Synthesis of a linear benzo[3]phenylene-[60]fullerene dyad

Article abstract of DOI:10.1016/j.tetlet.2005.09.174

The synthesis of a new linear benzo[3]phenylene-[60]fullerene dyad 1 is achieved over 10 steps in 15% overall yield by using an efficient sequence combining a double cobalt(I)-mediated cyclotrimerization with a Bingel reaction.

Full text of DOI:10.1016/j.tetlet.2005.09.174

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 8325–8328
Synthesis of a linear benzo[3]phenylene–[60]fullerene dyad
a,b
b
Sebastien Taillemite, Corinne Aubert,b Denis Fichoua,b, and Max Malacria
*
´
a
ˆ
CEA-Saclay, LRC Nanostructures et Semi-Conducteurs Organiques, SPCSI/DRECAM, Bat. 462, 91191 Gif-sur-Yvette, France
bUniversite´ P. et M. Curie, Laboratoire de Chimie, UMR 7611 CNRS-UPMC, Institut de Chimie Mole´culaire-FR 2769,
Tour 44-54, CC.229, 4 Place Jussieu, 75252 Paris Cedex 05, France
Received 22 July 2005; revised 27 September 2005; accepted 28 September 2005
Available online 18 October 2005
Abstract—The synthesis of a new linear benzo[3]phenylene–[60]fullerene dyad 1 is achieved over 10steps in 15% overall yield by
using an efficient sequence combining a double cobalt(I)-mediated cyclotrimerization with a Bingel reaction.
Ó 2005 Elsevier Ltd. All rights reserved.
The [N]phenylenes are linear polycyclic aromatic hydro-
carbons constituted an alternation of N benzene units
fused to N-1 cyclobutadiene rings. Similar to acenes,
they are promising candidates for molecular electronics
because of an extended p-conjugated system. As of to-
day, several [N]phenylenes have been synthesized1 and
some of them have even been studied spectroscopically2
and theoretically.3 However, to our knowledge the use
of [N]phenylenes as photo- or electroactive materials
have not been reported.
contrast, the first synthesis of fullerene adducts with tet-
racenes has been recently published8 and to our knowl-
edge, no example with [N]phenylenes has so far been
reported. Encouraged by our recent successful execution
of tetracene–[60]fullerene dyad and as part of our pro-
gram devoted to the construction of photovoltaic cells,
we turned our attention to a very efficient preparation
of [60]fullerene adducts bearing a [3]phenylene moiety.
[N]Phenylenes generally absorb between 400 and
500 nm with high molar extinction coefficients, but for
efficient photovoltaic conversion, absorption maximum
around 500–550 nm is preferred. Since the addition of
a fused benzene ring in the acene series tends to red-shift
the absorption by 100 nm,9 we envisioned to covalently
link C60 with various benzo[3]phenylenes acting as elec-
tron donors instead of the corresponding [3]phenylenes.
The small reorganization energy of fullerenes in electron
transfer reactions makes them particularly attractive as
electron accepting materials for energy conversion and
storage.4 Blends of functionalized [60]fullerenes mixed
together with conjugated polymers such as poly-p-phen-
ylenevinylene allow to build photovoltaic cells with con-
version efficiencies up to of a few percents.5 In these
systems, a fast photoinduced electron transfer from the
polymer donor moiety to the fullerene acceptor takes
place, followed by a slow charge recombination. Simi-
larly, donor-linked [60]fullerenes have been prepared
in view of developing solid state photovoltaic systems.6
Because of the ability of C60 to easily achieve close spatial
proximity with aromatic compounds via van der Waals
interactions,8 a sterically demanding group such as tri-
methylsilyl has been introduced on the adduct to avoid
a possible intramolecular p-stacking between benzo[3]-
phenylene and C60. Indeed, p-stacking would render
the separated charge state life-time too low and would
be inhibitory for further charge separation and efficient
photovoltaic effect. Thus, we report herein the successful
synthesis of the newly designed C60–benzo[3]phenylene
dyad 1 prepared by Bingel reaction,10 which has been
also recently employed to efficiently prepare [60]fullerene
adducts bearing carbazole moieties11 (Fig. 1).
