Synthesis and electron-donor ability of the first conjugated π-extended tetrathiafulvalene dimers

Article abstract of DOI:10.1021/jo049741z

A series of novel conjugated homo (16a,b) and heterodimers (20) of π-extended tetrathiafulvalenes with p-quinodimethane structures (exTTFs) linked by a conjugative vinyl spacer have been prepared by olefination Wittig-Horner reaction from the corresponding quinones (14, 19) and phosphonates (15a,b). The redox properties, determined by cyclic voltammetry, reveal a strong donor character and the presence of only one four-electron oxidation wave to form the tetracation species at oxidation potential values quite similar to those found for the related monomers. Theoretical calculations (PM3) show a planar central stilbene moiety and highly distorted exTTF units. The electronic spectra support as well as the electrochemical data and theoretical calculation the lack of significant communication between the exTTF units.

Full text of DOI:10.1021/jo049741z

Syn th esis a n d Electr on -Don or Ability of th e F ir st Con ju ga ted
π-Exten d ed Tetr a th ia fu lva len e Dim er s†
Marta C. D´ıaz, Beatriz M. Illescas, Carlos Seoane, and Nazario Mart´ın*
Departamento de Qu´ımica Orga´nica, Facultad de Ciencias Qu´ımicas, Universidad Complutense,
E-28040 Madrid, Spain
nazmar@quim.ucm.es
Received February 13, 2004
A series of novel conjugated homo (16a ,b) and heterodimers (20) of π-extended tetrathiafulvalenes
with p-quinodimethane structures (exTTFs) linked by a conjugative vinyl spacer have been prepared
by olefination Wittig-Horner reaction from the corresponding quinones (14, 19) and phosphonates
(15a ,b). The redox properties, determined by cyclic voltammetry, reveal a strong donor character
and the presence of only one four-electron oxidation wave to form the tetracation species at oxidation
potential values quite similar to those found for the related monomers. Theoretical calculations
(PM3) show a planar central stilbene moiety and highly distorted exTTF units. The electronic spectra
support as well as the electrochemical data and theoretical calculation the lack of significant
communication between the exTTF units.
In tr od u ction
of C60-wire-exTTF systems (7) over distances of 40 Å and
beyond, in which a strong paraconjugation takes place
between the π-conjugated oligomer and the exTTF elec-
tron donor, resulting in high coupling constant values
(V ∼ 5.5 cm-1)7 (Chart 1).
Tetrathiafulvalene (TTF, 1) is a well-known electron-
donor molecule that is currently receiving renewed
interest due to its application in fields other than
electrical conductivity.1 In particular, π-extended TTFs
with p-quinodimethane structure (exTTF, 2) incorporat-
ing an anthracene spacer between the dithiole rings2 have
been successfully used as electron-donating building
blocks in the preparation of photosynthetic models (3)3
or as materials with marked nonlinear optical properties
(4).4 Another remarkable applications involve crown-
annelated exTTFs (5), in which the crown ether moiety
is fused to the dithiole rings, as complexing agents for
metal ions recognition,5 as well as for the synthesis of
electroactive donor-acceptor dyads (6).6 Recently, a
molecular wire-like behavior has been found in a series
In contrast to the parent TTF, π-extended TTFs exhibit
only a single, quasireversible oxidation wave involving
two electrons to form stable dicationic species. In fact,
the oxidation potential for exTTF (2: R ) H, E1ox ) 0.44
V vs SCE) is slightly higher than that reported for the
parent TTF (1: E1 ) 0.34 V vs SCE). Formation of the
ox
oxidized state in exTTFs (2) occurs with a strong struc-
tural change from the highly distorted and non aromatic
neutral butterfly shape molecule to the planar and fully
aromatic dication state in which the 1,3-dithiolium
cations are in an almost orthogonal geometry to the
planar anthracene unit.8 This feature has been exploited
in our group to improve the lifetime of the charge-
separated state due to the gain of aromacity and planar-
ity associated with the oxidation process in the photo-
lytically generated radical pair in C60-exTTF dyads.9
* To whom correspondence should be addressed. Fax: +34-
913944103. Phone: +34-913944227.
† This work is dedicated to Professor J ose´ L. Soto on the occasion of
this retirement.
(1) (a) Bryce, M. R. J . Mater. Chem. 2000, 10, 589. (b) Segura, J . L.;
Mart´ın, N. Angew. Chem., Int. Ed. 2001, 40, 1372.
(2) (a) Bryce, M. R.; Moore, A. J .; Hasan, M.; Ashwell, G. J .; Fraser,
A. T.; Clegg, W.; Husthouse, M. B.; Karaulov, A. I. Angew. Chem., Int.
Ed. Engl. 1990, 29, 1450. (b) Yamashita, Y.; Kobayashi, Y.; Migashi,
T. Angew. Chem., Int. Ed. Engl. 1989, 8, 570.
One of the strategies followed to prepare novel TTF-
based donors with increased dimensionality as well as
to obtain multistep redox systems has been the synthesis
of molecular species bearing two or more TTF units, and
(3) (a) Mart´ın, N.; Pe´rez, I.; Sa´nchez, L.; Seoane, C. J . Org. Chem.
1997, 62, 5690. (b) Herranz, M. A.; Mart´ın, N. Org. Lett. 1999, 1, 2005.
(c) M. A. Herranz, N. Mart´ın, L. Sa´nchez, C. Seoane, D. M. Guldi, J .
Organomet. Chem. 2000, 2, 599. (d) Mart´ın, N.; Sa´nchez, L.; Guldi, D.
M. Chem Commun. 2000, 113. (e) Herranz, M. A.; Mart´ın, N.; Ramey,
J .; Guldi, D. M. Chem. Commun. 2002, 2968. (f) Gonza´lez, S.; Mart´ın,
N.; Swartz, A.; Guldi, D. M. Org. Lett. 2003, 5, 557. (g) Gonza´lez, S.;
Mart´ın, N.; Guldi, D. M. J . Org Chem. 2003, 68, 779.
