Sonogashira reactions for the synthesis of polarized pentacene derivatives

Article abstract of DOI:10.3906/kim-1505-117

Five dissymmetrically functionalized anthracene analogues (3a-e) were synthesized from commercially available 9,10-dibromoanthracene through an efficient bromine-iodine exchange followed by two successive Sonogashira coupling reactions. The resulting TMS-

Full text of DOI:10.3906/kim-1505-117

Turk J Chem
2015) 39: 1180 – 1189
Turkish Journal of Chemistry
(
http://journals.tubitak.gov.tr/chem/
¨
˙
⃝
c TUBITAK
Research Article
doi:10.3906/kim-1505-117
Sonogashira reactions for the synthesis of polarized pentacene derivatives
1
,∗
1
1
2
St ´e phane SCHWEIZER , Guillaume ERBLAND , Philippe BISSERET , Jacques LALEVEE ,
3
1,∗
Didier Le NOUEN , Nicolas BLANCHARD
1
Laboratory of Molecular Chemistry, University of Strasbourg, CNRS UMR 7509, ECPM, Strasbourg, France
2
Institute of Materials Science of Mulhouse IS2M, CNRS UMR 7361, University of Haute Alsace,
Mulhouse Cedex, France
3
Laboratory of Organic and Bioorganic Chemistry, EA4566, University of Haute Alsace, Donnet Research Institute,
Mulhouse Cedex, France
Received: 29.05.2015
•
Accepted/Published Online: 01.09.2015
•
Printed: 25.12.2015
Abstract: Five dissymmetrically functionalized anthracene analogues (3a–e) were synthesized from commercially avail-
able 9,10-dibromoanthracene through an efficient bromine–iodine exchange followed by two successive Sonogashira cou-
pling reactions. The resulting TMS-anthracene analogues are interesting building blocks for the preparation of highly
π-conjugated dissymmetric pentacene-based dyads, which could be used as active semiconducting layers for organic
field-effect transistors (OFETs).
Key words: Sonogashira reaction, anthracene, pentacene, organic field-effect transistors
1
. Introduction
During the past few years, organic field-effect transistors (OFETs) have attracted a great deal of interest due to
the possibility to design flexible, large-area, low-cost, and lightweight devices.1 Among all organic molecules
investigated, a lot of studies have been devoted to pentacene derivatives, which combine high reproducibility
of thin films and good electronic performance.8,9 Dissymmetric pentacenes-based dyads have particularly been
−7
widely examined as promising candidates for OFETs.1
0−15
Indeed, such compounds may be composed of both a
triisopropylsilylethynyl part, providing sufficient solubility of the pentacene core, and an extended π-conjugated
system, increasing the charge mobility and the degree of crystal formation in the film.16 Dissymmetric TIPS-
pentacenes were reported in a series of inspiring and insightful publications by Tykwinski,1
0−15
the aromatic
end-part being then composed of diverse acenes including phenyl, naphthyl, or anthracenyl groups. These
polycyclic aromatic hydrocarbons were attached to the pentacene through an ethynyl linker to provide extended
conjugation.11 Pentacene derivatives have also found potential applications in photoredox catalysis as pure
organic photocatalysts that can be an alternative to expensive iridium complexes.17
In this work, we report on the practical synthesis of dissymmetric TMS-anthracene building blocks 3 for
the preparation of new polarized pentacene derivatives 5 (Scheme 1). As indicated in the synthetic blueprint, the
first logical building block is commercially available 9,10-dibromoanthracene that needs to be first and selectively
alkynylated using a metal-catalyzed cross-coupling reaction with different phenylacetylenes substituted with
electron-withdrawing or electron-donating substituent in the para position. To achieve this selectivity, it was
∗
Correspondence: n.blanchard@unistra.fr, stephane.schweizer@yahoo.fr
1180

SCHWEIZER et al./Turk J Chem
envisioned to transform 9,10-dibromoanthracene into the corresponding mono-iodinated derivative 1. Then a
second metal-catalyzed cross-coupling reaction could be applied, leading to a series of anthracenes 3. The latter
could then undergo an in situ lithio-desilylation reaction, offering a transient lithium acetylide that could add
onto the known aromatic ketone 4.1
0−15
Completion of the synthesis of the pentacene dyads 5 finally calls for
a classical aromatization reaction.1
0−15
R
Desymmetrization
Br
Br
I
Br
Br
R
1st Sonogashira
coupling
commercially
available
1
2
R = H, EDG, EWG
TMS
R' Li
TMS
R
Li
R
2nd Sonogashira
coupling
Lithio-
desilylation
3
O
Addition of 4 followed
by aromatization
TIPS
R
OH
4
TIPS
5
Scheme 1. Synthetic blueprint for the preparation of the pentacene dyads 5.
