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 Mo(IV)/Mo(III) and Mo(III)/Mo(II) redox couples, around 1.0 V vs SCE. Mechanistic studies by (1)H 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.