Synthesis, structure and electrochemical properties of two new unsymmetrical tetrathiafulvalene derivatives

Article abstract of DOI:10.1002/jhet.5570420515

Two new unsymmetrical tetrathiafulvalene (TTF) derivatives, 2,3-bis(cyanoethylthio)-6,7-(methylethylenedithio)tetrathiafulvalene (6a) and 2,3-bis(cyanoethylthio)-6,7-(cyclopentodithio)tetrathiafulvalene (6b), have been prepared and characterized by NMR, MS, IR and Elemental analyses. The molecular structures have been determined by X-ray crystallography. Their redox properties have been investigated by cyclic voltammetry in dichloromethane solution and each compound shows two reversible single-electron redox couples.

Full text of DOI:10.1002/jhet.5570420515

Jul-Aug 2005
Synthesis, Structure and Electrochemical Properties of two new
Unsymmetrical Tetrathiafulvalene Derivatives
847
*
Ming Xu, Yong Ji, Jing-Lin Zuo, Yi-Zhi Li and Xiao-Zeng You
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University,
Nanjing 210093, China.
Received December 16, 2004
Two new unsymmetrical tetrathiafulvalene (TTF) derivatives, 2,3-bis(cyanoethylthio)-6,7-(methyl-
ethylenedithio)tetrathiafulvalene (6a) and 2,3-bis(cyanoethylthio)-6,7-(cyclopentodithio)tetrathiafulvalene
(6b), have been prepared and characterized by NMR, MS, IR and Elemental analyses. The molecular struc-
tures have been determined by X-ray crystallography. Their redox properties have been investigated by
cyclic voltammetry in dichloromethane solution and each compound shows two reversible single-electron
redox couples.
J. Heterocyclic Chem., 42, 847 (2005).
Introduction
thiones/ones in the presence of phosphine [19] or phos-
phite in one pot. In this paper, we adopt the similar method
to synthesize two new unsymmetrical TTF compounds,
2,3-bis(cyanoethylthio)-6,7-(methylethylenedithio)tetra-
thiafulvalene (6a) and 2, 3-bis(cyanoethylthio)-6,7-
(cyclopentodithio)tetrathiafulvalene (6b).
Over the past 20 years, there has been extensive research
in the synthesis of new tetrathiafulvalene (TTF) and related
derivatives with the aim of preparing organic conductors
and superconductors [1]. Recently, more interest in func-
tional molecular materials based on TTF (Scheme 1) mole-
cules has attracted much attention from chemists, physicists
and materials scientists. TTF moiety possesses a fully
extended electronically delocalized core and the delocaliza-
tion can be further extended by choice of appropriate R
groups [2-5]. The number and position of the sulfur atoms
in those substituents show significant effect on the packing
of the donor molecules in the crystalline structure. As a
consequence, it is possible by modifying the substituents on
the TTF core to obtain a wide range of structures and phys-
ical properties. They may have some potential applications,
such as in Langmuir-Blodgett film, chemosensors [6-8],
magnetic [9-11], non-linear optics [12-14], switches and
others [15]. In addition, the TTF moiety is also a prime can-
didate in the synthesis of macrocyclic hosts for electron-
deficient compounds [16-17]. Most reported TTF donors
are symmetrical because of their ease of synthesis. During
the past two decades, there has been much synthetic effort
on unsymmetrical tetrathiafulvalenes and their derivatives.
Some satisfactory results have been attained with approach
to the successful preparation of varieties of functionalized
unsymmetrical TTF [18]. But they are less studied com-
pared to the symmetric analogues. The reason is that the
separation and purification of unsymmetrical TTF are more
difficult and troublesome experimentally.
Results and Discussion.
Syntheses of Unsymmetrical TTF Derivatives.
The syntheses of the target molecules 6a and 6b started
from (Et N) [Zn(dmit) ] (dmit = 2-thioxo-1,3-dithiole-4,5-
4
2
2
bis(thiolato)) is shown in Scheme 2. Alkylation of
(Et N) [Zn(dmit) ] is usually carried out in acetonitrile,
4
2
2
acetone or tetrahydrofuran. Oligo(4,5-dihydro-1,3-dithiole-
2,4,5-trithione) (4) which can act as an effective 4π compo-
nent, reacted with cyclopentene by heating to form Diels-
Alder adduct compound 5 in yield of 30%. Compound 2
was converted to compound 3 by a conventional method in
high yield. Papavassiliou et al. prepared a series of unsym-
metrical TTF derivatives using two distinct 1,3-dithiole
heterocycles [20]. The method is the quickest, most general
route to unsymmetrical TTF and it gives the best yields. In
consideration of less reactive thione, we optimized this
reaction to achieve TTF framework by coupling the 1,3-
dithiole-2-thione and 1,3-dithiole-2-one. The homo-cou-
pling products have been observed and can be removed
through column chromatography. Apparently, due to the
polarity of the cyanoethyl group compared to the normal
alkylthio group, the symmetrical byproducts tetrakis(2'-
cyanoethylthio)tetrathiafulvalene and tetrakis(alkylthio)-
tetrathiafulvalene have R values close to 0 and 1, respec-
tively. Therefore chromatography and separation of the
middle fraction gives the pure mixed coupling product.
f
Scheme 1
Electrochemical Cyclic Voltammetry Studies.
The redox potentials of new electron donors 6a and 6b
were measured in dichloromethane by cyclic voltammetry
(0.1 M TBAClO as supporting electrolyte, carbon fiber
4
−1
electrode as working electrode, scan rate 100 mV S ).
Most of unsymmetrical TTF derivatives can success-
fully be available by refluxing their corresponding
Two reversible single-electron redox couples are observed.

