Modular synthesis of 1H-indenes, dihydro-s-indacene, and diindenoindacene - A carbon-bridged p-phenylenevinylene congener

Article abstract of DOI:10.1021/ja905626b

(Chemical Equation Presented) A variety of 1H-indenes, dihydro-s-indacenes, and diindenoindacenes, carbon-bridged phenylenevinylene derivatives, can be synthesized in good to high yields using as a synthetic module a 3-lithioindene compound made available

Full text of DOI:10.1021/ja905626b

Published on Web 09/03/2009
Modular Synthesis of 1H-Indenes, Dihydro-s-Indacene, and
Diindenoindacenesa Carbon-Bridged p-Phenylenevinylene Congener
Xiaozhang Zhu, Chikahiko Mitsui, Hayato Tsuji,* and Eiichi Nakamura*
Department of Chemistry, School of Science, The UniVersity of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Received July 8, 2009; E-mail: tsuji@chem.s.u-tokyo.ac.jp; nakamura@chem.s.u-tokyo.ac.jp
Linearly fused aromatic systems1 such as acenes2 and fluorenes3,4
are attracting much interest because of their utility in organic
electronic devices. Representing a carbon-bridged phenylenevi-
nylene structure, indacene derivatives are no less interesting.5,6 For
instance, diindenoindacene consisting of seven rings (7 in Scheme
2) represents a methylene-bridged p-(distyryl)benzene,7 and this
planar conjugated system may show better-defined physical proper-
ties than the parent compound, p-(distyryl)benzene. However, such
a compound cannot be easily synthesized by known synthetic
methods.8,9 Because indene represents a partial structure of in-
dacene, we felt that the development of a new indene synthesis10
may provide an expeditious route to indacenes. We report here a
simple and effective synthesis of indenes from commercially
available 1-bromo-2-iodobenzene that made available a variety of
indenes and indacenes in good to high yields as well as the
diindenoindacene 7. The latter, synthesized in 62% overall yield
in five steps from readily available 1,4-dibromo-2,5-diiodobenzene,
emits blue light (97% quantum yield) and showed high thermal
stability and high electron and hole mobilities on the order of 10-3
cm2 V-1 s-1, which is a very high value for amorphous materials.
Some of the observed physical properties of such compounds can
be attributed to the presence of the robust diphenylmethylene
bridges and are beneficial for their use as organic semiconductors.
After extensive investigation of the cyclization of 1-alkynyl-2-
diphenyl(methoxy)methylbenzene (1)11 and congeners under various
conditions, we found that treatment with lithium naphthalenide
(LiNaph) at room temperature in THF results in the loss of the
methoxy group and smooth formation of the desired indene 3a in
99% yield upon quenching with water (Table 1, entry 1; >96%
cross-coupling reactions were also performed after transmetalation
into zinc to obtain 3-phenyl, -pyridyl, and -alkenyl indenes 3g-i
in excellent yields (93-99%; entries 7-9). The p-phenylene-linked
bis(3-indenyl) compound 3j was also obtained in a similar manner
using 1,4-iodobenzene as an electrophile (71%; entry 10).
Table 1. Modular Synthesis of 1H-Indene Derivatives
1
deuterium incorporation upon D2O quenching, as judged by H
NMR spectroscopy; see the Supporting Information), indicating the
quantitative formation of 3-lithioindene intermediate 2 (Scheme 1).
Scheme 1. Reductive Cyclization To Obtain Substituted
1H-Indenes
a Isolated yield based on 1. b Ns ) N-4-nitrobenzenesulfonyl group.13
Utilizing the lithioindene 2 as a synthetic module, we obtained
a variety of 3-substituted indenes in good to excellent yields, as
shown in Table 1. Iodination of 2 with 1,2-diiodoethane gave
3-iodo-1H-indene 3b in 89% isolated yield (entry 2). The 3-lithio-
indene 2 added to benzophenone and N-4-nitrobenzenesulfonyl (Ns)
benzaldimine to give the expected tertiary alcohol 3c and amine
3d in 97 and 72% yields, respectively (entries 3 and 4). Copper-
mediated reactions of dimethyl 2-ethylidenepropanedioate and acetyl
chloride resulted in conjugate addition and acylation12 to give 3e
and 3f in 91 and 79% yields, respectively (entries 5 and 6). Negishi
The scope of this modular approach14 can be readily expanded
to the synthesis of dihydro-s-indacenes (hereafter called indacenes)
as well (Scheme 2). Thus, diacetylene 4 was treated with 4 equiv
of LiNaph at room temperature in THF for 30 min and then
quenched with either water or diiodoethane, affording a 3,7-
diprotonated or 3,7-diiodinated indacene derivative in excellent yield
(99 or 83% yield, respectively). We thus conclude that a dilithio
intermediate 5 formed quantitatively and hence served as a synthetic
module for indacene synthesis. For instance, diphenylation of 5
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10.1021/ja905626b CCC: $40.75  2009 American Chemical Society

