CyanobenzeneTTF-type donors; Synthesis and characterization

Article abstract of DOI:10.1016/j.tetlet.2014.10.111

Two cyanobenzeneTTF-type electron donors, which are also dithiolene ligand precursors, cyanobenzenedicyanoethylthiotetrathiafulvalene, (cbdc-TTF) and dicyanobenzenedicyanoethylthiotetrathiafulvalene, (dcbdc-TTF), were obtained through cross-coupling react

Full text of DOI:10.1016/j.tetlet.2014.10.111

Tetrahedron Letters 55 (2014) 6992–6997
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
CyanobenzeneTTF-type donors; synthesis and characterization
a
a
b
Sandra Rabaça a, , Sandrina Oliveira , Ana Cláudia Cerdeira , Dulce Simão ,
⇑
Isabel Cordeiro Santos a, Manuel Almeida a,
⇑
a C2TN, Instituto Superior Técnico/CFMCUL, Universidade de Lisboa, Estrada Nacional 10, P-2686-953 Sacavém, Portugal
b Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Two cyanobenzeneTTF-type electron donors, which are also dithiolene ligand precursors, cyanobenzene-
dicyanoethylthiotetrathiafulvalene, (cbdc-TTF) and dicyanobenzenedicyanoethylthiotetrathiafulvalene,
(dcbdc-TTF), were obtained through cross-coupling reactions with triethyl phosphite between 4,5-bis
(2-cyanoethylthio)-1,3-dithiole-2-one and 4,cyanobenzene-1,3-dithiole-2-thione or dicyanobenzene-
1,3-dithiole-2-thione, respectively. These reactions also yield 2,3,6,7-tetrakis(2-cyanoethylthio)-TTF
and the corresponding symmetric cyanobenzene TTF derivatives dicyanodibenzenetetrathiafulvalene
(dcdb-TTF) and tetracyanodibenzotetrathiafulvalene (TCN-DBTTF) resulting from the self-coupling
reactions of the ketone and the thiones. Compound dcdb-TTF was also synthesized by homo-coupling
reaction of the cyanobenzene-1,3-dithiole-2-ketone with triethyl phosphite. These compounds were
characterized namely by single crystal X-ray diffraction and cyclic voltammetry.
Received 11 August 2014
Revised 15 October 2014
Accepted 20 October 2014
Available online 27 October 2014
Keywords:
Tetrathiafulvalene
Ketones
Thiones
Cross-coupling
Cyanobenzene
Cyclic voltammetry
Ó 2014 Elsevier Ltd. All rights reserved.
The large majority of organic metals and superconductors that
have been developed during the last decades have been based on
derivatives from tetrathiafulvalene molecule (TTF).1 Their success
as building blocks for conducting materials is due to unique
More recently there has been increasing interest in TTF deriva-
tives containing N atoms in their periphery. Such compounds,
while retaining the electroactive behavior of TTF could in addition
be able to coordinate transition metals.4 Aiming at enlarging this
type of complexes we decided to explore new extended dithiolene
ligands that incorporate not only TTF, but also N containing units.
Along this line we recently reported the synthesis of the pzdc-TTF,
an extended TTF fused with a pyrazine moiety.5 Cyano groups
incorporated into TTF type donors, which besides possible metal
coordination can be engaged in weak intermolecular interactions
such as hydrogen and halogen bonding, have been however a lot
less explored. Literature examples are mostly restricted to salts
of 3-cyano-30,40-ethylenedithiotetrathiafulvalene (EDT-TTF-CN).6
In this Letter, we report the synthesis and characterization7 of
two new extended TTF-type donors fused with cyanobenzene and
dicyanobenzene moieties, the cyanobenzenedicyanoethylthiotet-
rathiafulvalene, (cbdc-TTF) (1a)8 and the dicyanobenzenedicyano-
ethylthiotetrathiafulvalene (dcbdc-TTF) (1b),9 which are also pre-
cursors for the preparation of new extended cyano-TTF fused
dithiolene ligands. A new symmetric cyanobenzene fused TTF-
based donor molecule, the dicyanodibenzenetetrathiafulvalene
(dcdb-TTF) (2a),10 is also reported.
p-donor properties of TTF and the possibility of extending the
delocalized -system by incorporation of additional sulfur or other
p
hetero atoms in the molecular periphery and chemical functional-
ization. The exploration of different TTF derivatives in this context
has been based on two guide lines. First, the extension of the p-sys-
tem in general renders more accessible the different oxidation
states, and maximizes the intermolecular interactions between
planar molecules that tend to be organized as stacks in the solid
state. Second, the incorporation of additional sulfur and other het-
ero atoms to the molecular periphery promotes the side intermo-
lecular interactions along the molecular plane, allowing
possible 2D or 3D character to the electronic interactions.
a
Some extended TTF derivatives have also been used in the last
decade as dithiolene ligands, to prepare extended transition metal
bisdithiolene complexes.2 These complexes deserved special atten-
tion since some of them, in their neutral state, were found to lead
metallic behavior, the so called single component molecular
metals.3
The key compounds for the synthesis of the cyanobenzene
substituted compounds (new extended TTF-type donors and sym-
metric TTF-type donors) are the thiones Ia (cyanobenzene-1,3-
dithiole-2-thione) and Ib (dicyanobenzene-1,3-dithiole-2-thione).
