Reactions of C702- with organic halides revisited: Unusual magnetic equivalence for the diastereotopic methylene protons in 2,5-(PhCH2)2C70

Article abstract of DOI:10.1021/jo4011848

The reactions of C₇₀^2- with organic halides result in several isomeric products. However, the structures of the isomers have not been identified unambiguously and the reactions still remain elusive even though the first report of the reaction appeared more than ten years ago. Herein, the reactions of C₇₀^2- with ArCH₂Br (Ar = Ph, o-, m-, and p-BrC₆H₄) are revisited. Two types of isomeric para-adducts of 2,5- and 7,23-(ArCH₂)₂C₇₀ are obtained and characterized with the X-ray single-crystal diffractions, HRMS, ¹H and ¹³C NMR, and UV-vis spectroscopies. An unusual singlet resonance instead of the typical AB quartet resonance is shown for the C2 diastereotopic methylene protons in ¹H NMR spectrum of 2,5-(PhCH₂)₂C₇₀ recorded at ambient temperature. The unexpected magnetic equivalence is studied with the variable-temperature (VT) NMR and density functional theory (DFT) calculations. The results show that the greater local curvature in the C₇₀ polar region is likely responsible for the unusual magnetic equivalence exhibited by the C2 diastereotopic methylene protons of 2,5-(PhCH₂) ₂C₇₀, indicating that under certain cases, it is improbable to elucidate the spectral data of fullerene derivatives with a less symmetrical carbon cage in analogy with those of the C₆₀ derivatives.

Full text of DOI:10.1021/jo4011848

Article
pubs.acs.org/joc
2−
Reactions of C70 with Organic Halides Revisited: Unusual Magnetic
Equivalence for the Diastereotopic Methylene Protons in 2,5-
(PhCH2)2C70
Shu-Hui Li, Zong-Jun Li, Wei-Wei Yang, and Xiang Gao*
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, University of Chinese Academy of
Sciences, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, Jilin 130022, China
S
* Supporting Information
2−
ABSTRACT: The reactions of C70 with organic halides
result in several isomeric products. However, the structures of
the isomers have not been identified unambiguously and the
reactions still remain elusive even though the first report of the
reaction appeared more than ten years ago. Herein, the
2−
reactions of C70 with ArCH2Br (Ar = Ph, o-, m-, and p-
BrC6H4) are revisited. Two types of isomeric para-adducts of
2,5- and 7,23-(ArCH2)2C70 are obtained and characterized
1
with the X-ray single-crystal diffractions, HRMS, H and 13C
NMR, and UV−vis spectroscopies. An unusual singlet
resonance instead of the typical AB quartet resonance is
1
shown for the C2 diastereotopic methylene protons in H
NMR spectrum of 2,5-(PhCH2)2C70 recorded at ambient
temperature. The unexpected magnetic equivalence is studied with the variable-temperature (VT) NMR and density functional
theory (DFT) calculations. The results show that the greater local curvature in the C70 polar region is likely responsible for the
unusual magnetic equivalence exhibited by the C2 diastereotopic methylene protons of 2,5-(PhCH2)2C70, indicating that under
certain cases, it is improbable to elucidate the spectral data of fullerene derivatives with a less symmetrical carbon cage in analogy
with those of the C60 derivatives.
the products have not been identified unambiguously due to
INTRODUCTION
■
The reactions of anionic fullerene species1−24 are important
supplements to the reactions of neutral fullerenes.25 Neutral
fullerenes are quite electron-deficient as evidenced by the
electrochemical study, where C60 and C70 undergo six
consecutive one-electron transfer reductions,26 and they are
typically involved in the reactions with nucleophiles.25 As for
the anionic fullerenes, they are electron-rich species and tend to
undergo reactions with electrophiles.1−24 Because of the
electron-deficiency of fullerenes, anionic fullerenes are stable
and readily available via either electrochemical1−6,16−18,23,24 or
chemical7−15,19−22 reductions.
the structural complications caused by the lower symmetry of
C70 cage.28 For the reaction of C70 with PhCH21Br, three
2−
regioisomers were proposed to form on the basis of H NMR
results,16 where two AB quartets and one singlet resonance are
shown for the methylene protons of the benzyls. The two AB
quartet resonances were assigned to the 7,23- (1a) and 7,19-
adducts (Scheme 1), respectively, and the singlet resonance was
assigned to the 7,38-adduct29,30 (Scheme 1) by reasoning with
1
the analogy of the H NMR results of C60 derivatives and also
computational calculations. However, only the 7,23-isomer has
been identified explicitly by the 13C INADEQUATE NMR
using 13C-enriched C70,21 while the structures of the other
products have never been confirmed.
The most conventional reactions studied for the anionic
fullerenes are the reactions of C60 dianion with organic
halides,1−4,7−15 which would form either the 1,4-adducts
(para-configuration, addition occurs at the carbon atoms across
one hexagon of fullerenes) or 1,2-adducts (ortho-configuration,
addition takes place at the carbon atoms between two hexagons
of fullerenes) depending on the size of addends, as a result of
the intrinsic stability difference between the two types of
adducts and the instability caused by the steric hindrance when
the addends are closely positioned.27 However, the reactions of
2−
Herein, we report the revisit of the reactions of C70 with
ArCH2Br (Ar = Ph, o-, m-, and p-BrC6H4). The reaction
products have been structurally characterized with the X-ray
single-crystal diffractions and various spectroscopic methods.
The results show unambiguously that 7,23- (1) and 2,5-isomers
(2) (Scheme 1) are obtained, while neither 7,19- nor 7,38-
isomer is formed from the reaction. VT 1H NMR and
computational calculations have also been performed to
2−
C70 with organic halides have remained elusive, even though
2−
the first report on the reaction of C70 with PhCH2Br
Received: May 30, 2013
Published: June 25, 2013
appeared more than 10 years ago,16 because the structures of
© 2013 American Chemical Society
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ORTEP diagrams of the resolved structures of 1b, 1c, 2a, and
2d, which unambiguously show that two types of para-adducts,
7,23- and 2,5-isomers, are produced from the reactions of C70
Scheme 1. Illustrated Structures of the 7,19-, 7,38-, and 7,23-
(PhCH2)2C70 Adducts Claimed in Ref 16 and the C70 7,23-
Adduct (1) and 2,5-Adduct (2) Obtained in This Work
2−
with organic halides, consistent with the addition preference of
benzyls when reacting with fullerene cages of C603,4 and M3N@
C80 (M = Lu, Sc).31 Notably, the phenyl rings in each
compound are all located over a hexagon of C70, suggesting a
possible interaction between the phenyl ring and the hexagon
of C70 cage. To the best of our knowledge, this is the first time
that single-crystal structures for the C70 7,23- and 2,5-adducts
have been obtained, and they may provide more structural
details for the 7,23-isomer and also the 2,5-isomer, which has
been proposed for C70 derivatives with addends of tert-
butylperoxo32 and trifluoromethyl33 on the basis of molecule
symmetry and computational calculations.
