Buckminsterfullerene-Aromaticity and Molecule@C60-  

May  27,  2013	
Kumiko  Yamamoto

Contents

1

Introduction-History of Buckminsterfullerene-How to Produce Fullerenes?

Aromaticity  of  Fullerenes-What is Aromaticity?!
-Aromaticity of Buckminsterfullerene

Endohedral  Fullerenes  Encapsulating  a  Molecule	-Why Endohedral Fullerenes?!
-Conventional Synthesis of Endohedral Fullerenes!
-“Molecular Surgery”!
H2@C60, H2O@C60

Summery  &  Outlook

http://www.ec.gc.ca/biosphere/

History  of  Buckminsterfullerene

Introduction	 2

1970! first prediction by E. Osawa!
E. Osawa, Kagaku 1970, 25, 854.!

1985! discovery of Buckminsterfullerene by H. W. Kroto, R. E. Smalley !
H. W. Kroto, J. R. Heath, S. C. O’Brien, R. F. Curl, R. E. Smalley, Nature 1985, 318, 162.!

© 1985 Nature Publishing Group© 1985 Nature Publishing Group

Buckminsterfullerene was named after !
Richard Buckminster Fuller.!
←Biosphere, Environment Museum

1990! preparation of substantial amounts of Buckminster fullerene by W. Krätschmer, D. R. Huffman!
W. Krätschmer, L. D. Lamb, K. Fostiropoulos, D. R. Huffman, Nature 1990, 347, 354.!

Downloaded from www.sciencemag.or

crystalquality were improved by exchanging thepyridine ligands for 4-tert-butylpyridine.
asoned that if C60 could
The observation of a single sharp chroay that broke its apparmatographic peak for the one-to-one adductry, it might crystallize suggested that it is a single regioisomer,der. We report here the rather than a mixture of the two regioiso1991! crystal
structure of Buckminsterfullerene !
e-to-one C60-osmium
mers which are possible from the proposednd its crystal structure soccer ball structure for C60. This would beball framework of C60.
t of the osmylation oft heteroatoms can befilllerene without disframework (13). Our
the addition of two osgiving the two-to-one
as a mixture of regioiChromatographic anal-

Introduction	
 3

History  of  Buckminsterfullereneheme I

action mixture revealed Fig. 1. ORTEP drawing (50% ellipsoids) of the
one-to-one
C60-osmium tetroxide adducts corresponding to theJ. M.
Hawkins, A. Meyer,showing
T. A. Lewis,
S. Loren, !
the reC60(OsO4)(4-tert-butylpyridine)2
llectively analyzes with lationshipof the osmyl unit with the carbon
F.
J.
Hollander,
Science
1991,
252,
312.!
ometry, and a single cluster.
SCIENCE, VOL. 252

W. I. F. David, R. M. Ibberson, J. C. Matthewman, K. Prassides, !
T. J. S. Dennis, J. P. Hare, H. W. Kroto, R. Talor, D. R. M. Walton, !
Nature 1991, 353, 147.!

1996! Nobel Prize in Chemistry; discovery of new carbon compounds called fullerenes

H. W. Kroto!

R. F. Curl!

R. E. Smalley!

arbonntities-presorkers
n waschamn, andessurenzene/
owed
c aroeavily
e [25].
s in aessuremasstech-

2. Equipment and techniques

Introduction	
 4How  to  Produce  Fullerenes?
A schematic of the reduced pressure fullerene com-bustion synthesis pilot apparatus is shown in Fig. 1.
The burner with a 0.25 m diameter porous refractory
laser-vaporization!
element is enclosed within a vacuum chamber (the combustion chamber of Fig. 1). The porous refractory burner and the thermal insulation in the chamber createan adiabatic reaction zone that extends 0.45 m fromthe burner. The combustion chamber is connected to asoot collection chamber and a heat exchanger, whichcools the exhaust gases before they enter the vacuum
pumps. The vacuum in the apparatus is supplied by vacuum pumps so as to control the pressures in the burnerchamber to 5.33 kPa (40 Torr). The soot collection
chamber includes a bag filter, which has a filter cleaning
・good generation efficiency of C60!
mechanism for dislodging captured soot witha nitrogen・smallscale
synthesis!
jet pulse and allows the combustion system to produce
篠原久典,  齋藤弥八,  『フラーレンとナノチューブの科学』,  	
fullerenes
continuously without halting the synthesiss and名古屋大学出版会,  2011.
process.
The soot collection chamber also has a ball
comvalve at its base, which allows the soot to fall into the
ed to
n the
mbus- combustion synthesis
could
e fullpararovesof thewaterd thisat themostechat wellbrium
n of ae andthese‘‘zip-

arc discharge

・low generation efficiency of C60!
・can obtain soot in gram scale!
篠原久典,  齋藤弥八,  『フラーレンとナノチューブの科学』,  	
名古屋大学出版会,  2011.

98% 1 g ¥14,600!
99.5% 1 g ¥34,800!
99.9% 1 g ¥70,600
Fig. 1. Reduced-pressure, premixed combustion fullerene synthesis
apparatus.

H. Takehara, M. Fujiwara, M. Arikawa, M. D. Diener, J. M. Alford, Carbon 2005, 43, 311.!

>99.5% 1 g ¥34,400!
>99.0% 1 g ¥27,200

99.9% 1 g ¥24,700

Introduction	
 5How  to  Produce  Fullerenes?
organic synthesis!
Mg, ether;Br acetaldehyde

PBr3

OH

97% yieldClbenzene
86% yield

ClO

71% yield

ClI2, propylene oxide,hν, cyclohexane
92% yield

NC
KOH, ethylene glycole;
SOCl2;
AlCl3, CH2Cl2

Cl

PPh3, toluene;
LiOEt, 2-naphthaldehyde,Cl
Br EtOH/CH2Cl2

51% yield

Cl

NBS, BPO, CCl4;
KCN, Bu4N(HSO4), H2O/CH2Cl2
93% yield

Cl

TiCl4, ODCB
85% yield
Cl

Cl

1100 °C, ca. 0.01 mm Hg
Flash Vacuum Pyrolysis

Cltotal 0.1-1.0% yield(12 steps)

L. T. Scott, M. M. Boorum, B. J. McMahon, !
S. Hagen, J. Mack, J. Blank, H. Wegner, !
A. Meijere, Science 2002, 295, 1500.

Contents

6

Introduction-History of Buckminsterfullerene-How to Produce Fullerenes?

Aromaticity  of  Fullerenes-What is Aromaticity?!
-Aromaticity of Buckminsterfullerene

Endohedral  Fullerenes  Encapsulating  a  Molecule	-Why Endohedral Fullerenes?!
-Conventional Synthesis of Endohedral Fullerenes!
-“Molecular Surgery”!
H2@C60, H2O@C60

Summery  &  Outlook

http://www.ec.gc.ca/biosphere/Aromaticity  of  Fullerenes	
 7

What  is  Aromaticity?
Reactivity  Criteria

Energetic  Criteria

electrophilic aromatic substitution

enhanced stability (large resonance energy)

Br2, FeBr3

resonancestabilization
152 kJ/mol

Br
E

+ H2

+ H2
208 kJ/mol

120 kJ/mol

Aromaticity
Structural  Criteria

Magnetic  Criteria

bond length equalization due to cyclic delocalization

ring current effects

H
HOMA etc.

NMR chemical shift!
diamagnetic susceptibility exaltation (Λ)!
NICS valueetc.
2011 LS by Kumiko Yamamoto

1.445(3) and1.432 (10)Spherical
Å, Aromaticity of Fullerenes
Structural  Criteria

Aromaticity  of  Fullerenes	
 8

Table 1. Calculated and Measured Bond Distances in
C60 [Å]

Table 2. Ca
C70tion in C60 is obviously notmethod[5,6]-bonds[6,6]-bonds
refof the σ framework. The
HF(STO-3G)
1.465
1.376
51
HF(7s3p/4s2p)
1.453
1.369
52
bond typbetween [6,6]- and [5,6]LDF(11s6p)
1.43
1.39
53
a
HF
1.448
1.370
54
b
MP2
1.446
1.406
55
d with the symmetry and
c
NMR
1.45
1.40
56
d
neutron diffraction
1.444
1.391
57
olecular π orbitals. The
earelectron diffraction
1.458
1.401
58
Figure
4.
O
r
t
h
o
-,
m
e
t
a
-and
p
f
X-ray
1.467
1.355
59
pes
of bonds
isstructure!
equivalent
the valencebond (VB)
gons within fullerenes.
ghhe π orbitals into localizedtures with adjacent pentagons. The destabilization
Data wehe hu, t1u, and t1g orbitals
of non-IPR fullerenes is due to an increase of strain(η -C )Ir(COenergy Aromaticity
caused by enforced bond angles accompanied
structure of
he degree of bond-lengthwith higher pyramidalization of the C atoms. In
Structural  Criteriaaddition, it was suggested that the pentalene-type 8
Table 3. El
y relatedto the situation
π-electron
substructures may lead to resonance deFully (Boldbond length equalization due to cyclic
delocalization
Icosahedra
stabilization.
The destabilizing effect of abutting
epending on the fillingofpentagons in fullerenes was investigated quantitalshell
th either 4N or 4N + tively
2 πby Fowler and Zerbetto. If, in addition to IPR0sviolating fullerenes, open-shell structures and unfa1pm the ideal Dnh takes placevorable para relationships of pentagons are avoided,2dthe huge number of possible isomers reduces conside icosahedral homologues
3ferably. With these constraints, magic
numberswholemolecule; 0.14!
67
same behavior.HOMAOnly
thefor
stable fullerenes C can be predicted, which areetc.
) 60 (one isomer), 70 (one isomer), 72HOMA(one isomer),4gvalues!
closed l ) 2 shell, nc )n7618)(one isomer), 78 (five isomers), etc. Next to C
andIC , structural assignment based on C NMR, 81
ll, nc ) 72) exhibit ideal
Figure 5. HOMA values for the
X-rayhcrystallography, and, in some cases by sup(Å)

a

2

70

30,31

a

32

31

33-38

n

70

60
13
T. M. Krygowski, A. Ciesielski, J. Chem. Inf. Comput. Sci. 1995, 35, 1001.!
M. Bühl, A. Hirsch, Chem. Rev. 2001, 101, 1153.