⇑
Corresponding authors. Tel.: +351 21 994 6203; fax: +351 21 955 0117 (S.R.);
tel.: +351 21 994 6171; fax: +351 21 955 0117 (M.A.).
E-mail addresses: sandrar@ctn.ist.utl.pt (S. Rabaça), malmeida@ctn.ist.utl.pt
(M. Almeida).
http://dx.doi.org/10.1016/j.tetlet.2014.10.111
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

S. Rabaça et al. / Tetrahedron Letters 55 (2014) 6992–6997
6993
(Scheme 1). Although similar results are expected to be achieved
from a reaction between ketones only, such route was not explored.
The hetero-coupling reactions leading to the compounds 1a and
1b also yielded other by-products (2a, 2b, and 3), resulting from the
self-coupling of the corresponding thiones (Ia and Ib) and ketone
(III). Dicyanodibenzenetetrathiafulvalene (dcdb-TTF) (2a) and
TCN-DBTTF (2b) result from the self-coupling of thiones Ia and Ib.
However, due to the insolubility in common organic solvents of
these compounds, this synthetic pathway is not a valuable option
to isolate 2a or 2b in large yields. Their insolubility prevents the
direct purification by column chromatography and a previous puri-
fication by Soxhlet extraction is required. One test in a small scale
was performed and 2a and 2b were isolated in 25% and 18% yields,
respectively. Both coupling reactions yield also to 2,3,6,7-tetrakis(2-
cyanoethylthio)TTF (3) resulting from the self-coupling of ketone
III,15 with a 21% and 14% yield, as a by-product of the preparation
of 1a or 1b, respectively. In alternative, compounds 2a (76% yield)
and 2b can be obtained in better yields by homo-coupling reactions
as previous reported by Decurtins et al.16 for 2b. Besides the prod-
ucts from the self-coupling of the thiones and ketones, reasonable
yields of 37% and 34% were achieved for 1a and 1b, respectively,
after column separation, using DCM/MeOH (v:v = 50:1) as eluent.
Compounds Ia, Ib, IIa, IIb, and 1b were easily recrystallized
affording single crystals suitable for their structural refinement
based on single crystal X-ray diffraction (Table 1).17
Thione Ia crystallizes in the Monoclinic system, space group
P2(1)/c, while thione Ib crystallizes in the Orthorhombic system,
space group Pbca. Both asymmetric units contain one independent
molecule in a general position.
Ketones IIa and IIb crystallize in the Orthorhombic system,
space group Pna2(1) and Pca2(1), respectively, with both asym-
metric units containing one independent molecule in a general
position. Figure 1 shows the ORTEP diagrams of Ia, Ib, IIa, and
IIb with the corresponding atomic numbering scheme. The thiones
(Ia and Ib) and ketones (IIa and IIb) are essentially planar (Rms
deviation of the fitted atoms: 0.0274 Å, 0.0196 Å, 0.0610 Å, and
0.0748 Å, respectively).
In the crystal structure of Ia and IIb the molecules are stacked
head to head in regular columns along the b axis (Fig. 2a1 and
b1, respectively) tilted approximately 24° and 21°, respectively,
toward the staking axis b. The shorter contacts, clearly below the
sum of van der Waals radii, are between neighboring columns,
either hydrogen bonds or Sꢀ ꢀ ꢀS contacts (Table 2), establishing
layers of closely connected molecules parallel to the a, c plane.
Scheme 1. Reagents and conditions: (i) K2S, CS2, DMF; (ii) P(OEt)3, toluene, 110 °C;
(iii) Hg(OAc)2, AcOH, DCM; (iv) P(OEt)3, toluene, 110 °C.
Thione Ia was recently described by us11 and thione Ib12 was pre-
pared in 59% yield following a similar procedure based on the reac-
tion of 2,3-dichlorocyanobenzene with potassium trithiocarbonate.
The corresponding ketones IIa13 and IIb14 (cyanobenzene-1,3-
dithiole-2-one and dicyanobenzene-1,3-dithiole-2-one), were used
to prepare the symmetric donors 2a and 2b by homocoupling reac-
tions. These ketones were obtained from a regular transchalcogen-
ation reaction of the corresponding thiones, accomplished with
mercuric acetate in dichloromethane and glacial acetic acid to give
IIa and IIb in 81% and 64% yields, respectively.
