Synthesis and properties of novel fullerene derivatives having dendrimer units and the fullerenyl anions generated therefrom

Article abstract of DOI:10.1039/b201334g

Benzyl-ether type dendrimers from the first to fourth generations having a fullerene cage as an electroactive core, GnC₆₀H (n = 1-4), were synthesized using convergent methods. All dendrimers were highly soluble in common organic solvents. Thei

Full text of DOI:10.1039/b201334g

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Synthesis and properties of novel fullerene derivatives having
dendrimer units and the fullerenyl anions generated therefrom
Yasujiro Murata, Miho Ito and Koichi Komatsu*
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
E-mail: komatsu@scl.kyoto-u.ac.jp; Fax: 81 774 38 3178; Tel: 81 774 38 3172
Received 5th February 2002, Accepted 15th March 2002
First published as an Advance Article on the web 16th April 2002
Benzyl-ether type dendrimers from the first to fourth generations having a fullerene cage as an electroactive
core, GnC60H (n ~ 1–4), were synthesized using convergent methods. All dendrimers were highly soluble in
1
common organic solvents. Their structures in solution were investigated by H and 13C NMR and UV-vis
spectroscopy and molecular dynamics calculations. The presence of an attractive interaction between the
dendrimer moieties and the fullerene cage was proved by an upfield shift of the NMR signals and the
2
appearance of a new absorption in the UV-vis spectra. The electrochemical study indicated that GnC60
(n ~ 1–4) anions can be electrochemically generated and are further reduced to the trianion stage. Anions
2
GnC60 (n ~ 1–4) were subjected to chemical one-electron oxidation with iodine and gave new fullerene dimers
carrying a dendrimer unit on each fullerene cage.
Introduction
Results and discussion
The synthesis and characterisation of dendrimers, cascade
molecules, and related hyper-branched systems is currently
attracting great interest in the field of materials science.1
Dendrimers are nanosized hyperbranched macromolecules
with well-defined three-dimensional structures and are poten-
tial building blocks for the construction of organised functional
materials with nanosize precision. Incorporation of functional
cores such as photoactive2 and/or redox-active3 moieties at the
center of dendrimers is one of the important issues in den-
drimer chemistry particularly from the viewpoint of utilization
of these dendrimers as molecular devices.4
Fullerene C60 is a spherically p-conjugated all-carbon molecule5
which can accept six electrons successively in solution.6 Thus, it
is considered as one of the most attractive units for incor-
poration as a functional core in dendrimers. Actually, a C60
cage has been used as a core7 as well as branches8 of the
dendrimers. In all the dendrimers having a fullerene cage as a
core reported so far,7,8 the dendrons are connected to the C60
cages by a formal [2 1 1] cycloaddition like pattern A shown
in Chart 1, including carbon, nitrogen, and iridium elements
directly attached to the C60 cage. On the other hand, C60-based
dendrimers with the addition pattern B are quite intriguing
because the electronic and chemical properties of the central
Synthesis
We chose benzyl-ether type dendrons [Gn]-Br (n ~ 0–3) as
building blocks, expecting the occurrence of some attractive
interactions between the dendrons and the fullerene core.7e,11
An acetylene unit was selected as a bridge between the den-
drons and the fullerene core because ethynylated fullerenes
having various substituents at the other end of the triple bond
are known to be synthesized in relatively high yield.9c,10,12
Thus, 2,6-dihydroxyethnylbenzene (5) as the junction moiety
was synthesized from 2,6-dihydroxyacetophenone (1) by
protection of hydroxy groups, chlorovinylation, and dehydro-
chlorination, followed by desilylation, using the reported
procedure for the synthesis of 2-ethynyl-1,3-dimethoxyben-
zene,13 as shown in Scheme 1.
Fre´chet’s method of convergent approach14 was applied for
the synthesis of dendritic phenylacetylenes GnA (n ~ 1–4).
Coupling of 2 equiv. of dendritic benzyl bromide [Gn]-Br
(n ~ 0–3)14 with 5 was performed in refluxing acetone in the
C
60 cage should be dramatically changed by abstraction of the
proton directly attached to the C60 cage.9,10 In this paper, we
report synthesis, characterisation, structure, and electrochemical
properties of the first C60-based dendrimers having various
generations of dendrons with the addition pattern B.
Chart 1 Addition patterns of organic addends to fullerene C60
.
Scheme 1 Synthesis of 2,6-dihydroxyethnylbenzene 5.
DOI: 10.1039/b201334g
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presence of K2CO3 and 18-crown-6 to afford dendritic
phenylacetylene GnA (n ~ 1–4) in good yields as shown in
Scheme 2. Previously we noticed that the reaction of fullerene
monitored by the change in appearance of the mixture from a
brown suspension to a dark green solution. It was observed
that the acetylide with a smaller dendron reacted faster
reflecting the smaller steric effects of the dendrons, the
approximate times required for completion of the reaction
ranging from a few minutes to 30 minutes at room temperature.
The dendritic fullerenes GnC60H (n ~ 1–4) are highly soluble in
common organic solvents. Their structures were characterised
as 1,2-addition products with the ethynyl group and a proton
added at a 6,6-bond on the fullerene cage, as previously
reported for the various nucleophilic additions,9c,10,12 by 1H
C
60 with lithium acetylides in THF can afford the ethynylated
C60 in high yields after protonation although the solubility of
starting C60 in THF is negligibly low.10 Similarly, the reaction
of C60 with lithium acetylides generated from GnA (n ~ 1–4) in
THF gave the desired fullerene derivatives having dendrimer
units GnC60H (n ~ 1–4) in good yields as brown powders.
No isolable amount of bisadduct was produced in any of these
reactions. The reaction of the acetylides and C60 could be
Scheme 2 Synthesis of fullerene derivatives GnC60H (n ~ 1–4) having dendrimer units.
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and 13C NMR, UV-vis, and MALDI-TOF MS spectroscopies
and elemental analysis.
Structure of dendrimers GnC60H (n ~ 1–4) in solution
Fullerene derivatives GnC60H (n ~ 1–4) synthesized as des-
cribed above have flexible benzyl-ether type dendrons sur-
rounding the fullerene core. Benzyl-ether type dendrimers are
reported to be able to act as a host for fullerene C60.11 Although
the intermolecular association constants reported for the for-
mation of the complex of C60 with these dendrimers are not so
high,11 the intramolecular association would be preferable in
GnC60H (n ~ 1–4) since the dendrimer units are located in such
close proximity to the C60 cage. Thus, the structures of GnC60H
(n ~ 1–4) in solution were studied by the use of NMR and
UV-vis spectra and molecular dynamics simulations.15
The dendritic fullerenes GnC60H (n ~ 1–4) 1H NMR spectra
in CDCl3 showed that the signal for the proton directly
attached to the C60 cage was upfield shifted as the generation
number of the dendrimer increased: i.e., d 7.12 ppm for
G1C60H, 7.01 for G2C60H, 6.99 for G3C60H, and 6.95 for
G4C60H. The chemical shift of d 7.12 for G1C60H is com-
parable to the one for the corresponding proton of the
phenylethynyl-C60 derivative, Ph-CMC-C60-H (d 7.13).12a Thus,
the observed upfield shifts are attributed to the ring current
effect of the increasing number of benzene rings of benzyl-ether
type dendrons located near the RC60H proton.
