Quinone-type methanofullerene acceptors: Precursors for organic metals

Article abstract of DOI:10.1021/jo951738f

We report details on the synthesis and electrochemistry of quinone-type methanofullerene derivatives in which, depending upon the substitution pattern on the cyclohexanedienone moiety, the reduction potential can be tuned, leading to novel fullerene deriv

Full text of DOI:10.1021/jo951738f

1306
J . Org. Chem. 1996, 61, 1306-1309
Qu in on e-Typ e Meth a n ofu ller en e Accep tor s: P r ecu r sor s for
Or ga n ic Meta ls
Toshinobu Ohno, Nazario Mart´ın,† Brian Knight, Fred Wudl,* Toshiyasu Suzuki,‡ and
Huinan Yu
Institute for Polymers and Organic Solids, Departments of Chemistry and Materials,
University of California, Santa Barbara, California 93106
Received September 22, 1995X
We report details on the synthesis and electrochemistry of quinone-type methanofullerene
derivatives in which, depending upon the substitution pattern on the cyclohexanedienone moiety,
the reduction potential can be tuned, leading to novel fullerene derivatives exhibiting better acceptor
properties than C60. We also present the lowest energy conformers of these spiroannulated
methanofullerenes. As expected, the anthrone derivative is not coplanar and is not perpendicular
to the ball’s surface.
The high electron affinity of buckminsterfullerene C60
derivatives exhibiting better acceptor properties than C60.
This opens up a potential route to fullerene derivatives
as precursors for charge-transfer complexes.
The intramolecular electronic interaction (periconju-
gation)8 between the pz-π orbitals of the quinone moiety
and the adjacent carbon atoms of C60, separated by a
spiro carbon atom, results in more extended conjugated
molecules showing good acceptor properties.
The synthesis of the novel methanofullerene deriva-
tives (3a -d ) was carried out according to Scheme 1 by
reaction of C60 with the corresponding 1,4-diazooxide
(1a -d ) by irradiation with a sun lamp (compounds 1a -
c) or by heating in 1,2-dichlorobenzene (compound 1d )
under nitrogen atmosphere (Table 1).
The starting diazo compounds 1a -d were prepared by
following previously described procedures (1a ,9 1b,10 1c,11
1d 12 ).
It is worth mentioning that, when compounds 1a -c
were allowed to react with C60 in chlorobenzene or 1,2-
dichlorobenzene at 100-115 °C or reflux temperature
they afforded the corresponding compounds 3a -c only
in trace amounts. However, compound 3d was obtained
by heating at different temperatures (60-70 °C or 100-
110 °C) overnight. Compounds 3a -d were purified by
flash chromatography (SiO2, chlorobenzene/hexane or
toluene/hexane, 1:1) producing air-stable solids which can
be stored at room temperature.
allows the addition of up to six electrons in solution.1 This
led, by reaction with metals and donor species, to the
2
formation of charge transfer salts such as K3C60 and
charge transfer complexes of type [TDAE]C60 [TDAE:
tetrakis(dimethylamino)ethylene],3 exhibiting supercon-
ducting and ferromagnetic properties, respectively.
These findings have encouraged the search of novel
fullerene derivatives showing better acceptor abilities. To
the best of our knowledge, only one example (C60F48)4 in
which the first reduction potential is considerably more
positive than in C60 is known. Several attempts to
prepare chemically modified fullerenes by combining the
electrochemical properties of C60 with other covalently
linked electroactive moieties have been described.5 How-
ever, the lack of conjugation between the two partners,
in addition to the loss of conjugation due to saturation
of one double bond in C60, was responsible for the
observation of adducts which are more electropositive
than the parent C60.6
In this paper we report more details on the synthesis
and electrochemistry of new quinone-type methano-
fullerene derivatives7 in which, depending upon the sub-
stitution pattern on the cyclohexanedienone moiety, the
reduction potential can be tuned, leading to novel fullerene
† On leave from Department of Organic Chemistry, Faculty of
Chemistry, Complutense University of Madrid, 28040-Madrid, Spain.
‡ Present address: Fundamental Research Laboratories, NEC
Corporation, 34, Miyukigaoka Tsukuba 305, J apan.
