Antimony Complexes for Electrocatalysis: Activity of a Main‐Group Element in Proton Reduction

Jiang, Jianbing; Materna, Kelly L.; Hedström, Svante; Yang, Ke; Crabtree, Robert H.; Batista, Víctor S.; Brudvig, Gary W.

doi:10.1002/ange.201704700

Cited by 17 publications

(9 citation statements)

References 26 publications

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“…11 The authors asserted that the hydrogenation of the porphyrin core is ultimately responsible for the loss of the catalyst activity (pathway (a) in Figure 1). 11,12 Based on this assumption it was theorized that the chlorin core is already reduced and thus less prone to further reductive decomposition compared to porphyrins. 12,13 However, in this work authors also performed a control CO 2 ERR experiment on a Zn porphyrin and the highresolution mass spectrometry (HRMS) analysis of the reaction mixture failed to detect the expected formation of hydrogenated products.…”

Section: Introductionmentioning

confidence: 99%

Resolving Deactivation Pathways of Co Porphyrin-Based Electrocatalysts for CO₂ Reduction in Aqueous Medium

et al. 2021

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Carbon-supported first-row transition metal complexes drive electroreduction of CO 2 to CO in aqueous medium with remarkable activity and selectivity. However, their durability under negative potentials is quite low and the deactivation mechanisms are still not clear. Herein, we present an in-depth mechanistic study on the stability of Co porphyrin-based catalysts during CO 2 reduction in an aqueous electrolyte. The mechanisms of the degradation reactions were evaluated for Co tetraphenylporphyrin (CoTPP) using a combination of spectral, electrochemical, and theoretical methods. Our evidence shows that two major pathways contribute to the gradual activity loss. The first route is oxidative and yields the catalytically inactive complex [Co III TPP]OH. The second pathway is based on reductive carboxylation of the porphyrin ring via transient formation of [Co 0 TPP] 2− and [Co 0 TPP-CO] 2− . The latter reaction disrupts the π-system of the porphyrin structure and leads to the complete disintegration of the macrocyclic core. In contrast to the earlier reports, we found that the direct poisoning by CO, demetallation, and reduction to chlorins play no significant role in the deactivation process. It was further determined that the bulky donating functional groups disfavor the formation of dianionic species and restrict access of CO 2 to the vulnerable meso-position of the porphyrin ligand, thus improving the catalyst stability. The effect was found to be especially strong for the −OMe-substituted complex CoTPP-(OMe) 8 that shows excellent reusability under overpotentials below 500 mV. In turn, electronegative substituents such as fluorine suppress the activity of the catalyst and provide no advantages in terms of durability.

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Section: Introductionmentioning

confidence: 99%

Resolving Deactivation Pathways of Co Porphyrin-Based Electrocatalysts for CO₂ Reduction in Aqueous Medium

et al. 2021

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“…19,20,24−26 For example, our previous work with Sb− porphyrin complexes has shown efficient hydrogen evolution but also irreversible porphyrin ligand reduction and thus low Faradaic efficiency. 20 In a series of rhenium−porphyrin dyads for CO 2 photoreduction, Windle et al found that photoabsorption by the porphyrin induced 2-electron hydrogenation to form a chlorin first followed by another 2-electron hydrogenation to form an isobacteriochlorin, ultimately completely altering the Q-band region of the porphyrin spectrum. 19 Such instability currently hinders the greater practical utility of porphyrins in applications to reductive electrocatalysis.…”

Section: ■ Introductionmentioning

confidence: 99%

Unusual Stability of a Bacteriochlorin Electrocatalyst under Reductive Conditions. A Case Study on CO₂ Conversion to CO

et al. 2018

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Photosynthetic CO2 fixation is mediated by the enzyme RuBisCo, which employs a nonredox-active metal (Mg2+) to bind CO2 adjacent to an organic ligand that provides reducing equivalents for CO2 fixation. Attempts to use porphyrins as ligands in reductive catalysis have typically encountered severe stability issues owing to ligand reduction. Here, a synthetic zinc–bacteriochlorin is reported as an effective and robust electrocatalyst for CO2 reduction to CO with an overpotential of 330 mV, without undergoing porphyrin-like ligand degradation (or demetalation) even after prolonged bulk electrolysis. The reaction has a CO Faradaic efficiency of 92% and sustains a total current density of 2.3 mA/cm2 at −1.9 V vs Ag/AgCl. DFT calculations highlight the molecular origin of the observed stability and provide insights into catalytic steps. This bioinspired study opens avenues for the application of bacteriochlorin compounds for reductive electrocatalysis with extended life beyond that seen with porphyrin counterparts.