2
2
. Results and discussion
.1. Desymmetrization of 9,10-dibromoanthracene
As shown in Scheme 2, commercially available 9,10-dibromoanthracene can be converted into 9-bromo-10-iodo-
anthracene 1 through a monoiodination reaction.18 Indeed, upon addition of 1 equivalent of n-butyllithium to
a THF solution of 9,10-dibromoanthracene, a very clean mono bromine-lithium exchange occurred. Addition of
iodine then led to the formation of the expected compound 1 in 79% isolated yield. This key transformation
is scalable and was routinely done on a decagram scale, allowing us to easily and selectively functionalize the
anthracenyl motif through two successive Sonogashira coupling reactions.
2
.2. Selective Sonogashira coupling reactions
A first Sonogashira coupling reaction was carried out between 9-bromo-10-iodo-anthracene 1 and a series of 5
para-substituted phenylacetylenes using 2 mol% of Pd(PPh3)4 and a copper(I) co-catalyst (2 mol%) in toluene
1
181

SCHWEIZER et al./Turk J Chem
◦
18
at 55 C (Scheme 3). The chemoselectivity of the cross-coupling was excellent as none of the 9,10-dialkynylated
anthracene was observed by 1 H NMR analysis of the crude material. As shown in the Table, this first coupling
reaction was very efficient and provided the 5 expected para-substituted bromoanthracenes 2 with excellent
yields either from phenylacetylene itself (2a, 74%, entry 1), or electron-deficient (2b, 2c, 67%–94%, entries 2
and 3) or electron-rich (2d, 2e, 72%–75%, entries 4 and 5) phenylacetylene derivatives.
1
. n-BuLi
THF
Br
Br
Br
I
2
. I2
9%
7
1
Scheme 2. Halogen swap of 9,10-dibromoanthracene according to Swager et al.
Pd(PPh ) (2 mol%)
3
4
CuI (2 mol%)
DIPA
Br
I
+
R
Br
R
Toluene
55 °C
20h
1
R =H, Cl, F, OMe, NMe2
2a-e
R = H, Cl, F, OMe, NMe2
TMS
Pd(PPh ) (6 mol%)
3
4
CuI (6 mol%)
DIPA
TMS
R
Toluene
80 °C
20h
3a-e
R = H, Cl, F, OMe, NMe2
Scheme 3. Successive Sonogashira coupling reactions.
Table. Two successive Sonogashira couplings on 9-bromo-10-iodo-anthracene 1.
Entry
R
1st coupling (Yield)a 2nd coupling (Yield)b
1
2
3
4
5
H
2a (74%)
2b (94%)
2c (67%)
2d (75%)
3a (66%)
3b (65%)
3c (90%)
3d (98%)
3e (93%)
4-Cl
4-F
4-OMe
4-NMe2 2e (72%)
a
◦
Reaction conditions: 1 (1 equiv.), alkyne (1 equiv.), Pd(PPh
3
)
4
(2%), CuI (2%) in toluene/diisopropylamine, 55 C,
(6%), CuI (6%) in toluene/diisopropylamine,
b
2
8
0 h. Isolated yields. 2 (1 equiv.), TMS-acetylene (1 equiv.), Pd(PPh
3
)
4
◦
0
C, 20 h. Isolated yields.
