Light-Driven Hydrogen Production from Aqueous Protons using Molybdenum Catalysts

Homogeneous light-driven systems employing molecular molybdenum catalysts for hydrogen production are described. The specific Mo complexes studied are six-coordinate bis­(benzenedithiolate) derivatives having two additional isocyanide or phosphine ligands to complete the coordination sphere. Each of the complexes possesses a trigonal prismatic coordination geometry. The complexes were investigated as proton reduction catalysts in the presence of [Ru­(bpy)3]2+, ascorbic acid, and visible light. Over 500 TON are obtained over 24 h. Electrocatalysis occurs between the MoIV/MoIII and MoIII/MoII redox couples, around 1.0 V vs SCE. Mechanistic studies by 1H NMR spectroscopy show that upon two-electron reduction the Mo­(CNR)2(bdt)2 complex dissociates the isocyanide ligands, followed by addition of acid to result in the formation of molecular hydrogen and the Mo­(bdt)2 complex.