Low Oxidation Potential Tetrathiafulvalene Analogues Based on 3,4-Dialkoxythiophene π-Conjugating Spacers

Article abstract of DOI:10.1021/jo981312b

Tetrathiafulvalene analogues involving dihexyloxythiophene (1), ethylenedioxythiophene (2), and bis(3,4-dihexyloxy-2-thienyl)ethylene (3) as conjugating spacer and diversely substituted at the 1,3-dithiole ring (R) have been synthesized. Electronic absorption spectra show the expected decrease of HOMO-LUMO gap when increasing the electron-releasing power of R or the length of the conjugating spacer. Cyclic voltammetry (CV) shows that whereas compounds 1 and 2 are reversibly oxidized into their cation radical and dication through two one-electron steps, for compounds 3 the dication is formed directly via a two-electron transfer. Comparison of the data for compounds 2 and 3 with those of their respective analogues based on thiophene and dithienylethylene shows that introduction of the electron-donating alkoxy groups at the 3 and 4 positions of the thiophene ring produces a 150-200 mV negative shift of the first redox potential (E°₁). On the other hand, CV data for compounds 1 and 2 reveal several unusual features such as E°₁ ≈ 0.10 V/SCE ranking among the lowest known to date and a Coulombic repulsion between positive charges in the dication larger than for the analogue π-donors based on unsubstituted thiophene. These results are interpreted by a major reorganization of the electronic distribution in the donor molecule due to alkoxy groups: the highest electron density moving from the 1,3-dithiole moiety toward the central thiophene ring.

Full text of DOI:10.1021/jo981312b

J . Org. Chem. 1999, 64, 4267-4272
4267
Low Oxid a tion P oten tia l Tetr a th ia fu lva len e An a logu es Ba sed on
3,4-Dia lk oxyth iop h en e π-Con ju ga tin g Sp a cer s
Said Akoudad, Pierre Fre`re, Nicolas Mercier, and J ean Roncali*,†
Inge´nierie Mole´culaire et Mate´riaux Organiques, CNRS UMR 6501, Universite´ d’Angers, 2 Bd Lavoisier,
49045 Angers Cedex, France
Received J uly 6, 1998
Tetrathiafulvalene analogues involving dihexyloxythiophene (1), ethylenedioxythiophene (2), and
bis(3,4-dihexyloxy-2-thienyl)ethylene (3) as conjugating spacer and diversely substituted at the
1,3-dithiole ring (R) have been synthesized. Electronic absorption spectra show the expected decrease
of HOMO-LUMO gap when increasing the electron-releasing power of R or the length of the
conjugating spacer. Cyclic voltammetry (CV) shows that whereas compounds 1 and 2 are reversibly
oxidized into their cation radical and dication through two one-electron steps, for compounds 3 the
dication is formed directly via a two-electron transfer. Comparison of the data for compounds 2
and 3 with those of their respective analogues based on thiophene and dithienylethylene shows
that introduction of the electron-donating alkoxy groups at the 3 and 4 positions of the thiophene
ring produces a 150-200 mV negative shift of the first redox potential (E°1). On the other hand,
CV data for compounds 1 and 2 reveal several unusual features such as E°1 ≈ 0.10 V/SCE ranking
among the lowest known to date and a Coulombic repulsion between positive charges in the dication
larger than for the analogue π-donors based on unsubstituted thiophene. These results are
interpreted by a major reorganization of the electronic distribution in the donor molecule due to
alkoxy groups: the highest electron density moving from the 1,3-dithiole moiety toward the central
thiophene ring.
In tr od u ction
lengthening of the spacer group, these compounds appear
more and more as end-capped conjugated oligomers in
which the HOMO energy level is raised by the electron-
releasing effect of the end 1,4-dithiafulvenyl groups
(DTF). As shown by many of the above examples, such
compounds in which the intrinsic properties of the
conjugating spacer are somewhat exalted represent
interesting models for analyzing the relative efficiency
of various structures of π-conjugating spacers as electron
relay.
While a major trend involves the lengthening of a
π-conjugating spacer of known structure such as poly-
enes10 or polythienylenevinylenes,8,11 we have recently
shown that rigidification of a simple dithienylethylene
spacer produces significant changes in the electrochemi-
cal behavior of the derived TTF analogues due to a
reorganization of the electronic distribution in both the
neutral and oxidized state.12 As a further step we report
here the synthesis of new series of TTF analogues built
Linearly extended tetrathiafulvalene (TTF) analogues
built by insertion of a π-conjugating spacer between two
1,4-dithiafulvenyl groups have been subject to intensive
studies over the past few years.1 Interest in these systems
was initially motivated by the increased dimensionality
and hence improved charge transport properties expected
for the corresponding cation radical salts in the general
frame of the chemistry of extended TTF analogues.2
However, more recent work has shown that these hybrid
π-conjugated systems are also potentially interesting as
small gap organic semiconductors3 or as building blocks
for push-pull or push-push chromophores for second-
or third-order nonlinear optics.4 While the first examples
of such π-conjugated systems were built around olefinic5
or simple heterocyclic systems such as furan, thiophene,
or pyrrole,6 extended TTF analogues involving oligomers
of the thiophene,7 thienylenevinylene,8 or furylenevi-
nylene9 series have been recently described. With the
(7) (a) Roncali, J .; Giffard, M.; Fre`re, P.; J ubault, M.; Gorgues, A.
