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Equilibrios entre los rotámeros estabilizados alfa- y beta-agóticos de los complejos secundarios de alquilo niobio
J Jaffart1, M Etienne, F Maseras
1Laboratoire de Chimie de Coordination du CNRS, UPR 8241, 205 Route de Narbonne, 31077 Toulouse Cedex 4, France.
Journal of the American Chemical Society
|June 21, 2001
Resumen
Este estudio revela que los complejos alquilo secundarios de niobio exhiben estructuras distintas beta-agóticas y alfa-agóticas, con su equilibrio influenciado por factores electrónicos y estéricos. Estos complejos se someten a un reordenamiento térmico a complejos alquilo lineales.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- Coordinación Química de la Coordinación
- Química del boro y su química.
Sus antecedentes:
- El estudio investiga la dinámica estructural de los complejos secundarios de alquilo que incluyen el ligando hidrotris-3,5-dimetilpirazolil) borato (TpMe2).
- La comprensión de las interacciones agósticas es crucial para predecir la reactividad y la estabilidad en los compuestos organometálicos.
Objetivo del estudio:
- Para dilucidar las preferencias conformacionales y los equilibrios dinámicos de los complejos secundarios de alquilo niobio.
- Explorar la influencia de los factores electrónicos y estéricos en las interacciones agósticas en estos sistemas.
- Caracterizar los parámetros termodinámicos y cinéticos que rigen los equilibrios y reordenamientos rotaméricos.
Principales métodos:
- Cristalografía de rayos X para determinar las estructuras de estado sólido.
- Solución Espectroscopia de Resonancia Magnética Nuclear (RMN) para el estudio de los equilibrios dinámicos y la cinética.
- Cálculos híbridos de mecánica cuántica / mecánica molecular (QM / MM) para el análisis teórico.
Principales resultados:
- El complejo de cloro isopropílico Tp(Me2) NbCl(i-Pr) ((PhCCMe) exhibe una estructura beta-agóstica en cristales, con un equilibrio entre los rotámeros beta- y alfa-agóticos en solución.
- Los diastereómeros del complejo sec-butilo muestran interacciones agósticas distintas en estados sólidos y disueltos, con equilibrios observables para un diastereómero.
- Los estudios de RMN proporcionaron parámetros termodinámicos y cinéticos para los equilibrios y la rotación alrededor del enlace Nb-C.
- Los efectos isotópicos y los estudios computacionales confirmaron la influencia de los factores estéricos y electrónicos en las preferencias agósticas.
Conclusiones:
- Los complejos secundarios de alquilo niobio muestran un comportamiento agóstico complejo impulsado por un equilibrio de efectos electrónicos y estéricos.
- La masa estérica del ligando Tp(Me2) juega un papel importante en la dirección de la conformación del grupo alquilo.
- Todos los complejos de alquilo secundarios estudiados se someten a un reordenamiento térmico a complejos de alquilo lineales a través de un proceso de primer orden.
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