Half-Sandwich Zirconium and Hafnium Amidoborane Complexes: Precursors of Hydride Derivatives

Half-sandwich zirconium(IV) and hafnium(IV) complexes with amidoborane and hydride ligands have been isolated in the stoichiometric reactions of mono(pentamethylcyclopentadienyl)metal alkyl and amido derivatives with the amine-boranes NHRBH (R = H, Me, HBu). Treatment of the tris(trimethylsilylmethyl) complexes [M(η-CMe)(CHSiMe)] with NHBH (3 equiv) gives the seven-coordinate species [M(η-CMe)(NHBH)] (M = Zr (), Hf ()) with three κ-NHBH ligands. The tris(neophyl) [M(η-CMe)(CHCMePh)] or tris(dimethylamido) [M(η-CMe)(NMe)] derivatives react with NHMeBH (≥3 equiv) to afford bis(dimethylamidoborane) hydride complexes [M(η-CMe)H(NMeBH)] (M = Zr (), Hf ()) via thermally unstable [M(η-CMe)(NMeBH)] species. The reaction of [M(η-CMe)(NMe)] and NHBuBH (≥4 equiv) affords analogous mixed amidoborane hydride derivatives [M(η-CMe)H(NHBuBH)(NMeBH)] (M = Zr (), Hf ()) with κ-NHBuBH and κ-NMeBH ligands. The addition of NHRBH (≥1 equiv) on the mono(dimethylamido) complexes [M(η-CMe)Cl(NMe)] in hexane leads to the precipitation of the ionic compounds [(NHR)BH][{M(η-CMe)Cl}(μ-H)] (R = Me, M = Zr (), Hf (); R = HBu, M = Zr (), Hf ()). Molecular hydride species [Cl(η-CMe)M(μ-Cl)(μ-H)M(η-CMe)Cl(NHBu)] (M = Zr (), Hf ()) could be isolated from mixtures of complexes [M(η-CMe)Cl(NMe)] and lower ratios of NHBuBH. The zirconium complex decomposes in solution to give the mononuclear -butylamido derivative [Zr(η-CMe)Cl(NHBu)] () along with other byproducts.