4544
J. Am. Chem. Soc. 1998, 120, 4544-4545
[16.16.16](1,3,5)Cyclophanetetracosayne (C60H6): A
Precursor to C60 Fullerene
Yoshito Tobe,*,† Nobuko Nakagawa,† Koichiro Naemura,†
Tomonari Wakabayashi,‡ Tadamasa Shida,‡ and Yohji Achiba§
Department of Chemistry
Faculty of Engineering Science
Osaka UniVersity, Toyonaka, Osaka 560, Japan
DiVision of Chemistry, Graduate School of Science
Kyoto UniVersity, Kyoto 606-01, Japan
Department of Chemistry
Tokyo Metropolitan UniVersity
Hachioji, Tokyo 192-03, Japan
ReceiVed January 29, 1998
Although C60 and some higher fullerenes are now readily
available from commercial sources, it is still important to
synthesize fullerenes on the basis of organochemical transforma-
tions because it would be possible to manipulate carbon cages in
a size-selective and structure-defined manner. It would also be
possible to encapsulate transition metals into the cage leading to
the yet-discovered endohedral transition metallofullerenes,1 which
are of tremendous interest as new materials. The first attempt to
the total synthesis of isosahedral C60 was set up by Chapman’s
school2 well before its first observation,3 which was followed by
several approaches.4 However, despite the numerous efforts, the
controlled chemical synthesis of fullerenes as well as that of
endohedral metallofullerenes have not been achieved yet.
of our strategy to generate reactive polyynes by [2 + 2]
cycloreversion of [4.3.2]propellatriene derivatives,9 we disclose
here the preparation of a stable precursor 3 [C60H6(Ind)6] which
would form C60H6 by extrusion of six aromatic fragments (indane
) Ind) and the observation of C60 as well as C60H6 ions in the
laser desorption mass spectra.10
According to the semiempirical calculations on the AM1 level,
the title compound 1 has a heat of formation about 500 kcal/mol
larger than that of the known hexahydrofullerene.11 Moreover,
since diaryl-substituted hexadecaoctaynes have been shown to be
the isolation limit of the linear polyynes,13 cage polyyne 1 must
be too reactive for isolation at room temperature. It is also
interesting to note that 1 is a member of polyyne-bridged
cyclophanes, a new family of strained cyclophanes, proposed
recently.14
To prepare unsymmetrically substituted diakynylpropellatriene,
the protective group of the known monoalkynylated propellatriene
4a9b was switched to the more readily removable Si(i-Pr)3 group
to give 4b. Introduction of the second alkynyl group followed
by selective deprotection of the SiMe3 group of 5a afforded diyne
5b. Pd-catalyzed hetero coupling15 of 5b with tris(bromoethynyl)-
benzene (6)5a afforded trispropellane 7a in 67% yield. After
Recently, Rubin et al. proposed a new route to fullerene
synthesis5 inspired by a postulated mechanism of the fullerene
formation, which includes intermolecular cycloaddition of cyclic
polyynes (coalescence) followed by skeletal isomerization (an-
nealing).6 Thus, cage polyyne C60H6 (1) was proposed as a
possible precursor to C60 fullerene, because it would cascade down
to the most stable icosahedral structure of Ih symmetry7 together
with the loss of hydrogen, just like the similar cascade known as
“adamantane rearrangement.”8 As an intial step to the synthesis
of C60H6, they prepared C60H18 (2), in which two double bonds
still remained in each of the polyyne bridge. In the ion cyclotron
resonance mass spectrum (negative mode) of 2, dehydrogenation
down to C60H14 was observed,5a suggesting the possibility of
-
complete dehydrogenation of C60H6 (2) to C60. As an extension
† Osaka University.
‡ Kyoto University.
§ Tokyo Metropolitan University.
