Synthesis and structure of tetrathiophene with a chiral 1,1′-binaphthyl kink

Article abstract of DOI:10.1039/b007355p

A chiral oligothiophene, possessing in-chain chirality, was prepared and its racemate was characterized by single crystal X-ray crystallography; the in-chain chiral 1,1′-binaphthyl moiety interrupts the π-conjugation and affects the solid state properties

Full text of DOI:10.1039/b007355p

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Synthesis and structure of tetrathiophene with a chiral 1,1A-binaphthyl
kink†
Andrzej Rajca,* Hua Wang, Visa Pawitranon, Tom J. Brett and John J. Stezowski
a Department of Chemistry and Center for Materials Research and Analysis, University of Nebraska,
Lincoln, NE 68588-0304, USA. E-mail: arajcal@unl.edu
Received (in Columbia, MO, USA) 14th August 2000, Accepted 10th April 2001
First published as an Advance Article on the web 22nd May 2001
A chiral oligothiophene, possessing in-chain chirality, was
prepared and its racemate was characterized by single
crystal X-ray crystallography; the in-chain chiral 1,1A-
binaphthyl moiety interrupts the p-conjugation and affects
the solid state properties of the oligothiophene.
Oligothiophenes are attracting attention as functional materials
for (opto)electronic devices.1,2 Soluble oligothiophenes are
especially valuable in applications where reproducible high
chemical purity is essential and recently developed solution
printing techniques can be utilized, e.g. in ‘plastic electronics’
based upon field effect transistors.2 The well-defined oligomers
are also studied as models for the parent polymers.3 The crystal
structures of a number of oligothiophenes have been re-
ported.2,4
The introduction of chirality into the oligo- or polythiophenes
is expected to provide an additional engineering tool for these
materials, arising not only from intrinsic chirooptical and
chiroelectronic properties but also from diastereomeric inter-
actions in the solid state.5,6 Polythiophenes with various chiral
pendant groups and in-chain 1,1A-binaphthyls have been
reported.7,8
We report on the synthesis and single crystal X-ray structure
determination of 6,6A-bis(5-phenyl-2,2A-bithiophen-5A-yl)-2,2A-
bis(decyloxy)-1,1A-binaphthyl (1), a chiral oligothiophene,
possessing in chain chirality.
Scheme 1 Synthesis of (R)-, (S)-, and rac-1, and the structure of the
reference compound 5.
1,1A-binaphthyl-2,2A-diols (3) with iododecane in the presence
of NaH in DMF.12 The modules 2 and 4 are linked via Negishi
coupling providing (R)-, (S)-, and rac-1 in 59–70% yields
(Scheme 1).13,14 Analogous synthetic procedures were used to
obtain the model bithiophene 5.
Orange, block-shaped crystals of rac-1 suitable for X-ray
diffraction experiments were grown by slow evaporation of the
solvent from a hexane–chloroform solution.15 The structure
displayed by 1 is that of a twisted binaphthyl with the alkoxy
chain of one naphthyl unit packing against the naphthyl–
thiophene–thiophene–phenyl p-system of the other half of the
molecule (Fig. 1). Each of the p-systems is nearly planar,
exhibiting small interplanar twist angles.16 Possible 2-fold
symmetry about an axis perpendicular to the C(1)–C(25)
binaphthyl linkage is broken by the differing conformations
displayed by the alkoxy chains. The difference is a single
torsion angle. The conformation about the C(2A)–C(3A) bond
is trans [C(1A)–C(2A)–C(3A)–C(4A) = 2176.2(4)°], whereas
the C(2B)–C(3B) conformer is gauche [C(1B)–C(2B)–C(3B)–
C(4B) = 268.8(5)°]. The remainders of both chains are in all-
trans conformations. Because of the difference in conformation,
the plane containing C(2B–10B) lies parallel to the adjacent p-
system, while the C(2A–10A) plane is essentially perpendicular
to the adjacent p-system. Both chains lie in close contact with
The convergent synthesis of (R)-, (S)-, and rac-1 is based
upon the connection of two achiral modules 2 to the chiral
module 4, which is available in the (R)-, (S)-, and racemic-
forms. 5A-Bromo-5-phenyl-2,2A-bithiophene (2) is obtained in
two steps: (1) 2,5-dibromothiophene is treated with 1 equiv. of
n-BuLi in diethyl ether, followed by oxidation with CuCl2 to
give 5,5A-dibromo-2,2A-bithiophene,9 (2) Suzuki coupling of
phenylboronic acid in the presence of an excess of 5,5A-
dibromo-2,2A-bithiophene gives 2 in 68% yield.10,11 6,6A-
Dibromo-2,2A-bis(decyloxy)-1,1A-binaphthyls (4) are prepared
according to the previously published procedures for analogous
bis(dodecyloxy) derivatives by etherification of 6,6A-dibromo-
† Electronic supplementary information (ESI) available: synthesis and
characterization data for 1, 2, 4, and 5; crystal packing plots for rac-1. See
http://www.rsc.org/suppdata/cc/b0/b007355p/
Fig. 1 The conformation for the crystal structure for rac-1. Ellipsoids are
shown at 50% probability.
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Chem. Commun., 2001, 1060–1061
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b007355p

