9,10-Disubstituted octafluoroanthracene derivatives via palladium-catalyzed cross-coupling

Article abstract of DOI:10.1021/jo8017268

(Chemical Equation Presented) 9,10-Dichlorooctafluoroanthracene (1) reacts with aryl boronic acids and terminal alkynes under palladium-catalyzed cross-coupling conditions to afford 9,10-diaryloctafluoroanthracenes (2a-e) and 9,10-dialkynyloctafluoroanthracenes (6a,b), respectively. Optical spectroscopy and cyclic voltammetry indicate that octafluoro-9,10-di(thiophen-2-yl)anthracene (2d) exhibits donor-acceptor character and a LUMO energy level of -3.27 eV relative to vacuum. A functionalized 5-bromothiophen-2-yl derivative (2e) was obtained in high yield by bromination of 2d with NBS. X-ray crystallographic analysis of octafluoro9,10-bis[(trimethylsilyl)ethynyl]anthracene (6a) reveals a solid-state structure that mimics the packing of columnar liquid crystals, with a .stacking distance of 3.39 A between the octafluoroanthracene cores. In addition, octafluoro-9,10-bis(mesitylethynyl)anthracene (6b) displays a LUMO energy level of -3.50 eV, which approaches the value of -3.65 eV measured for perfluoropentacene, making 9,10-dialkynyloctafiuoroanthracenes a promising new class of n-type organic materials.

Full text of DOI:10.1021/jo8017268

9,10-Disubstituted Octafluoroanthracene Derivatives via
Palladium-Catalyzed Cross-Coupling
John F. Tannaci, Masahiro Noji,‡ Jennifer L. McBee, and T. Don Tilley*
Department of Chemistry, UniVersity of California at Berkeley, Berkeley, California 94720
tdtilley@berkeley.edu
ReceiVed August 4, 2008
9,10-Dichlorooctafluoroanthracene (1) reacts with aryl boronic acids and terminal alkynes under palladium-
catalyzed cross-coupling conditions to afford 9,10-diaryloctafluoroanthracenes (2a-e) and 9,10-
dialkynyloctafluoroanthracenes (6a,b), respectively. Optical spectroscopy and cyclic voltammetry indicate
that octafluoro-9,10-di(thiophen-2-yl)anthracene (2d) exhibits donor-acceptor character and a LUMO
energy level of -3.27 eV relative to vacuum. A functionalized 5-bromothiophen-2-yl derivative (2e)
was obtained in high yield by bromination of 2d with NBS. X-ray crystallographic analysis of octafluoro-
9,10-bis[(trimethylsilyl)ethynyl]anthracene (6a) reveals a solid-state structure that mimics the packing
of columnar liquid crystals, with a π stacking distance of 3.39 Å between the octafluoroanthracene cores.
In addition, octafluoro-9,10-bis(mesitylethynyl)anthracene (6b) displays a LUMO energy level of -3.50
eV, which approaches the value of -3.65 eV measured for perfluoropentacene, making 9,10-
dialkynyloctafluoroanthracenes a promising new class of n-type organic materials.
Introduction
One strategy for affecting n-type behavior is the inclusion of
electron-withdrawing groups, especially fluorine.8 Suzuki et al.
synthesized perfluoropentacene from tetrafluorophthallic anhy-
dride and hydroquinone using Friedel-Crafts chemistry.9
Fluorine substitution stabilizes the LUMO energy level of
perfluoropentacene, leading to effective electron transport in both
n-type FETs and bipolar devices with pentacene. Recently, Bao
et al. measured an electron mobility of 0.72 cm2 V-1 s-1 for
N,N′-bis(heptafluorobutyl)-3,4:9,10-perylene diimide.10 Cyclic
voltammetry indicates a LUMO energy level of -3.85 eV for
the partially fluorinated diimide, with n-type FETs that are stable
in air for more than 50 days, presumably because of dense
packing in the solid state.
Progress in the field of organic electronics has enabled
applications such as light-emitting diodes (LEDs),1 field-effect
transistors (FETs),2 sensors,3 and photovoltaics.4 Because most
organic compounds are inherently p-type (hole-transporting)
semiconductors,5 considerable research has focused on n-type
(electron-transporting) materials for improved devices and
complementary circuits.6,7
‡ Current address: Meiji Pharmaceutical University, 2-522-1, Noshio, Kiyose,
Tokyo 204-8588, Japan.