In the 13C NMR spectra, 30 signals were observed for the sp2
carbons of the C60 cage, proving the presence of Cs symmetry
as depicted in Scheme 2. Fig. 1 (a) shows the sp2-carbon regions
of the 13C NMR spectra of GnC60H (n ~ 1–4) in CDCl3. The
averaged values of the chemical shifts of the 58 sp2 carbons
in the fullerene cage are 144.10 (Dd 0.00), 143.91 (Dd 20.19),
143.86 (Dd 20.25), and 143.80 (Dd 20.30), for G1C60H,
G2C60H, G3C60H, and G4C60H, respectively; the values in
parentheses are the differences in chemical shifts with reference
to that of G1C60H. Thus, an upfield shift increasing in the order
of the increasing generation number of the dendrimers is clearly
observed. The observed Dd values of 20.19, 20.25, and 20.30
are much larger than that reported for the intermolecular
complex of C60 with a benzyl-ether type dendrimer (Dd 20.003
at 25 uC).11b These results are taken as evidence that the
dendrimer units in GnC60H (n ~ 1–4) efficiently surround the
C60 cage located at the centre of the molecule by an attractive
interaction between the dendrimer units and the C60 cage in
solution.
In order to investigate which carbon in the C60 cage is
strongly influenced by the dendrimer units, the assignment of
each fullerene signal in the 13C NMR spectra was attempted by
comparison with the chemical shifts calculated by the use of
the GIAO method16,17 for the model compound, ethynylfuller-
ene 6. The structure of 6 was fully optimized with Cs symmetry
at the B3LYP/6-31G(d) level of theory and the GIAO calcu-
lations were conducted at the HF/6-311G(d,p) level using the
optimized geometry. The chemical shifts obtained by calcula-
tions are shown in Fig. 1 (b). The calculated 13C NMR chemi-
cal shifts are about 2 to 6 ppm more downfield shifted than the
experimental values, but the general tendency of the experi-
mental spectra are modestly well reproduced for GnC60H
(n ~ 1–4). By comparison of the calculated 13C NMR spectrum
for 6 with observed ones for GnC60H (n ~ 1–4), selected signals
for C1, C2, C3, C4, C27, C28, C29, and C30 (Fig. 1 (c)) were
assigned as shown in Fig. 1 (a). These assignments are in
good agreement with the reported ones for the osmylated C60
derivative with C2v symmetry experimentally determined by 2D
NMR.18
Fig. 1 13C NMR spectra of (a) dendrimers GnC60H (n ~ 1–4) observed
(75 MHz, CDCl3) and (b) model compound 6 calculated by GIAO
(SCF/6-311G(d,p)//B3LYP/6-31G(d)). The signals are numbered
based on the order of downfield shift and the corresponding carbons
are shown in (c).
according to the increase in the generation number of the
dendrimer, suggesting the presence of an attractive interac-
tion between the dendrimer units and the fullerene cage. The
selected carbon atoms are those closest to the saturated 6,6
bond (C1 and C2), those near the middle part of the cage (C27
and C28), and the furthest carbons from the saturated carbons
(C3 and C4). Among these carbons, C28 suffers the greatest
influence from the dendrimer units as shown by the greatest
change in Dd values, indicating that the probability of the
presence of the flexible dendrimer units is quite high near this
Based on the assignment described above, the chemical shifts
of selected carbons and the differences in chemical shifts with
reference to those of G1C60H are summarized in Table 1. The
upfield shifts of signals for all these carbons are observed
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Table 1 Observed chemical shifts (ppm) of sp2 carbons of the C60 cage for GnC60H (n ~ 1–4)
Compd C1 (Dd)a
C2 (Dd)a
C3 (Dd)a
C4 (Dd)a
C27 (Dd)a
C28 (Dd)a
C29 (Dd)a
C30 (Dd)a
G1C60
G2C60
G3C60
G4C60
H
H
H
H
151.99 (0.00)
151.93 (0.00)
147.65 (0.00)
147.39 (0.00)
140.46 (0.00)
140.29 (0.00)
136.18 (0.00)
135.20 (0.00)
151.80 (20.19) 151.76 (20.17) 147.51 (20.15) 147.26 (20.14) 140.25 (20.21) 139.94 (20.35) 136.01 (20.17) 135.05 (20.15)
151.72 (20.27) 151.69 (20.24) 147.49 (20.17) 147.24 (20.15) 140.23 (20.23) 139.85 (20.44) 135.92 (20.26) 135.00 (20.20)
151.71 (20.29) 151.67 (20.25) 147.40 (20.25) 147.17 (20.23) 140.19 (20.27) 139.80 (20.49) 135.87 (20.31) 134.95 (20.25)
aThe difference in chemical shifts (ppm) from that of G1C60H.
carbon. With respect to C3 and C4 which are furthest from the
saturated carbons, the upfield shifts are relatively small until
the third generation of the dendrimer and a considerable
upfield shift is observed for the fourth generation of the
dendrimer. This is attributed to the supposition that only the
fourth generation of the dendrimer can reach the bottom part
of the C60 cage.
The UV-vis spectra of GnC60H (n ~ 1–4) were measured in
o-dichlorobenzene (ODCB) in order to investigate the intra-
molecular electronic interaction between the dendrimer units
and the C60 cage, and are shown in Fig. 2. All the dendritic
fullerenes showed sharp absorptions at 435–436 nm and broad
absorptions at 704–708 nm, which are characteristic for C60
derivatives having a saturated 6,6-bond.19 To cancel out the
experimental errors in concentrations, absorbance corrections
using absorptions at 705 nm were applied to the spectra of all
dendrimers. Then the spectra of G1C60H and G2C60H were
found to be almost identical to each other. However, the
absorption around 436 nm is stronger for G3C60H and G4C60H
in the order of increasing generation number of the dendrimer.
This is supposed to be due to the intramolecular electronic
interaction between the benzyl ether moiety and the fullerene
cage.11b Thus, it is considered that fullerene derivatives
GnC60H (n ~ 1–4) have such structures that the flexible
dendrimer units surround the central fullerene cage in solution,
most efficiently in the case of G4C60H.
The effect of the solvent polarity upon the 1H NMR spectra
of G4C60H is expected to provide further evidence for the
intramolecular complexation. Fig. 3 shows the 1H NMR
spectra of G4C60H taken in CDCl3–CD3CN mixed solvents
of ratios varying from 1 : 0 to 1 : 2 by volume. In accord with the
increase in the solvent polarity, it was observed that the peaks
become broader and shift to the upfield region. This suggests
that the dendrimer units wrap the fullerene cage more tightly in
the more polar solvent system. A similar phenomenon has been
reported for the intramolecular folding of oligo(phenylene-
ethynylene) in a polar solvent.20
For the computational determination of minimum-energy
structures of dendrimers GnC60H (n ~ 1–4) at 0 K in the gas
phase, molecular dynamics (MD) simulations were carried out
with the MM1 forcefield implemented in the HYPERCHEM
program package15 to give the results shown in Fig. 4. The
Fig. 3 1H NMR (300 MHz) spectra of dendrimer G4C60H in different
solvent systems.
dense packing of the dendron branches around the fullerene
cage is clearly observed in all dendrimers. The presence of
favourable p–p stacking interactions is indicated by the face-to-
face arrangements of the fullerene cage with several aromatic
rings of the dendrons. Such interaction should have led to the
Fig. 2 UV-vis spectra (ODCB, 1 6 1024 M) of GnC60H (n ~ 1–4) after
absorbance correction at 705 nm.
