Tertiary amine substitution with a softer pyridine group and the inclusion of a conjugated bipyridine unit in a Co complex was used to study the structure-activity relationship of a catalytic hydrogen evolution reaction (HER). Improved catalytic stability and activity resulted from these modifications observed for electro- and photocatalytic HER in neutral water. The new ligand referred to as Py<sub>3</sub>Me-Bpy, 6-((6-(1,1-di(pyridin-2-yl)ethyl)pyridin-2-yl)methyl)-2,2'-bipyridine, catalyzes the HER electrolytically at 1.3 V (vs. SHE) for 20 hours with a turnover number (TON) of 266,300. The photolytic HER study was stable for two days with a TON of 15,000. Both studies occurred in aqueous pH 7 solutions. Increased stability towards the CoI species is likely the result of the softer ligand scaffold. Density functional theory (DFT) calculations suggest H<sub>2</sub> is released from the protonation of CoIIH species through a general electron transfer/proton transfer/electron transfer/proton transfer pathway.

Hydrogen evolution reaction enhancements via cobalt complexation with a softer polypyridyl ligand in neutral water

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