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| 2. |
- Abdelhamid, Hani Nasser, et al.
(author)
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Luminescence properties of a family of lanthanide metal-organic frameworks
- 2019
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In: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 279, s. 400-406
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Journal article (peer-reviewed)abstract
- Two isostructural series of lanthanide metal-organic frameworks denoted as SUMOF-7II (Ln) and SUMOF-7IIB (Ln) (Ln = La, Ce, Pr, Nd, Sm, Eu, and Gd) were synthesized using4,4',4 ''-(pyridine-2,4,6-triyl)tris(benzoic acid) (H(3)L2) and a mixture of H(3)L2 and 4,4',4 ''-(benzene-1,3,5-triyl)tris(benzoic acid) (H3BTB) as linkers, respectively. Both series were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermal analysis (TGA), and photoluminescence spectroscopy. Photoluminescence measurements show that Eu-MOFs demonstrate a red emission while Pr- and Nd-MOFs display an emission in the near-infrared (NIR) range. On the other hand, La-, Ce-, Sm- and Gd-MOFs exhibit only a ligand-centered emission. The average luminescence lifetimes in the SUMOF-7IIB series are 1.3-1.4-fold longer than the corresponding ones in the SUMOF-7II series. SUMOF-7IIs show a good photo- and thermal stability. Altogether, the properties of SUMOF-7II and SUMOF-7IIB render them promising materials for applications including sensing, biosensing, and telecommunications.
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| 3. |
- Valiente, Alejandro, et al.
(author)
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Aerobic Homocoupling of Arylboronic Acids Catalyzed by Regenerable Pd(II)@MIL-88B-NH2(Cr)
- 2019
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In: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 11:16, s. 3933-3940
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Journal article (peer-reviewed)abstract
- A fast and operationally simple method for the aerobic homocoupling of arylboronic acids is described. The process is catalyzed by Pd(II) complexes supported on the metal-organic framework MIL-88B-NH2(Cr). The benefits of this approach include the use of a benign oxidant/solvent mixture at room temperature with catalytic amounts of base, easy recovery of the catalyst, and easy isolation of the products. Very high conversions and good yields were achieved for a variety of substrates, and the process was also carried out on a larger scale with the same efficiency. The catalyst was found to suffer deactivation due to progressive reduction and agglomeration of palladium into inactive metal clusters/particles. An innovative procedure for the oxidative redispersion and regeneration of the active Pd(II)@MOF species is presented.
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| 4. |
- Valiente, Alejandro, 1992-, et al.
(author)
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Electrochemical Generation of Hydrides over a Nickel Foam for Z-Stereoselective Semihydrogenation/deuteration of Functionalized Alkynes
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Other publication (other academic/artistic)abstract
- Selective reduction strategies based on abundant-metal catalysts are very important in the production of chemicals. In this paper, we present a method for the electrochemical semihydrogenation and semideuteration of alkynes to form Z-alkenes using a simplenickel foam as catalyst and H3O+or D3O+as sources of hydrogen or deuterium. Good yields and excellent stereoselectivities (Z/E up to 20:1) are obtained under very mild reaction conditions. The reaction works with terminal and nonterminal alkynes, and with alkynes containing easily reducible functional groups, such as carbonyl groups, and aryl chlorides, bromides, and even iodides. The nickel-foam electrocatalyst can be recycled up to 14 times without any change in its catalytic properties.
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| 5. |
- Valiente, Alejandro, et al.
(author)
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Electrochemical Proton Reduction over Nickel Foam for Z-Stereoselective Semihydrogenation/deuteration of Functionalized Alkynes
- 2022
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In: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 15:1
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Journal article (peer-reviewed)abstract
- Selective reduction strategies based on abundant-metal catalysts are very important in the production of chemicals. In this paper, a method for the electrochemical semihydrogenation and semideuteration of alkynes to form Z-alkenes was developed, using a simple nickel foam as catalyst and H3O+ or D3O+ as sources of hydrogen or deuterium. Good yields and excellent stereoselectivities (Z/E up to 20 : 1) were obtained under very mild reaction conditions. The reaction proceeded with terminal and nonterminal alkynes, and also with alkynes containing easily reducible functional groups, such as carbonyl groups, as well as aryl chlorides, bromides, and even iodides. The nickel-foam electrocatalyst could be recycled up to 14 times without any change in its catalytic properties.
