- A biomimetic copper water oxidation catalyst with low overpotential
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Simply mixing a Cu(II) salt and 6,6′-dihydroxy-2,2′-bipyridine (H2L) in a basic aqueous solution afforded a highly active water oxidation catalyst (WOC). Cyclic voltammetry of the solution at pH = 12-14 shows irreversible catalytic current with an onset potential of ~0.8 V versus NHE. Catalytic oxygen evolution takes place in controlled potential electrolysis at a relatively low overpotential of 640 mV. Experimental and computational studies suggest that the L ligand participates in electron transfer processes to facilitate the oxidation of the Cu center to lead to an active WOC with low overpotential, akin to the use of the tyrosine radical by Photosystem II to oxidize the CaMn4 center for water oxidation.
- Zhang, Teng,Wang, Cheng,Liu, Shubin,Wang, Jin-Liang,Lin, Wenbin
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- Effect of the ortho-Hydroxyl Groups on a Bipyridine Ligand of Iridium Complexes for the High-Pressure Gas Generation from the Catalytic Decomposition of Formic Acid
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The hydroxyl groups of a 2,2′-bipyridine (bpy) ligand near the metal center activated the catalytic performance of the Ir complex for the dehydrogenation of formic acid at high pressure. The position of the hydroxyl groups on the ligand affected the catalytic durability for the high-pressure H2 generation through the decomposition of formic acid. The Ir complex with a bipyridine ligand functionalized with para-hydroxyl groups shows a good durability with a constant catalytic activity during the reaction even under high-pressure conditions, whereas deactivation was observed for an Ir complex with a bipyridine ligand with ortho-hydroxyl groups (2). In the presence of high-pressure H2, complex 2 decomposed into the ligand and an Ir trihydride complex through the isomerization of the bpy ligand. This work provides the development of a durable catalyst for the high-pressure H2 production from formic acid.
- Iguchi, Masayuki,Zhong, Heng,Himeda, Yuichiro,Kawanami, Hajime
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- Transfer hydrogenation in water via a ruthenium catalyst with OH groups near the metal center on a bipy scaffold
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The new ligand 6,6′-dihydroxy-2,2′-bipyridyl (dhbp) was synthesized via its tautomer, and this provides an efficient route to novel metal complexes of dhbp. In ruthenium complexes of dhbp, these OH groups enhance water solubility and may play a role in aq
- Nieto, Ismael,Livings, Michelle S.,Sacci, John B.,Reuther, Lauren E.,Zeller, Matthias,Papish, Elizabeth T.
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- New Access Routes to Privileged and Chiral Ligands for Transition-Metal Catalyzed Hydrogen Autotransfer (Borrowing Hydrogen), Dehydrogenative Condensation, and Alkene Isomerization Reactions
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A group of transition-metal catalyzed hydrogen moving reactions, encompassing hydrogen autotransfer (HAT; also called borrowing hydrogen, BH), dehydrogenative condensation (DHC) and alkene isomerization, displays high atom economy and relies on widely ava
- Hintermann, Lukas,Jandl, Christian,Klein, Philippe,Koller, Sebastian,Ochmann, Lukas,P?thig, Alexander,Reinhardt, Katja,Seitz, Antonia
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- Reinvestigating catalytic alcohol dehydrogenation with an iridium dihydroxybipyridine catalyst
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The examined catalyst [Cp*Ir(H2O)(6,6′-dhbp)]2+ (1; 6,6′-dhbp = 6,6′-dihydroxy-2,2′-bipyridine) was reported in 2012 as a highly efficient (92% conversion) and selective catalyst for the conversion of benzyl alcohol to benzaldehyde as the sole product via acceptorless dehydrogenation. We report herein that the observed conversion and selectivity data are not accurate but may have resulted, in part, from other products being produced that are not easily detected. Specifically, benzoic acid is formed as a byproduct via the disproportionation of benzaldehyde, but at high temperatures, most of the benzoic acid produced is converted in situ to benzene and carbon dioxide. While we can explain the observed selectivity, we cannot explain the observed conversion to products. In our hands, we observed 15% conversion to products under the original conditions. Other alcohol substrates were also examined and gave lower conversion to products and decreased selectivity in comparison with the original report. Acceptorless alcohol dehydrogenation to generate aldehydes is a potentially transformative technology which can allow chemists to replace stoichiometric oxidants that produce waste with efficient catalysts that only generate H2 gas as a byproduct. Thus, clarification of the 2012 report to indicate what conditions can lead to high efficiency and selectivity is a worthy topic of discussion in the literature.
- Brewster, Timothy P.,DeRegnaucourt, Alexa R.,Loadholt, Kylie H.,Papish, Elizabeth T.,Qu, Fengrui,Shrewsbury, Emily D.,Silprakob, Weerachai,Yao, Wenzhi
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supporting information
p. 3656 - 3662
(2020/11/23)
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- Iridium-catalysed primary alcohol oxidation and hydrogen shuttling for the depolymerisation of lignin
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Lignin is a potentially abundant renewable resource for the production of aromatic chemicals, however its selective depolymerisation is challenging. Here, we report a new catalytic system for the depolymerisation of lignin to novel, non-phenolic monoaromatic products based on the selective β-O-4 primary alcohol dehydrogenation with a Cp?Ir-bipyridonate catalyst complex under basic conditions. We show that this system is capable of promoting the depolymerisation of model compounds and isolated lignins via a sequence of selective primary alcohol dehydrogenation, retro-aldol (Cα-Cβ) bond cleavage and in situ stabilisation of the aldehyde products by transfer (de)hydrogenation to alcohols and carboxylic acids. This method was found to give good to excellent yields of cleavage products with both etherified and free-phenolic lignin model compounds and could be applied to real lignin to generate a range of novel non-phenolic monomers including diols and di-acids. We additionally show, by using the same catalyst in a convergent, one-pot procedure, that these products can be selectively channelled towards a single di-acid product, giving much simpler product mixtures as a result.
