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| 2. |
- Bornschein, Christoph, et al.
(author)
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Evaluation of Fe and Ru Pincer-Type Complexes as Catalysts for the Racemization of Secondary Benzylic Alcohols
- 2016
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In: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 22:33, s. 11583-11586
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Journal article (peer-reviewed)abstract
- Fe and Ru pincer-type catalysts are used for the racemization of benzylic alcohols. Racemization with the Fe catalyst was achieved within 30 minutes under mild reaction conditions, with a catalyst loading as low as 2 mol %. This reaction constitutes the first example of an iron-catalyzed racemization of an alcohol. The efficiency for racemization of the Fe catalyst and its Ru analogue was evaluated for a wide range of sec-benzylic alcohols. The commercially available Ru complex proved to be highly robust and even tolerated the presence of water in the reaction mixture.
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| 3. |
- Bratt, Emma, et al.
(author)
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A General Suzuki Cross-Coupling Reaction of Heteroaromatics Catalyzed by Nanopalladium on Amino-Functionalized Siliceous Mesocellular Foam
- 2014
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In: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 79:9, s. 3946-3954
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Journal article (peer-reviewed)abstract
- Suzuki-Miyaura cross-coupling reactions of heteroaromatics catalyzed by palladium supported in the cavities of amino-functionalized siliceous mesocellular foam are presented. The nanopalladium catalyst effectively couples not only heteroaryl halides with boronic acids but also heteroaryl halides with boronate esters, potassium trifluoroborates, MIDA boronates, and triolborates, producing a wide range of heterobiaryls in good to excellent yields. Furthermore, the heterogeneous palladium nanocatalyst can easily be removed from the reaction mixture by filtration and recycled several times with minimal loss in activity. This catalyst provides an alternative, environmentally friendly, low-leaching process for the preparation of heterobiaryls.
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| 4. |
- Das, Biswanath, et al.
(author)
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Bifunctional and regenerable molecular electrode for water electrolysis at neutral pH
- 2023
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 11:25, s. 13331-13340
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Journal article (peer-reviewed)abstract
- The instability of molecular electrodes under oxidative/reductive conditions and insufficient understanding of the metal oxide-based systems have slowed down the progress of H2-based fuels. Efficient regeneration of the electrode's performance after prolonged use is another bottleneck of this research. This work represents the first example of a bifunctional and electrochemically regenerable molecular electrode which can be used for the unperturbed production of H2 from water. Pyridyl linkers with flexible arms (–CH2–CH2–) on modified fluorine-doped carbon cloth (FCC) were used to anchor a highly active ruthenium electrocatalyst [RuII(mcbp)(H2O)2] (1) [mcbp2− = 2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine]. The pyridine unit of the linker replaces one of the water molecules of 1, which resulted in RuPFCC (ruthenium electrocatalyst anchored on –CH2–CH2–pyridine modified FCC), a high-performing electrode for oxygen evolution reaction [OER, overpotential of ∼215 mV] as well as hydrogen evolution reaction (HER, overpotential of ∼330 mV) at pH 7. A current density of ∼8 mA cm−2 at 2.06 V (vs. RHE) and ∼−6 mA cm−2 at −0.84 V (vs. RHE) with only 0.04 wt% loading of ruthenium was obtained. OER turnover of >7.4 × 103 at 1.81 V in 48 h and HER turnover of >3.6 × 103 at −0.79 V in 3 h were calculated. The activity of the OER anode after 48 h use could be electrochemically regenerated to ∼98% of its original activity while it serves as a HE cathode (evolving hydrogen) for 8 h. This electrode design can also be used for developing ultra-stable molecular electrodes with exciting electrochemical regeneration features, for other proton-dependent electrochemical processes.
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| 5. |
- Das, Biswanath, et al.