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parentheses are shown the differences in chemical shifts with
reference to that of G1C602. The signal for the anion centre
carbon appears at 120.71 (Dd 0.00), 120.33 (Dd 20.38), 120.29
(Dd 20.42), and 119.79 (Dd 20.92) ppm, corresponding to
G1C602, G2C602, G3C602, and G4C602, respectively. Thus,
2
also in the series of dendritic fullerenyl anions GnC60 (n ~
1–4), the upfield shift of the signals was observed according to
the increase in the generation number of the attached dendrons
as has been observed for the neutral dendrimers GnC60H
(n ~ 1–4). It appears that the benzyl-ether dendrimer units in
anions GnC602 (n ~ 1–4) also surround the negatively charged
C60 cage by the attractive interaction between the dendrimer
units and the C60 cage in the solution.
In order to assign the signals of the 13C NMR spectra to
appropriate carbons, the GIAO (SCF/6-311G(d,p)//B3LYP/
6-31G(d)) calculations were conducted for ethynylfullerenyl
anion 72 with Na1 as a counter cation and for free anion 72 as
model compounds for the core of the dendrimer anions
GnC602. As shown in Fig. 5 (b), the calculated 13C NMR
chemical shifts for the ion pair Na172 exhibited slightly better
agreement with those obtained experimentally than those
calculated for free 72. From this result, these fullerenyl anions
are supposed to be present as ion pairs with the counter cation
rather than free ions in solution. Although the agreement of the
calculated 13C NMR chemical shifts with experimental values
is not sufficient to assign all the carbons, the selected signals for
C1, C2, C30, and C2 were assigned as shown in Fig. 5 (a) and
Table 2. Again, upfield shifts of these selected signals are seen
according to the increase of the generation number of the
dendrimer.
Fig. 4 Minimum energy structures at 0 K of GnC60H (n ~ 1–4) after
molecular dynamics (MD) simulation. All structures were premini-
mized with the MM1 forcefield implemented in HYPERCHEM15 prior
to the MD simulation. During the MD simulations the structures were
heated to 1000 K and kept at this temperature for equilibration before
they were allowed to cool to 0 K to establish the minimum energy
structure. Conditions7d for the simulated annealing: heat time: 5 ps, run
time: 50 ps, cool time: 50 ps, step size: 0.001 ps, starting temperature:
0 K, simulation temperature: 1000 K, final temperature: 0 K, in vacuo,
data collection period: 1 time step.
Electrochemical properties of the dendritic fullerenyl anions
The redox behaviour of dendritic fullerenes GnC60H (n ~ 1–4)
was examined by the use of cyclic voltammetry in ODCB. It has
been reported that deprotonation is induced by electrochemical
reduction of hydrofullerenes such as C60(CN)H.9e Similarly, it
pronounced wrapping of the fullerene core with the dendron
units.7d
2
was observed that fullerenyl anions GnC60 (n ~ 1–4) were
generated on the electrode when a cathodic scan was conducted
over the potential range beyond 21.5 V vs. Fc/Fc1. Thus, the
2
Generation of the dendritic fullerenyl anions
electrochemical properties of anions GnC60 (n ~ 1–4) gener-
ated in the CV cell by the treatment of ButOK were studied
instead of GnC60H (n ~ 1–4). The voltammograms observed
for all the dendritic fullerenes are shown in Fig. 6, and the data
are summarized in Table 3.
From the voltammograms shown in Fig. 6, a general ten-
dency was observed that the redox current gradually decreased
according to the increase of the generation number of the
dendrimer. This is considered to be due to the decrease of the
diffusion coefficients as has been reported for the dendrimers
containing ferrocene as a core unit.3h
In these dendrimers, the redox active central cores are fullerene
moieties having a highly acidic proton9 directly attached to the
fullerene cage. The electronic properties of the central core
should be greatly changed when it is transformed to the anion
by abstraction of the acidic proton. When THF solutions of the
dendrimers GnC60H (n ~ 1–4) were treated with one equivalent
of ButOK, the initial brown solutions immediately turned into
dark green, indicating the formation of fullerenyl anions10
2
GnC60 (n ~ 1–4) (Scheme 3). Accordingly, new absorptions
at lmax 634–638 and 959–964 nm appeared in the vis-NIR
spectra, supporting the generation of GnC602 (n ~ 1–4) anions.
No significant difference in the maximum absorptions was
observed among these dendrimers.
Apparently the most unusual features are concerned with the
2
redox cycle at the lowest potential. For example, anion G1C60
?
is oxidised to radical G1C60 at 20.48 V, but the corresponding
2
reduction peak is cathodically shifted to 21.15 V, the difference
of peak potentials being 0.67 V. This large negative shift of the
cathodic peak is ascribed to some chemical process associated
with the electron transfer, and this would most probably cor-
The formation of GnC60 (n ~ 1–4) anions were further
confirmed by the 1H NMR spectra in THF-d8, in which the
signal for the proton attached to the C60 cage disappeared while
signals for all other protons corresponding to the dendrimer
moieties remained.
?
respond to a rapid dimerization of G1C60 to G1C60–G1C60
On the other hand, the 13C NMR spectra of all GnC60
2
(Scheme 4). The reduction of dimer G1C60–G1C60 to the
original monomeric anion G1C602 requires extra energy for the
bond dissociation and also for a subtle structural change in
(n ~ 1–4) anions indicated that they have Cs symmetry as
shown by the number of signals (30 signals) for the fullerenyl
sp2 carbons (Fig. 5 (a)). As has been reported previously,10
these signals of the fullerenyl anions exhibit a general downfield
shift as compared with those of the neutral molecules GnC60H
(n ~ 1–4). The averages of the chemical shifts of the 58 sp2
carbons (30 signals) are 147.01 (Dd 0.00), 146.89 (Dd 20.12),
146.89 (Dd 20.12), and 146.55 (Dd 20.46), corresponding to
G1C602, G2C602, G3C602, and G4C602, respectively: in the
the C60 framework, which could have caused the cathodic shift
as has been reported.10 The next two reductions (Ered1 and Ered
2
)
were nearly reversible as observed by individual redox waves at
E1/2 21.49 and 21.91 V, respectively. Other dendritic fullerenyl
2
anions GnC60 (n ~ 2–4) exhibited the same redox behaviour
as described above in spite of the larger size of the dendron
moiety. This fact indicates that the presence of such a sterically
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2
Scheme 3 Generation of fullerenyl anions having dendrimer units, GnC60 (n ~ 1–4).
demanding group as the fourth-generation dendrimer unit
cannot prevent the dimerization of the fullerenyl radical.
As to the values of the redox potentials, no systematic
change was observed depending on the generation number of
the attached dendron moieties.
been reported for singly bonded dimers.21 Thus, the presence of
the equilibrium between monomeric G4C60 and dimeric
G4C60–G4C60 was confirmed.
?
In exactly the same way, dimer G3C60–G3C60 was synthe-
sized in 41% yield, for which the MALDI-TOF MS spectrum
showed a molecular ion peak at 4615 (M2) and the ESR
spectrum displayed a broad ESR signal (g ~ 2.0023, peak-to-
peak width ~ 1.074 G). The 1H NMR of these dimers dis-
played very complicated spectra suggesting that they are
mixtures of meso and racemic structures.21b
In order to confirm that the formation of such a sterically
congested molecule as dimer G4C60–G4C60 is possible, the
molecular dynamics calculations of G4C60–G4C60 in both the
1,4- and 1,6-addition patterns were carried out. The results are
shown in Fig. 8. Thus, in spite of the presence of a seemingly
large addend the two C60 cages can be connected by a single
bond in the fashion of 1,4- or 1,6-addition patterns, owing
to the great flexibility of the benzyl-ether type dendrimer
structure.
