SET-promoted photoaddition reactions of fullerene C60 with tertiary N-trimethylsilylmethyl substituted α-aminonitriles. Approach to the synthesis of fulleropyrrolidine nitriles

Article abstract of DOI:10.1016/j.tet.2017.08.057

Photoaddition reactions of C₆₀ with tertiary N-arylmethyl-N-trimethylsilylmethyl substituted α-aminonitriles were explored. The results show that these photoreactions produce both trimethylsilyl- and cyano group containing fulleropyrrolidines as major products through pathways involving 1,3-dipolar cycloaddition of azomethine ylide intermediates. The ylides are formed either by SET from α-aminonitriles to the triplet excited state of C₆₀ (in N₂-purged solutions) followed by desilylation or deprotonation, or by hydrogen atom abstraction by singlet oxygen (in O₂-purged solutions). In contrast, photoreactions of C₆₀ with analogous amines that do not contain trimethylsilyl group form fulleropyrrolidines that contain aryl- and cyano substitutents on the pyrrolidine ring. The efficiencies of these photoaddition reactions are influenced by several factors including reaction condition (N₂ or O₂-purged), solvent polarity, the electronic and structural nature of α-aminonitriles and additive. The presence of trimethylsilyl group in the α-aminonitrile substrates plays a crucial role in enhancing the efficiencies of the fulleropyrrolidine forming reactions.

Full text of DOI:10.1016/j.tet.2017.08.057

Accepted Manuscript
SET-promoted photoaddition reactions of fullerene C with tertiary N-
60
trimethylsilylmethyl substituted α-aminonitriles. Approach to the synthesis of
fulleropyrrolidine nitriles
Suk Hyun Lim, Dae Won Cho, Jungkweon Choi, Hyunjun An, Jun Ho Shim, Patrick S.
Mariano
PII:
S0040-4020(17)30904-3
10.1016/j.tet.2017.08.057
TET 28951
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 8 August 2017
Revised Date: 29 August 2017
Accepted Date: 31 August 2017
Please cite this article as: Lim SH, Cho DW, Choi J, An H, Shim JH, Mariano PS, SET-promoted
photoaddition reactions of fullerene C with tertiary N-trimethylsilylmethyl substituted α-
60
aminonitriles. Approach to the synthesis of fulleropyrrolidine nitriles, Tetrahedron (2017), doi: 10.1016/
j.tet.2017.08.057.
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ACCEPTED MANUSCRIPT
SET-Promoted Photoaddition Reactions of Fullerene C60 with Tertiary Ν-Trimethylsilylmethyl
Substituted α-Aminonitriles. Approach to the Synthesis of Fulleropyrrolidine Nitriles
Suk Hyun Lim,1 Dae Won Cho,1* Jungkweon Choi,2 Hyunjun An,3 Jun Ho Shim,3
Patrick S. Mariano4*
1Department of Chemistry, Yeungnam University, Gyeongsan, Gyeongbuk 712-749, Korea
(dwcho00@yu.ac.kr)
2Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS),
Daejeon 305-701, Korea
3Department of Chemistry and Institute of Basic Science, Daegu University, Gyeongsan, Gyeongbuk
38453, Korea
4Department 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
Photoaddition reactions of C60 with tertiary N-arylmethyl-N-trimethylsilylmethyl substituted α-
aminonitriles were explored. The results show that these photoreactions produce both trimethylsilyl-
and cyano group containing fulleropyrrolidines as major products through pathways involving 1,3-
dipolar cycloadditon of azomethine ylide intermediates. The ylides are formed either by SET from α-
aminonitriles to the triplet excited state of C60 (in N2-purged solutions) followed by desilylation or
deprotonation, or by hydrogen atom abstraction by singlet oxygen (in O2-purged solutions). In
contrast, photoreactions of C60 with analogous amines that do not contain trimethylsilyl group form
fulleropyrrolidines that contain aryl- and cyano substitutents on the pyrrolidine ring. The efficiencies
of these photoaddition reactions are influenced by several factors including reaction condition (N2 or
O2-purged), solvent polarity, the electronic and structural nature of α-aminonitriles and additive. The
presence of trimethylsilyl group in the α-aminonitrile substrates plays a crucial role in enhancing the
efficiencies of the fulleropyrrolidine forming reactions.
3

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Introduction
Chemical transformation of fullerenes to organofullerene derivatives, which possess unique
photochemical and photophysical properties, is required for potential applications in the fields of
material and biological sciences.1-7 Among a number of organofullerene families probed so far, those
containing appended amine functionality have attracted interests owing to their synthetic
accessibility and well-defined structures. Especially interesting in this regard are fulleropyrrolidines
in which the fullerene ring system is fused to a five-membered N-heterocyclic ring.8-14 A variety of
thermal, metal-catalyzed and photochemical methods using α-amino acid derivatives have been
developed for the preparation of fulleropyrrolidines. For instance, the pioneering work of Prato and
co-workers7a,7b,8 led to the development of thermally promoted 1,3-dipolar cycloaddition reactions of
fullerene C60 with azomethine ylides. The ylide serving as the intermediate in this process is
generated through condensation reaction of N-methylglycine with formaldehyde followed by
decarboxylation. Since that time, related approaches have been devised to prepare fulleropyrrolidines
using a variety of other azomethine ylide precursors such as a combination of α-amino acids and
aldehydes,15 aziridinoesters8 and α-iminoesters (Scheme 1).13,14 Recently, during an exploration of
Prato type thermal reactions of C60, Wang and co-workers10a discovered that α-amino acids and α-
aminoesters undergo sequential deamination-decarboxylation to generate aldehydes, which then react
in situ with the starting α-amino acids/esters to form azomethine ylides that add to C60 to form
fulleropyrrolidines. More recently, Liu and co-workers9 reported that thermal reactions of C60 with
mixtures of arylmethylamines (ArCH2NHR, R = H, alkyl) and arylaldehydes (ArCHO) give rise to
stereoselective formation of 2,5-diaryl substituted pyrrolidine containing fullerene adducts.
Scheme 1.
4

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Metal-catalyzed cycloaddition reactions of amines with C60 also have been employed to prepare
fulleropyrrolidines. Martin and co-workers14 revealed that α-iminoesters, derived by reactions of
arylaldehydes with primary α-aminoesters, add to C60 in the presence of Cu(II) or Ag(I) at room
temperature to generate mixtures of diasteromeric fulleropyrrolidines (Scheme 2). Interestingly,
when these processes were conducted in the presence of chiral organic additives, stereoselective and
enantioselective formation of fulleropyrrolidine adducts took place. In addition, the results of a study
by Liu and co-workers12a showed that Fe(III)-catalyzed reactions of primary and secondary
arylmethylamines (ArCH2NHR, R = H, alkyl) with C60 occur to produce fulleropyrrolidines
stereoselectively.
Scheme 2.
O
Ar
H
O
Ar
O
M
O
C60
M+
Ar
N
+
OR2
NH
Ar HN
OR2
R1
CO2R2
R1
R1
H2N
OR2
(M+ = Cu(II) or Ag(I))
R1
(R2, R3 = H, alkyl)
5

