Electrocatalytic H₂ Generation from Water Relying on Cooperative Ligand Electron Transfer in "PN³ P" Pincer-Supported...

Water is the most sustainable source for H₂ production, and the efficient electrocatalytic production of H₂ from mixed water/acetonitrile solutions by using two new air-stable nickel(II) pincer complexes, [Ni(κ³ -2,6-{Ph₂ PNR}₂ (NC₅ H₃ )Br₂ ] (R=H I, Me II) is reported. Hydrogen generation from H₂ O/CH₃ CN solutions is initiated at -2 V against Fc^+/0 , and bulk electrocatalysis studies showed that the catalyst functions with an excellent Faradaic efficiency and a turnover frequency of 160 s^-1 . A DFT computational investigation of the reduction behavior of I and II revealed a correlation of H₂ formation with charge donation from electrons originating in a reduced ligand-localized orbital. As a result, these catalysts are proposed to proceed by a novel mechanism involving electron/proton transfer between a Ni^0I species bonded to an anionic PN³ P ligand ("L^- /Ni^0I ") and a Ni^I -hydride ("Ni-H"). Furthermore, these catalysts are able to reduce phenol and acetic acid, more active proton sources, at lower potentials that correlate with the substrate pK_a .