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Influencia de los factores estéricos en los agregados quirales de amida de litio
Chicheung Su1, Russell Hopson, Paul G Williard
1Department of Chemistry, Brown University , 324 Brook Street, Providence, Rhode Island 02912 United States.
Journal of the American Chemical Society
|January 24, 2014
Resumen
El impedimento estérico en las amidas quirales de litio dicta su estado de agregación con n-butilitio. Las amidas menos obstaculizadas forman agregados 2: 2, mientras que el aumento de la masa estérica favorece los agregados mixtos 2: 1, lo que influye en las estructuras de la solución.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- Química supramolecular de las moléculas.
- Espectroscopia de RMN y RMN.
Sus antecedentes:
- Las amidas quirales de litio son intermediarios clave en la síntesis asimétrica.
- Comprender su comportamiento de agregación en solución es crucial para controlar la reactividad.
- Los agregados mixtos con reactivos de organolitio pueden exhibir propiedades estructurales y químicas únicas.
Objetivo del estudio:
- Para investigar las estructuras de solución de agregados mixtos formados entre amidas quirales de litio y n-butilitio.
- Para aclarar el papel del obstáculo estérico en el control del estado de agregación.
- Para correlacionar las características estructurales con la naturaleza de los sustituyentes en la amida quiral.
Principales métodos:
- Espectroscopia de Resonancia Magnética Nuclear (RMN), incluida la RMN ordenada por difusión (DOSY) con correlación coeficiente de difusión-formula de peso (D-FW).
- Se emplearon técnicas de RMN unidimensional y bidimensional.
- Caracterización de los agregados en solución de tolueno-d8.
Principales resultados:
- El estado de agregación de agregados mixtos está controlado por el impedimento estérico de los grupos R1 y R2 de la amida de litio quiral.
- El litio (S) -N-isopropil-1- (((triisopropilsilyl) oxy) propan-2-amida forma un agregado mixto tipo escalera 2:2 con n-butilitio cuando R2 está menos obstaculizado.
- El aumento del obstáculo estérico promueve la formación de agregados mixtos 2: 1, con solo agregados 2: 1 observados para la amida más obstaculizada.
Conclusiones:
- El volumen estérico es un determinante primario del número de agregación y la estructura en estos sistemas mixtos de litio amida-n-butilitio.
- Una transición de 2:2 a 2:1 agregación se produce con el aumento de la demanda estéril.
- Los hallazgos proporcionan información sobre el autoensamblaje en estado de solución de las especies de organolitio quiral.
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