Catalytic H 2 Evolution by a Mononuclear Cobalt Complex with a Macrocyclic Pentadentate Ligand


The utilization of H 2 as fuel is considered as a potential solution for future energy demand, and there has been great interest in the design of metal catalysts for the H 2 evolution from water with light and/or electricity over the past years. A mononuclear water soluble polypyridyl cobalt complex [Co(N4-Py)(H 2 O)](PF 6 ) 3 (4b) (N4-Py = N-methylpyridine-2,11-diaza[3,3](2,6)pyridinophane) was synthesized and characterized by elemental analysis, mass spectrum, electrochemistry, and theoretical calculations. It is shown that 4b can catalyze both electro- and photocatalytic H 2 production in aqueous solutions. Photocatalytic H 2 production is achieved with a turnover number (TON) of 200 at pH 6 while electrolytic H 2 production is accomplished with a TON of 140 at pH 7. Results from DFT computations indicate that the penta-coordinated Co II species is the active catalyst in the homogeneous H 2 evolution by 4b, and the generation of H 2 from a Co II -H species occurring via mononuclear heterolytic coupling is favorable by –23.0 kcal/mol.

Publication Title

European Journal of Inorganic Chemistry