Creation of cyclic π-electron-conjugated systems through the functionalization of fullerenes and synthesis of their multinuclear metal complexes

Article abstract of DOI:10.1246/bcsj.81.320

This account article describes the synthesis of a cyclic benzenoid system, [10]cyclophenacene, using a one-step deca-fold addition reaction to [60]fullerene, and a double-decker buckyferrocene complex, [(FeCp) ₂(C₆₀Me₁₀)]. Luminescent and electronic communication properties for each material may give us new opportunities to study photo- and electrochemical functional materials. Theoretical studies on electronic structure of finite-length single-walled carbon nanotubes are also described with respect to the structure of cyclophenacenes.

Full text of DOI:10.1246/bcsj.81.320

320 Bull. Chem. Soc. Jpn. Vol. 81, No. 3, 320–330 (2008)
Ó 2008 The Chemical Society of Japan
Award Accounts
The Chemical Society of Japan Award for Young Chemists for 2005
Creation of Cyclic ꢀ-Electron-Conjugated Systems
through the Functionalization of Fullerenes and
Synthesis of Their Multinuclear Metal Complexes
Yutaka Matsuo
Nakamura Functional Carbon Cluster Project, ERATO, Japan Science and Technology Agency,
Hongo, Bunkyo-ku, Tokyo 113-0033
Received September 10, 2007; E-mail: matsuo@chem.s.u-tokyo.ac.jp
This account article describes the synthesis of a cyclic benzenoid system, [10]cyclophenacene, using a one-step
deca-fold addition reaction to [60]fullerene, and a double-decker buckyferrocene complex, [(FeCp)2(C60Me10)]. Lumi-
nescent and electronic communication properties for each material may give us new opportunities to study photo- and
electrochemical functional materials. Theoretical studies on electronic structure of finite-length single-walled carbon
nanotubes are also described with respect to the structure of cyclophenacenes.
tems [n]cyclacene8a,11 and [n]cyclophenacene8 (Fig. 1), which
can be formally generated by rolling a one-dimensional graph-
1. Introduction
The design and construction of functional molecules that can
act as active components in organic devices has received a great
deal of attention in recent years.1 In particular, incorporation of
fullerenes in such molecules has been a focus of this field due to
rich inherent functions of fullerenes, such as extraordinary elec-
tron affinity,2 small reorganization energy,3 and photo-respon-
sive properties,4 and nano-size structures can be used to modify
the fullerene structure. Chemical modification of fullerenes
by addition of organic and inorganic groups is a major approach
to prepare fullerene derivatives, which have functions of the
organic groups, the metal atoms, and fullerenes themselves.
Among the derivatives, multi-functionalized products that bear
these addends at defined positions on the fullerene sphere make
it possible to prepare stereochemically defined large structures.
In addition, selective multi-functionalization enables us to per-
form selective detraction5 of the spherical conjugation system
of fullerene, leading to the construction of new curved ꢀ-
conjugated systems. Such a new class of benzenoids provides
a scaffold to construct multi-metal fullerene complexes6 and
an opportunity to study the structure of single-walled carbon
nanotubes (SWCNTs).7 This account article describes the syn-
thesis of belt-shaped cyclic ꢀ-electron-conjugated benzenoid
systems, [10]cyclophenacenes (10 benzene rings arrange in a
cyclic way),8 by the destruction of ten double bonds of [60]full-
erene.9,10 Synthesis of dinuclear metal complexes and a theoret-
ical study on SWCNTs are also described in this article.
ite network into a ring, are an interesting class of compounds.
These benzenoid systems have attracted the interest of chem-
ists and physicists for 50 years, ever since Heilbronner’s pre-
diction,8 because of questions about their resonance structure
and chemical reactivities as well as their physical properties
and potential applications in materials science. They have also
become the subject of recent interest of the broader scientific
community, because they are a subunit of carbon nanotubes.
Such belt-shaped benzenoids, however, have remained a hypo-
thetical species despite a number of synthetic attempts.12
Spherical ꢀ-electron-conjugated system of [60]fullerene
contains a belt-shaped ꢀ-electron-conjugated system, [10]-
cyclophenacene (Fig. 2). We thought that belt-shaped aromatic
conjugation could be created by removal of two [5]radialene
ꢀ-electron-conjugated structures (20ꢀ-electrons) at the both
poles of [60]fullerene. We chose this unconventional synthetic
2. Syntheses and Structural Studies of Cyclic
ꢀ-Conjugated Systems, [10]Cyclophenacenes
Belt-shaped cyclic ꢀ-electron-conjugated benzenoid sys-
Fig. 1. Belt-shaped benzenoid systems.
Published on the web March 13, 2008; doi:10.1246/bcsj.81.320

Y. Matsuo
Bull. Chem. Soc. Jpn. Vol. 81, No. 3 (2008)
321
Scheme 1. One-step deca-addition of aryl groups to [60]fullerene. Isomers always form with respect to the relative location of the
hydrogen atom in the pentagon surrounded by five aryl groups. Only one isomer is shown in this figure.
Fig. 2. Detraction of the ꢀ-electron-conjugated system of
[60]fullerene.
strategy, which is opposite from ordinary building up methods
from small ꢀ-electron-conjugated systems. Our synthesis re-
lies on the selective addition of organic groups to the fullerene
Fig. 3. Absorption and emission (excited at ꢁ ¼ 366 nm)
ꢀ-conjugated system. Five-fold addition of an organocopper
spectra of 1–3. Emission spectra are shown in arbitrary
reagent, reported by Nakamura, Sawamura, et al. ten years
ago, to [60]fullerene selectively afforded a penta-adduct, C60-
unit. Inset: pictures of photoluminescence for 1–3.
Ar5H,13 and thus, we became intrigued by the possibility of
achieving a ten-fold addition to synthesize deca(organo)[60]-
fullerenes, C60Ar10H2, that have [10]cyclophenacene.
dryness, and methanol was added to obtain an orange solid.
The orange solid was collected by filtration and added to a
mixed solvent (toluene/acetonitrile = 5/5) to obtain a yellow
suspension, and then, the yellow precipitate was collected and
washed three times with the same mixed solvent to obtain 1
(570 mg, 20%) as yellow powder. There are three isomers of
compound 1, due to the relative location of two hydrogen
atoms.
It was found that pyridine is necessary for this organocopper
addition reaction to [60]fullerene. Although the detailed mech-
anism remains unclear, we think that weak coordination of
pyridine to the Cu atom of a plausible reaction intermediate,
Cu–C60Ar5, makes this reaction possible. A pyridine complex,
pyridine–Cu–C60Ar5, may form, preventing this intermediate
from reacting with more organocopper reagent to form an
intermediate ate complex, Ar–Cuꢃ–C60Ar5. The neutral pyri-
dine–Cu–C60Ar5 complex possibly undergoes further nucleo-
philic addition on the bottom of fullerene, whereas nucleo-
philic addition reaction to the ate complex Ar–Cuꢃ–C60Ar5
may not take place due to the negative charge of the top part
of the fullerene.
