Synthesis and structural characterization of hexa-tert-butyl-hexa-peri- hexabenzocoronene, its radical cation salt and its tricarbonylchromium complex

Article abstract of DOI:10.1002/(SICI)1521-3765(20000515)6:10<1834::AID-CHEM1834>3.0.CO;2-L

The hexa-tert-butyl substituted hexa-peri-hexabenzocoronene was synthesized in an overall yield of 83% from 4-tert-butylphenylacetylene. The key step was the oxidative cyclodehydrogenation of hexa(4-tert- butylphenyl)benzene with anhydrous FeCl₃ in CH₂Cl₂. The high solubility of hexa-tertbutyl-hexa-peri-hexabenzocoronene in common organic solvents allowed a comprehensive spectroscopic characterization of this compound in solution. Electrochemical oxidation at -30 °C in the presence of tetrabutylammonium hexafluoroarsenate led to the formation of a stable radical cation salt. Reaction of hexa-tert-butyl-hexa-peri-hexabenzocoronene with an excess of tricarbonyl(naphthalene)chromium in THF/dioxane afforded a mixture of mono- and bis-tricarbonylchromium complexes which could be separated by chromatography. The molecular structures of the parent compound, its radical cation salt and its mono- tricarbonylchromium complex were determined by X- ray analysis and discussed in detail. Remarkably, the crystal structures of these compounds are mainly dominated by the formation of dimers of the aromatic cores.

Full text of DOI:10.1002/(SICI)1521-3765(20000515)6:10<1834::AID-CHEM1834>3.0.CO;2-L

FULL PAPER
Synthesis and Structural Characterization of Hexa-tert-butyl-
hexa-peri-hexabenzocoronene, Its Radical Cation Salt and
Its Tricarbonylchromium Complex
Peter T. Herwig, Volker Enkelmann, Oliver Schmelz, and Klaus Müllen*[a]
Abstract: The hexa-tert-butyl substitut-
ed hexa-peri-hexabenzocoronene was
synthesized in an overall yield of 83%
from 4-tert-butylphenylacetylene. The
key step was the oxidative cyclodehy-
drogenation of hexa(4-tert-butylphe-
nyl)benzene with anhydrous FeCl3 in
CH Cl The high solubility of hexa-tert-
butyl-hexa-peri-hexabenzocoronene in
common organic solvents allowed a
comprehensive spectroscopic character-
ization of this compound in solution.
Electrochemical oxidation at À308C in
the presence of tetrabutylammonium
hexafluoroarsenate led to the formation
of a stable radical cation salt. Reaction
of hexa-tert-butyl-hexa-peri-hexabenzo-
coronene with an excess of tricarbonyl-
(naphthalene)chromium in THF/diox-
ane afforded a mixture of mono- and
bis-tricarbonylchromium complexes
which could be separated by chroma-
tography. The molecular structures of
the parent compound, its radical cation
salt and its mono- tricarbonylchromium
complex were determined by X-ray
analysis and discussed in detail. Re-
markably, the crystal structures of these
compounds are mainly dominated by
the formation of dimers of the aromatic
cores.
2
2.
Keywords: arene complexes ´ crys-
tal structure ´ cyclodehydrogenation
´
electrocrystallization ´ PAH
Introduction
properties and, on the other hand, allows the derivatization of
these compounds by chemical and electrochemical means.
Polycyclic aromatic hydrocarbons (PAHs) are of interest
because of their electronic and optoelectronic properties.[1]
Furthermore, large PAHs serve as unique model compounds
for graphite.[
Recently, we have described synthetic concepts toward
[5±10]
alkyl-substituted derivatives of PAHs.
