Reaction of C602- with organic halides revisited in DMF: Proton transfer from water to RC60- and unexpected formation of 1,2-Dihydro[60]fullerenes

Article abstract of DOI:10.1021/jo100430a

The reactions of dianionic C₆₀ with organic halides, which have been studied extensively in benzonitrile (PhCN), are revisited in a different solvent medium, N,N-dimethylformamide (DMF), by using ArCH₂Br (Ar = Ph, C₆H₄CH₃, C₆H₄Br). Interestingly, instead of the 1,4-R₂C₆₀ adducts, which are the typical products when the reactions are carried out in PhCN, the 1,2-dihydro[60]fullerenes (1,2-HRC₆₀) have been obtained as the major products in DMF, except for the case of o-CH₃C₆H ₄CH₂Br probably due to the steric effect. The obtained 1,2-dihydro[60]fullerenes have been characterized with single-crystal diffraction, ¹H and ¹³C NMR, high-resolution mass spectrometry (HRMS), and UV-vis. Further examination with deuterated reagents including PhCD₂Br, DMF-d₇, and D₂O has revealed that the fullerenyl hydrogen of 1,2-dihydrofullerenes originates from traces of water residue in DMF. When the reaction is re-examined in PhCN with the addition of an excessive amount of water, the yield of 1,2-dihydrofullerene increases significantly, but is still lower compared with that obtained in DMF, demonstrating a considerable solvent effect on the reactivity of C ₆₀^2-. A possible mechanism accounting for such a difference is proposed. The work has presented an alternative protocol for effective preparation of 1,2-dihydro[60]fullerenes, and may also provide clues toward a better understanding of the proton transfer process for anionic C ₆₀-mediated reducing reactions involving H₂O.

Full text of DOI:10.1021/jo100430a

pubs.acs.org/joc
Reaction of C602- with Organic Halides Revisited in DMF:
Proton Transfer from Water to RC60- and Unexpected Formation of
1,2-Dihydro[60]fullerenes
Wei-Wei Yang, Zong-Jun Li, and Xiang Gao*
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Graduate
School of Chinese Academy of Sciences, Chinese Academy of Sciences, 5625 Remin Street, Changchun, Jilin,
130022, China
xgao@ciac.jl.cn
Received March 8, 2010
The reactions of dianionic C60 with organic halides, which have been studied extensively in
benzonitrile (PhCN), are revisited in a different solvent medium, N,N-dimethylformamide (DMF),
by using ArCH2Br (Ar = Ph, C6H4CH3, C6H4Br). Interestingly, instead of the 1,4-R2C60 adducts,
which are the typical products when the reactions are carried out in PhCN, the 1,2-dihydro-
[60]fullerenes (1,2-HRC60) have been obtained as the major products in DMF, except for the case
of o-CH3C6H4CH2Br probably due to the steric effect. The obtained 1,2-dihydro[60]fullerenes have
been characterized with single-crystal diffraction, 1H and 13C NMR, high-resolution mass spectro-
metry (HRMS), and UV-vis. Further examination with deuterated reagents including PhCD2Br,
DMF-d7, and D2O has revealed that the fullerenyl hydrogen of 1,2-dihydrofullerenes originates from
traces of water residue in DMF. When the reaction is re-examined in PhCN with the addition of an
excessive amount of water, the yield of 1,2-dihydrofullerene increases significantly, but is still lower
compared with that obtained in DMF, demonstrating a considerable solvent effect on the reactivity
of C602-. A possible mechanism accounting for such a difference is proposed. The work has presented
an alternative protocol for effective preparation of 1,2-dihydro[60]fullerenes, and may also provide
clues toward a better understanding of the proton transfer process for anionic C60-mediated reducing
reactions involving H2O.
Introduction
electronegativity of the carbon atom, carbanions are usually
strong bases, good electron donors, and strong nucleophiles.
As a result, they are moisture and oxygen sensitive.1,2
Anionic C60, which is readily available by either chemical
or electrochemical reduction of electron-deficient neutral
C60,3 has shown promising potentials in the functionalization
of C60.4-6 Similar to typical carbanions, C60 anions are good
electron donors5,7 and strong bases.8 However, they are not
good nucleophiles due to the delocalization of the negative
charges over the C60 sphere.5b It is noteworthy that C60 anions
have displayed an unusual stability toward water, as shown by
the fact that C60-, C602-, [(γ-CD)2-C60]- (CD: cyclodextrin),
Carbanions are important intermediates in organometal-
lic and organic chemistry, and have played key roles in the
functionalization of organic compounds.1 Due to the weak
(1) (a) Buncel, E.; Durst, T. Comprehensive Carbanion Chemistry, Parts A,
B, and C; Elsevier: New York, 1980, 1984, 1987. (b) Bates, R. B.; Ogle, C. A. In
Carbanion Chemistry-Reactivity and Structure Concepts in Organic Chemis-
try; Hafner, K., Lehn, J.-M., Rees, C. W., Schleyer, P. v. R., Trost, B. M.,
Zahradnik, R., Eds.; Springer-Verlag: Berlin, Germany, 1983; Vol. 17. (c)
Snieckus, V. Advances in Carbanion Chemistry; JAI: Greenwich, CT, 1992,
1996; Vols. 1 and 2. (d) Heathcock, C. H.; Winterfeldt, E.; Schlosser, M. In
Modern Synthetic Methods-Topics in Carbanion Chemistry; Scheffold, R., Ed.;
VHCA and VCH: Basel, Switzerland, and Weinheim, Germany, 1992.
4086 J. Org. Chem. 2010, 75, 4086–4094
Published on Web 05/27/2010
DOI: 10.1021/jo100430a
r
2010 American Chemical Society

Yang et al.
JOCArticle
and [(γ-CD)2-C60]2- can be generated in the presence of large
amounts of water without protonation, although they are still
very sensitive toward oxygen.9-11
and photoirradiation.13 However, no such proton transfer
reaction has been recorded in the literature, even though
there are RC60- intermediates5 and traces of water residue14
available in the reaction system of C602- with RX. Instead,
strong proton donors such as trifluoroacetic acid have been
2-
Among various anionic C60, the chemistry of C60 has
drawn extensive attention4,5 since the early studies by Kadish
-
2-
and co-workers.4a C60 has been recognized as an impor-
tant building block for fullerene functionalization by reac-
used to protonate the RC60 intermediates, which are
formed either from anionic C604h,j,5b,8a or nucleophilic addi-
tion of organolithiums or Grignard reagents to C60.4l,15 The
water residue in the solvent has shown little effect on the bulk
2-
tions with organic halides (RX, X = I, Br, Cl), where C60
plays a key role in initiating the reactions via a single-electron
transfer to organic halides.5 In addition, C602- encapsulated
in bis-γ-cyclodextrins has also shown interesting catalytic
reducing activities, including CdO, CdC, and N;Nþ bond
reduction11 and dinitrogen fixation12 in the presence of
water, where protons are likely to be transferred from water
substrate to the reduced species mediated by C602-. How-
ever, little is known regarding such a proton transfer process
since no organofullerene intermediate has been reported
from the reactions.
