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Toward Controlling Water Oxidation Catalysis: Tunable Activity of Ruthenium Complexes with Axial Imidazole/DMSO Ligands
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. (Organisk kemi/O Ramström)ORCID iD: 0000-0003-1662-5817
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2012 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 45, 18868-18880 p.Article in journal (Refereed) Published
Abstract [en]

Using the combinations of imidazole and dimethyl :sulfoxide (DMSO) as axial ligands and 2,2'-bipyridine-6,6'-dicarboxylate (bda) as the equatorial ligand, we have synthesized six novel ruthenium complexes with noticeably different activity as water oxidation catalysts (WOCs). In four C-s symmetric Ru-II(kappa(3)-bda)(DMSO)L-2 complexes L = imidazole (1), N-methylimidazole (2), 5-methylimidazole (3), and 5-bromo-N-methylimidazole (4). Additionally, in two C-2v symmetric Ru-II(kappa(4)-bda)L-2 complexes L = 5-nitroimidazole (5) and 5-bromo-N-methylimidazole (6), that is, fully equivalent axial imidazoles. A detailed characterization of all complexes and the mechanistic investigation of the catalytic water oxidation have been carried out with a number of experimental techniques, that is, kinetics, electrochemistry and high resolution mass spectrometry (HR-MS), and density functional theory (DFT) calculations. We have observed the in situ formation: of a Ru-II-complex with the accessible seventh coordination position. The measured catalytic activities and kinetics of complex 1-6 revealed details about an important structure activity relation: the connection between the nature of axial ligands in the combination and either the increase or decrease of the catalytic activity. In particular, an axial DMSO group substantially increases the turnover frequency of WOCs reported in article, with the ruthenium-complex having one axial 5-bromo-N-methylimidazole and one axial DMSO: (4), we have obtained a high initial turnover frequency of similar to 180 s(-1). DFT modeling Of the binuclear reaction pathway of the O-O bond formation in catalytic Water oxidation further corroborated the concept of the mechanistic significance of the axial ligands and rationalized the experimentally observed difference in the activity of complexes with imidazole/DMSO and imidazole/imidazole combinations of axial ligands.

Place, publisher, year, edition, pages
2012. Vol. 134, no 45, 18868-18880 p.
Keyword [en]
O-O Bond, Redox Properties, Photosystem-Ii, Molecular Catalysts, Iridium Complexes, Dimer Complex, Mechanisms, Photosynthesis, Intermediate, Family
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-109191DOI: 10.1021/ja309805mISI: 000311192100060ScopusID: 2-s2.0-84869478208OAI: diva2:582858
Swedish Research CouncilKnut and Alice Wallenberg Foundation

QC 20130107

Available from: 2013-01-07 Created: 2012-12-21 Last updated: 2015-09-16Bibliographically approved
In thesis
1. Artificial Photosynthesis: Molecular Catalysts for Water Oxidation
Open this publication in new window or tab >>Artificial Photosynthesis: Molecular Catalysts for Water Oxidation
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Artificial photosynthesis provides a promising solution to the future sustainable energy system. Water is the only suitably sufficient protons and electrons supplier by the reaction of water oxidation. However, this reaction is both kinetically and thermodynamically demanding, leading to a sluggish kinetics unless the introduction of a catalyst.The theme of this thesis is to design, synthesize and evaluate molecular catalysts for water oxidation. This thesis consists of seven parts:The first chapter presents a general introduction to the field of homogenous catalysis of water oxidation, including catalysts design, examination and mechanistic investigation.The second chapter investigates the electronic and noncovalent-interaction effects of the ligands on the activities of the catalysts.In the third chapter, halogen substitutes are introduced into the axial ligands of the ruthenium catalysts. It is proved that the hydrophobic effect of the halogen atom dramatically enhanced the reactivity of the catalysts.Chapter four explores a novel group of ruthenium catalysts with imidazole-DMSO pair of axial ligands, in which the DMSO is proved to be crucial for the high efficiency of the catalysts.Chapter five describes the light-driven water oxidation including the three-component system and the sensitizer-catalyst assembled system. It is found that the common Ru(bpy)32+ dye can act as an electron relay and further benefit the electron transfer as well as the photo-stability of the system.In chapter six, aiming to the future application, selected ruthenium catalysts have been successfully immobilized on electrodes surfaces, and the electrochemical water oxidation is achieved with high efficiency.Finally, in the last chapter, a novel molecular catalyst based on the earth abundant metal ―nickel has been designed and synthesized. The activities as well as the mechanism have been explored.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 82 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:40
artificial photosynthesis, water oxidation, ruthenium complexes, nickel complexes, cerium, photo-catalysts, photosensitizer, electrochemistry, immobilization.
National Category
Organic Chemistry Physical Chemistry
Research subject
Chemistry; Energy Technology
urn:nbn:se:kth:diva-173622 (URN)978-91-7595-659-6 (ISBN)
Public defence
2015-10-13, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Swedish Energy Agency

QC 20150916

Available from: 2015-09-16 Created: 2015-09-15 Last updated: 2015-09-16Bibliographically approved

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