Synthesis of Poly(3-substituted thiophene)s of Remarkably High Solubility in Hydrocarbon via Nickel-Catalyzed Deprotonative Cross-Coupling Polycondensation

Article abstract of DOI:10.1021/acs.macromol.5b02524

Polythiophenes bearing a siloxane moiety in a substituent at the 3-position are prepared by deprotonative polycondensation of 2-bromo-3-substituted-thiophene with a bulky magnesium amide chloromagnesium 2,2,6,6-tetramethylpiperidine-1-yl lithium chloride salt (TMPMgCl·LiCl) catalyzed by a nickel complex. Deprotonation takes place at 60 °C for 1 h to form the corresponding thiophene magnesium species, which is subjected to the polymerization by addition of 0.1-5 mol % NiCl₂(PPh₃)IPr (IPr: 1,3-bis(2,6-diisopropylphenyl)imidazole-2-yl). Polymerization proceeds in a highly regioregular manner, and the molecular weight of the thus-obtained polymer is controllable by the ratio of monomer feed/catalyst loading to indicate M_n of up to 280 000 with narrow molecular weight distribution. Chlorothiophenes are also found to induce polymerization in a deprotonative manner with TMPMgCl·LiCl or nBuLi (the Murahashi coupling polymerization). The obtained polymers bearing a siloxane moiety in the substituent is revealed to be dissolved in a hydrocarbon allowing formation of thin film from hexane.

Full text of DOI:10.1021/acs.macromol.5b02524

Article
pubs.acs.org/Macromolecules
Synthesis of Poly(3-substituted thiophene)s of Remarkably High
Solubility in Hydrocarbon via Nickel-Catalyzed Deprotonative Cross-
Coupling Polycondensation
†
†
†
†
†
†
Keisuke Fujita, Yugo Sumino, Kenji Ide, Shunsuke Tamba, Keisuke Shono, Jian Shen,
†
,†
‡
Takashi Nishino, Atsunori Mori,* and Takeshi Yasuda
†
Department of Chemical Science and Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
‡
Organic Thin-Film Solar Cells Group, Photovoltaic Materials Unit, National Institute for Materials Science (NIMS), 1-2-1 Sengen,
Tsukuba, Ibaraki 305-0047, Japan
*
S Supporting Information
ABSTRACT: Polythiophenes bearing a siloxane moiety in a
substituent at the 3-position are prepared by deprotonative
polycondensation of 2-bromo-3-substituted-thiophene with a
bulky magnesium amide chloromagnesium 2,2,6,6-tetramethyl-
piperidine-1-yl lithium chloride salt (TMPMgCl·LiCl) cata-
lyzed by a nickel complex. Deprotonation takes place at 60 °C
for 1 h to form the corresponding thiophene magnesium
species, which is subjected to the polymerization by addition of
0
.1−5 mol % NiCl (PPh )IPr (IPr: 1,3-bis(2,6-diisopropyl-
2
3
phenyl)imidazole-2-yl). Polymerization proceeds in a highly
regioregular manner, and the molecular weight of the thus-obtained polymer is controllable by the ratio of monomer feed/
catalyst loading to indicate M of up to 280 000 with narrow molecular weight distribution. Chlorothiophenes are also found to
n
induce polymerization in a deprotonative manner with TMPMgCl·LiCl or nBuLi (the Murahashi coupling polymerization). The
obtained polymers bearing a siloxane moiety in the substituent is revealed to be dissolved in a hydrocarbon allowing formation of
thin film from hexane.
7
INTRODUCTION
details. Herein, we describe that the molecular weight of
polythiophene is controllable and highly dependent toward
catalyst loading with narrow polydispersities in the nickel-
catalyzed polymerization. Thus, the polythiophene with
molecular weight of >280 000 is successfully prepared, and
the polymer is shown to be still soluble in hexane. Synthesis of
additional polythiophene derivatives bearing different structures
at the polythiophene substituent to estimate the solubility in
hydrocarbon and polythiophene syntheses with other polymer-
ization protocols are also described.
■
Siloxanes that involve Si−O−Si bond incorporated into organic
and polymer framework show remarkable change in their
characteristics such as thermal behaviors, chemical stabilities,
1
mechanical properties, and miscibility in solvents. Introduction
of a siloxane moiety into organic and polymer molecules has
thereby been studied to date to induce a new class of chemical
and physical properties particularly improving processability as
materials. Since we have been engaged in developing practical
synthetic protocols in polythiophene synthesis,
2
3
−5
which
greatly contributes to the design of highly conjugated
molecules, it is intriguing to prepare highly regioregular
poly(3-substituted thiophene)s bearing a siloxane moiety,
which potentially show unprecedented characteristics in
polythiophene derivatives. However, there have been few
studies on such preparation of polymers as well as monomers as
their precursors due to the synthetic difficulties of thiophene
derivative bearing both a siloxane moiety and polymerizable
EXPERIMENTAL SECTION
■
General. Unless otherwise specified, organic and polymerization
reactions were carried out under nitrogen with standard Schlenk
technique. Purification of 2,2,6,6-tetramethylpiperidine (TMPH) was
performed by distillation and stored under a nitrogen atmosphere.
Knochel−Hauser base (chloromagnesium 2,2,6,6-tetramethyl-
piperidine-1-yl lithium chloride salt: TMPMgCl·LiCl) was prepared
by the reaction of 2,2,6,6-tetramethylpiperidine with isopropyl-
magnesium chloride lithium chloride salt in THF at room temperature
for 24 h, and the resulting solution was stored in the freezer as a 1.0 M
2
b,6
functionality.
We have recently shown as a preliminary
communication that polythiophene derivatives bearing a
pentamethyldisiloxy substituent at the ω-alkene on the 3-
position of thiophene can be prepared by deprotonative
polymerization with a nickel catalyst, and the obtained polymer
of molecular weight ca. >10 000 is easily dissolved in
hydrocarbon whereas the reaction has not been studied in
8
THF solution under nitrogen. THF and cyclopentyl methyl ether
Received: November 22, 2015
Revised: January 26, 2016
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.macromol.5b02524
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
(
CPME) employed as a solvent (anhydrous grade) for the
= 7.0, 10.2, 17.4 Hz, 1H), 5.05 (d, J = 17.4 Hz, 1H), 5.00 (d, J = 10.2
1
3
polymerization were purchased and used without further purification.
Hz, 1H), 2.67 (t, J = 8.7 Hz, 2H), 2.34 (dt, J = 7.0, 7.0 Hz, 2H).
