Bis(dithiomethyl-tetrathiafulvalene) with two phenyl-phosphino bridges

Article abstract of DOI:10.1016/j.crci.2010.04.010

The single crystal X-ray structure of the precursor dithiomethyl- tetrathiafulvalene (MeS)₂TTF is reported, together with theoretical calculations at DFT level, which afforded two energy minima corresponding to cis and trans orientations of the thiomethyl substituents. The bis(tetrathiafulvalene) reaction of this TTF derivative followed by the reaction with phenyldichlorophosphine provides a new rigid bis(tetrathiafulvalene [TTF]) containing a 1,4-dihydro-1,4-diphosphinine ring between the two redox active units. Its solid-state structure, determined by single crystal X-ray diffraction analysis, shows the coexistence of both cis and trans isomers. Cyclic voltammetry measurements are in accordance with the existence of a communication between the two TTFs, as illustrated by the splitting of the oxidation waves.

Full text of DOI:10.1016/j.crci.2010.04.010

C. R. Chimie 13 (2010) 1227–1232
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´
Full paper/Memoire
Bis(dithiomethyl-tetrathiafulvalene) with two phenyl-phosphino bridges
*
Ion Danila, Narcis Avarvari
ˆ
Laboratoire chimie et inge´nierie mole´culaire (CIMA), UMR 6200 CNRS-universite´ d’Angers, UFR Sciences, batiment K, 2, boulevard Lavoisier,
49045 Angers, France
A R T I C L E I N F O
A B S T R A C T
Article history:
The single crystal X-ray structure of the precursor dithiomethyl-tetrathiafulvalene
(MeS)2TTF is reported, together with theoretical calculations at DFT level, which afforded
two energy minima corresponding to cis and trans orientations of the thiomethyl
substituents. The bis(tetrathiafulvalene) reaction of this TTF derivative followed by the
reaction with phenyldichlorophosphine provides a new rigid bis(tetrathiafulvalene [TTF])
containing a 1,4-dihydro-1,4-diphosphinine ring between the two redox active units. Its
solid-state structure, determined by single crystal X-ray diffraction analysis, shows the
coexistence of both cis and trans isomers. Cyclic voltammetry measurements are in
accordance with the existence of a communication between the two TTFs, as illustrated by
the splitting of the oxidation waves.
Received 9 April 2010
Accepted after revision 14 April 2010
Keywords:
Tetrathiafulvalenes
Rigid phosphines
Crystalline structures
Mixed valence species
Main group chemistry
´
ß 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
The fused derivatives (o-DMTTF)2(SiMe2)2, (o-DMTTF)2
(GeMe2)2 [12], and (o-DMTTF)2(PPh)2 [11] have been
Tetrathiafulvalenes (TTF) and functional derivatives
represent a well-known wide family of electroactive sulfur
rich compounds [1], extensively used for various applica-
tions in molecular electronics and optoelectronics [2]. For
many of these applications, the occurrence of multiple
redox states is an important prerequisite. One of the
straightforward strategies to address this issue is the use of
dimeric TTF, in which, depending on the degree of the
through-bond or through-space interactions between the
redox active units, intramolecular mixed valence species
can be evidenced in solution and/or in the solid state [3]. A
particularly interesting family of bis(TTF) is that containing
either one heteroatomic linker connecting the TTF moieties
in close vicinity, such as the series X(TTF)2, with X = S or Se
[4], Te [5], PPh, SiMe2 or Hg [6], Me2Si–SiMe2 [7], and SbMe
[8], or two heteroatomic bridges as in the rigid derivatives
X2(TTF)2, with X = S [9], Te [10], PPh [11], SiMe2 and GeMe2
[12] (Scheme 1).
