The reactivity of the recently discovered Th2+ complex [K(18-crown-6)(THF)(2)] [Cp-3 '' Th], 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-3 '' ThH, 2, a reaction that formally involves a net two-electron reduction. Complex 1 also reacts in the solid state and in solution with H-2 to form a mixed-valent bimetallic product, [K(18-crown-6)(Et(2)Q)][Cp-2 '' ThH2](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 [(C2Me5)(2)ThH2](2). In the preSence of 18-croWn-6, this reaction forms an analogous mixed-valent product formulated as [K(18-crown-6)(THF)] [(C5Me5)(2)ThH2,]2; 4: A similar complex with (C5Me4H)(1-) ligands was not obtained, but reaction of (C5Me4H)(3)Th with H-2 in the presence of KC8 and 2.2'.2-cryptand at -45 degrees C produced two monometallic hydride products, namely, (C2Me4H)(3)ThH, 5, and [K(2.2.2-cryptand)]-[(C5Me4H)(2)[eta(1):eta(5)-C5Me3H(CH2)]ThHD, 6. Complex 6 contains a metalated tetramethylcyclopentadienyl dianion, [C5Me3H(CH2)](2-), that binds in a tuck-in mode.