J . Chem. Soc., Chem. Commun. 1993, 689. (b) Roncali, J .; Rasmussen,
L.; Thobie-Gautier, C.; Fre`re P.; Brisset, H.; Salle´, M.; Becher, J .;
Simonsen, O.; Hansen, T. K.; Benahmed-Gasmi, A.; Orduna, J .; Garin,
J .; J ubault, M.;. Gorgues, A. Adv. Mater. 1994, 6, 841.
(8) (a) Elandaloussi, E.; Fre`re, P.; Roncali, J .; Richomme, P.; J ubault,
M.; Gorgues, A. Adv. Mater. 1995, 7, 390. (b) Elandaloussi, E.; Fre`re,
P.; Roncali, J . Tetrahedron Lett. 1996, 37, 6121.
(9) (a) Elandaloussi, E.; Fre`re, P.; Benahmed-Gasmi, A.; Riou, A.;
Gorgues, A.; Roncali, J . J . Mater. Chem. 1996, 6, 1859. (b) Benahmed-
Gasmi, A.; Fre`re, P.; Elandaloussi, E.; Roncali, J .; Orduna, J .; Garin,
J .; J ubault, M.; Riou, A.; Gorgues, A. Chem. Mater. 1996, 8, 2291.
(10) (a) Nguyen, T. T.; Gouriou, Salle´, M.; Fre´re, P.; J ubault, M.;
Gorgues, A.; Toupet, L.; Riou, A. Bull. Soc. Chim. Fr. 1996, 133, 301.
(b) Ma¨rkl, G.; Po¨ll, A.; Aschenbrenner, G.; Schmaus, C.; Troll, T.;
Kreitmeier, P.; No¨th, H.; Schmidt, M. Helv. Chim. Acta 1996, 79, 1497.
(11) J estin, I.; Fre`re, P.; Levillain, E.; Roncali, J . Adv. Mater. 1999,
11, 134.
† e-mail: jean.roncali@univ-angers.fr.
(1) Roncali, J . J . Mater. Chem. 1997, 7, 2307.
(2) (a) Bryce, M. R. J . Mater. Chem. 1995, 5, 1481. (b) Adam, M.;
Mu¨llen, K. Adv. Mater. 1994, 6, 439. (c) Schukat G.; Fangha¨nel, E.
Sulfur Rep. 1996, 18, 1. Garin, J . Adv. Heterocycl. Chem. 1995, 62,
249. Misaki, Y.; Higuchi, N.; Fujiwara, H.; Yamabe, T.; Mori, T.; Mori,
H.; Tanaka, S. Angew. Chem., Int. Ed. Engl. 1995, 34, 1222
(3) Brisset, H.; Thobie-Gautier, C.; J ubault, M.; Gorgues, A.; Roncali,
J . J . Chem. Soc., Chem. Commun. 1994, 1765.
(4) (a) Rao, V. P.; J en, K.-Y.; Wong, K. Y.; Drost, K. J . Tetrahedron
Lett. 1993, 34, 1747. (b) Scho¨bert, U.; Salbeck, J .; Daub, J . Adv. Mater.
1992, 4, 41. (c) Sylla, M.; Zaremba, J .; Chevalier, R.; Rivoire, G.;
Khanous, A.; Gorgues, A. Synth. Met. 1993, 59, 111.
(5) Sugimoto, T.; Awaji, H.; Sugimoto, I.; Misaki, Y.; Kawase, T.;
Yoneda, S.; Yoshida, Z. Chem. Mater. 1989, 1, 535.
(6) (a) Hansen, T. K.; Lakshmikantam, M. V.; Cava, M. P.; Niziurski-
Mann, R. E.; J ensen, F.; Becher, J . J . Am. Chem. Soc. 1992, 114, 5035.
(b) Benahmed-Gasmi, A.; Fre`re, P.; Garrigues, B.; Gorgues, A.; J ubault,
M.; Carlier, R.; Texier, F. Tetrahedron Lett. 1992, 33, 6457.
(12) Brisset, H.; Le Moustarder, S.; Blanchard, P.; Illien, B.; Riou,
A.; Orduna, J .; Garin, J .; Roncali, J . J . Mater. Chem. 1997, 7, 2027.
10.1021/jo981312b CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/15/1999

4268 J . Org. Chem., Vol. 64, No. 12, 1999
Akoudad et al.
Ch a r t 1
Sch em e 1a
around π-conjugating spacers bearing dialkoxy electron-
releasing substituents such as 3,4-dihexyloxythiophene
(1a -c), 3,4-ethylenedioxythiophene (2a -c), and bis(3,4-
dihexyloxy-2-thienyl)ethylene (3a -c) (Chart 1). Charac-
terization of the structure and electronic properties of
these compounds by X-ray diffraction, UV-vis spectros-
copy, and cyclic voltammetry shows that the introduction
of alkoxy groups on the thiophenic spacer leads to new
π-donors with original electronic properties.