Owing to the good
solubility of these compounds a spectroscopic characteriza-
tion in solution became possible. Interestingly, the n-alkyl
substituted compounds form discotic mesophases with a
2]
Most of the smaller PAHs crystallize in a fashion in which
there is little p interaction between the molecules.[ A typical
structure found in this class of compounds is the herringbone
motif where the discs are oriented approximately perpendic-
ular to each other. If the diameter of the discs increases,
however, it is expected that at a certain point the herringbone
packing is no longer stable and that columnar structures with
strong p interactions are formed.[
3]
[6]
stack-like arrangement of the aromatic discs. Furthermore,
monomolecular adsorbate layers on graphite could be ob-
tained which were characterized by scanning tunneling
microscopy.[
5, 8, 10]
Herein we describe a synthetic route toward hexa-tert-
butyl-hexa-peri-hexabenzocoronene (1b). The good solubility
of this compound allows the formation of the stable radical
cation salt [1b] AsF upon electrochemical oxidation of 1b, as
3, 4]
One of the difficulties dealing with larger PAHs is the fact
that with increasing molecular weight the solubility of these
compounds decreases dramatically. For instance, hexa-peri-
hexabenzocoronene (1a) is so insoluble in common organic
solvents that crystals for the structure determination had to be
grown in pyrene melts.[
2
6
well as the synthesis of the tricarbonylchromium complexes
[1b]Cr(CO) (6) and [1b][Cr(CO) ] (7). The crystal structure
3
3 2
analyses of these compounds reveal a remarkable packing
behavior of the aromatic discs in the solid state.
4]
Sufficient solubility is, on the one hand, a prerequisite for
the structural investigation and characterization of physical
Results and Discussion
The synthesis of 1b, outlined in Scheme 1, starts with 4-tert-
butylphenylacetylene (2) which is coupled with 4-tert-butyl-
[
a] Prof. K. Müllen, P. T. Herwig, Dr. V. Enkelmann, O. Schmelz
Max-Planck-Institut für Polymerforschung
Ackermannweg 10, 55128 Mainz (Germany)
E-mail: muellen@mpip-mainz.mpg.de
iodobenzene (3) to yield di(4-tert-butylphenyl)acethylene (4)
(92%).[
11, 12]
The [Co (CO) ] mediated cyclotrimerization of 4
2 8
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Chem. Eur. J. 2000, 6, No. 10

1
834±1839
Table 1. Cyclic voltammetric data of compound 1b.[a]
solvent
E
1=21[V]
E
1=212[V]
reduction
oxidation
THF
CH Cl
2 2
À 2.10
‡ 0.99
À 2.40
‡ 1.42
[
a] Working and counter electrodes: Au; reference: SCE; supporting
À1
4 6
electrolyte: Bu PF (0.1m); scan rate: 100 mVsec .
Crystals suitable for X-ray structure analysis were obtained
by slow evaporation of the solution of 1b in THF/pentane at
room temperature. The crystal structure shows the formation
of dimers which are arranged in a herringbone-like motif
which according to the classification of Desiraju and Gav-
generated hexa(4-tert-butylphenyl)benzene (5) in a yield of
9
0%.[ The key step for the synthesis of 1b is the oxidative
13]
cyclodehydrogenation of 5. Using anhydrous FeCl as oxidant,
3
1
b was obtained in nearly quantitative yield after reductive
ezotti can be characterized as a sandwich herringbone packing
[14]
workup (Scheme 1).
[3]
(
Figure 1a).
It can be seen that the molecules are not strictly planar but
slightly bent owing to the steric interaction of the tert-butyl
groups. The largest deviation of the central atoms of the tert-
butyl groups from the best plane calculated for the aromatic
core is 0.56 Š (C55). Remarkably, the normal projection of
the sandwich is comparable to the one of two graphite planes,
that is each carbon atom in this projection is located in the
center of a six-membered ring of the neighboring molecule
(
Figure 1b).
The interplanar distance of 3.44 Š is only slightly larger
than in graphite (3.35 Š). This packing is quite different from
1
(
a which forms columns of flattened-out herringbones
according to Desiraju and Gavezotti called g motif).[
4]
Apparently the bulky tert-butyl substituents hinder the
formation of equidistant stacks so that strong p interaction
is found only in a pair of molecules. At room temperature, two
of the tert-butyl substituents are disordered, that is two
orientations are observed which differ by approximately a 608
rotation. In Figure 1 only the majority positions are shown for
clarity. It is interesting to note that these two substituents have
no interdimer contacts and have apparently a sufficiently
large cavity to perform a rotation. This motion is frozen in
when the temperature is lowered. The occupancy factor for
the majority methyl groups increases with decreasing temper-
ature so that at 230 K the disorder for one of the tert-butyl
groups is no longer observed. In the investigated temperature
range the thermal motion of the aromatic core can be treated
with good approximation as a rigid body motion and the
vibrational amplitudes decrease in the expected fashion.