848
M. Xu, Y. Ji, J.-L. Zuo, Y.-Z. Li and X.-Z. You
Vol. 42
Table 1
Crystal Data, Data Collection and Structure Refinement for 6a and 6b
Scheme 2
6a
6b
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
C
H
N S
C H N S
17 16 2 8
504.80
293(2)
0.71073
Monoclinic
15 14
2
8
478.76
293(2)
0.71073
Triclinic
P-1
7.8142(17)
11.479(3)
12.683(3)
64.206(4)
82.428(4)
79.266(4)
1004.7(4)
2
P2 /c
1
20.159(3)
8.3200(11)
12.9181(17)
90
99.359(3)
90
2137.8(5)
4
1.568
0.842
1040
γ (°)
3
Volume (Å )
Z
D
3
(g/cm )
1.583
0.891
492
calc
-1
µ (mm )
F (000)
Crystal size
θ range for data collection (°) 1.99-25.25
Index ranges
023 × 0.20 × 0.15 0.30 × 0.20 × 0.20
2.05-25.25
-24 ≤ h ≤ 23
-9 ≤ k ≤ 9
-15 ≤ l ≤ 10
10465
-9 ≤ h ≤ 8
-13 ≤ k ≤ 13
-15 ≤ l ≤ 7
5087
No. reflections collected
No. independent reflections
R(int)
3559
3869
0.0322
0.0235
Data/restraints/parameters
Goodness-of-fit on F
3559/0/227
1.031
3869/0/244
0.916
2
Final R indices [I>2σ(I)]
R = 0.0645,
R = 0.0512,
1
1
i) acetone, 40 °C, 2 d, 57%; ii) CH CN, reflux 1.5 h, 87%; iii) CH COOH/CHCl
3
3
3
wR = 0.1333
wR = 0.1374
2
2
(v/v 3:1), quantitative; iv) I , EtOH, acetone,-50 °C, 2 h, 95%; v) 1, 4-dioxane, 75
2
Largest difference peak
0.350 / -0.408
0.589 / –0.510
°C, 2 h, 33%; vi) P(OEt) , 110 °C, 2 h
3
-3
and hole(e· Å )
Preparation of unsymmetrical TTF derivatives
For 6a, the first one-electron oxidation peak (E = 0.635
1/2
+
V) is assigned to 6a/6a ; the second reversible peak (E
0.915 V) is assigned to 6a /6a . Compound 6b shows
=
1/2
+
2+
these peaks at E = 0.628 V and 0.916 V. The redox
1/2
potentials for both compounds are close, indicating that the
two substitution groups here show similar electron effect
on the TTF core.
Description of Crystal Structure of 6a and 6b.
For crystal structure analysis, the crystal data, data col-
lection conditions and refinement data are given in Table 1.
A perspective view of the asymmetric unit with the
atom-numbering scheme and the projection of the molecu-
lar entity in the lattices are shown in Figure 1. For com-
pound 6a, S(1), S(4), S(5), S(6), C(1) and C(6) atoms are
nearly coplanar, the other sulfur atoms deviate to the same
side of the core plane by 0.70-0.92 Å. The planes formed
by atoms S(1), S(4), C(2), C(5) and S(5), S(6), C(7), C(8)
make angles of 20.4 and 21.0°, respectively, with the cen-
tral tetrathiafulvalene plane. The two cyanoethyl groups in
compound 6a are greatly deviated from this plane and bent
toward the same direction. The shortest intermolecular
Figure 1. ORTEP view of 6a and 6b with atom numbering scheme:
Hydrogen atoms are omitted for clarity. Ellipsoids are drawn at the 50%
probability level.

