Synthesis of Fullerene-Fluorene Dyads through the Platinum-Catalyzed Reactions of [60]Fullerene with 9-Ethynyl-9 H-fluoren-9-yl Carboxylates

Article abstract of DOI:10.1021/acs.joc.9b00932

The single-step regio- and stereoselective platinum-catalyzed reactions of [60]fullerene with a series of 9-ethynyl-9H-fluoren-9-yl carboxylates afforded fullerene-fluorene dyads in their [2 + 2] cycloaddition forms. The presented reactions represent the

Full text of DOI:10.1021/acs.joc.9b00932

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Article
Synthesis of Fullerene–Fluorene Dyads through the Platinum-Catalyzed
Reactions of [60]Fullerene with 9-Ethynyl-9H-fluoren-9-yl Carboxylates
Michio Yamada, Mayu Takizawa, Yoko Nukatani, Mitsuaki Suzuki, and Yutaka Maeda
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00932 • Publication Date (Web): 17 Jun 2019
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Synthesis of Fullerene–Fluorene Dyads through the Platinum-Catalyzed Reactions of [60]Fullerene with 9-
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Ethynyl-9H-fluoren-9-yl Carboxylates
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Michio Yamada,*,† Mayu Takizawa,† Yoko Nukatani,† Mitsuaki Suzuki,‡ and Yutaka Maeda†
†Department of Chemistry, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan
‡Department of Chemistry, Josai University, Sakado, Saitama 350-0295, Japan
ABSTRACT
The single-step regio- and stereoselective platinum-catalyzed reactions of [60]fullerene with a series of 9-ethynyl-
9H-fluoren-9-yl carboxylates afforded fullerene–fluorene dyads in their [2+2] cycloaddition forms. The presented
reactions represent the first examples of the use of easily accessible fluorenyl carboxylates as fluorenylideneallene
precursors. In addition, the single-crystal X-ray structure of one of the dyads reveals a distorted cyclobutane ring.
Furthermore, the dyad forms a layered structure with close-packed arrays of C60 spheres in its crystals.
INTRODUCTION
Allenes are recognized as valuable precursors to a number of products in modern synthetic chemistry owing to
their abilities to undergo a variety of skeletal transformations.1 In particular, allene unsaturation, which is spread over
three carbon atoms, provides powerful access to carbo- and heterocycles through tandem or multistep reactions.2 In
addition, allenes have been used in a wide range of asymmetric catalytic and natural-product syntheses because they
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provide axially chiral scaffolds when appropriately substituted.3,4 Notably, allenes can be used to functionalize
fullerene, which has been a fascinating research topic in materials chemistry.5,6,7,8 The chemical reactivities, as well
as the electronic and optical properties of allenes can be tuned through the incorporation of substituents.
Fluorenylideneallenes have been reported to be highly reactive and to easily dimerize to form isomeric mixtures of
cyclobutanes even at low temperature.9,10 Therefore, fluorenylideneallenes have rarely been explored for synthetic
chemistry applications. Mcglinchey et al. developed a new synthetic route to tetracenes through the dimerization of
fluorenylideneallenes,9b while Alcarazo and coworkers reported the synthesis of organic frustrated Lewis pairs by
the reactions of fluorenylideneallenes with N-heterocyclic carbenes.11
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Recently, we demonstrated that transition-metal-catalyzed reactions of [60]fullerene (C60) and propargylic esters
yielded formal [2+2] cycloadducts (alkylidenecyclobutane-annulated fullerenes)12 and [4+2] cycloadducts
(cyclohexene-annulated fullerenes) in reasonable yields.8 We found that the choice of metal catalyst had a profound
effect on the outcome of the reaction; formal [2+2] cycloadducts were dominantly formed when CuCl was used, and
[4+2] cycloadducts were dominantly formed when AgOCOCF3 was loaded as the catalyst. In that case, the formal
[2+2] cycloadditions are likely to involve the formation of allene intermediates through 6-endo-dig cyclization
reactions aided by the transition-metal catalyst. This achievement motivated us to explore the reactivities of
fluorenylideneallenes with fullerenes by examining the reactions of C60 with 9-ethynyl-9H-fluoren-9-yl carboxylates.
We envisaged that treatment of these carboxylates with a transition metal catalyst would readily generate
fluorenylideneallene intermediates in-situ, and that these intermediates would be trapped by C60 to yield novel
fullerene–fluorene dyads in one step. In related work, Galloni, Gatto, and their coworkers reported the synthesis of
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two fullerene–fluorene dyads with different position linkage of the fluorene group by the Prato reaction, and revealed
that the ground and excited state properties of the molecules were modulated by changing the position of the fluorene
chromophore.13 The formation of [4+2] cycloadducts is prohibited in the proposed scheme because the introduction
of the fluorenylidene structure excludes the formation of 1,3-dienyl ester intermediates that facilitate the formal [4+2]
cycloaddition with C60. In this work, we found that the platinum-catalyzed reactions of C60 with the above-mentioned
carboxylates afforded the corresponding fullerene–fluorene dyads in their [2+2] cycloaddition forms in reasonable
yields and with high regio- and stereoselectivities, as described below.
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RESULTS AND DISCUSSION
The syntheses of the 9-ethynyl-9H-fluoren-9-yl carboxylates 2 and the fullerene–fluorene dyads 3 are summarized
in Scheme 1 and Table 1. These carboxylates were appended with different substituents (R1) on the acetylenic
terminal in order to investigate the substituent dependence of these reactions, while long alkyl chains were
incorporated into 2a–2c for solubility reasons. In a typical procedure, a mixture of C60 and 2 (6.0 equiv. based on
C60) in toluene was treated with a catalytic amount of PtCl2 (0.3 equiv. based on C60) at 80 ºC for 4–6 h. The reaction
was monitored by TLC and HPLC. The dyads were purified and isolated by silica-gel flash chromatography and, if
necessary, subsequent preparative HPLC using a Buckyprep column. The HPLC profiles of the reaction mixtures
provided contrasting features compared to those of 2a–2c (Figure S4). In the reaction of C60 with 2a, two fullerene
derivatives, Z-3a and E-3a, were obtained in yields of 3% and 25%, respectively (Table 1, entry 1). Notably, the
reactions of C60 with 2b or 2c gave Z-3b (45%) or Z-3c (12%) as the sole dyad (Table 1, entries 3 and 5). Increasing
the amount of 2c (12 equiv. based on C60) in the reaction with C60 had no beneficial effect on the yield of Z-3c (Table
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1, entry 6). In addition to dyads 3, a complex mixture of non-fullerene products was predominantly formed in the
reaction of C60 with 2b or 2c (see Figure S4). Although the separation and full characterization of such non-fullerene
products were difficult, they are likely to be isomeric mixtures of cyclobutanes formed by dimerization of in-situ
generated fluorenylideneallene intermediates (see Figure 1). The formation of these dimers was suggested by the
MALDI-TOF mass spectrometry (see Figure S8). Using CuCl as a catalyst instead of PtCl2 in the reactions of C60
with 2a–2c afforded none of the desired product; both the carboxylates and C60 were scarcely consumed after heating
at 80 ºC for 4 h (Table 1, entries 2, 4, and 7).