Packing and the distortion out of planarity are not affected by
temperature. Pertinent data on the temperature dependence
are summarized in Table 2.
Scheme 1. Synthesis of hexa-tert-butyl-hexa-peri-hexabenzocoronene
1b).
(
The presence of the tert-butyl groups in 1b improves the
solubility significantly. In contrast to the parent compound 1a,
b is soluble in several organic solvents (e. g. chlorinated
Many other smaller aromatic compounds form crystals of
radical cation salts which precipitate on the anode when a
solution is oxidized in the presence of a suitable supporting
1
aliphatic hydrocarbons and tetrahydrofuran) even at room
1
temperature and therefore can be fully characterized by H-
electrolyte (e. g. tetrabutylammonium hexafluoroarsen-
and 13C-NMR spectroscopy as well as UV/Vis spectroscopy.
The cyclovoltammetric determination of the first reduction
[15±17]
ate).
With 1b, however, an oxidation in methylene
chloride yielded a stable red solution from which upon
cooling at À308C shiny black crystals precipitated. The X-ray
structural analysis of these crystals (Figure 2a) shows the
formation of a radical cation salt with the stoichiometry
potentials shows the reversible formation of the mono- and
dianion (E1=21 ˆ À2.10 V, E
2
ˆ À2.40 V), the oxidation
1=2
occurs at E1=21 ˆ ‡0.99 V and E
2
ˆ ‡1.42 V and is rever-
1=2
sible as well (Table 1).
[1b] AsF .
2 6
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1835

K. Müllen et al.
FULL PAPER
Figure 1. a) Crystal structure of 1b. b) Normal projection of a dimer of 1b.
The radical cation salts of smaller aromatic compounds
form columnar structures in which stacks of the disc-like
molecules are placed in a fashion leaving channels in which
the counterions are found.[
15±17]
Here no continuous stacks are
formed, but a layer of solvent molecules is intercalated in the
stacks, separating pairs of 1b. The molecular overlap in such a
pair which is shown in Figure 2b differs from the graphite-like
arrangement of the parent compound. With respect to this
packing the rings are shifted by half a CÀC bond length so that
Figure 2. a) Crystal structure of [1b] AsF . b) Normal projection of a
dimer of [1b] AsF .
2 6
2
6
the centers of the bond intersect in the normal projection. This
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Chem. Eur. J. 2000, 6, No. 10

Hexabenzocoronenes
1834±1839
Table 2. Temperature dependence of the occupancy factors of the
disordered atoms and the eigenvalues of the mean square librational
Cr(CO) groups are placed at adjacent tert-butyl substituted
3
benzene rings. Due to the symmetry of this molecule, a dis-
crimination between the two possible sterioisomers, namely
the cis and the trans isomer, by spectroscopic methods is pre-
vented. However, due to repulsive interactions between the
amplitudes L
i
as determined by the TLS analysis.
room temperature
230 K
155 K
OCC (C441-C461)
0.71
0.59
0.91
2.35
3.45
1.0
1.0
OCC (C561-C581)
0.67
0.84
2.04
3.03
0.87
0.72
1.11
2.09
Cr(CO) ligands the formation of the trans isomer is more
3
2
L
L
L
1
2
3
(deg )
likely.
2
(deg )
2
In order to obtain information about the influence of the
tricarbonylchromium group on the packing behavior of the
aromatic core in the crystal, a X-ray structural analysis of 6
was performed. Suitable crystals were grown by slow diffusion
of ethanol into a solution of 6 in methylene chloride.
Remarkably, the crystal structure is again dominated by the
formation of dimers. The crystal structure of 6 is shown in two
projections in Figure 3.
(deg )
overlap pattern has been frequently observed in the radical
cation salts of other arenes, e. g. pyrene and perylene.[
15, 17]
The reason for the formation of segragated dimers in the
radical cation salt is not clear. As in 1b steric hindrance of the
bulky substituents is a possible explanation for this behavior.
