Synthesis, characterization and electrocatalysis of mono- and di-nickel tetraiminodiphenolate macrocyclic complexes as active site models of [NiFe]-hydrogenases

Martin, Maria da Graça Moraes Braga; Vidotti, Marcio; Nunes, Fábio Souza

doi:10.1016/j.ijhydene.2012.06.118

Cited by 6 publications

(2 citation statements)

References 32 publications

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“…In addition, there have also been studies on photocatalytic H + reduction using cobaloxime catalysts. − Given the number of different research groups working on cobaloxime complexes and the wide range of conditions used to study them, it is not surprising that there is some debate on the mechanism for H + reduction to H 2 . The three most common mechanistic cycles proposed for H + reduction are the heterolytic pathways of H + + Co III –H → H 2 + Co III , − or H + + Co II –H → H 2 + Co II , ,− and the bimolecular homolysis pathway of 2Co III –H → H 2 + 2Co II . ,,,− Several dinuclear nickel, iron, and nickel–iron complexes have been investigated for electrocatalytic H + reduction, − but surprisingly, very few dicobalt. To the best of our knowledge, few such examples have been reported, an octamethylene linked bis(cobaloxime) dimer by Gray et al, pyridazine based dicobalt complexes by Peters et al, and bis(pyridyl)pyrazolato bridged di-Co(terpyridine) by Llobet, Fukuzumi, and co-workers .…”

Section: Introductionmentioning

confidence: 99%

Electrocatalytic Proton Reduction by a Dicobalt Tetrakis-Schiff Base Macrocycle in Nonaqueous Electrolyte

2014

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A series of dicobalt complexes, Co2L(2+) and Co2LAc(+), where L is a N6O2 coordinating bis(phenolate) tetrakis-Schiff base ligand, have been synthesized and characterized via electrochemical and spectroscopic techniques. [Co2LAc](ClO4) crystallizes in the monoclinic space group P21/n, and the structure reveals a highly distorted octahedral geometry for the Co(II) ions, which are bridged by an acetate with a Co-Co distance of 3.2 Å. Cyclic voltammetry (CV) of Co2L(2+) and Co2LAc(+) in anhydrous acetonitrile reveals large anodic/cathodic peak splitting for the Co(II/III) redox transitions and a multielectron wave for the Co(II/I) reductions. The CVs for Co2L(2+) and Co2LAc(+) were also compared to those of Zn2LAc(+) and H4L(2+) to identify the ligand-center oxidations and reductions. Addition of trifluoroacetic acid (TFA) or acetic acid (AcOH) to the electrolyte solutions of Co2L(2+) results in an irreversible reduction wave that is consistent with electrocatalytic H(+) reduction. The catalytic rate law shows a first order dependence on [catalyst] and a second order dependence on [acid]. Using TFA as the acid source, the electrocatalytic H(+) reduction rate constant for Co2L(2+) was determined to be 138 M(-2) s(-1), while coordination of acetate slows the rate to 63 M(-2) s(-1) for Co2LAc(+). Controlled potential electrolysis of Co2L(2+) with AcOH generated H2 in 72-94% Faradaic efficiency as determined by gas chromatography. Initial studies suggest Co(I)2 as the catalytically active form of the complex. These complexes represent a new class of Co-based electrocatalytic H(+) reduction catalysts that utilize a bimetallic active site.

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Section: Introductionmentioning

confidence: 99%

Electrocatalytic Proton Reduction by a Dicobalt Tetrakis-Schiff Base Macrocycle in Nonaqueous Electrolyte

2014

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“…For long, H 2 evolution derived from the electrons and protons during the reduction process by molecular cobalt electrocatalysts has been studied extensively. Recently, interest in employing dinuclear transition metal complexes as HER electrocatalysts has been amplified due to advances in electrocatalytic proton reduction. − Surprisingly, the reports on dinuclear cobalt complexes as electrocatalysts for proton reduction to H 2 are rather rare. − Based on the design of the ligand scaffolds, dinuclear cobalt complexes have been proposed for the possibility of undergoing a uni-/bimolecular homolytic mechanistic catalytic route during electrocatalytic proton reduction. The studies by several research groups have shown that the mechanistic pathways were different for different molecular structures.…”

Section: Introductionmentioning

confidence: 99%

Ligand-Mediated Hydrogen Evolution by Co(II) Complexes and Assessment of the Mechanism by Computational Studies

et al. 2023

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In this work, two novel dinuclear cobalt complexes, [Co II (hbqc)-(H 2 O)] 2 (Co-Cl) and [Co II (hbqn)(H 2 O)] 2 (Co-NO 2 ), featuring benzimidazole derived redox-active ligand have been synthesized to investigate their catalytic activities toward electrocatalytic proton reduction (where hbqc is 2. The electrochemical responses in 95/5 (v/v) DMF/H 2 O with the addition of 24 equiv of AcOH as a proton source manifest high catalytic activity for proton reduction to H 2 . The catalytic reduction event yields H 2 at an applied potential of −1.9 V vs SCE. A faradaic efficiency of 85−89% was obtained from gas chromatography analysis. A series of experiments performed concluded the homogeneous behavior of these molecular electrocatalysts. Between the two complexes, the Cl-substituted analogue, Co-Cl, has an increased overpotential of 80 mV compared to its NO 2 -substituted counterpart, exhibiting lesser catalytic activity toward the reduction process. The high stability of electrocatalysts under the electrocatalytic conditions was established, as no noticeable degradation of catalysts was observed throughout the process. All these measurements were exploited to elucidate the mechanistic route by these molecular complexes for the reduction process. The mechanistic pathways were suggested to be operational with EECC (E: electrochemical and C: chemical). The overall reaction energy by NO 2 -substituted Co-NO 2 -catalyzed reaction is more exogenic than Cl-substituted Co-Cl-catalyzed reaction; the corresponding reaction energies are −88.9 and −85.1 kcal mol −1 . The computational study indicates that Co-NO 2 is more efficient toward molecular hydrogen formation reaction than Co-Cl.

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Molecular Catalysts for Proton Reduction Based on Non‐noble Metals

Elléouet

Pétillon

Schollhammer

2018

Non‐Noble Metal Catalysis

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Synthesis, characterization and electrocatalysis of mono- and di-nickel tetraiminodiphenolate macrocyclic complexes as active site models of [NiFe]-hydrogenases

Cited by 6 publications

References 32 publications

Electrocatalytic Proton Reduction by a Dicobalt Tetrakis-Schiff Base Macrocycle in Nonaqueous Electrolyte

Electrocatalytic Proton Reduction by a Dicobalt Tetrakis-Schiff Base Macrocycle in Nonaqueous Electrolyte

Ligand-Mediated Hydrogen Evolution by Co(II) Complexes and Assessment of the Mechanism by Computational Studies

Molecular Catalysts for Proton Reduction Based on Non‐noble Metals

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