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Scheme 1. Synthesis of 9-ethynyl-9H-fluoren-9-yl carboxylates 2a–2c and fullerene–fluorene dyads E/Z-3.
a) i) n-BuLi, trimethylsilylacetylene, Et2O, ii) K2CO3, THF, MeOH; 52% (1a). b) n-BuLi, 1-hexyne or 1-n-
butyl-4-ethynylbenzene, THF, then NH4Cl/H2O; 79% (1b), 93% (1c). c) n-octanoyl chloride, N,N-dimethyl-4-
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aminopyridine (DMAP), Et3N, CH2Cl2; 97% (2a). d) Ac2O, pyridine, K2CO3; 99% (2b), 87% (2c). e) C60,
catalyst, toluene. Yields are summarized in Table 1.
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Table 1. Transition-Metal-Catalyzed Reaction of C60 with 2
Entry
2
Catalyst Molar ratioa
Yieldb of Z-3
3% (3%)
0%
Yieldb of E-3
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PtCl2
CuCl
PtCl2
CuCl
PtCl2
PtCl2
CuCl
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6 : 1 : 0.3
6 : 1 : 0.3
6 : 1 : 0.3
6 : 1 : 0.3
12 : 1 : 0.3
6 : 1 : 0.3
25%( 29%)
0%
45% (67%)
0%
0%
0%
12% (67%)
11% (61%)
0%
0%
0%
0%
aMolar ratio refers to [2]:[C60]:[catalyst].
bYield of isolated product. The values in parentheses are conversion yields based on the amount of C60 consumed.
Dyads Z-3a, E-3a, Z-3b, and Z-3c were characterized by MALDI-TOF mass spectrometry as well as by absorption
and IR spectroscopy. The MALDI-TOF mass spectrum of each dyad exhibits the corresponding parent peak (see
Figure S7). However, the relative intensity of the parent peak was very weak in each case; instead, a strong fragment
peak due to the C60 cage was observed, which corresponds to the loss of the entire addend. These results suggest that
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the retro-cycloaddition takes place easily during mass spectrometry. The absorption spectra of dyads Z-3a, E-3a, Z-
3b, and Z-3c exhibit features characteristic of [6,6]-closed addition forms (see Figure S9). The 1H NMR spectra of
Z-3a and E-3a reveal that both dyads have Cs symmetry based on the pairwise equivalency of the fluorene aromatic
protons, which indicates the formation of the ,-cycloaddition product. In this context, we note that ,-
cycloaddition leads to C1 symmetric products (i.e., ,-cycloadduct 4) as shown in Figure 1. The vinylcarbenoid
addition to form a cyclopropanated derivative is also a possible pathway (see Scheme 2). The cyclopropane structure,
which must have C1 symmetry, was also excluded based on the molecular symmetry. The 13C NMR spectra of both
Z-3a and E-3a show 30 peaks in the ~137–153 ppm range, which are due to the sp2 carbon atoms of the C60 skeleton
and the fluorene core, and are consistent with structures of Cs symmetry.
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Figure 1. Structures of the fluorenylideneallene intermediates and the ,-cycloadducts.
The 1H NMR chemical shifts of the fluorene skeletons of Z-3a and E-3a are almost identical. On the other hand,
the chemical shifts of the olefinic protons in Z-3a (7.66 ppm) and E-3a (8.10 ppm) are quite different; this difference
is most likely due to the distance between the olefinic proton atom and the fullerene surface. In the E-,-cycloadduct,
the olefinic proton is more affected by the ring current of the fullerene surface because of its close proximity. On the
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other hand, the olefinic proton in the Z-,-cycloadduct is more distant from the fullerene surface. Therefore, Z-3a
and E-3a are assigned to be the Z-,- and E-,-cycloadducts, respectively. The observed 1H NMR chemical shifts
are also in good agreement with the chemical shifts calculated for model compounds Z-3d and E-3d (R1 = H, R2 =
CH3) at the GIAO14-B3LYP/6-31G(d) level of theory using the B3LYP/6-31G(d) optimized geometries (see Figures
S13 and S14).15 In addition, the E-3a geometry was assigned on the basis of NOESY NMR spectroscopy, in which
correlations between the octanoyl group and the fluorene moiety are clearly observed (see Figure S34). Similarly,
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the H and 13C NMR spectra of Z-3b and Z-3c are also consistent with Cs symmetry. In addition, the geometrical
assignments of both Z-3b and Z-3c were provided by NOESY spectroscopy in which the required correlations
between the butyl or butylphenyl groups and the fluorene moieties are clearly observed.
The detailed structure of Z-3b was revealed by single-crystal X-ray diffractometry (see Figure 2), which confirmed
the Z-,-cycloaddition form of Z-3b. Black plate crystals of the compound suitable for data collection were obtained
by gradual diffusion of n-hexane into a solution of Z-3b in CS2/n-hexane. The ORTEP drawing shown in Figure 2
represent the first example of an X-ray crystallographic study of an alkylidenecyclobutane-annulated fullerene. In
fact, known examples of crystallographically identified C60-based [2+2] cycloadducts are limited.16 The
alkylidenecyclobutane moiety is distorted: C1–C2 (1.609 Å), C2–C61 (1.521 Å), C61–C62 (1.528 Å), C1–C62
(1.616 Å), C61–C75 (1.322 Å), C2-C61-C62 (95.80º), C61-C62-C1 (87.30º), C62-C1-C2 (89.06º), and C1-C2-C61
(87.80º). The distortion seems to arise through angle strain at the C61 sp2 hybridized carbon. The fullerene C(sp3)–
C(sp3) bond length in Z-3b (i.e., C1–C2 in Figure 2a) is similar to those reported for methanofullerenes (1.57–
1.61Å)17 and Diels–Alder adducts (1.59–1.62 Å).18 The packing structure reveals that Z-3b forms layers parallel to
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the ab plane in which layers of C60 moieties alternate with layers of addends along the c axis. In fact, the plane of the
crystal plates is in accordance with the ab plane (see Figure S1). Within a layer, each C60 moiety is in close contact
(~3.36 Å) with six other C60 moieties, which constitutes a close-packed array of spheres. Such molecular packing of
two-dimensional crystalline ordering may be valuable in bulk heterojunction polymer solar cell applications.19
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(a)
(b)
(c)
b
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C75
C62
C1
C61
C2
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Figure 2. (a) ORTEP drawing of Z-3b with thermal ellipsoids shown at the 50% probability level; the
disordered n-butyl moiety is omitted for clarity. (b) Packing structure in which the fullerene cages are
highlighted in light blue. (c) Two orthogonal views of a single layer of fullerene spheres.
