AlCl3-mediated mono-, di-, and trihydroarylation of [60]fullerene

Article abstract of DOI:10.1002/anie.200700062

(Chemical Equation Presented) Functionalization of fullerenes can be achieved inexpensively by Friedel-Crafts reaction. For instance, treatment of [60]fullerene with AlCl₃ in toluene gave mono-, di-, and tritolyltrihydro[60]fullerenes in modera

Full text of DOI:10.1002/anie.200700062

Angewandte
Chemie
DOI: 10.1002/anie.200700062
Fullerene Chemistry
AlCl3-Mediated Mono-, Di-, and Trihydroarylation of [60]Fullerene**
Akihiko Iwashita, Yutaka Matsuo,* and Eiichi Nakamura*
Reported over 10 years ago by Olah et al.,[1] the AlCl3-
mediated Friedel–Crafts-type hydroarylationreaction
between [60]fullerene and benzene or toluene represents an
early example of multifunctionalization reactions of fullerene
molecules and still remains an intriguing reaction in several
respects. First, as it requires only an aromatic solvent and
AlCl3, it is potentially a very inexpensive and convenient
synthetic method. Second, the report described the formation
of a mixture of many compounds formulated as C60ArnHn
(Ar= Ph, C6H4Me; n = 1–3, 6, 12, 16), suggested low product
selectivity, and did not give any structure assignment. As a
[2]
result, there have beenno published reports
of attempts to
utilize this reactionfor the sytnhesis of useful materials
despite the known utility of polyaryl-[3,4] and polyhydrofuller-
ene[5,6] derivatives. We report hereinthat the Friedel–Crafts-
type reactionas reported by Olah et al. produces mono-, di-,
and trihydrofullerene derivatives in synthetically viable yields
under the conditions most suitable for the synthesis of each
class of compounds (Scheme 1). The reaction is applicable not
only to intact fullerene but also to those that are already
functionalized and is useful for the synthesis of new h5-
organometallic compounds.[7]
Scheme 1. AlCl3-mediated hydroarylations of fullerene.
Careful reexamination of the reaction using a variety of
conditions and substrates revealed that the reaction first
produces mono- and dihydroarylation products and progres-
sively gives higher hydroarylationproducts as the amount of
toluene is increased and as a longer reaction time is
employed. We noted that the hydroarylated products are
air-sensitive under ambient light, which may have caused
problems of structural identificationinprevious studies. For
instance, the reaction of a mixture of [60]fullerene (30 mg)
and AlCl3 (30 mg, 5.4 equiv) intoluene (20 mL) at 25 8C for
32 h indeed formed a complex mixture of tri-, tetra-, penta-,
and higher hydroarylated [60]fullerenes as determined by
HPLC analysis and mass spectrometry. The presence of water,
one equivalent to fullerene, is essential for a fast and
reproducible reaction. Under strictly anhydrous conditions
the reaction is very slow, and in the presence of a large
amount of water the reaction does not proceed. The use of
HCl gas without AlCl3 was ineffective. We therefore consider
that water produces HCl, which is further activated through
removal of chloride anion by an AlIII species to form a very
reactive protonsource. [8]
When we use a less reactive benzene derivative, we can
stop the reactionquite selectively at the monohydroarylation
stage. For instance, the reaction of [60]fullerene in chloro-
benzene in the presence of AlCl3 afforded C60(4-ClC6H4)H (1)
in39% yield with 50% recovery of fullerene (Scheme 1;
Table 1, entry 1). Anisole was less reactive and gave C60(4-
OMeC6H4)H (2) only in 10% yield with 80% recovery of
fullerene (Table 1, entry 2).[9] Inboth cases, the additiontook
place in a 1,2 manner as has been described for such reactions
under basic conditions.[10] 1,2-Dichlorobenzene and trifluor-
omethylbenzene were unreactive.
