Photoinduced Generation of a Durable Thermal Proton Reduction Catalyst with in Situ Conversion of Mn(bpy)(CO)₃Br to Mn(bpy)₂Br₂

The conversion of protons to H2 is a critical reaction for the design of renewable fuel generating systems. Robust, earth-abundant, metal-based catalysts that can rapidly facilitate this reduction reaction are highly desirable. Mn(bpy)(CO)3Br generates an active catalyst for the proton reduction reaction upon photolysis at a high, directly observed H2 production rate of 1,300,000 turnovers per hour, with a low driving force for this reaction. Through the use of FcMe10 as an electron source, a proton source (triflic acid, 4-cyanoanilinium, or tosylic acid), and MeCN/H2O as solvent, the thermal reaction at room temperature was found to proceed until complete consumption of the electron source. No apparent loss in catalytic activity was observed to the probed limit of 10,000,000 turnovers of H2. Interestingly, a catalytically competent complex (Mn(bpy)2Br2), which could be isolated and characterized, formed upon photolysis of Mn(bpy)(CO)3Br in the presence of acid.