Prospecting for a 5-center 4-electron (C-H-C-H-C)+ bonding array

Journal of the American Chemical Society

Volumn 125, Issue 14, 2003, Pages 4042-4043

  Tantillo, Dean J ^a   Hoffmann, Roald ^a  

^a Cornell University ^*  (United States)

Author keywords

[No Author keywords available]

Indexed keywords

HYDROCARBON;

ARTICLE; CALCULATION; CARBON NUCLEAR MAGNETIC RESONANCE; CHEMICAL BOND; CHEMICAL STRUCTURE; ELECTRON; PROTON NUCLEAR MAGNETIC RESONANCE; STRUCTURE ANALYSIS; THERMODYNAMICS;

EID: 0037427305     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja021394s     Document Type: Article

References (27)

1. For leading references on the pioneering work of Sorensen and McMurry on acyclic 3-center 2-electron carbocations, see: McMurry, J. E.; Lectka, T. Acc. Chem. Res. 1992, 25, 47-53. For general reviews that also describe cyclic 3-center 2-electron cations, see: Saunders: M.; Jimenez-Vazquez, H. A. Chem. Rev. 1991, 91, 375-397; Grob, C. A. Acc. Chem. Res. 1983, 16, 426-431; Brown, H. C. Acc. Chem. Res. 1983, 16, 432-440.
2. For leading references on the pioneering work of Sorensen and McMurry on acyclic 3-center 2-electron carbocations, see: McMurry, J. E.; Lectka, T. Acc. Chem. Res. 1992, 25, 47-53. For general reviews that also describe cyclic 3-center 2-electron cations, see: Saunders: M.; Jimenez-Vazquez, H. A. Chem. Rev. 1991, 91, 375-397; Grob, C. A. Acc. Chem. Res. 1983, 16, 426-431; Brown, H. C. Acc. Chem. Res. 1983, 16, 432-440.
3. For leading references on the pioneering work of Sorensen and McMurry on acyclic 3-center 2-electron carbocations, see: McMurry, J. E.; Lectka, T. Acc. Chem. Res. 1992, 25, 47-53. For general reviews that also describe cyclic 3-center 2-electron cations, see: Saunders: M.; Jimenez-Vazquez, H. A. Chem. Rev. 1991, 91, 375-397; Grob, C. A. Acc. Chem. Res. 1983, 16, 426-431; Brown, H. C. Acc. Chem. Res. 1983, 16, 432-440.
4. For leading references on the pioneering work of Sorensen and McMurry on acyclic 3-center 2-electron carbocations, see: McMurry, J. E.; Lectka, T. Acc. Chem. Res. 1992, 25, 47-53. For general reviews that also describe cyclic 3-center 2-electron cations, see: Saunders: M.; Jimenez-Vazquez, H. A. Chem. Rev. 1991, 91, 375-397; Grob, C. A. Acc. Chem. Res. 1983, 16, 426-431; Brown, H. C. Acc. Chem. Res. 1983, 16, 432-440.
5. (a) All calculations were performed with GAUSSIAN 98, revision A.9: Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, revision A.9; Gaussian, Inc.: Pittsburgh, PA, 1998.
6. (b) Geometries were optimized without symmetry constraints at the B3LYP/6-31G(d) level (Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652, Becke, A. D. J. Chem. Phys. 1993, 98, 1372-1377, Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1998, 37, 785-789, P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J. Phys. Chem. 1994. 98, 11623-11627). Several recent reports have discussed the use of B3LYP for computing geometries and energetics of 3-center 2-electron cations (Vrcek, I. V.; Vrcek, V.; Siehl, H.-U. J. Phys. Chem. A 2002, 106, 1604-1611 and Farcasiu, D.; Lukinskas, P.; Pamidighantam, S. V. J. Phys. Chem. A 2002, 106, 11672-11675.). These papers suggest that B3LYP tends to underestimate the stability of delocalized structures relative to MP2. but that B3LYP gives comparable results to CCSD.
7. (b) Geometries were optimized without symmetry constraints at the B3LYP/6-31G(d) level (Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652, Becke, A. D. J. Chem. Phys. 1993, 98, 1372-1377, Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1998, 37, 785-789, P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J. Phys. Chem. 1994. 98, 11623-11627). Several recent reports have discussed the use of B3LYP for computing geometries and energetics of 3-center 2-electron cations (Vrcek, I. V.; Vrcek, V.; Siehl, H.-U. J. Phys. Chem. A 2002, 106, 1604-1611 and Farcasiu, D.; Lukinskas, P.; Pamidighantam, S. V. J. Phys. Chem. A 2002, 106, 11672-11675.). These papers suggest that B3LYP tends to underestimate the stability of delocalized structures relative to MP2. but that B3LYP gives comparable results to CCSD.