Whena more reactive areen was used, the reaction
proceeded to the dihydroarylationstage. Thus, we obtained
diaryl dihydro[60]fullerene C60(4-MeC6H4)2H2 (3) in52%
yield after flash chromatography (Scheme 1; Table 1, entry 3)
when fullerene was treated with toluene (10 equiv), AlCl3
(5 equiv), and water (1 equiv) in 1,2-dichlorobenzene for
30 minat 25 8C. The atmospheric-pressure chemical ioniza-
tiontime-of-flight (APCI-TOF) mass spectrum of the product
exhibited a signal at m/z 903.11504 [MÀH+], whereas the
1H NMR spectrum exhibited only one set of 1H NMR signals
[*] Dr. Y. Matsuo, Prof. E. Nakamura
Nakamura Functional Carbon Cluster Project, ERATO
Japan Science and Technology Agency
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan)
Fax: (+81)3-5800-6889
E-mail: matsuo@chem.s.u-tokyo.ac.jp
nakamura@chem.s.u-tokyo.ac.jp
A. Iwashita
Department of Chemistry
The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan)
[**] We thank the 21st Century COE Program for Frontiers in Funda-
mental Chemistry for partial financial support.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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Table 1: Hydroarylation of [60]fullerene.[a]
Entry Solvent
ClC6H5
2
3
polarity with respect to silica gel
chromatography. The reactionpro-
ceeded faster when1,2-dichloro-
benzene was used as a cosolvent
and gave the tris adduct 4 in30 min
(entry 5). Heating of the mixture
4a,b at 808C afforded only 4b, an d
whenthe hydroarylationreaction
was carried out at 808C for 10 min
inthe presence of 20% 1,2-dichlor-
obenzene the reaction afforded
only 4b in50% yield (Table 1,
entry 6). The result strongly sug-
gests that 4a and 4b are isomeric
probably with respect to the posi-
tionof the hydrogenatoms rather
thanthe tolyl groups. The reaction
could be performed easily ona 1-g
T [8C]
t [min]
Main product
Yield [%]
1
25
80
25
25
25
80
25
25
25
25
120
1200
480
80
30
10
30
20
25
20
C60(4-ClC6H4)H (1)
39
10
52
52
56
50
51
17
31
27
MeOC6H5[b]/1,2-Cl2C6H4
toluene[c]/1,2-Cl2C6H4
toluene
C60(4-OMeC6H4)H (2)
C60(4-MeC6H4)2H2 (3)
C60(4-MeC6H4)3H3 (4a,b)
C60(4-MeC6H4)3H3 (4a,b)
C60(4-MeC6H4)3H3 (4b)
C60Ph3H3 (7)
C60(4-tBuC6H4)3H3 (8)
C60(3,4-Me2C6H3)3H3 (9)
C60(4-PhC6H4)3H3 (10)
4
5
6
toluene/1,2-Cl2C6H4 (4:1)
toluene/1,2-Cl2C6H4 (4:1)
benzene/1,2-Cl2C6H4 (4:1)
tBuC6H5/1,2-Cl2C6H4 (4:1)
o-xylene/1,2-Cl2C6H4 (4:1)
biphenyl[e]/1,2-Cl2C6H4
7[d]
8[d]
9[d]
10
[a] General conditions: C60 (72.0 mg, 0.10 mmol) and AlCl3 (66.7 mg, 0.50 mmol) were mixed in solvent
(20 mL single solvent or 25 mL mixed-solvent system) containing water (0.10 mmol). [b] Anisole
(10 equiv). [c] Toluene (10 equiv). [d] The reaction without 1,2-dichlorobenzene was slower because of
insufficient solubility of fullerene, but the yield was almost the same. [e] Biphenyl (100 equiv).
corresponding to the p-tolyl moiety and one singlet signal at
d = 5.78 ppm corresponding to two protons on the C60
scale (see Experimental Section). AlBr3 and GaCl3 similarly
catalyzed the reactionbut gave lower yields.
skeletonwhich idnicated
Cs symmetry of the molecule.
Compounds 4a and 4b were separated from each other by
preparative HPLC (RP-FULLERENE, Nomura Chemical
Co., toluene/acetonitrile = 4:6), and their structures were
Neither ortho- nor meta-substituted isomers formed probably
because of the steric effect of the bulky fullerene molecule.