2- 14
generation of C60
,
which further reacts with organic
halides to form 1,2- and/or 1,4-di(organo)fullerenes as the
major products depending on the size of addends,4,5,16 along
with minor products of methanofullerenes and 1,2-dihydro-
fullerenes.4i,k The formation of 1,2-dihydrofullerenes is quite
unusual, and the fullerenyl hydrogen has been proposed to
originate from the methylene protons of the organic halides
(XCH2A, A = ester, ketone; X = Br, I) via the formation of
C60H- intermediate.4i It is therefore of importance to investi-
gate if H2O is involved in the reaction of reduced C60 species, not
only because it may provide further information on the reaction
mechanism proposed for radical acylation of C60,13 but also
because it may provide clues on the proton transfer mechanism
from water molecule to the reduced species during anionic C60-
mediated reducing reactions, since the resulting fullerenyl proton
can also be easily removed from the C60 sphere.4h,j,l,8b
Orfanopoulos and co-workers have recently proposed the
-
reaction of RC60 with water moisture to account for the
partial formation of 1,2-dihydro[60]fullerenes for the radical
reactions of C60 with aldehydes mediated by decatungstate
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Benzonitrile is the most typical solvent medium used for the
bulk generation and reactions of anionic C60.4a,d,e,h,k,l,5,6 It has
a fair solubility for neutral C60,17 and a good solubility for
anionic C60.18 Other solvents, including CH3CN,4f,g,i,j a mix-
ture of toluene and CH3CN,4c and tetrahydrofuran (THF),4b,19
have also been used, even though it has been indicated that the
solubility of mono- and dianionic C60 is rather low in
CH3CN.18,20 Surprisingly, no report on using DMF as the
solvent medium for reactions of C602- with organic halides has
appeared, although it has been shown that DMF has a good
solubility for both the mono- and dianionic C60.18,21 Notably,
recent work by Nakamura and co-workers has shown that the
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Grignard reagents can be facilitated by addition of DMF.4l
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37, 7061–7064. (b) Kitagawa, T.; Tanaka, T.; Takata, Y.; Komatsu, K.
Tetrahedron 1997, 53, 9965–9976.
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7412. (b) Trulove, P. C.; Carlin, R. T.; Eaton, G. R.; Eaton, S. S. In Recent
Advances in the Chemistry and Physics of Fullerenes and Related Materials;
Ruoff, R. S., Kadish, K. M., Eds; The Electrochemical Society Proceedings Series;
The Electrochemical Society: Pennington, NJ, 1995; pp 362-370.
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Chem. 1994, 98, 1282–1287. (b) Takekuma, S.; Takekuma, H.; Matsumoto,
T.; Yoshida, Z. Tetrahedron Lett. 2000, 41, 4909–4912.
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2-
FIGURE 1. HPLC trace of the crude reaction mixture of C60
FIGURE 2. ORTEP drawing of 1,2-H(PhCH2)C60 with 50% ther-
mal ellipsoids. Selected bond distances (A) and bond angles (deg):
C1-C2, 1.577(6); C2-C3, 1.527(6); C3-C4, 1.354(6); C4-C5,
1.474(6); C5-C6, 1.371(6); C6-C1, 1.547(6); C1-C61, 1.580(6);
C61-C62, 1.498(6); C6-C1-C2, 113.4(4); C1-C2-C3, 115.8(4);
C1-C61-C62, 114.7(4).
with benzyl bromide (molar ratio of C602-/benzyl bromide = 1:10).
The mixture was eluted with toluene over a semipreparative Bucky-
prep column (20 ꢀ 250 mm) at a flow rate of 4.0 mL/min with the
detector wavelength set at 380 nm.
with a greater amount in DMF than that in PhCN due to the
miscibility of DMF with H2O.23 It is therefore of interest to
2-
study the reaction of C60 with organic halides in a DMF
solvent system other than PhCN. Herein, we report the reaction
2-
of C60 with ArCH2Br (Ar = Ph, C6H4CH3, C6H4Br) in
DMF. It shows explicitly that the water residue is involved in
2-
the reaction of C60 with organic halides, which is very
different from the case when PhCN is used.
Results and Discussion
Formation and Characterization of 1,2-Dihydrofullerenes
from the Reactions of Dianionic C60 with ArCH2Br (Ar = Ph,
2-
C6H4CH3, C6H4Br) in DMF. Procedures for generating C60
2-
FIGURE 3. Crystal packing diagram of 1,2-H(PhCH2)C60 viewed
along the b-axis. Space group = P21/c, a = 16.9920(18) A, b =
10.2389(11) A, c = 24.0163(18) A, R = 90°, β = 123.714(5)°, γ =
90°, and V = 3475.62 A3.
in DMF and reactions of C60 with organic halides were
carried out in a manner similar to those reported in PhCN,4k
and details of the synthesis and purification are described in the
Experimental Section. Figure 1 shows the HPLC chromato-
gram of the crude reaction mixture of C602- with benzyl bro-
mide. Three fractions appear at 5.4, 6.7, and 9.2 min, corres-
ponding to the 1,4-(PhCH2)2C60, 1,2-H(PhCH2)C60, and C60,
respectively, consistent with previous HPLC assignment.6a
Notably, different from the results obtained when PhCN is
used,4a,d,k,5 where 1,4-(PhCH2)2C60 is the exclusive major
product, 1,2-H(PhCH2)C60 is formed as the predominant
product when the same reaction is carried out in DMF, while
the amount of 1,4-(PhCH2)2C60 is greatly reduced, demonstrat-
ing a distinctive solvent effect on the reactivity of C602-. Under
typical conditions, the isolated yield is ca. 50%, 10%, and 25%
for 1,2-H(PhCH2)C60, 1,4-(PhCH2)2C60, and C60, respectively.
