Synthesis and properties of naphthalenes carrying two cofacially oriented α-oligothiophene units at the peri positions

Article abstract of DOI:10.1016/S0040-4039(00)60822-5

Two cofacially oriented (oligo)thiophene units of 1,8-di(2-thienyl)-, 1,8-bis(5,2'-bithiophene-2-yl)-, and 1,8-bis(5,2':5',2''-terthiophene-2-yl)naphthalenes, which were synthesized starting from 1,8-dibromonaphthalene, interact with each other to stabilize the radical cations of these compounds, thus decreasing their CV oxidation potentials.

Full text of DOI:10.1016/S0040-4039(00)60822-5

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Vol. 33, No. 49.
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Printed in
Synthesis and Properties of Naphthalenes
Carrying Two Cofacially Oriented
Units at the Positions
and Masamatsu
of
of
338, Japan
Noboru
Two cofacially oriented
and
units of
which
the
synthesized starting
cations of these
with each other to
thus
Recently, several
carbon atom
Oligothiophenes are attractive building blocks
electronic deviis.
molecules which have two perpendicular oligothiophene units bisected through a
As another approach
switches.1
have been synthesized with expectation of obtaining new
diited molecular devices, thin solid films. in which oligothiophene units am cofacially stacked
each other, have been obtained by using techniques? In this connection, we have
become interested in the preparation of naphthalene derivatives carrying two units at
the
positions. In such molecules, two thiophene units would be placed cofacially in close
proximity and interact with each other to produce additional new interesting physico-chemical
properties. In fact, X-ray single crystal structure analysis of
has revealed that
to the plane of
the approximately parallel planes of the two
the naphthalene ring.3
are at an angle of
We first attempted the preparation of
with
1 by coupling of
bromide catalyzed by [
However, the reaction carried out in refluxing ether gave
chloride
as the major product and the desired 1 as a minor product, We therefore
next used
instead of the diiodo compound as the starting material. The
reaction satisfactorily gave in 36% yield in addition to
in 30%
yield.
7553

7 5 5 4
Bromination of 1 wit h 2 equiv. of
The coupling of 2 with
(NBS) gave the dibromide in 63%
bromide in ether
yield
afforded expected
Similarly the reaction of 2 with
in refluxing ether afforded
36 as pale-yellow crystals in 77% yield
bromide in the presence of
47 as yellow
crystals in 60% yield. The reaction in refluxing
did not give the expected 4.
3
ether
4
For comparison with
and 4, monosubstituted naphthalene derivatives 5-7 were synthesized
Every reaction worked cleanly to give 5-7 in excellent yields.
in the manner depicted below.
ether
ether
6

7555
Both
and
NMR data show that two
of 1.3 and 4
rotating at room
However,
equivalent,
on NMR
is
thus revealing that the
bond is
scale. The same is true for
known to be separable into cis and
while two thiophene rings of
and
prepared from
magnesium bromide, still remain equivalent on NMR time scale. These observations. show that
The thiophene ring protons at C-3 and C-4 of
appear at 6.43 and 6.58 as doublet of doublet, while does not have any abosorption at higher field
1
is a less bulky substituent than phenyl.
This indicates that the preferred conformation of
1 is the one in which two thiophene
than
rings
approximately to each other, but not coplanar with the naphthalene ring, thus resulting
in the shielding of the thiophene ring protons by ring current effect. The same conclusion is also
reached for 3 and 4 by considering chemical shift differences between 3 and 6 and between 4 and
In
spectra in
(Table the highest
for 1 is slightly greater than that of
5, whereas the highest
for 3 and 4 are smaller than those of 6 and 7. These observations lead to
the same conclusion as that reached by NMR, although the conjugation between naphthalene ring and
thiophene units is more strictly inhibited for 3 and 4 than for 1.11
CV oxidation potential data (Table
determined with a platinum working
and 0.1
M electrolyte (tetrabutylammonium perchlorate) in acetonitrile, are of particular interest. Every
compound shows irreversible oxidation
probably because radical cations
very reactive
decrease with an
and undergo polymerization as many thiophenes do
increasing number of thiophene rings without any exception and
of 1.3 and 4 are lower than the
corresponding 5-7. Furthermore,
increase
that the radical cation formed in one thiophene unit is stabilized by the participation of the other
thiophene unit and such is mom effective in molecules having longer oligothiophene units.
differences between 1 and and 6, and beween 4 and 7
with an increasing number of thiophene rings. These observations strongly suggest
UV and Oxidation Potential Data of Naphthalenes
1 and 3-7.
Table 1.
Naphthalenes
Eox
Naphthalenes
Eox
1.11
0.84
0.7 1
299 9600)
335 (20800)
373 (32200)
1.05
0.75
0.59
312 (8200)
1
3
4
6
7
330 (32200)
365 (52200)
References and Notes
1. (a) Aviram, A. Am. Chem.
ibid., 1990,212, 662. Tour, J. M.; Wu, R.; J. S. Schumm, J. S. ibid, 1991. 113, 7064.
(d) Nakayama, J.; Fujimori, T. 1991, 1614.
1988,
5687. (b) Tour, J. M.; Wu, R.; Schumm, J. S.