Unambiguous structure assignment of 3 was achieved by X-
ray crystallographic analysis of a single crystal obtained by
1
studied by H an d13C NMR, and UV/Vis spectroscopy, and
high-resolutionAPCI-TOF mass spectrometry measure-
slow diffusionof hexane to a solutionof
3 in1,2-dichloro-
ments. The UV/Vis spectra of 4a and 4b showed a character-
benzene (Figure 1).[11] This is a rare example of crystallo-
graphic analysis obtained for a 1,2,3,4-tetrasubstituted adduct
of [60]fullerene.[12]
istic absorptionpattern(
lmax = 350 nm and 396 nm) as
previously reported for penta(organo)hydro[60]fullerenes.[3]
1
The H NMR spectrum of 4a exhibited signals at d = 4.90,
5.43, and 5.56 ppm assigned to the three hydrogen atoms
directly attached to the fullerene core (Figure 2). The first two
Figure 2. The 1H NMR chemical shifts [ppm] and coupling constants
for the hydrogen atoms of 4a and 4b.
Figure 1. Molecular structure of 3: a) ORTEP drawing with ellipsoids at
the 30% probability level (C ellipsoids, H spheres); b) space-filling
models of top and side views (C gray, H white).
signals are coupled with each other with a small coupling
5
constant 5JH-H = 3.6 Hz characteristic of JH-H coupling
between the protons on a hexagon in a dihydro[60]fullerene.[6]
The first and the third signals also exhibited a small coupling
4
Whenthe reactionwas carried out with a large excess of
toluene, the reaction continued to the trihydroarylation stage
to give triaryl trihydro[60]fullerene C60(4-MeC6H4)3H3 (4) in
52% yield as a moderately air-sensitive compound under
ambient light (Table 1, entry 4). This sensitivity is most likely
attributed to photooxidationof the hydrogenatoms attached
to the fullerene core. The product consisted of a mixture of
regioisomers 4a (80%) and 4b (20%) that display similar
constant JH-H = 0.9 Hz, indicating that these two hydrogen
atoms are neither in a 1,2 nor in a 1,4 relationship. In the
1H NMR spectrum of 4b, a large coupling constant between a
3
pair of the 1,2-hydrogenatoms was observed ( JH-H = 12 Hz)
5
while another pair of the hydrogen atoms exhibited JH-H
=
3.5 Hz. It is unclear at this time why 4b is thermodynamically
more stable than 4a, and how this prototropy reaction takes
place.
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The mixture of the triaryl trihydrofullerenes 4a,b was
converted into a single h5-organometallic complex,[7] which
gave support to the above structural assignment. Thus,
treatment of a mixture of 4a and 4b with KOtBu inTHF
gave a dark red solution,[13] which upontreat-
Treatment of C60(CH2SiMe2OiPr)H (11)[14] with five equiva-
lents of AlCl3 intoluene afforded a mixture of the dihy-
droarylated product C60(4-MeC6H4)2(CH2SiMe2OMe)H3
(12a,b) in57% yield (Scheme 3). The isopropyloxy group
ment with [RuCl2(CO)3]2 provided a rutheniu-
m(II)
complex
[Ru{C60(4-MeC6H4)3H2}-
Cl(CO)2] (5) in18% yield as shownin
Scheme 2. Whentreated with [RuCp-
(MeCN)3][PF6] (Cp: cyclopentadienyl), it
afforded
a bucky ruthenocene [Ru{C60(4-
MeC6H4)3H2}Cp] (6) in11% yield. From the
1H NMR spectra, compounds 5 and 6 dis-
played characteristic signals of Cs-symmetric
structures which indicate that the metal is
bonded in an h5 fashion and hence supports
the structural assignment of 4a,b. Onthe basis
Scheme 3. Hydroarylation of an alkylhydro[60]fullerene.
onthe siliconatom was replaced by a methoxy group upon
methanol workup. We expect that the flexibility of this
synthetic approach will allow us to synthesize a variety of new
types of organometallics and fullerene derivatives of interest
[15–17]
inmaterials science.
Experimental Section
Synthesis of 4 as a mixture of 4a and 4b: Toluene (280 mL) containing
water (25.0 mL, 1.39 mmol) was added to a mixture of C60 (1.00 g,
1.39 mmol) and aluminum(III) chloride (0.923 g, 6.94 mmol). The
reactionmixture was stirred for 80 minat 25 8C before water (2 mL)
was added. TLC analysis showed only one spot with Rf = 0.52 (CS2/
hexane = 2:1) while the rest of the product stayed near the baseline.