Aromaticity  of  Fullerenes	
 9Structural  Criteria

C606-!
[6,6]-bonds: 1.42 Å!
Figure 3. Schematicof one of the five
LUMO!representation[5,6]-bonds:
1.45 Å!
degenerate HOMOs (a) and one of the three degenerate
1156 Chemical Reviews, 2001, Vol. 101, No. 5

LUMOs (b) of C60. Each orbital is represented by a frontand side view. Only the exohedral part of the orbitals
projected to the corresponding C atoms
is Hirschshown forBühl andclarity.23

3).10,23,49,65,66,68,71 The lowest energy level is the hu
level, which in neutral C60 is completely filled withthe valence bond (VB) structure!
the 10 available electrons. The resulting hu10 groundstate is nondegenerate (Hund’s rule) and has theangular momentum quantum numbers L ) 0, S )0, J ) 0, and the many-electron hu10 configuration[6,6]-bonds: double bond character!
has Ag symmetry within the point group Ih. A[5,6]-bonds: single bond character!
comparison of the representations of the sets of σ*
orbitals along the [6,6]-bonds
with that of the π
HOMO!
(from calculations & experimental results)!
C60that! whenelectrons shows
filling the hu shell, theoccupied π orbitals form a set which is completely[6,6]-bonds:
1.45Å! along theequivalent to theset of localized
σ orbitals
65,66 Therefore, the molecular orbitals can[6,6]-bonds. [5,6]-bonds: 1.37 Å!
be weakly localized at these sides by a unitarytransformation. This distortion exactly corresponds
to the internal structural
10+! of freedom that theC60degree
molecule
has
without
Ih symC
60
Figure 3. Schematic
representationbreaking
of one of thethe five
65,66 Looking at the symmetries of the hmetry.HOMOsuno significant!
degenerate(a) and one ofbond-length
the three degenerate
orbitalsreveals
the [6,6]orbital isinteractions
represented withby a front
LUMOs(b) of C
60. Eachbonding
alternation
is expected!
Figure 2. PM3//MNDO-calculated π orbitals of C6010+. Theand sideview.
the exohedral
part ofinthebonds
andOnly
antibonding
interactions
theorbitals[5,6]-bonds
23,72
position of the C60 skeleton is the same in all orbitalprojectedtothecorresponding
C
atoms
is
shown
(Figure 3).
As a consequence, filling the hu fororbitals
23[6,6]-bonds:
1.48 Å!
presentations. The s orbital is also shown in wire meshclarity.
causes a shortening of the [6,6]-bonds, which leads
presentation. This makes the nodal plane visible, which is[5,6]-bonds:
1.44
Å!is
to an increase
inlowest
bond energy
andatthethesame
Theenergylevel
hu timehidden in the other presentations. (Reprinted with permis-3).10,23,49,65,66,68,71
favorslonger[5,6]-bondsbyreducing
antibonding
sion from ref 67. Copyright 2000 Wiley-VCH.)
level, which in neutral
C is completely filled with73 More60 pronounced distortions werethe 10interactions.
available electrons.
The resulting hu10 ground2+
symmetrically distributed, no distortion from spheri-state calculated
for the partiallyfilledC60the, C604+,is 6+
nondegenerate(Hund’srule)systems
and has8+
cal or icosahedral symmetry is expected in casesangular, and C60 . quantum
Here, evennumbers
a symmetry
C60 momentumL69)lowering
0, S ) was
where all states are completely filled. Hence, no0, J )predicted
to
D
or
C
,
respectively.
10
5
d
5
v
0, and the many-electron hu configuration
C60 has ambiguous aromaticcharacter;! alternation is expected forhas AgAdding
significant
bond-length
12 electrons
intopoint
the t1groupu and tI2u. orbitals
symmetry
within theh A
10+lengthsof theC60 . The B3LYP/6-31G*-calculated
would oflead
toa closed-shellofsituation
again.
comparison
therepresentations
the
sets
of
σ* In
aromatic hexagons and antiaromatic
pentagons
withinneutralC.
!
60 contrast to icosahedral C , however, an anomaly[6,6]- and [5,6]-bonds of C6010+ (Ih symmetry) are 1.48orbitals
is80
along the[6,6]-bonds
with thatthe 101,
π 1153.
Hirsch,Rev.ofderived
2001,
and 1.44 Å.67,69 Therefore, the bond-length alternation
observedM.
forBühl,
C60, A.
since
the Chem.
t1g orbitals
fromAromaticity  of  Fullerenes	
 10

Magnetic  Criteria

Aromaticity
Magnetic  Criteria
ring current effects

H
NMR chemical shift!
diamagnetic susceptibility exaltation (Λ)!
NICS valueetc.
2011 LS by Kumiko Yamamoto

Aromaticity  of  Fullerenes	
 11

Magnetic  Criteria
1H NMR chemical shift!

Haromatic
diatropic ring currentHanti aromaticparatropic ring current
H

H
H

9.28 ppm (outer protons)–2.99 ppm (inner protons)[18]annulene

H

H
2– H

H
H
2–

–1.13 ppm (outer protons)
29.5, 28.1 ppm (inner protons)
dianion of [18]annulene

J. F. M. Oth, E. P. Woo, F. Sondheimer, J. Am. Chem. Soc. 1973, 95, 7337.!

Aromaticity  of  Fullerenes	
 12

Magnetic  Criteria
diamagnetic susceptibility exaltation (Λ)!

Λ = χM − χM'Λ < 0: aromatic compounds!
Λ ~ 0: non aromatic compounds
χM:! the experimentally determined molar susceptibility of a compound!
χM’:!the susceptibility estimated for a cyclopolyene of that structurecompound!

χ M

χM’

compound!

－68.1! －68.1

0.0

－57.5

－58.3

0.8

－48.6

－49.3

0.7

－54.8

－41.1

－13.7

χM’
-

-

－17.2**－44.5! －38.0!     －6.5!
(－2.4**)!
--

32.6***All values of χM, χM’ and Λ are given in units of 10-6 cm3 mol-1 (ppm cgs). !
**The calculated magnetic susceptibility exaltations.

H. J. Dauben, Jr., J. D. Wilson, J. L. Laity, J. Am. Chem. Soc. 1968, 90, 811.!
H. J. Dauben, Jr., J. D. Wilson, J. L. Laity, J. Am. Chem. Soc. 1969, 91, 1991.!

Aromaticity  of  Fullerenes	
 13

Magnetic  Criteria
NICS (nucleus-independent chemical shift)!

absolute magnetic shieldings, computed at ring centers
NICS < 0: aromaticity!
NICS > 0: antiaromaticity

compound!

NICS

compound!

NICS          0.0－2.2－17.2**

－13.7

－9.7

－6.5!
    －3.2(－2.4**)!

–5.1

32.6**

－14.3

54.2

*All values of Λ are given in units of 10-6 cm3 mol-1 (ppm cgs) !
and NICS are given in units of ppm. !
**The calculated magnetic susceptibility exaltations.

19.0

P. v. R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao, N. J. R. van E. Hommes,!
J. Am. Chem. Soc. 1996, 118, 6317.!

Aromaticity  of  Fullerenes	
 14

Magnetic  Criteria

NMR chemical shift!
δRC = 2χM /r3!
⇒ 0.57 ppm
r: radius of the sphere
V. Elser, R. C. Haddon, Nature 1987, 325, 792.

diamagnetic susceptibility exaltation (Λ)!
χ M

χM’

－54.8

－41.1

－13.7

－260±20－262±402±60

compound!

C60

He

M’

60) = －6.3 ppm= [ring current] + [σ-bond anisotropy]

1172 *AllChemical
2001,
Vol.
No.(ppm
5 cgs).
values of χ , χReviews,
and Λ are given
in unitsof 10101,
cm molM

3He NMR: δ(He@C

-6

3

-1

R. C. Haddon, L. F. Schneemeyer, J. V. Waszczak, S. H. Glarum, R.
Tycko, G. Dabbagh, A. R. Kortan, A. J. Muller, A. M. Mujsce, M. J.
Rosseinsky, S. M. Zahurak, A. V. Makhija, F. A. Thiel, K. Raghavachari,
E. Cockayne, V. Elser, Nature 1991, 350, 46.!

NICS (nucleus-independent chemical shift)!

hexagons: -5.31 ppm!
pentagons: 8.89 ppm!
(benzene: -9.7 ppm)!
M. Bühl, Chem. Eur. J. 1998, 4, 734.

M. Saunders, H. A. J.-Vázquez, R. J. Cross, S. Mroczkowski,
D. I. Freedberg, F. A. L. Anet, Nature 1994, 367, 256.

sophisticated theoretical calculation!
δ(He@C60H60) = －5.2 ppm

fullerene reactivity).
reduction and adductare effectively added
system, respectively. T
ring-current chemical shift δRC(C60) = ca. －1 ppm
a summary of the conc
properties. Section V.2
C60 has ambiguousaromaticaboutcharacter.!
brought
by repla
fullerenes with hetero

M. Bühl, W. Thiel, H. Jiao, P. R. Schleyer, M. Saunders, F. A. L. Anetl,
J. Am. Chem. Soc. 1994, 116, 6005.

R. C. Haddon, Nature 1995, 378, 249.!
M. Bühl, A. Hirsch, Chem. Rev. 2001, 101, 1153.

Aromaticity  of  Fullerenes	
 15

Summary
Reactivity  Criteria

Energetic  Criteria

electrophilic aromatic substitution

enhanced stability (large resonance energy)

Br2, FeBr3

resonancestabilization
152 kJ/mol

Br
E

C60  has  	

+ H2

+ H2
120 kJ/mol

208 kJ/mol

ambiguous  aromatic  	
Aromaticity
character.	
Structural  Criteria
Magnetic  Criteria
bond length equalization due to cyclic delocalization

ring current effects

H
HOMA etc.

NMR chemical shift!
diamagnetic susceptibility exaltation (Λ)!
NICS valueetc.

Contents

16

Introduction-History of Buckminsterfullerene-How to Produce Fullerenes?

Aromaticity  of  Fullerenes-What is Aromaticity?!
-Aromaticity of Buckminsterfullerene

Endohedral  Fullerenes  Encapsulating  a  Molecule	-Why Endohedral Fullerenes?!
-Conventional Synthesis of Endohedral Fullerenes!
-“Molecular Surgery”!
H2@C60, H2O@C60

Summery  &  Outlook

http://www.ec.gc.ca/biosphere/Endohedral  Fullerenes  Encapsulating  a  Molecule	

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 17

endohedral fullerenes: fullerenes with atom(s) or molecule(s) encapsulated
Endhedral fullerenes which have been synthesized and isolated till May 2011

篠原久典,  齋藤弥八,  『フラーレンとナノチューブの科学』,  名古屋大学出版会,  2011,  pp.  207.

