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Article

Highly Stereoregular Syndiotactic Polypropylene Formation with Metallocene Catalysts via Influence of Distal Ligand Substituents

Supporting Info

Stephen A. Miller^† and John E. Bercaw*

Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125

Organometallics, 2004, 23 (8), pp 1777–1789

DOI: 10.1021/om030333f

Publication Date (Web): March 18, 2004

†

Current address: Department of Chemistry, Texas A&M University, College Station, TX 77843-3255.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Abstract

Highly stereoregular syndiotactic polypropylene is obtained with the catalyst systems Ph₂C(Oct)(C₅H₄)ZrCl₂/MAO (8/MAO) (Oct = octamethyloctahydrodibenzofluorenyl; MAO = methylaluminoxane) and Me₂C(Oct)(C₅H₄)ZrCl₂/MAO (12/MAO). The syndiotactic polypropylenes obtained are largely devoid of stereoerrors by ¹³C NMR analysis ([r] > 98%), and melting temperatures as high as 153 or 154 °C (from 8 and 12, respectively) are found for the thermally quenched polymers (without annealing). A related hafnium catalytic system, Ph₂C(Tet)(C₅H₄)HfCl₂/MAO (11/MAO) (Tet = tetramethyltetrahydrobenzofluorenyl), was found to be the most syndioselective of the hafnocenes tested (T_m = 141 °C). The metallocene dichloride precatalysts represent the first examples of transition metal complexes containing the Oct or Tet ligands. Reported are the solid state crystal structures of 8, the diprotio ligand precursor of 8 (Ph₂C(OctH)(C₅H₅)), and the zirconium analogue of 11, Ph₂C(Tet)(C₅H₄)ZrCl₂ (10). Distal ligand influences are thus demonstrated to have a dramatic effect on polymer stereochemistry.