Hydrogen Evolution Reactions Catalyzed by a Bis(thiosemicarbazone) Cobalt Complex: An Experimental and Theoretical Study

Abstract

The synthesis and characterization of a dinuclear bis(thiosemicarbazone) cobalt complex [Co L (NCS) ] is reported. This complex exhibits significant catalytic activity for hydrogen production in DMF by using triethylammonium (Et NHBF ) as the proton source. Cyclic voltammetry data allowed a maximum turnover frequency of 130 s for 1 m proton concentration to be determined. The catalytic nature of the process and the production of dihydrogen were confirmed by gas analysis during controlled potential electrolysis experiments. Quantum chemical calculations show that the complex displays a ligand-assisted metal-centered reactivity and supports a catalytic mechanism involving ligand-based reduction and protonation steps followed by metal-centered processes.

Artificial photosynthesis: opportunities and challenges of molecular catalysts

“…In addition to the above main series of HECs, many other well designed ligand platforms have been applied for housing transition metals as HECs. 313,326,[366][367][368][369] For example, the macrocyclic Ni complex 72 and its analogues were good electrochemical HECs under organic-aqueous solutions 370 and fully aqueous solutions. 371 Recent studies demonstrated that dithiolene complexes 73 and the nitrogen donor ligand stabilized complex 74 could efficiently catalyze both electrochemical and photochemical H 2 evolution from water reduction, [372][373][374] and a cobalt bis(iminopyridine) complex 75 could also act as an efficient electrocatalyst for H 2 production from an aqueous solution.…”

Ligand-based electronic effects on the electrocatalytic hydrogen production by thiosemicarbazone nickel complexes

“…20 Metal complexes based on thiosemicarbazone ligands are emerging as a new class of electrocatalyst for HER. [21][22][23][24][25][26] Indeed, it was suggested that the introduction of proton relays in the second coordination sphere of the metal center combined with the use of redox-active ligands can be exploited to enhance or promote catalytic activity. [27][28][29] These complexes thus present some interesting features relevant to electrocatalytic proton reduction: the thiosemicarbazone ligand has already been shown to be redox active while the presence of S-donors and several N-atoms allows for protonation of the ligand and can serve as proton relays.…”

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

“…Crystal X-ray diffraction analysis revealed that 68 exists as a dimer, which dissociates upon two-electron reduction. 178 Complex 68 is able to catalyse proton reduction when titrated with Et 3 NHBF 4 (pK a = 9.2) in DMF, as it exhibits a TON of 9 with a faradaic yield of 65% under CPE with an applied potential of −1.60 vs. Fc + /Fc for 4 h. Combined electrochemical, theoretical and kinetic ana- lyses suggested a possible catalytic mechanism involving a three-electron-reduced Co(I) species protonated on the coordinating nitrogen of the thiosemicarbazone ligand. The last step of the HER mechanism is the second protonation, proposed by the authors to take place on the Co(I) centre.…”