Oligothiophenes III: Synthesis of tetra-thienyl-substituted ethylenes including an abnormal Mcmurry coupling result

Article abstract of DOI:10.1080/00397910701199037

This article describes the synthesis of some selected tetra-thiophenyl- substituted ethenes by McMurry coupling of some selected thienyl ketones, including a surprising coupling product. The products were analyzed by MS, NMR, UV, and x-ray crystallography

Full text of DOI:10.1080/00397910701199037

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Oligothiophenes III: Synthesis of
Tetra‐thienyl‐Substituted Ethylenes Including
an Abnormal McMurry Coupling Result
Harald Halvorsen a , Jan Skramstad a & Håkon Hope b
a Department of Chemistry, University of Oslo, Oslo, Norway
b Department of Chemistry, University of California, Davis, California, USA
Version of record first published: 13 Oct 2010.
To cite this article: Harald Halvorsen , Jan Skramstad & Håkon Hope (2007): Oligothiophenes III: Synthesis
of Tetra‐thienyl‐Substituted Ethylenes Including an Abnormal McMurry Coupling Result, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:7,
1179-1187
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Synthetic Communicationsw, 37: 1179–1187, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701199037
Oligothiophenes III: Synthesis of
Tetra-thienyl-Substituted Ethylenes
Including an Abnormal McMurry
Coupling Result
Harald Halvorsen and Jan Skramstad
Department of Chemistry, University of Oslo, Oslo, Norway
˚
Hakon Hope
Department of Chemistry, University of California, Davis,
California, USA
Abstract: This article describes the synthesis of some selected tetra-thiophenyl-substi-
tuted ethenes by McMurry coupling of some selected thienyl ketones, including a sur-
prising coupling product. The products were analyzed by MS, NMR, UV, and x-ray
crystallography. Their cyclic voltagrams were recorded.
Keywords: Cyclic voltametry, McMurry coupling, oligothiophenes
INTRODUCTION
In the flourishing field of organic materials with interesting electrical and
optical properties, tetra-aryl substituted methanes and silanes have recently
attracted much interest. In particular, oligothiophenyl groups play an
important part in such tetrahedral compounds.[2] We are interested in the
planar analogues to these systems, (i.e., tetra-thiophenyl substituted
ethenes). In our laboratories, we are exploring different routes to these
systems. In the present communication,[1] we report the synthesis of selected
Received in the U.K. June 12, 2006
Address correspondence to Jan Skramstad, Department of Chemistry, University of
Oslo, P. O. Box 1033 Blindern, N-0315, Oslo, Norway. E-mail: jan.skramstad@kjemi.
uio.no
1179

1180
H. Halvorsen, J. Skramstad, and H. Hope
bithiophenyl-substituted ethenes by deoxygenative coupling of properly sub-
stituted ketones by the use of low-valent titanium, a method known as the
McMurry reaction.[3,4]
RESULTS
Our main results are depicted in Scheme 1.
The ketones I and II used as starting material for the first two coupling
reactions were prepared by reacting mono-lithiated 2,20-bithiophene with
thiophene-2-carbonitrile and benzonitrile, respectively. This gave the
ketones in higher yields and with better purity than the previously used
Friedel–Crafts acylation of 2,20-bithiophene with thiophene-2-carbonyl
chloride or benzoyl chloride.[5] The synthesis of the symmetrical di-2,20-
bithiophen-5-ylmethanone III was achieved by reacting two equivalents of
mono-lithiated 2,20-bithiophene with carbamic chloride.
The McMurry coupling reactions of these ketones were performed
according to the procedure given in the literature[3,4] (see Experimental). As
can be seen from Scheme 1, the yields are excellent. The products were
characterized by MS, NMR, and x-ray crystallography. Ortep plots are
given in Fig. 1.
An interesting observation was made during the coupling of the most
sterically crowded ketone III. When III was refluxed for only 24 h (instead
of the usual 72 h), an unexpected product could be isolated in 68% yield.
This product turned out to be the single bond analogue, VII, of the desired
Scheme 1. Synthesis of three thiophene substituted ethenes by McMurry coupling.