The HRMS of 1a−d and 2a−d (see the Supporting
Information) show M+ or [M + H]+ at 1022.11086,
1177.93290, 1178.93294, 1178.93607 and 1023.11635,
1178.93590, 1178.94001, 1178.93639, respectively, consistent
with the formation of the respective (ArCH2)2C70 molecules.
Compounds 1a and 1d are identified as the 7,23-adducts, while
compounds 2b and 2c are determined as the 2,5-adducts by
comparing the UV−vis absorptions with 1b,c and 2a,d,
respectively, since UV−vis spectroscopy has been shown to
be characteristic of the addition pattern rather than the types of
addends.34 The 13C NMR spectra of 1a−d (see the Supporting
Information) all display a similar pattern, with one resonance
for the methylene carbon (around 50 ppm) of the benzyl and
one resonance for the sp3 C70 carbon (around 56 ppm) bonded
to the benzyl for each compound, and a total of about 32 sp2
C70 resonances along with signals arising from the phenyl rings,
consistent with the C2 symmetry of the 7,23-adduct. As for 2a−
d, the 13C NMR spectra display two resonances for the
methylene carbons, two signals for the sp3 C70 carbons bonded
to the benzyls for each compound, and a total of about 60 sp2
C70 resonances along with signals due to the phenyl carbons,
consistent with the C1 symmetry of the 2,5-adduct as shown by
the crystal structure.
1
rationalize the unusual magnetic equivalence shown in the H
NMR spectrum of 2,5-(PhCH2)2C70, which has confused the
previous assignment of the product.
RESULTS AND DISCUSSION
■
2−
Reactions of C70 with ArCH2Br (Ar = Ph, o-, m-, p-
BrC6H4) and Structural Characterizations of the Prod-
2−
ucts. The reactions of C70 with organic halides were carried
out following procedures reported previously,16 except the
reaction temperature was elevated to 50 °C to improve the
yield of the products (see the Experimental Section). The crude
mixture consists of two major products, which are identified as
the 7,23-(ArCH2)2C70 (1) and 2,5-(ArCH2)2C70 (2) after a
two-stage HPLC purification, along with unreacted C70.
Single-crystals suitable for X-ray diffractions have been
obtained for 1b, 1c, 2a, and 2d. Figure 1 displays the
1H NMR of 2,5-(PhCH2)2C70: Singlet Resonance for the
C2 Diastereotopic Methylene Protons. The 1H NMR
spectra of the 7,23-adducts (1a−d) show one AB quartet for
the two sets of diastereotopic methylene protons of each
compound (see the Supporting Information), consistent the C2
symmetry of the molecule and in agreement with the
conventions exhibited by the diastereotopic methylene protons
3,12−15,35
31
bonded to the C60
and C80 cages.
1
Surprisingly, a totally different scenario is shown for the H
NMR spectrum of 2,5-(PhCH2)2C70 (2a). Figure 2a displays
the expanded 1H NMR spectrum (600 MHz) for the methylene
protons of 2a recorded at room temperature, which shows one
AB quartet (δ = 3.20 ppm, ABq, ΔνAB = 24.0 Hz, JAB = 18.0 Hz,
2H) and one singlet (δ = 3.65 ppm, 2H) resonances for the two
sets of methylene protons, consistent with the result reported
previously.16 The presence of an AB quartet is quite typical for
the diastereotopic methylene protons, as compared with the
counterpart of 1a−1d and also the adducts of C603,12−15,35 and
M3N@C80.31 However, the appearance of a singlet resonance
for the diastereotopic methylene protons at room temperature
is really unexpected, especially by analyzing the 1H NMR
results of the diastereotopic methylene protons bonded to C60
and C80 cages and also to the C70 cage at the equatorial 7,23-
positions. Previous work has shown that the diastereotopic
methylene protons of 1,4-(PhCH2)2C60 would exhibit a broad
Figure 1. ORTEP diagrams for 1b, 1c, 2a, and 2d molecules with 30%
thermal ellipsoids. The solvent molecules and hydrogen atoms are
omitted for clarity.
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Compounds 2,5-(ArCH2)2C70 (Ar = o-, m-, p-BrC6H4) (2b,
1
2c, and 2d) were also subjected to the H NMR character-
ization (see the Supporting Information). Different from the
result of 2,5-(PhCH2)2C70, the two sets of the methylene
protons both display AB quartets for the C70 derivatives with
the Br-substituted benzyls, implying that the exhibited magnetic
equivalence for the C2 diastereotopic methylene protons of 2,5-
(PhCH2)2C70 is rather delicate.
