Coordination chemistry of the early actinides in various oxidation states (+III to +V) with benzamidinate ligand

Compared to the lanthanides, which primarily exhibit the oxidation state +III, the early actinides up to plutonium can display a diverse range of oxidation states spanning from +I to +VII. In the context of exploring oxidation states and covalency of actinides complexes, it would be intriguing and valuable to compare compounds that share the same molecular scaffold but differ in their oxidation states. Amidinate ligands have been widely studied in the field of coordination chemistry due to their excellent capability to stabilize transition metal complexes in various oxidation states, including some early actinide metal complexes. Thus, N,N'-diisopropylbenzamidinate (iPr2BA) was selected as an appropriate model N-donor ligand for the current study. Our goal was to test the ligand’s ability to stabilize actinides in various oxidation states as well as its synthetic flexibility.
In order to gain insight into the bonding trends and electronic structures of each oxidation state, series of tetravalent actinide tris-iPr2BA chloride complexes [AnIVCl(iPr2BA)3] (An = Th, U, Np) were synthesized via salt metathesis, followed by subsequent synthetic transformations to obtain (pseudo)halide congeners and complexes in the +III and +V oxidation states. The synthesized complexes were analyzed by single crystal X-ray diffraction (SC-XRD) to examine their molecular structures in solid state. Furthermore, the combination of paramagnetic NMR experiments in solution and quantum chemical calculations enabled the comparison of the overall degree of covalency between different oxidation states within the same tris-amidinate complex scaffold.