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- Laine, Tanja M., 1979-
(författare)
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Development of Ruthenium Catalysts for Water Oxidation
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Li, Ying-Ying, et al.
(författare)
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Quantum Chemical Study of the Mechanism of Water Oxidation Catalyzed by a Heterotrinuclear Ru2Mn Complex
- 2019
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 12:5, s. 1101-1110
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Tidskriftsartikel (refereegranskat)abstract
- The heterotrinuclear complex A {[Ru-II(H2O)(tpy)](2)(mu-[Mn-II(H2O)(2)(bpp)(2)])}(4+) [tpy=2,2 ':6 ',2 ''-terpyridine, bpp=3,5-bis(2-pyridyl)pyrazolate] was found to catalyze water oxidation both electrochemically and photochemically with [Ru(bpy)(3)](3+) (bpy=2,2 '-bipyridine) as the photosensitizer and Na2S2O8 as the electron acceptor in neutral phosphate buffer. The mechanism of water oxidation catalyzed by this unprecedented trinuclear complex was studied by density functional calculations. The calculations showed that a series of oxidation and deprotonation events take place from A, leading to the formation of complex 1 (formal oxidation state of Ru1(IV)Mn(III)Ru2(III)), which is the starting species for the catalytic cycle. Three sequential oxidations of 1 result in the generation of the catalytically competing species 4 (formal oxidation state of Ru1(IV)Mn(V)Ru2(IV)), which triggers the O-O bond formation. The direct coupling of two adjacent oxo ligands bound to Ru and Mn leads to the production of a superoxide intermediate Int1. This step was calculated to have a barrier of 7.2 kcal mol(-1) at the B3LYP*-D3 level. Subsequent O-2 release from Int1 turns out to be quite facile. Other possible pathways were found to be much less favorable, including water nucleophilic attack, the coupling of an oxo and a hydroxide, and the direct coupling pathway at a lower oxidation state ((RuMnRuIV)-Mn-IV-Ru-IV).
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| 3. |
- Shatskiy, Andrey, et al.
(författare)
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Electrochemically Driven Water Oxidation by a Highly Active Ruthenium-Based Catalyst
- 2019
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 12:10, s. 2251-2262
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Tidskriftsartikel (refereegranskat)abstract
- The highly active ruthenium-based water oxidation catalyst [Ru-X(mcbp)(OHn)(py)(2)] [mcbp(2-)=2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine; n=2, 1, and 0 for X=II, III, and IV, respectively], can be generated in a mixture of Ru-III and Ru-IV states from either [Ru-II(mcbp)(py)(2)] or [Ru-III(Hmcbp)(py)(2)](2+) precursors. The precursor complexes are isolated and characterized by single-crystal X-ray analysis, NMR, UV/Vis, EPR, and FTIR spectroscopy, ESI-HRMS, and elemental analysis, and their redox properties are studied in detail by electrochemical and spectroscopic methods. Unlike the parent catalyst [Ru(tda) (py)(2)] (tda(2-)=[2,2:6,2-terpyridine]-6,6-dicarboxylate), for which full transformation into the catalytically active species [Ru-IV(tda)(O)(py)(2)] could not be carried out, stoichiometric generation of the catalytically active Ru-aqua complex [Ru-X(mcbp)(OHn)(py)(2)] from the Ru-II precursor was achieved under mild conditions (pH7.0) and short reaction times. The redox properties of the catalyst were studied and its activity for electrocatalytic water oxidation was evaluated, reaching a maximum turnover frequency (TOFmax) of around 40000s(-1) at pH9.0 (from foot-of-the-wave analysis), which is comparable to the activity of the state-of-the-art catalyst [Ru-IV(tda)(O)(py)(2)].
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