A Straightforward Synthesis to Novel 1,10-Phenanthrolines with Fused Thiophene Structure

Article abstract of DOI:10.1055/s-0037-1611022

We report here a straightforward synthesis for a series of new structures with fused 1,10-phenanthroline-thiophene connection. They are synthesized with a modified Hinsberg thiophene procedure, followed by successive modification to yield several 5,7-disubstituted thieno[3,4- f ][1,10]phenanthrolines, most notable thiophene-substituted compounds that could be potentially of use for organic electronics applications. For some selected examples, crystal structures were obtained, showing a nearly coplanar arrangement around the fused connection, also beneficial for an effective electron transfer in organic electronics or solar cells.

Full text of DOI:10.1055/s-0037-1611022

SYNLETT
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
©
Georg Thieme Verlag Stuttgart · New York
2018, 29, A–E
letter
A
en
Synlett
M. Tünnermann et al.
Letter
A Straightforward Synthesis to Novel 1,10-Phenanthrolines with
Fused Thiophene Structure
Maike Tünnermann
S
N
Pia Rehsies
Ulrich Flörke
Matthias Bauer*
COOEt
0
0
0
0-
0
0
0
2-9
2
9
4-6
0
7
6
COOMe
H
Paderborn University, Department of Chemistry,
Warburger Strasse 100, 33098 Paderborn, Germany
matthias.bauer@upb.de
COOH
S
Rx
N
N
O
O
N
N
N
N
N
S
EtOOC
S
COOEt
+
S
COOH
Rx
S
S
Br
Br
Received: 15.08.2018
Accepted after revision: 24.09.2018
Published online: 24.10.2018
The structural motif of interest is shown in Scheme 1. It
is generally unknown from literature studies, except for a
patent by Jung-Sub Lee, describing the fusion of a 2,9-
DOI: 10.1055/s-0037-1611022; Art ID: st-2018-k0525-l
9
phenanthroline to thiophene. Their proposed protocol did
Abstract We report here a straightforward synthesis for a series of
new structures with fused 1,10-phenanthroline-thiophene connection.
They are synthesized with a modified Hinsberg thiophene procedure,
followed by successive modification to yield several 5,7-disubstituted
thieno[3,4-f][1,10]phenanthrolines, most notable thiophene-substituted
compounds that could be potentially of use for organic electronics
applications. For some selected examples, crystal structures were
obtained, showing a nearly coplanar arrangement around the fused
connection, also beneficial for an effective electron transfer in organic
electronics or solar cells.
not yield the desired 5,7-disubstituted thieno[3,4-
f][1,10]phenanthrolines. Another structure, which shows
the highest similarity with the systems reported here pos-
sess a 1,10-phenanthroline with a fused imide ring at the
10
[
3,4-f]-position. These pyrrole-containing molecules were
synthesized based on a procedure described by Lash or Ono,
who used 5-nitro-1,10-phenanthroline, DBU, and different
isocyanoacetates to isolate the fused pyrrole structure.
Key words thiophene, 1,10-phenanthroline, fused thiophene, semi-
conductor, organic solar cells
COOH
N
N
O
O
N
N
base
+
COOEt
S
EtOOC
S
solvent
Thiophenes are versatile compounds that are used in
many different fields and they are gaining much interest
COOH
1
1
during the last years. They are often used in research areas
2,3
Scheme 1 General scheme for a modified Hinsberg thiophene
like organic electronics as semiconductors, organic light-
synthesis that results in a 1,10-phenanthroline backbone
4
,5
6
emitting diodes (OLEDs) or solar cells and as bioimaging
materials.
5,7
In these applications, the thiophene com-
pounds are mostly based on π-conjugated polymer struc-
tures. Some of these polymers contain fused thiophene
rings or organic structures that are fused with the thio-
phene backbone like 3,4-ethylenedioxythiophene (EDOT).8
Through the conjugated structure they possess the ability
to transfer electrons within the organic framework. While
most fused thiophene structures are based on fusion at the
We therefore chose the well-established Hinsberg thio-
phene synthesis to prepare compound 1 as precursor for
further 5,7-disubstituted thieno[3,4-f][1,10]phenanthro-
lines. The according reaction scheme is shown in Scheme 1.
