Diastereoselective syntheses and oxygenation of silyl fulleroids

Article abstract of DOI:10.1016/j.jorganchem.2009.01.046

The addition of silyl diazomethane (1a-d) to fullerene C₆₀ at room temperature provided the mono-adducts, the bis- and tris-adducts of silyl fulleroid (3a-d) in moderate yields. The structures of the silyl fulleroids were characterized by mass

Full text of DOI:10.1016/j.jorganchem.2009.01.046

Journal of Organometallic Chemistry 694 (2009) 1988–1997
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Diastereoselective syntheses and oxygenation of silyl fulleroids
a
a
a
a
Yoshio Kabe a, , Houjin Hachiya , Tomohisa Saito , Daisuke Shimizu , Masakatsu Ishiwata ,
*
Kazuharu Suzuki b, Yuko Yakushigawa b, Wataru Ando b
a Department of Chemistry, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka 259-1293, Japan
b Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The addition of silyl diazomethane (1a–d) to fullerene C60 at room temperature provided the mono-
adducts, the bis- and tris-adducts of silyl fulleroid (3a–d) in moderate yields. The structures of the silyl
fulleroids were characterized by mass spectroscopy, as well as 1H and 13C NMR. The gated 1H NMR and
13C–1H COLOC analyses of 3a–d showed a correlation between the methine proton resonances and three
fullerene carbons. These observations, as well as the 1H NMR chemical shifts of the methine protons, sug-
gest a remarkable diastereoselectivity, with the silyl groups located above a five-membered ring. Two
transition states of the thermal nitrogen-extrusion of pyrazoline intermediate (2a) were theoretically
obtained, the structures of which disclosed that the diastereoselectivity is a consequence of minimization
of the repulsive interaction between the silyl groups and the N2 moiety. The bridgehead C@C double bond
of the silyl fulleroid is thought to be reactive by POAV analyses. The silyl fulleroids (3a,b) were found to
react with singlet oxygen to afford the silyl enol ether (9a,b) via 1,3-silyl migration of a diketone (8a,b).
This is the first example of 1O2 oxygenation of fulleroids.
Received 2 December 2008
Received in revised form 26 January 2009
Accepted 27 January 2009
Available online 5 February 2009
Keywords:
Fullerene
Silicon
POAV analysis
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
proceed in a diastereoselective fashion to yield silyl fulleroids,
which undergo 1O2 oxygenation with 1,3-silyl group migration to
Among the various fullerene derivatives, fulleroids and their
nitrogen analog (azafulleroid) with [5,6] C60 open structures have
attracted great interest in the synthesis of open-cage fullerenes for
application as encapsulated and hetero fullerenes [1,2]. The addition
of diazo or azide compounds to C60 has been the only known route to
the formation of fulleroid or azafulleroid [3,4]. Concerted nitrogen-
extrusion of the [6,6] pyrazoline and triazoline intermediate (I)
(X = CR2 or NR, as shown in Scheme 1) formed initially takes place
to rearrange the [5,6] open fulleroid (III) via a retro [2+2+2] cyclore-
action of an unknown [5,6] closed methanofullerene (II) [5]. Subse-
quent oxidative C@C bond cleavage of the azafulleroids (IV; X = NR)
by singlet oxygen (1O2) is the key step in opening a hole in the fuller-
ene surface. Another approach is the bisfulleroid route, which in-
volves photochemical [4+4] cycloaddition of cyclohexadine
derivatives of C60 (V; E = N, CR1) followed by a retro [2+2+2] cyclore-
action (VI). Oxygenation of bisfulleroids (VII) also affords an open-
cage fullerene (VIII) having larger rings on its surface.
afford the silyl enol ether derivatives of C60. In order to explore
the diastereoselectivity of the first step, the mechanism of the
decomposition of the 1,3-dipolar adduct of silyl diazomethane
was theoretically investigated. The reactivity of the bridgehead
double bond of the silyl fulleroid and the related fullerene was esti-
mated by p-orbital axis vector (POAV) analysis.
2. Results and discussion
2.1. Diastereoselective formation of silyl fulleroids
The mono-silyl diazomethane (1a–d) was slowly added to a tol-
uene solution of C60 at room or reflux temperature, and the products
were separated by gel permeation chromatography (GPC). The
mono-adducts (3a–d) were isolated in 19–41% yield as well as the
bis- and tris-adducts (12–29% and 8–24% yield), and were analyzed
by FAB or TOF mass spectroscopy, as shown in Scheme 2 and Table 1.
