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Ligandos donantes axiales: una nueva estrategia para la catálisis de polimerización tardía de los metales de

Dennis H Leung¹, Joseph W Ziller, Zhibin Guan

¹Department of Chemistry, University of California, 1102 Natural Sciences 2, Irvine, California 92697-2025, USA.

Journal of the American Chemical Society

|May 23, 2008

Resumen

Un nuevo ligando alfa-diimine con un grupo piridina permite catalizadores metálicos tardíos altamente activos para la polimerización del etileno, produciendo polietileno lineal de alto peso molecular. Este ligando de piridina mejora significativamente el rendimiento del catalizador en comparación con los controles basados en fenilo.

Área de la Ciencia:

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

Sus antecedentes:

El desarrollo de catalizadores eficientes para la polimerización de olefinas es crucial para la producción de materiales poliméricos avanzados.
Los catalizadores de metales tardíos ofrecen perfiles de reactividad únicos para la polimerización.
Los ligandos alfa-diimina son plataformas versátiles para ajustar el rendimiento del catalizador.

Objetivo del estudio:

Para sintetizar y caracterizar un nuevo ligando alfa-diimine con un grupo de piridina axial.
Para evaluar el rendimiento de los complejos de níquel y paladio de este ligando en la polimerización de etileno.
Investigar el papel de la fracción de piridina y el cocatalizador en la actividad del catalizador y las propiedades del polímero.

Principales métodos:

Síntesis del ligando alfa-diimine (1) con un grupo de piridina.
Preparación de complejos de níquel (por ejemplo, 1-NiBr2) y paladio (por ejemplo, 1-PdMeCl).
Experimentos de polimerización de etileno utilizando estos complejos con el cocatalizador AlMe2Cl.
Análisis del peso molecular del polímero (Mn) y la ramificación mediante cromatografía de permeación de gel (GPC) y espectroscopia de RMN.

Principales resultados:

Los complejos de níquel y paladio del ligando (1) que contiene piridina mostraron una alta actividad para la polimerización del etileno.
Se produjo polietileno lineal de alto peso molecular (PE), con Mn de hasta 109.224 g/mol (Ni) y 880.379 g/mol (Pd).
Los catalizadores de control con un ligando de fenilo produjeron solo oligómeros ramificados de bajo peso molecular, destacando la efectividad del grupo piridina.

Conclusiones:

El grupo piridina axial en el ligando alfa-diimine es clave para lograr una alta actividad y producir PE lineal de alto peso molecular.
El cocatalizador AlMe2Cl juega un papel específico en la activación de los complejos basados en piridina, probablemente a través de interacciones bimetálicas.
La porción de piridina suprime la eliminación de beta-hidruro, lo que lleva a una reducción de la transferencia de la cadena y una mayor linealidad del polímero.

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