Synthesis of Benzothieno[60]fullerenes through Fullerenyl Cation Intermediates

Article abstract of DOI:10.1021/acs.joc.9b00549

Benzothieno[60]fullerenes were synthesized using fullerenyl cations as key intermediates. The reaction proceeded through a nucleophilic attack of the sulfur atom as a weak nucleophile to the fullerenyl cation electrophile. A monoarylated fullerene, (2-methylthiophenyl)hydro[60]fullerene, C₆₀ArH (Ar = C₆H₄-SMe-2 and so on; four derivatives) was subjected to deprotonation with KOtBu to form a fullerenyl anion ArC₆₀^-, followed by oxidation using I₂ to generate a fullerenyl cation ArC₆₀⁺, leading to intramolecular demethylative cyclization via fullerene cation-S interaction to the product. Electrochemical and computational studies revealed slightly narrower band gap of this compound than usual fullerene derivatives because of the relatively high-lying HOMO of the fused thieno moiety.

Full text of DOI:10.1021/acs.joc.9b00549

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Article
Synthesis of Benzothieno[60]fullerenes
Through Fullerenyl Cation Intermediates
Yutaka Matsuo, Yun Yu, Xiao-Yu Yang, Hiroshi Ueno, Hiroshi
Okada, Hiromasa Shibuya, Yeong Suk Choi, and Yong Wan Jin
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00549 • Publication Date (Web): 22 Apr 2019
Downloaded from http://pubs.acs.org on April 22, 2019
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The Journal of Organic Chemistry
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Synthesis of Benzothieno[60]fullerenes Through Fullerenyl
Cation Intermediates
Yutaka Matsuo*,1,2, Yun Yu1, Xiao-Yu Yang1, Hiroshi Ueno3, Hiroshi Okada2, Hiromasa Shibuya4,
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Yeong Suk Choi4, and Yong Wan Jin4
1 Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, 96 Jin-
zhai Road, Hefei, Anhui 230026, China
2 Department of Mechanical Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo
113-8656, Japan
3 School of Chemistry, Northeast Normal University, 5268 Renmin Street, Changchun, Jilin 130024, P.R. China
4 Material Research Center, Samsung Advanced Institute of Technology, 130 Samsung-ro, Yeongtong-gu, Suwon-si,
Gyeonggi-do 443-803, Korea
Supporting Information Placeholder
I–
R
S
R
H
S
R
1) base
2) I2
S
fullerenyl cation intermediate benzothieno[60]fullerene
ABSTRACT: Benzothieno[60]fullerenes were synthesized using fullerenyl cations as key intermediates. The reaction proceeded
through a nucleophilic attack of the sulfur atom as a weak nucleophile to the fullerenyl cation electrophile. A monoarylated fuller-
ene, (2-methylthiophenyl)hydro[60]fullerene, C60ArH (Ar = C6H4-SMe-2, and so on; four derivatives) was subjected to deprotona-
tion with KOtBu to form a fullerenyl anion ArC60–, followed by oxidation using I2 to generate a fullerenyl cation ArC60+ leading to
intramolecular demethylative cyclization via fullerene cation–S interaction to the product. Electrochemical and computational stud-
ies revealed slightly narrower band gap of this compound than usual fullerene derivatives because of the relatively high-lying
HOMO of the fused thieno moiety.
2–
transfer occurs to generate the reduced fullerene species, C60
.
INTRODUCTION
10
Sulfur-containing organic π-electron-conjugated systems are
In this study, we solved this issue by using oxidized fuller-
important semiconductors that are used in organic electronic
enes to enhance the electrophilicity of the fullerene core for
devices.1 They are represented by poly(thiophene)s2 and thio-
reactions with sulfur atoms to produce C60–S bond-containing
phene-fused aromatic compounds, such as benzodithiophenes,3
fullerene derivatives (Figure 1). We have demonstrated unique
and so on,4 and feature excellent electron-donating and charge
reactions that proceed through fullerenyl cation intermedi-
carrier transport properties for organic photovoltaics5 and or-
ates11–13 by utilizing newly generated frontier orbitals formed
ganic field-effect transistors.1,6 Thiophene-containing fullerene
by the removal of two electrons from organo[60]fullerenyl
derivatives have been reported widely,7 with some of them
anions. Herein, we found that these new orbitals interact with
used in applications research.8 Besides, there are few reports
the weakly nucleophilic sulfur atom to facilitate cyclization
on the modification of fullerene to produce compounds that
and produce dihydrobenzothieno[60]fullerene as a new heter-
contain fullerene–sulfur bonds,9 which is ascribable to the
ocycle-fused fullerene derivative. This reaction is facile when
lower nucleophilicity of the sulfur atom toward electrophilic
excess iodine is used as the oxidant, rather than the Cu(II)
fullerenes compared to carbanions and oxygen atoms. Thus,
oxidants employed in previous studies.13 The obtained prod-
well-known strategies that use nucleophiles are generally not
ucts have narrower band gaps than their oxygen-containing
suitable for the synthesis of C60–S compounds. For example,
NaSMe does not nucleophilically attack C60; instead, electron
congeners9e,13d,14 because of the fused thiophene rings. These
features are preferred for organic electronics applications;
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hence, the introduced methodology is expected to open up new
Page 2 of 8
was dark green in ortho-dichlorobenzene (o-DCB). This spe-
cies was oxidized in a one-pot process by the addition of ex-
cess iodine to afford the arylfullerenyl radical B and then the
arylfullerenyl cation C. A dimer was predominantly formed
through the radical coupling of B when one equivalent of I2
was used (Supporting Information). This result indicates that
the fullerenyl radical B does not react with the sulfur atom,
even though some other C60–S compounds are formed through
radical reactions.9 When 5.5 eq. of I2 were used to oxidize A,
the sulfur atom became involved in an unconventional nucleo-
philic attack to produce a cyclized compound, dihydroben-
zothieno[60]fullerene 2a in 42% isolated yield. The use of
excess iodine successfully oxidized the fullerenyl radical B to
the cation C in a manner that was superior to that using Cu(II)
halides as oxidants.13 In the last step, I–, which is formed by
the reduction of I2 with A and B, facilitated demethylation for
the cyclization through a thiophenium intermediate (Figure
2).13d Compound 2a is very stable in air, and no oxidized
product was observed by stirring a solution of 2a in o-DCB at
90 °C in air.