(1) Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S. A. Chem. Mater.
2004, 16, 4556.
(2) Zaumseil, J.; Sirringhaus, H. Chem. ReV. 2007, 107, 1296.
(3) Thomas, S. W., III; Joly, G. D.; Swager, T. M. Chem. ReV. 2007, 107,
1339.
Crystal engineering to afford extensive π stacking is well-
established for p-type organic semiconductors.11-14 Although
(4) Thompson, B. C.; Fre´chet, J. M. J. Angew. Chem., Int. Ed. 2008, 47, 58.
(5) Strukelj, M.; Papadimitrakopoulos, F.; Miller, T. M.; Rothberg, L. J.
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AdV. Mater. 2007, 19, 4028.
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Lin, Y.-Y.; Dodabalapur, A. Nature 2000, 404, 478.
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1003.
(9) Sakamoto, Y.; Suzuki, T.; Kobayashi, M.; Gao, Y.; Fukai, Y.; Inoue,
Y.; Sato, F.; Tokito, S. J. Am. Chem. Soc. 2004, 126, 8138.
(10) Oh, J. H.; Liu, S.; Bao, Z.; Schmidt, R.; Wu¨rthner, F. Appl. Phys. Lett.
2007, 91, 212107.
(11) Anthony, J. E. Angew. Chem., Int. Ed. 2008, 47, 452.
(12) Anthony, J. E. Chem. ReV. 2006, 106, 5028.
(13) Miao, Q.; Lefenfeld, M.; Nguyen, T.-Q.; Siegrist, T.; Kloc, C.; Nuckolls,
C. AdV. Mater. 2005, 17, 407.
(14) Chen, Z.; Mu¨ller, P.; Swager, T. M. Org. Lett. 2006, 8, 273.
10.1021/jo8017268 CCC: $40.75
Published on Web 09/13/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 7895–7900 7895

Tannaci et al.
pentacene organizes into a herringbone pattern in the solid state,
Anthony achieved a range of π-stacking motifs through alkynyl
substituents.11,12 Controlling the size and location of the alkyne
functional groups gives 2-D “bricklayer” arrangements that
exhibit high hole mobilities. However, there are few examples
of crystal engineering for n-type or ambipolar acenes,15 likely
because of a lack of appropriate building blocks. For instance,
with the exception of nucleophilic aromatic substitution,16,17
synthetic methodology related to perfluoroacenes is limited.
To circumvent this problem, the optimized synthesis and
preliminary C-C coupling chemistry of 9,10-dichlorooctafluo-
roanthracene (1) was reported.18 Suzuki-Miyaura coupling of
1 with phenylboronic acid generated octafluoro-9,10-dipheny-
lanthracene (2a) in 82% yield. Compound 2a has a stabilized
LUMO energy level of -3.04 eV and packs in the desired 2-D
“bricklayer” structure.
This paper describes the reactivity of 1 with a variety of
boronic acids and terminal alkynes under palladium-catalyzed
cross-coupling conditions. To further assess 1 as a potential
synthon for novel n-type organic semiconductors, the coupling
products have been characterized by a number of methods,
including UV-vis/fluorescence spectroscopy, cyclic voltam-
metry, and X-ray crystallography.
nylboronic acid is too electron deficient to transmetalate under
these conditions.19 Fagnou et al. overcame this issue by using
palladium acetate, S-Phos,19 and potassium carbonate to achieve
efficient coupling between fluorinated aromatics and aryl
halides,20 but similar reactions between pentafluorobenzene and
1 exhibited minimal conversion.
Synthesis of Terminal Alkynes. Most of the terminal alkynes
in this study are commercially available, while ethynylmesity-
lene was prepared as reported in the literature.21 Synthesis of
5-ethynyl-5′-hexyl-2,2′-bithiophene (4) was accomplished by
Sonogashira coupling22 of 5-bromo-5′-hexyl-2,2′-bithiophene
(5)23 with ethynyltrimethylsilane, followed by deprotection
under basic conditions (63% overall yield from 5). Compound
4 degrades from a pale yellow powder to a brown solid over
several days under ambient conditions, so it was stored in the
dark under nitrogen and used promptly after purification.
