Reductive electrochemistry of spiromethanofullerenes

Article abstract of DOI:10.1021/jo010297z

The synthesis and electrochemical properties of spiromethanofullerenes 1-6 are described. The syntheses were achieved via the diazomethane route, and the regioisomeric distribution of bis-adducts 3 was determined by ¹H NMR, UV-vis, and HPLC analysis. The electrochemistry of these compounds in dichloromethane exhibits, besides several reversible reductions, some irreversible waves. Reductive electrolysis of 1 and 3-5 in dichloromethane leads to the removal of the addend and thus to the formation of C₆₀. Reductive electrolysis of 1, 2 and 6 in dichloromethane leads to a different reaction, which we tentatively assign to a reaction with the solvent to form fullerene-CH₂Cl products. Electrolyses in the less reactive solvent THF lead to adduct removal for 1 and 3-5. Interestingly, significant formation of bis-adducts from the corresponding monoadducts was observed for 4 and 5. These electrochemically induced reactions, namely addend removal, reaction with the solvent, and addend transfer are influenced by the structure of the addend and by the choice of solvent.

Full text of DOI:10.1021/jo010297z

J . Org. Chem. 2001, 66, 4393-4398
4393
Red u ctive Electr och em istr y of Sp ir om eth a n ofu ller en es
Marcel W. J . Beulen,† J ose´ A. Rivera,‡ M. AÄ ngeles Herranz,§ Beatriz Illescas,§
Nazario Mart´ın,*,§ and Luis Echegoyen*,†
Department of Chemistry and Center for Supramolecular Science, University of Miami,
Coral Gables, Florida 33124, Department of Chemistry, Pontifical Catholic University of Puerto Rico,
Ponce, Puerto Rico 00731, and Departamento de Quı´mica Orga´nica, Facultad de Ciencias Qu´ımicas,
Universidad Complutense, E-28040 Madrid, Spain
echegoyen@miami.edu
Received March 19, 2001
The synthesis and electrochemical properties of spiromethanofullerenes 1-6 are described. The
syntheses were achieved via the diazomethane route, and the regioisomeric distribution of bis-
adducts 3 was determined by 1H NMR, UV-vis, and HPLC analysis. The electrochemistry of these
compounds in dichloromethane exhibits, besides several reversible reductions, some irreversible
waves. Reductive electrolysis of 1 and 3-5 in dichloromethane leads to the removal of the addend
and thus to the formation of C60. Reductive electrolysis of 1, 2 and 6 in dichloromethane leads to
a different reaction, which we tentatively assign to a reaction with the solvent to form fullerene-
CH2Cl products. Electrolyses in the less reactive solvent THF lead to adduct removal for 1 and
3-5. Interestingly, significant formation of bis-adducts from the corresponding monoadducts was
observed for 4 and 5. These electrochemically induced reactions, namely addend removal, reaction
with the solvent, and addend transfer are influenced by the structure of the addend and by the
choice of solvent.
Sch em e 1. Ad d u ct Rem ova l by Red u ctive
Electr och em istr y for Meth a n ofu ller en es 4,
5, a n d 10
In tr od u ction
The Bingel reaction, cyclopropanation of fullerenes by
the addition of malonate derivatives, has been widely
used as a synthetic tool for the preparation of fullerene
adducts.1 Its reverse, the electrochemical retro-Bingel
reaction, was recently reported by Diederich and Eche-
goyen (see Scheme 1, 10 to 11).2 The reaction, an
electrolytic reduction reaction typically performed in
dichloromethane, efficiently removes di[alkoxycarbonyl]-
methano adducts to yield the parent fullerenes. Interest-
ingly, partial electrolysis of bis- or tris-Bingel adducts of
C60 results in isomerization of the adducts.3 The “Bingel-
[retro-Bingel]” strategy can be used as a protection-
deprotection scheme and has been used for the isolation
We have also shown that addend removal via electro-
lytic reduction is not limited to Bingel-type adducts (see
fullerene 10), but can also occur for spiro-methano
adducts such as those on 4 and 5 (see Scheme 1). We
showed that controlled potential electrolysis (CPE) in
dichloromethane results in the efficient removal of these
adducts, to form the parent C60.6 Adduct removal for
these methanofullerenes during electrolysis is presum-
ably initiated by opening of the three-membered ring.7
Furthermore, reductive electrochemistry of 4 and 5 in
THF revealed, besides simple adduct removal, a second
reaction pathway leading to the formation of bis-adducts.8
2a
of enantiomerically pure C76 for the preparation of a
new C2v-C78 bis-adduct2b and in the separation of consti-
tutional isomers and enantiomers of C84.2c Bingel addends
can also be removed chemically using Mg/Hg in THF at
elevated temperatures,4 and both the electrochemical and
chemical procedures have been shown to act selectively
in the presence of several other adduct types.4,5
* To whom correspondence should be addressed.