On the other hand, it seems possible to form a columnar
structure by rotating adjacent molecules by 608 with respect to
each other thus avoiding this hindrance and allowing a close
stacking. Thus, another explanation is that the p-system in 1b
is already sufficiently extended in order to effectively stabilize
the charge in a dimer, whereas in the salts of smaller arenes
the infinite stack of molecules is needed to obtain a stable salt.
Many tricarbonyl(arene)chromium complexes can be syn-
thesized by treatment of the corresponding arene with
tricarbonyl(naphthalene)chromium.[ When 1b was reacted
with an excess of tricarbonyl(naphthalene)chromium in a
mixture of dioxane/tetrahydrofuran, complexes 6 and 7 were
formed, which could be separated by column chromatography
18]
(
Scheme 2).
Figure 3. Crystal structure of 6.
The structure contains two molecules CH Cl in the asym-
2
2
metric unit. A dimer is formed in which the Cr(CO) ligands
3
point in opposite directions and are located with maximal
distance at the periphery of the dimer. In some respects the
structure of the Cr(CO)3 complex resembles the parent
compound. The molecules are not strictly planar (maximal
deviation from the best plane 0.31 Š). The interplanar spacing
of 3.59 Š is well within the distance expected for aromatic
rings in the absence of any p ± p interaction. As in 1b the
packing can be described as a double herringbone structure
with almost graphite-like overlap within a dimer pair.
Conclusion
Compound 1b was obtained by a convenient three-step syn-
thesis in high yield. The presence of the tert-butyl substituents
in 1b led to a good solubility which allowed the trans-
formation of 1b into the radical cation salt [1b] AsF as well
Scheme 2. Synthesis of compounds 6 and 7.
2
6
as into the tricarbonylchromium complexes 6 and 7. X-ray
crystallographic analyses elucidated the molecular structures
of 1b, [1b] AsF , and 6. In contrast to the parent compound 1,
Both the H- and 13C-NMR spectra of 6 establish unequiv-
1
ocally the position of the Cr(CO) group, which is ligated to an
3
2
6
electron-rich, tert-butyl substituted benzene ring. In the case
of 7, inspection of the NMR spectra reveals that the two
the crystal structure of 1b is characterized by a sandwich-
herringbone packing. [1b] AsF forms dimers in the crystal
2
6
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1837

K. Müllen et al.
FULL PAPER
which are separated by solvent molecules. This result is in
sharp contrast to the crystal structures of the radical cation
salts of smaller aromatic compounds which are characterized
by the formation of continuous stacks. Finally, the tendency of
(100 mg, 0.12 mmol) in a mixture of dioxane/THF 3:1 (200 mL). The
solution was heated under reflux for 3 h with exclusion of light. The solvent
was removed in vacuo and the residue was purified by chromatography on
silica gel (pentane/CH Cl 5:1). The first fraction gave unreacted 1b, the
2 2
second fraction complex 6 [orange solid (23 mg, 20%); m.p.: 1728C
1
1
b to form dimers in the solid state is established by the
(decomp.); H NMR (500 MHz, CD
2
Cl
2
): d ˆ 1.77 (s, 9H), 1.81 (s, 18H),
1
2
3
1
.83 (s, 18H), 1.84 (s, 9H), 7.36 (s, 2H), 8.84 (s, 2H), 9.33 (m, 4H), 9.37 (s,
H), 9.38 (s, 2H); C NMR (125 MHz, CD
2.14, 35.22, 36.10, 36.16, 36.17, 86.77, 98.51, 100.35, 119.10, 119.59, 119.80,
19.87, 120.00, 121.26, 121.48, 122.05, 122.81, 123.64, 123.80, 123.95, 129.95,
crystal structure of 6. We are currently investigating the
chemical and physical properties of even larger, solubilized
PAHs. It will be of utmost interest to see whether the results
presented in this paper are a general feature of large, alkyl
substituted PAHs.