Isolationof this product was carried out inthe dark because of its
moderate air-sensitivity under light. The dark brown reaction mixture
was passed through a pad of silica gel (eluent: toluene), and the
solvent from the eluate was removed by evaporation. This crude
product was purified by columnchromatography (6 cm(ID) ” 25 cm,
350 g silica gel, CS2/hexane = 2:1; Rf = 0.52). The first pale brown
fraction (ca. 600 mL) contained a small amount of a mono and a bis
adduct. The following 400-mL fraction contained the desired tris
adducts, and the final 200-mL fraction contained a mixture of the
desired tris adduct and polyarylated fullerenes. This last fraction was
purified againon70 g silica gel (3 cm(ID) ” 20 cm, CS 2/hexane = 2:1).
The first brown fraction (ca. 50 mL) was collected and combined with
the second fraction from the first chromatography step. The
combined fractions were concentrated under vacuum until a solid
just began to appear on the inside wall of the flask. Methanol
(200 mL) was added to precipitate the product. The title compound 4
(693 mg, 50%; 4:1 mixture of 4a/4b) was obtained by filtration as a
brownpowder, which was over 95% pure according to 1H NMR
spectroscopic analysis. Spectroscopic data are described in the
Supporting Information.
Scheme 2. Synthesis of ruthenium fullerene complexes.
of the reported reactivity of h5-hydrofullerene metal com-
plexes,[6] we expect that the two hydrogenatoms in 5 and 6 can
be deprotonated and alkylated to provide access to further
functionalized products.
Table 1 illustrates the scope of the trihydroarylation
reaction with several different benzene derivatives in 1,2-
dichlorobenzene. The hydroarylation reactions took place
with benzene as well as substituted benzenes, tert-butylben-
zene, o-xylene, and biphenyl to afford the corresponding
triaryl trihydrofullerenes C60Ph3H3 (7), C60(4-tBuC6H4)3H3
(8), C60(3,4-Me2C6H3)3H3 (9), and C60(4-PhC6H4)3H3 (10) in
51%, 17%, 31%, and 27% yields, respectively (Table 1,
entries 7–10). In all cases, we isolated a single para regioiso-
mer with respect to the substitution pattern of the benzene
ring. We detected only a trace amount of dihydroarylated
products but observed higher hydroarylated products, whose
structures we could not assign with certainty.
Received: January 6, 2007
Published online: March 27, 2007
Keywords: aluminum · Friedel–Crafts reaction · fullerenes ·
.
hydroarylation · ruthenium
The present procedure can be applied not only to intact
[60]fullerene but also to a monoalkyl hydro[60]fullerene,
which then affords monoalkyl diaryl trihydro[60]fullerenes.
[1] a) G. A. Olah, I. Bucsi, C. Lambert, R. Aniszfeld, N. J. Trivedi,
D. K. Sensharma, G. K. S. Prakash, J. Am. Chem. Soc. 1991, 113,
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Communications
9387 – 9388; b) G. A. Olah, I. Bucsi, D. S. Ha, R. Aniszfeld, C. S.
[8] H2SO4 and CF3SO3H did not catalyze the reaction at all.
[9] The low reactivity of anisole may be attributed to complex
formationwith AlCl 3; see: G. A. Olah, . Molnµr, Hydrocarbon
Chemistry, 2nd ed., Wiley, Hoboken, NJ, 2003, pp. 215 – 283.
[10] a) A. Hirsch, T. Grösser, A. Skiebe, A. Soi, Chem. Ber. 1993, 126,
1061 – 1067; b) A. Hirsch, Synthesis 1995, 895 – 913.
[11] CCDC 632010 (3) contains the supplementary crystallographic
data for this paper. These data canbe obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[12] G. P. Miller, M. C. Tetreau, M. M. Olmstead, P. A. Lord, A. L.
Balch, Chem. Commun. 2001, 1758 – 1759.