C
1
13
H NMR (500, 400, and 300 MHz) and C NMR (125, 100, and 75
NMR (125 MHz): δ 141.1, 137.7, 128.4, 125.4, 115.5, 109.3, 33.8,
−1
MHz) spectra were measured on BRUKER Avance-500, JEOL
ECZ400, and Varian Gemini 300 as a CDCl solution. The chemical
shifts were expressed in ppm with CHCl (7.26 ppm for H) or CDCl
29.0. IR (ATR): 3077, 2978, 2925, 2854, 1639, 1409, 991, 913 cm .
The obtained 3 was directly employed for the next reaction without
further purification.
3
1
3
3
(
77.16 ppm for 13C) as internal standards. SEC analyses were carried
2-Bromo-3-(4-pentamethyldisiloxybutan-1-yl)thiophene (5). To a
solution of 3 (1.57 g, 7.26 mmol) were added pentamethyldisiloxane
(1.71 mL, 8.7 mmol) and one drop of (1,1,3,3-tetramethyl-1,3-
divinyldisiloxane)platinum(0) (2 wt % xylene solution). After stirring
the mixture at room temperature for 5 min, the resulting reaction
mixture was subjected to column chromatography on silica gel to
out by standard HPLC system equipped with a UV detector at 30 °C
using CHCl as an eluent with Shodex GPC KF-404HQ and KF-
3
4
02HQ. Molecular weights and molecular weight distributions were
estimated on the basis of the calibration curve obtained by eight
standard polystyrenes. MALDI-TOF mass spectra were measured by
Bruker Daltonics Flexscan ultrafleXtreme. Elemental analysis was
carried out at Quantum Beam Science Center Japan Atomic Energy
Agency, Harima, Japan, with vario MICRO cube. Measurements of
HRMS were carried out with JEOL JMS-T100LP AccuTOF LC-Plus
1
afford 2.50 g of 5 (94%). H NMR (300 MHz): δ 7.18 (d, J = 5.7 Hz,
1H), 6.79 (d, J = 5.7 Hz, 1H), 2.56 (t, J = 7.5 Hz, 2H), 1.54−1.65 (m,
2H), 1.29−1.42 (m, 2H), 0.51−0.59 (m, 2H), 0.05 (s, 9H), 0.04 (s,
6H). 13C NMR (125 MHz): δ 142.1, 128.4, 125.3, 108.9, 33.5, 29.3,
−
1
(
ESI) with a JEOL MS-5414DART attachment. IR spectra were
2
3.1, 18.3, 2.1, 0.5. IR (ATR): 2955, 2858, 1409, 1252, 840, 753 cm .
+
79
recorded on Bruker Alpha with an ATR attachment (Ge). Purification
by HPLC with preparative SEC column (JAI-GEL-2H) was performed
by JAI LC-9201. For thin-layer chromatography (TLC) analyses
HRMS (DART-ESI , M + H) calcd for C H BrOSSi : 365.0426;
13
26
2
found m/z 365.0427.
Synthesis of 2-Bromo-3-(4-pentamethyldisiloxypropan-1-yl)-
thiophene (6). The solution of 2 (0.78 mL, 6.0 mmol) in 12.0 mL
of acetone was treated with sodium iodide (1.8 g, 12.0 mmol) at 40 °C
for 1.5 h. After filtration of the solid material, concentration of the
filtrate under reduced pressure left a crude oil, which was dissolved in
THF (12 mL). The solution was subjected to the reaction of
vinylmagnesium bromide (6.0 mL, 6.0 mmol) in the presence of CuI
throughout this work, Merck precoated TLC plates (silica gel 60 F254
)
were used. HOMO energy levels of the polymer films were measured
by photoelectron yield spectroscopy (PYS) using an AC-3
spectrometer (Riken Keiki). The UV−vis spectrum was measured by
a Hitachi U-3010 UV−vis spectrometer. The photoluminescences
(
PL) spectrum was recorded by a Jasco FP-6500 spectrofluorometer.
XRD analysis was carried out with Rigaku RINT-2500. Observation of
atomic force microscope (AFM) was performed with SII Nanocute.
Regioregular poly(3-hexylthiophene) (P3HT) that was purchased
from the Luminescence Technology Corp. was used as a reference
material in the film state. Allylmagnesium chloride was purchased from
Sigma-Aldrich Co. Ltd. as a 2 M THF solution. A platinum catalyst for
hydrosilylation (1,1,3,3-tetramethyl-1,3-divinyldisiloxane)platinum(0)
(
114 mg, 0.6 mmol) and 2,2′-bipyridyl (95 mg, 0.6 mmol) at room
temperature for 1 h. The mixture was poured into water to separate
into two phases. Aqueous was extracted with diethyl ether, and the
combined organic layer was dried over anhydrous sodium sulfate.
Removal of the solvent left an oil, which was passed through a short
path silica gel column to afford crude 4 (0.49 g, 2.66 mmol).
Pentamethyldisiloxane (0.62 mL, 3.19 mmol) and one drop of
(
2 wt % xylene solution) was purchased from Sigma-Aldrich Co. Ltd.
(1,1,3,3-tetramethyl-1,3-divinyldisiloxane)platinum(0) (2 wt % xylene
and used as received. Although 2-bromo-3-bromomethylthiophene (2)
is commercially available, preparation of 2 was carried out by the
reaction of 2-bromo-3-methylthiophene (1) with N-bromo-
succinimide/AIBN, and the obtained crude 2 was directly employed
for further allylation and hydrosilylation reactions without isolation,
leading to 4 to avoid technical loss of volatile 2 and 3 during isolation.
solution) were added to 4, and the mixture was stirred at 60 °C for 3 h.
After cooling to room temperature, purification by column
chromatography on silica gel afforded 0.85 g of 6 (89%). 4: H
NMR (300 MHz): δ 7.19 (d, J = 4.5 Hz, 1H), 6.80 (d, J = 4.5 Hz, 1H),
1
13
5
.83−5.97 (m, 1H), 5.05−5.10 (m, 2H), 3.33 (d, J = 6.0 Hz, 2H).