described by us, together with the (o-DMTTF)2(S = PPh)2
compound and coordination bimetallic complexes based
on the last 1,4-dihydro-1,4-diphosphinine system [13]. In
these compounds we have isolated, in solution or solid
state, mixed valence species and demonstrated by
spectroscopic and theoretical investigations extensive
electron delocalization over both TTF units. One of the
possible modifications of this type of rigid dimeric system
consists of the variation of the lateral substituents on both
TTFs, while keeping the same heteroatomic bridges, in
order to extend the scope of these valuable precursors. We
have thus decided to replace the lateral methyl substi-
tuents by thiomethyl ones in the bis(TTF)-diphosphinine
fused system, since it is known that additional sulfur atoms
attached to the TTF skeleton can engage in intermolecular
S ꢀ ꢀ ꢀ S contacts in the solid state. Moreover, the thiomethyl
substituents are expected to insure a better solubility
of the rigid system. We describe herein the synthesis
and single crystal X-ray structure of the bis(TTF)
[(MeS)2TTF]2(PPh)2, preceded by the description of the
solid state structure and
precursor (MeS)2TTF.
a theoretical study of the
* Corresponding author.
E-mail address: narcis.avarvari@univ-angers.fr (N. Avarvari).
1631-0748/$ – see front matter ß 2010 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2010.04.010

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I. Danila, N. Avarvari / C. R. Chimie 13 (2010) 1227–1232
Scheme 1.
Scheme 2. Synthesis of 1.
2. Results and discussion
2.1. Structural and theoretical investigations on the
dithiomethyl-tetrathiafulvalene precursor
The precursor we have used for the preparation of the
bis(TTF) system was the dithiomethyl-tetrathiafulvalene
(MeS)2TTF (Scheme 2), prepared using the published
procedure involving the phosphite mediated cross cou-
pling of the bis(thiomethyl)-dithiolethione half with the
dithiolone-dicarboxylate half, followed by the double
decarboxylation of the TTF-diester [14]. The spectroscopic
data of the compound were in agreement with those
described in the literature [15]. In the course of our
investigations we have succeeded to crystallize this
precursor, for which the solid-state structure was
unknown. Large size orange single crystals of (MeS)2TTF
were grown after several hours from a solution of
(MeS)2TTF, in a small volume of diethyl ether, poured in
a large excess of hexane. The compound crystallizes in the
orthorhombic system, non-centrosymmetric space group
P212121, with one independent molecule in the unit cell
(Fig. 1).
Fig. 1. Molecular structure of (MeS)2TTF (a) and side view of the molecule
(b).
tions of the thiomethyl substituents with respect to the TTF
plane (Fig. 2).
The two minima are isoenergetic
(DEtrans–
cis = 0.39 kcal moleꢁ1) and are characterized by the folding
of the dithiole ring adjacent to the substituents, as
observed in the experimental solid-state structure. Never-
theless, the orientation of the thiomethyl substituents in
both equilibrium conformations is different with respect to
the experimental one, since in the trans geometry the
methyl groups are located above and below the TTF plane
All the bond lengths and angles are in the usual range of
neutral TTFs, together with the moderate folding of the
dithiole ring adjacent to the thiomethyl substituents,
amounting to 15.88 around the S3 ꢀ ꢀ ꢀ S4 hinge. Interesting-
ly, the thiomethyl substituents arrange in a nonsymmetric
manner, with the methyl group defined by C8 located
above the TTF mean plane (dihedral angle C8S6C6C5
of 1038), while the other methyl group defined by C7 lies
practically in the TTF plane (dihedral angle C7S5C5C6
of 1618). In order to evaluate whether this conformation
observed in the solid state corresponds to an equilibrium
geometry in the gas phase, we have undertaken theoretical
calculations at the DFT level, with the B3LYP hybrid
functional [16] and the 6-31(+)G(d) basis set. The
geometry optimizations provided two energy minima
(checked by frequency calculations which were all
positive) corresponding to relative trans and cis orienta-
Fig. 2. Optimized geometries for (MeS)2TTF: trans (a) and cis (b); DFT/
B3LYP/6-31(+)G(d).

I. Danila, N. Avarvari / C. R. Chimie 13 (2010) 1227–1232
1229
Fig. 3. Molecular structure of the cis isomer in the crystalline structure of 1.
