The Curious\nCase of [AnH(NR<sub>2</sub>)<sub>3</sub>] (An = Th, U; R = SiMe<sub>3</sub>): Two Monomeric Actinide Hydrides\nRevisited

The reaction of AnCl<sub>4</sub>(DME)<sub><i>x</i></sub> (An = Th, <i>x</i> = 2; An = U, <i>x</i> = 0)\nwith 4 equiv of NaNR<sub>2</sub> (R = SiMe<sub>3</sub>) in THF at\n65 °C results in the formation of [An{N(R)(SiMe<sub>2</sub>CH<sub>2</sub>)}(NR<sub>2</sub>)<sub>2</sub>] (An = U, <b>1</b>; An\n= Th, <b>2</b>), and not the reported monomeric actinide hydrides,\n[AnH(NR<sub>2</sub>)<sub>3</sub>], as expected. Both complexes <b>1</b> and <b>2</b> were characterized by X-ray crystallography.\nSurprisingly, their unit cell parameters are remarkably close to those\nreported for [AnH(NR<sub>2</sub>)<sub>3</sub>], suggesting that the\noriginal crystals of [AnH(NR<sub>2</sub>)<sub>3</sub>] were, in fact,\n[An{N(R)(SiMe<sub>2</sub>CH<sub>2</sub>)}(NR<sub>2</sub>)<sub>2</sub>], but were misidentified. Reduction of <b>1</b> with 1.1 equiv\nof KC<sub>8</sub> in THF, in the presence of 1 equiv of 2.2.2-cryptand,\nresults in the formation of [K(2.2.2-cryptand)][U{N(R)(SiMe<sub>2</sub>CH<sub>2</sub>)}(NR<sub>2</sub>)<sub>2</sub>] (<b>3</b>) in\ngood yield. Likewise, the reaction of <b>1</b> with 1 equiv\nof bis(diisopropylamino)cyclopropenylidene (BAC) results in the formation\nof the BAC adduct, [(BAC)U{N(R)(SiMe<sub>2</sub>CH<sub>2</sub>)}(NR<sub>2</sub>)<sub>2</sub>] (<b>4</b>), in moderate yield. Finally,\nthe addition of H<sub>2</sub> (10 bar) to <b>2</b> in C<sub>6</sub>D<sub>6</sub> at room temperature results in the formation\nof the targeted monomeric hydride, [ThH(NR<sub>2</sub>)<sub>3</sub>], in 32% yield, according to integrations against an internal standard.\nHowever, removal of the H<sub>2</sub> atmosphere results in rapid\nreformation of <b>2</b>. In contrast, the addition of H<sub>2</sub> (10 bar) to <b>1</b> in C<sub>6</sub>D<sub>6</sub> at\nroom temperature results in no apparent reaction.