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

The scandium dialkyl complex [Cp'Sc(CH(2)SiMe(3))(2)(THF)] (1-Sc, Cp' = C(5)Me(4)SiMe(3)) reacts rapidly with ammonia at room temperature to afford selectively a trinuclear hexaamido complex [Cp'Sc(mu-NH(2))(2)](3) (3-Sc) with release of SiMe(4). The reaction of the lutetium dialkyl complex [Cp'Lu(CH(2)SiMe(3))(2)(THF)] (1-Lu) with ammonia under the same conditions gives the analogous hexaamido Lu complex [Cp'Lu(mu-NH(2))(2)](3) (3-Lu) as a major product (92%) together with a tetranuclear octaamido complex [Cp'Lu(mu-NH(2))(2)](4) (4-Lu) as a minor product (8%). In contrast, reaction of tetranuclear rare-earth metal octahydride complexes [Cp'Ln(mu-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)(mu-NH(2))(6)(mu(3)-NH(2))(mu(4)-H)] (Ln = Y (5-Y), Lu (5-Lu)), in which a mu(4)-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.