To assess the thermal stabilities of these dyads, they were heated at elevated temperatures and monitored for
changes by HPLC. When the dyads were heated at 80 ºC for 1 h in toluene, they did not decompose (Figure S11).
Retro-cycloaddition dominated at 110 ºC and C60 was the major product after 1 h, indicating that the decomposition
pathway dominates in all cases (Figure S12). As for Z-3a, a small amount of E-3a was observed in addition to C60
produced by the retro-cycloaddition process. Similarly, a small amount of Z-3a was formed in addition to C60 when
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a toluene solution of E-3a was heated at 110 ºC. As for Z-3b and Z-3c, heating at 110 ºC for 1 h resulted in retro-
cycloaddition to give C60, while no other isomers, such as E-3b or E-3c, were detected. In this context, we conclude
that the products decompose negligibly during the presented PtCl2-catalyzed reactions of C60 with 2a–2c.
To gain insights into the selectivities, we computed the relative energies of possible structurally isomeric formal
[2+2] cycloadducts, as summarized in Figure 3. The ,-cycloadduct was calculated to be thermodynamically most
stable when R1 = H, while the Z- and E-,-cycloadducts are respectively 5.61 and 5.92 kcal mol–1 higher in energy
than the ,-cycloadduct. Given that the corresponding ,-cycloadducts were not observed experimentally, it is
reasonable to conclude that the ,-cycloaddition is a thermodynamically disfavored but kinetically favored process
when R1 = H. Meanwhile, the energy difference between the ,-cycloadduct and the E/Z-,-cycloadducts is very
small (< 0.50 kcal mol–1) when R1 = CH3. Furthermore, the E/Z-,-cycloadducts are more stable than the ,-
cycloadduct when R1 = Ph; notably, the Z-,-cycloadduct is 4.19 kcal mol–1 lower in energy than the ,-
cycloadduct. These results suggest that substituent R1 plays an important role in determining the relative energies of
these isomers; an alkyl or an aryl group leads to ,-cycloaddition thermodynamically favored over ,-cycloaddition.
The calculations also suggest that the Z-isomers are more stable than the E-isomers, regardless of the substituent on
the ,-cycloadduct. On the one hand, the mechanism of the intramolecular [2+2] cycloaddition has been an important
topic in allene chemistry, in which most examples have been explained by a stepwise diradical mechanism.11 It is
also noteworthy that transition metals can catalyze the [2+2] cycloadditions of allenes.20 Further information on the
reaction mechanism involved in the formation of the [2+2] cycloadducts presented herein is lacking; however, we
deem that the preferential formation of the ,-cycloadducts rather than the ,-cycloadducts may be governed by
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the favorable localization of either spin or charge over the fluorene moieties in the corresponding singly-bonded
intermediates (see Figure S3).21,22 In related work, Ryu et al. reported that PtCl2 catalyzes the reactions of propargylic
esters bearing phenylacetylene moieties but devoid of fluorene moieties (i.e., 1,3-diphenylprop-2-yn-1-yl pivalate
and 1-phenylhept-1-yn-3-yl pivalate) to give the corresponding ,-cycloadducts.7 Therefore, we conclude that the
reactivities of fluorenylideneallenes toward C60 is different from those of other allenol esters. The preferential
transformation of the E-,-cycloadduct into the Z-,-cycloadduct in the reaction of C60 with 2a is possibly due to
steric repulsion between the acetoxy group and the fullerene surface.
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Figure 3. Schematic structures and B3LYP/6-31G(d)+ZPVE-calculated relative energies (kcal mol–1) of
possible structural isomers of the formal [2+2] cycloadduct, where R2 = CH3.
It is also noteworthy that the presented reactivities of the 9-ethynyl-9H-fluoren-9-yl carboxylates toward C60 and
furans are different. Ohe et al. reported that 9-ethynyl-9H-fluoren-9-yl carboxylates react with furans in the presence
of PtCl2 in toluene at 50 ºC to give 9-acyloxy-9-ethynylfluorene derivatives in excellent yields.23 In that case, PtCl2
activates the alkyne to generate an electrophilic vinylcarbenenoid24 through a 5-exo-dig-mode 1,2-acyloxy migration,
and the resulting vinylcarbenoid promotes the subsequent ring-opening of the furan. These contrastive results suggest
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that the in-situ generated vinylcarbenenoids and fluorenylideneallenes are interconvertible in such systems and that
these interconversions take place through double 1,2-acyloxy migrations and/or combinations of 6-endo-dig-mode
1,3-acyloxy migrations and 5-exo-dig-mode 1,2-acyloxy migrations, as shown in Scheme 2. Known examples of
metal carbene complexes that exhibit reactivity toward C60 are limited.25,26
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Scheme 2. Proposed mechanism for the skeletal transformation of a 9-ethynyl-9H-fluoren-9-yl carboxylate.
Electronic properties were electrochemically characterized in 1,2-dichlorobenzene (1,2-DCB) containing 0.1 M
(n-Bu)4NPF6 (see Figure S15). The reduction potentials of dyads 3 and related compounds, such as ,-cycloadducts
27
4e and 4f as well as C60 reported previously, are summarized in Table 2. The fullerene–fluorene dyads exhibit
similar reversible reduction properties to those of other alkylidenecyclobutane-annulated fullerenes devoid of
fluorene moieties,8 suggesting that electronic interactions between the fullerene cores and the fluorene moieties are
very weak.
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Table 2. Reduction Potentialsa (V vs. Fc/Fc+) of Dyads 3 and Related Compounds
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Compound
E-3a
Z-3b
Z-3c
redE1
–1.25
–1.20
–1.17
–1.20
–1.23
–1.13
redE2
–1.62
–1.59
–1.56
–1.58
–1.63
–1.50
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4eb
4fb
c
C60
aDetermined using CV. bRef. 8. cRef.27.
CONCLUSIONS
In conclusion, we functionalized C60 with 9-ethynyl-9H-fluoren-9-yl carboxylates through platinum catalysis.
These transformations represent the first examples of the use of these carboxylates as fluorenylideneallene precursors.
