Synthesis of some new electron π-donors containing methoxy groups

Article abstract of DOI:10.1515/znb-2004-0716

The synthesis of some new electron π-donors carrying four or two methoxy groups is described. The precursor 5,6-dimethoxy-5,6-dihydro[1,3]dithiolo[4,5- b] [1,4]dithiin-2-thione was synthesized and by coupling reactions the symmetrical 5,6,5′,6′-tetramethoxy-5,6,5′,6′-tetrahydro- [2,2′]bi[[1,3]dithiolo[4,5-b][1,4]dithiinylidene] and unsymmetrical 5,6-dimethoxy-5,6,5′,6′-tetrahydro-[2,2′]bi[[1,3]-dithiolo[4, 5-[1,4]dithiinylidene], 2-(5,6-dimethoxy-5,6-dihydro-[1,3]dithiolo[4,5-b][1,4] dithiin-2-ylidene)-5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]-dioxine and (5,6-dimethoxy-5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]dithiin-2-ylidene)-6, 7-dihydro-5H-[1,3]dithiolo[4,5-6][1,4]dithiepine donors were prepared. They have been characterized spectroscopically and their redox potentials determined using cyclic voltammetry.

Full text of DOI:10.1515/znb-2004-0716

Note
839
metallic behavior down to liquid helium temperatures,
as well as superconducting salts with Cu2(NCS)−3 [5]
and ReO−4 [6]. The main advantages of the BEDO-
TTF molecule are the high solubility and the CH—
O type hydrogen bonding. To develop new oxygen–
based donors, TTF derivatives substituted with ethoxy,
methoxy, ethylenedioxy and ethylenethioxy groups
have been prepared so far.
In our search for new π-donors we introduced
methoxy groups into the 5,6,5’,6’ positions of the
BEDT-TTF skeleton in order to allow interactions by
hydrogen bonding and to increase the solubility. We
prepared also some unsymmetrical donors with two
methoxy groups. In this paper we describe the synthe-
sis and physical studies of some new symmetrical and
unsymmetrical π-donors with methoxy groups. The
method is a general route for the preparation of many
TTF derivatives with methoxy groups.
Synthesis of Some New Electron
π-Donors Containing Methoxy Groups
G. A. Mousdisa, G. C. Papavassilioua, N. Psaroudakisb,
and G. C. Anyfantisa,b
a National Hellenic Research Foundation, 48,
Vassileos Constantinou Ave., Athens, GR 116-35, Greece
University of Athens, Chemistry Department,
b
University Campus, Athens, GR 157-71, Greece
Reprint requests to Dr. G. A. Mousdis. Fax: 30210-7273794.
E-mail: gmousdis@eie.gr
Z. Naturforsch. 59b, 839 – 841 (2004);
received January 30, 2004
The synthesis of some new electron π-donors carrying
four or two methoxy groups is described. The precursor
5,6-dimethoxy-5,6-dihydro[1,3]dithiolo[4,5-b] [1,4]dithiin-
2-thione was synthesized and by coupling reactions the
symmetrical
5,6,5’,6’-tetramethoxy-5,6,5’,6’-tetrahydro-
[2,2’]bi[[1,3]dithiolo[4,5-b][1,4]dithiinylidene] and unsym-
metrical 5,6-dimethoxy-5,6,5’,6’-tetrahydro-[2,2’]bi[[1,3]-
dithiolo[4,5–[1,4]dithiinylidene], 2-(5,6-dimethoxy-5,6-di-
hydro-[1,3]dithiolo[4,5-b][1,4]dithiin-2-ylidene)-5,6-dihy-
dro-[1,3]dithiolo[4,5-b][1,4]-dioxine and (5,6-dimethoxy-
5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]dithiin-2-ylidene)-6,7-
dihydro–5H–[1,3]dithiolo[4,5-b][1,4]dithiepine donors were
prepared. They have been characterized spectroscopically
and their redox potentials determined using cyclic voltam-
metry.
Results and Discussion
The new series of tetrahetero-TTF donors 5a – c
and 7 reported here shows at least one 1,2-bis(meth-
oxy)ethane-1,2-diyl bridge between sulfur atoms out-
side the TTF nucleus. Their synthesis is described
in Scheme 1. The starting material 1,2-dichloro-1,2-
dimethoxyethane was prepared by chlorination of gly-
oxal with SOCl2 in methanol and separated from the
by-products by distillation [7].
