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Mononuclear Ruthenium Complexes that Catalyze Water to Dioxgen Oxidation
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. (Licheng SUN)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The theme of this thesis is the development of mononuclear Ru-based complexes that are capable of catalyzing the water oxidation (or O2-evolving) reaction, e.g. 2 H2O → O2 + 4 H+ + 4 e. Several families of mononuclear Ru water oxidation catalysts were designed and prepared. They feature with anionic ancillary ligands that contain carboxylate or phenolate donors. The properties of the catalysts were investigated in various aspects including coordination geometry, electrochemical behavior, and ligand exchange. All catalysts showed outstanding catalytic activity towards water oxidation in the presence of cerium(IV) ammonium nitrate as a sacrificial oxidant. High-valent Ru intermediates involved in the reactions were characterized both experimentally and theoretically. The kinetics of catalytic water oxidation was examined based on one catalyst and a prevailing catalytic pathway was proposed. The catalytic cycle involved a sequence of oxidation steps from RuII−OH2 to RuV=O species and O−O bond formation via water-nucleophilic-attack to the RuV=O intermediate. By comparing properties and catalytic performance of Ru catalysts herein with that of previously reported examples, the effect of anionic ancillary ligands was clearly elucidated in the context of catalytic water oxidation. Aiming to further application in an envisaged artificial photosynthesis device, visible light-driven water oxidation was conducted and achieved primarily in a homogeneous three-component system containing catalyst, photosensitizer, and sacrificial electron acceptor. Moreover, one model Ru catalyst was successfully immobilized on ordinary glass carbon surface through a facile and widely applicable method.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , 101 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:55
Keyword [en]
Ruthenium complex, Homogeneous catalysis, Water oxidation, O2 evolution, anionic ligand, Molecular catalyst, Electrocatalysis, Kinetics, Artificial photosynthesis, Light-driven, Immobilization of catalyst
National Category
Organic Chemistry Inorganic Chemistry Energy Systems
Identifiers
URN: urn:nbn:se:kth:diva-104765ISBN: 978-91-7501-517-0 (print)OAI: oai:DiVA.org:kth-104765DiVA: diva2:567277
Public defence
2012-11-30, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20121112

Available from: 2012-11-12 Created: 2012-11-12 Last updated: 2012-11-13Bibliographically approved
List of papers
1. Structural Modifications of Mononuclear Ruthenium Complexes: A Combined Experimental and Theoretical Study on the Kinetics of Ruthenium-Catalyzed Water Oxidation
Open this publication in new window or tab >>Structural Modifications of Mononuclear Ruthenium Complexes: A Combined Experimental and Theoretical Study on the Kinetics of Ruthenium-Catalyzed Water Oxidation
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2011 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 50, no 2, 445-449 p.Article in journal (Refereed) Published
Abstract [en]

Small change, big difference: A minor structural modification of water-oxidation catalysts changes the kinetics of O2 evolution from second- to first-order (see scheme). According to DFT calculations, the torsional flexibility of the chelating ligands and their reorganization through the catalytic cycle are implicated in pathway selectivity, and the auxiliary carboxylate group becomes involved in proton-coupled nucleophilic attack.

Keyword
density functional calculations, homogeneous catalysis, N, O ligands, ruthenium, water splitting
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-31388 (URN)10.1002/anie.201005141 (DOI)000286729300017 ()2-s2.0-78650882640 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
QC 20110314Available from: 2011-03-14 Created: 2011-03-14 Last updated: 2017-12-11Bibliographically approved
2. Water Oxidation Catalysis: Influence of Anionic Ligands upon the Redox Properties and Catalytic Performance of Mononuclear Ruthenium Complexes
Open this publication in new window or tab >>Water Oxidation Catalysis: Influence of Anionic Ligands upon the Redox Properties and Catalytic Performance of Mononuclear Ruthenium Complexes
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2012 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 51, no 6, 3388-3398 p.Article in journal (Refereed) Published
Abstract [en]

Aiming at highly efficient molecular catalyts for water oxidation, a mononuclear ruthenium complex Ru-II(hqc)(pic)(3) (1; H(2)hqc = 8-hydroxyquinoline-2-carboxylic acid and plc = 4-picoline) containing negatively charged carboxylate and phenolate donor groups has been designed and synthesized. As a comparison, two reference complexes, Ru-II(pdc)(pic)(3) (2; H(2)pdc = 2,6-pyridine-dicarboxylic acid) and Ru-II(tpy)(pic)(3) (3; tpy = 2,2':6',2 ''-terpyridine), have also been prepared. All three complexes are fully characterized by NMR, mass spectrometry (MS), and X-ray crystallography. Complex 1 showed a high efficiency toward catalytic water oxidation either driven by chemical oxidant (Ce-IV in a pH 1 solution) with a initial turnover number of 0.32 s(-1), which is several orders of magnitude higher than that of related mononuclear ruthenium catalysts reported in the literature, or driven by visible light in a three-component system with [Ru(bpy)(3)](2+) types of photosensitizers. Electrospray ionization MS results revealed that at the Rum state complex 1 undergoes ligand exchange of 4-picoline with water, forming the authentic water oxidation catalyst in situ. Density functional theory (DFT) was ernployed to explain how anionic ligands (hqc and pdc) facilitate the 4-picoline dissociation compared with a neutral ligand (tpy). Electrochemical measurements show that complex 1 has a much lower E(Ru-III/Ru-II) than that of reference complex 2 because of the introduction of a phenolate ligand. DFT was further used to study the influence of anionic ligands upon the redox properties of mononuclear aquaruthenium species, which are postulated to be involved in the catalysis cycle of water oxidation.

