Concise synthesis of halogenated chrysenes ([4]phenacenes) that favor π-stack packing in single crystals

Article abstract of DOI:10.1021/ol901693y

A concise synthesis of halogenated chrysene derivatives from 2,2,2-trifluoroethyl tosylate and halostyrene was established. Friedel-Crafts type cyclization of a 1,1 -difluoro-1 -alkene bearing halogenated phenyl moieties involved skeletal rearrangement an

Full text of DOI:10.1021/ol901693y

ORGANIC
LETTERS
2009
Vol. 11, No. 17
4026-4028
Concise Synthesis of Halogenated
Chrysenes ([4]Phenacenes) that Favor
π-Stack Packing in Single Crystals
Hiroyuki Isobe,*,† Shunpei Hitosugi,† Taisuke Matsuno,† Takeaki Iwamoto,† and
Junji Ichikawa‡
Department of Chemistry, Tohoku UniVersity, Aoba-ku, Sendai 980-8578, Japan, and
Department of Chemistry, Graduate School of Pure and Applied Sciences, UniVersity
of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
isobe@m.tains.tohoku.ac.jp
Received July 24, 2009
ABSTRACT
A concise synthesis of halogenated chrysene derivatives from 2,2,2-trifluoroethyl tosylate and halostyrene was established. Friedel-Crafts
type cyclization of a 1,1-difluoro-1-alkene bearing halogenated phenyl moieties involved skeletal rearrangement and dehydrogenation to afford
the title compound in good to moderate yield. X-ray analysis revealed that the halogen substituents induce π-stack packing of the molecules
in the crystals.
Polycyclic aromatic hydrocarbons (PAHs) are attracting
renewed interest as base molecules for electronic devices
such as field-effect transistors (FETs) or light-emitting diodes
(LEDs). Acenes, PAHs with fused benzene rings in a
rectilinear arrangement, have long been notable molecules
of particular interest, especially those with more than four
rings, and the derivatives of acenes with improved properties
such as thermal stability or packing structures have contrib-
uted significantly to the development of the field of organic
devices.1 Phenacenes, PAHs with fused benzene rings in a
zigzag arrangement, have recently emerged as new candidate
molecules with ideal properties, such as stability in FETs or
blue light emission in LEDs.2,3 However, synthetic access
to the phenacene derivatives is scarce,4,5 which hampers
further exploration of the potential applications of the
phenacenes. Here we report on a concise two-step method
for the synthesis of chrysene ([4]phenacene) derivatives.
Detailed analysis of the crystal structures revealed unique
packing features of the π-stack assembly in single crystals.
The method for the synthesis of chrysene derivatives was
found unexpectedly during an investigation into the synthesis
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Yamaji, M. J. Am. Chem. Soc. 2008, 130, 10470–10471
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† Tohoku University.
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C. W.; Yang, C.; Ellenstein, A. J. Am. Chem. Soc. 1997, 119, 2119–2124.
Hwang, K.-J.; O’Neil, J. P; Katzenellenbogen, J. A. J. Org. Chem. 1992,
‡ University of Tsukuba.
(1) Anthony, J. E. Chem. ReV. 2006, 106, 5028–5048. Coropceanu, V.;
Cornil, J.; Filho, S. D. A.; Olivier, Y.; Silbey, R.; Bre´das, J.-L. Chem. ReV.
2007, 107, 926–952. Anthony, J. Angew. Chem., Int. Ed. 2008, 47, 452–
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10.1021/ol901693y CCC: $40.75
Published on Web 08/10/2009
 2009 American Chemical Society

