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Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry
Published on: October 18, 2019
Mecanismo de la ciclohidroaminación catalítica por complejos de zirconio saliciloxazolina
Laura E N Allan1, Guy J Clarkson, David J Fox
1Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry CV7 4AL, UK.
Journal of the American Chemical Society
|October 14, 2010
Resumen
Este estudio investiga el mecanismo de hidroaminación / ciclización utilizando catalizadores de circonio. Un hallazgo clave es que la ruptura del enlace N-H, no el cierre del anillo, dicta la velocidad de reacción, lo que propone una formación reactiva de especies de imido.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- La catálisis es la catálisis.
- Mecanismo de reacción Elucidación.
Sus antecedentes:
- Las reacciones de hidroaminación/ciclización son cruciales para la síntesis de compuestos que contienen nitrógeno.
- Los catalizadores a base de zirconio ofrecen perfiles de reactividad únicos en las transformaciones orgánicas.
- Comprender los mecanismos de reacción es vital para el diseño y la optimización del catalizador.
Objetivo del estudio:
- Para aclarar el mecanismo detallado de la hidroaminación / ciclización catalizada por Cp * LZr (((NMe (((2)) ((2)) complejos.
- Para identificar la etapa de determinación de la velocidad (RDS) y los intermediarios clave involucrados en el ciclo catalítico.
- Investigar la influencia de la estructura del catalizador y las condiciones de reacción en las velocidades y vías de reacción.
Principales métodos:
- Estudios cinéticos para determinar la ley de velocidad y los parámetros de activación.
- Estudios estequiométricos y espectroscópicos de RMN in situ para caracterizar los productos intermedios.
- Cristalografía de rayos X para analizar la estructura del catalizador y los efectos estéricos.
Principales resultados:
- La ley de velocidad d[sustrato]/dt = k[catalizador](1) [sustrato](0) indica un paso de determinación de velocidad dependiente del catalizador e independiente del sustrato.
- Un efecto de isótopo cinético significativo (KIE) apunta a la ruptura del enlace N-H como el RDS, que precede al cierre del anillo.
- El aumento de la masa estérica en el catalizador aumenta las tasas de reacción, y la conversión del catalizador a una especie metaciclica a través de la activación de C-H se produce después de la reacción.
Conclusiones:
- El mecanismo implica la formación que determina la velocidad de una especie de imido reactiva, excluyendo un mecanismo de amido.
- El centro metálico no actúa como un ácido de Lewis en el RDS, pero el sustrato activado está involucrado.
- Se propone un ciclo catalítico, que culmina en la desactivación del catalizador a través de la activación C-H.
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