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, (( ^Ad,Me ArO) 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(SiMe ₃ ) ₂ ) ₃ ] (Ln = La, Ce, Pr, Sm, Yb) with the tris(phenol) ( ^Ad,Me ArOH) ₃ mes yielded the Ln ³⁺ complexes [(( ^Ad,Me ArO) 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)][(( ^Ad,Me ArO) 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 (( ^Ad,Me ArO) ₃ mes) ^4- ligands. Structural comparisons of the [(( ^Ad,Me ArO) ₃ mes)Ln] and [(( ^Ad,Me OAr) 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.