First fused perpendicular hybrid tetrathiafulvalene (TTF) dimers: A new strategy in π-extended and rigidified TTF

Article abstract of DOI:10.1021/ol025522t

(equation presented) The synthesis, theoretical calculations, and crystallographic and electrochemical properties of fused perpendicular tetrathiafulvalene (TTF) dimers incorporating both a TTF unit and a quinonoid π-extended TTF are described as a new st

Full text of DOI:10.1021/ol025522t

ORGANIC
LETTERS
2002
Vol. 4, No. 6
961-963
First Fused Perpendicular Hybrid
Tetrathiafulvalene (TTF) Dimers: A New
Strategy in π-Extended and Rigidified
TTF
Nicolas Gautier, Nuria Gallego-Planas, Nicolas Mercier, Eric Levillain, and
Pie´trick Hudhomme*
Inge´nierie Mole´culaire et Mate´riaux Organiques, UMR-CNRS 6501, 2 Bd LaVoisier,
49045 Angers, France
pietrick.hudhomme@uniV-angers.fr
Received January 7, 2002
ABSTRACT
The synthesis, theoretical calculations, and crystallographic and electrochemical properties of fused perpendicular tetrathiafulvalene (TTF)
dimers incorporating both a TTF unit and a quinonoid π-extended TTF are described as a new strategy for obtaining π-extended, rigidified,
and sulfur-rich analogues of TTF.
Since the discovery of tetrathiafulvalene (TTF) and its unique
properties as a π-donor, considerable work has been devoted
to the search for more sophisticated derivatives1 that are
prone to generation of charge-transfer complexes or radical
cation salts exhibiting two-dimensional networks upon
oxidation.2 This increase of dimensionality has been identi-
fied as a priority to prevent the metal-to-insulator transitions
at low temperature, as well as to achieve highly conducting
or superconducting materials.3 On this basis, space-extended
and sulfur-rich analogues of TTF constitute promising
candidates.4 Thus, bis(1,4-dithiafulven-6-yl)TTFs were proven
to afford original two-dimensional electroconductive materi-
als held by intermolecular intra- and interchain S‚‚‚S
contacts.5 Nevertheless, some difficulties were found in the
preparation of mixed valence salts from compound 1, the
crystals obtained being of insufficient quality to perform
physical measurements.6 The explanation found was an
unwanted intramolecular cyclization reaction occurring under
acidic or oxidative conditions.7
With the aim of suppressing such a side reaction, we
recently reported the “T-shaped” TTF dimer 2.8 This kind
of dimeric TTF derivative displaying multistage redox
behavior should provide the possibility of controlling the
stoichiometry and molecular assembly in the desired conduc-
(1) Segura, J. L.; Mart´ın, N. Angew. Chem., Int. Ed. 2001, 40, 1372.
(2) Bryce, M. R. J. Mater. Chem. 1995, 5, 1481.
(3) Farges, J. P. In Organic conductors. Fundamentals and applications;
Marcel Dekker Inc.: New York, 1994.
(5) (a) Salle´, M.; Jubault, M.; Gorgues, A.; Boubekeur, K.; Fourmigue´,
M.; Batail P.; Canadell, E. Chem. Mater. 1993, 5, 1196. (b) Salle´, M.;
Gorgues, A.; Jubault, M.; Boubekeur, K.; Batail P.; Carlier, R. Bull. Soc.
Chim. Fr. 1996, 133, 417.
(4) (a) Mart´ın, N.; Sa´nchez, L.; Seoane, C.; Ort´ı, E.; Viruela P. M.;
Viruela, R. J. Org. Chem. 1998, 63, 1268. (b) Pe´rez, I.; Liu, S.-G.; Mart´ın
N.; Echegoyen, L. J. Org. Chem. 2000, 65, 3796 and references therein.
(6) Morisson, V.; Salle´, M.; Fre`re, P.; Belyasmine, A.; Gorgues, A.;
Jubault, M.; Uriel, S.; Batail, P.; Boubekeur, K.; Orduna, J.; Gar´ın, J. Synth.
Met. 1995, 70, 1155.
10.1021/ol025522t CCC: $22.00 © 2002 American Chemical Society
Published on Web 02/23/2002

