Reaction of the C60 radical anion with alkyl halides

Article abstract of DOI:10.1039/c9nj01043b

The reaction of the C₆₀ radical anion (C₆₀^-) with α-bromo-1,3-dicarbonyl compounds selectively afforded the methanofullerene derivatives. The reaction with benzyl halide and 1,2-bis(dihalomethyl)benzene afforded the corresponding 1,4-dibenzylated C₆₀ derivative and cycloaddition product, respectively. The possible mechanisms for the formation of the fullerene adducts are proposed.

Full text of DOI:10.1039/c9nj01043b

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Reaction of C radical anion with alkyl halide †
6
0
a
a
a
a
a
Yutaka Maeda, * Makoto Sanno, Tatsunari Morishita , Kodai Sakamoto, Eiichiro Sugiyama, Saeka
a
a
a,b
Akita, Michio Yamada, Mitsuaki Suzuki
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Reaction of the C60 radical anion (C60.-) with α-bromo-1,3-dicarbonyl example,
compounds selectively afforded methanofullerene derivatives. The dichlorobenzene (1,2-DCB) to allow the expansion of a flow reactor
reaction with benzyl halide and 1,2-bis(dihalomethyl)benzene system. Understanding of the reactivity of C60 also contributes to
afforded the corresponding 1,4-dibenzylated C60 derivative and the understanding of metallofullerene and carbon nanotube
cycloaddition product, respectively. Possible mechanisms for the chemistry.
C
60 and
C
.-
60
have sufficient solubility in 1,2-
.-
formation of the fullerene adducts are proposed.
In a typical experiment, 10 equiv of alkyl halide was added to a
.-
-3
solution of C60 around 1.67 × 10 M that had been generated by
bulk electrolysis in 1,2-DCB containing 0.13 M tetrabutylammonium
perchlorate (TBAP). The reaction was monitored by vis near-infrared
The functionalization of fullerenes has attracted a great deal of
attention in disciplines such as material science, catalysis, and
medical science. A large number of reactions have been developed
in recent years to determine the chemical reactivity of fullerenes and
to control their physical and chemical properties. Activation of the
fullerenes by chemical or electrochemical reduction is an effective
method for their functionalization. Kadish et al. reported that an
electrochemically generated C60 dianion (C60 ) reacts with organic
halides to afford the corresponding bis-adducts. Chemical reduction
to generate C60 is advantageous for the activation of C60 because of
its simple operation.
(
NIR) absorption spectroscopy to confirm the disappearance of the
.-
24
characteristic peaks of C60 at 1089 nm. After the disappearance of
the characteristic peak of C60 , 1,2-DCB was removed under reduced
1
-7
.-
pressure and the reaction mixture was dissolved in carbon disulfide,
then filtered to remove precipitated TBAP. The products were
isolated either by preparative high-performance liquid
chromatography (HPLC) using a Buckyprep column or by flash
chromatography.
2
-
8
2
-
9
,10
These reductive alkylation reactions have
been applied to the functionalization of endohedral
metallofullerenes
utilizing the high oxidation reactivity of both C60 and alkylated C60
Scheme 1
1
1,12
13-15
and carbon nanotubes.
Recently, reactions
2
-
1
6
17-21
anion species have been reported. In addition, dihydrofuran-,
2
2
23
lactone-, and oxazoline-fused
C
60 can be synthesized from an
alkylated C60 radical anion or an alkylated C60 radical anion having a
β-carbonyl group.
In this communication, we report the reaction of C60 with alkyl
halides and alkyl dihalides (Scheme 1). It is well known that the C60
radical anion (C60 ) is an important intermediate in various electron
transfer systems. To handle active C60 , anaerobic conditions and
highly polar solvents, such as acetonitrile and benzonitrile, are
required. In contrast, C60 has higher stability and easier handling. For
.-
.-
2
-
The structures of the C60 derivatives were characterized using matrix-
assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass
spectrometry, NMR spectroscopy, and UV-vis NIR absorption
.-
2
5
26
27
28
29
30
spectroscopy. The spectral data of 2a, 2b, 2c, 2e, 4, and 6
are consistent with previous reports. For example, the MALDI-TOF
mass spectrum of 2a displayed a strong peak at m/z 878,
corresponding to the mono adduct of C60 and 1a. The visible
absorption spectrum of 2a showed an absorption maximum at 428
nm, which is characteristic of a 6,6-addition on C60. The NMR spectra
a. Department of Chemistry, Tokyo Gakugei University, Koganei, Tokyo 184-8501,
Japan.
