Synthesis and electrochemical studies of tetrathiafulvalene derivatives (TTF's) as redox active ligands

Article abstract of DOI:10.1002/jhet.5570390413

A simple route for synthesis of new tetrathiafulvalene dimethyl ester (TTF-DME) is reported. The tetrathifulvalene dimethylester (TTF-DME) has been prepared by introducing an ester coordination function as a bifunctional new donor. The redox behavior of t

Full text of DOI:10.1002/jhet.5570390413

Jul-Aug 2002
Synthesis and Electrochemical Studies of Tetrathiafulvalene
Derivatives (TTF's) as Redox Active Ligands
691
Abd El-Wareth A. O. Sarhan*, Makoto Murakami and Taeko Izumi
Department of Chemistry and Chemical Engineering
Faculty of Engineering, Yamagata University, 3-16 Jonan 4-Chome
Yonezawa 992-8510, Japan
Received September 10, 2001
A simple route for synthesis of new tetrathiafulvalene dimethyl ester (TTF-DME) is reported. The
tetrathifulvalene dimethylester (TTF-DME) has been prepared by introducing an ester coordination function
as a bifunctional new donor. The redox behavior of the TTF-DME was investigated in comparison to the
well-known dibenzotetrathiafulvene (DB-TTF) by cyclic voltammetry. A two-electron redox behavior was
observed as a two waves.
J. Heterocyclic Chem., 39, 691 (2002).
Since the discovery of the conducting properties of the
study of the electrochemical behavior in comparison with
the well-known dibenzotetrathiafulvene (DB-TTF) donor
11. We report the synthesis of the first example of TTF
substituted by two carboxylate coordination functions.
Introducing of two carboxylate esters into the TTF core
was also described. Methyl phenylpropiolate 4 was
obtained (40.5% yield) via reaction of phenyl acetylene 3
with methyl chloroformate in the presence of sodium
metal as shown in Scheme 1.
tetrathiafulvalene and its derivatives it has become a sub-
ject of great interest for electrochemical studies [1].
Chemical modifications of the tetrathiafulvenes (TTF's)
framework have been added to improve their electrical
conductance properties. Several tetrathiafulvalenes TTF's
were previously prepared via one step reaction with differ-
ent yields [2].
Bis-(ethylenedithio)tetrathiafulvalene (BEDT-TTF) (1)
has been widely used for the preparation of different
organic superconductors [3]. TTF's containing two or more
fused or covalently attached TTF's units have been also
used for preparing super conducting salts [4].
Scheme 1
Recently, Martin Bryce et al. reported the synthesis of a
crown-annulated derivative of TTF (2) as a redox active
ligand system [5]. The preparation of modified TTF's has
focused on dimeric TTF units [6], for example bis-TTF's,
higher oligomers [7] as well as polymers [8] and den-
drimers [9]. In addition, intensive studies on TTF deriva-
tives having more than one TTF unit with quinonoid struc-
ture as a conjugated spacer have been reported [10-13].
Tetrathiafulvalene substituted by coordination functions
such as dithiolene or phosphine ligands, which are not the
only ligands showing chelating ability towards various
transition metals have been described [14]. β-Diketones
and their enolate ions also show powerful chelating prop-
erties and form complexes with transition metals and main
group elements [15]. Tetrathifulvalenes substituted with
two electron-withdrawing ester groups are therefore per-
haps potential ligands, which can be involved in the forma-
tion of organic-inorganic materials [16].
The synthetic strategy described by Benitez and
Grunwell for the preparation of 1,3-dithiole-2-thione
derivative 5a [17] was adapted for compound 5b as shown
in Scheme 1. Treatment of Phenyl acetylene 3 or related
ester 4 with carbon disulfide at 140 °C using an autoclave
in the presence of bis-morphiline disulfide gave the corre-
sponding 1,3-dithiole-2-thione derivatives 5a-b as shown
in Scheme 1.