The TTF-based donors 1a and 1b were obtained following a syn-
thetic route first used by Underhill and co-workers2 involving the
coupling with triethyl phosphite between thiones and ketones
Table 1
Crystallographic details for compounds Ia, Ib, IIa, IIb, and 1b
(Ia)
(Ib)
(IIa)
(IIb)
(1b)
Crystal size (mm)
Crystal color and shape
Empirical formula
Molecular mass
Crystal system
Space group
a (Å)
0.60 ꢁ 0.10 ꢁ 0.03
Yellow plate
C8H3NS3
209.29
Monoclinic
P2(1)/c
15.8538(11)
3.8896(2)
15.5207(10)
90.00
118.032(2)
90.00
844.80(9)
4, 1.646
0.809
0.30 ꢁ 0.18 ꢁ 0.03
Yellow plate
C9H2N2S3
234.31
Orthorhombic
Pbca
7.8700(5)
14.3785(8)
16.5094(10)
90.00
90.00
90.00
0.30 ꢁ 0.28 ꢁ 0.10
Colorless prism
C8H3NOS2
193.23
Orthorhombic
Pna2(1)
7.3555(2)
12.3095(1)
8.5265(2)
90.00
90.00
90.00
772.01(3)
4, 1.663
0.627
0.20 ꢁ 0.20 ꢁ 0.06
Colorless plate
C9H2N2OS2
218.25
Orthorhombic
Pca2(1)
16.2207(9)
3.8093(2)
13.9027(9)
90.00
90.00
90.00
859.04(9)
4, 1.687
0.578
0.20 ꢁ 0.18 ꢁ 0.10
Orange block
C18H10N4S6
474.66
Triclinic
P-1
7.1703(2)
8.2429(2)
b (Å)
c (Å)
17.2712(4)
93.4710(10)
98.4740(10)
105.115(2)
969.47(4)
a
(°)
b (°)
c
(°)
V (Å3)
1868.18(19)
8, 1.666
0.745
Z, Dcalcd (mg/m3)
l
2, 1.626
0.719
, (mmꢂ1
)
F (000)
424
944
392
440
484
Index range (h, k, l)
Tmax/min
Final R1, [I > 2r(I)], wR2
ꢂ18/19; ꢂ3/4: ꢂ18/18
0.9761/0.6423
0.0290, 0.0759
ꢂ9/9; ꢂ16/17; ꢂ19/20
0.9780/0.8074
0.0349, 0.0831
ꢂ9/9; ꢂ15/15; ꢂ10/10
0.9400/0.8342
0.0222, 0.0539
ꢂ20/18; ꢂ4/4; ꢂ17/17
0.9662/0.8834
0.0259, 0.0259
ꢂ8/8; ꢂ10/10; ꢂ21/21
0.9316/0.8696
0.0296, 0.0697

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S. Rabaça et al. / Tetrahedron Letters 55 (2014) 6992–6997
The molecules are tilted toward the stacking axis by 60.4°. In the
unit cell there are 8 molecules arranged in four stacks with differ-
ent orientations connected through several short contacts (Table 2).
Molecules in different stacks make an angle of 120.8°. The crystal
structure of IIa is made of head to head regular stacks of molecules
along the a-axis with cyano groups alternating in different direc-
tions (Fig. 3b1 and b2). The molecules along these stacks are
connected by short contacts (C5ꢀ ꢀ ꢀC6) and tilted 68.4° toward the
a-axis. In the unit cell there are two chains of molecules making
an angle of 43.1° and connected by several short contacts listed
in Table 2.
The compound 1b crystallizes in the triclinic system, space
group P-1. Figure 4 shows ORTEP diagrams with the corresponding
atomic numbering scheme. The asymmetric unit contains one
independent dcbdc-TTF molecule located in a general position.
The central TTF core and the dicyanobenzene unit are essentially
planar (Rms deviation of fitted atoms: 0.0378 Å) while the chains
containing the cyanoethyl groups are drastically deviated from
the central molecular plane. Bond lengths and angles in the TTF
moiety are in the range expected for the neutral TTF derivatives.18
The crystal structure of 1b is composed by head to tail stacks of
dcbdc-TTF molecules along b (Fig. 5). These stacks are arranged
with molecules in the same orientation, making layers of cyano-
ethyl groups segregated from the TTF cores, which alternate along
c in layers parallel to the a,b plane. Molecules parallel to each other
are connected by short contacts and hydrogen bonds (C10ꢀ ꢀ ꢀC9;
C8ꢀ ꢀ ꢀS5; C16–H16Aꢀ ꢀ ꢀN1; C16–H16Aꢀ ꢀ ꢀN1) as listed in Table 2
and shown in Figure 5b.
Figure 1. ORTEP diagrams of: compounds Ia (a), Ib (b), IIa (c), and IIb (d), drawn at
30% probability level with the atomic numbering scheme.
The electrochemical behavior of these new donors was studied
by cyclic voltammetry.19 In each case, the two standard one-elec-
tron quasi-reversible redox waves typical of TTF donors were
observed at potentials listed in Table 3. The redox potentials of
the donors 1a and 1b were measured in dimethylformamide.