Resu lts a n d Discu ssion
The synthesis of the new compounds is depicted in
Scheme 1.
a
(a) C6H13Br, K2CO3, (b) NaOH, H2O, EtOH, (c) Cu2O, ∆, (d)
3,4-Dihydroxythiophene (4) prepared by the Hinsberg
method13 was reacted with 1-bromohexane in the pres-
ence of K2CO3 to give 2,5-dicarboethoxy-3,4-dihexyloxy-
thiophene (5) in 82% yield. Saponification of 5 with
NaOH and acidification afforded 2,5-dicarboxy-3,4-di-
hexyloxythiophene (6) in 78% yield. 3,4-Dihexyloxy-
thiophene (7a ) was then obtained in 78% yield by
decarboxylation of 6 in the presence of Cu2O. Vilsmeier
formylation of 7a afforded the monoaldehyde 7b in 92%
yield, while dialdehyde 7c was prepared in 58% yield by
reaction of DMF on the dilithiated derivative of 7a .
McMurry dimerization14 of monoaldehyde 7b gave (E)-
1,2-bis[2-(3,4-dihexyloxythienyl)]ethylene (8a ) in 72%
yield. This compound was then converted into the cor-
responding dicarbaldehyde (8b) by dilithiation and reac-
tion with DMF (yield 66%). 3,4-Ethylenedioxy-2,5-
thiophenedicarbaldehyde (9b) was prepared from 3,4-
ethylenedioxythiophene (9a ) (Bayer) by reaction of DMF
on the dilithiated derivative obtained using an excess of
t-BuOK and n-BuLi.
POCl3/DMF, CH2Cl2, (e) n-BuLi/DMF, TMEDA/hexane, (f) TiCl4/
Zn/pyridine/THF (g) n-BuLi, (h) n-BuLi, t-BuOK/LiBr, DMF/THF.
All target donor molecules 1-3a -c have been synthe-
sized by double Wittig (a ) or Wittig-Horner (b,c) olefi-
nation of the appropriate dicarbaldehyde using the
already described procedures and reagents.6-9,15
Monocrystals of 2a have been obtained by slow evapo-
ration of a CHCl3 solution. The X-ray structure was
determined from two independent molecules of donor and
one molecule of solvent. As shown by the side view in
Figure 1, the π-conjugated system in the molecule adopts
a planar conformation. For each molecule, the distance
between the sulfur atom of thiophene and those of the
1,4-dithiafulvenyl groups (3.074 and 3.122 Å) are inter-
mediate between twice the van der Waals radius of sulfur
(3.70 Å) and a covalent S-S bond (2.04 Å). These short
distances are characteristic of the strong 1-5 S- - -S
(15) (a) Akiba, K.; Ishikawa, K.; Inasoto, N. Bull. Chem. Soc. J pn.
1978, 51, 2674. (b) Hansen, T. K.; Lakshmikantham, M. V.; Cava, M.
P.; Metzger, R. M.; Becher, J . J . Org. Chem. 1991, 56, 2720. (c) Moore,
A. J .; Bryce, M. R.; Ando, D. T.; Hursthouse, M. B. J . Chem. Soc., Chem.
Commun. 1991, 320.
(13) Hinsberg, O. Ber. 1910, 43, 901.
(14) McMurry, J . E. Chem. Rev. 1989, 89, 1513.

Low Oxidation Potential Tetrathiafulvalene Analogues
J . Org. Chem., Vol. 64, No. 12, 1999 4269
F igu r e 1. ORTEP view of compound 2a .
Ta ble 1. UV-Vis Sp ectr oscop ic Da ta for Com p ou n d s
1-3a -c in Meth ylen e Ch lor id e
compd
λmax (nm)
λ0-0 (nm)
log ꢀmax
∆E (eV)
1a
1b
1c
2a
2b
2c
3a
3b
3c
421
440
442
427
446
446
484
492
505
446
465
471
449
474
476
511
528
537
4.68
4.73
4.68
4.43
4.44
4.43
4.64
4.67
4.61
2.77
2.66
2.62
2.75
2.61
2.60
2.42
2.34
2.30
intramolecular interactions that contribute to stabilize
the δ-syn conformation of both for the neutral and
oxidized states of TTF analogues containing thiophene
or furan spacers.7b,9a,12,16
Table 1 lists the main UV-vis spectral data for
compounds 1-3a -c in CH2Cl2. As for previous series of
extended TTF analogues, the various substituents (R)
attached at the DTF moiety have been selected in order
to analyze the effects of substitution on the electronic
properties of the π-conjugated system.6-9
F igu r e 2. Electronic absorption spectra recorded in methyl-
ene chloride: (top) 2a , (middle) 2b, (bottom) 2c.
of the absorption bands, the relative intensity of the low
energy absorption band increases with electron-donating
effect of R, i.e., in the order R ) CO2Me, SMe, n-propyl
(Figure 2).
For each type of spacer, the absorption maximum (λmax
)
shifts bathochromically when the electron-releasing effect
of R increases, i.e., in the order CO2Me, SMe, and
n-propyl, as already observed for other series of TTF
analogues.6-9 Comparison of the values of the HOMO-
LUMO energy gap (∆E) on the basis of the maximum of
the transition of lowest energy (λ0-0) shows that the effect
of R is roughly independent of the structure of the spacer.
