Stepwise synthesis of fullerene cyclopentadienide R5C60- and indenide R3C60-. An approach to fully unsymmetrically substituted derivatives

Article abstract of DOI:10.1021/ol005993k

(Equation presented) Fullerene cyclopentadienide (PhCH₂)₂Ph₃C₆₀^- and indenide (PhCH₂)₂PhC₆₀^-, each bearing two different organic groups, were efficiently sy

Full text of DOI:10.1021/ol005993k

ORGANIC
LETTERS
2
000
Vol. 2, No. 13
919-1921
Stepwise Synthesis of Fullerene
-
1
Cyclopentadienide R C and Indenide
5
60
-
R C . An Approach to Fully
3
60
Unsymmetrically Substituted Derivatives
,†
Masaya Sawamura,* Motoki Toganoh, Kazuhiro Suzuki, Atsushi Hirai,
Hitoshi Iikura, and Eiichi Nakamura*
Department of Chemistry, The UniVersity of Tokyo, Hongo, Bunkyo-ku,
Tokyo 113-0033, Japan
nakamura@chem.s.u-tokyo.ac.jp
Received April 27, 2000
ABSTRACT
Fullerene cyclopentadienide (PhCH
2
)
2
Ph
3
C
60- and indenide (PhCH
2
)
2
PhC60-, each bearing two different organic groups, were efficiently synthesized
) or a Grignard reagent (PhMgBr) followed
through regioselective reactions of 1,4-(PhCH
2
)
2
C60 with an organocopper reagent (PhMgBr/CuBr‚SMe
2
t
by deprotonation with KO Bu.
We reported earlier the synthesis of cyclopentadienes
We are currently postulating that the 5-fold organocopper
-
(R
5
HC60; R ) Ar, Me) and cyclopentadienides (R
5
C
60
)
addition to C60 proceeds through a sequential addition/
-
embedded in C60 through quantitative 5-fold organocopper
2
oxidation process involving nucleophilic attacks of R Cu
1
addition to C60. The pentakis addition is so effective that a
species and one-electron oxidation by a Cu(I) salt. Formation
-
2
variety of R
5
C
60 compounds have been prepared, in many
of a 1,4-diorgano-1,4-dihydro[60]fullerene (1,4-R
2
C60) and
cases, in a quantitative yield; nonetheless, the method is
totally unsuitable for the synthesis of compounds bearing
different R groups or for the synthesis of C60 derivatives
bearing fewer than five substituents. Here we report strategies
for the installation of two different R groups totaling three
and five in number as demonstrated through synthesis of new
1,4,11,30-tetraorgano-1,4,11,30-tetrahydro-[60]fullerene
3
(1,4,11,30-R
tulated. Along such a line of reasoning, we considered that
the reaction of 1,4-R 60 with an organocopper reagent
4
C60) as transient intermediates are being pos-
2
C
(2) (a) Nagashima, H.; Terasaki, H.; Kimura, E.; Nakajima, K.; Itoh, K.
J. Org. Chem. 1994, 59, 1246-1248. (b) Subramanian, R.; Kadish, M. K.;
Vijayashree, N. M.; Gao, X.; Jones, T. M.; Miller, D. M.; Krause, K. L.;
Suenobu, T.; Fukuzumi, S. J. Phys. Chem. 1996, 100, 16327-16335. (c)
Miki, S.; Kitao, M.; Fukunishi, K. Tetrahedron Lett. 1996, 37, 2049-2052.
(d) Kitagawa, T.; Tanaka, T.; Tanaka, Y.; Takeuchi, K.; Komatsu, K. J.
Org. Chem. 1995, 60, 1490-1491. (e) Wang, G.-W.; Murata, Y.; Komatsu,
K.; Wan, T. S. M. J. Chem. Soc., Chem. Commun. 1996, 2059-2060. (f)
Fukuzumi, S.; Suenobu, T.; Hirasaka, T.; Arakawa, R.; Kadish, K. M. J.
Am. Chem. Soc. 1998, 120, 9220-9227.
+
-
cyclopentadienide and indenides, K [(PhCH
2
)
2
Ph
3
C60] (3)
+
-
and K [(PhCH
2
2
) PhC60] (5).
†
E-mail: sawamura@chem.s.u-tokyo.ac.jp.
1) (a) Sawamura, M.; Iikura, H.; Nakamura, E. J. Am. Chem. Soc. 1996,
(
1
18, 12850-12851. (b) Sawamura, M.; Iikura, H.; Ohama, T.; Hackler, U.
E.; Nakamura, E. J. Organomet. Chem. 2000, 599, 32-36. (c) Sawamura,
M.; Toganoh, M.; Kuninobu, Y.; Kato, S.; Nakamura, E. Chem. Lett. 2000,
2
62-263. (d) Sawamura, M.; Iikura, H.; Hirai, A.; Nakamura, E. J. Am.
(3) Murata, Y.; Shiro, M.; Komatsu, K.. J. Am. Chem. Soc. 1997, 119,
8117-8118.
Chem. Soc. 1998, 120, 8285-8286.
1
0.1021/ol005993k CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/27/2000

