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Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

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Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
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Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
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Reduction of Alkenes: Catalytic Hydrogenation02:13

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Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...
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Catalysis02:50

Catalysis

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The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
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Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation01:28

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Unlike the easy catalytic hydrogenation of an alkene double bond, hydrogenation of a benzene double bond under similar reaction conditions does not take place easily. For example, in the reduction of stilbene, the benzene ring remains unaffected while the alkene bond gets reduced. Hydrogenation of an alkene double bond is exothermic and a favorable process. In contrast, to hydrogenate the first unsaturated bond of benzene, an energy input is needed; that is, the process is endothermic. This is...
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Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation02:47

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One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
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Isomerización de alqueno con un catalizador de níquel-hidruro heterogéneo

Alison Sy-Min Chang1, Melanie A Kascoutas1, Quinn P Valentine1

  • 1Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403, United States.

Journal of the American Chemical Society
|May 21, 2024
PubMed
Resumen

Un nuevo catalizador de níquel heterogéneo soportado en zirconio sulfatado (SZO300) demuestra una alta actividad y selectividad para la isomerización de alquenos. Este robusto catalizador, hecho de elementos abundantes en la Tierra, supera las limitaciones de los sistemas homogéneos y basados en metales preciosos.

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Área de la Ciencia:

  • Catálisis
  • Ciencias de los materiales
  • Química orgánica

Sus antecedentes:

  • Los catalizadores homogéneos ofrecen selectividad ajustable pero carecen de estabilidad y reciclabilidad.
  • Los catalizadores heterogéneos son robustos, pero a menudo carecen de especificidad del sitio activo y son difíciles de mejorar.
  • Los catalizadores heterogéneos existentes en un solo lugar utilizan metales preciosos y soportes complejos.

Objetivo del estudio:

  • Desarrollar un catalizador heterogéneo estable, reciclable y altamente activo para la isomerización de alquenos utilizando elementos abundantes en la Tierra.
  • Para superar los problemas de descomposición de los catalizadores homogéneos de níquel-hidruro.
  • Lograr una mayor selectividad y una mayor tolerancia de los grupos funcionales en comparación con los sistemas existentes.

Principales métodos:

  • Inmovilización de un sitio activo a base de níquel en zirconio sulfatado (SZO300).
  • Pruebas catalíticas para la isomerización de alquenos, la hidroalquenilación, la hidroboración y la hidrociliación.
  • Estudios cinéticos para comparar los catalizadores de níquel y paladio.

Principales resultados:

  • El catalizador Ni/SZO300 exhibe una alta actividad y selectividad para la isomerización de alquenos, superando a los catalizadores homogéneos y de metales preciosos.
  • Los problemas de descomposición del precursor homogéneo se evitan mediante la inmovilización.
  • El catalizador demuestra un amplio espectro de tolerancia y actividad del grupo funcional en otras reacciones.

Conclusiones:

  • La zirconia sulfatada es un soporte eficaz para la creación de catalizadores heterogéneos robustos y altamente activos a partir de metales abundantes en la Tierra.
  • El sistema Ni/SZO300 representa un avance significativo en la catálisis de isomerización de alquenos, ofreciendo una alternativa práctica y sostenible.
  • Este catalizador heterogéneo muestra potencial para varias transformaciones orgánicas importantes más allá de la isomerización.