One-step deca-fold arylation reaction with the use of
organocopper reagents in the presence of pyridine took place
onto the top and bottom of [60]fullerene to produce the cyclo-
phenacene derivatives, deca-aryl adduct C60Ar10H2 (1: Ar =
4-n-BuC6H4; compounds with Ar = Ph, 4-t-BuC6H4, 4-MeC6-
H4, 4-PhC6H4, etc. were also synthesized) in 20%–30% yield
(Scheme 1). The reaction also afforded a side addition product
2, which will be discussed in the next section. A typical proce-
dure is described below: To a suspension of CuBr SMe2 (8.64
ꢀ
g, 42 mmol) in THF (44 mL) was added a solution of 4-n-
BuC6H4MgBr (0.95 M, 45 mL, 42 mmol) in THF, pyridine
(34 mL), and a solution of [60]fullerene (1.0 g, 1.4 mmol) in
1,2-dichlorobenzene (40 mL). Note that the pyridine/THF/
1,2-Cl2C6H4 ratio was ca. 1:2:1. The resulting dark brown
suspension was gradually warmed to 40 ꢁC over 30 min.
After stirring for 40 h, the reaction was monitored by HPLC
(Develosil RPFullerene, eluent: toluene/acetonitrile = 5/5),
which showed the formation of 1 (retention time 6.5 min)
and its regioisomer 2 (see next section, retention time 9.2
min). The reaction was quenched with sat. NH4Cl (aq.) (ꢂ1
mL) and HCl (aq.) (ꢂ1 mL), followed by the removal of vola-
tile solvent under reduced pressure. The residual mixture was
diluted with toluene or CS2 (ꢂ200 mL) and filtered through a
pad of silica gel. An orange-colored eluent was concentrated to
Deca-aryl adduct 1 has a belt-shaped 40ꢀ-electron-conju-
gated system. This unique ꢀ-electron-conjugated system was
found to be chemically stable, and it fluoresced at ꢁmax
¼
562 and 612 nm (bimodal, quantum yield ꢂ ¼ 0:18) (Fig. 3).
Fullerenes are known not to be fluorescent (ꢂ ¼ 0:00032).14
The quantum yield for the present compound is the highest

322 Bull. Chem. Soc. Jpn. Vol. 81, No. 3 (2008)
AWARD ACCOUNTS
Fig. 4. Fused corannulenes. (a) The parent compound C30H12 (A). (b) Dibenzo-fused corannulene C38H16 (B) and p-phenylene-
bridged dibenzo-fused corannulene C44H20 (C). (c) Dibenzo-fused corannulene embedded into fullerene framework (2). (d) p-
Phenylene-bridged dibenzo-fused corannulene in fullerene framework (3). Color coding shows NICS-based aromaticity of the
rings (red and dark red: aromatic, NICS < ꢃ4:0. blue: non-aromatic, NICS > ꢃ4:0).
value among those for various fullerene derivatives.5a,15 The
photophysical properties of this unconventional ꢀ-electron-
conjugated system will be an interesting subject in the applica-
tion studies on organic electroluminescent devices. Aromaticity
of the cyclophenacene part was elucidated by using DFT cal-
ꢄ
culations (B3LYP/6-31G ), and the negative NICS (Nucleus
independent chemical shift)16 values for ten benzene rings
were ca. ꢃ11:5.
3. Another Unconventional ꢀ-Electron-Conjugated System
Large ꢀ-conjugated aromatic molecules have long attracted
chemists’ attention for a variety of reasons. Planar polycon-
Fig. 5. Selectivity of the bottom functionalization. (a) The
densed aromatic compounds17 belong to one class and spheri-
reaction affording 1. (b) The reaction affording 2 and 3.
cal fullerene molecules to another. Bowl-shaped condensed
aromatic compounds18 topologically link these two extremes
and have received considerable attention. Fused corannulene
(phenanthro[3,4-a:5,6-d]corannulene, C30H12, A, Fig. 4) is
an archetype of the bowl-shaped molecules and was synthe-
sized sometime ago from flat precursors.19 However, the yield
was low due to elaborate multi-step reactions. Given its effi-
ciency, which was demonstrated with the synthesis of the belt-
shaped aromatic compound,9 selective detraction of the ꢀ-
electron system of a spherical fullerene molecule is expected
to be a powerful synthetic route to bowl-shaped molecules.
We synthesized in one step two derivatives 2 and 3 of dibenzo-
fused corannulene B and its p-phenylene derivative C. The
overall yield of both compounds was ꢂ60% based on [60]full-
erene, which was enough material to investigate the structures
and properties of the fused corannulene compounds.
Compound 2, consisting of six regioisomers is relation to
the hydrogen atoms, was obtained from the pyridine-modified
deca-addition reaction, as described in the previous section
(Scheme 1). This reaction exclusively afforded 1 and 2 as a
ca. 1:2 mixture. The regioselectivity arises during the sixth ad-
dition of the ArCu reagent, which can take place either via
path (a) or path (b) shown in Fig. 5. In path (a), the sixth Ar
group is placed next to the carbon atom of the bottom penta-
gon, and then, the seventh to tenth Ar groups are placed around
the bottom pentagon to produce 1. In path (b), the sixth Ar
group attaches to the bottom carbon atom to produce 2. The
1:2 product ratio is ascribed to both the steric congestion of
the Ar groups and the high reactivity of the bottom five carbon
atoms. Compound 2 has a much higher solubility than that of 1
in common organic solvents; therefore, 2 can be easily separat-
ed from the mixture. Compound 2, which has a dibenzo-fused
corannulene-type curved ꢀ-electron-conjugated system, was
found to be luminescent and showed blue emission at ꢁmax
463 and 491 nm (Fig. 3). The luminescent quantum yield, ꢂ,
of 2 was 0.065.
