Video Experimental Relacionado

Updated: Jul 6, 2026

Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

Published on: June 21, 2017

Mecanismo de acoplamiento reversible de alquinos en el circonoceno: efectos auxiliares del ligando

Adam D Miller¹, Jennifer L McBee, T Don Tilley

¹Department of Chemistry, University of California, Berkeley, Berkeley, California 94720-1460, USA.

Journal of the American Chemical Society

|March 14, 2008

Resumen

Este estudio revela que el acoplamiento reversible de alquino en el zirconio se produce a través de un mecanismo disociativo. El volumen estérico de los ligandos auxiliares influye significativamente en las tasas de reacción de la escisión del zirconaciclopentadieno.

Área de la Ciencia:

Química organometálica Química orgánica de los metales.
Catalización de zirconio en la catálisis de zirconio.
Reacciones de acoplamiento alquino Reacciones de acoplamiento alquino

Sus antecedentes:

El acoplamiento reversible de alquinos es crucial en la síntesis orgánica.
Los circonaciclopentadienos son intermediarios clave en estas transformaciones.
La comprensión de los mecanismos de reacción es vital para el diseño de catalizadores.

Objetivo del estudio:

Para dilucidar el mecanismo de acoplamiento reversible de alquinos en el circonio.
Para investigar la cinética de la escisión del anillo de zirconaciclopentadieno.
Para determinar la influencia de los ligandos auxiliares en las velocidades de reacción.

Principales métodos:

Estudios cinéticos de la escisión del circonaciclopentadieno.
El uso de zirconaciclopentadienos sustituidos por trimetilsililo.
Empleando varios conjuntos de ligandos bis (cyclopentadienil) (Cp2, Me2C (eta) -C5H4) 2, CpCp*).
Análisis de los parámetros de activación utilizando el análisis de Eyring.

Principales resultados:

La reacción de escisión es de primer orden en la concentración de zirconaciclo y de orden cero en la fosfina.
Un mecanismo disociativo fue confirmado por los parámetros de activación.
Los complejos Ansa-bridged mostraron tasas de reacción significativamente alteradas en comparación con los complejos Cp2.
Las propiedades estéricas de los ligandos auxiliares se identificaron como los principales factores que influyen en la tasa.

Conclusiones:

El mecanismo de acoplamiento reversible de alquinos en el zirconio es disociativo.
Los estéricos de ligandos auxiliares juegan un papel crítico en la modulación de la cinética de la escisión del zirconaciclopentadieno.
Esto proporciona información sobre el control de la reactividad en el acoplamiento de alquino catalizado por zirconio.

Más Videos Relacionados

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)

Published on: January 17, 2020

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Published on: March 20, 2017

Videos de Conceptos Relacionados

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

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.

Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction

Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction

The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.

Aryldiazonium Salts to Azo Dyes: Diazo Coupling

Aryldiazonium Salts to Azo Dyes: Diazo Coupling

The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the para position.

Electrophilic Addition to Alkynes: Hydrohalogenation

Electrophilic Addition to Alkynes: Hydrohalogenation

Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.

Electrophilic Addition to Alkynes: Halogenation

Electrophilic Addition to Alkynes: Halogenation

Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.

E1 Reaction: Stereochemistry and Regiochemistry

E1 Reaction: Stereochemistry and Regiochemistry

One of the critical aspects of the E1 reaction mechanism, as also observed in E2, is the regiochemistry, with multiple regioisomers obtained as products. In the example discussed, the presence of water as a weak base favors elimination over substitution to generate two alkenes. Given that alkenes’ stability increases with the number of alkyl groups across the double bond, typically, E1 reactions lead to the Zaitsev product, for this is more substituted and stable than the Hofmann product.