Properties of Amine-Containing Ligands That Are Necessary for Visible-Light-Promoted Catalysis with Divalent Europium.

We describe a study of the influence of amine-containing ligands on the photoredox-relevant properties of EuII toward the rational design of EuII-containing catalysts for visible-light-promoted photoredox reactions. We report our observations of the effects of the degree of functionalization of amines, denticity, and macrocylic ligands on the absorbance of EuII. Ligands that contain secondary amines bathochromically shift the absorbance of EuCl2 relative to ligands that contain primary or tertiary amines. Similarly, ligands of larger denticity have a larger bathochromic shift of the absorbance than ligands of smaller denticity. We observed that macrocyclic ligands have a larger effect on the absorbance of EuCl2 than nonmacrocyclic ligands. Also, we report the photoredox reactivity of four new EuII-containing complexes. These observations are potentially influential in understanding the ligand properties that promote the use of EuII in visible-light-promoted photoredox catalysis.