Solvent-free reactions of fullerenes and N-alkylglycines with and without aldehydes under high-speed vibration milling

Article abstract of DOI:10.1016/S0040-4020(02)01478-3

The solvent-free reactions of fullerenes and N-alkylglycines with and without aldehydes (RCHO) 2a-e under high-speed vibration milling (HSVM) conditions have been investigated. Fulleropyrrolidines 4a-e (C₆₀(CH₂N(CH₃)CHR), R=H (4a), C₆H₅ (4b), p-NO₂-C₆H₄ (4c), p-CH₃O-C₆H₄ (4d), p-(CH₃)₂N-C₆H₄ (4e)) were obtained in moderate yields from reactions of C₆₀ with aldehydes 2a-e and N-methylglycine (Prato reaction). In all these solvent-free reactions, 4a was found to be formed besides 4b-e, indicating that fullerenes can react with N-substituted glycines in the absence of aldehyde to give fulleropyrrolidines. For this novel reaction, a possible reaction mechanism involving an electron transfer process has been proposed. Intrigued by this observation, the dependence of the yield on the reagent ratio for the reaction of C₆₀ with paraformaldehyde and/or N-methylglycine was examined to search the optimal conditions. The reaction of C₇₀ with paraformaldehyde and/or N-methylglycine under HSVM conditions was also studied and was found to give the positional isomers of [70]fulleropyrrolidines.

Full text of DOI:10.1016/S0040-4020(02)01478-3

Tetrahedron 59 (2003) 55–60
Solvent-free reactions of fullerenes and N-alkylglycines with and
without aldehydes under high-speed vibration milling
a
a
a
b
Guan-Wu Wang,a Ting-Hu Zhang, Er-Hong Hao, Li-Juan Jiao, Yasujiro Murata
,
*
and Koichi Komatsub
aDepartment of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
bInstitute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
Received 5 September 2002; revised 23 October 2002; accepted 14 November 2002
Abstract—The solvent-free reactions of fullerenes and N-alkylglycines with and without aldehydes (RCHO) 2a–e under high-speed
vibration milling (HSVM) conditions have been investigated. Fulleropyrrolidines 4a–e (C60(CH2N(CH3)CHR), R¼H (4a), C6H5 (4b), p-
NO2–C6H4 (4c), p-CH3O–C6H4 (4d), p-(CH3)2N–C6H4 (4e)) were obtained in moderate yields from reactions of C60 with aldehydes 2a–e
and N-methylglycine (Prato reaction). In all these solvent-free reactions, 4a was found to be formed besides 4b–e, indicating that fullerenes
can react with N-substituted glycines in the absence of aldehyde to give fulleropyrrolidines. For this novel reaction, a possible reaction
mechanism involving an electron transfer process has been proposed. Intrigued by this observation, the dependence of the yield on the
reagent ratio for the reaction of C60 with paraformaldehyde and/or N-methylglycine was examined to search the optimal conditions. The
reaction of C70 with paraformaldehyde and/or N-methylglycine under HSVM conditions was also studied and was found to give the
positional isomers of [70]fulleropyrrolidines. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
fullerene have been developed.7–14 The technique called
‘high-speed vibration milling (HSVM)’ has been used to
promote reactions of fullerenes under solvent-free con-
ditions. In this technique, the mechanical energy caused by
local high pressure, friction, shear strain, etc. can be used as
a driving force for the reaction. This HSVM technique has
been successfully utilized in the Reformatsky-type reaction
of C60,8 reactions of C60 to prepare fullerene dimers and
trimers catalyzed by various potassium salts, alkaline
metals, or solid amines,9 [4þ2] reactions of C60 with
condensed aromatics,10 with phthalazine11 and with di(2-
pyridyl)-1,2,4,5-tetrazine,12 reaction of C60 with dichlor-
odiphenylsilane and lithium,13 and reactions of C60 with
organic bromides and alkali metals.14 Preliminary work on
1,3-dipolar cycloadditions of C60 with diazo compounds and
with organic azides have also been reported.7b It is to be
noted that many of the functionalized fullerenes obtained in
these studies could only be produced by the HSVM
reactions and cannot be attained by conventional liquid-
phase reactions.9–11,13 We now report our study on the
solvent-free HSVM reactions of fullerenes with N-alkyl-
glycines and aldehydes 2a–e, and more importantly, the
novel reactions of fullerenes and N-alkylglycines without
aldehyde under HSVM conditions.