Thus, substitution of the CO2Me group by the n-propyl
one produces in every case a 0.12-0.15 eV decrease of
∆E, changes which are comparable to those observed for
other donors with spacers of different structure.6-9
Comparison of the UV-vis spectra of compounds 2
shows that in addition to the above-discussed red shifts
This enhancement of the resolution of the vibronic fine
structure suggests a parallel increase of the rigidity of
the molecule. In fact, it has been shown that the strength
of the 1-5 intramolecular interactions depends on the
electronic effect of R.16 The fact that this effect is less
apparent in the spectra of compounds 3 (not shown) could
be related to the larger degree of freedom of the molecule
allowed by the central double bond. Further comparison
of the data for compounds 1-3 shows, as expected, that
for compounds of series 3 the extension of the conjugating
spacer produces a bathochromic shift of the absorption
bands and a ca. 0.30 eV decrease of ∆E.
(16) (a) Hansen, T. K.; Bryce, M. R.; Howard, J . A. K.; Uffit, D. S.
J . Org. Chem. 1994, 59, 5324. (b) Elandaloussi, E.; Fre`re, P.; Riou, A.;
Roncali, J . New J . Chem. 1998, 1051. (c) Favard, J . F.; Fre`re, P.; Riou,
A.; Benahmed-Gasmi, A.; Gorgues, A.; J ubault, M.; Roncali, J . J . Mater.
Chem. 1998, 8, 363.
Cyclic Volt a m m et r y. Table 2 lists the main cyclic
voltammetric (CV) data for compounds 1-3 in CH2Cl2.
The CVs of compounds 1 and 2 exhibit two reversible one-

4270 J . Org. Chem., Vol. 64, No. 12, 1999
Akoudad et al.
Ta ble 2. Cyclic Volta m m etr ic Da ta for Com p ou n d s
1-3a -c (ca . 5 × 10-4 M in 0.10 M Bu 4NP F 6-CH2Cl2)a
compd
E°1 (V)
E°2 (V)
E°3
E°2 - E°1
1a
1b
1c
0.55
0.34
0.12
0.65
0.46
0.49
0.30
0.08
0.49
0.31
0.18
0.79
0.51
0.35
0.84
0.62
0.78
0.51
0.35
0.23
0.17
0.23
0.19
0.16
0.29
0.21
0.27
10a b
10bb
2a
2b
2c
3a
3b
1.58
1.30
1.40
3c
a
b
Pt electrodes, ref SCE, scan rate 100 mV s-1
.
From ref 8a.
F igu r e 4. Cyclic voltammogram of compound 3a ca. 5 × 10-4
M in 0.10 M Bu4NPF6/CH2Cl2. Pt electrodes, ref SCE, v ) 50
mV s-1
.
reach 0.10 V, which is among the lowest redox potentials
ever reported for TTF analogues.2b In fact under the same
conditions TTF shows E°1 and E°2 values of 0.40 and 0.80
V vs SCE. Furthermore, it is worth noting that until now
such low redox potentials have been reached at the price
of a considerable spatial extension of the analogue TTF
molecule.17
Comparison of the CV data for compounds 1 and 2 with
those of the parent donors based on unsubstituted
thiophene (10) shows that although compounds 1 and 2
have lower E°1 and E°2 values, they exhibit potential
differences E°2 - E°1 slightly larger than those for
compounds 10, thus indicating a larger Coulombic repul-
sion between positive charges in the dication. Since the
extent of the π-conjugated system is similar for com-
pounds 1, 2, and 10, this larger Coulombic repulsion
suggests that the distances between the maximum
density of positive charges in the dicationic state are
smaller in compounds 1 and 2 than in compound 10.
Previous theoretical works on extended TTF analogues
have shown that the end DTF groups bear the highest
HOMO coefficients in the ground state and the highest
density of positive charge in the cationic state.5,12 These
conclusions have been confirmed by recent X-ray data.16c
However, a recent study of extended TTFs based on
dithienylethylene (DTE) spacers has demonstrated that
the covalent bridging the DTE spacer produces a negative
shift of E°1 associated with an increase of Coulombic
repulsion. Theoretical calculations have shown that for
bridged compounds the highest HOMO coefficients in the
ground state and the highest density of positive charges
F igu r e 3. Cyclic voltammogram of compound 1c ca. 5 × 10-4
M in 0.10 M Bu4NPF6/CH2Cl2. Pt electrodes, ref SCE, v ) 50
mV s-1
.
electron oxidation steps which correspond to the succes-
sive generation of the cation radical and dication (Figure
3).
For compounds of series 1 and 2 the two redox
potentials E°1 and E°2 undergo a 0.40-0.45 V negative
shift when increasing the electron-donating effect of R,
as observed for other series of extended TTFs.7-9,12 For
compounds 3 E°1 decreases according to the same se-
quence; however, the smaller negative shifts observed
when changing R in this case could be related to the fact
that the first oxidation step corresponds to the direct
formation of the dication through a two-electron transfer.
Furthermore, a third redox system corresponding to the
formation of the trication radical is observed in this case
(Figure 4).
