Catalytic cycloaddition of diazo amides to fullerene C60

Article abstract of DOI:10.1016/j.tetlet.2013.02.037

A general catalytic procedure for the cycloaddition of diazo amides to fullerene C₆₀ in the presence of the three-component catalyst, Pd(acac)₂-PPh₃-Et₃Al, has been developed. Depending on the reaction conditions, pyrazolinofullerenes or methanofullerenes are formed.

Full text of DOI:10.1016/j.tetlet.2013.02.037

Tetrahedron Letters 54 (2013) 2146–2148
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Catalytic cycloaddition of diazo amides to fullerene C60
⇑
Airat R. Tuktarov , Liliya L. Khuzina, Natal’ya R. Popod’ko, Usein M. Dzhemilev
Institute of Petrochemistry and Catalysis, Russian Academy of Sciences, 141 Prospekt Oktyabrya, Ufa 450075, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
A general catalytic procedure for the cycloaddition of diazo amides to fullerene C60 in the presence of the
three-component catalyst, Pd(acac)2–PPh3–Et3Al, has been developed. Depending on the reaction condi-
tions, pyrazolinofullerenes or methanofullerenes are formed.
Received 8 December 2012
Revised 24 January 2013
Accepted 13 February 2013
Available online 20 February 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
[60]Fullerene
Diazo compounds
Diazo amides
Cycloaddition
Metal complex catalyst
Pyrazolinofullerene
Methanofullerene
1,3-Dipolar cycloaddition between diazo compounds and fuller-
ene C60 is the most effective and convenient route to homo- and
methanofullerenes, which are of special interest as new materials
for science and technology, as evidenced by numerous reviews1–6
covering methods for synthesizing fullerenes1–4 and aspects of
their use.5,6
Analysis of the literature, however, has shown that thermal cyc-
loadditions of diazo compounds to fullerene C60 proceed non-
selectively and produce a mixture of methano- and stereoisomeric
homofullerenes.7–11
Previously, we showed that the three-component catalytic sys-
tem, Pd(acac)2–PPh3–Et3Al, favoured cycloadditions of diazo al-
kanes,13–16 diazo acetates,17,20–23 diazo ketones24 and diazo
thioates18,25 to fullerene C60 with high yields and selectivity. These
studies also revealed that the ratios of the starting reagents defined
the direction of the reaction leading to the formation of homofulle-
renes or methanofullerenes. Taking into account these findings we
performed further research in this arena.
Our experiments revealed that the reaction between fullerene
C60 and a fivefold molar excess of N-cyclohexyl-2-diazoacetamide
(80 °C, 1 h, chlorobenzene),26 in the presence of 20 mol % of the
three-component catalytic system, Pd(acac)2–PPh3–Et3Al (1:2:4),
gave a single pyrazolinofullerene 127 in 40% yield relative to the
starting fullerene C60 (Scheme 1). An elevated temperature
(100 °C) and increased reaction time (3 h) did not significantly in-
crease the yield of the target [2+3] cycloadduct 1. This reaction,
without a catalyst, leads to a formation of a mixture of methano-
and stereoisomeric homofullerenes, as reported previously19 for
Metal complex catalysts (based upon palladium and rhodium)
can direct the cycloaddition reaction towards the predominant for-
mation of individual homo-, methano- or pyrazolinofullerenes.4,12–18
At the onset of our research, only a thermal reaction of diazo
amides with C60 to afford a mixture of 6,6-close and stereoisomeric
5,6-open cycloadducts had been described in the literature.19
Information concerning catalytic cycloadditions between diazo
amides and fullerenes was absent from the literature.
In continuation of our work13–18 on both the cycloaddition reac-
tions of diazo compounds to fullerenes under the action of metal
complex catalysts, and to develop effective methods for the syn-
thesis of synthetically important functionalized fullerenes, we
have studied the catalytic 1,3-dipolar cycloadditions of various dia-
the thermal cycloaddition of diazo amides to fullerene C60.
The MALDI–TOF mass spectrum of pyrazolinofullerene 1, which
was isolated by preparative HPLC, contained an intense molecular
ion peak [M+H]+ at m/z 888.112 (ca. 888.114) along with a frag-
ment ion peak [C60N2H]+ at m/z 749.033, which provided strong
evidence for the proposed structure.
zo amides to fullerene C60
.
