New redox active ligands involving a tetrathiafulvalene vinylogue backbone

Article abstract of DOI:10.1016/j.tet.2008.03.032

Two synthetic approaches towards a new bisthiopicoline substituted vinylogous tetrathiafulvalene (TTFV) are described. As evidenced by electrochemistry and ¹H NMR studies, this redox active ligand shows excellent coordinating properties towards Zn²⁺ metal ion.

Full text of DOI:10.1016/j.tet.2008.03.032

Tetrahedron 64 (2008) 5285–5290
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Tetrahedron
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New redox active ligands involving a tetrathiafulvalene vinylogue backbone
*
Michel Guerro, Ngoc Ha Pham, Julien Massue, Nathalie Bellec, Dominique Lorcy
ˆ
Sciences Chimiques de Rennes, UMR 6226 CNRS-Universite´ de Rennes 1, Campus de Beaulieu, Bat 10A, 35042 Rennes Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Two synthetic approaches towards a new bisthiopicoline substituted vinylogous tetrathiafulvalene
(TTFV) are described. As evidenced by electrochemistry and 1H NMR studies, this redox active ligand
shows excellent coordinating properties towards Zn2þ metal ion.
Received 31 January 2008
Received in revised form 5 March 2008
Accepted 11 March 2008
Available online 14 March 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Dithiafulvene
Tetrathiafulvalene vinylogue
Thiopicoline
Ligand
Redox behaviour
1. Introduction
we investigated the functionalization of each dithiole ring in order
to facilitate the complexation with one metal ion, sandwiched by
In recent years, a large amount of work has been devoted to the
search of novel hybrid organic–inorganic architectures based on
tetrathiafulvalene (TTF) due to their unique electronic properties.1
A novel trend in this research area consists in grafting various co-
ordination functions onto the TTF core, leading to numerous redox
active ligands mainly as O,2,3 S,4 N,5–8 P9,10 ligands or mixed (P,N),11
(N,S),12 (P,S)10a ligands. Among these ligands, some TTFs have been
used as redox-responsive receptors towards metal ions and have
also shown their efficiency as redox probes.4 A first p-extended TTF
framework, functionalized with binding site groups for transition
metal groups (Ni2þ, Pd2þ and Pb2þ), acting as a highly effective
redox sensor was very recently reported.13 As part of our ongoing
research, we focused on the studies of electroactive ligands based
on a tetrathiafulvalene vinylogue (TTFV) core, acting as potential
redox receptors.14 These TTFV, unlike simple TTF, exhibit different
motions upon electron transfer, depending on the structure of the
molecule,15 and we have recently shown that the complexation to
a metal ion can interfere with the electrochemically triggered
molecular movement.14 In order to further explore the intrinsic
properties of these TTFV as electroactive ligands, we have decided
to focus our attention on TTFV bearing two thiopicoline functions.
Indeed, in the TTF series, bis-substituted thiopicoline TTF
derivatives have shown their efficiency to form octahedral com-
plexes with various divalent transition metal ions.12 As the TTFV
substituted on the central conjugation are non-planar molecules,16
the two coordination functions of the same TTFV. In this paper, we
first describe two synthetic approaches to reach the target mole-
cules. Then, we present the complexation studies of the dithia-
fulvenes precursors as well as the complexation study carried out
on the TTFV in the presence of Zn2þ ions.
N
S
N
S
Me
Me
S
S
S
S
Ar = C6H5, C6H4CN
Ar
Ar
2. Results and discussion
2.1. Synthesis and redox properties of the donor molecules
TTFV can easily be synthesized from dithiafulvenes (DTF)
through their chemical oxidative coupling.16 In the literature, DTF
are generally prepared according to a Wittig17 or Wadsworth–
Emmons18 type reaction between a phosphonium or phosphonate
in basic medium with an aldehyde. The DTF 2a and 2b function-
alized by a thiopicoline group were prepared from the reaction
of the dithiolyl phosphonate anion generated by treating 1 with
n-BuLi followed by the addition of benzaldehyde or p-cyano-
benzaldehyde (Scheme 1). It can be observed on the NMR spectra
* Corresponding author. Fax: þ33 2 23 23 67 38.
E-mail address: dominique.lorcy@univ-rennes1.fr (D. Lorcy).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.03.032

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M. Guerro et al. / Tetrahedron 64 (2008) 5285–5290
N
S
N
S
N
Me
S
Me
S
Me
N
Me
S
S
S
S
i) n-BuLi, THF
i) I2
S
S
S
S
O
H
ii) Na2S2O4
H
Ar
P(O)(OEt)2
ii)
R
H
Ar
Ar
1
3a (ZZ/EE/ZE) Ar = C6H5
3b (ZZ/EE/ZE) Ar = C6H4CN
2a (Z/E) Ar = C6H5
2b (Z/E) Ar = C6H4CN
R = H, CN
Scheme 1.
that both dithiafulvenes 2a and 2b exist as Z and E isomers,
inseparable by column chromatography.