1
3
2
Cl
2
): d ˆ 31.63, 31.96, 32.10,
130.38, 130.89, 131.14, 131.23. 150.38, 150.58, 150.86; UV/Vis (cyclohex-
ane): Smax (lgM) ˆ 354 (5.01), 379 (4.58), 388 (4.55), 418 nm (4.08); MS
‡
(
FD): m/z (%): 995.8 (100) [M] ; anal. calcd for C69
H
66
O
3
Cr (995.28): C
8
3.27, H 6.68; found C 83.01, H 6.65], and the third fraction complex 7
Experimental Section
1
[
orange solid (32 mg, 25%); m.p.: 1708C (decomp.); H NMR (500 MHz,
CD Cl
): d ˆ 1.74 (s, 18H), 1.80 (s, 18H), 1.82 (s, 18H), 6.75 (s, 2H), 7.31 (s,
2H), 8.82 (s, 2H), 9.34 (m, 4H), 9.39 (s, 2H); C NMR (125 MHz, CD Cl ):
2
2
1
3
General: Commercially available reagents were used without further
purification unless otherwise stated. All reactions were carried out under
an atmosphere of argon with freshly distilled solvents under anhydrous
conditions. Melting points were determined on a Büchi melting point
apparatus and are uncorrected. UV/Vis spectra were recorded at room
temperature on Perkin ± Elmer Lambda9 or Perkin ± Elmer Lambda15
spectrophotometers. NMR spectra were recorded at ambient or specified
temperatures on Varian Gemini 2000, Bruker AM300 or Bruker AMX500
instruments and calibrated with the solvent as the internal reference. Mass
spectra were recorded on VG TRIO 2000 EI or ZAB2-SE-FPD equipment.
Elemental analyses were performed by the Institut für Organische Chemie,
Johannes Gutenberg-Universität in Mainz (Germany).
2
2
d ˆ 31.46, 31.87, 32.02, 35.19, 36.11, 36.18, 85.40, 86.33, 96.76, 98.71, 98.90,
119.37, 120.07, 120.20, 120.43, 121.25, 121.95, 122.62, 123.03, 123.22, 123.40,
129.34, 130.58, 131.07, 131.24, 151.03, 151.30, 233.62; UV/Vis (cyclohexane):
Smax (lgM) ˆ 346 (4.85), 381 (4.54), 420 nm (4.26); MS (FD): m/z (%):
‡
1130.8 (100) [M] ; anal. calcd for C H O Cr (1131.30): C 76.44, H 5.88;
7
2
66
6
2
found C 76.22, H 5.75].
X-ray crystallography: All data with the exception of the low-temperature
structures of 1b were collected on a Nonius CAD4 diffractometer using
[18]
graphite monochromated CuKa radiation (l ˆ 1.5418 Š). The latter were
collected on a Nonius KCCD diffractometer with MoKa radiation (l ˆ
0
.7107 Š). Data on the CAD4 diffractometer were collected in the q-2q
Di(4-tert-butylphenyl)acethylene (4):[12] At room temperature 3 (4.4 g,
scan mode. Data collections at low temperature were carried out with a
cooled nitrogen stream. Unit cell parameters were determined from a least-
squares fit of 25 reflections with q > 208. An empirical absorption
correction was applied to the data. The structures were solved with direct
methods (Shelxs) and refined by full matrix least-squares analyses on F
with anisotropic temperature factors for all non-hydrogen atoms. The latter
were placed at the calculated positions and included in the refinement with
fixed isotropic temperature factors in the riding mode. For the disordered
tert-butyl groups occupancy factors (x, 1 À x) were refined.
1
6.94 mmol) was added to a solution of [Pd(PPh
CuI (0.16 g, 0.85 mmol) in piperidine (250 mL). After stirring for 30 min, 2
2.67 g, 16.94 mmol) was added and stirring was continued for a further 6 h.
The mixture was diluted with CH Cl (200 mL), washed with saturated
NH ).
3 4
) ] (0.48 g, 0.42 mmol) and
(
2
2
4
Cl solution (2 Â 200 mL) and H
2
O ( 2Â 200 mL) and dried (MgSO
4
The solvent was removed in vacuo and the residue recrystallized from
MeOH/EtOH to furnish 4 as colorless crystals (4.52 g, 92%). M.p.: 1778C
[
12]
1
(
(
1
lit.: 177 ± 1788C ); H NMR (200 MHz, CDCl
3
): d ˆ 1.36 (s, 18H), 7.39
m, 4H), 7.50 (m, 4H); 1 C NMR (50 MHz, CDCl
21.08, 125.81, 131.84, 151.81; MS (EI): m/z (%): 290.0 (48) [M] ; anal.