The structure of 1,2-H(PhCH2)C60 is established by X-ray
single-crystal diffraction, 1H and 13C NMR, high-resolution
MS, and UV-vis spectroscopy. The single crystal of the
compound was obtained by slow evaporation of an n-hexane
solution, and the structure is shown in Figure 2. The benzyl
group is orientated toward the C60 core in the crystal
structure, while in fact the benzyl can be positioned with a
direction either toward or away from the C60 core as shown
in the single-crystal structures of C60 derivatives bearing two
benzyls.5a,6a Previous reports on the single-crystal structure
of 1,2-dihydrofullerene compounds are very limited, but
interestingly, the same orientation of the organic addend is
observed as compared with the single-crystal structure of
1,2-H(SiMe2OiPr)C60,4l suggesting that the orientation of
the organic addends for 1,2-dihydrofullerene compounds is
likely controlled by similar unidentified driving forces.
Figure 3 shows the crystal packing diagram of 1,2-H-
(PhCH2)C60 molecules viewed along the b-axis. It reveals
that the molecules are packed with the distance between the
centroids of C60 cages being 10.2, 12.5, and 13.7 A respec-
tively within the same layer, consistent with reported data
for organofullerenes.24 The molecules are organized into
well-aligned 1-D stacks probably due to the C C and
3 3 3
π
π van der Waals interactions between the closely posi-
3 3 3
tioned benzyl addend and C60 core, and the neighboring
columns of the stacks are antiparallel with each other. The
well-ordered 1-D stacking structure of fullerene molecules
suggests a potential application of the compound in the area
(23) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 84th ed.;
CRC Press: Boca Raton, FL, 2003; pp 3-218.
(24) Chancellor, C. J.; Thorn, A. A.; Beavers, C. M.; Olmstead, M. M.;
Balch, A. L. Cryst. Growth Des. 2008, 8, 976–980.
4088 J. Org. Chem. Vol. 75, No. 12, 2010

Yang et al.
JOCArticle
of organic electronic materials as photovoltaic devices.25 In
addition, it is noteworthy that there is no solvent molecule in
the crystal packings, which is quite unusual for the crystals of
C60 derivatives, but has been previously observed.4l
254, 304, and 324 nm, along with the characteristic absorption
for 1,2-C60 adducts at 431 nm.28 The spectroscopic data are
therefore consistent with the X-ray single-crystal diffraction
result for the structural assignment of the 1,2-H(PhCH2)C60.
1
The H NMR of 1,2-H(PhCH2)C60 (see the Supporting
To further examine the generality of the formation of 1,2-
2-
Information) shows two singlets at 4.77 and 6.65 ppm, which
correspond to the methylene protons of the benzyl group and
H-C60, respectively. The resonance of the methylene pro-
tons isupperfieldshiftedcomparedwiththat of1,2-(PhCH2)2-
C60 (5.03 ppm),4k but is lower field shifted with respect to that
of 1,4-(PhCH2)2C60 (3.71 ppm),4k demonstrating a subtle
influence of the addend and addition pattern on the electronic
structure of the derivatives. Previous work has shown that the
electronic structure of C60 derivatives is closely related to the
dihydrofullerenes from C60
in DMF, organic halides
including o-, m-, p-CH3PhCH2Br and m-, p-BrPhCH2Br
were used with a 10:1 molar ratio to C602-. The obtained
crude products were subjected to HPLC separation eluting
with toluene over a semipreparative Buckyprep column as
shown in Figure 4, with the isolation yield of ca. 10%, 35%,
45%, 40%, and 50% for the 1,2-dihydro[60]fullerene com-
pound from the reaction of C602- with o-, m-, p-CH3PhCH2Br
and m-, p-BrPhCH2Br, respectively. The structures of the
isolated 1,2-dihydrofullerenes have been characterized by
UV-vis, 1H and 13C NMR, and HRMS (see the Supporting
Information), while the formation of 1,4-di(organo)fullerenes
half-wave potentials of the first reductions (E1/2red1).26 It is
red1
therefore of interest to correlate the E1/2
values of the
compounds with the chemical shifts of the methylene protons.
The E1/2red1 for 1,2-(PhCH2)2C60, 1,2-H(PhCH2)C60, and 1,4-
(PhCH2)2C60 in PhCN containing 0.1 M TBAP is -0.62,4k
-0.54 (see the Supporting Information), and -0.52 V4k vs
SCE, respectively. This indicates that first, a 1,2-adduct is
much less electron-deficient than a 1,4-adduct by demonstrat-
ing a more cathodically shifted reduction potential (1,2-
(PhCH2)2C60 vs 1,4-(PhCH2)2C60), suggesting that more elec-
trons are pulled over toward the electron-deficient C60 sphere
from the benzyls when the addends are positioned with 1,2-
pattern than the case when the addends are positioned with
1,4-pattern; and second, it indicates that a stronger electron-
donating group (benzyl) can push more electrons to the C60
sphere via the inducing effect than a weaker electron-donating
group (H) (1,2-(PhCH2)2C60 vs 1,2-H(PhCH2)C60). Conse-
quently, the methylene protons of benzyls for the 1,2-adducts
are more deshielded than those for 1,4-adducts, and the
methylene protons of benzyls for 1,2-(PhCH2)2C60 are also
more deshielded than those for 1,2-H(PhCH2)C60, resulting in
the appearance of methylene protons of 1,2-(PhCH2)2C60,
1,2-H(PhCH2)C60, and 1,4-(PhCH2)2C60 in the order from
upper field to lower field as observed in the 1H NMR.