¼
A phenylene-bridged dibenzo-fused corannulene-type ꢀ-
electron-conjugated system is comprised of an octaaryl[60]full-
erene derivative that has five aryl groups on the top part of full-
erene and three aryl groups on another hemisphere. Octa-ad-
duct 3 forms when the reaction leading to 2 prematurely finish-
es after the addition of the eighth Ar group. The use of a large
excess of pyridine (60% v/v pyridine) was a synthetically vi-
able procedure that afforded octa-adduct 3 (50%) and deca-ad-
duct 1 (35%) (Scheme 2). Thus, the addition reaction first pro-
duces the cyclopentadienide anion of the penta-adduct, from
which deca-adduct 1 and octa-adduct 3 form. Further addition
of two aryl groups to 3 produces deca-adduct 2. This last reac-
tion must be difficult, because of steric congestion of the reac-
tion sites flanked by many aryl groups. We think that the reac-
tion to produce 2 from 3 is slower, likely due to low solubility
of the intermediate 3 in a 60% pyridine solution. Note that
compound 3 was smoothly converted into 2 in 90% yield by
the reaction of 3 with ArMgBr (30 molar amount) and CuBr
ꢀ
SMe2 (30 molar amount) in the presence of 1,4-dicyclohexyl-
1,4-diaza-1,3-butadiene (30 molar amount) in THF/o-dichloro-
benzene (1/1). Compound 3 has a bowl-shaped structure with
a cyclic p-phenylene-type ꢀ-system. This hybrid ꢀ-system
was found to emit red light at ꢁmax ¼ 652 and 715 nm with

Y. Matsuo
Bull. Chem. Soc. Jpn. Vol. 81, No. 3 (2008)
323
Scheme 2. Reaction yielding octa(aryl)[60]fullerenes.
Scheme 3. Electrophilic addition affording hepta(organo)[60]fullerenes.
ꢂ ¼ 0:015 (Fig. 3). From a comparison with the luminescence
maximum wavelengths of 1 (560 nm), the emission of 2 is
ꢂ100 nm blue-shifted and that of 3 is ꢂ100 nm red-shifted,
respectively. It should be noted that the p-phenylene-bridge
between the two benzene edges of the dibenzo-fused corannu-
lene ꢀ-conjugated system causes a large (200 nm) red-shift
for 3 compared to 2. Luminescence wavelengths reflect the
HOMO–LUMO gaps of each compound. Present result indi-
cates that luminescent properties of fullerene derivatives are
sensitively controlled by the location of the addends attached
to fullerene.
(" ¼ 5:03 ꢅ 103 Mꢃ1 cmꢃ1). Trianion 4 was useful nucleo-
philes (Scheme 3). Upon treatment of a black-green THF solu-
tion of 4 with excess molar amount of a benzylic halide at
25 ꢁC, the solution color change to dark red, and subsequent
protonation with aqueous HCl afforded a doubly alkylated
product as the predominant product. Hepta-adduct 5 was iso-
lated as a red crystalline solid, and it weakly luminesced at
ꢁmax ¼ 623 nm. This alternative method for destruction of
the ꢀ-system can be applied to metal-penta(organo)[60]full-
erene complexes9f and will be further expanded to other full-
erene ꢀ-systems.
Addition of nucleophiles to a fullerene is one method of
multi-functionalization as described. Another way to function-
alize a fullerene is electrophilic alkylation using fullerene
4. Syntheses and Electrochemistry of
Double-Decker Buckyferrocenes
2ꢃ
anions.20 For instance, fullerene-dianion C60
reacts with
Another interesting point of the cyclophenacene derivatives
is that it is possible to synthesize dinuclear metal complexes
since there are two cyclopentadiene parts on the top and bot-
tom of [60]fullerene. Synthesis and properties of dinuclear
metal complexes linked by ꢀ-electron-conjugated system have
been subjects of interests in recent years owing to the potential
applications in molecular-level electronics.21 Electronic inter-
actions between two metal centers have been examined for
various ꢀ-electron-conjugated systems as linkers: polyene,22
polyphenylenes,23 polyynes,24 cumulene,25 and polyaromat-
ics.26 Although [60]fullerene and its derivatives are considered
to be an ideal three-dimensional ꢀ-electron bridge between
multi-metal centers,27,28 electronic interactions between two
metal centers through the fullerene cage had not been evaluat-
ed, to the best of our knowledge, because most fullerene metal
benzyl bromide affording C60(CH2Ph)2.20b We applied this re-
action to penta(organo)[60]fullerenes to obtain unconventional
ꢀ-electron-conjugated systems.9c Thus, we chemically reduced
C60Ar5H (Ar = biphenyl and phenyl) and utilized the result-
ing trianions for substrates in the electrophilic addition to ob-
tain hepta(organo)[60]fullerenes C60Ar5R2H (R = CH2Ph
and CHPh2) that contain new curved ꢀ-electron-conjugated
systems.
Treatment of C60Ar5H with excess amount of potassium
metal in THF at 25 ꢁC afforded a dark green solution of penta-
aryl[60]fullerene-trianion [Kþ(thf)n]3[C60Ar53ꢃ] (4). After
removal of THF, an air and moisture sensitive black-green
powder of 4 was obtained. Trianion 4 exhibited absorbed
at ꢁmax ¼ 545 nm (" ¼ 5:17 ꢅ 103 Mꢃ1 cmꢃ1) and 692 nm

324 Bull. Chem. Soc. Jpn. Vol. 81, No. 3 (2008)
AWARD ACCOUNTS
Scheme 4. Syntheses of the double-decker buckyferrocenes 8 and 10.
complexes29 reported in the literature usually undergo cleav-
purification (Scheme 4, lower equation).32 The product has a
highly symmetric D5d structure, the same point group that
(5,5)-armchair carbon nanotubes have.
age of the fullerene–metal bond during redox cycles. We syn-
thesized di-iron [60]fullerene complexes, [(FeCp)2(C60R10)]
(Cp = C5H5), which have two ferrocene moieties embedded
on the top and bottom of [60]fullerene (Scheme 4) and evalu-
ated the electronic interaction between two irons through
the fullerene skeleton. We called these compounds ‘‘double-
decker buckyferrocenes.’’
The di-iron complexes were characterized by 1H and
13C NMR, high-resolution APCI-TOF mass spectra, and X-
ray single-crystal analyses (Figs. 6 and 7). X-ray analyses of 8
and 10 showed that the alternating bond pattern, characteristic
of [10]cyclophenacene,9 was not disturbed by the metal com-
plexation. Small bond alternation in the equatorial region of
[60]fullerene was observed similar to our previous non-
metallic [10]cyclophenacene derivatives.9 The fluorescence
observed in 1 and 6 was not observed in the buckyferrocenes,9
because of the heavy atom effect.
Multi-step reduction and oxidation behaviors of these di-
iron fullerene complexes were investigated. The double-decker
buckyferrocenes retain the basic electrochemical behaviors of
ferrocene and [60]fullerene and were found to undergo rever-
sible four-electron redox processes. Despite the equivalent en-
vironment of the two iron atoms in the decamethyl compound
10, cyclic voltammetry (CV) and differential pulse voltamme-
try (DPV) measurement exhibited a pair of resolved oxidation
waves. This observation indicates that two iron atoms interact
with each other through the fullerene ꢀ-electron-conjugated
system (vide infra). We consider that this dimetallic fullerene
molecule may provide useful information for the future study
of single molecular devices.