Due to poor solubility of donor 2a the solvent was in this case
replaced by benzonitrile. Donors 1a, 1b, and 2a show the typical
two redox processes of TTF-based donors. At lower potentials there
is a quasi-reversible process, at 0.38 V, 0.42 V, and 0.27 V, respec-
tively, corresponding to the formation of the cationic species and
a second irreversible process at 0.54 V, 0.59 V, and 0.60 V, due to
the formation of the dicationic species.
Comparing the redox potentials of the two new extended TTF
donors (1a and 1b) we can conclude that, as expected, the addi-
tional cyano substituent group reduces the donor properties, shift-
ing the redox potentials to higher values due to the electron-
withdrawing effect of the cyano groups.21
Figure 2. Crystal structure of compounds Ia and IIb viewed along b axis (a1 and b1)
and along c axis (a2) and a axis (b1), respectively.
Figure 2a2 and b2 shows these layers along the c and a axis,
respectively.
The crystal structure of Ib (Fig. 3a1 and a2) is composed by head
to tail slightly dimerized stacks of planar molecules connected
along the a-axis by short contacts (C1ꢀ ꢀ ꢀS1; C1ꢀ ꢀ ꢀS2; C3ꢀ ꢀ ꢀS1).
Table 2
Selected short contacts and hydrogen bonds in the crystal structure of Ia, Ib, IIa, IIb, and 1b
Ia
IIb
1b
C6–H6ꢀ ꢀ ꢀS1 (#a)
C3–H3ꢀ ꢀ ꢀN1 (#b)
C7–H7ꢀ ꢀ ꢀN1 (#c)
S1ꢀ ꢀ ꢀS1 (#d)
2.928 Å
2.636 Å
2.668 Å
3.519 Å
3.443 Å
C4–H4ꢀ ꢀ ꢀN2 (#h)
S1ꢀ ꢀ ꢀN2 (#i)
2.578 Å
3.273 Å
2.981 Å
3.179 Å
3.273 Å
2.692 Å
C10ꢀ ꢀ ꢀC9 (#1)
3.387 Å
3.481 Å
2.617 Å
2.707 Å
3.178 Å
3.280 Å
2.457 Å
C8ꢀ ꢀ ꢀS5 (#2)
C4ꢀ ꢀ ꢀO1 (#j)
C16–H16Aꢀ ꢀ ꢀN1 (#1)
C17–H17Aꢀ ꢀ ꢀN2 (#1)
S5ꢀ ꢀ ꢀN3 (#3)
S2ꢀ ꢀ ꢀN1 (#l)
S3ꢀ ꢀ ꢀS3 (#f), (#g)
S2ꢀ ꢀ ꢀN2 (#m)
C5–H5ꢀ ꢀ ꢀN1 (#n)
C18ꢀ ꢀ ꢀC18 (#4)
C13–H13Bꢀ ꢀ ꢀN4 (#3)
Ib
IIb
C1ꢀ ꢀ ꢀS2 (#j)
C1ꢀ ꢀ ꢀS1 (#j)
C3ꢀ ꢀ ꢀS1 (#j)
C5ꢀ ꢀ ꢀC9 (#j)
N2ꢀ ꢀ ꢀS1 (#o)
C9ꢀ ꢀ ꢀS1 (#o)
3.491 Å
3.495 Å
3.497 Å
3.394 Å
3.238 Å
3.444 Å
S3ꢀ ꢀ ꢀN1 (#p)
3.097 Å
3.326 Å
3.249 Å
2.736 Å
2.567 Å
O1ꢀ ꢀ ꢀC8 (#j)
3.213 Å
3.369 Å
3.272 Å
2.535 Å
2.497 Å
N1ꢀ ꢀ ꢀS2 (#q)
C5ꢀ ꢀ ꢀC6 (#j)
N2ꢀ ꢀ ꢀS2 (#r)
S2ꢀ ꢀ ꢀN1 (#j)
C3–H3ꢀ ꢀ ꢀN2 (#h)
C6–H8ꢀ ꢀ ꢀN1 (#x)
C7–H7ꢀ ꢀ ꢀO1 (#h)
C5–H5ꢀ ꢀ ꢀN1 (#h)
#a = x, ꢂ½ ꢂ y, ½ + z; #b = 2 ꢂ x, 1 ꢂ y, 2 ꢂ z; #c = 2 ꢂ x, ꢂ½ + y, 2.5 ꢂ z ; #d = 1 ꢂ x, ꢂ1 ꢂ y, 1 ꢂ z; #f = 1 ꢂ x, ꢂ½ + y, 1.5 ꢂ z; #g = 1 ꢂ x, ½ + y, 1.5 ꢂ z; #h = ½ + x, 1 ꢂ y, z;
#i = ½ + x, 1 ꢂ y, z; #j = 2 ꢂ x, ꢂy, ½ + z ; #l = 1.5 ꢂ x, ꢂ1 + y, ꢂ½ + z ; #m = 1.5ꢂx, y, ꢂ½ + z; #n = 1.5 ꢂ x, ꢂ1 + y, ꢂ½ + z; #o = ½ꢂx, 1ꢂy, ꢂ½ + z; #p = ꢂx, ꢂ½ + y, 1.5ꢂz;
#q = ꢂ½ + x, 1.5ꢂy, 2ꢂz; #r = x, 1.5 ꢂ y, ꢂ½ + z; #1 = ꢂx, 2 ꢂ y, ꢂz; #2 = ꢂx, 1 ꢂ y, ꢂz; #3 = 1 ꢂ x, 1 ꢂ y, 1 ꢂ z; #4 = 2 ꢂ x, 2 ꢂ y, 1 – z.

