Synthesis and structure of diamido ether uranium(iv) and thorium(iv) halide “ate” complexes and their conversion to salt-free bis(alkyl) complexes

Abstract

The high-yield synthesis, spectroscopic and structural determination of three new uranium(IV) and thorium(IV) “ate” complexes supported by three different diamido ether ligands are reported. The reaction of Li₂[2,6-ⁱPr₂PhN(CH₂CH₂)]₂O (Li₂[^DIPPNCOCN]) with 1 equiv. of UCl₄ in THF generates [^DIPPNCOCN]UCl₃Li(THF)₂ (1), while reaction in toluene/ether gives salt-free [^DIPPNCOCN]UCl₂·½C₇H₈ (2), which was identified by paramagnetically shifted ¹H NMR. Reaction of 0.5 equiv. of {[^tBuNON]UCl₂}₂ ([^tBuNON] = [(CH₃)₃CN(Si(CH₃)₂)]₂O²⁻) with 3.5 equiv. LiI in toluene and a minimal amount of THF results in [^tBuNON]UI₃Li(THF)₂ (3) and is very similar in structure to 1. {[^MesNON]ThCl₃Li(THF)}₂ (4), a dimeric complex with a Th₂Li₂Cl₆ core, is prepared by reaction of Li₂[2,4,6-Me₃PhN(Si(CH₃)₂)]₂O (Li₂[^MesNON]) with ThCl₄ in THF. The analogous reaction in toluene did not yield the salt-free complex but rather a sterically crowded diligated compound, [^MesNON]₂Th (5), which was also structurally characterized. Complex 5 was prepared rationally by reacting 2 equiv. Li₂[^MesNON] with ThCl₄ in toluene. The reaction of 1 and 3 with 2 equiv. of LiCH₂Si(CH₃)₃ generates the stable, salt-free organoactinides [^DIPPNCOCN]U(CH₂Si(CH₃)₃)₂ (6) and [^tBuNON]U(CH₂Si(CH₃)₃)₂ (7). Complex 6 was structurally characterized. These reactions illustrate the viability of “ate” complexes as useful synthetic precursors.