1
VT H NMR and DFT Computational Calculations. To
obtain a better understanding on the exhibited magnetic
equivalence of the C2 diastereotopic methylene protons of 2a,
VT 1H NMR was performed on the 2,5-(PhCH2)2C70, and the
results are displayed in Figure 3. As is shown in the Figure,
1
Figure 2. Expanded H NMR spectra (600 Hz) of (a) 2a and (b) 2f
showing the resonances of methylene protons recorded in CS2 with
benzene-d6 as the external lock solvent at room temperature. The
labeled numbers in brackets refer to the relative integration areas.
singlet resonance only at a high temperature of 370 K due to
the coalesce of the AB quartet,36 which is likely caused by the
accelerated rotation of the phenyl rings, whose conformation
significantly affects the magnetic equivalence of the diaster-
eotopic methylene protons as shown in previous work.37 This
ambient singlet resonance was unfortunately misassigned to the
7,38-C70 adduct (Scheme 1), by assuming that the two far-
separated benzyls might have much less interactions with each
other and thus rotate in a rather free manner.16,38
Two H/D labeling experiments were carried out to identify
which set of the diastereotopic methylene protons would
exhibit the magnetic equivalence. The first one was performed
by adding equal amounts of PhCD2Br and PhCH2Br
(nPh2C−D2Br:nPhCH2Br:nC70 = 10:10:1) simultaneously into the
C70 solution, and the obtained 2,5-adduct is designated as
2e. The second experiment was carried out by also using equal
Figure 3. Expanded VT 1H NMR spectra (600 Hz) of 2,5-
(PhCH2)2C70 from 213 to 333 K recorded in CS2 with acetone-d6
as the external lock solvent. The signals labeled with # and * in the
spectra (from 293 to 333 K) are likely due to the H2O residue
presented in CS2 and acetone-d6.
amounts of PhCD2Br and PhCH2Br (nPhCD2Br:nPhCH2Br:nC70
=
10:10:1), but with a stepwise addition manner, where PhCD2Br
was added first, followed by the addition of PhCH2Br with a
time interval of about 20 min (see the Experimental Section),
similar to the procedures reported previously,6,18,35 which can
effectively differentiate the benzyls added during different steps
of the reaction, by taking advantage of the stepwise nature of
the reaction between the dianion of fullerenes and organic
halides.8,10,16,17 The obtained 2,5-adduct is designated as 2f.
No significant SKIE (secondary kinetic isotope effect) is
observed between PhCH2Br and PhCD2Br as indicated by the
1H NMR spectrum of 2e (Figure S39, Supporting Informa-
tion), which shows both the singlet and the AB quartet
resonances consist of almost equal amount of PhCD2 and
when the temperature is low (213 and 233 K), the C2
diastereotopic methylene protons indeed exhibit an AB quartet;
while as the temperature reaches to 253 K and above, the C2
methylene protons exhibit a singlet resonance despite of their
diastereotopic nature. The results indicate that the exhibited
magnetic equivalence for the C2 diastereotopic methylene
protons at room temperature is likely caused by the same
mechanism that coalesces the AB quartet of 1,4-(PhCH2)2C60
at high temperature, i.e., the rapid rotation of the phenyl ring,37
suggesting that the barrier for the rotation of phenyl ring of the
C2 benzyl about the C71−C72 bond (Figure 1 for 2a) is less
than that for rotating the phenyl ring of the C5 benzyl about
the C78−C79 bond (Figure 1 for 2a) and also the one for
rotating the phenyl ring in 1,4-(PhCH2)2C60. Notably, the AB
quartet signal due to the C5 methylene protons also coalesces
into a singlet resonance as the temperature is increased to 333
K, suggesting that the barrier for the rotation of the phenyl ring
of the C5 benzyl about the C78−C79 bond is also less than the
respective one for rotating the phenyl ring in 1,4-(PhCH2)2C60.
DFT calculations were performed to rationalize the much
less rotational barrier for the C2 phenyl around the C2−C71
1
PhCH2. As for compound 2f, the H NMR spectrum (Figure
2b) shows that the singlet resonance has a much lower intensity
with respect to the AB quartet, indicating explicitly that the
2−
singlet originates from the benzyl added to C70 during the
first step. Previous work has demonstrated that C2 is the first
addition site since the C2-RC70 is more stable;17,18,39 the
−
results therefore show unambiguously that the C2 diaster-
eotopic methylene protons are the ones exhibiting the singlet
resonance in the 1H NMR spectrum, while the C5
diastereotopic methylene protons still exhibit the typical AB
quartet signal.
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Figure 4. (a) Simulated structure of 2,5-(PhCH2)2C70 used for calculations of the rotational barriers of the phenyl rings about the C71−C72 and
C78−C79 bonds; (b) the most hindered structures simulated by the rotation of the C2 phenyl; (c) the most hindered structures simulated by the
rotation of the C5 phenyl.
Figure 5. Calculated energy profiles on the rotation of the phenyl ring of (a) the C2 phenyl about the C71−C72 bond and (b) the C5 phenyl about
the C78−C79 bond.
bond. The geometry of the simulated structures were optimized
at the HF/6-31G level, and the rotational barriers were
calculated at the B3LYP/6-311G(d) level. It is noteworthy that
if a structure with the conformation similar to the crystal
structure of 2a (Figure 1), where the C5 benzyl is orientated
toward the C2 benzyl, is directly used for the simulation, the
C5 phenyl ring would experience a significant hindrance from
the interactions with the methylene protons of the C2 benzyl
during the simulated rotation due to the specific conformation
of the benzyls, indicating that it is unlikely for the C5 phenyl
ring to rotate over the hexagon located in the polar region,
rather the C5 phenyl ring would be likely to rotate over the
hexagon in the equatorial region, if such a configuration is also
an energy minimum and the rotation barrier for the C5 benzyl
about the C5−C78 bond (Figure 1, 2a) is small enough.
The evaluation of the rotation hindrance of respective benzyl
about the C2−C71 and C5−C78 bonds is therefore necessary
before assessing the rotational barriers of the C2 and C5 phenyl
rings about the C71−C72 and C78−C79 bonds. Simulated
molecules of 2,5-(PhCH2)HC70 and 2,5-H(PhCH2)C70 were
used to avoid the overestimation of the hindrance brought by
the interactions between the two benzyls if 2,5-(PhCH2)2C70
was used. The simulated molecules of 2,5-(PhCH2)HC70 and
2,5-H(PhCH2)C70 were constructed on the basis of the
optimized structure starting with the crystal structure of 2a,
where one benzyl was replaced with an H atom, while the other
benzyl was remained with the original conformation. A small
hindrance of 4.9 and 6.8 kcal/mol is predicted for the rotation
of the C2 and C5 benzyls about the C2−C71 and C5−C78
bond, respectively (see Figures S48 and S49, Supporting
Information, for the calculated energy profiles), suggesting that
it is possible for the C2 and C5 benzyl to adopt conformation
other than the one shown in the single-crystal structure.