1182

SCHWEIZER et al./Turk J Chem
The next step of the synthesis of the 5 building blocks 3 involved a second Sonogashira reaction between
the bromo-anthracene derivatives 2a–e and TMS-acetylene (Scheme 3).18 For this coupling, an excess of TMS-
◦
acetylene (3 equivalents) was employed and the reaction was carried out at 80 C in toluene using a threefold
amount of catalyst (6 mol%) and co-catalyst (6 mol%) compared to the first Sonogashira cross-coupling. As
shown in the Table, this second coupling reaction led to the formation of the 5 expected asymmetric anthracenes
3
a–e with good to excellent yields (65%–98%).
MeLi
TMS
Li
THF/HMPA (4:1)
40 °C, 45 min
-
3a
O
1
. 4, -78 °C then -20 °C,
0 min
3
TIPS
2
3
. -78 °C quench with
NH Cl
OH
4
aq.
4
TIPS
. SnCl , THF, 20 °C,
2
6
h
5a
Scheme 4. Preliminary results for the synthesis of 5a from 3a.
3
. Application to the synthesis of polarized pentacene derivatives
Having in hand these stable 9,10-dialkynylated anthracenes 3a–e, we briefly explored the reactivity of 3a as a
representative compound in the synthesis of extended π-conjugated pentacene-based dyads 5. It was quickly
discovered that the lithio-desilylation of 3a using methyllithium was not a trivial task, leading either to the
unchanged starting material or to complete degradation. After extensive experimentation, it was found that the
◦
optimal conditions for this lithio-desilylation required running the reaction at –40 C for 45 min, in a mixture
◦
of THF and HMPA (4:1). Addition of this lithium acetylide to the known ketone 41
0−15
at –78 C followed by
◦
warming the reaction mixture at –20 C for 20 min led to the desired product alongside numerous unidentified
◦
side products, even after a –78 C quench with aqueous ammonium chloride. Immediate aromatization of the
crude mixture using tin(II) chloride in degassed THF led to an intricate mixture from which several very apolar
and UV active products could be isolated as minor components (<10%) by flash chromatography. Although
the targeted pentacene derivative 5a was present in this green powder (as demonstrated by extensive 2D NMR
experiments), it was contaminated by inseparable isomers that seem to be partially reduced forms of one of the
alkynes embedded in 5a.
Further optimization of these last two steps is obviously required in order to provide a more general
synthetic access to this class of electronically diverse trialkynyl-pentacenes 5.
3
.1. Conclusions
We have reported an efficient synthesis of electronically diverse 9,10-dialkynylated anthracenes 3a–e thanks to
successive Sonogashira cross-coupling reactions. This sequence is practical and can be performed routinely on
2
1
183

SCHWEIZER et al./Turk J Chem
decagrams. The reactivity of these building blocks as competent partners for the synthesis of pentacene-based
dyads has been briefly explored and demonstrated that access to pentacenes such as 5 is not a trivial task.
Optimization of the last 2 steps of the sequence is currently under study and will be communicated in due
course.
4
4
. Experimental
.1. General remarks
NMR spectra were recorded on Bruker AV 300 or AV 400 spectrometer at 300 MHz or 400 MHz for 1
H
NMR, at 75 or 100 MHz for 13 C NMR, and at 376 MHz for 19 F NMR. The spectra were calibrated using
undeuterated solvent as internal reference, unless otherwise indicated. Coupling constants (J) were reported in
Hertz. Melting points were recorded on a B u¨ chi 510 melting point apparatus. All reactions were carried out in
oven-dried glassware under a nitrogen atmosphere using dry solvents, unless otherwise noted. Tetrahydrofuran
(
THF) was distilled under nitrogen from sodium-benzophenone, and toluene and dichloromethane were distilled
over CaH2 . Reagents were purchased from Aldrich, Acros, or Alfa Aesar. Yields refer to chromatographically
homogeneous materials, unless otherwise noted. Reactions were monitored by thin-layer chromatography (TLC)
carried out on Merck TLC silica gel 60 F254 glass-coated plates, using UV light or potassium permanganate as
visualizing agents. All separations were performed by flash chromatography on Merck silica gel 60 (40-63 µm),
on a Combiflash Companion from Teledyne Isco.
