2-Trimethylsilylamidopyridine complexes of uranium(IV)

Reaction of 2-trimethylsilylaminopyridine with n-butyl lithium or potassium hydride affords the alkali metal ligand transfer reagents [{Li(C5H4N-2-NSiMe3)(THF)}2] (1) and [K(C5H4N-2-NSiMe3)(THF)0.25] (2), respectively. The solid state structure of complex 1 was determined revealing a dimeric structure in the solid state constructed around a centrosymmetric trans-μ-amide-lithium Li2N2 core. The synthetic utility of 1 and 2 was demonstrated by their reactions with UCl4 and UI4(OEt2)2 to give the corresponding uranium(IV) complexes [U(Cl)(C5H4N-2-NSiMe3)3] (3) and [U(I)(C5H4N-2-NSiMe3)3] (4), respectively. Crystallographic analyses of 3 and 4 revealed heteroleptic monomeric complexes where all three trimethylsilyl groups are ‘up’ with respect to the halide co-ligand. The three 2-trimethylsilylamidopyridine ligands in 3 and 4 are arranged in a twist-propeller orientation around each uranium centre giving approximate C3 symmetry down the uranium-halide bond vector but crystals of 3 and 4 are racemic. Attempts to reduce 4 to give the hypothetical uranium(III) complex [U(C5H4N-2-NSiMe3)3] were unsuccessful and instead the only product that could be isolated from a variety of reactions was the homoleptic uranium(IV) complex [U(C5H4N-2-NSiMe3)4] (5). Complex 5 exhibits fluxionality in solution which was studied by variable-temperature 1H NMR spectroscopy revealing decoalescence at low temperature which is consistent with the presence of a structure in solution that is analogous to the solid state structure. Complexes 1–5 have been characterised by NMR and FTIR spectroscopy, Evans method magnetic moment determinations, CHN microanalyses, and X-ray crystallography for 1 and 3–5.