Regioselective Synthesis of [6,6]-Open and [5,6]-Closed C70(CF3)8[CH2] Methanofullerenes with Rapid [6,6]-to-[5,6] Phototransformation

Article abstract of DOI:10.1002/ejoc.201701610

Fullerene derivatives with >CH₂ addends in [6,6]-open or [5,6]-closed configuration are uncommon of fullerene derivatives, but they are readily accessible via treatment of C_s-C₇₀(CF₃)₈ with diazomethane followed by thermolysis or photolysis. Both thermodynamic and kinetic factors favor regioselective addition of diazomethane at the near-equatorial [5,6]-double bond of C_s-C₇₀(CF₃)₈ to give a thermally labile pyrazoline intermediate. Thermal extrusion of N₂ from the latter is a kinetically controlled process with orbital symmetry controlled Woodward–Hoffmann-allowed mechanism. It quantitatively yields the less thermodynamically favorable [6,6]-open isomer of C₇₀(CF₃)₈[CH₂] homofullerene, but the latter turns out to be capable of unexpectedly rapid quantitative phototransformation into the thermodynamically preferable [5,6]-closed methanofullerene isomer. The transformation involves the manifold of the triplet states that facilitate the required cleavage of the C_cage–CH₂ bonds.

Full text of DOI:10.1002/ejoc.201701610

A Journal of
Accepted Article
Title: Regioselective synthesis of [6,6]-open and [5,6]-closed
C70(CF3)8[CH2] methanofullerenes with rapid [6,6]-to-[5,6]
phototransformation
Authors: Olesya O. Semivrazhskaya, Nikita M. Belov, Alexey V.
Rybalchenko, Vitaliy Yu. Markov, Ilya N. Ioffe, Natalia S.
Lukonina, Sergey I. Troyanov, Erhard Kemnitz, and Alexey A
Goryunkov
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201701610
Link to VoR: http://dx.doi.org/10.1002/ejoc.201701610
Supported by

European Journal of Organic Chemistry
10.1002/ejoc.201701610
FULL PAPER
Regioselective synthesis of [6,6]-open and [5,6]-closed
C (CF ) [CH ] methanofullerenes with rapid [6,6]-to-[5,6]
7
0
3 8
2
phototransformation
[
a]
[a]
[a]
[a]
[a]
Olesya O. Semivrazhskaya, Nikita M. Belov, Alexey V. Rybalchenko, Vitaliy Yu. Markov, Ilya N. Ioffe,
[
a]
[a]
[b]
[a]
Natalia S. Lukonina, Sergey I. Troyanov, Erhard Kemnitz, and Alexey A. Goryunkov*
Abstract: Fullerene derivatives with >CH
5,6]-closed configuration are uncommon of fullerene derivatives, but
they are readily accessible via treatment of C -C70(CF (1) with
2
addends in [6,6]-open or
Specific addition patterns in the derivatives of C70 give rise
to further promising features. Recently, we demonstrated that
[
s
3
)
8
s 3 8 2
regioselective cyclopropanation of C -C70(CF ) with CX (X=F or
diazomethane followed by thermolysis or photolysis. Both
thermodynamic and kinetic factors favor regioselective addition of
aryl) at the near-equatorial [5,6]-bond provides compounds with
[19]
potential properties of molecular switches.
reversible open/closed transformations of the CX
Charge-controlled
bridge result
diazomethane at the near-equatorial [5,6]-double bond of
to give thermally labile pyrazoline intermediate 2. Thermal
extrusion of N from 2 is a kinetically controlled process with an
s
C -
2
C70(CF
)
3 8
in switching between connected and split states of the molecular
2
-system and considerably alter the electron-withdrawing
[
19]
orbital symmetry controlled Wodward-Hoffmann-allowed mechanism. properties. Those findings motivated us to try incorporating in
It quantitatively yields less thermodynamically favorable [6,6]-open -C70(CF other possible bridging moieties in a search of
isomer of C70(CF [CH ] homofullerene (3), but the latter turns out to
C
s
3 8
)
)
3 8
2
be capable of unexpectedly rapid quantitative phototransformation
into the thermodynamically preferable [5,6]-closed methanofullerene
isomer 4. The transformation involves the manifold of the triplet
2
states that facilitate the required cleavage of the Ccage–CH bonds.
Introduction
Spherical unsaturated fullerene skeleton serves a convenient
scaffold for engineering novel molecular materials with desired
optoelectronic properties by means of creating various addition
[
1–7]
patterns and thus shaping the conjugated -system.
facilitate that task, multitude of diverse fullerene
functionalization techniques were developed in the last two
To
further examples of uncommon behavior.
Fig. 1. General scheme of C -C70(CF ) methylenation with diazomethane.
s 3 8
a
Here we report the first results of methylenation of C
(1) through its reaction with diazomethane (see Fig. 1).
Two novel methanofullerenes C70(CF [CH ] (3, 4) have been
obtained that feature unusual [6,6]-open and [5,6]-closed
conformations of the CH bridge. Moreover, the [6,6]-isomer
s
-
[
8–14]
decades.
A remarkable recent example presents a family of
3 8
C70(CF )
mixed derivatives of C70 with same eight methoxy groups in the
equatorial part of the molecule and different further addends,
such as cyclopropane, epoxide, and hydroxide moieties, as
efficient fluorophores with peak emission wavelengths spanning
3
)
8
2
2
turned out to undergo rapid photochemically promoted
transformation into the [5,6]-one, and single crystal X-ray
characterization of the latter thus also clarified the structure of
the former. We further report MALDI MS, UV-vis and NMR data
on the novel compounds.
[
7]
the range of 450 to 650 nm. Another example of fine tuning of
optoelectronic properties via altering the addition pattern is
manifested by extensive families of trifluoromethylated fullerenes
[
15]
with 2 to 20 CF
3
groups.
Those polyadducts demonstrate, in
particular, strong dependence of the electron affinity values on
[
16–18]
the addition pattern
while also capable of efficient
[
5]
fluorescence (quantum yields up to 0.68).
Results and Discussion
Synthesis and structural elucidation
[
a]
Dr. O. O. Semivrazhskaya, N. M. Belov, A. V. Rybalchenko, D.Sc. V.
Yu. Markov, D.Sc. I. N. Ioffe, Dr. N. S. Lukonina, Prof. D.Sc. S. I.