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“… 22 Recent work from Grapperhaus and co-workers identified homogeneous proton reduction catalysts that proceed via ligand-centered reactions in which metal hydride species are not involved ( Chart 1 , D ), 23 and also nickel porphyrin HER catalysts have been shown to undergo reduction/protonation to lead to an organic hydride as the key intermediate generated by ligand-based [2e – /H + ] reactivity. 24 In addition to catalysts containing transition-metal centers, examples have been reported of main-group complexes that are active in hydrogen evolution, 25 as illustrated by Berben’s aluminum complexes with reduced pyridinediimine ligands ( Chart 1 , E ).…”

Section: Introductionmentioning

confidence: 99%

Reactivity of Two-Electron-Reduced Boron Formazanate Compounds with Electrophiles: Facile N–H/N–C Bond Homolysis Due to the Formation of Stable Ligand Radicals

Mondol

Otten

2018

Inorg. Chem.

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The reactivity of a boron complex with a redox-active formazanate ligand, LBPh2 [L = PhNNC(p-tol)NNPh], was studied. Two-electron reduction of this main-group complex generates the stable, nucleophilic dianion [LBPh2]2–, which reacts with the electrophiles BnBr and H2O to form products that derive from ligand benzylation and protonation, respectively. The resulting complexes are anionic boron analogues of leucoverdazyls. N–C and N–H bond homolysis of these compounds was studied by exchange NMR spectroscopy and kinetic experiments. The weak N–C and N–H bonds in these systems derive from the stability of the resulting borataverdazyl radical, in which the unpaired electron is delocalized over the four N atoms in the ligand backbone. We thus demonstrate the ability of this system to take up two electrons and an electrophile (E+ = Bn+, H+) in a process that takes place on the organic ligand. In addition, we show that the [2e–/E+] stored on the ligand can be converted to E• radicals, reactivity that has implications in energy storage applications such as hydrogen evolution.

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Antimony Complexes for Electrocatalysis: Activity of a Main‐Group Element in Proton Reduction

Cited by 17 publications

References 26 publications

Resolving Deactivation Pathways of Co Porphyrin-Based Electrocatalysts for CO₂ Reduction in Aqueous Medium

Resolving Deactivation Pathways of Co Porphyrin-Based Electrocatalysts for CO₂ Reduction in Aqueous Medium

Unusual Stability of a Bacteriochlorin Electrocatalyst under Reductive Conditions. A Case Study on CO₂ Conversion to CO

Reactivity of Two-Electron-Reduced Boron Formazanate Compounds with Electrophiles: Facile N–H/N–C Bond Homolysis Due to the Formation of Stable Ligand Radicals

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Antimony Complexes for Electrocatalysis: Activity of a Main‐Group Element in Proton Reduction

Cited by 17 publications

References 26 publications

Resolving Deactivation Pathways of Co Porphyrin-Based Electrocatalysts for CO2 Reduction in Aqueous Medium

Resolving Deactivation Pathways of Co Porphyrin-Based Electrocatalysts for CO2 Reduction in Aqueous Medium

Unusual Stability of a Bacteriochlorin Electrocatalyst under Reductive Conditions. A Case Study on CO2 Conversion to CO

Reactivity of Two-Electron-Reduced Boron Formazanate Compounds with Electrophiles: Facile N–H/N–C Bond Homolysis Due to the Formation of Stable Ligand Radicals

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Resolving Deactivation Pathways of Co Porphyrin-Based Electrocatalysts for CO₂ Reduction in Aqueous Medium

Resolving Deactivation Pathways of Co Porphyrin-Based Electrocatalysts for CO₂ Reduction in Aqueous Medium

Unusual Stability of a Bacteriochlorin Electrocatalyst under Reductive Conditions. A Case Study on CO₂ Conversion to CO