Facile synthesis of [6,6]-phenyl-C61/71-butyric acid methyl esters via sulfur ylides for bulk-heterojunction solar cell

Article abstract of DOI:10.1055/s-0033-1339481

A one-step, mild synthesis of methanofullerenes as electron acceptors for solution-processed bulk-heterojunction solar cells was developed. [6,6]-Phenyl-C₆₁-butyric acid methyl ester {[60]PCBM} was directly synthesized in good yields, by the reaction of fullerene with sulfur ylide derivatives in the presence of 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU) at room temperature. This method was also successfully applied to the preparation of [6,6]-phenyl-C₇₁-butyric acid methyl ester {[70]PCBM}. Georg Thieme Verlag Stuttgart, New York.

Full text of DOI:10.1055/s-0033-1339481

1988▌
LETTER
letter
Facile Synthesis of [6,6]-Phenyl-C61/71-Butyric Acid Methyl Esters via Sulfur
Ylides for Bulk-Heterojunction Solar Cell
[6,6]-Phenyl-C61/71-Butyric Acid Methyl Esters
Takatoshi Ito,* Toshiyuki Iwai, Fukashi Matsumoto, Koichi Hida, Kazuyuki Moriwaki, Yuko Takao, Takumi Mizuno,
Toshinobu Ohno*
Osaka Municipal Technical Research Institute, 1-6-50, Morinomiya, Joto-ku, Osaka 536-8553, Japan
Fax +81(6)69638049; E-mail: ito@omtri.or.jp; E-mail: ohno@omtri.or.jp
Received: 10.05.2013; Accepted after revision: 02.07.2013
More recently, power conversion efficiencies of 7–8%
Abstract: A one-step, mild synthesis of methanofullerenes as elec-
have been achieved for solution-processed BHJ solar cells
tron acceptors for solution-processed bulk-heterojunction solar
through the use of new conjugated polymer donor materi-
cells was developed. [6,6]-Phenyl-C61-butyric acid methyl ester
{[60]PCBM} was directly synthesized in good yields, by the reac-
als with PCBM.4 Despite the use of these improved con-
tion of fullerene with sulfur ylide derivatives in the presence of 1,8- jugated polymer donors, PCBM are still considered the
standard acceptors in organic photovoltaic systems.5 The
development of scalable and efficient methods for the
synthesis of PCBM should be further investigated for the
purpose of promoting their practical use.
diazabicyclo-[5.4.0]undec-7-ene (DBU) at room temperature. This
method was also successfully applied to the preparation of [6,6]-
phenyl-C71-butyric acid methyl ester {[70]PCBM}.
Key words: methanofullerene, PCBM, photovoltaics, sulfur ylide,
addition–elimination reaction
However, PCBM preparative methods have been restrict-
ed to the few procedures by Hummelen and Wudl et al.6
They originally cyclopropanated C60 with 1-phenyl-1-
Because of the many potential applications of fullerenes
[3-(methoxycarbonyl) propyl] diazomethane that was
in materials and nanotechnology, numerous fullerene de-
formed in situ through the base-induced decomposition of
rivatives have been synthesized over the past decade.1 The
the sodium salt of methyl 4-benzoylbutyrate p-tosylhy-
excellent electron-accepting capabilities of fullerenes of-
drazone. This method always produces isomeric interme-
fer promise as materials for organic photovoltaics.2 In par-
diates {primarily the [5,6]-open fulleroids}, which require
ticular, since Sariciftci et al. reported that a conversion
conversion into the thermodynamically stable [6,6]-
efficiency of 2.5–3.0% could be achieved using a polymer
closed methanofullerene {[60]PCBM} by tedious thermal
solar cell based on a bulk heterojunction (BHJ) of poly[2-
or photochemical processing. Although an efficient high-
methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinyl-
throughput synthesis for PCBM was recently reported us-
ene] (MDMO-PPV) and methanofullerenes, typically
ing a continuous-flow system, these problems still re-
[6,6]-phenyl-C61-butyric acid methyl ester {[60]PCBM}
mained because of the use of tosylhydrazones starting
or
[6,6]-phenyl-C71-butyric
acid
methyl
ester
marerials.7
{[70]PCBM}, the polymer/methanofullerene photovolta-
ic system has attracted a great deal of attention for its sig-
nificant promise (Figure 1).3
Among the various synthetic approaches to metha-
nofullerenes, addition–elimination reactions such as the
Bingel reaction,8 the reactions of stabilized sulfur ylides,9
the reactions of silylated nucleophiles derived from α-
halocarbonyls,10 and others11 efficiently afford only [6,6]-
closed methanofullerenes without conversion processes.