Oligothiophenes III
1181
Figure 1. Ortep plots of the three target molecules, IV, V, and VI.
compound VI. By reaction with selenium dioxide, compound VII could be
oxidized to VI in 81% yield (Scheme 1). As none of the other two ketones
gave single bond coupling products, it is tempting to speculate that this
outcome of the McMurry reaction is steric in origin. We have not been able
to find precedent in the literature for this surprising result, which could
throw new light on the mechanism of the McMurry reaction.
In the McMurry reaction, both E and Z isomers of the products are
possible. As can be seen from the structure plots, both IV and V have the E
configuration. It is also interesting to note that when phenyl groups are
attached to the central double bond (V), the sulfur atoms of the dithiophenes

1182
H. Halvorsen, J. Skramstad, and H. Hope
point the same way. When the substituents are all thiophenes, the sulfurs point
in opposite directions.
ELECTROCHEMICAL PROPERTIES
Cyclic voltametry (CV) was used to determine the redox potential for the
target molecules. The measurements were carried out in dichloromethane/
0.1 M Bu4NþPF26 at a platinum disk electrode vs. ferrocene/ferrocenium
couple (fc). The results are given in Fig. 2.
The CV of all the compounds exhibits reversible one-electron oxidation cor-
responding to the formation of a cation radical. For the phenyl-substituted
compound V, a second oxidation was observed, corresponding to formation of
a dication. A qualitative interpretation of this is that the removal of the second
electron possibly takes place on the other side of the ethylene bridge and that
is made more difficult because of conjugation with the charge through the bridge.
Figure 2. CV scans of target compounds IV, V, and VI. CV was measured in solution
containing 0.1 M Bu4NþPF62 1.0 mM substrate (n ¼ 1.0 V/s, 08C, d ¼ 0.4-mm
platinum disk electrode).

Oligothiophenes III
1183
Table 1. Electrochemical data extracted from the cyclic voltametric measurements of
compounds IV, V, and VI
Delta
Ep1
(mV)
Delta
Ep2
(mV)
Ep(f)1 Ep(r)1 E(0)1
(V)
Ep(f2) Ep(r)2 E(0)2
(V)
Compound
(V)
(V)
(V)
(V)
IV
V
0.41
0.46
0.29
0.35
0.37
0.22
0.38
0.42
0.25
61
88
66
0.55
0.46
0.51
90
VI
Compounds IV and VI may also undergo a two-electron oxidation and
here the removal of the second electron is not more difficult than removal
of the first electron. (The authors acknowledge this interpretation from
Professor Vernon Parker, Utah State University, USA.) Another observation
is that by increasing the number of thiophene moieties in the molecule
(IV ! VI), the E(0) value decreases. The relevant data are given in Table 1.
EXPERIMENTAL
Melting points are uncorrected. The infrared spectra were recorded on a
Nicolet Magna 550 FTIR spectrometer using an attenuated total reflectance
(ATR) ZnSe plate for solid samples. High-resolution NMR spectra (1H and
13C) were recorded on Bruker Avance DPX 300 and DRX 500 spectrometers.
J values are given in Hertz. The mass spectra were obtained using a Fison
Instrument VG Prospec Q, and the ultraviolet spectra were recorded on a
Shimadzu UV-260 spectrophotometer.
2,20-Bithiophen-5-yl(thiophen-2-yl)methanone (I)
2,20-Bithiophene (5 g, 30 mmol) was dissolved in dry diethyl ether (50 ml) and
cooled to 2108C. Then 1.6 M butyl lithium (18.8 ml, 30 mmol) in hexane was
added dropwise. The reaction mixture was warmed to room temperature and
stirred for 1 h. After cooling to 210 to 2208C, thiophene-2-carbonitrile
(3.06 g, 28 mmol) in benzene (15 ml) was added. The mixture was then heated
to reflux for 15 h, whereupon it was hydrolyzed by boiling with 30% hydrochloric
acid (250 ml). Substances boiling below 1008C were then distilled off. The
resulting solution was refluxed for 1 h, rendered basic with 40% sodium
hydroxide, and extracted with methylene dichloride. The organic layer was
dried (MgSO4) and filtered, and the solvent was removed. The residue was crys-
tallized to give the title compound as a yellow solid (5.01 g, 65%), mp 1048C
(pentane) (lit. 1048C).[6] dH (300 MHz, CD2Cl2) 7.08–7.11 (m, 1H), 7.21–7.23
(m, 1H), 7.27 (d, J 3.94, 1H), 7.37–7.39 (m, 2H), 7.73–7.75 (m, 1H), 7.83
(d, J 3.95, 1H), 7.90–7.92 (m, 1H). dC (75 MHz, CD2Cl2) 124.604, 126.128,