Synthesis of fullerene dimers
Since the formation of dimers GnC60–GnC60 (n ~ 1–4) on the
electrode was suggested by cyclic voltammetry, macroscopic
synthesis of the dimers was expected to be possible. Thus, the
chemical one-electron oxidation was attempted for the full-
erenyl anion bearing the largest dendron as an addend. When
the anion G4C602 was generated by deprotonation of G4C60H
with ButOK in THF and was then oxidized with iodine, the
separation by gel permeation chromatography (GPC) gave
dimer G4C60–G4C60 as a brown powder in 40% yield (Scheme 5)
together with some small amounts of G4C60H and a higher-
molecular-weight compound of unknown structure. The struc-
ture of dimer G4C60–G4C60 was confirmed by the MALDI-TOF
MS spectrum shown in Fig. 7, which clearly displays the
molecular ion peak at 8010 (M2) in addition to fragment peaks
Conclusion
2
at 4004 and 720 corresponding to G4C60 and C60, respec-
tively.
A series of fullerene derivatives having benzyl-ether type
dendrons, GnC60H (n ~ 1–4), were newly synthesized. All
dendrimers are highly soluble in common organic solvents.
1H and 13C NMR and UV-vis spectroscopy and molecular
dynamics calculations indicated the presence of certain attrac-
tive interactions between the dendrimer moieties and the
When a benzene solution of dimer G4C60–G4C60 was sub-
jected to ESR measurement, a single-line signal (g ~ 2.0023,
peak-to-peak width ~ 1.073 G) was observed, which most
?
probably corresponds to the fullerenyl radical G4C60 , as has
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prepared and was found to be in equilibrium with the radical
?
G4C60 as confirmed by ESR measurements. The MD calcu-
lations indicated that the dendron moieties do not prohibit
dimerization of the radical although they tend to wrap the
fullerene core efficiently. This is ascribed to the flexibility of the
benzyl-ether type dendrons.
This work was supported by a Grant-in-Aid for COE
Research on Elements Science (no. 12CE2005) from the
Ministry of Education, Culture, Sports, Science and Techno-
logy, Japan.
Experimental
General
All reagents and solvents were of commercial quality and were
dried where necessary using standard procedures. All reactions
were performed in standard glassware under an argon atmo-
sphere. Dendrimer units [Gn]-OH and [Gn]-Br (n ~ 0–3) were
synthesized according to the reported procedure.14 Thin layer
chromatography was performed on plastic plates coated
with 0.2 mm thickness of silica gel 60 F254 (Merck). Medium
pressure column chromatography (MPLC) was conducted by
using silica gel 60 (230–400 mesh, Merck) columns and a
Yamazen YFLC-540 pump. Recycling preparative gel permea-
tion chromatography (GPC) was performed on a JAI LC-908
chromatograph equipped with JAIGEL-1H and -2H GPC
columns using CHCl3 as an eluent. Elemental analyses were
performed at the Microanalysis Division of Institute for
Chemical Research, Kyoto University. UV-vis spectra (lmax
in nm (log e)) were measured on a Shimadzu UV-2100PC spec-
1
trometer. H NMR spectra were recorded on Varian Mercury
300 and JEOL JNM-AL300 spectrometers; chemical shifts (d)
are quoted in ppm, relative to tetramethylsilane as an internal
reference (0 ppm), and coupling constants (J) are quoted in Hz.
MALDI-TOF mass spectra were obtained on an Applied
Biosystems Voyager-DE STR spectrometer using dithranol as
a matrix. FAB mass and EI mass spectra were obtained on a
JEOL MStation JMS-700 spectrometer using 3-nitrobenzyl
alcohol as a matrix in the case of FAB. Cyclic voltammetry
(CV) was performed on a BAS CV-50W Voltammetric Ana-
lyser. The counter, working, and reference electrodes were Pt
wire, glassy carbon, and Ag/AgNO3, respectively. All solutions
were purged with argon and retained under an argon atmo-
sphere whilst the measurements were carried out. The poten-
tials were corrected against ferrocene used as an internal
standard added after each measurement.
Molecular Dynamics (MD) simulations were conducted
using HYPERCHEM 6, Hypercube Inc.15 All structure were
preminimized with the MM1 forcefield implemented in
HYPERCHEM prior to the MD simulation. During the MD
simulations the structures were heated to 1000 K and kept
at this temperature for equilibration before they were allowed
to cool to 0 K to establish the minimum energy structure.
Conditions7d for the annealing: heat time, 5 ps; run time, 15 ps;
cool time, 50 ps; step size, 0.001 ps; starting temperature, 0 K;
simulation temperature, 1000 K; final temperature, 0 K;
in vacuo; data collection period, 1 time step.
For the ab initio calculations, all the geometry optimizations
and single-point NMR chemical shift calculations were carried
out using the Gaussian 98 program.22 The Cs symmetry was
imposed throughout the calculations of 6, 72 and Na172. All
13C chemical shifts are referenced to those of TMS calculated at
the same level.
Fig. 5 13C NMR spectra of (a) dendritic GnC60 (n ~ 1–4) observed
2
(75 MHz, THF-d8) and (b) model compounds Na172 and free 72
calculated by GIAO (SCF/6-311G(d,p)//B3LYP/6-31G(d)). The sig-
nals are numbered based on the order of downfield shift and the
corresponding carbons are shown in (c).
fullerene cage. The electrochemical study indicated that
2
GnC60 (n ~ 1–4) anions can be electrochemically generated
and are further reduced to the trianion stage. The formed
anions were found to undergo facile dimerization upon re-
oxidation even when the fullerene core carried a large (G3 to
G4) dendritic addend. The dimer G4C60–G4C60 was chemically
2,6-Bis(tert-butyldimethylsilyloxy)acetophenone (2)
To a solution of 2,6-dihydroxyacetophenone (1) (1.00 g,
6.60 mmol) in dry N,N-dimethylforamide (10 cm3) was added
tert-butyldimethylchlorosilane (2.01 g, 13.31 mmol) and
J. Mater. Chem., 2002, 12, 2009–2020
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2
Table 2 Observed chemical shifts (ppm) of sp2 carbons of the C60 cage for GnC60 (n ~ 1–4)
Compd
C1 (Dd)a
C2 (Dd)a
C30 (Dd)a
C2 (Dd)a
2
G1C60
G2C60
G3C60
G4C60
175.27 (0.00)
158.95 (0.00)
135.46 (0.00)
120.71 (0.00)
2
2
2
174.91 (20.36)
174.72 (20.55)
174.11 (21.16)
158.60 (20.35)
158.53 (20.42)
158.09 (20.86)
135.27 (20.19)
135.23 (20.23)
134.87 (20.59)
120.33 (20.38)
120.29 (20.42)
119.79 (20.92)
2
aThe difference in chemical shifts (ppm) from that of G1C60
.
Scheme 5 Synthesis of fullerene dimers, G3C60–G3C60 and G4C60
G4C60.