tive complexes.9 Thus, compound 2 exhibited three reversible
oxidation peaks following the sequence: 2 h 22+ h 23.+ h
24+, in which the first two-electron process was related to
the π-extended TTF moiety and both TTF units appeared to
be electrochemically independent.
Scheme 2a
To increase the intramolecular interactions between the
TTF entities, we have designed new space-extended donors
3 in which the 1,3-dithiol-2-ylidene moieties of 1 are
connected using the vinylene group (Scheme 1).
Scheme 1
a Reagents and conditions: i, p-benzoquinone, CH3OH then
glacial AcOH, 80 °C, 68% (lit.12 63%); ii, Na2S‚9H2O, MeOH,
98% (lit.12 71%); then DDQ, 74% (lit.12 54% using p-benzo-
quinone); iii, cyclopentadiene, THF, 25 °C, 94%; iv, Hg(OAc)2,
CH2Cl2/glacial AcOH, 93%; v, phosphonate 9, n-BuLi, THF, -78
to 20 °C.
corresponding 2-thioxo-1,3-dithiole using sodium sulfide, the
oxidation was improved using DDQ to furnish 6 in 74%
yield.
Cyclic voltammetry of 6 exhibited two reversible one-
red
electron reduction peaks, the first one appearing at E1
)
- 0.15 V.13 To avoid the electron transfer of the phosphonate
anion of 9 to the quinonic functionality that occurred during
the following olefination step,8 the accepting character of 6
was suppressed by a prior Diels-Alder cycloaddition of
cyclopentadiene in THF, affording 2-thioxo-1,3-dithiole 7
in 94% yield (E1red ) - 0.87 V).13 The latter was converted
into the key intermediate 8 in 93% yield using the classical
transchalcogenation reaction (E1red ) - 0.95 V).13 The single-
crystal X-ray structure of 8 revealed that the unique kinetic
isomer with respect to the endo rule was compatible with
the reported cycloaddition of cyclopentadiene to p-benzo-
quinone.14
We then carried out a Horner-Wadsworth-Emmons
olefination to create the TTF core.8a After the reaction of 8
with phosphonate anion 9,15 a silica gel column chromatog-
raphy (CS2/CH2Cl2 (8/1) as the eluent) was used to separate
the bis-olefinated and tris-olefinated compounds 10 and 11,
respectively. The yields of the reaction appeared to be
dependent on the excess of phosphonate (for 6 equiv of 9a:
10a ) 32% and 11a ) 44%; for 10 equiv of 9b:10b ) 47%
and 11b ) 36%). Considering that the decomposition of 11a
and 11b occurred at 156 and 125 °C, respectively, cyclo-
pentadiene was removed quantitatively by thermal treatment
to reach the bis-fused TTF 3 (Scheme 3).8 All new
compounds gave satisfactory spectroscopic data.16
This constitutes the first example of a fused perpendicular
hybrid TTF dimer incorporating both the TTF unit and the
quinonoid π-extended TTF and introduces a new strategy
in bis-fused TTF. To our knowledge, this approach was
restricted to the synthesis of BDT-TTP10 and derivatives, for
which interest has significantly increased since the discovery
of the superconducting properties found from vinylogous
DTEDT.11
As described in Scheme 2, the synthesis first used
p-benzoquinone which reacted with the dithiocarbamate salt
(resulting from the addition of pyrrolidine to carbon disulfide)
in the presence of glacial acetic acid. The corresponding
Michae¨l addition was followed by aromatization, producing
compound 4 in 75% yield. The latter was oxidized using
p-benzoquinone, and the following cyclization upon treat-
ment with glacial acetic acid afforded iminium salt 5 in 68%
yield for both steps. After quantitative conversion into the
(7) (a) Benahmed-Gasmi, A.; Fre`re, P.; Belyasmine, A.; Malik, K. M.
A.; Hursthouse, M. B.; Moore, A. J.; Bryce, M. R.; Jubault M.; Gorgues,
A. Tetrahedron Lett. 1993, 34, 2131. (b) Fre`re, P.; Gorgues, A.; Jubault,
M.; Riou, A.; Gouriou Y.; Roncali, J. Tetrahedron Lett. 1994, 35, 1991.
(c) Me´zie`re, C.; Salle´, M.; Fourmigue´, M. Acta Crystallogr. 1998, C54,
2005.
(8) (a) Boulle, C.; Desmars, O.; Gautier, N.; Hudhomme, P.; Cariou,
M.; Gorgues, A. Chem. Commun. 1998, 2197. (b) Gautier, N.; Mercier,
N.; Riou, A.; Gorgues, A.; Hudhomme, P. Tetrahedron Lett. 1999, 40, 5997.
(9) For reviews on TTF dimers, see: (a) Otsubo, T.; Aso, Y.; Takimiya,
K. AdV. Mater. 1994, 6, 439. (b) Becher, J.; Lau, J.; Mørk, P. In Electronic
Materials: The Oligomer Approach; Mu¨llen, K., Wegner, G., Eds.; Wiley-
VCH: Weinheim, 1998; p 198.
(10) Misaki, Y.; Matsui, T.; Kawakami, K.; Nishikawa, H.; Yamabe T.;
Shiro, M. Chem. Lett. 1993, 1337.
(11) (DTEDT)[Au(CN)2]0.4 showed superconductivity below 4 K at
ambient pressure: Misaki, Y.; Higuchi, N.; Fujiwara, H.; Yamabe, T.; Mori,
T.; Mori H.; Tanaka, S. Angew. Chem., Int. Ed. Engl. 1995, 34, 1222.
The X-ray structure of a single crystal of 11a showed that
the π-extended unit presents a butterfly-shaped nonplanar
(12) Compound 6 was synthesized according to a previously described
methodology, with several yields being improved by modifications of
experimental procedures or reagents: Sun, D.; Krawiec, M.; Watson, W.
H. J. Chem. Crystallogr. 1997, 27, 515.
(13) Conditions of cyclic voltammetry: Pt electrode, 1.5 mM in CH2-
Cl2-n-Bu4NPF6 0.1 M, V ) 100 mV s-1, Ered in V/SCE.
(14) O’Brien D. F.; Gates, J. W., Jr J. Org. Chem. 1965, 30, 2593.
(15) Moore, A. J.; Bryce, M. R. Synthesis 1991, 26.
962
Org. Lett., Vol. 4, No. 6, 2002

