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Mechanisms of Stereoselective Polymerizations Luigi Cavallo Università di Salerno Italy Modeling Lab for Nanostructures And Catalysis.

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Presentation on theme: "Mechanisms of Stereoselective Polymerizations Luigi Cavallo Università di Salerno Italy Modeling Lab for Nanostructures And Catalysis."— Presentation transcript:

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 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 Polypropylene made

5 Milano, Italy, 53 years and 4 days ago 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 Polypropylene made

6 Consequences of the discovery About 100*10 6 tons/year of PE & PP in 2005 1 m 3 blocks would wrap the equator 2.5 times

7 The Catalysts Resconi Cavallo Fait Piemontesi Chem Rev 2000, 100, 1253 Coates Chem Rev 2000, 100, 1223 Brintzinger, Fischer, Mülhaupt, Rieger, Waymouth Angew Chem Int Ed 1995, 34, 1143 Ewen Scientific American May 1997 TiCl 3 /AlR 3 VCl 4 /AlR 3 19541988196220002001 1985 Ewen JACS 1984, 106, 6355 Kaminsky, Külper, Brintzinger, Wild ACIE Engl. 1985, 24, 507. Ewen, Jones, Razavi, Ferrara JACS 1988, 110, 6255 Fujita, Kashiwa et al. Macromol. Rapid Commun. 2001, 22, 1072 Tshuva, Goldberg, Kol JACS 2000, 122, 10706

8 The Catalysts TiCl 3 /AlR 3 VCl 4 /AlR 3 19541988196220002001 1985 Coates Chem Rev 2000, 100, 1223 Brintzinger, Fischer, Mülhaupt, Rieger, Waymouth Angew Chem Int Ed 1995, 34, 1143 Ewen Scientific American May 1997 Resconi Cavallo Fait Piemontesi Chem Rev 2000, 100, 1253

9 The Catalysts TiCl 3 /AlR 3 VCl 4 /AlR 3 19541988196220002001 1985 Coates Chem Rev 2000, 100, 1223 Brintzinger, Fischer, Mülhaupt, Rieger, Waymouth Angew Chem Int Ed 1995, 34, 1143 Ewen Scientific American May 1997 Resconi Cavallo Fait Piemontesi Chem Rev 2000, 100, 1253

10 Mechanism of Chain Growth + CH 2 =CH 2 Cossee, P. J. Catal. 1964, 3, 80

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

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

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

14 Possible Stereomistakes TiCl 3 /AlR 3 VCl 4 /AlR 3 Cp 2 TiCl 2 at low T Enantiomorphic-site sterocontrol Chain-end Sterocontrol

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

16 The Catalysts 19541989196220002001 TiCl 3 /AlR 3 VCl 4 /AlR 3 1985 Ewen JACS 1984, 106, 6355 Kaminsky, Külper, Brintzinger, Wild ACIE Engl. 1985, 24, 507. Resconi Cavallo Fait Piemontesi Chem Rev 2000, 100, 1253 Coates Chem Rev 2000, 100, 1223 Brintzinger, Fischer, Mülhaupt, Rieger, Waymouth Angew Chem Int Ed 1995, 34, 1143 Ewen Scientific American May 1997 System with well defined chemistry!

17 C 2 -symmetric systems (isospecific symmetry) (S) C 2 -axis (R) C 2 -axis Mirror plane

18 C 2 -symmetric systems (isospecific symmetry) (+)-Chain (–)-Chain (S)

19 C 2 -symmetric systems (isospecific symmetry) (+)-Chain (–)-Chain (S) Messenger! -chain – -chain monomer + – Mt P P Orientations of the growing chain

20 C 2 -symmetric systems (isospecific symmetry) (+)-Chain (–)-Chain Favored ! (S)

21 C 2 -symmetric systems (isospecific symmetry) or ? resi (+)-Chain (S)

22 C 2 -symmetric systems (isospecific symmetry) (S) si (+)-Chain (S) re

23 C 2 -symmetric systems (isospecific symmetry) (S) (+)-Chain sire Favored ! (+)-Chain (S) si

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

25 C 2 -symmetric systems (isospecific symmetry) (+)-Chain si (S) C 2 -axis

26 C 2 -symmetric systems (isospecific symmetry) (+)-Chain si (S) C 2 -axis 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.

