Complexes of triamidoamines with the early actinides. Synthetic routes to monomeric compounds of tetravalent uranium and thorium containing halide and amide ligands

The reaction of the lithiated triamidoamine [Li-3(NN'(3))(THF)(3)] [NN; = N (CH2CH2NSiMe2But)(3)] with AnCl(4) (An = U, Th) followed by sublimation giv es monomeric [An(NN'3)Cl]. Reaction of these complexes with SiMe3X (X = Br, I) gives [An(NN'3)X]. The amido derivatives [An(NN'3)(NEt2)] are prepared from H-3(NN;) and [U(NEt2)(4)] and from [Th(NN;)CI] and [Li(NEt2)]. In each case, the complexes [U(NN;)X] (X = Cl, Br, I, NEt2) are shown by X-ray cry stallography to contain a triamidoamine ligand disposed with 3-fold symmetr y about the metal center. The structures are distorted from trigonal bipyra midal by displacement of the uranium atoms out of the equatorial plane of t he three amido nitrogen atoms by ca. 0.8 Angstrom. The ligand backbone is d istorted in such a manner as to cause the tert-butyldimethylsilyl groups to encircle the equatorial plane of the metal atom rather than surround the a pical coordination site as is observed in the transition metal complexes of this type. Variation of the auxiliary ligand has little effect on the orie ntation, bond lengths, and angles within the (triamidoamine)uranium fragmen t. The tert-butydimethysilyl-substituted triamidoamine ligand is thus ideal ly suited for coordination to large metals since it stabilizes the formatio n of 3-fold symmetric structures while also allowing reactivity at the fift h coordination site.