intrinsically low, compared to that of C60 (ref 12) and C70 (ref 13),Endohedral  Fullerenes  Encapsulating  a  Molecule	
 18
because of the conduction mechanism through encapsulated metal
ions. Since the LUMO is dominated by the orbital of encapsulated	La, the intermolecular overlap of LUMOs should be very small,resulting in low mobilities.
The more critical cause of the low mobility is the crystallinity.
We have carried out X-ray and electron diffraction experiments
and found that the film is poorly crystalline displaying amorphous features. This indicates that intermolecular hopping is a
Paramagnetic Water-Soluble Metallofullerenes
Bioconjugate Chem., Vol. 12, No. 4, 2001 513
more plausible mechanism of conduction and that the activation
Arrhenius plot of conductivity. Right inset shows a schematicenergy ∆ observed in Figure 1 is regarded as a hopping barrier
La2@C80 molecule.
Left inset displays
absorption spectra for thinmolecular
electronics
MRI
agent which are irregularly stacked. On
NMR analysis
betweencontrast
neighboring molecules,
oluene solution of La2@C80.
C O Mimplies
M U N Ithat
C A theT I OmobilityNSthe other hand, the present resultofMe
field effect transistor
La2@C80 can be improved by fabrication of films with better Nfrom thestandard procedure, namely, (IDS)1/2 vs VGS plot at VDS )N
crystallinity.
80 V. TheInlow
mobilitywe
in havethe order
10-4 cm2/V thes givesa meansummary,first ofdemonstrated
n-typefield effect +free-pathextremely
smaller than the molecularsize,film.
indicatingtransistor
of dimetallofullerene
La2@C80 thin
Takingthat
the nature
the bandsuggestedfromFigure of
1 isthenotdevicecorrect.
of conduction
LUMO intomodelaccount,
the n-type
behavior
indicates
A morelikely mechanism
carrier transport
in the present
an occurrenceof carrierofconduction
through encapsulated
La ions.
La2@CThewould
be hopping
betweengrain boundaries
or field
80 filmpresent
experiment
revealed
the advantageof thin film
betweenneighboring
effecttransistormolecules.
technique in determining the carrier types andbenzene
The charge
mobilitytransportof electron
carriers in of
La2@C
to be
80 is expectedmechanisms
variousendohedral
metalloS. Kobayashi et al. "reflux, 2 hintrinsicallylow, comparedto that
C60 investigated.
(ref 12) and C70 (ref 13),
fullerenes,
which should
be of
more
J. Am. Chem. Soc. 2003, 125, 8166.
because of the conduction mechanism through encapsulated metal
Acknowledgment.
We thank
T. Nishikawa
and Seiko EPSON
ions. Since
the LUMO is dominatedby theorbital of encapsulated
Technology
Platform
ResearchCenterGroup forLa, theCorporationintermolecular
overlap of
LUMOs
should bevery Msmall,
He@C
theinphotolithography
was
in
part
supported
60:He@C
70 = 7:3
resulting
low mobilities. technique. This work
3622 J. Am. Chem. Sa.,Vol.
116, No. 8, 1994
Communications to the EbyaGrand-in
Aid
from
MEXT,
Japan.
The more critical cause of the low mobility is the crystallinity.
carried out X-ray and electron diffraction experiments
O 4.We(a)have
FigureT1References-weighted MRI of CDF1 mice before and 30 min after i.v. administration of Gd@C82(OH)40 via tail vein as the dosefound
is poorly
crystalline
displayingof 5 µmoland
Gd/kg[whichthat
wasthe
1/20film
of a typicalclinicaldose of Gd-DTPA(100 amorµmol Gd/kg)] (n ) 3), and (b) its time dependent signal
intensity phouschangeNin(1)variousorgans.
MRI see:conditions:
4.7H.
T Rep.
Unity
INOVA(Varian),
TR/TE ) 300 ms/11 ms. At 30 min. after i.v.
features.
This
indicatesthatintermolecular
hopping
is 63,
a atForarecentreview,
Shinohara,
Prog.
Phys.
2000,
843Drain-source current (IDS) is plotted as a function of drain-source
administrationof Gd@C892.
82(OH)40, enormous signal enhancement was observed at lung, liver, spleen, and kidney (Figure 4(b)).
O
moreplausible
mechanismofconduction
and
that
the
activation)forseveralvaluesofgate
voltage
(V
).
Data
sets
are
displayedDSGS(2) Alvarez,
M.; Gillan, E. G.; Holczer, K.; Kaner, R. B.; Min, K. S.;
N M.
NniusV plot
Right inset shows a schematic
15
fromofVconductivity.
in L.
Figure1 Chem.
is regarded
as10561-10563.
a hoppingGS ) -75 to 75 V. Inset shows a schematic diagramenergy ∆ observed
Thebarrier
present paramagnetic water-soluble metallofWhetten, R.
J. Phys.
1991, 95,
3+
molecule.
Left
inset
displaysabsorption
spectraforthin
80
Kobayashi, molecules,
K.; Nagase, which
S.; Akasaka,
T. Chem. Phys.
Lett. On
1995,
245,
Gd (3)
80 thin film transistor. S, D, and G denote source, drain, and gate,between
ullerenes(Gd-fullerenols),
which have extremely strong
neighboringare irregularly
stacked.
solutionofLa@C.
230-236.
2
80
ly.
MR
signalofenhancement ability, will be applied as novelOO
O the other(4)hand,thepresent
resultimpliesthatthemobility
Nishibori, E.;O
Takata, M.; Sakata, M.; Taninaka, A.;MRI
Shinohara,
H. Angew.
contrast
agents for the present anatomical and
Ed. 2001,by40,fabrication
2998-2999. of films with betterO
OLa2@C80 canChem.,
be Int.
improvedOOfunctional
imaging.
O
Suzuki, T.; Maruyama, Y.; Kato, T.; Kikuchi, K.; Nakao, Y.; Achiba, Y.; Furthermore, this will be a promisingage (VGS) values. Relatively large current flow wascrystallinity.
H (5) Kobayashi,
novel1995,
coreof MRI probes for high-quality
K.; Nagase, S. Angew. Chem., Int. Ed. Engl.
34, material
1094even at VGS ) 0 V. Application of positive (negative) In summary,
H 1096.we haveand future genetic imaging for next
first demonstrated the n-typemolecular/cellular
field effectincreases (reduces) the current IDS. These observationstransistor(6)Fujitsuka,
M.; Ito, O.;La
Kobayashi,K.; Nagase, S.; generation.
Yamamoto, K.; Kato,of T.;
dimetallofullerene
2@C80 thin film. Taking the nature
Wakahara, T.; Akasaka,
T. Chem. Lett.
2000, 902-903.
Gd-DTPA!
Gd@C
(OH)
! Y.;
hat the electron-type carriers are already unintentionally82of thenACKNOWLEDGMENT
of LUMOaccount,
the n-type
behavior
deviceindicates(7)intoTaninakaA.; Shino,K.; Sugai,T.; Heike,S.; Terada,
Hashizume, T.;
the nominally undoped material and that the transistoran occurrence
Shinohara
H.
Nano
Lett.
2003,
3,
337-341.
mono adductsofcarrier
conduction
through
encapsulated
La ions.
100μmol
Gd/kg!
5μmol
Gd/kg!
Of h 0(8) Dimitrakopoulos, C. D.; Malenfant, P. R. L. AdV. Mater.
14, 99This2002,
research
was financial supported by the Japanin the electron accumulation mode. According to theThe present
experiment
revealedtheadvantage
of
thin
film
field
117.
Society for Promotion of Science (JSPS) for the Future
al3 and experimental11 studies on individual La2@C80effect transistor(9) Kazaoui,S.; Ross,inR.;determining
Minami, N. Phys.
ReV. BProgram
1995,
R11665techniquethe carriertypes52,and
grant
on New Carbon Nano-Materials to H.S.
R11668. 1/20!
s, LUMO is dominantly formed of encapsulated La ions.charge transportmechanismsofvariousendohedral
metallo(10) Kubozono, Y.; Takabayashi, Y.; Shibata, K.; Kanbara,T.; Fujiki,CITEDS.;LITERATURE
he present observation of n-type operation of the thin filmfullerenes,
whichshouldbe moreKashino,S.; Fujiwara,A.; investigated.
Emura, S. To appear in Phys. ReV., B.
' ~7,' - '- "2 0, .'0 0 . '- 2.2 ,. 0 0 - 2 4 . 0 0 -26 00 - 2 9 . 0 0
I.
-6 00
-8.00
-10.00-12.00-14.00-16.00-18.00indicates that the carrier conduction through encapsulated
PPH and Wesbey,(11) Kato, T.; Okubo, S.; Matsuoka, H.; Dinse, K.-P.,
Proceedingsofthe(1) Weinmann, H.-J., Brasch, R. C., Press, W.-R.,
Figure 5. Biodistributionof Gd in CDF1 mice at 30 min, 1 h,
International
Symposiumon
Fullerenes,
Nanotubes,
andCarbonNanoH.
Shinoharaetal.
"Acknowledgment.
We
thank82(OH)T. Nishikawa
G.EPSON
E.
(1984)(381
Characteristics
of Gadolinium-DTPA
Figure1. Seiko
3He NMR
spectrumMHz) of the productof addition of azomethineComplex:
ylide to a 'He-labeled C&~J mixture. Another spectru
occurring in metallofullerene La2@C80 solids. The
originand
24 h afteri.v. administrationof ECS
Gd@C
Assay
ofand
clusters in 203rd
Meeting 40
in. Paris
2003,
13;
Kamat,
P.ofV.,
D. Contrast
acquiredafter
3HeGuldi,
bubbledthrough theAgent.
sample inAthe
A mL
Potentialm
Jal.
. Rtubea" diowith
logya. syringe
142, to create a reference peak.
ions wascarried outM.,
by Kadish,
ICP.
Theenhancementshown
Bioconjugate
Chem.
2001,
12,
510.!
M. Saunders
et. NMR
Corporation
Technology
Platform
ResearchCenterSociety,
M 1.5
Group
forwasNMR
s that exist without application of the gate voltageGd
remains
K.signal
M.,
Eds.;
The
ElectrochemicalInc.:
Pennington,
619-624.
in Figure 3 had good correspondencewith the concentration of
2003. Soc.
thephotolithography
technique.
This
work
was
in
part
supported
J.
Am.
Chem.
2003,
125,
4391.
J.
Am.
Chem.
Soc.
1994,
116,
arified. They may be ascribed to the unintentionally(2) Brasch, R. C., Weinmann, H.-J, and Wesbey, G. E. (1984) 3621.
Gd@C82(OH)40 found in these organs (Figure 4a and Figure 4b).
(12) Haddon, R. C.; Perel, A. S.; Morris, R. C.; Palstra, T. T. M.; Hebard, A.
Themadebiodistribution
indicated
Gd@C82Japan.
(OH)40 tends toContrast-Enhanced NMR Imaging: Animal Studies Usingby a Grand-in
Aid that
fromtheMEXT,
d carriers, though the measurement of Figure 2 wasWhy  Endohedral  Fullerenes?

Scientiﬁc  interest!!
+
expected  to  be  important  for  their  potential  use  in  various  ﬁelds  such  as…

'

I

'

I '

1 ' " ' '

I

I

" '

I

'

I

"

I

'

Conventional  Synthesis  of  Endohedral  Fullerenes	

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 19physical  methods  under  harsh  conditions  such  as…
co-vaporization of carbon and metal atoms!
→ metallofullerenes!

high-pressure/temperature treatment with gases!
→ non-metal doped fullerenes (noble gas atom@fullerene)!

laser-vaporization, arc discharge, etc. !
with composite graphite target rods; made bymixing metal powder with graphite powder,pressing, and carbonized by baking. !

650 ℃, 3000 atm, under noble gas atmosphere!
ca. 0.1% yield

tube furnace
C60 etc.

composite graphite!
target rod

quartz tube
laser

Ar or He

first example: M. Saunders et al. J. Am. Chem. Soc. 1994, 116, 2193.!
日本化学会編,  『π電子系の化学』,  化学同人,  2013.

laser-vaporization
first example: R. E. Smalley et al. J. Am. Chem. Soc. 1985, 107, 7779.!
篠原久典,  齋藤弥八,  『フラーレンとナノチューブの科学』,  名古屋大学出版会,  2011.

problems
difficult to control the reaction; no selectivity in controlling both the cage-size and product distribution. !
low yield & laborious purification; yield only mg quantities of pure product after tedious isolation procedures.

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 20“Molecular  Surgery”	1) ‘‘incision’’ of the fullerene cage to form an opening on the surface.!
2) insertion of some small atom(s) or molecule(s) through the opening.!
3) ‘‘suture’’ of the opening to reproduce the fullerene cage while retaining the guest species. !
Y. Rubin, K. N. Houk, M. Saunders, R. J. Cross et al. Angew. Chem. Int. Ed. 2001, 40, 1543.!
M. Murata, Y. Murata, K. Komatsu, Chem. Commun. 2008, 6083.

by Yves Rubin

1

2

3

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 21

Insertion  of  He  &  H2  Through  the  Oriﬁce  of  an  Open  Fullerene  	
synthesis!

14-membered-ring orifice!

N3

+

N3

N O

O N

o-Cl2C6H4
55 ºC, 4 days
C60

>12% yieldO2 or DDQ

N
N
N

NN
N

N

N

N
1O

O

O

N

N O

O N

2

–N2

G. Schick, T. Jarrosson, Y. Rubin, Angew. Chem. Int. Ed. 1999, 38, 2360.!

1G-+PI-., <SN,G/+; :;O+,M:G;OD

N:P<-G,G2+;T+Endohedral  Fullerenes  Encapsulating  a  Molecule	
 22+;MOJ O<GU+N

Insertion  of  He  &  H2  Through  the  Oriﬁce  of  an  Open  Fullerene  	insertion of He & H2!
tBu

tBu

N O

O N

tBu

tBu

N O

O N

R.2-+ 9D K,+N:PM+N .PM:V.M:G; 2.,,:+,O QG, :;O+,M:G; .;N P./+ +OP.L+3 .;N+;+,/:+O ZY?$&KB5'?90kkBBY?$&KB?'=903 ]P.- 1G-!9J GQ +;P.LOI-.M:G; QG, M<+
calculated
activation barrier;+IM,.- /I+OMO *+3 F+3 *= 3 F= 3 .;N `, /.O+O :;O:N+ M<+ GL+; QI--+,+;+ 2:O-.PM.1#D #;O+,M:G; M+1L+,.MI,+O .,+ +OM:1.M+N .O +[L-.:;+N :; M<+ M+[MD
0I+OM(G-I1+W==X
Wl?X%OMD :;O+,M:G;
M+1L+,.MI,+W!)X

Y.,,:+, MG:;O+,M:G;%;+,/S GQ+;P.LOI-.M:G;

Y.,,:+, MG+OP.L+

*+
*=
F+
F=
`,

99D>
96D>
97D5
?8D?
=AD6

9=7
?6@
?A7
988>
96?>

# =7D8# 79D7# 7>D5# 99=D7# 9?5D?

# >D=
# 9D7
! 9D9
# 8D5
# 5D9

# =7D?
# 7>D># 79D@# 9>5DA# 9?>D=,+Q+,+;P+ .M !
:;PG,LG,.M+N
I;N+, M<+ O.
?
*+e)5> Z>D9
1+M<GNDWA3 6X R
98> !)D *:/<+
M<+ Q,.PM:G; GQ.O . P,SOM.--:;
U:M<:; . P,:1
ZP.D @>>> LO:J?
*+e# U:M<?
*+e)5> OM.;
N:,+PM +[L+,:1
QG, +OP.L+ G,+-.M:V+ ?*+M+1L+,.MI,+O
M<+ ;G;N+PG1*+ G, * :;O+,M:G;O Z=880 .;N 8>=0 P1!93 ,+OL+PM:V+-SJ P-+.,-S
experimental= results
PG,,+OLG;N U:M< M<+ +[:MB+;M,.;P+ 1GM:G; GQ *+ G, *= D R<+
QI--+,+;+:MO+-Qatm,
I;N+,/G+O
L,.PM:P.--S;G N:OMG,M:G; :; M<:O
100 P./+℃, 3-424 h →
0.04% yield!
He
300 ℃, 475 atm, 7.5 h → 1.5% yield!"## 3He NMR: δ != "#$%&'()*-10.10 ppm(+,-./ 012*3 4'56789 "+:;<+:13 =>>9 97??'@A89B>9B7>>A
He and H2 are strongly shieldedby the fullerene π-electron shell
400 ℃, 100 atm, 48 h → 5% yield of the open fullerene.
H-H 1
H NMR: δ = -5.43 ppm“The important step of closing back the fullerene framework also needs to be studied.“!