Troyanov, and D.Sc. A. A. Goryunkov*
Chemistry Department
Lomonosov Moscow State University
Leninskie Gory, 1-3, 119991, Moscow, Russia
E-mail: aag@thermo.chem.msu.ru
https://thermolab.chem.msu.ru
Prof. Dr. E. Kemnitz
Institut für Chemie
Humboldt Universität zu Berlin
Several approaches have been developed to functionalize
fullerenes with
a
CH
2
moiety. They include addition of
diazomethane followed by thermolysis or photolysis of the
[20–22]
isolable intermediate 1-pyrazoline adducts, either without
or
[23]
with
a
catalyst,
reaction of electrochemically generated
[
24,25]
fullerene anions with dihalomethanes,
and the Simmons–
The rare example of [6,6]-open
methanofullerene C2v-C70(CH ) [CH group is inserted into [6,6]-
equatorial bond of C70 cage] has been prepared by modified
Kratchmer-Huffman method in presence of CH and via direct
[
26]
[
b]
Smith reaction.
2
2
Brook-Taylor-Str. 2, 12489 Berlin, Germany
Supporting information for this article is given via a link at the end of
the document.
4
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European Journal of Organic Chemistry
10.1002/ejoc.201701610
FULL PAPER
o
[27]
reaction of C70 and CH
60(CH ) and C70(CH ) methanofullerenes have been achieved
by means of oxidative cyclopropanation of the precursory
4
at 1100 C. High yields of [6,6]-closed
C
70(CF
3
)
8
[C(PhOMe)
2
] and C70(CF
[CH
The absorption onset in 2 was
3
)
8
X
2
, X=H, Cl, CN, as well as
C
2
2
below described [5,6]-C70(CF
Fig 4a and S4 in SI).
observed at 456 nm, within the range of 448–462 nm which is
typical of the addition pattern in question. Compared to the other
3
)
8
2
] of the present work (see
[
19,36–38]
[
28]
silylmethyl derivatives. Finally, selective preparation of mono-
and polymethanofullerenes has been effected through the
Bingel-decarboxylation” approach.
[
29]
“
However, none of the
3 8 2
C70(CF ) X compounds this onset is pronouncedly blueshifted,
above synthetic schemes has yet been applied to
trifluoromethylated fullerenes as substrates.
reflecting disruption of the -system into two smaller halves.
Therefore, it is safe to conclude that 1-pyrazoline moiety is fused
at near-equatorial [5,6]-bond in compound 2 as shown in Fig 1.
3 8 2
Figure 3. Structure of [5,6]-closed C70(CF ) [CH ] (4) obtained from XRD
analysis (thermal ellipsoids are shown at the 50% level of probability) and its
Schlegel diagram (the solid black circles and dumbbells denote attachment
3 2
positions of the CF and CH groups, respectively).
o
Heating of the reaction mixture at ca 90 C for 2–3 min led to
disappearance of the pyrazoline intermediate and its
2
replacement with compound 3, as can be seen from the HPLC
trace in Fig 2b. This product was isolated by HPLC and
identified by MALDI mass spectra as methanofullerene
Figure 2. HPLC traces (Cosmosil Buckyprep 4.6 mm I.D. × 25 cm, toluene, 1
–1
mL min ) of the reaction mixture of C
s
-C70(CF
and after its heating at ca 90 C (b). HPLC traces and negative ions MALDI
mass spectra of isomeric methanofullerenes C70(CF [CH ] 3 and 4 (c and d).
3 8
) with diazomethane at 0°C (a)
o
)
3 8
2
C
70(CF
3
)
8
[CH
fractions did not reveal any significant amounts of
[CH ]. Manipulations with the individual
2
] (Figure 2c). Mass spectra of other HPLC
Being interested in cyclopropanation at the near-equatorial
5,6]-bond of C -C70(CF , which is sterically obstructed by two
CF groups, we chose the diazomethane approach with its less
bulky reactant. Initially, the diazomethane pathway gives rise to
C70(CF
3
)
8
2
[
s
3 8
)
methanofullerene 3 led us to the observation that exposition of
its toluene solution to visible light (inert atmosphere, room
temperature) promotes quantitative transformation within 2–4
days into an isomeric methanofullerene 4 (see Figure 2d). This
transformation was somewhat unexpected, being not known for,
3
[
20–22]
formation of 1-pyrazoline fullerene intermediates.
subsequent photolysis is known to proceed through N
Their
2
extrusion
to give isomeric mixtures of [6,6]-closed and [5,6]-open C60(CH
or compounds. Alternatively, thermolysis of the
pyrazolines affords almost exclusively the [5,6]-open adducts.
The starting C -C70(CF (1) was synthesized using the well
established two-step ampoule protocol followed by HPLC
2
)
[20–22,39]
2 2 .
e.g., the related [5,6]-open C60(CH ) and C70(CH )
2
C70(CH )
To determine structure of isomeric methanofullerenes 3 and
4,
we attempted to obtain crystalline material via slow
s
3 8
)
evaporation of their solutions in toluene and chloroform. No
suitable crystalline material of compound 3 was obtained, but
compound 4 produced single crystals in both cases. We
obtained a total of three consistent XRD datasets – one for the
[
30,31]
separation.
Its treatment with diazomethane solution in
toluene at 0°C resulted in rapid formation of compound 2 as a
major product, which was identified as a 1-pyrazoline adduct
3 8 2
toluene crystallosolvate of C70(CF ) [CH ] and two more for its
3 8 2 2
C70(CF ) [CH N ] (Figures 1 and 2a). Similarly to 1-pyrazoline
pure crystals obtained from chloroform.
derivatives of pristine fullerenes C60 and C70, whose thermolysis
[
20–22]
X-Ray diffraction analysis of methanofullerene 4 revealed
attachment of the methano bridge to the near-equatorial [5,6]-
bond, i.e. to the same position as in the precursory 1-pyrazoline
adduct 2 (Figs. 1 and 3). As has been demonstrated earlier in
affords corresponding homofullerenes,
compound 2 proved
thermally unstable, and its isolation and characterization was
complicated by noticeable decomposition even at room
temperature. Nevertheless, the UV-vis spectrum of 2 obtained
directly with the HPLC detector provided crucial insights into its
molecular structure since the details of electronic spectra of
fullerene derivatives are known to be quite sensitive to the
numerous reactions with C
reactive toward sterically undemanding addends.
CH bridge forms a cyclopropane moiety with C–C bond length
s 3 8
-C70(CF ) , the said bond is the most
[
19,36–38,40]
The
2
[32–36]
between the bridgehead carbon atoms in the three crystal
structures available of 1.678(7), 1.683(7) and 1.691(6) Å. Those
values are similar to the isostructural [5,6]-closed
addition motifs.
similarity to the derivatives of C
functionalized near-equatorial [5,6]-double bond: [5,6]-closed
The spectrum was found to show large
s
-C70(CF with additionally
3 8
)
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European Journal of Organic Chemistry
10.1002/ejoc.201701610
FULL PAPER
[
19]
[35,40–43]
19
C
70(CF
3
)
8
[C(PhOMe)
the same time, addition of electron-withdrawing CF
same [5,6]-bond is known to cleave it to ca. 2.1 Å.
