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Los paladaciclos paramagnéticos con centros Pd(III) son catalizadores muy activos para las reorganizaciones

Simon H Eitel¹, Matthias Bauer, David Schweinfurth

¹Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.

Journal of the American Chemical Society

|February 11, 2012

Resumen

Los catalizadores de paladio más efectivos para reacciones de reordenamiento asimétrico presentan inesperadamente un centro Pd (III). Estos nuevos complejos Pd(III) son los primeros catalizadores enantioselectivos reconocidos, que utilizan un núcleo de ferroceno estable.

Área de la Ciencia:

Química organometálica Química orgánica de los metales.
La catálisis de la catálisis.
Síntesis asimétrica de síntesis.

Sus antecedentes:

Los catalizadores de paladio son cruciales para varias transformaciones orgánicas.
La reorganización asimétrica de los compuestos alelicos es sintéticamente importante.
Comprender la activación del catalizador es clave para mejorar la eficiencia.

Objetivo del estudio:

Para dilucidar la estructura y el estado de oxidación de catalizadores Pd altamente eficientes.
Para investigar el papel del núcleo de ferroceno en la actividad catalítica.
Para identificar nuevas especies catalíticas en síntesis asimétrica.

Principales métodos:

Utilizó una combinación de técnicas espectroscópicas: estructura de absorción de rayos X cercana al borde (XANES), estructura fina de absorción de rayos X extendida (EXAFS), cristalografía de rayos X.
Métodos empleados de resonancia electroquímica y resonancia magnética nuclear: RMN de 1H, resonancia paramagnética de electrones (EPR), espectroscopia de Mössbauer y voltametría cíclica.

Principales resultados:

Se demostró que los catalizadores Pd más eficientes poseen un centro Pd (III) en su forma oxidada activada.
Se demostró que el núcleo de ferroceno permanece en un estado Fe (II) estable durante la activación oxidativa.
Identificó estos complejos Pd(III) como los primeros catalizadores enantioselectivos reconocidos.

Conclusiones:

La especie catalítica activa en el reordenamiento asimétrico de los trifluoroacetimidatos alilicos es un complejo Pd(III).
La porción de ferroceno juega un papel crucial, permaneciendo sin cambios durante el ciclo catalítico.
Este descubrimiento abre nuevas vías para el diseño de catalizadores enantioselectivos avanzados.

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