† University of Miami.
‡ Pontifical Catholic University of Puerto Rico.
§ Universidad Complutense.
(5) Kessinger, R.; Fender, N. S.; Echegoyen, L. E.; Thilgen, C.;
Echegoyen, L.; Diederich, F. Chem. Eur. J . 2000, 6, 2184-2192.
(6) Beulen, M. W. J .; Echegoyen, L.; Rivera, J . A.; Herranz, M. A.;
Mart´ın-Domenech, A.; Mart´ın, N. Chem. Commun. 2000, 917-918.
(7) (a) Knight, B.; Mart´ın, N.; Ohno, T.; Ort´ı, E.; Rovira, C.; Veciana,
J .; Vidal-Gancedo, J .; Viruela, P.; Viruela, R.; Wudl, F. J . Am. Chem.
Soc. 1997, 109, 9871-9882. (b) Mart´ın, N.; Sa´nchez, L.; Illescas, B.;
Pe´rez, I. Chem. Rev. 1998, 98, 2527-2547. (c) Eiermann, M.; Haddon,
R. C.; Knight, B.; Chan Li, Q.; Maggini, M.; Mart´ın, N.; Ohno, T.; Prato,
M.; Suzuki, T.; Wudl, F. Angew. Chem., Int. Ed. Engl. 1995, 34, 1591-
1593. (d) Ohno, T.; Mart´ın, N.; Knight, B.; Wudl, F.; Suzuki, T.; Yu,
H. J . Org. Chem. 1996, 61, 1306-1309.
(1) Bingel, C. Chem. Ber. 1993, 126, 1957-1959.
(2) (a) Kessinger, R.; Crassous, J .; Herrmann, A.; Ru¨ttimann, M.;
Echegoyen, L.; Diederich, F. Angew. Chem., Int. Ed. Engl. 1998, 37,
1919-1922. (b) Boudon, C.; Gisselbrecht, J .-P.; Gross, M.; Herrmann,
A.; Ru¨ttimann, M.; Crassous, J .; Cardullo, F.; Echegoyen, L.; Diederich,
F. J . Am. Chem. Soc. 1998, 120, 7860-7868. (c) Crassous, J .; Rivera,
J . A.; Fender, N. S.; Shu, L.; Echegoyen, L.; Thilgen, C.; Herrmann,
A.; Diederich, F. Angew. Chem., Int. Ed. Engl. 1999, 38, 1613-1617.
(3) (a) Kessinger, R.; Go´mez-Lo´pez, M.; Boudon, C.; Gisselbrecht,
J .-P.; Gross, M.; Echegoyen, L.; Diederich, F. J . Am. Chem. Soc. 1998,
120, 8545-8546. (b) Echegoyen, L. E.; Djojo, F. D.; Hirsch, A.;
Echegoyen, L. J . Org. Chem. 2000, 65, 4994-5000.
(8) Beulen, M. W. J .; Rivera, J . A.; Herranz, M. A.; Mart´ın-
Domenech, A.; Mart´ın, N.; Echegoyen, L. Chem. Commun. 2001, 407-
408.
(4) Moonen, N. N. P.; Thilgen, C.; Echegoyen, L.; Diederich, F. Chem.
Commun. 2000, 335-336.
10.1021/jo010297z CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/22/2001

4394 J . Org. Chem., Vol. 66, No. 12, 2001
Beulen et al.
Sch em e 2. Syn th esis of Novel
Ch a r t 1. Sp ir om eth a n ofu ller en es 1-6
Stu d ied by Red u ctive Electr och em istr y
Sp ir om eth a n ofu ller en es fr om Dia zo Com p ou n d s
While some aspects of the electrochemical transforma-
tions of a few of these molecules have been discussed in
preliminary reports,6,8 here we report the synthesis of
some new methanofullerene derivatives (Chart 1), along
with the assignment of the regioisomers of bis-adducts
3 by detailed analysis using UV-vis, 1H NMR, and
HPLC. The products resulting from the reductive elec-
trochemistry of 1-6 in the solvents dichloromethane and
THF are also described for the first time along with an
overall picture of the electrochemistry of this class of
molecules. A previously unreported electrochemically
induced reaction is also presented, for which we tenta-
tively propose involvement of the solvent dichloromethane.
tosyl azide following the method previously reported in
the literature.12
As shown in Scheme 2, monoadduct 4 (43% yield, 62%
based on recovered C60) was obtained together with a
mixture of regioisomeric bis-adducts (3) in lower yield
(10%, 13% based on recovered C60).
