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Mecanismo de polimerización del metyaluminoxano (MAO) y modelo cinético desde la dinámica molecular ab initio y
Lacramioara Negureanu1, Randall W Hall, Leslie G Butler
1Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA.
Journal of the American Chemical Society
|December 21, 2006
Resumen
El metilaluminoxano (MAO) es crucial para los catalizadores de metaloceno. Este estudio revela las formas de MAO a través de la polimerización paso a paso de un monómero bifuncional, con [CH3) Al-O como la unidad estructural, utilizando simulaciones de dinámica molecular.
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 metilaluminoxano (MAO) es un co-catalizador vital en los sistemas de metallocenos para la polimerización de olefinas en un solo sitio.
- La estructura exacta de las especies catalíticamente activas en la MAO sigue siendo indeterminada, a pesar de los numerosos modelos propuestos.
- Comprender el mecanismo de formación de MAO es fundamental para optimizar su rendimiento catalítico.
Objetivo del estudio:
- Para dilucidar el mecanismo de formación del metilaluminoxano (MAO).
- Para identificar la molécula de bloque de construcción y la vía de polimerización de la MAO.
- Proponer un modelo cinético para la formación de MAO.
Principales métodos:
- Se emplearon simulaciones de dinámica molecular en el nivel teórico MP2.
- Las simulaciones se centraron en los pasos elementales en la formación de MAO a través de la hidrólisis del trimetilaluminio (TMA).
- Las barreras de activación para las reacciones se calcularon para comprender el proceso de polimerización.
Principales resultados:
- Se observó la producción de metano, consistente con los hallazgos experimentales.
- Se identificó una molécula de bloque de construcción estable, (CH3) 3Al-OH2 (TMA-OH2), que contiene un enlace único Al-O.
- Se formó un intermedio de jaula hexameric, con tres canales distintos identificados para un mayor crecimiento.
Conclusiones:
- La formación de MAO se produce a través de una polimerización paso a paso que implica un monómero bifuncional con [CH3) Al-O] como la unidad estructural.
- El modelo cinético propuesto y las estructuras identificadas se alinean con la evidencia cristalográfica de los aluminoxanos.
- Los hallazgos apoyan los datos experimentales sobre la composición química y el papel catalítico de la MAO.
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