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Autointercambio lento de átomos de hidrógeno entre los complejos de anilido Os(IV) y anilina Os(III): relaciones con
1Department of Chemistry, Campus Box 351700, University of Washington, Seattle, Washington 98195-1700, USA.
Journal of the American Chemical Society
|October 2, 2003
Resumen
Este estudio midió las tasas de las reacciones de transferencia de átomos de hidrógeno, protones y electrones que involucran complejos de osmio. Encontró que la transferencia concertada de átomos de hidrógeno es lenta, mientras que las transferencias de protones y electrones son mucho más rápidas, lo que sugiere la catálisis por ácidos y bases.
Área de la Ciencia:
- Química Inorgánica La Química Inorgánica es la química inorgánica.
- La cinética química es la cinética química.
- Reacciones de transferencia de electrones.
Sus antecedentes:
- Los complejos de osmio con ligandos de anilina y anilideo se estudian por sus propiedades redox.
- Comprender los mecanismos de la transferencia de átomos de hidrógeno (HAT) y la transferencia de electrones acoplados a protones (PCET) es crucial en química y biología.
Objetivo del estudio:
- Para determinar las tasas de autointercambio y de reacción cruzada para la transferencia de átomos de hidrógeno, protones y electrones en los sistemas Os{IV}/Os{III} anilina/anilida.
- Para comparar las tasas de HAT/PCET concertadas con vías de transferencia gradual de protones (PT) y de transferencia de electrones (ET).
- Investigar la influencia del obstáculo estérico y la catálisis ácido/base en estas reacciones de transferencia.
Principales métodos:
- Estudios cinéticos de Os(IV) y Os(III) complejos de anilina y anilideo.
- Medición de las tasas de autocambio para las reacciones HAT, PT y ET.
- Análisis de la cinética de la reacción cruzada con complejos estéricamente obstaculizados y radicales nitroxilo.
Principales resultados:
- La transferencia concertada de átomos de hidrógeno (HAT) entre Os{IV}NHPh y Os{III}NH{2) Ph es significativamente lenta (k{ex}H*) = 3 x 10{-3) M{-1}s{-1}).
- Las reacciones de autointercambio relacionadas de transferencia de protones (PT) y transferencia de electrones (ET) son mucho más rápidas (k = 10(3)-10(5) M(-1) s(-1)).
- El bulto estérico cerca del sitio activo retrasa tanto la transferencia de H* como la de H(+), mientras que los trazas de ácidos/basas catalizan la transferencia neta de H* a través de mecanismos escalonados.
Conclusiones:
- La lentitud de las HAT concertadas se atribuye a grandes plazos de trabajo para la formación de complejos precursores y / o dinámicas no adiabáticas, no a barreras intrínsecas.
- Los mecanismos escalonados que involucran ET y PT rápidos son favorecidos sobre el HAT / PCET concertado bajo ciertas condiciones.
- La catálisis ácido-base juega un papel importante en la facilitación de la transferencia neta de átomos de hidrógeno en estos sistemas de osmio.
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