2
]
and other methanofullerenes.
In
mirror symmetry, F NMR spectrum consists of four multiplets
A–D of equal intensity due to four pairs of equivalent CF groups
within the –δ range of 61–67 ppm (Fig. 4c). Proximity of the
CH group results in a slight upfield shift of the quartet signal A
due to the terminal CF groups with respect to the parent C
(–66.4 vs. –65.7 ppm ). H NMR spectrum features a
pair of coupled doublet signals of equal intensity at δ 2.2 and
4.8 ppm, JHH=6.9 Hz (Fig. 4d), thus reflecting different magnetic
shielding of the geminal CH hydrogen atoms situated over a
hexagon (H ) and over a pentagon (H ). Such picture is quite
common for [5,6]-adducts; for example, in the related [5,6]-open
), H and H signals demonstrated even higher degree of
inequivalence with δ
2
group to the
3
[
19]
In
F
[
44]
accordance with the Bent's rule, electron-withdrawing fluorine
atoms dictate increased contributions of the carbon 2p-orbitals
to the C–F bonds and, consequently, of the 2s-orbital to the C–C
bonds, which results in more pronounced opening of the C–CF
C angle compared to CH and CR adducts. The bridgehead
carbons of compound 4 have nearly planar configuration with
2
3
s
-
[
31]
1
C
3 8
70(CF )
2
–
H
3
2
2
2
[
45]
the π-orbital axis vectors (POAV) angle
the same carbon atoms in the parent
Interestingly, the related [5,6]-open CHal adducts at the same
of 1.7° (cf. 10.8° for
h
p
[
46]
s 3 8
C -C70(CF ) ).
2
C
60(CH
2
h
p
[19]
[47]
[20,21]
bond,
POAV value of 6.2°.
C
3
70(CF )
8
[CF
2
]
and [5,6]-C70(CCl
2
),
show larger
H
of 2.9 and 6.4 ppm, respectively.
Finally, H– C HMBC spectrum of 4 (Fig S3 in SI) demonstrated
the bridgehead carbon to have chemical shift δ = 60 ppm, i.e.
within the range typical for closed methanofullerenes.
1
13
The NMR data for compound 4 are in good agreement with
the X-ray results and DFT-GIAO calculations (see Table 1).
C
[
21,22,48]
s 3 8
Similarly to other derivatives of C -C70(CF ) that retain idealized
Figure 4. UV-vis spectra (within 430–800 nm range, toluene) of parent
70(CF [C(PhOMe) ] (DPM) and [5,6]-open C70(CF [CF
hypothetic 3b isomers, e). F and H NMR spectra of 4 (c, d) and 3 (f, g).
C
s
[
-C70(CF
3
)
8
,
compounds 2–4 prepared in this work, related [5,6]-closed
[CH ] 4 (b) and 3 (experimental 3a and
19]
C
)
3 8
2
)
3 8
2
] from our previous work (a). Schlegel diagrams of C70(CF
)
3 8
2
19
1
[
a]
3 8 2
Table 1. Experimental and DFT calculated data for isomeric C70(CF ) [CH ] compounds.
[
6,6]-Open isomer 3a
[5,6]-Open isomer 3b
[5,6]-Closed isomer 4
–1
f
Δ E / kJ mol
r(C...C) /Å
[78]
[76]
[0]
[b]
[2.17]
[2.18]
1.68 [1.69]
[
c]
[b]
POAV,
θ
p
/ °
[4.4, 3.2]
[6.0, 7.8]
1.7 [1.2]
δ
F
/ ppm
/ ppm
–61.5 (A), –65.7(H) [–60.1 (A), –66.8 (H)]
[–64.6 (A), –66.0 (H)]
[4.93 (H ), 4.98 (H )]
–66.4 (A) [–68.2 (A)]
δ
H
2.7 (H ), 5.5 (H ) [2.7 (H ), 5.6 (H )]
2.2 (H ), 4.8 (H ) [2.5 (H ), 4.7 (H )]
a
b
a
b
h
p
h
p
h
p
3
0.0 (CH
2
), 95.5 (Cbrh), 108.5 (Cbrh
)
46.9 (CH
2
), 59.7 (Cbrh)
δ
C
/ ppm
[39.9 (CH ), 148.4 (Cbrh), 155.9 (Cbrh)]
2
[29.5 (CH
2
), 88.4 (Cbrh), 104.6 (Cbrh)]
1.94 [1.67]
[41.2 (CH ), 65.8 (Cbrh)]
2
E
G
/ eV
[1.58]
[–4.42]
[–6.00]
2.65 [2.25]
[–4.11]
E
LUMO / eV
[–4.40]
[–6.07]
E
HOMO / eV
[–6.37]
[a]
[b]
[c]
[45]
DFT data values (PBE/TZ2P) are shown in square brackets.
bridgehead carbons, POAV of the respective near-equatorial carbons in C
Averaged value from X-ray data for three independent molecules.
π-Orbital axis vector angle of the
[46]
s
3 8
-C70(CF ) are 10.8° and 7.7° (X-ray data).
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European Journal of Organic Chemistry
10.1002/ejoc.201701610
FULL PAPER
Lack of crystalline material of compound 3, the initially
negligible effect on the adjacent bonds (length variation of
formed isomer of C70(CF
3
)
8
[CH
2
], restricted the means of its
0.001–0.009 Å), suggesting preservation of the basic features of
the electronic structure, similarly to other homofullerenes.
[
10,22,49]
identification to general chemical considerations and
interpretation of its NMR data with the aid quantum chemical
calculations (Table 1). The precursor of 3, pyrazoline derivative
2
,
and the product of its selective rearrangement,
methanofullerene 4, reveal addition to the same near-equatorial
5,6]-bond, and from the energetic considerations it looks highly
unlikely that nitrogen extrusion (2 to 3) or CH rearrangement (3
to 4) involve cleavage of both bonds between the addend and
the fullerene cage. Under the supposition that one C70–CH
bond persists, there are only two possible alternatives for the
compound 3 with CH moiety attached adjacently to the [5,6]-
bond in question: structures 3a or 3b as shown in Fig 4e. Both
[
2
2
2
1
9
1
molecules are non-symmetric, which agrees with F and
NMR spectra of compound 3 (Figure 4f, g). Furthermore, of the
two quartets signals A and H that belong to the terminal CF
groups, A is shifted downfield by ca 4 ppm, evidencing nearby
attachment of the CH addend.