(4) (a) Herranz, M. A.; Mart´ın, N.; Sa´nchez, L.; Gar´ın, J .; Orduna,
J .; Alcala´, R.; Villacampa, B.; Sa´nchez, C. Tetrahedron 1998, 54, 11651.
(b) Otero, M.; Herranz, M. A.; Seoane, C.; Mart´ın, N.; Gar´ın, J .; Orduna,
J .; Alcala´, R.; Villacampa, B. Tetrahedron 2002, 58, 7463.
(5) Bryce, M. R.; Batsanov, A. S.; Finn, T.; Hansen, T. K.; Howard,
J . A. K.; Kamenjicki, M.; Ledner, I. K.; Asher, S. A. Chem. Commun.
2000, 295.
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B.; Christensen, C. A.; Godbert, N.; Batsanov, A. S.; Levillain, E.;
McInnes, E. J . L.; Zhao, J . P. J . Am. Chem. Soc. 2002, 124, 14227.
(7) Giacalone, F.; Segura, J . L.; Martı´n, N.; Guldi, D. M. J . Am.
Chem. Soc. 2004, 126, 5340-5341.
(8) (a) Mart´ın, N.; Sa´nchez, L.; Seoane, C.; Ort´ı, E.; Viruela, P. M.;
Viruela, R. J . Org. Chem. 1998, 63, 1268. (b) For a recent review on
quinonoid exTTFs, see: Martı´n, N.; Ort´ı, E. In Handbook of Advanced
Electronic Photonic Materials and Devices; Nalwa, H. S., Ed.; Academic
Press: New York, 2001; Vol. 3, Chapter 6.
(9) D´ıaz, M. C.; Herranz, M. A.; Illescas, B. M.; Mart´ın, N.; Godbert,
N.; Bryce, M. R.; Luo, Ch.; Swartz, A.; Anderson, G.; Guldi, D. M. J .
Org. Chem. 2003, 68, 7711.
10.1021/jo049741z CCC: $27.50 © 2004 American Chemical Society
Published on Web 06/02/2004
4492
J . Org. Chem. 2004, 69, 4492-4499

Synthesis of Conjugated π-Extended Tetrathiafulvalene Dimers
CHART 1. Som e Rep r esen ta tive Exa m p les of F u n ction a l Molecu les Con ta in in g th e ExTTF Moiety
J . Org. Chem, Vol. 69, No. 13, 2004 4493

D´ıaz et al.
a wide variety of molecular, macromolecular and su-
pramolecular systems have been reported.1,10 In contrast,
only a very few examples of double donors involving one
exTTF unit are known,11 and only two dimeric systems
(8, 9) formed with exTTF have been reported so far. The
electrochemical study of compounds 812 and 913 reveals
the presence of only one oxidation wave, thus confirming
that both exTTF moieties, connected either by an oxygen
atom in 8 or by means of a more complex spacer involving
multiple single and double bonds in 9, behave indepen-
dently.
We have recently reported a suitably functionalyzed
exTTF dimer which has been covalently connected to the
C60 molecule affording a new electroactive triad (C60-
exTTF1-exTTF2, 10) in which the photoinduced electron
transfer gives rise to the radical pair C60•--exTTF1-
exTTF2•+ showing the highest lifetime reported so far for
a C60-based triad (∼100 µs).14 This remarkable finding
has been accounted for by the low reorganization energy
of the C60 molecule15 and the gain of aromaticity and
planarity undergone by the exTTF units upon oxidation.
To have a better understanding of unprecedented
exTTF dimers in which both exTTF units are covalently
connected through a conjugated bridge, in this paper we
report on the synthesis of a series of novel exTTF dimers
bound by a vinyl spacer. The presence of a conjugated
bridge linking both donor units could, in principle, lead
to a different electrochemical behavior than that found
for the twin-donors (8, 9) previously reported. The
geometry of the novel compounds has been determined
by semiempirical PM3 theoretical calculations in order
to determine the planarity of the novel donor molecules
and, hence, the degree of electronic communication
between the two exTTF units.
as shown in Scheme 1. It is worth mentioning that
suitably functionalized p-quinodimethane analogues of
TTF (exTTFs) have been less studied, and only recently,
the chemical functionalization of exTTFs has been un-
dertaken by different groups.16 Therefore, we decided to
carry out the synthesis of exTTFs 17 and 18 endowed
with iodine and vinyl groups, respectively. Compound 18
was synthesized in three steps from 2-amino-9,10-an-
thraquinone (11) by functional group transformation to
2-iodo-9,10-anthraquinone (12)17 and further Stille cou-
pling reaction with tritertbutylvinyltin in the presence
18
of Pd(PPh3)4 to afford 2-vinyl-9,10-anthraquinone 13.
Transformation of 13 into the exTTF 18 was carried out
by Wittig-Horner olefination reaction with phosphonate
15a . Phosphonates 15a ,b were in turn obtained in a
multistep synthetic procedure by following the procedure
reported in the literature.19
Compounds 17 and 18 are appealing building blocks
for the construction of conjugated exTTF dimers by Heck
coupling reaction. However, all attempts to obtain com-
pound 16a from its precursors (17 and 18) were unsuc-
cessful and formation of dimer 16a was only detected by
TLC and mass spectroscopy.