Following the literature procedure11 that uses NaOt-Bu for
the deprotonation of the thiodiacetate and t-BuOH as sol-
vent only 1,10-phenanthroline-5,6-diol was obtained in-
stead of the desired product 1. Consequently, a screening of
reaction parameters was carried out to realize the synthesis
of 1.12 The individual reaction components are summarized
in Table 1. Exchange of NaOt-Bu by KOt-Bu led to the
2
,3-position, a novel procedure to generate a fusion of 1,10-
phenanthroline at the 5,6-position with a thiophene ring at
,4-position is presented here.
3
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

B
Synlett
M. Tünnermann et al.
Letter
desired product, but only with a very low yield of 1.7 %
Table 1, entry 1). Contrary, changing the solvent to MeOH
and the base to KOMe increased the yield up to 96 % (Table
, entry 9). Isolation of the dicarboxylic acid required a
workup under strongly acidic conditions, which led to the
precipitation of the product.
ing was performed to ascertain the ideal conditions for the
C–C cross-coupling reaction of 5 with 2-thienylmagnesium
bromide (Table 2, entries 1–5), 2-thienyl boronic acid
(Table 2, entries 6–10), and 2-(tributylstannyl)thiophene
(Table 2, entry 11). The summarized screening results are
collected in Table 2. It was not possible to isolate the desired
extended thiophene structure 6 with a Ni- or Fe-catalyzed
Kumada coupling, while every Suzuki coupling yielded the
(
1
Table 1 Screening Parameter for a Modified Hinsberg Thiophene
Synthesis to Obtain 1
13
desired product 6, but with varying yields of 14.6–54.3 %.
The best result with a yield of 54.9 % was obtained with the
Stille coupling utilizing Pd(PPh ) as catalyst, and a solvent
mixture of toluene and DMF (4:1; Table 2, entry 11).
Entry
Solvent
Base
Order position Temp (°C) Yield (%)
of the base
3
4
1
2
3
4
5
6
7
8
9
t-BuOH
t-BuOH
t-BuOH
t-BuOH
EtOH
KOt-Bu
1st
r.t.
r.t.
0
2
–
2nd
cat. H2SO4
ROH
KOt-Bu
KOt-Bu
NaOt-Bu
KOt-Bu
KOt-Bu
KOt-Bu
KOMe
Δ
R1
R1
HOOC
COOH
H
H
2nd
2nd
2nd
–
X
X
X
3: R1
= COOMe 29 %
4
1
2
0
–
9
6 %
86 %
: R1 = COOEt 49 %
0
27
18
32
92
96
NBS H2O
MeOH
MeOH
MeOH
MeOH
2nd
r.t.
0
X=
2nd
Br
Br
X
1st
5
0
N
72 %
KOMe
2nd
0
S
N
S
Pd(PPh3)4
K3PO4
DMF
(HO)2B
If the reagents were suspended and added to the base
st
(
see Table 1, order position of base: 1 ) or the base was add-
S
S
ed to the suspended reagents (see Table 1, order position of
base: 2 ) had only minor influences on the obtained yield
X
6
4 %
nd
5
(91.5 % vs. 96.1 %). Compound 1 was utilized to realize a
series of new 5,7-disubstituted thieno[3,4-f][1,10]phenan-
throlines by using it as precursor in four different reactions.
According to Scheme 2, the decarboxylated product thie-
no[3,4-f][1,10]phenanthroline (2), the methyl (3), and ethyl
ester (4) of 1, and the 5,7-dibromo-substituted compound
NBS H2O
Br
Br
S
S
X
5
,7-dibromothieno[3,4-f][1,10]phenanthroline 5. All reac-
7
18 %
tions are depicted in Scheme 2. The synthesis of 2 was car-
ried out as a neat reaction, and the product sublimed as
colorless solid in vacuum. Although the yields were quite
low, esterifications of 1 to 3 and 4 produced the desired
products. For the synthesis of 5, N-bromosuccinimide (NBS)
was used as bromine source and water as solvent, which re-
sults in a yield of 72 %. Other solvents like CHCl or CH Cl
N
R2
R2
14: R2 =
15: R2 =
S
S
N
X
3
2
2
suffered from low solubility of 1 and did not yield any prod-
uct. Until now, only molecules with electron-withdrawing
groups that lower both, the HOMO and the LUMO, were
prepared. Hence, a system which provides different elec-
tronic properties was also synthesized. To achieve this, 5,7-
di(thiophen-2-yl)thieno[3,4-f][1,10]phenanthroline 6 with
terminal thiophene rings in the 5,7-position was prepared
to generate a system that is expected to feature a raised
HOMO and lowered LUMO due to the extended conjugation.
