The suitability of aryloxide ligands for stabilizing +2 oxidation states of the rare earth elements, Ln, i.e. Sc, Y, and the lanthanides, has been examined for comparison with the silylcyclopentadienyl and amide complexes, (Cp'3Ln)1−, (Cp''3Ln) 1−, and [Ln(NR2)3]1− [Cp' = (C5H4R); Cp'' = (C5H3R2-1,3); R = SiMe3]. The trivalent rare-earth metal aryloxide precursors, Ln(OAr′)3, (OAr′ = OC6H2tBu2-2,6-Me-4; Ln = Sc, Y, Gd, Ho, Er, Lu) were synthesized from the corresponding metal triflates, Ln(OSO2CF3)3 or trichlorides. Reductions of THF solutions of Ln(OAr′)3 with KC8 in the presence of 2.2.2-cryptand (crypt) at −30 °C yielded dark-colored solutions except for Ln = Gd. For Ln = Sc and Y, the EPR spectra at 77 K are characteristic of the Ln2+ ions: an eight-line spectrum for Sc (gave = 2.01 and Aave = 291 G) and a two-line spectrum for Y (g∥ = 1.99, g⊥ = 1.97, Aave = 154 G). The Y2+ aryloxide product decomposes within sixty seconds at room temperature, while the Sc analog persists up to 40 min at room temperature. The Sc complex was characterized by X-ray crystallography as [K(crypt)][Sc(OAr′)3] and constitutes only the second structurally characterized complex of Sc2+. The accessibility and stability of these aryloxide complexes as a function of metal will be compared with stability trends with the other ligands cited above for Ln2+ complexes using electronic and steric arguments.

Exploring aryloxide ligands in the synthesis of complexes of new +2 ions of the rare-earth metals

256th National Meeting (2018)

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