From branched hydrocarbon propellers to C3-symmetric graphite disks

Article abstract of DOI:10.1021/jo049452a

Branched hydrocarbon propellers (9 and 12) were prepared by stepwise palladium-catalyzed Hagihara-Sonogashira coupling reactions and Diels-Alder cycloadditions and submitted to oxidative cyclodehydrogenation by FeCl ₃ to afford two new giant graphite disks 2 and 3 with 3-fold symmetry in high yield. One of the precursors, the polyphenylene dendrimer 9 containing 150 carbon atoms, was crystallographically characterized. The poorly soluble graphite disks were characterized by isotope-resolved MALDI-TOF mass spectroscopy, and their electronic and vibrational properties were investigated by solid-state UV-vis and Raman spectroscopy. The effect of molecular size and geometry on their properties was discussed. The molecule 2 represents the largest, 3-fold-symmetric all-benzenoid graphite disk, and the five-membered rings in molecule 3 open the opportunity to synthesize large bowl-shaped PAHs.

Full text of DOI:10.1021/jo049452a

3
F r om Br a n ch ed Hyd r oca r bon P r op eller s to C -Sym m etr ic
Gr a p h ite Disk s
J ishan Wu, Zˇ eljko Tomovi c´ , Volker Enkelmann, and Klaus M u¨ llen*
Max-Planck Institut f u¨ r Polymerforschung, Ackermannweg 10, Mainz 55128, Germany
muellen@mpip-mainz.mpg.de
Received April 2, 2004
Branched hydrocarbon propellers (9 and 12) were prepared by stepwise palladium-catalyzed
Hagihara-Sonogashira coupling reactions and Diels-Alder cycloadditions and submitted to
oxidative cyclodehydrogenation by FeCl to afford two new giant graphite disks 2 and 3 with 3-fold
3
symmetry in high yield. One of the precursors, the polyphenylene dendrimer 9 containing 150 carbon
atoms, was crystallographically characterized. The poorly soluble graphite disks were characterized
by isotope-resolved MALDI-TOF mass spectroscopy, and their electronic and vibrational properties
were investigated by solid-state UV-vis and Raman spectroscopy. The effect of molecular size and
geometry on their properties was discussed. The molecule 2 represents the largest, 3-fold-symmetric
all-benzenoid graphite disk, and the five-membered rings in molecule 3 open the opportunity to
synthesize large bowl-shaped PAHs.
In tr od u ction
columns was observed, and this qualified the molecules
as promising semiconductors for organic field effect
transistors, light-emitting diodes, and photovoltaic de-
vices.6
Polycyclic aromatic hydrocarbons (PAHs) represent one
of the most intensively investigated classes of carbon-
rich compounds. Their synthesis, characterization, and
electronic properties have been widely studied since the
beginning of the 20th century. All-benzenoid PAHs such
1
The molecular size, symmetry, and nature of the
periphery have great influence on the electronic proper-
ties as well as the two- and three-dimensional super-
2
as triphenylene and hexa-peri-hexabenzocoronene (HBC)
possess high thermal and chemical stability and thus are
7
structures of these graphite disks. In our previous work,
various graphite molecules with D2h and D6h symmetry
have been prepared, and a D3h symmetric disk 1 (Chart
useful organic semiconductors in practical electronic and
optoelectronic devices.3 The synthesis of a series of
1
) with 96 carbons was synthesized by oxidative cyclo-
graphite molecules with different size and periphery has
been well developed in our group mainly based on
oxidative cyclodehydrogenation of branched oligophen-
dehydrogentation of a 1,3,5-tris(pentaphenylyl)benzene
8
propeller molecule in nearly quantitative yield. The
4
hexadodecyl-substituted molecule 1 possesses a surpris-
ingly high solubility in many organic solvents and gives
rise to a highly ordered room-temperature columnar
ylene precursors. Well-defined graphite disks carrying
up to 222 carbons were prepared, and the synthetic
concept was also used to prepare polydispersed graphite
9
5
liquid crystalline phase. The symmetry is thus expected
ribbons. Attachment of flexible substituents onto the
to have an important influence on its packing in the bulk
state. Herein, the synthesis and characterization of a new
extended D3h-symmetric graphite disk 2 (Chart 1) with
graphite disks improves the solubility and lowers the
melting point. Melting leads to remarkably stable discotic
mesophases with columnar superstructures.4b As a result,
1
3
50 carbons and another C -symmetric disk 3 (Chart 1)
a high one-dimensional charge carrier mobility along the
with 90 carbons are presented. Their electronic and
vibrational properties were studied by solid-state UV-
vis and Raman spectroscopy as a function of size.
Molecule 3, containing three five-membered rings and
*
To whom correspondence should be addressed. Fax: 0049 6131 379
3
1
50.
