Direct functionalization of polycyclic aromatics via radical perfluoroalkylation

Article abstract of DOI:10.1021/ol1007197

Direct functionalization of electron-deficient and electron-rich polycyclic aromatics via copper-mediated radical perfluoroalkylation was achieved in high yields.

Full text of DOI:10.1021/ol1007197

ORGANIC
LETTERS
2010
Vol. 12, No. 10
2374-2377
Direct Functionalization of Polycyclic
Aromatics via Radical Perfluoroalkylation
Yan Li,†,‡ Cheng Li,†,‡ Wan Yue,†,‡ Wei Jiang,†,‡ Ralf Kopecek,§ Jianqiang Qu,*,§
and Zhaohui Wang*,†
Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, China, Graduate School of the Chinese
Academy of Sciences, Beijing 100190, China, and Performance Chemicals Research,
BASF SE, Ludwigshafen 67056, Germany
wangzhaohui@iccas.ac.cn; jianqiang.qu@basf.com
Received March 27, 2010
ABSTRACT
Direct functionalization of electron-deficient and electron-rich polycyclic aromatics via copper-mediated radical perfluoroalkylation was achieved
in high yields.
Due to their remarkable electro-optical properties,1 perylene-
3,4,9,10-tetracarboxylic acid bisimides (PBIs) have received a
great deal of attention as promising organic n-type semiconduc-
tors which have found applications such as light-harvesting
arrays,2 field effect transistors,3 light-emitting diodes,4 and
photovoltaics5 in the past decades. Naphthalene bis(dicarbox-
imide)s (NBIs) were also identified recently as key polymer
building blocks to ensure a strong electron-depleted electronic
structure.6 Chemical modifications both at imide groups and in
bay regions are two different successful synthetic strategies for
rylene bisimide derivatives. However, the dramatic change of
optical and electronic properties can only be achieved by the
bay-functionalization because of nodes in the HOMO and
LUMO orbitals at the imide nitrogen atoms.
One of the key design principles for air-stable n-type
rylene-based semiconductor materials is to incorporate strong
electron-withdrawing groups. Core-cyanated and N-fluoro-
alkylated PBI and NBI derivatives have been reported to
exhibit high n-type mobilities and air stability.7 Core-
fluorinated perylene bisimides have also been synthesized
and achieved promising n-type semiconducting properties.8
Recently we have reported a highly efficient synthetic
methodology toward the bis-perfluoroalkylated perylene
bisimides from regioisomerically pure 1,7-dibromo PBIs.
† Institute of Chemistry, Chinese Academy of Sciences.
‡ Graduate School, Chinese Academy of Sciences.
§ Performance Chemicals Research, BASF SE.
(1) (a) Zollinger, H. Color Chemistry, 3rd ed.; VCH: Weinheim,
Germany, 2003. (b) Wu¨rthner, F. Chem. Commun. 2004, 14, 1564.
(2) Kelley, R. F.; Shin, W. S.; Rybtchinski, B.; Sinks, L. E.; Wasielewski,
M. R. J. Am. Chem. Soc. 2007, 129, 3173.
(6) (a) Katz, H. E.; Lovinger, A. J.; Johnson, J.; Kloc, C.; Siegrist, T.;
Li, W.; Lin, Y.-Y.; Dodabalapour, A. Nature 2000, 404, 478. (b) Guo, X.;
Watson, M. D. Org. Lett. 2008, 10, 5333. (c) Yan, H.; Chen, Z.; Zheng,
Y.; Newman, C.; Quinn, J. R.; Do¨tz, F.; Kastler, M.; Facchetti, A. Nature
2009, 457, 679.
(3) Schmidt, R.; Ling, M. M.; Oh, J. H.; Winkler, M.; Ko¨nemann, M.;
Bao, Z.; Wu¨rthner, F. AdV. Mater. 2007, 19, 3692.
(7) (a) Jones, B. A.; Ahrens, M. J.; Yoon, M.-H.; Facchetti, A.; Marks,
T. J.; Wasielewski, M. R. Angew. Chem., Int. Ed. 2004, 43, 6363. (b) Katz,
H. E.; Johnson, J.; Lovinger, A. J.; Li, W. J. Am. Chem. Soc. 2000, 122,
7787.
(4) Ego, C.; Marsitzky, D.; Becker, S.; Zhang, J.; Grimsdale, A. C.;
Mu¨llen, K.; MacKenzie, J. D.; Silva, C.; Friend, R. H. J. Am. Chem. Soc.
2003, 125, 437.
(5) Schmidt-Mende, L.; Fechtenko¨tter, A.; Mu¨llen, K.; Moons, E.;
Friend, R. H.; MacKenzie, J. D. Science 2001, 293, 1119.
(8) Wu¨rthner, F.; Osswald, P.; Schmidt, R.; Kaiser, T. E.; Mansikkama¨ki,
H.; Ko¨nemann, M. Org. Lett. 2006, 8, 3765.
10.1021/ol1007197  2010 American Chemical Society
Published on Web 04/22/2010

