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- Corpas, Javier, et al.
(författare)
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Interplay between the Directing Group and Multifunctional Acetate Ligand in Pd-Catalyzed anti-Acetoxylation of Unsymmetrical Dialkyl-Substituted Alkynes
- 2022
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 12:11, s. 6596-6605
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Tidskriftsartikel (refereegranskat)abstract
- The cooperative action of the acetate ligand, the 2-pyridyl sulfonyl (SO2Py) directing group on the alkyne substrate,and the palladium catalyst has been shown to be crucial forcontrolling reactivity, regioselectivity, and stereoselectivity in theacetoxylation of unsymmetrical internal alkynes under mildreaction conditions. The corresponding alkenyl acetates wereobtained in good yields with complete levels of beta-regioselectivityandanti-acetoxypalladation stereocontrol. Experimental andcomputational analyses provide insight into the reasons behindthis delicate interplay between the ligand, directing group, and themetal in the reaction mechanism. In fact, these studies unveil themultiple important roles of the acetate ligand in the coordinationsphere at the Pd center: (i) it brings the acetic acid reagent into close proximity to the metal to allow the simultaneous activation ofthe alkyne and the acetic acid, (ii) it serves as an inner-sphere base while enhancing the nucleophilicity of the acid, and (iii) it acts asan intramolecular acid to facilitate protodemetalation and regeneration of the catalyst. Further insight into the origin of the observedregiocontrol is provided by the mapping of potential energy profiles and distortion-interaction analysis
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| 2. |
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| 3. |
- Kong, Xiangrui, et al.
(författare)
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Surface solvation of Martian salt analogues at low relative humidities
- 2022
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Ingår i: Environmental Science: Atmospheres. - : Royal Society of Chemistry (RSC). - 2634-3606. ; 2:2, s. 137-145
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Tidskriftsartikel (refereegranskat)abstract
- Salt aerosols play important roles in many processes related to atmospheric chemistry and the climate systems on both Earth and Mars. Complicated and still poorly understood processes occur on the salt surfaces when interacting with water vapor. In this study, ambient pressure X-ray photoelectron spectroscopy (APXPS) is used to characterize the surface chemical environment of Martian salt analogues originating from saline lakes and playas, as well as their responses to varying relative humidities. Generally, APXPS shows similar ionic compositions to those observed by ion chromatography (IC). However, XPS is a surface-sensitive method while IC is bulk-sensitive and differences are observed for species that preferentially partition to the surface or the bulk. Element-selective surface enhancement of Cl− is observed, likely caused by the presence of SO42−. In addition, Mg2+ is concentrated on the surface while Na+ is relatively depleted in the surface layer. Hence, the cations (Na+ and Mg2+) and the anions (Cl− and SO42−) show competitive correlations. At elevated relative humidity (RH), no major spectral changes were observed in the XPS results, except for the growth of an oxygen component originating from condensed H2O. Near-edge X-ray absorption fine structure (NEXAFS) measurements show that the magnesium and sodium spectra are sensitive to the presence of water, and the results imply that the surface is fully solvated already at RH = 5%. The surface solvation is also fully reversible as the RH is reduced. No major differences are observed between sample types and sample locations, indicating that the salts originated from saline lakes commonly have solvated surfaces under the environmental conditions on Earth.
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