Trithiaazafulvalene: A promising building block between tetrathiafulvalene and dithiadiazafulvalene

Article abstract of DOI:10.1021/ol060705r

New electroactive building blocks, the trithiaazafulvalenes (TTAFs), were synthesized. These redox-active molecules, intermediate between tetrathiafulvalene (TTF) and dithiadiazafulvalene (DTDAF), show promising features for the elaboration of molecular materials.

Full text of DOI:10.1021/ol060705r

ORGANIC
LETTERS
2006
Vol. 8, No. 11
2377-2380
Trithiaazafulvalene: A Promising
Building Block between
Tetrathiafulvalene and
Dithiadiazafulvalene
Samar Eid, Michel Guerro, Thierry Roisnel, and Dominique Lorcy*
Sciences Chimiques de Rennes, UMR 6226 CNRS-UniVersite´ de Rennes 1, Campus de
Beaulieu, Baˆt 10A, 35042 Rennes Cedex, France
Dominique.lorcy@uniV-rennes1.fr
Received March 22, 2006
ABSTRACT
New electroactive building blocks, the trithiaazafulvalenes (TTAFs), were synthesized. These redox-active molecules, intermediate between
tetrathiafulvalene (TTF) and dithiadiazafulvalene (DTDAF), show promising features for the elaboration of molecular materials.
Intensive unabated studies have focused on the tetrathiaful-
valene (TTF) derivatives for the preparation of molecular
conductors for the last 30 years.1 Several modifications of
the TTF moiety have been performed either to achieve better
conductivity properties or to understand structure-activity
relationships. Among them, the replacement of two sulfur
atoms in the TTF framework by nitrogen atoms leads to the
dithiadiazafulvalenes (DTDAFs).2 Compared with TTFs,
DTDAFs exhibit higher electron-donating properties but an
instability upon air exposure leading to various oxidative
rearrangements.3 An interesting aspect of DTDAF chemistry
is the possibility to modify the R substituents on the nitrogen
atoms, for example, to obtain the cis isomer by connecting
the two thiazole cores by a N,N′-bridge or to use the R
substituent as a handle for further functionalization.2 As all
the DTDAFs, even those substituted with electron-withdraw-
ing groups,4 seem labile to oxygen, we decided to investigate
the synthesis of trithiaazafulvalene (TTAF) which should
exhibit intermediate properties between the DTDAF the TTF
derivatives and show the best features of each family, that
is, the excellent electron-donating properties of DTDAF and
the stability of TTF. The first TTAF was reported 30 years
ago from the reaction of 3-methylbenzothiazolium salt with
2-piperidino-1,3-benzodithiole affording a benzoannelated
TTAF.5 Ten years later, 3-methylbenzothiazolium salt was
also used in cross reactions with non-benzoannelated dithiole,
but none of these publications reported investigations on the
redox properties or the structural conformations of these
trithiazafulvalenes (TTAF).6 Benzoannelated derivatives of
TTF or DTDAF are usually easier to prepare and are more
stable as they exhibit higher oxidation potentials but are less
attractive as precursors of molecular materials than the
corresponding non-benzoannelated donor cores.1 Herein, we
report the synthesis and the structural and electrochemical
properties of non-benzoannelated TTAF using 4,5-dimethyl-
2-piperidino-1,3-dithiole and various substituted thiazolium
(1) Special issue on Molecular Conductors, Chem. ReV. 2004, 104, 4887.
(2) Lorcy, D.; Bellec, N. Chem. ReV. 2004, 104, 5185.
(3) (a) Vorsanger, J. J. Bull. Soc. Chim. Fr. 1964, 119. (b) Wanzlick, H.
W.; Kleiner, H. J.; Lasch, I.; Fu¨ldner, H. U.; Steinmaus, H. Liebigs Ann.
Chem. 1967, 708, 155. (c) Takamizawa, A.; Hirai, K.; Hamashima, Y.;
Sato, H. Chem. Pharm. Bull. 1969, 17, 1462. (d) Baldwin, J. E.; Walker, J.
A. J. Am. Chem. Soc. 1974, 96, 596. (e) Bssaibis, M.; Robert, A.;
Lemaguere`s, P.; Ouahab, L.; Carlier, R.; Tallec, A. J. Chem. Soc., Chem.
Commun. 1993, 601. (f) Koizumi, T.; Bashir, N.; Kennedy, A. R.; Murphy,
J. A. J. Chem. Soc., Perkin Trans. 1 1999, 3637.
(4) Tormos, G. V.; Bakker, M. G.; Wang, P.; Lakshmikantham, M. V.;
Cava, M. P.; Metzger, R. M. J. Am. Chem. Soc. 1995, 117, 8528.
(5) Buza, D.; Krasuski, W. Rocz. Chem. 1975, 49, 2007.
(6) Krasuski, W.; Regitz, M. Z. Naturforsch. 1984, 39b, 1806.
10.1021/ol060705r CCC: $33.50
© 2006 American Chemical Society
Published on Web 04/26/2006