1,3-Dithiole-2-thiones 5a-b were refluxed with
trimethylphosphite for 5 hours to afford a mixture of cis-
trans isomers of the corresponding TTF's 6a-b and 7a-b, in
addition to the formation of 2-dimethoxyphosphinyl-1,3-
dithioles (8a-b) in relatively good yield [18], Scheme 2.
Results and Discussions.
In this work we focused on synthesis of tetrathiafulva-
lene TTF with appropriate coordination functions and

692
A. A. O. Sarhan, M. Murakami and T. Izumi
Vol. 39
Scheme 2
Chart 2
Electrochemistry.
The redox behavior of diphenyltetrathiafulvene (DPh-
TTF 6a), tetrathifulvalene dimethylester (TTF-DME 7a)
and DB-TTF 11 was investigated by cyclicvoltammetry
and the results are listed in Table 1. As usually observed
for TTF's, these derivative exhibit two reversible mono-
electronic waves. One can see that the presence of the two
electron withdrawing groups (ester groups) slightly
decrease the donor ability of the TTF-DME compound 7a
compared with the DPh-TTF 6a and DB-TTF 11. The
The tetrathiafulvalenes 6a-b and 7a-b obtained were a
mixture of cis-trans isomers in a ratio of (86:14) and
(55:45) respectively ( HNMR analysis), Chart 1. The cis-
isomers 6a and 7a could only be obtained as single isomers
by column chromatography using silica gel (hexane/chlo-
roform 2:1) and used for cyclic voltammetric studies.
Furthermore, the trans-isomers 6b and 7b could not be
obtained as single isomers.
1
1/2
value of ∆E decreases in the direction of DB-TTF 11 >
DPh-TTF 6a > TTF-DME 7a suggesting that the intramol-
ecular Columbic repulsion energy decrease in this series.
DPh-TTF 6a
TTF-DME 7a
DB-TTF 11
12
10
8
Chart 1
6
4
2
0
-2
-4
-6
-8
Formation of cis-trans isomers in this reaction was
expected and this presumably involves initial thiophilic
addition of trialkyl phosphite to the thione, to give the 1,3-
dipolar intermediate 9. Reaction of 9 with further thione
leads to the intermediate 10, which is easily rationalized to
the cis-trans isomers 6a-b and 7a-b following the estab-
lished mechanism of this reaction [18], Scheme 3.
0
200
400
600
800
1000
1200
1400
E mV vs. Ag/AgCl
Figure 1. Cyclic volatmmogram of DPh-TTF 6a TTF-DME 7a, and DB-
-5
TTF 11 in CH Cl on a platinum electrode, concentration of (4.0x10 M).
Scan rate 200 mVs , base-electrolyte TBAP 0.1 M.
Scheme 3
2
2
-1
Table 1
Cyclic Voltammetry Data, of TTF's 6a, 7a and 11 in CH Cl on a
Platinum Electrode, Concentration of (4.0x10 M), Scan rate 200mVs ,
Base-Electrolyte TBAP 0.1 M
2
2
-5
-1
1/2
1/2
1/2
TTF
E
(1)/V
E
(2)/V
∆E /V
DB-TTF 11
DPh--TTF 6a
TTF-DME 7a
7.79
4.21
4.91
11.72
6.04
6.53
2.94
1.83
1.62
As shown in Figure 2, increasing the scan rate from 20
-1
-1
mVs to 400 mVs leads to the increasing of the oxida-
tion potential wave. Compounds 6a and 7a also showed
some common features depending on the scan rates effect.
The DB-TTF 11 was prepared according to the method
previously described [19] for comparison study of the
electrochemical behavior using the cyclicvoltammetry
spectra with the synthesized TTF's. Attempts are now
underway to synthesize the tetrazafulvalenes (TAF) 12 for
a comparison study of the electrochemical properties of
both DTF's, TTF's and TAF, Chart 2.