Diazo amides derived from glycine and cyclohexylamine were
selected as model compounds.
The one-dimensional (1H, 13C) and two-dimensional (COSY,
HSQC, HMBC) NMR experiments on compound 1 also gave evi-
dence for the presence of the pyrazoline ring linked to the amide
group. The 13C NMR spectrum of the pyrazoline moiety exhibited
three signals. Two of them (dC 80.09 and 87.30) were due to
⇑
Corresponding author. Tel./fax: +7 347 2842750.
E-mail address: tuktarovar@gmail.com (A.R. Tuktarov).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.02.037

A. R. Tuktarov et al. / Tetrahedron Letters 54 (2013) 2146–2148
2147
H
N
O
80 oC, 1 h
N
+
N2
N
H
chlorobenzene
Pd(acac)2-PPh3-Et3Al
(1:2:4)
N
H
O
1 (~40 %)
Scheme 1. Catalytic cycloaddition of N-cyclohexyl-2-diazoacetamide to [60]fullerene.
H
N
O
80 oC, 1 h
N
N2
N
H
R
+
Pd(acac)2−PPh3−Et3Al
(1:2:4)
N
H
R
O
2 5
Me
Me
2: R = Ph (~33%); 3: R =
(~39%); 4: R =
(~30%); 5: R=
(~36%)
Me
Scheme 2. Catalytic synthesis of pyrazolinofullerenes 2–5.
R
O
R
40 oC, 1 h
HN
+
N2
N
Pd(acac)2-PPh3-Et3Al
(1:2:4)
H
O
6
8
Scheme 3. Reactions of [60]fullerene with diazo amides bearing a substituent alpha to the diazo group.
annelated sp3 hybridized C-atoms of the fullerene skeleton, while
the third signal (dC 136.23) was assigned to the carbon atom at-
tached to the nitrogen of the five-membered heterocycle by a dou-
ble bond.
nofullerene formed giving rise to a [2+1] cycloadduct. In the hope
of developing a selective method for the synthesis of methanofulle-
renes, we studied the reactions between C60 and a-substituted dia-
zo amides derived from alanine, leucine, methionine and
Additionally, between dC 25 and dC 50 in the 13C NMR spectrum
of pyrazolinofullerene 1, we observed low frequency signals attrib-
utable to the cyclohexyl moiety [dC 25.38 (2C), 26.05 (1C), 33.31
(2C), 49.08 (1C)]. Also seen were high frequency signals character-
istic of the fullerene skeleton (25 signals in the region between dC
137 and dC 149), and the carbonyl carbon atom (dC 157.61).
In order to extend the application of this fullerene cycloaddition
and to investigate patterns in the yield and selectivity on the size
and structure of the substituent on the amide group of the diazo
compound, we studied the reactions between fullerene C60 and
sterically hindered diazo amides, based on glycine or aniline, and
also derived from adamantane-containing amines (Scheme 2).
Thus, under the optimized conditions [80 °C, 1 h, Pd(acac)2–
2PPh3–4Et3Al] the corresponding monoadducts 2–528–31 were ob-
tained in moderate yields (up to 40%). The experiments also
showed that bulky substituents on the amide group did not influ-
ence the reaction pathway.
cyclohexylamine.
The reactions between the above diazo amides and fullerene C60
under the optimized conditions (40 °C, 1 h) in the presence of
20 mol% of Pd(acac)2–PPh3–Et3Al (1:2:4), led exclusively, to met-
hanofullerenes 6–833–35 in 40–50% yields (Scheme 3).
The structures of methanofullerenes 6–8 were reliably estab-
lished by means of standard analytical (1D and 2D NMR, IR, UV,
MALDI–TOF) methods.
The intense molecular ion peak at m/z 873.120 (ca. 873.115) in
the MALDI–TOF spectrum of compound 6 provided strong evidence
for the formation of the [2+1]-cycloadduct.
The 13C NMR spectrum of compound 6 contained 27 reso-
nances in the fullerene region between dC 138 and dC 149,
and three with twice the intensity. The cyclopropane fragment
has a plane of symmetry and in the spectrum exhibited two
signals resonating at dC 78.30. The signals of the bridge carbon
atom (dC 62.00) bound to the amide group (dC 165.95) and the
methyl group (dC 17.32), which in the 1H NMR spectrum man-
ifested itself as a singlet at dH 2.54, also provided evidence for
the formation of the cyclopropane–annelated 6,6-substituted
fullerene.
