| 1. |
- 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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| 2. |
- Abdel-Magied, Ahmed F., et al.
(författare)
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Chemical and Photochemical Water Oxidation Mediated by an Efficient Single-Site Ruthenium Catalyst
- 2016
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 9:24, s. 3448-3456
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Tidskriftsartikel (refereegranskat)abstract
- Water oxidation is a fundamental step in artificial photosynthesis for solar fuels production. In this study, we report a single-site Ru-based water oxidation catalyst, housing a dicarboxylate-benzimidazole ligand, that mediates both chemical and light-driven oxidation of water efficiently under neutral conditions. The importance of the incorporation of the negatively charged ligand framework is manifested in the low redox potentials of the developed complex, which allows water oxidation to be driven by the mild one-electron oxidant [Ru(bpy)(3)](3+) (bpy = 2,2'-bipyridine). Furthermore, combined experimental and DFT studies provide insight into the mechanistic details of the catalytic cycle.
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| 3. |
- Abdel-Magied, Ahmed F., et al.
(författare)
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Substituent Effects in Molecular Ruthenium Water Oxidation Catalysts Based on Amide Ligands
- 2017
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Ingår i: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 9:9, s. 1583-1587
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Tidskriftsartikel (refereegranskat)abstract
- The production of clean and sustainable energy is considered as one of the most urgent issues for our society. Mastering the oxidation of water to dioxygen is essential for the production of solar fuels. A study of the influence of the substituents on the catalytic activity of a series of mononuclear Ru complexes (2a-e) based on a tetradentate ligand framework is presented. At neutral pH, using [Ru(bpy)(3)](PF6)(3) (bpy=2,2'-bipyridine) as the terminal oxidant, a good correlation between the turnover frequency (TOF) and the Hammett sigma(meta) parameters was obtained. Additionally, a general pathway for the deactivation of Ru-based catalysts 2a-e during the catalytic oxidation of water through poisoning by carbon monoxide was demonstrated. These results highlight the importance of ligand design for fine-tuning the catalytic activity of water oxidation catalysts.
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| 4. |
- Avetyan, David L., et al.
(författare)
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Scalable total synthesis of natural vanillin-derived glucoside omega-esters
- 2022
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Ingår i: Carbohydrate Research. - : Elsevier BV. - 0008-6215 .- 1873-426X. ; 522, s. 108683-
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Tidskriftsartikel (refereegranskat)abstract
- The first total synthesis of vanilloloside, calleryanin, and a series of naturally occurring omega-esters of vanilloloside was realized through direct glycosylation of vanillin-based aglycones or late-stage derivatization of vanilloloside. All aglycones and their fragments were synthesized from vanillin as the sole aromatic precursor. Subsequently, these intermediates were used to construct various vanillin-derived glucoside omega-esters using a mild acidic deacetylation as the key synthetic step, providing the final products in the total yields of 10-50% and general purity of >95%. Additionally, the first operationally simple and sustainable synthesis of litseafoloside B was realized on large scale, avoiding the use of toxic solvents and reagents, providing an attractive alternative to isolation of this and other similar compounds from plant sources.
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| 5. |
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| 6. |
- Chen, Y., et al.
(författare)
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Cooperative Silver- and Base-Catalyzed Diastereoselective Cycloaddition of Nitrones with Methylene Isocyanides : Access to 2-Imidazolinones
- 2020
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Ingår i: European Journal of Organic Chemistry. - : Wiley-VCH Verlag. - 1434-193X .- 1099-0690.
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Tidskriftsartikel (refereegranskat)abstract
- A protocol involving cooperative silver- and base-catalyzed diastereoselective cycloaddition of nitrones with isocyanides is described, providing access to a wide range of 2-imidazolinone derivatives with various functional groups as single diastereomers. Varying the base and temperature of the reaction allowed selective access to both diastereomers of the product. A plausible reaction mechanism is proposed and supported by DFT calculations.
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| 7. |
- Chen, Yan, et al.
(författare)
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Silver-Promoted (4+1) Annulation of Isocyanoacetates with Alkylpyridinium Salts : Divergent Regioselective Synthesis of 1,2-Disubstituted Indolizines
- 2021
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Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 23:19, s. 7555-7560
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Tidskriftsartikel (refereegranskat)abstract
- An unprecedented silver-promoted regioselective (4 + 1) annulation of isocyanoacetates with pyridinium salts is reported. The established protocol provides controlled, facile, and modular access to a range of synthetically useful N-fused heterocyclic scaffolds containing indolizines, pyrrolo[1,2-a]quinolines, pyrrolo[2,1-a]isoquinolines, and 1H-imidazo[4,5-a]indolizin-2(3H)-ones. A mechanistic pathway involving nucleophilic addition/protonation/elimination/cydoisomerization is proposed.
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| 8. |
- Das, Biswanath, et al.
