O–O bond formation in ruthenium-catalyzed water oxidation: single-site nucleophilic attack vs. O–O radical coupling

2017 ◽  
Vol 46 (20) ◽  
pp. 6170-6193 ◽  
Author(s):  
David W. Shaffer ◽  
Yan Xie ◽  
Javier J. Concepcion
Keyword(s):  
Water Oxidation ◽  
Bond Formation ◽  
Single Site ◽  
Nucleophilic Attack ◽  
Radical Coupling ◽  
Molecular Catalysts

A review of water oxidation by ruthenium-based molecular catalysts, with emphasis on the mechanism of O–O bond formation.

scholarly journals From Ru-bda to Ru-bds: a step forward to highly efficient molecular water oxidation electrocatalysts under acidic and neutral conditions

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jing Yang ◽  
Lei Wang ◽  
Shaoqi Zhan ◽  
Haiyuan Zou ◽  
Hong Chen ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Bond Formation ◽  
Density Functional Theory Calculations ◽  
Oxidation Catalyst ◽  
Nucleophilic Attack ◽  
Molecular Water ◽  
Formation Mechanisms ◽  
Equatorial Position ◽  
Neutral Conditions

AbstractSignificant advances during the past decades in the design and studies of Ru complexes with polypyridine ligands have led to the great development of molecular water oxidation catalysts and understanding on the O−O bond formation mechanisms. Here we report a Ru-based molecular water oxidation catalyst [Ru(bds)(pic)2] (Ru-bds; bds2− = 2,2′-bipyridine-6,6′-disulfonate) containing a tetradentate, dianionic sulfonate ligand at the equatorial position and two 4-picoline ligands at the axial positions. This Ru-bds catalyst electrochemically catalyzes water oxidation with turnover frequencies (TOF) of 160 and 12,900 s−1 under acidic and neutral conditions respectively, showing much better performance than the state-of-art Ru-bda catalyst. Density functional theory calculations reveal that (i) under acidic conditions, the high valent Ru intermediate RuV=O featuring the 7-coordination configuration is involved in the O−O bond formation step; (ii) under neutral conditions, the seven-coordinate RuIV=O triggers the O−O bond formation; (iii) in both cases, the I2M (interaction of two M−O units) pathway is dominant over the WNA (water nucleophilic attack) pathway.

scholarly journals Switching the O-O Bond Formation Pathways of Ru-pda Water Oxidation Catalyst by Third Coordination Sphere Engineering

Research ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yingzheng Li ◽  
Shaoqi Zhan ◽  
Lianpeng Tong ◽  
Wenlong Li ◽  
Yilong Zhao ◽  
...  
Keyword(s):  
Coordination Sphere ◽  
Water Oxidation ◽  
Density Functional ◽  
Electrochemical Polymerization ◽  
Bond Formation ◽  
Kinetic Studies ◽  
Oxidation Catalyst ◽  
Nucleophilic Attack ◽  
Formation Pathway ◽  
Axial Ligands

Water oxidation is a vital anodic reaction for renewable fuel generation via electrochemical- and photoelectrochemical-driven water splitting or CO2 reduction. Ruthenium complexes, such as Ru-bda family, have been shown as highly efficient water-oxidation catalysts (WOCs), particularly when they undergo a bimolecular O-O bond formation pathway. In this study, a novel Ru(pda)-type (pda2– =1,10-phenanthroline-2,9-dicarboxylate) molecular WOC with 4-vinylpyridine axial ligands was immobilized on the glassy carbon electrode surface by electrochemical polymerization. Electrochemical kinetic studies revealed that this homocoupling polymer catalyzes water oxidation through a bimolecular radical coupling pathway, where interaction between two Ru(pda)–oxyl moieties (I2M) forms the O-O bond. The calculated barrier of the I2M pathway by density-functional theory (DFT) is significantly lower than the barrier of a water nucleophilic attack (WNA) pathway. By using this polymerization strategy, the Ru centers are brought closer in the distance, and the O-O bond formation pathway by the Ru (pda) catalyst is switched from WNA in a homogeneous molecular catalytic system to I2M in the polymerized film, providing some deep insights into the importance of third coordination sphere engineering of the water oxidation catalyst.

The Ru-tpc Water Oxidation Catalyst and Beyond: Water Nucleophilic Attack Pathway versus Radical Coupling Pathway

ACS Catalysis ◽  
2017 ◽  
Vol 7 (4) ◽  
pp. 2956-2966 ◽  
Author(s):  
Ting Fan ◽  
Lele Duan ◽  
Ping Huang ◽  
Hong Chen ◽  
Quentin Daniel ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Oxidation Catalyst ◽  
Nucleophilic Attack ◽  
Radical Coupling

scholarly journals Formation of CoIV=O intermediate at the Boundary of the “Oxo-wall” Induces Water Oxidation

2020 ◽  
Author(s):  
Roman Ezhov ◽  
Alireza Ravari ◽  
Gabriel Bury ◽  
Paul Smith ◽  
Yulia Pushkar
Keyword(s):  
Hydrogen Bonding ◽  
Water Splitting ◽  
Oxygen Evolution ◽  
Water Oxidation ◽  
Artificial Photosynthesis ◽  
Bond Formation ◽  
Nucleophilic Attack ◽  
Earth Abundant ◽  
3D Elements

