Synthesis and characterization of tantalum(V) metallaheterocycle [([Me.sub.2]N).sub.3]TaN(Si[Me.sub.3])Si[Me.sub.2]C[H.sub.2] and chloro-mixed-amide [([Me.sub.2]N).sub.3]Ta(Cl)[[N(Si[Me.sub.3]).sub.2]]

A new mixed-amido complex (Me2N)3Ta(C1)[N[(Si[Me.sub.3]).sub.2]] (1) was prepared from the reaction of [([Me.sub.2]N).sub.3]Ta[Cl.sub.2] with 1 equiv, of LiN[(Si[Me.sub.3]).sub.2]. The reactions of 1 with 1 equiv, of LiN[(Si[Me.sub.3]).sub.2] or [([Me.sub.2]N).sub.3]Ta [Cl.sub.2] with 2 equiv, of LiN[(Si[Me.sub.3]).sub.2] gave [([Me.sub.2]N).sub.3]TaN(Si[Me.sub.3])Si[Me.sub.2]C[H.sub.2] (2) with a four-membered metallaheterocyclic ring through [gamma]-hydrogen abstraction. In the solid state, 1 adopts a distorted trigonal bipyramidal geometry with the -N[(Si[Me.sub.3]).sub.2] and -C1 ligands in the equatorial and axial positions, respectively. The X-ray structure of 2 reveals that it is in a distorted trigonal bipyramidal geometry with a planar metallaheterocyclic ring. Key words: tantalum, [gamma]-hydrogen abstraction, C-H activation, amido complexes, metallacycle.