The Curious Case of [AnH(NR 2 ) 3 ] (An = Th, U; R = SiMe 3 ): Two Monomeric Actinide Hydrides Revisited
The reaction of AnCl 4 (DME) x (An = Th, x = 2; An = U, x = 0) with 4 equiv of NaNR 2 (R = SiMe 3 ) in THF at 65 °C results in the formation of [An{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] (An = U, 1; An = Th, 2), and not the reported monomeric actinide hydrides, [AnH(NR 2 ) 3 ], as expected. Furthermore, both complexes 1 and 2 were characterized by X-ray crystallography. Surprisingly, their unit cell parameters are remarkably close to those reported for [AnH(NR 2 ) 3 ], suggesting that the original crystals of [AnH(NR 2 ) 3 ] were, in fact, [An{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ], but were misidentified. Reduction of 1 with 1.1 equiv of KC 8 in THF, in the presence of 1 equiv of 2.2.2-cryptand, results in the formation of [K(2.2.2-cryptand)][U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] (3) in good yield. Likewise, the reaction of 1 with 1 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) results in the formation of the BAC adduct, [(BAC)U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] (4), in moderate yield. Finally, the addition of H 2 (10 bar) to 2 in C 6 D 6 at room temperature results in the formation of the targeted monomeric hydride, [ThH(NR 2 ) 3 ], in 32% yield, according to integrations against an internal standard. However, removal of the H 2 atmosphere results in rapid reformation of 2. In contrast, the addition of H 2 (10 bar) to 1 in C 6 D 6 at room temperature results in no apparent reaction.