1184
H. Halvorsen, J. Skramstad, and H. Hope
127.033, 128.427, 128.685, 133.143, 133.657, 134.442, 136.532, 141.407,
143.111, 145.771, 178.404. IR (ATR, cm21) 3102 (s), 1587 (m).
2,20-Bithiophen-5-yl(phenyl)methanone (II)
2,20-Bithiophene (5 g, 30 mmol) was dissolved in dry diethyl ether (50 ml) and
cooled to 2108C. Then 1.6 M butyl lithium (18.8 ml, 30 mmol) in hexane was
added dropwise. The reaction was warmed to room temperature and stirred for
1 h. After adjusting the temperature to 210 to 208C, benzonitrile (2.9 g,
28 mmol) in benzene (15 ml) was added. The mixture was refluxed for 15 h
and then hydrolyzed by boiling with 30% hydrochloric acid (250 ml),
whereupon substances boiling below 1008C were removed by distillation. The
resulting solution was refluxed for 1 h, rendered basic with 40% NaOH, and
then extracted with CH2Cl2. The organic layer was dried (MgSO4) and filtered
and the solvent was removed. The residue was crystallized to give a yellow
solid (4.8 g, 63%), mp 74–768C (pentane) (lit. 74–768C).[7] dH (300 MHz,
CD2Cl2) 7.14 (dd, J1 1.43, J2 3.6, 1H), 7.36 (d, J 4.0, 1H), 7.51 (dd, J1 1.86,
J2 4.0, 1H), 7.55–7.65 (m, 5H), 7.87 (dd, J1 1.67, J2 7.96, 2H). dC (75 MHz,
CD2Cl2) 124.58, 125.33, 126.89, 127.98, 128.81, 129.38, 129.64, 133.05,
136.84, 138.79, 142.44, 146.43, 187.68. IR (ATR, cm21) 3069 (m), 1623 (m).
Di-2,20-bithiophen-5-ylmethanone (III)
2,20-Bithiophene (5 g, 30 mmol) was dissolved in THF (50 ml) and cooled to
2788 Butyl lithium (1.6 M, 18.8 ml, 30 mmol) in hexane was added dropwise.
After 30 min, carbamic chloride (1.2 g, 15 mmol) was added. The reaction
mixture was warmed to room temperature and stirred overnight. The reaction
was then quenched with water. The phases were separated, and the organic
phase was dried (MgSO4) and filtered. The solvent was evaporated, affording a
crude reaction product, which was dissolved in ether. The title compound crystal-
lized to give a yellow solid (3.77 g, 70%), mp 154–1558C (diethyl ether). dH
(300 MHz, CD2Cl2) 7.82 (d, J 4.04, 2H), 7.38–7.39 (m, 4H), 7.28 (d, J 4.04,
2H), 7.09–7.12 (dd, J1 3.74, J2 1.29). dC (75 MHz, CD2Cl2) 177.829,
145.660, 141.263, 136.563, 134.117, 128.708, 127.050, 126.146, 124.634. IR
(ATR, cm21) 3083 (b w), 1571 (s), 1442 (s). M/z: 358 (100), 330 (7.5), 193
(40). High-resolution MS: 357.961369; calculated for C17H10OS4: 357.961452.
(E)-1,2-Di(2,20-bithiophen-5-yl)-1,2-di(thiophen-2-yl)ethene (IV)
THF (50 ml) was cooled to 08C under argon atmosphere. TiCl4 (1.0 M,
8.0 ml, 8 mmol) in dichloromethane was added dropwise, and then zinc
(1.1 g, 16.8 mmol) was added. The reaction mixture was warmed to room

