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El hidruro de cobalto que nunca fue: revisando la "hidridocobaloxima" de Schrauzer
David C Lacy1, Gerri M Roberts1, Jonas C Peters1
1Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States.
Journal of the American Chemical Society
|March 24, 2015
Resumen
Un complejo de cobalto reinvestigado, que anteriormente se pensaba que era un hidruro, es en realidad una especie de cobalto. Este hallazgo tiene un impacto en los estudios mecanicistas de la reacción de evolución del hidrógeno (HER) utilizando cobaloximes.
Área de la Ciencia:
- Química Inorgánica La Química Inorgánica es la química inorgánica.
- La electrocatálisis por electrocatálisis.
- Reacción de Evolución del Hidrógeno (HER)
Sus antecedentes:
- Los complejos de cobalto-dimetilglioxima (dmg) son electrocatalisadores cruciales para los estudios de HER.
- El aislamiento de Schrauzer de un supuesto complejo de hidruro de cobalto proporcionó soporte para los intermediarios de Co (III) -H en HER.
- Este supuesto hidruro ha sido ampliamente citado en la investigación sobre los hidruros de cobaloxima y la catálisis de HER.
Objetivo del estudio:
- Para reevaluar la estructura del complejo cobalto-dmg estabilizado con fosfina de Schrauzer.
- Para aclarar la identidad de las especies relevantes para los mecanismos de reacción de evolución del hidrógeno (HER).
- Para corregir la atribución errónea de una señal de RMN de protones a una especie de hidruro.
Principales métodos:
- Cristalografía de rayos X para determinar la estructura del estado sólido.
- Análisis espectroscópico, incluyendo RMN de protones.
- Caracterización de complejos y impurezas de cobalto-dmg sintetizados.
Principales resultados:
- El complejo previamente identificado como un hidruro de cobalto (III) se reasigna como un complejo de cobalto (II), [Co (II) (dmgH) 2P (nBu) 3].
- Este complejo de cobalto (II) se dimeriza en estado sólido, formando un enlace Co-Co sin soporte.
- Una impureza paramagnética, erróneamente asignada como un hidruro, exhibe una señal de RMN de protones a -5.06 ppm.
Conclusiones:
- La ampliamente citada "hidridocobaloxima" no es un hidruro sino un complejo de cobalto (II).
- Esta reasignación estructural es fundamental para comprender los mecanismos de la reacción de evolución del hidrógeno (HER) catalizada por cobaloximes.
- Los hallazgos requieren una reevaluación de modelos mecánicos anteriores basados en la existencia de este hidruro de cobalto específico.
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