Reversible Photochemical Modifications in Dicarbene-Derived Metallacycles with Coumarin Pendants

Abstract

Molecular rectangles were obtained from two bis(NHC) ligands, each featuring two terminal coumarin groups and two Ag+, Au+, or Cu+ ions. Upon UV irradiation (λ=365 nm), the dinuclear complexes undergo photochemical modification through a [2+2] cycloaddition reaction of two adjacent coumarin moieties to give a macrocyclic tetra(NHC) ligand. The photodimerization of the coumarin pendants proceeds stereoselectively to give the syn-head-head isomers in all cases. Subsequent irradiation at λ=254 nm initiates a photocleavage reaction with reconstitution of the initial dinuclear complexes with coumarin pendants.