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avenues for the preparation of a variety of heterocyclic fuller-
ene derivatives for materials chemistry.
S
weak nucleophile
modification
S
S
oxidation
I2
organofullerenyl anion
organofullerenyl cation
enhanced electrophilicity
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Figure 1. Concept of this study. The oxidized fullerene (fullerenyl
cation) undergoes nucleophilic attack by the sulfur atom.
RESULTS AND DISCUSSION
The synthesis began with the preparation of a series of
monoarylated [60]fullerenes (C60ArH; Ar = C6H3(SMe)R; R =
t
OMe (1a), H (1b), Bu (1c), and CH2OMe (1d)), in which
methylthio groups are attached at the ortho-positions relative
to the ipso-carbon atom of the benzene rings (Scheme 1).
These compounds are prepared by the efficient DMSO-
mediated (or DMF-mediated) monoaddition reactions of Gri-
gnard reagents,15 which have been extensively investigated in
our previous studies. To that end, 4-methoxy-2-
(methylthio)phenylmagnesium bromide (1.5 eq.) was reacted
with C60 in the presence of anhydrous DMSO (15 eq.) at room
temperature to produce monoarylated fullerene 1a in 66%
I–
O
S
Figure 2. Demethylation of the thiophenium intermediate.
isolated yield. Side product 1a’ was obtained from this reac-
–
tion,
in
which
Ar–S–CH2
attacked
fullerene
Compounds 2b-d were synthesized using the same method.
Overall, unsubstituted compound 2b was poorly soluble for
silica-gel column chromatography, while 2a and 2c bearing
methoxy and tert-butyl groups were respectively well separat-
ed and soluble. Compound 2d bearing the methoxymethyl
group was superior to the other benzothienofullerenes in terms
of separation and solubility.
(C60(CH2SAr)H,16 described later), as evidenced by H NMR
spectroscopy and high-resolution mass spectrometry (HRMS),
in yields that ranged from 5 to 20%, and was found to depend
on the freshness of the Grignard reagent. The sulfur-
containing aryl Grignard reagents, C6H3(SMe)(R)MgBr, were
found to rearrange to the isomeric C6H4(R)SCH2MgBr (Sup-
porting Information). The side product 1a’ could be removed
by HPLC, or it could be carried through the next step and re-
moved afterwards.
1
1
Benzothieno compound 2a-d were characterized by H and
13C NMR spectroscopy, HRMS, UV-vis absorption spectros-
1
copy, and electrochemical studies. For example, the H NMR
R1
S
R2
R1
KOtBu
R1
R2
spectrum of 2a exhibits benzene-ring signals at 7.85, 6.99, and
6.86 ppm in addition to a signal due to the methoxy group at
3.92 ppm, while the 13C NMR spectrum displayed a pattern
consistent with a CS-symmetric structure. The UV-vis spec-
trum of 2a in toluene exhibited an absorption maximum at 430
nm characteristic of a 58π-fullerene derivative with a 1,2-
addition pattern (Supporting Information). Even though this
compound has a smaller band gap (vide infra) than dihydro-
benzofurano[60]fullerene, no obvious spectral change from
that of an ordinary 1,2-adduct was observed. We examined the
thermal stability of 2a by thermogravimetry; this compound
remained intact to ~440 °C (Supporting Information), which
S
H
(2.0 eq.)
then I2
R2
MgBr
(1.5 eq.)
(in THF)
(5.5 eq.)
S
o-DCB, rt
DMSO (15 eq.)
o-DCB, rt
2a (R1 = OMe; R2 = H), 42%
2b (R1 = R2 = H), 30%
1a-d
KOtBu
2c (R1 = H, R2 = tBu), 40%
2d (R1 = H; R2 = CH2OMe), 41%
(mechanism)
I–
R1
R2
R1
R2
R1
S
S
S
R2
I2
I2
– e–
oxidation
– e–
further
highlights
the
thermal
stability
of
this
ben-
zothieno[60]fullerene.
oxidation
A
B
C
The cyclic voltammogram of 2a in o-DCB showed reversi-
ble reduction waves at E1/2 = –1.15 and –1.49 V (vs. Fc/Fc+)
(Figure 3). Third and fourth reduction waves were observed,
but they were irreversible, which is likely due to structural
changes that occur at these potentials. Interestingly, the first
and second reduction potentials of 2a were close to those of
pristine C60; indeed they were positively shifted by only 40
and 10 mV from those of C60. The LUMO energies of 2a and
Scheme 1. Synthesis of benzothieno[60]fullerenes and associated
reaction mechanisms.
With the starting monoadducts 1a-d in hand, we next inves-
tigated the fullerenyl-cation-mediated cyclization reaction.
The key step is the oxidation of the fullerenyl anion to provide
a strongly electrophilic center for reaction with the weakly
nucleophilic sulfur atom. Deprotonation of 1a with KOtBu
generated the aryl[60]fullerenyl anion (A in Scheme 1), which
C60 were determined to be –3.65 and –3.69 eV using the equa-
red1
tion: E(LUMO) = –(E1/2
+4.80).15,17 However, the values
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from this method strongly depend on the solvent used during
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cyclic voltammetry. In addition, the first reduction potential of
C60 in the same o-DCB solution reported in the literature vary
by –1.08,18 –1.09,19 –1.10,20 –1.13,21 and –1.10 eV (in this
work), providing E(LUMO) values that range from –3.67 to –
3.72 eV; hence, caution is required. For instance, temperature
(e.g., room temperature) and concentration may affect the
measured reduction potentials. Nevertheless, the electrochem-
ical data acquired in the same solvent under the same experi-
mental conditions in this study suggest that 2a has a low-lying
LUMO level, which is slightly higher or almost comparable to
that of C60. We ascribe this observation to the slightly higher
electronegativity of the sulfur atom (2.58) compared to that of
the carbon atom (2.55). In addition, the reversible two-electron
reduction of 2a is advantageous for electrochemical stability,
since benzofurano[60]fullerene exhibits reversibility only in
the first reduction.13d
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Figure 4. Frontier orbitals with B3LYP/6-31G(d)-optimized
structures. (a) LUMO of 2b. (b) LUMO of benzo-
furano[60]fullerene. (c) HOMO of 2b. (d) HOMO of benzo-
furano[60]fullerene.