–
imidazole (1.79 g, 26.30 mmol), and the solution stirred at 60 uC
for 20 h. The resulting mixture was then poured into water and
extracted with diethyl ether. The extract was washed with
brine, dried over MgSO4, and evaporated to afford 2.4 g (96%)
of 2 as a white solid (Analysis found: C, 63.23; H, 9.63;
C20H36O3Si2 requires: C, 63.10; H, 9.53%); m/z (1FAB) 381
(M1 1 1); dH (CDCl3) 7.04 (1 H, t, J 8.4), 6.44 (2 H, d, J 8.4),
Fig. 6 Cyclic voltammograms of fullerenyl anions GnC602 (n ~ 1–4) in
ODCB (c ~ 1 mM): scan rate, 0.1 V s21; supporting electrolyte,
Bu4NBF4 (0.1 M).
Table 3 Results of cyclic voltammetrya
1
2
Compd
Epa
Epc
Ered
Ered
2
G1C60
G2C60
G3C60
G4C60
20.48
20.54
20.51
20.49
21.15
21.20
21.21
21.23
21.49
21.54
21.53
21.53
21.91
21.93
21.93
21.92
2
2
2
aPotential in volts vs. ferrocene/ferrocenium in ODCB with Bu4NBF4
as a supporting electrolyte (0.1 M); scan rate, 0.1 V s21
.
Fig. 7 MALDI-TOF MS (negative-ion, dithranol) of G4C60–G4C60
.
2
Scheme 4 Electrochemical reactions of GnC60 (n ~ 1–4) on the electrode.
2016
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resulting mixture was then poured into water and extracted
with diethyl ether. The extract was washed with brine and dried
over Na2SO4. The solvent was removed in vacuo to afford
150 mg of 5 in quantitative yield as a pale yellow solid, which
was found to be unstable and was used for further reactions
without purification; dH (CDCl3) 7.15 (1 H, t, J 8.2), 6.52 (2 H,
d, J 8.2), 5.56 (1 H, br), 3.80 (1 H, s); dC (CDCl3) 157.66,
131.37, 106.94, 96.84, 90.49, 73.84.
General procedure for the synthesis of phenylacetylene
derivatives having dendrimer units
A mixture of the appropriate dendritic benzyl bromide [Gn]-Br
(n ~ 0–3) (2.2 equiv.), 2,6-dihydroxy-1-ethynylbenzene (5)
(1.0 equiv.), potassium carbonate (2.5 equiv.), and 18-crown-6
(0.2 equiv.) in dry acetone was heated at reflux and stirred
vigorously for 20–48 h. The mixture was allowed to cool, added
to water and extracted with dichloromethane. The extracts
were dried over Na2SO4 and evaporated to dryness. The crude
product was purified as outlined below.
Fig. 8 Minimum energy structures at 0 K of 1,4- and 1, 6 derivatives
of G4C60–G4C60 after molecular dynamics (MD) simulation. All
structures were preminimized with the MM1 forcefield implemented in
HYPERCHEM15 prior to the MD simulation. During the MD
simulations the structures were heated to 1000 K and kept at this
temperature for equilibration before they were allowed to cool to 0 K to
establish the minimum energy structure. Conditions7d for the simulated
annealing: heat time, 5 ps; run time, 50 ps; cool time, 50 ps; step size,
0.001 ps; starting temperature, 0 K; simulation temperature, 1000 K;
final temperature, 0 K; in vacuo; data collection period, 1 time step.
G1A
This compound was prepared from [G0]-Br and purified by
MPLC [SiO2, hexane–ethyl acetate (7 : 1 v/v)] to give G1A
(84%) as a colourless oil (Analysis found: C, 84.05; H, 5.78;
C22H18O2 requires: C, 84.05; H, 5.77%); m/z (1EI) 314 (M1);
dH (CDCl3) 7.46–7.27 (10 H, m), 7.09 (1 H, t, J 8.5), 6.50 (2 H,
d, J 8.5), 5.14 (4 H, s), 3.54 (1 H, s); dC (CDCl3) 161.17, 136.81,
129.85, 128.41, 127.64, 126.73, 105.57, 101.99, 85.80, 76.18,
70.41.
2.46 (3 H, s), 0.95 (18 H, s), 0.20 (12 H, s); dC (CDCl3) 202.65,
152.61, 129.47, 126.66, 112.02, 32.38, 25.54, 18.02, 24.39.
2,6-Bis(tert-butyldimethylsilyloxy)-1-(1-chloroethenyl)benzene
(3)
G2A
To a solution of 2 (508 mg, 1.33 mmol) in dry benzene (3 cm3)
was added phosphorus trichloride (0.63 cm3, 7.22 mmol) and
phosphorus pentachloride (340 mg, 1.63 mmol), and the
solution stirred at room temperature for 20 h. The resulting
mixture was then poured into ice-water and extracted with
diethyl ether. The extract was washed with brine and dried over
MgSO4. The solvent was removed in vacuo and the residue was
chromatographed (SiO2, hexane) to give 206 mg (39%) of 3 as a
white solid (Analysis found: C, 59.92; H, 8.92; C20H35ClO2Si2
requires: C, 60.19; H, 8.84%); m/z (1FAB) 397 (M1); dH
(CDCl3) 7.07 (1 H, t, J 8.2), 6.50 (2 H, d, J 8.2), 5.68 (1 H, d,
J 0.9), 5.34 (1 H, d, J 0.9), 1.05 (18 H, s), 0.27 (12 H, s); dC
(CDCl3) 154.22, 133.36, 129.36, 123.16, 118.29, 111.93, 25.65,
18.17, 24.21.
This compound was prepared from [G1]-Br and purified by
GPC (CHCl3) to give G2A (68%) as a colourless oil (Analysis
found: C, 81.25; H, 5.72; C50H42O6 requires: C, 81.23; H,
5.73%); m/z (1FAB) 739 (M1 1 1); dH (CDCl3) 7.43–7.31 (10
H, m), 7.12 (1 H, t, J 8.7), 6.74 (4 H, d, J 2.4), 6.55 (2 H, t, J 2.4),
6.51 (2 H, d, J 8.7), 5.13 (4 H, s), 5.03 (8 H, s), 3.49 (1 H, s); dC
(CDCl3) 161.04, 160.04, 139.35, 136.70, 130.00, 128.53, 127.94,
127.52, 105.56, 105.44, 101.79, 101.41, 85.67, 76.38, 70.26,
69.98.
G3A
This compound was prepared from [G2]-Br and purified by
MPLC [SiO2, toluene–ethyl acetate (20 : 1 v/v)] to give G3A
(71%) as a colourless oil (Analysis found: C, 80.07; H, 5.69;
C
106H90O14 requires: C, 80.18; H, 5.71%); m/z (1MALDI-
2,6-Bis(tert-butyldimethylsilyloxy)-1-ethynylbenzene (4)
TOF) 1609 (M1 1 Na); dH (CDCl3) 7.38–7.13 (40 H, m), 7.05
(1 H, t, J 8.4), 6.69 (4 H, d, J 2.1), 6.43 (8 H, d, J 2.1), 6.53 (4 H,
t, J 2.1), 6.50 (2 H, t, J 2.1), 6.44 (2 H, d, J 8.4), 5.03 (16 H, s),
4.95 (8 H, s), 4.91 (4 H, s), 3.50 (1 H, s); dC (CDCl3) 161.03,
160.01, 159.89, 139.32, 139.15, 136.65, 128.94, 128.46, 128.13,
127.88, 127.70, 127.46, 106.21, 105.52, 101.74, 101.44, 85.84,
76.44, 70.22, 69.93, 69.80.