Fig. 4. Molecular structure of the trans isomer in the crystalline structure of 1.
(the dihedral angles C15S13C3C2 and C16S14C2C3 are
70.78 and 111.38, respectively), while in the cis geometry,
with the methyl groups on the same side of the TTF plane,
the angles are wider (125.1 and 123.28), probably because
of the larger steric hindrance. Therefore, it is very likely
that the rotation barrier of the two substituents is very
small and the packing effects are responsible for the
observed experimental conformation. Note that in the
monosubstituted (MeS)TTF the methyl group is also
arranged above the TTF plane in the optimized geometry
[17].
However, when diethyl ether was layered onto the top of a
solution of 1 in a small volume of THF, very small and thin
plate-like orange crystals have been obtained within
several hours. Variation of the crystallization conditions
did not afford any improvement of the crystal quality.
Single crystal X-ray analysis on a small crystalline plate
allowed the collection of a rather fair data set when taking
into account the size of the measured crystal. This explains
the mediocre quality of the crystal structure, with a large
value for the reliability factor R. However, the gross
connectivity between atoms could be undoubtedly
established; however, because of the relatively large
esd’s values, no fine analysis or comparison of the bond
lengths and angles will be further performed. The
compound crystallizes in the triclinic system, centrosym-
metric space group P–1, with one cis isomer and one half
trans isomer, located on an inversion center, in the
asymmetric unit (Fig. 3 for the cis and Fig. 4 for the trans
isomers).
As can be observed in Fig. 3, the solid-state conforma-
tion of the cis isomer does not present any symmetry
element. The most striking difference between the two TTF
units consists in the different arrangement of the SMe
substituents, since C1A and C2A methyl groups are in
relative cis position, while C15A and C16A are in trans,
although the dihedral angle for the latter is rather wide,
providing a conformation close to that observed in the
precursor (MeS)2TTF (vide supra). The central dipho-
sphinine ring is folded around the P ꢀ ꢀ ꢀ P hinge by about
38.68, to be compared to 30.48, the folding angle measured
in the case of the (o-DMTTF)2(PPh)2 analogue [11]. The
other component found in the crystal structure of 1 is the
trans isomer, which conformation is symmetric with
respect to the inversion center (Fig. 4).
2.2. Synthesis, structural analysis and electrochemistry of
[(MeS)2TTF]2(PPh)2
1
The preparation of 1 has been achieved in a one-pot
protocol, previously applied in the preparation of (o-
DMTTF)2(PPh)2 [11], upon bis(lithiation) of the precursor
(MeS)2TTF with LDA, followed by trapping the
bis(lithiated) TTF with PhPCl2 (Scheme 2).
The cis/trans ratio in the compound purified by
column chromatography, as determined by 31P NMR, is
4:1, with the chemical shift for the cis isomer appearing at
ꢁ21.1 ppm, and the one for the trans isomer at ꢁ25.4 ppm.
The cis and trans isomers of 1 arise from the relative
orientation of the phenyl rings on the phosphorous
atoms with respect to the central six-member ring. The
chemical shifts for the two isomers have been assigned
by comparison with the ones for the analogue (o-
DMTTF)2(PPh)2, for which the preferential crystallization
of the cis isomer from a toluene solution of the isomeric
mixture could be achieved [11]. By applying the same
crystallization conditions in the case of 1, we could not
grow any crystal, probably because of its better solubility.

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I. Danila, N. Avarvari / C. R. Chimie 13 (2010) 1227–1232
Fig. 5. Alternate stacking of trans/cis/cis isomers of 1 along c.
The methyl substituents are trans each other on both
cation–dication species (
potential, formation of trication–tetracation species
E = 80 mV) (Fig. 6). These wave separations are some-
what smaller than those measured for (o-DMTTF)2(PPh)2,
which were both of 120 mV [11], but in that case only
the cis isomer was measured and not the mixture.