Resonances due to the phenyl protons are observed be-
tween 7.46 and 7.84 ppm. The 13C NMR spectrum exhibits
27 signals from 155.4 to 131.6 ppm for the sp2 C60 carbons,
and two resonances at 66.0 and 59.1 ppm corresponding to
the sp3 C60 carbon atoms bonded to benzyl and hydrogen
atom respectively as shown by the heteronuclear multiple
quantum coherence (HMQC) NMR (see the Supporting
Information), in agreement with previous peak assignment.4d,27
In addition, resonances due to the sp2 benzyl carbon atoms are
also shown in the spectrum from 135.9 to 127.7 ppm. The
compound (C67H8) was also subjected to the negative ESI FI-
ICR (electrospray ionization Fourier transform ion cyclotron)
MS measurement, and the monoisotopic [M - H]- ion is
observed at 811.0543, which is deviated from the calculated
value (811.0553) by only -1.2 ppm. The UV-vis spectrum of
the compound shows typical absorptions of C60 derivatives at
1
is confirmed by H NMR. Two conclusions can be drawn
from the results. First, the yield of 1,2-dihydrofullerene is
improved significantly as compared with the case where
PhCN4a,d,k,5 or CH3CN4f,i,j is used as the reaction medium,
confirming that the solvent does have a significant effect on
the reactivity of C60 dianion; and second, there is a substituent
effect on the product distribution. For o-CH3PhCH2Br, the
1,4-di(organo)fullerene is still the predominant product, while
for m-CH3PhCH2Br and m-BrPhCH2Br, both 1,2-dihydro-
fullerene and 1,4-di(organo)fullerene are formed as the major
products, and as for the p-CH3PhCH2Br and p-BrPhCH2Br,
the 1,2-dihydrofullerenes are the exclusive products, and only
trace amounts of 1,4-di(organo)fullerenes are formed.
The observed product distribution difference for the
ortho-, meta-, and para-substituted organic halides is likely
due to the steric effect. For addend with substituent at the
ortho-position, it may exhibit a greater steric hindrance than
the one with the substituent at meta- or para-position, since
the ortho-substituent is closer to the C60 core. The ortho-
-
substituent is likely to restrain the access of the C2 of RC60
-•
formed by the radical coupling of C60 and R•, which are
generated via the electron transfer between C602- and RX,5
therefore decreasing the yield of 1,2-HRC60, and leading
to the formation of more 1,4-adducts via the subsequent
-
SN2 reaction of RC60 with RX,5 even though the ortho-
substituted benzyl bromide is actually the most unfavorable
substrate for the SN2 reaction among the ArCH2Br used. As
for the addend with para-substituent, the steric hindrance
between the addend and C60 is very small since the substituent
is far away from theC60 core, and theC2 is easilyaccessible by
water molecules, leading to 1,2-dihydrofullerene as the pre-
dominant product. The steric hindrance for addend with meta-
substituent is in between those for addends with ortho- and
para-substituent, consequently, both 1,2-dihydrofullerene and
1,4-di(organo)fullerene are found as major products in the
reactions.
Origin of the Hydrogen Atom in 1,2-Dihydrofullerenes. It is
surprising that the yields of 1,2-dihydrofullerenes improve
significantly for the reactions of C602- with organic halides
when DMF is used as the solvent medium. As for the same
reaction carried out in PhCN, the formation of 1,2-dihydro-
fullerenes is very unfavorable, and only a trace amount of
1,2-dihydrofullerenes can be detected even if the organic
addend is less hindered.4k One possible source for the full-
erenyl hydrogen has been proposed to be the methylene
(25) Kennedy, R. D.; Ayzner, A. L.; Wanger, D. D.; Day, C. T.; Halim,
M.; Khan, S. I.; Tolbert, S. H.; Schwartz, B. J.; Rubin, Y. J. Am. Chem. Soc.
2008, 130, 17290–17292.
(26) Suzuki, T.; Maruyama, Y.; Akasaka, T.; Ando, W.; Kobayashi, K.;
Nagase, S. J. Am. Chem. Soc. 1994, 116, 1359–1363.
(27) Miller, G. P.; Tetreau, M. C. Org. Lett. 2000, 2, 3091–3094.
(28) Smith, A. B., III; Strongin, R. M.; Brard, L.; Furst, G. T.;
Romanow, W. J.; Owens, K. G.; Goldschmidt, R. J.; King, R. C. J. Am.
Chem. Soc. 1995, 117, 5492–5502.
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FIGURE 4. HPLC traces of the crude reaction products containing 1,2-H(o-CH3PhCH2)C60, 1,2-H(m-CH3PhCH2)C60, 1,2-H(p-CH3PhCH2)C60,
1,2-H(m-BrPhCH2)C60, and 1,2-H(p-BrPhCH2)C60 eluted by toluene over a semipreparative Buckyprep column at a flow rate of 4.0 mL/min with
the detector wavelength set at 380 nm.
protons of ArCH2Br used for the reaction.4i Therefore,
PhCD2Br was used to examine if 1,2-dihydrofullerene with deu-
terated fullerenyl proton would be formed. 1H NMR (see the
Supporting Information) of the obtained 1,2-dihydrofullerene
shows that the singlet corresponding to the methylene protons
(δ 4.77 ppm) is missing, consistent with the use of PhCD2Br
for reaction. However, the integration ratio of fullerenyl proton
(δ 6.65 ppm) to phenyl protons (δ 7.84, 7.56, and 7.47 ppm) is
found to be exactly 1:5, indicating that the fullerenyl proton is
not from the methylene protons of ArCH2Br.
work has shown that the fullerenyl proton can come from the
carbonyl hydrogen of aldehydes.13 Consequently, DMF-d7
was used as the reaction medium to examine if it is the source
of fullerenyl proton. The 1H NMR of the isolated 1,2-
dihydrofullerene (see the Supporting Information) from
the reaction shows typical resonances for the compound,
with singlets at 4.77 and 6.65 ppm corresponding to the
methylene and fullerenyl protons, respectively, and reso-
nances at 7.84, 7.56, and 7.47 ppm due to the phenyl protons.
More importantly, the integration ratio of the fullerenyl
proton to the methylene protons is 1:2, indicating no deuter-
ium is attached directly to the C60 sphere, implying that the
One of the other possible sources for the fullerenyl hydro-
gen is DMF, the solvent medium of this reaction, since recent
4090 J. Org. Chem. Vol. 75, No. 12, 2010

Yang et al.
JOCArticle
FIGURE 5. 1H NMR spectrum of 1,2-dihydro[60]fullerene com-
pound obtained from the reaction of C60 with PhCH2Br in a
2-
DMF solution into which 30 μL of D2O was added. The spectrum
was recorded on a 600 MHz instrument in CDCl3. The number in
the parentheses refers to the integration area.
FIGURE 6. HPLC trace of the crude product obtained from the
reaction of C60 with PhCH2Br in PhCN into which 100 μL of
water was added. The mixture was eluted by toluene over a
semipreparative Buckyprep column at a flow rate of 4.0 mL/min
with the detector wavelength set at 380 nm.
2-
carbonyl hydrogen of DMF is not the source of the fullerenyl
proton, and DMF is not involved in the reaction.
