Synthesis of large poly cyclic aromatic hydrocarbons: Variation of size and periphery

Article abstract of DOI:10.1021/ja000832x

A new series of polycyclic aromatic hydrocarbons (PAHs) with different peripheries was synthesized via oxidative cyclodehydrogenation of suitable oligophenylene precursors under mild conditions. Such large PAHs are considered to be two-dimensional graphite sections whose electronic properties are expected to converge to those of macroscopic graphite. The synthetic buildup of the oligophenylene frameworks was mainly based either on Diels-Alder reactions or on cyclotrimerizations. They were subsequently converted into planar aromatic hydrocarbons containing up to 78 carbon atoms. Due to the insufficient solubility of extended PAHs, characterization was achieved by laser desorption/ionization time-of-flight mass spectrometry and UV/visible spectroscopy of thin films.

Full text of DOI:10.1021/ja000832x

J. Am. Chem. Soc. 2000, 122, 7707-7717
7707
Synthesis of Large Polycyclic Aromatic Hydrocarbons: Variation of
Size and Periphery
Florian Do1tz, Johann Diedrich Brand, Shunji Ito, Lileta Gherghel, and Klaus Mu1llen*
Contribution from the *Max-Planck-Institute for Polymer Research, Ackermannweg 10,
55128 Mainz, Germany
ReceiVed March 7, 2000
Abstract: A new series of polycyclic aromatic hydrocarbons (PAHs) with different peripheries was synthesized
via oxidative cyclodehydrogenation of suitable oligophenylene precursors under mild conditions. Such large
PAHs are considered to be two-dimensional graphite sections whose electronic properties are expected to
converge to those of macroscopic graphite. The synthetic buildup of the oligophenylene frameworks was mainly
based either on Diels-Alder reactions or on cyclotrimerizations. They were subsequently converted into planar
aromatic hydrocarbons containing up to 78 carbon atoms. Due to the insufficient solubility of extended PAHs,
characterization was achieved by laser desorption/ionization time-of-flight mass spectrometry and UV/visible
spectroscopy of thin films.
Introduction
Chart 1. A Variety of Extended, All-Benzenoid
Hydrocarbons
Due to its hexagonal symmetry, hexa-peri-hexabenzocoronene
(HBC, 1, Chart 1) serves as an intriguing homologue of benzene
with unique electronic properties.1 Polycyclic aromatic hydro-
carbons (PAHs) larger than HBC have also become accessible
that constitute molecularly defined models of graphite.2 Com-
pounds 2 (C60) and 3 (C78) are the first members of a
homologous series in which the HBC moiety is “extended”
along one symmetry axis.3 While in a formal sense 2 and 3 can
be described as consisting of three oligophenylene chains with
n, n + 1, and n benzene rings, the rhombus 4 (C54) establishes
still another topology, namely, that of three parallel terphenyl
chains, i.e., [3,3,3].4
The idea of using HBC as starting point of a benzene-like
chemistry of molecular graphite subunits suggests a series of
* Corresponding author: (fax) (+49) 6131-379350; (e-mail) muellen@
mpip-mainz.mpg.de.
(1) (a) Herwig, P.; Kayser, C. W.; Mu¨llen, K.; Spiess, H. W. AdV. Mater.
1996, 8, 510. (b) Stabel, A.; Herwig, P.; Mu¨llen, K.; Rabe, J. P. Angew.
Chem. 1995, 107, 1768; Angew. Chem., Int. Ed. Engl. 1995, 34, 1609. (c)
van de Craats, A. M.; Warman, J. M.; Mu¨llen, K.; Geerts, Y.; Brand, J. D.
AdV. Mater. 1998, 10, 36.
(2) (a) Clar, E. Aromatische Kohlenwasserstoffe-Polycyclische Systeme;
Springer, Berlin, 1952. (b) Clar, E. The Aromatic Sextet; Wiley: London,
1972. (c) Dias, J. R. Handbook of Polycyclic Hydrocarbons. Part a:
Benzenoid Hydrocarbons; Elsevier: Amsterdam, 1987. (d) Fetzer, J. C.
Polycycl. Aromat. Comput. 1996, 11 (1-4), 317. (e) Diederich, F.; Rubin,
Y. Angew. Chem. 1992, 104, 1123; Angew. Chem., Int. Ed. Engl. 1992, 31,
1101. (f) Hudgins, D. M.; Allamandola, L. J. J. Phys. Chem. 1995, 99,
3033. (g) Scott, L. T.; Cheng, P.-C.; Hashemi, M. M.; Bratcher, M. S.;
Meyer, D. T.; Warren, H. B. J. Am. Chem. Soc. 1997, 119, 10963. (h) Faust,
R. Angew. Chem. 1995, 107, 1559; Angew. Chem., Int. Ed. Engl. 1995, 34,
1429. (i) Mu¨ller, M.; Petersen, J.; Strohmaier, R.; Gu¨nther, C.; Karl, N.;
Mu¨llen, K. Angew. Chem. 1996, 108, 947; Angew. Chem., Int. Ed. Engl.
1996, 35, 886. (j) Iyer, V. S.; Wehmeier, M.; Brand, J. D.; Keegstra, M.
A.; Mu¨llen, K. Angew. Chem. 1997, 109, 1675; Angew. Chem., Int. Ed.
Engl. 1997, 36, 1604. (k) Mu¨ller, M.; Ku¨bel, C.; Mu¨llen, K. Chem. Eur. J.
1998, 4, 2099. (l) Ito, S.; Wehmeier, M.; Brand, J. D.; Ku¨bel, C.; Epsch,
R.; Rabe, J. P.; Mu¨llen, K. Chem. Eur. J., in press.
(3) (a) Iyer, V. S.; Yoshimura, K.; Enkelmann, V.; Epsch, R.; Rabe, J.
P.; Mu¨llen, K. Angew. Chem. 1998, 110, 2843; Angew. Chem., Int. Ed.
Engl. 1998, 37, 2696. (b) Iyer, V. S.;Wehmeier, M.; Brand, J. D.; Keegstra,
M. A.; Mu¨llen, K. Angew. Chem. 1997, 109, 1679; Angew. Chem., Int. Ed.
Engl. 1997, 36, 1607. (c) Broene, R. D.; Diederich, F. Tetrahedron Lett.
1991, 32, 5227.
further structural modifications.5 The first step would be to
maintain the hexagonal symmetry, but to proceed to the next
higher homologue of 1, i.e., the C114 compound 5. On the other
hand, the electronic structure of large PAHs has been shown to
10.1021/ja000832x CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/27/2000

7708 J. Am. Chem. Soc., Vol. 122, No. 32, 2000
Do¨tz et al.
Chart 2. A Variety of Extended, All-Benzenoid
Hydrocarbons and Exemplary Precursor Molecules
substituted derivatives of aromatic molecules such as tri-
phenylene or HBC form discotic liquid crystals and, therefore,
provide opportunities for materials with one-dimensional trans-
port processes such as energy migration, electric conductivity
and photoconductivity.12 Characterization and visualization of
monolayers of such compounds with molecular resolution can
be obtained by scanning tunneling microscopy (STM). PAHs
are therefore becoming increasingly important as functional
materials in optoelectronics and molecular electronics.1
We have recently reported that extended PAHs are readily
available by a two-step protocol.2k This includes the synthesis
of nonplanar oligophenylene precursors which are then subjected
to an intramolecular cyclodehydrogenation reaction forcing
planarization and formation of the polycyclic target structures.
The prototype of the cyclodehydrogenation is the successful
transformation of hexaphenylbenzene (11) into HBC (1).1b The
formation of 2 and 3 from 12 and 13, respectively, is impressive
but nevertheless a straightforward extension of this concept. The
design process leading to the appropriate oligophenylene
precursors of PAHs and the scope and limitation of the
subsequent cyclodehydrogenation process are key synthetic
issues of this paper.
The above-mentioned oligophenylene compounds are soluble
in organic solvents. In contrast, the corresponding PAHs are
nearly insoluble, which limits the role of conventional techniques
in structure elucidation. Two experimental aspects are therefore
important: laser desorption time-of-flight (LD-TOF) or matrix-
assisted laser desorption/ionization ) time-of-flight (MALDI-
TOF) mass spectrometry can prove the success of the cyclo-
dehydrogenation process and UV/visible spectroscopy, recorded
for thin solid films of PAHs, can provide information as to the
electronic structure.13,14 The synthetic approach mentioned above
can be modified to afford alkyl-substituted PAHs. Alkyl
substituents are important since they can render the PAHs
soluble and assist in their supramolecular ordering. Having
available soluble, alkyl-substituted derivatives of 1, 7, 8, and
9, we can also compare UV/visible spectra in solution with those
of thin solid films.
depend not only upon the size of the molecules but also upon
the nature of their periphery:6 While four different perimeter
types of hexagonal analogues of 1 have been envisaged, we
introduce here the hexagon 6 containing a “cove”-type rather
than an “armchair” periphery as occurring in 1-5.
