Addition of S-Heterocyclic Carbenes to Fullerenes: Formation and Characterization of Dithiomethano-Bridged Derivatives

Article abstract of DOI:10.1002/hlca.201900064

The reactions of novel S-heterocyclic carbenes (SHCs), which were prepared by the cycloaddition of disilenes and digermenes to CS₂, with C₆₀ and Sc₃N@I_h-C₈₀ afforded the corresponding methano-bridged

Full text of DOI:10.1002/hlca.201900064

DOI: 10.1002/hlca.201900064
FULL PAPER
Addition of S-Heterocyclic Carbenes to Fullerenes: Formation and
Characterization of Dithiomethano-Bridged Derivatives
Masahiro Kako,*a Yuki Arikawa,a Shinji Kanzawa,a Michio Yamada,b Yutaka Maeda,b
Makoto Furukawa,c and Takeshi Akasaka*b, c, d
a
Department of Engineering Science, The University of Electro-Communications, Chofu 182-8585, Japan,
e-mail: kako@e-one.uec.ac.jp
Department of Chemistry, Tokyo Gakugei University, Tokyo 184-8501, Japan,
b
e-mail: akasaka@tara.tsukuba.ac.jp
Foundation for Advancement of International Science, Tsukuba, Ibaraki 305-0821, Japan
c
d
School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei
430074, P. R. China
Dedicated to Professor François Diederich
The reactions of novel S-heterocyclic carbenes (SHCs), which were prepared by the cycloaddition of disilenes
and digermenes to CS2, with C60 and Sc3N@Ih-C80 afforded the corresponding methano-bridged fullerenes. The
[6,6]-closed and [6,6]-open structures were characterized for the SHC adducts of C60 and Sc3N@Ih-C80,
respectively. These derivatives exhibited relatively low oxidation potentials, indicative of the electron-donating
effects of the SHC addends. The electronic properties of the SHC derivatives were clarified by the density
functional theory calculations.
Keywords: fullerenes, cluster compounds, sulfur heterocycles, S-heterocyclic carbenes, disilenes, digermenes.
Introduction
most frequently employed reactions. Hitherto, the
Endohedral metallofullerenes (EMFs)[1–14] are of great radical malonate addition, the Bingel–Hirsch reaction,
interest because of their remarkable structures and reactions of carbenes and diazoalkanes, electrochem-
properties based on the encapsulated metal atoms ical synthesis, and zwitterion addition have been
and metallic clusters inside the carbon cages. Thus far, reported for the synthesis of methano-bridged EMFs.[7]
many EMFs with various cage structures and endohe- For example, the addition of carbenes to M3N@Ih-C80
dral species have been extensively investigated, stim- (M=Sc, Y, and Lu), Ih-C80-based trimetallic nitride
ulating their potential applications in biochemistry, template (TNT) EMFs, afforded two regioisomeric
nanomaterial science, and molecular electronics.[1–14] methanofullerenes at the [6,6] (two hexagons) and
To develop their applications to functional materials, [5,6] (a pentagon and a hexagon) ring junctions.[15–23]
exohedral derivatization plays an indispensable role In these cases, methano-bridged EMF derivatives have
via the modification of the fundamental properties of ‘open’ structures (also known as fulleroids), in which
EMFs, such as their solubilities and redox potentials.
the CÀ C bonds of the addition sites are cleaved. One
Among the several functionalization methods for of the most practical uses of methano-bridged full-
EMFs, the methano-bridge formation[7] is one of the erenes is the acceptor materials in organic photo-
voltaic (OPV) devices.[24] For example, phenyl-C61-
butyric acid methyl ester (PC61BM)[25] and the corre-
sponding C70 derivative (PC71BM)[26,27] are well known
Supporting information for this article is available on the
WWW under https://doi.org/10.1002/hlca.201900064
to be excellent electron acceptor materials for organic
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solar cells. For EMFs, similar Lu3N@Ih-C80 derivatives few studies based on chemical trapping experiments,
were reported as promising materials for OPV spectroscopic
observation,
and
theoretical
devices.[28–30] As the lowest unoccupied molecular calculations.[44,45]
orbital (LUMO) of Lu3N@Ih-C80 is higher than that of
Herein we report the reactions of Sc3N@Ih-C80,[46][47]
C60, the OPV devices fabricated using Lu3N@Ih-C80 the third most abundant fullerene after C60 and C70,
derivatives exhibited an increase in the open-circuit with novel SHCs, which are generated using syntheti-
voltage, affording higher power conversion efficien- cally more accessible precursors. The SHC adducts of
cies.
