Synthesis, electrochemical properties and catalytic behavior for electrochemical hydrogen production of [Ni(1,3-bis(diphenylphosphino)propane)((2-mercaptopyridinate)-κN,S)]BF4

Dissociation of Pyridinethiolate Ligands during Hydrogen Evolution Reactions of Ni-Based Catalysts: Evidence from X-ray Absorption Spectroscopy

“…This effect is explored for electrocatalysis by [Ni­(bpy)­(DMF) 4 ] 2+ in the presence of increasing amounts of pyS-H ligand in SI Section III (Figure S16). While the major pathway of pyS-H ligand dissociation has been demonstrated in the present work for complexes 1 – 3 only, the same mechanism likely plays a role for other molecular catalysts containing pyridinethiolate and related ligands, all of which propose the same mechanism of pyridyl N protonation and partial ligand dechelation. − Therefore, it is advisable to reassess the stability of those catalysts in the presence of a proton source and evaluate how ligand dissociation affects the reaction mechanism and efficiency of catalysis.…”

“…The crystal structure of a related fully protonated model system [Ni­(pyS-H) 4 ] 2+ (complex 3 , Figure A) provides the most compelling evidence to date for the proposed structure of [ 1 NH ] + . Despite the lack of direct experimental evidence for the structures of the protonated (and subsequently reduced) catalyst species, the same mechanism has been invoked to describe the reactions of several more recently demonstrated Ni- and Co-centered proton and CO 2 reduction catalysts containing pyS – or similar NS-coordinated ligands. − The mechanistic speculation for these catalysts includes pyridyl N protonation and partial dechelation at this site to form the protonated − or the reduced and protonated − catalyst species.…”

“…Protonation of the pyS – ligand and subsequent structural changes to the catalyst are critical in understanding the catalytic mechanisms of Ni-pyS and related complexes, as these steps are thought to create an open coordination site at the metal and enable the subsequent formation of the metal–hydride or metal–carboxylate species that are important intermediates in the H 2 evolution or CO 2 reduction reactions. − Therefore, the goal of the present work is experimental characterization of the protonated form of catalyst 1 . While it is difficult to separate the mechanistic roles of the metal and ligand reaction sites using optical spectroscopy methods, element-specific core level spectroscopy is well suited to probe changes in both the electronic structure and the coordination of a specific metal or ligand atom of the catalyst upon protonation.…”