We synthesized the target compounds through two different
routes. In the first route, we started with the previously report-
ed cyclophenacene compound 6,9a which is obtained by using
a four-step functionalization reactions of [60]fullerene. A di-
rect FeCp transfer reaction that was used for the synthesis of
buckyferrocenes 730 was employed for the synthesis of the
double-decker buckyferrocenes. Treatment of 6 with a 5 molar
amount of [FeCp(CO)2]2 in PhCN at 185 ꢁC afforded in a
single step a C5v symmetric pentamethyl–pentaphenyl double-
decker buckyferrocene, [(FeCp)2(C60Me5Ph5)] (8), in 26%
isolated yield (Scheme 4). We think that electron transfer from
the iron(I) complex to the fullerene derivative occurred first,
followed by intramolecular electron transfer to the cyclopenta-
dienyl moieties.31 This would lead to the loss of a hydrogen
atom, and eventually, 8 would be produced. Treatment of
decaaryl[60]fullerenes, such as 1, did not afford the di-iron
complexes, because of their relatively low solubility and low
reactivity.
The second route yielded an interesting decamethyl com-
pound. This route relies on stepwise methylation and complex-
ation reactions on the top and bottom of [60]fullerene, because
of the difficulty in the preparation of decamethyl precursors,
C60Me10H2. Thus, pentamethyl buckyferrocene Fe(C60Me5)Cp
(7) was treated with a methylcopper reagent in a pyridine/
THF/o-dichlorobenzene solution to obtain Fe(C60Me10H)Cp
(9), and then precursor 9 was reacted with [FeCp(CO)2]2 in
PhCN to afford a decamethyl double-decker buckyferrocene,
[(FeCp)2(C60Me10)] (10), in 3% isolated yield after HPLC
CV measurement of 10 exhibited a pair of slightly overlap-
ping but separated oxidation waves (Fig. 8). This separation of
oxidation potential was clearly confirmed with DPV study
(0.06 and 0.17 V vs. Fc/Fcþ (ferrocene/ferrocenium)) (Fig. 9).
The 110 mV difference in the two oxidation potentials (ꢀE) is
comparable to those of phenylene-linked diferrocenes (ꢀE ¼
131, 90, and 104 mV for o-, m-, and p-C6H4),23b,23c but larger
than that of a biphenylene-linked diferrocene (ꢀE ¼ 70
mV).23b,23c The appearance of two oxidation waves is indica-
tive of electronic interaction between iron atoms across the

Y. Matsuo
Bull. Chem. Soc. Jpn. Vol. 81, No. 3 (2008)
325
Fig. 6. X-ray crystal structure of 8. PhCl molecules in the
crystal packing are omitted for clarity. (a) ORTEP draw-
ing. (b) CPK model structure.
Fig. 8. Cyclic voltammogram of the decamethyl double-
decker buckyferrocene 10.
Fig. 7. X-ray crystal structure of 10. PhCl molecules in the
crystal packing are omitted for clarity. (a) ORTEP draw-
ing. (b) CPK model structure.
Fig. 9. Differential pulse voltammogram of the decamethyl
double-decker buckyferrocene 10.
bridging fullerene core via endohedral homo conjugation.31
DFT calculations on the model compound [(FeCp)2(C60H10)]
also showed endohedral homo conjugation between the cyclo-
pentadienide and the [10]cyclophenacene parts. Hence, the
fullerene cage of 10 is still a good ꢀ-electron bridge in spite
of the interruption of the sp2 conjugation by the ten sp3 carbon
atoms.
Complex 8 with C5v symmetry in PhCN showed two two-
electron oxidation waves at 0.08 and 0.36 V (vs. Fc/Fcþ).
Such a large difference in the first and the second potentials
is partly due to electronic communication between the two fer-
rocene moieties and partly due to rather large electronic effects
of the methyl and the phenyl groups that are connected to the
fullerene core through sp3 carbon atoms. By comparing the CV
of 8 to those of pentamethyl mono-ferrocene 7 and its penta-
phenyl analog,30d,30e the first wave was assigned to the oxida-
tion of the top iron atom surrounded by the electron-donating
methyl groups and the second one to the bottom iron atom.
Chemical oxidation and isolation of the cationic complexes
were performed by reacting with triarylaminium antimonate. A
monocation, [(FeCp)2(C60Me5Ph5)][SbCl6] (11), was obtained
by treating of 8 with one molar amount of [(4-BrC6H4)3N]-
[SbCl6]. The ferrocene moiety surrounded by five methyl
groups was oxidized. The geometry of the top ferrocene is
similar to that of the parent ferrocenium cation,33 whereas
that of the bottom one is similar to the neutral parent com-
pound (Fig. 10). The dication [(FeCp)2(C60Me10)][SbCl6]2
Fig. 10. X-ray crystal structure of cationic complex 11.
PhCN molecules found in a unit cell are omitted for clari-
ty. (a) ORTEP drawing. (b) CPK drawing.
(12) was synthesized and isolated by oxidating 10 with excess
[(4-BrC6H4)3N][SbCl6]. The X-ray crystal structure of 12
(Fig. 11) showed two ferrocenium structures with elongated
iron–carbon bonds in the ferrocenium part (Fe–C(Cp) = 2.10
˚
˚
˚
A and Fe–C(C60) = 2.13 A for 12 vs. Fe–C(Cp) = 2.05 A
˚
and Fe–C(C60) = 2.08 A for 10).
The [10]cyclophenacene part accepts two electrons and
forms 41- and 42ꢀ-electron-conjugated systems, as indicated
by the two reversible one-electron reduction waves in 8 at

326 Bull. Chem. Soc. Jpn. Vol. 81, No. 3 (2008)
AWARD ACCOUNTS
Fig. 12. UV–vis–NIR absorption spectra of 8 (black),
monoanion 13 (light green), and 14 dianion (green).
Fig. 11. X-ray crystal structure of cationic complex 12.
PhCN molecules found in a unit cell are omitted for clarity.
Scheme 5. Monoanion and dianion of the double-decker buckyferrocene.