[13] Y. Matsuo, K. Tahara, E. Nakamura, Chem. Lett. 2005, 34, 1078 –
1079.
[14] H. Nagashima, H. Terasaki, E. Kimura, K. Nakajima, K. Itoh, J.
Org. Chem. 1994, 59, 1246 – 1248.
[15] a) M. Sawamura, K. Kawai, Y. Matsuo, K. Kanie, T. Kato, E.
Nakamura, Nature 2002, 419, 702 – 705; b) Y. Matsuo, A.
Muramatsu, R. Hamasaki, N. Mizoshita, T. Kato, E. Nakamura,
J. Am. Chem. Soc. 2004, 126, 432 – 433; c) Y. Matsuo, A.
Muramatsu, Y. Kamikawa, T. Kato, E. Nakamura, J. Am.
Chem. Soc. 2006, 128, 9586 – 9587.
[16] S. Zhou, C. Burger, B. Chu, M. Sawamura, M. Nagahama, M.
Toganoh, U. E. Hackler, H. Isobe, E. Nakamura, Science 2001,
291, 1944 – 1947.
[17] a) F. Wudl, J. Mater. Chem. 2002, 12, 1959 – 1963; b) D. M. Guldi,
S. Fukuzumi in Fullerenes: From Synthesis to Optoelectronic
Properties (Eds.: D. M. Guldi, N. Martin), Kluwer, Dordrecht,
2003, pp. 237 – 265.
Lee, G. K. S. Prakash, Fullerene Sci. Technol. 1997, 5, 389 – 405.
[2] The synthesis of diaryl dihydro[60]fullerene was recently
described in oral presentation: S. Tochika, M. Kato, C. Kuang,
K. Kokubo, T. Oshima, 31st Fullerene Nanotubes General
Symposium (Mie, Japan) 2006, poster presentation 1P-4.
[3] a) M. Sawamura, H. Iikura, E. Nakamura, J. Am. Chem. Soc.
1996, 118, 12850 – 12851; b) M. Sawamura, H. Iikura, T. Ohama,
U. E. Hackler, E. Nakamura, J. Organomet. Chem. 2000, 599,
32 – 36; c) Y. Matsuo, A. Muramatsu, K. Tahara, M. Koide, E.
Nakamura, Org. Synth. 2006, 83, 80 – 87.
[4] a) R. Taylor, G. J. Langley, M. F. Meidine, J. P. Parsons, A. K.
Abdul-Sada, T. J. Dennis, J. P. Hare, H. W. Kroto, D. R. M.
Walton, J. Chem. Soc. Chem. Commun. 1992, 667 – 668; b) F.
Diederich, C. Thilgen, Science 1996, 271, 317 – 323; c) Y. Murata,
M. Shiro, K. Komatsu, J. Am. Chem. Soc. 1997, 119, 8117 – 8118.
[5] a) Y. Rubin, P. S. Ganapathi, A. Franz, Y.-Z. An, W. Qian, R.
Neier, Chem. Eur. J. 1999, 5, 3162 – 3184; b) J. Nossal, R. K.
Saini, L. B. Alemany, M. Meier, W. E. Billups, Eur. J. Org. Chem.
2001, 4167 – 4180.
[6] a) M. Toganoh, Y. Matsuo, E. Nakamura, Angew. Chem. 2003,
115, 3654 – 3656; Angew. Chem. Int. Ed. 2003, 42, 3530 – 3532;
b) M. Toganoh, Y. Matsuo, E. Nakamura, J. Am. Chem. Soc.
2003, 125, 13974 – 13975.
[7] a) M. Sawamura, Y. Kuninobu, M. Toganoh, Y. Matsuo, M.
Yamanaka, E. Nakamura, J. Am. Chem. Soc. 2002, 124, 9354 –
9355; b) Y. Matsuo, E. Nakamura, Organometallics 2003, 22,
2554 – 2563; c) Y. Matsuo, Y. Kuninobu, S. Ito, E. Nakamura,
Chem. Lett. 2004, 33, 68 – 69; d) Y. Matsuo, Y. Mitani, Y.-W.
Zhong, E. Nakamura, Organometallics 2006, 25, 2826 – 2832.
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