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Mechanisms of Stereoselective Polymerizations

Mechanisms of Stereoselective Polymerizations. Luigi Cavallo. Università di Salerno Italy lcavallo@unisa.it. Modeling Lab for Nanostructures And Catalysis http://www.chem.unisa.it/groups/molnac. Outline. Introduction Examples of Site Stereocontrol Examples of Chain-End Stereocontrol

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Mechanisms of Stereoselective Polymerizations

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  1. Mechanisms of Stereoselective Polymerizations Luigi Cavallo Università di Salerno Italy lcavallo@unisa.it Modeling Lab for Nanostructures And Catalysis http://www.chem.unisa.it/groups/molnac

  2. Outline • Introduction • Examples of Site Stereocontrol • Examples of Chain-End Stereocontrol • About Regiomistakes • Ion-Pairs • Final Remarks

  3. Outline • Introduction • Examples of Site Stereocontrol • Examples of Chain-End Stereocontrol • About Regiomistakes • Ion-Pairs • Final Remarks

  4. Milano, Italy, 53 years and 4 days ago Polypropylene made Nobel prize to Karl Ziegler and Giulio Natta in 1963 “Nature synthesizes many stereoregular polymers, for example cellulose and rubber. This ability has been so far thought to be a monopoly of Nature operating with biocatalysts known as enzymes. But now Prof. Natta has broken this monopoly… The scientific and technical consequences of your discovery are immense and cannot even now be fully estimated.” Presentation Speech, Stockholm, December 10 1963

  5. Milano, Italy, 53 years and 4 days ago Polypropylene made Nobel prize to Karl Ziegler and Giulio Natta in 1963 “Nature synthesizes many stereoregular polymers, for example cellulose and rubber. This ability has been so far thought to be a monopoly of Nature operating with biocatalysts known as enzymes. But now Prof. Natta has broken this monopoly… The scientific and technical consequences of your discovery are immense and cannot even now be fully estimated.” Presentation Speech, Stockholm, December 10 1963

  6. About 100*106 tons/year of PE & PP in 2005 • 1 m3 blocks would wrap the equator 2.5 times Consequences of the discovery

  7. Brintzinger, Fischer, Mülhaupt, Rieger, Waymouth Angew Chem Int Ed 1995, 34, 1143 The Catalysts Resconi Cavallo Fait Piemontesi Chem Rev 2000, 100, 1253 Ewen Scientific American May 1997 Coates Chem Rev 2000, 100, 1223 TiCl3/AlR3 VCl4/AlR3 1985 1954 1962 1988 2000 2001 Ewen JACS1984, 106, 6355 Kaminsky, Külper, Brintzinger, Wild ACIE Engl.1985, 24, 507. Tshuva, Goldberg, Kol JACS2000, 122, 10706 Ewen, Jones, Razavi, Ferrara JACS1988, 110, 6255 Fujita, Kashiwa et al. Macromol. Rapid Commun.2001, 22, 1072

  8. Brintzinger, Fischer, Mülhaupt, Rieger, Waymouth Angew Chem Int Ed 1995, 34, 1143 The Catalysts Resconi Cavallo Fait Piemontesi Chem Rev 2000, 100, 1253 Ewen Scientific American May 1997 Coates Chem Rev 2000, 100, 1223 TiCl3/AlR3 VCl4/AlR3 1985 1954 1962 1988 2000 2001

  9. Brintzinger, Fischer, Mülhaupt, Rieger, Waymouth Angew Chem Int Ed 1995, 34, 1143 The Catalysts Resconi Cavallo Fait Piemontesi Chem Rev 2000, 100, 1253 Ewen Scientific American May 1997 Coates Chem Rev 2000, 100, 1223 TiCl3/AlR3 VCl4/AlR3 1985 1954 1962 1988 2000 2001

  10. Mechanism of Chain Growth + CH2=CH2 Cossee, P. J. Catal.1964, 3, 80

  11. The Chain-Migratory Mechanism Step (i+1) Step (i)

  12. The Three Polypropylenes Same face enchainment Isotactic polypropylene (i-PP) Opposite faces enchainment n Syndiotactic polypropylene (s-PP) Random faces enchainment Atactic polypropylene (a-PP)

  13. The Three Polypropylenes Same face enchainment Isotactic polypropylene (i-PP) Opposite faces enchainment n Syndiotactic polypropylene (s-PP) Random faces enchainment Atactic polypropylene (a-PP)

  14. Possible Stereomistakes Chain-end Sterocontrol Enantiomorphic-site sterocontrol TiCl3/AlR3 Cp2TiCl2 at low T VCl4/AlR3

  15. Outline • Introduction • Examples of Site Stereocontrol • Examples of Chain-End Stereocontrol • About Regiomistakes • Ion-Pairs • Final Remarks

  16. Brintzinger, Fischer, Mülhaupt, Rieger, Waymouth Angew Chem Int Ed 1995, 34, 1143 The Catalysts Resconi Cavallo Fait Piemontesi Chem Rev 2000, 100, 1253 Ewen Scientific American May 1997 Coates Chem Rev 2000, 100, 1223 TiCl3/AlR3 VCl4/AlR3 1985 1954 1962 1989 2000 2001 System with well defined chemistry! Ewen JACS1984, 106, 6355 Kaminsky, Külper, Brintzinger, Wild ACIE Engl.1985, 24, 507.