S. Rabaça et al. / Tetrahedron Letters 55 (2014) 6992–6997
6995
Figure 3. Crystal structure of compounds Ib viewed along a axis (a1) and along c
axis (a2) and of compound IIa viewed along a axis (b1) and b axis (b2).
Figure 5. Crystal structure of 1b: (a) viewed along b axis, and (b) side view of one
column.
Table 3
Redox potentials (vs Ag/Ag+) of the TTF-type donors 1a, 1b, 2a, and 3 as well as of
related donors (Half wave potentials E1/2 except ⁄ where anodic peak values are given
instead)
Donor
Solvent
1E1/2 (V)
2E1/2 (V)
1a
1b
DMF
DFM
Benzonitrile
DMF
DCM
0.38
0.42
0.27
0.64
0.742
0.43
0.54*
0.59*
0.60*
0.84
1.152
0.63
2a
318d
DCET-BzTTF20
pzdc-TTF5
DMF
*
Anodic peak potentials.
Acknowledgments
Work partially supported by FCT (Portugal) through contract
PTDC/QEQ-SUP/1413/2012.
Figure 4. ORTEP diagrams of compound 1b drawn at 30% probability level, showing
the atomic numbering scheme in the top (a) and lateral (b) molecular views.
Supplementary data
Supplementary data (crystallographic data for the structural
analysis have been deposited with the Cambridge Crystallographic
Data Centre, CCDC 1015265-1015269 for compounds 1a, Ia, Ib, IIa,
IIb) associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.tetlet.2014.10.111. These data
include MOL files and InChiKeys of the most important compounds
described in this article.
In conclusion we have prepared a variety of new extended TTF-
type symmetric and asymmetric donors fused with cyanobenzene
and dicyanobenzene moieties. The crystal structures of these
donors are dominated by a large number of S mediated contacts.
The crystal structure of compound 1b presents a strong segrega-
tion of the ethyl cyano groups and the TTF cores in alternated lay-
ers. These new molecules are expected to be used directly as
electroactive donors or as precursors for the preparation of new
extended cyano-TTF fused dithiolene ligands with the potential
to provide solids with interesting electrical and magnetic proper-
ties. In particular these molecules will allow to further explore
the possible role of the cyano groups in crystal engineering, either
coordinating to transition metals or promoting weak intermolecu-
lar interactions such as hydrogen and halogen bonding with halo-
genated anions.
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Santos, I. C.; Almeida, M. Eur. J. Inorg. Chem. 2008, 4728–4734.
solution after cooling to ambient temperature. Mp 228–233 °C; Rf = 0.72. IR
(KBr) = 3069; 3051 (ArAH), 2981; 2937 (CH2), 2252; 2230 (C„N), 1563 (C@C),
1123 (ArAS), 522 (CAS) cmꢂ1 1H NMR (300 MHz, DMSO-d6, 25 °C, TMS)
.
d = 8.320 (s, 1H), 3.176 (t, J = 6.6 Hz, 2H), 2.890 (t, J = 6.6 Hz, 2H). 13C
(75.3373 MHz), DMSO-d6: d = 151.6, 143.9, 128.4, 127.4, 119.6, 116.2, 112.9,
109.4, 31.6, 18.9. Anal. Calcd for C18H10N4S6: C 45.54; H 2.14; N 11.80; S 40.53.
Found C 44.98, H 2.40, N 11.90, S 40.75.
It was possible to isolate one of the other two products of the coupling reaction
resultant from the self-coupling of the reactants: compound 3, 0.229 g;
0.0.42 mmol; yield = 15%; Mp 189 °C; Rf = 0.2. IR (KBr) = 2922 (CH2), 2249
(C„N), 1590 (C@C), 1233 (CAC), 771 (CAS) cmꢂ1 1H NMR (300 MHz, DMSO-d6,
.
25 °C, TMS) d = 3.16 (t, J = 9 Hz, 2H), 2.87 (t, J = 9 Hz, 2H). 13C (75.3373 MHz),
DMSO-d6: d = 127.62, 118.83, 109.47, 30.86, 18.23.
As in case of compound 2a, also compound 2b is insoluble in common organic
solvents. The insolubility of 2b did not allow the pure isolation of this
compound. It stays at the top of the silica gel column chromatography.
