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Olefin Metathesis: A Mechanistic and Kinetic Study

Olefin Metathesis: A Mechanistic and Kinetic Study. Chris Whipp November 20, 2008. Metathesis in Chemistry. What is Olefin Metathesis?. Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001 , 34 , 18. What is Olefin Metathesis?. Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001 , 34 , 18.

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Olefin Metathesis: A Mechanistic and Kinetic Study

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  1. Olefin Metathesis: A Mechanistic and Kinetic Study Chris Whipp November 20, 2008

  2. Metathesis in Chemistry

  3. What is Olefin Metathesis? Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res.2001, 34, 18.

  4. What is Olefin Metathesis? Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res.2001, 34, 18.

  5. What is Olefin Metathesis? Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res.2001, 34, 18.

  6. What is Olefin Metathesis? Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res.2001, 34, 18.

  7. What is Olefin Metathesis? Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res.2001, 34, 18.

  8. Metals in Metathesis Ti Ti V Cr Ru Nb Mo Ta W Re Os Ir Pt Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res.2001, 34, 18.

  9. Relative Reactivity of Metals Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res.2001, 34, 18. Tebbe, F. N.; Parshall, G. W.; Ovenall, D. N. J. Am. Chem. Soc.1979, 101, 5074.

  10. Industry: The Origin of Metathesis Mol, J. C. J. Mol. Cat. A2004, 213, 49. Banks, R. L.; Bailey, G. C. Ind. Eng. Chem., Prod. Res. Dev. 1964, 170.

  11. 2005 Nobel Prize for Metathesis Chauvin, Y.; Schrock, R. R.; Grubbs, R. H. Angew. Chem. Int. Ed.2006, 47, 3740.

  12. Metathesis Publications 1st Commerically available Grubbs catalyst 1st Commerically available Schrock catalyst

  13. Metathesis in Synthesis Hirama, M.; Oishi, T.; Uehara, H.; Inoue, M.; Maruyama, M.; Oguri, H.; Satake, M. Science2001, 294, 1904. Martin, S. F.; Humphrey, J. M.; Ali, A.; Hillier, M. C. J. Am. Chem. Soc.1999,121, 866. Faucher, A.-M. Org. Lett. 2004, 6, 2901.

  14. Outline • Establishment of the complete catalytic cycle • The Grubbs 1st and 2nd generation catalysts • Mechanistic studies on how these catalysts differ and why

  15. The Catalytic Cycle

  16. Mechanism of Olefin Coordination Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc.1997, 119, 3887.

  17. Mechanism of Olefin Coordination Active Catalyst 18 e- Active Catalyst Precatalyst 14 e- Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  18. Phosphine Dissociation Experiments Phosphine exchange monitored by 31P NMR experiments over a range of temperatures Catalyst will not carry out subsequent metathesis steps Intermediates are observable by NMR Key intermediates could not be observed by NMR Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  19. Phosphine Dissociation Experiments Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  20. Determining Dependence on Phosphine Rate shows no dependence on phosphine concentration Vary equivalents of phosphine k (s-1) PR3 (eq) Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  21. Phosphine Dissociation Experiments Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  22. Determining Entropy of Activation Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  23. The Eyring Equation k = reaction rate constant kB = Boltzmann’s constant h = Planck’s constant T = temperature DG = Gibbs energy of activation R = Gas constant Atwood, J. D. Inorganic and Organometallic Reaction Mechanisms; VCH: New York, 1997, p 13.

  24. The Eyring Equation y = mx + b Equation requires the variation of temperature ln(kB/h)+DS/R ln(k/T) -DH/R (1/T) Atwood, J. D. Inorganic and Organometallic Reaction Mechanisms; VCH: New York, 1997, p 13.

  25. Determining Entropy of Activation Eyring Plot ln(k/T) (1/T) Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  26. Determining Entropy of Activation Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  27. The Updated Catalytic Cycle What is the conformation? Intermediate or transition state?

  28. The Piers Catalyst Romero, P. E.; Piers, W. E.; McDonald. R. Angew. Chem. Int. Ed.2004, 43, 6161.

  29. Metallacyclobutane: Transition State or Intermediate? Intermediate Romero, P. E.; Piers, W. E. J. Am. Chem. Soc.2005, 127, 5032.

  30. The Updated Catalytic Cycle

  31. The Grubbs Catalysts Sholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett.1999, 1, 953.

  32. Gives electron density Removes electron density N-Heterocyclic Carbene Ligands Diez-Gonzalez, S.; Nolan, S. P. Coord. Chem. Rev.2006, 251, 874. Straub, B. F. Adv. Synth. Catal.2007, 349, 204.

  33. The Trans Effect and Ligand Dissociation Atwood, J. D. Inorganic and Organometallic Reaction Mechanisms; VCH: New York, 1997, p 51.

  34. The Trans Effect and Ligand Dissociation Atwood, J. D. Inorganic and Organometallic Reaction Mechanisms; VCH: New York, 1997, p 51.

  35. The Updated Catalytic Cycle

  36. Catalyst Activation by Phosphine Dissociation Catalyst activity is NOT directly proportional to phosphine dissociation Grubbs 2 must be more reactive once in the catalytic cycle Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  37. The Updated Catalytic Cycle

  38. Catalyst Propagation Studies Highly reactive, will favour metathesis Stable complex Not metathesis active Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  39. The Updated Catalytic Cycle Large excess of olefin will favour forward direction Key Assumption: All steps after olefin coordination are fast

  40. kobs (s-1) Olefin (eq) Catalyst Propagation Studies Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  41. Calculating the Rate Law A B C Rate Law for C Assume steady-state of B Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 6543.

  42. Calculating the Rate Law A B C Overall Rate Law Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 6543.

  43. At saturation: Saturation Kinetics A To get saturation kinetics, k-1 must be very small compared to k2 Will give pseudo first-order kinetics reactivity is different with Grubbs 1 and 2 Catalysts will reach saturation at different concentration of olefins Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 6543.

  44. At saturation: Catalyst Propagation Studies Does not reach saturation until 5300 eq. kobs (s-1) Under saturation kinetics at 5 eq. Olefin (eq) Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  45. At saturation: Saturation Kinetics A To get saturation kinetics, k-1 must be very small compared to k2 kobs (s-1) Grubbs 1 reaches saturation slowly k-1 might be important Grubbs 2 reaches saturation quickly May indicate large difference between k2, k-1 Olefin (eq) Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  46. The Updated Catalytic Cycle Key Assumption: All steps after olefin coordination are fast

  47. Computational Studies What is the conformation needed for metallacyclobutane formation? Straub, B. F. Angew. Chem. Int. Ed.2005, 44, 5974.

  48. Reaction Pathway of Grubbs 1 and 2 Straub, B. F. Angew. Chem. Int. Ed.2005, 44, 5974.

  49. Catalyst Activation by Phosphine Dissociation Grubbs 1 initiates faster Sanford, M. S.; Ulman, M.; Grubbs, R. H. J. Am. Chem. Soc.2001, 123, 749.

  50. Reaction Pathway of Grubbs 1 and 2 Straub, B. F. Angew. Chem. Int. Ed.2005, 44, 5974.

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