Creation of hoop- and bowl-shaped benzenoid systems by selective detraction of [60]fullerene conjugation. [10]Cyclophenacene and fused corannulene derivatives

Article abstract of DOI:10.1021/ja048683w

Selective penta-addition of a methylcopper reagent followed by addition of a phenylcopper reagent to a suitably modified synthetic intermediate results in creation of 40π-electron systems-hoop- and bowl-shaped cyclic benzenoid compounds, [10]cyclophenacene, and dibenzo-fused corannulene derivatives. The 40π-electron cyclophenacene derivatives have been found to be chemically stable, yellow-colored, luminescent (560 nm), and EPR-silent. X-ray crystallographic analysis provided precision structural data sets. The dibenzo-fused corannulene derivatives exhibit blue-green (460 nm) to red (649 nm) fluorescence.

Full text of DOI:10.1021/ja048683w

Published on Web 06/23/2004
Creation of Hoop- and Bowl-Shaped Benzenoid Systems by
Selective Detraction of [60]Fullerene Conjugation.
[10]Cyclophenacene and Fused Corannulene Derivatives
Yutaka Matsuo, Kazukuni Tahara, Masaya Sawamura,† and Eiichi Nakamura*
Contribution from the Department of Chemistry, The UniVersity of Tokyo, Hongo, Bunkyo-ku,
Tokyo 113-0033, Japan
Received March 8, 2004; E-mail: nakamura@chem.s.u-tokyo.ac.jp
Abstract: Selective penta-addition of a methylcopper reagent followed by addition of a phenylcopper reagent
to a suitably modified synthetic intermediate results in creation of 40π-electron systemsshoop- and bowl-
shaped cyclic benzenoid compounds, [10]cyclophenacene, and dibenzo-fused corannulene derivatives.
The 40π-electron cyclophenacene derivatives have been found to be chemically stable, yellow-colored,
luminescent (560 nm), and EPR-silent. X-ray crystallographic analysis provided precision structural data
sets. The dibenzo-fused corannulene derivatives exhibit blue-green (460 nm) to red (649 nm) fluorescence.
Introduction
Among numerous ways to look at [60]fullerene,1 there is a
structural chemists’ view to identify various unconventional
aromatic systems in this spherical molecule. For instance, one
may remove the “north pole” and the “south pole” of the
fullerene molecule to generate the polyene structure of a hoop-
shaped 40π-electron cyclic benzenoid A, [10]cyclophenacene
(Figure 1a).2-4 Having thus far remained hypothetical,5-7 such
hoop-shaped benzenoid compounds have attracted the interest
of chemists for half a century8 because of a questions about
their aromaticity,9 their potential utilities in materials science,5
and their structures that have challenged synthetic chemists for
a number of years.6 They have recently become the subject of
interest of the broader scientific community because they
comprise a part of carbon nanotubes (CNT).10-12 An alternative
Figure 1. [10]Cyclophenacene, fused corannulene, and its carbon-
substituted derivatives. (a) Hoop-shaped molecule C40H20 (A, D5d sym-
metry). (b) Bowl-shaped molecule, fused corannulene C30H12 (B, C2V
symmetry). (c) Dibenzo-fused corannulene C38H16 (C, C2V symmetry) and
p-phenylene-bridged dibenzo-fused corannulene C44H20 (D, Cs symmetry).
(d) [10]Cyclophenacene embedded in a fullerene framework C60R1 R2 H2
(1 and E). (e) p-Phenylene-bridged dibenzo-fused corannulene in a fullerene
framework (3 and F). (f) Dibenzo-fused corannulene in a fullerene
framework (4 and G).
† Present address: Department of Chemistry, Graduate School of Science,
Hokkaido University.
(1) PerspectiVes of Fullerene Nanotechnology; Osawa, E., Ed.; Kluwer
5
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Academic Publishers: Dordrecht, 2002.
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M. Chem. ReV. 2003, 103, 3449-3606.
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2003, 125, 2834-2835.
(4) Hoffmann, R. Int. J. Phil. of Chem. 2003, 9, 7-10.
(5) Schro¨der, A.; Mekelburger, H.-B.; Vo¨gtle, F. Top. Curr. Chem. 1994, 172,
179-201.
view of [60]fullerene may generate hemispherical bowl-shaped
aromatic systems.13,14 For instance, a bowl-shaped aromatic
system, fused corannulene B (C30H12, Figure 1b), can be
identified as a half of fullerene.15 In this article, we describe
(6) Cory, R. M.; McPhail, C. L. AdV. Theor. Interesting Mol. 1998, 4, 53-80.
(7) (a) Ashton, P. R.; Girreser, U.; Giuffrid D.; Kohnke, F. H.; Mathias, J. P.;
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Chem. Soc. 1993, 115, 5422-5429. (b) Godt, A.; Enkelmann, V.; Schlu¨ter,
A. D. Angew. Chem., Int. Ed. Engl. 1989, 28, 1680-1682. (c) Kuwatani,
Y.; Yoshida, T.; Kusaka, A.; Iyoda, M. Tetrahedron Lett. 2000, 41, 359-
363. (d) St. Martin, H. M.; Scott, L. T. The Tenth International Symposium
on Novel Aromatic Compounds, August 2001, San Diego, CA, Abstract
No. P77.
(11) Matsuo, Y.; Tahara, K.; Nakamura, E. Org. Lett. 2003, 5, 3181-3184.
(12) Bettinger, H. F. Org. Lett. 2004, 6, 731-734.
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1300.
(15) (a) Rabideau, P. W.; Abdourazak, A. H.; Folsom, H. E.; Marcinow, Z.;
Sygula, A.; Sygula, R. J. Am. Chem. Soc. 1994, 116, 7891-7892. (b)
Sygula, A.; Rabideau, P. W. J. Am. Chem. Soc. 1999, 121, 7800-7803.
(c) Hagen, S.; Bratcher, M. S.; Erickson, M. S.; Zimmermann, G.; Scott,
L. T. Angew. Chem., Int. Ed. Engl. 1997, 36, 406-408. (d) Mehta, G.;
Panda, G. Chem. Commun. 1997, 2081-2082. (e) Sygula, A.; Marcinow,
Z.; Fronczek, F. R.; Guzei, I.; Rabideau, P. W. Chem. Commun. 2000,
2439-2440.
(8) (a) Heilbronner, E. HelV. Chim. Acta 1954, 37, 921-935. (b) Vo¨gtle, F.
Top. Curr. Chem. 1983, 115, 157-159.
(9) (a) Choi, H. S.; Kim, K. S. Angew. Chem., Int. Ed. 1999, 38, 2256-2258.
(b) Houk, K. N.; Lee, P. S.; Nendel, M. J. Org. Chem. 2001, 66, 5517-
5521. (c) Tu¨rker, L. J. Mol. Struct. (Theochem) 1999, 491, 275-280. (d)
Aihara, J. J. Chem. Soc., Perkin Trans. 2 1994, 971-974. (e) Kanamitsu,
K.; Saito, S. J. Phys. Soc. Jpn. 2002, 71, 483-486.
(10) Saito, R.; Dresselhaus, G.; Dresselhaus, M. S. Physical Properties of Carbon
Nanotubes; Imperial College Press: London, 1998.
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10.1021/ja048683w CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 8725-8734
8725

A R T I C L E S
Matsuo et al.
Figure 2. Synthesis of [10]cyclophenacene derivatives and fused corannulene derivatives. Reaction conditions: a, (1) MeMgBr (30 equiv), CuBr‚SMe2 (30
t
equiv), DMI (30 equiv) in THF/o-dichlorobenzene, (2) NH4Cl/H2O; b, (1) BuOK (1.1 equiv) in THF, (2) TsCN (1.2 equiv) in PhCN; c, (1) PhMgBr (30
equiv), CuBr‚SMe2 (30 equiv), DMI (30 equiv) in THF, (2) NH4Cl/H2O; d, (1) Li+[C10H10]- (30 equiv) in PhCN, (2) NH4Cl/H2O; e, (1) PhMgBr (30 equiv),
CuBr‚SMe2 (30 equiv), 1,4-dicyclohexyl-1,4-diaza-1,3-butadiene (30 equiv) in THF/o-dichlorobenzene, (2) HCl/H2O; f, (1) KH in THF, (2) under air in
THF; g, (1) tBuOK (1.1 equiv) in THF, (2) [PdCl(π-allyl)]2; h, (1) tBuOK (1.1 equiv) in THF, (2) [RhCl(cod)]2; i, (1) Li+[C10H10]- (30 equiv) in PhCN, (2)
EtOH, (3) NH4Cl/H2O. For 1, 2, 3, 4, 7, 9, 10, and 11, isomers always formed with respect to the relative stereochemistry of the top and the bottom
pentagons (only one isomer is shown in this figure).
the full details of our recent communication on the creation of
the first hoop-shaped, [10]cyclophenacene conjugated structure
1 (Figure 1d) by selective detraction of the fullerene conjuga-
tion,3 as well as on the isolation of 3 and 4 (Figure 1e,f) that
possess a dibenzo-fused corannulene conjugation C and its
p-phenylene derivative D (Figure 1c).
later removed after the second penta-addition was achieved. The
second penta-addition to the nitrile 6 was successful with a
phenylcopper reagent to give, in 18% yield, the first hoop-shaped
aromatic compound, 2, as a mixture of three isomers, owing to
the relative position of the cyano group and the bottom hydrogen
atoms. The reaction of methylcopper to cyanide 6 was much
less clean than we hoped it would be. The cyano group was
removed by lithium naphthalenide reduction to give the di-protio
compound 1. Oxidation of its di-potassium compound with air
afforded the oxidized product 7. X-ray crystallographic analysis
of 7 and a palladium derivative, 8, gave the information on the
structure of the first hoop-shaped aromatics (vide infra).