(9) (a) Tobe, Y.; Fujii, T., Matsumoto, H.; Naemura, K.; Achiba, Y.;
Wakabayashi, T. J. Am. Chem. Soc. 1996, 118, 2758-2759. (b) Tobe, Y.;
Matsumoto, H.; Naemura, K.; Achiba, Y.; Wakabayashi, T. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 1800-1802. (c) Wakabayashi, T.; Kohno, M.; Achiba,
Y.; Shiromaru, H.; Momose, T.; Shida, T.; Naemura, K.; Tobe, Y. J. Chem.
Phys. 1997, 107, 4783-4687.
(1) For reviews, see: (a) Bethune, D. S.; Johnson, R. D.; Salem, J. R.; de
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Edelmann, F. T. Angew. Chem., Int. Ed. Engl. 1995, 34, 981-985.
(2) Ph.D. dissertations at UCLA: Jacobsen, R. H. 1986; Xiong, Y. 1987;
Loguercio, D., Jr. 1988; Shen, D. 1990. Cited in Diederich, F.; Whetten, R.
L. Acc. Chem. Res. 1992, 25, 119-126.
(10) Recently, we became aware that Rubin et al. synthesized a precursor
-
-
(3) Kroto, H. W.; Heath, J. R.; O’Brien, S. C.; Curl, R. F.; Smalley, R. E.
Nature (London) 1985, 318, 162-163.
to 1 annelated by cyclobutenedione units and observed C60H6 and C60 in
the negative mode ion cyclotron resonance mass spectrum: Rubin, Y.; Parker,
T. C.; Pastor, S.; Jalisatgi, S.; Boulle, C.; Wilkins, C. L. Angew. Chem.
In press.
(4) Fabre, C.; Rassat, A. C. R. Acad. Sci. Paris 1989, 308, 1223-1228.
(b) Rabidau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242.
(5) (a) Rubin, Y.; Parker, T. C.; Khan, S. I.; Holliman, C. L.; McElvany,
S. W. J. Am. Chem. Soc. 1996, 118, 5308-5309. (b) Rubin, Y. Chem. Eur.
J. 1997, 3, 1009-1016. (c) Saalfrank, R. W. Nature (London) 1996, 383,
124-125.
(11) The AM1-calculated ∆Hf° values for 2, 1,2,33,41,42,50-hexa-
hydrofullerene,11a and 1,2,5,10,21,24-hexahydrofullerene11b are 1341.5, 847.6,
and 840.3 kcal/mol, respectively. Calculations were performed by SPARTAN
version 5.0; Wavefunction Inc. For ab initio calculations of C60H6 isomers,
see: Cahill, P. A. Chem. Phys. Lett. 1996, 254, 257-262.
(12) (a) Meier, M. S.; Weedon, B. R.; Spielmann, H. P. J. Am. Chem. Soc.
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R.; Hitchcock, P. B.; Kroto, H. W.; Taylor, R.; Walton, D. R. M. Nature
(London) 1992, 357, 479-481. Birkett, P. R.; Avent, A. G.; Darwish, A. D.;
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1993, 1230-1232.
(13) (a) Armitage, J. B.; Entwistle, N.; Jones, E. R. H.; Whiting, M. C. J.
Chem. Soc. 1954, 147-154. (b) Johnson, T. R.; Walton, D. R. M. Tetrahedron
1972, 28, 5221-5236.
(14) Haley, M. M.; Langsdorf, B. L. Chem. Commun. 1997, 1121-1122.
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(7) Recently, a theoretical examination of a cascade isomerization mech-
anism, “fullerene rearrangement,” from various C60 isomers to Ih C60 was
undertaken: Ohsawa, E.; Ueno, H,; Yoshida, M.; Nishiyama, M. J. Chem. Soc.,
Perkin Trans. 2 Submitted for publication.
(8) Schleyer, P. v. R. In Cage Hydrocarbons; Olah, G. A., Ed.; Wiley-
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S0002-7863(98)00330-8 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/28/1998