Additional information regarding the structure of 3 was
H
3
Figure 5. DFT optimized structure of compound 3, [6,6]-open C70(CF ) [CH ]
3
8
2
2
(selected distances are given in Å, rear atoms are hidden for clarity).
The uncommon [6,6]-open configuration of 3 and [5,6]-
closed configuration of 4 give rise to certain characteristic details
in the UV-vis absorption data (see Figure 4a and S4 in SI). Thus,
UV-vis spectra of [5,6]-closed compounds 2 and 4 are show
much similarity to the related [5,6]-closed methanofullerene
1
13
derived from its H– C HMBC spectra (Table 1 and Figure S2 in
1
3
SI), which made possible to identify C chemical shifts in the
–Ccage moiety and in its direct vicinity. Thus, the four
C
cage–CH
2
cage carbons adjacent to the bridgehead ones gave rise to
resonances at 127, 130, 137, and 149 ppm. That evidenced, in
agreement with the structure of the proposed 3a or 3b, lack of
[
19]
C (CF ) [C(PhOMe) ].
7
0
3 8
2
In those compounds, the absorption
onset is blueshifted by 0.7–0.8 eV with respect to the parent Cs-
direct bonding between the bridgehead carbons and the CF
3
-
C (CF ) (1.97 eV), which reflects splitting of the connected
7
0
3 8
bearing ones, whose typical chemical shifts are generally found
62π-electron system of the latter into the disjoint 32π- and 28π-
electron fragments. Contrariwise, in the [6,6]-open
C (CF ) [CH ], the parent 62π-electron system is preserved,
and the spectral deviations from the parent C -C (CF ) are only
s 70 3 8
marginal. This definitive role of the π-system connectivity is
[
19]
around 61–62 ppm.
resonances of CH were, expectedly, observed at 30 ppm, while
the bridgehead carbon atoms at δ 95 and 108 ppm revealed
considerable deshielding compared to compound 4. Such
chemical shifts are typical of the open CH bridge configuration
cf. δ from 119 to >130 ppm in the open homofullerenes
60(CHR) and C70(CH
In the methano bridge itself, the
2
7
0
3 8
2
C
2
further illustrated by close coincidence of the absorption onset in
[19]
[
C
C
3 (1.94 eV) and in the [5,6]-open C (CF ) [CF ] (1.90 eV),
a
7
0
3 8
2
[
22,27,49]
2
)
vs. 56–72 ppm in the closed
formal analog of 4 but with connected conjugated system due to
openness of the CF2 bridge. Higher excitation energy in the
disjoint adducts is associated with rather symmetric changes in
the HOMO and LUMO levels (Table 1): compared to the open
compound 3, the HOMO in the closed adduct 4 is located 0.3 eV
below and the LUMO – 0.3 eV above.
[
21,22,29,48]
methanofullerenes
observed in the CF
for open and closed configurations, respectively).
]. Similar trends have also been
2
fullerene adducts (97–108 ppm vs. 69 ppm
[
50,48,19]
To make a choice between 3a and 3b, we involved GIAO
DFT calculations of the NMR chemical shifts (see Table S3 in SI
for predicted NMR shifts of the complete isomer list). It turned
out that both structures demonstrate open configuration of the
Reaction mechanism
CH
2
bridge, but in 3b the openness is more pronounced and
Selective addition of sterically undemanding addends to Cs-
C (CF ) at near-equatorial [5,6]-double bond is a common case
gives rise to much stronger deshielding of the bridgehead atoms
than observed in the experiment. As one can see from Table 1,
the DFT values for 3b strongly deviate from the experiment not
only in the C but also in the H, and F spectra. Structure 3a,
on the contrary, complies well with the experimental NMR data
for compound 3. Hence, we identify compound 3 as 3a, a rare
7
0
3 8
[
37,19,36]
favored by advantageous thermodynamics.
The examples
[
37]
[38]
include halogenation,
nucleophilic addition,
reductive
1
3
1
19
[36]
[19]
hydrogenation,
[2+1] cycloaddition,
and even suprafacial–
[
40]
suprafacial [2+2] dimerization.
With bulkier addends, e.g. in
the case of nucleophilic cyclopropanation following the Bingel-
Hirsh approach, addition occurs at better accessible double
[
6,6]-open CH
The molecular geometry of compound 3 optimized at the
DFT level of the theory (PBE/TZ2P) is shown in Fig. 5. The CH
bridge has open configuration with bridgehead carbons spaced
by 2.17 Å. This degree of opening is intermediate between C2v
2
-adduct (see Fig. 5).
[40]
bonds at the poles of C -C (CF ) . The size of diazomethane
s
70
3 8
2
is sufficiently moderate to avoid steric complications, so its
addition to a more favorable site is not surprising. Indeed, a DFT
survey of the whole set of theoretically possible
C (CF ) [CH N ] diastereomers identifies compound 2 as the
-
[27]
[48,50]
C
70(CH
2
) (2.31 Å)
being most close to the [5,6]-open C70(CCl
Insertion of CH bridge into [6,6]-bond of C -C70(CF
and C60/70(CF
2
) (2.06 and 2.09 Å)
) (2.135(1) Å).
has only
,
7
0
3 8
2
2
[
47]
–1
2
most stable isomer, ca. 40 kJ mol below the next stable ones
[
40]
2
s
3
)
8
that are isostructural to the bulky Bingel-Hirsch adducts of ref.
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European Journal of Organic Chemistry
10.1002/ejoc.201701610
FULL PAPER
(
see Table S1 in SI). Transition state calculations demonstrate
that the mechanism can be regarded as concerted 1,3-dipolar
cycloaddition and that the compound is also more
To obtain more information on transformation of 3 into 4, we
performed additional kinetic experiments. Individual compounds
o
2
3 and 4 in toluene solutions were heated at 90 C under inert
advantageous kinetically, the less stable isomers showing higher
activation barrier for diazomethane addition (Fig S9 in SI).
Furthermore, the calculated activation energy of the reverse
process of diazomethane detachment from those less stable
atmosphere with and without exposure to ambient light.
Monitoring of the reaction mixture composition was carried out
by means of HPLC (see Fig S5 and S6 in SI for compound 3).
As one would expect, methanofullerene 4 demonstrated thermal
and photochemical stability without any notable changes within 4
h of observations. Contrarywise 3 was found to transform into 4
even in the dark, indicatively of relatively low activation barrier.