Oligothiophenes III
1185
temperature with stirring. After 6 h, the mixture was cooled to 08C and pyridine
(2.5 ml) and I (1.55 g, 5.6 mmol) in THF (30 ml) were added. The reaction
mixture was allowed to reach room temperature. Finally, the reaction mixture
was refluxed for 72 h. After cooling, CH2Cl2 (250 ml) was added, and the
mixture was washed with 0.1 M HCl. The organic layer was dried (MgSO4)
and filtered, and the solvent was evaporated, affording the crude reaction
product, which was chromatographed on silica gel with chloroform–hexane
(10:1). The product was crystallized to give a yellow solid (1.37 g, 95%), mp
207–2088C (toluene). dH (300 MHz, CD2Cl2) 6.67 (d, J 3.99, 2H), 6.95–7.00
(m, 4H), 7.05–7.08 (m, 6H), 7.22 (dd, J1 1.11, J2 5.13, 2H), 7.46 (dd, J1 1.96,
J2 4.42, 2H). dC (75 MHz, CD2Cl2) 125.057, 125.073, 127.796, 127.805,
128.165, 128.253, 128.274, 128.352, 130.582, 130.690, 131.357, 143.200,
143.427. M/z: 520 (100), 260 (10). High-resolution MS: 519.956961; calculated
for C26H16S6: 519.957631. UV (CCl4), log e (lmax): 4.34 (230), 4.38 (330), 4.41
(424). Crystal data for C26H16S6: Monoclinic, space group P21/a; a ¼ 12.302(3)
˚
˚
˚
A, b ¼ 7.2878(15) A, c ¼ 14.012(4) A, b ¼ 115.26(2)8, V ¼ 1136.1(5)
3
˚
˚
A , T ¼ 120(1) K, l(Cu Ka) ¼ 1.54178 A, Z ¼ 2. Yellow prism,
0.26 ꢀ 0.16 ꢀ 0.13 mm. Data were collected with Siemens P4 diffractometer.
Ni-filtered Cu(Ka) radiation from a rotating anode. Empirical absorption correc-
tion was done with Xabs2.[8] Solution was created with SHELXS96[9] and
Fourier techinques. Full-matrix refinement with SHELX197[10] gave R ¼ 0.0582
for 1331 reflections with Io . 2s(Io), of 1502 independent.
(E)-1,2-Di(2,20-bithiophen-5-yl)-1,2-diphenylethene (V)
From II (1.55 g, 5.6 mmol) in THF (30 ml), following the procedure given pre-
viously for the synthesis of IV, the title compound was prepared as a yellow solid
(1.32 g, 93%), mp 193–1948C (toluene). dH (300 MHz, CD2Cl2) 7.44–7.47
(m, 10H), 7.15–7.17 (m, 2H), 6.80–6.94 (m, 4H), 6.80 (d, J 3.91, 2H), 6.25
(d, J 3.91, 2H). dC (75 MHz, CD2Cl2) 145.257, 142.004, 138.613, 137.574,
133.423, 131.373, 131.052, 129.448, 128.717, 128.160, 124.789, 123.737,
122.969. M/z: 508 (100), 254 (10). High-resolution MS: 508.042788; calculated
for C30H20S4: 508.044788. UV (CCl4), log e (lmax): 4.35 (229), 4.35 (332), 4.39
(406). Crystal data for C30H20S4: Monoclinic, space group P21/a; a ¼ 7.604(2)
˚
˚
˚
A, b ¼ 11.103 (3) A, c ¼ 13.952(3) A, b ¼ 95.25(2)8. V ¼ 1173.10(5)
3
˚
˚
A , T ¼ 90(1) K, l(Mo Ka) ¼ 0.71073 A, Z ¼ 2. Yellow needle,
0.37 ꢀ 0.16 ꢀ 0.12 mm. Data collected with Siemens (Bruker) SMART
CCD diffractometer. Solution and refinement were done as for (IV) which
gave R ¼ 0.041 for 2826 reflections with Io . 2s(Io), of 3645 independent.
1,1,2,2-Tetra(2,20-bithiophen-5-yl)ethene (VI)
From III (2.0 g, 5.6 mmol) in THF (30 ml), following the procedure given
previously for the synthesis of IV and V, the title compound was prepared