(1) (a) Clar E. Polycyclic Hydrocarbons; Academic Press: New York,
964; Vol. I/II. (b) Dias, J . R. Handbook of Polycyclic Hydrocarbons;
Elsevier: Amsterdam, 1988. (c) Harvey, R. G. Polycyclic Aromatic
Hydrocarbons; Wiley-VCH: New York, 1997.
(6) (a) van de Craats, A. M.; Warman, J . M.; Fechenk o¨ tter, A.;
Brand, J . D.; Harbison, M. A.; M u¨ llen, K. Adv. Mater. 1999, 11, 1469-
1472. (b) Schmidt-Mende, L.; Fechtenk o¨ tter, A.; M u¨ llen, K.; Moons,
E.; Friend, R. H.; MacKenzie, J . Science 2001, 293, 1119-1122. (c) van
de Craats, A. M.; Stutzmann, N.; Bunk, O.; Nielsen, M. M.; Watson,
M. D.; M u¨ llen, K.; Chanzy, H. D.; Sirringhaus, H.; Friend, R. H. Adv.
Mater. 2003, 15, 495-499.
(2) Carbon Rich Complex I/II. Top. Curr. Chem. 1998, 196, whole
issue.
(3) (a) Bushby, R. J .; Lozman, O. R. Curr. Opi. Solid. State Mater.
Sci. 2002, 6, 569-578. (b) Sage, I. C. In Handbook of Liquid Crystals;
Demus, D., Goodby, J ., Gray, G. W., Spiess, H. W., Vill, V., Eds.; Wiley-
VCH: Weinheim, 1998; Vol. 1, pp 731-762.
(4) See our review papers: (a) Watson, M.; Fechtenk o¨ tter, A.;
(7) (a) M u¨ ller, M.; K u¨ bel, C.; M u¨ llen, K. Chem. Eur. J . 1998, 4,
2099-2109. (b) D o¨ tz, F.; Brand, J . D.; Ito, S.; Gherghel, L.; M u¨ llen, K.
J . Am. Chem. Soc. 2000, 122, 7707-7717.
M u¨ llen, K. Chem. Rev. 2001, 101, 1267-1300. (b) Simpson, C. D.; Wu,
J .; Watson, M.; M u¨ llen, K. J . Mater. Chem. 2004, 494-504.
(5) (a) Simpson, C. D.; Brand, J . D.; Berresheim, A. J .; Przybilla,
(8) Iyes, V. S.; Wehmeier, M.; Brand, J . D.; Keegstra, M. A.; M u¨ llen,
K. Angew. Chem., Int. Ed. Engl. 1997, 36, 1604-1607.
(9) Tomovi c´ , Zˇ .; Watson, M. D.; M u¨ llen, K. Angew. Chem., Int. Ed.
2004, 43, 755-758.
L.; R a¨ der, H. J .; M u¨ llen, K. Chem. Eur. J . 2002, 8, 1424-1429. (b)
Wu, J .; Gherghel, L.; Watson, M. D.; Li, J .; Wang, Z.; Simpson, C. D.
M.; Kolb, U.; M u¨ llen, K. Macromolecules 2003, 36, 7082-7089.
1
0.1021/jo049452a CCC: $27.50 © 2004 American Chemical Society
Published on Web 07/03/2004
J . Org. Chem. 2004, 69, 5179-5186
5179

Wu et al.
CHART 1. Molecu la r Str u ctu r e of th e 3-F old Sym m etr ic Gr a p h ite Disk s
SCHEME 1 a
a
Key: (i) diphenyl ether, 230 °C; (ii) Co2(CO)8, dioxane, 125 °C, 5 h.
three naphthalene units, can serve as a reasonable
precursor of larger bowl-shaped PAHs, which were widely
studied by Scott et al.10 The single-crystal structure of
the precursor of 2, a branched oligophenylene propeller
molecule with 25 phenyl rings (9), was also analyzed to
understand the oxidative cyclodehydrogenation process.
3
C -symmetric molecule 6a (Scheme 1) was pursued first.
Diels-Alder cycloaddition between tetraphenylcyclopen-
tadienone and excess 4,4-bis(phenylethynyl)benzene (4)
gave the monophenylethynyl-substituted hexaphenyl-
2 8
benzene 5, which was then submitted to Co (CO) -
catalyzed cyclotrimerization reactions, however, affording
two inseparable structural isomers 6a , the desired pre-
cursor, and 6b.
