M C. White Chem 153 EM Polymerization-302 Week of november 18. 2002 Chiral metallocene catalysts Brinteinger's C2-symmetric catalysts/ enantiomorphic site control polymer chain-end control: the stereochemistry of the newest stereogenic center on the growing polymer controls the stereochemistry of monomer addition enantiomorphic site control: chiral ligand overrides the influence of the polymer chain end and controls the stereochemistry of monomer ois( tetrahydroindenyl) iconium dichloride zirconium dichloride polymer chain-end control MAO MAO MAO 91% isotacticity >99% Isotacticity 8 activity(kg pol/molZr-h), 7700 activity(kg pol/molzr-h) Mw=24.00 Paulus OM 1994(13)954. rintzinger ACIEE 1985(6)507 aulus OM 1994(13)954 Proposed model for isospecific polymerisation polyn in open quadrant H fin binds such that its stabilizing a-agostic interaction in the meso ligands give atactic a-substituent is trans to the TS is thought to rigidify the TS for olefin bulky substituent on the growing insertion thereby increasing the Grubbs Acc. Chem. Res. 1996(29)85 lymer chain stereospecificity of insertion Coates Chem. Rev. 2000(100)1223 Ewan JACS1984(106)6355M.C. White Chem 153 EM Polymerization -302- Week of November 18, 2002 Chiral metallocene catalysts Zr Cl Cl Brintzinger's C2-symmetric catalysts/ enantiomorphic site control Zr Cl Cl MAO MAO Me2Si Zr 1-Naphthyl 1-Naphthyl Me Me Cl Cl MAO polymer chain-end control: the stereochemistry of the newest stereogenic center on the growing polymer controls the stereochemistry of monomer addition. enantiomorphic site control: chiral ligand overrides the influence of the polymer chain end and controls the stereochemistry of monomer addition. LnM P LnM P polymer chain-end control: stereoerror is propagated. enantiomorphic site control: stereoerror is corrected by the catalyst. (±) ethylenebis(indenyl) zirconium dichloride (±) ethylenebis(tetrahydroindenyl) zirconium dichloride 60o 50 C oC 91% isotacticity, 7700 activity (kg pol/molZr·h), Mw = 12,000. Brintzinger ACIEE 1985 (6) 507. 78% isotacticity, 188 activity (kg pol/molZr·h), Mw =24,000. Paulus OM 1994 (13) 954. 50oC >99% isotacticity, 875 activity (kg pol/molZr·h), Mw = 920,000. Paulus OM 1994 (13) 954. Zr Proposed model for isospecific polymerization P H H polymer chain is in open quadrant olefin binds such that its α-substituent is trans to the bulky substituent on the growing polymer chain Zr P H H ‡ stabilizing α-agostic interaction in the TS is thought to rigidify the TS for olefin insertion thereby increasing the stereospecificity of insertion. Zr P Zr Cl Cl meso ligands give atactic polymers. Ewan JACS 1984 (106) 6355. Grubbs Acc. Chem. Res. 1996 (29) 85. Coates Chem. Rev. 2000 (100) 1223