When investigating the series of hexagons 1, 5, and 6, one
would also suggest combining different periphery types in one
and the same molecule.7 From a design aspect, this can readily
be achieved by removing one benzene ring from 1, thus arriving
at 7 (C36) with one core.8 Removal of a second benzene ring
would then furnish 8 (C30, Chart 2), again a subunit of 1 with
only “armchairs” in the periphery.9 Along the same line, one
can design models for hexagon 5 by adding benzene to the HBC
core, thus arriving at the new compounds 9 (C54), which is an
isomer of the rhombus 4, and 10 (C60).10
Increasing the size and varying the periphery of disk-type
PAH molecules should influence not only their electronic
properties but also their two- and three-dimensional superstruc-
tures. Typical examples are the formation of densely packed
monolayers of PAHs on surfaces that depend sensitively on the
coincidence of adsorbate and substrate symmetries and of stable
discotic mesophases with a stacking of the π-layers.3a,4,11 Alkyl-
Results and Discussion
The synthetic concept of the PAH family presented herein is
based on symmetry and size arguments. Different topologies
can be achieved either by extending the aromatic system along
one symmetry axis or by inducing a starburstlike growth in all
directions. In addition, different perimeter types can be intro-
duced. These design principlessclassifying PAHs according to
their symmetry and peripheryswere established by Stein and
Brown, who suggested two series of all-benzenoid PAHs starting
from benzene as the smallest subunit.6 The next member in both
series is HBC, which is followed in the first series by the PAH
5 containing 114 carbons and in the second one by the PAH 6,
which shows a “cove”-type periphery. The calculations of Stein
and Brown proved that resonance energies are strongly influ-
enced by the edge structure of the molecules, i.e., the periphery,
and the size of the PAHs. Interior carbon atoms several bond
(4) Mu¨ller, M.; Petersen, J.; Strohmaier, R.; Gu¨nther, C.; Karl, N.; Mu¨llen,
K. Angew. Chem. 1996, 108, 947, Angew. Chem., Int. Ed. Engl. 1996, 35,
886.
(5) Ito, S.; Herwig, P. T.; Bo¨hme, T.; Rabe, J. P.; Rettig, W.; Mu¨llen,
K. J. Am. Chem. Soc. 2000, 122, 7698-7706.
(6) Stein, S. E.; Brown, R. L. J. Am. Chem. Soc. 1987, 109, 3721.
(7) (a) Tong, L.; Lau, H.; Ho, D. M.; Pascal, R. A., Jr. J. Am. Chem.
Soc. 1998, 120, 6000. (b) Debad, J. D.; Bard, A. J. J. Am. Chem. Soc.
1998, 120, 2476.
(8) Clar et al. already synthesized the unsubstituted analogues, 7 and 8,
respectively, in a multistep procedure. See: (a) Clar, E.; Zander, M. J. Chem.
Soc. 1959, 142. (b) Clar, E.; Zander, M. J. Chem. Soc. 1958, 1861.
(9) Another approach to 8 via an intramolecular Diels-Alder cycload-
dition is given in: Mu¨ller, M.; Mauermann-Du¨ll, H.; Wagner, M.; Enkel-
mann, V.; Mu¨llen, K. Angew. Chem. 1995, 107, 1751; Angew. Chem., Int.
Ed. Engl. 1995, 34, 1583.
(11) Weiss, K.; Beernink, G.; Do¨tz, F.; Birkner, A.; Mu¨llen, K.; Wo¨ll,
Ch. Angew. Chem. 1999, 111, 3974; Angew. Chem., Int. Ed. Engl. 1999,
38, 3748.
(12) (a) van de Craats, A. M.; Warman, J. M.; Mu¨llen, K.; Geerts, Y.;
Brand, J. D. AdV. Mater. 1998, 10, 36. (b) Adam, D.; Schuhmacher, P.;
Simmerer, J.; Ha¨ussling, L.; Siemensmeyer, K.; Etzbach, K. H.; Ringsdorf,
H.; Haarer, D. Nature 1994, 371, 141.
(13) (a) Yoshimura, K.; Brand, J. D.; Wehmeier, M.; Ito, S.; Ra¨der, H.-
J.; Mu¨llen, K. Macromol. Chem. Phys., submitted. (b) Przybilla, L.; Brand,
J. D.; Ra¨der, H.-J.; Mu¨llen, K. Anal. Chem., submitted.
(14) Gherghel, L.; Mu¨llen, K., in preparation.
(10) Shifrina, Z. B.; Averina, M. S.; Rusanov, A. L.; Wagner, M.; Mu¨llen,
K. Macromolecules 2000, 33, 3525.

Synthesis of Large Polycyclic Aromatic Hydrocarbons
J. Am. Chem. Soc., Vol. 122, No. 32, 2000 7709
Scheme 1. Two Alternative Routes to Large
Oligophenylenes: Cyclotrimerization and Diels-Alder
Reactiona
and iron(III) chloride. Unfortunately, the use of the former
causes unfavorable side reactions such as chlorination;2k there-
fore, all of the cyclodehydrogenation reactions leading to
unsubstituted PAHs more extended than HBC, e.g., 2, 5, and
6, were carried out with the use of copper(II)-trifluoromethane-
sulfonate/aluminum(III) chloride. Contrary to that, optimization
of the appropriate cyclization conditions of alkyl-substituted
oligophenylenes proved iron(III) chloride to be superior to all
other reagents since it did not suffer from severe disadvantages
such as dealkylation, chlorination, or even migration of the alkyl
substituents.2j Retention of the desired substitution pattern was
achieved, and the cyclization reaction proceeded smoothly at
room temperature, in all cases being completed in less than 24
h.
Since nearly all of the investigated hydrocarbons in this study
show extremely low solubility, the applied analytical methods
are restricted to LD-TOF mass spectrometry and UV/visible
spectroscopy, i.e., solid-state characterization. These two tech-
niques represent the basic tools of structure elucidation for the
PAHs reported herein and, therefore, need to be proved with
respect to reliability and accuracy. Two compounds of the
presented PAH family, 7a and 8a (Scheme 2), respectively,
permit processing and characterization easily, due to their
solubilizing side chains and relatively small aromatic core.
Considering the small PAHs 7a and 8a as model compounds,
the reliability of the analytical methods could be shown by
simply comparing mass and UV/visible spectra of 7a and 8a
recorded for different conditions: measurements from solution
(field desorption, FD) or solid state (LD-TOF) concerning mass
spectrometry and from solution or in film concerning UV/visible
spectroscopy. No difference in the spectra was observed, which
proved both techniques to be suitable for the characterization
of still more extended PAHs.
a Conditions: (a) Co2(CO)8, 1,4-dioxane, 100 °C, 6 h, 99%
(RdC12H25); (b) diphenyl ether, reflux, 24 h, 69-95%.
lengths from an edge were found to have properties similar to
those in an infinite graphite sheet. These theoretical investiga-
tions show a progression from benzene via extended PAHs to
macroscopic graphite and, therefore, provide a guideline for our
research in this field.
In view of the well-established synthesis of HBCs from 16
and 17, the route to 7a and 8a is straightforward (Scheme 2).8,9
The oligophenylene precursor 20 was prepared by Diels-Alder
cycloaddition between tetraphenylcyclopentadienone 16 and
4-octyne (19), with concomitant extrusion of carbon monoxide
(44%, a relatively low yield due to difficulties in removing
diphenyl ether). The cyclodehydrogenation of 20 with iron(III)
chloride finally led to 8a. Cycloaddition between 16 and
4-dodecyl(phenyl)acetylene (21) under similar conditions af-
forded the precursor 22 (99%) and finally 7a.
Our synthetic approach to large PAH molecules consists
mainly of two steps: the synthesis of a nonplanar and soluble
oligophenylene precursor and its oxidative cyclodehydrogenation
to an all-benzenoid hydrocarbon. Two entries to the oligophen-
ylene precursors have turned out to be the most convenient and
successful. A quite elegant and facile access to large oligophen-
ylenes is the dicobaltoctacarbonyl-catalyzed trimerization of
suitably substituted diphenylacetylenes which leads to PAHs
with hexagonal symmetry (Scheme 1).15 Hexaphenylbenzene
is easily synthesized in this way, and this method can also be
extended to the preparation of higher hexaarylbenzenes as
potential precursors for HBC homologues such as 5. A more
general approach toward hexaphenylbenzenes is the Diels-
Alder cycloaddition between tetraarylcyclopentadienones and
diphenylacetylenes.16 This method requires more synthetic effort
but opens new possibilities of functionalization. Whereas the
cyclotrimerization route permits only uniform substitution of
all phenyl rings, the cycloaddition method leads to a broad
spectrum of various functionalized oligophenylenes. This has
recently allowed us to synthesize unsymmetrical HBCs with
different functional groups according to Scheme 1. Both routes
afford oligophenylene precursors that are easily characterized
and processable.
Having available the pure and reliably identified PAHs 7a
and 8a, one can now, for the first time, analyze their UV/visible
and NMR spectra in detail. The latter are well resolved and
support the expected structure; the former clearly show the three
bands typically observed for PAHs (R, â, p) and are in
agreement with Clar’s results.8 A more detailed discussion is
given below.
Another example of a moderately soluble PAH is the
arrowlike molecule 9a containing 54 core aromatic carbons
(Scheme 3). Introduction of four alkyl chains improves solubility
to such an extent that characterization could be achieved not
only by LD-TOF mass spectrometry and UV/visible spectros-
copy but also by NMR spectroscopy. The synthesis involves
four steps.
The final step in the synthesis of extended PAHs is the
oxidative cyclodehydrogenation of suitably substituted oligophen-
ylenes which is performed under Lewis acidic conditions.17
Commonly used are copper(II) chloride/aluminum(III) chloride,
copper(II)-trifluoromethanesulfonate/aluminum(III) chloride
Starting from 1,3,5-tribromobenzene (23), Pd(0)-catalyzed
Hagihara reaction with phenylacetylene afforded 3,5-dibromo-
diphenylacetylene (24) in 77% yield. The alkyne 25 was
obtained via Pd(0)-catalyzed Suzuki coupling of 24 with
phenylboronic acid, which was then converted into the oli-
gophenylene precursor 26 in a Diels-Alder cycloaddition with
tetraphenylcyclopentadienone (26, 77%; 26a, 92%). Cyclode-
(15) Vollhardt, K. P. C. Acc. Chem. Res. 1970, 10, 1.
(16) Dilthey, W.; Hurtig, G. Chem. Ber. 1934, 67, 495.
(17) Kovacic, P.; Jones, M. B. Chem. ReV. 1987, 87, 357.

7710 J. Am. Chem. Soc., Vol. 122, No. 32, 2000
Scheme 2. Synthesis of PAHs 7a and 8aa
Do¨tz et al.
a Conditions: (a) diphenyl ether, reflux, 24 h; 44% (b) FeCl3, CH2Cl2, 25 °C, 30 min, 24%; (c) o-xylene, reflux, 24 h, 99%; (d) FeCl3, CH2Cl2,
25 °C, 30 min, 53%.