The 1H NMR chemical shifts of the methine proton of 3a–d can be
used as a sensitive NMR probe for the segregated ring currents of
the fullerene core. For 3a–d, the methine protons appeared upfield
(2.47–3.43 ppm) of 1a–d, typical for a location above the six-mem-
bered ring of a bridged fullerene subunit. In the 1H-decoupled 13C
NMR spectra of 3a–d, 32 resonances were assigned to the C60 skel-
eton. Of the 32, 28 signals have a relative intensity of 2 and 4 signals
have an intensity of 1, indicating CS symmetry. Moreover, in the
Using the two essentially identical reaction routes, several deriv-
atives of open-cage fullerenes have been prepared [1,2]. However,
to date no information has been reported regarding the 1O2 oxygen-
ation of fulleroids (III; X = CR2) and their derivatives. Herein, the
reaction of silyl-substituted diazomethane with C60 is reported to
* Corresponding author. Tel./fax: +81 0463 59 4111.
E-mail address: kabe@kanagawa-u.ac.jp (Y. Kabe).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.01.046

Y. Kabe et al. / Journal of Organometallic Chemistry 694 (2009) 1988–1997
1989
Scheme 1.
Scheme 2.
Table 1
[7f]. The formation of 5 is thought to be the result of the dimeriza-
tion of silene, which was formed by trimehylsilyl migration from a
silicon atom to the carbon center shown in Scheme 3 [7]. Thus,
bulky bissilyl diazomethane seems to inhibit the [2+3] cycloaddi-
tion of diazomethane with C60, and silene is not added to C60 be-
cause of its bulkiness and electrophilicity.
Yields of monosilyldiazomethane adducts.
Reactant
(R3SiCHN2)
Yields (%) and ion peaks
Mono-adducts 3
Bis-adductsa
Tris-adductsb
1a: R3 = Me3
34, (M+ = 806)
24, (M+ = 892)
29, (M+ = 1016)
29, (M+ = 1138)
12, (M+ = 1265)
22, (M+ = 978)
1b: R3 = Me2Ph
1c: R3 = Me2Arc
1d: R3 = Ph3
41, (M+ = 868)
8, (M+ - H = 1164)
18, (M+ = 1348)
24, (M+ = 1537)
41, (M+ = 929)
Phenyltrimethylsilyl diazomethane (4g) combined with C60 un-
der reflux yielded the mono-adduct (6) in 46% yield. In the 13C
NMR spectrum of 6, two quaternary carbons appear in the aliphatic
region. The higher field resonance at 48.0 ppm is assigned to the
methano-bridged carbon, slightly lower than those of 3a-d (38.0–
40.7 ppm). The lower field resonance at 78.1 ppm is assigned to
the bridgehead carbon supporting the [6,6] closed methanofulle-
rene structure. These chemical shifts are very close to the reported
values (43.1 ppm and 75.6 ppm) of [6,6] closed methanofullere de-
rived from p-methoxyphenyldiazomethane combined with C60 [3f].
Whereas various reagent produce exclusively the [6,6] closed iso-
mers, diazoalkane addition is the only known route to the formation
of [5,6] open fulleroids. Most [5,6] fulleroids are quite labile, and
therefore thermally, photochemically and electrochemically isom-
erize to the [6,6] open methanofullerene [6]. The formation of 6 is
postulated to involve either thermal conversion of [5,6] fulleroid
or silyl carbene addition. In fact, the reaction of mono-silyldiazome-
thane 1d with C60, at higher temperature resulted in the formation
of the [6,6] closed isomer (7) in addition to the [5,6] open fulleroid
(3d), in 17.4% yield, as 1:2 mixture.
19 (17.4)d, (M+ = 992)
a
Bis-adducts: C60(R3SiCH)2.
Tris-sadduts: C60(R3SiCH)3.
Ar: 3,4-(OMe)2C6H4.
1:2 mixture of 7 and 3d.
b
c
d
gated 1H-coupled 13C NMR spectra of 3a–d, the three sets of fuller-
ene carbons at 136.7–137.0 ppm, 138.2–140.0 ppm and 143.7–
143.8 ppm are split into doublets (
2,3
J
= 5.3–7.4 Hz) by the
C–H
methine protons. 13C–1H COLOC analysis also showed a correlation
between the methine proton resonances and the same three fuller-
enes resonances. Typical spectra (3c) are shown in Figs. 1 and 2, and
Table 2. The 13C–1H long range coupling supports the conclusion
that 3a–d have [5,6] open fulleroid structures with silyl groups lo-
cated above a five-membered ring, as shown in Scheme 2. Recently,
it was reported that monoalkylated [3k,5d] and alkylphenylated
diazoalkanes [6b,c,e] react with C60 with remarkable regio- and dia-
stereoselectivity to yield stable fulleroids with the bulkier substitu-
ent located above a five-membered ring.
