Synthesis of substituted oligothiophenes and X-ray crystal structures of 3′-methyl-2,2′:5′,2″-terthiophene, 3,3″-dimethyl-2,2′:5′,2″-terthiophene and 5′-(2-thienyl)-2,2′:3′,2″-terthiophene

Article abstract of DOI:10.1039/a607254b

A range of substituted oligothiophenes has been prepared and characterised. Crystal structures were determined for three substituted terthiophenes. Both in solution and in the solid state, syn-conformers were found to be populated to a greater extent than expected.

Full text of DOI:10.1039/a607254b

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Synthesis of substituted oligothiophenes and X-ray crystal structures
of 3Ј-methyl-2,2Ј:5Ј,2Љ-terthiophene, 3,3Љ-dimethyl-2,2Ј:5Ј,2Љ-
terthiophene and 5Ј-(2-thienyl)-2,2Ј:3Ј,2Љ-terthiophene
Penny A. Chaloner,* Sumudu R. Gunatunga and Peter B. Hitchcock
School of Chemistry, Physics and Environmental Science, University of Sussex, Falmer,
Brighton, UK BN1 9QJ
A range of substituted oligothiophenes has been prepared and characterised. Crystal structures were
determined for three substituted terthiophenes. Both in solution and in the solid state, syn-conformers were
found to be populated to a greater extent than expected.
molecules adopting the anti-conformation. However, crystal
Introduction
structures tell us only a limited amount about solution con-
formation; for this solution NMR spectroscopy and UV
absorption data are more useful.
There is considerable interest in polythiophenes and oligothio-
phenes because they are conducting when doped, and may be
used for third harmonic generation.1 The structures of a range
of substituted and unsubstituted oligothiophenes including
bithiophene,2,3 substituted bithiophenes,4–8 terthiophene,9 sub-
stituted terthiophenes,10 tetrathiophenes11,12 and sexithio-
phenes13 have recently been established in diffraction studies.
We now report the synthesis and characterisation of some
bi- and ter-thiophenes with site-specific substitution of alkyl
groups.
1
The H NMR spectrum of 3,3Ј-dimethyl-2,2Ј-bithiophene 6
shows a singlet for the methyl groups and doublets (J 4.9 Hz)
for 4,4Ј-H (δ 7.01) and 5,5Ј-H (δ 7.33). The aromatic protons
were unambiguously assigned on the basis of an observation
of a 2.8% nuclear Overhauser enhancement (NOE) from the
methyl group to 4-H. Most of the 13C NMR resonances were
assigned from the proton coupled 13C NMR spectrum, with the
quaternary carbon atoms assigned by comparison with related
data from Barbarella and co-workers.17
Results and discussion
Terthiophenes
The 1H and 13C NMR spectra of terthiophene have been previ-
ously assigned,18 and provide a starting point for the assign-
ment of the spectra of substituted compounds. The structure of
terthiophene has been determined, with coplanar, anti, rings,
Synthesis of oligothiophenes
The compounds 1–11 were prepared by adaptations of known
methods (Scheme 1) for bromination and Grignard coupling
reactions. Bäuerle’s14 method for bromination of 3-hexyl-
thiophene was the most successful in our hands; use of other
solvents resulted in the isolation of considerable amounts
of side-chain brominated material. In the preparation of 3-
hexylthiophene, varying amounts of dodecane, produced by
homocoupling of the Grignard reagent, were detected by GLC
in the crude material. The amount of dodecane could be
reduced by using an excess of magnesium, and increasing the
time for Grignard formation. The products of homocoupling
of thienyl Grignard reagents were also detected in the prepar-
ations of 7, 8 and 9.
1
as in 13.9 The H NMR spectrum of 3,3Љ-dimethyl-2,2Ј:5Ј,2Љ-
terthiophene 7 was assigned by a combination of decoupling
and NOE experiments. In particular there was a 5.3% NOE
between the methyl groups and the 4,4Љ-hydrogens. More
surprisingly there was a 2.7% NOE from the CH3 to the 3Ј-
and 4Ј-hydrogens. This suggests that the molecule does not
exclusively adopt the all-anti-conformation 7a, but that 7b
and/or 7c are also significantly populated. Space filling models
suggest that 7b and 7c are significantly more hindered. The 13
C
NMR spectrum was assigned by two-dimensional one-bond
and long range C᎐H shift correlations.
Bithiophenes—NMR spectra and conformations;
models for higher oligomers
The 1H NMR spectrum of 3Ј-methyl-2,2Ј:5Ј,2Љ-terthiophene
8 is more complex, due to the lower symmetry. Selective decoup-
ling experiments allowed the grouping of the signals due to 3-
H, 4-H and 5-H, and 3Љ-H, 4Љ-H and 5Љ-H, but did not allow us
to assign the groups to the appropriate ring. NOEs were again
helpful, when all possible conformations were considered (8a–
8d). There is a 4.8% NOE between the methyl group and 4Ј-H,
as expected, but also a 1.5% NOE to 3Љ-H. This latter is only
possible if conformations 8b or 8d are populated. There was
also a 1.4% NOE between 4Ј-H and 3-H, possible only in 8c or
8d. Again it is clear that syn-conformations must be populated
in solution. The 13C NMR spectrum was assigned using short
and long range two-dimensional C᎐H correlations.
X-Ray diffraction data for oligothiophenes have been sparse
until recently, since the compounds do not crystallise well, tend
to decompose in the X-ray beam, and structures are frequently
disordered. The structure of 2,2Ј-bithiophene was initially
determined in the 1960s by Visser,15 but was of poor quality.
We 2 and Pelletier 3 have recently redetermined the structure, at
low temperature. Contrary to conventional wisdom, the struc-
ture does not consist exclusively of molecules in the anti-
conformation 12a, but contains 15% of the syn-conformation
12b. Disorder in solid-state structures of compounds contain-
ing a thiophene ring is relatively common.16 Substitution in
oligothiophenes may cause deviations from coplanarity,
unusual proportions of unexpected conformers, and changes in
bond lengths. For example, in 5,5Ј-dibromo-2,2Ј-bithiophene,
bond lengths and angles are slightly altered as a result of the
electronic effect of the bromine.5 In 2,2Ј-bithiophene-5-
carbaldehyde,8 the main conformation is syn with only 20% of
Similar analyses were applied to the 1H and 13C spectra of 3Ј-
hexyl-2,2Ј:5Ј,2Љ-terthiophene 9. In this instance the NOE from
the α-CH2 of the hexyl side chain was 5.6% to 4Ј-H and 2.6% to
3Љ-H. 4Ј-H showed an NOE of 2.7% to 3-H.
A polymer was prepared from 9 by ferric chloride oxidation.