In conclusion, for the first time, we have reported catalytic cyc-
loadditions between diazo amides and fullerene C60 under the
influence of the three-component catalytic system, Pd(acac)2–
PPh3–Et3Al, to produce pyrazolinofullerenes or methanofullerenes
depending on the reaction conditions.
It is known that pyrazolinofullerenes derived from fullerene C60
and diazo acetates17,32 or diazothioates18 can undergo thermal
transformations to afford the corresponding methanofullerenes.
Refluxing [2+3] cycloadducts 1–5 for 100 h in 1,2-dichlorobenzene
did not result in the formation of methanofullerenes, and in all the
experiments the starting pyrazolinofullerenes
unchanged.
remained
Earlier,18 we showed that the substituent alpha to the diazo
group of the diazo compound was able to destabilize the pyrazoli-

2148
A. R. Tuktarov et al. / Tetrahedron Letters 54 (2013) 2146–2148
2H, 2CH), 7.73 (m, 2H, 2CH), 8.81 (s, 1H, NH). 13C NMR (100 MHz, CDCl3): d
References and notes
62.90, 88.18, 119.92, 125.28, 127.67, 136.36, 137.06, 137.17, 140.33, 140.35,
141.93, 141.94, 142.27, 142.44, 142.56, 142.65, 142.69, 142.91, 142.96, 142.98,
143.19, 144.08, 144.20, 144.40, 144.64, 145.26, 145.29, 145.40, 145.85, 146.06,
146.61, 146.43, 146.49, 147.21, 147.57, 147.89, 148.69, 156.09. MALDI–TOF, m/
z 881.065 [M]+ (C68H7N3O).
1. Diederich, F.; Thilge, C. Science 1996, 271, 317.
2. Yurovskaya, M. A.; Trushkov, I. V. Russ. Chem. Bull. 2002, 51, 367.
3. Thilgen, C.; Diederich, F. Chem. Rev. 2006, 106, 5049.
4. Tuktarov, A. R.; Dzhemilev, U. M. Russ. Chem. Rev. 2010, 79, 585.
5. Troshin, P. A.; Lyubovskaya, R. N.; Razumov, V. F. Nanotechnol. Russ. 2008, 3,
242.
6. Da Ros, T.; Prato, M. Chem. Commun. 1999, 663.
7. Prato, M.; Lucchini, V.; Maggini, M.; Stimpfl, E.; Scorrano, G.; Eiermann, M.;
Suzuki, T.; Wudl, F. J. Am. Chem. Soc. 1993, 115, 8479.
8. Li, Z.; Bouhadir, K. H.; Shevlin, P. Tetrahedron Lett. 1996, 37, 4652.
9. Isaacs, L.; Wehrsig, A.; Diederich, F. Helv. Chim. Acta 1993, 76, 1231.
10. Zhu, C. C.; Xu, Y.; Liu, Y. Q.; Zhu, D. B. J. Org. Chem. 1997, 62, 1996.
11. Nakamura, Y.; Inamura, K.; Oomuro, R.; Laurenco, R.; Tidwell, T. T.; Nishimura,
J. Org. Biomol. Chem. 2005, 3, 3032.
12. Roberti, M.; Natalini, B.; Andrisano, V.; Seraglia, R.; Gioiello, A.; Pellicciari, R.
Tetrahedron 2010, 66, 7329.
13. Tuktarov, A. R.; Korolev, V. V.; Sabirov, D. Sh.; Dzhemilev, U. M. Russ. J. Org.
Chem. 2011, 47, 41.
14. Dzhemilev, U. M.; Tuktarov, A. R.; Korolev, V. V.; Khalilov, L. M. Petroleum Chem.
2011, 51, 123.
15. Tuktarov, A. R.; Korolev, V. V.; Tulyabaev, A. R.; Popod’ko, N. R.; Khalilov, L. M.;
Dzhemilev, U. M. Tetrahedron Lett. 2011, 52, 834.
16. Tuktarov, A. R.; Khuzin, A. A.; Korolev, V. V.; Dzhemilev, U. M. Russ. J. Org. Chem.
2012, 48, 99.