cores. At least one electron-withdrawing group on the
thiazole core was included to moderate the strength of the
electron-donating ability, and eventually, their lability toward
oxygen will enable us to compare them with the parent
donors.
to the procedure described above.4 Having these thiazolium
salts in hand, we prepared the 4,5-dimethyl-2-piperidino-
1,3-dithiole 6 for the cross-coupling experiment according
to literature procedure.11
On the basis of the experiments carried out previously for
the synthesis of benzoannelated TTAF, the thiazolium salts
5 were heated to reflux in acetonitrile with 1 equiv of
2-piperidino-1,3-dithiole 6 (Scheme 2). After 1 h at reflux,
The approach we chose for the synthesis of our target
precursors, the thiazolium salts, is outlined in Scheme 1.
Scheme 1. Synthesis of the Target Precursors
Scheme 2. Synthesis of TTAFs
the TTAFs 7a-c precipitated from the solution and were
isolated by filtration. It is noteworthy that these derivatives
can be purified by recrystallization and stored under ambient
conditions for months without alteration.
Single crystals were obtained for 7a and 7b, and the X-ray
molecular structures are given in Figure 1. Both TTAFs
Lithiation of heterocycles is a very useful route for the
preparation of various substituted derivatives.7 Metalation
of the 1,3-thiazoline-2-thione ring on the 5 position can be
realized using strong bases such as BuLi or lithium diiso-
propylamide (LDA) and the lithiated species can then react
with a variety of electrophiles.8
For our purpose, we use in this reaction the 3,4-dimethyl-
1,3-thiazoline-2-thione 19 that we lithiated with BuLi and
then reacted with either methyl chloroformate or dimethyl
formamide as the electrophile to give the monoester 2a or
the aldehyde 3. The conversion of the aldehyde 3 into the
corresponding nitrile 2b was realized through the dehydration
of the intermediate aldoxime 4. First, the thiazole-2-thione
aldehyde 3 was heated in the presence of hydroxylamine
hydrochloride to afford the aldoxime 4 which can be either
isolated (90% yield) or directly transformed into the nitrile
by simply heating with acetic anhydride. The resulting nitrile
2b is obtained with an overall yield of 72%. Thiazoline-2-
thiones 2a and 2b were converted to the corresponding
thiazolium salts 5a,b with hexafluorophosphoric acid and
hydrogen peroxide.10 We also synthesized thiazolium salt
5c from 1,3-thiazoline-2-thione 2c (R1 ) R2 ) CO2Me)
substituted with two electron-withdrawing groups according
Figure 1. X-ray crystal structure of 7a (left) and 7b (right) (CCDC
602405-602406). The displacement ellipsoids are drawn at the 50%
probability level.
present similar trends such as a fully planar donor core, a
head to tail organization of two neighboring TTAFs, and
formation of stacks (see Supporting Information). The
shortest intermolecular S‚‚‚S distances are equal to 3.860-
(17) and 3.995(6), respectively, for 7a and 7b. The bond
lengths in the TTAFs 7a and 7b are collected in Table 1
together with those of the tetramethyl TTF (TMTTF)12 and
the hexamethyl DTDAF.13 Comparison of these bond lengths
(11) Mora, H.; Fabre, J. M.; Giral, L.; Montginoul, C. Bull. Soc. Chim.
Belg. 1992, 101, 137.
(7) Chinchilla, R.; Najera, C.; Yus, M. Chem. ReV. 2004, 104, 2667.
(8) Bellec, N.; Lorcy, D.; Robert, A. Synthesis 1998, 1442.
(9) Bellec, N.; Lorcy, D.; Boubekeur, K.; Carlier, R.; Tallec, A.; Los, S.
Z.; Pukacki, W.; Trybula, M.; Piekara-Sady, L.; Robert, A. Chem. Mater.
1999, 11, 3147.
(10) Gue´rin, D.; Carlier, R.; Guerro, M.; Lorcy, D. Tetrahedron 2003,
59, 5273.
(12) Batsanov, A. S.; Bryce, M. R.; Chesney, A.; Howard, J. A. K.; John,
D. E.; Moore, A. J.; Wood, C. L.; Gershtenman, H.; Becker, J. Y.;
Khodorkovsky, V. Y.; Ellern, A.; Bernstein, J.; Perepichka, I. F.; Rotello,
V.; Gray, M.; Cuello, A. O. J. Mater. Chem. 2001, 11, 2181.
(13) Arduengo, A. J., III.; Goerlich, J. R.; Marshall, W. J. Liebigs Ann.
1997, 365.
2378
Org. Lett., Vol. 8, No. 11, 2006