However, these results suggest through-bond communi-
cation between the two-redox active units, as previously
emphasized in other heteroatom containing rigid dimers
[11,12].
The oxidation potential values are similar to those
measured for (o-DMTTF)2(PPh)2 and show that the new
rigid bis(TTF) system can serve as precursor for radical
cation salts, keeping in mind that intramolecular mixed
valence species could be in principle obtained.
DE = 60 mV), and then, at higher
sides of the molecule, thus corresponding to the optimized
trans conformation found in (MeS)2TTF. The central six-
member ring is planar. Interestingly, this represents the
first crystal structure of a trans isomer of the free ligand in
this series of compounds, since for (o-DMTTF)2(PPh)2 only
the cis isomer could be crystallized so far. In the crystalline
packing the two isomers are not isolated, but form mixed
stacks along c, with an alternation of a dyad of cis isomers,
corresponding each other through the inversion center,
and a trans isomer twisted by about 358 with respect to the
neighboring cis isomers, a likely consequence of the steric
hindrance due to the phenyl rings (Fig. 5).
(
D
Cyclic voltammetry measurements on the cis/trans
mixture of 1 reveal the splitting of both oxidation waves,
resulting into a pair of two closely spaced one-electron
processes, corresponding to the successive formation of
3. Conclusion
A
new rigid bis(TTF) system consisting in fused
(MeS)2TTF donors to a central 1,4-dihydro-1,4-dipho-
sphinine ring has been successfully prepared and struc-
turally characterized as a mixture of cis and trans isomers.
This represents the second example of this type of rigid
bis(TTF) with phosphino linkers, and the first one where
the trans isomer could be analyzed by single-crystal X-ray
diffraction. The (MeS)2TTF precursor has been also
structurally characterized. Theoretical calculations at
DFT level afforded two energy minima for this donor,
with cis or trans mutual orientations of the SMe
substituents. Both orientations have been found in the
solid state structure of the bis(TTF) donor. The electro-
chemical behaviour of [(MeS)2TTF]2(PPh)2, showing four-
one electron processes in cyclic voltammetry, demon-
strates electronic communication between the TTF units,
and, therefore, the isolation of mixed valence species can
be envisaged.
Fig. 6. Cyclic voltammetry of 1 (ref. Ag/AgCl, 0.1 M TBAPF6 in CH2Cl2/
MeCN, 0.1 V sꢁ1). Insert: The deconvoluted curves, better illustrating
the peak-to-peak separation of the one-electron processes. E11=2
0:54 V; E21=2 ¼ 0:60 V; E13=2 ¼ 0:92 V; E41=2 ¼ 1:00 V.
¼

I. Danila, N. Avarvari / C. R. Chimie 13 (2010) 1227–1232
1231
Table 1
Crystallographic data, details of data collection and structure refinement parameters.
(MeS)2TTF
1
Formula
Mw
C8H8S6
296.50
orthorhombic
P212121
8.8699(11)
10.3346(11)
13.6162(14)
90
C28H22P2S12 (1 cis +0.5 trans)
1207.67
triclinic
P-1
Cryst syst
Space group
˚
a (A)
14.641(8)
14.681(5)
15.218(8)
89.39(3)
72.90(4)
60.19(4)
2676.2
2
˚
b (A)
˚
c (A)
a
b
g
(deg)
(deg)
90
(deg)
90
3
˚
V (A )
1248.15
4
Z
T (K)
293(2)
1.578
293(2)
1.499
dcalcd, g cmꢁ3
m
(mmꢁ1
)
1.054
0.845
Total number of measured intensities
Abs correction
7722
8128
multi-scan
2419
multi-scan
4608
Number of unique data
Observed reflections
(I > 2s
(I))
1988
2361
Number of refined variables
˚
127
565
l
(A)
0.71073
0.0356
0.0472
0.988
0.71073
0.1227
0.2174
1.095
R(Fo)a
RwðFo2Þ
GoF
a
4. Experimental
graphite monochromator. The structures were solved
(SHELXS-97) by direct methods and refined (SHELXL-97)
by full-matrix least-square procedures on F2 [18]. All non-
hydrogen atoms of the donor molecules were refined
anisotropically, and hydrogen atoms were introduced at
calculated positions (riding model), included in structure
factor calculations but not refined. Crystallographic data for
the two structures of (MeS)2TTF and 1 have been deposited
with the Cambridge Crystallographic Data Centre, deposi-
tionnumberCCDC761647(DTM-TTF)andCCDC761648(1).
