Tanja M. Laine

Water Oxidation by Single-Site Ruthenium Complexes : Using Ligands as Redox and Proton Transfer Mediators

Water Oxidation by Single-Site Ruthenium Complexes : Using Ligands as Redox and Proton Transfer Mediators

A Dinuclear Ruthenium-Based Water Oxidation Catalyst: Use of Non-Innocent Ligand Frameworks for Promoting Multi-Electron Reactions

Insight into how H2O is oxidized to O2 is envisioned to facilitate the rational design of artificial water oxidation catalysts, which is a vital component in solar-to-fuel conversion schemes. Herein, we report on the mechanistic features associated with a dinuclear Ru-based water oxidation catalyst. The catalytic action of the designed Ru complex was studied by the combined use of high-resolution mass spectrometry, electrochemistry, and quantum chemical calculations. Based on the obtained results, it is suggested that the designed ligand scaffold in Ru complex 1 has a non-innocent behavior, in which metal–ligand cooperation is an important part during the four-electron oxidation of H2O. This feature is vital for the observed catalytic efficiency and highlights that the preparation of catalysts housing non-innocent molecular frameworks could be a general strategy for accessing efficient catalysts for activation of H2O.

Molecular ruthenium water oxidation catalysts carrying non-innocent ligands: mechanistic insight through structure–activity relationships and quantum chemical calculations

Robust catalysts that mediate H2O oxidation are of fundamental importance for the development of novel carbon-neutral energy technologies. Herein we report the synthesis of a group of single-site Ru complexes. Structure–activity studies revealed that the individual steps in the oxidation of H2O depended differently on the electronic properties of the introduced ligand substituents. The mechanistic details associated with these complexes were investigated experimentally along with quantum chemical calculations. It was found that O–O bond formation for the developed Ru complexes proceeds via high-valent RuVI species, where the capability of accessing this species is derived from the non-innocent ligand architecture. This cooperative catalytic involvement and the ability of accessing RuVI are intriguing and distinguish these Ru catalysts from a majority of previously reported complexes, and might generate unexplored reaction pathways for activation of small molecules such as H2O.

Cobalt selenium oxohalides: catalysts for water oxidation.

Two new oxohalides Co4Se3O9Cl2 and Co3Se4O10Cl2 have been synthesized by solid state reactions. They crystallize in the orthorhombic space group Pnma and the monoclinic space group C2/m respectively. The crystal structure of the two compounds are made up of similar building blocks; Co4Se3O9Cl2 is made up of [CoO4Cl2], [CoO5Cl] and [SeO3] polyhedra and Co3Se4O10Cl2 is made up of [CoO4Cl2] and [SeO3] polyhedra. As several Co-containing compounds have proved to be good catalysts for water oxidation, the activities of the two new compounds were compared with the previously found oxohalide Co5Se4O12Cl2 in reference to CoO and CoCl2. The one electron oxidant Ru(bpy)3(3+) was used as oxidizing species in a phosphate buffer and it was found that the activities of the oxohalide species were in between CoO and CoCl2. The roles of Cl(-) and PO4(3-) ions are discussed.

On the mechanism of water oxidation catalyzed by a dinuclear ruthenium complex: a quantum chemical study

The development of efficient and robust catalysts for H2O oxidation is an essential element in solar water splitting. The reaction mechanism for a previously reported dinuclear Ru water oxidation catalyst (1) has been investigated in detail through quantum chemical calculations. The predicted mechanism starts from a Ru2III,III complex with two aqua ligands. After three sequential oxidations, O–O bond formation occurs at a formal Ru2IV,V state via the direct coupling of two adjacent oxo moieties while the water nucleophilic attack mechanism was found to be associated with a higher energy barrier. Two H2O molecules are then inserted with subsequent release of O2, which was found to be the rate-limiting step with a barrier of 22.7 kcal mol−1. In a previous work, it was revealed that the ligand scaffold in the studied Ru complex has a non-innocent function. Here, we further highlight this behavior, where the ligand was shown to mediate proton transfer events and accept/donate electrons during the catalytic cycle, which can significantly decrease the redox potentials and facilitate the access to high-valent redox states. This study provides further insight into the H2O oxidation mechanism and principles for designing improved catalysts for activation of small molecules, such as H2O.