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In addition to these efforts, earlier studies by Foote,16 Gan11 and others10b,10c,10d showed that
irradiation of oxygenated (O2-purged or air-saturated) solutions of C60 containing aliphatic amines
possessing α-hydrogens gives rise to formation of fulleropyrrolidine adducts through pathways
involving singlet oxygen (1O2) and/or single electron transfer (SET) steps. In recent studies exploring
photochemical reactions of C60, we observed that irradiation of both O2 and N2-purged 10% EtOH-
toluene (v/v) solutions of C60 and tertiary α-aminoesters 1 (MeN(ArCH2)CH2CO2Et, Ar = para-
substituted phenyl) gives rise to formation of fulleropyrrolidines 6 via [3+2]-dipolar cycloaddition
between C60 and in situ generated azomethine ylides 3 (a in Scheme 3).17 More interesting results
came from an investigation of the photoreactions of C60 with α-aminoesters possessing the
trimethylsilyl group (2 (Me3SiCH2N(ArCH2)CH2CO2Et, Ar = para-substituted phenyl). Specifically,
irradiation of O2-purged 10% EtOH-toluene solutions containing C60 and α-aminoesters 2 resulted in
the formation of fulleropyrrolidines 7 (b in Scheme 3). Importantly, these reactions were more
efficient than those of the related non-trimethylsilyl substituted α-aminoester analogs 1. In contrast,
photoreaction of N2-purged solutions of C60 and trimethylsilyl substituted α-aminoesters 2 led to
predominant/exclusive formation of 1-aminomethyl-1,2-dihydrofullerenes 8, via addition of α-amino
-
radicals 5 to fullerene radical anions (C60ꢀ ), formed by SET from 2 to the excited state of C60.17 (c in
Scheme 3) These observations show that O2 plays an important role in governing pathways followed
in these photochemical processes.
Another interesting observation made relates to the different substitution patterns in the
fulleropyrrolidine adducts 6 and 7 that arise from photoreactions of non-trimethylsilyl- (1) and
trimethylsilyl (2) substituted α-aminoesters. Specifically, while irradiation of C60 in the presence of
non-trimethylsilyl containing α-aminoesters 1 (MeN(ArCH2)CH2CO2Et) led to formation of
products 6 arising from cycloaddition of ethoxycarbonyl- and aryl substituted azomethine ylides 3,
irradiation of C60 in solutions containing trimethylsilyl substituted α-aminoesters
2
6

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(Me3SiCH2N(ArCH2)CH2CO2Et) brought about formation of fulleropyrrolidines 7, derived from
ethoxycarbonyl- and trimethylsilyl substituted ylides 4 (Scheme 3).
Scheme 3.
In a continuing research program aimed at exploring the nature and range of photoaddition
reactions employed for the synthesis of fulleropyrrolidines, we designed, prepared and probed
photoaddition reactions of C60 with N-arylmethyl and N-trimethylsilylmethyl substituted tertiary α-
aminonitriles (Me3SiCH2N(ArCH2)CH2CN), in which the aryl groups contain either electron
donating or withdrawing substituents. Despite the simplicity of their preparation and their high utility
as potential azomethine ylide precursors,18 to the best of our knowledge, these amines have only
rarely been utilized in photochemical reactions. Because α-aminonitriles bearing α-hydrogens (pKa
ca. 25) can potentially serve as chemical equivalents of α-aminoesters (pKa ca. 25), they should be
useful substrates in photocycloaddition reactions leading to fulleropyrrolidines. Observation made in
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studies with these substances, summarized below, show that photoaddition reactions of trimethylsilyl
group containing α-aminonitriles with C60 occur stereoselectively to form fulleropyrrolidines in a
highly efficient manner, even when conducted using N2-purged conditions.
Results and Discussion
Synthesis and photochemistry. The N-arylmethyl and N-trimethylsilylmethyl substituted
tertiary α-aminonitriles 11a-11k, employed as substrates in photoreactions with C60, were prepared
by using sequences beginning with well-known base-catalyzed substitution reactions of
commercially available substituted benzylamines 9a-9k and iodomethyltrimethylsilane (ICH2SiMe3).
(Scheme 4) These processes produced secondary N-trimethylsilylmethyl-N-benzylamines 10a-10k,19
which then reacted with iodoacetonitrile (ICH2CN) in the presence of base (K2CO3) to form the
target tertiary α-aminonitriles 11a-11k (66-91 %).
Scheme 4.
Photoreactions were performed by irradiation (450W Hanovia medium pressure Hg lamp and
flint glass filter (>300 nm)) of 10% EtOH-toluene (v/v) and 10% EtOH-o-dichlorobenzene (ODCB)
solutions (220 mL, N2 or O2 purged condition) containing the α-aminonitriles (0.59 mmol) and C60
(0.28 mmol). The concentrated photolysates were then subjected to column chromatography to give
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the products and yields displayed in Scheme 5 and Tables 1-4.
Scheme 5.
Table 1. Products and yields of photoaddition reactions of C60 with α-aminonitriles 11a-11k in N2-
purged 10% EtOH-toluene solutions.
irradiation
conversion
entry
amine
product (%)b
Time (h)
(%)a
83
83
85
85
86
87
85
81
1
2c
3
2
2
2
2
2
2
2
6
12a (42), 13a (13)
12a (41), 13a (13)
12b (40)
11a
11a
11b
11c
11d
11e
11f
4
12c (42)
5
12d (42), 13d (17), 14 (4)
12e (50)
6
7
12f (43), 13f (15)
12g (39),
8
11g
9