One can observe the influence of the cyano electron with-
drawing group on the oxidation potentials of the dithiafulvenes, as
for DTF 2b the Epa amounts to 0.84 V versus SCE while for the DTF
2a Epa decreases to 0.79 V versus SCE. In order to prepare quanti-
tatively the TTFV 3a and 3b, we also performed the chemical oxi-
dative coupling of 2a and 2b in the presence of iodine; the formed
dicationic species in the medium being then reduced with Na2S2O4.
Work up of the reaction leads to the neutral TTFV 3a and 3b in
rather low yields (38 and 7%, respectively) (Scheme 1). The TTFV
3a,b were obtained as a mixture of three isomers (ZZ/EE/ZE) in
a statistical ratio, as observed on 1H NMR spectra but could not be
separated by column chromatography.
We investigated the redox properties of electroactive dithia-
fulvenes 2a and 2b using cyclic voltammetry. Both voltammograms
show similar trends: at the first anodic scan, an irreversible oxi-
dation wave and upon successive scans, the appearance of a novel
reversible oxidation system at a lower oxidation potential than the
first one (Fig. 1). This behaviour indicates that a novel redox active
derivative TTFV 3 is formed upon oxidation, resulting from
the coupling of two dithiafulvene radical cations followed by the
deprotonation of the dimer.19 Upon repetitive sweeps, the intensity
of the irreversible oxidation wave decreases while the one of the
reversible system increases.
We also investigated anotherapproach to insert the coordination
function in the last synthetic step. One attractive possibility consists
in preparing a TTFV containing cyanoethylthio-protected thiolate
groups; a strategy well developed by Becher and Simonsen.20 The
thiolate can be easily deprotected in basic medium and further
alkylated with various electrophiles. Nevertheless, the synthesis of
a dithiafulvene according to Scheme 1 involves the generation of the
phosphonate anion with n-BuLi, which would also deprotect the
thiolate. Therefore, we investigated another route to the TTFV 3a
involving the phosphite mediated cross-coupling of a dithiole thi-
one with an aldehyde, a route compatible with the basic-sensitive
protected thiolate group.21 This synthetic strategy starts from
dithiole mesoionic 422 as described in Scheme 2. Alkylation of 4 with
3-bromopropionitrile in refluxing CH2Cl2 followed by treatment of
dithiolium salt 5 with NaSH$H2O in acidic medium allows the
formation of dithiole-2-thione 6 in 70% yield. A mixture of dithiole 6
and benzaldehyde was then heated in stoichiometric amounts, in
neat triethyl phosphite at 100 ꢀC for 6 h. Dithiafulvene 2c was
obtained in 88% yield as a mixture of Z and E isomers.
Electrochemical study of this dithiafulvene 2c using cyclic
voltammetry, leads to the same-patterned cyclic voltammogram as
those obtained for 2a and 2b. The oxidation of 2c into the cation
radical occurs at Epa¼0.79 V versus SCE in CH2Cl2 (0.72 V vs SCE in
CH3CN). The chemical oxidative coupling of 2c was investigated in
Figure 1. Cyclic voltammogram of 2b in CH2Cl2 with 0.1 M n-Bu4NPF6 and E in V
versus SCE scanning rate 100 mV/s.
S-
Me
Me
SCH2CH2CN
Me
SCH2CH2CN
Me
SCH2CH2CN
S
S
S
S
+
S
S
+
S
S
BrCH2CH2CN
NC(H2C)2S
C6H5CHO
NaSH,CH3CO2H
Br-
N
N
P(OEt)3, Δ
S
6
H
2c (Z/E)
4
5
Me
Me
Me
S
Me
SCH2
S(CH2)2CN
H2CS
S
S
S
N
N
S
S
S
S
Ox/red
i) CsOH.H2O
ClCH2
ii)
N
3c (ZZ/EE/ZE)
3a (ZZ/EE/ZE)
Scheme 2.