The rotational barrier calculations for the C2 and C5 phenyl
about the C71−C72 bond and C78−C79 bonds were
performed by adopting a configuration as shown in Figure 4a,
where the C2 benzyl remains the similar conformation as that
shown in the crystal structure of 2a, while the C5 benzyl is
rotated over the equatorial hexagon of C70 that contains C5 for
the following reasons: First, the rotation barrier of the C5
benzyl about the C5−C78 bond is quite small, and such a
configuration is also an energy minimum, with only about 0.4
kcal/mol higher than the optimized configuration starting with
the single-crystal structure; second, with such conformation, it
would avoid the interactions between the two benzyls during
the simulated rotation of the C5 phenyl, suggesting that this is
more likely the actual rotation pathway for the C5 phenyl about
the C78−C79 bond.
Parts b and c of Figure 4 show the diagrams of the most
hindered structures simulated by the rotation of the phenyl
rings of the C2 and C5 benzyls, respectively. As is shown in
Figure 4, the rotation hindrance mainly arises from the
interactions of the phenyl ring with the C70 fullerene cage.
The shortest distance between the ortho H of C2 phenyl and
C
70 cage is 1.87 Å, while it is 1.81 Å between the ortho H of C5
phenyl and the C70 cage, suggesting a smaller barrier for the
rotation of the C2 phenyl than rotating the C5 phenyl.
Figure 5 shows the calculated energy profiles for the rotation
of the C2 and C5 phenyls about the C71−C72 and C78−C79
bonds. The calculations predict a barrier of about 17.8 kcal/mol
for the rotation of the C2 phenyl, and 21.9 kcal/mol for the
rotation of the C5 phenyl, consistent with the experimental
results that the C2 diastereotopic methylene protons exhibit a
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2−
Scheme 2. Proposed Mechanism for the Reaction of C70 with Organic Halides
−
singlet resonance, while the C5 ones exhibit an AB quartet
resonance in the 1H NMR spectrum for the compound and also
the simulated most hindered structures shown in parts b and c
of Figure 4.
or C7−RC70 to ArCH2Br, resulting in the 2,5- and 7,23-
isomers.
CONCLUSION
■
2−
The results indicate that the unusual magnetic equivalence
observed for the C2 methylene protons of 2,5-(PhCH2)2C70 is
likely caused by the free rotation of the C2 phenyl ring due to a
small rotation hindrance. Such a small barrier is probably
related to the specific shape of C70 carbon cage, where the polar
region has the greatest curvature, while the equatorial region is
much flatted. As is shown in parts b and c of Figure 4, the C2
phenyl is likely to have an interaction with the hexagon located
in the polar region, while the C5 phenyl would be likely have an
interaction with the hexagon in the equatorial region during
their respective rotation. Consequently, the C2 phenyl would
have a longer distance from the carbon cage due to the greater
curvature of the fullerene cage and experiences a less rotation
hindrance, while the C5 phenyl would be likely to have a
shorter distance from the carbon cage due to the flat surface of
equatorial region of C70, and experiences a greater rotation
hindrance. Notably, no such structural variance is encountered
for the spherical cages such as C60 and C80 with Ih symmetry,
suggesting that an addend bonded to a spherical carbon cage
may experience a different effect compared with the addend
bonded to a less symmetrical carbon cage, indicating that
cautions should be taken when structural elucidations of
fullerene derivatives with a less symmetrical carbon cage by
reasoning in analogy with the spectral results of C60 derivatives.
As for the Br-substituted 2,5-adducts, the Br may slightly
change the conformations of the aromatic rings, thus varying
the barrier for the rotation of the C2 phenyl, and results in the
exhibition of AB quartet resonance for the respective C2
methylene protons.
The reactions of C70 with organic halides have been
reinvestigated, and the reaction products have been identified
with the X-ray single-crystal diffractions and various spectro-
scopic characterizations. Experiment of H/D labeling has
identified the C2 diastereotopic methylene protons of 2,5-
(PhCH2)2C70 as the ones that exhibit the singlet resonance, and
such unusual magnetic equivalence is further studied with the
VT 1H NMR and DFT calculations. The results imply that the
curvature variance of a fullerene carbon cage may affect the 1H
NMR spectra of the derivatives, indicating that cautions should
be exercised when structural elucidations of fullerene
derivatives with a less symmetrical carbon cage by reasoning
1
in analogy with the H NMR results of C60 derivatives. The
understanding of the effect of less symmetrical fullerene carbon
1
cages toward the H NMR of the fullerene derivatives is of
significance, since the carbon cages of most higher fullerenes
are less symmetrical, and the study of the chemical reactivity of
higher fullerenes has been considered as one of the new
challenges in the fullerene chemistry,40 where the H NMR
1
spectroscopy is expected to play an important role, because it
requires much less samples than the 13C NMR and the
availability of higher fullerenes is very limited at current stage.
EXPERIMENTAL SECTION
■
General Methods. All reactions were carried out under an
atmosphere of argon. All reagents were obtained commercially and
used without further purification unless otherwise noted. Benzonitrile
(PhCN) was distilled over P2O5 under vacuum at 305 K prior to use.
Tetra-n-butylammonium perchlorate (TBAP) was recrystallized from
absolute ethanol and dried under vacuum at 313 K prior to use.
Controlled-potential bulk electrolysis was carried out on a
potentiostat/galvanostat using an “H” type cell which consisted of
two platinum gauze electrodes (working and counter electrodes)
separated by a sintered glass frit. A saturated calomel electrode (SCE)
was used as reference electrode. A fritted-glass bridge of low porosity
which contained the solvent/supporting electrolyte mixture was used
to separate the SCE from the bulk of the solution.
2−
Reaction Mechanism of C70 with Organic Halides.