Chemical modifications of fullerenes have been intensively
explored because of the potential applications of fullerene
derivatives in many fields.1 Over the past ten years,
numerous fullerene derivatives have been synthesized via
various functionalization methods.2 Among these methods,
the 1,3-dipolar cycloaddition of azomethine ylide to
fullerene, known as the Prato reaction, is one of the most
investigated reactions. A number of [60]fulleropyrrolidines
have been synthesized by the reaction of C60 with N-
substituted glycine or other amino acid and aldehydes or
ketones.3 The reaction of C70 with N-methylglycine and
paraformaldehye has also been investigated and the
formation of three positional isomers of monoadducts was
observed.4
Recently solvent-free organic reactions5 have attracted great
attention due to the increasing concern for protection of the
environment.6 On the other hand, the solubility of fullerenes
in common organic solvents is so low that the use of a large
amount of solvents is inevitable for their reactions. There-
fore, solvent-free reaction of fullerene is an attractive and
appealing method to synthesize functionalized fullerenes.
Recently the mechanochemical solvent-free reactions of
Keywords: fullerenes; Prato reaction; N-alkylglycine; solvent-free reaction;
high-speed vibration milling.
2. Results and discussion
*
Corresponding author. Tel.: þ86-551-360-7864; fax: þ86-551-360-7864;
e-mail: gwang@ustc.edu.cn.
The 1,3-dipolar cycloaddition of azomethine ylide generated
0040–4020/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)01478-3

56
G.-W. Wang et al. / Tetrahedron 59 (2003) 55–60
in situ from N-methylglycine and paraformaldehyde to C60 to
give fulleropyrrolidine was reported at a very early stage of
fullerene chemistry by Prato and co-workers.15 Since then
many fulleropyrrolidine derivatives with novel functional-
ities have been prepared. As a typical procedure, a mixture of
C60, N-methylglycine or other amino acids, and aldehydes or
ketones was reacted at elevated temperature (refluxing
toluene or chlorobenzene) to afford fulleropyrrolidine.3,4
Then we questioned if the HSVM technique could be applied
to this Prato reaction of C60 under solvent-free conditions. A
mixture of C60, 1 equiv. of N-methylglycine (3) and 1 equiv.
of aldehyde 2a–e was vigorously shaken by HSVM
technique for 1 h, and we found that the expected full-
eropyrrolidines 4a–e were obtained in moderate yields
(Scheme 1). The identities of the products were confirmed by
comparison of their spectral data with those reported in
literature.15,16
Table 1. Product yields and recovered C60 for the reactions of C60 with N-
methylglycine and aldehydes
Aldehyde
4 (Yield, %)
Recovered C60 (%)
2a
2b
2c
2d
2e
4a (30%)
43
50
53
56
58
4b (23%)þ4a (7%)
4c (29%)þ4a (12%)
4d (24%)þ4a (7%)
4e (18%)þ4a (9%)
of C60 and 3 was fixed at 1:1 and the amount of 2a was
varied; then the relative yields of produced 4a and C120 and
unchanged C60 at various equivalents of 2a were determined
to give the results shown in Figure 1. Second, the ratio of
C60 and 2a was fixed at 1:1, and the amount of 3 was varied;
then the yields of 4a, C60 and C120 were determined at
various equivalents of 3 to give the result shown in Figure 2.
As clearly seen in Figure 1, the yield of 4a changed little
when 2a varied from 1 to 6 equiv., and then decreased
gradually with the increase of recovered C60.
Noteworthy is the fact that in these solvent-free HSVM
reactions we unexpectedly isolated 4a as a minor product
besides the corresponding fulleropyrrolidines 4b–e in all
reactions of C60 with 3 and 2b–e. The yields of the products
and recovered C60 for these reactions of C60 with 3 and
aldehydes in a molar ratio of 1:1:1 are listed in Table 1.
Meanwhile, as shown in Figure 2, the yield of 4a increased
rapidly with the change in the amount of 3 from 0.3 to
1 equiv. and was maintained nearly constant until 2.3 equiv.
of 3; then it rapidly decreased until 3 equiv. of 3 and kept
gradually decreasing. In all cases, the formation of C120 was
negligible (,10%). From these results, we conclude that the
optimal amount for paraformaldehyde is 1–6 equiv. and
that for 3 is 1–2 equiv. relative to C60 to obtain high yield of
fulleropyrrolidine 4a for the present HSVM reaction.