  17. C2-symmetric systems(isospecific symmetry) Mirror plane (R) (S) (S) (R) C2-axis C2-axis

  18. C2-symmetric systems(isospecific symmetry) (+)-Chain (S) (S) (S) (S) (–)-Chain

  19. Orientations of the growing chain (+)-chain P monomer + monomer Mt Mt – P (–)-chain C2-symmetric systems(isospecific symmetry) Messenger! (+)-Chain (S) (S) (S) (S) (–)-Chain

  20. C2-symmetric systems(isospecific symmetry) Favored ! (+)-Chain (S) (S) (S) (S) (–)-Chain

  21. C2-symmetric systems(isospecific symmetry) ? or re si (+)-Chain (S) (S)

  22. C2-symmetric systems(isospecific symmetry) si (+)-Chain (S) re (S)

  23. C2-symmetric systems(isospecific symmetry) Favored ! si re (+)-Chain (+)-Chain (S) (S) si (S) (S)

  24. The Chain-Migratory Mechanism Step (i+1) Step (i)

  25. C2-symmetric systems(isospecific symmetry) (+)-Chain (S) (S) si si C2-axis (S) (S) (+)-Chain

  26. C2-symmetric systems(isospecific symmetry) Homotopic coordination positions: the same monomer enantioface is favored at each step (i.e. an isotactic polymer is formed) Cavallo, Corradini, Guerra, Vacatello Polymer 1991, 32, 1329. (+)-Chain (S) (S) si si C2-axis (S) (S) (+)-Chain

  27. The Catalysts Solved! TiCl3/AlR3 VCl4/AlR3 1985 1954 1962 1988 2000 2001

  28. The Catalysts Solved! TiCl3/AlR3 VCl4/AlR3 1985 1954 1962 1988 2000 2001

  29. Other systems Heterogeneous 1954 Metallocene 1985 Post-Metallocene 2000 Mechanism of the chiral orientation of the growing chain Corradini, Guerra, Cavallo Acc. Chem. Res. 2004, 37, 231

  30. The Catalysts Solved ? Solved! Solved! TiCl3/AlR3 VCl4/AlR3 1985 1954 1962 1988 2000 2001

  31. The Catalysts Solved ? Solved! Solved! TiCl3/AlR3 VCl4/AlR3 1985 1954 1962 1989 1988 2000 2001 Ewen, Jones, Razavi, Ferrara JACS1988, 110, 6255

  32. CS-symmetric systems(syndiospecific symmetry) Mirror plane

  33. CS-symmetric systems(syndiospecific symmetry) Mirror plane C2-axis

  34. CS-symmetric systems(syndiospecific symmetry) (+)-Chain si

  35. CS-symmetric systems(syndiospecific symmetry) (–)-Chain (+)-Chain si re Mirror plane

  36. CS-symmetric systems(syndiospecific symmetry) Enantiotopic coordination positions: opposite monomer enantiofaces are favored in successive steps (i.e. a syndiotactic polymer is formed) (–)-Chain (+)-Chain Cavallo, Corradini, Guerra, Vacatello Macromolecules1991, 24, 1784. si re Mirror plane

  37. The Catalysts Solved? Solved! Solved! Solved! TiCl3/AlR3 VCl4/AlR3 1985 1954 1962 1989 1988 2000 2001

  38. Stereoregular polymer Configuration of monomer insertion Configuration of the catalytic site Chain Orientation as Messenger(1,2 propagation, site stereocontrol) Flow of Information

  39. Stereoregular polymer Messenger! monomer monomer + – Configuration of monomer insertion (–)-chain (+)-chain Configuration of the chirally oriented growing chain Configuration of the catalytic site Chain Orientation as Messenger(1,2 propagation, site stereocontrol) Flow of Information

  40. P Experimental Validation of the Mechanism If the chiral orientation of the chain is the key element, without a long chain propene insertion shouldn’t be enantioselective…

  41. CH3 Experimental Validation of the Mechanism NMR study of propene insertion into the M-CH3 bond Zambelli Locatelli Sacchi Tritto Macromolecules1982, 15, 831.

  42. Experimental Validation of the Mechanism Enantioselectivity of propene insertion intoM-13CH3 13CH3 (50%) + 13CH3 (50%) Enantioselectivity of propene insertion intoM-13CH2CH3 (10%) 13CH2CH3 + (90%) 13CH2CH3 The mechanism of the chiral orientation of the growing chain is confirmed

  43. Outline • Introduction • Examples of Site Stereocontrol • Examples of Chain-End Stereocontrol • About Regiomistakes • Ion-Pairs • Final Remarks

  44. The Catalysts Solved? Solved! Solved! Solved! TiCl3/AlR3 VCl4/AlR3 1985 1954 1962 1989 1988 2000 2001 Fujita, Kashiwa et al. Macromol. Rapid Commun.2001, 22, 1072

  45. Regiochemistry of Insertion TiCl3/AlR3 1 1 2 2 Primary (1,2) Insertion 2 1 2 1 VCl4/AlR3 Secondary (2,1) Insertion

  46. Stereorigid Catalysts Heterogeneous Ti-catalysts The bridge confers stereorigidity Interconversion impossible (R) (S) (R) (S)

  47. Stereoflexible Catalysts Homogeneous V-catalysts Withouth a bridge stereoflexible complexes Possible Interconversion

  48. re-chain/D-site/si-propene (r-diad) E = 5.8 Steric stress! Steric stress! Chain-Site-Monomer Interaction E in kcal/mol

  49. re-chain/D-site/si-propene (r-diad) E = 5.8 E = 3.8 re-chain/L-site/re-propene (m-diad) Steric stress! Steric stress! Steric stress! Chain-Site-Monomer Interaction E in kcal/mol

  50. re-chain/D-site/si-propene (r-diad) E = 5.8 E = 3.8 E = 1.9 re-chain/L-site/re-propene (m-diad) Steric stress! re-chain/D-site/re-propene (m-diad) Steric stress! Steric stress! Steric stress! Chain-Site-Monomer Interaction E in kcal/mol

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