Compound 16 could be, however, prepared from bis-
anthraquinone 14 which was in turn obtained by reacting
quinones 12 and 13 by Heck coupling,20 using (CH3-
CN)2PdCl2 as the catalyst in refluxing toluene.21 Com-
pound 14 was thus obtained in 24% yield using trieth-
ylamine as base and tetrabutylammonium bromide as
phase-transfer agent. Other conditions used such as Pd-
(OAc)2 as a catalyst or adding LiCl led to 14 in lower
yields. Compound 14 was also prepared by an alternative
olefin metathesis reaction from 2-vinyl-9,10-anthraqui-
none 13 using the Grubbs ruthenium catalyst [Cl2Ru-
(Pcy3)2] in refluxing dichloromethane. However, this
cycloaddition/cycloreversion process led to bis-anthraqui-
none 14 in 18% yield.
Resu lts a n d Discu ssion
Olefination Wittig-Horner reaction of bis-anthraqui-
none 14 with the carbanion generated from the respective
phosphonate ester (15a ,b) in the presence of n-butyl-
lithium afforded exTTF dimers 16a ,b as orange stable
solids in reasonably good yields (54%-62%) (see the
Experimental Section). It is important to note that a
stoichiometric ratio of 1:10 (bis-anthraquinone/phospho-
nate) was found to be the most appropriate to complete
the reaction and to avoid major compounds containing
one or more unreacted free carbonyl groups. Anyway, a
further purification by careful flash cromatography is
needed for the separation of these byproducts which were
detected by TLC (Scheme 1).
Syn th esis. The preparation of the novel exTTF dimers
was carried out in a multistep synthetic procedure from
commercially available 2-amino-9,10-anthraquinone (11)
(10) (a) Adam, M.; Mu¨llen, K. Adv. Mater. 1994, 6, 439. (b)
J ørgensen, T.; Hansen, T. K.; Becher, J . Chem. Soc. Rev. 1994, 41. (c)
Otsubo, T.; Aso, Y.; Takimiya, K. Adv. Mater. 1996, 8, 203. (d)
Simonsen, K. B.; Becher, J . Synlett 1997, 1211. (e) Roncali, J . J . Mater.
Chem. 1997, 7, 2307. (f) Becher, J .; Lau, J .; Mørk, P. In Electronic
Materials: The Oligomer Approach; Mu¨llen, K., Wegner, G., Eds.;
Wiley-VCH: Weinheim, 1998; p 198. (g) Bryce, M. R.; Davenport, W.;
Goldenberg, L. M.; Wang, C. Chem. Commun. 1998, 945. (h) Bryce,
M. R. Adv. Mater. 1999, 11, 11. (i) Nielsen, M. B.; Lomholt, C.; Becher,
J . Chem. Soc. Rev. 2000, 29, 153. (j) Bryce, M. R. J . Mater. Chem. 2000,
10, 589.
(11) (a) Cerrada, E.; Bryce, M. R.; Moore, A. J . J . Chem. Soc., Perkin
Trans. 1 1993, 537. (b) Marshallsay, G. J .; Bryce, M. R. J . Org. Chem.
1994, 59, 6847. (c) Boulle, C.; Desmars, O.; Gautier, N.; Hudhomme,
P.; Cariou, M.; Gorgues, A. Chem. Commun. 1998, 2197. (d) Gautier,
N.; Mercier, N.; Riou, A.; Gorgues, A.; Hudhomme, P. Tetrahedron Lett.
1999, 40, 5997. (e) Supramolecular Engineering of Synthetic Metallic
Materials: Conductors amd Magnets; Veciana, J ., Rovira, C., Am-
abilino, D. B., Eds.; NATO ASI Series, Vol. 518; Kluwer: Dordrecht,
1999. (f) Pe´rez, I.; Liu, S. G.; Mart´ın, N.; Echegoyen, L. J . Org. Chem.
2000, 65, 9092. (g) Gautier, N.; Gallego-Planas, N.; Mercier, N.;
Levillain, E.; Hudhomme, P. Org. Lett. 2002, 4, 961.
The structure of exTTF dimers 16a ,b was established
by their analytical and spectroscopic data. The FTIR
spectrum showed the absence of carbonyl band, thus
(16) (a) Bryce, M. R.; Finn, T.; Moore, A. J . Tetrahedron Lett. 1999,
40, 3271. (b) Christensen, C. A.; Bryce, M. R.; Batsanov, A. S.; Howard,
J . A. K.; J eppesen, J . O.; Becher, J . Chem. Commun. 1999, 2433. (c)
D´ıaz, M. C.; Illescas, B.; Mart´ın, N. Tetrahedron Lett. 2003, 44, 945.
(17) House, H. O.; Koepsell, D. G.; Campbell, W. J . J . Org. Chem.
1972, 37, 1003.
(18) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508.
(19) (a) Bryce, M. R.; Moore, A. J . Synthesis 1991, 26. (b) Parg, R.
P.; Kilburn, J . D.; Ryan, T. G. Synthesis 1994, 195 and references
therein.
(12) Mart´ın, N.; Pe´rez, I.; Sa´nchez, L.; Seoane, C. J . Org. Chem.
1997, 62, 870.
(13) Godbert, N.; Bryce, M. R.; Dahaoui, S.; Batsanov, A. S.; Howard,
J . A. K.; Hazendok, P. Eur. J . Org. Chem. 2001, 749.
(14) Sa´nchez, L.; Pe´rez, I.; Mart´ın, N. Guldi, D. M. Chem. Eur. J .
2003, 9, 2457.
(20) Heck, R. F. Acc. Chem. Res. 1979, 12, 146.
(15) (a) Guldi, D. M.; Prato, M. Acc. Chem. Res. 2000, 33, 695. (b)
Guldi, D. M. Chem. Commun. 2000, 321.
(21) Davies, D. G.; Hodge, P.; Yates, P. J . Chem. Soc., Perkin Trans.
1 1973, 850.