Abstract Development of economically viable artificial photosynthesis requires use of 3d metal-based catalysts. Water oxidation by [Co4O4]n+ cubane mimics water splitting by CaMn4O5 cluster in Nature but the exact mechanism of O-O bond formation is presently unknown. We demonstrate first in situ detection CoIV=O (~ 1.67 Å) moiety formed upon activation of [Co4O4Py4Ac4]0 (Py = pyridine and Ac = CH3COO−) towards O-O bond formation. Combined spectroscopic and DFT analyses show that the intermediate active in O-O bond formation has two CoIV centers and at least one CoIV=O unit of strong radicaloid character that participates in O-O bond formation via water nucleophilic attack. The multimetallic structure of the cubane provides unique stabilization for CoIV=O + H2O = Co-OOH + H+ transition with the carboxyl accepting the proton and the bridging oxygen stabilizing the peroxide via hydrogen bonding. Results are important for development of oxygen evolution catalysts based on Earth-abundant 3d elements.

scholarly journals Hydrazine Formation via NiIII-NH2 Radical Coupling in Ni-Mediated Ammonia Oxidation

2020 ◽  
Author(s):  
Nina Gu ◽  
Paul H. Oyala ◽  
Jonas Peters
Keyword(s):  
Water Oxidation ◽  
Ammonia Oxidation ◽  
Bond Formation ◽  
Oxidation States ◽  
Bond Forming ◽  
Radical Coupling ◽  
Multiply Bonded ◽  
Ni Species ◽  
Oxidation Mechanisms ◽  
Metal Ligand

<p>Given the diverse mechanistic possibilities for the overall 6e<sup>-</sup>/6H<sup>+</sup> transformation of ammonia to dinitrogen, identification of M(NH<sub>x</sub>) intermediates involved in N–N bond formation is a central mechanistic challenge. In analogy to water oxidation mechanisms, which widely invoke metal oxo intermediates, metal imide and nitride intermediates have commonly been proposed for ammonia oxidation, and stoichiometric demonstration of N–N bond formation from these metal-ligand multiply bonded species is well-precedented. In contrast, while the homocoupling of M–NH<sub>2</sub> species to form hydrazine has been hypothesized as the key N–N bond forming step in certain molecular ammonia oxidation systems, well-defined examples of this transformation from M–NH<sub>2</sub> complexes are essentially without precedent. This work reports the first example of net ammonia oxidation mediated by a molecular Ni species, a transformation carried out via formal Ni<sup>II</sup>/Ni<sup>III</sup> oxidation states. The available data are consistent with a Ni<sup>III</sup>–NH<sub>2</sub> intermediate featuring substantial spin at N undergoing N–N bond formation to generate a Ni<sup>II</sup><sub>2</sub>(N<sub>2</sub>H<sub>4</sub>) complex. Additional and structurally unusual Ni<sub>x</sub>(N<sub>y</sub>H<sub>z</sub>) species – including a Ni<sub>2</sub>(<i>trans</i>-N<sub>2</sub>H<sub>2</sub>) complex – are characterized and studied as intermediates in the Ni-mediated ammonia oxidation cycle described herein.</p>

scholarly journals Hydrazine Formation via NiIII-NH2 Radical Coupling in Ni-Mediated Ammonia Oxidation

2020 ◽  
Author(s):  
Nina Gu ◽  
Paul H. Oyala ◽  
Jonas Peters
Keyword(s):  
Water Oxidation ◽  
Ammonia Oxidation ◽  
Bond Formation ◽  
Oxidation States ◽  
Bond Forming ◽  
Radical Coupling ◽  
Multiply Bonded ◽  
Ni Species ◽  
Oxidation Mechanisms ◽  
Metal Ligand

<p>Given the diverse mechanistic possibilities for the overall 6e<sup>-</sup>/6H<sup>+</sup> transformation of ammonia to dinitrogen, identification of M(NH<sub>x</sub>) intermediates involved in N–N bond formation is a central mechanistic challenge. In analogy to water oxidation mechanisms, which widely invoke metal oxo intermediates, metal imide and nitride intermediates have commonly been proposed for ammonia oxidation, and stoichiometric demonstration of N–N bond formation from these metal-ligand multiply bonded species is well-precedented. In contrast, while the homocoupling of M–NH<sub>2</sub> species to form hydrazine has been hypothesized as the key N–N bond forming step in certain molecular ammonia oxidation systems, well-defined examples of this transformation from M–NH<sub>2</sub> complexes are essentially without precedent. This work reports the first example of net ammonia oxidation mediated by a molecular Ni species, a transformation carried out via formal Ni<sup>II</sup>/Ni<sup>III</sup> oxidation states. The available data are consistent with a Ni<sup>III</sup>–NH<sub>2</sub> intermediate featuring substantial spin at N undergoing N–N bond formation to generate a Ni<sup>II</sup><sub>2</sub>(N<sub>2</sub>H<sub>4</sub>) complex. Additional and structurally unusual Ni<sub>x</sub>(N<sub>y</sub>H<sub>z</sub>) species – including a Ni<sub>2</sub>(<i>trans</i>-N<sub>2</sub>H<sub>2</sub>) complex – are characterized and studied as intermediates in the Ni-mediated ammonia oxidation cycle described herein.</p>

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