The poor yield (18%) of 2 was due to formation of numerous
side products, resulting largely from the formation of two side-
way adducts 3 and 4, each of which comprises many isomers
due to the relative location of the hydrogen atoms attached to
the fullerene core. Careful product identification and optimiza-
tion of the reaction conditions allowed us to isolate 3 in 32%
yield and to convert it to 4 in high yield. The structure
determination of this side-way adduct was achieved by conver-
sion to rhodium complex 9 followed by X-ray crystallographic
analysis. Alternatively, we could optimize the conditions to
obtain the dibenzo-fused corannulene conjugation system, 4,
Results and Discussion
Synthetic Strategy. Our approach shown in Figure 2 relies
on our own synthetic method that converts [60]fullerene
exclusively and quantitatively into a cyclopentadiene compound,
5, by the reaction of [60]fullerene with a methylcopper reagent
derived from MeMgBr and CuBr‚SMe2.16 Repetition of the
reaction on the bottom 50π-electron part of 5 should directly
produce the desired cyclic 40π-electron system in three overall
steps from [60]fullerene. However, it did not take place at all;
the copper reagent deprotonates 5 to generate the corresponding
cyclopentadienyl anion, which is entirely unreactive toward
further addition reactions (because of the homoconjugation
between the cyclopentadienide and the bottom 50π-electron
system).17 To circumvent this problem, we temporarily protected
the acidic hydrogen atom in 5 with a cyano group, which was
(16) (a) Sawamura, M.; Iikura, H.; Nakamura, E. J. Am. Chem. Soc. 1996, 118,
12850-12851. (b) Sawamura, M.; Toganoh, M.; Kuninobu, Y.; Kato, S.;
Nakamura, E. Chem. Lett. 2000, 270-271. (c) Nakamura, E.; Sawamura,
M. Pure Appl. Chem. 2001, 73, 355-359.
(17) Iikura, H.; Mori, S.; Sawamura, M.; Nakamura, E. J. Org. Chem. 1997,
62, 7912-7913.
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Creation of Hoop- and Bowl-Shaped Benzenoid Systems
A R T I C L E S
Figure 3. Crystal structure of 6‚(CH2Cl2)0.5. (a) ORTEP drawing. CH2Cl2
molecules found in the unit cell and disordered carbon and nitrogen atoms
of the cyano group are omitted for clarity. (b) Top view of CPK model. (c)
Side view of CPK model.
Figure 4. Crystal structure of 7‚(C6H5Cl)1.5. (a) ORTEP drawing. C6H5Cl
molecules found in the unit cell and disordered oxygen atoms are omitted
for clarity. (b) Top view of CPK model. (c) Side view of CPK model.
directly from 6. The formation of two products, 2 and 4, is
obviously due to the presence of six radialene-type pentagons
in 6, all of which can react with the organocopper reagent. The
details of the synthesis and the properties of the [10]cyclo-
phenacene and the dibenzo-fused corannulene are described
below.
Figure 5. Oxidation product of the [60]fullerene pentagon.
Synthesis of [10]Cyclophenacenes and Dibenzo-Fused
Corannulenes. The synthesis started with penta-methylated
[60]fullerene 5,16b which was synthesized in 92% isolated
t
yield from [60]fullerene. It was treated first with BuOK and
then with p-toluenesulfonyl cyanide (TsCN) in benzonitrile to
obtain the cyano fullerene 6 in 81% yield. The structure of this
compound was confirmed by X-ray crystallographic analysis
(Figure 3). In this synthetic sequence, the electronegative cyano
protective group also acts to increase the electrophilicity of
the 50π-electron system (the first reduction potential of 6
is -1.35 V (Fc/Fc+) in tetrahydrofuran (THF); those of 5 and
[60]fullerene are -1.48 V (Fc/Fc+) in THF and -0.98 V in
toluene/acetonitrile, respectively).18
Figure 6. Crystal structure of 8‚C6H5Cl. (a) ORTEP drawing of one of
the two crystallographically independent molecules of 8. C6H5Cl molecules
found in the unit cell and disordered cyano groups are omitted for clarity.
(b) Side view of CPK model. (c) Bottom view of CPK model.
Treatment of 6 with a phenylcopper reagent in the presence
of N,N′-dimethylimidazolidinone (DMI) afforded the [10]cyclo-
phenacene C60(CN)Me5Ph5H (2) in 14% isolated yield as a
mixture of three isomers.19 The cyanide group in 2 was
reductively removed by treatment with lithium naphthalenide
in benzonitrile to obtain C60Me5Ph5H2 (1) in 82% yield. This
compound was found not to give any EPR signals (solid, at
4 K). In agreement with its closed-shell, aromatic (vide infra)
character, the 40π-electron system was found to be chemically
stable.
Conversion of the sp2 carbon atoms in the polar cyclo-
pentadiene moieties into sp3 hybridization was then examined.
Treatment of 1 with potassium hydride followed by exposure
to molecular oxygen afforded the penta-oxygenated product
C60Me5Ph5O3(OH)2 (7). High-resolution APCI-TOF MS of 7
showed that five oxygen atoms attached to the fullerene core.
X-ray structural analysis of 7 revealed the molecular structure
(Figure 4). In the north pole of 7, the cyclopentadienyl anion
was oxidized into a hydroxy bis(epoxide) (Figure 5, I). A similar
part structure has been reported by Taylor et al.20 on C60Me5O2-
(OH), obtained by a reaction of C60Cl621 with excess MeLi. The
south pole cyclopentadienyl anion was oxidized into a hydroxy
mono-epoxide (Figure 5, II). Our oxidation procedure, via a
dianion compound, cleanly gives the epoxide of the pentaphenyl
derivative II, but none of the benzo-furan compound III reported
previously.22 Bis-epoxidation giving I-type product did not take
place on the south pole, likely because of both steric and
electronic effects of the five phenyl groups. The hoop-shaped
40π-electron system was not oxidized at all under these
conditions (or any other conditions so far).
t
Deprotonation of the cyclopentadiene in 2 with BuOK in
THF afforded an anion [K(THF)n][C60(CN)Me5Ph5], which
reacted with [PdCl(π-allyl)]2 to give a palladium complex, Pd-
[C60(CN)Me5Ph5](π-allyl) (8),23 as a single isomer in 57% yield.
The 13C NMR data showed the Cs symmetric structure of 8,
whose signals due to the cyclophenacene carbon atoms appeared
at 144-158 ppm. The crystal structure of 8 is shown in Figure
6. The metrical data of 7 and 8 will be discussed in detail in
the following section.
Thorough analysis and separation of a product mixture of
the reaction of cyanide 6 and phenylcopper reagents allowed
(18) Reed, C. A.; Bolskar, R. D. Chem. ReV. 2000, 100, 1075-1120.
(19) The reaction of methylcopper with cyanide 6 was much less clean than
that of phenylcopper and, hence, was not pursued further.
(20) Al-Matar, H.; Hitchcock, P. B.; Avent, A. G.; Taylor, R. Chem. Commun.
2000, 1071-1072.
(21) Birkett, P. R.; Avent, A. G.; Darwish, A. D.; Kroto, H. W.; Taylor, R.;
Walton, D. R. M. J. Chem. Soc., Chem. Commun. 1993, 1230-1232.
(22) Avent, A. G.; Birkett, P. R.; Darwish, A. D.; Kroto, H. W.; Taylor, R.;
Walton, D. R. M. Chem. Commun. 1997, 1579-1580.
(23) For other nickel, palladium, and platinum complexes of the penta(organo)-
[60]fullerenes, Pd(C60R5)(π-allyl) (R ) Me, Ph), see: Kuninobu, Y.;
Matsuo, Y.; Toganoh, M.; Sawamura, M.; Nakamura, E. Organometallics
2004, 23, 3259-3266.
9
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A R T I C L E S
Matsuo et al.
Figure 7. Crystal structure of 9‚(THF)3. (a) ORTEP drawing. THF
molecules found in the unit cell and disordered cyano group due to a mixture
of three regioisomers are omitted for clarity. (b) Top view of CPK model.
(c) Side view of CPK model.
Figure 8. NICS values in C40H20 (A, D5d symmetric constant) and
C60H12 (E, C2h symmetric constant). Color coding shows NICS-based
aromaticity of the rings (red, aromatic, NICS < -4.0; blue, nonaromatic,
NICS > -4.0). The NICS calculations were performed at the GIAO-SCF/
6-31G*//HF/6-31G* level for the B3LYP/6-31G* geometry.
us to identify the dibenzo-fused corannulene, C60(CN)Me5Ph3H
(3), and its phenylene derivative, C60(CN)Me5Ph5H (4), as a
mixture of isomers with respect to the position of the cyano
group and the hydrogen atom attached to the fullerene core.