of halogenated [4]helicene derivatives using a method
developed by one of the authors.6 Thus, we prepared the
starting material, difluoroalkene 1a bearing a 4-bromophenyl
group, by a slightly modified method in 66% yield from
commercially available CF3CH2OTs (Scheme 1),7 and 1a was
after the addition of magic acid within a few minutes,8
which is followed by the formation of chrysene derivative
3a as the result of the skeletal rearrangement and
dehydrogenation. Since a similar rearrangement of non-
halogenated tetrahydro[4]helicene 2 is promoted by poly-
phosphoric acid,5 we suppose that the present reaction is
also initiated by the protonation of 2 with magic acid.
However, the nonhalogenated tetrahydro[4]helicene itself
did not afford 3 under the present reaction conditions, and
hence we assume that the rearrangement and subsequent
dehydrogenation may also involve the reaction/interaction
of aromatic moieties with magic acid.9,10 Details of the
reaction may be of theoretical interest and will be investigated
in a further mechanistic study.
Scheme 1. Synthesis of Halogenated Chrysene Derivatives
The halogen substituents provide an access to further
derivatization of chrysene, and we preliminarily examined
two basic transformations (Scheme 2). Thus, lithium-halogen
Scheme 2. Derivatization of Halogenated Chrysenes
subjected to the acid-promoted reaction conditions previously
optimized for nonhalogenated [4]helicene derivatives. To-
gether with the expected tetrahydro[4]helicene derivative 2,
an aromatic compound was obtained as a white precipitate.
Structural analysis of this aromatic compound by NMR
spectroscopy and X-ray diffraction of the single crystal (Vide
infra) unequivocally showed that the compound was the
unexpected product 3,9-dibromo-6,12-dimethylchrysene 3a.
We then optimized the reaction conditions simply by
extending the reaction time to six hours, and obtained 3a in
72% yield (Scheme 1). A similar reaction involving the
skeletal rearrangement and dehydrogenation took place with
other difluoroalkenes 1 with different halogen substituents
or regiochemistry, and we obtained a series of halogenated
chrysene derivatives 3b-3f in 14-70% yields (Scheme 1).
The reaction of 1 bearing nonhalogenated phenyl moieties
or 2-bromophenyl moieties did not afford the corresponding
chrysene derivatives.
exchange reaction and protonation afforded 6,12-dimethyl-
chrysene 4 in 74% yield, and Suzuki-Miyaura coupling
reaction with arylboronate gave 3,9-di(tert-butylphenyl)-6,12-
chrysene 5 in 83% yield.
We obtained single crystals of all the halogenated chrysene
derivatives 3 as well as the nonhalogenated congener 4 and
found that the halogen substituents induce π-stack packing
of the molecules in the crystals. Defining the x and y vectors
along the short and long axes of the molecule, we measured
the packing parameters of nearest-neighbor cofacial mol-
ecules in the crystal structures in order to determine the
(9) Olah, G. A.; Schilling, P.; Gross, I. M. J. Am. Chem. Soc. 1974, 96,
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4090
.
When we analyzed the reaction of 1a, tetrahydro[4]-
helicene 2 was detected as the immediate intermediate
(11) Curtis, M. D.; Cao, J.; Kampf, J. W. J. Am. Chem. Soc. 2004, 126,
4318–4328.
(12) Burns, D. M.; Iball, J. Proc. R. Soc. London, Ser. A. 1960, 257,
491–514.
(6) Ichikawa, J.; Yokota, M.; Kudo, T.; Umezaki, S. Angew. Chem.,
Int. Ed. 2008, 47, 4870–4873.
(13) Moon, H.; Zeis, R.; Borkent, E. -J.; Besnard, C.; Lovinger, A. J.;
Siegrist, T.; Kloc, C.; Bao, Z. J. Am. Chem. Soc. 2004, 126, 15322–15323.
(14) Robertson, J. M. In Crystal Engineering; Desiraju, G. R., Ed.;
Elsevier: New York, 1989; Chapter 6.
(7) The synthesis with halogenated series using the reported method
afforded the desired product 1a in 4% yield. The order of the addition of
bromine and methoxide as well as the reaction temperature for the first
migration step after the addition of vinyllithium has been modified. See
Supporting Information for the details.
(15) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112,
5525–5534.
(8) When we terminated the reaction within a shorter period,
tetrahydro[4]helicene 2 was obtained as a major product in 57% yield,
and the subsequent dehydrogenation with Ph3C•BF4 afforded dibromo[4]-
helicene derivatives.
(16) Jaeger, H. M.; Swenson, D. W. H.; Dykstra, C. E. J. Phys. Chem.
A 2006, 110, 6399–6407.
(17) Hunter, C. A.; Lawson, K. R.; Perkins, J.; Urch, C. J. J. Chem.
Soc., Perkin Trans. 2001, 2, 651–669.
Org. Lett., Vol. 11, No. 17, 2009
4027

