Fullerene-Acene Chemistry: Diastereoselective Synthesis of a cis,cis-Tris[60]fullerene Adduct of 6,8,15,17-Tetraphenylheptacene

Article abstract of DOI:10.1021/ol0356791

(Equation presented) A one-pot, diastereoselective synthesis of a cis,cis-tris[60]fullerene adduct of 6,8,15,17-tetraphenylheptacene has been demonstrated starting from [60]fullerene and 5,7,9,14,16,18-hexahydro-6,8,15,17- tetraphenylheptacene.

Full text of DOI:10.1021/ol0356791

ORGANIC
LETTERS
2
003
Vol. 5, No. 22
203-4206
Fullerene−Acene Chemistry:
Diastereoselective Synthesis of a
cis,cis-Tris[60]fullerene Adduct of
4
6,8,15,17-Tetraphenylheptacene
Glen P. Miller* and Jonathan Briggs
Department of Chemistry, UniVersity of New Hampshire,
Durham, New Hampshire 03824
gpm@cisunix.unh.edu
Received September 2, 2003
ABSTRACT
A one-pot, diastereoselective synthesis of a cis,cis-tris[60]fullerene adduct of 6,8,15,17-tetraphenylheptacene has been demonstrated starting
from [60]fullerene and 5,7,9,14,16,18-hexahydro-6,8,15,17-tetraphenylheptacene.
Numerous supramolecular assemblies involving electron-poor
60]fullerene and electron-rich arenes are known. The elec-
donor-acceptor interactions cannot be invoked to explain
the syn addition of [60]fullerenes across 6,13-disubstituted
pentacenes. Instead, the [60]fullerene-[60]fullerene interac-
tions are purely van der Waals (i.e., π-stacking) in nature.
[
1
2
tron-rich arenes include hydroquinone, cyclotriveratrylene,
3
and calixarenes. In each case, weak π-π donor-acceptor
interactions contribute to the supramolecular assembly, while
fullerene-arene van der Waals interactions help to stabilize
the resulting complex. Recently, we demonstrated4,5 the use
of a different noncovalent interaction, namely, [60]fullerene-
6
An X-ray crystal structure of the cis-bis[60]fullerene adduct
of 6,13-diphenylpentacene, 1, confirms the syn addition and
the importance of van der Waals interactions in stabilizing
this adduct.
[
60]fullerene π-stacking, during the diastereoselective syn
In an effort to further exploit [60]fullerene-[60]fullerene
π-stacking interactions for the assembly of interesting struc-
tures, we now report a highly diastereoselective synthesis
of a cis,cis-tris[60]fullerene adduct of 6,8,15,17-tetraphen-
ylheptacene, 2. Compound 2 is prepared in one pot starting
with [60]fullerene and 5,7,9,14,16,18-hexahydro-6,8,15,17-
addition of [60]fullerenes across 6,13-disubstituted penta-
cenes. Since [60]fullerene is a weak electron donor, π-π
(1) (a) Ermer, O. HelV. Chim. Acta 1991, 74, 1339. (b) Blanc, E.; Restori,
R.; Schwarzenbach, D.; Burgi, H. B.; Fortsch, M.; Venugopalan, P.; Ermer,
O. Acta Crystallogr., Sect. B 2000, B56 (6), 1003. (c) Ermer, O.; Roebke,
C. J. Am. Chem. Soc. 1993, 115, 10077.
(
2) (a) Steed, J. W.; Junk, P. C.; Atwood, J. L.; Barnes, M. J.; Raston,
(4) (a) Miller, G. P.; Mack, J. Org. Lett 2000, 2, 3979. (b) Miller, G. P.;
Briggs, J., Fullerenes, Proceedings of the International Symposium on
Fullerenes, Nanotubes, and Carbon Nanoclusters; Kamat, P. V., Guldi, D.
M., Kadish, K. M., Eds.; The Electrochemical Society: Pennington, NJ,
2002; Vol. 12, p 279.
