Metal versus Ligand Reduction in Ln(3+) Complexes of a Mesitylene-Anchored Tris(Aryloxide) Ligand

The synthesis of 4f(n) Ln(3+) complexes of the tris(aryloxide) mesitylene ligand, (((ArO)-Ar-Ad,Me)(3)mes)(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) ((ArOH)-Ar-Ad,Me)(3)mes yielded the Ln(3+) complexes [(((ArO)-Ar-Ad,Me)(3)mes)Ln] (Ln = La, Ce, Pr, Sm, Yb), 1-Ln. Single electron reduction of each 4f(n) complex, 1-Ln, using potassium yielded the reduced products, [K(2.2.2-cryptand)][(((ArO)-Ar-Ad,Me)(3)mes)Ln] (Ln = La, Ce, Pr, Sm, Yb), 2-Ln. The Sm and Yb complexes have properties consistent with the presence of Ln(2+) ions with traditional 4f(n+1) electron configurations. However, the La, Ce, and Pr complexes appear to formally contain Ln(3+) ions and (((ArO)-Ar-Ad,Me)(3)mes)(4-) ligands. Structural comparisons of the [(((ArO)-Ar-Ad,Me)(3)mes)Ln] and [(((OAr)-O-Ad,Me)(3)mes)Ln](1-) complexes along with UV-vis absorption and EPR spectroscopy as well as density functional theory calculations support these ground state assignments.