After dedoping the material produced was found to be partially
J. Chem. Soc., Perkin Trans. 2, 1997
1597

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Hexyl
Br
H3′
H4′
[NiCl2(dppp)]
70%
+ HexylMgBr
S
S
S
1
S
S
S
S
S
S
H3′
H4′
7a
7b
NBS (1 mol), CCl4, ∆
63%
Br
H3′
H4′
S
2
S
S
S
NBS (2 mol), CCl4, ∆
7c
65%
Br
Br
S
H3′′
H4′
3
H4′
Hexyl
Br
S
S
S
NBS (1 mol), dark, –20 °C, DMF
52%
1
S
S
S
S
8a all anti
8b anti-syn
4
Hexyl
NBS (2 mol), dark, –20 °C, DMF
70%
H3′′
H3
H3
H4′
H4′
Br
Br
S
S
5
S
S
S
S
8c syn-anti
8d all syn
[NiCl2(dppp)]
2 +
61%
MgBr
hexylthiophene) in both doped and undoped states. It is of
interest that the oligomeric material is conducting in its doped
state, since sexithiophenes have been the subject of much atten-
tion as models for polythiophene.19,20 The chloroform-insoluble
fraction was black in both the doped and undoped states, but
the soluble fraction underwent a shift in its UV absorption from
454 nm in the undoped state (greenish yellow) to 508 nm in the
doped state (blue-black). It was predictable that the polymer
derived from hexylterthiophene would be less soluble than that
from 3-hexylthiophene, since it is the alkyl groups that confer
solubility. Equally its higher conductivity was to be expected,
since there are fewer side chains to impede planarity.
S
S
S
6
[NiCl2(dppp)]
+ 2
Br
15%
Br
Br
MgBr
MgBr
S
S
S
S
S
S
S
7
R
R
[NiCl2(dppp)]
+ 2
Br
S
S
S
R = Methyl, 3
R = Hexyl, 5
R = Methyl, 8, 48%
R = Hexyl, 9, 40%
By-products of the synthesis of 3Ј-hexyl-2,2Ј:5Ј,2Љ-terthiophene 9
The synthesis of 9 involved the coupling of 2-bromo-
magnesiothiophene with 2,5-dibromo-3-hexylthiophene 5. The
crude material obtained was shown by TLC to contain 2-
bromothiophene, 2,5-dibromo-3-hexylthiophene and bithio-
phene (formed by Grignard homocoupling) as well as three
other components with rather similar Rf values. The starting
materials and bithiophene were readily removed by chroma-
tography, but the other materials were only fully separated by
chromatography on three successive columns. The first com-
pound isolated was 9 and the others were identified by 1H NMR
spectroscopy as 2,2Ј:3Ј,2Љ-terthiophene 14, and 5Ј-(2-thienyl)-
2,2Ј:3Ј,2Љ-terthiophene 15. The formation of 14 and 15 was
(+ by-products)
NBS, DMF, dark, –20 °C
80%
Br
Br
S
S
S
S
10
[NiCl2(dppp)]
10 + 2
MgBr
56%
S
S
S
S
S
11
Scheme 1 Synthesis of substituted oligothiophenes
S
S
S
S
S
S
12a
12b
S
S
S
S
S
S
S
14
S
15
S
Br
13
soluble in chloroform suggesting that there was an oligomeric
and a polymeric fraction. The most abundant component of
the chloroform-soluble material was shown by mass spec-
trometry and 1H NMR spectroscopy to be a dihexylsexi-
thiophene, although neither spectrum could be fully analysed.
Conductivity measurements (4-probe technique on pressed
pellets) are given in Table 1 for both fractions, and for poly(3-
Br
S
16
surprising. Compound 15 was isolated in reasonable quantity
and fully characterised by X-ray diffraction (vide infra). Only a
small amount of 14 was obtained, and this was characterised by
1598
J. Chem. Soc., Perkin Trans. 2, 1997

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Table 1 Conductivity measurements on doped and undoped fractions
from 3Ј-hexyl-2,2Ј:5Ј,2Љ-terthiophene polymerisation, and on poly(3-
hexythiophene) at 25 ЊC
Table 2 Selected bond lengths and angles for 3,3Љ-dimethyl-2,2Ј;5Ј2Љ-
terthiophene 7
Bond lengths, d/Å
Bond angles, θ/Њ
Conductivity/S cmϪ1a
S(3)᎐C(9)
1.768(3)
1.707(4)
1.345(4)
1.355(4)
1.905(6)
1.70(3)
C(3)᎐C(4)᎐C(5)
C(4)᎐C(5)᎐C(6)
S(2)᎐C(8)᎐C(9)
C(8)᎐C(9)᎐C(10)
C(9)᎐C(10)᎐C(11)
C(11)᎐C(12)᎐S(3)
C(9)᎐C(10a)᎐C(11a)
C(11a)᎐C(12a)᎐S(3a)
128.3(2)
128.2(2)
123.5(2)
134.5(2)
113.5(2)
111.0(3)
116(1)
Material
Undoped
Doped (I2)
S(3)᎐C(12)
C(9)᎐C(10)
C(11)᎐C(12)
S(3a)᎐C(9)
S(3a)᎐C(12a)
C(9)᎐C(10a)
C(11a)᎐C(12a)
Chloroform-soluble fraction
Chloroform-insoluble fraction
Poly(3-hexylthiophene)
0
43.5
446.0
239.0
0.0027
0
1.18(2)
1.33(2)
a
Data given are an average of measurements on five separate pellets.
115(1)
4′′
3′′
5′′
S
3′′
S
3
4
4
3
4′′′
5′′′
3′′′
3′′′ 4′
4′
4′′′
5
5′′′
5
S
S
S
S
S
S
15a
15b
Fig. 1 Conformations of 5Ј-(2-thienyl)-2,2Ј:3Ј,2Љ-terthiophene 15
1H NMR spectroscopy and mass spectrometry. Control
experiments with 2-bromomagnesiothiophene and [NiCl2-
(dppp)] (dppp = 1,3-bisdiphenylphosphinopropane) or bithio-
phene and 2-bromomagnesiothiophene did not yield 14 or 15.
Branched ter- and quater-thiophenes have been previously
prepared by Perrine21 and Kankare22 from diketones. However,
we found it more convenient to prepare an authentic sample of
15 for comparison by reaction of three molar equivalents of 2-
bromomagnesiothiophene with 2,3,5-tribromothiophene in the
presence of [NiCl2(dppp)]. Compound 15 was obtained in 80%
yield after recrystallisation.
Fig. 2 Structure of 3,3Љ-dimethyl-2,2Ј:5Ј,2Љ-terthiophene 7. ORTEP
diagram, 50% thermal ellipsoids, H atoms as spheres of arbitrary size.
1
Most of the H NMR spectrum could be assigned by com-
parison with lower congeners. The assignments were confirmed
by the observation of a 4.5% NOE between the methyl groups
and H-4 and H-4ٞ, and of 1.7% between the methyl groups and
H-3Ј and H-4Љ (as before this latter implies population of cisoid
conformers). The 13C spectrum was assigned by long and short
range C᎐H correlation experiments.
1
Assignment of the H and 13C NMR spectra of 15 required
selective decoupling, NOE and short- and long-range C᎐H cor-
relation experiments. A key argument, which also gave inform-
ation about the conformation of 15 in solution, involves the
NOEs from the protons at the 3, 3Љ and 3ٞ sites (Fig. 1). From
coupling constant data it was known that the signals at δ 7.101,
7.152 and 7.223 must be assigned to H-3, H-3Љ and H-3ٞ, but
not which was which. Irradiation of H-4Ј showed partial satur-
ation of the signal at δ 7.223 and 2.3% NOE to the signal at
δ 7.101. This means that the signal at δ 7.101 must be H-3Љ or
H-3ٞ; H-3 could not show an NOE to H-4Ј. This allows us to
assign the signal at δ 7.152 to H-3. Irradiation of the signal at
δ 7.101 gave a 4.2% NOE to H-4Ј, and 3.1 and 4.9% NOEs to
the signals at δ 7.152 and δ 7.223. This allows its unequivocal
identification as H-3Љ; by rotating ring D, this proton may
be in proximity to either H-3 or H-3ٞ (Fig. 1). Thus the NOE
measurements were useful in assigning the spectra, and also
showed that some cisoid conformations must be populated.
