A New Building Block for Diels-Alder Reactions in π-Extended Tetrathiafulvalenes: Synthesis of a Novel Electroactive C60-Based Dyad

Article abstract of DOI:10.1021/ol9911674

(Matrix Presented) The synthesis of quinonoid π-extended tetrathiafulvalene (TTF) derivatives bearing two hydroxymethyl groups on one 1,3-dithiole ring (10) have been prepared in seven steps from commercially available ethylene trithiocarbonate. From thes

Full text of DOI:10.1021/ol9911674

ORGANIC
LETTERS
1999
Vol. 1, No. 12
2005-2007
A New Building Block for Diels−Alder
Reactions in π-Extended
Tetrathiafulvalenes: Synthesis of a
Novel Electroactive C -Based Dyad
60
a
M Angeles Herranz and Nazario Mart´ın*
Departamento de Qu´ımica Orga´nica, Facultad de Qu´ımica, UniVersidad Complutense,
E-28040 Madrid, Spain
nazmar@eucmax.sim.ucm.es
Received October 19, 1999
ABSTRACT
The synthesis of quinonoid π-extended tetrathiafulvalene (TTF) derivatives bearing two hydroxymethyl groups on one 1,3-dithiole ring (10)
have been prepared in seven steps from commercially available ethylene trithiocarbonate. From these compounds, the transient 4,5-dimethylene
intermediate (12) has been favorably generated and trapped in situ by the reactive dienophile C60 to form the first Diels−Alder cycloaduct of
a π-extended TTF (13).
Tetrathiafulvalene (TTF) derivatives with extended π-con-
jugation are an important class of electron-donor systems
which present remarkable differences with the parent TTF
in terms of oxidation potential values, geometry, and charge
delocalization.1-3 In particular, p-quinodimethane analogues
of TTF such as 1 and 2 (Figure 1) show a saddle-shaped
structure, due to the steric hindrance caused by benzoannu-
lation of the quinonoid moiety,4 which is in contrast to the
almost planar structure of the TTF molecule.5
Despite the highly distorted geometry, compound 1 forms
electrically conducting charge-transfer complexes with tetra-
cyano-p-quinodimethane.3 Other properties such as nonlinear
optics6 or photovoltaics,7 when the compounds are covalently
linked to an electron-acceptor unit, have been also reported.
However, a chemical functionalization is still required for
the systematic study of the properties shown by these
quinonoid π-extended TTFs. Although some derivatives
(1) Akiba, K.; Ishikawa, K.; Inamoto, N. Bull. Chem. Soc. Jpn. 1978,
51, 2674.
(2) Yamashita, Y.; Kobayashi, Y.; Miyashi, T. Angew. Chem., Int. Ed.
Engl. 1989, 28, 1052-1053.
(3) Bryce, M. R.; Moore, A. J.; Hasan, M.; Ashwell, G. J.; Fraser, A.
T.; Clegg, W.; Hursthouse, M. B.; Karaulov, A. I. Angew. Chem., Int. Ed.
Engl. 1990, 29, 1450-1452
(4) Mart´ın, N.; Sa´nchez, L.; Seoane, C.; Ort´ı, E.; Viruela, P. M.; Viruela,
R. J. Org. Chem. 1998, 63, 1268-1279 and references therein.
(5) Viruela, R.; Viruela, P. M.; Pou-Ame´rigo, R.; Ort´ı, E. Synth. Met.
1999, 103, 1991-1993.
(6) Herranz, M. A.; Mart´ın, N.; Sa´nchez, L.; Gar´ın, J.; Orduna, J.; Alcala´,
R.; Villacampa, B.; Sa´nchez, C. Tetrahedron 1998, 54, 11651-11658.
(7) Mart´ın, N.; Sa´nchez, L.; Guldi, D. M. Unpublished results.
Figure 1.