All the obtained spiromethanofullerenes 1-6 were the
thermodynamically more stable [6,6] closed methano-
fullerene isomer showing the typical absorption peak at
around 430 nm in the UV-vis spectra. The 13C NMR
spectra of the spiromethanofullerenes show, in addition
to the carbonyl groups at 184-191 ppm, the presence of
the cyclopropane carbons in the region between 40 and
77 ppm for 1, 2, 4, and 5. The FTIR and FABMS spectra
are also consistent with the assigned structures.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of th e Meth a n o-
fu ller en es. The synthesis and electrochemical properties
of 4-6 in dichloromethane were described previously.6,7,9
Compounds 1-3 have somewhat similar structures but
were designed to probe the effects of the different groups
on the electrochemical reactions. Thus, 1 is a structural
hybrid between 5 and 6, while 2 contains phenyl groups
on the quinone instead of the methyl groups in 6.
Compound 3 is the regioisomeric mixture of bis-adducts
corresponding to the monoadduct 4.
1
It is worth mentioning that the H NMR spectra show
a remarkable downfield shift of the protons nearest to
the C60 surface for compounds 1, 2, 5, and 6 in comparison
to those of the parent diazo starting materials as it has
been previously observed for other compounds7d,13 due to
the magnetic deshielding effect of the ring currents of
the C60 sphere.
Bis-adducts of [6,6]methanofullerenes can consist of
eight possible regioisomers: trans-1-4, e, and cis-1-3.
Unambiguous assignment of regioisomers of several
fullerene bis-adducts has been described in detail by
Hirsch et al.14 For example, synthesis of bis-Bingel
adducts of C60 leads to the following regioisomer distribu-
tion: 2% trans-1, 13% trans-2, 30% trans-3, 9% trans-4,
38% e, 6% cis-3, and 2% cis-2.14 The regioisomer distribu-
tion that results during the synthesis of the bis-adducts
The synthesis of the spiromethanofullerenes 1-4 was
carried out by reaction of C60 with the respective diazo
compounds 7-9 by irradiation with a sun lamp (7 and
8) or by heating in 1,2-dichlorobenzene (o-DCB) (9) under
a nitrogen atmosphere (see the Experimental Section)
(Scheme 2).
The starting diazo compounds 710 and 811 were pre-
pared by Bamford-Stevens reaction from the respective
p-benzoquinone derivatives and p-tosylhydrazone under
basic conditions. Diazo compound 9 was prepared from
commercially available indandione by reaction with p-
(12) Spangler, R. J .; Kim, J . H.; Cava, M. P. J . Org. Chem. 1977,
42, 1697-1703.
(13) Prato, M.; Suzuki, T.; Wudl, F. J . Am. Chem. Soc. 1993, 115,
7876-7877.
(14) (a) Hirsch, A.; Lamparth, I.; Karfunkel, H. R. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 437-438. (b) Hirsch, A.; Lamparth, I.;
Karfunkel, H. R. Fullerenes: Recent advances in the chemistry and
physics of fullerenes and related materials. In The regiochemistry of
nucleophilic addition reactions to C60; Kadish, K. M., Ruoff, R. S., Eds.;
The Electrochemical Society, Inc.; Pennington, NJ , 1994; pp 734.
(9) Methanofullerene 6 is unstable under reductive conditions.
Products obtained after electrolysis of methanofullerene 6 do not
contain any C60 or starting material. Main peak in Maldi-Tof is at
m/z 890.
(10) Ried, W.; Dietrich, R. Chem. Ber. 1961, 94, 387.
(11) Nikiforov, G. A.; Plekhanova, L. G.; De J onge, K.; Ershov, V.
V. Izv. Akad. Nauk SSSR, Ser. Khim. 1978, 12, 2752.

Reductive Electrochemistry of Spiromethanofullerenes
J . Org. Chem., Vol. 66, No. 12, 2001 4395
F igu r e 1. HPLC graph of the regioisomers of bis-adduct 3.