,-Cycloaddition proceeded smoothly to afford novel fullerene–fluorene dyads through formal [2+2] cycloadditions
involving in-situ generated fluorenylideneallene intermediates. Acetylene-capped carboxylates 2b and 2c displayed
uniform regio- and stereoselectivities in their cycloadditions to C60. The structure of dyad Z-3b was unambiguously
elucidated by X-ray crystallography, which revealed that the adducts formed layered structures containing close-
packed arrays of C60 spheres. This study demonstrated that these carboxylates undergo a variety of skeletal
transformations that serve as powerful methods for the functionalization of fullerenes, yielding new structural motifs
such as fullerene–polyarene dyads. We expect that the presented reaction is applicable to other polyarenes, such as
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indenofluorenes and sumanene.
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EXPERIMENTAL SECTION
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Reagents and solvents were purchased as reagent grade from commercial suppliers and used as received unless
otherwise noted. Diethyl ether (Et2O) and dichloromethane (CH2Cl2) were distilled over CaH2. 1,2-Dichlorobenzene
(1,2-DCB) was freshly distilled from CaH2. Dehydrated tetrahydrofuran (THF) and toluene were purchased as Super
plus grade from Kanto Kagaku and purified with a Glass Contour Solvent Dispensing System (Nikko Hansen & Co.,
Ltd.). All reactions were performed under an inert atmosphere by applying a positive pressure of argon unless
otherwise stated. A personal organic synthesizer equipped with aliminum heating block units (ChemiStation PPV;
EYELA) was used for reactions that require heating. When basification of silica gel was required for TLC analysis
and column chromatography, the following amine-pretreatment was conducted prior to use: Silica gel 60 (particle
size 0.040–0.050 mm, Kanto Chemical) or TLC plates (aluminum sheets coated with silica gel 60 F254 obtained from
Merck) was immersed in n-hexane containing ca. 10vol% triethylamine and stand at room temperature over night.
The amine-treated silica gel was packed in a column and washed with eluents for separation, or, the amine-treated
TLC plates were taken out and was air-dried before use. Analytical high-performance column chromatography
(HPLC) was run on a JASCO chromNAVI system equipped with a JASCO LC-Net II interface, a JASCO PU-2080
pump, a JASCO UV-2075plus UV-detector (330 nm) and a Buckyprep column (Nacalai Tesque; 40ºC in a column
oven JASCO CO-2060plus) at flow rate of 1.0 mL min–1 with eluent of toluene unless otherwise stated. Preparative
HPLC was performed using a chromatograph (LC-918; Japan Analytical Industry Co.) that was monitored using UV
absorption at 330 nm. 1D and 2D NMR spectra were measured on a JEOL JNM-ECX400P spectrometer (400 MHz)
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at room temperature unless otherwise stated. Chemical shifts  are given in ppm relative to tetramethylsilane (TMS)
and were referenced to internal TMS or residual non-deuterated solvent for 1H and 13C NMR spectra. Infrared spectra
(IR) were recorded on a JASCO FT/IR4100 spectrometer equipped with a diamond ATR unit. Absorption spectra
were recorded on a JASCO V670 spectrophotometer. MALDI-TOF mass spectra were measured on a Bruker
Daltonics autoflex III smartbeam with 1,1,4,4-tetraphenylbuta-1,3-diene (TPB) as the matrix. Isotope distribution
patterns were simulated using ChemCalc.28 Electrochemical measurements were performed using an ALS
electrochemical analyzer (model 630DT; BAS). A platinum disc and a platinum wire were used as the working
electrode and the counter electrode, respectively. The reference electrode was a saturated calomel reference electrode
(SCE). Analytes were dissolved in 1,2-DCB with (n-Bu)4NPF6 (0.1 M). They were deaerated using freeze–pump–
thaw cycles under reduced pressures. The measurement settings were as follows: scan rate = 20 mV s–1 for cyclic
voltammetry (CV) measurements and pulse amplitude = 50 mV, pulse width = 200 msec, pulse period = 500 msec
for differential pulse voltammetry (DPV) measurements. All potentials are referenced to the ferrocene/ferrocenium
couple (Fc/Fc+) as the standard. DFT calculations including zero-point vibration energy (ZPVE) correction were
performed using Gaussian 09 (Rev. D.01)29 at the B3LYP/-31G(d)30 level of theory.
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Synthesis of Substrates
9-Ethynyl-9H-fluoren-9-ol (1a). The title compound 1a was prepared according to a literature procedure.31
Trimethylsilylacetylene (1.3 mL, 9.4 mmol) was dissolved in Et2O (10 mL) in an oven-dried two-necked round
bottom flask. The solution was cooled to –10 ºC and n-BuLi (1.6 M in n-hexane, 8.0 mL, 12.8 mmol) was added
dropwise using a syringe, after which the solution was stirred for 1 h. 9H-Fluoren-9-one (1.99 g, 11.0 mmol) was
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dissolved in Et2O (15 mL) in a separate flask and cooled to –10 ºC. The 9H-fluoren-9-one solution was then added
to the trimethylsilylacetylene/n-BuLi solution by syringe. The mixture was warmed to room temperature and stirred
overnight, after which it was diluted with water (30 mL) and extracted with Et2O (3  20 mL). The combined organic
layers were dried over MgSO4. The solution was concentrated under reduced pressure and the residue was
recrystallized from CH2Cl2/n-hexane to afford crude 9-(trimethylsilyl)ethynyl-9H-fluoren-9-ol (2.17 g) as pale
yellow crystals. The crude mixture (2.17 g) and K2CO3 (6.51 g, 47.1 mmol) were dissolved in a mixture of THF (35
mL) and methanol (35 mL) and stirred overnight at room temperature. Water (20 mL) was added to the mixture, after
which was extracted with EtOAc (2  30 mL). The combined organic layers were dried over MgSO4 and the solvent
was removed under reduced pressure. The residue was purified by silica-gel flash chromatography (SiO2; EtOAc/n-
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1
hexane 1:3) to afford 1a (1.17 g, 52%). White solid; Rf = 0.28 (SiO2; EtOAc/n-hexane 1:3); H NMR (400 MHz,
CDCl3):  2.48 (s, 3H; CH3), 2.62 (brs, 1H; OH), 7.36 (dd, J = 7.6, 1.2 Hz, 2H; Ar-H), 7.41 (dd, J = 7.6, 1.2 Hz, 2H;
Ar-H), 7.60–7.64 (m, 2H; Ar-H), 7.69–7.73 (m, 2H; Ar-H) ppm; 13C{1H} NMR (100 MHz, CDCl3):  71.5, 74.5,
83.9, 120.2, 124.3, 128.6, 129.8, 139.1, 146.6 ppm. The NMR data are in accord with the literature values.