In CH Cl on a Pt electrode and at ambient temperature
the TTF 6a and 7a showed two oxidation waves at peak
potentials of 550 mV, 979 mV for 6a, and 763 mV, 1108
mV for 7a at scans rates 200 mVs . For 6a and 7a, such a
2
2
-1

Jul-Aug 2002
Synthesis and Electrochemical Studies of Tetrathiafulvalene Derivatives
693
FAB-MS spectra were obtained using a JEOL JMS-AX505HA
(Nihon Denshi Ltd, 3-1-2, Musashino, Akishima-shi, Tokyo,
Japan). Cyclic voltammetry was measured on a cyclic voltammo-
gram spectrometer (Model CS-1090/Model CS-1087, Cypress
System Inc., Lawrence, Kansas, USA). Column chromatography
was performed on silica gel 60 (230-400 Mesh ASTM). Solvents
were distilled before use. 4-Phenyl-1,3-dithiole-2-thione (5a) was
obtained according to the reported method as yellow crystals in
44% yield, mp 117-118 °C, lit. 117-118 °C [17].
process is electrochemically reversible or quasi-reversible
1
2
1
(∆Ep 85 mV and ∆Ep 97 mV) for 6a and (∆Ep 90 mV
2
2
and ∆Ep 92 mV) for 7a respectively. The ∆Ep was also
observed with the increase of scan rate from 20 mV to 400
-1
mVs at ambient temperature as shown in Figure 2.
10
8
6
Methyl phenylpropiolate (4).
4
2
A mixture of phenyl acetylene (3; 1.02 g, 10.0 mmol) and sodium
metal (0.26 g, 11.3 mmol) was stirred at room temperature for one
hour. The sodium acetylide thus formed is dissolved in ether (25 ml)
and methyl chloroformate (1.0 ml) in ether (10 ml) was added drop
wise with stirring over a period of 15 minutes. The reaction mixture
is stirred at room temperature for further 5 hours. The ether is
removed under vacuum and the residue washed with water, the dark
brown oil thus formed is extracted by ether and dried over sodium
sulfate. The reaction mixture is filtered off and chromatographed on
silica gel using hexane/ethyl acetate mixture (10:3) to give 0.630 g
of yellow oil of the corresponding methyl phenylpropiolate (4) in
40.5% yield; ir (neat) ν 3023w, 2952m, 2225m, 1712s, 1596w,
0
-2
-4
-6
0
200
400
600
800
1000
1200
1400
E / mV vs. Ag/AgCl
Figure 2. Cyclic volatmmogram of TTF-DME 7a in CH Cl on a plat-
inum electrode, concentration of (4.0x10 M). Scan rate 20 ~ 400 mVs ,
base-electrolyte TBAP 0.1 M.
2
2
-5
-1
-1
1
1496s, 1434s, 1288s, 1201s, 1170s, 757s, 688s cm ; H nmr
Conclusion.
(CDCl ): δ 7.6-7.5 (dd, J = 8 Hz, J = 1 Hz, 2H, aromatic-H), 7.4 (m,
3
+
3H, aromatic-H), 3.84 (s, 3H, OCH ); ms: m/z 160 (M ).
The TTF's 6a, 7a and 11 were synthesized using the
methods described in this text and their structures were
confirmed by spectral analyses. The electrochemical
behaviors of these compounds were studied using cyclic
voltammetry at ambient temperature on a Pt working elec-
trode, using TBAP as the supporting electrolyte. The CV
3
4-Methoxycarbonyl-5-phenyl-1,3-dithiole-2-thione (5b).
Following the method reported in reference [17], a mixture of
methyl phenylpropiolate (4; 2.73 g, 17 mmol) and bis-morphiline
disulfide (1.0 g, 4.0 mmol) in a 4:1 molar ratio was dissolved in 75
ml of CS , and the resulting solution was poured in a one liter Parr
2
exhibited good donor properties, showing a two-electron
bomb reactor (autoclave). The apparatus was flushed with N and
2
2+
heated to 140 °C for 24 hours. The Pressure was raised to 140 psi.
