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Mecanismo de la metátesis de enyne catalizada por los complejos de rutenio-carbeno de Grubbs: un estudio de DFT
Jörg J Lippstreu1, Bernd F Straub
1Department Chemie und Biochemie der Ludwig-Maximilians-Universität München, Germany.
Journal of the American Chemical Society
|May 19, 2005
Resumen
El modelado computacional revela el ciclo catalítico de los complejos de Grubbs de rutenio carbeno en la metátesis de enyne. La metátesis de alquenos es rápida y reversible, mientras que la inserción de alquinos es lenta y determina la regioselectividad, formando complejos de vinilcarbenos en lugar de rutenaciclobutenos.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- La catálisis es la catálisis.
- Química computacional es la química computacional.
Sus antecedentes:
- Los complejos de carbeno de rutenio de Grubbs son catalizadores vitales para las reacciones de metátesis de olefinas.
- La metátesis de Enyne ofrece una ruta versátil hacia los dienes conjugados.
Objetivo del estudio:
- Para dilucidar el ciclo catalítico completo de la metátesis de enyne utilizando catalizadores de Grubbs.
- Identificar las vías mecanicistas clave y las etapas que determinan la tasa.
Principales métodos:
- Cálculos de la Teoría Funcional de Densidad (DFT) en el nivel B3LYP/LACV3P//B3LYP/LACVP.
- Modelado de las estructuras de sustrato y catalizador del núcleo, incluidos el eteno, la etina y los catalizadores Grubbs simplificados.
Principales resultados:
- El ciclo catalítico implica una metátesis de alqueno rápida y reversible seguida de una inserción de alquino más lenta e irreversible.
- Los complejos de vinilcarbeno se forman directamente, evitando los intermediarios de rutenaciclobuteno.
- Las etapas de inserción de alquinas y ciclo-reversión tienen barreras comparables en la metátesis de alquinas intermoleculares.
- La metástasis de enyne intramolecular implica una metástasis inicial de alqueno seguida por la inserción de alquino intramolecular.
Conclusiones:
- El estudio proporciona una visión mecanicista detallada de la metátesis de enyne catalizada por Grubbs.
- La regioselectividad está controlada cinéticamente por el paso de inserción de alquinos.
- La atmósfera de eteno (condiciones de Mori) mejora las velocidades de reacción al mantener una alta concentración de alquenos para la etapa de ciclo-reversión que limita la velocidad.
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