Metal versus Ligand Reduction in Ln³⁺ Complexes of a Mesitylene-Anchored Tris(Aryloxide) Ligand

The synthesis of 4f^<i>n</i> Ln³⁺ complexes of the tris­(aryloxide) mesitylene ligand, ((^Ad,MeArO)₃mes)^3–, with Ln = La, Ce, Pr, Sm, and Yb, and their reduction with potassium have revealed that this ligand system can be redox active with some metals. Protonolysis of [Ln­(N­(SiMe₃)₂)₃] (Ln = La, Ce, Pr, Sm, Yb) with the tris­(phenol) (^Ad,MeArOH)₃mes yielded the Ln³⁺ complexes [((^Ad,MeArO)₃mes)­Ln] (Ln = La, Ce, Pr, Sm, Yb), <b>1-Ln</b>. Single electron reduction of each 4f^<i>n</i> complex, <b>1-Ln</b>, using potassium yielded the reduced products, [K­(2.2.2-cryptand)]­[((^Ad,MeArO)₃mes)­Ln] (Ln = La, Ce, Pr, Sm, Yb), <b>2-Ln</b>. The Sm and Yb complexes have properties consistent with the presence of Ln²⁺ ions with traditional 4f^<i>n</i>+1 electron configurations. However, the La, Ce, and Pr complexes appear to formally contain Ln³⁺ ions and ((^Ad,MeArO)₃mes)^4– ligands. Structural comparisons of the [((^Ad,MeArO)₃mes)­Ln] and [((^Ad,MeOAr)₃mes)­Ln]^1– complexes along with UV–vis absorption and EPR spectroscopy as well as density functional theory calculations support these ground state assignments