C
NMR (125 MHz): δ 139.2, 135.3, 128.5, 125.5, 116.3, 109.6, 33.9. 6:
2
-Bromo-3-bromomethylthiophene (2). To a solution of 2-bromo-
1
H NMR (300 MHz): δ 7.19 (d, J = 4.5 Hz, 1H), 6.79 (d, J = 4.5 Hz,
3
-methylthiophene (1: 4.92 mL, 44.0 mmol) in CCl (44.0 mL) was
4
1
0
1
1
H), 2.58 (t, J = 7.5, 2H), 1.57−1.65 (m, 2H), 0.51−0.61 (m, 2H),
.06 (s, 9H), 0.05 (s, 6H). 13C NMR (125 MHz): δ 142.0, 128.4,
25.3, 109.1, 33.1, 23.8, 18.3, 2.2, 0.5. IR (ATR): 2956, 1408, 1340,
added AIBN (0.22 g, 1.3 mmol). N-Bromosuccinimide (NBS) (3.13 g,
7.6 mmol) was added to the resulting solution, and stirring was
1
continued at 80 °C for 1 h. AIBN (0.07 g, 0.44 mmol) and NBS (2.35
g, 13.2 mmol) were further added to the reaction mixture, and the
solution was stirred at 80 °C for 1 h. The above procedure was
repeated, and further stirring was continued for 2 h. The reaction
mixture was cooled to room temperature and poured into water to
result in separation into two phases. Aqueous was extracted with
hexanes, and the combined organic phase was dried over anhydrous
sodium sulfate. Removal of the solvent under reduced pressure left a
crude oil, which was purified by column chromatography on silica gel
using hexanes as an eluent to afford 6.94 g of 2 (62%), whose
spectroscopic properties were identical with those of the authentic
−1
252, 1172, 1054, 995, 839, 809, 753, 687, 634, 623 cm . HRMS
+
79
(
DART-ESI , M + H) calcd for C H BrOSSi : 351.0270; found m/
12 24 2
z 351.0273.
2
-Chloro-3-(4-pentamethyldisiloxybutan-1-yl)thiophene (7). To a
2
0 mL Schlenk tube equipped with a Teflon-coated magnetic stirring
bar was added 5 (124 mg, 0.34 mmol) under a nitrogen atmosphere.
The mixture was cooled to 0 °C, and ethylmagnesium chloride (0.43
mL of 0.95 M THF solution, 0.41 mmol) was added dropwise to the
mixture. After stirring the mixture at 60 °C for 1.5 h, N-
chlorosuccinimide (NCS) (45 mg, 0.34 mmol) and THF (0.43 mL)
were added to the resulting solution, and stirring was continued at
room temperature overnight. The reaction mixture was cooled to
room temperature and poured into saturated aqueous solution of
sodium thiosulfate to result in separation into two phases. The
aqueous phase was extracted with diethyl ether twice, and the
combined organic layer was washed with brine and then with water.
The solvent was removed under reduced pressure to leave a crude oil.
Column chromatography on silica gel using hexanes as an eluent
9
1
sample. H NMR (300 MHz): δ 7.26 (d, J = 5.7 Hz, 1H), 7.00 (d, J =
.7 Hz, 1H), 4.46 (s, 2H).
-Bromo-3-(3-buten-1-yl)thiophene (3). To a 100 mL Schlenk
5
2
tube equipped with a Teflon-coated magnetic stirring bar under a
nitrogen atmosphere were added 2 (2.24 mL, 17.2 mmol) and THF
(
34.4 mL). The mixture was cooled to 0 °C, and allylmagnesium
chloride (11.2 mL of 2.0 M THF solution, 22.4 mmol) was added
dropwise to the mixture. After stirring the mixture for 1.5 h, the
solution was poured into water (50 mL) to result in phase separation.
The aqueous phase was extracted with diethyl ether twice (30 × 2
mL), and the combined organic layer was washed with brine and then
with water. The solvent was removed under reduced pressure to leave
a colorless oil, which was passed through silica gel column using
1
afforded 109 mg of 7 (>99%). H NMR (500 MHz): δ 7.02 (d, J = 7.5
Hz, 1H), 6.80 (d, J = 7.5 Hz, 1H), 2.59 (t, J = 7.5 Hz, 2H), 1.57−1.66
(m, 2H), 1.32−1.42 (m, 2H), 0.53−0.59 (m, 2H), 0.07 (s, 9H), 0.05
(s, 6H). 13C NMR (125 MHz): δ 139.3, 128.0, 124.6, 122.1, 33.4, 27.8,
23.1, 18.3, 2.1, 0.5. IR (ATR): 2956, 2856, 1413, 1252, 1054, 840, 807,
1
−1
hexanes as an eluent to afford 3.61 g of crude 3 (97%). H NMR (300
783, 753, 712, 686, 638 cm . Anal. Calcd for C H ClOSSi : C,
13
25
2
MHz): δ 7.19 (d, J = 5.7 Hz, 1H), 6.81 (d, J = 5.7 Hz, 1H), 5.85 (ddt, J
48.60; H, 7.79%. Found: C, 48.74; H, 7.82%.
B
DOI: 10.1021/acs.macromol.5b02524
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Scheme 1. Preparation of Thiophene Monomers (Precursors) Bearing Siloxane
2
-Bromo-3-(4-triethylsilylbutan-1-yl)thiophene (8). Synthesis of 8
Preparation of 10 was also carried out in a larger scale with 0.66 g of
bromothiophene 5 (1.8 mmol) and TMPMgCl·LiCl (2.0 mL, 2.0
mmol) at 60 °C for 1 h (deprotonation) and polymerization at 60 °C
was carried out in a similar manner to the synthesis of 5 from 3 (0.13
g, 0.60 mmol), triethylsilane (84 mg, 0.72 mmol), and one drop of
1,1,3,3-tetramethyl-1,3-divinyldisiloxane)platinum(0) (2 wt % xylene
solution) at room temperature for 2.5 h (>99%). H NMR (400
(
for 24 h with NiCl (PPh )IPr (0.15 mol %, 14 mg, 1.8 μmol) in THF
2 3
1
(18 mL) to afford 10 (0.49 g, 74%). M = 296 000; M /M = 1.26. HT
n w n
regularity >99%.
MHz): δ 7.18 (d, J = 5.5 Hz, 1H), 6.79 (d, J = 5.5 Hz, 1H), 2.58 (t, J =
7
.5 Hz, 2H), 1.66−1.56 (m, 2H), 1.41−1.30 (m, 2H), 0.93 (t, J = 8.0
Poly(3-(4-triethylsilylbutan-1-yl)thiophen-2,5-diyl) (11). Synthesis
of 11 was carried out in a similar manner to the synthesis of 10 from 2-
bromo-3-(4-triethylsilylbutan-1-yl)thiophene (8, 183 mg, 0.55 mmol),
TMPMgCl·LiCl (0.66 mL, 0.66 mmol, 1 M in THF), and
13
Hz, 9H), 0.59−0.47 (m, 8H). C NMR (100 MHz): δ 142.1, 128.3,
1
2
HRMS (DART-ESI , M + H) calcd for C H BrSSi: 333.0708;
found m/z 333.0710.