M. Guerro et al. / Tetrahedron 64 (2008) 5285–5290
5287
has an influence on the 1H NMR spectrum, especially on the set of
signals attributed to the picoline group, which resonate at lower
field. For instance, in CDCl3 the methylene resonates at 4.03 ppm
for the free ligand 2b and at 4.31 ppm in (2b)2$ZnCl2. We also
investigated the redox behaviour of (2b)2$ZnCl2 by cyclic voltam-
metry. As observed for 2b, an irreversible peak is observed upon the
first anodic scan while a reversible oxidation system appeared on
the voltammogram upon successive scans, demonstrating the oxi-
dative coupling of the dithiafulvene cores into the corresponding
TTFV in solution. Two possibilities can be envisioned concerning
the oxidative coupling since the two dithiafulvenes can form either
a cyclic TTFV or a polymeric derivative via, respectively, an intra- or
an intermolecular coupling. Actually it is interesting to note that the
complexation does not modify the oxidation potential of the
dithiafulvene core, as for (2b)2$ZnCl2 Epa¼0.86 V versus SCE and for
2b Epa¼0.85 V versus SCE in dichloromethane. Contrariwise, the
reversible process due to TTFV formed in situ occurs at a higher
oxidation potential (E¼0.60 V vs SCE) than for metal-free TTFV
3b at E¼0.55 V versus SCE. In previous studies, we noticed that
the only noticeable modification in terms of redox properties was
a positive shift in the oxidation potentials when going from non-
cyclic derivatives to cyclic ones, such as those represented on Chart
1. The derivatives 7–9 exhibit one reversible oxidation system at
E¼0.651 V for 7, E¼0.717 V for 8 (n¼4) and E¼0.736 V for 9 (n¼3).15
We can therefore conclude that the TTFV core formed here is the
result of an intramolecular oxidative coupling and the positive shift
observed is due to steric hindrance generated by the metal com-
plexation. The complexation of ZnCl2 constrains the binding groups
linked to the dithiole rings, which induces in return a positive shift
in the oxidation process. Unfortunately, when oxidizing
(2b)2$ZnCl2, either chemically or electrochemically, the resulting
TTFV (3b)$ZnCl2 was not isolatable from the other salts formed in
the medium.
Table 1
Redox potentials of compounds 3a–3c
E in CH3CN
E
1 in CH2Cl2
E2 in CH2Cl2
3a
3b
3c
0.40
0.50
0.48
0.40
0.55
0.53
0.49
–
0.64
E in V versusSCE, Pt workingelectrodewith 0.1 M n-Bu4NPF6, scanning rate100 mV/s.
the presence of two different oxidizing agents, iodine23 and
AgBF4.24 The coupling reaction of 2c was realized in the presence of
2 equiv of the oxidizing agent in refluxing dichloromethane under
inert atmosphere followed by reduction of the medium with
Na2S2O4 (Scheme 2). The use of AgBF4 allowed us to isolate 3c in
70% yield while the oxidation with iodine afforded 3c in lower yield
(20%). The target molecule 3a was prepared from 3c by depro-
tection of the two thiolate functions with CsOH$H2O followed by
alkylation with picoline chloride. According to this strategy, 3a was
obtained in 80% yield, and the purification step was much easier to
achieve than from the oxidative coupling reaction described in
Scheme 1.
Redox behaviour of the three TTFV 3a–3c has been studied by
cyclic voltammetry in dichloromethane and in acetonitrile and the
data are gathered in Table 1. All the derivatives exhibit only one
single bielectronic reversible oxidation wave in acetonitrile. On the
contrary, in dichloromethane, two distinct behaviours can be ob-
served: either two close reversible monoelectronic waves for 3a
and 3c or one bielectronic wave for 3b. This behaviour is reminis-
cent to what was previously observed with other TTFV, where the
redox behaviour was found to be strongly dependant both on
the donating properties of the phenyl group and on the steric in-
teractions on the central conjugation. As seen in Table 1, when
decreasing the electron withdrawing strength, the bielectronic
wave observed for 3b splits into two close monoelectronic ones for
3a.25 This presence of the cyano group decreases also significantly
the donating ability of the TTFV as the oxidation potential is posi-
tively shifted.
(CH2)n
Me
SMe
S
S
Me
Me
S
S
S
S
NC
S
S
2.2. Metal complexes
CN
S
S
Recently, Decurtins et al. showed that TTF derivatives
substituted by two thiopicoline substituents can easily coordinate
divalent metal ions such as Ni(II), Co(II), and Zn(II).12 In order to
follow the complexation not only through electrochemical studies
but also through 1H NMR studies, we realized these complexations
only with the diamagnetic ion Zn2þ, either on the dithiafulvene 2b
or on the vinylogous TTF 3a.
Addition of half equivalent of ZnCl2 to an acetonitrile solution of
2b and refluxing the medium for 1 h leads to a 2:1 complex where
two dithiafulvenes 2b are coordinated to one Zn2þ ion, Scheme 3.
This complex (2b)2$ZnCl2, has been isolated as a brown powder in
72% yield and fully characterized. Complexation of the metal ion
CN
NC
MeS
Me
8 n = 4
9 n = 3
7
Chart 1.