17. Tuktarov, A. R.; Khuzina, L. L.; Dzhemilev, U. M. Russ. Chem. Bull. 2011, 60, 662.
18. Tuktarov, A. R.; Khuzin, A. A.; Popod’ko, N. R.; Dzhemilev, U. M. Tetrahedron
Lett. 2012, 53, 3123.
19. Skiebe, A.; Hirsch, A. J. Chem. Soc., Chem. Commun. 1994, 335.
20. Tuktarov, A. R.; Akhmetov, A. R.; Kamalov, R. F.; Khalilov, L. M.; Pudas, M.;
Ibragimov, A. G.; Dzhemilev, U. M. Russ. J. Org. Chem. 2009, 45, 1168.
21. Tuktarov, A. R.; Akhmetov, A. R.; Sabirov, D. Sh.; Khalilov, L. M.; Ibragimov, A.
G.; Dzhemilev, U. M. Russ. Chem. Bull. 2009, 58, 1724.
22. Tuktarov, A. R.; Akhmetov, A. R.; Kirichenko, G. N.; Glazunova, V. I.; Khalilov, L.
M.; Dzhemilev, U. M. Russ. J. Appl. Chem. 2010, 83, 1238.
23. Tuktarov, A. R.; Akhmetov, A. R.; Khasanova, L. L.; Khalilov, L. M.; Dzhemilev, U.
M. Russ. Chem. Bull. 2010, 59, 1959.
29. N-[1-(1-Adamantyl)ethyl]carboamidyl-10H-[1,2]pyrazolino[40,50:1,9](C60–Ih)-
[5,6]fullerene (3) (isolated yield 39%). IR: 526, 752, 1180, 1448, 1520,
1671 cmꢀ1. UV (CHCl3), kmax, nm: 257, 316, 427. 1H NMR (400 MHz, CDCl3):
d 1.29 (d, 3H, CH3, J = 5.6 Hz), 1.55 (m, 6H, 3CH2), 1.79 (m, 6H, 3CH2), 2.13 (m,
3H, 3CH), 3.96 (m, 1H, CH), 6.94 (d, 1H, NH, J = 9.6 Hz), 8.01 (s, 1H, NH). 13C
NMR (100 MHz, CDCl3): d 14.76, 29.01, 36.40, 37.46, 38.79, 53.81, 76.14,
136.24, 136.31, 137.08, 137.19, 140.28, 140.30, 141.86, 141.89, 141.95, 141.97,
142.23, 142.26, 142.41, 142.53, 142.68, 142.87, 142.88, 142.90, 142.93, 142.94,
143.18, 144.18, 144.37, 144.41, 144.43, 145.67, 144.69, 145.23, 145.25, 145.41,
145.43, 145.77, 146.02, 146.05, 146.06, 146.37, 146.38, 146.45, 147.17, 147.54,
147.62, 147.86, 148.47, 158.20. MALDI–TOF, m/z 968.221 [M+H]+ (C74H21N3O).
30. N-(1-Adamantyl)carboamidyl-10H-[1,2]pyrazolino[40,50:1,9](C60–Ih)-
[5,6]fullerene (4) (isolated yield 30%). IR: 523, 750, 1181, 1455, 1519,
1672 cmꢀ1. UV (CHCl3), kmax, nm: 257, 327, 424. 1H NMR (400 MHz, CDCl3):
d 1.76 (m, 6H, 3CH2), 2.05 (m, 6H, 3CH2), 2.21 (m, 3H, 3CH), 6.84 (s, 1H, NH),
8.08 (s, 1H, NH). 13C NMR (100 MHz, CDCl3): d 30.10, 36.66, 41.86, 53.16, 66.09,
80.03, 136.22, 140.27, 140.32, 141.89, 141.94, 142.25, 142.41, 142.52, 142.67,
142.86, 142.93, 142.99, 144.19, 144.39, 144.48, 144.68, 145.22, 145.24, 145.42,
145.75, 146.01, 146.05, 146.36, 146.45, 147.16, 147.57, 147.84, 148.71, 157.25.
MALDI–TOF, m/z 940.147 [M+H]+ (C72H17N3O).