Key words: π-Donors, Tetrathiafulvalenes,
Cyclic Voltammetry
Introduction
Since the discovery of the first organic metal TTF-
TCNQ in 1972 [1], the synthesis of new π-donors
based on tetrathiafulvalene and its derivatives re-
mained at the forefront of research in the field of
organic metals [2]. Up to now a large number of
TTF and TSF derivatives have been synthesized, that
gave a plethora of organic conductors and some
superconductors [2]. Among them, the most attrac-
tive are bis(ethylene-dithio)-tetrathiafulvalene BEDT-
TTF, which holds the record among the organic su-
perconductors regarding the transition temperature
[3], and bis(ethylenedioxy)-tetrathiafulvalene (BEDO-
TTF) [4]. BEDO-TTF is an oxygen analogue of BEDT-
TTF and has afforded a great number of salts with a
Scheme 1.
c
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840
Note
Table 1. Redox potentials of the new donors 5a – c, 7 and 6a.
the glyoxal, cooled with an ice-salt bath, and 24 ml of SOCl2
was added dropwise so that the inside temperature did not
exceed 5 ◦C. After 50% of SOCl2 had been added a vigorous
gas evolution started and the reaction became endothermic.
At this moment the cooling bath was replaced by a heating
bath and the rest of SOCl2 was added faster keeping the in-
side temperature at 20 – 30 ◦C. The procedure took place in
Compound
BEDT-TTF (6a)
E1∗ (V)
0.48
0.55
0.54
0.47
0.53
E2∗ (V)
0.89
0.96
0.96
0.89
0.97
E2 −E1 (V)
0.41
7
5a
5b
0.41
0.42
0.42
0.44
5c
∗
vs SCE, 1.0 mM solutions in CH2Cl2 with 0.1 M Bu4NPF6; scan 3 h. The solution was stirred overnight. The excess of SOCl2
rate 100 mV/s.
and the solvent were evaporated under vacuum. Our product
was purified by distillation under reduced pressure (19 Torr)
◦
at 78 – 80 ◦C (lit. 79 C [7]). The product, when placed in a
The nucleophilic displacement reaction of 2 [8] with
1 in one step using dry THF as solvent gave thione 3
in a 88% yield. The same product was obtained by the
reaction of (Bu4N)2[Zn(dmit)2] (dmit = 1, 3-dithiol-2-
thione-4, 5-dithiolate) with 1 but the yield was lower
than 50%.
refrigerator, crystallized as transparent crystals (18.0 g, yield
68%), m.p. 72 ◦C. – 1H NMR (300 MHz, CDCl3): δ = 5.45
(s, 1H, CHCl), 3.55 (s, 3H, OMe).
Compound 3 was prepared as follows: To a solution of
2.4 g (10 mmol) of 2 [8] in 50 ml of CH3CN a solution of
1.58 g (10 mmol) of 1 in 10 ml of CH3CN was added. The
mixture was stirred for 15 min under N2 at room tempera-
ture. During this time the color changed from red to orange-
yellow. The mixture was filtered. The filtrate was evaporated
in vacuo and the residue was purified by column chromatog-
raphy on SiO2 with CH2Cl2 as eluent to give 3 (2.2 g, yield
Coupling reaction of thione 3 in dry benzene with an
excess of triethyl phosphite gave alkene 7. The prod-
uct was purified by column chromatography on silica
gel with CH2Cl2 as eluent. Coupling reactions of the
thione 3 with ketones 4a, 4b, 4c in benzene with an ex-
cess of triethyl phosphite gave a mixture of symmetri-
cal and unsymmetrical π-donors. The mixture was sep-
arated by column chromatography. The donors can be
obtained also by the use of the corresponding thiones
instead of ketones but the yields are lower. By this
method we can prepare many TTF derivatives with
methoxy groups, using thiones or ketones similar to 4.
As expected, the cyclovoltammograms of the new
donors exhibit two 1e− reversible oxidation peaks cor-
responding to the successive generation of the radi-
cal cation and the dication (Table 1). The MeO group
increases the redox potentials, but they are compara-
ble with those of BEDT-TTF indicating that the new
donors are suitable for the preparation of conducting
radical cation salts.