To a stirred solution of 3 (2.34 g, 5.86 mmol) in dry THF
(10 cm3) was added a 2.0 M solution of lithium diisopropyl-
amide in THF (14.7 cm3, 29.4 mmol) at 278 uC and the
solution stirred at 0 uC for 3 h. The resulting mixture was then
poured into water and extracted with diethyl ether. The extract
was washed with saturated NH4Cl solution and dried over
Na2SO4. The solvent was removed in vacuo and the residue was
chromatographed [SiO2, hexane–toluene (97 : 3 v/v)] to give
1.47 g (69%) of 4 as a white solid (Analysis found: C, 66.11; H,
9.60; C20H34O2Si2 requires: C, 66.24; H, 9.45%); m/z (1EI) 362
(M1); dH (CDCl3) 7.02 (1 H, t, J 8.2), 6.45 (2 H, d, J 8.2), 3.30
(1 H, s), 1.02 (18 H, s), 0.22 (12 H, s); dC (CDCl3) 158.55,
129.17, 112.69, 108.20, 84.89, 78.17, 25.77, 18.30, 24.24.
G4A
This compound was prepared from [G3]-Br and purified by
MPLC [SiO2, toluene–ethyl acetate (25 : 1 v/v)] to give G4A
(92%) as a colourless oil (Analysis found: C, 80.19; H, 5.71;
C218H186O30 requires: C, 79.69; H, 5.71%); m/z (1MALDI-
TOF) 3308 (M1 1 Na); dH (CDCl3) 7.43–7.16 (80 H, m), 7.03
(1 H, t, J 8.1), 6.68 (4 H, d, J 2.1), 6.64 (16 H, d, J 2.1), 6.62 (8 H,
d, J 2.1), 6.53 (8 H, t, J 2.1), 6.51 (2 H, t, J 2.1), 6.50 (4 H, d,
J 2.1), 6.42 (2 H, d, J 8.1), 5.02 (4 H, s), 4.97 (32 H, s), 4.90
(24 H, s), 3.51 (1 H, s); dC (CDCl3) 161.08, 160.09, 159.99,
139.24, 139.17, 136.79, 128.53, 127.95, 127.53, 106.34, 101.55,
85.11, 77.22, 70.04, 69.93.
2,6-Dihydroxy-1-ethynylbenzene (5)
To a stirred solution of 4 (406 mg, 1.12 mmol) in THF (3 cm3)
was added acetic acid (0.15 cm3) and a 1.0 M solution of
tetrabutylammonium fluoride in THF (2.43 cm3, 2.43 mmol),
and the solution stirred at room temperature for 1 h. The
J. Mater. Chem., 2002, 12, 2009–2020
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General procedure for the synthesis of GnC60H (n ~ 1–4)
145.98, 145.65, 145.44, 145.29, 145.24, 145.12, 145.07, 144.46,
144.30, 142.78, 142.34, 142.21, 141.93, 141.88, 141.79, 141.66,
141.39, 141.34, 140.19, 139.80, 139.22, 139.12, 139.09, 136.74,
135.87, 134.95, 130.40, 128.51, 127.92, 127.49, 106.44, 106.01,
102.68, 101.60, 101.27, 77.21, 70.97, 70.04, 69.98, 62.08, 55.69.
To a vigorously stirred suspension of fullerene C60 (50–100 mg)
in THF (7–15 cm3), obtained by irradiation in a ultrasonic bath
for 60 min, was added at room temperature the appropriate
lithium acetylide (2 equiv.), prepared from GnA (n ~ 1–4) and
BunLi in THF. The mixture was stirred for 30 min, during
which time the color changed into dark green. To the mixture
was added two drops of trifluoroacetic acid to give a dark
brown suspension. The solvent was removed in vacuo and the
crude product was purified as outlined below.
General procedure for the generation and measurement of 1H and
2
13C NMR spectra of GnC60 (n ~ 1–4) anions
A solution of ButOK in THF (1.1 equiv.) was added to GnC60H
(n ~ 1–4) (17–23 mg, 0.005–0.02 mmol) in a glass tube (outer
diameter, 8 mm) equipped with an NMR tube as a side arm
under an argon atmosphere to give a dark green solution. The
whole system was connected to a vacuum line, and the solvent
was evaporated. To the residue was added THF-d8 (0.8 cm3,
distilled over Na mirror) by vacuum distillation and the whole
system was subjected to a freeze–pump–thaw cycle three times.
The whole system was sealed under vacuum (v 1024 mmHg).
The solution was transferred into the NMR tube, which was
sealed off and subjected to NMR measurements.
G1C60H
This compound was prepared from G1A and purified by
MPLC [SiO2, CS2–toluene (5 : 1 v/v)] to give G1C60H (52%) as
a brown powder (Analysis found: C, 95.12; H, 1.69; C82H18O2
requires: C, 95.16; H, 1.75%); m/z (–MALDI-TOF) 1034 (M2);
vis (ODCB) 435 (3.70), 705 (2.6); dH (CDCl3) 7.67 (4 H, d,
J 6.9), 7.38–7.23 (7 H, m), 7.11 (1 H, s), 6.77 (2 H, d, J 8.4), 5.32
(4 H, s); dC (CDCl3) 161.25, 151.99, 151.93, 147.65, 147.39,
146.79, 146.42, 146.25, 145.93, 145.64, 145.48, 145.40, 144.75,
144.61, 143.23, 142.60, 142.58, 142.18, 142.08, 142.05, 141.73,
141.63, 140.46, 140.29, 136.97, 136.18, 135.20, 130.41, 128.51,
127.85, 126.81, 105.85, 102.77, 100.61, 77.18, 70.65, 62.13,
55.78.
2
G1C60
This anion was prepared from G1C60H; dH (THF-d8) 7.89 (4 H,
d, J 8.1), 7.33–7.24 (5 H, m), 7.13 (2 H, t, J 7.2), 6.86 (2 H, d,
J 8.4), 5.38 (4 H, s); dC (THF-d8) 175.25, 162.16, 158.95, 154.39,
152.62, 152.41, 151.53, 151.33, 150.69, 150.18, 148.09, 147.96,
146.91, 146.72, 145.80, 145.75, 144.98, 144.58, 143.71, 143.68,
143.52, 143.31, 143.20, 142.65, 141.19, 139.54, 138.94, 138.75,
138.49, 135.46, 130.10, 129.33, 128.08, 127.47, 120.71, 107.11,
106.26, 101.20, 80.16, 71.22, 54.79.
G2C60H
This compound was prepared from G2A and purified by
MPLC [SiO2, CS2–toluene (1 : 1 v/v)] to give G2C60H (68%) as
a brown powder (Analysis found: C, 90.30; H, 2.88; C110H42O6
requires: C, 90.52; H, 2.90%); m/z (–MALDI-TOF) 1458 (M2);
vis (ODCB) 435 (3.67), 705 (2.6); dH (CDCl3) 7.36–7.15 (21 H,
m), 7.01 (1 H, s), 6.87 (4 H, d, J 2.4), 6.73 (2 H, d, J 8.4), 6.49
(2 H, t, J 2.4), 5.22 (4 H, s), 4.97 (8 H, s); dC (CDCl3) 161.15,
160.08, 151.80, 151.76, 147.51, 146.75, 146.26, 146.21, 146.10,
145.75, 145.62, 145.40, 145.33, 145.23, 145.19, 144.58, 144.40,
142.95, 142.44, 142.37, 142.03, 141.96, 141.87, 141.76, 141.52,
141.44, 140.25, 139.94, 139.19, 136.61, 136.00, 135.05, 130.37,
128.53, 127.94, 127.53, 106.49, 105.90, 102.70, 101.46, 101.25,
77.19, 70.96, 70.03, 62.09, 55.71.