Although these reactions proceed under mild conditions,
the resulting methanofullerene cyclopropane rings pos-
sess two carbonyl groups or their equivalents in the Bingel
reaction, or one carbonyl group in the reaction of sulfur
ylides, which limits the preparation of various functional-
ized methanofullerenes. To the best of our knowledge, the
reaction of a sulfur ylide stabilized with a phenyl group (a
so-called semistabilized ylide12) with a fullerene has nev-
er been reported. We herein report an alternative, one-pot,
[6,6]-direct, mild, and efficient synthesis of PCBM with a
semistabilized sulfur ylide generated in situ from the cor-
responding novel sulfonium salts (Scheme 1).
OMe
OMe
O
O
[60]PCBM
[70]PCBM
Figure 1
As the precursors of the PCBM, the sulfonium salts, di-
methyl (5-methoxy-5-oxo-1-phenylpentyl) sulfonium tri-
flate (2a) or dimethyl (5-methoxy-5-oxo-1-phenylpentyl)
sulfonium tetrafluoroborate (2b), were successfully pre-
SYNLETT 21709013, 2415, 1988–1992
Advanced online publication: 14.08.2013
DOI: 10.1055/s-0033-1339481; Art ID: ST-2013-U0436-L
© Georg Thieme Verlag Stuttgart · New York
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1
4
3
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2
0
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6

LETTER
[6,6]-Phenyl-C61/71-Butyric Acid Methyl Esters
1989
previous work
OMe
O
OMe
base
heat or hν
C60
+
[6,6]-closed PCBM
N
O
NH
Ts
([60]PCBM)
[5,6]-open
fulleroid
Me
Me
this work
S+
OMe
OMe
base
r.t.
C60
[6,6]-closed PCBM
O
+
S+
O
([60]PCBM)
–
Me
Me
X–
Scheme 1 Synthetic protocols of PCBM
pared in two steps. Facile bromination of methyl 5- 21% of [60]PCBM (Table 1, entry 6). Among the organic
phenylpentanoate at the benzyl position generated 1, fol- bases, it was found that the relatively strong basicity16 of
lowed by nucleophilic substitution of the bromide with di- DBU promoted the reaction to afford the corresponding
methyl sulfide (Scheme 2).13
PCBM in 55% yield with 28% of recovered C60 (Table 1,
entry 8). Furthermore, by increasing the quantities of sul-
fonium salt 2a and base relative to C60,17 the yield of
PCBM was improved to 58% (Table 1, entry 11), together
with 7% of the bisadducts and 24% of recovered C60.
Equally good results were achieved through the use of sul-
fonium salt 2b (Table 1, entry 12). The pure monoadduct
could be obtained after a silica gel column chromatogra-
Br
O
O
cat. BPO,
NBS
OMe
OMe
CCl4, reflux,
2 h
1 89%
X–
S+
1
phy. The H NMR and 13C NMR spectra of the product
Me
Me
O
suggested the formation of the [6,6]-closed methano-
fullerene {[60]PCBM}, which exhibited only one singlet
for methyl ester proton at δ = 3.68 ppm, and a bridgehead
cyclopropane carbon at δ = 79.87 ppm.7b It was important
that the desired [6,6] isomer {[60]PCBM} was directly
obtained without the corresponding [5,6]-open fulleroid.