On the other hand, bis(trimethylsilyl) diazomethane (4e) did
not react with C60 under similar conditions, even under reflux
and photolysis, as shown in Scheme 3. Trimethylsilyl pentame-
thyldisilyl diazomethane (4f) reacts with C60 under photolysis in
toluene to afford 5 in 56% yield with recovered C60. The structure
of 5 was elucidated by reported spectral data and X-ray analysis
2.2. Theoretical studies on thermal nitrogen-extrusion of [6,6] closed
silylpyrazoline
In order to elucidate the origin of the diastereoselectivity in
the addition of silyldiazomethanes to C60, the mechanism of N2

1990
Y. Kabe et al. / Journal of Organometallic Chemistry 694 (2009) 1988–1997
Fig. 1. 13C NMR (top) and gated decoupled 13C NMR (bottom) of the fullerene region of 3c. X denotes 13C–1H long couplings.
conformers, as shown in Scheme 4. In the closed [6,6]/5 conformer
(IX), the silyl group (R = SiR03) faces the pentagonal ring, whereas in
the closed [5,6]/6 conformer (XII) the silyl group (R = SiR03) faces
the hexagonal ring. Schemes 4 and 5 show the concerted and step-
wise nitrogen-extrusion mechanisms, respectively. Because of the
high energy of the stepwise mechanism [5c] and the same stereo-
chemical consequence on both mechanisms [5d], the stepwise
mechanism was neglected in the remainder of arguments. Thermal
nitrogen-extrusion of the two conformers of pyrazoline (IX and
XII) takes place leading to the corresponding opened [5,6]/5 and
[5,6]/6 fulleroid (XI and XIV) via the closed [5,6]/5 and [5,6]/6 met-
hanofullerenes (X and XIII), respectively. Experimentally, only the
opened [5,6]/5 fulleroid (XI) was isolated, not the [5,6]/6 fulleroid
(XIV). During the formation of the fulleroids, the silyl groups
(R = SiR03) have to move toward the N2 moieties, or move from it,
no matter which mechanism, concerted or stepwise, is considered.
The transition state (TSs) of two reaction pathways for trimethyl-
silyl pyrazoline (2a, R = SiMe3) were analyzed using RHF/STO-3G, as
shown in Fig. 3. In TS1, the silyl groups move away from the N2 moi-
ety. For TS2, the silyl groups move toward the N2 moiety. The two TSs
corresponding to the thermal extrusion of nitrogen from pyrazoline
were located at the RHF/STO-3G level. Vibrational analyses verified
that both are first-order saddle points corresponding to the extru-
sion of N2 with imaginary frequencies of ꢀ1164 and ꢀ1046 cmꢀ1
for TS1 and TS2, respectively. RHF/STO-3G calculation favors TS1
over TS2 by more than 6.9 kcal molꢀ1, in agreement with experi-
mental results. To confirm that TS1 and TS2 are connected to the
closed [6,6] pyrazoline and the opened [5,6] fulleroids, the intrinsic
reaction coordinates (IRCs) starting from these TSs were con-
structed, as shown in Fig. 4. In fact, it was found that the two TSs
are connected to the closed [6,6] pyrazoline. Interestingly, the two
TSs are also connected the closed [5,6] methanofullerenes,
which are located in very shallow minima. In all cases, the most
favorable pathway is for the sterically demanding silyl group to
Fig. 2. 13C–1H COLOC NMR spectrum of 3c.
Table 2
Selected 1H and 13C NMR spectral data for 3a–d.
1H NMR d/ppm 13C NMR d/ppm
H at bridging C Bridging C (1JC–H, Hz) Fullerene carbons (2,3JC–H, Hz)
3a 2.47
3b 2.69
3c 2.69
3d 3.43
40.5 (126.5)
40.3 (125.8)
40.7 (125.8)
38.0 (127.3)
136.7 (5.9), 140.0 (6.1), 143.7 (6.0)
136.7 (6.3), 139.5 (6.0), 143.7 (6.3)
136.7 (6.3), 139.9 (6.4), 143.7 (5.3)
137.1 (6.4), 139.3 (6.4), 143.7 (6.1)
extrusion from the silylpyrazoline intermediate was studied by ab
initio Hartree–Fock methods. For the silylpyrazoline, two possible
conformers exist, the closed [6,6]/5 (IX) and closed [6,6]/6 (XII)

Y. Kabe et al. / Journal of Organometallic Chemistry 694 (2009) 1988–1997
1991
Scheme 3.