The mechanism of formation of 14 and 15 in the synthesis of
9 remains obscure. The cleavage of the hexyl group may involve
a radical–photochemical process, or may involve MgBr2 acting
as a source of bromine for ipso-substitution of the hexyl group
by bromine. If we can postulate the formation of 16, then 15
could be produced by two further couplings, and 14 by a coup-
ling, Grignard exchange and protonation on work-up. How-
ever, since oligomers of these branched materials are likely to be
too twisted to be valuable as conductors, we did not pursue the
matter further.
Crystals which appeared to be satisfactory for an X-ray struc-
ture determination were grown from hexane, and a low quality
structure was obtained.23 However, the structure is made up of
two independent molecules that are almost related by a non-
crystallographic translation of 0.5 ϩ x, 0.5 ϩ y, z. The two
terminal rings were closely related in this way, but the inner
rings had different orientations in the two molecules. Because
of the high correlation, the two molecules were refined in alter-
nating cycles of least squares. Three of the carbon atoms
became non-positive definite, and were reset isotropic. The final
difference map showed residual density at sites corresponding
to pseudo-symmetry-related sulfur atoms, and a satisfactory R
value could not be obtained.
Structure of 3,3Љ-dimethyl-2,2Ј:5Ј,2Љ-terthiophene 7
Good quality crystals were grown by the slow evaporation of a
hexane solution of 7 at room temperature. The structure is
shown in Fig. 2, and selected bond lengths and angles in Table
2. The structure contains a single unique molecule which is
disordered in the ring containing S(3). The prevailing conform-
ation (85%) is 7b with 15% of 7a. The C᎐S bonds are elongated
[1.747(4)–1.768(3) Å] compared with 8 (vide infra) or 3,4Ј,4Љ-
trimethyl-2,2Ј:5Ј;2Љ-terthiophene [1.708(6)–1.744(5) Å],10 but
whether this reflects crowding or disorder is difficult to discern.
Structure of 3Ј-methyl-2,2Ј:5Ј,2Љ-terthiophene 8
The structure of 8 was determined in an X-ray diffraction
study, good quality crystals having been obtained by slow sub-
limation at atmospheric pressure. Selected bond lengths and
angles are given in Table 3. For 8 the diffraction was rather
weak (only 1755 significant reflections out of 5105 measured)
and did not justify anisotropic refinement of the carbon atoms.
Fig. 3 shows the three crystallographically distinct molecules in
each unit cell. Two of these (A and B) had the expected geo-
metry with transoid ring junctions, and were close to planar
Tetrathiophenes
Bromination of bithiophene gave 5,5Ј-dibromo-2,2Ј-bithio-
phene 10 in 80% yield.14 This was coupled with two molar
equivalents of 2-bromomagnesio-3-methylthiophene to give
3,3ٞ-dimethyl-2,2Ј:5Ј,2Љ:5Љ,2ٞ-quaterthiophene
11.
The
material initially obtained was rather dark in colour, but could
be readily decolourised over charcoal, to give, after recrystal-
lisation, a yellow flaky solid.
J. Chem. Soc., Perkin Trans. 2, 1997
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Table 3 Selected bond lengths and angles for 3Ј-methyl-2,2Ј:5Ј,2Љ-terthiophene 8
Bond lengths, d/Å Bond angles, θ/Њ
Molecule
Molecule
A
A
B
C
B
C
S(1)᎐C(1)
S(1)᎐C(4)
S(2)᎐C(5)
S(2)᎐C(8)
S(3)᎐C(9)
S(3)᎐C(12)
C(2)᎐C(3)
C(3)᎐C(4)
1.70(2)
1.71(2)
1.61(2)
1.67(2)
1.748(15)
1.717(13)
1.662(14)
1.66(2)
S(1)᎐C(1)᎐C(2)
C(1)᎐C(2)᎐C(3)
S(1)᎐C(2)᎐C(3)
S(3)᎐C(9)᎐C(10)
S(3)᎐C(12)᎐C(11)
C(2)᎐C(3)᎐C(4)
C(3)᎐C(4)᎐C(5)
S(2)᎐C(5)᎐C(4)
113(1)
111(1)
108(1)
111(1)
113(1)
115(1)
127(1)
118(1)
112(1)
115(1)
110(1)
109(1)
114(1)
110(1)
128(1)
116.9(9)
118(1)
118(1)
1.730(5)
1.732(14)
1.739(14)
1.721(14)
1.665(15)
1.41(2)
1.750(14)
1.732(13)
1.714(14)
1.756(14)
1.689(14)
1.44(2)
114.4(8)
110(1)
110(1)
95.8(8)
121(1)
120(1)
1.57(2)
1.64(2)
1.38(2)
1.41(2)
Table 4 Selected bond lengths and angles for 5Ј-(2-thienyl)-2,2Ј:3Ј,2Љ-
terthiophene 15
Bond lengths, d/Å
Bond angles, θ/Њ
S(3)᎐C(1)
S(3)᎐C(4)
C(1)᎐C(2)
C(3)᎐C(4)
C(4)᎐C(5)
S(2)᎐C(8)
S(2)᎐C(11)
C(8)᎐C(9)
C(10)᎐C(11)
C(5)᎐C(12)
C(6)᎐C(7)
1.65(2)
1.656(14)
1.33(2)
1.58(2)
1.50(2)
1.72(2)
1.62(2)
1.59(2)
1.31(2)
1.32(2)
1.42(2)
C(1)᎐S(3)᎐C(4)
S(3)᎐C(4)᎐C(3)
C(1)᎐C(2)᎐C(3)
C(2)᎐C(3)᎐C(4)
C(4)᎐C(5)᎐C(12)
C(8)᎐S(2)᎐C(11)
S(2)᎐C(8)᎐C(9)
C(8)᎐C(9)᎐C(10)
C(9)᎐C(10)᎐C(11)
C(6)᎐C(5)᎐C(12)
S(1)᎐C(7)᎐C(6)
95.6(8)
113.2(9)
121(2)
99.0(9)
125(1)
92.4(8)
115.6(9)
96.7(9)
117(1)
118(1)
115(1)
Fig. 4 Structure of 5Ј-(2-thienyl)-2,2Ј:3Ј,2Љ-terthiophene, 15. The
ORTEP diagram shows the non-H atom as 50% thermal ellipsoids.
ent in the solid state. The bond lengths and angles of the trisub-
stituted ring of 15 compare closely with those in other ter-
thiophenes. However, in this case no ring is coplanar with
any other (interplanar angles range from 29 to 88Њ as was noted
with the 3Ј-aryl and heteroaryl substituted terthiophenes
reported by Kankare22). Again, apparent peculiarities in bond
lengths and angles are artefacts of the disorder.
Fig. 3 The three crystallographically distinct molecules in the struc-
ture of 3Ј-methyl-2,2Ј:5Ј,2Љ-terthiophene 8
with only minor bowing. However, in the third molecule, there
is disorder between two orientations related by a 180Њ rotation
about one ring–ring bond, corresponding to conformations 8a
and 8b. The two sites have equal occupancy and were given an
average scattering factor. It is somewhat surprising that the dis-
order occurs at what seems to be the less likely site, in which one
would expect the greatest hindrance between the methyl group
and the adjacent C᎐H. Apparent changes in bond lengths and
angles in the outer rings are artefacts created by the averaging
over the disorder.