Table 1. Calculated HOMO and LUMO levels of 2b and benzo-
furano[60]fullerene and their energy band gap (Eg = LUMO–
HOMO).
HOMO levels
[eV]
LUMO levels
[eV]
Eg
[eV]
benzothienoC60, 2b
benzofuranoC60
–5.71
–5.80
–3.21
–3.22
2.51
2.57
Lastly, we found that by-product 1b’ formed in the first re-
action can be converted into a six-membered sulfur- contain-
ing ring compound. Starting from a mixture of 1b and 1b’,
deprotonation with KOtBu, followed by oxidation with I2 (5.5
eq.) produced a mixture of 2b and 2b’ (Scheme 2). Although
product 2b’ does not contain a fullerene–S bond, elucidation
of the structure of this side product by careful analysis provid-
ed insight and in-depth understanding of this chemistry. A
plausible mechanism for the formation of 2b’ involves cation–
π interactions between the fullerenyl cation and the benzene
ring for Friedel–Crafts cyclization.
Figure 3. Cyclic voltammograms of 2a (upper) and C60 (lower) in
o-DCB containing n-Bu4N+TFSI− as the supporting electrolyte.
Scan rate = 100 mV/sec; working and counter electrodes are Pt;
the reference electrode is Ag/Ag+.
To obtain a deeper understanding of the differences between
benzothieno- and benzofurano[60]fullerenes, unsubstituted
compounds were examined computationally. Figure 4 shows
the B3LYP/6-31G(d)-optimized structures of 2b and the cor-
responding oxygen-containing benzofurano[60]fullerene con-
gener calculated using the Gaussian09 program, along with
their GaussView-generated HOMOs and LUMOs. Their
LUMO distributions are almost identical and localized on the
C60 cage (Figure 4a,b). In contrast, the HOMO of 2b displays
a large distribution onto the benzothieno moiety (Figure 4c),
which is not evident in the HOMO of the benzo-
furano[60]fullerene congener (Figure 4d). This difference in
HOMO distribution is reflective of the frontier orbital energy
levels (Table 1). While the LUMO levels are almost the same
in the two compounds, the HOMO level of 2b is clearly higher
than that of benzofurano[60]fullerene. We surmise that this is
due to electron donation from the benzothieno moiety to the
fullerene core. This difference results in a slightly smaller
energy gap (Eg = LUMO–HOMO) for 2b (2.51 eV) than ben-
zofurano[60]fullerene (2.57 eV).
H
S
H
S
S
S
+
+
1) base
2) iodine
1b
1b'
(plausible mechanism for 2b')
2b'
2b
– H+
S
cation-π interaction
Scheme 2. Formation of six-membered 2b’ from by-product 1b’
through Friedel–Crafts cyclization.
CONCLUSION
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crude products. Analytical HPLC (Buckyprep) revealed two main
In summary, we demonstrated the synthesis of ben-
zothieno[60]fullerene through a key fullerenyl cation interme-
diate generated by the facile oxidation of the fullerenyl anion
with excess iodine. The reaction mechanism involves intramo-
lecular nucleophilic attack22 of the weakly nucleophilic sulfur
atom at the fullerenyl cation to form the cyclized product. This
study demonstrates the use of our fullerene cation chemistry as
a frontier technique for the modification of fullerenes. The
obtained products are thiophene-fused fullerene derivatives
that exhibit higher HOMO levels than the corresponding oxy-
gen congeners owing to their fused thiophene moieties; this
affords fullerene derivatives with slightly lower band gaps
compared to ordinary fullerene derivatives. The present work
contributes to developing methodology for the preparation of
new heterocyclic fullerenes bearing other main group atoms,
such as silicon.23 In addition, because of air and thermal stabil-
ities of 2a-d, thiophene-fused fullerenes are expected to be of
interest to device scientists in the organic electronics field.
peaks with retention times of 10.906 and 11.675 min (Buckyprep
4.6 φ × 250 mm; eluent: toluene/2-propanol = 8/2) for com-
pounds 1b and 1b’, respectively. The faster eluting compound
was separated by preparative HPLC to give 1b in 52% isolated
yield. 1H NMR (400 MHz, CDCl3/CS2): δ 8.33 (d, J = 8.0 Hz, 1H,
C6H4), 7.69 (d, J = 8.0 Hz, 1H, C6H4), 7.55 (d, J = 0.8 Hz, 1H, C6H4),
7.43 (s, 1H, C6H4), 6.81 (s, 1H, C60H), 2.87 (s, 3H, SMe). 13C{1H}
NMR (100 MHz, CDCl3/CS2): δ 51.28, 59.23, 65.11, 127.34, 129.38,
131.07, 136.00, 136.42, 136.46, 140.15, 140.27, 141.57, 141.66,
141.98, 142.07, 142.27, 142.55, 142.59, 143.23, 144.47, 144.69,
145.34, 145.41, 145.60, 145.73, 145.86, 146.15, 146.19, 146.37,
146.40, 146.88, 147.24, 147.24, 147.44, 153.40, 153.75. High-
resolution MALDI-TOF MS [M+]: m/z calcd. for C67H8S, 844.0347;
found, 844.0324.
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Synthesis
of
(5-tert-butyl-2-
(methylthio)phenyl)hydro[60]fullerene (1c). A THF solution
of 5-tert-butyl-2-(methylthio)phenylmagnesium bromide (0.220
mL, 0.95 mol/L, 0.209 mmol, 1.5 equiv.) was added to a solution
of C60 (100 mg, 0.139 mmol) and DMSO (0.150 mL, 2.09 mmol, 15
equiv.) in o-DCB (30 mL) under Ar at room temperature. The
mixture was stirred for 40 min at room temperature, after which
aqueous NH4Cl (0.2 mL, 1.0 mol/L) was added to quench the reac-
tion. The volatile solvents were removed by rotary evaporation
and excess methanol was added to precipitate the crude products.
