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La cooperatividad entre metales y ligandos redox permite una catálisis de oxidación de agua robusta y eficiente a pH

Pablo Garrido-Barros¹, Dooshaye Moonshiram², Marcos Gil-Sepulcre¹

¹Institute of Chemical Research of Catalonia (ICIQ), Barcelona Institute of Science and Technology (BIST), Avinguda Països Catalans, 16, 43007 Tarragona, Spain.

Journal of the American Chemical Society

|September 16, 2020

Resumen

Un nuevo complejo de cobre con un ligando macrocíclico de tetraamidato (TAML) altamente deslocalizado demuestra una catálisis de oxidación de agua superior. Este catalizador avanzado logra una alta eficiencia y estabilidad a pH neutro, superando a los sistemas relacionados con ligandos menos deslocalizados.

Área de la Ciencia:

Química inorgánica
Catálisis
Fotosíntesis artificial

Sus antecedentes:

La catálisis de la oxidación del agua es crucial para los dispositivos de fotosíntesis artificial.
Los complejos metálicos de transición de primera fila tardía ofrecen plataformas de catalizador de bajo costo.
Los desafíos incluyen el acceso a altos estados de oxidación y labilidad de enlace metal-ligando.

Objetivo del estudio:

Para explorar un complejo de cobre con un ligando macrocíclico de tetraamidato extendido π-delocalizado (TAML) como catalizador de oxidación de agua.
Para comparar su actividad y estabilidad con sistemas análogos con menor deslocalización π.
Investigar el papel de la cooperatividad metal-ligando y la deslocalización de la carga en el rendimiento catalítico.

Principales métodos:

Síntesis y caracterización de complejos de cobre con ligando π-delocalización variable.
Evaluación de la actividad catalítica de la oxidación del agua en condiciones de pH neutro.
Análisis de las vías de degradación catalítica y de los mecanismos de estabilización.

Principales resultados:

El complejo de cobre con el ligando TAML extendido (1^2-) exhibe una mayor cooperatividad metal-ligando para acomodar equivalentes oxidativos.
La deslocalización eficiente de la carga en 1^2- estabiliza las cargas oxidativas, lo que conduce a una mejora significativa en el rendimiento catalítico (k_obs = 140 s^-1 a 200 mV de sobrepotencial).
Los complejos análogos con menor deslocalización π (2^2-) se degradan, y los complejos acíclicos (3^2-) son inestables a pH neutro.

Conclusiones:

La deslocalización π extendida en el ligando TAML es esencial para estabilizar las cargas oxidativas y lograr una alta actividad catalítica de oxidación de agua.
La cooperatividad metal-ligando, facilitada por la deslocalización de la carga, es clave para el rendimiento superior y la robustez del complejo de cobre basado en TAML.
La estabilización macrocíclica es crítica para la longevidad y el rendimiento del catalizador a pH neutro.

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