Furthermore, the organic field effect transistors (OFETs)
incorporating this new n-type semiconductor show remark-
able air-stability and good charge carrier mobility.9 While
these approaches are attractive, new methods for the direct
perfluoroalkylation of polycyclic aromatics remain highly
desirable in terms of atom and step economy by avoiding a
“prefunctionalization” process.
Scheme 2. Perfluoroalkylation of NBI
In the past several decades, many efforts have been made
to direct C-H functionalization/C-C bond formation,10
which provides a viable alternative to a traditional cross-
coupling reaction. To date, great elegant progress has been
achieved for electron-rich arenes and heterocycles with a
directing group that can be ortho-functionalized by aryl or
alkyl halides, boronates, and olefins under palladium,11
ruthenium,12 or rhodium13 catalysis. Direct C-H bond
transformation of unreactive arenes is, however, still a
challenge. Very recently, Shinokubo and his co-workers have
reported success with Ru-catalyzed alkylation and arylation
of PBIs;14 meanwhile, we have also reported direct alkylation
of PBIs by palladium-catalyzed C-H functionalization.15
Herein, we present the direct functionalization of electron-
deficient and electron-rich polycyclic aromatics via copper-
mediated radical perfluoroalkylation.
perylene bisimides, which makes it difficult to introduce a single
function group to the bay region. What is interesting is that the
perfluoroalkyl group is regioselectively introduced to the bay
region. Meanwhile, 1,6- and 1,7-perfluoroalkylated PBIs were
also obtained in about 20% yields in a ratio of 1:5.
Initially, a highly electron-deficient perylene bisimide 1 was
chosen as a model substrate for this study. Direct copper-
mediated perfluoroalkylation of 1 with perfluoroalkyl iodides
gives excellent yields of mono-core-perfluoroalkylated PBIs
(Schemes 1, compounds 2 and 4). It should be noted that
Scheme 3
.
Regioselective Perfluoroalkylation of Electron-Rich
Molecules
Scheme 1. Regioselective Perfluoroalkylation of PBI
Under the optimized reaction conditions above, the
substrate scope was also explored. Recently, Watson reported
Stille coupling of regioisomerically pure dibromonaphthalene
bisimides (NBIs) with various stannylated thiophene-based
monobrominated perylene bisimides are relatively not so easily
available compared with dibrominated and tetrabrominated
(12) (a) Kakiuchi, F.; Matsuura, Y.; Kan, S.; Chatani, N. J. Am. Chem.
Soc. 2005, 127, 5936. (b) Kakiuchi, F.; Murai, S. Acc. Chem. Res. 2002,
35, 826. (c) Ackermann, L.; Nova´k, P.; Vicente, R.; Hofmann, N. Angew.
Chem., Int. Ed. 2009, 48, 6045. (d) Kakiuchi, F.; Kan, S.; Igi, K.; Chatani,
N.; Murai, S. J. Am. Chem. Soc. 2003, 125, 1698.
(9) Li, Y.; Tan, L.; Wang, Z.; Qian, H.; Shi, Y.; Hu, W. Org. Lett. 2008,
10, 529.
(10) (a) Shilov, A. E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879. (b)
Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. ReV. 2002, 102., 1731. (c) Alberico,
D.; Scott, M. E.; Lautens, M. Chem. ReV. 2007, 107, 174. (d) Hassan, J.;
Se´vignon, M.; Gozzi, C.; Schuluz, E.; Lemaire, M. Chem. ReV. 2002, 102,
1359.
(13) Oi, S.; Watanabe, S.; Fukita, S.; Inoue, Y. Tetrahedron Lett. 2003,
44, 8665.
(14) (a) Nakazono, S.; Imazaki, Y.; Yoo, H.; Yang, J.; Sasamori, T.;
Tokitoh, N.; Ce´dric, T.; Kageyama, H.; Kim, D.; Shinokubo, H.; Osuka,
A. Chem.sEur. J. 2009, 15, 7530. (b) Nakazono, S.; Easwaramoorthi, S.;
Kim, D.; Shinokubo, H.; Osuka, A. Org. Lett. 2009, 11, 5426.
(15) Yue, W.; Li, Y.; Jiang, W.; Zhen, Y.; Wang, Z. Org. Lett. 2009,
11, 5430.
(11) (a) Okazawa, T.; Satoh, T.; Miura, M.; Nomura, M. J. Am. Chem.
Soc. 2002, 124, 5286. (b) Stuart, D. R.; Fagnou, K. Science 2007, 316, 1172.
(c) Zaitsev, V. G.; Daugulis, O. J. Am. Chem. Soc. 2005, 127, 4156. (d) Cai,
G.; Fu, Y.; Li, Y.; Wan, X.; Shi, Z. J. Am. Chem. Soc. 2007, 129, 7666.
Org. Lett., Vol. 12, No. 10, 2010
2375

