Activation of the (Trimethylsilyl)tetramethylcyclopentadienyl Ligand in Zirconocene Complexes

Reduction of [ZrCl2{η5-C5Me4(SiMe3)}2] (1) with excess magnesium in tetrahydrofuran
affords a mixture of the monomeric zirconocene hydride [ZrH{η1:η5-C5Me4(SiMe2CH2)}{η5-C5Me4(SiMe3)}] (2) and the dimeric, tetranuclear Zr(III)− and Zr(IV)−magnesium hydride
complexes 3 and 4, respectively. In the presence of bis(trimethylsilyl)ethyne (btmse), a similar
reduction yields the η2-alkyne complex [Zr{η5-C5Me4(SiMe3)}2(η2-btmse)] (5) as the major
product and compounds 2−4 as minor impurities. Upon thermolysis under vacuum, 5
undergoes a 2-fold hydrogen transfer from trimethylsilyl groups in the zirconocene
intermediate to leaving btmse to afford [Zr{η5:η1-C5Me4(SiMe2CH2)}2] (6) and a mixture of
alkenes (E)- and (Z)-Me3SiCHCHSiMe3 (E ≫ Z). Crystal structures of compounds 2 and
4−6 were determined by X-ray crystallography.