Optimization of the conditions by the use of DMI as an additive
led to the production and isolation (silica gel column chroma-
tography with CS2/toluene elution) of the triphenyl compound
3 in 32% yield as a mixture of five isomers. While 3 was found
not to react further with the phenylcopper reagent under the
same conditions, it reacted smoothly in the presence of 1,4-
dicyclohexyl-1,4-diaza-1,3-butadiene to afford the dibenzo-fused
corannulene (4) in 91% isolated yield (an inseparable mixture
of 13 regioisomers). Alternatively, treatment of 6 with the
phenylcopper reagent in the presence of the diazabutadiene
directly afforded 4 in 32% yield and 2 in 18% yield. The cyano
group in 3 and 4 was removed by lithium naphthalenide
reduction in benzonitrile to give di-protio products 10 and 11,
respectively. Rigorous structural identification of 3 and 4 was
hampered by the presence of many isomers, but it was finally
achieved for 3 through the synthesis and crystallographic
analysis of a rhodium derivative (Figure 7). Compound 3 was
converted to the corresponding potassium salt, which was treated
with [RhCl(cod)]2 to afford a rhodium 1,5-cyclooctadiene
complex Rh[C60(CN)Me5Ph3](cod) (9) in 88% yield. The
complex, 9, is an η5-indenylmetal complex, similar to the one
reported for a [70]fullerene derivative,24 and consisted of a
mixture of three regioisomers with respect to the location of
the cyano group. The structural features of the bowl-shaped
aromatic system are described in the following section. On the
basis of the product ratio (18% for 2 and 32% for 4), the carbon
atom on the south pole pentagon appears to be slightly more
reactive than those on the remaining five pentagons in the
“southern hemisphere”.
Table 1. Experimental Data (Standard Deviation in Parentheses)
from X-ray Crystallographic Analysis and Theoretical Optimized
Structures of Model Compounds A (C40H20) and E (C60H12
)
bond length (Å)a,b
compounds
a
b
c
d
e
f
g
7 (X-ray)
8 (X-ray)
A (HF)
A (B3LYP) 1.37
A (PM3)
E (HF)
1.37(2) 1.44(2) 1.43(1) 1.40(2) 1.43(1) 1.45(1) 1.36(1)
1.36(1) 1.45(1) 1.43(1) 1.40(2) 1.44(2) 1.44(2) 1.37(2)
1.35
1.44
1.44
1.43
1.44
1.45
1.44
1.43
1.45
1.44
1.43
1.44
1.44
1.38
1.42
1.40
1.38
1.39
1.40
1.36
1.35
E (B3LYP) 1.37
E (PM3) 1.37
a a, b, c, d, average lengths of five equivalent bonds; e, f, g, average
lengths of 10 equivalent bonds. Calculated data for A and E refer to the
geometry optimized structures (D5d symmetry and C2h symmetry, respec-
tively) obtained by the hybrid density functional method (B3LYP), the
Hartree-Fock ab initio method (HF) using the 6-31G* basis set, and the
semiempirical PM3 method. b Bond coding (a-g) is shown in Figure 8.
structure. This experimental structure obviously does not
conform to the “ideal graphitic structure”, which was assumed
in most of the previous theoretical studies of CNTs.25 The
geometries of the model compounds C40H20 (A) and C60H12 (E)
(Figures 1 and 8) were optimized with quantum mechanical
calculations at various levels of theory (semiempirical, Hartree-
Fock, and hybrid density functional methods)26 and were found
to reproduce the experimental data very well (Table 1). Note
that, in contrast to the [10]cyclophenacenes, there is distinctive
bond alternation in [60]fullerene (1.36 vs 1.47 Å),27 in 1,3-
butadiene (1.35 vs 1.47 Å),28 and in 20π cyclic cis-polyacetylene
(1.36 vs 1.46 Å, B3LYP/6-31G*-optimized, see Supporting
Information).
Structure and Properties of [10]Cyclophenacene. (a)
Structural Analysis. X-ray crystallographic structures were
determined for [10]cyclophenacene derivatives 7 and 8 (Table
1; refer to Figure 8 for the location of bonds a-g). Whereas
the double bonds on the edge are quite short (bonds a and g are
1.36(2) and 1.37(2) Å for 7 and 1.36(1) and 1.37(2) Å for 8,
respectively), bond alternation in the “equator” region is very
small (c, e ) 1.43(1) and d ) 1.40(2) Å for 7, and c ) 1.43(1),
e ) 1.44(2), and d ) 1.40(2) Å for 8, respectively). The
unsymmetrical substitution (methyl vs phenyl groups) and the
coordination of the palladium atom have little effect on the
(b) Aromaticity of [10]Cyclophenacenes. Nucleus indepen-
dent chemical shift (NICS)29 is a useful measure of the magnetic
(25) (a) Rochefort, A.; Salahub, D. R.; Avouris, P. J. Phys. Chem. B 1999,
103, 641-646. (b) Cioslowski, J.; Rao, N.; Moncrieff, D. J. Am. Chem.
Soc. 2002, 124, 8485-8489. (c) Tanaka, K.; Ago, H.; Yamabe, T.; Okahara,
K.; Okada, M. Int. J. Quantum Chem. 1997, 63, 637-644. (d) Liu, L.;
Jayanthi, C. S.; Guo, H.; Wu, S. Y. Phys. ReV. B 2001, 64, 033414.
(26) (a) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys.
Chem. 1994, 98, 11623-11627 and references therein. (b) Ditchfield, R.;
Hehle, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54, 724-728. (c) Hehre,
W. J.; Ditchfield, R.; Pople. J. A. J. Chem. Phys. 1972, 56, 2257-2261.
(d) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213-222.
(27) Liu, S.; Lu, Y.; Kappes, M. M.; Ibers, J. A. Science 1991, 254, 408-410.
(28) Kveseth, K.; Seip, R.; Kohl, D. A. Acta Chem. Scand. 1980, A34, 31-42.
(29) (a) Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; Hommes, N. J.
R. v. E. J. Am. Chem. Soc. 1996, 118, 6317-6318. (b) Bu¨hl, M.; Hirsch,
A. Chem. ReV. 2001, 101, 1153-1183.
(24) Toganoh, M.; Matsuo, Y.; Nakamura, E. J. Organomet. Chem. 2003, 683,
295-300.
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8728 J. AM. CHEM. SOC. VOL. 126, NO. 28, 2004

Creation of Hoop- and Bowl-Shaped Benzenoid Systems
A R T I C L E S
Table 2. Bond Lengths of the Dibenzo-Fused Corannulene Moiety in 9, C, D, F, and G
bond length (Å)a
compounds
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
9b (X-ray)
C (PM3)
C (B3LYP) 1.436
1.44(2) 1.43(1) 1.40(2) 1.44(2) 1.40(1) 1.37(1) 1.44(2) 1.46(1) 1.43(2) 1.40(2) 1.44(1) 1.42(1) 1.42(2) 1.37(1) 1.44(2)
1.432
1.464
1.486
1.487
1.451
1.471
1.451
1.447
1.449
1.446
1.441
1.396
1.409
1.385
1.394
1.405
1.388
1.402
1.388
1.402
1.379
1.445
1.431
1.426
1.446
1.353
1.351
1.328
1.370
1.380
1.393
1.374
1.368
1.379
1.368
1.377
1.366
1.375
1.355
1.430
1.420
1.413
1.445
1.437
1.446
1.438
1.445
1.438
1.432
1.452
1.446
1.448
1.445
1.440
1.461
1.454
1.460
1.455
1.452
1.430
1.435
1.435
1.442
1.442
1.444
1.439
1.443
1.439
1.437
1.376
1.383
1.359
1.381
1.390
1.384
1.397
1.384
1.397
1.373
1.461
1.472
1.476
1.451
1.467
1.454
1.452
1.453
1.451
1.448
1.403
1.407
1.400
1.419
1.421
1.432
1.422
1.430
1.422
1.415
1.391
1.447
1.427
1.393
1.434
1.393
1.408
1.391
1.407
1.386
1.383
1.388
1.375
1.380
1.388
1.375
1.384
1.375
1.383
1.364
1.397
1.400
1.392
1.420
1.423
1.436
1.433
1.428
1.425
1.419
C (HF)
1.435
1.442
Dc (PM3)
Dc (B3LYP) 1.442
1.4.37 1.374
Fc (PM3)
Fc (B3LYP) 1.438
G (PM3) 1.445
G (B3LYP) 1.438
G (HF) 1.435
1.444
1.458
1.451
1.458
1.450
1.445
1.381
1.396
1.381
1.397
1.374
a Bond coding (a-o) is shown in Figure 9 C. Bond coding in other geometries is similar to the bond coding of C in dizenzo-fused corannulene part
structure. Calculated data for C, D, F, and G refer to the geometry optimized structures (C2h symmetry for C and G, Cs symmetry for D, and C1 symmetry
for F, respectively) obtained by the hybrid density functional method (B3LYP), the Hartree-Fock ab initio method (HF) using 6-31G* basis set, and the
semiempirical PM3 method. b Average bond lengths from X-ray single-crystal analysis (standard deviation in parentheses). c Average bond lengths from
optimized geometry.
shielding effect of aromatic ring current. Analysis of the NICS
values for six-membered rings of cyclophenacene in the model
compounds A and E indicates that the hoop-like 40π-electron
system is aromatic (Figure 8, NICS ) -8.62 and NICS )
-11.46 to -11.99, respectively) and the other rings in E are
nonaromatic (NICS ) -1.27 to 0.30). The center of gravity
(CG; NICS ) -7.25 and NICS ) -11.58) is predicted to be
subject to an aromatic shielding effect (a value experimentally
provable by 3He NMR experiments).30 We ascribe the difference
in the NICS values between A and E to the effect of the σ
skeleton.31
Since Heilbronner proposed hypothetical hoop-shaped ben-
zenoid “cyclacene” in 1954,8a the aromaticity of cyclic ben-
zenoids has attracted much interest, and chemists have attempted
in vain to synthesize such molecules in the past half century.
