Water and Air Stable Copper(I) Complexes of Tetracationic Catenane Ligands for Oxidative C−C Cross‐Coupling

Aqueous soluble and stable Cu(I) molecular catalysts featuring a catenane ligand composed of two dicationic, mutually repelling but mechanically interlocked macrocycles are reported. The ligand interlocking not only fine‐tunes the coordination sphere and kinetically stabilizes the Cu(I) against air oxidation and disproportionation, but also buries the hydrophobic portions of the ligands and prevents their dissociation which are necessary for their good water solubility and a sustained activity. These catenane Cu(I) complexes can catalyze the oxidative C−C coupling of indoles and tetrahydroisoquinolines in water, using H2O2 as a green oxidant with a good substrate scope. The successful use of catenane ligands in exploiting aqueous Cu(I) catalysis thus highlights the many unexplored potential of mechanical bond as a design element for exploring transition metal catalysis under challenging conditions. Copper(I) molecular catalysts that are water soluble and stable against oxidative degradation are obtained by the strategic use of multiply charged catenane ligands. By using the new catalysts, oxidative C−C cross‐coupling is realized in water using H2O2 as a green and convenient oxidant, highlighting the potential of ligand interlocking in leveraging transition metal catalysis under challenging conditions.