Selective ammonolysis of half-sandwich rare-earth metal dialkyl and polyhydride complexes: synthesis of polyamido rare-earth complexes having novel structures

Abstract

The scandium dialkyl complex [Cp′Sc(CH₂SiMe₃)₂(THF)] (1-Sc, Cp′ = C₅Me₄SiMe₃) reacts rapidly with ammonia at room temperature to afford selectively a trinuclear hexaamido complex [Cp′Sc(μ-NH₂)₂]₃ (3-Sc) with release of SiMe₄. The reaction of the lutetium dialkyl complex [Cp′Lu(CH₂SiMe₃)₂(THF)] (1-Lu) with ammonia under the same conditions gives the analogous hexaamido Lu complex [Cp′Lu(μ-NH₂)₂]₃ (3-Lu) as a major product (92%) together with a tetranuclear octaamido complex [Cp′Lu(μ-NH₂)₂]₄ (4-Lu) as a minor product (8%). In contrast, reaction of tetranuclear rare-earth metal octahydride complexes [Cp′Ln(μ-H)₂]₄(THF) (Ln = Y (2-Y), Lu (2-Lu)) with ammonia under similar conditions yields selectively the heptaamido/monohydrido complexes [(Cp′Ln)₄(μ-NH₂)₆(μ₃-NH₂)(μ₄-H)] (Ln = Y (5-Y), Lu (5-Lu)), in which a μ₄-H ligand remains at the center of the tetrahedral metal framework. Exposure of heptaamido/monohydrido complex 5-Lu to an ammonia atmosphere at room temperature for a long time (two days) affords the octaamido complex 4-Lu quantitatively. The molecular structures of 3-Sc, 3-Lu, 4-Lu, 5-Y, and 5-Lu have been determined by X-ray analyses.