3 can be studied by HPLC, and the chromatogram is
shown in Figure 1. We separated the regioisomeric bis-
adducts 3 on a preparative HPLC column (eluent: tolu-
ene; column: Supelco SPLC-Si silica semipreparative
column). Five fractions were isolated and their structures
were assigned by 1H NMR spectroscopy (Figure 2), UV-
vis spectroscopy (Figure 3), and using polarity argu-
ments. The signals in the 1H NMR spectrum of the
monoadduct 4 are typical of an AA′XX′ spin-system, as
expected for an ortho-substituted benzene derivative; see
1
Figure 2.15 The H NMR spectra for the isolated regio-
isomers of 3 (spin-system AA′BB′XX′YY′) are generally
quite complex (Figure 2), but symmetry arguments
enabled the unambiguous assignment of the third frac-
tion as that corresponding to the e isomer. This is the
case because it has Cs symmetry and it is the only
regioisomer with one adduct in the plane of symmetry.
This results in a more complicated 1H NMR spectrum
compared to the other regioisomers, as visualized by the
1
distribution of the peaks. The H NMR spectrum of the
F igu r e 2. 1H NMR spectra of the regioisomers of bis-adduct
3 (HPLC fractions 1-5), bis-adduct 3, and monoadduct 4.
e regioisomer consists of two sets of two peaks with the
following number of protons: 2H/3H and 1H/2H, whereas
the other 1H NMR spectra consist of two sets of peaks
with a 4H and 2H/2H distribution.16 The other isomer
that could have been immediately assigned if it had been
isolated would have been the highly symmetric trans-1
(with D2h-symmetry), but this was not observed. The
other isomers were assigned by UV-vis spectroscopy and
by their polarity, as reflected in the order of elution on
the HPLC column. It was assumed that the HPLC elution
order would follow the polarity of the regioisomers
(increasing polarity from trans-1 to cis-1), as observed
by Hirsch for the Bingel bis-adducts.14 Assignment of the
second fraction to the trans-3 regioisomer (and not trans-
4) was based on the UV-vis spectrum. The following
regioisomer distribution of the bis-adducts was found for
the diazomethane synthetic product mixture: 14% trans-
2, 16% trans-3, 41% e, 5% cis-3, 19% cis-2 (Figure 1). No
detectable amount of the trans-4 regioisomer was iso-
lated, perhaps because it elutes very close to the e or the
trans-3 isomers. The distribution is similar to that of the
bis-Bingel addend fullerenes determined by Hirsch et
F igu r e 3. UV-vis spectra of the regioisomers of bis-adduct
3.
(15) Gu¨nther, H. In NMR Spectroscopy; J ohn Wiley & Sons: Chich-
ester, 1980.
(16) Fraction 3 (e isomer) contains a small amount (7%) of the
trans-3 isomer, causing the NMR-signal denoted with X.
al.,14 with trans-3 and e as predominant regioisomers and
cis-3 as one of the minor ones.

4396 J . Org. Chem., Vol. 66, No. 12, 2001
Beulen et al.
isolated after the electrolysis. We recently showed that
dichloromethane reacts efficiently with the [60]fullerene
trianion to form methanofullerenes of the type
C60>(CH2)n,17 and it also forms similar adducts with C84
(C84>(CH2)n) during the reductive retro-Bingel reaction
of di[alkoxycarbonyl]methano adducts of C84.2c We think
that a similar process is taking place during the elec-
trolysis of 1 and 6. These anions can react with dichlo-
romethane to form products of the type methanofullerene-
CH2Cl, which presumably acquires another proton during
or after oxidation, leading to the observed mass increase
of 50 amu. Due to the small amounts of material
available, it has not been possible to carry out an
1
assignment (e.g., by H NMR) of the structures of these
+50 amu products.18
CPE of 2 (964 amu) was performed after the third wave
(arrow B, Figure 4) discharging 3.2 electrons. Reoxidation
and purification yielded two fullerene products in a 1:1
ratio with a total 58% yield. Some starting material was
isolated indicating that this compound is relatively stable
under reductive electrolysis conditions. Furthermore an
unknown product with a mass of 1014 amu was isolated,
which again is assigned to a reaction product with
dichloromethane, leading to 2-CH2Cl.
F igu r e 4. Cyclic voltammograms vs ferrocene of 1-3 in
dichloromethane.
