Synthesis, Molecular Structure, and Racemate−Meso Interconversion for rac-(Me_2Si)_2{η^5-C_5H-3-(CHMe_2)-5-Me}_2MCl_2 (M = Ti and Zr)

Abstract

Doubly [SiMe_2]-bridged group IV metallocenes, rac-(Me_2Si)_2{η^5-C_5H-3-(CHMe_2)-5-Me}_2MCl_2 (M = Ti, Zr), have been synthesized, and a crystal structure of rac-(Me_2Si)_2{η^5-C_5H-3-(CHMe_2)-5-Me}_2TiCl_2 has been determined by X-ray diffraction methods. Racemate−meso interchange occurs in benzene solution just above room temperature, affording an approximately 1:1 mixture of rac-(Me_2Si)_2{η^5-C_5H-3-(CHMe_2)-5-Me}_2TiCl_2 and meso-(Me_2Si)_2{η^5-C_5H-3-(CHMe_2)-5-Me}_2TiCl_2. Measurements of the kinetics of the approach to equilibrium reveal ΔH^⧧ = 18(1) kcal·mol^(-1) and ΔS^⧧ = −7(2) eu. The corresponding zirconium compound is configurationally stable.

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