Y. Rubin, T. Jarrosson, G.-W. Wang, M. D. Bartberger, K. N. Houk, G. Schick, M. Saunders, R. J. Cross, Angew. Chem. Int. Ed. 2001, 40, 1543.!

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 23

Encapsulation  of  H2  in  C60  by  Organic  Synthesis	
‘‘incision’’ of the fullerene cage!

Py

N

Ph

HN N
+

Ph
Py

N

Ph

Py
O

Ph

1O

o-Cl2C6H4
180 ºC, 17 h
50% yield
C60

N

Ph

Koichi Komatsu! Yasujiro Murata!
小松紘一
村田靖次郎
Py
O

Ph

O
S8 (1 eq)
TDAE (1 eq)

2

CCl4, hυunder air, 6 h
60% yield

N

Ph
Ph

O
S

o-Cl2C6H4
180 ºC, 30 min
77% yield
Me2N

NMe2

Me2N
NMe2
TDAE

Y. Murata, M. Murata, K. Komatsu, Chem. Eur. J. 2003, 9, 1600.!

Encapsulation  of  H2  in  C60  by  Organic  Synthesis	
8-membered-ring orifice!

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 241600 ± 1609

PhN
fullerenes∫
and ™zipping up(Scheme 1) having a 2-pyridyl group at the 3-position andPyPh
onnection with the latter ™ziptwo phenyl
Ph groups at the 5- and 6-positions. We conducted a
HN N
N reaction with one equivalent of C60 in o-dichloroon of C60 has been detected bythermalPh+[12]
Py
precursors, and, most imporbenzene (ODCB) at 180 !C for 17 h. The reaction was foundthesis of C60 has recently been
workers using flash vacuum
the synthesis.[13] Although this
2C6H
mising for providing o-Cl
access
to4
180
ºC,
17
yet unknown fullerenes, it hash
50% yield
thesis of endohedral fullerene
C60
ess has, however,been attained
X-ray structure
y for the endohedral complexes.
e gases such as helium, neon,
have been incorporated
intoPh
N !C, 3000 atm)
itions (such as 600
PyPh
gases, albeit in yields typically
as
Ph
HN N
N
y one molecule +of C60 out ofPh
Pys contains the gas atom.Diels-AlderIt isn state, a bond on the C60 cage is
hat can incorporate these gas
15]
In a recent study, Rubin and8-membered-ring orifice!
actam derivative of C60 having a
Scheme 1. Synthesis of open-cage fullerene derivative 5.
6]and succeeded in the encap1.5 %) or molecular hydrogenf 300 !C and 475 atm or 400 !C
to proceed smoothly, giving almost a single product, which

Y. Murata, M. Murata, K. Komatsu, Chem. Eur. J. 2003, 9, 1600.!

Encapsulation  of  H2  in  C60FULL
  by  Organic  Synthesis	
PAPER

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 25

K. Komatsu et al

12-membered-ring orifice!

N

Py
C2

1.406(4) Å C3

Ph
Ph
C5
C4 1.403(4) Å

1.511(4) ÅC2-C3 and C4-C5 have double bond character.!
HOMO is localized primarily at C2-C3 and C4-C5.!
⇒ O2 addition is expected to take Figure
place
onX-raythesebonds.
1. Thestructureof open-cage fullerene derivative 5 with

Py

N

Ph
Ph

displacement ellipsoids drawn at the 50 % probability level. Selecteddistances [ä], bond angles [!], and dihedral angles [!]: C1!C2 1.521(4),C2!C3 1.406(4), C3!C4 1.511(4), C4!C5 1.403(4), C5!C6 1.517(4), C6!C7
1.540(4), C7!N1 1.270(4), N1!C1 1.457(3), C2!C13 2.274(4), C5!C14
2.279(4); C1-C2-C3 124.0(3), C2-C3-C4 129.8(2), C3-C4-C5 128.7(2), C4C5-C6 124.6(2); C1-C2-C3-C4 ! 39.0(4) C3-C4-C5-C6 38.8(4), C2-C3-C4C5 0.4(5).

Figure 2. The optimized structure of open-cage fullerene derivative 5 withthe contour of the HOMO, calculated at the B3LYP/6 ± 311G** level otheory.

Phwith theaddition of O2 as shown by FAB MS, in 60%, 31 %Ph
N of 9 and 10
N 2 % yields, respectively. The IR
Pyspectra
and
Ph
Ph
Py
exhibited Ph
strong carbonyl stretching
O bands at 1747 and!1with the dihedral angle between the two double bonds being O1748 cm , respectively, whereas no carbonylband wasO
only 0.4(5)!. O
observed for 11.
O mechanism for the formation of 5 is
A probable reaction
Because comparisonof the experimental and calculated
H-H
1O
13
2 shown in Scheme 1 b. A [4"2] cycloaddition of triazine 4 to
C NMR spectra seemed to be crucial for the structura
C60 affords 6, and the following extrusion of nitrogen gives
determination of 9, 10, and 11, we first examined the validity
CCl4, hυof such a comparison 51.8
using the spectrum of compound 5, for
2-aza-1,3-cyclohexadiene-fused C60 derivative 7, which would
which the structurekcal/mol
was confirmed by X-ray crystallography
under air,undergo
6 h a formal intramolecular [4"4] cycloaddition to give
To determine which level of theory is the most accurate for8, and then a retro [2"2"2] reaction affords 5.
60% yield
reproducing the experimental 13C NMR spectrum of 5, the⇒ further enlargement !
Enlargement of the orifice in open-cage fullerene 5: It hasgauge-independant atomic orbital (GIAO)[20,21] calculationsof theopening
is necessary
been reported both by us and another group that one of theon 5 wereconductedusing Hartree± Fock (HF) and density
[22]
[23]
double bonds in the eight-membered-ring orifice in an
openfunctional
theory(B3LYP
and
B3PW91) methods
with
Y. Murata, M. Murata, K. Komatsu, Chem. Eur. J. 2003,
9, 1600.!
[24]
cage fullerene can undergo oxidative cleavage by the M.
action
of
both
the
6
±
311G**
and
TZV
basis
sets,
based
on
Murata, Y. Murata, K. Komatsu, Chem. Commun. 2008, 6083.the
N

Ph

Py
O

for 9 at the B3LYP/6 ± 311G** level of theory demonstrated

Endohedral  Fullerenes  Encapsulating  a  Moleculethat the LUMO of 9 is relatively localized at the conjugated	
 26

Encapsulation  of  H2  in  C60  by  Organic  Synthesis	
Figure 9. UV/Vis spectra of open-cage fullerene derivatives: blue line (5),black (9), green (10), red (11), and brown (15).

butadiene part, C9"C10"C11"C12, on the rim of the orifice(Figure 6); the numbering is shown in Scheme 3. The absolutetions at 253, 317, and 442 nm. Compound 15, which has theorifice among the compounds examined in this study,
13-membered-ring orifice! largest
showed maximum absorptions at 257 and 319 nm as well as a

top view

Figure 8. The X-ray structure of open-cage fullerene derivative 15 with thedisplacement ellipsoids model drawn at the 50 % probability level: a) sideview and b) top view. Selected distances [ä]: N1!C1 1.445(3), C1!C2
1.584(4), C2!O1 1.209(3), C2!C9 1.492(4), C9!C10 1.398(4), C10!S1
1.780(3), S1!C11 1.754(3), C10!C11 2.546(4), C11!C12 1.367(4), C12!C3
1.518(4), C3!O2 1.202(3), C3!C4 1.553(4), C4!C5 1.380(4), C5!C6
1.552(3), C6!C7 1.545(4), C7!N1 1.281(3).

Compounds 9 and 10, which are isomeric, showed quite
similar absorptions, that is, strong maximum absorptions in
the UV region (257 and 325 nm for 9; 259 and 324 nm for 10),which are commonly observed in C60 derivatives, and a small
absorption in the visible region (424 nm for 9; 423 nm for 10)
as well as the long-wavelength visible absorption extending toapproximately 700 nm. These absorptions are different fromthose of an enol-ketone derivative 16, which has a similar 12elliptic shape!
membered-ring orifice. This showed maximum absorptions at
453 and 751(14-membered
nm.[10a] Compound 11ring)
showed maximum absorp1606

broad absorption at 430 nm. With the increase in the size ofthe orifice in the order 5, 9 and 10, and 15, the absorption at
the visible region lost their structure. The colors of thesolutions of 5, 9, 10, 11, and 15 in CHCl3 were purple, brown,
brown, red-brown, and bright red, respectively.

To examine the electronic properties of the open-cagefullerene derivatives 5, 9, 10, 11, and 15, their redox behaviors
were studied by cyclic voltammetry (CV) and differential
pulse voltammetry (DPV) in ODCB using Bu4NBF4 as asupporting electrolyte. Despite the significant change in the !electronic system resulting from the transformation in thefullerene skeleton made for these derivatives, all compounds
showed four quasi-reversible redox waves in the negative
scans upon CV. These were quite similar to those observed for
C60 itself. The corresponding four one-electron reduction
peaks were observed upon DPV measurements. As an
example, the CV and DPV results for compound 10 are
shown in Figure 10, together with those for C60 .
The reduction potentials determined by DPV are summarized in Table 1, together with the LUMO energy levels
calculated by the B3LYP/6 ± 31G* level of theory. As shownby the values in Table 1, the reduction potentials of compounds 5 and 11 were found to be rather similar to those of
C60 , indicating that the fully conjugated !-electron systems
made of 60 sp2 carbons in 5 and 11 retain the high electron
affinities characteristic of C60 . Most noteworthy is theobservation that compounds 9 and 10 exhibited first reduction
waves at potentials as low as ! 0.97 and ! 0.98 V versus theferrocene/ferrocenium couple, respectively, 8which are approximately 0.2 V lower than that of C60 measured under the

X-ray structure

Py
O

N

Ph
Ph

O

Py
O
0.29 C9
C10

Figure 6. The optimized structure of open-cage fullerene derivative 9 withthe contour of the LUMO, calculated at the B3LYP/6 ± 311G** level oftheory.

NO

Ph LUMO is relatively localized
Ph

at C9-C10-C11-C12.