Synthesis of 9,10-Dialkynyloctafluoroanthracenes (6). Ethy-
nylbenzene and 1-ethynyl-4-methoxybenzene were initially
chosen for Sonogashira coupling with 1. Both reactions gener-
ated orange solids, and mass spectrometry indicated the presence
of the desired 9,10-dialkynyloctafluoroanthracenes, but the
limited solubilities of the two products precluded full charac-
terization. Attempts to improve solubility by use of hexyl-
substituted 4 as a coupling partner were unsuccessful and
afforded an intractable dark green powder.
Results and Discussion
Fortunately, bulkier coupling partners gave soluble 9,10-
dialkynyloctafluoroanthracenes in high yields under modified
Sonogashira conditions (eq 2). The trimethylsilyl derivative 6a
is light-sensitive in solution and must be handled appropriately,
and this hinders both the characterization of electronic properties
and deprotection to the terminal dialkyne. However, octafluoro-
9,10-bis(mesitylethynyl)anthracene (6b) was isolated as a stable,
bright red solid in 73% yield.
Synthesis of 9,10-Diaryloctafluoroanthracenes (2). Com-
pound 1 was synthesized from commercially available tetrafluo-
rophthallic acid and coupled with phenylboronic acid under
modified Suzuki-Miyaura conditions19 as previously de-
scribed.18 Similar conditions were applied in coupling reactions
of 1 with a series of aryl boronic acids (Scheme 1). Compared
to 2a, the resulting 9,10-diaryloctafluoroanthracenes contain
electron-donating (2b), electron-withdrawing (2c), and heteroaryl
(2d) groups in order to probe substituent effects on the electronic
properties and solid-state packing of the octafluoroanthracene
core. Bromination of 2d was also explored to provide synthetic
handles for further C-C coupling chemistry (eq 1). Treatment
of 2d with excess NBS in glacial acetic acid at ambient
temperature for 72 h afforded octafluoro-9,10-bis(5-bro-
mothiophen-2-yl)anthracene (2e) in 94% yield.
Electronic Properties. The electronic properties of four new
9,10-disubstituted octafluoroanthracene derivatives were exam-
ined using optical spectroscopy and cyclic voltammetry. Each
derivative was compared to 2a to assess substituent effects on
HOMO and LUMO energy levels, photoluminescence quantum
yield, donor-acceptor character, and potential n-type behavior.
Optical data is compiled in Table 1, and representative
UV-vis/fluorescence spectra of 2c are shown in Figure 1. The
9,10-diaryloctafluoroanthracenes display CdC vibrational cou-
pling,24 while 9,10-dialkynyloctafluoroanthracene 6b has one
broad absorption band centered at 490 nm. Methoxyphenyl
Repeated attempts to prepare the perfluorinated 9,10-diphe-
nylanthracene, via coupling reactions with pentafluorophenyl-
boronic acid, were unsuccessful. It appears that pentafluorophe-
(20) Lafrance, M.; Shore, D.; Fagnou, K. Org. Lett. 2006, 8, 5097.
(21) Ishihara, K.; Kobayashi, J.; Nakano, K.; Ishibashi, H.; Yamamoto, H.
Chirality 2003, 15, 135.
(22) Marsden, J. A.; Haley, M. M. In Metal-Catalyzed Cross-Coupling
Reactions; de Meijere, A., Diederich, F., Eds.; Wiley-VCH: Weinheim, 2004;
Vol. 1, pp 317-394.
(23) Nicolas, Y.; Blanchard, P.; Levillain, E.; Allain, M.; Mercier, N.; Roncali,
J. Org. Lett. 2004, 6, 273.
(15) Tang, M. L.; Reichardt, A. D.; Miyaki, N.; Stoltenberg, R. M.; Bao, Z.
J. Am. Chem. Soc. 2008, 130, 6064.
(16) Geramita, K.; McBee, J.; Shen, Y.; Radu, N.; Tilley, T. D. Chem. Mater.
2006, 18, 3261.
(17) Nitschke, J.; Tilley, T. D. J. Am. Chem. Soc. 2001, 123, 10183.
(18) Tannaci, J. F.; Noji, M.; McBee, J.; Tilley, T. D. J. Org. Chem. 2007,
72, 5567.
