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Activación meta-selectiva de enlaces C-H catalizada por paladio con una plantilla que contiene nitrilo: estudio

Yun-Fang Yang¹, Gui-Juan Cheng, Peng Liu

¹Laboratory of Computational Chemistry and Drug Design and Laboratory of Chemical Genomics, Peking University Shenzhen Graduate School , Shenzhen 518055, China.

Journal of the American Chemical Society

|December 10, 2013

Resumen

La teoría funcional de la densidad revela que los heterodímeros Pd-Ag son clave para las olefinaciones meta-selectivas de C-H utilizando plantillas de nitrilo. Esto dirige el paladio a la meta posición, controlando los resultados de la reacción.

Área de la Ciencia:

Química organometálica Química orgánica de los metales.
La catálisis de la catálisis.
Química computacional es la química computacional.

Sus antecedentes:

La funcionalización C-H catalizada por el paladio es crucial para la síntesis orgánica.
Lograr la regioselectividad en estas reacciones, particularmente la meta-selectividad, sigue siendo un desafío.
Las plantillas que contienen nitrilo ofrecen una estrategia para dirigir la activación de C-H.

Objetivo del estudio:

Aclarar el mecanismo y los orígenes de la meta-regioselectividad en las olefinaciones de C-H catalizadas por Pd (II).
Para investigar el papel de diferentes especies catalíticas de paladio en la reacción.
Para entender cómo las plantillas de nitrilo influyen en la regioselectividad.

Principales métodos:

Se emplearon investigaciones de la Teoría Funcional de Densidad (DFT).
Análisis de cuatro pasos clave: activación de C-H, inserción de alqueno, eliminación de beta-hidruro y eliminación reductiva.
Evaluación de varias especies catalíticas: el monomérico Pd(II), el dimérico Pd2(OAc) 4, el heterodímero PdAg(OAc) 3 y el trímero Pd3(OAc) 6.

Principales resultados:

El paso de activación C-H, que procede a través de una vía concertada de metalización-deprotonación (CMD), dicta la velocidad y la regioselectividad.
Se identificó un estado de transición heterodímero Pd-Ag como la vía más favorable para la activación de meta-C-H.
El grupo nitrilo se coordina con Ag, posicionando Pd para la activación meta-selectiva de C-H, superando la favorabilidad energética del dimérico Pd2 ((OAc) 4.

Conclusiones:

El mecanismo heterodímero Pd-Ag explica la alta meta-selectividad observada en estas reacciones.
Las especies monoméricas y triméricas de Pd favorecen los orto-productos, que requieren mayores energías de activación.
La estructura de la plantilla y las energías de distorsión impactan significativamente el mecanismo de reacción y la regioselectividad, ofreciendo vías para el diseño de nuevos catalizadores.

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