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9
6
6
8
8
84
69
85
80
12h (41)
12i (40)
12j (44)
12k (40)
11h
11i
10
11
12
11j
11k
aDetermined based on recovered C60. bIsolated yields.
cExcess of α-amino nitrile 11a (2.95 mmol) is used.
As the results in Scheme 5 and Table 1 show, 2 h irradiation of a N2-purged 10% EtOH-toluene
solution containing C60 and α-aminonitrile 11a gave rise to formation of the N-benzyl, trimethylsilyl-
and cyano group substituted fulleropyrrolidine 12a as the major photoadduct, along with a minor
amount of cycloadduct 13a that does not contain the trimethylsilyl group (entry 1 in Table 1). No
change in the percent conversion or product ratio occurred when a molar excess of 11a (2.95 mmol)
was used (entry 2 in Table 1). Similar product distributions arose from photoreactions of p-Me (11d)
and p-OMe (11f) substituted analogs (entries 5 and 7 in Table 1). Interestingly, reaction of 11d with
C60 also generated the N-trimethylsilyl, toluyl- and cyano group substituted fused pyrrolidine 14 as a
minor photoproduct. Moreover, photoreactions of C60 in the presence of α-aminonitriles 11b, 11c,
11e and 11g-11k generated the corresponding trimethylsilyl- and cyano group substituted
fulleropyrrolidines 12 as sole photoadducts (39-44%) (entries 3, 4, 6, 8-12 in Table 1). Notably, in
contrast to those of p-H and p-electron donating group substituted analogs 11a-11f (2 h),
photoreactions of electron withdrawing (F and CF3) group substituents containing cyanoamines 11g-
11k with C60 required much longer irradiation times (6-8 h) to bring about high conversions of C60.17-
18
It is noteworthy to compare the product profiles of photoreactions of the α-aminonitriles with
those arising from α-aminoesters (c in Scheme 3). While photoreactions of trimethylsilyl containing
α-aminoesters 2 (Scheme 3) occurred under anaerobic conditions to produce 1-aminomethyl-1,2-
10

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dihydrofullerenes 8 predominantly,17 those of the corresponding α-aminonitriles produced
fulleropyrrolidines solely. (Scheme 5) It should be noted that photoreactions of C60 with all of the α-
aminonitriles examined in this effort led to stereoselective formation of trans-isomers of the
fulleropyrrolidines 12a-12k (see below).
Studies were carried out to assess the nature of photoaddition reactions of oxygenated (O2-
purged) 10% EtOH-toluene solutions containing C60 and α-aminonitriles 11a-11k. As can be seen by
viewing the results in Scheme 5 and Table 2, the product distributions of these reactions were quite
similar to those arising from reactions in N2-purged solutions. However, relatively shorter irradiation
times were required in all cases to bring about high conversion of C60 (> 90%) and modest product
yields (39-50%). Moreover, photoreactions of respective α-aminonitriles 11a, 11d and 11f gave rise
to exclusive formation of trimethylsilyl- and cyano group substituted fulleropyrrolidines 12a, 12d
and 12f (entries 1, 4 and 6 in Table 2).
Table 2. Products and yields of photoaddition reactions of C60 with α-aminonitriles 11a-11k in O2-
purged 10% EtOH-toluene.
Irradiation
Conversion
entry
amine
Product (%)b
Time (h)
(%)a
94
1
2
3
4
5
6
1
1
1
1
1
1
12a (44), 13a (3)
12b (47)
11a
11b
11c
11d
11e
11f
95
96
12c (50)
96
12d (44), 13d (5), 14 (1)
12e (49)
96
96
12f (49), 13f (5)
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7
8
3
3
3
5
5
93
94
86
90
91
12g (48)
12h (48)
12i (43)
12j (53)
12k (44)
11g
11h
11i
9
10
11
11j
11k
aDetermined based on recovered C60. bIsolated yields.
We observed earlier that solvent polarity is an important factors in governing the efficiencies of
SET-promoted photochemical reactions of C60 with amines.10b,10c,17,19-21 As a result, photoaddition
reactions of C60 with 11a-11k in the 10% EtOH-o-dichlorobenzene (ODCB), which is less polar
solvent system than 10% EtOH-toluene, were explored. Photoreactions of N2-purged 10% EtOH-
ODCB solutions containing C60 and 11a-11k took place less efficiently than those of N2-purged 10%
EtOH-toluene solutions to produce fulleropyrrolidines exclusively (Table 3). For example, even 10 h
irradiation of solutions containing o,p-di-F (11j) and p-CF3 (11k) aryl ring substituted α-
aminonitriles resulted in low conversion of C60 (entries 10-11 in Table 3). Another interesting
observation was that photoreactions of C60 with 11a, 11d and 11f produce the trimethylsilyl- and
cyano group containing fulleropyrrolidines 12a, 12d and 12f exclusively. The product distributions
were comparable to those from reactions of N2-purged 10% EtOH-toluene solutions containing the
same α-aminonitriles.
Table 3. Products and yields of photoaddition reactions of C60 with α-aminonitriles 11a-11k in N2-
purged 10% EtOH-ODCB.
Entry
amine
irradiation conversion (%)a
product (%)b
12