Absolute values of the

C12
S (1 eq)
coefficients of C10 and C11
S
0.35
0.25
TDAE (1 eq)
are 0.35 and 0.32.!
C11
0.32¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/03/0907-1606 $ 20.00+.50/0
Chem. Eur. J. 2003, 9, No. 7
o-Cl2C6H4
Scheme 3. Synthesis of open-cagederivative 15.
⇒ Sfullerene
8 inserted into !
the largest hole!
180 ºC, 30 min
the C10-C11 bond.
(at that time)
77% yield
values of the coefficients of the LUMO at C9, C10, C11, andabsolute
C12 of 9values
are 0.29, 0.35, 0.32, and 0.25, respectively. Thus, it isrelatively circular shape!
assumedthat the sulfur atom has been inserted into theofthecoefficients(13-membered ring)
C10"C11 bond to give the novel open-cage fullerene deriv-

15 havingK.a Komatsu,
13-membered-ringorificeThe
Y. Murata,ative
M. Murata,
Chem. Eur.
J. (Scheme
2003, 9,3).
1600.!

Received April 1, 2003; E-mail: komatsu@scl.kyoto-u.ac.jp

Encapsulation  of  H2  in  C60  by  Organic  Synthesis	Endohedral  Fullerenes  Encapsulating  a  Molecule	
 27dohedral fullerene complexes incorporating noble gases1 or
2 haveinsertionof H
ic nitrogenbeen
prepared by insertion of these atoms
2!
PhPh
pristine C60 under forced conditions.
However,the yields of Py N
Py N
Ph
PhIf a sufficiently O-5%.
materials have been as low as 0.4%
to
10
O
O
orifice is opened on a fullerene surface,O such atoms would
capsulated efficiently by insertion throughthe orifice.H-H
In thisS
S
3
ct, Rubin et al. prepared an open-cage fullerene derivative 2
ucceeded in introducing a He atom and a H2 molecule in 1.5%
the largest
hole! 4 To achieve 100% encapsulation of
5% yields,
respectively.
(at that time)
gas molecules, it is desirable to have a larger orifice on the
structre
Figure 1. Structures calculatedof open-cagefullerene derivatives
relatively circular shape!
ene surface. We recently synthesizedanopen-cage
fullerene
optimized structure of H2@1 calculated at the B3LYP/6(13-membered ring)theory. The H2 molecule is shown as a space-filling modative 1, which has a 13-membered-ring orifice on a C60 cage
molecule is shown as a stick model.
re 1).calculated
The derivative
1 has
an orifice5.64 Åofalongtheactivation
barrier
for theof
insertion
H2 (kcal/mol)
experimental results
axis and 3.75 Å along the short axis5 and is expected to be aenergy of!than barrier
200 ℃, 800 atm, 8 h → 100% yieldr host molecule for smallbarrier
atoms to!
and molecules
2. Hereto!
encapsulation
how that encapsulation of ainsertion
H2 molecule
into 1 does takeescapeplacestable at room temp. for more than 3 months.
Ph
Py N
1H NMR: δ = -7.25 ppm
oduce the endohedral
complex H2@1 in 100% yield, and thatPhOO
C60 can be generated
in the gas phase by restoration of the
MALDI-TOF mass: H2@open-cage fullerene !
S
28.7
age from H2@1 upon laser30.1
irradiation. 1.4
open-cage fullerene!
C60!
examine the feasibility of insertion of small atoms andH2@C60cules through the orifice of 1, theoretical calculations usingd density functional theory (B3LYP/6-31G**//B3LYP/3-21G)
X-ray diffraction study
Figure 2. 1H NMR spectrum (300 MHz, o-dichlorobenze
conducted.6 The energies required for insertion of He, Ne,
41.4
1.4
40.4
together with the values of the spin-lattice relaxation timend Ar into 1 were calculated to be 18.9, 26.2, 30.1, and 97.7
a vacuum-sealed sample for some selected signals. In paren
by Rubin etconsiderablyal.
mol, respectively,
lower than the corresponding
the T1 values obtained for the oxygen-saturated sample.
ies for 2 (24.5, 40.6, 41.4, and 136.3 kcal/mol),4 indicating
ncapsulation of atoms and molecules as small as He, Ne, andwith the intensities of well-resolved aromatic-proto
Y. Murata, M. Murata, K. Komatsu, J. Am. Chem. Soc. 2003, 125, 7152.!

Encapsulation  of  H2  in  C60  by  Organic  Synthesis	
characterization of H2@ATOCF!
Py
O

N

Ph
Ph

Py
O

O
S

H-H

N

Ph
Ph
O

S

X-ray

construct a three-dimensional
he diffraction data by using theMEM). The MEM analysis was
rogram[7] at a resolution of 128 !
ors of the final MEM charge
24 for H2@ATOCF and empty-dimensional representations ofties of H2@ATOCF and empty
2. The equal-density levels are at

H-H

Figure 3. MEM electron-density distributions of a) empty ATOCF and
H2@ATOCF
for observed1) horizontal division
2) verticaldivision.
Theelectronb)density
wasat theandcenterof thefullerene
cage.!
centerfigureshows
thepositionsofdivision
for
(1)
and
(2).
The
the number of electrons was calculated tobe 2.0 ± 0.1 (= H2).!
!3
contour maps are drawn from 0.01 to 0.11 e ! .

H. Sawa, Y. Wakabayashi, Y. Murata, M. Murata, K. Komatsu, Angew. Chem. Int. Ed. 2005, 44, 1981.!

Encapsulation  of  H2  in  C60  by  Organic  Synthesis	
‘‘suture’’ of the opening!
Py
O

N

Ph
Ph

Py
O

O
S

N
O

m-CPBA
toluenert, 13 h
99% yield

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 28

Ph
Ph

Py
O

O

N

Ph
Ph

O

S
toluene, visible lightrt, 17 h
42% yield
TiCl4, Zn
o-DCB/THF
80 °C, 2 h
88% yield
Py

N

Ph
Ph

340 °C, 2 h
61% yield
H2@C60
total 5.2% yield

K. Komatsu, M. Murata, Y. Murata, Science 2005, 307, 238.!

Downloaded from www.sciencemag.org on May 1

Relative intensity

Relative intensity

Absorbance

Relative intensity

Relative intensity

AbsorbanceEncapsulation  of  H   in  C   by  Organic  Synthesis	

Downloaded from www.sciencemag.org on May 1

esired, step productD). The desired product
Endohedral  Fullerenes  Encapsulating  a  Molecule	
 29
ted
mg,withcontaminated9%with 9%67%
as obtained
yield byin 67% yield by
2
60
bon
lutiondisulfideof the solution of the-gelthroughcolumn.
a silica-gel column.
whenwere Hobtained
when H2@5of H @C !
@5
2purification
2
60
300-C
urs, at for
320-C
24 hours, at 320-C
2r at
min.
400-C
Thus,for 2 min. Thus,
total
ynthesizedyield ofin a total yield ofrecycling
HPLC (20 cycles)!
Fig. 3. Structural Fig.
char-3.by
Structural
charH2@C60 B
H2@C60H2@C60B@2,e obtained
which canin be Aobtained inH2@C60A
acterization of H2@C
acterizationof H2@C60.
60.
13C 19).
m(18,consumed19). C60 (18,
NMR
0.5
NMR
(A) Expanded 13C (A)Expanded 13C NMR
eof
that
thetheorificeclosure of the orifice
λmax (log ε)spectrum(75
MHz,
spectrumoMHz, o⇒(75“very
weak but appreciable van der Waals
mally
way allowedof a thermally allowed 10:1
212 (5.14)
DCB-d
DCB-d
4 ) of H 2 @C
60 4 ) of H 2 @C 60
HPLC
0.4
258 (5.17)
þyclizationp2s^ electrocyclization
rereC60
C60
contaminatedbycontaminated
9% interaction
by 9% must be operating between the inner
330 (4.67)
13. C(B) Expanded 13CSpectroscopic Data. (B)Expanded
C60405C
propaneduces tworings
cyclopropane rings
60(3.42)
0.3
NMR
spectrum NMR(75 hydrogen
spectrum (75 molecule and the π-electron cloud of
543 (2.84)
eavageential radical
and a cleavage and a
600 (2.80)) of o-DCB-dMHz,o-DCB-d 4MHz,%T4 ) of”.!
ction
s2s þproduces2s^ reaction produce
outerC
622 (2.52)H @C purified
x 50
.
(C)
@C
. 60
(C)
purified
H
100
2
60
2
60
0.2
142.80 143.00 142.60 142.80
142.60143.00143.00 and 142.80 143.00 142.60 142.80
142.60ng
pyridine
off 2-cyanopyridine
and
MALDI-TOF mass MALDI-TOF
specmass specChemical shift (ppm) Chemical shift (ppm)
Chemical shift (ppm) Chemical shift (ppm)
ene.
trum (positive ionization
trum (positive ionization
1429.2 1182.3
0.1
MRf thespectrum
desired of the desiredmode, dithranol matrix)
mode, dithranol matrix)
576.7
D
D
C
C
of purified H2@C60of. (D)purified H2@C60. (D)ed
142.844a signalppm
at d 0 142.844 ppm
Predicted isotopePredicted
disisotope
dis0
ignal
a veryat small
d 0 signal at d 0
90
200
300
400
500
600 tribution
700
800
pattern
tributionforpattern fore (Fig.
latter 3A),
cor- the latter corH2@C60.
H2@C60.
wavelength / nm
actly
nal oftoempty
thesignal of empty
characterization
of
H
@C
!
2
60
anded
obtained
spectrumwith obtained with
Figure S3 Ultraviolet-visible spectrum (cyclohexane) of H2@C60 (3.18 x 10−5 M).
ppmoints FAB
spectral
for a 50-ppm
spectralSpectroscopic Data
mass!
UV-vis spectrum!
IR spectrum!
80
526.5
egratedeas of thesepeak areas of these
MALDI-TOF
mass!
on of
estimated
H
ratio
of
H
@C
@C
%T
2
60
2
60
1.0
4600
4000 100
3000
2000
1500
1000
400
of 10:1.
714
718
714
718
722 714726 718
722
726
722 714726 718
722
726
−1
wavenumber / cm
elemental
analysis!
λmax (log ε)
m/z
m/z
m/z
m/z
medCH
@C
throughfromCthrough602
60
60
212 (5.16)
0.8
1182.3Figure S1 Infrared spectrum (KBr) of H2@C1429.2
1H NMR!
60.
quid-performance
chromaliquid chroma258 (5.18)
576.7
H2@C60330 (4.67)
ave semipreparative
CosmosilCosmosil
13C NMR!
0.6
405(3.41)
H2@C60connected
mn (two directlycol- connected col%T
90543 (2.86)
Scheme1.
Scheme 1. 100
diameter,y 10 mmwith
inner diameter, with
600 (2.84)
0.4622 (2.58)
mobilew rate,phase;
4 ml flow rate, 4 ml
x 50
on
n for
time,
C60395andmin for C60 and
80
0.2
H
ted
H260@C). 60
Isolated H2@C60
C60
2@C1429.2 1182.3
80nbethe100%
basispureof on the basis of
526.5
60
575.7
0
NMR
142.844
signalppmat 142.844 ppm
200
300
400
500
600
700
800
4600
4000
3000
2000
1500
1000
400
solutionesults of fasthigh-resolution fast−1
wavelength / nmwavenumber / cm
mentometrymass(calcuspectrometry (calcu40
Figure S1 Infrared spectrum (KBr) of H2@C60.
for C60H2: 722.0157;
H2weight: 722.0157;
Figure S4 Ultraviolet-visible spectrum (cyclohexane) of C60 (5.99 x 10−5 M).
⇒
UV-visspectrum
is
also
the
same
!
63),
eementandofthetheagreement of theas that of C60.!

20

S8/S11www.sciencemag.org
www.sciencemag.org
SCIENCE VOL 307
SCIENCE
14 JANUARY
VOL 307 2005
14 JANUARY 2005

239

4600

526.5

%T
4000 100

239

3000

2000

wavenumber / cm

1000

400

−1

Figure S2 Infrared spectrum (KBr) of C60.