Me2S, AgX
OMe
CH2Cl2, r.t., 4 h
2a X = OTf 81%
2b X = BF4 90%
Scheme 2 Preparation of sulfonium salts as precursor of PCBM
To increase throughput in the synthesis of [60]PCBM, a
higher concentration would be desirable. The method was
also successfully applied at 20 mM C60 concentration with
similar efficiency (53% yield by HPLC analysis, 45% iso-
lated yield, together with 5% of the bisadducts and 22% of
recovered C60, after column chromatography, Scheme
3).18
Initially, we examined the reactions between the sulfoni-
um salts and fullerene C60. o-Dichlorobenzene (ODCB)
and 1,2,4-trimethylbenzene (TMB) were chosen as the
solvents because of the high solubility of C60 therein.14 A
brief, small-scale optimization of the reaction conditions
was performed using 1.5 equivalents of sulfonium salt 2a
with C60 in the presence of various bases (1.5 equiv) in
ODCB at room temperature for six hours. The reactions
were monitored by HPLC,15 which showed the presence
of a monoaddition product in conjunction with unreacted
C60 and small amounts of bisadducts. The results are sum-
marized in Table 1.
–
BF4
OMe
DBU
C60
[60]PCBM
+
S+
O
r.t., 6 h
Me
Me
2 mM 57%
2b
20 mM 53% (isolated yield 45%)
In the reactions with inorganic bases such as K2CO3 and
Cs2CO3, the starting material was completely recovered Scheme 3 Preparation of [60]PCBM using sulfonium salt
because of the low solubility of the bases in ODCB (Table
1, entries 1 and 2). Various organic bases were then exam-
Next, our attention turned to the preparation of the higher
ined. In the cases of pyridine, Et3N, and 1,4-diazabicyc-
fullerene analogue, [70]PCBM, which exhibits a stronger
lo[2.2.2]octane (DABCO), no reaction occurred (Table 1,
absorption in the visible-light region than [60]PCBM.
entries 3–5). The use of DBN gave polar compounds with
Therefore, this material has often been used in photovol-
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 1988–1992

1990
T. Ito et al.
LETTER
Table 1 Optimization of the Synthesis of [60]PCBM via Sulfur Ylidea
Entry
Sulfonium salt (equiv)
Base (equiv)
Solventc
Yield of [60]PCBM (%)b
1
2
2a (1.5)
2a (1.5)
2a (1.5)
2a (1.5)
2a (1.5)
2a (1.5)
2a (1.5)
2a (1.5)
2a (1.5)
2a (1.0)
2a (2.0)
2b (1.5)
K2CO3 (3.0)
Cs2CO3 (3.0)
pyridine (3.0)
Et3N (3.0)
ODCB
ODCB
ODCB
ODCB
ODCB
ODCB
TMB
0
0
3
0
4
0
5
DABCO (3.0)
DBN (3.0)
DBU (3.0)
DBU (3.0)
DBU (3.0)
DBU (2.0)
DBU (4.0)
DBU (3.0)
0
6
21
25
55
16
45
58
57
7
8
ODCB
ODCB
ODCB
ODCB
ODCB
9d
10
11
12
a All reactions were carried out by using C60 (2.0 μmol), bases, and sulfonium salts in organic solvents (1 mL) for 6 h at r.t.
b Yields were determined by HPLC analysis.15
c ODCB: o-dichlorobenzene, TMB: 1,2,4-trimethylbenzene.
d Reaction was carried out at 0 °C.