The mixture was subjected to silica-gel column and HPLC
(Buckyprep) to obtain the title compound as a brown powder in
45% isolated yield. 1H NMR (400 MHz, CS2/DMSO-d6 inner tube):
δ 8.32 (s, 1H, C6H3), 7.63 (d, J = 8.4 Hz, 1H, C6H3), 7.54 (d, J = 8.4
Hz, 1H, C6H3), 6.80 (s, 1H, C60H), 2.83 (s, 3H, Me), 1.44 (s, 9H, tBu).
13C{1H} NMR (100 MHz, CDCl3/CS2): δ 31.42, 51.89, 53.67, 59.27,
65.35, 126.54, 131.64, 132.49, 136.56, 140.27, 140.39, 141.72,
141.77, 141.78, 142.10, 142.19, 142.39, 142.67, 142.71, 143.33,
144.61, 144.82, 145.47, 145.53, 145.68, 145.86, 146.01, 146.27,
146.31, 146.49, 146.51, 147.05, 147.36, 147.55, 150.70, 153.65,
154.04. HR MALDI-TOF MS [M+]: m/z calcd. for C71H16S, 900.0973;
found, 900.0968.
EXPERIMENTAL SECTION
General remarks. All reagents commercially available were used
as received without further purification. 1H and 13C NMR spectra
were recorded at 400 MHz and 100 MHz on Bruker AVANCE III 400
spectrometer, respectively. High-resolution mass spectra were ob-
tained by MALDI using a time-of-flight mass analyzer on a Bruker
Ultra exTOF/TOF spectrometer. UV–visible spectra were recorded on
a JASCO V-570 spectrometer. CV experiments were performed with
a Hokuto Denko HZ-5000 voltammetric analyzer. The synthetic
schemes for the synthesis of the starting materials 3–5 are in the sup-
porting information.
Synthesis
of
(4-methoxy-2-
(methylthio)phenyl)hydro[60]fullerene (1a). A THF solution of 4-
methoxy-2-(methylthio)phenylmagnesium bromide (0.347 mL, 0.90
mol/L, 0.313 mmol, 1.5 equiv.) was added to a solution of C60 (150
mg, 0.208 mmol) and DMSO (0.225 mL, 3.13 mmol, 15 equiv.) in o-
DCB (45 mL) under Ar at room temperature. The mixture was stirred
for 40 min at room temperature, after which aqueous NH4Cl (0.2 mL,
1.0 mol/L) was added to quench the reaction. The volatile solvents
were removed by rotary evaporation and excess methanol was added
to precipitate the crude products. The mixture was subjected to silica
gel column chromatography to obtain a mixture of 1a and 1a’. This
mixture was separated by HPLC (Buckyprep) to give pure 1a as a
brown powder in 66% isolated yield. In addition, by-product 1a’ was
obtained in 20% isolated yield.
Synthesis
of
(5-(methoxymethyl)-2-
(methylthio)phenyl)hydro[60]fullerene (1d). A THF solution
of 5-(methoxymethyl)-2-(methylthio)phenyl magnesium bromide
(0.337 mL, 0.62 mol/L, 0.209 mmol, 1.5 equiv.) was added to a
solution of C60 (100 mg, 0.139 mmol) and DMSO (0.150 mL, 2.09
mmol, 15 equiv.) in o-DCB (30 mL) under Ar at room tempera-
ture. The mixture was stirred for 40 min at room temperature,
after which aqueous NH4Cl (0.2 mL, 1.0 mol/L) was added to
quench the reaction. The volatile solvents were removed by rota-
ry evaporation and excess methanol was added to precipitate the
crude products. The mixture was subjected to silica gel column
with CS2 as the eluent to provided 1d as an air-stable dark brown
solid in 54% yield.
Compound 1d, 1H NMR (400 MHz, CS2/CDCl3): δ 8.20 (d, J = 2.0
Hz, 1H, C6H3), 7.65 (d, J = 8.0 Hz, 1H, C6H3), 7.49 (dd, J = 8.0 Hz, J =
2.0 Hz, 1H, C6H3), 6.79 (s, 1H, C60H), 4.54 (s, 2H, CH2O), 3.43 (s, 3H,
OMe), 2.86 (s, 3H, SMe); 13C{1H} NMR (100 MHz, CS2/CDCl3): δ
19.30, 59.10, 62.27, 69.34, 74.90, 128.97, 130.16, 130.47, 137.82,
140.75, 141.19, 142.14, 142.62, 142.79, 143.03, 143.07, 143.50,
143.54, 144.19, 145.44, 145.71, 146.26, 146.34, 146.48, 146.67,
146.98, 147.00, 147.21, 147.22, 147.71, 148.07, 148.38, 154.43.
HR MALDI-TOF MS [M+] m/z calcd. for C69H12OS, 888.0614; found
888.0612.
Compound 1d’, 1H NMR (400 MHz, CS2/CDCl3): δ 7.72 (d, J = 8.4
Hz, 2H, C6H4), 7.33 (d, J = 8.8 Hz, 2H, C6H4), 6.75 (s, 1H, C60H), 4.91
(s, 2H, CH2O), 4.43 (s, 2H, CH2S), 3.36 (s, 3H, OMe); 13C{1H} NMR
(100 MHz, CS2/CDCl3): δ 52.48, 58.79, 60.08, 65.97, 74.70, 129.10,
132.00, 135.69, 137.29, 137.31, 138.96, 141.00, 141.12, 142.39,
142.49, 142.81, 142.90, 143.09, 143.38, 143.43, 144.03, 145.30,
145.51, 146.23, 146.26, 146.44, 146.67, 146.97, 147.01, 147.19,
147.22, 147.70, 148.05, 148.24, 154.21, 154.57. HR MALDI-TOF
MS [M – H+]: m/z calcd. for C69H12OS, 887.0606; found 887.1866.