⇒ “slight repulsive interaction 1182.3
with the inner1429.2H2 molecule caused a very slight deformation
575.7
of the spherical cage of H2@C60”.!
80

S7/S11

M. Murata, Y. Murata, K. Komatsu,!
J. Am. Chem. Soc. 2006, 128, 8024.!

1500

60

H2

OD

OD

O

O
Py SN PhPhH NMR (300 MHz, ODCB-d4) spectra of H2@4, HO
2@5, H
2@6, and H2@7
H O
HEndohedral  Fullerenes  Encapsulating  a  Molecule	
 30

H2O

ODCB

ODCB

Encapsulation  of  H2  in  C60  by  Organic  Synthesis	SPhPy HN@4
H2 H Ph1
H NMR (300 MHz, ODCB-d4) spectra of H2@4, HO
2@5, H2@6, and H2@7
O

ODCB

8

ODCB

10

ODCB

8

ODCB

10

H2O

4

2

6

4

2

0

H2O

8

6

6

6

× impurity

ODCB

10

ODCB

8
ODCB

10

ODCB

about H NMR chemical shift!

4

2

4

2

0

H
S2@4
−2
−4
Py N PhO H H Ph
O
−2

−4

S Ph
H
@4
Py N 2
Ph
O
H H
O
O
Ph
−2
0 Py S
N
Ph−4
H2@4
O
O
H
H
O
S
Ph
0 Py H−2
−4
HN
H Ph
2@5
O
O
O
HS−2
2@5 −40Ph
Py N
O H H PhO
0
−4
O−2
Py N Ph
HS2@5 PhOOH H
Py N Ph
−2
0 O
−4
Ph
O
HH2@5
H

−6

−8

−10 δ/ppm−6−8−10 δ/ppm-7.25 ppm
−6−8

−10 δ/ppm−6−8−10 δ/ppm

NICS values

Synthesis and Properties of Endohedral C60

Py
O

N

Ph
Ph
O

S

Py
O

N

ART

Ph
Ph
O

S

Murata et a

ARTICLES

H2O
H2O
H2O
H2O

-6.33 ppm

-5.80 ppm

H2O

-2.95 ppm

ODCB

ODCB

H2O

ODCB ODCB

o-dichlorobenzene
ODCB ODCB

H2O
O
H
2

H2O

ODCB

ODCB

H2O

H2O

× impurity

ODCB

× impurity
× impurity

ODCB

ODCB

ODCB

ODCB

ODCB
ODCB

ODCB

ODCB ODCBODCB ODCB

ODCB

ODCB

issue.42 The NMR signal for encapsulated hydrogen wa
Figure 9. NICS patterns of the open-cage fullerene derivatives 5, 7, and 8, calculated at the B3LYP/6-31G* level of theory: red regions are f
Ph
Ph ppm, pink for δ ) 0 to -5, pale blue for δ ) +5 to +10, and blue forobserved
δ > +10. in ODCB-d4 at δ -3.27 ppm for H2@16 (upfield
Py N
Py N
shifted from dissolved free hydrogen by ∆δ, 7.81 ppm), -4.30
PhPh
ppm for H2@17 (∆δ, 8.84 ppm), and -4.64 ppm for H2@18
O
O
Table 1. Experimental and Calculated NMR Chemical Sh
4
2
10
8
6
−6
−8
δ/ppm
the paramagnetic property of the encapsulated species. In accord(∆δ, 9.18
ppm). These
upfield ofshiftsare quite
similar toFullere
thosOO
Encapsulated
Hydrogena Seriesof Open-CageOOwith a very minute effect of encapsulated hydrogen, the IR
and H2signal@C60 of 3He encapsulated in threportedDerivatives
for the NMR
3
spectrum was almost the same as that of empty C60, exhibitingS
S
corresponding derivatives
H2@5 for He@C
H2@6 60 (∆δ,
H2@7 8.06, 9.11,
H2@8 and
4
2
10
8
6
−6
−8
δ/ppm
four absorption bands at 1429.2, 1182.3, 576.7, and 526.5 cm-1
9.45 ppm, exp
respectively)
being constantly
lessshielded -2.95
by 0.23a
-7.25
-6.33
-5.80
2a Thus,b(to be compared with 1429.2, 1182.3, 575.7, and 526.5 cm-1
0.27 ppm.calcd
theinside molecularhydrogenof-0.17
C60 can
-5.87
-4.72
-3.85
∆
1.38 probe 1.61
1.95 the chemica
2.78
for empty C60 measured under exactly the same conditions).
also be used
as a good
to investigate-1
Only the band at 576.7 cm of H2@C60, corresponding to anreactions ata the exterior of the fullerene
cage, just as the 3H
At A300
in SODCB-d4. b Calculated at
the GIAOSynthesis and Properties of Endohedral C60
TMHz,
ICLE
out-of-plane vibration mode,32 is slightly higher in energy thanatom inside
the R
fullerene
cagelevelhas ofbeen
utilized.19
311G**//B3LYP/6-31G*
theory.
4
2
10
8
6
−6
−8
δ/ppm
that of empty C60 by 1.0 cm-1. This might be taken as evidence
Figure 10.that
NICS
pattern repulsiveof the open-cagefullerene with
derivatives
6, calculateda slight
interaction
the inner
H2 molecule
The observed gradual downfield shift must be d
Ph
PhB3LYP/6-31G*
at theof theory.
has caused levela veryslight deformation of the spherical cage ofchange in magnetic environment of this hydrogen, resul
Py N
Py N
Ph
PhH2@C60. The UV-vis spectrum was also the same as that of
the change in diamagnetic and paramagnetic ring cuOOfrom H2@8, 1.50 ppm downfield shift was observed. The NICS
empty C60. An attempt to measure the Raman spectrum of
Py N PhOO values forhexagons and pentagons, and the consequent total ring
C60, calculated in the same way as above, are -2.4
H−2 H −4
4
2
10
8
6
0
−6
−8
δ/ppm
H2@C
of strong fluorescence fromPh
60 was unsuccessful because 36a
O H2@6of the fullerene cage. To prove this, the diamagnet
for the hexagon and +11.8 for the pentagon, clearly indicatingO
the outer C cage. Further trials are now underway.
paramagneticity of all the π-conjugated five- and six-mthat the aromaticity60of the hexagon is considerably decreased
The endohedral fullerene H2@C60 is thermally stable. Uponrings in the open-cage fullerenes 5-8 and of C60 were
and the antiaromaticity of pentagons is increased, despite theheatingthepuresample
of
H
@C
at
500
°C
for
10
min
under
H
@6
2
60
by the NICS (nucleus-independent chemical shifts)
2 Ph −4
formation of a completely π-conjugated system. Again, the
δ/ppm
10
8
6
0 Py −2−6−842
vacuum, there was no decomposition or release of incorporated
tions.33,35,36 The obtained NICS values for each pentN
pyramidalization of all 60 carbons and the resulting
increase of13
O H OH Ph
hydrogen at all, as judged from the C NMR and HPLC.
hexagon are shown in the Schlegel diagrams of Figure
strain should
be related to the lowering of the overall aroma1H NMR Chemical Shift of AHydrogen
Synthesis and Properties of Endohedral C60
R T I C L EInsideS
theOpenremoval of the sulfur atom from the orifice of 5, whic
ticity. In addition, this last step is accompanied by the formation
Ph
δ/ppm
10
8
6
0
−4
−6
−8
−2
4
2
Cageπ-conjugated
Fullerenes. antiaromatic
At each step pentagons
in the chemicaltransformation
a 1.45 ppm downfield shift, the aromatic character oNof two fullycompared
toPyPh
to reduce
theareorificegradualdownfield
shiftswere
observed
H2@6
hexagonsout of 18) decreased (decrease in
Figure 9. NICS patterns of the open-cagefullerene
derivatives
5,
7,
andsize,8, calculated
atthe together
B3LYP/6-31G*
levelof theory: red theregions
are for δ(14
< -5
8.
All
these
effects
assumed
to
be
added
to
cause
1
Ph pink for δ ) 0 to -5, pale blue for Ph
ppm,δ ) +5forto +10,
and
blue
for
δ
>
+10.
theshift
H NMR
of encapsulatedhydrogen: H2@5, δ
NICS value, 0.5-2.2 ppm) with the exception of t
H H
of the signal
H2 NMRsignal.
N
N the downfield
Ph
-7.25
ppm;
H
@6,
δ
-6.33
ppm;
H
@7,
δ
-5.80
ppm;
H
@8,
2
2
2
(increaseinabsolute
value,
0.1-0.6 ppm), whPh
Ph oxidation of the sulfur atom of H2@5, a 0.92 ppm
Py
Py
Upon
Electrochemical BehaviorNICS
of H
2@C60. To clarify th
N
Table 1.
Experimental
andCalculated NMR Chemical
Shiftsforδ -2.95
ppm;
H2@C60even, δ -1.45
ppm.
To
examineof
ifthetheoreticalPyantiaromaticcharacter
of in
most
pentagons(8 conducted
out of 9)Ph
downfield
shift
wasthoughthestructureelectronic
properties
of
H2@C60more
detail, we
the paramagnetic property of the encapsulated
species.
Inobserved,
accordEncapsulated
HydrogenofaSeriesofOpen-Cage
Fullerene
δ/ppm
10
8
6
0
−4
−6 H H−8−242
canwasreproduce this tendency,
wevalues
first ofconducted
by 1.1-2.2. (CV)A similar
trend is also
seenvoltammetry
in the ca
fullerenecalculations
skeletonitselfTheandNICS
cyclic voltammetry
and differential
pulsewith a very minute effect of encapsulatedhydrogen,the IR not affected.
Derivatives
H2@C
60
H2@6
37
the
GIAO
(gauge-independent
atomicorbital)calculationsatchemicaltransformationof 7 to 8, which cause
sulfoxide
6 indicatedthat the oxidation of S to HSO
influenced(DPV).
Upon
measurements
spectrum was almost the same as thatof empty
C60, exhibiting
H2@6
H2@7
H2@8
H2@C60 at room temperature for the rang
2@5
theof theorythe structuresby+)2.85
ppm (calculated
3.68-1 its level
not only
theB3LYP/6-311G**
carbocycles
vicinity
but alsoforalmost
all of optiof 0.0 todownfield-2.0 V (vsshift
Fc/Fc
in ODCBand for thevalue,
range of
0.0
H NMR (300 MHz, ODCB-d4) spectra of H2@4, H2@5, H2@6, and H2@7
four absorption bands at 1429.2, 1182.3,
576.7,
and526.5 cminaexplevel,
-7.25
-6.33
-5.80
-2.95
-1.45
Ph
mized
at
the
B3LYP/6-31G*
onaseriesoftheopenthis
way,
the
size
reductionofthreethe orificein eachstep-1
the cyclicof cm
the fullerenecalcd
cage(Figuretheto +1.0 V in
1,1,2,2-tetrachloroethane,reversible
reductionb
HN H(to be compared with 1429.2, 1182.3,
575.7, systems
and 526.5-5.87 10):
-4.72
-3.85
-0.17
+1.79
33
cage
and closed-cagefullerenes
containing
H2. AllchemicalPy H2@7 Ph
to1/2lower
the aromaticcharacterof thefullerene
cageonas+) andmagnetic
characteristics
ofmosthexagons
andpentagons
are
waves
(E
)
-1.13,-1.54,
-1.99
V
vs
Fc/Fc
∆
1.38
1.61
1.95
2.78
3.24
for
empty
C
measuredunderexactlythesameconditions).
60
δ/ppm
10
8
6
0
−4
−6
−8
−2
4
2
shiftsaretheexpressed
as the values
reference
to oftetramethA seriesof thesesize
reduction
processes
shto makeoverallof with
6 lowerthan that
irreversible
oxidation
peakorifice(Epa )+1.62
V) wereobserved
Only the band at 576.7 cm-1 of Hchanged
to an aromaticity
2@C60, correspondingatheb TablePh
ylsilanealsocalculated
using
same
level.
As
shown
in
At
300
MHz,
in
ODCB-d.
Calculatedatthe
GIAO-B3LYP/6be
accompaniedbyveryslightbut
gradualincrease
in
4
32
Py N
5. This higher
is presumably
characteristic
respectively, virtually at the same potentials as those for empty
out-of-plane vibration mode, is slightly
in energydue
thanto an electronegative
311G**//B3LYP/6-31G*
leveltheory.ofPh
1, thegroup.
GIAOAscalculations
were
found
to reproduce
theoftrend
the fullerene’s
which should
gradually
10
8
6
0
−4
−6 H2@7
−8
δ/ppm
4
2
the SdOa related example,
it hasbeen reported
C60. However,when weσ-frameworks,
applied more negative
potential
using
O −2
that of empty C60 by 1.0 cm-1. Thisofmight
be taken
as evidencePh
gradualdownfield
shifts,although
there
was
a
tendency
to3
3He@C the extent
of theby
total
π-conjugationon the fullerene su
Taylorand co-workers
that theNMR
signalof-5−1.44Op.p.m.
theshiftconditions
reported
Echegoyen
in toluene-acetonitrilN
thatderivatives
a slight 5,repulsive
interaction
withthe inner
Hlevel
9. NICS patterns of the open-cage fullerene
7, and 8, calculated
at by
the
B3LYP/6-31G*of theory:
redHe
regionsarefor δ <
60
2 moleculeTheobserved
gradualmust beduetaken
to thePy H HFigure
Phpink for δ ) 0 to -5, pale blue for δ ) +5 to +10, and blue for δ > +10.
underestimate
the2.8magnetic
shieldingeffectsof thedownfield
fullerenePh
together43asthe
thereduction
reason forof
observedppm,
Cl6 (δ
ppm)cageisdownfield
shiftedcompared(5.4:1)
atThese-10are°Callunderfromvacuum,H2@C6dN
has caused a very slight deformationof )the-12.3
spherical
of ppmPh
Py change
in magnetic
environment
ofof
this hydrogen,resulting
cage
in
the
extentwhich
gradually
increased
in
the
order
3
shiftsupon
thereductionoftheorificeS
to that
He@Cas60Ph
-15.1
ppm)
due to theand paramagnetic
was found toring
becomeslightly
but gradually moresize.
difficult than
H2@C60. The UV-vis spectrum wasalso ofthe samethat5Clof (δ )the
10
8
6
0
−4
−6
−8
δ/ppm
−2
4
2
changeindiamagnetic
currentsof
H2@5and
(∆δ
1.38)
to H
19mChemical
2@C
60 (∆δ 3.24).
Inas thefinal step,cagein whichorganic
adden
1. electronegative
Experimental
Calculated
ShiftsA
forsimilar tendency ofchloroaddends.
empty C60totaltheacquiresthemore
numberso
empty
C60.InAn
attempt toTable
measurethe Raman
spectrumof NMR
hexagons
and pentagons,
and the consequent
ringfullerene
currents,
the paramagnetic property of the encapsulated
species.
accord
11.8NMR
underestimationofthechemical
shift of encapsulated
H H
Encapsulated
Hydrogenofof
Fullerenecompletely
and theoriginal11,
C60 thestructurewas
H2@7
electrons
up to six.removed
As andshown
in Figurereduction
examinethea Series
effectof Open-Cageencapsulatedhydrogencage.
uponTotheprove this,H2@C60 was unsuccessful
because ofTostrongfluorescencefrom- S-3 of thefullerene
the diamagneticity
the IR
Derivatives and Hspecies
2@C60 in the GIAO-DFT
methodhas been reportedand
H Hwith a very minute effect of encapsulatedthehydrogen,potentials estimatedfrom the differential pulse voltammogram
reactivityof the outer fullerene
the solid-stateofmechano-2.4cage,
now underway.
60 cage. Further trials areparamagneticity
andsix-membered
spectrum was almost the same as that of emptyouter
C60, Cexhibiting(35)
Schleyer,P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; Hommdiscussed
in detail.H33,34
H2@5
H2@6
H2@8
H2@C60 all the π-conjugated five2@7
wereand-0.95,-1.89,and ca. -3.5 V fo
dimerization
H2@C
conducted
under the fullerenes
samev.-1.37,
E.
J. Am.
Chem. -2.39,
Soc. 1996,-2.95,
118, 6317.
60 wasThe
H2@Cchemical
stable.ofUpon
60 is thermallyrings
in the open-cage
5-8
of C60wereassessedfour absorption bands at 1429.2, 1182.3, 576.7,
andendohedral
526.5 cm-1fullerene expa38 It was -1.45(36)(a) Bühl,
M. Chem.sEur.
J. 1998,-1.37,
4, 734. -1.88,(b) Chen, -2.35
Z.; Cio
H
@4
-7.25
-6.33
-5.80
-2.95
H
@C
to
be
comparedwith -0.95,
found
that
the
conditionsaswepreviously
reported.
2
2
60
10
8
6
0
−4
−6
−8
δ/ppm
−2
4
2
heatingthepuresample
of
H
@C
at
500
°C
for
10
min
under
-1
2
by-0.17
the NICS(nucleus-independentchemical Rao,shifts)calcula- S-3 b 60
N.; Moncrieff,
D.; Bühl, M.; Hirsch, A.; Thiel, W. Theor.
(32) Bakowies,
W. Chem.
Phys.
1991,+1.79
151,
309.
(to be compared with 1429.2, 1182.3, 575.7, and 526.5 cm
calcd
-5.87
-4.72 D.; Thiel,-3.85-2.88,forand-3.35
forandempty C60. Thus the difference indumbbell-shaped
dimer,(H@CMalkina,)2, 2.78
wasin J.30%
2001,
106,V364.
(33) (a)M.; Kaupp,O.
L.;obtained
Malkin,V. G.
Comput.
Chem.
33,35,36
2M.;
60tions.
there was no decomposition
or releaseofBühl,
incorporated
Theobtained
NICS
valueseach
pentagon
∆
1.38
1.61
1.95
3.24
for empty C60 measured under exactly thevacuum,same conditions).
*
(37)
The
aromatic
characterinallhexagons
decreased
(by
the
abs
1999,
20,
91.
(b)
Bühl,
M.;
Hirsch,
A.
Chem.
ReV.
2001,
101,
1153.
*
H2@7
13
reduction potential
reachesnearly 0.15 V at the stage of six
isolatedyield
similarly
to the reactionof emptyGuo,
CshownApparently,
60.Q.-X.;hydrogen at all, as judged from the
C NMR
and
HPLC.
hexagon
inWu,
theY.-D.
Schlegel
Figureppm),
9. Uponand the antiaromatic character of all pentagon(34) Wang,
G.-W.; Zhang, X.-H.;
Zhan, H.;areJ. Org.diagrams of0.7-3.1
Only the band at 576.7 cm-1 of H2H@C@C
60, corresponding to an@C
C60
b Calculated
2601H NMR Chemical Shifta ofelectronreduction.
Although
the0.7-5.3
extentppm).
is so minute, this resul
At
300
ODCB-datHremovalthethe MHz,
insideinInsidehydrogen
theGIAO-B3LYP/6reactivityof theatom
outerfrom the(bywhichthe absolutevalue,
Chem. the2003,
68, not
6732.affect
4.doesHydrogen
Openofthesulfurorificeof
5,
causedout-of-plane vibration mode,32 is slightly higher
in energy than
311G**//B3LYP/6-31G*
level ofsignal
theory.for the inside hydrogen was observed
is taken characteras clear evidence
that hydrogen, as a slightly electro
42−2
The NMR
10
88
66
0
−4
−10
10
−4
−6
−8
−10 Cδ/ppm
60 cage.
-1
Cage Fullerenes. At each step in C
thechemicaltransformation
a 1.45 ppm downfield shift, the aromaticof most ofthat of empty
60 by 1.0 cm . This might be taken as evidence
9 VOL. repulsion
J.anAM.
CHEM. SOC.
128, NO. 24,
2
10
8
6
0
−4
−6
−8 δ / p.p.m.
δ/ppm
4
2
positive(decrease
molecule,inexerts
appreciable
electronic
withas a singlet
at δwere-4.04
ppm,39 whichtheis 8.58 ppm upfield
reduceorifice size, gradual downfield
shiftsobserved(14theoutshiftedof 18) decreased
absolute- S-3- −2
that a slight repulsive interaction with thetoinnerH2themolecule
The observed
gradualdownfield
shift
musthexagons
be3He@C
due to
the
outer
C
cage
when
the
π-system of the latter is charged
1
from
free
hydrogen,similar
to
the
case
for
(8.81
ppm
60
60
forsphericalthe H NMR
signal of encapsulated hydrogen: H2@5, δNICSvalue,
0.5-2.2
ppm)
with
the
exception
of
two
rings
has
causedaveryslightdeformation
of
the
cage
of
change in magnetic
environment
this
1
38bhydrogen, resulting from
moreppm),
than fourelectrons.
fromfreeH32of
He).
Figure S5 H NMR (300 MHz, o-dichlorobenzene-d4) spectrum of H2H@C.
-7.25 ppm; H2@6,ofδ -6.33 ppm; upfield
H2@7, δshift
-5.80
ppm;
@8,
(increasein absolute
NICS value,with
0.1-0.6
whereasthe60
2@C
60. The UV-vis spectrum was also the same as thatthe change
in diamagnetic
and paramagnetic
ring
additional
fullerene
derivatives,
H2currents
@16,
H2of
@17,ofandδ -2.95spectrum
ppm; H2@C
ppm.Three
To examine
if theoreticalantiaromaticcharactermost pentagons(8 out of 9) increased
empty C60. An attempt to measure the Ramanof 60, δ -1.45
SummaryPh* Impurities of the solvent.
hexagons and pentagons, and the consequent
total ring currents,
40
H2O