9-(Hex-1-yn-1-yl)-9H-fluoren-9-ol (1b). The title compound 1b was prepared according to a literature procedure.32
1-Hexyne (1.3 mL, 11.4 mmol) was dissolved in THF (40 mL) in an oven-dried two-necked round bottom flask. The
solution was cooled to –78 ºC and n-BuLi (1.6 M in n-hexane, 7.8 mL, 12.0 mmol) was added dropwise using a
syringe. The solution was stirred for 0.5 h. To the flask was added 9H-fluoren-9-one (1.50 g, 8.35 mmol) in THF (10
mL) dropwise by syringe. The mixture was warmed to room temperature and stirred overnight, after which it was
quenched with saturated aqueous NH4Cl (280 mL) and extracted with EtOAc (3  30 mL). The combined organic
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layers were washed with saturated aqueous NH4Cl (30 mL) and brine (30 mL), and dried over MgSO4. The solvent
was removed under reduced pressure and the residue was purified by silica-gel flash chromatography (SiO2;
EtOAc/n-hexane 1:6) to afford 1b (1.74 g, 79%). Yellow oil; Rf = 0.23 (SiO2; EtOAc/n-hexane 1:6); 1H NMR (400
MHz, CDCl3):  0.88 (t, J = 7.2 Hz, 3H; CH3), 1.32–1.43 (m, 2H; CH2), 1.43–1.53 (m, 2H; CH2), 2.21 (t, J = 7.2 Hz,
2H), 2.49 (brs, 1H; OH), 7.34 (dd, J = 7.6, 1.2 Hz, 2H; Ar-H), 7.38 (dd, J = 7.6, 1.2 Hz, 2H; Ar-H), 7.59–7.63 (m,
2H; Ar-H), 7.67–7.71 (m, 2H; Ar-H) ppm; 13C{1H} NMR (100 MHz, CDCl3):  13.7, 18.7, 22.1, 30.7, 75.1, 80.0,
84.5, 120.3, 124.3, 128.6, 129.6, 139.1, 147.8 ppm. The NMR data are in accord with the literature values.
9-((4-n-Butylphenyl)ethynyl)-9H-fluoren-9-ol (1c). 1-n-Butyl-4-ethynylbenzene (2.0 mL, 11.4 mmol) was
dissolved in THF (40 mL) in an oven-dried two-necked round bottom flask. The solution was cooled to –78 ºC and
n-BuLi (1.6 M in n-hexane, 7.8 mL, 12.0 mmol) was added dropwise using a syringe, after which the solution was
stirred for 0.5 h. To the flask was added 9H-fluoren-9-one (1.51 g, 8.37 mmol) in THF (10 mL) dropwise by syringe.
The mixture was warmed to room temperature and stirred overnight, after which it was quenched with saturated
aqueous NH4Cl (60 mL) and extracted with EtOAc (3  20 mL). The combined organic layers were washed with
brine (30 mL) and dried over Na2SO4. The solvent was removed under reduced pressure and the residue was purified
by silica-gel flash chromatography (SiO2; EtOAc/n-hexane 1:4) to afford 1c (2.65 g, 93%). Viscous pale yellow solid;
Rf = 0.30 (SiO2; EtOAc/n-hexane 1:4); m.p. 73–74ºC; 1H NMR (400 MHz, CDCl3):  0.93 (t, J = 7.4 Hz, 3H; CH3),
1.34 (sext, J = 7.4 Hz, 2H; CH2); 1.58 (quint, J = 7.4 Hz, 2H; CH2), 2.59 (t, J = 7.4 Hz, 2H; CH2), 2.75 (brs, 1H;
OH), 7.10 (AA’BB’, J = 8.0 Hz, 2H; Ar-H), 7.34–7.45 (m, 6H; Ar-H), 7.64 (d, J = 7.2 Hz; Ar-H), 7.79 (d, J = 7.2
Hz; Ar-H) ppm; 13C{1H} NMR (100 MHz, CDCl3)  14.0 (CH3), 22.3 (CH2), 33.3 (CH2), 35.5 (CH2), 75.2, 83.4,
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88.4, 119.5, 120.2 (CH), 124.4 (CH), 128.3 (CH), 128.5 (CH), 129.6 (CH), 131.9 (CH), 139.0, 143.6, 147.3 ppm. IR
(ATR): ~ = 3243, 3060, 3025, 2954, 2921, 2852, 2310, 1506, 1448, 1376, 1286, 1269, 1186, 1053, 994, 937, 903,
838, 824, 767, 744, 730, 607 cm–1; HR-ESI-TOF-MS (positive mode): m/z calcd. for C25H22ONa: 361.1568, found:
361.1557 [M+Na]+.
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9-Ethynyl-9H-fluoren-9-yl octanoate (2a). The title compound 2a was prepared according to a slightly modified
literature procedures in which esterification was carried out after desilylation.23 n-Octanoyl chloride (1.2 mL, 7.01
mmol) was slowly added to a solution of 1a (1.17 g, 5.67 mmol) and N,N-dimethyl-4-aminopyridine (DMAP) (16.2
mg, 0.133 mmol) in CH2Cl2 (10 mL) and triethylamine (1.7 mL) at 0 ºC under argon. The mixture was allowed to
warm up to room temperature and stirred for 2 h, after which it was poured into ice water (30 mL). The organic layer
was separated, the aqueous layer was extracted with CH2Cl2 (2  10 mL), and the combined organic layers were dried
over MgSO4. The solvent was removed under reduced pressure and the residue was purified by silica-gel flash
chromatography (amine-treated SiO2: CH2Cl2/n-hexane 1:20) to afford 2a (1.82 g, 97%). Yellow oil; Rf = 0.35
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(amine-treated SiO2; CH2Cl2/n-hexane 1:20); H NMR (400 MHz, CDCl3):  0.89 (t, J = 7.2 Hz, 3H; CH3), 1.20–
1.35 (m, 8H; CH2), 1.58–1.65 (m, 2H; CH2), 2.31 (t, J = 7.6 Hz, 2H; CH2), 2.63 (s, 1H; CH), 7.35 (dd, J = 7.6, 1.2
Hz; Ar-H), 7.43 (dd, J = 7.6, 1.2 Hz; Ar-H), 7.64 (d, J = 7.6 Hz; Ar-H), 7.85 (d, J = 7.6 Hz; Ar-H) ppm; 13C{1H}
NMR (100 MHz, CDCl3):  14.1, 22.6, 24.9, 28.9, 29.0, 31.7, 34.8, 73.8, 78.7, 80.9, 120.1, 125.9, 128.5, 130.1,
140.0, 143.9, 172.1 ppm. The NMR data are in accord with the literature values.
