Catálisis de oxidación de complejos de Nb ((salan): epoxidación asimétrica de alcoholes alílicos utilizando peróxido de hidrógeno acuoso como oxidante

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Hiromichi Egami¹, Takuya Oguma, Tsutomu Katsuki

¹Department of Chemistry, Faculty of Science, Graduate School, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.

Journal of the American Chemical Society

|April 3, 2010

Resumen

Los complejos ópticamente activos de niobio (sal) catalizan la epoxidación asimétrica. Los complejos monoméricos que utilizan peróxido de hidrógeno acuoso logran una alta enantioselectividad, marcando una primera para este oxidante en la epoxidación de alcohol alílico.

Área de la Ciencia:

Química organometálica Química orgánica de los metales.
Catalización asimétrica por catálisis asimétrica.
Las reacciones de oxidación son reacciones de oxidación.

Sus antecedentes:

Se han explorado complejos de niobio con ligandos salan para aplicaciones catalíticas.
La epoxidación asimétrica de los alcoholes alílicos es crucial para la síntesis de moléculas quirales.
Los métodos anteriores a menudo requerían oxidantes especializados.

Objetivo del estudio:

Para sintetizar y caracterizar los complejos ópticamente activos de niobio (salón).
Investigar su eficacia como catalizadores para la epoxidación asimétrica de los alcoholes alílicos.
Para explorar el uso de peróxido de hidrógeno acuoso como un oxidante sostenible.

Principales métodos:

Síntesis del complejo dimérico mu-oxo Nb ((salan) a partir de Nb ((OiPr) 5 y el ligando salan.
Preparación de complejos monoméricos de Nb (sal) in situ.
Epoxidación asimétrica catalítica utilizando el adducto de peróxido de urea-hidrógeno y el peróxido de hidrógeno acuoso.
Análisis de la cinética de la reacción y la enantioselectividad (ee).

Principales resultados:

Un complejo dimérico mu-oxo Nb ((salan) mostró buena enantioselectividad, pero se disoció en especies monoméricas activas.
Los complejos monoméricos Nb ((salan) catalizaron la epoxidación con alta enantioselectividad (83-95% ee) utilizando agua H2O2.
La reacción fue efectiva en soluciones de CHCl3/salmuera o tolueno/salmuera.
La epoxidación del alcohol cinnamyl produjo un moderado ee del 74%.

Conclusiones:

Los complejos monoméricos de Nb (sal) son las especies activas en la reacción de epoxidación.
El peróxido de hidrógeno acuoso se puede utilizar eficazmente con los catalizadores Nb (sal) para la epoxidación altamente enantioselectiva.
Este trabajo presenta la primera epoxidación altamente enantioselectiva de alcoholes alílicos utilizando peróxido de hidrógeno acuoso.

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