Synthesis and properties of 1,6,7,12,13,18,19,24- octamethylacenaphthyleno[b,l]tetraphenylene

Article abstract of DOI:10.1039/b416820h

The X-ray crystal structure and photophysical properties of 1,6,7,12,13,18,19,24-octamethylacenaphthyleno[b,l]tetraphenylene, which has been synthesized via a Diels-Alder reaction of 5,6,11,12-tetradehydrodibenzo[a,e] cyclooctene and 6,7-dihydro-6-hydroxy-7,9-dimethyl-8H-cyclopenta[a] acenaphthylene-8-one, are reported.

Full text of DOI:10.1039/b416820h

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C O M M U N I C A T I O N
Synthesis and properties of 1,6,7,12,13,18,19,24-
octamethylacenaphthyleno[b,l]tetraphenylene
Eric L. Elliott,a Akihiro Orita,b Daiki Hasegawa,b Peter Gantzel,a Junzo Oterab and
Jay S. Siegel*a,c
a Department of Chemistry, University of California, San Diego, La Jolla, California,
92093-0358, USA
b Department of Applied Chemistry, Okayama University of Science, Okayama, Japan
c Organisch-chemisches Institut, Universita¨t Zu¨rich, Winterthuererstr. 190, Zu¨rich, 8057,
Switzerland. E-mail: jss@oci.unizh.ch; Fax: 41 1 6356888
Received 2nd November 2004, Accepted 17th December 2004
First published as an Advance Article on the web 19th January 2005
The X-ray crystal structure and photophysical properties
of 1,6,7,12,13,18,19,24-octamethylacenaphthyleno[b,l]te-
traphenylene, which has been synthesized via a Diels–Alder
reaction of 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene
and 6,7-dihydro-6-hydroxy-7,9-dimethyl-8H-cyclopenta-
[a]acenaphthylene-8-one, are reported.
Non-planar polycyclic aromatic hydrocarbons with a parabolic
curvature result from perturbations caused by the incorpora-
tion of a five-membered ring into a planar graphite surface.1
Fullerenes, buckybowls, and buckytubes are all manifesta-
tions of this effect.2 Related perturbations, caused by the
incorporation of larger rings (7 or 8 members), can be ob-
served in the saddle-like structures of [7]circulene (1)3 and
dibenzo[def ,pqr]tetraphenylene (2).4 Herein, we report the syn-
thesis and properties of a novel saddle-shaped tetraphenylene
derivative (3) containing two fluoranthene subunits.
Scheme 2 Synthesis of 3.
octamethyldibenzo[def ,pqr]tetraphenylene (3) in good yield
(Scheme 2).8
The X-ray crystal structure of 3 (Fig. 1)† reveals a C2
symmetric molecule with a severely twisted surface. The twisting
is continuous from one naphthalene subunit, through the
tetraphenylene core, to the naphthalene of the other fluoran-
thene subunit. The angle between the mean planes of the
naphthalene and benzene units is 19.55◦. Although the parent
fluoranthene (7) is flat, a similar degree of twisting is observed
for the sterically similar 1,6,7,10-tetramethylfluoranthene (8).9
Aside from minor twisting, the tetraphenylene core of 3 is
unchanged by this perturbation. Another interesting structural
feature is the proximity of the methyl groups in the 7,12,19,24-
positions to the benzene protons of the tetraphenylene subunit
The synthesis of fluoranthene derivatives can be accomplished
via Diels–Alder reaction between a cyclopentadienone and an
acetylene (or masked acetylene).1,5 Thus, tetraphenylene 3 can
be envisioned to come from 5,6,11,12-tetradehydrodibenzo-
[a,e]cyclooctene (4) and cyclopentadienone 5 (Scheme 1).
Scheme 1 Retrosynthesis of 3.
Diyene 4 is readily prepared in high yield through a
double elimination protocol recently reported by Otera and
coworkers.6 Immediately after purification, diyne 4 and the
previously reported 6,7-dihydro-6-hydroxy-7,9-dimethyl-8H-
cyclopenta[a]acenaphthylene-8-one (6)2e were heated to 100 ◦C
in acetic anhydride for 12 h. Gratifyingly, the highly strained
acetylenic bonds7 of 4 reacted rapidly with cyclopentadienone
5, formed in situ from 6, to produce 1,6,7,12,13,18,19,24-
Fig. 1 Two perspectives of the X-ray crystal structure of 3: (left) along
C2 axis; (right) view through cleft.†
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
O r g . B i o m o l . C h e m . , 2 0 0 4 , 3 , 5 8 1 – 5 8 3
5 8 1
©

