Chain Propagation for Polyethylene and Polypropylene Polymerization with Late Metal Homogeneous Catalysts Dean M. Philipp, Richard P. Muller, and William A. Goddard, III. I. Why Late Metal Homogeneous Catalysts? II. What Makes a Good Catalyst? III. General Mechanism for Polymerization by Late Metal Homogeneous Catalysts IV. What Is Involved in Chain Propagation Calculations? V. Results for Chain Propagation Calculations Using Various Metals, Ligands, and Monomer Units VI. Conclusions

I. Why Late Metal Homogeneous Catalysts? Alternative to other methods of polymerization - could be more active. Like Ziegler-Natta catalysts, they offer control of branching and stereoselectivity. Homogeneous catalysts are relatively easy to model. Linear Polyethylene Highly Branched Polyethylene Isotactic Polypropylene Syndiotactic Polypropylene Can use Mixed QM/MM methodsCan use full QM + +

II. What Makes a Good Catalyst? Low barrier to insertion. Strong enough affinity for the incoming monomer - but not too strong Large barriers for termination pathways. Ability to control branching Ability to control tacticity Other factors that are more difficult to address theoretically such as: –Stability under reaction conditions –Ease of synthesis –Cost –Ability to for from precursor + co-catalyst

III. General Mechanism for Polymerization by Late Metal Homogeneous Catalysts

Need to find complexation energy of incoming monomer unit,  E comp Need to find energy for insertion of monomer into growing polymer chain,  E in Need to find barrier to monomer insertion,  E † in Computational details: –B3LYP density functional theory –Jaguar program –6-31G** basis set used, except for LACVP** on metal and 6-31G on coordinating ligand atoms not directly connected to metal IV. What Is Involved in Chain Propagation Calculations? Need to find

Calculated Results for Varying the Ligand on Pd

Calculated Results for Propylene as Monomer Unit

VI. Conclusions Ethylene complexation energy increases as metal is changed to one further down or further to the left in the periodic table Insertion energy barrier increases as metal is changed to one further down. It increases as one moves to the left for the second and third transition series, but decreases towards the left for the first series. The weaker the trans influence of the coordinating ligand, the larger the observed complexation energies and insertion energy barriers. Using propylene instead of ethylene yields slightly larger complexation energies and insertion barriers. The two propagation pathways explored for polypropylene were energetically similar, with the second pathway slightly lower in energy for all points, but with a slightly larger insertion barrier.

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