9-(Hex-1-yn-1-yl)-9H-fluoren-9-yl acetate (2b). 1b (0.870 g, 3.32 mmol) was dissolved in pyridine (1.9 mL, 23.5
mmol) and acetic anhydride (3.5 mL, 20.1 mmol) under argon in an oven-dried two-necked round bottom flask. The
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mixture was stirred for 48 h at room temperature, after which it was poured into aqueous K2CO3 (100 mL, 10% w/v)
and extracted with CH2Cl2 (4  20 mL). The combined organic layers were dried over MgSO4. The solvent was
removed under reduced pressure and the residue was purified by silica-gel flash chromatography (amine-treated SiO2;
EtOAc/n-hexane 1:10) to afford 2b (1.00 g, 99%). Viscous pale yellow solid; Rf = 0.38 (amine-treated SiO2;
EtOAc/n-hexane 1:10); m.p. 53–55ºC; 1H NMR (400 MHz, CDCl3):  0.84 (t, J = 7.4 Hz, 3H; CH3), 1.33 (sext, J =
7.4 Hz, 2H; CH2), 1.43 (quint, J = 7.4 Hz, 2H; CH2), 1.96 (s, 3H; CH3), 2.18 (t, J = 7.4 Hz, 2H; CH2), 7.28 (dd, J =
7.6, 0.8 Hz, 2H; Ar-H), 7.33 (dd, J = 7.6, 0.8 Hz, 2H; Ar-H), 7.56 (d, J = 7.6 Hz, 2H; Ar-H), 7.80 (d, J = 7.6 Hz, 2H;
Ar-H) ppm; 13C{1H} NMR (100 MHz, CDCl3):  13.5 (CH3), 18.5 (CH2), 21.7 (CH3), 21.7 (CH2), 30.3 (CH2), 77.0,
79.5, 86.7, 119.9 (CH), 125.7 (CH), 128.2 (CH), 129.6 (CH), 139.6, 144.7, 168.9 (C=O) ppm; IR (ATR): ~ = 3063,
2962, 2930, 2866, 2241, 1740, 1449, 1365, 1317, 1289, 1223, 1174, 1141, 1090, 1013, 974, 927, 768, 757, 733, 682,
640, 603, 567 cm–1; HR-ESI-TOF-MS (positive mode): m/z calcd. for C21H20O2Na: 327.1361, found: 327.1365
[M+Na]+.
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9-((4-n-Butylphenyl)ethynyl)-9H-fluoren-9-yl acetate (2c). 1c (1.02 g, 3.01 mmol) was dissolved in pyridine (1.9
mL, 23.5 mmol) and acetic anhydride (3.5 mL, 20.1 mmol) under argon in an oven-dried two-necked round bottom
flask. The mixture was stirred for 29 h at room temperature, after which it was poured into aqueous K2CO3 (100 mL,
10% w/v) and extracted with CH2Cl2 (4  20 mL). The combined organic layers were dried over Na2SO4. The solvent
was removed under reduced pressure and the residue was purified by silica-gel flash chromatography (amine-treated
SiO2; EtOAc/n-hexane 1:7) to afford 2b (0.999 g, 87%). Viscous pale yellow solid; Rf = 0.38 (amine-treated SiO2;
EtOAc/n-hexane 1:10); m.p. 77–78ºC; 1H NMR (400 MHz, CDCl3):  0.98 (t, J = 7.2 Hz, 3H; CH3), 1.38 (sext, J =
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7.4 Hz, 2H; CH2), 1.62 (quint, J = 7.4 Hz, 2H; CH2), 2.12 (s, 3H; CH3), 2.63 (t, J = 7.4 Hz, 2H; CH2), 7.15 (AA’BB’,
J = 8.0 Hz, 2H; Ar-H), 7.39–7.51 (m, 6H; Ar-H), 7.70 (d, J = 7.2 Hz, 2H; Ar-H), 8.02 (d, J = 7.2 Hz, 2H; Ar-H) ppm;
13C{1H} NMR (100 MHz, CDCl3):  14.0 (CH3), 21.9 (CH3), 22.3 (CH2), 33.3 (CH2), 35.6 (CH2), 79.8, 85.4, 85.8,
119.4, 120.1 (CH), 126.0 (CH), 128.3 (CH), 128.4 (CH), 129.9 (CH), 132.0 (CH), 139.9, 143.8, 144.4, 169.2 (C=O)
ppm; IR (KBr): ~ = 3057, 2954, 2926, 2867, 2848, 2231, 1748, 1505, 1449, 1365, 1288, 1225, 1206, 1057, 1011,
968, 955, 903, 776, 742, 649, 564 cm–1; HR-ESI-TOF-MS (positive mode): m/z calcd. for C27H24O2K: 419.1413,
found: 419.1398 [M+K]+.
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Synthesis of fullerene–fluorene dyads Z-3a and E-3a. 2a (224 mg, 0.675 mmol) was dissolved in toluene (15 mL)
under argon in an oven-dried two-necked flask, and degassed using three freeze–pump–thaw cycles under reduced
pressures. Fullerene C60 (81.4 mg, 0.113 mmol) and PtCl2 (9.2 mg, 0.034 mmol) were placed in a Pyrex tube under
argon. The toluene solution of 2a and additional dry toluene (66 mL) were added to the tube using a syringe. The
mixture was heated at 80 ºC and the reaction was monitored by TLC and HPLC. After completion of the reaction,
the mixture was passed through a cotton plug and the solvent was removed under reduced pressure. Purification and
isolation was accomplished by silica-gel flash chromatography (SiO2; toluene/n-hexane 1:3, 1:2, then 1:1) followed
by preparative HPLC (Buckyprep 20  250 mm; Cosmosil; Nacalai Tesque Inc., toluene/n-hexane 1:1, flow rate
9.9 mL min–1) to give Z-3a (3.1 mg, 3%) and E-3a (30.2 mg, 25%) together with unreacted C60 (11.3 mg, 14%).