H2O

hexaneH2O-1.45 ppm

2

60

“the size reduction of theorifice in each step isshown to lower thearomatic character of thefullerene cage as a whole”.!

M. Murata, Y. Murata, K. Komatsu, J. Am. Chem. Soc. 2006, 128, 8024.!

Encapsulation  of  H2  in  C60  by  Organic  Synthesis	Endohedral  Fullerenes  Encapsulating  a  Molecule	
 31

properties of H2@C60!
N
a

NH2

−1.99
−1.54Vibration
High-speed
milling−1.13
5 µA
rt, 30 min
(CV)
−2.50
30%yield−2.02−1.16 −1.57

H2@C60

C60

−1.11

−1.52

2 µA
(DPV)

−1.99

C60

b

−1.15

1

0

−1.56

−2.02

⇒ “the inside hydrogen does
not affect the reactivity of theouter C60 cage”.!

−2.49

the same condition+
V vs Fc/Fc−1−230%yieldFigure S7 Cyclic voltammetry (CV) and differential pulse voltammetry (DPV).

H @C

2 60 and60 b, C60: 0.5 mM in o-dichlorobenzene, 0.05 M Bu4NBF4, scana, H2@C−1

rate 0.02 V s . Values of potential are read with reference to ferroceneferrocenium couple.

and!Properties of Endohedral C
electronic property of HSynthesis
2@C60

60

ARTICLESof the same kind (two directly connected Buckyprep columns, 10 mm
× 250 mm) for preparative purpose. Fullerene C60 was purchased from
H2@C60
Matsubo Co. m-Chloroperbenzoic acid was purchased from Aldrich
Co. Zinc (sandy) and titanium(IV) chloride were purchased from Wako
10 µA
Co.
Computational Method. All calculations were conducted using theGaussian98
260series of electronic structure program. The geometries were
−1.44
+1.62
fully optimized with the restricted Becke hybrid (B3LYP) method for
−1.07
C60
all calculations. The GIAO calculations were performed at the B3LYP/b
6-311G** level of theory using the optimized structures at the B3LYP/
6-31G* level of theory. NICS calculations were performed at theB3LYP/6-31G* level of theory using the optimized structures at theB3LYP/6-31G* level.
+1.63
Cyclic Voltammetry and Differential Pulse Voltammetry of+
H2@C60. The measurements were conducted on a BAS electrochemical
V vs Fc/Fc2
10−1
analyzer ALS600A using a four-necked flask equipped with threeplatinum wires serving as reference, counter, and working electrodes.
Figure S8 Cyclic voltammetry (CV). Figurea, H2@C
and
b,
C
:
0.5
mM
in
60 of (a) H2@C60 and (b) C60 in toluene-CH3CN
11.60 CV and DPV
About
× 10-4 M solutionsof H2@C
and C60 wereused. TBAPF
K.2Komatsu,
M. Murata,
Y. 60Murata,
Science
2005,6 307, 238.!
−1(5.4:1)
at -10 °C.
1,1,2,2-tetrachloroethane, 0.1 M Bu4NPF
6, scan rate 0.02 V s . Values(0.1M)
was usedK.asKomatsu,
supporting electrolyte.
For a low-temperature
M. Murata, Y. Murata,
J. Am. Chem.
Soc. 2006, 128, 8024.!
a

−1.07

−1.44

⇒ H @C becomes more difficult
to be reduced as it acquires morethan three electrons.!