Chemical and Photochemical Water Oxidation Mediated by an Efficient Single-Site Ruthenium Catalyst

Abstract Water oxidation is a fundamental step in artificial photosynthesis for solar fuels production. In this study, we report a single‐site Ru‐based water oxidation catalyst, housing a dicarboxylate‐benzimidazole ligand, that mediates both chemical and light‐driven oxidation of water efficiently under neutral conditions. The importance of the incorporation of the negatively charged ligand framework is manifested in the low redox potentials of the developed complex, which allows water oxidation to be driven by the mild one‐electron oxidant [Ru(bpy)3]3+ (bpy=2,2’‐bipyridine). Furthermore, combined experimental and DFT studies provide insight into the mechanistic details of the catalytic cycle.

An Oxofluoride Catalyst Comprised of Transition Metals and a Metalloid for Application in Water Oxidation

The application of the recently discovered oxofluoride solid solution (Cox Ni1-x )3 Sb4 O6 F6 as a catalyst for water oxidation is demonstrated. The phase exhibits a cubic arrangement of the active metal that forms oxo bridges to the metalloid with possible catalytic participation. The Co3 Sb4 O6 F6 compound proved to be capable of catalyzing 2H2 O→O2 +4H(+) +4e(-) at 0.33 V electrochemical and ≤0.39 V chemical overpotential with a TOF of 4.4⋅10(-3) , whereas Ni3 Sb4 O6 F6 needs a higher overpotential. Relatively large crystal cubes (0.3-0.5 mm) are easily synthesized and readily handled as they demonstrate both chemical resistance to wear after repeated in situ tests under experimental conditions, and have a mechanical hardness of 270 V0.1 using Vickers indentation. The combined properties of this compound offer a potential technical advantage for incorporation to a catalytic interface in future sustainable fuel production.

Substituent Effects in Molecular Ruthenium Water Oxidation Catalysts Based on Amide Ligands

The production of clean and sustainable energy is considered as one of the most urgent issues for our society. Mastering the oxidation of water to dioxygen is essential for the production of solar fuels. A study of the influence of the substituents on the catalytic activity of a series of mononuclear Ru complexes (2 a–e) based on a tetradentate ligand framework is presented. At neutral pH, using [Ru(bpy)3](PF6)3 (bpy=2,2’‐bipyridine) as the terminal oxidant, a good correlation between the turnover frequency (TOF) and the Hammett σmeta parameters was obtained. Additionally, a general pathway for the deactivation of Ru‐based catalysts 2 a–e during the catalytic oxidation of water through poisoning by carbon monoxide was demonstrated. These results highlight the importance of ligand design for fine‐tuning the catalytic activity of water oxidation catalysts.

Catalyst–solvent interactions in a dinuclear Ru-based water oxidation catalyst

Photocatalytic water oxidation represents a key process in conversion of solar energy into fuels and can be facilitated by the use of molecular transition metal-based catalysts. A novel straightforward approach for covalent linking of the catalytic units to other moieties is demonstrated by preparation of a dinuclear complex containing two [Ru(pdc)(pic)3]-derived units (pdc = 2,6-pyridinedicarboxylate, pic = 4-picoline). The activity of this complex towards chemical and photochemical oxidation of water was evaluated and a detailed insight is given into the interactions between the catalyst and acetonitrile, a common co-solvent employed to increase solubility of water oxidation catalysts. The solvent-induced transformations were studied by electrochemical and spectroscopic techniques and the relevant quantitative parameters were extracted.

Visible Light-Driven Water Oxidation Catalyzed by Ruthenium Complexes

A shift in energy dependence from fossil fuels to sustainable and carbon-neutral alternatives is a daunting challenge that faces the human society. Light harvesting for the production of solar fuels has been extensively investigated as an attractive approach to clean and abundant energy. An essential component in solar energy conversion schemes is a catalyst for water oxidation. Ruthenium-based catalysts have received significant attention due to their ability to efficiently mediate the oxidation of water. In this context, the design of robust catalysts capable of driving water oxidation at low overpotential is a key challenge for realizing efficient visible light-driven water splitting. Herein, recent progress in the development within this field is presented with a focus on homogeneous ruthenium-based systems and surface-immobilized ruthenium assemblies for photo-induced oxidation of water.