10. Dicyanodibenzenetetrathiafulvalene, dcdb-TTF (2a): The compound IIa (0.79 g,
4.09 mmol) was suspended in the mixture of triethyl phosphite (10 mL) and
toluene (10 mL). The mixture was heated up to 120 °C under nitrogen
atmosphere and stirred for 3 h. During the reaction a yellow precipitate was
formed. After cooling to room temperature, 20 mL of methanol was added to
the reaction mixture to complete the precipitation. The product was isolated
by filtration as a yellow powder, washed with methanol, and dried under
vacuum (0.553 g, 1.56 mmol, yield = 76%). Mp >254 °C. IR (KBr pellet) = 3056
(ArAS), 2227 (C„N), 1577 (C@C), 1452 (C@C), 1122 (ArAS), 582 (CAS); Anal.
Calcd for C16H6N2S4: C 54.21; H 1.71; N 7.90; S 36.18. Found C 54.67; H 1.87; N
7.76; S 36.24.
5. Rabaça, S.; Oliveira, S.; Santos, I. C.; Almeida, M. Tetrahedron Lett. 2013, 54,
6635–6639.
6. Devic, T.; Bertran, J. N.; Domercq, B.; Canadell, E.; Avarvari, N.; Auban-Senzierc,
P.; Fourmigue, M. New J. Chem. 2001, 25, 1418–1424.
7. Whenever required, the solvents were dried and purified by standard
procedures,22 freshly distilled, and saturated with nitrogen prior to use. All
starting reagents were purchased from commercial sources and used without
further purification or synthesized from published methods. The thione Ia was
prepared as previously described.11 The ketone III was obtained after a regular
S to O exchange reaction of the 4,5-cyanoethylthio)-1,3-dithiole-2-thione.15
Other chemicals were commercially obtained and used without further
purification. Yields were calculated for the pure compounds. Column chroma-
tography was carried out using silica gel (0.063 0.2 mm) from SDS. IR spectra
were obtained on a Perkin–Elmer 577 spectrophotometer. 1H and 13C NMR
spectra were recorded with an Oxford Varian Unity 300 with DMSO-d6 as
solvent and using TMS as internal reference. Elemental analyses of the isolated
compounds were performed at CTN analytical services using an EA 110 CE
Instruments automatic analyzer. Melting points were performed on a Stuart
Scientific SMP2.
8. Cyanobenzenedicyanoethylthiotetrathiafulvalene, cbdc-TTF (1a): Compound Ia
(0.55 g; 2.62 mmol) and III (0.8 g; 2.77 mmol) were suspended in 10 mL of
triethyl phosphite (P(OEt)3). The mixture was heated up to 90 °C under
nitrogen atmosphere and stirred for 16 h. During the reaction an orange
precipitate was formed. Upon cooling to ambient temperature the precipitate
was filtered off and washed with 3 ꢁ 10 mL of methanol and dried under
vacuum.
The insolubility in common organic solvents prevents further characterization
of this compound by NMR techniques.
11. Cerdeira, A. C.; Afonso, M. L.; Santos, I. C.; Pereira, L. C. J.; Coutinho, J. T.; Rabaça,
S.; Simão, D.; Henriques, R. T.; Almeida, M. Polyhedron 2012, 44, 228–237.
12. 4,5-Cyanobenzene-1,3-dithiole-2-thione (Ib): A mixture of potassium sulfide
(43%, 3 g, 11.7 mmol), carbon disulfide (2 mL, 33 mmol) and
dimethylformamide (8 mL) was stirred at room temperature for 3 h. To the
resulting
red
suspension
of
potassium
trithiocarbonate,
4,5-
dichlorophthalonitrile (1.97 g, 10 mmol) was added, and the mixture was
further stirred for 24 h at 50 °C. The mixture was then poured into water
(100 mL), filtered, dried in vacuum, and compound Ib (1.38 g, 5.9 mmol,
yield = 59%) was isolated as a yellow solid after separation by silica gel column
chromatography. Mp 247–250 °C; Rf = 0.45 (CH2Cl2/hexane, 3:1). IR
(KBr) = 3076 (ArAH), 2227 (C„N), 1568 (C@C), 1220 (CAC), 1120 (ArAS),
1085 (C@S), 692 (CAS) cmꢂ1 1H NMR (300 MHz, DMSO-d6, 25 °C, TMS):
.
d = 8.633 (s, 1H), 13C (75.3373 MHz, DMSO-d6): d = 113.6, 116.1, 128.4, 147.0,
213.0. Anal. Calcd for C9H2N2S3: C 46.13, H 0.86, N 11.96, S 41.05. Found C
46.00, H 0.59, N 11.45, S 39.38.
