Prueba de los límites de la reactividad desequilibrada de CPET: cruce mecánico en la abstracción de átomos de H por
Norman Zhao1, McKenna K Goetz1, Joseph E Schneider1
1Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States.
Journal of the American Chemical Society
|March 3, 2023
Resumen
Este estudio revela que el aumento de la basicidad de los complejos de cobalto-oxo puede alterar los mecanismos de activación de enlaces C-H. Los complejos altamente básicos muestran un cambio de la transferencia concertada de protones-electrones a las vías graduales, impactando las tasas de reacción.
Área de la Ciencia:
- Química organometálica
- Catálisis
- Mecanismos de reacción
Sus antecedentes:
- Los complejos de metal de transición-oxo son intermediarios cruciales en las reacciones de oxidación, en particular la activación de enlaces C-H.
- Las tasas de reacción en la activación de C-H a menudo están vinculadas a la energía libre de disociación de enlaces de sustrato a través de la transferencia concertada de protones-electrones (CPET).
- Las vías alternativas por etapas que involucran la acidez/basicidad del sustrato/metal-oxo o los potenciales redox también pueden influir en la dinámica de reacción.
Objetivo del estudio:
- Investigar los límites de la activación de enlaces C-H regidos por la basicidad por complejos de metal de transición-oxo.
- Para sintetizar y estudiar un complejo más básico de cobalto-oxo, PhB ((AdIm) 3CoIIIO, y comparar su reactividad con un análogo menos básico.
- Explorar el cruce mecánico entre las vías concertadas y escalonadas en la activación de enlaces C-H y O-H.
Principales métodos:
- Síntesis de un nuevo complejo terminal más básico de cobalto-oxo, PhB ((AdIm) 3CoIIIO.
- Estudios de reactividad con donantes de átomos de hidrógeno y sustratos de fenol.
- Análisis termodinámico de los procesos de transferencia de protones (PT) y de transferencia de electrones (ET).
Principales resultados:
- El complejo PhB ((AdIm) 3CoIIIO más básico exhibe una mayor reactividad desequilibrada de CPET en comparación con PhB ((Im) 3CoIIIO.
- La activación O-H de los sustratos de fenol muestra un cambio mecanicista de CPET a la transferencia gradual de protones-electrones (PTET).
- Se identificó un punto de cruce termodinámico entre la reactividad concertada y la gradual.
Conclusiones:
- La basicidad juega un papel crítico en dictar el mecanismo de activación de enlaces C-H por complejos de cobalto-oxo.
- Los sistemas con máximo desequilibrio pueden lograr tasas de CPET rápidas hasta que se produzca un cruce mecanicista a vías graduales.
- Este punto de cruce conduce a una formación de productos más lenta, lo que pone de relieve el delicado equilibrio entre la reactividad concertada y gradual.
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