4494 J . Org. Chem., Vol. 69, No. 13, 2004

Synthesis of Conjugated π-Extended Tetrathiafulvalene Dimers
SCHEME 1
showing the purity of the final compounds which was
confirmed by elemental analysis and electrospray mass
spectrometry.
in refluxing toluene. Compound 19 contains the strong
electron donor exTTF conjugated with the electron ac-
ceptor 9,10-anthraquinone, and consequently, its elec-
tronic spectrum shows the presence of an intense in-
tramolecular charge-transfer band centered at λmax ≈ 520
nm (Figure 1). This absorption band is responsible for
the violet color of this compound and suggests the
interest of this compound, as well as other further
D-π-A derivatives prepared by transformation of the
quinone moiety into other acceptors, in the field of
nonlinear optics.
Conjugated hetero exTTF dimer 20 was finally pre-
pared from 19 by following the standard above procedure
for the introduction of the 1,3-dithiole rings by Wittig-
Horner olefination reaction using a stoichiometry 19/
phosphonate of 1:6 (Scheme 1).
1
The H NMR and 13C NMR spectra of 16a ,b showed
only the half of the expected signals due to the existence
1
of a C2 rotational axis. Therefore, the H NMR spectra
of 16a ,b showed, in addition to the expected aromatic
and dithiole ring signals, the vinyl protons as a singlet
at δ ∼7.2. The E configuration of the vinyl moiety was
confirmed by the IR band appearing at 968 cm-1
.
As shown in Scheme 1, the synthetic procedure fol-
lowed for obtaining exTTF dimers (16a ,b) is limited to
the preparation of symmetric systems bearing the same
substituents on the 1,3-dithiole ring. Therefore, we have
carried out a different synthetic strategy to obtain
asymmetric dimers which is based in the preparation of
the valuable intermediate 19 constituted by one exTTF
unit and one anthraquinone moiety able to undergo
further chemical transformations.
Thus, compound 20 was obtained as a stable orange
solid in 58% yield. The structure of 20 was confirmed by
analytical and spectroscopic data and the 1H and 13C
NMR spectra revealed the lack of symmetry. The UV-
vis spectrum of 20 is similar to that of 16a ,b and shows
a significant hypsochromic shift in comparison with its
Intermediate 19 was synthesized by Heck coupling
reaction between iodine-containing exTTF (17) and vi-
nylanthraquinone (13) using (CH3CN)2PdCl2 as catalyst
J . Org. Chem, Vol. 69, No. 13, 2004 4495

D´ıaz et al.
F IGURE 1. UV-vis absorption spectra of compounds 19 and
20 in dichloromethane.
F IGURE 2. Room-temperature cyclic voltammograms of 16a ,
16b, and 20 in MeCN/CH2Cl2 (1/1).
TABLE 1. Red ox P oten tia ls (V vs Ag/AgCl) of Novel
Don or s Syn th esized a
In agreement with the above data, functionalized
exTTFs 17 and 18 show only one oxidation wave to form
the dication species at the same value as reported for the
parent unsubstituted 2a under the same experimental
conditions. Iodine substituted compound 17 showed,
however, a sligthly poorer oxidation potential than 2a
(see Table 1), due to the presence of the iodine atom and
its electronegative character.
The CV of all three new dimers 16a ,b and 20 show
several common features. All of the compounds es-
sentially retain the electronic porperties of both exTTF
moieties. Thus, compounds 16a ,b showed only one oxida-
tion wave involving 4e- at values quite similar to those
found for the respective monomer components (2a and
2b, respectively). In contrast, heterodimer 20 showed two
oxidation waves corresponding to the formation of the
dication and tetracation species of the two constituent
exTTF units of the dimer. The first anodic peak corre-
sponding to the oxidation of the exTTF unit with the
unsubtituted 1,3-dithiole rings and the second one cor-
responding to the exTTF unit bearing the SCH3 groups.
Interestingly, these values are sligthly shifted to lower
oxidation potentials compared to the respective dimers
16a ,b (Figure 2).
The reduction wave at positive values is associated to
the process of formation of the neutral molecule from the
tetracation state. As shown in Figure 2, the cyclic
voltammograms of the novel dimeric donors exhibit a
chemically reversible behavior which is in contrast to
other irreversible behaviors observed for exTTFs under
different experimental conditions.24
Interestingly and most importantly, when comparing
the CVs of the dimeric exTTF donors 16a ,b and 20 with
those of the model compounds 2a ,b and 18, it is obvious
that the CV of the dimers is not exactly the sum of the
CVs of the respective monomers. This could suggest the
presence of weak electronic interactions between the two
donor moieties (Table 1). This small electronic interaction
in the ground state is in agreement with the recorded
electronic spectra. The UV-vis spectra of the dimers is
dominated by the absorption of the exTTF moiety in the
b
compd
E1,ox
Epc
E1,red
λmaxc (nm)
pa
pc
2a (R ) H)
0.33 (2e-)
0.47 (2e-)
0.38 (2e-)
0.36 (2e-)
0.36 (4e-)
0.46 (4e-)
0.37 (2e-)
415
435
430
434
428
434
523
2b (R ) SCH3)
17
18
16a
16b
19
0.19
0.11
0.17
0.25
-0.86
-1.19
20
0.32 (2e-)
0.44 (2e-)
0.25
0.34
443
a
In MeCN/CH2Cl2 (1/1), Ag/AgCl vs Pt, scan rate 100 mVs-1
.
b
Reduction process from the dication to the neutral molecules.
c In CH2Cl2.
precursor 19 as a consequence of the lack of the donor-
acceptor character in 20 (Figure 1).
Electr och em istr y. The redox properties of the novel
π-extended dimers (exTTF) were measured by cyclic
voltammetry (CV) in CH3CN/CH2Cl2 (1/1) as solvent at
room temperature using a glassy carbon (GC) as working
electrode, the standard Ag/AgCl as reference electrode,
and using tetrabutylammonium perchlorate (0.1 M) as
the supporting electrolyte. The data are collected in Table
1 together with the parent exTTF (2: R ) H; R ) SCH3)
as references.