13. 4-Cyanobenzene-1,3-dithiole-2-one (IIa): Under Argon, a solution of mercuric
acetate (1.54 g, 4.84 mmol) in acetic acid (30 mL) was drop wise added to a
solution of 4-cyanobenzene-1,3-dithiole-2-thione (0.47 g, 2.2 mmol) in
dichloromethane (125 mL) and stirred for 3 h. The resulting solution was
filtered under Celite, washed with a saturated solution of NaHCO3 (3 ꢁ 50 mL),
H2O (3 ꢁ 50 mL), and then dried with MgSO4. The dichloromethane was
evaporated and the light yellow residue was purified on a silica gel column
using dichloromethane as eluent. After evaporating the solvent, the resulting
pale yellow powder, compound IIa (0.346 g, 1.79 mmol, yield = 81.4%), was
dried overnight under vacuum. Mp 179 °C; Rf = 3.5 (CH2Cl2). IR (KBr) = 3083
(ArAH), 2229 (C„N), 1680 (C@O), 1560 (C@C), 1199 (CAC), 1122 (ArAS), 702
The pure compound 1a (0.436 g; 0.97 mmol, yield = 37%) was isolated as an
orange solid after separation by silica gel column chromatography, using DCM/
MeOH (v:v = 50:1) as eluent. Mp 192 °C; Rf = 0.76. IR (KBr) = 3074 (ArAH),
2960; 2923 (CH2), 2252; 2225 (C„N), 1463; 1564 (C@C), 1120 (ArAS), 582
(CAS) cmꢂ1 1H NMR (300 MHz, DMSO-d6, 25 °C, TMS) d = 8.07 (s, 1H), 7.786 (d,
.
J = 8 Hz, 1H), 7.683 (d, J = 8 Hz, 1H), 3.112 (t, J = 6.6 Hz, 2H), 2.758 (t, J = 6.6 Hz,
2H). 13C (75.3373 MHz), DMSO-d6: d = 151.6, 142.9, 131.0, 128.0, 126.3, 124.0,
119.6, 118.0, 109.8, 31.6, 18.9. Anal. Calcd for C17H11N3S6: C 45.41; H 2.47; N
9.34; S 42.78. Found C 44.58; H 2.53; N 9.11; S 42.42.
(CAS) cmꢂ1 1H NMR (300 MHz, CDCl3, 25 °C, TMS) d = 7.79 (d, J = 1.2 Hz, 1H),
.
7.64–7.58 (m, 2H). 13C (75.3373 MHz, CDCl3, TMS): d = 187.4, 138.2, 134.0,
129.9, 126.1, 123.6, 117.4, 111.0. Anal. Calcd for C8H3NOS2: calcd C 49.73, H
1.56, N 7.25, S 33.18; found C 49.57, H 1.84, N 7.32, S 33.24.
It was possible to isolate one of the other two products of the coupling reaction
resultant from the self-coupling of the reactants: compound 3, 0.3169 g;
0.582 mmol; yield = 21%; Mp 189 °C; Rf = 0.2. IR (KBr) = 2922 (CH2), 2249
14. 4,5-Cyanobenzene-1,3-dithiole-2-one (IIb): Under anaerobic conditions, the
(C„N), 1590 (C@C), 1233 (CAC), 771 (CAS) cmꢂ1
.
1H NMR (300 MHz, DMSO-d6,
mercuric acetate (1.16 g, 3.63 mmol) was added to
cyanobenzene-1,3-dithiole-2-thione (0.28 g, 1.21 mmol) in
a
solution of 4,5-
mixture of
25 °C, TMS) d = 3.16 (t, J = 9 Hz, 2H), 2.87 (t, J = 9 Hz, 2H). 13C (75.3373 MHz),
DMSO-d6: d = 127.62, 118.83, 109.47, 30.86, 18.23. Anal. Calcd for C18H16N4S8:
C 39.99; H 2.96; N 10.28; S 47.08. Found C 39.51; H 3.12; N 10.63; S 47.16.
The poor solubility of 2a in common organic solvents did not allow the pure
isolation of this compound using the procedure described above. The
compound 2a stays at the top of the silica gel column chromatography,
mixed with some silica gel (the crude mixture, before the chromatography
separation, is mixed with some silica gel to facilitate the introduction of the
crude in to the column). An alternative procedure was tested on a smaller scale.
Before the column chromatography the crude product was purified by soxhlet
extraction with hot DCM to isolate the insoluble compound 2a. The extracted
DCM solution was evaporated to dryness and the mixture product was
chromatographed, using DCM/MeOH (v:v = 50:1) as eluent.
a
chloroform and acetic acid (3:1) (45 mL) and stirred overnight. The resulting
solution was filtered under celite, and washed firstly with a fraction of water
(40 ml), then with a saturated solution of NaHCO3 (40 ml) and to finish with
other fraction of water (40 ml) and then dried with MgSO4 (30 min). The
solvent was evaporated and the resulting light yellow precipitated, compound
IIb (0.17 g, 0.78 mmol, yield = 64.4%), was dried overnight under vacuum. Mp
>247 °C; Rf = 3.0 (CH2Cl2). IR (KBr) 3086 (ArAH), 2233 (C„N), 1692 (C@O),
1574 (C@C), 1218 (CAC), 1125 (ArAS) cmꢂ1 1H NMR (400 MHz, CDCl3):
.
d = 8.68 (s, 2H). 13C NMR (75.3373 MHz, DMSO-d6): d = 189.32, 139.28, 123.57,
129.39, 116.12, 113.1. Anal. Calcd for C9H2N2OS2: C 49.53; H 0.92; N 12.84; S
29.38. Found C 49.19; H 1.02; N 12.18; S. 28.24.
15. (a) Svenstrup, N.; Becher, J. Synthesis 1995, 215–235; (b) Svenstrup, N.;
Rasmussen, K. M.; Hansen, T. H.; Becher, J. Synthesis 1994, 809–812.
