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Alkyne Metathesis

Michael Holtz-Mulholland Literature Meeting September 28 th 2011. Alkyne Metathesis. About Me. I ’ m from Montreal. Contents. The Reaction Mechanism Catalyst Systems Reaction Aspects Applications. Alkyne Metathesis. Exchange of termini Metal catalyzed.

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Alkyne Metathesis

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  1. Michael Holtz-Mulholland Literature Meeting September 28th 2011 Alkyne Metathesis

  2. About Me • I’m from Montreal

  3. Contents • The Reaction • Mechanism • Catalyst Systems • Reaction Aspects • Applications

  4. Alkyne Metathesis • Exchange of termini • Metal catalyzed Montreaux, A.; Blanchard, M. J. Chem. Soc. Chem. Comm., 1974, 786.

  5. Mechanism • 1981: Schrock demonstrated alkylidyne is an active species • 1982: Schrock successfully isolated a metallacyclobutadiene from metathesis conditions Wengrovius, J.H.; Sancho, J.; Schrock, R.R. J. Am. Chem. Soc. 1981, 103, 3932. Pedersen, S.F.; Schrock, R.R.; Churchill, M.R.; Wasserman, H.J. J. Am. Chem. Soc., 1982, 104, 6808.

  6. Catalyst Systems

  7. a • Mo(CO)6 and phenol • Earliest examples • Relatively stable • Low functional group tolerance • Requires high temperature • Ill-defined active species

  8. a – effect of the phenol • Grela: optimization of the phenol source • Optimal Pka between 8 and 9 Grela, K.; Ignatowska, J. Org. Lett., 2002, 4, 3747. Sashuk, V.; Ignatowska, J.; Grela, K. J. Org. Chem., 2004, 69, 7748.

  9. b • Commercially available • Highly active • First well defined catalyst • Air/moisture sensitive • Improved compatibility

  10. Synthesis of b Schrock, R.R.; Clark, D.N.; Sancho, J.; Wengrovius, J.H.; Rocklage, S.M.; Pedersen, S.F. Organometallics, 1982, 1, 1645. Listemann, M.L.; Schrock, R.R., Organometallics, 1985, 4, 74.

  11. c • Highly sensitive • Must be handled under argon • Precatalyst is capable of activating nitrogen • High reactivity • Good functional group tolerance

  12. Synthesis of c Laplaza, C.E.; Odom, A.L.; Davis, W.M.; Cummins, C.C.; Protasiewicz, J.D. J. Am. Chem. Soc., 1995, 117, 4999. Furstner, A.; Mathes, C.; Lehmann, C.W. Chem. Eur. J., 2001, 7, 5299.

  13. C synthesis of carbyne complexes • More efficient due to reductive recycle strategy • Allows access to a variety of alkylidynes Zhang, W.; Kraft, S.; Moore, J.S. Chem. Commun., 2003, 832.

  14. d • High air and moisture resistance • In situ generation of alkylidyne active species • Provides reactivity and functional group tolerance of Molybdenum carbyne complexes

  15. Synthesis of d Bindl, M.; Stade R.; Heilmann, E.K.; Picot, A.; Goddard, R. Furstner, A. J. Am. Chem. Soc., 2009, 131, 9468.

  16. Functional Group Compatibility • High lewis acidity lowers compatibility

  17. Comparison of Reactivity • Standard RCM

  18. Reaction Requirements • Substrate bearing a non-terminal alkyne • Catalyst compatible with substrate fuctional groups • Appropriate temperature • Driven by removal of byproduct • 2-Butyne requires high temperature and vacuum to remove • Formation of insoluble byproducts is more effective Zhang, W.; Moore, J.S.; J. Am. Chem. Soc., 2004, 126, 12796.

  19. Controlling the Stereochemistry of Alkenes • Reductive method controls the stereochemistry

  20. Applications of Alkyne Metathesis • Polymerization • Cross metathesis • RCM • Total Synthesis/Materials

  21. ROMP • Early examples are non-living • Effective when opening strained systems

  22. ROMP • First example • Non-living polymerization of cyclooctyne • High PDI Krouse, S.A.; Schrock, R.R. Macromolecules, 1989, 22, 2569.