(19) Barder, T. E.; Walker, S. D.; Martinelli, J. R.; Buchwald, S. L. J. Am.
Chem. Soc. 2005, 127, 4685.
(24) Berlman, I. B. Handbook of Fluorescence Spectra of Aromatic Mol-
ecules; Academic Press, Inc.: New York, 1965.
7896 J. Org. Chem. Vol. 73, No. 20, 2008

9,10-Disubstituted Octafluoroanthracene DeriVatiVes
SCHEME 1. Synthesis of 9,10-Diaryloctafluoroanthracenes
TABLE 1. Optical Data for 9,10-Disubstituted
Octafluoroanthracene Derivatives
FIGURE 1. Absorbance (dashed line) and emission (solid line) spectra
of 2c in THF.
abs
em
em
λmax
λmax
λmax
(nm) in
cyclohexane (eV)a Φfb
op
(nm) in (nm) in
THF
Eg
TABLE 2. Electrochemical Data for 9,10-Disubstituted
Octafluoroanthracene Derivativesa
substituents
phenyl (2a)c
p-C6H5OMe (2b)
p-C6H5CF3 (2c)
thiophen-2-yl (2d)
mesitylethynyl (6b)
THF
377
379
377
388
490
441
458
439
d
438
442
439
d
3.00
2.94
2.99
2.89
2.28
0.12
0.04
0.41
0.00
e
substituents
phenyl (2a)c
p-C6H5OMe (2b)
p-C6H5CF3 (2c)
HOMOb (eV)
LUMOb (eV)
Egel (eV)
-5.93
-5.82
-6.02d
-5.88
-5.70
-3.04
-3.02
-3.14e
-3.27
-3.50e
2.89
2.80
2.88
2.61
2.20
560
e
thiophene-2-yl (2d)
mesitylethynyl (6b)f
a Eg
calculated from the onset of absorbance in THF.
op
b Photoluminescence quantum yield determined in cyclohexane by
comparison with 9,10-diphenylanthracene. c See reference 18.
d Negligible fluorescence was observed in THF, cyclohexane, and
chlorobenzene. e Not measured.
a In acetonitrile, (Bu)4NPF6 electrolyte, Ag/AgNO3 reference, 200
mV/s scan rate. b HOMO and LUMO energy levels (relative to vacuum)
calculated from the onset of oxidation and reduction, respectively. c See
ref 18. d Scan rate of 500 mV/s. e Scan rate of 50 mV/s. f In
dichloromethane.
derivative 2b and thiophenyl derivative 2d, with electron-
donating substituents, exhibit smaller optical HOMO-LUMO
energy gaps (Egop) of 2.94 and 2.89 eV, respectively. A
substantially lower Egop of 2.28 eV is observed for 6b because
of extended conjugation.
Fluorescence spectroscopy of the 9,10-diaryloctafluoroan-
thracenes is consistent with donor-acceptor character in the
excited state. Solvatochromism was measured by comparing
fluorescence spectra in cyclohexane and THF (Table 1).
Trifluorotolyl derivative 2c has the same fluorescence maximum
em
(λmaxem) in both solvents, while the λmax of 2b undergoes a
bathochromic shift of 18 nm in THF, suggesting a polarized
excited state. Surprisingly, solvatochromism of 2d, with the most
electron-donating substituents, could not be measured because
of negligible fluorescence. To ensure that aggregation was not
quenching the emission, a fluorescence spectrum of 2d was
collected in chlorobenzene, and again no photoluminescence
was detected. Increased donor-acceptor character is known to
reduce photoluminescence quantum yields (Φf),25 and this trend
is reflected in the 9,10-diaryloctafluoranthracenes. Compound
2c has a moderate Φf of 0.41, which decreases by an order of
magnitude to 0.04 for 2b, and no photoluminescence was
observed for 2d.
FIGURE 2. Cyclic voltammogram of 6b.
oxyphenyl substituents destabilize the HOMO energy level
without affecting the LUMO energy level, creating a small
decrease of 0.08 eV in Egel, but thiophenyl groups do not
continue this trend. Compound 2d has a slightly higher HOMO
energy level, while the LUMO energy level is stabilized by 0.23
eV. Probably because of sterics, the thiophenyl subtituents seem
to have better π overlap with the octafluoroanthracene core,
Cyclic voltammetry corroborated the Egop values and revealed
substituent effects on the HOMO and LUMO energy levels.