To further understand the chelating abilities of these derivatives,
(3a)$ZnCl2 has been directly prepared using similar reaction con-
ditions, from preformed TTFV 3a in the presence of 1 equiv of ZnCl2.
Filtration of the precipitate in suspension followed by analysis of
both precipitate and filtrate show that the precipitate contains the
remaining free ligand TTFV 3a while the filtrate contains the 1:1
N
Me
Me
Me
S
NC
S
NC
S
S
S
N
ZnCl
N
Zn Cl
N
S
S
S
S
S
ZnCl2
ox/red
Cl
Cl
S
CH3CN
N
S
S
S
S
NC
NC
NC
Me
Me
2b
(2b)2.ZnCl2
Scheme 3.

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M. Guerro et al. / Tetrahedron 64 (2008) 5285–5290
complex with 3a as shown in Scheme 4. This reluctance of the TTFV
3a to fully complex the Zn2þ cation is due to the fact that TTFV 3a is
obtained during its synthesis as a mixture of three isomers (EE/EZ/
ZZ), which are represented below in Scheme 5.
In the EE or EZ configuration, the two thiopicolines are too far
away from each other to allow intramolecular complexation
whereas in the ZZ configuration, they are much closer, which
favours complexation to the metal ion.
Cl
N
N
Zn
Me
S
Me
S
S
Cl
SCH2
H2CS
Me
Me
S
N
S
S
N
S
S
S
S
ZnCl2
CH3CN
As previously noticed for the DTF 2b, comparison of the 1H NMR
spectra in (CD3)2CO of the free ligand 3a with the (3a)$ZnCl2
complex shows that complexation influences the set of signals
attributed to the picoline group, which resonate at lower field. The
methylene group resonates at 4.04 ppm for 3a and at 4.52 ppm
in (3a)$ZnCl2. Similarly, as can be seen in Figure 2, the signals
3a (ZZ/EE/ZE)
3a.ZnCl2
Scheme 4.
N
N
H2C
S
N
CH2
H2C
N
N
N
Me
Me
S
Me
S
Me
Me
SCH2
H C
S
2
Me
H2CS
S
S
S
S
S
S
S
S
S
S
S
S
Ar
Ar
3a EZ
Ar
3a EE
Ar
Ar
Ar
3a ZZ
Scheme 5.
Figure 2. 1H NMR ((CD3)2CO, 200 MHz) spectra of the aromatic protons of 3a (left) and 3a$ZnCl2 (right).

M. Guerro et al. / Tetrahedron 64 (2008) 5285–5290
5289
Figure 3. Schematic representation of the stretch motion for 3a (left) and the clip motion for (3a)$ZnCl2 (right) upon oxidation.
attributed to the pyridine proton exhibit significant chemical shift
differences, for example, the closest proton from the nitrogen atom
resonates at 8.56 ppm in 3a while in (3a)$ZnCl2 it is observed at
8.96 ppm.
a platinum disk electrode (A¼1 mm2). The potentials were mea-
sured versus saturated calomel electrode.
4.2. Synthesis
The redox potentials of the complex (3a)$ZnCl2 was investigated
in dichloromethane by cyclic voltammetry. Complexation of the
two dithiole rings through the thiopicoline groups modifies the
shape of the voltammogram as only one reversible oxidation wave
is observed at E¼0.47 V versus SCE for (3a)$ZnCl2 instead of the two
close reversible oxidation processes observed for the free ligand 3a
(Table 1). The shift of the oxidation potential towards more positive
value as well as the coalescence of the two monoelectronic waves
into one bielectronic process has already been observed when
passing from TTFV to their constrained cyclic TTFV.15 This modifi-
cation of the redox behaviour was the result of two different mo-
lecular motions generated by the electron transfer. Indeed a stretch
movement was observed for the TTFV while a clip movement
occurred for constrain cyclic TTFV. Therefore the modification of
the shape of the voltammogram in (3a)$ZnCl2 compared to 3a
implies that complexation impedes the stretch movement
observed for TTFV (Fig. 3).
4.2.1. Dithiafulvenes (2a) and (2b)
To a solution of dithiole phosphonate 1 (1 g, 2.70 mmol) in THF
(20 mL) under inert atmosphere and at ꢁ78 ꢀC was added dropwise
n-BuLi 1.6 M in hexane (1.82 mL, 2.97 mmol). After 30 min under
stirring, the aldehyde was added (benzaldehyde: 0.30 mL; 4-cya-
nobenzaldehyde: 420 mg, 3.24 mmol). The reaction mixture was
then allowed to reach room temperature and stirred for 12 h. The
medium was concentrated in vacuo and CH2Cl2 (30 mL) was added.
