New versatile building block for the construction of tetrathiafulvalene- based donor-acceptor systems

Article abstract of DOI:10.1021/ol060011i

A new dissymmetrical tetrathiafulvalene (TTF) derivative 1 was synthesized as a versatile building block to reach TTF-based donor-acceptor assemblies incorporating C₆₀ in triad C₆₀-TTF-C₆₀ 2 and/or p-benzoquinone (Q) in fu

Full text of DOI:10.1021/ol060011i

ORGANIC
LETTERS
2006
Vol. 8, No. 7
1307-1310
New Versatile Building Block for the
Construction of Tetrathiafulvalene-Based
Donor−Acceptor Systems
Je´roˆme Baffreau, Fre´de´ric Dumur, and Pie´trick Hudhomme*
Laboratoire de Chimie, Inge´nierie Mole´culaire et Mate´riaux d’Angers (CIMMA),
Groupe Synthe`se Organique et Mate´riaux Fonctionnels (SOMaF), UMR CNRS 6200,
UniVersite´ d’Angers, 2 Bd LaVoisier, F-49045 Angers, France
pietrick.hudhomme@uniV-angers.fr
Received January 3, 2006
ABSTRACT
A new dissymmetrical tetrathiafulvalene (TTF) derivative 1 was synthesized as a versatile building block to reach TTF-based donor
assemblies incorporating C60 in triad C60 TTF C60 2 and/or p-benzoquinone (Q) in fused dyad Q TTF 3 and triad Q TTF C60 4.
−acceptor
−
−
−
−
−
Tetrathiafulvalene (TTF) derivatives are intensively studied
because of their unique π-electron donating properties.
Discovery of the first metallic charge-transfer TTF-based
complex1 has initiated major research activities in search of
new molecular conductors.2 Efforts are particularly devoted
to direct intermolecular interactions in TTF-based crystalline
molecular conductors. This concerns specifically TTF mol-
ecules functionalized by hydrogen-bonding donor and ac-
ceptor groups such as alcohols, carboxylic acids, and amides.3
Intensive work is also carried out to modify the TTF
framework to achieve new original applications using this
π-donor.4 During the past few years, the utility of TTF
derivatives as building blocks in supramolecular structures,5
as well as the incorporation of this donor moiety in donor-
acceptor (D-A) systems, has made TTF one of the most
extensively studied heterocycles.6 Particular attention is still
given to the construction of TTF-acceptor systems for
intramolecular charge-transfer interaction,7 to photoinduced
electron-transfer processes by association with fullerene C60,8
and to reach low HOMO-LUMO gap TTF-based materials
as targets for the realization of unimolecular electronic
devices.9
This work describes the synthesis of novel TTF deriv-
ative 1 as an attractive building block to obtain donor-
acceptor ensembles that are easily amenable to further
functionalization.
The accessibility to the hydroquinone (HQ) template or
the quinone (Q) moiety10 and the possibility of converting
(1) Ferraris, J.; Cowan, D. O.; Walatka, V. V.; Perlstein, J. H. J. Am.
Chem. Soc. 1973, 95, 948.
(2) Batail, P. Molecular Conductors (Thematic issue). Chem. ReV. 2004,
104, issue 11.
(3) Fourmigue´, M.; Batail, P. Chem. ReV. 2004, 104, 5379.
(4) (a) Bryce, M. R. J. Mater. Chem. 2000, 10, 589. (b) Segura, J. L.;
Mart´ın, N. Angew. Chem., Int. Ed. 2001, 40, 1372.
(5) Nielsen, M. B.; Lomholt, C.; Becher, J. Chem. Soc. ReV. 2000, 29,
153.
(6) TTF Chemistry. Fundamentals and applications of tetrathiafulValene;
Yamada, J., Sugimoto, T., Eds.; Springer-Verlag: New York, 2004.
(7) Bryce, M. R. AdV. Mater. 1999, 11, 11.
(8) Mart´ın, N.; Sa´nchez, L.; Illescas, B.; Pe´rez, I. Chem. ReV. 1998, 98,
2527.
(9) Bendikov, M.; Wudl, F.; Perepichka, D. F. Chem. ReV. 2004, 104,
4891.
(10) Gautier, N.; Dumur, F.; Lloveras, V.; Vidal-Gancedo, J.; Veciana,
J.; Rovira, C.; Hudhomme, P. Angew. Chem., Int. Ed. 2003, 42, 2765.
10.1021/ol060011i CCC: $33.50
© 2006 American Chemical Society
Published on Web 02/28/2006

