9994
J. Am. Chem. Soc. 1999, 121, 9994-9998
Search for Long-Lived 1,3-Carbodications and Preparation of the
Persistent 1,1,3,3-Tetracyclopropyl-1,3-propanediyl Dication1
George A. Olah,* V. Prakash Reddy,* Golam Rasul, and G. K. Surya Prakash*
Contribution from the Donald P. and Katherine B. Loker Hydrocarbon Research Institute and Department
of Chemistry, UniVersity of Southern California, Los Angeles, CA, 90089-1661
ReceiVed July 6, 1999
Abstract: Several substituted versions of 1,3-propanediol were ionized under a variety of superacidic conditions,
and the product carbocations and carboxonium species were characterized by 1 C NMR spectroscopy at low
temperatures. 1,1,3-Triphenyl-1,3-propanediol (19), and 1,1,3,3-tetraphenyl-1,3-propanediol (20), upon ionization
in FSO3H/SO2ClF or SbF5-FSO3H/SO2ClF solution at -78 °C gave the disproportionated cationic species,
3
1
,1-diphenylethyl cation (24) and protonated benzaldehyde (25) or protonated benzophenone (26). At lower
temperatures (-130 °C) they yielded the allyl cations, 29 and 30, as the only products. Diol 23 was also
ionized at -78 °C to give a 1:1 mixture of tricyclopropylmethyl cation (27) and O-protonated dicyclopropyl
ketone (28). The ionization of 1,1,3,3-tetracyclopropyl-1,3-propanediol (21) in SbF5/SO2ClF, on the other hand,
gave the stable 1,3-carbodication, that is, 1,1,3,3-tetracyclopropyl-1,3-propanediyl dication (33). The structures
1
3
and the C NMR chemical shifts for the carbodication 33 and the allyl cations 29 and 30 were also computed
using DFT/IGLO methods.
Introduction
2,3-dimethyl-2-butyl cation (5), and the O-protonated acetone
6). Higher level theoretical studies [up to Gaussian-2 (G2)
(
Carbodications, the readily observable species in the gas
theory], however, predict that even the parent 1,3-propanediyl
dication (i.e., protonated allyl cation) is a minimum, with
significant hyperconjugative interactions.
2
phase, have received renewed interest both experimentally and
3
3c
theoretically. Olah and co-workers have prepared many car-
bodications in which the charged centers are separated from
each other by at least two carbons, and their structural
13
information was probed through C NMR spectroscopic stud-
4
ies. Interestingly, the carbodications show enhanced charge-
dispersal as compared to their related carbomonocations, as
13
reflected by their relatively shielded C NMR absorptions for
the cationic centers. However, attempted preparations of the 1,3-
carbodications, in which the charge centers are separated by
only one methylene group, were mostly unsuccessful. The
ionization of 2,4-dichloro-2,4-dimethylpentane (1) and 2,3,3,4-
tetramethyl-2,4-pentanediol (3) did not yield the expected 1,3-
5
carbodications. The former reaction gave 3-penten-2-yl cation,
More recently, in a study to probe Y-aromaticity, formally
,3-carbodications involving Y-conjugationsthe hexaphenyl-
whereas the latter gave only the products of disproportionation,
1
trimethylene)-methane dication (7) and its substituted versionss
(
1) Stable Carbocations, Part 310, For Part 309, see: Prakash, G. K. S.;
Weber, K.; Olah, G. A.; Prinzbach, H.; Wollenweber, M.; Etzkorn, M.;
were obtained by the ionization of their corresponding diols in
Voss, T.; Herges, R. Chem. Commun. 1999, 1029-1030.
13
FSO3H/SbF5. The C NMR spectra of these dications displayed
(
2) (a) Prakash, G. K. S. Pure Appl. Chem. 1998, 70, 2001-2006. (b)
13
δ C(C+) values around 208, quite similar to that of trityl cation,
implicating the absence of the Y-aromaticity due to the 2π-
electronY-conjugatedsysteminthesecarbodications. Theabsence
Laali, K. K. Chem. ReV. 1996, 96, 1873-1906 and references therein. (c)
Prakash, G. K. S.; Rawdah, T. N.; Olah, G. A. Angew Chem., Int. Ed. Engl.
1
983, 22, 390-401. (d) Pagni, R. M.; Peebles, W.; Haddon, R. C.;
Chichester, S. V. J. Org. Chem. 1990, 55, 5595-5601. Olah, G. A. Angew.
Chem., Int. Ed. Engl. 1993, 32, 767-788. (e) Heagy, M. D.; Wang, Q.;
Olah, G. A.; Prakash, G. K. S. J. Org. Chem. 1995, 60, 7351-7354. (f)
Mills, N. S.; Malinky, T.; Malandra, J. L.; Burns, E. E.; Crossno, P. J.
Org. Chem. 1999, 64, 511-517.
(5) (a) Prakash, G. K. S. Pure Appl. Chem. 1998, 70, 2001-2006. (b)
Laali, K. K. Chem. ReV. 1996, 96, 1873-1906 and references therein. (c)
Prakash, G. K. S.; Rawdah, T. N.; Olah, G. A. Angew Chem., Int. Ed. Engl.
1983, 22, 390-401. (d) Pagni, R. M.; Peebles, W.; Haddon, R. C.
Chichester, S. V. J. Org. Chem. 1990, 55, 5595-5601. Olah, G. A. Angew.
Chem., Int. Ed. Engl. 1993, 32, 767-788. (e) Heagy, M. D.; Wang, Q.;
Olah, G. A.; Prakash, G. K. S. J. Org. Chem. 1995, 60, 7351-7354. (f)
Mills, N. S.; Malinky, T.; Malandra, J. L.; Burns, E. E.; Crossno, P. J.
Org. Chem. 1999, 64, 511-517.
(3) (a) Lammertsma, K.; Schleyer, P. v. R.; Schwarz, H. Angew, Chem.,
Int. Ed. Engl. 1989, 28, 1321-1341. (b) Lammertsma, K.; Guner, O. F.;
Thibvodeaux, A. F.; Schleyer, P. v. R. J. Am. Chem. Soc. 1989, 111, 8995-
9
002. (c) Mayer, P. M.; Radom, L. Chem. Phys. Lett. 1997, 244-250.
(4) Olah, G. A.; Grant, J. C.; Spear, R.; Bollinger, J. M.; Serianz, A.;
Sipos, G. J. J. Am. Chem. Soc. 1976, 98, 2501-2507.
1
0.1021/ja992321k CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/14/1999