10.1021/ol9911674 CCC: $18.00 © 1999 American Chemical Society
Published on Web 11/09/1999

bearing a functional group on the central hydrocarbon
skeleton (2) are known,8 the synthesis of appropriately
monofunctionalized quinonoid π-extended derivatives 3 has
been only recently reported.9
Scheme 1
In this Letter we report on the preparation of novel 4′,5′-
functionalized 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydro-
anthracene derivatives 10 and 11 as precursors of the elusive
intermediate 4′,5′-dimethylene derivative 12. This o-quino-
dimethane analogue10 of the 1,3-dithiol-2-ylidene moiety 12
undergoes a rapid [4 + 2] cycloaddition reaction with [60]-
fullerene as the dienophile to form a novel C60-based donor-
acceptor dyad (13).
This first example of a Diels-Alder reaction involving a
quinonoid π-extended TTF derivative facilitates the use of
cycloadditions as a useful tool for the preparation of other
more sophisticated π-extended TTF derivatives. In this
regard, our present approach complements the recently
reported [4 + 2] cycloadditions of the parent 2,3-dimethyl-
ene-TTF to C60.11
The synthesis of the novel diols 10a-c is shown in
Scheme 1. Thus, reaction of the anion of anthrone 4 with
the dithiolium salt 5, prepared in a three-step synthetic
procedure by following the method reported in the litera-
ture,12 affords compound 6 in 54% yield. Introduction of the
second 1,3-dithiol unit in 6 requires the previous protection
of hydroxyl groups, which was carried out with tert-
t
butyldiphenylsilyl chloride (ClSiPh2 Bu) in 81% yield. Ole-
fination reaction of bis-protected diol 7 with the anion of
the phosphonate esters 8a-c13 generated in the basic medium
led to the protected quinonoid π-extended TTFs 9a-c in
good yields. Further deprotection of 9a-c was carried out
by using tetrabutylammonium fluoride to give diols 10a-
c,14 which were further purified by flash chromatography
using hexane:ethyl acetate (1:1) as eluant.
9-(4,5-Dihydroxymethyl-1,3-dithiol-2-ylidene)-10-(1,3-
dithiol-2-ylidene)-9,10-dihydroanthracenes 10 are interesting
electron donors for the preparation of salts and charge-
transfer complexes since, in addition to their strong electron-
donor character, they present two -OH groups which are able
to form a net of hydrogen bonds, thus increasing the
dimensionality in the solid state. Bryce has recently reviewed
the importance of TTF systems endowed with hydroxy
substituents in order to gain control of crystal architectures.15
In this regard, the strength, directionality, and selectivity of
the hydrogen bond make it an excellent candidate to increase
the dimensionality and hence the conductivity in π-extended
TTF derivatives.
(8) Mart´ın, N.; Pe´rez, I.; Sa´nchez, L.; Seoane, C. J. Org. Chem. 1997,
62, 5690-5695.
(9) Bryce, M. R.; Finn, T.; Moore, A. J. Tetrahedron Lett. 1999, 40,
3271-3274.
(10) For a very recent review on o-quinodimethanes, see: Segura, J. L.;
Mart´ın, N.; Chem. ReV. 1999, 99, 3199.
(11) (a) Llacay, J.; Mas, M.; Molins, E.; Veciana, J.; Powell, D.; Rovira,
C. Chem. Commun. 1997, 659-660. (b) Boulle, C.; Rabreau, J. M.;
Hudhomme, P.; Cariou, M.; Jubault, M.; Gorgues, A.; Orduna, J.; Gar´ın, J.
Tetrahedron Lett. 1997, 38, 3909-3910. (c) Llacay, J.; Veciana, J.; Vidal-
Gancedo, J.; Bourdelande, J. L.; Gonza´lez-Moreno, R.; Rovira, C. J. Org.
Chem. 1998, 63, 5201-5210.
Diols 10 react with phosphorus tribromide in THF/CCl4
at 0 °C to form dibromomethyl derivatives 11. Thus, when
compound 10b was treated with PBr3 under these conditions,
11 was obtained in 71% yield as an orange solid which could
be stored in the refrigerator for a few days without
decomposition.