Ta ble 1. Red ox P oten tia ls of Meth a n ofu ller en es 1-6 vs
F er r ocen e in Dich lor om eth a n e
Electrolysis of 4 after the first reduction wave resulted
in the formation of C60 in a relatively high yield (58%).6
We performed several electrolysis experiments with the
corresponding bis-adducts 3. CPE of 3 at a potential
slightly cathodic of the second wave (arrow D, Figure 4)
discharged 3.4 electrons and yielded 75% of fullerene
products.19 Purification and analysis showed the exclu-
sive formation of C60. Isomers 3 also exhibit adduct
removal induced by reductive electrochemistry. Elec-
trolysis at less negative potentials, e.g., after the first
two-electron wave (arrow C, Figure 4), discharged 2.5
electrons and yielded 70% of fullerene products. Purifica-
tion and analysis showed the formation of C60 (35%) and
monoadduct 4 (35%). We observed that this electrochemi-
cal adduct removal reaction is a relatively slow reaction
and can be inhibited considerably if the electrolysis
mixture is immediately reoxidized after completing the
reductive electrolysis.20 CPE after the first oxidation
wave (arrow C, Figure 4) yielded 30% monoadduct 4 and
65% unreacted bis-adduct 3, whereas CPE after the
second reduction wave (arrow D, Figure 4) resulted in
5% C60, 30% monoadduct 4, and 19% bis-adduct 3. The
regioisomer distribution of the bis-adducts isolated in
these electrolyses was very similar to that found for the
starting material 3.
E1
E2
E3
E4
E5
1
2
3
4
5
6
-951a
-832c
-965e
-971e
-1038
-859
-1096b
-1092d
-1335
-1598
-1383c
-1119c
-1207
-1487
-2069c
-2015
-1492
-1522
-1486
-1915
-1841
-1893
-1926
a
Electrochemically irreversible reduction, oxidation wave at
b
-595 mV. Electrochemically irreversible reduction, oxidation
wave at -724 mV. c Electrochemically irreversible reduction.
d
Electrochemically irreversible reduction, oxidation wave at -666
mV. e Two-electron process.
Electr och em istr y in Dich lor om eth a n e. The cyclic
voltammograms (CVs) of 1-3 in dichloromethane are
presented in Figure 4. Compound 1 exhibits two chemi-
cally irreversible redox waves, followed by three revers-
ible ones. The CV of 2 consists of two irreversible redox
waves followed by two reversible waves. Compound 3
starts with a two-electron wave, followed by a one-
electron wave and an irreversible wave. Similar to the
electrochemistry of 4-6,6 1-3 exhibit, besides reversible
reductions, several irreversible reductions. The redox
potentials of 1-6 vs ferrocene are reported in Table 1.
Compound 1 was subjected to controlled potential
electrolysis (CPE) after the fourth reduction wave (arrow
A, Figure 4), which discharged 3.4 electrons per molecule.
The CV of 1 completely changed upon electrolysis. After
reoxidation at 0 V, the reaction mixture was purified by
column chromatography (eluent: toluene) to yield 38%
of fullerene-based products. Characterization by HPLC,
UV-vis spectroscopy, and Maldi-Tof mass spectrometry
showed that no starting material was recovered while
two products, in a roughly 1:1 ratio, were isolated. One
of the products was identified as C60, and the other was
an unknown product with a mass of 926 amu (1: 876
amu). So adduct removal is one of the main reaction
pathways for 1, but a secondary pathway affords a new,
still uncharacterized product. Interestingly, the electroly-
sis of 6 under identical conditions resulted in the forma-
tion of a product whose mass is also 50 amu larger than
that of the starting material (6, 840 amu; electrolysis
product, 890 amu).6 However, in the case of 6, no C60 was
CPE of 5 after the third reduction wave discharged 4.7
electrons and yielded, after reoxidation, purification and
characterization 65% of C60.6
Thus, adduct removal is a very general reaction, which
occurs for 1 and 3-5. Furthermore, a secondary reaction
pathway with the solvent is observed for 1, 2 and 6. This
(17) Beulen, M. W. J .; Echegoyen, L. Chem. Commun. 2000, 1065-
1066.
(18) We attempted to prove the presence of chlorine in these
structures by the isotope pattern in the Maldi-Tof spectrum
(
35Cl/37Cl ) 76:24). However, as was shown by simulations, the
dominating factor in the isotope pattern for these molecules is not
chlorine but the high number of carbons (1-CH2Cl contains 72
carbons), rendering the identification of chlorine by Maldi-Tof some-
what ambiguous.
(19) CPE at even more negative potentials leads to uncontrolled
reactions; no fullerene products could be isolated after reoxidation.
(20) Monitoring of the CPE-experiment by electrochemical (CV,
OSWV) and ESR measurements normally requires a period of 30-60
min. between the reductive electrolysis and the oxidative electrolysis.

Reductive Electrochemistry of Spiromethanofullerenes
J . Org. Chem., Vol. 66, No. 12, 2001 4397
Ta ble 2. Resu lts of CP E a t Meth a n ofu ller en es 1-6 in th e
The mechanism was supported by molecular modeling
studies.