UV–VIS spectra
The UV absorption spectra of oligothiophenes24–26 are gener-
ally assigned in terms of the strong absorption band at longer
wavelength being associated with the π → π* electron trans-
fer of the entire chromophore, and the less intense band with
the π → π* local excitation of the hetero-nucleus.27 Our data
are given in Table 5, in comparison with the earlier work of van
Pham.28 It is clear that substitution results in a blue shift of the
stronger band, relative to the unsubstituted system. This is to be
expected, since substitution is likely to result in the greater
population of more twisted, and hence less conjugated con-
formers. One curious effect is that λmax was concentration
dependent, particularly for 6 and 7. For example, for 6, λmax was
218.5 and 255.5 nm at 0.003  concentration, but 219.5 and
252.0 nm at 0.0003 . This concentration dependence may
account for the differences between our data and those reported
Structure of 5Ј-(2-thienyl)-2,2Ј:3Ј,2Љ-terthiophene 15
Good quality crystals of 15 were obtained by slow evaporation
of an ethanol solution. The structure is shown in Fig. 4 and
selected bond lengths and angles are given in Table 4. The mole-
cule is disordered in two of the rings. The ring containing S(2) is
disordered 60:40 between the sites labelled S(2) and C(9), and
the ring containing S(3) is disordered 72:28 between the sites
S(3) and C(3). Thus a range of conformational isomers is pres-
1600
J. Chem. Soc., Perkin Trans. 2, 1997

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Table 5 UV–VIS data for oligothiophenes in CHCl3
λmax/nm (ε)
solvent removed under reduced pressure. Fractional distillation
gave 3-hexylthiophene (17.6 g, 70%), bp 60–61 ЊC, 0.77 mmHg
(lit.30 62–63 ЊC, 0.7 mmHg). δH (360 MHz, CDCl3) 1.13 (3H, t,
J 6.9, CH3), 1.56 (6H, m, 3 × CH2), 1.84 (2H, m, CH2), 2.84
(2H, t, J 7.4, ArCH2) 7.0 (1H, m, 2-H), 7.13 (1H, dd, J 1.2, 4.9,
5-H), 7.39 (1H, dd, J 2.9, 5.1, 4-H); δC(62.5 MHz, CDCl3) 13.92
(CH3), 22.62 (CH2CH3), 29.32 (ArCH2CH2CH2), 29.67
(ArCH2), 30.47 (ArCH2CH2), 31.4 (CH2CH2CH3), 119.73 (5-
C), 124.95 (2-C), 128.17 (4-C), 143.11 (3-C).
Compound
(local excitation)
λmax/nm (ε)
12
6
243a
219.5
302a
252 (8440)
270a (7460)
355a
343 (17 760)
344a (17 340)
352 (13 550)
336a (15 980)
348 (16 100)
352 (47 400)
13
7
245a
252
276.5 (sh)
253 (6390)
8
Synthesis of 2-bromo-3-methylthiophene 2
A mixture of 3-methylthiophene (5 g, 0.05 mol) and NBS (9.08
g, 0.05 mol) in tetrachloromethane (150 cm3) was heated under
reflux for 5 h. The reaction mixture was cooled and filtered and
the solvent removed under reduced pressure. Distillation gave 2
as a colourless liquid (5.62 g, 63%), bp 14–16 ЊC, 0.3 mmHg,
(lit.31 27 ЊC, 1.8 mmHg). δH (360 MHz, CDCl3) 2.24 (3H, s,
CH3), 6.81 (1 H, d, J 5.5, 4-H), 7.19 (1H, d, J 5.5, 5-H); δC(62.5
MHz, CDCl3) 15.0 (CH3) 109.2 (2-C), 124.9 (5-C), 129.1 (4-C),
137.0 (3-C).
9
15
244 (11 400)
245 (49 000)
294 (57 100)
248a
α-Quaterthiophene
390a
11
250 (6950)
383 (14 600)
a
Data taken from ref. 23.
by van Pham. Whilst many organic chromophores do show
such dependence, this phenomenon might also be related to
stacking effects in solution; we hope to study this further by an
examination of the variation of the 1H NMR spectra with
concentration.
Synthesis of 2,5-dibromo-3-methylthiophene 3
The same procedure was used as for 2-bromo-3-
methylthiophene, except that the quantity of NBS was doubled
(18.16 g, 0.1 mol). Distillation gave 3 (8.35 g, 65%) as a colour-
less liquid, bp 35–37 ЊC, 0.3 mmHg, (lit.31 55 ЊC, 2 mmHg).
δH (250 MHz, CDCl3) 2.15 (3 H, d, J 0.4, CH3), 6.74 (1H, d, J
0.4, CH); δC(62.5 MHz, CDCl3) 15.1 (CH3), 108.3, 110.1 (2-C,
5-C), 131.7 (4-C), 137.8 (3-C).
Conclusions
Oligothiophenes with a range of substituents at specific sites
can be prepared by coupling reactions. Both in the solid state
and in solution they adopt a range of conformations, with the
‘disfavoured’ syn-isomers quite highly populated. Both the
NOE data in solution, and the prevalence of disorder in the
solid-state structures, suggest that the difference in energy
between syn- and anti-conformations is small. As expected,
substitution leads to twisting of the oligothiophenes, and
shorter conjugation paths.
Synthesis of 2-bromo-3-hexylthiophene 4
A solution of 3-hexylthiophene (3 g, 0.18 mol) in dimethylform-
amide (DMF ) (50 cm3) was protected from light and cooled to
Ϫ20 ЊC. To this was slowly added a solution of NBS (3.178 g,
0.18 mol) in DMF (50 cm3). The mixture was stirred at Ϫ20 ЊC
for 30 min, and then allowed to warm to room temperature.
Stirring was continued for 5 h, and the mixture was poured into
ice (50 g) and extracted with dichloromethane (3 × 100 cm3).
The combined organic extracts were dried (Na2SO4) and the
solvent removed under reduced pressure. Fractional distillation
gave 4 (2.31 g, 52%), bp 95–96 ЊC, 0.1 mmHg, which was used
without further purification; δH (360 MHz, CDCl3) 0.95 (3H, t,
J 6.5, CH3), 1.36 (6H, m, 3 × CH2), 1.63 (2H, m, CH2), 2.61
(2H, t, J 7.5, ArCH2), 6.83 (1H, d, J 5.6, 4-H), 7.20 (1H, d, J
5.5, 5-H).
Experimental
1H and 13C NMR spectra were recorded in CDCl3 with
Si(CH3)4 as an external standard, using a Bruker AC250Y
(250.13, 62.85 MHz), a Bruker WM360 (360.53, 90.36 MHz)
or a Bruker AMX500 (500.73, 125.77 MHz) spectrometer.
J values are in Hz. Mass spectra were measured on either an
MS25 Kratos GC/MS spectrometer or a VG Autospec Fissions
instrument using the EI technique. Microanalyses were per-
formed on a Perkin-Elmer 2400 analyser at the University of
Sussex, or by Medac Ltd. IR spectra were recorded on a Perkin-
Elmer 1710 FTIR spectrometer. Data are reported for 10 scans
at a resolution of 4 cmϪ1. UV–VIS spectra were obtained on a
Philips PU8720 spectrometer.
2-Bromothiophene and 3-bromothiophene were kindly
donated by Synthetic Chemicals Ltd. N-Bromosuccinimide
(NBS) was recrystallised from nitromethane immediately before
use. Solvents were freshly distilled from an appropriate
desiccant before use. Reactions were performed under dry
nitrogen unless otherwise stated.
