Electronic Effects on Single‐Site Iron Catalysts for Water Oxidation

Codolà, Zoel; Garcia‐Bosch, Isaac; Acuña‐Parés, Ferran; Prat, Irene; Luis, Josep M.; Costas, Miguel; Lloret‐Fillol, Julio

doi:10.1002/chem.201301112

Cited by 119 publications

(123 citation statements)

References 42 publications

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“…These experiments provided support for a mechanism in which a [ 396 To shed light on the mechanism of the final part of the reaction, that is, the generation of O 2 from the [Fe IV (O)-(OH 2 )(L N4 )] 2+ species, the authors decided to address this in a subsequent study. 397 In this study, a family of structural analogues of complex 303 ( Figure 81) hosuing different This work gave additional insight into the mechanism of the crucial O−O bond formation and also revealed that structural modifications of the ligand backbone had a significant effect on the catalytic performance. Carrying out the reaction with 12.5 μM of complex 312 and 10.000 equiv of CAN at pH 0.7 resulted in the most efficient reaction, affording a TON of 180 over 2 h and a maximum TOF of 0.23 s −1 .…”

Section: Molecular Water Oxidation Catalysts Based On Ironmentioning

confidence: 96%

Artificial Photosynthesis: Molecular Systems for Catalytic Water Oxidation

et al. 2014

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Section: Molecular Water Oxidation Catalysts Based On Ironmentioning

confidence: 96%

Artificial Photosynthesis: Molecular Systems for Catalytic Water Oxidation

et al. 2014

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“…1,2 While in attempts to mimic nature the first catalysts were based on manganese, more recently catalytically active compounds for water oxidation have been reported based on cobalt, 3-7 nickel, [8][9][10] iron, [11][12][13] copper, 14-20 ruthenium [21][22][23][24][25][26][27][28][29][30][31][32][33][34] and iridium. [35][36][37][38][39] Generally, the catalytic activity of these compounds is investigated using the oxidant (NH4)2[Ce(NO3)6] (CAN).…”

Section: Introductionmentioning

confidence: 99%

Rate and Stability of Photocatalytic Water Oxidation using [Ru(bpy)₃]²⁺ as Photosensitizer

2016

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The kinetics of homogeneous photocatalytic water oxidation is reported using [Ru(bpy)3]Cl2 as photosensitizer, Na2S2O8 as sacrificial electron acceptor, and three different water-oxidation catalysts: the ruthenium catalyst [Ru(bda)(isoq)2] ([1], H2bda = 2,2'-bipyridine-6,6'-dicarboxylic acid, isoq = isoquinoline), Co(NO3)2 ([2]), or [Ir(Cp*)(dmiz)(OH)2] ([3], Cp* = pentamethylcyclopentadienyl, dmiz = 1,3-dimethylimidazol-2-ylidene). At pH=7.0, in a phosphate buffer, and under blue light irradiation, the production of O2 at the catalyst is rate determining when [2] or [3] are used as water-oxidation catalysts. However, when [1] is used as catalyst in identical conditions the turn over at the wateroxidation catalyst is not the rate-limiting step of the photocatalysis. Instead, the step limiting dioxygen production is the transfer of electrons from the catalyst to the photooxidized photosensitizer [Ru(bpy)3] 3+ . Due to the instability of [Ru(bpy)3] 3+ in neutral aqueous solutions, slow electron transfer results in significant photosensitizer decomposition, which limits the overall stability of the photocatalytic system. When the catalyst [1] is used decomposition of both the photosensitizer and the catalyst [1] occurs in parallel. However, the photosensitizer and the catalyst also stabilize each other, i.e., the TON increases when more photosensitizer is added, while the photocatalytic turnover number PTON increases when more catalyst [1] is added. These data demonstrate that not only new and more stable water oxidation catalysts should be developed in the future, but that new and more stable photosensitizers are needed as well.

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“…10,15,porphyrin, with a highly electron-deficient meso-dimethylimidazolium porphyrin, was the most effective catalyst. The O 2 formation rate was 170 nmol·cm −2 ·min −1 (k obs = 1.4 × 10 3 s −1 ) with a Faradaic efficiency near 90%.…”

mentioning

confidence: 99%

Efficient water oxidation catalyzed by homogeneous cationic cobalt porphyrins with critical roles for the buffer base

Wang

Groves

2013

Proc. Natl. Acad. Sci. U.S.A.

