A Density Functional Study of the Insertion Mechanism in MAO (Methylaluminoxane)- Activated, Cp 2 ZrMe 2 -Catalyzed Olefin Polymerization Eva Zurek, Tom.

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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 and Functional: LDA along with gradient corrected exchange functional of Becke; correlation functional of Perdew. Basis-set: double-  STO basis with one polarization function for H, C, Al, O; triple-  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 C  -C ethylene distance.

Single-Site Homogeneous Catalysis Catalysts: L 1 L 2 MR 1 R 2 ; L=Cp, NPR 3, NCR 2 ; M=Ti, Zr, R=methyl, propyl, etc. Co-Catalyst (Anion): B(C 6 F 5 ) 3, MAO (Methylaluminoxane) MAO + Cp 2 Zr(CH 3 ) 2  Cp 2 ZrCH MAOMe -

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

‘Real’ (TMA-Containing) MAO

Reactive MAO (R-MAO) Cages

Active & Dormant Species Active Species: [Cp 2 ZrMe] + [AlMe 3 Me(R-MAO)] - Dormant Species: [Cp 2 ZrMe] + [Me(R-MAO)] -

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

First Insertion: ‘Dormant’ Species Zr-O: Zr-O: Cis-Attack Trans-Attack Zr-O: Zr-O: Transition State  E gas = kcal/mol  E toluene = kcal/mol  -complex  E gas = kcal/mol  E toluene = kcal/mol  -complex  E gas = kcal/mol  E toluene = kcal/mol Transition State  E gas = kcal/mol  E toluene = kcal/mol

First Insertion: ‘Active’ Species Cis-Attack Trans-Attack Zr-Me: Zr-Me:  -complex  E gas = kcal/mol  E toluene = kcal/mol Transition State  E gas = kcal/mol  E toluene = kcal/mol Transition State  E gas = kcal/mol  E toluene = kcal/mol  -complex  E gas = kcal/mol  E toluene = kcal/mol Zr-Me: 3.938Zr-Me: 2.501

Second Insertion: Trans  -complexes kcal/mol kcal/mol 4.161Å 4.387Å 9.13 kcal/mol 4.652Å kcal/mol 4.637Å 4.405Å kcal/mol 4.229Å kcal/mol, gas

Second Insertion: Cis  -complexes 4.343Å 4.792Å 9.73 kcal/mol 4.819Å 9.30 kcal/mol 4.169Å kcal/mol kcal/mol 4.326Å kcal/mol Å kcal/mol (gas)

Second Insertion: Trans TS Transition State  E gas = kcal/mol  E toluene = kcal/mol Transition State  E gas = 21.26kcal/mol  E toluene = kcal/mol Zr-Me: 2.517ÅZr-Me:4.658Å  -complex  E gas = kcal/mol  E toluene = kcal/mol

Second Insertion: Cis TS Zr-Me: 2.503Å Transition State  E gas = kcal/mol  E toluene = kcal/mol Transition State  E gas = 21.81kcal/mol  E toluene = kcal/mol Zr-Me:4.925Å Transition State  E gas = kcal/mol  E toluene = kcal/mol Zr-Me:4.089Å

Comparison with Free Cation  -agostic TS  -agostic TS

Do the Cation & Anion Associate? Transition StateAssociated Product

Conclusions [Cp 2 ZrMe] + [AlMe 3 Me(R-MAO)] - is an active species and [Cp 2 ZrMe] + [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: -  -complexes with a  -agostic bond are more stable than those with an  -agostic or with no agostic bonds - associated TS’s are higher in energy than dissociated TS’s - trans-approach with  -agostic bond yields no insertion barrier; uptake barrier must be found - lower barrier than first insertion

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 ($$$) Miscellaneous