Steric Effects on the Oxygen Reduction Reaction with Cobalt Porphyrin Atropisomers

Liu, Tao; Qin, Haonan; Xu, Yuhan; Peng, Xinyang; Zhang, Wei; Cao, Rui

doi:10.1021/acscatal.4c01295

“…Metalloenzymes, such as cytochrome c oxidase and cytochrome P450, demonstrate that first row transition metals can indeed efficiently activate O 2 . − Heme enzymes, in particular, have inspired a variety of homogeneous and heterogeneous electrocatalysts for ORR consisting of first-row transition metals and either porphyrin, corrole, or phthalocyanine ligands. − Although most of these electrocatalysts are highly selective for the four electron reduction of O 2 to H 2 O, they require effective overpotentials that are likely too high for practical use . Cobalt complexes with porphyrin, corrole, and phthalocyanine ligands tend to have lower overpotentials but slower activity and lesser selectivity for H 2 O than their iron-containing analogs. − …”

Section: Introductionmentioning

confidence: 99%

Installing Quinol Proton/Electron Mediators onto Non-Heme Iron Complexes Enables Them to Electrocatalytically Reduce O₂ to H₂O at High Rates and Low Overpotentials

Obisesan,

Parvin,

Tao

et al. 2024

Inorg. Chem.

0

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We prepare iron(II) and iron(III) complexes with polydentate ligands that contain quinols, which can act as electron proton transfer mediators. Although the iron(II) complex with N-(2,5-dihydroxybenzyl)-N,N′,N′-tris(2-pyridinylmethyl)-1,2-ethanediamine (H 2 qp1) is inactive as an electrocatalyst, iron complexes with N,N′-bis(2,5-) were found to be much more active and more selective for water production than a previously reported cobalt-H 2 qp1 electrocatalyst while operating at low overpotentials. The catalysts with H 2 qp3 can enter the catalytic cycle as either Fe(II) or Fe(III) species; entering the cycle through Fe(III) lowers the effective overpotential. On the basis of their TOF 0 values, the successful iron−quinol complexes are better electrocatalysts for oxygen reduction than previously reported iron-porphyrin compounds, with the Fe(III)−H 2 qp3 arguably being the best homogeneous electrocatalyst for this reaction. With iron, the quinol-for-phenol substitution shifts the product selectivity from H 2 O 2 to water with little impact on the overpotential, but unlike cobalt, this substitution also greatly improves the activity, as assessed by TOF max , by hastening the protonation and oxygen binding steps. The addition of a second quinol further enhances the activity and selectivity for water but modestly increases the effective overpotential.

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The “Pull Effect” of a Hanging Zn^II on Improving the Four‐Electron Oxygen Reduction Selectivity with Co Porphyrin

Han,

Tan,

Guo

et al. 2024

Angewandte Chemie

0

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Due to the challenge of cleaving O−O bonds at single Co sites, mononuclear Co complexes typically show poor selectivity for the four‐electron (4e−) oxygen reduction reaction (ORR). Herein, we report on selective 4e− ORR catalyzed by a Co porphyrin with a hanged ZnII ion. Inspired by Cu/Zn‐superoxide dismutase, we designed and synthesized 1‐CoZn with a hanging ZnII at the second sphere of a Co porphyrin. Complex 1‐CoZn is much more effective than its Zn‐lacking analogues to catalyze the 4e− ORR in neutral aqueous solutions, giving an electron number of 3.91 per O2 reduction. With spectroscopic studies, the hanging ZnII was demonstrated to be able to facilitate the electron transfer from CoII to O2, through an electronic “pull effect”, to give CoIII‐superoxo. Theoretical studies further suggested that this “pull effect” plays crucial roles in assisting O−O bond cleavage. This work is significant to present a new strategy of hanging a ZnII to improve O2 activation and O−O bond cleavage.

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The “Pull Effect” of a Hanging Zn^II on Improving the Four‐Electron Oxygen Reduction Selectivity with Co Porphyrin

Han,

Tan,

Guo

et al. 2024

Angew Chem Int Ed

3

0

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Due to the challenge of cleaving O−O bonds at single Co sites, mononuclear Co complexes typically show poor selectivity for the four‐electron (4e−) oxygen reduction reaction (ORR). Herein, we report on selective 4e− ORR catalyzed by a Co porphyrin with a hanged ZnII ion. Inspired by Cu/Zn‐superoxide dismutase, we designed and synthesized 1‐CoZn with a hanging ZnII at the second sphere of a Co porphyrin. Complex 1‐CoZn is much more effective than its Zn‐lacking analogues to catalyze the 4e− ORR in neutral aqueous solutions, giving an electron number of 3.91 per O2 reduction. With spectroscopic studies, the hanging ZnII was demonstrated to be able to facilitate the electron transfer from CoII to O2, through an electronic “pull effect”, to give CoIII‐superoxo. Theoretical studies further suggested that this “pull effect” plays crucial roles in assisting O−O bond cleavage. This work is significant to present a new strategy of hanging a ZnII to improve O2 activation and O−O bond cleavage.

show abstract

Steric Effects on the Oxygen Reduction Reaction with Cobalt Porphyrin Atropisomers

Cited by 12 publications

References 64 publications

Installing Quinol Proton/Electron Mediators onto Non-Heme Iron Complexes Enables Them to Electrocatalytically Reduce O₂ to H₂O at High Rates and Low Overpotentials

Installing Quinol Proton/Electron Mediators onto Non-Heme Iron Complexes Enables Them to Electrocatalytically Reduce O₂ to H₂O at High Rates and Low Overpotentials

The “Pull Effect” of a Hanging Zn^II on Improving the Four‐Electron Oxygen Reduction Selectivity with Co Porphyrin

The “Pull Effect” of a Hanging Zn^II on Improving the Four‐Electron Oxygen Reduction Selectivity with Co Porphyrin

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Steric Effects on the Oxygen Reduction Reaction with Cobalt Porphyrin Atropisomers

Cited by 12 publications

References 64 publications

Installing Quinol Proton/Electron Mediators onto Non-Heme Iron Complexes Enables Them to Electrocatalytically Reduce O2 to H2O at High Rates and Low Overpotentials

Installing Quinol Proton/Electron Mediators onto Non-Heme Iron Complexes Enables Them to Electrocatalytically Reduce O2 to H2O at High Rates and Low Overpotentials

The “Pull Effect” of a Hanging ZnII on Improving the Four‐Electron Oxygen Reduction Selectivity with Co Porphyrin

The “Pull Effect” of a Hanging ZnII on Improving the Four‐Electron Oxygen Reduction Selectivity with Co Porphyrin

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Installing Quinol Proton/Electron Mediators onto Non-Heme Iron Complexes Enables Them to Electrocatalytically Reduce O₂ to H₂O at High Rates and Low Overpotentials

Installing Quinol Proton/Electron Mediators onto Non-Heme Iron Complexes Enables Them to Electrocatalytically Reduce O₂ to H₂O at High Rates and Low Overpotentials

The “Pull Effect” of a Hanging Zn^II on Improving the Four‐Electron Oxygen Reduction Selectivity with Co Porphyrin

The “Pull Effect” of a Hanging Zn^II on Improving the Four‐Electron Oxygen Reduction Selectivity with Co Porphyrin