The organic phase was washed with water (2ꢂ50 mL), dried over
MgSO4 and concentrated. After column chromatography on silica
gel using CH2Cl2/n-pentane 1:1 as eluent (Rf¼0.65 for 2a; Rf¼0.60
for 2b), Dithiafulvene 2a and 2b were obtained as thick oils.
4.2.1.1. Compound 2a. Yield 42%; 1H NMR (CDCl3, 300 MHz) d 1.67
(s, 3H, CH3), 3.98 (s, 2H, CH2), 6.42 (s, 1H, CH), 7.11–8.56 (m, 9H, CH
Ar); 13C NMR (CDCl3, 75 MHz) d 14.3, 41.8, 113.1, 113.3, 115.8, 122.2,
123.4, 125.5 126.6, 128.5, 132.5, 135.9, 136.5, 149.8, 157.1; HRMS
calcd for C17H15NS3: 329.0366, found: 329.0379.
3. Conclusion
4.2.1.2. Compound 2b. Yield 65%; 1H NMR (CDCl3, 300 MHz) d 1.78
(s, 3H, CH3), 4.03 (s, 2H, CH2), 6.44 (s, 1H, CH), 7.20–7.30 (m, 3H, CH
Ar), 7.49–7.71 (m, 4H, CH Ar), 8.57 (d, 1H, CH Ar); 13C NMR (CDCl3,
75 MHz) d 15.2, 42.2, 107.8, 111.3, 119.6, 122.9, 123.9, 127.8, 132.6,
136.8, 137.2, 138.2, 139.4, 141.1, 147.6, 150.0, 157.1; HRMS calcd for
In summary we have presented two synthetic approaches to
a novel redox active ligand able to coordinate divalent metal ions
such as Zn2þ. Considering the fact that the binding sites of this li-
gand are far away from the redox active core, it is unlikely that the
positive shift observed during the electrochemical investigations
of the complex is the result of Coulombic repulsion between the
oxidized TTFV core and the charged ion. Instead, due to the high
stability of the complex, the Zn2þ plays the role of a linker between
the two thiopicoline groups impeding the stretch molecular mo-
tions triggered by electron transfer. Consequently the oxidation of
the TTFV core to the dication occurs in one bielectronic process in
the complex instead of the two monoelectronic steps for the free
ligand. Further work will be undertaken on the chelating ability of
this redox active ligand towards other transition metal ions.
C18H14N2S3: 354.0319, found: 354.0307. Anal. Calcd for C18H14N2S3:
C, 60.98; H, 3.98; N, 7.90. Found: C, 61.01; H, 3.95; N, 8.41.
4.2.2. General procedure for the synthesis of TTFV (3a) and (3b) by
oxidative coupling of (2a) and (2b)
To a CH2Cl2 (40 mL) solution of dithiafulvene 2a (1 g, 3.04 mmol)
or 2b (1.08 g, 3.04 mmol), under inert atmosphere, was added I2
(2.02 g, 8 mmol) and the resulting solution was stirred under reflux
for 1 h. To the reaction mixture a large excess of Na2S2O4 (2 g) was
added and the reaction mixture was stirred under reflux for 12 h.
The reaction mixture was filtered on Celite and the organic phase
was washed with water 2ꢂ50 mL, dried over MgSO4. The solvent
was removed and the residue was purified by silica gel column
chromatography using CH2Cl2/Et2O 9:1 as eluent. TTFV 3b was
obtained as a yellow thick oil. Yield 7%; 1H NMR (200 MHz, CDCl3)
d 1.75 (s, 3H, CH3), 1.78 (s, 3H, CH3), 4.05 (s, 2H, CH2), 4.08 (s, 2H,
CH2), 7.19–7.75 (m,14H, CH), 8.58 (m, 2H, CH). TTFV 3a was obtained
as a yellow thick oil. Yield 38%. Three isomers are observed on the
1H NMR spectrum. 1H NMR (300 MHz, (CD3)2CO) d 1.65 (s, 3H, CH3),
1.70 (s, 3H, CH3), 1.73 (s, 3H, CH3), 1.75 (s, 3H, CH3), 3.98 (s, 2H, CH2),
4.04 (s, 2H, CH2), 7.10–7.70 (m, 16H, CH), 8.56 (m, 2H, CH); 13C NMR
(75 MHz, CD3Cl) d 13.9, 41.7, 116.8, 122.2, 123.7, 124.2, 126.5, 126.6,
128.5, 136.2, 136.5, 136.7, 137.5, 149.8, 156.9; HRMS calcd
4. Experimental
4.1. General
1H NMR spectra were recorded at 200 or 300 MHz and 13C NMR
spectra at 75 MHz with tetramethylsilane as internal reference.