4
.2. Synthesis of 9-bromo-10-iodo-anthracene (1)18
A round-bottom flask, equipped with a magnetic stirring bar and dry nitrogen inlet, was successively charged
with 9,10-dibromoanthracene (10.0 g, 29.9 mmol) and THF (200 mL). n-BuLi (2 M in hexane, 16 mL, 32.3
◦
◦
◦
mmol) was then added at –78 C to the solution and the mixture was stirred at –78 C for 3 h. At –78 C,
a solution of iodine (9.9 g, 38.9 mmol) in THF (50 mL) was then slowly added on the anion and the mixture
was stirred at room temperature for 16 h. The solvent was evaporated under reduced pressure (to 10% of the
initial volume) and a saturated aqueous Na2 S2 O3 solution was added thus triggering the formation of a yellow
precipitate. The solid was recovered by filtration and washed with a saturated aqueous solution of Na2 S2 O3 ,
water, and cold ethanol. Compound 1 was obtained as a yellow powder (9.0 g, 79% yield).
Mp: 221 C. 1 H NMR (CDCl3 , 300 MHz) δ (ppm) 8.58–8.55 (m, 4H), 7.60–7.63 (m, 4H). 13 C NMR
◦
(
CDCl3 , 75 MHz) δ (ppm) 134.6, 134.4, 134.2, 128.7, 128.1, 127.6, 125.7, 106.6.
This product has been previously described and spectral data are in agreement with those reported in
the literature.18
4
.3. General procedure for the first Sonogashira coupling
A round-bottom flask, equipped with a magnetic stirring bar and a dry nitrogen inlet, was successively charged
with 1 (500 mg, 1.31 mmol), toluene (5.6 mL), diisopropylamine (2.4 ml), and the corresponding alkyne (1
equiv.). Copper(I) iodide (5 mg, 0.026 mmol) and palladium(0)tetrakis(triphenylphosphine) (30 mg, 0.026
◦
mmol) were added to the solution and the mixture was stirred at 55 C for 20 h. Dichloromethane was added
at room temperature to dissolve the precipitate and the resulting clear solution was successively washed with
water and brine. The organic layer was dried over magnesium sulfate, filtered, and the solvent was evaporated
under reduced pressure. The crude material was purified by column chromatography on silica gel to provide
the desired product 2.
1184

SCHWEIZER et al./Turk J Chem
4
.3.1. 9-Bromo-10-(2-phenylethynyl)anthracene (2a)
Compound 2a was obtained following the general procedure from phenylacetylene (143 µL, 1.31 mmol). The
crude material was purified by chromatography on silica gel (cyclohexane) to afford 2a as a yellow powder (345
mg, 74%).
Mp: 171 C. 1 H NMR (CDCl3 , 300 MHz) δ (ppm) 8.68–8.73 (m, 2H), 8.56–8.61 (m, 2H), 7.76–7.80 (m,
◦
2
1
H), 7.60–7.69 (m, 4H), 7.42–7.50 (m, 3H). 13 C NMR (CDCl3 , 100 MHz) δ (ppm) 133.1, 131.8, 130.4, 128.9,
27.7, 128.4, 127.6, 127.4, 126.9, 124.3, 123.5, 118.4, 101.9, 86.1.
This product has been previously described and spectral data are in agreement with those reported in
the literature.18
4
.3.2. 9-Bromo-10-[2-(4-chlorophenyl)ethynyl]anthracene (2b)
Compound 2b was obtained following the general procedure from 4-chlorophenylacetylene (178 mg, 1.31 mmol).