Scheme 3. Synthesis of Arrowlike PAHs 9 and 9aa
a (a) phenylacetylene, Pd(PPh3)4, CuI, piperidine, 25 °C, 24 h, 77%; (b) Pd(PPh3)4, toluene, K2CO3, EtOH, H2O, reflux, 24 h, 99%; (c)
tetraphenylcyclopentadienone, diphenyl ether, reflux, 16 h, 77%; (d) Cu(OSO2CF3)2, AlCl3, CS2, 25 °C, 24 h, 75%.
hydrogenation of 26 with copper(II)trifluoromethanesulfonate/
aluminum(III) chloride and 26a with iron(III) chloride yielded
the desired PAHs 9 and 9a, respectively, as a brownish orange
powder (9, 75%; 9a, 73%). The four dodecyl chains of 9a
provide sufficient solubility for characterization so that the
proposed structure could be proven unambiguously. A 1H NMR
spectrum was recorded at 140 °C. As expected, due to lack of
symmetry, the spectrum is complex and difficult to interpret.
Strong π-π-interactions between single molecules favor ag-
gregation leading to broad resonance signals in the NMR
spectrum and disallow complete assignment of all signals. Mass
spectrometry and elemental analysis gave satisfying results and
were in full accordance with the theoretically expected values.
This example demonstrates again the problems of structure
elucidation of PAHs with insufficient solubility and process-
ability, where a molecule as small as 9a is on the verge of being
unprocessable. Whereas the unsubstituted analogue 9 is com-
pletely insoluble, the poor solubility of 9a allows purification
by column chromatography.
A comparison of the proton NMR shifts of the structurally
related compounds 7a, 8a, and 9a reveals interesting informa-
tion. The observed chemical shifts result from a complex
interplay of ring size, perimeter type, and aggregation. A
complete assignment of all signals was achieved by a combina-
tion of 1D NOE difference and H,H COSY measurements. As
expected from the deshielding effects induced by stronger ring
current, protons inside a bay (e.g., H1, Scheme 2) absorb at lower
field than those offside a bay (H2). This becomes clear when
comparing the shifts for H1 and H2 in 7a and 8a, respectively
(7a: H1, δ ) 8.97 ppm; H2, δ ) 7.64 ppm. 8a: H1, δ ) 8.40
ppm; H2, δ ) 7.42 ppm). A comparison between the two slightly
different bay types in 7a and 8a (8a contains a propyl group

Synthesis of Large Polycyclic Aromatic Hydrocarbons
J. Am. Chem. Soc., Vol. 122, No. 32, 2000 7711
Scheme 4. Synthesis of PAH 10a
a Conditions: (a) phenylboronic acid, Pd(PPh3)4, toluene, K2CO3, EtOH, H2O, reflux, 24 h, 91%; (b) NBS, CCl4, reflux, 18 h, 94%; (c) Fe(CO)5,
NaOH, PTC, CH2Cl2, H2O, reflux, 18 h, 31%; (d) benzil, nBu4NOH, 1,4-dioxane, reflux, 1 h, 47%; (e) diarylacetylene, diphenyl ether, reflux, 16
h, 95%; (f) Cu(OSO2CF3)2, AlCl3, CS2, 25 °C, 24 h, 87%.
where 7a bears a proton, H7) clearly demonstrates that both
ring current-induced deshielding and van der Waals shielding
effects influence chemical shifts. However, both resonances for
H1 and H2 appear at lower field in 7a whereas the strongest
ring current-induced deshielding is seen for the cove-type proton
H7 in 7a. Surprisingly, the analogous proton in 9a (Scheme 3)
resonates at significantly higher field. However, the broad
signals in the proton NMR spectrum of 9a suggest that ring
protons could be placed in the shielding region of a neighboring
disk-type π-system due to aggregation effects and would,
therefore, lead to an absorption at higher field.
At this point it should be noted that we have been able to
perform a detailed NMR analysis of the parent compound 7
since it had been sufficiently soluble in tetrachloroethane at 80
°C. Also, we could subject 7 to X-ray crystal structure analysis.18
It should be mentioned that 7 is planar within the limit of
accuracy, which is important since one might have anticipated
that a steric interaction of protons in the cove (H1, H7) might
cause a bending of the π-system and would also influence
chemical shifts.
Extending the π-system in only one direction by adding two
additional phenyl rings to 9 leads to the “cove”-type PAH 10
(Scheme 4). 3,5-Diphenyltoluene (28) was prepared by Suzuki
coupling of 3,5-dibromotoluene (27) with phenylboronic acid
in 91% yield. NBS bromination of 28 afforded the benzyl
bromide derivative 29, which was converted into bis(3,5-
diphenylbenzyl) ketone (30) under the use of iron pentacarbonyl.
Knoevenagel condensation of 30 with benzil gave cyclopenta-
dienone 31, which was then subjected to Diels-Alder cycload-
dition with diphenylacetylene to yield the oligophenylene 32
(95%). Oxidative cyclodehydrogenation under conditions men-
tioned above resulted in the PAH 10 as a brown powder (87%).
An alternative route leading to 10 will be published elsewhere.10
The synthesis of the starlike PAH 6 with a “cove”-type
periphery required an unsymmetrically substituted diketone,
which was synthesized via Hagihara coupling of 3-bromobi-
phenyl (33) with phenylacetylene and subsequent oxidation of
the resulting acetylene 34 to the benzil derivative 35 (Scheme
5). Condensation to the cyclopentadienone 36 and subsequent
Diels-Alder addition with dienophile 34 afforded an inseparable
mixture of the regioisomers 37a and 37b in 95% yield.
Nevertheless, cyclodehydrogenation of the isomers resulted in
the PAH 6 because oxidative formation of 12 carbon-carbon
bonds led to the same target molecule in both cases.
The next higher homologue of HBC is the C114 compound
5. The intended synthesis involves three steps starting from the
brominated o-terphenyl 38 (Scheme 6):19 Pd(0)-catalyzed
coupling to the diarylacetylene 39 (78%) was followed by
trimerization with dicobaltoctacarbonyl, which afforded the
precursor 40. Unexpectedly, subsequent cyclodehydrogenation
afforded not only the desired PAH 5 but also species of slightly
higher molecular weight, as will be discussed later.
A brief discussion of the physical properties of the PAHs 5,
6, 9, and 10 clearly points out the difficulties in investigating
the chemistry and proving the structure of such extended
aromatic systems. All four compounds are completely insoluble;
purification was therefore limited to extensive washing and
extraction, and structure elucidation was restricted to mass
spectrometry, UV spectroscopy, and elemental analysis. UV
spectra could only be recorded by smearing the sample onto a
quartz substrate, as will be discussed later. Due to their poor
processability, unsubstituted PAHs more extended than the
perylene derivative 7 exceed the limits of conventional tech-
niques of characterization, which requires the development of
new sophisticated methods of structure proof. The most powerful
tool for identifying extended PAHs has turned out to be LD-
TOF or MALDI-TOF mass spectrometry. PAHs 6, 9, and 10
have been investigated by LD-TOF mass spectrometry and the
obtained highly resolved spectra gave unambiguous evidence
for a complete cyclization since the formation of each chemical
bond between adjacent phenyl rings reduces the molecular
weight by two mass units.13a The observed isotopic distribution
pattern was in all cases in good correspondence to the theoreti-
cally expected distribution (Figure 1).
However, LD-TOF mass spectrometry also suffers from a
severe problem: Probably due to their dominating π-π-
interactions, more extended PAHs require high laser power for
desorption of the analyte molecules, which easily leads to
unfavorable side reactions such as fragmentation or hydrogen
(18) Ku¨bel, C.; Eckhardt, K.; Enkelmann, V.; Wegner, G.; Mu¨llen, K.
J. Mater. Chem. 2000, 10, 879.
(19) Sato, T.; Shimada, S.; Hata, K. Bull. Chem. Soc. Jpn. 1969, 42, 6.

7712 J. Am. Chem. Soc., Vol. 122, No. 32, 2000
Scheme 5. Synthesis of Star-like PAH 6a
Do¨tz et al.
a Conditions: (a) phenylacetylene, Pd(PPh3)4, CuI, piperidine, 25 °C, 24 h, 94%; (b) I2, DMSO, reflux, 18 h, 81%; (c) 30, nBu4NOH, 1,4-
dioxane, reflux, 15 min, 59%; (d) 34, diphenyl ether, reflux, 2 h, 68%; (e) Cu(OSO2CF3)2, AlCl3, CS2, 25 °C, 24 h, 89%.
Scheme 6. Synthesis of PAH 5a
a Conditions: (a) Pd(PPh3)4, toluene, 120 °C, 72 h, 78%; (b)
Co2(CO)8, 1,4-dioxane, 100 °C, 14 h, 36%; (c) Cu(OSO2CF3)2, AlCl3,
CS2, 25 °C, 24 h, 89%.
elimination. As a consequence, the obtained spectra get more
complex and tedious to interpret. These difficulties can be clearly
demonstrated when large PAHs are investigated with LD
techniques.13 The results of the MALDI-TOF measurements will
be discussed later. LD characterization of the PAH 5 containing
114 carbons revealed yet a further unforeseen problem: Contrary
to PAHs 6, 9, and 10, the LD spectrum shows not only the
desired molecular peak at m/z ) 1398, but also two other peaks
Figure 1. LD-TOF spectra of PAHs 6, 9, and 10. Samples were
of comparable intensity which are four and six mass units higher.
suspended in tetrachloroethane and ultrasonificated to prevent formation
These two additional peaks cannot be explained satisfactorily
of aggregates.
by partially cyclized or chlorinated species because extension
of reaction time only led to increased chlorination and the
observed peaks remained unchanged, which suggests that they
do not originate from incomplete cyclization. From a thermo-
dynamic point of view, incomplete cyclization would also be
unfavorable because only the formation of a fully dehydroge-
nated system gains a major increase of resonance energy. On

Synthesis of Large Polycyclic Aromatic Hydrocarbons
J. Am. Chem. Soc., Vol. 122, No. 32, 2000 7713
Scheme 7. Rearrangement and Formation of the PAHs 42
and 44
o-terphenyl unit. However, such a hypothesis is not in ac-
cordance with Allen and Pingert’s results. In the case of the
starlike PAH 6, rearrangement of a m-terphenyl unit into an
o-terphenyl unit is possible in general. On the other hand, the
cyclodehydrogenation was completed in 24 h at room temper-
ature, which makes such a phenyl shift less probable. Therefore,
the possibility of rearrangements under our reaction conditions
seems to be restricted to oligophenylenes that bear o-terphenyl
units.