Elemental analysis results and Mass spectra were carried out at the
Centre de Mesures Physiques de l’Ouest, Rennes. The dithiole
phosphonate 1 was synthesized starting from dithiole mesoionic 4
according to published procedure.18,26 Cyclic voltammetry were
carried out on a 10ꢁ3 M solution of the compounds in dichloro-
methane or in acetonitrile, containing 0.1 M n-Bu4NPF6 as sup-
porting electrolyte. Voltammograms were recorded at 0.1 V/s on
for
C34H28N2S6: 679.0475, found: 679.0477. Anal. Calcd for

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M. Guerro et al. / Tetrahedron 64 (2008) 5285–5290
C34H28N2S6$0.5CH2Cl2: C, 59.27; H, 4.15; N, 4.01. Found: C, 59.44; H,
4.39; N, 3.94.
CH), 7.24–7.28 (m, 4H, CH Ar), 7.34–7.37 (m, 4H, CH Ar), 7.57–7.63
(m, 4H, CH Ar), 7.84–8.07 (m, 2H, CH Ar), 8.88 (m, 2H, CH Ar); 13C
NMR (CDCl3, 75 MHz) d 13.2, 14.1, 39.1, 106.6, 110.5, 114.7, 118.1,
123.1, 124.9, 125.8, 131.3, 136.6, 137.1, 137.9, 139.6, 147.5, 147.9, 155.9,
206.4; HRMS calcd for C36H28Cl2N4S6Zn [MþH]: 842.9385, found:
842.9390. Anal. Calcd for (C36H28Cl2N4S6Zn.Et2O): C, 52.25; H, 4.16;
N, 6.09. Found: C, 52.51; H, 3.81; N, 6.52.
4.2.3. 3-[(5-Methyl-2-thioxo-1,3-dithiol-4-yl)thio]propanenitrile (6)
A solution of mesoionic-2-piperidino-1,3-dithiolium-4-thiolate
4 (13.9 g, 6 mmol) and 3-bromopropionitrile (9.4 g, 7 mmol) in
CH2Cl2 was heated to reflux for 12 h. After evaporation of the
solvent, the oil was washed several times with diethylether and
dried. Dithiolium 5 was obtained in 93% yield as an oily product and
used for the next step without further purification. 1H NMR (CDCl3,
300 MHz) d 1.48–1.60 (m, 6H, CH2), 2.23 (s, 3H, CH3), 2.66 (m, 2H,
SCH2), 2.87 (m, 2H, CH2), 3.61 (m, 4H, NCH2). A solution of dithio-
lium 5 (2 g, 5 mmol) and 2 g of NaSH$H2O in DMF (20 mL) and
acetic acid (20 mL) was stirred at 100 ꢀC for 2 h. After cooling at
room temperature, water (20 mL) and dichloromethane (40 mL)
were added. The organic phase was washed with water (2ꢂ30 mL)
and with NaHCO3 (30 mL). The organic layer was separated and
dried over Na2SO4. The solution was concentrated in vacuo and the
residue was purified on column chromatography using ether/pe-
troleum ether 1:2 as eluent to give 6 (820 mg) as yellow crystals in
70% yield. Mp¼78–80 ꢀC; 1H NMR (CDCl3, 300 MHz) d 2.44 (s, 3H,
CH3), 2.74 (m, 2H, CH2), 3.05 (m, 2H, CH2); 13C NMR (CDCl3, 75 MHz)
d 15.3, 18.6, 32.1, 117.3, 125.8, 148.6, 210.9. Anal. Calcd for C7H7NS4:
C, 36.02; H, 3.02; N, 6.00. Found: C, 35.75; H, 2.95; N, 5.75. FTIR
4.3.2. Synthesis of complex (3a)$ZnCl2
Similar procedure as the one described above for 2b using 3a
(250 mg, 0.3 mmol) and 1 equiv of ZnCl2 (0.4 g, 0.3 mmol). The
solvent was evaporated under reduced pressure and the uncom-
plexed 3a and ZnCl2 were precipitated by the addition Et2O. The
complex (3a)$ZnCl2 was obtained as a brown thick oil in 35% yield.
1H NMR ((CD3)2CO, 200 MHz) d 1.65 (s, 3H, CH3), 1.74 (s, 3H, CH3),
4.52 (s, 4H, CH2), 7.2–7.6 (m, 12H, CH), 7.79 (m, 2H, CH), 8.15 (m, 2H,
CH), 8.96 (m, 2H, CH); HRMS calcd for C34H28Cl2N2S6Zn [MþH]:
790.9324, found: 790.9355 and calcd for [MꢁCl]: 754.9557, found:
754.9535.