CV and DPV of H2@C60 and C60!

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 32

Encapsulation  of  H2  in  C60  by  Organic  Synthesis	
summary!
Py

N

Ph

HN N
+

Ph
Py

Ph

N

Py
O

Ph

1O

o-Cl2C6H4
180 ºC, 17 h
50% yield

Ph

N

Py
O

Ph

O
S8 (1 eq)
TDAE (1 eq)

2

CCl4, hυunder air, 6 h
60% yield

N

Ph
Ph
O

S

o-Cl2C6H4
180 ºC, 30 min
77% yield

C60
H-H

total 5.2% yield(800 atm)
200 ºC
8h
100% yield

・H2@C60 and C60 showed almost the same properties.!
・the endohedral chemical shift for the H2 is sensitive !
to the transformation of the outer cage.
H2@C60
Py

N

Ph
Ph

340 °C, 2 h Py N
O
61% yield
O

Ph

Py
O

Ph

O
S

TiCl4, Zn
o-DCB/THF
80 °C, 2 h
88% yieldNtoluenevisible lightrt, 17 h
42% yield

Ph
Ph

Py
O

O
m-CPBA
toluenert, 13 h
99% yield

N

Ph
Ph
O

S

Contents

33

Introduction-History of Buckminsterfullerene-How to Produce Fullerenes?

Aromaticity  of  Fullerenes-What is Aromaticity?!
-Aromaticity of Buckminsterfullerene

Endohedral  Fullerenes  Encapsulating  a  Molecule	-Why Endohedral Fullerenes?!
-Conventional Synthesis of Endohedral Fullerenes!
-“Molecular Surgery”!
H2@C60, H2O@C60

Summery  &  Outlook

http://www.ec.gc.ca/biosphere/Encapsulation  of  H2O  in  C60  by  Organic  Synthesis	Endohedral  Fullerenes  Encapsulating  a  Molecule	
 34

REPORTSsynthesis!

Ar =

N

tBu

O

X-ray

Ar =

Bu

Ar

O
O

HO
Fig. 1. (A) Synthetic route of open-cage C60 5 (1-chloronaphthalene being abbreviated as 1-ClNp) and (B) the x-ray structure of 5a at the 50% probability
level. The solvent molecules were omitted for clarity.
t

Ar
O

Downloaded from www.sciencemag.org on May 13, 2013Ar

5a was observed and a new species, probably 4a of the integrated peak areas. The encapsulation erated in situ, followed by addition of a water(fig. S19), wasAr
detected with high-performance ratio is apparently lower than the reported values molecule to regenerate 5b encapsulating an H2O
liquid chromatography (HPLC) (Buckyprep, by Iwamatsu et al. (75%) (11) and by Gan and co- molecule. The 1H NMR spectrum of H2O@5b
N Nanalysis. However, because this com- workers (88%) (12), reflecting the smaller size of displayed a strongly shielded sharp signal at –9.87
toluene)Ar
4b than those on their parts per million (ppm), corresponding
pound+quickly went back to hydrate 5 at roomAr the opening on tetraketone
Ar
Ar to the enO H2O molecule (11, 12). The encapsulatemperature, characterization of 4 was not achieved compounds. However, quantitative encapsulation capsulated
O by fast atom bombardment
yet. As a similar reaction is known in the litera- of an H2O molecule inside 5b was achieved when tion was also supported
ture (17), the conversion between 5a and 4a this process was conducted under the high pres- mass spectrometry analysis displaying the mowould be performed quantitatively. The size of sure of 9000 atm at 120°C for 36 hours (Fig. 2 lecular ion peak at a mass-to-charge ratio m/z
1
NMMO
the opening on tetraketone 4 is greater than that and figs. S20 to S22). The high pressure O
1139 (M+H+), corresponding to H2O@5b
is critical;(15).
2
of hydrate 5, implying that insertion of an H2O only 40% encapsulation was observed under
Our synthetic pathway for closing the 135000 atm under the similar
conditions.
membered-ring opening on H2O@5b is a coupling
molecule into 4 could be possible.
1-ClNp1-ClNp-CS
THF
2, hυ
The formation of H2O@5b can be explained reaction of two carbonyl groups with a phosphite
When hydrate 5b was refluxed in wet toluene
260ºC,and40thehresult- by the dynamic control of the opening
rt, 23-27
h ester (18). As shown in Fig. 2, the reaction
rt, 3of h(15 mL of water in 10 mL
toluene)size. Eliming product was analyzed by 1H nuclear magnetic ination of a water molecule
H
from
5b
generates
4b.
O@5b
with
excessive
amountsof
P(Oi-Pr)2
3
43% yield (2 steps)
88% yield
resonance (NMR), an H2O molecule encapsulated The insertion of an H2O molecule into 4b takes (i-Pr, isopropyl) in refluxing toluene gave H2O@2bC5binside60was detected in 8% yield by comparison place through the 16-membered-ring opening gen- in 50% isolated yield without the loss of the

H2O

Ar
O

Ar
O
O
HO

Fig. 2. Encapsulation
Kurotobi, Y. Murata, Science 2011, 333, 613.!
of an HK.
2O molecule toEncapsulation  of  H2O  in  C60  by  Organic  Synthesis	Endohedral  Fullerenes  Encapsulating  a  Molecule	
 35

synthesis!
O

Ar
O

O

Ar

Ar
O
O

O
O

O

–H2O

H2O

–H2O

Ar

Ar

O

O

Ar

Ar

O
HO

encapsulation of H2O was supported by!
1H NMR: δ = -9.87 ppm!
FAB mass!

Ar

O

O
HO

HO
toluene/H2O (667:1)
9000 atm
120 °C, 36 h
quant

O
HO

K. Kurotobi, Y. Murata, Science 2011, 333, 613.!

Encapsulation  of  H2O  in  C60  by  Organic  Synthesis	Endohedral  Fullerenes  Encapsulating  a  Molecule	
 35

synthesis!

Ar
O

O

Ar

Ar
O

O

Ar

O
O
–2 O=P(OiPr)3
ca. 60% yield–H2O–2 O=P(OiPr)3

H2O

Ar
Ar

H2O@C60

O

Ar

Ar
O

Al2O3

P(OiPr)3

360 °C, 1 h
29% yield

toluene120 °C, 15 h
50% yield

HO

O
HO

K. Kurotobi, Y. Murata, Science 2011, 333, 613.!

encapsulated species: Dd 0.02 ppm for He (25),
Dd 0.08 ppm for H2 (8), Dd 0.17 ppm for Ar(26), Dd 0.39 ppm for Kr (27), and Dd 0.95 ppm

Downloaded from w

structure of the outer C60 cage (15).
No escape of the encapsulated H2O moleculem H2O@C60 was observed when the powder

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 36

10
Encapsulation  of  H2O  in  C60  by  Organic  Synthesis	

3 A

UV-Vis spectra(solid)(dot)-1.08 -1.46 -1.91 -2.38(-1.08) (-1.47) (-1.92) (-2.39)⇒ “no detectable electronic interaction present !
1
0
-1
-2
betweenthe encapsulated
H2O and C
60 cage”.!
-2 V vs Fc/Fc+

0 and DPV!
-1
CV

Figure S36. Dif f erential pulse voltammetry (DPV) of H2O@C60 (solid) and C60 (dot).

13C NMR:SCIENCEVOLδ
333
29 JULY 2011
= 142.89
ppm (C1 60: 143.78ppm)! 615 0.1 M Bu4NPF6, scan rate: 20 mVs-1.
mM
in o-dichlorobenzene,! ⇒ “rapid rotation of the encapsulated
H2O”.!
Values of potential(C60 in parentheses) are read with ref erence to f errocene/f errocenium
APCI mass!
couple.
no escape of H2O was observed (420 ℃, 30 min)!
ODCB“wet fullerene”!
“polar C60”

3 A

S28 / S36
H2O

mag.org

properties!

+1.32(+1.32)

Fig. 3. X-ray structure of the molecular complex H2O@C60·(NiOEP)2 at the 50% probability
X-ray
oftwoHfive-membered
2O@C60・(NiOEP)
level. (A) The viewpointfrom therings overlapped 2with hydrogen atoms
x-membered rings overlapped with displaying hydrogen atoms determined experimentally for H2O
just at the center of the C60 cage1
1H NMR: δ = -4.81 ppm!

-2

104M-1cm-1

evidence for the existence of the encapsulated H2O!

-1

+1.32
(+1.32)
1

H2O@C600-1.08 -1.46 -1.91 -2.38(-1.08) (-1.47) (-1.92) (-2.39)-1-2⇒ encapsulated H2O is electrochemically stable.!
K. Kurotobi, Y. Murata, Science 2011, 333, 613.!

Endohedral  Fullerenes  Encapsulating  a  Molecule	
 37

Encapsulation  of  H2O  in  C60  by  Organic  Synthesis	
summary!
Ar

N N
+

Ar

Ar
Ar

Ar
O

Ar

1O

1-ClNp260 ºC, 40 h

O

Ar

Ar
O

O

2

1-ClNp-CS2, hυ
rt, 23-27 h
43% yield (2 steps)

O

HO

NMMO

HO

THF
rt, 3 h88% yield

C60
Ar =

total 5.2% yield

H
N

H
tBu

toluene9000 atm
120 °C, 36 h
95% yield

・single molecule of H2O without any hydrogen bonds!
can be completely isolated.!
・bulk synthesis of H2 O@C60 allow the study of !
the intrinsic properties of a single molecule of H2O.!
Ar

H2O@C60

Ar
O

Ar

Ar
O

Al2O3

P(OiPr)

360 °C, 1 h
29% yield

toluene120 °C, 15 h
50% yield

3

O

HO

O
HO

Contents

38

Introduction-History of Buckminsterfullerene-How to Produce Fullerenes?

Aromaticity  of  Fullerenes-What is Aromaticity?!
-Aromaticity of Buckminsterfullerene

Endohedral  Fullerenes  Encapsulating  a  Molecule	-Why Endohedral Fullerenes?!
-Conventional Synthesis of Endohedral Fullerenes!
-“Molecular Surgery”!
H2@C60, H2O@C60

Summery  &  Outlook

http://www.ec.gc.ca/biosphere/Summary  &  Outlook
Introduction-History of Buckminsterfullerene-How to Produce Fullerenes?

Aromaticity  of  Fullerenes-What is Aromaticity?!
-Aromaticity of Buckminsterfullerene
C60 has ambiguous aromatic character.!

Endohedral  Fullerenes  Encapsulating  a  Molecule	-Why Endohedral Fullerenes?!
-Conventional Synthesis of Endohedral Fullerenes!
-“Molecular Surgery”!
H2@C60, H2O@C60
total 5.2% yield

total 5.2% yield

39

40

Summary  &  Outlook
Endohedral  Fullerenes  Encapsulating  a  Molecule	
Scientific interest!!
+
expected to have high potential such as…
-synthesis of new endohedral fullerenes which can’t be obtained by conventional methodologies!
-highly efficient (gram scale) synthesis of endohedral fullerenes → material sciences!
-control π-electron system from the inside of fullerenes!
-completely “isolated” molecule!
-encapsulation of highly active species!
etc.