◦
88%) as a yellow solid, m.p. 123 C. – UV/vis (CH2Cl2):
λ
max1(lgε) = 403 nm (4.12), λmax2(lgε) = 273 nm (3.88). –
1H NMR (300 MHz, CDCl3): δ = 3.58 (s, 6H, 2 OMe) and
5.32 (s, 2H, 2 OCH). – C7H8O2S5 (284.3): calcd. C 29.56,
H 2.83; found C 29.42, H 2.81.
Compounds 5a, 5b, 5c were prepared as follows: A
mixture of 3 (300 mg, 1.05 mmol), and 4a or 4b or 4c
(1.05 mmol) and triethyl phosphite (2 ml, 12 mmol) was re-
fluxed in 10 ml of dry benzene for 4 h. The mixture was
evaporated in vacuo and the residue was purified by col-
umn chromatography on SiO2 with CH2Cl2 as eluent. The
first fraction contained 6, the second 5a or 5b or 5c, and
the third 7. Physico-chemical data for 5a: yellow-orange
crystals, 13% yield, m.p. 180 – 181 ◦C. – UV/vis (CH2Cl2):
λmax1(lgε) = 346 nm (4.05), λmax2(lgε) = 318 nm (4.18). –
1H NMR (300 MHz, CDCl3): δ = 3.55 (s, 6H, 2 OMe), 3.29
(s, 4H, 2 SCH2) and 5.23 (s, 2H, 2 CH). – C12H12O2S8
(444.5): calcd. C 32.41, H 2.72; found C 32.22, H 2.92.
Physico-chemical data for 5b: orange crystals, 10% yield,
m.p. 179 ◦C. – UV/vis (CH2Cl2): λmax1(lgε) = 350 nm
(4.26), λmax2(lgε) = 323 nm (4.51), λmax3(lgε) = 310 nm
(4.46). – 1H NMR (300 MHz, CDCl3): δ = 3.54 (s, 6H,
2 OMe), 4.25 (s, 4H, 2 CH2) and 5.22 (s, 2H, 2 CH). –
C12H12O4S6 (412.6): calcd. C 34.93, H 2.93; found C 34.81,
H 2.93. Physico-chemical data for 5c: orange crystals, 21%
The electron donating properties of these new
donors were tested by preparing conducting radical
cation salts with I3− and PF−6 . The properties of these
salts and others with different anions will be reported
elsewhere.
Experimental Section
Compound 2 was prepared by methods reported in [8].
Compound 1 was prepared by a method similar to that re- yield, m.p. 187 – 188 ◦C. – UV/vis (CH2Cl2): λmax1(lgε) =
ported in [7], as follows: A mixture of 9.6 g (165 mmol) of 346 nm (3.93), λmax2(lgε) = 318 nm (4.14). – 1H NMR
glyoxal, 13 ml of anhydrous MeOH and 1 ml of SOCl2 were (300 MHz, CDCl3): δ = 2.40 (m, 2H, CH2), 2.69 (m, 4H,
introduced in a three-necked flask, equipped with a ther- 2 CH2), 3.54 (s, 6H, 2 OMe), and 5.22 (s, 2H, 2 CH). –
mometer, a pressure equalizing dropping funnel and a con- C13H14O2S8 (458.8): calcd. C 34.03, H 3.08; found C 34.11,
denser with a CaCl2 tube. The mixture was heated to dissolve H 2.99.
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Note
841
Compound 7 was prepared as follows: A mixture of 3 C14H16O4S8 (504.8): calcd. C 33.31, H 3.19; found C 33.45,
(300 mg, 1.05 mmol) and triethyl phosphite (2 ml, 12 mmol) H 3.08.
was refluxed in 10 ml of dry benzene for 4 h. The mix-
ture was evaporated in vacuo and the residue was purified
Acknowledgements
by column chromatography on SiO2 with CH2Cl2 as elu-
Partial support of this work through the project “Excellence
in the Research Institutes supervised by the General Secre-
tariat for Research and Technology/ Ministry of Develop-
ment in Greece” (Project Code 64769) is gratefully aknowl-
edged.
ent to give 7 as orange-yellow crystals, 60% yield, m.p.
◦
186 – 187 C. – UV/vis (CH2Cl2): λmax1(lgε) = 339 nm
(4.13), λmax2(lgε) = 311 nm (4.17). – 1H NMR (300 MHz,
CDCl3): δ = 3.56 (s, 12H, 4 OMe) and 5.23 (s, 4H, 4 CH). –
Strioby Crouch, W. K. Kwok, J. E. Chirber, D. L.
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