-
R′
2
Cu would afford the mixed organohydrofullerene R
2
R′
3
-
purification (Bucky Prep), gave (PhCH
72% yield as a mixture of two isomers (100% conversion
of C60). The structure of (PhCH PhHC60 was assigned in
the manner similar to the one employed for 2; namely,
2 2
) PhHC60 (4a,b) in
60 (1)2
b,c,f
as a starting
HC60. We have chosen (PhCH
2
)
2
C
material of the present studies because of its availability and
the high solubility in organic solvent. To our satisfaction,
the reaction of 1 (1,2-dichlorobenzene/THF, 25 °C, 2 h) with
an excess amount of an organocopper reagent prepared from
2 2
)
t
deprotonation with KO Bu formed a single C
1
symmetric
+
-
potassium salt K [(PhCH ) PhC60] (5) (Scheme 2).
2 2
PhMgBr (15 equiv) and CuBr‚SMe
2
(15 equiv) (after
Ph H (2a-
quenching with aqueous NH Cl) gave (PhCH
4
2
)
2
3
c) quantitatively as a mixture of three isomers (Scheme 1).
Scheme 2
Scheme 1
Optimized structure of a C
s
symmetric model compound
(*)
C H K (6) (HF/3-21G , total energy ) -2857.00417344
60 3
5
hartree, Figure 1a) shares some important features with that
Purification by HPLC (Bucky Prep, Nacalai Tesque Co.)
afforded an analytically pure material in 86% yield. Treat-
ment of the solution of the isomeric mixture of 2 in THF
t
with an excess KO Bu (1.2 equiv) at 20 °C caused immediate
1
color change from dark red to very dark brown. The H and
1
3
C NMR (THF-d
convergedintoasinglecyclopentadienideK [(PhCH
3) with C symmetry. This result indicates that the isomerism
8
) showed that the isomeric mixture
+
-
2 2 3 60
) Ph C ]
(
s
Figure 1. (a) Part of the optimized structure of 6 at the HF/3-
in 2 arises from the positional isomers of the cyclopentadiene
moiety as shown for 2a-c and, therefore, that the three
phenyl groups were regioselectively installed in such a
manner that one of the C60 pentagons became isolated from
the remainder of the C60 core to form a cyclopentadiene.
2
1G(*) level. C-C bond lengths (Å) are affixed to the respective
bonds. K-C bond lengths (Å): K-C(1), 3.08; K-C(2), 2.98;
K-C(3), 2.93. (b) HOMO surface of 6.
1d
3
of its C70 analogue, C70H Li reported previously. Thus, the
It is known that a Grignard reagent reacts with C60 in a
4
fully delocalized 10-π indenyl framework is separated from
the remaining 48-π electron system by the seven surrounding
1
,2-monoaddition manner. We have conjectured that the
2
reaction of 1,4-R C60 with a Grignard reagent will take place
6
C-C bonds of rather long bond lengths (1.47-1.52 Å). The
only once to give a triorganomonohydrofullerene. In light
of our previous knowledge on a regioselectivity in the 3-fold
addition reaction of C70, we considered that the reaction
would give 5. According to this scenario, we have carried
pentagon of the indenyl moiety coordinates to the metal
5
center in an η -fashion. The HOMO surface of 6 depicted
in Figure 1b represents a typical indenyl HOMO and shows
3
remarkable resemblance to that of C70H Li. Such an effective
out the reaction of 1,4-(PhCH
reaction of 1 proceeded smoothly in 1,2-dichlorobenzene at
2 °C in the presence of 3.6 equiv of PhMgBr (1 M in THF)
and, after hydrolysis with aqueous NH Cl and HPLC
2 2
) C60 (1) with PhMgBr. The
π electron delocalization within the indenyl framework of 6
2
(
5) Hehre, W.; Radom, L.; Schleyer, P. v. R.; Pople, J. A. Ab Initio
4
Molecular Orbital Theory; Wiley: New York, 1986.
(
6) The most obvious difference is found in the shorter C(3)-C(4) bond
(4) (a) Fagan, P. J.; Krusic, P. J.; Evans, D. H.; Lerke, S. A.; Johnston,
length (1.39 Å) of 6.
E. J. Am. Chem. Soc. 1992, 114, 9697-9699. (b) Hirsch, A.; Gr o¨ sser, T.;
Skiebe, A.; Soi, A. Chem. Ber. 1993, 126, 1061-1067.
(7) Note that the indenyl plane of C70H3Li is rather flat due to the
decreased degree of curvature in the equatorial belt region of C70 cage.
1920
Org. Lett., Vol. 2, No. 13, 2000

is surprising if one consider the highly bent structure of the
indenyl plane.
on application of the densely functionalized, geometrically
well-defined compounds in various fields.
7
In conclusion, we have shown that the cyclopentadiene
1
2
1
R HC60) and cyclopentadienide (R1
2
2
-
(
R
R
2
R
3
HC60, R
2
2
R
C
3 60
,
Acknowledgment. This work was supported by Mon-
busho, Grant-in-Aid for Scientific Research on Priority Area
No. 283, Innovative Synthetic Reactions).
1
2
-
2
R C60 ) bearing two different organic substituents can
efficiently be synthesized by stepwise methods by way of
,4-diorganofullerene. Since unsymmetrical 1,4-diorgano-
(
2
1
fullerene RR′C60 of various combination of R and R′ can be
Supporting Information Available: Experimental pro-
-
2d-f
prepared through trapping of RC60 with an electrophile,
we can fully expect that one can now synthesize a wide
variety of analogues of R HC60 and R HC60 bearing various
cedures and characterization for compounds 2-5. This
material is available free of charge via the Internet at
http://pubs.acs.org.
5
3
different organic substituents. The structure diversity thus
created on a spherical platform will open new opportunities
OL005993K
Org. Lett., Vol. 2, No. 13, 2000
1921