Autoxidation of transition-metal complexes. Reaction of a 1:1 cobalt-molecular oxygen complex with acids to yield hydrogen peroxide. Kinetics and mechanism

Pignatello, Joseph J.; Jensen, Frederick R.

doi:10.1021/ja00514a012

Cited by 13 publications

(6 citation statements)

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“…The Co III (O 2 • ) species reacts rapidly upon the addition of a strong acid, DMF-H + , resulting in the disappearance of most of the EPR signal (Figure c). This behavior is consistent with an autoxidation pathway to generate Co III species, as has been reported previously. − In contrast, no reaction was observed between the Co III (O 2 • ) species and the weak acid, DCAH (Figure d).…”

Section: Resultssupporting

confidence: 91%

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Brønsted Acid Scaling Relationships Enable Control Over Product Selectivity from O₂ Reduction with a Mononuclear Cobalt Porphyrin Catalyst

et al. 2019

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The selective reduction of O 2 , typically with the goal of forming H 2 O, represents a long-standing challenge in the field of catalysis. Macrocyclic transition-metal complexes, and cobalt porphyrins in particular, have been the focus of extensive study as catalysts for this reaction. Here, we show that the mononuclear Co-tetraarylporphyrin complex, Co(por OMe ) (por OMe = meso-tetra(4-methoxyphenyl)porphyrin), catalyzes either 2e – /2H + or 4e – /4H + reduction of O 2 with high selectivity simply by changing the identity of the Brønsted acid in dimethylformamide (DMF). The thermodynamic potentials for O 2 reduction to H 2 O 2 or H 2 O in DMF are determined and exhibit a Nernstian dependence on the acid p K a , while the Co III/II redox potential is independent of the acid p K a . The reaction product, H 2 O or H 2 O 2 , is defined by the relationship between the thermodynamic potential for O 2 reduction to H 2 O 2 and the Co III/II redox potential: selective H 2 O 2 formation is observed when the Co III/II potential is below the O 2 /H 2 O 2 potential, while H 2 O formation is observed when the Co III/II potential is above the O 2 /H 2 O 2 potential. Mechanistic studies reveal that the reactions generating H 2 O 2 and H 2 O exhibit different rate laws and catalyst resting states, and these differences are manifested as different slopes in linear free energy correlations between the log(rate) versus p K a and log(rate) versus effective overpotential for the reactions. This work shows how scaling relationships may be used to control product selectivity, and it provides a mechanistic basis for the pursuit of molecular catalysts that achieve low overpotential reduction of O 2 to H 2 O.

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Section: Resultssupporting

confidence: 91%

“…This behavior is consistent with an autoxidation pathway to generate Co III species, as has been reported previously. 73−76 In contrast, no reaction was observed between the Co III (O 2 • ) species and the weak acid, DCAH (Figure 6d).…”

Section: Resultsmentioning

confidence: 95%

Brønsted Acid Scaling Relationships Enable Control Over Product Selectivity from O₂ Reduction with a Mononuclear Cobalt Porphyrin Catalyst

et al. 2019

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“…The above mechanism is similar to that proposed by Pignatello and Jensen [27] for the decomposition of [Co(acacen)O,(py)] in pyridine at -10" where second-order kinetics in cobalt, and an inverse first-order dependence on oxygen pressure were observed. The authors concluded that there was rapid formation of a binuclear q':q'-complex which is then protonated to give [Co(acacen)(py)]+ and H,O,.…”

Section: Mechanism Ojdecomposition Of [Co(cn)o]-i-supporting

confidence: 85%

The Reactivity of the Pentacyano(η¹‐Dioxygen)cobaltate(III) Ion in Aqueous Solution

Gubelmann

Riittimann

Bocquet

et al. 1990

Helvetica Chimica Acta

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The mononuclear η1‐dioxygen complex [Co(CN)5O2]3− (A) decomposes in aqueous solution to the hydroxo‐complex [Co(CN)5OH]3− (B) and the hydroperoxo complex [Co(CN)5CoO2N]3 (C). The mechanism involves partial dissociation of A to give [Co(CN)5]3− (E) which binds with unreacted A to give the η1:η1‐peroxo complex [(CN)5Co02Co(CN)5]6− (F) which is hydrolysed to B and C. The mechanism is supported by the effects of pH, dioxygen concentration, and ionic strength on the rate of decomposition, and by the trapping of oxidation products of E and F. Complex A reacts readily with reducing agents to give directly the hydroperoxo complex C.

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“…Moreover, the crown ether ringÕs special conformation in MnL n 2 Cl ðn ¼ 1-4Þ can offer large steric hindrance, and possibly favor the formation of and stabilize the active Mn@O species. The possible mechanism of styrene oxidation involves free radical processes since peroxide L n 2 MnOOHðM@MnðIIIÞClÞ could be formed an MnO 2 complexes in the presence of acid [8], and the above peroxide can oxidize styrene to benzaldehyde through a free hydroxyl radical intermediate C(OOH)-C Å , which is derived from interaction between a hydroperoxyl radical and the carbon-carbon double bond [9].…”

mentioning

confidence: 99%

The effect of aza crown ring bearing salicylaldimine Schiff bases Mn(III) complexes as catalysts in the presence of molecular oxygen on the catalytic oxidation of styrene

Zeng

Qin

2006

Inorganic Chemistry Communications

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Autoxidation of transition-metal complexes. Reaction of a 1:1 cobalt-molecular oxygen complex with acids to yield hydrogen peroxide. Kinetics and mechanism

Cited by 13 publications

References 20 publications

Brønsted Acid Scaling Relationships Enable Control Over Product Selectivity from O₂ Reduction with a Mononuclear Cobalt Porphyrin Catalyst

Brønsted Acid Scaling Relationships Enable Control Over Product Selectivity from O₂ Reduction with a Mononuclear Cobalt Porphyrin Catalyst

The Reactivity of the Pentacyano(η¹‐Dioxygen)cobaltate(III) Ion in Aqueous Solution

The effect of aza crown ring bearing salicylaldimine Schiff bases Mn(III) complexes as catalysts in the presence of molecular oxygen on the catalytic oxidation of styrene

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Autoxidation of transition-metal complexes. Reaction of a 1:1 cobalt-molecular oxygen complex with acids to yield hydrogen peroxide. Kinetics and mechanism

Cited by 13 publications

References 20 publications

Brønsted Acid Scaling Relationships Enable Control Over Product Selectivity from O2 Reduction with a Mononuclear Cobalt Porphyrin Catalyst

Brønsted Acid Scaling Relationships Enable Control Over Product Selectivity from O2 Reduction with a Mononuclear Cobalt Porphyrin Catalyst

The Reactivity of the Pentacyano(η1‐Dioxygen)cobaltate(III) Ion in Aqueous Solution

The effect of aza crown ring bearing salicylaldimine Schiff bases Mn(III) complexes as catalysts in the presence of molecular oxygen on the catalytic oxidation of styrene

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Brønsted Acid Scaling Relationships Enable Control Over Product Selectivity from O₂ Reduction with a Mononuclear Cobalt Porphyrin Catalyst

Brønsted Acid Scaling Relationships Enable Control Over Product Selectivity from O₂ Reduction with a Mononuclear Cobalt Porphyrin Catalyst

The Reactivity of the Pentacyano(η¹‐Dioxygen)cobaltate(III) Ion in Aqueous Solution