After cooling, the apparatus was opened, the brown solution was
transferred to a round-bottom flask, and the excess carbon disulfide
was removed under vacuum. The dark residue was chromatographed
on silica gel using hexane/chloroform as an eluent to give in the sec-
ond fractions the 4-methoxycarbonyl-5-phenyl-1,3-dithiole-2-thione
(5b) as yellow crystals, 1.3 g, 28.4% yield, mp. 87-89 °C; ir (KBr): ν
3060m, 3027m, 2962s, 1727s, 1577m, 1544s, 1488s, 1434s, 1268s,
quazireversible oxidation wave to the dications TTF
.
The oxidation potential values, and in a larger extent the
reduction potential values processes, are strongly influ-
enced by the scan rates. A two-electron redox behavior
was observed as two waves. The advantage of introducing
the electron-withdrawing ester substituents into the donor
7a is that ester group raises the oxidation potentials rela-
tive to TTF [20].
-1 1
1211s, 1083s, 761s, 732s cm ; H nmr (CDCl ): δ 7.4 (m, 5H, aro-
3
+
matic-H), 3.7 (s, 3H, OCH ); ms: m/z 268 (M ).
3
Considering the fact that these donors contain two simi-
lar types of donor moieties, it was important to determine
the oxidation/reduction process by changing the scan rates.
Thereby a double two-electron oxidation process encoun-
tered quasireversible process in CH Cl as a solvent.
Synthesis of Tetrathiafulvalenes (TTF-DME) 7a-b and 2-
Dimethoxyphosphinyl-1,3-dithiole derivatives (8b).
A sample of 5b (0.2 g, 0.74 mmol) was refluxed in
trimethylphosphite (3.0 ml) for 2 hours. The reaction mixture
was cooled, diluted with methanol and kept over night at room
temperature. The brown crystals thus formed, were collected by
filtration to give 36 mg, 10% yield of cis-trans isomers of TTF-
2
2
EXPERIMENTAL
+
DME 7a-b (M = 472). The residue was concentrated under vac-
uum and chromatographed on silica gel, hexane/chloroform 1:1
to give 8b as brown yellow oil, 95 mg 37% yield, M = 346.
Melting points were recorded on a Gallencamp melting point
apparatus and are uncorrected. Infrared spectra (IR) were mea-
sured on a Hitachi 260-10 spectrometer (Hitachi Ltd, 1-5-1,
Marunouchi, Chiyod-ku, Tokyo, Japan). HNMR and CNMR
spectra were recorded at room temperature on INOVA-Varian
Nuclear Magnetic Resonance Spectrometer (500 MHz). Chemical
shifts are denoted in δ units (ppm), relative to tetramethylsilane
+
cis-trans-Tetrathiafulvalenes (7a-b).
1
13
Compounds 7a-b have ir (KBr): ν 1722s, 1637s, 1556m,
-1
1
1430m, 1257s, 1203s, 1058w, 738s, 688s cm ; H nmr (CDCl ,
3
500 MHz): δ 7.41-7.39 (m, 10H, aromatic-H), 3.67 (s, 6H,
13
(TMS) as internal standard, J values are given in Hz. CDCl is
OCH ), 3.65 (s, OCH ); C nmr (CDCl , 125 MHz): δ 159.82
3
3
3
3
used as a deuterated solvent unless otherwise stated. MS and
(CO, ester), 148.67, 148.29 (C-4), 131.22, 129.89, 129.87,

694
Vol. 39
A. A. O. Sarhan, M. Murakami and T. Izumi
71516, Egypt.
[1] J. L. Segura and N. Martin, Angew. Chem. Int. Ed. Engl., 40,
1372 (2001).
128.99, 128.96, 128.28 (aromatic-C), 119.96, 119.60 (C-5),
+
108.57, 108.40 (C=C), 52.43 (OCH ); ms: m/z 472 (M ).
3
cis-Tetrathiafulvalene (TTF-DME 7a).
[2a] G. Coustumer and Y. Moller, J. Chem. Soc. Chem. Commun.,
38 (1980); [b] Z. Yoshida, T. Kawase, H. Awaji, I. Sugimoto, T. Sugimoto
and S. Yoneda, Tetrahedron Lett., 24, 3469 (1983); [c] A. Khanous, A.