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˚
(2.9–3.3 A). Such an arrangement brings to mind the possibility
twisting of the methylated derivatives (8 and 9) nor the proximity
of chromophores in 3 lead to any statistically relevant deviation
in the quantum efficiency.
of ring-closure of a suitable precursor to an [8]circulene type
structure, with alternating six- and five-membered rings.
The distortion of 3 from D2h (planar) to C2 (ground state)
gives rise to the possibility of dynamic behavior. The two
possible dynamic modes of interest are the inversion of the
core eight-membered ring through the plane and the twisting
of the fluoranthene subunit. The former process is highly
unlikely at room temperature, for example, an exceptional
Acknowledgements
This work was supported by the US National Science Founda-
tion, the Swiss National Science Foundation, and the Japanese
Society for the Promotion of Science.
thermal racemization barrier of 67.2
0.8 kcal mol−1 was
measured for dibenzo[b,h]tetraphenylene.10 The barrier to ring-
inversion for tetraphenylene derivatives is commonly between
25 and 45 kcal mol−1,11,12 thus, the central ring is essentially
locked in place. In 3, the twisting of the fluoranthene subunits
should occur with a much lower barrier, either stepwise, among
diastereomeric complexes, or correlated between enantiomers
through an effective C2v transition form.
The methyl groups of 3 appear as only a single set of signals
in the proton NMR, expressing the time-averaged symmetry of
the dynamically twisting racemate. If a frozen solution structure
akin to that seen in the X-ray crystal structure could be obtained,
two sets of methyl signals, exo and endo, should be seen. This
would only be observable at lower temperatures.
Notes and references
† CCDC reference number 255954. See http://www.rsc.org/suppdata/
ob/b4/b416820h/ for crystallographic data in .cif format. Crystal
data 3 (0.30 × 0.20 × 0.10 mm3): Formula C52H40; formula weight
˚
664.84; crystal system monoclinic;◦ a = 17.705(2) A, b = 21.289(2)
3
˚
˚
˚
A, c = 19.354(2) A, b = 96.336(3) , V = 7250.4(15) A , T = 296(2)
K; space group C2/c; Z = 8; m = 0.069 mm−1; q = 1.218 mg
m−3; reflections collected 18208; independent reflections 6303 [R(int) =
0.0306]; data/restraints/parameters 6303/0/477; goodness of fit on F2
0.875; final R indices [I > 2r(I)] R1 = 0.0401, wR2 = 0.0997; R indices
(all data) R1 = 0.0693, wR2 = 0.1080; largest diff. peak and hole 0.126
−3
˚
and −0.134 e A
.
1 R. G. Harvey, Polycyclic Aromatic Hydrocarbons, Wiley-VCH, New
York, NY, 1997.
In an attempt to measure the barrier to twisting in 3, dynamic
2 (a) G. N. Sastry, Curr. Sci., 2003, 85, 125; (b) D. T. Colbert and
R. E. Smalley in Perspectives of Fullerene Nanotechnology, ed.
E. Osawa, Kluwer Academic Publishers, Dordrecht, Amsterdam,
2002, 3; (c) K. K. Baldridge and J. S. Siegel, Theor. Chem. Acc., 1997,
97, 67; (d) H. Sakurai, T. Daiko and T. Hirao, Science, 2003, 301,
1878; (e) T. J. Seiders, E. L. Elliott, G. H. Grube and J. S. Siegel,
J. Am. Chem. Soc., 1999, 121, 7804; (f) L. T. Scott, P.-C. Cheng,
M. M. Hashemi, M. S. Bratcher, D. T. Meyer and H. B. Warren,
J. Am. Chem. Soc., 1997, 119, 10963.
1H-NMR spectra were recorded at temperatures from −120 to
◦
25 C in dichlorofluoromethane-d.13 However, no splitting of
the signal set was observed, implying an upper limit to the
twisting barrier of ca. 7.5 kcal mol−1. This conclusion is given
additional support by the recently reported barrier to twisting of
8,9-diacetoxy-1,6,7,10-tetramethylfluoranthene (DG‡ < 7.0 kcal
mol−1).9
Luminescence was observed during the isolation of 3. This
is not surprising given the fluorescent properties of the parent
fluoranthene (7), however, perturbations of the electronic spectra
of 3 could reveal something about the coupling between
the juxtaposed chromophores. Thus, it was decided to study
the photophysics of the series of fluoranthenes: 8,9-diphenyl-
1,6,7,10-tetramethylfluoranthene (9),14 and 3.
3 K. Yamamoto, T. Harada, M. Nakazaki, T. Naka, Y. Kai, S. Harada
and N. Kasai, J. Am. Chem. Soc., 1983, 105, 7171.
4 D. N. Leach and J. A. Reiss, J. Org. Chem., 1978, 43, 2484.
5 E. Clar, R. Schoental, Polycyclic Hydrocarbons; Academic Press,
New York, ch. 1, 1964.
6 (a) A. Orita, D. Hasegawa, T. Nakano and J. Otera, Chem. Eur. J.,
2002, 8, 2000; (b) For the original report of 4 see: H. N. C. Wong,
P. J. Garratt and F. Sondheimer, J. Am. Chem. Soc., 1974, 96, 5604.
7 R. Destro, T. Pilati and M. Simonetta, J. Am. Chem. Soc., 1975, 97,
658.
8 1,6,7,12,13,18,19,24-Octamethylacenaphthyleno[b,l]tetraphenylene
(3). 6,7-Dihydro-6-hydroxy-7,9-dimethyl-8H-cyclopenta[a]acena-
phthylene-8-one (6) (440 mg, 1.58 mmol) and 5,6,11,12-
tetradehydrodibenzo[a,e]cyclooctene (4) (79 mg, 0.40 mmol)
were dissolved in acetic anhydride (20 mL) under an argon
atmosphere. The suspension was heated to 100 ◦C and gently
stirred for 12 h. The resulting solution was cooled to ambient
temperature, diluted with toluene (20 mL) and quenched slowly
with 2 M NaOH. The organic layer was washed three times with
additional 2 M NaOH (50 mL), dried over MgSO4 and then passed
through a short plug of silica gel. The crude product was purified
by column chromatography on silica gel with 5% ethylacetate in
hexane as the eluent to yield an orange solid (210 mg, 78%). Mp
354 ◦C (d). 1H NMR (CDCl3, 500 MHz), ppm: 2.47 (s, 12H), 2.70 (s,
12H), 7.21–7.26 (m, 8H), 7.29 (d, 3J = 8, 4H), 7.61 (d, 3J = 8, 4H)
13C NMR (CDCl3, 125 MHz), ppm: 22.5, 24.9, 126, 126.5, 126.53,
126.7, 129.7, 131.69, 131.72, 134, 135.1, 139.7, 141.6. UV (CH3CN)
The UV kmax displays a predictable red shift upon methyl
or phenyl substitution (Table 1) concomitant with twisting of
the plane. Somewhat surprising is the lack of any significant
differences among 8, 9, and 3, however, the severely distorted
central ring prevents conjugation, and allows the two fluo-
ranthene substructures to behave like isolated units. The only
noticeable change is a slight increase in molar absorptivity. The
change in the fluorescent emission throughout the series is one
of spectral structure rather than wavelength. The parent displays
two maxima, but only the longer wavelength emission persists
in 8, 9, and 3. The quantum efficiencies (φf ) were measured by
comparison to 9,10-diphenylanthracene in cyclohexane15 and
are the same, within experimental error. Thus, neither the severe
l
max, nm (e): 250 (7 × 104), 277 (4 × 104), 288 (4 × 104), 298 (4 ×
104), 338 (1 × 104), 373 (2 × 104). HRMS: found 664.3155, calcd.
(C52H40) 664.3130.
9 A. Borchardt, K. Hardcastle, P. Gantzel and J. S. Siegel, Tetrahedron
Lett., 1993, 34, 273.
10 P. Rashidi-Ranjbar, Y. M. Man, J. Sandstrøm and H. N. C. Wong,
J. Org. Chem., 1989, 54, 4888.
11 A. Rosdahl and J. Sandstrøm, Tetrahedron Lett., 1972, 4187.
12 G. H. Senkler, Jr., D. Gust, P. K. Riccobono and K. Mislow, J. Am.
Chem. Soc., 1972, 94, 8626.
Table 1 Photophyscial properties of 3 and 7–9
13 J. S. Siegel and F. A. L. Anet, J. Org. Chem., 1988, 53, 2629.
14 8,9-Diphenyl-1,6,7,10-tetramethylfluoranthene (9). 6,7-Dihydro-
6-hydroxy-7,9-dimethyl-8H-cyclopenta[a]acenaphthylene-8-one (6)
(552 mg, 2.0 mmol) and diphenylacetylene (373 mg, 2.1 mmol) were
dissolved in acetic anhydride (20 mL) under an argon atmosphere.
The suspension was heated to reflux and gently stirred for 3 d. The
resulting solution was cooled to ambient temperature, diluted with
toluene (20 mL) and quenched slowly with 2 M NaOH. The organic
kmax/nm
kem/nm
φf
7
8
9
3
358
369
374
373
431, 455
452
458
0.20 0.02
0.19 0.02
0.21 0.03
0.17 0.02
461
5 8 2
O r g . B i o m o l . C h e m . , 2 0 0 4 , 3 , 5 8 1 – 5 8 3