E1=2 ¼ ꢃ2:24 and ꢃ2:63 V (vs. Fc/Fcþ in THF). Chemical re-
duction of 10 with potassium metal under anaerobic conditions
(Scheme 5) afforded the NMR-silent green-colored mono-
anion 13, followed by the dark green-colored dianion 14 as
the amount of the reducing agent was increased. Absorptions
at 750 and 1190 nm for the monoanion and 680 and 1000 nm
for the dianion are characteristic of polyanions of substituted
fullerenes (Fig. 12).9c,34 The mono- and dianions are thermally
stable (for 2 days at 25 ꢁC), but are rapidly oxidized by molec-
ular oxygen to reproduce 10.
search. To the best of our knowledge, there has been no exper-
imental structural data accurate enough to discuss the C–C
bond lengths, bonding pattern, aromaticity, and chemical reac-
tivities of CNTs. Theoreticians working on CNTs have gener-
ally relied on ideal graphite structures (i.e., equal C–C
length),42 and have seldom tried structure optimization.42f,42g
On the basis of the experimental data on cyclophenacene
1, we obtained geometry-optimized structures of a series of
finite-length armchair [n,n] single-wall carbon nanotubes
(n ¼ 5 and 6) by using theoretical calculations. We found that
chemical structure falls into three different classes, which may
5. Structure and Aromaticity of Finite-Length
Armchair [n,n] Single-Wall Carbon Nanotubes
´
be referred to as Kekule and incomplete Clar and complete
Clar networks (Fig. 13, Table 1). The optimized bond lengths
indicated that the shortest [5,5] carbon nanotube C40H20 has an
Chemical modification of single-walled carbon nanotubes
(SWCNTs) has become an important subject owing to the at-
tractive properties of functionalized SWCNTs.35 Chemically
modified SWCNTs have been already applied to supramolec-
ular recognition of DNA,36 bioimmobilization of metallopro-
teins and enzymes,37 covalent coupling of quantum dots to
SWCNTs,38 chemical adsorption of toxic substances,39 fluores-
cent materials,40 and support for homogeneous catalysts.41 In
modern chemistry, accurate information on the chemical struc-
ture of a molecule is essential for studies on its chemical reac-
tivity; however, such information is lacking in the CNT re-
´
aromatic Kekule structure with little bond alternation, as dis-
cussed above. In the case of C50H20, an aromatic Clar row is
surrounded by weakly aromatic six-membered rings. C60H20
is a complete Clar network. In the next series, C70H20 has a
´
pair of the Kekule structures, C80H20 has a pair of Clar chains
surrounded by olefin edges, and C90H20 is a perfect Clar net-
work, similar to C60H20. In the third series, C100H20 has three
´
rows of delocalized Kekule structures, and so on. This trend
continues to at least C200H20. The NICS data pattern also oscil-
lates periodically.

Y. Matsuo
Bull. Chem. Soc. Jpn. Vol. 81, No. 3 (2008)
327
ence between the [5,5] and [6,6] carbon nanotubes is that the
latter exhibits larger negative NICS values (Fig. 13), likely be-
cause of the increased planarity and hence better ꢀ-overlaps.
HOMO–LUMO gaps correlate to the chemical structures.
As the structure oscillates, the energy of the frontier orbitals
and the HOMO/LUMO gap also oscillate (Fig. 14). Generally,
the HOMO energy tends to increase and the LUMO energy
decreases within each period. Thus, within one period, the
´
Kekule structure shows a larger HOMO/LUMO gap than the
other two, and the complete Clar network has the smallest
gap. The HOMO/LUMO contour surface pattern also oscil-
lates. Since aromaticity and frontier molecular orbital energies
represent certain measures of thermodynamic and kinetic sta-
bilities, we expect that the chemical properties of the finite-
length carbon nanotubes with different tube lengths will
depend critically on the exact length of the tube.
The structural study of the finite-length armchair single-wall
carbon nanotubes gave precise structures, which were catego-
´
rized into three typical structures types: Kekule, incomplete
Clar and complete Clar. These three structures periodically
´
emerge, because of matching/mismatching Kekule and Clar
networks. The HOMO/LUMO gap and aromaticity also oscil-
lated periodically, depending on the tube lengths. Structures
and local aromaticities of the tubes should give us important
information concerning local chemical reactivities of the each
part of the tubes. The present study suggests that chemical re-
activities of finite-length single-wall carbon nanotubes signifi-
cantly depend both on the tube lengths and location of the
tubes and, therefore, that regioselective chemical functionali-
zation of the short single-wall carbon nanotubes may be
achieved using suitable reagents and conditions.
6. Conclusion
A cyclic benzenoid-type ꢀ-electron-conjugated system,
[10]cyclophenacene (1) was synthesized for the first time by
selective detraction of the [60]fullerene ꢀ-electron array. The
synthesis of the [10]cyclophenacene compounds provided the
first information on their structure and chemical and physical
properties, such as their luminescent function. To expand the
research of this material, development of an efficient synthetic
method is particularly important in order to prepare a variety
of fullerene derivatives. In this regard, the deca-fold function-
alization reaction described in this article takes place in
one-step on a large scale, affording cyclic ꢀ-conjugated com-
pounds. Selective detractions of the 60ꢀ-spherical conjugation
of [60]fullerene also gave two new varieties of bowl-shaped
ꢀ-conjugated aromatic systems: dibenzo-fused corannulenes
2 and its phenylene-bridged derivative 3. We demonstrated
that the photophysical properties drastically change with the
change in the shape of the fullerene ꢀ-systems. We expect
further functionalization of the deca-aryl fullerene system,
especially 2, will provide several undiscovered ꢀ-conjugated
systems.
Fig. 13. Schematic structures and NICS maps of finite-
length [n,n] carbon nanotubes (n ¼ 5 and 6). Hydrogen
atoms are omitted for clarity. Chemical bonds are sche-
matically represented by using single bond (solid single
˚
line; bond length > 1.43 A), double bond (solid double
˚
line; bond length < 1.38 A), single bond half way to dou-
˚
ble bond (solid-dashed line; 1.43 A > bond length > 1.38
˚
A), and Clar structures (i.e., ideal benzene). NICS coding:
red, aromatic < ꢃ4:5; blue, non-aromatic > ꢃ4:5. NICS
ꢄ
values were obtained by GIAO-SCF/6-31G //HF/6-
ꢄ
31G level calculations.
A cyclic benzenoid derivative with ten organic groups is
useful as a scaffold to obtain dinuclear metal fullerene com-
plexes. Electrochemical studies of 10 showed that the two iron
atoms interact with each other through the ꢀ-conjugation of
the cyclophenacene. This is the first evaluation of electronic
communication ability of fullerene by directly connecting
Geometry optimized structures of [6,6] carbon nanotubes
also exhibited the same trend in the structure and aromaticity.
