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Molecular ruthenium water oxidation catalysts carrying non-innocent ligands: mechanistic insight through structure-activity relationships and quantum chemical calculations
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
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Number of Authors: 7
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.

Place, publisher, year, edition, pages
2016. Vol. 6, no 5, 1306-1319 p.
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-129099DOI: 10.1039/c5cy01704aISI: 000371607600006OAI: oai:DiVA.org:su-129099DiVA: diva2:921095
Available from: 2016-04-19 Created: 2016-04-14 Last updated: 2016-10-24Bibliographically approved
In thesis
1. Development of Ruthenium Catalysts for Water Oxidation
Open this publication in new window or tab >>Development of Ruthenium Catalysts for Water Oxidation
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
homogeneous catalysis, O-O bond formation, photocatalysis, ruthenium, water oxidation
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-134824 (URN)978-91-7649-508-7 (ISBN)978-91-7649-509-4 (ISBN)
Public defence
2016-12-09, Magnéli Hall, Arrhenius Laboratory, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
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Available from: 2016-11-16 Created: 2016-10-19 Last updated: 2016-11-04Bibliographically approved

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Kärkäs, Markus D.Laine, Tanja M.Siegbahn, Per E. M.Åkermark, Björn
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