Resu lts a n d Discu ssion
This obstacle was overcome by the design and synthe-
sis of a novel C -symmetric precursor 9 as shown in
3
Scheme 2. The synthesis started with a 3-fold Hagihara-
Sonogashira coupling between 1,3,5-tris(3′′-iodo-2′-bi-
Syn th esis of Com p ou n d 2. The two key steps toward
the graphite disk 2 are the synthesis of the branched
oligophenylene precursor and the subsequent oxidative
cyclodehydrogenation. A possible precursor such as the
5
180 J . Org. Chem., Vol. 69, No. 16, 2004

Branched Hydrocarbon Propellers
SCHEME 2 a
a
Key: (i) phenylacetylene, Pd(PPh3)4, CuI, piperidine, rt, 88%; (ii) diphenyl ether, reflux, 82%; (iii) FeCl3/CH3NO2, dichloromethane,
1
9 h.
phenylyl)benzene (7)11 and phenylacetylene to afford
compound 8 in 88% yield and was followed by the 3-fold
Diels-Alder cycloaddition between tetraphenylcyclopen-
tadienone and compound 8 in refluxing diphenyl ether
to give the branched oligophenylene 9 in 82% yield. The
good solubility of 9 allows full structural characterization
by NMR and mass spectroscopy (Figure 1a) as well as
single-crystal analysis (see later). The key starting mate-
rial 7 was synthesized from the corresponding 3-trim-
ethylsilyl-substituted tris(1,3,5-biphenylbenzene), which
was prepared by 3-fold Suzuki coupling reaction between
the 1,3,5-tribromobenzene and a biphenylboronic acid.11
The molecule 9 is expected to adopt a three-dimensional
propeller-like conformation similar to other polyphe-
nylene dendrimers,12 raising the question of whether it
can be fused to a planar graphite disk under oxidative
cyclodehydrogenation conditions. Surprisingly, upon treat-
3
ment with 180 equiv of FeCl , compound 9 lost exactly
60 hydrogen atoms to afford the desired disk 2 as an
insoluble powder. Due to the very poor solubility of the
graphite disk, NMR characterization failed. Elemental
analysis of such kind of insoluble graphite disks can-
not provide reliable information about the elemental
composition because of the incomplete combustion dur-
ing the measurements. Alternatively, isotope-resolved
matrix-assisted laser desorption ionization time-of-flight
(MALDI-TOF) mass spectroscopy using a solid-state
sample preparation method with 7,7,8,8-tetracyanoquin-
odimethane (TCNQ) as matrix played a major role in the
(
10) (a) Scott, L. T.; Bratcher, M. S.; Hagen, S. J . Am. Chem. Soc.
996, 118, 8743-8744. (b) Hagen, S.; Bratcher, M. S.; Erickson, M.
S.; Zimmermann, G.; Scott, L. T. Angew. Chem., Int. Ed. Engl. 1997,
control of the reactions and the determination of the
1
13
degree of cyclodehydrogenation. It appeared that FeCl
3
(180 equiv) in dichloromethane was a more efficient oxi-
3
6, 406-408; Angew. Chem. 1997, 109, 407-409. (c) Reisch, H. A.;
Bratcher, M. S.; Scott, L. T. Org. Lett. 2000, 2, 1427-1430. (d)
dant than Cu(OTf) (180 equiv) in carbon disulfide
-AlCl
2
3
Marcinow, Z.; Grove, D. I.; Rabideau, P. W. J . Org. Chem. 2002, 67,
but required a longer time for complete reaction. The
3
537-3539. (e) Scott, L. T.; Boorum, M. M., McMahon, B. J .; Hagen,
S.; Mack, J .; Blank, J .; Wegner, H.; de Meijere, A. Science 2002, 295,
MALDI-TOF mass spectrum of a sample of 2 synthesized
by FeCl in 19 h is shown in Figure 1b, and the molecular
3
ion peak with good isotopic distribution (inset) indicates
an exact loss of 60 hydrogen atoms during the reaction.
1
500-1503. (e) Seiders, T. J .; Baldridge, K. K.; Siegel, J . S. J . Am.
Chem. Soc. 1996, 118, 2754-2755. (f) Havenith, R. W. A.; J iao H.;
J enneskens, L. W.; van Lenthe, J . H.; Sarobe, M.; von Ragu e´ Schleyer,
P.; Kataoka, M.; Necula, A., Scott, L. T. J . Am. Chem. Soc. 2002, 124,
2
363-2370. (g) Havenith, R. A.; van Lenthe, J . H.; Dijkstra, F.,
J enneskens, L. W. J . Phys. Chem. A 2001, 105, 3838-3845. (h) Soncini,
A.; Havenith, R. W. A.; Fowler, P. W.; J enneskens, L. W.; Steiner, E.
J . Org. Chem. 2002, 67, 4753-4758.
(12) Berresheim, A. J .; M u¨ ller, M.; M u¨ llen, K. Chem. Rev. 1999, 99,
1747-1785.
