In-Plane Thorium(IV), Uranium(IV), and Neptunium(IV) Expanded Porphyrin Complexes.

Here we report the first series of in-plane thorium(IV), uranium(IV), and neptunium(IV) expanded porphyrin complexes. These actinide (An) complexes were synthesized using a hexa-aza porphyrin analogue, termed dipyriamethyrin, and the nonaqueous An(IV) precursors, ThCl4(DME)2, UCl4, and NpCl4(DME)2. The molecular and electronic structures of the ligand, each An(IV) complex, and a corresponding uranyl(VI) complex were characterized using nuclear magnetic resonance (NMR) and UV-vis spectroscopies as well as single-crystal X-ray diffraction analysis. Computational analyses of these complexes, coupled to their structural features, provide support for the conclusion that a greater degree of covalency in the ligand-cation orbital interactions arises as the early actinide series is traversed from Th(IV) to U(IV) and Np(IV). The axial ligands in the present An(IV) complexes proved labile, allowing for the electronic features of these complexes to be further modified.