.39 (s, 2H), 4.87 (broad s, 1H), 4.32 (d, JZ
6 Hz, 2H), 3.89 (t, JZ7 Hz, 4H), 1.75 (m, 4H), 1.43 (s, 9H),
1.30 (m, 36H), 0.88 (t, JZ7 Hz, 6H); 13C NMR (75 MHz,
CDCl3): 163.3, 163.2, 160.4, 155.8, 145.1, 145.05, 145.0,
144.95, 144.85, 144.8, 144.6, 144.5, 144.4, 143.8, 143.7,
143.0, 142.9, 142.8, 142.1, 141.8, 141.7, 140.8, 140.7,
139.6, 139.1, 138.8, 136.4, 133.6, 129.1, 127.7, 107.0,
101.6, 79.5, 71.3, 68.8, 68.5, 68.1, 51.7, 44.3, 31.9, 29.7,
29.6, 29.4, 29.3, 29.2, 28.4, 26.1, 22.7, 14.1. Anal. Calcd for
C107H73O8N: C 85.64, H 4.90, N 0.93. Found: C 85.41, H
4.90, N 0.84.
4.1.7. Compounds 2, 3, and 4. A 3.2 M solution of
BF3$OEt2 (0.2 mL) in CHCl3 was added to a stirred solution
of 13 (334 mg, 1 mmol) and 10 (340 mg, 1 mmol) in CHCl3
(200 mL) at room temperature under argon. The resulting
dark red solution was stirred for 1 h and p-chloranil
(367 mg, 1.5 mmol) added. The mixture was then refluxed
for 1 h and evaporated. Column chromatography (SiO2)
gave 2 (eluent: CH2Cl2/MeOH 90:10, 54 mg, 14%), 3
(eluent: CH2Cl2/MeOH 88:12, 73 mg, 11%), 4 (eluent:
CH2Cl2/MeOH 85:15, 80 mg, 12%).
Compound 3. Dark purple solid. UV–vis (CH2Cl2): 422
(230,000), 519 (10,700), 546 (7300), 594 (6500), 645
(6600); 1H NMR (CDCl3, 300 MHz): 8.88 (s, 8H), 8.07 (d,
JZ2 Hz, 4H), 7.80 (t, JZ2 Hz, 2H), 7.77 (broad s, 2H),
7.74 (broad d, JZ7 Hz, 2H), 7.23 (d, JZ7 Hz, 2H), 4.46 (t,
JZ6 Hz, 4H), 4.29 (t, JZ6 Hz, 4H), 4.13 (t, JZ6 Hz, 4H),
3.97 (t, JZ6 Hz, 4H), 3.93 (m, 4H), 3.81 (m, 8H), 3.78 (m,
12H), 1.53 (s, 36H), K2.74 (broad s, 2H).
4.1.4. Compound 1. A solution of 9 (393 mg, 0.26 mmol)
and CF3CO2H (20 mL) in CH2Cl2 (40 mL) was stirred at
room temperature for 4 h. The mixture was then washed
with water, dried (MgSO4), filtered and evaporated to
dryness. Recrystallization from CH2Cl2/hexane yielded 1
(397 mg, 99%) as a dark brown solid. UV–vis (CH2Cl2):
1
257 (130,200), 326 (36,900), 425 (3200), 687 (180); H
NMR (300 MHz, CDCl3): 7.46 (AB, JZ8 Hz, 4H), 6.51 (d,
JZ2 Hz, 2H), 6.37 (t, JZ2 Hz, 1H), 5.46 (s, 2H), 5.37 (s,
2H), 4.16 (s, 2H), 3.86 (t, JZ7 Hz, 4H), 1.67 (m, 4H), 1.25
(m, 36H), 0.87 (t, JZ7 Hz, 6H); 13C NMR (75 MHz,
CDCl3): 163.4, 163.3, 160.4, 145.2, 145.1, 144.9, 144.6,
144.4, 143.8, 142.9, 142.1, 141.8, 141.7, 140.9, 140.8,
139.3, 138.6, 136.4, 136.1, 129.4, 129.1, 107.3, 101.8, 71.2,
69.0, 68.2, 51.6, 31.9, 29.7, 29.5, 29.4, 29.3, 26.2, 22.7,
14.2; FAB-MS: 1401.5 ([MKCF3COK2 ]C, calcd for
C102H66O6N: 1401.6). Anal. Calcd for C104H66O8NF3$0.8
CH2Cl2: C 79.54, H 4.31, N 0.89. Found: C 79.74, H 4.35, N
0.83.