C O M M U N I C A T I O N S
proceeded under the conditions of Negishi coupling to afford the
octaphenylindacene 6c in 94% yield. Similarly, addition of ben-
zophenone to 5 afforded the diol 6d (92%). Intramolecular
Friedel-Crafts reaction using BF3 ·OEt2 gave diindenoindacene 7,
which has a carbon-bridged phenylenevinylene skeleton, in 99%
yield as a yellow solid.
a lower temperature (mp 268 °C).17 We consider that the planarity
of the compounds contributes to the high mobilities and the high
stability.
In conclusion, we have developed efficient modular syntheses
of 1H-indenes, dihydro-s-indacenes, and a diindenoindacene con-
taining a carbon-bridged phenylenevinylene framework. Because
of the beneficial presence of the robust diphenylmethylene bridges,
these compounds showed clear signs of enhanced π-conjugation:
red-shift in absorption, high quantum yield of light emission, high
carrier mobilities, and high thermal stability. The balanced ambi-
polar mobility profile of 7 is noteworthy and suggests the potential
of the indacene class of materials for use in organic semiconductor
devices.
Scheme 2. Modular Synthesis of Dihydro-s-indacenes 6 and
Diindenoindacene 7
Acknowledgment. We thank Dr. Yoshiharu Sato for helpful
discussions and MEXT for financial support (KAKENHI for E.N.,
no. 18105004, H.T., no. 20685005, and the Global COE Program
for Chemistry Innovation). Z.X. thanks the JSPS for a Postdoctoral
Fellowship for Foreign Researchers (no. P 09046). C.M. thanks
JSPS for the Research Fellowship for Young Scientists (No.
21·9262).
Supporting Information Available: Experimental details and
photophysical and electrochemical data. This material is available free
of charge via the Internet at http://pubs.acs.org.
References
(1) (a) Grimsdale, A. C.; Mu¨llen, K. Angew. Chem., Int. Ed. 2005, 44, 5592.
(b) Yamaguchi, S.; Tamao, K. Chem. Lett. 2005, 34, 2.
(2) Anthony, J. E. Angew. Chem., Int. Ed. 2008, 47, 452.
(3) Cho, S. Y.; Grimsdale, A. C.; Jones, D. J.; Watkins, S. E.; Holmes, A. B.
J. Am. Chem. Soc. 2007, 129, 11910.
(4) (a) Scherf, U.; Mu¨llen, K. Makromol. Chem., Rapid Commun. 1991, 12,
489. (b) Jacob, J.; Sax, S.; Piok, T.; List, E. J. W.; Grimsdale, A. C.; Mu¨llen,
K. J. Am. Chem. Soc. 2004, 126, 6987. (c) Wong, K.-T.; Chien, Y.-Y.;
Chen, R.-T.; Wang, C.-F.; Lin, Y.-T.; Chiang, H.-H.; Hsieh, P.-Y.; Wu,
C.-C.; Chou, C. H.; Su, Y. O. J. Am. Chem. Soc. 2002, 124, 11576.
(5) Adams, C.; Morales-Verdejo, C.; Morales, V.; MacLeod-Carey, D.;
Manr´ıquez, M.; Cha´vez, I.; Mun˜oz-Castro, A.; Delpech, F.; Castel, A.;
Gornitzka, H.; Rivie`re-Baudet, M.; Rivie`re, P.; Molins, E. Eur. J. Inorg.
Chem. 2009, 784.
The maximum absorption wavelengths of two indacenes, oc-
taphenylindacene 6c and diindenoindacene 7, are 353 and 419 nm,
respectively, in CH2Cl2 (spectra shown in the Supporting Informa-
tion). The longer absorption wavelength of 7 relative to 6c is
consistent with the more enhanced conjugation in 7, which possesses
two additional diphenylmethylene bridges (see the Supporting
Information). Upon photoexcitation, both compounds 6c and 7
showed blue emission, with maximum wavelengths of 439 and 433
nm, respectively. The emission quantum yields of the two com-
pounds are very high: 0.82 for 6c and 0.97 for 7, as determined by
the absolute method.
We next examined the solid-state properties (carrier mobilities
and thermal stability) of 6c and 7. The carrier mobilities were