Solven ts Dich lor om eth a n e a n d THF
total yield
CPE (%)
starting
60 (%) material (%)
other
products (%)
CPE of isomers 3 after the second wave discharged 3.0
electrons. Reoxidation and purification yielded 30%
fullerene products, consisting of 14% C60 and 16% mono-
adduct 4. CPE after the first reduction wave discharged
2.0 electrons and yielded, after reoxidation and purifica-
tion, 14% of C60, 33% monoadduct 4, as well as 33% of
bis-adducts 3. No tris-adducts were isolated. The regio-
isomer distribution of the recovered bis-adducts 3 had
changed considerably in comparison with the starting
material, with an increase of the cis-3 isomer from 5%
to 13%. This apparent isomerization, which favors the
cis-3 regioisomer, can follow an intermolecular (via the
mono- or tris-adduct) or intramolecular pathway. Cur-
rently we are investigating the mechanism of this
isomerization.
C
DCM
1
2
3
38
19
29
35
75
19 (1-CH2Cl)
58
29 (2-CH2Cl)
70a
75b
80
35 (monoadduct 4)
4
5
6
58
65
22
65
60
60 (6-CH2Cl)
THF
1
2
3
32
50
32e
50e
33
80a
30b
81a
84b
91
14
14
40
35
41
33 (monoadduct 4)
16 (monoadduct 4)
14 (bis-adduct 3)c
19 (bis-adduct 3)d
11 (bis-adduct of 5)
4
27
30
39
5
a
b
Electrolysis after first reduction wave. Electrolysis after
Con clu sion s
second reduction wave. c trans-2, 3%; trans-3, 7%, ee 37%; cis-3,
49%. trans-2, 6%; trans-3, 11%, ee 43%; cis-3, 37%. e Main
d
In conclusion, we have synthesized several new metha-
nofullerene derivatives by the diazomethane route. As-
signment of the regioisomers of the bis-adduct 3 were
product, not totally pure.
confirms that dichloromethane is not a good solvent for
electrochemical measurements of fullerenes.17 On the
basis of these observations, it was decided to investigate
the electrochemical behavior of the methanofullerenes in
the less reactive solvent THF.
Electr och em istr y in THF . The CVs of the metha-
nofullerene derivatives in the solvents dichloromethane
and THF are very similar. Electrolysis of 1 at the same
potential as shown by arrow A in Figure 4 discharged
2.7 electrons. Reoxidation of the electrolysis mixture
yielded fullerene products in a 32% yield, mainly consist-
ing of C60.
Electrolysis of 2 was performed after the third reduc-
tion wave, as indicated by arrow B in Figure 4 for DCM,
and it discharged 2.5 electrons. Essentially no changes
were observed in the cyclic voltammogram, and reoxida-
tion and purification yielded 50% of fullerene products,
mainly recovery of the starting material.
1
made by H NMR, UV-vis, and HPLC. These methano-
fullerenes exhibit interesting electrochemistry in dichlo-
romethane and THF. Reductive electrolysis of the metha-
nofullerene 1 and 3-5 in dichloromethane leads to
removal of the addends to form C60. This could be used
as a protective group in synthetic fullerene chemistry.
Interestingly, an alternative reaction pathway was ob-
served for 1, 2, and 6, which leads to the formation of
methanofullerene-CH2Cl products of unspecified struc-
ture. Reductive electrolyses in THF shows clean adduct
removal for 1 and 3-5. Another reaction pathway was
observed in THF for 4 and 5, an intermolecular addend
crossover reaction leading to bis-adducts. We are cur-
rently investigating the mechanisms and possible ap-
plications of these new electrochemical reactions.
Exp er im en ta l Section
Gen er a l Deta ils. 1H NMR and 13C NMR spectra were
obtained using a Varian VXR-300, a Bruker Avance-300, and
a Bruker AMX-500. Mass spectra were recorded using a VC
Autospec EBE spectrometer operating at 30 kV by using a
bombardment of Cs+ ions and 2-NPOE or 3-NBA as matrix or
Maldi-Tof MS: PerSeptive Biosystems Voyager-DE STR
spectrometer. FTIR spectra were recorded using a Nicolet
Magna-IR spectrometer 5550. UV-vis: Shimadzu UV 2101
PC spectrometer. HPLC: Varian ProStar with a SiO2 column.
All chromatography was performed using Merck silica gel (70-
230 mesh). All reagents were used as purchased unless
otherwise stated. All solvents were dried according to standard
procedures.
