Electrocatalytic reduction of protons to hydrogen by a copper complex of the pentadentate ligand Dmphen-DPA in a nonaqueous electrolyte

A copper complex based on the pentadentate aminopyridine ligand [(9-methyl-1,10-phenanthrolin-2-yl)methyl]bis-(pyridin-2-ylmethyl)amine (Dmphen-DPA), namely [Cu(Dmphen-DPA)](ClO 4 ) 2 ( 1 ), was synthesized and characterized by elemental analysis, HR-MS spectroscopy and X-ray single crystal diffraction. The complex has five-coordinated solid-state structures, but has an open coordination site in acetonitrile. The electrochemical studies reveal that complex 1 has an electrocatalytic proton reduction activity in acetonitrile, when using acetic acid as a proton source with i cat / i p ∼ 2.5. DFT calculations suggest that the parent copper complex undergoes two successive reductions to generate the radical species [Cu( i )(Dmphen-DPA&z.rad; − )] 0 , which is protonated at the low-valence copper center to afford a reactive Cu II -H intermediate. The Cu II -H species combines bimolecularly and generates H 2 via reductive elimination. An aminopyridine-based copper complex was synthesized and investigated for its electrocatalytic proton reduction activity and the plausible mechanism.