Present address: Department of Chemistry, Faculty of Science, Josai University,
Sakado, Saitama 350-0295, Japan.
E-mail: ymaeda@u-gakugei.ac.jp
b.
c.
†
Electronic
Supplementary
Information
(ESI)
available:
See
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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of 2a displayed the proton signals of the ethyl groups at 1.48 and 4.52
ppm, as well as the carbon signals of the ethyl groups at 14.3 and
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The reaction of C60.- with 10 equiv of benzyl bromide afforded 1,4-
DOI: 10.1039/C9NJ01043B
1
3
6
3.1 ppm. The C NMR spectrum also showed one quaternary dibenzylated C60 in low yield (entry 8). In this reaction, the rate of the
3
.-
carbon peak corresponding to the sp carbon atoms of C60 at 71.5 disappearance of the characteristic absorption peaks of C60 was
ppm and one carbonyl carbon peak at 163.0 ppm. In addition, the
NMR showed 13 peaks in the range of 139-145 ppm for the C60 cage the reaction rate and yield of 4 were increased by increasing the
due to the overlapping of 3 peaks.
1
3
C
slower than those of the β-dicarbonyl compounds. In contrast, both
amount of benzyl bromide or by using benzyl iodide instead of benzyl
.-
2-
As summarized in Table 1, the reaction of C60 is extended to β- bromide (entries 9 and 10). The reaction of C60 with an alkyl dihalide
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1-33
dicarbonyl compounds, such as a diester (entry 1), keto esters is also well known as one of the cycloaddition reactions.
The
entries 2 and 3), and β-diketones (entries 4 and 5), which afforded reaction of C60 with 1f and 5 formed the corresponding
.
-
(
the corresponding methanofullerenes (2a-2e). The mono-adducts cycloaddition products 2a and 6, respectively (entries 6, 11, and 12).
were selectively formed in high conversion yields based on the When the amount of alkyl halide used was decreased, the yields of
consumption of C60. The bis-adducts were separated in 4% yield as 2a and 6 were increased (entries 7 and 13).
.-
.-
isomer mixtures from the reaction of C60 with 1a. The high recovery To confirm the reaction mechanism, C60 was reacted with 50
.-
(39-63%) of C60 as the neutral form suggests that two C60 molecules equiv of butyl bromide. As shown in Figure S2, it took a longer
.-
were consumed for every methanofullerene molecule formed. The time for the characteristic absorption peaks assigned to C60 to
relatively low yield of 2e might be because of reduced purification decrease after the addition of butyl bromide compared with
efficiency due to its low solubility.
that after the addition of substrates 1, 3, and 5. After the
reaction, insoluble materials were obtained along with C60. This
lower reactivity of butyl bromide as compared with that of
Table 1. The substrate equivalents and yields for the reaction of C60.-
with 1, 3, and 5. Yields in parentheses are based on the amount of substrates 1, 3, and 5 excludes an S 2 reaction mechanism for
N
.
-
C
60 consumed.
60
the reaction of C . It is consistent with the low nucleophilicity
.
-
of C60 due to its 60π electron system.
Fukuzumi et al. reported detail studies on the electron transfer
2
-
.-
from C60 , C60 , and four semiquinone radical anions to three
allyl halides and manganase(III) dodecaphenylporphyrin, and
determined the rate constants of these electron transfer
3
4
reactions. These rate constants showed linear correlation with
oxidation potential of donors. The electron transfer rate
.-
2-
constants from C60 to acceptors were lower than that from C60
to acceptors depending on its lower oxidation potential. From
the comparison of the reduction potential of acceptors, the
.-
35
electron transfer from C60 to 1a (-1.13 V vs SCE) is
3
6
energetically feasible than that to allyl bromide (-1.4 V vs SCE).