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Time (h)
1
2
3
3
87
80
79
80
82
89
65
62
62
52
41
12a (39), 13a (3)
12b (35)
11a
11b
11c
11d
11e
11f
3
3
12c (35)
4
3
12d (37), 13d (5)
12e (43)
5
3
6
3
12f (46), 13f (trace)
12g (26)
7
6
11g
11h
11i
8
6
12h (30)
9
6
12i (33)
10
11
10
10
12j (26)
11j
12k (23)
11k
aDetermined based on recovered C60. bIsolated yields.
Photoreactions of O2-purged 10% EtOH-ODCB solutions containing C60 and 11a-11k were also
conducted (Table 4). Interestingly, the results showed that photoreactions of all of α-aminonitriles,
including 11a, 11d and 11f, take place efficiently and give rise to trimethylsilyl- and cyano group
containing fulleropyrrolidiens 12a-12k solely. Moreover, photoreactions of the respective o,p-di-F
(11j) and p-CF3 (11k) substituted α-aminonitriles took place with increased conversion efficiencies
and chemical yields (entries 10-11 in Table 4).
Table 4. Products and yields of photoaddition reactions of C60 with α-aminonitriles 11a-11k in O2-
purged 10% EtOH-ODCB.
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irradiation
entry
amine
conversion (%)a
Time (h)
product (%)b
1
2
2
2
85
83
82
84
93
96
89
86
88
76
74
12a (45)
12b (39)
12c (39)
12d (44)
12e (46)
12f (52)
12g (43),
12h (46)
12i (46)
12j (39)
12k (37)
11a
11b
11c
11d
11e
11f
3
2
4
2
5
2
6
2
7
5
11g
11h
11i
8
5
9
5
10
11
10
10
11j
11k
aDetermined based on recovered C60. bIsolated yields.
Solvent effect. In earlier studies,17a we explored the effects of the EtOH content in EtOH-
toluene solvent systems on the efficiencies of SET-promoted photoaddition reactions between
tertiary N-α-silylamines 15 and C60. The results showed that the presence of EtOH in the mixed
solvent system was essential for formation of 1-aminomethyl-1,2-dihydrofullerenes 17 (Scheme 6).
This observation is consistent with the sequential SET-desilylation mechanism for these
photoreactions (Scheme 6).
Scheme 6.
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The earlier findings stimulated us to probe the effect of EtOH content in toluene or ODCB
solutions on photoreactions of C60 with α-aminonitriles 11a-11k. For this purpose, photoreactions of
C60 with two α-aminonitriles 11a and 11d were performed in N2 or O2-purged pure toluene solutions
(Table 5). While photoreactions of N2-purged pure toluene solutions of 11a and 11d (entries 1-2 in
Table 5) took place less efficiently than those in 10% EtOH-toluene solutions (see entries 1 and 5 in
Table 1), no significant differences existed in the photoreactions of O2-purged pure (entries 3-4 in
Table 5) and EtOH-toluene mixed solutions (entries 1 and 4 in Table 2).
Table 5. Products and yields of photoaddition reactions of C60 with α-amino nitriles 11a and 11d in
pure toluene.
reaction irradiation conversion
entry
1
amine
product (%)b
condition
N2
time (h)
2
(%)a
77
12a (32), 13a (2)
11a
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2
3
4
N2
O2
O2
2
1
1
77
93
95
12d (26), 13d (8)
12a (46), 13a (2)
12d (42), 13d (10)
11d
11a
11d
aDetermined based on recovered C60. bIsolated yields.
The same probes were made in photoaddition reactions of C60 with α-aminoesters 20-21 in O2-
purged pure toluene solutions (Scheme 7 and Table 6). In a previous study,17b we found that
photoaddition reactions of α-aminoesters 20-21 in O2-purged 10% EtOH-toluene solutions give rise
to fulleropyrrolidines 22-23, respectively (entries 1-2 in Table 6). While the reactions of 20-21 in O2-
purged pure toluene solutions also produced 22-23, they required much longer irradiation times to
bring about the same conversions.
Scheme 7.
Table 6. Products and yields of photoaddition reactions of C60 with α-aminoesters 20-21 in O2-
purged 10% EtOH-toluene or pure toluene solutions.
irradiation conversion
entry
amine
product (%)b
time (h)
(%)a
89
1c
2c
2
2
22 (57)
23 (56)
20
21
90
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3d
4d
5
5
85
87
22 (50)
23 (50)
20
21
aDetermined based on recovered C60. bIsolated yields. cReaction in 10% EtOH-toluene.
dReaction in pure toluene
Effect of trimethylsilyl group. As mentioned above (Scheme 3), not only the efficiencies but
also the product distributions of photoaddition reactions of α-aminoesters to C60 are highly
dependent on the presence of a α-trimenthylsilyl group.17 To explore if this effect also plays a role in
photoreactions with α-aminonitriles, we prepared and explored the photochemistry of the non-
trimethylsilyl α-aminonitrile analogs 24-2622 (Scheme 8). The results showed that photoreactions of
24-26 with C60 are comparable to those of the trimethylsilyl group containing α-aminonitriles. For
example, no photoreactions took place when N2-purged 10%-EtOH solutions of 24-26 were
irradiated even for long irradiation period (entries 1, 4 and 7 in Table 7). In contrast, photoreactions
of 24-26 did occur upon prolonged irradiation of O2-purged 10% EtOH-toluene solutions to form
trans- and cis-diastereomeric mixtures of the corresponding fulleropyrrolidines 27-29, along with
13a (from 24) and 13d (from 25).
Scheme 8.
Table 7. Products and yields of photoaddition reactions of C60 with non-trimethylsilyl containing α-
17

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aminonitriles 24-26 in 10% EtOH-toluene solutions.
reaction irradiation conversion
product
entry
amine
condition
N2
time (h)
(%)a
(% yield, trans:cis ratio)b
c
c
1
2
3
4
5
6
7
8
9
8
8
-
-
24
24
24
25
25
25
26
26
26
O2
54
77
27 (38, 1: 0.7), 13a (2)
27 (44, 1: 0.7), 13a (4)
O2
15
8
c
c
N2
-
-
O2
8
53
78
28 (33, 1: 0.3), 13d (4)
28 (46, 1: 0.3), 13d (8)
O2
15
15
15
40
c
c
N2
-
-
O2
10
28
29 (4, 1: 0.9)
29 (14, 1: 0.9)
O2
aDetermined based on recovered C60. bIsolated yields and trans:cis isomer molar ratio.
cNo reaction
Another interesting observation concerned the stereochemistry features of photoproducts 27-29.
Specifically, in contrast to the trans-specific formation of fulleropyrrolidines (12a, 12d and 12i) in
photoreactions of the trimethylsilyl group containing α-aminonitriles 11a, 11d and 11i,
photoreactions of the non-trimethylsilyl counterparts 24-27 produced trans- and cis- isomeric
mixtures of fulleropyrrolidines products 27-29. A possible explanation for the lack of
stereoselectivity observed in photoreactions of C60 with the non-trimethylsilyl containing α-
aminonitriles comes from a proposal made by Liu and co-workers9a,12a that the conformation of in-
situ formed azomethine ylides are responsible for stereochemistry of these photoreactions of
fulleropyrrolidines. Accordingly, azomethine ylides generated from trimethylsilyl group containing
α-aminonitriles should prefer to have conformation 31, which minimizes steric repulsion between
18

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the sterically bulky benzyl, cyano and trimethylsily groups. In contrast, the conformations 32 and 33
of ylides generated from non-trimethylsilyl containing α-aminonitriles 24-26 are energetically more
similar. (Scheme 9)
Scheme 9.
ylide forming
E = SiMe3
SiMe3
CN
SiMe3
CN
SiMe3
CN
Ar
N
Ar
N
Ar
N
E
30
31
Ar
N
CN
Me
Me
Me
ylide forming
E = H
Ar = substituted
phenyl
Ar
N
Ar
N
CN
Ar
N
CN
CN
32
33
Structural and stereochemical assignments. Structural assignments of the fulleropyrrolidines
photoproducts formed in the reactions described above were made by using 1H and 13C NMR, FT-IR,
UV-visible spectroscopy and HRMS (see Experimetnal Section and Supplementary data), as well as
1
by comparing the data to those previously reported for related fulleropyrrolidines.9a,12a,14,16-19 In H
NMR spectra of fulleropyrrolidines 12a-12k, the presence of two stereogenic carbons adjacent to the
nitrogen atom caused the the benzyl protons to appear as AB quartets in the ca. 4.0-5.0 ppm region.
In addition, the two methine protons on carbons bearing trimethylsilyl and cyano groups appeared as
singlet peaks at ca. 4.3-4.4 and 5.3-5.4 ppm region, respectively. In the 13C NMR spectra of 12a-12k,
the quaternary sp3 carbons in the hydro-C60 core resonated at ca. 68-74 ppm region and the methine
carbons possessing the trimethylsilyl and cyano groups resonated at ca. 66-67 ppm. Importantly,
cyano carbon resonated at ca. 114-115 ppm in all cases. FT-IR spectra of 12a-12k also clearly
contained characteristic absorptions at 2260 cm-1 for cyano stretching vibrations. Fulleropyrrolidines
13a, 13d, 13f contain one chiral center and, as a result, 1H NMR showed that their methylene protons
appear as AB quartets at ca. 4.2-4.6 ppm and their benzyl protons appear at ca. 4.5-4.7 ppm as AB
19

