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Explicación mecanicista alternativa para las selectividades dependientes de ligandos en las reacciones de N- y
Hai-Zhu Yu1, Yuan-Ye Jiang, Yao Fu
1Department of Chemistry, Joint Laboratory of Green Synthetic Chemistry, University of Science and Technology of China, Hefei 230026, China.
Journal of the American Chemical Society
|December 8, 2010
Resumen
Este estudio propone un mecanismo alternativo de adición oxidativa/eliminación reductora para explicar las selectividades dependientes de los ligandos en las reacciones de tipo Ullmann catalizadas por el cobre, ofreciendo nuevos conocimientos sobre los resultados de la N- vs. O-arilación.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- La catálisis es la catálisis.
- Mecanismos de reacción Mecanismos de reacción
Sus antecedentes:
- Las reacciones de tipo Ullmann son cruciales para la formación de enlaces C-N y C-O.
- Estudios anteriores atribuyeron selectividades dependientes de ligandos en reacciones catalizadas por cobre a los mecanismos de transferencia de electrones individuales y de transferencia de átomos de yodo.
- El papel de la carga del ligando y la coordinación del sustrato en la determinación de las vías de reacción sigue siendo un área de investigación activa.
Objetivo del estudio:
- Investigar un mecanismo alternativo de adición oxidativa/eliminación reductora para las reacciones de tipo Ullmann.
- Para dilucidar cómo diferentes ligandos (β-diketona frente a 1,10-fenantrolina) influyen en la selectividad de la reacción.
- Explorar computacionalmente los factores que rigen la N-arilación frente a la O-arilación en la catálisis del cobre.
Principales métodos:
- Modelado computacional y cálculos teóricos.
- Análisis de estados de transición y energética de reacción.
- Comparación del mecanismo propuesto con las vías de transferencia de un solo electrón existentes.
Principales resultados:
- Un complejo neutro Cu(I) -β-diketona facilita la adición oxidativa de ArI antes de la coordinación del aminoalcohol, favoreciendo la N-arilación.
- Un complejo de Cu (I) -1,10-fenantrolina cargado positivamente requiere la desprotonación del sustrato para la adición oxidativa, favoreciendo la O-arilación.
- El paso de coordinación es limitante de velocidad para los ligandos β-diketona, mientras que la adición oxidativa es limitante de velocidad para los ligandos 1,10-fenantrolina.
Conclusiones:
- El mecanismo de adición oxidativa/eliminación reductora proporciona una explicación alternativa viable para las selectividades dependientes de los ligandos en las reacciones de tipo Ullmann catalizadas por cobre.
- Las propiedades de los ligandos, específicamente la carga, dictan el mecanismo de reacción y el sitio preferido de arilación (N vs. O).
- La comprensión de estos matices mecánicos es clave para diseñar sistemas catalíticos más eficientes y selectivos para la arilación de aminas y alcoholes.
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