Catalyst free, visible-light promoted photoaddition reactions between C60 and N-trimethylsilylmethyl-substituted tertiary amines for synthesis of aminomethyl-1,2-dihydrofullerenes

Article abstract of DOI:10.1016/j.tet.2017.11.064

An efficient and benign method for the preparation of aminomethyl-substituted fullerenes has been developed. The process, involving catalyst free, visible-light irradiation of 10% EtOH-toluene solutions containing fullerene C₆₀ and N-trimethyls

Full text of DOI:10.1016/j.tet.2017.11.064

Accepted Manuscript
Catalyst free, visible-light promoted photoaddition reactions between C and
60
N-trimethylsilylmethyl-substituted tertiary amines for synthesis of aminomethyl-1,2-
dihydrofullerenes
Suk Hyun Lim, Dae Won Cho, Patrick S. Mariano
PII:
S0040-4020(17)31230-9
10.1016/j.tet.2017.11.064
TET 29144
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 12 October 2017
Revised Date: 20 November 2017
Accepted Date: 23 November 2017
Please cite this article as: Lim SH, Cho DW, Mariano PS, Catalyst free, visible-light promoted
photoaddition reactions between C and N-trimethylsilylmethyl-substituted tertiary amines for synthesis
60
of aminomethyl-1,2-dihydrofullerenes, Tetrahedron (2018), doi: 10.1016/j.tet.2017.11.064.
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Graphical Abstract
1

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Catalyst Free, Visible-Light Promoted Photoaddition Reactions between C60 and N-
Trimethylsilylmethyl-Substituted Tertiary Amines for Synthesis of Aminomethyl-1,2-
dihydrofullerenes
Suk Hyun Lim,1 Dae Won Cho1*, Patrick S. Mariano2*
1Department of Chemistry, Yeungnam University, Gyeongsan, Gyeongbuk 712-749, Korea
(dwcho00@yu.ac.kr)
2Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque,
New Mexico 97131, USA
(mariano@unm.edu)
1

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Graphical Abstract
2

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Abstract
An efficient and benign method for the preparation of aminomethyl-substituted fullerenes has
been developed. The process, involving catalyst free, visible-light irradiation of 10% EtOH-toluene
solutions containing fullerene C60 and N-trimethylsilylmethyl-substituted amines by using a 20 W
compact fluorescent lamp, leads to formation of aminomethyl-substituted fullerene adducts in a
highly efficient manner. The photoaddition reaction takes place via a pathway initiated by visible
light absorption by C60, followed by SET from the amine to the triplet excited state of C60. Ethanol-
promoted desilylation of the resulting aminium radical then generates the corresponding α-amino
radical which couples with the C60 radical anion to form the anion precursor of the fullerene adducts.
The new approach using visible-light takes place under mild conditions and it does not require the
use of photocatalysts. Thus, the method developed in this effort could broadens the range of
functionalized fullerene derivatives that can be readily prepared.
3

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Introduction
Owing to the potential need for fullerene derivatives in many scientific research fields,1-5
a
number of studies have focused on the preparation of functionalized fullerene derivatives which not
only maintain the unique photophysical and redox properties of the parent fullerenes but also have
novel physical/chemical characteristics.6 For instance, addition reactions of diverse organic
substances across the [6,6]-juncture (or [5,6]-juncture) of C60 have been shown to generate fullerene
derivatives which have tunable properties,7 while maintaining high electron affinities,8,9 small
reorganization energies10,11 and high electron transporting abilities.12,13
The most common protocols developed to date to synthesize fullerene derivatives involve
thermal cycloaddition reactions of 1,3-dipolar azomethine ylides (known as the Prato reaction),14,15
base/organometal-promoted nucleophilic additions,16-18 transition metal mediated free radical
reactions19,20 and single electron transfer (SET)-promoted photoaddition reactions.21-24 Owing to the
excellent electron accepting ability of fullerene C60 (Ered = -0.42 V vs SCE in PhCN), photoinduced
SET-promoted reactions take place between excited states of fullerene C60 and proper electron
donating substrates under mild conditions with high quantum and chemical efficiencies.
Among the number of potentially available electron donating substances, tertiary aliphatic and
aromatic amines (ca. Eox < +1 V vs Ag/AgCl) have been utilized extensively in SET-promoted
photoaddition reactions with C60.21a,25-27 The results of these studies reveal that irradiation of C60 in
the presence of amines 1 leads to formation of aminomethyl-1,2-dihydrofullerenes 5 (i.e., 1,2-
4

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adducts) by a pathway involving thermodynamically favorable SET from the amines 1 to the triplet
*
*
excited state of C60 (3C60 , Ered(3C60 ) = 1.56 V),11b,21b,28 formed by efficient intersystem crossing
*
(ISC) from its singlet excited state of C60 (1C60 , ΦISC = 1).29 This process produces the radical anion
-
of C60 (C60ꢀ ) (Scheme 1) and an amine radical cation 2, the latter of which undergoes α-CH
deprotonation (E = H) to form a carbon centered α-amino radical 3, which couples with C60 - to form
ꢀ
an anion (6) precursor of aminomethyl-substituted 1,2-adduct 5. Alternatively, proton transfer can
-
ꢀ
occur between the amine radical cation 2 (E = H) and C60 to generate α-amino radical 4 and the
25a,30
ꢀ
hydrofullerene radical 3 (H-C60 ) which can then couple to generate the 1,2-adducts 4 directly.
Scheme 1. Mechanistic pathway for SET-promoted photoaddition reactions between tertiary amines
and C60.
Recently, we explored SET-promoted photoaddition reactions of C60 with tertiary aliphatic
amines that possess N-trimethylsilylmethyl substituents.31-33 The results showed that photoreactions
of C60 with the amines 1 (E = SiMe3) gave rise to formation of 1,2-adducts 5 with much higher
5

