H2 Oxidation Electrocatalysis Enabled by Metal-to-Metal Hydrogen Atom Transfer: A Homolytic Approach to a Heterolytic Reaction.

Oxidation of H2 in a fuel cell converts the chemical energy of the H-H bond into electricity. Electrocatalytic oxidation of H2 by molecular catalysts typically requires one metal to perform multiple chemical steps: bind H2 , heterolytically cleave H2 , and then undergo two oxidation and two deprotonation steps. The electrocatalytic oxidation of H2 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 H2 to cleave the H-H bond, while Fe interfaces with the electrode. Neither metal is required to heterolytically cleave H2 , so this system provides a very unusual example of a homolytic reaction being a key step in a molecular electrocatalytic process.