ACCEPTED MANUSCRIPT
13
quartets. In addition, the C NMR spectra of 13a, 13d, 13f contained peaks that correspond to two
quaternary sp3 carbons, two methylene carbons and one methine carbon. The UV-visible absorption
spectra of all of photoproducts contained maxima at ca. 431-433 nm, which are characteristic of 1,2-
adducts formed by addition across the [6,6]-juncture of C60.10b,10c,17-21 Finally, spectroscopic data for
the isomeric mixtures of 27-29 and comparisons of these data with those for 12a-12k and 14 enabled
assignments of their structures of photoproducts. These data clearly showed the characteristic peaks
corresponding to fulleropyrrolidines 27-29.
1
It should be noted that H and 13C NMR spectral data provide no information to enable
assignments of stereochemistry (trans versus cis) to the generated fulleropyrrolidines. In addition,
despite repeated attempts to obtain clear x-ray crystallographic data on photoproducts, we met with
failure. We recently became aware of studies by Liu and co-workers9a,12a in which the
stereochemistry of isomeric fulleropyrrolidines was assigned by using NOESY. As a result, we
utilized this technique to assign stereochemistry of 12a-12k. Based on the results of previous
studies,9a,12a we expected that while the methine protons in trans-fulleropyrrolidines would display
no correlation NOE peaks owing to their great spatial separation, the analogous cis-
fulleropyrrolidines would display strong NOE correlation peaks between the two methine protons. In
fact, NOESY spectra of trans-fulleropyrrolidines 12a, 12d and 14 did not display any NOE
correlation peaks for the two methine protons on the trimethylsilyl and cyano substituted carbons
(Supporting Information). Analysis of NOESY data for the isomers of fulleropyrrolidines 27-29,
produced by photoreactions of C60 with non-trimethylsilyl containing α-aminonitriles 24-26, support
the proposal that the absence or presence of NOE correlation peaks would be decisive in assigning
stereochemistry. Although separation of the cis and trans isomers of fulleropyrrolidines 27-29 was
exceedingly difficult, it was possible to isolate isomerically pure cis-27 and trans-28. The results of
NOESY analysis of these substances showed that, as expected, cis-27 displays strong NOE
20

ACCEPTED MANUSCRIPT
correlation peaks and trans-28 does not (Supporting Information).
Additive effect. To gain information about factors governing the efficiencies of photoaddition
reactions leading to formation of the trimethylsilyl (12a-12k) and non-trimethylsilyl (13a, 13d and
13f) containing fulleropyrrolidines, photoreactions of N2 and O2-purged pure toluene solutions
containing C60 and α-aminonitriles 11a and 11d along with pyridine were explored. In the absence of
pyridine, 2 h irradiation of N2-purged solutions of 11a and 11d brought about high conversion of C60
(77%) and relatively low yields of fulleropyrrolidines (12a+13a (34%), 12d+13d (34%), entries 1-2
in Table 5). Interestingly, in the presence of pyridine (1.26 mM), 2 h photoreactions of these
substances occurred with higher conversions (> 94%), higher yields (> 54%) and greater degrees of
chemoselectivity favoring the trimethylsilyl group containing adducts (entries 1-2 in Table 8).
However, pyridine had no significant effects on both the conversions (C60) and yields (12a+13a and
12d+13d) on photoreactions of oxygenated toluene solutions containing these substrates (entries 3-4
in Table 5 and Table 8), a finding that has mechanistic implications.
Table 8. Products and yields of photoaddition reactions of pure toluene solutions containing C60 and
α-aminonitriles 11a and 11d in the presence of pyridine (1.26 mM).
reaction irradiation conversion
entry
amine
product (%)b
condition
time (h)
(%)a
94
1
2
3
4
N2
N2
O2
O2
2
2
1
1
12a (54)
12d (55)
11a
11d
11a
11d
95
95
12a (50), 13a (3)
12d (53), 13d (2)
96
aDetermined based on recovered C60. bIsolated yields.
21

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Mechanistic analysis. The observations outlined above enabled the proposal of feasible
mechanistic pathways for formation of the trimethylsilyl and non-trimethylsilyl containing
fulleropyrrolidines formed in the photoreactions of C60 with the α-aminonitriles. The routes for
reactions taking place in N2 purged solutions (Scheme10) are initiated by SET from the α-
*
aminonitrile 34 to the triplet excited state of C60 (3C60 ), generated by efficient intersystem crossing
1
*
of C60 (ΦISC = 1).23 This process forms a radical ion pair consisting of the fullerene radical anion
-
radicals (C60ꢀ ) and aminium radicals 35. The generated aminium radicals undergo competitive α-CH
deprotonation by C60 - vs ethanol promoted desilylation to give the respective trimethylsilyl and non-
ꢀ
ꢀ
trimethylsilyl containing α-amino radicals 36 and 37, along with the hydrofullerene radical (H-C60 ).
Although it is known that typical α-silyl substituted aminium radicals undergo solvent assisted
desilylation with rates that exceed those of α-CH deprotonation,24-25 the latter process could
overwhelm desilylation when, like in the current case, the acidity of the aminium radicals is
enhanced by α-substituents. The α-amino radicals 36 and 37, generated by deprotonation or
desilylation, are oxidized by SET to either H-C60ꢀ or C60, to form the respective iminium ions 38 and
-
39 along with the hydrofullerene anion (H-C60 ). Deprotonation of 38 and 39 then produces the
respective ylides 40 and 41. Alternatively, desilylation of 38 can also generate 41. The processes are
then terminated by [3+2]-dipolar cycloaddition to give fulleropyrrolidine adducts 42. If a much
stronger base such as pyridine (pKa ca. 5.2) rather than H-C60- (pKa ca. 4.7) is present, deprotonation
of aminium radical 35 occurs more rapidly, explaining why the reaction efficiency increases and the
products arising from azomethine ylides 40 are more predominant.
Scheme 10.
22