(13) Przybilla, L.; Brand, J . D.; Yoshimura, K.; R a¨ der, J .; M u¨ llen,
K. Anal. Chem. 2000, 72, 4591-4597.
(11) Wu, J .; Baumgarten, M.; Debije, M.; Warman, J . M.; M u¨ llen,
K. Angew. Chem., Int. Ed. 2004, submitted for publication.
J . Org. Chem, Vol. 69, No. 16, 2004 5181

Wu et al.
single-crystal structure of such branched oligophenylenes
to understand the process of their planarization. Single-
crystal growth and analysis of large hydrocarbons are a
challenge, and recently, crystallographic structures of
polyphenylene dendrimers containing up to 222 carbon
atoms have been determined.14 Herein, a single crystal
was grown by slow evaporation of a saturated solution
of 9 in dichloromethane. Projection of the single-crystal
structure of 9 and its three-dimensional packing are
shown in Figure 2.15 Similar to the other polyphenylene
dendrimers, the phenylene rings in molecular 9 remain
planar and the dihedral angles between the neighboring
covalently linked phenylene rings are in the range of 40-
7
0°. Interestingly, the three hexaphenylbenzene arms are
arranged on the same side of the plane of the center
benzene ring instead of forming a C -symmetric three-
3
bladed propeller. This unexpected structure can be
related to the energy-favored three-dimensional packing.
Molecule 9 possesses a triclinic unit cell with a P-1 space
group; i.e., it contains two molecules in each unit cell.
Cavities exist between the molecules which are filled with
dichloromethane molecules. The molecular composition
of the crystal is formulated as C150
H
2 2
102‚2CH Cl .
The above crystallographic analysis clearly shows that
the molecule 9 is branched with all the neighboring
phenyl rings twisted to each other. While the detailed
mechanism of the cyclodehydrogenation is not clear, the
successful transformation of 9 to planar 2 reflects the
magic of iron chloride as an oxidant in the planarization
of branched polyphenylene dendrimers. It should be
pointed out that a similar oxidative cyclodehydrogenation
of 7 also gives a planar hexa-peri-hexabenzocoronene
carrying three iodo functional groups, which allows
versatile functionalization according to our new synthetic
concept.1
1,16
Syn th esis of Com p ou n d 3. The synthesis of 3 is
similar to that of 1 (Scheme 3). Three-fold Diels-Alder
cycloaddition of commercially available 1,3,5-triethynyl-
benzene (10) with excess (3.3 equiv) 7,9-diphenyl-8H-
cyclopenta[l]acenaphthylen-8-one (11)17 in refluxing o-
xylene gave the propeller-like precursor 12 in 90% yield.
Cyclodehydrogenation of 12 with 45 equiv of FeCl
3
afforded compound 3 as a dark-brown, fluorescent solid.
The MALDI-TOF mass spectrum of 3 revealed a single
species with good isotope distribution (Figure 1c). NMR
characterization is impossible due to the poor solubility.
Further attempts toward intramolecular cyclodehydro-
(14) (a) Bauer, R. E.; Enkelmann, V.; Wiesler, U. M.; Berresheim,
A. J .; M u¨ llen, K. Chem. Eur. J . 2002, 8, 3858-3864. (b) Pasacal, R.
A., J r.; Hayashi, N.; Ho, D. M. Tetrahedron 2001, 57, 3549-3555. (c)
Shen, X.; Ho, D. M.; Pascal, R. A., J r. Org. Lett. 2003, 5, 369-371. (d)
Tong, L.; Ho, D. M.; Vogelaar, N. J .; Schutt, C. E.; Pascal, R. A., J r. J .
Am. Chem. Soc. 1997, 119, 7291-7302.
F IGURE 1. MALDI-TOF mass spectra of compounds 9, 2, and
, TCNQ as matrix; inset is the isotope distribution which is
in agreement with the simulated results.
(15) Crystal structure determination was carried out on a KCCD
3
diffractometer with graphite-monochromated Mo KR irradiation. The
structure was solved by direct methods (SHELXS-97). 23 797 unique
reflections (υ < 27.5°) were measured of which 6124 were considered
and used in the refinement. Refinement was done with anisotropic
temperature factors for C and Cl, and the hydrogen atoms were refined
with fixed isotropic temperature factors in the riding mode. Some of
Sin gle-Cr ysta l Str u ctu r e of Com p ou n d 9. The
successful synthesis of the fully closed graphite disk 2
from a branched precursor 9 is a surprise because its
three hexaphenylbenzene units deviate more from the
plane of the center benzene ring compared with the
precursor 6a and such a comformation requires more
energy to compensate for the loss of entropy during the
cyclodehydrogention. Thus, it is helpful to inspect the
the solvent molecules are disordered. Refinement gave: C150
Cl , a ) 14.2289(7) Å, b ) 18.0347(7) Å, c ) 25.1367(9) Å, R )
x
2.471(1)°, â ) 88.187(1)°, γ ) 80.469(1)°, V ) 7064.9 Å , Z ) 2, D )
2
H102‚2CH -
2
3
7
-3
-1
1.227 g cm , µ ) 0.242 mm , R ) 4.21%, R ) 4.31%.
w
(
16) Wu, J .; Watson, M. D.; M u¨ llen, K. Angew. Chem., Int. Ed. 2003,
2, 5329-5333.
