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Reactividad dirigida por ligandos en la unión de oxígeno y agua a cis-[Pd(NHC) ₂ ((η²-O₂) ]

Taryn D Palluccio¹, Xiaochen Cai², Subhojit Majumdar²

¹Department of Chemistry, Tufts University , 62 Talbot Avenue, Medford, Massachusetts 02155, United States.

Journal of the American Chemical Society

|November 28, 2017

Resumen

Este estudio revela un nuevo complejo de peróxido de paladio, cis-[Pd(IPr) ₂, que reacciona aún más con el oxígeno para formar un complejo bis-superóxido único, trans-[Pd(IPr) ₂. El aumento de la reactividad de este complejo está relacionado con factores estéricos que influyen en la unión de oxígeno.

Área de la Ciencia:

Química organometálica
Química de coordinación
Catálisis

Sus antecedentes:

Los complejos de paladio con carbenos N-heterocíclicos (NHC) son cruciales en la catálisis.
Comprender la reactividad de los complejos de paladio con el oxígeno es vital para desarrollar nuevos procesos catalíticos y prevenir la degradación del catalizador.

Objetivo del estudio:

Para investigar la reacción de un complejo de paladio con oxígeno molecular (O₂).
Caracterizar la estructura y las propiedades de los productos de reacción.
Elucidar los factores que influyen en la reactividad y estabilidad de estos complejos.

Principales métodos:

Síntesis y caracterización de los complejos de paladio-NHC.
Estudios de reacción a baja temperatura con O2 y H2O.
Estudios espectroscópicos que incluyen magnetometría de calamares y EPR.
Cristalografía de rayos X para la determinación estructural.
Cálculos de la Teoría Funcional de la Densidad (DFT) para conocimientos mecanicistas.

Principales resultados:

El descubrimiento de un complejo de peróxido lábil, cis-[Pd(IPr) ₂, y su posterior reacción para formar un complejo de bis-superóxido, trans-[Pd(IPr) ₂.
El complejo bis-superoxido exhibe un estado fundamental diradical singlet con un estado triplet accesible.
cis-[Pd(IPr)₂(η²-O₂) reacciona con el agua para producir trans-[Pd(IPr)₂(OH)
La mayor reactividad del ligando IPr en comparación con los IMes se atribuye a la reducción de la repulsión de los interligantes, lo que lleva a una unión O₂ más débil.

Conclusiones:

La masa estérica del ligando NHC influye significativamente en la reactividad de los complejos de paladio-oxígeno.
Los factores cinéticos juegan un papel crucial en la formación de complejos de bis-superóxido, incluso cuando se favorecen termodinámicamente.
El estudio proporciona una comprensión completa de las vías de reacción y las propiedades electrónicas de las especies de oxígeno-paladio.

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