Unlike the parent TTF, exTTFs 2a ,b exhibit only one,
two-electron, quasireversible oxidation wave to form a
dication, which has been confirmed by Coulombimetric
analysis.22 The coalescence of the two one-electron pro-
cesses into one two-electron process reveals that the
presence of the quinonoid structure between the two 1,3-
dithiole rings leads to unstable, highly distorted, non-
planar, radical cations.8 Only recently, the first experi-
mental evidence for the formation of the π-radical cation
and dication species of a series of exTTFs by using time-
resolved and steady-state radiolytic techniques, has been
reported.23
(22) Moore, A. J .; Bryce, M. R. J . Chem. Soc., Perkin Trans. 1 1991,
157.
(23) (a) Guldi, D. M.; Sa´nchez, L.; Mart´ın, N. J . Phys. Chem. 2001,
105, 7139. (b) J ones, A. E.; Christensen, Ch. A.; Perepichka, D. F.;
Batsanov, A. S.; Beeby, A.; Low, P. J .; Bryce, M. R.; Parker, A. W.
Chem. Eur. J . 2001, 7, 973.
(24) (a) Pe´rez, I.; Liu, S.-G.; Mart´ın, N.; Echegoyen, L. J . Org. Chem.
2000, 65, 3796. (b) Otsubo, T.; Kochi, Y.; Bitoh, A.; Andura, F. Chem.
Lett. 1994, 2047.
4496 J . Org. Chem., Vol. 69, No. 13, 2004

Synthesis of Conjugated π-Extended Tetrathiafulvalene Dimers
visible region (∼430 nm), and the found values for the
λmax of the dimers are slightly shifted in comparison with
the respective monomers (see Table 1).
These electrochemical findings are in agreement with
those found for other related doubly donor molecules such
as the TTF-CHdCH-exTTF heterodimer, for which a
weak electronic interaction between the two donor (TTF
and exTTF) moieties was observed by CV.24a In contrast,
this weak interactions were not reported for the related
TTF dimer (TTF-CHdCH-TTF) which showed only two
redox couples, implying that there is no Coulombic effect
between the two TTF units.24b
Finally, D-π-A compound 19 showed, in addition to
the oxidation wave of the exTTF unit (0.34 V), the two
single-electron reduction waves to form the radical anion
and dianion species of the anthraquinone moiety, thus
confirming its amphoteric redox behavior.
Molecu la r Str u ctu r e. The molecular structure of the
parent exTTF dimer 16a has been optimized by using
semiempirical calculations at the PM3 level. Previous
theoretical calculations carried out on exTTFs (2) have
shown a good agreement with experimental data and
demonstrated that the PM3 method provides a good
description, even better than ab initio HF/6-31G* calcu-
lations, for the molecular structure of this type of
compounds.8
The minimum energy conformations (A and B) found
for 16a reveal an energy difference of only 0.272 kcal/
mol. As expected, the exTTF units show a butterfly-
shaped nonplanar geometry due to the strong steric
hindrance between the peri hydrogens and the sulfur
atoms (1.78 Å). To avoid these interactions, the molecule
is distorted out of the planarity with the central ring in
a boat conformation (distance S‚‚‚H, 2.53 Å).
F IGURE 3. Syn (A) and anti (B) minimum energy PM3-
optimized conformations for compound 16a .
Wittig-Horner olefination reaction with the respective
phosphonates of 1,3-dithiole rings. The starting bis-
anthraquinone was prepared either by Heck coupling
reaction or by olefination metathesis. A new donor
heterodimer involving two different exTTF units with
different substitution pattern on the 1,3-dithiole rings
was prepared from D-π-A molecule 19 constituted by
one exTTF unit connected by a vinyl spacer to the
anthraquinone moiety.
The electrochemical data reveal a similar redox be-
havior in the exTTF dimers showing only one quasire-
versible oxidation wave to form the corresponding tet-
racation species. This finding suggest that although a
certain degree of electronic interaction takes place be-
tween the exTTF units, both electroactive units behave
independently and, therefore, no significant electronic
communication occurs between the 1,3-dithiole rings in
the ground state. This electrochemical behavior is in
agreement with that previously reported for the analogue
system constituted by two TTF units connected by a vinyl
spacer which showed only two oxidation waves corre-
sponding to the radical cation and dication species of each
TTF moiety.25
Distortions from planarity in the exTTF units can be
described in terms of the angles R and γ. Angle R
corresponding to the angle formed by the outer benzene
rings (the wings of the butterfly), and γ defines the tilting
of the dithiole units and is obtained as the supplement
of the C7-C2-C6-C5 dihedral angle.8 The calculated
angles are basically the same for both exTTF units, being
R ) 140.0° and γ ) 33.2° for the more stable conformation
(B). Theses values are in good agreement with those
determined experimentally in the crystal for compound
2 (R ) SCH3)22 (R ) 143.8° and γ ) 33.3°) (Figure 3).
Although two different geometries [syn (A) and anti
(B)] are possible for 16a depending upon the orientation
of the two dithiole rings in each exTTF moiety (up and
down), no significant energy differences were found
between them. Finally, the planarity of the vinyl group
connecting the two benzene rings has been determined
by the dihedral angle C18-C25-C26-C27. The calcu-
lated value of 179.3° as well as the dihedral angles C17-
C18-C25-C26 ) 178.0° and C25-C26-C27-C28 )
175.4° confirm that both π-extended TTF units are in
conjugation through the vinyl spacer, thus supporting the
electronic communication between both benzene rings of
the exTTF units.
