Synthesis of Cp* Terphenylamido U(III) Iodide Complexes with a Substitutable Iodide Position to Generate Terminal U(III)–(κ 3 -BH 4 ) Complexes

Reaction of Cp*UI2(THF)3 (Cp* = pentamethylcyclopentadienide; THF = tetrahydrofuran) with NaR3TerNH (R3Ter = 2,6(2,4,6-R3C6H2)2C6H3; R = Me, Et, iPr) gave the U(III) monoiodide complexes Cp*(R3TerNH)UI (R = Me, 1-Me; R = Et, 2-Et; R = iPr, 3-iPr). These complexes contain a functionalizable iodide position which reacts favorably with NaBH4 to give the κ3-borohydride complexes Cp*(R3TerNH)U(H3BH) (R = Me, 4-Me; R = Et, 5-Et; R = iPr, 6-iPr). All compounds were experimentally characterized by SC-XRD, 1H and 11B NMR spectroscopy as well as UV–vis–NIR and FTIR analyses. DFT calculations corroborate the experimental findings, confirming the 5f3 U(III) configuration across the entire series and revealing an increased U 5f orbital contribution in the borohydride derivatives. All compounds exhibit small but non-negligible U(III)–(η6-arene) δ-back-bonding interactions arising from the unpaired 5f electrons. Calculated steric parameters show progressively greater shielding of the U(III) center with increasing bulk of the terphenyl substituents from Me to iPr.