In this context, the photoinduced electron transfer be-
tween fullerenes and a number of polycyclic hydrocar-
bons, which have been covalently linked as donor
moieties to C60 has been extensively investigated.7 In
Keywords: [60]Fullerene dyad; Benzo[3]phenylene; Cyclotrimerization;
Bingel reaction.
*
Our strategy for the synthesis of the benzo[3]phenylene
was based upon a classical iterative sequence including
Corresponding author. Tel.: +33 1 69 08 43 74; fax: +33 1 69 08 84
46; e-mail: fichou@drecam.cea.fr
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.09.174

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S. Taillemite et al. / Tetrahedron Letters 46 (2005) 8325–8328
Scheme 2. Reagents and conditions: (a) 1. MeMgBr, THF, rt, 1 h; 2.
(CH2O)n, rt, 4 h. (b) NBS, CH2Cl2, rt, 30min. (d) 7, Et3N, DMAP,
CH2Cl2, rt, 3 h.
Preparation of the quite stable triyne 8 was carried out
from 6 following Scheme 2. The silylated tether was
introduced according to the reported procedure for the
construction of unsymmetrical silaketals and silyl
ethers.15 Our first attempts to cyclize 8 with only a cat-
alytic amount of CpCo(CO)2 were quite unsuccessful,
only traces of the cycloadduct 9 were observed. As for
linear [4]phenylene,16 we suppose that CpCo was com-
plexed to the cycloadduct, thus consuming the catalyst
and requiring a stoichiometric amount of the complex.
Therefore, the target benzo[3]phenylene 9 was obtained
in 27% yield by using one equivalent of CpCo(CO)2
(Scheme 3). Thus, the opening of the silylether was car-
ried out with MeLi and led quantitatively to
benzo[3]phenylene 10. However, the overall yield for
its formation is 5.4% from 2,3-dihydroxynaphthalene
and appears not satisfying for synthetic purposes.
Figure 1. Newly designed C60–benzo[3]phenylene dyad 1.
palladium-catalyzed alkynylations followed by cobalt-
catalyzed cyclotrimerizations.12 A Sonogashira coupling
of trimethylsilylacetylene (TMSA) with 2, obtained in
92% yield from commercially available naphthalene-
2,3-diol,13 followed by desilylation of the triple bonds
afforded diyne 3 in 83% yield over two steps (Scheme
1). The first [2+2+2] cyclization was performed by slow
addition of a dilute solution of compound 3 in boiling
bis(trimethylsilyl)acetylene (BTMSA),12b under irradia-
tion. The benzobiphenylene 4, obtained in 94% yield,
was then sequentially submitted to iododesilylation, pal-
ladium-catalyzed coupling and desilylation to furnish
diyne 6 in 79% yield over three steps.
At the same time, the bimolecular cyclization of diyne 6
with silylated propargylic alcohol was attempted17
(Scheme 4).
As in the approach of linear [3]phenylenes, the second
bimolecular cyclotrimerization has been reported to be
generally less efficient than the first one,12b we antici-
pated that an intramolecular cyclization could be a
higher yielding alternative. Thus, we considered to pre-
pare linear benzo[3]phenylenes via an intramolecular
cycloaddition through temporary silicon tethers. The
use of disposable tethers in the sequence of the cycliza-
tion followed by the displacement of the silicon group
allows the chemo- and regioselective formation of poly-
substituted arenes.14
Indeed, in the presence of a stoichiometric amount of
CpCo(CO)2, the bimolecular cycloaddition led surpris-
ingly to higher yield than the intramolecular one. The
cycloadduct 11 was obtained in 61% yield, boosting
Scheme 3. Reagents and conditions: (a) CpCo(CO)2 (1 equiv), toluene,
hm, D. (b) MeLi, 0 °C, THF.
