SiCl 3 + and SiCl+ affinities for pyridines determined by using the kinetic method with multiple stage mass spectrometry: Agostic effects in the gas phase

  • Sheng Sheng Yang
  • Philip Wong
  • Shuguang Ma
  • R. Graham Cooks


Cluster ions, Py1SiCl 3 + Py2 and Py1SiCl+Py2, where Py1 and Py2 represent substituted pyridines, formed upon reactive collisions of mass-selected SiCl 3 + or SiCl+ cations with a mixture of pyridines, are shown to have loosely bound structures by multiple stage mass spectrometry experiments in a pentaquadrupole mass spectrometer. The fragment ion abundance ratio, ln([Py1SiCl n + ]/[Py2SiCl n + ]) (n=1 or 3) is used to estimate the relative SiCl 3 + or SiCl+ affinities of the constituent pyridines by the kinetic method. In the case of clusters comprised of meta- and/or para-substituted pyridines (unhindered pyridines), the SiCl 3 + and SiCl+ affinities are shown to display excellent linear correlations with the proton affinities (PAs). On the assumption that the effective temperatures of the SiCl 3 + - and SiCl+-bound dimers are 555 K (i. e., the same as those of the corresponding Cl+-bound dimers), SiCl 3 + and SiCl+ affinities of the substituted pyridines, relative to pyridine, are estimated to be 3-MePy (2.1 kcal/mol), 4-MePy (3.2 kcal/mol), 3-EtPy (3.7 kcal/mol), 4-EtPy (4.2 kcal/mol), 3,5-diMePy (4.8 kcal/mol), and 3,4-diMePy (5.4 kcal/mol). The SiCl 3 + and SiCl+ cation affinities are related to the proton affinities by the expressions: relative (SiCl 3 + ) affinity = 0.95 ΔPA and relative (SiCl+) affinity = 0.60 ΔPA. The smaller constant in the relationship between the relative SiCl affinity and the relative proton affinity is the result of weaker bonding.

Steric effects between the ortho-substituted alkyl group and the central SiCl 3 + cation reduce the SiCl 3 + affinities of dimers that contain ortho-substituted pyridines. The magnitude of the steric acceleration of fragmentation is used to measure a set of gas-phase steric parameters (S k). The steric effects in the SiCl 3 + dimers are similar in magnitude to those in the corresponding Cl+-bound dimers but weaker than those produced by the bulky [OCNCO]+ group. An inverted steric effect is observed in those SiCl+-bound dimers that incorporate ortho-substituted pyridines and is ascribed to auxiliary Si-H-C bonding, which stabilizes the ortho-substituted pyridine-SiCl+ bond. This auxiliary bonding appears to correspond to agostic bonding, which is well characterized in solution and occurs in competition with steric effects that weaken the pyridine-SiCl+ interaction.