These data can be obtained free of charge from CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (e-mail: deposit@ccdc.
cam.ac.uk or http://www.ccdc.cam.ac.uk).
4.1. General
Reactions were carried out under argon. THF was
distilled from Na/benzophenone. NMR spectra were
recorded on a Bruker Avance DRX 500 spectrometer
operating at 202.39 MHz for 31P. Chemical shifts are
expressed in parts per million (ppm). The following
abbreviations are used: s, singlet. The (MeS)2TTF was
synthesized according to the published procedure [14].
4.2. Synthesis of [(MeS)2TTF]2(PPh)2
1
LDA (lithium diisopropylamide) (11 ml of a solution
0,79 M in hexane; 8,7 mmol) was added drop wise to a
solution of ortho-dithiomethyl-TTF (MeS)2TTF (1,184 g;
4 mmol) in 60 ml dry THF at ꢁ78 8C. The mixture was
stirred for 4 hours, following which PPhCl2 (0.57 ml; 4.
2 mmol) was added drop wise. After returning to room
temperature during the night, the solution was partially
evaporated and the compound was precipitated by adding
hexane. The precipitate was washed with methanol,
dissolved in toluene and purified by chromatography on
a silica column, eluant toluene/hexane 1:1. Yield 222 mg
4.4. Theoretical calculations
The optimized geometries have been obtained with the
Gaussian03 [19] package at the DFT level of theory. The
B3LYP functional [16] with the 6-31 + G* basis set has been
used. Vibrations frequency calculations performed on the
optimized structures at the same level of theory yielded
only positive values.
4.5. Cyclic voltammetry measurements
(0.3 mmol, 15%) of brown solid. 31P NMR (THF):
d
= ꢁ21.1
Cyclic voltammetry measurements were performed
using a three-electrode cell equipped with a platinum
millielectrode of 0.126 cm2 area, a silver wire pseudo-
reference electrode, and a platinum wire counter elec-
trode. The potential values were then readjusted with
respect to the Ag/AgCl electrode, using ferrocene as
internal reference. The electrolytic media involved a
0.1 mol Lꢁ1 solution of (n-Bu4N)PF6 in a CH2Cl2/MeCN
mixture. All experiments have been performed at room
temperature at 0.1 V sꢁ1. Experiments have been carried
(s, cis), ꢁ25,4 (s, trans).
4.3. X-Ray structure determinations
Details about data collection and solution refinement
are given in Table 1. X-ray diffraction measurements were
performed on a Bruker Kappa CCD diffractometer for 1, and
on a Stoe Imaging Plate System for (MeS)2TTF, both
˚
operating with a Mo-Ka (l = 0.71073 A) X-ray tube with a

1232
I. Danila, N. Avarvari / C. R. Chimie 13 (2010) 1227–1232
(b) J.D. Martin, E. Canadell, J.Y. Becker, J. Bernstein, Chem. Mater 5
(1993) 1199.
[6] M. Fourmigue´, Y.-S. Huang, Organometallics 12 (1993) 797.
[7] A. Hameau, F. Guyon, M. Knorr, C. Da¨schlein, C. Strohmann, N. Avarvari,
Dalton Trans (2008) 4866.
out with an EGG PAR 273A potentiostat with positive
feedback compensation.
Acknowledgements
[8] M. Ashizawa, H.M. Yamamoto, A. Nakao, R. Kato, Tetrahedron Lett 47
(2006) 8937.
