Macrocycles with bithiophene units: Synthesis, structure, and electrochemical properties

Article abstract of DOI:10.1016/j.tetlet.2013.01.027

Bithiophene macrocycles with oligo(oxyethylene) loops were synthesized in good yields by reacting 4,40-bis(hydroxymethyl)-2,20-bithiophene with ditosylated oligoethyleneglycols. The structures of the macrocycles were elucidated by NMR spectroscopy and MS spectrometry. The electronic and electrochemical properties of the macrocyclic compounds were determined using cyclic voltammetry and UV-Vis spectroscopy. Copyright

Full text of DOI:10.1016/j.tetlet.2013.01.027

Tetrahedron Letters 54 (2013) 1460–1462
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Macrocycles with bithiophene units: synthesis, structure,
and electrochemical properties
Dora Demeter a,b, Claudia Lar a, Jean Roncali b, , Ion Grosu a,
⇑
⇑
a Babeßs-Bolyai University, Center of Supramolecular Organic and Organometallic Chemistry (CSOOMC), Cluj-Napoca, 11 Arany Janos str., 400028 Cluj-Napoca, Romania
b Group Linear Conjugated Systems, CNRS, MOLTECH-Anjou, University of Angers, 2 Bd Lavoisier, 49045 Angers, France
a r t i c l e i n f o
a b s t r a c t
Bithiophene macrocycles with oligo(oxyethylene) loops were synthesized in good yields by reacting 4,40-
bis(hydroxymethyl)-2,20-bithiophene with ditosylated oligoethyleneglycols. The structures of the macro-
cycles were elucidated by NMR spectroscopy and MS spectrometry. The electronic and electrochemical
properties of the macrocyclic compounds were determined using cyclic voltammetry and UV–Vis
spectroscopy.
Article history:
Received 20 October 2012
Revised 17 December 2012
Accepted 8 January 2013
Available online 16 January 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Bithiophenes
Macrocycles
Electropolymerization
Cyclic voltammetry
UV–Vis spectra
Electroactive conjugated polymers obtained by electropolymer-
ization of thiophene derivatives have attracted significant interest
in various aspects of sensor applications.1
via a flexible spacer chain6 (I, Fig. 1); to thiophene macrocycles
which include in their ring the 3 and 4 positions of the thiophene
unit (II),7 or to transannular macrocyclic compounds containing
bithiophene (III, IV),8 or larger terthiophene,9 quaterthiophene,10
and sexithiophene10 entities (V).
As with many sensors based on conjugated systems, the sensing
mechanism of
p-conjugated thiophenic systems involves a revers-
ible alteration of the electronic properties of the extended
p
-conju-
In this work, we report the synthesis and properties of transan-
nular macrocylic systems 5–7, (Scheme 1) which possess bithioph-
ene units connected at their 4,40 positions to oligo(oxyethylene)
chains via CH2 groups. The target compounds 5–7 were obtained
by the macrocyclization of 4,40-bis(hydroxymethyl)-2,20-bithioph-
ene (1) with ditosylated oligoethyleneglycols 2–4 (Scheme 1).11
The diol 1 was obtained by a multi-step approach starting from
thiophene-3-carboxylic acid (8) using procedures described in the
literature (Scheme 2).
gated chain. In the case of electrogenerated electroactive polymers,
the interactions of the sensor with the analyte species can be de-
tected through a modification of the optical and/or electrochemical
properties of the system. The origin of this modification can be
electrostatic or correlated with changes in the geometry of the p-
conjugated system. While a fully planar geometry leads to optimal
electron delocalization, the interactions of the functional conju-
gated system with the analyte inducing a torsion of the conjugated
structure, and thus a reduction of electron delocalization inducing
changes in the optical and redox properties of the conjugated sys-
tem.2–5
Polythiophenes functionalized with macrocyclic polyethers,
either via a linker or as a macrocyclic loop, attached at two differ-
ent points of the conjugated system, combine the advantages of
enhanced hydrophilicity brought about by the polyether moiety
with the metal–cation complexing properties of the macrocycles.
The main classes of structures reported in the literature correspond
to compounds bearing macrocycles attached to the thiophene units
The acid 8 was brominated with Br2/acetic acid,12 and the
resulting acid 9 was esterified using SOCl2 and methanol,13 while
the coupling reaction (synthesis of 11) was based on the Ulmann
reaction of bromoester 10.14 The last step was the reduction of
diester 11 with LiAlH4 in THF.
The structures of the products were determined using NMR (1D
and 2D), UV–Vis spectroscopy, and MS, while the electropolymer-
ization and electrochemical properties were investigated using
cyclic voltammetry.
The UV–Vis spectra of 5–7 (Fig. 2, Table 1) showed maxima
around 310 nm. A slight hypsochromic shift was observed when
increasing the length of the polyether chain (e.g., kmax = 304 nm
for compound 7).
⇑
Corresponding authors. Tel.: +40 264593833; fax: +40 264590818.
E-mail address: igrosu@chem.ubbcluj.ro (I. Grosu).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.01.027