(författare)
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The Impact of Ligand Carboxylates on Electrocatalyzed Water Oxidation
- 2021
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Ingår i: Accounts of Chemical Research. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 54:17, s. 3326-3337
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Forskningsöversikt (refereegranskat)abstract
- Fossil fuel shortage and severe climate changes due to global warming have prompted extensive research on carbon-neutral and renewable energy resources. Hydrogen gas (H-2), a clean and high energy density fuel, has emerged as a potential solution for both fulfilling energy demands and diminishing the emission of greenhouse gases. Currently, water oxidation (WO) constitutes the bottleneck in the overall process of producing H-2 from water. As a result, the design of efficient catalysts for WO has become an intensively pursued area of research in recent years. Among all the molecular catalysts reported to date, ruthenium-based catalysts have attracted particular attention due to their robust nature and higher activity compared to catalysts based on other transition metals. Over the past two decades, we and others have studied a wide range of ruthenium complexes displaying impressive catalytic performance for WO in terms of turnover number (TON) and turnover frequency (TOF). However, to produce practically applicable electrochemical, photochemical, or photo-electrochemical WO reactors, further improvement of the catalysts' structure to decrease the overpotential and increase the WO rate is of utmost importance. WO reaction, that is, the production of molecular oxygen and protons from water, requires the formation of an O-O bond through the orchestration of multiple proton and electron transfers. Promotion of these processes using redox noninnocent ligand frameworks that can accept and transfer electrons has therefore attracted substantial attention. The strategic modifications of the ligand structure in ruthenium complexes to enable proton-coupled electron transfer (PCET) and atom proton transfer (APT; in the context of WO, it is the oxygen atom (metal oxo) transfer to the oxygen atom of a water molecule in concert with proton transfer to another water molecule) to facilitate the O-O bond formation have played a central role in these efforts. In particular, promising results have been obtained with ligand frameworks containing carboxylic acid groups that either are directly bonded to the metal center or reside in the close vicinity. The improvement of redox and chemical properties of the catalysts by introduction of carboxylate groups in the ligands has proven to be quite general as demonstrated for a range of mono- and dinudear ruthenium complexes featuring ligand scaffolds based on pyridine, imidazole, and pyridazine cores. In the first coordination sphere, the carboxylate groups are firmly coordinated to the metal center as negatively charged ligands, improving the stability of the complexes and preventing metal leaching during catalysis. Another important phenomenon is the reduction of the potentials required for the formation of higher valent intermediates, especially metal-oxo species, which take active part in the key O-O bond formation step. Furthermore, the free carboxylic acid/carboxylate units in the proximity to the active center have shown exciting proton donor/acceptor properties (through PCET or APT, chemically noninnocent) that can dramatically improve the rate as well as the overpotential of the WO reaction.
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| 9. |
- Das, Biswanath, et al.
(författare)
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Water oxidation catalyzed by molecular di- and nonanuclear Fe complexes: importance of a proper ligand framework
- 2016
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Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 45:34, s. 13289-13293
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of two molecular iron complexes, a dinuclear iron(III,III) complex and a nonanuclear iron complex, based on the di-nucleating ligand 2,2-(2-hydroxy-5-methyl-1,3-phenylene)bis(1H-benzo[d]imidazole-4-carboxylic acid) is described. The two iron complexes were found to drive the oxidation of water by the one-electron oxidant [Ru(bpy)(3)](3+).
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| 10. |
- Fedorova, Dariya D., et al.
(författare)
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Divergent Synthesis of Natural Benzyl Salicylate and Benzyl Gentisate Glucosides
- 2020
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Ingår i: Journal of Natural Products. - : American Chemical Society (ACS). - 0163-3864 .- 1520-6025. ; 83:10, s. 3173-3180
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Tidskriftsartikel (refereegranskat)abstract
- Herein is reported the first total synthesis of benzyl salicylate and benzyl gentisate glucosides present in various plant species, in particular the Salix genus, such as Populus balsamifera and P. trichocarpa. The method permits the synthesis of several natural phenolic acid derivatives and their glucosides starting from salicylic or gentisic acid. The divergent approach afforded access to three different acetylated glucosides from a common synthetic intermediate. The key step in the total synthesis of naturally occurring glycosides-the selective deacetylation of the sugar moiety-was achieved in the presence of a labile benzyl ester group by employing mild deacetylation conditions. The protocol permitted synthesis of trichocarpine (4 steps, 40% overall yield), isotrichocarpine (3 steps, 51% overall yield), trichoside (6 steps, 40% overall yield), and deoxytrichocarpine (3 steps, 42% overall yield) for the first time (>95% purity). Also, the optimized mild deacetylation conditions allowed synthesis of 2-O-acetylated derivatives of all four glycosides (5-17% overall yield, 90-95% purity), which are rare plant metabolites.
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