Compound 1a, 1H NMR (400 MHz, CDCl3/CS2): δ 8.25 (d, J = 8.0,
1H, C6H3), 7.22 (m, 1H, C6H3), 6.93 (d, J = 8.0 Hz, 1H, C6H3), 6.83 (s,
1H, C60H), 3.96 (s, 3H, OMe), 2.85 (s, 3H, SMe). 13C{1H} NMR (100
MHz, CDCl3/CS2): δ 51.22, 55.28, 59.39, 65.27, 113.26, 116.56,
123.19, 130.35, 136.60, 136.63, 137.33, 140.32, 140.45, 141.74,
141.83, 142.15, 142.24, 142.44, 142.72, 142.77, 143.37, 144.65,
144.86, 145.51, 145.58, 145.77, 145.90, 146.04, 146.32, 146.36,
146.54, 146.57, 147.05, 147.41, 147.60, 153.58, 153.91, 160.19.
High-resolution (HR) MALDI-TOF MS [M+]: m/z calcd. for
C68H10OS, 874.0452; found, 874.0446.
1
Compound 1a’, H NMR (400 MHz, CDCl3/CS2): δ 7.32 (dt, J =
3.2 Hz, J = 1.6 Hz, 1H, C6H4), 7.29 (d, J = 7.6 Hz, 1H, C6H4), 7.26 (t, J
= 2.0 Hz, 1H, C6H4), 6.80 (ddd, J = 5.2 Hz, J = 4.0 Hz, J = 2.4 Hz, 1H,
C6H4), 4.92 (s, 2H, CH2S), 3.84 (s, 3H, MeO). HR MALDI-TOF MS
[M+]: m/z calcd. for C68H10OS, 874.0452; found, 874.0451.
Synthesis of (2-(methylthio)phenyl)hydro[60]fullerene
(1b). A THF solution of 2-(methylthio)phenylmagnesium bromide
(0.068 mL, 1.33 mol/L, 0.090 mmol, 1.3 equiv.) was added to a
solution of C60 (50 mg, 0.069 mmol) and DMSO (0.075 mL, 1.04
mmol, 15 equiv.) in o-DCB (15 mL) under Ar at room tempera-
ture. The mixture was stirred for 40 min at room temperature,
after which aqueous NH4Cl (0.1 mL, 1.0 mol/L) was added to
quench the reaction. The volatile solvents were removed by rota-
ry evaporation and excess methanol was added to precipitate the
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The Journal of Organic Chemistry
Synthesis of MeO-benzothieno[60]fullerene (2a). A THF so-
HR MALDI-TOF MS [M+]: m/z calcd. for C70H12S, 884.0660; found,
884.0665.
Synthesis of MeOCH2-benzothieno[60]fullerene (2d). A THF
lution of t-BuOK (1.0 M, 24 µL, 24 µmol) was added to a solution
of 1a (10 mg, 11 µmol) in o-DCB (2.0 mL) under Ar at room tem-
perature. A dark green solution of the potassium salt of deproto-
nated 1a immediately formed. After stirring for 30 min, I2 (18 mg,
69 µmol) was added to the dark green solution, after which the
reaction mixture was stirred for 60 min at ambient temperature.
The resulting dark brown solution (suspension) was passed
through a pad of silica gel with CS2 as the eluent. The obtained
solution was concentrated in vacuo and the residue was purified
by column chromatography on silica gel (CS2) to obtain the title
compound as a blackish microcrystalline powder in 42% isolated
yield. 1H NMR (400 MHz, CDCl3/CS2): δ 7.87 (d, J = 8.8 Hz, 1H,
C6H3), 7.01 (d, J = 2.4 Hz, 1H, C6H3), 6.88 (dd, J = 8.4 Hz, J = 2.4 Hz,
1H, C6H3), 3.94 (s, 3H, OMe). 13C{1H} NMR (100 MHz, CDCl3/CS2): δ
31.04, 56.16, 108.40, 113.36, 128.45, 128.98, 135.67, 140.96,
141.18, 141.56, 142.50, 142.86, 142.95, 142.99, 143.18, 143.26,
143.50, 143.53, 144.03, 144.58, 145.20, 145.35, 145.97, 145.98,
146.01, 146.13, 146.78, 146.88, 146.92, 147.08, 148.30, 148.55,
151.52, 152.24, 161.54. HR MALDI-TOF MS [M+]: m/z calcd. for
C67H6OS, 858.0134; found, 858.0123.
Synthesis of benzothieno[60]fullerene (2b). A THF solution
of t-BuOK (1.0 M, 27 µL, 27 µmol) was added to a solution of 1b
(20 mg, 24 µmol) in o-DCB (2.0 mL) under Ar at room tempera-
ture. A dark green solution of KC60(C6H4-2-SMe) immediately
formed. After stirring for 20 min, I2 (24 mg, 95 µmol) was added
to the dark green solution, after which the reaction mixture was
stirred for 60 min at ambient temperature. The resulting dark
brown solution (suspension) was passed through a pad of silica
gel with CS2 as the eluent. The obtained solution was concentrat-
ed in vacuo, and the residue was subjected to preparative HPLC
(Buckyprep) and reprecipitation by the addition of methanol. An
inseparable mixture of 2b and 2b’, which exhibited overlapping
HPLC peaks with retention times of 15.03 and 15.52 min
(Buckyprep 4.6 φ × 250 mm; eluent: toluene/2-propanol = 7/3)
was obtained. Repeated silica gel column chromatography with
CS2/n-hexane gradient eluent was used to carefully separate this
mixture to provide the desired compound 2b (the HPLC peak at
15.03 min) in 30% yield (6 mg) as a dark brown powder. 1H NMR
(400 MHz, CDCl3/CS2): δ 7.35 (t, 1H, C6H4), 7.44 (t, 1H, C6H4), 7.52
(d, 1H, C6H4), 8.01 (d, 1H, C6H4). We were unable to obtain a 13C
NMR spectrum due to very low solubility of unsubstituted com-
pound 2b. HR MALDI-TOF MS [M+]: m/z calcd. for C66H4S,
828.0034; found, 828.0012.