[9] (a) V.Y. Khodorkovsky, J.Y. Becker, J. Bernstein, Synth. Met 56 (1993)
1931;
(b) E. Aqad, J.Y. Becker, J. Bernstein, A. Ellern, V. Khodorkovsky, L.
Shapiro, J. Chem. Soc. Chem. Commun (1994) 2775.
[10] (a) C. Wang, A. Ellern, J.Y. Becker, J. Bernstein, Tetrahedron Lett 35
(1994) 8489;
Financial support from the Ministry of Education and
Research (grant to I.D.) is gratefully acknowledged. This
work was also supported by the CNRS.
References
(b) C. Wang, A. Ellern, V. Khodorkovsky, J.Y. Becker, J. Bernstein, J.
Chem. Soc. Chem. Commun (1994) 2115;
[1] (a) J.L. Segura, N. Martin, Angew. Chem. Int. Ed 40 (2001) 1372;
(b) J.-L. Yamada, TTF Chemistry: fundamentals and applications
o;f tetrathiafulvalene, Springer-Verlag, Berlin and Heidelberg, 2004
(c) E. Ojima, H. Fujiwara, H. Kobayashi, A. Kobayashi, Adv. Mater 11
(1999) 1527.
[11] N. Avarvari, M. Fourmigue´, Chem. Commun (2004) 2794.
[12] F. Biaso, M. Geoffroy, E. Canadell, P. Auban-Senzier, E. Levillain, M.
Fourmigue´, N. Avarvari, Chem. Eur. J 13 (2007) 5394.
´
(c) D. Lorcy, N. Bellec, M. Fourmigue, N. Avarvari, Coord. Chem. Rev
253 (2009) 1398;
´
´
(d) D. Canevet, M. Salle, G. Zhang, D. Zhang, D. Zhu, Chem. Commun
[13] I. Danila, F. Biaso, H. Sidorenkova, M. Geoffroy, M. Fourmigue, E.
(2009) 2245.
Levillain, N. Avarvari, Organometallics 28 (2009) 3691.
[14] G.C. Papavassiliou, J.S. Zambounis, G.A. Mousdis, V. Gionis, S.Y. Yian-
nopoulos, Mol. Cryst. Liq. Cryst 156 (1988) 269.
[15] M. Fourmigue´, F. Krebs, J. Larsen, Synthesis 5 (1993) 509.
[16] (a) A.D. Becke, J. Chem. Phys 84 (1986) 4524;
[2] (a) M.R. Bryce, Adv. Mater 11 (1999) 11;
(b) M. Bendikov, F. Wudl, D.F. Perepichka, Chem. Rev 104 (2004)
4891;
(c) M. Mas-Torrent, C. Rovira, J. Mater. Chem 16 (2006) 433;
(d) M. Mas-Torrent, C. Rovira, Chem. Soc. Rev 37 (2008) 827.
[3] (a) T. Otsubo, Y. Aso, K. Takimiya, Adv. Mater 8 (1996) 203;
(b) M. Iyoda, M. Hasegawa, Y. Miyake, Chem. Rev 104 (2004)
5085.
[4] M.R. Bryce, G. Cooke, A.S. Dhindsa, D.J. Ando, M.B. Hursthouse, Tetra-
hedron Lett 33 (1992) 1783.
[5] (a) J.Y. Becker, J. Bernstein, M. Dayan, L. Shahal, J. Chem. Soc. Chem.
Commun (1992) 1048;
(b) A.D. Becke, J. Chem. Phys 98 (1993) 5648;
(c) C.T. Lee, W.T. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[17] C. Re´thore´, A. Madalan, M. Fourmigue´, E. Canadell, E.B. Lopes, M.
Almeida, R. Cle´rac, N. Avarvari, New J. Chem 31 (2007) 1468.
[18] G.M. Sheldrick, SHELXL91, release 97-2, program for the refinement of
crystal structures, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[19] Pople J.A. et al., Gaussian03, Revision B.03; Gaussian, Inc.: Wallingford
CT, 2004.