(author)
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Cobalt Electrocatalyst on Fluorine Doped Carbon Cloth – a Robust and Partially Regenerable Anode for Water Oxidation
- 2022
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In: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 14:18
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Journal article (peer-reviewed)abstract
- The low stability of the electrocatalysts at water oxidation (WO) conditions and the use of expensive noble metals have obstructed large-scale H2 production from water. Herein, we report the electrocatalytic WO activity of a cobalt-containing, water-soluble molecular WO electrocatalyst [CoII(mcbp)(OH2)] (1) [mcbp2−=2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine] in homogeneous conditions (overpotential of 510 mV at pH 7 phosphate buffer) and after anchoring it on pyridine-modified fluorine-doped carbon cloth (PFCC). The formation of cobalt phosphate was identified only after 4 h continuous oxygen evolution in homogeneous conditions. Interestingly, a significant enhancement of the stability and WO activity (current density of 5.4 mA/cm2 at 1.75 V) was observed for 1 after anchoring onto PFCC, resulting in a turnover (TO) of >3.6×103 and average TOF of 0.05 s−1 at 1.55 V (pH 7) over 20 h. A total TO of >21×103 over 8 days was calculated. The electrode allowed regeneration of∼ 85 % of the WO activity electrochemically after 36 h of continuous oxygen evolution.
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| 6. |
- Das, Biswanath, et al.
(author)
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The Impact of Ligand Carboxylates on Electrocatalyzed Water Oxidation
- 2021
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In: Accounts of Chemical Research. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 54:17, s. 3326-3337
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Research review (peer-reviewed)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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| 7. |
- Deiana, Luca, et al.
(author)
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Combined Heterogeneous Metal/Chiral Amine : Multiple Relay Catalysis for Versatile Eco-Friendly Synthesis
- 2014
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In: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 53:13, s. 3447-3451
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Journal article (peer-reviewed)abstract
- Herein is described a versatile and broad synergistic strategy for expansion of chemical space and the synthesis of valuable molecules (e.g. carbocycles and heterocycles), with up to three quaternary stereocenters, in a highly enantioselective fashion from simple alcohols (31examples, 95:5 to >99.5:0.5 e.r.) using integrated heterogeneous metal/chiral amine multiple relay catalysis and air/O-2 as the terminal oxidant. A novel highly 1,4-selective heterogeneous metal/amine co-catalyzed hydrogenation of enals was also added to the relay catalysis sequences.
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| 8. |
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| 9. |
- Deiana, Luca, 1982-, et al.
(author)
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Enantioselective Heterogeneous Synergistic Catalysis for Asymmetric Cascade Transformations
- 2014
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In: Advanced Synthesis and Catalysis. - : Wiley. - 1615-4150 .- 1615-4169. ; 356:11-12, s. 2485-2492
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Journal article (peer-reviewed)abstract
- A modular design for a novel heterogeneous synergistic catalytic system, which simultaneously activates the electrophile and nucleophile by the combined activation modes of a separate metal and non-metal catalyst, for asymmetric cascade transformations on a solid surface is disclosed. This modular catalysis strategy generates carbocycles (up to 97.5: 2.5 er) as well as spirocyclic oxindoles (97.5: 2.5 to > 99: 0.5 er), containing all-carbon quaternary centers, in a highly enantioselective fashion via a one-pot dynamic relay process.
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| 10. |
- Deiana, Luca, 1982-, et al.
(author)
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Highly Enantioselective Cascade Transformations by Merging Heterogeneous Transition Metal Catalysis with Asymmetric Aminocatalysis
- 2012
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 2, s. 851-
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Journal article (peer-reviewed)abstract
- The concept of combining heterogeneous transition metal and amine catalysis for enantioselective cascade reactions has not yet been realized. This is of great advantage since it would allow for the recycling of expensive and non-environmentally friendly transition metals. We disclose that the use of a heterogeneous Pd-catalyst in combination with a simple chiral amine co-catalyst allows for highly enantioselective cascade transformations. The preparative power of this process has been demonstrated in the context of asymmetric cascade Michael/carbocyclization transformations that delivers cyclopentenes bearing an all carbon quaternary stereocenters in high yields with up to 30: 1 dr and 99% ee. Moreover, a variety of highly enantioselective cascade hetero-Michael/carbocyclizations were developed for the one-pot synthesis of valuable dihydrofurans and pyrrolidines (up to 98% ee) by using bench-stable heterogeneous Pd and chiral amines as co-catalysts.
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