-Bromo-3-(4-bistrimethylsiloxysilylbutan-1-yl)thiophene (9).
25.3, 108.9, 33.9, 29.2, 23.7, 11.3, 7.6, 3.5. IR (ATR): 2952, 2910,
−1
874, 1749, 1413, 1376, 1168, 1012, 915, 828, 724, 685, 635 cm .
+
79
26
NiCl (PPh )IPr (4.3 mg, 5.5 μmol) in THF (5.5 mL) at 60 °C for
2 3
1
14
2
4 h (70%) (HT regularity >99%, M = 14 400, M /M = 1.05). H
n w n
NMR (400 MHz): δ 6.97 (brs, 1H), 2.76−2.85 (br, 2H), 1.77−1.67
2
(
8
2
br, 2H), 1.49−1.39 (br, 2H), 0.96−0.90 (br, 9H), 0.63−0.45 (m,
Synthesis of 9 was carried out in a similar manner to the synthesis
of 5 from 3 (0.14 g, 0.64 mmol), 1,1,1,3,5,5,5-heptamethyltrisiloxane
H). 13C NMR (100 MHz): δ 139.9, 133.9, 130.6, 128.7, 34.9, 29.4,
4.1, 11.4, 7.7, 3.5.
(
0.21 mL, 0.77 mmol), and one drop of (1,1,3,3-tetramethyl-1,3-
Poly(3-(4-bistrimethylsiloxysilylbutan-1-yl)thiophen-2,5-diyl)
12). Synthesis of 12 was carried out in a similar manner to the
divinyldisiloxane)platinum(0) (2 wt % xylene solution) at room
temperature for 1 h (96%). H NMR (300 MHz): δ 7.18 (d, J = 6.0
Hz, 1H), 6.79 (d, J = 6.0 Hz, 1H), 2.56 (t, J = 7.5 Hz, 2H), 1.54−1.64
(
1
synthesis of 10 from 2-bromo-3-(4-bistrimethylsiloxysilylbutan-1-
yl)thiophene (9, 220 mg, 0.50 mmol), TMPMgCl·LiCl (0.6 mL, 0.6
mmol, 1 M in THF), and NiCl (PPh )IPr (3.9 mg, 5 μmol) in THF
(
m, 2H), 1.30−1.41 (m, 2H), 0.45−0.52 (m, 2H), 0.08 (s, 18H),
0.01 (s, 3H). 1 C NMR (125 MHz): δ 142.0, 128.4, 125.3, 109.0,
3
2
3
−
3
9
(
1
1
5.0 mL) at 60 °C for 24 h (64%) (HT > 99%, M = 37 200, M /M =
n w n
1
3.3, 29.3, 22.9, 17.6, 2.0, −0.1. IR (ATR): 2957, 1409, 1256, 1045,
.09). H NMR (400 MHz): δ 6.97 (brs, 1H), 2.76−2.85 (br, 2H),
+
93, 839, 798, 782, 754, 714, 686, 652, 633. HRMS (DART-ESI , M +
.67−1.77 (br, 2H), 1.51−1.39 (br, 2H), 0.49−0.58 (br, 2H), 0.08
79
H) calcd for C H O BrSSi : 439.0614; found m/z 439.0625.
13
15
32
2
3
(brs, 18H), 0.02 (brs, 3H). C NMR (100 MHz): δ 139.9, 133.9,
Typical Synthetic Procedure for the Polymerization of 2-Halo-3-
Substituted Thiophenes Bearing Siloxane Moiety Representative as
the Case with 2-Bromo-3-(4-Pentamethyldisiloxybutan-1-yl)-
thiophene (5). To 2-bromo-3-(4-pentamethyldisiloxybutan-1-yl)-
thiophene 5 (0.18 g, 0.50 mmol) under a nitrogen atmosphere was
added a 1.0 M THF solution of TMPMgCl·LiCl (0.55 mL, 0.55
mmol) at room temperature. After stirring at 60 °C for 1 h, THF (5
mL) and NiCl (PPh )IPr (3.9 mg, 0.5 μmol) were added to the
resulting mixture, which was further stirred at 60 °C for 24 h.
Hydrochloric acid (0.1 M, 2 mL) and methanol were added to the
mixture to quench the reaction, the formed precipitate was filtered off,
and the residue was washed with methanol repeatedly to leave dark
purple solid, which was dried under reduced pressure to afford 70.9 mg
of poly(3-(4-pentamethyldisiloxybutan-1-yl)thiophen-2,5-diyl) (10)
1
30.7, 128.7, 34.3, 29.4, 23.4, 17.7, 2.0, −0.1.
Poly(3-(4-pentamethyldisiloxypropan-1-yl)thiophen-2,5-diyl)
(
13). Synthesis of 13 was carried out in a similar manner to the
synthesis of 10 from 2-bromo-3-(4-pentamethyldisiloxypropan-1-
yl)thiophene (6, 175 mg, 0.50 mmol), TMPMgCl·LiCl (0.6 mL, 0.6
mmol, 1 M in THF), and NiCl (PPh )IPr (3.9 mg, 5 μmol) in THF
2
3
(
5.0 mL) at 60 °C for 24 h (99%) (HT > 99%, M = 32 200, M /M =
n w n
1
2
3
1
1
9
1
.18). H NMR (400 MHz): δ 6.98 (brs, 1H), 2.78−2.88 (br, 2H),
.76−1.71 (br, 2H), 0.62−0.72 (br, 2H), 0.08 (brs, 6H), 0.07 (brs,
H). C NMR (100 MHz): δ 139.9, 133.9, 130.8, 128.8, 33.2, 24.7,
8.8, 2.2, 0.6.
13
Polymerization of chlorothiophene 7 (91.2 mg, 0.28 mmol) was
carried out with 1 M THF solution of TMPMgCl·LiCl (0.31 mL, 0.31
mmol) and NiCl (PPh )IPr (2.2 mg, 2.8 μmol) under the above-
mentioned conditions to afford 72.7 mg of 10 (90%) (HT > 99%, Mn
= 29 800, M /M = 1.17).
