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From Hexa-peri-hexabenzocoronene to УSuperacenesФ.

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Angew.
Chem.Int. Ed. Engl. 1997,36,No. 15
0 VCH VerlagsgesellschajimbH,0-69451Weinheim,1997
0570-0833/97/3607-1603
$17.50 + SO/O
1603
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-
From Hexa-peri-hexabenzocoronene to
“Superacenes”* *
Vivekanantan S. Iyer, Mike Wehmeier, J. Diedrich
Brand, Menno A. Keegstra, and Klaus Mullen*
We recently synthesized soluble derivatives of hexa-peri-hexabenzocoronene (1) by cyclodehydrogenation.[’] Compounds
such as 1 are building blocks for supramolecular architectures;
thus l a shows a stable discotic mesophase with a hexagonal
superstructure over a wide temperature range[’] and forms
monomolecular layers on suitable substrates.[’]
l:R=H
l a : R = n-Cq2H25
R
F
R
and disclose the syntheses of some extremely large polycyclic
aromatic hydrocarbons (PAHs) derived from 1. If, from a design point of view, one considers the hexagonal structure of 1 as
“superbenzene”, fusion reactions of 1can lead to various homologues such as “supernaphthalene” (Z), “supertriphenylene”
(3), or the “phenalenyl” framework 17.[41
Our synthesis of PAHs is based on two steps: 1) construction
of a soluble polyphenylene precursor of well-defined structure
with a close spatial arrangement of the phenyl rings, which is
similar to the framework of the target molecule, and
2) planarization of this precursor to the PAH by intramolecuar
cyclodehydrogenation. Whereas cyclotrimerization of substituted diphenylacetylenes is restricted to PAH precursors with sixfold symmetry,[61Diels-Alder reaction of tetraphenylcyclopentadienones with diarvlacetvlenes is a well-established method
for the construction of polyaryl compounds.[71By this process,
each Diels-Alder reaction (followed by extrusion of CO) adds
five phenyl rings to an existing alkyne in a one-pot reaction.
Therefore, the task of designing the precursor is simplified to
choosing the right alkyne. It appears that the known
would be a suitable precursor to 2. Alkyl substitution is a key
step towards the synthesis of soluble PAHs. The 1,2-diketone
synthesis by Mueller-Westerhoff‘81 and our improved synthesis
of 1,3-diarylacetonesrg1expedite the synthesis of alkyl-substituted tetraphenylcyclopentadienones (Scheme 1, Table 1).
tBu+Br
R
R
4
2: R = H. 2a: R = tBu
6:R=H
6a: R = tBu
R
?:R=H
?a: R = tBu
8: R, R = H
8a: R. R = tBu
8b: R = tBu, R = H
Scheme 1. a) nBuLi/THF/ - 78 “ C ; b) 1,4-dirnethylpiperazine-2,3-dione, 60%
(two steps); c) [Fe(CO),] (0.5 equiv)/NaOH/CH,CI,/H,0/5 mol% dodecyltrimethylammonium bromide, 65%; d) KOH/EtOH/reflux/3 h, 90-95%.
3: R = H. 3a: R = tBu
A key question concerns the change in the two- and three-dimensional superstructures upon further increasing the size and
varying the periphery of the disc molecules. Their shape is particularly important when attempting to achieve densely packed
layers on surfaces.[31Here we outline a general synthetic strategy
[‘I
[**I
Prof. Dr. K. Mullen, Dr. V. S. Iyer, Dip1.-Chem. M. Wehmeier,
DipLChem. I. D. Brand, Dr. M. A. Keegstra
Max-Planck-lnstitut fur Polymerforschung
Ackermannweg 10, D-55128 Mainz (Germany)
Fax: Int. code +(6131)379-350
e-mail: muellen@mpip-mainz.mpg.de
This work was supported by the Volkswagenstiftung and the Bundesministerium fur Bildung und Forschung. V. S. I. thanks the Max-Planck-Gesellschaft
for a fellowship.
1604
0 VCH VerlagsgeseIi.~chafimbH, 0-69451 Weinherm, 1997
Diels-AIder reaction of alkyne 9 with two equivalents of 8 or
8a resulted in the corresponding polyphenylene compounds 10
and 10a, respectively, in nearly quantitative yields. Similarly, 12
and 12a were obtained from triyne 11 and three equivalents of
8 or 8b (Scheme 2, Table 1 ) .
