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

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journal contribution
posted on 19.02.2018, 13:04 by Chad T. Palumbo, Dominik P. Halter, Vamsee K. Voora, Guo P. Chen, Alan K. Chan, Megan E. Fieser, Joseph W. Ziller, Wolfgang Hieringer, Filipp Furche, Karsten Meyer, William J. Evans
The synthesis of 4fn 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), 1-Ln. Single electron reduction of each 4fn complex, 1-Ln, using potassium yielded the reduced products, [K­(2.2.2-cryptand)]­[((Ad,MeArO)3mes)­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 4fn+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.