Three characteristic structures occurred upon the layer-by-
layer addition of 12 carbon atoms, suggesting that this is a gen-
eral trend among armchair carbon nanotubes. One small differ-

328 Bull. Chem. Soc. Jpn. Vol. 81, No. 3 (2008)
AWARD ACCOUNTS
a),b)
˚
Table 1. Bond Lengths (A) of Optimized Structures of Finite-Length [5,5] Carbon Nanotubes
a
b
c
d
e
f
g
h
i
j
k
l
C40H20
C50H20
C60H20
C70H20
C80H20
C90H20
1.366
1.361
1.384
1.372
1.366
1.381
1.373
1.368
1.380
1.435
1.445
1.418
1.432
1.441
1.421
1.430
1.438
1.422
1.452
1.422
1.468
1.451
1.435
1.465
1.452
1.440
1.462
1.415
1.426
1.416
1.416
1.422
1.417
1.417
1.420
1.417
1.444
1.428
1.438
1.441
1.435
1.439
1.440
1.435
1.441
1.434
1.428
1.438
1.435
1.430
1.437
1.409
1.413
1.424
1.415
1.415
1.423
1.437
1.418
1.430
1.436
1.421
1.446
1.436
1.423
1.444
C100H20
C110H20
C120H20
1.417
1.424
1.419
1.437
1.431
1.435
a) Bond coding (a–l) is shown in Fig. 13. b) Structure optimization was performed by density functional calculations at the B3LYP
ꢄ
level with the 6-31G basis set.
his collaborators listed in the references, in particular Dr.
Kazukuni Tahara, for his considerable experimental contribu-
tion in this work.
References
1 S.-S. Sun, N. S. Sariciftci, Organic Photovoltaics, CRC
Press, Boca Raton, 2005.
2
a) P.-M. Allemand, A. Koch, F. Wudl, Y. Rubin, F.
Diederich, M. M. Alvarez, S. J. Anz, R. L. Whetten, J. Am. Chem.
Soc. 1991, 113, 1050. b) C. A. Reed, R. D. Bolskar, Chem. Rev.
2000, 100, 1075.
3 a) D. M. Guldi, P. Neta, K.-D. Asmus, J. Phys. Chem.
1994, 98, 4617. b) H. Imahori, Y. Sakata, Adv. Mater. 1997, 9,
537.
4
J. W. Arbogast, A. P. Darmanyan, C. S. Foote, Y. Rubin,
F. N. Diederich, M. M. Alvarez, S. J. Anz, R. L. Whetten, J. Phys.
Chem. 1991, 95, 11.
Fig. 14. HOMO/LUMO levels and band gap oscillation of
the finite-length [5,5] carbon nanotubes. The values are
determined by the PM3 level calculations, and the trend
parallels the one observed in the B3LYP/6-31G calcula-
tions from C40H20 to C120H20.
5
a) G. Schick, M. Levitus, L. Kvetko, B. A. Johnson, I.
ꢄ
Lamparth, R. Lunkwitz, B. Ma, S. I. Khan, M. A. Garcia-Garibay,
Y. Rubin, J. Am. Chem. Soc. 1999, 121, 3246. b) K. Hutchison,
J. Gao, G. Schick, Y. Rubin, F. Wudl, J. Am. Chem. Soc. 1999,
121, 5611.
6 Y. Matsuo, K. Tahara, E. Nakamura, J. Am. Chem. Soc.
2006, 128, 7154.
two metal atoms. We believe that dinuclear metal fullerene
complexes, e.g., 10, will become a subject of interdisciplinary
research between chemistry and physics as well as currently
emerging single molecular electronics research. Given the
self-assembling behavior of penta(organo)fullerene deriva-
tives43 and photo-induced charge separation function44 of the
metal fullerene complexes,45 supramolecular organization of
this photo-electronically active compound will be also an intri-
guing project for further studies.
7
3181.
8
Y. Matsuo, K. Tahara, E. Nakamura, Org. Lett. 2003, 5,
a) E. Heilbronner, Helv. Chim. Acta 1954, 37, 921. b) J.
Aihara, J. Chem. Soc., Perkin Trans. 2 1994, 971. c) L. Turker,
THEOCHEM 1999, 491, 275.
¨
9
a) E. Nakamura, K. Tahara, Y. Matsuo, M. Sawamura,
J. Am. Chem. Soc. 2003, 125, 2834. b) Y. Matsuo, K. Tahara,
M. Sawamura, E. Nakamura, J. Am. Chem. Soc. 2004, 126,
8725. c) Y. Matsuo, E. Nakamura, J. Am. Chem. Soc. 2005,
127, 8457. d) Y. Matsuo, E. Nakamura, in Cyclophenacene Cut
Out of Fullerene in Functional ꢀ-System: Syntheses and Strat-
The cyclic benzenoid system also allows us to study the
electronic structures of the finite-length [5,5] single-wall
carbon nanotubes (SWCNTs). Theoretical calculations showed
that three structures periodically appear as the tube is elongat-
ed and that the aromaticities and the HOMO–LUMO gaps also
oscillate similarly. The results suggest that the chemical reac-
tivities of the finite-length tubes change periodically. Such
information will be useful in future studies on the chemical
functionalization of carbon nanotubes.
egies, ed. by T. J. J. Muller, U. H. F. Bunz, Wiley-VCH,
¨
Weinheim, 2007, pp. 59–80. e) Y. Matsuo, K. Tahara, K. Morita,
K. Matsuo, E. Nakamura, Angew. Chem., Int. Ed. 2007, 46, 2844.
f) Y. Matsuo, T. Fujita, E. Nakamura, Chem. Asian J. 2007, 2,
948.
10 a) L. T. Scott, Angew. Chem., Int. Ed. 2003, 42, 4133.
The author expresses his sincerest appreciation to Prof.
Eiichi Nakamura (The University of Tokyo/ERATO-JST)
for his continuous support and guidance. The author acknowl-
edges Prof. Masaya Sawamura (Hokkaido University) for his
foresight in the early stage of this study. The author thanks
´
b) M. Randic, Chem. Rev. 2003, 103, 3449. c) R. Hoffmann,
Int. J. Philos. Chem. 2003, 9, 7.
11 a) H. S. Choi, K. S. Kim, Angew. Chem., Int. Ed. 1999, 38,
2256. b) K. N. Houk, P. S. Lee, M. Nendel, J. Org. Chem. 2001,
66, 5517.

Y. Matsuo
Bull. Chem. Soc. Jpn. Vol. 81, No. 3 (2008)
329
12 a) A. Godt, V. Enkelmann, A. D. Schluter, Angew. Chem.,
¨
26 a) J. M. Manriquez, M. D. Ward, W. M. Reiff, J. C.
Calabrese, N. L. Jones, P. J. Carroll, E. E. Bunel, J. S. Miller,
Int. Ed. 1989, 28, 1680. b) P. R. Ashton, G. R. Brown, N. S.
Isaacs, D. Giuffrida, F. H. Kohnke, J. P. Mathias, A. M. Z. Slawin,
D. R. Smith, J. F. Stoddart, D. J. Williams, J. Am. Chem. Soc.
1992, 114, 6330. c) U. Girreser, D. Giuffrida, F. H. Kohnke,
J. P. Mathias, D. Philp, J. F. Stoddart, Pure Appl. Chem. 1993,
65, 119. d) Y. Kuwatani, T. Yoshida, A. Kusaka, M. Iyoda, Tetra-
hedron Lett. 2000, 41, 359.
