Synthesis, Molecular Structure, and Racemate−Meso Interconversion for rac-(Me2Si)2{η5-C5H-3-(CHMe2)-5-Me}2MCl2 (M = Ti and Zr)

Doubly [SiMe 2 ]-bridged group IV metallocenes, rac -(Me 2 Si) 2 {η 5 -C 5 H-3-(CHMe 2 )-5-Me} 2 MCl 2 (M = Ti, Zr), have been synthesized, and a crystal structure of rac -(Me 2 Si) 2 {η 5 -C 5 H-3-(CHMe 2 )-5-Me} 2 TiCl 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 2 Si) 2 {η 5 -C 5 H-3-(CHMe 2 )-5-Me} 2 TiCl 2 and meso -(Me 2 Si) 2 {η 5 -C 5 H-3-(CHMe 2 )-5-Me} 2 TiCl 2 . Measurements of the kinetics of the approach to equilibrium reveal Δ H ⧧ = 18(1) kcal·mol - 1 and Δ S ⧧ = −7(2) eu. The corresponding zirconium compound is configurationally stable.