H-2 Oxidation Electrocatalysis Enabled by Metal-to-Metal Hydrogen Atom Transfer: A Homolytic Approach to a Heterolytic Reaction

Oxidation of H-2 in a fuel cell converts the chemical energy of the H-H bond into electricity. Electrocatalytic oxidation of H-2 by molecular catalysts typically requires one metal to perform multiple chemical steps: bind H-2, heterolytically cleave H-2, and then undergo two oxidation and two deprotonation steps. The electrocatalytic oxidation of H-2 by a cooperative system using Cp*Cr(CO)(3)H and [Fe(diphosphine)(CO)(3)](+) has now been invetigated. A key step of the proposed mechanism is a rarely observed metal-to-metal hydrogen atom transfer from the Cr-H complex to the Fe, forming an Fe-H complex that is deprotonated and then oxidized electrochemically. This division of chemical labor features Cr interacting with H-2 to cleave the H-H bond, while Fe interfaces with the electrode. Neither metal is required to heterolytically cleave H-2, so this system provides a very unusual example of a homolytic reaction being a key step in a molecular electrocatalytic process.