Theoretical calculations (PM3) carried out on com-
pound 16a reveal two highly distorted exTTF units and
a planar moiety involving the vinyl group and the two
adjacent benzene rings. This geometry favors the elec-
tronic communication between the adjacent benzene
Con clu sion s
In summary, we have synthesized a series of novel
exTTF dimers covalently connected through a vinyl
spacer from the corresponding bis-anthraquinone by
(25) Green, D. C.; Allen, R. W. J . Chem. Soc., Chem. Commun. 1978,
832.
J . Org. Chem, Vol. 69, No. 13, 2004 4497

D´ıaz et al.
NMR (CDCl3, 300 MHz) δ 7.69-7.64 (m, 4H, ArH), 7.49 (d,
2H, J 1 ) 8.2 Hz, ArH), 7.30-7.25 (m, 4H, ArH), 7.23 (s, 2H),
units and, at the same time, shows the lack of planarity
between the 1,3-dithiole rings in the ground state, thus
underpinning the lack of a strong electronic interaction
between the donor 1,3-dithiole rings as is also suggested
by the electrochemical results.
7.01 (d, 2H, J 2 ) 2.4 Hz, ArH), 6.61 (dd, 2H, J 1 ) 8.2 Hz, J 2
)
2.4 Hz, ArH), 6.29 (s, 4H), 6.27 (s, 4H); 13C NMR (CDCl3, 75
MHz) δ 135.4, 134.1, 132.2, 131.7, 130.8, 130.3, 128.8, 128.0,
127.2, 125.9, 124.9, 117.3, 117.2, 117.1; FTIR (KBr) 2922, 2850,
1545, 1514, 1454, 1444, 1259, 1091, 1020, 800, 754, 654 cm-1
;
Exp er im en ta l Section
UV-vis (CH2Cl2) λmax 428, 363, 279, 239 nm; MS (EI) m/z 784
(M+). Anal. Calcd for C42H24S8: C, 64.25; H, 3.08. Found: C,
64.42; H, 3.25.
2-Amino-9,10-anthraquinone (11) and n-butyllithium (1.6
M) were commercially available. 2-Iodo-9,10-anthraquinone
(12)17 and phosphonate esters (15a ,b)19 were obtained by
previously reported procedures.
1,2-Di{9,10-bis[4,5-bis(m eth ylth io)-1,3-dith iol-2-yliden e]-
9,10-d ih yd r oa n th r a cen -2-yl}eth ylen e (16b): 62% yield; mp
194-195 °C; 1H NMR (CDCl3, 300 MHz) δ 7.55-7.51 (m, 4H,
ArH), 7.36 (d, 2H, J 1 ) 8.2 Hz, ArH), 7.32-7.28 (m, 4H, ArH),
2-Vin yl-9,10-a n th r a qu in on e (13). To a stirred solution of
2-iodo-9,10-anthraquinone (12) (334 mg, 1 mmol) in dry
toluene (20 mL) was added Pd(PPh3)4 (58 mg, 0.05 mmol)
under argon atmosphere. While stirring, tributyl(vinyl)tin (634
mg, 2 mmol) was added. The resulting reaction mixture was
refluxed for 20 h. The solvent was then removed under vacuum
and the residue extracted with ethyl acetate (2 × 100 mL).
The combined organic extracts were washed with brine (3 ×
75 mL). After drying over MgSO4, the solvent was removed
under reduced pressure to afford a solid, which was further
purified by column chromatography on silica gel using hexane/
dichloromethane (1:1): 71% yield; mp 175-177 °C (lit.26 mp
175-176 °C dec); 1H NMR (CDCl3, 300 MHz) δ 8.35-8.26 (m,
4H, ArH), 7.83-7.78 (m, 3H, ArH), 6.87 (dd, 1H, J 1 ) 17.6
Hz, J 2 ) 10.7 Hz), 6.05 (d, 1H, J 1 ) 17.4 Hz), 5.54 (d, 1H,
J 2 ) 10.7 Hz); 13C NMR (CDCl3, 75 MHz) δ 183.2, 179.9, 143.3,
135.4, 134.1, 134.0, 133.6, 132.6, 131.4, 127.8, 127.3, 127.2,
124.8, 118.3; FTIR (KBr) 1678, 1626, 1589, 1325, 1290, 995,
933, 920, 899, 740, 710 cm-1; UV-vis (CH2Cl2) λmax 334, 267
nm; MS (EI) m/z 234 (M+). Anal. Calcd for C16H10O2: C, 82.04;
H, 4.30. Found: C, 82.23; H, 4.36.
7.20 (s, 2H), 6.86 (d, 2H, J 2 ) 2.3 Hz, ArH), 6.63 (dd, 2H, J 1
)
8.2 Hz, J 2 ) 2.3 Hz, ArH), 2.39 (s, 24H, SCH3); 13C NMR (CD3-
COCD3, 75 MHz) δ 147.8, 134.7, 134.1, 133.7, 129.3, 126.6,
126.5, 126.3, 125.2, 125.1, 125.0, 124.8, 124.6, 124.3, 124.2,
124.0, 121.8, 111.6, 110.2, 18.6 (SCH3), 18.4 (SCH3); FTIR
(KBr) 2918, 1618, 1560, 1533, 1499, 1471, 1417, 1292, 1252,
968, 879, 758, 675 cm-1; UV-vis (CH2Cl2) λmax 434, 368, 276,
242 nm; MS (ES), m/z 1154 (M+). Anal. Calcd for C50H40S16
:
C, 52.04; H, 3.49. Found: C, 52.26; H, 3.55.
P r ep a r a tion of Don or s 17 a n d 18. Gen er a l P r oced u r e.