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layer was washed three times with additional 2 M NaOH (50 mL),
dried over MgSO4 and then passed through a short plug of silica gel.
The crude product was purified by column chromatography on silica
gel with 5% ethylacetate in he◦xane as the eluent to yield a yellow solid
(371 mg, 45%). Mp 196–197 C. 1H NMR (CDCl3, 500 MHz), ppm:
2.42 (s, 6H), 2.82 (s, 6H), 7.1–7.12 (m, 6H), 7.18 (d, 3J = 7.5, 2H), 7.41
(d, 3J = 8, 2H), 7.73 (d, 3J = 8, 2H). 13C NMR (CDCl3, 125 MHz),
ppm: 23.3, 24.7, 126, 126.2, 126.6, 127.5, 128.2, 130.8, 131.8, 132.1,
134, 135, 140, 141.6, 142.2. UV (CH3CN) lmax, nm (e): 251 (7 × 104),
276 (3 × 104), 287 (4 × 104), 295 (3 × 104), 338 (1 × 104), 374 (1 ×
104). HRMS: found 410.2024, calcd. (C32H26) 410.2029.
15 J. N. Dema and G. A. Crosby, J. Phys. Chem., 1971, 75, 991.
O r g . B i o m o l . C h e m . , 2 0 0 4 , 3 , 5 8 1 – 5 8 3
5 8 3