Actinide Hydride Complexes as Multielectron Reductants: Analogous Reduction Chemistry from [(C₅Me₅)₂UH]₂, [(C₅Me₅)₂UH₂]₂, and [(C₅Me₅)₂ThH₂]₂

Methods to separate the components of the equilibrium mixture of [(C5Me5)2UH]2 and [(C5Me5)2UH2]2 have been developed that allow their reductive chemistry to be studied. These actinide hydrides can act as four-, six-, and eight-electron reductants depending on the substrate with H2 as the byproduct of a H- → e- + 1/2 H2 redox couple. This hydride reduction chemistry allows complexes of redox-inactive Th4+ such as [(C5Me5)2ThH2]2 to be four- and six-electron reductants. [(C5Me5)2UH]2 and [(C5Me5)2UH2]2 cleanly reduce 2 equiv of PhEEPh (E = S, Se) to form 2 equiv of (C5Me5)2U(SPh)2 and (C5Me5)2U(SePh)2 in an overall four-electron reduction in each case. [(C5Me5)2UH]2 and [(C5Me5)2UH2]2 also effect a six-electron reduction of 3 equiv of 1,3,5,7-cyclooctatetraene to [(C5Me5)(C8H8)U]2(C8H8) and an eight-electron reduction of 2 equiv of PhNNPh to form 2 equiv of the U6+ imido complex (C5Me5)2U(NPh)2. In each reaction, H2 is a byproduct. This hydride-based reduction is also successful with the tetravalent thorium hydride [(C5Me5)2ThH2]2, which reduces 2 equiv of PhSSPh to (C5Me5)2Th(SPh)2 and 3 equiv of C8H8 to [(C5Me5)(C8H8)Th]2(C8H8) with concomitant formation of H2. X-ray crystallographic data are reported on [(C5Me5)2UH]2, [(C5Me5)2UH2]2, and (C5Me5)2U(SePh)2 as well as the thorium reduction products (C5Me5)2Th(SPh)2 and [(C5Me5)(C8H8)Th]2(C8H8).