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La no inocencia de redox de ligando en los complejos afecta la formación de nitreno
Nicolaas P van Leest, Martijn A Tepaske, Jean-Pierre H Oudsen
1Department of Chemistry , Johns Hopkins University , Baltimore , Maryland 21218 , United States.
Journal of the American Chemical Society
|December 18, 2019
Resumen
Se confirma la no inocencia redox del ligando macrocíclico tetraamido (TAML) en los complejos cobalto-TAML. Este estudio revela radicales centrados en ligandos en el cobalto-TAML oxidado, cruciales para las reacciones de transferencia de nitreno catalítico.
Área de la Ciencia:
- Química inorgánica
- Química organometálica
- Espectroscopia
- Química computacional
Sus antecedentes:
- El comportamiento redox de los andamios de ligando tetraamido macrocíclico (TAML) en complejos de cobalto se ha debatido desde 2006.
- La comprensión de la no inocencia redox del ligando es crítica para elucidar los mecanismos de reacción en la catálisis.
Objetivo del estudio:
- Para demostrar definitivamente la no inocencia redox de la columna vertebral TAML en los complejos de cobalto-TAML.
- Caracterizar la estructura electrónica de las especies de cobalto-TAML oxidadas y su papel en las reacciones de transferencia de nitreno.
Principales métodos:
- Utilizó una variedad de técnicas espectroscópicas (EPR, XANES, UV-vis) para la caracterización.
- Se emplean espectrometría de masas de alta resolución y mediciones de momento magnético.
- Se han realizado cálculos de referencia múltiple (CASSCF) para determinar la estructura electrónica.
Principales resultados:
- Se confirmó que la columna vertebral TAML en los complejos aniónicos de cobalto-TAML no es redox, formando un radical centrado en el ligando tras la oxidación de un electrón.
- La estructura electrónica del complejo oxidado es un doblete (S = 1/2) que surge de un centro de cobalto S = 1 acoplado a un radical ligando.
- La reacción con los precursores de nitrógeno (PhINNs) conduce a la oxidación centrada en TAML, formando complejos de radicales de nitrógeno ([Co(TAML) ((NNs) ] y [Co(TAML) ((NNs) 2)) cruciales para la transferencia catalítica de nitrógeno.
Conclusiones:
- El ligando TAML en los complejos de cobalto exhibe una no inocencia redox significativa, actuando como un componente redox activo.
- Los radicales centrados en los ligandos son intermediarios clave en el mecanismo de transferencia de nitreno catalítico mediado por estos complejos de cobalto-TAML.
- El estado redox del ligando TAML dicta la formación de complejos de radicales mono o bis-nitreno.
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