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Los efectos electrónicos dirigen el mecanismo de hidrogenaciones asimétricas de alquenos aril-sustituidos no
Yubo Fan1, Xiuhua Cui, Kevin Burgess
1Department of Chemistry, Texas A & M University, Box 30012, College Station, TX 77842-3012, USA.
Journal of the American Chemical Society
|December 23, 2004
Resumen
Los cálculos de la teoría funcional de la densidad revelan cómo los complejos de iridio catalizan la hidrogenación asimétrica de los alquenos. Las interacciones estéricas con el grupo adamantilo del ligando dictan principalmente la selectividad de la enantiofaz en estas reacciones.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- Catalización asimétrica por catálisis asimétrica.
- Química computacional es la química computacional.
Sus antecedentes:
- La hidrogenación asimétrica es crucial para la síntesis de moléculas quirales.
- Los complejos de iridio con ligandos de carbenos N-heterocíclicos son catalizadores efectivos.
- La comprensión de los mecanismos de reacción y los determinantes de la selectividad es clave para el diseño del catalizador.
Objetivo del estudio:
- Para dilucidar el mecanismo de hidrogenación asimétrica de alquenos catalizados por un complejo de iridio imidazolilidina oxazolina.
- Investigar los factores que rigen la selectividad de la superficie enantioficial en este sistema catalítico.
- Para validar las predicciones computacionales contra las observaciones experimentales.
Principales métodos:
- Cálculos de la teoría funcional de densidad (DFT) utilizando las funciones PBE y B3LYP.
- Modelado de las etapas de coordinación de alquenos, inserción migratoria y liberación de productos.
- Análisis de los factores estéricos y electrónicos que influyen en la estereoselectividad.
Principales resultados:
- La coordinación de alqueno ocurre preferentemente trans al ligando del carbeno.
- La hidrogenación procede a través de una reacción secuencial con H2 y transferencia de hidruro.
- Las interacciones estéricas con el grupo adamantilo del ligando son los principales impulsores de la selectividad de la enantiofaz para los alquenos trisubstituidos.
Conclusiones:
- El modelo DFT predice con precisión las enantioselectividades experimentalmente observadas.
- El estudio proporciona una comprensión mecanicista de la hidrogenación asimétrica catalizada por iridio.
- El diseño de los ligandos, particularmente el volumen estérico, es crítico para controlar la enantioselectividad.
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