and the intramolecular S‚‚‚S distances (3.22 Å) confirm the
trend observed for the experimental X-ray data. These
theoretical calculations were extended to compound 3 (R )
H) for which the recovery of the quinonoid structure induces
an important gain of planarity (γ ) 6.8°). The calculated
angle was compared with the one computed for compound
2 (γ ) 19.2°), the difference being attributed to the S‚‚‚S
interactions (3.08 Å) between both TTF moieties in 3.
Comparison of deconvoluted cyclic voltammograms (CV)
of the dimeric TTF 2 and the fused TTF-extended TTF 3b
gave fundamental structural information (Figure 2). Although
Scheme 3a
a Reagents and conditions: for 11a, refluxing o-dichlorobenzene;
for 11b, refluxing chlorobenzene, quantitative yields.
geometry (Figure 1).4a This distortion from planarity could
be described in terms of the angle γ which defines the tilting
of the dithiole units and is obtained as the supplement of
the C16-C4-C22-C3 dihedral angle. This crystallographic
angle (γ ) 20°) was found to be remarkably lower than the
one observed for the equivalent precursor of 2 (γ ) 34.5°),
in which the conformation is strongly controlled by the short
distance between the peri-hydrogens of the benzene ring and
the sulfur atoms of the 1,3-dithiole units.17 In the case of
compound 11a, this gain in planarity is justified by strong
intramolecular S‚‚‚S interactions, with the distances S1‚‚‚
S7 ) 3.029(3) Å and S2‚‚‚S9 ) 3.055(3) Å, lower than the
sum of van der Waals radii (3.70 Å) and in good agreement
with the distances observed for derivatives of 1.5
Figure 2. Deconvoluted cyclic voltammograms of 2 (left) and 3b
(right): Pt electrode; n-Bu4NPF6 0.1 M in CH2Cl2; V ) 100 mV
s-1
.
the CV for 2 was characterized by both CVs of extended
TTF and TTF moieties, the interesting feature of dimer 3
concerns its ability to undergo four sequential reversible
oxidation processes. With this phenomenon being indepen-
dent of the concentration, the existence of intramolecular
electronic interactions is clearly shown. These separated
oxidation processes could arise from Coulombic repulsions
between the two different TTF moieties in the oxidized states.
In these preliminary results, we have introduced a new
strategy for perpendicular bis-fused TTF. Further electro-
chemical studies and electrocrystallizations to reach promis-
ing radical cation salts from 3 are in progress.
Acknowledgment. Financial support was provided by the
MENRT for a research studentship to N. Gautier. All
theoretical calculations were performed at the national
CINES computing center.
Figure 1. ORTEP views of 11a. Ellipsoids are drawn at 50%
probability.
OL025522T
Density functional theory (DFT) calculations were per-
formed with the GAUSSIAN 9818 package at the B3LYP/
6-31G* level of theory for a full geometry optimization of
compound 11 (R ) H). The calculated angle (γ ) 24.7°
(18) Gaussian 98 (Revision A.9). Frisch, M. J.; Trucks, G. W.; Schlegel,
H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.;
Montgomery, J. A.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam,
J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith,
T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.;
Challacombe, M.; Gill, P. M. W.; Johnson, B. G.; Chen, W.; Wong, M.
W.; Andres, J. L.; Head-Gordon, M.; Replogle E. S.; Pople, J. A. Gaussian,
Inc., Pittsburgh, PA, 1998.
(16) Crystal data for 11a: C27H26S14, M ) 799.4, monoclinic, a ) 14.189-
(2), b ) 9.568(1), and c ) 26.106(1) Å, â ) 96.09(1)°, V ) 3524(1) Å3,
space group P21/n, Z ) 4, calculated density 1.5 (λMo
) 0.71069). A
KR
total of 6595 reflections werer collected in the 2.5-25°θ range; 235
parameters from 2989 reflections with I/σ(I) > 3 converged to R ) 0.052,
RW ) 0.074.
(17) This X-ray structure analysis will be published later. Gautier, N.
Thesis of Nantes and Angers UniVersities, France, October 24th 2000.
Org. Lett., Vol. 4, No. 6, 2002
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