Synthesis, Molecular Structure, and Racemate−Meso Interconversion for rac-(Me2Si)2{η5-C5H-3-(CHMe2)-5-Me}2MCl2 (M = Ti and Zr)
摘要:
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 structure of rac-(Me2Si)(2){eta(5)-C5H3-(CHMe2)-5-Me}(2)TiCl2 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-(Me2Si)(2){eta(5)-C5H-3-(CHMe2)-5-Me}(2)TiCl2 meso-(Me2Si)(2){eta(5)-C5H-3-(CHMe2)-5-Me}(2)TiCl2. Measurements of the kinetics of the approach to equilibrium reveal Delta H double dagger = 18(1) kcal.mol(-1) and Delta S double dagger = -7(2) eu. The corresponding zirconium compound is configurationally stable.