Houk et al.9b and Kim et al.9a predicted that “cycloanthracene”
has a double “trannulene” structure and a small HOMO-LUMO
gap, making it rather unstable. On the other hand, “cyclophen-
acene” was suggested by Aihara et al.9d and Tu¨rker et al. to
enjoy a large degree of conjugative stabilization.9c The 40π-
electron conjugated system in compounds 1 and 7 showed low
chemical reactivity and was EPR-silent. In addition, delocalized
benzenoid structures were found by the X-ray single-crystal
Figure 9. NICS values of the model compounds B, C, D, F, and G
analysis of 7 and 8. This class of compounds has rather large
(GIAO-SCF/6-31G*//HF/6-31G* for the B3LYP/6-31G* geometry). Color
HOMO-LUMO gaps,11 and the NICS values of model com-
coding shows NICS-based aromaticity of the rings (red, aromatic, NICS <
-4.0; blue, nonaromatic, NICS > -4.0). Refer also to Figure 1 for whole
structures of F and G.
pounds A and E also revealed large aromatic shielding effects
at all hexagons in the 40π-electron system. We thus conclude
that the 40π-electron cyclic benzenoid molecules stabilize
themselves by conjugative stabilization, as has been predicted.
Subsequently, a theoretical study on a series of [5,5] and [6,6]
armchair nanotubes up to the carbon number of 20011 showed
that the present cyclophenacene represents the first compound
in a series of finite CNTs, whose chemical properties are
predicted to change periodically as the tube is elongated by a
layer-by-layer addition of carbon atoms. This prediction based
on the frontier molecular orbital energies was recently confirmed
by the theoretical study on the reactivity of CNTs toward
fluorine atom and a carbene-reactive intermediate.12,32
Structure and Properties of Dibenzo-Fused Corannulene.
(a) Structural Analysis. The X-ray crystallographic analysis
of 9 provided the experimental structural data of this intriguing
aromatic system, a dibenzo-fused corannulene embedded in a
fullerene skeleton (Table 2). The bond alternation found in the
crystal structure is as shown in Figure 9 and closely follows
the pattern found in [60]fullerene. The bond lengths obtained
from the experimental structure of 9 agrees within 1.1% error
with the calculated structures of the two model fullerene-derived
compounds F and G and shows a bond alternation pattern
similar to those of corannulene and tetramethyl-fused corannu-
lene.15e Such agreement of bond lengths indicates that the
fullerene framework and the dibenzo-conjugation added to
the parent corannulene structure have a rather small structural
effect despite a rather large difference of hybridization of the
carbon atoms.33
(30) Saunders, M.; Jimenez-Vazquez, H. A.; Cross, R. J.; Mroczkowski, S.;
Freedberg, D. I.; Anet, F. A. L. Nature 1994, 367, 256-285.
(31) Dihedral angles between the two planes including the bonds [a and b] and
[d and e] on the 10 hexagons ) 22.9° (A) and 2.9(4)° (E).
(32) Lu, X.; Tian, F.; Xu, X.; Wang, N.; Zhang, Q. J. Am. Chem. Soc. 2003,
125, 10459-10464.
9
J. AM. CHEM. SOC. VOL. 126, NO. 28, 2004 8729

A R T I C L E S
Matsuo et al.
are in qualitative agreement with the HOMO-LUMO gap
calculated for simplified model compounds E, F, and G.34 We
expect that the photophysical properties of the compounds can
also be modified by changing the R1/R2 organic groups.35-37
Metal complexes 8 and 9, however, are not luminescent,
probably because of quenching of the excited state by the
transition metals.
Summary
In summary, we have accomplished the first synthesis of a
hoop-shaped cyclic benzenoid system, [10]cyclophenacene, by
selective removal of conjugation out of the [60]fullerene
π-electron array and have also found an effective synthetic
route to corannulene-type π-electron conjugated systems. The
experimental data on the [10]cyclophenacenes provided the first
information on the precision structure and chemical and physical
properties of a class of hoop-shaped cyclic benzenoid, which
enjoys a high degree of conjugative stabilization. The present
route offers flexibility of installation of functional groups to
these new benzenoid systems35-38 so that, for instance, we can
control the solubility, synthesize metal complexes, and make
composite materials out of these functionalized molecules. The
syntheses of palladium complex 8 and rhodium complex 9
suggest that the compounds 1, 10, and 11 can be used as starting
materials for the synthesis of previously unavailable classes of
organometallics.39 Finally, we expect that similar multiple-
addition reactions would also be possible for higher fullerenes
to provide an access to other classes of novel aromatic
compounds.
Figure 10. Absorption and emission spectra of [10]cyclophenacene
derivatives and dibenzo-fused corannulene derivatives. (a) C60Me5Ph5H2
(1, 1.0
×
10-5
M in cyclohexane) and C60Me5Ph5O3(OH)2 (7,
1.0 × 10-5 M in cyclohexane). (b) C60Me5Ph5H2 (1, 1.0 × 10-5 M in
cyclohexane), C60(CN)Me5Ph3H (3, 1.0 × 10-5 M in cyclohexane), and
C60(CN)Me5Ph5H (4, 1.0 × 10-5 M in cyclohexane). The intensities of
emission spectra of 3 and 4 are magnified ×8 and ×2, respectively.
Experimental Section
(b) Aromaticity of Dibenzo-Fused Corannulenes. In light
of good agreement of the calculated and experimental geometry
(vide supra), we studied the aromaticity NICS calculations. The
NICS data for various compounds are summarized by red/blue
color coding in Figure 9. All hexagons are aromatic (colored
in red, NICS ) -14.26 to -4.04), and the two five-membered
rings are nonaromatic (blue, NICS ) -1.94 to 7.12). These
results agree with the pattern of bond alternation found by
experiment and by theory.
Absorption and Emission Spectra of [10]Cyclophenacenes
and Dibenzo-Fused Corannulenes. The absorption spectra of
the [10]cyclophenacene molecules (1 and 7 in cyclohexane) are
similar to each other, showing a maximum at ca. 260 nm, with
broad absorption that extends to ca. 500 nm (Figure 10a). The
[10]cyclophenacene derivatives 1 and 7 emit bright yellow
light (λmax ) ∼560 nm and ∼620 nm) with quantum efficiency
(Φ) of 0.10 in cyclohexane (irradiation at 366 nm, rhodamin B
as standard, see Experimental Section). The dibenzo-fused
corannulene 4 exhibits blue-green fluorescence, with a maximum
at 460 nm (Φ ) 0.028, Figure 10b), and the p-phenylene-
bridged compound 3 emits red light, with a maximum at 649
nm (Φ ) 0.012). The maximum wavelength of 3 is red-
shifted ca. 100 nm and that of 4 is blue-shifted ca. 100 nm, as
compared with 1, respectively. The large shift of the maximum
wavelength between 3 and 4 indicates that cyclic conjugation
in the p-phenylene-bridge compound 3 greatly affects the photo-
luminescent property. The wavelengths of the luminescence
General. All manipulations involving air- and moisture-sensitive
compounds were carried out using the standard Schlenk technique under
nitrogen or argon. Hexane and THF were distilled from Na/K alloy
and thoroughly degassed by trap-to-trap distillation before use. Toluene
was distilled from Na and thoroughly degassed by trap-to-trap distil-
lation. Chloroform-d was distilled from CaH2 and thoroughly degassed
by trap-to-trap distillation. THF-d8 was distilled from Na/K alloy and
thoroughly degassed by trap-to-trap distillation. o-Dichlorobenzene was
distilled from CaH2 under nitrogen and stored over molecular sieves.
Benzonitrile was distilled from P2O5 under nitrogen and stored over
molecular sieves. All commercially available reagents were distilled
or recrystallized before use. tBuOK in THF was purchased from Aldrich
Inc. and used as received. 1,4-Dicyclohexyl-1,4-diaza-1,3-butadiene was
prepared according to the literature.40
1H (400 MHz, 500 MHz) and 13C (100 MHz, 125 MHz) NMR
spectra were measured on JEOL EX 400 and ECA 500 spectrometers.
(34) HOMO-LUMO gaps of model compounds E, F, and G obtained from
B3LYP/6-31G* calculation are 2.9647, 3.3663, and 3.4173 eV, respectively.
(35) (a) Sawamura, M.; Kawai, K.; Matsuo, Y.; Kanie, K.; Kato, T.; Nakamura,
E. Nature 2002, 419, 702-705. (b) Matsuo, Y.; Muramatsu, A.; Hamasaki,
R.; Mizoshita, N.; Kato T.; Nakamura, E. J. Am. Chem. Soc. 2004, 126,
432-433.