Triyne 15 was synthesized by trimerization of 3-bromoacetophenone (13; commercially available) with tetrachlorosilane
in ethanol“ ‘I followed by palladium-catalyzed coupling of tribromide 14 with phenylacetylene. Diels-Alder reaction of 15
with three equivalents of 8 or 8a resulted in the precursors 16
and 16a, respectively, in greater than 90% yield (Scheme 3,
Table 1).
Similar to our results from the cvclodehvdroaenation reactions of hexaarylbenzenes to give derivatives of 1,“. 1 2 1 cyclodehydrogenation of the unsubstituted precursors 12 and 16 proceeded smoothly with copper(I1) trifluoromethane sulfonate and
aluminum(II1) chloride to give the desired planar PAHs 17 and
3, respectively (Scheme 4), which were identified by laser-desorption time-of-flight mass spectrometry (LD-TOF-MS; 17:
M + =1183 gmol-’; 3 : M + = 1633 gmol-I). Cyclodehydrogenation of 10 with copper(r1) chloride and aluminum(ii1) chlo-
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Angew. Chem Int. Ed. Engi. 1997. 36, No. 15
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Table 1. Selected spectroscopic data [a] of 2, 2a, 3,3a, 10a, 12, 12a, 16, 16a, 17, 17a,
and 20 [15]
niiz (%) = 891(100) [ M t (calcd
]
for C,,H2, = 891).
2 a . MS (MALDI-TOF)- m i i (%)=1340(100) [ M ' ] (calcd for
C,,,H,, =1339.86). UV/Vis (1,1.2,2-tetrachloroethane):i.,,
=
,362, 415. 478,
505 nm.
2: MS (LD-TOF)
3:MS (LD-TOF): ni,: (%) =1633.6(100) [ M t(calcd
]
for C,,,H,, = 1633.48).
3 a : MS (MALDI-TOF): mi2 (%) = 23034(100) [M'] (calcd for C,,,H,,, =
2-tetrachloroethane): i,,, = 363, 397, 424, 487, 522 nm.
364 1 ( l O O ) [ M + (calcd
]
forC,,,H,,, = 1364.05);
2-tetrachloroethane, 140°C): 6 = 31.22, 31.27,
, 34.16, 118.96, 125.05, 125.27, 130.67, 132.50,
133.29. 133.78, 13391, 136.93, 137.29, 137.99, 138.14, 138.42, 138.95, 139.57,
140.63, 141.68, 142.66, 147.25, 147.48, 147.76, 147.88, 148.26, 148.30, 157.13.
12: MS (FD. 8 kV) mi- ( X ) =1219.6(100) [M'] (calcd for C,,H,,=1219.58);
"C NMR (125 MH7. [D2]1,1,2,2-tetrachloroethane,140'-C): d =125.2, 125.5,
125.7, 126.2. 126.5. 126.8. 127.0, 127.4, 130 2, 130.4, 131.2, 121.8. 132.0, 139.4,
140 5, 140.7. 140.8. 141.7, 142 3.
12a: M S ( F D . 8 kV):n?i(%) =15564(100)[Mt](calcdforC,,,H,,,=1556.23);
I3C NMR (125 MHz. [D,]1,1,2,2-tetrachloroethane,140'C): 6 = 31.02, 31.38,
31.76. 34.12, 123.24 123.54, 123.74, 126.99, 127.41, 127.53, 130.60, 131.20. 131.56,
131.76, 132.23. 137 64. 137.91, 139 26, 139.74, 140.49, 140.63, 140.73, 140.91,
142.19. 148.13, 14X 44.
b
-
16:MS (FD, 8 kV). I)? :(%) =1676.2(100) [ M ' ] (calcd for C,,,H,, =1676.17);
3C NMR (125 MHz. [D,]l
2-tetrachloroethane, 140 "C): 6 = 123.4, 124.37,
124.44. 125.2, 125.4, 126.6, 126.8, 126.9, 129.9, 131.0. 139.5, 140.3, 140.6, 140.77,
140.84, 14097, 141 00, 141.1, 141.3, 141.9.
16a:MS(FD.8 kV):m;z(%) = 2343 8(100)[Mt~(calcdforC,,,H,,, = 2343 41);
I3C NMR (125 MHz. [D,]1.1,2,2-tetrachloroethane,140°C): 6 = 31.4, 34.1, 124.2,
124.3, 125.2. 131.1. 131.2, 131.9, 132.0, 138.3, 139.6, 140.0, 140.1, 140.6, 140.7,
141.1, 141.2. 141.5. 141.6. 142.0, 147.5, 148.0, 148.1.
