Photo- and Electrocatalytic Hydrogen Production Using Valence Isomers of N₂S₂-Type Nickel Complexes

Abstract

Three Schiff-base-type nickel(II) complexes (1a-3a) and the corresponding noninnocent-type complexes (1b-3b) were synthesized, and the equilibria between these valence isomers were observed in tetrahydrofuran (THF) at room temperature. The electronic state of the noninnocent-type nickel complex was also confirmed by isolation of the one-electron-reduced species. The catalytic ability for the photogeneration of hydrogen from water was examined about 1a-3a and 1b-3b in the presence of a photosensitizer and a sacrificial electron donor. Then, a Schiff-base-type complex with chlorine atoms (2a) and a noninnocent-type complex with methyl groups (3b) on the pendant phenyl rings being present as the minor species in THF exhibited high activity of over 400 turnover numbers. The dynamic light scattering and transmission electron microscopy measurements suggested the formation of NiS-like aggregate species under photocatalytic conditions. The electrocatalytic activities of the nickel complexes for hydrogen production were also investigated, and a plausible reaction mechanism was proposed on the basis of a combined electrochemical and density functional theory study.

Recent advances in the mechanisms of the hydrogen evolution reaction by non-innocent sulfur-coordinating metal complexes

“…Six nickel complexes with an S2N2-ligand framework similar to complex 47 were synthesized and used as photocatalysts and electrocatalysts for hydrogen production. 168 Complexes 57a-c possess Schiff-base type macrocyclic ligands and are found to be in an equilibrium state with their noninnocent type 56a-c isomers in THF solution 169 (Scheme 25a). Irradiation (λ > 400 nm) together with [Ir( ppy) 2 (bpy)] + (ref.…”

“…Notably, these macrocyclic complexes have much larger overpotentials than both their amine-thiolate analogue, 47, probably because nitrogen protonation is coupled with reduction in the latter case. 168 In another study, two S2N2-type Ni(II) complexes bearing different chelating-ring sizes, 58 and 59, were synthesized and examined as photocatalysts and electrocatalysts for proton reduction. In the photocatalytic system [Ru(bpy) 3 ] 2+ was used as a photosensitizer and sodium ascorbate as a sacrificial electron donor in aqueous solution at pH 4.0. electronic structures, a clear definition of the metal oxidation state is not straightforward.…”

Synthesis, Characterization, and Electrocatalytic Behavior for Hydrogen Evolution of a Dinuclear Copper(II) Complex of 1‐[(2‐Carboxymethyl) benzene]‐3‐[2‐carboxybenzene] triazene

“…The reaction mixture was filtered, and the solid was purified by crystallization at -4°C from 8:2 ethyl acetate/hexanes to obtain yellow crystals, which were collected and dried in vacuo (65 %). Found (calcd) for C 15…”

“…[13] To mimic the behavior of this natural process, people focus their works on the design and development of catalysts based on transition metal complexes for electrochemical driven hydrogen production via water or proton reduction, and several transition metal compounds have been developed as electro-catalysts for H 2 evolution. [14][15][16][17] Based on that the deprotonation makes the triazenido species, […”

Experimental and Theoretical Study of Photochemical Hydrogen Evolution Catalyzed by Paddlewheel‐Type Dirhodium Complexes with Electron Withdrawing Carboxylate Ligands

“…In contrast, the development of HEC remains in the developmental stages. Recent research efforts dedicated towards HEC can be mainly divided into two categories; one is the earth‐abundant 3d metal complexes, and the other is the noble 4d and 5d metal complexes . The former serve as HEC with relatively low over‐potentials, while their catalytic activities in the photochemical reactions are relatively low.…”