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| 6. |
- Valiente, Alejandro, 1992-, et al.
(author)
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Tetrameric Aryl Palladium Bromide Intermediates Leading to Easy Transmetalation in Suzuki – Miyaura Cross-Couplings with Pd @ MIL-101-NH2
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Other publication (other academic/artistic)abstract
- The composition and structure of catalytic intermediates in the context of the Suzuki – Miyaura cross-coupling reaction catalyzed by Pd @ MIL-101-NH2 has been investigated. Trimeric and tetrameric palladium species with formula [Br-Pd-Ar] n Br -(n = 3–4) have been identified by electrospray ionization mass spectrometry (ESI-MS) and density-functional theory (DFT) calculations, and their role in the transmetalation step has been studied. The weak nature of the bonds between Pd and the bridging halides in these species enables a very easy transmetalation step, with an estimated activation free energy of only 10 kcal / mol. Further experimental support for Pd speciation was obtained using scanning transmission electron microscopy (STEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and fluorine-19 nuclear magnetic resonance spectroscopy (19 F NMR).
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| 7. |
- Valiente Sánchez, Alejandro, 1992-
(author)
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Catalytic and Electrocatalytic Transformations with Palladium and Nickel : Scope and mechanistic investigations
- 2021
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Doctoral thesis (other academic/artistic)abstract
- The work presented in this thesis is based on methodology development and mechanistic investigations using heterogeneous palladium and nickel catalysts. Following the introduction (Chapter 1), Chapter 2 presents a summary of the synthesis and characterization of the MOF-supported Pd catalysts (Pd @ MOF) that are used in this thesis. Chapters 3, 4 and 5 are based on the use of heterogeneous Pd @ MOF catalysts for CC bond forming reactions, whilst Chapter 6 deals with the use of nickel foam for hydrogenation reactions. In Chapter 3, the speciation of the ligandless Suzuki-Miyaura reaction catalyzed by Pd @ MOF is investigated. Here, questions regarding the composition, structure and reactivity of leached palladium are studied by means of electrospray ionization mass spectrometry (ESI-MS), density-functional theory (DFT) calculations, nuclear magnetic resonance (NMR) spectroscopy and scanning-transmission electron microscopy (STEM). (Paper I)The next chapter (Chapter 4) deals with the study of the Mizoroki-Heck reaction catalyzed by Pd @ MOF under working conditions. In this study, catalyst activation, catalyst deactivation and the role of the MOF support are studied. (Paper II) Chapter 5 concerns the use of MOF-supported Pd (II) complexes for the aerobic homocoupling of boronic acids. A mild oxidation method for regenerating active catalytic palladium species, which enables its recyclability, is described. (Paper III)The last chapter (Chapter 6) describes the use of a commercially available nickel foam for the stereoselective semireduction of alkynes using electrochemically generated hydrides from acidic water. As the method tolerates numerous functional groups, it could be applied to a large variety of alkynes. The use of deuterated solvents provided easy access to a library of deuterated Z -olefins. (Paper IV)
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| 8. |
- Yuan, Ning, et al.
(author)
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Probing the Evolution of Palladium Species in Pd@MOF Catalysts during the Heck Coupling Reaction: An Operando X-ray Absorption Spectroscopy Study
- 2018
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 140:26, s. 8206-8217
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Journal article (peer-reviewed)abstract
- The mechanism of the Heck C-C coupling reaction catalyzed by Pd@MOFs has been investigated using operando X-ray absorption spectroscopy (XAS) and powder X-ray diffraction (PXRD) combined with transmission electron microscopy (TEM) analysis and nuclear magnetic resonance (H-1 NMR) kinetic studies. A custom-made reaction cell was used, allowing operando PXRD and XAS data collection using high-energy synchrotron radiation. By analyzing the XAS data in combination with ex situ studies, the evolution of the palladium species is followed from the as-synthesized to its deactivated form. An adaptive reaction mechanism is proposed. Mononuclear Pd(II) complexes are found to be the dominant active species at the beginning of the reaction, which then gradually transform into Pd nanoclusters with 13-20 Pd atoms on average in later catalytic turnovers. Consumption of available reagent and substrate leads to coordination of Cl- ions to their surfaces, which causes the poisoning of the active sites. By understanding the deactivation process, it was possible to tune the reaction conditions and prolong the lifetime of the catalyst.
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