Macromolecular Science and Engineering Tuesday June 1 PM MA3 Regatta Advances In Olefin Polymerization Organizer - H. Zahalka Chair - H. Zahalka 13:30-14:00.

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Macromolecular Science and Engineering Tuesday June 1 PM MA3 Regatta Advances In Olefin Polymerization Organizer - H. Zahalka Chair - H. Zahalka 13:30-14: Olefin Polymerization Catalysts Beyond Group-IV Metallocenes Ziegler T., Deng L., Schmid R., Margl P.

Fe

Brookhart Polymerization Catalyst C&EN Feb. 5, 1996: “Polymer Catalyst System: Dupont Eyes New Polyolefin Business” Brookhart catalyst highly linear to moderately branched Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995, 117, high MWs good activities temperature: Temp  branching  monomer pressure: [Et]  branching  bulk of substituents: bulk  branching  MW 

GibsonBrookhart - Robust - Low-cost - Simple to make - High activities - High selectivity

Experimental Observations 1 R = R’ = i-Pr 2 R = R’ = Me 3 R = t-Bu, R’=H 4 R = i-Pr, R’ = H 5 R = Et, R’ = H 6 R = Me, R’ = H Fe/Co catalyst highly linear high density Gibson, V. C. et al. Chem. Commun., 1998, 849. Small, B.L.; Brookhart, M.; Bennett, A.M.A. J. Am. Chem. Soc. 1998, 120, Small, B.L.; Brookhart, M.; J. Am. Chem. Soc. 1998, 120, monomer pressure: [Et] activities: Fe Co no change bulk of substituents: bulk MW no branching Metals : activities of Fe complexes = activities of analogous Co ones no mechanistic details!

Deng,L.;Margl, P.; Ziegler, T., J.Am. Chem. Soc.,1999, in press a b a. Olefin complex resting state: axial C  -conformation preferred electronically  E complex = kcal/mol  E ins = 23 kcal/mol  E BHT = 4 kcal/mol b. Olefin complex: the insertion precursor equatorial C  -conformation disfavored electronically  E complex = kcal/mol  E ins = 7.4 kcal/mol

Neutral Ni(II)-Based Catalyst for Ethylene Polymerization Wang and Grubbs et al. Organometallics, 1998, 17, Experiment: Highly active for Polymerization of ethylene Calculation: Without bulky substituents, the insertion and termination barrier About the same both as high as 26 kcal/mol

M L 'L R M = Ti, V, Cr, Mn L = NH 3, NH 2 - R = Me, Et Possible Polymerization Catalysts First row transition metals Cationic high-spin complexes Two nitrogen ligands Me or Et as model for the growing polymer chain

Olefin Binding Energy d1d1 d2d2 d3d3 d4d4 Olefin binding energy for R = Me Olefin binding energy correlates with the number of d- electrons. d 3 and d 4 systems have lowest binding energy because of destabilized the acceptor orbital for the  -d-interaction.

M MR M M R R R M R MR MR MR d-levels a.b. b. sp 3 OC IN   Orbital Interactions during the Olefin Insertion for example: a d 1 system SOMO becomes significantly destabilized during the insertion. b. = bonding; a.b. = antibonding

Termination Reactions BHE reaction is in most cases less facile than the BHT reaction. BHT reaction coordinate involves a shift of the olefin in the BHT plane similar to the insertion reaction. The major contribution for BHT barrier stems from the breaking of the C-H bond. M C H 2 CH 2 'L L OC BHT H M H 2 C CH 2 'L L H CH 2 H 2 C

Nobel-Price 1998 in Chemistry for “The Theory” W. Kohn (DFT) and J. Pople (ab initio) Theory as a valuable tool in chemical research