Additionally, 6 is theoretically capable of showing an effi-
cient electron transfer, too. With this modification, a larger
π-system is created that should be beneficial for efficient
electron-transport properties. Therefore, a second screen-
Scheme 2 Synthetic route for the synthesis of six different fused
thiophene structures
The synthesis of 5,7-bis(5-bromothiophen-2-yl)thie-
no[3,4-f][1,10]phenanthroline 7 was conducted as de-
scribed before for the preparation of 5 with NBS in water.
Synthesis of 5,7-bis[5-(pyridin-3-yl)thiophen-2-yl]thie-
no[3,4-f][1,10]phenanthroline 14 and 5,7-bis[5-(2,6-di-
methylpyridin-3-yl)thiophen-2-yl]thieno[3,4-
f][1,10]phenanthroline 15 by C–C cross-coupling reactions
of
7 with 3-pyridinylmagnesium bromide and (2,6-
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M. Tünnermann et al.
Letter
Table 2 C–C Cross-Coupling Reaction for the Reaction to Obtain 6
Entrya,b
THF
Et
O
DME/H
O
DMF
Toluene
NidpppCl
Fe(acac)
Pd(PPh
)
Pd(ac)
Pd(dppf)Cl
Time (h)
Yield (%)
2
2
2
3
3
4
2
2
1
2
3
4
5
6
7
8
9
x
x
x
21
68
2
–
–
x
x
x
–
x
x
x
24
72
21
23
41
62
142
70
–
x
–
x
x
x
x
–
x
x
x
x
x
39c
22c
15d
54d
55e
x
x
x
1
0
1
1
x
a
b
c
Entries 1–5 were conducted with 2-ThioMgBr as coupling reagent.
Entries 6–10 were conducted with 2-ThioB(OH) as coupling reagent.
Na CO was used as base in entries 6–8.
PO was used as base in entries 9 and 10.
2
2
3
d
e
K
3
4
3
Entry 11 was conducted with 2-ThioSnBu as coupling reagent.
S
possible to obtain the two last structures of 14 and 15.14
Bu3Sn
R
N
R
R
N
R
NBS
After the termination of the reaction, the products precipi-
tated as pale-yellow solids. They are the most promising
structures for novel photocatalytic systems because addi-
tional to the large π-system, they also possess two separate
Pd(PPh3)4
toluene
DMF
CHCl3
CH3COOH
(1:1)
S
Br
R = H or CH3
8: R = H
: R = CH3 91 %
79 %
9
15
coordination sides. These can be used to obtain bimetallic
R
N
R
R
N
R
systems as active photocatalytic hydrogen evolving sys-
n-BuLi
SnBu3Cl
tems.16
S
S
Br
64 %
THF
SnBu3
The synthesized compounds were characterized and
confirmed by NMR spectroscopy, mass spectrometry, and
elemental analysis. Additionally, it was possible to collect
single-crystal X-ray data for 5, 6, 7, and 15. All four struc-
tures exhibit a nearly coplanar arrangement of the 1,10-
phenanthroline and the thiophene ring with a maximum
torsion angle of 4.66° for structure 6. This plane orientation
supports the assumed effective electron transfer in these
compounds.17 The more extended structures (6, 7, and 15)
show an additional twist of ca. 70–75° around the terminal
thiophene rings in 6 and 7 and between the thiophene and
the pyridine rings in 15 with angles around 45°. The molec-
ular structure of 15 is shown in Figure 1, and the other
crystal structures are included in the Supporting Informa-
tion.