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efficiencies than photoreactions utilizing analogous, non-α-trimethylsilyl group containing amines 1
(E = H) (Scheme 1). The enhanced chemical efficiencies of photoreactions of N-trialkylsilylmethyl-
substituted amines is a consequence of the fact that trimethylsilyl-substituted amine radical cations 2
(E = SiMe3) undergo silophilic solvent-assisted desilylation much more rapidly than α-CH
deprotonation of the non-trimethylsilyl analogs 1 (E = H).29–31
Because photoaddition reactions of C60 with amines are highly desirable processes to synthesize
functionalized fullerene derivatives, we embarked on an effort to develop mild and eco-friendly
conditions to conduct these reactions in an efficient manner. For the most part, these reactions have
been promoted in the past using high energy UV-light.25,31,32a However, visible light is advantageous
as most organic compounds do not absorb in this region and product decomposition and unwanted
side products are easily avoided. In addition, C60 can absorbs light in the visible region and therefore
no catalysts are necessary. As a result, we designed a study to explore the viability of these
photoaddition reactions using visible light as the energy source. At the outset of this investigation,
we were aware of studies by Nishibayashi and his coworkers31a that demonstrated that visible-light
could be utilized to promote iridium complex photocatalyzed reactions of C60 with N-
trimethylsilylmethyl-substituted arylamines (Me3SiCH2NAr2, Ar = aryl) that produce aminomethyl-
substituted fullerene derivatives. In addition, Troshin35, Gan36 and others26,37 showed that visible-
light initiated photoaddition reactions of C60 with secondary/tertiary amines occurred to produce the
corresponding fullerene derivatives. Although these reactions are simple and efficient, their wide use
6

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is limited because highly intense light sources (high pressure Hg lamp equipped with a filter and
cooling water bath or intense Xenon light bulb), and expensive and laboriously synthesized iridium
(Ir) catalysts31a are required. In the effort described below, we have shown that catalyst-free, direct
visible-light promoted photoaddition reactions between C60 and N-trimethylsilylmethyl-substituted
amines take place efficiently. To the best of our knowledge, the observations are the first that show
that a methodology, in which a cheap and commercially available visible light source (and eventually
even sunlight) is used, has great potential for the preparation of uniquely functionalized fullerenes.
Results and Discussion
The N-trimethylsilylmethyl-substituted tertiary amines used in this study were prepared using
methods devised in our previous studies31 (see supplementary data). Photochemical reactions were
performed by irradiation of N2 purged, 10% EtOH-toluene (v/v) solutions (10 mL) containing C60
(0.17 mM) and the amines (0.35 mM) using a 20 W commercial compact fluorescent lamp (CFL) for
fixed time periods. (Emitted wavelength range and relative intensity of 20W CFL is shown in ESI)
Photoproduct yields were determined by utilizing HPLC and UV-visible spectrometric analysis of
1
the crude photolysates. Structural determination of photoproducts were made by comparison of H
and 13C NMR spectroscopic data to those previously reported.31,32
Photoreactions of N-trimethylsilylmethyl-N,N-dialkylamines 7-12. Photoreactions of C60
with the Ν−trimethylsilylmethyl-N,N-dialkylamines 7-1231a were explored first. The results, given in
7