The crude material was purified by chromatography on silica gel (cyclohexane) to afford 2b as a yellow powder
(
485 mg, 94%).
Mp: 187 C. 1 H NMR (CDCl3 , 300 MHz) δ (ppm) 8.65–8.69 (m, 2H), 8.56–8.60 (m, 2H), 7.73–7.78 (m,
◦
2
1
H), 7.61–7.68 (m, 4H), 7.13–7.19 (m, 2H). 13 C NMR (CDCl3 , 75 MHz) δ (ppm) 134.9, 133.1, 132.9, 130.4,
29.1, 128.4, 127.6, 127.2, 127.1, 124.7, 122.0, 117.9, 100.7, 87.1.
4
.3.3. 9-Bromo-10-[2-(4-fluorophenyl)ethynyl]anthracene (2c)
Compound 2c was obtained following the general procedure from 1-ethynyl-4-fluorobenzene (150 µL, 1.31
mmol). The crude material was purified by chromatography on silica gel (cyclohexane) to afford 2c as a yellow
powder (326 mg, 67%).
Mp: 204 C. 1 H NMR (CDCl3 , 400 MHz) δ (ppm) 8.65–8.69 (m, 2H), 8.56–8.60 (m, 2H), 7.76 (dd,
◦
1
3
JH−H = 8.6 Hz, JH−F = 3.5 Hz, 2H), 7.61–7.68 (m, 4H), 7.16 (t, J = 8.6 Hz, 2H). C NMR (CDCl3 , 75
MHz) δ (ppm) 163.0 (d, JC−F = 249 Hz), 133.7 (d, JC−F = 8 Hz), 133.1, 130.4, 128.4, 127.6, 127.3, 127.0,
1
9
1
24.4, 119.6, 116.1 (d, JC−F = 21 Hz), 105.8, 100.8, 85.8.
F NMR (CDCl3 , 376 MHz) δ (ppm) –109.2 (tt,
J = 8.6 Hz, J = 5.7 Hz). HRMS-ESI m/z calcd for C22 H12 BrF [M+H]+ 375.0179, found 375.0178).
4
.3.4. 9-Bromo-10-[2-(4-methoxyphenyl)ethynyl]anthracene (2d)
Compound 2d was obtained following the general procedure from 4-(methoxyphenyl)acetylene (169 µL, 1.31
mmol). The crude material was purified by chromatography on silica gel (cyclohexane) to afford 2d as a yellow
powder (378 mg, 75%).
Mp: 132 C. 1 H NMR (CDCl3 , 300 MHz) δ (ppm) 8.65–8.71 (m, 2H), 8.53–8.58 (m, 2H), 7.69 (d, J =
◦
8
1
.8 Hz, 2H), 7.57–7.66 (m, 4H), 6.97 (d, J = 8.8 Hz, 2H), 3.87 (s, 3H). 13 C NMR (CDCl3 , 100 MHz) δ (ppm)
60.2, 133.3, 133.0, 130.4, 128.3, 127.5, 127.5, 126.8, 123.8, 118.8, 115.6, 114.4, 102.2, 84.9, 55.5.
This product has been previously described and spectral data are in agreement with those reported in
the literature.19
1
185

SCHWEIZER et al./Turk J Chem
4
.3.5. 4-[2-(10-Bromoanthracen-9-yl)ethynyl]-N,N -dimethylaniline (2e)
Compound 2e was obtained following the general procedure from 4-ethynyl-N, N -dimethylaniline (190 mg, 1.31
mmol). The crude material was purified by chromatography on silica gel (cyclohexane) to afford 2e as an orange
powder (374 mg, 72%).
Mp: 233 C. 1 H NMR (CDCl3 , 300 MHz) δ (ppm) 8.70–8.75 (m, 2H), 8.53–8.58 (m, 2H), 7.65 (d, J =
Hz, 2H) 7.60–7.64 (m, 4H), 6.75 (d, J = 9 Hz, 2H), 3.05 (s, 6H). 13 C NMR (CDCl3 , 100 MHz) δ (ppm)
50.9, 133.3, 133.1, 130.8, 128.5, 128.0, 127.8, 126.8, 123.2, 120.0, 112.4 (2C), 104.1, 84.6, 40.7.