While the electrochemical properties of compounds 3
are qualitatively similar to those of other series of
extended TTF analogues, those of compounds 1 and 2
present some unusual and interesting features. Thus, the
combined effects of the alkoxy substituent at the 3,4-
positions of the thiophene ring and of the n-propyl chains
on the DTF moieties allow the 1c and 2c E°1 values to
(17) Belyasmine, A.; Fre`re, P.; Gorgues, A.; J ubault, M.; Duguay,
G.; Hudhomme, P.; Tetrahedron Lett. 1993, 34, 4008. Salle´, M.; J ubault,
M.; Gorgues, A.; Boubekeur, K.; Fourmigue´, M.; Batail, P.; Canadell,
E. Chem. Mater. 1993, 5, 1196.

Low Oxidation Potential Tetrathiafulvalene Analogues
J . Org. Chem., Vol. 64, No. 12, 1999 4271
with water and the organic phase is dried over MgSO4.
Evaporation of the excess of 1-bromohexane leaves 20.15 g
(82%) of crude product which can be directly used for the next
step: 1H NMR (CDCl3) δ ppm 4.30 (m, 4H), 4.14 (t, 4H), 2.00-
1.53 (m, 8H), 0.8 (t, 6H); 13C NMR (CDCl3) 148.2, 112.1, 71.47,
33.5, 25.4, 14.2.
in the dication are homogeneously delocalized over the
whole molecule, in sharp contrast with the unbridged
compounds.12
The similarity of the electrochemical behavior of these
bridged compounds with that of the new donors 1 and 2
suggests that substitution of thiophene by dialkoxy
groups produces a major reorganization of the electronic
distribution of the molecule; the highest densities of
positive charges in the dication which are essentially
localized on the DTF groups in compounds 10,16c move
toward the middle of the molecule, thus leading to an
increased Coulombic repulsion.
2,5-Dica r boxy-3,4-d ih exyloxyth iop h en e (6). A mixture
of compound 5 (76.2 g, 0.178 mol), 145 mL of 10% NaOH, and
120 mL of ethanol is refluxed for 2 h. After cooling to room
temperature water is added and hydrochloric acid (25%) is
added until precipitation occurs. The product is dried by
1
filtration to give 51.4 g (78%) of a white compound: H NMR
(CDCl3) δ ppm 13.0 (s, 2H), 4.1 (t, 4H), 2.0-1.5 (m, 8H), 0.8
(t, 6H); 13C NMR (CDCl3) 148.2, 112.2, 71.5, 33.5, 25.4, 14.
3,4-Dih exyloxyth iop h en e (7a ). A mixture of 30 g of
compound 6 and 1 g of Cu2O is introduced in a round-bottom
flak equipped with a distillation apparatus. The mixture is
heated gently until ca. 2 L of CO2 is recovered and then
Preliminary attempts to electrocrystallize cation radi-
cal salts of compounds 1b and 2b have remained unsuc-
cessful, and further experiments are in progress. How-
ever, to gain some information on the electrical properties
of these compounds, the four-probe conductivity of a
compacted pellet of compound 1a has been measured
distilled under reduced pressure to give 17.86 g (78%) of the
1
title compound: Eb(0.19
154 °C; H NMR δ (ppm, CDCl3)
mbar):
6.16 (s, 2H), 4.00 (t, 4H), 1.98-1.4 (m, 16H), 0.96 (t, 6H); 13C
NMR 147.46, 96.69, 70.47, 31.51, 28.92, 25.58, 22.53, 13.97;
MS (EI) 284 (M+•, 100%). Anal. (Calcd) C 67.56 (67.60), H 9.86
(9.92), S 11.11 (11.27).
after iodine doping, giving a value of 5 × 10-3 S cm-1
.
Con clu sion
3,4-Dih exyloxyth iop h en e-2-ca r ba ld eh yd e (7b). A mix-
ture of 8 g (28.2 mmol) of compound 7a and 4.47 mL of DMF
(56.4 mmol) in 100 mL of dichloroethane is cooled to 0 °C,
POCl3 (4.31 mL, 45 mmol) is slowly added, and the solution is
refluxed for 2 h. After cooling to room temperature 250 mL of
1 M aqueous sodium acetate is introduced and the mixture is
stirred for 30 min and extracted with methylene chloride. The
organic phase is washed with water and dried (MgSO4).
Evaporation of the solvent and column chromatography (silica
gel, 1:1 CH2Cl2/petroleum ether) gave 8.1 g (92%) of a yellow
oil: 1H NMR (CDCl3) 10.0 (s, 1H), 7.11 (s, 1H), 4.25-3.96 (2t,
4H), 1.96-0.7 (m, 22H); 13C NMR 182.0, 147.5, 98.2, 70.5, 31.5,
29.1, 25.7, 22.6, 14.0; MS (EI) 312 (M+ 100%).
3,4-Dih exyloxyth iop h en e-2,5-d ica r ba ld eh yd e (7c). To
a solution of 5.5 g (19 mmol) of compound 7a and 3.85 mL (20
mmol) of TMEDA in 10 mL of hexane is added 15.88 mL of
n-BuLi (1.6 M in hexanes) under an inert atmosphere, and
the mixture is refluxed for 30 min. After cooling to room
temperature THF (30 mL) is added, the mixture is cooled to
-40 °C, and 2.47 mL (32 mmol) of DMF is added dropwise.
