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 (R-2 = H-2, Me-2, HtBu). Treatment of the tris(trimethylsilylmethyl) complexes [M(eta(5)-C5Me5)(CH2SiMe3)(3)] with NH3BH3 (3 equiv) gives the seven-coordinate species [M(eta(5)-C5Me5)(NH2BH3)(3)] (M = Zr (1), Hf (2)) with three kappa N-2,H-NH2BH3 ligands. The tris(neophyl) [M(eta(5)-C5Me5)(CH2CMe2Ph)(3)] or tris(dimethylamido) [M(eta(5)-C5Me5)(NMe2)(3)] derivatives react with NHMe2BH3 (>= 3 equiv) to afford bis(dimethylamidoborane) hydride complexes [M(eta(5)-C5Me5)H(NMe2BH3)(2)] (M = Zr (3), Hf (4)) via thermally unstable [M(eta(5)-C5Me5)(NMe2BH3)(3)] species. The reaction of [M(eta(5)-C5Me5)(NMe2)(3)] and NH(2)tBuBH(3) (>= 4 equiv) affords analogous mixed amidoborane hydride derivatives [M(eta(5)-C5Me5)H(NHtBuBH(3))(NMe2BH3)] (M = Zr (5), Hf (6)) with kappa N-2,H-NHtBuBH(3) and kappa N-3,H,H-NMe2BH3 ligands. The addition of NHR2BH3 (>= 1 equiv) on the mono(dimethylamido) complexes [M(eta(5)-C5Me5)Cl-2(NMe2)] in hexane leads to the precipitation of the ionic compounds [(NHR2)(2)BH2][{M(eta(5)-C5Me5)Cl-2}(2)(mu-H)(3)] (R-2 = Me-2, M = Zr (7), Hf (8); R-2 = HtBu, M = Zr (9), Hf (10)). Molecular hydride species [Cl-2(eta(5)-C5Me5)M(mu-Cl)(mu-H)(2)M(eta(5)-C5Me5)Cl(NH(2)tBu)] (M = Zr (11), Hf (12)) could be isolated from mixtures of complexes [M(eta(5)-C5Me5)Cl-2(NMe2)] and lower ratios of NH(2)tBuBH(3). The zirconium complex 11 decomposes in solution to give the mononuclear tert-butylamido derivative [Zr(eta(5)-C5Me5)Cl-2(NHtBu)] (13) along with other byproducts.