C. L.; Burkhalter, R. S. J. Am. Chem. Soc. 1994, 116, 10346. (b) Matsubara,
H.; Oguri, S.-y.; Asano, K.; Yamamoto, K. Chem. Lett. 1999, 431. (c) Rio,
Y.; Nierengarten, J.-F. Tetrahedron Lett. 2002, 43, 4321.
(3) (a) Atwood, J. L.; Koutsantonis, G. A.; Raston, C. L. Nature 1994,
3
68, 229. (b) Susuki, T.; Nakashima, K.; Shinkai, S. Chem. Lett. 1994,
(5) Miller, G. P.; Mack, J.; Briggs, J. Org. Lett 2000, 2, 3983.
(6) Miller, G. P.; Briggs, J.; Mack, J.; Lord, P. A.; Olmstead, M. M.;
Balch, A. L. Org. Lett. 2003, 5, 4199.
699. (c) Atwood, J. L.; Barbour, L. J.; Heaven, M. W.; Raston, C. L. Angew.
Chem., Int. Ed. 2003, 42, 3254.
1
0.1021/ol0356791 CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/10/2003

1
13
6
,8,15,17-tetraphenylheptacene-7,16-quinone, 6. H and C
NMR spectra suggest that 6 forms via an endo,exo Diels-
Alder sequence analogous to the carefully studied reaction
8
between 1,3-diphenylisobenzofuran and p-benzoquinone. A
double dehydration of 6 with p-tosic acid in benzene affords
previously unknown 6,8,15,17-tetraphenylheptacene-7,16-
quinone, 7. Reduction of 7 with hydriodic acid in acetic acid
gives compound 3 in quantitative yield.
Quantitative formation of 3 was an unexpected but wel-
come result. Similar reductive conditions have been utilized
for over 100 years on smaller acene quinones and related
9
systems. Thus, Liebermann showed that HI and red phos-
phorus would reduce 9,10-anthraquinone at elevated tem-
peratures to form a mixture of anthrone, 9,10-dihydroan-
10
thracene, and anthracene. More recently, Harvey noted that
mixtures of HI and acetic acid convert polycyclic aromatic
quinones into their corresponding arenes or dihydroarenes
in good to excellent yields. We expected the HI/AcOH
reduction of 7 to produce either 7,16-dihydro-6,8,15,17-
tetraphenylheptacene or 6,8,15,17-tetraphenylheptacene, 4,
but not the “over-reduced” 3. Only a small number of other
hydrogenated heptacenes are known for comparison to 3.
Figure 1. cis-Bis[60]fullerene adduct of 6,13-diphenylpentacene,
(top), and cis,cis-tris[60]fullerene adduct of 6,8,15,17-tetraphen-
ylheptacene, 2 (bottom).
1
1
1
Hart observed spontaneous isomerization of 5,9,14,18-
tetrahydroheptacene into the thermodynamically preferred
tetraphenylheptacene, 3. Compound 3 does not react with
5,8,15,18-tetrahydroheptacene. With its alternating benzenoid
[60]fullerene but can be oxidized in situ to afford 6,8,15,-
rings and intact terphenyl moieties, compound 3 persists
indefinitely and can be considered a protected, stable version
of acene 4.
17-tetraphenylheptacene 4, which readily adds 3 equiv of
[60]fullerene in a diastereoselective fashion.
Our synthesis of 3 utilizes 1,3-diphenylnaphtho[2,3-c]-
Because acenes larger than pentacene are known to
furan, 5, an excellent diene for Diels-Alder chemistry.
Lustrous red crystals of compound 5 were prepared using a
1
2
13
degrade via photooxidation and photodimerization reac-
tions, we sought to prepare and react heptacene 4 in situ.