Murahashi Coupling Polymerization of Chlorothiophene (7). To
a solution of 2-chloro-3-(4-pentamethyldisiloxybutan-1-yl)thiophene
(7, 116 mg, 0.36 mmol) in 5.4 mL of CPME was added a hexane
solution of 1.6 M n-butyllithium (0.23 mL, 0.36 mmol) at −78 °C, and
the resulting mixture was stirred with raising the temperature to 0 °C
over 30 min. Then, NiCl (PPh )IPr (2.8 mg, 0.36 μmol) was added,
2
3
(
77% yield). Molecular weight and the molecular weight distribution
were estimated by SEC analysis to show M = 28 100, M /M = 1.07.
n
w
n
w
n
1
Analysis by H NMR (thienyl−CH − signals) at δ 2.80 (H−T) and δ
.60 (T−T), respectively, suggested HT (head-to-tail) regioregularity
as >99%. H NMR (300 MHz): δ 6.98 (brs, 1H), 2.72−2.87 (br, 2H),
.64−1.80 (br 2H), 1.38−1.53 (br, 2H), 0.55−0.64 (m, 2H), 0.06
brs, 15H). 13C NMR (125 MHz): δ 140.0, 133.9, 130.7, 128.8, 34.4,
9.4, 23.6, 18.5, 2.2, 0.6.
2
2
1
1
(
2
2
3
C
DOI: 10.1021/acs.macromol.5b02524
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a
Table 1. Estimation of the Deprotonation of 5 at the 5-Position of Thiophene
b
c
b
c
temp (°C)
time (min)
conversion (%)
temp (°C)
time (min)
conversion (%)
25
10
54
72
81
82
81
60
10
30
38
61
77
97
93
91
3
6
0
0
45
1
3
80
00
60
120
1
80
a
The reaction was carried out with thiophene 5 (0.2 mmol) and TMPMgCl·LiCl (0.22 mmol) in THF (0.22 mL). The reaction mixture was
b
c
1
quenched with DMF (3.0 mmol). The reaction period of deprotonation. Conversion was estimated by H NMR analysis. (See also Supporting
Information).
Scheme 2. Deprotonative Polymerization of 5 with TMPMgCl·LiCl and a Nickel(II) Catalyst
Figure 1. MALDI-TOF MS of polythiophene 10 bearing disiloxane moiety in the side chain.
and further stirring was continued for 30 min. The reaction mixture
was poured into a mixture of hydrochloric acid (1.0 M, 2 mL) and
methanol to form a precipitate, which was filtered off to leave a dark
purple solid. After washing with methanol repeatedly, the solid was
dried under reduced pressure to afford 62 mg of 10 (61% isolated
yield). SEC analysis showed Mn = 28 200, M /M = 1.29. HT
organic layer was concentrated under reduced pressure to leave a
crude oil, which was subjected to 1H NMR analysis to confirm
formation of 2-bromo-3-(4-pentamethyldisiloxybutan-1-yl)-5-formyl-
thiophene comparing proton signals of formylated product and the
remaining 5: H NMR (300 MHz) δ 7.45 (s, 0.97 H) and 6.79 ppm
(d, J = 5.7 Hz, 0.03 H), respectively (corresponding to the 4-position
of thiophene rings).
1
w
n
regioregularity >99%.
Studies on Deprotonation of 5 with TMPMgCl·LiCl. To a solution
of 2-bromo-3-(4-pentamethyldisiloxybutan-1-yl)thiophene (5, 73 mg,
Fabrication and Characterization of Organic Field-Effect
Transistors (OFETs). To estimate the hole mobilities of the siloxane-
bearing polythiophene, OFETs with a top-contact geometry were
fabricated and characterized as follows. A glass/Au gate electrode/
0
.2 mmol) was added a 1.0 M THF solution of TMPMgCl·LiCl (0.22
mmol, 0.22 mL). After stirring at 60 °C for 60 min, N,N-
dimethylformamide (DMF) (3.0 mmol, 0.23 mL) was added in one
portion, and stirring was continued at room temperature overnight.
The resulting mixture was poured into a mixture of hydrochloric acid,
and aqueous was extracted with diethyl ether twice. The combined
Parylene-C insulator substrate was prepared. The polymer 10 (M =
n
12 200) was spin-coated from hexane solution onto the Parylene-C
layer. The coated substrate was then transferred to a N -filled glovebox
2
where it was dried for 10 min at 110 °C. Au (40 nm) source-drain
D
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electrodes were thermally evaporated onto the substrates through
shadow masks. The channel length and width were fixed at 75 μm and
5
mm, respectively. The OFET measurements were conducted using a
Keithley 2636A System source meter under vacuum. The average
values with standard deviations of OFET parameters were calculated
from the results of four OFETs.
RESULTS AND DISCUSSION
Synthesis of several thiophene monomers bearing siloxane was
carried out as summarized in Scheme 1 starting from 2-bromo-
■
Table 2. Relationship in the Polymerization of 5 with the
a
Reaction Period
b
−3
c
c
time, h
conversion,
%
M × 10
n
M /Mn
w
0
1
3
9
4
.5
70
79
83
86
86
12.5
25.5
26.7
28.2
28.1
1.26
1.17
1.17
1.09
1.07
Figure 2. Relationship of the molecular weight (M ) and molecular
n
weight distribution (M /M ) of polythiophene 10 with the ratio of
w n
monomer feed/catalyst loading (20−1000). ●: M ; ▲: M /M . The
2
n
w
n
a
dotted line indicates theoretical value based on the monomer feed/
catalyst loading.
The reaction was carried out with 1 mol % nickel catalyst,
bromothiophene 5 (0.3 mmol), and TMPMgCl·LiCl (0.33 mmol)
in 3 mL of THF at 60 °C. Conversion was estimated by H NMR
analysis of the filtrate after isolation of polymer 10 with
b
1
c
pentachlorobenzene as an internal standard. M and M /M were
n
w
n
measured by SEC analysis.
Table 3. Relationship of the Molecular Weight of
Polythiophene 10 with the Ratio of Catalyst Loading/
a
Monomer Feed
b
catalyst loading/monomer feed
mol/mol)
conversion
(%)
M ×
n
−3
c
c
(
10
M /Mn
w
2
5
0
0
73
81
86
77
83
82
4.1
1.12
1.24
1.07
1.26
1.44
1.19
12.1
28.1
1
2
5
00
00
00
42.4
126.6
280.8
1
000
Figure 3. SEC profile of 10 with different monomer feed/catalyst
loading ratio.
a
The reaction was carried out with 5 (0.5 mmol) and TMPMgCl·LiCl
0.55 mmol) (deprotonation at 60 °C for 1 h) and polymerization
(
b
with NiCl (PPh )IPr in 5.0 mL THF (at 60 °C for 24 h). Conversion
2
3
1
summarized in Table 1, it was found that deprotonation of 5
at room temperature for 3 h resulted in 82% conversion.
