[2+1] Cycloaddition of nitrene onto C60 revisited: Interconversion between an aziridinofullerene and an azafulleroid

Article abstract of DOI:10.1002/anie.200704410

(Figure Presented) An open and closed case: The reversible interconversion of a [1,2]aziridinofullerene and a [1,6]azafulleroid represents the first such example for a monosubstituted fullerene. While the [1,2]aziridinofullerene rearranges thermally to th

Full text of DOI:10.1002/anie.200704410

Communications
DOI: 10.1002/anie.200704410
Fullerene Chemistry
[2+1] Cycloaddition of Nitrene onto C60 Revisited: Interconversion
between an Aziridinofullerene and an Azafulleroid**
Tsukasa Nakahodo, Mitsunori Okada, Hiroyuki Morita, Toshiaki Yoshimura,
Midori O. Ishitsuka, Takahiro Tsuchiya, Yutaka Maeda, Hisashi Fujihara, Takeshi Akasaka,*
Xingfa Gao, and Shigeru Nagase*
It is known that organic azides react with a [6,6] bond of C60
through a 1,3-dipolar [3+2] cycloaddition to afford triazo-
lines.[1] Thermolysis of a triazoline, followed by concomitant
loss of nitrogen, gives rise to a [1,6]azafulleroid 1 and a
[1,2]aziridinofullerene 2 (Scheme 1).[2] Both 1 and 2 can also
nature of the substituent.[3] Furthermore, azides have major
associated problems in regards to toxicityand explosibility.
Thus, new useful methods for the preparation of azafulleroids
and aziridinofullerenes are expected.
[4]
Sulfilimines[5] are known to generate an N-substituted
nitrene in thermal and photochemical reactions. Recently, it
has been reported that N-sulfenylsulfilimine generates a
sulfenylnitrene under mild conditions. Nitrenes readily react
with alkenes to afford the corresponding three-membered
aziridines.[6] In this context, a nitrene is expected to be a key
intermediate, instead of an azide, in the aziridination of
fullerene.
be obtained directlyfrom the reaction of C and azides at
60
higher temperatures, but the ratio of 1:2 depends on the
In the course of our studyon the development of synthetic
[2]
methodologyfor the preparation of [1,2]aziridinofullerene,
we carried out the photoreaction of C60 with an
N-p-toluenesulfonylsulfilimine[7] having a dibenzothiophene
structure (3; Scheme 2) to accomplish the regioselective
Scheme 1. Structures of 1 and 2.
[*] M. Okada, Dr. M. O. Ishitsuka, Dr. T. Tsuchiya, Prof. Dr. T. Akasaka
Center for Tsukuba Advanced Research Alliance
University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan)
Fax: (+81)29-853-6409
E-mail: akasaka@tara.tsukuba.ac.jp
Homepage: http://www.tara.tsukuba.ac.jp/~akasaka-lab/
Dr. X. Gao, Prof. Dr. S. Nagase
Department of Theoretical Molecular Science
Institute for Molecular Science, Okazaki, Aichi 444-8585 (Japan)
Fax: (+81)56-453-4660
E-mail: nagase@ims.ac.jp
Dr. T. Nakahodo, Prof. Dr. H. Fujihara
Department of Applied Chemistry
Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502 (Japan)
Scheme 2. Photoreaction of C60 with N-tosylsulfilimine 3.
Ts =tosyl=p-toluenesulfonyl.
Dr. Y. Maeda
Department of Chemistry
Tokyo Gakugei University, Koganei, Tokyo 184-8501 (Japan)
synthesis of N-tosyl[1,2]aziridinofullerene ([6,6]-closed
C60NTs, 4). It is well known that 1,6-azafulleroids 1 readily
cyclize thermally and photochemically to afford [1,2]aziridi-
nofullerenes 2, while the reverse reaction hardlyoccurs. [8] This
finding mayindicate that 2 is more thermallystable than 1.
Prof. Dr. H. Morita, Prof. Dr. T. Yoshimura
Department of Applied Chemistry
Graduate Schoolof Science and Engineering
University of Toyama, Gofuku, Toyama 930-8555 (Japan)
[**] We thank Dr. H. Sawa for his experimentalhepl at the Photon
Factory. We also thank T. Wakahara for interesting discussions. This
work was supported in part by a Grant-in-Aid and the 21st Century
COE Program, Nanotechnology Support Project, The Next Gener-
ation Super Computing Project (Nanoscience Project), and Scien-
tific Research on Priority Area from the Ministry of Education,
Culture, Sports, Science, and Technology of Japan.
