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Las porfirinas de manganeso catalizan las halogenaciones selectivas de enlaces C-H
1Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.
Journal of the American Chemical Society
|September 3, 2010
Resumen
Los catalizadores de porfirina de manganeso permiten la cloración selectiva de enlaces C-H de alcano utilizando hipoclorito de sodio. Este método logra una alta regioselectividad, incluso en moléculas complejas, a través de una vía radical intermedia.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- La catálisis es la catálisis.
- Metodología sintética de la metodología sintética.
Sus antecedentes:
- La funcionalización del enlace C-H alifático sigue siendo un desafío significativo en la síntesis orgánica.
- El desarrollo de métodos de cloración selectivos y eficientes para los alcanos no activados es crucial para acceder a valiosos intermediarios de cloruro de alquilo.
- Las porfirinas de manganeso han demostrado potencial como catalizadores en varias reacciones de oxidación.
Objetivo del estudio:
- Desarrollar un nuevo sistema mediado por porfirina de manganeso para la cloración selectiva de enlaces alifáticos C-H no activados.
- Investigar la regioselectividad y el alcance del sustrato de este nuevo método de cloración.
- Para aclarar la vía mecanicista que involucra a los radicales intermedios y las especies de manganeso-oxo.
Principales métodos:
- Utilizando las porfirinas de manganeso (Mn(TPP)Cl y Mn(TMP)Cl) como catalizadores.
- Empleando hipoclorito de sodio como fuente de cloro.
- Empleando un catalizador de transferencia de fase para facilitar la reacción.
- Analizar los productos de reacción utilizando técnicas estándar de síntesis orgánica y métodos espectroscópicos.
Principales resultados:
- Clorinación selectiva de varios alcanos no activados para formar cloruros de alquilo con oxigenación mínima.
- Clorado exitoso de alcanos con fuertes enlaces C-H (por ejemplo, neopentano).
- Evidencia de un intermediario radical de carbono de larga vida, indicado por productos reordenados de la cloración de norcarano.
- Alta regioselectividad lograda con un catalizador obstaculizado (Mn(TMP) Cl), favoreciendo los enlaces C-H del metileno.
- Aplicación a sustratos complejos como el 5α-colestano y el sclareolide, que producen productos clorados específicos.
Conclusiones:
- Se ha establecido un nuevo y eficiente sistema catalizado por porfirina de manganeso para la cloración alifática de enlaces C-H.
- La reacción procede a través de un mecanismo que involucra especies de manganeso-oxo y radicales alquilo intermedios.
- Las propiedades estéricas del catalizador influyen significativamente en la regioselectividad, permitiendo la funcionalización específica de moléculas complejas.
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