Advances in the Molecular Catalysis of Dioxygen Reduction

Machan, Charles W.

doi:10.1021/acscatal.9b04477

Cited by 97 publications

(72 citation statements)

References 149 publications

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“…Those that survived evolved to exploit the presence of O 2 , using it to release the energy that cells will use for their maintenance and growth. The oxygen reduction reaction is also crucial for emerging energy technologies, such as solar fuels production [3–5] …”

Section: Introductionmentioning

confidence: 99%

DpgC‐Catalyzed Peroxidation of 3,5‐Dihydroxyphenylacetyl‐CoA (DPA‐CoA): Insights into the Spin‐Forbidden Transition and Charge Transfer Mechanisms**

Ortega

Zanchet

Sanz-Sanz

et al. 2020

Chemistry A European J

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Despite being a very strong oxidizing agent, most organic molecules are not oxidized in the presence of O2 at room temperature because O2 is a diradical whereas most organic molecules are closed‐shell. Oxidation then requires a change in the spin state of the system, which is forbidden according to non‐relativistic quantum theory. To overcome this limitation, oxygenases usually rely on metal or redox cofactors to catalyze the incorporation of, at least, one oxygen atom into an organic substrate. However, some oxygenases do not require any cofactor, and the detailed mechanism followed by these enzymes remains elusive. To fill this gap, here the mechanism for the enzymatic cofactor‐independent oxidation of 3,5‐dihydroxyphenylacetyl‐CoA (DPA‐CoA) is studied by combining multireference calculations on a model system with QM/MM calculations. Our results reveal that intersystem crossing takes place without requiring the previous protonation of molecular oxygen. The characterization of the electronic states reveals that electron transfer is concomitant with the triplet–singlet transition. The enzyme plays a passive role in promoting the intersystem crossing, although spontaneous reorganization of the water wire connecting the active site with the bulk presets the substrate for subsequent chemical transformations. The results show that the stabilization of the singlet radical‐pair between dioxygen and enolate is enough to promote spin‐forbidden reaction without the need for neither metal cofactors nor basic residues in the active site.

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Section: Introductionmentioning

confidence: 99%

DpgC‐Catalyzed Peroxidation of 3,5‐Dihydroxyphenylacetyl‐CoA (DPA‐CoA): Insights into the Spin‐Forbidden Transition and Charge Transfer Mechanisms**

Ortega

Zanchet

Sanz-Sanz

et al. 2020

Chemistry A European J

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“…(3). 41 Considering the pKa of AcOH in MeCN as 23.51, 34 4Considering these standard potentials (vs. Fc +/0 ) for the reduction of O2 to water in MeCN and aqueous electrolyte, we then estimated the overpotentials for the ORR catalyzed by 1 within the applied potential ( ) between the onset ( ) and the catalytic peak potential ( , Figure 15). For the homogeneous case, 1 exhibited an overpotential ( / )…”

Section: Standard Potentials and Overpotential Analysismentioning

confidence: 99%

Electrocatalytic O2 Reduction by an Organometallic Pd(III) Complex via a Binuclear Pd(III) Intermediate

