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Heterogeneous Catalysis

Heterogeneous Catalysis

Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...

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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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The addition of a hydrogen halide to 1,3-butadiene gives a mixture of 1,2- and 1,4-adducts. Since more substituted alkenes are more stable, the 1,4-adduct is expected to be the major product. However, the product distribution is strongly influenced by temperature; low temperature favors the 1,2-adduct, whereas the 1,4-adduct is predominant at high temperature.

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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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Mono-oxidación de las bisfosfinas bidentadas en la activación del catalizador: estudios cinéticos y mecánicos de una

Yining Ji¹, R Erik Plata¹, Christopher S Regens²

¹Department of Chemistry, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States ;

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|October 14, 2015

Resumen

Este resumen es generado por máquina.

La mono-oxidación de los ligandos de bis-fosfina es crucial para la activación de los catalizadores de paladio en la arilación C-H. El ligando de monoóxido resultante es catalíticamente activo, lo que permite reacciones de acoplamiento eficientes catalizadas por paladio.

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Área de la Ciencia:

Química organometálica
Catálisis
Síntesis orgánica

Sus antecedentes:

La arilación C-H catalizada por el paladio es una herramienta vital en la síntesis orgánica.
La comprensión de los mecanismos de activación del catalizador es clave para optimizar la eficiencia de la reacción.

Objetivo del estudio:

Para aclarar el papel de los ligandos de la fosfina en la arilación C-H catalizada por el paladio.
Identificar las especies catalíticas activas y su mecanismo de acción.

Principales métodos:

Estudios cinéticos, espectroscópicos y cristalográficos.
Modelado computacional.
Análisis de rayos X de los intermediarios catalíticos.

Principales resultados:

La mono-oxidación de los ligandos de bis-fosfina es crítica para la formación del catalizador activo de paladio.
El monóxido de bisfosfina actúa como un ligando bidentado hemilabil.
El monóxido intermedio es catalíticamente competente, correspondiendo a la actividad del precursor.

Conclusiones:

Los ligandos de monóxido de fosfina juegan un papel clave en las reacciones de acoplamiento catalizadas por paladio.
Una base de carboxilato tiene una doble función en la activación y rotación del catalizador.
El exceso de ligando de fosfina inhibe el proceso catalítico.