1
1
0: R = H
1: R = CH3 100 %
12: R = H 91 %
13: R = CH3 82 %
R
Br
S
N
N
R
N
S
S
Br
N
N
5
S
Pd(PPh3)4
toluene
DMF
R
N
R
1
1
4: R = H
70 %
5: R = CH3 69 %
Scheme 3 Synthetic route for the synthesis of 14 and 15
In conclusion, we have identified straightforward syn-
thesis protocols for a series of new 5,7-disubstituted thie-
no[3,4-f][1,10]phenanthroline structures. The crucial step
for the successful syntheses of these new structures was
the modification of the Hinsberg thiophene synthesis to
obtain the starting material 1 used for the preparation of all
derivatives. It is the first time that a 1,10-phenanthroline is
reported with a fused 3,4-thiophene ring in the backbone.
All molecules were characterized by standard methods as
well as crystal structure analysis for 5, 6, 7, and 15. Due to
dimethylpyridin-3-yl)magnesium bromide and Ni(dppf)Cl2
as catalyst failed. Hence, the synthetic strategy was altered,
and we went two steps back to introduce 5 to Stille cross-
coupling reactions with 12 and 13. These two molecules
were also prepared via another Stille coupling to obtain 8
and 9, subsequent brominations to 10 and 11 that were
finally converted into 12 and 13. This new synthetic route is
depicted in Scheme 3. With this modified procedure it was
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

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M. Tünnermann et al.
Letter
their coplanar arrangement, these new fused systems con-
taining thiophene rings are theoretically promising candi-
dates for the application as molecular electronics. Although
the actual application in organic electronics is not the aim
of the current work, the synthesized compounds may find
suitable applications in that field. However, in the near
future we will report promising results obtained with these
structures as ligands in photocatalytic hydrogen evolution
experiments as components in two-component as well as
one-component applications.
(3) Yu, H.; Park, K. H.; Song, I.; Kim, M.-J.; Kim, Y.-H.; Oh, J. H. J. Mater.
Chem. C 2015, 3, 11697.
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Chem. 2010, 8, 4819.
(
6) (a) Krishnamoorthy, T.; Kunwu, F.; Boix, P. P.; Li, H.; Koh, T. M.;
Leong, W. L.; Powar, S.; Grimsdale, A.; Grätzel, M.; Mathews, N.;
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(
7) (a) Xu, S.; Zhu, Y.; Li, R.; Su, J.; Li, S.; Zhou, H.; Wu, J.; Tian, Y.
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Rodriguez, L.; Belfield, K. D. J. Org. Chem. 2010, 75, 3975.
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Ali, S. S.; Manna, S. RSC Adv. 2015, 5, 24274.
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1589. (b) Turbiez, M.; Frère, P.; Allain, M.; Videlot, C.;
Ackermann, J.; Roncali, J. Chem. Eur. J. 2005, 11, 3742.
9) Lee, J.-S. US 20150155497, 2015.
(
(
10) (a) Ono, N.; Hironaga, H.; Simizu, K.; Ono, K.; Kuwano, K.;
Ogawa, T. J. Chem. Soc., Chem. Commun. 1994, 1019. (b) Lash, T.
D.; Novak, B. H.; Lin, Y. Tetrahedron Lett. 1994, 35, 2493.
(c) Villegas, J. M.; Stoyanov, S. R.; Rillema, D. P. Inorg. Chem.
2
2
002, 41, 6688. (d) Swavey, S.; DeBeer, M.; Li, K. Inorg. Chem.
015, 54, 3139. (e) Yao, H.; Zhang, L.; Peng, Y.; Carroll, P. J.;
Gong, L.; Meggers, E. Inorg. Chim. Acta 2014, 421, 489.
(
(
11) Wynberg, H.; Kooreman, H. J. J. Am. Chem. Soc. 1965, 87, 1739.