Gorgues and M. Jubault, Synth. Metals, 41-43, 2327 (1991).
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A. J. Shultz, U. Geiser, K. D. Carlson, A. M. .Kini, H. H.Wang, W. K.
Kwow, M. H. Whango and J. E. Schirber, Science, 252, 1501 (1991).
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Misaki, T. Ohta, N. Higuchi, H. Fujiwara, T. Yamabe, T. Mori, H. Mori
and S. Tanaka, J. Mater. Chem., 5, 570 (1995).
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Howard, M. Kamenjicki, I. K. Lednev and S. A. Asher, Chem. Commun.,
295 (2000).
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[7] J. Becher, J. Lau and P. Mork, Oligotetrathiafulvalenes. In The
Oligomer Approach, K. Müullen and G. Vegner, 1998, Ed., Wiley-VCH:
Weinheim.
Compound 7a has ir (KBr): ν 1722s, 1637s, 1556m, 1430m,
-1
1
1257s, 1203s, 1058w, 738s, 688s cm ; H nmr (CDCl , 500
3
MHz): δ 7.41-7.39 (m, 10H, aromatic-H), 3.65 (s, 6H, OCH );
3
+
ms: m/z 472 (M ).
4-Methoxycarbonyl-5-phenyl-2-dimethoxyphosphinyl-1,3-
dithiole (8b).
Compound 8b has ir (neat): 3056w, 2954s, 2925s, 2854s,
-1
1731s, 1563m, 1461s, 1376s, 1294s, 1259s, 1039s, 755m cm ;
1
H nmr (CDCl , 500 MHz): δ 7.39-7.35 (m, 5H, aromatic-H),
3
4.82-4.81 (d, J = 5Hz, 1H, CH-2
), 3.96-3.76 (m, 2 OCH
AB system
3
13
and 1H, CH-2
) 3.62 (s, 3H, OCH ); C nmr (CDCl ,
AB system
3
3
125 MHz): δ 160.84 (CO, ester), 147.22 (C-4), 131.11, 129.82,
129.11, 128.18 (aromatic-C), 117.11 (C-5), 55.03, 54.38 (2
+
OCH ), 52.2 (OCH ), 41.68 (PCH-2); ms: m/z 346 (M ).
3
3
Synthesis of Tetrathiafulvalenes (DPh-TTF) 6a-b and 2-
Dimethoxyphosphinyl-1,3-dithiole derivatives (8a).
[8] J. Roncali, J. Mater. Chem., 7, 2307 (1997).
[9] M. R. Bryce, W. Devonport, L. M. Goldenberg and Ch. Wang,
Chem. Commun., 945 (1998).
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62, 870 (1997).
[11] C. Boulle, O. Desmars, N. Gautier, P. Hudhomme, M. Carion
and A. Gorges, Chem. Commun., 2197 (1998).
According to the method described for synthesis of TTF-DME
7a-b and 1,3-dithiole derivative 8b, the DPh-TTF 6a-b and 8a
were obtained after chromatography using silica gel
(hexane/chloroform 1:1) in 26% and 35.9% respectively
cis-trans-Tetrathiafulvalenes (DPh-TTF) 6a-b.
[12] I. Pérez, S. Liu, N. Martin and L. Echegoyen, J. Org. Chem.,
65, 3796 (2000).
[13] A. A. O. Sarhan, M. Murakami and T. Izumi, Monatsh.
Chem., In Press --- (2002).
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Trans., 1309 (2000); [b] M. Fourmigué and P. Batail, Bull. Chim. Fr., 129,
29 (1992); [c] M. Fourmigué, and Y. S. Huang, Organometallics, 12, 797
(1993); [d] M. Fourmigué, C. E. Uzelmeier, K. Boubekeur, S. L. Bartley
and K. R. Dunbar, J. Organomet. Chem., 529, 343 (1997); [e] G. Schukat
and E. Fanghanel, Sulfur Reports, 18, 1 (1996); [f] P. Pellon, E. Brulé, N.