Ion-molecule reactions of pyridines with halosilicon radical cations SiCl 2 + and SiCl 4 + as well as alkylated halosilicon cations Si(CH3)2Cl+ and Si(CH3)Cl 2 + also are investigated. In these cases, charge exchange and associated reactions are the main reaction channels, and clustering is not observed.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. 1.(a)
    Oppenstein, A.; Lampe, F. W. In Review of Chemical Intermediates; Strsusz, O. P., Ed.; Elsevier: Amsterdam, 1986; Vol. 6, p 275;Google Scholar
  2. 1.(b)
    Schwartz, H. In The Chemistry of Organic Silicon Compounds; Patai,, S.; Rappoport, Z., Eds.; Wiley: New York, 1989; p 445;CrossRefGoogle Scholar
  3. 1.(c)
    Depuy, C. H.; Damrauer, R.; Bowie, J. H.; Sheldon, J. C. Acc. Chem. Res. 1987, 20, 127;CrossRefGoogle Scholar
  4. 1.(d)
    Bowie, J. H. Mass Spectrom. Rev. 1984, 3, 1.CrossRefGoogle Scholar
  5. 2.
    Murthy, S.; Beauchamp, J. L. J. Phys. Chem. 1992, 96, 1247.CrossRefGoogle Scholar
  6. 3.
    Li, X.; Stone, J. A. Int. J. Mass Spectrom. Ion Processes 1990, 101, 149.CrossRefGoogle Scholar
  7. 4.
    Weber, M. E.; Armentrout, P. B. J. Phys. Chem. 1989, 93, 1596.CrossRefGoogle Scholar
  8. 5.(a)
    Sieck, L. W.; Lias, S. G. J. Phys. Chem. Ref. Data 1976, 5, 1123.CrossRefGoogle Scholar
  9. 5.(b)
    Meot-ner (Mautner), M. In Gas Phase Ion Chemistry Bower, M. T., Ed.; Academic: New York, 1979; Vol. 2;Google Scholar
  10. 5.(c)
    Depuy, C. H.; Bierbaum, V. M. Acc. Chem. Res. 1981, 14, 146.CrossRefGoogle Scholar
  11. 6.(a)
    Foucaud, A. In The Chemistry of Functional Groups; Patai, S.; Rappoport, Z.; Eds.; Wiley: New York 1983; Suppl. D, Chap. 11, p 441;Google Scholar
  12. 6.(b)
    Lwowski, W., Ed. Nitrenes; Interscience: New York, 1970;Google Scholar
  13. 6.(c)
    Jones, M., Jr.; Moss, R. A., Eds. Carbenes; Wiley-Interscience: New York, 1973; Vol. 1;Google Scholar
  14. 6.(d)
    Saunders, M.; Jimnet-Vazueez, H. A. Chem. Rev., 1991, 91, 375;CrossRefGoogle Scholar
  15. 6.(e)
    Lammertsma, K. Rev. Chem. Intermed. 1988, 9, 141;CrossRefGoogle Scholar
  16. 6.(f)
    Cox, R. A. Org. React. Mech. 1989, 283;Google Scholar
  17. 6.(g)
    Creary, X., Ed. Advances in Carboncation Chemistry; JAI Press: Greenwich, CT, 1989.Google Scholar
  18. 7.(a)
    Kotiaho, T.; Shay, B. J.; Cooks, R. G.; Eberlin, M. N. J. Am. Chem. Soc. 1993, 115, 1004.CrossRefGoogle Scholar
  19. 7.(b)
    Bortolini, O.; Yang, S. S.; Cooks, R. G. Org. Mass Spectrom. 1993, 28, 1313.CrossRefGoogle Scholar
  20. 8.(a)
    Patrick, J. S.; Kotiaho, T.; McLuckey, S. A.; Cooks, R. G. Mass Spectrom. Rev. 1994, 33, 287;Google Scholar
  21. 8.(b)
    Cooks, R. G.; Kruger, T. L. J. Am. Chem. Soc. 1981, 203, 3274;Google Scholar
  22. 8.(c)
    Wright, L. G.; McLuckey, S. A.; Cooks, R. G.; Wood, K. V. Int. J. Mass Spectrom. Ion Processes 1982, 42, 115.CrossRefGoogle Scholar
  23. 9.(a)
    O’Hair, R. A. J.; Bowie, J. H.; Gronert, S. Int. J. Mass Spectrom. Ion Processes 1992, 117, 23;CrossRefGoogle Scholar
  24. 9.(b)
    Bojesen, G. J. Am. Chem. Soc. 1987, 209, 5557;CrossRefGoogle Scholar
  25. 9.(c)
    Wu, Z.; Fenselau, C. Tetrahedron 1993, 49, 9197;CrossRefGoogle Scholar
  26. 9.(d)
    Cheng, X. H.; Wu, Z.; Fenselau, C. J. Am. Chem. Soc. 1993, 115, 4844;CrossRefGoogle Scholar
  27. 9.(e)
    Zhang, K.; Zimmerman, D. M.; Chung-Phillips, A.; Cassady, C. J. Am. Chem. Soc. 1993, 115, 10812.CrossRefGoogle Scholar