12) The reaction was conducted under inert atmosphere. Potassium
(
3.51 g, 89.8 mmol, 4 equiv) was dissolved in dry MeOH (15
mL). 1,10-Phenanthroline-5,6-dione (5.01 g, 23.8 mmol,
equiv) and diethyl-2,2′-thiodiacetate (4.99 g, 24.2 mmol, 1
1
equiv) were mixed in dry MeOH (40 mL) at 0 °C in a second
flask, and the potassium methanolate solution was added
slowly. During this process, the color changed from yellow to
black. The solution was stirred for 3 h at ambient temperature.
After this time a solid was formed. Water (500 mL) was added to
the mixture, and the reaction solution was concentrated to
Figure 1 Molecular structure of 15 with anisotropic displacement
ellipsoids drawn at the 50 % probability level
Funding Information
2
50 mL. The suspension was filtered, and concentrated HCl (65
M. Tünnermann thanks the Deutsche Bundesstiftung Umwelt (DBU)
for a Ph.D. scholarship. The German ministry of research and educa-
tion is acknowledged for funding in frame of project TrExHigh.()
mL) was added. The obtained solid 1 was filtered, washed with
diethyl ether, and dried under vacuum; yield 7.42 g (96 %)
1
H
3
NMR (500 MHz, DMSO-d ): δ = 8.18 (dd, J = 8.5, 4.9 Hz, 2 H),
6
HH
.15 (dd, JHH = 4.9 Hz, JHH = 1.4 Hz, 2 H), 10.00 (dd, 3JHH = 8.5
3
4
9
4
13
Hz, J = 1.4 Hz, 2 H) ppm. C NMR (125 MHz, DMSO-d ): δ =
Supporting Information
HH
6
125.7 (CH or Cq), 126.5 (Cq), 132.9 (Cq), 134.0 (Cq), 139.2 (Cq),
15
Supporting information for this article is available online at
141.5 (CH), 147.3 (CH), 163.3 (Cq) ppm. N NMR (70.9 MHz,
DMSO-d
H] .
https://doi.org/10.1055/s-0037-1611022.
S
u
p
p
orit
n
g Inform ati
o
n
S
u
p
p
orti
n
g Inform ati
o
n
6
): δ = 245.83 (s) ppm. MS-ESI (pos): m/z = 325.03 [M +
+
(
13) The reaction was carried out under Ar atmosphere. Compd 5
(0.16 g, 0.4 mmol, 1 equiv), 2-thienylboronic acid (0.12 g, 1.0
mmol, 2.5 equiv) and K PO (0.28 g, 1.3 mmol, 3.5 equiv) were
References and Notes
3
4
(
1) (a) Wu, Z.-S.; Zheng, Y.; Zheng, S.; Wang, S.; Sun, C.; Parvez, K.;
Ikeda, T.; Bao, X.; Müllen, K.; Feng, X. Adv. Mater. 2017, 29,
602960. (b) Zhang, W.; Han, Y.; Zhu, X.; Fei, Z.; Feng, Y.; Treat,
added to a Schlenk flask. Afterwards, Pd(PPh3)4 (0.06 g,
51.9 μmol, 0.1 equiv) was added to the flask with dry, oxygen-
free DMF (5 mL) and heated to 100 °C. After the reaction time of
142.5 h the mixture was allowed to cool down to r.t., extracted
1
N. D.; Faber, H.; Stingelin, N.; McCulloch, I.; Anthopoulos, T. D.;
Heeney, M. Adv. Mater. 2016, 28, 3922.
with CHCl , and washed with EDTA solution to remove palla-
3
(2) Yang, Y.; Zhang, Z.-G.; Bin, H.; Chen, S.; Gao, L.; Xue, L.; Yang, C.;
Li, Y. J. Am. Chem. Soc. 2016, 138, 15011.
dium residuals. The crude product of 6 was purified by column
1
chromatography over SiO with THF; yield 0.08 g (54 %)
H NMR
2
3
(
500 MHz, CDCl ): δ = 7.23 (dd, J = 5.2, 3.5 Hz, 2 H), 7.27 (dd,
3
HH
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

E
Synlett
M. Tünnermann et al.
Letter
3JHH = 8.4, 4.4 Hz, 2 H), 7.31 (dd, J = 3.5 Hz, 4JHH = 1.2 Hz, 2 H),
3
24.3 (CH ), 121.1 (CH), 123.1 (CH), 125.7 (Cq), 127.9 (CH), 130.0
HH
3
3
4
3
7
.59 (dd, J = 5.2 Hz, J = 1.2 Hz, 2 H), 8.15 (dd, J = 8.4 Hz,
= 1.7 Hz, 2 H), 8.95 (dd, J = 4.4 Hz, J = 1.7 Hz, 2 H) ppm.