taic cells instead of [60]PCBM, and higher current densi-
ties have been achieved.19 In general, [70]PCBM has been
OMe
synthesized via the conventional method used for
O
[60]PCBM, starting from methyl 4-benzoylbutyrate tosyl-
hydrazone.3b
The synthesis of [70]PCBM was performed analogously
to the procedure described above for [60]PCBM; the cor-
responding [6,6]-closed [70]PCBM was successfully ob-
tained in good yield (45% isolated yield, Scheme 4).20 The
O
products consisted of a mixture of three regioisomers,
with a similar component ratio (ca. 85:15) to that observed
with the conventional method. Additionally, the use of ex-
MeO
bis[70]PCBM
cess sulfonium salt afforded bisadducts (bis[70]PCBM),
Figure 2
in 64% yield, as well as 24% of the monoadducts (Figure
2).21
OMe
O
OMe
O
–
BF4
OMe
DBU (2.0 equiv)
C70
+
S+
O
+
ODCB, r.t., 6 h
45%
+
Me
Me
O
OMe
2b
(2.0 equiv)
major isomer
minor isomers
Scheme 4 Preparation of [70]PCBM using sulfonium salt
Synlett 2013, 24, 1988–1992
© Georg Thieme Verlag Stuttgart · New York

LETTER
[6,6]-Phenyl-C61/71-Butyric Acid Methyl Esters
1991
Kinbara, K.; Saigo, K. Tetrahedron Lett. 2001, 42, 5069.
(c) Tada, T.; Ishida, Y.; Saigo, K. J. Org. Chem. 2006, 71,
1633.
In conclusion, we demonstrated an alternative method for
the preparation of PCBM which provided [6,6]-closed
PCBM under simple, mild conditions. The novel sulfoni-
um salts 2a and 2b were obtained as useful synthetic pre-
cursors and the direct syntheses of [60] and [70]PCBM,
via the in situ generated semistabilized sulfur ylide were
successfully demonstrateed.
(10) (a) Ito, H.; Kishi, Y.; Nishikawa, Y.; Tada, T.; Ishida, Y.;
Saigo, K. Synlett 2010, 1811. (b) Hino, T.; Kinbara, K.;
Saigo, K. Tetrahedron Lett. 2001, 42, 5065.
(11) (a) Tokuyama, H.; Nakamura, M.; Nakamura, E.
Tetrahedron Lett. 1993, 34, 7429. (b) Bestmann, H. J.;
Hadawi, D.; Röder, T.; Moll, C. Tetrahedron Lett. 1994, 35,
9017.
Acknowledgment
(12) Appel, R.; Hartmann, N.; Mayr, H. J. Am. Chem. Soc. 2010,
132, 17894.
This research was supported in part by Core Research for Evolutio-
nal Science and Technology (CREST) of Japan Science and Tech-
nology Agency (JST) and JSPS KAKENHI Grant Number
23750232, 22550176.
(13) Methyl 5-Bromo-5-phenylpentanoate (1)
Commercially available methyl 5-phenylpentanoate (3.65 g,
19.0 mmol) was dissolved in CCl4 (50 mL) and treated with
NBS (3.68 g, 20.7 mmol) and a trace amount of dibenzoyl
peroxide. The mixture was refluxed for 2 h and then cooled
and filtered, followed by solvent removal in vacuo. After the
residue was purified by silica gel chromatography, product 1
was obtained in 89% yield (4.61 g). 1H NMR (300 MHz,
CDCl3): δ = 7.40–7.25 (m, 5 H), 4.95 (t, J = 6.9 Hz, 1 H),
3.65 (s, 3 H), 2.37–2.14 (m, 4 H), 1.92–1.56 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 173.42, 141.80, 128.71,
128.40, 127.20, 54.72, 51.57, 39.20, 33.12, 23.60. IR (neat):
2951, 1737, 1455, 1436, 1204, 1174, 759, 697 cm–1. ESI-
MS: m/z calcd for C12H15BrO2Na: 293.0; found: 292.8 [M +
Na]+.
References and Notes
(1) (a) Thilgen, C.; Diederich, F. Chem. Rev. 2006, 106, 5049.
(b) Nambo, M.; Segawa, Y.; Itami, K. J. Am. Chem. Soc.
2011, 133, 2402. (c) Lu, S.; Jin, T.; Kwon, E.; Bao, M.;
Yamamoto, Y. Angew. Chem. Int. Ed. 2012, 51, 802.
(d) Hashiguchi, M.; Obata, N.; Maruyama, M.; Yeo, K. S.;
Ueno, T.; Ikebe, T.; Takahashi, I.; Matsuo, Y. Org. Lett.