Scheme 1. Two Routes for the Synthesis of TTF Building Block 1
ester groups into functional intermediates allowing the
cording to a reported three-step procedure17 including thio-
alkylation in quantitative yield, reduction of resulting
compound 10 with NaBH4, and dethioalkylation with HBF4‚
Et2O in 95% overall yield. Treatment with trimethyl phos-
phite in the presence of NaI according to an Arbuzov-type
reaction18 afforded new phosphonate 12 in 80% yield. It
should be noted that this compound constitutes a valuable
synthetic intermediate for further applications in TTF
chemistry. The generation of a carbanion from 12 proceeded
smoothly under basic conditions by treatment with the non-
nucleophilic reagent LDA, which was preferred to n-BuLi
in agreement with the presence of ester functionalities.
Nevertheless, despite many modifications on the experimen-
tal procedure, the yield in compound 1 as the result of this
HWE reaction using 2-oxo-1,3-dithiole 13 could not exceed
36%. Consequently, although route A does not lead to a
selective synthesis, this still remains the most efficient access
to compound 1 at the multigram scale level.
attachment of C6011 are utilized to reach A-D-A triad C60-
TTF-C60 2, fused A′-D dyad Q-TTF 3, and A′-D-A
triad Q-TTF-C60 4.
Two different strategies were considered for the synthesis
of target TTF 1 (Scheme 1). Route A employed the
straightforward nonselective cross-coupling involving 2-oxo-
1,3-dithiole 612 and 2-thioxo-1,3-dithiole 7.13 The draw-
back of this strategy is the formation of both symmetrical
species besides the dissymmetrical TTF.14 Nevertheless, the
polarity of the three products was sufficiently different to
allow an easy purification of TTF 1 by chromatography on
silica gel. Whereas symmetrical TTFs resulting from the self-
condensation of 2-thioxo-1,3-dithiole 7 and 2-oxo-1,3-
dithiole 6 were isolated in low yields (6 and 12% for TTFs
8 and 9,15 respectively), dissymmetrical TTF 1 was isolated
in 55% yield.
To suppress the formation of these self-coupling products,
we applied the selective Horner-Wadsworth-Emmons
(HWE) olefination to create the TTF core (route B).16 This
reaction is based on the nucleophilic addition of the phos-
phonate anion generated from compound 12 onto 2-oxo-1,3-
dithiole derivative 13.13 First, tetrafluoroborate dithiolium
salt 11 was synthesized from corresponding thione 5 ac-
The synthetic scope of building block 1 was investigated.
TTF-hydroquinone (HQ-TTF) dyad 14 was isolated in 80%
yield after deprotection of silyl groups using Bu4NF and
subsequent acidic hydrolysis using p-TsOH‚H2O. To our
knowledge, this constitutes the first example of a fused HQ-
TTF dyad.19 The synthetic potential of the hydroquinone
functionality was exploited through its transformation into
the corresponding triad 2.20 Esterification of HQ-TTF 14
with PCBA 15,21 prepared by acidic hydrolysis of PCBM,22
in the presence of DCC as an activating coupling reagent
(11) Gorgues, A.; Hudhomme, P.; Salle´, M. Chem. ReV. 2004, 104, 5151.
(12) Parg, R. P.; Kilburn, J. D.; Petty, M. C.; Pearson, C.; Ryan, T. G.
Synthesis 1994, 613.
(13) Dumur, F.; Gautier, N.; Gallego-Planas, N.; S¸ahin, Y.; Levillain,
E.; Mercier, N.; Hudhomme, P.; Masino, M.; Girlando, A.; Lloveras, V.;
Vidal-Gancedo, J.; Veciana, J.; Rovira, C. J. Org. Chem. 2004, 69, 2164.
(14) Fabre, J.-M. Chem. ReV. 2004, 104, 5133.
(15) Pittman, C. U., Jr.; Narita, M.; Liang, Y. F. J. Org. Chem. 1976,
41, 2855.
(17) (a) Llacay, J. PhD Thesis, University of Barcelona, 1997. (b) Llacay,
J.; Mata, I.; Molins, E.; Veciana, J.; Rovira, C. AdV. Mater. 1998, 3, 330.
(18) Moore, A. J.; Bryce, M. R. Synthesis 1991, 26.
(16) (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.
(c) Gautier, N.; Gallego-Planas, N.; Mercier, N.; Levillain, E.; Hudhomme,
P. Org. Lett. 2002, 4, 961.
(19) HQ-TTF-HQ and TTF-HQ-TTF triads were reported in, re-
spectively: (a) Watson, W. H.; Eduok, E. E.; Kashyap, R. P.; Krawiec, M.
Tetrahedron 1993, 49, 3035. (b) Frenzel, S.; Mu¨llen, K. Synth. Met. 1996,
80, 175. A nonfused HQ-TTF dyad was previously described in: Segura,
J. L.; Mart´ın, N.; Seoane, C.; Hanack, M. Tetrahedron Lett. 1996, 37, 2503.
1308
Org. Lett., Vol. 8, No. 7, 2006