(36) Isobe, H.; Mashima, H.; Yorimitsu, H.; Nakamura, E. Org. Lett. 2003, 5,
4461-4463.
(37) Hamasaki, R.; Matsuo, Y.; Nakamura, E. Chem. Lett. 2004, 33, 328-329.
(38) Nakamura, E.; Isobe, H. Acc. Chem. Res. 2003, 36, 807-815.
(39) (a) Sawamura, M.; Kuninobu Y.; Nakamura E. J. Am. Chem. Soc. 2000,
122, 12407-12408. (b) Sawamura, M.; Kuninobu, Y.; Toganoh, M.;
Matsuo, Y.; Yamanaka, M.; Nakamura, E. J. Am. Chem. Soc., 2002, 124,
9354-9355. (c) Nakamura, E. Pure Appl. Chem. 2003, 75, 427-434. (d)
Matsuo, Y.; Nakamura, E. Organometallics 2003, 22, 2554-2563. (e)
Toganoh, M.; Matsuo, Y.; Nakamura, E. Angew. Chem., Int. Ed. 2003, 42,
3530-3532. (f) Toganoh, M.; Matsuo, Y.; Nakamura, E. J. Am. Chem.
Soc. 2003, 125, 13974-13975. (g) Matsuo, Y.; Kuninobu, Y.; Ito, S.;
Nakamura, E. Chem. Lett. 2004, 33, 68-69.
(33) Compounds 9, F, and G show larger p-orbital axis vector (POAV) angles
(8.0-12.8°) than C (0.0-11.0°). For the POAV angle, see: (a) Haddon,
R. C.; Scott, L. T. Pure Appl. Chem. 1986, 58, 137-142. (b) Haddon, R.
C. Acc. Chem. Res. 1988, 21, 243-249. (c) Haddon, R. C. Science 1993,
261, 1545-1550.
(40) (a) Kliegman, J. M.; Barnes, R. K. Tetrahedron 1970, 26, 2555-2560. (b)
Kliegman, J. M.; Barnes, R. K. J. Org. Chem. 1970, 35, 3140-3143. (c)
van Koten, G.; Vrieze, K. AdV. Organomet. Chem. 1982, 21, 151-239.
9
8730 J. AM. CHEM. SOC. VOL. 126, NO. 28, 2004

Creation of Hoop- and Bowl-Shaped Benzenoid Systems
A R T I C L E S
Table 3. Crystal Data and Structure Analysis Results for 6, 7, 8, and 9
6‚(CH Cl2)0.5
7‚(C H Cl)1.5
8‚C H Cl
9‚(C H O)3
2
6
5
6
5
4 8
formula
C
68.5H16N1Cl1
C
104H46Cl1.5O4
C
105H50Cl1N1Pd1
C100H66N1Rh1
crystal system
space group
R, Rw (I > 2σ(I))
R1, wR2 (all data)
GOF on F2
a (Å)
orthorhombic
Fdd2 (No. 43)
0.033, -
-, 0.036a
3.112
29.7502(4)
24.2689(7)
20.0769(7)
90
monoclinic
P 21/a (No. 14)
0.145, 0.365
0.243, 0.427
1.265
19.7450(15)
16.5410(20)
20.0340(30)
90
91.6750(60)
90
6540.4(13)
4
monoclinic
P 21/n (No. 14)
0.105, 0.270
0.180, 0.324
0.993
14.9920(17)
27.5470(20)
32.7300(14)
90
97.044(5)
90
13415(5)
8
orthorhombic
P 212121 (No. 19)
0.079, 0.198
0.096, 0.216
1.040
14.3460(7)
14.5830(14)
32.1220(3)
90
90
90
6720.2(9)
4
b (Å)
c (Å)
R (deg)
â (deg)
90
90
γ (deg)
V (Å3)
14495.6(7)
8
Z
T (K)
293(2)
153(2)
173(2)
173(2)
crystal size (mm)
D
0.50, 0.33, 0.25
1.58
0.20, 0.05, 0.05
1.435
0.25, 0.21, 0.20
1.453
0.50, 0.20, 0.15
1.463
calcd (g/cm3)
2θmin, 2θmax (deg)
4.58, 51.22
12396
4267
654
0.25, -0.33
4.54, 51.3
9281
3456
1433
1.29, -1.58
4.12, 51.5
21958
9462
1944
2.696, -1.773
4.72, 51.24
6563
5385
910
0.182, -0.831
no. refln measured (unique)
no. refln measured (I > 2σ(I))
no. parameters
∆ (eÅ-3
)
a A final R index is calculated with I > 3σ(I).
When chloroform-d and THF-d8 were used as solvent, the spectra were
referenced to residual solvent protons in the H NMR spectra (7.26
Electrochemical Measurements. Cyclic voltammetry (CV) was
performed using a BAS CV-50W voltammetric analyzer and three-
electrode cell, with a glassy carbon working electrode and a platinum
wire counter electrode. All potentials were recorded vs a Ag/Ag+
reference electrode and corrected against Fc/Fc+. CV was measured at
a scan rate of 100 mV/s.
1
and 3.58 ppm, respectively) and to solvent carbons in the 13C NMR
spectra (77.0 and 67.4 ppm, respectively). Other spectra were recorded
by the use of the following instruments: IR spectra, JASCO IR-420
and ReactIR 1000; UV/vis spectra, Hitachi U3500; fluorescence spectra,
Hitachi F4010; and mass spectra, Shimadzu LCMS-QP8000 and JEOL
JMS SX102.
UV-Vis Absorption and Fluorescence Measurements. Fluores-
cence spectra were measured on the HITACHI F4010 spectrometer
using a 1.0 × 10-5 M solution of 1, 3, 4, and 7. All solutions were
prepared in spectrograde cyclohexane that was purged with argon prior
to the measurements. Fluorescence quantum yields were determined
using recrystallized rhodamin B (Φ ) 0.71 in ethanol) as a standard.44
Preparation of C60Me5H (5). A white suspension of CuBr‚SMe2
(4.28 g, 20.8 mmol) in THF (30 mL) was treated at 23 °C with a
solution of MeMgBr (1.0 M, 20.8 mL, 20.8 mmol) in THF and with
DMI (2.25 mL, 20.8 mmol). To the resulting yellow suspension, a
solution of C60 (500 mg, 0.694 mmol) in o-dichlorobenzene (50 mL)
was added. After being stirred for 1 h at 23 °C, the reaction was
quenched with NH4Cl (aqueous, 0.5 mL). The mixture was diluted with
toluene (250 mL) and filtered through a pad of silica gel. A red-colored
eluent was concentrated to a small volume and then precipitated with
Et2O (300 mL). The precipitate was washed with EtOH and ether and
dried in vacuo to obtain 1 (507 mg, 92% yield, 95% purity determined
by HPLC). IR (KBr) 2957, 2918, 2856, 1575, 1548, 1521, 1444, 1417,
1370, 1343, 1324, 1285, 1262, 1235, 1200, 1170, 1146, 1127, 1092,
1054, 1034, 1011, 953, 830, 807, 745, 683 cm-1; 1H NMR (400 MHz,
X-ray Crystallographic Analysis. Single crystals of 6, 7, 8, and 9
suitable for X-ray diffraction study were grown and subjected to data
collection. The data sets were collected on a MacScience DIP2030
imaging plate diffractometer using Mo KR (graphite monochromated,
λ ) 0.71069 Å) radiation. Crystal data and data statistics are
summarized in Table 3. The structure of 6 was solved by the directed
method (SIR97).41 The positional and thermal parameters of non-
hydrogen atoms were refined anisotropically on F2 by the full-
matrix least-squares method, using SHELXL-97.42 Hydrogen atoms
were placed at calculated positions and refined “riding” on their
corresponding carbon atoms. In the subsequent refinement, the function
∑ω(Fo - Fc2)2 was minimized, where |Fo| and |Fc| are the observed
2
and calculated structure factor amplitudes, respectively. The agreement
indices are defined as R1 ) ∑(||Fo| - |Fc||)/∑|Fo| and wR2 )
[∑ω(Fo - Fc2)2/∑(ωFo )]1/2. The crystal of 8 contains two crystallo-
graphically independent molecules. While both compounds 6 and 8
consist of single isomers, crystallographic disorder of the cyano groups
was observed. The crystal of 9 consists of a mixture of three
regioisomers with respect to the cyano group. It could not be determined
whether compound 7 (obtained as five regioisomers) crystallizes into
a single isomer or not, since the structure of 7, except for disordered
oxygen atoms, has pseudo-C5 symmetry.
2
4
CDCl3) δ 2.30 (s, 6H, CH3), 2.32 (s, 6H, CH3), 2.42 (s, 3H, CH3); 13
C
NMR (100 MHz, CDCl3) δ 26.91 (2C, CH3), 27.26 (2C, CH3), 32.86
(1C, CH3), 50.98 (2C, C60), 51.12 (1C, C60), 53.13 (2C, C60), 59.22
(1C, C60), 142.89 (2C, C60), 143.52 (2C, C60), 143.74 (2C, C60), 144.04
(2C, C60), 144.08 (2C, C60), 144.28 (2C, C60), 144.64 (2C, C60), 144.82
Theoretical Calculations. All theoretical calculations were per-
formed with the Gaussian 98 package.43 The PM3, the Hartree-Fock,
and the B3LYP calculations with the 6-31G* basis sets were used for
the geometry optimization of model compounds (A, B, C, D, E, F,
and G). The nucleus-independent chemical shift (NICS) at the ring
centers was calculated at the GIAO-SCF/6-31G*//HF/6-31G* level
for the B3LYP/6-31G* geometries.