Sc3N@Ih-C80 as well as those of C60 are characterized
In our ongoing study on the derivatization of on the basis of spectroscopic, electrochemical, and
fullerenes with carbenes,[7] the formation of S- theoretical studies. These results provided a basis for
heterocyclic carbene (SHC) 3[31] was previously understanding the electronic properties of these
reported in the photoreaction of tricyclic octasilane compounds, revealing the electronic effects of SHCs as
1[32] and CS2 (Scheme 1). The subsequent addition of nucleophilic carbenes.
Results and Discussion
Syntheses of SHC Adducts of Fullerenes
Novel SHCs 7, 10a, and 10b were synthesized using
disilene 6[48] and digermenes 9a[49] and 9b,[50] respec-
tively (Scheme 2). To prepare compound 6, trisilane
Scheme 1. Reaction of S-heterocyclic carbene 3 with C60.
3 to C60 produced the corresponding [6,6]-closed
methanofullerene 4.[31] The formation of 3 was easily
rationalized by the [2+3] cycloaddition of in situ
generated cyclic disilene 2 with CS2 as reported for
an isolable disilene reported by Wiberg and co-
workers.[33] However, the synthetic yield of 1 was
not sufficient to perform studies on 3 because the
preparation of 1 requires multiple step syntheses
Scheme 2. Formation of SHCs 7, 10a, and 10b.
and subsequent separation by high-performance
liquid chromatography (HPLC).[32]
Since the discovery of a stable carbene, 1,3-di-1-
adamantylimidazol-2-ylidene,[34] N-heterocyclic car- 5[48] was employed as the disilene precursor. Because
benes (NHCs) have been extensively studied from the photolysis of 5 requires short-wavelength ultra-
fundamental viewpoints as well as with respect to the violet (UV) irradiation, we conducted the following
application to catalysts or ligands for metallic stepwise procedure involving the photolytic synthesis
complexes.[34–36] In fullerene chemistry, the NHC of 6 and subsequent formation of 7. Thus, a benzene
adducts as the Lewis donor–acceptor complexes have solution of 5 was subjected to photolysis in a quartz
been studied for C60,[37] C70,[37] and a few EMFs.[38–41] tube by a low-pressure mercury arc lamp for 4 h. Then,
Nevertheless, examples of cyclic carbenes containing the resultant solution containing 6 was added to a
other heteroatoms such as phosphorus and sulfur are benzene solution of C60 and CS2 (Scheme 3). The
extremely sparse compared with those of NHCs.[42,43] subsequent preparative HPLC separation of the reac-
As compounds related to SHCs, the studies of 1,3- tion mixture afforded 11 in 36% yield. The matrix-
dithiocarbenes (RSÀ CÀ SR) also have been limited in assisted laser desorption ionization time-of-flight
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photolysis for 2 h, the mixture was separated by
preparative HPLC to afford the corresponding adduct
12 in 22% yield. As described above for 11, the [6,6]-
closed structure of 12 was confirmed by the MALDI-
TOF, UV/Visible (Figure 1), and 13C-NMR spectra (Fig-
ure S12). Selective formation of 11 and 12 as the
[6,6]-closed adducts was consistent with the result
obtained previously for the addition of 3 to C60.[6]
Subsequently, these synthetic procedures for the
derivatization with SHCs were applied to Sc3N@Ih-C80.
After the addition of 6 into a solution of CS2 and
Sc3N@Ih-C80, the mixture was separated by preparative
HPLC to give 13 (Scheme 4). For derivatization using
Scheme 3. Reactions of C60 with SHCs 7 and 10a.
Figure 1. UV/Visible absorption spectra of 11 and 12 in CH2Cl2.
Scheme 4. Reactions of Sc3N@Ih-C80 with SHCs 7 and 10b.