On the other hand, in the case of acceptors having relatively
high reduction potential such as benzyl bromide (-1.85 V vs
3
7
2-
SCE), there is a possibility to form C60 dianion (C60 ) via
.-
disproportionation of C60 . Recently, Gao et al. reported that
-
the benzylated C60 anion (BnC60 ) was detected by in situ
2
-
measurements of absorption spectra in the reaction of C60
3
8
with benzyl bromide. The characteristic absorption peaks at
2
-
-
9
54 nm assigned to C60 and at 660 nm assigned to BnC60 were
.-
not observed in the reaction of C60 with benzyl bromide,
although the results do not exclude the possibility of
contribution of the disproportionation pathway (Figure S2).
Thus, we assume that the reaction proceeds via electron
transfer from C60 to the alkyl halide, and the generated alkyl
radical then attacks C60. Subsequent radical coupling reaction of
the alkylated C60 radical accompanied by hydrogen abstraction
affords 2. In this hydrogen abstraction, another radical species
is required, and two C60 molecules are consumed in the
formation of the mono adducts. For the formation of 4 and 6,
addition of the alkyl radical to the alkylated C60 radical
intermediates takes place instead of the hydrogen abstraction.
Thus, the high recovery of C60 from the reaction is consistent
with the proposed reaction mechanism. Very recently, Wang et
al. and Hirsch et al. have reported independently, that the
.-
.-
2
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11 F.-F. Li, A. Rodríguez-Fortea, J. M. Poblet and L. VEiecwheArgtioclyeeOnnl,inJe.
reaction of C60 with 1a and 5a to give 2a (51%) and 6 (21%),
respectively.3
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Am. Chem. Soc., 2011, 133, 2760.
DOI: 10.1039/C9NJ01043B
They proposed that the reaction involved a
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2 F.-F. Li, A. Rodríguez-Fortea, P. Peng, G. A. C. Chavez, J. M.
.-
single-electron transfer process from C60 to the alkyl halides.
Poblet and L. Echegoyen, J. Am. Chem. Soc., 2012, 134, 7480.
.-
It is interesting that the reaction of C60 with β-dicarbonyl
compounds affords methanofullerenes selectively, even though
the proposed intermediates are similar to the intermediates in
13 J. Chattopadhyay, A. K. Sadama, F. Liamg, J. M. Beach, Y. Xiao,
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1
7-22
the formation of dihydrofuran-fused C60
60 with carbonyl compounds promoted by manganese(III)
acetate over 80˚C, it was proposed that the radical
.
In the reaction of
5 Y. Maeda, S. Minami, Y. Takehana, J.-S. Dang, S. Aota, K.
Matsuda, Y. Miyauchi, M. Yamada, M. Suzuki, R.-S. Zhao, X.
Zhao and S. Nagase, Nanoscale, 2016, 8, 16916.
C
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intermediates, alkylated C60 radicals, afford corresponding 16 H.-L. Hou and X. Gao, J. Org. Chem. 2012, 77, 2553.
enolate salt and oxidized by the manganese(III) to give
dihydrofuran- or lactone-fused
methanofullerenes and dihydrofuran-fused C60 were formed
competitively from aromatic methyl ketones in the presence of
manganese(III) acetate or cupper(II) acetate. In the related
studies reported by X. Gao et al., it was proposed that
dihydrofuran-fused C60 is produced from alkylated C60 radical in
the presence of excessive hydroxide and iodide. Therefore,
the results showed that the reaction products are different
depending on the reaction methods and additives even if the
intermediates, alkylated C60 radicals, are the same.
1
7 G.-W. Wang, T.-H. Zhang, Y.-J. Li, P. Lu, H. Zhan, Y.-C. Liu, Y.
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5 C. Bingel, Chem. Ber., 1993, 126, 1957.
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26 T.-H. Zhang, G.-W. Wang, P. Lu, Y.-J. Lo. R.-F. Peng, Y.-C. Liu, Y.
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Conflicts of interest
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