Molecular Thorium Compounds with Dichalcogenide Ligands: Synthesis, Structure, 77Se NMR Study, and Thermolysis.

A series of dimeric thorium disulfides and diselenides have been prepared with sterically undemanding ancillary ligands. Five complexes, (py)6Th2I4(μ2-S2)2, (py)6Th2Br2(SC6F5)2(μ2-S2)2, (py)6Th2I4(μ2-Se2)2, (py)6Th2I2(SC6F5)2(μ2-Se2)2, and (py)6Th2Br2(SC6F5)2(μ2-Se2)2, were isolated in high yields by first reducing mixtures of I2, F5C6SSC6F5, PhSeSePh, or PhSSPh, and PhSeBr with elemental Th, followed by in situ ligand-based redox reactions with elemental sulfur or selenium. These are the first examples of thorium compounds with bridging dichalcogenide ligands. Attempts to prepare chloride derivatives gave mixtures of (py)4ThCl4 and either (py)6Th2Cl2(SC6F5)2(μ2-S2)2 or (py)8Th4Se4(SePh)4(SC6F5)4. All products were characterized by single-crystal and powder X-ray diffraction and IR, UV-visible, and NMR spectroscopy. A computational analysis of experimental 77Se NMR chemical shifts reveals that the solvated dimeric structures with two bridging dichalcogenides are maintained in solution. Thermolysis of (py)6Th2I4(μ2-Se2)2 leads to reduction of the bridging Se22- moieties, oxidation of the I- ligand, and formation of solid-state ThSe2 and I2.