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A Density Functional Study of the Insertion Mechanism in MAO (Methylaluminoxane)-Activated, Cp 2 ZrMe 2 -Catalyzed Olefi

A Density Functional Study of the Insertion Mechanism in MAO (Methylaluminoxane)-Activated, Cp 2 ZrMe 2 -Catalyzed Olefin Polymerization. Eva Zurek, Tom Ziegler*, University of Calgary. Computational Details. DFT Calculations: performed with ADF 2.3.3 and 2000.

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A Density Functional Study of the Insertion Mechanism in MAO (Methylaluminoxane)-Activated, Cp 2 ZrMe 2 -Catalyzed Olefi

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  1. A Density Functional Study of the Insertion Mechanism in MAO (Methylaluminoxane)-Activated, Cp2ZrMe2-Catalyzed Olefin Polymerization Eva Zurek, Tom Ziegler*, University of Calgary

  2. Computational Details • DFT Calculations: performed with ADF 2.3.3 and 2000. • Functional: LDA along with gradient corrected exchange functional of Becke; correlation functional of Perdew. • Basis-set: double-z STO basis with one polarization function for H, C, Al, O; triple-z STO basis with one polarization function for Zr. • Solvation: COnductor-like Screening Model (COSMO). • Transition States:geometry optimizations along a fixed reaction coordinate. TS where gradient less than convergence criteria. For insertion barriers this is Ca-Cethylene distance.

  3. Single-Site Homogeneous Catalysis • Catalysts: L1L2MR1R2; L=Cp, NPR3, NCR2; M=Ti, Zr, R=methyl, propyl, etc. • Co-Catalyst (Anion): B(C6F5)3, MAO (Methylaluminoxane) • MAO + Cp2Zr(CH3)2 Cp2ZrCH3+ + MAOMe-

  4. ‘Pure MAO’ Percent Distribution average unit formula of (AlOMe)18.41, (AlOMe)17.23 , (AlOMe)16.89, (AlOMe)15.72 at 198K, 298K, 398K and 598K

  5. ‘Real’ (TMA-Containing) MAO

  6. Reactive MAO (R-MAO) Cages

  7. Active & Dormant Species Dormant Species: [Cp2ZrMe]+[Me(R-MAO)]- Active Species: [Cp2ZrMe]+[AlMe3Me(R-MAO)]-

  8. Possible Mechanisms Trans Approach: ‘Dissociative’ Transition State Cis Approach: ‘Associative’ Transition State

  9. First Insertion: ‘Dormant’ Species Cis-Attack Zr-O: 3.658 Zr-O: 3.336 p-complex DEgas= 31.88 kcal/mol DEtoluene= 28.43 kcal/mol Transition State DEgas= 38.80 kcal/mol DEtoluene= 35.55 kcal/mol Trans-Attack Zr-O: 4.539 Zr-O: 4.209 Transition State DEgas= 35.37 kcal/mol DEtoluene= 29.26 kcal/mol p-complex DEgas= 34.65 kcal/mol DEtoluene= 26.96 kcal/mol

  10. First Insertion: ‘Active’ Species Zr-Me: 3.938 Zr-Me: 2.501 p-complex DEgas= 14.97 kcal/mol DEtoluene= 12.32 kcal/mol Transition State DEgas= 16.63 kcal/mol DEtoluene= 18.36 kcal/mol Cis-Attack Zr-Me: 3.999 Zr-Me: 4.108 p-complex DEgas= 20.73 kcal/mol DEtoluene= 16.22 kcal/mol Transition State DEgas= 21.87 kcal/mol DEtoluene= 17.00 kcal/mol Trans-Attack

  11. Second Insertion: Trans p-complexes 4.161Å 4.652Å 4.229Å 13.69 kcal/mol 9.13 kcal/mol 26.61 kcal/mol, gas 4.405Å 4.637Å 4.387Å 19.19 kcal/mol 10.93 kcal/mol 15.26 kcal/mol

  12. Second Insertion: Cis p-complexes 3.988 Å 4.792Å 4.343Å 17.70 kcal/mol (gas) 9.30 kcal/mol 19.28 kcal/mol 4.326Å 4.169Å 4.819Å 14.48 kcal/mol 9.73 kcal/mol 15.58 kcal/mol

  13. Second Insertion: Trans TS Zr-Me: 2.517Å Zr-Me:4.658Å Transition State DEgas= 22.29 kcal/mol DEtoluene= 24.11 kcal/mol Transition State DEgas= 21.26kcal/mol DEtoluene= 16.40 kcal/mol p-complex DEgas= 18.70 kcal/mol DEtoluene= 13.69 kcal/mol

  14. Second Insertion: Cis TS Zr-Me: 2.503Å Zr-Me:4.925Å Transition State DEgas= 16.39 kcal/mol DEtoluene= 18.25 kcal/mol Transition State DEgas= 21.81kcal/mol DEtoluene= 16.85 kcal/mol Zr-Me:4.089Å Transition State DEgas= 20.05 kcal/mol DEtoluene= 14.90 kcal/mol

  15. Comparison with Free Cation b-agostic TS a-agostic TS

  16. Do the Cation & Anion Associate? Transition State Associated Product

  17. Conclusions • [Cp2ZrMe]+[AlMe3Me(R-MAO)]- is an active species and [Cp2ZrMe]+[Me(R-MAO)]- is a dormant species (‘R-MAO’ is one of the seven reactive MAO cages) in olefin polymerization First insertion: - cis-approach has an associated TS; trans-approach has a dissociated TS - trans-approach has lower insertion barrier Second insertion: - p-complexes with a b-agostic bond are more stable than those with an a-agostic or with no agostic bonds - associated TS’s are higher in energy than dissociated TS’s - trans-approach with a-agostic bond yields no insertion barrier; uptake barrier must be found - lower barrier than first insertion

  18. Miscellaneous • Future Work: - to finish calculating uptake & insertion barriers for the second insertion; examine termination barriers. • Acknowledgements: - Kumar Vanka, Artur Michalak, Michael Seth, Hans Martin Senn, Zhitao Xu and other members of the Ziegler Research Group for their help and fruitful discussions - Novacor Research and Technology (NRTC) of Calgary ($$$) - NSERC ($$$) - Alberta Ingenuity Fund ($$$)

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