Synthesis of a short-chain fullerene dimer

Article abstract of DOI:10.1016/j.tetlet.2006.08.061

The synthesis of a short-chain fullerene dimer via bifunctional cycloaddition is demonstrated. A mono-functionalised C₆₀ species is isolated, and has the potential for further organic functionalisation.

Full text of DOI:10.1016/j.tetlet.2006.08.061

Tetrahedron Letters 47 (2006) 7413–7415
Synthesis of a short-chain fullerene dimer
*
Timothy J. Hingston, Mark R. Sambrook, Kyriakos Porfyrakis and G. Andrew D. Briggs
Department of Materials, Oxford University, Oxford, OX1 3PH, United Kingdom
Received 18 July 2006; revised 7 August 2006; accepted 17 August 2006
Abstract—The synthesis of a short-chain fullerene dimer via bifunctional cycloaddition is demonstrated. A mono-functionalised C60
species is isolated, and has the potential for further organic functionalisation.
ꢀ
2006 Elsevier Ltd. All rights reserved.
Multi-fullerene systems, in which the carbon cages are
covalently linked, are of great interest as they provide
simple models of polymeric or coalesced fullerenes
and, if linked by optically or electrochemically active
2,3-dimethylbutadiene followed by a twofold N-bromo-
1
7
succinimide (NBS) bromination
butyronitrile (AIBN) as an initiator. This was then
reacted with C60 by iodine-induced elimination of the
using azobisiso-
1
8
1
19
chains, may possess novel electronic properties. The
bromine groups in the presence of 18-crown-6. Since
photophysical properties of numerous C -based dimer
this step is normally carried out in dimethylformamide,
and fullerenes have a poor solubility in this solvent, the
synthesis had to be transferred to toluene using 18-
6
0
2
molecules, including those linked by thiophenes, tetra-
3
4
thiafulvenes and p-conjugated oligomers, have been
studied and, in some cases, such molecules are investi-
gated as components in photovoltaic devices. Fullerene
crown-6 as a phase transfer catalyst. This gave both
5
20
the monofunctionalised C
1
in 75% yield and a sym-
6
0
2
1
dimers can be prepared by either dimerisation of fuller-
ene cages or fullerene derivatives or through bifunc-
tional cycloadditions. Only a limited number of short-
chain dimers have so far been reported and all involve
direct modification of the fullerene cages. These systems,
prepared by either solution chemistry or solid-state high
metrical C60 dimer 2 in 12% yield (Scheme 1). A suc-
cessful separation of the reaction mixture was achieved
by HPLC, with the monomer eluting after 6.23 min
and the dimer after 19.68 min (Buckyprep-M
À1
20 · 250 mm, toluene, 18 ml min ). In addition, unre-
acted C (13%) eluted after 7.03 min.
6
0
6
speed vibration milling (HSVM) include the directly
7
,8
9,10
bonded C120
,
oxygen bridged C120O,
and
MALDI mass spectrometric analysis of the monomer
and dimer gave peaks at m/z 959.9 and 1521.1, respec-
tively, corresponding to the molecular ions of the two
species (Fig. 1).
1
1
12
C120O , carbon bridged C
germanium and silicon bridged dimers. In 1993,
and the more unusual
2
121
1
3
14
Belik et al. reported the reaction of C60 with o-quino-
1
5
dimethane as a route to stable C60 derivatives, and this
cycloaddition strategy has been employed many times in
preparing fullerene dimers with controlled cage separa-
tion.1 In all cases an aromatic core is covalently linked
to fullerene cages through cyclohexene rings. Herein, we
report a related synthesis in which a tetrabromoalkene
undergoes cycloaddition to two fullerene cages to pro-
duce a short-chain fullerene dimer.
UV–vis absorption spectra of C , monomer 1 and di-
6
0
mer 2 revealed that the main C60 features are retained
in both functionalised species, although in the monomer
the relative intensities of the main absorption peaks were
altered. The shoulder observed at 435 nm is highly
characteristic of 1,2-addition across a 6:6 bond in C
6
6
0
2
2
(Fig. 2).
1
13
The starting material 2,3-bis-(bromomethyl)-1,4-di-
bromo-2-butene was synthesised by the bromination of
The monomer was characterised by H and C NMR
1
spectroscopy, and the dimer by H NMR only due to
its poor solubility. The H NMR spectrum of monomer
1
1
revealed two doublets at d = 4.19 and 4.56 ppm corre-
Keywords: Fullerenes; Dimers; Cycloadditions.
*
Corresponding author. Tel.: +44 (0) 1865 273724; e-mail: mark.
sambrook@materials.ox.ac.uk
sponding to the CH and CH Br proton environments,
respectively. The C NMR spectrum showed a total
2
2
1
3
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.08.061