1
2
3
4
5
6
7
8
solution of t-BuOK (1.0 M, 36 µL, 36 µmol) was added to a solu-
tion of 1d (20 mg, 23 µmol) in o-DCB (4.0 mL) under Ar at room
temperature. A dark green solution containing the potassium salt
of deprotonated 1d immediately formed. After stirring for 30 min,
I2 (39 mg, 153 µmol) was added to the dark green solution, after
which the reaction mixture was stirred for 120 min at ambient
temperature. The resulting dark brown solution (suspension) was
passed through a pad of silica gel with CS2 as the eluent. The ob-
tained solution was concentrated in vacuo, and the residue was
purified by column chromatography on silica gel (CS2) to obtain
the title compound as a blackish microcrystalline powder in 41%
9
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15
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19
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23
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27
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1
isolated yield. H NMR (400 MHz, CDCl3/CS2): δ 7.94 (dd, J = 1.6
Hz, J = 0.8 Hz, 1H, C6H3), 7.48 (d, J = 8.0 Hz, 1H, C6H3), 7.40 (dd, J =
8.0 Hz, J = 0.8 Hz, 1H, C6H3), 4.51 (s, 2H, CH2O), 3.41 (s, 3H, OMe).
13C{1H} NMR (100 MHz, CDCl3/CS2): δ 30.09, 58.18, 74.09, 122.62,
126.86, 129.12, 134.73, 135.06, 136.23, 136.81, 137.98, 140.22,
140.75, 141.70, 142.07, 142.20, 142.25, 142.51, 142.71, 142.76,
143.24, 143.82, 144.39, 144.56, 145.24, 145.27, 145.34, 145.37,
146.00, 146.10, 146.12, 146.14, 146.35, 147.53, 147.78, 150.53,
151.37. HR MALDI-TOF MS [M+]: m/z calcd. for C68H8OS,
872.0296; found, 872.0285.
Synthesis of O-(2-bromo-5-methoxyphenyl) dimethylcar-
bamothioate (3a). To
a
stirred solution of Bromo-4-
methoxyphenol of 5.18 g and 1,4-diazabicyclo[2,2,2]octane of
5.75 g in 50 mL DMF was slowly added dimethylthiocarbamoyl
chloride in four separate portions over 30 min. When the addition
was complete, the mixture was stirred overnight (18 h) under a
nitrogen atmosphere. At the end of this period, the mixture was
poured into distilled water with rapid stirring. The mixture was
extracted with DCM. The organic layer was dried over Na2SO4,
subjected to filtration, and concentrated in vacuo. The crude
product was purified by column chromatography on silica gel (40:
2: 1 = PE: EA: Et3N) to afford the product as white crystals of 4.80
g. The yield is 65%. 1H NMR (400 MHz, CDCl3): δ 7.46 (d, J = 9.2 Hz,
1H, C6H3), 7.26 (s, 1H, C6H3), 6.73 (s, 1H, C6H3), 3.80 (s, 3H, OMe),
3.48 (s, 3H, NMe), 3.39 (s, 3H, NMe).24a
Synthesis of S-(2-bromo-5-methoxyphenyl) dimethylcar-
bamothioate (4a). A solution of 3a of 4.80 g and 15 mL N,N-
diethylaniline was vacuum-degassed and then heated under re-
flux under nitrogen for 6 h. The resulting brown solution was
concentrated. And the residue was poured into ice cold 6 M HCl
with rapid stirring. The mixture was cooled to room temperature.
The mixture was extracted with diethyl ether. The organic layer
was dried over MgSO4, subjected to filtration, and concentrated in
vacuo. The crude product was purified by column chromatog-
raphy on silica gel (100 : 2 : 1 = PE : EA : Et3N) to afford the prod-
uct as white crystals of 4.00 g. The yield is 83%. 1H NMR (400
MHz, CDCl3): δ 7.55 (d, J = 8.8 Hz, 1H, C6H3), 7.19 (d, J = 3.2 Hz, 1H,
C6H3), 6.82 (dd, J = 8.8 Hz, J= 2.8 Hz, 1H, C6H3), 3.79 (s, 3H, OMe),
3.11 (brs, 3H, NMe), 3.06 (brs, 3H, NMe).24a
Synthesis of (2-bromo-5-methoxyphenyl)(methyl)sulfane
(5a). To a stirred solution of KOH (7.02 g) in 30 mL of methanol
was added 4.00 g of 4a. The mixture was heated under reflux
under a nitrogen atmosphere for 4h, then cooled to 0 °C, and neu-
tralized with 100 mL of 6 M HCl. The mixture was cooled to 0 °C
and extracted with DCM. The organic extracts were combined,
dried over Na2SO4, filtered, and concentrated under reduced pres-
sure to give a light brown liquid of 2.50 g. This 2.50 g was dis-
solved in 35 mL of anhydrous DMF and treated with 3.80 g of
anhydrous K2CO3. The resulting mixture was stirred for 20 min,
and then, 1.5 mL of methyl iodide was slowly added over 15 min.
The resulting mixture was stirred at room temperature under a
nitrogen atmosphere overnight (18 h). At the end of this period,
the reaction mixture was poured into 200 mL of distilled water
and extracted with diethyl ether. The organic layers were com-
bined, dried over MgSO4, filtered, and concentrated under re-
The fraction with the longer retention time (15.52 min, com-
pound 2b’) was also characterized. 1H NMR (400 MHz,
CDCl3/CS2): δ 4.60 (d, 2H, CH2), 7.37 (t, 1H, C6H4), 7.39 (t, 1H,
C6H4), 7.74 (d, 1H, C6H4), 8.48 (d, 1H, C6H4). High-resolution
MALDI-TOF MS [M+]: m/z calcd. for C67H6S, 842.0190; found,
842.0217.
Synthesis of tBu-benzothieno[60]fullerene (2c). A THF solu-
tion of t-BuOK (1.0 M, 24 µL, 24 µmol) was added to a solution of
C60(C6H3-2-SMe-5-t-Bu)H (1c, 10 mg, 11 µmol) in o-DCB (2.0 mL)
under Ar at room temperature. A dark green solution of
KC60(C6H3-2-SMe-5-t-Bu) immediately formed. After stirring for
40 min, I2 (18 mg, 69 µmol) was added to the dark green solution,
after which the reaction mixture was stirred for 60 min at ambi-
ent temperature. The resulting dark brown solution (suspension)
was passed through a pad of silica gel with CS2 as the eluent. The
obtained solution was concentrated in vacuo, and the residue was
purified by column chromatography on silica gel (CS2) to provide
the title compound in 40% yield. 1H NMR (400 MHz, CDCl3/CS2): δ
7.37–7.35 (m, 1H, C6H3), 7.20–7.19 (m, 2H, C6H3), 1.24 (s, 9H, tBu).