Electrochemical data is collected in Table 2, and a representative
cyclic voltammogram of 6b is shown in Figure 2. Compared to
2a, trifluorotolyl groups, which are electron-withdrawing,
stabilize both the HOMO and LUMO energy levels to the same
extent (∼0.1 eV), leading to minimal change in the electro-
el
thereby decreasing Eg to 2.61 eV.
The electrochemistry of 9,10-dialkynyloctafluoroanthracene
6b is particularly interesting. Extended conjugation causes a
significant decrease in Egel (down to 2.20 eV), and the HOMO
energy level is moderately higher at -5.70 eV relative to
vacuum. More importantly, compared to 2a, the LUMO energy
level is stabilized by 0.46 eV, and a second, irreversible
reduction occurs at an onset potential of -1.58 V (Ag/AgNO3
reference). The LUMO energy level of 6b (-3.50 eV) is similar
el
chemical HOMO-LUMO energy gap (Eg ). In contrast, meth-
(25) Zhu, Y.; Gibbons, K. M.; Kulkarni, A. P.; Jenekhe, S. A. Macromol-
ecules 2007, 40, 804.
J. Org. Chem. Vol. 73, No. 20, 2008 7897

Tannaci et al.
FIGURE 3. Space-filling view of the 2-D “bricklayer” structure in
crystals of 2a; phenyl groups removed for clarity (see ref 18).
to the value of -3.65 eV measured for perfluoropentacene,9
making 9,10-dialkynyloctafluoroanthracenes promising candi-
dates for n-type organic materials.
Solid-State Structure. Substituent effects on the packing of
the octafluoroanthracene core were examined through X-ray
crystallographic studies of 2b, 2d, and 6a. Previously reported
phenyl derivative 2a exhibits the 2-D “bricklayer” structure
associated with efficient charge transport (Figure 3).11,12,18
Because of greater electron-density on the central anthracene
ring, one might expect tighter π stacking for 2b and 2d, as has
been observed in pentacene systems with enhanced donor-
acceptor interactions between fluorinated and nonfluorinated
rings.26 However, the increased steric bulk of the methoxy
groups in 2b appears to disrupt the desired “bricklayer” structure,
leading to herringbone packing with a tilt angle of 42° (Figure
4). Neighboring parallel molecules have a short interplanar
distance of 3.1 Å, but significant translation (4.3 Å) along the
short axis of the octafluoroanthracene core prevents π stacking.
As a heteroaryl analogue of 2a, a 2-D “bricklayer” structure
was anticipated for 2d. Instead, thiophenyl derivative 2d displays
extended 1-D π stacking with an interplanar distance of 3.46 Å
as shown in Figure 5. Slippage occurs in each π stack, with
translational values of 5.3 and 0.6 Å down the long axis and
short axis, respectively, of the octafluoroanthracene core.
Adjacent π stacks are arranged in a herringbone pattern with a
75° tilt angle.
FIGURE 4. Two views of the crystal structure of 2b; methoxyphenyl
groups removed for clarity.
The alkynyl groups of 6a seem to promote columnar π
stacking of the molecules in the solid state. As shown in Figure
6, compound 6a π stacks with a 1° tilt between octafluoroan-
thracene planes and a distance of 3.39 Å between the aromatic
cores. When viewed down the a-axis (Figure 7), the rectangular
face-centered cross-section resembles columnar liquid crystals
(Colr).27,28 Each column has an alternating AB structure, with
molecule B rotated about the a-axis by 52° relative to molecule
A. Extended π stacks are insulated from neighboring columns
by the alkynyl substituents, and solvent molecules (dichlo-
romethane, ∼0.4 equiv) partially fill the remaining void space
between columns. Nonfluorinated and partially fluorinated acene
analogues, including those with similar size ratios between the
alkyne functional group and the aromatic core,29 do not exhibit
this π-stacking motif, indicating that the electron-deficient
octafluoroanthracene framework is important for columnar
packing.30
FIGURE 5. Space-filling view of the crystal structure of 2d; thiophenyl
groups removed for clarity.