and both DMAP and HOBT afforded C60-TTF-C60 triad 2
in 52% yield (calculated from 1). On the other hand, in situ
oxidation of HQ-TTF 14 using DDQ afforded fused
Q-TTF 3 which was isolated as blue crystals in 73% yield
(Scheme 2).
Considering the chemical versatility of ester functionalities,
we transformed building block 1 into bis(hydroxymethyl)-
TTF 16 using NaBH4 associated with ZnCl2 (88% yield).24
Subsequent TTF derivative 1725 was conveniently synthe-
sized in 78% yield upon treatment with PBr3, referring to a
reaction previously applied in the TTF series.26 Reductive
elimination upon treatment of compound 17 with KI in the
presence of 18-crown-6 gave rise to transient diene 18 which
was trapped by C60 according to a Diels-Alder cyclo-
addition.27
Scheme 2. Transformations of TTF 1 in Triad
C60-TTFC-C60 2 Using the Hydroquinone Template 14 and
Fused Dyad Q-TTF 3
Resulting TTF-C60 dyad 19 was easily isolated in 37%
yield by column chromatography on silica gel using CS2 as
the eluent (Scheme 3). Deprotection of silyl protecting groups
Scheme 3. Syntheses of Dyad TTF-C60 19 and Triad
Q-TTF-C60
4
The UV-visible spectrum of 1 presents a maximum
absorption band in CS2 at 452 nm, whereas this band is
hypsochromatically shifted to 439 nm in compound 3.
Moreover, a weak charge-transfer band at 810 nm indicates
an electronic interaction between TTF and quinone moieties
(Figure 1). This charge-transfer absorption has a pronounced
gave the intermediate HQ-TTF-C60 as a supramolecular
template with the presence of two hydroxy groups. We were
able to isolate TTF-C60 triad 4 in 63% yield after subsequent
oxidation of the hydroquinone group using DDQ. Despite
its insolubility, this material was characterized by its infrared
spectrum, which showed both the typical band of quinone
(1650 cm-1) and the radial vibration of C60 (527 cm-1)
moieties, and its maldi-tof mass spectrum. The latter exhibits
the molecular ion peak at m/z 1030 with an isotopic
(20) A C60-TTF-C60 triad was previously synthesized by esterification
using bis(hydroxymethyl)TTF and PCBA 15: Ravaine, S.; Delhae`s, P.;
Leriche, P.; Salle´, M. Synth. Met. 1997, 87, 93. Or a fulleropyrrolidine
carboxylic acid derivative: Segura, J. L.; Priego, E. M.; Mart´ın, N.; Luo,
C.; Guldi, D. M. Org. Lett. 2000, 2, 4021.
(21) [6,6]-phenyl-C61-butyric acid (PCBA) was previously used in
esterification reactions: (a) Ravaine, S.; Vicentini, F.; Mauzac, M.; Delhaes,
P. New J. Chem. 1995, 19, 1. (b) Giacalone, F.; Segura, J. L.; Mart´ın, N.
J. Org. Chem. 2002, 67, 3529.
(22) Hummelen, J. C.; Knight, B. W.; LePeq, F.; Wudl, F. J. Org. Chem.
1995, 60, 532.
Figure 1. Absorption spectra of 1 (dashed line), 2 (solid line),
and 3 (dotted line) in CS2 (c ) 5 × 10-4 M).
(23) λmax (nm) of compound 3 ) 810 (CS2), 793 (CCl4), 776 (CH2Cl2),
768 (toluene), 727 (DMF), 723 (THF), 713 (DMSO), 697 (CH3CN).
(24) Blanchard, P.; Duguay, G.; Cousseau, J.; Salle´, M.; Jubault, M.;
Gorgues, A.; Boubekeur, K.; Batail, P. Synth. Met. 1993, 55-57, 2113.
(25) Its maldi-tof mass spectrum exhibits the molecular ion peak at m/z
948 and successive fragmentations of each bromine atom corresponding to
peaks at m/z 868 and 788, respectively.
(26) Hudhomme, P.; Liu, S.-G.; Kreher, D.; Cariou, M.; Gorgues, A.
Tetrahedron Lett. 1999, 40, 2927.
(27) Kreher, D.; Cariou, M.; Liu, S.-G.; Levillain, E.; Veciana, J.; Rovira,
C.; Gorgues, A.; Hudhomme, P. J. Mater. Chem. 2002, 12, 2137.
negative solvatochromism; the maximum wavelength of
Q-TTF 3 decreased while the polarity increased.23 By
comparison with compound 1, triad 2 exhibits the charac-
teristic weak absorption band of fullerene derivatives at 702
nm.
Org. Lett., Vol. 8, No. 7, 2006
1309