17) Wehmeier, M.; Wagner, M.; M u¨ llen, K. Chem. Eur. J . 2001, 7,
2197-2205.
4
(
5
182 J . Org. Chem., Vol. 69, No. 16, 2004

Branched Hydrocarbon Propellers
F IGURE 2. Single-crystal structure and packing of compound 9.
SCHEME 3 a
a
Key: (i) o-xylene, 170 °C, 90%; (ii) FeCl3/CH3NO2, dichloromethane, 45 min.
genation at the peripheries by using large excesses of
oxidant or by applying longer reaction times did not
succeed, indicating a high energy requirement to make
the bowl-shaped PAH. The molecule 3 has enough
solubility in a normal organic solvent such as THF,
allowing standard UV-vis and fluorescence spectroscopic
characterization (see below). Molecule 3, containing five-
membered rings and naphthalene units, should display
different electronic and optoelectronic properties com-
pared with the all-benzenoid PAHs 1 and 2.
UV-vis a n d Ra m a n Sp ectr oscop ic Ch a r a cter iza -
tion of Com p ou n d s 1-3. The poor solubility of com-
pounds 1 and 2 limits their conventional spectroscopic
characterizations in solution. Alternatively, solid-state
UV-vis and Raman spectroscopy are standard tools for
the characterization of insoluble PAHs and nanosized
graphite domains.4 The UV-vis spectra of compounds
,5,7
F IGURE 3. Solid-state UV-vis spectra of compounds 1 and
1
and 2 were recorded on mechanically “smeared” films
2
.
on quartz and shown in Figure 3. Compound 1 possesses
a broad absorption band centered at λmax ) 491 nm, red-
shifted by about 10 nm with respect to its bands in dilute
solution owing to solid aggregation. Compound 2, how-
ever, displays well-resolved absorption bands with the
J . Org. Chem, Vol. 69, No. 16, 2004 5183

Wu et al.
F IGURE 4. UV-vis and fluorescence spectra of compound 3
F IGURE 5. Raman spectra of compounds 1-3.
symmetry of the molecules. Two Raman peaks at 1580
in THF (the spectra were normalized).
λmax ) 575 nm (Figure 3). The bathochromic shift of 84
-
1
and 1330 cm appear in the spectrum of disordered
graphite, usually referred to as the G and the D band,
respectively. The first band (G) is the only feature
observed in the first-order Raman spectrum of highly
ordered, crystalline graphite. The D peak originates from
imperfections and small conjugated domains with finite
size.20 From a structural point of view, molecules 1-3
can be regarded as nanosized, disorded graphitic islands.
nm with respect to compound 1 can be explained by the
extended π-conjugation upon going from 1 to 2. The
appearance of well-resolved peaks instead of a broad
band is somewhat surprising since the increasing mo-
lecular size is supposed to also increase the face-to-face
overlap between the disks. One explanation is that the
overlap between molecules of 2, after rotation some angle
along the columnar axes, is less efficient than that of
molecules 1; i.e., the parts far from the center of 2 do
not overlap and thus their electronic structures are less
disturbed by the π-stacking. The UV-vis and fluores-
cence spectra of compound 3 were recorded in solution
-
1
The line centered at 1600 cm thus can be assigned to
the G band and the lines located around 1220 and 1350
-
1
cm to the D bands. For disordered graphite, the ratio
of the intensities of the peaks at the D band and G band
[I(D)/I(G)] varies inversely with the extension of the
(Figure 4). Well-resolved absorption bands centered at
π-conjugation, i.e., the larger the conjugation, the smaller
the value of I(D)/I(G).21 This relationship was applied
herein to qualitatively evaluate the size effect on the
Raman spectra. The values of I(D)/I(G) for 1, 2, and 3
are about 0.76, 0.70, and 2.94, respectively, in accordance
with the sequence of size 3 < 1 < 2. The I(D)/I(G) relation
of molecule 3 is much higher than that of 1 and 2,
indicating a less ordered packing in 3.
4
75 nm were observed, suggesting an extended conjuga-
tion. The appearance of well-resolved peaks instead of
broad absorption bands as observed in compound 1 can
be explained by the decreased symmetry in molecule 3
as well as possible distortion of the molecular plane owing
to the steric hindrance between the naphthalene units
and the center triangular graphite segment. An ap-
proximate mirror-imaged fluorescence spectrum (λem,max
)
594 nm) with a small Stokes shift was observed, in
accordance with the highly fluorescent nature of com-
pound 3 even in the solid state.