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1. hv/ C60
Ar
Ar
2. ISC
C60
Me3Si
N
CN
Me3Si
N
CN
3. SET from
-aminonitriles
35
34
~ H+
EtOH
+
~ SiMe3
Ar
Ar
H
C60
H
C60
N
CN
Me3Si
N
CN
37
36
SET to
C60 or H-C60
SET to
C60 or H-C60
Ar
Ar
H
C60
+
N
CN
H
C60
+
Me3Si
N
CN
39
38
Ar
Ar
+
H2 C60
+
N
CN
H2 C60
Me3Si
N
CN
C60
41
40
C60
R
Ar
N
CN
42 (R =SiMe3 or H)
*
In photoreactions occurring in O2-purged solutions, the triplet excited state of C60 (3C60 )
participates in energy transfer to form singlet oxygen (1O2).23 As suggested by Foote,16b reactions of
1O2 with amines take place through α-H atom abstraction to generate α-amino radicals 36. This
process with α-aminonitriles generates α-amino radicals 36 along with the hydroperoxy radicals
(HOOꢀ) in pathways leading to the production of the key azomethine ylides 40 and 41, which
cycloadd to C60 to produce fulleropyrrolidines 42.
23

ACCEPTED MANUSCRIPT
Conclusion
In the study described above, photoaddition reactions of C60 with N-arylmethyl-N-
trimethylsilylmethyl substituted tertiary α-aminonitriles were explored. The results show that
photoreactions of C60 with trimethylsilyl group containing α-aminonitriles produce predominantly
trimethylsilyl and cyano group containing pyrrolidine ring fused fullerenes in a trans-stereoselective
manner through a pathway involving azomethine ylide intermediates. The azomethine ylides,
generated by either SET process or H-atom abstraction, cycloadd to C60 at [6,6]-juncture positions to
form fulleropyrrolidines. In contrast, photoreaction of C60 with non-trimethylsilyl containing amine
analogs give rise to inefficient formation of trans- and cis isomers of phenyl- and cyano group
containing pyrrolidine ring fused fullerenes. Importantly, the efficiencies of photoaddition reactions
of C60 with α-aminonitriles are influenced by several factors including reaction condition (N2 or O2-
purged), solvent polarity, the electronic and structural nature of the α-aminonitriles and additive. For
example, photoreactions occurring in either oxygenated (O2 purged) or 10% EtOH-toluene solutions,
rather than either deoxygenated (N2-purged) or 10% EtOH-ODCB solutions, require much shorter
irradiation times to bring about high conversions of C60 as well as high product yields. In addition,
short period irradiation of solutions containing C60 and α-aminonitriles, possessing arene rings that
are either un-substituted or substituted with electron donating groups (H, Me and OMe), promotes
high conversions and product yields. Finally, presence of trimethylsilyl group in α-aminonitrile
substrates plays a crucial role in enhancing reaction efficiencies.
Finally, in contrast to thermal and photochemical strategies developed previously for
fulleropyrrolidine synthesis, the currently developed SET-promoted photoaddition reactions of C60
with trimethylsilyl group containing amine substrates are mild and efficient, and as a results they
should be highly useful in preparing a broader library of functionalized fulleropyrrolidines.
24

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Experimental
1
General Procedure H and 13C NMR spectra were recorded using CDCl3 solutions and
chemical shifts are reported in parts per million relative to CHCl3 (7.24 ppm for 1H and 77.0 ppm for
13C) as an internal standard. High resolution (HRMS) mass spectra were obtained by using an
electrospray ionization unless otherwise noted. All starting materials used in the synthetic routes
came from commercial sources. All new compounds described were isolated in >90% purity (by
NMR analysis) unless noted otherwise.
General procedure for synthesis of N-arylmethyl-N-trimethylsilylmethyl substituted α-
aminonitriles 11a-11k. Individual solutions of secondary N-α-trimethylsilylmethyl-N-
benzylamines19 (5 mmol) in acetonitrile (100 mL) containing K2CO3 (10 mmol) and 2-
iodoacetonitrile (4.5 mmol) were stirred for 12 h at room temperature and concentrated in vacuo to
give residues that were partitioned between water and CH2Cl2. The CH2Cl2 layers were dried and
concentrated in vacuo to afford residues that were subjected to silica gel column chromatography
(EtOAc/hexane = 1: 15 - 1: 30) to yield corresponding α-aminonitiriles 11a18 (91%), 11b (74%), 11c
(78%), 11d (85%), 11e (75%), 11f (75%), 11g (74%), 11h (75%), 11i (78%), 11j (78%) and 11k
(66%).
11a (liq): 1H-NMR 0.12 (s, 9H), 2.18 (s, 2H), 3.40 (s, 2H), 3.62 (s, 2H), 7.27-7.34 (m, 5H).
11b (liq): 1H-NMR 0.13 (s, 9H), 2.20 (s, 2H), 2.40 (s, 3H), 3.36 (s, 2H), 3.63 (s, 2H), 7.17-7.21
(m, 3H), 7.29-7.32 (m, 1H); 13C-NMR -1.9, 18.9, 44.1, 46.2, 60.0, 114.5, 125.6, 127.5, 129.7, 130.3,
135.1, 137.4; HRMS (ESI) m/z 269.1449 (M+Na, C14H22N2SiNa requires 269.1450).
11c (liq): 1H-NMR 0.15 (s, 9H), 2.18 (s, 2H), 2.36 (s, 3H), 3.39 (s, 2H), 3.58 (s, 2H), 7.09-7.15
(m, 3H), 7.20-7.25 (m, 1H); 13C-NMR -1.8, 21.2, 44.7, 46.3, 61.0, 114.5, 125.7, 128.2, 128.3, 129.3,
137.3, 137.9; HRMS (ESI) m/z 269.1461 (M+Na, C14H22N2SiNa requires 269.1450).
25