Sinha¹,

Mirica

2021

Preprint

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The development of electrocatalysts for the selective O2-to-H2O conversion, the O2 reduction reaction (ORR), is of great interest for improving the performance of fuel cells. In this context, molecular catalysts that are known to mediate the 4H+/4e– reduction of O2 to H2O tend to be marred by limited stability and selectivity in controlling the multi-proton and multi-electron transfer steps. Thus, evaluation of new transition metal complexes, including organometallic species, for ORR reactivity could uncover new molecular catalysts with improved properties. We have previously reported the synthesis and characterization of various organometallic PdIII complexes stabilized by the tetradentate ligand N,N′-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane (tBuN4). These complexes were shown to react with O2 and undergo oxidatively-induced C–C and C–heteroatom bond formation reactions in the presence of O2. These O2-induced oxidative transformations prompted us to evaluate the ORR reactivity of such organometallic Pd complexes, which to the best of our knowledge has never been studied before for any molecular Pd catalyst. Herein, we report the ORR reactivity of the [(tBuN4)PdIIIMeCl]+ complex, under both homogeneous and heterogeneous conditions in a non-aqueous and acidic aqueous electrolyte, respectively. Cyclic voltammetry and hydrodynamic electrochemical studies for [(tBuN4)PdIIIMeCl]+ revealed the electrocatalytic reduction of O2 to H2O proceeds with Faradaic efficiencies (FE) of 50-70% in the presence of acetic acid (AcOH) in MeCN. The selectivity toward H2O production further improved to a FE of 80-90% in an acidic aqueous medium (pH 0), upon immobilization of the molecular catalyst onto edge plane graphite (EPG) electrodes. Analysis of electrochemical data suggests the formation of a binuclear PdIII intermediate in solution, likely a PdIII-peroxo-PdIII species, which dictates the thermochemistry of the ORR process for [(tBuN4)PdIIIMeCl]+ in MeCN, and thus being a rare example of a bimolecular ORR process. The maximum second-order turnover frequency TOFmax(2) = 2.76 x 108 M–1 sec–1 was determined for 0.32 mM of [(tBuN4)PdIIIMeCl]+ in the presence of 1 M AcOH in O2-saturated MeCN with an overpotential of 0.32 V. By comparison, a comparatively lower TOFmax(2) = 1.25 x 105 M–1 sec–1 at a higher overpotential of 0.8 V was observed for [(tBuN4)PdIIIMeCl]PF6 adsorbed onto EPG electrodes in O2-saturated 1 M H2SO4 aqueous solution. Overall, reported herein is a detailed ORR reactivity study using a novel PdIII organometallic complex and benchmark its selectivity and energetics toward O2 reduction in MeCN and acidic aqueous solutions.

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“…The concept of storing the solar energy into higherenergy chemicals is the basis of artificial photosynthesis, which is dedicated to producing fuels/high-value chemicals such as H 2 , methane, methanol, or hydrogen peroxide. A number of molecular catalysts have been developed for water splitting [3][4][5][6][7][8][9][10][11][12], CO 2 reduction [13][14][15][16][17][18][19][20][21], and O 2 reduction [22,23]. However, the molecular catalysts in homogeneous solution often suffer from low stability in redox conditions.…”

Section: Introductionmentioning

confidence: 99%

Immobilization of molecular catalysts for artificial photosynthesis

Whang

2020

Nano Convergence

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Artificial photosynthesis offers a way of producing fuels or high-value chemicals using a limitless energy source of sunlight and abundant resources such as water, CO2, and/or O2. Inspired by the strategies in natural photosynthesis, researchers have developed a number of homogeneous molecular systems for photocatalytic, photoelectrocatalytic, and electrocatalytic artificial photosynthesis. However, their photochemical instability in homogeneous solution are hurdles for scaled application in real life. Immobilization of molecular catalysts in solid supports support provides a fine blueprint to tackle this issue. This review highlights the recent developments in (i) techniques for immobilizing molecular catalysts in solid supports and (ii) catalytic water splitting, CO2 reduction, and O2 reduction with the support-immobilized molecular catalysts. Remaining challenges for molecular catalyst-based devices for artificial photosynthesis are discussed in the end of this review.

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Advances in the Molecular Catalysis of Dioxygen Reduction

Cited by 97 publications

References 149 publications

DpgC‐Catalyzed Peroxidation of 3,5‐Dihydroxyphenylacetyl‐CoA (DPA‐CoA): Insights into the Spin‐Forbidden Transition and Charge Transfer Mechanisms**

DpgC‐Catalyzed Peroxidation of 3,5‐Dihydroxyphenylacetyl‐CoA (DPA‐CoA): Insights into the Spin‐Forbidden Transition and Charge Transfer Mechanisms**

Electrocatalytic O2 Reduction by an Organometallic Pd(III) Complex via a Binuclear Pd(III) Intermediate

Immobilization of molecular catalysts for artificial photosynthesis

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