Kosei Yamauchi

The one-electron-reduced form of methylviologen (MV(+*)), generated in situ by bulk electrolysis of methylviologen (MV(2+)), was for the first time reacted with various Pt(II) complexes in aqueous media without light irradiation to reveal that thermal reduction of water into molecular hydrogen is indeed highly promoted by the Pt(II)-based molecular catalysts.

A nickel pyrazinedithiolate ([Ni(dcpdt)₂ ]^2- ; dcpdt=5,6-dicyanopyrazine-2,3-dithiolate), bearing a NiS₄ 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 %

A macrocyclic N-heterocyclic carbene (NHC)-cobalt complex was found to act as an improved H2-evolving catalyst in a [Ru(bpy)3](2+)-sensitized photosystem using methylviologen as a redox acceptor (MV(2+) + e(-) → MV(+)˙, MV(2+) = N,N'-dimethyl-4,4'-bipyridinium), which provides a driving force of only 150 meV for H2 evolution at pH 5.0.

Abstract Proton abstraction leading to the formation of a hydride species required to evolve H 2 largely relies on the basicity of d orbital of the metal responsible for this action. Here we report that a square‐planar Ni II (bpy)(dcbdt) hydrogen evolution catalyst shows substantial acceleration in the proton abstraction rate due to the increased basicity at the filled Ni d z 2 orbital after formation of [Ni I (bpy −. )(dcbdt)] 2− via consecutive two one‐electron reductions (bpy=2,2′‐bipyridine;

Abstract A nickel pyrazinedithiolate ([Ni(dcpdt) 2 ] 2− ; dcpdt=5,6‐dicyanopyrazine‐2,3‐dithiolate), bearing a NiS 4 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

Two new nickel dithiolate derivatives have been examined for their electrocatalytic activity for the hydrogen evolution reaction (HER) in attempts to clarify whether the overpotential for the HER can be tuned upon varying the ligand-centered reduction potential that triggers the HER by the catalysts. We demonstrate the validity of this approach to achieve desirable tunability in the overpotential for the HER.

Our DFT results demonstrate that hydrogen evolution from water catalyzed by a nickel pyradinedithiolate (dcpdt) molecular hydrogen evolution catalyst [NiII(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 [NiII(dcpdtH2)(dcpdtH)]-, afforded as a result of two consecutive ligand-based reductions of [NiII(dcpdt)(dcpdtH)]- through proton-coupled electron tra

A Pt(ii)-based photo-hydrogen-evolving molecular device tethered to dimethyl-substituted viologens (Pt(bpy)(dmMV²⁺)₂), providing higher driving force for hydrogen evolution reaction (HER) than the non-methylated analogue (Pt(bpy)(MV²⁺)₂), is found to exhibit improved photocatalytic performance. The observed behaviors are explained by the multiple HER pathways taken by evolving H₂ by the doubly and triply reduced species generated via consecu

The first negatively charged PtCl(tpy) (tpy = 2,2':6',2''-terpyridine) derivative, formulated as Na2[PtCl(tctpy)]·5H2O (tctpy = 2,2':6',2''-terpyridine-4,4',4''-tricarboxylate), was prepared, characterized, and investigated in detail for its activity as a single-component photocatalyst that drives water reduction to H2 in the presence of a sacrificial electron donor (EDTA). This compound was confirmed to exist in its fully deprotonated form [PtCl(tctpy)](2-) in aqueous media at pH > 4.4. Despite

Herein we report a water-soluble cobalt porphyrin that efficiently catalyzes the photoreduction of CO 2 in fully aqueous media with a good selectivity over H 2 production.

To answer the question of whether Pt(II)-based H(2)-evolving catalysts are stable upon exposure to H(2), the behaviours of some platinum(II) complexes in the presence of H(2) (5 × 10(-4) - 1 atm) have been followed spectrophotometrically. The results reveal that some catalysts are highly stable upon exposure to H(2).

The catalytic role of the hydride intermediate in the reduction of CO2 to formate (HCOO–) by NiII-NHC complexes is investigated in detail by density functional theory (DFT) calculations. It is found that a NiII-hydride is sufficiently hydridic to facilitate the efficient transfer of hydride to the carbon center of CO2, leading to HCOO– production. Importantly, the direct hydride transfer path proposed here bypasses the conventional insertion of CO2 into a metal–hydride bond. This mechanism is el

The catalytic performance of photochemical H₂ evolution from water by <bold>Co-NHC-1</bold> is dramatically improved by rational redox tuning of an electron relay.

The factors controlling the catalytic activity in photochemical hydrogen evolution reaction (HER) are studied in detail for two macrocyclic cobalt compounds bearing two N-heterocyclic carbenes and two pyridyl donors (<b>Co-NHC1</b> and <b>Co-NHC2</b>, where <b>Co-NHC2</b> has a methoxy substituent on each pyridyl ligand). The present study adopts an aqueous photosystem consisting of EDTA, [Ru(bpy)₃]²⁺ (bpy = 2,2'-bipyridine), and MV²⁺ (MV²⁺ = methylvio

Water oxidation is a key to achieving sustainable energy cycles, for which higher-valent metal-oxo species often play a key role to accelerate the rate-limiting O-O bond formation. The present study undertook efforts to clarify one of the steps postulated for the water oxidation (WO) catalyzed by [Ru^II(terpy)(bpy)(OH₂)]²⁺ (terpy = 2,2':6',6″-terpyridine, bpy = 2,2'-bipyridine). This study focuses on inner-sphere electron transfer for the Ce^IV-driven ox