Compound 4. Dark purple solid. UV–vis (CH2Cl2): 422
(280,000), 520 (19,400), 552 (14,300), 594 (9700), 646
(9500); 1H NMR (CDCl3, 300 MHz): 8.88 (m, 8H), 8.08 (d,
JZ2 Hz, 2H), 8.07 (d, JZ2 Hz, 2H), 7.81 (t, JZ2 Hz, 1H),
7.80 (t, JZ2 Hz, 1H), 7.78 (m, 2H), 7.74 (m, 2H), 7.23 (m,
2H), 4.46 (m, 4H), 4.29 (m, 4H), 4.12 (m, 4H), 3.97 (m, 4H),
3.90 (m, 4H), 3.82 (m, 8H), 3.78 (m, 12H), 1.54 (s, 18H),
1.53 (s, 18H), K2.73 (broad s, 2H).
4.2. ES-MS
Samples for ES-MS were prepared from stock solutions of
1, 2, 3, and 4 in CH2Cl2 to achieve a concentration of 10K5 M.
Positive ES mass spectra were obtained on an ES triple
quadrupole mass spectrometer Quattro II with a mass-to-
charge (m/z) ratio range extended to 8000 (Micromass,
Altrincham, UK). The electrospray source was heated to
40 8C. Sample solutions were introduced into the mass
spectrometer source with a syringe pump (Harvard type 55
1111: Harvard Apparatus Inc., South Natick, MA, USA)
with a flow rate of 3 mL minK1. The extraction cone voltage
(Vc) was systematically changed from 20 to 180 V.
Calibration was performed using protonated horse myo-
globin. Scanning was performed in the MCA (Multi
Channel Analyzer) mode, and several scans were summed
to obtain the final spectrum.
4.1.5. Compound 2. A 3.2 M solution of BF3$OEt2
(200 mL) in CHCl3 was added to a stirred solution of 10
(170 mg, 0.50 mmol), 11 (140 mL, 2.02 mmol) and 12
(331 mg, 1.51 mmol) in CHCl3 (200 mL) at room tempera-
ture under argon. The resulting solution was stirred for 1 h
and p-chloranil (382 mg, 1.56 mmol) added. The mixture
was then refluxed for 1 h and evaporated. Column
chromatography (SiO2, CH2Cl2/MeOH 90:10) gave 2
(75 mg, 13%) as a dark purple solid. UV–vis (CH2Cl2):
421 (455,000), 517 (16,500), 553 (9800), 592 (5300), 648
(5300); 1H NMR (CDCl3, 300 MHz): 8.90 (s, 8H), 8.09 (d,
JZ2 Hz, 4H), 8.08 (d, JZ2 Hz, 2H), 7.80 (t, JZ2 Hz, 2H),
7.79 (d, JZ2 Hz, 1H), 7.78 (t, JZ2 Hz, 1H), 7.76 (dd, JZ7,
2 Hz, 1H), 7.24 (d, JZ7 Hz, 1H), 4.47 (t, JZ6 Hz, 2H),
4.30 (t, JZ6 Hz, 2H), 4.14 (t, JZ6 Hz, 2H), 3.98 (t, JZ

´
N. Solladie et al. / Tetrahedron 62 (2006) 1979–1987
1987
Tat, F. T.; Jarowski, P. D.; Schuster, D. I. Chem. Commun.
2003, 226–227.
4.3. Determination of the association constant Ka by
NMR titration
´
7. Solladie, N.; Walther, M. E.; Gross, M.; Figueira Duarte,
T. M.; Bourgogne, C.; Nierengarten, J.-F. Chem. Commun.
2003, 2412–2413.
1
The H NMR binding studies were performed at 298 K in
CDCl3. The concentration of 1 was kept constant (0.5 mM).
Increasing amounts of 14 were added (0.2–2 mM; 12 data
points) and the chemical shift (d) of the aromatic protons in
1 were observed. The complexation-induced variation of the
chemical shift (Dd) was plotted against the concentration of
14. The complexation data (Ka, DG0, Ddsat) were obtained
by iteration using a nonlinear regression analysis curve-
fitting software developed in the laboratories of Prof.
Franc¸ois Diederich.23 The experiment was performed in
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