Con clu sion
The oxidative cyclodehydrogenation of two propeller-
like hydrocarbons by iron chloride gave two giant graph-
ite disks with 3-fold symmetry axis. The single-crystal
structure of one of the hydrocarbon precursors (9) dis-
closed a highly branched conformation, which, however,
did not forbid the subsequent cyclodehydrogenation
Raman spectroscopy has been demonstrated to be a
powerful tool in the determination of extended π-conjuga-
tion and ordering of cyclodehydrogenated products.5
The first-order Raman spectra of 1-3 were recorded from
solid samples using 514 nm excitation laser wavelength
b,18
(
Figure 5). All spectra are characterized by two charac-
-
1
teristic features, a first band situated around 1600 cm
(19) (a) Castiglioni, C.; Mapelli, C.; Negri, F.; Zerbi, G. J . Chem.
and a second band with resolved peaks in the range of
Phys. 2001, 114, 963-974. (b) Castiglioni, C.; Negri, F.; Rigolio, M.;
Zerbi, G. J . Chem. Phys. 2001, 115, 3769-3778. (c) Negri, F.; Cas-
tiglioni, C.; Tommasini, M.; Zerbi, G. J . Phys. Chem. A 2002, 106,
-
1
1
220 to 1350 cm . The Raman spectra of various all-
benzenoid PAHs with different but well-defined structure
3
306-3317. (d) Mapelli, C.; Castiglioni, C.; Zerbi, G.; M u¨ llen, K. Phys.
1
9
and size have been studied by Zerbi et al. and revealed
Rev. B 1999, 60, 12710-12725. (e) Mapelli, C.; Castiglioni, C.; Meroni,
E.; Zerbi, G. J . Mol. Struct. 1999, 481, 615-620. (f) Rigolio, M.;
Castiglioni, C.; Zerbi, G.; Negri, F. J . Mol. Struct. 2001, 563-564, 79-
-
1
as a common feature a line near 1600 cm and two or
-
1
more lines near 1300 cm . The number of the peaks in
8
7.
-
1
the region around 1300 cm , their relative intensities,
and their positions changed according to the size and the
(
20) (a) Dressellhaus, M. S.; Dressellhaus, G.; Eklund, P. C. Science
of Fullerenes and Carbon Nanotubes; Academic Press: San Diego,
996. (b) Riedo, E.; Magnano, E.; Rubini, S.; Sancrotti, M.; Baborini,
1
E.; Pieseri, P.; Milani, P. Solid State Commun. 2000, 116, 287-292.
(21) Ferrari, A. C.; Robertson, J . Phys. Rev. B 2000, 61, 14095-
14107.
(
18) Shifrina, Z. B.; Averina, M. S.; Rusanov, A. L.; Wagner, M.;
M u¨ llen, K. Macromolecules 2000, 33, 3525-3529.
5
184 J . Org. Chem., Vol. 69, No. 16, 2004

Branched Hydrocarbon Propellers
process. Molecule 2 represents up to now the largest
solution after being stirred at room temperature for 3.5 h
under argon atmosphere. The crude product was extracted by
dichloromethane, and the organic layer was washed with water
three times and dried over magnesium sulfate. After solvent
was removed, the residue was purified by column chromatog-
raphy (silica gel, peltroleum ether/dichloromethane ) 5:1) to
afford 177 mg of 8 as a white powder (88%): FD-MS (8 kV)
3
-fold symmetric graphite disk, and molecule 3 is one of
1
0
the largest PAHs containing five-membered rings. Their
structure and the electronic and vibrational properties
of the graphitic molecules had good correlations with the
molecular size, geometry, and stacking. Self-assembly of
these disks on the solid-liquid interface which can be
studied by scanning tunneling microscopy (STM) and
+
1
m/z 834.7 [M ] (calcd for C H 835.0); H NMR (250 MHz,
6
6
42
CD
142.3, 141.0, 140.5, 139.9, 133.1, 131.9, 131.0, 130.9, 130.6,
30.4, 130.1, 128.8, 128.7, 128.3, 128.1, 89.72 (C≡C), 89.7
C≡C). Anal. Calcd: C, 94.93; H, 5.07. Found: C, 94.53; H,
.33.
Com p ou n d 9. Compound 8 (140 mg, 0.168 mmol), tetra-
2
Cl
2
) δ 7.0-7.8 (broad); 13C NMR (125 MHz, CD
2 2
Cl ) δ
2
2
spectroscopy (STS) is a subject of future work.
1
(
5
Exp er im en ta l Section
Unless otherwise noted, all starting materials were com-
1
7
phenylcyclopentadienones (443 mg, 1.15 mmol), and diphenyl
ether (2 mL) were heated to reflux under argon for 19 h. After
cooling, the mixture was poured into 30 mL of methanol and
the precipitate was purified by column chromatography (silica
gel, PE/DCM ) 4:1 then 2:1 and finally pure dichloromethane)
to afford 260 mg of compound 9 as a white powder (82%):
mercially available and used as received. Compounds 11 and
1
1
7
were prepared according to the literature.
H NMR and C NMR spectra were recorded in deuterated
1
13
2 2 2 2 4
solvents such as CD Cl and C D Cl . Field desorption (FD)
mass spectra were obtained under a working voltage of 8 kV.