Electr och em istr y. Details of the experimental electro-
chemical setup for the CV, Osteryoung square wave voltam-
metry (OSWV), and bulk electrolysis measurements have been
described elsewhere.24 Briefly, electrochemical measurements
were performed using a BAS 100W electrochemical analyzer
(Bioanalytical systems). An electrochemical cell designed to
carry out CV, OSWV, and bulk electrolysis under high vacuum
was used. For CV and OSWV, a glassy-carbon working
electrode, a silver wire pseudoreference electrode, and a Pt-
mesh counter electrode were used. Bulk electrolysis was
carried out using Pt mesh electrodes for both working and
counter electrode. As supporting electrolyte, tetrabutylammo-
Previously, we reported that electrolysis of 4 and 5 in
THF resulted in clean adduct removal and formation of
C60. However, an alternative reaction pathway also led
to the formation of bis-adducts for 4 and 5, but not for
the other compounds. The formation of bis-adducts from
the electrolysis of 4 was easily proven by comparison with
the synthetically prepared bis-adducts 3. The formation
of bis-adducts for 5 was proven by HPLC and Maldi-
Tof.21 Detailed studies showed that electrolysis of 4 after
the first or after the second reduction wave yielded
mainly the e and cis-3 regioisomeric bis-adducts (see
Table 2). The formation of the cis-3 regioisomer in such
a high percentage is unprecedented in fullerene deriva-
tive synthesis, except when it is selected using the tether-
directed remote functionalization method, designed for
that particular isomer.22 We have tentatively proposed
a mechanism that involves the presence of fullerene-
dimer23 intermediates to rationalize these observations.8
(21) Main peaks in Maldi-Tof spectrum at 1004 (bis-adduct), 912,
and 720 amu. Maldi-Tof spectra for fullerenes always shows frag-
mentation in the mass-spectrometer (720 amu ) C60; 912 ) mono-
adduct 5). HPLC measurements show that the sample itself does not
contain any of these two fragments.
(22) Nierengarten, J .-F.; Habicher, T.; Kessinger, R.; Cardullo, F.;
Diederich, F.; Gramlich, V.; Gisselbrecht, J .-P.; Boudon, C.; Gross, M.
Helv. Chim. Acta 1997, 80, 2238-2276.
(23) Segura, J . L.; Mart´ın, N. Chem. Soc. Rev. 2000, 29, 13-25.
(24) Diekers, M.; Hirsch, A.; Pyo, S.; Rivera, J . A.; Echegoyen, L.
Eur. J . Org. Chem. 1998, 1111, 1-1121.

4398 J . Org. Chem., Vol. 66, No. 12, 2001
Beulen et al.
nium hexafluorophosphate was used. Dichloromethane was
distilled over silica, THF over Na/K before use.
4H), 8.21 (s, 2H); 13C NMR (75 MHz, CDCl3/CS2) δ 40.8, 77.2,
128.2, 128.3, 128.5, 129.1, 129.3, 129.8, 132.2, 135.6, 137.1,
138.3, 141.9, 142.0, 142.9, 143.5, 143.9, 144.7, 144.8, 144.9,
145.0, 145.4, 146.0, 147.0, 185.7; MS m/z 964 (M+, 20), 720
(C60, 100); UV-vis (CHCl3) λmax/nm 258, 328, 436.
S p ir o [1′(2′,7′-in d a n d io n e )-1′,61-m e t h a n o [60]fu ll-
er en e] (4). An o-dichlorobenzene solution of C60 (100 mg, 0.138
mmol) and 2-diazo-1,3-indandione12 (9, 478 mg, 0.27 mmol)
was heated to reflux under argon atmosphere for 4 h. The
solvent was removed under reduced pressure, and the crude
material was carefully chromatographed on a silica gel column
using cyclohexane/toluene 1/1 as eluent. Unreacted C60 eluted
first, followed by the monoaddition product (4), and finally,
the regioisomeric mixture of the bis-adducts 3 was obtained.
Further purification was accomplished by repetitive precipita-
tion and centrifugation using hexane, methanol, and diethyl
ether as solvents.
Ma ter ia ls. We previously reported the synthesis of the
methanofullerenes 5 and 6.7d
P r ep a r a tion of Dia zo Com p ou n d s 7-9. 3-Methyl-1-
diazonaphthalene-4-oxide (7) was prepared from 2-methyl-1,4-
naphthoquinone by reaction with p-tosylhydrazine and sub-
sequent base-catalyzed decomposition.10 3,5-Diphenyl-1-diazo-
benzene-4-oxide (8) was obtained by reaction of 2,6-diphenyl-
1,4-benzoquinone similarly to 7.11 2-Diazo-1,3-indandione (9)
was prepared from 1,3-indandione and tosyl azide at low
temperature according to the procedure reported in the
literature.12 The diazo compounds 7-9 were used immediately
in the next step.