Jul-Aug 2005
Synthesis, Structure and Electrochemical Properties
849
S⋅⋅⋅S contacts between S(2) ⋅⋅⋅S(4') and S(2)⋅⋅⋅S(5')
(Figure 2) are 3.629(2) Å and 3.680(2) Å (related by the
symmetry operators of (1+x, y, z)), respectively, which are
less than the sum of the van der Waals radii (3.70 Å). From
the packing diagram of compound 6a, the crystal consists
of columns of molecules along a direction. The shorter
intermolecular C(1)-H⋅⋅⋅ S(8') contact is 3.599(7) Å (sym-
metry code : 1+x, −1+y, 1+z).
Figure 3. The packing diagram of compound 6b view along the b axis
(the dotted line representing shorter C-H···N interactions).
240C analyzer. The ir spectra were taken on a Vector22 Bruker
−1
Spectrophotometer (400-4000cm ) with KBr pellets. NMR
spectra were measured on a Bruker AM 500 spectrometer.
Chemical shifts were measured as δ units (ppm) relative to
tetramethylsilane. EI-MS spectra were recorded on a Varian MAT
311A instrument. Melting points were determined with a X-4
digital micro melting point apparatus and uncorrected. The cyclic
voltammetry was performed by a CHI660a-Analyser with the
electrochemical cell using a carbon fiber as the working elec-
trode, a platinum plate as auxiliary electrode and Ag/AgCl as ref-
erence electrode. Measurements were made in CH Cl solution
Figure 2. The packing diagram of compound 6a view along the a axis
(the dotted line representing S···S non-bonded contacts less than 3.7 Å).
2
2
and using 0.1 M tetrabutylammonium perchlorate as supporting
electrolyte. (Et N) [Zn(dmit) ] and oligo (1,3-dithiole-2,4,5-
4
2
2
trithione) were prepared by literature method [21].
Compound 6b has nearly the same flat tub conformation
and the most obvious difference is that the two cyanoethyl
groups bent such that they point in opposite directions rel-
ative to each other (Figure 3). No short intermolecular
S⋅⋅⋅S contact is observed, which may arise from the differ-
ent packing modes of the external units for these two com-
pounds. The shorter intermolecular interactions occur at
C(12)-H(12A)⋅⋅⋅N(2') (3.360(5) Å, symmetry code: x, 1/2-
y, -1/2+z); C(12)- H(12B)⋅⋅⋅N(2') (3.413(6) Å, symmetry
code: x, -1+y, z) and C(15)-H(15B)⋅⋅⋅N(2') (3.361(5) Å,
symmetry code: x, 3/2-y, 1/2+z).
X-ray Structure Determination.
The single crystal of compound 6a suitable for the X-ray struc-
ture analysis was grown from dichloromethane/diethyl ether.
Single crystals of 6b were obtained upon recrystallization from
CH Cl /CH OH. Intensity data were measured on a Bruker
2
2
3
Smart Apex CCD diffractometer with graphite monochromated
Mo-Kα (λ = 0.71073 Å) radiation using ω/2θ scan mode at 20
°C. The highly redundant data sets were reduced using SAINT
and corrected for Lorentz and polarization effects. Absorption
corrections were applied using SADABS supplied by Bruker.
Structures were solved by direct methods using the program
SHELXL−97. Non-hydrogen atoms were found in alternating
difference Fourier syntheses and least-squares refinement cycles
and, during the final cycles, refined anisotropically. All hydrogen
atoms were positioned geometrically and refined as riding, with
EXPERMENTAL
C-H distances of 0.97 Å and with U (H) = 1.2Ueq (C).
All the commercial reagents used were analytically pure and
without further purification. Schlenk techniques were used in car-
rying out manipulation under nitrogen atmosphere. Elemental
analyses for C, H, and N were performed on a Perkin-Elmer
iso
Crystallographic parameters and agreement factors are contained
in Table 1. CCDC-257504 and 257505 contain the supplementary
crystallographic data for this paper. These data can be obtained