(12) Fox, M. A.; Pan, H.-L. J. Org. Chem. 1994, 59, 6519-6527.
(13) (a) Bryce, M. R.; Moore, A. J. Synthesis 1991, 26-28. (b) Parg, R.
P.; Kilburn, J. D.; Ryan, T. G.; Synthesis 1994, 195-198 and references
therein.
(14) Selected spectroscopic data for 10b: 79% yield; FTIR (KBr disk)
V (cm-1) 2922, 2853, 1528, 1499, 1445, 1385, 1283, 1171, 1049, 999, 947,
858, 779, 756, 675, 644, 625; 1H NMR (DMSO-d6, 300 MHz) δ 7.61-
7.58 (2H, m), 7.51-7.48 (2H, m), 7.40-7.36 (4H, m), 5.43 (2H, t, J )
5.8, -OH), 4.27 (2H, dd, J1 ) 13.7, J2 ) 5.8), 4.19 (2H, dd, J1 ) 13.7, J2
) 5.8), 2.4 (6H, s); 13C NMR (DMSO-d6, 50 MHz) δ 134.4, 134.1, 133.6,
129.6, 129.4, 126.7, 126.2, 125.3, 125.0, 124.8, 123.6, 120.8, 56.0
(-CH2OH), 18.4 (-SCH3); UV-vis (CH2Cl2) λmax (log ꢀ) nm 242 (4.52),
266 (4.21), 364 (4.15), 430 (4.40); MS (m/z) 532 (M+, 100%), 514 (M -
18, 68%).
Among the different methods reported in the literature for
the generation of o-quinodimethanes and related hetero-
analogues,10 iodide-induced 1,4-dehydrohalogenation has
played a very important role. By using this method, in the
presence of 18-crown-6 ether, the transient 4,5-dimethylene
(15) Bryce, M. R. J. Mater. Chem. 1995, 5, 1481-1496.
Org. Lett., Vol. 1, No. 12, 1999
2006

intermediate 12 was generated in situ and reacted with a good
dienophile such as C60 to form the Diels-Alder cycloaduct
as a yellow-brown solid in 25% yield (37% yield based on
recovered C60).16
different temperatures. The oxidation potentials are anodi-
cally shifted as the temperature decreases [Eox(40 °C) ) 0.55
V; Eox(rt) ) 0.60 V; Eox(0 °C) ) 0.67 V; Eox(-78 °C) )
0.89 V], which indicates a greater difficulty in the formation
of the dication species. A much more remarkable effect is
observed in the wave associated with the process donor2+
f donor°, which undergoes a drastic cathodic shift when
the temperature is decreased [Ered(40 °C) ) 0.17 V; Ered(rt)
) 0.10 V; Ered(0 °C) ) 0.01 V, Ered(-78 °C) ) -0.27 V].
This behavior has been interpreted as an indication of the
high stability of the former dications.17
The UV-vis spectrum of 13 shows absorption bands at
424 (4.33) and 442 (4.39) nm which are assigned to the
π-extended donor moiety (10b: 420 and 430 nm), thus hiding
the characteristic weak absorption band at λ ) 430 nm of
dihydrofullerenes. The 13C NMR spectrum shows a peak
observed at 77.4 ppm, characteristic of those quaternary sp3-
hybridized carbons of attachment to the substituent, thus
confirming the linkage of the organic addend on a [6,6] ring
junction of the C60 core. Confirmation of the structure was
carried out by MALDI-TOF (matrix-assisted laser desorption/
ionization time-of-flight) mass spectrometry which showed
the molecular ion at m/z 1219.
C60-Based dyad 13 shows, in addition to the oxidation
wave of the donor fragment to form the dication, the presence
of four quasireversible reduction waves, similar to those
observed for the parent C60. These reduction potentials are
slightly shifted to more negative values than those of C60
due to the saturation of a double bond which raises the
LUMO energy of the molecule (Table 1).18 It is important
to note that the redox values are remarkably shifted in
comparison with both donor and acceptor independent units
which suggests a kind of electronic interaction between them.
