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Acoplamiento diastereo-selectivo de Ullmann a los bicelicenos por tocoquímica de la superficie

Anaïs Mairena¹, Christian Wäckerlin¹, Martin Wienke²

¹Empa, Swiss Federal Laboratories for Materials Science and Technology , 8600 Dübendorf , Switzerland.

Journal of the American Chemical Society

|November 2, 2018

Resumen

El autoensamblaje del 9,9′-bisheptaheliceno en las superficies de oro produce un exceso diastereomérico del 50% de la mesoforma. Esta estereoselectividad surge de los efectos topoquímicos inducidos por la superficie durante la síntesis en la superficie.

Área de la Ciencia:

Química orgánica
Ciencias de la superficie
Química supramolecular

Sus antecedentes:

Los helicenos son hidrocarburos aromáticos policíclicos quirales con propiedades estructurales y electrónicas únicas.
La síntesis en la superficie ofrece una poderosa plataforma para construir moléculas orgánicas complejas con arquitecturas controladas.
Comprender los procesos de autoensamblaje es crucial para el diseño de nanomateriales funcionales.

Objetivo del estudio:

Investigar el comportamiento de autoensamblaje del 9,9′-bisheptaheliceno en la superficie Au{11}.
Para comparar el resultado del autoensamblaje con la síntesis en la superficie de la misma molécula.
Para aclarar los factores que rigen la estereoselectividad en estos procesos.

Principales métodos:

Se utilizó la microscopía de túnel de barrido (STM) para estudiar el autoensamblaje del 9,9′-bisheptaheliceno en Au{111).
Se realizó una síntesis en la superficie a través del acoplamiento de Ullmann de 9-bromoheptaheliceno para obtener la molécula diana.
El análisis de las imágenes STM permitió la determinación de las relaciones diastereoméricas.

Principales resultados:

El autoensamblaje del 9,9′-bisheptaheliceno en Au(111) dio lugar a un exceso diastereomérico (de) del 50% para la forma meso (M, P).
La síntesis en la superficie también arrojó el mismo exceso diastereomérico, lo que indica resultados estereoquímicos consistentes.
La estereoselectividad observada se atribuyó a un efecto topoquímico.

Conclusiones:

La alineación superficial de los reactivos e intermedios favorece estéricamente el estado de transición (M, P) durante la síntesis en la superficie.
El control topoquímico es un factor clave para lograr una alta estereoselectividad en las reacciones mediadas por la superficie.
Este estudio proporciona información sobre el diseño racional de las moléculas quirales con disposiciones espaciales específicas en las superficies.

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