Expanding Thorium Hydride Chemistry Through Th<sup>2+</sup>, Including the Synthesis of a Mixed-Valent Th<sup>4+</sup>/Th<sup>3+</sup> Hydride Complex

The reactivity of the recently discovered Th<sup>2+</sup> complex [K­(18-crown-6)­(THF)<sub>2</sub>]­[Cp″<sub>3</sub>Th], <b>1</b> [Cp′′ = C<sub>5</sub>H<sub>3</sub>(SiMe<sub>3</sub>)<sub>2</sub>-1,3], with hydrogen reagents has been investigated and found to provide syntheses of new classes of thorium hydride compounds. Complex <b>1</b> reacts with [Et<sub>3</sub>NH]­[BPh<sub>4</sub>] to form the terminal Th<sup>4+</sup> hydride complex Cp″<sub>3</sub>ThH, <b>2</b>, a reaction that formally involves a net two-electron reduction. Complex <b>1</b> also reacts in the solid state and in solution with H<sub>2</sub> to form a mixed-valent bimetallic product, [K­(18-crown-6)­(Et<sub>2</sub>O)]­[Cp″<sub>2</sub>ThH<sub>2</sub>]<sub>2</sub>, <b>3</b>, which was analyzed by X-ray crystallography, electron paramagnetic resonance and optical spectroscopy, and density functional theory. The existence of <b>3</b>, which formally contains Th<sup>3+</sup> and Th<sup>4+</sup>, suggested that KC<sub>8</sub> could reduce [(C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>ThH<sub>2</sub>]<sub>2</sub>. In the presence of 18-crown-6, this reaction forms an analogous mixed-valent product formulated as [K­(18-crown-6)­(THF)]­[(C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>ThH<sub>2</sub>]<sub>2</sub>, <b>4</b>. A similar complex with (C<sub>5</sub>Me<sub>4</sub>H)<sup>1–</sup> ligands was not obtained, but reaction of (C<sub>5</sub>Me<sub>4</sub>H)<sub>3</sub>Th with H<sub>2</sub> in the presence of KC<sub>8</sub> and 2.2.2-cryptand at −45 °C produced two monometallic hydride products, namely, (C<sub>5</sub>Me<sub>4</sub>H)<sub>3</sub>ThH, <b>5</b>, and [K­(2.2.2-cryptand)]­{(C<sub>5</sub>Me<sub>4</sub>H)<sub>2</sub>[η<sup>1</sup>:η<sup>5</sup>-C<sub>5</sub>Me<sub>3</sub>H­(CH<sub>2</sub>)]­ThH]}, <b>6</b>. Complex <b>6</b> contains a metalated tetramethylcyclopentadienyl dianion, [C<sub>5</sub>Me<sub>3</sub>H­(CH<sub>2</sub>)]<sup>2–</sup>, that binds in a tuck-in mode.