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1 A Density Functional Study on Activation and Ion-Pair Formation in Group IV Metallocene and Related Olefin Polymerization Catalysts Mary S.W. Chan,

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Presentation on theme: "1 A Density Functional Study on Activation and Ion-Pair Formation in Group IV Metallocene and Related Olefin Polymerization Catalysts Mary S.W. Chan,"— Presentation transcript:

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2 1 A Density Functional Study on Activation and Ion-Pair Formation in Group IV Metallocene and Related Olefin Polymerization Catalysts Mary S.W. Chan, Kumar Vanka, Cory C. Pye and Tom Ziegler Department of Chemistry, University of Calgary Calgary, Alberta Canada T2N 1N4

3 2Introduction Activation of the Precatalyst by B(C 6 F 5 ) 3 Yang, X.; Stern, C.L.; Marks, T. J. J.Am. Chem. Soc. 1994, 116, 10015. Metallocenes are not very effective as polymerization catalysts by themselves. They require activation by a Lewis acid such as B(C 6 F 5 ) 3. The product of this reaction was characterized experimentally and crystal structures like the one shown on the right was used as model geometry for computational studies

4 3Introduction Possible Reactions of the Contact Ion-Pair A: activation of the precatalyst B:dissociation into infinitely separated ions C:insertion of a solvent molecule in the contact ion-pair D:insertion of an olefin molecule in the contact ion-pair E:dissociation of solvent separated ion-pair F: dissociation of olefin separated ion-pair

5 4 Major Sections Mono- cyclopentadienyl Constrained Geometry Bis- cyclopentadienyl M = Ti or Zr R = methyl group à Reactions of the contact ion-pair à Activation of various catalyst precursors by the co-catalyst B(C 6 F 5 ) 3 Areas for In-depth Study Catalyst Systems for In-depth Study

6 5 Computational Details The density functional theory calculations were carried out using the Amsterdam Density Functional (ADF) program version 2.3.3. 1 Geometry optimizations were carried out using the local exchange-correlation potential of Vosko et al. 2 A triple-zeta basis set was used to describe the outer most valence orbitals for the titanium and zirconium whereas a double- zeta basis set was used for the non-metals. The frozen-core approximation was used to treat the core orbtials for all atoms. The gas phase energy differences between stationary points were calculated by augmenting the LDA energy with Predew and Wang’s non-local correlations and exchange corrections. 3 The energy differences in solution was corrected from the gas phase energies by accounting for the solvation energy calculated by the Conductor-like Screening Model (COSMO). 4 The solvation energy calculations were carried out with a dielectric constant of 2.38 to represent toluene as the solvent. The charge distribution study was carried out by the Hirshfeld analysis. 5 1. (a) Baerends, E.J.; Ellis, D.E.; Ros, P. Chem. Phys. 1973, 2, 41. (b) Baerends, E.J.; Ros, P. Chem. Phys. 1973, 2, 52. 2. Vosko, S.H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200. 3. Perdew, J. P. Phys. Rev. B 1992, 46, 6671. 4. Pye, C.C.; Zielger T. Theor. Chem. Acc. 1999. (DOI10.1007/s00214990m184, in press pulbished online March 16, 1999). 5. Hirshfeld, F.L. Theoret. Chim. Act. 1977, 44, 129.

7 6 Enthalpy Change of Methide Abstraction ∆H M = Ti -12.2 kcal/mol M = Zr -14.9 kcal/mol ∆H M = Ti -14.4 kcal/mol M = Zr -17.5 kcal/mol ∆H M = Ti -16.3 kcal/mol M = Zr -19.1 kcal/mol Activation by a -catalyst Activation by a Co-catalyst

8 7 Activation by a Co-catalyst Charge Analysis of Ligands and Functional Groups in the Neutral Precursor and Ion-Pair + cyclopentadienyl 0.02 Ti 0.41 methyl-0.15 methyl-0.13 B 0.11 C 6 F 5 -0.04 C 6 F 5 -0.03 C 6 F 5 -0.04 cyclopentadienyl 0.13 Ti 0.43 methyl-0.07 Methyl-0.07  -methyl-0.03 B-0.01 C 6 F 5 -0.09 C 6 F 5 -0.13 C 6 F 5 -0.15 Flow of electron density from cyclopentadienyl and methyl ligand to the boron and pentafluorophenyl groups is observed.

9 8 Activation by a Co-catalyst Effect of Alkyl Substitution on the Constrained Geometry Catalyst ∆H ∆HTotalTotalChange in R gas phase COSMOCharge inCharge inCharge (kcal/mol)(kcal/mol)NeutralIon-PairDensity H-13.9-14.4-0.21-0.170.04 Methyl-16.1-16.4-0.19-0.130.06 Isopropyl-16.9-17.0-0.18-0.120.06 tert-Butyl-18.4-18.0-0.19-0.100.09

10 9 Activation by a Co-catalyst Effect of Methyl Substitution on Cp Rings ∆H (kcal/mol) Substitution on Cp gas phase COSMOExperimental a H-19.1-19.1-23.1 1,2-Dimethyl-23.8-24.0-24.3 Pentamethyl-27.5-27.8-36.7 a Obtained from: Deck, P.A.; Beswick, C.L.; Marks, T.J. J. Chem. Soc. 1998, 120, 1772.

11 10 Reactions of the Contact Ion-Pair Toluene Complexed Ions and Ion-Pairs from the CpZrMe 3 Precursor

12 11 Reactions of the Contact Ion-Pair Toluene Complexed Ions and Ion-Pairs from the H 2 SiCp(NH)ZrMe 2 Precursor

13 12 Reactions of the Contact Ion-Pair Toluene Complexed Ions and Ion-Pairs from the Cp 2 ZrMe 2 Precursor

14 13 Reactions of the Contact Ion-Pair Olefin Complexed Ions and Ion-Pairs from the CpZrMe 3 Precursor

15 14 Reactions of the Contact Ion-Pair Olefin Complexed Ions and Ion-Pairs from the H 2 SiCp(NH)ZrMe 2 Precursor

16 15 Reactions of the Contact Ion-Pair Olefin Complexed Ions and Ion-Pairs from the Cp 2 ZrMe 2 Precursor

17 16 Reactions of the Contact Ion-Pair Initial Stages of Polymerization for CpMMe 3 and H 2 SiCp(NH)MMe 2 Systems

18 17 Reactions of the Contact Ion-Pair Initial Stages of Polymerization for Cp 2 MMe 2 Systems

19 18 Future Work Search for the structure of resting state(s) incorporating the counter ion Molecular dynamics simulation of olefin uptake and insertion from the contact ion-pair

20 19 Electronic factors play a predominant role in determining the enthalpy change of methide abstraction to form a contact ion-pair. Mechanism of olefin complexation dependant on the structure of the catalyst precursor and solvent. Mono-cyclopentadienyl and constrained geometry catalysts show a strong tendency to co-ordinate with toluene The steric bulk of the bis-cyclopentadienyl catalysts prevent optimal co- ordination with toluene and makes olefin complexation more favorable. Conclusions Acknowledgement This investigation was supported by the Natural Science and Engineering Research Council of Canada (NSERC) and by Novacor Research and Technology of Calgary.

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