A Nickel Dithiolate Water Reduction Catalyst Providing Ligand‐Based Proton‐Coupled Electron‐Transfer Pathways

Abstract

A nickel pyrazinedithiolate ([Ni(dcpdt) ] ; dcpdt=5,6-dicyanopyrazine-2,3-dithiolate), bearing a NiS core similar to the active center of [NiFe] hydrogenase, is shown to serve as an efficient molecular catalyst for the hydrogen evolution reaction (HER). This catalyst shows effectively low overpotentials for HER (330-400 mV at pH 4-6). Moreover, the turnover number of catalysis reaches 20 000 over the 24 h electrolysis with a high Faradaic efficiency, 92-100 %. The electrochemical and DFT studies reveal that diprotonated one-electron-reduced species (i.e., [Ni (dcpdt)(dcpdtH )] or [Ni (dcpdtH) ] ) forms at pH<6.4 via ligand-based proton-coupled electron-transfer (PCET) pathways, leading to electrocatalytic HER without applying the highly negative potential required to generate low-valent nickel intermediates. This is the first example of catalysts exhibiting such behavior.

New Cobalt‐Bisterpyridyl Catalysts for Hydrogen Evolution Reaction

“…[16][17][18][19] As far as C8 is concerned, our DFT analysis finds ad ifferent operating mechanism,w hich is likely to also apply to C6 and C7 (see Scheme 2). Notably,m echanismsi nvolving activei ntermediates created upon protonation of the ligands rather than formationo f metal hydrides have already been reported in the literature.…”

Ligand‐Based PCET Reduction in a Heteroleptic Ni(bpy)(dithiolene) Electrocatalyst Giving Rise to Higher Metal Basicity Required for Hydrogen Evolution

“…), choice of other more stable sulfur‐donating ligands may help researchers to advance the studies on the metal‐sulfur systems. In this context, researchers attempting to explore artificial hydrogenase mimics have paid great attention to dithiolene ligands (L; examples are shown in Scheme a) in order to examine the catalytic activity of various homoleptic ML 2 ‐type complexes with M=Fe, Co, Ni, Mo, Rh, and W ,. We also reported on the electrocatalytic activity of several NiL 2 ‐type complexes, showing their unique reaction paths permitting the formation of hydride intermediates via two consecutive ligand‐based proton‐coupled electron transfer (PCET) processes (Scheme (3)) ,,…”

“…In this context, researchers attempting to explore artificial hydrogenase mimics have paid great attention to dithiolene ligands (L; examples are shown in Scheme 1a) in order to examine the catalytic activity of various homoleptic ML 2 -type complexes with M=Fe, [18][19][20] Co, [21][22][23][24] Ni, [25][26][27][28][29][30][31][32][33] Mo, [34] Rh, [35] and W. [36,37] We also reported on the electrocatalytic activity of several NiL 2 -type complexes, showing their unique reaction paths permitting the formation of hydride intermediates via two consecutive ligand-based proton-coupled electron transfer (PCET) processes (Scheme 2(3)). [30,32,33] On the other hand, our previous efforts involve mechanistic studies on the HER catalyzed by various artificial systems with different metal and ligand geometries. The platinum(II) catalysts, such as PtCl 2 (bpy) derivatives (bpy = 2,2'-bipyridine), are important examples shown to give a hydridoplatinum(III) intermediate via a metal-ligand-centered PCET pathway, [38] depicted in Scheme 2(2).…”

Homolytic versus Heterolytic Hydrogen Evolution Reaction Steered by a Steric Effect

“…The viability of a hydrogen‐based energy society is depended on efficient and durable production of hydrogen . Recent efforts have resulted in the identification of many molecular catalysts for hydrogen evolution . Despite these achievements, however, understanding and further controlling reaction processes are still highly challenging .…”