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

The synthesis of 4f n Ln3+ 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(SiMe3 )2 )3 ] (Ln = La, Ce, Pr, Sm, Yb) with the tris(phenol) (Ad,Me ArOH)3 mes yielded the Ln3+ 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 Ln2+ ions with traditional 4f n+1 electron configurations. However, the La, Ce, and Pr complexes appear to formally contain Ln3+ 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.