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 NHR 2 BH 3 (R 2 = H 2 , Me 2 , H t Bu). Treatment of the tris(trimethylsilylmethyl) complexes [M(η 5 -C 5 Me 5 )(CH 2 SiMe 3 ) 3 ] with NH 3 BH 3 (3 equiv) gives the seven-coordinate species [M(η 5 -C 5 Me 5 )(NH 2 BH 3 ) 3 ] (M = Zr ( 1 ), Hf ( 2 )) with three κ 2 N,H -NH 2 BH 3 ligands. The tris(neophyl) [M(η 5 -C 5 Me 5 )(CH 2 CMe 2 Ph) 3 ] or tris(dimethylamido) [M(η 5 -C 5 Me 5 )(NMe 2 ) 3 ] derivatives react with NHMe 2 BH 3 (≥3 equiv) to afford bis(dimethylamidoborane) hydride complexes [M(η 5 -C 5 Me 5 )H(NMe 2 BH 3 ) 2 ] (M = Zr ( 3 ), Hf ( 4 )) via thermally unstable [M(η 5 -C 5 Me 5 )(NMe 2 BH 3 ) 3 ] species. The reaction of [M(η 5 -C 5 Me 5 )(NMe 2 ) 3 ] and NH 2 t BuBH 3 (≥4 equiv) affords analogous mixed amidoborane hydride derivatives [M(η 5 -C 5 Me 5 )H(NH t BuBH 3 )(NMe 2 BH 3 )] (M = Zr ( 5 ), Hf ( 6 )) with κ 2 N,H -NH t BuBH 3 and κ 3 N,H,H -NMe 2 BH 3 ligands. The addition of NHR 2 BH 3 (≥1 equiv) on the mono(dimethylamido) complexes [M(η 5 -C 5 Me 5 )Cl 2 (NMe 2 )] in hexane leads to the precipitation of the ionic compounds [(NHR 2 ) 2 BH 2 ][{M(η 5 -C 5 Me 5 )Cl 2 } 2 (μ-H) 3 ] (R 2 = Me 2 , M = Zr ( 7 ), Hf ( 8 ); R 2 = H t Bu, M = Zr ( 9 ), Hf ( 10 )). Molecular hydride species [Cl 2 (η 5 -C 5 Me 5 )M(μ-Cl)(μ-H) 2 M(η 5 -C 5 Me 5 )Cl(NH 2 t Bu)] (M = Zr ( 11 ), Hf ( 12 )) could be isolated from mixtures of complexes [M(η 5 -C 5 Me 5 )Cl 2 (NMe 2 )] and lower ratios of NH 2 t BuBH 3 . The zirconium complex 11 decomposes in solution to give the mononuclear tert -butylamido derivative [Zr(η 5 -C 5 Me 5 )Cl 2 (NH t Bu)] ( 13 ) along with other byproducts.