(43) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann,
R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,
K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi,
R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ciowlowski, J.; Ortiz,
J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Conzalez, C.; Challacombe, M.; Gill, P. M. W.;
Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon,
M.; Replogle, E. S.; Pople, J. A. Gaussian 98, revision A.7; Gaussian,
Inc.: Pitsburgh, PA, 1998.
(41) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115-119.
(42) Sheldrick, G. M. Programs for Crystal Structure Analysis (Release 97-
2); Institut fu¨r Anorganische Chemie der Universita¨t:Go¨ttingen, Germany,
1998.
(44) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991.
9
J. AM. CHEM. SOC. VOL. 126, NO. 28, 2004 8731

A R T I C L E S
Matsuo et al.
(2C, C60), 145.27 (2C, C60), 145.37 (2C, C60), 146.39 (1C, C60), 146.55
(2C, C60), 146.66 (2C, C60), 147.49 (2C, C60), 147.53 (2C, C60), 147.69
(2C, C60), 147.76 (1C, C60), 147.93 (2C, C60), 148.00 (2C, C60), 148.26
(2C, C60), 148.32 (2C, C60), 148.38 (2C, C60), 149.57 (2C, C60), 153.70
(2C, C60), 153.74 (2C, C60), 154.02 (2C, C60), 157.17 (2C, C60); APCI-
MS (+) m/z ) 796 [M+].
31.58-33.22, 50.62-53.22, 54.82-54.84, 55.53-55.83, 57.45-57.65,
59.97-60.88, 118.65-118.70, 127.16-129.07, 134.01-160.33; HRMS
(APCI-TOF, negative) m/z calcd for C84H30N1 [M-H]-, 1052.2378;
found, 1052.2396.
Synthesis of [10]Cyclophenacene C60Me5Ph5H2 (1). To a solution
of C60(CN)Me5Ph5H (80 mg, 66 mmol) in PhCN (20 mL) in a Schlenk
tube was added a solution of lithium naphthalenide (2.6 mL, 0.76 M
in THF, 2.0 mmol). The color of the solution changed immediately
from yellow to dark red, indicating decyanation and formation of a
bis-cyclopentadienyl dianion. After it was stirred for 1 h at 23 °C, the
reaction mixture was quenched by the addition of saturated NH4Cl
(aqueous, 0.10 mL). The color of the resulting solution changed
immediately from dark red to light red, indicating the protonation of
the bis-cyclopentadienyl dianion took place. The mixture was diluted
with toluene (100 mL) and filtered though a pad of silica gel. A red-
colored eluent was evaporated to a small volume, and precipitation
with MeOH afforded a crude product. This mixture was purified by
HPLC (Nacalai Tesque, Buckyprep, 250 mm, toluene/2-propanol, 7:3).
The fractions containing C60Me5Ph5H2 were collected and evaporated
to a small volume. Precipitation with MeOH afforded C60Me5Ph5H2
(65 mg, 82% yield) of 98% purity by HPLC as a mixture of three
isomers. NMR and IR spectra were measured for the mixture of the
stereoisomers. IR (ReactIR, diamond prove) 3064, 3024, 2959, 2918,
2857, 1599, 1521, 1492, 1445, 1370, 1345, 1318, 1262, 1210, 1185,
t
Synthesis of C60Me5CN (6). A solution of BuOK (0.69 mL, 0.69
mmol, 1.0 M in THF) was added to a suspension of C60Me5H (500
mg, 0.63 mmol, 94% purity) in PhCN (10 mL) at 23 °C. The color of
the reaction mixture changed from red to black. A solution of TsCN
(3.0 mL, 0.25 M in PhCN, 0.75 mmol) was added to the mixture. After
it was stirred for 10 min, the reaction was quenched with HCl (aqueous,
0.20 mL). The solvent was removed, and the resulting red-colored solid
was dissolved with CS2. Purification on a pad of silica gel (CS2 and
toluene as eluent) afforded the fractions containing 6. The fractions
were evaporated to a small volume. Precipitation with EtOH and then
washing with Et2O and hexane afforded 6 (416 mg, 81% yield, 99%
HPLC purity). Slow diffusion of ethanol to a methylene chloride
solution of 6 gave a single crystal suitable for X-ray analysis. IR (KBr)
2963, 2920, 2860, 2229 (CN), 1641, 1547, 1445, 1418, 1374, 1264,
1239, 1200, 1106, 684, 658, 552, 522 cm-1
;
1H NMR (400 MHz,
CDCl3) δ 2.38 (s, 6H, CH3), 2.39 (s, 6H, CH3), 2.64 (s, 3H, CH3); 13
C
NMR (100 MHz, CDCl3) δ 25.36 (2C, CH3), 26.80 (2C, CH3), 32.35
(1C, CH3), 51.12 (2C, C60), 51.37 (1C, C60), 52.62 (2C, C60), 55.46
(1C, C60), 118.08 (1C, CN), 143.02 (2C, C60), 143.07 (2C, C60), 143.93
(2C, C60), 144.03 (2C, C60), 144.10 (4C, C60), 144.31 (2C, C60), 144.35
(2C, C60), 144.50 (2C, C60), 145.10 (2C, C60), 145.27 (2C, C60), 146.71
(1C, C60), 146.83 (2C, C60), 146.85 (2C, C60), 147.77 (2C, C60), 147.91
(2C, C60), 147.98 (1C, C60), 148.03 (2C, C60), 148.15 (2C, C60), 148.31
(2C, C60), 148.33 (2C, C60), 148.50 (2C, C60), 148.56 (2C, C60), 148.68
(2C, C60), 151.75 (2C, C60), 152.24 (2C, C60), 152.98 (2C, C60), 156.37
(2C, C60); HRMS (APCI-TOF, negative) m/z calcd for C66H15N1 (M-),
821.12045; found, 821.12261.
1
1158, 1076, 1031, 950, 922, 812, 789, 752, 727, 682, 660 cm-1; H
NMR (400 MHz, THF-d8) δ 2.37-2.50 (s, 15H, CH3), 4.847, 4.853
and 4.868 (s, 1H, three signals of C60-H), 5.527 and 5.545 (s, 1H, three
signals of C60-H), 7.00-7.20, 7.30-7.33, 7.45-7.50, 7.60-7.70 and
7.89-7.91 (m, 25H, C6H5); UV-vis spectra (cyclohexane, ꢀ) 261
(33 400), 278 (32 600), 334 (10 900), 380 (2500), 425 (2000), 454
(2900), 460 (3000) nm; HRMS (FAB, positive) m/z calcd for C95H42
(M+), 1182.3356; found, 1182.3320.
Synthesis of Dibenzo-Fused Corannulene (4). Method A: Syn-
thesis from 6. To a brown suspension of CuBr‚SMe2 (150 mg, 0.73
mmol) and 1,4-dicyclohexyl-1,4-diaza-1,3-butadiene (161 mg, 0.73
mmol) in THF (2.0 mL) was added a solution of PhMgBr (0.97 M in
THF, 0.75 mL, 0.73 mmol) at 23 °C. To the resulting yellow suspension,
a solution of 6 (20 mg, 23 µmol) in o-dichlorobenzene (2.0 mL) was
transferred though a cannula. After it was stirred for 40 h at 40 °C, the
reaction was stopped by the addition of an aqueous HCl. The mixture
was diluted with toluene (20 mL) and filtered though a pad of silica
gel. An orange-colored eluent was concentrated and purified by HPLC
(Nomura Chemical, RPFullerene, 250 mm, toluene/acetonitrile, 2:3).
The fractions containing 4 were collected, and the solvent was
evaporated to a small volume. Precipitation with MeOH afforded 4
(9.5 mg, 32% isolated yield with 98% HPLC purity) as a mixture of
stereoisomers. NMR and IR spectra were measured for the mixture of
the stereoisomers. IR (ReactIR, diamond prove) 3056, 3024, 2962, 2921,
2863, 2227 (CN), 1598, 1582, 1492, 1445, 1374, 1262, 1096, 1075,
1030, 753, 694 cm-1; 1H NMR (500 MHz, CDCl3) δ 1.05-1.30, 1.47-
1.77, 2.02-2.25, 2.36-2.67 and 2.82 (s, 15H, CH3), 4.303, 4.343,
4.349, 4.414, 4.559, 4.618, 4.670, 4.719, 4.713, 4.723, 4.741 and 4.778
(s, 1H, C60-H),45 6.85-8.00 (m, 25H, C6H5); HRMS (APCI-TOF,
negative) m/z calcd for C96H40N1 [M - H]-, 1206.3161; found,
1206.3142.