(MALDI-TOF) mass spectrum and the UV-visible spec- 10b, the photolysis of a toluene solution of Sc3N@Ih-
trum (Figure 1) of 11 confirmed the formation of a C80, 8b, and CS2 using a medium-pressure mercury arc
[6,6]-closed adduct of C60 and 7. The 13C-NMR lamp for 1 h afforded the corresponding adduct 14.
spectrum of 11 (Figure S10 in the Supporting Informa- The MALDI-TOF mass spectra of 13 and 14 show
tion) showed 17 peaks for sp2 carbon atoms of the C60 molecular ion peaks for the SHC adduct of Sc3N@Ih-
cage, 13 signals of which exhibited doubled inten- C80, with the fragment ion peak for Sc3N@Ih-C80. In the
sities, indicative of the C2v symmetry of the C60 cage Vis/NIR spectra, gentle curves with absorption should-
by assuming the inversion of the SHC ring and rotation ers around 760 nm were observed, which was similar
of the mesityl (Mes) groups within the NMR timescale. to those of pristine Sc3N@Ih-C80, as well as its [6,6]- and
In addition, signals corresponding to the sp3 carbon [5,6]-open methano-derivatives,[17–19,21–23] suggesting
atom of the C60 cage, and to the spirocarbon atom of fulleroid structures of 13 and 14 (Figure 2). It is well
the SHC addend were also observed at 80.19 ppm and known that fulleroid structures exhibit absorption
50.83 ppm, respectively. These chemical shifts are spectra that resemble to those of the corresponding
similar to those of 4,[31] confirming the [6,6]-closed parent fullerenes due to the preservation of π-
structure of 11.
electronic systems.
In the case of 10a and 10b, cyclotrigermanes
In the 13C-NMR spectrum, 14 showed 44 sp2 carbon
8a[49] and 8b[50] were photolyzed in the presence of signals corresponding to the Ih-C80 cage, in which
C60 and CS2 because 8a and 8b are reactive for the eight signals were observed in half-intensities (Fig-
extrusion of 9a and 9b, respectively, under long- ure S16). Among the signals, two signals observed at
wavelength UV irradiation (Scheme 2). Hence, it is 123.88 ppm and 122.10 ppm were assigned to those
feasible to conduct the derivatization of fullerenes of bridgehead carbon atoms of the methano-addition
with SHCs 10a and 10b for one-pot syntheses. For site. In the upfield region, one quaternary carbon
this purpose, a toluene solution of C60, CS2, and 8b signal (56.82 ppm) was observed for the dithiocarbon
was irradiated in a Pyrex tube using a medium- atom. These results are consistent with the [6,6]-open
pressure mercury arc lamp (Scheme 3). After the structure of 14 with C2 symmetry by assuming that
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lower than 12-II by 5.43 kcal/mol, supporting the
selective formation of 11 and 12 as the [6,6]-open
adduct.
In the case of 14, optimized structures were
calculated for the [6,6]-open adducts 14-I–VII and the
[5,6]-open adducts 14-VIII–XI, by the M06-2X[54]
methods (Figures 4, S19, and S20). In addition, the
Figure 2. Vis/NIR absorption spectra of 13, 14, and Sc3N@Ih-C80
in CS2.
the Sc3N cluster possibly does not affect the molecular
symmetry on the NMR timescale by its rotation inside
the C80 cage. In addition, methyl and aromatic carbon
signals of the Mes groups were observed as broad-
ened peaks probably due to the restricted ring
rotation by their steric congestion. In contrast, no
[5,6]-open SHC adduct was obtained in these results,
which may be attributed to its low yield. In fact, the
reactions of adamantylidene carbene to Sc3N@Ih-C80
afforded low yields of the [5,6]-open adduct along
with the [6,6]-open adduct as the predominant
product, respectively.[23] The 13C-NMR spectrum of 13
also shows similar results indicating the [6,6]-open
structure of 13.
Theoretical Calculations
Structural and electronic properties of the SHC
adducts were investigated by the density functional
theory calculations. The optimized structures of 11
and 12 were obtained as 11-I and 12-I, respectively,
by the B3LYP[51–53] method (Figures 3 and S18). The
corresponding [5,6]-open adducts were also calculated
as 11-II and 12-II, respectively. As a result, 11-I is lower
in energy than 11-II by 10.87 kcal/mol, 12-I is also
Figure 4. Representation of 14-I–XI and the orientations of
Sc3N cluster. Values in the parentheses are the relative energies
in kcal/mol compared to that of 14-III.
orientations of the Sc3N cluster were changed in these
isomers to examine the dependence of the relative
energies on the orientations of the Sc3N cluster.