Since the reagents commonly used for all these reactions are
C60 and 3, 4a may have resulted from the direct reaction
between these two. To test this hypothesis, we treated the
mixture of C60 and 3 (1:1) under the HSVM conditions for
1 h. The reaction mixture was separated by a silica-gel
column chromatography eluted with toluene to give 4a in
19% (35% based on the consumed C60). Its structure was
1
confirmed by H and 13C NMR, HRMS, IR and UV–Vis
We have also investigated the dependence of the relative
product yield on reagent ratios for the reaction of C60 with 3
in the absence of aldehydes. The relative yields of 4a, C60
and C120 at various equivalents of 3 are shown in Figure 3.
spectra.15 Then, as a much less soluble product, which was
eluted out by o-dicholorobenzene, the fullerene dimer
9a
C120 was obtained in 23% (42% based on the consumed
C60) (Scheme 2). When 3 was substituted by N-ethylglycine,
the same kind of reaction occurred, N-ethyl fulleropyrroli-
dine (5) and C120 were obtained in 16% (36% based on the
consumed C60) and 19% (43% based on the consumed C60)
yields, respectively (Scheme 2). Fulleropyrrolidine 5
exhibited 17 lines for the sp2 carbons of the C60 cage in
its 13C NMR, which is consistent with its C2v symmetry. Its
13C NMR pattern for the C60 cage carbons and UV-vis
spectrum were the same as those of 4a.
As shown in Figure 3, the fulleropyrrolidine (4a) was
formed in the range of 0.3–4 equiv. of 3, while C120 was
formed at the all range of 3. The yield of 4a increased from
0.3 to 2 equiv. of 3, then decreased gradually and finally
dropped to zero after 4 equiv. of 3. Meanwhile, there is a
plateau for the yield of C120 around 20% from 1 to 2 equiv.
of 3, then the yield increased rapidly and reached nearly the
maximum (,40%), and then was almost unchanged until
7 equiv. of 3. Thus, C120 can be obtained selectively without
contamination of 4a when more than 5 equiv. of 3 was used.
Compound 5 was also obtained in 26% (52% based on the
consumed C60) from the mechanochemical HSVM reaction
of C60 with N-ethylglycine and paraformaldehyde under the
HSVM conditions for 1 h (Scheme 3).
Previously, it has been reported that the HSVM treatment of
9b
C60 with solid amines can give 30–40% of C120
.
Another aspect of interest is how the mass of the reaction
mixture affects the product yield in the present HSVM
reaction. The reagent ratio was kept unchanged, but the total
amount of the reaction mixture was altered to see how the
product yield was affected. The reaction of C60 with N-
methylglycine (3) and paraformaldehye (2a) was chosen for
this purpose. It was found that the increase of C60 from 7.2
To examine how the reagent ratio affects the product
distribution and yield, we monitored the reaction mixtures at
various reagent ratios by the use of HPLC analysis. Two
series of experiments have been conducted. First, the ratio
Scheme 1.
Scheme 2.

G.-W. Wang et al. / Tetrahedron 59 (2003) 55–60
57
Scheme 3.
to 28.8 mg for the reaction of C60 with 2a and 3 in the ratio
of 1:1:1 has almost no effect on the yield of 4a. The same
phenomenon was true for the reaction of C70 with 2a and 3
(vide infra). The milling time can be made shorter, the
reactions of 20–30 min gave almost the same yield of 4a
and also the functionalized C70, i.e. 6, 7, 8. However, the
increase of the total amount for the reaction of C60 with 2b–
e and 3 decreased the yield of 4b–e, and even did not give
any 4b or 4d for the reaction of C60 with 2b or 2d and 3.
Therefore, we kept the amount of C60 at 7.2 mg for each run
to compare the product yields for different aldehydes. The
exact reason for this dependence of the product yield on the
quantity of reaction mixture is not quite clear at the moment,
but probably the high temperature required for these
reactions is critical. When a smaller amount of the reaction
mixture was used the temperature of the reaction mixture
could get higher because of the greater degree of the direct
contact of the milling ball with the inner surface of the
capsule causing greater friction.
Figure 2. Distributions of 4a, C60, and C120 at various equivalents of 3 for
the reaction of C60 with 2a and 3 conducted under the HSVM conditions for
1 h.
reaction temperature under HSVM is lower than the boiling
point of toluene.
To find out if a similar reaction of C60 with N-methylglycine
occurs for C70, a mixture of C70 and N-methylglycine was
treated with HSVM. It turned out that the reaction indeed
proceeded and gave monoadducts 6 and 7 in total yield of
23% with relative ratio of 1.5:1 (Scheme 5). The reason for
the absence of 8 is not known.
We have also explored the reaction of [70]fullerene with N-
methylglycine and paraformaldehyde under HSVM con-
ditions. This reaction gave three monoadduct isomers
(Scheme 4).