The measurements reveal first-order kinetics with half-
transformation times of 130 min in the dark and 50 min under
ambient light.
–
1
isomers is below 100 kJ mol ; hence, even had they formed,
they would have been converted into C -C70(CF upon heating
on the N extrusion stage.
6,6]-Open methanofullerene 3 that forms via thermally
activated N extrusion from 2 turns out to be considerably
s
3 8
)
2
[
2
–1
unfavorable energetically: 78 kJ mol above the final [5,6]-
closed methanofullerene 4, which was found to be the most
stable (see Tables 1 and S2 in SI). In fact, direct conversion of 2
into 4 could hardly be expected from the sterical point of view,
since it would require mostly accomplished preliminary
elimination of N
above considered alternative structure 3b that does not form is
effectively isoenergetic with and likewise sterically
2 2
before closing the CH bridge. However, the
3
unobstructed. Thus, thermolysis of 2 is a kinetically controlled
process likely governed by some electronic effects. The same is
known to be true for [6,6] diazomethane adducts of pristine C60
[
20–22]
and C70 that decompose into [5,6]-open methanofullerenes
–
1
1
(
0–20 kJ mol less stable that their [6,6]-closed counterparts
[
51,52]
B3LYP/6-31G(d)).
rationalizes thermal-induced N
methanofullerenes as an eight-electron [2π
concerted process controlled by orbital symmetry.
was later corroborated by ab initio and density functional
An explanation by Diederich et al.
extrusion to give [5,6]-open
+2π +2σ +2σ
This view
2
s
s
s
a
]
[
53]
[54]
calculations of the related model systems.
In Fig. 6a, we present our DFT results for the possible
alternative pathways of N extrusion from pyrazoline 2 (see Fig.
S10 in SI for further details). To reduce the computational cost,
we replaced actual C -C70(CF with the model pyramidalized
polyene C32
region of interest.
2
s
3 8
)
H
10(CH
2
19]
)
2
that is known to reasonably mimic the
The thermally activated reaction does,
[
indeed, proceed via concerted transition states, and the barrier
–
1
toward the missing 3b turns out to be 40 kJ mol higher than
the one toward 3, likely reflecting lack of compliance of the 3b
pathway with the Woodward-Hoffman rules.
The more stable methanofullerene 4 quantitatively forms
from 3 upon room temperature visible light irradiation for 2–4
days. No similar transformation is known for [5,6]-open
Figure 6. (a) Possible alternative mechanisms of thermolysis 1-pyrazoline
[20–22,39]
homofullerenes C60(CH
2
), C70(CH
2
),
and monoalkylated
derivative 2 through N
6,6]-open and [5,6]-open products 3 and 3b. (b) Reaction pathways of
thermally/light-induced isomerisation of methanofullerene 3 to 4 (green) and
2
extrusion via two alternative transition states yielding
[
55]
[
5,6]-open
C60(CHR),
though it can be initiated
[
photochemically, thermally, or electrochemically in the
compounds with monoarylated and bis-alkylated methano
2 2
related transformation [5,6]-open C60(CH ) to [6,6]-closed C60(CH ) (blue, the
[
32,22,56–59]
bridge,
advantageously in the presence of electron
–1
energy values are given in kJ mol ).
[60]
acceptors. The reaction rate was observed to increase in the
order dialkyl<arylalkyl<diaryl,
with the extent of stabilization of the biradical intermediate ( I
Further studies of the photoinduced transformation of 3 were
performed under RT conditions using a deuterium+halogen light
source (290–2500 nm; see more detail in the Experimental).
Shorter-wavelength absorption onset in 4 made possible to
selectively monitor the absorption of 3 near its red edge.
Continuous acquisition of the UV-vis spectra confirmed first-
order kinetics with apparent half-life time (t1/2) of 16 min under
argon atmosphere (Fig S7a) and slower 42 min in presence of
[
57]
which is evidently associated
3
1
of
Fig. 6b, c). It is generally accepted the transformation is the di-π-
methano (Zimmerman) rearrangement that proceeds via the
[
32]
triplet manifold,
and its kinetics in photoinduced cases was
[
56,59,60]
measured to be zero-order.
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European Journal of Organic Chemistry
10.1002/ejoc.201701610
FULL PAPER
oxygen (Fig. S7b) with oxygenated species as side products.
Interestingly, no reaction was observed with the halogen source
alone, despite its spectral window (500–2500 nm) overlaps with
the absorption spectrum of 3.
The inhibitory effect of O corroborates previous suggestions
2
that the process does proceed via the triplet manifold and
thermodinamically
unfavorable
[6,6]-open
homofullerene
C70(CF
3
)
8
[CH ] 3 in quantitative yields. Quite unexpectedly,
2
visible light irradiation and/or prolonged thermal treatment of the
[6,6]-open homofullerene 3 was found to promote quantitative
and irreversible isomerisation to thermodynamic the most
preferable methanofullerene 4 through formation of the triplet
follows the general scheme of Fig. 6b. For comparison, we also
provide the computational data for [5,6]-open C60(CH ). The first
2
step is photoexcitation of [6,6]-open methanofullerene 3 to an
state. Such rearrangement is not paralleled in C60(CH
quantum-chemical computations reveal the facilitating effect of
the C70(CF backbone compared to C60
Noteworthy, [6,6]-open and [5,6]-closed isomers of
[CH ] show remarkable variability in electronic structure
according to experimental . Thus, their DFT calculated LUMO
and HOMO levels differ by ca. –0.3/+0.3 eV, respectively. The
distinction comes from splitting of the connected 62π-electron
2
), and the
3
)
8
.
electronically excited singlet state with subsequent intersystem
3
crossing (ISC) to the lowest triplet state 3 (ISC rates are known
C70(CF
3
)
8
2
[
61,62]
to be relatively high in fullerene compounds),
while for the
dark conditions one can assume equilibrium thermal population
3
of 3. As one can see from Fig. 6b, the relative energy of the
3
3
triplet state of both compounds 3 and 4 ( 3 and 4, respectively),
exceeds the ca. 0.98 eV triplet-singlet gap in molecular oxygen,
so triplet oxygen is able to quench both triplet forms back to the
ground state. However, the relative energy values suggest
s 3 8
system of the parent C -C70(CF ) retained in the [6,6]-open
isomer 3 into the disjoint 32π- and 28π-electron fragments in the
[5,6]-closed compound 4. We therefore expect the developed
2
method of regioselective CH insertion in the near-equatorial
3
prevalence of the initially forming 3 even if equilibrium is
region of -C70(CF (and, probably, other known C70X
C
s
3
)
8
8
established in the triplet state. Thence, in accordance with the
derivatives with this common addition pattern) to become a
useful tool in rational design of next generation fullerene
derivatives with desired optoelectronic properties.
experimental data, molecular oxygen must predominantly
3
quench
3 back into the ground state, thus inhibiting
photoinduced isomerization.
