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Monofosfitos de triskelion helical como ligandos en la catálisis asimétrica
Manfred T Reetz1, Hongchao Guo, Jun-An Ma
1Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany. reetz@mpi-muelheim.mpg.de
Journal of the American Chemical Society
|March 3, 2009
Resumen
Se sintetizaron nuevos ligandos quirales de fosfito triskelion con estructuras helicoidales. Estos ligandos voluminosos logran una alta enantioselectividad en reacciones de hidrogenación asimétricas, lo que demuestra su potencial en la catálisis.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- Catalización asimétrica por catálisis asimétrica.
- Diseño del ligando diseño de ligando.
Sus antecedentes:
- Los ligandos quirales son cruciales para la síntesis enantioselectiva.
- El desarrollo de nuevas arquitecturas de ligandos puede mejorar la eficiencia catalítica y la selectividad.
- Las estructuras helicoidales en los ligandos pueden impartir un control estereoquímico único.
Objetivo del estudio:
- Síntesis y caracterización de una nueva familia de ligandos monofosfitos quirales, C(3)-simétricos.
- Para investigar el impacto de la masa estérica y la rigidez conformacional en el rendimiento de los ligandos.
- Evaluar la eficacia de estos nuevos ligandos en la hidrogenación asimétrica catalizada por Rh.
Principales métodos:
- Síntesis en dos pasos que incluye monoacilación de diolos quirales (BINOL) seguido de fosforilación.
- Caracterización mediante cristalografía de rayos X y espectroscopia de RMN.
- Aplicación como ligandos en la hidrogenación asimétrica catalizada por Rh de los alcoholes homoalílicos.
Principales resultados:
- Se prepararon con éxito nuevos ligandos de monofosfito helical C(3)-simétrico.
- El ligando más estéricamente obstaculizado, derivado del adamantano, adoptó una rígida conformación sin con una geometría parecida a una hélice y una helicidad definida.
- Estos voluminosos ligandos helicoidales lograron altas enantioselectividades (79-98% ee) en la hidrogenación asimétrica.
- Los análogos menos rígidos exhibieron flexibilidad conformacional y dieron como resultado una escasa enantioselectividad (32% ee).
Conclusiones:
- Los ligandos de fosfito helicoidales voluminosos y conformacionalmente rígidos derivados del BINOL son efectivos para la hidrogenación asimétrica.
- La flexibilidad conformacional del ligando impacta negativamente en la enantioselectividad.
- Los ligandos sintetizados representan una nueva clase prometedora para la catálisis quiral.
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