13 a) M. Sawamura, H. Iikura, E. Nakamura, J. Am. Chem.
Soc. 1996, 118, 12850. b) Y. Matsuo, A. Muramatsu, K. Tahara,
M. Koide, E. Nakamura, Org. Synth. 2006, 83, 80.
´
J. Am. Chem. Soc. 1995, 117, 6182. b) G. Alfonso, I. Chavez,
V. Arancibia, J. M. Manriquez, M. T. Garland, A. Roig, E.
Molins, R. F. Baggio, J. Organomet. Chem. 2001, 620, 32.
c) A. M. Gilbert, T. J. Katz, W. E. Geiger, M. P. Robben, A. L.
Rheingold, J. Am. Chem. Soc. 1993, 115, 3199.
27 H. Park, J. Park, A. K. L. Lim, E. H. Anderson, A. P.
Alivisatos, P. L. McEuen, Nature 2000, 407, 57.
28 S. Nakanishi, M. Tsukada, Phys. Rev. Lett. 2001, 87,
126801.
14 a) M. Lee, O.-K. Song, J.-C. Seo, D. Kim, Y. D. Suh, S. M.
Jin, S. K. Kim, Chem. Phys. Lett. 1992, 196, 325. b) D. Kim, M.
Lee, Y. Do. Suh, S. K. Kim, J. Am. Chem. Soc. 1992, 114, 4429.
15 a) R. M. Williams, J. M. Zwier, J. W. Verhoeven, J. Am.
Chem. Soc. 1995, 117, 4093. b) S.-K. Lin, L.-L. Shiu, K.-M.
Chien, T.-Y. Luh, T.-I. Lin, J. Phys. Chem. 1995, 99, 105.
c) Y.-P. Sun, G. E. Lawson, J. E. Riggs, B. Ma, N. Wang,
D. K. Moton, J. Phys. Chem. A 1998, 102, 5520. d) C. Luo, M.
Fujitsuka, A. Watanabe, O. Ito, L. Gan, Y. Huang, C. H. Huang,
J. Chem. Soc., Faraday Trans. 1998, 94, 527. e) Y. Matsubara, H.
Muraoka, H. Tada, Z. Yoshida, Chem. Lett. 1996, 373. f) K.
Hutchison, J. Gao, G. Schick, Y. Rubin, F. Wudl, J. Am. Chem.
Soc. 1999, 121, 5611.
29 a) O. Gunnarsson, Rev. Mod. Phys. 1997, 69, 575. b) K.
Funasaka, K. Sugiyama, K. Yamamoto, T. Takahashi, J. Phys.
Chem. 1995, 99, 1826. c) A. L. Balch, M. M. Olmstead, Chem.
Rev. 1998, 98, 2123.
30 a) M. Sawamura, Y. Kuninobu, M. Toganoh, Y. Matsuo,
M. Yamanaka, E. Nakamura, J. Am. Chem. Soc. 2002, 124,
9354. b) M. Toganoh, Y. Matsuo, E. Nakamura, J. Am. Chem.
Soc. 2003, 125, 13974. c) Y. Matsuo, Y. Kuninobu, S. Ito, E.
Nakamura, Chem. Lett. 2004, 33, 68. d) R. H. Herber, I. Nowik,
Y. Matsuo, M. Toganoh, Y. Kuninobu, E. Nakamura, Inorg.
Chem. 2005, 44, 5629. e) Y. Matsuo, H. Isobe, T. Tanaka, Y.
Murata, M. Murata, K. Komatsu, E. Nakamura, J. Am. Chem.
Soc. 2005, 127, 17148.
16 a) P. v. R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao,
N. J. R. van E. Hommes, J. Am. Chem. Soc. 1996, 118, 6317.
31 H. Iikura, S. Mori, M. Sawamura, E. Nakamura, J. Org.
Chem. 1997, 62, 7912.
32 The chemical yield was poor because it was difficult to
b) M. Buhl, A. Hirsch, Chem. Rev. 2001, 101, 1153.
¨
¨
17 M. D. Watson, A. Fechtenkotter, K. Mullen, Chem. Rev.
2001, 101, 1267.
separate the mixture of regioisomers for 9.
˚
¨
˚
33 Bond lengths Fe–C(Cp) (2.11 A) and Fe–C(C60) (2.13 A)
of the ferrocenium moiety surrounded by the methyl groups are
18 P. W. Rabideau, A. Sygula, Acc. Chem. Res. 1996, 29, 235.
19 a) P. W. Rabideau, A. H. Abdourazak, H. E. Folsom, Z.
Marcinow, A. Sygula, R. Sygula, J. Am. Chem. Soc. 1994, 116,
7891. b) A. Sygula, P. W. Rabideau, J. Am. Chem. Soc. 1999,
121, 7800. c) S. Hagen, M. S. Bratcher, M. S. Erickson, G.
Zimmermann, L. T. Scott, Angew. Chem., Int. Ed. Engl. 1997,
36, 406. d) G. Mehta, G. Panda, Chem. Commun. 1997, 2081.
20 a) C. Caron, R. Subramanian, F. D’Souza, J. Kim, W.
Kutner, M. T. Jones, K. M. Kadish, J. Am. Chem. Soc. 1993,
115, 8505. b) R. Subramanian, K. M. Kadish, M. N. Vijayashree,
X. Gao, M. T. Jones, M. D. Miller, K. L. Krause, T. Suenobu, S.
Fukuzumi, J. Phys. Chem. 1996, 100, 16327. c) S. Fukuzumi, T.
Suenobu, T. Hirasaka, R. Arakawa, K. M. Kadish, J. Am. Chem.
Soc. 1998, 120, 9220. d) F. Cheng, Y. Murata, K. Komatsu,
Org. Lett. 2002, 4, 2541. e) S. Miki, M. Kitao, K. Fukunishi,
Tetrahedron Lett. 1996, 37, 2049.
˚
˚
longer than those (Fe–C(Cp) = 2.07 A and Fe–C(C60) = 2.08 A)
of the ferrocene moiety surrounded by the phenyl groups.
34 a) Y. Matsuo, K. Tahara, E. Nakamura, Chem. Lett. 2005,
34, 1078. b) I. Aprahamian, D. Eisenberg, R. E. Hoffman, T.
Sternfeld, Y. Matsuo, E. A. Jackson, E. Nakamura, L. T. Scott,
T. Sheradsky, M. Rabinovitz, J. Am. Chem. Soc. 2005, 127, 9581.
35 a) A. Hirsch, Angew. Chem., Int. Ed. 2002, 41, 1853.
b) J. L. Bahr, J. M. Tour, J. Mater. Chem. 2002, 12, 1952. c) S.