Bellec, K. Chamontin and D. Lorcy, J. Chem. Soc., Perkin Trans. 1, 4409
(2000).
Compounds 6a-b were obtained in 26% yield (40 mg), mp
206-208 °C, Lit [2a], mp 208 °C; ir (KBr): ν 1590m, 1565s,
1548s, 1488s, 1440s, 1250m, 1205m, 1031m, 921s, 823s, 738s,
-1 1
698s cm ; H nmr (CDCl , 500 MHz): δ 7.43-7.25 (m, 10H, aro-
3
13
matic-H), 6.55 (s, 2H, trans-CH-5), 6.52 (s, 2H, cis-CH-5);
C
nmr (CDCl , 125 MHz): δ 136.10 (C-4), 132.47, 128.96 (aro-
3
matic-C), 128.47, 126.28 (aromatic-CH), 113.37, 113.30 (C=C),
+
110.52 (CH-5); FAB-ms: m/z 356 (M ).
cis-Tetrathifulvalenes (DPh-TTF) (6a).
[15] A. R. Siedle In Comprehensive Coordination Chemistry; G.
Wilkinson, R. D. Gillard and J. A. McCleverty, Eds. Diketone and
Related Ligands. Pergamon Press: Oxford, 1987, Vol. 2, pp. 365-412.
[16a] N. Bellec and D. Lorcy, Tetrahedron Lett., 42, 3189 (2001);
[b] H. Tanaka, Y. Okano, H. Kobayashi, W. Suzuki and A. Kobayashi,
Science, 291, 285 (2001).
[17] F. M. Benitez and J. R. Grunwell, J. Org. Chem., 43, 2917
(1978); [b] D. Leaver, W. A. H. Robertson and D. M. Mckinnon, J. Chem.
Soc., 5104 (1962).
1
Compound 6a has H nmr (CDCl , 500 MHz): δ 7.43-7.29 (m,
3
10H, aromatic-H), 6.52 (s, 2H, CH-5 and CH-5').
4-Phenyl-2-dimethoxyphosphinyl-1,3-dithiole (8a).
Compound 8a was obtained in 35.9% yield (250 mg), mp 85-
87 °C, Lit. mp 87-88 °C[21]; ir (KBr): 3054w, 2950m, 2850w,
1560m, 1462s, 1372s, 1290s, 1251s, 1064s, 1037s, 746s, 665s
-1
1
cm ; H nmr (CDCl , 500 MHz): δ 7.40-7.31 (m, 5H, aromatic-
3
[18a] R. P. Parg, J. D. Kilburn and T. G. Ryan, Synthesis, 195
(1994); [b] G., Scherowsky and J. Weiland, Chem. Ber., 107, 3155
(1974); [c] M. Narita, C. U. Pittman, Jr., Synthesis, 489 (1976).
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Nielsen, N. Thorup and J. Becher, J. Org. Chem., 65, 5794 (2000); [c] K.
Lerstrup, D. Talham, A. Bloch and D. Cowan, J. Chem. Soc., Chem.
Commun., 336 (1982).
H), 6.23 (s, 1H, CH-5), 5.06-5.05 (d, J = 4.5 Hz, CH-2), 3.91 (s,
3H, OCH ), 3.89 (s, 3H, OCH ).
3
3
Acknowledgment.
This work was partially supported by a Grant-Aid for
Scientific Research No. 12650844 from the Ministry of
Education, Sciences, Sports and Culture (Japan).
[20a] D. C. Green, J. Org. Chem., 44, 1476 (1979); [b] A. S.
Batsanov, M. R. Bryce, J. N. Heaton, A. J. Moore, P. J. Skabara, J. A. K.
Howard, E. Ortí, P. M. Veruella, and R. Veruella, J. Mater. Chem., 5, 1689
(1995).
REFERENCES AND NOTES
*
E-mail: elwareth@acc.aun.eun.eg; Permanent Address:
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51, 2674 (1978).
Chemistry Department, Faculty of science, Assiut University, Assiut