Syntheses and Crystal Structures of Bis[(trimethylsilyl)tetramethylcyclopentadienyl]titanium Dichloride and Monochloride

(Trimethylsilyl)tetramethylcyclopentadiene (Cp'H) was obtained from the lithium salt of tetramethylcyclopentadiene and trimethylsilyl chloride. Bis[(trimethylsilyl)tetramethylcyclopentadienyl]titanium dichloride ( 1 ) and monochloride ( 2 ) were prepared by the generally known procedures. The X-ray crystal structures of 1 and 2 showed the placement of the bulky trimethylsilyl groups in side positions on opposite sides of the CE-Ti-CE planes. The steric congestion between the two chlorine atoms and two trimethylsilyl groups in 1 resulted in the nearly eclipsed conformation of the rings. Consequently, the steric hindrance between the methyl groups at the hinge position of the Cp' ligands led to a decrease in the angle between the Cp' ring planes by 4.8°, compared with the value of 44.6° in (C 5 Me 5 ) 2 TiCl 2 . The titanocene skeleton in 2 is virtually the same as in (C 5 Me 5 ) 2 TiCl. The electronic effect of the trimethylsilyl group upon various properties of 1 and 2 appeared to be ambiguous. Based on the position of λ max of electronic absorption bands of 1 the trimethylsilyl group exerted a stronger electron donation effect than the methyl group, however, the affinity of 2 to 2-methyltetrahydrofuran put the effect of the trimethylsilyl group close to that of hydrogen and the anisotropy of the EPR g -tensor of 2 close to that of the methyl group.