2012, 14, 3276. (e) Yoshimura, K.; Matsumoto, K.; Uetani,
Y.; Sakumichi, S.; Hayase, S.; Kawatsura, M.; Itoh, T.
Tetrahedron 2012, 68, 3605. (f) Li, F.-B.; You, X.; Wang,
G.-W. J. Org. Chem. 2012, 77, 6643. (g) Morinaka, Y.;
Nobori, M.; Murata, M.; Wakamiya, A.; Sagawa, T.;
Yoshikawa, S.; Murata, Y. Chem. Commun. 2013, 49, 3670.
(2) Brabec, C. J.; Sariciftci, N. S.; Hummelen, J. C. Adv. Funct.
Mater. 2001, 11, 15.
Dimethyl (5-Methoxy-5-oxo-1-phenylpentyl) Sulfonium
Triflate (2a)
To a solution of methyl 5-bromo-5-phenylpentanoate (1, 271
mg, 1.0 mmol) and Me2S (186 mg, 3.0 mmol) in CH2Cl2 (1
mL) was added AgOTf (257 mg, 1.0 mmol) at 0 °C. The
reaction mixture was stirred and gradually warmed to r.t. for
4 h. After filtration through Celite to remove the precipitate,
the filtrate was concentrated under reduced pressure. The
residue was then washed twice by decantation with hexane
(10 mL). The solvent was removed in vacuo and the
sulfonium salt 2a was obtained in 81% yield (324 mg). 1H
NMR (300 MHz, CDCl3): δ = 7.49–7.42 (m, 5 H), 4.94 (t,
J = 7.8 Hz, 1 H), 3.63 (s, 3 H), 3.03 (s, 3 H), 2.64 (s, 3 H),
2.36 (dt, J = 6.9, 2.1 Hz, 2 H), 2.25 (sext, J = 7.5 Hz, 2 H),
1.73–1.50 (m, 2 H). 13C NMR (75 MHz, CDCl3): δ = 173.05,
130.50, 130.10, 129.74, 129.11, 120.44 (q, JC–F = 317 Hz)
59.82, 51.43, 32.45, 29.52, 23.64, 22.30, 21.53. IR (neat):
3021, 2935, 1731, 1436, 1258, 757, 712, 638 cm–1. ESI-MS:
m/z calcd for C14H21O2S: 253.1; found: 253.0 [M –
CF3SO3]+.
(3) (a) Shaheen, S. E.; Brabec, C. J.; Sariciftci, N. S.; Padinger,
F.; Fromherz, T.; Hummelen, J. C. Appl. Phys. Lett. 2001,
78, 841. (b) Wienk, M. M.; Kroon, J. M.; Verhees, W. J.;
Knol, J.; Hummelen, J. C.; van Hal, P. A.; Janssen, R. A. J.
Angew. Chem. Int. Ed. 2003, 42, 3371.
(4) (a) Gendron, D.; Morin, P.-O.; Berrouard, P.; Allard, N.;
Aïch, B. R.; Garon, C. N.; Tao, Y.; Leclerc, M.
Macromolecules 2011, 44, 7188. (b) Su, M.-S.; Kuo, C.-Y.;
Yuan, M.-C.; Jeng, U. S.; Su, C.-J.; Wei, K.-H. Adv. Mater.
2011, 23, 3315. (c) Price, S. C.; Stuart, A. C.; Yang, L.;
Zhou, H.; You, W. J. Am. Chem. Soc. 2011, 133, 4625.
(d) Piliego, C.; Holcombe, T. W.; Douglas, J. D.; Woo, C.
H.; Beaujuge, P. M.; Fréchet, J. M. J. J. Am. Chem. Soc.
2010, 132, 7595.