  23. ROMP • Living polymerization Fischer, F.R.; Nuckolls, C. Angew. Chem. Int. Ed., 2010, 49, 7257.

  24. ROMP • Effect of phenol on living polymerization • Phenol replaces the amide ligand Fischer, F.R.; Nuckolls, C. Angew. Chem. Int. Ed., 2010, 49, 7257.

  25. Cross Metathesis • Can be highly selective • Can be pushed to completion by removal of 2-butyne

  26. Cross Metathesis • Homodimerization Furstner, A.; Mathes, C. Org. Lett., 2001, 3, 221.

  27. Cross Metathesis Kaneta, N.; Hikichi, K.; Asaka, S.; Uemaura, M.; Mori, M. Chem. Lett., 1995, 1055.

  28. Cross Metathesis Furstner, A.; Mathes, C. Org. Lett., 2001, 3, 221.

  29. Cross Metathesis • Synthesis application Furstner, A.; Dierkes, T. Org. Lett., 2000, 2, 2463.

  30. Cross Metathesis • Synthesis application Furstner, A.; Mathes, C. Org. Lett., 2001, 3, 221.

  31. Cross Metathesis Polymeriztion • Allows access to high molecular weight polymers • Copolymerization is possible • Polymers can be heavily conjugated • Useful for semiconducting materials For an overview see: Bunz, U. H. F. Acc. Chem. Res., 2001, 34, 998.

  32. Cross Metathesis Polymerization • Conjugated polymers Kloppenburg, L.; Song, D.; Bunz, U.H.F. J. Am. Chem. Soc., 1998, 120, 7973. See also: Zhang, W.; Moore, J.S. Macromolecules, 2004, 37, 3973. Brizius, G.; Kroth, S.; Bunz, U.H.F. Macromolecules, 2002, 35, 5317.

  33. Cross Metathesis Polymerization • Copolymers Brizius, G.; Kroth, S.; Bunz, U.H.F. Macromolecules, 2002, 35, 5317.

  34. RCM • Allows access to the Z olefin via subsequent metathesis/reduction reactions • Useful for controlling the geometry of macrocyclic products

  35. RCM Furstner, A.; Guth, O.; Rumbo, A.; Seidel, G. J. Am. Chem. Soc. 1999, 121, 11108.

  36. RCM Furstner, A.; Guth, O.; Rumbo, A.; Seidel, G. J. Am. Chem. Soc. 1999, 121, 11108.

  37. RCM in Synthesis • Alkyne used to give access to the Z isomer Furstner, A.; Grela K. Angew. Chem. Int. Ed., 2000, 39, 1234.

  38. RCM in Synthesis • Alkyne used to form exclusively the E isomer Furstner, A.; Bonnekessel, M.; Blank, J. T.; Radkowski, K.; Seidel, G.; Lacombe, F.; Gabor, B.; Mynott, R. Chem. Eur . J., 2007, 13, 8762.

  39. RCM in Synthesis Furstner, A.; Castanet, A.-S.; Radkowski, K.; Lehmann, C. W. J. Org. Chem. 2003, 68, 1521.

  40. RCM in Synthesis Benson, S.; Collin, M-P.; Arlt, A.; Gabor, B.; Goddard, R.; Furstner, A. Angew. Chem. Int. Ed., 2011, 50, 8739.

  41. Cyclooligomerization • Requires high dilution to be efficient • Early example shown • 0.19 M Ge, P.-H.; Fu, W.; Herrmann, W.A.; Herdtweck, E.; Campana, C.; Adams, R.D.; Bunz, U.H.F. Angew. Chem. Int. Ed., 2000, 39, 3607.

  42. Cyclooligomerization Pschirer, N.G.; Fu, W.; Adams, R.D.; Bunz, U.H.F Chem. Comm., 2000, 87.

  43. Cyclooligomerization • Byproduct precipitates to drive the reaction • Major increase in isolated yield • No need to remove butyne at high temperature Zhang, W.; Moore, J.S.; J. Am. Chem. Soc., 2004, 126, 12796.

  44. Summary • Allows selective access to E or Z olefins • Selective ring closing in the presence of alkenes • Alkyne can be used to perform many synthetically useful transformations • Gives easy access to useful heavily conjugated materials

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