31. N-(3,5-Dimethyl-1-adamantyl)carboamidyl-10H-
[1,2]pyrazolino[40,50:1,9](C60–Ih)-[5,6]fullerene (5) (isolated yield 36%). IR:
526, 754, 1180, 1454, 1518, 1674 cmꢀ1. UV (CHCl3), kmax, nm: 260, 326, 427.
1H NMR (400 MHz, CDCl3): d 1.13 (s, 6H, 2 CH3), 1.3–1.5 (m, 10H, 5CH2), 2.06
(m, 1H, CH), 2.21 (m, 2H, CH2), 6.86 (s, 1H, NH), 8.08 (s, 1H, NH). 13C NMR
(100 MHz, CDCl3): d 30.46, 31.38, 32.36, 38.35, 40.49, 42.83, 47.52, 48.59,
50.71, 66.21, 79.98, 136.30, 140.29, 140.31, 141.73, 141.93, 142.16, 142.40,
142.48, 142.59, 142.86, 142.94, 143.18, 144.11, 144.34, 144.49, 144.72, 145.15,
145.31, 145.74, 146.15, 146.21, 147.16, 147.31, 147.69, 148.13, 148.95, 149.40,
158.70. MALDI–TOF, m/z 967.208 [M]+ (C74H21N3O).
32. Wang, G.-W.; Li, Y.-J.; Peng, R.-F.; Liang, Z.-H.; Liu, Y.-C. Tetrahedron 2004, 60,
3921.
33. 10-Methyl-10-[N-cyclohexylamidyl](C60–Ih)[5,6]fullero[20,30:1,9]cyclopropane
(6) (isolated yield 50%). IR: 527, 577, 722, 748, 1021, 1182, 1431, 1456,
1685 cmꢀ1. UV (CHCl3), kmax, nm: 259, 328, 426. 1H NMR (400 MHz, CDCl3): d
1.39 and 2.18 (both m, 4H, 2CH2), 1.52 and 1.93 (both m, 4H, 2CH2), 1.77 (m,
2H, CH2), 2.54 (s, 3H, CH3), 4.29 (m, 1H, CH). 13C NMR (100 MHz, CDCl3): d
17.32, 25.46, 26.05, 33.53, 49.69, 62.00, 78.30, 138.07, 138.82, 139.33, 141.19,
141.54, 141.69, 142.04, 142.24, 142.31, 142.48, 142.83, 143.04, 143.18, 143.56,
143.71, 143.84, 143.90, 144.01, 144.13, 144.33, 144.54, 144.87, 145.23, 145.55,
146.39, 147.65, 148.32, 165.95. MALDI–TOF, m/z 873.120 [M]+ (C69H15NO).
34. 10-iso-Butyl-10-[N-cyclohexylamidyl](C60–Ih)[5,6]fullero[20,30:1,9]cyclopropane
(7) (isolated yield 47%). IR: 527, 573, 1093, 1176, 1448, 1508, 1636 cmꢀ1. UV
(CHCl3), kmax, nm: 261, 329, 427. 1H NMR (400 MHz, CDCl3): d 0.99 (d, 6H,
2CH3, J = 6.0 Hz), 1.30 (m, 1H, CH), 1.38 and 2.15 (both m, 4H, 2CH2), 1.51 and
1.83 (both m, 4H, 2CH2), 1.60 (m, 2H, CH2), 1.72 (m, 2H, CH2), 4.23 (m, 1H, CH).
13C NMR (100 MHz, CDCl3): d 24.12, 25.30, 25.97, 26.20, 33.47, 40.34, 49.23,
63.98, 79.32, 137.95, 138.14, 138.71, 138.41, 140.51, 141.42, 141.56, 142.11,
142.19, 142.27, 142.29, 142.52, 142.90, 143.13, 143.18, 143.24, 143.51, 143.63,
143.87, 144.22, 144.78, 144.87, 145.17, 145.28, 147.32, 147.61, 148.87, 165.88.
MALDI–TOF, m/z 915.169 [M]+ (C72H21NO).
24. Tuktarov, A. R.; Akhmetov, A. R.; Khalilov, L. M.; Dzhemilev, U. M. Russ. Chem.
Bull. 2010, 59, 611.
25. Tuktarov, A. R.; Khuzin, A. A.; Popod’ko, N. R.; Dzhemilev, U. M. Fullerenes
Nanotubes
Carbon
Nanostruct.
