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Origen de la diferencia de reactividad entre los catalizadores Ir para la borilación de enlaces C-H

Raphael J Oeschger¹, Matthew A Larsen¹, Alessandro Bismuto¹

¹Department of Chemistry , University of California , Berkeley , California 94720 , United States.

Journal of the American Chemical Society

|September 21, 2019

Resumen

El estudio revela que los catalizadores de iridio con ligandos de 3,4,7,8-tetrametilfenantrolina (tmphen) ofrecen mayores rendimientos en las reacciones de boroilación C-H debido a una mayor estabilidad, no solo a la reactividad. Esta mejora de la vida útil del catalizador es clave para una borilación eficiente.

Área de la Ciencia:

Química organometálica
Catálisis
Síntesis orgánica

Sus antecedentes:

Los catalizadores de iridio son cruciales para las reacciones de boroilación C-H.
La elección del ligando tiene un impacto significativo en el rendimiento y la estabilidad del catalizador.
La comprensión de las vías de desactivación del catalizador es esencial para optimizar las reacciones.

Objetivo del estudio:

Investigar el origen mecánico de las diferencias de reactividad entre los catalizadores de iridio.
Para comparar el rendimiento de los catalizadores de iridio ligados por 3,4,7,8-tetrametilfenantrolina (tmphen) y 4,4'-di-tert-butilbipiridina (dtbpy).
Elucidar los factores que contribuyen a un mayor rendimiento en las reacciones de borilación C-H.

Principales métodos:

Se han realizado reacciones catalíticas de borilación C-H utilizando bis ((pinacolato) diboro (B2pin2) con varios sustratos.
Se utilizan catalizadores de iridio generados a partir de [Ir ((COD)) ((OMe)) ]2 combinados con los ligandos tmphen o dtbpy.
Se analizaron las propiedades electrónicas y la reactividad estequiométrica de los catalizadores de iridio.

Principales resultados:

Los catalizadores de iridio-tmfeno produjeron rendimientos de producto sustancialmente más altos en comparación con los catalizadores de iridio-dtbpy en condiciones de reacción exigentes.
La vida útil del catalizador, en lugar de la reactividad intrínseca, se identificó como el factor principal para mejorar los rendimientos con Ir-tmphen.
El catalizador ligado dtbpy se descompone a través de la disociación del ligando y la borilación rápida en las posiciones alfa-nitrógeno.

Conclusiones:

La estabilidad superior del catalizador de iridio ligado con tmphen, atribuida a una mayor constante de unión, conduce a rendimientos de reacción generales más altos.
La longevidad del catalizador es un determinante crítico para el éxito en el desafío de las reacciones de borilación C-H.
Las ideas mecánicas sobre las vías de descomposición del catalizador informan el diseño de sistemas catalíticos más robustos.

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