Olefin Polymerizations Catalyzed by Late Transition Metal Complexes

1. Olefin Polymerizations Catalyzed by Late Transition Metal Complexes Maurice Brookhart University of North Carolina

2. Polyolefins Total : 100 billions / year 16lbs / person on Earth / year ! • Inexpensive monomers • Little waste in production • Attractive physical properties, long term stabilities

3. Polymer Microstructure — Key to Properties Polypropylene Tm = 160°C Stereoregular Tm = 165°C Completely amorphous Polyethylene • High Density PE (HDPE) Tm= 136°C • Linear Low Density PE (LLDPE) • Tm = 115~130°C • Low Density PE (LDPE) Tm= 105~115°C

4. Polyolefins Primarily Produced via Metal-Catalyzed Processes • Catalyst Structures Control: • polymer microstructures • polymer molecular weights, molecular weight distributions • comonomer incorporation Late Metal Catalysts (Pd, Ni, Co) Early Metal Catalysts (Ti, Zr, Cr)

5. General Mechanism for Polymer Formation

6. Olefin Polymerizations Using Late Metal Catalysts (Ni, Pd) • Why Late Metals ? • Potentially different enchainment mechanisms => • new microstructures • Less oxophilic — functional group compatible • But… • Normally lower insertion barriers • Chain transfer competitive with propagation => • dimers, short chain oligomers

7. α–Diimine Based Catalysts ■ High molecular weight polymers with unique microstructures from: ● ethylene ● α – olefins ● cyclopentene ● trans-1,2-disubstituted olefins ■ Copolymers of ethylene with certain polar vinyl monomers

8. Catalysts Modeled on α–Diimine Systems

9. Polyethylene

10. Poly (α–Olefins)

11. 1,2–Disubstituted Olefins

12. Mechanistic StudiesGeneration of Cationic Alkyl Complexes

13. 1H, 13C NMR Studies – Pd(II)

14. Insertion Kinetics – Ni(II)

15. Activation Barriers to Insertion (ethylene)

16. Mechanistic Model

17. Blocking of Axial Coordination Sites

18. Chain Transfer Mechanisms

19. Mechanistic Model

20. Formation of Agostic Ethyl Complex

21. Dynamics of Agostic Ethyl Complex

22. Cationic Metal Alkyl Intermediates –Ethylene Trapping Experiments

23. Cationic Metal Alkyl Intermediates –Ethylene Trapping Experiments

24. Mechanistic Model

25. Commercial Copolymers of Ethylene and Polar Vinyl Monomers ● Radical Initiation ● High temperatures, very high ethylene pressure

26. Examination of Pd and Ni Diimine Catalysts for Copolymerizations of Ethylene and:

27. Problems Connected with Copolymerization 1. Monomer Binding through the Functional Group 2. β-Elimination of G

28. 3. Weak Competitive Binding of 4. Strong Chelate Formation Following Insertion

29. 5. High Barrier to Insertion of Open Chelate

30. Examples: G = -CN ; -Br, -Cl

31. Ethylene / Acrylate Copolymerization - Pd

32. Mechanism of Copolymerization

33. Examination of Pd and Ni Diimine Catalysts for Copolymerizations of Ethylene and:

34. Ethylene / Alkoxy Vinyl Silane CopolymersVersipol Group - DuPont

35. Vinyl Alkoxy Silane Insertion Chemistry -

36. Evidence for Reversible C2H4 Coordination

37. Advantages of Vinyl Alkoxy Silane Comonomers • Insertion barriers of vinyl alkoxy silanes into Pd-R and Ni-R bonds are similar to ethylene insertion barriers. • Chelates resulting from vinyl alkoxy silane insertions are readily opened with ethylene. • Open chelates readily insert ethylene. • Relative binding affinities favor ethylene, but not to a prohibitive extent.