The assumed rotation in the precursor molecule 41 around a
biphenyl bond is not sterically hindered. Quantification of the
relative amounts of the target molecule 5 and the two rearranged
species is rather difficult, since desorption and ionization
probabilities strongly depend on the molecules’ structure.
However, close similarity of the molecular structure and LD
peak intensities suggest that all three species are formed in
comparable amounts, which means that our cyclodehydroge-
nation route does not selectively lead to the desired PAH 5.
To prove this hypothesis and to offer an additional approach
to an extended PAH containing 114 carbons, the synthesis of a
polyalkylated derivative of 5 containing 12 alkoxy chains is
now underway. Since the cyclization product is expected to
provide sufficient solubility for detailed characterization, insight
should be provided into the cyclization mechanism of large
oligophenylenes that bear o-terphenyl units.
The above-mentioned LD technique for the characterization
of large, insoluble PAHs is supplemented by a complementary
method, MALDI-TOF spectrometry, which induces desorption
of the sample more smoothly by distributing the analyte
molecules in an appropriate matrix.13 PAHs 5, 6, 9, and 10 were
also investigated by MALDI-TOF spectrometry and found to
contain traces of partially cyclized as well as monochlorinated
compounds. Quantification of these impurities is still a challenge
since desorption and ionization probabilities of the impurities
and the target molecule are usually different. Nevertheless,
considering both techniques, LD- and MALDI-TOF spec-
trometry, the amount of the organic side products can be
estimated to be less than 2% in an even more extended PAH
containing 222 carbon atoms.13b
the other hand, chlorination would result in peaks corresponding
with molecular weights several mass units higher. We therefore
tentatively attribute these two peaks to the PAHs 42 and 44
which are formed by rearrangement of the precursor 40 and
subsequent cyclization (Scheme 7).
A prerequisite to the formation of the oligophenylenes 41
and 43 is a 1,2-phenyl shift and a rotation around a biphenyl
bond. We suggest that the 1,2-phenyl shift is catalyzed by the
strong Lewis acid aluminum(III) chloride, a reaction that has
precedence in the observations of Allen and Pingert in the case
of o-terphenyl.20 Rearrangement at low temperature led to m-
and p-terphenyl, whereas at high temperature, triphenylene was
yielded. However, the rearrangement of o-terphenyl to p-
terphenyl via the meta derivative occurred under relatively
drastic conditions, i.e., refluxing benzene and extended reaction
times. Complete conversion of the ortho to a mixture of meta
and para isomers was observed after 3 days and after 11 days
only p-terphenyl was found. Therefore, it can be concluded that
rearrangement of the meta to the para derivative requires several
days and elevated temperatures even for a small aromatic
molecule if a stepwise mechanism is assumed. The precursor
of the extended PAH 5, the oligophenylene compound 40, also
contains o-terphenyl units, which makes the proposed 1,2-phenyl
shift most probable.13a Since the other extended, unsubstituted
PAHs 6, 9, and 10 show only the desired molecular peak in the
LD spectrum, hypothetical rearrangements, i.e., 1,2-phenyl
shifts, would have to result in species with exactly the same
molecular weight to be indistinguishable by mass spectrometry.
For PAHs 9 and 10, this would require a phenyl shift in the
opposite direction; i.e., a m-terphenyl unit rearranges into an
Mass spectrometry can quantify organic side products in the
final cyclization reaction, whereas inorganic impurities such as
aluminum, copper, and chlorine were found to be less than 1%
according to energy-dispersive X-ray spectroscopy (EDX) and
electron energy loss spectroscopy (EELS).21
All the results obtained so far by mass spectrometry provide
reliable proof for the structure of extended PAHs. Since our
interest focuses not only on the synthesis and characterization
of large PAHs but also on their optical properties, UV/visible
spectroscopy remains an important method to deliver informa-
tion in this field. However, nearly all of the large PAHs
investigated in this study show extremely low solubility,
insufficient to record their optical absorption spectra in solution.
Even high-boiling solvents as xylene could not break up
aggregation. For example, PAHs 6, 9, and 10 were refluxed in
o-xylene for several days and no UV/visible spectra were
obtained from these solutions.22 Thus, the only possibility to
determine these properties for large unsubstituted PAHs is
measurement in thin films (solid-state characterization). Thin
films may be prepared mechanically by simply smearing
samples on a quartz substrate. Model studies were first
conducted to ensure the reliability of the solid-state method;
(21) Ku¨bel, C. Ph.D. Thesis, Johannes Gutenberg-University, Mainz,
1998.
(22) Brand, J. D.; Ph.D. Thesis, Johannes Gutenberg-University, Mainz,
1999.
(20) Allen, C. F. H.; Pingert, F. P. J. Am. Chem. Soc. 1942, 64, 1365.

7714 J. Am. Chem. Soc., Vol. 122, No. 32, 2000
Do¨tz et al.
Figure 3. UV/visible spectra of thin films (quartz substrate) of PAHs
6, 9, and 10: Note the bathochromic shift of the â-bands, a consequence
of extending the π-system of PAHs. Arbitrary units were chosen for
the ordinate because no extinction coefficients could be determined
for the thin film measurements.
symmetry and size considerations. The synthetic route follows
a two-step protocol involving the buildup of appropriate
precursor molecules and subsequent cyclodehydrogenation to
planar all-benzenoid hydrocarbons. In principle, this route can
be extended to even larger PAHs than presented here provided
that planarization is still sterically possible. However, nonalkyl-
substituted PAHs suffer from meager solubility so that char-
acterization and purification still remain a challenge. Therefore,
structure elucidation basically focuses on sophisticated tech-
niques of laser desorption time-of-flight mass spectrometry as
well as UV/visible spectroscopy. Although LD-TOF mass
spectrometry can definitely prove the success of the final
cyclodehydrogenation, the question of rearrangements concern-
ing the most extended PAH of the presented series, 5, still has
to be elucidated further. Nevertheless, they seem to be restricted
to oligophenylenes with o-terphenyl units; the other members
of the PAH family reported herein could be synthesized in
moderate to high yields. The UV spectra recorded for thin films
consistently exhibit a significant bathochromic shift of the
â-bands, and current research on the optical properties of even
more extended PAHs is still going on in our laboratories. These
investigations should be the key to increase our knowledge on
large aromatic compounds, which are considered to be the still
missing link between benzene and macroscopic graphite.
Figure 2. UV/visible spectra of PAHs 8a (a) and 9a (b): solution
and thin-film (quartz substrate) spectra displaying the same optical
properties. Arbitrary units were chosen for the ordinate because no
extinction coefficients could be determined for the thin-film measure-
ments. For solution spectra, extinction coefficients are given in
parentheses.
i.e., smaller analogues (e.g., 7a, 8a, 9a) with solubilizing
substituents were characterized both in solution and as thin film
and good correlation was seen between the two methods.
We have observed similar peaks in the thin-film UV-visible
spectra, although the optical absorption bands in the solid state
are broad and weakly red shifted (2-3 nm), compared to the
corresponding solution spectra of the alkyl-substituted analogue
compounds (Figure 2).
Experimental Section
The UV/visible spectra of 7a and 8a clearly show three types
(groups) of bands (R, â, p) which are typical of aromatic
hydrocarbons, in solution as well as in film.2a The spectra of
8a are given as an example in Figure 2a. The detection of the
R-band (510 nm) of 9 is difficult because of the extremely low
intensity of this band, but both spectra (solution and film)
distinctly show the â-bands (∼385 nm) and p-bands (∼460 nm).
Having established its reliability, we applied this method to
the larger hydrocarbons. With extending size of the π-system,
the spectra are progressively red shifted and this trend is most
easily observed in the stronger absorption bands, the â-bands.
More specifically, this absorption peak is steadily shifted from
387 nm for 9 to 440 nm for 6 as the size of the chromophore
increases as shown in Figure 3. Similar investigations of the
optical behavior of other PAHs and a detailed discussion of
the obtained results will be published elsewhere.14
1,2,3,4-Tetrakis(4-dodecyl)phenyl-5,6-dipropylbenzene (20). 4-Oc-
tyne (19; 0.95 g, 8.62 mmol) and 2,3,4,5-tetrakis(4-dodecylphenyl)-
cyclopentadienone (16; 2.02 g, 1.91 mmol) were dissolved in diphenyl
ether (14 mL) under an argon atmosphere and the resultant mixture
was refluxed for 16 h. Solvent was removed in vacuo, and the obtained
residue was purified by column chromatography (petrolether/dichlo-
romethane) to give a yellowish oil (0.96 g, 44%): 1H NMR (250 MHz,
C2D2Cl4) δ 6.86 (d, J ) 8.2 Hz, 4H), 6.81 (d, J ) 8.2 Hz, 4H), 6.50
(d, J ) 8.2 Hz, 4H), 6.44 (d, J ) 8.2 Hz, 4H), 2.40 (t, J ) 7.3 Hz, 8H,
RCH2,dodecyl), 2.18 (t, J ) 7.4 Hz, 4H, RCH2,propyl), 1.59-0.89 (m, 84H,
H
alkyl), 0.80 (t, J ) 6.8 Hz, 12 H, CH3,dodecyl), 0.65 (t, J ) 7.3 Hz, 3 H,
CH3,propyl); 13C NMR (125 MHz, C2D2Cl4, 33 °C) δ 141.06, 139.83,
139.12, 139.06, 138.88, 138.63, 138.09 (all Caromat), 131.49, 130.79,
127.18, 126.35 (all CaromatH), 36.03, 35.78, 35.58, 33.45, 32.26, 31.65,
31.55, 30.07, 30.02, 29.85, 29.72, 29.28, 29.14, 25.03, 23.05 (all Calkyl),
15.25, 14.55 (all CH3); MS (FD, 8 kV) m/z (%) 1139.5 (100) [M+]
(calcd for C84H130, 1140.0). Anal. Calcd for C84H130: C, 88.51; H, 11.49.