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Scheme 2 and Table 1, show that 5 h visible light irradiation of N2-purged, 10% EtOH-toluene
solutions containing C60 and the N-trimethylsilylmethyl-substituted N,N-dialkylamines amines 7-11
led to production of the respective aminomethyl-substituted 1,2-adducts 13-1731a in high conversions,
product yields and material recoveries (entries 1-5 in Table 1). In contrast, reaction of the N,N-di-
carboxymethyl-substituted amine 12 formed the corresponding adduct 1831a in a low yield (27%,
entry 6), which could be significantly improved by using much longer irradiation times (entries 7-8
in Table 1). Importantly, the aminomethylated 1,2-adducts were not generated when reactions were
carried out by irradiation of either O2-purged (entries 9-10 in Table 1) or pure toluene containing
(entries 11-12 in Table 1) solutions. It is noteworthy that, in contrast to those of
Ν-
trimethylsilylmethyl-substituted amines, analogous non-α-trimethylsilyl-substituted amines (N-
methyl in place of N-trimethylsilylmethyl) did not undergo photoaddition reactions with C60 under
these conditions even when much longer irradiation times (100 h) were utilized.
Scheme 2. Visible light promoted photoaddition reactions of C60 with N-trimethylsilylmethyl-N,N-
dialkylamines 7-12.
Table 1. Products, conversions and yields of photoaddition reactions promoted by visible-light
irradiation of N2-purged 10% EtOH-toluene solutions containing C60 and N-trimethylsilylmethyl-
N,N-dialkylamines 7-12.
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irradiation conversion product
entry
amine
R3
R4
time (h)
5
(%)a
(%)
1
2
CH2(CH2)4CH3
CH2(CH2)4CH3
CH2(CH2)4CH3
CH2(CH2)4CH3
CH2CH(Et)(CH2)3CH3
CH2CH2OCH3
100
13 (91)
7
8
5
5
88
86
14 (80)
15 (74)
16 (79)
17 (54)
18 (25)
18 (49)
18 (87)
n.re
3
9
4
CH2CH(Et)(CH2)3CH3 CH2CH2OCH2CH2OH
5
91
10
11
12
12
12
7
5
CH2(CH2)4CH3
CH2CO2CH2CH3
CH2CO2CH2CH3
CH2CO2CH2CH3
CH2(CH2)4CH3
CH2(CH2)4CH3
CH2(CH2)4CH3
CH2(CH2)4CH3
CH2CO2CH2CH3
CH2CO2CH2CH3
CH2CO2CH2CH3
CH2CO2CH2CH3
CH2(CH2)4CH3
CH2CO2CH2CH3
CH2(CH2)4CH3
CH2CO2CH2CH3
5
68
6
5
35
7
10
24
24
24
24
24
58
8
91
9b
10b
11c
12c
n.re
n.re
n.re
n.re
n.re
11
7
n.re
n.re
11
aDetermined based on recovered C60. bPhotoreactions in O2-purged 10% EtOH-toluene solution.
cPhotoreaction in N2-purged, pure toluene solution. eNo reaction
Photoreactions of N-trimethylsilylmethyl-N-alkyl-N-benzylamines 19-29. Photoreactions of
C60 with N-trimethylsilylmethyl-substituted N-alkyl-N-benzylamines 19-29,31a,32b in which the alkyl
substituents possess various functional groups, were performed using the conditions described above.
As can be seen by viewing the data in Scheme 3 and Table 2, visible-light promoted photoreactions
of C60 with amines 19-22, 24-25 and 28 took place to produce the corresponding 1,2-adducts 30-
3331a, 35-3631a,32b and 3932b with high conversions, product yields and material recoveries. In contrast,
photoreactions of C60 with benzylamines 23 and 26-27, which possess either electron withdrawing
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(CH2CH2CO2CH2CH3 or p-F-Ph) or bulky (t-Bu) N-substituents, occurred to form the respective
photoadducts 3431a and 37-3832b (65-79%) in only moderate to low yields. Moreover, reaction of C60
with benzylamine 29, which possesses both an electron withdrawing para-F substituted phenyl ring
and a bulky N-tert-butyl group, was highly inefficient as reflected in a low conversion (52%) and
yield (33%) of adduct 40.32b Here again, no 1,2-aminomethyl-adducts were produced when
photoreactions of 19-29 were performed using either O2-purged solutions or pure toluene as the
solvent. Likewise, non-α-trimethylsilyl amine anologs of these substances (N-methyl in place of N-
trimethylsilylmethyl) did not undergo SET-promoted photoaddition reactions to C60 when irradiated
under the same conditions.
Scheme 3. Visible light promoted photoaddition reactions of C60 with N-trimethylsilylmethyl-N-
alkyl-N-benzylamines 19-29.
Table 2. Products, conversions and yields of photoaddition reactions promoted by visible-light
irradiation of N2-purged 10% EtOH-toluene solutions containing C60 with N-trimethylsilylmethyl-N-
alkyl-N-benzylamines 19-29.
irradiation conversion
entry
amine
R5
X
product (%)
time (h)
5
(%)a
1
2
3
CH2(CH2)4CH3
CH2(CH2)4OH
H
H
H
85
30 (81)
31 (73)
32 (74)
19
20
21
5
5
85
82
CH2CH2OCH2CH2OH
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4
5
CH2CH2OCH2CH2OCH3
H
H
5
5
5
5
5
5
5
5
82
75
99
99
91
86
89
52
33 (72)
34 (65)
35 (91)
36 (95)
37 (79)
38 (69)
39 (75)
40 (33)
22
23
24
25
26
27
28
29
CH2CH2CO2CH2CH3
6
CH3
CH3
CH3
t-Bu
t-Bu
t-Bu
H
7
CH3
F
8
9
H
10
CH3
F
11
aDetermined based on recovered C60.
The products formed in the visible light promoted reactions described above are comparable to
those generated using UV-irradiation of N2-purged, 10% EtOH-toluene solutions of the same tertiary
N-trimethylsilylmethyl-substituted amines and C60 (Table 3).31a,32b Inspection of the data arising from
the earlier study (Table 3) showed that while much shorter times were required to bring about high
conversions of C60 when UV-irradiation was used, in most cases the yields of the 1,2-aminomethyl-
adduct, reflected in much lower mass recoveries, were comparatively lower than those arising from
visible light promoted reactions.
Table 3. Products and yields of photoaddition reactions promoted by UV-light irradiation of N2-
purged 10% EtOH-toluene solutions containing C60 and N-trimethylsilylmethyl amines 7-12 and 19-
29.a
conversion
(%)b
irradiation
time (min)
entry
amine
product (%)
1c
2c
3c
4
4
4
100
93
13 (92)
14 (90)
15 (54)
7
8
9
69
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4c
5c
8
60
60
8
100
85
16 (51)
17 (42)
18 (23)
30 (47)
31 (43)
32 (57)
33 (56)
34 (54)
35 (86)
36 (69)
37 (53)
38 (61)
39 (66)
40 (52)
10
11
12
19
20
21
22
23
24
25
26
27
28
29
6c
68
7c
100
100
88
8c
8
9c
8
10c
11c
12c
13d
14d
15d
16d
17d
8
93
8
82
8
100
94
15
60
30
30
120
84
89
91
77
aAmine/C60 is 0.56:0.28 mmol in 220 mL of 10% EtOH-toluene and irradiated 450 W Hg lamp
with a flint glass filter (>300 nm). bDetermined based on recovered C60. cData from ref. 31a.
dData from ref. 32b.
Photoreactions of N-trimethylsilylmethyl-N,N-dibenzylamines 41-53. Catalyst free, visible-
light promoted photoaddition reactions of C60 with N-trimethylsilylmethyl-N,N-dibenzylamines 41-
5331b, in which the arene ring on the benzyl groups contains various electron donating (CH3, OCH3)
and electron withdrawing (F, CF3) substituents, were carried out under the same conditions described
above. As the results depicted in Scheme 4 and Table 4 show, in contrast to the parent phenyl group
containing substrate 41 (entry 1, Table 3), irradiation of 10% EtOH-toluene solutions of amines 42-
45, which possess either one or two electron donating phenyl substituents (i.e., CH3, OCH3),
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underwent SET-promoted photoaddition reactions with C60 to produce the respective aminomethyl-
substituted 1,2-adducts 55-5831b in high conversions and product yields (entries 1-5 in Table 4).
However, photoreactions of amines 46-53, containing one or two electron withdrawing phenyl
substituents (i.e., F, CF3), took place less efficiently than the reaction of 41 to give the respective
photoadducts 59-6631b (entries 6-13 in Table 3) even when a longer irradiation time (24 h) was used
(entries 11-13 in Table 4). Another interesting observation was that 24 h irradiation of a solution of
C60 and the two CF3 group substituted benzylamine 53 led to formation of the aminomethyl adduct
66 along with the pyrrolidine-fused fullerene 67 (4%).31b
Scheme 4. Visible-light promoted photoaddition reactions of C60 with N-trimethylsilylmethyl-N,N-
dibenzylamines 41-53.
Table 4. Products, conversions and yields of photoaddition reactions promoted by visible-light
irradiation of N2-purged 10% EtOH-toluene solutions containing C60 and N-trimethylsilylmethyl-
N,N-dibenzylamines 41-53.
irradiation
time (h)
conversion
(%)a
entry
1
amine
X
H
Y
H
product (%)
5
65
54 (58)
41
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2
3
H
H
CH3
OCH3
CH3
OCH3
F
5
5
95
95
98
100
30
17
59
38
42
54
28
22
55 (88)
56 (84)
42
43
44
45
46
47
48
49
50
51
52
53
4
CH3
OCH3
H
5
57 (92)
5
5
58 (94)
6
5
59 (26)
7
H
CF3
F
5
60 (11)
8
CH3
CH3
OCH3
F
5
61 (54)
9
CF3
CF3
F
5
62 (22)
10
11
12
13
5
63 (29)
24
24
24
64 (41)
F
CF3
CF3
65 (17)
CF3
66 (14), 67 (4)
aDetermined based on recovered C60.
Photoreactions of N-trimethylsilylmethyl-N-benzylglycinate esters 68-72. Observations
made in an earlier study32a demonstrated that UV-irradiation induced photoaddition reactions
between C60 and N-trimethylsilylmethyl-N-benzyl substituted glycinate esters were unique in that the
nature and distribution of photoproducts are highly dependent on reaction conditions. Specifically,
while UV irradiation of N2-purged, 10% EtOH-toluene solutions of C60 and these amines32a for short
time periods (1 h) leads to formation of expected aminomethyl-substituted 1,2-adducts32a exclusively,
irradiation of O2-purged 10% EtOH-toluene solutions leads to exclusive formation of the
corresponding fulleropyrrolidines.32a In the current effort, we briefly explored catalyst free, visible-
light promoted reactions between C60 and N-trimethylsilylmethyl-N-benzylglycinate esters 68-72
14