(5) Troshin, P. A.; Hoppe, H.; Renz, J.; Egginger, M.;
Mayorova, J. Y.; Goryachev, A. E.; Peregudov, A. S.;
Lyubovskaya, R. N.; Gobsch, G.; Sariciftci, N. S.; Razumov,
V. F. Adv. Funct. Mater. 2009, 19, 779.
(6) (a) Hummelen, J. C.; Knight, B. W.; LePeq, F.; Wudl, F.;
Yao, J.; Wilkins, C. L. J. Org. Chem. 1995, 60, 532.
(b) Janssen, R. A. J.; Hummelen, J. C.; Wudl, F. J. Am.
Chem. Soc. 1995, 117, 544.
(7) (a) Rossi, E.; Carofiglio, T.; Venturi, A.; Ndobe, A.;
Muccini, M.; Maggini, M. Energy Environ. Sci. 2010, 4,
725. (b) Seyler, H.; Wong, W. H.; Holmes, A. B. J. Org.
Chem. 2011, 76, 3551.
(8) (a) Bingel, C. Chem. Ber. 1993, 126, 1957. (b) Camps, X.;
Hirsch, A. J. Chem. Soc., Perkin Trans. 1 1997, 1595.
(c) Nierengarten, J.-F.; Nicoud, J.-F. Tetrahedron Lett.
1997, 38, 7737. (d) Wang, G-W.; Zhang, T.-H.; Li, Y.-J.;
Lu, P.; Zhan, H.; Liu, Y.-C.; Murata, Y.; Komatsu, K.
Tetrahedron Lett. 2003, 44, 4407.
Dimethyl (5-Methoxy-5-oxo-1-phenylpentyl) Sulfonium
Tetrafluoroborate (2b)
The procedure was similar to that described above, except
for the use of AgBF4 (195 mg, 1.0 mmol). The sulfonium salt
2b was obtained in 90% yield (306 mg). 1H NMR (300 MHz,
CDCl3): δ = 7.51–7.44 (m, 5 H), 4.83 (t, J = 8.4 Hz, 1 H),
3.63 (s, 3 H), 3.01 (s, 3 H), 2.62 (s, 3 H), 2.38 (dt, J = 7.2, 3.2
Hz, 2 H), 2.26 (sext, J = 7.6 Hz, 2 H), 1.72–1.52 (m, 2 H).
13C NMR (75 MHz, CDCl3): δ = 173.19, 130.74, 130.20,
129.99, 129.26, 60.38, 51.63, 32.56, 29.78, 23.70, 22.39,
21.69. IR (neat): 3030, 2951, 1734, 1456, 1437, 1203, 1177,
1061, 701 cm–1. ESI-MS: m/z calcd for C14H21O2S: 253.1;
found: 252.9 [M – BF4]+.
(14) (a) Ruoff, R. S.; Tse, D. S.; Malhotra, R.; Lorents, D. C.
J. Phys. Chem. 1993, 97, 3379. (b) Scrivens, W. A.; Tour, J.
M. J. Chem. Soc., Chem. Commun. 1993, 1207.
(15) HPLC conditions were as follows: column,
CHEMCOSORB5-ODS-UH (4.6 × 150 mm); column
temperature, 40 °C; flow rate, 1.2 mL/min; detection, UV at
λ = 340 nm; eluent toluene–MeOH (60:40, v/v). The
(9) (a) Wang, Y.; Cao, J.; Schuster, D. I.; Wilson, S. R.
Tetrahedron Lett. 1995, 36, 6843. (b) Hamada, M.; Hino, T.;
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 1988–1992

1992
T. Ito et al.
LETTER
absolute calibration method was used for the quantification
of analytes.
(16) (a) Costa, M.; Chiusoli, G. P.; Rizzardi, M. Chem. Commun.
1996, 1699. (b) Streitwieser, A.; Kim, Y. J. J. Am. Chem.
Soc. 2000, 122, 11783.
(17) The reactions of benzylic branched sulfur ylides have often
resulted in extensive decomposition by the Sommelet–
Hauser rearrangement and β-elimination of affording
styrene-type compounds.Krief, A.; Billen, S. D.