Figure 4 shows partial structures of 14-I–XI in addition
to their relative energies [kcal/mol] in parentheses. The
results revealed that the 14-I–V, in which one of the
Sc atoms is oriented to the addition sites, respectively,
are lower in energy than 4-VI–VII that exhibit the
Figure 3. Structures of 11-I, 11-II, 12-I, and 12-II.
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Figure 5. Cyclic voltammograms (CV) and differential pulse voltammograms (DPV) of a) 11, b) 12, c) 13, and d) 14 in ODCB
containing 0.1 M (Bu)4NPF6. In DPVs, peaks of the adducts and pristine EMFs are indicated by circles and squares, respectively.
Conditions: working electrode, a glassy carbon electrode; counter-electrode, Pt wire; reference electrode, SCE; scan rate, 50 mV/s.
slantwise and horizontal orientations of the Sc3N Electronic Effects of SHC Addends on Fullerenes
clusters. Furthermore, the relative energies of 4-I–V
fall within the range of 3.12 kcal/mol, suggesting that To obtain insight into the electronic properties of 11–
the Sc3N cluster possibly rotates around an axis 14, cyclic voltammetry (CV) and differential pulse
pointing to the addition sites. Similar results were voltammetry (DPV) were conducted in o-dichloroben-
obtained for the [5,6]-adducts 14-VIII–XI. Such orienta- zene (ODCB) as shown in Figure 5. Their redox
tions of the Sc3N clusters have been reported potentials are summarized in Table 1 with those of the
commonly for the [6,6]-open and [5,6]-open methano- corresponding parent fullerenes. Both the reduction
bridged M3N@Ih-C80 (M=Sc, Y) structurally determined (Ered) and the oxidation (Eox) potentials of 11–14
by X-ray crystallography.[16,18,22,23] By the comparison shifted to more negative values relative to those of
of the adducts with the vertical orientations of the pristine fullerenes, respectively, indicative of the
Sc3N cluster, the [6,6]-adducts 14-I–V are energetically electron-donating effects of SHCs as nucleophilic
lower than the [5,6]-adducts 14-VIII–X. This result may carbenes. In particular, the Eox potentials of 13 and 14
support the experimentally observed predominant are slightly lower than those of the related methano-
production of the [6,6]-open adducts although low bridged Sc3N@Ih-C80 derivatives 15–19 (Fig-
yield formation of the [5,6]-open adducts cannot be ure 6).[19,21,22] It is also noteworthy that 12 and 14
excluded. On the basis of these results, the most stable exhibited slightly lower Eox1 potentials than 11 and 13,
structure, 14-III is employed for the theoretical consid- respectively, suggesting that the energetically lower
eration of the electronic properties of 14.
molecular orbitals of Ge–Ge bonds contribute more
than those of SiÀ Si bonds. Previously, the similar slight
cathodic shift of the Eox potential has been reported
1
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Table 1. Redox potentials [V] of 11–14[a] and related com-
12-I, and 14-III. The HOMO and LUMO levels of 11-I
are higher than those of C60 by +0.42 eV and
+0.21 eV, respectively. Similarly, 12-I, and 14-III also
exhibited shifts of the HOMOs and LUMOs to more
positive values compared with those of the corre-
sponding pristine fullerenes. These shifts in the MO
levels are qualitatively consistent with the experimen-
tal cathodic shifts of the redox potentials, thereby
confirming the electron-donating effects of SHCs.
pounds.
Compound
Eox
Ered
Ered
2
1
1
[b]
C60
+1.21
+0.90
+0.76
+0.59
+0.48
+0.45
+0.52
+0.56
+0.52
+0.50
+0.52
À 1.12
À 1.24
À 1.23
À 1.26
À 1.35
À 1.34
À 1.24
À 1.34
À 1.37
À 1.48
À 1.51
À 1.50
À 1.66
À 1.64
À 1.62
À 1.77
À 1.74
À 1.96
À 1.90
À 1.93
À 2.01
À 1.61
11
12
[c]
Sc3N@Ih-C80
13
14
15[c]
16[c]
17[c]
18[d]
19[e]
Conclusions
The preparation of SHCs was established by the
cycloaddition of synthetically more accessible disilenes
and digermenes to CS2. The reactions of SHCs with C60
and Sc3N@Ih-C80 produced the corresponding [6,6]-
methanofullerenes 11–14, which were characterized
using spectroscopic, electrochemical, and theoretical
studies. The preferential formation of the [6,6]-meth-
anofullerenes over the [5,6]-isomers is consistent with
the previous examples of carbene addition to C60 and
Sc3N@Ih-C80, and supported by relative stabilities of
optimized structures of the [6,6]-isomers. The electron-
donating effect of the SHC addends was also indicated
for 11–14, for which relatively low oxidation poten-
tials were obtained. The cathodic shifts of redox
potentials of 11, 12, and 14 were verified by the
calculated energies of HOMOs and LUMOs with those
of C60 and Sc3N@Ih-C80.
