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Complejos de diironio μ-carbino, μ-hidruro de valencia mixta: implicaciones para la nitrogenasa

Charles H Arnett¹, Isabel Bogacz², Ruchira Chatterjee²

¹Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States.

Journal of the American Chemical Society

|September 25, 2020

Resumen

Los intermediarios del cofactor FeMo de la nitrogenasis fueron modelados utilizando complejos de diirón μ-carbina. La química redox reveló cambios en la covalencia metal-ligando, cruciales para facilitar las transformaciones multielectrónicas de fijación de nitrógeno.

Área de la Ciencia:

Química bioorgánica
Química organometálica
La bioquímica

Sus antecedentes:

La nitrogenasa FeMo-cofactor (FeMoco) se une a N₂ después de la transferencia de 4e^- y 4H⁺.
La estructura y la electrónica de este intermediario de valor mixto son poco conocidas.
Los estudios de EPR de pulso sugieren que existen dos fracciones de Fe- ((μ-H) -Fe.

Objetivo del estudio:

Para entender el grupo bioorganometálico de la nitrogenasa.
Caracterización espectral de los complejos modelo de Fe ((μ-C) ((μ-H) Fe activos en EPR.
Investigar la influencia de la deslocalización de valencia en los ligandos μ-hidruro.

Principales métodos:

Síntesis y manipulación redox de complejos de diirón μ-carbina.
Espectroscopia de resonancia paramagnética de electrones por pulso (EPR).
Espectroscopia de absorción de rayos X, estudios de Fe Mössbauer y cálculos de DFT.

Principales resultados:

Se caracterizaron dos complejos Fe-C-H-Fe EPR-activos, que se asemejan a los estados de la nitrogenasa E3 y E4.
Ambas especies exhiben estados S = 1/2 a bajas temperaturas.
La química redox indujo cambios significativos en la covalencia de Fe-C (-50% con una reducción de 2e).

Conclusiones:

Los ligandos hidrógenos en el estado FeMoco E₄(4H) probablemente cruzan los centros isovalentes Fe^III.
La covalencia cambia el exceso de carga en los metales redistribuyéndolo al carbono puente.
Este mecanismo facilita las transformaciones multielectrónicas esenciales para la fijación del nitrógeno.

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