Metal-Ligand Cooperative Effect on Intramolecular Electron Transfer in Macrocycle-Encircled Copper-Oxygen Species

Reproduction of ubiquitous metal-ligand cooperativity in copper-oxygen enzyme mimics is crucial for the comprehension of catalytic mechanisms in copper containing enzymes and copper-catalyzed chemical transformations. Here we describe the synthesis and reduction behavior of a series of encapsulated dinuclear copper-oxygen species by systematically altering the size and geometric structure of peripheral macrocyclic ligands. Along with the occurrence of a single-electron reduction, these macrocycleencircled dicopper complexes show distinct electron transfer pathways as a function of differently sized and substituted macrocyclic ligands. Detailed structural characterization and density functional theory calculations reveal that a coupled metal-ligand and bimetallic cooperativity is involved in the single electron reduction of hydroxyl-bridged dicopper species within macrocyclic homologue ligands Py[7]Ph [1] and Py[7]Ph[1]-Me. The highly flexible configurations of macrocyclic ligands are conducive to stabilizing copper-oxygen intermediates with different valence states and facilitating an intramolecular electron transfer between macrocyclic ligands and the central copper-oxygen moiety. Correlation of biased electron transfer behaviors of copper-oxygen species with their peripheral macrocyclic ligands provides a new means of tuning redox properties of metal cluster species and opens a broader prospect on the mechanistic study of copper-containing enzymes and copper-catalyzed transformations.