In conclusion, we have reported the synthesis of dihy-
droxymethyl quinonoid π-extended TTF derivatives 10 which
are appealing systems for the preparation of salts and CT
complexes with higher dimensionality. These compounds
(10) have been used as starting materials for obtaining the
respective dibromides (11) which can favorably generate the
first heteroanalogue o-QDM of a π-extended TTF. The facile
generation of these reactive intermediates paves the way for
use of cycloadditions for the design and synthesis of more
elaborate π-extended TTF derivatives. As a practical ap-
plication, we have prepared the first C60-based donor-
acceptor dyad by Diels-Alder reaction of C60 and a
π-extended TTF derivative, which has been spectroscopically
and electrochemically characterized. These dyads bearing
π-extended TTFs connected to the C60 core through a rigid
spacer are excellent candidates for photovoltaic devices.19
Photophysical studies on these novel systems (13) as well
as preparation of CT complexes by mixing donors 10 with
strong electron acceptors are currently in progress.
The solution redox properties of the new compounds have
been investigated by cyclic voltammetry. 4,5-Dihydroxy-
methyl π-extended TTF derivatives 10 showed the presence
of a quasireversible oxidation wave involving a two-electron
process to form the dication. This fact had been previously
confirmed by Coulometric analysis of other related π-ex-
tended derivatives (Table 1).17
Table 1. Cyclic Voltammetry Data at Room Temperature for
π-Extended TTFs (10) and C60-TTF Dyad (13)a
compound
E1
E1
E2
E3
E4
red
ox
red
red
red
C60
13
10a
10b
1a b
-0.60
-0.72
-1.00
-1.17
-1.52
-1.75
-2.04
-2.30
0.75 (2e-)
0.53 (2e-)
0.60 (2e-)
0.44 (2e-)
a Experimental conditions: toluene:MeCN (4:1), V vs SCE, GCE as
-
working electrode, Bu4N+ClO4 as supporting electrolite; 200 mV s-1
.
b Measured in CH2Cl2.
Substitution on the 1,3-dithiole ring in 10 results in a shift
of the oxidation potential to more positive values. The
electrochemical redox behavior of 10b was studied at
Acknowledgment. Financial support by the DGICYT
through project PB95-0428-CO2 is gratefully acknowledged.
M.A.H. in indebted to MEC of Spain.
(16) Selected spectroscopic data for 13: 25% yield (37% based on
recovered C60); FTIR (KBr disk) V (cm-1) 2915, 1522, 1496, 1443, 1426,
1281, 1182, 968, 766, 752, 696, 674, 642, 623, 575, 553, 526; 1H NMR
(CDCl3, 300 MHz) δ 7.84-7.79 (2H, m), 7.57-7.54 (2H, m), 7.38-7.29
(4H, m), 4.38 (2H, d, J ) 14.7), 4.31 (2H, d, J ) 14.7), 2.43 (6H, s);
UV-vis (CH2Cl2) λmax (log ꢀ) nm 260 (4.99), 316 (4.52), 424 (4.33), 442
(4.39), MALDI-TOF m/z 1219 (M+ 82%), 498 (diene, 100%).
(17) Bryce, M. R.; Moore, A. J. J. Chem. Soc., Perkin Trans. 1 1991,
157-168.
OL9911674
(18) (a) Suzuki, T.; Maruyama, Y.; Akasaba, T.; Ando, W.; Kobayashi,
K.; Nagase, S. J. Am. Chem. Soc. 1994, 116, 1359-1363. For a recent
review, see: Echegoyen, L.; Echegoyen, L. E. Acc. Chem. Res. 1998, 31,
593-601.
(19) Mart´ın, N.; Sa´nchez, L.; Illescas, B.; Pe´rez, I. Chem. ReV. 1998,
98, 2527-2548.
Org. Lett., Vol. 1, No. 12, 1999
2007