Synthesis, molecular structure, and racemate-meso interconversion for rac-(Me2Si)(2){eta(5)-C5H-3-(CHMe2)-5-Me}(2)MCl2 (M = Ti and Zr)

Doubly [SiMe2]-bridged group IV metallocenes, rac-(Me2Si)(2){eta(5)-C5H-3-( CHMe2)-5-Me}(2)MCl2 (M = Ti, Zr), have been synthesized, and a crystal stru cture of rac-(Me2Si)(2){eta(5)-C5H3-(CHMe2)-5-Me}(2)TiCl2 has been determin ed by X-ray diffraction methods. Racemate-meso interchange occurs in benzen e solution just above room temperature, affording an approximately 1:1 mixt ure of rac-(Me2Si)(2){eta(5)-C5H-3-(CHMe2)-5-Me}(2)TiCl2 meso-(Me2Si)(2){et a(5)-C5H-3-(CHMe2)-5-Me}(2)TiCl2. Measurements of the kinetics of the appro ach to equilibrium reveal Delta H double dagger = 18(1) kcal.mol(-1) and De lta S double dagger = -7(2) eu. The corresponding zirconium compound is con figurationally stable.