27 The Catalysts 19541988196220002001 TiCl 3 /AlR 3 VCl 4 /AlR 3 1985 Solved!

28 The Catalysts TiCl 3 /AlR 3 VCl 4 /AlR 3 19541988196220002001 1985 Solved!

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

30 The Catalysts TiCl 3 /AlR 3 VCl 4 /AlR 3 19541988196220002001 1985 Solved! Solved ?

31 The Catalysts 1989 TiCl 3 /AlR 3 VCl 4 /AlR 3 19541988196220002001 1985 Solved! Solved ? Ewen, Jones, Razavi, Ferrara JACS 1988, 110, 6255

32 C S -symmetric systems (syndiospecific symmetry) Mirror plane

33 C S -symmetric systems (syndiospecific symmetry) C 2 -axisMirror plane

34 C S -symmetric systems (syndiospecific symmetry) (+)-Chain si

35 C S -symmetric systems (syndiospecific symmetry) (+)-Chain (–)-Chain resi Mirror plane

36 C S -symmetric systems (syndiospecific symmetry) (+)-Chain (–)-Chain resi Enantiotopic coordination positions: opposite monomer enantiofaces are favored in successive steps (i.e. a syndiotactic polymer is formed) Mirror plane Cavallo, Corradini, Guerra, Vacatello Macromolecules 1991, 24, 1784.

37 The Catalysts 1989 TiCl 3 /AlR 3 VCl 4 /AlR 3 19541988196220002001 1985 Solved! Solved?Solved!

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

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

40 Experimental Validation of the Mechanism If the chiral orientation of the chain is the key element, without a long chain propene insertion shouldnt be enantioselective… P

41 Experimental Validation of the Mechanism NMR study of propene insertion into the M-CH 3 bond Zambelli Locatelli Sacchi Tritto Macromolecules 1982, 15, 831. CH 3

42 Experimental Validation of the Mechanism 13 CH 2 CH 3 + (10%) (90%) 13 CH 3 + (50%) Enantioselectivity of propene insertion into M- 13 CH 3 Enantioselectivity of propene insertion into M- 13 CH 2 CH 3 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 1989 TiCl 3 /AlR 3 VCl 4 /AlR 3 19541988196220002001 1985 Solved! Solved?Solved! Fujita, Kashiwa et al. Macromol. Rapid Commun. 2001, 22, 1072

45 Primary (1,2) Insertion Secondary (2,1) Insertion Regiochemistry of Insertion 1 1 2 2 1 2 1 2 TiCl 3 /AlR 3 VCl 4 /AlR 3

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

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

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

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

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

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

52 A Possible Overall Picture E in kcal/mol Ti-P n re-chain/ -site Ti-P n+1 si-chain/ -site Ti-P n+1 si-chain/ -site Ti-P n+2 re-chain/ -site Site Isomerization Site Isomerization si-propene re-propene Stereoerror re-propene E = 1.9 Stereoerror si-propene E = 1.9

53 Proposed Mechanism Dissociative Mechanism on the basis of NMR-studies Bickley & Serpone Inorg. Chem. 1979, 18, 2002 Bei, Dale, Swenson, Jordan OM 1997, 16, 3282 -complex G racemization = 10 ÷ 20 kcal/mol (Mt = Ti, Zr)

54 Monomer Assisted Dissociation DFT calculations E dissociation = 14.9 kcal/mol Dissociation

55 Site Chirality as Messenger (1,2 propagation, site stereocontrol) Flow of Information Configuration of the fluxional octahedral active species Configuration of the growing chain Configuration of monomer insertion Stereoregular polymer -site Messenger!

56 Other systems re-chain/ -site/si-propene (r-diad) re-chain/ -site/si-propene (r-diad) Mechanism of the chiral orientation of the growing chain Milano Guerra Cavallo JACS. 2004, 37, 231 First proposed: Corradini, Guerra, Pucciariello Macromolecules 1985, 13,42

57 The Catalysts 1989 TiCl 3 /AlR 3 VCl 4 /AlR 3 19541988196220002001 1985 Solved! Solved?Solved!

58 Outline Introduction Examples of Site Stereocontrol Examples of Chain-End Stereocontrol About Regiomistakes Ion-Pairs Final Remarks

59 Enantioselectivity of Regiomstakes C 2 -symmetric metallocene C S -symmetric metallocene Regiomstakes are enantioselective Guerra Cavallo Moscardi Vacatello Corradini J. Am. Chem. Soc. 1994, 116, 2988. P Favored re P si P re P Favored si

60 Enantioselectivity in 1,2 vs 2,1 insertion C 2 -symmetric metallocene C S -symmetric metallocene Opposite enantiofaces are favored in propagation and regiomistakes The same enantioface is favored in propagation and regiomistakes Guerra Cavallo Corradini Longo Resconi J. Am. Chem. Soc. 1997, 119, 4394. P re P si P P

61 Selectivity in 2-butene/ethene Copolymerization C 2 -symmetric metallocene C S -symmetric metallocene P re P si P P P cis P trans + =

62 Ethene/2-butene Copolymerization Tests P cis P trans cis-butene is selectively copolymerized trans-butene is selectively copolymerized Guerra Longo Corradini Cavallo J. Am. Chem. Soc. 1999, 121, 8651. C 2 -symmetric metallocene C S -symmetric metallocene