Synthesis of 2,5-dibromo-3-hexylthiophene 5
In the absence of light, NBS (6.36 g, 0.036 mol) dissolved in
DMF (30 cm3) was added in portions to a solution of 3-
hexylthiophene (3 g, 0.018 mol) in DMF (50 cm3) at Ϫ20 ЊC,
and the mixture stirred for 5 h while warming to room temper-
ature. The mixture was poured into ice (50 g) and extracted with
dichloromethane (3 × 50 cm3). The combined organic layers
were washed with water (2 × 100 cm3) and dried (Na2SO4).
Fractional distillation gave the colourless 5 (4.12 g, 70%), bp
142–145 ЊC, 0.3 mmHg (Found: C, 36.9; H, 4.3. Calc. for
C10H14Br2S: 36.8; H, 4.3%); δH (250 MHz, CDCl3) 0.91 (3H, t, J
7.1, CH3) 1.28–1.36 (6H, m, 3 × CH2), 1.54 (2H, m, CH2), 2.52
(2H, t, J 7.2, ArCH2), 6.7 (1H, s, 4-H); δC(62.5 MHz, CDCl3)
14.1 (CH3), 22.6 (CH2CH3), 28.8, 29.4, 29.5, 31.55 (4 × CH2),
107.9, 110.3 (2-C, 5-C), 130.9 (4-C), 142.9 (3-C); m/z (%) 328
(58, Mϩ), 326 (100), 324 (56), 255 (46), 177 (79), 175 (77).
[NiCl2(dppp)] was prepared in 92% yield according to the
method of van Hecke.29
Synthesis of 3-hexylthiophene 1
Magnesium (5 g, 0.21 mol) was suspended in diethyl ether (100
cm3) at 0 ЊC under nitrogen. A solution of 1-bromohexane (29.7
g, 0.18 mol) in diethyl ether (150 cm3) was added dropwise and
the mixture stirred at room temperature for 2 h. The Grignard
reagent was then added in portions to 3-bromothiophene (24.25
g, 0.15 mol) and [NiCl2(dppp)] (0.2 g) in diethyl ether (100 cm3)
and the mixture stirred for 3 h. The reaction mixture was then
quenched with water (100 cm3), the organic phase separated,
and the aqueous phase extracted (diethyl ether, 2 × 50 cm3).
The combined organic phases were dried (MgSO4) and the
Synthesis of 3,3Ј-dimethyl-2,2Ј-bithiophene 6
A solution of 2-bromo-3-methylthiophene (5 g, 0.028 mol)
in diethyl ether (75 cm3) was added dropwise over 1 h to
magnesium (0.72 g, 0.03 mol) suspended in diethyl ether (25
cm3). The Grignard reagent was added in small portions to a
mixture of 2-bromo-3-methylthiophene (5 g, 0.028 mol) and
[NiCl2(dppp)] (0.1 g) in diethyl ether (100 cm3) and stirred for
J. Chem. Soc., Perkin Trans. 2, 1997
1601

View Article Online
3 h. The reaction was quenched with water (100 cm3) and
extracted with diethyl ether (3 × 50 cm3). The combined organic
layers were dried and the solvent removed under reduced pres-
sure. Column chromatography (SiO2, light petroleum, bp 40–
60 ЊC) gave 6 (3.26 g, 61%) as a colourless liquid, bp 27–29 ЊC,
0.3 mmHg (Found: C, 62.0; H, 5.1. Calc. for C10H10S2: C, 61.8;
H, 5.2%); δH (500 MHz, CDCl3) 2.28 (6H, s, CH3), 7.00 (2H, d, J
4.9, 4,4Ј-H), 7.33 (2H, d, J 4.9, 5,5Ј-H); δC(125 MHz, CDCl3)
14.27 (CH3), 124.9 (5,5Ј-C), 129.9 (4,4Ј-C) 129.3 (3.3Ј-C), 136.3
(2,2Ј-C); m/z (%) 194 (100, Mϩ) 179 (51), 161 (19), 143 (18), 97
(11).
components. Further chromatography of this mixture (SiO2,
light petroleum, bp 30–40 ЊC) gave 9 as a viscous green oil (3.32
g, 40%), 2,2Ј:3Ј,2Љ-terthiophene 14 (0.137 g) and 5Ј-(2-thienyl)-
2,2Ј:3Ј,2Љ-terthiophene 15 (1.05 g) the latter two components
being identified spectroscopically (vide infra) (Found: C, 65.5;
H, 6.1. Calc. for C18H20S3: C, 65.0; H, 6.1%); δH (500 MHz,
CDCl3) 0.89 (3H, t, J 7.2, CH3), 1.31 (4H, m, 2 × CH2), 1.38
(2H, m, CH2), 1.66 (2H, m, CH2), 2.74 (2H, t, J 7.9, ArCH2)
7.04 (1H, dd, J3,4 3.6, J4,5 5.1, 4-H), 7.05 (1H, s, 4Ј-H), 7.09 (1H,
dd, J4Љ,5Љ 5.1, J3Љ,4Љ 3.6, 4Љ-H), 7.16 (1H, dd, J3Љ,5Љ 1.1, J3Љ,4Љ 3.5, 3Љ-
H) 7.19 (1H, dd, J3,5 1.1, J3,4 3.5, 3-H) 7.23 (1H, dd, J3,5 1.1, J4,5
5.1, 5-H), 7.33 (1H, dd, J3Љ,5Љ 1.1, J4Љ,5Љ 5.1, 5Љ-H); δC(125 MHz,
CDCl3) 14.0 (CH3), 22.6 (CH2CH3), 29.2 (ArCH2), 29.3
(ArCH2CH2CH2), 30.5 (ArCH2CH2), 31.6 (CH2CH2CH3) 123.4
(3Љ-C), 124.2 (5Љ-C), 125.2 (5-C), 125.7 (3-C), 126.4 (4Ј-C),
127.3 (4-C), 127.7 (4Љ-C), 129.4 (2-C), 135.0 (5Ј-C), 135.8 (2-C),
137.1 (2Љ-C), 140.1 (3Ј-C); m/z (%) 332 (100, Mϩ), 261 (55), 227
(15).
2,2Ј:3Ј,2Љ-Terthiophene 14. δH (500 MHz, CDCl3) 7.004 (1H,
dd, J 3.6, 5.2, 4-H or 4Љ-H), 7.028 (1H, dd, J 3.6, 5.1, 4-H or 4Љ-
H), 7.053 (1H, dd, J 1.3, 3.6, 3-H or 3Љ-H), 7.130 (1H, dd, J 1.1,
3.6, 3-H or 3Љ-H), 7.180 (1H, d, J 5.3, 4Ј-H or 5Ј-H), 7.267 (1H,
dd, J 1.2, 5.3, 5-H or 5Љ-H), 7.290 (1H, d, J 5.3, 4Ј-H or 5Ј-H),
7.324 (1H, dd, J 1.2, 5.1, 5-H or 5Љ-H); m/z (%) 248 (Mϩ, 100),
203 (53), 171 (15), 69 (25).