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(Scheme 5 and Table 5). We observed that 20 W CFL irradiation of N2-purged 10% EtOH-toluene
solutions of C60 and glycinates 68-72 led to production of the respective 1,2-aminomethyl adducts
73-77 solely. As anticipated (see above), the conversion and yield of the reaction of the p-CF3
substituted substrate 72 were relatively low (Table 5).
Scheme 5. Visible-light promoted photoaddition reactions of C60 with N-trimethylsilylmethyl-N-
benzylglycinate esters 68-72.
Table 5. Products, conversions and yields of photoaddition reactions promoted by visible-light
irradiation of N2-purged 10% EtOH-toluene solutions containing C60 and N-trimethylsilylmethyl-N-
benzylglycinate esters 68-72.
conversion
(%)a
irradiation
time (h)
entry
amine
Z
product (%)
1
2
3
4
5
6
7
8
H
H
5
24
5
60
88
68
90
86
94
41
64
73 (56)
73 (86)
74 (66)
74 (90)
75 (72)
75 (86)
76 (30)
76 (55)
68
68
69
69
70
70
71
71
CH3
CH3
OCH3
OCH3
F
24
5
24
5
F
24
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9
CF3
5
9
77 (2)
72
72
10
CF3
24
47
77 (43)
aDetermined based on recovered C60.
Photoreactions of N-trimethylsilylmethyl-N-methylanilines 78-80. Visible-light induced
photoreactions of C60 with α-trimethylsilyl-substituted N-methylanilines 78-8038 were also explored
by using the same irradiation conditions. (Scheme 6 and Table 6) As the data in Table 6 show,
irradiation of N2-purged 10% EtOH-toluene solutions containing C60 and anilines 78-80 gave rise to
the corresponding aminomethyl-substituted 1,2-adducts 81-83. In addition, both conversion and
product yields were enhanced as the irradiation time increase. Finally, no aminomethyl photoadducts
were produced when these processes were performed under O2-purged irradiation conditions.
Scheme 6. Visible-light promoted photoaddition reactions of C60 with N-trimethylsilylmethyl-N-
methylanilines 78-80.
Table 6. Products, conversions and yields of photoaddition reactions promoted by visible-light
irradiation of N2-purged 10% EtOH-toluene solutions containing C60 and N-trimethylsilylmethyl-N-
methylanilines 78-80.
conversion
(%)a
irradiation
time (h)
entry
amine
X
product (%)
16