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Z-3a: Brown solid; Rf = 0.10 (SiO2, toluene/n-hexane 1:3); H
NMR (400 MHz, CDCl3):  0.84 (t, J = 7.2 Hz, 3H; CH3), 1.15–
1.30 (m, 8H; CH2), 1.62 (quint, J = 7.5 Hz, 2H; CH2), 2.43 (t, J
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= 7.5 Hz, 2H; CH2), 7.49–7.56 (m, 4H; Ar-H), 7.66 (s, 1H; C=CH), 7.85–7.88 (m, 2H; Ar-H), 8.47–8.51 (m, 2H; Ar-
H) ppm; 13C{1H} NMR (100 MHz, CDCl3):  14.25 (C83), 22.74 (CH2), 24.80 (CH2), 29.01 (CH2), 29.11 (CH2),
31.68 (CH2), 34.23 (CH2), 65.79 (C62), 70.54 (C2), 120.43 (C67), 127.49 (C64), 128.00 (C65 or C66), 129.01 (C66
or C65), 129.24, 134.75 (C75), 138.17, 138.35, 140.39, 140.97, 141.34, 141.64, 142.21, 142.26, 142.56, 142.82,
143.01, 143.18, 144.62, 144.74, 145.37, 145.41, 145.49, 145.52, 145.60, 146.02, 146.15, 146.22, 146.31, 146.62,
147.19, 147.22, 147.88, 151.03, 152.46, 169.84 (C76) ppm (45 resonances out of 49 expected ones due to peak
overlap); max = 438, 707 nm (in CS2); (KCl)/cm–1 3094, 3062, 3036, 2961, 2925, 2853, 1757, 1446, 1260, 1187,
1094, 1030, 800, 742, 526; MALDI-TOF MS (negative mode): m/z calcd. for C83H24O2: 1052.178, found: 1052.178
[M]–.
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E-3a: Brown solid; Rf = 0.15 (SiO2, toluene/n-hexane 1:3); 1H NMR
(400 MHz, CDCl3/CS2 1:1):  0.91 (t, J = 7.2 Hz, 3H; CH3), 0.96–
1.21 (m, 8H; CH2), 1.24–1.33 ((m, 2H; CH2), 1.93 (t, J = 7.4 Hz, 2H;
CH2), 7.44–7.49 (m, 4H; Ar-H), 7.78–7.82 (m, 2H; Ar-H), 8.10 (s,
1H; C=CH), 8.39–8.44 (m, 2H; Ar-H) ppm; 13C{1H} NMR (100 MHz, CDCl3/CS2 1:1):  14.37 (C83), 22.98 (CH2),
24.32 (CH2), 28.94 (CH2), 28.96 (CH2), 31.78 (CH2), 33.80 (CH2), 66.13 (C62), 69.49 (C2), 76.09 (C1), 120.09 (C67),
127.04 (C64), 127.70 (C65 or C66), 128.65 (C66 or C65), 129.88 (C61), 134.31 (C75), 137.84, 138.37, 140.18,
140.96, 141.29, 141.42, 142.02, 142.12, 142.44, 142.69, 142.74, 142.83, 143.02, 144.47, 144.57, 145.16, 145.20,
145.29, 145.34, 145.52, 145.85, 145.94, 145.98, 146.06, 146.10, 146.54, 147.02, 147.06, 151.11, 152.66, 169.10
(C76) ppm (47 resonances out of 49 expected ones due to peak overlap); max = 438, 709 nm (in CS2); (KCl)/cm–1
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3066, 2921, 2848, 1751, 1690, 1446, 1198, 1129, 1104, 905, 741, 526; MALDI-TOF MS (negative mode): m/z calcd.
for C83H24O2: 1052.178, found: 1052.177 [M]–.
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Synthesis of Fullerene–fluorene dyad Z-3b. Fullerene C60 (81.2 mg, 0.113 mmol), 2b (205.5 mg, 0.676 mmol),
and PtCl2 (9.3 mg, 0.035 mmol) were placed in a Pyrex tube under argon. Dry toluene (81 mL) was added to the tube
using a syringe. The mixture was heated at 80 ºC and the reaction was monitored by TLC and HPLC. After
completion of the reaction, the mixture was passed through a cotton plug and the solvent was removed under reduced
pressure. Purification and isolation was accomplished by silica-gel flash chromatography (SiO2; toluene/n-hexane
1:2) and subsequent preparative HPLC (Buckyprep 20  250 mm; Cosmosil; Nacalai Tesque Inc., toluene/n-hexane
1:1, flow rate 9.9 mL min–1) if required to give Z-3b (52.0 mg, 45%) together with unreacted C60 (26.8 mg, 33%).
Z-3b: Brown solid; Rf = 0.28 (SiO2, toluene/n-hexane 1:2); 1H NMR (400 MHz, CDCl3/CS2 1:1):  0.56 (t, J = 7.4
Hz, 3H; CH3), 0.97 (sext, J = 7.4 Hz, 2H; CH2), 1.18 (quint, J = 7.4 Hz, 2H; CH2),
1.78 (t, J = 7.4 Hz, 2H; CH2), 2.06 (s, 3H; CH3), 7.45–7.54 (m, 4H; Ar-H), 7.79–7.83
(m, 2H; Ar-H), 8.47–8.51 (m, 2H; Ar-H) ppm; 13C{1H} NMR (100 MHz, CDCl3/CS2
1:1):  13.65 (C79), 20.64 (C81), 22.32 (C78), 28.03 (C77), 29.46 (C76), 65.95 (C62), 70.66 (C1 or C2), 75.28 (C2
or C1), 120.25 (C67), 127.48 (C64), 127.87 (C65 or C66), 128.85 (C66 or C65), 129.56 (C61), 137.89, 138.25,
140.19, 140.74, 141.17, 141.44, 141.99, 142.11, 142.21, 142.43, 142.58, 142.64, 142.81, 143.03, 144.47, 144.53,
145.19, 145.34, 145.81, 145.92, 145.97, 146.06, 146.59, 146.98, 147.03, 150.68 (C75), 150.99, 152.20, 168.18 (C80)
ppm (42 resonances out of 47 expected ones due to peak overlap); max = 438, 708 nm (in CS2); (KCl)/cm–1 3059,
3016, 2959, 2937, 2858, 1759, 1715, 1462, 1447, 1427, 1366, 1199, 1181, 1165, 742, 526; MALDI-TOF MS
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(negative mode): m/z calcd. for C81H20O2: 1024.146, found: 1024.143 [M]–.
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Synthesis of Fullerene–fluorene dyad Z-3c. Fullerene C60 (81.1 mg, 0.113 mmol), 2c (257.3 mg, 0.676 mmol), and
PtCl2 (9.2 mg, 0.035 mmol) were placed in a Pyrex tube under argon. Dry toluene (81 mL) was added to the tube
using a syringe. The mixture was heated at 80 ºC and the reaction was monitored by TLC and HPLC. After
completion of the reaction, the mixture was passed through a cotton plug and the solvent was removed under reduced
pressure. Purification and isolation was accomplished by silica-gel flash chromatography (SiO2; toluene/n-hexane
1:1) and subsequent preparative HPLC (Buckyprep 20  250 mm; Cosmosil; Nacalai Tesque Inc., toluene/n-hexane
1:1, flow rate 9.9 mL min–1) if required to give Z-3c (14.3 mg, 12%) together with unreacted C60 (67.1 mg, 83%).
