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Efectos electrónicos y del medio sobre la tasa de activación del areno C [enlace] H por los complejos catiónicos Ir

David M Tellers¹, Cathleen M Yung, Bruce A Arndtsen

¹Division of Chemical Sciences, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA.

Journal of the American Chemical Society

|February 14, 2002

Resumen

Este estudio revela que los complejos de iridio activan enlaces C-H en arenas a través de un mecanismo de pares de iones, donde la disociación de triflados precede a la activación. La reactividad se ve reforzada por sustituyentes donantes de electrones tanto en el complejo de iridio como en el sustrato de areno.

Área de la Ciencia:

Química organometálica Química orgánica de los metales.
La catálisis por catálisis.
Mecanismos de reacción Mecanismos de reacción

Sus antecedentes:

La activación de Arene C-H es una transformación crucial en la química organometálica.
Comprender las vías mecanicistas es clave para diseñar catalizadores eficientes.

Objetivo del estudio:

Investigar el mecanismo detallado de la activación del areno C-H por complejos Cp(L) IrMe(X) en solución de diclorometano.
Para aclarar el papel de la formación de pares de iones y la disociación de ligandos en el ciclo catalítico.

Principales métodos:

Estudio mecanicista detallado utilizando complejos Cp (L) IrMe (X) con diferentes ligandos (L) y contrarios (X).
Análisis cinético en solución de CH(2)Cl(2), incluyendo estudios con sales añadidas para sondear las interacciones de pares de iones.
Computaciones de la Teoría Funcional de Densidad (DFT) para apoyar interpretaciones mecanicistas.

Principales resultados:

La disociación del triflato de Cp (L) IrMe (OTf) para formar pares iónicos precede a la activación de C-H.
La reactividad es dependiente del medio y puede ser significativamente mejorada por el "efecto sal especial" utilizando aniones de coordinación débil como BAr f).
Los sustituyentes donantes de electrones en el areno aumentan la tasa de activación C-H, mientras que los efectos electrónicos del ligando de fosfina influyen principalmente en la disociación del ligando de pre-equilibrio.

Conclusiones:

El mecanismo de activación C-H implica la disociación inicial del triflato para formar intermedios de iridio catiónico.
La velocidad de reacción global es optimizada por grupos donantes de electrones tanto en el complejo de iridio como en el sustrato de areno.
Los cálculos de DFT apoyan el modelo mecanicista propuesto, destacando la importancia de la labilidad del ligando y el emparejamiento iónico.

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