Tuning Selectivity and Stability in Heteroleptic Lanthanide Adducts by Ligand Design.

Terdentate ligands - and their heteroleptic [Ln(hfac)] complexes (Ln = La, Eu, Gd, Er, or Y; H-hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) exhibit multifactorial correlations between the ligand's structural frameworks, including their level of preorganization and steric congestion and their affinities and selectivities for catching the trivalent lanthanide containers [Ln(hfac)]. The polyaromatic ligand scaffolds could be stepwise modulated via lanthanide-template synthetic strategies, using intermolecular rhodium-catalyzed insertion reactions. The increasing level of preorganization along the → → series leads to a duality in which larger thermodynamic formation constants with lanthanides in CDCl are accompanied by an unexpected decrease in the Ln-N affinities in the solid state, which could be assigned to a limited match between the lanthanide size and the enlarged preorganized cavities.