Minimal Proton Channel Enables H2 Oxidation and Production with a Water-Soluble Nickel-Based Catalyst

Hydrogenase enzymes use first-row transition metals to interconvert H-2 with protons and electrons, reactions that are important for the storage and recovery of energy from intermittent sources such as solar, hydroelectric, and wind. Here we present Ni((P2N2Gly)-N-Cy)(2), a water-soluble molecular electrocatalyst with the amino acid glycine built into the diphosphine ligand framework. Proton transfer between the outer coordination sphere carboxylates and the second coordination sphere pendant amines is rapid, as observed by cyclic voltammetry and FTIR spectroscopy, indicating that the carboxylate groups may participate in proton transfer during catalysis. This complex oxidizes H-2 (1-33 s(-1)) at low overpotentials (150-365 mV) over a range of pH values (0.1-9.0) and produces H-2 under identical solution conditions (>2400 s(-1) at pH 0.5). Enzymes employ proton channels for the controlled movement of protons over long distances-the results presented here demonstrate the effects of a simple two-component proton channel in a synthetic molecular electrocatalyst.