Found: C, 87.87; H, 11.38.
1,2,3,4,5-Pentakis(4-dodecyl)phenylbenzene (22). 4-(Dodecyl)-
phenylacetylene (21; 1.00 g, 3.70 mmol) and 16 (4.31 g, 4.07 mmol)
were dissolved in o-xylene (20 mL) under an argon atmosphere and
Conclusions and Outlook
In this paper, we have introduced a new series of PAHs with
different perimeter types, which have been designed based on

Synthesis of Large Polycyclic Aromatic Hydrocarbons
J. Am. Chem. Soc., Vol. 122, No. 32, 2000 7715
refluxed for 16 h. Solvent was removed in vacuo, and the obtained
residue was purified by column chromatography (petroleum ether/
dichloromethane) to give a yellowish oil which crystallized upon
phenylphosphine) (1.40 g, 1.21 mmol), and CuI (442.1 mg, 2.32 mmol)
in piperidine (300 mL), phenylacetylene (5.21 mL, 4.85 g, 47.44 mmol)
was added. The resulting mixture was stirred at room temperature for
24 h under an argon atmosphere. The reaction mixture was poured into
NH4Cl solution and extracted with dichloromethane. The organic layer
was washed with NH4Cl solution and water and then dried with MgSO4.
After the solvent was removed in vacuo, the residue was purified by
column chromatography (petroleum ether) to afford 24 (12.32 g, 77%)
as colorless crystals: mp 107.0-107.9 °C; 1H NMR (300 MHz, CDCl3)
δ 7.61 (t, J ) 1.8 Hz, 1H), 7.59 (d, J ) 1.8 Hz, 2H), 7.53-7.46 (m,
2H), 7.38-7.32 (m, 3H); 13C NMR (75 MHz, CDCl3) δ 133.89, 132.99,
131.74, 128.96, 128.46, 126.76, 122.62, 122.27, 91.96, 86.38; MS (FD,
8 kV) m/z (%) 336.1 (100) [M+] (calcd for C14H8Br2, 335.90). Anal.
Calcd for C14H8Br2: C, 50.04; H, 2.40; Br, 47.56. Found: C, 49.84;
H, 3.15.
1
standing (4.77 g, 99%): mp 29 °C; H NMR (250 MHz, THF-d8) δ
7.38 (s, 1H, Hcove), 6.93 (d, J ) 8.2 Hz, 4H, Hcove.), 6.85 (d, J ) 7.9
Hz, 4H, Hcove.), 6.64-6.59 (m, 8H), 6.56-6.52 (m, 8H), 2.48-2.36
(m, 4H, RCH2), 2.36-2.22 (m, 6H, RCH2), 1.52-1.27 (m, 10H, âCH2),
1.26-0.97 (m, 90H, Halkyl), 0.85-0.73 (m, 15H, CH3); 13C NMR (125
MHz, CD2Cl2, 33 °C) δ 142.88, 141.69, 141.40, 140.81, 140.45, 140.17,
140.09, 138.86, 138.53 (all Caromat), 132.25, 132.19, 131.92, 130.62,
128.35, 127.69, 127.34 (all CaromatH), 36.33, 36.18, 32.81, 32.25, 32.19,
32.15, 30.61, 30.56, 30.52, 30.41, 30.38, 30.25, 30.22, 30.15, 29.74,
23.55 (all Calkyl), 14.73 (CH3); MS (FD, 8 kV) m/z (%) 1299.4 (100)
[M+] (calcd for C96H146, 1300.2). Anal. Calcd for C96H146: C, 88.68;
H, 11.32. Found: C, 88.11; H, 11.09.
PAH 7a. (Since the systematic names according to the IUPAC
nomenclature do not contribute to the clarity of the molecular structure
as can easily be seen for the smallest and the largest PAH presented
herein, 8a and 5, respectively, we decided not to give the full IUPAC
names, but just the numbers of compounds as shown in the schemes.)
PAH 8a: 3,6,9,12-Tetra(dodecyl)-15,16-dipropyl(tribenzo[e;g,h,i;k])-
perylene.
PAH 5: Bisbenzo[5′′,6′′]naphthaceno[2′′,1′′,12′′,11′′,10′′,9′′:5′,6′,7′,8′,9′]-
heptaceno[1′,18′,17′,16′,15′,14′,13′:3,4,5,6,7,8,9,10]hexaceno[2,1,16,
15,14,13,12,11-defghijklmno:2′,1′,16′,15′,14′,13′,12′,11′-stuVwxyza1b1c1d1]-
heptacene
3,5-Diphenyldiphenylacetylene (25). To a deoxygenated solution
of phenylboronic acid (8.78 g, 71.99 mmol) and K2CO3 (41.5 g, 300.3
mmol) in water (150 mL) and ethanol (75 mL), a deoxygenated solution
of 24 (6.00 g, 17.85 mmol) in toluene (300 mL) and palladium(0)-
tetrakis(triphenylphosphine) (2.03 mg, 1.756 mmol) was added. The
resulting mixture was heated at reflux for 24 h under an argon
atmosphere. The reaction mixture was poured into water and extracted
with toluene. The organic layer was washed with water and dried with
MgSO4. After the solvent was removed in vacuo, the residue was
purified by column chromatography (dichloromethane/petroleum ether)
to afford 25 (5.84 g, 99%) as colorless crystals: mp 127.0-128.1 °C;
1H NMR (300 MHz, CDCl3) δ 7.77 (t, J ) 1.7 Hz, 1H), 7.75 (d, J )
1.7 Hz, 2H), 7.66 (d, J ) 6.9 Hz, 4H), 7.58 (dd, J ) 7.1 Hz, 2.5 Hz,
2H), 7.47 (dd, J ) 7.4 Hz, 6.9 Hz, 4H), 7.42-7.34 (m, 5H); 13C NMR
(75 MHz, CDCl3) δ 142.00, 140.40, 131.69, 129.15, 128.86, 128.39,
127.72, 127.22, 126.13, 124.19, 123.20, 89.60, 89.36; MS (FD, 8 kV)
m/z (%) 330.3 (100) [M+] (calcd for C26H18, 330.43). Anal. Calcd for
C26H18: C, 94.51; H, 5.49. Found: C, 95.14; H, 5.03.
22 (1.03 g, 0.80 mmol) was dissolved in dichloromethane (200 mL)
in a Schlenk flask under an argon atmosphere. Throughout the whole
reaction, a constant stream of Ar was bubbled through the mixture to
remove HCl formed in situ. A solution of iron(III) chloride (1.64 g,
10.11 mmol) in nitromethane was added dropwise, and the mixture
stirred for 30 min at room temperature. Methanol (100 mL) was added,
and a beige solid precipitated which was filtered, dried, and purified
by column chromatography (petrolether/dichloromethane). Recrystal-
lization from n-heptane yielded an orange solid (545 mg, 53%): NOE
difference 1H NMR; H,H COSY 1H NMR (500 MHz,C2D2Cl4) δ 10.11
(s, 1H, H7), 8.97 (d, J ) 8.3 Hz, 2H, H1), 8.83 (s, 2H, H6), 8.80 (s, 2H,
H5), 8.70 (s, 2H, H4), 8.59 (s, 2H, H3), 7.58 (d, J ) 8.3 Hz, 2H, H2),
3.15-3.0 (m, 6H, RCH2), 3.0-2.85 (m, 4H, RCH2), 2.0-1.70 (m, 10H,
âCH2), 1.60-0.95 (m, 90H, Halkyl), 0.85-0.65 (m, 15H, CH3); 13C NMR
(125 MHz, CS2/CDCl3) δ 141.17, 140.43, 136.34, 131.53, 130.32,
129.61, 129.51 (all Caromat), 129.31 (CaromatH), 128.08 (Caromat), 126.41
(CaromatH), 123.46 (CaromatH), 123.15 (Caromat), 122.49 (Caromat), 122.01
(CaromatH), 121.53 (CaromatH), 37.52, 36.74, 35.07, 32.61, 32.29, 31.98,
30.10, 30.04, 29.74, 25.91, 23.12 (all Calkyl), 14.81, 14.41 (all CH3);
MS (LD-TOF) m/z (%) 1292.1 (100) [M+] (calcd for C96H138, 1292.2).
Anal. Calcd for C96H138: C, 89.24; H, 10.76. Found: C, 88.80; H, 10.59.