Thus, compound 3 was heated in benzene along with excess
7
modified Cava procedure and then reacted with 0.5 equiv
of p-benzoquinone (Scheme 1). The double-Diels-Alder
2
,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and
[60]fullerene (Scheme 2). After rinsing with ethanol to
Scheme 1. Synthesis of
5,7,9,14,16,18-Hexahydro-6,8,15,17-tetraphenylheptacene, 3
Scheme 2. Synthesis of cis,cis-Tris[60]fullerene Adduct of
6,8,15,17-Tetraphenylheptacene, 2
remove hydroquinone byproduct and excess DDQ, trisadduct
was obtained in 74% crude yield based on mass balance
2
1
1
and H NMR integration. A H NMR spectrum of the crude
(
8) Oniciu, D. C.; Ghiviriga, I.; Iordache, F.; Istrate, D.; Dinulescu, I.
G. ReV. Roum. Chim. 1992, 37, 1285.
9) (a) Grabe, C.; Liebermann, C. Justus Liebigs Ann. Chem., Suppl.
870, 7, 287. (b) Liebermann, C.; Topf, C. Chem. Ber. 1876, 9, 1201. (c)
Liebermann, C. Justus Liebigs Ann. Chem. 1882, 212, 1.
10) Harvey, R. G.; Leyba, C.; Konieczny, M.; Fu, P. P.; Sukumaran,
K. B. J. Org. Chem. 1978, 43, 3423.
11) Luo, J.; Hart, H., J. Org. Chem. 1987, 52, 4833.
(
1
addition is complete within a few minutes at room temper-
ature and yields a single diastereomer of 6,17,8,15-diepoxy-
(
(
(7) (a) Cava, M. P.; VanMeter, J. P., J. Org. Chem. 1969, 34, 538. (b)
(12) (a) Allen, C. F. H.; Bell, A. J. Am. Chem. Soc. 1942, 64, 1253. (b)
EÄ tienne, A.; Beauvois, C. Compt. Rend. 1954, 239, 64.
Cava, M. P.; VanMeter, J. P., J. Am. Chem. Soc. 1962, 84, 2008.
4204
Org. Lett., Vol. 5, No. 22, 2003

phenylheptacene. These are C2V symmetric cis,cis-trisadduct
, C2V symmetric trans,trans-trisadduct 8 and C symmetric
2
s
cis,trans-trisadduct 9. The reaction is highly diastereoselec-
1
tive for only one of these compounds. A H NMR spectrum
of the pure product reveals a molecule with C2V symmetry,
thereby eliminating compound 9 from consideration. Thus,
two methine singlets integrating for 4 and 2 protons are
observed at 5.69 and 5.80 ppm, respectively, confirming three
[
60]fullerene cycloadditions and two planes of symmetry.
1
The only other H NMR signals attributable to the heptacene
backbone are a single set of AA′MM′ signals at 7.45 and
7
.53 ppm. These can only correspond to the two equivalent,
terminal benzene rings of the heptacene backbone. Conse-
quently, 3 equiv of [60]fullerene must cycloadd across the
(
C5,C18), (C7,C16), and (C9,C14) carbons of heptacene 4.
A total of 63 C NMR signals are expected for either 2
1
3
or 8. These include 32 signals for the terminal [60]fullerene
moieties, 17 signals for the central [60]fullerene moiety, 8
signals for the heptacene backbone, and 6 signals for the
13
phenyl substituents (slowly rotating, vide infra). A C NMR
3
spectrum of pure product reveals four unique sp carbons.
These are assigned to the two unique methine carbons on
the heptacene backbone (52.2 and 55.1 ppm) and two unique
quaternary carbons on the [60]fullerene skeletons (72.1 and
1
3
7
2.5 ppm). A total of 53 distinct C signals are observed in
2
the sp region between 125 and 156 ppm, whereas 59 signals
are expected. A close examination of this congested region
indicates several shoulders alongside discernible signals,
indicating instances of coincidental overlap.