Sp ir o[1′(5′-m et h ylb en zocycloh exa d ien -4′-on e)-1′,61-
m eth a n o[60]fu ller en e] (1). To a solution of C60 (177 mg, 0.25
mmol) in o-dichlorobenzene (15 mL) was added 3-methyl-4-
oxodiazonaphthalene10 (7, 50 mg, 0.27 mmol), and the reaction
mixture was irradiated with a sun lamp at 0-10 °C under
argon atmosphere for 3 h. The solvent was removed under
reduced pressure. The resulting solid was purified by silica
gel chromatography using cyclohexane/toluene 1/1 as eluent:
17% yield (34% based on consumed C60); FTIR (KBr) ν/cm-1
1664, 1661, 1659, 1459, 1185, 765, 714, 587, 526; 1H NMR (300
MHz, CDCl3) δ 2.37 (d, 3H, J ) 1.5 Hz), 7.67 (dt, 1H, J ) 7.7,
1.1 Hz), 7.76 (dt, 1H, J ) 7.7, 1.8 Hz), 8.41 (d, 1H, J ) 1.5
Hz), 8.50 (dd, 1H, J ) 7.7, 1.8 Hz), 9.14 (dd, 1H, J ) 7.7, 1.1
Hz); 13C NMR (75 MHz, CDCl3/CS2) δ 29.8, 40.6, 77.2, 78.4,
125.4, 128.5, 128.7, 131.9, 134.0, 137.7, 138.7, 138.8, 139.2,
139.9, 140.0, 141.1, 141.3, 141.6, 142.1, 142.2, 143.1, 143.2,
143.3, 143.9, 144.0, 144.5, 144.7, 144.8, 144.9, 145.0, 145.3,
145.4, 147.3, 148.3, 184.6; MS m/z 876 (M+, 19), 720 (C60, 100);
UV-vis (CHCl3) λmax/nm 258, 282, 322, 436, 690.
S p ir o [1′(2′,7′-in d a n d io n e )-1′,61-m e t h a n o [60]fu ll-
er en e] (4): 43% yield (62% based on consumed C60); FTIR
(KBr) ν/cm-1 1712, 1515, 1503, 1264, 1228, 744, 711, 698, 526;
1H NMR (300 MHz, CDCl3) δ 8.22-8.15 (m, 2H), 8.02-7.95
(m, 2H); 13C NMR (125 MHz, CDCl3/CS2 1/1) δ 64.4, 74.1,
123.3, 135.8, 140.9, 141.4, 141.5, 141.7, 142.1, 142.9 (2C),
143.0, 143.6, 143.8, 144.4, 144.5, 144.6, 144.7, 144.9, 145.1,
191.0; MS m/z 864 (M+, 55), 720 (C60, 80); UV-vis (CHCl3)
λmax/nm 290, 338, 432, 510, 660.
Bis [1′(2′,7′-in d a n d ion e)]-1′,61-m et a n o[60]fu ller en es
(3): 10% yield (13% based on consumed C60); FTIR (KBr)
ν/cm-1 1716, 1593, 1458, 1378, 1350, 1323, 1231, 1044, 939,
792, 780, 755, 740, 722, 698, 525; 1H NMR (300 MHz, CDCl3)
δ 8.31-7.85 (m, 8H); MS m/z 1009 (M+, 100), 864 (4, 16); UV-
vis (CH2Cl2) λmax/nm 250, 282, 314, 428, 482.
Sp ir o[1′(3′,5′-d ip h e n ylcycloh e xa d ie n -4′-on e )-1′,61-
m eth a n o[60]fu ller en e (2). To a solution of C60 (156 mg, 0.22
mmol) in dry o-dichlorobenzene (15 mL) was added 3,5-
diphenyl-4-oxadiazobenzene11 (8, 80 mg, 0.29 mmol), and the
reaction mixture was irradiated with a sun lamp at 0-10 °C
under argon atmosphere for 2.5 h. Flash chromatography of
the reaction mixture, using cyclohexane/toluene 1/1 as eluent,
gave pure adduct: 17% yield (84% based on consumed C60);
FTIR (KBr) ν/cm-1 649, 1625, 897, 816, 737, 714, 697, 525; 1H
NMR (300 MHz, CDCl3) δ 7.47-7.55 (m, 6H), 7.72-7.74 (m,
Ack n ow led gm en t. Financial support for this work
from the National Science Foundation through grant
CHE-9816503, The Netherlands Organization for Sci-
entific Research (NWO, talent stipendium, M.W.J .B.),
and the DGICYT of Spain (PB98-0818) is greatly ap-
preciated. We also thank to the Fulbright Foundation
(Project 99125) for financial support.
J O010297Z