8. (b) Geometries were optimized without symmetry constraints at the B3LYP/6-31G(d) level (Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652, Becke, A. D. J. Chem. Phys. 1993, 98, 1372-1377, Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1998, 37, 785-789, P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J. Phys. Chem. 1994. 98, 11623-11627). Several recent reports have discussed the use of B3LYP for computing geometries and energetics of 3-center 2-electron cations (Vrcek, I. V.; Vrcek, V.; Siehl, H.-U. J. Phys. Chem. A 2002, 106, 1604-1611 and Farcasiu, D.; Lukinskas, P.; Pamidighantam, S. V. J. Phys. Chem. A 2002, 106, 11672-11675.). These papers suggest that B3LYP tends to underestimate the stability of delocalized structures relative to MP2. but that B3LYP gives comparable results to CCSD.
9. (b) Geometries were optimized without symmetry constraints at the B3LYP/6-31G(d) level (Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652, Becke, A. D. J. Chem. Phys. 1993, 98, 1372-1377, Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1998, 37, 785-789, P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J. Phys. Chem. 1994. 98, 11623-11627). Several recent reports have discussed the use of B3LYP for computing geometries and energetics of 3-center 2-electron cations (Vrcek, I. V.; Vrcek, V.; Siehl, H.-U. J. Phys. Chem. A 2002, 106, 1604-1611 and Farcasiu, D.; Lukinskas, P.; Pamidighantam, S. V. J. Phys. Chem. A 2002, 106, 11672-11675.). These papers suggest that B3LYP tends to underestimate the stability of delocalized structures relative to MP2. but that B3LYP gives comparable results to CCSD.
10. (b) Geometries were optimized without symmetry constraints at the B3LYP/6-31G(d) level (Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652, Becke, A. D. J. Chem. Phys. 1993, 98, 1372-1377, Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1998, 37, 785-789, P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J. Phys. Chem. 1994. 98, 11623-11627). Several recent reports have discussed the use of B3LYP for computing geometries and energetics of 3-center 2-electron cations (Vrcek, I. V.; Vrcek, V.; Siehl, H.-U. J. Phys. Chem. A 2002, 106, 1604-1611 and Farcasiu, D.; Lukinskas, P.; Pamidighantam, S. V. J. Phys. Chem. A 2002, 106, 11672-11675.). These papers suggest that B3LYP tends to underestimate the stability of delocalized structures relative to MP2. but that B3LYP gives comparable results to CCSD.
11. (b) Geometries were optimized without symmetry constraints at the B3LYP/6-31G(d) level (Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652, Becke, A. D. J. Chem. Phys. 1993, 98, 1372-1377, Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1998, 37, 785-789, P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J. Phys. Chem. 1994. 98, 11623-11627). Several recent reports have discussed the use of B3LYP for computing geometries and energetics of 3-center 2-electron cations (Vrcek, I. V.; Vrcek, V.; Siehl, H.-U. J. Phys. Chem. A 2002, 106, 1604-1611 and Farcasiu, D.; Lukinskas, P.; Pamidighantam, S. V. J. Phys. Chem. A 2002, 106, 11672-11675.). These papers suggest that B3LYP tends to underestimate the stability of delocalized structures relative to MP2. but that B3LYP gives comparable results to CCSD.
12. (c) Structure 8 was characterized as a minimum by frequency calculations at the B3LYP/3-21G level (we are aware of the issues associated with using B3LYP/3-21G calculations to characterize the nature of this stationary point, but all attempts to perform frequency calculations on 8 with the larger 6-31G(d) basis set proved computationally unfeasible: we believe, on the basis of our experience with related systems, that B3LYP/6-31G(d) frequency calculations would also show 8 to be a true minimum).
13. Tantillo, D. J.; Hoffmann, R. J. Am. Chem. Soc., 2002, 124, 6836-6837.