337

306

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A series of cationic cobalt porphyrins was found to catalyze electrochemical water oxidation to O 2 efficiently at room temperature in neutral aqueous solution. 10,15,porphyrin, with a highly electron-deficient meso-dimethylimidazolium porphyrin, was the most effective catalyst. The O 2 formation rate was 170 nmol·cm −2 ·min −1 (k obs = 1.4 × 10 3 s −1 ) with a Faradaic efficiency near 90%. Mechanistic investigations indicate the generation of a Co IV -O porphyrin cation radical as the reactive oxidant, which has accumulated two oxidizing equivalents above the Co III resting state of the catalyst. The buffer base in solution was shown to play several critical roles during the catalysis by facilitating both redox-coupled proton transfer processes leading to the reactive oxidant and subsequent O-O bond formation. More basic buffer anions led to lower catalytic onset potentials, extending below 1 V. This homogeneous cobalt-porphyrin system was shown to be robust under active catalytic conditions, showing negligible decomposition over hours of operation. Added EDTA or ion exchange resin caused no catalyst poisoning, indicating that cobalt ions were not released from the porphyrin macrocycle during catalysis. Likewise, surface analysis by energy dispersive X-ray spectroscopy of the working electrodes showed no deposition of heterogeneous cobalt films. Taken together, the results indicate that Co-5,10,15,20-tetrakis-(1,3-dimethylimidazolium-2-yl)porphyrin is an efficient, homogeneous, single-site water oxidation catalyst.ater oxidation is a key step in photosynthesis that efficiently harvests and stores solar energy (1). The oxidation of H 2 O to O 2 is a four-electron, four-proton process in which O-O bond formation is the key chemical step. In photosystem II, these proton-coupled electron transfers (PCETs) occur via a tyrosine at the Mn 4 Ca oxygen-evolving complex (2). An important thermodynamic aspect of photosynthesis is the efficient conversion of photonic energy to electrical potential, thus providing 99% of the driving force required to convert CO 2 to carbohydrates (Eqs. 1 and 2):andThe development of synthetic catalysts that can mediate water oxidation under mild conditions with a minimal energy cost has become an appealing challenge for chemists (3-7). Among various approaches, homogeneous molecular catalysts have shown attractive features such as controllable redox properties, ease of investigating reaction mechanisms, and strategies for the characterization of reactive intermediates (8,9). Recently, such efforts have resulted in the development of a significant number of systems based on single-site and multinuclear transition metal complexes including Mn, Fe, Co, Cu, Ru, and Ir (9-15). Examples of cobalt-based molecular catalysts include a cobalt phthalocyanine (16), a cobalt "hangman" corrole (17), multipyridine cobalt complexes (18, 19), a dinuclear Co-peroxo species (20), and most recently, Co-porphyrins (21). Determining if these molecular complexes retain their homogenous nature during catalysis or ...

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Electronic Effects on Single‐Site Iron Catalysts for Water Oxidation

Cited by 119 publications

References 42 publications

Artificial Photosynthesis: Molecular Systems for Catalytic Water Oxidation

Artificial Photosynthesis: Molecular Systems for Catalytic Water Oxidation

Rate and Stability of Photocatalytic Water Oxidation using [Ru(bpy)₃]²⁺ as Photosensitizer

Efficient water oxidation catalyzed by homogeneous cationic cobalt porphyrins with critical roles for the buffer base

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Electronic Effects on Single‐Site Iron Catalysts for Water Oxidation

Cited by 119 publications

References 42 publications

Artificial Photosynthesis: Molecular Systems for Catalytic Water Oxidation

Artificial Photosynthesis: Molecular Systems for Catalytic Water Oxidation

Rate and Stability of Photocatalytic Water Oxidation using [Ru(bpy)3]2+ as Photosensitizer

Efficient water oxidation catalyzed by homogeneous cationic cobalt porphyrins with critical roles for the buffer base

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Rate and Stability of Photocatalytic Water Oxidation using [Ru(bpy)₃]²⁺ as Photosensitizer