Scheme 4.
move away from the N2 moiety. For the more bulky triphenylsilyl-
pyrazoline 2d, the energy difference between the two TSs increased
Fig. 3 shows that the pronounced diastereoselectivity is a conse-
quence of the minimization of the repulsive interaction between
the silyl groups and the N2 moiety, which produce the fulleroid with
the silyl group located above a five-membered ring.
to 9.4 kcal molꢀ1
,
with imaginary frequencies of ꢀ1169 and
ꢀ1032 cmꢀ1 for TS1 and TS2, respectively. Single-point calculations
using density functional theory B3LYP/6-31G**//HF/STO-3G were
also carried out. The calculations lowered the energy differences be-
tween TS1 and TS2 with 2.1 and 3.0 kcal molꢀ1 for 2a and 2d, respec-
tively. For comparison, for the carbon analog IX and XII (R = CMe3),
RHF/STO-3G calculations predicted a 9.7 kcal molꢀ1 energy differ-
ence, with imaginary frequencies of ꢀ1100 and ꢀ815 cmꢀ1 for TS1
and TS2, respectively. Close inspection of TS1 and TS2 shown in
2.3. POAV analyses of silyl fulleroids
As shown in Scheme 1, azafulleroid (III; X = NR) and bisfulleroid
(VII; E = N, CR) undergo regioselective oxidative cleavage of the
bridgehead double bond by singlet oxygen. However, there is no
information regarding fulleroids. The calculated structure of aza-

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Y. Kabe et al. / Journal of Organometallic Chemistry 694 (2009) 1988–1997
fulleroids, were carried out (Table 3). Inspection of Table 3, the
pyramidalization angles of fulleroids at C6 and C9 and those of bis-
fulleroid at C6 and C7 are large values, while the values of fulleroids
at C1 and C5 and those of bisfulleroids at C5 and C8 are small values.
At least, within the values at C6 and C9, when changing from parent,
phenyl and silyl fulleroids, the pyramidalization angles tend to in-
crease. Thus the calculations on the silyl-substituted fulleroid pre-
dict the reactivity toward 1O2 at the C1–C9 and C5–C6 bonds.
Scheme 5.
fulleroid is known to have a shorter bridgehead bond length (1–9
and 5–6 bonds) and more pyramidalization than the parent fulle-
roid, violating Bredt’s rule by POAV analyses [8]. Actually, the pyra-
midalization angles of azafulleroid C60NH (C1, C5 (8.1°) and C6, C9
(10.2°)) is reported to be greater than the parent fulleroid (C1, C5
(7.6°) and C6, C9 (9.5°)), but in all cases are reduced from the values
that are implicit in the parent C60 molecules (11.6°). Whereas 1O2
oxygenations of mixture of diphenyl-substituted fulleroid and met-
hanofullerene were carried out, the 1H NMR spectrum of the fulle-
roid region (7.3–8.0 ppm) showed no change in comparison with
the initial spectrum [9]. Thus, the fulleroid does not appear to show
any evidence of reaction at the 1–9 and 5–6 bonds. However, intro-
duction of a substituent at the bridged carbon is thought to make
this the site more reactive under certain circumstance. So, POAV
analyses of phenyl- and silyl-substituted fulleroids, as well as bis-
Fig. 4. IRC calculations of N2 extrusion from the closed [6,6]/5 and [6,6]/6
pyrazolines. [a] Energies were estimated relative to TS1 as 0.0 kcal/mol.
Fig. 3. Calculated (RHF/STO-3G) structures of TS1 and TS2 with terminal structures of IRC calculations.

Y. Kabe et al. / Journal of Organometallic Chemistry 694 (2009) 1988–1997
1993
Table 3
Calculated fulleroid pyramidalization angles (°).a
Fulleroid (left)b
C1, C5
C2, C4
C3
C6, C9
C7, C8
R1 = R2 = H
R1 = R2 = Ph
R1 = SiMe3, R2 = H
7.9
7.0
7.7
9.4
9.2
9.4
10.4
10.3
10.2
9.3
8.9
9.4
11.1
11.2
11.0
Bisfulleroid (right)b
C1, C12 C2, C11 C3, C10
7.3 8.1 10.0
7.1, 6.5 8.0, 8.0
C4, C9
8.6
C5, C8
5.9
C6, C7
9.7
E = C, R3 = R4 = H
E = N, R3 = Py,
R4 = Ph
Fig. 5. Partial atomic numbering of fulleroid (left) and bisfulleroid (right).
9.9, 9.9 8.6, 8.3 5.7, 6.2 9.6, 9.5
Geometries optimized using B3LYP/6-31G** basis set.
See Fig. 5.
a
Due to the low solubility of 9a, it was not possible to obtain the 13C
NMR spectrum. However, the 13C NMR spectrum of 9b displayed
two signals at 199.7 ppm for carbonyl carbon and at 97.68 ppm
for olefinic methine carbon, as shown in Fig. 6. Silyl enol ether
derivatives of bisfulleroids were reported that 13C NMR chemical
shifts of enol methine carbons are 101.54 ppm [10]. In the fullerene
carbon region of 9b, 54 signals were observed, indicating that 9b
has C1 symmetry. The IR spectra of 9a and 9b showed strong bands
at 1733 cmꢀ1 corresponding to a carbonyl group and a strong band
at 1100 cmꢀ1 corresponding to Si–O groups. Although, 13C NMR
characterization of 9a was precluded, all data are in agreement
with silyl enol ether structures of 9a and 9b. The [2+2] cycloaddi-
tion of 3a,b with 1O2 followed by symmetrical ring opening of 7a,b
is thought to occur to give the diketone derivative 8a,b. Subse-
quent 1,3-silicon migration of 8b affords the silyl enol ether deriv-
atives of C60. The 1,3-silicon migration is highly dependent upon
the silicon atom substituent [11]. Oxygenation of 3d in CS2 at
ꢀ60 °C proceeded similarly. Three assignable new peaks 5.81,
5.91 and 5.96 ppm in 1H NMR spectra were observed. However,
due to the instability of products, all attempts of isolation and
characterization met with failure.