Compared with the deprotonation of 2-bromo-3-hexylthio-
was estimated by H NMR analysis of the filtrate after isolation of
polymer 10 with pentachlorobenzene as an internal standard. M and
M /M were measured by SEC analysis.
c
n
w
n
3c,h
phene, which completed within 3 h at room temperature,
3
-methylthiophene (1). Radical bromination with NBS in the
the reaction of 5 was found to proceed slightly slower. Further
stirring for 5 h did not improve the conversion. Deprotonation
was revealed to be induced more efficiently when the reaction
was carried out at 60 °C for 1 h to show 97% conversion
whereas shorter reaction period for 10, 30, and 45 min resulted
in 38%, 61%, and 77% conversions, respectively.
presence of AIBN afforded bromomethylated intermediate 2,
which was subjected to allylation with a Grignard reagent to
give ω-olefinic product 3 in an excellent yield. Hydrosilylation
of 3 with a platinum catalyst led to the silylation product 5 in
a quantitative yield. By contrast, the related vinylation with
vinylmagnesium bromide did not proceed smoothly to result in
giving 4 in ca. 25% yield. Transformation of 2 into the
corresponding iodide followed by the reaction with vinyl
Grignard reagent proceeded smoothly to afford 4, which was
subjected to hydrosilylation in a similar manner to that of 3 to
afford 6 in excellent yields (overall yield: 89%). Chlorothio-
phene 7 bearing a siloxane moiety was obtained by halogen−
metal exchange of bromide 5 with EtMgCl followed by
treatment of N-chlorosuccinimide (NCS).
10
With the optimized deprotonation conditions in hand,
halothiophene 5 was subjected to polymerization with a nickel
catalyst. After treatment of 5 with TMPMgCl·LiCl at 60 °C for
11
12
1 h, nickel(II) catalyst NiCl (PPh )IPr was added to the
2
3
mixture to initiate polymerization. When 1 mol % nickel
catalyst was employed, the corresponding polymer bearing
disiloxane moiety was obtained in 77% isolated yield (86%
conversion) after stirring 60 °C for 24 h. SEC analysis of the
thus-obtained polymer revealed to show M = 28 100 and M /
n
w
1
We first examined deprotonation conditions in the reaction
M = 1.07. H NMR analysis of the obtained polymer 10
n
8
of halothiophene bearing siloxane 5 with TMPMgCl·LiCl, and
the progress of deprotonation was estimated by the reaction
with DMF leading to the corresponding aldehyde. As
showed that the head-to-tail regioregularity was >99% as well as
the presence of pentamethyldisiloxy group in the side chain
(Scheme 2). Figure 1 shows MALDI-TOF MS of the siloxane-
E
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Scheme 3. Polymerization of Thiophene Derivatives Bearing Organosilicon Moiety in the Alkyl Substituent
n
Scheme 4. Polymerization of Chlorothiophene 7 by Deprotonation with TMPMgCl·LiCl and BuLi
containing polymer 10 (Mn = ca. 4000), indicating the
repeating interval of ca. 285 Da, which reasonably agreed
with the corresponding monomer unit (284.6 Da). Peaks
observed as 3131.9 and 3210.8 Da also showed correspondence
ization with catalyst loading of 0.1 mol % afforded
3a,d,14
polythiophene of ca. 281 000 (Mn).
These results suggest
that deprotonative polymerization of a thiophene derivative
bearing a siloxane moiety in the substituent at the 3-position
15
with the polymer bearing end groups as H-(thienyl) -H and
11
proceeds in a catalyst transfer manner to result in chain
growth polymerization despite polycondensation (Figures 2
and 3).
Br-(thienyl) -H (theoretical M = 3132.1 and 3210.8 Da,
11
respectively).
The deprotonative cross-coupling polymerization was
studied under several conditions to exhibit that the molecular
weight of the polymer was increased as the progress of the
reaction period as shown in Table 2. Polymerization was mostly
complete in 9 h (86% conversion) at 60 °C, whereas the
reaction reached to ca. 70% within 1 h. The molecular weight
distribution was found constant to ca. 1.0−1.3 during the
polymerization. We also examined the reaction with different
monomer feed/catalyst loading as summarized in Table 3.
Thiophene derivatives bearing different silicon moieties were
then studied. Preparation of other monomer precursors was
performed as shown in Scheme 3, and thiophene derivatives
were subjected to polymerization under similar conditions at 60
°
C (deprotonation at 60 °C for 1 h) with 1.0 mol % nickel
catalyst. In addition to the formation of 5 and 6, formation of
thiophenes bearing triethylsilyl group 8 and branched siloxane
moiety 9 also proceeded in a similar manner. The reaction of
the thus-obtained bromothiophenes 6, 8, and 9 was performed
with TMPMgCl·LiCl (deprotonation) and NiCl (PPh )IPr
When 1 mol % of the nickel catalyst was employed, M was
n
2
3
2
8 100, whose value support that the molecular weight was
5
(polymerization) to afford the corresponding polymers (13, 11,
controlled by the concentration of the nickel catalyst. Increase
of catalyst loading produced the polymers with lower molecular
weights, which also showed reasonable correspondence with
the monomer feed/catalyst loading ratio. The reaction with
much lower catalyst loading such as 0.5−0.1 mol % also
afforded 10 with much higher molecular weight and relatively
small M /M values. It should be pointed out that polymer-
and 12, respectively) with good to excellent conversions (81−
9
9%). The M values of polymers bearing siloxane moiety
n
13
agreed with the theoretical molecular weight based on the
monomer/catalyst ratio whereas the molecular weight of 11
bearing triethylsilyl group was relatively inferior to those of 10,
12, and 13.
w
n
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Table 4. Optical Properties and Energy Levels of Polymers
in Film States
Egopt
b
PL
λmax (nm)
HOMO
(eV)
c
LUMO
(eV)
d
abs
λmax (nm)
polymer
(eV)
a
P3HT
554, 601
519
1.94
2.00
726
−4.74
−4.96
−2.80
−2.96
1
1
1
0
645, 706
(
12.2 kDa)
0
(
527
1.99
655, 716
−4.98
−2.99
280 kDa)
3
519
2.02
646, 682
−4.96
−2.94
a
b
Spin-coated from o-dichlorobenzene solution. Estimated from the
absorption onset in the film state. Estimated from photoelectron yield
spectroscopy. E
c
d
opt
= Eg + EHOMO.
