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Síntesis controlada por quelantes de las racemas ansa-zirconocenas

Matthew D Lococo¹, Xingwang Zhang, Richard F Jordan

¹Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, USA.

Journal of the American Chemical Society

|November 19, 2004

Resumen

Este estudio revela que los complejos de amida de zirconio forman preferentemente ansa-metalocenos racémicos debido a las conformaciones de torsión en el anillo de amidato de zirconio, influyendo en la estereoquímica durante la síntesis.

Área de la Ciencia:

Química organometálica Química orgánica de los metales.
Coordinación Química de la Coordinación
La catálisis de la catálisis.

Sus antecedentes:

Los complejos de zirconio con ligandos de amidato son precursores clave en la síntesis del metaloceno.
El resultado estereoquímico de la formación de metalloceno es crucial para las aplicaciones catalíticas.
Comprender las preferencias conformacionales en los complejos de zirconio es vital para controlar la selectividad del producto.

Objetivo del estudio:

Para investigar la síntesis de ansa-metalocenos utilizando un precursor específico de amidato de zirconio.
Para dilucidar el comportamiento conformacional del ligando de amidato de zirconio y su influencia en la estereoselectividad.
Determinar los factores que rigen la formación preferente de isómeros racémicos sobre los mesoisómeros.

Principales métodos:

Síntesis de complejos de amidato de zirconio y su reacción con reactivos de litio ansa-bis-indenilo.
Caracterización de productos mediante la espectroscopia de resonancia magnética nuclear (RMN).
Determinación de las estructuras moleculares a través de la cristalografía de rayos X.

Principales resultados:

Se obtuvieron altos rendimientos de ansa-metalocenos racémicos (rac-(XBI) Zr[PhN(CH((2)) (((3) NPh), sin que se pudieran detectar sus mesoisómeros.
La cristalografía de rayos X reveló conformaciones de torsión en los anillos Zr[PhN(CH(2))(3) NPh, posicionando los grupos N-Ph lejos del plano N-Zr-N.
Esta conformación observada complementa la estructura de los metallocenos racémicos y desestabiliza los mesoisómeros.

Conclusiones:

Se propone que la conformación de torsión del anillo Zr[PhN(CH(2))(3) NPh] dirija la estereoquímica durante la adición del segundo ligando indenilo.
Esta preferencia conformacional en el estado de transición conduce a un fuerte sesgo para la formación de productos racémicos.
Los hallazgos proporcionan información sobre el estereocontrol en la síntesis de metalloceno y están respaldados por estudios con otros precursores de amida de zirconio.

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