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1
2
3
4
5
6
7
8
9
H
H
5
7
65
76
87
72
81
89
44
54
61
81 (57)
81 (60)
81 (75)
82 (59)
82 (72)
82 (79)
83 (32)
83 (46)
83 (49)
78
78
78
79
79
79
80
80
80
H
10
5
CH3
CH3
CH3
F
7
10
5
F
7
F
10
aDetermined based on recovered C60.
The results of studies with the N-trimethylsilylmethyl-substituted N-methylanilines are
comparable to those observed arising from the work of Nishibayashi and co-workers.30a This earlier
effort showed that 9 h visible light (440 nm) irradiation (250W Hg lamp with filter) of a o-
dichlorobenzene (ODCB)-H2O (v/v = 200: 1) solution containing C60 and the N-
trimethylsilylmethyl-substituted aniline 78 in the absence of a photocatalyst (i.e., iridium complex)
gave rise to production of the 1,2-adduct 81 in a very low product yield (15 %). In addition, although
photoreaction in the presence of an iridium photocatalyst occurred with an enhanced efficiency, the
yield (36 %) was still low (Scheme 7).
Scheme 7. The results of Nishibayashi and co-workers’ study of visible light promoted photoreaction
of C60 with aniline 78 in the presence/absence of iridium photocatalyst.
17

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Although it is not possible to compare the observations made earlier by Nishibayashi and by us in
the current effort because different conditions (e.g., light sources, photochemical apparatus and
reaction conditions) were employed, the largely different yields of the processes are most likely
caused by the different solvents used. To explore how solvent governs the efficiencies of
photoreactions of C60 with N-trimethylsilylmethyl-substituted anilines, N2-purged 10% EtOH-ODCB
solutions of C60 and anilines 78-80 were subjected to visible-light irradiation. As can be seen by
reviewing the results in Table 7, although photoreactions in this solvent system took place to produce
aminomethylated 1,2-adducts, the yields were dramatically lower than when the 10% EtOH-toluene
solvent system was utilized. The differing in product yields depending on solvent system appear to
be highly associated with chemoselectivity. In the HPLC analysis of photoproducts (see
supplementary data), we found that while photoreactions of C60 with aniline derivatives 78-80 in 10%
EtOH-toluene solution gave rise to formation of single products 81-83 (i.e., one peak in HPLC data
was observed), however, reactions in 10% EtOH-ODCB produced multiple products, in which one of
them was aminomethyl 1,2-dihydrofullerenes 81-83 (i.e., two or three peaks in HPLC data were
observed).
Table 7. Products, conversions and yields of photoaddition reactions promoted by visible-light
irradiation of N2-purged 10% EtOH-ODCB solutions containing C60 and N-trimethylsilylmethyl-N-
methylanilines 78-80.
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conversion
(%)a
irradiation
time (h)
entry
amine
product (%)
1
2
4
5
7
8
5
10
5
46
71
52
72
29
60
81 (22)
81 (34)
82 (25)
82 (35)
83 (16)
83 (36)
78
78
79
79
80
80
10
5
10
aDetermined based on recovered C60.
Conclusion
Visible-light promoted photochemical reactions have recently attracted great attention because
of their wide application in organic synthesis and their use of sustainable and green energy sources.
In the study described above, an efficient and environmentally benign method for the preparation of
variously substituted aminomethyl-1,2-dihydrofullerenes has been developed. Observations made in
this study show that photocatalyst free, visible-light promoted photoreactions of 10% EtOH-toluene
solutions containing fullerene C60 and N-trimethylsilylmethyl-substituted amines generate
aminomethyl substituted fullerene adducts in a highly efficient manner, although reactions with
electron deficient amines give rise to limited conversion and product yields. Importantly, the results
confirm our earlier observations that show that presence of an N-trimethylsilylmethyl group and the
electronic nature of amine substrates play critical roles in governing the efficiencies of these
photoaddition reactions. In comparison to typical thermal and photochemical methods developed
previously for the preparation of aminomethylated fullerene derivatives, the new approach using
19