Conclusion
9,10-Diaryloctafluoroanthracenes and 9,10-dialkynyloctafluo-
roanthracenes were synthesized from 1 using palladium-
catalyzed cross-coupling, and initial structure-property rela-
tionships were probed. Recent literature has highlighted the
advantages of donor-acceptor architectures for organic elec-
tronic applications, including small band gaps, broad absorption
bands, balanced charge injection, and ambipolar transport.25,31
Based on optical spectroscopy, compounds 1 and 2e should
(26) Swartz, C. R.; Parkin, S. R.; Bullock, J. E.; Anthony, J. E.; Mayer,
A. C.; Malliaras, G. G. Org. Lett. 2005, 7, 3163.
(27) Laschat, S.; Baro, A.; Steinke, N.; Giesselmann, F.; Ha¨gele, C.; Scalia,
G.; Judele, R.; Kapatsina, E.; Sauer, S.; Schreivogel, A.; Tosoni, M. Angew.
Chem., Int. Ed. 2007, 46, 4832.
(28) Sergeyev, S.; Pisula, W.; Geerts, Y. H. Chem. Soc. ReV. 2007, 36, 1902.
(29) Anthony, J. E.; Eaton, D. L.; Parkin, S. R. Org. Lett. 2002, 4, 15.
(30) Foster, E. J.; Jones, R. B.; Lavigueur, C.; Williams, V. E. J. Am. Chem.
Soc. 2006, 128, 8569.
(31) Hancock, J. M.; Gifford, A. P.; Champion, R. D.; Jenekhe, S. A.
Macromolecules 2008, 41, 3588.
7898 J. Org. Chem. Vol. 73, No. 20, 2008

9,10-Disubstituted Octafluoroanthracene DeriVatiVes
and water (1 mL) was transferred via cannula onto the solids, and
the resulting solution was stirred under reflux at 95 °C for 13 h.
The crude product was extracted with chloroform and washed with
aq NaHCO3. The organic layer was passed through a plug of silica
gel (hexanes eluant) and then concentrated under vacuum to give
a pale yellow solid. Slow cooling of a toluene solution gave 0.32 g
(78%) of yellow crystals. Mp (DSC): 326 °C. 1H NMR: δ 7.29 (d,
J ) 9 Hz, 4 H), 7.01 (d, J ) 9 Hz, 4 H), 3.93 (s, 6 H). 19F NMR:
δ -135.4 (d, J ) 13 Hz, 4 F), -156.4 (d, J ) 13 Hz, 4 F). GC-MS
(EI) m/z: 534 (M+). Anal. Calcd for C28H14F8O2: C, 62.93; H, 2.64.
Found: C, 62.93; H, 2.53.
1,2,3,4,5,6,7,8-Octafluoro-9,10-bis[4-(trifluoromethyl)phenyl]an-
thracene (2c). The procedure for 2b was repeated with 4-(trifluo-
romethyl)phenylboronic acid (0.38 g, 2.00 mmol) and a reaction
time of 12 h. Slow cooling of an ethanol solution gave 0.37 g (79%)
FIGURE 6. Space-filling view of the crystal structure of 6a; alkynyl
substituents and solvent molecules removed for clarity.
1
of yellow crystals. Mp (DSC): 299-300 °C. H NMR: δ 7.76 (d,
J ) 8 Hz, 4 H), 7.53 (d, J ) 8 Hz, 4 H). 19F NMR: δ -63.7 (s, 6
F), -134.2 (d, J ) 13 Hz, 4 F), -154.5 (d, J ) 13 Hz, 4 F).
GC-MS (EI) m/z: 610 (M+). Anal. Calcd for C28H8F14: C, 55.10;
H, 1.32. Found: C, 54.90; H, 1.38.
1,2,3,4,5,6,7,8-Octafluoro-9,10-di(thiophen-2-yl)anthracene
(2d). The procedure for 2b was repeated with 2-thiophenylboronic
acid (0.25 g, 2.00 mmol) and a reaction time of 18 h. Slow cooling
of a hexanes solution gave 0.28 g (75%) of yellow crystals. Single
crystals for X-ray diffraction were obtained by slow evaporation
1
of a chloroform-d/dichloromethane/pentane solution. H NMR: δ
7.57 (dd, J ) 5 and 1 Hz, 2 H), 7.18 (dd, J ) 5 and 4 Hz, 2 H),
7.12 (dd, J ) 4 and 1 Hz, 2 H). 19F NMR: δ -137.3 (d, J ) 12
Hz, 4 F), -154.7 (d, J ) 12 Hz, 4 F). GC-MS (EI) m/z: 486 (M+).
