Dinuclear Cobalt Complexes with a Decadentate Ligand Scaffold: Hydrogen Evolution and Oxygen Reduction Catalysis

Giovanni, Carlo Di; Gimbert‐Suriñach, Carolina; Nippe, Michael; Benet‐Buchholz, Jordi; Sala, Xavier; Llobet, Antoni

doi:10.1002/chem.201503567

Cited by 42 publications

(50 citation statements)

References 67 publications

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“…Care should be taken when comparing these results with catalyst 5 , as we found evidence of an equilibrium with a dinuclear structure (Scheme S1) when crystallized from protic solvents (Figure S3). Dinuclear cobalt complexes have already been reported to reduce protons under photocatalytic conditions . Thus, we cannot exclude that 5 is active in its dimeric form and should not be directly compared to the other catalysts since it probably represents a class of its own.…”

Section: Resultsmentioning

confidence: 67%

Structure–Activity and Stability Relationships for Cobalt Polypyridyl‐Based Hydrogen‐Evolving Catalysts in Water

et al. 2017

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A series of eight new and three known cobalt polypyridyl‐based hydrogen‐evolving catalysts (HECs) with distinct electronic and structural differences are benchmarked in photocatalytic runs in water. Methylene‐bridged bis‐bipyridyl is the preferred scaffold, both in terms of stability and rate. For a cobalt complex of the tetradentate methanol‐bridged bispyridyl–bipyridyl complex [CoIIBr(tpy)]Br, a detailed mechanistic picture is obtained by combining electrochemistry, spectroscopy, and photocatalysis. In the acidic branch, a proton‐coupled electron transfer, assigned to formation of CoIII−H, is found upon reduction of CoII, in line with a pKa(CoIII−H) of approximately 7.25. Subsequent reduction (−0.94 V vs. NHE) and protonation close the catalytic cycle. Methoxy substitution on the bipyridyl scaffold results in the expected cathodic shift of the reduction, but fails to change the pKa(CoIII−H). An analysis of the outcome of the benchmarking in view of this postulated mechanism is given along with an outlook for design criteria for new generations of catalysts.

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Section: Resultsmentioning

confidence: 67%

Structure–Activity and Stability Relationships for Cobalt Polypyridyl‐Based Hydrogen‐Evolving Catalysts in Water

et al. 2017

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“…Dicobalt complexes with a diamond Co III 2 (OH) 2 stabilized by the six coordinate ligand, dipyridylethane naphthyridine (DPEN), also act as electrocatalysts for the four‐electron/four‐proton reduction of O 2 with CF 3 COOH in MeCN . In the case of a binuclear cobalt‐ μ ‐1,2‐peroxo complex with a decadentate dinucleating ligand containing a pyridazine bridging group and pyridylic arms, however, the peroxo complex catalyzed only two‐electron/two‐proton reduction of O 2 by Me 8 Fc in the presence of CF 3 COOH to produce H 2 O 2 . Thus, the cleavage of Co−O or O−O bond in the binuclear cobalt‐ μ ‐1,2‐peroxo complex is determined by the ligand, but the factors to control the Co−O or O−O bond cleavage pathways are yet to be clarified.…”

Section: Cobalt Complex Catalystsmentioning

confidence: 99%

Mechanisms of Two‐Electron versus Four‐Electron Reduction of Dioxygen Catalyzed by Earth‐Abundant Metal Complexes

2017

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The two‐electron reduction of dioxygen with two protons produces hydrogen peroxide, which is directly used as a liquid fuel in hydrogen peroxide fuel cells, whereas the four‐electron reduction of dioxygen is combined with the two‐electron oxidation of hydrogen in hydrogen fuel cells. Platinum (Pt)‐based nanocomposites are the most efficient commercial electrocatalysts for the oxygen reduction reaction (ORR). However, the poor stability, scarcity and high cost of these Pt‐based oxygen electrocatalysts are major barriers for the large‐scale implementation of fuel cell technologies. Replacing noble metal‐based electrocatalysts with highly efficient and inexpensive earth‐abundant metal‐based oxygen electrocatalysts has been of critical importance for practical applications. To develop efficient catalysts for the two‐electron and four‐electron reduction of dioxygen, it is crucially important to clarify the catalytic mechanisms of two‐electron/two‐proton versus four‐electron/four‐proton reduction of dioxygen with earth‐abundant metal complexes. This review focused on the factors that control the two‐electron/two‐proton versus four‐electron/four‐proton reduction of dioxygen by electron donors (one electron reductants) such as ferrocene, catalyzed by earth‐abundant metal complexes such as iron, cobalt, copper, manganese and nickel complexes in the homogeneous phase, by detecting catalytic intermediates, which determine the catalytic pathways of the two‐electron versus four‐electron reduction of dioxygen. The electrocatalytic two‐electron or/and four‐electron reduction of dioxygen with earth‐abundant metal complexes and metal oxides has also been discussed in relation with the homogeneous catalysis.

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“…Cooperative effects have been proposed by Dinolfo and co‐workers for a binuclear Co II catalyst in a bicompartmental Robson/Okawa‐type [N 6 O 2 ] macrocycle with a Co−Co distance of 3.22 Å, whereas Gray and co‐workers evaluated oxime‐based Co III catalysts with both flexible hydrocarbon and rigid BO 4 bridges that revealed no significant catalytic enhancement. Similarly, the lack of cooperativity observed in dicobalt complexes featuring pyrazolato bridges was attributed either to the large distance of 3.95 Å between the Co centers or to the flexibility of the ligand. To date it is unclear what factors control metal cooperativity in proton reduction, and this lack of understanding prevents a more rational design of Co 2 catalysts.…”

Section: Introductionmentioning

confidence: 99%

Bimetallic Cooperativity in Proton Reduction with an Amido‐Bridged Cobalt Catalyst

Kpogo

Mazumder

Wang

et al. 2017

Chemistry A European J

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The bimetallic catalyst [Co (L )(bpy) ]ClO (1), in which L is an [NN' O ] fused ligand, efficiently reduced H to H in CH CN in the presence of 100 equiv of HOAc with a turnover number of 18 and a Faradaic efficiency of 94 % after 3 h of bulk electrolysis at -1.6 V (vs. Ag/AgCl). This observation allowed the proposal that this bimetallic cooperativity is associated with distance, angle, and orbital alignment of the two Co centers, as promoted by the unique Co-N -Co environment offered by L . Experimental results revealed that the parent [Co Co ] complex undergoes two successive metal-based 1 e reductions to generate the catalytically active species [Co Co ], and DFT calculations suggested that addition of a proton to one Co triggers a cooperative 1 e transfer by each of these Co centers. This 2 e transfer is an alternative route to generate a more reactive [Co (Co -H )] hydride, thus avoiding the Co -H required in monometallic species. This [Co (Co -H )] species then accepts another H to release H .

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Dinuclear Cobalt Complexes with a Decadentate Ligand Scaffold: Hydrogen Evolution and Oxygen Reduction Catalysis

Cited by 42 publications

References 67 publications

Structure–Activity and Stability Relationships for Cobalt Polypyridyl‐Based Hydrogen‐Evolving Catalysts in Water

Structure–Activity and Stability Relationships for Cobalt Polypyridyl‐Based Hydrogen‐Evolving Catalysts in Water

Mechanisms of Two‐Electron versus Four‐Electron Reduction of Dioxygen Catalyzed by Earth‐Abundant Metal Complexes

Bimetallic Cooperativity in Proton Reduction with an Amido‐Bridged Cobalt Catalyst

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