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 NHR2BH3 (R2 = H2, Me2, HtBu). Treatment of the tris (trimethylsilylmethyl) complexes M (η5-C5Me5) (CH2SiMe3) 3 with NH3BH3 (3 equiv) gives the seven-coordinate species M (η5-C5Me5) (NH2BH3) 3 (M = Zr (1), Hf (2) ) with three κ2N, H-NH2BH3 ligands. The tris (neophyl) M (η5-C5Me5) (CH2CMe2Ph) 3 or tris (dimethylamido) M (η5-C5Me5) (NMe2) 3 derivatives react with NHMe2BH3 (≥3 equiv) to afford bis (dimethylamidoborane) hydride complexes M (η5-C5Me5) H (NMe2BH3) 2 (M = Zr (3), Hf (4) ) via thermally unstable M (η5-C5Me5) (NMe2BH3) 3 species. The reaction of M (η5-C5Me5) (NMe2) 3 and NH2tBuBH3 (≥4 equiv) affords analogous mixed amidoborane hydride derivatives M (η5-C5Me5) H (NHtBuBH3) (NMe2BH3) (M = Zr (5), Hf (6) ) with κ2N, H-NHtBuBH3 and κ3N, H, H-NMe2BH3 ligands. The addition of NHR2BH3 (≥1 equiv) on the mono (dimethylamido) complexes M (η5-C5Me5) Cl2 (NMe2) in hexane leads to the precipitation of the ionic compounds (NHR2) 2BH2M (η5-C5Me5) Cl22 (μ-H) 3 (R2 = Me2, M = Zr (7), Hf (8) ; R2 = HtBu, M = Zr (9), Hf (10) ). Molecular hydride species Cl2 (η5-C5Me5) M (μ-Cl) (μ-H) 2M (η5-C5Me5) Cl (NH2tBu) (M = Zr (11), Hf (12) ) could be isolated from mixtures of complexes M (η5-C5Me5) Cl2 (NMe2) and lower ratios of NH2tBuBH3. The zirconium complex 11 decomposes in solution to give the mononuclear tert-butylamido derivative Zr (η5-C5Me5) Cl2 (NHtBu) (13) along with other byproducts.