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visible-light takes place under mild conditions and it does not require the use of photocatalysts. Thus,
the method developed in this study could broaden the scope of methods to functionalize fullerenes
using amine substrates.
Experimental
1
General. Commercially available fullerene C60 (>99% HPLC pure) was used as received. H
and 13C NMR spectra (300 MHz) were recorded using CDCl3 solutions, and chemical shifts are
reported in parts per million relative to CHCl3 (7.24 ppm for 1H NMR and 77.0 ppm for 13C NMR)
as an internal standard. High resolution (HRMS) mass spectra were obtained by using a quadrupole
mass analyzer and electron impact ionization unless otherwise noted.
Synthesis of α-trimethylsilylamines 7-9 and 11.31a Individual solutions of N-
(trimethylsilyl)methyl-N-hexylamine (16 mmol) in MeCN (100 mL) containing K2CO3 (36 mmol)
and alkyl halide (20 mmol of 1-hexyl bromide, 2-ethyl-1-hexyl iodide, and 2-methoxy-1-ethyl iodide,
and ethyl 2-bromoacetate) were stirred for 12 h at room temperature and concentrated in vacuo to
give residues that were in vacuo to afford residues, which were subjected to column chromatography
(EtOAc: Hex = 1: 10) to yield 7 (85%), 8 (62%), 9 (68%) and 11 (80%).
Synthesis of α-trimethylsilylamine 10.31a A 100 mL MeCN solution of N-
(trimethylsilyl)methyl-N-hyroxyethoxyamine (10.5 mmol) containing K2CO3 (41.8 mmol) and 2-
ethyl-1-hexyl bromide (15 mmol) was stirred for 12 h at room temperature and concentrated in vacuo
20