PAH 8a. 20 (768 mg, 0.67 mmol) was dissolved in dichloromethane
(30 mL) in a Schlenk flask under an argon atmosphere. Throughout
the whole reaction, a constant stream of argon was bubbled through
the mixture to remove HCl formed in situ. A solution of iron(III)
chloride (982 mg, 6.10 mmol) in nitromethane was added dropwise,
and the mixture stirred for 30 min at room temperature. Methanol (100
mL) was added, and a yellow solid precipitated which was purified by
column chromatography (petroleum ether/dichloromethane). Recrys-
tallization from n-heptane yielded a yellow solid (184 mg, 24%): NOE
(3,5-Diphenylphenyl)pentaphenylbenzene (26). A mixture of 25
(1.00 g, 3.03 mmol) and tetraphenylcyclopentadienone (1.20 g, 3.13
mmol) in diphenyl ether (10 mL) was heated at reflux for 16 h under
an argon atmosphere. After cooling to room temperature, ethanol (100
mL) was added to the reaction mixture. The precipitated crystals were
collected by filtration and purified by recrystallization from dichlo-
romethane/ethanol to afford 26 (1.60 g, 77%) as colorless crystals: mp
1
>300 °C; H NMR (500 MHz, CDCl3) δ 7.37-7.19 (m, 11H), 7.108
(d, J ) 1.8 Hz, 2H), 7.01-6.86 (m, 25H); 13C NMR (125 MHz, CDCl3)
δ 140.82, 140.63, 140.61, 140.51, 140.43, 139.98, 139.90, 139.80,
131.63, 131.47, 131.44, 129.91, 128.43, 127.05, 126.93, 126.80, 126.60,
125.49, 125.24, 123.04; MS (FD, 8 kV) m/z (%) 686.8 (100) [M+]
(calcd for C54H38, 686.30). Anal. Calcd for C54H38: C, 94.42; H, 5.58.
Found: C, 94.83; H, 4.84.
PAH 9. (Due to incomplete combustion, elemental analyses for
carbon-rich compounds often yield too low carbon contents which can
be seen for the PAHs 5, 6, 9, and 10.)
To a mixture of copper(II)-trifluoromethanesulfonate (2.53 g, 6.93
mmol) and aluminum(III) chloride (981.5 mg, 7.361 mmol) in carbon
disulfide (50 mL), 26 (100.0 mg, 0.15 mmol) was added. After stirring
at room temperature for 1 h under an argon atmosphere, the mixture
was poured into 10% HCl solution. The precipitated crystals were
collected by filtration, washed with 10% NH4OH solution, water, carbon
disulfide, and dichloromethane, and dried in vacuo to afford 9 (73.2
mg, 75%) as an orange brown powder: mp >300 °C; MS (MALDI-
TOF) m/z (%) 670.7 (100) [M+] (calcd for C54H22, 607.17). Anal. Calcd
for C54H22: C, 96.69; H, 3.31. Found: C, 83.51; H, 3.26.
4-Dodecylphenylboronic Acid. To a solution of 4-bromododecyl-
benzene (10.00 g, 30.74 mmol) in dry tetrahydrofuran (200 mL) at
-78 °C, an n-butyllithium solution (1.6 M, 57.5 mL, 92.0 mmol) in
hexane was added dropwise. After stirring at the same temperature for
1 h, trimethoxyborane (10.5 mL, 9.61 g, 92.46 mmol) was added to
the mixture dropwise. After removing the dry ice acetone bath, the
mixture was stirred for another 16 h. Then the mixture was poured
into 2 N HCl (300 mL) and extracted with dichloromethane. The organic
layer was washed with water, dried with Na2SO4, and concentrated
under reduced pressure to afford the 4-dodecylphenylboronic acid as a
pale yellow oil which was used without further purification.
1
difference H NMR (500 MHz, C2D2Cl4) δ 8.75 (s, 2H, H5), 8.61 (s,
2H, H4), 8.46 (d, J ) 1.2 Hz, 2H, H3), 8.40 (d, J ) 8.3 Hz, 2H, H1),
7.42 (dd, J ) 8.3 Hz, J ) 1.2 Hz, 2H, H2), 3.66-3.55 (m, 4H,
RCH2,propyl), 3.09 (t, J ) 7.7 Hz, 4H, RCH2,R), 2.87 (t, J ) 8.0 Hz, 4H,
RCH2,R′), 2.10-1.95 (m, 4H, âCH2), 1.95-1.85 (m, 4H, âCH2), 1.85-
1.75 (m, 4H, âCH2), 1.65-1.25 (m, 82H, Halkyl), 1.05-0.87 (m, 18H,
CH3); 13C NMR (125 MHz, CDCl3) δ 141.75, 141.03, 136.79, 131.31,
130.30, 129.43, 128.05, 126.84, 123.52, 123.03, 122.30, 122.13, 121.76
(all Caromat), 99.82, 37.38 (Calkyl), 36.63, 35.15, 32.73, 32.25, 32.00,
30.00, 29.96, 29.93, 29.70, 25.98, 23.05 (all Calkyl), 15.06 (CH3), 14.57
(CH3); MS (FD, 8 kV) m/z (%) 1134.3 (100) [M+] (calcd for C84H124
,
1133.9). Anal. Calcd for C84H124: C, 88.98; H, 11.02. Found: C, 88.20;
H, 11.04.
3,5-Dibromodiphenylacetylene (24). To a solution of 1,3,5-tribro-
mobenzene (23; 30.40 g, 96.57 mmol), palladium(0)-tetrakis(tri-

7716 J. Am. Chem. Soc., Vol. 122, No. 32, 2000
Do¨tz et al.
3,5-Di(4-dodecylphenyl)diphenylacetylene (25a). To a deoxygen-
ated solution of 4-dodecylphenylboronic acid (12.36 g, 42.59 mmol)
and K2CO3 (27.6 g, 199.7 mmol) in water (100 mL) and ethanol (50
mL), a deoxygenated solution of 24 (4.00 g, 11.90 mmol) in toluene
(200 mL) and palladium(0)-tetrakis(triphenylphosphine) (688.8 mg,
0.60 mmol) was added. The resulting mixture was heated at reflux for
24 h under an argon atmosphere. The reaction mixture was poured into
water and extracted with toluene. The organic layer was washed with
water and dried with MgSO4. After the solvent was removed in vacuo,
the residue was purified by column chromatography (petrolether) to
3,5-Diphenylbenzyl Bromide (29). A mixture of 28 (8.80 g, 36.02
mmol) and NBS (7.05 g, 39.62 mmol) in carbon tetrachloride (300
mL) was heated at reflux for 18 h. After cooling to room temperature,
precipitated crystals were removed by filtration. The filtrate was
concentrated under reduced pressure. The residue was purified by
recrystallization from ethanol to afford 29 (10.91 g, 94%) as colorless
1
needles: mp 91.6-93.1 °C; H NMR (300 MHz, CDCl3) δ 7.72 (t, J
) 1.5 Hz, 1H), 7.63 (d, J ) 6.9 Hz, 4H), 7.59 (d, J ) 1.5 Hz, 2H),
7.60 (dd, J ) 7.3 Hz, 6.9 Hz, 4H), 7.36 (t, J ) 7.3 Hz, 2H), 4.61 (s,
2H); 13C NMR (75 MHz, CDCl3) δ 142.45, 140.55, 138.75, 128.85,
127.69, 127.25, 126.75, 126.26, 33.41; MS (FD, 8 kV) m/z (%) 321.1
(100) [M+] (calcd for C19H15Br, 322.04). Anal. Calcd for C19H15Br:
C, 70.60; H, 4.68; Br, 24.72. Found: C, 69.74; H, 4.85.
1
afford 25a (1.77 g, 22%) as colorless crystals: mp 42.7-44.2 °C; H
NMR (300 MHz, CDCl3) δ 7.74 (t, J ) 1.7 Hz, 1H), 7.70 (d, J ) 1.7
Hz, 2H), 7.59-7.54 (m, 6H), 7.38-7.32 (m, 3H), 7.26 (d, J ) 8.0 Hz,
4H), 2.65 (t, J ) 7.6 Hz, 4H), 1.65 (p, J ) 7.6 Hz, 4H), 1.39-1.20
(m, 36H), 0.87 (t, J ) 6.9 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ
142.59, 141.87, 137.75, 131.68, 128.90, 128.71, 128.35, 128.27, 127.02,
125.82, 124.01, 123.30, 89.58, 89.35, 35.64, 31.92, 31.46, 29.67, 29.64,
29.60, 29.53, 29.35, 22.68, 14.09; MS (FD, 8 kV) m/z (%) 666.7 (100)
[M+] (calcd for C50H66, 666.52). Anal. Calcd for C50H66: C, 90.03; H,
9.97. Found: C, 90.18; H, 9.82.
1,3-Bis(3,5-diphenylphenyl)acetone (30). To a mixture of 29 (11.80
g, 36.51 mmol), NaOH (8.98 g, 224.57 mmol), and benzyltriethyl-
ammonium chloride (318.5 mg, 1.40 mmol) in dichloromethane (120
mL) and water (6 mL), iron pentacarbonyl (3.6 mL, 5.36 g, 27.38 mmol)
was added. The resulting mixture was refluxed for 18 h under an argon
atmosphere. The reaction mixture was then poured into 6 N HCl
solution and extracted with dichloromethane. The organic layer was
washed with water, dried with MgSO4, and concentrated in vacuo. The
residue was purified by column chromatography (dichloromethane/
petroleum ether) to afford 30 (2.88 g, 31%) as colorless crystals: mp
213.8-215.5 °C; 1H NMR (500 MHz, CDCl3) δ 7.64 (s, 2H), 7.54 (d,
J ) 7.9 Hz, 8H), 7.40 (dd, J ) 7.9 Hz, 7.6 Hz, 8H), 7.34 (t, J ) 7.6
Hz, 4H), 7.337 (s, 4H), 3.90 (s, 4H); 13C NMR (125 MHz, CDCl3) δ
205.26, 142.36, 140.82, 134.97, 128.77, 127.52, 127.27, 125.02, 49.54;
MS (FD, 8 kV) m/z (%) 514.5 (100) [M+] (calcd for C39H30O, 514.23).
Anal. Calcd for C39H30O: C, 91.02; H, 5.88; O, 3.11. Found: C, 90.26;
H, 6.16.
3,5-Di(4-dodecylphenyl)-4′′,4′′′-didodecylhexaphenylbenzene (26a).