Preparation of 3,3Љ-dimethyl-2,2Ј:5Ј,2Љ-terthiophene 7
The Grignard derivative of 2-bromo-3-methylthiophene (7.8 g,
0.034 mol) in diethyl ether (150 cm3) was prepared as before,
and added to 2,5-dibromothiophene (18 g, 0.07 mol) and
[NiCl2(dppp)] (0.3 g) in diethyl ether (150 cm3). The mixture
was stirred for 3 h at room temperature, before work-up as
previously described. TLC indicated a mixture of six com-
pounds. Column chromatography (SiO2, light petroleum, bp
30–40 ЊC) allowed the separation of 2,5-dibromothiophene
and 2-bromo-3-methylthiophene, as well as 7. Crystallisation
(EtOH) gave pure material (2.8 g, 15%), mp 40–44 ЊC as a pale
yellow opaque solid (Found: C, 60.4; H, 4.55. Calc. for
C14H12S3: C, 60.8; H, 4.4%); λmax(CHCl3)/nm 276, 344; δH (500
MHz, CDCl3) 2.43 (6H, s, CH3), 6.90 (2H, d, J 5.1, 4,4Љ-H),
7.09 (2H, s, 3Ј-H, 4Ј-H), 7.16 (2H, d, J 5.1, 5,5Љ-H); δC(125
MHz, CDCl3) 15.43 (CH3), 123.3 (5,5Љ-C), 125.7 (3Ј,4Ј-C),
130.8 (3,3Љ-C), 131.4 (4,4Љ-C), 134.0 (2,2Љ-C), 136.2 (2Ј,5Ј-C);
m/z (%) 276 (100, Mϩ).
Synthesis of 5Ј-(2-thienyl)-2,2Ј:3Ј,2Љ-terthiophene 15
2-Bromothiophene (22.57 g, 0.138 mol) in diethyl ether (100
cm3) was added dropwise to magnesium (3.35 g, 0.138 mol)
suspended in diethyl ether (50 cm3) and stirred under nitrogen
for 1 h. The Grignard reagent was added in portions to 2,3,5-
tribromothiophene (14.8 g, 0.046 mol) and [NiCl2(dppp)] (0.1
g) in diethyl ether (100 cm3) and stirred for 3 h. The reaction was
then quenched with water (100 cm3) and the organic phase
separated. The aqueous phase was extracted with diethyl
ether (3 × 50 cm3). The combined organic phases were dried
(Na2SO4), decolourised over charcoal, and the solvent removed
under reduced pressure. The product was purified by column
chromatography (SiO2, light petroleum, bp 40–60 ЊC) and
recrystallised from ethanol (12.1 g, 80%), mp 57–58 ЊC (Found:
C, 58.1; H, 3.0. Calc. for C16H10S4: C, 58.15; H, 3.05%); δH (500
MHz, CDCl3) 7.029 (1H, dd, J3,4 3.6, J4,5 5.1, 4-H), 7.034 (1H,
dd, J3Љ,4Љ 3.6, J4Љ,5Љ 5.1, 4Љ-H), 7.055 (1H, dd, J3ٞ,4ٞ 3.6, J4ٞ,5ٞ 5.1,
4ٞ-H), 7.101 (1H, dd, J3Љ,4Љ 3.6, J3Љ,5Љ 1.2, 3Љ-H), 7.152 (1H, dd,
J3,4 3.6, J3,5 1.2, 3-H), 7.223 (1H, dd, J3ٞ,4ٞ 3.6, J3ٞ,5ٞ 1.2, 3ٞ-H),
7.24 (1H, s, 4Ј-H), 7.266 (1H, dd, J4ٞ,5ٞ 5.1, J3ٞ,5ٞ 1.2, 5ٞ-H), 7.307
(1H, dd, J4Љ,5Љ 5.1, J3Љ,5Љ 1,2, 5Љ-H), 7.317 (1H, dd, J4,5 5.1, J3,5
1.2, 5-H); δC(125 MHz, CDCl3) 124.1 (3ٞ-C), 124.9 (5ٞC),
125.7 (5Љ-C), 126.3 (4Ј-C), 126.7 (5-C), 126.8 (3Љ-C), 127.1 (4Љ-
C), 127.2 (4-C), 127.7 (3-C), 127.8 (4ٞ-C), 130.5 (2Ј-C), 132.5
(2Љ-C), 134.7 (2-C), 135.8 (5Ј-C), 136.5 (2ٞ-C), 137.0 (3Ј-C); m/z
(%) 330 (Mϩ, 100), 296 (18), 285 (33).
Synthesis of 3Ј-methyl-2,2Ј:5Ј,2Љ-terthiophene 8
2-Bromomagnesiothiophene was prepared by reacting 2-
bromothiophene (6.4 g, 0.039 mol) with Mg (1.87 g, 0.078 mol)
in diethyl ether (100 cm3). This was added to 2,5-dibromo-3-
methylthiophene (5 g, 0.019 mol) and [NiCl2(dppp)] (0.1 g) in
diethyl ether (100 cm3), and the mixture stirred for 3 h. The
reaction was quenched and worked up as before. Column
chromatography (SiO2, light petroleum, bp 40–60 ЊC) allowed
the successive isolation of 2-bromothiophene, 2,5-dibromo-3-
methylthiophene, 2,2Ј-bithiophene (from Grignard homocoup-
ling) and 8. On removal of the solvent 8 was initially obtained
as a yellow oil, which slowly solidified to long yellow needles,
mp 36–37 ЊC (2.4 g, 48%) (Found: C, 59.8; H, 3.9. Calc. for
C13H10S3: C, 59.5; H, 3.8%); λmax(CHCl3)/nm 353; δH (500 MHz,
CDCl3) 2.79 (3H, s, CH3), 6.99 (1 H, s, 4Ј-H), 7.02 (1 H, dd, J4Љ,5Љ
5.1, J3Љ,4Љ 3.5, 4Љ-H), 7.08 (1H, dd, J4,5 5.1, J3,4 3.5, 4-H), 7.16
(1H, dd, J3,5 1.2, J3,4 3.5, 3-H), 7.17 (1H, dd, J3Љ,5Љ 1.1, J3Љ,4Љ 3.5,
3Љ-H), 7.22 (1H, dd, J3Љ,5Љ 1.1, J4Љ,5Љ 5.1, 5Љ-H), 7.31 (1H, dd, J3,5
1.1, J4,5 5.1, 5-H); δC(125 MHz, CDCl3) 15.5 (CH3), 123.6 (3Љ-
C), 124.2 (5Љ-C), 125.0 (5-C), 125.3 (3-C), 127.3 (4-C), 127.91,
127.93 (4Ј,4Љ-C), 129.95 (5Ј-C), 134.5 (3Ј-C), 134.6 (2Ј-C), 136.2
(2-C), 137.1 (2Љ-C) ppm; m/z (%) 262 (100, Mϩ), 229 (14), 217
(8), 203 (5), 184 (10), 171 (7).
Synthesis of 5,5Ј-dibromo-2,2Ј-bithiophene 10
In the dark, under an atmosphere of nitrogen, NBS (8.58 g,
0.48 mol) in DMF (50 cm3) was added in portions to a solution
of 2,2Ј-bithiophene (5 g, 0.024 mol) in DMF (100 cm3) at
Ϫ20 ЊC, and the mixture stirred for 4 h. The mixture was
poured onto ice (100 g) and the precipitate collected by filtration
and washed with water. Drying over P2O5 and recrystallisation
(EtOH–hexane) gave 5,5Ј-dibromo-2,2Ј-bithiophene 10 as a pale
green solid (6.2 g, 80%), mp 145–146 ЊC (lit.14 146 ЊC); δH (500
MHz, CDCl3) 6.85 (2H, d, J 3.8, 4-H, 4Ј-H), 6.96 (2H, d, J 3.8,
3-H, 3Ј-H); m/z (%) 326 (61), 324 (100), 322 (55).
