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Development of Ruthenium Catalysts for Water Oxidation
Stockholm University, Faculty of Science, Department of Organic Chemistry. (Björn Åkermark)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

An increasing global energy demand requires alternative fuel sources. A promising method is artificial photosynthesis. Although, the artificial processes are different from the natural photosynthetic process, the basic principles are the same, i.e. to split water and to convert solar energy into chemical energy. The energy is stored in bonds, which can at a later stage be released upon combustion. The bottleneck in the artificial systems is the water oxidation. The aim of this research has been to develop catalysts for water oxidation that are stable, yet efficient. The molecular catalysts are comprised of organic ligands that ultimately are responsible for the catalyst structure and activity. These ligands are often based on polypyridines or other nitrogen-containing aromatic compounds. This thesis describes the development of molecular ruthenium catalysts and the evaluation of their ability to mediate chemical and photochemical oxidation of water. Previous work from our group has shown that the introduction of negatively charged groups into the ligand frameworks lowers the redox potentials of the metal complexes. This is beneficial as it makes it possible to drive water oxidation with [Ru(bpy)3]3+-type oxidants (bpy = 2,2’-bipyridine), which can be photochemically generated from the corresponding [Ru(bpy)3]2+ complex. Hence, all the designed ligands herein contain negatively charged groups in the coordination site for ruthenium.

The first part of this thesis describes the development of two mononuclear ruthenium complexes and the evaluation of these for water oxidation. Both complexes displayed low redox potentials, allowing for water oxidation to be driven either chemically or photochemically using the mild one-electron oxidant [Ru(bpy)3]3+.

The second part is a structure–activity relationship study on several analogues of mononuclear ruthenium complexes. The complexes were active for water oxidation and the redox potentials of the analogues displayed a linear relationship with the Hammet σmeta parameter. It was also found that the complexes form high-valent Ru(VI) species, which are responsible for mediating O–O bond formation.

The last part of the thesis describes the development of a dinuclear ruthenium complex and the catalytic performance for chemical and photochemical water oxidation. It was found that the complex undergoes O–O bond formation via a bridging peroxide intermediate, i.e. an I2M–type mechanism.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University , 2016. , 67 p.
Keyword [en]
homogeneous catalysis, O-O bond formation, photocatalysis, ruthenium, water oxidation
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-134824ISBN: 978-91-7649-508-7ISBN: 978-91-7649-509-4OAI: oai:DiVA.org:su-134824DiVA: diva2:1038808
Public defence
2016-12-09, Magnéli Hall, Arrhenius Laboratory, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2016-11-16 Created: 2016-10-19 Last updated: 2016-11-04Bibliographically approved
List of papers
1. Efficient photochemical water oxidation by a dinuclear molecular ruthenium complex
Open this publication in new window or tab >>Efficient photochemical water oxidation by a dinuclear molecular ruthenium complex
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2015 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 51, no 10, 1862-1865 p.Article in journal (Refereed) Published
Abstract [en]

Herein is described the preparation of a dinuclear molecular Ru catalyst for H2O oxidation. The prepared catalyst mediates the photochemical oxidation of H2O with an efficiency comparable to state-of-the-art catalysts.

National Category
Chemical Sciences
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-114259 (URN)10.1039/c4cc08606f (DOI)000348213200020 ()25525645 (PubMedID)
Note

AuthorCount:8;

Available from: 2015-03-26 Created: 2015-02-25 Last updated: 2016-10-24Bibliographically approved
2. Water Oxidation by Single-Site Ruthenium Complexes: Using Ligands as Redox and Proton Transfer Mediators
Open this publication in new window or tab >>Water Oxidation by Single-Site Ruthenium Complexes: Using Ligands as Redox and Proton Transfer Mediators
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2012 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 51, no 46, 11589-11593 p.Article in journal (Refereed) Published
Keyword
electrochemistry, homogeneous catalysis, photocatalysis, ruthenium, water oxidation
National Category
Chemical Sciences
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-85016 (URN)10.1002/anie.201205018 (DOI)000310875700033 ()
Funder
Knut and Alice Wallenberg Foundation
Note

AuthorCount:9;

Available from: 2013-01-04 Created: 2013-01-04 Last updated: 2016-10-24Bibliographically approved
3. A Dinuclear Ruthenium-Based Water Oxidation Catalyst: Use of Non-Innocent Ligand Frameworks for Promoting Multi-Electron Reactions
Open this publication in new window or tab >>A Dinuclear Ruthenium-Based Water Oxidation Catalyst: Use of Non-Innocent Ligand Frameworks for Promoting Multi-Electron Reactions
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2015 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 21, no 28, 10039-10048 p.Article in journal (Refereed) Published
Abstract [en]

Insight into how H2O is oxidized to O-2 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.

Keyword
density functional calculations, electrochemistry, ligands, ruthenium, water splitting
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-119297 (URN)10.1002/chem.201406613 (DOI)000357026700014 ()
Available from: 2015-08-04 Created: 2015-08-03 Last updated: 2016-10-24Bibliographically approved
4. Molecular ruthenium water oxidation catalysts carrying non-innocent ligands: mechanistic insight through structure-activity relationships and quantum chemical calculations
Open this publication in new window or tab >>Molecular ruthenium water oxidation catalysts carrying non-innocent ligands: mechanistic insight through structure-activity relationships and quantum chemical calculations
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2016 (English)In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 6, no 5, 1306-1319 p.Article in journal (Refereed) Published
Abstract [en]

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 Ru-VI 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 Ru-VI 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.

National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-129099 (URN)10.1039/c5cy01704a (DOI)000371607600006 ()
Available from: 2016-04-19 Created: 2016-04-14 Last updated: 2016-10-24Bibliographically approved

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