On the basis of the product structures and previous work on
the reaction of fullerene dianions,8,10,16,17 the reactions of C70
2−
with organic halides are finally clarified, and a reaction
mechanism for the formation of diorgano C70 para-adducts is
proposed as shown in Scheme 2. A single-electron transfer
2−
Synthesis of 7,23- and 2,5-(ArCH2)2C70 (Ar = Ph, o-, m-, and
p-BrC6H4). Typically, C70 (100 mg, 0.12 mmol) was electrolyzed at
−1.10 V versus SCE in freshly distilled PhCN solution containing 0.1
M TBAP under an argon atmosphere. The potentiostat was switched
off after the electrolytic formation of C702− was complete, and a 50-fold
excess of ArCH2Br was added into the solution under inert
atmosphere. The reaction was allowed to proceed for about 3 h
(SET) occurs between C70 and ArCH2Br with the formation
•
−
of C70•− and ArCH2 , which consequently form the C2−RC70
−
and C7−RC70 intermediates via radical coupling reaction
owing to the stability of these two species as supported by the
DFT calculations.17 A subsequent para-addition of the second
−
benzyl would then take place via the SN2 attack of C2−RC70
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with stirring at 50 °C. The mixture was dried with a rotary evaporator
under reduced pressure, and the residue was washed with methanol to
remove TBAP and excessive ArCH2Br. The obtained crude mixture
was put into toluene and sonicated for 10 min, and the soluble part
was further purified by HPLC over a two-stage chromatographic
procedure. At the first stage, the crude mixture was eluted with toluene
over a semipreparative Buckyprep column with a flow rate of 3.7 mL/
min, and the two fractions of the products were collected together. At
the second stage, the collected product mixture during the first stage
was eluted with a mixture of toluene and n-hexane (v:v = 7:3) over a
semipreparative Buckyprep column. Satisfactory separations of 1a
from 2a and 1b from 2b were achieved when the flow rate was 3.7
mL/min; and satisfactory separations of 1c from 2c and 1d from 2d
were achieved when the flow rate was 2.5 mL/min. Under typical
conditions, the isolated yield for the 7,23-(ArCH2)2C70 is 33% (40
mg) for 1a, 21% (29 mg) for 1b, 24% (34 mg) for 1c, and 33% (46
mg) for 1d; while it is 36% (44 mg) for 2a, 31% (43 mg) for 2b, 35%
(49 mg) for 2c, and 26% (36 mg) for 2d. The recovery yield of C70 is
18% (18 mg), 26% (26 mg), 27% (27 mg), and 26% (26 mg) for the
Spectral Characterization of 1b. Positive ESI FT-ICR MS: m/z
+
1
calcd for M+ (C84H12Br2 ), 1177.93003; found, 1177.93290. H NMR
(600 MHz, in CS2 with benzene-d6 as the external lock solvent) δ =
7.86 (d, 2H), 7.66 (d, 2H), 7.57 (t, 2H), 7.47 (t, 2H), 4.18 (ABq, Δν =
48.0 Hz, J = 12.0 Hz, 4H). 13C NMR (125 MHz, CS2/CDCl3): δ =
157.83 (2C), 151.76 (2C), 150.83 (2C), 150.43 (2C), 149.75 (2C),
149.00 (2C), 148.84 (2C), 148.72 (2C), 148.54 (2C), 148.38 (2C),
147.53 (2C), 147.36 (2C), 147.21 (2C), 147.07 (2C), 146.94 (2C),
146.20 (2C), 146.04 (2C), 145.35 (2C), 145.32 (2C), 145.28 (2C),
144.64 (2C), 144.54 (2C), 144.40 (2C), 144.00 (2C), 142.89 (2C),
142.43 (2C), 142.16 (2C), 141.19 (2C), 139.54 (2C), 139.35 (2C),
135.59 (2C, Ph), 134.21 (2C), 134.18 (2C), 133.70 (2C), 133.66 (2C,
Ph), 132.80 (2C, Ph), 132.28 (2C), 129.25 (2C, Ph), 127.19 (2C, Ph),
126.33 (2C, Ph) 56.95 (2C, sp3, C70), 47.84 (2C, CH2). UV−vis
(toluene): λ max/nm = 403, 438, 624, and 785.
X-ray Single-Crystal Diffraction of 1b. Black crystals of 1b were
obtained by slowly diffusing ethanol into a CS2 solution of 1b at room
temperature. Single-crystal X-ray diffraction data were collected on an
instrument equipped with a CCD area detector using graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å) in the scan range
1.35° < θ < 26.11°. The structure was solved with the direct method of
SHELXS-97 and refined with full-matrix least-squares techniques using
the SHELXL-97 program within WINGX. Crystal data of 1b·CS2:
C84H12Br2·CS2, Mw = 1256.89, monoclinic, space group P2(1)/c, a =
14.0028(8) Å, b = 10.9052(5) Å, c = 30.6099(16) Å, α = 90°, β =
98.8290(10)°, γ = 90°, V = 4618.6(4) Å3, Z = 4, Dcalcd = 1.808 Mg
m−3, μ = 1.910 mm−1, T = 295(2) K, crystal size 0.39 × 0.26 × 0.21
mm; reflections collected 25222, independent reflections 9164; 5228
with I > 2σ(I); R1 = 0.0857 [I > 2σ (I)], wR2 = 0.2337 [I > 2σ(I)]; R1
= 0.1481 (all data), wR2 = 0.2714 (all data), GOF (on F2) = 1.104.
Spectral Characterization of 2b. Positive ESI FT-ICR MS: m/z
2−
reactions of C70 with PhCH2Br and o-, m-, p-BrC6H4CH2Br
respectively. No data on the melting point of the C70 derivatives
could be obtained, since the compounds would decompose before
reaching to the melting point.