LUMO
the reaction was performed with 1 mol % catalyst loading, the
corresponding polythiophene 10 was obtained (M = 29 800;
n
M /M = 1.17; 84% conversion). It was also found that
w
n
16
polymerization proceeded by Murahashi coupling, which is
the cross-coupling reaction with organolithium, using BuLi
as a deprotonating agent resulting in giving 75% conversion in
17
n
3
0 min at 0 °C with M = 28 200 and M /M = 1.29.
n w n
The obtained polythiophenes bearing a silyl group in the side
Figure 4. Photographs of the polymerization mixture of (a) for the
synthesis of P3HT and (b) 10 bearing siloxane moiety in the side
chain performed by the reaction with TMPMgCl·LiCl and
NiCl (PPh )IPr. Solubility test of polythiophenes in organic solvents
chain were found to be highly soluble in various organic
solvents. Figure 4 shows the deprotonative polymerization
mixture of 2-bromo-3-hexylthiophene to give poly(3-hexyl-
2
3
(
1 mg/mL). (c) Polythiophene 10 (M = 12 500) bearing a disiloxane
3i
n
thiophene): P3HT (a) and the related thiophene bearing
moiety in the side chain in hexane. (d) P3HT (M = 12 500) in
n
pentamethyldisiloxy group in the side chain 7 (b) with a nickel
catalyst in THF suggesting that (a) showed color change to
dark purple along with progress of the polymerization caused
by aggregation of polymer chains. On the other hand, the
mixture of (b) maintained clear orange solution throughout
polymerization to show excellent solubility of polymer 10 in
THF.
hexane. (e) P3DT (M = 14 900) in hexane. (f) 10 (M = 280 000) in
n
n
hexane. (g) 10 (M = 12 500) dissolved in 1-butanol (1 mg/mL). (h)
n
The mixture (e) after heating to 100 °C.
It was also found that the isolated polymer 10 was soluble in
a hydrocarbon such as hexane. Figure 4 shows the result of
solubility test of polythiophenes in hexane (1 mg/mL) at room
temperature indicating excellent solubility of 10 (c) in hexane,
whereas P3HT was hardly soluble under similar conditions (d)
and even poly(3-dodecylthiophene) bearing a longer alkylene
chain (e) only showed much inferior solubility. The polymer
with higher molecular weight (ca. 280 000) was also found to
be soluble in hexane (f). Worthy of note is that polythiophene
Figure 5. Solubility tests of polythiophene poly-3-(CH ) Si-thiophen-
2
n
2
,5-diyl) (11: Si = SiEt , n = 4; 12: Si = SiMe(OSiMe ) , n = 4; 13: Si
3
3 2
=
Si(CH ) OSi(CH ) , n = 3).
3
2
3 3
1
0 was dissolved in 1-butanol. Although the solubility of 10 was
much lower at room temperature, heating the mixture to 100
C resulted in complete dissolution (g and h). Polythiophene
°
bearing branched siloxane 12 and that with shorter alkylene
chain 13 similarly showed excellent solubilities in organic
solvents THF and hexane. On the other hand, polythiophene
bearing a triethylsilyl group in the side chain 11 was found
much less soluble in hexane, whereas 11 was dissolved in THF
(
Figure 5). These results suggest that siloxane group plays a key
2
role to dissolve polythiophene in hydrocarbon regardless of its
molecular weight; however, considering the result on the effect
of triethylsilyl group the presence of silicon atom does not
necessarily improve the solubility of the polymer albeit steric
bulkiness.
Figure 6. UV−vis spectra (normalized) of (a) 10 in the film state (M
n
=
12 200: solid; M = 280 000: dotted), (b) 13 (hexane solution:
n
dotted; thin film: solid).
Optical properties of siloxane-bearing polythiophenes in
solution and film states were examined. As described in the
preliminary communication, measurement of UV−vis absorp-
Synthesis of polythiophene bearing a siloxane substituent was
also found to be achieved with the corresponding chlorothio-
phene 7, which was prepared by halogen exchange with
bromothiophene 5. Deprotonation of 7 was carried out in a
similar manner to the case of 5 (60 °C, 1 h) and following
addition of nickel catalyst induced the polymerization. When
3
h
tion spectrum of a hexane solution of 10 (M = 12 200)
n
exhibited the λmax of 446 nm, and that in the film spin coated
from hexane solution followed by annealing at 110 °C for 107
min exhibited λmax = 519 nm to reveal red-shift of 73 nm.
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Figure 7. AFM images (5 × 5 μm region) of siloxane-bearing polythiophenes 10 ((a) M = 12 200 and (b) 280 000), (c) 13, and (d) P3HT.
n
Figure 8. XRD profiles of siloxane-bearing polythiophenes 10 ((a) M = 12 200 and (b) 280 000), (c) 13, and (d) P3HT.
n
H
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Figure 9. (a) Output and (b) transfer characteristics (at a drain voltage of −100 V) of OFET of 10 (M = 12 200).
n
Siloxane-baring polythiophene 10 of higher molecular weight
M = 280 000) showed λ of 527 nm, which slightly red-
in the 10 (M = 280 000) film probably due to the formation of
n
(
random orientation which is also observed in the film of P3HT
n
max
20
shifted ca. 8 nm compared with that of lower M as shown in
with high Mn.
n
Figure 6a. On the other hand, an analogous siloxane-bearing
polymer of shorter alkylene length 13 exhibited mostly similar
λmax (519 nm in the film and 444 nm in hexane) (Figure 6b).
A comparison of optical properties, HOMO−LUMO energy
levels, and morphology for thin films based on siloxane-bearing
polythiophenes with those for regioregular P3HT is a major
concern since the siloxane-bearing polythiophenes have a steric
hindrance on the top of their alkyl chains. The absorbance
spectra of P3HT displayed a shoulder peak on red-shifted side
To estimate a hole mobility as electric properties of the
siloxane-bearing polythiophene, we fabricated and characterized
OFETs. Figure 9 shows the output and transfer characteristics
(at a drain voltage of −100 V) of the OFETs based on 10 (Mn
= 12 200). Above the threshold voltage, the field-effect hole
mobility can be calculated from the slope of the plot of the
square root of the drain current versus gate voltage. From the
plot, the field-effect hole mobility for the OFET based on 10
= 12 200) was calculated to be (1.1 ± 0.1) × 10− cm V
5
2
−1
(M
n
18
−1
of the maximum absorbance peak. This feature is known to
be enhanced by the coplanarization of thiophene main chains
due to the ease of π−π stacking in P3HTs with normal alkyl
s , with a threshold voltage of −22 ± 3 V and an on/off ratio
2
of (2.4 ± 0.5) × 10 . Field-effect hole mobilities of P3HT were
−
4
−4
2
−1
reported to be ranging from 0.12 × 10 to 6.2 × 10 cm V
1
9
−1
21
chains, leading to the long effective conjugation length and
the narrow HOMO−LUMO energy gap (red-shifted absorp-
tion and photoluminescence spectra) in P3HTs compared to
siloxane-bearing polythiophenes. The lack of fine shoulder
peaks in the absorption spectra of siloxane-bearing poly-
thiophene films is most likely due to the large steric hindrance
on the top of their alkyl chains disturbing the π−π stacking.