References and notes
1. Special issue on molecular conductors, Chem. Rev. 2004, 104.
2. Delogu, G.; Fabbri, D.; Dettori, M. A.; Salle, M.; Le Derf, F.; Blesa, M. J.; Allain, M.
J. Org. Chem. 2006, 71, 9096 and references therein.
3. (a) Massue, J.; Bellec, N.; Chopin, S.; Levillain, E.; Roisnel, T.; Cle´rac, R.; Lorcy, D.
Inorg. Chem. 2005, 44, 8740; (b) Zhu, Q.-Y.; Bian, G.-Q.; Zhang, Y.; Dai, J.; Zhang,
D.-Q.; Lu, W. Inorg. Chim. Acta 2006, 359, 2303; (c) Bellec, N.; Massue, J.; Roisnel,
T.; Lorcy, D. Inorg. Chem. Commun. 2007, 10, 1172.
(KBr) n CN¼2250 cmꢁ1
.
4.2.4. 2-Benzylidene-4,5-bis(methylthio)-1,3-dithiole (2c)
To a suspension of 1,3-dithiole-2-thione (1 g, 4.3 mmol) in
P(OEt)3 (10 mL) was added benzaldehyde (460 mg, 4.3 mmol). The
reaction mixture was stirred at 100 ꢀC for 6 h. The solvent was
removed under reduced pressure and the residue was purified on
column chromatography using CH2Cl2 as eluent. The dithiole 2c
was obtained as a mixture of two isomers as a yellow oil in 88%
yield. 1H NMR (CDCl3, 300 MHz) d 2.20 (s, 3H, CH3), 2.66 (m, 2H,
CH2), 2.93 (m, 2H, CH2), 6.50 (s, 1H, CH) for one isomer and 6.47 (s,
1H, CH) for the other one, 7.21–7.38 (m, 5H, Ar); 13C NMR (CDCl3,
75 MHz) d 14.8, 18.4, 30.7, 114.1, 117.7, 125.9, 126.7, 128.6, 131.6,
136.3, 136.5, 137.3. Anal. Calcd for C14H13NS3: C, 57.69; H, 4.50; N,
4. Kobayashi, A.; Fujiwara, E.; Kobayashi, H. Chem. Rev. 2004, 104, 5243 and
references cited therein.
5. Jia, C.; Liu, S.-X.; Tanner, C.; Leiggener, C.; Neels, A.; Sanguinet, L.; Levillain, E.;
Leutwyler, S.; Hauser, A.; Decurtins, S. Chem.dEur. J. 2007, 13, 3804.
6. (a) Liu, S.-X.; Dolder, S.; Pilkington, M.; Decurtins, S. J. Org. Chem. 2002, 67, 3160;
(b) Liu, S.-X.; Dolder, S.; Rusanov, E. B.; Stoeckli-Evans, H.; Decurtins, S. C. R.
Chim. 2003, 6, 657; (c) Dolder, S.; Liu, S.-X.; Beurer, E.; Ouahab, L.; Decurtins, S.
Polyhedron 2006, 25, 1514.
7. (a) Iwahori, F.; Golhen, S.; Ouahab, L.; Carlier, R.; Sutter, J.-P. Inorg. Chem. 2001,
40, 6541; (b) Setifi, F.; Ouahab, L.; Golhen, S.; Yoshida, Y.; Saito, G. Inorg. Chem.
2003, 42, 1791.
8. Devic, T.; Avarvari, N.; Batail, P. Chem.dEur. J. 2004, 10, 3697.
9. (a) Fourmigue´, M.; Batail, P. Bull. Soc. Chim. Fr. 1992, 129, 29; (b) Avarvari, N.;
4.81. Found: C, 56.97; H, 4.49; N, 4.72. FTIR (KBr) n CN¼2249 cmꢁ1
.
´
Martin, D.; Fourmigue, M. J. Organomet. Chem. 2002, 643–644, 292; (c) Devic, T.;
Batail, P.; Fourmigue´, M.; Avarvari, N. Inorg. Chem. 2004, 43, 3136.
10. (a) Pellon, P.; Gachot, G.; Le Bris, J.; Marchin, S.; Carlier, R.; Lorcy, D. Inorg. Chem.
2003, 42, 2056; (b) Gachot, G.; Pellon, P.; Roisnel, T.; Lorcy, D. Eur. J. Inorg. Chem.
2006, 13, 2604.