14. (a) Related architectures have been proposed as supports for σ-allyl cations, but the C - C distances in such systems appear to be too large to allow for direct carbon-carbon interaction. See, for example: Olson, L. P. Org. Lett. 2000, 2, 3059-3062 and Lipkowitz, K. B.; Larter, R. M.; Boyd, D. B. J. Am. Chem. Soc. 1980, 102, 85-92.
15. (a) Related architectures have been proposed as supports for σ-allyl cations, but the C - C distances in such systems appear to be too large to allow for direct carbon-carbon interaction. See, for example: Olson, L. P. Org. Lett. 2000, 2, 3059-3062 and Lipkowitz, K. B.; Larter, R. M.; Boyd, D. B. J. Am. Chem. Soc. 1980, 102, 85-92.
16. (b) For a discussion of hypothetical polyradicals built from similar triple acene architectures, see: Hoffmann, R.; Eisenstein, O.; Balaban, A. T. Proc. Natl. Acad. Sci. U.S.A. 1980, 77, 5588-5592.
17. 24 and its relatives. See Merschrod, E. F.; Hoffmann, R. Chem. Mater. 1999, 11, 341-351 and references therein. We might ponder further extension of 8 towards an infinite one-dimensional polycation.
18. (a) A related 3-center 4-electron O-C-O cation, supported by a monoanthracene framework, also boasts a central trigonal bipyramidal carbon, in this case substituted by four oxygen atoms. See: Akiba, K.; Yamashita, M.; Yamamoto, Y.; Nagase, S. J. Am. Chem. Soc. 1999, 121, 10644-10645.
19. (b) Trigonal bipyramidal carbons have also been found in some cases where a carbon atom is surrounded by five metals (such as Li or Au). See, for example: Jemmis, E. D.; Chandrasekhar, J.; Würthwein, E.; Schleyer, P. v. R. J. Am. Chem. Soc. 1982, 104, 4275-4276 and Scherbaum, F.; Grohmann, A.; Muller, G.; Schmidbaur, H. Angew. Chem., Int. Ed. Engl. 1989, 28, 463-465.
20. (b) Trigonal bipyramidal carbons have also been found in some cases where a carbon atom is surrounded by five metals (such as Li or Au). See, for example: Jemmis, E. D.; Chandrasekhar, J.; Würthwein, E.; Schleyer, P. v. R. J. Am. Chem. Soc. 1982, 104, 4275-4276 and Scherbaum, F.; Grohmann, A.; Muller, G.; Schmidbaur, H. Angew. Chem., Int. Ed. Engl. 1989, 28, 463-465.
21. 2 units) has subsequently been shown to also boast a 5-center 4-electron array. P. v. R. Schleyer, personal communication, a "holiday gift" to us, 12/13/02.
22. 2 For a classic example of the use of computed chemical shifts in characterizing carbocation structures, see: Schleyer, P. v. R.; Laidig, K.; Wiberg, K. B.; Saunders: M.; Schindler, M. J. Am. Chem. Soc. 1988, 110, 300-301.
23. 13C chemical shifts as probes of electron density in carbocations, see: Forsyth, D. A.; Spear, R. J.; Olah, G. A. J. Am. Chem. Soc. 1976, 98, 2512-2518.
24. (c) In some cases, using absolute chemical shifts as a measure of local electron density can be a somewhat risky endeavor (See, for example: Bethell, D. In Reactive Intermediates; Jones, M., Jr., Moss, R. A., Eds.; Wiley: New York, 1978; Chapter 4, Vol. 1). but we believe that the risk is minimal in our case due to the fact that we are primarily interested in relative shifts for closely related structures.
25. For comparison, we compute a chemical shift of +191 ppm for the central carbon of fully relaxed trityl cation (the experimental value is +211 ppm; see: Ray, G. J.; Kurland, R. J.; Colter, A. K. Tetrahedron 1971, 27, 735-752, Abarca, B.; Asensio, G.; Ballesteros, R.; Varea, T. J. Org. Chem. 1991, 56, 3224-3229 and references therein) and a shift of +370 ppm for the carbon in naked methyl cation (all relative to TMS).
26. For comparison, we compute a chemical shift of +191 ppm for the central carbon of fully relaxed trityl cation (the experimental value is +211 ppm; see: Ray, G. J.; Kurland, R. J.; Colter, A. K. Tetrahedron 1971, 27, 735-752, Abarca, B.; Asensio, G.; Ballesteros, R.; Varea, T. J. Org. Chem. 1991, 56, 3224-3229 and references therein) and a shift of +370 ppm for the carbon in naked methyl cation (all relative to TMS).
27. Extended Hückel calculations were performed with Greg Landrum's Yet Another Extended Hückel Molecular Orbital Package (YAeHMOP), available through http://sourceforge.net/projects/yaehmop/.