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Reacción del O2 con el PdHCl: evidencia de una vía intramolecular [H-L]+ de "eliminación reductiva"
Nattawan Decharin1, Brian V Popp, Shannon S Stahl
1Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States.
Journal of the American Chemical Society
|July 28, 2011
Resumen
Este estudio desafía los modelos anteriores de catálisis de oxidación aeróbica. Un nuevo mecanismo de eliminación reductora, no la abstracción bimolecular del átomo H, explica la reacción de los intermediarios de hidruro de paladio con el oxígeno.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- La catálisis de la catálisis.
- Reacciones de oxidación Reacciones de oxidación.
Sus antecedentes:
- Los complejos de paladio (II) con ligandos de nitrógeno quelantes, como la (-) -sparteína (Sp), catalizan las reacciones de oxidación aeróbica.
- Un paso clave implica la reacción de O(2) con un intermediario Pd(II) -hidruro, (Sp) Pd(H) Cl.
- Estudios computacionales anteriores propusieron la inserción de O(2) a través de la abstracción del átomo H.
Objetivo del estudio:
- Para investigar el mecanismo de oxigenación del intermediario (Sp) Pd(H) Cl.
- Para desafiar la vía de abstracción bimolecular de átomo H propuesta.
- Para aclarar el papel de los ligandos de nitrógeno quelantes en las oxidaciones aeróbicas catalizadas por el paladio.
Principales métodos:
- Generación in situ y oxigenación de (Sp) Pd (H) Cl.
- Estudios cinéticos para determinar el orden de reacción con respecto a O(2).
- Teoría de la Densidad Funcional (DFT) estudios computacionales.
Principales resultados:
- La oxigenación de (Sp) Pd ((H) Cl mostró una dependencia de orden cero en la concentración de O ((2).
- Estos datos cinéticos contradicen un mecanismo de abstracción bimolecular del átomo H.
- Los cálculos de DFT identificaron una nueva vía de eliminación reductiva intramolecular que involucra la desprotonación del ligando.
Conclusiones:
- La reacción de O(2) con (Sp) Pd(H) Cl procede a través de un nuevo mecanismo de eliminación reductora, no de la abstracción del átomo H.
- Este hallazgo sugiere un nuevo paradigma mecanicista para las oxidaciones aeróbicas catalizadas por el paladio que involucran ligandos quelantes de nitrógeno.
- El estudio sugiere la reevaluación de los sistemas catalíticos relacionados.
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