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 [Li3(NN‘3)(THF)3] [NN‘3 = N(CH2CH2NSiMe2But)3] with AnCl4
(An = U, Th) followed by sublimation gives 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 H3(NN‘3) and [U(NEt2)4]
and from [Th(NN‘3)Cl] and [Li(NEt2)]. In each case, the complexes [U(NN‘3)X] (X = Cl, Br, I, NEt2) are shown
by X-ray crystallography to contain a triamidoamine ligand disposed with 3-fold symmetry about the metal center.
The structures are distorted from trigonal bipyramidal by displacement of the uranium atoms out of the equatorial
plane of the three amido nitrogen atoms by ca. 0.8 Å. The ligand backbone is distorted in such a manner as to
cause the tert-butyldimethylsilyl groups to encircle the equatorial plane of the metal atom rather than surround
the apical coordination site as is observed in the transition metal complexes of this type. Variation of the auxiliary
ligand has little effect on the orientation, bond lengths, and angles within the (triamidoamine)uranium fragment.
The tert-butydimethysilyl-substituted triamidoamine ligand is thus ideally suited for coordination to large metals
since it stabilizes the formation of 3-fold symmetric structures while also allowing reactivity at the fifth coordination
site.