Trivalent Rare-Earth-Metal Bis(trimethylsilyl)amide Halide Complexes by Targeted Oxidations

In contrast to previously applied salt metathesis protocols the targeted rare-earth-metal compounds Ln­[N­(SiMe₃)₂]₂(halogenido) were accessed by oxidation of Ln­(II) silylamide precursors. Treatment of Sm­[N­(SiMe₃)₃]₂(thf)₂ with 0.5 equiv of C₂Cl₆ or 0.25 equiv of TeBr₄ in thf and crystallization thereof gave [Sm­{N­(SiMe₃)₂}₂(μ-X)­(thf)]₂ (X = Cl, Br). A similar reaction/crystallization procedure performed with 0.5 equiv of 1,2-diiodoethane gave monomeric Sm­[N­(SiMe₃)₂]₂I­(thf)₂. Switching to Yb­[N­(SiMe₃)₂]₂(thf)₂, the aforementioned oxidants generated monomeric five-coordinate complexes Yb­[N­(SiMe₃)₂]₂X­(thf)₂ (X = Cl, Br, I). The reaction of Eu­[N­(SiMe₃)₂]₂(thf)₂ with 0.5 equiv of C₂Cl₆ in thf yielded the separated ion pair [Eu­{N­(SiMe₃)₂}₃Cl]­[(thf)₅Eu­(μ-Cl)₂Eu­(thf)₅]. Performing the chlorination in <i>n</i>-hexane led to oxidation followed by rapid disproportionation into EuCl₃(thf)_<i>x</i> and Eu­[N­(SiMe₃)₂]₃. The bromination reaction did not afford crystalline material, while the iodination gave crystals of divalent EuI₂(thf)₅. Use of trityl chloride (Ph₃CCl) as the oxidant in thf accomplished the Eu­(III) species [Eu­{N­(SiMe₃)₂}₂(μ-Cl)­(thf)]₂. In situ oxidation of putative [Tm­{N­(SiMe₃)₂}₂(thf)_<i>x</i>] using 0.5 equiv of C₂Cl₆ in thf followed by crystallization from <i>n</i>-hexane led to the formation of a mixture of [Tm­{N­(SiMe₃)₂}₂(μ-Cl)­(thf)]₂ and Tm­[N­(SiMe₃)₂]₃. Switching the oxidant to 0.5 equiv of 1,2-diiodoethane and crystallizing from thf repeatedly afforded the bis-halogenated complex Tm­[N­(SiMe₃)₂]­I₂(thf)<sub>3