ACCEPTED MANUSCRIPT
1
11d (liq): H-NMR 0.10 (s, 9H), 2.14 (s, 2H), 2.32 (s, 3H), 3.36 (s, 2H), 3.54 (s, 2H), 7.12 (d,
2H, J = 8.1 Hz), 7.20 (d, 2H, J = 8.1 Hz); 13C-NMR -1.1, 21.6, 45.3, 46.9, 61.4, 115.1, 129.3, 129.7,
135.0, 137.7; HRMS (ESI) m/z 269.1473 (M+Na, C14H22N2SiNa requires 269.1450).
1
11e (liq): H-NMR 0.15 (s, 9H), 2.20 (s, 2H), 2.33 (s, 3H), 2.37 (s, 3H), 3.35 (s, 2H), 3.60 (s,
2H), 6.97-6.70 (m, 2H), 7.19 (d, 1H, J = 7.5 Hz); 13C-NMR -1.9, 18.8, 20.7, 43.9, 46.2, 59.8, 114.4,
126.2, 129.8, 131.1, 132.0, 137.0, 137.2; HRMS (FAB) m/z 283.1609 (M+Na, C15H24N2SiNa
requires 283.1606).
1
11f (liq): H-NMR 0.10 (s, 9H), 2.12 (s, 2H), 3.33 (s, 2H), 3.50 (s, 2H), 3.75 (s, 3H), 6.83 (d,
2H, J = 8.7 Hz), 7.21 (d, 2H, J = 8.7 Hz); 13C-NMR -1.9, 44.4, 46.0, 54.8, 60.3, 113.6, 114.4, 129.3,
129.7, 158.8; HRMS (FAB) m/z 285.1397 (M+Na, C14H22N2OSiNa requires 285.1399).
1
11g (liq): H-NMR 0.09 (s, 9H), 2.15 (s, 2H), 3.39 (s, 2H), 3.64 (s, 2H), 6.98-7.04 (m, 1H),
7.06-7.11 (m, 1H), 7.20-7.28 (m, 1H), 7.32-7.37 (m, 1H); 13C-NMR -1.9, 44.9, 46.3, 54.2, 114.5,
115.4 (d, JC-F = 86.7 Hz), 123.9 (d, JC-F = 14.1 Hz), 124.2 (d, JC-F = 56.4 Hz), 129.3 (d, JC-F = 32.7
Hz), 130.9 (d, JC-F = 16.5 Hz), 161.2 (d, JC-F = 985.8 Hz); HRMS (FAB) m/z 273.1196 (M+Na,
C13H19FN2SiNa requires 273.1199).
1
11h (liq): H-NMR 0.09 (s, 9H), 2.13 (s, 2H), 3.38 (s, 2H), 3.57 (s, 2H), 6.90-6.96 (m, 1H),
13
7.01-7.08 (m, 2H), 7.22-7.29 (m, 1H); C-NMR -1.9, 44.8, 46.1, 60.6, 114.3, 114.4 (d, JC-F = 76.5
Hz), 115.2 (d, JC-F = 85.2 Hz), 124.1 (d, JC-F = 11.1 Hz), 129.9 (d, JC-F = 32.7 Hz), 140.1 (d, JC-F
=
28.2 Hz), 162.8 (d, JC-F = 978.6 Hz); HRMS (FAB) m/z 273.1193 (M+Na, C13H19FN2SiNa requires
273.1199).
1
11i (liq): H-NMR 0.09 (s, 9H), 2.13 (s, 2H), 3.37 (s, 2H), 3.55 (s, 2H), 6.97-7.04 (m, 2H),
7.25-7.30 (m, 2H); 13C-NMR -2.3, 44.2, 45.6, 60.1, 113.9, 114.8 (d, JC-F = 84.6 Hz), 129.9 (d, JC-F
=
31.5 Hz), 133.0 (d, JC-F = 12.9 Hz), 161.7 (d, JC-F = 977.1 Hz); HRMS (FAB) m/z 273.1221 (M+Na,
C13H19FN2SiNa requires 273.1199).
26

ACCEPTED MANUSCRIPT
1
11j (liq): H-NMR 0.06 (s, 9H), 2.11 (s, 2H), 3.37 (s, 2H), 3.58 (s, 2H), 6.70-6.84 (m, 2H),
13
7.26-7.34 (m, 1H); C-NMR -2.1, 44.7, 46.0, 53.7, 10.7 (t, JC-F = 101.7 Hz), 111.0 (dd, JC-F = 83.6
Hz, 15Hz), 114.3, 120.2 (dd, JC-F = 57.5 Hz, 14.7 Hz), 131.7 (dd, JC-F = 38.1 Hz, 23.1 Hz), 161.2 (dd,
JC-F = 996.5 Hz, 47.1 Hz), 162.2 (dd, JC-F = 989.1 Hz, 47.4 Hz); HRMS (FAB) m/z 291.1104 (M+Na,
C13H18F2N2SiNa requires 291.1105).
1
11k (liq): H-NMR 0.10 (s, 9H), 2.16 (s, 2H), 3.39 (s, 2H), 3.65 (s, 2H), 7.44 (d, 2H, J = 7.8
Hz), 7.57 (d, 2H, J = 7.8 Hz); 13C-NMR -1.8, 45.0, 46.3, 60.8, 114.3, 125.4 (q, JC-F = 15 Hz), 128.9,
141.7; HRMS (FAB) m/z 301.1333 (M+H, C14H20F3N2Si requires 301.1342).
General procedure of photoreactions of C60 with α-aminonitriles 11a-11k. Photochemical
reactions were conducted using an apparatus consisting of a 450 W Hanovia medium vapor pressure
mercury lamp surrounded by a flint glass filter (>300 nm). Nitrogen or oxygen-purged 10% EtOH-
toluene or 10% EtOH-ODCB solutions (220 mL) containing C60 (0.278 mmol, 1.26 mM) and the α-
aminonitriles 11a-11k (0.555 mmol, 2.5 mM) were irradiated for a fixed time period given below.
Photolysates were concentrated in vacuo and the unreacted C60 was recovered by filtration using
CHCl3 to determine conversion yields. Photoproducts were separated by using silica gel column
chromatographic isolation (CS2) of crude photolysates.
Photoreaction of C60 with 11a. In N2-purged, 10% EtOH-toluene solution: 2 h irradiation (83%
conversion), column chromatography (CS2) to yield 12a (42%) and 13a (13%). In O2-purged, 10%
EtOH-toluene solution: 1 h irradiation (94% conversion), column chromatography (CS2) to yield 12a
(44%) and 13a (3%); In N2-purged, 10% EtOH-ODCB solution: 3 h irradiation (87% conversion),
column chromatography (CS2) to yield 12a (39%) and 13a (3%). In O2-purged, 10% EtOH-ODCB
solution: 2 h irradiation (85% conversion), column chromatography (CS2) to yield 12a (45%).
12a (sol, mp > 400 oC): 1H-NMR 0.58 (s, 9H), 4.04 (d, 1H, J = 12.3 Hz), 4.37 (s, 1H), 4.90 (d,
1H, J = 12.3 Hz), 5.34 (s, 1H), 7.35-7.40 (m, 1H), 7.43-7.48 (m, 2H), 7.70 (d, 1H, J = 7.2 Hz); 13C-
27