C NMR (125 MHz, CDCl ): δ = 123.0 (CH), 125.8 (Cq), 128.2
CH), 128.9 (CH), 129.6 (CH), 130.3 (Cq), 130.9 (Cq), 132.6 (CH),
(CH), 130.0 (Cq), 131.0 (Cq), 132.6 (CH), 135.0 (Cq), 138.3 (CH),
HH
HH
HH
4
3
4
15
J
144.7 (Cq), 147.1 (Cq), 149.8 (CH), 155.3 (Cq), 157.7 (Cq).
N
HH
HH
HH
1
3
NMR (50.7 MHz, CDCl ): δ = 305.9 (s), 313.1 (s) ppm. MS-ESI
3
3
+
+
(
1
(pos): m/z = 633.12 [M + Na] , 611.14 [M + H] , 306.07 [M +
2H] . Anal. Calcd for CHN S : N, 9.17; C, 70.79; H, 4.29; S, 15.75.
15
2+
34.7 (Cq), 147.0 (Cq), 149.6 (CH) ppm. N NMR (50.7 MHz,
4
3
CDCl3): δ = 305.59 (s) ppm. MS-ESI (pos): m/z = 823.02 [2M +
Found: N, 8.76; C, 69.69; H, 4.67; S, 14.5.
+
+
Na] , 401.02 [M + H] . Anal. Calcd for C22H12S N : C, 65.97; H,
(15) We have prepared bimetallic systems with these ligands that
show high activities as hydrogen-evolving devices in photocata-
lytic proton reduction. The results will be published in the near
future.
3
2
3
2
.02; N, 6.99; S, 24.01. Found: C, 65.15; H, 3.59; N, 6.78; S,
2.19.
(
14) The reaction was conducted under inert atmosphere. Compd 5
0.04 g, 0.1 mmol, 1 equiv) and 13 (0.10 g, 0.2 mmol, 2 equiv)
were added to a Schlenk flask with dry and oxygen-free toluene
2 mL) and DMF (0.5 mL). Pd(PPh ) (0.01 g, 8.7 μmol, 0.1 equiv)
(
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(b) Venkataraman, L.; Klare, J. E.; Nuckolls, C.; Hybertsen, M. S.;
Steigerwald, M. L. Nature 2006, 442, 904. (c) Benniston, A. C.;
Harriman, A. Coord. Chem. Rev. 2008, 252, 2528. (d) Woitellier,
S.; Launay, J. P.; Joachim, C. Chem. Phys. 1989, 131, 481.
(
3
4
was added in counterflow to the mixture, and the reaction was
stirred at 105 °C for 72 h. The mixture was allowed to cool down
to ambient temperature while a white solid precipitated. The
solvent was filtered off, and the solid was washed with toluene.
The powder was dried under vacuum and identified as the
1
desired product 15; yield 0.04 g (69 %). H NMR (500 MHz,
3
CDCl ): δ = 2.62 (s, 6 H), 2.78 (s, 6 H), 7.10 (d, J = 7.72 Hz, 2
3
HH
3
3
H), 7.22 (d, J = 3.65 Hz, 2 H), 7.33 (d, J = 3.65 Hz, 2 H), 7.34
d, JHH = 4.43 Hz, 2 H), 7.70 (d, JHH = 7.85 Hz, 2 H), 8.37 (dd,
HH
HH
3
3
(
3
4
3
4
JHH = 8.35 Hz, J = 1.60 Hz, 2 H), 9.00 (dd, J = 4.43 Hz, J =
HH
HH
HH
13
1
.60 Hz, 2 H) ppm. C NMR (125 MHz, CDCl3): δ = 24.1 (CH3),
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E