Anal. Calcd for C22H6F8S2: C, 54.32; H, 1.24; S, 13.18. Found: C,
54.49; H, 1.20; S, 12.99.
1,2,3,4,5,6,7,8-Octafluoro-9,10-bis(5-bromothiophen-2-yl)an-
thracene (2e). Compound 2d (0.04 g, 0.08 mmol) and NBS (0.07
g, 0.39 mmol) were stirred in glacial acetic acid (10 mL) under
ambient conditions for 48 h. A second portion of NBS (0.07 g,
0.39 mmol) was added, and the reaction was stirred for an additional
24 h. The resulting yellow solution was quenched with water (100
mL) and ether (15 mL). The organic layer was washed with water
and then passed through a plug of silica gel (hexanes eluant).
Concentration under vacuum gave 0.05 g (94%) of a yellow solid.
Mp: 253-255 °C. 1H NMR: δ 7.12 (d, J ) 4 Hz, 2 H), 6.86 (d, J
) 4 Hz, 2 H); 19F NMR: δ -136.7 (d, J ) 12 Hz, 4 F), -153.7 (d,
J ) 12 Hz, 4 F). MS (FAB) m/z: 644 (M+). Anal. Calcd for
C22H4Br2F8S2: C, 41.02; H, 0.63; S, 9.96. Found: C, 40.86; H, 0.27;
S, 9.62.
5-Ethynyl-5′-hexyl-2,2′-bithiophene (4). Triphenylphosphine
(0.06 g, 0.23 mmol), dichlorobis(triphenylphosphine)palladium(II)
(0.08 g, 0.11 mmol), copper(I) iodide (0.04 g, 0.23 mmol), and
523 (1.25 g, 3.80 mmol) were loaded into a flask under positive
nitrogen pressure. Degassed triethylamine (40 mL) was transferred
via cannula onto the solids, followed by addition of ethynyltrim-
ethylsilane (0.47 g, 4.75 mmol). A condenser was attached, and
the resulting solution was stirred under reflux for 12 h. The crude
product was extracted with hexanes and washed successively with
ammonium chloride, water, and brine. The organic layer was passed
through a plug of silica gel (hexanes eluant) and then concentrated
under vacuum. Trimethylsilyl groups were removed by stirring for
4 h with aq KOH (0.40 g, minimal water) in methanol (40 mL).
The resulting terminal alkyne was extracted with ether and washed
with water and brine. Concentration of the organic layer afforded
a tan solid that was recrystallized from hexanes to give 0.66 g (63%)
of pale yellow powder. This product degrades to a brown solid
over several days under ambient conditions, so it was used promptly
after purification. 1H NMR (C6D6): δ 6.90 (d, J ) 4 Hz, 1 H), 6.78
(d, J ) 4 Hz, 1 H), 6.65 (d, J ) 4 Hz, 1 H), 6.39 (d, J ) 4 Hz, 1
H), 2.94 (s, 1 H), 2.49 (t, J ) 8 Hz, 2 H), 1.47 (m, 2 H), 1.09-1.27
(m, 6 H), 0.86 (t, J ) 7 Hz, 3 H). 13C NMR (100 MHz, C6D6): δ
14.7, 23.3, 29.4, 30.7, 32.17, 32.21, 77.6, 83.0, 120.9, 123.3, 124.9,
125.7, 134.60, 134.66, 140.5, 146.7. GC-MS (EI) m/z: 274 (M+).
FIGURE 7. Space-filling view down the a-axis in crystals of 6a; solvent
molecules and hydrogen atoms removed for clarity.
provide synthetic access to new donor-acceptor oligomers and
polymers. Moreover, the solid-state packing of 6a is novel for
linear acenes and warrants further studies on related molecules
to discern the factors that direct this structural arrangement. Both
the synthesis and device performance of a range of 9,10-
dialkynyloctafluoroanthracenes are currently being explored, as
the stabilized LUMO energy levels and columnar π stacking
of these compounds could lead to high-performance n-type
organic materials. Future efforts will also involve attempts to
obtain oligomers and polymers via cross-coupling with dichlo-
ride 1. In addition, dibromide 2e is expected to provide a range
of donor-acceptor structures through straightforward coupling
reactions.