Spectral Characterization of 1a. Positive ESI FT-ICR MS: m/z
calcd for M+ (C84H14+) 1022.10900, found 1022.11086. 1H NMR (600
MHz, in CS2 with benzene-d6 as the external lock solvent) δ = 7.62−
7.56 (m, 10H), 3.96 (ABq, Δν = 24.0 Hz, J = 18.0 Hz, 4H). 13C NMR
(125 MHz, CS2/CDCl3): δ = 158.35 (2C), 151.12 (2C), 150.66 (2C),
150.58 (2C), 149.82 (2C), 148.93 (2C), 148.85 (2C), 148.72 (2C),
148.50(2C), 148.39 (2C), 147.49 (2C), 147.38 (2C), 147.16 (2C),
147.09 (2C), 146.97 (2C), 146.21 (2C), 146.00 (2C), 145.45 (2C),
145.35 (2C), 145.29 (2C), 144.92 (2C), 144.63 (2C), 144.42 (2C),
143.74 (2C), 143.20 (2C), 142.96 (2C), 142.18 (2C), 141.25 (2C),
140.14 (2C), 139.44 (2C), 135.71 (2C,Ph), 134.24 (2C), 134.17 (2C),
133.71 (2C), 132.19 (2C), 130.68 (4C, Ph), 128.48 (4C, Ph), 127.71
+
1
calcd for [M + H]+ (C84H13Br2 ) 1178.93785, found 1178.93590. H
NMR (600 MHz, in CS2 with benzene-d6 as the external lock solvent)
δ = 7.96 (d, 1H), 7.82 (d, 1H), 7.74 (d, 1H), 7.70 (t, 1H), 7.56−
7.53(m, 2H), 7.49 (t, 1H), 7.36 (t, 1H), 4.00 (ABq, Δν = 144.0 Hz, JAB
= 12.0 Hz, 2H), 3.47 (ABq, Δν = 96.0) Hz, JAB = 12.0 Hz, 2H). 13C
NMR (150 MHz, CS2/CDCl3) all signals represent 1C except noted:
δ = 168.10, 159.45, 156.70, 154.71, 151.71, 151.51, 151.06, 150.38,
150.07, 149.59 (2C), 149.54, 149.05, 149.00, 148.85, 148.69, 148.36
(2C), 148.01, 147.72, 147.62, 147.57, 147.53, 147.44, 147.36, 147.29,
146.92, 146.75, 146.52, 146.48, 146.24, 146.06, 145.88, 145.53, 145.47,
145.33, 145.09, 144.94, 144.84, 144.72, 144.37, 144.36, 144.19, 143.76,
143.69, 143.55, 143.50, 142.89, 142.72, 142.60 (2C), 142.39, 142.04,
141.33, 138.80, 137.55, 136.87, 136.40, 135.86 (2C), 134.47, 133.44
(Ph), 133.13 (Ph), 132.77 (2C), 132.70 (Ph), 132.53, 132.45 (Ph),
132.16, 131.08, 130.76, 129.43, 129.06 (Ph), 128.94 (Ph), 128.74
(Ph), 128.15 (Ph), 127.29 (Ph), 127.02 (Ph), 126.33 (Ph), 125.97
(2C, Ph), 57.48 (2C, sp3), 50.04 (2C, CH2). UV−vis (toluene): λ max
nm = 403, 438, 624, and 785.
/
Spectral Characterization of 2a. Positive ESI FT-ICR MS: m/z
calcd for [M + H]+ (C84H15+) 1023.11683, found 1023.11635. 1H
NMR (600 MHz, in CS2 with C6D6 as the external lock solvent) δ =
7.72 (d, 2H), 7.68 (t, 2H), 7.56 (t, 1H), 7.52 (t, 2H), 7.44 (t, 1H),
7.38 (d, 2H), 3.65 (s, 2H), 3.20 (ABq, Δν = 24.0 Hz, J = 18.0 Hz, 2H).
13C NMR (150 MHz, in CS2 with DMSO- d6 as the external lock
solvent) all signals represent 1C except noted: δ = 168.52, 159.59,
156.25, 154.22, 151.16, 150.97, 150.40, 149.79, 149.61, 149.19, 149.05,
149.02, 148.48 (2C), 148.37 (2C), 147.80 (2C), 147.40, 147.19,
147.14, 147.01 (2C), 146.93, 146.83, 146.76, 146.35, 146.12,146.97,
145.95, 145.68, 145.51, 145.38, 145.01 (2C), 144.81, 144.52 (2C),
144.26, 144.19, 143.87, 143.82, 143.67, 143.48, 143.16, 143.03, 142.97,
142.37, 142.20, 142.04, 142.02, 141.85, 141.52, 140.95, 138.29, 136.81,
136.41, 136.06 (2C), 135.70 (2C), 135.31, 133.83, 132.22, 132.18,
132.00, 131.62, 130.55, 130.25 (2C, Ph), 129.91 (2C, Ph), 129.02
(Ph), 128.31 (Ph), 127.87 (2C, Ph), 127.62 (2C, Ph), 126.82 (Ph),
126.77 (Ph), 57.23 (sp3, C70), 55.67 (sp3, C70), 46.31 (CH2), 42.85
(CH2). UV−vis (toluene): λ max/nm =355, 415, 602, and 701.
X-ray Single-Crystal Diffraction of 2a. Black crystals of 2a were
obtained by slowly diffusing ethanol into a CS2 solution of 2a at room
temperature. Single-crystal X-ray diffraction data were collected on an
instrument equipped with a CCD area detector using graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å) in the scan range
1.19° < θ < 25.05°. The structure was solved with the direct method of
SHELXS-97 and refined with full-matrix least-squares techniques using
the SHELXL-97 program within WINGX. Crystal data of 2a·CS2:
C84H14·CS2, Mw = 1099.10, monoclinic, space group P2(1)/c, a =
19.190(3) Å, b = 13.797(2) Å, c = 19.557(2) Å, α = 90°, β =
120.635(11)°, γ = 90°, V = 4455.3(11) Å3, Z = 4, Dcalcd = 1.639 Mg
m−3, μ = 0.184 mm−1, T = 188(2) K, crystal size 0.28 × 0.18 × 0.14
mm; reflections collected 24446, independent reflections 7864; 3297
with I > 2σ(I); R1 = 0.1412 [I > 2σ (I)], wR2 = 0.2409 [I > 2σ(I)]; R1
= 0.2668 (all data), wR2 = 0.2877 (all data), GOF (on F2) = 0.992.
3
(Ph), 56.96 (sp3, C70), 55.36 (sp , C70), 45.65 (CH2), 42.32 (CH2).
UV−vis (toluene): λ max/nm =355, 415, 602, and 701.