C
&6
dB
R
R
0 0
O
+gq+
R
0 0 0 0 0
~ 0 0 0 0 0 0
R
R
17:MS (LD-TOF): 117,: (%) =1182.6(100) [M'] (calcd for C,,H,, =1183.29)
I7a:MS (LD-TOF): wilz ( % ) =1520.3(100) [ M t ] (calcd for C,,,H,, =1519.
20:MS (FD. 8 kV): niii (Oh)= 2815 4(100) [ M + ](calcd for C,,,H,,, = 2815.2);
"CNMR (125 MHz. CDCI,, 30'C): d =141.78, 141.67, 140.63, 140.54, 140.45,
140.08, 140.01. 139.92. 139.12, 139.00, 138.44, 138.13, 131.65, 131.56, 131.53,
131.17, 129.96, 128.33, 127.51. 126.85, 126.74, 126.53, 126.18, 125.51, 125.26.
4
R
R
16: R = H
16a: R = tBu
Scheme 3. a) SiCl,/EtOH/25 'C/5 d, 55%; b) phenylacetylene (3.1 equiv)/piperidine/toluene/[Pd(PPh,),]/CuI/80"C, 2 d, 65%; c) derivatives 8 or 8a (3 equiv):
250"C/Ph,O, 90-95%.
[a] All LD-TOF and MALDI-TOF mass specta were calibrated with C,,and C,,.
9-Nitroanthrdcene was used as the matrix for the MALDI-TOF measurements.
MALDI = matrix-assisted laser-desorption ionization.
9
$-
Fz
a
+
oder b
R
L%
10: R = H
IOa: R = tBu
0
A
2: R = H,
2a. R = tBu
A
10: R = H,
IOa: R = tBu
$"
12:R=H
12a: R = tBu
L
I1
R
Scheme 2. a ) Derivatives 8 or 8a (2 equiv)/250 'C/Ph20/6--8h, 2100%;
b) derivat~ves8 or 8b (3 equiv):250'C/Ph,O/4-6
h, 4 100%.
T2: R = H
12a: R = tBu
17:R=H
17a: R = tBu
16
ride led to a mixture of chlorinated derivatives of 2 (up to 26 C1
atoms by LD-TOF-MS). However, the crude mixture was successfully dechlorinated by treating the solid with an excess of
tert-butyllithium followed by an aqueous quench. DechlorinatA n g e x Shem. In!. Ed Enxi. 1997, 36, N o . f5
16a
3
4
3a
Scheme 4. a) CuCl,/AIC1,/25'CiCS,,
1 d ; fBuLi (excess). H,O. > 9 0 % ;
b) FeCI,/CH,Cl,/2-3 h, 30% @a), 50% (3a). >SO% (17a). c ) copper(1r) trifluoromethane sulfonate/AlC1,/25 "C/CS,/14 d, >90%.
VCH Verlugsgesellschaft mbH, 0-69451 Weinheim. 1997
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1605
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ed 2 was again identified by LD-TOF-MS (M' = 891 gmol- I ) .
Extensive attempts to dissolve (in high-boiling solvents or ionic
or sublime (under ultra-high vacuum)['41 the cyclized planar compounds for purification were unsuccessful.
To obtain soluble analogues of 2, 3, and 17 we prepared the
tert-butyl precursors 10a, 16a, and 12a. The latter was derived
from cyclopentadienone 8b, and 10a and 16a from 8a. Cyclizations of all precursors were carried out with iron(m) chloride as
the oxidizing agent. Due to the HCI formed in the course of the
reaction, the expected products were invariably obtained together with chlorinated, cyclized products. Nevertheless, it was
possible to isolate the non-chlorinated, fully cyclized products
from these mixtures. Compound 2a was isolated from the reaction mixture after reductive work-up (treatment with water/
methanol followed by 5 % aqueous Na,SO,) and multiple precipitation from dichloromethane (yield about 30 YO).
Likewise,
3a was isolated in about 50% yield.
Whereas 2a and 3a are slightly soluble in many solvents, 17a
is insoluble. Presumably the six tert-butyl groups are not enough
to solubilize this large, planar PAH. UV spectra of 2a and 3a,
recorded in tetrachloroethane, are characterized by broad absorptions from 320-500 tailing to 530 nm (Figure 1). Attempts
2
0
18
8
yD--c+&
19
ib
I
Alnm
-
Figure 1. Absorption spectra of 2a (solid line) and 3a (dotted line) recorded in
1,1,2,2-tetrachloroethane.