We examined the stabilityof the newlysynthesized
4 and
found that it thermallyrearranges to a [1,6]azafulleroid ([5,6]-
open C60NTs, 5) and that the photochemical reversible
reaction also takes place.[9] Here we report for the first time
the reversible interconversion between 1 and 2. The structures
of both adducts were successfullydetermined bysingle-crystal
X-rayanalyses.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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Chemie
The photoreaction of C60 with one equivalent of sulfili-
mine 3 afforded the corresponding monoadduct (C60NTs, 4)
as a major product with 80% conversion. The absorption
band at 430 nm in the UV/Vis spectrum of 4 is indicative of
the formation of a 1,2-addition product of C60 (Figure 1).[10]
Figure 2. X-ray crystalstructures of 4 (left) and 5 (right) with thermal
ellipsoids at the 50% probability level; only one orientation is shown
and CS2 is omitted for clarity.
calculated at the B3LYP/6-31G(d,p) level.[15] Azafulleroid 5
has two geometric isomers (5a and 5b) with different
conformations of the N-tosyl group (see the Supporting
Information for the optimized structures of 5a and 5b). Both
5a and 5b are slightlymore stable than 4 (Table 1). These
Figure 1. UV/Vis spectra of aziridinofullerene 4 and azafulleroid 5.
To examine the thermal stabilityof the monoadduct, a
solution of 4 in o-dichlorobenzene (ODCB) was heated at
1808C for 10 hours (Scheme 3). HPLC analysis of the reaction
Table 1: Relative energies (kcalmolÀ1) and HOMO/LUMO energies (eV)
of 4 and 5.
Isomers
Relative
energies
HOMO
LUMO
HOMO/LUMO
gap
[6,6]-closed 4
[5,6]-open 5a
[5,6]-open 5b
0.00
À0.04
À0.75
À5.82
À6.01
À5.93
À3.21
À3.32
À3.21
2.61
2.69
2.72
Scheme 3. Interconversion between 4 and 5.
results are consistent with the fact that 4 thermallyrearranges
to 5. This situation is different from the known thermal
isomerizaiton of 1 to 2. This unusual phenomenon may
originate from the introduction of a tosylated amine bridge.
In conclusion, it has been shown that the addition of a
nitrene generated bythe photochemical reaction of sulfili-
mine 3 occurs at the [6,6] junction of C60 to afford the
[1,2]aziridinofullerene 4. It is found that 4 thermallyrear-
ranges to the [1,6]azafulleroid 5, and is the first example for a
monosubstituted fullerene.[16] Moreover, photochemical ring-
closure of 5 also takes place to afford 4. The structures of 4
and 5 have been characterized byNMR spectroscopyand X-
ray crystallographic analyses.[17]
mixture showed that the peak intensityof 4 decreased while
that of a new peak increased in size. The MALDI-TOF mass
spectrum of the product exhibited a molecular ion signal at
m/z 889. A band at 430 nm, which is characteristic of a
1,2-addition product,[10] did not appear in its UV/Vis spec-
trum. These data reveal that 5 maybe a regioisomer of
4
which has an open structure.[3] It was found that the isomer-
ization of 4 occurs in good yield upon heating. A reverse
isomerization of 5 to 4 was also observed photochemically
(see the Supporting Information).
Although a [5,6]-open azafulleroid 1 has been shown to
isomerize readilyto a [6,6]-closed type aziridinofullerene 2,[11]
the single-crystal X-ray analysis of 1 had not been reported.
We have succeeded in the structural determination of both
[6,6]-closed aziridinofullerene 4 and [5,6]-open azafulleroid 5
by single-crystal X-ray analysis (Figure 2).[12,13] The dihedral
angles of the N-tosyl ligand on C60 (f(N-S-Cipso = Cortho)) in 4
and 5 are 95.68 and 104.08, respectively, for the aryl
sulfonamide conformations.[14]
Experimental Section
General: Toluene was distilled over benzophenone sodium ketyl
under argon prior to use in the reactions. ODCB was distilled over
P2O5 under vacuum prior to use. CS2 was distilled over P2O5 under
argon prior to use. HPLC isolation was performed on a LC-908
system (Japan Analytical Industry Co., Ltd.). Toluene was used as the
eluent. Mass spectrometric analysis was performed on a Bruker
BIFLEX III spectrometer in the negative mode with 1,1,4,4-
tetraphenylbutadiene used as the matrix. The UV/Vis spectra were
To clarifythe reversible rearrangement, the relative
stabilities and HOMO/LUMO energies of 4 and 5 were
measured between 400 and 800 nm in toluene solution on
a
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Communications
SHIMADZU UV-3150 spectrophotometer. NMR spectra were
[2] J. Averdung, J. Mattay, Tetrahedron 1996, 52, 5407 – 5420.