13C{1H} NMR (100 MHz, CDCl3/CS2): δ 31.27, 34.17, 47.03, 58.80,
126.12, 130.64, 130.69, 132.68, 138.34, 139.59, 141.79, 142.05,
142.21, 142.43, 142.71, 143.23, 143.25, 143.41, 143.46, 143.67,
144.12, 144.34, 144.38, 144.43, 144.49, 144.56, 144.62, 144.65,
145.19, 146.89, 146.95, 147.00, 147.25, 147.27, 148.78, 149.84.
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Page 6 of 8
synthetic procedure for 5a, similarly we synthesized compound 5d as
oil in 95% yield. H NMR (400 MHz, CDCl3) δ 7.52 (d, J = 1.6 Hz,
duced pressure to give pale yellow liquid of 2.40 g. The yield is
90%. H NMR (400 MHz, CDCl3): δ 7.40 (d, J = 8.8 Hz, 1H, C6H3),
1
1
1
2
3
4
1H, C6H3), 7.27 (dd, J = 8.0 Hz, J = 1.6 Hz, 1H, C6H3), 7.11 (d, J =
8.0 Hz, 1H, C6H3), 4.39 (s, 2H, CH2), 3.38 (s, 3H, OMe), 2.48 (s, 3H,
SMe). 13C{1H} NMR (100 MHz, CDCl3): δ 58.36, 73.28, 77.23,
121.17, 127.16, 127.38, 131.99, 135.27, 138.81. EI-TOF MS [M+]:
m/z calcd. for C9H11BrOS, 245.9714; found, 245.9710.
6.68 (s, 1H, C6H3), 6.59 (dd, J = 8.8 Hz, J = 2.4 Hz, 1H, C6H3), 3.80 (s,
3H, OMe), 2.46 (s, 3H, SMe).24a
Synthesis of O-(2-bromo-4-(tert-butyl)phenyl) dimethyl-
carbamothioate (3c). According to the synthetic procedure for
1
5
3a, similarly we synthesized compound 3c in 67% yield. H NMR
(400 MHz, CDCl3): δ 7.58 (d, J = 2.0 Hz, 1H, C6H3), 7.35 (dd, J = 2.4
Hz, J = 8.4 Hz, 1H, C6H3), 7.08 (d, J = 8.4 Hz, 1H, C6H3), 3.48 (s, 3H,
NMe), 3.39 (s, 3H, NMe), 1.32 (s, 9H, tBu). 13C{1H} NMR (100 MHz,
CDCl3): δ 31.29, 34.66, 38.89, 43.46, 116.38, 124.38, 125.31,
130.20, 148.65, 150.62, 186.44. ESI-TOF MS [M + H+]: m/z calcd.
for C13H19BrNOS, 316.0371; found, 316.0360.
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9
ASSOCIATED CONTENT
Supporting Information
High-resolution mass spectra, H and 13C NMR spectra, Schemes
for the synthesis of the starting materials, HRMS data, data for the
rearrangement of the Grignard reagent, the reaction result with
less amount of iodine, UV-vis spectra, thermogravimetry data,
and theoretical calculations. This material is available free of
charge via the Internet at http://pubs.acs.org.
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Synthesis of S-(2-bromo-4-(tert-butyl)phenyl) dimethyl-
carbamothioate (4c). According to the synthetic procedure for
1
4a, similarly we synthesized compound 4c in 74% yield. H NMR
(400 MHz, CDCl3): δ 7.68 (d, J = 2.0 Hz, 1H, C6H3), 7.53 (d, J = 8.0
Hz, 1H, C6H3), 7.34 (dd, J = 8.4 Hz, J = 2.0 Hz, 1H, C6H3), 3.11–3.05
(m, 6H, NMe2), 1.31 (s, 9H, tBu). 13C{1H} NMR (100 MHz, CDCl3): δ
31.06, 34.82, 36.99, 125.18, 126.91, 130.48, 130.59, 137.70,
154.74, 165.67. ESI-TOF MS [M + H+]: m/z calcd. for C13H19BrNOS,
316.0371; found, 316.0360.
AUTHOR INFORMATION
Corresponding Author
* E-mail: matsuo@ustc.edu.cn
Notes
The authors declare no competing financial interest.
Synthesis
of
(2-bromo-4-(tert-
butyl)phenyl)(methyl)sulfane (5c). According to the synthetic
procedure for 5a, similarly we synthesized compound 5c in 88%
1
yield. H NMR (400 MHz, CDCl3): δ 7.54 (d, J = 2.4 Hz, 1H, C6H3),
ACKNOWLEDGMENT
7.32 (dd, J = 8.4 Hz, J = 2.0 Hz, 1H, C6H3), 7.09 (d, J = 8.4 Hz, 1H,
C6H3), 2.46 (s, 3H, SMe), 1.29 (s, 9H, tBu). 13C{1H} NMR (100 MHz,
CDCl3): δ 16.08, 31.31, 34.57, 122.10, 125.15, 125.73, 130.06,
136.10, 149.73. EI-TOF MS [M+]: m/z calcd. for C11H15BrS,
258.0078; found, 258.0075.
Funding from the University of Science and Technology of China
is gratefully acknowledged. This work was also supported by
Grants-in-Aid for Scientific Research (JSPS KAKENHI Grant
Numbers JP15H05760, JP16H04187, JP17K19116 and
17K04970) from the Ministry of Education, Culture, Sports, Sci-
ence and Technology (MEXT), Japan. The computational work
was performed at Research Center for Computational Science,
Okazaki, Japan.