The solution is allowed to warm to room temperature, poured
into 300 mL of 0.5 M aqueous HCl, and stirred vigorously for
15 min. After neutralization with 0.5 M NaHCO3, the aqueous
phase is extracted with diethyl ether, the organic phase is
washed with water and dried (MgSO4), and the solvent is
evaporated. Column chromatography (silica gel, CH2Cl2/
petroleum ether 2:3) gave 3.8 g (58%) of the target compound
as an orange oil: 1H NMR (CDCl3) 10.2 (s, 1H), 4.25-3.96 (2t,
4H), 1.97-0.7 (m, 22H); 13C NMR 182.0, 147.6, 97.2, 71.5, 31.5,
25.7, 22.6, 14.0; MS (EI) 340 (M+ 100%).
TTF analogues built around π-conjugating spacers
based on 3,4-dialkoxythiophenes have been synthesized.
The electron-releasing effect of the dialkoxy groups
contribute to strongly enhancing the π-donor properties
of the system, allowing for oxidation potentials lower
than 0.10 V, which are among the lowest reported so far
for TTF-based π-electron donors. On the other hand, the
increase of the Coulombic repulsion in the dication
suggests that the dialkoxy groups induce a major reor-
ganization of the electronic distribution in the molecule.
While a detailed understanding of this unusual behavior
requires further experimental and theoretical work, these
results show that TTF analogues with strong π-donor
ability can be reached at the cost of a limited spatial
extension of the molecule.
Exp er im en ta l Section
X-r a y Str u ctu r a l An a lysis. Cr ysta l Da ta for 2a . The
structure of C45S10O20Cl3H37 (Mw ) 1324.78) is triclinic P-1, Z
) 2, a ) 12.921(3) Å, b ) 15.164(3) Å, c ) 15.767(3) Å, R )
109.82(2)°, â ) 97.41(2)°, γ ) 101.13(3)°, V ) 2788(1) Å3,
calculated density 1.58 g cm-3
.
A single crystal of the title compound was selected by optical
examination, and X-ray diffraction data were collected at 293
K on an Enraf Nonius MACH3 four-circle diffractometer. The
crystal cell was obtained from a set of 25 reflections randomly
found in the 10-16° θ range; 9676 reflections were collected
by the ω scan technique in the 2-25° θ range (λMo KR ) 0.71069,
h 0,15; k -18,18; l -18,18)). A total of 5913 independent
reflections (R ) 0.018) with I/σ(I) > 3 were available for
structure refinement. A starting set of non-hydrogen atomic
coordinates was obtained from the direct methods (SIR). Two
independent C22S5O10H18 molecules were found in the struc-
ture, as a consequence of one well-ordered CHCl3 solvent
molecule. Refinement of structure did not allow for location
of hydrogen atoms which were then fixed at 0.95 Å from carbon
atoms (Hydro program). Finally, refinement of all non-H
atomic coordinates and anisotropic thermal factors led to R )
0.052, Rw ) 0.075 (use of F magnitude, 703 parameters for
5913 reflections). All calculations were performed using the
MolEN package.
(E)-1,2-Bis[2-(3,4-dih exyloxyth ien yl)]eth ylen e (8a). TiCl4
(5.27 mL, 46 mmol) and 6.3 g of Zn (96 mmol) are added
portionwise to 100 mL of dry THF at 0 °C under an inert
atmosphere, and the mixture is refluxed for 30 min. After
cooling to 0 °C, a solution consisting of 7.49 g (24 mmol) of
aldehyde 7b and 5 mL of pyridine in 20 mL of THF is slowly
added. The mixture is refluxed for 2 h and allowed to cool to
room temperature. After addition of ice and 100 mL of CH2-
Cl2, the mixture is stirred for 15 min and filtrated over
hyflosupercel. The solution is washed with dilute HCl and then
with water to neutrality and dried over Na2SO4. Column
chromatography (silica gel, CH2Cl2/petroleum ether 1:1) and
recrystallization in methanol give 5.37 g (76%) of the target
1
compound: mp 86 °C; H NMR (CDCl3) 6.96 (s, 2H), 5.99 (s,
2H), 4.05 (t, 4H), 3.94 (t, 4H), 1.78-1.30 (m, 32H), 0.93-0.90
(m, 12H); 13C NMR (CDCl3) 150.4, 143.95, 125.08, 116.86,
93.92, 69.88, 31.62, 31.47, 29.99, 29.07, 25.74, 22.63, 14.04;
MS (EI) 592 (M+ 100%). Anal. (Calcd) C 68.25 (68.87), H 9.52
(9.52), O 10.98 (10.79), S 10.86 (10.81).