These optical properties and HOMO−LUMO energy levels are
summarized in Table 4 (see also Supporting Information Figure
S2).
s , which were dependent on solvents used for spin-coating.
Additionally, field-effect hole mobilities of regioregular poly(3-
alkylthiophene)s (P3ATs) were reported to be ranging from
0.19 × 10− to 5.2 × 10 cm V s , which were dependent
4
−4
2
−1 −1
22
on the alkyl chain length. Even though the hole mobility of
the siloxane-bearing polythiophene is several orders of
magnitude lower than that of P3ATs due to the steric
hindrance on the top of their alkyl chains, the use of the
siloxane side chain for polythiophenes offers an advantage of
high solubility even in hexane. P3HTs with lower M may also
n
be soluble in hexane. However, the field-effect hole mobility of
AFM image for the P3HT film in Figure 7d shows a
significant roughness (the root-mean-square (RMS) roughness
of 6.33 nm), indicating the presence of P3HT aggregates due to
the ease of crystallization in P3HT. The out-of-plane XRD
diffraction patterns (diffraction angle 2θ = 5.4°, 10.8°, and
P3HT with the low M (= 2200) was reported to be quite low
n
mobility of 5.5 × 10− cm V s . Thus, our experimental
results will provide one of strategies for molecular design of
highly soluble conjugated polymers compatible with increasing
hole mobilities.
7
2
−1 −1 23
1
6.1° for the primary (100), secondary (200), and tertiary
(300) peaks in Figure 8d) indicate highly crystalline states in
CONCLUSION
the P3HT film. In contrast, homogeneous surfaces (RMS
roughness ranging from 0.93 to 1.45 nm) were observed for the
films of siloxane-bearing polythiophenes as shown in Figures
■
In conclusion, we have shown that polythiophene derivatives
bearing a siloxane moiety in a substituent of the thiophene ring
at the 3-position was successfully synthesized by nickel(II)-
catalyzed deprotonative polymerization of 2-bromo-3-substi-
tuted thiophenes with bulky magnesium amid Knochel−Hauser
base. The reaction was revealed to proceed to afford
regioregular head-to-tail-type polythiophene, in which the
molecular weight is controllable by the monomer feed/catalyst
loading ratio. The deprotonative polymerization was also
shown to proceed with the related chlorothiophene with
Knochel−Hauser base or butyllithium (Murahashi coupling
polymerization). The obtained siloxane-containing polythio-
phenes were shown to be dissolved in a variety of organic
solvents, particularly in hexanes. Characterization of thin films
8
a−c. Even though the layer distance of (100), which is a
interchain spacing between thiophene main chains through the
long side chains, is observed to some extent in XRD diffraction
patterns of 10 (M = 12 200) and 13 films, the lack of fine
n
shoulder peaks in absorption spectra and the homogeneous
surfaces observed in AFM images for the films based on
siloxane-bearing polythiophenes indicate a weak π−π inter-
action between neighboring polymer chains. XRD analysis of
siloxane-bearing polymer 13 with shorter alkylene length
indicated a peak at 2θ = 4.42° (100) suggesting layer distance
of 19.97 Å, which was shorter than that of 20.48 Å in the 10
(
M = 12 200) film, while a remarkable peak was not observed
n
I
DOI: 10.1021/acs.macromol.5b02524
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of siloxane containing polythiophenes by AFM and XRD was
performed, and the hole mobility of the thin film was studied.
Further researches on physical and mechanical properties of the
obtained polythiophenes are in progress, which will be
described in due course.
(6) (a) Mohamed, F. A.; Mohamed, A. I.; El-Shabouri, S. R. J. Pharm.
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(
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(
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A. H.; Knochel, P. Org. Lett. 2008, 10, 113−116.
ASSOCIATED CONTENT
■
*
S
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.macro-
mol.5b02524.
Experimental details and analytical data (PDF)
(9) Commercially available from Sigma-Aldrich Co. Ltd.
(
10) (a) Lewis, L. N.; Lewis, N. J. Am. Chem. Soc. 1986, 108, 7228−
231. (b) Chandra, G.; Lo, P. Y.; Hitchcock, P. B.; Lappert, M. F.
Organometallics 1987, 6, 191−192.
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010, 66, 9602−9609.
12) (a) Tamba, S.; Ide, K.; Shono, K.; Sugie, A.; Mori, A. Synlett
7
AUTHOR INFORMATION
■
*
(
2
(
Corresponding Author
E-mail amori@kobe-u.ac.jp (A.M.).
Notes
2
013, 24, 1133−1136. (b) Tanaka, S.; Tamba, S.; Sugie, A.; Mori, A.
The authors declare no competing financial interest.
Heterocycles 2012, 86, 255−266. (c) Tanaka, S.; Tamba, S.; Tanaka, D.;
Sugie, A.; Mori, A. J. Am. Chem. Soc. 2011, 133, 16734−16737.
(d) Tanaka, S.; Tanaka, D.; Tatsuta, G.; Murakami, K.; Tamba, S.;
ACKNOWLEDGMENTS
■
2
Sugie, A.; Mori, A. Chem. - Eur. J. 2013, 19, 1658−1665. (e) Tanaka,
S.; Tatsuta, G.; Sugie, A.; Mori, A. Tetrahedron Lett. 2013, 54, 1976−
This work was partially supported by KAKENHI B (No.
5288049), Special Coordination Funds for Promoting Science
and Technology, Creation of Innovation Centers for Advanced
Interdisciplinary Research Areas (Innovative Bioproduction
Kobe) by MEXT, Japan, and ASTEP by JST, MEXT, Japan.
S.T. thanks JSPS for the Research Fellowship for Young
Scientists.
1
4
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