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packing and materials properties of chiral molecular hinges in
the neutral and doped states are in progress.
This research was supported by the National Science
Foundation (CHE-9806954 to A. R. and CHE-9812146 to
J. J. S.). We thank Drs Lianhe Yu, Nai Xing Wang, and Jun Li
for preparation of synthetic intermediates and conductivity
measurements. We thank Dr R. Cerny of the Nebraska Center
for Mass Spectrometry for the mass spectral determinations.
Notes and references
1 (a) Handbook of Conducting Molecules and Polymers, ed. H. S. Nalwa,
Wiley, New York, 1997; (b) Conjugated Oligomers, Polymers, and
Dendrimers: From Polyacetylene to DNA, ed. J. L. Bredas, De Boeck
Universite, Paris, Bruxelles, 1999.
2 D. Fichou, Chem. Mater., 2000, 10, 571.
3 R. E. Martin and F. Diedrich, Angew. Chem., Int. Ed., 1999, 38,
1351.
4 (a) G. Barbarella, M. Zambianchi, L. Antolini, P. Ostoja, P. Maccag-
nani, A. Bongini, E. A. Marseglia, E. Tedesco, G. Gigli and R.
Cingolani, J. Am. Chem. Soc., 1999, 121, 8920; (b) G. Grüner, T.
Debaerdemaeker and P. Bäuerle, Chem. Commun., 1999, 1097; (c) U.
Mitschke, E. M. Osteritz, T. Debaerdemaeker, M. Sokolowski and P.
Bäuerle, Chem. Eur. J., 1998, 11, 2211; (d) D. D. Graf, R. G. Duan, J. P.
Campbell, L. L. Miller and K. R. Mann, J. Am. Chem. Soc., 1997, 119,
5888; (e) P. A. Chaloner, S. R. Gunatunga and P. B. Hitchcock, J. Chem.
Soc., Perkin Trans. 2, 1997, 1597.
5 Circularly polarized electroluminescence from chiral poly(p-pheny-
lenevinylene): E. Peeters, M. P. T. Christiaans, R. A. Janssen, H. F. M.
Schoo, H. P. J. M. Dekkers and E. W. Meijer, J. Am. Chem. Soc., 1997,
119, 9909.
6 E. L. Eliel and S. H. Wilen, Stereochemistry of Organic Compounds,
Wiley, New York, 1994, ch. 13.
Fig. 2 Crystal packing for rac-1: stereoview (approximately bc-plane) of the
tetramer fragment of the zig-zag chain extending along the c-axis. The
enantiomers are color-coded.
7 Selected polythiophenes with chiral pendant groups: M. Lemaire, D.
Delabouglise, R. Garreau, A. Guy and J. Roncali, Chem. Commun.,
1988, 658; D. Kotkar, V. Joshi and P. K. Ghosh, Chem. Commun., 1988,
917; B. M. W. Langeveld-Voss, R. A. J. Janssen, M. P. T. Christiaans,
S. C. J. Meskers, H. P. J. M. Dekkers and E. W. Meijer, J. Am. Chem.
Soc., 1996, 118, 4908; J. L. Bredas, D. A. dos Santos, J. Cornil, D.
Beljonne and Z. Shuai in ref. 1(b), ch. 7.
each p-system, with alkyl hydrogens pointing towards the p-
systems. We suggest that this interaction influences the
conformation of the binaphthyl core. The binaphthyl twist
displayed [C(9)–C(1)–C(25)–C(33) = 107.3(3)°] is larger than
that observed in binaphthyl (101.4°)17 and most other 2,2-disub-
stituted binaphthyls, e.g. 2,2A-dihydroxy-1,1A-binaphthyl
(92.5°)18 and 2,2A-bis(bromomethyl)-1,1A-binaphthyl (86.8°).19
For the discussion of the crystal packing in rac-1, the two p-
conjugated moieties of 1 may be viewed as a molecular hinge.
The phenyl–bithiophene–naphthyl moieties from the mirror
image enantiomers form a quasi-one-dimensional zig-zag chain
extending along the c axis (Fig. 2). Such a chain of molecular
hinges is facilitated by the alternating enantiomers. Along the a
axis, the chains pack side-by-side to form quasi-two-dimen-
sional zig-zag layers, which pack on top of each other in a ‘lock-
and-key pattern’. The homochiral p–p interactions are negli-
gible as the phenyl–bithiophene–naphthyl moieties form
alternating stacks with the alkyl chains.
8 L. Pu, Chem. Rev., 1998, 98, 2405; K. Y. Musick, Q.-S. Hu and L. Pu,
