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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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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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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.
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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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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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A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
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Catalizadores de hidroformilación de cobalto catiónico altamente activo

Drew M Hood1, Ryan A Johnson1, Alex E Carpenter2

  • 1Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA.

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Resumen

Los nuevos catalizadores catiónicos de cobalto ofrecen una alta actividad y selectividad para la hidroformilación de alquenos, acercándose al rendimiento del rodio. Estos catalizadores demuestran una larga vida útil y estabilidad, especialmente para los alquenos internos.

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Área de la Ciencia:

  • Química organometálica
  • Catálisis
  • Síntesis orgánica

Sus antecedentes:

  • La hidroformilación utiliza tradicionalmente catalizadores de cobalto o de rodio.
  • Los catalizadores de rodio son muy activos pero caros.
  • Los catalizadores de cobalto existentes tienen limitaciones en cuanto a actividad y selectividad.

Objetivo del estudio:

  • Desarrollar nuevos catalizadores de cobalto con mayor actividad y selectividad.
  • Comparar el rendimiento de los nuevos catalizadores de cobalto con los estándares industriales existentes.
  • Investigar la regioselectividad de estos catalizadores para diferentes tipos de alquenos.

Principales métodos:

  • Síntesis de cobalto catiónico (II) complejos de hidrido-carbonilo de bisfosfina.
  • Evaluación de la actividad catalítica en la hidroformilación de alquenos.
  • Análisis de la regioselectividad lineal a ramificada (L:B) para varios alquenos.
  • Evaluación de la estabilidad y la vida útil del catalizador.

Principales resultados:

  • Los nuevos catalizadores catiónicos de cobalto presentan una actividad significativamente mayor que los catalizadores tradicionales de cobalto.
  • La actividad del catalizador se acerca a la de los costosos catalizadores de rodio-fosfina.
  • Se observa una baja regioselectividad L:B para alquenos lineales simples.
  • Se obtiene una alta regioselectividad L:B para alquenos internos con ramas alquilo debido a la isomerización y los efectos estéricos.
  • Los catalizadores muestran una larga vida útil y resistencia a la degradación.

Conclusiones:

  • Los catalizadores catiónicos de cobalto bisfosfina representan un avance prometedor en la hidroformilación.
  • Estos catalizadores ofrecen una alternativa rentable a los catalizadores de rodio.
  • Con estos nuevos sistemas se puede lograr una selectividad adaptada a los alquenos internos.