[3] L. Ulmer, J. Mattay, Eur. J. Org. Chem. 2003, 2933 – 2940.
[4] M. Prato, Q. C. Li, F. Wudl, V. Lucchini, J. Am. Chem. Soc. 1993,
115, 1148 – 1150.
1
obtained on a Bruker AVANCE 500 spectrometer. The H and 13C
shifts were calibrated with tetramethylsilane (TMS) as an internal
reference (d = 0.0).
3: A solution of dibenzothiophene (2.0 g, 10.73 mol), chloramine-
T (4.53 g, 16.10 mol), and MgSO4 (1.93 g, 16.10 mol) in acetonitrile
(20 mL) was stirred at 508C for 18 h. The reaction mixture was then
cooled to room temperature and the MgSO4 removed byfilteration.
The filtrate was extracted with CHCl3 (20 mL ” 3), and the organic
layer then dried over MgSO4 and evaporated under reduced pressure.
The resulting solid was recrystallized from MeOH to give 3 (1.42 g,
[5] a) N. Furukawa, M. Fukumura, T. Nishio, S. Oae, J. Chem. Soc.
Perkin Trans. 1 1977, 96 – 98; b) Y. Hayashi, D. Swern, J. Am.
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430.
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2001, 1256 – 1257.
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Chem. Eur. J. 1998, 4, 2037 – 2042.
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Ishii, Y. Araki, O. Ito, J. Am. Chem. Soc. 2002, 124, 13364 –
13365.
[10] A. Hirsch, T. Groesser, A. Skiebe, A. Soi, Chem. Ber. 1993, 126,
1061 – 1067.
[11] J. Averdung, J. Mattay, Tetrahedron 1996, 52, 5407 – 5420.
[12] The X-raydiffraction data collection of [5,6]-open azafulleroid 5
was performed on beamline BL-1B at the Photon Factory, KEK,
Japan.
1
38%) as a colorless solid. H NMR (300 MHz, CDCl3, 293 K): d =
2.44 (s, 3H), 7.26 (d, J = 8.3 Hz, 2H), 7.44–7.47 (m, 2H), 7.63–7.67 (m,
4H), 7.83 (d, J = 8.4 Hz, 2H), 7.87 ppm (d, J = 8.3 Hz, 2H); 13C NMR
(75 MHz; CDCl3, 293 K): d = 21.7, 122.7, 126.9, 127.8, 129.6, 130.3,
133.2, 137.5, 137.7, 141.5, 142.2 ppm; m.p. 171.5–173.08C; MALDI-
TOF MS: m/z 353 [M]À; UV/Vis: lmax (e) 320 (1313) nm.
Photoreaction of C60 with 3 (Scheme 2): A solution of C60
(15.0 mg, 2.8 ” 10–3m) and sulfilimine 3 (7.4 mg, 2.8 ” 10À3 m) in
toluene was placed in a pyrex tube and degassed by freeze-thaw cycles
under reduced pressure before irradiating with a high-pressure
mercurylamp ( > 300 nm) at 208C for 30 min. The reaction mixture
was analyzed by HPLC as follows: column, Buckyprep f4.6 ”
[13] a) Crystal data for 4·CS2: C136.53H14N2O4S7.06, Mr = 1972.33, black
250 mm; eluent, toluene; flow rate, 1.0 mLminÀ1
;
temperature,
needles, 0.50 ” 0.14 ” 0.06 mm, triclinic, space group P1 (no. 2),
¯
1
408C; detector, UV 320 nm. 4: H NMR (300 MHz, [D6]acetone in
a capillary/CS2, 293 K): d = 1.95 (s, 3H), 6.81 (d, J = 8.3, 2H),
7.44 ppm (d, J = 8.3, 2H); 13C NMR (125 MHz; [D6]acetone in a
capillary/CS2, 293 K): d = 22.47, 80.10, 128.98, 130.35, 136.43, 141.18,
141.61, 142.14, 142.47, 143.05, 143.36, 143.42, 143.69, 144.18, 144.28,
144.46, 144.76, 145.21, 145.29, 145.37, 145.39, 145.54 ppm; MALDI-
TOF MS: m/z 889 [MÀ], 734 [MÀ(tosyl)]À, 720 [MÀ(N-tosyl)]À.
