Synthesis of Bis(2,6-Diadamantyl Aryloxide) Ln(II) Complexes of Samarium, Europium, and Ytterbium and Their Ln(III) Precursors

The syntheses of Ln­(II) bis(aryloxide) complexes of Sm, Eu, and Yb have been examined with the bulky aryloxide ligand (OC6H2-2,6-Ad2-4- t Bu)1– [(OAr*)1–; Ad = 1-adamantyl]. These LnII(OAr*)2(THF)2 complexes were pursued for comparison with the tris(aryloxide) Ln­(II) complexes [LnII(OAr*)3]1– (Ln = La, Ce, Nd, Gd, Dy, and Lu), which have 4fn5d1 electron configurations, and with 4f14 [YbII(OAr*)3]1–. Although the Ln­(II) chemistry of Sm, Eu, and Yb is often similar since they all adopt 4f n+1 electron configurations, their chemistry is surprisingly diverse with (OAr*)1–. Reactions of LnIII2(THF)2 with KOAr* in THF form the bis(aryloxide) Ln­(II) complexes LnII(OAr*)2(THF)2, 1-Ln, that were characterized by X-ray diffraction for 1-Sm and 1-Yb, but crystals of 1-Eu have been elusive. Reduction of the tris(aryloxide) Sm­(III) complex, SmIII(OAr*)3, 2-Sm, prepared from SmIII(NR2)3 (R = SiMe3) and HOAr* in refluxing toluene, generated the bis(aryloxide) complex, 1-Sm, and KOAr* rather than a Sm analogue of [YbII(OAr*)3]1–. Reduction of EuIII(OAr*)3, 2-Eu, prepared from EuCl3 with KOAr* in THF, caused an immediate dark blue-purple to bright red-orange color change, but crystals of the product were elusive. Neither reduction of TmIII(OAr*)3, 2-Tm, nor the reaction of TmIII2(DME)3 with KOAr* provided crystalline Tm­(II) complexes.