All the methanofullerenes 3a -d were the thermody-
namically more stable methanofullerene (“[6,6]”) isomer,
and the UV spectra showed typical peaks at ca. 440, 500,
and 700 nm. The methanofullerene structure was as-
certained by the 13C NMR of the bridgehead carbons in
the 74-85 ppm region. The FTIR and FABMS are also
X Abstract published in Advance ACS Abstracts, J anuary 15, 1996.
(1) Allemand, P.-M; Koch, A.; Wudl, F.; Rubin, Y.; Diederich, F.;
Alvarez, M. M.; Anz, S. J .; Whetten, R. L. J . Am. Chem. Soc. 1991,
113, 1050. Xie, Q.; Pe´rez-Cordero, E.; Echegoyen, L. J . Am. Chem. Soc.
1992, 114, 3978.
(2) Haddon, R. C. Acc. Chem. Res. 1992, 25, 127.
(3) Allemand, P.-M.; Khemani, K. C.; Koch, A.; Wudl, F.; Holczer,
K.; Donovan, S.; Gru¨ner, G.; Thompson, J . D. Science 1991, 253, 301.
Stephens, P. W.; Cox, D.; Lauer, J . W.; Mihali, L.; Wiley, J . B.;
Allemand, P.-M.; Hirsch, A.; Holczer, K.; Li, Q.; Thompson, J . D.; Wudl,
F. Nature 1992, 355, 331.
(4) Zhou, F.; van Berkel, G. J .; Donovan, B. T. J . Am. Chem. Soc.
1994, 116, 5485.
1
consistent with the assigned structure, and the H NMR
spectra show the typical resonance signals of the cyclo-
hexanedienone moiety. However, the aromatic protons
nearest to the spheroid in compound 3d are shifted
downfield in comparison to the related anthrone. This
effect has also been previously observed in non-quinoid
(5) Suzuki, T.; Maruyama, Y.; Akasaka, T.; Ando, W.; Kobayashi,
K.; Nagase, S. J . Am. Chem. Soc. 1994, 116, 1359.
(6) Haddon, R. C. Science 1993, 261, 1545. Arias, F.; Xie, Q.; Wu,
Y.; Lu, Q.; Wilson, S. R.; Echegoyen, L. J . Am. Chem. Soc. 1994, 116,
6388. Beer, E.; Feuerer, M.; Knorr, A.; Mirlach, A.; Daub, J . Angew.
Chem., Int. Ed. Engl. 1994, 33, 1097. Maggini, M.; Karlsson, A.;
Scorrano, G.; Sandona, G.; Farnia, G.; Prato, M. J . Chem. Soc., Chem.
Commun. 1994, 589.
(7) Very recently, the synthesis of a fullerene derivative containing
the p-benzoquinone moiety has been reported by Iyoda, M.; Sultana,
F.; Sasaki, S.; Yoshida, M. J . Chem. Soc., Chem. Commun. 1994, 1929.
The first reduction potential was assigned to the reduction of the
p-benzoquinone part which behaves independently of the C60 moiety.
(8) Wudl, F.; Suzuki, T.; Prato, M. Synth. Methods 1993, 59, 297.
Eiermann, M.; Haddon, R. C.; Knight, B.; Li, Q.; Maggini, M.; Mart´ın,
M.; Ohno, T.; Prato, M.; Suzuki, T.; Wudl, F. Angew. Chem., Int. Ed.
Engl. 1995, 34, 1591. Because the arrangement of “π”-orbitals in C60
is orthogonal to those in other spiroannulated molecules, there is no
possibility of spiroconjugation in 3a -3d .
(9) Puza, M.; Doetschman, D. Synthesis 1971, 48, 1.
(10) Ried, W.; Dietrich, R. Ber. 1961, 94, 387.
(11) Koser, G. F.; Pirkle, W. H. J . Am. Chem. Soc. 1967, 1992.
(12) 2. Fleming, J . C.; Shechter, H. J . Org. Chem. 1969, 34, 3962.