ACCEPTED MANUSCRIPT
NMR (CDCl3 + CS2) 0.5, 55.7, 66.6, 66.8, 73.1, 74.2, 114.8, 128.2, 128.6, 129.1, 136.3, 136.4, 136.6,
137.3, 138.7, 138.8, 139.8, 139.9, 141.3, 141.4, 141.6 (2C), 141.8, 141.9, 142.0, 142.4, 142.5, 142.8,
142.9, 144.1, 144.2, 144.4, 144.9, 145.0, 145.1, 145.3 (2C), 145.4, 145.8 (2C), 146.1, 146.7, 147.0;
HRMS (MALDI-TOF) m/z 949.1163 (M-H, C73H17N2Si requires 949.1166).
o
1
13a (sol, mp > 400 C): H-NMR 4.30 (d, 1H, J = 12.9 Hz), 4.57 (d, 1H, J = 9.9 Hz), 4.58 (d,
1H, J = 12.9 Hz), 4.71 (d, 1H, J = 9.9 Hz), 5.44 (s, 1H), 7.37-7.42 (m, 1H), 7.46-7.51 (m, 2H), 7.72
(d, 1H, J = 6.9 Hz); 13C-NMR (CDCl3 + CS2) 55.5, 64.2, 65.5, 68.6, 71.9, 114.4, 128.1, 128.7, 128.9,
135.5, 135.8, 136.3, 136.9, 137.8, 139.7, 139.8, 140.0, 140.1, 141.5 (2C), 141.6 (2C), 141.7 (3C),
141.8, 141.9, 142.0, 142.3, 142.4, 142.5, 142.8, 144.1, 144.2, 144.7 (2C), 145.1, 145.2 (2C), 145.4
(2C), 145.5, 145.6, 145.8, 145.9, 146.0, 146.1 (2C), 147.1, 147.2, 149.3, 151.6, 151.9, 154.0; HRMS
(MALDI-TOF) m/z 877.0775 (M-H, C70H9N2 requires 877.0771).
Photoreaction of C60 with 11b. In N2-purged, 10% EtOH-toluene solution: 2 h irradiation (85%
conversion), column chromatography (CS2) to yield 12b (40%). In O2-purged, 10% EtOH-toluene
solution: 1 h irradiation (95% conversion), column chromatography (CS2) to yield 12b (47%); In N2-
purged, 10% EtOH-ODCB solution: 3 h irradiation (80% conversion), column chromatography (CS2)
to yield 12b (35%). In O2-purged, 10% EtOH-ODCB solution: 2 h irradiation (83% conversion),
column chromatography (CS2) to yield 12b (39%) (sol, mp > 400 oC). 1H-NMR 0.58 (s, 9H), 2.76 (s,
3H), 4.11 (d, 1H, J = 12 Hz), 4.37 (s, 1H), 4.89 (d, 1H, J = 12 Hz), 5.23 (s, 1H), 7.28-7.32 (m, 3H),
13
7.68-7.71 (m, 1H); C-NMR (CDCl3 + CS2) 0.8, 19.9, 54.9, 66.9, 72.9, 74.2, 115.1, 126.4, 128.4,
130.1, 131.0, 134.3, 136.1, 136.2, 137.3, 137.4, 138.6, 138.8, 139.7, 141.3, 141.4, 141.5 (2C), 141.7,
141.8 (2C), 141.9, 142.0, 142.4 (2C), 142.5, 142.7, 142.8, 144.1 (2C), 144.3 (2C), 144.4, 144.9,
145.0 (2C), 145.1, 145.2, 145.3, 145.4 (2C), 145.7 (2C), 145.8, 146.1, 146.9, 147.0, 150.3, 151.9,
153.2, 153.8; HRMS (MALDI-TOF) m/z 963.1331 (M-H, C74H19N2Si requires 963.1323).
Photoreaction of C60 with 11c. In N2-purged, 10% EtOH-toluene solution: 2 h irradiation (85%
28

ACCEPTED MANUSCRIPT
conversion), column chromatography (CS2) to yield 12c (42%). In O2-purged, 10% EtOH-toluene
solution: 1 h irradiation (96% conversion), column chromatography (CS2) to yield 12c (50%); In N2-
purged, 10% EtOH-ODCB solution: 3 h irradiation (79% conversion), column chromatography (CS2)
to yield 12c (35%). In O2-purged, 10% EtOH-ODCB solution: 2 h irradiation (82% conversion),
column chromatography (CS2) to yield 12c (39%) (sol, mp > 400 oC). 1H-NMR 0.58 (s, 9H), 2.46 (s,
3H), 4.01 (d, 1H, J = 12.3 Hz), 4.38 (s, 1H), 4.88 (d, 1H, J = 12.3 Hz), 5.38 (s, 1H), 7.19 (d, 1H, J =
7.5 Hz), 7.35 (t, 1H, J = 7.5 Hz), 7.48 (s, 1H), 7.54 (d, 1H, J = 7.5 Hz); 13C-NMR (CDCl3 + CS2) 0.6,
21.4, 55.7, 66.7, 66.8, 73.1, 74.3, 115.0, 125.7, 129.0 (2C), 129.4, 136.4, 136.6, 138.5, 138.7, 138.8,
139.8, 141.4 (2C), 141.5, 141.6 (2C), 141.8, 141.9, 142.0 (2C), 142.4, 142.5, 142.8, 144.1 (2C),
144.3, 144.4 (2C), 145.1, 145.2, 145.3 (2C), 145.4 (2C), 145.7, 145.8 (2C), 146.1, 146.7, 147.0 (2C),
150.5, 152.2, 153.1, 153.5; ; HRMS (MALDI-TOF) m/z 963.1333 (M-H, C74H19N2Si requires
963.1323).
Photoreaction of C60 with 11d. In N2-purged, 10% EtOH-toluene solution: 2 h irradiation (86%
conversion), column chromatography (CS2) to yield 12d (42%), 13d (17%) and 14 (4%). In O2-
purged, 10% EtOH-toluene solution: 1 h irradiation (96% conversion), column chromatography (CS2)
to yield 12d (44%), 13d (5%) and 14 (1%); In N2-purged, 10% EtOH-ODCB solution: 3 h irradiation
(80% conversion), column chromatography (CS2) to yield 12d (37%) and 13d (5%). In O2-purged,
10% EtOH-ODCB solution: 2 h irradiation (84% conversion), column chromatography (CS2) to yield
12d (44%).
12d (sol, mp > 400 oC): 1H-NMR 0.58 (s, 9H), 2.43 (s, 3H), 4.02 (d, 1H, J = 12.3 Hz), 4.38 (s,
1H), 4.88 (d, 1H, J = 12.3 Hz), 5.38 (s, 1H), 7.28 (d, 2H, J = 7.8 Hz), 7.61 (d, 2H, J = 7.8 Hz); 13C-
NMR (CDCl3 + CS2) 0.6, 21.2, 55.4, 66.6, 66.7, 73.0, 74.3, 115.0128.6, 129.7, 133.6, 136.3, 136.4,
137.8, 138.7 (2C), 139.8, 141.2, 141.3, 141.4, 141.5 (2C), 141.7 (2C), 141.9, 142.0, 142.3, 142.4,
142.5, 144.1, 144.3 (2C), 144.4, 144.8, 145.0, 145.1 (2C), 145.2, 145.3 (2C), 145.4, 145.7 (2C),
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