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Adsorbados moleculares Intercambio de catálisis heterogénea: Inducción de la reactividad por carbenos

Johannes B Ernst¹, Christian Schwermann², Gen-Ichi Yokota

¹Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster , Corrensstrasse 40, 48149 Münster, Germany.

Journal of the American Chemical Society

|June 22, 2017

Resumen

La activación de carbenos N-heterocíclicos (NHC) de un catalizador de paladio sobre alumina (Pd/Al2O3) permite una aminación de Buchwald-Hartwig eficiente. La coordinación NHC modifica las propiedades electrónicas del paladio, facilitando la activación del haluro de arilo a través de un mecanismo heterogéneo.

Área de la Ciencia:

Catálisis heterogénea
Química orgánica de los metales
Ciencias de la superficie

Sus antecedentes:

Los catalizadores de paladio sobre alumina (Pd/Al2O3) son típicamente no reactivos para ciertas reacciones de acoplamiento cruzado.
Los carbenos N-heterocíclicos (NHC) son ligandos conocidos que pueden modificar las propiedades del catalizador metálico.

Objetivo del estudio:

Investigar la activación de un catalizador Pd/Al2O3 mediante el uso de ligandos NHC.
Explorar la aplicación de este catalizador modificado en las reacciones de aminación de Buchwald-Hartwig.
Para aclarar el mecanismo de activación del catalizador inducido por NHC.

Principales métodos:

Técnicas de análisis de superficie (por ejemplo, espectroscopia) para caracterizar la interacción NHC-Pd.
Cálculos ab initio para modelar los efectos electrónicos de la coordinación del CNS.
Prueba catalítica del catalizador Pd/Al2O3 modificado en la aminación de Buchwald-Hartwig.
Pruebas de heterogeneidad para determinar el mecanismo de reacción.

Principales resultados:

Se confirmó la coordinación del NHC con las partículas de paladio.
La modificación del NHC alteró las propiedades electrónicas del paladio, mejorando la actividad catalítica.
El catalizador modificado facilitó con éxito la aminación de Buchwald-Hartwig de cloruros de arilo, bromuros y yoduros.
La evidencia sugiere que la reacción se produce a través de una especie activa heterogénea.

Conclusiones:

Los ligandos NHC pueden activar catalizadores Pd/Al2O3 que de otro modo no serían reactivos.
La donación de electrones inducida por NHC en el paladio reduce la barrera de activación para el acoplamiento de haluro de arilo.
El catalizador Pd/Al2O3 modificado por NHC es eficaz para la aminación de Buchwald-Hartwig, operando a través de una vía heterogénea.

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