4.2.5. Synthesis of TTFV (3c)
To a solution of 2c (430 mg, 1.5 mmol) in 10 mL of dry degassed
CH2Cl2, AgBF4 (580 mg, 3 mmol) was added at 0 ꢀC. The solution
was stirred at 0 ꢀC for 2.5 h and then Na2S2O4 (2 g) was added. After
30 min stirring the solution was washed with water (2ꢂ20 mL) and
dried over Na2SO4. Chromatography over silica gel using ether/
pentane (1:2) mixture as the eluent afforded the TTFV in 70% yield
as a thick oil. 1H NMR (CDCl3, 300 MHz) d 2.18 (s, 6H, CH3), 2.65 (m,
4H, CH2), 2.92 (m, 4H, CH2), 7.15–7.55 (m, 10H, Ar); HRMS calcd for
´
´
´
11. (a) Rethore, C.; Fourmigue, M.; Avarvari, N. Chem. Commun. 2004, 1384; (b)
Perruchas, S.; Avarvari, N.; Rondeau, D.; Levillain, E.; Batail, P. Inorg. Chem. 2005,
44, 3459.
12. (a) Liu, S.-X.; Dolder, S.; Franz, P.; Neels, A.; Stoeckli-Evans, H.; Decurtins, S.
Inorg. Chem. 2003, 42, 4801; (b) Liu, S.-X.; Ambrus, C.; Dolder, S.; Neels, A.;
Decurtins, S. Inorg. Chem. 2006, 45, 9622.
13. Dolder, S.; Liu, S.-X.; Le Derf, F.; Salle, M.; Neels, A.; Decurtins, S. Org. Lett. 2007,
9, 3753.
14. Massue, J.; Bellec, N.; Guerro, M.; Bergamini, J. F.; Hapiot, P.; Lorcy, D. J. Org.
Chem. 2007, 72, 4655.
15. Guerro, M.; Carlier, R.; Lorcy, D.; Hapiot, P. J. Am. Chem. Soc. 2003, 125, 3159.
16. Guerro, M.; Lorcy, D. Tetrahedron Lett. 2005, 46, 5499 and references cited.
17. Hansen, T. K.; Lakshmikantham, M. V.; Cava, M. P.; Metzger, R. M.; Becher, J.
J. Org. Chem. 1991, 56, 2720.
C
28H24N2S6: 580.0263, found: 580.0237. Anal. Calcd for C28H24N2S6:
C, 57.99; H, 4.16; N, 4.82. Found: C, 57.55; H, 4.25; N, 4.88. FTIR (KBr)
n CN¼2250 cmꢁ1
.
18. Akiba, K.; Ishikawa, K.; Inamoto, N. Bull. Chem. Soc. Jpn. 1978, 51, 2674.
4.3. Metal complexes
`
19. (a) Lorcy, D.; Carlier, R.; Robert, A.; Tallec, A.; Le Magueres, P.; Ouahab, L. J. Org.
Chem. 1995, 60, 2443; (b) Hapiot, P.; Lorcy, D.; Tallec, A.; Carlier, R.; Robert, A.
J. Phys. Chem. 1996, 100, 14823.
20. Simonsen, K. B.; Becher, J. Synlett 1997, 1211.
4.3.1. Synthesis of complex (2b)2$ZnCl2
To a solution of dithiafulvene 2b (1 g, 2.82 mmol) in CH3CN
(40 mL), ZnCl2 (192 mg, 1.41 mmol) dissolved in H2O (5 mL) was
added. The reaction mixture was stirred under reflux for 1 h and
then 3 h at room temperature. The solvent was evaporated under
reduced pressure and the complex (2b)2$ZnCl2 was precipitated by
the addition Et2O. The precipitate was washed with ether to afford
(2b)2$ZnCl2 as a light brown compound (854 mg; 72%). 1H NMR
(CDCl3, 300 MHz) d 1.79 (s, 6H, CH3), 4.31 (s, 4H, CH2), 6.44 (s, 2H,
21. (a) Leriche, P.; Roquet, S.; Pillerel, N.; Mabon, G.; Frere, P. Tetrahedron Lett. 2003,
44, 1623; (b) Christensen, C. A.; Batsanov, A.; Bryce, M. R. J. Org. Chem. 2007, 72,
1301.
22. Souizi, A.; Robert, A. Synthesis 1982, 1059.
23. Mu¨ller, H.; Salhi, F.; Divisia-Blohorn, B. Tetrahedron Lett. 1997, 38, 3215; (b)
Lorcy, D.; Rault-Berthelot, J.; Poriel, C. Electrochem. Commun. 2000, 2, 382.
24. Guerro, M.; Roisnel, T.; Pellon, P.; Lorcy, D. Inorg. Chem. 2005, 44, 3347.
25. Bellec, N.; Boubekeur, K.; Carlier, R.; Hapiot, P.; Lorcy, D.; Tallec, A. J. Phys. Chem.
A 2000, 104, 9750.
26. Lorcy, D.; Le Paillard, M. P.; Robert, A. Tetrahedron Lett. 1993, 34, 5289.