Synthesis of 3Ј-hexyl-2,2Ј:5Ј,2Љ-terthiophene 9
2-Bromomagnesiothiophene was prepared as before from 2-
bromothiophene (8.18 g, 0.05 mol) and magnesium (1.3 g, 0.054
mol) in diethyl ether (100 cm3). The solution was added in por-
tions to a mixture of 2,5-dibromo-3-hexylthiophene (8.15 g,
0.025 mol) and [NiCl2(dppp)] (0.2 g) in diethyl ether (150 cm3).
The mixture was stirred for 3 h, then quenched with water (200
cm3). the organic phase was separated and the aqueous phase
extracted with diethyl ether (3 × 50 cm3). The organic fractions
were combined and dried (Na2SO4), and the solvent removed
under reduced pressure to give a brown oil (8.83 g). Column
chromatography (SiO2, light petroleum, bp 30–40 ЊC) allowed
Synthesis of 3,3ٞ-dimethyl-2,2Ј:5Ј,2Љ:5Љ,2ٞ-quaterthiophene 11
2-Bromomagnesio-3-methylthiophene was prepared from 2-
bromo-3-methylthiophene (10.9 g, 0.062 mol) as previously
described. The Grignard reagent was then added dropwise to
a solution of 5,5Ј-dibromo-2,2Ј-bithiophene (10 g, 0.031 mol)
separation of
a mixture of 2-bromothiophene and 2,5-
dibromo-3-hexylthiophene (2.08 g), 2,2Ј-bithiophene (1.16 g,
from Grignard homocoupling) and a mixture of three other
1602
J. Chem. Soc., Perkin Trans. 2, 1997

View Article Online
Table 6 Crystallographic data for compounds 7, 8 and 152
Crystal data
7
8
15
Molecular formula
M
C14H12S3
276.4
C13H9S3
261.4
C16H10S4
330.5
Crystal system
a/Å
b/Å
c/Å
monoclinic
8.072(3)
14.023(3)
12.058(2)
107.52(2)
1301.6
monoclinic
5.653(6)
36.977(8)
17.645(5)
94.54(5)
3676
monoclinic
15.823(7)
5.637(2)
16.373(8)
96.63(4)
1457.3
β/Њ
V/Å3
Parameters for cell determination
25 reflections
8 < θ < 10Њ
0.710 69
P21/c
4
1.41
25 reflections
8 < θ < 9Њ
0.710 69
P21/c
12
1.42
25 reflections
7 < θ < 10Њ
0.710 69
P21/c
4
λ/Å
Space group
Z
Dx/g cmϪ3
1.51
Appearance
Crystal dimensions/mm
Yellow blocks
0.3 × 0.2 × 0.2
cut from block
5.5
Pale yellow needles
0.6 × 0.1 × 0.08
cut from needle
5.5
Yellow needles
0.4 × 0.1 × 0.05
µ(Mo-Kα)/cmϪ1
6.1
Data collection and processing
Diffractometer type
Collection method
Radiation
CAD4
θ–2θ
Graphite
CAD4
θ–2θ
Graphite
CAD4
θ–2θ
Graphite
monochromated Mo-Kα
monochromated Mo-Kα
monochromated Mo-Kα
Reflections measured
3475
5105
2059
Independent reflections
3272
4568
1992
Rint
0.02
0.04
0.06
Observed reflections
Criterion for observed
h
k
2237
1755
1001
|F2| > 2σ(F2)
0→10
0→18
Ϫ15→15
2, 28
|F2| > 2σ(F2)
|F2| > 2σ(F2)
0→16
0→5
0→5
0→39
l
Ϫ18→18
Ϫ17→17
2, 22
θmin,max/Њ
2, 22
Max. change in standard reflections (%)
Decay correction
Absorption correction
T/K
Ϫ0.2
No
No
173
Ϫ0.6
No
Ϫ0.7
No
No
DIFABS32 max, min 1.29, 0.75
293
173
Structure analysis and refinement
Method, program
Direct, SHELXS-8633
Enraf-Nonius MolEN 34
Direct, SHELXS-8633
Enraf-Nonius MolEN 34
Direct, SHELXS-8633
Enraf-Nonius MolEN 34
¹
¹
¹
Weighting scheme
σ(F2) = [σ2(I) ϩ 0.04I2]²/Lp
σ(F2) = [σ2(I) ϩ 0.04I2]²/Lp
σ(F2) = [σ2(I) ϩ 0.04I2]²/Lp
w = σϪ2(F)
w = σϪ2(F)
w = σϪ2(F)
Σw(|Fo)| Ϫ |Fc|)2 minimised
Σw(|Fo)| Ϫ |Fc|)2 minimised
Σw(|Fo)| Ϫ |Fc|)2 minimised
R
RЈ
S
0.041
0.045
1.2
0.074
0.085
1.8
0.103
0.102
2.1
Variables
(∆/σ)max
(∆ρ)max,min/e ÅϪ3
222
0.01
ϩ0.36, Ϫ0.14
243
0.01
ϩ0.52, Ϫ0.20
101
0.02
ϩ0.96, Ϫ0.74
and [NiCl2(dppp)] (0.1 g) in tetrahydrofuran–diethyl ether
(1:1; 100 cm3). The reaction mixture was stirred at 23 ЊC for
3 h, then quenched with water (200 cm3) and worked up in the
usual manner. Removal of the solvent under reduced pressure,
followed by charcoal decolourisation, gave 11 (6.2 g, 56%) as a
yellow solid, mp 108–109 ЊC (from hexane) (Found: C, 60.45;
H, 3.9; S, 35.95. Calc. for C18H14S4: C, 60.3; H, 3.9; S, 35.8%);
δH (500 MHz, CDCl3) 2.44 (6H, s, CH3), 6.90 (2H, d, J 5.1,
4-H, 4ٞ-H), 7.05 (2H, d, J 3.7, 4Ј-H, 3Љ-H), 7.16 (2H, d, J 5.1,
5-H, 5ٞ-H), 7.14 (2H, d, J 3.7, 3Ј-H, 4Љ-H); δC(125 MHz,
CDCl3) 15.49 (CH3), 123.4 (5-C, 5ٞ-C), 123.8 (4Ј-C, 3Љ-C),
126.0 (3Ј-C, 4Љ-C), 130.8 (2-C, 2ٞ-C), 131.5 (4-C, 4ٞ-C), 134.1
(3-C, 3ٞ-C), 135.6 (5Ј-C, 2Љ-C), 136.5 (2Ј-C, 5Љ-C); m/z (%) 358
(Mϩ, 100).
methanol in a Soxhlet apparatus for 52 h. The material was
then extracted with chloroform, and choloroform-soluble and
-insoluble fractions dried under reduced pressure. For conduct-
ivity measurements the materials were pressed into pellets and
doped by exposure to iodine under ambient conditions.
Synthesis of poly(3-hexylthiophene)
The method described above was used with 3-hexylthiophene
(1 g, 0.006 mol) and iron() chloride (4 g, 0.025 mol). After
removal of iron() chloride, the polymer was dried under
reduced pressure to give pristine undoped poly(3-hexyl-
thiophene) (0.69 g, 69%) as a black powder.