However, the trithiaazafulvalenes described here suffer from
this drawback only upon chromatography whereas they are
stable for months in the solid state, a striking difference from
the DTDAF.
Table 1. Bond Lengths (Å) for TTAFs 7a, 7b, TMTTF, and
DTDAF
To get information on the redox properties of these new
donors, we performed cyclic voltammetry experiments. The
oxidation potentials of TTAFs 7a-c are listed in Table 2
7a
7b
DTDAF
TTF
a
b
1.360(9)
1.418(8)
1.747(13)
1.754(13)
1.773(7)
1.37(1)
1.757(10)
1.769(10)
1.771(12)
1.362(8)
1.336(8)
1.346(4)
1.406(3)
1.760(4)
1.763(3)
1.762(4)
1.364(5)
1.750(2)
1.758(2)
1.395(4)
1.326(4)
1.317(4)
1.341(2)
1.438(2)
1.392(2)
1.779(2)
1.762(2)
1.397(2)
1.432(2)
1.764(2)
1.769(2)
1.339(2)
1.329(2)
1.359(2)
Table 2. Oxidation Potentials in V vs SCE for TMTTF, 7a-c,
and 9a-ca
b′
c
c′
d
d′
e
e′
f
f ′
1.764(2)
1.761(3)
1.765(3)
1.769(2)
1.343(2)
R1
R2
E1
E2
∆E (mV)
TMTTF
7a
9a
7b
9b
0.23
-0.04
-0.33
0.04
-0.09
0.12
0.59
0.35
-0.09
0.40
0.12
0.48
360
390
240
360
210
360
230
Me
Me
Me
Me
CO2Me
CO2Me
CO2Me
CO2Me
CN
CN
CO2Me
CO2Me
7c
9c
-0.08
0.15
aPt working electrode with 0.1 M Bu4NPF6 in CH3CN has a scan rate of
100 mV/s.
is instructive. As can be seen in Table 1, each heterocycle
in TTAF maintains its characteristic bond lengths. The
thiazole core and the dithiole core of the TTAFs are
comparable to that of the DTDAF and the TTF, respectively,
as well as the central CdC bonds.
together with those of the parent donors DTDAFs 9a-c and
TMTTF for comparison. For that purpose, we prepared the
corresponding DTDAFs 9a-c directly from thiazolium salts
5 (Scheme 4).
Interestingly, we also tried to purify by column chroma-
1
tography the derivative 7c. In this case, H NMR and 13C
NMR data and X-ray crystal structure determination proved
this compound to be a novel oxygen-containing product, the
spiroamide 8 (Scheme 3 and Figure 2).
Scheme 4. Synthesis of DTDAF 9
Scheme 3. Oxidation on Silica Gel of DTDAF 7c
The base-catalyzed deprotonation of the thiazolium salts
was realized in acetonitrile using triethylamine under an inert
atmosphere. After 20 min, the DTDAFs formed in the
medium precipitate were quickly filtered off and directly
electrochemically analyzed without isolation because of the
strong air sensitivity mentioned above.
The behavior of 7c parallels that of DTDAFs which upon
air exposure are easily oxidized and converted into such spiro
amide derivatives or a 10-membered ring compound.3
For all the donors, two monoelectronic reversible processes
were detected indicating that each donor possesses three
redox states: neutral, cation radical, and dication. Redox
potentials of the TTAFs are intermediate between those of
the TTF and DTDAF donors. Interestingly, one can notice
the larger potential difference between the two oxidation
waves (∆E ) E2 - E1) of TTAFs 7a-c when compared to
DTDAFs 9a-c, which indicates that for TTAF the cation
radical species is stable in a wider potential window than
that for DTDAF. Actually, these ∆E values for 7 are
comparable with the one observed for TMTTF.
Figure 2. X-ray structure of the spiroamide 8 (CCDC 602407).
The displacement ellipsoids are drawn at the 50% probability level.
DFT calculations [B3LYP/6-31G(d)] were performed on
the unsubstituted model derivatives, the N-methyl-TTAF, the
Org. Lett., Vol. 8, No. 11, 2006
2379

