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Acoplamiento bimolecular en la metátesis de olefinas: estructura y descomposición correlacionadas para catalizadores

Daniel L Nascimento¹, Marco Foscato², Giovanni Occhipinti²

¹Center for Catalysis Research & Innovation, and Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Canada K1N 6N5.

Journal of the American Chemical Society

|July 16, 2021

Resumen

Los catalizadores de rutenio-ciclo-alquilo-aminocarbeno, aunque avanzados, se descomponen rápidamente. Este estudio revela su descomposición mejorada a través de un mecanismo de influencia trans, ofreciendo nuevas vías para mejorar la estabilidad del catalizador y la productividad de la metátesis de olefinas.

Área de la Ciencia:

Catálisis
Química organometálica
Síntesis orgánica

Sus antecedentes:

La descomposición bimolecular es un desafío crítico en la catálisis de la metátesis de olefinas.
Los catalizadores de rutenio-ciclo-alquilo-aminocarbeno (CAAC) ofrecen una alta productividad pero son propensos a la descomposición.
Los detalles mecánicos de esta vía de descomposición han permanecido en gran medida desconocidos.

Objetivo del estudio:

Elucidar los factores estéricos y electrónicos que rigen la descomposición bimolecular en los catalizadores de rutenio-CAAC.
Proporcionar información mecanicista detallada sobre la descomposición de las especies activas clave.
Comprender la relación entre la iniciación del catalizador y las tasas de descomposición.

Principales métodos:

Estudios computacionales experimentales y teóricos combinados.
Aislamiento y caracterización de los aductos de piridina estabilizados transitoriamente (RuCl2
Análisis cinético de la descomposición del catalizador a -10 °C.

Principales resultados:

Todos los catalizadores CAAC estudiados se descomponen a través de la cinética de segundo orden.
Los catalizadores CAAC se descomponen más de 1000 veces más rápido que los análogos del carbeno N-heterocíclico (NHC).
La descomposición acelerada se atribuye a una influencia trans más fuerte en los ligandos CAAC, debilitando el enlace Ru-piridina y aumentando la concentración de especies activas de metilideno.

Conclusiones:

La iniciación rápida del catalizador, un rasgo deseable, acelera inadvertidamente la descomposición bimolecular.
La inhibición de la descomposición bimolecular presenta oportunidades significativas para mejorar la productividad y la utilidad del catalizador en la metátesis de olefinas.
La comprensión de estas vías de descomposición es clave para desbloquear todo el potencial de la metástasis de la olefina.

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