b
2.4. 1O2 oxygenation of silyl fulleroids
Based on the POAV analyses, 1O2 oxygenation of 3a, 3b and 3d
were carried out. A solution of 3a,b in o-dichlorobenzene was
exposed to a halogen lamp (300 W) for 5 h under an oxygen
stream. Although the reaction in o-dichlorobenzene at room tem-
perature was sluggish, using CS2 as a solvent at ꢀ60 °C resulted
in a relatively clean reaction. The 1H NMR spectrum of the reaction
mixture of 3a showed two new singlet at 0.57 and 5.87 ppm, in
addition to those observed for 3a at 0.60 and 2.57 ppm for the
SiMe3 and CH protons. Similarly, the 1H NMR spectrum of the reac-
tion mixture of 3b showed three singlet at 0.84, 0.85 and 5.90 ppm,
in addition to those observed of 3b at 0.75 and 2.69 ppm for SiMe2
with CH protons. In the case of 3b the non equivalence of SiMe sug-
gested C1 symmetry of oxidation product. After GPC, 9a,b were ob-
tained in 15% and 12% yields, from 3a and 3b, respectively.
The product 9a,b are proposed to be a silyl enol ether on the ba-
sis of spectroscopic characteristics, as shown in Scheme 6. The
molecular ion peak at 831 ([M+1]+) of 9a and 901 ([M+1]+) of 9b
were detected by MALDI-TOF mass spectroscopy, indicating that
the product were formed by addition of O2 to 3a and 3b. The 1H
NMR resonance of the CH protons was shifted to lower field
(5.87 and 5.90 ppm) for 3a and 3b, assigned to the olefin protons.
Theoretical calculations also support the 1,3-silyl migration.
The optimized structures of the silyl enol ether 9a and diketone
8a calculated at B3LYP/6-31G level of theory, as shown in Fig. 7.
The relative energy of diketone 9a is calculated lower than that
of 8a by 21 kcal molꢀ1. The NMR chemical shifts of 8a and 9a were
also estimated by GIAO calculations (B3LYP/6-31G). The calculated
Scheme 6.
Fig. 6. 13C NMR sp2 carbon region of 9b in CS2: CDCl3 solution. X denotes as toluene.

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Y. Kabe et al. / Journal of Organometallic Chemistry 694 (2009) 1988–1997
the solvent under reduced pressure, the crude product was purified
by gel permeation liquid chromatography (GPC) to afford 19 mg of
3a (34%) as a dark brown solid together with the bis- and tris-ad-
ducts (15 mg and 15 mg) in 24% and 22% yields (Table 1).
For 3a: 1H NMR (400 MHz, C6D6:CS2 = 1:1) d 0.51 (s, 9H), 2.47 (s,
1H); 13C NMR (100 MHz, C6D6: CS2 = 1:1) d ꢀ0.32 (q), 40.47 (d),
133.02, 136.76, 137.64, 137.85, 138.17, 138.62, 140.06, 140.13,
141.50, 142.11, 142.98, 143.09, 143.18, 143.33, 143.36, 143.50,
143.54, 143.57, 143.66, 143.77, 143.82, 143.95, 144.04, 144.34,
145.25, 145.32, 148.52; 29Si NMR (80 MHz, C6D6: CS2 = 1:1) d 7.83;
UV–vis (cyclohexane) kmax/nm (e) 539 (250); MS (FAB) calcd for
C64H10Si (M+), 806, found, 806.
3.3.2. Dimethylphenylsilyldiazomethane (1b) with C60
To a solution of C60 (60 mg, 0.083 mmol) in toluene (25 ml) was
added a solution of 1b (21 mg, 0.12 mmol) in ether at room tem-
perature. The mixture was stirred for 40 h. After removal of the sol-
vent under reduced pressure, the crude product was purified by
GPC to afford 30 mg of 3b (41%) as a dark brown solid together
with the bis- and tris-adducts (25 mg and 7 mg) in 29% and 8%
yield (Table 1).
Fig. 7. B3LYP/6-31G optimized structures of 8a (left) and 9a (right).