20
Scheme 5 . a) Cyclopentadienone
(2 equiv)/Ph,O,
b) [Co,(CO),]/dioxane/5 d, lOO"C, 71 %.
to measure 'H NMR spectra of 2a and 3a are hampered by poor
solubility in a wide range of deuterated solvents. For example,
2a has a solubility of less than 0.1 mg per 10mL in [DJodichlorobenzene at 150 0C.1161
Using the design principles presented in the introduction it is
possible to envisage even larger PAH structures such as the
hexagonal C,,, hydrocarbon 21. However, this extension meets
with problems due to the lack of appropriate methods for structural proof. Triyne 18 undergoes Diels-Alder reaction with two
equivalents of tetraphenylcyclopentadienonein diphenyl ether
at 190" exclusively at the outer, sterically less encumbered
acetylene units to give 19 (yield 66%; Scheme 5 ) . In spite of the
voluminous pentaphenyl substituents at the triple bond of 19, its
cyclotrimerization in dioxane proceeds smoothly to form 20 in
71 YOyield.
The soluble, fully characterized hydrocarbon 20, which contains 37 benzene rings, serves as a precursor for the C,,,
graphite unit 21. Treatment of 20 with alurninum(n1) chloride
and copper triflate in carbon disulfide affords a black solid,
which is insoluble in all common solvents. Monitoring the intramolecular cyclodehydrogenation by LD-TOF-MS reflects
the loss of hydrogen atoms by the formation of a broad signal
in the mass range expected for 21. However, signal broadening
1606
0 VCH Verlugsgesellschuft
mbH. 0-694Sl Weinheim. 1997
11 h,
19O"C,
66%;
21
does not allow an exact molecular-weight determination and
does not provide proof of the quantitative removal of 108 hydrogen atoms. Work directed toward the manipulation and
OS70-0833/97/36lS-l606$ 1 7 . 5 0 + 3010
Angew. Chem
Inr
Ed. Engl. 1997,36, No I S
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~~
characterization of extremely large PAHs (>CzZ2)is in progress.
Received: December 11, 1996 [Z9867IE]
German version: Angew. Chem. 1997,109, 1675-1679
Keywords: arenes * cycloadditions * cyclodehydrogenations
Diels-Alder reactions * superacenes
for graphite.“. 21 We showed that the oxidative cyclodehydrogenation of oligophenylene precursors, for example the cyclization of hexaphenylbenzene (HPhB, 1) to hexa-peri-hexabenzocoronene (HBC, 2; Scheme I), can serve as a mild method for
-
s
B
[I] A. Stabel, P. Herwig. K. Miillen, J. P. Rabe, Angem. Chem. 1995,107, 17681770. Angrrr. Chrm. Int. Ed. Engl. 1995,34, 1609-1611.
[2] P. Herwig, C Kayser. H. W. Spiess, K. Miillen, Adv. Muter. 1996,8,510-513.
[3] G.Desiraju, A. Gavezzoti, J Chem Soc Chem. Commun. 1989,621 -622.
[4] The name “superbenzene” has been associated with 1 [5a] and “kekulene” [Sb]
in terms of possible enhanced aromaticity. We use this term simply to outline
our synthetic design of the large PAHs.
[5] a) E. Clar, The Aromafrc Sextet, Wiley, London, 1972;b) H. A. Staab, F.
Diederich, Angeii.. Client. 1978, YO, 383-385; Angen. Chem. Ini. Ed. Engl.
1978. 17. 372--374; H A Staab, F. Diederich, Chem. Ber. 1983, 116, 34873503: see also J. Aihara. J Am. Chem. SOL.1992,114, 865-868.
161 N. Schore in (’nmprehmsive Organic Sjnfhesi.r. Vol. 5 (Eds.: B. M. Trost, 1.
Fleming), Pergamon Press. Oxford, 1991,pp. 1129-1 162.
[7] M. A. Ogliaruco. M. G. Romanelli, E. 1 Becker, Chem. Rev. 1965,65, 261361.
[S] 1.2-Diaryl-l .‘-diketones are easily accessible from the corresponding aryllithium compounds and 1.4-dimethyIpiperdzine-2.3-dione:U T. Mueller-Westerhoff. M. Zhou, J Org. Cliem. 1994,59, 4988-4992.
[9]Our improved synthesis of 1.3-diarylacetones. which gives consistent yields, is
based on the following: Y. Kimura, Y. Tomito, S. Nakdnishi, Y. Otsuji, Chem.
Leir 1979.321 -322; H. des Abbdyes. J. Clement, P.Laurent, G. Tanguy, N.