The isomerization profile in 3 is shown in more detail in Fig.
S12 of the SI, and some key energy values are shown in Fig 6b,
3
Experimental Section
General information
c with C60(CH
2
) added for the sake of comparison. The initially
forming 3 is characterized by closed cyclopropane configuration
of the CH bridge (C–C bond length of 1.58 Å), the spin density
3
2
All reagents were obtained from commercial suppliers and used without
further purification. Solvents were dried by the usual methods and
distilled before use.
being distributed over the carbon cage with ca. 36 % localization
on carbon atoms C3 and C6 adjacent to cyclopropane moiety
3
(
for numeration see Fig 5). 3 undergoes relatively easy
2
cleavage of one of the Ccage–CH bonds to form an intermediate
High performance liquid chromatography. HPLC analyses of the
samples were performed using Agilent 1100 Series LC system (diode
array detector (DAD) operated at 190–950 nm wavelength range, Agilent
Technologies, Inc.) equipped by Cosmosil Buckyprep (Nacalai Tesque,
Inc.) analytic column (4.6 mm I.D. × 25 cm). HPLC separation was
carried out using Breeze LC Systems (UV-vis λ2 detector operated at
•
•
3
3
C70(CF
3
)
8
2 1
– CH biradical I that then recyclizes into 4. The
activation barrier of the transformation amounts to moderate 54
–1
3
kJ mol . Finally, intersystem crossing from 4 back to the
ground state produces compound 4.
Comparison
with
C
2
60(CH )
clearly
shows
why
190–700 nm, Waters, Inc.). LC system was equipped by Cosmosil
thermodynamically allowed isomerization of [5,6]-C60(CH
2
) into
Buckyprep (Nacalai Tesque, Inc.) semi-preparative column (10 mm I.D. ×
the more stable [6,6]-isomer has not yet been observed. Indeed,
2
2
5 cm). Toluene was used as eluent. HPLC traces were registered at
90 nm at the room temperature (for analytical purposes column was
3
the transformation barrier of its triplet state [5,6]-C60(CH
2
) to
being 86 kJ mol . Clearly, the
formation rate of [6,6]-C60(CH ) must be many orders lower than
], thus limiting the overall transformation
3
–1
biradical intermediate
I
1
thermostated at 25±0.8 °C).
3
2
3
3 8 2
of [5,6]-C70(CF ) [CH
UV/Vis spectra. The absorption spectra of the samples in toluene
solutions were recorded during the HPLC analysis via a DAD within
wavelength range of 190–950 nm with 2 nm resolution. Optical band
rate considerably.
opt
opt
gaps (E
G
) were estimated from the absorption band onsets as E
G
=
1240/λonset
.
Conclusions
Mass spectrometry. Negative ion MALDI mass spectra were acquired
using a Bruker AutoFlex II Rf-TOF device (N -laser, 337 nm, 2.5 ns
pulse). 2-trans-[3-(4-tert-butylphenyl)-2-methyl-2-
propenilyden]malononitrile (DCTB, ≥98%, Sigma-Aldrich) was used as a
matrix. AB Sciex TripleTOF 5600+ quadrupole-time-of-flight device was
applied to acquire positive ion APPI high-resolution mass spectra
(HRMS), resolving power being over 50000.
The novel C70(CF
open and [5,6]-closed configurations of the methano bridge are
readily accessible by treatment of -C70(CF with
diazomethane. Favored by both thermodynamic and kinetic
factors, addition of diazomethane molecule regioselectively
3 8 2
) [CH ] methanofullerenes with rare [6,6]-
2
C
s
3 8
)
proceeds at near-equatorial [5,6]-double bond of C
s 3 8
-C70(CF )
yielding thermally labile pyrazoline intermediate 2.
1
13
19
Orbital symmetry controlled Wodward-Hoffmann allowed
thermal extrusion of from process affords
NMR spectroscopy. H, C and F NMR spectra were registered at
00.3, 150.9 and 564.7 MHz, respectively, using a Bruker Avance III
spectrometer for samples dissolved in chloroform-d with a small amount
6
N
2
2
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European Journal of Organic Chemistry
10.1002/ejoc.201701610
FULL PAPER
of hexafluorobenzene (C F , δ
6 6 F
–162.90 ppm) and tetramethylsilane
Synthetic procedures
(
Me Si, δ 0.00 ppm) as internal standards.
4
H
s 3 8 3
Synthesis of precursory C -C70(CF ) . An excess of CF I (P&M-Invest,
X-ray crystallography. Two types of single crystals suitable for X-ray
diffraction analysis were obtained by slow evaporation of both chloroform
and toluene from solution of compound 4 under inert atmosphere. X-ray
diffraction data for both crystals were collected at 100K on a MAR225
CCD detector using synchrotron radiation (λ=0.8950 Å) at the BESSY
storage ring (BL14.3, PSF of the Free University, Berlin, Germany). The
structures were solved and anisotropically refined using the SHELX
98%; ca 1 mL) was condensed under cooling by liquid nitrogen to a glass
ampoule with fullerene C70 (Fullerene-center, 99.8%; 25 mg). Then
ampoule was sealed and heated in a gradient furnace at 420 °C for 72 h.
Obtained mixture of higher trifluoromethylated fullerenes C70(CF )
3 12–20
(40 mg) and additional amount of fullerene C70 (15 mg) were heated in
sealed glass ampoule at 450 °C for 40 h. Synthesized product mixture
s 3 8
was enriched by C -C70(CF ) isomer. Isolation of individual compound
was carried out by means of semi-preparative HPLC (Cosmosil
[
63]
package.
P2 /c, a=25.213(2), b=17.156(1), c=21.559(1) Å, β=91.920(8)°,
V=9320.2(10) Å , Z=8,
reflections and 1868 parameters. Two independent
molecules were found. Crystal data for [CH
498.94, monoclinic, P2 /c, a=20.217(2), b=18.379(1), c=14.351(1) Å,
β=99.053(9)°, V=5266.0(7) Å , Z=4,
248/11674 reflections and 1067 parameters. Solvated toluene molecule
Crystal data for C70(CF
3
)
8 2
[CH ]: M = 1406.81, monoclinic,
1
Buckyprep 10 mm I.D. × 25 cm) using toluene as an eluent (flow rate 4.6
3
2
–1
R
1
(F)/wR
2
(F )=0.079/0.169 for 9137/18611
[CH
]·PhMe: M =
mL min ).