Interconversion between 4 and 5: Thermal rearrangement: A
solution of 4 (4.2 ” 10À4 m) in [D4]ODCB was degassed byfreeze-thaw
cycles under reduced pressure and then heated at 1808C in the dark
for 10 h. Photochemical rearrangement: The solution was heated for
5 h and then photoirradiated with a halogen lamp fitted with a filter
a = 18.572(2), b = 21.376(2), c = 10.0431(13) Š, a = 92.632(3),
b = 105.614(3), g = 94.808(2)8, V= 3816.7(8) Š3, Z = 2; 1calcd
=
1.716 gcmÀ3
, , qmax = 20.828, T= 120 K,
m(MoKa) = 2.88 cmÀ1
12109 measured reflections, 5858 independent reflections, 1367
refined parameters, GOF = 1.128, R1 = 0.0906 and wR2 = 0.2020
for all data; R1 = 0.0905 for 5850 independent reflections (I >
2.0s(I)), min./max. electron density0.89/ À0.63 eŠÀ3; b) crystal
data for 5·CS2: C68H7NO2S3, Mr = 965.99, black plates, 0.20 ”
0.15 ” 0.10 mm, orthorhombic, space group Pnma (no. 62), a =
18.2815(6), b = 13.6431(5), c = 14.5987(5) Š, V= 3641.2(2) Š3,
Z = 4; 1calcd = 1.762 gcmÀ3
,
wavelength = 0.68880 Š, m =
2.71 cmÀ1, qmax = 35.718, T= 123 K, 30606 measured reflections,
6656 independent reflections, 641 refined parameters, GOF =
1.186, R1 = 0.0954 and wR2 = 0.1700 for all data; R1 = 0.0791 for
5738 independent reflections (I > 2.0s(I)), min./max. electron
density1.05/ À0.86 eŠÀ3; c) CCDC 665365 (4) and 665366 (5)
contain the supplementarycrystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif
(cut-off < 400 nm) at 208C for 15 min. These reactions were
1
monitored by H NMR spectroscopy(500 MHz, [D ]ODCB, 293 K)
4
and HPLC as follows: column, Buckyprep Mf4.6 ” 250 mm; eluent,
toluene; flow rate, 1.0 mLminÀ1; temperature, 258C; detector, UV
400 nm. 5: 1H NMR (300 MHz, [D6]acetone in a capillary/CS2,
293 K): d = 1.82 (s, 3H), 6.65 (d, J = 8.3, 2H), 7.24 ppm (d, J = 8.3,
2H); 13C NMR (125 MHz; [D6]acetone in a capillary/CS2, 293 K): d =
22.35, 129.27, 130.08, 134.54, 135.12, 136.06, 136.52, 138.15, 138.23,
138.62, 138.87, 139.97, 140.31, 141.98, 143.01, 143.04, 143.29, 143.51,
143.72, 143.92, 143.97, 144.08, 144.23, 144.27, 144.36, 144.44, 144.53,
144.65, 144.98, 147.69, 148.54 ppm; MALDI-TOF MS: m/z 889 [M]À.
Recrystallization of 4 and 5: Black crystals of 4 and 5 were
obtained byslow evaporation of CS 2 at 08C.
[14] a) V. Petrov, V. Petrova, G. V. Girichev, H. Oberhammer, N. I.
Giricheva, S. Ivanov, J. Org. Chem. 2006, 71, 2952 – 2956; b) F.
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F. Diederich, Angew. Chem. 2006, 118, 2193 – 2196; Angew.
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[15] Geometries were optimized with hybrid density functional
theoryat the B3LYP/6-31G(d,p) level using the Gaussian 03
program. For B3LYP, see a) A. D. Becke, Phys. Rev. A 1988, 38,
3098 – 3100; b) A. D. Becke, J. Chem. Phys. 1993, 98, 5648 – 5652;
c) C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785 – 789;
for 6-31G(d,p), see d) W. J. Hehre, R. Ditchfield, J. A. Pople, J.
Chem. Phys. 1972, 56, 2257 – 2261; e) P. C. Hariharan, J. A.
Pople, Theoret. Chim. Acta 1973, 28, 213 – 222.
[16] I. P. Romanova, G. G. Yusupova, O. A. Larionova, A. A. Balan-
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Rusinov, O. G. Sinyashin, Russ. Chem. Bull. Int. Ed. 2006, 55,
502 – 506.
[17] When this studywas presented at the annual meeting of the
Japan Chemical Society, in April, 2007, H. Hachiya and Y. Kabe
informed us that theywere also able for the first time to
characterize a [5,6]-monoazafulleroid byX-raycrystallographic
analysis.
Received: September 25, 2007
Published online: January8, 2008
Keywords: azafulleroids · fullerenes · photochemistry ·
.
rearrangement · structuraldetermination
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