A mixture of 25a (1.01 g, 1.52 mmol) and 3,4-di(4-dodecylphenyl)-
2,5-diphenylcyclopentadienone (1.09 g, 1.51 mmol) in diphenyl ether
(10 mL) was refluxed for 18 h under an argon atmosphere. After cooling
to room temperature, ethanol (100 mL) was added to the reaction
mixture. The solvent was decanted, and the residual oil was purified
by column chromatography (petroleum ether) to afford 26a (1.89 g,
92%) as a pale yellow oil: 1H NMR (500 MHz, CDCl3) δ 7.25 (t, J )
1.5 Hz, 1H), 7.11 (d, J ) 8.2 Hz, 4H), 7.07 (d, J ) 8.2 Hz, 4H), 7.00
(d, J ) 1.5 Hz, 2H), 6.93-6.82 (m, 15H), 6.72-6.72 (m, 8H), 2.576
(t, J ) 7.4 Hz, 4H), 2.35 (t, J ) 7.4 Hz, 2H), 2.34 (t, J ) 7.4 Hz, 2H),
1.60 (p, J ) 7.4 Hz, 4H), 1.43-1.06 (m, 76H), 0.88 (t, J ) 6.9 Hz,
12H); 13C NMR (125 MHz, CDCl3) δ 141.71, 141.13, 141.07, 141.03,
140.92, 140.74, 140.70, 140.42, 140.16, 139.90, 139.65, 139.34, 139.32,
138.77, 137.94, 137.91, 131.72, 131.59, 131.33, 131.29, 129.56, 128.49,
126.85, 126.72, 126.67, 126.59, 126.50, 125.36, 125.26, 125.02, 122.63,
35.59, 35.32, 31.93, 31.52, 31.15, 29.73, 29.68, 29.64, 29.60, 29.53,
29.38, 29.36, 28.81, 22.69, 14.10; MS (FD, 8 kV) m/z (%) 1360.4 (100)
[M+] (calcd for C102H134, 1360.05). Anal. Calcd for C102H134: C, 90.07;
H, 9.93. Found: C, 90.95; H, 9.24.
PAH 9a. To a stirred solution of 26a (1.00 g, 0.74 mmol) in
dichloromethane (200 mL), a solution of iron(III) chloride (11.85 g,
730.51 mmol) in nitromethane (30 mL) was added dropwise. An argon
stream was bubbled through the mixture throughout the course of the
reaction. After stirring for another 30 min, the reaction was quenched
with methanol (60 mL). The resulting mixture was poured into water
and extracted with hot toluene. The extract was purified by column
chromatography (hot toluene/petroleum ether) to afford 9a (723.3 mg,
73%) as an orange powder: 1H NMR (500 MHz, CDCl2CDCl2, 140
°C) δ 9.03 (br, 1H), 8.21 (br, 14H), 7.54 (br, 3H), 3.14 (br, 8H), 2.16
(br, 8H), 1.89-1.36 (br m, 72H), 1.00 (br, 12H); MS (FD, 8 kV) m/z
(%) 1342.9 (100) [M+] (calcd for C102H118, 1343.92); MS (MALDI-
TOF) m/z (%) 1342.7 (100) [M+] (calcd for C102H118, 1343.92). Anal.
Calcd for C102H118: C, 91.15; H, 8.85. Found: C, 91.16; H, 8.78.
3,5-Diphenyltoluene (28). To a deoxygenated solution of phenyl-
boronic acid (19.51 g, 160.01 mmol) and K2CO3 (66.34 g, 480.01 mmol)
in water (240 mL) and ethanol (120 mL), a deoxygenated solution of
3,5-dibromotoluene (27; 10.00 g, 40.01 mmol) in toluene (500 mL)
and palladium(0)-tetrakis(triphenylphosphine) (4.62 g, 4.00 mmol) was
added. The resulting mixture was heated at reflux for 4 days under an
argon atmosphere. The reaction mixture was poured into water and
extracted with toluene. The organic layer was washed with water and
dried with MgSO4. After the solvent was removed in vacuo, the residue
was purified by recrystallization from ethanol to afford 28 (8.88 g,
91%) as colorless crystals: mp 131.4-131.9 °C; 1H NMR (300 MHz,
CDCl3) δ 7.65 (d, J ) 7.6 Hz, 4H), 7.62 (s, 1H), 7.46 (dd, J ) 7.6 Hz,
7.3 Hz, 4H), 7.41 (s, 2H), 7.36 (t, J ) 7.3 Hz, 2H), 2.50 (s, 3H); 13C
NMR (75 MHz, CDCl3) δ 141.80, 141.32, 138.75, 128.72, 127.28,
127.26, 126.96, 123.40, 21.58; MS (FD, 8 kV) m/z (%) 244.2 (100)
[M+] (calcd for C19H16, 244.13). Anal. Calcd for C19H16: C, 93.40; H,
6.60. Found: C, 93.51; H, 6.57.
2,5-(3,5-Diphenylphenyl)-3,4-diphenylcyclopentadienone (31). To
a refluxing solution of 30 (1.00 g, 1.95 mmol) and diphenyl diketone
(415.8 mg, 1.98 mmol) in 1,4-dioxane (2 mL), a tetrabutylammonium
hydroxide solution (0.8 M, 1.2 mL, 0.96 mmol) in methanol was added.
The resulting mixture was heated at reflux for 1 h under an argon
atmosphere. The reaction mixture was poured into water and extracted
with dichloromethane. The organic layer was washed with water, dried
with MgSO4, and concentrated under reduced pressure. The residue
was purified by column chromatography (dichloromethane/petroleum
ether) to afford 31 (634.5 mg, 47%) as purple crystals: mp 225.4-
1
227.9 °C; H NMR (300 MHz, CDCl3) δ 7.67 (t, J ) 1.8 Hz, 2H),
7.50 (d, J ) 1.8 Hz, 4H), 7.45 (d, J ) 8.0 Hz, 8H), 7.41-7.25 (m,
18H), and 7.09 (d, J ) 8.4 Hz, 4H); 13C NMR (75 MHz, CDCl3) δ
200.23, 155.18, 141.38, 140.90, 133.31, 131.46, 129.37, 128.66, 128.33,
128.00, 127.30, 127.15, 125.26, 125.19; MS (FD, 8 kV) m/z (%) 687.5
(100) [M+] (calcd for C53H36O, 688.28). Anal. Calcd for C53H36O: C,
92.41; H, 5.27; O, 2.32. Found: C, 91.49; H, 6.59.
1,4-Bis(3,5-diphenylbenzene)-2,3,5,6-tetraphenylbenzene (32). A
mixture of diphenylacetylene (131.4 mg, 0.74 mmol) and 31 (500.5
mg, 0.73 mmol) in diphenyl ether (5 mL) was heated at reflux for 16
h under an argon atmosphere. After cooling to room temperature,
ethanol (100 mL) was added to the reaction mixture. The precipitated
crystals were collected by filtration and purified by recrystallization
from dichloromethane/ethanol to afford 32 (579.5 mg, 95%) as colorless
crystals: mp >300 °C; 1H NMR (500 MHz, CDCl3) δ 7.35 (t, J ) 7.5
Hz, 8H), 7.33 (t, J ) 1.5 Hz, 2H), 7.29 (t, J ) 7.2 Hz, 8H), 7.22 (d,
J ) 7.2 Hz, 8H), 7.11 (d, J ) 1.5 Hz, 4H), 7.03-6.96 (m, 16H), 6.93
(t, J ) 6.7 Hz, 4H); 13C NMR (125 MHz, CDCl3) δ 141.37, 141.12,
140.82, 140.61, 140.22, 139.94, 131.68, 129.93, 128.44, 127.08, 126.95,
126.85, 125.56, 123.10; MS (FD, 8 kV) m/z (%) 837.7 (100) [M+]
(calcd for C66H46, 838.36). Anal. Calcd for C66H46‚4H2O: C, 87.00;
H, 5.97; O, 7.02. Found: C, 87.31; H, 5.53.
PAH 10. To a mixture of copper(II)-trifluoromethanesulfonate (5.20
g, 14.37 mmol) and aluminum(III) chloride (2.00 g, 15.01 mol) in
carbon disulfide (200 mL), 32 (200.4 mg, 0.24 mmol) was added. After
stirring at room temperature for 24 h under an argon atmosphere, the
resulting mixture was poured into 10% HCl solution. The precipitated
crystals were collected by filtration, washed with 10% NH4OH solution,
water, carbon disulfide, and dichloromethane, and dried in vacuo to
afford 10 (171.4 mg, 88%) as a brown powder: mp >300 °C; MS

Synthesis of Large Polycyclic Aromatic Hydrocarbons
J. Am. Chem. Soc., Vol. 122, No. 32, 2000 7717
(FD, 8 kV) m/z (%) (100) [M+] (calcd for C66H26, 818.20). Anal. Calcd
for C66H26: C, 96.80; H, 3.20. Found: C, 86.67; H, 3.26.
130.53, 130.29, 130.16, 129.97, 129.87, 129.85, 129.73, 128.46, 127.37,
127.22, 127.15, 127.10, 127.04, 127.00, 126.88, 125.81, 125.79, 124.44,
123.25, 123.21; MS (FD, 8 kV) m/z (%) 991.1 (100) [M+] (calcd for
C78H54, 990.42). Anal. Calcd for C78H54: C, 94.51; H, 5.49. Found:
C, 93.70; H, 6.08.
PAH 6. To a mixture of copper(II)-trifluoromethanesulfonate (5.26
g, 14.55 mmol) and aluminum(III) chloride (2.25 g, 16.84 mol) in
carbon disulfide (200 mL), the mixture of 37a and 37b (200.0 mg,
0.20 mmol) was added. After stirring at room temperature for 24 h
under an argon atmosphere, the resulting mixture was poured into 10%
HCl solution. The precipitated crystals were collected by filtration,
washed with 10% NH4OH solution, water, carbon disulfide, and
dichloromethane, and dried in vacuo to afford 6 (174.2 mg, 89%) as a
brown powder: mp >300 °C; MS (MALDI-TOF) m/z (%) 965.9 (100)
[M+] (calcd for C78H30, 966.23). Anal. Calcd for C78H30: C, 96.87; H,
3.13. Found: C, 92.07; H, 3.46.
3-Phenyldiphenylacetylene (34). To a solution of 3-bromobiphenyl
(33) (5.54 g, 23.79 mmol), palladium(0)-tetrakis(triphenylphosphine)
(1.24 g, 1.07 mmol), and CuI (408.6 mg, 2.15 mmol) in piperidine
(200 mL), phenylacetylene (4.7 mL, 4.39 g, 42.98 mmol) was added.