~ ~ 7,
~ 2293-2299.
U N ~ C S
Thilmont. O ~ ~ ~ I U ~ J1988.
[lo] Compounds IOand I2 are described: W.Ried, D. Freitag, Angem. Chem. 1968,
XO. 932-942. Angew. C‘hen?.In!. Ed. Engl. 1968,7, 835-844.
[ I l l S . S . Elmorsq. A. Pelter. K Smith, Tetrahedron Lett. 1991, 4175-4176.
[I21 M. Miiller. H. Mauermann-Dull, M. Wagner, V. Enkelmann, K. Miillen,
Angrit. Cheni. 1995. 107, 1751-1754; Angen. Chem. In:. Ed. Engl. 1995,34,
1583 - 1586.
[I31 We thank DipILChem. M. Miiller for conducting theexperiments and Prof. K.
Seddon for his hospitality and providing us with 1-ethyl-3-methylimidazolium
tetrachloroaluminate, the ionic liquid used in these experiments.
[I41 Experiments conducted by Prof. N Karl, Universitat Stuttgart (Germany).
[I 51 All polyphenylene precursors show temperature-dependent N M R spectra, indicating the presence of several rotational isomers. The ‘T N M R chemical
shifts given in Table 1 were obtained above the coalescence temperatures of
these compounds.
[I61 Many other high-boiling solvents were tried, but the highest solubility (which
was not enough to obtain a ‘ H N M R spectrum) was observed for [DJodichlorobenrene
Scheme 1. Oxidative cyclodehydrogenation of hexaphenylben7ene (HPhB, 1) to
hexa-peri-hexabenzocoronone (HBC, 2 ) .
the synthesis of PAHs in high yield^.[^.^] In this case the
oligophenylenes must render planarization to PAHs possible by
eIimination of hydrogen and formation of C-C bonds.
The work reported here involves oligophenylenes in which
planarization is hindered by spatial superposition of phenyl
units or by strained rings other than six-membered rings. For
the intramolecular cyclodehydrogenation, surprisingly smooth
skeletal rearrangements can lead to planar PAHs from “nonplanarizable” oligophenylenes by removal of steric strain.
The oligophenylene derivative 6, which is a positional isomer
of oligophenylene 5,[51 was obtained from 1,3-di(phenylethyny1)benzene (4) by double Diels-Alder addition with
1,2,3,4-tetraphenylcyclopenta-1,3-dienone (tetracyclone) and
extrusion of carbon monoxide (Scheme 2). The crystal structure
of 6 (Figure 1) shows clearly the spatial superposition of the two
phenyl units directed towards the center of the molecule.r61
*
3
Polycyclic Aromatic Hydrocarbons by Cyclodehydrogenation and Skeletal Rearrangement of
Oligophenylenes**
Markus Miiller, Vivekanantan S. Iyer, Christian Kiibel,
Volker Enkelmann, and Klaus Miillen*
Polycyclic aromatic hydrocarbons (PAHs) are becoming
increasingly important in the areas of molecular electronics and
optoelectronics. They are also of theoretical interest as models
[*] Prof. Dr. K. Miillen, DipLChem. M. Miiller, Dr. V. S . Iyer,
Dipl.-Chem. C Kiibel, Priv.-Doz. Dr. V. Enkelmann
Max-Planck-Institut fur Polymerforschung
Ackermannweg 10, D-55128 Mainz (Germany)
Fax. Int. code +(6131)379-100
e-mail: muellen:o mpip-mainz.mpg.de
[**I This work was supported financially by the Volkswagenstiftung and the Bundesministerium fur Bildung und Forschung. We thank Dr. J. Rider and Dipl:
Chem. K. Martin for recording the LD-TOF mass spectra, and Prof. F.-G.
Klhrner and DipLChem. M. Kamieth for awstdnce with the MM3* and AM1
calculations. V. S. I . thanks the Max-Planck-Gesellschaft, and C. K. the Fonds
der Chemischen lndustrie for a scholarship.
Anxebr. Chm. Ini. E d Engl
1997.36, No. 15
f;
4
.)I
0 0 0 0 0
5
6
7
Scheme 2. a) and b) 1,2,3,4-Tetraphenylcyclopenta-1.3-dienone
220 ‘C!Ph,O/2 d ;
a) 97%, b) 95%; c) and d) copper(r1) triflate or CuCI,, respectively/AICl,/RT/
CSJ2 d/quantitative yield.
VCH Verlagsgesellschaft mbH, D-69451 Weinhelm. 1997
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