Spectral Characterization of 1c. Positive ESI FT-ICR MS: m/z
+
1
calcd for [M + H]+ (C84H13Br2 ) 1178.93785, found 1178.93924. H
NMR (600 MHz, in CS2 with benzene-d6 as the external lock solvent)
δ = 7.69−7.66 (m, 4H), 7.51−7.47 (m, 4H), 3.86 (ABq, Δν = 24.0 Hz,
J = 12.0 Hz, 4H). 13C NMR (125 MHz, CS2/CDCl3): δ = 157.63
(2C), 150.95 (2C), 150.76 (2C), 150.50 (2C), 149.95 (2C), 148.94
(2C), 148.88 (2C), 148.84 (2C), 148.50 (2C), 148.47 (2C), 147.48
(2C), 147.36 (2C), 147.18 (4C), 147.01 (2C), 146.22 (2C), 146.07
(2C), 145.43 (2C), 145.37 (2C), 145.35 (2C), 144.74 (2C), 144.65
(2C), 144.52 (2C), 143.93 (2C), 143.05 (2C), 142.69 (2C), 142.35
(2C), 141.23 (2C), 139.81 (2C), 139.19 (2C), 137.89 (2C,Ph), 134.22
(2C), 134.19 (2C), 133.72 (2C), 133.57 (2C, Ph), 132.09 (2C),
130.91 (2C, Ph), 129.91 (2C, Ph), 129.12 (2C, Ph), 123.03 (2C, Ph),
56.99 (2C, sp3, C70), 49.44 (2C, CH2). UV−vis (toluene): λ max/nm =
403, 438, 624, and 785.
X-ray Single-Crystal Diffraction of 1c. Black crystals of 1c were
obtained by slowly diffusing n-hexane into a CS2 solution of 1c at
room temperature. Single-crystal X-ray diffraction data were collected
on an instrument equipped with a CCD area detector using graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å) in the scan range
1.90° < θ < 26.13°. The structure was solved with the direct method of
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Article
SHELXS-97 and refined with full-matrix least-squares techniques using
the SHELXL-97 program within WINGX. Crystal data of 1c·0.5CS2:
C84H12Br2·0.5CS2, Mw = 1218.80, triclinic, space group P-1, a =
10.7742(8) Å, b = 11.1529(9) Å, c = 20.3030(16) Å, α =
98.8240(10)°, β = 104.7000(10)°, γ = 101.0710(10)°, V =
2262.8(3) Å3, Z = 2, Dcalcd = 1.789 Mg m−3, μ = 1.901 mm−1, T =
293(2) K, crystal size 0.42 × 0.21 × 0.10 mm; reflections collected
12538, independent reflections 8843; 5779 with I > 2σ (I); R1 =
0.0641 [I > 2σ(I)], wR2 = 0.1638 [I > 2σ(I)]; R1 = 0.1063 (all data),
wR2 = 0.1860 (all data), GOF (on F2) = 1.038.
50.558(3) Å, b = 10.0753(6) Å, c = 20.1387(12) Å, α = 90°, β = 90°, γ
= 90°, V = 10258.4(10) Å3, Z = 8, Dcalcd = 1.726 Mg m−3, μ = 1.803
mm−1, T = 293(2) K, crystal size 0.38 × 0.26 × 0.14 mm; reflections
collected 49745, independent reflections 9025; 5935 with I > 2σ(I);
R1 = 0.0717 [I > 2σ(I)], wR2 = 0.1797 [I > 2σ(I)]; R1 = 0.1158(all
data), wR2 = 0.2041 (all data), GOF (on F2) = 1.053.
H/D Labeling Experiment. Route 1: Typically, 150 mg (0.18
mmol) of C70 was electrolyzed at −1.10 V vs SCE in 100 mL of freshly
distilled PhCN solution containing 0.1 M TBAP under an argon
atmosphere. The potentiostat was switched off after the electrolytic
2−
formation of C70 was achieved. Then a 10-fold excess of PhCD2Br
Spectral Characterization of 2c. Positive ESI FT-ICR MS: m/z
+
1
calcd for [M + H]+ (C84H13Br2 ) 1178.93785, found 1178.94001. H
NMR (600 MHz, in CS2 with benzene-d6 as the external lock solvent)
δ = 7.87 (s, 1H), 7.72−7.69 (t, 2H), 7.62−7.59 (t, 2H), 7.55 (s, 1H),
7.45 (t, 1H), 7.36 (d, 1H), 3.64 (ABq , Δν = 30.0 Hz, JAB = 12.0 Hz,
2H), 3.21(ABq, Δν = 24.0 Hz, JAB = 12.0 Hz, 2H). 13C NMR (150
MHz, CS2/CDCl3) all signals represent 1C except noted: δ=168.71,
159.70, 156.53, 154.76, 151.76, 151.58, 150.85, 150.39, 150.18, 149.68
(2C), 149.62, 149.07 (2C), 148.91, 148.77, 148.45, 148.35, 148.00,
147.76, 147.70, 147.61 (2C), 147.52, 147.40, 147.36, 146.97, 146.64,
146.51 (2C), 146.27, 146.09, 145.98, 145.63, 145.58, 145.40, 145.19,
145.11, 144.90, 144.77, 144.46, 144.42, 144.18, 143.85, 143.75, 143.58,
143.55, 142.90 (2C), 142.84, 142.66, 142.56, 142.39, 142.23, 141.51,
138.89, 138.77, 138.58, 137.13, 136.98, 135.88, 134.19, 133.67 (Ph),
133.38 (Ph), 132.83, 132.79, 132.61, 132.23, 131.14, 130.80, 130.56
(Ph), 130.50 (Ph), 129.87 (Ph), 129.62 (Ph), 129.47 (Ph), 129.12
(Ph), 128.80 (Ph), 127.88 (Ph), 122.78 (Ph), 122.50 (Ph), 57.36 (sp3,
C70), 55.76 (sp3, C70), 46.27 (CH2), 42.81 (CH2). UV−vis (toluene):
(1.8 mmol, 213 μL) and a 10-fold excess of PhCH2Br (1.8 mmol, 213
μL) were added simultaneously into the reaction mixture to react for 3
h with stirring at 50 °C. The workup for the purification of 2e is the
same as that for 2a. Route 2: Typically, 150 mg (0.18 mmol) of C70
was electrolyzed at −1.10 V vs SCE in 100 mL of freshly distilled
PhCN solution containing 0.1 M TBAP under an argon atmosphere.
The potentiostat was switched off after the electrolytic formation of
C702− was complete. A 10-fold excess of PhCD2Br (1.8 mmol, 213 μL)
was added into the solution, and the reaction was allowed to proceed
for 20 min, followed by adding a 10-fold excess of PhCH2Br (1.8
mmol, 213 μL). The reaction was allowed to proceed for about 3 h
with stirring at 50 °C. The workup for the purification of 2f is the same
as that for 2a.
