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.
A versatile, monoanionic, chelating (bis)carbene ligand (2) was used to prepare a thorium dihalide complex (3) and a direduced-bpy derivative (4). CASSCF calculations suggest the involvement of a multiconfigurational open-shell singlet, with the main configuration corresponding to a Th(III)bpy(−1) (f 1 π* 1 ) electronic structure. The reactivity of 4 was explored in various transformations, including reactions with carbonyls and organic azides; the latter gave rise to an unusual terminal Th-imido bpy complex (6).
The bis(NHC)borate-supported thorium-bis(mesitylphosphido) complex (1) undergoes reversible intramolecular C-H bond activation enabling the catalytic hydrophosphination of unactivated internal alkynes. Catalytic and stoichiometric experiments support a mechanism involving reactive Th-NHC metallacycle intermediates (Int and 2).
The synthesis, characterization, and reductive elimination reactivity of a bis(NHC)borate-supported thorium bis(phosphido) complex (2 Mes ) is described. Treating 2 Mes with 2,2′-bipyridine leads to the reductive elimination of dimesityldiphosphine (4) and the formation of the previously reported NHC−thorium−bpy complex (3). The kinetics of the bpy-induced reductive elimination were studied by 31 P NMR and suggest the presence of an intermediate. Treatment with alternative oxidants also leads to diphosphine elimination, but the corresponding thorium species have not been isolated cleanly. Additional primary (2 Ph ) and secondary (2 PPh2 ) Th−bis(phosphido) complexes were synthesized but do not demonstrate the same facile reductive elimination as 2 Mes .
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