Syn th esis. 2,5-Dicarboethoxy-3,4-dihydroxythiophene (4)
was prepared according to the Hinsberg method.13
2,5-Dica r boeth oxy-3,4-d ih exyloxyth iop h en e (5). A mix-
ture of 15 g of compound 4, 16 g (2 equiv) of K2CO3, and 178
mL (22 equiv) of 1-bromohexane is heated at 110-120 °C for
30 h. After cooling to room temperature the solution is washed
(E)-1,2-Bis(5-for m yl-3,4-d ih e xyloxy-2-t h ie n yl)e t h yl-
en e (8b). Compound 8a (1.7 g, 2.86 mmol) is dissolved in 25

4272 J . Org. Chem., Vol. 64, No. 12, 1999
Akoudad et al.
mL of dry ether, and the solution is cooled to 0 °C. After
dropwise addition of 4.47 mL (7.15 mmol) of n-BuLi (1.6 M in
hexanes), the solution is stirred for 15 min and DMF (0.7 mL
13.4 mmol) is added. The mixture is allowed to warm to room
temperature, aqueous NH4Cl is added, and the solution is
extracted with ether. The organic phase is dried (Na2SO4), and
the solvent is evaporated to leave a brown solid. Recrystalli-
zation in methanol gives 1.22 g (66%) of an orange powder:
dark red solid; mp 162 °C; 1H NMR (CDCl3) 6.59 (s, 2H), 4.22
(s, 4H), 3.88-3.85 (2s, 12H); 13C NMR 159.0, 136.4, 131.2,
130.79, 105.20, 64.82, 53.37; UV-vis (λmax nm, log ꢀ) 427, 4.43;
MS (EI) 602 (M+, 100%); HRMS calcd for C22H18O10S5 601.9503
found 601.9513.
2,5-Bis[4,5-b is(m e t h ylsu lfa n yl)-2H -1,3-d it h iol-2-yli-
den em eth yl]-3,4-eth ylen edioxyth ioph en e 2b: red oil, yield
27%; 1H NMR (CDCl3) 6.61 (s, 2H), 4.21 (s, 4H), 246-243 (2s,
12H); 13C NMR 136.26, 128.32, 125.18, 104.85, 64.82, 19.24,
18.95; UV-vis (λmax nm, log ꢀ) 446, 4.44; MS (EI) 554 (M+,
100%); HRMS calcd for C18H18O2S9 553.8793, found 553.8773.
1
mp 81 °C; H NMR (CDCl3) 9.98 (s, 2H), 7.19 (s, 2H), 4.31 (t,
4H), 4.00 (t, 4H), 1.85-1.24 (m, 32H), 0.91 (t, 12H); 13C NMR
(CDCl3) 180.87, 156.66, 147.32, 135.11, 122.68, 119.84, 31.54,
31.44, 29.91, 25.58, 22.59, 14.00; IR (KBr) 1667 (CdO); MS
(EI) 648 (M+, 100%).
2,5-Bis[4,5-b is(n -p r op yl)-2H -1,3-d it h iol-2-ylid en em e-
th yl]-3,4-eth ylen ed ioxyth iop h en e 2c: red oil, yield 50%; 1H
NMR (CDCl3 6.60 (s, 2H), 4.2 (s, 4H), 2.56-2.25 (m, 8H), 1.69-
1.50 (m, 8H), 0.98-0.75 (m, 12H); 13C NMR 135.28, 127.94,
127.33, 101.85, 64.81, 31.93, 31.79, 30.56, 23.57, 22.20, 15.24,
14.63, 13.79, 13.60, 13.52; UV-vis (λmax nm, log ꢀ) 446, 4.43;
MS (EI) 538 (M+, 100%); HRMS calcd for C26H34O2S5 538.1162,
found 538.1152.
3,4-Eth ylen ed ioxy-2,5-th iop h en ed ica r ba ld eh yd e (9b).
Under an inert atmosphere ethylenedioxythiophene (1.4 g 10
mmol) and t-BuOK (3.36 g 30 mmol) are added to in 30 mL of
dry THF under stirring. The mixture is cooled to -90 °C, and
12 mL (30 mmol) of n-BuLi (1.6 M in hexanes) is added
dropwise. The mixture is stirred for 30 min, LiBr (2.61 g, 30
mmol) is slowly added, and the solution is stirred for another
30 min before the slow addition of 50 mL of DMF. The mixture
is allowed to warm to room temperature, hydrolyzed with 3 N
aqueous HCl, and extracted with CH2Cl2. The organic phase
is washed with 1 M NaHCO3 and water and dried over Na2-
SO4. After solvent removal the crude solid is chromatographed
(silica gel, CH2Cl2/petroleum ether 3:2) to give 50 mg of
starting compound, 0.4 g of monoaldehyde, and 0.4 g (26%) of
the desired dialdehyde: mp 155 °C; 1H NMR (CDCl3) 10.2 (s,
2H), 4.31 (t, 4H); 13C NMR 180.87, 142.10, 110.25, 67; MS (EI)
316 (M+ 100%).
1,2-Bis{5-[4,5-b is(m et h oxyca r b on yl)-2H -1,3-d it h iol-2-
yliden em eth yl]-2-(3,4-dih exyloxy)th ien yl}eth en e 3a: yield
41%, red solid; mp 105 °C; 1H NMR (CDCl3) 6.99-6.98 (2s,
2H), 6.62 (s, 2H), 4.08 (q, 8H), 3.88-3.87 (2s, 12H), 1.70 (m,
16H), 1.05 (2s, 12H); 13C NMR 160.18, 159.72, 146.97, 145.11,
132.10, 130.13, 126.37, 125.28, 115.93, 106.09, 53.45, 53.02,
31.59, 29.92, 25.63, 25.60, 22.62, 14.03; UV-vis (λmax nm, log
ꢀ) 484, 4.64; (MS EI) 1052 (M+, 100%); HRMS calcd for
C
50H68O12S6 1052.3035, found 1052.3065.