D. Demeter et al. / Tetrahedron Letters 54 (2013) 1460–1462
1461
0.4
O
O
O
O
O
O
O
0.3
O
O
n
O
X
0.2
0.1
0.0
X = O, CH2O
S
S
S
I
II
O
X
O
n
O
O
S
S
S
O
300
400
500
λ (nm)
600
700
800
S
S
X
III
X = O, CH2O
IV
Figure 2. UV–Vis (CH2Cl2) spectrum of compound 5.
n
O
O
n
O
O
Table 1
Absorption maxima (CH2Cl2) and oxidation potential values (5 mM, in 0.10 M
S
S
O
O
Bu4NPF6, MeCN, scan rate 100 mV sꢀ1) for compounds 5–7
S
Compound
5
6
7
S
S
kmax (nm)
Eox (V/SCE)
309
1.24
310
1.30
304
1.30
S
S
m
V
VI
m = 1, 2, 4
The cyclic voltammogram (CV) of products 5–7 revealed that
irreversible oxidation correlated with the formation of the radi-
cal-cation of the bithiophene unit (1.24–1.30 V; for 5, see: Fig. 3a,
Table 1). Clear electropolymerization was observed only for 5; with
6 the polymer formed did not adhere to the electrode, while for 7
no clear deposition of the polymer on the electrode was observed.
The CVs resulting from the application of recurrent potential
scans between 0.0 and +1.30 V were different for compounds
5–7. For macrocycles 5 and 6, application of repetitive potential
scans led to the progressive development of a broad redox system
[0.60–1.00 V for 5 (Fig. 3b) and 0.80–1.00 V for 6] characteristic of
the electrodeposition of an electroactive material on the anode sur-
face, while for 7 electrodeposition of the polymer was not observed.
This peculiar situation for 7 might be due to the high solubility of the
polymer, or to passivation of the electrode surface.
Figure 1. Thiophene or poly(thiophene) macrocyclic derivatives.
O
n
O
n
O
O
OH
OH
OTs
TsO
O
O
n = 1
n = 2
n = 3
2
3
4
S
S
S
S
NaH
1
5
6
7
n = 1 (32%)
n = 2 (31%)
n = 3 (33%)
Scheme 1.
The electrochemical properties of polymers 5 and 6 were inves-
tigated by cyclic voltammetry using monomer-free electrolyte
solutions. The CV of poly(5) and poly(6) exhibited anodic peak
potentials at 1.10 V for poly(5) and at 1.13 V for poly(6). The higher
value obtained for poly(6) reflects a shorter conjugation length
caused by the larger steric effect of the longer polyether chain.
The electrosynthesis of poly(5) and poly(6) was also carried out
under optimized potentiostatic conditions. The polymers were
deposited on Pt microelectrodes at a charge density of 2 mC/cm2
and at potentials of 1.15 V for poly(5) and 1.20 V for poly(6).
A preliminary analysis of the cation complexing properties of
poly(5) and poly(6) was undertaken by recording the CV response
of the polymers in the presence of different metal cations. In the case
of poly(6) no change in the electrochemical response was observed
when replacing Bu4N+ by cations such as Li+, Ag+, or Ba2+. In contrast,
for poly(5), replacing Bu4N+ with Li+ produced a ca 70 mV negative
shift of the main anodic peak potential (Fig. 4), but no change in the
CV was observed with other metal cations. This result suggests that
complexation of Li+ by the macrocyclic loop results in planarization
of the bithiophene unit which is initially twisted by steric effects.
In conclusion, crown-annelated bithiophenes 5–7 have been
synthesized in good yields and characterized, and the electrosyn-
O
O
OH
O
OH
SOCl2
reflux
Br2
AcOH
74%
CH3OH
76%
S
8
Br
S
9
OCH3
H3COOC
COOCH3
reflux
S
S
Br
S
Cu
11
10
DMF
26%
OH
OH
LiAlH4
THF
90%
S
S
1
Scheme 2.