[a] Values obtained by DPV are in volts relative to the ferrocene/
ferrocenium couple. [b] Data from ref. [31]. [c] Data from ref. [19].
[d]
[e]
Data from ref. [21]. Data from ref. [22].
Figure 6. Partial structures of Sc3N@Ih-C80-based methanofuller-
enes 15–19.
Experimental Section
Materials and General Method
Table 2. Calculated HOMO/LUMO Levels [eV].
All chemicals were reagent grade, purchased from
Wako Pure Chemical Industries Ltd. Sc3N@Ih-C80 was
purchased from Luna Innovations Inc. o-Dichloroben-
zene (ODCB) was distilled from P2O5 under vacuum
before use. Toluene was distilled from benzophenone
sodium ketyl under dry N2 prior to use. Reagents were
used as purchased unless otherwise specified. HPLC
was performed on an LC-908 apparatus (Japan
Analytical Industry Co. Ltd.) monitored using a UV3702
detector. Analytical HPLC was performed on a PU-1586
pump with a UV-1575 detector (JASCO Corp.). Bucky-
Compound
HOMO
LUMO
[a]
C60
À 5.99
À 5.57
À 5.52
À 6.44
À 6.14
À 3.23
À 3.02
À 2.96
À 2.78
À 2.15
11-I[a]
12-I[a]
[b]
Sc3N@Ih-C80
14-III[b]
[a] B3LYP/6-31G(d). [b] M06-2X/LanL2DZ[Sc, Ge], 6-31G(d)[C, H, N,
S].
for the digermirane adduct of Lu3N@Ih-C80 compared prep-M and 5PBB(Nacalai, ϕ 10 mm×250 mm, ϕ
to the corresponding silicon analog.[55]
4.6 mm×250 mm) columns were used for HPLC sepa-
Furthermore, the electronic properties of 11–14 ration. Toluene was used as the eluent for HPLC. The
were evaluated by the theoretical calculations. Table 2 1H- and 13C-NMR measurements were conducted on a
summarizes the energies of the highest occupied JEOL ECA-500 spectrometer (JEOL Ltd.). MALDI-TOF
molecular orbitals (HOMOs) and the LUMOs of 11-I, mass experiments were performed on an Autoflex III
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Smartbeam mass spectrometer (Bruker Daltonics) with 16 H); 0.97 (br. s, 24 H). 13C-NMR (CDCl3/CS2 1:1):
1,1,4,4-tetraphenyl-1,3-butadiene (TPB) as the matrix in 148.58 (8 C); 148.02 (4 C); 145.85 (4 C); 145.28 (4 C);
both positive and negative ion modes. Absorption 145.19 (4 C); 144.96 (2 C); 144.73 (4 C); 144.70 (2 C);
spectra were measured using a UV-3150 spectropho- 144.32 (4 C); 143.97 (4 C); 143.06 (4 C); 143.01 (4 C);
tometer (Shimadzu Corp.). IR Spectra were obtained by 142.84 (2 C); 142.21 (4 C); 142.14 (4 C); 140.42 (4 C);
an FT-730 spectrometer (HORIBA, Ltd.). Cyclic voltam- 139.22 (4 C); 138.40 (4 C); 129.99 (4 C); 126.38 (8 C);
mograms and differential pulse voltammograms were 80.96 (2 C); 51.62 (1 C); 30.48 (8 C); 15.13 (8 C). MALDI-
recorded on a BAS CV50W electrochemical analyzer TOF MS (TPB): 1474 (M+), 720 (C60+).