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Z-3c: Brown solid; Rf = 0.30 (SiO2, toluene/n-hexane 1:1); H NMR (400 MHz,
CDCl3):  0.87 (t, J = 7.4 Hz, 3H; CH3), 1.20 (sext, J = 7.4 Hz, 2H; CH2), 1.43 (quint,
J = 7.4 Hz, 2H; CH2), 2.19 (s, 3H; CH3), 2.41 (t, J = 7.4 Hz, 2H; CH2), 6.76 (AA’BB’,
J = 8.2 Hz, 2H; Ar-H), 6.82 (AA’BB’, J = 8.2 Hz, 2H; Ar-H), 7.43–7.48 (m, 4H; Ar-
H), 7.82–7.85 (m, 2H; Ar-H), 8.46–8.51 (m, 2H; Ar-H) ppm; 13C{1H} NMR (100
MHz, CDCl3):  14.07 (C85), 21.13 (C87), 22.28 (C84), 33.27 (C83), 35.39 (C82), 67.43 (C62), 71.93 (C1 or C2),
75.67 (C2 or C1), 120.46 (C67), 126.11 (C77), 127.50 (C64), 127.97 (C65 or C66), 128.17 (C78), 128.93 (C66 or
C65), 129.63 (C76), 131.25, 138.30, 138.44, 140.39, 140.81, 141.45, 141.64, 142.20, 142.30, 142.43, 142.56, 142.75,
142.82, 143.02, 143.21, 143.99 (C79), 144.68, 144.74, 145.41, 145.58, 146.03, 146.07, 146.16, 146.25, 146.29,
147.25, 147.29, 147.63 (C75), 151.37, 152.22, 169.11 (C86) ppm (46 resonances out of 51 expected ones due to peak
overlap); max = 433, 700 nm (in CS2); (ATR)/cm–1 3064, 2953, 2924, 2854, 1766, 1655, 1608, 1559, 1541, 1509,
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1448, 1427, 1364, 1261, 1197, 1153, 1082, 1067, 1039, 895, 871, 801, 621, 597, 575, 562, 551; MALDI-TOF MS
(negative mode): m/z calcd. for C87H24O2: 1100.178, found: 1100.178 [M]–.
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X-ray crystallographic analysis of Z-3b. X-Ray diffraction (XRD) measurements were performed at 90 K on a
Bruker AXS APEX III machine equipped with a Photon II detector with MoK radiation ( = 0.71073 Å). A
specimen of C81H20O2, approximate dimensions 0.060 mm  0.269 mm  0.284 mm, was used for the X-ray
crystallographic analysis. The integration of the data using an orthorhombic unit cell yielded a total
of 76675 reflections to a maximum θ angle of 27.10° (0.78 Å resolution), of which 9438 were independent (average
redundancy 8.124, completeness = 99.7%, Rint = 6.04%, Rsig = 4.34%) and 6489 (68.75%) were greater than
2σ(F2). The final cell constants of a = 19.3947(6) Å, b = 17.2114(5) Å, c = 25.7129(8) Å, volume = 8583.2(5) Å3,
are based upon the refinement of the XYZ-centroids of 9934 reflections above 20 σ(I). The calculated minimum and
maximum transmission coefficients (based on crystal size) are 0.9740 and 0.9940. The structure was solved and
refined using the Bruker SHELXTL Software Package, using the space group Pbca, with Z = 8 for the formula
unit, C81H20O2. The final anisotropic full-matrix least-squares refinement on F2 with 769 variables converged at R1
= 5.97%, for the observed data and wR2 = 17.70% for all data. The goodness-of-fit was 1.054. The largest peak in
the final difference electron density synthesis was 0.645 e–/Å3 and the largest hole was –0.628 e–/Å3 with an RMS
deviation of 0.075 e–/Å3. On the basis of the final model, the calculated density was 1.586 g/cm3 and F(000), 4176 e-.
CCDC 1887323 (Z-3b) contains the supplementary crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Thermal stability experiments
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A solution of dyad 3 (3.3  10–4 M) and C70 (2.0  10–4 M) in toluene (100 L) was placed in a Pyrex tube. After
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degassing through three freeze–pump–thaw cycles under reduced pressure, the tube was sealed and heated at 80ºC
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or 110 ºC for 1 h. The decomposition process was monitored by HPLC.
ASSOCIATED CONTENT
Supporting Information
Crystallographic data, HPLC chromatograms, mass spectra, IR spectra, absorption spectra, NMR spectra,
electrochemical data, and computational results. The Supporting Information is available free of charge on the ACS
Publications website.
AUTHOR INFORMATION
Corresponding Author
* E-mail: myamada@u-gakugei.ac.jp
NOTES
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was supported by the Japan Prize Foundation and TOBE MAKI Scholarship Foundation, and was partly
supported by a Grant-in-Aid for Young Scientists (B) (16K17890) and a Grant-in-Aid for Scientific Research (B)
(17H02735) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. The authors also
thank Prof. Takashi Hirano of the University of Electro-Communications for performing ESI-TOF mass
measurements.
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Catalyzed Cycloisomerization of Allenynes, Synlett 2006, 575–578.
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(21) The PtCl2-catalyzed reaction of C60 with 2b was not affected by the protection from ambient light and by the
presence of TEMPO (36 equiv. based on C60), suggesting that both photoactivated species and free radical species
are not involved in the reaction.
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(22) Recent DFT calculations revealed that [2+2] cycloaddition of benzyne to C60 involves stepwise processes with
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(23) Miki, K.; Senda, Y.; Kowada, T.; Ohe, K. Platinum- and Palladium-Catalyzed Sequential Reactions:
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(24) (a) Miki, K.; Fujita, M.; Uemura, S.; Ohe, K. Ru-Catalyzed Ring-Opening and Substitution Reactions of
Heteroaromatic Compounds Using Propargylic Carboxylates as Precursors of Vinylcarbenoids, Org. Lett. 2006, 8,
1741-1743. (b) Ikeda, Y.; Murai, M.; Abo, T.; Miki, K.; Ohe, K. Transition Metal-Catalyzed Ring-Opening,
Substitution, and Cyclopropanation Reactions via Vinylcarbene Complexes Generated from O-Propargyl
Thiocarbamates, Tetrahedron Lett. 2007, 48, 6651-6654.
(25) Yamada, M.; Akasaka, T.; Nagase, S. Carbene Additions to Fullerenes, Chem. Rev. 2013, 113, 7209-7264.
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1994, 35, 9529-9532. (b) Bespalova, N. B.; Bovina, M. A.; Rebrov, A. I.; Sergeeva, M. B. Cyclopropanation of
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