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to give residue that was in vacuo to afford residues, which were subjected to column chromatography
(EtOAc: Hex = 1: 5) to yield 10 (57%).
Synthesis of α-trimethylsilylamine 12.31a A 100 mL MeCN solution of N,N-bis-
ethylcarboxymethylamine
(15.5
mmol)
containing
K2CO3
(41.8
mmol)
and
(iodomethyl)trimethylsilane (20 mmol) was stirred for 12 h at room temperature and concentrated in
vacuo to give residue that was in vacuo to afford residues, which were subjected to column
chromatography (EtOAc: Hex = 1: 8) to yield 10 (69%).
Synthesis of α-trimethylsilylamines 19 and 22-23.31a Individual solutions of N-
(trimethylsilyl)methyl-N-benzylamine (15.5 mmol) in MeCN (100 mL) containing K2CO3 (31 mmol)
and alkyl halide (30 mmol of 1-hexyl bromide, 2-(2-methoxyethoxy)ethyl iodide, ethyl 2-
bromopropionate) were stirred for 12 h at room temperature and concentrated in vacuo to give
residues that were triturated with CH2Cl2. The triturates were dried and concentrated in vacuo to
afford residues, which were subjected to column chromatography (EtOAc: Hex = 1: 8) to yield 19
(81%), 22 (90%) and 23 (44%).
Synthesis of α-trimethylsilylamine 20.31a A 100 mL MeCN solution of N-5-hydroxypentyl-N-
benzylamine (15.5 mmol) containing K2CO3 (41.8 mmol) and (iodomethyl)trimethylsilane (20 mmol)
was stirred for 12 h at room temperature and concentrated in vacuo to give residue that was triturated
with CH2Cl2. The triturate was dried and concentrated in vacuo to afford residues, which were
subjected to column chromatography (EtOAc: Hex = 1: 8) to yield 20 (45%).
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Synthesis of α-trimethylsilylamine 21.31a A 100 mL MeCN solution of N-
(trimethylsilyl)methyl-N-hydroxyethoxyamine (10.5 mmol) containing K2CO3 (41.8 mmol) and
benzyl bromide (21 mmol) was stirred for 12 h at room temperature and concentrated in vacuo to
give residue that was triturated with CH2Cl2. The triturate was dried and concentrated in vacuo to
afford residues, which were subjected to column chromatography (EtOAc: Hex = 1: 5) to yield 21
(49%).
Synthesis of α-trimethylsilylamines 24-26.32b Individual solutions of N-trimethylsilylmethyl-
N-benzylamine derivatives (11 mmol) in MeCN (120 mL) containing K2CO3 (18 mmol) and methyl
iodide (9.5 mmol) were stirred for 12 h at room temperature and concentrated in vacuo to give
residues that were extracted with CH2Cl2. The extracts were dried and concentrated in vacuo to
afford residues, which were subjected to silica gel column chromatography (EtOAc/hexane = 1: 8) to
yield corresponding amine substrates 24 (62%), 25 (76%) and 26 (75%).
Synthesis of α-trimethylsilylamines 27-29.32b Individual solutions of N-(trimethylsilyl)methyl-
N-t-butylamines (11 mmol) in MeCN (120 mL) containing K2CO3 (18 mmol) and p-substituted (H,
Me, F) phenyl containing benzyl iodide (9 mmol) were stirred for 12 h at room temperature and
concentrated in vacuo to give residues that were extracted with CH2Cl2. The extracts were dried and
concentrated in vacuo to afford residues, which were subjected to silica gel column chromatography
(EtOAc/hexane = 1: 8) to yield 27 (89%), 28 (88%) and 29 (92%).
Synthesis of α-trimethylsilylamines 41-53.31b Individual solutions of N-trimethylsilylmethyl-
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N-benzylamine derivatives (13 mmol) in MeCN (120 mL) containing K2CO3 (20 mmol) and p-
substituted benzyl halides (20 mmol) were stirred for 12 h at room temperature and concentrated in
vacuo to give residues which were extracted with CH2Cl2. The extracts were dried and concentrated
in vacuo to afford residues, which were subjected to silica gel column chromatography to yield 41
(72%), 42 (62%), 43 (68%), 44 (73%), 45 (47%), 46 (63%), 47 (87%), 48 (39%), 49 (96%), 50
(82%), 51 (71%), 52 (94%) and 53 (73%).
Synthesis of α-trimethylsilylamines 68-72.32a Individual solutions of N-trimethylsilylmethyl-
N-benzylamine derivatives (10 mmol) in MeCN (100 mL) containing K2CO3 (2.7 g, 19 mmol) and
ethyl bromoacetate (12 mmol) were stirred for 12 h at room temperature and concentrated in vacuo
to give residues which were triturated with CH2Cl2. The triturates were dried and concentrated in
vacuo to afford residues, which were subjected to silica gel column chromatography (EtOAc: hexane
= 1: 20) to yield 68 (66%), 69 (53%), 70 (70%), 71 (88%) and 72 (56 %).
Synthesis of α-trimethylsilylamines 78-80.38 To individual solutions of N-methyl-N-
phenylamine derivatives (9.3 mmol) in THF (30 mL) was added n-BuLi (12 mmol) at -78 oC. After
stirred for 1 h, (iodomethyl)trimethylsilane (10.3 mmol) was added dropwise to the solutions and the
resulting solutions were stirred for 5 h at room temperature. Then, the solutions were quenched by aq.
NH4Cl and triturated with CH2Cl2. The triturates were dried and concentrated in vacuo to afford
residues, which were subjected to silica gel column chromatography (hexane) to yield 78 (75%), 79
(44%) and 80 (60%).
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General procedure for photoreaction of C60 with tertiary α-trimethylsilylamines.
Independent N2-purged 10% EtOH-toluene (v/v) solutions (10 mL) containing C60 (0.17 mM) and α-
trimethylsilylamine (0.35 mM) in quartz tubes were simultaneously irradiated by using 20 W
compact fluorescent lamp (CFL) in a merry-go-round apparatus for a certain period time. Each
photolysate was subjected to HPLC analysis by comparison with authentic photoproducts. The
results were summarized below.
irradiation conversion
product
(% yield)
1331a (91)
1431a (80)
1531a (74)
1631a (79)
1731a (54)
1831a (25)
18 (49)
amine
time (h)
(%)
100
88
86
91
68
35
58
91
85
85
82
82
75
99
99
91
86
89
52
65
95
95
98
100
5
5
7
8
5
9
5
10
11
5
5
10
24
5
12
18 (87)
19
20
21
22
23
24
25
26
27
28
29
41
42
43
44
45
3031a (81)
3131a (73)
3231a (74)
3331a (72)
3431a (65)
3532b (91)
3632b (95)
3732b (79)
3832b (69)
3932b (75)
4032b (33)
5431b (58)
5531b (88)
5631b (84)
5731b (92)
5831b (94)
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
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5
5
30
17
59
38
42
54
28
22
60
88
68
90
86
94
41
64
9
5931b (26)
6031b (11)
6131b (54)
6231b (22)
6331b (29)
6431b (41)
6531b (17)
6631b (14), 6731b (4)
7332a (56)
73 (86)
46
47
48
49
50
51
52
53
5
5
5
24
24
24
5
68
69
70
71
72
24
5
7432a (66)
24
5
74 (90)
7532a (72)
75 (86)
7632a (30)
24
5
24
5
76 (55)
7732a (2)
24
47
77 (43)
Photoreaction of C60 with 78. In 10% EtOH-toluene solution: 5h irradiation, 65% conversion,
HPLC analysis to yield 81 (57%); 7h irradiation, 76% conversion, HPLC analysis to yield 81 (60%);
10h irradiation, 87% conversion, HPLC analysis to yield 81 (75%). In 10% EtOH-ODCB solution:
5h irradiation, 46% conversion, HPLC analysis to yield 81 (22%); 10h irradiation, 71% conversion,
HPLC analysis to yield 81 (34%). 1H-NMR (CDCl3) 3.52 (s, 3H), 5.34 (s, 2H), 6.49 (s, 1H), 6.78 (t,
13
1H, J = 7.2 Hz), 7.15-7.7.18 (m, 2H), 7.26-7.31 (m, 2H); C-NMR (CS2+CDCl3) 40.8, 57.8, 67.1,
67.5, 112.7, 118.0, 129.2, 135.2, 135.8, 139.8, 140.0, 141.3 (2H), 141.6 (2H), 141.8, 142.2, 142.8,
144.1, 144.2, 144.9, 145.0, 145.1, 145.3, 145.7, 145.8, 145.9, 146.0, 146.5, 146.6, 146.9, 148.9,
153.2, 153.9; HRMS (FAB) m/z 842.0966 (M+H, C68H12N require 842.0964).
Photoreaction of C60 with 79. In 10% EtOH-toluene solution: 5h irradiation, 72% conversion,
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HPLC analysis to yield 82 (59%); 7h irradiation, 81% conversion, HPLC analysis to yield 82 (72%);
10h irradiation, 89% conversion, HPLC analysis to yield 82 (79%). In 10% EtOH-ODCB solution:
5h irradiation, 52% conversion, HPLC analysis to yield 82 (25%); 10h irradiation, 72% conversion,
HPLC analysis to yield 82 (35%). 1H-NMR (CDCl3) 2.3 (s, 3H), 3.5 (s, 3H), 5.3 (s, 2H), 6.51 (s, 1H),
13
7.09 (s, 4H); C-NMR (CS2+CDCl3) 20.4, 41.1, 57.9, 67.6, 67.7, 113.1, 126.8, 129.8, 135.3, 135.9,
139.9, 140.0, 141.4 (2H), 141.5, 141.7, 141.8, 141.9, 142.3, 142.9, 144.2, 144.3, 145.0, 145.1, 145.2,
145.5, 145.8, 145.9, 146.0, 146.1, 146.7 (2H), 147.0, 147.1, 153.4, 154.2; HRMS (FAB) m/z
856.1122 (M+H, C69H14N require 856.1121).
Photoreaction of C60 with 80. In 10% EtOH-toluene solution: 5h irradiation, 44% conversion,
HPLC analysis to yield 83 (32%); 7h irradiation, 54% conversion, HPLC analysis to yield 83 (46%);
10h irradiation, 61% conversion, HPLC analysis to yield 83 (49%). In 10% EtOH-ODCB solution:
5h irradiation, 29% conversion, HPLC analysis to yield 83 (16%); 10h irradiation, 60% conversion,
1
HPLC analysis to yield 83 (36%). H-NMR (CDCl3) 3.49 (s, 3H), 5.29 (s, 2H), 6.47 (s, 1H), 6.95-
13
7.01 (m 2H), 7.1-7.14 (m, 2H); C-NMR (CS2+CDCl3) 41.5, 58.0, 67.5, 68.0, 114.1 (d, JC-F = 28.8
Hz), 115.6 (d, JC-F = 87.6 Hz), 135.2, 135.9, 139.8, 140.1, 141.3, 141.4 (2H), 141.7 (2H), 141.8,
142.3, 142.7, 142.9, 144.1, 144.2, 145.0 (2H), 145.1, 145.4, 145.7 (2H), 145.8, 145.9, 146.0 (2H),
146.6 (2H), 146.9, 147.0, 153.1, 153.8, 155.7 (d, JC-F = 949.2 Hz); HRMS (FAB) m/z 860.0873
(M+H, C68H11F require 860.0870).
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Acknowledgements
This investigation was financially supported by 2016 Yeungnam University Research Grant
(2016A380047).
Appendix A. Supplementary data
Supplementary data related to this article can be found at https://
References
1. (a) Hebard AF, Rosseinsky MJ, Haddon RC, et al. Nature. 1990;350:600;
(b) Anthopoulos, TD, Tanase C. Setayesh S, et al. Adv Mater. 2004;16:2174;
(c) Yang, Y. Nature. 1992;356:585.
2. (a) Allemand, PM, Khemani, KC, Koch, A, et al. Science. 1991;253:301;
(b) Yu G, Gao J, Hummelen JC, Wudl F, Heeger AJ. Science. 1995;270:1789;
(c) Bendikov M, Wudl F. Chem Rev. 2004;104:4891.
3. (a) Matsuo Y. Ichiki T, Nakamura E. J Am Chem Soc. 2011;133:9932;
(b) Brunetti FG, Kumar R, Wudl F. J Mater Chem. 2010;20:2934;
(c) Mateo-Alonso A, Iliopoulos K, Couris S, Prato M. J Am Chem Soc. 2008;130:1534.
4. (a) Takenaka S, Yasmashita K, Takagi N, Hatta T, Tsuge O. Chem Lett. 1999;321;
(b) Friedman SH, DeCamp DL, Sijbesma RP, Srdanov G, Wudl F, Keyton GL. J Am Chem Soc.
27