Structure of 3,3Љ-dimethyl-2,2Ј:5Ј,2Љ-terthiophene 7
Good quality crystals were obtained by slow evaporation of a
hexane solution of 7 at room temperature. Data are given in
Table 6. Non-H atoms were refined anisotropically except the
lower occupancy sites, which were refined isotropically. H
atoms were freely refined isotropically except for the lower
occupancy sites, which were omitted. The five-membered ring
containing S(3) had 85% occupancy in the orientation shown in
Polymerisation of 3Ј-hexyl-2,2Ј:5Ј,2Љ-terthiophene 9
3Ј-Hexyl-2,2Ј:5Ј,2Љ-terthiophene (1.6 g, 0.005 mol) in tetra-
chloromethane (10 cm3) was added to a suspension of iron()
chloride (3.12 g, 0.019 mol) in tetrachloromethane (150 cm3)
and stirred for 4 h. The mixture was poured into methanol (500
cm3), and the precipitate collected. This was extracted with
J. Chem. Soc., Perkin Trans. 2, 1997
1603

View Article Online
6 M. Yu. Antipin and Yu. T. Struchkov, Zh. Strukt. Khim., 1980, 21,
190.
7 E. F. Paulus, K. Siam, K. Wolinski and L. Schäfer, J. Mol. Struct.,
1989, 196, 171.
8 S. P. Armes, P. A. Chaloner, P. B. Hitchcock and M. R. Simmons,
Acta Crystallogr., Sect. C, 1994, 50, 1945.
9 F. van Bolhuis, H. Wynberg, E. E. Havinga, E. W. Meijer and
E. G. J. Staring, Synth. Met., 1989, 30, 381.
10 G. Barbarella, M. Zambianchi, A. Bongoni and L. Antolini, Adv.
Mater., 1994, 6, 561.
11 G. Barbarella, M. Zambianchi, A. Bongoni and L. Antolini, Adv.
Mater., 1992, 4, 282.
12 S. Hotta and K. Waragai, J. Mater. Chem., 1991, 1, 835.
13 J. K. Herrema, J. Wildeman, F. van Bolhuis and G. Hadziioannou,
Synth. Met., 1993, 60, 239.
Fig. 2 and 15% occupancy in the orientation related by a 180Њ
rotation about the C(8)᎐C(9) bond.†
Structure of 3Ј-methyl-2,2Ј:5Ј,2Љ-terthiophene 8
Good quality crystals were obtained by slow sublimation at
atmospheric pressure. Data are given in Table 6. Refinement of
sulfur was anisotropic and carbon isotropic. The weakness of
the data did not justify anisotropic refinement of C atoms.
Hydrogen atoms were fixed at calculated positions with
Uiso = 1.3Ueq for parent atom. There are three independent
molecules in the asymmetric unit. They have similar geometry
except that in molecule C one ring is disordered equally
between two orientations related by a 180Њ rotation about the
ring–ring bond. The two sites having 50:50 S/C occupancy were
given an average scattering factor and the H-atom involved was
omitted.†
14 P. Bäuerle, F. Würthner, G. Götz and F. Effenberger, Synthesis,
1993, 1099.
15 G. J. Visser, G. J. Heeres, J. Wolters and A. Vos, Acta Crystallogr.,
Sect. B, 1968, 24, 467.
16 I. Novak, S. C. Ng, K. F. Mok, C. Y. Mok and H. H. Huang,
J. Chem. Res. (S), 1992, 350.
Structure of 5Ј-(2-thienyl)-2,2Ј:3Ј,2Љ-terthiophene 15
17 C. Arbizzani, G. Barbarella, A. Bongini, M. Mastragostino and
M. Zambianchi, Synth. Met., 1992, 52, 329.
18 F. Martinez, R. Voelkel, D. Naegele and H. Naarmann, Mol. Cryst.
Liq. Cryst., 1989, 167, 227.
19 D. Fichou, G. Horowitz and F. Garnier, Synth. Met., 1990, 39, 125.
20 D. Deglabouglise, M. Hmyene, G. Horowitz, A. Yassar and
F. Garnier, Adv. Mater., 1992, 4, 107.
21 D. M. Perrine, D. M. Bush, E. P. Kornak, M. Zhang, Y. H. Cho and
J. Kagan, J. Org. Chem., 1991, 56, 5095.
22 J. Kankare, J. Lukkari, P. Pasanen, R. Sillanpää, H. Laine,
K. Harmaa and C. Visy, Macromolecules, 1994, 27, 4327.
23 Details may be obtained from P. A. C.
24 R. F. Curtis and G. T. Phillips, Tetrahedron, 1967, 23, 4419.
25 J. W. Sease and L. Zechmeister, J. Am. Chem. Soc., 1947, 69, 270.
26 D. Bimbaum and B. E. Kohler, J. Chem. Phys., 1991, 95, 4783.
27 J. N. Murrell, J. Chem. Soc., 1956, 3779.
Good quality crystals were obtained by slow evaporation from
a saturated solution in ethanol. Refinement of sulfur was aniso-
tropic and carbon isotropic. Hydrogen atoms were fixed at cal-
culated positions with Uiso = 1.3Ueq for parent atom. There is
disorder in two of the rings. S(2) is disordered 0.6:0.4 between
the sites labelled S(2) and C(9), and S(3) is disordered 0.72:0.28
between sites labelled S(3) and C(3). The atoms at these sites
were given an average scattering factor, and hydrogen atoms
were included at the sites attached to C(3) and C(9) at appropri-
ate occupancies. Because of the disorder, attempts to refine C
atoms with anisotropic thermal vibrations resulted in many
non-positive definite values.†
† Atomic coordinates, bond lengths and angles, and thermal para-
meters have been deposited at the Cambridge Crystallographic Data
Centre (CCDC). For details of the deposition scheme, see ‘Instructions
for Authors’, J. Chem. Soc., Perkin Trans. 2, 1997, Issue 1. Any request
to the CCDC for this material should quote the full literature citation
and the reference number 188/74.
28 C. van Pham, A. Burkhardt, R. Shabana, D. D. Cunningham,
H. B. Mark and H. Zimmer, Phosphorus, Sulfur, Silicon, 1989, 46,
153.
29 G. R. van Hecke and W. deW. Horrocks, Inorg. Chem., 1966, 5, 1968.
30 R. Harrison, BSc Thesis, University of Sussex, 1990.
31 K. Dittmer, R. P. Martin, W. Herz and S. J. Cristol, J. Am. Chem.
Soc., 1949, 71, 1201.
32 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158.
33 G. M. Sheldrick, 1985, SHELXS-86, Program for the Solution of
Crystal Structures, Univ. of Gottingen, Germany.
34 C. K. Fair, 1990, MolEN, An Interactive Intelligent System for
Crystal Structure Analysis, Enraf-Nonius, Delft, The Netherlands.
References
1 J. Roncali, Chem. Rev., 1992, 92, 711.
2 P. A. Chaloner, S. R. Gunatunga and P. B. Hitchcock, Acta Crystal-
logr., Sect. C, 1994, 50, 1941.
3 M. Pelletier and F. Brisse, Acta Crystallogr., Sect. C, 1994, 50, 1942.
4 E. F. Paulus, R. Dammel, G. Kämpf, P. Wegener, K. Siam,
K. Wolinski and L. Schäfer, Acta Crystallogr., Sect. B, 1988, 44,
509.
5 G. J. Pyrka, Q. Fernando, M. B. Inoue, M. Inoue and E. F.
Velazquez, Acta Crystallogr., Sect. C, 1988, 44, 562.
Paper 6/07254B
Received 24th November 1996
Accepted 27th March 1997
1604
J. Chem. Soc., Perkin Trans. 2, 1997