7556
2.
3.
4.
Nakayama, J.;
D.
M.;
K. Thin Solid Films,
House,
0.;
W. J. Org. Chem.,
1003.
Tamao, K.; Kodama S.;
38. 3347.
Kumada, M.; Minato, A.; Suzuki, K.
5.
104-105
NMR (400
7.44
CDC13) 7.84 (dd, 8.0 and 1.2
7.55
7.1 and 1.2
8.0 and 7.1
4.9 and 0.8
13C NMR (100
144.14, 135.37, 132.43, 132.33, 130.53. 129.17, 127.60. 126.70, 125.05. 123.94;
6.58
4.9 and 3.5 Hz, 2H). 6.43 (dd, 3.5 and 0.8
[electron impact
145-146
292
6.
NMR (400
CDC13) 7.93 (dd, 8.2 and 1.3 Hz,
7.62 (dd,
7.03
6.41 (d.
7.2 and 1.3
7.53 (dd, 8.2 and 7.2 Hz,
7.15 (dd, 5.1 and 1.1
6.71 3.7 Hz,
(dd, 3.6 and 1.1 Hz,
6.96 (dd, 5.1 and 3.6 Hz,
3.7
NMR (100
CDC13) 143.37, 137.59, 136.13, 135.46, 132.17,
131.62, 130.70, 129.53, 128.58, 127.62, 125.17, 124.08, 123.80, 123.38;
456
7.63
3.7
(M+).
7.
172
(decomp.);
NMR (400
7.54 (dd, 8.5 and 7.0 Hz,
7.02 3.7 Hz,
CDC13) 7.94 (dd, 8.5 and 1.2
7.17 (dd, 5.0 and 1.1
6.96-6.93 6.72
(dd, 7.0 and 1.2 I-Ix,
7.08 (dd, 3.8 and 1.1
NMR (100 MHz, CDC13) 143.64, 137.26, 136.38.
136.11, 135.98, 135.47, 132.18, 131.74, 130.73, 129.65, 128.70, 127.79, 125.21,
123.91, 123.74, 123.51; (El) 620
(a) House, H. 0.; Bashe, II. R. W.
Campbell, W. J. ibid., 1815.
9. Clough, R. L.; and Roberts, J. D. Am.
Hz,
6.43
3.7 I-Ix,
8.
Org. Chem.,
784. (b) House, H. 0.;
1018.
10. X-Ray single crystal structure analysis of 3 performed by Professor Ohba’s group of Keio
University shows that the approximately parallel planes of the two thiophene units are at an angle
of approximately
to the plane of the naphthalene ring.
11.
is known to be a nearly planar molecule in the crystalline state; van
Bolhuis, F.; Wynberg. H.;
E. E.; Meijer, E. W.; Stating, E. G. J. Synthetic
1989.30, 381.
12. (a)
R. J.;
J.;
A. F.
185.
1459. (b) Yumoto, Y.;
Yoshimura, S.
(Received in Japan 10 August 1992)