The resulting mixture was stirred at 80 °C for 5 h under an argon
atmosphere. The reaction mixture was poured into NH4Cl solution and
extracted with dichloromethane. The organic layer was washed with
NH4Cl solution and water and then dried with MgSO4. After the solvent
was removed in vacuo, the residue was purified by column chroma-
tography (petroleum ether) to afford 34 (5.66 g, 94%) as a colorless
oil: 1H NMR (300 MHz, CDCl3) δ 7.57 (t, J ) 1.5 Hz, 1H), 7.41-
7.10 (m, 13H); 13C NMR (75 MHz, CDCl3) δ 141.42, 140.36, 131.64,
130.34, 128.80, 128.78, 128.35, 128.29, 127.58, 127.10, 127.08, 123.74,
123.24, 89.52, 89.37; MS (FD, 8 kV) m/z (%) 254.3 (100) [M+] (calcd
for C20H14, 254.11).
Bis(4,1′:2′,1′′terphen-1-yl)acetylene (39). To a deoxygenated solu-
tion of 4-bromo-1,1′:2′,1′′-terphenyl (38; 4.50 g, 14.60 mmol)19 in
toluene (60 mL), palladium(0)-tetrakis(triphenylphosphine) (1.52 g,
1.32 mmol) and bis(tributylstannyl)acetylene (5.86 g, 9.70 mmol) were
added under an argon atmosphere and refluxed for 62 h. After the
solvent was removed in vacuo, the residue was purified by column
chromatography (petroleum ether/dichloromethane)) to afford 39 (2.74
g, 78%) as colorless crystals: mp 253 °C; 1H NMR (500 MHz, CDCl3)
δ 7.42-7.41 (m, 8H); 7.33 (d, J ) 8.6 Hz, 4H), 7.24-7.18 (m, 6H),
7.14-7.11 (m, 4H), 6.36 (d, J ) 8.6 Hz, 4H); 13C NMR (125 MHz,
CDCl3) δ 141.59, 141.27, 140.61, 139.86, 131.12, 130.68, 130.39,
129.88, 129.86, 127.99, 127.76, 127.54, 126.60, 121.34, 89.69; MS
(FD, 8 kV) m/z (%) 482.1 (100) [M+] (calcd for C38H26, 482.20);
1,2,3,4,5,6-Hexakis(4,1′:2′,1′′terphen-1-yl)benzene (40). To a deoxy-
genated solution of 39 (500 mg, 1.03 mmol) in 1,4-dioxane (100 mL),
dicobaltoctacarbonyl (118 mg, 0.35 mmol) was added under an argon
atmosphere and the resultant mixture refluxed for 14 h. After the solvent
was removed in vacuo, the obtained residue was purified by column
chromatography (petroleum ether/dichloromethane)) to afford 40 (180
mg, 36%) as colorless crystals: mp 335 °C; 1H NMR (500 MHz,
CDCl3) δ 7.45-7.29 (m, 18H); 7.25-7.19 (m, 6H), 6.03 (t, J ) 7.6
Hz, 12H), 6.85 (d, J ) 7.9 Hz, 12H), 6.80 (t, J ) 7.3 Hz, 6H), 6.61 (d,
J ) 8.4 Hz, 12H), 6.50 (d, J ) 8.4 Hz, 12H); 13C NMR (125 MHz,
CDCl3) δ 141.54, 140.64, 140.50, 140.09, 139.10, 138.20, 131.72,
131.00, 130.90, 130.09, 128.44, 127.91, 127.59, 127.52, 126.63; MS
(FD, 8 kV) m/z (%) 1446.7 (100) [M+] (calcd for C114H78, 1446.6).
Anal. Calcd for C114H78: C, 94.57; H, 5.43. Found: C, 94.40; H, 5.51.
PAH 5. To a mixture of copper(II)-trifluoromethanesulfonate (3.51
g, 9.70 mmol) and aluminum(III) chloride (1.30 g, 9.71 mol) in carbon
disulfide (100 mL), 40 (50 mg, 0.033 mmol) was added. After stirring
at room temperature for 14 days under an argon atmosphere, the
resulting mixture was poured into methanol (50 mL). The precipitated
crystals were collected by filtration and washed with 10% NH4OH
solution, 10% HCl solution, and water. After drying, the residue was
washed again with ethanol, carbon disulfide, and hot toluene. The
obtained black solid (42 mg, 91%) was dried in vacuo: mp >300 °C;
MS (MALDI-TOF) m/z (%) 1398.4 (100) [M+] (calcd for C114H30,
1398.3). Anal. Calcd for C114H30: C, 97.84; H, 2.16. Found: C, 79.79;
H, 2.37.
3-Phenyl Diphenyl Diketone (35). A solution of 34 (3.00 g, 11.80
mmol) and iodine (1.53 g, 7.14 mmol) in DMSO (50 mL) was heated
at reflux for 18 h under an argon atmosphere. The reaction mixture
was poured into Na2SO3 solution and extracted with dichloromethane.
The organic layer was washed with water, dried with MgSO4, and
concentrated under reduced pressure. The residue was purified by
column chromatography (dichloromethane/petroleum ether) to give 35
1
(2.75 g, 81%) as yellow crystals: mp 71.5-72.1 °C; H NMR (300
MHz, CDCl3) δ 8.20 (t, J ) 1.7 Hz, 1H), 8.02-7.85 (m, 4H), 7.69-
7.33 (m, 8H); 13C NMR (75 MHz, CDCl3) δ 194.48, 194.43, 142.29,
139.61, 134.90, 133.56, 133.48, 133.03, 129.94, 129.47, 129.03, 128.97,
128.79, 128.26, 128.05, 127.18; MS (FD, 8 kV) m/z (%) 286.5 (100)
[M+] (calcd for C20H14O2, 286.10). Anal. Calcd for C20H14O2: C, 83.90;
H, 4.93; O, 11.18. Found: C, 83.95; H, 4.86.
2,5-(3,5-Diphenylphenyl)-3-phenyl-4-(3-biphenyl)cyclopentadi-
enone (36). To a refluxing solution of 30 (1.50 g, 2.92 mmol) and
3-phenyl diphenyl diketone35 (840.8 mg, 2.94 mmol) in 1,4-dioxane
(3 mL), a tetrabutylammonium hydroxide solution (0.8 M, 1.8 mL,
1.44 mmol) in methanol was added. The resulting mixture was heated
at reflux for 15 min under an argon atmosphere. The reaction mixture
was poured into water and extracted with dichloromethane. The organic
layer was washed with water, dried with MgSO4, and concentrated under
reduced pressure. The residue was purified by column chromatography
(dichloromethane/petroleum ether) to afford 36 (1.32 g, 59%) as purple
1
crystals: mp 148.4-150.2 °C; H NMR (300 MHz, CDCl3) δ 7.70 (t,
J ) 1.6 Hz, 1H), 7.68 (t, J ) 1.6 Hz, 1H), 7.56 (d, J ) 1.6 Hz, 2H),
7.53 (d, J ) 1.6 Hz, 2H), 7.50-7.43 (m, 8H), 7.41-7.26 (m, 22H),
7.21-7.09 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 200.21, 155.15,
154.92, 141.51, 141.41, 141.20, 140.90, 140.49, 133.55, 133.49, 131.54,
131.42, 129.46, 128.75, 128.70, 128.67, 128.56, 128.47, 128.22, 128.03,
127.47, 127.44, 127.32, 127.17, 126.97, 125.47, 125.35, 125.30, 125.22;
MS (FD, 8 kV) m/z (%) 763.6 (100) [M+] (calcd for C59H40O, 764.31).
Anal. Calcd for C59H40O: C, 92.64; H, 5.27; O, 2.09. Found: C, 91.84;
H, 5.76.
1,4-Bis(3,5-diphenylbenzene)-2,5-Di(3-phenylbenzene)-3,6-Diphen-
ylbenzene (37a) and 1,4-Bis(3,5-diphenylbenzene)-3,5-Di(3-phen-
ylbenzene)-2,6-Diphenylbenzene (37b). A mixture of 34 (343.8 mg,
1.35 mmol) and 36 (1.00 g, 1.31 mmol) in diphenyl ether (5 mL) was
heated at reflux for 2 h under an argon atmosphere. After cooling to
room temperature, ethanol (100 mL) was added to the reaction mixture.
The precipitated crystals were collected by filtration and purified by
recrystallization from dichloromethane/ethanol to afford 37a and 37b
(882.8 mg, 68%) as colorless crystals: mp 287.5-288.4 °C; 1H NMR
(500 MHz, CDCl3) δ 7.37-6.94 (m, 54H); 13C NMR (125 MHz,
CDCl3) δ 141.42, 141.36, 141.33, 141.25, 141.13, 141.05, 140.82,
140.67, 140.64, 140.57, 140.54, 140.47, 140.42, 140.35, 140.23, 140.03,
139.88, 139.87, 131.85, 131.80, 131.75, 131.72, 131.32, 131.26, 130.61,
Acknowledgment. Financial support by the Volkswagen-
stiftung, the European Commission (TMR-Program SISITO-
MAS), and Sony International (Europe) is gratefully acknowl-
edged. S.I. thanks the Humboldtstiftung for a scholarship; the
authors thank Dr. M. Watson for valuable insight toward the
preparation of this paper.
JA000832X