Table 1. Packing Parameters of Nearest-Neighbor Cofacial
Molecules in Single Crystals of Chrysene Derivatives
packing structure d (Å) R (deg) P (deg) dp (Å) dr (Å)
3a
3b
3c
3d
3e
4
π-stack
π-stack
π-stack
π-stack
π-stack
herringbone
3.42
3.40
3.36
3.39
3.41
7.39
2.3
2.1
1.0
0.3
37.7
13.2
58.3
39.1
59.1
59.2
32.6
17.4
5.54
2.76
5.61
5.69
2.18
1.73
0.14
0.13
0.06
0.02
2.64
2.31
induces the “rolled” π-stack of 3e (motif C; Figure 2, Table
1). The halogenated chrysene molecules in this study have
quadrupolar charge fields on the π-systems due to the
halogen substituents at the symmetric positions, and such
characteristics may have allowed the structural variations in
the π-stack motifs.16,17 It is also interesting to note that both
the pitched or rolled slides resulted in the shift of the
molecules along the nodal plane of HOMO wave functions
and maintain the intermolecular in-phase overlap of the
orbitals (Figures 1b and c).18-20
In summary, we have developed a concise method for the
synthesis of halogenated chrysene derivatives. The synthesis,
which can be easily upscaled and tolerate the structural
variations especially at 6,12-positions, may facilitate further
investigation of the molecules in organic electronics. Cofacial
π-stacking of phenacene molecules in single crystals has
rarely been observed, and the first π-stack motifs of
halogenated series may be useful for designs of device
molecules.1,2,11,13 The fine-tuning of electronic and packing
structures of π-systems with halogenated phenacenes and
derivatives may be of great interest in future studies.
Figure 1. Structural features of chrysene derivatives in single
crystals. (a) Definition of the packing parameters (angles and
distances) listed in Table 1. (b) Three π-stack motifs observed with
halogenated chrysenes in single crystals. A for X ) F, Cl, Br; B
for X ) I; C for X ) Br. Bond orders are not shown for clarity.
See Supporting Information for the details of crystal structures. Red
dotted lines show the nodal plane of HOMO wave functions
generated by the halogen substituents. (c) A HOMO wave function
of chrysene π-systems with blue dotted lines showing the nodal
plane.
Acknowledgment. We thank Dr. W. Nakanishi (Tohoku
University) for helpful discussion, JEOL for generous time
of DART MS measurment, Central Glass Co. for the gift of
HFIP and Nacalai Tesque for a sample column. This work
was partly supported by KAKENHI (20108015/21685005)
and by Nagase Foundation. S.H. thanks Global COE program
(Molecular Complex Chemistry) for predoctoral fellowship.
angular and lateral deviations from the perfect cofacial
π-stack (Figure 1a, Table 1).11 The structure of the nonha-
logenated chrysene derivative 4 was a herringbone packing,
similar to that of the parent chrysene,12 and showed that two
cofacial molecules were far separated by a distance of 7.4
Å (Table 1). On the other hand, all the halogenated chrysene
derivatives 3 showed π-stack structures with distances in the
range of a typical π-π contact distance (∼3.4 Å). The results
show that the halogen substituents induce the cofacial contact
of chrysene molecules, which is similar to what is observed
with haloarenes such as halogenated tetracenes in FET
devices.13-15
Supporting Information Available: Experimental pro-
cedures, spectral data and crystallographic data (CIF) of
3a-e, 4 and dibromo[4]helicene derivative. This material
is available free of charge via the Internet at http://pubs.acs.org.
Among the π-stack structures we observed three different
motifs that differed in the angular and lateral deviation from
the perfect cofacial stack (Figure 1b). Thus, halogen sub-
stituents on the roll-side (3,9-position) of the molecule induce
the “pitched” π-stack (motif A for F, Cl, Br and motif B for
I), and the bromine substituent on the pitch-side (2,8-position)
OL901693Y
(18) Bre´das, J. L.; Calbert, J. P.; da Silva Filho, D. A.; Cornil, J. Proc.
Natl. Acad. Sci. U.S.A. 2002, 99, 5804–5809
(19) Kazmaier, P. M.; Hoffmann, R. J. Am. Chem. Soc. 1994, 116, 9684–
.
9691
.
(20) Wiberg, K. B. J. Org. Chem. 1997, 62, 5720–5727
.
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