To a solution of the phosphonate ester (15a ) (1 mmol) in dry
THF (20 mL) at -78 °C and under argon atmosphere was
added n-butyllithium (1.6 M) (1.1 mmol). After 1 h at -78 °C,
a solution of the corresponding quinone (12 or 13) (0.25 mmol)
in dry THF (15 mL) was added with a syringe. The mixture
was stirred for 1 h at -78 °C and then allowed to warm to 20
°C and kept at this temperature overnight. The THF was
evaporated under reduced pressure, water (75 mL) was added,
and the residue was extracted with CH2Cl2 (3 × 50 mL). The
combined extracts were dried (MgSO4) and filtered, and the
solvent was removed under reduced pressure. Purification of
products was achieved by column chromatography on silica
gel using hexane/dichloromethane (9:1) as eluent.
1,2-Di(a n th r a qu in on -2-yl)eth ylen e (14). To a solution of
2-iodo-9,10-anthraquinone (12) (428 mg, 1.3 mmol) and 2-vinyl-
9,10-anthraquinone (13) (300 mg, 1.3 mmol), in dry toluene
(250 mL) and under argon atmosphere, were added (MeCN)2-
PdCl2 (111 mg, 427 µmol), NBu4Br (413 mg, 1.3 mmol) and
triethylamine (4.3 mL). The resulting reaction mixture was
refluxed for 48 h. The solvent was removed under vacuo, and
the residue was chromatographed on silica gel using hexane/
dichloromethane (3:7) as eluent: 24% yield; mp > 250 °C (lit.21
2-Iod o-9,10-b is(1,3-d it h iol-2-ylid en e)-9,10-d ih yd r oa n -
1
th r a cen e (17): 62% yield; mp 259-260 °C; H NMR (CDCl3,
300 MHz) δ 8.01 (d, 1H, J 2 ) 1.8 Hz, ArH), 7.71-7.66 (m, 2H,
ArH), 7.60 (dd, 1H, J 1 ) 8.2 Hz, J 2 ) 1.8 Hz, ArH), 7.43 (d,
1H, J 1 ) 8.2 Hz, ArH), 7.32-7.28 (m, 2H, ArH), 6.33 (s, 2H),
6.31 (s, 2H); 13C NMR (CDCl3, 75 MHz) δ 146.2, 142.3, 139.8,
139.3, 134.0, 132.0, 128.8, 127.9, 127.1, 119.6, 117.2, 114.3;
FTIR (KBr) 2924, 2852, 2183, 1545, 1516, 1452, 1394, 756,
646, 623, 501 cm-1; UV-vis (CH2Cl2) λmax 430, 366, 238 nm;
MS (EI) m/z 506 (M+, 68), 380 (M+ - I, 36). Anal. Calcd for
1
mp 434 °C); H NMR (CDCl3, 300 MHz) δ 8.33-8.26 (m, 4H,
ArH), 8.21 (d, 2H, J 2 ) 1.7 Hz, ArH), 8.17 (d, 2H, J 1 ) 8.1 Hz,
ArH), 7.82-7.79 (m, 4H, ArH), 7.62 (dd, 2H, J 1 ) 8.1 Hz, J 2
)
1.7 Hz, ArH), 6.95 (s, 2H); 13C NMR (CDCl3, 50 MHz) δ 183.3,
180.1, 154.7, 134.9, 134.3, 133.7, 133.3, 132.9, 129.6, 126.4,
126.3, 121.1, 118.1; FTIR (KBr) 2924, 1672, 1626, 1587, 1572,
1344, 1305, 1282, 986, 932, 847, 712, 663 cm-1; UV-vis (CH2-
Cl2) λmax 570, 428, 330, 255 nm; MS (EI) m/z 440 (M+). Anal.
Calcd for C30H16O4: C, 81.81; H, 3.66. Found: C, 82.03; H,
3.84.
C
20H11IS4: C, 47.43; H, 2.19. Found: C, 47.23; H, 2.09.
2-Vin yl-9,10-bis(1,3-d ith iol-2-ylid en e)-9,10-d ih yd r oa n -
1
th r a cen e (18): 65% yield; mp 186-187 °C; H NMR (CDCl3,
300 MHz) δ 7.77 (d, 1H, J 2 ) 1.7 Hz, ArH), 7.71-7.68 (m, 2H,
ArH), 7.66 (d, 1H, J 1 ) 8.2 Hz, ArH), 7.34-7.28 (m, 3H, ArH),
6.77 (dd, 1H, J 1 ) 17.4 Hz, J 2 ) 11.0 Hz), 6.32 (s, 2H), 6.31 (s,
ExTTF Dim er s 16a ,b. Gen er a l P r oced u r e. To a solution
of the corresponding phosphonate ester (15a ,b) (10 mmol) in
dry THF (200 mL) at -78 °C and under argon atmosphere
was added n-BuLi (1.6 M) (11 mmol) with a syringe. After 30
min at -78 °C, the quinone 14 (1 mmol) in dry THF (50 mL)
was added with a syringe into the solution of the phosphonate
carbanion. The mixture was stirred for 1 h at -78 °C and then
allowed to warm to 20 °C and kept at this temperature
overnight. The THF was evaporated under reduced pressure,
water (100 mL) was added, and the residue was extracted with
CH2Cl2 (3 × 75 mL). The combined extracts were dried
(MgSO4) and filtered, and the solvent was removed under
reduced pressure. Purification of products was achieved by
column chromatography on silica gel using hexane/dichlo-
romethane as eluent.
2H), 5.80 (d, 1H, J 1 ) 17.4 Hz), 5.28 (d, 1H, J 2 ) 11.0 Hz); 13
C
NMR (CDCl3, 75 MHz) δ 136.6, 135.7, 135.3, 125.9, 125.1,
124.9, 123.9, 122.6, 117.2, 113.8; FTIR (KBr) 2924, 2852, 2362,
2345, 1630, 1545, 1508, 995, 800, 752, 648 cm-1; UV-vis (CH2-
Cl2) λmax 434, 370, 287 (sh), 250 nm; MS (EI), m/z 406 (M+).