Another possible source of the fullerenyl proton is the
water residue in DMF. It has been shown that the water
residue is extremely difficult to be completely removed from
the organic solvent even after strict drying treatment.14
Under our experimental conditions, the amount of water
residue is about 180 ppm in the freshly distilled DMF, as
determined using the Karl Fischer titration method; it is
therefore of interest to examine the reaction with the addi-
tion of a small amount of D2O.
solution, a significant increase in the formation of 1,2-H-
(PhCH2)C60 is observed in the HPLC (Figure 6), confirming
that water molecules are involved in the reaction of C60
with organic halides. However, different from the case where
DMF is used, the 1,4-(PhCH2)2C60 is still formed as the
major product, even though the amount of water in PhCN is
much more than that in DMF, suggesting that the water
residue in PhCN is less reactive than that in DMF.
2-
Solvent Effect of DMF and PhCN on the Reactivity of H2O
toward RC60-. To further explore the reaction of C602- with
organic halides involving H2O, the reaction was carried out
in freshly distilled PhCN by first adding 10-fold benzyl
Figure 5 shows the 1H NMR spectrum of the isolated 1,2-
dihydrofullerene obtained from a DMF solution into which
30 μL of D2O was added. The most notable feature is the
intensity decrease of the H-C60 resonance at 6.65 ppm, the
integration ratio of this proton to the methylene protons at
4.77 ppm is only 0.6:2.0, significantly less than the expected
1:2 value, indicating that some of the fullerenyl hydrogen
atoms have been replaced by deuterium atoms, demonstrat-
ing unambiguously that the fullerenyl hydrogen atoms are
from the water residue in DMF. The result also suggests that
H/D exchange between the benzyl group and D2O is unlikely
to occur during the reaction, since the integration ratio of the
methylene protons to the phenyl hydrogen atoms remains
exactly 2:5.
2-
bromide into the C60 solution, followed by addition of
250 μL of H2O after about 2-4 min reaction time between
C60 and benzyl bromide. The solution turned from the
2-
deep red of C602- to dark-green, which is the typical color of
-
RC60 intermediate.4h,j,5a,19 The reaction was allowed to
proceed under stirring for about 3 h. Visible and near-IR
spectroscopy was used to follow the reaction, and the results
are shown in Figure 7. The dianionic C60 displays a strong
absorption band at 954 nm, consistent with results recorded
in literature.14 The intensity of the band decreases rapidly
after adding benzyl bromide to the C602- solution, and this is
Reaction in Benzonitrile Containing a Large Amount of
Water. Similar to DMF, there is also water residue in freshly
distilled PhCN under our experimental conditions. The
amount of water residue is measured to be about 90 ppm,
corresponding to about 4.5 μL of H2O in 50 mL of PhCN
used as the reaction solvent medium, which is about three
times more than the theoretical amount of water (1.25 μL)
needed for reaction with 50 mg of C60. However, no sig-
nificant formation of 1,2-H(PhCH2)C60 has been observed
when the reaction is carried out in PhCN solution as shown
previously.4k To gain a better understanding on the reactiv-
ity of water residue in PhCN, 100 μL of water was added into
50 mL of PhCN before electrolysis, which makes the water
content about 2100 ppm including the 90 ppm water residue.
Small water droplets can be seen in this PhCN solution due to
the very low solubility of water. After addition of benzyl
accompanied by the increase of a new absorption band at 660
- 5b
nm, which has been assigned to the absorption of RC60
,
indicating that PhCH2C60- has formed after the addition of
benzyl bromide into the C602- solution. In the mean time, the
-•
absorption band due to C60 at 1078 nm also increases,
-•
indicating that C60 has also formed during the reaction.
The observations are consistent with the previous proposed
reaction mechanism, which shows that reaction is initiated
-•
by the electron transfer between C602- and RX to form C60
-
and R•, followed by the formation of RC60 via radical
coupling.5 Deaerated water was then added into the system,
and no apparent change is observed in the visible-near-IR
spectrum, suggesting that protonation of RC60 is a rather
-
slow process. After about 2.5 h, the absorptions corresponding
to anionic C60 species disappear completely, along with the
appearance of new absorption bands in the range from 420 to
480 nm due to the formed organofullerenes, suggesting that
2-
bromide (molar ratio: PhCH2Br/C60 = 10:1) to this C60
J. Org. Chem. Vol. 75, No. 12, 2010 4091

Yang et al.
JOCArticle
the real cause for the reactivity difference of water residue
toward RC60- in DMF and PhCN. Since it has been shown
that traces of water residue may form hydrogen bonding with
carbanions to affect their reactivities in different solvents,22
the observed steric effect indicates that the availability of the
-
C2 of RC60 to water molecules is crucial in forming 1,2-
HRC60, suggesting that the solvent effect of DMF and PhCN
is likely related to the availability of water residue to the
RC60- intermediates.
Both DMF and PhCN have large solubility for anionic
-
C60 species, including the reaction intermediates of RC60
,
suggesting that the formed RC6-0- can be well solvated by the
solvent molecules.30 The RC60 intermediates can undergo
either protonation by water to form 1,2-HRC60, or an SN2
reaction with benzyl bromide to form di(organo)[60]fullerenes.
In the case of DMF, since water residue is miscible with the
solvent,23 it can be present in the DMF solvation shell in a
significant amount, and form hydrogen bonding with
PhCH2C60- in a manner similar to that of other carbanions.22
The formation of such a hydrogen bonding may facilitate the
subsequent proton transfer from water molecule to C60 sphere,
and decrease the nucleophilicity of PhCH2C60- for further SN2
reaction with PhCH2Br, resulting in 1,2-H(PhCH2)C60 as the
major product. In contrast, the water molecules are very
ineffective in entering into the PhCN solvation shell since
they are immiscible with PhCN,31 making it difficult for H2O
to approach PhCH2C60-, resulting in the formation of
1,4-(PhCH2)2C60 as the major product via the SN2 pathway
instead. The increase of the amount of water in PhCN can
help more water molecules to enter into the PhCN solvation
shell, leading to the formation of more 1,2-HRC60. However,
the water molecules are still not effective in approaching
FIGURE 7. In situ electronic absorption spectra observed for the
reaction of C602- (1.0 ꢀ 10-4 M) with the addition of (a) PhCH2Br
(1.0 ꢀ 10-3 M) (about 90 s interval) and (b) H2O (2.0 ꢀ 10-2 M) (top
to bottom, t = 1, 30, 150 min) in PhCN. The small peak at 1080 nm
labeled with an asterisk in the initial C602- spectrum is likely due to a
2-
slight amount of C60-• produced during the handling of C60
.