Synthesis of [10]Cyclophenacene C60(CN)Me5Ph5H (2) and p-
Phenylene-Bridged Dibenzo-Fused Corannulene C60(CN)Me5Ph3H
(3). To a white suspension of CuBr‚SMe2 (3.75 g, 18.3 mmol) in THF
(31 mL) was added a solution of PhMgBr (0.93 M in THF, 20.0 mL,
18.6 mmol) at 23 °C, and then N,N′-dimethylimidazolidinone (2.05
mL, 25.4 mmol) was added immediately. To the resulting dark yellow
solution, a solution of C60(CN)Me5 (515 mg, 0.608 mmol) in o-
dichlorobenzene (50 mL) was transferred though a cannula. After being
stirred for 24 h at 23 °C, the reaction was stopped with an addition of
saturated NH4Cl (aqueous, 0.20 mL). The mixture was diluted with
toluene (200 mL) and filtered though a pad of silica gel. The solvent
of an orange-colored eluent was evaporated, and the orange residue
was purified by silica gel column chromatography (toluene/CS2, 3:97).
The fractions containing 2 were collected, and the solvent was
evaporated to a small volume. Precipitation with MeOH afforded 2
(111 mg, 14% isolated yield) as a mixture of three stereoisomers. The
fractions containing 3 were collected, and the solvent was evaporated
to a small volume. Precipitation with MeOH afforded 3 (205 mg, 32%
isolated yield) as a mixture of five stereoisomers. NMR and IR spectra
were measured for the mixture of the stereoisomers.
2: IR (ReactIR, diamond prove) 3056, 3026, 2963, 2922, 2860, 2229
(CN), 1600, 1493, 1445, 1316, 1210, 1116, 1032, 1003, 950, 913, 684,
1
658 cm-1; H NMR (400 MHz, CDCl3) δ 2.44-2.49 (s, 12H, CH3),
Method B: Synthesis from p-Phenylene-Bridged Dibenzo-Fused
Corannulene (3). To a brown suspension of CuBr‚SMe2 (64 mg, 0.31
mmol) and 1,4-dicyclohexyl-1,4-diaza-1,3-butadiene (69 mg, 0.31
mmol) in THF (2.0 mL) was added PhMgBr (0.97 M in THF, 0.32
mL, 0.31 mmol) at 24 °C. A solution of C60(CN)Me5Ph3H (11 mg, 10
µmol) in o-dichlorobenzene (2.0 mL) was transferred to the yellow
phenylcopper reagent though a cannula. After being stirred for 14 h at
2.66-2.68 (s, 3H, CH3), 5.421, 5.424 and 5.448 (s, 1H, three signals
of C60-H), 7.12-7.27, 7.32-7.38, 7.43-7.47, 7.61-7.70 and 7.82-
7.89 (m, 25H, C6H5); HRMS (FAB-MS, positive) m/z calcd for
C96H41N1 [M]+, 1207.3230; found, 1207.3236.
3: IR (ReactIR, diamond prove) 3059, 3027, 2962, 2923, 2863, 2229,
1593, 1583, 1493, 1445, 1375, 1297, 1243, 1156, 1031, 922, 759, 692,
676 cm-1; 1H NMR (400 MHz, CDCl3) δ 2.03-2.19, 2.38-2.50, 2.68-
2.76 and 3.02 (s, 15H, CH3), 5.04, 5.07, 5.08, 5.09 and 5.12 (s, 1H,
five signals of C60-H), 7.16-7.38, 7.42-7.52, 7.57-7.82 and 8.12-
8.16 (m, 15H, C6H5); 13C NMR (125 MHz, CDCl3) δ 24.99-27.32,
(45) Although the reaction may give 13 isomers due to the stereochemistry of
the cyano group and the hydrogen atom on the C60 exterior, 12 signals due
to the C60-H were observed in the 1H NMR measurement. One C60-H signal
was missing because of overlap with other C60-H signals.
9
8732 J. AM. CHEM. SOC. VOL. 126, NO. 28, 2004

Creation of Hoop- and Bowl-Shaped Benzenoid Systems
A R T I C L E S
40 °C, the reaction was quenched with saturated HCl (aqueous, 10 µL).
The mixture was diluted with toluene (20 mL) and filtered though a
pad of silica gel. A yellow-colored eluent was evaporated to a small
volume. Precipitation with MeOH afforded C60(CN)Me5Ph5H (4) (12
mg, 91% isolated yield with 100% HPLC purity) as a mixture of
stereoisomers.
52.92 (1C, C60), 55.42 (1C, C60), 57.12 (2C, CH2CH), 59.28 (2C, C60),
59.36 (1C, C60), 59.39 (2C, C60), 99.87 (1C, CHCH2), 118.96 (1C, CN),
121.28 (1C, C60), 121.45 (2C, C60), 122.32 (2C, C60) 127.00 (5C,
p-C6H5) 127.63 (10C, m-C6H5), 128.24 (10C, o-C6H5), 143.90 (2C, C60),
144.16 (2C, C60), 144.27 (2C, C60), 144.34 (1C, ipso-C6H5), 144.38
(2C, C60), 144.46 (2C, C60), 144.93 (2C, C60), 145.52 (2C, C60), 146.02
(2C, C60), 146.41 (2C, C60), 146.63 (2C, C60), 146.66 (2C, C60), 146.88
(2C, C60), 147.76 (2C, C60), 151.09 (2C, C60), 151.27 (2C, C60), 153.37
(2C, C60), 153.40 (2C, C60), 154.05 (2C, C60), 154.26 (2C, C60), 154.59
(2C, C60), 155.07 (2C, C60), 156.41 (2C, C60), 158.04 (2C, C60); HRMS
(APCI-TOF, positive) m/z calcd for C99H45N1105Pd1 (M+), 1352.26028;
found, 1206.25577.
Synthesis of Penta-oxygenated Compound (7). C60Me5Ph5H2 (1,
10 mg, 8.5 mmol) and KH (3.2 mg, 80 mmol) were dissolved in THF
(5.0 mL) in a Schlenk tube. The color of the solution changed
immediately from yellow to blackish-brown, indicating the formation
of a bis-cyclopentadienyl dianion, [K]2[C60Me5Ph5]. The dianion was
allowed to react with oxygen in air to afford oxidized products. This
mixture was purified by column chromatography on silica gel (30-
70% toluene in hexane) to obtain C60Me5Ph5O3(OH)2 (4.5 mg, 42%
yield) as a mixture of isomers. Single crystals suitable for X-ray
structure analysis were obtained by slow diffusion of MeOH to a
saturated chlorobenzene solution of C60Me5Ph5O3(OH)2. IR (ReactIR,
diamond prove) 3501 (OH), 3484 (OH), 3084, 3058, 3031, 3025, 2963,
2923, 2860, 1598, 1583, 1494, 1446, 1373, 1365, 1345, 1323, 1224,
1070, 1019, 927, 807, 752, 723, 685 cm-1; 1H NMR (400 MHz, CDCl3)
δ 2.14-2.46 (s, 15H, CH3), 3.86-3.91 (s, 1H, OH), 4.59-4.60 (s, OH),
7.13-7.17 7.26-7.35, 7.42-7.48, 7.55-7.57, 7.78-7.80, 7.86-7.90
and 8.09-8.12 (m, 25H, C6H5); UV-vis spectra (cyclohexane, ꢀ) 256
(32 600), 282 (22 000), 335 (9600), 414 (1000), 424 (1600), 452 (3300)
nm; HRMS (APCI-TOF, positive) m/z calcd for C95H41O5 (M - 1)+,
1261.2954; found, 1261.29370.
Synthesis of [K(THF)n][C60(CN)Me5Ph3]. To a THF-d8 (0.50 mL)
solution of C60(CN)Me5Ph3H (3, 7.0 mg, 6.6 µmol) in an NMR tube,
a tBuOK solution (13 µL, 1.0 M in THF, 13 µmol) was added at room
temperature. The color of the solution changed immediately from orange
to black, indicating the formation of the cyclopentadienyl anion with
three structural isomers of [K(THF)n][C60(CN)Me5Ph3]. 1H NMR (400
MHz, THF-d8) δ 2.08-2.10, 2.36-2.42, 2.62-2.64 and 2.92 (m, 15H,
CH3), 7.00-7.35, 7.85-7.97 and 8.41-8.48 (m, 15H, C6H5).
Synthesis of Rh[C60(CN)Me5Ph5](cod) (9). To a solution of
C60(CN)Me5Ph3H (3, 15 mg, 14 µmol) in THF (2.0 mL) was added a
t
solution of BuOK (17 µL, 1.0 M in THF, 17 µmol). The color of
the solution changed from orange to black, indicating formation
of [K(THF)n][C60(CN)Me5Ph3]. To the reaction mixture was added
[RhCl(cod)]2 (21 mg, 43 µmol), and the mixture was stirred for 10
min at 26 °C. Precipitation with MeOH afforded Rh[C60(CN)Me5Ph3]-
(cod) (16 mg, 88% yield) as a mixture of three isomers. Single crystals
suitable for X-ray structure analysis were obtained by slow diffusion
of methanol to a THF solution of 9. NMR and IR spectra were measured
for the mixture of the stereoisomers. IR (ReactIR, diamond prove)
3058, 3028, 2961, 2921, 2864, 2831, 2227, 1599, 1494, 1445, 1373,
Synthesis of [K(THF)n][C60(CN)Me5Ph5]. To a THF-d8 (0.50 mL)
solution of C60(CN)Me5Ph5H (2, 27 mg, 22 µmol) in a NMR tube was
t
added a THF solution of BuOK (30 µL, 1.0 M in THF, 30 µmol) at
room temperature. The color of the solution changed immediately from
yellow to black, indicating the formation of cyclopentadienyl anion.