◦
9
1
This product has been previously described and spectral data are in agreement with those reported in
the literature.20
4
4
.4. Procedures for the second Sonogashira coupling
.4.1. Trimethyl({2-[10-(2-phenylethynyl)anthracen-9-yl]ethynyl})silane (3a)
A sealed tube, equipped with a magnetic stirring bar, was successively charged with 2a (270 mg, 0.76 mmol),
toluene (3.5 mL), diisopropylamine (1.6 mL), and trimethylsilylacetylene (325 µL, 2.27 mmol). Copper(I)
iodide (9 mg, 0.045 mmol) and palladium(0)tetrakis(triphenylphosphine) (52 mg, 0.045 mmol) were added to
◦
the solution and the mixture was stirred at 80 C for 20 h. Dichloromethane was added at room temperature to
dissolve the precipitate and the resulting clear solution was filtered through a pad of silica gel. The solvent was
evaporated under reduced pressure and the crude material was purified by column chromatography on silica gel
(
cyclohexane) to afford 3a as a yellow powder (186 mg, 66% yield).
Mp: 129 C. 1 H NMR (CDCl3 , 300 MHz) δ (ppm) 8.65–8.70 (m, 2H), 8.58–8.63 (m, 2H), 7.76–7.79 (m,
◦
2
1
H), 7.60–7.66 (m, 4H), 7.42–7.50 (m, 3H), 0.44 (s, 9H). 13 C NMR (CDCl3 , 75 MHz) δ (ppm) 132.5, 132.1,
31.8, 128.8, 128.7, 127.4, 127.3, 127.0, 126.9, 123.5, 118.8, 118.4, 108.2, 102.6, 101.8, 86.6, 0.4.
This product has been previously described and spectral data are in agreement with those reported in
the literature.18
4
.4.2. (2-{10-[2-(4-Chlorophenyl)ethynyl]anthracen-9-yl} ethynyl)trimethylsilane (3b)
A sealed tube, equipped with a magnetic stirring bar, was successively charged with 2b (420 mg, 1.07 mmol),
toluene (5.3 mL), diisopropylamine (2.3 mL), and trimethylsilylacetylene (458 µL, 3.22 mmol). Copper(I)
iodide (12 mg, 0.064 mmol) and palladium(0)tetrakis(triphenylphosphine) (74 mg, 0.064 mmol) were added to
◦
the solution and the mixture was stirred at 80 C for 20 h. Dichloromethane was added at room temperature to
dissolve the precipitate and the resulting clear solution was passed through a pad of silica gel. The solvent was
evaporated under reduced pressure and the crude material was purified by column chromatography on silica gel
(
cyclohexane) to afford 3b as a yellow powder (283 mg, 65% yield).
Mp: 173 C. 1 H NMR (CDCl3 , 300 MHz) δ (ppm) 8.57–8.66 (m, 4H), 7.69 (d, J = 8.6 Hz, 2H),
.60–7.66 (m, 4H), 7.43 (d, J = 8.6 Hz, 2H), 0.44 (s, 9H). 13 C NMR (CDCl3 , 100 MHz) δ (ppm) 134.9, 133.0,
32.5, 132.1, 129.1, 127.5, 127.2, 127.1, 127.0, 122.0, 118.7, 118.3, 108.5, 101.6, 101.3, 87.5, 0.3. HRMS-ESI
◦
7
1
m/z calcd for C27 H21 ClSi [M+H]+ 409.1174, found 409.1175).