Anal. Calcd for C22H14S4: C, 64.98; H, 3.47. Found: C, 64.75;
H, 3.18.
1-(An th r aqu in on -2-yl)-2-[9,10-bis(1,3-dith iol-2-yliden e)-
9,10-d ih yd r oa n th r a cen -2-yl]eth ylen e (19). To a solution of
the exTTF iodo derivative (17) (230 mg, 0.45 mmol) and
2-vinyl-9,10-anthraquinone (13) (106 mg, 0.45 mmol), in dry
toluene (100 mL) and under argon atmosphere, were added
(MeCN)2PdCl2 (39 mg, 150 µmol), NBu4Br (145 mg, 0.45 mmol)
and triethylamine (1.5 mL). The resulting reaction mixture
was refluxed for 22 h. The solvent was removed under vacuo,
and the residue was chromatographed on silica gel using
hexane/dichloromethane (1:1) as eluent. The isolated product
was obtained as a deep red solid: 31% yield; mp 204-205 °C;
1,2-Di[9,10-b is(1,3-d it h iol-2-ylid en e)-9,10-d ih yd r oa n -
th r a cen -2-yl]eth ylen e (16a ): 54% yield; mp 225-227 °C; 1H
(26) Ferna´ndez-Refojo, M.; Pan, Y.-L.; Kun, K. A.; Cassidy, H. G. J .
Org. Chem. 1960, 25, 416.
4498 J . Org. Chem., Vol. 69, No. 13, 2004

Synthesis of Conjugated π-Extended Tetrathiafulvalene Dimers
1H NMR (DMSO-d6, 300 MHz) δ 8.41 (s, 1H, ArH), 8.26-8.21
(m, 4H, ArH), 8.00 (s, 1H, ArH), 7.96-7.93 (m, 2H, ArH), 7.73-
7.66 (m, 5H), 7.58 (d, 1H, J ) 16.3 Hz), 7.39-7.36 (m, 2H,
ArH), 6.79 (m, 4H); 13C NMR (DMSO-d6, 75 MHz) δ 182.5 (CO),
181.9 (CO), 143.0, 137.2, 137.1, 135.2, 134.8, 134.5, 134.4,
134.2, 133.5, 133.1, 133.0, 132.2, 131.6, 131.5, 127.5, 127.0,
126.6, 126.2, 125.0, 124.9, 124.6, 123.3, 120.4, 120.3, 118.3,
118.2, 118.0; FTIR (KBr) 2924, 2363, 2343, 1672, 1591, 1545,
1508, 1327, 1298, 957, 933, 750, 708, 658 cm-1; UV-vis (CH2-
Cl2) λmax 523, 428, 371, 317, 252 nm; MS (ES) m/z 612 (M+).
Anal. Calcd for C36H20O2S4: C, 70.56; H, 3.29. Found: C, 70.28;
H, 3.36.
1-[9,10-Bis(1,3-d it h iol-2-ylid en e)-9,10-d ih yd r oa n t h r a -
cen -2-yl]-2-{9,10-bis[4,5-bis(m eth ylth io)-1,3-d ith iol-2-yl-
id en e]-9,10-d ih yd r oa n th r a cen -2-yl}eth ylen e (20). To a
solution of the phosphonate ester (15b) (1.8 g, 6 mmol) in dry
THF (120 mL) at -78 °C and under argon atmosphere was
added n-butyllithium (1.6 M) (4.1 mL, 6.6 mmol). After 1 h at
-78 °C, a solution of the quinone 19 in dry THF (612 mg, 1
mmol) was added with a syringe. The mixture was stirred for
1 h at -78 °C and then allowed to warm to 20 °C and kept at
this temperature overnight. The THF was evaporated under
reduced pressure, water (100 mL) was added, and the residue
was extracted with CH2Cl2 (3 × 50 mL). The combined extracts
were dried (MgSO4) and filtered, and the solvent was removed
under reduced pressure. Purification of the product was
achieved by column chromatography on silica gel using hexane/
dichloromethane (2:1) as eluent. The purified product was
isolated as a yellow solid: 58% yield; mp 232-233 °C; 1H NMR
(CDCl3, 300 MHz) δ 7.89-7.85 (m, 1H, ArH), 7.72-7.68 (m,
4H, ArH), 7.59-7.53 (m, 3H), 7.48-7.41 (m, 2H, ArH), 7.36-
7.28 (m, 4H, ArH), 7.19-7.17 (m, 2H, ArH), 6.30 (d, 4H, J )
1.5 Hz), 2.39 (s, 12H, 4SMe), 13C NMR (CDCl3, 75 MHz) δ
135.9, 135.8, 135.7, 135.6, 135.5, 135.3, 135.2, 135.0, 134.8,
134.5, 133.8, 131.2, 131.0, 129.0, 128.9, 128.2, 126.4, 126.3,
125.9, 125.7, 125.6, 125.4, 125.3 (2C), 124.9, 124.4, 124.3,
123.6, 123.5, 123.4, 123.1, 123.0, 122.9, 122.8, 117.3, 117.2
(2C), 117.1, 19.2 (SCH3), 19.1 (SCH3); FTIR (KBr) 2920, 2852,
2281, 1701, 1545, 1508, 1498, 1452, 1420, 1257, 959, 800, 754,
638 cm-1; UV-vis (CH2Cl2) λmax 443, 396, 327, 273, 236 nm;
MS (ES), m/z 968 (M+). Anal. Calcd for C46H32S12: C, 56.99;
H, 3.33. Found: C, 57.25; H, 3.48.
Ack n ow led gm en t. This work has been supported
by the MCYT of Spain (Project BQU2000-0790 and
BQU2002-00855).
J O049741Z
J . Org. Chem, Vol. 69, No. 13, 2004 4499