63 Regiochemistry in Octahedral Systems

64 Secondary Insertion E Regio kcal/mol Octahedral-systems : Ligand Effect Primary Insertion 0.33.6 Slightly favored Strongly favored

65 Octahedral-systems : Chain Effect Growing Chain E Regio kcal/mol 3.6 -2.0 1.4 i-Bui-Pr 0.3 Growing Chain i-Bui-Pr Steric stress! A secondary chain pushes insertion towards another secondary insertion

66 Origin of Different Regiochemistry Phenoxy-imine Phenoxy-amine Talarico Busico Cavallo JACS 2003, 125, 7172.

67 Origin of Different Regiochemistry Phenoxy-imine Phenoxy-amine Talarico Busico Cavallo JACS 2003, 125, 7172. weak antibonding interaction strong antibonding interaction Growing Chain Growing Chain Alkene Me

68 Outline Introduction Examples of Site Stereocontrol Examples of Chain-End Stereocontrol About Regiomistakes Ion Pairs Final Remarks

69 Ion-Pairs Metallocene/Borate H 2 Si(Cp) 2 ZrMe + /B(C 6 F 5 ) 4 - Metallocene/Borane H 2 Si(Cp) 2 ZrMe + /MeB(C 6 F 5 ) 3 - Excellent NMR study on Metallocenium Ion-Pairs Zuccaccia, Stahl, Macchioni, Chen, Roberts, Marks J. Am. Chem. Soc. 2004, 126, 1448 Energetic and structure of ion-pairs fundamental to understand activity, copolymerizations, microstructure Static methods (i.e. classical QM calculations) not particularly suited

70 Dynamics of Ion-Pairs System simulated 1 Metallocenium ion-pair swollen in roughly 1100 benzene molecules Conditions : P = 1 atm, T = 25 °C Sampling time : 5 ns (can be longer) Correa and Cavallo J. Am. Chem. Soc. 2006, 128, 10952 Classical Molecular Dynamics Simulations (i.e. no Quantum Mechanics)

71 Performance of the Model Excellent agreement with several structural properties Correa and Cavallo JACS 2006, 128, 10952 The Metallocene/Borane Ion-pair

72 Insight into the Metallocene/Borate Ion-Pair F2 F3 (ps) The unclear NMR data are due to a continous fluctuation between different geometries (as found in our MD simulations) Correa and Cavallo JACS 2006, 128, 10952

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76 Dynamic Behavior of the Metallocene/Borate Ion-pair (Forming and breaking of M…F interactions) Future Applications of Classical Molecular Dynamics of the Catalyst/Counterion Pair : Moving to other metallocenes and to non-metallocenesPolymer chain extended to 10, 100, 1000 monomeric unitsCounterion displacement by a coordinating monomerKey to explain activity and copolymerizations ?

77 Outline Introduction Examples of Site Stereocontrol Examples of Chain-End Stereocontrol About Regiomistakes Ion-Pairs Final Remarks

78 Understanding the Mechanics… a previous teaching Flying machine Codex B, f.74 (1485) Aerial screw Codex B, f.83 (1489) Leonardo da Vinci (1452-1519) Self-portrait

79 Stereospecific Olefins Polymerization aka The best understood organometallic reaction Theoreticians Paolo Corradini Gaetano Guerra Tom Ziegler Tom Woo Keiji Morokuma Giuliano Lanza Experimentalists Karl Ziegler Giulio Natta John Ewen Tobin Marks Maurice Brookhart Jim Stevens Bob Waymouth Richard Jordan Hans-Herbert Brintzinger Walter Kaminsky Gerhard Fink Norio Kashiwa Tominaga Keii Kazuo Soga Terunori Fujita Adolfo Zambelli Umberto Giannini Luigi Resconi Vincenzo Busico Moshe Kol All these people synergically contributed to understand the mechanisms of this reaction Absolutely not a comprehensive list!

80 Final Slide Why to understand ? It is key for the rational design of new catalysts It allows to develop new catalysts faster It is an intellectual pleasure Computational chemistry It is a powerful tool for the rationalization and prediction of chemical behavior The New Lab Strong interaction between theoreticians and experimentalists

81 Acknowledgments The Crew Dr. Computers U of Salerno Dr. G. Milano U of Salerno Dr. A. Correa U of Salerno Dr. C. Costabile U of Salerno Dr. G. Talarico U of Napoli Dr. L.Caporaso U of Salerno Dr. G. Moscardi Basell PolyolefinsDr. H. Jacobsen U of Tulane Dr. J. M. Ducéré U of Salerno Dr. J. Budria U of Eindhoven Financial Basell Polyolefins U of Salerno MURST PRIN-2004 projectMURST FISR project Cineca Grant SuperCalcoloINSTM Italia

82 dōmo arigatō


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