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.