Macromolecules, 1998, 31, 2933.
9 5,5A-Dibromo-2,2A-bithiophene: ref 4(e) and references therein.
10 Our melting point for 5A-bromo-5-phenyl-2,2A-bithiophene is about
20 °C higher than previously claimed: S. E. Burkart and R. B. Phillips,
PCT Int. Appl., 1986, WO 86/05949; Chem. Abstr., 1986, 106,
98 155.
11 N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457.
12 (a) J. Cuntze, L. Owens, V. Alcazar, P. Seiler and F. Diedrich, Helv.
Chim. Acta, 1995, 78, 367; (b) 1,1A-binaphthyl-2,2A-diol: non-racemic,
Aldrich (ee 99%); racemic, K. Ding, Y. Wang, L. Zhang, Y. Wu and T.
Matsuura, Tetrahedron, 1996, 52, 1005.
13 E. Negishi, A. O. King and N. Okukado, J. Org. Chem., 1977, 42,
1821.
14 The experimental procedures and characterisation data are available as
ESI.†
15 Crystal data for rac-1: C68H70O2S4, M = 1047.48, monoclinic, a =
12.587(1), b = 17.684(1), c = 26.299(1) Å, b = 100.136(1)°, T =
293(3) K, space group P21/c (no. 14), Z = 4, MoKa (l = 0.71073), Dc
= 1.207 g cm23, crystal size 1.0 3 0.4 3 0.1 mm. Structure solved by
direct methods and refined by full matrix least squares on F2. Final
refinement statistics: R1 = 0.0691, wR2 = 0.1630, and GooF = 1.333
for 4598 reflections with Fo > 4s(Fo). CCDC 163086. See http://
www.rsc.org/suppdata/cc/b0/b007355p/ for crystallographic data in .cif
or other electronic format.
16 Angles between least-squares planes composed of the following atoms:
C(19–24) and S(2)/C(15–18) = 5.4(2)°; S(2)/C(15–18) and S(1)/C(11–
14) = 3.6(2)°; S(1)/C(11–14) and C(1–10) = 3.5(2)°; C(25–34) and
S(3)/C(35–38) = 5.2(1)°; S(3)/C(35–38) and S(4)/C(39–42) = 7.7(2)°;
S(4)/C(39–42) and C(43–48) = 5.8(2)°.
17 The torsional angles (measured analogously to rac-1) are 101.4° and
69.5° for the enantiomeric and the racemic forms of binaphthyl,
respectively: R. B. Kress, E. N. Duesler, M. C. Etter, I. C. Paul and D. Y.
Curtin, J. Am. Chem. Soc., 1980, 102, 7709.
18 F. Toda, K. Tanaka, H. Miyamoto, H. Koshima, I. Miyahara and K.
Hirotsu, J. Chem. Soc., Perkin Trans. 2, 1997, 1877.
With bithiophene 5 as a reference, UV-vis spectra of 1 reveal
that the nonplanar chiral binaphthyl moiety highly attenuates
the p-conjugation.8 The broad p–p* transitions (lmax = 393
nm) for 1 and 5 are essentially superposable, except for the
molar absorptivities, which in 1 are approximately twice those
in 5 (log emax = 4.9 and 4.6). The fingerprint regions of the IR
spectra of solid (R)- and (S)-1 show small differences compared
to the IR spectrum of rac-1. Also, the melting point of rac-1 is
about 40–50 °C higher than those for the (R)- and (S)-
enantiomers, suggesting the presence of a racemic compound.20
Moreover, the melting point of bithiophene 5 is even higher,
about 95 °C above rac-1. The solubility in chloroform (g mL21
)
increases in the following order: (S)-1 (2 3 1021) > rac-1 (8 3
1024) > 5 (2 3 1025), i.e. the opposite order to the melting
points. These significant differences in solubilites are of
importance for the solution processability of oligothiophenes.
In summary, the introduction of chirality into the oligothio-
phene chain leads to significant differences in solid state
properties between stereoisomers and should be an important
factor in their solution processability. Further studies on crystal
19 K. Harata and J. Tanaka, Bull. Chem. Soc. Jpn., 1973, 46, 2747.
20 J. Jacques, A. Collet and S. H. Wilen, Enantiomers, Racemates, and
Resolutions, Krieger, Malabar, Florida, 1994, ch. 2.
Chem. Commun., 2001, 1060–1061
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