A Convenient Method for the Synthesis of Zirconocene Hydrido Chloride, Isobutyl Hydride, and Dihydride Complexes Using tert-Butyl Lithium

Preparation of zirconocene hydrido chloride complexes has been accomplished via addition of 1 equiv of tert-butyllithium to the corresponding zirconocene dichlorides. In this manner, both Cp*Cp‘ ‘Zr(H)Cl and Cp‘ ‘₂Zr(H)Cl (Cp* = C₅Me₅, Cp‘ ‘ = 1,3-(SiMe₃)₂C₅H₃) were prepared in high yield. Further addition of ^tBuLi to Cp*Cp‘ ‘Zr(H)Cl affords the isobutyl hydride complex Cp*Cp‘ ‘Zr(CH₂CHMe₂)(H), which upon addition of 1 atm of dihydrogen undergoes rapid hydrogenolysis yielding the monomeric dihydride Cp*Cp‘ ‘ZrH₂. In the absence of dihydrogen, the zirconocene dihydride undergoes reversible C−H activation of a cyclopentadienyl trimethylsilyl group, affording the “tuck-in” derivative Cp*(η⁵-1-SiMe₃C₅H₃-3-(η¹-SiMe₂CH₂))ZrH. Addition of 2 equiv of ^tBuLi to the ansa-zirconocene ⁱPr₂Si(η⁵-3-SiMe₃C₅H₃)(η⁵-3,4-(SiMe₃)₂C₅H₂)ZrCl₂ results in the corresponding zirconocene isobutyl hydride complex, which upon exposure to H₂ affords the dimeric dihydride [ⁱPr₂Si(η⁵-3-SiMe₃C₅H₃)(η⁵-3,4-(SiMe₃)₂C₅H₂)ZrH₂]₂. In a similar procedure the substituted indenyl complexes rac-(1-CMe₃−C₉H₆)Zr(H)Cl and rac-(1-CMe₃−C₉H₆)Zr(CH₂CHMe₂)(H) have been prepared. This synthetic methodology allows for the preparation of metallocene alkyl hydrides and dihydrides inaccessible by more traditional routes.