For 3b:1HNMR(400 MHz, C6D6:CS2 = 1:1)d0.75(s, 6H), 2.69(s, 1H),
7.25–7.61 (m, 5H); 13CNMR(100 MHz,C6D6:CS2 = 1:1)dꢀ1.92 (q), 40.32
(d), 128.25 (s), 128.53 (d), 130.37 (d), 133.62 (d), 135.14, 136.21, 136.81,
137.60, 137.87, 138.10, 138.62, 139.56, 140.15, 141.52, 142.13, 142.97,
143.13, 143.17, 143.29, 143.35, 143.52, 143.56, 143.66, 143.82, 143.97,
144.04, 144.32, 144.36, 145.42, 148.55; 29Si NMR (80 MHz, C6D6:
chemical shifts of carbonyl carbons at 213 ppm and enol carbons at
119 and 159 ppm for 9a are comparable with experimental values
of 9b, while the calculated values for 8a of carbonyl carbons at 202,
210 ppm and methine carbon at 69 ppm are not.
In conclusion, the unique diastereoselective formation of silyl
fulleroid has been accomplished. The origin of the diastereoselec-
tivity is understood in terms of minimization of the repulsive
interaction between the silyl groups and the N2 moiety in the
decomposition of the pyrazoline intermediate, based on theoretical
calculations. The bridgehead C@C double bond of the silyl fulleroid
showed reactivity toward electrophiles such as 1O2, based on POAV
analyses. 1O2 oxygenation of silyl fulleroids affords the silyl enol
ether derivatives via 1,3-silyl migration of the diketone derivatives.
CS2 = 1:1) d 0.90; UV–vis (cyclohexane) kmax/nm (
e) 536 (1200); MS
(FAB) calcd for C69H12Si (M+), 868, found, 868.
3.3.3. Dimethylveratrylsilyldiazomethane (1c) with C60
To a solution of C60 (72 mg, 0.10 mmol) in toluene (50 ml) was
added a solution of 1c (1.0 ml, 0.13 mmol) in ether at room tem-
perature. The mixture was stirred for 15 h. After removal of the sol-
vent under reduced pressure, the crude product was purified by
GPC to afford 44 mg of 3c (41%) as dark brown solid together with
the bis- and tris-adducts (38 mg and 28 mg) in 29% and 18% yields
(Table 1).
3. Experimental
3.1. General data
For 3c: 1H NMR (500 MHz, C6D6: CS2 = 1:1) d 0.62 (s, 6H), 2.69 (m,
1H), 3.59 (s, 3H), 3.64 (s, 3H), 6.72 (d, 1H), 7.07 (s, 1H), 7.16 (d, 1H);
13C NMR (125 MHz, C6D6: CS2 = 1:1) d ꢀ1.48 (q), 40.65 (d), 55.40 (q),
55.92 (q), 112.30 (d), 116.02 (d), 126.64, 128.30, 132.94, 136.17 (s),
136.66 (s), 137.48, 137.62 (s), 137.94, 138.53, 139.88, 140.05,
141.43, 142.05, 142.94, 143.05, 143.11, 143.13, 143.22, 143.28,
143.46, 143.48, 143.50, 143.61, 143.69, 143.74, 143.78, 143.89,
143.98, 144.26, 144.29, 145.22, 145.25, 148.52, 149.64 (s), 151.93
(s); 29Si NMR (60 MHz, C6D6: CS2 = 1:1) d ꢀ13.92; MS (FAB) calcd
for C71H16O2Si ([M+H]+), 929, found, 929.
The 1H and 13C NMR spectra were recorded on a Bruker AM-500
and JEOL JNM-ECP500 operating at 500 or 125 MHz, respectively.
IR spectra were recorded on a JASCO FT/IR-4100. Mass spectra
were recorded on a JEOL SX102A, JEOL JMS-AX505H and Shimadzu
AXIMA-CFR. UV spectra were recorded on a JASCO V-550. GPLC (gel
permeation liquid chromatography) was performed on an LC-908
(Japan Analytical Industry, Co., Ltd.) equipped with JAIGEL 1H
and 2H columns (eluent: toluene). Melting points were determined
using a Yanaco MP-S3.
3.3.4. Triphenylsilyldiazomethane (1d) with C60
3.2. Materials
To a solution of C60 (72.0 mg, 0.10 mmol) in toluene (50 ml)
was added a solution of 1d (30.1 mg, 0.10 mmol) in toluene
(5 ml). The reaction mixture was refluxed at 110 °C for 24 h. After
the removal of the solvent under reduced pressure, the crude prod-
uct was purified by GPC to afford 14.5 mg in 17.4% yield of ca 1:2
mixture of 7 and 3d as a dark brown solid together with the bis-
and tris-adducts (15.4 and 17.6 mg) in 12.2% and 24.0% yields
(Table 1).