MM2 calculations have proven to be a valuable and
convenient tool for comparing diastereomeric bis[60]fullerene
6
Figure 2. Relative MM2 strain energies (kcal/mol) for C2V
symmetric cis,cis-trisadduct 2 (top), C2V symmetric trans,trans-
adducts of 6,13-disubstituted pentacenes. They fare far better
in this regard than either AM1 or PM3 semiempirical
s
trisadduct 8 (middle), and C symmetric cis,trans-trisadduct 9
15
calculations, presumably because the latter do not consider
van der Waals forces. Compared to 8 and 9, compound 2
maximizes [60]fullerene-[60]fullerene π-stacking interac-
tions and is predicted by MM2 calculations to be the
thermodynamically preferred isomer (Figure 2).
Further evidence for formation of a cis,cis structure (i.e.,
) comes from a careful examination of the H NMR
spectrum for the pure product. As in the case of cis-bisadduct
(bottom).
reaction mixture reveals a reasonably clean transformation
to trisadduct 2. Minor byproduct signals are observed and
appear to be consistent with oligomerization reactions in
which, for example, a single [60]fullerene bridges two
acenes.
1
2
4
,5
1
1
,
five separate phenyl H NMR signals are observed,
13
As expected, a C NMR spectrum indicated the presence
of excess [60]fullerene in the crude reaction mixture.
Isolating trisadduct 2 from the excess [60]fullerene proved
to be difficult. TLC analyses indicate that trisadduct 2 and
indicating slow rotation of the phenyl groups on the NMR
time scale. One set of ortho protons gives rise to a quasi-
doublet at 6.86 ppm and is considerably shielded compared
(14) NMR data for 2: 1H NMR (CS /CDCl ) δ 5.69 (s, 4H), 5.80 (s,
[60]fullerene have nearly identical retention behaviors on
2
3
2
7
7
H), 6.84-6.87 (m, 4H), 7.05-7.09 (m, 4H), 7.32-7.37 (m, 4H), 7.41-
silica under all solvent conditions tested. Consequently, silica
column chromatography is complicated by coelution of
13
.47 (m, 8H), 7.49-7.56 (m, 8H); C NMR (CS2/CDCl3) δ 52.16, 55.09,
2.12, 72.47, 125.55, 127.24, 127.58, 128.20, 128.42, 128.70, 129.19,
[
60]fullerene and 2. Compound 2 was eventually obtained
129.90, 136.20, 136.59, 136.72, 136.86, 138.82, 138.84, 139.57, 139.79,
1
1
39.83, 141.35, 141.48, 141.57, 141.81, 141.82, 141.85, 141.88, 141.94,
42.32, 142.35, 142.40, 142.41, 142.44, 142.48, 142.54, 142.76, 144.42,
14
pure, albeit in a modest 20% isolated yield, via successive
runs on a flash silica column with neat CS as the eluant.
2
144.46, 144.50, 145.06, 145.10, 145.12, 145.18, 145.22, 145.44, 145.45,
1
1
45.95, 145.98, 146.00, 146.22, 146.26, 146.27, 147.30, 147.32, 154.96,
55.46.
(15) MM2 calculations correctly predict that cis-bis[60]fullerene adduct
is preferred to the corresponding trans isomer. Moreover, the 3.08 Å
In principle, three tris[60]fullerene adducts can form
Figure 2) upon reacting [60]fullerene with 6,8,15,17-tetra-
(
1
(
atoms of closest contact) and 9.84 Å (fullerene centroid-to-centroid)
(
13) (a) Birks, J. B.; Appleyard, J. H.; Pope, R. Photochem. Photobiol.
distances between adjacent [60]fullerenes predicted by MM2 are remarkably
close to the 3.065 and 9.805 Å distances observed in the X-ray structure of
1. AM1 and PM3 calculations place the atoms of closest contact on adjacent
[60]fullerenes ∼4.2 Å apart and the fullerene centroid-to-centroid distance
at ∼10.9 Å. See ref 3 for more details.
1
(
963, 2, 493. (b) Clar, E.; Macpherson, I. A. Tetrahedron 1962, 18, 1411.
c) Bowen, E. J.; Tanner, D. W. Trans. Faraday Soc. 1955, 51, 475. (d)
Coulson, C. A.; Orgel, L. E.; Taylor, W.; Weiss, J. J. Chem. Soc. 1955,
961.
