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

Abstract: Synthetic pathways to several salts of the anion [Cp*2ZrH3]- have been developed. Reaction of Cp*2ZrH2 (3) prepared from [Cp*2Zr(N2)]2(-N2) (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 1and 4, purification of 2 is problematic. Another preparation involving the reaction of Cp*2ZrCl2 with 3 equiv of n-BuLi under H2 affords 4?0.5(LiCl?THF). Alternatively, reaction of Cp*2ZrCl2 with LiAlH4 afforded the species Cp*2ZrH(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 1H NMR spectra and H/D scrambling experiments for 4 and 4- d 3 are consistent with the hydride exchange process mediated by ion pairing while T1 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.