Rational Design of a Tripodal Ligand for U(IV): Synthesis and Characterization of a U-Cl Species and Insights into Its Reactivity

The rational design and synthesis of the Trapen ligand (1, tris(2-aminobenzyl)amine) with a tripodal scaffold is reported. Treatment of Trapen with n-BuLi and TMSCl results in the formation of the corresponding complex [(Trapen(TMS))(Li)(3)] (2). In particular, 2 reacts with UCl4 to give the important synthon uranium(IV) complex [U(Trapen(TMS))(Cl)] (3) with all of the nitrogen atoms bound to the uranium(IV) center. Moreover, the pseudohalogen congener [U(Trapen(TMS))(OCP)] (4) or the azide analogue [U(Trapen(TMS))(N-3)] (5) could be obtained when [U(Trapen(TMS))(Cl)] (3) was treated with NaOCP(dioxane)(2)(.5) or NaN3 by a salt metathesis approach. In addition, the reaction of KC8 with [U(Trapen(TMS))(Cl)] (3) did not afford the desired U(III) complex but produced the unexpected bridging diuranium oxo complex [U(Trapen(TMS))(2)(mu-O)] (6). All of the compounds were isolated in the solid state and characterized by NMR, X-ray crystal diffraction, and FT-IR, and UV-vis-NIR as well as elemental analyses and SQUID magnetization measurements. The combined experimental analyses and chemical calculations support all of the formal uranium(IV) species.