ACCEPTED MANUSCRIPT
1993;115:6506;
(c) Cataldo F, Da Ros T. Medicinal Chemistry and Pharmacological Potential of Fullerenes and
Carbon Nanotubes. Netherlands: Springer; 2008.
5. (a) Sun D, Zhu Y, Liu Z, Liu G, et al. Chin Sci Bull. 1997;42:748;
(b) Boutorine A, Tokuyama H, Takasugi M, Isobe H, Nakamura E, Helene C. Angew Chem Int Ed
Engl. 1994;33:2462;
(c) Tokuyama H, Yamago S, Nakamura E, Shiraki T, Sugiura Y. J Am Chem Soc.
1993:115:7918;
(d) Kato S, Aoshima H, Saitoh Y, Miwa N. Bioorg Med Chem Lett. 2009;19:5293.
6. (a) Prato M. Top Curr Chem 1999;199:173;
(b) Guldi DM, Martın N. Fullerenes: From Synthesis to Optoelectronic Properties. Netherlands:
Kluwer Academic Publishers: 2002.
7. (a) Li C-Z, Yip H-L, Jen AK-Y. J Mater Chem. 2012;22:4161;
(b) Clarke TM, Durrant JR. Chem Rev. 2010;110:6736;
(c) Gunes S, Neugebauer H, Sariciftci NS. Chem Rev. 2007;107:1324;
(d) He YJ, Li YF. Phys Chem Chem Phys. 2011;13:1970.
8. (a) Reed CA, Bolskar RD. Chem Rev. 2000;100:1075;
(b) Krusic PJ, Wasserman E, Keizer PN, Morton JR, Preston KF. Science. 1991;254:1183.
9. McEwen CN, McKay RG, Larsen BS. J Am Chem Soc. 1992;114:4412.
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