2-
reaction of C60 with PhCH2Br and H2O is finished. The
results demonstrate explicitly that the proton transfer from H2O
-
to C60 core takes place after the formation of RC60
.
The HPLC of the crude product (see the Supporting
Information) shows the formation of both 1,4-(PhCH2)2C60
and 1,2-H(PhCH2)C60 as major products, similar to the
result when the reaction was carried out in PhCN containing
an excessive amount of water before electrolysis. The results
are consistent with the mechanism hypothesis proposed by
Orfanopoulos and co-workers regarding the involvement of
RC60- during the acyl radical reactions; however, different
from their work, where the carbonyl proton of aldehydes is
shown to be the major source of fullerenyl hydrogen,13 the
current work demonstrates that the fullerenyl hydrogen is
exclusively from water.
On the basis of the results of reactions of ArCH2Br (Ar =
Ph, C6H4CH3, C6H4Br) with C602- in DMF and benzonitrile,
a better understanding of the solvent effect can be inferred.
First, the rate difference in DMF and PhCN for the SN2
reaction of RC60- with RX, which leads to the formation of
1,4-R2C60, has to be considered. Both DMF and PhCN are
aproticsolvents, withDMF beingmorepolar thanPhCN. Itis
therefore expected that the SN2 reaction rate involving carba-
nions is faster in DMF than that in benzonitrile since the
cations are better solvated by DMF and the nucleophiles are
freed,29 consistent with the reported DMF-enhanced nucleo-
philic addition of Grignard reagents to C60.4l Consequently,
more 1,4-R2C60 is expected to form when the reaction is
carried out in DMF. In contrast, 1,2-HRC60 is obtained as
the major product when the reaction is carried out in DMF as
long as R is less hindered, and 1,4-R2C60 is obtained as the
major product in DMF only when the most unfavorable SN2
substrate of a bulky ortho-substituted benzyl bromide is used,
indicating that the SN2 reactionratedifference is unlikelytobe
-
RC60 due to the immiscibility of water with PhCN. The
2-
reaction mechanism showing the different reactivity of C60
in DMF and PhCN is therefore proposed based on the above
discussionsand previousstudy,5 andis illustrated inScheme1.
Notably, previous work has shown that no water residue is
involved in the reaction of C602- with organic halides when
the reaction is carried out in CH3CN, where the major
products are only the di(organo)[60]fullerenes4f,i,j although
CH3CN is miscible with H2O.32 Such a discrepancy between
the results obtained in DMF and CH3CN is likely due to the
involvement of anionic C60 species with lower oxidation
states such as C603-, when the reaction was carried out in
CH3CN. Previous work has indicated that the solubility of
2-
C602- in CH3CN is very low.18,20 The low solubility of C60
in CH3CN is also confirmed by controlled-potential bulk
electrolysis.33 In addition, the reported utilization of C602- in
CH3CN for fullerene functionalization was carried out by
chemical reducing methods,4f,i,j which is less selective in
(30) Noviandri, I.; Bolskar, R. D.; Lay, P. A.; Reed, C. A. J. Phys. Chem.
B 1997, 101, 6350–6358.
(31) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 84th ed.;
CRC Press: Boca Raton, FL, 2003; pp 3-42.
(32) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 84th ed.;
CRC Press: Boca Raton, FL, 2003; pp 3-4.
(33) Controlled-potential bulk electrolysis was performed to examine the
solubility of C602- in CH3CN. In 50 mL of CH3CN containing 0.1 M TBAP,
40 mg of C60 was added. The reducing potential was set at -1.00 V vs SCE,
which is about 170 mV more negative than the E1/2 of the C60-/C602- redox
couple in CH3CN. After the theoretical number of coulombs required for a
complete conversion of C60 to C602- had been reached, there were still large
amounts of insoluble species in the solvent, and no clear solution could be
obtained, indicating that the dianionic C60 is either insoluble or only very
slightly soluble in CH3CN.
(29) (a) Magnera, T. F.; Caldwell, G.; Sunner, J.; Ikuta, S.; Kebarle, P.
J. Am. Chem. Soc. 1984, 106, 6140–6146. (b) Mitsuhashi, T.; Yamamoto, G.;
Hirota, H. Bull. Chem. Soc. Jpn. 1994, 67, 831–838. (c) Reichardt, C. Solvents
and Solvent Effects in Organic Chemistry, 3rd ed.; Wiley-VCH: Weinheim,
Germany, 2003; pp 93-145.
4092 J. Org. Chem. Vol. 75, No. 12, 2010

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JOCArticle
SCHEME 1. Proposed Reaction Mechanism of C602- with PhCH2Br Involving Water Residue in DMF and PhCN
generating anionic C60 with specific oxidation state than the
potential-controlled bulk electrolysis. It is therefore likely
that anionic C60 species with lower oxidation state such as
stirring. 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 semipreparative Buckyprep
column with toluene as the eluent. NMR spectra were measured with
a 600 MHz instrument, using CDCl3 as solvent. Mass spectrometry
experiments were performed on a FT-ICR MS equipped with a 7.0 T
actively shielded superconducting magnet. The quantity of water
residue in the solvent is determined by using the Karl Fischer titration
method.
3-
C60 is involved in the reported reaction carried out in
CH3CN, thus resulting in stronger nucleophilicity of the
subsequently formed anionic intermediate (RC602-), which
may favor the SN2 reaction with organic halides rather than
protonation by H2O.
Conclusion
Spectral Characterization of 1,2-H(PhCH2)C60. Negative ESI
FT-ICR MS: C67H8, m/z [M - H]- calcd 811.0553, found
811.0543; 1H NMR (600 MHz, CDCl3) δ 7.84 (d, J = 7.5 Hz,
2H), 7.56 (t, J = 7.5 Hz, 2H), 7.47 (d, J = 7.5 Hz, 1H), 6.65 (s,
1H), 4.77 (s, 2H); 13C NMR (150 MHz, CDCl3) δ 155.4 (2C),
153.9 (2C), 147.5 (1C), 147.3 (1C), 147.0 (2C), 146.5 (2C), 146.4
(2C), 146.4 (2C), 146.3 (2C), 146.2 (2C), 145.9 (2C), 145.5 (2C),
145.4 (6C), 144.8 (2C), 144.6 (2C), 143.3 (2C), 142.6 (2C), 142.3
(4C), 142.1 (2C), 142.0 (2C), 142.0 (2C), 141.7 (2C), 141.6 (2C),
140.2 (2C), 140.0 (2C), 136.4 (2C), 136.1 (2C), 135.9 (1C, Ph),
131.3 (2C, Ph), 128.7 (2C, Ph), 127.7 (1C, Ph), 66.0 (1C, sp3,
C-CH2), 59.1 (1C, sp3, C-H), 53.1(1C, sp3, CH2); UV-vis
(hexane) λmax/nm 254, 304, 324, and 431.
