The anionic zirconocene trihydride: [Cp*2ZrH3](-)

Synthetic pathways to several salts of the anion [Cp*2ZrH3](-) have been developed, Reaction of Cp*2ZrH2 (3) prepared from [Cp*Zr-2(N-2)](2)(mu-N-2) (2), with KH in THF, afforded [Cp*2ZrH3]K (1) in a 74% yield, In a similar manner, addition of LiH gave [Cp*2ZrH3]Li (4). While this synthetic pathway provides reproducible routes to land 4, purification of 2 is problematic. Another preparation involving the reaction of Cp*2ZrCl2 with 3 equiv of n-BuLi under H-2 affords 4 . 0.5(LiCl . THF). Alternatively, reaction of Cp*2ZrCl2 with LiAlH4 afforded the species Cp*2ZrH(mu(2)-H2AlH2 (5) in virtually quantitative yield. Subsequent reaction of 5 with n-BuLi afforded the direct and high-yield conversion to 4, Deuteration and NMR studies infer attack of BuLi occurs at the Al center exclusively prompting transfer of a hydride to Zr and liberation of the Zr trihydride anion. Variable-temperature H-1 NR IR spectra and H/D scrambling experiments for ? and 4-d(3) are consistent with the hydride exchange process mediated by ion pairing while T-1 studies infer a classical trihydride formulation is appropriate. Crystallographic studies of 4 . 0.5(LiCl . THF), 5, and 4 also affirm cation-anion pairing in 4 and 4 . 0.5(LiCl . THF) and hydride bridging between Al and Zr in 5.