measured by the time-of-flight method for vacuum-deposited
amorphous films of the compounds, which showed a dispersive
transient current for both hole and electron upon irradiation with a
laser pulse. Octaphenylindacene 6c showed a hole mobility of 2 ×
10-3 cm2 V-1 s-1 (at an electric field E ) 2.5 × 105 V/cm) and an
electron mobility of 1 × 10-3 cm2 V-1 s-1 (at E ) 3.3 × 105 V/cm)
at room temperature. Diindenoindacene 7 showed higher hole and
(6) Fukazawa, A.; Li, Y.; Yamaguchi, S.; Tsuji, H.; Tamao, K. J. Am. Chem.
Soc. 2007, 129, 14164.
(7) (a) Hancock, J. E. H.; Pavia, D. L. J. Org. Chem. 1961, 26, 4350. (b)
Hellwinkel, D.; Hasselbach, H.-J.; La¨mmerzahl, F. Angew. Chem., Int. Ed.
Engl. 1984, 23, 705.
(8) Bell, W. L.; Curtis, C. J.; Eigenbrot, C. W.; Pierpont, C. G.; Robbins, J. L.;
Smart, J. C. Organometallics 1987, 6, 266.
(9) Dahrouch, M. R.; Jara, P.; Mendez, L.; Portilla, Y.; Abril, D.; Alfonso,
G.; Chavez, I.; Manriquez, J. M.; Rivie`re-Baudet, M.; Rivie`re, P.; Castel,
A.; Rouzaud, J.; Gornitzka, H. Organometallics 2001, 20, 5591.
(10) (a) Miyamoto, M.; Harada, Y.; Tobisu, M.; Chatani, N. Org. Lett. 2008,
10, 2975. (b) Ali Khan, Z.; Wirth, T. Org. Lett. 2009, 11, 229. (c) Yang,
S.; Li, Z.; Jian, X.; He, C. Angew. Chem., Int. Ed. 2009, 48, 3999.
(11) When the methoxy group in 1 was replaced by a chlorine atom and the
chloride compound was treated with BuLi (halogen-lithium exchange),
the cyclization did not take place; instead, the reaction gave the corre-
sponding dechlorinated, protonated product. When the diphenylmethyl
group in 1 was replaced by a diisopropyl group and treated with LiNaph,
the cyclization reaction did not take place either. The observations suggest
that the reported cyclization takes place via a radical anion species.
(12) Yoshikai, N.; Iida, R.; Nakamura, E. AdV. Synth. Catal. 2008, 350, 1063.
(13) Kan, T.; Fukuyama, T. Chem. Commun. 2004, 353.
(14) For examples, see: (a) Tsuji, H.; Mitsui, C.; Ilies, L.; Sato, Y.; Nakamura,
E. J. Am. Chem. Soc. 2007, 129, 11902. (b) Ilies, L.; Tsuji, H.; Sato, Y.;
Nakamura, E. J. Am. Chem. Soc. 2008, 130, 4240.
(15) (a) Lee, S. H.; Yasuda, T.; Tsutsui, T. J. Appl. Phys. 2004, 95, 3825. (b)
Inigo, A. R.; Chiu, H.-C.; Fann, W.; Huang, Y.-S.; Jeng, U.-S.; Lin, T.-L.;
Hsu, C.-H.; Peng, K.-Y.; Chen, S.-A. Phys. ReV. B 2004, 69, 075201. (c)
Choulis, S. A.; Nelson, J.; Kim, Y.; Poplavskyy, D.; Kreouzis, T.; Durrant,
J. R.; Bradley, D. D. C. Appl. Phys. Lett. 2003, 83, 3812.
electron mobilities: 5 × 10-3 and 6 × 10-3 cm2 V-1 s-1
,
respectively, at E ) 2.5 × 105 V/cm. The mobilities of these
compounds are 1-3 orders of magnitude higher than those of
poly(phenylenevinylene) compounds15 and on the same order of
magnitude as those of oligofluorenes.16
Because of their structural rigidity, compounds 6c and 7 are
thermally very stable. The temperature at which these compounds
lose 5% of their mass is as high as 378 °C (evaporation after melt
at 339-341 °C) and 472 °C (decomposition). In contrast, the
nonbridged counterpart, trans,trans-1,4-distyrylbenzene, melts at
(16) Wu, C.-C.; Liu, T.-L.; Hung, W.-Y.; Lin, Y.-T.; Wong, K.-T.; Chen, R.-
T.; Chen, Y.-M.; Chien, Y.-Y. J. Am. Chem. Soc. 2003, 125, 3710.
(17) Renak, M. L.; Bartholomew, G. P.; Wang, S.; Ricatto, P. J.; Lachicotte,
R. J.; Bazan, G. C. J. Am. Chem. Soc. 1999, 121, 7787.
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