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Conocimientos mecanicistas sobre la catálisis heterogénea organometálica molecular a través de estudios de resonancia
Matthew R Gyton1,2, Cameron G Royle1,3, Simon K Beaumont4
1Department of Chemistry, University of York, York YO10 5DD, U.K.
Journal of the American Chemical Society
|January 23, 2023
Resumen
Este estudio revela cómo un catalizador de rodio hidrogena eficientemente alquenos y alquinas utilizando parahidrógeno (para-H2) a través de la RMN de polarización inducida por parahidrógeno (PHIP). Se observó una alta hiperpolarización incluso con cilindros de gas de hidrógeno estándar.
Área de la Ciencia:
- Química organometálica
- Catálisis
- Espectroscopia de resonancia magnética nuclear (RMN)
Sus antecedentes:
- Las reacciones heterogéneas de gas sólido que involucran catalizadores de rodio e hidrocarburos insaturados son cruciales en la síntesis química.
- La polarización inducida por parahidrógeno (PHIP) es una técnica poderosa para mejorar las señales de RMN en las reacciones de hidrogenación.
- Comprender la especiación del catalizador y los mecanismos de reacción a nivel molecular es esencial para optimizar la eficiencia catalítica.
Objetivo del estudio:
- Explorar las reacciones sólido-gas de un complejo específico de rodio-propeno con varios sustratos insaturados utilizando RMN en fase gaseosa.
- Investigar la eficiencia de la transferencia catalítica de para-H2 en pares y los cambios en la especiación del catalizador.
- Obtener espectros de RMN de alta calidad de los productos de hidrogenación y estudiar la cinética de la reacción.
Principales métodos:
- Espectroscopia de resonancia magnética nuclear en fase gaseosa bajo condiciones de lote a 25 °C.
- Utilizando la polarización inducida por parahidrógeno (PHIP) para monitorear el flujo catalítico y la especiación a nivel molecular.
- Estructura fina de absorción de rayos X extendida (EXAFS) para la estructura del catalizador de la sonda.
Principales resultados:
- El complejo de rodio [Rh ((L2) ((propeno)) ] [BArF4] hidrogena eficientemente el propeno, el 1-buteno, la propina y el 1-buteno, produciendo altos niveles iniciales de polarización (> 85% para el propano).
- El complejo 1 reacciona con H2 para formar una especie dimérica [Rh(L2) ((H) ((μ-H) ]2[BArF4]2 (4), con 1 y 4 convirtiendo para-H2 en orto-H2 a diferentes velocidades.
- Las reacciones concurrentes observadas incluyen la ciclotrimerización de propina y la isomerización de 1-butina a butadieno, seguidas de una hidrogenación más lenta.
Conclusiones:
- El estudio demuestra la alta eficiencia del catalizador de rodio en las reacciones de hidrogenación mediadas por para-H2, evidenciada por fuertes efectos PHIP.
- Los efectos de hiperpolarización son alcanzables incluso con gas hidrógeno directamente de los cilindros estándar a temperatura ambiente.
- Las modificaciones en el ligando de fosfina quelante pueden influir en las eficiencias iniciales de polarización, pero pueden conducir a vías de desactivación del catalizador.
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