Me3SiCHN2 (1a), Me2PhSiCHN2 (1b), (3,4-(OMe)2C6H4Me2-
SiCHN2) (1c) and Ph3SiCHN2 (1d) were prepared by published pro-
cedure [11]. Because of the instability of silyldiazo compounds
except 1d, they were used as ether solution without further purifi-
cation. (Me3Si)2CN2 (4a) and Me3SiCN2SiMe2SiMe3 (4b) were pre-
pared using 1a or phenyldiazomethane followed by coupling
with Me3SiCl, Me3SiCN2Ph (4c), Me3SiMe3SiCl [7,12,13] .
For 3d+7: 1H NMR (500 MHz, C6D6: CS2 = 1:1) d 3.48, 4.01, 7.26–
7.36, 7.74–7.76, 7.95–7.97; 13C NMR (125 MHz, C6D6: CS2 = 1:1) d
28.4 (d), 38.0 (d), 72.9 (s), 128.6 (s), 130.2, 130.8 (d), 130.9 (s),
132.77, 132.82, 133.0, 134.9, 135.3, 136.1, 136.67 (d), 136.70 (d),
136.9, 137.0, 137.2, 137.7, 138.2, 138.4, 139.4, 140.1, 140.8, 141.3,
141.5, 141.6, 142.2, 142.3, 142.4, 142.9, 143.0, 143.07, 142.12, 143.16,
143.20, 143.3, 143.4, 143.45, 143.48, 143.51, 143.6, 143.7, 143.81,
3.3. Reaction of monosilyldiazomethane with C60
3.3.1. Trimethylsilyldiazomethane (1a) with C60
To a solution of C60 (50 mg, 0.069 mmol) in toluene (25 ml) was
added a solution of 1a (17 mg, 0.15 mmol) in ether at room
temperature. The mixture was stirred for 30 h. After removal of

Y. Kabe et al. / Journal of Organometallic Chemistry 694 (2009) 1988–1997
1995
143.82, 143.9, 144.0, 144.2, 144.3, 144.6, 144.7, 144.8, 145.0, 145.25,
3.5. Photooxygenation of silylfulleroid 3a,b
3.5.1. Photooxygenation of silylfulleroid 3a
145.33, 145.8, 146.0, 148.6, 150.0, 152.6; 29Si NMR (60 MHz, C6D6:
CS2 = 1:1) dꢀ13.92; MS (FAB) calcd for C79H16Si (M+), 992, found, 992.
A
mixture of C60 (50 mg, 0.069 mmol) and 1d (63 mg,
A solution of 3a (58.7 mg, 0.07 mmol) in o-dichlorobenzene
(20 ml) in a pyrex tube was irradiated with a halogen lamp under
bubbling oxygen for 4 h. After removal of the solvent under re-
duced pressure, an insoluble powder was filtered off. Purification
of the residue by GPC gave 9.3 mg of 9b, as a dark brown solid in
15% yield.
0.21 mmol) in o-dichlrobenzene (5 ml) was heated at 90 °C for
6 h. After removal of the solvent under reduced pressure, the crude
product was purified by GPC to afford 10 mg of 3d (19%) as a dark
brown solid.
For 3d:1H NMR (500 MHz, CDCl3:CS2 = 2:3)d3.43 (s, 1H), 7.27–7.53
(m, 15H); 13C NMR (125 MHz, CDCl3: CS2 = 2:3) d 37.46, 124.91, 127.74,
128.15, 129.51, 129.89, 130.50, 132.30, 132.35, 134.78, 136.21, 136.40,
136.53, 136.65, 137.19, 137.32, 137.76, 137.90, 139.61, 140.96, 141.66,
142.41, 142.57, 142.61, 142.63, 142.68, 142.82, 142.92, 142.98, 143.08,
143.18, 143.34, 143.41, 143.69, 143.79, 144.77, 148.13; MS (MALDI)
calcd for C79H16Si (M+), 992, found, 992.
For 9a: 1H NMR (500 MHz, CDCl3: CS2 = 1:1) d 0.57 (s, 9H), 5.87
ꢀ
(s, 1H); IR (KBr)
m
= 1733, 1100 cmꢀ1; MS (MALDI) calcd for
C64H10O2Si ([M+H]+), 839, found, 839.
3.5.2. Photooxygenation of silylfulleroid 3b
A solution of 3b (130.0 mg, 0.15 mmol) in o-dichlorobenzene
(40 ml) in a pyrex tube was irradiated with a halogen lamp under
bubbling oxygen for 5 h. After removal of the solvent under reduced
pressure, an insoluble powder was filtered off. Purification of the
residue by GPC gave 18.7 mg of 9b, as a dark brown solid in 12%
yield.