7414
T. J. Hingston et al. / Tetrahedron Letters 47 (2006) 7413–7415
Scheme 1. Synthesis of novel fullerene monomer 1 and dimer 2 from reaction of 2,3-bis-(bromomethyl)-1,4-dibromo-2-butene with C60. (a) KI, 18-
crown-6, toluene, reflux.
3
of 20 peaks, with three sp carbon environments at
Br
Br
d = 30.1, 44.5 and 65.0 ppm. These correspond to
1
3
CH Br, CH and C sp carbon environments, respec-
2
2
60
Br
Br
Br
Br
a)
+
tively. The C2v symmetry of the molecule arises due to
rapid ring flipping of the cyclohexene unit, and was con-
firmed by the other 17 peaks found in the range
+
2
d = 135.5–155.5 ppm. These all correspond to sp car-
1
bon environments. The H NMR spectrum of the dimer
2
revealed two doublets at d = 8.09 and 8.40 ppm corre-
sponding to the two different proton environments in
the compound.
Figure 1. MALDI mass spectrum of dimer 2. Inset: isotopic distribu-
tion pattern theoretically (above) and actual (below).
1
.4
.2
1
1
435 nm
0.8
0.6
0.4
0.2
0
370
390
410
430
450
470
490
200
300
400
500
Wavelength (nm)
600
700
800
Figure 2. UV–vis spectrum (toluene, 273 K) of C60
(
), C60 monomer 1 (
) and C60 dimer 2 (
). Inset: enlargement of region between 370 nm
and 500 nm showing the shoulder at 435 nm indicating 1,2-addition across the 6:6 bond in C60
.

T. J. Hingston et al. / Tetrahedron Letters 47 (2006) 7413–7415
7415
The FTIR spectra of C , 2,3-bis-(bromomethyl)-1,4-
13. Murata, Y.; Han, A.; Komatsu, K. Tetrahedron Lett.
003, 44, 8199.
4. Fujiwara, K.; Komatsu, K. Org. Lett. 2002, 4, 1039.
15. Belik, P.; G u¨ gel, A.; Spickermann, J.; M u¨ llen, K. Angew.
Chem., Int. Ed. Engl. 1993, 32, 78.
6
0
2
dibromo-2-butene, the C60 monomer and the C60 dimer
showed a number of interesting features. The C
1
6
0
À1
absorption band at 525 cm was retained in both the
monomer and dimer. Also observed in both products
À1
16. Paquette, L. A.; Graham, R. J. J. Org. Chem. 1995, 60,
were the CH stretching peaks at ꢀ2970 cm and CH2
2
2
958.
7. Cope, A. C.; Kagan, F. J. Am. Chem. Soc. 1958, 80, 5499.
18. Synthesis of 2,3-bis-(bromomethyl)-1,4-dibromo-2-butene:
,3-dimethylbutadiene (8.4 ml, 0.078 mol) was dissolved in
carbon tetrachloride (CCl4) (50 ml). Bromine (12 g,
0.075 mol) dissolved in CCl (50 ml) was added dropwise
over 3 h at 0 ꢁC with stirring. After this time, NBS (26.7 g,
.15 mol), AIBN (cat.) and CCl (15 ml) were added. The
À1
deformations at ꢀ1250 cm appearing in the products
1
and the bromine-bearing reagent, but not in C .
6
0
2
A short-chain fullerene dimer prepared from readily
available starting materials has been successfully synthes-
ised and characterised. A monomer intermediate has been
isolated and has the potential for functionalisation with a
wide range of organic molecules or other fullerenes.
4
0
4
reaction mixture was heated under reflux for 12 h. The
resulting solution was filtered while hot to remove
succinimide, with the liquid cooled to form crystals of
the impure product. The crystals were filtered cold, and
Acknowledgements
recrystallised from ethyl acetate to give the pure product
1
(
(
2
8.98 g, 30%). H NMR (500 MHz, CDCl
3
): d = 4.15
This research is a part of QIP IRC www.qipirc.org (GR/
S82176/01). G.A.D.B. thanks EPSRC for a Professorial
Research Fellowship (GR/S15808/01). We thank the
EPSRC National Mass Spectrometry Service Centre,
University of Wales, Swansea, for MALDI analysis.
13
s, 8H; CH2). C NMR (125.8 MHz, CDCl ): d = 137.1,
3
À1
7.82. FTIR (KBr disc) 2970 cm (CH stretch (w)), 1440
2
(
CH
2
bend (s)), 1250 (C–H deformation (s)), 720 (CH
2
À
rocking (m)). EI MS m/z: 399.7321 M Calculated mass
399.7319.
1
9. Synthesis of monomer 1 and dimer 2: C60 (474 mg,
0
.658 mmol) and 2,3-bis-(bromomethyl)-1,4-dibromo-2-
References and notes
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2
stretch
(w)), 1440 (CH
2
bend (s)), 1250 (C–H deformation (s)),
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À1
À1
nm 290 (e/dm mol cm 52,004), 330 Sh (33,662), 436
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À
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9
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2
2
stretch (w)), 1440 (CH bend (s)),
1250 (C–H deformation (s)), 720 (CH
(C60 (s)). UV–vis k (Toluene)/nm 286 (e/dm mol cm
2
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3
À1
À1
24,135), 330 (41,399), 434 Sh (4,672). MALDI m/z:
À
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