Amidophenolate Lanthanide Complexes and Their Multielectron Reactivity

A general approach to achieving multielectron reactivity with redox-restricted lanthanide complexes is to utilize redox-active ligands, which allow for facile electron transfer at the ligand throughout a reaction. Our group has successfully utilized an iminoquinone (iq) ligand capable of undergoing two-electron reduction events to form an iminosemiquinone (isq) and an amidophenolate (ap), respectively, on a variety of metals to achieve multielectron reactivity. Here, we report the synthesis and characterization of two tris-ligated lanthanide complexes, [Nd(ap)₃]K₃ (<b>Nd-L3</b>) and [Yb(ap)₃]K₃ (<b>Yb-L3</b>), and a bis-ligated complex, [Yb(ap)₂]K (<b>Yb-L2</b>). Compounds <b>Nd-L3</b> and <b>Yb-L3</b> were treated with elemental sulfur. In the presence of S₈, rapid ligand oxidation was observed, leading to the dissociation of a potassium iminosemiquinone ligand and the formation of a S₇^2- chain. Alternatively, when S₈ was added to <b>Yb-L2</b>, ligand oxidation was noted with the formation of a twist-boat metallocycle, [Yb(S₅)(isq)₂](K18c6) (<b>Yb-S</b>_<b>5</b>). All complexes were fully characterized by using ¹H NMR spectroscopy, electronic absorption spectroscopy, and X-ray crystallography to fully assign ligand oxidation states.