As shown in Figure 3, the energy of the HOMO of TTAF is
indeed located between those of TTF and DTDAF but is
closer in energy to the DTDAF system. Note also the very
small coefficient at the C4 carbon atom of the thiazole ring,
located R to the NMe group. This evolution of the HOMOs
was anticipated from our experience in the electrochemistry
of the symmetrical DTDAF molecules,2 hence the function-
alization of the TTAF core with electron-withdrawing groups
(-CN, -CO2Me) described above. The same calculations
were therefore performed with -CN substituted donor
molecules. Indeed, the HOMO of TTF is stabilized by 0.567
eV in TTF-CN. Concerning the TTAF, in that case, two
position isomers can be considered, with the CN group on
the C4 (close to the NMe group) or the C5 carbon atom of
the thiazole ring. A sizable difference is observed between
the two isomers, and the HOMO of the C4-substituted isomer
is more strongly stabilized than that of the C5-substituted
isomer. The stabilizing effect of the CN can also be partially
counterbalanced by the four methyl groups as shown in
Figure 3 for the 7b derivative discussed above. In these cases,
a strong stabilization of the HOMO of the TTAF is obtained,
which brings these molecules to energy levels comparable
to that of TTF itself.
In summary, we have shown that TTAF is a novel class
of electron-donor molecules whose electronic properties and
stability compare with those of TTF, provided that an
electron-withdrawing group is introduced on the thiazole ring.
Further investigations will be devoted to the elaboration,
either chemically or electrochemically, of ion radical salts
with these TTAF derivatives.
Figure 3. Molecular orbital surfaces and HOMO levels of
unsubstituted TTF, TTAF, DTDAF, monocyano TTF and TTAF,
and 7b.
Supporting Information Available: Experimental condi-
tions and characterization data for compounds 7 and 8, details
of calculations, and X-ray data. This material is available
free of charge via the Internet at http://pubs.acs.org.
N,N′-dimethyl-DTDAF, and the TTF, to determine the
evolution of their HOMO energies as well as their shape.
OL060705R
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Org. Lett., Vol. 8, No. 11, 2006