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.