3
): d ˆ 31.71, 35.26, 89.43,
3
Compound 1b (room temperature): monoclinic, P2
/c, a ˆ 15.0568(9), b ˆ
1
‡
3
1
8.094(1), c ˆ 18.136(1) Š, b ˆ 94.976(5)8, Vˆ 4922.4 Š , Z ˆ 4,
D
x
ˆ
calcd for C22
H
26 (290.03): C 90.98, H 9.02; found C 90.93, H 9.03.
À3
À1
1
.159 gcm , m ˆ 4.547 cm , 8449 reflections measured (qmax ˆ 648) 3234
Hexa(4-tert-butylphenyl)benzene (5): [Co
2
(CO) ] (150 mg, 0.43 mmol) was
8
observed (I > 3s(I)), R ˆ 0.064, R ˆ 0.067 (unit weights).
w
added to a solution of 4 (4.11 g, 14.17 mmol) in dioxane (200 mL). The
mixture was stirred and heated under reflux for 20 h. After the reaction
mixture had been allowed to cool down to room temperature, the
crystalline precipitate was filtered off and dissolved in CS . Filtration of
2
this solution and removal of the solvent under reduced pressure afforded
Compound 1b (230 K): monoclinic, P2
1
/c, a ˆ 15.0800(2), b ˆ 18.0961(5),
3
À3
c ˆ 18.1310(5) Š, b ˆ 95.059(1)8, Vˆ 4928.5 Š , Z ˆ 4, D
x
ˆ 1.158 gcm
,
À1
m ˆ 0.61 cm , 12511 reflections measured (qmax ˆ 298) 4617 observed (I >
3
s(I)), R ˆ 0.055, R
w
ˆ 0.055 (unit weights).
Compound 1b (155 K): monoclinic, P2
1
/c, a ˆ 15.0703(6), b ˆ 18.0203(7),
pure compound 5 as a white microcrystalline powder (3.7 g, 90%). M.p.: >
3
À3
c ˆ 18.0498(6) Š, b ˆ 94.917(2)8, Vˆ 4883.8 Š , Z ˆ 4, D
x
ˆ 1.169 gcm
,
1
3
1
3
008C; H NMR (500 MHz, C
2
D
2
Cl
4
, 1008C): d ˆ 1.06 (s, 54H), 6.65 (m,
À1
m ˆ 0.61 cm , 12410 reflections measured (qmax ˆ 298) 4745 observed (I >
2H), 6.74 (m, 12H); 13C NMR (125 MHz, C
D
Cl
, 100 C): d ˆ 31.44,
o
2
2
4
3
s(I)), R ˆ 0.053, R
w
ˆ 0.054 (unit weights).
(CH Cl
12: triclinic, P À 1, 165 K, a ˆ 18.869(5), b ˆ
4.13, 123.00, 131.53, 138.45, 140.42, 147.60; MS (FD): m/z (%): 870.1 (100)
‡
Compound [1b]
2
AsF
6
2
2
)
[
M] ; anal. calcd for C66
H
78 (870.1): C 90.98, H 9.02; found C 90.89, H 9.06.
1
6
1.354(5), c ˆ 28.771(5) Š, a ˆ 87.979(8), b ˆ 90.058(9), g ˆ 88.237(8)8, Vˆ
Hexa-tert-butyl-hexa-peri-hexabenzocoronene (1b): Anhydrous FeCl
1.78 g, 11.02 mmol) was added to a solution of 5 (0.2 g, 0.229 mmol) in
CH Cl (100 mL). The resulting green rection mixture was stirred for 18 h
at room temperature and then quenched with MeOH (10 mL), whereupon
the color turned yellow. The solution was washed with 5n hydrochloric acid
3
3
À3
À1
157 Š , Z ˆ 2, D
x
ˆ 1.302 gcm , m ˆ 32.857 cm , 15113 reflections meas-
(
ured (qmax ˆ 608) 8909 observed (I > 3s(I)), R ˆ 0.074, R ˆ 0.077 (unit
w
2
2
weights).