Keyword
Molecular Catalysts, Excited-States, Density, Thermochemistry, Solvation, Dioxygen, Kinetics, Energy, Cells, Dimer
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-95121 (URN)10.1021/ic201348u (DOI)000301624500008 ()2-s2.0-84863338735 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
QC 20120515Available from: 2012-05-15 Created: 2012-05-14 Last updated: 2017-12-07Bibliographically approved
3. Catalytic Water Oxidation by Mononuclear Ru Complexes with an Anionic Ancillary Ligand
Open this publication in new window or tab >>Catalytic Water Oxidation by Mononuclear Ru Complexes with an Anionic Ancillary Ligand
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2013 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 52, no 5, 2505-2518 p.Article in journal (Refereed) Published
Abstract [en]

Mononuclear Ru-based water oxidation catalysts containing anionic ancillary ligands have shown promising catalytic efficiency and intriguing properties. However, their insolubility in water restricts a detailed mechanism investigation. In order to overcome this disadvantage, complexes [Ru-II(bpc)(bpy)OH2](+) (1(+), bpc = 2,2'-bipyridine-6-carboxylate, bpy = 2,2'-bipyridine) and [Ru-II(bpc)(pic)(3)](+) (2(+), pic = 4-picoline) were prepared and fully characterized, which features an anionic tridentate ligand and has enough solubility for spectroscopic study in water. Using Ce-IV as an electron acceptor, both complexes are able to catalyze O-2-evolving reaction with an impressive rate constant. On the basis of the electrochemical and kinetic studies, a water nucleophilic attack pathway was proposed as the dominant catalytic cycle of the catalytic water oxidation by 1(+), within which several intermediates were detected by MS. Meanwhile, an auxiliary pathway that is related to the concentration of Ce-IV was also revealed. The effect of anionic ligand regarding catalytic water oxidation was discussed explicitly in comparison with previously reported mononuclear Ru catalysts carrying neutral tridentate ligands, for example, 2,2':6',2 ''-terpyridine (tpy). When 2(+) was oxidized to the trivalent state, one of its picoline ligands dissociated from the Ru center. The rate constant of picoline dissociation was evaluated from time-resolved UV-vis spectra.

Keyword
Dinuclear Ruthenium Complex, Molecular Catalysts, Spectral Properties, Redox Properties, Photosystem-Ii, Dimer Complex, Site, Mechanism, Evolution, IV
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-104805 (URN)10.1021/ic302446h (DOI)000315763300034 ()2-s2.0-84874636594 (Scopus ID)
Funder
Swedish Research CouncilVinnovaKnut and Alice Wallenberg Foundation
Note

QC 20130408. Updated from manuscript to article in journal.

Available from: 2012-11-13 Created: 2012-11-13 Last updated: 2017-12-07Bibliographically approved
4. Visible light-driven water oxidation catalyzed by a highly efficient dinuclear ruthenium complex
Open this publication in new window or tab >>Visible light-driven water oxidation catalyzed by a highly efficient dinuclear ruthenium complex
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2010 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 46, no 35, 6506-6508 p.Article in journal (Refereed) Published
Abstract [en]

Visible light-driven water oxidation has been achieved by the dinuclear ruthenium complex 1 with a high turnover number of 1270 in a homogeneous system in the presence of a Ru polypyridine complex photosensitizer.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-26833 (URN)10.1039/c0cc01250e (DOI)000281237600022 ()2-s2.0-77956042575 (Scopus ID)
Note
QC 20101206Available from: 2010-12-06 Created: 2010-11-29 Last updated: 2017-12-11Bibliographically approved
5. Oxygen evolution at functionalized carbon surfaces: A strategy for immobilization of molecular water oxidation catalysts
Open this publication in new window or tab >>Oxygen evolution at functionalized carbon surfaces: A strategy for immobilization of molecular water oxidation catalysts
2012 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 48, no 80, 10025-10027 p.Article in journal (Refereed) Published
Abstract [en]

A molecular Ru(ii) water oxidation catalyst was immobilized on a conductive carbon surface through a covalent bond, and its activity was maintained at the same time. The method can be applied to other materials and may inspire development of artificial photosynthesis devices.

Keyword
Mononuclear Ruthenium Complexes, Electrolysis, Chemistry, Azide
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-103519 (URN)10.1039/c2cc35379b (DOI)000308653800022 ()2-s2.0-84866391677 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20121017

Available from: 2012-10-17 Created: 2012-10-15 Last updated: 2017-12-07Bibliographically approved

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