33.67, 22.37. IR (KBr): 2921, 2849, 1735, 699, 573, 550,
526, 482, 453 cm–1. MS (MALDI): m/z calcd for C72H14O2:
910.1; found: 910.1 [M]+.
(19) Troshin, P. A.; Hoppe, H.; Peregudov, A.; Egginger, S. M.;
Shokhovets, S.; Gobsch, G.; Sariciftci, N. S.; Razumov, V.
F. ChemSusChem 2011, 1194.
(20) [6,6]-Phenyl-C71-butyric Acid Methyl Ester
{[70]PCBM}7b
1H NMR (300 MHz, CDCl3): δ = 7.92–7.40 (m, 5 H), 3.74
(minor isomer, s, 0.26 H), 3.67 (major isomer, s, 2.55 H),
3.51 (minor isomer, s, 0.19 H), 2.53–2.42 (m, 4 H), 2.25–
1.99 (m, 2 H). 13C NMR (75 MHz, CDCl3): δ = 173.38,
149.43–128.20, 69.82, 51.68, 33.80, 21.70. IR (KBr): 2941,
2923, 1737, 1429, 795, 726, 699, 674, 643, 579, 534, 459
cm–1. MS (MALDI): m/z calcd for C72H14O2: 1030.1; 1030.2
[M]+.
Tetrahedron Lett. 2002, 43, 5871.
(18) Preparation of [6,6]-Phenyl-C61-butyric Acid Methyl
Ester {[60]PCBM}7b
To a stirred mixture of sulfonium salt 2b (85 mg, 0.25 mmol)
and fullerene C60 (100 mg, 0.14 mmol) in ODCB (7 mL) was
added DBU (46 mg, 0.30 mmol) in one portion at r.t. After
stirring for 6 h, AcOH (ca. 3 equiv) was added. The reaction
mixture was concentrated to ca. 3 mL under reduced
pressure. The residue was purified by silica gel column
chromatography {eluent, stepwise gradient of CH2Cl2 (0–
80%) in toluene}. The obtained product was dissolved in a
small amount of toluene and poured into MeOH. The
resulting suspension was centrifuged, and the supernatant
was decanted. The product was dried in vacuo at 60 °C.
[60]PCBM was obtained in 45% isolated yield (57 mg).
Unreacted C60 (22 mg, 22%) and bisadducts (8 mg, 5%) were
isolated in the same manner. 1H NMR (300 MHz, CDCl3):
δ = 7.92 (d, J = 8.7 Hz, 2 H), 7.60–7.44 (m, 3 H), 3.68 (s, 3
H), 2.94–2.88 (m, 2 H), 2.52 (t, J = 7.5 Hz, 2 H), 2.23–2.13
(m, 2 H). 13C NMR (75 MHz, CDCl3): δ = 173.40, 148.79–
136.71, 132.06, 128.43, 128.24, 79.87, 51.85, 51.64, 33.87,
(21) Bis[70]PCBM
To a stirred mixture of sulfonium salt 2b (51 mg, 0.15 mmol)
and fullerene C70 (25 mg, 0.030 mmol) in ODCB (12 mL)
was added DBU (23 mg, 0.15 mmol) in one portion at r.t.
After stirring for 7 h, AcOH (ca. 3 equiv) was added and
treatments in the same manner of ref. 18, bis[70]PCBM was
obtained in 64% isolated yield (23 mg). Unreacted C70 (0.6
mg, 2%) and monoadducts (7.5 mg, 24%) were isolated.1H
NMR (300 MHz, CDCl3): δ = 7.93–7.37 (m, 5 H), 3.67–3.65
(m, 3 H), 2.50–2.10 (m, 6 H). MS (MALDI): m/z calcd for
C72H14O2: 1220.2; found: 1220.2 [M]+. Spectroscopic data
were in good agreement with the literature: Lenes, M.;
Shelton, S. W.; Sieval, A. B.; Kronholm, D. F.; Hummelen,
J. C.; Blom, P. W. M. Adv. Funct. Mater. 2009, 19, 3002.
Synlett 2013, 24, 1988–1992
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