Scheme 1. Reagents and conditions: (a) TMSA, PdCl2(PPh3)2, CuI,
Et2NH, D, 30h. (b) KOH, MeOH, rt, 30min, 83% from 2. (c)
BTMSA, CpCo(CO)2, o-xylene, D, hm, 94%. (d) ICl, CCl4, 0 °C to rt,
45 min, 81%. (e) TMSA, PdCl2(PPh3)2, CuI, Et2NH, D, 1 h. (f) KOH,
MeOH, 30min, 97% over two steps.
Scheme 4. Reagents and conditions: (a) CpCo(CO)2 (1.1 equiv),
o-xylene, hm, D.

S. Taillemite et al. / Tetrahedron Letters 46 (2005) 8325–8328
8327
In summary, by using an efficient sequence combining a
double cobalt(I)-mediated cyclotrimerization together
with a Bingel reaction, we succeeded in synthesizing a
new linear benzo[3]phenylene–[60]fullerene dyad, which
was obtained over 10steps in 15% overall yield from
naphthalene-2,3-diol. The photophysical properties of
dyad 1 are currently under study in solution and the
solid state as well as its use in photovoltaic solar cells.
Beside further substitution on the central six-membered
ring should induce a lowering of the energy of the first
excited state. Therefore, we are now working on the
preparation of benzo[3]phenylene derivatives absorbing
at wavelengths longer than 500 nm.
Scheme 5. Reagents and conditions: (a) DCC, DMAP, CH2Cl2, 0 °C
to rt, 20h. (b) C 60, I2, toluene, rt, 6 h.
Acknowledgement
the overall yield of the sequence to 34%. N,N0-Dicyclo-
hexylcarbodiimide mediated esterification of benzylic
alcohol 11 was performed with carboxylic acid 12, which
was prepared in 70% yield from 3,5-dihydroxybenzyl
alcohol,18 the presence of the 3,5-bis(dodecyloxy)benz-
ylic substituents ensuring the solubility of the dyad in
organic solvents. Thus, malonate 13 derived from 11
was obtained in 82% yield (Scheme 5).
This study has been realized in the framework of the
EURO-PSB European Project (5th PCRD, No.
ENK5-CT2002-00687).
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.
2005.09.174 (experimental procedures and characteriza-
tion data of the compounds 3–10).
Finally, the reaction of C60 with 13 under Bingel condi-
1
tions10 afforded the target dyad 1 in 52% yield.19 In H
NMR spectrum, the resonance of the protons of the
trimethylsilyl group of 1 is deshielded from 0.30 to
0.35 ppm as compared to 13, which probably indicates
the close spatial proximity of C60 with the silicon group,
which plays exactly the part as it was devoted.
References and notes
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The UV–visible spectrum of the dyad 1 is given in Fig-
ure 2 and fits well with the sum of the absorption spectra
of the donor, 13 and methano[60]fullerene. This obser-
vation indicates the absence of significant interaction be-
tween benzo[3]phenylene and C60 moieties in the ground
state. However, a small red-shift is observed in the
absorption maximum of 13 (kmax = 452 nm) as com-
pared to [3]phenylene (kmax = 432 nm).12b Such a small
shift has already been observed with naphthelyno-
cyclobutabenzene and is probably due to the partial
electron localization in linear [N]phenylene. Finally,
in agreement with what has already been reported for
linear [3]phenylene,2a compounds 11, 12, 13 and dyad
1 are not fluorescent.
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Figure 2. UV–visible absorption spectra of 1 (—) and 13 (- - -) in THF
(c = 10À3 mol LÀ1).

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S. Taillemite et al. / Tetrahedron Letters 46 (2005) 8325–8328
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mixture gave after a successive recrystallization in benzene
11 (0.153 g, 61%). Rf (toluene/AcOEt 9/1) = 0.35. FT-IR
6. (a) Eckert, J. F.; Nicoud, J. F.; Nierengarten, J. F.; Liu, S.
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4984.
(ATR) 2952, 1412, 1179, 1094, 868, 836, 748 cmÀ1 1H
.