1H NMR (400 MHz, THF-d8) δ 2.36 (s, 12H, CH3), 2.52 (s, 3H, CH3),
7.00-7.07 (m, 15H, m- and p-C6H5), 7.90-7.98 (m, 10H, o-C6H5);
13C NMR (100 MHz) δ 26.06 (2C, CH3), 27.22 (2C, CH3), 32.09 (1C,
CH3), 51.13 (1C, C60), 51.56 (2C, C60), 53.09 (1C, C60), 56.34 (1C,
C60), 62.58 (2C, C60), 62.68 (2C, C60), 62.73 (1C, C60), 119.75 (1C,
CN), 125.69 (2C, p-C6H5), 125.70 (3C, p-C6H5), 125.81 (1C, C60)
126.03 (2C, C60) 127.03 (2C, C60), 127.98 (10C, three signals of
m-C6H5), 129.50 (8C, two signals of o-C6H5), 129.54 (2C, o-C6H5),
143.49 (2C, C60), 143.78 (2C, C60), 144.03 (2C, C60), 144.46 (2C, C60),
145.65 (2C, C60), 147.10 (2C, C60), 147.55 (3C, two signals of ipso-
C6H5), 147. 63 (2C, ipso-C6H5), 148.54 (2C, C60), 149.31 (2C, C60),
149.56 (4C, two signals of C60), 149.77 (2C, C60), 151.01 (2C, C60),
152.37 (2C, C60), 153.45 (2C, C60), 154.70 (2C, C60), 156.40 (2C, C60),
158.15 (2C, C60), 159.33 (2C, C60), 159.53 (2C, C60), 160.15 (2C, C60),
160.80 (2C, C60), 160.90 (2C, C60).
1297, 1243, 1155, 1033, 1004, 963, 921, 861, 745, 733, 695, 678 cm-1
;
1H NMR (400 MHz, CDCl3) δ 1.74-1.77 (m, 8H, cod), 1.78-1.80
(m, 2H, cod), 2.22-2.32, 2.45-2.54, 2.67-2.77 and 2.92 (s, 15H,
CH3), 3.42 (br, 2H, cod), 7.12-7.32, 7.47-7.67, 7.75-7.79 and
9.28-9.35 (m, 15H, C6H5); HRMS (APCI-TOF, positive) m/z calcd
for C92H42N1103Rh1 (M+), 1263.23723; found, 1263.23883.
Synthesis of p-Phenylene-Bridged Dibenzo-Fused Corannulene
C60Me5Ph3H2 (10). To a solution of C60Me5CNPh3H (3, 40 mg, 38
µmol) in PhCN (10 mL) in a Schlenk tube was added a solution of
lithium naphthalenide (1.5 mL, 0.76 M in THF, 1.1 mmol) under an
argon atmosphere. The color of the solution changed immediately from
yellow to blackish-red, indicating the decyanation and formation of
bis-cyclopentadienide had occurred. After it was stirred for 1 h at 23
°C, the reaction was quenched by the addition of EtOH (0.10 mL) and
saturated NH4Cl (aqueous, 0.05 mL). The color of the solution changed
immediately from dark red to light red. The mixture was diluted with
toluene (50 mL) and filtered though a pad of silica gel, which was
done with a small amount of MeOH. A red-colored eluent was
evaporated to a small volume, and precipitation with MeOH afforded
a crude product. This mixture was purified by HPLC (Nacalai Tesque,
Buckyprep, 250 mm, toluene/2-propanol, 5:5) under an argon atmo-
sphere. The fractions containing 10 were collected and concentrated
to a small volume. Precipitation with MeOH afforded 10 (23 mg,
59% yield), with 98% HPLC purity, as a mixture of five isomers. IR
(ReactIR 1000, diamond prove) 3059, 3030, 2960, 2918, 2859, 1598,
1493, 1445, 1241, 1155, 1072, 1031, 921, 911, 748, 731, 714, 685,
660 cm-1; 1H NMR (400 MHz CDCl3) δ 1.80-2.04, 2.34-2.39, 2.46-
2.49, 2.60-2.61 and 2.74 (s, 15H, CH3), 4.445, 4.458, 4.591, 4.615
and 4.686 (s, 1H, C60-H), 4.991, 5.108, 5.029, 5.034 and 5.063 (s, 1H,
C60-H), 7.00-7.43, 7.45-7.52, 7.62-7.73, 7.75-7.79 and 8.12-8.15
(m, 15H, C6H5); APCI-MS (-) m/z ) 1027 [(M - 1)-].
Synthesis of Pd[C60(CN)Me5Ph5](π-allyl) (8). A THF solution of
tBuOK (0.50 M, 73 µL, 36 µmol) was added to a solution of
C60(CN)Me5Ph5H (2, 40 mg, 33 µmol) in THF (4.0 mL). The color of
the solution changed from yellow to black, indicating formation of
[K(THF)n][C60(CN)Me5Ph5]. [Pd(π-allyl)Cl]2 (7.3 mg, 20 µmol) was
added to the solution. After it was stirred at 26 °C for 10 min, the
reaction was quenched with saturated NH4Cl (aqueous, 0.10 mL). The
crude mixture was diluted with toluene (10 mL), and the organic layer
was collected. After being dryed over MgSO4, the solution was
concentrated in vacuo. The resulting orange solid was purified by HPLC
(Nacalai Tesque, Buckyprep, 250 mm, toluene/hexane, 3:7). The
fractions containing 8 were collected and evaporated to a small volume.
Precipitation with MeOH afforded 8 (26.0 mg 57% yield). Recrystal-
lization from a two-layered solution of chlorobenzene and ethanol gave
1
a single crystal of 8. H NMR (400 MHz, CDCl3) δ 2.17 (d, JH-H
)
12.0 Hz, 2H, allyl-CH2(anti)), 2.41 (s, 6H, CH3), 2.44 (s, 6H, CH3),
2.66 (s, 3H, CH3), 3.14 (d, JH-H ) 6.4 Hz, 2H, allyl-CH2(syn)), 4.78
(ddt, 1H, allyl-CH), 7.16-7.30 (m, 10H + 5H, o,m-C6H5), 7.84-7.86
(m, 10H, p-C6H5,); 13C NMR (100 MHz, CDCl3) δ 25.46 (2C, CH3),
26.70 (2C, CH3), 31.55 (1C, CH3), 50.99 (1C, C60), 51.41 (2C, C60),
Synthesis of Dibenzo-Fused Corannulene C60Me5Ph5H2 (11). To
a solution of C60(CN)Me5Ph5H (4, 15 mg, 12 µmol) in PhCN (4.0 mL)
in a Schlenk tube was added a solution of lithium naphthalenide (0.74
9
J. AM. CHEM. SOC. VOL. 126, NO. 28, 2004 8733

A R T I C L E S
Matsuo et al.
mL, 0.50 M in THF, 0.37 mmol). The color of the solution changed
immediately from yellow to dark red, indicating decyanation and
formation of a bis-cyclopentadienide. After being stirred for 1 h at 23
°C, the reaction mixture was quenched by the addition of EtOH and
then saturated NH4Cl (aqueous, 0.10 mL). The color of the resulting
solution changed immediately from dark red to light red, indicating
that the protonation of the bis-cyclopentadienyl dianion took place. The
mixture was diluted with toluene (20 mL) and filtered though a pad of
silica gel. A red-colored eluent was evaporated to a small volume, and
precipitation with MeOH afforded a crude product. This mixture was
purified by HPLC (Nacalai Tesque, Buckyprep, 250 mm, toluene/
2-propanol, 7:3). The fractions containing 11 were collected and
concentrated to a small volume. Precipitation with MeOH afforded 11
(9.1 mg, 63% yield), with 95% HPLC purity, as a mixture of isomers.
IR (ReactIR, diamond prove) 3085, 3058, 3027, 2958, 2919, 2861,
1600, 1584, 1493, 1445, 1372, 1181, 1156, 1136, 1078, 1032, 1003,
4.126, 4.313, 4.320, 4.557, 4.593 and 4.636 (s, 2H, C60-H), 6.92-7.24,
7.31-7.36, 7.39-7.41, 7.42-7.47, 7.51-7.54, 7.57-7.66 and 7.71-
7.82 (m, 25H, C6H5); HRMS (APCI, negative) m/z calcd for C95H41
[(M - H)-], 1181.3208; found, 1181.3256.
Acknowledgment. The present research was supported by a
Grant-in-Aid for Scientific Research (Specially Promoted
Research) and the 21st Century COE Programs for Frontiers in
Fundamental Chemistry. We thank Frontier Carbon Corp. for
the generous supply of [60]fullerene.
Supporting Information Available: Optimized geometry
(A-G) and CIF files, including lists of positional parameters,
thermal displacement parameters, bond lengths, and bond angles
for 6, 7, 8, and 9. This material is available free of charge via
the Internet at http://pubs.acs.org.
1
928, 754, 694, 675 cm-1; H NMR (500 MHz, CDCl3) δ 1.14-1.27,
1.37-1.64 and 2.04-2.68 (s, 15H, CH3), 3.946, 3.974, 3.986, 4.103,
JA048683W
9
8734 J. AM. CHEM. SOC. VOL. 126, NO. 28, 2004