Synthesis of 2-bromo-4-(hydroxymethyl)phenol. To a solution of
3-bromo-4-hydroxybenzaldehyde of 6.00 g in 100 mL EtOH was
added NaBH4 (1.50 g) at 0 °C. The clear solution was allowed to
warm to room temperature and stirred for 12 h. The reaction was
quenched by addition of 150 mL EtOAc and 50 mL water. The organ-
ic layer was separated, washed with water and brine, and dried
(Na2SO4). Concentration in vacuo gave a light-yellow solid of 5.56 g
REFERENCES
1
(1) (a) Tsumura, A.; Koezuka, H.; Ando, T. Macromolecular elec-
tronic device: Field effect transistor with a polythiophene thin
film. Appl. Phys. Lett. 1986, 49, 1210. (b) Katz, H. E. Organic mo-
lecular solids as thin film transistor semiconductors. J. Mater.
Chem. 1997, 7, 369–376.
(2) (a) Roncali, J.; Conjugated poly(thiophenes): synthesis,
functionalization, and applications. Chem. Rev. 1992, 92, 711–738.
(b) Roncali, J.; Synthetic principles for bandgap control in linear
π-conjugated systems. Chem. Rev. 1997, 97, 173–206. (c)
McCullough, R. D.; The chemistry of conducting polythiophenes.
Adv. Mater. 1998, 10, 93–116.
(3) (a) Kobayashi, K.; Gajurel, C. L. Thiophene-fused tetracy-
anoquinodimethanes as electron acceptors for conducting charge-
transfer salts. J. Chem. Soc., Chem. Commun. 1986, 1779–1780. (b)
Yoshida, S.; Fujii, M.; Aso, Y.; Otsubo, T.; Ogura, F. Novel electron
acceptors bearing a heteroquinonoid system. 4. Syntheses, prop-
in 92% yield. H NMR (400 MHz, DMSO-d6) δ 10.08 (s, 1H, OH),
7.40 (d, J = 2.0 Hz, 1H, C6H3), 7.10 (dd, J = 8.4 Hz, J = 2.0 Hz, 1H,
C6H3), 6.89 (d, J = 8.4 Hz, 1H, C6H3), 5.12 (s, 1H, C6H3OH), 4.37 (s,
2H, CH2).24b
Synthesis of 2-bromo-4-(methoxymethyl)phenol. To a solution of
2-bromo-4-(hydroxymethyl)phenol (5.56 g) in 50 mL CH3OH was
added a drop of conc. HCl at 90 °C. The clear solution was allowed to
stirred for 18 h. Concentration in vacuo gave white solid of 4.48 g in
1
75% yield. H NMR (400 MHz, CDCl3) δ 7.46 (d, J = 2.0 Hz, 1H,
C6H3), 7.18 (dd, J = 8.0 Hz, J = 2.0 Hz, 1H, C6H3), 6.99 (d, J = 8.4
Hz, 1H, C6H3), 5.53 (s, 1H, OH), 4.36 (s, 2H, CH2), 3.37 (s, 3H,
OMe).24c
Synthesis of O-(2-bromo-4-(methoxymethyl)phenyl) dimethyl-
carbamothioate (3d). According to the synthetic procedure for 3a
procedure, similarly we synthesized compound 3d in 90% yield. 1H
NMR (400 MHz, CDCl3) δ 7.59 (d, J = 2.0 Hz, 1H, C6H3), 7.30 (dd, J
= 1.6 Hz, J = 8.4 Hz, 1H, C6H3), 7.13 (d, J = 8.4 Hz, 1H, C6H3), 4.44
(s, 2H, CH2), 3.48 (s, 3H, OMe), 3.40 (s, 6H, NMe2). 13C{1H} NMR
(100 MHz, CDCl3): δ 15.57, 28.38, 58.22, 73.92, 111.14, 120.90,
121.34, 125.01, 126.65, 129.01, 129.67. ESI-TOF MS [M + H+]: m/z
calcd. for C11H15BrNO2S, 304.0007; found, 304.0006.
erties,
bis(dicyanomethylene)-2,7-dihydrobenzo[2,1-b:3,4-
b']dithiophene, 2,7-bis(dicyanomethylene)-2,7-
dihydrobenzo[1,2-b:4,3-b']dithiophene, and 2,6-
bis(dicyanomethylene)-2,6-dihydrobenzo[1,2-b:4,5-
and
charge-transfer
complexes
of
2,7-
Synthesis of S-(2-bromo-4-(methoxymethyl)phenyl) dimethyl-
b']dithiophene. J. Org. Chem. 1994, 59, 3077–3081. (c) Laquinda-
num, G. L.; Katz, H. E.; Lovinger, A. J.; Dodabalapur, A. Benzodithi-
ophene rings as semiconductor building blocks. Adv. Mater. 1997,
9, 36–39. (d) Takimiya, K.; Konda, Y.; Ebata, H.; Niihara, N.;
Otsubo, T. Facile synthesis, structure, and properties of benzo[1,2-
b:4,5-b’]dichalcogenophenes. J. Org. Chem. 2005, 70, 10569–
10571.
(4) (a) Wudl, F.; Haddon, R. C.; Zellers, E. T.; Bramwell, F. B.
3,4:3',4'-Bibenzo[b]thiophene. J. Org. Chem. 1979, 44, 2491–2493.
(b) Nakasuji, K. New multi-stage redox systems and new organic
molecular metals. Pure Appl. Chem. 1990, 62, 477–482.
carbamothioate (4d). According to the synthetic procedure for 4a,
1
similarly we synthesized compound 4d in 78% yield. H NMR (400
MHz, CDCl3) δ 7.67 (d, J = 2.0 Hz, 1H, C6H3), 7.59 (d, J = 7.6 Hz,
1H, C6H3), 7.28 (dd, J = 1.6 Hz, J = 8.0 Hz, 1H, C6H3), 4.45 (s, 2H,
CH2), 3.39 (s, 3H, OMe), 3.14–3.04 (m, 6H, NMe2). 13C{1H} NMR
(100 MHz, CDCl3): δ 37.02, 58.38, 73.23, 126.59, 129.35, 130.61,
132.03, 138.04, 141.84, 165.35. ESI-TOF MS [M + H+]: m/z calcd.
for C11H15BrNO2S, 304.0007; found, 303.9994.
Synthesis
of
(2-bromo-4-
(methoxymethyl)phenyl)(methyl)sulfane (5d). According to the
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The Journal of Organic Chemistry
(5) (a) Li, G.; Shrotriya, V.; Huang, J. S.; Yao, Y.; Moriarty, T.; Em-
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