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Videos de Conceptos Relacionados

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 Alkenes: Asymmetric Catalytic Hydrogenation02:17

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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 Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

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Introduction
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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Nitriles to Amines: LiAlH4 Reduction00:55

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Nitriles are reduced to amines in the presence of strong reducing agents like lithium aluminum hydride through a typical nucleophilic acyl substitution. The reaction requires two equivalents of the reducing agent. The reducing agent acts as a source of hydride ions.
As shown below, the mechanism involves three steps. Firstly, the hydride ion acting as a nucleophile attacks the nitrile carbon to form an anion. In the second step, a second equivalent of the hydride ion attacks the anion to...
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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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Preparation of Amines: Reductive Amination of Aldehydes and Ketones01:38

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Carbonyl compounds and primary amines undergo reductive amination first to produce imines, followed by secondary amines in the same reaction mixture, using selective reducing agents like sodium cyanoborohydride or sodium triacetoxyborohydride. Reductive amination produces different degrees of substitution of amines depending on the starting amine substrate.
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Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
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Catálisis de aminación C-H eficiente mediante el uso de complejos de níquel-dipirrina

Yuyang Dong1, Ryan M Clarke1, Gerard J Porter1

  • 1Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States.

Journal of the American Chemical Society
|May 29, 2020
PubMed
Resumen
Este resumen es generado por máquina.

Un nuevo catalizador de níquel permite una aminación intramolecular eficiente de las azidas alifáticas a temperatura ambiente. Esta reacción procede a través de un paso de abstracción del átomo de hidrógeno que determina la velocidad, formando N-heterociclos con amplio alcance de sustrato y tolerancia de grupo funcional.

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Área de la Ciencia:

  • Química organometálica
  • Catálisis
  • Síntesis orgánica

Sus antecedentes:

  • La aminación C-H intramolecular es una transformación crucial para la síntesis de heterociclos N.
  • El desarrollo de sistemas catalíticos suaves y eficientes para la funcionalización de C-H sigue siendo un desafío importante.
  • La catálisis del níquel ofrece una vía prometedora para activar enlaces C-H inertes.

Objetivo del estudio:

  • Desarrollar un nuevo catalizador de níquel para la aminación de C-H intramolecular utilizando azidas alifáticas.
  • Investigar el alcance, la quimioselectividad y la tolerancia del grupo funcional del sistema catalítico.
  • Aclarar el mecanismo de reacción, incluido el paso que determina la velocidad y el estado de reposo catalítico.

Principales métodos:

  • Síntesis y caracterización de un catalizador de níquel soportado por dipirrina.
  • Exploración del alcance del sustrato para la aminación C-H, incluidos varios tipos de enlaces C-H y grupos funcionales.
  • Estudios mecánicos mediante espectroscopia de resonancia magnética nuclear (RMN), mediciones del efecto isotópico cinético (EIC) y análisis de Eyring.

Principales resultados:

  • El catalizador (AdFL) Ni(py promueve eficientemente la aminación intramolecular C-H de las azidas alifáticas en condiciones suaves (temperatura ambiente, carga de 0,1-2 mol%).
  • La reacción exhibe un amplio alcance de sustrato, aminando con éxito enlaces bencílicos, terciarios, secundarios y primarios C-H con alta quimioselectividad para enlaces C-H más débiles.
  • Las investigaciones mecánicas revelan un paso de abstracción del átomo de hidrógeno que determina la velocidad, que probablemente involucra el túnel del átomo H, con el estado de reposo del catalizador identificado como un radical de níquel iminyl.

Conclusiones:

  • Se ha desarrollado un catalizador de níquel altamente eficaz para la aminación intramolecular de C-H, que permite la síntesis de heterociclos N.
  • La reacción se produce en condiciones suaves y demuestra una excelente tolerancia funcional del grupo y quimioselectividad.
  • Los estudios mecanicistas proporcionan información crítica sobre el ciclo catalítico, destacando la importancia de la abstracción y el túnel del átomo de hidrógeno.