Consecutive ligand-based PCET processes affording a doubly reduced nickel pyrazinedithiolate which transforms into a metal hydride required to evolve H2

Abstract

Our DFT results demonstrate that hydrogen evolution from water catalyzed by a nickel pyradinedithiolate (dcpdt) molecular hydrogen evolution catalyst [Ni^II(dcpdt)₂]²⁻ proceeds via the formation of a square-planar nickel(II) hydride intermediate which is given by unprecedented structural transformation of a doubly reduced triply protonated species [Ni^II(dcpdtH₂)(dcpdtH)]⁻, afforded as a result of two consecutive ligand-based reductions of [Ni^II(dcpdt)(dcpdtH)]⁻ through proton-coupled electron transfer (PCET) pathways.