2013.
http://dx.doi.org/10.1080/
1536383X.2012.690463.
26. Catalytic cycloaddition of diazo amides to [60]fullerene (general procedure).
Pd(acac)2 (0.00278 mmol) in chlorobenzene (0.2 mL) and PPh3 (0.00556 mmol)
in chlorobenzene (0.21 mL) were loaded into a glass reactor. The mixture was
cooled to ꢀ5 to 0 °C. Et3Al (0.01112 mmol) in toluene (0.1 mL) was added
under a dry argon current, and on stirring the mixture, the color changed from
light-yellow to light-brown. To the obtained catalyst, fullerene C60
(0.0139 mmol) in chlorobenzene (1.5 mL) was added at ꢁ20 °C and the
solution became deep-green in color. The mixture was heated to 80 °C, the
diazo compound (0.0695 mmol) in chlorobenzene (0.2 mL) was added
dropwise over 2–3 min, and the mixture was stirred for 1 h. The mixture
was cooled to ꢁ20 °C and treated with aqueous HCl. Toluene (7 mL) was added,
and the organic layer passed through a column containing a small amount of
silica gel. The reaction products and the starting fullerene C60 were separated
by preparative HPLC, with toluene as the eluent.
35. 10-[200-(Methylthio)ethyl]-10-[N-cyclohexylamidyl](C60–Ih)[5,6]fullero[20,30:1,9]
cyclopropane (8) (isolated yield 40%). IR: 525, 578, 735, 1028, 1182, 1428,
1675 cmꢀ1. UV (CHCl3), kmax, nm: 260, 328, 426. 1H NMR (400 MHz, CDCl3): d
1.39 and 2.74 (both m, 4H, 2CH2), 1.54 and 1.88 (both m, 4H, 2CH2), 1.78 (m,
2H, CH2), 2.14 (s, 3H, CH3), 3.12 (t, 2H, CH2, J = 7.2 Hz), 3.25 (t, 2H, CH2,
J = 7.2 Hz), 4.27 (m, 1H, CH). 13C NMR (100 MHz, CDCl3): d 16.20, 25.64, 25.73,
30.17, 31.33, 33.31, 49.35, 63.82, 79.07, 137.09, 137.87, 138.10, 138.16, 139.19,
140.53, 141.44, 141.79, 142.15, 142.20, 142.26, 142.37, 142.44, 142.99, 143.16,
143.26, 143.48, 143.74, 143.90, 144.23, 144.35, 144.53, 144.80, 144.88, 145.13,
145.25, 145.39, 145.53, 146.57, 147.30, 147.53, 147.85, 165.93. MALDI–TOF, m/
z 933.193 [M]+ (C71H19NOS).
27. N-Cyclohexylcarboamidyl-10H-[1,2]pyrazolino[40,50:1,9](C60–Ih)-[5,6]fullerene
(1) (isolated yield 40%). IR: 527, 750, 1179, 1457, 1523, 1633 cmꢀ1. UV (CHCl3),
kmax, nm: 260, 316, 427. 1H NMR (400 MHz, CDCl3): d 1.37 and 1.78 (both m,
2H, CH2), 1.46 and 2.16 (both m, 4H, 2CH2), 1.88 (m, 4H, 2CH2), 4.01 (m, 1H,
CH), 6.78 (s, 1H, NH), 8.08 (s, 1H, NH). 13C NMR (100 MHz, CDCl3): d 25.38,
26.05, 33.31, 49.08, 80.09, 136.23, 137.11, 140.28, 141.87, 141.94, 142.29,
142.41, 142.52, 142.67, 142.87, 142.93, 143.17, 144.18, 144.38, 144.67, 145.23,
145.41, 145.76, 146.02, 146.06, 146.36, 146.45, 147.17, 147.53, 147.86, 148.39,
157.61. MALDI–TOF, m/z 888.027 [M+H]+ (C68H13N3O).
28. N-Phenylcarboamidyl-10H-[1,2]pyrazolino[40,50:1,9](C60–Ih)-[5,6]fullerene (2)
(isolated yield 33%). IR: 526, 756, 1180, 1364, 1480, 1635 cmꢀ1. UV (CHCl3),
kmax, nm: 260, 330, 430. 1H NMR (400 MHz, CDCl3): d 7.23 (m, 1H, CH), 7.43 (m,