1462
D. Demeter et al. / Tetrahedron Letters 54 (2013) 1460–1462
Acknowledgments
We are grateful for the financial support of this work by CNCS-
UEFISCDI (Project PN-II-ID-PCCE-2011-2-0027) and to POSDRU/89/
1.5/S/60189 for the fellowship given to Claudia Lar.
References and notes
1. (a) Blanchard, P.; Leriche, P.; Frère, P.; Roncali, J. In Advanced Functional
p-
Conjugated Polythiophenes Based on Tailored Precursors, Handbook of Conducting
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Figure 3. Single potential scan of 5 (a) and potentiodynamic electropolymerization
11. NaH (2.5 equiv) was added in small portions, at room temperature (rt), under
argon, with stirring to a solution of 4,40-bis(hydroxymethyl)-2,20-bithiophene
(1) (1 equiv) in 50 ml of dried and degassed DMF and the mixture was allowed
to stir for 1 h at rt. Next, a solution of ditosylated oligoethyleneglycol (1 equiv)
in 20 ml of dried and degassed DMF was added dropwise. Once the addition
was complete, stirring was continued for 72 h at rt. CH2Cl2 (300 ml) was added
and the mixture was washed with H2O (4 ꢁ 150 ml), and the organic layer was
dried over MgSO4 and the solvent removed in vacuo. The pure target
macrocycles were isolated by silica gel column chromatography using EtOAc
as the mobile phase.
of compound 5; (b) 5 mM in 0.10 M Bu4NPF6 (MeCN); scan rate 100 mV sꢀ1
.
40,400-(2,5,8,11-Tetraoxadodecane-1,12-diyl)-20,200-bithiophene (5)
Yield: 32% (30 mg), white solid; mp = 155–156 °C, Rf (EtOAc) = 0.58. Calculated
for C16H20O4S2; C, 56.44; H, 5.92; S, 18.84. Found: C, 56.61; H, 6.03; S, 18.68. 1
H
NMR (500 MHz, CDCl3): d = 3.69–3.63 (m, 8H), 3.74 (s, 4H), 4.59 (s, 4H), 6.86 (d,
2H, J = 1.5 Hz), 7.61 ppm (d, 2H, J = 1.5 Hz); 13C NMR (125.7 MHz, CDCl3):
d = 65.8, 69.2, 71.2, 71.5, 118.9, 124.3, 137.6, 141.5 ppm. MS (MALDI-TOF) m/
z = 340 [M]+.
40,400-(2,5,8,11,14-Pentaoxapentadecane-1,15-diyl)-20,200-bithiophene (6)
Yield: 31% (33 mg), white solid; mp = 141–142 °C, Rf (EtOAc) = 0.41. Calculated
for C18H24O5S2; C, 56.23; H, 6.29; S, 16.68. Found: C, 56.49; H, 6.16; S, 16.48. 1
H
NMR (500 MHz, CDCl3): d = 3.71–3.59 (m, 16H), 4.53 (s, 4H), 6.96 (s, 2H),
7.37 ppm (s, 2H); 13C NMR (125.7 MHz, CDCl3): d = 68.4, 69.2, 70.5, 70.7, 70.9,
121.0, 124.1, 137.9, 140.8 ppm. MS (MALDI-TOF) m/z = 384 [M]+, 407, [M+Na]+,
423 [M+K]+.
40,400-(2,5,8,11,14,17-Hexaoxaoctadecane-1,18-diyl)-20,200-bithiophene (7)
Yield: 33% (26 mg), white solid; mp = 129–130 °C, Rf (EtOAc) = 0.30. Calculated
for C20H28O6S2; C, 56.05; H, 6.59; S, 14.96. Found: C, 56.22; H, 6.81; S, 14.82. 1
H
NMR (500 MHz, CDCl3): d = 3.54–3.60 (m, 20H), 4.52 (s, 4H), 7.25 (s, 2H), 7.34
(s, 2H); 13C NMR (75 MHz, CD3COCD3): d = 69.64, 71.21, 72.22, 72.33, 72.38,
123.29, 126.15, 139.19, 143.43, MS (EI, 70 eV) m/z (%) = 428 (43) [M]+, 234
(5.9), 221 (6.5), 207 (31.3); 192 (100), 179 (9.3), 147 (23.5), 133 (32.8) 115 (10),
103 (5.7), 96 (63.2), 89 (54.8), 73 (7.6), 59 (6.6), 45 (76.7).
Figure 4. Cyclic voltammograms of poly(5). Black line: in 0.10 Bu4NPF6 (MeCN), red
line: in 0.10 M LiClO4 (MeCN), scan rate 100 mV sꢀ1
.
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thesis of polymers poly(5) and poly(6) has been achieved. Analysis
of the electrochemical properties of the polymers in the presence
of various metal cations revealed a remarkable negative shift of
the oxidation potential of poly(5) upon complexation with Li+.
The ability of poly(5) for the complexation of Li+ and the high
selectivity of this process are attributed to a conformational
change of the bithiophene conjugated system.
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