C
70(CF
3
)
8
2
]
C
70(CF
3
)
8
2
C
s
-C70(CF
Buckyprep 4.6 mm I.D. × 25 cm, toluene, 1 mL min ); F NMR (564.7
MHz, CDCl , 25 °C, C ): –δ =61.4–61.5 (m, 12F; 4CF ), 61.7 (m, 6F;
CF ), 65.7 ppm (q, J(F,F)=16.1 Hz, 6F; 2CF ). UV-vis (toluene):
max=412, 418, 454, 482 nm; MS MALDI: m/z (%): 1392.0 (100%,
3 8 R
) (compound 1). Yield 23% (15 mg). t 4.5 min (Cosmosil
–1
19
1
1
3
2
1 2
R (F)/wR (F )=0.066/0.152 for
3
F
6 6
F
3
6
2
λ
3
3
is disordered over two positions. CCDCs 1569331 and 1569332 contain
the supplementary crystallographic data for this paper. These data can
–
–
3 8
[C70(CF ) ], [M ]).
*
be obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Synthesis of precursory diazomethane. Caution! Diazomethane is
highly toxic and explosive. The operation must be carried out in a good
hood with an adequate shield. Diazomethane was prepared by treatment
of a toluene solution of N-nitroso-N-methylurea with aqueous potassium
Kinetics of light induced isomerisation of 3. The light induced
isomerisation was studied by means of continuous monitoring of UV/Vis
spectra of compound 3 in toluene during its irradiation with deuterium
halogen source [AvaLight-DH-S-BAL equipped with SMA-terminated 800
μm fiber-optic cable FC-UV800-1M, Avantes BV; optical ranges (optical
powers) are 215–500 nm (58 μW) and 500–2500 nm (287 μW) for
deuterium and halogen lamps, correspondingly] at ambient temperature
under Ar or air atmospheres. The degassed solution of methanofullerene
in toluene (toluene cut-off value of 285 nm) was put in quartz suprasil
cuvette (spectral range of 200–2500 nm, light path of 10 mm) which was
placed in cuvette sample holder (CUV-ALL-UV/VIS, Avantes BV)
connected with the light source and spectrometer by means of fibber-
optic cables. Cuvette holder has a 5 mm wide slit to hold filters,
collimating lenses, and a cover to prevent ambient light. All spectra were
recorded using the spectrometer within wavelength range of 290–1100
nm (AvaSpec-2048, optical resolution of 2.4 nm, Avantes BV).
[
68]
hydroxide solution according to procedure from ref.
hydroxide (40 % wt. solution in H O, 5 mL) was added to toluene (10 mL)
and cooled to 0°C followed by addition of N-nitrozo-N-methylurea (20 mg,
.19 mmol) under continuous cooling and stirring. Resulting light-yellow
Potassium
2
0
toluene solution containing diazomethane was used without further
purification.
Reaction of C
diazomethane solution in toluene (1 mL) was added to solution of C
(14.6 mg, 9.8 μmol) in toluene (15 mL) and the reaction
s 3 8
-C70(CF ) with diazomethane. Freshly prepared cooled
s
-
3 8
C70(CF )
mixture was stirred for 20 min under continues cooling at 0°C using ice
bath. Progress of the reaction was monitored out by means of HPLC
(
Cosmosil Buckyprep 4.6 mm I.D. × 25 cm, toluene, flow rate of 1 mL
–1
min ). Then the reaction mixture was filtered through silica gel using
toluene as an eluent, heated at 90°C (2–3 min) for complete thermolysis
of 1-pyrazoline intermediates and cooled to room temperature. The
products of the reaction were separated into individual compounds by
HPLC (Cosmosil Buckyprep 10 mm I.D. × 25 cm, toluene, flow rate of 4.6
Quantum chemical calculations. Initially, molecular geometry of the
each structure in question was optimized at the AM1 level of theory with
[
64]
the use of the Firefly 8.2 software partly based on the GAMESS (US)
[
65]
source code.
This was followed DFT optimization with electronic
–1
mL min ) and their molecular composition was determined by means of
structure and GIAO calculations (GIAO=gauge-including atomic orbitals)
of the NMR chemical shifts for selected subsets of the structures. The
latter tasks were carried out with the use of the PRIRODA v. 6 software
MALDI mass spectrometry.
[
5,6]-closed C70(CF
integration). t 6.5 min (Cosmosil Buckyprep 4.6 mm I.D. × 25 cm,
toluene, 1 mL min ). UV-vis (toluene): λmax=304, 356 (sh.), 420 (sh.),
98 (sh.), 456 nm.
3 8 2 2
) [CH N ] (compound 2). Yield 39% (HPLC trace
[
66]
that implements efficient RI approximation (PBE exchange-correlation
R
[
67]
functional
and
a
built-in basis set of of triple-ζ quality with
–1
(
(
11s6p2d)/[6s3p2d] contraction scheme for first row atoms and
5s1p)/[3s1p] for hydrogen atoms were used). The analysis of the
3
isomerisation pathways was performed for model polyene C34
H
10(CH
2
)
)
2
C
1
-C70(CF
(Cosmosil Buckyprep 4.6 mm I.D. × 25 cm, toluene, 1 mL min ).
NMR (600.15 MHz, CDCl , 25 °C, TMS): δ =2.69 (d, J(H,H)=11.2 Hz, 1H,
CH ), 5.52 ppm (d, J(H,H)=11.0 Hz, 1H, CH
CDCl , 25 °C, C ): –δ =60.4 (m, 3F, CF ), 61.3 (m, 3F, CF
J(F,F)=17.2 Hz, 3F, CF ), 61.6 (m, 3F, CF ), 61.9 (m, 3F, CF
F, CF ), 62.8 (m, 3F, CF ), 65.7 ppm (q, J(F,F)=15.6 Hz, 3F, CF
NMR (600.3 MHz, CDCl , 25 °C), δ
), 65.6 (С(СF )), 67.4 (С(СF
4.5 (С(СF )), 74.9 (С(СF
СF ), 125.3, 125.9, 127.1, 127.7, 128.2, 128.5, 128.7, 128.8, 129.0,
30.4, 130.6, 131.0, 136.4, 137.0, 137.7, 137.8, 137.9, 141.9, 142.5,
3 8 2 R
) [CH ] (compound 3). Yield 40% (6.5 mg). t 6.0 min
that mimic, at least partly, the topology of the π-system of C -C70(CF
s
3
8
–1
1
[
19]
H
as was recently shown. The model polyene with two methano bridges
3 8
as geometry constraints reproduces the unsaturated part of C -C70(CF ) ,
3
H
s
19
2
2
). F NMR (564.7 MHz,
), 61.5 (q,
), 62.4 (m,
encompassed its portion centered around the [5,6]-bond in question. All
located transition states possess only one imaginary frequency and a
single minimal energy reaction path connects reactants and products,
according to the intrinsic reaction coordinate method. For further details
see supporting information.