monomers that yields high molecular weight donor-acceptor
conjugated polymers.6b Yan demonstrated a highly soluble
and printable n-channel NBI-thiophene copolymer exhibit-
ing unprecedented OTFT characteristics (electron mobilities
up to 0.45-0.85 cm2 V-1 s-1) under ambient conditions in
combination with Au contacts and various polymeric
dielectrics.6c Direct copper-mediated perfluoroalkylation of
naphthalene bis(dicarboximide)s with perfluoroalkyl iodides
gave excellent yields of mono- perfluoroalkylated NBIs.
Different perfluoroalkyl iodides (iodononafluorobutane, 1-io-
doperfluorohexane, and 1-iodoperfluorooctane) were chosen
to react with NBI and the isolated yield was from 60% to
70%. However, it should be mentioned that there is no
desired product detected, when bromo NBIs react with
perfluoroalkyl iodides under the same conditions.
A great variety of perfluoroalkylated polycyclic aromatics,
such as naphthalene, pyrene, and perylene, could be prepared
via this method with high yields. What should be noticed
here is that perfluoroalkyl chain was regioselectively intro-
duced to the 1 position of naphthalene and pyrene, and the
3 position of perylene.
To assess the effect of the perfluoroalkyl groups on the
molecular order in the solid state, attempts were devoted to
single-crystal growth. Ultimately, crystals suitable for single-
crystal X-ray analysis were obtained by slow evaporation
of an ethanol solution of 3b and a dichloromethane solution
of 13, respectively. The molecular structures of 3b and 13
are depicted in Figure 1.
and arranged in a sandwich herringbone packing including
dimeric species probably due to the notable dipole-dipole
interaction, and not the stacks along the R-axis of the unit
cell for 1,7-perfluoroalkyl-substituted PBIs.9 The subtle
changes in molecular structures lead to dramatically different
packing arrangements in the solid state and were also
expected to have a strong influence on the charge transporting
properties.
The summarized electro-optical data of perfluoroalkylated
polycyclic aromatics are shown in Table 1, and the UV-vis
Table 1. Electro-optical Properties of Perfluoroalkylated
Polycyclic Aromatics
a
a
λabs (nm)
ε (M-1 cm-1
)
λem (nm)
E1
E2
2
521
510
512
521
510
512
380
384
384
384
376
380
58 219
55 329
45 986
53 757
57 220
56 351
31 475
25 298
23 833
22 375
32 478
23 191
538
526
536
537
526
539
360
360
359
360
361
361
358
377
460
-0.82
-0.67
-0.68
-0.82
-0.67
-0.68
-1.05
-0.89
-0.87
-0.86
-0.88
-0.68
-1.11
-0.99
-1.03
-1.09
-0.99
-1.04
-1.53
-1.46
-1.47
-1.49
-1.37
-1.22
3a
3b
4
5a
5b
6a
7a
8
9
6b
7b
11
13
15
346
446
37 489
28 410
a Half-wave potentials (in V vs Fc/Fc+) measured in a 0.1 M solution
of Bu4NPF6 in dichloromethane with a scan rate of 50 mV/s.
absorption, fluorescence spectra, and cyclic voltammograms
were given in the Supporting Information.
The absorption spectra of 2-5 show well-defined vibronic
fine structures of the S0-S1 transitions with maxima at 521
nm for 2 and 4, 510 nm for 3a and 5a, and 512 nm for 3b
and 5b, hypsochromically shifted by 5, 16, and 14 nm,
respectively, in comparison with parent PBI derivatives,
probably due to the electron-withdrawing effect of perfluo-
roalkyl substituents.
The absorption maxima of 1,6-perfluoroalkylated PBIs (3b
and 5b) bathochromically shifted only 2 nm in comparison
with that of 1,7-perfluoroalkylated PBIs (3a and 5a);
however, 1,7-perfluoroalkylated PBIs show a higher absorp-
tion coefficient than 1,6-perfluoroalkylated PBIs. Mono- and
bis-perfluoroalkylated PBIs presented here possess Stokes
shifts between 16 and 27 nm, and exhibit very high
fluorescence quantum yields (0.86-0.92). The absorption
spectra maxima of perfluoroalkylated NBI (7a and 7b)
bathochromically shifted by 4 nm in comparison with 6a
and 6b, and the absorption maxima spectra of 13 and 15
bathochromically shifted by 8 nm in comparison with 12
and 14.
Figure 1. Molecular structure of 3b (a) and 13 (b). Crystal packing
of 3b (c) and 13 (d).
Four molecules of 3b and 13 were found in the unit cell.
As shown in Figure 1a, owing to the steric encumbrance
effect of perfluoroalkyl substituents, the perylene cores are
highly twisted as expected. The twisting of the central six-
membered ring was unsymmetrical with dihedral angles of
28.5° and 29.9°. The crystals of 3b and 13 have been found
Cyclic voltammograms of perfluoroalkylated PBIs and
NBIs in CH2Cl2 show two reversible reduction waves. The
half-wave reduction potentials vs Fc/Fc+ are -0.82 and
2376
Org. Lett., Vol. 12, No. 10, 2010