0022-3263/96/1961-1306$12.00/0 © 1996 American Chemical Society

Quinone-Type Methanofullerene Acceptors
J . Org. Chem., Vol. 61, No. 4, 1996 1307
Sch em e 1
Ta ble 1. Novel Meth a n ofu ller en e Der iva tives P r ep a r ed
Ta ble 2. P ea k Red u ction P oten tia ls Rela tive to
Fc/Fc+ (m V)
conditions, time
yield
(%)
compound
R1
R2
solvent
°C
(h)
E1,red
E2,red
E3,red
E4,red
-2016
3a
3b
3c
3d
H
H
H
H
o-DCBa
o-DCB
o-DCB
hν 0-10
hν 0-10
hν 0-10
60-70
1
1
2
16 (47)b
13 (43)
26 (57)
3a
3b
3c
3d
-1081a,b
-1042c
-1097d
-1215
-1559
1197c
Me
t-Bu
-1602
-2037
-1670c
-1913
-1620
-1525c
-1455
-2026e
-2097c
-2223c
-2172e
(-CHdCH-)2 o-DCB
24 47 (65)
-2090
-2383
C60
-1123
a
b
o-DCB: o-dichlorobenzene. Based on the recovered C60
.
BQf
-1166e
-1287e
-1365e
-1587e
Me2BAg
(tBu)2BQh
AQi
a
b
Peak position depends upon scan rate. Scan rate ) 10 mV/
s. c Electrochemically and chemically irreversible. Two-electron
d
process. e Electrochemically irreversible, but chemically reversible.
f Benzoquinone. 2,5-Dimethylbenzoquinone. 2,5-Di-tert-butyl-
g
h
i
benzoquinone. Anthraquinone.
compound 3d by carrying out the reaction at lower
temperatures (60-70 °C) led solely to the more stable
methanofullerene isomer.
In addition to the monoadduct 3d , the bis-adduct 4 (n
) 2) as well as the tris-adduct 4 (n ) 3) of the corre-
sponding 1,4-diazoanthrone (1d ) were also separated by
chromatography. However, the mixture of isomers could
not be resolved in this way.
The cyclic voltammetry (CV) measurements of the
novel acceptors were carried out in 1,2-dichlorobenzene
at room temperature with tetrabutylammonium tet-
rafluoroborate as the supporting electrolyte. The metha-
nofullerene derivatives 3a -c were found to be better
acceptors than the parent C60. In contrast, compound
3d (Figure 1) showed a more negative first reduction
potential (Table 2). All the compounds 3a -d showed
three or four reduction waves and, unlike most organo-
fullerenes reported, these compounds do not behave
reversibly in the CV. This finding could suggest the
opening of the cyclopropane ring when the molecule
accepts an electron.8 However, attempts to capture the
expected phenolate of the radical-anion with strong
alkylating reagents were unsuccessful.
Taking into account that compound 3b presents an
irreversible first redox potential, in Table 2 are collected
the peak-potentials for the first reduction to the corre-
sponding anion-radical. The OSWV14 was recorded and
also confirms the peaks observed (Figure 1) showing
additional waves at more negative values.
The better acceptor ability of compounds 3a -c could
be rationalized by the periconjugation of the pz-π orbitals
of the cyclohexadienone moiety and the orbitals of the
F igu r e 1. Cyclic voltammogram (CV) and Osteryoung square
wave voltammogram (OSWV) of compound 3d in o-DCB.
related molecules13 as a consequence of the magnetic
deshielding effect of the π-electrons of the buckyball.
No evidence of the fulleroid (“[5,6]”) isomer was ob-
served. Attempts to prepare the fulleroid isomer of
(13) Prato, M.; Suzuki, T.; Wudl, F. J . Am. Chem. Soc. 1993, 115,
7876.
(14) OSWV acronym for Osteryoung square Wave Voltammetry:
Osteryoung, J . G.; O’dea, J . J .; In Electroanalytical Chemistry; Bard,
A. J ., Ed.; Dekker: New York, 1986; Vol. 14.

1308 J . Org. Chem., Vol. 61, No. 4, 1996
Ohno et al.
F igu r e 2. Molecular geometry of compounds 3a and 3d by molecular mechanics calculations. In 3d , unlike the cyclohexadienone
in 3a , the anthrone moiety is not perpendicular to the ball’s surface.
fullerene carbon atoms adjacent to the cyclopropane ring.8
The crude reaction mixture was submitted to flash chroma-
tography (SiO2, 1:1-toluene/hexane) to give 240 mg (47% yield)
of pure compound (65% based on consumed C60). Further
The more negative reduction potential value found for
the anthrone derivative 3d may be due to the steric
interaction of the aromatic peri-hydrogens with the
spheroid leading to a significant deviation from the
purification was accomplished by recrystallization in toluene-
hexane to yield deep brown crystals. 1H NMR (CS2/500
MHz): δ 8.40 (dd, J ) 7.5, 1.5 Hz, 2H), 8.16 (dd, J ) 6.5, 2.0
orthogonality and hence to the loss of periconjugation.