The main purpose of this coupling reaction was the hetero coupling of the Ia
and III with the synthesis of compound 1a in a good yield, compounds 2a and 3
were considered side products of the reaction result of the reactants homo
coupling.
16. (a) Loosli, C.; Jia, C.; Liu, S.; Haas, M.; Dias, M.; Levillain, E.; Neels, A.; Labat, G.;
Hauser, A.; Decurtins, S. J. Org. Chem. 2005, 70, 4988–4992; (b) Jia, C.; Liu, S.;
Ambrus, C.; Labat, G.; Neels, A.; Decurtins, S. Polyhedron 2006, 25, 1613–1617.
17. The X-ray diffraction data for compounds Ia, Ib, IIa, IIb, and 1b were collected
on a Bruker APEXII CCD diffractometer equipped with an Oxford Cryosystems
9. Dicyanobenzenedicyanoethylthiotetrathiafulvalene,
dcbdc-TTF
(1b):
This
compound was prepared using the same method described for 1a, using
precursor Ib (0.6 g; 2.56 mmol) instead of precursor Ia. The crude obtained was
purified by column chromatography with DCM/MeOH (v:v = 50:1) as eluent.
The pure compound 1b (0.413 g; 0.87 mmol, yield = 34%) was isolated as a red
solid after column chromatography. Single crystals of 1b, suitable for RX
measurements were obtained from slow evaporation of a refluxed chloroform
low-temperature device at 150 K in the
x and u scan mode. A semi empirical
absorption correction was carried out using SADABS.23 Data collection, cell
refinement, and data reduction were done with the SMART and SAINT
programs.24 The structures were solved by direct methods using SIR9725 and
refined by full-matrix least-squares methods with the SHELXL9726 program

S. Rabaça et al. / Tetrahedron Letters 55 (2014) 6992–6997
6997
using the WINGX27 software package. Nonhydrogen atoms were refined with
anisotropic thermal parameters whereas H-atoms were placed in idealized
positions and allowed to refine riding on the parent C atom. Molecular graphics
were prepared using ORTEP328 and MERCURY 1.4.2.29
21. Rabaça, S.; Cerdeira, A. C.; Neves, A. I. S.; Dias, S. I. G.; Mézière, C.; Santos, I. C.;
Pereira, L. C. J.; Fourmigué, M.; Henriques, R. T.; Almeida, M. Polyhedron 2009,
28, 1069–1078.
22. Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals;
Pergamon: Oxford, 1988.
23. Sheldrick, G. M. SADABS; Bruker AXS: Madison, Wisconsin, USA, 2004.
24. Bruker SMART and SAINT; Bruker AXS: Madison, Wisconsin, USA, 2004.
25. Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.;
Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. App. Crystallogr.
1999, 32, 115–119.
18. (a) Bouguessa, S.; Gouasmia, A. K.; Golhen, S.; Ouahab, L.; Fabre, J. M.
Tetrahedron Lett. 2003, 44, 9275–9278; (b) Liu, S.-X.; Dolder, S.; Rusanov, E. B.;
Stoeckli-Evans, H.; Decurtins, S. C. R. Chimie 2003, 6, 657–662; (c) Devic, T.;
Avarvari, N.; Batail, P. Chem. Eur. J. 2004, 10, 3697–3707; (d) Belo, D.; Figueira,
M. J.; Nunes, J. P. M.; Santos, I. C.; Almeida, M.; Crivillers, N.; Rovira, C. Inorg.
Chim. Acta 2007, 360, 3909–3914.
19. Cyclic voltammetry data were obtained using
a
BAS C3 Cell Stand. The
26. Sheldrick, G. M. SHELXL97, Programs for Crystal Structure Analysis (Release97-2);
Institut fur Anorganische Chemie der Universitat: Tammanstrasse 4, D-3400
Goettingen, Germany, 2008.
27. Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.
28. Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
measurements were performed at room temperature in dimethylformamide
solutions, containing [n-Bu4]PF6 (0.1 M) as supporting electrolyte, with a scan
rate of 100 mV/s using platinum wire working and counter electrodes and a
Ag/Ag+ reference electrode.
20. Boudiba, L.; Kaboub, L.; Gousamia, A.; Fabre, J. M Synthesis 2005, 8, 1291–
1296.
29. Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Shields, G. P.; Taylor, R.;
Towler, M.; van de Streek, J. J. Appl. Crystallogr. 2006, 39, 453–457.