Making Hydrogen from Water Using a Homogeneous System Without Noble Metals

A photocatalytic noble metal-free system for the generation of hydrogen has been constructed using Eosin Y (1) as a photosensitizer, the complex [Co(dmgH)(2)pyCl](2+) (5, dmgH = dimethylglyoximate, py = pyridine) as a molecular catalyst, and triethanolamine (TEOA) as a sacrificial reducing agent. The system produces H-2 with an initial rate of 100 turnovers per hour upon irradiation with visible Light (lambda > 450 nm). Addition of free dmgH(2) greatly increases the durability of the system addition of 12 equiv of dmgH(2) (vs cobalt) to the system produces similar to 900 turnovers of H-2 after 14 h of irradiation. The rate of H-2 evolution is maximum at pH = 7 and decreases sharply at more acidic or basic pH. Spectroscopic study of photolysis solutions suggests that hydrogen production occurs through protonation of a Co-I species to give a Co-III hydride, which then reacts further by reduction and protolysis to give Co-II and molecular hydrogen.