Hz, 2H), 7.60-7.54 (m, 4H). 13C NMR (Cl2CD-CDCl2/CS2): δ
This result was confirmed by molecular mechanics cal-
culations using a Silicon-Graphics Iris computer (molec-
ular mechanics calculations were performed using the
Insight II molecular modeling system, Biosym Technolo-
gies Inc., San Diego, CA 92121) which revealed an
orthogonal disposition of the quinone moiety for com-
pounds 3a -c and a strong deviation for 3d . In agree-
ment with these data, the 13C NMR spectra of compound
3b showed 15 peaks for the fullerene moiety indicating
two planes of symmetry, and 23 peaks for 3d revealing
the presence of only one plane of symmetry in this
molecule (Figure 2).
In summary, we have carried out the synthesis of novel
methanofullerene derivatives bearing a cyclohexanedi-
enone moiety by photolysis of 1,4-diazooxides and C60 and
also by thermolysis. The good acceptor properties of
these molecules, better than C60, could be rationalized
in terms of periconjugation. This effect also explains the
anomalous behavior of the anthrone derivative 3d . The
13C NMR and the molecular geometry obtained by mo-
lecular mechanics calculations are in good agreement
with the CV data. These novel methanofullerene accep-
tors are precursors for organic metals. Work is in
progress in order to form charge-transfer complexes with
electron-donor molecules and to prepare the respective
TCNQ and DCNQI-type analogs.
186.93 (CO), 148.73, 146.31, 145.14, 145.05, 144.84, 144.71,
144.58, 144.52, 144.23, 143.84, 143.49, 143.02, 142.84, 142.76,
141.96, 141.84, 141.31, 140.90, 140.14, 139.26, 138.99, 137.46,
136.26, 130.82, 129.02, 128.58, 127.31, 81.87 (bridgehead C),
74.03 (bridgehead C), 48.08 (bridge). FTIR (KBr): 1670(CO)
s, 1595 m, 1465 w, 1450 w, 1430 w, 1300 m, 1260 m, 1185 w,
1160 w, 930 w, 800 w, 770 w, 750 w, 735 w, 715 w, 690 w, 560
w, 527 s cm-1
.
FABMS (toluene/NBA): m/z 913 (M + H)+,
720(C60). Anal. Calcd for C74H8O: C, 97.36; H, 0.88. Found:
C, 97.21; H, 0.95. UV-vis (toluene) λmax (nm): 286, 332, 410-
(sh), 436, 496, 696.
P r ep a r a tion of 1,4-Dia zooxid es. 1-Diazobenzene 4-oxide
was prepared by the dehydrochlorination of p-diazophenol with
freshly prepared silver oxide as described.9 3,5-Dimethyl-1-
diazobenzene 4-oxide was prepared by reaction of 2,6-dimethyl-
1,4-benzoquinone with p-tosylhydrazine and subsequent base-
catalyzed decomposition.10 3,5-di-tert-butyl-1-diazobenzene
4-oxide was prepared by the modified method of 3,5 dimethyl-
1-diazobenzene 4-oxide and confirmed by comparison of physi-
cal data with the literature.11
2,6-Di-ter t-b u t ylb en zoq u in on e 4-p -t osylh yd r a zon e:
solid, mp 94-96 °C dec; 1H NMR (CDCl3) δ 1.44 (s, 18H), 2.46
(s, 3H), 7.75 (s, 2H), 7.38 (d, 2H), 7.90 (d, 2H); FTIR (KBR)
3226m, 2957m, 1647m, 1633m, 1625m, 1365m, 1335m, 1319m,
1157s, 902m, 890s, 884m, 682m cm-1
C
.
Anal. Calcd for
21H28O3N2S: C, 64.92; H, 7.26; N, 7.21; S, 8.26. Found: C,
64.63; H, 7.18, N, 7.39; S, 8.50.
3,5-Di-ter t-b u t yl-1-d ia zob en zen e 4-oxid e: 1H NMR
(CDCl3) δ 1.33 (s, 18H), 7.19 (s, 2H); FTIR (KBR) 3007w
2955m, 2076s, 1593s, 1565s, 1353m, 1183s, 882m cm-1; UV-
vis (cyclohexane) λmax 210, 262, 350, 500.