2
Org. Lett., Vol. 5, No. 22, 2003
4205

to the other set of ortho protons that give rise to a quasi-
doublet at 7.46 ppm. Likewise, a quasi-triplet at 7.07 ppm
corresponds to a set of shielded meta protons. We assign
the shielded ortho and meta H signals, respectively, to those
protons on 2 that are syn to the [60]fullerene moieties (Figure
1
Table 1. H NMR Chemical Shifts (δ) for Syn-Ortho and
a
Anti-Ortho Protons on [60]Fullerene-Acene Compounds
1
compd
syn δo
anti δo
∆δo (anti δo - syn δo)
1
2
1
1
7.09
6.86
7.32
7.01
7.65
7.46
7.61
7.38
0.56
0.60
0.29
0.37
3). These protons are shielded due to secondary anisotropic
0
1
a
All spectra were recorded in CS2-CDCl3 solvent.
Figure 3. Two views of a partial [60]fullerene-acene structure
additional work would be required to quantify the relation-
ship. Given the small number of molecules impacted, this
may not be reasonable. Qualitatively, however, we can expect
significant shielding of all syn-ortho protons on related [60]-
with ortho and meta phenyl protons shown. The syn-ortho protons
(in boldface above) on 1, 2, 10, and 11 are approximately 3 Å
removed from a [60]fullerene cage.
1
fullerene-acene adducts. To this end, the H NMR spectrum
of the tris[60]fullerene product is consistent with cis,cis-2
but not trans,trans-8. Thus, both sets of ortho protons on 8
are subject to [60]fullerene shielding and the corresponding
fields created by π-bonds on the [60]fullerene surface. The
syn-ortho protons on 2 sit almost directly above and
approximately 3 Å removed from two 6-5 bonds, one on
each of two flanking [60]fullerene moieties. Each 6-5 bond
is one bond removed from a quaternary carbon and is
formally part of a benzene ring substructure on the corre-
sponding [60]fullerene surface.
∆
δ
o
value should be substantially less than that observed
for 1. Instead, the ∆δ value for 2 is modestly larger than
o
that observed for 1, consistent with a structure bearing one
and only one set of shielded syn-ortho protons.
In summary, a diastereoselective synthesis of a cis,cis-
tris[60]fullerene adduct of 6,8,15,17-tetraphenylheptacene,
Although relatively few [60]fullerene-acene compounds
with appropriately positioned phenyl substituents are known,
2
, has been demonstrated starting with [60]fullerene and
[
60]fullerene shielding of syn phenyl and especially syn-
5,7,9,14,16,18-hexahydro-6,8,15,17-tetraphenylheptacene. The
ortho protons is a common feature of those available for
assignment of a cis,cis stereochemistry for 2 is based
upon previous results for structurally similar compounds,
MM2 calculations, and a careful analysis of NMR data.
The successful synthesis of 2 suggests that [60]fullerene-
comparison. The syn-ortho protons on compounds 1, 10, and
11 all exhibit substantial upfield shifts relative to their anti-
ortho proton counterparts (Table 1). The shielding of syn-
ortho protons on 10 and 11 indicates that two [60]fullerene
moieties are not required. However, the extent of shielding
is greater when a syn-ortho proton is syn to two [60]fullerene
moieties as in 1 and 2. This is perhaps best gauged by
comparing the chemical shift difference between syn-ortho
[60]fullerene π-stacking should be added to the synthetic
chemist’s list of noncovalent interactions that can drive the
assembly of interesting structures.
Supporting Information Available: 1H and 13C NMR
spectra for compounds 2, 3, 5-7, 10, and 11. This material
is available free of charge via the Internet at http://pubs.acs.org.
and anti-ortho protons for each molecule (∆δ
o
values, Table
1). Thus, compounds 1 and 2 with two [60]fullerenes
o
surrounding each syn-ortho proton have ∆δ values that are
roughly twice those of compounds 10 and 11. Considerable
OL0356791
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Org. Lett., Vol. 5, No. 22, 2003