NMR (400 MHz, C6D6) d 0.21 (s, 9H), 4.31 (s, 2H), 6.23
(s, 1H), 6.26 (s, 1H), 6.44 (s, 1H), 6.47 (s, 1H), 6.64 (s, 1H),
6.72 (s, 1H), 7.10(m, 4H). 13C NMR (100 MHz, C6D6) d
0.66, 65.5, 111.2, 111.6, 113.1, 113.2, 116.7, 120.8, 126.2,
128.4, 129.3, 135.2, 146.4, 148.4, 151.0, 152.7. UV–vis
(THF) kmax 311, 327, 337, 353, 396, 425, 453. HMRS
calcd: 378.1447. Found: 378.1439.
Typical procedure for the preparation of 13: At 0 °C, N,N0-
dicyclohexylcarbodiimide (DCC, 0.051 g, 0.25 mmol,
1.5 equiv) was added to a solution of 128,18 (0.140 g,
0.25 mmol, 1.5 equiv) and 11 (0.059 g, 0.16 mmol, 1 equiv)
in presence of 4-DMAP (0.01 g, 0.08 mmol, 0.5 equiv) in
CH2Cl2 (8 mL). After being stirred for 1 h, the mixture
was warmed up to rt and was stirred for an additional 5 h.
After having removed the solvents in vacuo, the crude
residue was purified by flash chromatography (PE/AcOEt
95/5 then 9/1) to give 13 as a viscous solid (0.118 g, 82%).
Rf (PE/AcOEt 8/2) = 0.8. FT-IR (ATR) 2921, 2852, 1734,
9. Dabestani, R.; Ivanov, I. N. Photochem. Photobiol. 1999,
70, 10–34.
1597, 1463, 1326, 1249, 1129, 869, 838, 754 cmÀ1
.
1H
10. (a) Bingel, C. Chem. Ber. 1993, 126, 1957–1959; (b)
Nierengarten, J.-F.; Gramlich, V.; Cardullo, F.; Diede-
rich, F. Angew. Chem., Int. Ed. Engl. 1996, 35, 2101–2103.
11. Nakamura, Y.; Suzuki, M.; Imai, Y.; Nishimura, J. Org.
Lett. 2004, 6, 2797–2799.
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23, 536–556; (b) Berris, B. C.; Hovakeemian, G. H.; Lai,
Y.-H.; Mestdagh, H.; Vollhardt, K. P. C. J. Am. Chem.
Soc. 1985, 107, 5670–5687.
NMR (400 MHz, CDCl3) 0.30 (s, 9H), 0.89 (t,
d
J = 6.6 Hz, 6H), 1.26 (m, 32H), 1.43 (m, 4H), 1.76 (m,
4H), 3.50(s, 2H), 3.91 (t, J = 6.6 Hz, 4H), 5.06 (s, 2H),
5.11 (s, 2H), 6.41 (m, 3H), 6.48 (d, J = 2.3 Hz, 2H), 6.55 (s,
1H), 6.67 (m, 3H), 7.19 (dd, J = 6.6, 3.0Hz, 2H), 7.36 (dd,
J = 6.6, 3.0Hz, 2H). 13C NMR (100 MHz, CDCl3) d 0.3,
14.2, 22.8, 26.1, 29.3, 29.4, 29.5, 29.7, 32.0, 41.6, 67.3, 67.5,
68.1, 101.1, 106.4, 111.2, 111.6, 113.2, 117.3, 120.6, 126.1,
128.4, 135.1, 137.2, 140.2, 141.2, 146.2, 149.1, 151.1, 151.3,
151.4, 152.4, 153.3, 160.5, 166.2, 166.4. UV–vis (THF)
kmax (e) 311 (78,000), 338 (22,800), 354 (28,200), 426
(19,200), 452 (30,600).
13. Nicolaou, K. C.; Dai, W. M.; Hong, Y. P.; Baldridge, K.
K.; Siegel, J. S.; Tsay, S. C. J. Am. Chem. Soc. 1993, 115,
7944–7953.
