Soluble Metallocene Cataysts Polyethylene Bis(cyclopentadienyl)zirconium dichloride Plus methylaluminoxane (MAO) 5,000 kg PE / g Zr / hr (indefinitely active)

Soluble Metallocene Cataysts Polypropylene

Soluble Metallocene Cataysts Used a mixture of meso and racemic ansa-titanocenes Stereo-rigid Ethylene-bridged Rac: chiral with C2-symmetric axis Meso: achiral

Rac Ansa Catalysts Non-superimposable Mirror Images

Soluble Metallocene Cataysts Ewen J. Am. Chem. Soc. 1984

PP from ansa-Metallocene Catalysts Methyl pentad region Fractions of iso-PP versus atactic-PP tracks with ratio of racemic to meso catalyst levels MWs on each sample were similar indicating that both stereo-isomers of the catalyst give rise to similar propagation and termination rate constants

Soluble Metallocene Cataysts Confirmed Ewen’s proposal that it was the chiral ansa-metallocene that was responsible for the formation of isotactic PP Made the zirconium derivative 7,700 kg PP / mol Zr / hr (!) 1985 Kaminsky and Britzinger

Mechanism for Isotactic PP Conformational modeling studies (Corradini 1991) The growing polymer chain is forced into the open region Chirality of the metallocene is relayed to the incoming monomer through the orientation of the methyl group Since C2-symmetry, both reactions sites are homotopic Therefore selective for the same olefin enantioface Giving rise to isotactic PP

Soluble Metallocene Cataysts Polypropylene

Rac Ansa Catalysts C2 Axis of Symmetry Binding Sites are Homotopic

H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H

Cs symmetry Cp of different size Steric bulk flanking the metallocene wedge with an open region in center

How to make this? Hemi-isotactic Hemi-syndiotactic

… … m m r r m m m m r r r r m m m m r

Unbridged metallocene catalysts Rapid isomerization, low barriers What kind of polymer is produced?

Unbridged metallocene catalysts Added phenyl group to indene Inhibits rate of ligand rotation

Physical Properties of Polypropylene

Olefin Polymerizations with Early Metal Catalysts ~ 2 × 1011 lbs/year polyethylenes(PE), polypropylenes(PP) produced worldwide! Metallocene Catalysts: Technological advance A) Incremental B) Major: 1) New Materials 2) Detailed mechanistic understanding Not a black box anymore…

Olefin Polymerizations with Early Metal Catalysts Metallocene Catalysts: Incremental technological advance ● Increased activities/productivities ● Many different grades of ethylene/ α-olefin copolymers ● Control of MW, MWD bimodal, unimodal, PDI < 5.0! Existing markets are being extended into new applications

Metallocene Catalysts Major Technological Advance New Materials Syndiotactic polystyrene Tm = 270 °C, 40-50% X-tal w/ good rate of x-tallization Syndiotactic and elastomeric PP Cyclic Olefin Copolymers Hoechst’s TopazTM (Tg = 140 – 200 °C)

Chemical Review 2000, Issue 4 “FRONTIERS IN METAL-CATALYZED POLYMERIZATION” Also Angew. Chem. Int. Ed. 1999, 38, 428 ± 447