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Frustración por la eliminación del cloruro beta. La alquilación selectiva de areno por alfa-cloronorboreno catalizado
Aswini K Dash1, Tryg R Jensen, Charlotte L Stern
1Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA.
Journal of the American Chemical Society
|September 30, 2004
Resumen
Los nuevos catalizadores de polimerización de un solo sitio alquila de manera eficiente las moléculas aromáticas con alfa-cloronorboreno. Estos catalizadores producen regioselectivamente productos de exo-1-cloro-2-arilnorbornano con altas frecuencias de rotación.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- La catálisis de la catálisis.
- Síntesis orgánica La síntesis orgánica.
Sus antecedentes:
- Los catalizadores de polimerización de un solo sitio ofrecen un control preciso de la estructura del polímero.
- El metaloceno y los complejos relacionados son catalizadores versátiles en las transformaciones orgánicas.
- La activación de complejos alquilo metálicos con contrarios no coordinados genera especies altamente electrófilas.
Objetivo del estudio:
- Investigar la actividad catalítica de nuevos catalizadores de polimerización de un solo sitio para la alquilación aromática.
- Para explorar la regioselectividad y la estereoselectividad de la reacción de alquilación.
- Para dilucidar el mecanismo de reacción e identificar los intermediarios clave.
Principales métodos:
- Generación in situ de catalizadores a partir de los precursores Cp*MMe(3), (CGC)MMe(2) y Cp(2)ZrMe(2) (M = Ti, Zr).
- Activación utilizando Ph(3)C(+)B(C(6)F(5))(4)(-) o complejos aislados de pares de iones.
- Reacción de las moléculas aromáticas (benceno, tolueno) con el alfa-cloronorboreno.
- Caracterización de productos utilizando RMN, GC-MS y análisis elemental.
- Análisis estereoquímico a través de RMN 2D y cristalografía de rayos X.
Principales resultados:
- Los catalizadores regionales ofrecen selectivamente productos de exo-1-cloro-2-arilnorbornano con buenos rendimientos.
- Los productos etiquetados con deuterio fueron sintetizados utilizando disolventes aromáticos deuterizados.
- Se observaron altas frecuencias de rotación superiores a 120 h ((-1).
- La estereoquímica del grupo arilo se confirmó como exo.
- Es probable que el mecanismo implique la participación de electrófilos metálicos.
Conclusiones:
- Los nuevos catalizadores de un solo sitio son efectivos para la alquilación regioselectiva de aromáticos.
- La reacción procede con una alta exo-estereoselectividad.
- El sistema catalítico demuestra una alta eficiencia y potencial para un mayor desarrollo en la síntesis orgánica.
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