Synthesis and structural characterization of novel mixed-valent samarium and divalent ytterbium and europium complexes supported by amine bis(phenolate) ligands

Abstract

The amine-elimination reactions of Ln[N(SiMe₃)₂]₂(THF)₂ (Ln = Sm, Yb and Eu) with amine bis(phenol)s (L¹H₂ = [BuⁿN(CH₂-2-OC6H₂-3,5-Bu^t₂)₂]H₂; L²H₂ = [Me₂NCH₂CH₂N(CH₂-2-OC₆H₂-3,5-Bu^t₂)₂]H₂) were investigated. It was found that the number of heteroatom(s) in the ligands has a profound effect on the reaction outcome for the samarium systems. Reaction of the tetradentate diamino-bis(phenol)s L²H₂ with Sm[N(SiMe₃)₂]₂(THF)₂ afforded a yellow solution, which indicated the complete oxidation of the Sm(II) species, yellow being the characteristic color of Sm(III) species, while the same reaction with Eu[N(SiMe₃)₂]₂(THF)₂ gave a divalent complex with a dimeric structure (EuL²)₂1. Using the tridentate amine bis(phenol)s L¹H₂ as the reagent, the novel mixed-valent samarium complex Sm^III₂Sm^IIL¹₄2 was prepared by the same reaction. Both reactions of L¹H₂ with Yb[N(SiMe₃)₂]₂(THF)₂ and Eu[N(SiMe₃)₂]₂(THF)₂ yielded the normal divalent lanthanide complexes: monomeric complex for Yb(II), YbL¹(THF)₃3 and dimeric complex for Eu(II), (EuL¹)₂4. All of the complexes are well characterized with elemental analyses, IR and ¹H NMR spectra for 1, 3 and 4, as well as X-ray crystal structure determination in the cases of complexes 1, 2, and 3.