1,2-Bis{5-[4,5-b is(m e t h ylsu lfa n yl)-2H -1,3-d it h iol-2-
2,5-Bis[4,5-b is(m e t h oxyca r b on yl)-2H -1,3-d it h iol-2-
ylid en em eth yl]-3,4-d ih exyloxyth iop h en e 1a : yield 90%,
ylid en em eth yl]-2-(3,4-d ih exyloxy)th ien yl}eth en e 3b: red
oil, yield 33%; 1H NMR (CDCl3) 6.96 (s, 2H), 6.69 (s, 2H), 4.11-
3.93 (m, 8H), 2.70-2.11(m, 12H), 1.97-0.85 (m, 44H); 13C NMR
146.88, 144.46, 128.45, 127.99, 125.56, 124.64, 122.01, 115.64,
105.52, 74.00, 54.76, 54.65, 42.81, 40.47, 31.62, 29.92, 25.64,
19.23, 14.09, 14.04; UV-vis (λmax nm, log ꢀ) 492, 4.67; MS (EI)
1004 (M+, 100%); HRMS calcd for C46H68O4S10 1004.2324,
found 1004.2333.
1
dark red solid; mp 89 °C; H NMR (CDCl3) 6.64 (s, 2H), 3.96
(t, 4H), 3.88-3.85 (2s, 12H), 1.91-1.15 (m, 16H) 0.8 (t, 6H);
13C NMR 160.07, 159.98, 144.74, 130.88, 126.17, 122.52,
105.98, 74.05, 53.37, 31.53, 29.85, 29.66, 25.57, 22.59, 14.00;
UV-vis (λmax nm, log ꢀ) 421, 4.68; MS (EI) 744 (M+, 100%);
HRMS calcd for C32H40O10S5 744.1225, found 744.1225.
2,5-Bis[4,5-b is(m e t h ylsu lfa n yl)-2H -1,3-d it h iol-2-yli-
1
1,2-Bis{5-[4,5-b is(n -p r op yl)-2H -1,3-d it h iol-2-ylid en e-
m et h yl]-2-(3,4-d ih exyloxy)-t h ien yl}et h en e 3c: red oil,
d en em eth yl]-3,4-d ih exyloxyth iop h en e 1b: yield 84%; H
NMR (CDCl3) 6.69 (s, 2H), 3.97 (t, 4H), 2.58-2.26 (m, 12H),
1.80-0.77 (m, 22H); 13C NMR 144.16, 128.32, 127.48, 122.62,
105.61, 3.56, 29.91, 22.60, 19.23, 14.03; UV-vis (λmax nm, log
ꢀ) 440, 4.73; MS (EI) 696 (M+, 100%); HRMS calcd for
1
yield 67%; H NMR (CDCl3) 6.96 (s, 2H), 6.69 (s, 2H), 4.15-
3.95 (m, 8H), 2.58-2.43 (m, 8H), 1.69-1.5 (m,8H), 1.8-1.2 (m,
32H), 1.10-0.75 (m, 24H); 13C NMR 146.69, 143.52, 131.34,
128.42, 127.55, 123.52, 123.17, 115.29, 102.49, 73.89, 31.62,
31.60, 30.7, 29.9, 25.65, 23.15, 23.0, 22.6, 22.5, 14.05, 14.02;
UV-vis (λmax nm, log ꢀ) 505, 4.61; MS (EI) 989 (M+, 100%);
HRMS calcd for C54H84O4S6 988.4693, found 988.4673.
C
28H40O2S9 696.0531, found 696.0531.
2,5-Bis[4,5-b is(n -p r op yl)-2H -1,3-d it h iol-2-ylid en em e-
th yl]-3,4-d ih exyloxyth iop h en e 1c: yield 87%; 1H NMR
(CDCl3) 6.66 (s, 2H), 3.97 (t, 4H), 2.58-2.43 (m, 8H), 1.69-
1.5 (m, 8H), 1.8-1.2 (m, 16H), 1.12-0.78 (t, 18H); 13C NMR
143.18, 129.44, 128.06, 122.76, 102.69, 46.17, 31.58, 29.94,
25.63, 23.09, 22.60, 14.01; UV-vis (λmax nm, log ꢀ) 442, 4.68;
MS (EI) 680 (M+, 100%); HRMS calcd for C36H56O2S5 680.2894,
found 680.2894.
Su p p or tin g In for m a tion Ava ila ble: Tables giving posi-
tional and thermal parameters and bond distances for 2a . This
material is available free of charge via the Internet at
http://pubs.acs.org.
2,5-Bis[4,5-b is(m e t h oxyca r b on yl)-2H -1,3-d it h iol-2-
yliden em eth yl]-3,4-eth ylen edioxyth ioph en e 2a: yield 40%,
J O981312B