14. Chouraqui, G.; Petit, M.; Aubert, C.; Malacria, M. Org.
Lett. 2004, 6, 1519–1521.
15. Petit, M.; Chouraqui, G.; Aubert, C.; Malacria, M. Org.
Lett. 2003, 5, 2037–2040.
16. Hirthammer, M.; Vollhardt, K. P. C. J. Am. Chem. Soc.
1986, 108, 2481–2482.
17. It is worthy of note that the bimolecular cyclization of
diyne 6 with propargylic alcohol in the presence of either
CpCo(CO)2 or Wilkinson catalyst failed.
Typical procedure for the preparation of 1: To a solution of
C60 (0.136 g, 0.19 mmol, 1.5 equiv), iodine (0.035 g,
0.14 mmol, 1.1 equiv), 13 (0.116 g, 0.13 mmol, 1 equiv) in
freshly distilled toluene (100 mL) was added DBU
(0.048 g, 0.32 mmol, 2.5 equiv). After being stirred for
6 h at rt, the reaction mixture was concentrated in vacuo
to 25% of the initial volume, filtered on silica gel pad and
then concentrated. The crude residue was purified by flash
chromatography (toluene/PE 1/1) to furnish 1 (0.107 g,
52%). Rf (toluene/PE 1/1) = 0.1. FT-IR (ATR) 731, 839,
´
18. Felder, D.; Gutierrez Nava, M.; del Pillar Carreon, M.;
Eckert, J.-F.; Luccisano, M.; Schall, C.; Masson, P.;
Gallani, J.-L.; Heinrich, B.; Guillon, D.; Nierengarten,
J.-F. Helv. Chim. Acta 2002, 85, 288–319.
1228, 1463, 1597, 1746, 2851, 2923 cmÀ1 1H NMR
.
(400 MHz, CDCl3) d 0.35 (s, 9H), 0.88 (t, J = 6.9 Hz,
6H), 1.29 (m, 32H), 1.41 (m, 4H), 1.74 (m, 4H), 3.89 (t,
J = 6.6 Hz, 4H), 5.38 (s, 2H), 5.42 (s, 2H), 6.42 (s, 1H),
6.45 (s, 2H), 6.57 (m, 2H), 6.63 (s, 1H), 6.69 (m, 3H), 7.21
(m, 2H), 7.38 (m, 2H). 13C NMR (100 MHz, CDCl3) d 0.8,
14.3, 22.9, 26.3, 29.4, 29.5, 29.6, 29.8, 29.9, 32.1, 52.0, 68.3,
69.1, 71.5, 101.8, 107.1, 111.4, 111.9, 113.4, 118.0, 120.7,
126.3, 135.2, 136.6, 139.2, 140.7, 141.0, 141.9, 142.0, 142.3,
143.1, 143.9, 144.6, 144.8, 145.0, 145.1, 145.2, 145.3, 145.4,
146.3, 149.6, 151.3, 151.4, 151.6, 152.5, 153.3, 160.6, 163.4,
19. Typical procedure for the preparation of 11: In a flame-
dried flask under argon, a solution of diyne 6 (0.165 g,
0.66 mmol), 3-(trimethylsilanyl)-prop-2-yn-1-ol (0.190 g,
1.49 mmol, 2.25 equiv) and CpCo(CO)2 (85 lL, 1 equiv)
in o-xylene (5 mL) and THF (3 mL) was added with a
syringe pump to boiling degassed o-xylene (5 mL). Light
from a projector lamp (300 W, 50% of its power) was
directed at the reaction mixture during the addition. After
the mixture was refluxed and irradiated for an additional
15 min, the solvents were removed by vacuum transfer.
Flash chromatography (toluene/AcOEt 9/1) of the crude
+Å
þÅ
163.6. MS (FAB, m/z) 720[C 60 ], 1642 [M ]. UV–vis
(THF) kmax (e) 313 (113,000), 327 (81,300), 354 (47,900),
403 (12,300), 426 (22,000), 453 (32,000).