2-
The well-studied reactions of C60 with organic halides
have been revisited in DMF. It shows that traces of water
residue in DMF are involved in the reaction of C602-, leading
to the formation of 1,2-dihydro[60]fullerenes via the proton
transfer from H2O to the intermediate of RC60-. The reacti-
vity difference of the water content in DMF and PhCN is
ascribed to the miscibility of the solvent with water. This is the
first time thatwater has been shownto be ableto participate in
the reaction of C602-. The result not only provides a new
method in the preparation of 1,2-dihydro[60]fullerenes, which
have been shown to be important precursors for further
generation of a various of organofullerenes,4l but may also
provide clues toward a better understanding of the proton
transfer mechanism from water to the reduced species for the
reducing reactions mediated by C602-, since the fullerenyl
proton can be easily removed from C60 core as shown in the
literature.4h,j,l,8b
Spectral Characterization of 1,2-H(o-CH3PhCH2)C60. Nega-
tive ESI FT-ICR MS: C68H10, m/z [M - H]- calcd 825.0710,
1
found 825.0730; H NMR (600 MHz, CDCl3) δ 7.77 (d, J =
7.1 Hz, 1H), 7.30 (m, 3H), 6.63 (s, 1H), 4.85 (s, 2H), 2.72 (s, 3H);
13C NMR (150 MHz, CDCl3) δ 155.3 (2C), 153.9 (2C), 147.5
(1C), 147.3 (1C), 147.0 (2C), 146.6 (2C), 146.5 (2C), 146.4 (2C),
146.3 (2C), 146.2 (2C), 145.9 (2C), 145.5 (2C), 145.5 (2C), 145.4
(4C), 144.7 (2C), 144.6 (2C), 143.3 (2C), 142.6 (2C), 142.6 (2C),
142.2 (2C), 142.1 (2C), 142.0 (2C), 141.9 (2C), 141.7 (2C), 141.6
(2C), 140.3 (2C), 139.7 (2C), 137.6 (2C), 136.4 (2C), 135.7 (1C,
Ph), 134.2 (1C, Ph), 132.3 (1C, Ph), 131.2 (1C, Ph), 127.8 (1C,
Ph), 126.1 (1C, Ph), 66.4 (1C, sp3, C-CH2), 60.4 (1C, sp3,
C-H), 49.8(1C, sp3, CH2), 21.0 (1C, sp3, CH3); UV-vis
(hexane) λmax/nm 254, 306, 324, and 431.
Experimental Section
General Methods. C60 (99.5%) was purchased and used with-
out further purification. Electrochemical grade tetra-n-butylam-
monium perchlorate (TBAP) was recrystallized from absolute
ethanol and dried in a vacuum at 298 K prior to use. PhCN was
distilled over P2O5 under vacuum at 305 K prior to use. DMF was
distilled over P2O5 under vacuum at 300 K prior to use. C6H5-
CH2Br (98%), o-CH3C6H4CH2Br (98%), m-CH3C6H4CH2Br
(96%), p-CH3C6H4CH2Br (97%), m-BrC6H4CH2Br (99%),
p-CH3C6H4CH2Br (98%), benzyl bromide-R,R-d2 (98 atom % D),
and other chemicals were commercially obtained and used as
received. Controlled-potential bulk electrolyses were carried out with
a potentiostat/galvanostat. Typically, 50 mg (69.4 μmol) of C60 was
electrolyzed at -1.10 V versus SCE in 50 mL of freshly distilled
DMF or PhCN solution containing 0.1 M TBAP under an argon
atmosphere. The potentiostat was switched off after the electroge-
Spectral Characterization of 1,2-H(m-CH3PhCH2)C60. Nega-
tive ESI FT-ICR MS: C68H10, m/z [M - H]- calcd 825.0710,
1
found 825.0718; H NMR (600 MHz, CDCl3) δ 7.65 (s, 2H),
7.45 (t, J = 8.0 Hz, 1H), 7.43 (partially overlapped with the
solvent, 1H), 6.65 (s, 1H), 4.72 (s, 2H), 2.50 (s, 3H); 13C NMR
(150 MHz, CDCl3) δ 155.6 (2C), 154.0 (2C), 147.5 (1C), 147.4
(1C), 147.1 (2C), 146.5 (2C), 146.4 (2C), 146.4 (2C), 146.3
(2C), 146.2 (2C), 145.9 (2C), 145.5 (2C), 145.4 (6C), 144.7
(2C), 144.6 (2C), 143.3 (2C), 142.6 (4C), 142.3 (2C), 142.1
(2C), 142.0 (2C), 142.0 (2C), 141.7 (2C), 141.6 (2C), 140.2
(2C), 140.0 (2C), 138.4 (1C, Ph), 136.4 (2C), 136.0 (2C), 135.8
(1C, Ph), 132.3 (1C, Ph),128.7 (1C, Ph), 128.6 (1C, Ph), 128.5
(1C, Ph), 65.9 (1C, sp3, C-CH2), 59.0 (1C, sp3, C-H), 52.9 (1C,
2-
neration of C60 was complete, and a 10-fold excess of ArCH2Br
(Ar=Ph, C6H4CH3, C6H4Br) was added to the solution under inert
atmosphere. The reaction was allowed to proceed for about 3 h with
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Yang et al.
JOCArticle
sp3, CH2), 21.7 (1C, sp3, CH3); UV-vis (hexane) λmax/nm 254,
305, 324, and 431.
Spectral Characterization of 1,2-H(p-CH3PhCH2)C60. Nega-
(1C, Ph), 65.7 (1C, sp3, C-CH2), 59.2 (1C, sp3, C-H), 52.4 (1C,
sp3, CH2); UV-vis (hexane) λmax/nm 253, 307, 321, and 431.