- Lancefield, Christopher S.,Teunissen, Lucas W.,Weckhuysen, Bert M.,Bruijnincx, Pieter C. A.
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supporting information
p. 3214 - 3221
(2018/07/31)
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- En Route to a Practical Primary Alcohol Deoxygenation
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A long-standing scientific challenge in the field of alcohol deoxygenation has been direct catalytic sp3 C-O defunctionalization with high selectivity and efficiency, in the presence of other functionalities, such as free hydroxyl groups and amines widely present in biological molecules. Previously, the selectivity issue had been only addressed by classic multistep deoxygenation strategies with stoichiometric reagents. Herein, we propose a catalytic late-transition-metal-catalyzed redox design, on the basis of dehydrogenation/Wolff-Kishner (WK) reduction, to simultaneously tackle the challenges regarding step economy and selectivity. The early development of our hypothesis focuses on an iridium-catalyzed process efficient mainly with activated alcohols, which dictates harsh reaction conditions and thus limits its synthetic utility. Later, a significant advancement has been made on aliphatic primary alcohol deoxygenation by employing a ruthenium complex, with good functional group tolerance and exclusive selectivity under practical reaction conditions. Its synthetic utility is further illustrated by excellent efficiency as well as complete chemo- and regio-selectivity in both simple and complex molecular settings. Mechanistic discussion is also included with experimental supports. Overall, our current method successfully addresses the aforementioned challenges in the pertinent field, providing a practical redox-based approach to the direct sp3 C-O defunctionalization of aliphatic primary alcohols.
- Dai, Xi-Jie,Li, Chao-Jun
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supporting information
p. 5433 - 5440
(2016/05/19)
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- Pyridazine and Pyrrole Compounds, Processes For Obtaining Them and Uses
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The present invention relates to nonlinear oligopyridazine compounds, to processes for obtaining them, to their uses, and also to their reduction to oligopyrroles and to the uses of the pyridazinylpyrrole and oligopyrrole compounds obtained. The invention relates in particular to the uses as medicaments, in particular for treating pathologies such as cancer, bacterial infections or parasitic infections, and also the uses in the materials, environmental, electronics and optics field.
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- Synthesis, Properties, and Reactivity of N,N'-Difluorobipyridinium and Related Salts and Their Applications as Reactive and Easy-To-Handle Electrophilic Fluorinating Agents with High Effective Fluorine Content
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N,N′-Difluoro-2,2′-, -2,4′-, -3,3′-, -4,4′-bipyridinium and substituted N,N′-difluoro-2,2′-bipyridinmm bis(triflates), bis(tetrafluoroborates), bis(hexafluorophosphates), and bis(hexafluoroantimonates) 1-9 were synthesized in high yields by the direct fluorination of a mixture of a bipyridyl and a Lewis acid, a Br?nsted acid, or the alkali metal salt of an acid. The higher homologues, trimer 10 and polymer 11, were also synthesized. Unsubstituted or electron-donating group-substituted N,N′- difluorobipyridinium salts are stable nonhygroscopic crystals, while the electron-withdrawing group- substituted N,N′-diflurobipyridinium salts 3, 5, and 6 are moisture-sensitive crystals. Hydrolysis of 1b in boiling water gave 3,3′-dihydroxy-2,2′-bipyridyl. The reactivity determination indicated that the fluorinating capability decreased in the order 2,2′- ? 2,4' > 3,3′- ≈ 4,4′-isomer ? N-fluoropyridinium salt and that the two N-F moieties in a molecule were effective for fluorination. This fluorination occurred in a step-by-step manner, and the reactivity difference between the first and second fluorinations was very small. N,N′-Difluoro-2,2′-bipyridinium bis(tetrafluoroborate) (1b) is thus shown to be a highly reactive and easy-to-handle electrophilic fluorinating agent with the high effective fluorine content (103.3 g/kg) for preparing many fluoro organic compounds.
- Umemoto, Teruo,Nagayoshi, Masayuki,Adachi, Kenji,Tomizawa, Ginjiro
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p. 3379 - 3385
(2007/10/03)
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- Syntheses of Hydroxylated Bipyridines, III. - Synthesis of Unsymmetrically and Symmetrically Structured Dihydroxybipyridines
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Fifteen symmetrical and asymmetrical dimethoxybipyridines and the pertinent diols are prepared and characterized.Reductive cross coupling of halopyridines with Ni(0) may result in complex mixtures.The same is true for an alternative reaction of (trimethylstannyl)pyridines with halopyridines in the presence of Pd(0).UV, 1H-, and 13C-NMR spectra of the bipyridine derivatives are tabulated.Key Words: Bipyridinediols / Pyridines / Stannylpyridines
- Dehmlow, Eckehard V.,Sleegers, Arthur
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p. 953 - 960
(2007/10/02)
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