(BAS Inc.). The reference electrode was a saturated
calomel reference electrode (SCE). The glassy carbon
Synthesis of 13. The procedure was similar to that
electrode was used as the working electrode, and a for 11. A solution containing 6 prepared from 5[48]
platinum wire was used as the counter electrode. All (200 mg, 0.49 mmol) in benzene (4 ml) was added to a
potentials are referenced to the ferrocene/ferrocenium benzene solution of Sc3N@Ih-C80 (0.6 mg, 5.4×
couple (Fc/Fc+) as the standard. (Bu)4NPF6 (0.1 M) in 10À 4 mmol) and CS2 (0.4 ml), and stirred for 12 h under
ODCB was used as the supporting electrolyte solution. an argon atmosphere in the dark. Preparative HPLC
The cyclic voltammograms were recorded using a scan separation of the mixture with a Buckyprep-M column
rate of 50 mV/s. The differential pulse voltammograms (ϕ 10×250 mm) afforded 11 in 36% yield. Vis/NIR
were obtained using a pulse amplitude of 50 mV, a (CS2): 750. IR (KBr) 1026. 1H-NMR (CDCl3/CS2 1:1): 6.76–
pulse width of 50 ms, a pulse period of 200 ms, and a 6.46 (m, 8 H); 3.08–2.58 (m, 24 H); 2.34–2.14 (m, 12 H).
scan rate of 50 mV/s.
13C-NMR (CDCl3/CS2 1:1): 153.04 (2 C); 151.96 (2 C);
149.86 (2 C); 147.84 (8 C); 146.81 (2 C); 146.77 (2 C);
Synthesis of 11. A solution of 5[48] (400 mg, 146.56 (2 C); 144.97 (2 C); 144.82 (2 C); 144.80 (2 C);
0.97 mmol) in benzene (3 ml) in a quartz tube was 144.48 (2 C); 144.20 (1 C); 144.10 (1 C); 143.86 (4 C);
degassed using freeze-pump-thaw cycles under re- 143.59 (2 C); 143.25 (2 C); 142.99 (2 C); 142.57 (4 C);
duced pressure, and irradiated by a 125 W low- 142.32 (1 C); 141.53 (2 C); 141.22 (2 C); 140.97 (2 C);
pressure mercury lamp for 20 h. Subsequently, the 140.89 (2 C); 140.23 (4 C); 140.03 (4 C); 139.78 (4 C);
resultant solution containing 6 was added to a 139.36 (2 C); 139.15 (1 C); 138.93 (2 C); 138.82 (2 C);
benzene solution of C60 (10 mg, 1.4×10À 2 mmol) and 138.75 (2 C); 137.67 (2 C); 135.36 (2 C); 135.20 (2 C);
CS2 (0.8 ml) under an argon atmosphere in the dark. 134.63 (1 C); 134.33 (2 C); 130.84 (4 C); 130.45 (8 C);
After stirring the solution for 12 h, preparative HPLC 128.91 (2 C); 128.41 (1 C); 98.45 (1 C); 97.75 (1 C); 56.11
separation of the reaction mixture with a 5PBB column (1 C); 27.12 (4 C); 25.38 (8 C). MALDI-TOF MS (TPB):
(ϕ 10×250 mm) afforded 11 in 36% yield. UV/Vis 1717 (MÀ ), 1109 (Sc3N@Ih-C80À ).
(CS2): 430. IR (KBr) 1026. 1H-NMR (CDCl3/CS2 1:1):
6.78–6.56 (m, 8 H); 2.75–2.41 (br. s, 12 H); 2.33–2.01
Synthesis of 14. The procedure was similar to that
(m, 24 H). 13C-NMR (CDCl3/CS2 1:1): 148.13 (4 C); for 12. A toluene solution (25 ml) of 8a[49] (75.0 mg,
147.52 (4 C); 145.90 (8 C); 145.29 (4 C); 145.21 (4 C); 8.0×10À 2 mmol),
Sc3N@Ih-C80
(3.0 mg,
2.7×
144.95 (2 C); 144.84 (4 C); 144.73 (6 C); 144.33 (4 C); 10À 3 mmol), and CS2 (6.0 ml) in a Pyrex tube was
143.95 (4 C); 143.03 (4 C); 142.99 (4 C); 142.84 (2 C); degassed using freeze-pump-thaw cycles under re-
142.25 (4 C); 142.19 (4 C); 140.20 (4 C); 139.63 (8 C); duced pressure, and irradiated by a 125 W medium-
130.43 (8 C); 80.14 (2 C); 50.83 (1 C); 27.30 (4 C); 25.14 pressure mercury lamp for 2 h. Preparative HPLC
(8 C). MALDI-TOF MS (TPB): 1329 (MÀ ), 720 (C60À ).