  28. 10.
    Hoke, S. H. II; Yang, S. S.; Cooks, R. G.; Hrovat, D. A.; Borden, W. T. J. Am. Chem. Soc. 1994, 116, 4888.CrossRefGoogle Scholar
  29. 11.
    Eberlin, M. N.; Kotiaho, T.; Shay, B. J.; Yang, S. S.; Cooks, R. G. J. Am. Chem. Soc. 1994, 116, 2457.CrossRefGoogle Scholar
  30. 12.
    Yang, S. S.; Bortolini, O.; Steinmetz, A.; Cooks, R. G. J. Mass Spectrom. 1995, 30, 184.CrossRefGoogle Scholar
  31. 13.
    Yang, S. S.; Chen, G.; Ma, S.; Cooks, R. G.; Gozo, F.; Eberlin, M. N. J. Mass Spectrom. 1995, 30, 807.CrossRefGoogle Scholar
  32. 14.
    Schwartz, J. C.; Schey, K. L.; Cooks, R. G. Int. J. Mass Spectrom. Ion Processes 1990, 1, 101.Google Scholar
  33. 15.(a)
    Schwartz, J. C.; Wade, A. P.; Enke, C. G.; Cooks, R. G. Anal. Chem. 1990, 62, 1809.CrossRefGoogle Scholar
  34. 15.(b)
    Cooks, R. G.; Amy, J.; Bier, M.; Schwartz, J. C.; Schey, K. L. Adv. Mass Spectrom. 1989, 11A, 33.Google Scholar
  35. 16.
    Cooks, R. G.; Rockwood, A. L. Rapid Commun. Mass Spectrom. 1991, 5, 93.Google Scholar
  36. 17.
    Cedra B. A.; Wesdemiotis C. Presented at the 42nd ASMS Conference on Mass Spectrometry and Allied Topics, Chicago, IL., June 1994.Google Scholar
  37. 18.(a)
    Gallo, R.; Roussel, C.; Berg, U. In Advances in Heterocyclic Chemistry; Katritzky, A. R., Ed.; Academic Press: New York, 1988, Vol. 43, p 173;Google Scholar
  38. 18.(b)
    Berg, U.; Gallo, R.; Klatte, G.; Metzger, J. J. Chem. Soc., Perkin Trans. 1980, 2, 1350;Google Scholar
  39. 18.(c)
    Meyerson, S.; Weitkamp, A. W. Org. Mass Spectrom 1968, 1, 659;CrossRefGoogle Scholar
  40. 18.(d)
    Tureček, T. Collect. Czech. Chem. Commun. 1987, 52, 1928;CrossRefGoogle Scholar
  41. 18.(e)
    Turecek, F. Int. J. Mass Spectrom. Ion Processes 1991, 108, 137;CrossRefGoogle Scholar
  42. 18.(f)
    Green, M. M. Tetrahedron 1980, 36, 2687;CrossRefGoogle Scholar
  43. 18.(g)
    Jenkins, H. D. B.; Kelly, E. J.; Samuel, C. J. Tetrahedron Lett. 1994, 35, 6543;CrossRefGoogle Scholar
  44. 18.(h)
    Splitter; Tureček, F., Eds. Application of Mass Spectrometry to Organic Stereochemistry; VCH Publishers: New York, 1994.Google Scholar
  45. 19.
    Wright, L. G.; McLuckey, S. A.; Cooks, R. G.; Wood, K. V. Int. J. Mass. Spectrom. Ion Phys. 1982, 42, 115.CrossRefGoogle Scholar
  46. 20.
    Graul, S.; Schnute, M. E.; Squires, R. R. Int. J. Mass Spectrom. Ion Processes 1990, 96, 181.CrossRefGoogle Scholar
  47. 21.
    Brookhart, M.; Green, M. L. H. J. Organomet. Chem. 1983, 250, 395.CrossRefGoogle Scholar
  48. 22.(a)
    Green, M. L. H. Pure Appl. Chem. 1984, 56, 47.CrossRefGoogle Scholar
  49. 22.(b)
    Brookhart, M.; Green, M. L. H.; Wong, L-L.. In Progress in Inorganic Chemistry; Lippard, S. J., Ed.; Wiley: New York, 1988; Vol. 36, p 1.CrossRefGoogle Scholar
  50. 23.
    Crabtree, R. H.; Holt, E. M.; Lavin, M.; Morehouse, S. M. Inorg. Chem. 1985, 24, 1986.CrossRefGoogle Scholar
  51. 24.
    Carmona, E.; Contreras, L.; Poveda, M. L. Sànchez. J. Am. Chem. Soc. 1991, 113, 4322.CrossRefGoogle Scholar

Copyright information

© American Society for Mass Spectrometry 1996

Authors and Affiliations

  • Sheng Sheng Yang
    • 1
  • Philip Wong
    • 1
  • Shuguang Ma
    • 1
  • R. Graham Cooks
    • 1
  1. 1.Department of ChemistryPurdue UniversityWest LafayetteUSA

Personalised recommendations