Oxygen−Oxygen Bond Formation by the Ru-Hbpp Water Oxidation Catalyst Occurs Solely via an Intramolecular Reaction Pathway

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.

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Ligand Geometry Directs OO Bond-Formation Pathway in Ruthenium-Based Water Oxidation Catalyst

Angewandte Chemie ◽

10.1002/ange.201201356 ◽

2012 ◽

Vol 124 (24) ◽

pp. 6069-6072 ◽

Cited By ~ 23

Author(s):

Somnath Maji ◽

Laura Vigara ◽

Francesca Cottone ◽

Fernando Bozoglian ◽

Jordi Benet-Buchholz ◽

...

Keyword(s):

Water Oxidation ◽

Bond Formation ◽

Oxidation Catalyst ◽

Formation Pathway

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Impact of the Ligand Flexibility and Solvent on the O–O Bond Formation Step in a Highly Active Ruthenium Water Oxidation Catalyst

Inorganic Chemistry ◽

10.1021/acs.inorgchem.8b00619 ◽

2018 ◽

Vol 57 (21) ◽

pp. 13063-13066 ◽

Cited By ~ 23

Author(s):

Nitish Govindarajan ◽

Ambuj Tiwari ◽

Bernd Ensing ◽

Evert Jan Meijer

Keyword(s):

Water Oxidation ◽

Bond Formation ◽

Oxidation Catalyst ◽

Highly Active ◽

Formation Step

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

Research ◽

10.34133/2021/9851231 ◽

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.

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