1186

SCHWEIZER et al./Turk J Chem
4
.4.3. (2-{10-[2-(4-Fluorophenyl)ethynyl]anthracen-9-yl} ethynyl)trimethylsilane (3c)
A sealed tube, equipped with a magnetic stirring bar, was successively charged with 2c (291 mg, 0.78 mmol),
toluene (3.9 mL), diisopropylamine (1.7 mL), and trimethylsilylacetylene (331 µL, 2.33 mmol). Copper(I)
iodide (9 mg, 0.046 mmol) and palladium(0)tetrakis(triphenylphosphine) (54 mg, 0.046 mmol) were added to
◦
the solution and the mixture was stirred at 80 C for 20 h. Dichloromethane was added at room temperature to
dissolve the precipitate and the resulting clear solution was passed through a pad of silica gel. The solvent was
evaporated under reduced pressure and the crude material was purified by column chromatography on silica gel
(
cyclohexane) to afford 3c as a yellow powder (275 mg, 90% yield).
Mp: 154 C. 1 H NMR (CDCl3 , 400 MHz) δ (ppm) 8.54–8.59 (m, 4H), 7.69 (dd, JH−H = 8.8 Hz,
◦
1
3
JH−F = 3.3 Hz, 2H), 7.55–7.59 (m, 4H), 7.10 (t, J = 8.8 Hz, 2H), 0.42 (s, 9H). C NMR (CDCl3 , 100 MHz)
δ (ppm) 163.0 (d, JC−F = 250 Hz), 133.7 (d, JC−F = 8 Hz), 132.5, 132.1, 127.5, 127.2, 127.1, 127.0, 119.6 (d,
1
9
JC−F = 4 Hz), 118.6, 118.5, 116.1 (d, JC−F = 22 Hz), 108.4, 101.7, 101.4, 86.3, 0.4. F NMR (CDCl3 , 376
MHz) δ (ppm) –105.6 (tt, J = 8.6 Hz, J = 5.7 Hz). HRMS-ESI m/z calcd for C27 H21 FSi [2M+H]+ 785.2866,
found 785.2865).
4
.4.4. (2-{10-[2-(4-Methoxyphenyl)ethynyl]anthracen-9-yl} ethynyl)trimethylsilane (3d)
A sealed tube, equipped with a magnetic stirring bar, was successively charged with 2d (354 mg, 0.91 mmol),
toluene (4.6 mL), diisopropylamine (2 mL), and trimethylsilylacetylene (390 µL, 2.74 mmol). Copper(I) iodide
(
11 mg, 0.055 mmol) and palladium(0)tetrakis(triphenylphosphine) (63 mg, 0.055 mmol) were added to the
◦
solution and the mixture was stirred at 80 C for 20 h. Dichloromethane was added at room temperature to
dissolve the precipitate and the resulting clear solution was passed through a pad of silica gel. The solvent was
evaporated under reduced pressure and the crude material was purified by column chromatography on silica gel
(
cyclohexane/dichloromethane 9:1) to afford 3d as an orange powder (361 mg, 98% yield).
Mp: 150 C. 1 H NMR (CDCl3 , 300 MHz) δ (ppm) 8.64–8.70 (m, 2H), 8.56–8.62 (m, 2H), 7.71 (d, J =
◦
8
.8 Hz, 2H), 7.59–7.65 (m, 4H), 6.98 (d, J = 8.8 Hz, 2H), 3.89 (s, 3H), 0.43 (s, 9H). 13 C NMR (CDCl3 , 100
MHz) δ (ppm) 160.2, 133.3, 132.6, 132.0, 127.4, 127.4, 127.0, 126.8, 119.3, 117.9, 115.7, 114.4, 108.0, 102.8,
01.8, 85.4, 55.3, 0.4. HRMS-ESI m/z calcd for C28 H24 OSi [M+H]+ 405.1669, found 405.1671).
