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Compuestos arylallylic de litio, coordinados internamente versus externamente: comparación de sus estructuras y
Gideon Fraenkel1, Xiao Chen, Judith Gallucci
1Department of Chemistry, Ohio State University, Columbus, Ohio 43210, USA. fraenkel@mps.ohio-state.edu
Journal of the American Chemical Society
|March 7, 2008
Resumen
Este estudio compara la coordinación interna y externa en arylallyllithiums utilizando rayos X y RMN. Los compuestos coordinados internamente muestran litio cerca de los carbonos de alilo, influyendo en las barreras de rotación del fenilo.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- Química del estado sólido.
Sus antecedentes:
- Los arylallyllithiums son intermediarios clave en la síntesis orgánica.
- Comprender la coordinación del litio es crucial para predecir la reactividad.
Objetivo del estudio:
- Para comparar la coordinación interna y externa en arylallyllithiums.
- Para investigar la influencia de la coordinación del litio en la rotación del grupo fenilo.
Principales métodos:
- Cristalografía de rayos X para la determinación estructural.
- Espectroscopia de Resonancia Magnética Nuclear (RMN), que incluye RMN de litio-7 y 7Li{1H} HOESY.
- Análisis de las formas de las líneas de RMN para determinar las barreras de rotación.
Principales resultados:
- Los arylallyllithiums coordinados internamente (7 y 8) presentan litio cercano a los carbonos de alilo con endofeniles.
- Los análogos coordinados externamente (5 y 6) tienen exofeniles y proximidad variable al litio.
- Los estudios de RMN revelan estructuras electrónicas deslocalizadas y una rápida rotación del grupo fenilo.
- Las barreras de rotación disminuyen con la disminución de la separación de litio-anión, particularmente en compuestos coordinados internamente.
Conclusiones:
- La coordinación del litio tiene un impacto significativo en la estructura y la dinámica de los arylallyllithiums.
- La proximidad del litio al sistema de alelos facilita la rotación del grupo fenilo.
- Estos hallazgos proporcionan información sobre los mecanismos de los reordenamientos del organolitio.
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