2
G2C60
This anion was prepared from G2C60H; dH (THF-d8) 7.35 (8 H,
d, J 6.9), 7.25–7.15 (13 H, m), 6.92 (4 H, d, J 2.1), 6.74 (2 H, d, J
8.7), 6.49 (2 H, t, J 2.1), 5.41 (4 H, s), 5.02 (8 H, s); dC (THF-d8)
174.91, 162.32, 161.39, 158.60, 154.26, 152.52, 152.32, 151.42,
151.19, 150.61, 150.05, 148.05, 147.84, 146.82, 146.61, 145.67,
144.90, 144.44, 143.65, 143.56, 143.40, 143.18, 141.38, 141.15,
139.44, 138.73, 138.58, 138.48, 135.27, 129.79, 129.15, 128.50,
128.36, 120.33, 108.37, 106.77, 102.46, 101.93, 80.25, 72.26,
70.73, 56.18.
G3C60H
2
This compound was prepared from G3A and purified by
MPLC (SiO2, toluene) to give G3C60H (67%) as a brown
powder (Analysis found: C, 86.66; H, 3.85; C166H90O14
requires: C, 86.37; H, 3.93%); m/z (–MALDI-TOF) 2307
(M2); vis (ODCB) 436 (3.64), 707 (2.5); dH (CDCl3) 7.39–7.16
(41 H, m), 6.99 (1 H, s), 6.87 (4 H, d, J 2.4), 6.76 (2 H, d, J 8.7),
6.60 (8 H, d, J 2.1), 6.50 (4 H, t, J 2.1), 6.47 (2 H, t, J 2.1), 5.20
(4 H, s), 4.96 (16 H, s), 4.90 (8 H, s); dC (CDCl3) 161.14, 160.04,
159.98, 151.72, 151.69, 147.49, 147.24, 146.69, 146.22, 146.15,
146.08, 145.71, 145.49, 145.33, 145.31, 145.19, 145.12, 144.53,
144.36, 142.85, 142.42, 142.29, 141.97, 141.94, 141.84, 141.69,
141.44, 141.40, 140.23, 139.85, 139.12, 138.99, 136.61, 135.92,
135.00, 130.41, 128.55, 127.98, 127.57, 125.26, 106.40, 105.83,
102.45, 101.44, 101.26, 77.20, 70.92, 70.03, 69.92, 62.07, 55.66.
G3C60
This anion was prepared from G3C60H; dH (THF-d8) 7.35–7.12
(41 H, m), 6.91 (4 H, d, J 2.1), 6.76 (2 H, d, J 8.4), 6.66 (8 H, d,
J 2.1), 6.48 (2 H, t, J 2.1), 6.47 (4 H, t, J 2.1), 5.37 (4 H, s), 4.96
(24 H, s); dC (THF-d8) 174.72, 162.42, 161.33, 161.25, 158.53,
154.28, 152.50, 152.32, 151.38, 151.17, 150.60, 150.06, 149.98,
148.15, 147.85, 146.82, 146.62, 145.66, 144.93, 144.45, 143.69,
143.61, 143.44, 143.20, 143.15, 142.57, 141.28, 141.18, 141.03,
139.46, 138.67, 138.58, 138.48, 135.23, 129.92, 129.21, 128.96,
128.47, 128.41, 120.19, 108.43, 107.10, 106.72, 106.60, 106.25,
102.54, 102.28, 102.11, 80.36, 72.39, 70.70, 56.06.
2
G4C60
This anion was prepared from G4C60H; dH (THF-d8) 7.35–7.09
(81 H, m), 6.91 (4 H, d, J 2.1), 6.70 (2 H, d, J 8.4), 6.65 (8 H, d, J
2.4), 6.64 (16 H, d, J 2.4), 6.50 (8 H, t, J 2.1), 6.48 (2 H, t, J 2.1),
6.46 (4 H, t, J 2.1), 5.32 (4 H, s), 4.95 (24 H, s), 4.89 (24 H, s); dC
(THF-d8) 174.11, 162.03, 160.97, 160.91, 160.83, 158.09,
153.93, 152.04, 151.95, 150.99, 150.80, 150.22, 146.71, 149.61,
147.83, 147.51, 146.51, 146.28, 145.32, 145.28, 144.63, 144.14,
143.35, 143.30, 143.15, 142.88, 142.80, 142.27, 140.94, 140.87,
140.70, 140.59, 140.41, 139.14, 138.31, 138.27, 138.19, 134.87,
129.50, 128.97, 128.91, 128.74, 128.70, 128.67, 128.30, 128.24,
128.19, 128.06, 127.94, 127.84, 119.79, 106.95, 106.85, 106.53,
102.47, 102.26, 102.07, 80.30, 72.28, 70.71, 70.57, 55.98.
G4C60H
This compound was prepared from G4A and purified by
MPLC [SiO2, CS2–diethyl ether (40 : 1 v/v)] to give G4C60H
(76%) as a brown powder (Analysis found: C, 83.38; H, 4.80;
C
278H186O30 requires: C, 83.34; H, 4.68%); m/z (–MALDI-
TOF) 4005 (M2); vis (ODCB) 436 (3.71), 708 (2.5); dH (CDCl3)
7.38–7.12 (81 H, m), 6.95 (1 H, s), 6.84 (4 H, d, J 2.1), 6.68 (2 H,
d, J 8.7), 6.61 (16 H, d, J 2.1), 6.56 (8 H, d, J 2.1), 6.52 (8 H, t,
J 2.1), 6.47 (2 H, t, J 2.1), 6.45 (4 H, t, J 2.1), 5.12 (4 H, s), 4.95
(32 H, s), 4.85 (24 H, s); dC (CDCl3) 161.19, 160.08, 160.00,
151.71, 151.67, 147.40, 147.17, 146.65, 146.15, 146.07, 146.01,
2018
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1997, 1215; (i) M. Plevoets, F. Vo¨gtle, L. De Cola and V. Balzani,
New J. Chem., 1999, 23, 63; (j) F. Vo¨gtle, M. Plevoets, M. Nieger,
G. C. Azzellini, A. Credi, L. De Cola, V. De Marchis, M. Venturi
and V. Balzani, J. Am. Chem. Soc., 1999, 121, 6290.
(a) P. J. Dandliker, F. Diederich, M. Gross, C. B. Knobler,
A. Louati and E. M. Sadford, Angew. Chem., Int. Ed. Engl., 1994,
33, 1739; (b) G. R. Newkome, R. Guther, C. N. Moorefield,
F. Cardullo, L. Echegoyen, E. Perez-Cordero and H. Luftmann,
Angew. Chem., Int. Ed. Engl., 1995, 34, 2023; (c) P. J. Dandliker,
F. Diederich, J.-P. Gisselbrecht, A. Louati and M. Gross, Angew.
Chem., Int. Ed. Engl., 1995, 34, 2725; (d) H.-F. Chow, I. Y.-K.
Chan, D. T. W. Chan and R. W. M. Kwok, Chem. Eur. J., 1996, 2,
1085; (e) R. Sadamoto, N. Tomioka and T. Aida, J. Am. Chem.