1
Spectral Characterization of 2e. H NMR (600 MHz, in CS2
with benzene-d6 as the external lock solvent): δ = 7.75 (d, 2H), 7.71 (t,
2H), 7.58 (t, 1H), 7.58 (t, 2H), 7.47 (t, 1H), 7.40 (d, 2H), 3.68 (s,
1.00H), 3.23 (ABq, Δν = 24.0 Hz, J = 18.0 Hz, 1.02H).
1
Spectral Characterization of 2f. H NMR (600 MHz, in CS2
λ
max/nm = 355, 415, 602, and 701.
with benzene-d6 as the external lock solvent): δ = 7.72 (d, 2H), 7.68 (t,
2H), 7.56 (t, 1H), 7.52 (t, 2H), 7.44 (t, 1H), 7.38 (d, 2H), 3.66 (s,
0.28H), 3.21 (ABq, Δν = 24.0 Hz, J = 12.0 Hz, 1.32H).
Spectral Characterization of 1d. Positive ESI FT-ICR MS: m/z
+
1
calcd for [M + H]+ (C84H13Br2 ) 1178.93785, found 1178.93607. H
NMR (600 MHz, in CS2 with benzene-d6 as the external lock solvent)
δ= 7.32 (d, 4H), 7.06 (d, 4H), 3.48 (ABq, Δν = 18.0 Hz, J = 12.0 Hz,
4H). 13C NMR (125 MHz, CS2/CDCl3): δ = 157.72 (2C), 150.96
(2C), 150.75 (2C), 150.52 (2C), 149.94 (2C), 148.91 (2C), 148.87
(2C), 148.84 (2C), 148.48 (2C), 148.47 (2C), 147.47 (2C), 147.35
(2C), 147.18 (4C), 147.01 (2C), 146.22 (2C), 146.06 (2C), 145.42
(2C), 145.37 (4C), 144.79 (2C), 144.64 (2C), 144.51 (2C), 143.90
(2C), 143.06 (2C), 142.71 (2C), 142.36 (2C), 141.23 (2C), 139.87
(2C), 139.20 (2C), 134.56 (2C, Ph), 134.22 (2C), 134.19 (2C),
133.71 (2C), 132.15 (4C, Ph), 132.12 (2C), 131.67 (4C, Ph), 122.55
(2C, Ph), 57.05 (2C, sp3, C70), 49.46 (2C, CH2). UV−vis (toluene): λ
max/nm = 403, 438, 624, and 785.
Computational Methods. The geometry of 2,5-(PhCH2)2C70 was
optimized with Gaussian03 at the Hartree−Fock (HF) level with the
6-31G basis set, followed by harmonic frequency calculations at the
same level to confirm them as the energy minima. DFT calculations
with Guassian03 were performed at the B3LYP/6-311G(d) level to
evaluate the barriers for rotating the benzyls of simulated structures of
2,5-(PhCH2)HC70 and 2,5-H(PhCH2)C70, and the barriers for rotating
the phenyl rings of 2,5-(PhCH2)2C70.
ASSOCIATED CONTENT
■
S
* Supporting Information
Spectral Characterization of 2d. Positive ESI FT-ICR MS: m/z
X-ray crystallographic files for compounds 1b,c and 2a,d (CIF),
+
1
calcd for [M + H]+ (C84H13Br2 ) 1178.93785, found 1178.93639. H
NMR (600 MHz, in CS2 with C6D6 as the external lock solvent) δ =
7.82 (d, 2H), 7.64 (d, 4H), 7.28 (d, 2H), 3.72 (ABq, Δν = 30.0 Hz, JAB
= 12.0 Hz, 2H), 3.28 (ABq, Δν = 18.0 Hz, JAB = 12.0 Hz, 2H). 13C
NMR (150 MHz, CS2/CDCl3) all signals represent 1C except noted:
δ = 168.48, 159.67, 156.64, 154.91, 151.76, 151.58, 150.95, 150.37,
150.14, 149.67 (2C), 149.61, 149.07 (2C), 148.88, 148.77, 148.43,
148.35, 148.01, 147.75, 147.69, 147.62, 147.60, 147.51, 147.40, 147.35,
146.95, 146.79, 146.52, 146.50, 146.27, 146.08, 145.96, 145.58 (2C),
145.40, 145.18, 145.04, 144.87, 144.76, 144.44, 144.40, 144.16, 143.79,
143.72, 143.58, 143.55, 142.89, 142.84, 142.71, 142.65, 142.39, 142.20,
141.51, 138.74, 137.12, 137.03, 135.91, 135.51 (Ph), 135.11 (Ph),
134.19, 132.83, 132.77, 132.59, 132.30 (2C, Ph), 132.22, 132.06 (2C),
131.96 (2C, Ph), 131.56 (2C, Ph), 131.42 (2C), 131.28 (2C, Ph),
131.13, 121.84 (Ph), 121.72 (Ph), 57.37 (sp3, C70), 55.76 (sp3, C70),
HPLC of the crude product, HRMS, UV−vis, H and 13C
1
NMR spectra of compounds 1a−d and 2a−d, HMBC NMR
1
spectrum of compounds 2a and 2b, H NMR of deuterated
compounds 2e and 2f, and calculation details. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: xgao@ciac.jl.cn.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
46.39 (CH2), 42.96 (CH2). UV−vis (toluene): λ
and 701.
= 355, 415, 602,
■
max
This work was supported by NSFC (20972150, 21172212 for
X.G. and 21202157 for Z.J.L.) and the Solar Energy Initiative of
the CAS (KGCX2-YW-399 + 9).
X-ray Single-Crystal Diffraction of 2d. Black crystals of 2d were
obtained by slowly diffusing n-hexane into a CS2 solution of 1c at
room temperature. Single-crystal X-ray diffraction data were collected
on an instrument equipped with a CCD area detector using graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å) in the scan range
0.81° < θ < 25.03°. The structure was solved with the direct method of
SHELXS-97 and refined with full-matrix least-squares techniques using
the SHELXL-97 program within WINGX. Crystal data of 2d·2CS2:
C84H12Br2·2CS2, Mw = 1333.02, Orthorhombic, space group Pbcn, a =
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Article
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