High-resolution MALDI mass spectra were recorded using a
+
37 nm nitrogen laser with TCNQ as matrix.13 UV-vis spectra
MALDI-TOF MS m/z 1905.02 (100) [M ] (calcd for C150H
102
3
1
1
904.49); H NMR (250 MHz, CD
2
Cl
2
) δ 7.7-6.5 (m). Anal.
Calcd: C, 94.60; H, 5.40. Found: C, 94.49; H, 5.46.
were recorded on a “smeared” thin film on quartz plate at room
temperature. The fluorescence spectrum of compound 3 was
recorded in a diluted solution in THF. Raman spectra were
examined in KBr pellets and recorded by a liquid nitrogen
cooled CCD detector and Raman microscopically unit. An
Gr a p h ite Disk C150 42 (2). A solution of 50 mg (0.0263
H
mmol) of compound 9 in 50 mL of dichloromethane was
degassed by bubbling argon for 15 min, and then 765 mg (4.72
mmol) of iron(III) chloride dissolved in 3 mL of nitromethane
was added dropwise via a syringe. A constant argon stream
was carried out during the entire reaction, and the reaction
was quenched by adding methanol after 19 h. The dark
precipitate was collected and washed repetitively with metha-
nol and dried under vacuum to give 42 mg 2 as a black
+
excitation source Ar laser has been used.
1
,4-Bis(p h en yleth yn yl)ben zen e (4). 1,4-Diiodobenzene
50 g, 0.15 mol), Pd(PPh Cl (5.33 g, 7.6 mmol), CuI (2.88 g,
5.2 mmol), and PPh (3.97 g, 15.2 mmol) were mixed together
(
1
3
)
2
2
3
with 500 mL of triethylamine and 200 mL of toluene. The
mixture was degassed by bubbling argon for 15 min, and then
+
3
4 g (0.33 mol) phenylacetylene was added. After being stirred
powder: MALDI-TOF MS m/z 1844.12 (100) [M ] (calcd for
at room temperature overnight, the mixture was poured into
saturated aqueous ammonium chloride solution and 150 mL
of toluene was added. The organic layer was washed by water
two times and dried over magnesium sulfate, and the solvent
was removed under vacuum. The residue was purified by
column chromatography (silica gel, PE/dichloromethane (DCM)
150
C H42 1844.01); isotopic distribution calcd m/z 1842.33
(59.71), 1843.33 (100.00), 1844.33 (83.18), 1845.34 (45.82),
1846.34 (18.80), 1847.35 (6.13); found m/z 1843.12 (73.71),
1844.12 (100.00), 1845.12 (87.96), 1846.12 (47.43), 1847.11
(21.39), 1848.05 (10.45).
Com p ou n d 12. 1,3,5-Triethynylbenzene (10; 192 mg, 1.28
mmol) and 7,9-diphenyl-8H-cyclopenta[l]acenaphthylen-8-one
)
8:1) to give 37.5 g white powder (89%): FD-MS (8 kV) m/z
+
1
2
78.4 [M ] (calcd for C22
H
14 278.4); H NMR (250 MHz, C
2 2
D -
(
11; 1.50 g, 4.21 mmol) were dissolved in o-xylene (10 mL)
1
3
Cl
4
) δ 7.54-7.24 (m); C NMR (175 MHz, C Cl , 100 °C) δ
2
D
2
4
under an argon atmosphere, and the resultant mixture was
heated for 18 h at 170 °C (oil bath temperature). After the
mixture was cooled to room temperature, ethanol (20 mL) was
added. The precipitate was filtered, washed with ethanol (300
mL), and dried in a vacuum to afford 12 as a slightly yellow,
strongly fluorescent solid (1.30 g, 90%): FD MS (8 kV) m/z
1
31.9, 131.8, 128.6, 128.6, 123.6, 123.5, 91.8 (C≡C), 89.6 (C≡C).
Anal. Calcd: C, 94.93; H, 5.07. Found: C, 95.01; H, 4.99.
