Expanding Thorium Hydride Chemistry Through Th2+, Including the Synthesis of a Mixed-Valent Th4+/Th3+ Hydride Complex

The reactivity of the recently discovered Th2+ complex [K­(18-crown-6)­(THF)2]­[Cp″3Th], 1 [Cp′′ = C5H3(SiMe3)2-1,3], with hydrogen reagents has been investigated and found to provide syntheses of new classes of thorium hydride compounds. Complex 1 reacts with [Et3NH]­[BPh4] to form the terminal Th4+ hydride complex Cp″3ThH, 2, a reaction that formally involves a net two-electron reduction. Complex 1 also reacts in the solid state and in solution with H2 to form a mixed-valent bimetallic product, [K­(18-crown-6)­(Et2O)]­[Cp″2ThH2]2, 3, which was analyzed by X-ray crystallography, electron paramagnetic resonance and optical spectroscopy, and density functional theory. The existence of 3, which formally contains Th3+ and Th4+, suggested that KC8 could reduce [(C5Me5)2ThH2]2. In the presence of 18-crown-6, this reaction forms an analogous mixed-valent product formulated as [K­(18-crown-6)­(THF)]­[(C5Me5)2ThH2]2, 4. A similar complex with (C5Me4H)1– ligands was not obtained, but reaction of (C5Me4H)3Th with H2 in the presence of KC8 and 2.2.2-cryptand at −45 °C produced two monometallic hydride products, namely, (C5Me4H)3ThH, 5, and [K­(2.2.2-cryptand)]­{(C5Me4H)2[η1:η5-C5Me3H­(CH2)]­ThH]}, 6. Complex 6 contains a metalated tetramethylcyclopentadienyl dianion, [C5Me3H­(CH2)]2–, that binds in a tuck-in mode.