850
M. Xu, Y. Ji, J.-L. Zuo, Y.-Z. Li and X.-Z. You
Vol. 42
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or
from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK [Fax: + 44-1223/336-033;
Email: deposit@ccdc.cam.ac.uk].
Science Foundation of China (NSF20201006 and 90101028).
REFERENCES AND NOTES
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In a typical procedure, 1 (6 mmol, 1.34 g) and compound 3 (4
mmol, 1.15 g) in 35 ml of P(OEt) were placed in a 50 ml round
3
bottom 3-neck flask fitted a reflux condenser. The mixture was
then heated to 110 °C. After reacting for 1 h, the red solution was
cooled to room temperature and 50 ml of methanol was added.
The mixture was further cooled in a refrigerator. A crude precipi-
tate was obtained at -20 °C and it was dissolved into
dichloromethane. 6a was isolated by silica gel column chro-
matography. The solution was concentrated, ethanol added and
cooled to −20 °C. Orange yellow needle crystals were obtained.
−1
Yield: 35% (based on 3), mp 128−130 °C; ir (KBr) (ν , cm ):
max
1410 (C-S), 1634 (C=C), 2248 (C≡N); MS (EI): m/z(%) = 478
+
1
(M , 22); H nmr (500 MHz, CDCl ): δ 1.50 (d, 3H, J = 6.90 Hz,
3
CH ), 2.74 (t, 4H, J = 6.90 Hz, SCH CH CN), 3.05 (dd, 1H, J =
3
2
2
12.9 Hz, J = 7.60 Hz, SCHHCH), 3.09 (t, 4H, J = 6.90 Hz,
SCH CH CN), 3.22 (dd , 1H, J = 12.9 Hz, J = 2.60 Hz,
2
2
13
SCHHCHCH ), 3.69 (m, 1H, J = 2.60 Hz, SCHCH ); C nmr
(500 MHz, CDCl ): δ 128.45, 117.80, 39.43, 37.39, 31.76,
21.28, 19.29.
Anal. Calcd for C
Found: C, 37.74; H, 2.98; N, 5.74.
3
3
3
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11 (1999).
H N S : C, 37.65; H, 2.92; N, 5.58.
15 14 2 8
2, 3-Bis(cyanoethylthio)-6,7-(cyclopentodithio)tetrathiafulva-
lene (6b).
Compound 6b was obtained in a similar method as an orange
yellow needle crystal in 38% yield. mp 133−134 °C; ir (KBr)
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−1
(ν , cm ): 1404 (C-S), 1627 (C=C), 2249 (C≡N); MS (EI):
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max
+
1
m/z(%) = 504 (M , 18); H nmr (500 MHz, CDCl ): δ 1.82 (dd,
2H, J = 14.0 Hz, J = 6.0 Hz, CH CH CH ), 1.98 (q, 2H, J = 4 Hz,
3
2
2
2
SCHCHHCH ), 2.21 (q, 2H, J = 5.5 Hz, SCHCHHCH ), 2.75 (t,
4H, J = 6 Hz, SCH CH CN ), 3.10 (t, 4H, J = 6 Hz,
2
2
2
2
13
SCH CH CN), 3.81 (dd, 2H, J = 5.5 Hz, J = 6 Hz, SCHCH );
C
2
2
2
nmr (500 MHz, CDCl ): δ 128.44, 125.75, 117.88, 54.36, 33.33,
31.85, 25.29, 19.38.
Anal. Calcd for C
Found: C, 40.42; H, 3.22; N, 5.59.
3
H N S : C, 40.47; H, 3.17; N, 5.55.
17 16 2 8
Acknowledgements.
This work was supported by The Major State Basic Research
Development Program (G2000077500), the National Natural