Mono- and bimetallic Ir(III) based catalysts for the homogeneous photocatalytic reduction of CO2 under visible light irradiation. New insights into catalyst deactivation

Mononuclear iridium(III) complexes [Ir(mppy)(tpy)X] (mppy = 4-methyl-2-phenylpyridine, X = Cl, I) and binuclear analogues with various bis(2-phenylpyridin-4-yl) bridging ligands were synthesized and characterized by their spectroscopic and electrochemical properties. Kinetic measurements concerning the photocatalytic two electron reduction of CO2 to CO were investigated in order to determine the influence of intermolecular interactions between two active centers. A detailed comparison between the monometallic and the bimetallic complexes indicates an enhanced lifetime (TON) of the covalently linked complexes, causing an increased overall conversion of CO2. Additionally the deactivation pathways of the catalysts are examined.