1186
H. Halvorsen, J. Skramstad, and H. Hope
as a yellow solid (1.61 g, 84%), mp 194–1958C (toluene). dH (300 MHz,
CD2Cl2) 6.92 (d, J 3.90, 4H), 6.98–7.01 (dd, J1 1.09, J2 5.17, 4H),
7.07(d, J 3.90, 4H), 7.14–7.15 (dd, J1 1.09, J2 3.64, 4H), 7.23–7.24 (dd,
J1 1.09, J2 5.17, 4H). dC (75 MHz, CD2Cl2) 123.76, 124.30, 125.15,
127.39, 128.30, 131.68, 137.46, 139.96, 143.17. m/z: 684 (34), 344 (100),
121 (80). High-resolution MS: 683.929774; calculated for C34H20S8:
683.929774. UV (CCl4), log e (lmax): 4.65 (319), 4.63 (345), 4.35 (440).
Crystal data for C34H20S8: Monoclinic, space group P21/n;
˚
˚
˚
a ¼ 16.0424(10) A, b ¼ 5.5536(3) A, c ¼ 17.4351(11) A, b ¼ 105.960(2)8.
3
˚
˚
V ¼ 1493.47(16) A , T ¼ 90(1) K, l(Mo Ka) ¼ 0.71073 A, Z ¼ 2. Yellow
needle, 0.39 ꢀ 0.07 ꢀ 0.04 mm. Data collection, structure solution, and
refinement were done as for (V). Terminal thiophene rings are disordered.
The thiophene rings were restrained to have the same geometry.
R ¼ 0.0435 for 2540 reflections with Io . 2s (Io), of 4794 independent. In
all structures, the terminal thiophene rings are disordered. The majority con-
formations range from 59% to 93%.The thiophene rings were restrained to
have the same geometry.
1,1,2,2-Tetra(2,20-bithiophen-5-yl)ethane (VII)
THF (50 ml) was cooled to 08C under an argon atmosphere. Then, 8.0 ml of 1.0 M
TiCl4 (0.008 mol) in dichloromethane were added dropwise before zinc (1.1 g,
0.0168 mol) was added, and the reaction mixture was warmed to room temp-
erature. After 1 h, the mixture was heated for 5 h before it was cooled to
08C. Pyridine (2.5 ml) was added. Di(2,20-bithienyl) ketone (2.0 g,
5.6 mmol) in 30 ml THF was added, and the reaction mixture was warmed
to room temperature and then heated to reflux for 24 h. After cooling, the
mixture was added to CH2Cl2 (250 ml) and washed with 0.1 M HCl. The
organic layer was then dried (MgSO4). After filtration and evaporation of the
solvent, the crude reaction product was chromatographed on silica gel with
chloroform–hexane (1:1). Yield 1.3 g (68%) of a yellow solid melting at
168–1698C. dH (300 MHz, CD2Cl2) 5.11 (2H, S), 6.82 (4H, d, J 3.7), 6.94
(4H, d, J 3.7), 6.97–7.00 (4H, dd J 3.6 and 5.2), 7.10–7.12 (4H, dd, J 1.1,
and 3.6), 7.19–7.21 (4H, dd, J 1.1, and 5.2). dC (75 MHz, CD2Cl2) 50.208,
123.461, 123.939, 124.730, 126.972, 128.147, 136.955, 137.533, 144.810.
This compound could be converted to 1,1,2,2-tetra(2,20-bithiophen-5-
yl)ethene (VI) by the following procedure:
1,1,2,2-Tetra(2,20-bithienyl)ethane (VII) (1.3 g, 1.89 mmol) was mixed
with 0.21 g (1.89 mmol) of SeO2 and 40 ml of xylene and heated to reflux.
After 16 h of reflux, the reaction mixture was filtered through cellulose.
After evaporation of the solvent, the crude reaction product was chromato-
graphed on silica gel with chloroform–hexane (10:1). Yield was 1.0 g
(81%) of a yellow solid melting at 194–1958C, and spectroscopic data
(NMR and MS) are in accordance with those given above for compound VI.

Oligothiophenes III
1187
REFERENCES
1. Halvorsen, H.; Hope, H.; Skramstad, J. J. Synth. Comm. 2007, 1–11.
2. Brasselet, S.; Cherioux, F.; Audebert, P.; Zyss, J. Chem. Mater. 1999, 11,
1915–1920.
3. McMurry, J. E. Chem. Rev. 1989, 89 (7), 1513–1524.
4. Fu¨rstner, A.; Bogdanovic, B. Angew. Chem., Int. Ed. Engl. 1996, 35, 2442.
5. Hegedu, L. S. In Comprehensive Organometallic Chemistry II; Abel, E. W.,
Stone, F. G. A., and Wilkinson, G., (eds); Oxford: Pergamon, 1995; Vol. 12,
and references cited therein.
6. Lescot, E., Jr.; Buu-Hoi, N. P.; Xuong, N. D. J. Chem. Soc. 1959, 3234–3237.
7. Krishnaswamy, N. R.; Kumar, C. S. S. R. Indian J. Chem.; Sect. B 1993, 32B (7),
766–71.
8. Parkin, S.; Moezzi, B.; Hope, H. J. Appl. Cryst. 1995, 28, 53–56.
9. Sheldrick, G. M. Acta Cryst. 1990, A46, 467–473.
¨
10. Sheldrick, G. M. SHELXL97; University of Gottingen: Germany, 1997.