3
F
6 6
F
3
3
3
3
3
13
3
3
3
3
).
), 108.6
)), 74.4 (С(СF )),
)), 122.2–124.7
C
3
C
: 30.1 (CH
2
), 95.6 (Ccage–CH
2
(
C
cage–CH
2
3
3
)), 71.3 (С(СF
3
3
7
(
1
3
3
)), 75.0 (С(СF
3
)), 76.1 (С(СF
3
3
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201701610
FULL PAPER
1
1
1
1
1
43.1, 143.1, 144.1, 144.6, 145.0, 145.3, 145.5, 145.6, 145.7, 145.9,
46.0, 146.1, 146.2, 146.9, 147.2, 148.0, 148.1, 148.3, 148.4, 148.5,
48.8, 149.0, 149.1, 149.6, 149.7, 149.9, 149.9, 150.0, 150.2, 150.4,
50.8, 150.9, 151.0, 151.1, 151.3, 152.4, 152.7, 153.1, 153.2, 153.7,
[16] A. A. Popov, I. E. Kareev, N. B. Shustova, E. B. Stukalin, S. F.
Lebedkin, K. Seppelt, S. H. Strauss, O. V. Boltalina, L. Dunsch, J. Am.
Chem. Soc. 2007, 11551–11568.
[17] E. V. Bukovsky, B. W. Larson, T. T. Clikeman, Y.-S. Chen, A. A. Popov,
O. V. Boltalina, S. H. Strauss, J. Fluor. Chem. 2016, 185, 103–117.
[18] O. O. Semivrazhskaya, A. V. Rybalchenko, M. P. Kosaia, N. S.
Lukonina, O. N. Mazaleva, I. N. Ioffe, S. I. Troyanov, N. B. Tamm, A. A.
2
1
56.3 ppm (62 of 62 awaited resonances within sp -C atoms region). H–
1
3
C HMBC NMR (600.3, 150.9 MHz, CDCl
represented as doublets at 2.7 and 5.5 ppm correlate with following
resonances: 30 (>CH , satellite), 95.4 (Cbrh1–CH ), 108.5 (Cbrh2–CH
27.7 (Ccage), 130.7 (Ccage), 137.6 (Ccage), 149.9 ppm (Ccage); UV-vis
toluene): λmax=398, 418, 448, 474, 558, 604 nm. MALDI MS: m/z (%):
3
, 25 °C): both hydrogen atoms
13
C
2
2
2
),
Goryunkov,
Electrochimica
Acta
2017,
1
(
DOI:10.1016/j.electacta.2017.09.161.
[19] A. V. Rybalchenko, M. G. Apenova, O. O. Semivrazhskaya, N. M. Belov,
V. Y. Markov, S. I. Troyanov, I. N. Ioffe, N. S. Lukonina, L. N. Sidorov, T.
V. Magdesieva, et al., Electrochimica Acta 2016, 191, 980–986.
–
–
–
–
3 8 1 3 8 2
1392.0 (6, [C70(CF ) ], [M ]); 1406.0 (100, [C70(CF ) (CH ) ], [M ]).
[
[
[
20] T. Suzuki, Q. Li, K. C. Khemani, F. Wudl, J. Am. Chem. Soc. 1992, 114,
7301–7302.
C
s
-C70(CF
3 8 2 R
) [CH ] (compound 4). Yield 95% (6.1 mg). t 4.6 min
–1
1
(Cosmosil Buckyprep 4.6 mm I.D. × 25 cm, toluene, 1 mL min ).
H
21] A. B. Smith III, R. M. Strongin, L. Brard, G. T. Furst, W. J. Romanow, K.
G. Owens, R. C. King, J. Am. Chem. Soc. 1993, 115, 5829–5830.
22] A. B. I. Smith, R. M. Strongin, L. Brard, G. T. Furst, W. J. Romanow, K.
G. Owens, R. J. Goldschmidt, R. C. King, J. Am. Chem. Soc. 1995, 117,
NMR (600.15 MHz, CDCl
CH ), 4.8 ppm (d, J(H,H)=6.9 Hz, 1H, CH
5 °C, C ): –δ =61.4 (m, 6F, 2CF
CF ), 66.4 ppm (q, J(F,F)=15.6 Hz, 6F, 2CF
, 25 °C): both hydrogen atoms represented as
3
, 25 °C, TMS): δ
H
1
=2.2 (d, J(H,H)=6.9 Hz, 1H,
9
2
2
). F NMR (564.7 MHz, CDCl
3
,
2
2
6
F
6
F
3 3
), 61.6 (m, 6F, 2CF ), 61.8 (m, 6F,
1
13
3
3
). H– C HMBC NMR
5492–5502.
(
600.3, 150.9 MHz, CDCl
doublets at 2.2 and 4.8 ppm correlate with following C resonances: 59.7
), 129.4 (Ccage), 147.2 ppm (Ccage). UV-vis (toluene): λmax=426,
3
13
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(CH
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European Journal of Organic Chemistry
10.1002/ejoc.201701610
FULL PAPER
FULL PAPER
A pirouette on a cage: Rare fullerene
Fullerenes
derivatives with >CH
6,6]-open or
2
addends in
[5,6]-closed
[
O. O. Semivrazhskaya, N. M. Belov, A.
V. Rybalchenko, V. Yu. Markov, I. N.
Ioffe, N. S. Lukonina, S. I. Troyanov, E.
Kemnitz, and A. A. Goryunkov*
configuration are readily accessible
via treatment of -C70(CF with
C
s
3 8
)
diazomethane followed by thermolysis
or photolysis. Thermodynamically less
favorable
undergoes
quantitative phototransformation into
the thermodynamically preferable
[6,6]-open
unexpectedly
isomer
rapid
Page No. – Page No.
Regioselective synthesis of [6,6]-
open and [5,6]-closed C70(CF
methanofullerenes with rapid [6,6]-to-
5,6] phototransformation
3 8 2
) [CH ]
[
5,6]-closed methanofullerene via
[
triplet manifold.
This article is protected by copyright. All rights reserved.