separation of the reaction mixture with a 5PBB column
(ϕ 10×250 mm) afforded 14 in 59% yield. Vis/NIR
Synthesis of 12. A toluene solution (25 ml) of 8b[50] (CS2): 742. IR (KBr) 1020. 1H-NMR (CDCl3/CS2 1:1):
(99.0 mg, 9.7×10À 2 mmol), C60 (10.0 mg, 1.4× 6.78–6.75 (m, 8 H); 2.43–2.34 (m, 24 H); 2.24 (s, 6 H);
10À 2 mmol), and CS2 (3.2 ml) in a Pyrex tube was 2.22 (s, 6 H). 13C-NMR (CDCl3/CS2 1:1): 152.96 (2 C);
degassed using freeze-pump-thaw cycles under re- 151.88 (2 C); 150.57 (2 C); 150.36 (2 C); 149.80 (2 C);
duced pressure, and irradiated by a 125 W medium- 147.92 (2 C); 146.80 (2 C); 146.69 (2 C); 146.48 (2 C);
pressure mercury lamp for 2.5 h. Preparative HPLC 145.88 (1 C); 145.06 (1 C); 144.98 (2 C); 144.81 (2 C);
separation of the reaction mixture with a 5PBB column 144.73 (2 C); 144.45 (2 C); 144.18 (1 C); 143.81 (2 C);
(ϕ 10×250 mm) afforded 12 in 22% yield. UV/Vis 143.53 (2 C); 143.28-142.93 (4 C); 142.87 (2 C); 142.56
1
(CS2): 437. IR (KBr) 1072. H-NMR (CDCl3/CS2 1:1): 7.23 (2 C); 142.46 (2 C); 141.49 (2 C); 141.19 (2 C); 140.92
(t, J=7.5, 4 H); 7.05 (d, J=7.5, 8 H); 3.19–2.71 (br. s, (4 C); 140.88 (2 C); 140.10 (2 C); 140.08 (2 C); 139.67
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[5] X. Lu, L. Feng, T. Akasaka, S. Nagase, ‘Current status and
(2 C); 139.54 (2 C); 139.36 (2 C); 139.23 (1 C); 139.03
(1 C); 138.82 (2 C); 137.71 (2 C); 135.46 (1 C); 135.28
(4 C); 134.69 (2 C); 134.42 (2 C); 133.95 (2 C);132.54
(4 C); 130.14 (4 C); 129.96 (4 C); 123.88 (1 C); 122.10
(1 C); 56.82 (1 C); 25.22-24.67 (8 C); 21.17-20.91 (4 C).
MALDI-TOF MS (TPB): 1804–1812 (M+), 1109 (Sc3N@Ih-
C80+).
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Computational Method
All calculations were conducted using the
Gaussian09[56] program. Optimized structures were
obtained at the B3LYP[51–53] and the M06-2X[54] level of
theory using basis sets of 6-31G(d)[57] [C, H, N, Si, S],
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Acknowledgements
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Endohedral Metallofullerenes with Reactive Silicon and
Germanium Compounds’, Molecules 2017, 22, 1179–1195.
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This work was supported by a Grant-in-Aid for
Scientific Research on Innovative Areas (No. 20108001,
‘pi-Space’), Grants-in-Aid for Scientific Research (A)
(No. 202455006), (B) (No. 24350019), (C) (No.
17K05797), and a Grant for Specially Promoted
Research (No. 22000009) from the Ministry of Educa-
tion, Culture, Sports, Science, and Technology of
Japan.
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C. J. Chancellor, M. M. Olmstead, A. Rodríguez-Fortea, J. P.
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Author Contribution Statement
M. K. and T. A. designed this project. M. K. planned the
experimental work, and performed the computational
calculations. Y. A. and S. K. conducted the experimental
work. M. Y. and Y. M. carried out the analysis of the
compounds. M. K., M. F., and T. A. contributed to the
writing of the manuscript.
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H. Azurmendi, C. Wang, K. Harich, H. C. Dorn, H. W. Gibson,
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Received February 23, 2019
Accepted March 28, 2019
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