Fulleropyrrolidines were obtained from reactions of full-
erenes with N-alkylglycine and aldehydes under HSVM
conditions most probably through the expected 1,3-dipolar
cycloaddition of the azomethine ylide. To explain the
formation of [60]fulleropyrrolidines and C120 from the
direct reactions of C60 and N-alkylglycine, we propose the
following reaction pathways as a possible reaction mech-
anism (Scheme 6).
A mixture of monoadducts 6–84 was isolated by column
chromatography in total yield of 41%. The relative amount
1
of 6–8 was determined as 47:36:16 by H NMR. It was
reported that the above Prato reaction of C70 tended to
produce more 7 at the expense of 8 at higher reaction
temperature and under microwave irradiation.4 The
obtained ratio under the present HSVM conditions is closest
to that in refluxing toluene, and quite different from that
under microwave irradiation. A larger amount of mono-
adduct isomer 8 was obtained under HVSM conditions than
that in refluxing chlorobenzene and o-dichlorobenzene, and
under microwave irradiation. These facts hint that the local
The first step is the electron transfer from N-alkylglycine to
C60 to form C60 radical anion and 9 ((a) in Scheme 6).
Radical cation 9 loses CO2 and a proton to afford radical 11.
The proposed formation of radical 11 from C60 and glycines
has precedent in the literature.17 Radical 11 adds to the 6,6-
bond of C60 to form intermediate 12, which undergoes
intramolecular electron transfer to give 13, and then couples
Figure 1. Distributions of 4a, C60 and C120 at various equivalents of 2a for
the reaction of C60 with 2a and 3 conducted under the HSVM conditions for
1 h.
Figure 3. Distributions of 4a, C60, and C120 at various equivalents of 3 for
the reaction of C60 with 3 conducted under the HSVM conditions for 1 h.

58
G.-W. Wang et al. / Tetrahedron 59 (2003) 55–60
Scheme 4.
with radical 11 to afford anion 14. Amines are known to
easily transfer an electron to C60.18 The formed 14 transfers
one electron to C60 to give intermediate 15, which cyclizes
with the loss of the alkyl amine radical to afford the
fulleropyrrolidine 16 ((b) in Scheme 6). Cyclization
accompanied with unusual C–N bond breaking has been
noticed before.19 Alternatively, the anion 14 can transfer
one electron to C60 to form radical 17, which cyclizes with
the loss of alkyl amine radical to afford the fulleropyrro-
lidine ((c) in Scheme 6). C120 is supposed to be formed by
the coupling of C60 radical anion with C60 to form C120
radical anion 18, which transfers one electron to another
molecule of C60 to give C120 diradical 19, which couples to
afford C120 ((d) in Scheme 6). Thus, C120 can be formed
once the C60 radical anion is produced by the process (a) as
has been suggested before.9b
Scheme 6.
ditions were investigated by the use of the HSVM
technique. Not only the expected products 4a–e were
produced but the simplest N-methyl fulleropyrrolidine 4a
was obtained from all the reactions regardless of the type of
aldehyde. From this observation, a novel reaction of C60 or
C70 with N-alkylglycine was found. A possible reaction
mechanism was proposed for the reaction of C60 with N-
alkylglycine to explain the formation of fulleropyrrolidine
C70 should react with N-alkylglycine via the same pathway
as that of C60 with N-alkylglycine to give [70]fulleropyrro-
lidines. It should be noted that there is no evidence of the
formation of C70 dimer, C140. This is consistent with the
failure of formation of C140 from the reactions of C70 with
potassium salts, metals, and amines.9c
The synthesized fulleropyrrolidines can be converted to the
corresponding fullerene-containing amphiphiles bearing
ammonium head group. These amphiphiles are water-
soluble and expected to form interesting supramolecular
assemblies in water and polar organic solvents. Work along
this line is in progress.
and also the fullerene dimer, C120
.
3. Experimental
3.1. General procedures
In conclusion, the reactions of C60 with aldehydes and N-
methylglycine (Prato reaction) under solvent-free con-
1H and 13C NMR spectra were recorded at 300 or 400 and
75 MHz, respectively, in CS2–CDCl3. IR spectra were
recorded on a Shimadzu 8600 FT IR spectrometer. UV-vis
spectra were obtained on a Shimadzu UV-2100PC
spectrometer.
High-performance liquid chromatography analysis was
conducted on an Agilent 1100 liquid chromatograph with
a diode-array detector using a Cosmosil Buckyprep column
(4.6 mm£250 mm) with toluene as the eluent. For the
reaction of C60 with N-methylglycine and paraformalde-
hyde, the retention time for the product, 4a, C60, and C120
were 6.0, 8.0 and 18.9 min, respectively, at the flow rate of
1 mL min21. For the HPLC measurements, the reaction
mixture was monitored at 326 nm, and the relative ratios of
C60 and its derivatives’ peak areas were taken as the relative
Scheme 5.