Niyogi, M. A. Hamon, H. Hu, B. Zhao, P. Bhowmik, R. Sen,
M. E. Itkis, R. C. Haddon, Acc. Chem. Res. 2002, 35, 1105.
d) J. Liu, A. G. Rinzler, H. Dai, J. H. Hafner, R. K. Bradley,
P. J. Boul, A. Lu, T. Iverson, K. Shelimov, C. B. Huffman, F.
Rodriguez-Macias, Y.-S. Shon, T. R. Lee, D. T. Colbert, R. E.
Smalley, Science 1998, 280, 1253.
36 a) K. A. Williams, P. T. M. Veenhuizen, B. G. de la Torre,
R. Eritja, C. Dekker, Nature 2002, 420, 761. b) S. E. Baker,
W. Cai, T. L. Lasseter, K. P. Weidkamp, R. J. Hamers, Nano Lett.
2002, 2, 1413.
21 a) S. Barlow, D. O’Hare, Chem. Rev. 1997, 97, 637. b) D.
Astruc, Acc. Chem. Res. 1997, 30, 383. c) C. Joachim, J. K.
Gimzewski, A. Aviram, Nature 2000, 408, 541.
22 A.-C. Ribou, J.-P. Launay, M. L. Sachtleben, H. Li, C. W.
Spangler, Inorg. Chem. 1996, 35, 3735.
37 B. R. Azamian, J. J. Davis, K. S. Coleman, C. B. Bagshaw,
M. L. H. Green, J. Am. Chem. Soc. 2002, 124, 12664.
38 B. R. Azamian, K. S. Coleman, J. J. Davis, N. Hanson,
M. L. H. Green, Chem. Commun. 2002, 366.
39 R. Q. Long, R. T. Yang, J. Am. Chem. Soc. 2001, 123,
2058.
23 a) E. E. Bunel, P. Campos, J. Ruz, L. Valle, I. Chadwick,
M. S. Ana, G. Gonzalez, J. M. Manriquez, Organometallics 1988,
7, 474. b) C. Patoux, C. Coudret, J.-P. Launay, C. Joachim, A.
Gourdon, Inorg. Chem. 1997, 36, 5037. c) R. Chukwu, A. D.
Hunter, B. D. Santarsiero, S. G. Bott, J. L. Atwood, J.
Chassaignac, Organometallics 1992, 11, 589.
40 J. Chen, M. A. Hamon, H. Hu, Y. Chen, A. M. Rao, P. C.
Eklund, R. C. Haddon, Science 1998, 282, 95.
24 a) C. LeVanda, D. O. Cowan, C. Leitch, K. Bechgaard,
J. Am. Chem. Soc. 1974, 96, 6788. b) R. D. Adams, B. Qu,
M. D. Smith, Organometallics 2002, 21, 3867.
25 B. Bildstein, M. Schweiger, H. Angleitner, H. Kopacka, K.
Wurst, K.-H. Ongania, M. Fontani, P. Zanello, Organometallics
1999, 18, 4286.
41 S. Banerjee, S. S. Wong, J. Am. Chem. Soc. 2002, 124,
8940.
42 a) K. Tanaka, H. Ago, T. Yamabe, K. Okahara, M. Okada,
Int. J. Quantum Chem. 1997, 63, 637. b) A. Rochefort, D. R.
Salahub, P. Avouris, J. Phys. Chem. B 1999, 103, 641. c) T. Sato,
M. Tanaka, T. Yamabe, Synth. Met. 1999, 103, 2525. d) T.

330 Bull. Chem. Soc. Jpn. Vol. 81, No. 3 (2008)
AWARD ACCOUNTS
Yamabe, M. Imade, M. Tanaka, T. Sato, Synth. Met. 2001, 117,
61. e) L. Liu, C. S. Jayanthi, H. Guo, S. Y. Wu, Phys. Rev. B
2001, 64, 033414. f) K. Kanamitsu, S. Saito, J. Phys. Soc. Jpn.
2002, 71, 483. g) J. Cioslowski, N. Rao, D. Moncrieff, J. Am.
Chem. Soc. 2002, 124, 8485.
43 a) M. Sawamura, K. Kawai, Y. Matsuo, K. Kanie, T. Kato,
E. Nakamura, Nature 2002, 419, 702. b) Y. Matsuo, A.
Muramatsu, R. Hamasaki, N. Mizoshita, T. Kato, E. Nakamura,
J. Am. Chem. Soc. 2004, 126, 432. c) Y. Matsuo, A. Muramatsu,
Y. Kamikawa, T. Kato, E. Nakamura, J. Am. Chem. Soc. 2006,
128, 9586. d) Y.-W. Zhong, Y. Matsuo, E. Nakamura, J. Am.
Chem. Soc. 2007, 129, 3052.
44 D. M. Guldi, G. M. A. Rahman, R. Marczak, Y. Matsuo,
M. Yamanaka, E. Nakamura, J. Am. Chem. Soc. 2006, 128, 9420.
45 a) M. Sawamura, Y. Kuninobu, E. Nakamura, J. Am.
Chem. Soc. 2000, 122, 12407. b) Y. Matsuo, E. Nakamura,
Organometallics 2003, 22, 2554. c) Y. Matsuo, Y. Kuninobu, S.
Ito, E. Nakamura, Chem. Lett. 2004, 33, 68. d) Y. Kuninobu, Y.
Matsuo, M. Toganoh, M. Sawamura, E. Nakamura, Organometal-
lics 2004, 23, 3259. e) Y. Matsuo, A. Iwashita, E. Nakamura,
Organometallics 2005, 24, 89. f) Y. Matsuo, E. Nakamura, Inorg.
Chim. Acta 2006, 359, 1979. g) Y. Matsuo, Y. Mitani, Y.-W.
Zhong, E. Nakamura, Organometallics 2006, 25, 2826. h) Y.-W.
Zhong, Y. Matsuo, E. Nakamura, Chem. Asian J. 2007, 2, 358.
Yutaka Matsuo was born in Osaka, Japan, in 1974. He graduated from Osaka University (1996)
and received his Ph.D. (2001) from Osaka University under the guidance of Profs. K. Tani and
K. Mashima. Then, he joined the Department of Chemistry, the University of Tokyo (Prof. E.
Nakamura) as an Assistant Professor. In 2004, he moved to the Nakamura Functional Carbon
Cluster Project, ERATO, Japan Science and Technology Agency as a Group Leader. His research
interests lie in organometallic chemistry, carbon cluster chemistry, and materials science (photo-
voltaics, liquid crystals, luminescent materials, and molecular devices). He was awarded The
Chemical Society of Japan Award for Young Chemists (2005) and The 3rd Osawa Award of
the Fullerenes and Nanotubes Research Society (2007).