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Published February 23, 1994 | metadata_only
Journal Article

Theoretical Studies of Ziegler-Natta Catalysis: Structural Variations and Tacticity Control


Models for the likely active catalysts in homogeneous Ziegler-Natta systems have been studied using ab initio quantum chemical methods. We investigated the geometries of the isoelectronic model complexes, X_2M-R where X = Cl or Cp = (η^5-C_5H_5); where M = Sc and Ti^+ (and also Ti); and where R = H, CH_3, or SiH_3. The general trend is that the M = Sc compounds strongly prefer a planar configuration, whereas the M = Ti^+ cases generally prefer pyramidal geometries. This difference in geometry can be related to the differing ground-state electronic configurations for the metals: Sc is (4s)^2(3d)^1, whereas Ti^+ is (4s)^1(3d)^2. The nonplanar geometry for [Cp_2Ti-R]^+ suggests an explanation for the origin of stereospecificity in the syndiotactic polymerization by unsymmetric metallocene catalysts. These results suggest that {(η^5-C_5H_4)CMe_2(η^5-fluorenyl)}Sc-R would not catalyze syndiotactic polymerization under these conditions.

Additional Information

© 1994 American Chemical Society. Received June 30, 1992. Revised Manuscript Received November 22, 1993. We wish to thank Dr. Jason Perry for many helpful discussions. E.P.B. wishes to acknowledge a generous grant from the ARCS foundation. This research was supported by a grant from the National Science Foundation (CH91-100284) and the USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER113431). The facilities of the Materials and Molecular Simulation Center are also supported by grants from NSF-GCAG, DOE-AICD, Allied-Signal, Asahi Glass, Asahi Chemical, BP America, Chevron, BF Goodrich, Teijin Chemical, and Xerox.

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August 20, 2023
August 20, 2023