X-ray Crystallographic Data Collection and Structure Refine-
ment. Black lamellar crystals of 1,2-H(PhCH2)C60 suitable for
an X-ray analysis were obtained by slow evaporation of a
hexane solution, which was achieved by first dissolving the
compound in neat CS2, and then eluted over a silica gel column
with n-hexane as the eluent. Single-crystal X-ray diffraction data
were collected on an instrument equipped with a CCD area
detector, using graphite-monochromated Mo KR radiation
(λ = 0.71073 A) in the scan range 1.44° < θ < 25.14°. The
structure was solved with direct methods using SHELXS-97 and
refined with full-matrix least-squares techniques using the
SHELXL-97 program within WINGX. Non-hydrogen atoms
were refined anisotropically. Crystal data of 1,2-H(PhCH2)C60:
C67H8, Mw = 812.73, dark brown, monoclinic, space group =
P21/c, a = 16.9920(18) A, b = 10.2389(11) A, c = 24.0163(18) A,
β = 123.714(5)°, and V = 3475.62 A3, z = 4, Dcalcd = 1.553 Mg
m-3, μ = 0.089 mm-1, T = 296(2) K, crystal size 0.216 ꢀ 0.121 ꢀ
0.102 mm3; reflections collected 20452, independent reflections
6199; 3419 with I > 2σ(I); R1 = 0.0750 [I > 2σ(I)], wR2 = 0.1966
[I > 2σ(I)]; R1 = 0.1294 (all data), wR2 = 0.2199 (all data), GOF
(on F2) = 1.043.
tive ESI FT-ICR MS: C68H10, m/z [M - H]- calcd 825.0710,
found 825.0710; H NMR (600 MHz, CDCl3) δ 7.73 (d, J =
1
7.8 Hz, 2H), 7.36 (d, J = 7.8 Hz, 2H), 6.64 (s, 1H), 4.72 (s, 2H),
2.45 (s, 1H); 13C NMR (150 MHz, CDCl3) δ 155.6 (2C), 154.0
(2C), 147.5 (1C), 147.4 (1C), 147.1 (2C), 146.4 (3C), 146.4 (2C),
146.3 (2C), 146.2 (2C), 145.9 (2C), 145.5 (2C), 145.4 (6C), 144.7
(2C), 144.6 (2C), 143.3 (2C), 142.6 (3C), 142.3 (2C), 142.1 (2C),
142.0 (2C), 142.0 (2C), 141.7 (2C), 141.6 (2C), 140.2 (2C), 140.0
(2C), 137.4 (1C, Ph), 136.4 (2C), 136.1 (2C), 132.8 (1C, Ph),
131.3 (2C, Ph), 129.5 (2C, Ph), 66.1 (1C, sp3, C-CH2), 59.0 (1C,
sp3, C-H), 52.6 (1C, sp3, CH2), 21.3 (1C, sp3, CH3); UV-vis
(hexane) λmax/nm 253, 305, 323, and 431.
Spectral Characterization of 1,2-H(m-BrPhCH2)C60. Nega-
tive ESI FT-ICR MS: C67H7Br, m/z [M - H]- calcd 888.9658,
found 888.9646; H NMR (600 MHz, CDCl3) δ 7.98 (s, 1H),
1
7.78 (d, J = 7.6 Hz, 1H), 7.60 (d, J = 7.9 Hz, 1H), 7.43 (t, J =
7.8 Hz, 1H), 6.58 (s, 1H), 4.72 (s, 2H); 13C NMR (150 MHz,
CDCl3) δ 154.8 (2C), 153.6 (2C), 147.6 (1C), 147.4 (1C), 146.9
(2C), 146.5 (2C), 146.5 (2C), 146.3 (2C), 146.25 (2C), 146.18
(2C), 145.8 (2C), 145.6 (2C), 145.5 (6C), 144.8 (2C), 144.6 (2C),
143.3 (2C), 142.6 (4C), 142.2 (2C), 142.1 (2C), 142.0 (2C), 141.9
(2C), 141.7 (2C), 141.6 (2C), 140.3 (2C), 140.0 (2C), 138.2 (1C,
Ph), 136.3 (2C), 136.1 (2C), 134.3 (1C, Ph), 131.0 (1C, Ph), 130.3
(1C, Ph), 130.0 (1C, Ph), 122.8 (1C, Ph), 65.6 (1C, sp3, C-CH2),
59.1 (1C, sp3, C-H), 52.4 (1C, sp3, CH2); UV-vis (hexane)
Acknowledgment. We are grateful to Mr. Yi-jie Wu of
National Research and Analytical Center of Electrochemistry
and Spectroscopy, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, for NMR measurement. The
work was supported by the National Natural Science Founda-
tion of China (Grant No. 20972150), Solar Energy Initiative of
the Chinese Academy of Sciences, and the State Key Labora-
tory of Electroanalytical Chemistry of China.
λmax/nm 253, 306, 324, and 431.
Spectral Characterization of 1,2-H(p-BrPhCH2)C60. Negative
ESI FT-ICR MS: C67H7Br, m/z [M - H]- calcd 888.9658, found
888.9661; 1H NMR (600 MHz, CDCl3) δ 7.69 (d, J = 8.3 Hz,
2H), 7.67 (d, J = 8.3 Hz, 2H), 6.56 (s, 1H), 4.72 (s, 2H); 13C
NMR (150 MHz, CDCl3) δ 154.8 (2C), 153.6 (2C), 147.5 (1C),
147.4 (1C), 147.0 (2C), 146.5 (2C), 146.5 (2C), 146.3 (2C), 146.2
(4C), 145.8 (2C), 145.6 (2C), 145.5 (6C), 144.8 (2C), 144.6 (2C),
143.3 (2C), 142.6 (4C), 142.2 (2C), 142.1 (2C), 142.0 (2C), 141.9
(2C), 141.7 (2C), 141.6 (2C), 140.3 (2C), 140.0 (2C), 136.3 (2C),
136.1 (2C), 134.9 (1C, Ph), 133.1 (2C, Ph), 131.9 (2C, Ph), 122.0
Supporting Information Available: X-ray crystallographic
files of 1,2-H(PhCH2)C60 (CIF), 1H and 13C NMR spectra, MS
spectra of all compounds, HMQC NMR spectrum, and cyclic
voltammogram of 1,2-H(PhCH2)C60. This material is available
free of charge via the Internet at http://pubs.acs.org.
4094 J. Org. Chem. Vol. 75, No. 12, 2010