-1.11 V for 2, -0.67 and -0.99 V for 3a, -0.68 and -1.03
V for 3b, -0.89 and -1.46 V for 7a, and -0.68 and -1.22
V for 7b respectively (Table 1). Both first and second
reduction waves appeared at higher potentials with com-
parison to parent PBIs and NBIs, indicating that core-
perfluoroalkylation induces strong electron-accepting ability.
Due to the additional electron affinity of fluoroalkyl chains
at the N-substituents, the reduction potentials of 7b are less
negative than those of 7a. The absorption, emission spectra,
and cyclic voltammograms are not significantly influenced
by the number of fluorine substituents when the fluorinated
alkyl chain contains more carbon atoms.
Perfluoroalkyl iodides have been widely utilized as sources
of perfluoroalkyl radicals. The free-radical chain addition to
alkenes and the homolytic aromatic substitution by ther-
molysis are well-known processes.16 To gain some under-
standing of the investigated perfluoroalkylation reaction of
polycyclic aromatics, radical scavenger, TEMPO, was added
to the reaction mixture in the same equivalent as perfluo-
roalkyl iodides. The reaction was completely inhibited and
just returns the reactant, which supports the radical perfluo-
roalkylation mechanism.
In conclusion, a copper-mediated regioselective perfluo-
roalkylation process of highly electron-deficient rylene dyes
and electron-rich polycyclic aromatics has been achieved.
The generality and unique properties of perfluoro-alkylated
polycyclic aromatics may expand the scope of this reaction
to more academic and industrial applications.
Acknowledgment. We thank Prof. Zhangjie Shi (Peking
University) for valuble suggestions. We thank the National
Natural Science Foundation of China, 973 Program, Chinese
Academy of Sciences, and BASF SE for financial support
of this research.
Supporting Information Available: Experimental pro-
cedure and characterization of new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
(16) (a) Tiers, G. V. D. J. Am. Chem. Soc. 1960, 82, 5513. (b) Cowell,
A. B.; Tamborski, C. J. Fluorine Chem. 1981, 17, 345. (c) Bravo, A.;
Bjørsvik, H. R.; Fontana, F.; Liguori, L.; Mele, A.; Minisci, F. J. Org.
Chem. 1997, 62, 7128.
OL1007197
Org. Lett., Vol. 12, No. 10, 2010
2377