1
4
.4.5. N,N -Dimethyl-4-(2-{10-[2-(trimethylsilyl)ethynyl]anthracen-9-yl} ethynyl)aniline (3e)
A sealed tube, equipped with a magnetic stirring bar, was successively charged with 2e (328 mg, 0.82 mmol),
toluene (2.1 mL), diisopropylamine (1.8 mL), and trimethylsilylacetylene (350 µL, 2.46 mmol). Copper(I)
iodide (9 mg, 0.049 mmol) and palladium(0)tetrakis(triphenylphosphine) (57 mg, 0.049 mmol) were added to
◦
the solution and the mixture was stirred at 80 C for 20 h. Dichloromethane was added at room temperature to
dissolve the precipitate and the resulting clear solution was passed through a pad of silica gel. The solvent was
evaporated under reduced pressure and the crude material was purified by column chromatography on silica gel
(
cyclohexane/dichloromethane: 9/1) to afford 3e as a red powder (317 mg, 93% yield).
Mp: 208 C. 1 H NMR (CDCl3 , 300 MHz) δ (ppm) 8.65–8.70 (m, 2H), 8.53–8.59 (m, 2H), 7.62 (d, J =
◦
8
.9 Hz, 2H), 7.55–7.62 (m, 4H), 6.73 (d, J = 8.9 Hz, 2H), 3.03 (s, 6H), 0.41 (s, 9H). 13 C NMR (CDCl3 , 100
MHz) δ (ppm) 150.6, 133.0, 132.6, 131.7, 127.6, 127.3, 127.0, 126.5, 120.2, 117.0, 112.0, 110.2, 107.6, 104.6,
02.0, 84.9, 40.4, 0.4. HRMS-ESI m/z calcd for C29 H27 NSi [M+H]+ 418.1986, found 418.1987).
1
1
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4
.5. Synthesis of a pentacene derivative [2-(13-{2-[10-(2-Phenylethynyl)anthracen-9-yl]ethynyl}
pentacen-6-yl)ethynyl]-tris(propan-2-yl)silane (5)
In a round-bottom flask equipped with a magnetic stirring bar, a dry nitrogen inlet, and a septum, MeLi (1.28
◦
M) (1.41 mL, 1.8 mmol) was added at –40 C to a solution of 3a (704 mg, 1.88 mmol) in THF (6 mL) and
◦
HMPA (1.5 mL). The reaction mixture was stirred at –40 C for 45 min and the resulting anion solution was
◦
added at –78 C to a solution of 4 (184 mg, 0.38 mmol) in THF (2 mL). The mixture was then stirred for 30 min
◦
◦
at –20 C and quenched with NH4 Cl sat. at –78 C. After extraction with dichloromethane, the organic phase
was dried over MgSO4 , filtered, and the solvents were removed under reduced pressure. The crude material
was then dissolved in degassed THF (4 mL) and a solution of tin(II) chloride dihydrate (270 mg, 1.2 mmol)
in degassed THF (4 mL) was added. The reaction mixture was stirred at room temperature for 6 h. After
addition of water, the green/blue mixture was extracted with dichloromethane and the organic layer was dried
over MgSO4 . After filtration, the solvents were evaporated under reduced pressure. From an intricate crude
material, several very apolar and UV active products could be isolated as minor components (22 mg, <10%)
by flash chromatography (cyclohexane/dichloromethane: 8/2). Although the targeted pentacene derivative 5a
was present in this green powder, it was contaminated by inseparable isomers that seem to be partially reduced
forms of one of the alkynes embedded in 5a as demonstrated by HRMS (HRMS-APCI m/z calcd for C57 H48 Si
[
M+H]+ 761.3604, found 761.3579). Extensive 2D NMR experiments demonstrated that 5a was present as a
mixture with (at least) three other compounds. Data for 5a: 1 H NMR (CDCl3 , 400 MHz) δ (ppm) 9.41 (s,
2
8
H), 9.28 (s, 2H), 8.85 (d, J = 8.0 Hz, 2H), 8.80 (d, J = 8.8 Hz, 2H), 8.00 (d, J = 8.8 Hz, 2H), 7.93 (d, J =
.4 Hz, 2H), 7.73–7.22 (13H), 1.43 (s, 3H), 1.41 (s, 18H).
Acknowledgments
The authors thank the University of Strasbourg and the CNRS for financial support.
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