Compound 6 (CH
2
Cl
2
)
2
: monoclinic, P2
1
/n, 165 K, a ˆ 17.162(1), b ˆ
3
1
2.187(1), c ˆ 29.315(2) Š, b ˆ 91.140(4)8, Vˆ 6130 Š , Z ˆ 4,
D
x
ˆ
(
5 Â 200 mL), H
silica gel (CH Cl
0.196 g, 98%). M.p.: > 3008C; H NMR (300 MHz, CDCl
2
O ( 2Â 200 mL) and dried over MgSO
4
. Filtration over
À3
À1
1.262 gcm
,
m ˆ 35.493 cm
,
11490 reflections measured (qmax ˆ 608)
ˆ 0.077 (unit weights).
2
2
) afforded the pure compound 1b as a yellow solid
1
5890 observed (I > 3s(I)), R ˆ 0.071, R
w
(
5
1
3
): d ˆ 1.81 (s,
4H), 9.30 (s, 12H); 13C NMR (125 MHz, CDCl
): d ˆ 32.02, 35.73, 118.91,
3
20.51, 124.04, 130.55, 149.04; UV/Vis (cyclohexane): Smax (lgM) ˆ 340
‡
Acknowledgement
(
4.76), 355 (5.11), 387 nm (4.72); MS (FD): m/z (%): 858.52 (100) [M] ;
anal. calcd for C66
Radical cation salt [1b]
tetrabutylammonium hexafluoroarsenate (8.62 g, 20 mmol) in CH
200 mL) was cooled to À308C and electrolyzed between platinum-wire
electrodes at a constant low current (2 mA) under an atmosphere of argon.
H
66 (859.25): C 92.26, H 7.74; found C 91.90, H 7.70.
AsF : A solution of 1b (400 mg, 0.46 mmol) and
Cl
Financial support by the Volkswagen-Stiftung and the TMR European
Research Programme through the Sisitomas project is gratefully acknowl-
edged.
2
6
2
2
(
2 6
After two days, shiny black crystals of compound [1b] AsF were collected
and subjected to X-ray analysis.
[
1] E. Clar, The Aromatic Sextet, Wiley, Chichester, 1972.
Tricarbonylchromium complexes 6 and 7: Tricarbonyl(naphthalene)chro-
mium-tricarbonyl (317 mg, 1.2 mmol) was added to a solution of 1b
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0947-6539/00/0610-1838 $ 17.50+.50/0
Chem. Eur. J. 2000, 6, No. 10

Hexabenzocoronenes
1834±1839
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[12] An alternative synthesis of compound 4 has already been described:
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4695.
6
21.
[
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[
[
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[19] Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-142006 for 1b (room temp.), CCDC-142007 for 1b (230 K),
1
604.
[
8] V. S. Iyer, K. Yoshimura, V. Enkelmann, R. Epsch, J. P. Rabe, K.
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3
7, 2696.
[
9] M. Müller, C. Kübel, K. Müllen, Chem. Eur. J. 1998, 4, 2099.
[
10] S. Ito, M. Wehmeier, J. D. Brand, C. Kübel, R. Epsch, J. P. Rabe, K.
Müllen, Chem. Eur. J. 2000, in press.
CCDC-142008 for 1b (155 K), CCDC-142009 for [1b]
AsF (CH Cl 12 and CCDC-142010 for 6 ´ ( CH Cl . Copies of the
2
6
2
2
)
2
2 2
)
[
11] a) L. Cassar, J. Organometal. Chem. 1975, 93, 253; b) H. A. Dieck,
F. R. Heck, J. Organometal. Chem. 1975, 93, 259; c) K. Sonogashira, Y.
Tohda, N. Hagihara, Tetrahedron Lett. 1975, 4467.
data can be obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB21EZ, UK (fax: (‡44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
Received: July 13, 1999 [F1909]
Chem. Eur. J. 2000, 6, No. 10
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0947-6539/00/0610-1839 $ 17.50+.50/0
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