Table 1. Cyclic Voltammograms Recorded in Bu4NPF6 0.1 M Solution as the Supporting Electrolyte and Platinum Wires as Counter-
and Working Electrodesa
compd
solvent
E1/2red4
E1/2red3
E1/2red2
E1/2red1
E1/2ox1
E1/2ox2
1
1
2
CH2Cl2
+0.27
+0.25
+0.42
+0.74
+0.72
+0.91
o-C6H4Cl2/CH2Cl2 (2:1)
o-C6H4Cl2/CH2Cl2 (2:1)
o-C6H4Cl2/CH2Cl2 (2:1)
CH2Cl2
CH2Cl2
o-C6H4Cl2/CH2Cl2 (2:1)
-1.93b
-1.20
-1.21
-0.71
-2.13
-1.87b
-2.10
-2.01
-1.59
-1.60
-1.33
PCBM
3
8
19
+0.48
+0.12
+0.32
+0.85
+0.63
+0.56
-2.05
-1.56
-1.19
a Scan rate: 100 mV/s. V vs Fc+/Fc. Triad Q-TTF-C60 4 was insoluble in these media to carry out cyclic voltammetry. b Irreversible reduction process
is attributed to the ester functionality.
distribution in agreement with the calculated pattern and the
presence of both peaks at m/z 720 (C60) and 310 (diene 18)
resulting from the retro Diels-Alder reaction.
Electrochemical properties of these building block and
donor-acceptor systems were investigated by cyclic voltam-
metry to determine the influence of substituents on the redox
properties of TTF and the electrochemical HOMO-LUMO
difference inside D-A systems. TTF derivatives present two
reversible oxidation peaks corresponding to the cation radical
TTF+‚and dication TTF2+ species, respectively. By com-
anion radical TTF-Q‚- and dianion TTF-Q2- from the
quinone moiety of compound 3.
Cyclic voltammograms of TTF-C60 dyad 19 and TTF-
(C60)2 triad 2 were compared to those of building block 1
and PCBM. Whereas the dyad 19 showed the expected two
reversible oxidation peaks (E1/2ox1 ) +0.32 V and E1/2ox2
)
+0.56 V) and three reduction peaks close to those of PCBM,
we noted the appearance of an irreversible reduction peak
(E1/2red3 ) -1.87 V) in the case of triad 2 (Figure 2). Being
that this irreversible reduction process was also present in
reference compound 1, we unambiguously demonstrated that
this phenomenon was resulting in the reduction of the bis-
(methoxycarbonyl) functionality attached to the TTF moiety.
In summary, we propose an efficient scalable synthetic
strategy to elaborate a new building block in the TTF series
and exciting TTF-based donor-acceptor systems involving
p-benzoquinone and/or fullerene C60 with the aim of first
exploiting the synthetic richness of this platform. We believe
that future developments will allow the preparation of
promising molecular conductors’ architectures governed by
hydrogen-bond interactions using the potential of not only
the hydroquinone or quinone templates but also the hy-
droxymethyl, carboxylic acid, or amide functionalities ac-
cessible from the ester group.
parison with oxidation potentials of compound 8 (E1/2ox1
)
+0.12 V and E1/2ox2 ) +0.63 V vs Fc+/Fc), as expected,
the electron-withdrawing effect of both methoxycarbonyl
groups on the TTF framework in compound 1 resulted in an
increase of oxidation potentials (E1/2ox1 ) +0.27 V and E1/2ox2
) +0.74 V) (Table 1). This effect was more importantly
evidenced with the subsequent introduction of the quinone
moiety in dyad TTF-Q 3 (E1/2ox1 ) +0.48 V and E1/2ox2
)
+0.85 V) for TTF+‚-Q and TTF2+-Q species, respectively.
Two reversible reduction waves at E1/2red1 ) -0.71 V and
E1/2red2 ) -1.33 V were assigned to the formation of the
Acknowledgment. This work was supported by grants
from the Conseil Ge´ne´ral du Maine et Loire for J. Baffreau
and F. Dumur. We particularly thank Dr. C. Rovira (ICMAB
Barcelona) for fruitful discussions with regard to the prepara-
tion of tetrafluoroborate dithiolium salt 11. Special thanks
are extended to M. Pouvreau and N. Cocherel for their
contribution to the synthesis of starting materials and to J.
Delaunay for mass spectrometry experiments.
Supporting Information Available: Experimental details
and characterization data for new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
Figure 2. Cyclic voltammogram of triad C60-TTF-C60 2 and its
deconvolution in the inset.
OL060011I
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Org. Lett., Vol. 8, No. 7, 2006