Exp er im en ta l Section
Gen er a l P r oced u r e for P h otolysis of 1,4-Dia zooxid es
in o-Dich lor oben zen e Solu tion of C60. To a solution Of C60
(100 mg, 0.14 mmol) in o-dichlorobenzene (7 mL), 1,4-diaz-
ooxide (0.19 mmol) was added, and the reaction mixture was
Sp ir o[10-a n th r on e-9,61′-m eth a n ofu ller en e]. To a solu-
tion of C60 (400 mg, 0.55 mmol) in dry o-dichlorobenzene (35
mL) was added 10-diazoanthrone (135 mg, 0.61 mmol), and
the reaction mixture was stirred at 60-70 °C overnight.

Quinone-Type Methanofullerene Acceptors
J . Org. Chem., Vol. 61, No. 4, 1996 1309
irradiated with a sun lamp at 0-10 °C under N2 for 1 h. Flash
chromatography of the reaction mixture gave pure adducts.
Sp ir o[2,5-cycloh exa d ien on e-4,61′-m eth a n ofu ller en e]:
very insoluble solid, 16% yield (47% based on consumed C60);
143.35, 144.08, 144.74, 144.90, 145.13, 145.30, 145.57, 147.87,
151.45, 183.70. FTIR (KBr) 2952w, 1653 (CdO)s, 1635m,
1463m, 1456m, 1454m, 1427m, 1356m, 1188m, 897m, 757m,
738m, 713m, 587m, 554m, 526s cm-1; FABMS m/z 926 (M +
H)+, 721 (C60 + H). Anal. Calcd for C74H20O: C, 96.09; H,
FTIR (KBr) 1657 (CdO)s, 1499m, 1174m, 856m, 527s cm-l
;
FABMS m/z 814 (M + H)+. Anal. Calcd for C66H4O: C, 97.54;
H, 0.50. Found: C, 95.21; H, 0.78. UV-vis (cyclohexane) λmax
225, 262, 327, 440.
2.18. Found: C, 94.68; H, 1.99. UV-vis (cyclohexane); λmax
220, 260, 315, 440, 520.
:
Th er m olysis of 3,5-Dim eth yl-1-d ia zoben zen e 4-Oxid e
in Ch lor oben zen e Solu tion of C60. To a solution of C60 (100
mg, 0.14 mmol) in chlorobenzene (7 mL) was added 3,5-
dimethyl 1,4-diazooxide (0.19 mmol), and the reaction mixture
was refluxed under N2 for 24 h. Though comparison of TLC
(eluent, chlorobenzene) with an authentic sample indicated
generation of the adduct, it could not be isolated.
Sp ir o[2,6-d im et h yl-2,5-cycloh exa d ien on e-4,61′-m et h -
a n ofu ller en e]: solid, TLC Rf 0.4, chlorobenzene; isolated in
26% yield (57% based on consumed C60) by flash chromatog-
1
raphy with chlorobenzene; H NMR (CS2) δ 2.20 (s, 6H), 7.77
(s, 2H); FTIR (KBR) 2920w, 1658m, 1636 (CdO)s, 1427m,
1033m, 738m, 714m, 555m, 527s cm-1. FABMS m/z 842 (M
+ H)+. Anal. Calcd for C68H8O: C, 97.14; H, 0.96. Found:
C, 95.83; H, 1.06. UV-vis (cyclohexane) λmax: 222, 260, 330,
440, 500.
Ack n ow led gm en t. We are grateful to the Nation-
al Science Foundation for support through Grant
DMR 95-00888. N.M. is indebted to Universidad Com-
plutense for a research fellowship (Beca del Amo).
Spir o[2,6-di-ter t-bu tyl-2,5-cycloh exadien on e-4,61′-m eth -
a n ofu ller en e]: flash chromatographed with a 1/1 solution of
chlorobenzene and hexane; TLC Rf 0.6, 1/1 hexane/chloroben-
zene; 19% yield (43% based on consumed C60); 1H NMR (CS2)
δ 1.42 (s, 18H), 7.72 (s, 2H). 13C NMR (CS2) δ 29.56, 40.20,
77.21, 85.81, 131.74, 138.03, 141.38, 141.42, 142.27, 143.13,
J O951738F