Computational evidence that the inverse kinetic isotope effect for reductive elimination of methane from a tungstenocene methyl-hydride complex is associated with the inverse equilibrium isotope effect for formation of σ-complex intermediate

Chemical Communications

Volumn , Issue 1, 2003, Pages 22-23

  Janak, Kevin E ^a   Churchill, David G ^a   Parkin, Gerard ^a  

^a Och Spine at New York Presbyterian Hospitals   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ISOTOPE; METHANE; TUNGSTEN DERIVATIVE;

ARTICLE; CALCULATION; COMPLEX FORMATION; DISSOCIATION; KINETICS; OXIDATION;

EID: 0037223563     PISSN: 13597345     EISSN: None     Source Type: Journal    
DOI: 10.1039/b209684f     Document Type: Article

References (20)

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4. For recent reviews, see: (a) W. D. Jones, Acc. Chem. Res. in press (b) R. M. Bullock and B. R. Bender, 'Isotope Methods in Homogeneous Catalysis' in Encyclopedia of Catalysis, ed. I. T. Horváth, Wiley, New York, 2003.
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7. D. G. Churchill, K. E. Janak, J. S. Wittenberg and G. Parkin, J. Am. Chem. Soc., in press.
8. DFT B3LYP (Jaguar 4.1): Geometry optimizations and frequency calculations (6-31G** and LACVP** basis sets); single point calculations (cc-pVTZ(-f) and LACV3P** basis sets).
9. 2M(Me)H (M = Mo,W) derivatives, see: (a) J. C. Green and C. N. Jardine, J. Chem. Soc., Dalton Trans., 1998, 1057; (b) J. C. Green, J. N. Harvey and R. Poli, J. Chem. Soc., Dalton Trans., 2002, 1861; (c) M.-D. Su and S.-Y. Chu, J. Phys. Chem. A, 2001, 105, 3591.
10. 2M(Me)H (M = Mo,W) derivatives, see: (a) J. C. Green and C. N. Jardine, J. Chem. Soc., Dalton Trans., 1998, 1057; (b) J. C. Green, J. N. Harvey and R. Poli, J. Chem. Soc., Dalton Trans., 2002, 1861; (c) M.-D. Su and S.-Y. Chu, J. Phys. Chem. A, 2001, 105, 3591.
11. 2M(Me)H (M = Mo,W) derivatives, see: (a) J. C. Green and C. N. Jardine, J. Chem. Soc., Dalton Trans., 1998, 1057; (b) J. C. Green, J. N. Harvey and R. Poli, J. Chem. Soc., Dalton Trans., 2002, 1861; (c) M.-D. Su and S.-Y. Chu, J. Phys. Chem. A, 2001, 105, 3591.
12. B. K. Carpenter, Determination of Organic Reaction Mechanisms, Wiley-Interscience, New York, 1984.
13. We have also determined the isotope effects using the modification that employs the Redlich-Teller product rule, i.e. KIE = SYM·V-P·EXC·ZPE, and (ii) the thermodynamic values obtained directly from the DFT calculations. Significantly, the three methods yield very similar results, thereby providing an indication of the reliability of the calculations. See supporting information for comparison of the three methods.
14. 2]Rh(Me)H has also demonstrated that the inverse EIE for reductive coupling is a result of the normal kinetic isotope effect for reductive coupling being smaller than the normal kinetic isotope effect for oxidative coupling. See: T. O. Northcutt, D. D. Wick, A. J. Vetter and W. D. Jones, J. Am. Chem. Soc., 2001, 123, 7257.
15. As such, the derived transition state is not a well defined stationary point on the enthalpy surface; nevertheless, we have also calculated frequencies at other points on the singlet dissociation surface and find similar values.
16. Although there are no experimentally determined EIE values for dissociation of methane from σ-complexes (or association of methane), related values have been reported for other alkanes. Interestingly, both normal and inverse values have been observed. See, for example: (a) S. Geftakis and G. E. Ball, J. Am. Chem. Soc., 1998, 120, 9953; (b) A. A. Bengali, R. H. Schultz, C. B. Moore and R. G. Bergman, J. Am. Chem. Soc., 1994, 116, 9585.
17. Although there are no experimentally determined EIE values for dissociation of methane from σ-complexes (or association of methane), related values have been reported for other alkanes. Interestingly, both normal and inverse values have been observed. See, for example: (a) S. Geftakis and G. E. Ball, J. Am. Chem. Soc., 1998, 120, 9953; (b) A. A. Bengali, R. H. Schultz, C. B. Moore and R. G. Bergman, J. Am. Chem. Soc., 1994, 116, 9585.
18. re), thereby corresponding to the most extreme inverse value for the system.
19. 14a,b However, the validity of this claim has been questioned. See refs. 2(a) and 5. (a) H. C. Lo, A. Haskel, M. Kapon and E. Keinan, J. Am. Chem. Soc., 2002, 124, 3226; (b) M. A. Iron, H. C. Lo, J. M. L. Martin and E. Keinan, J. Am. Chem. Soc., 2002, 124, 7041.
20. 14a,b However, the validity of this claim has been questioned. See refs. 2(a) and 5. (a) H. C. Lo, A. Haskel, M. Kapon and E. Keinan, J. Am. Chem. Soc., 2002, 124, 3226; (b) M. A. Iron, H. C. Lo, J. M. L. Martin and E. Keinan, J. Am. Chem. Soc., 2002, 124, 7041.