,2,3,4,5-P en ta p h en yl-6-(4′p h en yleth yn ylp h en yl)ben -
1
zen e (5). Compound 4 (10 g, 35.92 mmol), tetraphenylcyclo-
pentadienone (6 g, 15.61 mmol), and diphenyl ether (11 mL)
were heated at 230 °C under argon overnight. After cooling,
the mixture was poured into methanol and the precipitate was
purified by column chromatography (silical gel, PE/DCM ) 7/3)
to give 4.6 g of 5 as a light yellow powder (47%): FD-MS (8
+
1
1
135.6 (100) [M ] (calcd for C90
H54 1135.4); H NMR (500 MHz,
C
2
D
2
Cl , 100 °C) δ 7.70-7.50 (m, 21H), 7.33 (t, J ) 7.6 Hz,
4
3
6
H), 7.27-7.16 (m, 18H), 7.10 (t, J ) 7.3 Hz, 3H), 6.86 (s, 3H),
.75 (s, 3H), 6.71 (d, J ) 7.0 Hz, 3H); C NMR (125 MHz,
13
+
1
kV) m/z 634.8 [M ] (calcd for C50
Cl
7.6 Hz, 2H), 6.85-6.70 (m, 27H); C NMR (125 MHz, C
H
34 634.8); H NMR (500 MHz,
2 2 4
C D Cl , 100 °C) δ 141.2, 141.0, 139.8, 139.6, 138.1, 138.1,
C
)
Cl
2
D
2
4
) δ 7.42-7.34 (br, 2H), 7.29-7.20 (br, 3H), 6.98 (d, J
1
1
1
37.2, 136.5, 136.4, 135.8, 133.4, 131.5, 130.8, 130.2, 130.1,
29.6, 128.7, 128.6, 128.0, 127.9, 127.8, 127.5, 126.7, 123.5,
23.0. Anal. Calcd: C, 95.21; H, 4.79. Found: C, 95.10; H, 5.01.
1
3
2
D
2
-
4
, 120 °C) δ 141.6, 140.9, 140.8, 140.75, 140.5, 139.8, 131.7,
30.1, 128.4, 128.2, 126.8, 126.6, 125.5, 125.3, 123.8, 120.1,
1
9
Gr a p h ite Disk C90H36 (3). Compound 12 (150 mg, 0.13
0.5 (C≡C), 89.3 (C≡C). Anal. Calcd: C, 94.60; H, 5.40.
mmol) was dissolved in dichloromethane (100 mL) in a 250
mL two-necked round-bottom flask. A constant stream of argon
was bubbled into the solution through a glass capillary. A
Found: C, 94.53; H, 5.47.
1
,3,5-Tr is[(3′′-ph en yleth yn yl)biph en ylyl-2′]ben zen e (8).
Compound 7 (220 mg, 0.241 mmol), Pd(PPh (21 mg, 0.018
3 4
)
3 3 2
solution of FeCl (0.96 g, 5.92 mmol) in CH NO (5 mL) was
mmol), CuI (7 mg, 0.037 mmol), and piperidine (5 mL) were
mixed together in a 25 mL Schlenck tube. The mixture was
degassed by two “freeze-pump-thaw” cycles, and then 150
mg (1.47 mmol) of phenylacetylene was added. The reaction
then added dropwise via syringe. Throughout the whole
reaction, a constant stream of argon was bubbled through the
mixture to remove HCl formed in situ. The reaction was stirred
for 45 min and then quenched by adding methanol (120 mL).
The precipitate was collected by filtration, washed with
methanol (300 mL), and dried in a vacuum to afford 138 mg
was quenched by 15 mL of 2 M saturated aqueous NH
4
Cl
(
22) (a) Samori, P.; Fechtenk o¨ tter, A.; J a¨ ckel, F.; B o¨ hme, T.; M u¨ llen,
of 3 as a dark brown solid: mp > 300 °C; MALDI-TOF MS:
K.; Rabe, J . P. J . Am. Chem. Soc. 2001, 123, 11462-11467. (b)
Tchebotareva, N.; Yin, X.; Watson, M. D.; Samori, P.; Rabe, J . P.;
M u¨ llen, K. J . Am. Chem. Soc. 2003, 125, 9734-9739. (c) Ito, S.; Herwig,
P. T.; B o¨ hme, T.; Rabe, J . P.; Rettig, W.; M u¨ llen, K. J . Am. Chem. Soc.
000, 122, 7698-7706. (d) Samori, P.; Severin, N.; Simpson, C. D.;
M u¨ llen, K.; Rabe, J . P. J . Am. Chem. Soc. 2002, 124, 9454-9457.
+
m/z 1117.89 (100) [M ] (calcd for C90
H
36:1117.29); isotopic
distribution calcd m/z 1116.28 (99.36), 1117.29 (100.00),
118.29 (49.77), 1119.29 (16.33), 1120.30 (3.97), found 1116.90
95.10), 1117.89 (100.00), 1118.89 (47.75), 1119.84 (22.90),
1120.75 (9.34).
1
(
2
J . Org. Chem, Vol. 69, No. 16, 2004 5185

Wu et al.
(
3
G5RD-CT-2000-00321) and MAC-MES (Grd2-2000-
0242). We thank Lileta Gherghel for solid-state UV-
Ack n ow led gm en t. This work was financially sup-
ported by the Zentrum f u¨ r Multifunktionelle Werkstoffe
und Miniaturisierte Funktionseinheiten (BMBF 03N
vis and Hansj o¨ rg Menges for the Raman spectroscopic
measurements.
6
500), EU-TMR project SISITOMAS, the Deutsche
Forschungsgemeinschaft (Schwerpunkt Organische Fel-
deffekttransistoren) as well as the EU projects DISCEL
J O049452A
5
186 J . Org. Chem., Vol. 69, No. 16, 2004