Soc., 1996, 118, 3978; (f) P. Bhyrappa, J. K. Young, J. S. Moore
and K. S. Suslick, J. Am. Chem. Soc., 1996, 118, 5708;
(g) C. B. Gorman, B. L. Parkhurst, W. Y. Su and K.-Y. Chen,
J. Am. Chem. Soc., 1997, 119, 1141; (h) C. M. Cardona and
A. E. Kaifer, J. Am. Chem. Soc., 1998, 120, 4023.
General procedure for the generation and the measurement of
2
vis-NIR spectra of GnC60 (n ~ 1–4) anions
One drop of diazabicyclo[5.4.0]undec-7-ene (ca. 7 mg, ca.
50 mmol) was added to a solution of GnC60H (n ~ 1–4) in
ODCB under an argon atmosphere to give a dark green
solution. The solution was transferred to a 10 mm cell under a
nitrogen atmosphere and subjected to measurement.
2
G1C60
2
3
4
This anion was generated from G1C60H (1.038 mg, 1.003 6
1023 mmol) in ODCB (10 cm3); vis-NIR (ODCB) 542 (3.47),
638 (3.63), 963 (3.44).
2
G2C60
This anion was generated from G2C60H (1.562 mg, 1.070 6
1023 mmol) in ODCB (10 cm3); vis-NIR (ODCB) 540 (3.47),
637 (3.61), 964 (3.40).
2
G3C60
This anion was generated from G3C60H (1.154 mg, 4.999 6
1024 mmol) in ODCB (5 cm3); vis-NIR (ODCB) 543 (3.47), 636
(3.61), 959 (3.39).
2
G4C60
This anion was generated from G4C60H (1.603 mg, 4.001 6
1024 mmol) in ODCB (4 cm3); vis-NIR (ODCB) 543 (3.47), 636
(3.61), 959 (3.39).
General procedure for the generation and CV measurement of
2
GnC60 (n ~ 1–4) anions
A solution of ButOK in THF (0.0945 M, 0.03 cm3, 1 equiv.)
was added to a 1 mM solution of GnC60H (n ~ 1–4) in 0.1 M
solution of Bu4NBF4 in ODCB (2.0 cm3) under an argon
atmosphere to give a dark green solution. The solution was
subjected to the measurement of cyclic voltammetry.
(a) S. Hechet and J. M. J. Fre´chet, Angew. Chem. Int. Ed., 2001, 40,
75; (b) C. M. Cardona, S. Mendoza and A. E. Kaifer, Chem. Soc.
Rev., 2000, 29, 37.
A. Hirsch, The Chemistry of the Fullerenes, Thieme, New York,
1994.
5
6
7
Q. Wie, E. Perez-Cordero and L. Echegoyen, J. Am. Chem. Soc.,
1992, 114, 3978.
Dimer G3C60–C60G3
(a) K. L. Wooley, C. J. Hawker and J. M. J. Fre´chet, J. Am. Chem.
Soc., 1993, 115, 9836; (b) C. J. Hawker, K. L. Wooley and
J. M. J. Fre´chet, J. Chem. Soc., Chem. Commun., 1994, 925; (c)
J.-F. Nierengarten, T. Habicher, R. Kessinger, F. Cardullo,
F. Diederich, V. Gramlich, J.-P. Gisselbrecht, C. Boudon and
M. Gross, Helv. Chim. Acta, 1997, 80, 2238; (d) X. Camps,
H. Scho¨nberger and A. Hirsch, Chem. Eur. J., 1997, 3, 561;
(e) V. J. Catalano and N. Parodi, Inorg. Chem., 1997, 36, 537;
(f) X. Camps and A. Hirsch, J. Chem. Soc., Perkin Trans. 1, 1997,
1595; (g) M. Brettreich and A. Hirsch, Tetrahedron Lett., 1998, 39,
2731; (h) X. Camps, E. Dietel, A. Hirsch, S. Pyo, L. Echegoyen,
S. Hackbarth and B. Ro¨der, Chem. Eur. J., 1999, 5, 2362; (i) Y.
Rio, J.-F. Nicoud, J.-L. Rehspringer and J.-F. Nierengarten,
Tetrahedron Lett., 2000, 41, 10207; (j) A. Herzog, A. Hirsch and
O. Vostrowsky, Eur. J. Org. Chem., 2000, 171; (k) M. Schwell,
N. K. Wachter, J. H. Rice, J.-P. Galaup, S. Leach, R. Taylor and
R. V. Bensasson, Chem. Phys. Lett., 2001, 339, 25.
To a solution of G3C60H (10.2 mg, 4.42 6 1023 mmol) in THF
(5 cm3) was added a 0.0945 M solution of ButOK in THF
(0.051 cm3, 4.7 6 1023 mmol) at room temperature under
an argon atmosphere to give a dark green solution and the
solution stirred at room temperature for 10 min. To the
reaction mixture was added a 0.0039 M solution of iodine in
THF (0.56 cm3, 2.2 6 1023 mmol) at room temperature. The
solvent was removed in vacuo and the residue was purified by
GPC to afford 4.1 mg (41%) of G3C60–C60G3 as a brown solid;
m/z (–MALDI-TOF) 4615 (M2); dH (CDCl3) 7.45–7.10 (m),
6.63–6.30 (m), 5.10–4.65 (m).
Dimer G4C60–C60G4
To a solution of G4C60H (15.6 mg, 3.89 6 1023 mmol) in THF
(5 cm3) was added a 0.0945 M solution of ButOK in THF
(0.045 cm3, 4.3 6 1023 mmol) at room temperature under an
argon atmosphere to give a dark green solution and the solu-
tion stirred at room temperature for 10 min. To the reaction
mixture was added a 0.0039 M solution of iodine in THF
(0.52 cm3, 2.0 6 1023 mmol) at room temperature. The solvent
was removed in vacuo and the residue was purified by GPC
to give 5.6 mg (40%) of G4C60–C60G4 as a brown solid; m/z
(–MALDI-TOF) 8010 (M2); dH (CDCl3) 7.36–7.21 (m), 6.67–
6.26 (m), 5.09–4.58 (m).
8
(a) J.-F. Nierengarten, D. Felder and J.-F. Nicoud, Tetrahedron
Lett., 1999, 40, 269; (b) J.-F. Nierengarten, D. Felder and J.-F.
Nicoud, Tetrahedron Lett., 1999, 40, 273; (c) J.-F. Nierengarten,
D. Felder and J.-F. Nicoud, Tetrahedron Lett., 2000, 41, 41;
(d) D. Felder, H. Nierengarten, J.-P. Gisselbrecht, C. Boudon,
E. Leize, J.-P. Nicoud, M. Gross, A. V. Dorsselaer and
J.-F. Nierengarten, New J. Chem., 2000, 24, 687; (e) J.-F.
Nierengarten, Chem. Eur. J., 2000, 6, 3667.
(a) P. J. Fagan, P. J. Krusic, D. H. Evans, S. A. Lerke and
E. Johnston, J. Am. Chem. Soc., 1992, 114, 9697; (b) M. E.
Niyazymbetov, D. H. Evans, S. A. Lerke, P. A. Cahill and C. C.
Henderson, J. Phys. Chem., 1994, 98, 13093; (c) P. Timmerman,
H. L. Anderson, R. Faust, J. L. Nierengarten, T. Habicher,
P. Seiler and F. Diederich, Tetrahedron, 1996, 52, 4925; (d) R. G.
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9
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