On the radical Brook and related reactions: an ab initio study of some (1,2)-silyl, germyl and stannyl translocations

Abstract

Ab initio molecular orbital calculations using a (valence) double-ζ pseudopotential basis set (DZP) with (MP2, QCISD) and without (SCF) the inclusion of electron correlation predict that the transition states (12–14) involved in homolytic (1,2)-translocation reactions of silyl (SiH₃), germyl (GeH₃) and stannyl (SnH₃) groups between carbon centres, between carbon and nitrogen, and between carbon and oxygen proceed via homolytic substitution mechanisms involving front-side attack at the group (IV) heteroatom. While migrations between carbons are predicted to be unlikely, with calculated activation barriers of 71–137 kJ mol^–1, depending on the level of theory, migrations from carbon to nitrogen and from carbon to oxygen are predicted to be facile. For example, rearrangement of the (silylmethyl)aminyl radical (H₃SiCH₂NH˙) to the silylaminomethyl species (H₃SiNHCH₂˙) is predicted to proceed with a barrier of 50.8–63.2 kJ mol^–1 when electron correlation is included, in excellent agreement with experimental data. In addition, the analogous translocation to oxygen in the silylmethoxyl radical (H₃SiCH₂O˙), the prototypical radical Brook rearrangement, is calculated to require only 19.9 kJ mol^–1 at the MP2/DZP + ZPVE level. Somewhat unexpectedly, MP2/DZP calculations predict that the stannylmethoxyl radical (H₃SnCH₂O˙) rearranges to the stannyloxymethyl radical (H₃SnOCH₂˙) without barrier.

References

1. C. H. Schiesser and L. M. Wild, Tetrahedron, 1996, 52, 13 265 and references cited therein.
2. J. C. Dalton and R. A. Bourque, J. Am. Chem. Soc., 1981, 103, 699; Y.-M. Tsai and C.-D. Cherng, Tetrahedron Lett., 1991, 32, 3515.
3. S. Kim and J. S. Koh, J. Chem. Soc., Chem. Commun., 1992, 1377; S. Kim, S. Lee and J. S. Koh, J. Am. Chem. Soc., 1991, 113, 5106; S. Kim and K. M. Lim, J. Chem. Soc., Chem. Commun., 1993, 1152; S. Kim and K. M. Lim, Tetrahedron Lett., 1993, 34, 4851; S. Kim, J. Y. Do and K. M. Lim, J. Chem. Soc., Perkin Trans. 1, 1994, 2517.
4. S. Kim, J. Y. Do and K. M. Lim, Chem. Lett., 1996, 669.
5. A. G. Davies and M.-W. Tse, J. Organomet. Chem., 1978, 155, 25; P. J. Barker, A. G. Davies, J. A.-A. Hawari and M.-W. Tse, J. Chem. Soc., Perkin Trans. 2, 1980, 1488.
6. A. Alberti and A. Hudson, Chem. Phys. Lett., 1977, 48, 331; A. I. Prokof'ev, T. I. Prokof'eva, I. S. Belostotskaya, N. N. Bubnov, S. P. Solodovnikov, V. V. Ershov and M. I. Kabachnik, Tetrahedron, 1979, 35, 2471; Y. J. Lee, C. P. Lee, Y. T. Jeon, P. S. Mariano, U. C. Yoon, D. U. Kim, J. C. Kim and J. G. Lee, Tetrahedron Lett., 1993, 34, 5855.
7. C. G. Pitt and M. S. Fowler, J. Am. Chem. Soc., 1968, 90, 1928.
8. R. West and P. Boudjouk, J. Am. Chem. Soc., 1973, 95, 3983; J. M. Harris, I. MacInnes, J. C. Walton and B. Maillard, J. Organomet. Chem., 1991, 403, C25.
9. J. M. Harris, J. C. Walton, B. Maillard, S. Grelier and J.-P. Picard, J. Chem. Soc., Perkin Trans. 2, 1993, 2119.
10. B. P. Roberts and A. R. Vazquez-Persaud, J. Chem. Soc., Perkin Trans. 2, 1995, 1087.
11. M. C. Fong and C. H. Schiesser, Aust. J. Chem., 1992, 45, 475.
12. B. P. Roberts, J. Chem. Soc., Perkin Trans. 2, 1996, 2719.
13. C. H. Schiesser, M. L. Styles and L. M. Wild, J. Chem. Soc., Perkin Trans. 2, 1996, 2257.
14. C. H. Schiesser and M. L. Styles, unpublished.
15. M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. J. P. Stewart, M. Head-Gordon, C. Gonzalez and J. A. Pople, Gaussian 94, Revision B.3, Gaussian Inc., Pittsburgh, PA, 1995.
16. W. J. Hehre, L. Radom, P. v. R. Schleyer and P. A. Pople, Ab Initio Molecular Orbital Theory, Wiley, New York, 1986.
17. W. R. Wadt and P. J. Hay, J. Chem. Phys., 1985, 82, 284; P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 270; P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 299.
18. A. Höllwarth, M. Böhme, S. Dapprich, A. W. Ehlers, A. Gobbi, V. Jonas, K. F. Köhler, R. Stegmann, A. Veldkamp and G. Frenking, Chem. Phys. Lett., 1993, 208, 237.
19. T. H. Dunning and P. J. Hay, Modern Theoretical Chemistry, Plenum, New York, 1976, ch. 1, pp. 1–28.
20. C. H. Schiesser and B. A. Smart, Tetrahedron, 1995, 51, 6051; C. H. Schiesser, B. A. Smart and T.-A. Tran, Tetrahedron, 1995, 51, 3327; C. H. Schiesser, B. A. Smart and T.-A. Tran, Tetrahedron, 1995, 51, 10 651; C. H. Schiesser and B. A. Smart, J. Comput. Chem., 1995, 16, 1055.
21. J. T. Russell, H. S. Rzepa and D. A. Widdowson, J. Chem. Soc., Chem. Commun., 1983, 625.
22. M. J. S. Dewar, E. G. Zoebisch, E. F. Healy and J. J. P. Stewart, J. Am. Chem. Soc., 1985, 107, 3902; M. J. S. Dewar, C. Jie and J. Yu, Tetrahedron, 1993, 49, 5003.