Experimental Section32
1,2,3,4,5,6,7,8-Octafluoro-9,10-bis(4-methoxyphenyl)an-
thracene (2b). Phosphine 3 (0.03 g, 0.06 mmol), tris(dibenzylide-
neacetone)dipalladium(0) (0.01 g, 0.01 mmol), sodium carbonate
(0.21 g, 2.00 mmol), 4-methoxyphenylboronic acid (0.30 g, 2.00
mmol), and 1 (0.30 g, 0.77 mmol) were loaded into a flask in a
glovebox. A degassed mixture of toluene (3 mL), THF (3 mL),
(32) See the Supporting Information for general experimental details.
(33) Compound 3a is light-sensitive in solution, so it must either be purified
quickly or handled in the dark. Yellow needles of 3a are stable indefinitely under
ambient conditions.
J. Org. Chem. Vol. 73, No. 20, 2008 7899

Tannaci et al.
Anal. Calcd for C16H18S2: C, 70.02; H, 6.61; S, 23.37. Found: C,
69.82; H, 6.71; S, 23.59.
The crude product was extracted with chloroform and washed
successively with ammonium chloride, water, and brine. The
organic layer was passed through a plug of silica gel (hexanes
eluant) and then concentrated under vacuum. Slow cooling of a
toluene/methanol solution gave a bright red solid (0.17 g, 73%).
1,2,3,4,5,6,7,8-Octafluoro-9,10-bis[(trimethylsilyl)ethynyl]an-
thracene (6a).33 Triphenylphosphine (0.02 g, 0.08 mmol), dichlo-
robis(triphenylphosphine)palladium(II) (0.03 g, 0.04 mmol), cop-
per(I) iodide (0.02 g, 0.08 mmol), and 1 (0.30 g, 0.77 mmol) were
loaded into a flask under positive nitrogen pressure. Degassed
triethylamine (10 mL) was transferred via cannula onto the solids,
followed by addition of ethynyltrimethylsilane (0.19 g, 1.92 mmol).
A condenser was attached, and the resulting solution was stirred
under reflux for 16 h. The crude product was extracted with ether
and washed successively with ammonium chloride, water, and brine.
The organic layer was passed through a plug of silica gel (hexanes
eluant) and then concentrated under vacuum. Slow cooling of a
hexanes solution gave 0.30 g (76%) of fine yellow needles. Single
crystals for X-ray diffraction were obtained by slow evaporation
1
Mp: 266-267 °C. H NMR: δ 6.95 (s, 4 H), 2.53 (s, 12 H), 2.34
(s, 6H). 19F NMR: δ -137.7 (d, J ) 14 Hz, 4 F), -155.5 (d, J )
14 Hz, 4 F). HRMS (EI): calcd for C36H22F8 606.1594 (M+), found
606.1588.
Acknowledgment. This work was supported by the National
Science Foundation (research grant no. CHE0314709). We thank
Professor Barry Thompson for helpful discussions on organic
electronics.
1
Supporting Information Available: General experimental,
UV-vis/fluorescence spectra of 2b, 2d, and 6b, cyclic volta-
mmograms of 2b-d, NMR spectra of new compounds, and
crystallographic data for 2b, 2d, and 6a. This material is
available free of charge via the Internet at http://pubs.acs.org.
of a dichloromethane/pentane solution. H NMR: δ 0.34 (s, 9 H).
19F NMR: δ -137.2 (d, J ) 13 Hz, 4 F), -154.7 (d, J ) 13 Hz,
4 F). GC-MS (EI) m/z: 514 (M+). Anal. Calcd for C24H18F8Si2:
C, 56.02; H, 3.53. Found: C, 55.73; H, 3.56.
1,2,3,4,5,6,7,8-Octafluoro-9,10-bis(mesitylethynyl)an-
thracene (6b). The procedure for 6a was repeated using ethynylm-
esitylene21 (0.14 g, 0.96 mmol) and stirring under reflux for 24 h.
JO8017268
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