3.4. Reaction of bissilyl and silylphenyldiazomethane with C60
3.4.1. Bistrimethylsilyldiazomethane (4e) with C60
A
mixture of C60 (20 mg, 0.028 mmol) and 4e (21 mg,
For 9b: 1H NMR (500 MHz, CDCl3: CS2 = 1:1) d 0.84 (s, 3H), 0.85 (s,
3H), 5.90 (s, 1H), 7.39–7.83 (m, 5H); 13C NMR (125 MHz, CDCl3:
CS2 = 1:1) d 0.88, 97.68, 127.48, 130.06, 130.36, 133.82, 135.13, 135.29,
135.43, 135.75, 135.93, 136.12, 137.00, 137.26, 137.49, 137.67, 138.57,
138.97, 139.23, 139.63, 140.16, 141.63, 141.76, 142.06, 142.28, 142.70,
142.92, 143.01, 143.10, 143.14, 143.30, 143.39, 143.72, 143.93, 144.41,
144.86, 145.27, 145.63, 145.70, 145.74, 145.77, 145.86, 146.08, 146.32,
146.62, 147.08, 147.05, 145.08, 147.21, 147.39, 147.85, 148.14, 148.47,
ꢀ
0.11 mmol) in o-dichlrobenzene (10 ml) was degassed and sealed
in a pyrex tube. The reaction mixture was heated at 110 °C for
12 h. After removal of the solvent under reduced pressure, the res-
idue was separated by GPC to afford 8 mg of recovered C60
.
A
solution of C60 (10 mg, 0.014 mmol) and 4e (25 mg,
0.13 mmol) in toluene (10 ml) was degassed and sealed in a pyrex
tube. The reaction mixture was irradiated with a high pressure
mercury lamp using a glass filter (cut off 350 nm) for 6 h. After re-
moval of the solvent under reduced pressure, the residue was sep-
148.59, 149.98, 150.33, 199.76; IR (KBr) m
= 1733, 1100 cmꢀ1; MS (MAL-
DI) calcd for C69H12O2Si ([M+H]+), 901, found, 901.
arated by GPC to afford 7 mg of recovered C60
.
3.6. Computational studies
3.4.2. Pentamethyldisilyltrimethylsilyldiazomethane (4f) with C60
mixture of C60 (10 mg, 0.014 mmol) and 4f (31 mg,
A
Calculations were carried out on an HPC-P4/GLW and HPC3000-
XC104T workstation provided by HPC Inc. of Japan. Ab initio calcu-
lations were performed using the Gaussian 03 computer program
[14]. The initial geometries for the pyrazolines, fulleroids and oxy-
genation products were constructed using the Chem 3D graphical
interface provided by Cambridge Software Inc. All geometry opti-
mizations were performed on cartesian coordinate using the en-
ergy gradient minimization method. Transition states were
formed by the QST2 technique in the Gaussian 03 program. The
vibrational analyses were carried out using the MolStudio R4
graphical interface from NEC. The POAV/3D-HMO analyses were
performed using the POAV3 program [8c].
0.13 mmol) in o-dichlorobenzene (10 ml) was degassed and sealed
in a pyrex tube. The reaction mixture was heated at 155 °C for 30 h.
After removal of the solvent under reduced pressure, the residue
was separated by GPC to afford 7 mg of recovered C60
.
A
solution of C60 (10 mg, 0.014 mmol) and 4f (95 mg,
0.39 mmol) in toluene (10 ml) was degassed and sealed in a pyrex
tube. The reaction mixture was irradiated for 36 h. After removal of
the solvent under reduced pressure, the residue was separated by
GPC to afford 47 mg of 5 as colorless crystals in 56% yield.
For 5: 1H NMR (500 MHz, C6D6) d 0.32 (s, 36H), 0.53 (s, 12H); 13
C
NMR (125 MHz, C6D6) d 8.02 (q), 9.16 (q), 13.2 (s); 29Si NMR
(80 MHz, C6D6)
d
ꢀ1.78, 4.23; MS (EI) calcd for C18H48Si6
([MꢀCH3]+), 417, found, 417.
Acknowledgments
3.4.3. Phenyltrimethylsilyldiazomethane (4 g) with C60
This work was supported by a Grant-in Aid for a High-Tech Re-
search Center Project from the Ministry of Education, Culture,
Sports, Science and Technology, Japan. The authors are grateful to
the Shin-Etsu Chemical Co. Ltd. and the Asai Germanium Co. Ltd
for providing the chlorosilanes and tetrachlorogermane.
To a solution of C60 (72.0 mg, 0.10 mmol) in toluene (50 ml),
was added
a solution of 4g (35 mg, 0.18 mmol) in toluene
(10 ml). The reaction mixture was refluxed at 110 °C for 25 h. After
removal of the solvent under reduced pressure, the crude product
was purified by GPC to afford 30.4 mg of 6 (46%) as a dark
brown solid. The bis- and tris-adducts (10.0 mg and 7.8 mg)
were obtained in 13% and 9% yields, respectively, based on the
molecular ions peaks (1045 (M++H) and 1207 (M+)) from mass
spectroscopy.
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