G.-W. Wang et al. / Tetrahedron 59 (2003) 55–60
59
1
amounts of C60 and its derivatives. Their actual amounts are
slightly different due to the slightly different molar
extinction coefficients for C60 and its derivatives at
326 nm. However, this treatment does not affect the
distribution trends shown in Figures 1–3.
792.0825; H NMR (300 MHz, CS2–CDCl3 (2:1)) d 4.40
(s, 4H), 3.14 (q, 2H, J¼7.3 Hz), 1.55 (t, 3H, J¼7.3 Hz); 13C
NMR (75 MHz, CS2–CDCl3 (2:1)) d 154.70 (4C), 146.98
(2C), 145.95 (4C), 145.76 (4C), 145.75 (4C), 145.39 (2C);
145.17 (4C), 144.98 (4C); 144.28 (4C), 142.83 (2C), 142.35
(4C), 141.95 (4C), 141.80 (4C), 141.62 (4C), 139.92 (4C),
136.02 (4C), 70.31 (2C), 67.54 (CH2N), 49.15 (NCH2CH3),
14.10 (NCH2CH3).
All solvent-free reactions were performed using a high-
speed vibration mill that consists of a capsule and a milling
ball made of stainless steel. The capsule containing the
milling ball was fixed on a vibration arm of a home-built
mill, and was vibrated vigorously at a rate of 3500 cycles
per minute.
Compound 5 (16%) and C120 (19%) along with recovered
C60 (56%) were obtained from the reaction of C60 with N-
ethylglycine using the same procedure as described above.
C60 (.99.9%) and C70 (98%) were purchased from 3D
Carbon Cluster Material Co. of Wuhan University in China.
All other reagents were commercial material.
3.1.4. Reaction of C70 with aldehydes and/or N-methyl-
glycine. A mixture of C70 (8.4 mg, 0.01 mmol), N-
methylglycine (0.9 mg, 0.01 mmol) and paraformaldehyde
(0.3 mg, 0.01 mmol) was vigorously shaken by HSVM for
1 h. The combined reaction mixture from six runs was
separated on a silica gel column with toluene/petroleum
ether as the eluent to afford recovered C70 (22.7 mg, 45%)
and a mixture of monoadducts 6–84 (22.1 mg, 41%). The
3.1.1. Reaction of C60 with N-methylglycine and alde-
hydes. A mixture of C60 (7.2 mg, 0.01 mmol), N-methyl-
glycine (0.9 mg, 0.01 mmol) and p-nitrobenzaldehyde (2c)
(1.5 mg, 0.01 mmol) was vigorously shaken by HSVM for
1 h. The combined reaction mixture from six runs was
separated on a silica gel column with toluene/petroleum
ether as the eluent to afford recovered C60 (22.9 mg, 53%),
4c (15.5 mg, 29%), and 4a (5.6 mg, 12%). Similar results
were obtained from reactions of C60 with N-methylglycine
and other aldehydes. All fulleropyrrolidines 4a–e were
characterized by NMR, UV-vis, and their structures were
confirmed by comparison of their spectral data with those
reported in literature.15,16
1
ratio of 6–8 was determined to be 47:36:16 by H NMR.
Monoadducts 6 and 7 (1.5:1) in a total yield of 23% along
with 62% of recovered C70 can also be obtained by the
reaction of C70 with N-methylglycine using the same
procedure as described above.
Acknowledgements
We are grateful for financial support from the ‘Hundred
Talents Program’ of the Chinese Academy of Sciences,
National Science Fund for Distinguished Young Scholars
(20125205), Anhui Provincial Natural Science Foundation
(00045306), and USTC Environment and Resource
Research Base Foundation.
3.1.2. Reaction of C60 with N-methylglycine. A mixture of
C60 (7.2 mg, 0.01 mmol) and N-methylglycine (0.9 mg,
0.01 mmol) was vigorously shaken by HSVM for 1 h. The
combined reaction mixture from six runs was separated on a
silica gel column with toluene/petroleum ether as the eluent
to afford recovered C60 (19.9 mg, 46%) and a black solid
(8.9 mg, 19%), which was proven to be the same product as
that from the reaction of C60 with N-methylglycine and
paraformaldehyde by comparison their 1H NMR, 13C NMR,
MS, IR, UV–Vis spectra, and was further confirmed by
high-resolution mass spectroscopy as 4a. 4a: MS (2APCI)
m/z 777 (M2); HRMS (þFAB) calcd for C63H8N (Mþ1),
778.0656, found 778.0609.
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